JPH0364703A - Method for laminating film for polarizing plate - Google Patents

Abstract

PURPOSE:To improve adhesive strength, moisture and heat resistances by carrying out adhesion through a soln. of an adhesive contg. PVA having specified degrees of polymn. and saponification in the solid component under a specified pressure. CONSTITUTION:Polarizing films are adhered through a soln. of an adhesive at 35-90 deg.C under 3-30kg/cm<2> pressure. The adhesive contains >=60wt.% PVA having 1,500-4,000 degree of polymn. and 90-100mol% degree of saponification in the solid component. When the degree of polymn. of the PVA is <1,500, adhesive strength is not satisfactory and the moisture and heat resistances of the polarizing films are deteriorated. When the degree exceeds 4,000, coating viscosity is increased and stability of performance is not ensured. When the degree of saponification of the PVA is <90mol%, the moisture and heat resistances of the films are deteriorated and interlaminar exfoliation is caused at high temp. and humidity. When the amt. of the PVA is <60wt.%, transparency is lost and wet readhesion cannot be carried out. By this method, moisture and heat resistances and adhesive strength are remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a film for a polarizing plate. More details 1. < relates to a method for laminating a high-quality film for a polarizing plate that has strong adhesive strength and good heat and humidity resistance.

[Prior Art] Polarizing plates are incorporated into liquid crystal display panels and are widely used in display devices such as digital watches, liquid crystal televisions, automobile front instrument panels, and digital desk calculators.

Such display devices tend to become larger year by year, and they are also required to be used in increasingly harsh conditions such as high temperature and high humidity.Therefore, it is necessary to develop a polarizing plate that satisfies the required specifications. is an urgent need.

Currently used as a polarizing plate for the above applications, one side of a laminated film (film for polarizing plate) is a polyvinyl alcohol film on which a dichroic dye is adsorbed and fixed, and a protective film is laminated on both sides of the film via an adhesive layer. , a structure having an adhesive layer made of a polyacrylic acid polymer and a release film is known.

Adhesives used to bond the polyvinyl alcohol base film and the protective film include adhesives made from water-soluble polymers such as polyvinyl alcohol, partially saponified polyvinyl alcohol, and carboxymethyl cellulose, polyacrylic adhesives, and polyurethane adhesives. , epoxy adhesives, etc. have been proposed.

[Problems to be Solved by the Invention] However, water-soluble adhesives such as polyvinyl alcohol, partially saponified polyvinyl alcohol, and carboxymethyl cellulose do not have water resistance and swell, resulting in reduced adhesive strength.
Poor heat and humidity resistance. Furthermore, when polyacrylic, polyurethane, or epoxy adhesives are used, the coating viscosity becomes high, which not only makes it impossible to apply the adhesive to a uniform thickness, but also makes it impossible to rewet and bond the adhesive, which is easy to process.

The object of the present invention is to improve such problems and propose a lamination method for easily producing a high-quality polarizing plate film with good heat and humidity resistance and few optical defects required for a polarizing plate film for a large-sized liquid crystal display. It is in.

[Means for Solving the Problems] In order to achieve the above object, as a result of intensive research, the present invention has been completed. That is, the present invention provides (1) a method for laminating a film for a polarizing plate in which a protective film is laminated on at least one side of a polyvinyl alcohol film as a base film via an adhesive layer, in which polymerization is present in the solid content of the adhesive; degree 1500~4000, saponification degree 90~100m
3-30k containing 5Qwt% or more of polyvinyl alcohol of ol%, through a solution of the adhesive at 35-90°C.
A method for laminating a film for a polarizing plate characterized by adhesion by applying a pressure of g/crl, (2) laminating a protective film on at least one side of a polyvinyl alcohol film as a base film via an adhesive layer. In the method for laminating films for polarizing plates, the solid content of the adhesive contains a polymerization degree of 15.
00-4000. Containing 60vt% or more of polyvinyl alcohol with a degree of saponification of 90 to 100 mol%, the adhesive is swollen at a temperature of 35 to 90°C to produce 3 to 30 kg/cf.
This is a method for laminating films for polarizing plates, characterized by applying pressure of Ir for bonding.

In the lamination method of the present invention, polyvinyl alcohol is polymerized as an adhesive used for laminating a polyvinyl alcohol film containing a dichroic dye (hereinafter referred to as a base film) and a protective film when it becomes a film for a polarizing plate. The degree is 1500-4000, preferably 2000-3
It is 800.

If the degree of polymerization is less than 1500, the adhesive force will not be sufficient and the heat and humidity resistance of the polarizing film will be poor. Moreover, if the degree of polymerization exceeds 4000, the coating viscosity becomes high, the coating thickness becomes uneven during lamination, the adhesive strength becomes uneven, and performance stability is lacking. The degree of saponification of polyvinyl alcohol used as an adhesive is required to be in the range of 90 to 10Q n+o1% in terms of heat and humidity resistance and adhesiveness. When the degree of saponification is less than 90no1%, the heat and humidity resistance decreases, and delamination of the polarizing film occurs under high temperature and high humidity. The solid content of the adhesive may contain a water resistant agent such as boric acid, glyoxal, methylol urea, active vinyl compound, epoxy compound, polycarboxylic acid, isocyanate, etc. in an amount less than 40 wt%, but if the polyvinyl alcohol component is If it is less than 5Qvt%, not only will transparency be lost, but rewet adhesion will not be possible, so the polyvinyl alcohol component in the solid content of the adhesive needs to be 60W1% or more.

In the present invention, the solution temperature or swelling temperature of the adhesive needs to be 35°C to 90°C, preferably 40°C to 80°C. If the temperature is less than 35° C., the compatibility at the interface between the base film and the adhesive is poor, and the heat and humidity resistance of the film for polarizing plate is poor. Moreover, if the temperature exceeds 90° C., air bubbles are likely to be generated between the adhesive layers, causing optical defects.

Lamination pressure during adhesion is 3-30 kg/e11f
Within this range, the film for the polarizing plate has good heat and humidity resistance, the number of bubbles between the laminated fill points is small (and there are no defects such as scratches on the surface of the laminating roll accompanying lamination processing). Further, deformation of the laminated film group can be prevented.

Next, the method for laminating the film for polarizing plate of the present invention will be explained in more detail.

First, in the present invention, the base film ε refers to a film made of polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyvinyl acetal, or poly(ethylnon-vinyl acetate) copolymer.

These films are uniaxially stretched 2 to 8 times by a conventional stretching method under wet heat in a temperature range of 30° C. to 1,80° C. (1) under dry heat. The adsorption of the dichroic dye onto the base film is achieved by dipping the base 4rA film into a liquid containing the dichroic dye for 10 minutes.
~200 seconds immersion treatment 1. Let's do it.

Dichroic dyes in the film for polarizing plates (7) include iodine, azo, anthraquinone, beryone, quinophthalone, and naphthoquinone, which exhibit dichroism in the -axis-oriented substrate film. , tetrazine-based dichroic dyes or pigments can be used, or they may be used in combination.

(Thus, a base film containing a dichroic dye is obtained.

The protective film is preferably a resin film with excellent transparency and tensile strength. For example, triacetylcellulose (TA
C), diacetyl cellulose (DAC), polyethylene telemeth (PET), polyether sulfone (PES), polycarbonate (PC), polyvinyl acetate (PVAe), and other resin films can be used.

Among these, films made of I-liacetylcellulose (TAC) and diacetylcellulose (DAC), in which more than 5Qmol% of the film surface has been completely saponified, have high transparency (and excellent mechanical strength), and This film is particularly preferred due to its high adhesive strength (2).

Next, a method for laminating the base film and the protective film will be described.

For laminating the base film and the protective film, a device that applies pressure using one or more pairs of nip rolls can be used.

The protective film and the base film may be laminated either before or after immersion treatment in a liquid containing a dichroic dye.

The temperature between the base film and the protective film before lamination is 35~
Apply an adhesive solution dropwise or sprayed at 90°C, preferably with a concentration of 1 to 20 wt%, and use a laminating roll at a pressure of 3 = 30 kg/e, f, preferably (7 or 35 to 90 wt%). After pressing at a temperature of 40-1320℃
Let it dry and you'll be able to glue it together. Water is the solvent for adhesive solution! , 1 is preferably alcohol or a mixture thereof.Also, the adhesive solution is applied to the surface of the protective film in advance to a thickness of 0.02-□5 μm using a metering bar, gravure roll, kiss roll, sprayer, etc. After coating, a protective film with adhesive was prepared by drying (7), and when laminated, it was heated to a temperature of 35 to 90°C between the protective film with adhesive and the base film. While applying the solvent of the polyvinyl alcohol adhesive, the adhesive may be swollen (preferably, rewetting may be performed at a temperature of 35 to 90° C. and a pressure of 3 to 30 kg/enf).

There are two types of lamination methods as described above, and either method requires the adhesive layer specified in the present invention to be interposed (12) and a specific pressure (1) to be satisfied during lamination. It is important that you

Further, in the following two lamination methods, the case where the layers are laminated on one side of the base film has been described, but when laminating on both sides of the base film, the lamination method 47 is similarly used.

[Method for Measuring Physical Properties and Evaluating Effects] The methods for measuring physical property values and evaluating the effects of the present invention are as follows.

(1) A sample of a heat-and-moisture resistant polarizing plate film and a 1 mm thick glass plate bonded together using a butyl acrylate-1 adhesive with a transmittance of 9068% was measured using a spectrophotometer in the wavelength range 400 to 700.
For each wavelength iQnm in the range of III11, calculate the average transmittance (T) of a single polarizing film, and further calculate the average transmittance (T+) when two polarizing films are stacked in parallel to the polarization axis direction, The average transmittance (T
2) was measured and the degree of polarization (V) was determined from the following calculation formula.

T+: Average transmittance (%) when the polarizing axes of two polarizing films are arranged in parallel T2: Average transmittance (%) when the polarizing axes of two polarizing films are arranged orthogonally The heat and humidity resistance of the polarizing film is determined by placing the polarizing film attached to a glass plate in a constant temperature and humidity chamber at 60°C and 90% RH, and measuring the transmittance and degree of polarization using a spectrophotometer after 300 hours. , the initial transmittance before the test, and the initial polarization degree are each expressed as ΔY1ΔV. The smaller the value of ΔY1ΔV, the better the heat and humidity resistance.

(2) One end of the laminate consisting of the adhesive base film and the protective film
After immersing in water at 0℃ and peeling it off, dry it and then peel it off again at 20℃.
The peel force at both ends of the film was determined at a film width of 25 M using a constant speed moving type tensile tester in a room at 65% RH, and the adhesive strength was judged according to the following criteria.

◎: Dry adhesion strength is extremely large and excellent. (The film was cut without peeling) ○: Dry adhesion strength was large and good. (Peeling force is 3kg)
exceed. ) △: Dry adhesion strength is small and inferior. (Peeling force is 1 to 3 kg) ×: Adhesive force is extremely small and cannot be used. (Peeling force is 1
(3) Cut a laminated sample of a wet release base film and a protective film to a width of 25mm and a length of 170mm, peel off one end, hang a load (15g) on one end of the film, and remove the film. Wet adhesive strength was evaluated by measuring the time (seconds) from when the other end of the sample was immersed in 40°C warm water until the adhesive surface was completely peeled off. Naturally, the longer the peeling time, the better.

(4) Appearance quality The appearance quality of the laminated product consisting of the base film and the protective film was judged according to the following criteria.

◎: Excellent visual quality. (There are less than 5 point defects such as bubbles of 0.2 mm or more in size, push scratches, and dents per 1rd layer of the laminate, and the transparency is extremely good.

) O: Appearance quality is good. (The number of the above-mentioned point defects present per 1 d of the laminate is 5 or more and less than 20, and the transparency is satisfactory.) Δ: Poor in visual quality. (Laminated product 1
20 or more of the above point defects exist around d lOO
or the transparency is poor, which poses a practical problem. ) ×: Appearance quality is poor. (The laminate product 1d has 100 or more of the above point-like defects, or the transparency is so poor that it cannot be put to practical use.) [Examples] The present invention will be explained based on Examples.

Examples 1 to 3 A polyvinyl alcohol film (#7500 manufactured by Kuraray ■) having a thickness of 75 μm was coated with 0.1 wt % of iodine, 0.2 wt % of potassium iodide, and 4.0 wt % of boric acid. After immersion treatment in a 35°C aqueous solution containing 4.0% boric acid. ．． The film was stretched 3.8 times in the running direction of the film in a 40° C. aqueous solution containing Ovt%, further washed with water, and then dried at 50° C. to obtain a polyvinyl alcohol base film. Subsequently, the degree of polymerization and degree of saponification are respectively 1500/98.9 fflor%, 20
00/99°9 mol%, 3800/99. On+o
An adhesive solution prepared by dissolving 1% polyvinyl alcohol resin in hot water to a concentration of 10 wt% and adjusting the temperature to 50°C was dripped and spread between the base film and a triacetyl cellulose film with a thickness of 80 μm while rolling the laminating roll. The films for polarizing plates of Examples 1 to 3 in which the base film and the protective film were laminated were obtained by pressing at a pressure of 10 kg/cnr and drying at 60°C.

Comparative example 1.・2 Example 1. The polymerization degree and saponification degree of the adhesive and the polyvinyl alcohol used in I~ are 1200/9, respectively.
9.2 mo! %, 5100/99.2 mol% and J7
Example J except that. Comparative Examples 1 and 2 were manufactured under the same conditions.
A film for a polarizing plate was obtained.

Examples 4 to 6 A polyvinyl alcohol film (#7500 manufactured by Kuraray ■) having a thickness of 75 μm was stretched using a roll-type longitudinal stretching machine equipped with a heating roll at 140°C between a slow-driving roll and a fast-driving roll.
．． The film was stretched 0 times to obtain a uniaxially oriented polyvinyl alcohol film. On the other hand, the degree of polymerization is 3500 and the degree of saponification is 90.
゜2 n+o1%, 97, 5 mol%, 99゜9
mol% polyvinyl alcohol resin with warm water to a concentration of 2w
t% and a temperature of 50° C. was applied to one surface of a triacetyl cellulose film with a thickness of 80 μm using a gravure coater, and then dried to obtain a triacetyl cellulose film having an adhesive layer. The previously obtained uniaxially oriented polyvinyl alcohol film and triacetyl cellulose having an adhesive layer are arranged so that the adhesive layer is on the bonding surface 12, and water at 50°C is added to the polyvinyl alcohol adhesive layer to form an adhesive layer. A laminated product of polyvinyl alcohol film and triacetyl cellulose film was obtained by pressure bonding at 1°Okg/cnf using a laminating roll while swelling the film.

This laminated film contains 0.1 wt% of iodine, 2 wt% of potassium iodide/-Q, and 4.0 wt% of boric acid. After being immersed in an aqueous solution containing Owt% at 35° C., the film was dried in J7 to obtain a film for a polarizing plate of Example 4-6.

Comparative Example 3 A product was manufactured under the same conditions as in Example 4 except that the degree of saponification of the polyvinyl alcohol resin used as the adhesive in Example Rin was 86.9 mol%.

Examples 7-9 Example 1. The degree of polymerization of polyvinyl alcohol used as an adhesive was 3800, and the degree of saponification was 99.9.
Strain the mol% and adjust the temperature of the adhesive solution before application to 35°C and 60°C.
Example 1 except that the temperature was 90°C. Manufactured under the same conditions as
~, films for polarizing plates of Examples 7 to 9 were obtained.

Comparative Examples 4 and 5 In Example 7, the temperature of the adhesive solution before application was 26°C, 9
Films for polarizing plates of Production J7 and Comparative Examples 4 and 5 were obtained under the same conditions as in Example 7 except that the temperature was 8°C.

Examples 1.0 to 12 In Example 3, the adhesion pressure of the polyvinyl alcohol film and triacetyl cellulose film after applying the adhesive with the laminating roll was 5 kg/ci, 18 kg.
/ al, Example 3 except that it was 30 kg/at.
Polarizing plate films h of Examples 10 to 12 were obtained under the same conditions as above.

Comparative Examples 6 and 7 In Example 10, the degree of polymerization and degree of saponification of polyvinyl alcohol used after applying the adhesive were 3500.
97.5vt%ε, adhesive pressure 1-kg/cffl
The films for polarizing plates of Comparative Examples 6 and 7 were obtained by manufacturing under the same conditions as Examples J and 0, except that the weight was 33 kg/ci.

Examples 13 and 14 In Example 1, the degree of polymerization of the polyvinyl alcohol used as the adhesive was 3500, and the adhesive composition was 60 wt%/40 w of polyvinyl alcohol/methylol urea.
The film for polarizing plate of Example 13ε14 was obtained by manufacturing under the same conditions as in Example 1 except that t% and 80wt%/20wt% were used.

Comparative Example 8 Example 1.3 was produced under the same conditions as Example J3, except that the adhesive composition was 45% by weight of polyvinyl alcohol and 55% by weight of methylol urea.

As is clear from Table 10, the film for polarizing plate produced by the method of the present invention is excellent in both heat and humidity resistance and appearance quality.

[Effects of the Invention] The present invention provides adhesives that contain at least 60 wt% or more of a polyvinyl alcohol component with a degree of polymerization of 1500=40001 and a degree of saponification of 90 to 100 mol% in the solid content of the adhesive in the step of laminating a base film and a protective film. By adhering under a specific pressure through a layer of adhesive, it is possible to significantly improve moisture and heat resistance and adhesive strength, and to provide excellent quality with few optical defects, greatly improving the reliability of large liquid crystal displays, etc. It is raised to

Claims (3)

[Claims] (1) In a method for laminating a film for a polarizing plate, in which a protective film is laminated on at least one side of a polyvinyl alcohol film as a base film via an adhesive layer, the solid content of the adhesive has a polymerization degree of 1500 to 4000, degree of 9
60wt of 0-100mol% polyvinyl alcohol
% or more, and bonding is carried out by applying a pressure of 3 to 30 kg/cm^2 through a solution of the adhesive at 35 to 90°C. (2) In a method for laminating a film for a polarizing plate, in which a protective film is laminated on at least one side of a polyvinyl alcohol film as a base film via an adhesive layer, the solid content of the adhesive has a polymerization degree of 1500 to 4000, degree of 9
60wt of 0-100mol% polyvinyl alcohol
% or more, the adhesive is swollen at a temperature of 35 to 90°C, and bonded by applying a pressure of 3 to 30 kg/cm^2. (3) Claim (1) or (2) characterized in that the protective film is a cellulose film.
A method for laminating a film for a polarizing plate as described in 1.