JP3274549B2 - Polarizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate for a liquid crystal display used in personal computers, word processors, televisions and the like.

[0002]

2. Description of the Related Art Liquid crystal displays used in personal computers, word processors, watches, calculators, and the like are often used in harsh environments such as touch panels, optical shutters, and liquid crystal displays for automobiles. Is coming. Therefore, the polarizing plate used in the liquid crystal display also has durability such as no deterioration under high temperature and high humidity and excellent dimensional stability so that the characteristics do not change even in a severe environment. Required.

That is, the polarizing plate used in the liquid crystal display has a structure in which a polarizing film and a protective film are adhered to one or both surfaces thereof. As the polarizing film, uniaxially oriented polyvinyl alcohol (PVA) is used. What adsorbed iodine and / or a dichroic dye is generally used, and cellulose triacetate (TAC) having good light transmittance and small birefringence is generally used as a protective film.
Since the properties of the protective film dominate the durability of the polarizing plate, the protective film has good moisture-heat resistance such as no deterioration under high temperature and high humidity and excellent dimensional stability. Is naturally required.

A conventional protective film of cellulose triacetate contains 15 to 20% by weight of a plasticizer such as a phosphate ester in the protective film in order to impart appropriate flexibility to the film. However, when such a polarizing plate is used under high temperature and high humidity, problems such as cracks in the protective film, peeling of the protective film from the polarizing film, and coloring of the protective film occur.

In order to solve the above problem, a polarizing plate using a protective film containing a plasticizer such as a phosphate ester in an amount of 10% by weight or less has been proposed (JP-A-61-24340).
No. 7). Furthermore, a polarizing plate using a protective film containing no plasticizer has also been proposed (Japanese Patent Application Laid-Open No. 1-214802). However, although these protective films have improved durability (moisture and heat resistance) under high temperature and high humidity, the protective film itself becomes brittle due to reduced flexibility, and the protective film forming process, slitting Various problems occur in the processing, the step of bonding the polarizing film and the protective film, or the step of processing the polarizing plate (such as a punching step). That is, cracks are generated in the process of forming cellulose triacetate, which is a protective film, poor adhesion between the polarizing film and the protective film, and chips are often generated especially in the slitting and punching processes, and the chips adhere to the product. As a result, many products having defects in transparency and the like are manufactured. Furthermore, since the cut surface cut in this way has a sawtooth shape due to fine cracks, the slit film may be torn during transportation (winding).

[0006]

Accordingly, the present inventor has
Various studies have been made on the protective film (cellulose ester-based film such as cellulose triacetate) of the polarizing plate in order to improve the wet heat resistance without reducing the flexibility. And as a result of repeated studies focusing on the plasticizer concentration distribution in the thickness direction of the cellulose triacetate film, the plasticizer concentration on the film surface was lowered, and the plasticizer concentration was maintained to some extent as a whole film. It has been clarified that the wet heat resistance can be improved while maintaining flexibility as a whole. A cellulose ester-based film having such good flexibility, excellent workability, and good heat and moisture resistance such as no deterioration under high temperature and high humidity and excellent dimensional stability is used as a polarizing plate. By using it as a protective film, a polarizing plate having excellent wet heat resistance can be obtained with high productivity.

Accordingly, an object of the present invention is to provide a polarizing plate having good wet heat resistance such as no deterioration under high temperature and high humidity and excellent dimensional stability. Further, another object of the present invention is to provide a polarizing plate having high productivity (easy to manufacture and high yield) and excellent in wet heat resistance.

[0008]

According to the present invention, there is provided a polarizing plate comprising a polarizing film and a protective film having a thickness of 50 μm or more provided on at least one surface of the polarizing film, wherein the protective film contains a plasticizer. A cellulose ester-based film, wherein the plasticizer content of the surface layer in the range from the surface of the protective film to a depth of 10 μm is 3 to 9% by weight, and the average concentration of the plasticizer in the entire protective film is 11%;偏光 18% by weight. As a protective film of the above polarizing plate,
It is preferable that the surface layer has a plasticizer content of 3 to 9% by weight in a range from the surface to a depth of 10 μm on both side surfaces.

Preferred embodiments of the polarizing plate of the present invention are as follows.

(1) The above polarizing plate, wherein the plasticizer is a phosphate ester plasticizer.

(2) The above-mentioned polarizing plate, wherein the cellulose ester is cellulose triacetate.

(3) The above polarizing plate, wherein the protective film is obtained by casting a solution.

(4) The above polarizing plate, wherein the surface layer extending from the surface of the protective film to a depth of 10 μm contains 5 to 7% by weight of a plasticizer.

(5) The protective film as a whole contains the plasticizer in an amount of 13 to
The above polarizing plate containing 16% by weight.

(6) The protective film has a thickness of 50 to 150 μm.
m.

[Detailed Description of the Invention] The polarizing plate of the present invention comprises:
It has a basic structure in which a polarizing film and a protective film are provided on at least one surface of the polarizing film. 1 and 2 schematically show cross sections of a basic configuration of the polarizing plate of the present invention.

FIG. 1 shows a polarizing plate in which a protective film 12 is formed on one surface of a polarizing film 11 with an adhesive layer 13 interposed therebetween. The protective film is generally adhered to the polarizing film surface by the adhesive (adhesive) as described above. A hard coat layer may be further formed on the protective film.

FIG. 2 shows a polarizing plate in which protective films 22a and 22b are formed on both surfaces of the polarizing film 21 via adhesive layers 23a and 23b, respectively.

Known polarizing films can be used for the polarizing plate of the present invention. For example, a polarizing film in which iodine and / or a dichroic dye is adsorbed and oriented on a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and a saponified film of an ethylene / vinyl acetate copolymer; A polarizing film obtained by dehydrating a polyvinyl alcohol-based film to orient polyene; and a polarizing film obtained by dehydrochlorinating a polyvinyl chloride film to orient polyene.

The cellulose ester used for the protective film of the polarizing plate of the present invention is an ester of cellulose and a fatty acid. Examples thereof include cellulose diacetate, cellulose triacetate, cellulose tripropionate and cellulose tributyrate. it can. Further, a copolymer such as cellulose acetate butyrate may be used. Further, these may be used alone or in combination. Among the above, cellulose triacetate is preferred. The degree of acetylation of cellulose triacetate is
It is preferably from 50 to 70%, particularly preferably from 55 to 65%. The weight average molecular weight is preferably from 70,000 to 120,000, particularly preferably from 80,000 to 100,000. Further, the cellulose triacetate may be partially esterified with not only acetic acid but also a fatty acid such as propionic acid and butyric acid, as long as the acetylation degree is satisfied. Alternatively, the cellulose triacetate may contain other cellulose esters such as cellulose propionate and cellulose butyrate as long as the total amount satisfies the degree of acetylation.

The protective film of the polarizing plate of the present invention contains a plasticizer. Examples thereof include phosphate-based plastics such as triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, cresyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and tributoxyethyl phosphate. Phthalic acid esters such as diethyl phthalate, dimethoxyethyl phthalate and dimethyl phthalate; and triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, op
Glycerol esters such as tolueneethylsulfonamide, glycerol triacetate and butylphthalylbutylglycolate. Of these, phosphate ester plasticizers are preferred.

The protective film of the polarizing plate of the present invention is a cellulose ester-based (preferably cellulose triacetate) film, and the above phosphate ester-based film in a surface layer extending from the surface of the protective film to a depth of 10 μm. Has a plasticizer content of 3 to 9% by weight, and the average concentration of the plasticizer in the entire protective film is 11 to 18% by weight. FIG. 3 schematically shows a cross section of the configuration of the protective film of the present invention. Of the protective film 31, a layer ranging from the surface to a depth of 10 μm is a surface layer 32.
a, 32b, so that the protective film 31 is
It is the whole protective film including a and 32b. As long as the surface layer contains a plasticizer such as a phosphate ester in an amount of 3 to 9% by weight, the content of the plasticizer in the surface layer may be uniform or non-uniform. Further, the entire protective film is made of a plasticizer of 11 to 11.
As long as it is contained at an average concentration of 18% by weight, the content of the plasticizer in the protective film excluding the surface layer may be uniform or non-uniform. Generally, the content of the plasticizer is low in a region near the surface layer and high in the inside.

The above-mentioned surface layer preferably contains a phosphate ester plasticizer in an amount of 5 to 7% by weight, and the entire protective film contains the phosphate ester plasticizer in an amount of 13 to 16% by weight.
Is preferably contained in an amount of When the content of the phosphate ester plasticizer in the surface layer exceeds 9% by weight, cracks easily occur in the protective film under high temperature and high humidity (reduction in wet heat resistance). When the content is less than 3%, slit processing is performed. The cut surface becomes saw-toothed, and the film (protective film) is easily torn during transportation (rolling). If the content of the phosphate ester plasticizer in the protective film (entire) exceeds 18% by weight, the plasticizer may bleed to the surface over time, and if it is less than 3%, chips may be generated during production. In many cases, chips are easily attached to a product to form a protective film having a defect (such as transparency). The thickness of the protective film is preferably in the range of 50 to 150 μm, particularly preferably in the range of 70 to 120 μm.

The protective film of the present invention may contain an ultraviolet absorber. For example, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone can be mentioned.

The protective film of the present invention may contain fine particles of an inorganic or organic compound in order to impart lubrication. Examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate,
Mention may be made of hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate. Silicon oxide, titanium dioxide and zirconium oxide are preferred, and silicon dioxide is particularly preferred. Examples of the organic compound (polymer) include a silicone resin, a fluorine resin, and an acrylic resin. Silicone resins are preferred.

The solvent used for producing the film of the present invention by the solution casting method may be any solvent as long as it can dissolve cellulose triacetate. Any material that can be dissolved by mixing with a solvent can be used.
Examples of the solvent include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, isooctane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; methyl chloride, methylene chloride (methylene chloride), carbon tetrachloride And halogenated hydrocarbons such as trichloroethane; alcohols such as methanol, ethanol, isopropyl alcohol and n-butyl alcohol;
And esters such as methyl formate, ethyl formate, methyl acetate and ethyl acetate can be mentioned.

In general, a mixed solvent of methylene chloride and methanol is used. Unless a cellulose ester is precipitated (during the preparation of the dope or at the time of adding the fine particle dispersion later), another solvent such as isopropyl alcohol or n- Butyl alcohol may be used. The ratio between the cellulose ester and the solvent in the dope is 1 by weight.
The range of 0:90 to 30:70 is preferred.

Next, a method for producing the protective film of the present invention will be described. i) 1 solvent, cellulose triacetate and a plasticizer are charged into a mixing tank for dope, and stirred (under heating,
The dope is prepared by dissolving the cellulose triacetate (if necessary under pressure). ii) When using an ultraviolet absorber, etc., put the solvent and the ultraviolet absorber into a separate mixing tank and stir to dissolve the ultraviolet absorber (if adding fine particles that improve slipperiness, Further, the mixture is charged and transferred to a dispersing machine, and the fine particles are sufficiently dispersed to prepare a dispersion liquid). iii) The above-mentioned dope or a mixed solution of the above-mentioned dope and a solution containing an ultraviolet absorber is sent to a casting port through a dope filter as appropriate, and the dope (mixed solution) is cast on a drum from the casting port. iv) After the mixed solution (dope) has been cast on the drum from the casting port, the cast layer is dried to the extent that it has a self-supporting property during one rotation of the drum, and then separated from the drum. After being dried sufficiently (80 to 130 ° C.), it is wound up on a drum. An endless band may be used instead of the drum. v) In the present invention, in order to form a surface layer having a low plasticizer content, the film is further heated at 140 to 160 ° C for 1 minute to 6 minutes.
Heat treatment is performed for 0 minutes (preferably at 140 to 160 ° C. for 3 to 30 minutes) to volatilize the plasticizer on the surface, thereby producing the protective film of the present invention.

As another method for forming the surface layer having a low plasticizer content, a co-casting method described in JP-A-61-94725 can be used. That is, when co-casting a dope (B) in which cellulose triacetate is dissolved in a mixed solvent such as methylene chloride and methanol, a mixed solvent in which the proportion of a poor solvent such as an alcohol is higher than that of the mixed solvent of the dope (B) is used. The dope (A) used and having a lower concentration of cellulose triacetate than the dope (B) is placed on both sides of the dope (B) to perform co-casting, thereby shortening the film formation time (time until peeling from the drum). It can be shortened. In this method, if the ratio of the plasticizer of the dope (A) to the cellulose triacetate is reduced and co-casting is performed, the protective film of the present invention can be produced without performing the drying step of v). it can.

As a method of forming the surface layer having a small content of the plasticizer, a method of casting a support at a temperature of 10 ° C. or less described in JP-A-62-37113 can be used. . That is, when the dope of cellulose triacetate is cast on a support having a temperature of 10 ° C. or less, the dope is transferred to a drying step in a state where the proportion of the solvent is large. Film can be manufactured. That is, since the solubility of the plasticizer is overwhelmingly greater than that of cellulose triacetate, when a large amount of the solvent is rapidly moved to the film surface and volatilized by the rapid drying, the plasticizer near the film surface is also volatilized with the solvent. It is thought to be.

The cellulose ester-based film such as the above-mentioned cellulose triacetate film for a protective film is then cut into small widths by a slitter and sent to the next polarizing plate manufacturing step. In the polarizing plate manufacturing process, a polarizing plate can be manufactured by applying an adhesive to one surface of a cellulose ester film serving as a protective film and then bonding the adhesive to one or both surfaces of the polarizing film. In the case of a liquid crystal display, an adhesive is further applied to one surface of the protective film, a release paper is temporarily bonded, and a punching process is performed to perform punching.

Further, at the time of preparing the dope or the dispersion, various known additives such as a dispersant, a fluorescent dye, an antifoaming agent, a lubricant, an anti-fading agent and a preservative may be used, if necessary.

[0033]

【Example】

[Example 1] Cellulose triacetate (degree of acetylation: 61)
%), 15 parts by weight of TPP (triphenyl phosphate), 360 parts by weight of methylene chloride, 40 parts by weight of methanol and 20 parts by weight of 1-butanol were mixed and heated and stirred to dissolve the cellulose triacetate and dope. Prepared. A solution casting apparatus for dope prepared above (consisting of dope casting port and drum)
, And then the dope was cast on the drum from the casting port. Thereafter, the film peeled from the drum was dried by being conveyed through a heat treatment apparatus (100 ° C.) having a large number of rolls to produce a cellulose triacetate film having a thickness of 80 μm. The film was further conveyed to the above heat treatment apparatus and heat-treated at 150 ° C. for 10 minutes to volatilize the plasticizer on the film surface to obtain a protective film.

The obtained protective film was punched to form two protective films, and a polyurethane-based adhesive was applied to one surface of the two films to form a polyvinyl alcohol / dichroic dye polarizing film (30 μm). To produce a polarizing plate.

Example 2 100 parts by weight of cellulose triacetate (degree of acetylation: 61%), 22 parts by weight of TPP (triphenyl phosphate), methylene chloride 36
0 parts by weight, 40 parts by weight of methanol and 1-butanol 2
By mixing and heating and stirring with 0 parts by weight, cellulose triacetate was dissolved to prepare a dope. The prepared dope was sent to a casting port of a solution casting apparatus, and then the dope was cast on a drum from the casting port. Thereafter, the film peeled from the drum was dried by being conveyed through a heat treatment apparatus (100 ° C.) having a large number of rolls to produce a cellulose triacetate film having a thickness of 80 μm. The film was further conveyed to the above heat treatment apparatus and heat-treated at 150 ° C. for 15 minutes to volatilize the plasticizer on the film surface to obtain a protective film.

Using the obtained protective film, a polarizing plate was produced in the same manner as in Example 1.

Comparative Example 1 A cellulose triacetate film was prepared in the same manner as in Example 1 except that the heat treatment at 150 ° C. after drying was not performed for 10 minutes.

[Comparative Example 2] In Example 1, instead of the heat treatment at 150 ° C. for 10 minutes after drying, 140 ° C.
A cellulose triacetate film was prepared in the same manner as in Example 1 except that the heat treatment was performed for 5 minutes.

Comparative Example 3 100 parts by weight of cellulose triacetate (degree of acetylation: 61%), 7 parts by weight of TPP (triphenyl phosphate), methylene chloride 360
Parts by weight, 40 parts by weight of methanol and 20 of 1-butanol
By mixing and heating and stirring the parts by weight, the cellulose triacetate was dissolved to prepare a dope. The prepared dope was sent to a casting port of a solution casting apparatus, and then the dope was cast on a drum from the casting port. Thereafter, the film peeled from the drum was dried by being conveyed through a heat treatment apparatus (100 ° C.) having a large number of rolls, thereby producing a cellulose triacetate film (protective film) having a thickness of 80 μm. Using the obtained film for a protective film, a polarizing plate was produced in the same manner as in Example 1.

The properties of the protective film and polarizing plate obtained above were evaluated by the following methods.

1) Plasticizer Concentration in Film (Surface Layer and Entire Film) With respect to the protective film obtained in each example, a 0.5 g sample was obtained by shaving the surface layer from the film surface to a depth of 10 μm. A sample was similarly taken of the other surface of the film, and the film was cut in the thickness direction to obtain 0.5 g of a sample of the whole membrane. Only in Comparative Example 2, a surface layer from the surface of the film to a depth of 5 μm was collected. 0.5 g of each of the above samples was dissolved in 40 ml of chloroform, and 2 μl was injected into a vaporization chamber for gas chromatography to obtain a gas chromatogram. The concentration of the plasticizer was determined using a calibration curve.

The measurement conditions by the above gas chromatography are as follows. Gas chromatography used: GC-15A (Co., Ltd.)
Column: Silicon OV, 2%, 1.6m, 3φ, 260
℃ Carrier gas: nitrogen 50 ml / min Detector: FID, hydrogen 0.6 kg / cm ² , air 0.5
kg / cm ² vaporization chamber: 280 ° C

2) Suitability for processing The film for a protective film obtained in each example was slit (cut), and the amount of chips generated at that time was observed.
Further, the degree of unevenness of the slit film cut was observed with a microscope and evaluated as follows. AA: There was almost no generation of chips, and the cut edge was smooth. BB: Chips were slightly generated, and the cut was somewhat saw-toothed. CC: There were many chips and the cut was saw-like.

3) Moisture and heat resistance The obtained polarizing plate was cut into a size of 100 mm x 100 mm, and bonded to a glass plate using an acrylic adhesive.
After leaving for 500 hours in an atmosphere of 5 ° C. and 90% RH,
Observe cracking of the polarizing plate, peeling of the protective film, coloring, etc.,
The evaluation was as follows. AA: None of cracking, peeling, or coloring occurred. CC: Several cracks occurred and some coloring was observed. DD: Cracking, peeling, and coloring occurred.

The results of the above measurement are shown in Table 1 below.

[0046]

[Table 1] Table 1 Plasticizer concentration (wt% ) Processing Suitability Moisture / heat resistance Comprehensive evaluation Surface layer Whole film ──────────────────────────────────── Example 1 6.3 / 6.0 11.2 BB AA Good Example 2 5.5 / 5.2 14.5 AA AA Excellent ─────────────────────────────────── ─ Comparative Example 1 14.2 / 13.8 12.5 BB DD Not possible Comparative Example 2 10.8 / 10.5 12.5 BB CC Not possible Comparative Example 3 7.2 / 7.0 6.4 CC AA Not possible ─────────────────── ─────────────────

As is clear from the above results, the polarizing plates of the present invention obtained in Examples 1 and 2 were excellent in both processability and wet heat resistance. On the other hand, Comparative Examples 1 and 2
The polarizing plate obtained in (1) has good workability but does not have sufficient wet heat resistance. In particular, regarding the protective film of the polarizing plate obtained in Comparative Example 2, when the plasticizer concentration of the surface layer up to a depth of 5 μm was also measured, low values of 7.5 and 7.3% by weight were obtained. Nevertheless, it shows inferior wet heat resistance, indicating that a surface layer satisfying the plasticizer concentration of the present invention needs to have a depth of 10 μm. Furthermore, a polarizing plate using a protective film having a low plasticizer concentration of less than 10% by weight (Comparative Example 3) has good wet heat resistance due to a low plasticizer concentration, but has a problem in workability.

[0048]

As described above, the protective film constituting the polarizing plate of the present invention contains a suitable amount of plasticizer as a whole, while keeping the plasticizer concentration in the surface layer low. This allows
The present invention solves both the problem of a decrease in wet heat resistance when the plasticizer concentration is appropriate and the problem of a decrease in processability due to a decrease in flexibility when the plasticizer concentration is low. Therefore, when manufacturing a polarizing plate using the protective film of the present invention, since the film for the protective film has flexibility, the generation of chips during slit processing is small, and the particles adhere to the protective film. There is no decrease in the transparency of the polarizing plate, and the cut edge when the film is slit is smooth, so that it is not torn and cut during transportation, and chips are also generated in the polarizing plate punching process. And the generation of various problems associated with the attachment of debris to the polarizing plate. Therefore,
The polarizing plate of the present invention obtained by bonding the protective film and the polarizing film has advantages of being easy to manufacture, having a high yield, and exhibiting high productivity. Furthermore, since the protective film constituting the polarizing plate of the present invention has a low plasticizer concentration in the surface layer of the protective film,
In addition to having flexibility, there is no occurrence of cracking, coloring, etc. under high temperature and high humidity (that is, it has excellent moisture and heat resistance). In addition, there is almost no occurrence of peeling, coloring, etc. of the protective film, and the film has excellent wet heat resistance. Therefore, the liquid crystal display in which the polarizing plate of the present invention is incorporated does not deteriorate even if it is used for a long time under high temperature and high humidity.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a basic configuration of a polarizing plate of the present invention.

FIG. 2 is a schematic cross-sectional view of another basic configuration of the polarizing plate of the present invention.

FIG. 3 is a schematic view of a cross section of a protective film constituting a polarizing plate of the present invention.

[Explanation of symbols]

 11, 21 Polarizing film 12, 22a, 22b, 31 Protective film 13, 23a, 23b Adhesive layer 32a, 32b Surface layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-243407 (JP, A) JP-A-61-129604 (JP, A) JP-A-61-151502 (JP, A) 177801 (JP, A) JP-A-61-94725 (JP, A) JP-A-62-37113 (JP, A) JP-A-1-214802 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/30

Claims (2)

(57) [Claims] 1. A polarizing plate comprising a polarizing film and a protective film having a thickness of 50 μm or more provided on at least one surface of the polarizing film, wherein the protective film is a cellulose ester film containing a plasticizer, and The plasticizer content of the surface layer in the range from the surface of the protective film to a depth of 10 μm is 3 to 9% by weight, and the average concentration of the plasticizer in the entire protective film is in the range of 11 to 18% by weight. A polarizing plate, characterized in that: 2. On both sides of the protective film, a depth of 1 from the surface.
The plasticizer content of the surface layer in the range up to 0 μm is 3 to
The polarizing plate according to claim 1, wherein the polarizing plate is formed so as to be 9% by weight.