TW201350938A - Retardation film and polarizer - Google Patents

Abstract

The object of this invention is to provide a retardation film and a polarizer. The retardation film can provide easy and reliable adjustment of retardation and can be easily laminated, and has a small retardation variation due to environmental conditions. The retardation film of this invention is formed by stretching the sheet that is made of acetate propionate fiber by extrusion molding. Preferably, the retardation value is R448 when tested by using the light with 448.1 nm of wavelength, and is R589 when tested by using the light with 589 nm of wavelength, the retardation value is R800 when tested by using the light with 800nm of wavelength, and preferably, the resulting value of (R800/R589-R448/R589)/(800-589) for the retardation film is greater than 0.001 and less than 0.003.

Description

Phase difference film and polarizing plate

The present invention relates to a retardation film and a polarizing plate.

Conventionally, there has been known a retardation film formed by stretching a sheet made of polycarbonate or a sheet made of a cycloolefin polymer. The retardation film is used, for example, for a polarizing plate. Specifically, a polarizer protective film made of cellulose triacetate or the like is laminated on both surfaces of a polarizing plate (polarizer) to form a polarizer, and the retardation film is made of water-based glue (water paste) or the like. A polarizing plate is produced by laminating and bonding on the polarizer.

The resin of the retardation film made of polycarbonate has a relatively high photoelastic coefficient of 60 or more and 80 or less. If the retardation film made of polycarbonate is deformed by the temperature and humidity of the use environment, the refractive index changes and is delayed. The problem of change. Therefore, it is difficult to use a retardation film made of a polycarbonate as a retardation film which is laminated on a circularly polarizing plate for antireflection of an organic EL display, for example, as a retardation film which does not like a retardation change.

Since the retardation film made of a cycloolefin polymer has high gas barrier properties and low moisture permeability, it cannot be bonded using an aqueous glue containing a cellulose resin as a main component, and thus it is difficult to laminate and bond with a polarizing plate or the like.

Further, a retardation film made of cellulose acetate propionate is proposed in Japanese Laid-Open Patent Publication No. 2007-131681. The retardation film described in the above publication is obtained by dissolving cellulose acetate propionate in a solvent to form a solution, and then casting the solution into a sheet form. Therefore, the solvent remains in the retardation film described in the above-mentioned publication, and there is a problem in that it is difficult to obtain a balance between the retardation in the plane direction and the retardation in the thickness direction due to the residual solvent.

Prior art literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2007-131681

In view of the above-described problems, an object of the present invention is to provide a retardation film which can easily and reliably adjust the retardation, can be easily laminated and bonded, and has a small change in retardation due to conditions of the use environment. Further, the present invention provides a polarizing plate having a retardation film capable of reliably adjusting retardation, which is easy to manufacture and which has little change in optical characteristics due to conditions of use environment.

In order to solve the above problems, the present invention provides a retardation film which is a retardation film formed by stretching a sheet made of an extrusion-formed cellulose acetate propionate resin.

The retardation film is a retardation film formed by stretching an extruded sheet of cellulose acetate propionate in an oblique direction inclined with respect to the longitudinal direction of the sheet.

Since the retardation film is made of cellulose acetate propionate, the retardation change due to the conditions of the use environment is small compared with the conventional polycarbonate sheet or the like. Further, the retardation film exhibits a phase difference by being stretched, and it is easy to obtain surface retardation and thickness as compared with a conventional retardation film produced by using a solution in which cellulose acetate propionate is dissolved in a solvent. The balance of the direction delay is such that the retardation film has an excellent balance of the plane direction retardation and the thickness direction retardation. In addition, the retardation film can be bonded to a polarizing plate or the like easily and reliably by using an aqueous glue which has been conventionally used and which is mainly composed of a cellulose-based resin.

In the retardation film, it is preferable that the retardation in the plane direction measured by the light of 448.1 nm is R448, the retardation in the plane direction measured by the light of 589 nm is R589, and the plane direction measured by the light of 800 nm. When the retardation is R800, (R800/R589-R448/R589)/(800-448.1) is 0.001 or more and 0.003 or less.

Thus, the plane direction retardation measured with light of a high wavelength (800 nm) becomes larger than the plane direction retardation measured by light of a low wavelength (448.1 nm), and the ratio of the enlargement is within the numerical range, So you can play against the light with the light The length of the corresponding surface direction is delayed, and a desired phase difference can be exhibited for a wide range of wavelength regions.

In the retardation film, it is preferable that the retardation in the plane direction measured by the light of 448.1 nm is R448, the retardation in the plane direction measured by the light of 589 nm is R589, and the plane direction measured by the light of 800 nm. When the retardation is R800, (1-R448/R589)/(589-448) is 0.0013 or more and 0.003 or less, and (R800/R589-1)/(800-589) is 0.0006 or more and 0.003 or less.

Thus, in the low wavelength region (448.1 to 589 nm), the plane direction retardation measured with the high wavelength (589 nm) light becomes larger than the plane direction retardation measured with the low wavelength (448.1 nm) light, and the The proportion that becomes larger is within the numerical range, and therefore the light for the low-wavelength region can exhibit a plane direction delay corresponding to the wavelength of the light. Further, in the high wavelength region (589 to 800 nm), the plane direction retardation measured by the high wavelength (800 nm) light becomes larger than the plane direction retardation measured with the low wavelength (589 nm) light, and the enlargement becomes large. The ratio is within the range of values, so that the light for the high wavelength region can exhibit a plane direction delay corresponding to the wavelength of the light. That is, by adopting the above configuration, a desired phase difference can be exhibited for a wide range of wavelength regions.

Further, it is preferable that (R800/R589-1)/(1-R448/R589) is 0.4 or more and 1 or less. Thus, the ratio of the rate of change of the retardation in the plane direction in the high wavelength region (589 to 800 nm) to the rate of change in the plane direction in the low wavelength region (448.1 to 589 nm) is within the numerical range, and is low. In the wavelength region and the high-wavelength region, the surface direction retardation can be made to be accurately increased corresponding to the wavelength of the transmitted light, and thus the desired phase difference can be easily exhibited in a wide range of wavelength regions.

In the retardation film, it is preferable that the retardation in the plane direction measured by light having a wavelength of 589 nm is 130 nm or more and 150 nm or less. Thereby, the retardation film can function as a quarter-wave plate.

In the retardation film, it is preferable that the retardation in the thickness direction measured by light having a wavelength of 589 nm is 70 nm or more and 300 nm or less. Thereby, the retardation film A good balance between the thickness direction retardation and the plane direction retardation can be easily and reliably obtained.

In the retardation film, it is preferable that the stretching ratio in the longitudinal direction of the sheet is 30% or more and 250% or less. Thereby, the delay of the desired range can be easily and accurately expressed.

Further, the present invention provides a polarizing plate comprising: the retardation film; and a polarizing plate laminated and bonded to the retardation film by an adhesive layer.

Since the polarizing plate has the retardation film of the above configuration, it has the advantage of the retardation film described above. In other words, the polarizing plate has a small change in optical characteristics due to a change in the use environment, and the retardation film has excellent balance between the retardation in the plane direction and the retardation in the thickness direction. By using an adhesive layer such as an aqueous glue containing a cellulose resin as a main component, which has been conventionally used, the retardation film of the polarizing plate can be easily and reliably laminated.

As described above, the retardation film of the present invention can easily and reliably adjust the retardation, and can be easily laminated and bonded, and the retardation change due to the conditions of the use environment is small.

1‧‧‧ phase difference film

1a‧‧‧ piece forming material

3‧‧‧Polarizer

5‧‧‧Binder layer

10‧‧‧Polar plate

Fig. 1 is a schematic front view showing a retardation film according to an embodiment of the present invention.

FIG. 2 is a schematic explanatory view for explaining a stretching method of the method for producing the retardation film of FIG. 1. FIG.

Fig. 3 is a schematic front view showing a polarizing plate using the retardation film of Fig. 1;

4 is a view showing a relationship between a wavelength of a transmitted ray and a retardation in a plane direction, with respect to the retardation film of the embodiment of the present invention and the retardation film of Comparative Examples 1 and 2. FIG.

Fig. 5 is a table for comparing values 1 to 4 according to Fig. 4.

Hereinafter, an embodiment of the present invention will be described. First, a retardation film 1 according to an embodiment of the present invention will be described.

Phase difference film 1

The retardation film 1 of the present invention is a sheet made of extrusion-formed cellulose acetate propionate. A retardation film formed by stretching in an oblique direction inclined with respect to the longitudinal direction of the sheet. The sheet is obtained by extrusion molding a resin composition containing cellulose acetate propionate as a main component. Here, cellulose acetate propionate is a substance in which at least a part of the hydroxyl group of cellulose is substituted with an ethyl fluorenyl group and a propyl fluorenyl group.

The average degree of substitution (DSac + DSpR) of the ethyl fluorenyl group and/or the propyl fluorenyl group in the cellulose acetate propionate is preferably 2.0 or more. When the average degree of substitution is less than the lower limit, the retardation film 1 having a larger retardation (absolute value) at a shorter wavelength has a problem that the display quality of the liquid crystal display device is lowered. Further, the average degree of substitution (DSac + DSpR) of the ethyl fluorenyl group and/or the propyl fluorenyl group in the cellulose acetate propionate can be determined, for example, by the method described in ASTM-D817-96. Further, the upper limit of the average degree of substitution (DSac + DSpR) is 3, and in this case, all of the hydroxyl groups are acetylated or propylated.

Further, the average degree of substitution (DSac) of the ethyl fluorenyl group in the cellulose acetate propionate is preferably 0.1 or more and 1.6 or less, and further, the average degree of substitution of the fluorenyl group in the cellulose acetate propionate. (DSpR) is preferably 0.1 or more and 2.4 or less, more preferably 0.5 or more and 2.0 or less, still more preferably 1.0 or more and 2.0 or less.

The cellulose acetate propionate may have other substituents other than an ethyl fluorenyl group and a propyl fluorenyl group. The other substituent may, for example, be an ether group such as another ester group such as butyrate or an alkyl ether group or an aralkyl ether group.

The weight average molecular weight (Mw) of the cellulose acetate propionate is preferably 5,000 or more and 140,000 or less, more preferably 15,000 or more and 110,000 or less, and still more preferably 50,000 or more and 105,000 or less. When the weight average molecular weight of cellulose acetate propionate exceeds the upper limit, there is a problem that thermal fluidity at the time of extrusion molding is lowered to cause thermoforming. On the other hand, when the weight average molecular weight of the cellulose acetate propionate is less than the lower limit, there is a problem that the mechanical strength of the obtained film is lowered and the obtained film does not have a sufficient phase difference. Further, the weight average molecular weight (Mw) can be calculated by measurement of gel permeation chromatography (GPC).

The cellulose acetate propionate may be composed of a single compound, but in order to easily adjust optical characteristics such as in-plane retardation, a compound having a different degree of substitution of a propyl fluorenyl group and an acetamidine group may be used in combination.

The cellulose acetate propionate can be produced by a known method. For example, the cellulose is treated with a concentrated caustic soda solution into an alkali cellulose, and the alkali cellulose is thiolated using a mixture of acetic anhydride and propionic anhydride. The obtained cellulose ester has an average degree of substitution (DSac + DSpR) of substantially 3, and by partially hydrolyzing the thiol group, cellulose acetate propionate having a target degree of substitution can be produced. Further, by changing the ratio of acetic anhydride to propionic anhydride at the time of thiolation, the target degree of substitution of propylene is obtained.

Further, the resin composition as the sheet forming material may contain other compounds than the main component of cellulose acetate propionate. The other compound may, for example, be another cellulose ester such as cellulose butyrate or a cellulose ether such as methyl cellulose or ethyl cellulose. Among them, ethyl cellulose which is excellent in developability in the inner surface direction and excellent in compatibility with cellulose acetate propionate is preferable. The amount of the ethyl cellulose blended is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 8 parts by mass or less, and still more preferably 100 parts by mass of the cellulose acetate propionate. 6 parts by mass or more and 8 parts by mass or less.

From the viewpoint of improving the processing properties at the time of stretching, it is preferred that the resin composition contains a plasticizer. The plasticizer is not particularly limited, and examples thereof include diethyl phthalate and a polyol compound. Among them, diethyl phthalate is preferable because it has good compatibility with cellulose acetate propionate and has little influence on retardation in the opposite direction.

The content of the plasticizer is preferably 5% by mass or more and 20% by mass or less, and more preferably 8% by mass or more and 16% by mass or less based on the total amount of the resin composition. If the content of the plasticizer exceeds the upper limit, there is a problem that the mechanical strength is lowered. On the other hand, when the content of the plasticizer is less than the lower limit, there is a problem that the effect of adding the plasticizer cannot be sufficiently exhibited, and the hot forming and stretching steps cannot be improved.

Further, it is preferable that the resin composition contains a phosphite (or salt)-based coloring inhibitor. By containing a phosphite (or salt)-based coloring inhibitor, an excellent coloring prevention effect can be obtained even when the molding temperature is in a high temperature range.

As the phosphite (or salt)-based coloring preventive agent, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diyldiphosphoric acid can be exemplified. Ester, tetrakis(2,6-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diyldiphosphite, tetrakis(2,6-di-tert-butylphenyl-4 -Methyl)[1,1-biphenyl]-4,4'-diyldiphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, double (2-tert-Butyl-4-cumylphenyl) pentaerythritol diphosphite, bis(4-tert-butyl-2-cumylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl) Pentaerythritol dipenta phosphate, bis(2,4-di-tert-butyl-6-methylphenyl)pentaerythritol diphosphite, etc., among which pentaerythritol excellent in coloring prevention effect is preferable. system.

The amount of the phosphite (or salt)-based coloring preventive agent is preferably 0.005% by mass or more and 0.5% by mass or less based on the total amount of the resin composition. If the amount of the phosphite (or salt)-based coloring preventive agent exceeds the upper limit, there is a problem that a sufficient effect corresponding to the added amount cannot be obtained. On the other hand, when the mixing amount of the phosphite (or salt)-based coloring preventive agent is less than the lower limit, there is a problem that the coloring prevention effect is lowered.

Further, the resin composition may contain other additives insofar as it does not impair the effects of the present invention. As other additives, a heat stabilizer, a UV stabilizer, a nucleating agent, a matting agent, a pigment, an antifungal agent, an antibacterial agent, a flame retardant, a hydrophilic agent, and the like can be exemplified.

As described above, the retardation film 1 is formed by stretching the sheet in an oblique direction, and the stretching ratio in the oblique direction of the sheet is preferably 30% or more and 250% or less. It is preferably 40% or more and 220% or less, and more preferably 50% or more and 120% or less. If it is less than the lower limit value, there is a problem that the phase difference cannot be sufficiently exhibited. On the other hand, if the upper limit is exceeded, then there is The problem of phase difference cannot be fully controlled. Further, the stretching method in the oblique direction will be described later.

The retardation film 1 has a fast axis that is inclined by 40 or more and 50 or less with respect to the longitudinal direction of the sheet. Further, in the present invention, the inclination angle of the fast axis is not particularly limited, but the angle of inclination of the fast axis is about 45°, which can be suitably used as a retardation film for a polarizing plate.

The retardation film 1 has a retardation in the plane direction measured by light having a wavelength of 589 nm of 130 nm or more and 150 nm or less. Further, in the present invention, the surface direction retardation is not necessarily limited to the above range, but by delaying the surface direction of the retardation film 1 within the above range, it can be suitably used as a quarter-wave plate. Further, the retardation (Re) as the plane direction is a numerical value obtained by the following equation.

Re=(ny-nx)×d

Where nx is the refractive index of the fast axis of the retardation film (the axis parallel to the plane direction), and ny is the refractive index of the slow axis of the retardation film (the axis parallel to the plane direction and perpendicular to the fast axis), and d is the phase The thickness of the film is poor.

Further, the retardation film 1 has a retardation in the thickness direction measured by light having a wavelength of 589 nm of 70 nm or more and 300 nm or less. Further, in the present invention, the thickness direction retardation is not necessarily limited to the above range, but by delaying the thickness direction of the retardation film 1 within the range, the thickness direction retardation and the plane direction can be easily and reliably obtained. The balance of delay. In addition, the thickness direction retardation (Rth) is a numerical value obtained by the following formula.

Rth=((nx+ny)/2-nz)×d

Here, nz is the refractive index of the retardation film 1 in the thickness (direction perpendicular to the plane direction).

Further, for example, an automatic birefringence measuring device (for example, manufactured by Oji Scientific Instruments Co., Ltd., trade name: KOBRA-WR) is used to transmit light of a specific wavelength (for example, 589 nm) in an environment of 23 ° C and 50% RH. The three-dimensional refractive index measurement can be obtained by determining the refractive indices nx, ny, and nz. Delay in thickness direction.

Further, in the case where the plane direction retardation measured by the light of 448.1 nm is R448, the plane direction retardation measured by the light of 589 nm is R589, and the plane direction retardation measured by the light of 800 nm is R800, it is preferable. The retardation film 1 satisfies the following conditions.

The value obtained by dividing the difference between R800 and R448 and R589 (R800/R589 and R448/R589) by the amount of change in wavelength of light (800-448.1) (hereinafter sometimes referred to as value 1), preferably 0.001 the above.

Specifically, it is preferable to satisfy the following calculation formula (1).

The left side of the calculation formula (1) (value 1) means that the surface direction retardation measured by the high wavelength (800 nm) light is larger than the surface direction retardation measured by the low wavelength (448.1 nm) light. By setting the numerical value 1 to be equal to or higher than the lower limit value, it is possible to function as a quarter-wave plate in a wide wavelength region. Further, the lower limit value is preferably 0.0009.

Further, the numerical value 1 is preferably 0.003 or less. If the value 1 exceeds the upper limit value, the retardation in the plane direction of the high-wavelength (800 nm) light becomes too large or the retardation in the plane direction of the low wavelength (448.1 nm) becomes too small, and the result cannot be in a wide range. In the wavelength region, it functions as a function of a quarter-wave plate. Further, the upper limit of the numerical value 1 is more preferably 0.002.

The value obtained by dividing the difference between R800 and R589 and R589 (R800/R589 and 1) by the amount of change in wavelength of light (800-589) (hereinafter sometimes referred to as "value 2") is preferably 0.0006 or more.

Specifically, it is preferable to satisfy the following calculation formula (2).

The left side (value 2) of the calculation formula (2) refers to a ratio in which the plane direction retardation in the high wavelength region (589 to 800 nm) becomes larger corresponding to the wavelength of the transmitted light, by setting the value 2 under the Above the limit, it can be used in high wavelength regions It is a function of 1/4 wave plate.

Further, the numerical value 2 is preferably 0.003 or less. This is because if the value 2 exceeds the upper limit value, conversely, there is a problem that the function as a quarter-wave plate cannot be exhibited in the high-wavelength region. Further, the upper limit value of the numerical value 2 is more preferably 0.002.

The value obtained by dividing the ratio of R448 and R589 to R589 (R448/R589 and 1) by the amount of change in wavelength of light (589-448.1) (hereinafter sometimes referred to as the value 3) is preferably 0.0013 or more.

Specifically, it is preferable to satisfy the following calculation formula (3).

The left side (value 3) of the calculation formula (3) refers to a ratio in which the plane direction retardation in the low wavelength region (448.1 to 589 nm) becomes larger corresponding to the wavelength of the transmitted light, by setting the value 3 under the Above the limit value, it can function as a quarter-wave plate in a low-wavelength region. Further, the lower limit value is more preferably 0.0014.

Further, the numerical value 3 is preferably 0.003 or less. This is because if the numerical value 3 exceeds the upper limit value, conversely, there is a problem that the function as a quarter-wave plate cannot be exhibited in a wide wavelength region in the low-wavelength region. Further, the upper limit of the numerical value 3 is more preferably 0.002 or less.

The ratio of the value 2 to the value 3 is preferably 0.4 or more.

Specifically, it is preferable to satisfy the following calculation formula (4).

The left side (value 4) of the calculation formula (4) is a ratio of the rate of change of the plane direction retardation in the high wavelength region to the rate of change of the plane direction retardation in the low wavelength region (448.1 to 589 nm) by making the value 4, above the lower limit value, the plane direction retardation in the low wavelength region and the high wavelength region can be accurately increased in accordance with the wavelength of the transmitted light, and thus can be used as a quarter wave in a wide wavelength region. The function of the piece. Further, the lower limit value is more preferably 0.42.

Further, it is preferred that the value 4 is 1 or less. If the value 4 exceeds The upper limit value makes it difficult to manufacture the retardation film 1. Further, the upper limit of the numerical value 4 is more preferably 0.8 or less, still more preferably 0.7 or less.

The average thickness of the retardation film 1 is preferably 40 μm or more and 250 μm or less, more preferably 40 μm or more and 200 μm or less, and still more preferably 40 μm or more and 150 μm or less. If the average thickness of the retardation film 1 exceeds the upper limit value, there is a problem that it is inconsistent with the demand for thinness and light weight. On the other hand, in the case where the average thickness of the retardation film 1 is smaller than the lower limit value, there is a problem that a sufficient phase difference cannot be exhibited.

Further, the average thickness of the sheet before stretching of the retardation film 1 is preferably 50 μm or more and 500 μm or less, more preferably 100 μm or more and 300 μm or less, and still more preferably 120 μm or more and 250 μm or less. Thereby, the retardation film 1 having the above average thickness can be produced after stretching.

The light transmittance of the retardation film 1 is preferably 85% or more, and more preferably 90% or more. When the light transmittance of the retardation film 1 is smaller than the lower limit, there is a problem that the amount of light from the light source is lowered and the visibility of the screen is lowered.

The haze of the retardation film 1 is preferably 2% or less, and more preferably 1% or less. If the haze of the retardation film 1 exceeds the upper limit, problems such as a decrease in light transmittance and a decrease in sharpness of a transmission image are caused.

Method of manufacturing retardation film 1

The method for producing the retardation film 1 includes a step of melting a sheet forming material whose main component is cellulose acetate propionate, a step of extruding the melted sheet forming material into a sheet shape, and forming an extruded sheet-like sheet. The step of stretching the material and the step of punching the stretched sheet forming material into a quadrangular shape.

The melting step and the extrusion step can be carried out by a conventional melt extrusion method. For example, the sheet forming material can be melted and extruded from a T die to form a sheet.

The stretching step is a step of continuously stretching the sheet forming material extruded as described above in an oblique direction inclined with respect to the longitudinal direction of the sheet. In this process, the stretching temperature It is preferably 130 ° C or more and 170 ° C or less, and more preferably 140 ° C or more and 160 ° C or less. When the stretching temperature is less than the lower limit value, there is a problem that the sheet-like forming material is broken at the time of stretching. On the other hand, if the stretching temperature exceeds the upper limit value, there is a problem that a sufficient phase difference cannot be exhibited by stretching.

In the stretching step, the sheet forming material is stretched in the longitudinal direction (longitudinal direction of the sheet) while the sheet forming material is also stretched in the lateral direction (the short side direction of the sheet), thereby forming the sheet forming material along Stretched in an oblique direction inclined to the longitudinal direction of the sheet. The longitudinal and transverse stretching can be carried out, for example, by a stretching device as shown in Fig. 2. The stretching device shown in FIG. 2 grips both end portions of the sheet forming material 1a with a jig, respectively, so that the jigs of the two end portions are along the longitudinal direction of the sheet in a manner faster than the sheet extrusion speed. The traveling is performed by making the traveling speed of one jig faster than the traveling speed of the other jig, thereby stretching the sheet in an oblique direction inclined with respect to the longitudinal direction of the sheet.

Here, as described above, the stretching ratio is preferably 30% or more and 250% or less. The stretching ratio refers to the distance of the pair of jigs which are widened after stretching (the length W2 from the sheet forming material after stretching in the oblique direction (fast axis direction) minus the sheet formation before stretching The ratio of the value of the material W1 in the short-side direction to the distance between the pair of jigs before stretching (the length W1 (width) of the sheet-forming material 1a before stretching in the short-side direction). Specifically, the draw ratio can be obtained by the following calculation formula (5).

Stretching ratio (%) = ((distance of a pair of jigs after stretching) / (distance of a pair of jigs before stretching)) *100-100... Calculation formula (5)

Further, in the present invention, the stretching method is not limited to the method described, and for example, it is also considered to be inclined by stretching in one direction (for example, the longitudinal direction) and stretching in the other direction (for example, the lateral direction). The method of stretching in the direction. In this case, the draw ratio can be obtained by the calculation formula (6).

Stretching ratio (%) = ((stretching magnification in one direction) ² + (stretching magnification in the other direction) ² ) ^1/2 ...calculation formula (6)

Further, in the present invention, the case where the stretching step and the extrusion step are continuously provided has been described, but the present invention is not limited thereto. For example, a sheet formed by extruding into a sheet may be temporarily used. The roll is taken up into a roll-shaped original piece, and thereafter, the sheet is taken out from the roll-shaped original piece and subjected to a stretching process. In this case, as a pre-stretching step, it is preferred to carry out a step of preheating the sheet.

In the punching step, the long side or the short side of the punched quadrilateral is punched so as to be parallel to the longitudinal direction of the stretched sheet forming material. As described above, since the sheet forming material is stretched in the oblique direction with respect to the longitudinal direction, the fast axis of the punched sheet (the retardation film 1) becomes inclined with respect to the longitudinal direction of the sheet. Tilt in direction.

Method of manufacturing polarizing plate 10

Next, a method of manufacturing the polarizing plate 10 using the retardation film 1 will be described.

The method of manufacturing the polarizing plate 10 includes a step of laminating the phase difference film 1 on the polarizing plate 3. Here, as the polarizing plate 3, a conventional polarizing plate can be used, and for example, a polarizing obtained by dyeing and uniaxially stretching a polyvinyl alcohol resin film with a dichroic substance such as iodine or a dichroic dye can be used. sheet. The degree of polymerization of the polyvinyl alcohol constituting the polyvinyl alcohol resin film is preferably 500 or more, and more preferably 1,000 or more. The polyvinyl alcohol resin film can be formed by a known method (for example, a casting method or a casting method in which a resin obtained by dissolving a resin in water or an organic solvent is cast into a film). The thickness (average thickness) of the polarizing plate 3 varies depending on the purpose and use of the liquid crystal display device or the like using the polarizing plate 10, and is typically 5 μm or more and 100 μm or less. The polarizing plate 3 may contain any components other than the polyvinyl alcohol resin and the dichroic material as long as it does not interfere with the polarizing function and optical transparency. As a typical production method of the polarizing plate 3, a series of manufacturing steps including a step of swelling, dyeing, crosslinking, stretching, washing, and drying a polyvinyl alcohol resin film can be employed. In addition to the drying process, in each treatment process, by using polyvinyl alcohol resin The membrane was immersed in a solution bath used in the respective steps for treatment. The order, the number of times, and whether or not each treatment of swelling, dyeing, cross-linking, stretching, water washing, and drying can be carried out can be appropriately set depending on the purpose, materials used, conditions, and the like. For example, the stretching treatment may be carried out before the dyeing treatment, or may be carried out simultaneously with the swelling treatment or the like. Further, it is preferred that the crosslinking treatment be performed before and after the stretching treatment.

In the lamination bonding step in the method of manufacturing the polarizing plate 10, the polarizing plate 3 and the retardation film 1 are laminated and bonded by a binder. As the binder, a conventionally known binder can be used. For example, a water-soluble binder can be used, and an aqueous binder containing a cellulose resin as a main component can be suitably used.

Polarizer 10

Next, the polarizing plate 10 using the retardation film 1 will be described with reference to Fig. 3 . The polarizing plate 10 of FIG. 3 includes a polarizing plate 3 and the retardation film 1, and the retardation film 1 is laminated and bonded to both faces of the polarizing plate 3 via an adhesive layer 5 composed of the adhesive.

Here, the pair of the retardation films 1 laminated on the both surfaces of the polarizing plate 3 are laminated and bonded to the polarizing plate 3 so as to face each other at a predetermined angle in the fast axis direction. Specifically, one of the retardation films 1 is laminated and bonded to the polarizing plate 3 so that the fast axis direction thereof is inclined by +45° with respect to the transmission axis direction of the polarizing plate 3 in plan view, and the other retardation film 1 is viewed from above. The polarizing plate 3 was laminated and bonded in such a manner that its fast axis direction was inclined by -45° with respect to the transmission axis direction of the polarizing plate 3. Therefore, the pair of the retardation films 1 are laminated and bonded to the polarizing plate 3 so as to have an angle of 90° with respect to the fast axis direction of each other. Further, a predetermined angle formed by looking down the direction of the fast axis direction of the pair of retardation films 1 is preferably 80° or more and 100° or less. Further, the angle between the fast axis direction of the retardation film 1 and the transmission axis direction of the polarizing plate 3 in plan view is preferably an absolute value of 40° or more and 50° or less.

Advantages of the invention

Since the retardation film 1 has the above-described structure, the retardation film 1 is made of cellulose acetate propionate, so that it is conventional. In the polycarbonate sheet or the like, the change in retardation due to the conditions of the use environment is small, and the polarizing plate 10 is less likely to change in optical characteristics due to the conditions of the use environment.

Further, the retardation film 1 exhibits a phase difference by stretching, and it is easy to obtain a balance between the retardation in the plane direction and the retardation in the thickness direction as compared with the retardation film which has been conventionally produced with a solvent. Therefore, the retardation film 1 is obtained. A good balance of surface direction retardation and thickness direction retardation can be obtained. Therefore, the retardation film can be easily and reliably produced, for example, as a retardation film which can function as a positive A plate, and the retardation film can be easily and reliably produced, for example, as a negative C plate. The phase difference film acts.

In addition, the retardation film 1 can be bonded to the polarizing plate 3 easily and reliably by using an aqueous glue which has been conventionally used and which is a cellulose-based resin as a main component.

Further, since the retardation in the plane direction of the retardation film varies within the range due to the transmitted light (refer to calculation formulas (1) to (4)), it is suitable as a quarter-wave plate in a wide wavelength region. use.

Further, the retardation film 1 exhibits a phase difference by being stretched in an oblique direction, and can punch the stretched sheet by a long side or a short side parallel to the longitudinal direction of the sheet. Since it is manufactured, compared with the conventional technique of punching in the oblique direction, the number of manufacturing processes is small and loss is unlikely to occur, so that cost reduction can be achieved.

Example 1

Next, an embodiment of the retardation film of the present invention will be described.

In the present embodiment, a sheet forming material prepared by adding cellulose acetate propionate (the average degree of substitution of acrylonitrile to 2.0) to 100 parts by weight of the main component is added as a plasticizer. The weight fraction of the TPP of the Big Eight Chemical Industry and the 5 parts by weight of the #8 Chemical Industry's #10. The sheet forming material was melted and extruded through a T die to obtain a sheet-like sheet forming material, and the sheet-like sheet forming material was stretched at a stretching ratio of 155 ° C at a stretching ratio of 165%. The retardation film of this example was obtained. Further, the retardation film has an average thickness of 145 μm. (240 μm before stretching).

With respect to the retardation film of the above-described embodiment, the transmitted light for each wavelength was measured in an environment of 23 ° C and 50% RH using an automatic birefringence measuring device (manufactured by Oji Scientific Instruments Co., Ltd., trade name: KOBRA-WR). The face direction is delayed. The result is shown in Fig. 4.

Further, as a comparative example, the retardation film (manufactured by Teijin Chemicals Co., Ltd.) having a trade name of WRF-W was measured under the same conditions as described above. The result is shown in Fig. 4.

Further, in Fig. 4, the horizontal axis represents the wavelength of the transmitted light at the time of measurement. The vertical axis represents the ratio of the plane direction retardation measured by the transmitted light of each wavelength to the plane direction retardation measured by the transmitted light of the wavelength of 589 nm.

As is apparent from the above-described FIG. 4, the retardation film of the present embodiment has a larger retardation in the plane direction as the transmitted light ray moves from a lower wavelength to a higher wavelength than the retardation film of the comparative example, in a wide wavelength region. It functions as a quarter-wave plate.

More specifically, as shown in Fig. 5, the numerical value 1 (the numerical value on the left side of the calculation formula (1)) is about 0.00093 in the present embodiment, and is about 0.00079 in the comparative example. Further, the numerical value 2 (the value on the left side of the calculation formula (2)) which has been described is about 0.00060 in the present embodiment, and is about 0.00051 in the comparative example. Further, as already described, the value 3 (the value on the left side of the calculation formula (3)) is about 0.00143 in the present embodiment, and is 0.00120 in the comparative example. This embodiment is compared with the comparative example, with the transmitted light. When moving from a low wavelength to a high wavelength, the surface direction retardation gradually increases, and functions as a quarter-wave plate in a wide wavelength region. Further, the numerical value 4 (the numerical value related to the calculation formula (4)) which has been described is about 0.42 in the present embodiment and the comparative example.

Other embodiments

Further, the present invention is not limited to the embodiment, and various modifications and improvements can be implemented. For example, the polarizing plate 10 of the embodiment performs a polarizing plate having a three-layer structure (excluding the adhesive layer 5) of a pair of retardation film 1 and a polarizing plate 3 sandwiched therebetween. In addition, for example, the polarizing plate 10 may have a two-layer structure of the polarizing plate 3 and the retardation film 1 as well, and may be a three-layer structure as in the above-described embodiment. The outer surface of the retardation film 1 is further laminated with a structure of a protective film.

Industrial applicability

As described above, the retardation film and the polarizing plate of the present invention are suitably used in various fields such as a liquid crystal display device and polarized glasses used in mobile phones, PC displays, televisions, calculators, clocks, and automobile instruments.

1‧‧‧ phase difference film

Claims (8)

A retardation film which is a retardation film formed by stretching a sheet made of an extruded cellulose acetate propionate resin. The retardation film according to the first aspect of the invention, wherein the retardation in the plane direction measured by the light of 448.1 nm is R448, the retardation in the plane direction measured by the light of 589 nm is R589, and the light is measured by 800 nm. When the arrival direction retardation is R800, (R800/R589-R448/R589)/(800-448.1) is 0.0008 or more and 0.003 or less. The retardation film according to the first aspect of the invention, wherein the retardation in the plane direction measured by the light of 448.1 nm is R448, the retardation in the plane direction measured by the light of 589 nm is R589, and the light is measured by 800 nm. When the retardation in the plane direction is R800, (1-R448/R589)/(589-448) is 0.0013 or more and 0.003 or less, and (R800/R589-1)/(800-589) is 0.0006 or more and 0.003 or less. The retardation film according to the third aspect of the invention, wherein (R800/R589-1)/(1-R448/R589) is 0.4 or more and 1 or less. The retardation film according to the first aspect of the invention, wherein the retardation in the plane direction measured by light having a wavelength of 589 nm is 130 nm or more and 150 nm or less. The retardation film according to the first aspect of the invention, wherein the retardation in the thickness direction measured by light having a wavelength of 589 nm is 70 nm or more and 300 nm or less. The retardation film according to the first aspect of the invention, wherein the stretching ratio in the stretching direction is 30% or more and 250% or less. A polarizing plate comprising: the retardation film according to any one of claims 1 to 7; and a polarizing plate laminated and bonded to the retardation film by an adhesive layer.