JP2019038190A - Moisture absorbing film, packaging bag and method for producing moisture absorbing layer - Google Patents

Abstract

To provide a moisture absorbing film which can absorb moisture also with a drying agent which does not precipitate the surface.SOLUTION: There are provided a moisture absorbing film 1 which is formed by laminating a resin base material layer 2, a moisture absorbing layer 3 formed of a polyvinyl alcohol-based resin having a porous structure containing an inorganic substance 5, and a sealant layer 4 in this order; and a method for producing a moisture absorbing layer which includes a step of preparing a mixed liquid of a completely saponified type polyvinyl alcohol having a degree of saponification of 98.0% and a partially saponified type polyvinyl alcohol having a degree of saponification of 94.5%, a step of mixing an inorganic substance with the mixture, a step of forming a coated film using a mixed liquid containing an inorganic substance, and a step of washing and removing a part of the coated film formed of the partially saponified type polyvinyl alcohol to form a moisture absorbing layer formed from the polyvinyl alcohol-based resin having a porous structure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hygroscopic film that selectively adsorbs only moisture, a laminated film using the hygroscopic film, and a packaging bag.

  Conventionally, a desiccant is bundled for the purpose of preventing quality deterioration caused by moisture in various articles such as foods and drinks, pharmaceuticals, chemicals, daily necessities, and the like. When the desiccant is bundled, it was used by packing silica gel, calcium chloride, etc. in a sachet and enclosing it in the package, but the workability is poor, and the sachet is broken and the desiccant is mixed into the internal product. Or, there is a risk of accidental ingestion, and as a material for solving these problems, a film using a material having a hygroscopic property for the packaging material itself is used as the packaging material. For example, there is one in which polyvinyl alcohol is formed on the surface of a film substrate as a water-absorbing organic polymer (for example, see Patent Document 1).

  A desiccant film in which a desiccant is mixed into the packaging material is used as the packaging material. For example, as a desiccant, there is a desiccant obtained by kneading synthetic zeolite into a resin, extruding a kneaded resin (desiccant-containing resin) by a T-die method, and performing uniaxial stretching (for example, see Patent Document 2).

  However, the present inventor has found that the above-described technique has the following problems. That is, in Patent Document 1, when a water-absorbing polymer is formed on the surface of a film substrate, moisture can be absorbed only from the outermost surface of the water-absorbing polymer, and there is a problem that moisture cannot be absorbed efficiently. Further, in Patent Document 2, when a desiccant is kneaded into a resin, extruded and uniaxially stretched, only the desiccant deposited on the surface can absorb water, and there is a problem that moisture cannot be absorbed efficiently.

JP 2001-145982 A JP 2002-206046 A

  This invention is made | formed in view of the said situation, Comprising: It makes it a subject to provide the moisture absorption film which can also adsorb | suck a desiccant which has not precipitated on the surface.

  According to one aspect of the present invention, the above-mentioned laser diffraction / scattering method for an inorganic substance, comprising: a resin base layer; a moisture absorption layer made of a porous polyvinyl alcohol resin containing an inorganic substance; and a sealant layer. The hygroscopic film is characterized in that the average diameter is from 0.5 to 20.0 μm, and the thickness of the hygroscopic layer is from 30 μm to 250 μm.

  The hygroscopic film of the present invention has a hygroscopic property capable of selectively adsorbing only moisture due to the above configuration.

  The inorganic substance is preferably contained in an amount of 5 to 100% by mass with respect to the porous polyvinyl alcohol resin.

Similarly, it is desirable that the inorganic substance contains diatomaceous earth, zeolite, activated carbon, pumice, perlite, calcium oxide, calcium silicate, or a combination thereof because of its high moisture selective adsorptivity. .

  Similarly, the inorganic substance is desirably contained in an amount of 5 to 100% by weight based on the porous polyvinyl alcohol resin because it has high moisture selective adsorption.

  It is good also as a packaging bag using the said moisture absorption film.

  Further, a step of preparing a mixed solution of fully saponified polyvinyl alcohol having a saponification degree of 98.0% and a partially saponified polyvinyl alcohol having a saponification degree of 94.5% or less, and mixing an inorganic substance into the mixed liquid A step of forming a coating film using a mixed solution containing an inorganic substance, a step of forming a coating film comprising a partially saponified polyvinyl alcohol, and removing a part of the coating film by washing with water to absorb moisture comprising a porous polyvinyl alcohol resin. It is possible to manufacture the moisture absorbing layer used for the moisture absorbing film by a method for manufacturing a moisture absorbing layer comprising a step of forming a layer.

  According to the present invention, a moisture absorbing film capable of selectively adsorbing only moisture is provided.

Sectional drawing which shows schematically the moisture absorption film which concerns on one Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, about the element which has the same or similar function, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 1 is a cross-sectional view schematically showing a layer structure of a moisture absorption film according to an embodiment of the present invention. The moisture-absorbing film 1 according to the present invention is formed by laminating a moisture-absorbing layer 3 containing an inorganic substance 5 and a sealant layer 4 on a resin base layer 2 that is the lowermost layer.

  This moisture absorption film 1 is a self-supporting film having a multilayer structure. The term “self-supporting film” as used herein means a film that can be handled by itself without being supported by a support such as a substrate.

  The hygroscopic film 1 may be used alone, but can also be used in the form of a multilayer film further including one or more other layers.

<Resin substrate layer>
The resin base material layer 2 is not particularly limited as long as it can support the moisture absorption layer 3 and is made of the following resin film. For example, cellulose esters such as polyester film, polyethylene film, polypropylene film, cellophane, cellulose diacetate film, cellulose acetate butyrate film, cellulose acetate phthalate film, cellulose acetate propionate film (CAP film), cellulose triacetate and cellulose nitrate Films made of the above or derivatives thereof, polyvinylidene chloride film, polyvinyl alcohol film, ethylene vinyl alcohol film, syndiotactic polystyrene film, polycarbonate film, norbornene resin film, polymethylpentene film, polyether ketone film, polyether Sulfone film, polysulfone film Arm, polyether ketone imide film, a polyamide film, a fluororesin film, a nylon film, polymethyl methacrylate film, acrylic film, and polyarylate films.

  The thickness of the resin base material layer 2 is not limited, but is preferably in the range of 6 to 700 μm, more preferably in the range of 40 to 250 μm, and in the range of 50 to 150 μm. More preferably it is.

<Hygroscopic layer>
As illustrated in FIG. 1, the moisture absorption layer 3 is a water-washing treatment of a polyvinyl alcohol-based resin film prepared from a coating solution in which fine particles made of an inorganic substance are mixed in a mixed aqueous solution of completely saponified polyvinyl alcohol and partially saponified polyvinyl alcohol. The porous structure containing the inorganic substance produced by this is provided.

  Therefore, innumerable pores 6 are formed inside the moisture absorption layer 3 and fine cavities are formed. Fine particles made of the added inorganic substance 5 (average diameter measured by laser diffraction / scattering method is 0.5 to 20.0 μm) are exposed in the space formed by the cavity. Moisture that has permeated through the resin base layer 2 and the sealant layer 4 reaches the moisture absorption layer 3 and is adsorbed by the inorganic substance 5. The pores 6 are considered to have a function of facilitating the movement of moisture inside the moisture absorption layer 3.

[Polyvinyl alcohol]
In the polyvinyl alcohol having a porous structure, the polyvinyl alcohol used in the portion forming the matrix is called a completely saponified type having a saponification degree of 98.0% or more, preferably close to 100% and industrially 99.9% or less. Are preferred. The degree of polymerization is preferably 500 or more and 2000 or less. If the degree of polymerization is less than 500, the strength of the film is weak and the molecular chain becomes too short, making it difficult to take a network structure. On the other hand, when the degree of polymerization exceeds 2000, the viscosity of the aqueous solution becomes too high, which makes the handling inconvenient and makes it difficult to produce a thin film. The concentration of the fully saponified polyvinyl alcohol in the aqueous solution is preferably 5% by weight or more, more preferably 10% by weight or more. If it is less than 5% by weight, the molecular chains are dispersed and it is difficult to form a three-dimensional network structure of the matrix.

  The polyvinyl alcohol used for the portion removed by extraction is preferably a partially saponified type having a saponification degree of preferably 50.0% or more and 94.5% or less. If the degree of saponification is less than 50.0%, it becomes insoluble in water, and if it exceeds 94.5%, phase separation becomes difficult. Like the complete saponification type, the polymerization degree is preferably 500 or more and 2000 or less. The concentration of the partially saponified polyvinyl alcohol in the aqueous solution is preferably less than 5% by weight, more preferably less than 4% by weight. If it is 5% by weight or more, molecular chains are entangled, making it difficult to form pores by washing with water. In the phase separation of partially saponified polyvinyl alcohol, the degree of saponification is sufficiently different and the surface tension is different, so that phase separation occurs naturally in a normal state.

[Inorganic substances]
The inorganic substance 5 is dispersed inside and on the surface of the porous polyvinyl alcohol, and has a function of selectively absorbing moisture. As the inorganic substance 5, a hygroscopic substance can be selected. For example, diatomaceous earth, zeolite, activated carbon, pumice, perlite, calcium oxide, calcium silicate and the like can be mentioned.

  The average particle size of the inorganic substance is preferably 0.1 to 20 μm, more preferably 0.1 to 10 μm. If the average particle size is less than 0.1 μm, the portion that appears on the surface of the polyvinyl alcohol having a porous structure is small, so the hygroscopicity is low. On the other hand, when the average particle diameter exceeds 20 μm, the hygroscopicity is lowered because particles appearing on the surface of the polyvinyl alcohol having a porous structure are easily removed during film formation or lamination, or the sealant layer is pierced. Here, the average particle diameter (or average diameter) refers to the average diameter obtained by the laser diffraction / scattering method, and the same applies hereinafter.

  The amount of the inorganic substance 5 added to the porous polyvinyl alcohol is preferably 5 to 100% by weight, more preferably 10 to 70% by weight. When the addition amount is less than 5% by weight, the amount of the inorganic substance that appears on the surface of the porous polyvinyl alcohol is small, so the hygroscopicity is low.

<Adjustment of moisture absorption layer>
The hygroscopic layer 3 is adjusted by uniformly mixing the above-described two types of polyvinyl alcohol aqueous solution and the inorganic substance 5. For this mixing, for example, although not particularly limited, a stirrer such as a disper mixer, an ultra mixer, a homogenizer, and a planetary stirring deaerator can be used.

<Manufacture of moisture absorption layer>
For example, the moisture absorption layer 3 is formed by applying the coating liquid of the moisture absorption layer 3 to the resin base layer 2 and subjecting the coating film to heat treatment. Thereafter, the coating film is washed with water to remove the partially saponified polyvinyl alcohol to obtain a moisture-absorbing layer 3 having a porous structure.

  Although there is no restriction | limiting in particular in the application | coating method of the moisture absorption layer 3, For example, the die coating method, the dipping method, the method of using a wire bar, the roll coat method, the gravure coat method, the reverse coat method, the air knife coat method, the comma coat method, Known methods such as a curtain method, a screen printing method, a spray coating method, and a gravure offset method can be used.

  Although there is no restriction | limiting in particular in the heat processing method of the moisture absorption layer 3, For example, heating methods, such as hot air drying, hot roll drying, high frequency irradiation, condensation drying, and infrared irradiation, can be used individually or in combination of 2 or more types. . The heating temperature is preferably in the range of 80 to 140 ° C. If it is less than 80 degreeC, it cannot fully dry. Moreover, when it exceeds 140 degreeC, a coating film becomes weak and it will be easy to collapse.

  The thickness of the moisture absorption layer 3 is preferably in the range of 30 to 250 μm, more preferably in the range of 40 to 200 μm, and still more preferably in the range of 50 to 150 μm. When the thickness is less than 30 μm, the amount of moisture absorption in the thickness direction is small and the hygroscopicity is low. On the other hand, if the thickness exceeds 250 μm, the hygroscopic layer becomes hard and flexibility cannot be obtained.

<Sealant layer>
The uppermost sealant layer 4 of the moisture-absorbing film 1 has a function of adjusting the moisture absorption and covering the rough surface of the moisture-absorbing layer 3. The top layer is used because it can be sealed at the time of packaging. The sealant layer 4 includes a low density polyethylene (hereinafter referred to as LDPE) linear low density polyethylene (hereinafter referred to as LLDPE), an ethylene-vinyl alcohol copolymer (hereinafter referred to as EVA), and an ethylene-acrylic acid copolymer (hereinafter referred to as EAA). ), Ethylene-acrylic acid ester copolymer (EAE), ionomer, and ethylene-methacrylic acid copolymer (EMAA).

  The thickness of the sealant layer 4 is not limited, but is preferably in the range of 10 to 100 μm, and more preferably in the range of 20 to 50 μm. When the thickness is less than 10 μm, the rough surface of the moisture absorption layer cannot be sufficiently covered. On the other hand, if it exceeds 100 μm, the effect of the hygroscopic layer is cut off and the hygroscopicity is lowered.

  The lamination of the sealant layer 4 to the moisture absorption layer is not particularly limited, but a known method such as a dry lamination method can be used.

  The hygroscopic film 1 may include a multilayer structure of two or more layers that are sequentially laminated with the hygroscopic layer and the sealant layer 4 as one structure.

  Since the moisture-absorbing film 1 is provided with the sealant layer 4 as the uppermost layer, it can also be used as a packaging bag by thermally bonding the sealant layers together.

  Since the moisture absorption film 1 is excellent in the property of selectively adsorbing only moisture, it can be used for the purpose of preventing quality deterioration caused by moisture in various articles such as foods and drinks, pharmaceuticals, chemicals, daily necessities, and the like.

  Examples of the present invention will be described below. However, the present invention is not limited to the matters described below.

<Example 1>
The moisture absorption film 1 shown in FIG. 1 was produced in the following procedures.
Specifically, first, polyvinyl alcohol (A and B) and water were dispersed and charged with stirring using a planetary stirring deaerator (Mazerustar KK5000, manufactured by KURABO) so as to have the following composition and concentration. The mixture was heated to 95 ° C. and completely dissolved. Thereafter, an inorganic substance having a particle diameter of 5 μm (average diameter by laser diffraction / scattering method) shown below was added at a ratio of 10 parts by mass with respect to 10 parts by mass of the polyvinyl alcohol solid content and uniformly dispersed.
Completely saponified polyvinyl alcohol (A): 7% by mass of PVA117 (manufactured by Kuraray)
Partially saponified polyvinyl alcohol (B): 4% by mass of PVA417 (manufactured by Kuraray)
Inorganic substance (C): Diatomaceous earth (Celite 505) (manufactured by Tokyo Imano)

  Next, using this coating solution, a polyethylene terephthalate (PET) sheet (S10, manufactured by Toray Industries, Inc.) having a thickness of 125 μm was applied by a die coating method so that the film thickness after drying was 50 μm. . This coating film was put into a 130 ° C. hot air drying oven for 5 minutes and dried to obtain a film. Then, this film was immersed in warm water of 50 ° C. for 20 hours to elute partially saponified polyvinyl alcohol and washed away to obtain a moisture absorbing layer.

  Next, a sealant layer was laminated by laminating low density polyethylene (Petrocene 203, manufactured by Tosoh Corporation) having a thickness of 50 μm on this moisture absorption layer by a dry lamination method, and the moisture absorption film of Example 1 was obtained.

<Example 2>
A hygroscopic film was produced in the same manner as in Example 1 except that the content of the inorganic substance relative to the polyvinyl alcohol solid content was 30 parts by mass.

<Example 3>
A hygroscopic film was produced in the same manner as in Example 1 except that the content of the inorganic substance relative to the polyvinyl alcohol solid content was 50 parts by mass.

<Example 4>
A film was produced in the same manner as in Example 1 except that the content of the inorganic substance relative to the polyvinyl alcohol solid content was 70 parts by mass.

<Example 5>
A hygroscopic film was produced in the same manner as in Example 1 except that the thickness of the hygroscopic layer was 100 μm.

<Example 6>
A hygroscopic film was produced in the same manner as in Example 1 except that the thickness of the hygroscopic layer was 200 μm.

<Comparative Example 1>
A hygroscopic film was produced in the same manner as in Example 1 except that the inorganic substance was diatomaceous earth (Celite 545) (manufactured by Tokyo Imano Co., Ltd.) having a particle diameter of 35 μm.

<Comparative example 2>
A hygroscopic film was produced in the same manner as in Example 1 except that the thickness of the hygroscopic layer was 350 μm.

<Comparative Example 3>
Using a coating liquid in which an inorganic substance having a particle diameter of 5 μm is added to a 7% by mass aqueous solution of PVA117 (manufactured by Kuraray Co., Ltd.) in a proportion of 10 parts by mass with respect to 10 parts by mass of polyvinyl alcohol solid content and the moisture absorption layer is uniformly dispersed. A hygroscopic film was produced in the same manner as in Example 1 except that the film was formed as a non-porous hygroscopic layer.

<Evaluation>
The hygroscopicity and film appearance of the hygroscopic film produced by the method described above were evaluated by the following methods.

<Measurement method of hygroscopicity>
The produced hygroscopic film is cut into dimensions of 100 mm in length and 100 mm in width and left for 240 hours in an environment of temperature 25 ° C. and humidity 50% RH, and the moisture absorption rate and saturated water absorption are obtained from the amount of change in the weight of the hygroscopic film. Evaluation of hygroscopicity was made. The amount of water absorption after 1 hour was defined as the moisture absorption rate (mg / hr), and the amount of water absorption when the increase in the amount of water absorption ceased until 240 hours was defined as the saturated water absorption amount (mg).

<Film appearance>
Whether the moisture-absorbing layer was visually cracked or curled in the film was evaluated as “No appearance defect”: “Good”, “External appearance defect”: “No” The evaluation results are summarized in Table 1 below.

  As shown in Table 1 above, the hygroscopic films according to Examples 1 to 6 have higher hygroscopicity than the non-porous film of Comparative Example 3.

On the other hand, in Comparative Example 1, the particle size of the inorganic substance was as large as 35 μm, and the inorganic substance adhered to the surface of the hygroscopic layer when the sealant layer was laminated was peeled off, and the hygroscopicity was inferior compared with Examples 1-6. .
Further, in Comparative Example 2, the moisture absorption layer was as thick as 350 μm, so the saturated water absorption amount was larger than those in Examples 1 to 6, but the moisture absorption layer was cracked when the sealant layer was laminated, and the appearance was poor.

DESCRIPTION OF SYMBOLS 1 ... Hygroscopic film 2 ... Resin base material layer 3 ... Hygroscopic layer 4 ... Sealant layer 5 ... Inorganic substance 6 ... Fine pore

Claims (5)

A resin base layer;
A hygroscopic layer made of a polyvinyl alcohol-based resin having a porous structure containing an inorganic substance;
A sealant layer,
The inorganic substance has an average diameter of 0.5 to 20.0 μm by a laser diffraction / scattering method,
A moisture-absorbing film, wherein the moisture-absorbing layer has a thickness of 30 μm to 250 μm.   2. The moisture-absorbing film according to claim 1, wherein the inorganic substance is contained in an amount of 5 to 100% by mass relative to the porous polyvinyl alcohol resin.   The moisture-absorbing film according to claim 1 or 2, wherein the inorganic substance contains diatomaceous earth, zeolite, activated carbon, pumice, pearlite, calcium oxide, calcium silicate, or a combination thereof.   The packaging bag using the moisture absorption film in any one of Claims 1-3. It is a manufacturing method of the moisture absorption layer according to claim 1,
A step of preparing a mixture of a completely saponified polyvinyl alcohol having a saponification degree of 98.0% and a partially saponified polyvinyl alcohol having a saponification degree of 94.5% or less;
Mixing an inorganic substance with the mixed solution;
Forming a coating film using a mixed liquid containing an inorganic substance;
And a step of forming a moisture absorbing layer made of a polyvinyl alcohol resin having a porous structure by washing and removing a part of the coating film made of the partially saponified polyvinyl alcohol. .

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