TECHNICAL FIELD

The present disclosure relates to a water-soluble film including a polyvinyl alcohol resin as a main component, and more specifically, to a water-soluble film that has excellent mechanical characteristics, such as a high tensile strength and a high tensile elongation, and that does not cause bleed-out before formation of a package, and a chemical agent package obtained by using the film.

A polyvinyl alcohol is hereinafter sometimes abbreviated as “PVA”, and a water-soluble film including a polyvinyl alcohol resin as a main component is hereinafter sometimes abbreviated as “PVA water-soluble film” or simply as “water-soluble film”.

BACKGROUND ART

A PVA film is a film formed of a PVA resin that has water solubility while being a thermoplastic resin, and the film is largely different from a hydrophobic film that is frequently used for a packaging film or the like in ordinary cases, such as a polyethylene terephthalate film or a polyolefin film, in, for example, various film physical properties and texture.

In addition, a chemical agent portion package (unit package) obtained by incorporating any one of various chemical agents, such as an agricultural chemical and a detergent, into a bag formed of a film of the PVA resin through the exploitation of the water solubility of the PVA resin has heretofore been proposed, and has been used in a wide variety of applications.

As a water-soluble unit packaging bag to be used in such applications, for example, there has been known a water-soluble film obtained by blending 100 parts by weight of a PVA with 5 parts by weight to 30 parts by weight of a plasticizer, 1 part by weight to 10 parts by weight of starch, and 0.01 parts by weight to 2 parts by weight of a surfactant (see, for example, PTL 1), or a water-soluble film formed of a resin composition containing 20 parts by weight to 50 parts by weight of a plasticizer, 2 parts by weight to 30 parts by weight of a filler, and 0.01 parts by weight to 2.5 parts by weight of a surfactant with respect to 100 parts by weight of an anionic group-modified PVA resin having a 4 wt % aqueous solution viscosity at 20° C. of from 10 mPa·s to 35 mPa·s, an average saponification degree of from 80.0 mol % to 99.9 mol %, and an anionic group modification amount of from 1 mol % to 10 mol % (see, for example, PTL 2).

RELATED ART DOCUMENT

Patent Document

PTL 1: JP-A-2001-329130

PTL 2: JP-A-2004-161823

SUMMARY

Each of the water-soluble films disclosed in PTL 1 and PTL 2 described above is excellent in water solubility and hence can be used as a chemical agent package having packaged therein a liquid detergent or the like. However, the plasticizer in the film bleeds out when the film is in the state of a film roll before the formation of the package, and the bleed-out causes a problem, such as the contamination of a package-forming apparatus or the whitening of the film, in some cases. Accordingly, a water-soluble film from which a plasticizer does not bleed out has been desired.

In view of the foregoing, under such background, according to the present disclosure, there are provided a water-soluble film that has excellent mechanical characteristics, such as a high tensile strength and a high tensile elongation, and that does not cause bleed-out before the formation of a package, and a chemical agent package obtained by packaging various chemical agents with the water-soluble film.

To provide such water-soluble film and chemical agent package, the inventor has made extensive investigations in view of such circumstances, and as a result, has found that, when three kinds of plasticizers having different melting points are used in combination as plasticizers in a water-soluble film including a PVA resin as its main component, a water-soluble film that has excellent mechanical characteristics, such as a high tensile strength and a high tensile elongation, and that does not cause bleed-out before the formation of a package can be obtained without the impairment of the water solubility of the film.

That is, the gist of the present disclosure relates to a water-soluble film, including: a PVA resin (A); and a plasticizer (B), wherein the plasticizer (B) contains a polyhydric alcohol (b1) having a melting point of more than 50° C. and 100° C. or less, a polyhydric alcohol (b2) having a melting point of 50° C. or less, and a polyhydric alcohol (b3) having a melting point of more than 100° C.

According to one embodiment of the present disclosure, there is also provided a chemical agent package, including: a package bag obtained by bonding the water-soluble films to each other; and a liquid chemical agent included in the package bag.

The water-soluble film of the present disclosure is a water-soluble film that has excellent water solubility, has excellent mechanical characteristics, such as a high tensile strength and a high tensile elongation, and does not cause bleed-out before the formation of a package. Accordingly, the film can be used in various packaging applications, and is particularly useful in an application where a chemical agent or the like is packaged as a unit.

In addition, when the water-soluble film of the present disclosure includes an anionic group-modified polyvinyl alcohol resin as the polyvinyl alcohol resin (A), its solubility in water further increases.

Further, when the water-soluble film of the present disclosure includes an anionic group-modified polyvinyl alcohol resin and an unmodified polyvinyl alcohol as the polyvinyl alcohol resin (A), its water sealability further increases.

In addition, when the content of the plasticizer (B) in the water-soluble film of the present disclosure is 25 parts by weight or more with respect to 100 parts by weight of the polyvinyl alcohol resin (A), the easy formability of the water-soluble film further increases.

In addition, when the content ratio (b1/b3) of the polyhydric alcohol (b1) having a melting point of more than 50° C. and 100° C. or less to the polyhydric alcohol (b3) having a melting point of more than 100° C. in the water-soluble film of the present disclosure is from 1 to 40 in terms of weight ratio, the bleed-out resistance of the film further increases.

When the water-soluble film has a water content of from 3 wt. % to 15 wt. %, the mechanical strength and sealability of the film further increases.

The chemical agent package including the package bag obtained by bonding the water-soluble films to each other and the liquid chemical agent included in the package bag serves as a suitable use form of the chemical agent because the chemical agent package holds such a shape as to include the liquid chemical agent therein at the time of its conveyance or storage, and is smoothly dissolved in water to diffuse the included chemical agent in the water at the time of its use. In addition, the chemical agent package is suitable as a package in which a chemical agent is individually packaged.

In addition, in the chemical agent package of the present disclosure, in the case where the liquid chemical agent shows a pH value of from 6 to 12 when dissolved or dispersed in water, and the liquid chemical agent has a water content of 15 wt. % or less, the films do not gel or become insoluble. Accordingly, the chemical agent package is more smoothly dissolved at the time of its use, and hence does not inhibit the diffusion of the liquid chemical agent.

