JP2007121351A - Retardation film, method for producing the same and optical compensation polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film capable of properly adjusting even phase difference when seen from an oblique direction, having uniformity of in-plane optical characteristics, and also having such uniform optical compensation ability as to ensure no local contrast reduction even in a large liquid crystal display device. <P>SOLUTION: The retardation film comprises one film produced by a solvent cast method and ensures a larger frontal phase difference Re at a longer wavelength. The angle between a slow axis direction in the film surface and a flow direction of the film is within ±1.5°. A refractive index in the flow direction of the film at a wavelength of 586.7 nm is larger than a refractive index in the width direction of the film. With respect to a refractive index nx in the slow axis direction in the film surface, a refractive index ny in a quick axis direction and a refractive index nz in the thickness direction, value calculated by (nx-nz)/(nx-ny) is 1.00 to <1.20. A frontal phase difference is 70-100 nm, a photoelastic coefficient is 3.0×10<SP>-11</SP>m<SP>2</SP>/N, and thickness variation in the width direction is less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a retardation film that has a larger retardation in a visible light region and has a larger viewing angle characteristic and can be used for a liquid crystal display device. Furthermore, this invention relates to the manufacturing method of such retardation film. The present invention also relates to an optical compensation polarizing plate using these retardation films.

  The retardation film is widely used in display devices such as liquid crystal display devices. In general, a polymer film made of polycarbonate, cyclic polyolefin or the like is used as the retardation film. An example of such a retardation film is a quarter wave plate having a phase difference of ¼ of the wavelength, and has a function of converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light, and is combined with a polarizing plate. It can be used for reflective liquid crystal display devices.

  In recent years, the use of retardation films has been expanded, and accordingly, more advanced functions have been required. One particularly important function is that the longer the wavelength in the visible light region, the higher the phase difference. It is desirable that the above-described retardation film used as a quarter wavelength plate has a retardation corresponding to a quarter wavelength for each wavelength of visible light. However, in the case of retardation films such as polycarbonate that are widely used in general, the longer the wavelength, the smaller the retardation, and in the case of displaying black in a liquid crystal display device using such retardation film showing wavelength dependence, May not be able to completely block the light from the screen, resulting in a decrease in contrast and gradation display.

On the other hand, the polycarbonate phase difference film which shows a high phase difference is disclosed, so that it is a long wavelength by bonding two phase difference films at a predetermined angle (for example, refer to patent documents 1). thing). 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 retardation 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, a retardation film composed of a single film of cellulose acetate having a higher retardation as the wavelength is longer (see, for example, Patent Document 2), and positive refractive index anisotropy. There has been proposed a retardation film comprising a copolymer of a high molecular monomer and a high molecular monomer having negative refractive index anisotropy (for example, see Patent Document 3).

Furthermore, a method of improving the viewing angle characteristic by adjusting the phase difference when viewed from an oblique direction has a higher phase difference as the wavelength is longer (for example, see Patent Document 4). See
JP-A-5-100114 JP 2000-137116 A International Publication WO00 / 26705 Pamphlet JP 2003-73485 A

  In the retardation film composed of a single film of cellulose acetate described in Patent Document 2, it is difficult to control the refractive index in all directions of the film, and the retardation when viewed from an oblique direction is appropriately adjusted. Was difficult. Further, the polycarbonate-based retardation film described in Patent Document 3 has a large change in retardation when stress is applied to the film, that is, a large photoelastic coefficient, and a decrease in contrast when used in a large liquid crystal display device such as a television. There was a problem of inviting.

  Furthermore, the retardation film using the special stretching method described in Patent Document 4 increases the manufacturing cost and gives a uniform optical property over the entire surface of the film because the special stretching method is used. It was difficult to use for a large liquid crystal display device.

  In addition, if there is unevenness due to the thickness pattern on the film surface, there is a problem that the image is distorted due to the dispersion of the retardation or the so-called lens effect. Has been required to have a uniform thickness. In this regard, for example, Japanese Patent Application Laid-Open No. 2005-128360 discloses a film having a controlled thickness pattern as an optical film formed by a melt extrusion method capable of obtaining a uniform display even under a high-luminance backlight. However, even if it is a retardation film made from a film formed by a solvent cast method, which is generally easier to ensure film thickness uniformity over a larger area than this melt extrusion method, By using only the casting method, the uniformity of the film thickness was insufficient to obtain sufficient viewing angle characteristics in a large area.

  The present invention has been made in view of the above-described problems, and its purpose is to have a higher phase difference as the wavelength is longer in the visible light region, and also to have a phase difference when viewed from an oblique direction. Provided are a retardation film that can be adjusted as appropriate, has in-plane thickness and uniformity of optical characteristics, and can be used for a large-sized liquid crystal display device, a method for producing the same, and an optical compensation polarizing plate using them There is to do.

As a result of intensive studies, the present inventors have found that a retardation film comprising a single film formed by a solvent cast method and having specific optical characteristics can solve the above-mentioned problems, and makes the present invention. It came to. That is, the present invention consists of a single film, the refractive index in the film flow direction at a wavelength of 586.7 nm is larger than the refractive index in the film width direction, and the following A, B, C, D, E, And F is satisfied.
A: The front phase difference Re (λ) at the wavelength λnm satisfies the following formula 1.

B: Value of NZ calculated by the following formula 2 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 586.7 nm. However, it satisfy | fills following Numerical formula 3, and a photoelastic coefficient is 3.0 * 10 < ^-11 > m < ² > / N or less.

C: Film thickness d is 50 μm or more and 90 μm or less.
D: Front phase difference Re (550) at a wavelength of 550 nm satisfies the following formula 4.

E: The thickness of the film from the top of the adjacent peak to the bottom of the valley when the thickness is measured at an interval of 1 mm in the film width direction is 0.5 μm or less in terms of the total film width, and the film thickness represented by Formula 5 Is 0.15 μm / mm or less in terms of the total width of the film.

Note that (height) in Equation 5 is the height (μm) from the top of the adjacent mountain to the bottom of the valley, and (width) in Equation 5 is the width from the top of the adjacent mountain to the bottom of the valley. (Mm).
F: The angle formed by the slow axis direction in the film plane and the film flow direction is within ± 1.5 °.

  Furthermore, in the retardation film of this invention, it is preferable to contain a cellulose derivative 80weight% or more.

  Furthermore, in the retardation film of the present invention, the cellulose derivative is preferably a cellulose acylate in which a hydroxyl group of cellulose is substituted with an acyl group having 4 or less carbon atoms.

  Furthermore, in the retardation film of this invention, it is preferable that the substitution degree of the said acyl group is 2.0 or more and 2.9 or less.

  Furthermore, in the retardation film of the present invention, it is preferable that when the acyl group is an acetyl group and a propionyl group and the degree of acetyl substitution is represented by DSac and the degree of propionyl substitution is represented by DSpr, the following formula 6 is satisfied.

Furthermore, in the retardation film of the present invention, the cellulose acylate may be composed of a plurality of types in which at least one of the acetyl substitution degree and the propionyl substitution degree has a different value.

  Furthermore, in the retardation film of the present invention, 1 part by weight or more and 20 parts by weight or less of cellulose ether in which a hydroxyl group of cellulose is substituted with an alkoxy group having 4 or less carbon atoms with respect to 100 parts by weight of the cellulose acylate. You may contain.

  Furthermore, in the retardation film of this invention, it is preferable that the said alkoxy group is an ethoxy group and an ethoxy substitution degree (DSet) satisfy | fills following Numerical formula 7.

Furthermore, this invention relates to the manufacturing method of the said retardation film. That is, the present invention includes a step of longitudinally stretching a film, and a step of maintaining the film at a temperature of (Tg + 5) ° C. or higher with respect to the glass transition temperature (Tg) of the film during the longitudinal stretching step. Furthermore, it is related with the manufacturing method of retardation film characterized by including.

  Furthermore, in the method for producing a retardation film of the present invention, a film transport apparatus having two pairs of nip rolls, each having a pair of inlet side nip rolls and two pairs of outlet side nip rolls, each capable of adjusting the circumferential speed, And a method for producing a retardation film, wherein the film is processed using a longitudinal stretching machine including a film heating device having a plurality of zones each capable of controlling the temperature, the film comprising an inlet side nip roll, a low temperature zone, While moving in the order of the high temperature zone adjusted to a temperature higher than the low temperature zone and the outlet nip roll, the longitudinal stretching is performed due to the peripheral speed difference between the two pairs of nip rolls, and the temperature of the high temperature zone is set to (Tg + 5) ° C. or more. It is preferable to adjust the temperature.

  Furthermore, in the manufacturing method of the retardation film of this invention, it is preferable to temperature-control the said low temperature zone and the said high temperature zone so that the temperature difference between them may be 5 degreeC or more.

  Furthermore, in the method for producing a retardation film of the present invention, it is preferable to adjust the temperature of the low temperature zone to (Tg−5) ° C. or more and (Tg + 5) ° C. or less.

Furthermore, in the method for producing a retardation film of the present invention, the peripheral speed v _{1 of} the inlet nip roll, the peripheral speed v ₂ of the outlet nip roll, the width W _{1 of the} film in the inlet nip roll, and the outlet side the width W ₂ of the film in the nip rolls, it is preferable to the longitudinal stretching so as to satisfy the following equation 8.

Furthermore, this invention relates to the optical compensation polarizing plate formed by laminating | stacking the said retardation film and polarizing plate.

  According to the present invention, a retardation film and an optical compensation polarizing plate having specific optical characteristics and a method for producing the same are provided, and a uniform display can be obtained even in a large liquid crystal display device. Furthermore, since the phase difference when viewed from an oblique direction can be adjusted as appropriate, the function of eliminating the viewing angle dependency in the liquid crystal display device can be exhibited.

  The retardation film of the present invention is formed by a solvent cast method. By forming the film by the solvent cast method, the thickness pattern can be easily controlled, and a film having a uniform thickness can be obtained. Furthermore, the retardation film of the present invention comprises a single film, and the refractive index in the film flow direction at a wavelength of 586.7 nm is larger than the refractive index in the film width direction. It is preferable to form a single film because an increase in processes and a decrease in yield due to the bonding of the films can be prevented. A retardation film having a refractive index in the film flow direction larger than a refractive index in the film width direction usually has a heating furnace between two pairs of nip rolls, and is stretched by a difference in peripheral speed between the two pairs of nip rolls. Although it can be obtained by stretching, such longitudinal stretching is preferable in that the retardation in the film plane and the uniformity of the slow axis can be maintained as compared with lateral stretching using a pin tenter or clip tenter. Furthermore, the retardation film of the present invention is characterized in that the front retardation Re (λ) at the wavelength λnm satisfies Re (450) <Re (550) <Re (650). If the wavelength dependence is out of this range, for example, when linearly polarized light in the visible light region is incident on this film, the obtained polarization state is a perfect circularly polarized light at a specific wavelength, but at other wavelengths. There may be a problem that it is greatly deviated from circularly polarized light. The wavelength dependency of the phase difference is preferably Re (450) / Re (550) <0.98, more preferably Re (450) / Re (550) <0.95, even within the above range. preferable. Further, Re (650) / Re (550) <1.01 is preferable, and Re (450) / Re (550) <1.03 is more preferable. Such wavelength dependency is a value peculiar to the resin used for the film, and can be obtained by appropriately selecting the resin to be used.

  The front phase difference Re referred to here is a refractive index nx in the slow axis direction, a refractive index ny in the fast axis direction, a refractive index nz in the thickness direction, and a film thickness d in the film plane. expressed.

In the retardation film of the present invention, the value of NZ represented by the following formula 2 at a wavelength of 586.7 nm is 1.00 or more and less than 1.20, preferably 1.10 or less, and more preferably. Is 1.05 or less.

When the value of NZ is large, the difference between the retardation values when the film is viewed from the front and when viewed from an oblique direction is large. The smaller the NZ, the smaller these differences are, and NZ = 0.5. At some point, these differences are zero. When the retardation 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. In the present invention, the film is formed or stretched. By appropriately selecting the method, NZ can be adjusted within the above range. Such a retardation film can be used for any liquid crystal display device. In particular, in a vertical alignment (VA) type liquid crystal display, a polarizer, a polarizer protective film, and a retardation film having the NZ value of the present invention. By using the optical compensation polarizing plate laminated in this order, it has a suitable optical compensation ability and can prevent a decrease in contrast even when viewed from an oblique direction.

  Furthermore, the retardation film of the present invention preferably has a film thickness d of 50 μm or more and 90 μm or less, more preferably 55 μm or more and 85 μm or less, and further preferably 60 μm or more and 80 μm or less. A retardation film is obtained by orienting molecules in the stretching direction by stretching an unstretched film, but generally the thickness decreases before and after stretching. The amount of change in thickness varies depending on conditions such as stretching temperature and magnification. In the present invention, the thickness of the film before stretching is preferably 55 μm or more and 100 μm or less, and preferably 60 μm or more and 95 μm or less. More preferably, it is 65 μm or more and 90 μm or less. Since the phase difference is expressed by the product of birefringence and thickness, if the thickness is too small, the achievable phase difference range becomes small, and a desired phase difference may not be obtained. If the thickness is too large, the range of retardation that can be achieved is widened, but not only is it difficult to obtain a film having a uniform thickness, but the productivity by the solvent cast method tends to be inferior.

  Furthermore, in the retardation film of the present invention, it is preferable that the front retardation at a wavelength of 550 nm satisfies the following mathematical formula 4.

In a quarter wavelength plate used for an antireflection plate of a reflective liquid crystal display device or an organic EL display device, the retardation value at 550 nm is ideally 137.5 nm, but in other liquid crystal display devices, Good display characteristics can be obtained without necessarily showing a phase difference of ¼ of the wavelength. Furthermore, as described above, in order to show a phase difference of ¼ of the wavelength, it is necessary to increase the thickness of the film. However, increasing the film thickness tends to reduce the thickness accuracy, and in order to obtain a uniform optical compensation capability, the retardation value is preferably within the above range.

  Furthermore, the thickness uniformity of the retardation film of the present invention will be described below. In the retardation film of the present invention, when the thickness is measured at intervals of 1 mm in the film width direction, the height from the top of the adjacent mountain to the bottom of the valley is preferably 0.5 μm or less in the entire film width, It is more preferably 0.3 μm or less, and further preferably 0.2 μm or less. Furthermore, the inclination of the film thickness represented by Formula 5 is preferably 0.15 μm / mm or less, more preferably 0.10 μm / mm or less, and 0.07 μm / mm or less in the entire film width. More preferably.

Note that (height) in Equation 5 is the height (μm) from the top of the adjacent mountain to the bottom of the valley, and (width) in Equation 5 is the width from the top of the adjacent mountain to the bottom of the valley. (Mm).

  In general, the thickness variation of the film is expressed by the difference between the maximum value and the minimum value of the full width. The correlation between the difference and the inclination is strong, and the smaller the numerical value, the higher the uniformity of the retardation, and the retardation film with less display distortion due to the so-called lens effect can be obtained.

  In the present invention, a method for measuring the height from the top of the adjacent peak to the bottom of the valley and the inclination of the film thickness will be described. The film is cut out with a width of 5 cm in the flow direction, and a strip-shaped film sample is obtained with the flow direction of 5 cm as one side and the film width as one side orthogonal to the one side. About this film sample, thickness is measured continuously in the film width direction, data are obtained by sampling those values in units of 1 mm, and the obtained data is plotted in two dimensions. For the measurement of the thickness, a film thickness meter that can measure the thickness continuously with a contact type measurement accuracy within 0.1 μm, for example, a film thickness meter KG601A manufactured by Anritsu Corporation is used. The height from the apex of the adjacent mountain to the bottom of the valley is obtained by (a) in FIG. Further, the inclination is obtained by (a) / (b) using (a) and (b) of FIG. In FIG. 1, (a) represents the height from the top of the adjacent mountain to the bottom of the valley, and (b) represents the width from the top of the adjacent mountain to the bottom of the valley.

  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 °, more preferably within ± 0.6 °. 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. Further, 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 °, more preferably within 1.0 °, Preferably, it is within 0.8 °.

Furthermore, in the retardation film of the present invention, the photoelastic coefficient is preferably 3.0 × 10 ⁻¹¹ m ² / N or less, more preferably 2.5 × 10 m ² / N or less, and still more preferably 2 0.0 × 10 ⁻¹¹ m ² / N or less. When the photoelastic coefficient exceeds the above range, uneven bonding when the retardation film is bonded together with the liquid crystal layer and the polarizing plate, thermal expansion difference between constituent materials due to receiving heat from the backlight and the external environment, polarizing film The change in phase difference due to the influence of stress caused by the shrinkage of the liquid crystal becomes large, which may cause display defects such as a decrease in contrast in the liquid crystal display device.

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

Next, polymers that can be used in the retardation 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 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 the cellulose derivative include cellulose esters 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. Among these, an amorphous polymer having excellent heat resistance can be preferably used.

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 retardation films. 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 in the above range, it is possible to maintain the wavelength dependence of the retardation of such a 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 indicates how much the three hydroxyl groups present at positions 2, 3, and 6 in the D-glucose molecule are esterified on average 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 esterified. When a film made of cellulose acylate having a substitution degree of 3 in which all the hydroxyl groups in the cellulose molecule are esterified with either an acetyl group or a propionyl group is uniaxially stretched, a negative direction in which the direction perpendicular to the stretch direction is the slow axis The retardation film having the optical anisotropy is obtained. The wavelength dispersion of retardation of this film shows a tendency that the longer the wavelength, the smaller the retardation (absolute value).

  When the degree of substitution is made smaller than 3, the ease of expression of retardation due to stretching decreases, and a film with little phase difference even when stretched at about 2.8 to 2.9 is obtained. If is reduced, the stretching direction becomes the slow axis, and a retardation film having positive optical anisotropy is obtained. Along with this, the chromatic dispersion of the phase difference tends to have a larger phase difference (absolute value) 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. The phase difference is shown. The degree of substitution showing a certain phase difference regardless of 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.

  For the above reasons, the substitution degree with an acyl group does not exceed 3, and 2.0 or more is appropriate from the viewpoint of wavelength dispersion of retardation. 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.

  Further, when cellulose acylate is used in the present invention, the acyl group is an acetyl group and a propionyl group, and the ratio of acetyl substitution degree (DSac) to propionyl substitution degree (DSpr) (DSpr / DSac) is 2 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 2003-240948 A. As disclosed in JP-A-2003-315538 and the like, the object can be achieved by replacing the hydroxyl group in the cellulose molecule with an acetyl group or a propionyl group. 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, from the viewpoint of solvent recovery equipment, it should be dissolved in a single solvent. Is preferred. 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. In particular, when methylene chloride is used, a remarkable difference is recognized, and it is a preferable configuration because it can be dissolved in a single solvent by increasing the degree of propionyl substitution.

  Accordingly, the propionyl substitution degree (DSpr) is preferably higher, and the ratio (DSpr / DSac) to the acetyl substitution degree (DSac) is 2.0 or more, more preferably 5.0 or more, and further preferably 10.0 or more. is there.

  Furthermore, in the retardation film of the present invention, a plurality of cellulose acylates having different substitution degrees are mixed and used for the purpose of appropriately adjusting the wavelength dispersion of retardation and the expression of retardation. You can also.

  Cellulose acylate can be produced by a known method. 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 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, the retardation film of the present invention may further contain a specific amount of a specific cellulose ether for the purpose of appropriately adjusting the wavelength dispersion of the retardation and the expression of the retardation. The cellulose ether used in the retardation 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 has a methoxy group, an ethoxy group, or a propoxy group. A cellulose ether substituted with one or more of a group and a butoxy group is more preferred, and a cellulose ether substituted with one or more of a methoxy group and an ethoxy group is particularly preferred. Since such cellulose ether has high retardation development property, the selection range of the retardation of the retardation 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 used as a retardation film.

  In the retardation film according to the present invention, the 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. If the cellulose ether content is less than 1 part by weight, the effect of improving the retardation when stretched may not be sufficient. Further, 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, and there is a case that the longer the wavelength, the higher the phase difference is.

  The retardation film according to the present invention can improve the retardation development property by further containing cellulose ether. Further, by setting the addition amount in the above range, the longer the wavelength, the higher the retardation. The characteristic of having can be maintained.

  Moreover, the cellulose ether used suitably in the polymer film which concerns on this invention has a specific substitution degree. Specifically, a cellulose ether having an ethoxy substitution degree (DSet) of 2.0 or more and 2.8 or less is preferable. The preferable range of the substitution degree of cellulose ether will be described below.

  DSet represents the average number of ethoxylations of the three hydroxyl groups present at positions 2, 3, and 6 in the D-glucose molecule, which is the basic unit of the cellulose molecule, in the cellulose molecule. 3 indicates that all hydroxyl groups in the cellulose molecule are ethoxylated. The degree of substitution at each position may be equal, or may be biased to any position. The degree of ether substitution can be quantified by the method described in ASTM D4794-94.

  Cellulose ethers are known to vary greatly in solubility in solvents depending on the degree of substitution. However, when the polymer film according to the present invention is produced by the solvent cast method, both the cellulose ether and the cellulose acylate described above are used. It is necessary to select a solvent that dissolves. 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.

  The cellulose ether used in the polymer film according to the present invention can be produced by a known method. For example, it is produced by treating cellulose with a strong caustic soda solution to obtain alkali cellulose, which is reacted with methyl chloride or ethyl chloride and etherified.

  The number average molecular weight of the cellulose ether is preferably 22000 to 100,000, more preferably 30000 to 80000, and still more preferably 35000 to 65000. An excessively high molecular weight may cause problems such as lowering the solubility in the solvent, the viscosity of the resulting solution being too high to be suitable for the solvent casting method, making thermoforming difficult and lowering the transparency of the film. is there. On the other hand, an excessively low molecular weight tends to decrease the mechanical strength of the obtained film.

  Thus, the retardation film according to the present invention may be composed of a single cellulose acylate, or may be composed of a plurality of cellulose acylates having different degrees of substitution, and is a mixture of cellulose acylate and cellulose ether. May be. Furthermore, you may contain the other polymer and additive which are compatible with these polymers.

  In the retardation 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 retardation 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 retardation film according to the present invention can be obtained by a solvent cast method in which a resin is dissolved in a solvent and the film thickness is adjusted by a known coater such as a die method or a comma method. In particular, when high flatness is required, such as optical compensation of a liquid crystal display device, the solvent cast method is advantageous in that a uniform film thickness can be obtained. The present application relates to a method of forming a film before stretching by this solvent casting method, and more particularly, to a method of forming a retardation film having a more uniform film thickness than that of the conventional film, more effectively exhibiting the characteristics of this 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.

  When forming into a film by this solvent cast method, after melt | dissolving resin and an additive in a solvent and making dope, it casts to a support body and dries to make 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.

  In order to make the film uniform thickness, it is important to prevent sudden solvent scattering at the initial stage of drying, and the ambient temperature immediately after coating the dope on the support should be below the boiling point of the solvent. Is preferred. Moreover, when the atmospheric temperature immediately after coating is lowered, the atmospheric temperature further decreases due to evaporation of the solvent, so that moisture in the drying furnace may be condensed and the film may be whitened. In order to prevent such whitening due to condensation, it is preferable to supply dry air or a gas having a low water content such as nitrogen into the furnace at the initial stage of drying, and keep the humidity in the furnace at 20% or less. From such a state, conditions are set so that the atmospheric temperature increases as drying proceeds, and the atmospheric temperature is preferably (solvent boiling point +50) ° C. or lower until the film surface is in a dry state. Drying conditions. When the film thickness accuracy is out of the range of the present invention, it is effective to lower the drying temperature or to reduce the linear velocity in the flow direction of the support for the purpose of lowering the drying rate.

  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.

  In order to obtain a retardation film, the film obtained above can be subjected to an orientation treatment by a known stretching method to impart a uniform retardation. In producing the retardation film of the present invention, the stretching method is not particularly limited, but it is preferable to use a method of longitudinal stretching due to a difference in peripheral speed between two pairs of nip rolls. Furthermore, in such a stretching method, the length of the heating furnace disposed between the two pairs of nip rolls is preferably 1.0 times or more, more than 1.5 times the film width before stretching. More preferably. By setting the furnace length in such a range, the range of deviation of the slow axis of the film can be reduced. Further, the length of the heating furnace is preferably 15 times or less, more preferably 10 times or less with respect to the film width before stretching. If the furnace length is excessively long, not only will the equipment cost increase, but when the film is stretched, the film will sag due to its own weight and lose its self-supporting property, and the film will rub against the nozzle of the hot air heater, etc. It may cause appearance defects such as scratches.

  Furthermore, in the method for producing a retardation film of the present invention, in order to make NZ a 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, etc., in order to reduce NZ. Requires special biaxial stretching as disclosed in JP-A-5-157911. However, in such special biaxial stretching, it is necessary to bond a heat-shrinkable film, etc., so that the number of processes increases, yield tends to deteriorate, and cost tends 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 a retardation 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 in-plane uniformity of retardation and reducing the shift 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, as shown in FIG. 2, 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, 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. When the temperature is out of the temperature range, the effect of improving the uniformity of the phase difference or reducing the shift of the slow axis may be diminished.

  The reason why the slow axis shift and phase difference can be reduced by such a zone stretching method is not clear, but in our estimation, 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 a retardation film of the present invention, the peripheral speed v ₁ of the nip roll on the inlet side, the peripheral speed v ₂ of the nip roll on the outlet side, the film width W ₁ on the nip roll on the inlet side, and the nip roll on the outlet side it is preferable that the film width W ₂ satisfies the following formula 8 in, it is more preferred to satisfy the equation 10.

In the normal longitudinal stretching method, W ₂ is generally W ₁ × (v ₂ / v ₁ ) ^−1/2 , but in the retardation film of the present invention, the film width after stretching is reduced to the above range. Thereby, NZ can be made into a desired range. To the film width W ₂ after stretching and the range, to increase the stretching temperature, it is effective to promote the widthwise shrinkage 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.

  Furthermore, in the method for producing a retardation film of the present invention, the width direction as described in JP-A No. 2000-241628 is used for the purpose of improving the 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 a retardation film, for example, a retardation film provided with an adhesive layer on one or both sides, a polarizing film and / or an isotropic transparent resin layer or glass layer via 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 retardation film of the present invention and a polarizing plate. Moreover, when laminating a retardation film and a polarizing plate to form an optical compensation polarizing plate, only one retardation film of the present invention may be used, or two or more retardation films may be used. Furthermore, it can also be used in combination with this invention retardation film and another optical compensation film. 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, a polarizing plate having a transparent protective layer on both sides of a polarizing film is widely used. As a polarizing film, a polyvinyl alcohol (PVA) film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer system are used. From a stretched film made by adsorbing iodine and / or a dichroic dye on a hydrophilic polymer film such as a partially saponified film, or a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product And the like. 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. As the transparent protective layer, a triacetyl cellulose (TAC) film is generally used. Generally, such a transparent protective film is called a polarizer protective film.

  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. This has the 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 also be formed by using the retardation 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 retardation film and the polarizing plate can be appropriately determined. For example, it can be carried out by a method of sequentially laminating separately in the manufacturing process of the liquid crystal display device, but by laminating the retardation film and the polarizing plate in advance, 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. Moreover, the method of improving the adhesiveness with an adhesive agent etc. by surface-treating the retardation film of this invention by corona discharge etc., and preventing peeling of an adhesive agent etc. are also used preferably. 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 retardation 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, a retardation film, and a polarizing plate and an illumination system as necessary, and incorporating a drive circuit. The retardation film according to the invention is not particularly limited except that the retardation film is used for optical compensation and 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 retardation film is more preferably disposed between the liquid crystal cell and the polarizing plate, particularly the polarizing plate on the viewing side, from the viewpoint of the compensation effect. In the arrangement, the optical compensation polarizing plate described above can also be used.

  In addition, each layer such as the above-described retardation film, polarizing plate, transparent protective layer, and adhesive layer is made of, for example, 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 retardation film and / or 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. In particular, the effect is remarkable when it is used for the purpose of suppressing the change in the visibility due to the viewing angle of the VA liquid crystal display device.

  As mentioned above, the objective of this invention consists of one film, The retardation film of the film flow direction in wavelength 586.7nm is larger than the refractive index of a film width direction, Furthermore, the retardation film which satisfy | fills the various characteristics mentioned above, and The production method and an optical compensation polarizing plate using the same are not provided by the film, the stretching condition, the retardation value, and the like specifically described in the present specification. Therefore, the retardation film and the optical compensation polarizing plate formed by laminating the retardation film 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 sample of 50 mm square is cut out from the center in the width direction of the film, and the wavelength dispersion of retardation is measured by 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 by an automatic birefringence meter KOBRA-WR manufactured by Oji Scientific Instruments at a measurement wavelength of 586.7 nm, with a plane phase difference and a film slow axis as the rotation axis at 45 °. The phase difference at the time of tilting was measured, and the thickness direction phase difference (Rth) and NZ were calculated by a program attached to the apparatus. Rth is a value calculated by the following mathematical formula 11.

(3) Film thickness, height from top of adjacent mountain to bottom of valley, and slope of film thickness Cut out the film with a width of 5 cm in the flow direction, set the flow direction of 5 cm as one side, and the film width as the one side. A strip-shaped film sample having one side orthogonal to each other was obtained. About this film sample, thickness was measured continuously in the film width direction, and data was obtained by sampling those values in 1 mm units. The average thickness at this time was defined as the film thickness. In addition, the obtained data is plotted in two dimensions, and the height (a) from the top of the adjacent mountain to the bottom of the valley (a) and the bottom of the valley as shown in FIG. The distance (b) was calculated, and the thickness gradient was determined from (a) / (b). These were performed from the apex of all adjacent peaks to the bottom of the valley, and the maximum value in the film width direction was determined.

(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 stepwise from 0N to 10N in increments of 1N by an X-axis ant type stage B05-11BM manufactured by Suruga Seiki. . The tension was monitored with a sensor separate type digital force gauge ZPS-DPU-50N manufactured by Imada Corporation. The phase difference value in a 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 phase difference measurement, the sample was removed from the jig, and the thickness (d) of the phase difference measurement part was measured. From each measured value, the cross-sectional area of the film (S) = 15 mm × d, stress (= tension / S), birefringence (= phase difference value / d) are calculated, the stress is plotted on the horizontal axis, and the vertical axis The birefringence was plotted on the line, and the slope of the straight line obtained by the least square method was taken as the photoelastic coefficient.
(8) Slow axis misalignment and phase difference distribution As shown in FIG. 3, first, at 5 locations in the flow direction of the film 1m and twice in the flow direction at intervals of 5cm, over the entire width of the film. By cutting the film, five strip-shaped films were cut out. This strip-like film has a width of 5 cm and the length is the width of the film. Next, each of these samples was equally divided into 10 in the film width direction to obtain a total of 50 samples. The phase difference values of these 50 points in total and the deviation between the flow direction and the slow axis of the film were measured at a measurement wavelength of 586.7 nm by KOBRA-WR manufactured by Oji Scientific Instruments, and the average value of these 50 point samples. The maximum value and the minimum value were calculated.
(9) Amount of residual solvent About 10 g of a sample was cut out from the vicinity of the center in the width direction of the film, and after measuring the weight, it was heated in an oven at 150 ° C. for 60 minutes, and then the weight was measured again.

Example 1
A cellulose acetate propionate (cellulose ester CAP482-20 manufactured by Eastman Chemical Co., hereinafter 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. 50 parts by weight, 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 25000 (cellulose ester CAP482-0.5 manufactured by Eastman Chemical) A dope containing 50 parts by weight of Compound B), 2 parts by weight of diethyl phthalate, and 566 parts by weight of methylene chloride was prepared. A comma coater is applied on a biaxially stretched PET film having a width of 1650 mm and a thickness of 125 μm in a state where a stress of 1.0 × 10 ⁶ N / m ² is applied in the flow direction in an environment of 23 ° C. and 15% humidity. Used for continuous casting. The support and the cast dope are continuously conveyed 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. After that, it was further dried by passing through a hot air oven whose temperature was raised stepwise from 60 ° C. to 90 ° C. to form a web, which was integrated with the support into a winding roll shape. The obtained roll-shaped web was peeled off from the PET film and further dried in a hot air oven with an atmospheric temperature of 100 ° C., and then both ends of the film were cut off to obtain a long film having a thickness of 71.5 μm, a width of 1490 mm, and a length of 1400 m. Got. The resulting film had a residual solvent amount of methylene chloride of 1.2% and a glass transition temperature of 138 ° C. (this film is referred to as “unstretched film 1”).

Using the non-stretched film 1, the peripheral speed ratio (v ₂ / v ₁ ) = 1 of the nip roll v ₁ on the inlet side and the nip roll v ₂ on the outlet side of a roll stretching machine having a furnace length of 4 m and an atmospheric temperature in the furnace of 148 ° C. = 1 .67 was continuously stretched in the film flow direction to obtain a roll-like retardation film having a thickness of 63.2 μm.

(Example 2)
The film was continuously stretched in the film flow direction in the same manner as in Example 1 except that the unstretched film 1 was used and the atmospheric temperature in the furnace was 144 ° C. and (v ₂ / v ₁ ) = 1.59. A 6 μm roll retardation film was obtained.

(Comparative Example 1)
A roll-like retardation having a thickness of 61.9 μm was continuously stretched in the film flow direction in the same manner as in Example 1 except that the atmospheric temperature in the furnace was 138 ° C. and (v ₂ / v ₁ ) = 1.50. A film was obtained.

(Comparative Example 2)
A long film having a thickness of 105.3 μm, a width of 1490 mm, and a length of 1400 m was obtained under the same conditions as the unstretched film 1 except for the thickness at the time of coating. The obtained film had a methylene chloride residual solvent amount of 1.5% and a glass transition temperature of 138 ° C. (this film is referred to as “unstretched film 2”). Using this non-stretched film 4, it was continuously stretched in the film flow direction under the same conditions as in Example 1 except that (v ₂ / v ₁ ) = 1.39, and a roll-shaped film having a thickness of 101.9 μm. A retardation film was obtained.

(Comparative Example 3)
A long film having a thickness of 41.5 μm, a width of 1490 mm, and a length of 1400 m was obtained under the same conditions as in the production of the unstretched film 1 except for the thickness at the time of coating. In the obtained film, the residual solvent amount of methylene chloride was 0.9%, and the glass transition temperature was 138 ° C. (this film is referred to as “unstretched film 3”). Using this unstretched film 3, it was continuously stretched in the film flow direction under the same conditions as in Example 1 to obtain a roll-shaped retardation film having a thickness of 37.9 μm.

(Comparative Example 4)
When the film was continuously stretched in the film flow direction under the same conditions as in Comparative Example 3 except that the unstretched film 3 was used and (v ₂ / v ₁ ) = 1.90, the film became extremely cloudy and provided for practical use. It wasn't something to get.

(Example 3)
Using a non-stretched film 1, a furnace length of 4 m, and a roll stretching machine that is partitioned every 2 m and can be independently temperature-controlled, the first zone and the second zone (hereinafter referred to as 1Z and 2Z, respectively) The temperature was 138 ° C., 148 ° C., and (v ₂ / v ₁ ) = 1.67, and the film was continuously stretched in the film flow direction to obtain a roll-shaped retardation film having a thickness of 62.9 μm. An outline of the stretching machine is shown in FIG.

Example 4
The film was continuously stretched in the film flow direction in the same manner as in Example 3 except that the unstretched film 1 was used and the temperatures of 1Z and 2Z were 145 ° C., 148 ° C. and (v ₂ / v ₁ ) = 1.71, respectively. A roll-shaped retardation film having a thickness of 63.1 μm was obtained.

(Example 5)
The film was continuously stretched in the film flow direction in the same manner as in Example 3 except that the unstretched film 1 was used and the temperatures of 1Z and 2Z were 132 ° C., 148 ° C. and (v ₂ / v ₁ ) = 1.66, respectively. A roll-shaped retardation film having a thickness of 63.3 μm was obtained.

(Example 6)
Using the unstretched film 1, the film was continuously stretched in the film flow direction in the same manner as in Example 3 except that the temperatures of 1Z and 2Z were 148 ° C., 138 ° C. and (v ₂ / v ₁ ) = 1.69, respectively. A roll-shaped retardation film having a thickness of 63.1 μm was obtained.

(Example 7)
An unstretched film 1 is used, and an infrared panel heater divided into 10 in the width direction is arranged in the furnace 2Z of the roll stretching machine used in Example 3, and 175, 175, 165, 160, 155, 155 are arranged in order from the end. , 160, 165, 175, 175 ° C., 1Z and 2Z temperatures of 138 ° C., 148 ° C. and (v ₂ / v ₁ ) = 1.67, respectively, and continuously stretched in the film flow direction to obtain a thickness A 62.9 μm roll-like retardation film was obtained.

(Example 8)
A dope containing 30 parts by weight of Compound A, 70 parts by weight of Compound B, and 500 parts by weight of methylene chloride was prepared. Using this dope, a long film having a thickness of 71.3 μm, a width of 1471 mm, and a length of 1400 m was obtained in the same manner as in Example 1. In the obtained film, the residual solvent amount of methylene chloride was 1.1%, and the glass transition temperature was 147 ° C. (this film is referred to as “unstretched film 4”).

Using the non-stretched film 4, the panel heater of the roll stretching machine having the infrared panel heater used in Example 7 was set to 180, 180, 170, 165, 160, 160, 165, 170, 180, 180 ° C. in order from the end. Then, with the temperature of 1Z and 2Z being 147 ° C., 157 ° C. and (v ₂ / v ₁ ) = 1.71, respectively, a roll-like retardation film having a thickness of 60.9 μm was stretched continuously in the film flow direction. Obtained.

Example 9
A dope containing 93 parts by weight of Compound A, 9 parts by weight of ethyl cellulose (Ethcel MED70 manufactured by Dow Chemical) having an average degree of substitution of 2.3 and a number average molecular weight of 51,000 and 650 parts by weight of methylene chloride was prepared. Using this dope, a long film having a thickness of 63.7 μm, a width of 1465 mm, and a length of 1400 m was obtained in the same manner as in Example 1. In the obtained film, the residual solvent amount of methylene chloride was 0.9%, and the glass transition temperature was 147 ° C. (this film is referred to as “unstretched film 5”).

The film was continuously stretched in the film flow direction in the same manner as in Example 1 except that the unstretched film 5 was used and the atmospheric temperature in the furnace was set to 157 ° C. and (v ₂ / v ₁ ) = 1.63. An 8 μm roll retardation film was obtained.

(Example 10)
The film was continuously stretched in the film flow direction in the same manner as in Example 9 except that the unstretched film 5 was used and the atmospheric temperature in the furnace was 159 ° C. and (v ₂ / v ₁ ) = 1.73. A 5 μm roll retardation film was obtained.

(Example 11)
The film was continuously stretched in the film flow direction in the same manner as in Example 3 except that the unstretched film 5 was used and the temperatures of 1Z and 2Z were 149 ° C., 159 ° C. and (v ₂ / v ₁ ) = 1.75, respectively. A roll-like retardation film having a thickness of 58.8 μm was obtained.

(Comparative Example 5)
A dope containing 100 parts by weight of polycarbonate (Teijin Kasei Panlite C-1400) made of bisphenol A (the following monomer [A]) as a bisphenol component and 400 parts by weight of methylene chloride was prepared. Using this dope, a long film having a thickness of 24.3 μm, a width of 1430 mm, and a length of 1400 m was obtained in the same manner as in Example 1. The obtained film had a methylene chloride residual solvent amount of 1.7% and a glass transition temperature of 148 ° C. (this film is referred to as an unstretched film 6).

The unstretched film 6 was continuously stretched in the film flow direction in the same manner as in Example 1 except that the atmospheric temperature in the furnace was 157 ° C. and (v ₂ / v ₁ ) = 1.11, and the thickness was 20.1 μm. A roll-like retardation film was obtained.

(Comparative Example 6)
A reaction vessel equipped with a stirrer, a thermometer and a reflux condenser was charged with an aqueous sodium hydroxide solution and ion-exchanged water, and bisphenol A (the following monomer [A]) and biscresol fluorene (the following monomer [B]) were added to this: The mixture was dissolved at a ratio of 60 (mol%), and a small amount of hydrosulfite was added. Next, methylene chloride was added thereto, and phosgene was blown in at about 20 ° C. over about 60 minutes. Further, p-tert-butylphenol was added to emulsify, and then triethylamine was added and stirred at 30 ° C. for about 3 hours to complete the reaction. After completion of the reaction, the organic phase was separated and methylene chloride was evaporated to obtain a polycarbonate copolymer. The obtained copolymer was dissolved in deuterated benzene, and the copolymerization ratio was calculated from the proton intensity ratio of methyl groups of components A and B by proton NMR using Varian NMR INOVA AS600. A]: [B] = 43: 57.

  A dope containing 100 parts by weight of this copolymer and 450 parts by weight of methylene chloride was prepared. Using this dope, a long film having a thickness of 80.2 μm, a width of 1430 mm, and a length of 1400 m was obtained in the same manner as in Example 1. The obtained film had a residual solvent amount of methylene chloride of 1.1% and a glass transition temperature of 227 ° C. (this film is referred to as “unstretched film 7”).

The unstretched film 7 was continuously stretched in the film flow direction in the same manner as in Example 1 except that the atmospheric temperature in the furnace was 234 ° C. and (v ₂ / v ₁ ) = 1.77, and the thickness was 70.1 μm. A roll-like retardation film was obtained.

The properties of the unstretched films 1 to 5 are shown in Table 1, and the properties of the stretched films obtained in Examples and Comparative Examples are shown in Table 2 and Table 3.

(Example 12) A PVA film (thickness 30 μm) containing iodine was prepared as an absorbing dichroic polarizing film, and a TAC film (thickness 40 μm) was used as a transparent protective film on both sides of the polarizing film with a PVA adhesive. By sticking together, a polarizing plate having a total thickness of 110 μm was prepared (referred to as polarizing plate A). An optical compensation polarizing plate (referred to as polarizing plate B) was obtained by laminating with an acrylic adhesive so that the transmission axis of polarizing plate A and the stretching axis of the retardation film obtained in Example 1 were parallel. . A polarizing plate A is placed on a backlight having an illuminance of 10,000 lux in a dark room, and further, a polarizing plate B is placed on the backlight so as to be orthogonal to the transmission axis of the polarizing plate A, and the presence or absence of light leakage is visually evaluated. As a result, light leakage could not be confirmed.

(Comparative Example 7)
The optical compensation polarizing plate (referred to as polarizing plate C) was obtained by pasting together with an acrylic adhesive so that the transmission axis of polarizing plate A and the stretching axis of the retardation film obtained in Comparative Example 1 were parallel. . When the same light leakage evaluation was carried out using the polarizing plate C instead of the polarizing plate B of Example 12, no light leakage was observed when viewed from the front, but it was viewed from a direction of 45 degrees obliquely. A streaky light leak was observed.

As shown in the above examples, it consists of a single film formed by the solvent cast method, and the refractive index in the film flow direction at a wavelength of 586.7 nm is larger than the refractive index in the film width direction. A retardation film characterized by satisfying all of A, B, C, D, E, and F can be obtained.
A: The front phase difference Re (λ) at the wavelength λnm satisfies the following formula 1.

B: Value of NZ calculated by the following formula 2 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 586.7 nm. However, it satisfy | fills following Numerical formula 3, and a photoelastic coefficient is 3.0 * 10 < ^-11 > m < ² > / N or less.

C: Film thickness d is 50 μm or more and 90 μm or less.
D: Front phase difference Re (550) at a wavelength of 550 nm satisfies the following formula 4.

E: The thickness of the film from the top of the adjacent peak to the bottom of the valley when the thickness is measured at an interval of 1 mm in the film width direction is 0.5 μm or less in terms of the total film width, and the film thickness represented by Formula 5 Is 0.15 μm / mm or less in terms of the total width of the film.

Note that (height) in Equation 5 is the height (μm) from the top of the adjacent mountain to the bottom of the valley, and (width) in Equation 5 is the width from the top of the adjacent mountain to the bottom of the valley. (Mm).
F: The angle formed by the slow axis direction in the film plane and the film flow direction is within ± 1.5 °.

  Further, as shown in Example 3, Example 7, Example 8, and Example 11, a longitudinal stretching machine having two or more temperature-controllable heating zones in the film flow direction between two pairs of nip rolls is used. The temperature is set so that the film passes through the high temperature zone after the low temperature zone, and the temperature of the high temperature zone is set to (Tg + 5) ° C. or higher with respect to the glass transition temperature (Tg) of the film. It can be seen that the range of axial misalignment can be reduced.

  Further, as shown in Example 12, the optical compensation polarizing plate made of a retardation film satisfying the above conditions has good display characteristics with no light leakage.

In this invention, it is a schematic diagram of the measuring method of the height from the peak of an adjacent peak to the bottom of a valley, and the inclination of film thickness. It is a schematic diagram of the longitudinal stretch machine which has two or more temperature-controllable heating zones in the film flow direction between two pairs of nip rolls used in the retardation film manufacturing method of the present invention. In measuring the distribution of the slow axis deviation of the retardation film of the present invention, a method for cutting out a measurement sample is schematically shown. It is the schematic diagram of the longitudinal stretch machine which has two heating zones which can be temperature-controlled in the film flow direction between two pairs of nip rolls used in the Example of this invention.

Claims (14)

It consists of one film formed by the solvent cast method, and the refractive index in the film flow direction at a wavelength of 586.7 nm is larger than the refractive index in the film width direction. Furthermore, the following A, B, C, D, A retardation film satisfying all of E and F.
A: The front phase difference Re (λ) at the wavelength λnm satisfies the following formula 1.
B: Value of NZ calculated by the following formula 2 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 586.7 nm. However, it satisfy | fills following Numerical formula 3, and a photoelastic coefficient is 3.0 * 10 < ^-11 > m < ² > / N or less.
C: Film thickness d is 50 μm or more and 90 μm or less.
D: Front phase difference Re (550) at a wavelength of 550 nm satisfies the following formula 4.
E: The thickness of the film from the top of the adjacent peak to the bottom of the valley when the thickness is measured at an interval of 1 mm in the film width direction is 0.5 μm or less in terms of the total film width, and the film thickness represented by Formula 5 Is 0.15 μm / mm or less in terms of the total width of the film.
Note that (height) in Equation 5 is the height (μm) from the top of the adjacent mountain to the bottom of the valley, and (width) in Equation 5 is the width from the top of the adjacent mountain to the bottom of the valley. (Mm).
F: The angle formed by the slow axis direction in the film plane and the film flow direction is within ± 1.5 °.   The retardation film according to claim 1, comprising a cellulose derivative in an amount of 80% by weight or more.   The retardation film according to claim 2, wherein 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.   The retardation film according to claim 3, wherein the substitution degree of the acyl group is 2.0 or more and 2.9 or less. 5. The retardation film according to claim 4, wherein the acyl group is an acetyl group and a propionyl group, and satisfies the following Expression 6 when the acetyl substitution degree is represented by DSac and the propionyl substitution degree is represented by DSpr.
  The retardation film according to claim 5, wherein the cellulose acylate comprises a plurality of types in which at least one of the acetyl substitution degree and the propionyl substitution degree is different.   The cellulose ether in which the hydroxyl group of cellulose is substituted with an alkoxy group having 4 or less carbon atoms is further contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the cellulose acylate. 6. The retardation film according to any one of 6 above. The retardation film according to claim 7, wherein the alkoxy group is an ethoxy group, and an ethoxy substitution degree (DSet) satisfies the following formula 7.
  It is a manufacturing method of phase contrast film given in any 1 paragraph of Claims 1-8, Comprising: The process of carrying out longitudinal stretching of a film, and in the glass transition temperature (Tg) of this film during this longitudinal stretching process A method for producing a retardation film, further comprising a step of holding the film at a temperature of (Tg + 5) ° C. or higher. Film conveying apparatus having two pairs of nip rolls, each having a pair of inlet side nip rolls and two pairs of outlet side nip rolls, each capable of adjusting the peripheral speed, and film heating having a plurality of zones each capable of temperature adjustment The method for producing a retardation film according to claim 9, wherein the film is processed using a longitudinal stretching machine including an apparatus,
The film is stretched in the longitudinal direction due to a difference in peripheral speed between the two pairs of nip rolls while moving the film in the order of an inlet nip roll, a low temperature zone, a high temperature zone adjusted to a temperature higher than the low temperature zone, and an outlet nip roll; The method for producing a retardation film, wherein the temperature of the high temperature zone is adjusted to (Tg + 5) ° C. or higher.   The method for producing a retardation film according to claim 10, wherein the temperature of the low-temperature zone and the high-temperature zone is adjusted so that a temperature difference between them is 5 ° C. or more.   The temperature of the said low temperature zone is temperature-controlled to (Tg-5) degreeC or more and (Tg + 5) degreeC or less, The manufacturing method of the retardation film of any one of Claim 10 or 11 characterized by the above-mentioned. The peripheral speed v _{1 of} the inlet-side nip roll, the peripheral speed v _{2 of} the outlet-side nip roll, the width W _{1 of the} film in the inlet-side nip roll, and the width W _{2 of the} film in the outlet-side nip roll The method for producing a retardation film according to claim 10, wherein the longitudinal stretching is performed so as to satisfy.
  A retardation film according to any one of claims 1 to 8, or a retardation film formed by the production method according to any one of claims 9 to 13, and a polarizing plate, An optical compensation polarizing plate.