JP3029209B2 - Method for producing polyvinyl alcohol-based retardation film with improved properties - Google Patents

Description

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

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

A so-called quarter-wave plate having a function of generating a quarter-wave phase difference with respect to the wavelength λ of an incident light beam is currently commercially available as a retardation film and is in practical use. This is an interchangeable element between linearly polarized light and circularly polarized light.
It is used for a beam splitter of a laser beam or in combination with a linear polarizer to form a circularly polarizing plate.

In an STN-type liquid crystal display (STN-LCD), a phase difference film is used to prevent color shift of the 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 is made of polyvinyl chloride, polystyrene, polyamide, polycarbonate, or the like. Although it has been studied and used for retardation films, the properties (retardation value (R value)) of the retardation film fluctuate greatly in a high-heat atmosphere due to poor heat resistance, and PVA films or sheets are used alone. Therefore, there is a need for a method of improving the heat resistance problem of the film or sheet.

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

[Means for Solving the Problems] The present inventors have conducted intensive studies to solve such problems, and as a result, formed a film of a polyvinyl alcohol-based resin aqueous solution containing boric acid or borax, and obtained a film or sheet. The present inventors have found a method for producing a polyvinyl alcohol-based retardation film having improved properties characterized by uniaxially stretching the film, and have completed the present invention.

In order to produce the retardation film of the present invention, an aqueous solution in which a PVA-based resin, boric acid or borax is mixed is used.

The content of boric acid or borax in aqueous solution is 0.05-
1% by weight is required. When the content is less than 0.05% by weight, the effect of the present invention is hardly obtained.

The content of the PVA resin is 10 to 30% by weight, preferably 1 to 30% by weight.
0-20% by weight is preferred.

If necessary, known additives such as ultraviolet absorbers and various stabilizers may be added to the aqueous solution.

The PVA-based resin is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. However, the present invention is not limited to this, and a small amount of unsaturated carboxylic acid (salt, ester, amide, nitrile And the like, olefins, vinyl ethers, unsaturated sulfonates, and the like, which may be copolymerized with vinyl acetate. or
PVA reacted with aldehydes in the presence of acid, for example, polyvinyl butyral resin, so-called polyvinyl acetal resin such as polyvinyl formal resin and other PV
A derivatives include, but are not limited to. Among these, PVA having a high degree of saponification and a high degree of polymerization is preferred from the viewpoint of good heat resistance. That is,
The degree of saponification is preferably 95% or more, more preferably 99% or more, particularly 99.5% or more, and the degree of polymerization is 1000 or more, preferably 1,000 to 3,000.

The aqueous solution is formed into a sheet or film by a known method such as a casting method and an extrusion method.

The formed film film or sheet is subsequently prepared in the order of 1.1 to 4
It is uniaxially stretched about twice. The stretching operation first preheats the raw film and sheet at a temperature of 120 to 200 ° C for 30 seconds to 5 minutes,
Subsequently, the film is stretched at a temperature of 150 to 230 ° C, preferably 170 to 200 ° C, about 1.1 to 4 times.

Finally, heat setting is performed for 1 to 5 minutes at a temperature not higher than the stretching temperature to 130 ° C. If necessary, the water-resistant treatment may be performed at any of the above stages.

The film thus obtained has a thickness of about 30 to 100 μm,
Preferably, the base material has a retardation value of about 100 to 700 nm and does not yet have moisture resistance.

In order to obtain a retardation film 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 uniform 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 film having small optical spots, a neck-in rate (100 × (A−)) defined by a film width A before stretching and a film width B after stretching.
B) / 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 according to the intended use of the retardation film. That is, the retardation value is 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 enters at the same phase, is defined by the wavelength (λ) of the light beam used.
For example, when the stretching process is performed to have a value of 1/4, a 1/4 wavelength plate is obtained, and when the stretching process is performed to be a value of 1/2, A wave plate will be 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.

The obtained retardation film is practically used as it is, or is laminated on 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, PVA containing boric acid or borax is used.
By uniaxially stretching a film or sheet obtained from an aqueous solution of a base resin, a retardation film having excellent heat resistance while maintaining moisture resistance can be obtained.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 PVA and boric acid having a polymerization degree of 1700 and an average saponification degree of 99.8 mol% were dissolved in water to obtain an aqueous solution having a PVA concentration of 18% by weight and a boric acid concentration of 0.3% by weight.

The solution was dripped onto a polyethylene terephthalate film and dried to obtain a film having a thickness of 75 μm.

The film was uniaxially stretched by a tenter method under the following conditions.

Preheating step: 180 ° C., 2 minutes Stretching step: 190 ° C., 1.12 times drawing Heat setting step: 150 ° C., 2 minutes Nikon POH-1
(Light source is white light)
It was 390 nm, and the quality was good.

Next, a cellulose triacetate film was adhered to both surfaces of the retardation film using a PVA-based resin viscosity agent, and further bonded to glass using an acrylic adhesive to obtain a retardation film (total thickness). Is 170 μm). 40 ° C x 95
When left for 250 hours under the condition of% RH (case I), the R value was 384 nm, and when left for 250 hours under the condition of 70 ° C x 65% RH (case II), the R value was 394 nm. It was also found that it had excellent heat resistance.

Comparative Example 1 The same experiment as in Example 1 was performed except that the use of boric acid was omitted.

The R value of the retardation film was 392 nm, and the R value of the retardation plate was 403 nm in case I and 380 nm in case II.

Examples 2-3 As PVAs, those having a degree of polymerization of 3000 and a degree of saponification of 99.5 mol% were used (Example 2), and the same PVA as in Example 1 was used, but the stretching ratio was changed to 1.2 times (Example) Except for 3), the same method as in Example 1 was performed.

 The results were as follows.

Examples 4 to 5 The content of boric acid was changed to 0.2% by weight (Example 4).
The same experiment as in Example 1 was conducted except that borax and 0.5% by weight of borax were used (Example 5).

 The results were as follows.

[Effect] Since the retardation film of the present invention contains boric acid or borax, the retardation film does not vary in retardation value even in a high-humidity or high-temperature atmosphere and has good quality.

Claims (3)

(57) [Claims] 1. A method for producing a polyvinyl alcohol-based retardation film having improved properties, comprising forming a film of an aqueous solution of a polyvinyl alcohol-based resin containing boric acid or borax, and uniaxially stretching the resulting film or sheet. Method. 2. An aqueous polyvinyl alcohol resin solution having a boric acid or borax content of 0.05 to 1% by weight and a polyvinyl alcohol resin content of 10 to 30% by weight is used. The manufacturing method as described. 3. The method according to claim 1, wherein the uniaxially stretched polyvinyl alcohol resin film or sheet is heat-treated at a stretching temperature of 130 ° C.