JPH09324096A - Water-soluble film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a water-soluble film which is excellent in low-temp. solubility, does not exhibit any changes in physical properties with changes in temp. and humidity, and does not undergo the degradation in quality even when kept in contact with chemicals such as an alkali by compounding a specific modified PVA resin and a specific PVA resin. SOLUTION: This compsn. comprises a modified PVA resin having anionic groups (pref. carboxyl and/or sulfo groups) pref. in an amt. of 2.0-40mol% (in terms of degree of modification) and a degree of polymn. of pref. 200-8,000 and a PVA resin having a degree of saponification of 70-99mol% and a degree of polymn. of pref. 200-8,000. The modified PVA resin having carboxyl groups is produced by subjecting PVA to the Michael addition reaction with acrylonitrile or acrylamide and partly or fully hydrolyzing the reaction product, and the one having sulfo groups is produced by subjecting PVA to the Michael addition reaction with vinylsulfonic acid, etc. The wt. ratio of the modified PVA resin to the PVA resin is pref. (95:5)-(5:95).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold water quick-soluble type water-soluble film and a water-soluble packaging material, and more particularly to a cold water fast-soluble type polyvinyl alcohol film and a water-soluble packaging material formed of the film.

[0002]

2. Description of the Related Art Conventionally, polyvinyl alcohol (hereinafter referred to as PVA) can be formed into a film relatively easily and has excellent strength, so that it exhibits water solubility such as packaging of a water-soluble film and a cleaning agent. Widely used as packaging material.

[0003] The PVA used in these compounds has a water solubility of 80 to 80, particularly a low temperature water solubility (low temperature solubility).
90% saponified products are commonly used.

[0004]

However, in the conventional PVA film, the PV of the partially saponified product described above is used.
Even if A is used as the raw material, the solubility at low temperatures may be insufficient, and therefore, in applications where fast solubility at low temperatures is required, satisfactory performance is not always obtained.

Further, at low temperature and low humidity, the saponification reaction proceeds due to film breakage such as cracking and contact with an alkaline substance, so that the solubility in cold water is further lowered and it cannot be used for packaging alkaline substances. There was a problem.

Further, since these PVA films may generate insolubilized products when exposed to high temperatures during heat-sealing, in pesticide packaging and the like, nozzle clogging occurs when pesticides are used in a sprayer. It has been pointed out.

On the other hand, the applicant previously mentioned that modified polyvinyl alcohol in which an anionic group was introduced into PVA (hereinafter referred to as "modified P
VA ”) has been proposed (Japanese Patent Application No. 7-179064), which has very good quick water solubility in cold water, deterioration due to alkali, and film damage at low temperature and low humidity. Can also be prevented.
However, if the modification rate is increased to improve the quick water solubility in cold water, the hygroscopicity of the film increases, so that the modified PVA
In the production of such films and packaging materials, there is the problem that humidity must be controlled.

The object of the present invention is to solve the above problems.
A-based water-soluble film, that is, it has excellent low-temperature solubility, has little change in physical properties with respect to temperature and humidity, does not deteriorate in the packaging of alkaline substances, and minimizes the generation of insoluble substances, and is used as a packaging material. Having the strength of
An object is to provide a water-soluble film.

[0009]

DISCLOSURE OF THE INVENTION In view of the above problems, the present inventors have made earnest studies, and as a result, modified P having an anionic group was found.
VA and PVA having a saponification degree in a specific range are blended at a fixed ratio, and the obtained film has a fast solubility in cold water which is much higher than expected when simply mixed, and also with respect to temperature and humidity. The present invention has been found to solve the problems of small changes in physical properties, film breakage at low temperatures and low humidity, and insolubilization by alkalis, leading to the present invention. That is, it is a water-soluble film comprising (A) a modified polyvinyl alcohol having an anionic group and (B) a polyvinyl alcohol having a saponification degree of 70 to 99 mol%.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION First, the anionic modified PVA which is the component (A) of the present invention will be described in detail below.

The degree of polymerization of the anion-modified PVA used in the present invention is not particularly limited, but is preferably 200 to 8,000, and more preferably 300 to 4,000. Degree of polymerization is 2
If it is less than 00, there is a problem that sufficient film strength cannot be obtained and hygroscopicity becomes large. On the other hand, when the degree of polymerization exceeds 8,000, not only the rapid solubility in cold water is lowered but also the viscosity of the aqueous solution is high, so that it cannot be dissolved in a high concentration,
There is a problem that productivity drops.

The modification ratio of the anionic group is 2.0 to
40 mol% is preferable, and 4.0 to 30 mol% is preferable. If it is less than 2.0 mol%, the rapid solubility in cold water may decrease and the film may be damaged at low temperature and low humidity. On the other hand, if it exceeds 40 mol%, the production is difficult.

Examples of the type of anionic group include a carboxyl group, a sulfone group, a phosphoric acid group and the like, and a carboxyl group and a sulfone group are preferable in terms of economy and ease of production.

Carboxyl group-modified P used in the present invention
Examples of VA include so-called copolymerized modified PVA obtained by copolymerizing vinyl acetate and itaconic acid or maleic acid and then saponifying, and so-called post-modified PVA in which a carboxyl group is directly introduced into PVA.

As a method of introducing a carboxyl group into PVA by post-modification, PVA is monoesterified with maleic anhydride or the like, PVA is replaced with monochloroacetic acid or the like, or acrylic acid is added to PVA by a Michael addition reaction. Similarly, there is a method in which acrylonitrile, acrylamide or the like is subjected to a Michael addition reaction and then partially or completely hydrolyzed. Among them, a method of adding acrylonitrile or acrylamide with Michael and then hydrolyzing it is preferable from the viewpoint that a high conversion rate and a high modification rate can be obtained.

On the other hand, as a method of introducing a sulfone group into PVA, for example, vinyl acetate and vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (hereinafter AMPS) and the like, followed by saponification, vinyl sulfonic acid or its salt, AM
There is a method of adding PS or a salt thereof to PVA by Michael. Among them, AMPS or a salt thereof is added to P in terms of high reaction rate and high modification.
A method of adding Michael to VA is preferable.

Examples of the AMPS salt include Na salt and K salt.

As a matter of course, in the production of anion-modified PVA, two or more of the above anionizing agents and modification methods may be used in combination.

Next, the component (B) PVA will be described in detail. The degree of saponification of PVA as the component (B) used in the present invention is 70 to 99 mol%, preferably 80 to 95 mol%.

When the degree of saponification is less than 70 mol%, the rapid solubility in cold water is lowered and the performance is not satisfied in terms of alkali resistance. On the other hand, if it exceeds 99 mol%, the rapid solubility in cold water (insolubilization in cold water) and film cracking at low temperature and low humidity tend to occur.

The degree of polymerization is preferably 200 to 8,000, and more preferably 300 to 8,000 for the same reason as the above-mentioned component (A).
4,000 is good.

The mixing ratio of the component (A) and the component (B) can be arbitrarily selected within the range of (A) :( B) = 95 to 5: 5 to 95% by weight. The mixing method is not particularly limited, and as long as it is a solid one, it can be mixed as a powder as it is, or can be mixed as an aqueous solution.

Regarding the film formation of the PVA composition thus obtained, the production method is not particularly limited, but the production method similar to that of the conventionally known PVA film can be applied mutatis mutandis.

For example, a casting method is generally used in which an aqueous solution of these PVA-based compositions is prepared and then cast on a belt, a plastic film such as PET, a release paper or a drum, and dried.

The thickness of the film of the present invention can be arbitrarily set according to the purpose of use, but the thickness of the film finally obtained by any of the film forming methods is 10 in terms of mechanical strength and water fast solubility. ˜100 μm is preferable, and more preferably 10 to 70 μm.

Further, the film of the present invention may contain a plasticizer, if necessary, in order to impart flexibility. As a plasticizer used for these, a plasticizer used for an ordinary PVA film can be used. In particular, ethylene glycol, glycerin, diglycerin, and low molecular weight polyethylene glycol (molecular weight: 600 or less) are preferable. . Further, a colorant, a release agent, etc. may be blended or applied within a range that does not impair the gist of the present invention. Further, the film may be subjected to a concavo-convex process such as embossing in order to prevent blocking and improve aesthetics.

The water-soluble PVA-based film of the present invention obtained as described above has an excellent fast solubility even in cold water, and does not deteriorate in the packaging of chemicals such as alkaline substances.
Furthermore, it is a material that also has strength as a packaging material. Therefore, it has very excellent performance as a packaging material for agricultural chemicals and the like.

In the present invention, the rapid solubility in cold water means that the water temperature is 10
The high-speed solubility of the film shown at 0 ° C or lower. The film of the present invention is also suitable as a water transfer film and various unit packaging materials, which are the applications of conventionally used water-soluble films, but it requires fast solubility at low water temperature, which has been particularly limited in conventional use. It can be used as a packaging material.

[0029]

The present invention will be described in more detail with reference to the following examples. In the text, parts and% are based on weight unless otherwise specified.

Production Example of Component (A) Production Example 1 75 parts of vinyl acetate, 500 parts of methanol, 4.85 parts of itaconic acid, 1.10 parts of NaOH and 0.3 parts of azobisisobutyronitrile were charged in a separable flask. , 70
Polymerized at 9 ° C. for 9 hours. At this time, the polymerization rate was 81%. After removing unreacted vinyl acetate,
10 NaOH was added and saponified at 40 ° C. for 5 hours. The degree of polymerization of the obtained carboxy-modified PVA is 1,200,
The degree of saponification was 96.3 mol%. In addition, as analyzed by NMR, the carboxyl modification rate was 3.3 mol%.

Production Example 2 PVA (polymerization degree: 50) was added to a horizontal blender having a capacity of 4 liters.
0, saponification degree 88.2 mol%) 490 parts, NaOH 20
0 parts, 420 parts of a 50% -monochloroacetic acid aqueous solution and 200 parts of isopropyl alcohol were added, and the mixture was stirred at 60 ° C. for 8 hours. The obtained product was purified with methanol, dried, and analyzed by colloid titration to find that the carboxy modification rate was 16.2 mol%.

Production Example 3 PVA (polymerization degree: 2,5) was added to a horizontal blender having a capacity of 4 liters.
00, degree of saponification 98.8 mol%) 440 parts, 30% -N
200 parts of an aOH aqueous solution and 484 parts of a 50% -acrylamide aqueous solution were added, and the mixture was stirred at 60 ° C for 8 hours. Next, 100 parts of 50% -NaOH was added, and hydrolysis was performed at 90 ° C. for 1 hour. When the obtained powder was analyzed by NMR, the carboxyl modification ratio was 29.3 mol%.

Production Example 4 The same procedure as in Production Example 3 was carried out except that 250 parts of acrylonitrile was used instead of 484 parts of 50% -acrylamide aqueous solution. When the obtained powder was analyzed by NMR, the carboxyl modification rate was 37.6 mol%.

Production Example 5 PVA (polymerization degree: 1,7) was added to a horizontal blender having a capacity of 4 liters.
00, degree of saponification 98.5 mol%) 440 parts, 50% -N
280 parts of aOH aqueous solution and 50% -AMPS aqueous solution 8
28 parts were added and stirred at 80 ° C. for 7 hours. When the obtained powder was analyzed by NMR, the sulfone group modification rate was 14.
3 mol%.

Production Example 6 PVA (polymerization degree: 5,0) was added to a horizontal blender having a capacity of 4 liters.
00, saponification degree 98.2 mol%) 440 parts, 30% -N
70 parts of an aOH aqueous solution and 284 parts of a 50% -acrylamide aqueous solution were added, and the mixture was stirred at 60 ° C. for 4 hours. Then 5
125 parts of 0% -NaOH was added, and the mixture was hydrolyzed at 70 ° C. for 1 hour.

Then, 460 parts of 50% -AMPS sodium salt aqueous solution was added, and the mixture was stirred at 80 ° C. for 4 hours. When the obtained powder was analyzed by NMR, the carboxyl modification rate was 17.3 mol% and the sulfone group modification rate was 6.5 mol%.

Examples 1 to 6 and Comparative Examples 1 to 2 Components (A) and (B) were mixed in the proportions shown in Table 1,
Eight types of test films were prepared by the following method.

[0038]

[Table 1]

Preparation of Film First, the modified PVA as the component (A) and the PVA as the component (B) are mixed in a desired ratio, and the PVA-based mixture obtained and this PVA are mixed.
3% glycerin 15000-2 for VA-based mixture
5000 mPa · s (BH viscometer, 20 rpm, 25
It was dissolved in water at 80 ° C. so that the viscosity became (° C.). After cooling to room temperature, it was cast on a PET film, left standing for 24 hours, and then dried at 100 ° C. for 1 hour to prepare a test film having a thickness of 40 μm. The obtained film was subjected to a performance test by the following method. The results are shown in Table 2.

Dissolution rate test in water Cut the film into 1 cm x 1 cm, mark + with an aqueous magic, prepare 500 cc of water at 10 ° C in a 1 liter beaker in advance, drop the film on the still water surface,
The time until the + sign disappeared completely was measured. If the film curled or adhered to the side surface of the beaker, remeasurement was performed. The results were averaged three times and displayed in units (seconds). Further, in the same manner as above, 5 ° C
The water temperature was also evaluated. Those that did not dissolve in 300 seconds were designated as "insoluble".

Mechanical strength test film was kept at 20 ° C. and 65% RH for 72 hours, and
Tensile strength (TB: kg / cm according to IS K7127
Strength) and elongation (EB:%) were measured, and JIS
The tear strength (TR: kg / cm) was measured according to K7128.

Generation test of insoluble matter The test film was cut into a piece of 5 cm × 5 cm, and 2 pieces were hot-pressed.
Pressed at 00 ° C for 1 minute. Then, this film 30
It was dissolved in 0 cc of tap water, filtered and dried to measure the insoluble matter.

The alkali resistance test test film was cut into 1 cm × 1 cm placed in a petri dish, the film obscures by Na ₂ CO ₃ put a Na ₂ CO ₃ from the top of the film, one month in an oven at 40 ° C. After standing, the dissolution rate in water was measured. Those that did not dissolve in 300 seconds were regarded as insoluble.

Hygroscopicity The weight change of the film was measured under the conditions of 25 ° C. and RH 80%. The equilibrium moisture content at the time when the weight increase reached equilibrium was calculated as the moisture absorption rate, and evaluated according to the following criteria. Moisture absorption rate: <20% Hygroscopicity: small, moisture absorption rate: 20-30
% Moisture Absorption: Medium, Moisture Absorption:> 30% Moisture Absorption: Large

Film breakage The film left for 48 hours under the conditions of 0 ° C. and RH of 20% was bent, and the presence or absence of film cracking was evaluated.

Comprehensive Evaluation Performance test results were comprehensively judged and evaluated in five levels. (Good) 5 → 4 → 3 → 2 → 1 (bad)

[0047]

[Table 2]

[0048]

The PVA-based film of the present invention comprises anion-modified PVA having excellent quick water solubility, alkali resistance and the like and PVA excellent in mechanical strength and humidity stability. When both are uniformly mixed to form a film. Excellent performance is provided by the synergistic effect. That is, the PVA-based film of the present invention comprises: It also dissolves quickly in cold water. 2. It does not easily deteriorate even when it comes into contact with chemicals such as alkalis. 3. Stable to temperature and humidity with little change in physical properties. For example, it is possible to prevent film cracking and the like under low temperature and low humidity (0 ° C., 20%). 4. Excellent mechanical strength as a film or packaging material. And so on.

Therefore, when used in the PVA film pesticide packaging material or the like of the present invention, it is possible to prevent clogging of the nozzle of the sprayer, and the quality of the packaging material due to chemicals or in an environment where the temperature and humidity conditions are poor. Deterioration can be suppressed.

Claims (4)

[Claims] 1. A water-soluble film comprising (A) a modified polyvinyl alcohol having an anionic group and (B) a polyvinyl alcohol having a saponification degree of 70 to 99 mol%. 2. The water-soluble film according to claim 1, wherein the modified polyvinyl alcohol is a modified polyvinyl alcohol obtained by Michael-adding a vinyl compound to polyvinyl alcohol and then partially or completely hydrolyzing the vinyl compound. 3. The water-soluble film according to claim 1, wherein the modified polyvinyl alcohol is a modified polyvinyl alcohol obtained by partially or completely hydrolyzing acrylonitrile or acrylamide to polyvinyl alcohol by Michael addition. . 4. A water-soluble packaging material comprising the water-soluble film according to claim 1.