JP2005215700A - Polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the occurrence of the warpage of a polarizing plate in the case of sticking different protection films to both surfaces of a polarizing film. <P>SOLUTION: The polarizing plate 11 is manufactured by sticking the 1st and the 2nd protection films 13 and 14 different from each other to both surfaces of the polarizing film 12. When it is assumed that the hygroscopic swelling coefficients of the 1st and the 2nd protection films 13 and 14 in the absorption axis direction of the polarizing plate 11 are X1 and X2 respectively, the film satisfying 0.65X2<X1<1.55X2 is used as the 1st and the 2nd protection films 13 and 14. The 1st and the 2nd protection films 13 and 14 are set so that a warpage value may be ≤7mm when they are made a 10cm×10cm square where the absorption axis direction of the polarizing plate 11 is set as a diagonal line before they are stuck to the polarizing film 12. Thus, the polarizing plate whose warpage is decreased after sticking is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polarizing plate, and relates to a polarizing plate used for an electronic display including an optical compensation film and a liquid crystal panel.

  A polarizing film called an iodine type, which is most widely used in electronic displays, is generally obtained by impregnating an aqueous solution of iodine-potassium iodide with a polymer film mainly composed of a polyvinyl alcohol-based polymer, and stretching and orienting it. Is manufactured by. Since the above-mentioned iodine-type polarizing film impairs the polarizing performance due to the presence or heating of water, a protective film is usually provided on both sides thereof. The polarizing plate generally has a polarizing film and protective films on both sides as a basic configuration.

  Conventionally, the protective film to be laminated on both sides of the polarizing film is pasted as a protective film on both sides of the polarizing film with the same kind of main component polymer, film thickness, physical properties, etc. It was common. However, in recent years, it has been required to provide the protective film with functions such as optical compensation, retardation, controllability, anti-glare and the like. The correspondence which bonds the protective film from which a characteristic differs mutually is achieved.

  As the protective film, a cellulose acylate film such as a cellulose acetate film is widely used from the viewpoint of low birefringence, transparency, and easy handling. The cellulose acylate film has the characteristics that it has transparency, moderate moisture permeability, and high mechanical strength. As the polarizing film, a polyvinyl alcohol polymer film is widely used.

  The cellulose acylate film is manufactured by a solution casting method. In this method, after the polymer is doped with a solvent, the dope is cast from a casting die to a support, and a drying process or necessary. Accordingly, it is a basic process that the film is peeled off from the support as a film through a cooling process and dried while being conveyed using a conveying means. In addition, as a conveyance means, the roller conveyance which conveys a film using a conveyance roller while applying tension in the conveyance direction, and the tenter conveyance that holds the side edge of the film and conveys the film while applying tension in the width direction. And there is a conveyance that combines these two conveyances.

  However, when different protective films are bonded to both surfaces of the polarizing film, the polarizing plate may be warped. This leads to a problem that not only the appearance is bad but also the handling property when the polarizing plate is bonded to the liquid crystal panel is poor.

  This invention is made | formed in view of the said subject, and it aims at providing the polarizing plate which suppressed the curvature produced by bonding a protective film to a polarizing film.

  In the present invention, in order to solve the above problems, the polarizing film and a pair of protective films laminated on both sides of the polarizing film, and any one of the film thickness, physical characteristics, and components of the protective film is provided. In the polarizing plates different from each other, the water absorption expansion coefficient in the absorption axis direction of the polarizing plate of the first protective film bonded to one surface of the polarizing film is X1, and the second protective film bonded to the other surface is When it is X2, the first and second protective films satisfy the condition of 0.65X2 <X1 <1.55X2 and are 10 cm × in which the absorption axis direction is a diagonal before the bonding. A warp value is 7 mm or less when it is a 10 cm square shape.

  When the thickness of the first protective film is Y1 (unit: μm) and the thickness of the second protective film is Y2 (unit: μm), the absolute value of the difference between Y1 and Y2 is greater than 2 and less than 100 It is preferable that

  By this invention, the polarizing plate which reduced the curvature at the time of bonding a protective film to a polarizing film can be obtained, and this polarizing plate is excellent in an external appearance and handleability.

  FIG. 1 shows an embodiment of the present invention and is a sectional view of a polarizing plate. The polarizing plate 11 has a structure in which a first protective film 13 and a second protective film 14 are bonded to both surfaces of the polarizing film 12, respectively. The first protective film 13 on one surface and the second protective film 14 on the other surface are different from each other. Here, being different from each other means that the types of polymers constituting the first and second protective films 13 and 14 are different from each other, or the types and blending ratios of various additives added to the protective film are different from each other. I mean. Furthermore, even when the components are composed of the same compound and blending ratio, the physical properties such as film thickness, molecular orientation, and elastic modulus are different from each other.

  Here, regarding the absorption axis direction X of the polarizing plate, the water absorption expansion coefficient (unit:%) of the first protective film 13 is X1, and that of the second protective film 14 is X2. Further, the thicknesses (unit: μm) of the first protective film 13 and the second protective film 14 are Y1 and Y2, respectively, and Y1 and Y2 have different values. In the present embodiment, the first and second protective films 13 and 14 having a water absorption expansion coefficient X1 and X2 satisfying 0.65X2 <X1 <1.55X2 are used. Accordingly, even when the first and second protective films 13 and 14 are bonded to the polarizing film 12, the occurrence of warpage as the polarizing plate 11 can be reduced.

  The first protective film 13 preferably has a water absorption expansion coefficient X1 that is greater than 0.70 times and less than 1.40 times the water absorption expansion coefficient X2 of the second protective film 14, and more preferably greater than 0.85 times. Most preferably, the value is smaller than 20 times. However, considering the measurement accuracy of the water absorption expansion coefficients X1 and X2 and the selection of materials for the first protective film 13 and the second protective film 14, substantially X1> 0.02 or X2> 0.02. . In the present embodiment, the front and back of the polarizing plate 11 are not distinguished.

  Further, regarding the respective film thicknesses Y1 and Y2 of the first and second protective films 13 and 14, the effect of reducing warpage is particularly great when the absolute value of the difference between Y1 and Y2 is greater than 2 and less than 100.

  FIG. 2 is a plan view of a measurement sample of the submersion expansion rates X1 and X2. The sample piece 21 of the protective film 12 is a strip having a length LD of 120 mm with respect to the absorption axis direction X of the polarizing film. The specific method of measurement is as follows. First, after leaving the sample piece 21 to stand at 23 ° C. and a relative humidity of 65% for 2 hours, two holes 21a having a diameter of 6 mm are opened at an interval L of 100 mm. When the sample piece 21 is not formed into a strip shape but is, for example, a square, the hole 21a is formed so that the measurement direction of the interval L coincides with the absorption axis direction X of the polarizing plate.

  The distance L between the holes 21a is measured with a commercially available pin gauge having a minimum memory of 1/1000 mm, and is set as a reference dimension L1. Next, after immersing the sample piece 21 in 20 ° C. water for 30 minutes, the distance L between the two holes is immediately measured with the pin gauge, and this value is taken as the water absorption dimension L2. The reference dimension L1 and the wet dimension L2 measured in this way are substituted into the calculation formula (L2-L1) / L1 × 100, and these are set as the water absorption expansion coefficients X1 and X2.

  In the present invention, as the polymer of the first and second protective films 13 and 14, cellulose acylate such as cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate is preferable, and cellulose acetate is most preferable. However, it is not limited to this, In addition, the various polymers as a well-known protective film can be used. For example, in addition to polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polycarbonate, polystyrene, polyamide, various polyolefins and the like can be mentioned. Among them, ZEONEX, ZEONOR (both trade names, ZEON CORPORATION) And polyolefins such as ARTON (trade name, JSR Co., Ltd.) are suitable.

  When a cellulose acylate or the like is formed into a film by a solution casting method, generally, various properties of the film vary depending on the film forming conditions. The same applies to the water absorption expansion coefficients X1 and X2, and is affected by, for example, the material and temperature of the support, the drying speed, and the like. In the solution casting method, first, in order to form a film, the components are dissolved or dispersed with a solvent to prepare a dope. As the adjustment method, dissolution at normal temperature is common, but a cooling dissolution method or a high temperature dissolution method can be applied as necessary.

  In the cooling dissolution method, first, a polymer such as cellulose acylate and an additive are gradually added to a solvent simultaneously or sequentially with stirring at a temperature around -10 to 40 ° C. In some cases, a solution or dispersion of each component is prepared and then these solutions are mixed. The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of the solid component of the dope and the solvent is solidified. Furthermore, when this is heated to approximately 0 to 200 ° C., a solution in which each component flows in the solvent is obtained. The temperature can be raised by simply leaving it at room temperature or in a warm bath.

  In the high-temperature dissolution method, first, a polymer such as cellulose acylate and an additive are gradually added to a solvent with stirring at a temperature of about −10 to 40 ° C. around room temperature. Next, the solvent is heated to 70 to 240 ° C. under a pressure of approximately 0.2 MPa to 30 MPa. The heating temperature is preferably 80 to 220 ° C. Next, the heated solution or dispersion is cooled below the boiling point of the lowest boiling solvent among the solvents used. In general, this is cooled to −10 to 50 ° C. and returned to normal pressure. Preferably, it cools by apparatus cooling using various refrigerant | coolants, such as cooling water.

  The obtained dope is cast on a support by a die as a dope supply means. As the support, a metal band, a drum, a glass plate, or the like is used. The dope is dried to some extent on the above support to give rigidity, and peeled from the support as a film. Next, the solvent is removed by passing through the drying section by various conveying means, and films for the first and second protective films 13 and 14 are obtained.

  As the polymer as the main component of the polarizing film of the present invention, a polyvinyl alcohol-based polymer is most preferable. Examples of the polyvinyl alcohol-based polymer include alkyl-modified polyvinyl alcohol in addition to polyvinyl alcohol. Polyvinyl alcohol polymers are usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but unsaturated carboxylic acids and derivatives thereof (for example, salts, esters, amides, nitriles, etc.), olefins, vinyl ethers. Further, a compound obtained by copolymerizing a small amount of a compound copolymerizable with vinyl acetate such as an unsaturated sulfonate may be used. The alkyl-modified polyvinyl alcohol has an alkyl group at the terminal and preferably has a saponification degree of 80% or more and a polymerization degree of 200 or more.

  Examples of polymers other than polyvinyl alcohol that can be used as the polarizing film 12 in the present invention include polycarbonate polymers and cellulose polymers.

  When a polyvinyl alcohol polymer is used as the main component of the polarizing film 12, the film is dyed by a gas phase adsorption method or a liquid phase adsorption method which is a general dyeing method. Although the liquid phase adsorption method is used in the present embodiment, the present invention does not depend on the staining method.

  For dyeing by liquid phase adsorption, iodine is used here, but the present invention is not limited to this. The polyvinyl alcohol film was immersed in an iodine / potassium iodide (KI) aqueous solution with an immersion time of 30 seconds to 5000 seconds. The aqueous solution at this time preferably has an iodine concentration of 0.1 g / liter to 20 g / liter and a potassium iodide concentration of 1 g / liter to 100 g / liter. Moreover, it is preferable that the temperature of the aqueous solution at the time of immersion is set to the range of 5 degreeC or more and 50 degrees C or less.

  The liquid phase adsorption method is not limited to the above immersion method, and a known method such as a method of applying iodine or other dye solution to the polyvinyl alcohol film or a method of spraying may be applied. Dyeing may be performed before or after the polyvinyl alcohol film is stretched, but the polyvinyl alcohol film is appropriately swelled and easily stretched by being dyed, so that the stretching step It is particularly preferable to provide a dyeing step before the step.

  It is also preferable to dye with a dichroic dye instead of iodine. Examples of dichroic dyes include dye compounds such as azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes, anthraquinone dyes. it can. A water-soluble dye-based compound is preferable, but not limited thereto. Further, it is preferable that a hydrophilic functional group such as a sulfonic acid group, an amino group, or a hydroxyl group is introduced into the molecule of these dichroic dyes.

  As dichroic dyes, C-I Direct Yellow 12, C-I Direct Orange 39, C-I Direct Orange 72, C-I Direct Red 39, C-I Direct Red Red 79, Sea Eye Direct Red 81, Sea Eye Direct Red 83, Sea Eye Direct Red 89, Sea Eye Direct Violet 48, Sea Eye Direct Blue 67, Sea Eye Examples include Direct Blue 90, Sea Eye Direct Green 59, Sea Eye Acid Red 37, and the like.

  Furthermore, JP-A-1-161202, JP-A-1-172906, JP-A-1-172907, JP-A-1-183602, JP-A-1-248105, JP-A-1-265205, Examples thereof include the dyes described in JP-A-7-261024. These dichroic dye compounds are used as free acids, alkali metal salts, ammonium salts, and salts of amines.

  By blending two or more of the above dichroic dye compounds, polarizers having various hues can be produced. As a polarizing element or a polarizing plate, a compound that exhibits black when the polarization axes are orthogonal to each other, or a compound in which various dichroic dye compounds are blended so as to exhibit black, has both a single-plate transmittance and a polarization rate. It is excellent and preferable.

  When producing a polarizing film by stretching a dyed polyvinyl alcohol film, a compound that crosslinks polyvinyl alcohol is used. Specifically, in an arbitrary step, a polyvinyl alcohol film is immersed in a crosslinking agent solution to contain a crosslinking agent. Instead of soaking, the cross-linking agent solution may be applied to the film or sprayed. The polyvinyl alcohol film is sufficiently hardened by the inclusion of the crosslinking agent, and as a result, appropriate orientation is imparted. In addition, as a crosslinking agent of a polyvinyl alcohol-type polymer, a well-known crosslinking agent other than what is described in US reissue specification 232897 can be used, However, Boric acids are the most preferable.

  The first and second protective films 13 and 14 and the polarizing film 12 may be bonded by a method of laminating them with an adhesive, or by chemical modification of at least one bonded surface of the protective films 13 and 14 or the polarizing film 12. A known bonding method such as a method of laminating with adhesion by surface treatment such as, can be applied. When cellulose acylate is used as a protective film, acid treatment, alkali treatment, corona discharge treatment, glow discharge treatment, ultraviolet irradiation treatment, etc. are particularly preferred as the surface treatment method.

  In the present embodiment, after the surface treatment of the first and second protective films 13 and 14, the protective films 13 and 14 and the polarizing film 12 are bonded together with an adhesive. This surface treatment is saponification with alkali. Specifically, the cellulose acylate films to be the first and second protective films 13 and 14 were immersed in an alkaline solution, neutralized with an acidic solution, washed with water, and dried. As the alkaline solution, an aqueous solution of sodium hydroxide or potassium hydroxide is preferably used and the concentration is preferably 0.1 to 3.0N. Moreover, it is preferable to make the temperature of an alkaline solution into the range of room temperature-90 degreeC.

  When the polarizing film 12 and the first and second protective films 13 and 14 are bonded together with an adhesive, various known adhesives can be used. Among these, an aqueous solution of a polyvinyl alcohol polymer or a boron compound containing a modified polyvinyl alcohol having an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group or the like is preferable. This adhesive is preferably applied so that the thickness after drying is 0.01 μm or more and 10 μm or less, and more preferably 0.05 μm or more and 5 μm or less.

  Furthermore, an antireflection layer, an antiglare layer, a slip-imparting layer, an easy adhesion layer, or the like can be provided on the surface of the first or second protective film 13 or 14. Furthermore, an optical compensation sheet can be bonded to the surface of the protective film constituting the polarizing plate and used as an optical compensation film. These products can also constitute part of a liquid crystal display device.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Two types of dopes I and II are prepared, and five types of films A, B, C, D, and E are prepared from each of the dopes I and II by solution casting, and these are used as the first and second protective films 13 and 14. It was. The blending ratio and preparation method of each dope I and II, the production conditions of the films A to E to be the first and second protective films 13 and 14, and the production method of the polarizing plate 11 are as follows.

(Dope I)
Cellulose triacetate 89.3% by weight
(Acetyl group substitution degree 2.8)
Triphenyl phosphate (TPP) 7.1% by weight
Biphenyl diphenyl phosphate 3.6% by weight
For solids consisting of
92% by weight of dichloromethane
Methyl alcohol 8% by weight
A dope I having a solid content concentration of 18.5% by weight was obtained by appropriately adding a mixed solvent of and stirring.

(Dope II)
Cellulose triacetate 89.5% by weight
(Acetyl group substitution degree 2.8)
Triphenyl phosphate (TPP) 7.0% by weight
Biphenyl diphenyl phosphate 3.5% by weight
For solids consisting of
Dichloromethane 82% by weight
Methyl alcohol 15% by weight
n-Butyl alcohol 3% by weight
A dope II having a solid content concentration of 23.5% by weight was obtained by appropriately adding a mixed solvent of and stirring.

(Preparation of film A)
The dope I was cast on a support and peeled off as a film when it had self-supporting properties. The film after peeling was sufficiently dried in a tenter device and a roller drying chamber, and wound up as film A. The support used is a metal band. The thickness of the film A was 80 μm, and the water absorption expansion coefficient in the longitudinal direction of the film was 0.49%.

(Preparation of film B)
The dope I was cast on a support and peeled off as a film when it had self-supporting properties. The film after peeling was sufficiently dried in a tenter device and a roller drying chamber, and wound up as a film B. The support used is a metal band. The thickness of the film B was 60 μm, and the water absorption expansion coefficient in the longitudinal direction of the film was 0.49%.

(Preparation of film C)
The dope II was cast on a support and peeled off as a film when it had self-supporting properties. The film after peeling was sufficiently dried in a tenter device and a roller drying chamber, and wound up as film C. The support used was a metal drum, and the temperature of the metal drum during casting was -3 ° C. The thickness of the film C was 80 μm, and the water absorption expansion coefficient in the longitudinal direction of the film was 0.25%.

(Preparation of film D)
The dope II was cast on a support and peeled off as a film when it had self-supporting properties. The film after peeling was sufficiently dried in a tenter device and a roller drying chamber, and wound up as a film D. The support used was a metal drum, and the temperature of the metal drum during casting was -3 ° C. The thickness of the film D was 108 μm, and the water absorption expansion coefficient in the longitudinal direction of the film D was 0.28%.

(Preparation of film E)
Dope II was cast on a support, dried, and peeled off as a film. The film after peeling was fixed to a steel frame and dried for 30 minutes in a thermostatic bath set at 120 ° C. to obtain a film E. The thickness of the film E was 80 μm, and the water absorption expansion coefficient in the longitudinal direction of the film E was 0.35%.

(Preparation of polarizing film)
A polyvinyl alcohol film (made by Kuraray Co., Ltd.) having a thickness of 75 μm was immersed in an aqueous solution at 25 ° C. with an iodine concentration of 0.3 g / liter and a potassium iodide concentration of 18.0 g / liter. This was further stretched 5.0 times in an aqueous solution at 50 ° C. with a boric acid concentration of 80 g / liter and a potassium iodide concentration of 30 g / liter to obtain a polarizing film.

(Preparation of polarizing plate)
The films A to E were treated with a 1.5N aqueous solution of sodium hydroxide at 50 ° C. for 180 seconds, then neutralized and washed with water. Immediately after that, the protective films 13 and 14 were formed on both sides of the polarizing film 12 according to the combinations shown in Table 1. As pasted together. In Table 1, the description of the first and second protective films 13 and 14 represents the type of film used. In addition, the longitudinal direction at the time of producing films A to E was made to coincide with the stretching direction of polyvinyl alcohol, and the adhesive was interposed. As the adhesive, a 4% by weight aqueous solution of polyvinyl alcohol (trade name: PVA-117H, manufactured by Kuraray Co., Ltd.) was used. After bonding, this was dried for 30 minutes in an air thermostat set at 80 ° C. to obtain a polarizing plate. In addition, three types of polarizing plates using the same first and second protective films 13 and 14 were prepared, and these were designated as Reference Experiments 1 to 3 in Table 1.

(Evaluation of warpage of polarizing plate)
The produced polarizing plate 11 was cut into a square having a length of 10 cm and a width of 10 cm so that the absorption axis thereof was a diagonal line, and this was left for 30 minutes in a normal temperature and humidity environment. This was placed on a smooth glass plate, and the height of the apex of the square floating from the glass plate from the glass plate was measured with a scale. Among the heights, the maximum value is set as a warp value (unit: mm). Further, according to the value, a preferable one as a polarizing plate is indicated by ○, and an unfavorable one is indicated by ×.

  As a result of this example, the warpage value is small in any of the polarizing plates produced in Experiments 1 to 4, and it can be seen that the polarizing plate and the production method of the present invention are very effective.

It is sectional drawing of the polarizing plate of this invention. It is an embodiment of the present invention, and is a plan view of a sample for measuring the water absorption expansion coefficient of a protective film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Polarizing plate 12 Polarizing film 13 1st protective film 14 2nd protective film 21 Sample piece of water absorption expansion coefficient measurement X Absorption axis direction of polarizing plate Y1 Thickness of first protective film Y2 Thickness of second protective film

Claims (2)

In a polarizing plate having a polarizing film and a pair of protective films laminated on both sides of the polarizing film, and any of the film thickness, physical characteristics, and components of the protective film are different from each other,
The water absorption expansion coefficient in the absorption axis direction of the polarizing plate of the first protective film bonded to one surface of the polarizing film is X1, and that of the second protective film bonded to the other surface is X2. And when
The first and second protective films satisfy a condition of 0.65X2 <X1 <1.55X2, and are formed into a 10 cm × 10 cm square shape so that the absorption axis direction is a diagonal line before the bonding. A polarizing plate characterized by having a warp value of 7 mm or less. When the thickness of the first protective film is Y1 (unit; μm) and the thickness of the second protective film is Y2 (unit; μm), the absolute value of the difference between Y1 and Y2 is larger than 2. The polarizing plate according to claim 1, wherein the polarizing plate is less than 100.

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