JP2007310105A - Optical compensation film, its manufacturing method, optical compensation polarizing plate and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensation film in which the retardation becomes larger as wavelength is longer, the retardation in the thickness direction is relatively small as compared to the retardation in the front surface direction and the coefficient of photo-elasticity is small. <P>SOLUTION: The optical compensation film has an X-ray diffraction intensity based upon an X-ray diffraction method of ≥3,000 cps and ≤15,000 cps and satisfies the following (A), (B), and (C): (A) The front surface retardation Re(λ) at wavelength λnm satisfies the numerical relation (1), Re(450)<Re(550)<Re(650); (B) Re(550) is ≥30 nm and is ≤500 nm; and (C) NZ value at wavelength 590 nm satisfies the numerical relation (3), 1.00≤NZ<1.20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical compensation film having optical characteristics such that the longer the wavelength in the visible light region, the greater the retardation, while having excellent viewing angle characteristics and practically sufficient mechanical strength. The present invention further relates to a method for producing such an optical compensation film. The present invention also relates to an optical compensation polarizing plate and a liquid crystal display device using these optical compensation films.

  The use of optical compensation films has been expanding in recent years, and higher functions have been demanded accordingly. One particularly important function is that the longer the wavelength in the visible light region, the higher the retardation. However, since most optical compensation films made of polymers have a smaller retardation at longer wavelengths, when displaying black on a liquid crystal display device using such an optical compensation film exhibiting such wavelength dependence, the light from the backlight is completely lost. In some cases, the light cannot be shielded from light, resulting in a decrease in contrast and gradation display.

  On the other hand, cellulose derivatives such as cellulose acetate can obtain an optical film having a higher retardation as the wavelength is longer by controlling the substituent and degree of substitution (see, for example, Patent Document 1). ). Furthermore, by using an acyl group having a large number of carbon atoms other than the acetyl group, an optical film made of cellulose acylate having a large retardation in the thickness direction has been proposed, and there is little light loss when viewed from an oblique direction. Is disclosed (for example, see Patent Document 2). However, only by using an optical film using these technologies in a liquid crystal display device, light leakage from an oblique direction can be reduced at a specific wavelength, but chromatic dispersion of a liquid crystal cell and chromatic dispersion of an optical film. Therefore, there is a problem in that light of other wavelengths in the visible light region is lost when viewed from an oblique direction, and complete black display cannot be realized.

Therefore, the longer the wavelength, the larger the retardation, the retardation in the thickness direction is relatively smaller than the retardation in the front direction, the longer the wavelength, the smaller the retardation, and the thickness direction. There has been proposed a VA mode liquid crystal display element capable of displaying almost achromatic black with little light leakage over the entire wavelength in the visible light region by combining an optical compensation film having a retardation that is relatively larger than the retardation in the front direction ( For example, see Patent Document 3). However, when an optical compensation film made of a polycarbonate-based polymer as described in the examples of Patent Document 3 is used, tension when the optical compensation film is bonded to a polarizing plate, etc., and a polarizing plate after bonding There is a problem that the retardation value changes due to a change in dimensions of the liquid crystal display, and therefore, it is not suitable for a large-sized liquid crystal display device such as a television.
JP 2000-137116 A JP 2001-188128 A International Publication WO03 / 032060 Pamphlet

In view of the above viewpoint, the present inventor has an optical compensation film having a smaller photoelastic coefficient as an optical compensation film having a larger retardation as a longer wavelength and a relatively smaller retardation in the thickness direction than the retardation in the front direction. I thought it was necessary to prepare. However, the optical compensation film whose retardation in the thickness direction is relatively smaller than the retardation in the front direction has a large molecular orientation in a specific direction in the plane, so that the orientation direction is prone to cracking and the film handling properties are poor. was there. Furthermore, in durability tests such as a thermal shock test, there may be a problem in strength such as cracks.

As a result of intensive studies to solve such problems, it is possible to obtain an optical compensation film having sufficient strength while maintaining desired optical characteristics by setting the crystallinity of the film within a specific range. The headline and the present invention were made. That is, the present invention is an optical compensation characterized in that it comprises a single film, has an X-ray diffraction intensity by an X-ray diffraction method of 3000 cps or more and 15000 cps or less, and further satisfies all of the following A, B, and C. Related to film.
A: The front retardation Re (λ) at the wavelength λnm satisfies the following formula 1.
Re (450) <Re (550) <Re (650) (Formula 1)
B: Front retardation Re (550) at a wavelength of 550 nm is 30 nm or more and 500 nm or less.
C: 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 at a wavelength of 590 nm, the value of NZ calculated by the following formula 2 is The following formula 3 is satisfied.
NZ = (nx-nz) / (nx-ny) (Formula 2)
1.00 ≦ NZ <1.20 (Formula 3)

  Furthermore, in the optical compensation film of the present invention, the angle formed by the slow axis direction in the film plane and the film longitudinal direction is within ± 1.0 ° at an arbitrary point within the range of 90% of the central portion in the width direction of the film. It is preferable that

  Furthermore, in the optical compensation film of the present invention, the cellulose derivative is a cellulose acylate in which a hydroxyl group of cellulose is substituted with an acyl group having 4 or less carbon atoms, and the total substitution degree of acyl groups is 2.0 or more. 2.9 or less is preferable.

Furthermore, in the optical compensation film of the present invention, it is preferable that the acyl group is an acetyl group and a propionyl group, and the ratio of the acetyl substitution degree (DSac) to the propionyl substitution degree (DSpr) satisfies the following formula 4.
DSpr / DSac> 2.0 (Formula 4)

  Furthermore, in the optical compensation film of the present invention, the cellulose acylate is a cellulose acylate having two or more cellulose acylates having different values of at least one of acetyl substitution degree and propionyl substitution degree. It is preferable that it is contained so as to be 80 parts by weight or more with respect to the part.

Furthermore, the optical compensation film of the present invention preferably has a photoelastic coefficient of 3.0 × 10 ⁻¹¹ m ² / N or less.

  Furthermore, this invention relates to the manufacturing method of the optical compensation film in any one of the said. The method for producing an optical compensation film of the present invention includes a film longitudinal stretching step, and the film is heated to a temperature of (Tg + 5) ° C. or higher with respect to the glass transition temperature (Tg) of the film during the longitudinal stretching step. It is preferable to include the process of hold | maintaining.

  Furthermore, in the method for producing an optical compensation film of the present invention, the draw ratio in the longitudinal direction is preferably 20% or more.

Furthermore, in the method for producing an optical compensation film of the present invention, the longitudinal stretching step includes an inlet-side nip roll and an outlet-side nip roll, the peripheral speed v _{1 of} the inlet-side nip roll, the peripheral speed v ₂ of the outlet-side nip roll, The film is preferably stretched in the longitudinal direction so that the width W _{1 of the} film in the inlet nip roll and the width W _{2 of the} film in the outlet nip roll satisfy the following formula 5.
(W ₂ / W ₁ ) ≦ 0.90 × (v ₂ / v ₁ ) ^−1/2 (Formula 5)

  Furthermore, the present invention relates to an optical compensation polarizing plate comprising at least one optical compensation film described above.

  Furthermore, the present invention relates to a liquid crystal display device including at least one of the optical compensation film according to any one of the above and the optical compensation polarizing plate.

  The present invention provides an optical compensation film having specific optical characteristics and strength, a method for producing the same, an optical compensation polarizing plate and a liquid crystal display device using the same. Further, in the optical compensation polarizing plate and the liquid crystal display device using this optical compensation film, even in a large-sized liquid crystal display device such as a television, uniform display with little light leakage when viewed from an oblique direction can be realized.

  The optical compensation film of the present invention comprises a single film, and the front retardation Re (λ) at the wavelength λnm preferably satisfies Re (450) <Re (550) <Re (650). Re (450) <Re (550) <Re (650) means that the longer the wavelength, the larger the retardation. As such an optical compensation film, a plurality of optical compensation films are attached to JP-A-5-27118, JP-A-5-27119, JP-A-5-100114, JP-A-10-68816, and the like. Although it is described that it can be realized by combining them, it is preferable that one optical compensation film has a larger retardation as the wavelength increases because of a decrease in yield and an increase in cost due to a complicated bonding process. Also, the wavelength dependence of retardation is preferably Re (450) / Re (550) <0.98, particularly Re (450) / Re (550) <0.95, in the above range. Is more preferable. Further, Re (650) / Re (550) <1.01 is preferable, and Re (650) / Re (550) <1.03 is more preferable. If the wavelength dependence of retardation is out of the above range, even if the optical characteristics of a specific wavelength can be compensated in the visible light region, the optical characteristics of other wavelengths cannot be sufficiently compensated, and as a result, It may be difficult to obtain an achromatic black display. Moreover, such wavelength dependence can be expressed by using a cellulose derivative as described in detail below.

The front retardation Re (λ) at the wavelength λnm referred to here means the refractive index nx in the slow axis direction, the refractive index ny in the fast axis direction, the refractive index nz in the thickness direction in the film plane at the measurement wavelength λ, When it is set as film thickness d, it represents with the following Numerical formula 6.
Re = (nx−ny) × d (Formula 6)

In the optical compensation film of the present invention, at a wavelength of 590 nm, the value of NZ represented by the following formula 2 is 1.00 or more and less than 1.20, preferably 1.10 or less, more preferably 1.05 or less.
NZ = (nx-nz) / (nx-ny) (Formula 2)

  When the optical compensation film is used for the purpose of compensating the viewing angle of the liquid crystal display device, the value of NZ needs to be adjusted according to the type of liquid crystal used and the characteristics of the polarizing plate. The difference in retardation value when viewed from an oblique direction becomes large, and light leakage may occur when viewed from an oblique direction. In addition, as a method of adjusting NZ in said range, the method explained in full detail below can be used conveniently.

Furthermore, in the optical compensation film of the present invention, the photoelastic coefficient is preferably 3.0 × 10 ⁻¹¹ m ² / N or less, more preferably 2.5 × 10 ⁻¹¹ m ² / N or less. More preferably, it is 2.0 × 10 ⁻¹¹ m ² / N or less. When the photoelastic coefficient exceeds the above range, uneven bonding when the optical compensation film is bonded together with the liquid crystal layer and the polarizing plate, difference in thermal expansion between the constituent materials due to receiving heat from the backlight and the external environment, polarizing film In some cases, the retardation change caused by the stress caused by the dimensional change or the like becomes large, resulting in a decrease in contrast in the liquid crystal display device. In particular, since the tendency is remarkable in a large-sized liquid crystal display device such as a television, it is important that an optical compensation film used for large-sized liquid crystal display has a small photoelastic coefficient.

In view of the above viewpoint, the smaller the photoelastic coefficient, the smaller the change in retardation due to tension, which is preferable. On the other hand, if the photoelastic coefficient is excessively small, the retardation that can be imparted by stretching or the like is small, and the desired The value may not be reached. From such a viewpoint, the photoelastic coefficient is preferably 5.0 × 10 ⁻¹² m ² / N or more.

  In the optical compensation film of the present invention, the front retardation Re (550) at a wavelength of 550 nm is preferably 30 nm or more and 500 nm or less, more preferably 50 nm or more and 300 nm or less, and 200 nm or less. Is more preferable. If the retardation is smaller than the above range, the optical compensation ability may not be sufficient. Moreover, since it is necessary to make a film excessively thick in order to make retardation larger than the said range, it may be inferior to the productivity and handling property of a film.

  Moreover, since an increase in the haze of the film leads to a decrease in contrast of the display device, the haze is preferably 3.0% or less, and more preferably 2.0% or less. Although the haze can be separated into an internal haze and a surface haze, the optical film is used by being bonded to another film or a member such as glass and an adhesive layer in a scene for practical use such as a liquid crystal display device. The haze is filled with the adhesive. For this reason, there is little effect of light being scattered by surface haze in a scene for practical use, and it is difficult to reduce the contrast. On the other hand, since the internal haze is not reduced even by using an adhesive or the like, it often leads to a decrease in contrast. Therefore, the internal haze value is preferably 1.5% or less, more preferably 1.2% or less, and further preferably 1.0% or less. In view of the above viewpoint, the internal haze is preferably small. However, since the optical compensation film of the present invention has a predetermined crystallinity, the internal haze is generally 0.2% or more. is there.

  Regarding the measurement of the haze of a film, it can be measured using an integrating sphere haze meter according to the method described in JIS K7105. The haze measured by this method is the total haze of the film, that is, the sum of internal haze and surface haze. The internal haze of the film should be measured with the haze meter after immersing the film in a cell filled with water after setting a blank cell such as quartz filled with water in the haze meter and performing a blank measurement. Can be measured by.

  The optical compensation film having the optical characteristics described so far can be used for any liquid crystal display device, but in particular, as described in the pamphlet of International Publication No. WO03 / 032060, etc., vertical alignment (VA) type liquid crystal. The display has a suitable optical compensation capability, and a display with little color change can be obtained even when viewed from an oblique direction.

  Next, polymers that can be used in the optical compensation film of the present invention will be described. The polymer that can be used in the present invention is preferably selected from thermoplastic polymers that have film-forming ability and transparency and can be formed by a melt extrusion method or a solution casting method. Among such polymers, it is preferable to use a cellulose derivative from the viewpoint of the wavelength dispersion of the retardation and the photoelastic coefficient. Examples of cellulose derivatives include cellulose acylates such as cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate, cellulose ethers such as methyl cellulose and ethyl cellulose, and other cellulose derivatives. .

  In particular, in the present invention, among the cellulose derivatives, it is preferable to contain cellulose acylate in which the hydroxyl group of cellulose is substituted with an acyl group having 4 or less carbon atoms. As such a cellulose acylate, specifically, one in which the hydroxyl group of cellulose is substituted with any one of an acetyl group, a propionyl group, and a butyryl group is preferable. That is, as the cellulose acylate suitably used in the polymer film according to the present invention, a plurality of types such as cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate are used. The thing which has an acyl group is mentioned. These have high transparency and can be suitably used for optical applications such as an optical compensation film. Among these, cellulose acetate or cellulose acetate propionate can be particularly preferably used because it can be generally produced or obtained at a low cost.

  The content of the cellulose derivative is preferably 80 parts by weight or more, and more preferably 90 parts by weight or more with respect to 100 parts by weight of the film. By setting the content of the cellulose derivative within the above range, it is possible to maintain the wavelength dependency of retardation of the polymer and optical characteristics such as a photoelastic coefficient within a desired range.

  Furthermore, in the present invention, the cellulose acylate preferably has a specific degree of substitution. Specifically, the total of the acetyl substitution degree, propionyl substitution degree, and butyryl substitution degree is preferably 2.0 or more and 2.9 or less, more preferably 2.3 or more and 2.9 or less, More preferably, it is 2.5 or more and 2.8 or less.

  Here, the preferable range of the substitution degree of cellulose acylate will be described. Cellulose molecules are polysaccharides in which D-glucose, which is a basic unit, is linked in a straight chain by β-1,4 bonds. The degree of substitution of cellulose acylate represents the average acylation of the three hydroxyl groups present at 2, 3, and 6 positions in the D-glucose molecule in the cellulose molecule. The degree of substitution may be equal or may be biased to any position. Moreover, the substitution degree of an acyl group can be quantified by the method described in ASTM-D817-96.

  “Degree of substitution = 3” indicates that all hydroxyl groups in the cellulose molecule are acylated. When a film made of cellulose acylate having a substitution degree of 3 in which all hydroxyl groups in the cellulose molecule are esterified with either acetyl group or propionyl group is uniaxially stretched, the direction perpendicular to the stretch direction becomes the slow axis. It becomes an optical compensation film having a so-called negative birefringence. The wavelength dispersion of retardation of this film shows a tendency that the retardation (absolute value) is smaller as the wavelength is longer.

  If the degree of substitution is made smaller than 3, the ease of developing retardation due to stretching decreases, and a film with almost no retardation even when stretched at about 2.8 to 2.9 is obtained. If the ratio is reduced, the stretching direction becomes the slow axis, and an optical compensation film having positive birefringence is obtained. Along with this, the wavelength dispersion of retardation shows a tendency that the retardation (absolute value) becomes larger as the wavelength is longer, and when the degree of substitution is further reduced, this tendency is lost and is almost constant regardless of the wavelength. Shows the retardation of. The degree of substitution showing a certain retardation without depending on the wavelength is slightly in the range of 2.0 to 2.3, although it varies slightly depending on the type and ratio of the substituent. In general, as the degree of substitution decreases, the expression of retardation increases and NZ, which is an index of birefringence in the thickness direction, tends to increase, and it is difficult to obtain an optical compensation film with NZ = 1. It may become.

  For the above reasons, the degree of substitution with an acyl group does not exceed 3, and 2.0 or more is suitable from the viewpoint of retardation wavelength dispersion. A more preferable numerical range of the degree of substitution is 2.3 or more and 2.9 or less, and further preferably 2.5 or more and 2.8 or less.

  Furthermore, when cellulose acylate is used in the present invention, the acyl group is an acetyl group and a propionyl group, the acetyl substitution degree (DSac) is 0.1 or more, and the propionyl substitution degree (DSpr) is 2.0 or more. It is preferable.

  Here, the types and ratios of substituents will be described below. As described above, cellulose acetate and cellulose acetate propionate are preferably used as the cellulose derivative. However, from the viewpoint of wavelength dispersion, JP 2000-137116 A and JP 2002-71957 A. As disclosed in JP-A-2003-240948, JP-A-2003-315538, etc., the objective is achieved even if the hydroxyl group in the cellulose molecule is substituted with an acetyl group or a propionyl group. be able to. However, in the case of forming a film with good thickness accuracy by the solvent cast method, it is desired that a high-concentration solution can be prepared, and further, it is preferable to dissolve in a single solvent at a high concentration. A paper by CJMalm et al. (Ind.Eng.Chem., 43, 688, 1951) states that cellulose propionate is much more soluble in organic solvents than cellulose acetate. Cellulose acetate propionate with a high propionyl substitution degree (DSpr) is superior to a cellulose acetate propionate with a high degree of acetyl substitution (DSac). Is possible. From this viewpoint, the propionyl substitution degree (DSpr) is preferably higher, and the ratio to the acetyl substitution degree (DSac) (DSpr / DSac) is 2.0 or more, more preferably 3.0 or more, and further preferably 5 0.0 or more.

  In addition, since cellulose acylate adjusts the degree of substitution according to the saponification conditions and the like as described above, it may be difficult to make the degree of substitution always constant. In view of such a viewpoint, in the present invention, a plurality of cellulose acylates having different degrees of substitution, in particular, two or more cellulose acylates having at least one of different values of acetyl substitution degree and propionyl substitution degree are used in combination. It is preferable to adjust the wavelength dispersion of retardation and the expression of retardation to obtain an optical compensation film having a certain optical characteristic. Further, by adjusting the mixing ratio, it is possible to adjust the expression of the desired retardation and wavelength dispersion characteristics. In general, in the optical compensation of a liquid crystal display, it is necessary to adjust the wavelength dispersion and retardation value of the retardation of the optical compensation film depending on the configuration of the liquid crystal cell and other optical members used. The purpose can be achieved by adjusting the mixing ratio of the rates. For example, the ratio of cellulose acylate having a high degree of substitution can be increased to obtain a product having a large chromatic dispersion, and the ratio of cellulose acylate having a low degree of substitution can be increased to obtain a product having a low chromatic dispersion. That's fine.

  The preferred number average molecular weight of the cellulose acylate is 5,000 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.

  Furthermore, in the optical compensation film of the present invention, other polymers can be blended and used for the purpose of adjusting the wavelength dispersion of retardation and the expression of retardation. May be contained in a specific amount. The cellulose ether particularly preferably used in the optical compensation film according to the present invention is one in which the hydroxyl group of cellulose is substituted with an alkoxy group having 4 or less carbon atoms. Specifically, the hydroxyl group of cellulose is a methoxy group or an ethoxy group. , Cellulose ethers substituted by any one or more of propoxy group and butoxy group. Among these, those substituted by one or more of methoxy group and ethoxy group are preferable. Since such cellulose ether has high retardation development property, the selection range of retardation of the optical compensation film of the present invention can be widened. Furthermore, such a cellulose ether is preferable because it exhibits good compatibility with the above-described cellulose acylate and can maintain transparency when it is used as an optical compensation film.

  In the optical compensation film according to the present invention, a preferable range of the content of cellulose ether is 1 part by weight or more and 20 parts by weight or less, more preferably 2 parts by weight or more, 15 parts by weight with respect to 100 parts by weight of cellulose acylate. Parts by weight or less, more preferably 3 parts by weight or more and 10 parts by weight or less. When the content of cellulose ether is less than the above range, the effect of improving the retardation expression when stretched may not be sufficient. Further, if the content of cellulose ether is larger than the above range, the retardation change due to wavelength change tends to approach a certain value, and the longer the wavelength, the more the retardation of the present invention may be deviated. .

  Furthermore, the optical compensation film of the present invention is characterized in that the X-ray diffraction intensity by the X-ray diffraction method is 3000 cps or more and 15000 cps or less, more preferably, the X-ray diffraction intensity is 4000 cps or more and 10,000 cps or less. More preferably, it is 5000 cps or more and 8000 cps or less. If the degree of crystallinity is too high, the haze of the film, particularly the internal haze described above, increases, which may cause a decrease in contrast in the liquid crystal display device. If the crystallinity is too low, the strength of the film may be inferior.

  In the film described in the prior art of this specification, the retardation in the thickness direction is relatively larger than the retardation in the front direction, the refractive index nx in the slow axis direction and the refractive index ny in the fast axis direction in the film plane. Nx ≧ ny> nz with respect to the refractive index nz in the film thickness direction, and NZ is larger than 1. Those having such characteristics generally have high mechanical strength. This is presumably because the molecular chains are oriented in both the slow axis direction and the fast axis direction in the film plane. On the other hand, a film with NZ close to 1.0 as in the present invention has nx> ny ≧ nz and tends to crack in the slow axis direction, and the larger the retardation value of the front, the more The trend is remarkable. This is presumably because in such a film, the orientation of molecular chains in the in-plane slow axis direction is large, and cracks are likely to occur along the orientation direction.

  Therefore, there has been a problem that the film is torn due to a minute notch or the like generated during film conveyance. In addition, the durability of the product at high and low temperatures, especially in the state of being bonded to other members such as polarizing plates and glass, the dimensional change rate in overheating and cooling of these members and the film of the present invention is different. Due to the rapid expansion and contraction of the film in the impact test, there was a problem in its practicality such that cracks were likely to occur along the slow axis direction with low strength. In particular, as the NZ of the optical compensation film is smaller and approaches 1.0, and the front retardation value is larger, such a problem becomes more prominent. The present invention has been found that by setting the X-ray diffraction intensity of the optical compensation film within a predetermined range, the film strength can be improved and such problems can be solved.

  Here, the “X-ray diffraction intensity” is obtained from a diffraction peak intensity value (scanning range: 2θ = 3 to 35 °) detected by X-ray diffraction measurement. Specifically, it is measured by the intensity difference between the perpendicular from the diffraction peak position at the Bragg angle 2θ = 5 ° to 10 ° and the baseline connecting the intensity values of the Bragg angles 2θ = 5 ° and 2θ = 10 °. Can do. Details are shown in FIG.

  In order to increase the degree of crystallinity of the film, for example, as described in JP-A-2005-206696, etc., in the drying process when film-forming by the solvent cast method, the residual solvent amount is high and the temperature is high. Examples thereof include a treatment method and a method for adjusting the substituent and degree of substitution of cellulose acylate as described in JP-A-2006-45422. However, usually these methods alone are not sufficient to increase the degree of crystallinity, and it has been difficult to obtain a film having a practically sufficient strength. Among them, cellulose acylate having a degree of substitution of 2.8 or less tends to have a low crystallinity because of low structural objectivity compared to cellulose acylate having a degree of substitution close to 3.0. Generally, the crystallinity of the film is outside the scope of the present invention, as described in the examples of the publication. In such a case, it is preferable to use the method described later.

  On the other hand, the cellulose acylate resin used in the cellulose acylate retardation film of the present invention preferably has an X-ray diffraction intensity of 2000 cps or more and 13000 cps or less, more preferably an X-ray diffraction intensity of 2500 cps or more and 90000 cps or less. More preferably, it is 4000 cps or more and 8000 cps or less. The X-ray diffraction intensity of the cellulose acylate resin can be measured by the same method as the X-ray diffraction intensity of the optical compensation film. By setting the X-ray diffraction intensity of the cellulose acylate resin in the above range, the crystallinity when the optical compensation film is obtained can be set to a target value.

  In order to increase the strength of the film, the same effect may be obtained by increasing the molecular weight of the polymer without increasing the crystallinity. However, as described above, when the molecular weight is excessively increased, the solubility is decreased, and a high-concentration solution cannot be prepared. In this invention, it is useful at the point which can obtain the film which has sufficient intensity | strength without accompanying such a fall of productivity. That is, according to the present invention, it is possible to obtain a retardation film having mechanical strength that can be put to practical use without a decrease in productivity due to an increase in molecular weight.

  In view of such a viewpoint, the film manufacturer may select a cellulose acylate resin having a high degree of crystallinity as a film raw material, and the present invention is limited depending on the production method of the cellulose acylate resin. Although it is not a thing, as a manufacturing method of the cellulose acylate resin which raised the crystallinity degree, the amount of catalyst at the time of acylating cellulose with an acid anhydride, reaction temperature, reaction time, or when saponifying, for example Can be obtained by adjusting the catalyst amount, the saponification temperature, the saponification time, etc., and the knowledge described in paragraphs 18 to 21 of JP-A-10-36401 can be used (for example, By reducing the amount of sulfuric acid catalyst during the acetylation reaction of cellulose, the distribution of acetyl groups can be made uniform and the crystallinity can be increased. Moreover, after making a cellulose acylate resin into a film and raising crystallinity, the method of grind | pulverizing a film and using it as a cellulose acylate resin etc. can also be used.

  Further, the tear strength in the slow axis direction, that is, the stretching direction is preferably 0.7 N / mm or more, more preferably 0.9 N / mm or more, and further preferably 1.0 N / mm or more. Moreover, although there is no upper limit in the preferable range of tear strength, it is generally 5.0 N / mm or less. The tear strength can be measured by a JISK-7128-1 (trouser tear method) using a tensile tester.

  In the optical compensation film of the present invention, it is preferable that the film longitudinal direction and the slow axis are substantially parallel. Here, “substantially parallel” in the present invention means that the angle formed by both is in the range of ± 5 °, preferably within ± 3 °, preferably within ± 2 °. Further preferred. Such an optical compensation film in which the refractive index in the film flow direction is larger than the refractive index in the film width direction usually has a heating furnace between two pairs of nip rolls, and is stretched due to a difference in peripheral speed between the two pairs of nip rolls. Although obtained by longitudinal stretching, such longitudinal stretching is preferable because NZ can be reduced as compared with lateral stretching using a pin tenter, a clip tenter, or the like.

  Furthermore, in the retardation film of the present invention, the angle formed by the slow axis direction in the film plane and the film flow direction is preferably within ± 1.5 °, more preferably at any position in the film plane. Within ± 1.0 °, more preferably within ± 0.8 °. Here, the arbitrary point in the film plane means an arbitrary point within the range of 90% of the central portion in the width direction of the film, but an arbitrary point within the range of 95% of the central portion in the width direction of the film. More preferably, the angle formed by the slow axis direction and the film flow direction is within the above range. By setting the slow axis in the above range, it is possible to prevent a local decrease in contrast due to the shift of the axis. In particular, when used in a large liquid crystal display device, it is important to reduce the variation in the axis. Furthermore, for the same reason as described above, the range of the angle variation between the slow axis direction in the film plane and the film flow direction is preferably within 1.5 °, and more preferably within 1.0 °. preferable.

  Next, a method for producing the optical compensation film of the present invention will be described. In the optical compensation film according to the present invention, in order to prevent a decrease in film strength due to moisture present during film formation, resins, pellets, solvents, and the like used for film formation may be dried in advance. The optical compensation film according to the present invention may further contain additives such as a plasticizer and a deterioration inhibitor.

  The plasticizer can be used for the purpose of improving processing characteristics such as stretching or toughness. Examples of the plasticizer include phosphoric acid esters and carboxylic acid esters. Examples of the phosphoric acid ester include triphenyl phosphate and tricresyl phosphate. Examples of the carboxylic acid ester include phthalic acid ester and citric acid ester, and examples of the phthalic acid ester include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diphenyl phthalate, and diethyl hexyl phthalate. Citric acid esters include triethyl O-acetyl citrate and tributyl O-acetyl citrate. Other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, various trimellitic acid esters, and the like. In the polymer film according to the present invention, it is preferable to use a phthalic acid-based or phosphoric acid-based plasticizer.

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

  The amount of the additive such as a plasticizer is preferably 0.5 to 5.0 parts by weight, more preferably 1.0 to 4.0 parts by weight, based on 100 parts by weight of the polymer. preferable. When the added amount exceeds 5.0 parts by weight, the effect cannot be obtained, and conversely, the film tends to ooze out or the transparency is lowered. Moreover, when the addition amount is less than 0.5 parts by weight, the effect of the deterioration inhibitor may not be sufficiently obtained.

  The optical compensation 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, such as optical compensation of a liquid crystal display device, it is preferably manufactured by a solvent cast method.

  The solvent used for dissolving the cellulose acylate and additives is not particularly limited as long as it dissolves the cellulose acylate, and is selected from known solvents such as ketones, esters, halogenated hydrocarbons and the like. . 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 the cellulose acylate is 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. Furthermore, a poor solvent for cellulose acylate can be added to the above-mentioned solvent for the purpose of lightening the peeling of the web from the support. As the poor solvent, alcohols having 10 or less carbon atoms are preferable, and alcohols having 4 or less carbon atoms, that is, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and t-butyl alcohol are more preferable. Preferably used. The amount of the poor solvent is preferably 1 part by weight or more and 20 parts by weight or less, preferably 2 parts by weight or more and 15 parts by weight or less, more preferably 3 parts by weight or more when the total amount of the solvent is 100 parts by weight. More preferably, it is 10 parts by weight or less. If the amount of the poor solvent is small, the effect of reducing peeling due to gelation may not be sufficient. In addition, when the amount of the poor solvent is too large, the solubility is decreased, the viscosity of the solution is increased, the productivity in the solvent cast method is inferior, or the gel component may be mixed into the film to become a bright spot. .

  Regarding the preparation of the solution, the method is not particularly limited, but a method of dissolving the resin and the additive in a solvent, a method of dissolving the resin and the additive separately, and mixing using a static mixer or the like are preferable. It can also be used. Furthermore, a method of dissolving cellulose acylates having different degrees of substitution individually and mixing them can also be suitably used.

  The preferable viscosity of the solution is preferably 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 at the liquid temperature when cast on the support. It is as follows. If the viscosity is smaller than the above range, a lot of energy is required to disperse the solvent, and the productivity may be inferior. Moreover, when larger than the said range, it may become difficult to obtain a uniform film.

  The film 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. For the drying of the film, a float method, a tenter or a roll conveyance method can be generally used. 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. Furthermore, in this drying step, as described in JP-A-2005-206696, etc., the degree of crystallinity can be increased by heating to a high temperature while the solvent remains.

  The thickness of the film 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. On the other hand, 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 sufficient retardation 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 uniform retardation. In producing the optical compensation film of the present invention, the stretching method is not particularly limited. However, as described above, it is preferable to use a method of longitudinal stretching due to a difference in peripheral speed between two pairs of nip rolls. Further, in such a stretching method, the length of the heating furnace arranged between the two pairs of nip rolls is preferably 1.0 times or more, more than 2.0 times the film width before stretching. It is more preferable that it is 2.5 times or more. By setting the furnace length in such a range, the range of deviation of the slow axis of the film can be reduced.

  Further, in the method for producing an optical compensation film of the present invention, in order to set NZ within the target range, the stretching temperature is preferably (Tg + 5) ° C. or higher with respect to the glass transition temperature Tg of the film, and (Tg + 7 ) It is preferable that the temperature is not lower than ° C. 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 within a range of 10 mm from the film in the furnace for carrying out the drawing. Other points in the furnace may be out of the temperature range. The upper limit of the stretching temperature is not particularly limited as long as it is lower than the melting point of the film. However, if the temperature is excessively high, the expression of retardation may be lowered, and therefore it is preferably (Tg + 30) ° C. or lower.

  The glass transition temperature can be measured by a method described in JIS K-7121 using differential thermal analysis (DSC).

  In general, when a film made of a cellulose derivative is uniaxially stretched at the free end, the value of NZ often exceeds 1.20 as disclosed in Examples of JP-A-2000-137116. In order to reduce NZ, special biaxial stretching as shown in JP-A-5-157911 can also be used. However, in such special biaxial stretching, bonding of a heat-shrinkable film is performed. Therefore, the number of processes increases, yield tends to deteriorate, and costs tend to increase. In the present invention, the NZ range is 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 to the above range. Therefore, it is a preferable method in terms of yield improvement and cost reduction by reducing the number of processes.

  Furthermore, in the method for producing an optical compensation film of the present invention, two or more temperature adjustments are performed in the film flow direction between two pairs of nip rolls for the purpose of improving the in-plane uniformity of retardation and reducing the deviation of the slow axis. Using a longitudinal stretching machine having a possible heating zone, the temperature is adjusted so that the film passes through the high temperature zone after the low temperature zone, and the temperature of the high temperature zone is (Tg + 5) with respect to the glass transition temperature (Tg) of the film. ) A method of at least ° C can be suitably used. In such a configuration, the simplest and preferable mode is a mode in which the film is divided into a low temperature zone and a high temperature zone in the film flow direction as shown in FIG. 1, and heat is supplied to the high temperature zone and the low temperature zone. The temperature control is possible for each zone. Furthermore, a zone having an intermediate temperature may be provided between the high temperature zone and the low temperature zone, a high temperature zone may be provided before the low temperature zone, or a preheating zone having a lower temperature may be provided. In addition, providing a temperature-controlled hot roll between the high-temperature zone and the nip roll on the outlet side is a preferable configuration because generation of wrinkles due to rapid cooling of the film can be prevented.

  In the case of using such a zone stretching method, the temperature of the high temperature zone is preferably (Tg + 5) ° C. or higher, and preferably (Tg + 7) ° C. or higher. However, the temperature here does not mean that all the temperatures in the zone where the stretching is performed must be uniform at this temperature, but the maximum temperature within the range of 10 mm from the film in the high temperature zone. Other points in the furnace may be out of the temperature range. The upper limit of the temperature of the high temperature zone is not particularly limited as long as it is lower than the melting point of the film. However, if the temperature is excessively high, the expression of retardation may be lowered, and therefore it is preferably (Tg + 30) ° C. or lower. .

  Further, in such a zone stretching method, the temperature difference between the low temperature zone and the high temperature zone is preferably 5 ° C. or more, and more preferably 7 ° C. or more. Furthermore, the temperature of the low temperature zone is preferably (Tg-5) ° C. or higher and (Tg + 5) ° C. or lower, more preferably (Tg-5) ° C. or higher and (Tg + 3) ° C. If the temperature is out of such a range, the effect of improving the uniformity of retardation or reducing the shift of the slow axis may be diminished.

  The reason why the slow axis misalignment and retardation can be reduced by such a zone stretching method is not clear, but the inventors estimate that the longitudinal stretching method is a process that shrinks in the width direction and stretches in the flow direction. These processes are considered to occur because the uniformity of stretching increases when they occur individually rather than at the same time. That is, these two processes can be performed individually by shrinking the film in the width direction to some extent in the low temperature zone and stretching in the flow direction in the high temperature zone. Therefore, when the temperature of the low temperature zone is too low, the shrinkage in the width direction of the film in the low temperature zone does not occur so much, and the shrinkage process in the width direction and the stretching process in the flow direction do not occur simultaneously in the high temperature zone. It is estimated that. Further, when the temperature difference between the low temperature zone and the high temperature zone is small, it is estimated that the effect is reduced from the same idea. Such a principle is only an estimation, and the present invention is not limited to these principles.

Furthermore, in the method for producing an optical compensation film of the present invention, the ratio (v ₂ / v ₁ ) between the peripheral speed v ₁ of the inlet-side nip roll and the peripheral speed v ₂ of the outlet-side nip roll is the draw ratio. The draw ratio is preferably 20% or more, more preferably 25% or more, and further preferably 30% or more. When the draw ratio is low, the tension during film drawing becomes insufficient, and the film loosens in the drawing furnace, and in particular, the shift of the slow axis at the end of the film may increase. The upper limit of the magnification is not limited, but is generally 200% or less, preferably 100% or less, and more preferably 80% or less. Even when the draw ratio is set to a certain value or more, the retardation value does not increase sufficiently, and on the contrary, the film may be whitened to reduce the function as an optical compensation film.

In the method for producing an optical compensation film of the present invention, it is preferable that v ₁ , v ₂ and the film width W ₁ at the inlet side nip roll and the film width W _{2 at the} outlet side nip roll satisfy the following formula 5. It is further preferable to satisfy Equation 7.
(W ₂ / W ₁ ) ≦ 0.90 × (v ₂ / v ₁ ) ^−1/2 (Formula 5)
(W ₂ / W ₁ ) ≦ 0.85 × (v ₂ / v ₁ ) ^−1/2 (Formula 7)

When stretched at a temperature in the vicinity of Tg by a normal longitudinal stretching method, the shrinkage rate in the film width direction and the thickness direction are substantially equal, so W ₂ is approximately W ₁ × (v ₂ / v ₁ ) ^−1/2 . However, in the method for producing an optical compensation film of the present invention, the film width after stretching can be reduced to the above range by increasing the stretching temperature, whereby NZ can be set to a desired range. In order to set the film width W ₂ after stretching in the above range, it is effective to increase the stretching temperature and promote shrinkage in the width direction of the film.

  In a film in which molecules are not oriented at all and are in a random state, 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 are nx = ny = nz. In the actual film, in the case of solvent casting, the stress received from the support when the solvent volatilizes, the tension received during transportation, etc., and in the case of the melting method, the shear stress or the tension received during transportation In most cases, the molecules are oriented and the values of nx, ny, and nz are different. In particular, when a cellulose derivative is formed by a solvent cast method, there is a tendency that nx≈ny> nz. In such a film, in order to reduce NZ after stretching, the stretching temperature is appropriately adjusted, It is effective to set the film width after stretching within the above range.

  Further, in the method for producing an optical compensation film of the present invention, the width direction as described in JP-A No. 2000-241628 is used for the purpose of improving retardation uniformity and reducing the shift of the slow axis. It is also a preferable configuration to combine with the method of stretching by dividing the temperature by dividing.

  In practical use of the optical compensation film, for example, an optical compensation film provided with an adhesive layer on one or both sides, a polarizing film and / or an isotropic transparent resin layer or glass layer through the adhesive layer. It can also be applied as an optical member of an appropriate form composed of a laminate of two layers or three or more layers, such as a laminate obtained by bonding and laminating a protective layer composed of, for example. In particular, an optical compensation polarizing plate can be obtained by laminating the optical compensation film of the present invention and a polarizing plate. In addition, when the optical compensation film and the polarizing plate are bonded to form an optical compensation polarizing plate, only one optical compensation film of the present invention may be used, or two or more optical compensation films may be used. Furthermore, the optical compensation film of the present invention can be used in combination with other optical compensation films. When using an optical compensation film other than the present invention, the purpose is to improve the compensation effect, and the optical compensation film is not particularly limited. For example, a stretched product such as a uniaxial or biaxial polymer film, a discotic system or a nematic system is used. A liquid crystal alignment layer such as a birefringent layer made of a non-liquid crystalline polymer described in JP-A No. 2003-344856 can be preferably used.

  Moreover, what is used as a polarizing plate is not specifically limited, A suitable thing can be used. In general, polarizing plates with transparent protective layers on both sides of the polarizing film are widely used. However, polarizing films include polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer systems partially saponified. A film made by adsorbing iodine and / or a dichroic dye to a hydrophilic polymer film such as a film, a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product, etc. Is given. Although the orientation method of a polarizing film is not specifically limited, Generally, what extended | stretched the film to the flow direction and / or the width direction is used. In particular, from the viewpoint of productivity, the polarizing film is more preferably stretched in the film flow direction.

  The polarizing plate, particularly the polarizing film, may have a transparent protective layer on one side or both sides thereof. The polarizing plate may be of a reflective type having a reflective layer. The reflective polarizing plate is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side) and displays a liquid crystal display that can omit the incorporation of a light source such as a backlight. It has an advantage that the display device can be easily thinned.

  The transparent protective layer can be appropriately formed as a polymer coating layer, a laminate of protective films, etc., and a polymer excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, etc. is preferably used for the formation. It is done. Examples thereof include cellulose resins such as triacetyl cellulose, polyester resins, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, Alternatively, thermosetting type such as acrylic type, urethane type, acrylic urethane type, epoxy type, silicone type, or ultraviolet curable type resin can be used. The surface of the transparent protective layer may be formed in a fine concavo-convex structure by containing fine particles. In particular, when a cellulose-based resin such as triacetylcellulose is used, the film surface can be saponified to increase the adhesion. Furthermore, an optical compensation polarizing plate can be formed by using the optical compensation film of the present invention with a transparent protective layer of a polarizing film.

  The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is provided on one side of the polarizing plate via a transparent resin layer or the like as necessary. Specific examples thereof include a surface of a transparent resin layer such as a protective film that is mat-treated if necessary, with a foil or vapor deposition film made of a reflective metal such as aluminum, or the surface of the transparent resin layer containing fine particles. For example, a metal reflective layer provided on the fine concavo-convex structure by an appropriate method such as vapor deposition or plating.

  In the optical compensation polarizing plate of the present invention, the method of laminating the optical compensation film and the polarizing plate can be appropriately determined. For example, it can be carried out by a method of sequentially laminating sequentially in the manufacturing process of the liquid crystal display device, but by pre-laminating the optical compensation film and the polarizing plate, it has excellent quality stability and laminating workability. There is an advantage that the manufacturing efficiency of the liquid crystal display device can be improved. For the lamination, an appropriate transparent adhesive or pressure-sensitive adhesive can be used, and the type of the adhesive is not particularly limited. When layers having different refractive indexes are laminated, an adhesive having an intermediate refractive index is preferably used from the viewpoint of suppressing reflection loss. In addition, a method of improving the adhesion with an adhesive or the like by surface-treating the optical compensation film of the present invention with corona discharge or plasma or the like and preventing the adhesive or the like from peeling off is also preferably used. Also, from the viewpoint of preventing changes in optical properties, a lamination method using an adhesive layer that does not require curing, drying, or the like that requires a long process at a high temperature during lamination is preferable. The adhesive layer is not particularly limited, but an acrylic layer is preferably used from the viewpoint of heat resistance and optical characteristics.

  For the adhesive layer, for example, natural or synthetic resins, glass fibers or glass beads, fillers or pigments made of metal powder or other inorganic powders, coloring agents, antioxidants, etc. Various additives can also be blended. Moreover, it can also be set as the adhesion layer which contains microparticles | fine-particles and shows light diffusibility.

  The liquid crystal display device using the optical compensation film and / or the optical compensation polarizing plate according to the present invention can be formed according to a known method. In other words, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, an optical compensation film, and, if necessary, a polarizing plate and an illumination system, and incorporating a drive circuit. The optical compensation film according to the invention is not particularly limited except that it is used for optical compensation and is provided on one side or both sides of the liquid crystal cell.

  Accordingly, it is possible to form an appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector that is used in an illumination system. In the case of a liquid crystal display device using a polarizing plate, the optical compensation film is preferably disposed between the liquid crystal cell and the polarizing plate, particularly the viewing-side polarizing plate, in view of the compensation effect. In the arrangement, the optical compensation polarizing plate described above can also be used.

  In addition, each of the above-described optical compensation film, polarizing plate, transparent protective layer, adhesive layer, and the like includes ultraviolet rays such as salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Ultraviolet absorbing ability can be provided by a method of treating with an absorbent.

  The optical compensation film and / or the optical compensation polarizing plate according to the present invention is used for the purpose of compensating for the birefringence of a liquid crystal cell, such as widening the viewing angle and improving the contrast, TN type, STN type, VA type, IPS type, It can be used for any liquid crystal cell such as OCB type. Among them, the effect is remarkable when used for the purpose of suppressing the change in visibility due to the viewing angle of the VA liquid crystal display device. For example, as described in the pamphlet of International Publication WO 03/032060, biaxiality is used. By using together with other optical compensation layers having different wavelength dispersion, a liquid crystal display device having excellent viewing angle characteristics can be obtained.

  As described above, the object of the present invention is to contain at least 80 parts by weight of the cellulose derivative with respect to 100 parts by weight of the total weight, the X-ray diffraction intensity by the X-ray diffraction method is 3000 cps to 15000 cps, It is to provide an optical compensation film having the same, a method for producing the same, and an optical compensation polarizing plate and a liquid crystal display device using the same, and the technical scope thereof is the type of resin specifically described in the present specification and its It does not exist in the production method, the degree of crystallinity, or the conditions for forming a film, the stretching conditions, the retardation value that the film has. Therefore, the above optical compensation film, and the optical compensation polarizing plate and the liquid crystal display device using the same belong to the scope of the present invention regardless of the raw materials.

  It should be noted that the specific embodiments made in the section of the best mode for carrying out the invention and the following examples are merely to clarify the technical contents of the present invention, and to such specific examples. It is not to be construed as limiting in any way whatsoever, and those skilled in the art can implement the invention within the spirit of the invention and the scope of the appended claims.

  Moreover, all the academic literatures and patent literatures described in this specification are incorporated herein by reference.

  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) Wavelength dispersion of retardation value A 50 mm square sample was cut out from the center in the width direction of the film, and the wavelength dispersion of retardation was measured with an automatic birefringence meter KOBRA-WR manufactured by Oji Scientific Instruments. In addition, Re (450), Re (550), and Re (650) were calculated from the program attached to the apparatus.

(2) Thickness direction retardation and NZ
A 35 mm square sample was cut out from the center in the width direction of the film, and measured with an automatic birefringence meter KOBRA-WR manufactured by Oji Scientific Instruments at a measurement wavelength of 586.7 nm, with a plane direction retardation and 45 ° with the film slow axis as the rotation axis. The retardation at the time of tilting was measured, and the thickness direction retardation (Rth) and NZ were calculated by a program attached to the apparatus. Rth is a value calculated by the following formula 8.
Rth = {(nx + ny) / 2−nz} × d (Formula 8)

(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 From the center in the width direction of the film, a film cut into a rectangle of 15 mm × 60 mm with the stretching direction as the long side direction was used. Both ends in the long side direction of the cut out film were fixed so that the distance between chucks was 45 mm, and tension was applied to the film in steps of 10N from 0N to 100N by Suruga Seiki's X-axis ant stage B05-11BM. . The tension was monitored with a sensor separate type digital force gauge ZPS-DPU-50N manufactured by Imada Corporation. The retardation value in the state where each tension was applied was measured at a measurement wavelength of 586.7 nm using KOBRA-WR manufactured by Oji Scientific Instruments. After the retardation measurement, the sample was removed from the jig, and the thickness (d) of the retardation measurement portion was measured. From each measured value, the cross-sectional area of the film (S) = 15 mm × d, stress (= tension / S), birefringence (= retardation value / d) are calculated, the stress is plotted on the horizontal axis, and the vertical axis The birefringence was plotted on the graph, and the slope of the straight line obtained by the least square method was taken as the photoelastic coefficient.

(8) Slow axis misalignment As shown in FIG. 2, first, the film is cut over the entire width of the film twice at 5 cm intervals in the flow direction at 5 locations at intervals of 1 m in the flow direction. Thus, five strip-shaped films were cut out. This strip-like film has a short side of 5 cm and a long side of the film width. A range of 90% of the central part of the long side (= film width) of this strip-shaped film was divided into 10 equal parts, and 50 samples were obtained. The difference between the stretching direction and the slow axis of the central part of each of these 50 samples was measured at a measurement wavelength of 586.7 nm using KOBRA-WR manufactured by Oji Scientific Instruments, and the maximum and minimum values of the slow axis were measured. Was calculated.

(9) X-ray diffraction intensity Using a rotation counter-cathode X-ray diffractometer Geigerflex RAC-rA manufactured by Rigaku Denki Co., Ltd., an angular range 2θ = 3 ° to 35 °, a scanning speed of 2 ° / with Cu · Kα rays (intensity 40 kV, 120 mA) Minute, sampling interval 0.02 °, divergence slit 1 °, receiving slit 0.6 mm, scatter slit 1 °. Based on the measured X-ray diffraction intensity chart, as shown in FIG. 1, the diffraction peak intensity in each region of Bragg 2θ = 5 to 10 °, the perpendicular from the peak position, and the Bragg angles 2θ = 5 ° and 2θ = It calculated | required from the intensity | strength difference with the base line which tied the intensity | strength value of 10 degrees.

(10) Tear strength Tear strength in the stretching direction was measured by a trouser tear method (JIS-K7128-1) using Shimadzu Corporation tensile tester Autograph S-100-C. A value obtained by dividing the average value of the tearing force by the thickness was taken as the tear strength in each test, and the average value obtained by conducting the test at N = 5 was taken as the tear strength of each film.

(Non-stretched film creation example 1)
100 parts by weight of cellulose acetate propionate (hereinafter referred to as Resin A) having an acetyl group substitution degree of 0.1, a propionyl group substitution degree of 2.4, a number average molecular weight of 32000, and an X-ray diffraction intensity of 4200 cps, A dope containing 3 parts by weight of diethyl phthalate and 566 parts by weight of methylene chloride was prepared. On a biaxially stretched polyphthalate film having a thickness of 125 μm and a width of 1650 mm in a state where a stress of 1.0 × 10 ⁶ N / m ² is applied in the flow direction in an environment of room temperature (23 ° C.) and humidity of 15% Then, it was continuously cast by a comma coater so that the gap between the support and the comma roll was 480 μm. The support and the cast solution are continuously transported into a drying furnace adjusted to an ambient temperature of 35 ° C. by a far infrared heater, and thereafter pass through the furnace in which the ambient temperature is gradually raised to 50 ° C. I let you. Moreover, this drying furnace kept the humidity at 15% or less by continuously supplying dehumidified air having a dew point of −23 ° C., and prevented whitening of the film due to moisture. Then, it was further dried by passing through a hot air oven whose temperature was raised stepwise from 60 ° C. to a maximum of 80 ° C. to form a web, and a roll was formed integrally with the support. The obtained roll-shaped film is peeled off from the support film, further transported in a roll-suspended dryer and dried, then both ends of the film are cut off, and a long cellulose acylate film having a width of 1520 mm and a thickness of about 80 μm. Was obtained (referred to as unstretched film 1).

(Non-stretched film creation examples 2-8)
Applying the resin shown in Table 1 and the drying conditions shown in Table 2 and adjusting the gap between the support and the comma roll so as to achieve the target thickness, the same as in Film Preparation Example 1, Obtained. As shown in Table 3, in Film Production Examples 2 and 6, the crystallinity of the film was increased by increasing the initial drying temperature in the roll suspension dryer.

Example 1
Using the non-stretched film 1, the peripheral speed ratio (v ₂ / v ₁ ) of the nip roll v ₁ on the inlet side and the nip roll v ₂ on the outlet side of a roll stretcher having a furnace length of 4 m and an atmospheric temperature in the furnace of 147 ° C. = 1 .47 was continuously stretched in the film flow direction to obtain a roll-shaped optical compensation film. Table 3 shows the stretching conditions and the properties of the obtained optical compensation film.

(Examples 2-5 and Comparative Examples 1-4)
A roll-shaped optical compensation film was obtained in the same manner as in Example 1 except that the unstretched films 1 to 9 were used and the stretching conditions in Table 3 were applied.

  The properties of resins A to E are shown in Table 1, the production conditions of unstretched films 1 to 9 and the properties of the film are shown in Table 2, the production conditions of Examples 1 to 6 and Comparative Examples 1 to 4 are shown in Table 3, and the stretched film The characteristics are shown in Table 4.

  As shown in the above Examples and Comparative Examples, it can be seen that the cellulose acylate retardation film having a crystallinity within the range of the present invention satisfies predetermined optical characteristics and satisfies the film strength.

3 shows an X-ray crystal diffraction chart of the retardation film of Example 3 in the present specification. Point A and point B are diffraction values of 2θ = 5 ° and 10 °, point C is a diffraction peak at 2θ = 5 ° to 10 °, and point D is an intersection of a straight line descending from C and a line segment AB It is. The distance between point C and point D represents the X-ray diffraction intensity in this specification. The method of cutting out the sample for a measurement in measuring the distribution of slow axis deviation and retardation of the optical compensation film of the present invention is schematically shown.

Claims (11)

It contains 80 parts by weight or more of cellulose derivative with respect to 100 parts by weight of the total film weight, X-ray diffraction intensity by X-ray diffraction method is 3000 cps or more and 15000 cps or less, and further satisfies all of A, B, and C below. A characteristic optical compensation film.
A: The front retardation Re (λ) at the wavelength λnm satisfies the following formula 1.
Re (450) <Re (550) <Re (650) (Formula 1)
B: Front retardation Re (550) at a wavelength of 550 nm is 30 nm or more and 500 nm or less.
C: 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 at a wavelength of 590 nm, the value of NZ calculated by the following formula 2 is The following formula 3 is satisfied.
NZ = (nx-nz) / (nx-ny) (Formula 2)
1.00 ≦ NZ <1.20 (Formula 3)   The angle formed by the slow axis direction in the film plane and the film longitudinal direction is within ± 1.0 ° at an arbitrary point within the range of 90% of the central portion in the width direction of the film. The optical compensation film described in 1.   The cellulose derivative is a cellulose acylate in which a hydroxyl group of cellulose is substituted with an acyl group having 4 or less carbon atoms, and the total substitution degree of acyl groups is 2.0 or more and 2.9 or less. The optical compensation film according to any one of claims 1 and 2. The optical compensation film according to claim 3, wherein the acyl group is an acetyl group and a propionyl group, and a ratio of an acetyl substitution degree (DSac) to a propionyl substitution degree (DSpr) satisfies the following formula 4.
DSpr / DSac> 2.0 (Formula 4)   The cellulose acylate according to claim 4, wherein at least one of the acetyl substitution degree and the propionyl substitution degree has a different value, the sum of the cellulose acylates is 80 parts by weight with respect to 100 parts by weight of the total film weight. An optical compensation film characterized by being contained so as to be at least part by weight. ^6. The optical compensation film according to claim 1, wherein the photoelastic coefficient is 3.0 × 10 ⁻¹¹ m ² / N or less.   It is a manufacturing method of the optical compensation film of any one of Claim 1 to 6, Comprising: The longitudinal stretch process of a film is included, and with respect to the glass transition temperature (Tg) of this film during this longitudinal stretch process And a step of holding the film at a temperature of (Tg + 5) ° C. or higher.   The method for producing an optical compensation film according to claim 7, wherein a stretching ratio in the machine direction is 20% or more. The longitudinal stretching step includes an inlet-side nip roll and an outlet-side nip roll, a peripheral speed v _{1 of} the inlet-side nip roll, a peripheral speed v ₂ of the outlet-side nip roll, a width W _{1 of the} film in the inlet-side nip roll, 9. The method for producing an optical compensation film according to claim 7, wherein the film is stretched in the longitudinal direction so that a width W _{2 of the} film in the exit side nip roll satisfies Formula 5 below.
(W ₂ / W ₁ ) ≦ 0.90 × (v ₂ / v ₁ ) ^−1/2 (Formula 5)   An optical compensation polarizing plate comprising at least one optical compensation film according to any one of claims 1 to 6.   A liquid crystal display device comprising at least one of the optical compensation film according to any one of claims 1 to 6 and the optical compensation polarizing plate according to claim 10.

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