JP2016050280A - Water soluble polyvinyl alcohol-based film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water soluble polyvinyl alcohol-based film which has high solubility in water, and furthermore requires a certain time of duration before being completely dissolved after contacting with water, and a method for producing the water soluble polyvinyl alcohol-based film.SOLUTION: The water soluble polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin is provided in which amount of a hydroxyl group is 40 mole% or more, a crystallinity index measured by X-ray diffraction is 19% or more, and a dissolution time, when the water soluble polyvinyl alcohol-based film is immersed in water at 23°C, is 3 hours or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a water-soluble polyvinyl alcohol film used for temporary substrates such as films for packaging pharmaceuticals such as agricultural chemicals and detergents, laundry bags, waste disposal products, nursery sheets, seed tapes, and embroidery base fabrics.

Conventionally, water-soluble films have been used for packaging of pharmaceuticals such as agricultural chemicals and detergents (unit packaging), laundry bags, waste disposal products, seedling sheets, seed tapes, temporary substrates such as embroidery base fabrics, etc. Yes.

In particular, for waste disposal products and seedling sheet / seed tape applications, only immediate solubility is not required, and it may take a certain time for the water-soluble film to dissolve after the water-soluble film comes into contact with moisture. Desired. In addition, in unit packaging applications, after putting a medicine packaged with functions such as sterilization and rust prevention treatment capacity into water and dissolving it over time, it can be dissolved in water tanks, pipes, etc. at desired positions. The drug can function.

Thus, as a method of suppressing the dissolution of the water-soluble film to a certain extent, there are a method of using a modified polyvinyl alcohol-based resin containing a hydrophobic group in the molecule or adding a certain amount of a hardly soluble resin.
For example, Patent Document 1 proposes a melt-molded product comprising a melt-moldable polyvinyl alcohol resin and a saponified ethylene-vinyl acetate copolymer.
Patent Document 2 discloses a melt-molded product comprising an oxyalkylene group-containing polyvinyl alcohol resin, a polyolefin resin modified with an unsaturated carboxylic acid or an anhydride thereof, and a polyamide resin. ing.
Furthermore, as another method for suppressing the dissolution of the water-soluble film to a certain degree, there is a method of covering one side or both sides of the water-soluble film with a hydrophobic material. For example, Patent Document 3 discloses that on the inner side of a water-soluble film, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene, polymethyl methacrylate, boriaacrylonitrile, butyral. Shown is a waste storage bag provided with a layer having a thickness of 0.1 to 10 μm of a hydrophobic material selected from a resin, an epoxy resin or an organosilane compound.

However, when using a modified polyvinyl alcohol resin containing a hydrophobic group in the molecule or adding a poorly soluble resin to produce a water-soluble film, a material with poor water solubility is used, so the resin is dissolved in water. There has been a problem that it is not possible to adopt the process of forming by molding. Therefore, the melt molding method will be adopted, but since it becomes a high-temperature process of 180 ° C or higher, the problem that the polyvinyl alcohol-based resin is discolored and the water-soluble film additive has heat resistance of 180 ° C or higher There was a problem of being limited to.
On the other hand, in the method of coating one or both surfaces of a water-soluble film with a hydrophobic material, it is possible to suppress discoloration of the polyvinyl alcohol resin by adopting a process of dissolving a normal polyvinyl alcohol resin in water. However, since a hydrophobic material is used, there is a problem that undissolved material is generated when dissolved in water. In addition, since a hydrophobic material is coated or laminated on a water-soluble film, the number of processes is increased, resulting in a high cost.

JP 2002-105269 A Japanese Patent No. 5177925 JITTO No. 2518203

In view of the present situation, the present invention is a water-soluble polyvinyl alcohol film that requires a certain amount of time to completely dissolve after being in contact with moisture while having high solubility in water, and the water-soluble polyvinyl alcohol film. An object is to provide a manufacturing method.

The present invention is a water-soluble polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin, wherein the polyvinyl alcohol-based resin has a hydroxyl amount of 40 mol% or more and a crystallinity of 19 measured by X-ray diffraction. It is a water-soluble polyvinyl alcohol film having a dissolution time of 3 hours or less when the water-soluble polyvinyl alcohol film is immersed in water at 23 ° C.
Hereinafter, the present invention will be described in detail.

The water-soluble polyvinyl alcohol film of the present invention contains a polyvinyl alcohol resin. The said polyvinyl alcohol-type resin becomes a main structural component of the water-soluble polyvinyl alcohol-type film of this invention.

The polyvinyl alcohol-based resin is obtained by polymerizing a vinyl ester according to a conventionally known method to obtain a polymer, and then saponifying, ie, hydrolyzing the polymer. In general, alkali or acid is used for saponification. An alkali is preferably used for saponification. As said polyvinyl alcohol, only 1 type may be used and 2 or more types may be used together.

Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate and vinyl benzoate. Of these, vinyl acetate is preferred.

The method for polymerizing the vinyl ester is not particularly limited. Examples of the polymerization method include a solution polymerization method, a bulk polymerization method, and a suspension polymerization method.

Examples of the polymerization catalyst used when polymerizing the vinyl ester include 2-ethylhexyl peroxydicarbonate (“TrigonoxEHP” manufactured by Tianjin McEIT), 2,2′-azobisisobutyronitrile (AIBN), t-butyl. Peroxyneodecanoate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propylperoxydicarbonate, di-n-butylperoxydicarbonate, di-cetylperoxydicarbonate and di-s-butylperoxy Examples include dicarbonate. As for the said polymerization catalyst, only 1 type may be used and 2 or more types may be used together.

Since the degree of saponification is easily controlled within a suitable range, the polymer obtained by polymerizing the vinyl ester is preferably a polyvinyl ester. The polymer obtained by polymerizing the vinyl ester may be a copolymer of the vinyl ester and another monomer. That is, the polyvinyl alcohol-based resin may be formed using a copolymer of vinyl ester and another monomer. Examples of the other monomers, that is, comonomers to be copolymerized, include olefins, (meth) acrylic acid and salts thereof, (meth) acrylic acid esters, (meth) acrylamide derivatives, N-vinylamides, vinyl ethers, and nitriles. , Vinyl halides, allyl compounds, maleic acid and salts thereof, maleic acid esters, itaconic acid and salts thereof, itaconic acid esters, vinylsilyl compounds, and isopropenyl acetate. As for the other monomer, only one kind may be used, or two or more kinds may be used in combination.

Examples of the olefins include ethylene, propylene, 1-butene and isobutene. Examples of the (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, and (meth) acrylic acid n-. Examples include butyl and 2-ethylhexyl (meth) acrylate. Examples of the (meth) acrylamide derivative include acrylamide, n-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, and (meth) acrylamidepropanesulfonic acid and salts thereof. Examples of the N-vinyl amides include N-vinyl pyrrolidone. Examples of the vinyl ethers include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl ether. Examples of the nitriles include (meth) acrylonitrile. Examples of the vinyl halides include vinyl chloride and vinylidene chloride. Examples of the allyl compound include allyl acetate and allyl chloride. Examples of the vinylsilyl compound include vinyltrimethoxysilane.

The polyvinyl alcohol-based resin may be subjected to a modification treatment by adding a predetermined functional group.
Although it does not specifically limit as a functional group provided as a result of the said modification | denaturation process, A formal group, an acetoacetal group, a butyral group, an amino group, an amide group, a carboxyl group, a sulfo group etc. are mentioned.

When the polyvinyl alcohol-based resin is a modified product, the modification amount is preferably 15 mol% or less, more preferably 5 mol% or less. That is, in a total of 100 mol% of the structural unit derived from the vinyl ester in the modified PVA and the structural unit derived from the other monomer, the structural unit derived from the vinyl ester is preferably 85 mol% or more, more preferably 95 mol%. The structural unit derived from the other monomer is preferably at most 15 mol%, more preferably at most 5 mol%.
In this specification, the polyvinyl alcohol-based resin includes modified polyvinyl alcohol (modified PVA). The water-soluble polyvinyl alcohol film includes a water-soluble modified polyvinyl alcohol (modified PVA) film obtained by forming a modified polyvinyl alcohol (modified PVA) into a film.

The polyvinyl alcohol resin has a hydroxyl group content of 40 mol% or more.
When the amount of the hydroxyl group is less than 40 mol%, water solubility is insufficient, and undissolved matter is generated even when dissolved in water. The amount of hydroxyl groups in the polyvinyl alcohol-based resin is preferably 70 mol% or more, and preferably 99.99 mol% or less.
In addition, when the said polyvinyl alcohol-type resin does not contain a modification group, the value of the said hydroxyl group can substitute the value of the saponification degree shown to a [0020] paragraph. Moreover, when the said polyvinyl alcohol resin contains a modified group, it can calculate by multiplying the value of saponification degree from the amount of remaining vinyl alcohol type components, after clarifying the amount of modified groups by NMR analysis.

The saponification degree of the polyvinyl alcohol resin is preferably 95 mol% or more. When the saponification degree is 95 mol% or more, the crystallization of the film easily proceeds and the dissolution time can be further increased. The saponification degree of the polyvinyl alcohol-based resin is more preferably 97 mol% or more, and preferably 99.99 mol% or less.

The saponification degree is measured according to JIS K6726. The saponification degree indicates the proportion of units that are actually saponified to vinyl alcohol units among the units converted to vinyl alcohol units by saponification.
The method for adjusting the saponification degree is not particularly limited. The degree of saponification can be appropriately adjusted according to the saponification conditions, that is, the hydrolysis conditions.

The degree of polymerization of the polyvinyl alcohol resin is not particularly limited. The polymerization degree of the polyvinyl alcohol-based resin is preferably 300 to 4000. When the degree of polymerization is within the above range, the strength as a film is maintained, and the film can be easily formed into a film shape. The degree of polymerization is more preferably 500-2700. The degree of polymerization is measured according to JIS K6726.

The polyvinyl alcohol resin has a crystallinity of 19% or more as measured by X-ray diffraction. By setting the crystallinity to 19% or more, the water-soluble film becomes difficult to dissolve, so that the dissolution time can be extended. The more preferable lower limit of the crystallinity is 21%, and the preferable upper limit is 40%.
In this specification, the degree of crystallinity is determined by separating the scattering peak derived from the crystalline substance detected by X-ray diffraction and the halo derived from the amorphous part by fitting, and calculating the intensity integral of each, It can obtain | require by calculating the ratio of the crystalline part.

In 100% by weight of the water-soluble polyvinyl alcohol film of the present invention, the content of the polyvinyl alcohol resin is preferably 60 to 97% by weight.
When the content of the polyvinyl alcohol-based resin is within the above range, both the mechanical strength necessary for the water-soluble film and the flexibility that makes it difficult to break before being immersed in water can be ensured.

The water-soluble polyvinyl alcohol-based film of the present invention includes a plasticizer, a surfactant, a preservative, a colorant, a fragrance, a bulking agent, a defoaming agent, a release agent, an ultraviolet absorber, a compatibilizing agent, and a lubricant as necessary. Ordinary additives such as inorganic powder may be added.

(Dissolution time measured by immersion method)
The water-soluble polyvinyl alcohol film of the present invention has a dissolution time of 3 hours or less when immersed in water at 23 ° C.
Since the dissolution time by the above immersion method is 3 hours or less, since the film does not remain in the aqueous solution, it can be suitably used as a unit packaging film or a laundry bag for chemicals having functions such as detergent and sterilization. It becomes.
The dissolution time by the above immersion method is preferably 30 minutes or less, and preferably 60 seconds or more.
In the present specification, the dissolution time by the dipping method means that after the film is cut into a 40 mm × 25 mm rectangle, the film is sandwiched between slide mounts and immersed in water kept at 23 ° C. without any flow due to stirring. , A method measured by measuring the time until the film is completely invisible visually.

(Dissolution time measured by slide mount method)
The water-soluble polyvinyl alcohol film of the present invention preferably has a dissolution time in water at 23 ° C. measured by a slide mount method of 20 seconds or longer.
The dissolution time of 20 seconds or more by the above slide mount method means that it takes a certain time until it completely dissolves after contact with moisture. It can be used suitably for a use.
The dissolution time by the slide mount method is more preferably 30 seconds or more, and preferably 5 minutes or less.
In this specification, the dissolution time by the slide mount method is specifically defined such that the film is cut into a rectangle of 40 mm × 25 mm and then sandwiched between the slide mounts so that the slide mounts are perpendicular to the flow direction. In this case, after the film swells and breaks, it is a value obtained by measuring the time until the film still attached is completely separated from the slide mount.

The thickness of the water-soluble polyvinyl alcohol film of the present invention is preferably 20 to 150 μm. When the thickness of the water-soluble polyvinyl alcohol film is within the above range, the film can be used without being broken before being immersed in water.

The water-soluble polyvinyl alcohol film of the present invention is suitably used for temporary substrates such as films for packaging pharmaceuticals such as agricultural chemicals and detergents, laundry bags, waste disposal products, nursery sheets, seed tapes and embroidery base fabrics. be able to.

The water-soluble polyvinyl alcohol film of the present invention includes, for example, a step (A) of mixing a water-soluble resin containing a polyvinyl alcohol resin having a hydroxyl group content of 40 mol% or more and a raw material composition containing water, the raw material composition A step (B) of extruding a product from a mold to form a sheet-like composition, and a step (C) for volatilizing water by bringing the sheet-like raw material composition into contact with a support and heating It is preferable that the sheet-like composition extruded from the mold is produced using a production method in which the time until contact with the support is 2 seconds or more. A method for producing such a water-soluble polyvinyl alcohol film is also one aspect of the present invention.

In the production method of the present invention, first, the step (A) of mixing a water-soluble resin containing a polyvinyl alcohol-based resin having a hydroxyl group content of 40 mol% or more and a raw material composition containing water is performed.

As the above-mentioned step (A) and the following step (B), a method of dissolving in a stirring vessel such as a tank while heating and then transporting it to a mold with a pump or the like, or a multi-screw extruder And a conventionally known method such as a method of transporting to a mold with a pump or the like and making it into a sheet-like composition, since it can be dissolved with a small amount of solvent. The method using is preferable.
As the multi-screw extruder, a twin-screw extruder or a twin-screw extruder may be used in addition to a twin-screw extruder, but a twin-screw extruder is preferably used from the viewpoint of cost.

When performing the said process (A), it is preferable to perform the process of throwing in the raw material composition containing water-soluble resin and water prior to that.
Examples of the method of charging the raw material composition include a method of charging from a raw material supply port installed in the barrel of the multi-screw extruder.
One place may be sufficient as the place which throws the said raw material composition into a multi-screw extruder, and two or more places may be sufficient as it. Moreover, the water-soluble resin and water may be added simultaneously or separately.

The step of mixing the raw material composition is preferably performed by rotating a screw installed inside the barrel of the multi-screw extruder.
Although it does not specifically limit as a structure of the screw of the said multi-screw extruder, It is preferable that the screw element of a full flight and a kneading disk is included at least.
The full flight has the ability to transport the raw material composition, and the kneading disc has the ability to mix and dissolve the raw material composition in a shorter time, thereby increasing the production rate. .

The shape of the water-soluble resin is not particularly limited, and a wet cake-like water-soluble resin containing pellets, powder, and water to be charged into a multi-screw extruder later may be used.

The raw material composition contains water in addition to the water-soluble resin.
Moreover, the said raw material composition may contain the other liquid in addition to water.

Examples of the other liquid include ethanol, methanol, propanol, isopropanol, acetone, methyl ethyl ketone, acetic acid, methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, glycerin, ethylene glycol, propylene glycol, butylene glycol, diglycerin, Examples include polyethylene glycol.
The other liquids may be used alone or in combination of two or more.

The raw material composition may further contain a conventionally known plasticizer, surfactant, and preservative.
Examples of the plasticizer include glycerin, diglycerin, triglycerin, polyglycerin, ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, trimethylolpropane, triethylene glycol, polyethylene glycol, polypropylene glycol, pentaerythritol, and mannitol. , Polyhydric alcohol plasticizers such as sorbitol, fructose and glucose, and mixtures thereof.

The raw material composition may contain a conventionally known surfactant. By including the surfactant, the film surface at the time of film formation can be smooth, and the peelability of the film containing liquid from the substrate can be improved.

The water-soluble resin content in the raw material composition is preferably 50 to 80% by weight.
When the content of the water-soluble resin is more than 80% by weight, the water-soluble resin is not sufficiently dissolved in water and a non-uniform film can be obtained, or the viscosity of the raw material composition is increased, so that the multiaxial extrusion is performed. The pressure inside the machine may rise too much, making it impossible to form a film. Further, when the content of the water-soluble resin is less than 50% by weight, the cost and efficiency of the step of removing the liquid may be deteriorated. Preferably it is 55 to 70% by weight.
The water-soluble resin content can be calculated from the amount of raw material composition charged into the multi-screw extruder per unit time.
Moreover, it is preferable that the water content in the said raw material composition is 20 to 45 weight%.

In the said process (A), it is preferable that the temperature at the time of mixing with a raw material composition shall be 80-120 degreeC.
In particular, in the production method of the present invention, in the step (A), it is preferable that the raw material composition is heated to 80 ° C. or higher and then cooled to 50 ° C. or lower. By performing such a cooling step, crystallization of the polyvinyl alcohol-based resin is promoted, and the dissolution time can be extended. The cooling step is more preferably 20 to 40 ° C.
In addition, the said cooling process can be performed by cooling a flow path by using a cooling adapter etc. in the flow path for the mixed raw material composition to advance to the next process, for example. Such a cooling adapter is preferably designed so that the average residence time of a normally used adapter raw material composition is 5 minutes or more.

Next, in the production method of the present invention, the step (B) of extruding the raw material composition from a mold to form a sheet-like composition is performed.

In the said process (B), it does not specifically limit as a kind of metal mold | die used, Conventionally well-known metal mold | dies, such as a circular die and a T die, can be used, A T die is especially preferable.

In the said process (B), it is preferable that the moisture content of the sheet-like composition in a metal mold exit is 20 to 50 weight%.
By making the water content of the sheet-like composition at the mold outlet 20% by weight or more, the solubility of the water-soluble resin in water increases, and a sheet-like composition is obtained without clogging in the mold. Can do. When the moisture content of the sheet-like composition at the mold outlet exceeds 50% by weight, the viscosity of the sheet-like composition extruded from the mold decreases, the neck-in amount increases, and the thickness is uniform in the width direction. A film cannot be obtained. In addition, it is preferable that the moisture content of the sheet-like composition in the said metal mold | die exit is 25 to 45 weight%.
The “moisture content of the sheet-like composition at the mold outlet” refers to the moisture content of the sheet-like raw material composition immediately after being extruded from the mold.

In the said process (B), it is preferable that the die clearance of the metal mold | die used is 50-2000 micrometers.
Moreover, it is preferable that the discharge speed | rate of the sheet-like raw material composition in a metal mold | die exit is 0.1-20 m / min.

In the present invention, next, the step (C) for volatilizing water by bringing the sheet-shaped raw material composition into contact with the support and heating it is performed. A water-soluble polyvinyl alcohol film can be obtained by drying and forming the sheet-shaped raw material composition extruded from the mold through the step (C).

The support may have a planar shape or a curved shape.
A roller is preferably used as the curved surface, and examples thereof include an iron roller, a casting roller, and a rubber roller.
The roller may be a single roller or a plurality of rollers.

In the said process (C), it is preferable that the rotational speed of a roller is 0.3-30 m / min.
Moreover, in the said process (C), it is preferable that the surface temperature of the said roller is 60 degreeC or more. When the surface temperature of the roller is less than 60 ° C., the sheet-like raw material composition immediately after being extruded from the mold is not sufficiently dried and is not uniformly peeled off from the casting roller. In addition, it is preferable that the surface temperature of the said roller is 60-100 degreeC.

In the production method of the present invention, the time until the sheet-like composition extruded from the mold comes into contact with the support surface is 2 seconds or more. When the time is less than 2 seconds, the sheet-like composition discharged from the mold is cooled by the outside air, and the crystallinity can be increased.
The time is preferably 2 to 60 seconds.
The time until the sheet-like composition extruded from the mold comes into contact with the support surface is the distance between the mold outlet and the support surface, the speed at which the sheet-like composition is extruded from the mold. It can be calculated by calculation based on the numerical values of the lip clearance, the moving speed of the support surface, and the film thickness when contacting the support surface.

In the production method of the present invention, the distance between the mold outlet and the support surface is preferably 10 to 600 mm. By setting it within the above-mentioned range, it is possible to secure time until contact with the support surface.
The distance between the mold outlet and the support surface can be determined by a linear distance between x and y, where x is the mold outlet and y is the contact point between the sheet-like composition and the support surface. it can.

By using the production method of the present invention, it is possible to increase the crystallinity of the polyvinyl alcohol-based resin. The required water-soluble polyvinyl alcohol film can be preferably produced.

According to the present invention, there is provided a water-soluble polyvinyl alcohol-based film that has a high solubility in water and requires a certain time until it is completely dissolved after being in contact with moisture, and a method for producing the water-soluble polyvinyl alcohol-based film. Can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
A polyvinyl alcohol resin (SELVOL 518, manufactured by SEKISUI SPECIALTY CHEMICALS) having a saponification degree of 88 mol% was charged at 7 kg / Hr from a raw material supply port (hopper). At the same time, water and glycerin were charged from two liquid inlets. From the liquid inlet a, water was supplied to the inside of the barrel 2 at 4.9 kg / Hr, and from the liquid inlet b, glycerin was supplied at 1.0 kg / Hr. The liquid was supplied at a position where water touched the resin before glycerin.
As the extruder, a twin-screw extruder was used, the screw rotation speed was 350 rpm, the barrel, adapter and mold set temperature was 90 ° C., and the raw material composition consisting of the raw resin and liquid was extruded from the mold. The mold had a discharge part width of 2400 mm and an opening degree of 300 μm.
In this case, the discharge speed from the mold is calculated by the formula of (total amount of raw material input [kg / Hr]) / (density of raw material mixture [t / m ³ ]) / (die opening area [m ² ]). Is required. Since the density of the raw material composition was 1.15 t / m ³ , in Example 1, the discharge speed was calculated to be 0.26 m / min by calculation.

Next, the raw material mixture extruded from the mold outlet is received by an iron roller having a diameter of 500 mm and a surface temperature of 25 ° C., rotated at 0.60 m / min to form a film, and then peeled off and dried in an oven at 90 ° C. A 75 μm film was obtained.
The distance (air gap) between the die outlet and the iron roller surface was 150 mm, and the required time was calculated. As a result, it was about 23 seconds.

(Examples 2-7, Comparative Examples 1-2)
As shown in Table 1, a film was obtained by using the same method as in Example 1 except that the raw material composition and the production conditions were changed. In Table 1, the numerical value of water concentration was calculated by dividing the amount of water added by the total amount of all raw materials (water-soluble resin, water, and glycerin) input.
In Examples 4 to 7, instead of polyvinyl alcohol resin having a saponification degree of 88 mol% (SELVOL 518, SEKISUI SPECIALTY CHEMICALS), saponification 99 mol% modified polyvinyl alcohol resin (acrylamidopropanesulfonic acid modified, modified amount 4 0.5 mol%) was used.
In Comparative Example 2, a polyvinyl alcohol resin (SELVOL325, SEKISUI SPECIALTY CHEMICALS) having a saponification degree of 99 mol% was used instead of the polyvinyl alcohol resin (SELVOL518, SEKISUI SPECIALTY CHEMICALS) having a saponification degree of 88 mol%.
In Example 7, a cooling adapter (tube diameter: 40 mm, length: 5 m) was installed between the extruder and the mold, and the adapter wall surface temperature was adjusted to 30 ° C. The resin temperature at the cooling adapter outlet was It was 40 ° C. The other adapters and the mold were set at a wall surface temperature of 90 ° C., and the film temperature immediately after being discharged from the mold was measured with an infrared thermometer.

<Evaluation>
The following evaluation was performed about the film obtained by the Example and the comparative example. The results are shown in Table 1.

(Crystallinity)
About the obtained film, the range of 2 (theta) / (theta) 10-60 degrees was scanned with the electric current of 45 kV and 200 mA using the X-ray-diffraction apparatus (the Rigaku make, SmartLab).
The obtained data was subjected to waveform separation into a crystalline component and an amorphous component with numerical analysis software (manufactured by Wavemetrics, IGOR Pro), and the crystallinity was calculated based on the following formula.
Crystallinity (%) = (Crystal component area) / (Crystal component area + Amorphous component area) × 100

(Dissolution time)
(1) Immersion method After the obtained film is cut into a 40 mm × 25 mm rectangle, it is sandwiched between slide mounts and immersed in water kept at 23 ° C. without any flow caused by stirring, and then the film is taken every minute. The appearance was observed and the time until the film was completely invisible was measured.

(2) Slide mount method 500 mL of water was put into a 600 mL beaker, the water temperature was adjusted to 23 ° C., and the mixture was stirred with a magnetic stirrer. The rotation speed was adjusted so that the lower end of the spiral generated at this time was in a 300 mL line.
The obtained film was cut into a 40 mm × 25 mm rectangle and then sandwiched between slide mounts (opening 35 mm × 18 mm), and the slide mount was placed so as to be perpendicular to the flow direction. After the film swells and breaks, the time required for the film still attached to the film to completely separate from the slide mount is taken as the dissolution time.

According to the present invention, there is provided a water-soluble polyvinyl alcohol-based film that has a high solubility in water and requires a certain time until it is completely dissolved after being in contact with moisture, and a method for producing the water-soluble polyvinyl alcohol-based film. Can be provided.

Claims (5)

A water-soluble polyvinyl alcohol film containing a polyvinyl alcohol resin,
The polyvinyl alcohol-based resin has a hydroxyl group amount of 40 mol% or more and a crystallinity measured by X-ray diffraction of 19% or more.
A water-soluble polyvinyl alcohol film characterized by having a dissolution time of 3 hours or less when the water-soluble polyvinyl alcohol film is immersed in water at 23 ° C. The water-soluble polyvinyl alcohol film according to claim 1, wherein the dissolution time in water at 23 ° C measured by a slide mount method is 20 seconds or more. The water-soluble polyvinyl alcohol film according to claim 1 or 2, wherein the polyvinyl alcohol resin has a saponification degree of 95 mol% or more. A method for producing a water-soluble polyvinyl alcohol film according to claim 1, 2 or 3,
A step (A) of mixing a water-soluble resin containing a polyvinyl alcohol resin having a hydroxyl group content of 40 mol% or more and a raw material composition containing water, and extruding the raw material composition from a mold to form a sheet-like composition. A step (B) and a step (C) for volatilizing water by bringing the sheet-shaped raw material composition into contact with a support and heating it,
A method for producing a water-soluble polyvinyl alcohol film, wherein the time until the sheet-like composition extruded from the mold comes into contact with the support surface is 2 seconds or more. The method for producing a water-soluble polyvinyl alcohol film according to claim 4, wherein in the step (A), the raw material composition is heated to 80 ° C or higher and then cooled to 50 ° C or lower.