JP6764150B2 - Manufacturing method of optical resin material - Google Patents

Description

The present invention particularly relates to an optical resin material in which the temperature dependence of the intrinsic birefringence of a polymer is suppressed (that is, the intrinsic birefringence does not change depending on the measurement temperature), and the intrinsic birefringence is adjusted to almost zero or a desired value. The present invention relates to a method for producing the optical resin material, an optical resin member made of these materials, and a polarizing plate made of the member.

In recent years, the spread and development of liquid crystal displays has been remarkable, and it is no exaggeration to say that they are used in all kinds of electronic devices. In addition, the size of desktop personal computer monitors and LCD TVs is increasing, and many products of 40 inches or more are on the market. A liquid crystal panel generally used for a liquid crystal display has a structure in which a liquid crystal display cell in which a liquid crystal component is sandwiched between two glass substrates and a polarizing plate are laminated, and on the surface of each substrate, Generally, it has a structure in which optical members such as an optical film capable of exhibiting various functions such as a polarizing film, a retardation film, and an antireflection film are laminated. As a material for such an optical member, a light-transmitting resin called "optical resin" or "optical polymer" is widely used. Further, the optical member made of these resin materials is used not only for the above-mentioned liquid crystal display but also for various optical related devices. For example, in addition to the above, as a functional member required to have better optical characteristics, such as a lens in a signal reading lens system of an optical disk, a Fresnel lens for a projection screen, and a plastic lens such as a lenticular lens. Is also used.

Here, the resin film is manufactured by, for example, melt extrusion molding, stretching, or the like because of its productivity. In various optical films and plastic lenses made of the optical polymer produced in this way, the polymer molecules are oriented in either direction for various reasons, and the light is not in an ideal amorphous state. It is known that a state in which the refractive index differs depending on the polarization direction of the light, that is, birefringence occurs. There are several known types of birefringence of polymers, but they are important for optical films for liquid crystal displays used in the above-mentioned various optical-related devices and transparent polymers used for plastic lenses and the like. Those are "orientation birefringence" and "photoelastic birefringence", which particularly affect the optical characteristics.

On the other hand, a method is known in which one of orientation birefringence and photoelastic birefringence is almost eliminated by selecting an additive to a light-transmitting polymer and its concentration, or by selecting a combination of copolymerization and a composition ratio. However, the method of reducing one was insufficient to reduce the other. Under such circumstances, the inventors of the present application have proposed a method of simultaneously reducing and almost eliminating the orientation birefringence and photoelastic birefringence of the optical resin material, and both the orientation birefringence and the photoelastic birefringence Both propose very small optical resins (optical polymers) and applications of the resins to optical members (optical elements, optical components, etc.) (see Patent Document 1).

Specifically, for an optical material having a composite component system of three or more components including a birefringent system or more, the optical material orients the combination and component ratio (composition ratio) of the components of the composite component system. We have proposed a method of selecting so that both birefringence and photoelastic birefringence are canceled at the same time, thereby obtaining an optical resin in which both orientation birefringence and photoelastic birefringence are very small. .. As a result, the problem of light leakage due to birefringence can be improved, and by using the obtained optical resin, "color unevenness phenomenon", "light leakage", "color change depending on the observation angle", etc. that occur in the screen, etc. It is possible to suppress.

Japanese Patent No. 4624845

However, as a result of further studies, the present inventors have conducted both oriented birefringence and photoelastic birefringence in a composite component system having three or more components including a binary system or a copolymerized system in the above-mentioned conventional technique. Although very small optical resins can be obtained in both cases, the optical characteristics of this optical film are those at room temperature, and it has been newly recognized that there are the following technical problems in the actual usage environment. .. Specifically, in the above-mentioned prior art, the composite component system is determined by utilizing the intrinsic birefringence of each homopolymer corresponding to each monomer constituting each component of the copolymer, and in that case, the intrinsic birefringence is determined. We considered refringence at room temperature (normal temperature), but we newly found that intrinsic birefringence has temperature dependence, and in particular, the tendency increases as the temperature rises, and the present inventors have found this point. I came to recognize that it is necessary to consider. That is, as described above, optical films are used in various optical-related devices, but for example, mobile phones and personal computers are not always used at so-called normal temperature, and are not always used at so-called normal temperature, and are extremely cold or extremely hot. It is also used in various temperature environments, and in particular, since these devices generate heat during operation, various heat dissipation and cooling means are considered, but the temperature of the optical film rises locally. Something is happening. On the other hand, if a product that considers the temperature dependence of the intrinsic birefringence newly found by the present inventors, which affects the optical characteristics, can be obtained, it is extremely useful in practical use.

Therefore, an object of the present invention is to provide a resin product such as an optical film that takes into consideration the temperature dependence of the intrinsic birefringence (that is, the orientation birefringence inherent to the polymer) that affects the optical properties newly found by the present inventors. Providing a technology that can be stably and surely obtained, and further, stably and surely obtain a resin material that has very small intrinsic birefringence and whose temperature dependence is reduced, which is useful for optical applications. It is to provide the technology that can be used. If such a technology is provided, "color unevenness phenomenon", "light leakage", etc. that occur in the screen due to the optical film used in various optical related devices used in various temperature ranges, etc. It becomes possible to reliably suppress "color change depending on the observation angle", and it becomes possible to design a stable high-performance liquid crystal display or the like. Another object of the present invention is useful for optical applications in which the intrinsic birefringence is set to a desired value in consideration of temperature dependence by appropriately using the above technique, and the temperature dependence is reduced. It is an object of the present invention to provide a technique that enables the resin material to be stably and reliably adjusted, and for example, to synthesize a polymer that easily develops orientation birefringence. If such a technique is provided, for example, in the case of a retardation film for a liquid crystal display, it is necessary to adjust the orientation birefringence and the thickness so as to obtain a desired retardation by stretching the film in the manufacturing process. However, since a film having a desired orientation and birefringence can be obtained at a draw ratio that is easy to manufacture, a great merit in manufacturing can be obtained.

As a result of diligent studies on the above-mentioned problems of the prior art, the present inventors have, for example, a composite component system having two or more components including a binary system or more copolymer system and a uniyuan system or more (co) polymerization system. When designing the combination of the types of monomer components constituting the composite component system and the component ratio (composition ratio) of the optical resin material having the above, the present inventors have newly found uniqueness that affects the optical characteristics. We have found a method for reducing the temperature dependence in birefringence (that is, the orientation birefringence peculiar to a polymer), and have arrived at the present invention.

The above object is achieved by the following invention. That is, the present invention is an optical resin material containing a composite component system in which the number of components z defined under the condition of including the element number x (x ≧ 1) of the (co) polymer in the number of components and counting is 2 or more. Therefore, the composite component system is polarized only with a polymer having an element x of 2 or more, or a polymer having an element x of 1 or a copolymer having an element x of 2 or more. It is composed of at least one kind of low molecular weight organic compound which has anisotropy of ratio and can be oriented in the polymer, and the combination of the components constituting the composite component system forms the copolymer or the polymer. At least one of the intrinsic compound refraction temperature coefficient of each homopolymer corresponding to each monomer component and the intrinsic compound refraction temperature coefficient that the low molecular weight organic compound commonly exhibits in each homopolymer is different from the others. The component ratios of the components selected to be the symbols and constituting the composite component system are such that the intrinsic double refraction temperature dependence is canceled by utilizing the heterogeneous sign relationship with respect to the intrinsic copolymer temperature coefficient. Provided is an optical resin material characterized by being selected.

As a preferable form of the optical resin material, a uniaxially stretched film composed of the composite component system is used, and the temperature of the film is controlled stepwise in the range of 15 to 70 ° C., and the intrinsic birefringence at each temperature is performed. The absolute value of the intrinsic birefringence temperature coefficient dΔn ⁰ / dT at 15 ° C. to 70 ° C., which was obtained by measuring Δn ⁰ as the amount of change in the intrinsic birefringence per 1 ° C. from the obtained measurement results, was 1.0 × 10. It is in the range of ^-5 (° C ^-1 ) or less, and the temperature dependence of the intrinsic birefringence is reduced.

Further, the present invention is an optical resin material containing a composite component system in which the number of components z defined under the condition of including the element number x (x ≧ 2) of the copolymer in the number of components and counting is 3 or more. The composite component system is composed of only a copolymer having a element number x of 3 or more, or is in a polymer having an anisotropy of a polarization rate with a copolymer having an element number x of 2 or more. It is composed of at least one kind of low molecular weight organic compound that can be oriented, and the combination of the components constituting the composite component system is the intrinsic birefringence of each homopolymer corresponding to each monomer component forming the copolymer. At least one of the symbols of the above and the orientation birefringent symbols that the low molecular weight organic compound commonly shows in each of the homopolymers has a different code from the others, and is unique to each of the homopolymers. Of the birefringence temperature coefficient and the intrinsic birefringence temperature coefficient that the low molecular weight organic compound commonly exhibits in each of the homopolymers, at least one is selected so as to have a different sign from the others, and the composite component system is used. The component ratio of each component constituting the above is dependent on the intrinsic birefringence and the intrinsic birefringence temperature indicated by the optical resin by utilizing the different sign relationship regarding the orientation birefringence and the different sign relationship regarding the intrinsic birefringence temperature coefficient. Provided is an optical resin material characterized in that are selected to be offset at the same time.

The following are preferable forms of the optical resin material. Using the uniaxially stretched film composed of the composite component system, the intrinsic birefringence Δn ⁰ at each temperature was measured and obtained in a state where the temperature of the film was controlled stepwise in the range of 15 to 70 ° C. The absolute value of the intrinsic birefringence temperature coefficient dΔn ⁰ / dT at 15 ° C to 70 ° C, which was obtained from the measurement results as the amount of change in the intrinsic birefringence per 1 ° C, is in the range of 1.0 × ^10-5 (° C ^-1 ) or less. It is inside, and the temperature dependence of the intrinsic birefringence is reduced; it is an optical resin material composed of a copolymer composed by copolymerizing monomer components having three or more kinds of components, and the above three kinds. The combination of the above monomer components and the composition ratio of these monomer components set the natural birefringence Δn ⁰ at 25 ° C. of the uniaxially stretched film composed of each homopolymer corresponding to each monomer component and the temperature of the film from 15 to 70. The intrinsic birefringence Δn ⁰ at each temperature was measured in a state of being controlled stepwise in the range of ° C., and the intrinsic birefringence temperature coefficient obtained as the amount of change in the intrinsic birefringence per 1 ° C. from the obtained measurement results. Determined using dΔn ⁰ / dT, the intrinsic birefringence Δn ^{0 at} 25 ° C. measured using the uniaxially stretched film made of the copolymer has an absolute value of 3.0 × 10 ^-3 or less. , Or adjusted so that the absolute value of the intrinsic birefringence at 25 ° C is 0.01 or more, and in any case, the 15 ° C. The temperature dependence of the intrinsic birefringence is reduced, adjusted so that the absolute value of the intrinsic birefringence temperature coefficient dΔn ⁰ / dT at ~ 70 ° C is 1.0 × 10 ^-5 (° C ^-1 ) or less. That is.

Further, as another embodiment, the present invention is a method for producing any of the above optical resin materials, in which the type of the monomer component of the composite component system to be selected as the raw material is determined, and two or more selected types are selected. It has a raw material adjusting step that determines the composition ratio of the monomer components, and in the raw material adjusting step, the temperature of the film is stepwise in the range of 15 to 70 ° C. for the birefringent film made of each homopolymer corresponding to each monomer component. The intrinsic birefringence at each temperature was measured in the controlled state, and the intrinsic birefringence temperature coefficient dΔn ⁰ / dT, which is the amount of change in the intrinsic birefringence per 1 ° C., was calculated from the obtained measurement results. A relational graph between the intrinsic birefringence temperature coefficient dΔn ⁰ / dT and the intrinsic birefringence Δn ⁰ measured at 25 ° C. was created, and from the relational graph, the intrinsic birefringence Δn ⁰ measured at 25 ° C. and the intrinsic birefringence temperature were obtained. A combination in which there may be a composition in which both the coefficients dΔn ⁰ / dT are zero, or when the intrinsic birefringence temperature coefficient dΔn ⁰ / dT is zero and the absolute value of the intrinsic birefringence at 25 ° C. is 0.01 or more. By selecting a combination in which a composition having a desired value can be present, the type of the monomer component is determined, and the uniqueness measured at 25 ° C., which is unique to the copolymer obtained by copolymerizing the selected monomer component. When the birefringence Δn ⁰ becomes zero, or the absolute value of the intrinsic birefringence measured at 25 ° C. becomes a desired value of 0.01 or more, and the intrinsic birefringence temperature coefficient dΔn ⁰ / dT becomes zero. Assuming, by calculating the mass ratio of each monomer component, the composition ratio of the monomer component to be combined is determined, and the monomer component of the type selected and determined above is used, and the composition ratio of the monomer component is determined above. Provided is a method for producing an optical resin material, which comprises synthesizing a copolymer by copolymerizing the monomers blended as described above.

As a preferable form of the method for producing an optical resin material, when determining the composition ratio of the monomer components to be combined, there are N types of monomer components (where N is an integer of 3 or more), and these monomer components are copolymerized. Assuming that the intrinsic compound refraction and the intrinsic compound refraction temperature coefficient peculiar to the copolymer obtained are both 0 (zero) or the desired values, the mass fraction of each monomer is calculated using the following simultaneous equations. It is possible to calculate and determine the composition ratio of the monomers constituting the copolymer.
In [the formula (i), [Delta] n ⁰ ₁ represents the intrinsic birefringence of the first homopolymer, [Delta] n ⁰ ₂ denotes the intrinsic birefringence of the second homopolymer, [Delta] n ⁰ _N is the Represents the intrinsic birefringence of the Nth homopolymer. In the above formula _{^{(ii), dΔn 0 1 /}} dT represents the intrinsic birefringence temperature coefficient of the first homopolymer, d.DELTA.n ⁰ ₂ / dT represents the intrinsic birefringence temperature coefficient of the second homopolymer , DΔn ⁰ _N / dT represent the temperature coefficient of intrinsic birefringence of the Nth homopolymer. In the above formula (iii), W ₁ , W ₂ , and W _N represent the first, second, and Nth monomer mass fractions (%), respectively. ]

Further, the present invention is characterized in that any of the above optical resin materials is formed in the form of a film and is adjusted so as not to cause the temperature dependence indicated by the intrinsic birefringence. Provide members. A preferred form thereof further includes a film-shaped optical resin member having an adhesive layer formed on at least one surface of the film. The present invention also provides a polarizing plate made of these film-shaped optical resin members.

Here, in the present specification, "nearly zero" of the intrinsic compound refraction Δn ⁰ means zero or a value close to zero, which can be regarded as almost zero. It means that the absolute value is 3.0 × 10 ^-3 or less, but more preferably 1.0 × 10 ^-3 or less. In addition, "the temperature dependence of the intrinsic birefringence has been reduced" means that, numerically speaking, the temperature of the uniaxially stretched film is controlled stepwise in the range of 15 to 70 ° C. When each birefringence is measured and the intrinsic birefringence temperature coefficient "dΔn ⁰ / dT", which is the amount of change in the intrinsic birefringence per 1 ° C., is calculated from these measurement results, the absolute value is 1.0 ×. It means that it is within the range of ^10-5 (° C- ¹ ) or less.

According to the present invention, for example, a resin product such as an optical film which is useful for optical applications having very small orientation birefringence and in consideration of the temperature dependence of intrinsic birefringence which affects optical characteristics A technique that can be stably and surely obtained is provided. As a result, "color unevenness", "light leakage" and "observation" that occur in the screen due to the optical film used in various optical-related devices that are used in various temperature ranges and generate heat during operation. It becomes possible to reliably suppress "color change depending on the angle" and the like, and it becomes possible to design a stable high-performance liquid crystal display or the like. Further, according to the present invention, there is provided a technique that makes it possible to adjust the orientation birefringence to a desired value in consideration of temperature dependence and to synthesize a polymer that easily develops orientation birefringence. Will be done. For example, in the case of a retardation film for a liquid crystal display, it is necessary to adjust the orientation birefringence and the thickness so that the desired retardation is obtained by stretching the film in the manufacturing process. In that case, the stretching is easy to manufacture. It is extremely useful in industry, such that a film having a desired orientation birefringence can be obtained at a magnification, and a resin material useful for optical applications with reduced temperature dependence can be stably and reliably prepared. Effect can be obtained. Further, a liquid crystal display uses an optical resin member formed by forming an adhesive layer on at least one surface of a film obtained by further processing the film-shaped optical resin material provided by the present invention with an adhesive. By doing so, it becomes possible to control "color unevenness phenomenon", "light leakage", "color change depending on the observation angle", etc., which have been problems in the past, which is an extremely useful effect in practical use. ..

The intrinsic compound refraction Δn ^{0 at} 25 ° C. measured using a film formed of each homopolymer corresponding to each of the four types of monomers, and the specific amount of change in the intrinsic compound refraction per 1 ° C. obtained for these homopolymers. As a copolymer consisting of a compound refraction coefficient dΔn ⁰ / dT and, in that case, a combination of these monomers, three types in which Δn ⁰ and dΔn ⁰ / dT of the copolymer are both 0 (zero). It is a figure which showed that there are two kinds of combinations of the monomers of. The intrinsic birefringence at 25 ° C. formed by a ternary copolymer P (MMA / TFEMA / BzMA = 52.0 / 42.0 / 6.0) obtained by copolymerizing three kinds of monomers is almost zero. is a diagram showing temperature dependence of the orientation birefringence [Delta] n _or a formed in the polymer film. MMA is an abbreviation for methyl methacrylate, TFEMA is an abbreviation for 2,2,2-trifluoroethyl methacrylate, and BzMA is an abbreviation for benzyl methacrylate. It is a figure which showed the temperature dependence of the intrinsic birefringence Δn ⁰ of the film formed by the polymer which made by copolymerizing three kinds of monomers shown in FIG. 2 and having almost zero intrinsic birefringence at 25 degreeC. It is a figure which showed the temperature dependence of the intrinsic birefringence Δn ⁰ of the film formed by the two-component copolymer P (MMA / MeMI = 82/18) which is made by copolymerizing two kinds of monomers. MeMI is an abbreviation for methylmaleimide. (A) Orientation birefringence in each of the three-component copolymer P (MMA / PhMA / BzMA = 39/23/38) prepared in Example 1 and the homopolymer PMMA of MMA, which is one of the monomers used. It is a graph which shows the relationship between the refringence Δn _or and the degree of orientation, and (b) the figure which showed the temperature dependence of the intrinsic birefringence Δn ⁰ . Uniqueness in each of the three-component copolymer P (MMA / PhMA / EMI = 29/54/17) prepared in Example 3 and the homopolymer of MMA (abbreviated as PMMA), which is one of the monomers used. It is a figure which showed the temperature dependence of birefringence Δn ⁰ . PhMA is an abbreviation for phenylmethacrylate, and EMI is an abbreviation for ethylmaleimide. It is a conceptual diagram of the temperature control device of the sample film used when investigating the temperature dependence of the intrinsic birefringence. The intrinsic birefringence Δn ^{0 at} 25 ° C. measured using a film formed of each homopolymer corresponding to the three types of monomers and the photoelastic constant C obtained from the photoelastic birefringence measured using the film. It is a relational graph, and it is a figure which showed that the composition of the copolymer (copolymer) in which Δn ⁰ and C are both 0 (zero) exists in the combination of these monomers.

Next, the present invention will be described in more detail with reference to preferred embodiments for carrying out the invention.
First, each term used in the present invention will be described. "Orientation double refraction" is a double refraction that is generally expressed by orienting the main chain of a chain polymer (polymer chain). For example, a manufacturing process by extrusion molding / stretching of a polymer film, injection molding, etc. It occurs in the manufacturing process of various polymer optical elements and parts. That is, the polymer chains oriented by stress in these molding processes are generally not completely relaxed during cooling and solidification, and exist in a state in which the main chain is oriented in the film / optical element, which becomes a source of orientation birefringence. ..

The above-mentioned "orientation birefringence" generally refers to a commercially available birefringence measuring device at room temperature after heating a polymer film to be measured to a temperature equal to or higher than the glass transition temperature, uniaxially stretching the polymer film in a softened state, and then cooling and solidifying the polymer film. It can be measured by such means. At that time, as shown in the equation (1), the polymer main chain is parallel to the linearly polarized light having a polarization plane (a plane including the traveling direction of light and the vibration direction of the electric field) in the direction parallel to the uniaxial stretching direction and the direction orthogonal to the uniaxial stretching direction. direction of the difference between the refractive index _{n d} of the refractive index _{n p} orthogonal directions _(n p -n _d), defined as the orientation birefringence [Delta] n _or.
Δn _or = ( _np −n _d ) (1)

Then, when the Δn _or is not zero is called the "birefringence has occurred", is calling its value as the "orientation birefringence". When Δn _or is a positive value, that is, when the refractive index in the parallel direction is larger, it is called “positive orientation birefringence”, and when Δn _or is a negative value, that is, the refractive index in the orthogonal direction is larger. The case where is larger is called "negative orientation birefringence". It is known that zero birefringence can be achieved at the molecular level by randomly copolymerizing a positively oriented birefringent monomer and a negatively oriented birefringent monomer at an appropriate ratio. It has also been put to practical use as a polymer for use.

In the above, when linearly polarized light is incident on the stretched film, the passing light is decomposed into two orthogonal linearly polarized light, and birefringence causes a retardation. The retardation Re has a relationship as shown in the following formula (2) with the orientation birefringence and the thickness d of the film.
Re = Δn _or × d (2)

Many general measuring devices can measure the above retardation. This is, by dividing the result of retardation obtained by measuring film thickness d, which means that it is possible to determine the orientation birefringence [Delta] n _or, by calculation.

Here, the orientation birefringence [Delta] n _or has a degree of orientation f described above, the intrinsic birefringence [Delta] n ^0, can be related by the equation (3). That is, the degree of orientation of the polymer main chain is called the degree of orientation and is represented by "f", and "f" has a value between zero and one.
Δn _or = f × Δn ⁰ (3)

f = 1 means a state in which all the polymer molecules are aligned (a state in which the polymer molecules are completely stretched), and f = 0 means a state in which the polymer molecules are completely random. The “unique birefringence” Δn ⁰ corresponds to the orientation birefringence when the degree of orientation f = 1, and is a property peculiar to the type of polymer. This degree of orientation f can be measured by an infrared two-color method or the like. Therefore, by measuring the degree of orientation f and the orientation birefringence Δn _or , respectively, it is possible to obtain the “inherent birefringence Δn ⁰ ” in the polymer film to be measured. As described above, the orientation birefringence is a value caused by the fact that the main chain exists in the film / optical element in an oriented state because it cannot be completely relaxed during cooling and solidification after the polymer is melted. The present inventors believe that by examining in detail the value of "inherent birefringence" peculiar to the polymer species, it is possible to select a material that does not cause orientation birefringence, which is ideal for optical applications using polarized light. We are conducting various studies.

In addition, in the optical element / component formed of the polymer, in addition to the above-mentioned orientation birefringence, the volume shrinkage that generally occurs when the optical element / component is cooled from the vicinity of the glass transition temperature (Tg) to a temperature lower than that, and Tg or less. There is photoelastic birefringence caused by external stress applied at temperature. This photoelastic constant is a property unique to the type of polymer. As described above, the present inventors have so far produced the optical film by a general-purpose method such as melt extrusion in which birefringence is likely to occur, but the above-mentioned "orientation birefringence" and "photoelasticity". We are proposing a design method that can obtain an optical film that does not cause light leakage and that does not cause "birefringence" at the same time.

Industrially manufactured polymer-based optical elements and parts are generally "methods of heating a polymer above the glass transition temperature, molding it in a molten state, and cooling and solidifying it" such as extrusion molding, stretching, and injection molding. Often manufactured by. Therefore, as described above, orientation birefringence is likely to occur, and photoelastic birefringence is likely to occur when stress is applied to the obtained optical element at a temperature equal to or lower than the glass transition temperature. These birefringences are factors that reduce the performance of optical films for liquid crystal displays and various lenses that are required to maintain the polarized state of incident polarized light. On the other hand, the present inventors have already paid attention to the above-mentioned intrinsic birefringence and photoelastic constants, and selected three or more kinds of monomer components (repeating unit structures) so as to be a combination of different codes in each of them. By adjusting the copolymerization composition ratio so as to be approximately zero in each case, a polymer that essentially does not cause orientation birefringence and photoelastic birefringence is obtained. By using the polymer synthesized by such a method, it is possible to obtain an optical film, an optical element, and a component having almost zero birefringence, which is an extremely important technique in applications requiring such low birefringence. It becomes.

Further, by applying this technique, it is possible to adjust the intrinsic birefringence to an appropriate value and synthesize a polymer that easily develops oriented birefringence. For example, in the case of a retardation film for a liquid crystal display, in the manufacturing process, the orientation birefringence and the thickness are adjusted so as to obtain a desired retardation by stretching the film, but industrially, the characteristics of the manufacturing equipment and the like are adjusted. Therefore, the range of stretching conditions such as the stretching ratio is also practically limited. That is, in order to obtain a desired orientation birefringence at a draw ratio that is easy to manufacture, it is desirable that the range has inherent birefringence.

Several types of retardation films are industrially manufactured and commercially available, and are appropriately selected and used according to the mode and configuration of the liquid crystal display. The range of intrinsic birefringence preferable in terms of design will be described below by taking a quarter wave plate used in many liquid crystal displays as an example. In principle, a quarter wave plate imparts retardation of a quarter of the wavelength, but the polymer has a wavelength dependence of birefringence, and visible light is not a single wavelength but a wavelength of about 400 nm to 800 nm. In general, it is often designed based on the wavelength of green light having high visual sensitivity (for example, around 550 nm). Again, when designing based on the wavelength of 550 nm, the first quarter wavelength is 137.5 nm. Commercially available retardation films usually have a thickness of about 100 μm or less, but in recent years, research and development have been carried out with the aim of further reducing the thickness by about 20 μm. Here, with respect to the film having a thickness of 100 [mu] m, orientation birefringence [Delta] n _or from the equation (2) is about 1.4 × ^{10 -3,} high degree of orientation f = 0 obtained by the conventional stretching. In No. 1, the intrinsic birefringence Δn ⁰ calculated from the above equation (3) is about 0.014. Recent improvements in stretching technology have made it possible to obtain a higher degree of orientation, so that the absolute value of intrinsic birefringence required for film materials is low. Considering them, the desired absolute value of the intrinsic birefringence in producing a retardation film is 0.01 or more, more preferably 0.05 or more, and more preferably 0.1 or more. The degree of orientation f can be measured by an infrared absorption two-color method or the like as described later. Incidentally, when it is difficult to measure the degree of orientation, in the low crystallinity polymer, if the absolute value of the orientation birefringence [Delta] n _or about 1.4 × 10 ^-3 or more at a thickness 100μm approximately following the film, It can be estimated that the absolute value of the intrinsic birefringence is 0.01 or more. The reason for this presumption is that, except for crystalline polymers, few polymers that do not meet this condition have been reported. As described above, in some applications such as optical films for liquid crystal displays, it is particularly important to adjust the intrinsic birefringence of the polymer to approximately zero or an appropriate desired value. The material is designed in consideration of this point.

In the process of developing an optical film such as a retardation film designed by the above-mentioned method as a product that meets the above-mentioned demands, the present inventors have found the following important facts, and at the same time, have found the optical film. Considering the fact that the environment in which the used product is used is extremely diverse, and that the temperature of the optical film may rise due to the heat generated during the operation of the mounted product, the method proposed above has been improved. I came to recognize that it is necessary to add. That is, when the present inventors measured the temperature dependence of the intrinsic birefringence of the polymer in the process of conducting a detailed study, the value of the intrinsic birefringence was not constant with respect to the temperature but changed, and in particular, We have obtained a new finding that has never been recognized in the past that the tendency increases as the temperature rises. So far, the intrinsic birefringence of a polymer has usually been measured at room temperature (normal temperature), and various discussions have been made on this as a value unique to the polymer. This means that various developments have been carried out on the premise of product quality under room temperature (normal temperature) conditions. On the other hand, for example, the usage environment of a liquid crystal display to which an optical film is applied is diverse, and the conditions of intense heat exceeding 60 ° C. such as in extremely cold conditions, in a vehicle in midsummer, or in a work environment with heat generation. Often used below. Further, it is known that the electronic devices themselves generate heat during operation, and the optical film is also affected by the temperature in this respect. In view of these circumstances, the present inventors can stably develop better performance by considering the temperature dependence of the intrinsic birefringence of the polymer found by the present inventors in the development of the optical film. We recognized that it was necessary to provide an optical film product that could be used. According to the studies by the present inventors, for example, the intrinsic birefringence of the stretched tack of the retardation plate used in the polarizing plate for VA liquid crystals used in liquid crystal televisions is temperature-dependent and temperature-dependent. The tendency was large. This means that at least in order for the polarizing plate mounted on the product that generates heat during operation to have higher quality performance than the conventional one, it is necessary to reduce the temperature dependence of the intrinsic birefringence found by the present inventors. This means that it is important to develop materials for products that take temperature dependence into consideration.

Therefore, the present inventors have investigated the temperature dependence of the intrinsic birefringence of the polymer in more detail, and found the following. First, the temperature dependence of the intrinsic birefringence due to the orientation of the main chain of this polymer chain is similarly temperature-dependent even in the polymer species in which the intrinsic birefringence is almost zero (that is, there is almost no orientation). I confirmed that there was. Furthermore, as a result of measuring the rate of change of the intrinsic birefringence with respect to the temperature (inherent birefringence temperature coefficient) for various polymers, it was confirmed that these are also polymer-specific properties, and that there are positive and negative signs. did.

As described above, the present inventors utilize the conventional measurement results for the intrinsic birefringence and the photoelastic constant, and three or more kinds of monomer components (repeating unit structure) such that each of them has a combination of different codes. ) Is selected, and it is proposed to adjust the copolymerization composition ratio so that all of them become approximately zero, and a polymer that essentially does not cause orientation birefringence and photoelastic birefringence is obtained. However, the above-mentioned new findings are based on the measurement results of the intrinsic birefringence of each homopolymer, which was conventionally considered to show an intrinsic value regardless of the temperature, which was used when determining the above-mentioned monomer composition. Due to its temperature dependence, the present inventors have observed an optical film in which excellent performance is stably maintained even in an environment of a wide range of operating temperatures or when the mounted equipment generates heat due to operation. We have come to recognize that it is necessary to develop new technology in consideration of this point in order to provide. As a result of detailed studies based on the above recognition, the present inventors have further obtained a new finding that the rate of change of the intrinsic birefringence with respect to temperature (the temperature coefficient of intrinsic birefringence) is also a property peculiar to the polymer. Taking advantage of this, the present invention has been achieved by finding that it is possible to realize a polymer design in which the influence of temperature changes is suppressed in consideration of the temperature dependence in the intrinsic birefringence.

More specifically, the present invention focuses on the fact that some homopolymers have positive or negative temperature dependence (inherent birefringence temperature coefficient) of the intrinsic birefringence, and is composed of the monomer compositions thereof. Provided is a technique for obtaining a desired intrinsic birefringence temperature-dependent copolymer (polymer) or the like by appropriately selecting a repeating unit structure and adjusting it to an appropriate copolymer composition ratio. A polymer with almost zero intrinsic birefringence and a zero temperature coefficient of intrinsic birefringence (the birefringence does not change with temperature and is always zero), or intrinsic birefringence, realized by the technique provided by the present invention. A polymer having a desired appropriate size and a zero intrinsic birefringence temperature coefficient is considered to be particularly promising when used as a retardation film for a liquid crystal display, as described below. The retardation film is used to compensate for the birefringence of the liquid crystal layer of the liquid crystal panel and other optical films (three-dimensionally cancel the birefringence and eliminate the influence of the birefringence), and is temperature-dependent. It would be extremely useful if birefringence could be stably compensated without. Further, according to the technique provided in the present invention, the birefringence of, for example, a liquid crystal layer or another optical film may change depending on the temperature, so that it can be canceled out. It is also possible to appropriately impart the intrinsic birefringence temperature coefficient of the above, and it is possible to obtain a remarkable practical effect that the compensation method can be various.

Further, as described above, a resin in which a material exhibiting a desired value of intrinsic birefringence can be stably and reliably obtained, its temperature dependence is reduced, and the intrinsic birefringence is suppressed from changing with temperature. If the material can be obtained reliably and stably, the optical film such as the retardation film obtained by using this material will have the intrinsic birefringence stably maintained with respect to the temperature change. Its performance is maintained stable. For this reason, a liquid crystal display constructed using such a retardation film or the like stabilizes high performance even when it is used in a variety of temperature environments or when the mounted equipment generates heat due to operation. It will be an excellent product that can be maintained.

The optical resin material with reduced temperature dependence of the intrinsic birefringence of the present invention is used in the case of obtaining the polymer proposed by the present inventors having a intrinsic birefringence of almost zero and a photoelastic coefficient of zero. It can be done in the same way as the design method. As a result, as will be described later, a resin material useful for optical applications in which the intrinsic birefringence is very small and the temperature dependence is reduced, which is the object of the present invention, and the intrinsic birefringence can be obtained at a desired value. A resin material that is useful for optical applications and whose temperature dependence is reduced can be easily obtained by designing the monomer composition by the following formula and determining the resin synthesis conditions so as to match the obtained monomer composition. An optical film having stable performance can be obtained reliably and reliably.

Here, first, regarding the design method proposed earlier by the present inventors in the case of obtaining a copolymer having substantially zero intrinsic birefringence and zero photoelastic coefficient, methyl methacrylate (MMA) and Methyl methacrylate (MMA) are used. A ternary copolymer composed of 2,2,2-trifluoroethyl methacrylate (TFEMA) and benzyl methacrylate (BzMA) will be specifically described as an example.

The specific birefringence Δn ⁰ of the ternary copolymer obtained by synthesizing the above three types of monomer components so as to have mass ratios of W _PMMA , W _PTFEMA , and W _PBzMA is each of the homopolymers synthesized from each monomer. It is obtained by the following equation (4) using intrinsic birefringence. Further, the photoelastic constant C of the ternary copolymer obtained by synthesizing the above-mentioned monomer components so as to _have the mass ratio of W _PMMA , W _PTFEMA , and W _PBzMA is the photoelastic constant of each homopolymer synthesized from each monomer. Is obtained by the following equation (5) using. The following formula (6) is a formula showing the monomer composition of the ternary copolymer, and shows that the three types of monomer components are copolymerized at the mass ratio (%) of W _PMMA , W _PTFEMA , and W _PBzMA. ing.

In the above formula (4), Δn ⁰ _PMMA represents the intrinsic birefringence of the homopolymer (PMMA) of MMA, Δn ⁰ _PTFEMA represents the intrinsic birefringence of the homopolymer (PTFEMA) of _TFEMA , and Δn ⁰ _PBzMA is Represents the intrinsic birefringence of a BzMA homopolymer (PBzMA). Further, in the above formula (5), C _PMMA represents the photoelastic constant of the homopolymer of MMA, C _PTFEMA represents the photoelastic constant of the homopolymer of _TFEMA , and C _PBzMA represents the photoelastic constant of the homopolymer of BzMA. Represents a constant.

In the above formula (4), the value of the intrinsic birefringence Δn ⁰ of the ternary copolymer on the left side is set to zero (Δn ⁰ = 0), and in the above formula (5), the light of the ternary copolymer on the left side is set. A polymer in which both the intrinsic birefringence Δn ⁰ and the photoelastic constant C become zero by solving the equation by setting the value of the elastic constant C to zero (C = 0) and combining it with Eq. (6) (hereinafter, zero). The monomer composition of MMA, TFEMA and BzMA, which enables the synthesis of (also called zero birefringent polymer), W _PMMA / W _PTFEMA / W _PBzMA = 52.0 / 42.0 / 6.0 is required. Then, when a ternary copolymer having such a monomer composition is actually synthesized and its natural birefringence and photoelastic constant are measured, it becomes almost zero under a temperature condition of 25 ° C.

The method for designing a ternary copolymer based on the above-mentioned simultaneous equations is easier to understand when considered with reference to FIG. FIG. 8 is a graph in which the photoelastic constant is on the vertical axis and the intrinsic birefringence is on the horizontal axis, which the present inventors call a “birefringence map”. The values of the homopolymers composed of the monomers in PMMA, PTFEMA and PBzMA are plotted in FIG. 8, and it can be seen that the triangle connecting these includes the origin. As is mathematically clear, in this case, a solution can be obtained by making the left sides of the above equations (4) and (5) simultaneous with each other as zero. Furthermore, by measuring the intrinsic birefringence and photoelastic constants of various homopolymers in this way and plotting these values in the birefringence map, it is possible to obtain a copolymer of any kind of monomer combination. For example, it becomes possible to visually judge whether a zero-zero birefringent polymer can be obtained. Then, for a combination in which a solution including the origin (zero) can be obtained, if the monomer composition is obtained by solving equations (4)-(6), both the intrinsic birefringence and the photoelastic constant are zero birefringence easily and surely. Polymers can be prepared.

(Measuring method of birefringence)
The "inherent birefringence of the polymer" in the present specification is measured by the following method. First, an appropriate organic solvent is used to prepare a polymer solution to be measured, a film is prepared from the solution, and the obtained film is used to measure orientation birefringence and its degree of orientation as described below. Then, the intrinsic birefringence of the polymer was determined from these measured values obtained. Taking the three-component polymer composed of the above monomers as an example, first, the obtained polymer was placed in a glass sample tube together with tetrahydrofuran in a mass ratio of 4 times and stirred to sufficiently dissolve the polymer. Then, the polymer solution was developed into a glass plate shape using a knife coater to a thickness of about 0.3 mm, left at room temperature for one day, and dried. Next, the obtained film was peeled off from the glass plate, dried in a vacuum dryer at 60 ° C. for another 48 hours, and the obtained polymer film having a thickness of about 40 μm was processed into a dumbbell shape, and Tensilon general-purpose testing machine (Co., Ltd.) Uniaxial stretching was performed by Orientec). At this time, the stretching temperature was 120 to 140 ° C., and the stretching speed was 2 to 30 mm / min. , The draw ratio was adjusted in the range of 1.1 to 3.0, and several films having a degree of orientation f were prepared. Then, the orientation birefringence of the film after stretching was measured using an automatic birefringence measuring device ABR-10A (manufactured by Uniopt Co., Ltd.). In addition, the degree of orientation of the film after stretching was measured by an infrared absorption two-color method. Then, the value of the orientation birefringence measured as described above was divided (or extrapolated) by the degree of orientation of the stretched film to determine the intrinsic birefringence of the polymer. The intrinsic birefringence of the film made of the polymer measured by the above method was 0.16 × 10 ^-3 at 25 ° C., which was a size that could be regarded as almost zero at room temperature.

(Temperature dependence of intrinsic birefringence)
Using a polymer composed of the ternary copolymer (MMA / TFEMA / BzMA = 52.0 / 42.0 / 6.0) obtained as described above and having almost zero intrinsic birefringence, the temperature was 102 ° C. and 40 mm. The temperature dependence of the intrinsic birefringence of a sample that was thermally stretched by 40 mm at / min and stored at room temperature for 24 hours after stretching was examined while controlling the temperature at 16 ° C. to 70 ° C. Specifically, the retardation (Re) when the temperature was raised by the temperature control device was measured. FIG. 2 shows the measurement results of orientation birefringence. This was obtained by dividing the measured retardation by the film thickness of 28 μm. Further, the intrinsic birefringence shown in FIG. 3 is obtained by dividing this by the degree of orientation f = 0.107 of the polymer molecular chains in the polymer film. As can be seen from these figures, the birefringence was zero near room temperature of 25 ° C., but the birefringence increased as the temperature increased. As can be seen from these figures, this temperature dependence had a relatively linear relationship with temperature. Further, when the value of orientation birefringence 0.10 × 10 ^-3 is multiplied by the thickness of a general polarizing plate protective film of 80 μm, it can be seen that the retardation corresponds to 8 nm. In general, the 1 nm retardation can be visually recognized when placed between orthogonal Nicols (orthogonal polarizing plates), and thus it can be seen that the influence of the birefringence change due to this temperature change is large.

(Examination of temperature dependence of intrinsic birefringence of polymer)
From the above results, the present inventors conducted similar tests on optical films having various monomer compositions to investigate the temperature dependence of the intrinsic birefringence, and FIG. 4 shows an example of the results.

The example shown in FIG. 4 is a two-component copolymer composed of MMA / MeMI (methylmaleimide), and the copolymer composition is MMA / MeMI = 80/20. As shown in FIG. 4, it was confirmed that the intrinsic birefringence of the polymer exhibits temperature dependence, as in the case of the three-component copolymer exemplified in FIG. 3 shown above. The temperature coefficient of intrinsic birefringence dΔn ⁰ / dT was 2.9 × 10 ^-5 ° C ^-1 . Further, although not shown, it was confirmed that both the polymer showing positive intrinsic birefringence at room temperature and the polymer having negative intrinsic birefringence at room temperature are temperature-dependent.

(Temperature dependence of the intrinsic birefringence of each homopolymer)
The polymers shown in FIGS. 3 and 4 all showed a positive correlation with temperature, but it was found that the degree was not uniform and differed depending on the monomer composition. Therefore, in order to examine the difference in the degree, the degree of correlation was compared for the homopolymers corresponding to various monomers by the amount of change of Δn per 1 ° C. Table 1 shows the value of the intrinsic birefringence Δn ⁰ at 25 ° C. (room temperature) of each polymer and the amount of change in Δn per 1 ° C. obtained by measuring while controlling the temperature at 15 ° C. to 70 ° C. The results of the temperature coefficient of intrinsic birefringence dΔn ⁰ / dT are shown. As a result, the degree of correlation with temperature tended to depend on the side chain structure of each polymer. For example, it was suggested that it was low for polymers with a rigid structure and high for polymers with a structure that was not rigid and had a large polarizability anisotropy. In Table 1, PPhMA is an abbreviation for phenylmethacrylate homopolymer, PMI is an abbreviation for homopolymer corresponding to polymaleimide, PMeMI is an abbreviation for homopolymer corresponding to polymethylmaleimide, and PEMI is an abbreviation for homopolymer. , An abbreviation for a homopolymer corresponding to polyethylmaleimide, PCHMI is an abbreviation for a homopolymer corresponding to polycyclohexylmaleimide, and the other is an abbreviation for a homopolymer similar to that described above.

The copolymers constituting the optical resin material of the present invention or the monomers forming the polymers are not limited to the above-mentioned monomers, and for example, aromatic monomers, acrylic monomers, vinyl monomers, and maleimides as listed below. A system monomer, a polar monomer, or the like can be appropriately used.

Examples of the aromatic monomer include styrene, alpha-methylstyrene, benzyl (meth) acrylate, alkylphenoxypolyalkylene glycol (meth) acrylate, 6- (4,6-dibromo-2-isopropylphenoxy) -1-hexyl acrylate, and the like. 6- (4,6-dibromo-2-s-butylphenoxy) -1-hexyl acrylate, 2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecylphenyl acrylate, 2- (1) -Naphthyloxy) -1-ethyl acrylate, 2- (2-naphthyloxy) -1-ethyl acrylate, 6- (1-naphthyloxy) -1-hexyl acrylate, 6- (2-naphthyloxy) -1-hexyl Examples include acrylates, 8- (1-naphthyloxy) -1-octyl acrylates, 8- (2-naphthyloxy) -1-octyl acrylates, 2-phenylthio-1-ethyl acrylates and phenoxyethyl (meth) acrylates. Not limited to them.

Examples of the acrylic monomer include alkyl (meth) acrylates and (meth) acrylates having an alkyl cyclic compound or a heterocycle in the side chain. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl ( Meta) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, isodecyl (meth) Examples thereof include meta) acrylate, n-dodecyl (meth) acrylate, n-tridecyl (meth) acrylate, and n-tetradecyl (meth) acrylate. These may be used alone or in combination of two or more. The alkyl (meth) acrylate means an alkyl acrylate and / or an alkyl methacrylate.

Examples of the vinyl-based monomer include vinyl acetate, vinyl chloride, vinyltoluene, and various vinyl ethers.

Examples of maleimide-based monomers include N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethyl) phenylmaleimide, N- (2-isopropyl) phenylmaleimide, and N- (3-methylphenyl). ) Maleimide, N- (3-ethylphenyl) maleimide, N- (4-methylphenyl) maleimide, N- (4-ethylphenyl) maleimide, N- (2,6-dimethylphenyl) maleimide, N- (2, 6-diethylphenyl) maleimide, N- (2,6-diisopropylphenyl) maleimide, N- (2,4,6-trimethylphenyl) maleimide, N-carboxyphenyl maleimide, N- (2-chlorophenyl) maleimide, N- Examples thereof include (2,6-dichlorophenyl) maleimide, N- (2-bromophenyl) maleimide, N- (perbromophenyl) maleimide, N- (2,4-dimethylphenyl) maleimide, and paratril maleimide. In addition to the above phenylmaleimides, examples of N-alkyl-substituted maleimides include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-i-propylmaleimide, and Nn-butylmaleimide. N-i-butylmaleimide, Ns-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N Examples thereof include N-alkyl-substituted maleimides such as −lauryl maleimide, N-stearyl maleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide, N-cyclohexylmaleimide and N-methylcitraconimide.

Examples of the polar monomer include ethylene-based unsaturated carboxylic acid, ethylene-based unsaturated sulfonic acid, ethylene-based unsaturated phosphoric acid, hydroxyl group-containing monomer, and nitrogen-containing monomer.

Examples of the ethylene-based unsaturated carboxylic acid include acrylic acid, methacrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

Other polar monomers include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl (meth) acrylate; (meth) acrylamide, N, N- Amid group-containing monomers such as dimethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, and N-butoxymethyl (meth) acrylamide; 2- (N, N-dimethylamino) Amino group-containing monomer such as ethyl (meth) acrylate; Glysidyl group-containing monomer such as glycidyl (meth) acrylate; propyltrimethoxysilane (meth) acrylate, propyldimethoxysilane (meth) acrylate, propyltriethoxysilane ( An alkoxysilyl group-containing monomer such as meta) acrylate; (meth) acrylonitrile, N- (meth) acryloylmorpholine, N-vinyl-2-pyrrolidone and the like can be mentioned.

In addition, examples of other monomers include acrylonitrile and methacrylonitrile. Furthermore, neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, dipentaerythritol hexa ( Examples thereof include those having two or more polymerizable functional groups such as meth) acrylate.

The above (co) polymer can be produced by ordinary solution polymerization, bulk polymerization, emulsion polymerization or suspension polymerization, active radiation polymerization and the like.

The optical resin material of the present invention is composed of a copolymer or polymer formed of the above-mentioned monomers and a low-molecular-weight organic compound that can be oriented in these polymers, and thus has a temperature dependence of intrinsic birefringence. It is also possible to use a resin material with a reduced amount of. Examples of the low-molecular-weight organic compound that can be used at that time and has anisotropy of polarizability and can be oriented in the polymer include various plasticizers as described below. Typical plasticizers include, for example, polyoxyethylene aryl ether, dialkyl adipate, 2-ethylhexyl diphenyl phosphate, t-butylphenyl diphenyl phosphate, di (2-ethylhexyl) adipate, toluene sulfonamide, dipropylene glycol dibenzoate, etc. Examples include polyethylene glycol dibenzoate, polyoxypropylene aryl ether, dibutoxyethoxyethylformal, and dibutoxyethoxyethyl adipate. In the present invention, a compound containing two aromatic groups is particularly effective. For example, 1,2-diphenylethane (also known as trans-stylben) or diphenylsulfide, as a benzoic acid ester system, diethylene glycol dibenzoate, di Examples thereof include propylene glycol dibenzoate, benzylbenzoate and 1,4-cyclohexanedimethanol dibenzoate. The number of "aromatic groups" is counted as one condensed ring such as a naphthalene ring.

According to the study by the present inventors, by adding the low-molecular-weight organic compound as described above to the (co) polymer described above, the (co) polymer has unique birefringence (Δn ⁰ ). The temperature coefficient of birefringence (Δn ⁰ / dT) can be changed. The results of the study on this point are shown below. Specifically, taking trans-stilben and diphenylsulfide as examples of low-molecular-weight organic compounds, an optical resin material obtained by adding these low-molecular-weight organic compounds to PMMA was formed into a film, and each film was uniquely birefringent. The refringence (Δn ⁰ ) and the intrinsic birefringence temperature coefficient (Δn ⁰ / dT) were measured, respectively. The results are summarized in Table 2 below. At that time, the amount of the low molecular weight organic compound added to PMMA was set to 2 types, 3% by mass and 10% by mass, and films were prepared for each. For comparison, PMMA's original intrinsic birefringence (Δn ⁰ ) and intrinsic birefringence temperature coefficient (Δn ⁰ / dT) without the addition of low molecular weight organic compounds are also shown in Table 2. As shown in Table 2, by adding a low molecular weight organic compound to PMMA, which is a (co) polymer, the intrinsic birefringence (Δn ⁰ ) and the intrinsic birefringence of the (co) polymer are determined according to the amount of addition. It was confirmed that the refringence temperature coefficient (Δn ⁰ / dT) was changed. This means that the inherent birefringence temperature dependence of the obtained film can be reduced by a simple method of adding the low molecular weight organic compound as described above to the (co) polymer in an appropriate amount. It means that it can be designed.

The optical resin material in which the temperature dependence of the intrinsic birefringence defined in the present invention is reduced can be easily and surely obtained by the following method. For example, the intrinsic birefringence and the intrinsic birefringence temperature coefficient peculiar to the copolymer obtained by copolymerizing the above-mentioned monomer components are both 0 (zero), or the intrinsic birefringence is used for producing a retardation film or the like. Solving the following simultaneous equations, assuming that the absolute value of the intrinsic birefringence at a suitable 25 ° C. is 0.01 or more and the intrinsic birefringence temperature coefficient is 0 (zero). Therefore, the mass fraction of each monomer can be calculated, and the composition ratio of the monomers constituting the copolymer exhibiting the above-mentioned target performance can be determined. Therefore, the copolymer exhibiting the desired performance is polymerized by blending the monomers in consideration of the reactivity of each monomer, the reaction conditions, etc. so as to obtain the desired monomer composition ratio obtained above. Can be easily obtained with.
In [the formula (i), [Delta] n ⁰ ₁ represents the intrinsic birefringence of the first homopolymer, [Delta] n ⁰ ₂ denotes the intrinsic birefringence of the second homopolymer, [Delta] n ⁰ _N is the Represents the intrinsic birefringence of the Nth homopolymer. In the above formula _{^{(ii), dΔn 0 1 /}} dT represents the intrinsic birefringence temperature coefficient of the first homopolymer, d.DELTA.n ⁰ ₂ / dT represents the intrinsic birefringence temperature coefficient of the second homopolymer , DΔn ⁰ _N / dT represent the temperature coefficient of intrinsic birefringence of the Nth homopolymer. In the above formula (iii), W ₁ , W ₂ , and W _N represent the first, second, and Nth monomer mass fractions (%), respectively. ]

More specifically, for example, a resin material useful for an optical film having a polymer having almost zero or a desired value of intrinsic birefringence, which is the object of the present invention, and having reduced temperature dependence of these intrinsic birefringences. In the case of a copolymer composed of three kinds of monomers, it can be obtained by the following method. First, the type of monomer component capable of forming a polymer having almost zero intrinsic birefringence is selected by the method shown in FIG. 8 described above. Here, it is assumed that the three types of monomers from the first to the third are selected. Next, for each film composed of homopolymers corresponding to each of these three types of monomers, the temperature dependence of the intrinsic birefringence was investigated by the method described above, and the respective intrinsic birefringence temperature coefficients dΔn. Find ⁰ / dT. Then, assuming that the mass fractions (%) of the three types of monomers from the first to the third are W ₁ , W ₂ , and W ₃ , respectively, the simultaneous equations (iv)-(vi) below are used. Stand up. Then, for example, the left side of the equation (iv) is set to zero (Δn ⁰ = 0), and the left side of the equation (v) is set to zero (dΔn ⁰ / dT = 0), and the solutions of W ₁ , W ₂ , and W ₃ are obtained. Therefore, it is possible to obtain a polymer having almost zero intrinsic birefringence and having a zero intrinsic birefringence temperature coefficient and having no temperature dependence on orientation birefringence. At this time, if the value on the left side of Eq. (Iv) and the value on the left side of Eq. (V) are set to desired values, the orientation birefringence is adjusted to the desired value, and the temperature dependence is reduced. It is possible to obtain an optical film useful for a retardation film or the like of a liquid crystal display.

The following formula is obtained by converting the above formulas (i) to (iii) into a three-component (N = 3) formula.

Design of a ternary copolymer according to the simultaneous equations (iv)-(vi) described above, for example, to obtain a polymer having almost zero intrinsic birefringence and zero intrinsic birefringence temperature coefficient. The method is easier to understand when considered with reference to FIG. 1, as in FIG. 8 described above. FIG. 1 shows an example described later, which was also used for designing a monomer composition ratio for synthesizing an optical resin material. The first monomer in the above formula is MMA, and the corresponding homopolymer. Is PMMA, the second monomer in the above formula is PhMA, the corresponding homopolymer is PPhMA, the third monomer in the above formula is EMI or BzMA, and the corresponding homopolymers are PEMI. Alternatively, it is PBzMA. In FIG. 1, the horizontal axis has the intrinsic birefringence Δn ⁰ at 25 ° C. (room temperature), and the vertical axis has the intrinsic birefringence temperature coefficient dΔn ⁰ / dT, which are homopolymers corresponding to each monomer, PMMA, PPhMA, For PBzMA and PEMI, the intrinsic birefringence Δn ⁰ and the temperature coefficient of intrinsic birefringence dΔn ⁰ / dT are plotted, respectively.

From FIG. 1, it can be seen that the triangle connecting the plots of PMMA, PPhMA and PEMI and the triangle connecting the plots of PMMA, PPhMA and PBzMA include the origin (Δn ⁰ = dΔn ⁰ / dT = 0). As is mathematically clear, in these cases, a solution can be obtained by simultaneously setting the left sides of the above equations (iv) and (v) to zero. Further, in this way, for various homopolymers, the intrinsic birefringence Δn ⁰ at 25 ° C. (room temperature) and the intrinsic birefringence temperature coefficient dΔn ⁰ / dT obtained by examining the temperature dependence were measured and shown in the map. By plotting these values, it is possible to determine what kind of monomer combination copolymer can be used as a polymer having almost zero birefringence and zero temperature coefficient of intrinsic birefringence. You will be able to judge visually. Then, if the monomer composition is obtained by solving equations (iv)-(vi) for the combination in which the solution including the origin can be obtained, the orientation birefringence is almost zero and the temperature at the orientation birefringence is almost zero. A composition ratio of a polymer capable of obtaining an optical film having no dependence can be obtained. Therefore, by using the optical resin material of the present invention prepared by copolymerizing a plurality of monomers under the above design, the temperature dependence of the intrinsic birefringence of the resin is reduced, and under various temperatures. It is possible to provide an optical film product that is more useful for optical applications and exhibits stable optical characteristics even when used. Further, not limited to the explanation here, the intrinsic birefringence is almost zero by solving the equation of any N component in the above equations (i)-(iii) under Δn ⁰ = dΔn ⁰ / dT = 0. Moreover, it is possible to design a polymer in which the temperature coefficient of intrinsic birefringence is almost zero and the temperature dependence of intrinsic birefringence is reduced. Usually, when the number of components is 4 or more, a plurality of monomer compositions of the copolymer that can solve the equation can be obtained.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, "part" or "%" in the text is based on mass unless otherwise specified.

[Example 1]
(Design of monomer composition ratio)
In this embodiment, the three types of monomers shown in FIG. 1, PhMA (first monomer), BzMA (second monomer) and EMI (third monomer) are selected, and these are selected. When a copolymer was obtained from a combination of monomers, the optical film produced by the obtained copolymer was designed so that both the intrinsic compound refraction and the intrinsic compound refraction temperature coefficient were zero. Specifically, the composition ratios of the above three types of monomers were calculated by calculation using the following formulas (iv) to (vi) as described above.

Specifically, in this embodiment, in order to design a copolymer capable of obtaining an optical film in which both the intrinsic birefringence and the temperature coefficient of intrinsic birefringence are zero, the above-mentioned simultaneous equations (iv) to (vi) are used. Was used to calculate the monomer composition as follows. Substituting the intrinsic birefringence and the temperature coefficient of intrinsic birefringence for each homopolymer used above into equations (iv) to (vi), the following equations (vii), (viii), and (ix) are obtained. ..
Then, when the simultaneous equations are calculated with the left side of the equation (vii) and the equation (viii) as 0 (zero), the monomer composition of MMA / PhMA / BzMA = 33/34/33 in mass fraction (%). In the case of a copolymer synthesized by a ratio, it is expected that both the intrinsic birefringence and the temperature coefficient of intrinsic birefringence of the optical film made of the copolymer will be zero.

(Synthesis of polymer)
The procedure for synthesizing the polymer so that the mass fractions of the three types of monomers calculated in the above example have a monomer composition of MMA / PhMA / BzMA = 33/34/33 will be described below. Aiming at a copolymer that satisfies the above composition ratio obtained by calculation, in consideration of the reactivity of each monomer used for polymerization, methyl methacrylate (MMA) and phenyl methacrylate (PhMA) were added to a glass sample tube. , Benzyl methacrylate (BzMA) was blended so as to have a mass ratio of 41/22/37. Further, perbutyl O (trade name, manufactured by NOF CORPORATION) was added as a polymerization initiator in an amount of 0.2% by mass based on the total amount of these monomers. These raw materials were mixed and stirred to make them sufficiently uniform, then filtered through a membrane filter and transferred to a test tube. These test tubes were placed in a hot water bath at 70 ° C. and polymerized for 24 hours. Subsequently, heat treatment was performed for 24 hours in a dryer at 90 ° C.

The polymer thus obtained was dissolved in 10 times the amount of methylene chloride, and the obtained polymer solution was added dropwise to methanol to precipitate the polymer. The polymer was filtered and sufficiently dried to remove the remaining monomers to obtain a ternary copolymer. As a result of measuring the copolymerization ratio of this copolymer using ¹³ CNMR, a good agreement with the target mass fraction was obtained.

The intrinsic birefringence at 25 ° C. calculated from the above equations (iv) and (v) with the measured monomer ratio of the copolymer is Δn ⁰ = 0.11 × 10 ^-3 , and the intrinsic birefringence The temperature coefficient of refringence was dΔn ⁰ / dT ⁼ 0.32 × 10 ^-5 ° C ^-1 .

(Measurement of optical properties of films made from polymers)
A film was prepared from the polymer obtained above as described below, and the optical properties of the obtained film were further investigated. First, the obtained polymer was placed in a glass sample tube together with 5 times the mass ratio of methylene chloride, stirred, and sufficiently dissolved. Next, the obtained polymer solution was developed into a glass plate shape using a knife coater to a thickness of about 0.3 mm, and allowed to stand at room temperature for one day to dry. Then, the obtained film was peeled off from the glass plate and dried in a vacuum dryer at 90 ° C. for another 24 hours. The polymer film having a thickness of about 40 μm obtained as described above was processed into a dumbbell shape and uniaxially stretched by a Tensilon general-purpose testing machine (manufactured by Orientec Co., Ltd.). At this time, the stretching temperature was 114 ° C. and the stretching speed was 50 mm / min. , The draw ratio was adjusted in the range of 1.5 to 2.5, and several films having a degree of orientation f were prepared. Then, the birefringence of the stretched film was measured using an automatic birefringence measuring device ABR-10A (manufactured by Uniopt Co., Ltd.). In addition, the degree of orientation of the film after stretching was measured by an infrared absorption two-color method. As a result, the intrinsic birefringence of the film produced above was −0.16 × 10 ^-3 at 25 ° C., which was a size that could be regarded as almost zero.

(Temperature dependence of the inherent birefringence of the film)
The temperature dependence of the orientation birefringence and the intrinsic birefringence of the sample obtained by storing the heat-stretched film obtained as described above at room temperature for 24 hours after stretching while controlling the temperature at 12 ° C. to 70 ° C. Examined. Specifically, the retardation (Re) when the temperature was raised by the temperature control device was measured. The orientation birefringence was obtained by dividing this by the film thickness, and the result of plotting with respect to the degree of orientation f of the polymer is shown in FIG. 5 (A). Further, the intrinsic birefringence was obtained from the orientation birefringence and the degree of orientation f, and the temperature change was measured and shown in FIG. 5 (B). Here, the degree of orientation f was regarded as constant in the measurement temperature range. As can be seen from these figures, in the film made of the copolymer prepared in this example, the birefringence hardly changed even when the temperature increased, and the temperature dependence was reduced. The temperature coefficient of intrinsic birefringence of the prepared film was dΔn ⁰ / dT ⁼ 0.15 × ^10-5 ° C- ¹ . The intrinsic birefringence temperature coefficient was calculated from the data at 15 ° C to 70 ° C. In each case of the present specification, the intrinsic birefringence temperature coefficient was calculated from the data of 15 ° C. to 70 ° C. Also, for comparison, the measurement results of PMMA were similarly plotted in FIG.

[Example 2]
The film obtained from the copolymer was prepared in the same manner as in Example 1 except that the copolymer was prepared in which the mass ratio of the monomers of the copolymer was MMA / PhMA / BzMA = 40/27/33. The intrinsic birefringence and the temperature coefficient of intrinsic birefringence at 25 ° C. were determined. As a result, the intrinsic birefringence at 25 ° C. is Δn ⁰ = −0.22 × 10 ^-3 , and the intrinsic birefringence temperature coefficient is dΔn ^{0 /} dT = 0.38 × ^10-5 ° C. ^-1 . In the film made of the copolymer prepared in this example, the birefringence hardly changed even when the temperature increased, and the temperature dependence was reduced.

[Example 3]
The monomer composition was designed and obtained in the same manner as in Example 1 except that a three-component copolymer was prepared in which the mass ratio of the monomers of the copolymer was MMA / PhMA / EMI = 29/54/17. The copolymer was synthesized so as to have the obtained monomer composition. Then, for the film obtained from this copolymer, the intrinsic birefringence and the intrinsic birefringence temperature coefficient at 25 ° C. were determined. The result is shown in FIG. As a result, the intrinsic birefringence at 25 ° C. is Δn ⁰ = −0.47 × 10 ^-3 , and the intrinsic birefringence temperature coefficient is dΔn ⁰ / dT ⁼ −0.12 × 10 ⁻⁵ ° C. ^-1. In the film made of the copolymer prepared in the examples, the birefringence hardly changed even when the temperature increased, and the temperature dependence was reduced.

(Measurement of temperature dependence of polymer's intrinsic birefringence)
In the present invention, when investigating the temperature dependence of the intrinsic birefringence, the film sample having the configuration shown in FIG. 7 is used as the temperature control device for the film sample, and the film sample at the time of measuring the birefringence is surely desired. The temperature was set to. Reference numeral 1 in FIG. 7 is a sample holder having an empty cylinder at the center, and by arranging a film sample in the empty cylinder portion, the sample can be surely set to a desired temperature. This sample holder has two thermocouples shown by 2 and 3 in FIG. 7, and the temperature of the sample is measured by these thermocouples. By appropriately operating the closed circulation type handy cooler TRL, 108H, LM (manufactured by Thomas Kagaku Kikai Co., Ltd.) shown in FIG. 7 in FIG. 7, the temperature of these thermocouples can be adjusted to the desired temperature. , The sample is set to a desired temperature, and the birefringence is measured in that state. Reference numeral 5 denotes a recorder for recording information from a thermocouple. In the present invention, a touch-type paperless recorder TR / V550 (trade name, manufactured by KEYENCE CORPORATION) was used. Using such a device, the intrinsic birefringence was measured using a film sample with strict temperature control.

1: Sample holder 2, 3: Thermocouple 4: Sealed circulation type handy cooler 5: Recorder

Claims (2)

A method for producing an optical resin material having a composite component system of three or more components and having reduced temperature dependence of intrinsic birefringence.
It has an adjustment step for adjusting each component constituting the copolymer which is a composite component system of three or more components.
Uniaxially stretched film made of the copolymer is adjusted by said adjusting step, while the temperature stepwise controlled in the range of 15 to 70 ° C. of the film, the intrinsic birefringence [Delta] n ⁰ at the individual temperature below respectively The absolute value of the intrinsic birefringence temperature coefficient dΔn ⁰ / dT at 15 ° C. to 70 ° C., which was obtained as the amount of change in the intrinsic birefringence per 1 ° C. from the obtained measurement results, was 1.0 ×. Make sure that the intrinsic birefringence Δn ^{0 at} 25 ° C is within the range of ^10-5 (° C ^-1 ) or less and whose absolute value is 3.0 × 10 ^-3 or less, which is almost zero. A characteristic method for producing an optical resin material.
(1) Measurement of retardation Re of the uniaxially stretched film
(2) dividing the measurement value of the retardation Re of the film with a thickness d of the film determine the orientation birefringence [Delta] n _or
(3) The degree of orientation of the uniaxially stretched film is measured, and the degree of orientation birefringence Δn _or when the degree of orientation f = 1 obtained by using the measured degree of orientation is the intrinsic birefringence Δn ^{0 at} each temperature. To be the measured value of A method for producing an optical resin material having a composite component system of three or more components and having reduced temperature dependence of intrinsic birefringence.
It has an adjustment step for adjusting each component constituting the copolymer which is a composite component system of three or more components.
Uniaxially stretched film made of the copolymer is adjusted by said adjusting step, while the temperature stepwise controlled in the range of 15 to 70 ° C. of the film, the intrinsic birefringence [Delta] n ⁰ at the individual temperature below respectively The absolute value of the intrinsic birefringence temperature coefficient dΔn ⁰ / dT at 15 ° C. to 70 ° C., which was obtained as the amount of change in the intrinsic birefringence per 1 ° C. from the obtained measurement results, was 1.0 ×. It is characterized in that it is within the range of ^10-5 (° C- ¹ ) or less, and the measured natural birefringence Δn ^{0 at} 25 ° C is set to a desired value whose absolute value is 0.01 or more. A method for manufacturing an optical resin material.
(1) Measurement of retardation Re of the uniaxially stretched film
(2) dividing the measurement value of the retardation Re of the film with a thickness d of the film determine the orientation birefringence [Delta] n _or
(3) The degree of orientation of the uniaxially stretched film is measured, and the degree of orientation birefringence Δn _or when the degree of orientation f = 1 obtained by using the measured degree of orientation is the intrinsic birefringence Δn ^{0 at} each temperature. To be the measured value of