JPH04173844A - Production of polyvinyl alcohol phase-difference film having improved property - Google Patents

Abstract

PURPOSE:To obtain the subject film free from scattering of retardation value even in a hot humid atmosphere and having excellent heat-resistance by forming a film from an aqueous solution of a PVA resin containing boric acid, etc., and uniaxially drawing the obtained film. CONSTITUTION:The objective film is produced by forming a film from an aqueous solution of a PVA resin (preferably having a PVA resin concentration of 10-30wt.%) containing preferably 0.05-1wt.% of boric acid or borax, uniaxially drawing the obtained film or sheet and heat-treating the product preferably at a temperature between the drawing temperature and 130 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses polyvinyl alcohol (PV) with improved heat resistance.
A) Regarding a method for producing a retardation film.

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

As a retardation film that is currently commercially available and in practical use, there is a so-called 1/4 wavelength plate that has a function of generating a retardation of 1/4 λ with respect to the wavelength λ of an incident light beam.

This is used as a beam splitter for laser beams as an interchanging element for linearly polarized light and circularly polarized light, or used in combination with a linear polarizer to construct a circularly polarizing plate.

In addition, STN type liquid crystal display (5TN-LCD)
In recent years, retardation films have been used to prevent color shift in 5TN-LCDs.

[Problems to be Solved by the Invention] A film or sheet made of PVA or a derivative thereof, together with a cellulose acetate film uniaxially stretched, polyvinyl chloride, polystyrene, polyamide, polycarbonate, etc. The properties of the retardation film (retardation value (R value)) change greatly in a high-temperature atmosphere due to poor heat resistance, and PVA-based film or sorting alone Because of the problem that it cannot be used in films or sheets, it is desired to develop a method to improve the heat resistance problem.

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

[Means for Solving the Problem L] As a result of intensive studies to solve the problem, the present inventors formed a film from a polyvinyl alcohol resin aqueous solution containing boric acid or borax, and produced a film or We have discovered a method for producing a polyvinyl alcohol retardation film with improved properties, which involves uniaxially stretching a sheet, and have completed the present invention.

In order to manufacture the retardation film of the present invention, an aqueous solution containing a PVA resin, boric acid, or borax is used.

The content of boric acid or borax in the aqueous solution is 005~
1% by weight is required. If it is less than 0.05% by weight, it is difficult to obtain the effects of the present invention, while if it exceeds 1% by weight, the film-forming properties deteriorate.

Further, the content of the PVA resin is preferably 10 to 30% by weight, preferably 10 to 20% by weight.

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

PVA-based resins are usually produced by polymerizing vinyl acetate and saponifying polyvinyl acetate, but the present invention is not limited to this, and a small amount of unsaturated carbonic acid (salt, ester) is produced. , amides, nitriles, etc.), olefins, vinyl ethers, unsaturated sulfonates, etc.
It may contain a component copolymerizable with vinyl acetate.

Examples include, but are not limited to, so-called polyvinyl acetal resins such as polyvinyl butyral resin, polyvinyl alcohol resin, and other PVA derivatives in which PVA is reacted with aldehydes in the presence of an acid. Among these, PVA with a high degree of saponification and a high degree of polymerization is preferred because it has good heat resistance.

That is, the degree of saponification is preferably 95% or more, more preferably 99%.
% or more, especially 99.5% or more, and the degree of polymerization is 10
00 or more, preferably 1000 to 3000.

The aqueous solution is sorted or formed into a film according to a known method such as a casting method or an extrusion method.

The formed raw film or sheet is then processed in steps 1.1 to 4.
It is uniaxially stretched to about twice the original size. In the stretching operation, first the raw film and the sort are heated for 30 seconds to 5 molecules at a temperature of 120 to 200°C, then heated to 150 to 230°C, preferably 170 to
Stretching is performed at 200°C by about 1.1 to 4 times.

Finally, heat setting is performed for 1 to 5 minutes at a temperature below the stretching temperature to 130°C. Water resistance treatment may be performed at any of the above steps as necessary.

The film thus obtained has a thickness of about 30 to 100 μm, preferably about 40 to 80 μm, and has a retardation value of about 100 to 700 nm in terms of physical properties.
This is a base material that does not yet have moisture resistance.

In order to obtain a retardation film with a constant optical principal axis and little optical color shift, it is preferable that the original film or notebook has good thickness accuracy and is as optically homogeneous as possible. It is undesirable for Gly lines to occur on the film or notebook during film formation.

In order to obtain a retardation film with optically small color shift in the present invention, the neck-in rate (100X(A-
It is preferable to suppress B)/A) to 20% or less.

The uniaxial stretching method includes, for example, a method in which the film is preheated by passing it between a number of rolls, and then stretched to a predetermined magnification by two pairs of stretching rolls, and a method in which the film is passed between a number of rolls. Methods such as a method in which preheating and stepwise stretching are simultaneously performed during the stretching to reach a predetermined magnification, and a transverse uniaxial stretching method in which stretching is performed in the width direction using a tenter method may be employed.

Stretching is carried out as appropriate depending on the intended use of the retardation film. In other words, the retardation value is the main stretching direction (
The MD force direction and the direction perpendicular to this (linearly polarized light defined as the product of the refractive index difference (n, D4, D) in the TD force direction and the thickness (d) of the retardation film or sheet, which have an orthogonal relationship) In this case, the stretching process is performed so that the retardation value (R value), which means the phase difference of transmitted light when the light is incident in the same phase, is, for example, 1/4 of the wavelength (λ) of the used light beam. In this case, a 1/4-wavelength plate is obtained, and if the stretching process is performed so that the value becomes 1/2, a 172-wavelength plate is obtained.If the light used is visible light, The retarder value as a 174 wavelength plate is 95~
The range is 170 nm.

Therefore, by combining a quarter-wave plate in this range and a linear polarizer, it is possible to obtain circularly polarized light that is accurate to a certain visible light beam.

In practical use, the obtained retardation film is used as it is or by laminating an optically non-oriented and transparent polymer film or sheet on both or one side using an adhesive. Examples of such polymer films 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 agents, urethane type,
Acrylic and epoxy types are often used.

[Function] In the present invention, P V containing boric acid or borax
By uniaxially stretching the film obtained from the A-based resin aqueous solution, a retardation film having excellent heat resistance while retaining moisture resistance can be obtained.

lExample Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 PVA with polymerization degree of 1700 and average saponification degree of 998 mol%
And boric acid was dissolved in water to obtain an aqueous solution with a PVA concentration of 18% by weight and a boric acid concentration of 0.3% by weight.

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

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

Preheating step = 180°C, 2 minutes Stretching step: 190°C, 1,12 times stretching Heat setting step 150°C, 2 minutes The R value of the obtained retardation film (thickness 72 μm) was measured using a polarizing microscope equipped with a Babinet compensator. Nicon POH-1
When measured using a compensation method (the light source was white light), it was found to be 390r++++, and was of good quality.

Next, a cellulose trisulfate film was adhered to both sides of the above retardation film using a PVA resin adhesive, and then laminated with glass using an acrylic adhesive to obtain a retardation plate (all The thickness is 170 μm). This retardation plate was heated at 40°C.
The R value when left for 250 hours under ×95% RH conditions (Case I) is 384 nm, and the R value when left for 250 hours under 70°C × 65% RH conditions (Case ■) is 39.
It was found that the film had a diameter of 4 nm, had moisture resistance, and had excellent heat resistance.

Control Example I 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 for case (■) and 380 nm for case (2).

Examples 2 to 3 PVA with a polymerization degree of 3000 and a saponification degree of 99.5 mol%
(Example 2), and the same PV as Example 1
A was used, but the stretching ratio was changed to 1.2 times (Example 3
) The same method as in Example 1 was performed except for the following.

The results were as follows.

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

The results were as follows.

[Effects] Since the retardation film of the present invention contains boric acid or borax, it has good quality with no variation in retardation value even in a high humidity or high temperature atmosphere.

Claims (1)

[Claims] 1. Polyvinyl alcohol retardation with improved properties, characterized by forming a film from an aqueous polyvinyl alcohol resin solution containing boric acid or borax, and uniaxially stretching the resulting film or sheet. Film manufacturing method. 2. The content of boric acid or borax is 0.05 to 1% by weight,
2. The manufacturing method according to claim 1, wherein an aqueous polyvinyl alcohol resin solution having a polyvinyl alcohol resin content of 10 to 30% by weight is used. 3. The manufacturing method according to claim 1, wherein the uniaxially stretched polyvinyl alcohol resin film or sheet is heat-treated at a stretching temperature to 130°C.