JP7556809B2 - Pellet manufacturing method - Google Patents

Description

The present invention relates to a new method for producing pellets (resin pellets), etc.

Acrylic resins, such as polymethyl methacrylate (PMMA), are used as optical materials because of their high transparency. Among these acrylic resins, acrylic polymers with ring structures in the main chain are being developed because of their heat resistance. For example, Patent Document 1 discloses a copolymer having methyl (meth)acrylate units, methacrylic acid units, and glutaric anhydride units.

International Publication No. 2017/022393

The object of the present invention is to provide a novel method for producing pellets (resin pellets, resin composition) (and further, pellets themselves).

Another object of the present invention is to provide a new molding method (a method for manufacturing molded products).

As mentioned above, acrylic resins are widely used, and attempts are being made to introduce ring structures into acrylic resins from the standpoint of heat resistance, etc. It has been difficult to stably manufacture pellets of such acrylic resins using the strand method, etc. This tendency is particularly noticeable in acrylic resins that have a ring structure and are relatively hard and brittle.

In this situation, the present inventor obtained pellets of acrylic resin (particularly acrylic resin having a ring structure) by the hot-cut method, etc., but found that when such pellets (hot-cut pellets, etc.) are used for molding, the measurement in the molding machine (injection molding machine, etc.) becomes unstable, and appearance and molding defects (for example, silver streaks in molded products) are likely to occur.

That is, as shown in FIG. 1, a molding machine (such as an injection molding machine) typically includes a cylinder (cylinder section) 2, a nozzle section Hn equipped with a nozzle 1 connected to the front end of the cylinder 2, and a hopper 3 connected to the rear section H3 of the cylinder 2 for feeding molding material (such as resin pellets) into the cylinder 2.

The cylinder 2 contains a screw consisting of a front section (metering section) S1, a middle section (compression section) S2, and a rear section (supply section) S3, which correspond to the front section (metering section) H1, middle section (compression section) H2, and rear section (supply section) H3 of the cylinder 2 when the screw is pushed in (the screw is moved toward the nozzle).

Temperature measuring devices (thermocouples, etc.) 4 are installed in each part of the cylinder, and a cooling device (a cooling jacket such as a water-cooled jacket) H4 is installed around the rear part H3 of the cylinder (and further around the base end of H3, below the hopper 3) so as to surround its periphery (outer periphery). This cooling device H4 can also be called the cooling means (device) for the rear part H3 of the cylinder (or its base end, below the hopper).

The molding material is introduced and transported from hopper 3 and melted in cylinder 2. This molten molding material is then fed through nozzle 1 to a mold (not shown) to produce the desired molded body.

In this type of molding machine, as described above, molding material such as pellets is fed from hopper 3 to supply section H3 (S3). However, if the pellets (hot-cut pellets, etc.) are acrylic resin (particularly acrylic resin having a ring structure) (or a material containing said resin), it has been found that the weighing in weighing section S1 (H1) may become unstable.

The reason for this instability is unclear, but one possible reason is that for some reason (for example, the pellets cracking after being fed into the feed section (before melting)), it is difficult for the pellets to receive shear (by the screw) inside the cylinder, and the pellets are measured in the measuring section in an insufficiently melted state.

On the other hand, according to the inventor's research, it was found that when acrylic resins (especially acrylic resins having a ring structure) are used in injection molding, the frequency of occurrence of appearance and molding defects such as silver streaks, coloring or color tone (YI) varies depending on the injection molding conditions. The reason for this is also unclear, but some reason (for example, unstable weighing makes it difficult for gas to escape, or fluctuations in thermal history make it easier for gas to be generated by thermal decomposition, etc.) is thought to be one of the contributing factors.

In this situation, the present inventor discovered that a new method for producing pellets can be provided by specifying the pellet size, and that the pellets obtained by this method (e.g., hot-cut pellets) can improve the unstable metering (and even silver streaks) described above, even when an acrylic resin having a ring structure [particularly an acrylic resin having a relatively small Mw or a relatively large MFR or having a ring structure (e.g., a cyclic ester structure)] is used (and even when hot-cut pellets, etc. are used), and that silver streaks (and even unstable metering, etc.) can be improved by specifying the cooling conditions of the supply section in the injection molding machine (injection device) in relation to the physical properties of the molding material (resin) used, thereby completing the present invention.

That is, the present invention relates to the following inventions, etc.
[1]
A method for producing resin pellets, comprising the steps of:
The resin comprises an acrylic resin (A),
A method in which a resin is cut (so that the major axis is 4.5 mm or less) to produce pellets (resin pellets) having a major axis of 4.5 mm or less.
[2]
The method according to [1], wherein the acrylic resin (A) has a ring structure.
[3]
The method according to [1] or [2], wherein the acrylic resin (A) has a cyclic ester structure.
[4]
The method according to any one of [1] to [3], wherein the acrylic resin (A) (or resin) has a melt flow rate of 2 g/10 min or more at 230° C. under a load of 3.8 kg as determined in accordance with JIS K 7210.
[5]
The method according to any one of [1] to [4], wherein the weight average molecular weight of the acrylic resin (A) (or the resin) is 100,000 or less.
[6]
The method according to any one of [1] to [5], wherein the molecular weight distribution of the acrylic resin (A) (or the resin) is 2.5 or less.
[7]
The method according to any one of [1] to [6], wherein the acrylic resin (A) satisfies at least one of the following properties selected from a melt flow rate of 2 g/10 min or more at 230° C. under a load of 3.8 kg, a weight average molecular weight of 100,000 or less, and a molecular weight distribution of 2.5 or less, as determined in accordance with JIS K 7210, and has a cyclic ester structure.
[8]
The method according to any one of [1] to [7], wherein a molten resin is cut (hot cut).
[9]
The method according to any one of [1] to [8], wherein a resin extruded from a die of an extruder (extrusion die) is cut in a molten state (hot cut).
[10]
The method according to any one of [1] to [9], wherein the pellet has a minor axis of 4.5 mm or less.
[11]
The method according to any one of [1] to [10], wherein the pellet has a major axis and a minor axis of 4.0 mm or less.
[12]
The method according to any one of [1] to [11], wherein the pellet has a thickness of 3.5 mm or less.
[13]
The method according to any one of [1] to [12], wherein the pellets are for injection molding [for use in an injection molding machine (injection device)].
[14]
A pellet produced by any one of the methods according to [1] to [13].
[15]
A method for injection molding a resin (a method for producing a molded product by injection molding), comprising the steps of:
The resin comprises an acrylic resin (A),
When the temperature of a cooling device installed in the supply section (or below the hopper) of the cylinder of an injection molding machine (injection unit) is Tj (°C), and the glass transition temperature of the resin is Tg (°C), this method ensures that Tg - Tj (°C) is 80 or less.
[16]
The method according to [15], wherein the acrylic resin (A) has a ring structure.
[17]
The method according to [15] or [16], wherein the acrylic resin (A) has a cyclic ester structure.
[18]
The method according to any one of [15] to [17], wherein the acrylic resin (A) (resin (A)) has a melt flow rate of 2 g/10 min or more at 230° C. under a load of 3.8 kg as measured in accordance with JIS K 7210.
[19]
The method according to any one of [15] to [18], wherein the weight average molecular weight of the acrylic resin (A) is 100,000 or less.
[20]
The method according to any one of [15] to [19], wherein the molecular weight distribution of the acrylic resin (A) (or the resin) is 2.5 or less.
[21]
The method according to any one of [15] to [20], wherein the acrylic resin (A) has a cyclic ester structure.
[22]
The method according to any one of [15] to [21], wherein pellets having a major axis of 4.5 mm or less are used as the resin.
[23]
The method according to any one of [15] to [22], wherein Tg-Tj (°C) is 70 or less.
[24]
the acrylic resin (A) is an acrylic resin having a cyclic ester structure and satisfying at least one of the following: a melt flow rate of 2 g/10 min or more at 230° C. under a load of 3.8 kg, a weight average molecular weight of 100,000 or less, and a molecular weight distribution of 2.5 or less, all of which are in accordance with JIS K 7210;
The method according to any one of [15] to [23], wherein pellets having a major axis and a minor axis of 4.0 mm or less are used as the resin.
[25]
The method according to any one of [15] to [24], further comprising a pellet production step of producing resin pellets by the method according to any one of [1] to [13], and using the resin pellets obtained in the pellet production step as the resin.

According to one aspect of the present invention, a method for producing novel pellets (resin pellets, resin compositions) can be provided. In this method, the pellet size is adjusted to a specific size, and even if the resin constituting the pellet is an acrylic resin such as an acrylic resin having a ring structure (particularly an acrylic resin having a ring structure with a small Mw or a large MFR), the metering during molding can be efficiently stabilized (and silver streaks in the molded product can be efficiently prevented).

According to another aspect of the present invention, a new molding method (a method for manufacturing a molded product) can be provided. In this method, the cooling conditions during molding (in the molding machine) are adjusted to specific conditions in relation to the physical properties (glass transition temperature) of the resin used, and appearance or molding defects in molded products such as silver streaks (and even unstable weighing during molding) can be efficiently improved.

And according to these aspects of the present invention, pellets and molded products produced by the above-mentioned methods can also be provided.

FIG. 1 is a diagram (cross-sectional view) showing a general molding machine (injection molding machine, injection unit).

<Method of manufacturing pellets>
In one aspect of the present invention, a method for producing resin pellets is provided.

[resin]
The resin is not limited, but may usually contain at least an acrylic resin (sometimes referred to as acrylic resin (A) etc.). Such an acrylic resin may have a ring structure, as described later.
The acrylic resin is generally a thermoplastic resin (resin, polymer). The method for producing such an acrylic resin is not particularly limited, but the acrylic resin may be produced by the method described below.

The acrylic resin (A) may usually have (meth)acrylic acid ester units [units (structural units) derived from (meth)acrylic acid esters].

The (meth)acrylic acid ester constituting the (meth)acrylic acid ester unit is not particularly limited, and examples thereof include aliphatic (meth)acrylates [for example, (meth)acrylic acid alkyl esters (for example, C 1-18 alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, _butyl (meth)acrylate, etc.)], alicyclic (meth)acrylates [for example, (meth)acrylic acid cycloalkyl esters (for example, (meth)acrylic acid C _3-20 cycloalkyl esters such as cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, etc.), crosslinked cyclic (meth)acrylates (for example, isobornyl (meth)acrylate), etc.], aromatic (meth)acrylates [for example, (meth)acrylic acid aryl esters (for example, (meth)acrylic acid C _6-20 aryl esters such as phenyl (meth)acrylate, o-tolyl (meth)acrylate, etc.), (meth)acrylic acid aralkyl esters (for example, (meth)acrylic acid C _6-10 aryl esters such as benzyl (meth)acrylate, etc.), _1-4 alkyl), phenoxyalkyl (meth)acrylate (for example, phenoxy C _1-4 alkyl (meth)acrylate such as phenoxyethyl (meth)acrylate), and the like.

The (meth)acrylic acid ester also includes a (meth)acrylic acid ester having a substituent (for example, a hydroxy group, an alkoxy group, a glycidyl group, etc.). Examples of such a (meth)acrylic acid ester include a methacrylic acid ester having a hydroxy group [for example, a hydroxyalkyl (meth)acrylic acid ester (for example, a hydroxy C _1-12 alkyl (meth)acrylate such as 2-hydroxyethyl (meth)acrylate)], a (meth)acrylic acid ester having an alkoxy group [for example, an alkoxyalkyl (meth)acrylic acid ester (for example, a C _1-12 alkoxy C _1-12 alkyl methacrylate such as 2-methoxyethyl (meth)acrylate)], and a (meth)acrylic acid ester having a glycidyl group (for example, glycidyl (meth)acrylate).

The (meth)acrylic acid ester unit may be formed by using one or more types of (meth)acrylic acid ester in combination.

The (meth)acrylic acid ester units will vary depending on the desired physical properties, but it is particularly preferable for them to contain at least methacrylic acid ester units.

Examples of the methacrylic acid ester constituting the (meth)acrylic acid ester unit include aliphatic methacrylates [e.g., alkyl methacrylates (e.g., C 1-18 alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, heptyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, and octadecyl methacrylate, preferably C 1-18 alkyl methacrylates such as C _1-18 alkyl methacrylates, cycloalkyl methacrylates (e.g., cycloalkyl methacrylates (e.g., cyclopropyl methacrylate, cyclobutyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, and other cycloalkyl methacrylates, preferably C _3-20 cycloalkyl methacrylates, e.g., C _{1-12 alkyl} methacrylates, etc.); _3-12 cycloalkyl), bridged cyclic methacrylates (for example, isobornyl methacrylate, etc.), etc.], aromatic methacrylates [for example, methacrylic acid aryl esters (for example, phenyl methacrylate, o-tolyl methacrylate, m-tolyl methacrylate, p-tolyl methacrylate, 2,3-xylyl methacrylate, 2,4-xylyl methacrylate, 2,5-xylyl methacrylate, 2,6-xylyl methacrylate, 3,4-xylyl methacrylate, 3,5-xylyl methacrylate, 1-naphthyl methacrylate, 2-naphthyl methacrylate, binaphthyl methacrylate, anthryl methacrylate, etc., C _6-20 aryl methacrylate, preferably C _6-10 aryl methacrylate), methacrylic acid aralkyl esters (for example, C _6-10 aryl methacrylate, such as benzyl methacrylate, _1-4 alkyl), phenoxy alkyl methacrylate (for example, phenoxy C _1-4 alkyl methacrylate such as phenoxyethyl methacrylate), and the like.

From the viewpoint of improving transparency, among the methacrylic acid ester units, the (meth)acrylic acid ester unit preferably contains at least a methacrylic acid alkyl ester unit (for example, a methacrylic acid C _1-18 alkyl unit), and more preferably contains at least a methyl methacrylate unit.

The acrylic resin may contain units derived from other polymerizable monomers (monomers) than the (meth)acrylic acid ester units, as necessary. Examples of such other monomers include acid group-containing monomers (methacrylic acid, acrylic acid, etc.), styrene-based monomers [for example, styrene, vinyl toluene, styrenes having a substituent (for example, a halogen group, an alkoxy group, an alkyl group, a hydroxyl group, etc.) (for example, α-methylstyrene, chlorostyrene, etc.), styrenesulfonic acid or a salt thereof, etc.], vinyl esters (for example, vinyl acetate, etc.), unsaturated nitriles (for example, acrylonitrile, methacrylonitrile, etc.), olefin-based monomers (for example, C olefins such as ethylene, propylene, 1-butene, isobutylene, 1-octene, etc.), and the like. _2-10 alkenes), amide group-containing vinyl monomers [for example, (meth)acrylamide, N-substituted (meth)acrylamides (for example, N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide; N-cycloalkyl(meth)acrylamides such as N-cyclohexyl(meth)acrylamide; N-aryl(meth)acrylamides such as N-phenyl(meth)acrylamide; N-aralkyl(meth)acrylamides such as N-benzyl(meth)acrylamide, etc.)], 2-(hydroxymethyl)acrylic acid esters (for example, alkyl esters such as ethyl 2-(hydroxymethyl)acrylate), and the like.

The other monomers may be used alone or in combination with two or more other monomers to form units derived from the other monomers.

The content of (meth)acrylic acid ester units in the acrylic resin (or the constituent units of the acrylic resin) can be selected from the range of, for example, 10% by mass or more (e.g., 20% by mass or more), preferably 30% by mass or more (e.g., 35% by mass or more), more preferably 40% by mass or more (e.g., 45% by mass or more), and may be 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 80% by mass or more, etc.

When the acrylic resin contains methacrylic acid ester units, the content of the methacrylic acid ester units in the acrylic resin (or the constituent units of the acrylic resin) can be selected from a range of, for example, 10% by mass or more, and may be 20% by mass or more, preferably 30% by mass or more (e.g., 35% by mass or more), and more preferably 40% by mass or more (e.g., 45% by mass or more), or may be 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 80% by mass or more, etc.

When the acrylic resin contains methacrylic acid ester units, the content of the methacrylic acid ester units in the (meth)acrylic acid ester units may be, for example, 10% by mass or more (e.g., 20% by mass or more), preferably 30% by mass or more (e.g., 40% by mass or more), more preferably 50% by mass or more (e.g., 60% by mass or more), and may be 70% by mass or more, 80% by mass or more, 90% by mass or more, etc.

When the acrylic resin contains methacrylic acid alkyl ester units, the content of the methacrylic acid alkyl ester units in the (meth)acrylic acid ester units may be, for example, 10% by mass or more (e.g., 20% by mass or more), preferably 30% by mass or more (e.g., 40% by mass or more), more preferably 50% by mass or more (e.g., 60% by mass or more), and may be 70% by mass or more, 80% by mass or more, 90% by mass or more, etc.

When the acrylic resin contains methyl methacrylate units, the content of methyl methacrylate units in the (meth)acrylic acid ester units may be, for example, 10% by mass or more (e.g., 20% by mass or more), preferably 30% by mass or more (e.g., 40% by mass or more), and more preferably 50% by mass or more (e.g., 60% by mass or more), or may be 70% by mass or more, 80% by mass or more, 90% by mass or more, etc.

When the acrylic resin contains acrylic acid ester units, the content of the acrylic acid ester units in the acrylic resin may be relatively small from the viewpoint of heat resistance and refractive index, and may be selected, for example, from the range of less than 10% by mass (e.g., 8% by mass or less), preferably 5% by mass or less (e.g., 4% by mass or less), and more preferably 3% by mass or less (e.g., 2% by mass or less).

When the acrylic resin contains units derived from other polymerizable monomers, the content of the units in the acrylic resin is not particularly limited and can be selected appropriately. In particular, when an acid group-containing monomer is contained as the other polymerizable monomer, the content of the acid group-containing monomer units may be relatively low from the viewpoint of transparency, coloration, etc., and may be, for example, 10% by mass or less (e.g., 5% by mass or less), preferably 2% by mass or less (e.g., 1% by mass or less), and more preferably 0.5% by mass or less.

The acrylic resin (A) may have a ring structure. The ring structure is usually present in the main chain of the acrylic resin (polymer chain, acrylic polymer).
Acrylic resins having a ring structure (and furthermore, acrylic resins having a relatively large MFR and/or a relatively small Mw) appear to be significantly affected by pellet size with respect to metering, and therefore the present invention can be suitably applied thereto.

In addition, by having a ring structure in the acrylic resin, various physical properties [for example, heat resistance, moist heat resistance, yellowing resistance, hardness (strength), solvent resistance, surface hardness, barrier properties against oxygen and water vapor, optical properties, dimensional stability, shape stability, etc.] can be imparted, improved or enhanced in the acrylic resin.
In addition, since the acrylic resin has a ring structure, it is possible to efficiently produce a molded article (for example, a lens) having a thinner film thickness than polymethyl methacrylate or the like.

Specific examples of ring structures include cyclic imide structures (e.g., structures derived from N-substituted maleimide monomers, glutarimide structures, etc.), cyclic amide structures (e.g., lactam structures, etc.), cyclic ester structures (e.g., lactone ring structures, etc.), and acid anhydride structures (e.g., structures derived from maleic anhydride monomers, glutaric anhydride structures).

The ring structure may in particular be a non-anhydride structure [e.g., a ring structure that is not a structure derived from maleic anhydride monomer, a glutaric anhydride structure, etc. (e.g., a cyclic imide structure, a cyclic amide structure, a cyclic ester structure, etc.)].

The acrylic resin may have one or more ring structures. When the acrylic resin has two or more ring structures, the two or more ring structures may be ring structures of the same type (e.g., two or more cyclic imide structures, etc.) or ring structures of different types (e.g., a combination of a cyclic imide structure and a lactone structure, etc.).

Examples of glutarimide structures and glutaric anhydride structures include structures represented by the following formula (1):

(In the formula, ^R1 and ^R2 are each independently a hydrogen atom or an alkyl group, ^R3 is a hydrogen atom or a substituent, and ^X1 is an oxygen atom or a nitrogen atom. When ^X1 is an oxygen atom, n=0, and when ^X1 is a nitrogen atom, n=1.)

In R ¹ and R ² of formula (1), examples of the alkyl group include C _1-8 alkyl groups (e.g., methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, n-hexyl group, isohexyl group, n-heptyl group, isoheptyl group, n-octyl group, 2-ethylhexyl group, etc.).

R ¹ and R ² are particularly preferably a hydrogen atom or a C _1-4 alkyl group.

In ^R3 of formula (1), examples of the substituent include a hydrocarbon group.
Examples of the hydrocarbon group include an aliphatic group, an alicyclic group, an aromatic group, etc. The hydrocarbon group may further have a substituent such as a halogen.

In R ³ of formula (1), examples of the aliphatic group include C _1-10 alkyl groups (e.g., methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, n-hexyl group, isohexyl group, n-heptyl group, isoheptyl group, n-octyl group, 2-ethylhexyl group, etc.). Of these alkyl groups, C _1-4 alkyl groups, particularly methyl group, are preferred.

In ^R3 of formula (1), examples of the alicyclic group include a _C3-12 cycloalkyl group (e.g., a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, etc.). Of these cycloalkyl groups, a _C3-7 cycloalkyl group, in particular a cyclohexyl group, is preferred.

In R ³ of formula (1), examples of the aromatic group include a C _6-20 aromatic group [for example, a C _6-20 aryl group (e.g., a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 2,3-xylyl group, a 2,4-xylyl group, a 2,5-xylyl group, a 2,6-xylyl group, a 3,4-xylyl group, a 3,5-xylyl group, a 1-naphthyl group, a 2-naphthyl group, a binaphthyl group, an anthryl group, etc.), a C _7-20 aralkyl group (e.g., a benzyl group, etc.)]. Among these aromatic groups, a phenyl group and a tolyl group are preferred.

Typically, in formula (1), R ¹ and R ² are each independently a hydrogen atom or a methyl group, R ³ may be a C _1-10 alkyl group, a C _3-12 cycloalkyl group, or a C _6-20 aromatic group, preferably, R ¹ and R ² are each independently a hydrogen atom or a methyl group, R ³ may be a C _1-4 alkyl group, a C _3-7 cycloalkyl group, a C _6-20 aryl group, or a C _7-20 aralkyl group, more preferably, R ¹ and R ² are each independently a hydrogen atom or a methyl group, R ³ may be a methyl group, a cyclohexyl group, a phenyl group, or a tolyl group, most preferably, R ¹ and R ² are each independently a hydrogen atom or a methyl group, R ³ may be a cyclohexyl group or a phenyl group. From the viewpoint of suppressing coloration of the acrylic polymer, R ³ may be a hydrogen atom, a methyl group, or a cyclohexyl group, and from the viewpoint of improving the strength of the molded body, R ³ may be a hydrogen atom or a methyl group.

The ring structure may have one or more structures represented by formula (1).

In particular, when the ring structure has a structure represented by formula (1), it preferably has a glutarimide structure which is a cyclic non-anhydride structure (that is, a structure in which X ¹ in formula (1) is a nitrogen atom).

In addition, a glutaric anhydride structure (i.e., a structure in which ^X1 is an oxygen atom in formula (1)) may be hydrolyzed or have an increased acid value, which may reduce water resistance or hot water resistance or cause fluctuations in optical properties. Therefore, it may be preferable that the ring structure does not substantially have a glutaric anhydride structure, or contains only a small amount of the glutaric anhydride structure.

Examples of structures derived from maleimide monomers (particularly N-substituted maleimide monomers) and maleic anhydride monomers include the structure represented by the following formula (2).

(In the formula, R ⁴ and R ⁵ are each independently a hydrogen atom or a methyl group, R ⁶ is a hydrogen atom or a substituent, and X ² is an oxygen atom or a nitrogen atom. When X ² is an oxygen atom, n=0, and when X ² is a nitrogen atom, n=1.)

In R ⁶ of formula (2), examples of the substituent include a hydrocarbon group.
Examples of the hydrocarbon group include aliphatic groups {for example, alkyl groups [for example, C1-6 alkyl groups such as _C1-6 linear alkyl groups (for example, methyl group, ethyl group, etc.), _C1-6 branched alkyl groups (for example, _isopropyl group, etc.)], etc.}, alicyclic groups (for example, _C3-20 cycloalkyl groups such as cyclopentyl group, cyclohexyl group, etc.), aromatic groups {for example, _C6-20 aromatic groups [for example, _C7-20 aralkyl groups (for example, benzyl group, etc.), _C6-20 aryl groups (for example, phenyl group, etc.)]}, etc. The hydrocarbon group may further have a substituent such as a halogen.

When ^X2 is an oxygen atom, the ring structure represented by formula (2) is a structure derived from a maleic anhydride monomer.

On the other hand, when ^X2 is a nitrogen atom, the ring structure represented by formula (2) is a structure derived from an N-substituted maleimide monomer.

In formula (2), when ^X2 is a nitrogen atom, preferably, ^R4 and ^R5 are each independently a hydrogen atom, and ^R6 is a _C3-20 cycloalkyl group or a _C6-20 aromatic group, more preferably, ^R4 and ^R5 are each independently a hydrogen atom, and ^R6 is a cyclohexyl group, a benzyl group, or a phenyl group. From the viewpoint of suppressing coloration of the acrylic polymer, ^R6 may be a hydrogen atom, a methyl group, or a cyclohexyl group, and from the viewpoint of improving the strength of a molded article, ^R6 may be a hydrogen atom or a methyl group.

The ring structure may have one or more structures represented by formula (2).

In particular, when the ring structure has a structure represented by formula (2), it preferably has a structure derived from a maleimide monomer which is a cyclic non-anhydride structure (i.e., a structure in which ^X2 in formula (2) is a nitrogen atom).

In the above formula (2), when ^X2 is an oxygen atom (and n=0), the above formula (2) becomes a structure derived from a maleic anhydride monomer. Such a structure derived from a maleic anhydride monomer may be hydrolyzed or have an increased acid value, which may reduce water resistance or hot water resistance or cause fluctuations in optical properties. Therefore, it may be preferable that the ring structure does not substantially have a structure derived from a maleic anhydride monomer, or contains only a small amount of such a structure.

The lactone ring (cyclic ester) structure is not particularly limited and may be, for example, a 4- to 8-membered ring, but a 5- or 6-membered ring is preferred, and a 6-membered ring is more preferred, due to the excellent stability of the ring structure.

The lactone ring structure may be, for example, a structure disclosed in JP 2004-168882 A, and examples thereof include the structure represented by the following formula (3).

(In the formula, R ⁷ , R ⁸ and R ⁹ are each independently a hydrogen atom or a substituent.)

In the formula (3), examples of the substituent include organic residues such as hydrocarbon groups.
Examples of the hydrocarbon group include aliphatic groups (for example, _C1-20 alkyl groups such as methyl group, ethyl group, and propyl group, and _C2-20 unsaturated aliphatic hydrocarbon groups such as ethenyl group and propenyl group), aromatic groups (for example, _C6-20 aromatic hydrocarbon groups such as phenyl group and naphthyl group), and the like.

The hydrocarbon group may contain an oxygen atom, and one or more hydrogen atoms may be substituted with at least one type of group selected from a hydroxyl group, a carboxyl group, an ether group, and an ester group.

In formula (3), preferably, R ⁹ may be a hydrogen atom or a methyl group, and R ⁷ and R ⁸ may each independently be a hydrogen atom or a C _1-20 alkyl group, and more preferably, R ⁹ may be a hydrogen atom or a methyl group, and R ⁷ and R ⁸ may each independently be a hydrogen atom or a methyl group.

The ring structure may contain one or more structures represented by formula (3).

The lactam ring structure is not particularly limited, and examples thereof include a pyrrolidinone ring structure represented by the following formula (4).

The pyrrolidinone ring structure has a five-membered amide ring structure (cyclic amide structure) as the basic skeleton. This cyclic amide structure is also a five-membered lactam structure (γ-lactam structure). Having a pyrrolidinone ring structure in the main chain means that at least one of the five atoms that make up the basic skeleton of the five-membered pyrrolidinone ring structure, typically the three carbon atoms that do not make up an amide bond (-N(R)CO-), is located in the main chain of the polymer and forms the main chain.

(In the formula, R ¹⁰ to R ¹² are each independently a hydrogen atom or a substituent.)

In the formula (4), examples of the substituent for R ¹⁰ include a hydrocarbon group or a —NHCOR ¹³ group (R ¹³ is a hydrogen atom or a hydrocarbon group).

Examples of the hydrocarbon group in R ¹⁰ or R ¹³ include an aliphatic group, an alicyclic group, and an aromatic group.
Examples of the aliphatic group include C _1-18 alkyl groups (for example, C _1-18 straight-chain or branched alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl groups).
Examples of alicyclic groups include C _3-18 cycloalkyl groups (eg, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc.).
Examples of aromatic groups include C _6-20 aromatic groups [for example, C _6-20 aryl groups (for example, phenyl, tolyl, xylyl, naphthyl, anthryl, etc.), C _7-20 aralkyl groups (for example, benzyl, etc.)].

As R ¹⁰ , a hydrogen atom, a C _1-18 linear alkyl group (eg, a methyl group, etc.) and the like are particularly preferable.
Furthermore, particularly preferred examples of R ¹³ include a hydrogen atom, a C _1-18 linear alkyl group (preferably a C _1-12 linear alkyl group, more preferably a C _1-4 linear alkyl group, etc.), a C _6-20 aryl group (for example, a phenyl group, etc.), a C _3-18 cycloalkyl group (preferably a C _3-12 cycloalkyl group, more preferably a C _3-6 cycloalkyl group, etc.), etc.

In the formula (4), examples of the substituent for R ¹¹ include a -COOR ¹⁴ group (R ¹⁴ is a hydrogen atom or a hydrocarbon group).

Examples of the hydrocarbon group for R ¹⁴ include the hydrocarbon groups exemplified for R ¹⁰ or R ¹³ .
Moreover, particularly preferred embodiments of R ¹⁴ are the same as those of R ¹³ .

In the formula (4), examples of the substituent for R ¹² include a -COR ¹⁵ group (R ¹⁵ is a hydrogen atom or a hydrocarbon group).

Examples of the hydrocarbon group for R ¹⁵ include the hydrocarbon groups exemplified for R ¹⁰ or R ¹³ .
Moreover, particularly preferred embodiments of R ¹⁵ are the same as those of R ¹³ .

The ring structure of the acrylic resin may be appropriately selected depending on the desired physical properties (e.g., heat resistance, hardness (strength), solvent resistance, surface hardness, oxygen and water vapor barrier properties, optical properties, dimensional stability, shape stability, etc.). For example, from the viewpoint of heat resistance, etc., the ring structure may preferably include a lactone ring structure or a cyclic imide structure (e.g., a structure derived from an N-substituted maleimide monomer, a glutarimide structure, etc.).

In addition, from the viewpoint of water resistance, hot water resistance, etc., the ring structure may preferably contain a cyclic non-anhydride structure [for example, a lactone ring structure, a cyclic imide structure (particularly a glutarimide structure, or a structure derived from an N-substituted maleimide monomer)].

Furthermore, from the viewpoint of surface hardness, solvent resistance, barrier properties, optical properties, etc., the ring structure may preferably contain a lactone ring structure, a glutarimide structure, etc.

In particular, the ring structure may contain at least one ring structure selected from a cyclic imide structure (in particular, a glutarimide structure or a structure derived from an N-substituted maleimide monomer) and a lactone ring structure, and among these, may contain at least a lactone ring structure.
Acrylic resins having a lactone ring (cyclic ester) structure appear to be prone to unstable weighing (for example, the pellet size has a large effect on weighing), and the present invention can be suitably applied thereto.

The content of the ring structure can be selected according to the application, desired physical properties, etc., and is not particularly limited. For example, it can be selected from a range of about 0.1% by mass or more (e.g., 0.5% by mass or more) in the acrylic resin, and may be 1% by mass or more, preferably 3% by mass or more, and more preferably 5% by mass or more, and may be 10% by mass or more, 15% by mass or more, 20% by mass or more, 22% by mass or more, 25% by mass or more, etc.

The content ratio of the ring structure (or its upper limit) is not particularly limited, and may be, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, etc., in the acrylic resin.

A high content of ring structures is preferable in terms of heat resistance, hardness (strength), solvent resistance, surface hardness, dimensional stability, etc.

These upper and lower limits may be appropriately combined to set an appropriate range (e.g., 1-70% by mass, 3-60% by mass, 5-60% by mass, 5-50% by mass, etc.) (the same applies to other range descriptions).

In particular, when the acrylic resin has a glutarimide structure, the content of the glutarimide structure may be preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and may be 90% by mass or less, preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

When the acrylic resin has a structure derived from an N-substituted maleimide monomer, the content of the structure derived from the N-substituted maleimide monomer may be, for example, 5 to 90% by mass, preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 10 to 30% by mass.

When the acrylic resin has a lactone ring structure, the content of the lactone ring structure may be, for example, 1 to 80% by mass, preferably 3 to 70% by mass, and more preferably 5 to 60% by mass (e.g., 10 to 50% by mass), and may also be 15% by mass or more (e.g., 18 to 55% by mass), 20% by mass or more (e.g., 23 to 50% by mass), 25% by mass or more (e.g., 26 to 45% by mass, 28 to 40% by mass, etc.), etc.

When the acrylic resin has a lactam ring structure, the content of the lactam ring structure may be, for example, about 1 to 80% by mass, preferably about 5 to 70% by mass, and more preferably about 10 to 50% by mass.

The content of the ring structure may be, for example, 1 to 80% by mass, preferably 3 to 70% by mass, and more preferably 5 to 60% by mass (e.g., 10 to 50% by mass), or may be a relatively high content, for example, 10% by mass or more [e.g., 13 to 60% by mass, 15% by mass or more (e.g., 18 to 55% by mass), 20% by mass or more (e.g., 23 to 50% by mass), 25% by mass or more (e.g., 26 to 45% by mass, 28 to 40% by mass, etc.)].

By introducing a ring structure into the acrylic resin at a relatively high content, it is possible to efficiently obtain a resin (molded product) having extremely excellent heat resistance (for example, high glass transition temperature) and moist heat resistance.
On the other hand, as the content of ring structures increases, it may easily lead to unstable weighing (for example, the effect of pellet size on weighing becomes greater), and from this viewpoint, an acrylic resin having a relatively large number of ring structures (for example, having ring structures in a proportion of 10 mass % or more, 15 mass % or more, 20 mass % or more, etc.) may be preferably used.

In the present invention, even if the acrylic resin contains a high proportion of ring structures (e.g., ring structures that include at least a lactone ring structure), coloring (yellowing) can be effectively suppressed.

The proportion of ring structures in the acrylic resin can be determined by a conventional method depending on the type of ring structure, etc. For example, the proportion of cyclic ester structures (lactone ring structures) may be determined based on the dealcoholization reaction rate, and the proportion of non-cyclic ester structures (e.g., cyclic imide structures, cyclic amide structures, acid anhydride structures, etc.) may be determined based on NMR (e.g., ¹ H-NMR, ¹³ C-NMR, etc.) analysis. In the NMR analysis (NMR measurement), the analysis (measurement) conditions can be appropriately selected, and for example, the analysis (measurement) may be performed using a predetermined measurement solvent (e.g., CDCl ₃ , DMSO-d ₆ ) at a predetermined measurement temperature (e.g., 40° C.).

As an example, we will explain a method based on the dealcoholization reaction rate.

First, the amount of weight loss that occurs when all hydroxyl groups from the polymer composition obtained by polymerization are dealcoholized as methanol was used as a standard, and the dealcoholization reaction rate was calculated from the weight loss due to the dealcoholization reaction from 150°C, before the weight loss began, to 300°C, before decomposition of the polymer began, in dynamic TG measurement.
That is, in dynamic TG measurement of a polymer having a lactone ring structure, the weight loss rate is measured between 150° C. and 300° C., and the obtained actual weight loss rate is designated as (X). On the other hand, based on the composition of the polymer, it is assumed that all hydroxyl groups contained in the polymer composition are involved in the formation of lactone rings and become alcohols, and are dealcoholized, and the theoretical weight loss rate (i.e., the weight loss rate calculated on the assumption that a 100% dealcoholization reaction occurs in that composition) is designated as (Y).
More specifically, the theoretical weight reduction rate (Y) can be calculated from the molar ratio of a raw material monomer having a structure (hydroxyl group) involved in a dealcoholization reaction in the polymer, i.e., the content of the raw material monomer in the polymer composition.
These values (X) and (Y) are used to calculate dealcoholization:
1-(Actual weight reduction rate (X)/Theoretical weight reduction rate (Y))
By substituting the above into the above equation and expressing the value as a percentage, the dealcoholization reaction rate can be obtained.

The acrylic resin may contain atoms or groups derived from components used during polymerization.

For example, the acrylic resin may contain sulfur atoms. In a more specific embodiment, the acrylic resin may have a sulfur-containing group (sulfur-containing skeleton) at least at the molecular end.

Such acrylic resins having sulfur atoms or sulfur-containing groups can be obtained, for example, by using a thiol compound (such as the thiol compound described below) as a chain transfer agent.

When the acrylic resin is a copolymer, the form of the copolymerization is not particularly limited, and it may be a random copolymer, a block copolymer, an alternating copolymer, a graft copolymer, etc.

For example, acrylic resins are generally considered to be copolymers because they have a ring structure, but the manner in which the ring structure is introduced is not particularly limited, and the ring structure may be introduced randomly, or in a block, alternating, graft, or other manner.

The melt flow rate (MFR) of the acrylic resin (A) (or resin) is, at a temperature of 230°C and a load of 3.8 kg, for example, 0.1 g/10 min or more (e.g., 0.2 g/10 min or more), preferably 0.3 g/10 min or more (e.g., 0.4 g/10 min or more), and more preferably 0.5 g/10 min or more (e.g., 0.6 g/10 min or more, 0.7 g/10 min or more, 0.8 g/10 min or more). /10 min or more, 1 g/10 min or more, 1.5 g/10 min or more, 1.6 g/10 min or more), or 1.8 g/10 min or more (e.g., 2 g/10 min or more, 2.2 g/10 min or more, 2.5 g/10 min or more, 2.8 g/10 min or more, 3 g/10 min or more, 3.2 g/10 min or more, 3.5 g/10 min or more, 3.8 g/10 min or more, 4 g/10 min or more).

The upper limit of the melt flow rate of the acrylic resin (A) (or resin) at a temperature of 230°C and a load of 3.8 kg may be, for example, 10 g/10 min or less, 9.8 g/10 min or less, 9.6 g/10 min or less, 9.4 g/10 min or less, 9.2 g/10 min or less, 9 g/10 min or less, 8.8 g/10 min or less, 8.6 g/10 min or less, 8.4 g/10 min or less, 8.2 g/10 min or less, 8 g/10 min or less, 7.8 g/10 min or less, 7.6 g/10 min or less, 7.4 g/10 min or less, 7.2 g/10 min or less, 7 g/10 min or less, 6.5 g/10 min or less, 6 g/10 min or less, 5.5 g/10 min or less, 5.2 g/10 min or less, or 5 g/10 min or less.

Specific ranges for the melt flow rate of the acrylic resin (A) (or resin) include combinations of the above ranges, and may be, for example, 0.1 to 10 g/10 min, 1.8 to 9 g/10 min, or 2 to 8 g/10 min at a temperature of 230°C and a load of 3.8 kg.

The melt flow rate of the acrylic resin (or resin) may be measured in accordance with JIS K 7210.

By having excellent melt fluidity (high melt fluidity), discoloration during molding (for example, melt molding such as injection molding) is reduced, and molded products (melt molded products such as injection molded products) with low yellowness can be obtained efficiently.

In addition, the high melt fluidity allows molding processing at lower temperatures, and by suppressing the thermal history during the molding process, discoloration of the molded product can be reduced. In addition, the time required for the heating and cooling process of the injection device can be shortened, which is expected to improve productivity.

On the other hand, acrylic resins (e.g., acrylic resins having a ring structure) with high melt flowability (e.g., MFR of 1.8 g/10 min or more, 2 g/10 min or more) tend to make metering unstable (and are prone to silver streaks, etc.); however, the method of the present invention can efficiently stabilize metering (and reduce silver streaks, etc.) even with such resins.

The weight average molecular weight (Mw) of the acrylic resin (A) (or resin) may be 5000 or more (e.g., may be selected from a range of about 7000 or more, e.g., 10000 or more (e.g., 12000 or more), preferably 15000 or more (e.g., 18000 or more), more preferably 20000 or more (e.g., 25000 or more), or may be 30000 or more (e.g., 35000 or more, 38000 or more, 40000 or more, 42000 or more, 45000 or more, 48000 or more, 50000 or more, 52000 or more, 55000 or more, 58000 or more, 60000 or more, 62000 or more, 65000 or more, etc.).

The weight average molecular weight (Mw) of the acrylic resin (A) (or resin) may be, for example, 500,000 or less, 400,000 or less, 300,000 or less, 250,000 or less, 200,000 or less, 180,000 or less, 150,000 or less, 120,000 or less, or may be 110,000 or less (for example, 105,000 or less, 100,000 or less, less than 100,000, 98,000 or less, 95,000 or less, 90,000 or less, etc.).

The specific range of the weight average molecular weight (Mw) of the acrylic resin (A) (or resin) may be, for example, 20,000 to 200,000, 30,000 to 150,000, 50,000 to 100,000, etc., from the viewpoint of moldability, etc.

Acrylic resins (e.g., 110,000 or less, 100,000 or less, 95,000 or less, etc.) with a relatively low Mw (e.g., 110,000 or less, 100,000 or less, 95,000 or less, etc.) (especially acrylic resins having a ring structure) tend to have unstable metering (and are prone to silver streaks, etc.), but the method of the present invention can efficiently stabilize the metering (and reduce silver streaks, etc.) even with such resins.

The molecular weight distribution (Mw/Mn) of the acrylic resin (A) may be, for example, about 1 to 10 (e.g., 1.1 to 7.0), preferably about 1.2 to 5.0 (e.g., 1.5 to 4.0), or about 1.5 to 3.0, or may be 2.8 or less, 2.7 or less, 2.6 or less, particularly 2.5 or less (e.g., 2.4 or less, 2.3 or less, 2.2 or less), etc.

The acrylic resin (A) (or any other resin) may have a relatively narrow molecular weight distribution (Mw/Mn) from the viewpoints of melt flowability, strength of a molded product, and the like.
On the other hand, acrylic resins (particularly acrylic resins having a ring structure) with narrow molecular weight distributions (for example, 2.5 or less, 2.3 or less, etc.) tend to have unstable metering (and are prone to silver streaks and the like), possibly due to their relationship with melt fluidity. However, according to the method of the present invention, it is possible to efficiently stabilize the metering (and reduce silver streaks and the like) even with such resins.

The molecular weight (and molecular weight distribution) may be measured, for example, using GPC and converted into polystyrene.

The acid value of the acrylic resin (A) (or resin) varies depending on the application, etc., and a small acid value may be suitably used, and may be, for example, about 10 mmol/g or less, preferably 5 mmol/g or less, and more preferably 3 mmol/g or less (e.g., 1.5 mmol/g or less), or may be 1.2 mmol/g or less (e.g., 1 mmol/g or less, 0.8 mmol/g or less, 0.7 mmol/g or less, 0.6 mmol/g or less, 0.5 mmol/g or less, 0.4 mmol/g or less, 0.35 mmol/g or less, etc.).
An acrylic resin (A) having a low acid value may easily lead to unstable metering (for example, the strength is low, and the pellets are easily broken, resulting in a large effect of the pellet size). However, according to the present invention, even with such an acrylic resin (A) having a low acid value, it is possible to efficiently stabilize the metering (and further reduce silver streaks, etc.).

The acid value can be measured by a conventional method. For example, it can be measured and calculated based on the amount of acid groups contained in the acrylic resin [including acid groups generated by hydrolysis (neutralization) of an acid anhydride] and the amount of base (e.g., sodium hydroxide) used for neutralization. Specifically, it can be measured and calculated by the method described below.

The glass transition temperature (Tg) of the acrylic resin (A) may be, for example, 70° C. or higher (e.g., 80 to 200° C.), preferably 90° C. or higher (e.g., 100 to 180° C.), and more preferably about 110° C. or higher (e.g., 112 to 170° C.), or about 115° C. or higher (e.g., 118 to 160° C.), or may be 120° C. or higher [e.g., 120 to 160° C., 125° C. or higher (e.g., 126 to 155° C.), 128° C. or higher (e.g., 129 to 150° C.)], or the like.
The glass transition temperature can be efficiently adjusted, for example, by the type and ratio of the (meth)acrylic monomer, and when the acrylic resin contains a ring structure, the type and ratio of the ring structure, etc. Usually, an acrylic resin having a ring structure often has a relatively high glass transition temperature, and among acrylic resins having a ring structure, an acrylic resin having a larger ratio of the ring structure often has a higher glass transition temperature.

Tg may be measured, for example, by the method described below.

The acrylic resin may be a commercially available product or may be manufactured. The manufacturing method of the acrylic resin is described below.

(Acrylic resin manufacturing method)

Acrylic resin (acrylic polymer) can be produced through at least a process of polymerizing the polymerization components (polymerization process).

The polymerization components are monomers that are the raw materials for the acrylic resin, and correspond to the (meth)acrylic acid esters and other monomers exemplified above. The types and preferred aspects of the monomers are the same as those described above.

The acrylic resin may have a ring structure, and depending on the type of ring structure, the polymerization components may contain a monomer that constitutes the ring structure or a monomer that is a raw material for the ring structure.

For example, in the case of producing an acrylic resin having a structure derived from a maleimide monomer or maleic anhydride monomer, the polymerization components may contain, for example, maleic anhydride, maleimide-based monomers [for example, maleimide; N-substituted maleimides such as N-alkylmaleimides (for example, N-C _1-10 alkylmaleimides such as N-methylmaleimide and N-ethylmaleimide), N-cycloalkylmaleimides (for example, N-C _3-20 cycloalkylmaleimides such as cyclohexylmaleimide), N-arylmaleimides (for example, N-C _6-10 arylmaleimides such as N-phenylmaleimide), and N-aralkylmaleimides (for example, N-C _7-10 aralkylmaleimides such as N-benzylmaleimide)].

When producing an acrylic resin having a lactone ring structure, the polymerization components may contain a monomer that serves as a raw material for the lactone ring, such as a 2-(hydroxymethyl)acrylic acid ester (e.g., an alkyl ester such as ethyl 2-(hydroxymethyl)acrylate).

When producing an acrylic resin having a lactam ring structure, the polymerization components may contain lactam monomers [for example, N-vinylpyrrolidone monomers (for example, N-vinylpyrrolidone, N-vinyl-4-butylpyrrolidone, N-vinyl-4-propylpyrrolidone, N-vinyl-4-ethylpyrrolidone, N-vinyl-4-methylpyrrolidone, N-vinyl-4-methyl-5-ethylpyrrolidone, N-vinyl-4-methyl-5-propylpyrrolidone, N-vinyl-5-methyl-5-ethylpyrrolidone, N-vinyl-5-propylpyrrolidone, N-vinyl-5-butylpyrrolidone, etc.), N-vinylcaprolactam monomers (for example, N-vinylcaprolactam, N-vinyl-6-methylcaprolactam, N-vinyl-6-propylcaprolactam, N-vinyl-7-butylcaprolactam, etc.)], etc.].

The polymerization may typically be radical polymerization.

The polymerization may be carried out in the presence of a polymerization initiator (particularly a radical polymerization initiator).

Polymerization initiators (radical polymerization initiators) are not particularly limited, but include, for example, organic peroxides [e.g., peroxides (dialkyl peroxides, diacyl peroxides, etc.), peroxy monocarbonates, peroxy esters, peroxy ketals, etc.], azo compounds, etc.

Specific examples of polymerization initiators include organic peroxides [e.g., tert-amylperoxyisononanoate, t-amylperoxy-2-ethylhexanoate, tert-butylperoxy-3,5,5-trimethylhexanate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, tert-hexylperoxyisopropyl monocarbonate, tert-butylperoxyacetate, 1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butylperoxy2-ethylhexanoate, tert-butylperoxylaurate, tert-butyl ...laurate, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, tert-butylperoxylaurate, tert-butylperoxyisopropyl monocarbonate, xanate, tert-butylperoxyisobutyrate, tert-hexylperoxy 2-ethylhexanate, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, etc.], azo compounds [for example, 2-(carbamoylazo)-isobutyronitrile, 1,1'-azobis(1-cyclohexanecarbonitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), dimethyl 2,2'-azobisisobutyrate, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), etc.], etc.].

The polymerization initiators may be used alone or in combination of two or more.

In particular, at least an organic peroxide (such as a peroxy ester) may be preferably used as the polymerization initiator.

The amount (usage ratio) of the polymerization initiator used will vary depending on the type of polymerization initiator, but may be, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, particularly 0.15 parts by mass or more, relative to 100 parts by mass of the polymerization components, or 0.2 parts by mass or more (e.g., 0.25 parts by mass or more, 0.28 parts by mass or more, 0.3 parts by mass or more, 0.32 parts by mass or more, 0.35 parts by mass or more, 0.38 parts by mass or more, 0.4 parts by mass or more, 0.42 parts by mass or more, 0.45 parts by mass or more, 0.48 parts by mass or more, 0.5 parts by mass or more, 0.52 parts by mass or more).

The upper limit of the amount of polymerization initiator used is not particularly limited, but may be, for example, 10 parts by mass, 9 parts by mass, 8 parts by mass, 7 parts by mass, 6 parts by mass, 5 parts by mass, 4.5 parts by mass, 4 parts by mass, 3.5 parts by mass, 3.2 parts by mass, 3 parts by mass, 2.8 parts by mass, 2.5 parts by mass, 2.2 parts by mass, 2 parts by mass, 1.8 parts by mass, 1.5 parts by mass, 1.2 parts by mass, 1 part by mass, 0.9 parts by mass, 0.8 parts by mass, 0.7 parts by mass, etc., relative to 100 parts by mass of the polymerization components.

In particular, the proportion of polymerization initiator used per 100 parts by mass of polymerization components may be relatively large [e.g., 0.2 parts by mass or more, 0.3 parts by mass or more, 0.4 parts by mass or more (e.g., 0.4 to 0.8 parts by mass), etc.].

By using a relatively large amount of polymerization initiator in this way, it is easy to efficiently obtain an acrylic resin that has advantages in terms of melt fluidity, etc. Even when a chain transfer agent is used, it is easy to ensure a sufficient polymerization reaction rate, and an acrylic resin with good melt fluidity can be efficiently obtained.

The polymerization may be carried out in the presence of a chain transfer agent.

The chain transfer agent is not particularly limited, but examples thereof include thiol compounds {for example, primary thiols [for example, aliphatic primary thiols (for example, primary alkyl mercaptans such as butanethiol, octanethiol, decanethiol, dodecanethiol (n-dodecyl mercaptan), hexadecanethiol, octadecanethiol, and decanetrithiol, preferably primary C _3-30 alkyl mercaptans), etc.)], secondary thiols [for example, aliphatic secondary thiols (for example, secondary alkyl mercaptans such as 2-propanethiol, 2-butanethiol, 2-methyl-1-propanethiol, 3-methyl-2-butanethiol, 3-pentanethiol, 2-decanethiol, 3-decanethiol, 4-decanethiol, 5-decanethiol, 2-hexadecanethiol, 5-hexadecanethiol, 8-octadecanethiol, etc., preferably secondary C _3-30 alkyl mercaptans), alicyclic secondary thiols (for example, cycloalkyl mercaptans such as cyclohexanethiol, cyclopentanethiol, etc., preferably C _3-20 cycloalkyl mercaptans), aromatic secondary thiols (for example, aryl mercaptans such as thiophenol, etc., preferably C _6-20 aryl mercaptan), etc.], tertiary thiols [for example, aliphatic tertiary thiols (for example, tert-alkyl mercaptans such as tert-butyl mercaptan, tert-dodecyl mercaptan, tert-nonyl mercaptan, tert-hexyl mercaptan, etc., preferably C _3-30 tert-alkyl mercaptan), etc.]}, and the like.

When the chain transfer agent contains a polyfunctional thiol, the proportion of the polyfunctional thiol in the chain transfer agent may be small. The amount (proportion) of the polyfunctional thiol used in the chain transfer agent may be, for example, 20% by mass or less (e.g., 15% by mass or less), preferably 10% by mass or less (e.g., 5% by mass or less), more preferably 3% by mass or less, 1% by mass or less, 0.5% by mass or less, etc.

Chain transfer agents can be used in one or more combinations.

The amount (proportion) of the chain transfer agent used may be, for example, 0.001 parts by mass or more, preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, particularly 0.015 parts by mass or more, or may be 0.02 parts by mass or more, per 100 parts by mass of the polymerization components.

The upper limit of the amount of chain transfer agent used is not particularly limited, but may be, for example, 5 parts by mass, 4 parts by mass, 3 parts by mass, 2 parts by mass, 1.5 parts by mass, 1 part by mass, 0.5 parts by mass, 0.25 parts by mass, 0.2 parts by mass, 0.15 parts by mass, 0.1 parts by mass, 0.08 parts by mass, 0.07 parts by mass, etc., relative to 100 parts by mass of the polymerization components.

In particular, even when a chain transfer agent is used, the proportion of the chain transfer agent used relative to 100 parts by mass of the polymerization components may be relatively small (e.g., 0.5 parts by mass or less, 0.1 parts by mass or less (e.g., 0.001 to 0.1 parts by mass)) from the viewpoint of reducing discoloration, and it is not necessary to use a chain transfer agent.

In this way, it is easy to efficiently obtain an acrylic resin that is advantageous in terms of melt flowability, etc., even without using a chain transfer agent or using a relatively small amount of chain transfer agent.

The mass ratio of the chain transfer agent and the polymerization initiator may be preferably 1/2 or less, more preferably 1/3 or less, 1/4 or less, or 1/5 or less, from the viewpoints of suppressing discoloration of the acrylic resin and melt fluidity. The mass ratio of the chain transfer agent and the polymerization initiator is calculated by (mass of the chain transfer agent)/(mass of the polymerization initiator).

The polymerization may be carried out in the presence of a polymerization initiator, a chain transfer agent, and other components (e.g., a pH adjuster, various catalysts, etc.) as necessary.

The polymerization may be any of bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc., and in particular may be solution polymerization from the viewpoint of obtaining a polymer that does not contain impurities and has stable fluidity. In solution polymerization, the polymerization can be carried out relatively uniformly, and compared to bulk polymerization, the production of polymers with significantly high molecular weights seems to be suppressed, making it easier to efficiently obtain polymers with stable fluidity. In addition, compared to suspension polymerization and emulsion polymerization, it does not contain impurities such as emulsifiers, making it easier to efficiently obtain polymers with high transparency.

When the polymerization is carried out in a solvent (e.g., in the case of solution polymerization), the solvent can be appropriately selected depending on the type of polymerization components, and is not particularly limited. Examples of the solvent include organic solvents [aromatic hydrocarbons (e.g., benzene, toluene, xylene, ethylbenzene, etc.), aliphatic or alicyclic hydrocarbons (e.g., cyclohexane, methylcyclohexane, etc.), halogenated solvents (e.g., chloroform, methylene chloride, carbon tetrachloride, etc.)], ketones (e.g., acetone, methyl ethyl ketone, etc.), esters (e.g., ethyl acetate, butyl acetate, etc.), ethers [e.g., chain ethers (e.g., diethyl ether, etc.), cyclic ethers (e.g., tetrahydrofuran, dioxane, etc.), amides [e.g., N-substituted amides (N-alkyl-substituted alkanamides such as N,N-dimethylformamide)], alcohols (e.g., alkanols such as methanol, ethanol, isopropanol), glycol ethers (e.g., monoalkyl ethers of alkanediols or polyalkanediols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol monoethyl ether, etc.)], etc.

Solvents may be used alone or in combination of two or more.

In the polymerization, the concentration of the polymerization components in the entire polymerization system may be, for example, 20% by mass or more (e.g., 20 to 70% by mass), preferably 35% by mass or more (e.g., 35 to 65% by mass), more preferably 40% by mass or more (e.g., 40 to 60% by mass), and particularly 45% by mass or more (e.g., 45 to 55% by mass), from the viewpoints of suppressing molecular weight increase and productivity.

The components (e.g., polymerization components, polymerization initiator, chain transfer agent, other components, solvent, etc.) may all be present (charged) in the reaction system (reactor) at the start of polymerization, or may be added (or mixed) as the polymerization progresses, or a combination of these may be used. In such cases, the addition speed and addition time of each component can be appropriately selected.

Each component may be added to the reaction system in multiple portions (two or more portions, for example, 2 to 5 portions).
In particular, the polymerization components (monomers) may be added to the reaction system as the polymerization proceeds, in which case the polymerization components may be added in multiple divided portions or may be added dropwise. When the polymerization components are added dropwise to the reaction system, an acrylic resin having a relatively narrow molecular weight distribution is easily obtained.
Also, a polymerization initiator may be added to the reaction system as the polymerization proceeds. In particular, when the polymerization components are added to the reaction system by dropping, it is preferable to add the polymerization initiator to the reaction system by dropping. By adding the polymerization initiator to the reaction system as the polymerization proceeds, it is expected that safety can be ensured or a polymer having a relatively narrow molecular weight distribution can be obtained.
When the polymerization components and the polymerization initiator are added by dropwise addition, the dropwise addition speed is not particularly limited. However, from the viewpoint of easily obtaining an acrylic resin having a relatively small molecular weight, it is preferable to add them slowly, and they may be added over 1 hour or more (for example, 1 to 10 hours).

Polymerization is usually carried out at a given temperature (or under heating). The polymerization temperature (reaction temperature) can be appropriately selected depending on the type of polymerization components, polymerization initiator, solvent, etc., and may be, for example, 20°C or higher, preferably 30°C or higher (e.g., 35 to 180°C), more preferably 40°C or higher (e.g., 45 to 170°C), particularly 50°C or higher (e.g., 55 to 160°C), and particularly preferably 60°C or higher (e.g., 65 to 150°C), and may usually be about 70 to 140°C (e.g., 80 to 130°C).

The polymerization temperature may be changed as the polymerization progresses, but even if it is changed in this way, the polymerization is usually carried out within the above temperature range.

The polymerization may be carried out under stirring. The polymerization may also be carried out in air or in an inert atmosphere (such as nitrogen, helium, or argon).

The polymerization time (if aging is performed) can be appropriately selected depending on the amount of polymerization components, polymerization temperature, etc., and is not particularly limited, but may be, for example, 30 minutes or more (e.g., 40 minutes to 24 hours), preferably 1 hour or more (e.g., 1.5 to 16 hours), and more preferably 2 hours or more (e.g., 2.5 to 12 hours).

When the acrylic resin has a ring structure, such a ring structure may be formed during the polymerization as described above depending on the type of ring structure (for example, in the case of a structure derived from a maleimide monomer or maleic anhydride monomer, a lactam ring structure, etc.), and after polymerization, the ring structure can be formed or introduced into the acrylic resin through a step of forming or introducing the ring structure. The method for forming or introducing the ring structure is not particularly limited, and can follow any known method.

For example, the lactone ring structure can be formed or introduced by cyclizing (cyclization condensation, cyclization treatment) an acrylic resin containing units derived from a monomer that is the raw material for the lactone ring [e.g., 2-(hydroxymethyl)acrylic acid ester], as described above. The cyclization may be carried out in the presence of a cyclization catalyst [e.g., a phosphorus-based catalyst (e.g., a phosphate ester such as stearyl phosphate)].

The glutarimide structure can be formed or introduced into the acrylic polymer by known methods such as imidizing (meth)acrylic acid ester units (for example, the methods described in JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328329, JP-A-2006-328334, JP-A-2006-337491, JP-A-2006-337492, JP-A-2006-337493, JP-A-2007-009182, etc.).

The glutaric anhydride structure can be formed or introduced into the acrylic polymer, for example, by a method of intramolecular dealcoholization reaction between adjacent (meth)acrylic acid ester units and (meth)acrylic acid units (e.g., the methods described in JP-A-2006-283013, JP-A-2006-335902, JP-A-2006-274118, etc.).

Through this polymerization process (and optionally a cyclization process), an acrylic resin is obtained.

The resin obtained through the polymerization process may be purified and separated as appropriate using conventional methods.

[Other resins]
The resin (or pellets) may contain other resins (resins other than acrylic resins) as necessary [the resin composition (or pellets thereof) may be constituted together with the other resins].

The other resins can be appropriately selected depending on the desired physical properties, applications, etc., and are not particularly limited. They may be thermoplastic resins, curable resins, or combinations of these.
The other resins may be used alone or in combination of two or more kinds.

Specific examples of other resins include olefin-based polymers (e.g., polyethylene, polypropylene, ethylene-propylene copolymers, poly(4-methyl-1-pentene), etc.), halogen-based polymers (e.g., vinyl halide polymers such as polyvinyl chloride, polyvinylidene chloride, polyvinyl chloride, etc.), styrene-based polymers [e.g., polystyrene, styrene-based copolymers (e.g., styrene-methyl methacrylate copolymers, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene block copolymers (ABS resins), etc.)], polyester-based polymers (e.g., poly aromatic polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate), polyamide resins (for example, aliphatic polyamide resins such as polyamide 6, polyamide 66, and polyamide 610), polyacetal resins, polyphenylene oxide resins, polyphenylene sulfide resins, polyether ether ketone resins, polysulfone resins, polyether sulfone resins, and rubber polymers [for example, styrene resins (for example, styrene copolymers such as ABS resins) blended with rubber (polybutadiene rubber, acrylic rubber, etc.)].

Other resins include cellulose-based resins. Examples of cellulose-based resins (cellulose derivatives) include cellulose esters [e.g., cellulose acylates such as cellulose acetate (cellulose diacetate, cellulose triacetate), cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate], cellulose ethers [e.g., alkyl celluloses (e.g., methyl cellulose, ethyl cellulose), hydroxyalkyl celluloses (e.g., hydroxyethyl cellulose, hydroxyalkyl cellulose), carboxyalkyl celluloses (e.g., carboxymethyl cellulose)], and cyanoethyl cellulose.

The other resins include thermoplastic elastomers. Thermoplastic elastomers are not particularly limited, but examples include styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, and amide-based elastomers.

[Other ingredients]
The resin (or pellets) may contain other components as necessary (the resin composition (or pellets thereof) may be formed together with the other components).
Such other components can be selected according to the desired application, physical properties, etc. The other components are not particularly limited, and examples thereof include ultraviolet absorbers, colorants, antioxidants (e.g., phenol-based antioxidants, thioether-based antioxidants, phosphoric acid-based antioxidants, etc.), stabilizers, reinforcing materials, flame retardants, antistatic agents, organic fillers, inorganic fillers, antiblocking agents, resin modifiers, organic fillers, inorganic fillers, plasticizers, lubricants, retardation reducing agents, etc.

The other ingredients may be used alone or in combination of two or more.

The ultraviolet absorbing ability of the ultraviolet absorber (UVA) may be in the wavelength range of 300 to 380 nm, and may have a molar absorption coefficient (chloroform solution) of 10,000 (L·mol ⁻¹ ·cm ⁻¹ ) or more for light of a wavelength at which absorption by UVA is maximum.

Ultraviolet absorbers (UVA) are not particularly limited, but examples include benzophenone-based compounds, salicylate-based compounds, benzoate-based compounds, triazole-based compounds, and triazine-based compounds.

Examples of triazole compounds include 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(3,5-di-t-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-t-butylphenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(t-butyl)phenol, 2-(2H-benzotriazol-2-yl)-4,6-di-t-butylphenol, 2-(2H-benzotriazol-2-yl)-4,6-di-t-butylphenol, )-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 branched 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-C _7-9 branched and linear alkyl esters, and the like. Triazole compounds having a halogen atom, such as a chlorine atom, are preferred because of their high ultraviolet absorbing ability.

Examples of triazine 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, 2,4-diphenyl-(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-dodecyl oxyphenyl)-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-hexyloxy-3-methylphenyl)-1,3,5-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-alkyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine skeleton (alkyloxy; long chain alkyloxy group such as octyloxy, nonyloxy, decyloxy, etc.). Among these, UVAs having a 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-alkyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine skeleton (alkyloxy; long-chain alkyloxy groups such as octyloxy, nonyloxy, and decyloxy) are preferred because of their excellent ultraviolet absorbing properties.

The molecular weight of the UVA is not particularly limited, but is preferably 600 or more. The upper limit of the molecular weight of the UVA may be, for example, 10,000, 8,000, 5,000, etc.

UV absorbers may be used alone or in combination of two or more.

The colorant is not particularly limited and can be appropriately selected depending on the application of the composition, and may be, for example, a pigment (e.g., inorganic pigment, organic pigment), a dye, etc.

The colorant may also have bluing properties (the property of compensating (countering) and reducing the color (e.g., yellow) of the acrylic resin or composition).
Such a colorant may be a colorant (compound) having a maximum absorption wavelength in the range of 520 to 600 nm, 540 to 580 nm, or the like, depending on the color to be corrected.

Such a colorant can be appropriately selected depending on the type (wavelength) of the color to be corrected, and examples thereof include compounds having an anthraquinone skeleton (anthraquitone-based compounds), compounds having a phthalocyanine skeleton (phthalocyanine-based compounds), compounds having an azo skeleton (azo-based compounds), and compounds having a triarylmethane skeleton (triarylmethane-based compounds).
Among these, compounds having an anthraquinone skeleton may be preferably used from the viewpoint of heat resistance and the like.

Specific colorants (colorants having bluing properties, bluing agents) include anthraquinone dyes [e.g., Solvent Violet 13 (CA. No. (Color Index Number) 60725), Solvent Violet 14, Solvent Violet 31 (CA. No. 68210), Solvent Violet 33 (CA. No. 60725), Solvent Violet 36 (CA. No. 68210), Solvent Blue 45 (CA. No. 61110), Solvent Blue 94 (CA. No. 61500), Solvent Blue 87, Solvent Blue 97, Disperse Examples of the dyes include Solvent Violet 28, phthalocyanine dyes (e.g., Solvent Blue 25 (CA. No. 74350) and the like), monoazo dyes (e.g., Solvent Violet 21, etc.), and triarylmethane dyes (e.g., Solvent Blue 2 (CA. No. 42563) and the like).

As such colorants, commercially available products such as "Macrolex (registered trademark) Violet B", "Macrolex (registered trademark) Violet 3R", "Macrolex (registered trademark) Blue RR" (manufactured by LANXESS KK), "Sumiplast (registered trademark) Violet B", "Sumiplast (registered trademark) Green G" (manufactured by Sumika Chemtex Co., Ltd.), "Polysynthren (registered trademark) Blue RLS" (manufactured by Clariant), "Diaresin Violet D", "Diaresin Blue G", "Diaresin Blue N" (manufactured by Mitsubishi Chemical Corporation) may be used.

In addition, a black dye may be used as the colorant to obtain an excellent jet black (piano black-like) appearance.

As such black dyes, for example, organic dyes such as compounds having an anthraquinone skeleton (anthraquinone-based compounds), compounds having a perinone skeleton (perinone-based compounds), compounds having a perylene skeleton (perylene-based compounds), compounds having an azo skeleton (azo-based compounds), compounds having a methine skeleton (methine-based compounds), and compounds having a quinone skeleton (quinone-based compounds) are preferably used. As anthraquinone-based compounds, organic dyes such as blue, purple, and green may be preferably used, and as perinone-based compounds, organic dyes such as red and orange may be preferably used.

Black dyes are commercially available. For example, "Oplus (registered trademark) Black 838", "Nubian (registered trademark) Black PC-0870", "Nubian (registered trademark) Black PC-5856", "Nubian (registered trademark) Black PC-5857", "Nubian (registered trademark) Black PC-8550" (manufactured by Orient Chemical Industries Co., Ltd.), "Sumiplast (registered trademark) Black H3B", "Sumiplast (registered trademark) Black HLG", "Sumiplast (registered trademark) Black HB" (manufactured by Sumika Chemtex Co., Ltd.), etc. may be used.

The colorants may be used alone or in combination of two or more.

[Proportion of each ingredient]
In the resin (or pellets), the proportion of the acrylic resin (A) (or the proportion of the acrylic resin (A) in the resin components) may be selected from the range of, for example, 10% by mass or more (e.g., 20% by mass) and may be 30% by mass or more (e.g., 40% by mass or more), preferably 50% by mass or more (e.g., 60% by mass or more), and more preferably 70% by mass or more (e.g., 80% by mass or more, 90% by mass or more).

When the resin (or pellets) contains other resins, the content of the other resins can be selected from a range of, for example, about 70% by mass or less (e.g., 0.1 to 60% by mass) relative to the entire resin (pellets) [or resin components (total amount of acrylic resin (A) and other resins)], and may be 50% by mass or less (e.g., 0.5 to 40% by mass), preferably about 30% by mass or less (e.g., 1 to 25% by mass), or may be 20% by mass or less (e.g., 15% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1 to 10% by mass, etc.), etc.

In addition, from the viewpoint of efficiently expressing the physical properties of the acrylic resin (A), even if other resins are included, it is preferable that the proportion of the other resins is not too large.

When the resin (pellet) contains other components (additives), the proportion of the other components may be, for example, about 0.01 to 10% by mass (e.g., 0.05 to 5% by mass) relative to the entire resin (pellet).

[Method of manufacturing pellets]
In one aspect of the present invention, pellets of the resin described above are produced in a particular manner.

In other words, in this method, the resin is cut (for example, hot cut) to produce pellets. At this time, the pellets (pellets after cooling or in a solidified state) are cut to a specific size.

The shape of the pellets may vary depending on the melting and cutting methods, but may be, for example, columnar (cylindrical), flat, circular (disc-shaped), or the like.
Among these shapes, the present invention may suitably use circular pellets, etc. By using pellets of such a shape, it is possible to more efficiently stabilize the metering (and further reduce silver streaks, etc.).

The size of the pellets (hot cut pellets, etc.) may be selected from a range of about 5 mm or less in the major axis (major axis of the cut surface, maximum width of the cut surface), and may be 4.5 mm or less, preferably 4.2 mm or less, and more preferably 4.0 mm or less (e.g., 3.9 mm or less, 3.8 mm or less).

The short diameter of the pellet (short diameter of the cut surface, minimum width of the cut surface) may be selected from a range of about 5 mm or less, and may be 4.5 mm or less, preferably 4.2 mm or less, and more preferably 4.0 mm or less (e.g., 3.9 mm or less, 3.8 mm or less).

When the major axis of the pellet is L (mm) and the minor axis of the pellet is S (mm), the value of L-S may be 0 mm or more (e.g., 0 to 4 mm, 0 to 3.5 mm), and may preferably be 2 mm or less (e.g., less than 2 mm, 1.8 mm or less, 1.5 mm or less, 1.2 mm or less, 1.0 mm or less).
In the present invention, such pellets having a small L-S value may be preferably used. By using such pellets, it is possible to more efficiently stabilize the metering (and further reduce silver streaks, etc.).

The thickness (or length) of the pellets depends on the cutting method, etc., but may be selected from a range of, for example, about 10 mm or less (e.g., 8 mm or less, 7 mm or less, 6 mm or less), or may be 5 mm or less (e.g., 4.5 mm or less), preferably 4.2 mm or less (e.g., 4.0 mm or less), and more preferably 3.5 mm or less (e.g., 3.2 mm or less, 3.0 mm or less).

The major axis, minor axis, and thickness may be the average values (arithmetic mean value, etc.) of multiple pellets.

The major axis, minor axis, and thickness can be measured by conventional methods, for example, by the method described below.

The thickness of the pellet may be equal to or less than the major axis of the pellet (particularly, smaller than the major axis of the pellet), or may be equal to or less than the minor axis of the pellet (particularly, smaller than the minor axis of the pellet).

In such a case, when the major axis of the pellet is L (mm), the minor axis of the pellet is S (mm), and the thickness of the pellet is T (mm), the value of L-T or the value of S-T may be 0 mm or more (e.g., 0 to 4 mm, 0 to 3.5 mm), or may be 0.1 mm or more (e.g., 0.2 to 3.5 mm), 0.3 mm or more (e.g., 0.4 to 3.2 mm), or 0.5 mm or more (e.g., 0.5 to 3 mm).
In the present invention, pellets having such an L-T value or S-T value (for example, pellets having a relatively similar major axis (or minor axis) and thickness) may be preferably used. By using such pellets, it is possible to more efficiently stabilize the metering (and further reduce silver streaks, etc.).

In cutting the resin, the state of the resin (the resin to be cut) is not limited, but typically, the resin in a molten state may be cut (particularly, the molten resin may be cut in a molten state (hot cut)).
Hot-cut pellets are susceptible to the effects of unstable weighing, etc., but according to the present invention, such unstable weighing, etc. can be suppressed, making it possible to realize stable (efficient) production of hot-cut pellets.

The method for melting the resin (melting means) is not particularly limited, and for example, an extruder can be used.

When producing pellets containing other resins and other components in addition to the acrylic resin, the other resins and other components may be melted in advance in the acrylic resin, or may be melted (melt-kneaded) while being mixed with the acrylic resin in the melting means (extruder).

The cutting method (cutting means) is not particularly limited, but for example, a cutter (a cutter used in a hot-cut method) can be used. Specific cutting means (pelletizers) include, for example, a hot-cut pelletizer, a watering pelletizer, a mist-cut pelletizer, an underwater pelletizer, a rotary knife pelletizer, a centrifugal pelletizer, and a strand-cut pelletizer.

In a typical method, from the viewpoint of stable pellet production, the resin extruded from a melting means (such as an extruder) through a die (such as an extrusion die) may be cut (hot cut) in the molten state.

The die may usually have multiple holes.

The resin may be cooled at an appropriate stage depending on the cutting method, etc. For example, when cutting by hot cutting, the resin after cutting (for example, in a molten state) may be cooled.
The method for cooling (solidifying) the resin (for example, in the case of hot cutting, the cut resin or the molten resin) is not particularly limited, and may be natural cooling (air cooling), water cooling, etc., depending on the type of pelletizer, etc.

The cooling may be performed on the resin (e.g., the cut resin), but in many cases, the resin is cooled so that it immediately solidifies. For example, the resin (e.g., the cut resin, or the molten resin) may be cooled so that it solidifies within 1 minute (e.g., within 30 seconds, within 20 seconds, within 10 seconds, within 5 seconds, etc.) after cutting.

[pellet]
Pellets are obtained in the manner described above. The size and other details of such pellets are as described above.

The uses of the pellets are not particularly limited, but they may be suitable for melt molding, particularly injection molding.

Acrylic resin pellets can sometimes be metered unstably in an injection molding machine (injection device), but pellets obtained as described above can be metered relatively stably when used in injection molding. Furthermore, by using such pellets, molded products (injection molded products) with fewer appearance and molding defects such as silver streaks can be efficiently manufactured.

In particular, such pellets (or the method for producing pellets) may be combined (applied) with the methods of other aspects of the present invention described below. By combining in this way, it may be possible to more efficiently produce molded products with stable weighing and fewer appearance and molding defects such as silver streaks, depending on the type of acrylic resin.

<Method of molding resin>
In another aspect of the present invention, a method for molding a resin (a method for manufacturing a molded product) is provided.

In such a method, the resin may be the same as the resin described above (the resin described in one embodiment of the present invention). That is, the resin may usually contain acrylic resin (A), and the preferred embodiment of acrylic resin (A), other resins, other components, etc. may also be the same as those described above.

For example, the acrylic resin (A) may be an acrylic resin having a ring structure (e.g., a cyclic ester structure), or may be an acrylic resin having the above-mentioned MFR (e.g., MFR of 2 g/10 min or more), Mw (e.g., Mw of 100,000 or less), Mw/Mn (e.g., Mw/Mn of 2.5 or less), etc.

Such acrylic resins are also suitable for the production of molded products (injection molded products) that have relatively stable weighing and few appearance and molding defects such as silver streaks, even in the methods of other aspects of the present invention.

The resin may be in the form of pellets. Such pellets may be similar to the pellets in one embodiment of the present invention described above [e.g., similar in major axis, minor axis, thickness, and the difference between these (e.g., major axis 4.5 mm or less, minor axis 4.5 mm or less, thickness 3.5 mm or less, etc.)] or may be different, but similar pellets may be preferably used.

When pellets are used as the resin, the pellets may be resin obtained in the same manner as in one embodiment of the present invention (e.g., hot-cut pellets obtained by cutting a molten resin), and typically, pellets obtained by the method of one embodiment of the present invention (e.g., hot-cut pellets) may be used.

The use of such pellets may be incorporated into the method of another aspect of the present invention. That is, the method of another aspect of the present invention may include a pellet production step in which pellets are produced by the method of the one aspect of the present invention, and the pellets of the resin obtained in this production step may be used as the resin.

In another embodiment of the present invention, the resin is injection molded [or the resin is injection molded to produce a molded product (injection molded product)].

The molding machine (injection molding machine, injection device) used in injection molding has the structure described above in Figure 1.

That is, as shown in FIG. 1, a molding machine (such as an injection molding machine) typically comprises a cylinder (cylinder section) 2, a nozzle section Hn equipped with a nozzle 1 connected to the front end of the cylinder 2, and a hopper (feeding port) 3 connected to the rear section H3 of the cylinder 2.

The cylinder 2 contains a screw consisting of a front section (metering section) S1, a middle section (compression section) S2, and a rear section (supply section) S3, which correspond to the front section (metering section) H1, middle section (compression section) H2, and rear section (supply section) H3 of the cylinder 2 when the screw is pushed in (the screw is moved toward the nozzle).

In addition, temperature measuring devices (thermocouples, etc.) 4 may be installed in each part of the cylinder.

A cooling device (a cooling jacket such as a water-cooled jacket) H4 is installed at the rear of the cylinder H3 (or at the base end of H3, below the hopper 3). This type of cooling device is usually installed so as to surround the periphery (outer periphery) of H3.

The resin (pellets, etc.) is fed from the hopper 3 into the supply section H3 (S3) and melted in the cylinder 2 (melted by the shearing force of the screw). This molten resin is then weighed in the weighing section S1 (H1) and fed through the nozzle 1 into a mold (not shown) to produce the desired molded product.

Here, in another aspect of the method of the present invention, the temperature (set temperature) of the cooling device (H4) is adjusted in relation to the glass transition temperature of the resin.

In other words, when the temperature of the cooling device is Tj (°C) and the glass transition temperature of the resin is Tg (°C), Tg-Tj may be 80 or less (e.g., 75 or less), preferably 70 or less, more preferably 65 or less (e.g., 62 or less), and particularly preferably 60 or less (e.g., 58 or less), or may be 55 or less (e.g., 52 or less, 50 or less, 48 or less, etc.).

The lower limit of Tg-Tj (°C) may be, for example, 3, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, etc., and may typically be 20 or more (for example, 20, 25, 30, etc.).

The reason why such a temperature makes it easier to stabilize weighing and improve silver streaks is unclear, but one possible reason is that it makes it easier for moisture and remaining volatile components in the pellets to escape. Furthermore, when using the above-mentioned pellets, it is thought that this, combined with the fact that the pellets are less likely to crack, makes it even easier to achieve the above improvements.

As mentioned above, in the injection molding machine, the resin (molten resin) is weighed in the weighing section, and such weighing can be stabilized by adjusting the temperature of the cooling device.

Therefore, the method of the present invention can also be described as a method (or a method of stabilizing the metering) of resin (molten resin) measured [the molten resin to be discharged (injected) into a mold (through a nozzle)] by setting Tg-Tj (°C) to a specific temperature (e.g., 80 or less, 70 or less, etc.) in injection molding or an injection molding machine (or a method of injection molding and manufacturing a molded product).

Other molding (injection molding) conditions (conditions other than the temperature of the cooling device, such as the set temperatures of the supply section, compression section, metering section and nozzle section, compression conditions, etc.) are not particularly limited and can be appropriately selected according to conventional methods.

<Molded products, etc.>
Through at least the above-mentioned method (the method of one aspect of the present invention and/or the method of another aspect of the present invention), pellets (resin pellets, resin composition) or molded articles (molded bodies) can be obtained.

The yellowness index (YI) of such molded products (or resin pellets) may be relatively small, depending on the components, and may be, for example, 4 or less, preferably 3.5 or less, more preferably 3 or less, or may be 2.8 or less, 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2.0 or less, 1.9 or less, 1.8 or less, etc.

The lower limit of the yellowness may be 0 (or the detection limit) or a finite value (e.g., 0.01, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc.).

The yellowness index may be, for example, a value in a thickness of 3 mm (e.g., a sheet [sheet-shaped molded product (injection molded product)] having a thickness of 3 mm, etc.) [e.g., a value measured in accordance with the provisions of JIS K7373 using a spectrophotometer (Shimadzu Corporation, UV-3600) with a C2 degree light source and a wavelength range of 380 nm to 780 nm], or in detail, a value measured by the method described below.

The shape of the molded product is not particularly limited, and may be either a two-dimensional shape [e.g., a film (or sheet)] or a three-dimensional shape (e.g., a block shape).

The molded article can be used for various purposes, but since it often has excellent transparency (and low colorability) and excellent optical properties due to the acrylic resin (A), it may be suitable for use in optical applications (even as an optical component), for example.

Specific examples of applications include light guiding members, film applications [for example, protective films (optical protective films, etc.), optical films (optical sheets), etc.], lenses (optical lenses, etc.), covers (lens covers, etc.), foam (foam molded articles) applications (for example, cushioning materials, heat-retaining/thermal insulating materials, vibration-damping materials, soundproofing materials, sealing materials, packing materials, etc.), and interior material applications [for example, interior material applications for vehicles (automobiles, etc.) such as front panels of in-vehicle displays and meter covers].
Examples of lenses (optical lenses, etc.) include Fresnel lenses, linear Fresnel lenses, lenticular lenses, flat prisms, fly's eye lenses, aspheric lenses, condenser lenses, microlenses, collimator lenses, concave lenses, convex lenses, and diffractive lenses.
Examples of applications of lenses (lens members) include head-up displays, cameras (e.g., in-vehicle cameras), LIDAR devices, etc. Examples of lenses for such applications include Fresnel lenses and condenser lenses used in head-up displays, and Fresnel lenses, condenser lenses, collimator lenses, convex lenses, etc. used in LIDAR devices.

Examples of light-guiding members include light guides [or lighting devices, such as lamps or lights]. The light guides may be for automobiles, motorcycles, etc. The location (or application) where the light guide is provided is not particularly limited, and examples of applications include headlamps, tail lamps, brake lamps, side mirror lamps, and daytime running lights (DRLs) in automobiles.

Specific examples of components (light-guiding components) include light covers and light guides (light guides for vehicle lamps [e.g., light guides for automobile headlamps (e.g., light guides for DRLs)]).

Examples of protective films include protective films for various optical disk (VD, CD, DVD, MD, LD, etc.) substrates, and polarizer protective films used in polarizing plates for liquid crystal display devices.

Examples of optical films (optical sheets) include retardation films, zero retardation films (with extremely small in-plane and thickness direction retardation), viewing angle compensation films, light diffusion films, reflective films, anti-reflection films, anti-glare films, brightness enhancement films, conductive films for touch panels, diffusion plates, light guides, retardation plates, zero retardation plates, and prism sheets.

In particular, in the present invention, as described above, a melt molding method such as injection molding can be applied, so the molded body may be a molded body having a three-dimensional shape.

In particular, molded articles for optical applications (optical components) may require high transparency (and further low colorability, high surface hardness, etc.), and the method of the present invention can be suitably used for producing such molded articles.

The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Unless otherwise specified, "%" below means "% by mass (weight)" and "parts" means "parts by mass (weight)".

Measurements and evaluations of various physical properties were performed using the following methods.

[Weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn)]
The weight average molecular weight and molecular weight distribution of the resin were determined in terms of polystyrene using gel permeation chromatography (GPC) using the following apparatus and conditions:
System: Tosoh GPC system HLC-8320
Measurement column configuration Guard column: Tosoh TSKguardcolumn SuperHZ-L
Separation column: Tosoh Corporation, TSKgel SuperHZM-M, two columns connected in series Reference column configuration Reference column: Tosoh Corporation, TSKgel SuperH-RC
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade)
Flow rate of developing solvent: 0.6 mL/min. Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Column temperature: 40°C

[Glass transition temperature (Tg)]
The glass transition temperature was measured in accordance with the provisions of JIS K7121-1987. Specifically, a differential scanning calorimeter (Rigaku's "Thermo plus EVO DSC-8230") was used to measure the glass transition temperature by the starting point method from a DSC curve obtained by heating about 10 mg of a sample from room temperature to 200°C (heating rate 20°C/min) in a nitrogen gas atmosphere. α-alumina was used as a reference.

[Melt flow rate (MFR)]
The melt flow rate was measured in accordance with JIS K 7210-1:2014 Method A at a temperature of 230°C and a load of 3.8 kg (37 N).

[Proportion of lactone ring structure contained in acrylic resin]
First, the amount of weight loss that occurs when all hydroxyl groups from the polymer composition obtained by polymerization are dealcoholized as methanol was used as a standard, and the dealcoholization reaction rate was calculated from the weight loss due to the dealcoholization reaction from 150°C, before the weight loss began, to 300°C, before decomposition of the polymer began, in dynamic TG measurement.
That is, in dynamic TG measurement of a polymer having a lactone ring structure, the weight loss rate is measured between 150° C. and 300° C., and the obtained actual weight loss rate is designated as (X). On the other hand, based on the composition of the polymer, it is assumed that all hydroxyl groups contained in the polymer composition are involved in the formation of lactone rings and become alcohols, and are dealcoholized, and the theoretical weight loss rate (i.e., the weight loss rate calculated on the assumption that a 100% dealcoholization reaction occurs in that composition) is designated as (Y).
More specifically, the theoretical weight reduction rate (Y) can be calculated from the molar ratio of a raw material monomer having a structure (hydroxyl group) involved in a dealcoholization reaction in the polymer, i.e., the content of the raw material monomer in the polymer composition.
These values (X) and (Y) are used to calculate dealcoholization:
1-(Actual weight reduction rate (X)/Theoretical weight reduction rate (Y))
By substituting the above into the above equation and expressing the value as a percentage, the dealcoholization reaction rate can be obtained.
The ratio of lactone ring structures in the pellets obtained in Production Example 6 (Production Example 7) described later is calculated. The theoretical weight reduction rate (Y) of this polymer is calculated as follows: the molecular weight of methanol is 32, the molecular weight of methyl 2-(hydroxymethyl)acrylate is 116, and the content (mass ratio) of methyl 2-(hydroxymethyl)acrylate in the polymer is 13 mass% in terms of composition, so that it is (32/116) x 13 ≒ 3.59 mass%. On the other hand, the actual weight reduction rate (X) measured by dynamic TG measurement was 0.08 mass%. When these values are applied to the above dealcoholization calculation formula, it becomes 1-(0.08/3.59) ≒ 0.978, so the dealcoholization reaction rate is 97.8%.
In the case of Production Example 1, the content of methyl 2-(hydroxymethyl)acrylate in the copolymer was 13.0% by mass, the calculated dealcoholization reaction rate was 97.8% by mass, and the formula weight of the lactone cyclized structural unit produced when methyl 2-(hydroxymethyl)acrylate having a molecular weight of 116 is condensed with methyl methacrylate is 170. Therefore, the content of lactone rings in the copolymer was 8.6 (13.0 × 0.978 × 170/116)% by mass.

[Acid value]
The acid value was measured by the following method. First, 0.15 g of the polymer was dissolved in 24.94 g of methylene chloride. 14.85 g of methanol was added to the obtained solution and stirred for 3 hours. Next, 2 drops of a 1 wt% phenolphthalein ethanol solution were added to the solution. While stirring the obtained solution, a 0.1 N aqueous sodium hydroxide solution was added, and stirring was continued at room temperature for 1 hour. At this time, the amount of the 0.1 N aqueous sodium hydroxide solution added is defined as A ml. Next, 0.1 N hydrochloric acid was dropped into the solution. The amount of 0.1 N hydrochloric acid added until the color of the solution (red purple) disappeared is defined as B ml.
Next, a mixed solution of 24.94 g of methylene chloride and 14.85 g of methanol was prepared. Two drops of a 1 wt% phenolphthalein ethanol solution were added to this mixed solution. Next, while stirring this mixed solution, a 0.1 N aqueous sodium hydroxide solution was added, and stirring was continued for 1 hour at room temperature. At this time, the amount of the 0.1 N aqueous sodium hydroxide solution added is defined as C ml. Next, 0.1 N hydrochloric acid was dropped into this mixed solution. The amount of 0.1 N hydrochloric acid added until the color of the mixed solution (reddish purple) disappeared is defined as D ml.
The acid value (mmol/g) of the polymer was calculated from the following formula: The acid value represents the amount of sodium hydroxide required to neutralize the acidic groups contained in 1 g of the polymer and the acidic groups generated by hydrolysis of the acid anhydride groups.
[Acid value (mmol/g)]=0.1×[(AB)-(CD)]/0.15

[Yellowness index (YI)]
The yellowness was measured on a 3 mm thick molded body using a spectrophotometer (Shimadzu Corporation, UV-3600) with a C2 degree light source and a wavelength range of 380 nm to 780 nm in accordance with the provisions of JIS K7373: 2006. The molded body was prepared by drying the obtained pellets at 100°C for 12 hours or more at 100°C using an injection molding machine (Nissei Plastics, NS40-5A) under the injection molding machine set temperature conditions described below, in a mold with a size of 100 mm x 100 mm x 3 mm thickness, and at a mold temperature of 100°C (100 mm x 100 mm x 3 mm thick injection molded body).

[Three-point bending test]
The three-point bending test was performed in accordance with the provisions of JIS K7171: 2016 using a bending tester (Instron universal testing machine model 185). The pellets obtained were dried at 100 ° C. for 12 hours or more, and then molded bodies were produced using a manual heat press molding machine (manufactured by Imoto Seisakusho Co., Ltd.) at a molding temperature of 220 ° C. and a mold size of 127 mm × 12.7 mm × thickness 3.2 mm.
The bending test was performed under the measurement conditions of a span of 60 mm and a test speed of 2 mm/min, and the maximum bending stress (bending strength) and bending elastic modulus were measured.

[Pellet size]
The pellet size was measured using a digital caliper. Twenty of the obtained pellets were fixed with double-sided tape so that the cross-sectional direction of each pellet was horizontal to the flat plate. The average values of the major axis and minor axis of the pellet cross-section were calculated for these arranged pellets. Furthermore, the average value of the maximum height of the pellet cross-section was calculated as the thickness of the pellet.

[Weighing time and weighing variation]
The pellets thus obtained were dried at 100°C for 12 hours or more, and then molded using an injection molding machine (NS40-5A, manufactured by Nissei Plastics Co., Ltd.) under the temperature setting conditions of the injection molding machine described below. The weighing times during 20 continuous shots were measured, and the average value and standard deviation were calculated. The average value was taken as the weighing time, and the standard deviation was taken as the weighing variation.
The shorter the weighing time, the better the weighing stability.

[Silver Streak Occurrence Rate]
The obtained pellets were dried at 100°C for 12 hours or more, and then a molded body (injection molded body having a size of 100 mm x 100 mm x thickness of 3 mm) was produced using an injection molding machine (NS40-5A, manufactured by Nissei Plastics Co., Ltd.) at a mold temperature of 100°C in a mold having a size of 100 mm x 100 mm x thickness of 3 mm under the injection molding machine set temperature conditions described below.
The number of molded products on which silver streaks occurred among the 20 molded products was visually confirmed, and the result was calculated as the silver streak occurrence rate according to the following formula.
Silver streak occurrence rate (%) = [number of sheets with silver streaks/20] x 100

(Production Example 1 [Production of Acrylic Resin Pellets (B1)])
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen inlet tube, and a dropping pump was charged with 11.5 parts by mass of methyl 2-(hydroxymethyl)acrylate (RHMA), 38.5 parts by mass of methyl methacrylate (MMA), 90.7 parts by mass of toluene, and 0.05 parts by mass of tris(2,4-di-tert-butylphenyl)phosphite, and the temperature was raised to 105° C. while passing nitrogen through.
As an initial initiator, a solution consisting of 4.3 parts by mass of toluene and 0.29 parts by mass of t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added dropwise over 8 minutes to carry out solution polymerization at 105 ° C. to 110 ° C. Then, 22 minutes later, a solution consisting of 5.0 parts by mass of toluene and 0.30 parts by mass of t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added dropwise over 170 minutes as a dropping initiator. In addition, 25 minutes after the initial initiator was added, a solution consisting of 11.5 parts by mass of 2-(hydroxymethyl) methyl acrylate (RHMA) and 38.5 parts by mass of methyl methacrylate (MMA) was added dropwise over 180 minutes to carry out solution polymerization at 105 ° C. to 110 ° C., and then aged for 1.5 hours.
To the obtained polymerization solution, a solution consisting of 1.25 parts by mass of toluene and 0.30 parts by mass of stearyl phosphate (Phoslex A-18, manufactured by Sakai Chemical Industry Co., Ltd.) was added as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction for forming a lactone ring structure was allowed to proceed under reflux at about 90° C. to 110° C. for 2 hours.
Next, the obtained polymerization solution was passed through a multi-tube heat exchanger maintained at 240 ° C. to complete the cyclization condensation reaction, and then introduced into a vent-type screw twin-screw extruder (L / D = 52) with a leaf disk-type polymer filter (filtration accuracy 5 μm) at the tip at a processing rate of 90 parts by weight / hour in terms of resin amount, and the polymerization solution was devolatilized to obtain resin pellets (B1). The number of rear vents of the vent-type screw twin-screw extruder used was 1, the number of fore vents was 4 (referred to as the first, second, third, and fourth vents from the upstream side), the barrel temperature was 240 ° C., and the degree of vacuum was 13.3 to 400 hPa (10 to 300 mmHg). During devolatilization, ion-exchanged water was introduced from behind the first and third vents at a rate of 1.3 parts by weight / hour, and a mixed solution of a bluing agent and an antioxidant prepared separately was introduced from behind the second vent at a rate of 0.30 parts by weight / hour. As a mixed solution of bluing agent and antioxidant, a solution consisting of 0.27 parts by weight of a solution obtained by dissolving 1.0 part by weight of bluing agent (Sumiplast (registered trademark) Violet B manufactured by Sumika Chemtex Corporation) in 99 parts by weight of toluene, 3.6 parts by weight of two types of antioxidants (Irganox 1010 manufactured by BASF Japan Ltd. and Adeka STAB AO-412S manufactured by ADEKA Corporation), and 112.5 parts by weight of toluene was used.

(Production Example 2 [Production of Acrylic Resin Pellets (A1)])
The resin pellets (B1) obtained in Production Example 1 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 225° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 2.3 kg/h from a die (narrow hole) having a diameter of 1.5 mmφ provided in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.012 g pieces by rotating (1600 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A1) having a major axis of 3 mm, a minor axis of 3 mm, and a thickness of 2.4 mm.

The weight average molecular weight of the obtained resin pellets (A1) was 80,000, the molecular weight distribution was 2.1, the glass transition temperature was 132°C, the melt flow rate was 4.0, the proportion of ring structures was 28.8% by mass, and the acid value was 0.3 mmol/g or less.

(Production Example 3 [Production of Acrylic Resin Pellets (A2)])
The resin pellets (B1) obtained in Production Example 1 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 225° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 3 kg/h from a die (narrow hole) having a diameter of 2 mmφ provided in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.016 g pieces by rotating (1600 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A2) having a major axis of 3.5 mm, a minor axis of 3.5 mm, and a thickness of 2.4 mm.

The weight average molecular weight of the obtained resin pellets (A2) was 80,000, the molecular weight distribution was 2.1, the glass transition temperature was 132°C, the melt flow rate was 4.0, the proportion of ring structures was 28.8% by mass, and the acid value was 0.3 mmol/g or less.

(Production Example 4 [Production of acrylic resin pellets (A3)])
The resin pellets (B1) obtained in Production Example 1 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 225° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 3.6 kg/h from a die (narrow hole) having a diameter of 2.5 mmφ of the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.021 g pieces by rotating (1750 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A3) having a major axis of 3.8 mm, a minor axis of 3.8 mm, and a thickness of 2.7 mm.

The weight average molecular weight of the obtained resin pellets (A3) was 80,000, the molecular weight distribution was 2.1, the glass transition temperature was 132°C, the melt flow rate was 4.0, the proportion of ring structures was 28.8% by mass, and the acid value was 0.3 mmol/g or less.

(Production Example 5 [Production of Acrylic Resin Pellets (A4)])
The resin pellets (B1) obtained in Production Example 1 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 225° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 3.6 kg/h from a die (narrow hole) having a diameter of 3 mmφ provided in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.03 g pieces by rotating (1250 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A4) having a major axis of 4.6 mm, a minor axis of 4.6 mm, and a thickness of 2.7 mm.

The weight average molecular weight of the obtained resin pellets (A4) was 80,000, the molecular weight distribution was 2.1, the glass transition temperature was 132°C, the melt flow rate was 4.0, the proportion of ring structures was 28.8% by mass, and the acid value was 0.3 mmol/g or less.

(Production Example 6 [Production of acrylic resin pellets (B2)])
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen inlet tube, and a dropping pump was charged with 6.5 parts by mass of methyl 2-(hydroxymethyl)acrylate (RHMA), 43.5 parts by mass of methyl methacrylate (MMA), 90.7 parts by mass of toluene, and 0.05 part by mass of tris(2,4-di-tert-butylphenyl)phosphite, and the temperature was raised to 105° C. while passing nitrogen through.
As the initial initiator, a solution consisting of 4.3 parts by mass of toluene and 0.22 parts by mass of t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added dropwise over 8 minutes to carry out solution polymerization at 105 ° C. to 110 ° C. Then, 22 minutes later, a solution consisting of 5.0 parts by mass of toluene and 0.28 parts by mass of t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added dropwise over 180 minutes to carry out solution polymerization at 105 ° C. to 110 ° C. while dropping a solution consisting of 6.5 parts by mass of 2-(hydroxymethyl) methyl acrylate (RHMA) and 43.5 parts by mass of methyl methacrylate (MMA) over 180 minutes, and then aged for 1.5 hours.
To the obtained polymerization solution, a solution consisting of 1.25 parts by mass of toluene and 0.075 parts by mass of stearyl phosphate (Phoslex A-18, manufactured by Sakai Chemical Industry Co., Ltd.) was added as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 1.5 hours under reflux at about 90° C. to 110° C.
Next, the obtained polymerization solution was passed through a multi-tube heat exchanger maintained at 220 ° C. to complete the cyclization condensation reaction, and then introduced into a vent-type screw twin-screw extruder (L / D = 52) with a leaf disk-type polymer filter (filtration accuracy 5 μm) at the tip at a processing rate of 90 parts by weight / hour in terms of resin amount, and the polymerization solution was devolatilized to obtain resin pellets (B2). The number of rear vents of the vent-type screw twin-screw extruder used was 1, the number of fore vents was 4 (referred to as the first, second, third, and fourth vents from the upstream side), the barrel temperature was 220 ° C., and the degree of vacuum was 13.3 to 400 hPa (10 to 300 mmHg). During devolatilization, ion-exchanged water was charged from behind the first, second, and third vents at a charging rate of 1.3 parts by weight / hour.

(Production Example 7 [Production of acrylic resin pellets (A5)])
The resin pellets (B2) obtained in Production Example 6 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 225° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 2.3 kg/h from a die (narrow hole) having a diameter of 1.5 mmφ provided in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.012 g pieces by rotating (1600 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A5) having a major axis of 3 mm, a minor axis of 3 mm, and a thickness of 2.4 mm.

The weight average molecular weight of the obtained resin pellets (A5) was 88,000, the molecular weight distribution was 2.2, the glass transition temperature was 123°C, the melt flow rate was 4.5, the proportion of ring structures was 18.6% by mass, and the acid value was 0.2 mmol/g or less.

(Production Example 8 [Production of acrylic resin pellets (B3)])
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube and a nitrogen inlet tube was charged with 10 parts by weight of 2-(hydroxymethyl)methyl acrylate (RHMA), 40 parts by weight of methyl methacrylate (MMA), 0.025 parts by weight of tris(2,4-di-tert-butylphenyl)phosphite and 50 parts by weight of toluene as a polymerization solvent. Next, the temperature was raised to 105°C while introducing nitrogen gas into the reaction vessel, and when refluxing accompanying the temperature rise began, 0.05 parts by weight of tertiary amyl peroxy isononanoate (manufactured by Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added as a polymerization initiator. At the same time, dropwise addition of 0.10 parts by weight of the above tertiary amyl peroxy isononanoate was started, and while dropping this over 2 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110°C. After the dropwise addition was completed, the reaction vessel was continued to be heated for 4 hours to perform aging.

Next, 0.05 parts by weight of stearyl phosphate (Phoslex A-18, manufactured by Sakai Chemical Industry Co., Ltd.) was added to the polymerization solution thus obtained as a catalyst for the cyclization reaction, and the cyclization condensation reaction to form a lactone ring structure was carried out under reflux at approximately 90°C to 110°C for 2 hours.

Next, the obtained polymerization solution was passed through a multi-tube heat exchanger maintained at 240°C to complete the cyclization condensation reaction, and then introduced into a vent-type twin-screw extruder (L/D = 52) equipped with a leaf disk-type polymer filter (filtration accuracy 5 μm) at the tip at a processing speed of 90 parts by weight/hour in terms of resin amount, and the polymerization solution was devolatilized to obtain resin pellets (B3). The vent-type twin-screw extruder used had one rear vent and four fore vents (referred to as the first, second, third, and fourth vents from the upstream side), a side feeder was placed between the third and fourth vents, the barrel temperature was 240°C, and the degree of vacuum was 13.3 to 400 hPa (10 to 300 mmHg). During devolatilization, ion-exchanged water was fed at a rate of 1.3 parts by weight/hour from behind the second vent, and a separately prepared solution of a cyclization catalyst deactivator was fed at a rate of 0.6 parts by weight/hour from behind the third vent. As the solution of the cyclization catalyst deactivator, a solution in which 1.0 part by weight of zinc octylate (manufactured by Nippon Kagaku Sangyo Co., Ltd., product name: Nikka Octyx Zinc 10% by weight) was dissolved in 0.3 parts by weight of toluene was used.

(Production Example 9 [Production of acrylic resin pellets (A6)])
The resin pellets (B3) obtained in Production Example 8 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 250° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 3.6 kg/h from a die (narrow hole) having a diameter of 3 mmφ provided in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.03 g pieces by rotating (1250 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A6) having a major axis of 4.6 mm, a minor axis of 4.6 mm, and a thickness of 2.7 mm.

The weight average molecular weight of the obtained resin pellets (A6) was 116,000, the molecular weight distribution was 2.6, the glass transition temperature was 130°C, the melt flow rate was 0.8, the proportion of ring structures was 28.6% by mass, and the acid value was 0.3 mmol/g or less.

(Production Example 10 [Production of Acrylic Resin Pellets (B4)])
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen inlet tube, and a dropping pump was charged with 12 parts by mass of methyl 2-(hydroxymethyl)acrylate (RHMA), 83.5 parts by mass of methyl methacrylate, 90.4 parts by mass of toluene, 0.05 part by mass of tris(2,4-di-tert-butylphenyl)phosphite, and 0.07 part by mass of n-dodecyl mercaptan as a chain transfer agent, and the temperature was raised to 105° C. while passing nitrogen through.
0.09 parts by mass of t-amyl peroxy isononanoate (Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added as an initial initiator, and 5 minutes later, a solution consisting of 4.5 parts by mass of styrene (St), 8.14 parts by mass of toluene, and 0.179 parts by mass of a dropping initiator t-amyl peroxy isononanoate (Arkema Yoshitomi Co., Ltd., Luperox (registered trademark) 570) was added dropwise over 2 hours while carrying out solution polymerization at 100°C to 110°C, and further aging was carried out over 4 hours.
To the obtained polymerization solution, 0.075 parts by mass of stearyl phosphate (Phoslex A-18, manufactured by Sakai Chemical Industry Co., Ltd.) was added as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction for forming a lactone ring structure was allowed to proceed under reflux at about 90° C. to 110° C. for 1.5 hours.
Next, the obtained polymerization solution was passed through a multi-tube heat exchanger maintained at 240 ° C. to complete the cyclization condensation reaction, and then introduced into a vent-type screw twin-screw extruder (L / D = 52) with a leaf disk-type polymer filter (filtration accuracy 5 μm) at the tip at a processing rate of 90 parts by weight / hour in terms of resin amount, and the polymerization solution was devolatilized to obtain resin pellets (B4). The number of rear vents of the vent-type screw twin-screw extruder used was 1, the number of fore vents was 4 (referred to as the first, second, third, and fourth vents from the upstream side), the barrel temperature was 240 ° C., and the degree of vacuum was 13.3 to 400 hPa (10 to 300 mmHg). During devolatilization, ion-exchanged water was introduced from behind the first and second vents at a rate of 1.3 parts by weight / hour, and a solution of a cyclization catalyst deactivator separately prepared was introduced from behind the third vent at a rate of 0.3 parts by weight / hour. As the solution of the cyclization catalyst deactivator, a solution in which 1.0 part by weight of zinc octylate (manufactured by Nippon Kagaku Sangyo Co., Ltd., trade name: Nikka Octyx Zinc 10% by weight) was dissolved in 0.3 parts by weight of toluene was used.

(Production Example 11 [Production of acrylic resin pellets (A7)]
The resin pellets (B4) obtained in Production Example 10 were melt-kneaded using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (manufactured by Tanabe Plastics Machinery Co., Ltd., RP40) at the tip at a cylinder temperature of 240° C. and a screw rotation speed of 25 rpm, and the molten acrylic resin was extruded at 3.6 kg/h from a die (narrow hole) having a diameter of 3 mmφ in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.03 g pieces by rotating (1250 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A7) having a major axis of 4.6 mm, a minor axis of 4.6 mm, and a thickness of 2.7 mm.

The weight average molecular weight of the obtained resin pellets (A7) was 130,000, the molecular weight distribution was 2.7, the glass transition temperature was 123°C, the melt flow rate was 1.6, the proportion of ring structures was 16.9% by mass, and the acid value was 0.2 mmol/g or less.

(Production Example 12 [Production of acrylic resin pellets (A8)]
Pellets of a commercially available acrylic resin (Sumipex MH, manufactured by Sumitomo Chemical Co., Ltd., an acrylic resin having no ring structure and composed mainly of methyl methacrylate) were melt-kneaded at a cylinder temperature of 225°C and a screw rotation speed of 25 rpm using an extruder (φ=40 mm, L/D=16) equipped with a small hot-cut pelletizer (RP40, manufactured by Tanabe Plastics Machinery Co., Ltd.) at the tip, and the molten acrylic resin was extruded at 2.8 kg/h from a die (fine hole) having a diameter of 3 mmφ in the extrusion die.
The molten acrylic resin extruded from the extrusion die was cut into approximately 0.023 g pieces by rotating (1250 rpm) a cutter blade attached to the tip of the extruder, to obtain disk-shaped resin pellets (A8) having a major axis of 4.8 mm, a minor axis of 4.7 mm, and a thickness of 2.1 mm.

The weight average molecular weight of the resulting resin pellets (A8) was 93,000, the molecular weight distribution was 2.0, the glass transition temperature was 110°C, and the melt flow rate was 2.0.

Table 1 shows the evaluation results of the acrylic resin pellets (A) obtained in each production example.

Example 1
The acrylic resin pellets (A1) obtained in Production Example 2 were dried at 100°C for 12 hours or more, and then, using an injection molding machine (NS40-5A, manufactured by Nissei Plastics Co., Ltd.) having the same injection device as in FIG. 1, a molded body (size 100 mm x 100 mm x thickness 3 mm injection molded body) was produced at a mold temperature of 100°C in a mold having a size of 100 mm x 100 mm x thickness 3 mm at the set temperature of the injection molding machine shown in Table 2.

Example 2
A molded article was produced in the same manner as in Example 1, except that the pellets of the acrylic resin (A2) obtained in Production Example 3 were used.

Example 3
A molded article was produced in the same manner as in Example 1, except that the pellets of the acrylic resin (A3) obtained in Production Example 4 were used.

Example 4
A molded body was produced in the same manner as in Example 1, except that the pellets of the acrylic resin (A3) obtained in Production Example 4 were used and the set temperature of the injection molding machine was changed.

Example 5
In Example 1, the pellets of the acrylic resin (A5) obtained in Production Example 7 were used, and a molded body was produced in the same manner as in Example 1, except that the set temperature of the injection molding machine was changed to 90° C.

(Example 6)
A molded article was produced in the same manner as in Example 1, except that the pellets of the acrylic resin (A4) obtained in Production Example 5 were used.

(Example 7)
A molded body was produced in the same manner as in Example 1, except that the pellets of the acrylic resin (A6) obtained in Production Example 9 were used and the set temperature of the injection molding machine was changed.

(Example 8)
In Example 1, the pellets of the acrylic resin (A7) obtained in Production Example 11 were used, and a molded body was produced in the same manner as in Example 1, except that the set temperature of the injection molding machine was changed to 90°C.

(Example 9)
In Example 1, the pellets of the acrylic resin (A8) obtained in Production Example 12 were used, and a molded body was produced in the same manner as in Example 1, except that the set temperature of the injection molding machine was changed to 80° C.

Example 10
A molded body was produced in the same manner as in Example 1, except that the pellets of the acrylic resin (A4) obtained in Production Example 5 were used and the set temperature of the injection molding machine was changed.

Table 2 shows the set temperatures of the injection molding machine and the evaluation results for each example.

As is clear from the table above, by adjusting the pellet size or the temperature of the cooling device to a specific value, it was possible to relatively reduce the occurrence of measurement variations and silver streaks.

In detail, the results of Examples 6, 10, and 7 show that for acrylic resins with a ring structure that have a relatively small MFR or a relatively large Mw, or for acrylic resins that do not have a ring structure, simply adjusting the temperature of the cooling device to a specific value can reduce the occurrence of measurement variations and silver streaks.

On the other hand, the results of Examples 1 to 5 and Examples 6 and 10 show that for acrylic resins with a ring structure that has a relatively large MFR or a relatively small Mw, the occurrence of metering variations and silver streaks can be efficiently reduced to a higher level by combining adjustment of the pellet size and adjustment of the cooling device temperature.

In addition, the results of Examples 6 and 10 show that by keeping the difference in the cooling device temperature (Tg-Tj) specified in the present invention within a specified range (for example, Tg-Tj is 70°C or less), it is possible to more efficiently reduce the variation in weighing (and even coloring).

The present invention provides a novel method for producing pellets.

1 Nozzle Hn Nozzle section 2 Cylinder H1 Cylinder front section (metering section)
H2 Cylinder middle section (compression section)
H3 Cylinder rear (supply section)
S1 Front of the screw (metering section)
S2: Middle screw section (compression section)
S3 Rear of the screw (supply section)
H4 Cooling device (cooling means)
3 Hopper 4 Temperature measuring device

Claims (19)

A method for injection molding a resin, comprising the steps of:
The resin comprises an acrylic resin (A),
As the resin, pellets with a major axis of 4.0 mm or less are used.
When Tj (°C) is the temperature of the cooling device installed in the supply section of the cylinder of the injection molding machine and Tg (°C) is the glass transition temperature of the resin, this method ensures that Tg - Tj (°C) is 72 or less. 2. The method according to claim 1 , wherein the acrylic resin (A) has a ring structure. The method according to claim 1 or 2 , wherein the acrylic resin (A) has a cyclic ester structure. The method according to any one of claims 1 to 3 , wherein the acrylic resin (A) has a melt flow rate of 2 g/10 min or more at 230°C under a load of 3.8 kg as measured in accordance with JIS K 7210. The method according to any one of claims 1 to 4 , wherein the weight average molecular weight of the acrylic resin (A) is 100,000 or less. The method according to any one of claims 1 to 5 , wherein the molecular weight distribution of the acrylic resin (A) is 2.5 or less. The method according to any one of claims 1 to 6 , wherein the acrylic resin (A) has a cyclic ester structure. The method according to any one of claims 1 to 7 , wherein the resin is in the form of pellets having a major axis of 3.8 mm or less. The method according to any one of claims 1 to 8 , wherein Tg-Tj (°C) is 50 or less. the acrylic resin (A) is an acrylic resin having a cyclic ester structure and satisfying at least one of the following: a melt flow rate of 2 g/10 min or more at 230° C. under a load of 3.8 kg, a weight average molecular weight of 100,000 or less, and a molecular weight distribution of 2.5 or less, all of which are in accordance with JIS K 7210;
The method according to any one of claims 1 to 9 , wherein pellets each having a major axis and a minor axis of 3.8 mm or less are used as the resin. As the resin, pellets with a major axis of 3.8 mm or less are used.
The method according to any one of claims 1 to 10, wherein Tg-Tj (°C) is 50 or less. The method according to any one of claims 1 to 11, wherein the pellet has a thickness of 3.5 mm or less. The method according to any one of claims 1 to 12, wherein the resin is in the form of pellets having a major axis of 3.8 mm or less and a thickness of 3.5 mm or less, and Tg-Tj (°C) is 50 or less. The method according to any one of claims 1 to 13, wherein the resin is in the form of pellets having a major axis of 3.8 mm or less and a thickness of 2.7 mm or less, and Tg-Tj (°C) is 50 or less. The acrylic resin (A) is an acrylic resin having a cyclic ester structure and a melt flow rate of 3.5 g/10 min or more at 230° C. under a load of 3.8 kg, as determined in accordance with JIS K 7210;
The method according to any one of claims 1 to 14, wherein pellets having a major axis of 3.8 mm or less and a thickness of 2.7 mm or less are used as the resin, and Tg-Tj (°C) is 50 or less. The injection molding machine includes a cylinder, a nozzle portion having a nozzle connected to a front end of the cylinder, and a hopper connected to a rear end of the cylinder;
A screw composed of a metering section, a compression section, and a supply section is housed in the cylinder, and these sections correspond to the metering section, the compression section, and the supply section of the cylinder when the screw is pushed in, respectively;
A cooling device is installed under the hopper at the base end of the cylinder supply section,
The method according to any one of claims 1 to 15, wherein the pellets are fed from a hopper into a supply section of the cylinder. The method according to any one of claims 1 to 16 , further comprising a pellet production step of cutting the resin to produce resin pellets, and using the resin pellets obtained in the pellet production step as the resin. 18. The method according to claim 17, wherein the resin is cut in a molten state during the pelletizing process. 19. The method according to claim 17 or 18, wherein in the pellet production step, the resin extruded from a die of an extruder is cut in a molten state.