JP4796781B2 - Polymer film and optical compensation film - Google Patents

Description

  The present invention relates to a polymer film comprising a mixture of cellulose ester and cellulose ether. More specifically, the present invention relates to an optical compensation film that can be used in a liquid crystal display device and the like and has a larger phase difference as the wavelength increases in the visible light region.

  Optical compensation films are widely used in display devices such as liquid crystal display devices. In general, a transparent film made of polycarbonate or cyclic polyolefin is used as the optical compensation film.

  The application of the optical compensation film is further expanded, and a higher function has been demanded accordingly. Of these requirements, those that have a higher phase difference for longer wavelengths are required in the visible light region. For example, a quarter-wave plate whose phase difference is ¼ of the wavelength has a function of converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. Can be used.

  It is desirable that the optical compensation film used as the quarter wavelength plate has a phase difference corresponding to a quarter wavelength for each wavelength of visible light. However, the polycarbonate optical compensation film that is currently widely used has a smaller phase difference as the wavelength increases. When a black color is displayed on a reflective TFT liquid crystal display device using such an optical compensation film exhibiting wavelength dependence, Since the light from the light cannot be completely blocked, the contrast and the gradation display are lowered.

On the other hand, the optical compensation film which shows a phase difference high as a long wavelength is disclosed also by a polycarbonate film by bonding two optical compensation films at a predetermined angle (for example, refer patent document 1). . However, in the above-described method, two retardation films are required, and two retardation films need to be bonded at a predetermined angle. Requires labor. Furthermore, when applied to a retardation film of polycarbonate, the photoelastic coefficient is usually as large as 70 × 10 ⁻¹² m ² / N, so that the desired retardation is shifted due to the tension when the optical compensation film is bonded. In addition, there is a problem that the retardation value changes due to shrinkage of the polarizing plate after bonding. In addition, when applied to a retardation film made of a cyclic polyolefin polymer, there is a problem that the film thickness of the film becomes large and the handling property is inferior because the retardation development property is small.

In order to solve these problems, there has been proposed an optical compensation film that uses cellulose acetate and has a higher retardation for a longer wavelength with a single film (see, for example, Patent Document 2). A single film of cellulose acetate is a preferable configuration because it has a relatively low photoelastic coefficient and has a larger phase difference at longer wavelengths. However, the phase difference developability of cellulose acetate alone is not sufficient, and it has been required to further increase the phase difference developability. Further, a retardation increasing agent has been proposed in order to increase the retardation development property of cellulose acetate (see, for example, Patent Document 3). However, when these retardation increasing agents are used to obtain sufficient retardation, the transparency of the film is impaired, and haze increases.
JP-A-5-100114, JP 2000-137116 A WO00 / 65384 specification

  An object of the present invention is to provide an optical compensation film having a phase difference that is higher for a longer wavelength in a visible light region and having a sufficient phase difference by a single film.

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, they have found that a film containing cellulose acylate and cellulose ether can achieve the intended purpose, and have reached the present invention. That is, the present invention comprises a mixture of cellulose acylate in which the hydroxyl group of cellulose is substituted with an acyl group having 4 or less carbon atoms and cellulose ether in which the hydroxyl group of cellulose is substituted with an alkoxyl group having 4 or less carbon atoms, and cellulose acylate The present invention relates to a polymer film comprising 1 part by weight or more and 20 parts by weight or less of cellulose ether with respect to 100 parts by weight. By adding cellulose ether, it is possible to maintain the characteristics that it has a sufficient retardation, and the addition amount is in the above range, so that the longer wavelength has a higher retardation.

  The present invention also relates to an optical compensation film formed by stretching in at least a uniaxial direction.

  The front phase difference Re (λ) at the wavelength λnm satisfies Re (450) <Re (550) <Re (650), and the refractive index nx in the slow axis direction in the film plane at the wavelength 550 nm, the fast axis direction When the refractive index ny of (nx−ny) ≧ 0.0012 is satisfied, an optical compensation film having a larger phase difference and a sufficient phase difference in the visible light region can be obtained.

  Furthermore, in another aspect, the present invention is characterized in that free end uniaxial stretching is performed at (Tg + 5) ° C. or more and (Tg + 30) ° C. or less with respect to the glass transition temperature Tg of the film. When NZ = (nx−nz) / (nx−ny) with respect to the refractive index nx in the slow axis direction, the refractive index ny in the fast axis direction, and the refractive index nz in the thickness direction in the film plane, It can be set as 1.00 <= NZ <= 1.20, and the uniaxiality of an optical compensation film can be maintained.

  According to the present invention, it is possible to obtain an optical compensation film having a single film having a larger retardation and longer retardation as the wavelength is longer.

  In the present invention, cellulose acylate in which the hydroxyl group of cellulose is substituted with any of acetyl group, propionyl group, butyryl group, or a plurality of lower fatty acids, and the hydroxyl group of cellulose is methoxyl group, ethoxyl group, propoxyl group, butoxyl group Or a mixture of cellulose ethers substituted with one or more alkoxyl groups.

  Transparency is important for optical compensation films such as liquid crystal display devices. The light transmittance of the film is preferably 85% or more, and more preferably 90% or more. The haze of the film is preferably 2% or less, more preferably 1% or less. Usually, when a plurality of different types of polymer compounds are mixed, there is a problem that a highly transparent film cannot be obtained due to the compatibility problem. On the other hand, since the cellulose acylate and cellulose ether used in the present invention show good compatibility and the light transmittance and haze can be within the above ranges, they are preferable as an optical compensation film material.

  The preferable range of the content of cellulose ether with respect to 100 parts by weight of cellulose acylate is 1 part by weight or more and 20 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less, and further preferably 3 parts by weight. More than 10 parts by weight. When the content of cellulose ether is less than 1 part by weight, the expression of retardation when stretched tends to be insufficient. Moreover, when the content of cellulose ether is larger than 20 parts by weight, the phase difference due to the wavelength tends to approach a certain value, which may be out of the object of the present invention that the longer wavelength has a higher phase difference.

  Next, the cellulose acylate used in the present invention will be described in detail below. The cellulose acylate used in the present invention is one in which the hydroxyl group of cellulose is substituted with an acyl group having 4 or less carbon atoms. Specifically, the hydroxyl group of cellulose is one of acetyl group, propionyl group, butyryl group or a plurality of lower fatty acids. Is replaced by Specifically, cellulose acylate substituted with a single fatty acid such as cellulose acetate, cellulose propionate or cellulose butyrate, or cellulose acylate substituted with a mixed fatty acid such as cellulose acetate propionate or cellulose acetate butyrate. The rate can be suitably used. In particular, cellulose acetate and cellulose acetate propionate are preferable because they can be manufactured at low cost. Among them, those having an acetyl substitution degree (DSac) and a propionyl substitution degree (DSpr) satisfying the following (I) 2.0 ≦ DSac + DSpr ≦ 2.9 and (II) DSpr / DSac ≧ 2 are preferably used. be able to.

  The meaning of the formula (I) is as follows. DSac + DSpr represents on average how much the three hydroxyl groups present at positions 2, 3, 6 in the cellulose molecule are esterified, and the degree of substitution at each position may be equal, or at any position. It may be biased. Moreover, the substitution degree of an acyl group can be quantified by the method described in ASTM-D817-96.

  A degree of substitution of 3 indicates that all hydroxyl groups are esterified. When a film made of cellulose acetate propionate having a DSac + DSpr of 3 in which all hydroxyl groups are esterified with either an acetyl group or a propionyl group is uniaxially stretched, a negative optical in which the direction orthogonal to the stretch direction is the slow axis An optical compensation film having anisotropy is obtained. The wavelength dependence of the retardation of this film shows that the longer the wavelength, the smaller the retardation (absolute value). When DSac + DSpr is made smaller than 3, the ease of developing a phase difference due to stretching decreases, and even when stretched at about 2.8 to 2.9, the phase difference hardly appears, and DSac + DSpr is further decreased. Then, the stretching direction becomes the slow axis, and the optical compensation film has a positive optical anisotropy. Accordingly, the wavelength dependence of the phase difference shows a tendency that the phase difference (absolute value) increases as the wavelength increases. When DSac + DSpr is further reduced, this tendency is lost, and a constant phase difference does not depend on the wavelength. Will come to show. DSac + DSpr, which shows a constant phase difference regardless of the wavelength, varies depending on the ratio of DSac and DSpr, but is generally in the range of 2.0 to 2.3.

  For the above reasons, DSac + DSpr does not exceed 3, and 2 or more is appropriate from the viewpoint of wavelength dependence of the phase difference. A more preferable numerical range of DSac + DSpr is 2.3 or more and 2.9 or less, and more preferably 2.5 or more and 2.8 or less.

  Next, the meaning of the formula (II) will be described. From the viewpoint of the above-described wavelength dependence, as disclosed in JP-A-2000-137116, the hydroxyl group of cellulose can achieve its purpose even if it is substituted with an acetyl group or a propionyl group. . However, in order to form a film having a good thickness accuracy by the solvent cast method, it is desired that a high concentration solution can be prepared, and further, it is desirable that the film be dissolved in a single solvent at a high concentration. From this point of view, cellulose acetate propionate with a high propionyl substitution degree (DSpr) is much more soluble in organic solvents than cellulose acetate propionate with a high degree of acetyl substitution (DSac). A marked difference is observed when methylene chloride is used. Accordingly, the propionyl substitution degree (DSpr) is preferably higher, and the relationship with the acetyl substitution degree (DSac), that is, the value represented by DSpr / DSac is 2.0 or more, more preferably 5.0 or more, and still more preferably Is preferably 10.0 or more.

  Cellulose acylate can be produced by a method known per se. For example, cellulose is treated with a strong caustic soda solution to obtain alkali cellulose, which is acylated with an acid anhydride. The degree of substitution of the obtained cellulose acylate is about 3. By hydrolyzing this, a cellulose acylate having the desired degree of substitution can be produced.

  The preferred number average molecular weight of cellulose acylate is 50,000 to 100,000, more preferably 20,000 to 80,000. When the number average molecular weight is below this range, the mechanical strength of the film tends to be insufficient. When the number average molecular weight is above this range, the solubility in a solvent is reduced, and the productivity when producing a film by the solvent cast method is increased. May be inferior.

  Next, the cellulose ether used in the present invention will be described in detail below. The cellulose ether used in the present invention is one in which the hydroxyl group of cellulose is substituted with an alkoxyl group having 4 or less carbon atoms. Specifically, the hydroxyl group of cellulose is substituted with one or a plurality of alkoxyl groups of methoxyl group, ethoxyl group, propoxyl group, butoxyl group. In particular, those substituted by a single or a plurality of alkoxyl groups of methoxyl group and ethoxyl group are preferable, and among them, ethyl cellulose having an ethoxyl substitution degree (DSet) satisfying 2.0 ≦ DSet ≦ 2.8 can be suitably used. .

  DSet represents the average ethoxylation of the three hydroxyl groups present at positions 2, 3, 6 in the cellulose molecule. When the degree of substitution is 3, all hydroxyl groups are ethoxylated. Indicates. The degree of substitution at each position may be equal, or may be biased to any position. Further, the degree of ether substitution can be quantified by the method described in ASTM D4794-94.

  Ethylcellulose is known to have a large change in solubility in solvents depending on the degree of substitution. Must be selected. If the degree of substitution is less than 2.0, the type of solvent that can be dissolved alone is limited, and the water absorption rate of the film increases, resulting in a lack of dimensional stability. In addition, even if the degree of substitution exceeds 2.9, the type of solvent that dissolves is not limited, and the resin itself tends to be expensive. Therefore, the preferable range of DSet is 2.0 or more and 2.8 or less, and more preferably 2.2 or more and 2.6 or less.

  Cellulose ether can be produced by a method known per se. For example, it is produced by treating cellulose with a strong caustic soda solution to make alkali cellulose, which is etherified by reacting it with methyl chloride or ethyl chloride.

  The number average molecular weight of the cellulose ether is preferably 22,000 to 100,000, more preferably 30,000 to 80,000, still more preferably 35,000 to 65,000. The unnecessarily high molecular weight reduces the solubility in the solvent, causes the problem that the viscosity of the resulting solution is too high to be suitable for the solvent casting method, makes thermoforming difficult, and lowers the transparency of the film. . On the other hand, too low molecular weight tends to reduce the mechanical strength of the resulting film.

  Cellulose acylate and cellulose ether may be dried in advance in order to prevent a decrease in film strength due to moisture present during film formation, such as resin, pellets, and solvents used for film formation. Additives such as plasticizers and deterioration inhibitors can also be added.

  The plasticizer is used for the purpose of improving processing characteristics such as stretching and toughness. As the plasticizer, for example, phosphate ester or carboxylic acid ester can be used. Examples of the phosphoric acid ester include triphenyl phosphate and tricresyl phosphate. Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of the phthalic acid ester include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diphenyl phthalate and diethyl hexyl phthalate. Examples of the citrate ester include triethyl O-acetylcitrate and tributyl O-acetylcitrate. Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, various trimellitic acid esters, and the like.

  As the deterioration preventing agent, an antioxidant that suppresses deterioration due to oxidation, a heat stabilizer that imparts stability at high temperatures, and an ultraviolet absorber that prevents deterioration due to ultraviolet rays are used. An acid absorbent that absorbs free acid generated by decomposition can also be used for chlorinated resins and plasticizers. As the deterioration preventing agent, the above-mentioned phosphate ester compounds, phenol derivatives, epoxy compounds, amine derivatives and the like are used. Phenol derivatives include octylphenol, pentaphenone, diamylphenol and the like, and examples of amine derivatives include diphenylamine and the like.

  The addition amount of the additive is preferably 0.01 to 5.0 parts by weight and preferably 0.05 to 2.0 parts by weight with respect to 100 parts by weight of the total of cellulose acylate and cellulose ether. Further preferred. Even if the addition amount is 1 part by weight or more, the effect is hardly increased, and conversely, bleeding onto the film surface is observed or transparency tends to be lowered. When the addition amount is less than 0.01 parts by weight, the effect of the deterioration preventing agent is hardly recognized.

  The film according to the present invention can be obtained by a known film forming method such as a melt molding method such as a melt extrusion method or an inflation method, or a solvent cast method. In particular, when high flatness is required as in an optical compensation film, it is preferably produced by a solvent cast method.

  Solvents that can be used in the solvent casting method are selected from known solvents such as ketones, esters, and halogenated hydrocarbons. As the ketones, acetone, methyl ethyl ketone, methyl isobutyl ketone and the like can be used. As the esters, ethyl acetate, methyl acetate, butyl acetate, ethyl propionate, methyl propionate, or the like can be used. As the halogenated carbon, methylene chloride, chloroform and the like can be used. Among them, methylene chloride has an advantage that both cellulose acylate and cellulose ether are easily dissolved, and the productivity is high because the boiling point is low. Furthermore, since it is highly safe against a fire during drying, it is most suitably used when producing the retardation film of the present invention.

  In the case of forming a film by the solvent cast method, the resin and additives are dissolved in a solvent to prepare a dope, and then cast on a support and dried to form a film. Regarding the dope adjustment, it is also possible to use a method in which only the resin is first dissolved in a solvent and then the additive is mixed using a static mixer or the like.

  A preferable viscosity of the dope is 1.0 Pa · s or more and 10.0 Pa · s or less, more preferably 1.5 Pa · s or more and 8.0 Pa · s or less. Preferred supports include stainless steel endless belts, polyimide films, biaxially stretched polyethylene terephthalate films, and the like. Moreover, when using films, such as a polyimide and a biaxially-stretched polyethylene terephthalate, as a support body, in order to control the adhesiveness of a support body and a cellulose film, you may perform support body surface coating and discharge treatment. Specifically, the adhesion can be improved to such an extent that the support and the cellulose film can be appropriately peeled by coating or electric discharge treatment.

  The film of the present invention can be dried while being supported on the support, but if necessary, the pre-dried film can be peeled off from the support and further dried. In general, a float method, a tenter or a roll conveying method can be used for drying the film. In the case of the float process, the film itself is subjected to complicated stress, and optical characteristics are likely to be uneven. In the case of the tenter method, it is necessary to balance the film width shrinkage due to solvent drying and the tension to support its own weight depending on the distance between the pins or clips that support both ends of the film. There is a need. On the other hand, in the case of the roll conveyance method, since the tension for stable film conveyance is in principle applied to the film flow direction (MD direction), it has a characteristic that the direction of stress is easily made constant. Therefore, the film is most preferably dried by a roll conveyance method. Further, drying in an atmosphere kept at a low humidity so that the film does not absorb moisture when the solvent is dried is an effective method for obtaining the film of the present invention having high mechanical strength and transparency.

  The thickness of the film of the present invention is 10 μm to 500 μm, preferably 30 μm to 300 μm, and more preferably 50 μm to 130 μm. When the thickness of the film exceeds the above range, productivity by the solvent cast method tends to be inferior. Moreover, when the thickness of the film is below the above range, not only the handleability of the film is inferior, but also there is a tendency that a sufficient phase difference cannot be obtained by stretching.

  In order to obtain an optical compensation film, the film obtained above can be subjected to an orientation treatment by a known stretching method to give a uniform retardation.

  The front retardation value of the optical compensation film can be selected in accordance with the purpose between 5 nm and 1000 nm. (However, the “front phase difference value” here refers to a phase difference value measured in the normal direction of the film, and in the present invention, it is simply referred to as “phase difference value” unless otherwise specified.) In particular, when the film of the present invention is used as a quarter wavelength plate, the retardation value at a wavelength of 550 nm is preferably 120 to 155 nm, more preferably 125 to 150 nm, and further preferably 130 to 145 nm. If the phase difference is within this range, linearly polarized light can be converted into circularly polarized light, which can be suitably used for a reflective liquid crystal display device or the like. In addition, the wavelength dependence of the phase difference is important for the quarter wavelength plate, and the longer the wavelength, the higher the phase difference is required. In other words, the front phase difference Re (λ) at the wavelength λnm is preferably Re (450) <Re (550) <Re (650). If the wavelength dependence of the phase difference is out of this range, when linearly polarized light in the visible light region is incident on this film, the polarization state obtained is completely circularly polarized at a specific wavelength, but otherwise There may be a problem that the wavelength is greatly deviated from circularly polarized light.

  Further, in terms of expression of retardation, 0.0012 when the refractive index in the slow axis direction in the film plane at a wavelength of 550 nm is nx and the refractive index in the fast axis direction is ny (nx−ny). It is preferable that it is above, and more preferably 0.0014 or more. If (nx-ny) is below this range, the thickness of the quarter-wave plate film will generally exceed 130 μm, which is not suitable for mobile applications and is inferior in film productivity and handling properties. There is a tendency. Since the film of the present invention can satisfy these requirements, it can be used as an optical compensation film having a higher retardation in the visible light region and a sufficient retardation.

  Furthermore, it is preferable that the refractive index in the three-dimensional direction can be controlled as a characteristic of the optical compensation film. Regarding the control of the three-dimensional refractive index, when the refractive index in the film plane is nx, the refractive index in the fast axis direction is ny, and the refractive index in the thickness direction is nz, NZ = (nx−nz) / (nx− ny).

  When uniaxiality is required for the optical compensation film, the range of NZ is preferably 1.00 or more and 1.20 or less, more preferably 1.00 or more and 1.10 or less.

  The retardation value and the three-dimensional refractive index can be adjusted to desired values by the stretching method, stretching temperature, stretching ratio, and the like.

  As the stretching method, a uniaxial or biaxial thermal stretching method can be employed. Furthermore, it is possible to increase the refractive index in the film thickness direction by performing special biaxial stretching as disclosed in JP-A-5-157911.

  In general, the draw ratio is 1.01 to 4 times, and the draw temperature is preferably in the range of (Tg−30) ° C. to (Tg + 30) ° C. with respect to the glass transition temperature Tg. A particularly preferred stretching temperature is in the range of (Tg−20) ° C. or higher and (Tg + 20) ° C. or lower, more preferably Tg−10) ° C. or higher and (Tg + 15 ° C.) or lower. However, the drawing temperature here does not mean that all the temperatures in the furnace for carrying out the drawing must be uniform at this temperature, but represents the maximum temperature in the furnace for carrying out the drawing, Other points in the furnace may be out of the temperature range. The glass transition temperature can be measured by a method described in JIS K-7121 using differential thermal analysis (DSC).

  If the stretching temperature is smaller than the above range, the film tends to break during stretching or haze tends to increase. If it is larger than the above range, there is a tendency that a sufficient phase difference cannot be obtained. By setting it within this temperature range, film whitening during stretching can be prevented, and variation in retardation of the obtained optical compensation film can be reduced.

  In particular, when the optical compensation film is required to be uniaxial, a method of free end uniaxial stretching at a temperature of (Tg + 5) ° C. or higher and (Tg + 30) ° C. or lower can be suitably used. As disclosed in the examples of JP-A-2000-137116, when a film made of a cellulose derivative is generally uniaxially stretched at the free end, the value of NZ obtained exceeds 1.20. In order to further reduce NZ, special biaxial stretching as shown in JP-A-5-157911 is required, but it is necessary to bond a heat shrink film, etc. Yield tends to deteriorate and costs increase. In the present invention, the range of NZ can be controlled to 1.00 or more and 1.20 or less, and further 1.00 or more and 1.10 or less by free end uniaxial stretching by controlling the stretching temperature. This is a preferable method in terms of yield improvement and cost reduction by decreasing the number.

Further, the photoelastic coefficient, that is, the change rate of birefringence when subjected to a stress load is preferably 20 × 10 ⁻¹² m ² / N or less. If the photoelastic coefficient is large, the unevenness of bonding when bonded together with the liquid crystal layer or polarizing plate, the difference in thermal expansion between constituent materials due to heat from the backlight or the external environment, the stress caused by the contraction of the polarizing film, etc. The change in phase difference due to the influence becomes large, and the color unevenness of the display device tends to be deteriorated or the contrast tends to be lowered. The photoelastic coefficient of the known polycarbonate is 70 × 10 ⁻¹² m ² / N, whereas the photoelastic coefficient of the optical compensation film of the present invention satisfies the previous range and the change in retardation is small, so that it is particularly large. It can also be suitably used for a screen liquid crystal display device.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  (Measuring method) The material characteristic values and the like described in the present specification are obtained by the following evaluation methods.

(1) Phase difference value The wavelength dispersion of the phase difference is measured by an automatic birefringence meter KOBRA-WR manufactured by Oji Scientific Instruments, and Re (450), Re (550), Re (650) was calculated.

(2) NZ
The automatic birefringence meter KOBRA-WR manufactured by Oji Scientific Instruments was used to measure the phase difference in the plane direction and the phase difference when tilted by 45 ° with the film slow axis as the rotation axis, and NZ was calculated by a program attached to the apparatus.

(3) Thickness Measured with an Anritsu electronic micrometer.

(4) Total light transmittance It measured by the method of 5.5 of JIS K7105-1981 with the Nippon Denshoku Industries integrating sphere type haze meter 300A.

(5) Haze The haze was measured by the method described in 6.4 of JIS K7105-1981 using an integrating sphere haze meter 300A manufactured by Nippon Denshoku Industries Co., Ltd.

(6) Glass transition temperature It measured by the method as described in JISK-7121 by Seiko Electronics Industry differential scanning calorimeter DSC220C.

(7) Photoelastic coefficient A film obtained by cutting a film into a rectangle such that the stretching direction is the long side direction and the short side is 5 cm was used. Oji Scientific Instruments phase difference meter One short side of the sample was fixed with a tape on the stage of KOBRA-WR, and the phase difference was measured at a measurement wavelength of 590 nm. (The phase difference at this time is assumed to be R (0).) In a state where a weight of 500 g is hung on the short side of the film opposite to the one fixed on the stage, and tension is applied in the long side direction at 590 nm. The phase difference was measured. (The phase difference at this time is R (W).) After the phase difference measurement, the sample was removed from the rail, and the thickness (d) of the phase difference measurement part was measured. The photoelastic coefficient is
[(R (W) −R (0)) / D] / [W × G / (50 mm × D)]
Is calculated by However, W represents the mass of the weight, and G represents the gravitational acceleration = 9.8 m / s ² .

(Reference Example 1)
12.6 parts by weight of cellulose acetate propionate (referred to as compound A) having an acetyl group substitution degree of 0.1, a propionyl group substitution degree of 2.6 and a number average molecular weight of 75,000, and an average substitution degree of 2. 3. A dope containing 0.4 parts by weight (hereinafter referred to as Compound B) of ethyl cellulose having a number average molecular weight of 51,000 and 87 parts by weight of methylene chloride was prepared. The long side direction on a biaxially stretched PET film having a thickness of 125 μm in a state where a stress of 1.0 × 10 ⁶ N / m ² is applied to the long side direction in an environment of room temperature 23 ° C. and humidity 15%. After casting in the casting direction, drying was performed at room temperature for 4 minutes, at 60 ° C. for 4 minutes, and at 80 ° C. for 4 minutes. After the obtained film was peeled from the PET film, it was further dried at 110 ° C. for 30 minutes with a stress of 2.0 × 10 ⁵ N / m ^{2 applied in} the casting direction to obtain a polymer film having a thickness of 100 μm. It was. The glass transition temperature of the obtained film was 147 ° C.

(Reference Example 2)
A dope containing 11.7 parts by weight of Compound A, 1.3 parts by weight of Compound B, and 87 parts by weight of methylene chloride was prepared. Using this dope, a polymer film having a thickness of 80 μm was obtained in the same manner as in Reference Example 1. The glass transition temperature of the obtained film was 147 ° C.

(Reference Example 3)
A dope containing 11.0 parts by weight of Compound A, 2.0 parts by weight of Compound B, and 87 parts by weight of methylene chloride was prepared. Using this dope, a polymer film having a thickness of 75 μm was obtained in the same manner as in Reference Example 1. The glass transition temperature of the obtained film was 147 ° C.

(Reference Example 4)
12.6 parts by weight of cellulose acetate propionate having a substitution degree of acetyl group of 0.1, a substitution degree of propionyl group of 2.4 and a number average molecular weight of 25,000, 0.4 part by weight of compound B, methylene chloride A dope containing 87 parts by weight was prepared. Using this dope, a polymer film having a thickness of 90 μm was obtained in the same manner as in Reference Example 1. The film glass transition temperature obtained was 145 ° C.

(Reference Example 5)
A dope containing 10 parts by weight of cellulose acetate having an acetyl group substitution degree of 2.6, 81 parts by weight of methylene chloride, and 9 parts by weight of ethanol was prepared. Using this dope, a polymer film having a thickness of 160 μm was obtained in the same manner as in Reference Example 1. The film glass transition temperature obtained was 167 ° C.

(Reference Example 6)
A dope containing 5 parts by weight of Compound A, 5 parts by weight of Compound B, and 90 parts by weight of methylene chloride was prepared. Using this dope, a polymer film having a thickness of 80 μm was obtained in the same manner as in Reference Example 1. The resulting film had a glass transition temperature of 145 ° C.

(Reference Example 7)
A dope containing 20 parts by weight of polycarbonate composed of bisphenol A and 80 parts by weight of methylene chloride as a bisphenol component was prepared. The long side direction on a biaxially stretched PET film having a thickness of 125 μm in a state where a stress of 1.0 × 10 ⁶ N / m ² is applied to the long side direction in an environment of room temperature 23 ° C. and humidity 15%. After casting in the casting direction, drying was performed at room temperature for 2 minutes, at 60 ° C. for 1 minute, and at 80 ° C. for 1 minute. After peeling off the obtained film from the PET film, it was further subjected to a stress of 2.0 × 10 ⁵ N / m ^{2 in} the casting direction at 80 ° C. for 10 minutes, at 100 ° C. for 10 minutes, and 110 ° C. For 10 minutes to obtain a polymer film having a thickness of 66 μm. The resulting film had a glass transition temperature of 145 ° C.

Example 1
The film obtained in Reference Example 1 was stretched at a stretching ratio of 50% by free end uniaxial stretching at a stretching temperature of 155 ° C.

(Example 2)
The film obtained in Reference Example 1 was stretched at a stretching temperature of 160 ° C. by free end uniaxial stretching at a stretching ratio of 50%.

(Example 3)
The film obtained in Reference Example 2 was stretched at a stretching temperature of 160 ° C. by free end uniaxial stretching at a stretching ratio of 32%.

Example 4
The film obtained in Reference Example 3 was stretched at a stretching temperature of 160 ° C. by free end uniaxial stretching at a stretching ratio of 24%.

(Example 5)
The film obtained in Reference Example 4 was stretched at a stretching ratio of 47% by free end uniaxial stretching at a stretching temperature of 160 ° C.

(Comparative Example 1)
The film obtained in Reference Example 5 was stretched at a stretching ratio of 50% by free end uniaxial stretching at a stretching temperature of 155 ° C.

(Comparative Example 2)
The film obtained in Reference Example 6 was stretched at a stretching temperature of 155 ° C. by free end uniaxial stretching at a stretching ratio of 23%.

(Comparative Example 3)
The film obtained in Reference Example 7 was stretched at a stretching temperature of 150 ° C. by free end uniaxial stretching at a stretching ratio of 5%.

  Table 1 summarizes the properties of the stretched films obtained in Examples and Comparative Examples.

According to the present invention, there is provided an optical compensation film having a higher retardation as a longer wavelength in a visible light region and having a sufficient retardation development property by a single film.

Claims (8)

It consists of a mixture of hydroxyl groups of cellulose and cellulose acetate propionate substituted by an acetyl group and a propionyl group, a hydroxyl group of cellulose with a cellulose ether substituted with an alkoxyl group having 4 or less carbon atoms, cellulose acetate propionate 100 parts by weight 1 part by weight or more and 20 parts by weight or less of cellulose ether, and the degree of acetyl substitution (DSac) and propionyl substitution (DSpr) in cellulose acetate propionate is the following (I) 2.0 ≦ A polymer film characterized by satisfying DSac + DSpr ≦ 2.9 and (II) DSpr / DSac ≧ 2 . 2. The polymer film according to claim 1, wherein the alkoxyl group of the cellulose ether is an ethoxyl group, and the substitution degree DSet is 2.0 ≦ DSet ≦ 2.8. The polymer film according to claim 1 or 2 , which is produced by a solvent cast method using methylene chloride as a solvent. The polymer film according to any one of claims 1 to 3, wherein light transmittance is 85% or more and haze is 2% or less. An optical compensation film obtained by stretching the film according to any one of claims 1 to 4 in at least a uniaxial direction. The front phase difference Re (λ) at the wavelength λnm satisfies Re (450) <Re (550) <Re (650), and the refractive index nx in the slow axis direction in the film plane at the wavelength 550 nm, the fast axis direction The optical compensation film according to claim 5 , wherein a refractive index ny of (nx−ny) ≧ 0.0012 is satisfied. When NZ = (nx−nz) / (nx−ny) with respect to the in-plane refractive index nx in the slow axis direction, the refractive index ny in the fast axis direction, and the refractive index nz in the thickness direction, the optical compensation film according to claim 5 or 6, characterized in that it is 00 ≦ NZ ≦ 1.20. The glass transition temperature Tg of the film, (Tg + 5) ° C. or higher, (Tg + 30) The optical compensation film of any one of claims 5 7, characterized in that the free-end uniaxial stretching at ° C. or less.