JPH06254958A - Polyvinyl alcohol resin stretched film - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a stretched film of polyvinyl alcohol resin having excellent optical properties, heat resistance and moisture resistance. A polyvinyl alcohol resin stretched film obtained by immersing and stretching a polyvinyl alcohol resin film formed from an aqueous solution of a boron compound-containing polyvinyl alcohol resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretched film of polyvinyl alcohol resin having excellent optical properties, and more specifically, it has excellent heat resistance and moisture resistance which can be used for retardation plates or polarizing plates. The present invention relates to a polyvinyl alcohol-based resin stretched film.

[0002]

2. Description of the Related Art Films of polyvinyl alcohol resin have been widely used in the fields of food packaging, industrial packaging, etc. due to their high barrier properties such as packaging materials for textile products, etc. Against the background of development, the range of applications is expanding to the optical fields such as retardation plates and polarizing plates. In the optical field, a polycarbonate film has conventionally been the mainstream as a film for a retardation plate / polarizing plate, but a stretched polyvinyl alcohol-based resin has been produced by a fusion of a polyvinyl alcohol-based resin film-forming technology and a high-precision stretching technology. Various optical properties of the film have been improved, and the film has been widely used in the optical field. In this optical field, a polyvinyl alcohol-based resin film having excellent optical characteristics and durability such as heat resistance and moisture resistance is particularly required. Among these, as a method for improving heat resistance, the present applicant has a method of forming a polyvinyl alcohol-based resin aqueous solution containing a boron compound and uniaxially stretching the obtained film or sheet (Japanese Patent Application No. 2-301478). Gazette).

[0003]

However, with the recent expansion of applications, a polyvinyl alcohol resin which is required to have durability under more severe conditions and has excellent heat resistance and moisture resistance and which is excellent in durability. A film was desired.

[0004]

[Means for Solving the Problems] Therefore, the inventors of the present invention have conducted diligent research to obtain a polyvinyl alcohol resin stretched film having improved heat resistance and humidity resistance and excellent optical characteristics. , A polyvinyl alcohol-based resin stretched film formed from an aqueous solution of a boron compound-containing polyvinyl alcohol-based resin is immersed in an acidic aqueous solution, and the stretched polyvinyl alcohol-based resin stretched film has excellent optical characteristics, and has conventional heat resistance and moisture resistance. The present invention has been completed by discovering that it has a durability exceeding the property. About the polyvinyl alcohol-based resin stretched film of the present invention,
The details will be described below.

The polyvinyl alcohol resin used for the stretched film is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not limited to this. A small amount of unsaturated carboxylic acid (including salts, esters, amides, nitriles, etc.), olefins, vinyl ethers, unsaturated sulfonates and the like, which may be copolymerized with vinyl acetate, may be contained. Further, a polyvinyl butyral resin obtained by reacting a polyvinyl alcohol resin with an aldehyde in the presence of an acid, a so-called polyvinyl acetal resin such as a polyvinyl formal resin, and other polyvinyl alcohol-based resin derivatives are included, but are not limited thereto. . Of these, PVA having a high degree of saponification and a high degree of polymerization is preferable because it has good heat resistance. That is, the saponification degree is preferably 95 mol% or more, more preferably 99 mol%.
It is preferably a mol% or more, particularly 99.5 mol% or more, and a polymerization degree of 1000 or more, preferably 1000 to 5000.

In order to produce the stretched polyvinyl alcohol resin film of the present invention, an aqueous solution prepared by mixing the above polyvinyl alcohol resin with a boron compound such as boric acid or borax is used. The content of the boron compound such as boric acid or borax in the aqueous solution is preferably 0.01 to 15% by weight, more preferably 0.05 to 1% by weight. If it is less than 0.01% by weight, the heat resistance will decrease, while 1
If it exceeds 5% by weight, the film-forming property deteriorates. The content of the polyvinyl alcohol resin is preferably 1 to 20% by weight, more preferably 5 to 20% by weight. The boron compound is 0.01 to 5 with respect to the polyvinyl alcohol resin.
Used in a weight percentage.

The pH of the aqueous solution is preferably 4 or higher, more preferably 7 or higher. In adjusting the pH at this time, it is preferable to add sodium hydroxide within a limit of 15% by weight. If the pH of the aqueous solution is too low, the effect of adding the boron compound cannot be sufficiently exhibited, which is not preferable. Further, known additives such as an ultraviolet absorber and various stabilizers may be added to the aqueous solution, if necessary. The aqueous solution is formed into a film by a known method such as a casting method or an extrusion method.

The present invention is most characterized in that the film formed as described above is dipped in an acidic aqueous solution, and a film excellent in optical properties, and further in durability such as heat resistance and moisture resistance is obtained by this dipping treatment. You can get it. That is, the film contains an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, boric acid, phosphoric acid and the like, and a metal salt such as sodium salt, potassium salt, magnesium salt, etc., and an acidic aqueous solution having a pH of 6 or less, preferably 5 or less. To be immersed in. The immersion treatment is preferably performed in an atmosphere of 50 ° C. for about 1 to 20 minutes. Next, the film subjected to the dipping treatment is subjected to a known stretching treatment to become a polyvinyl alcohol resin stretched film.

As an example of the stretching method, a uniaxial stretching method is adopted for use as a film for retardation film.
It is stretched to about 4 times. For the stretching operation, first, the film subjected to the immersion treatment is preheated at a temperature of 120 to 200 ° C. for 30 seconds to 5 minutes, and subsequently 150 to 230 ° C., preferably 170 to 230 ° C.
Stretching is performed at 200 ° C. to about 1.1 to 4 times. Finally, heat setting is performed for 1 to 5 minutes at a temperature of not higher than the stretching temperature to 130 ° C. Water resistance treatment can be performed at any of the above stages, if necessary. The film thus obtained has a thickness of 30 to 100.
It has a retardation value of 100 to 700 in terms of physical properties.
It is about nm.

In order to obtain a retardation film having a constant optical principal axis and a small number of optical color spots, the original film or sheet is required to have a good thickness accuracy and be as optically as uniform as possible. preferable. It is not preferable that die lines or the like be generated during film formation. In order to obtain a retardation film having an optically small color spot in the present invention, a neck-in ratio (100 × (A−B) / A defined by a film width A before stretching and a film width B after stretching. ) Is preferably suppressed to 20% or less. The uniaxially stretching method includes, for example, preheating the film by passing the film between a large number of rolls, then stretching the film at a predetermined ratio with two pairs of stretching rolls, and passing the film between a large number of rolls. While performing preheating and stepwise stretching concurrently during the heating, methods such as a method of obtaining a predetermined draw ratio and a lateral 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 film. That is, the retardation value means the difference between the refractive index difference (II _MD- II _TD ) and the thickness (d) of the retardation film or sheet in the main stretching direction (MD direction) and the direction perpendicular to this (TD direction). The retardation value (R value), which is defined by the product and means the phase difference of transmitted light when linearly polarized light having an orthogonal relationship is incident in the same phase, is, for example, 1/4 of the wavelength (λ) of the used light beam. When a stretching process is performed so that a 1/4 wavelength plate is obtained, and when a stretching process is performed so that the value becomes 1/2, a 1/2 wavelength plate is obtained. Becomes When the light used is visible light, the retardation value as a 1/4 wavelength plate is 95-1.
The range is 70 nm. Therefore, by combining a 1/4 wavelength plate and a linear polarizer in this range, accurate circularly polarized light in a certain visible light can be obtained.

The uniaxial stretching method is also used for polarizing film applications, and iodine dyeing is added in any step to form a polarizing film. That is, the acid-treated film is stretched and dyed with iodine, stretched and dyed simultaneously, or stretched after iodine dyeing. Whichever means is used, it is necessary to stretch, and it is preferable to perform uniaxial stretching of 4 times or more, preferably 6 times or more in the uniaxial direction. The temperature conditions during stretching are
It is preferable to select from 50 to 130 ° C. In order to carry out such stretching, roll stretching, tenter stretching and the like similar to those for the retardation film are optionally carried out, but roll stretching is usually carried out.

The film is dyed with iodine, that is, the adsorption of the polarizing element is carried out by bringing the film into contact with a liquid containing the polarizing element. Usually, an iodine-potassium iodide aqueous solution is used, and the concentration of iodine is 0.1 to 2
g / l, the concentration of potassium iodide is 10 to 50 g / l, and the weight ratio of iodine / potassium iodide is 20 to 100. The dyeing time is practically about 30 to 500 seconds, and a small amount of an organic solvent compatible with water may be contained in addition to the water solvent. As the contact means, immersion is preferable, but any means such as coating and spraying can be adopted.

In both the retardation film and the polarizing film, the stretched and dyed film is then treated with a boron compound when further durability is required. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.5 to 2 mol / l, and it is practically desirable to allow a small amount of potassium iodide to coexist in the solution. A dipping method is desirable as the treatment method,
Of course, a coating method and a spraying method can also be implemented. The treatment temperature is preferably 50 to 70 ° C., and the treatment time is preferably 5 to 20 minutes.
If necessary, a stretching operation may be carried out during the treatment or after the treatment.

The retardation film or polarizing film thus obtained is used by laminating a protective film having excellent optical transparency and mechanical strength on both sides or one side with an adhesive and drying. To be done. As such a protective film, cellulose triacetate, cellulose-based films such as cellulose diacetate, polycarbonate-based films, polymethylmethacrylate-based films, polystyrene-based films, polyester-based films such as polyethylene terephthalate,
Examples of the adhesive include polysulfone-based films, and urethane-based, acrylic-based, and epoxy-based adhesives are often used. The polyvinyl alcohol-based resin stretched film of the present invention is very useful in the optical field such as retardation film / polarizing film applications as described above, but in addition to such applications, various packaging films including food applications It can be used for applications.

[0016]

The polyvinyl alcohol-based resin stretched film of the present invention is subjected to a specific acid treatment at the time of film production, so that it is possible to obtain a film having excellent optical properties and further durability such as heat resistance and moisture resistance. , It is very useful in the optical field such as retardation film and polarizing plate film.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, "parts" and "%" are based on weight unless otherwise specified. Example 1 Polyvinyl alcohol resin having an average degree of polymerization of 1700 and an average saponification degree of 99.5 mol%, boric acid and sodium hydroxide in an amount of 2% by weight, 1.7% by weight and 1.6% by weight, respectively.
Was dissolved in water to prepare an aqueous solution. The pH of the aqueous solution at this time was 11.5 (20 ° C.). Next, the aqueous solution is treated with PET (polyethylene terephthalate).
After casting on a film, it was dried to obtain a film having a thickness of 75 μm. 1% by weight of sulfuric acid and 30% of sodium sulfate
It was dipped in an acidic aqueous solution of pH 3.3 containing 5% by weight at 55 ° C. for 5 minutes to obtain an unstretched film having a thickness of 75 μm and a water content of about 15% by weight after drying. The film was uniaxially stretched under the following conditions by a tenter method to obtain a uniaxially stretched film having a thickness of 72 μm. -Preheating step: 180 ° C, 2 minutes-Stretching step: 190 ° C, 1.12 times stretching-Heat setting step: 150 ° C, 2 minutes

(Phase difference characteristics) The R value of the obtained uniaxially stretched film was measured by a compensation method using a polarizing microscope (Nikon POH-1 type) equipped with a Babinet type compensator (light source was white light) and found to be 390 nm. there were. In addition, the cellulose triacetate film was adhered to both sides of the above retardation film using a polyvinyl alcohol-based resin adhesive, and the retardation plate was obtained by bonding it to glass using an acrylic adhesive (total thickness). Is 170 μ). This retarder is 40 ℃ × 9
When left for 750 hours under the condition of 5% RH (Case I)
And the R value when left to stand in a dryer at 70 ° C. for 750 hours (Case II).

Example 2 Polyvinyl alcohol resin having an average degree of polymerization of 3000 and an average saponification degree of 99.5 mol%, boric acid and potassium hydroxide were adjusted to 5% by weight, 3% by weight and 2.2% by weight, respectively. Was dissolved in water to prepare an aqueous solution. The pH of the aqueous solution at this time was 12.2 (20 ° C.). Then, the aqueous solution is cast on a PET film and then dried to a film thickness of 75.
A film of μ was obtained. The film was immersed in an acidic aqueous solution of pH 3.0 containing 1% by weight of hydrochloric acid and 30% by weight of sodium chloride at 55 ° C. for 3 minutes, and dried to obtain an unstretched film having a thickness of 75 μ and a water content of about 15% by weight. The film was uniaxially stretched by the tenter method under the following conditions to obtain a uniaxially stretched film having a thickness of 72 μm. -Preheating step: 180 ° C, 2 minutes-Stretching step: 190 ° C, 1.15 times stretching-Heat setting step: 150 ° C, 2 seconds

(Retardation property) The R value of the obtained uniaxially stretched film was measured by a compensation method using a polarizing microscope (Nikon POH-1 type) equipped with a Babinet type compensator (light source was white light) and found to be 390 nm. there were. In addition, the cellulose triacetate film was adhered to both sides of the above retardation film using a polyvinyl alcohol-based resin adhesive, and the retardation plate was obtained by bonding it to glass using an acrylic adhesive (total thickness). Is 170 μ). This retarder is 40 ℃ × 9
When left for 750 hours under the condition of 5% RH (Case I)
And the R value when left to stand in a dryer at 70 ° C. for 750 hours (Case II).

Example 3 Polyvinyl alcohol resin having an average degree of polymerization of 1700 and an average degree of saponification of 99.9 mol%, boric acid and sodium hydroxide in amounts of 2% by weight, 1.7% by weight and 1% by weight, respectively. Was dissolved in water to prepare an aqueous solution. At this time, the pH of the aqueous solution was 11.7 (20 ° C.). next,
The aqueous solution was cast on a PET film and then dried to a film thickness of 7
A film of 5μ was obtained. The film was immersed in an acidic aqueous solution of pH 3.3 containing 1% by weight of sulfuric acid and 30% by weight of sodium sulfate at 55 ° C. for 5 minutes to obtain an unstretched film having a thickness of 75 μm and a water content of about 15% by weight after drying.

(Polarizing property) The film was mounted on a chuck, dipped in an aqueous solution containing 0.2 g / l of iodine and 60 g / l of potassium iodide at 30 ° C. for 4 minutes, and then 70 g of boric acid.
/ L, potassium iodide 30 g / l, and a boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching 6.0 times. A polarizing plate was obtained by laminating a cellulose triacetate film having a thickness of 80 μm on both surfaces of the film using a polyvinyl alcohol-based adhesive. The obtained polarizing plate was bonded to a glass plate having a thickness of 1 mm via an adhesive sheet to prepare a measurement sample, and the single-body transmittance and the polarization degree were measured. Further, the single-body transmittance and the polarization degree were measured after standing for 10 days in an atmosphere of relative humidity of 90% and 60 ° C.

Example 4 Polyvinyl alcohol resin having an average degree of polymerization of 4000 and an average saponification degree of 99.5 mol%, boric acid and potassium hydroxide were adjusted to 2% by weight, 1.7% by weight and 1% by weight, respectively. Was dissolved in water to prepare an aqueous solution. At this time, the pH of the aqueous solution was 11.7 (20 ° C.). Then, the aqueous solution is cast on a PET film and then dried to a film thickness of 75.
A film of μ was obtained. The film was dipped in an acidic aqueous solution of pH 3.1 containing 1% by weight of hydrochloric acid and 20% by weight of potassium chloride at 55 ° C. for 5 minutes, dried to a thickness of 75 μ, and a water content of about 1
An unstretched film of 5% by weight was obtained.

(Polarizing property) The film was mounted on a chuck, immersed in an aqueous solution containing 0.2 g / l of iodine and 60 g / l of potassium iodide at 30 ° C. for 4 minutes, and then 70 g of boric acid.
/ L, potassium iodide 30 g / l, and a boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching 6.0 times. A polarizing plate was obtained by laminating a cellulose triacetate film having a thickness of 80 μm on both surfaces of the film using a polyvinyl alcohol-based adhesive. The obtained polarizing plate was bonded to a glass plate having a thickness of 1 mm via an adhesive sheet to prepare a measurement sample, and the single-body transmittance and the polarization degree were measured. Further, the single-body transmittance and the polarization degree were measured after standing for 10 days in an atmosphere of relative humidity of 90% and 60 ° C.

Comparative Examples 1 to 4 In each of Examples 1 to 4, the retardation characteristics or the polarization characteristics were measured in the same manner except that the immersion treatment was not performed in the acidic aqueous solution. Table 3 shows the measurement results of Examples and Comparative Examples.

[0026]

[Table 1] Polyvinyl alcohol-based resin aqueous solution cast film PVA-based resin Boron compound Alkaline pH Thickness P Sv amount Amount (μ) Example 1 1700 99.5 2.0 Boric acid 1.7 NaOH 1.6 11.5 75 〃 2 3000 99.5 5.0 Boric acid 3.0 KOH 2.2 12.2 75 〃 3 1700 99.9 2.0 Boric acid 1.7 NaOH 1.0 11.7 75 〃 4 4000 99.5 2.0 Boric acid 1.7 KOH 1.0 11.7 75 Comparative Example 1 1700 99.5 2.0 Boric acid 1.7 NaOH 1.6 11.5 75 〃 2 3000 99.5 5.0 Boric acid 3.0 KOH 2.2 12.2 75 〃 3 1700 99.9 2.0 Boric acid 1.7 NaOH 1.0 11.7 75 〃 4 4000 99.5 2.0 Boric acid 1.7 KOH 1.0 11.7 75 Note) PVA; polyvinyl alcohol P; average degree of polymerization Sv; saponification degree (mol%) amount; included All quantities are in weight percent.

[0027]

[Table 2]Acidic aqueous solution Unstretched film acid Metal salt pH thickness Moisture content Quantity Quantity (μ) (%) Example 1 Sulfuric acid 1.0 Sodium sulfate 30 3.3 75 15 〃 2 Hydrochloric acid 1.0 Potassium hydrochloric acid 30 3.0 75 15 〃 3 Sulfuric acid 1.0 Sodium sulfate 30 3.3 75 15〃 4 hydrochloric acid 1.0 potassium chloride 20 3.1 75 15 Comparative Example 1 No acid immersion treatment 〃 2 No acid immersion treatment 〃 3 No acid immersion treatment〃 4 without acid dipping  Note) Amount; All contents are in weight percent.

[0028]

[Table 3] Phase difference characteristics * Polarization characteristics ** (Case I) (Case II) Transmittance (%) Polarization degree (%) Example 1 382 396 --- --- 〃 2 383 395 ---- -〃 3 --- --- 40.1 / 42.8 99.9 / 99.7 〃 4 --- --- 43.2 / 44.0 99.9 / 99.8 Comparative example 1 375 402 --- --- 〃 2 376 399 --- --- 〃 3 --- --- 40.1 / *** 99.9 / *** 〃 4 --- --- 43.2 / *** 99.9 / *** *; Represents each R value, the unit is nm . **: Each value represents before / after moisture resistance treatment. ***: Decolorization was observed and measurement was not possible.

[0029]

EFFECTS OF THE INVENTION The stretched film of polyvinyl alcohol resin of the present invention is subjected to a specific acid treatment during the production of the film, so that a film having excellent optical properties and further durability such as heat resistance and moisture resistance can be obtained. Therefore, it is very useful in the optical field such as a film for retardation plate and polarizing plate.

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[Procedure amendment]

[Submission date] May 10, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

As an example of the stretching method, a uniaxial stretching method is adopted for use as a film for retardation film.
It is stretched to about 4 times. For the stretching operation, first, the film subjected to the immersion treatment is preheated at a temperature of 120 to 200 ° C. for 30 seconds to 5 minutes, and subsequently 150 to 230 ° C., preferably 170 to 230 ° C.
Stretching is performed at 200 ° C. to about 1.1 to 4 times. Finally, heat setting is performed for 1 to 5 minutes at a temperature of not higher than the stretching temperature to 130 ° C. Water resistance treatment can be performed at any of the above stages, if necessary. The film thus obtained has a thickness of 30 to 100.
It has a retardation value of 10 to 700 n in terms of physical properties.
It is about m .

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

The retardation film or polarizing film thus obtained is used by laminating a protective film having excellent optical transparency and mechanical strength on both sides or one side with an adhesive and drying. To be done. As such a protective film, cellulose triacetate, cellulose-based films such as cellulose diacetate, polycarbonate-based films, polymethylmethacrylate-based films, polystyrene-based films, polyester-based films such as polyethylene terephthalate,
Examples thereof include polysulfone-based films, and as adhesives, urethane-based, acrylic-based, epoxy-based , and water-soluble adhesives are often used. The polyvinyl alcohol-based resin stretched film of the present invention is very useful in the optical field such as retardation film / polarizing film applications as described above, but in addition to such applications, various packaging films including food applications It can be used for applications.

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Claims (6)

[Claims] 1. A stretched polyvinyl alcohol-based resin film, comprising a polyvinyl alcohol-based resin film formed from an aqueous solution of a boron compound-containing polyvinyl alcohol-based resin, immersed in an acidic aqueous solution, and stretched. 2. The polyvinyl alcohol resin stretched film according to claim 1, wherein the aqueous solution of the boron compound-containing polyvinyl alcohol resin has a pH ≧ 4. 3. The stretched polyvinyl alcohol resin film according to claim 1, wherein the acidic aqueous solution has a pH ≦ 6. 4. The polyvinyl alcohol resin stretched film according to claim 1, wherein the acidic aqueous solution comprises an inorganic acid and a metal salt thereof. 5. The stretched polyvinyl alcohol resin film according to any one of claims 1 to 4, wherein the stretched polyvinyl alcohol resin film is a film for retardation plate. 6. The stretched polyvinyl alcohol resin film according to any one of claims 1 to 4, wherein the stretched polyvinyl alcohol resin film is a polarizing film that has been subjected to an iodine dyeing treatment.