JP3050589B2 - Manufacturing method of polyvinyl alcohol phase retarder with improved moisture resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to polyvinyl alcohol (PV) having improved moisture resistance.
A) It relates to a method for producing a system retardation plate.

[Prior Art] A retardation plate is a film or sheet having birefringence. Since the light that has passed through the phase difference plate has a different refractive index in two directions orthogonal to each other, a phase difference occurs between the orthogonal light beams after passing through the phase difference plate.

A so-called quarter-wave plate having a function of producing a phase difference of 1/4 .lamda. With respect to the wavelength .lamda. Of an incident light beam is currently commercially available as a retardation plate and is in practical use. This is used as an interchangeable element of linearly polarized light and circularly polarized light in a beam splitter of a laser beam, or in combination with a linear polarizer to form a circularly polarizing plate.

In addition, a phase difference plate is used to prevent color shift of an STN-type liquid crystal display (STN-LCD).

[Problems to be Solved by the Invention] A film or a sheet made of PVA or a derivative thereof is made of a cellulose acetate-based film uniaxially stretched or a film made of polyvinyl chloride, polystyrene, polyamide, polycarbonate or the like. It has been studied and used as a retardation plate, but its properties (retardation value (R value), film and sheet weight, dimensions, etc.) fluctuate greatly in a high-humidity atmosphere due to poor moisture resistance. However, there is a problem that the PVA film or sheet cannot be used alone. In fact, ST
In an STN-LCD in which a retardation plate is attached to an N liquid crystal cell, moisture absorption from a cut surface (side surface) is a problem.

As a method of solving the problem, there is a method of sealing the peripheral portion with a sealant. However, since the cost is high, it is desired to develop a method of improving the moisture absorption problem in the film or sheet. I have.

The present invention has been made to solve the problem of poor moisture resistance when the PVA film is used as a retardation film.

[Means for Solving the Problems] As a result of intensive studies to solve such problems, the present inventors treated a polyvinyl alcohol-based uniaxially stretched film or sheet with boric acid or an aqueous solution containing borax,
Further, the present inventors have found a method for producing a polyvinyl alcohol-based retardation plate with improved moisture resistance, which is further characterized by being treated with an alkyl ester of orthophosphoric acid and, if necessary, an alcohol solution containing boric acid or borax, and completed the present invention. I came to.

In the present invention, a PVA-based uniaxially stretched film or sheet is used.

As the PVA-based material constituting the film or sheet, PVA, reacted with aldehydes in the presence of an acid of PVA, for example, polyvinyl butyral resin, so-called polyvinyl acetal resin such as polyvinyl formal resin, and other PVA by copolymerization Derivatives include, but are not limited to. Among these, from the viewpoint of good heat resistance, high saponification degree and high polymerization degree
PVA is preferred. That is, the degree of saponification is preferably 95% or more, more preferably 99% or more, particularly 99.5% or more,
Polymerization degree of 1000 or more, desirably 1000 to 3000 is preferable.

The PVA-based uniaxially stretched film or sheet is PVA.
An original film or sheet obtained by forming a film of a system resin by a usual method such as a casting method, an extrusion method, and a calendar method is used in a method of 1.1 to
Uniaxially stretched about 4 times, and about 30 to 60 μm, preferably about 40 to 50 μm in thickness obtained by heat treatment at 150 to 250 ° C. for about 10 to 30 seconds, preferably about 200 to 230 ° C. for about 10 to 25 seconds. It is a substrate that has a retardation value of about 50 to 200 nm in physical properties and does not yet have moisture resistance.

In order to obtain a retardation plate having a constant optical principal axis and little optical color unevenness, it is preferable that the raw film or sheet has good thickness accuracy and is as optically as possible as possible. It is not preferable that a die line or the like is generated during film formation on a film or a sheet.

In the present invention, in order to obtain a retardation plate having small optical spots, a neck-in ratio (100 × (AB) /) defined by a film width A before stretching and a film width B after stretching.
A) is preferably suppressed to 20% or less.

Examples of the method of uniaxial stretching include, for example, preheating the film by passing the film between a number of rolls, and then stretching the film to a predetermined magnification with two pairs of stretching rolls, and passing the film between a number of rolls. While preheating and stepwise stretching are performed concurrently during the heating, a method such as a method of bringing the film to a predetermined magnification or a transverse uniaxial stretching method of stretching in the width direction by a tenter method can be adopted.

Stretching is appropriately performed depending on the intended use of the retardation plate. That is, the retardation value is defined as the product of the refractive index difference (II _MD -II _TD ) in the main stretching direction (MD direction) and the direction perpendicular thereto (TD direction) and the thickness (d) of the retardation film or sheet. The retardation value (R value), which means the phase difference of transmitted light when linearly polarized light having an orthogonal relationship is incident at the same phase, is defined as, for example, 1/4 of the wavelength (λ) of the light beam used. If the stretching process is performed so that
When a 波長 wavelength plate is obtained and stretched so as to have a value of 1/2, a 波長 wavelength plate is obtained. When the light used is a visible light, the retardation value as a quarter wavelength plate is in the range of 95 to 170 nm. Therefore, by combining a quarter-wave plate and a linear polarizer in this range, accurate circularly polarized light in a certain visible ray can be obtained.

Various additives such as an ultraviolet absorber and a stabilizer may be added to the PVA-based retardation plate according to the present invention.

The molecular orientation is made permanent by heat treatment performed after the stretching.

In the present invention, the PVA manufactured as described above
The system uniaxially stretched film or sheet is treated with an aqueous solution containing boric acid or borax. This processing is performed to improve the durability of the film or sheet.

The boric acid or borax-containing aqueous solution is not only an aqueous solution of so-called orthoboric acid (H ₃ BO ₃ ) or borax, but also an aqueous solution of metaboric acid or tetraboric acid. This is a concept that includes an aqueous solution, but also includes an aqueous solution.

As the concentration of the boric acid or borax-containing aqueous solution, 20
1 to 5% in terms of solubility in water of about 35 ° C, shortening the time required for treatment, enhancing the effectiveness of treatment, etc.
(% By weight, the same applies hereinafter), and more preferably about 1.5 to 3%.

The temperature of the aqueous solution when the PVA-based uniaxially stretched film or sheet is treated with the boric acid or borax-containing aqueous solution is preferably about 20 to 35 ° C, and 25 to 30 ° C in view of the efficiency of the next step. The degree is more preferred.

As a method for treating a PVA-based uniaxially stretched film or sheet with an aqueous solution containing boric acid or borax, for example, the film or sheet is immersed in an aqueous solution having a predetermined concentration and temperature by a continuous method or a batch method for a predetermined time. Specific examples thereof include a method, and a method of spraying an aqueous solution containing boric acid or borax.

The PVA-based uniaxially stretched film or sheet thus treated with the boric acid or borax-containing aqueous solution is treated with an alcohol solution containing an alkyl ester of orthophosphoric acid as it is or after washing with water. This process is performed to further improve the moisture resistance. As the alkyl group of the alkyl ester of orthophosphoric acid, those having about 1 to 5 carbon atoms are practical, and methyl orthophosphate, ethyl orthophosphate and propyl orthophosphate are useful. (The ester may be any of mono, di and tri.) It is preferable to use boric acid or borax in combination to enhance the effect.

The alcohol used to prepare the alcohol solution is not particularly limited as long as it has good solubility in the orthophosphoric acid alkyl ester. For example, methanol, ethanol, 1-propanol, 2-propanol, -Butanol, 2-butanol, t-butanol and the like.

The concentration of the ester in the alcohol solution containing oritoric acid ester is preferably about 4 to 15%, and 8 to 12%.
The degree is more preferred.

Also, the concentration of boric acid or borax is desirably 4 to 15%, preferably about 8 to 12%. The ester / boric acid or borax ratio can be anywhere from 1 / 0.5 to 1/3.

The temperature of the alcohol solution in the case of treating with the alcohol solution containing fortphosphate is 25
The temperature is preferably about 30 ° C.

Further, as the treatment method, the same method as in the case of treating with a boric acid-containing aqueous solution can be adopted.

In the treatment, the concentration of the boric acid-containing aqueous solution exceeds about 5%, the temperature of the boric acid-containing aqueous solution exceeds about 35 ° C., the concentration of the orthophosphoric acid alkyl ester-containing alcohol solution exceeds about 15%, When the temperature of the alcohol solution exceeds about 30 ° C., the treated film or sheet tends to whiten. Further, when the concentration of the aqueous solution containing boric acid is less than about 1% and the concentration of the alcohol solution containing alkyl orthophosphate is less than about 4%, effects such as durability cannot be sufficiently obtained.

PVA-based uniaxially stretched film or sheet treated with an orthophosphoric acid alkyl ester-containing alcohol solution is usually washed with alcohol at about 50 to 200 ° C., preferably 100 to 200 ° C.
A heat treatment which also serves as drying at about 200 ° C. for about 1 to 3 minutes is performed.

The PVA-based retardation film or sheet produced by the method of the present invention as described above has a retardation value of not more than 600 nm, a weight change of 12 when left at 40 ° C. and 95% RH for 12 days.
% Or less, the dimensional change is 3% or less in the MD direction and 4% or less in the TD direction, thereby improving the moisture resistance.

In practical use, the PVA-based retardation film or sheet is used as it is or by laminating an optically non-oriented and transparent polymer film or sheet on both sides or one side using an adhesive. Examples of such a polymer film include cellulose films such as cellulose triacetate and cellulose diacetate, polycarbonate films, polymethyl methacrylate films, polystyrene films, polyester films such as polyethylene terephthalate, and polysulfone films. As the agent, urethane-based, acrylic-based, and epoxy-based agents are frequently used.

[Action] In the present invention, a phase difference film having excellent durability can be obtained by treating a PVA-based uniaxially stretched film with boric acid or borax and then with an alkyl orthophosphate.

[Examples] Hereinafter, the method of the present invention will be described based on examples.

Examples 1-2 A 50 μm-thick uniaxially stretched polyvinyl alcohol film having a degree of polymerization of 2,000 and an average degree of saponification of 99.7 mol% (stretch ratio of 1.2)
And then heat-treated at 200 ° C. for 15 seconds after stretching) and immersed in an aqueous solution containing boric acid and a methanol solution containing an alkyl orthophosphate under the conditions shown in Table 1. Then, after washing by immersion in methanol,
The heat treatment which also served as drying for minutes was performed.

Using the obtained retardation film, the weight change rate, the dimensional change rate and the R
The change in the value was measured by the following method. The results are shown in Table 1.

(Rate of change in weight) The weight of the retardation film when absolutely dried in a desiccator and the weight of the film after the moisture resistance test are measured, and are obtained by the following equation.

(Dimensional change rate) The length when the retardation film is absolutely dried in a desiccator and the length of the film after the moisture resistance test are measured, and are obtained by the following equation.

(Change in R value) Polarizing microscope with a Babinet-type compensator (Nikon PO
H-1) by the compensation method. The light source is white light.

Comparative Example 1 Evaluation was made in the same manner as in Example 1 except that the treatment with the boric acid-containing alcohol solution was omitted. The results are shown in Table 1.

Comparative Example 2 Evaluation was performed in the same manner as in Example 1 except that the treatment with the aqueous solution containing an orthophosphoric acid alkyl ester was omitted. The results are shown in Table 1.

Comparative Example 3 The uniaxially stretched film used in Example 1 was evaluated in the same manner as in Example 1 without treatment. The results are shown in Table 1.

Example 3 In Example 1, the degree of polymerization of polyvinyl alcohol was 170.
A retardation film was prepared and evaluated in the same manner as in Example 1, except that the saponification degree was changed to 99.8 mol% and the stretching ratio was 1.15 times. The results are shown in Table 1.

[Effect] The PVA-based retardation film according to the method of the present invention has improved moisture resistance over the conventional PVA-based retardation film,
This solves the problem of the A-system retarder.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J ^7/ 00-7/18 G02B 5/30

Claims (1)

(57) [Claims] 1. A polyvinyl alcohol-based uniaxially stretched film or sheet is treated with an aqueous solution containing boric acid or borax, and further treated with an alkyl ester of orthophosphoric acid and, if necessary, an alcohol solution containing boric acid or borax. A method for producing a polyvinyl alcohol-based retardation plate having improved moisture resistance.