JPH05249315A - Optical phase difference plate and its production - Google Patents

Abstract

PURPOSE:To simultaneously satisfy the stability and flatness of the retardation of the optical phase difference film consisting of a vinylidene fluoride resin and a methyl methacrylate resin. CONSTITUTION:This optical phase difference film is an oriented film in which the vinylidene fluoride resin consists mainly of a beta type structure and has a heat absorption peak temp. at >=80 deg.C in DSC aside from the crystal m. p. and the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 60/40 to 85/15. This film is obtd. by subjecting the oriented film in which the vinylidene fluoride resin consists mainly of the beta type structure and the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 60/40 to 85/15, to a heat treatment at 90 to 160 deg.C, then laminating the film which has 1 to 6% shrinkage rate on heating and is the same as s the above-mentioned film or is different therefrom via a tacky adhesive agent onto the oriented film and subjecting the films in this state to a heat treatment at 70 to 155 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical retardation plate used in a light control element.

[0002]

2. Description of the Related Art Describing on the basis of a transmissive black-and-white display, incident light first passes through a polarizing plate on the back surface to become linearly polarized light, and then enters a liquid crystal layer and changes to elliptically polarized light. When the elliptically polarized light is emitted through the polarizing plate as it is, the degree of the elliptically polarized light differs depending on the wavelength, and therefore the intensity of the transmitted light is different, and the display is colored. Therefore, in order to prevent coloring, phase compensation for returning elliptically polarized light to linearly polarized light is necessary, and an optical retardation plate is used for this purpose. Although liquid crystals have been used for a long time, today's black-and-white 2-mode liquid crystal displays always use polymer optical retarders regardless of whether they are transmissive or reflective. As is well known, the reason why the polymer film is used is to reduce the weight and thickness of the display, to have a cost advantage by improving the assembly yield, and to improve the contrast.

Regarding the color display, both the STN method and the TFT method have been studied, but the TFT is becoming the mainstream in terms of high image quality. TFT-LCD
Although a TN liquid crystal is used for the TN liquid crystal, the TN liquid crystal also has a drawback that the viewing angle is narrow because it has a slight birefringence.
Therefore, the polymer film is still useful for improving the viewing angle.

The optical characteristics required for such a polymer film include retardation unevenness, viewing angle, wavelength dispersion characteristics,
Optical axis disorder, resistance to temperature and humidity, optical defects due to foreign substances, light transmittance, photoelastic coefficient, etc. are listed, and other factors such as film flatness and waist strength are enumerated.

Among these, the optical characteristics determined by the nature of the polymer raw material include photoelastic coefficient and wavelength dispersion characteristics. Oriented films made of a composition of vinylidene fluoride-based resin and methyl methacrylate-based resin, which are known to be highly compatible among combinations of polymers, are polymers having a photoelastic coefficient conventionally used in this field. -Smaller than the bone.
Therefore, it has a feature that a change in birefringence due to a partial distortion of the film when mounted on a display, that is, a retardation spot is less likely to occur.

Depending on the type of liquid crystal used, matching of wavelength dispersion characteristics is also good, and since the film softening temperature range during stretching is wide, any retardation can be easily obtained and retardation unevenness can be controlled. Also has the feature of being easy.

Another characteristic of the oriented film composed of the composition of vinylidene fluoride resin and methyl methacrylate resin is that the vinylidene fluoride resin having a positive intrinsic birefringence and the negative intrinsic birefringence are Since it is a composition with a methyl methacrylate-based resin having, the intrinsic birefringence can be adjusted arbitrarily. Therefore, especially for a TFT color display, a retardation plate of several tens nm is required, but a low nm film can be easily obtained without paying attention to the thickness of the oriented film.

At this point, the intrinsic birefringence is about 100 × 10 ^-3.
In the case of polycarbonate, the film thickness must be extremely thin, and as a result, if a uniform low-nm film is to be obtained, it is necessary to control the film thickness uniformly, which is far beyond common sense. Skills are needed and encounter difficult situations.

Further, since the above-mentioned photoelastic coefficient is large, the birefringence of the film is apt to change due to an external force, so that the low nm,
In other words, when trying to obtain a low birefringence index, even a slight orientation operation is not allowed, so the film forming conditions must be set strictly.

From the viewpoints of such intrinsic birefringence and photoelastic coefficient, an oriented film made of a composition of vinylidene fluoride resin and methyl methacrylate resin is used for forming a retardation plate for a TFT color display. Another feature is that it can be obtained under a wide range of conditions.

Further, the vinylidene fluoride resin has a very high transparency because it is a β-type crystal, unlike the α-type spherulites, and is basically sufficient for a film in this field. It has optical characteristics. Above all, in JP-A-3-15005, such a film is
We propose a stable retardation by heat treatment at ~ 160 ° C.

[0012]

However, when the film obtained by the above-mentioned prior art is actually used as an optical retardation plate, the retardation rises to a value at which the liquid crystal phase cannot be corrected, and finally the liquid crystal display. There was a problem that the parts started to be colored. After the tension heat treatment,
It has been found that the annealing stabilizes the retardation but impairs the flatness.
Thus far, there has been no product that satisfies both the retardation and the flatness at the same time. The present invention is to solve such a problem.

[0013]

When such a film is used as an optical retardation plate, it is fixed on a glass plate with an adhesive and used. In addition, the temperature resistance test should be at least 25 at 70 ° C or lower in such a fixed state.
Need 0 hours. On the other hand, the above-mentioned JP-A-3-155
As the temperature resistance test conditions in the examples shown in Japanese Patent Publication No. 005, 70 ° C. and 50 hours were adopted without restraining the film at all. It was thought that the effect would be the same in any of these prior arts.

However, it is inferred from various findings that the following things will occur in the subsequent research. That is, in the case of the temperature resistance test in the form of being used as an optical retardation plate, there is a contribution that the orientation is relaxed and the birefringence is reduced as the paracrystal that melts at 70 ° C. or lower is melted. On the other hand, the birefringence increases due to the isothermal crystallization of the paracrystal after melting and the progress of the secondary crystallization at other sites. Further, even if an attempt is made to shrink the volume due to the progress of crystallization, the dimension is not changed due to being constrained by the glass plate, and the film is placed in a tension state. For this reason, the tie chain between the crystals is strained and the orientation is increased, which is also a factor in increasing the birefringence. As a whole, the contribution of increasing the birefringence is larger than the contribution of decreasing the birefringence, and the retardation is increased.

On the other hand, in the case of the temperature resistance test of the above-mentioned prior art film under unrestrained conditions, the contribution of the decrease in the birefringence is that the film is not in the restricted state and the volume due to the increase of crystallization is increased. There are two factors that cause the shrinkage and at the same time the orientation relaxation of the crystal proceeds without any tension in the thai chain, and the orientation relaxes with the melting of the paracrystal that melts at 70 ° C. or less. On the contrary, as the contribution to increase the birefringence, there is isothermal crystallization of the paracrystal and an increase in secondary crystallization due to heat treatment of other portions. Overall, the birefringence of the film is slightly reduced. Further, the retardation does not change much because the thickness increases due to the relaxation of the orientation. In other words, the heat treatment of the above-mentioned prior art seemed to be good in appearance, but it was found that the heat treatment was insufficient under actual conditions.

Theoretical consideration of the above phenomenon is as follows. It should be noted that this consideration is based on the perfect uniaxial orientation mode, and therefore cannot be applied to all orientation modes. However, the present invention is not limited to such a complete uniaxially oriented form, and can be applied to a general uniaxially oriented film and, of course, a biaxially oriented film within a range where viewing angle characteristics are not affected.

As is well known, the retardation is represented by the product of the birefringence (Δn) and the thickness (d) of the film.

In the state where the film is fixed to the glass plate, the dimensional change of the film is extremely small, so that the thickness change can be ignored, and the retardation change depends only on the birefringence change.

By the way, the birefringence is Δn = V [f _C · Δn _C · X + f _a · Δn _a · (1-X)]
+ [F _P · Δn _P ] · [1-V], where V: volume ratio of vinylidene fluoride resin, f _C : crystal orientation coefficient of vinylidene fluoride resin, Δn _C : Crystalline intrinsic birefringence of vinylidene fluoride resin, X: Crystallization fraction of vinylidene fluoride resin, f _a : Amorphous orientation coefficient of vinylidene fluoride resin, Δn _a : Amorphous vinylidene fluoride resin Birefringence, f _P : orientation coefficient of methyl methacrylate resin, Δn _P : intrinsic birefringence of methyl methacrylate resin, the first term is the birefringence index of vinylidene fluoride resin, and the second term is It corresponds to the birefringence of methyl methacrylate resin. Since the intrinsic birefringence of the methyl methacrylate resin is negative, Δn of the entire system decreases as the molecular chains are oriented.

In the above formula, the methyl methacrylate resin has a glass transition temperature of about 100 ° C., and at 70 ° C. which is the temperature of the above-mentioned temperature resistance test condition, the molecular motion is almost frozen, so that the birefringence is Although the refractive index does not change, since the vinylidene fluoride resin has a glass transition temperature of about -45 ° C, the birefringence can change sufficiently. By the way, looking at an example of the relative change of the retardation, that is, the relative change of the birefringence during the process of 250 hours at 70 ° C. after fixing to a glass plate, a change curve divided into two regions as shown in FIG. Indicates.

In the figure, the change in the region (A) is mainly due to the increase in the orientation coefficient of the vinylidene fluoride resin due to the generation of the tension molecular chains by the glass plate, and the change in the region (B) is mainly the vinylidene fluoride resin. It is considered that this is due to an increase in the crystallinity of. Therefore, it is known that the change in the retardation thereafter is almost eliminated only by performing the heat treatment including the (A) region and the (B) region.

The present inventors have found a new heat treatment that includes such regions (A) and (B) and at the same time secures planarity, and the vinylidene fluoride system obtained by such heat treatment. The inventors have also found that the resin has a new structure, and completed the present invention.

One feature of the present invention is that the vinylidene fluoride resin mainly has a β-type structure, has an endothermic peak temperature of 80 ° C. or more in DSC, and has a vinylidene fluoride-based structure. The mixing ratio of the system resin to the methyl methacrylate resin is 85/15 or less by weight and 6
The optical retardation plate is composed of an oriented film of 0/40 or more. Hereinafter, the present invention will be described in detail.

Here, the fact that the crystal structure of the vinylidene fluoride resin is mainly of β type structure means that β is in the infrared absorption spectrum.
It means that the crystallization fraction of the type structure is 0.5 or more, that is, the crystallization fraction of the α type structure is less than 0.5, and the crystallization fraction of the β type structure is preferably 0.6 or more, It is preferably 0.7 or more.

The measuring method is the method of S. Osaki et al. (Journal o
f Polymer Science Vol.13, 1071-1083 (1975)). That is, there is a peak for a crystal having an α-type structure at a wave number of 530 cm ^{−1 in} the infrared absorption spectrum, and a peak for a crystal having a β-type structure at a wave number of 510 cm ⁻¹ . From the absorption at each peak position, the absorbance for the α-type structure is D ₅₃₀ = log ₁₀ (I ₀ / I) ₅₃₀ The absorbance for the β-type structure is D ₅₁₀ = log ₁₀ (I ₀ / I) ₅₁₀ Thus, the crystallization fraction of β-type structure can be calculated by the following formula. Crystallization fraction of β-type structure = {D ₅₁₀ /(0.81D ₅₃₀ +
D ₅₁₀ )}

As the vinylidene fluoride resin in the present invention, not only vinylidene fluoride homopolymer but also copolymer containing vinylidene fluoride as a constituent unit in an amount of 50 mol% or more, and two or more polymers of these polymers are used. -May be a blend. Suitable examples of copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trifluorochloroethylene, vinyl fluoride and the like.

The vinylidene fluoride resin in the present invention is
It has an endothermic peak temperature of 80 ° C. or higher in addition to the crystal melting point of α crystal observed at about 159 ° C. and the crystal melting point of β crystal observed at about 173 ° C. Here, an endothermic peak temperature of 80 ° C. or higher means a differential scanning calorimeter (DS
In C), it is the endothermic peak temperature observed when the temperature is raised at a rate of 10 ° C./min in a nitrogen atmosphere. The endothermic peak temperature is preferably 90 ° C or higher, more preferably 10 ° C.
The temperature is 0 ° C. or higher, and the higher the temperature, the better. Further, those having no endothermic peak temperature below 80 ° C, more preferably below 90 ° C, particularly preferably below 100 ° C are used. It is considered that this endothermic peak temperature is based on the melting point of paracrystal (quasicrystal).

The methyl methacrylate resin used in the present invention includes, in addition to methyl methacrylate homopolymer, 70 mol% or more of a methyl methacrylate monomer as a constitutional unit, other than acrylic acid ester or methyl methacrylate. Of the copolymer containing 30 mol% or less of the methacrylic acid ester, and a polymer blend comprising two or more of these polymers. In addition, ethyl methacrylate, propyl methacrylate, etc. in the above-mentioned copolymer, ethyl methacrylate, propyl methacrylate, etc. are illustrated as a suitable thing as methacrylic acid ester other than methacrylmethyl. In addition to this, the optical retardation plate may contain a small amount of the third component.

The optical retardation plate of the present invention comprises such a vinylidene fluoride resin and a polymethylmethacrylate resin and is oriented. The orientation is preferably uniaxial orientation from the viewpoint of viewing angle characteristics, but biaxial orientation is also used. Especially when it is used for a color display, uniaxial orientation or orientation by flow orientation alone is sufficient, but stretch orientation is preferably used. In addition, the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 85/15 or less by weight and 60/4.
0 or more, preferably 80/20 or less and 65/45
That is all. 60 / even if it exceeds 85/15
If it is less than 40, the transparency will be impaired, and if it is much less than 60/40, the transparency will be improved but the birefringence will be insufficient, and the retardation will be insufficient. Further, in the present invention, the optical retardation plate may be either a transmission type or a reflection type.

Such an optical retardation plate of the present invention can be obtained, for example, by the following method. The main point is that the vinylidene fluoride resin has a β-type structure as a main component, and the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 85/15 or less by weight, which is 60/4.
A first heat treatment step of heat-treating an oriented film composed of a vinylidene fluoride resin and a methyl methacrylate resin, which is 0 or more, at 90 to 160 ° C., and then a heat shrinkage ratio of 1 to
6%, and in the state where the heat-resistant polymer film which is the same as or different from the above-mentioned film and the above-mentioned oriented film are laminated on one side or both sides of the above-mentioned oriented film via an adhesive, the temperature is lower than the first heat treatment temperature, And 70-155 ℃
In the second heat treatment step, the relaxation heat treatment is performed for 5 hours or more. The invention of this manufacturing method will be described in detail below.

The above vinylidene fluoride resin mainly has a β type structure, and the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 85/15 or less and 60/40 or more by weight. An oriented film composed of a vinylidene chloride resin and a methyl methacrylate resin can be produced, for example, as follows. First, a mixture of a vinylidene fluoride resin and a methyl methacrylate resin in which the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 85/15 or less and 60/40 or more by weight is uniformly kneaded. And melt extrude. Then, it is formed into a film or a sheet by melt extrusion and then rapidly cooled so that the crystal structure of the vinylidene fluoride resin in the film or the sheet is mainly the β type structure. When it is used for a color display, it is not always necessary to carry out a stretching operation after that, but usually, the film or sheet is coated with
Stretching is performed at 5 to 150 ° C.

First, the first heat treatment step is performed at 90 to 160 ° C., preferably 110 to 130 ° C. This is because if the temperature is lower than 90 ° C., sufficient molecular kinetic energy for crystallization cannot be imparted, and stable crystals or crystal growth cannot be promoted. If the temperature is higher than 160 ° C., β-type crystallites melt, After one heat treatment step, recrystallized again, and
This is because it is not possible to suppress changes in the application.

The first heat treatment step is carried out by relaxation heat treatment under tension or at a relaxation rate other than 100% for further flatness, and relaxation heat treatment is required for further dimensional stability. The heat treatment time is about 20 minutes under hot air,
When using a heat roll, about 1 minute is sufficient.

The second heat treatment step is performed at 70 ° C. or higher and 155 ° C. or lower, preferably 75 to 140 ° C., more preferably 80 to 130 ° C. Since it is not possible to apply sufficient molecular kinetic energy for crystallization at lower temperatures, long-term treatment is required, which is not practical, while at 155 ° C.
If it is higher, melting of β crystallites occurs again, and paracrystals having an endothermic peak temperature at 70 ° C or less are again generated. This paracrystal melts and isothermally recrystallizes in the subsequent temperature resistance test, and thus the crystal layer of the crystal layer is formed. This is because the orientation is increased and, as a result, the change in retardation cannot be suppressed.

In the second heat treatment step, for example, the composition ratio of the vinylidene fluoride resin and the methyl methacrylate resin is 85/1.
Usually, a relaxation heat treatment is performed, although it may be performed under tension when the crystallization is sufficiently performed, as in the case close to 5.

In the second heat treatment step, an oriented film made of a vinylidene fluoride resin and a methyl methacrylate resin, and a polymer film having a heat shrinkage of 1 to 6%, which is the same as or different from the above oriented film (hereinafter, This film is referred to as a “protective film.” When the protective film is an oriented film composed of a vinylidene fluoride resin and a methyl methacrylate resin, in the following, “from a vinylidene fluoride resin and a methyl methacrylate resin is used. (Hereinafter referred to as “oriented protective film”) is laminated with a pressure sensitive adhesive between them and heat treated.

If the second heat treatment is performed without using the protective film, the flatness is impaired. Further, if a large number of oriented films made of a vinylidene fluoride resin and a methyl methacrylate resin that have undergone only one-step heat treatment are stacked and heat-treated without laminating a protective film, blocking between the films occurs. As a result, not only the flatness is deteriorated but also birefringence unevenness is generated in that portion, which is not practical. This phenomenon becomes more remarkable as the film becomes thinner. When a film different from the above oriented film is used as the protective film, polyethylene, polyethylene terephthalate, etc. are preferably used, and polyethylene is particularly preferably used. However, depending on the second heat treatment temperature, the protective film may be deformed,
In such a case, a heat-resistant film that does not deform should be used.

The protective film is laminated on both sides or one side of the oriented film. Normally it is laminated on both sides,
When the shrinkage rate of the protective film and the shrinkage rate of the oriented film are the same, they may be laminated on only one side.

Moreover, the protective film, the vinylidene fluoride resin and the oriented film composed of the methyl methacrylate resin are laminated via an adhesive. Even if a large number of oriented films are simply stacked and heat-treated with the protective film interposed therebetween, the oriented films shrink due to shrinkage of the oriented films. It is presumed that such a distortion may be due to the oriented film undergoing the heat treatment, shrinking while being considerably softened, and being secondary crystallized as it is. On the other hand, even if the oriented film is softened by laminating the protective film and the oriented film via the adhesive, it is supported by the protective film through the adhesive, and the flatness of the protective film is deteriorated due to shrinkage. It is thought that this is because it can be avoided. As the adhesive, for example, ethylene vinyl acetate type or acrylic type adhesive is used.

The heat shrinkage of the protective film is 1 to 6%, preferably 2 to 4%. Here, the heat shrinkage is a shrinkage that occurs when the protective film alone is 100% relaxed and heat-treated for a time corresponding to the second heat treatment step. If the shrinkage ratio is less than 1%, the oriented film composed of the vinylidene fluoride resin and the methyl methacrylate resin curls when the protective film is removed after the heat treatment. If the shrinkage ratio exceeds 6%, wrinkles are generated in the protective film during the heat treatment, and the shrinkage stress causes the orientation film composed of the vinylidene fluoride resin and the methyl methacrylate resin to change its orientation. , The birefringence unevenness occurs. Moreover, the flatness is impaired by this slight stress.

The second heat treatment time is 5 hours or more, preferably 8 hours or more, and usually 96 hours or less is sufficient.
If it is less than 5 hours, a slight secondary crystallization still proceeds even after the heat treatment according to the present invention, which is unsuitable. The second heat treatment time requires such a long time, but there is no problem even if the heat treatment is performed in the form of stacking films. For example, even if the film is put in a shelf form and subjected to a batch heat treatment of 100 sheets × 5 stages, no curling is observed even during the heat treatment and when the protective film is removed after the heat treatment. An increase in the birefringence of the same can be used as an optical retardation plate.

[0042]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. The characteristics shown in each example were measured by the following methods.

The retardation value was determined by using a microscopic polarization spectrophotometer (TFM-120AFT) manufactured by Oak Corporation. The flatness is visually observed.

The shrinkage ratio of the protective film is 50 cm long and 30 cm wide, and the sample before heating is heated in a constant temperature bath for a time corresponding to the second heat treatment time, and then left at room temperature for 2 hours. The shrinkage ratio with respect to the length is obtained in the length direction.

[Example 1] A composition of polyvinylidene fluoride (Kureha Chemical Industry Co., Ltd., trade name KF # 850) and polymethylmethacrylate (Sumitomo Chemical Co., Ltd., trade name Sumipex LO) And the former has a weight fraction of 70/30 and a thickness of 130 .mu.m.
A uniaxial stretching operation was performed at 0 ° C. and a stretching ratio of 1.2 times to obtain a film having an in-plane birefringence of 1.69 × 10 ⁻³ . This film was subjected to a constant length heat treatment at a temperature of 120 ° C. for 2 minutes. The β-type crystallization fraction of polyvinylidene fluoride in the stretched film before the constant-length heat treatment was 0.9.

Next, the heat shrinkage rate at 80 ° C. on both sides of the film was about 3% regardless of the second heat treatment time shown in Table 1 at the end of Example 1, and polyethylene was used with ethylene vinyl acetate as the adhesive. A protective film (using a trade name PAC-3 manufactured by San-E Chemical Co., Ltd.) was laminated, and a second heat treatment was performed at 80 ° C. for a time shown in Table 1 in a state of 100 cm × 50 cm in length and width of the film. The β-type crystal fraction of polyvinylidene fluoride was the same as that before the heat treatment.

As a result, no curling was observed even when the protective film was removed during the heat treatment or after the heat treatment, and the increase in birefringence due to the heat treatment was uniform in the plane, so that an optical retardation plate was obtained. It could be used. Further, the temperature showing the endothermic peak of the uniaxially stretched film after the heat treatment was as shown in Table 1.

Further, an acrylic adhesive (Souken Chemical Co., Ltd.)
Manufactured by trade name KH-1371) and fixed to a glass plate, the change in birefringence before and after heat treatment at 70 ° C. for 250 hours was observed to be 2% at all measured points as shown in Table 1. It was below. Table 1 shows the main experimental conditions and results of Examples and Comparative Examples. Further, there was no endothermic peak other than the endothermic peaks and melting points shown in Table 1.

[0049]

[Table 1]

[Example 2] Second heat treatment temperature 8 in Example 1
The same procedure as in Example 1 was performed except that 0 ° C. was 100 ° C. and the heat treatment time was 7 hours. The β-type crystal fraction of polyvinylidene fluoride after the second heat treatment was 0.9. The heat shrinkage rate of the protective film at 100 ° C. is 4%. The results are shown in Table 1.

[Embodiment 3] Second heat treatment temperature 8 in Embodiment 1
The composition was such that 0 ° C. was 120 ° C., the heat treatment time was 7 hours, and the heat shrinkage ratio at 120 ° C. was about 4% regardless of the second heat treatment time shown in Table 1 at the end of Example 1 as a protective film. The ratio is the same as that of the retardation film, the same procedure as in Example 1 is performed except that an oriented protective film made of a vinylidene fluoride resin and a methyl methacrylate resin is used and an acrylic adhesive is used as the adhesive. It was The results are shown in Table 1.
It was as shown in. The β-type crystal fraction of polyvinylidene fluoride after the second heat treatment was 0.9.

Example 4 The ratio of polyvinylidene fluoride to polymethyl methacrylate in Example 1 was 65 /
A sheet having a thickness of 80 and a thickness of 80 μm was uniaxially stretched at a stretch ratio of 1.10 times at 80 ° C.
A retardation plate for TFT color liquid crystal having a size of 5 × 10 ⁻³ was obtained.
This film was subjected to a constant length heat treatment at a temperature of 120 ° C. for 2 minutes. Then, as in Example 1, a second heat treatment was performed at 80 ° C. for 72 hours. The results are shown in Table 1 and could be used as an optical retardation plate. The β-type crystallization fraction of polyvinylidene fluoride after the heat treatment is 0.
It was 9.

[Comparative Example 1] Four sets of two first heat-treated films in Example 1 were prepared, and the second heat-treated films were stacked without a protective film, and the temperatures were 60 ° C. and 80, respectively.
C., 100.degree. C., 120.degree. C. for 1 hour. In both cases, blocking occurred between the films, the flatness was deteriorated, and large retardation unevenness was generated at the blocking site, which was not practical.

[Comparative Example 2] Second heat treatment temperature 8 in Example 1
The same procedure as in Example 1 was performed except that 0 ° C. was changed to 60 ° C. and the treatment time was changed to 96 hours. The obtained film was the same as in Example 1 in that curls did not occur even when the protective film was removed, and the in-plane birefringence was equally increased, but the film was fixed by a glass plate with an adhesive. As shown in Table 1, the change in birefringence after heating at 70 ° C. for 250 hours was significantly higher than 3%. The β-type crystal fraction of polyvinylidene fluoride after the heat treatment was 0.9.

Comparative Example 3 The ratio of polyvinylidene fluoride to polymethyl methacrylate in Example 1 was 80 /
A sheet having a thickness of 20 and a thickness of 130 μm is 80 ° C. and 1.28
The film was subjected to a uniaxial stretching operation at a stretch ratio of 2 to obtain a film having an in-plane birefringence of 4.23 × 10 ⁻³ . The second heat treatment of this film was performed in the same manner as in Example 1 except that the heat treatment was performed at 80 ° C. for 1 hour. As a result, there was no problem in the flatness of the film. However, when a temperature resistance test was carried out at 70 ° C. for 250 hours while fixing with a glass plate with an adhesive, the change in the retardation was not uniform in the film plane, and it exceeded 3% at the film edge in the stretching direction. It was
Further, peeling from the glass plate occurred due to the shrinkage of the film at this portion, and it was substantially unusable as a retardation plate. The β-type crystallization fraction of polyvinylidene fluoride in the stretched film after the heat treatment was 0.8.

[0056]

The retardation of the optical retardation plate of the present invention is stable, and the flatness is maintained. Therefore, for both the transmissive type and the reflective type, or two colors of black and white, color
Widely used for both.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a relative change in retardation of an optical retardation plate in a conventional technique.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display area B29L 7:00 4F

Claims (6)

[Claims] 1. A vinylidene fluoride-based resin, a methylmethacrylate-based resin of vinylidene fluoride-based resin, which has a β-type structure as a main component and has an endothermic peak temperature of 80 ° C. or higher in DSC in addition to a crystal melting point. The mixing ratio by weight is 85/1
An optical retardation plate comprising an oriented film having a ratio of 5 or less and a ratio of 60/40 or more. 2. The optical retardation plate according to claim 1, which has no endothermic peak temperature at room temperature or higher and lower than 80 ° C. in DSC. 3. The vinylidene fluoride resin mainly has a β-type structure, and the mixing ratio of the vinylidene fluoride resin to the methyl methacrylate resin is 85/15 or less by weight.
90 to 16 for an oriented film composed of a vinylidene fluoride resin and a methyl methacrylate resin, which is 0/40 or more.
A first heat treatment step of heat treatment at 0 ° C., and then a heat resistant film having a heat shrinkage of 1 to 6% and the same or different from the above film is laminated on one side or both sides of the above oriented film via an adhesive. In the state, the second heat treatment step of performing heat treatment at a temperature lower than the first heat treatment temperature and at 70 to 155 [deg.] C. for 5 hours or more is performed. 4. The method for manufacturing an optical retardation plate according to claim 3, wherein the second heat treatment step is relaxation heat treatment. 5. The method for producing an optical retardation plate according to claim 3, wherein one of the heat resistant films is a film made of the same material as the optical retardation plate. 6. The method for producing an optical retardation plate according to claim 3, wherein the heat resistant film is a film made of polyethylene or polyethylene terephthalate.