JP2010065085A - Method for producing polyvinyl alcohol film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively producing a high-quality film comprising PVA resin and an inorganic salt. <P>SOLUTION: The method for producing the polyvinyl alcohol film includes thermofusion molding of a blend comprising 100 pts.wt. of polyvinyl alcohol resin and 55-145 pts.wt. of an inorganic salt hydrate by using a die adjusted to a temperature of 100-150°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polyvinyl alcohol film. More specifically, the present invention relates to a method for producing a polyvinyl alcohol film in which an inorganic salt hydrate is blended in a polyvinyl alcohol resin and hot melt molded.

  A film made of polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) is excellent in film forming property, transparency, strength, and the like, and thus is widely used taking advantage of its properties.

  Furthermore, attempts have been made to improve various physical properties by adding various additives to PVA. For example, Patent Document 1 describes that a water-soluble polymer molding material such as a film is obtained by mixing a water-soluble polymer such as PVA with an aqueous solution containing an inorganic salt such as magnesium nitrate. Patent Document 2 describes that PVA is added to an aqueous solution containing a salt such as sodium chloride and molded to obtain a PVA molded body such as a film. Furthermore, as a method for producing such a PVA film containing an inorganic salt, Patent Document 3 discloses that a transparent and elastic film is dried after adding a water-soluble inorganic salt to a PVA aqueous solution under specific conditions. Etc. are described.

  In these documents, when producing a PVA film, first a film-forming stock solution is prepared. At this stage, it is necessary to dissolve at a high temperature (100 ° C.) or to dissolve for a long time in order to prepare a uniform film-forming solution having no undissolved material. Further, the obtained film is dried for a long time. There is a need. As a result, although the obtained film had excellent physical properties, it was difficult to produce the film industrially and inexpensively.

Japanese Patent Laid-Open No. 61-115936 International Publication WO01 / 068746 Pamphlet JP 2004-149694 A

  Then, the objective of this invention is providing the method of manufacturing the high quality film which consists of PVA resin and inorganic salt at low cost.

  As a result of intensive studies to achieve the above object, the present inventors have adjusted a blend of 100 parts by weight of PVA resin and 55 to 145 parts by weight of inorganic salt hydrate to a temperature of 100 to 150 ° C. The present invention has been completed by reaching a method for producing a PVA film characterized by hot-melt molding using a die obtained.

  In this case, it is preferable that the blend is formed into a pellet using an extruder and then the pellet is subjected to hot melt molding.

  The inorganic salt hydrate used in the present invention is preferably magnesium nitrate hexahydrate.

  The polymerization degree of the PVA resin is preferably 500 to 3000, and the saponification degree is preferably 85.0 mol% or more.

  According to the method of the present invention, a film comprising a PVA resin and an inorganic salt can be produced industrially and inexpensively without drying water.

The present invention is described in detail below.
The PVA resin used in the present invention can be produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like. Among these, vinyl acetate is preferably used from the viewpoints of availability, ease of production of PVA resin, cost, and the like.

  The PVA resin is not limited to a saponified vinyl ester homopolymer, and a copolymer of vinyl ester and a small amount of other copolymerizable monomers as long as the effects of the present invention are not impaired. A saponified product, polyvinyl acetal in which a part of hydroxyl groups of the PVA resin are crosslinked, and the like can also be used.

  Here, as another copolymerizable monomer that can be used for copolymerization with a vinyl ester, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (Meth) acrylic acid and salts thereof; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, ( (Meth) acrylates such as i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate ; (Meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylami , (Meth) acrylamide derivatives such as diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid and salts thereof, (meth) acrylamide propyldimethylamine and salts thereof, N-methylol (meth) acrylamide; N-vinylformamide, N -N-vinylamides such as vinylacetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl Vinyl ethers such as vinyl ether; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl chloride, vinylidene chloride, vinyl fluoride, vinyl fluoride Allyl compounds such as allyl acetate and allyl chloride; maleic acid, its salts and esters; itaconic acid, its salts and esters; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; Saturated sulfonic acid etc. can be mentioned. These copolymerizable monomers can be used alone or in combination of two or more.

  Examples of the polyvinyl acetal in which a part of the hydroxyl group of the PVA resin is crosslinked include polyvinyl acetal in which a part of the hydroxyl group of the PVA resin is crosslinked with aldehydes such as formaldehyde, butyraldehyde, and benzaldehyde.

  The degree of polymerization of the PVA resin used in the present invention is preferably 500 to 3000 from the viewpoint of the mechanical properties of the film. There is a possibility that the melt viscosity of PVA becomes high and the hot melt moldability becomes poor. On the other hand, if the polymerization degree of the PVA resin is less than 500, the film may become brittle. The polymerization degree of the PVA resin is more preferably 700 to 2500, and even more preferably 1000 to 2000. In addition, the polymerization degree of PVA resin as used in this specification means the polymerization degree measured according to JIS K 6726.

  The degree of saponification of the PVA resin is preferably 85 mol% or more, more preferably 90 mol% or more, and even more preferably 97 mol% or more, from the viewpoint of improving the moldability of the resulting PVA film. 98 mol% or more is the most preferable. When the degree of saponification of PVA is less than 85 mol%, the affinity with water is increased, the adhesiveness of the PVA film is increased, and the PVA film is continuously produced industrially by a hot melt molding method. There is a risk that it will not be possible. The saponification degree of the PVA resin is actually the total number of moles of units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification among the structural units constituting the polymer. The ratio (mol%) of the unit saponified into the vinyl alcohol unit. The degree of saponification of the PVA resin can be measured according to the method described in JIS K 6726.

  The inorganic salt hydrate used in the present invention is not particularly limited. For example, a halide, nitrate, nitrite, carbonate, borate, sulfate, phosphate, monohydrogen phosphate, dihydrogen Examples of the cationic species corresponding to these anionic species include calcium and magnesium. Specific examples of inorganic salt hydrates include calcium chloride dihydrate, magnesium chloride hexahydrate, magnesium nitrate hexahydrate, and the like. These inorganic salt hydrates can be used alone or in combination of two or more. Among the inorganic salt hydrates, magnesium nitrate hexahydrate is particularly preferable in terms of transparency and cost.

  It is important that the inorganic salt hydrate is blended in an amount of 55 to 145 parts by weight with respect to 100 parts by weight of the PVA resin, preferably 60 to 120 parts by weight, and more preferably 70 to 100 parts by weight. When the blending amount of the inorganic salt hydrate is less than 55 parts by weight, the melt viscosity becomes high and the heat meltability becomes poor. Moreover, when the compounding quantity of an inorganic salt hydrate exceeds 145 weight part, it will become easy to color, and adhesiveness will become high too much and will cause a melt molding defect.

  In the method for producing a PVA film of the present invention, a blend comprising a PVA resin and an inorganic salt hydrate is hot-melt molded. In the case of producing a film from a conventional aqueous solution of PVA, it takes a very long time to dry water, so that only a film having a thickness of about 100 μm can be obtained industrially. In addition, the production speed is extremely slow, and a large amount of energy is required for drying. According to the production method of the present invention, it is possible to produce a film having a thickness of more than 100 μm, and further, it is possible to suppress the production cost because a drying step is unnecessary.

  In this case, it is important to add a considerable amount of inorganic salt hydrate to the PVA resin as described above in order to improve the hot melt moldability. Further, water may be further added to the blend composed of PVA resin and inorganic salt hydrate. A blend composed of PVA resin and inorganic salt hydrate can hold more water than PVA resin alone. For example, a blend of 100 parts by weight of PVA and 100 parts by weight of magnesium nitrate hexahydrate is about 1 to 26 parts by weight. Can hold water. Therefore, even if water is added in this range, a PVA film can be produced without drying later.

  In addition to the PVA resin and the inorganic salt hydrate, a plasticizer can be blended with the above blend. As the plasticizer, polyhydric alcohol is preferably used, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. These plasticizers can be used alone or in combination of two or more. Among these, it is particularly preferable to use glycerin from the viewpoints of volatility and plasticity.

  In addition, it is preferable to add a surfactant to the above blend for improving the handleability of the film. Of these, anionic or nonionic surfactants are preferred. As the anionic surfactant, sodium alkylbenzene sulfonate is particularly preferable, and as the nonionic surfactant, polyoxyethylene alkyl ether is particularly preferable.

  Moreover, you may mix | blend antioxidant, an antifreezing agent, pH adjuster, a concealing agent, a coloring inhibitor, an oil agent, an inorganic filler, etc. with said formulation as needed.

Next, an example of hot melt molding by an extrusion method will be described.
In order to blend the PVA resin, the inorganic salt hydrate, and other components, these components may be uniformly mixed with a mixer such as a mixer. The compound thus obtained may be directly subjected to melt molding, or the compound may be kneaded using a uniaxial or biaxial extruder or the like into a composition and pelletized. From the viewpoint of sufficiently mixing and from the viewpoint of stabilizing the quality of the obtained film, it is particularly preferable to knead the blend using a biaxial stretching machine to form a composition and pelletize. The kneading conditions at this time are not particularly limited, and the kneading temperature is generally in the range of 100 to 150 ° C.

In the melt molding, a blend containing all the above components or a pellet of the composition is supplied to another extruder, melt-kneaded, and extruded from a die connected to the extruder to be molded. The temperature of the die at this time needs to be adjusted to 100 to 150 ° C, preferably 100 to 140 ° C, and more preferably 110 to 130 ° C. When the temperature of the die is less than 100 ° C., unmelted material remains and a load is applied during extrusion. On the other hand, when the die temperature exceeds 150 ° C., the inorganic salt hydrate is decomposed and foamed, and a good PVA film cannot be obtained.
The thickness of the film thus obtained is 2 to 200 μm in view of industrial continuous production.

  The present invention will be specifically described below with reference to examples and the like, but the present invention is not limited to the following examples.

  80 parts by weight of magnesium nitrate hexahydrate was added to 100 parts by weight of PVA resin having an average degree of polymerization of 1700 and a saponification degree of 98.5 mol%, and these were put in a bag and mixed for 15 minutes. The resulting blend was melt-extruded using a 25φ twin-screw extruder (L / D = 25) at a die temperature of 115 ° C. to obtain a strand-shaped molded product. A pellet of a composition made of PVA resin and magnesium nitrate hexahydrate having a diameter of 3 mm was obtained from this molded article using a pelletizer. The pellets were supplied to a 20φ single-screw extruder (L / D = 20) provided with a die and melt extrusion was performed at a die temperature of 120 ° C. to obtain 10 m of a 1 mm thick film. When the obtained film was observed, no foaming or coloring was observed.

  The amount of magnesium nitrate hexahydrate mixed with the PVA resin is set to 60 parts by weight, the temperature of the die of the twin screw extruder into which the blend of PVA resin and magnesium nitrate hexahydrate is added is set to 130 ° C. A film was obtained in the same manner as in Example 1 except that the temperature of the die of the single screw extruder into which the pellets were charged was changed to 135 ° C. When the obtained film was observed, no foaming or coloring was observed.

  Except that the amount of magnesium nitrate hexahydrate mixed with the PVA resin was changed to 140 parts by weight, and the temperature of the die of the single screw extruder into which the pellets of the composition were charged was changed to 130 ° C., the same as in Example 1. To obtain a film. When the obtained film was observed, no foaming or coloring was observed.

  Except that the PVA resin to be used was changed to a PVA resin having an average polymerization degree of 500 and a saponification degree of 98.5 mol%, and the temperature of the die of the single screw extruder for introducing the pellets of the composition to 115 ° C. A film was obtained in the same manner as in 1. The obtained film was slightly brittle, but when observed, no foaming or coloring was observed.

  The temperature of the die of the twin screw extruder in which the mixture of PVA resin and magnesium nitrate hexahydrate is added to PVA resin having an average polymerization degree of 2400 and a saponification degree of 98.5 mol% is set to 130 ° C. A film was obtained in the same manner as in Example 1 except that the temperature of the die of the single screw extruder into which the pellets of the composition were charged was changed to 140 ° C. When the obtained film was observed, a slight coloration was observed, but there was no problem, and no foaming was observed.

  A film was obtained in the same manner as in Example 1 except that the temperature of the die of the single screw extruder into which the pellets of the composition were charged was changed to 145 ° C. When the obtained film was observed, a slight coloration was observed, but there was no problem, and no foaming was observed.

  Except that the PVA resin used is a PVA resin having an average polymerization degree of 1700 and a saponification degree of 87.8 mol%, and the temperature of the die of the single screw extruder for charging the composition pellets is changed to 130 ° C. A film was obtained in the same manner as in 1. The obtained film was slightly high in tackiness, but when observed, no foaming or coloring was observed.

Comparative Example 1
The amount of magnesium nitrate hexahydrate mixed with PVA resin was changed to 50 parts by weight, and the temperature of the die of the twin screw extruder into which the blend of PVA resin and magnesium nitrate hexahydrate was charged was changed to 135 ° C. Except for the above, melt extrusion was attempted in the same manner as in Example 1, but the melt had a high melt viscosity and could not be extruded.

Comparative Example 2
Example 1 except that the amount of magnesium nitrate hexahydrate mixed with PVA resin was changed to 150 parts by weight and the temperature of the die of the single screw extruder into which the pellets of the composition were charged was changed to 130 ° C. Attempts were made to melt-extrusion, but since the coloration of the melt was observed, the production of the film was abandoned.

Comparative Example 3
A film was obtained in the same manner as in Example 1 except that the temperature of the die of the single screw extruder into which the pellets of the composition were charged was changed to 90 ° C. When the obtained film was observed, an unmelted product was observed.

Comparative Example 4
100 parts by weight of PVA resin having an average degree of polymerization of 1700 and a degree of saponification of 98.5 mol% and 80 parts by weight of magnesium nitrate hexahydrate were dissolved in 500 parts by weight of water, and the resulting aqueous solution was dissolved in 50 cm square polytetrafluoroethylene. The film was poured into a mold and dried in an environment of 20 ° C. and 40% RH to obtain a film. It took 5 days to finish the drying, and during that time, the molds had to be always placed horizontally, making industrial production difficult.

  The above results are summarized in Table 1.

  According to the present invention, a high-quality film comprising a PVA resin and an inorganic salt can be produced at a low cost.

Claims (5)

Production of a polyvinyl alcohol film, characterized in that a composition comprising 100 parts by weight of a polyvinyl alcohol resin and 55 to 145 parts by weight of an inorganic salt hydrate is hot melt molded using a die adjusted to a temperature of 100 to 150 ° C. Method. The method for producing a polyvinyl alcohol film according to claim 1, wherein the compound is pelletized using an extruder, and then the pellet is hot-melt molded. The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein the inorganic salt hydrate is magnesium nitrate hexahydrate. The manufacturing method of the polyvinyl alcohol film of any one of Claims 1-3 whose polymerization degree of the said polyvinyl alcohol resin is 500-3000. The manufacturing method of the polyvinyl alcohol film of any one of Claims 1-4 whose saponification degree of the said polyvinyl alcohol resin is 85.0 mol% or more.