JP7535404B2 - Transparent moldings for optical elements - Google Patents

Description

The present invention relates to a transparent molded body for optical elements.

Traditionally, glass has been used for optical components such as lenses and prisms, but in recent years, plastics have come to be used in response to the need for greater design freedom, such as for lightweight, compact lenses and aspheric lenses. Plastics commonly used for optical components include methacrylic resins, styrene resins, polycarbonates, and cyclic olefin resins.

In general, the quality of optical plastics as optical products is greatly affected by impurities contained in the raw materials, gels generated during polymerization, foreign matter mixed in during the manufacturing process, resin fading due to thermal history during molding processing, and foreign matter generated or mixed in by the molding machine or external environment, so thorough measures against foreign matter and management are carried out.
Among foreign bodies, bright spot foreign bodies that become bright spots by diffusing and reflecting light are sometimes considered important in optical applications. For example, the above-mentioned black or brown foreign bodies, which are thought to be caused by resin scorching due to thermal history, absorb light and are therefore unlikely to become bright spots, but foreign bodies that are mainly composed of inorganic compositions and are thought to be caused by the external environment, are likely to become bright spots because they tend to reflect light.

Conventionally, measures against foreign matter have been implemented to reduce foreign matter larger than several micrometers or larger than 20 micrometers, regardless of whether the foreign matter is a bright spot or not, by filtering out the foreign matter using, for example, a polymer filter having a filtering accuracy of about 5 micrometers or 10 micrometers.
For example, Patent Document 1 discloses an acrylic resin packaging body in which the number of foreign particles having a diameter of 2 micrometers or more as measured with a liquid particle counter is less than 500 per gram by filtering molten acrylic resin with a polymer filter.
Furthermore, Patent Document 2 discloses pellets of an acrylic resin composition in which a heat-resistant acrylic resin is filtered through a polymer filter having a filtration accuracy of 10 micrometers or less, and the pellets contain 100 or less foreign matter particles having a particle size of 20 micrometers or more per gram as measured using a particle counter.

However, filtration using polymer filters such as those described above is intended to remove impurities contained in the raw resin materials, gels that are generated during polymerization, and foreign matter that gets mixed in during the manufacturing process, so there is a possibility that foreign matter that comes from the molding process, transportation, and the external environment will not be removed and will remain.

As described above, the amount of bright spot foreign matter in resins is not clearly measured and controlled, and transparent molded articles for optical elements in which the amount of bright spot foreign matter is highly reduced are desired.

Patent No. 4819952 Patent No. 5536011

Therefore, the present invention aims to provide a transparent molded body for optical elements that reduces the decrease in visibility caused by minute bright spot foreign matter.

As a result of extensive research into solving the problems of the conventional technology described above, the inventors discovered that the above problems could be solved by creating a clean environment in each manufacturing and molding process and reducing bright spot foreign matter mainly originating from the external environment by eliminating static electricity from the entire space, and thus completed the present invention.

That is, the present invention is as follows.
[1]
A method for producing a transparent molded body for optical elements, the method comprising the steps of: providing a transparent molded body for optical elements having a content of bright spot foreign matter having a size of 10 micrometers or more, which becomes a bright spot due to diffuse reflection when light is incident thereon, the content of bright spot foreign matter being 1 piece/cm3 or ^less per unit volume;
A resin pellet manufacturing process, comprising: manufacturing and packaging resin pellets in an environment in which the space is controlled to a cleanliness level of Class 6 (ISO 14644-1) and in which a bar-type ionizer is installed to neutralize the entire space;
a molding step of a transparent molded body for optical elements, comprising removing foreign matter adhering to the packaging surface of the packaged resin pellets obtained in the manufacturing step of the resin pellets with an air gun equipped with a static elimination function, moving the packaged resin pellets to an environment that is a space controlled to a cleanliness level of Class 6 (ISO 14644-1) and that is equipped with a bar-type ionizer for static elimination in the entire space and an injection molding machine, and injection molding the transparent molded body for optical elements using the resin pellets with the injection molding machine.

The present invention provides a transparent molded body for optical elements that reduces the loss of visibility caused by minute bright spot foreign matter.

The following provides a detailed explanation of the form for carrying out the present invention (hereinafter referred to as the "present embodiment"); however, the present invention is not limited to the following description, and can be carried out in various modifications within the scope of the gist of the invention.

<Transparent molded body for optical elements> The transparent molded body for optical elements of this embodiment is characterized in that the content of bright spot foreign matter of 10 micrometers or more that becomes bright spots due to diffuse reflection when light is incident on it is 1 piece/cm3 or ^less per unit volume.
In the present disclosure, a "bright spot" is a point that is brighter than the surroundings by diffusing and reflecting light, and can be detected as a bright part when, for example, light is incident on any surface of a transparent molded body, in a state where the illumination light does not reach the observer (dark field). More specifically, a "bright spot" is a part whose brightness in dark field observation is 3 mcd/ ^m2 or more, which is the range in which a person can confirm the outline.
In addition, in the present disclosure, a "bright spot foreign matter" refers to a foreign matter that becomes a bright spot due to diffuse reflection when light is incident on the transparent molded body.

The size of the bright spot foreign matter targeted in the transparent molded body for optical elements of this embodiment is set to 10 micrometers or more, taking into consideration that the brightness may be recognized as a bright spot by humans. It is preferable to reduce bright spot foreign matter of less than 10 micrometers as much as possible from the viewpoint of improving quality, but it is considered that the actual control range in consideration of mass productivity is about 10 micrometers as the control lower limit.
In the transparent molded article for optical elements of this embodiment, the content of bright foreign matter having a size of 10 micrometers or more is 1 piece/cm3 or ^less per unit volume, preferably 0.9 pieces/ ^cm3 or less, and more preferably 0.8 pieces/ ^cm3 or less. When the content of bright foreign matter having a size of 10 micrometers or more is within the above range, the visibility of the transparent molded article for optical elements is good.
Methods for controlling the content of bright spot foreign matter within the above range include filtering and refining the resin with a polymer filter or the like during the polymerization process, constructing a clean environment by installing a clean booth or the like in each step from the resin manufacturing process to the molding process of the transparent molded body for optical elements, and reducing bright spot foreign matter mainly originating from the external environment by eliminating electricity from the entire space using an ionizer or the like. In particular, in the area where electricity is eliminated, eliminating electricity from the entire space, not just localized locations such as each device, is effective in reducing bright spot foreign matter.
The size of the bright spot foreign matter is a value expressed as the size (maximum diameter) of the bright spot measured in a dark field using a digital microscope.

The standard for determining whether a foreign object is a bright spot foreign object is that when light is incident on any surface of a transparent molded body, if the foreign object is a bright spot foreign object that diffusely reflects light in a dark field, the reflected light will reach the observer, and so a foreign object that is observed to be brighter than its surroundings in a dark field is a bright spot foreign object. Therefore, foreign objects that absorb or transmit the incident light are not considered to be bright spots because the reflected light does not reach the observer and they are not considered to be bright spots. For example, black or brown foreign objects such as resin burns caused by thermal history during the manufacturing process, and transparent foreign resins that are thought to have been mixed in from the outside during transportation, are unlikely to be bright spot foreign objects because they absorb or transmit light. On the other hand, inorganic foreign objects such as metals and minerals, and colored foreign objects such as fibers, although this varies depending on the type and surface shape, are observed as bright spots because they diffusely reflect light, and are considered to be bright spot foreign objects.

Bright spot foreign matter may be observed by a human being through visual inspection, but as detection becomes more difficult, especially for small bright spot foreign matter, it is preferable to observe using a microscope such as a stereo microscope or digital microscope. From the standpoint of quantitative evaluation and time saving, it is also acceptable to make a judgment through automatic measurement using an automatic appearance inspection device, etc.

A more specific method for inspecting for internal bright spot foreign bodies in a transparent molding is to use depth synthesis with a digital microscope to obtain a depth synthesis image that captures only the inside of the transparent molding, and from this depth synthesis image, it is possible to extract only the bright spot foreign bodies that exist inside the transparent molding, excluding the surface portion of the transparent molding.
In the present disclosure, the "interior of the transparent molded body" and the "surface portion of the transparent molded body" refer to a portion from the surface up to a specific distance in a direction perpendicular to the surface as the "surface portion of the transparent molded body", and the remaining portion as the "interior of the transparent molded body", and may be determined according to a desired inspection range of the transparent molded body. For example, the portion from the surface up to less than 2 millimeters in a direction perpendicular to the surface may be defined as the surface portion of the transparent molded body, and the remaining portion (a portion 2 millimeters or more away from the surface in a direction perpendicular to the surface) may be defined as the "interior of the transparent molded body".

Here, the relationship between lens magnification and focal depth (depth of field) is such that the lower the lens magnification, the wider the field of view but the shallower the focal depth (depth of field), and the higher the lens magnification, the narrower the field of view but the deeper the focal depth (depth of field).
On the other hand, the resolution of the captured image increases as the lens magnification increases, because the projection area per pixel of the image sensor on the depth of field side decreases. In other words, by selecting an appropriate lens magnification of the digital microscope for the transparent molded object to be observed and adjusting the height range for depth synthesis of the digital microscope from the range of resolution and depth of field, it is possible to obtain a depth synthesis image of only the inside of the transparent molded object, excluding the surface portion.

By separately preparing an external light source as a light source for irradiating light onto any surface of the transparent molded body, it is possible to quantitatively evaluate internal bright spot foreign matter, including tiny internal bright spot foreign matter of about 10 micrometers.
Examples of external lighting for directing light to any surface of the transparent molded body include a light source with diffusivity such as an LED, a light source with high linearity such as a laser, and a parallel light source focused by an optical fiber or a lens.

The wavelength of the light source to be irradiated is not particularly limited and can be freely selected as long as it is white light or monochromatic light, or any other light with a wavelength that can be identified as a bright spot in the captured image. However, from the perspective of a person judging a bright spot foreign object, there are situations in which using a monochromatic light source makes it easier for a person to judge a bright spot foreign object. Also, white LEDs are usually made white by mixing a blue LED with a yellow phosphor, and depending on the light distribution characteristics, there is a possibility that the anisotropy of the emitted light color resulting from the highly directional blue and the highly diffusive yellow may cause differences in the appearance of bright spot foreign objects. For this reason, it is preferable to use a monochromatic light source.

Furthermore, removing noise light (stray light) caused by reflection from foreign matter, scratches, etc. present on the surface makes it possible to detect bright spots more clearly in dark-field observation, and to detect bright spot foreign matter more precisely. Therefore, it is preferable that the method for inspecting bright spot foreign matter has a means for removing noise light caused by the surface of the transparent molded body.
As a means for removing noise light caused by the surface of the transparent molded body, it is preferable to provide an optical slit between the transparent molded body and a light source that makes light incident on an arbitrary surface of the transparent molded body. By making the slit width of this optical slit narrower than the width of the surface of the transparent molded body that makes light incident on, foreign matter, scratches, etc. present on the surface of the transparent molded body are not irradiated by external illumination, so that the above-mentioned noise light is reduced and bright foreign matter inside the transparent molded body can be clearly detected.
Also, instead of providing a slit, the external illumination may be highly parallel and the light may be irradiated only inside the transparent molded body without irradiating the surface of the transparent molded body, thereby eliminating noise light. However, it is not easy to prepare strictly parallel light, and when the thickness or size of the transparent molded body changes, it is necessary to prepare a suitable light source each time. However, with an optical slit, it is possible to easily respond by preparing several types of optical slits with slit widths that match the size of the transparent molded body.

[Resin composition containing methacrylic resin having a ring structure in the main chain]
The transparent molded article for an optical element of the present embodiment preferably contains a resin composition containing a methacrylic resin having a ring structure in the main chain.
The resin composition containing a methacrylic resin having a ring structure in the main chain may optionally contain additives, and may also contain a thermoplastic resin, a rubbery polymer, or the like other than the methacrylic resin having a ring structure in the main chain, or may consist only of a methacrylic resin having a ring structure in the main chain.

(Methacrylic resin having a ring structure in the main chain)
The methacrylic resin having a ring structure in the main chain of this embodiment is a methacrylic resin containing a structural unit (A) derived from a methacrylic acid ester monomer and a structural unit (B) having a ring structure in the main chain. The structural unit (B) having a ring structure in the main chain is selected from a structural unit (B-1) derived from an N-substituted maleimide monomer, a glutarimide structural unit (B-2), a lactone ring structural unit (B-3), and the like. In addition, the methacrylic resin optionally contains other vinyl monomer units (C) copolymerizable with the methacrylic acid ester monomer.
The content of the methacrylic resin having a ring structure in the main chain in 100% by mass of the resin composition is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

Each monomer structural unit is explained below.

-Structural unit (A) derived from methacrylic acid ester monomer-
First, the structural unit (A) derived from a methacrylic acid ester monomer will be described.
The structural unit (A) derived from a methacrylic acid ester monomer is formed, for example, from a monomer selected from the methacrylic acid esters shown below.
Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, cyclooctyl methacrylate, tricyclodecyl methacrylate, dicyclooctyl methacrylate, tricyclododecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 1-phenylethyl methacrylate, 2-phenoxyethyl methacrylate, 3-phenylpropyl methacrylate, and 2,4,6-tribromophenyl methacrylate.
These monomers may be used alone or in combination of two or more kinds.
Among the above methacrylic acid esters, methyl methacrylate and benzyl methacrylate are preferred in that the resulting methacrylic resin having a ring structure in the main chain has excellent transparency and weather resistance.
The structural unit (A) derived from a methacrylic acid ester monomer may be contained in one type or in two or more types.

The content of the structural unit (A) derived from a methacrylic acid ester monomer is preferably 50 to 97% by mass, more preferably 55 to 97% by mass, even more preferably 55 to 95% by mass, still more preferably 60 to 93% by mass, and particularly preferably 60 to 90% by mass, based on 100% by mass of the methacrylic resin, from the viewpoint of imparting sufficient heat resistance to the methacrylic resin having a ring structure in the main chain by the structural unit (B) having a ring structure in the main chain described later.
The content of the structural unit (A) derived from the methacrylic acid ester monomer can be determined by ¹ H-NMR measurement and ¹³ C-NMR measurement. ¹ H-NMR measurement and ¹³ C-NMR measurement can be performed, for example, using CDCl ₃ or DMSO-d ₆ as a measurement solvent at a measurement temperature of 40° C.

The structural unit (B) having a ring structure in the main chain is described below.

--Structural unit (B) having a ring structure in the main chain--
--Structural unit derived from N-substituted maleimide monomer (B-1)--
Next, the structural unit (B-1) derived from the N-substituted maleimide monomer will be described.
The structural unit (B-1) derived from an N-substituted maleimide monomer may be at least one selected from a monomer represented by the following formula (1) and/or a monomer represented by the following formula (2), and is preferably formed from both of the monomers represented by the following formula (1) and the following formula (2).

式（１）中、Ｒ^１は、炭素数７～１４のアリールアルキル基、炭素数６～１４のアリール基のいずれかを示し、Ｒ^２及びＲ^３は、それぞれ独立に、水素原子、炭素数１～１２のアルキル基、炭素数６～１４のアリール基のいずれかを示す。
また、Ｒ^２がアリール基の場合には、Ｒ^２は、置換基としてハロゲンを含んでいてもよい。
また、Ｒ^１は、ハロゲン原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基、ニトロ基、ベンジル基等の置換基で置換されていてもよい。

In formula (1), R ¹ represents either an arylalkyl group having 7 to 14 carbon atoms or an aryl group having 6 to 14 carbon atoms, and R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
When ^R2 is an aryl group, ^R2 may contain a halogen as a substituent.
Furthermore, R ¹ may be substituted with a substituent such as a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a nitro group, or a benzyl group.

式（２）中、Ｒ^４は、水素原子、炭素数３～１２のシクロアルキル基、炭素数１～１２のアルキル基のいずれかを示し、Ｒ^５及びＲ^６は、それぞれ独立に、水素原子、炭素数１～１２のアルキル基、炭素数６～１４のアリール基のいずれかを示す。

In formula (2), R ⁴ represents any one of a hydrogen atom, a cycloalkyl group having 3 to 12 carbon atoms, and an alkyl group having 1 to 12 carbon atoms, and R ⁵ and R ⁶ each independently represent any one of a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, and an aryl group having 6 to 14 carbon atoms.

Specific examples are given below.
Examples of the monomer represented by formula (1) include N-phenylmaleimide, N-benzylmaleimide, N-(2-chlorophenyl)maleimide, N-(4-chlorophenyl)maleimide, N-(4-bromophenyl)maleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)maleimide, N-(2-methoxyphenyl)maleimide, N-(2-nitrophenyl)maleimide, and N-(2,4,6-trimethylphenyl)maleimide. N-(4-benzylphenyl)maleimide, N-(2,4,6-tribromophenyl)maleimide, N-naphthylmaleimide, N-anthracenylmaleimide, 3-methyl-1-phenyl-1H-pyrrole-2,5-dione, 3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1,3-diphenyl-1H-pyrrole-2,5-dione, 1,3,4-triphenyl-1H-pyrrole-2,5-dione, and the like.
Among these monomers, N-phenylmaleimide and N-benzylmaleimide are preferred because the resulting methacrylic resin having a ring structure in the main chain has excellent heat resistance and optical properties such as birefringence.
These monomers may be used alone or in combination of two or more kinds.

Examples of the monomer represented by formula (2) include N-methylmaleimide, N-ethylmaleimide, N-n-propylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-isobutylmaleimide, N-s-butylmaleimide, N-t-butylmaleimide, N-n-pentylmaleimide, N-n-hexylmaleimide, N-n-heptylmaleimide, N-n-octylmaleimide, N-laurylmaleimide, and N-stearylmaleimide. Examples of such maleimide include allylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, 1-cyclohexyl-3-methyl-1-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3-phenyl-1H-pyrrole-2,5-dione, and 1-cyclohexyl-3,4-diphenyl-1H-pyrrole-2,5-dione.
Among these monomers, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-cyclohexylmaleimide are preferred because the weather resistance of the methacrylic resin having a ring structure in the main chain is excellent, and N-cyclohexylmaleimide is particularly preferred because it has excellent low moisture absorption properties, which are required for optical materials in recent years.
These monomers may be used alone or in combination of two or more.

In the methacrylic resin having a ring structure in the main chain of the present embodiment, it is particularly preferable to use a monomer represented by formula (1) and a monomer represented by formula (2) in combination in order to develop highly controlled birefringence characteristics.
The molar ratio (B1/B2) of the content (B1) of the structural unit derived from the monomer represented by formula (1) to the content (B2) of the structural unit derived from the monomer represented by formula (2) is preferably more than 0 and 15 or less, more preferably more than 0 and 10 or less.
When the molar ratio B1/B2 is within this range, the molded article containing the methacrylic resin having a ring structure in the main chain of this embodiment maintains its transparency, is not yellowed, and does not lose its environmental resistance, and exhibits good heat resistance and good photoelastic properties.

The content of the structural unit (B-1) derived from the N-substituted maleimide monomer is not particularly limited as long as the resulting composition satisfies the glass transition temperature range of the present embodiment, but is preferably in the range of 5 to 40 mass %, more preferably in the range of 5 to 35 mass %, based on 100 mass % of the methacrylic resin.
When it is within this range, a molded article containing a methacrylic resin having a ring structure in the main chain can obtain a more sufficient heat resistance improving effect, and can obtain more preferable improving effects in weather resistance, low water absorption, and optical properties. Note that, setting the content of the structural unit (B-1) derived from the N-substituted maleimide monomer to 40 mass% or less is effective in preventing a decrease in the physical properties of a molded article containing a methacrylic resin having a ring structure in the main chain, which is caused by a decrease in the reactivity of the monomer component during the polymerization reaction and an increase in the amount of unreacted remaining monomer.

--Glutarimide structural unit (B-2)--
The methacrylic resin having a glutarimide structural unit (B-2) in the main chain is, for example, a methacrylic resin having a glutarimide structural unit (B-2) described in JP-A-2006-249202, JP-A-2007-009182, JP-A-2007-009191, JP-A-2011-186482, Republished Japanese Patent Publication No. 2012/114718, etc., and can be formed by the method described in the publications.

The glutarimide structural unit (B-2) constituting the methacrylic resin having a ring structure in the main chain of the present embodiment may be formed after polymerization of the resin.
Specifically, the glutarimide structural unit (B-2) may be represented by the following general formula (3).

上記一般式（３）において、好ましくはＲ^７及びＲ^８は、それぞれ独立して、水素又はメチル基であり、Ｒ^９は、水素、メチル基、ブチル基、シクロヘキシル基のいずれかであり、より好ましくは、Ｒ^７は、メチル基であり、Ｒ^８は、水素であり、Ｒ^９は、メチル基である。
グルタルイミド系構造単位（Ｂ－２）は、単一の種類のみを含んでいてもよいし、複数の種類を含んでいてもよい。
グルタルイミド系構造単位（Ｂ－２）を有するメタクリル系樹脂において、グルタルイミド系構造単位（Ｂ－２）の含有量については、本実施形態の組成物として好ましいガラス転移温度の範囲を満たすものであれば特に制限はないが、メタクリル系樹脂を１００質量％として、好ましくは５～７０質量％の範囲、より好ましくは５～６０質量％の範囲である。
グルタルイミド系構造単位（Ｂ－２）の含有量が上記範囲にあると、成形加工性、耐熱性、及び光学特性の良好な樹脂が得られることから好ましい。
グルタルイミド系構造単位（Ｂ－２）を有するメタクリル系樹脂は、必要に応じて、芳香族ビニル単量体単位をさらに含んでいてもよい。
芳香族ビニル単量体としては特に限定されないが、スチレン、α－メチルスチレンが挙げられ、スチレンが好ましい。
グルタルイミド系構造単位（Ｂ－２）を有するメタクリル系樹脂における芳香族ビニル単位の含有量としては、特に限定されないが、グルタルイミド系構造単位（Ｂ－２）を有するメタクリル系樹脂を１００質量％として、０～２０質量％が好ましい。
芳香族ビニル単位の含有量が上記範囲にあると、耐熱性と優れた光弾性特性との両立が可能となり好ましい。

In the above general formula (3), preferably, ^R7 and ^R8 are each independently hydrogen or a methyl group, and ^R9 is any one of hydrogen, a methyl group, a butyl group, and a cyclohexyl group, and more preferably, ^R7 is a methyl group, ^R8 is hydrogen, and ^R9 is a methyl group.
The glutarimide structural unit (B-2) may contain only one type, or may contain a plurality of types.
In the methacrylic resin having the glutarimide structural unit (B-2), the content of the glutarimide structural unit (B-2) is not particularly limited as long as it satisfies the preferred glass transition temperature range for the composition of the present embodiment, but is preferably in the range of 5 to 70 mass %, more preferably in the range of 5 to 60 mass %, based on 100 mass % of the methacrylic resin.
It is preferable that the content of the glutarimide structural unit (B-2) is within the above range, since a resin having good moldability, heat resistance and optical properties can be obtained.
The methacrylic resin having the glutarimide structural unit (B-2) may further contain an aromatic vinyl monomer unit, if necessary.
The aromatic vinyl monomer is not particularly limited, but examples thereof include styrene and α-methylstyrene, with styrene being preferred.
The content of aromatic vinyl units in the methacrylic resin having a glutarimide structural unit (B-2) is not particularly limited, but is preferably 0 to 20% by mass, based on 100% by mass of the methacrylic resin having a glutarimide structural unit (B-2).
When the content of the aromatic vinyl unit is within the above range, it is possible to achieve both heat resistance and excellent photoelasticity, which is preferable.

--Lactone ring structural unit (B-3)--
Methacrylic resins having a lactone ring structural unit (B-3) in the main chain can be formed by the methods described in, for example, JP-A-2001-151814, JP-A-2004-168882, JP-A-2005-146084, JP-A-2006-96960, JP-A-2006-171464, JP-A-2007-63541, JP-A-2007-297620, JP-A-2010-180305, and the like.
The lactone ring structural unit (B-3) constituting the methacrylic resin of this embodiment may be formed after the resin polymerization.
The lactone ring structural unit (B-3) in this embodiment is preferably a six-membered ring because this provides excellent stability of the ring structure.
As the 6-membered lactone ring structural unit (B-3), for example, a structure represented by the following general formula (4) is particularly preferred.

上記一般式（４）において、Ｒ^１０、Ｒ^１１及びＲ^１２は、互いに独立して、水素原子、又は炭素数１～２０の有機残基である。
有機残基としては、例えば、メチル基、エチル基、プロピル基等の炭素数１～２０の飽和脂肪族炭化水素基（アルキル基等）；エテニル基、プロペニル基等の炭素数２～２０の不飽和脂肪族炭化水素基（アルケニル基等）；フェニル基、ナフチル基等の炭素数６～２０の芳香族炭化水素基（アリール基等）；これら飽和脂肪族炭化水素基、不飽和脂肪族炭化水素基、芳香族炭化水素基における水素原子の一つ以上が、ヒドロキシ基、カルボキシル基、エーテル基、エステル基からなる群から選ばれる少なくとも１種の基により置換された基；等が挙げられる。
ラクトン環構造は、例えば、ヒドロキシ基を有するアクリル酸系単量体と、メタクリル酸メチル等のメタクリル酸エステル単量体とを共重合して、分子鎖にヒドロキシ基とエステル基又はカルボキシル基とを導入した後、これらヒドロキシ基とエステル基又はカルボキシル基との間で、脱アルコール（エステル化）又は脱水縮合（以下、「環化縮合反応」ともいう）を生じさせることにより形成することができる。
重合に用いるヒドロキシ基を有するアクリル酸系単量体としては、例えば、２－（ヒドロキシメチル）アクリル酸、２－（ヒドロキシエチル）アクリル酸、２－（ヒドロキシメチル）アクリル酸アルキル（例えば、２－（ヒドロキシメチル）アクリル酸メチル、２－（ヒドロキシメチル）アクリル酸エチル、２－（ヒドロキシメチル）アクリル酸イソプロピル、２－（ヒドロキシメチル）アクリル酸ｎ－ブチル、２－（ヒドロキシメチル）アクリル酸ｔ－ブチル）、２－（ヒドロキシエチル）アクリル酸アルキル等が挙げられ、好ましくは、ヒドロキシアリル部位を有する単量体である２－（ヒドロキシメチル）アクリル酸や２－（ヒドロキシメチル）アクリル酸アルキルであり、特に好ましくは２－（ヒドロキシメチル）アクリル酸メチル、２－（ヒドロキシメチル）アクリル酸エチルである。

In the above general formula (4), R ¹⁰ , R ¹¹ and R ¹² are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms.
Examples of the organic residue include saturated aliphatic hydrocarbon groups (e.g., alkyl groups) having 1 to 20 carbon atoms, such as a methyl group, an ethyl group, a propyl group, etc.; unsaturated aliphatic hydrocarbon groups (e.g., alkenyl groups) having 2 to 20 carbon atoms, such as an ethenyl group, a propenyl group, etc.; aromatic hydrocarbon groups (e.g., aryl groups) having 6 to 20 carbon atoms, such as a phenyl group, a naphthyl group, etc.; and groups in which one or more hydrogen atoms in these saturated aliphatic hydrocarbon groups, unsaturated aliphatic hydrocarbon groups, and aromatic hydrocarbon groups have been substituted with at least one group selected from the group consisting of a hydroxy group, a carboxyl group, an ether group, and an ester group.
The lactone ring structure can be formed, for example, by copolymerizing an acrylic acid monomer having a hydroxy group with a methacrylic acid ester monomer such as methyl methacrylate to introduce a hydroxy group and an ester group or a carboxyl group into the molecular chain, and then causing dealcoholization (esterification) or dehydration condensation (hereinafter also referred to as a "cyclization condensation reaction") between the hydroxy group and the ester group or the carboxyl group.
Examples of the acrylic acid monomer having a hydroxy group used in the polymerization include 2-(hydroxymethyl)acrylic acid, 2-(hydroxyethyl)acrylic acid, alkyl 2-(hydroxymethyl)acrylates (e.g., methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl 2-(hydroxymethyl)acrylate, n-butyl 2-(hydroxymethyl)acrylate, t-butyl 2-(hydroxymethyl)acrylate), alkyl 2-(hydroxyethyl)acrylates, and the like. Preferred are 2-(hydroxymethyl)acrylic acid and alkyl 2-(hydroxymethyl)acrylates, which are monomers having a hydroxyallyl moiety, and particularly preferred are methyl 2-(hydroxymethyl)acrylate and ethyl 2-(hydroxymethyl)acrylate.

The content of the lactone ring structural unit (B-3) in the methacrylic resin having the lactone ring structural unit (B-3) in the main chain is not particularly limited as long as it satisfies the range of the glass transition temperature of the methacrylic resin having a ring structure in the main chain of this embodiment, but is preferably 5 to 40 mass %, more preferably 5 to 35 mass %, relative to 100 mass % of the methacrylic resin.
When the content of the lactone ring structural unit (B-3) is within this range, the effects of introducing a ring structure, such as improved solvent resistance and improved surface hardness, can be achieved while maintaining moldability.
The content of the lactone ring structural unit (B-3) in the methacrylic resin having a ring structure in the main chain can be determined by the method described in the aforementioned patent document.

From the viewpoint of the heat resistance, thermal stability, strength, and fluidity of the methacrylic resin having a ring structure in the main chain of this embodiment, the content of the structural unit (B) having a ring structure in the main chain is preferably 3 to 40% by mass, with the methacrylic resin being 100% by mass, and the lower limit is more preferably 5% by mass or more, even more preferably 7% by mass or more, and even more preferably 8% by mass or more, and the upper limit is more preferably 30% by mass or less, even more preferably 28% by mass or less, even more preferably 25% by mass or less, particularly preferably 20% by mass or less, especially more preferably 18% by mass or less, and most preferably less than 15% by mass.

-Other vinyl monomer units copolymerizable with methacrylic acid ester monomers (C)-
Examples of other vinyl monomer units (C) (hereinafter, may be referred to as monomer units (C)) copolymerizable with the methacrylic acid ester monomer and capable of constituting the methacrylic resin having a ring structure in the main chain of the present embodiment include aromatic vinyl monomer units (C-1), acrylic acid ester monomer units (C-2), vinyl cyanide monomer units (C-3), and monomer units (C-4) other than these.
The other vinyl monomer units (C) copolymerizable with the methacrylic acid ester monomer may be used alone or in combination of two or more.

The monomer unit (C) can be selected from an appropriate material depending on the properties required of the methacrylic resin having a ring structure in the main chain, but when properties such as thermal stability, fluidity, mechanical properties, and chemical resistance are particularly required, at least one selected from the group consisting of aromatic vinyl monomer units (C-1), acrylic acid ester monomer units (C-2), and vinyl cyanide monomer units (C-3) is preferred.

[Aromatic vinyl monomer unit (C-1)]
The monomer constituting the aromatic vinyl monomer unit (C-1) constituting the methacrylic resin having a ring structure in the main chain of the present embodiment is not particularly limited, but is preferably an aromatic vinyl monomer represented by the following general formula (5).

前記一般式（４）中、Ｒ^１３は、水素原子、又は炭素数が１～６のアルキル基を表し、当該アルキル基は、例えば、水酸基で置換されていてもよい。
Ｒ^１４は、水素原子、炭素数が１～１２のアルキル基、炭素数が１～１２のアルコキシ基、炭素数が６～８のアリール基、炭素数が６～８のアリーロキシ基からなる群より選択されるいずれかであり、Ｒ^１４は、全て同じ基であっても、異なる基であってもよい。また、Ｒ^１４同士で環構造を形成してもよい。
ｎは、０～５の整数を表す。

In the general formula (4), R ¹³ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and the alkyl group may be substituted with, for example, a hydroxyl group.
R ¹⁴ is any one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 8 carbon atoms, and an aryloxy group having 6 to 8 carbon atoms, and R ¹⁴ may be all the same group or different groups. In addition, R ¹⁴ may form a ring structure together.
n represents an integer of 0 to 5.

Specific examples of the monomer represented by the general formula (5) include, but are not limited to, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, p-tert-butylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 1,1-diphenylethylene, isopropenylbenzene (α-methylstyrene), isopropenyltoluene, isopropenylethylbenzene, isopropenylpropylbenzene, isopropenylbutylbenzene, isopropenylpentylbenzene, isopropenylhexylbenzene, isopropenyloctylbenzene, α-hydroxymethylstyrene, and α-hydroxyethylstyrene.
Of the above, styrene and isopropenylbenzene are preferred, and styrene is more preferred from the viewpoints of imparting fluidity and reducing unreacted monomers by improving the polymerization conversion rate.
These may be appropriately selected depending on the properties required for the methacrylic resin having a ring structure in the main chain of this embodiment.

When aromatic vinyl monomer units (C-1) are used, the content is preferably 23% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, when the total amount of monomer units (A) and structural units (B) is taken as 100% by mass, taking into consideration the balance between heat resistance, reduction in residual monomer species, and flowability.

When the aromatic vinyl monomer unit (C-1) is used in combination with the maleimide structural unit (B-1) described above, the ratio (mass ratio) of the content of the (C-1) monomer unit to the content of the (B-1) structural unit (i.e., (C-1) content/(B-1) content) is preferably 0.3 to 5, from the viewpoints of flowability during processing of a film and the effect of reducing silver streaks by reducing residual monomers.
From the viewpoint of maintaining good color tone and heat resistance, the upper limit is preferably not more than 5, more preferably not more than 3, and even more preferably not more than 1. From the viewpoint of reducing residual monomers, the lower limit is preferably not less than 0.3, and more preferably not less than 0.4.
The above-mentioned aromatic vinyl monomer (C-1) may be used alone or in combination of two or more kinds.

[Acrylic acid ester monomer unit (C-2)]
The monomer constituting the acrylate monomer unit (C-2) constituting the methacrylic resin having a ring structure in the main chain of the present embodiment is not particularly limited, but is preferably an acrylate monomer represented by the following general formula (6).

前記一般式（６）中、Ｒ^１５は、水素原子、又は炭素数が１～１２のアルコキシ基を表し、Ｒ^１６は、炭素数が１～１８のアルキル基、炭素数が３～１２のシクロアルキル基、炭素数が６～１４のアリール基のいずれかを表す。

In the general formula (6), R ¹⁵ represents a hydrogen atom or an alkoxy group having 1 to 12 carbon atoms, and R ¹⁶ represents any one of an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, and an aryl group having 6 to 14 carbon atoms.

As a monomer for forming the acrylic acid ester monomer unit (C-2), from the viewpoint of enhancing weather resistance, heat resistance, fluidity, and thermal stability in the methacrylic resin for the film of this embodiment, preferred are methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, and the like, more preferred are methyl acrylate, ethyl acrylate, and n-butyl acrylate, and from the viewpoint of easy availability, methyl acrylate and ethyl acrylate are even more preferred.
The acrylic acid ester monomer unit (C-2) may be used alone or in combination of two or more kinds.

When the acrylic acid ester monomer unit (C-2) is used, the content is preferably 5% by mass or less, and more preferably 3% by mass or less, when the total amount of the (A) monomer unit and the (B) structural unit is taken as 100% by mass, from the viewpoint of heat resistance and thermal stability.

[Cyanide vinyl monomer unit (C-3)]
The monomer constituting the vinyl cyanide monomer unit (C-3) constituting the methacrylic resin having a ring structure in the main chain of the present embodiment is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, ethacrylonitrile, vinylidene cyanide, and the like. Among these, acrylonitrile is preferred from the viewpoints of availability and chemical resistance.
The vinyl cyanide monomer unit (C-3) may be used alone or in combination of two or more kinds.

When vinyl cyanide monomer units (C-3) are used, their content is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, when the total amount of monomer units (A) and structural units (B) is taken as 100% by mass, from the viewpoint of maintaining solvent resistance and heat resistance.

[Monomer unit (C-4) other than (C-1) to (C-3)]
The monomer constituting the monomer unit (C-4) other than (C-1) to (C-3) constituting the methacrylic resin having a ring structure in the main chain of the present embodiment is not particularly limited, and examples thereof include amides such as acrylamide and methacrylamide; glycidyl compounds such as glycidyl (meth)acrylate and allyl glycidyl ether; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and the like, and semi-esterified products or anhydrides thereof; unsaturated alcohols such as methallyl alcohol and allyl alcohol; olefins such as ethylene, propylene, and 4-methyl-1-pentene; and vinyl compounds or vinylidene compounds other than those mentioned above, such as vinyl acetate, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinyl pyrrolidone, and N-vinyl carbazole.
Further, examples of crosslinkable compounds having a plurality of reactive double bonds include compounds in which both terminal hydroxyl groups of ethylene glycol or its oligomers are esterified with acrylic acid or methacrylic acid, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate; compounds in which hydroxyl groups of two alcohols are esterified with acrylic acid or methacrylic acid, such as neopentyl glycol di(meth)acrylate and di(meth)acrylate; compounds in which polyhydric alcohol derivatives, such as trimethylolpropane and pentaerythritol, are esterified with acrylic acid or methacrylic acid; and polyfunctional monomers, such as divinylbenzene.

Among the monomers constituting the above-mentioned (C) monomer unit, at least one selected from the group consisting of methyl acrylate, ethyl acrylate, styrene, and acrylonitrile is preferred from the viewpoint of ease of availability.

The content of the other vinyl monomer unit (C) copolymerizable with the methacrylic acid ester monomer is 0 to 20 mass%, preferably 0 to 18 mass%, and more preferably 0 to 15 mass%, based on 100 mass% of the methacrylic resin, from the viewpoint of enhancing the effect of imparting heat resistance by the structural unit (B).
In particular, when a crosslinkable polyfunctional (meth)acrylate having a plurality of reactive double bonds is used as the (C) monomer unit, the content of the (C) monomer unit is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.2% by mass or less, from the viewpoint of the fluidity of the polymer.

In particular, in this embodiment, from the viewpoint of the heat resistance and optical properties of a molded product containing a methacrylic resin having a ring structure in the main chain, when the total amount of the (B) structural unit and the (C) monomer unit is taken as 100 mass%, the content of the (B) structural unit is 45 to 100 mass%. At this time, the content of the (C) structural unit is 0 to 55 mass%. And, the content of the (B) structural unit is preferably 50 to 100 mass%, more preferably 50 to 90 mass%, and even more preferably 50 to 80 mass%.

The characteristics of the methacrylic resin having a ring structure in the main chain of this embodiment are described below.

(Glass transition temperature of methacrylic resin having a ring structure in the main chain)
The glass transition temperature (Tg) of the methacrylic resin having a ring structure in the main chain of this embodiment is preferably higher than 120° C. and 160° C. or lower.
If the glass transition temperature of the methacrylic resin having a ring structure in the main chain exceeds 120° C., it is possible to more easily obtain the necessary and sufficient heat resistance required for a transparent molded body for an optical element. From the viewpoint of dimensional stability under the temperature of the usage environment, the glass transition temperature (Tg) is more preferably 125° C. or higher, and even more preferably 130° C. or higher.
On the other hand, when the glass transition temperature (Tg) of the methacrylic resin having a ring structure in the main chain is 160° C. or less, melt processing at extremely high temperatures can be avoided, thermal decomposition of the resin, etc. can be suppressed, and a good product can be obtained. For the above-mentioned reasons, the glass transition temperature (Tg) is preferably 150° C. or less.
The glass transition temperature (Tg) can be determined by measuring in accordance with JIS-K7121. Specifically, it can be measured by the method described in the examples below.

(Photoelastic coefficient of methacrylic resin having a ring structure in the main chain)
The photoelastic coefficient C of the methacrylic resin having a ring structure in the main chain of this embodiment is preferably −3.0×10 ⁻¹² to +3.0×10 ⁻¹² Pa ⁻¹ , more preferably −2.0×10 ⁻¹² to +2.0×10 ⁻¹² Pa ⁻¹ , and even more preferably −1.0×10 ⁻¹² to +1.0×10 ⁻¹² Pa ⁻¹ . When the photoelastic coefficient C is within the above range, the resin has excellent transparency, low birefringence, and high heat resistance, and can be suitably used in applications requiring high optical properties among optical elements.
The photoelastic coefficient is described in various documents (for example, see Chemical Review, No. 39, 1998 (published by the Academic Society Publishing Center)) and is defined by the following formulas (ia) and (ib). It can be seen that the closer the value of the photoelastic coefficient C is to zero, the smaller the change in birefringence due to an external force is.
C=Δn/σ...(e)
Δn=nx-ny...(f)
(In the formula, C is the photoelastic coefficient, σ is the stretching stress, Δn is the birefringence, nx is the refractive index in the stretching direction, and ny is the refractive index in the in-plane direction perpendicular to the stretching direction.)
If the absolute value of the photoelastic coefficient C of the methacrylic resin having a ring structure in the main chain of this embodiment is 3.0×10 ⁻¹² Pa ⁻¹ or less, the birefringence generated by stress generated when the injection molded article is fitted into a product as a part will be sufficiently small.
The photoelastic coefficient C of the methacrylic resin having a ring structure in the main chain can be determined specifically by the method described in the Examples below.

The methacrylic resin having a ring structure in the main chain of the present embodiment has a weight average molecular weight (Mw) in terms of polymethyl methacrylate measured by gel permeation chromatography (GPC) in the range of preferably 65,000 to 220,000, more preferably 80,000 to 180,000, and even more preferably 90,000 to 150,000.
When the weight average molecular weight (Mw) is within the above range, the balance between mechanical strength and flowability is excellent.
Regarding the ratios among the Z-average molecular weight (Mz), weight-average molecular weight (Mw), and number-average molecular weight (Mn) as parameters representing molecular weight distribution, in the methacrylic resin of the present embodiment, taking into consideration the balance between fluidity and mechanical strength, Mw/Mn is preferably 1.5 to 3.0, more preferably 1.6 to 2.5, and even more preferably 1.6 to 2.3; Mz/Mw is preferably 1.3 to 2.0, more preferably 1.3 to 1.8, and even more preferably 1.4 to 1.7.
The weight average molecular weight and number average molecular weight of the methacrylic resin can be measured by the method described in the Examples below.

The composition distribution of the ring structure in the methacrylic resin having a ring structure in the main chain of this embodiment can be determined by observing the molecular weight dependence of the composition ratio of the structural unit containing a ring structure in the methacrylic resin, specifically, by determining the abundance ratio of the structural unit having a ring structure for each component obtained by molecular weight fractionation of the methacrylic resin by preparative GPC. When the abundance ratio of the structural unit having a ring structure in the methacrylic resin component obtained by molecular weight fractionation is expressed in mass%, the difference in the abundance ratio of the structural unit having a ring structure between the fractionated component having a peak top molecular weight of 40,000 to 50,000 and the fractionated component having a peak top molecular weight of 240,000 to 260,000 is preferably 3.0 mass% or less, more preferably 2.5 mass% or less, even more preferably 2.0 mass% or less, and even more preferably 1.5 mass% or less. Here, a fraction having a peak top molecular weight of 40,000 to 50,000 refers to any fraction having a peak top molecular weight in this range, and a fraction having a peak top molecular weight of 240,000 to 260,000 refers to any fraction having a peak top molecular weight in this range.
The method for molecular weight fractionation of the methacrylic resin and the abundance ratio of structural units having a ring structure in each fractionated component can be measured by the method described in the Examples below.

(Methacrylic resin manufacturing method)
Hereinafter, a method for producing the methacrylic resin having a ring structure in the main chain according to this embodiment will be described.

In the production method of this embodiment, a batch system, a semi-batch system, or a continuous system can be used as the polymerization system. Here, the batch system is a process in which the reaction is started and progressed after the entire amount of raw materials is charged into a reactor, and the product is recovered after the reaction is completed. The semi-batch system is a process in which either the raw material is charged or the product is recovered simultaneously during the reaction, and the continuous system is a process in which both the raw material is charged and the product is recovered simultaneously during the reaction. As a method for producing a methacrylic resin having a ring structure in the main chain in this embodiment, a semi-batch system in which a part of the raw material is charged after the reaction is started is preferable from the viewpoint of precisely controlling the copolymer composition.
In the method for producing a methacrylic resin having a ring structure in the main chain in this embodiment, polymerization of monomers by radical polymerization is preferably used.

Hereinafter, a method for producing a methacrylic resin containing an N-substituted maleimide structural unit (B-1) as the structural unit (B) having a ring structure in the main chain will be described in detail.
In this embodiment, the method for producing the methacrylic resin having the structural unit (B-1) derived from an N-substituted maleimide monomer in the main chain is preferably a solution polymerization method.

The polymerization solvent to be used is not particularly limited as long as it can increase the solubility of the maleimide copolymer obtained by polymerization and can appropriately maintain the viscosity of the reaction solution for the purpose of preventing gelation, etc.
Specific examples of the polymerization solvent that can be used include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and isopropylbenzene; ketones such as methyl isobutyl ketone, butyl cellosolve, methyl ethyl ketone, and cyclohexanone; and polar solvents such as dimethylformamide and 2-methylpyrrolidone.
Furthermore, alcohols such as methanol, ethanol, and isopropanol may be used in combination as a polymerization solvent within a range that does not inhibit dissolution of the polymerization product during polymerization.
These may be used alone or in combination of two or more.

There are no particular restrictions on the amount of solvent used during polymerization, so long as the polymerization proceeds without causing precipitation of the copolymer or monomers used during production and the amount can be easily removed. For example, if the total amount of the monomers to be mixed is 100 parts by mass, it is preferable to use 10 to 200 parts by mass. More preferably, it is 25 to 200 parts by mass, even more preferably 50 to 200 parts by mass, and even more preferably 50 to 150 parts by mass.

There are no particular limitations on the polymerization temperature as long as it is a temperature at which the polymerization proceeds, but it is preferably 70 to 180°C, more preferably 80 to 160°C, even more preferably 90 to 150°C, and even more preferably 100 to 150°C. From the viewpoint of productivity, it is preferable to set the temperature at 70°C or higher, and it is preferable to set the temperature at 180°C or lower in order to suppress side reactions during polymerization and obtain a polymer with the desired molecular weight and quality.

The polymerization time is not particularly limited as long as it is a time that can obtain the required degree of polymerization at the required conversion rate, but from the viewpoint of productivity, etc., it is preferably 2 to 15 hours, more preferably 3 to 12 hours, and even more preferably 4 to 10 hours.

In the present embodiment, the polymerization conversion rate at the end of polymerization of the methacrylic resin having the structural unit (B-1) derived from an N-substituted maleimide monomer in the main chain is preferably 93 to 99.9%, more preferably 95 to 99.9%, and even more preferably 97 to 99.8%.
Here, the polymerization conversion rate is the ratio of the total mass of the monomers added to the polymerization system minus the total mass of the monomers remaining at the end of the polymerization to the total mass of the monomers added to the polymerization system.

Furthermore, the amount of N-substituted maleimide monomer remaining in the solution after polymerization (N-substituted maleimide residual amount) is preferably from 50 to 5,000 ppm by mass, more preferably from 100 to 3,000 ppm by mass, and even more preferably from 200 to 1,000 ppm by mass.
The higher the polymerization conversion rate and the smaller the remaining amount of N-substituted maleimide, the less monomer will be circulated to the solvent recovery system, and the load on the purification system will be reduced and the unit consumption will increase, which is economical. However, if the polymerization conversion rate is made too high or the remaining amount of N-substituted maleimide is reduced too much, the amount of colorable low-molecular-weight components will increase, which may have an adverse effect on the color tone and moldability.

During the polymerization reaction, a chain transfer agent may be added as necessary.
As the chain transfer agent, any chain transfer agent used in general radical polymerization can be used, and examples thereof include mercaptan compounds such as n-butyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, and 2-ethylhexyl thioglycolate; halogen compounds such as carbon tetrachloride, methylene chloride, and bromoform; unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, dipentene, and terpinolene; and the like.
These may be used alone or in combination of two or more.
These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and there are no particular limitations on the addition stage.
The amount of the chain transfer agent added may be 0.01 to 1 part by mass, and preferably 0.05 to 0.5 part by mass, based on 100 parts by mass of the total amount of monomers used in the polymerization.

During the polymerization reaction, a polymerization initiator may be added.
As the polymerization initiator, any initiator generally used in radical polymerization can be used. Examples of the polymerization initiator include organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, t-amylperoxyisononanoate, and 1,1-di-t-butylperoxycyclohexane; and azo compounds such as 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and dimethyl-2,2'-azobisisobutyrate.
These may be used alone or in combination of two or more.
These polymerization initiators may be added at any stage as long as the polymerization reaction is in progress.
The amount of the polymerization initiator added may be 0.01 to 1 part by mass, and preferably 0.05 to 0.5 part by mass, based on 100 parts by mass of the total amount of the monomers used in the polymerization.

In solution polymerization, it is important to reduce the dissolved oxygen concentration in the polymerization solution as much as possible. For example, the dissolved oxygen concentration is preferably 10 ppm or less.
The dissolved oxygen concentration can be measured, for example, using a dissolved oxygen meter DO Meter B-505 (manufactured by Iijima Electronics Co., Ltd.) Methods for reducing the dissolved oxygen concentration can be appropriately selected from a method of bubbling an inert gas into the polymerization solution, a method of repeatedly pressurizing a container containing the polymerization solution to about 0.2 MPa with an inert gas before polymerization and then releasing the pressure, a method of passing an inert gas through a container containing the polymerization solution, and the like.

In order to reduce the difference in the bound monomer composition in copolymers with different molecular weights, it is preferable to carry out polymerization while additionally adding some monomer units so that the monomer composition in the polymerization system during polymerization becomes as uniform as possible. For example, the type, amount and timing of additionally adding the monomer are adjusted so that the difference in the consumption rate of each monomer at the time when about 70% of the total amount of monomers finally added to the system is consumed is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less.
The consumption rate of a certain monomer at a certain point in time means the proportion of that monomer consumed in the polymerization reaction to the total amount of that monomer added, and the total amount of that monomer added includes both the monomer that has already been added at a certain point in time and the monomer that has not yet been added.

Furthermore, the polymerization is carried out so that the difference in final conversion rate between each monomer at the end of the polymerization is 10% or less, more preferably 5% or less, and even more preferably 3% or less.

The method for recovering the polymer from the polymerization liquid obtained by solution polymerization is not particularly limited, and examples thereof include a method in which the polymerization liquid is added to a liquid containing an excess amount of a poor solvent such as a hydrocarbon solvent or an alcohol solvent in which the polymerization product obtained by polymerization is not dissolved, followed by treatment with a homogenizer (emulsion dispersion), and then pretreatment such as liquid-liquid extraction or solid-liquid extraction is performed to separate the unreacted monomer from the polymerization liquid; or a method in which the polymerization solvent and unreacted monomer are separated via a step called a devolatilization step, and the polymerization product is recovered; and the like.
The devolatilization step refers to a step of removing volatile matters such as the polymerization solvent, residual monomers, and reaction by-products under heating and reduced pressure conditions.

Examples of the equipment used in the devolatilization step include a devolatilization apparatus consisting of a tubular heat exchanger and a devolatilization tank; thin-film evaporators such as Wiblen and Exeva manufactured by Kobelco Environmental Solutions Co., Ltd., and Contra and tilted blade Contra manufactured by Hitachi, Ltd.; and vented extruders having sufficient residence time and surface area to exhibit devolatilization performance.
A devolatilization step using a devolatilization apparatus that combines two or more of these devices can also be used.

The processing temperature in the devolatilizer is preferably 150 to 350°C, more preferably 170 to 300°C, and even more preferably 200 to 280°C. Setting the temperature at or above the lower limit temperature can suppress the remaining volatile matter, while setting the temperature at or below the upper limit temperature can suppress discoloration and decomposition of the resulting acrylic resin.

The degree of vacuum in the volatilizer is preferably in the range of 10 to 500 Torr, and more preferably in the range of 10 to 300 Torr. By setting the degree of vacuum to the upper limit or less, the amount of remaining volatile matter can be suppressed. Also, a degree of vacuum equal to or greater than the lower limit is practical for industrial implementation.
The treatment time is appropriately selected depending on the amount of remaining volatile matter, but in order to suppress coloration and decomposition of the resulting acrylic resin, the shorter the treatment time, the better.

The polymer recovered through the devolatilization step may be processed into pellets in a step called a granulation step.
In the granulation step, the molten resin may be extruded in the form of strands through a multi-hole die and processed into pellets by a cold cut method, an air hot cut method, or an underwater cut method.

When a vented extruder is used as the devolatilizer, the devolatilizer process may be combined with the granulation process.

Next, an example of a method for producing a methacrylic resin having a glutarimide structural unit (B-2) will be described.

First, a (meth)acrylic acid ester polymer is produced by polymerizing a (meth)acrylic acid ester such as methyl methacrylate. When an aromatic vinyl unit is to be included in the methacrylic resin having the glutarimide structural unit (B-2), a (meth)acrylic acid ester and an aromatic vinyl (e.g., styrene) are copolymerized to produce a (meth)acrylic acid ester-aromatic vinyl copolymer.

Next, an imidization reaction is carried out by reacting the (meth)acrylic acid ester polymer or the methacrylic acid ester-aromatic vinyl copolymer with an imidization agent (imidization step). This allows the production of a methacrylic resin having glutarimide structural units (B-2).

The imidizing agent is not particularly limited as long as it can generate the glutarimide structural unit (B-2) represented by the general formula (3) above.
Specifically, the imidizing agent may be ammonia or a primary amine. Examples of the primary amine include aliphatic hydrocarbon group-containing primary amines such as methylamine, ethylamine, n-propylamine, i-propylamine, n-butylamine, i-butylamine, tert-butylamine, and n-hexylamine; alicyclic hydrocarbon group-containing primary amines such as cyclohexylamine; and the like.
Of the above imidizing agents, ammonia, methylamine and cyclohexylamine are preferred from the standpoint of cost and physical properties, with methylamine being particularly preferred.

In this imidization step, the content of glutarimide structural units (B-2) in the resulting methacrylic resin having glutarimide structural units (B-2) can be adjusted by adjusting the ratio of the imidization agent added.

The method for carrying out the imidization reaction is not particularly limited, and a conventionally known method can be used. For example, the imidization reaction can be carried out using an extruder or a batch-type reaction tank.
The extruder is not particularly limited, but for example, a single screw extruder, a twin screw extruder, a multi-screw extruder, etc. can be used.
Among these, it is preferable to use a twin-screw extruder, which can promote mixing of the raw material polymer and the imidizing agent.
Examples of twin-screw extruders include non-intermeshing co-rotating, intermeshing co-rotating, non-intermeshing counter-rotating, and intermeshing counter-rotating.

The above-mentioned extruders may be used alone or in combination of a plurality of extruders connected in series.
It is particularly preferable to equip the extruder to be used with a vent port capable of reducing the pressure to below atmospheric pressure, since this makes it possible to remove the imidizing agent, by-products such as methanol, and monomers of the reaction.

In producing a methacrylic resin having a glutarimide structural unit (B-2), in addition to the above-mentioned imidization step, an esterification step of treating the carboxyl group of the resin with an esterification agent such as dimethyl carbonate can be included. In this case, a catalyst such as trimethylamine, triethylamine, or tributylamine can also be used in combination for the treatment.
The esterification step can be carried out, for example, by using an extruder or a batch reaction tank, in the same manner as in the imidization step.
For the purpose of removing excess esterifying agent, by-products such as methanol, or monomers, the apparatus used is preferably equipped with a vent port capable of reducing the pressure to atmospheric pressure or below.

The methacrylic resin that has been subjected to the imidization step and, if necessary, the esterification step is molten and extruded in the form of strands from an extruder equipped with a multi-hole die, and processed into pellets by a cold cut method, an in-air hot cut method, an underwater cut method, or the like.
In order to reduce the number of foreign matters in the resin, it is also preferable to use a method in which the methacrylic resin is dissolved in an organic solvent such as toluene, methyl ethyl ketone, or methylene chloride, the obtained methacrylic resin solution is filtered, and then the organic solvent is removed.

The imidization reaction is preferably carried out at 130 to 250°C, and more preferably at 150 to 230°C. The reaction time is preferably 10 minutes to 5 hours, and more preferably 30 minutes to 2 hours. After the imidization process, an esterification process is carried out as necessary, followed by a devolatilization and granulation process.

Hereinafter, a method for producing a methacrylic resin containing a lactone ring structural unit (B-3) as the structural unit (B) having a ring structure in the main chain will be described in detail.
In the present embodiment, the method for producing the methacrylic resin having the lactone ring structural unit (B-3) in the main chain is preferably solution polymerization using a solvent in order to promote the cyclization reaction. Here, the lactone ring structural unit (B-3) may be formed by a cyclization reaction after polymerization.

Examples of the polymerization solvent to be used include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; and ketones such as methyl ethyl ketone and methyl isobutyl ketone.
These solvents may be used alone or in combination of two or more.
The amount of the solvent during polymerization is not particularly limited as long as the polymerization proceeds and gelation can be suppressed. For example, the amount of the solvent is preferably 50 to 200 parts by mass, and more preferably 100 to 200 parts by mass, assuming that the total amount of the monomers to be blended is 100 parts by mass.
In order to sufficiently suppress gelation of the polymerization liquid and promote the cyclization reaction after polymerization, it is preferable to carry out the polymerization so that the concentration of the produced polymer in the reaction mixture obtained after polymerization is 50 mass % or less.
It is also preferable to appropriately add the polymerization solvent to the reaction mixture to control the amount to 50 mass% or less. The method for appropriately adding the polymerization solvent to the reaction mixture is not particularly limited, and for example, the polymerization solvent may be added continuously or intermittently. The polymerization solvent to be added may be a single solvent of only one type or a mixed solvent of two or more types.

There are no particular limitations on the polymerization temperature as long as the polymerization proceeds at that temperature, but from the viewpoint of productivity, a temperature of 50 to 200°C is preferable, and a temperature of 80 to 180°C is more preferable.

The polymerization time is not particularly limited as long as the desired conversion rate is achieved, but from the viewpoint of productivity, etc., it is preferably 0.5 to 10 hours, and more preferably 1 to 8 hours.

In this embodiment, the polymerization conversion rate at the end of polymerization of the methacrylic resin having a lactone ring structural unit (B-3) in the main chain may be the polymerization conversion rate disclosed in the method for preparing the methacrylic resin having the structural unit (B-1) derived from the N-substituted maleimide monomer.

During the polymerization reaction, a chain transfer agent may be added as necessary.
As the chain transfer agent, a chain transfer agent used in general radical polymerization can be used. For example, the chain transfer agents disclosed in the preparation method of the methacrylic resin having the structural unit (B-1) derived from the N-substituted maleimide monomer can be used.
These may be used alone or in combination of two or more.
These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and there are no particular limitations on the addition stage.
The amount of the chain transfer agent to be added is not particularly limited as long as it is within a range in which a desired degree of polymerization can be obtained under the polymerization conditions used, but is preferably 0.01 to 1 part by mass, and more preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the total amount of the monomers to be used in the polymerization.

The dissolved oxygen concentration in the polymerization solution may be, for example, the value disclosed in the method for preparing a methacrylic resin having structural units (B-1) derived from the N-substituted maleimide monomer.

During the polymerization reaction, a polymerization initiator may be added.
The polymerization initiator is not particularly limited, but for example, the polymerization initiators disclosed in the method for preparing the methacrylic resin having the structural unit (B-1) derived from the N-substituted maleimide monomer can be used.
These polymerization initiators may be used alone or in combination of two or more kinds.
The amount of the polymerization initiator to be added may be appropriately set depending on the combination of monomers, reaction conditions, and the like, and is not particularly limited. When the total amount of the monomers to be used in the polymerization is taken as 100 parts by mass, the amount may be 0.01 to 1 part by mass, and preferably 0.05 to 0.5 parts by mass.

In the polymerization of the methacrylic resin having the lactone ring structural unit (B-3) in this embodiment, a polymerization initiator and, if necessary, a monomer are added during the polymerization, and the amounts added are controlled, whereby it is possible to reduce fluctuations in the ratio of the monomer concentration to the radical concentration in the system during the polymerization, suppress the generation of low molecular weight components at the end of the polymerization, and improve colorability and moldability.
The methacrylic resin having the lactone ring structural unit (B-3) in this embodiment can be obtained, for example, by carrying out a cyclization reaction after the completion of the polymerization reaction. Therefore, it is preferable to subject the polymerization reaction liquid to the lactone cyclization reaction while it contains the solvent, without removing the polymerization solvent from the polymerization reaction liquid.
When the copolymer obtained by polymerization is heat-treated, a cyclization condensation reaction occurs between the hydroxyl groups (hydroxyl groups) and the ester groups present in the molecular chain of the copolymer, forming a lactone ring structure.
In the heat treatment for forming the lactone ring structure, a reaction apparatus equipped with a vacuum device or a volatilizing device, an extruder equipped with a volatilizing device, or the like can be used to remove alcohol that may be by-produced by the cyclocondensation.

When forming the lactone ring structure, a heat treatment may be carried out using a cyclization condensation catalyst, if necessary, in order to promote the cyclization condensation reaction.
Specific examples of the cyclization condensation catalyst include monoalkyl phosphite esters, dialkyl esters, or triesters of phosphites such as methyl phosphite, ethyl phosphite, phenyl phosphite, dimethyl phosphite, diethyl phosphite, diphenyl phosphite, trimethyl phosphite, and triethyl phosphite; monoalkyl phosphate esters, dialkyl esters, or trialkyl esters of phosphates such as methyl phosphate, ethyl phosphate, 2-ethylhexyl phosphate, octyl phosphate, isodecyl phosphate, lauryl phosphate, stearyl phosphate, isostearyl phosphate, dimethyl phosphate, diethyl phosphate, di-2-ethylhexyl phosphate, diisodecyl phosphate, dilauryl phosphate, distearyl phosphate, diisostearyl phosphate, trimethyl phosphate, triethyl phosphate, triisodecyl phosphate, trilauryl phosphate, tristearyl phosphate, and triisostearyl phosphate; and the like.
These may be used alone or in combination of two or more.

The amount of the cyclization condensation catalyst used is not particularly limited, but is, for example, preferably 0.01 to 3 parts by mass, more preferably 0.05 to 1 part by mass, per 100 parts by mass of the methacrylic resin.
If the amount of the catalyst used is less than 0.01 parts by mass, the reaction rate of the cyclocondensation reaction may not be sufficiently improved, whereas if the amount of the catalyst used is more than 3 parts by mass, the resulting polymer may be colored or crosslinked, making melt molding difficult.

The timing of adding the cyclization condensation catalyst is not particularly limited, and for example, it may be added at the beginning of the cyclization condensation reaction, or during the reaction, or it may be added at both times.
When the cyclization condensation reaction is carried out in the presence of a solvent, it is also preferable to simultaneously carry out devolatilization.
The apparatus used when the cyclocondensation reaction and the devolatilization step are carried out simultaneously is not particularly limited, but a devolatilization apparatus consisting of a heat exchanger and a devolatilization tank, an extruder equipped with a vent, or an apparatus in which a devolatilization apparatus and an extruder are arranged in series is preferable, and a twin-screw extruder equipped with a vent is more preferable.
The vented twin-screw extruder used is preferably one having a plurality of vent ports.

When a vented extruder is used, the reaction temperature is preferably 150 to 350° C., more preferably 200 to 300° C. If the reaction temperature is less than 150° C., the cyclization condensation reaction may be insufficient, resulting in a large amount of residual volatile matter. Conversely, if the reaction temperature exceeds 350° C., the resulting polymer may become discolored or decomposed.
When a vented extruder is used, the degree of vacuum is preferably 10 to 500 Torr, more preferably 10 to 300 Torr. If the degree of vacuum exceeds 500 Torr, volatile matter may easily remain. Conversely, if the degree of vacuum is less than 10 Torr, industrial implementation may be difficult.

When the above cyclization condensation reaction is carried out, it is also preferred to add an alkaline earth metal and/or amphoteric metal salt of an organic acid during granulation in order to deactivate the remaining cyclization condensation catalyst.
Examples of the alkaline earth metal and/or amphoteric metal salt of an organic acid that can be used include calcium acetylacetate, calcium stearate, zinc acetate, zinc octoate, and zinc 2-ethylhexylate.

After the cyclocondensation reaction step, the methacrylic resin is molten and extruded in the form of strands from an extruder equipped with a multi-hole die, and processed into pellets by a cold cut method, an in-air hot cut method, or an underwater cut method.
The lactonization for forming the lactone ring structural unit (B-3) may be carried out after the production of the resin and before the production of the resin composition (described later), or may be carried out during the production of the resin composition, together with melt-kneading of the resin and components other than the resin.

In this embodiment, the methacrylic resin having a ring structure in the main chain preferably has at least one ring structural unit selected from the group consisting of structural units (B-1) derived from N-substituted maleimide monomers, glutarimide structural units (B-2), and lactone ring structural units (B-3). Among these, it is particularly preferable to have structural units (B-1) derived from N-substituted maleimide monomers, since this makes it easy to highly control optical properties such as the photoelastic coefficient without blending with other thermoplastic resins.

-Additives-
The resin composition containing the methacrylic resin having a ring structure in the main chain according to this embodiment may contain various additives within the range that does not significantly impair the effects of the present invention.
The additives are not particularly limited, and examples thereof include antioxidants, light stabilizers such as hindered amine light stabilizers, ultraviolet absorbers, release agents, other thermoplastic resins, softeners/plasticizers such as paraffinic process oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane, and mineral oil, flame retardants, antistatic agents, inorganic fillers such as organic fibers and pigments such as iron oxide, reinforcing agents such as glass fibers, carbon fibers, and metal whiskers, colorants, organic phosphorus compounds such as phosphites, phosphonites, and phosphate esters, other additives, and mixtures thereof.

--Antioxidants--
The resin composition containing the methacrylic resin having a ring structure in the main chain according to this embodiment preferably contains an antioxidant that suppresses deterioration and coloration during molding or use.
The antioxidant is not limited to the following, but examples thereof include hindered phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. The methacrylic resin of the present embodiment is suitably used in various applications such as melt extrusion, injection molding, and film molding. The heat history during processing varies depending on the processing method, ranging from about several tens of seconds in an extruder to several tens of minutes to several hours in the molding processing of thick-walled products and sheet molding.
When subjected to a long-term heat history, it is necessary to increase the amount of heat stabilizer added in order to obtain the desired heat stability. From the viewpoint of suppressing bleed-out of the heat stabilizer and preventing the film from sticking to the roll during film formation, it is preferable to use multiple types of heat stabilizers in combination, for example, it is preferable to use at least one selected from a phosphorus-based antioxidant and a sulfur-based antioxidant in combination with a hindered phenol-based antioxidant.
These antioxidants may be used alone or in combination of two or more.

Examples of the hindered phenol-based antioxidant include, but are not limited to, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the like. , 3,3',3'',5,5',5''-hexa-tert-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis(dodecylthiomethyl)-o-cresol, ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene bis[ 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris[(4-tert-butyl-3-hydroxy-2,6-xylin)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2 ,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamine)phenol, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate, and the like.
Particularly preferred are pentaerythritol terakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate.

In addition, as the hindered phenol-based antioxidant as the antioxidant, a commercially available phenol-based antioxidant may be used. Examples of such commercially available phenol-based antioxidants include, but are not limited to, Irganox 1010 (Irganox 1010: pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by BASF), Irganox 1076 (Irganox 1076: octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, manufactured by BASF), Irganox 1330 (Irganox 1330: octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, manufactured by BASF), and Irganox 1330 (Irganox 1330: octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, manufactured by BASF). 1330: 3,3',3'',5,5',5''-hexa-t-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol, manufactured by BASF Corporation), Irganox 3114 (Irganox 3114: 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, manufactured by BASF Corporation), Irganox 3125 (Irganox 3125, manufactured by BASF), Adeka STAB AO-60 (pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by ADEKA), Adeka STAB AO-80 (3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, manufactured by ADEKA), Sumilizer BHT (Sumilizer BHT, manufactured by Sumitomo Chemical), Cyanox 1790 (Cyanox 1790, manufactured by Cytec), Sumilizer GA-80 (Sumilizer GA-80, manufactured by Sumitomo Chemical), Sumilizer GS (Sumilizer Examples of the acrylate copolymer include GS (2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, manufactured by Sumitomo Chemical), Sumilizer GM (2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate, manufactured by Sumitomo Chemical), and Vitamin E (manufactured by Eisai).
Among these commercially available phenol-based antioxidants, Irganox 1010, Adeka STAB AO-60, Adeka STAB AO-80, Irganox 1076, Sumilizer GS, and the like are preferred from the viewpoint of the effect of imparting thermal stability to the resin.
These may be used alone or in combination of two or more.

Examples of the phosphorus-based antioxidant as the antioxidant include, but are not limited to, tris(2,4-di-t-butylphenyl)phosphite, bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl)ethyl ester phosphorous acid, tetrakis(2,4-di-t-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methyl phenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, tetrakis(2,4-t-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonite, di-t-butyl-m-cresyl-phosphonite, 4-[3-[(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphepin)-6-yloxy]propyl]-2-methyl-6-tert-butylphenol, and the like.
Furthermore, a commercially available phosphorus-based antioxidant may be used as the phosphorus-based antioxidant. Examples of such commercially available phosphorus-based antioxidants include, but are not limited to, Irgafos 168 (Irgafos 168: tris(2,4-di-t-butylphenyl)phosphite, manufactured by BASF), Irgafos 12 (Irgafos 12: tris[2-[[2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphen-6-yl]oxy]ethyl]amine, manufactured by BASF), Irgafos 38 (Irgafos 38: bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl)ethyl ester phosphorous acid, manufactured by BASF), and ADK STAB 329K (ADK STAB 329K). STAB-229K, manufactured by ADEKA), ADK STAB PEP-36 (ADK STAB PEP-36, manufactured by ADEKA), ADK STAB PEP-36A (ADK STAB PEP-36A, manufactured by ADEKA), ADK STAB PEP-8 (ADK STAB PEP-8, manufactured by ADEKA), ADK STAB HP-10 (ADK STAB HP-10, manufactured by ADEKA), ADK STAB 2112 (ADK STAB 2112, manufactured by ADEKA), ADK STAB 1178 (ADKA STAB 1178, manufactured by ADEKA), ADK STAB 1500 (ADK STAB 1500, manufactured by ADEKA) Sandstab Examples of such an agent include P-EPQ (manufactured by Clariant), Weston 618 (manufactured by GE), Weston 619G (manufactured by GE), Ultranox 626 (manufactured by GE), Sumilizer GP (4-[3-[(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphepin)-6-yloxy]propyl]-2-methyl-6-tert-butylphenol, manufactured by Sumitomo Chemical Co., Ltd.), and HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, manufactured by Sanko Co., Ltd.).
Among these commercially available phosphorus-based antioxidants, from the viewpoint of the effect of imparting thermal stability to the resin and the effect of using them in combination with various types of antioxidants, Irgafos 168, ADK STAB PEP-36, ADK STAB PEP-36A, ADK STAB HP-10, and ADK STAB 1178 are preferred, and ADK STAB PEP-36A and ADK STAB PEP-36 are particularly preferred.
These phosphorus-based antioxidants may be used alone or in combination of two or more kinds.

In addition, examples of the sulfur-based antioxidant as the antioxidant include, but are not limited to, 2,4-bis(dodecylthiomethyl)-6-methylphenol (Irganox 1726, manufactured by BASF Corporation), 2,4-bis(octylthiomethyl)-6-methylphenol (Irganox 1520L, manufactured by BASF Corporation), 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1 ,3-diylbis[3-dodecylthio]propionate] (ADEKA STAB AO-412S, manufactured by ADEKA Corporation), 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diylbis[3-dodecylthio]propionate] (ChemiNox PLS, manufactured by Chemipro Chemical Co., Ltd.), and di(tridecyl) 3,3'-thiodipropionate (AO-503, manufactured by ADEKA Corporation).
Among these commercially available sulfur antioxidants, Adeka STAB AO-412S and Cheminox PLS are preferred from the viewpoints of the effect of imparting thermal stability to the resin, the effect of using them in combination with various types of antioxidants, and ease of handling.
These sulfur-based antioxidants may be used alone or in combination of two or more kinds.

The content of the antioxidant may be an amount that provides the effect of improving thermal stability. If the content is excessive, problems such as bleeding out during processing may occur, so the content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, even more preferably 0.8 parts by mass or less, even more preferably 0.01 to 0.8 parts by mass, and particularly preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of methacrylic resin.

There are no particular limitations on the timing of adding the antioxidant, and examples of the antioxidant include adding it to the monomer solution before polymerization and then initiating polymerization, adding it to the polymer solution after polymerization and mixing it and then subjecting it to the devolatilization step, adding it to the molten polymer after devolatilization and mixing it and then pelletizing it, and adding it and mixing it when the pellets after devolatilization and pelletization are melt-extruded again. Among these, from the viewpoint of preventing thermal deterioration and coloration in the devolatilization step, it is preferable to add the antioxidant to the polymer solution after polymerization and mix it, add it before the devolatilization step, and then subject it to the devolatilization step.

--Hindered amine light stabilizer--
The resin composition according to the present embodiment that contains a methacrylic resin having a ring structure in the main chain may contain a hindered amine light stabilizer.
The hindered amine light stabilizer is not particularly limited, but is preferably a compound containing three or more ring structures. Here, the ring structure is preferably at least one selected from the group consisting of an aromatic ring, an aliphatic ring, an aromatic heterocycle, and a non-aromatic heterocycle, and when one compound has two or more ring structures, they may be the same or different from each other.

Examples of the hindered amine light stabilizer include, but are not limited to, bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate, a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidylsebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, N ,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-N,N'-diformylhexamethylenediamine, polycondensation product of dibutylamine/1,3,5-triazine/N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{2,2,6,6-tetramethyl- 4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, 1,2,2,6,6-pentamethyl-4-piperidiol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5. reaction product of 2,2,6,6-tetramethyl-4-piperidiol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol, reaction product of 2,2,6,6-tetramethyl-4-piperidiol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol, bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, and 2,2,6,6-tetramethyl-4-piperidyl methacrylate.
Among these, bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, a polycondensate of dibutylamine, 1,3,5-triazine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine, and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, and poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl} Preferred are {2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], a reaction product of 1,2,2,6,6-pentamethyl-4-piperidiol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol, and a reaction product of 2,2,6,6-tetramethyl-4-piperidiol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol.

The content of the hindered amine light stabilizer may be an amount that provides the effect of improving light stability. If the content is excessive, problems such as bleeding out during processing may occur, so the content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, even more preferably 0.8 parts by mass or less, even more preferably 0.01 to 0.8 parts by mass, and particularly preferably 0.01 to 0.5 parts by mass, relative to 100 parts by mass of the methacrylic resin.

--Ultraviolet absorbing agent--
The resin composition according to the present embodiment that contains a methacrylic resin having a ring structure in the main chain may contain an ultraviolet absorber.
The ultraviolet absorbent is not particularly limited, but is preferably an ultraviolet absorbent having a maximum absorption wavelength of 280 to 380 nm, and examples thereof include benzotriazole-based compounds, benzotriazine-based compounds, benzophenone-based compounds, oxybenzophenone-based compounds, benzoate-based compounds, phenol-based compounds, oxazole-based compounds, cyanoacrylate-based compounds, and benzoxazinone-based compounds.

Benzotriazole compounds include 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-benzotriazol-2-yl-4,6-di-tert-butylphenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-t-butylphenol, 2-(2H-benzotriazol-2-yl)-4,6-di-t-butylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1 ,3,3-tetramethylbutyl)phenol, 2-(2H-benzotriazol-2-yl)-4-methyl-6-(3,4,5,6-tetrahydrophthalimidylmethyl)phenol, methyl 3-(3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate/polyethylene glycol 300 reaction products, 2-(2H-benzotriazol-2-yl)-6-(linear and side chain dodecyl)-4-methylphenol, 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-C7-9 side chain and straight chain alkyl esters.
Among these, benzotriazole-based compounds having a molecular weight of 400 or more are preferred. Examples of commercially available products include Kemisorb (registered trademark) 2792 (manufactured by Chemipro Chemicals), Adeka STAB (registered trademark) LA31 (manufactured by ADEKA Corporation), and Tinuvin (registered trademark) 234 (manufactured by BASF).

Benzotriazine compounds include 2-mono(hydroxyphenyl)-1,3,5-triazine compounds, 2,4-bis(hydroxyphenyl)-1,3,5-triazine compounds, and 2,4,6-tris(hydroxyphenyl)-1,3,5-triazine compounds. Specific examples of the benzotriazine compounds include 2,4-diphenyl-6-(2-hydroxy-4-methoxyphenyl)-1,3,5-triazine, 2,4-diphenyl-6-(2-hydroxy-4-ethoxyphenyl)-1,3,5-triazine, 2,4-diphenyl-(2-hydroxy-4-propoxyphenyl)-1,3,5-triazine, and 2,4-diphenyl-6-(2-hydroxy-4-methoxyphenyl)-1,3,5-triazine. 1-(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine, 2,4-diphenyl-6-(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine, 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine, 2,4-diphenyl-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2,4-diphenyl-6-(2-hydroxy-4-dodecyloxyphenyl)-1,3,5-triazine, 2,4-diphenyl-6-(2-hydroxy-4-benzyloxyphenyl)-1,3,5-triazine , 2,4-diphenyl-6-(2-hydroxy-4-butoxyethoxy)-1,3,5-triazine, 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3-5-triazine, 2,4,6-tris(2-hydroxy-4-methoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-ethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-propoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine , 2,4,6-tris(2-hydroxy-4-butoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-dodecyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-benzyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-ethoxyethoxyphenyl)-1,3,5-triazine, 2 ,4,6-tris(2-hydroxy-4-butoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-propoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-methoxycarbonylpropyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-ethoxycarbonylethyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-(1-(2-ethoxyhexyloxy)-1-oxopropan-2-yloxy)phenyl)-1,3,5-triazine azine, 2,4,6-tris(2-hydroxy-3-methyl-4-methoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-ethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-propoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4- 2,4,6-tris(2-hydroxy-3-methyl-4-hexyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-octyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-dodecyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-benzyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-ethoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyethoxyphenyl)-1 ,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-propoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-methoxycarbonylpropyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-ethoxycarbonylethyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-(1-(2-ethoxyhexyloxy)-1-oxopropan-2-yloxy)phenyl)-1,3,5-triazine, and the like.
As the benzotriazine-based compound, commercially available products may be used, such as Kemisorb 102 (manufactured by Chemipro Chemicals), LA-F70 (manufactured by ADEKA Corporation), LA-46 (manufactured by ADEKA Corporation), TINUVIN 405 (manufactured by BASF), TINUVIN 460 (manufactured by BASF), TINUVIN 479 (manufactured by BASF), and TINUVIN 1577FF (manufactured by BASF).
Among these, ultraviolet absorbers having a 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-alkyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine skeleton (wherein "alkyloxy" refers to a long-chain alkyloxy group such as octyloxy, nonyloxy, decyloxy, etc.) are more preferably used because of their high compatibility with acrylic resins and excellent ultraviolet absorbing properties.

As ultraviolet absorbents, benzotriazole-based compounds and benzotriazine-based compounds having a molecular weight of 400 or more are preferred from the viewpoints of compatibility with resins and volatility when heated, and benzotriazine-based compounds are particularly preferred from the viewpoint of suppressing decomposition of the ultraviolet absorbent itself due to heating during extrusion processing.

The melting point (Tm) of the ultraviolet absorber is preferably 80° C. or higher, more preferably 100° C. or higher, even more preferably 130° C. or higher, and even more preferably 160° C. or higher.
The ultraviolet absorber preferably has a weight loss rate of 50% or less, more preferably 30% or less, even more preferably 15% or less, even more preferably 10% or less, and even more preferably 5% or less, when heated from 23° C. to 260° C. at a rate of 20° C./min.

These ultraviolet absorbents may be used alone or in combination of two or more.
By using two types of ultraviolet absorbents having different structures in combination, ultraviolet rays in a wide wavelength range can be absorbed.

The content of the UV absorber is not particularly limited as long as it does not impair heat resistance, moist heat resistance, thermal stability, and moldability and exerts the effects of the present invention, but is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass or less, more preferably 0.25 to 3 parts by mass, and even more preferably 0.3 to 3 parts by mass, relative to 100 parts by mass of methacrylic resin. When it is within this range, an excellent balance of UV absorption performance, moldability, etc. is achieved.

--Release agent--
The resin composition containing the methacrylic resin having a ring structure in the main chain of the present embodiment may contain a release agent. Examples of the release agent include, but are not limited to, fatty acid esters, fatty acid amides, fatty acid metal salts, hydrocarbon lubricants, alcohol lubricants, polyalkylene glycols, carboxylate esters, and hydrocarbon paraffin mineral oils.

The fatty acid ester that can be used as the release agent is not particularly limited, and any of the conventionally known fatty acid esters can be used.
Examples of fatty acid esters that can be used include ester compounds of fatty acids having 12 to 32 carbon atoms, such as lauric acid, palmitic acid, heptadecanoic acid, stearic acid, oleic acid, arachic acid, and behenic acid, with monohydric aliphatic alcohols, such as palmityl alcohol, stearyl alcohol, and behenyl alcohol, and polyhydric aliphatic alcohols, such as glycerin, pentaerythritol, dipentaerythritol, and sorbitan; and complex ester compounds of fatty acids, polybasic organic acids, and monohydric aliphatic alcohols or polyhydric aliphatic alcohols.
Examples of such fatty acid ester lubricants include cetyl palmitate, butyl stearate, stearyl stearate, stearyl citrate, glycerin monocaprylate, glycerin monocaprate, glycerin monolaurate, glycerin monopalmitate, glycerin dipalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, glycerin monooleate, glycerin dioleate, glycerin trioleate, glycerin monolinoleate, and the like. glycerin monobehenate, glycerin mono 12-hydroxystearate, glycerin di-12-hydroxystearate, glycerin tri-12-hydroxystearate, glycerin diacetomonostearate, glycerin citrate fatty acid ester, pentaerythritol adipic acid stearate, partially saponified montanic acid ester, pentaerythritol tetrastearate, dipentaerythritol hexastearate, and sorbitan tristearate.
These fatty acid ester-based lubricants may be used alone or in combination of two or more.
Examples of commercially available products include the Rikemal series, Poem series, Rikestar series, and Rikemaster series manufactured by Riken Vitamin Co., Ltd., and the Excel series, Leo D'or series, Exepar series, and Coconard series manufactured by Kao Corporation. More specific examples include Rikemal S-100, Rikemal H-100, Poem V-100, Rikemal B-100, Rikemal HC-100, Rikemal S-200, Poem B-200, Rikestar EW-200, Rikestar EW-400, Excel S-95, and Leo D'or MS-50.

There are also no particular limitations on the fatty acid amide-based lubricant, and any of the conventionally known lubricants can be used.
Examples of fatty acid amide lubricants include saturated fatty acid amides such as lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide; unsaturated fatty acid amides such as oleic acid amide, erucic acid amide, and ricinoleic acid amide; substituted amides such as N-stearyl stearic acid amide, N-oleyl oleic acid amide, N-stearyl oleic acid amide, N-oleyl stearic acid amide, N-stearyl erucic acid amide, and N-oleyl palmitic acid amide; methylol amides such as methylol stearic acid amide and methylol behenic acid amide; methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, and ethylene bisstearic acid amide (ethylene saturated fatty acid bisamides such as ethylene bisstearylamide, ethylene bisisostearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene bishydroxystearic acid amide, N,N'-distearyl adipamide, and N,N'-distearyl sebacic acid amide; unsaturated fatty acid bisamides such as ethylene bisoleic acid amide, hexamethylene bisoleic acid amide, N,N'-dioleyl adipamide, and N,N'-dioleyl sebacic acid amide; and aromatic bisamides such as m-xylylene bisstearic acid amide and N,N'-distearyl isophthalic acid amide.
These fatty acid amide-based release agents may be used alone or in combination of two or more.
Examples of commercially available products include the Diamid series (manufactured by Nippon Kasei Chemical Industry Co., Ltd.), the Amide series (manufactured by Nippon Kasei Chemical Industry Co., Ltd.), the Nikka Amide series (manufactured by Nippon Kasei Chemical Industry Co., Ltd.), the Methylol Amide series, the Bis Amide series, the Slipax series (manufactured by Nippon Kasei Chemical Industry Co., Ltd.), the Kaowax series (manufactured by Kao Corporation), the Fatty Acid Amide series (manufactured by Kao Corporation), and ethylene bis stearic acid amides (manufactured by Dainichi Chemical Industry Co., Ltd.).

The fatty acid metal salt refers to a metal salt of a higher fatty acid, and examples thereof include lithium stearate, magnesium stearate, calcium stearate, calcium laurate, calcium ricinoleate, strontium stearate, barium stearate, barium laurate, barium ricinoleate, zinc stearate, zinc laurate, zinc ricinoleate, zinc 2-ethylhexoate, lead stearate, dibasic lead stearate, lead naphthenate, calcium 12-hydroxystearate, and lithium 12-hydroxystearate. Among these, calcium stearate, magnesium stearate, and zinc stearate are particularly preferred because the resulting transparent resin composition has excellent processability and extremely excellent transparency.
Examples of commercially available products include the SZ series, SC series, SM series, and SA series manufactured by Sakai Chemical Industry Co., Ltd.
When the fatty acid metal salt is used, its content is preferably 0.2% by mass or less relative to 100% by mass of the resin composition containing the methacrylic resin having a ring structure in the main chain, from the viewpoint of maintaining transparency.

The above release agents may be used alone or in combination of two or more.

The release agent to be used is preferably one having a decomposition onset temperature of 200° C. or higher. Here, the decomposition onset temperature can be measured based on the 1% mass loss temperature by TGA.
The content of the release agent may be an amount that can obtain the effect as a release agent, and if the content is excessive, problems such as bleed-out during processing and extrusion failure due to screw slippage may occur, so the content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, even more preferably 0.8 parts by mass or less, even more preferably 0.01 to 0.8 parts by mass, and particularly preferably 0.01 to 0.5 parts by mass, relative to 100 parts by mass of the methacrylic resin. When the release agent is added in an amount within the above range, the decrease in transparency due to the addition of the release agent is suppressed, and there is a tendency for release failure during injection molding and sticking to a metal roll during sheet molding to be suppressed, which is preferable.

--Other thermoplastic resins--
The resin composition according to the present embodiment containing a methacrylic resin having a ring structure in the main chain may also contain other thermoplastic resins in addition to the methacrylic resin, as long as the object of the present invention is not impaired.
Other thermoplastic resins include, for example, polyacrylates such as polybutyl acrylate; styrene-based polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene block copolymer; and further, for example, acrylic rubber particles having a 3-4 layer structure described in JP-A-59-202213, JP-A-63-27516, JP-A-51-129449, JP-A-52-56150, etc.; rubbery polymers disclosed in JP-B-60-17406 and JP-A-8-245854; methacrylic rubber-containing graft copolymer particles obtained by multistage polymerization described in WO 2014-002491; and the like.
Among these, from the viewpoint of obtaining good optical properties and mechanical properties, rubber-containing graft copolymer particles having, on their surface layer, a graft portion made of a composition compatible with a styrene-acrylonitrile copolymer or a methacrylic resin containing a structural unit (B) having a ring structure in the main chain, are preferred.
The average particle size of the above-mentioned acrylic rubber particles, methacrylic rubber-containing graft copolymer particles, and rubber polymer is preferably 0.03 to 1 μm, and more preferably 0.05 to 0.5 μm, from the viewpoint of improving the impact strength and optical properties of a molded article obtained from the composition of this embodiment.

The content of the other thermoplastic resin is preferably 0 to 50 parts by mass, more preferably 0 to 25 parts by mass, based on 100 parts by mass of the methacrylic resin.

(Method for producing a resin composition containing a methacrylic resin having a ring structure in the main chain)
Examples of methods for producing a resin composition containing a methacrylic resin having a ring structure in the main chain include a method of kneading using a kneader such as an extruder, a heated roll, a kneader, a roller mixer, or a Banbury mixer. Among these, kneading using an extruder is preferred in terms of productivity. The kneading temperature may be in accordance with the preferred processing temperature of the polymer constituting the methacrylic resin or the other resin to be mixed, and is generally in the range of 140 to 300°C, preferably 180 to 280°C. In addition, it is preferable to provide a vent port in the extruder in order to reduce volatile content.

(Glass transition temperature of resin composition containing methacrylic resin having a ring structure in the main chain)
The glass transition temperature (Tg) of the resin composition of the present embodiment is preferably higher than 120° C. and not higher than 160° C.
If the glass transition temperature of the resin composition exceeds 120° C., it is possible to more easily obtain sufficient heat resistance as a transparent molded body for optical elements. From the viewpoint of dimensional stability under the temperature of the usage environment, the glass transition temperature (Tg) is more preferably 125° C. or higher, and further preferably 130° C. or higher.
On the other hand, when the glass transition temperature (Tg) of the resin composition is 160° C. or lower, melt processing at extremely high temperatures can be avoided, thermal decomposition of the resin, etc. can be suppressed, and a good product can be obtained. For the reasons described above, the glass transition temperature (Tg) is preferably 150° C. or lower.
The glass transition temperature (Tg) can be determined by measuring in accordance with JIS-K7121. Specifically, it can be measured by the method described in the examples below.

(Photoelastic coefficient of resin composition containing methacrylic resin having a ring structure in the main chain)
The photoelastic coefficient C of the resin composition of this embodiment is preferably −3.0×10 ⁻¹² to +3.0×10 ⁻¹² Pa ⁻¹ , more preferably −2.0×10 ⁻¹² to +2.0×10 ⁻¹² Pa ⁻¹ , and even more preferably −1.0×10 ⁻¹² to +1.0×10 ⁻¹² Pa ⁻¹ . When the photoelastic coefficient C is within the above range, the optical resin composition has excellent transparency, low birefringence, and high heat resistance, and can be suitably used for applications requiring high optical properties among optical elements.
The photoelastic coefficient is described in various documents (for example, see Chemical Review, No. 39, 1998 (published by the Academic Society Publishing Center)) and is defined by the following formulas (ia) and (ib). It can be seen that the closer the value of the photoelastic coefficient C is to zero, the smaller the change in birefringence due to an external force is.
C=Δn/σ...(e)
Δn=nx-ny...(f)
(In the formula, C is the photoelastic coefficient, σ is the stretching stress, Δn is the birefringence, nx is the refractive index in the stretching direction, and ny is the refractive index in the in-plane direction perpendicular to the stretching direction.)
If the absolute value of the photoelastic coefficient C of the resin composition of this embodiment is 3.0×10 ⁻¹² Pa ⁻¹ or less, birefringence caused by stress generated when the injection molded article is fitted into a product as a part becomes sufficiently small.
Specifically, the photoelastic coefficient C of the resin composition can be determined by the method described in the Examples below.

(Method for producing transparent molded article for optical element)
The method for producing the transparent molded body for optical elements of the present embodiment can use various molding methods such as extrusion molding, injection molding, compression molding, calendar molding, inflation molding, blow molding, etc. Among these, it is preferable to apply injection molding and injection compression molding from the viewpoint of productivity.
Typically, injection molding consists of: (1) an injection process in which resin is melted and the molten resin is filled into a temperature-controlled mold cavity; (2) a pressure holding process in which pressure is applied to the cavity until the gate is sealed, and an amount of resin is injected equivalent to the amount of molten resin filled in the injection process that comes into contact with the mold, cools, and shrinks; (3) a cooling process in which, after the pressure holding is released, the molded body is held until the resin is cooled; and (4) the mold is opened and the cooled molded body is removed.

In this case, the molding temperature is preferably in the range of Tg+100° C. to Tg+160° C., and more preferably in the range of Tg+110° C. to Tg+150° C., based on the glass transition temperature of the resin composition containing the methacrylic resin having a ring structure in the main chain. Here, the molding temperature refers to the controlled temperature of the band heater wrapped around the injection nozzle.
The mold temperature is preferably in the range of Tg-70°C to Tg, more preferably in the range of Tg-50°C to Tg-20°C, based on the glass transition temperature (Tg) of the resin composition containing a methacrylic resin having a ring structure in the main chain.

The injection speed can be appropriately selected depending on the thickness and dimensions of the injection molded article to be obtained, and can be appropriately selected, for example, from the range of 200 to 1000 mm/sec.
The pressure for holding can be appropriately selected depending on the shape of the injection molded article to be obtained, and can be appropriately selected, for example, within the range of 30 to 120 MPa. In the case of a thin-walled molded article with a fast solidification speed, holding pressure may not be applied.
The pressure for holding the pressure referred to here is the pressure maintained by a screw for further feeding the molten resin from a gate after the molten resin has been filled.

Injection compression molding is an injection molding method in which the mold is opened slightly before the start of injection molding, and molten resin is filled into the mold at high speed and low pressure. After that, the mold clamping pressure is increased at high speed and a compression and holding pressure process is added to uniformly hold the pressure over the entire surface of the resin. This makes it possible to mold molded articles with excellent surface and optical properties.
When attempting to obtain a thinner injection molded article, for example one having a thickness of less than 1 mm and a diagonal dimension of more than 100 mm, it is particularly preferable to employ injection compression molding, since this method produces a molded article with excellent optical properties and color tone.

In addition, when the injection molded article obtained using the resin composition containing the methacrylic resin having a ring structure in the main chain is used as a light guide plate, the surface may be molded with fine irregularities. By providing such fine irregularities, it is preferable because it is not necessary to provide a reflective layer by separate printing or the like. The fine irregularities are not particularly limited, but examples include irregularities with clear structural units such as rectangular parallelepiped, cylindrical, elliptical cylinder, triangular prism, sphere, aspheric surface, etc., irregularities with a matte or hairline shape but with unclear structural units or combinations thereof, and irregularities with clear structural units but with changes in shape, particularly size. Examples of the shape of the irregularities include a height or recess of 0.1 to 500 μm, and a pitch distance between the irregularities of 10 to 1000 μm.

The methacrylic resin having a ring structure in the main chain of this embodiment and various molded articles using the resin composition thereof can be further subjected to surface functionalization treatments such as anti-reflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, and gas barrier treatment.

(Applications of transparent molded bodies for optical elements)
According to the transparent molded article for optical elements of this embodiment, not only is it possible to highly reduce bright spot foreign matter that becomes bright spots due to diffuse reflection, but it is also possible to obtain a molded article containing a methacrylic resin composition that is excellent in transparency and heat resistance and has highly controlled birefringence, and the molded article can be suitably used for applications such as optical components in household products, office automation equipment, AV equipment, battery electrical equipment parts, lighting equipment, automobiles, etc.
Examples of optical components in household products, office automation equipment, AV equipment, battery-powered electrical equipment parts, lighting equipment, and the like include light guide plates, display front panels, and touch panels used in displays of smartphones, PDAs, tablet PCs, liquid crystal televisions, and the like, as well as lenses for smartphones and tablet PC cameras, and optical lens parts for head-mounted displays and liquid crystal projectors, such as prism elements, waveguides, and lenses, and particularly optical lenses having a small, thin, irregular thickness shape, optical fibers, coating materials for optical fibers, lenses, Fresnel lenses, phase plates equipped with microlens arrays, and optical cover parts.
Examples of optical members for automobiles and the like include light guide plates for in-vehicle displays; in-vehicle meter panels; optical members for head-up displays such as front panels, combiners, and optical cover parts for car navigation systems; in-vehicle camera lenses, light guide rods, and the like.
In addition to the above, the present invention can also be preferably used as a camera focusing screen, or as a component for a digital signage display device that displays information on a thin display connected to a network for the purpose of publicity, advertising, etc., in places such as outdoors, in stores, public institutions, and transportation facilities.

The present invention will be specifically described below with reference to examples and comparative examples. Note that the present invention is not limited to the following examples.

<1. Measurement of polymerization conversion rate>
A part of the polymerization solution in each of the examples and comparative examples was collected, and the amount of monomer remaining in this polymerization solution sample was measured by dissolving the sample in chloroform to prepare a 5% by mass solution, adding n-decane as an internal standard substance, and measuring the concentration of the monomer remaining in the sample using gas chromatography (GC-2010 manufactured by Shimadzu Corporation) to determine the total mass (a) of the monomer remaining in the polymerization solution. The polymerization conversion rate (%) was calculated from this total mass (a), the total mass (b) assuming that all the monomers added up to the time when the sample was collected remained in the polymerization solution, and the total mass (c) of the monomers to be added up to the end of the polymerization step, according to the formula (b-a)/c x 100.

2. Analysis of structural units
The structural units of the produced methacrylic resin having a ring structure in the main chain were identified by ¹ H-NMR measurement and ¹³ C-NMR measurement, and the amount of each was calculated. The measurement conditions for ¹ H-NMR measurement and ¹³ C-NMR measurement were as follows.
・Measuring equipment: Bruker DPX-400
Measurement solvent: CDCl ₃ or DMSO-d ₆
Measurement temperature: 40°C

<3. Measurement of molecular weight and molecular weight distribution>
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resins having a ring structure in the main chain produced in the examples and comparative examples described later were measured using the following apparatus and under the following conditions.
Measurement device: gel permeation chromatography (HLC-8320GPC) manufactured by Tosoh Corporation
Measurement conditions:
Column: One TSKguard column SuperH-H, two TSKgel SuperHM-M, and one TSKgel SuperH2500 were connected in series. Column temperature: 40° C.
Developing solvent: tetrahydrofuran, flow rate: 0.6 mL/min, and 0.1 g/L of 2,6-di-t-butyl-4-methylphenol (BHT) was added as an internal standard.
Detector: RI (differential refractive index) detector, detection sensitivity: 3.0 mV/min Sample: 0.02 g of methacrylic resin or 20 mL of tetrahydrofuran solution of methacrylic resin. Injection amount: 10 μL
Standard sample for calibration curve: The following ten types of polymethyl methacrylate (PMMA Calibration Kit MM-10, manufactured by Polymer Laboratories) having known monodisperse weight peak molecular weights and different molecular weights were used.
Weight peak molecular weight (Mp)
Standard sample 1 1,916,000
Standard sample 2 625,500
Standard sample 3 298,900
Standard sample 4 138,600
Standard sample 5 60,150
Standard sample 6 27,600
Standard sample 7 10,290
Standard sample 8 5,000
Standard sample 9 2,810
Standard sample 10 850
Under the above conditions, the RI detection intensity was measured versus the elution time of the methacrylic resin.
Based on the calibration curve obtained by measuring the standard samples for the calibration curve, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the methacrylic resin were determined.

<4. Glass transition temperature>
The glass transition temperature (Tg) (° C.) of the methacrylic resin having a ring structure in the main chain was measured in accordance with JIS-K7121.
First, from a sample that had been conditioned (left to stand at 23° C. for one week) under standard conditions (23° C., 65% RH), test pieces of about 10 mg each were cut out at four points (four locations).
Next, a differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer Japan Co., Ltd.) was used under the condition of a nitrogen gas flow rate of 25 mL/min, where the sample was heated from room temperature (23°C) to 200°C (first heating) at 10°C/min, held at 200°C for 5 minutes to completely melt the sample, then cooled from 200°C to 40°C at 10°C/min, held at 40°C for 5 minutes, and heated again under the above heating conditions (second heating). Among the DSC curves drawn during this period, the intersection point (midpoint glass transition temperature) between the step-like change partial curve during the second heating and a straight line equidistant in the vertical direction from each baseline extension line was measured as the glass transition temperature (Tg) (°C). Four points were measured per sample, and the arithmetic average (rounded off to the nearest whole number) of the four points was taken as the measured value.

<5. Measurement of composition distribution of structural units>
The methacrylic resins having a ring structure in the main chain obtained in the examples and comparative examples were subjected to molecular weight fractionation using the following apparatus and conditions.
Fractionation device: LC-908 manufactured by Japan Analytical Industry Co., Ltd.
・Isolation conditions:
Column: SHODEX K-2004
Eluent: chloroform, flow rate: 3 mL/min, detector: UV detector (254 nm)
Sample: 3% by mass chloroform solution. Fractionation method: 3 mL of the sample was injected, and fractions were collected at 1-minute intervals from elution time 18 to 43 minutes.
The fractionation operation was repeated three times, and a sample selected from the obtained fractions was subjected to determination of the composition ratio of structural units according to the above-mentioned <2. Analysis of structural units>, and the molecular weight distribution was measured according to <3. Measurement of molecular weight and molecular weight distribution>, and the peak top molecular weight (Mp) was calculated from the position of the apex of the peak.

<6. Measurement of bright spot foreign matter on transparent molded bodies>
For the four rectangular molded pieces obtained in the examples and comparative examples, a digital microscope manufactured by Keyence Corporation VHX-7000 was used to inspect for bright spot foreign matter in a dark field. The lens magnification was set to 80 times, and the width direction of the rectangular molded piece was perpendicular to the stage of the digital microscope, and the length direction of the rectangular molded piece was in the left-right direction of the digital microscope, so that the rectangular molded piece was placed on the digital microscope. Next, light was incident from an external light source on each of the two opposing 20 mm x 3 mm side surfaces of the rectangular molded piece to generate bright spots. Of the height (width) of the rectangular molded piece of 20 mm, a range of 16 mm excluding a range of 2 mm from the top and bottom surfaces as the surface part of the rectangular molded piece was taken as the inside of the rectangular molded piece, and depth synthesis was performed by imaging. Furthermore, the depth synthesis images obtained were linked for a total range of 50 mm from the center of the rectangular molded piece to 25 mm in the length direction.
As external lighting for generating bright spots, two blue LED lights (CCS Corporation's line LED light "LDL2-158X16BL2", peak emission wavelength 467 nm) were used. The blue LED light, the rectangular molded piece, and the blue LED light were arranged in a line at intervals of about 1 mm in order, with the 20 mm x 3 mm side surface facing the light-emitting surface of the blue LED light so that light was incident on each of the two opposing 20 mm x 3 mm side surfaces of the rectangular molded piece.
Furthermore, for each of the four rectangular molded pieces, bright spot foreign matter of 10 micrometers or more present in an area of 2.5 mm thickness × 16 mm width × 50 mm length in the connected depth composite image was counted and calculated as the number per ^cm3 volume.

<7. Measurement of photoelastic coefficient>
The methacrylic resin obtained in each of the examples and comparative examples was first formed into a press film using a vacuum compression molding machine to prepare an unstretched sample.
As specific sample preparation conditions, the methacrylic resin was placed in a 150 μm thick polyimide frame, sandwiched between two polyimide films and two iron plates, and set in a vacuum compression molding machine (manufactured by Shinto Metal Industries, SFV-30 type), preheated at 260 ° C. under reduced pressure (about 10 kPa) for 10 minutes, compressed at 260 ° C. and about 10 MPa for 5 minutes, and then transferred to a cooling compression molding machine for cooling and solidification after releasing the reduced pressure and press pressure. The obtained pressed film was aged for 24 hours or more in a constant temperature and humidity room adjusted to 23 ° C. and 50% humidity, and then used as an unstretched sample.
A film-like test piece with a width of 6 mm was cut out from this unstretched sample, and the photoelastic coefficient C (Pa ^-1 ) was measured using a birefringence measuring device described in detail in Polymer Engineering and Science 1999, 39, 2349-2357.
The film-like test piece was placed in a film tensioning device (manufactured by Imoto Manufacturing Co., Ltd.) similarly installed in a constant temperature and humidity chamber so that the distance between the chucks was 50 mm. Next, a birefringence measuring device (manufactured by Otsuka Electronics, RETS-100) was placed so that the optical path of the device was located at the center of the film, and the birefringence of the test piece was measured at a wavelength of 550 nm while applying a tensile stress with a distance between the chucks of 50 mm and a chuck movement speed of 0.1 mm/min.
From the relationship between the measured birefringence (Δn) and the tensile stress (σ), the slope of the line was determined by least squares approximation, and the photoelastic coefficient (C) (Pa ⁻¹ ) was calculated. Data for the tensile stress in the range of 2.5 MPa≦σ≦10 MPa was used for the calculation.
C = Δn/σ
Here, the birefringence (Δn) has the value shown below.
Δn=nx−ny
(nx: refractive index in the stretching direction, ny: refractive index in the in-plane direction perpendicular to the stretching direction)

8. Visibility Evaluation
The rectangular molded pieces obtained in the examples and comparative examples were visually evaluated for visibility under a white LED light applied from the side surface (20 mm x 3 mm surface) of the molded body. The evaluation results were judged as good visibility (◯) or poor visibility (×).

[Raw materials]
The raw materials used in the production examples described later are shown below.

[[monomer]]
Methyl methacrylate: manufactured by Asahi Kasei Corporation. N-Phenylmaleimide (phMI): manufactured by Nippon Shokubai Co., Ltd. N-Cyclohexylmaleimide (chMI): manufactured by Nippon Shokubai Co., Ltd.

[[Polymerization initiator]]
1,1-di(t-butylperoxy)cyclohexane: "Perhexa C" manufactured by NOF Corporation

[[Chain transfer agent]]
n-Octyl mercaptan: manufactured by Kao Corporation

[Example 1]
358.6 kg of methyl methacrylate (hereinafter referred to as MMA), 29.4 kg of N-phenylmaleimide (hereinafter referred to as phMI), 67.7 kg of N-cyclohexylmaleimide (hereinafter referred to as chMI), 0.77 kg of n-octyl mercaptan as a chain transfer agent, and 224.3 kg of meta-xylene (hereinafter referred to as mXy) were weighed out, and added to a 1.25 m3 reactor equipped with a jacketed temperature control device and a stirring blade, and the mixture was stirred to obtain a mixed monomer solution.
Next, 88.0 kg of MMA, 6.3 kg of phMI, and 142.4 kg of mXy were weighed and added to Tank 1 with stirring to obtain a mixed monomer solution for additional addition.
The liquid in the reactor was bubbled with nitrogen at a rate of 30 L/min for 1 hour, and the liquid in Tank 1 was bubbled with nitrogen at a rate of 10 L/min for 30 minutes to remove dissolved oxygen.
Thereafter, steam was blown into the jacket to raise the solution temperature in the reactor to 115° C., and polymerization was initiated by adding a polymerization initiator solution prepared by dissolving 0.487 kg of 1,1-di(t-butylperoxy)cyclohexane in 1.888 kg of mXy at a rate of 1.0 kg/hour while stirring at 50 rpm.
During the polymerization, the solution temperature in the reactor was controlled at 115±2° C. by adjusting the temperature with the jacket. Thirty minutes after the start of polymerization, the addition rate of the initiator solution was reduced to 0.5 kg/hour. Starting one hour after the start of polymerization, the entire amount of the additional mixed monomer solution was added from tank 1 at a constant rate over a period of four hours.
Furthermore, the addition rate of the initiator solution was reduced to 0.25 kg/hour 3.5 hours after the start of polymerization, and the addition was stopped 5 hours after the start of polymerization.
After 12 hours had elapsed since the start of polymerization, a polymer solution containing a methacrylic resin having structural units with a ring structure in the main chain was obtained.
The polymer solution was sampled 2 hours and 12 hours after the start of polymerization, and the polymerization conversion was analyzed from the remaining monomer concentration. The polymerization conversion after 2 hours was 78.9% MMA, 77.3% phMI, and 70.4% chMI, and after 12 hours it was 97.9% MMA, 99.4% phMI, and 99.3% chMI. Taking into account the monomers added after 2 hours from the start of polymerization, the polymerization conversion after 2 hours was converted as the consumption rate relative to the total amount of each monomer added by the end of polymerization, and was 67.2% MMA, 67.1% phMI, and 70.4% chMI.
This polymer solution was fed to a concentrator consisting of a tubular heat exchanger and a vaporizer previously heated to 250°C, and devolatilization was carried out. The degree of vacuum in the vaporizer was set to 10 to 15 Torr. The resin flowing down the vaporizer was discharged by a gear pump, extruded from a strand die, cooled with water, and pelletized to obtain a methacrylic resin. The environment in which the manufacturing equipment was located was a space controlled to a cleanliness level of Class 6 (ISO14644-1), and a bar-type ionizer was installed to neutralize the entire space.
The composition of the obtained pellet-like polymer was confirmed, and it was found that the structural units derived from the MMA, phMI and chMI monomers accounted for 81.0 mass %, 6.6 mass % and 12.4 mass %, respectively.
The weight average molecular weight was 108,000, and Mw/Mn was 2.04.
The glass transition temperature was 134°C.
The measurement results of the composition distribution of the structural units were Mp: 253,000 (MMA: 81.4 mass%, phMI: 6.5 mass%, chMI: 12.1 mass%), Mp: 176,000 (MMA: 81.1 mass%, phMI: 6.6 mass%, chMI: 12.3 mass%), Mp: 111,000 (MMA: 80.9 mass%, phMI: 6.7 mass%, chMI: 12.4 mass%), Mp: 88,000 (MMA: 80.8 mass%, phMI: 6.7 mass%, chMI: 12.5 mass%), and Mp: 48,000 (MMA: 80.4 mass%, phMI: 6.8 mass%, chMI: 12.8 mass%).
A press film was produced using the obtained methacrylic resin, and the photoelastic coefficient was evaluated, finding that it was −0.3×10 ⁻¹² Pa ⁻¹ .
Next, the obtained methacrylic resin was injection molded using an injection molding machine (EC-100SX manufactured by Toshiba Machine Co., Ltd.) and a strip mold having a side gate and a thickness of 3 mm x width of 20 mm x length of 220 mm at a cylinder temperature of 280°C and a mold temperature of 70°C to obtain a strip molded piece for measuring bright spot foreign matter.
The environment in which the injection molding machine was located was a space controlled to a cleanliness level of Class 6 (ISO14644-1). In particular, a bar-type ionizer was installed to eliminate static electricity from the entire space, and any foreign matter that had adhered to the packaging surface due to exposure to the external environment after pellet packaging was removed with an air gun equipped with a static elimination function before moving to the environment where molding was performed.
When the above-mentioned measurement of bright spots was carried out on four rectangular molded bodies, a total of seven bright spots of 10 μm or more were found. In other words, the number of bright spots per ^cm3 of volume was calculated to be 0.875/ ^cm3 .
In addition, when the visibility was evaluated, it was found to be good (◯).

[Example 2]
A methacrylic resin was prepared in the same manner as in Example 1, except that the polymer solution was purified by filtration through a polymer filter having a pore size of 10 μm.
Similarly, four rectangular molded products were measured for bright spots, and a total of six bright spots of 10 μm or more were found. The number of bright spots per cm ³ of volume was calculated to be 0.75/cm ³ .
In addition, when the visibility was evaluated, it was found to be good (◯).
The polymerization conversion rate, structural units, weight average molecular weight (Mw), molecular weight distribution (Mw/Mn), glass transition temperature, composition distribution of structural units, and photoelastic coefficient were the same as those in Example 1.

[Comparative Example 1]
In a general environment without a clean booth or the like, a methacrylic resin was produced from the same raw materials as in the polymerization recipe described in Example 1. In the injection molding using the obtained methacrylic resin, molding was performed in a space controlled to the same cleanliness as the clean environment described in Example 1.
The four obtained rectangular molded products were subjected to measurement of bright foreign points, and a total of 76 bright foreign points of 10 μm or more were found. The number of bright foreign points per cm ³ of volume was calculated to be 9.5/cm ³ .
Moreover, when the visibility was evaluated, it was found to be poor (×).
The polymerization conversion rate, structural units, weight average molecular weight (Mw), molecular weight distribution (Mw/Mn), glass transition temperature, composition distribution of structural units, and photoelastic coefficient were the same as those in Example 1.

[Comparative Example 2]
The methacrylic resin obtained in Comparative Example 1 was used to obtain a rectangular molded piece by injection molding in a general environment without a clean booth or the like.
The four obtained rectangular molded products were subjected to measurement of bright foreign particles, and a total of 192 bright foreign particles having a size of 10 μm or more were found. The number of bright foreign particles per cm ³ of volume was calculated to be 24 particles/cm ³ .
Moreover, when the visibility was evaluated, it was found to be poor (×).
The polymerization conversion rate, structural units, weight average molecular weight (Mw), molecular weight distribution (Mw/Mn), glass transition temperature, composition distribution of structural units, and photoelastic coefficient were the same as those in Example 1.

It can be seen that the transparent molded body for optical elements of the embodiment has a high degree of reduction in bright spot foreign matter and has good visibility.

The transparent molded article of the present invention in which bright spot foreign matter is highly reduced is used as an optical component in household goods, office automation equipment, AV equipment, battery-powered electrical equipment parts, lighting equipment, and the like, for example, light guide plates, display front panels, touch panels used in displays of smartphones, PDAs, tablet PCs, LCD televisions, and the like, as well as lenses for smartphones and tablet PC cameras, and optical lens components for head-mounted displays and LCD projectors, for example, prism elements, waveguides, lenses, and particularly small, thin-walled, irregular-thickness optical lenses, optical fibers, coating materials for optical fibers, lenses, Fresnel lenses, phase plates equipped with microlens arrays, optical cover components, and the like.
Examples of optical members for automobiles and the like include light guide plates for in-vehicle displays; in-vehicle meter panels; optical members for head-up displays such as front panels, combiners, and optical cover parts for car navigation systems; in-vehicle camera lenses, light guide rods, and the like.
In addition to the above, the present invention can also be preferably used as a camera focusing screen, or as a component for a digital signage display device that displays information on a thin display connected to a network for the purpose of publicity, advertising, etc., in places such as outdoors, in stores, public institutions, and transportation facilities.

Claims (1)

A method for producing a transparent molded article for optical elements, the method comprising the steps of: providing a transparent molded article for optical elements having a content of bright spot foreign matter having a size of 10 micrometers or more, which becomes a bright spot due to diffuse reflection when light is incident thereon, the content of which is 1 piece/ ^cm3 or less per unit volume;
A resin pellet manufacturing process, comprising: manufacturing and packaging resin pellets in an environment in which the space is controlled to a cleanliness level of Class 6 (ISO 14644-1) and in which a bar-type ionizer is installed to neutralize the entire space;
a molding step of a transparent molded body for optical elements, comprising removing foreign matter adhering to the packaging surface of the packaged resin pellets obtained in the manufacturing step of the resin pellets with an air gun equipped with a static elimination function, moving the packaged resin pellets to an environment that is a space controlled to a cleanliness level of Class 6 (ISO 14644-1) and that is equipped with a bar-type ionizer for static elimination in the entire space and an injection molding machine, and injection molding the transparent molded body for optical elements using the resin pellets with the injection molding machine.