JPH0611796B2 - Polyvinyl alcohol molding and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) molded product and a method for producing the same, and in particular, a mat-shaped product composed of a single crystal aggregate of PVA. The present invention relates to a PVA molded product having a high strength and a high elastic modulus, which is suitable for use as an industrial material by stretching a product. As will be understood later, the molded article of the present invention means a linear article, a tape article, and a film article.

<Prior Art> Conventionally, PVA fibers have higher strength and elastic modulus than fibers of polyamide, polyester, polyacrylonitrile, etc., and have been used as a reinforcing material for industrial materials and cement. No high strength and high modulus fiber represented by aramid) fiber or ultra high molecular weight polyethylene fiber was obtained.

Various methods have been proposed to improve the strength and elastic modulus of PVA fibers. For example, a method of wet spinning using dimethyl sulfoxide as a solvent in an organic solvent such as methanol as disclosed in JP-B-43-16675, and adding boric acid to a spinning dope as disclosed in JP-B-37-14422 or JP-B-47-32142. Methods such as these are known, but these have a PVA fiber strength of 1 gigapascal (GPa) or less and an elastic modulus of 30 G.
It was below Pa. Meanwhile, JP-A-60-126312 and JP-A-5
No. 9-130314 describes a method for producing a PVA fiber having a strength of 1.5 GPa or more and a modulus of 40 GPa or more by gel spinning. However, even against this, there has been a demand for PVA fibers or molded products having higher performance than ultrahigh molecular weight polyethylene fibers and aramid fibers.

<Problems to be Solved by the Invention> In light of the above background, the present inventors have conducted extensive research to obtain even higher performance for PVA molded products. As a result P
Unlike the above-mentioned known technique in which a spinning dope having a VA concentration of several% or more is extruded from a nozzle and is made into fibers by a rapid cooling gel, a solution having a PVA concentration of less than 2% reduces the entanglement points of PVA molecular chains, and the single crystal aggregate is gradually cooled. It was found that when a mat-like product was obtained by precipitating the above, the mat-like product could be stretched at a high ratio, and thereby a PVA molded product having high strength and high elastic modulus could be obtained.

<Means for Solving Problems> That is, the present invention is "(1) a molded product obtained from a single crystal mat of polyvinyl alcohol, having a breaking strength of 1.2 Gpa or more,
A polyvinyl alcohol molded product having a tensile modulus of 30 Gpa or more.

(2) The polyvinyl alcohol molded product according to claim 1, having a strength of 1.8 gigapascal or more and an elastic modulus of 50 gigapascal or more.

(3) Polyvinyl alcohol having a viscosity average degree of polymerization of 1500 or more is heated and dissolved in a solvent so that the concentration becomes 2% by weight or less, and the obtained solution is gradually cooled to obtain a polyvinyl alcohol single crystal aggregate. A method for producing a polyvinyl alcohol molded product, which comprises depositing, followed by desolvation treatment to form a mat-like product, and stretching the mat-like product at least 15 times or more.

(4) The method for producing a polyvinyl alcohol molded product according to claim 3, wherein the viscosity average degree of polymerization is 5000 or more.

(5) The method for producing a polyvinyl alcohol molded product according to claim 3 or 4, wherein the solution has a polyvinyl alcohol concentration of 0.5% by weight or less.

(6) The method for producing a polyvinyl alcohol molded article according to any one of claims 3 to 5, wherein the mat-like material is stretched by extrusion stretching and tensile stretching.

(7) The method for producing a polyvinyl alcohol molded product according to any one of claims 3 to 6, wherein the mat-like material is stretched so that the total stretching ratio is 25 times or more. .

It is about.

The contents of the present invention will be described in more detail below.

The PVA polymer used in the present invention is a straight-chain polyvinyl having an average degree of polymerization of 1,500 or more determined by the following method in an aqueous solution at 30 ° C., a saponification degree of 99 mol% or more and a low branching degree. It is an alcohol polymer.

The polymer is obtained by copolymerizing 1 mol% or less of another vinyl compound, or 2 wt% or less of an antioxidant,
Those containing UV absorbers, pigments and other modifiers can improve other properties without substantially lowering the basic properties, and are included in the PVA polymer referred to in the present application.

As the PVA used, the higher the average degree of polymerization, the higher the possibility of obtaining a molded product having high strength and high elastic modulus.
It is 6,000 or more, more preferably 10,000 or more. Further, it is desirable that PVA be formed into a mat-like material in a state where the concentration of PVA in the solvent is lowered and the entanglement of molecular chains is reduced by crystallization.

Solvents for dissolving PVA include polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol and glycerin, dimethyl sulfoxide,
Any solvent can be used as long as it produces a single crystal, such as diethylformamide, diethylenetriamine, a mixed solvent of two or more kinds of these, or a mixed solvent of water or an alcohol and the above solvent, without any problem. However, in view of easiness of producing a single crystal mat, a polyhydric alcohol based poor solvent is preferable.

The heating dissolution is performed by stirring at a temperature near the boiling point of the solvent. It is preferable to add an antioxidant in order to prevent oxidative deterioration of PVA or to carry out the heating and melting in a stream of an inert gas such as nitrogen gas. Further, in order to completely eliminate the bubbles in the polymer, it is preferable to decompress-cool-thaw the mixed solution of PVA and the solvent, or to reduce the bubbles in the solution by depressurizing the mixture.

The PVA concentration is preferably 2% by weight or less, particularly 0.05 to 0.5
Weight percent is preferred. If the PVA concentration exceeds 2% by weight, the number of entanglements in the molecular chain increases and the draw ratio tends to decrease.

Next, a single crystal aggregate of PVA is precipitated from this heated dissolution solution. Examples of the crystallization method include cooling the solution to a temperature at which the solution is heated or below, or mixing the solution with a non-solvent for PVA, such as alcohols and ketones. Specific cooling of the solution can be carried out by cold crystallization in which the heated solution is cooled at a rate at which gel is not generated, or isothermal crystallization in which the solution is maintained at a constant temperature at which crystals can precipitate. Where to set the constant temperature for the isothermal crystallization is appropriately selected depending on the kind of the solvent, the concentration of the solution and the like. For example, in a 0.2 wt% ethylene glycol solution, the temperature is kept at about 80 ° C.

The obtained single crystal aggregate is filtered and then subjected to desolvation treatment (for example, solvent extraction treatment with alcohols, ketones or a mixture thereof with a solvent, solvent evaporation treatment, etc.) to obtain a mat-like form. And finally 1 solvent
It is used as a sample for stretching by adjusting the content to 0% by weight or less, preferably 1% by weight or less. When the residual amount of the solvent is large, the PVA tends to be colored and decomposed during the dry heat drawing, which will be described later.
It is difficult to obtain a VA molded product.

The mat-like material is composed of a single crystal aggregate of PVA and is in a unique crystalline state in which the entanglement of PVA molecules is released as much as possible, so that the stretchability is remarkably improved.

The stretching can be performed by a conventional method such as extrusion stretching and tensile stretching. However, in order to obtain a higher stretch ratio and performance, it is preferable to perform a two-stage stretching in which extrusion stretching is performed and then tensile stretching is performed. Examples of the extrusion stretching include solid phase extrusion and draft stretching with a roller.

For solid-phase extrusion, for example, a billet having a diameter of 10 mm and a length of 100 mm obtained by melt-molding high-density polyethylene or polypropylene having a normal molecular weight is divided into two in the longitudinal direction, and the above-mentioned divided billets are placed between the divided billets. The single crystal aggregate mat-shaped product is sandwiched between the solid-state extruder and a die (for example, inlet diameter 10 mm, die angle 2).
There is a method of coextrusion through 0 ° and an outlet diameter of 1.5 to 5.7 mm). In this case, the target extrudate can be easily separated from the extrudate of the split billet obtained at the same time.

Extrusion stretching of the single crystal aggregate mat-like material in the present invention,
The temperature is 30 to 200 ° C, preferably 130 to 170 ° C,
The extrusion ratio (stretch ratio) is 2 to 10, and the extrusion pressure is usually 500 to
It is preferably carried out at 3000 atm. Solid phase extrusion can be repeated twice or more. Usually, the target properties are not reached by this extrusion stretching alone, so the extrudate is re-stretched. Re-stretching of the extrudate can be carried out by a conventional method such as nip stretching or inter-roller stretching, but the nip stretching is preferable because it gives the molded product particularly excellent physical properties. This re-stretching may be performed in two or more stages.

The above stretching treatment may use any one or two or more of dry heat stretching in air or nitrogen or wet heat stretching in hot water or oil, but the final stretching is preferably dry heat stretching. The final stage dry heat drawing temperature is preferably 200 to 230 ° C., and PV
It is desirable to stretch as slowly as possible to a high magnification within the range in which the coloring and decomposition of A do not occur.

The total draw ratio (extrusion draw ratio x tensile draw ratio) is at least 15 times or more, preferably 25 times or more. If it is less than 15 times, it is difficult to obtain a PVA molded product having a breaking strength of 1.2 GPa or more and a tensile elastic modulus of 30 GPa or more.

As is clear from the above-mentioned production method, the high-polymerization degree PVA molded product of the present invention is a mat-like product formed from a single crystal aggregate by forming a single crystal in a state where the PVA molecular chain is small using a dilute solution of PVA. Stretched at high magnification, breaking strength is 1.2 GPa or more, especially 2.0 GPa or more, tensile elastic modulus is 30 GPa
It has physical properties of a or more, especially 50 GPa or more.

The present invention will be specifically described below with reference to examples.

Example 1 PVA having a viscosity average degree of polymerization of 6600 and a saponification degree of 99.9 mol% was added to ethylene glycol as a solvent in an amount of 0.2% by weight, and at the same time, an antioxidant was added in an amount of 0.5% by weight with respect to PVA to obtain 170 in a nitrogen gas stream. It was heated to ℃ and dissolved while stirring. The obtained solution having a PVA concentration of 0.2% by weight was allowed to stand in a constant temperature bath at 80 ° C. for about 15 hours for isothermal crystallization. After cooling to room temperature,
The precipitated crystals were filtered with filter paper to obtain a solution crystallized mat. This mat was immersed in methanol to remove most of the solvent, and then dried under reduced pressure at 80 ° C. to obtain a mat-like material having a solvent residual rate of 1.5% by weight and a thickness of 0.5 mm. The solvent residual rate was calculated by immersing the solvent in methanol three times and then changing the weight before and after drying under reduced pressure at 160 ° C. for 24 hours.

A film-like product having a width of 10 mm and a length of 100 mm is cut out from the mat-like product and divided billets (made of polypropylene, diameter 10
mm, length 100 mm billet divided into two in the vertical direction), inlet diameter 10 mm, die angle 20 °, outlet diameter
Extrusion temperature 160 ℃ Extrusion pressure 800 through 1.9mm die
An extrudate having a stretching ratio of 6 times was obtained at atmospheric pressure.

After separating the stretched PVA mat from the extrudate, a part of the stretched PVA mat was cut out, and both ends having a length of 10 mm were sandwiched between paper and sandpaper and fixed with an epoxy resin. This sample was fixed to a chuck of a stretching device (Tensilon HTM-100) and nip-stretched at 220 ° C. in a constant temperature air chamber at a crosshead speed of 1 cm / min to obtain a stretched molded product having a total stretching ratio of 30 times. The breaking strength of this stretched molded product is 2.1 GPa, and the tensile elastic modulus is 62 GPa.
Met. Tensilon HTM is used to measure the performance of stretch molded products.
-100 was used at room temperature with a sample length of 100 mm and an initial strain rate of 1 × 10 ⁻³ sec ⁻¹ .

Example 2 PVA having a viscosity average degree of polymerization of 3400 and a degree of saponification of 99.8 mol%
0.006 of antioxidant and 600 g of glycerin were added to 1.2 g, and the mixture was heated to 180 ° C. and dissolved with stirring. Next, the solution was allowed to stand at 120 ° C. for 24 hours for isothermal crystallization.

After cooling to room temperature, the precipitated crystals were filtered and washed with water and methanol for a long time to obtain a mat-like substance having a residual solvent amount of 4.6% by weight. This mat-like material is dried under reduced pressure at 120 ° C to form a molded product having a thickness of 0.7 mm, and then a film-like material having a width of 5 mm is cut out and fixed to a chuck of a manual stretching machine with an effective sample length of 10 mm, and dried with hot air at 180 ° C. It was stretched 9 times in the container at a pulling speed of about 5 cm / min.

Next, the same apparatus was used to draw at a draw rate of about 1 cm / min at a temperature of 230 ° C. for a further 2.5 times to obtain a stretch-formed product having a total draw ratio of 22.5 times. The breaking strength of this molded product is 1.6 GPa and the breaking elongation is 5.7.
The% tensile modulus was 45 GPa.

Example 3 A 0.1 wt% ethylene glycol solution was prepared using PVA having a viscosity average degree of polymerization of 11000, and solid phase coextrusion was carried out in the same manner as in Example 1 to obtain a stretched extrudate having a stretch ratio of 8 times.

Then, the polypropylene for billet was separated from the extrudate, and the PVA film was taken out. Then, the billet made of polypropylene was again sandwiched and solid phase coextrusion similar to that in Example 1 was carried out and stretched to 3.5 times. The obtained PVA film was cut to a length of 60 mm, fixed on a chuck of a manual stretching machine, and stretched 1.8 times at 237 ° C. under a nitrogen stream to obtain a stretched molded product having a total stretching ratio of 50.4 times.

This molded product had almost no coloration and had a breaking strength of 2.6 GPa and a tensile modulus of 74 GPa.

Example 4 PVA having a viscosity average degree of polymerization of 18,000 was dissolved in triethylene glycol at 220 ° C. to obtain a 0.1 wt% solution. Then, while slowly cooling in a silicon oil bath, the mixture was allowed to stand at 190 ° C. for 4 hours, 150 ° C. for 1 hour, and 100 ° C. for 1 hour.
After hours, it was brought to room temperature.

The obtained single crystal was filtered, washed with water and methanol, and dried to obtain a mat-like substance, and then solid-state coextrusion was performed at a draw ratio of 6 times in the same manner as in Example 1 to obtain a PVA extrudate.

Then, the resulting PVA extrudate was cut into a length of 10 mm, fixed on a chuck of a manual stretching machine, and stretched 6.4 times at a pulling speed of about 2 cm / min in a hot air dryer at 228 ° C.,
A stretched molded product having a total stretching ratio of 38.4 times was obtained. The breaking strength of this molded product was 2.2 GPa, and the tensile modulus was 61 GPa.

Comparative Example 1 PVA having a viscosity average degree of polymerization of 3400 and glycerin were put into a kneading extruder so that the PVA concentration was 70% by weight, and 200 ° C.
Was made into a solution and then discharged from a slit die having a width of 1 mm and a length of 10 mm to obtain a tape-shaped molded product. After removing most of glycerin from this molded product by extraction with methanol and drying under reduced pressure, it was manually stretched in hot air at 230 ° C., but the maximum stretch ratio was 12 times, the breaking strength was 0.6 GPa, and the tensile elastic modulus was as low as 21 GPa. It was a thing.

Claims (7)

[Claims] 1. A molded product obtained from a single crystal mat of polyvinyl alcohol, which has a breaking strength of 1.2 Gpa or more and a tensile modulus of 30 Gpa or more. 2. The strength is 1.8 Gpa or more and the elastic modulus is 5.
The polyvinyl alcohol molded product according to claim 1, which has a viscosity of 0 gigapascal or more. 3. Polyvinyl alcohol having a viscosity average degree of polymerization of 1500 or more is dissolved by heating in a solvent so that its concentration is 2% by weight or less, and the resulting solution is gradually cooled to obtain a single crystal aggregate of polyvinyl alcohol. A method for producing a polyvinyl alcohol molded product, which comprises: precipitating a body, followed by desolvation treatment to form a mat-like product, and stretching the mat-like product at least 15 times or more. 4. The method for producing a polyvinyl alcohol molded product according to claim 3, which has a viscosity average degree of polymerization of 5000 or more. 5. The method for producing a polyvinyl alcohol molded product according to claim 3 or 4, wherein the polyvinyl alcohol concentration of the solution is 0.5% by weight or less. 6. The method for producing a polyvinyl alcohol molded product according to any one of claims 3 to 5, wherein the mat-like material is stretched by extrusion stretching and tensile stretching. 7. The polyvinyl alcohol molded product according to any one of claims 3 to 6, wherein the mat-shaped product is stretched so that the total stretching ratio is 25 times or more. Production method.