JP7577952B2 - Highly moisture-absorbent, flexible film - Google Patents

Description

The present invention relates to a highly moisture-absorbing, flex-resistant film that has excellent moisture absorption, flex resistance, and impact resistance, and is flexible and highly adhesive, as well as a highly moisture-absorbing, flex-resistant packaging material and a highly moisture-absorbing, flex-resistant package made from the highly moisture-absorbing, flex-resistant film.

Packaging materials are known that are intended for the transport or long-term storage of contents such as metal products and chemicals made of metal materials or parts using metal, particularly medical instruments and pharmaceuticals, and that can maintain the quality and functionality of the contents while having a simple layer structure and being manufactured through a simple manufacturing process.
These products employ methods of preventing moisture from reaching the contents or of treating them with anti-rust agents in order to prevent the contents from deteriorating in quality or generating rust due to moisture absorption. For example, Patent Documents 1 to 3 propose packaging laminates in which a resin contains a highly volatile anti-rust agent that volatilizes at room temperature and exerts an anti-rust effect, with the aim of preventing rust on the contents of metal products.
However, packaging materials that do not use volatile rust inhibitors are desired because they require a tightly sealed exterior, and there are concerns that vaporized rust inhibitors may have effects other than the rust-preventing effect, such as deterioration of the contents or functional impairment if they come into contact with the contents, and their removal is also troublesome and limited in scope.
PTP packaging and blister packaging are widely used for packaging food and medicine, but in the past, many of them had insufficient moisture resistance, and to compensate for this, aluminum foil pillow bags were used as outer bags and a desiccant was further packed in. However, with this method, the moisture resistance after opening the outer bag is insufficient, and there are many accidents where the desiccant is accidentally ingested.

JP 2010-254350 A JP 2007-308726 A JP 2010-052751 A

The present invention aims to solve the above problems and provide a highly moisture-absorbent, flex-resistant film that is easy to work with during laminate production, has a small total number of constituent layers, is thin and flexible, has high heat sealability, is highly hygroscopic, and produces few pinholes under bending load, as well as a highly moisture-absorbent, flex-resistant packaging material and a highly moisture-absorbent, flex-resistant package made from the highly moisture-absorbent, flex-resistant film.

As a result of various studies, the inventors have found that a highly moisture-absorbing, flexible-resistant film having at least one moisture-absorbing layer and two heat-sealing layers, in which the moisture-absorbing layer contains a specific resin and moisture absorbent, can achieve the above-mentioned objective.

The present invention is characterized in the following points.
1. A highly moisture-absorbing and flexible film having at least one moisture-absorbing layer and two heat-sealing layers,
the moisture absorbing layer contains a polyethylene resin, a flexible resin, an adhesive reinforcing resin, and a moisture absorbing agent, and is sandwiched and laminated between the two heat seal layers;
The flexible resin contains a polyethylene-based elastomer and/or a polyethylene-based plastomer,
The adhesive reinforcing resin contains a functional group-containing modified polyolefin,
the heat seal layer contains a polyethylene resin but does not contain the moisture absorbent, and is a layer on both surfaces of the highly moisture-absorbing and flexible film;
A highly moisture-absorbing and flexible film, wherein the polyethylene resins contained in each of the two heat seal layers or in the moisture absorbing layer are the same or different.
2. The content of the flexible resin in the moisture absorption layer is 2% by mass or more and 20% by mass or less,
The content of the adhesive reinforcing resin in the moisture absorption layer is 2% by mass or more and 20% by mass or less,
2. The highly moisture-absorbing and bending-resistant film described in 1 above, characterized in that the content of the moisture absorbent in the moisture absorption layer is 40% by mass or more and 70% by mass or less.
3. The highly moisture-absorbing and flexible resistant film according to the above item 1 or 2, wherein the polyethylene elastomer has a density of 0.86 g/cm ³ or more and 0.935 g/cm ³ or less.
4. The highly moisture-absorbing and flexible film according to any one of 1 to 3 above, wherein the polyethylene plastomer has a density of 0.86 g/cm ³ or more and 0.935 g/cm ³ or less.
5. The highly moisture-absorbing and flexible film according to any one of 1 to 4 above, wherein the adhesive reinforcing resin is maleic anhydride-modified polyethylene.
6. The highly moisture-absorbing and bending-resistant film according to any one of 1 to 5 above, wherein the moisture absorbent is a metal oxide.
7. The highly moisture-absorbing and flexible film according to 6 above, wherein the metal oxide is one or more selected from the group consisting of calcium oxide, magnesium oxide, barium oxide, and hydrophilic zeolite.
8. The highly moisture-absorbing and flex-resistant film according to any one of 1 to ⁷ above, characterized in that the moisture absorption amount for 14 days at 23° C. and 50% RH is 6 g/m ² or more and 10 g/m 2 or less.
9. The highly moisture-absorbing and flex-resistant film according to any one of 1 to 8 above, characterized in that the number of pinholes generated after 1,000 flexes in a Gelbo flex test in accordance with ASTM F392 is 0 or more and 7 or less.
10. The highly moisture-absorbent and flexible film according to any one of 1 to 9 above, characterized in that the impact strength in an impact breaking test in accordance with ASTM D3420 Standard Test Method for Pendulum Impact Resistance of Plastic Films is 1.5 J or more and 3 J or less.
11. A highly moisture-absorbent and flexible packaging material produced using the highly moisture-absorbent and flexible film according to any one of 1 to 10 above.
12. A highly moisture-absorbent and flexible packaging product, which is packaged using the highly moisture-absorbent and flexible packaging material described in 11 above.

According to the present invention, it is possible to obtain a highly moisture-absorbent, flex-resistant film that is easy to work with during film production, has a small total number of constituent layers, is thin and flexible, has high heat sealability, is highly moisture-absorbent, and generates few pinholes under bending load, as well as a highly moisture-absorbent, flex-resistant packaging material and a highly moisture-absorbent, flex-resistant package made from the highly moisture-absorbent, flex-resistant film.

1 is a schematic cross-sectional view showing an example of a layer structure of a highly moisture-absorbing and flexible film of the present invention.

The highly moisture-absorbent, flex-resistant film of the present invention, as well as the highly moisture-absorbent, flex-resistant packaging material and highly moisture-absorbent, flex-resistant packaging body made from the highly moisture-absorbent, flex-resistant film, are described in detail below with reference to the drawings.

In the present invention, the total number of constituent layers refers to the detailed number of layers constituting the laminate, such as inorganic vapor deposition layers, crack resistance-imparting adhesive layers, inorganic vapor deposition layer support layers, substrate layers, sealant layers, and adhesive layers, and refers to the number of layers including special treatment coating layers such as vapor deposition layers and anchor coat layers in each layer. For example, a PET film layer with an aluminum vapor deposition layer is counted as two layers.
The laminate according to the present invention and the packaging material and packaging bag made of the laminate will now be described.
The resin names used in the present invention are those commonly used in the industry. Furthermore, the present invention is not limited to the specific examples listed below.
In the present invention, films and sheets are collectively referred to as films.

<Highly moisture-absorbent and bending-resistant film>
The highly moisture-absorbing and flex-resistant film of the present invention has at least one moisture-absorbing layer and two heat-sealable layers, and has a layer structure in which the moisture-absorbing layer is sandwiched between the two heat-sealable layers.
The layers may be laminated with an adhesive layer between them.
The moisture absorbing layer contains a polyethylene resin, a flexible resin, an adhesive reinforcing resin, and a moisture absorbent, the flexible resin may be a polyethylene elastomer and/or a polyethylene plastomer, and the adhesive reinforcing resin preferably contains a functional group-containing modified polyolefin.
The heat seal layer is a layer containing a polyethylene resin, and preferably does not contain a moisture absorbent in order to have good heat sealability. In addition, it is preferable that each of the two heat seal layers is a surface layer on both surfaces of the highly moisture-absorbing and flexible film.
Here, the polyethylene resins contained in each of the two heat seal layers or the moisture absorbing layer may be the same or different.
The polyethylene resin is preferably LLDPE and/or LDPE, more preferably LLDPE.

The content of the flexible resin in the moisture-absorbing layer is preferably 2% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less. If it is less than the above range, the bending resistance and impact resistance of the highly moisture-absorbing, bending-resistant film may be insufficient, and if it is more than the above range, the rigidity of the moisture-absorbing layer and/or the highly moisture-absorbing, bending-resistant film as a whole may be too low, tending to make it unsuitable as a packaging material.

The content of the adhesive reinforcing resin in the moisture absorption layer is preferably 2% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less. If it is less than the above range, the adhesive strength of the moisture absorption layer interface and the heat sealability, flex resistance, and impact resistance of the highly moisture-absorbent, flex-resistant film may be insufficient. If it is more than the above range, the adhesive strength of the moisture absorption layer interface and the heat sealability, flex resistance, and impact resistance of the highly moisture-absorbent, flex-resistant film will not be significantly improved.

The content of the moisture absorbent in the moisture absorption layer is preferably 40% by mass or more and 70% by mass or less, and more preferably 43% by mass or more and 65% by mass or less. If it is less than the above range, the moisture absorption may be insufficient, and if it is more than the above range, the film formability and interfacial adhesive strength may decrease, and the flex resistance may be insufficient.

The thickness of the highly moisture-absorbent, flex-resistant film of the present invention is not particularly limited, but is preferably 20 μm or more and 200 μm or less, more preferably 30 μm or more and 150 μm or less, and more preferably 30 μm or more and 100 μm or less. If it is thinner than the above range, the moisture absorption of the highly moisture-absorbent, flex-resistant film may be insufficient and it may tend to tear easily, and if it is thicker than the above range, the rigidity of the highly moisture-absorbent, flex-resistant film may be too strong, making it less suitable as a packaging material.

The thickness of the moisture-absorbing layer is not particularly limited, but is preferably 10 μm to 100 μm, more preferably 15 μm to 75 μm, and even more preferably 15 μm to 50 μm. If the thickness is thinner than the above range, the moisture absorption of the highly moisture-absorbing and bending-resistant film may be insufficient, and if the thickness is thicker than the above range, the moisture absorption is not significantly improved and the rigidity of the highly moisture-absorbing and bending-resistant film may become too strong, making it less suitable as a packaging material.

The thickness of the heat seal layer is not particularly limited, but is preferably 5 μm or more and 50 μm or less, more preferably 7 μm or more and 40 μm or less, and more preferably 10 μm or more and 30 μm or less. If it is thinner than the above range, the heat sealability of the highly moisture-absorbing and flexible-resistant film may be insufficient, and if it is thicker than the above range, the rigidity of the highly moisture-absorbing and flexible-resistant film may be too strong, making it less suitable as a packaging material.

The bending resistance of the highly moisture-absorbent, bending-resistant film of the present invention can be evaluated by the number of pinholes that occur after bending treatment. For example, the bending resistance of the highly moisture-absorbent, bending-resistant film is preferably such that the number of pinholes that occur after 1,000 bending cycles in a Gelbo flex test according to ASTM F392 is 0 or more and 7 or less.

The impact resistance of the highly moisture-absorbent, flexible film of the present invention is preferably such that the impact strength in an impact destruction test conforming to ASTM D3420 standard test method for pendulum impact resistance of plastic films is 1.5 J or more and 3 J or less.

The moisture absorption of the highly moisture-absorbing and flex-resistant film of the present invention is preferably such that the moisture absorption amount at 23° C. and 50% RH for 14 days is 6 g/m ² or more and 10 g/m ² or less.

<Moisture absorption layer>
The moisture absorbing layer is a layer that is responsible for the moisture absorption properties of the highly moisture absorbing and bending resistant film, and is a layer that contains a moisture absorbent, a thermoplastic resin as a binder resin, and an adhesive reinforcing resin.
The moisture absorbing layer may be one layer in the highly moisture absorbing and flexible film, or it may be two or more layers having the same or different compositions.
The binder resin contained in the moisture absorbing layer is preferably a thermoplastic resin having excellent bending resistance, affinity suitable for dispersing the moisture absorbent, and excellent film forming properties, and more preferably a thermoplastic resin having excellent heat sealing properties.

Such a thermoplastic resin preferably contains a polyethylene resin, more preferably contains LLDPE and a flexible resin. The combination of a polyethylene resin, particularly LLDPE, and a flexible resin has a synergistic effect, and has high bending resistance and high affinity with a moisture absorbent, making it excellent as a binder resin for the moisture absorption layer of a highly moisture-absorbing and bending-resistant film.
The adhesive reinforcing resin contained in the moisture absorbing layer reinforces the interlayer adhesive strength at the interface where the moisture absorbing layer contacts and the heat seal strength of the highly moisture absorbing and flexible film.

The moisture-absorbing layer can contain multiple types of thermoplastic resins in combination, as long as they do not have a significant adverse effect on bending resistance, moisture absorption, heat sealability, film-forming properties, etc.

<Heat seal layer>
The heat seal layer is preferably a surface layer on both sides of the highly moisture-absorbing and flexible film, and preferably contains a thermoplastic resin having excellent film-forming properties and heat sealability.
Such a thermoplastic resin is preferably a polyethylene-based resin, and more preferably contains LLDPE.
The content of LLDPE in the heat seal layer is preferably 75% by mass or more and 100% by mass or less, and more preferably 85% by mass or more and 100% by mass or less.

Many types of thermoplastic resins can be used in the heat seal layer as long as they do not have a significant adverse effect on heat sealability, film-forming properties, etc.

<Adhesive Layer>
There is no particular limitation on the adhesive used in the adhesive layer, and adhesives for DL (dry lamination), adhesives for EC (extrusion coating), adhesives for non-solvent lamination, any anchor coating agent, etc. can be used.
The adhesive may be of any of the following types: heat-curable, ultraviolet-curable, and electron-beam-curable types; and may be in any form, such as aqueous, solution, emulsion, and dispersion types. The adhesive may be in any form, such as film/sheet, powder, and solid. The adhesive mechanism may be any of the following types: chemical reaction, solvent volatilization, thermal melting, and thermal pressure.

Examples of components that form such adhesive layers include polyvinyl acetate adhesives such as polyvinyl acetate and vinyl acetate-ethylene copolymers, polyacrylic acid adhesives consisting of copolymers of polyacrylic acid and polystyrene, polyester, polyvinyl acetate, etc., cyanoacrylate adhesives, ethylene copolymer adhesives consisting of copolymers of ethylene and monomers such as vinyl acetate, ethyl acrylate, acrylic acid, and methacrylic acid, cellulose adhesives, polyurethane adhesives, polyester adhesives, polyamide adhesives, polyimide adhesives, polyolefin adhesives such as LDPE, amino resin adhesives consisting of urea resin or melamine resin, phenol resin adhesives, epoxy adhesives, reactive (meth)acrylic adhesives, elastomer adhesives consisting of chloroprene rubber, nitrile rubber, styrene-butadiene rubber, etc., silicone adhesives, inorganic adhesives consisting of alkali metal silicates, low melting point glass, etc.

<About each ingredient>
[Moisture absorbent]
The moisture absorbent contained in the highly moisture-absorbing and flexible film of the present invention is preferably a metal oxide.
The metal oxide is preferably one or more selected from the group consisting of calcium oxide, magnesium oxide, barium oxide, and hydrophilic zeolite.

The moisture absorbent may be of any external shape, such as spherical, rod-like, or elliptical, and may be in any form, such as powder, lump, or granule. However, from the viewpoints of uniform dispersibility, kneading characteristics, and film-forming properties when dispersed in a resin, a powder form is preferred.

In the present invention, the average particle diameter of the moisture absorbent can be appropriately selected from any average particle diameter depending on the application, but the average particle diameter is preferably 0.01 μm or more and 15 μm or less, and more preferably 1 μm or more and 12 μm or less. Here, the average particle diameter is a value measured by a dynamic light scattering method.
If the average particle size is smaller than the above range, the hydrophilic zeolite tends to aggregate and the dispersibility tends to decrease.If the average particle size is larger than the above range, the film-forming property of the layer containing the hydrophilic zeolite tends to be poor, so it tends to be difficult to add a large amount of hydrophilic zeolite, and the surface area is also reduced, so there is a possibility that a sufficient moisture absorption effect cannot be obtained.

(hydrophilic zeolite)
In the present invention, the hydrophilic zeolite used as the moisture absorbent preferably contains one or more types selected from the group consisting of A-type zeolite, CHA-type zeolite, and MFI-type zeolite.
Here, the A-type zeolite preferably has a pore diameter of 0.3 to 0.5 nm, the CHA-type zeolite preferably has a pore diameter of about 0.38 nm, and the MFI-type zeolite preferably has a pore diameter of about 0.55 nm and/or a specific surface area of 300 to 400 m ² /g.
In addition to water, the above zeolites can absorb gases with molecular sizes according to their pore sizes and gases in amounts according to their specific surface areas. For example, CHA-type zeolites are excellent in the ability to adsorb lower hydrocarbons and carbon dioxide, while MFI-type zeolites are excellent in the ability to adsorb carbon dioxide, lower hydrocarbons, lower aldehydes, lower organic acids, and lower alcohols.
On the other hand, the above-mentioned zeolites have low affinity for organic gases having low polarity, and are inferior in their ability to adsorb such gases.

(Method of dispersing moisture absorbent)
The moisture absorbent is preferably incorporated via a master batch in which the moisture absorbent is melt-blended with a thermoplastic resin.
Specifically, it is preferable to prepare a master batch by melt blending a moisture absorbent into a thermoplastic resin at a relatively high concentration, and then dry blending the master batch with components such as a binder resin to obtain a moisture absorbent concentration.
The moisture absorbent and the thermoplastic resin to be melt blended may each be of one type or two or more types, and one master batch may contain one or two or more types of moisture absorbent.

The content of the moisture absorbent in the master batch is preferably 10% by mass or more and 90% by mass or less, and more preferably 30% by mass or more and 70% by mass or less. Within the above range, it is easy to contain a necessary and sufficient amount of the moisture absorbent in a dispersed state.
The above thermoplastic resin may be the same as or different from the thermoplastic resin contained as the binder resin in the moisture absorbing layer.

<Thermoplastic resin>
The thermoplastic resins used in combination as binder resins in the moisture absorption layer and the heat seal layer, and the thermoplastic resins used in the master batch may be the same thermoplastic resin for each layer, or different thermoplastic resins may be used depending on the required performance.

Specific examples of the thermoplastic resin include polyolefin resins, polyester resins, polyamide resins, polyaramid resins, polycarbonate resins, polyacetal resins, fluorine resins, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers (EVOH), polyvinyl alcohol, polyacrylonitrile, etc. These resins may be used alone or in combination of two or more.
Among these resins, polyolefin resins are preferred from the viewpoint of film-forming properties.

Specific examples of polyolefin resins include polyethylene resins, polypropylene resins, unsaturated carboxylic acid modified resins of polyolefin resins, cyclic polyolefin resins, cyclic olefin copolymers, methylpentene polymers, etc. As unsaturated carboxylic acids, it is preferable to use acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, etc. These polyolefin resins may be used alone or in combination of two or more, or in a multilayer structure containing different types of resins. These copolymerized unsaturated carboxylic acids may be used alone or in combination of two or more.
Among these polyolefin resins, polyethylene resins are preferred from the viewpoint of film-forming properties.

<Heat sealable resin>
The heat sealable resin that can be used in the highly moisture-absorbing and flexible film of the present invention is
Any known heat-sealable resin can be used without any particular limitation, so long as it is a thermoplastic resin that can be melted and fused by heat.
Specific examples of heat-sealable resins include polyethylene, very low density polyethylene (hereinafter referred to as VLDPE), low density polyethylene (hereinafter referred to as LDPE), medium density polyethylene (hereinafter referred to as MDPE), high density polyethylene (hereinafter referred to as HDPE), LLDPE, metallocene polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-ethyl (meth)acrylate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, polyolefin resins obtained by modifying polyolefin resins such as polyethylene or polypropylene with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, and the like, terpolymer resins of ethylene-(meth)acrylic acid ester-unsaturated carboxylic acid, cyclic polyolefin resins, cyclic olefin copolymers, polyethylene terephthalate (PET), polyacrylonitrile (PAN), and the like.

Among these, polyolefin-based resins are preferred, and among polyolefin-based resins, polyethylene-based resins are more preferred, and among polyethylene-based resins, LDPE and LLDPE are further preferred, with LLDPE being particularly preferred.
In the highly moisture-absorbing and flexible film of the present invention, it is preferable to select the resin from those used as binder resins.

<Polyethylene resin>
Specific examples of polyethylene resins include HDPE, MDPE, LDPE, LLDPE, VLDPE, metallocene polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-ethyl (meth)acrylate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, unsaturated carboxylic acid modified resin of polyethylene polyolefin resin, etc. As the unsaturated carboxylic acid, it is preferable to use acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, etc.

Among the above polyethylene resins, LDPE, LLDPE, and VLDPE are more preferred, and VLDPE is even more preferred. These polyethylene resins may be used alone or in combination of two or more.

[Polyethylene elastomer]
The polyethylene elastomer in the present invention is a copolymer having a hard segment and a soft segment derived from an ethylene monomer and another monomer, and is classified into a random copolymer type and a block copolymer type depending on the arrangement of the repeating units derived from each monomer. These may be used alone or in combination of two or more types.
In general, the random copolymer type is relatively softer and has a lower melting point (softening point) than the block copolymer type.
Specific examples of polyethylene-based elastomers include ethylene-propylene block copolymers, ethylene/butene random copolymers, ethylene/octene block copolymers, and copolymers of ethylene and various cyclic olefins.
The random copolymerization type polyethylene elastomer is an ethylene copolymer in which repeating units derived from each monomer are arranged randomly.
For example, the main chain structure of a random copolymer consisting of monomer A and monomer B is represented by -ABAABABABBBAB- and the like.
The block copolymer type polyethylene elastomer is an ethylene copolymer in which several consecutive repeating units derived from one type of monomer form a block, and then several consecutive repeating units derived from another type of monomer form a block.
For example, the main chain structure of a block copolymer consisting of monomer A and monomer B is -A-A-A
It is represented as -A-B-B-B-B-B-A-A-A-, etc.
A polyethylene elastomer has extremely high elasticity at room temperature like rubber, and has a lower density, a lower elastic modulus, and a lower softening point than ordinary polyethylene resins.
The polyethylene elastomer in the present invention preferably has a density of 0.86 g/cm ³ or more and 0.935 g/cm ^{3 or} less, and more preferably has a density of 0.88 g/cm ³ or more and 0.915 g/cm ³ or less.

[Polyethylene plastomer]
A plastomer is a polymeric compound that exhibits plasticity at room temperature, like plastic.
The polyethylene plastomer in the present invention is a polyethylene whose main chain is mainly composed of ethylene monomer units, but due to the influence of the side chains and a narrow molecular weight distribution, it exhibits elasticity and thermoplasticity at the same time.
Polyethylene plastomers have both plastic and elastic properties, and are superior in flexibility, transparency, low-temperature sealing properties, and impact resistance to ordinary polyethylene resins.
The polyethylene plastomer used in the highly moisture-absorbing and flexible film of the present invention preferably has a density of 0.86 g/cm ³ or more and 0.935 g/cm ³ or less, and more preferably 0.88 g/cm ³ or more and 0.915 g/cm ³ or less.

<Adhesive reinforced resin>
The adhesive reinforcing resin is a resin that reinforces adhesiveness, and can improve the interfacial adhesion strength around layers contained in the highly moisture-absorbing, flexible film, and the heat seal strength of the highly moisture-absorbing, flexible film.
In the present invention, the adhesive reinforcing resin preferably contains a functional group-containing modified polyolefin.
Since the moisture-absorbing layer containing the adhesively-reinforcing resin contains LLDPE and a flexible resin, the main skeleton of the adhesively-reinforcing resin is preferably a polyolefin-based skeleton that has high affinity with these resins, and is preferably modified to contain functional groups in order to enhance adhesion.
The functional group-containing modified polyolefin is more preferably maleic anhydride modified polyethylene.
When the main skeleton of the polyethylene-based resin and flexible resin contained in the moisture-absorbing layer is polyethylene-based, it is preferable that the main skeleton of the adhesive reinforcing resin contained in the same moisture-absorbing layer is also polyethylene-based, as this will have higher affinity.In order to have high adhesion, it is preferable for the resin to have a highly polar functional group, and a polyethylene-based resin modified with maleic anhydride is more preferable.

[Method for producing highly moisture-absorbent and flexible film]
The preparation method described below is an example and is not intended to limit the present invention.
The film formation and lamination of each layer constituting the highly moisture-absorbing and flexible laminate is not particularly limited, and any known or commonly used film formation and lamination method can be applied. For example, any method such as wet lamination, dry lamination, solventless dry lamination, extrusion lamination, T-die coextrusion molding, coextrusion lamination, inflation method, etc. can be used.
The highly moisture-absorbing and flexible film may be obtained by laminating the film on another layer such as a release film by extrusion or coextrusion, using an extrusion coating method, and then peeling the film off. Even in the case of the extrusion coating method, the film may be laminated via an adhesive layer as necessary.
The obtained highly moisture-absorbing and flexible laminate can be subjected to secondary processing for the purpose of imparting surface functions such as chemical functions, electrical functions, magnetic functions, mechanical functions, friction/wear/lubrication functions, optical functions, thermal functions, and biocompatibility.

Examples of secondary processing include embossing, painting, gluing, printing, metallizing (plating, etc.), machining, surface treatment (antistatic treatment, corona discharge treatment, plasma treatment, photochromic treatment, physical vapor deposition, chemical vapor deposition, coating, etc.), etc.

Below, an example is described for producing a highly moisture-absorbent, flexible film (highly moisture-absorbent, flexible packaging material) having a layer structure of adhesive reinforcement layer/moisture absorption layer/heat seal layer.

A resin composition for the adhesion reinforcing layer, a resin composition for the moisture absorbing layer, and a resin composition for the heat seal layer are each prepared, and a highly moisture absorbing and bending resistant film having the following layer structure is obtained by an inflation method.
Layer structure: Adhesive reinforcement layer/moisture absorption layer/heat seal layer

≪High moisture absorption bending resistant packaging material≫
The highly hygroscopic and flexible packaging material of the present invention is a packaging material produced by using the highly hygroscopic and flexible film of the present invention, and may be the same as the highly hygroscopic and flexible film. Depending on the circumstances, various functional layers, printed layers, and the like may also be included.
The highly moisture-absorbing and flexible packaging material of the present invention can also be subjected to lamination (dry lamination or extrusion lamination), bag making, and other post-treatments.

≪High moisture absorption bending resistant packaging≫
The highly moisture-absorbent and flexible packaging body of the present invention is a packaging body packaged with the highly moisture-absorbent and flexible packaging material of the present invention.
The highly hygroscopic and flexible packaging body of the present invention can be prepared, for example, by folding the highly hygroscopic and flexible packaging material of the present invention in half, or by preparing two sheets of the highly hygroscopic and flexible packaging material, The heat seal layers are laminated with their faces facing each other, and the peripheral edges are sealed with, for example, a side seal type, a two-sided seal type, a three-sided seal type, a four-sided seal type, an envelope seal type, a joint seal type (pillow By heat sealing in a variety of heat sealing configurations, such as a flat bottom seal type, a pleated seal type, a square bottom seal type, a gusset type, etc., highly moisture-absorbent and flexible packaging bodies of various configurations can be produced.
In the above, the heat sealing can be performed by a known method such as bar sealing, rotary roll sealing, belt sealing, impulse sealing, high frequency sealing, ultrasonic sealing, etc.

Details of the raw materials used in the examples are as follows.
[Moisture absorbent]
Metal oxide 1: Calcium oxide F-Lime 1300-K manufactured by Calfine Co., Ltd. Average particle size: 4.3 μm.
Metal oxide 2: Kyowamag 30 magnesium oxide manufactured by Kyowa Chemical Industry Co., Ltd. Average particle size: 3.16 μm.
Metal oxide 3: hydrophilic zeolite 4A manufactured by Tomoe Engineering Co., Ltd. Average particle size: 10 μm.

[Thermoplastic resin]
LLDPE1: Evolue SP1540, LLDPE manufactured by Prime Polymer Co., Ltd. Density: 0.913 g/cm ³ , MFR: 3.8 g/10 min.

[Flexible resin]
Elastomer 1: Polyethylene elastomer, Toughmer A8050S, manufactured by Mitsui Chemicals, Inc. Density 0.885 g/cm3, MFR 3.6 g/10 min.
Elastomer 2: INFUSE 9107, a polyethylene elastomer manufactured by The Dow Chemical Company, Ltd. Density: 0.866 g/cm ³ , MFR: 1 g/10 min.
Plastomer 1: Polyethylene plastomer, Kernel KS340T, manufactured by Japan Polyethylene Co., Ltd. Density: 0.880 g/cm ³ , MFR: 3.5 g/10 min.
Plastomer 2: Polyethylene plastomer manufactured by Japan Polyethylene Co., Ltd., Kernel KF282, density 0.915 g/cm ³ , MFR 2.2 g/10 min.

[Adhesive reinforced resin]
Adhesive reinforcement resin 1: Admer NF557, maleic anhydride modified polyethylene manufactured by Mitsui Chemicals, Inc. Density 0.903 g/cm ³ , MFR 1.7 g/10 min.
Adhesive strengthening resin 2: Maleic anhydride modified polyethylene manufactured by Dow Chemical Co., Amplify TY1052H, density 0.87 g/cm ³ , MFR 1.25 g/10 min.

[Preparation of Masterbatch]
The masterbatch used in the gas adsorption layer was prepared as follows.

(Preparation of Masterbatch 1)
LLDPE 1 and metal oxide 1 were melt-blended in the following ratio to obtain master batch 1 (MB1).
LLDPE1 30 parts by mass Metal oxide 1 70 parts by mass

[Preparation of Masterbatches 2 and 3]
According to the formulation in Table 1, the raw materials were melt-blended in the same manner as for Masterbatch 1 to obtain Masterbatches 2 and 3 (MB2 and MB3).

[Example 1]

(Preparation of moisture absorbing layer resin composition)
The moisture-absorbing layer resin composition used in the moisture-absorbing layer was prepared as follows.

MB1, LLDPE1, elastomer1, and adhesive reinforcing resin1 were dry blended in the following ratio to obtain a moisture absorbing layer resin composition.
MB1 72 parts by mass LLDPE1 20 parts by mass Elastomer 1 5 parts by mass Adhesive reinforced resin 1 3 parts by mass

(Preparation and evaluation of highly moisture-absorbent and flexible film)
The moisture absorbing layer resin composition obtained above and LLDPE1 were formed into a film and laminated by co-extrusion to obtain a highly moisture absorbing and flexible film (60 μm thick) having the following layer structure. Various evaluations were then carried out.
Layer structure: heat seal layer 1/moisture absorption layer/heat seal layer 2=LLDPE1 (15 μm thick)/moisture absorption layer resin composition 1 (30 μm thick)/LLDPE1 (15 μm thick)

[Examples 2 to 7, Comparative Examples 1 to 5]
Using the materials shown in Table 2, and following the same procedure as in Example 1, moisture-absorbing layer resin compositions and highly water-absorbent, flex-resistant films were prepared and similarly evaluated.

<Evaluation method>
[Film-forming ability]
The appearance of the highly water-absorbent and flex-resistant film was observed and evaluated sensorily according to the following criteria.
○: Film formation is possible without wrinkles or bumps.
×: Numerous wrinkles and bumps were generated, making film formation difficult.

[Heat sealability]
The highly moisture-absorbent and flexible film was cut into a size of 100 mm x 100 mm, and the heat seal layer was overlapped. Using a heat seal tester (TP-701-A manufactured by Tester Sangyo Co., Ltd.), an area of 10 mm x 100 mm was heat sealed under the following conditions to prepare a test piece for peel strength in which the ends were not heat sealed and not bonded, but were divided into two.
This test piece was cut into a strip of 15 mm width, and each bifurcated end was attached to a tensile tester to measure the peel strength (N/15 mm) under the conditions described below, and the pass/fail judgment was made according to the pass/fail judgment criteria described below.
Heat sealing conditions Temperature: 160°C
Pressure: 1 kgf/ ^cm2
Time: 1 second Test conditions Test speed: 300 mm/min Load range: 50 N
Pass/fail criteria: ◯: 30N/15mm or more, passed.
×: Less than 30N/15mm, not acceptable.

[Moisture absorption amount]
The highly moisture-absorbent and flexible film was cut into a size of 100 mm x 100 mm, and the weight was measured in an environment of 23°C and 50% RH, and the moisture absorption amount was calculated according to the following formula.
Moisture absorption (g/ ^m2 ) = [wet weight after 2 weeks (g) - initial dry weight (g)]/0.01 ( ^m2 )

[Impact strength]
The impact strength of the highly moisture-absorbent flex-resistant film was measured by an impact destruction test in accordance with ASTM D3420 Standard Test Method for Pendulum Impact Resistance of Plastic Films.
The measurement conditions were an impact weight of 3 J, a 0.5 inch impact head (12.7 mm diameter, made of brass) was attached, and the measurement was performed at room temperature (25° C.).

[Number of pinholes]
The highly moisture-absorbent and flex-resistant film was formed into a cylindrical shape, and a Gelbo flex test was carried out in accordance with ASTM F392 using a Gelbo flex tester manufactured by Star Industries Co., Ltd., and the number of pinholes that had formed was counted.
Measurement conditions Environment: 23°C 50% RH
Stroke: 80mm
Bending motion: 400°/80mm
Bending speed: 40cpm
Number of flexes: 1000

<Summary of results>
The highly moisture-absorbing and flexible resistant films of all the Examples exhibited good film-forming properties, moisture absorption properties, pinhole resistance and impact strength.
However, Comparative Examples 1, 2, and 4, which did not contain a flexible resin or an adhesive reinforcing resin or contained too little of them, showed poor pinhole resistance and impact strength, Comparative Example 3, which contained too little moisture absorbent, showed insufficient moisture absorption, and Comparative Example 3, which contained too much moisture absorbent, showed insufficient film-forming properties.
Comparative Example 5, in which the content of the flexible resin was too high, exhibited poor film-forming properties and heat sealability.

1 Highly moisture-absorbing and bending-resistant film 2 Pinhole-resistant moisture-absorbing packaging material 3a Heat seal layer 3b Moisture-absorbing layer 3c Moisture absorbent

Claims (11)

A highly moisture-absorbing and flexible film having at least one moisture-absorbing layer and two heat-sealing layers,
the moisture absorbing layer contains a polyethylene resin, a flexible resin, an adhesive reinforcing resin, and a moisture absorbing agent, and is sandwiched and laminated between the two heat seal layers;
The flexible resin contains a polyethylene-based elastomer and/or a polyethylene-based plastomer,
The adhesive reinforcing resin contains a functional group-containing modified polyolefin,
The content of the flexible resin in the moisture absorption layer is 2% by mass or more and 20% by mass or less,
The content of the adhesive reinforcing resin in the moisture absorption layer is 2% by mass or more and 20% by mass or less,
The content of the moisture absorbent in the moisture absorbing layer is 40% by mass or more and 70% by mass or less,
the heat seal layer contains a polyethylene resin but does not contain the moisture absorbent, and is a layer on both surfaces of the highly moisture-absorbing and flexible film;
A highly moisture-absorbing and flexible film, wherein the polyethylene resins contained in each of the two heat seal layers or in the moisture absorbing layer are the same or different. 2. The highly moisture-absorbent and flexible resistant film according to claim 1 , wherein the polyethylene elastomer has a density of 0.86 g/cm3 ^or more and 0.935 g/cm3 or ^less . 3. The highly moisture-absorbent and flexible film according to claim 1 , wherein the polyethylene plastomer has a density of 0.86 g/cm3 ^or more and 0.935 g/ ^cm3 or less. 4. The highly moisture-absorbent and flexible film according to claim 1, wherein the adhesive reinforcing resin is maleic anhydride-modified polyethylene. The highly moisture-absorbing and flexible film according to any one of claims 1 to 4 , wherein the moisture absorbent is a metal oxide. 6. The highly moisture-absorbing and flexible film according to claim 5 , wherein the metal oxide is one or more selected from the group consisting of calcium oxide, magnesium oxide, barium oxide, and hydrophilic zeolite. The highly moisture-absorbing and flex-resistant film according to any one of claims 1 to 6 , characterized in that the moisture absorption amount for 14 days at 23°C and 50% RH is 6 g/m2 or ^more and 10 g/ ^m2 or less. The highly moisture-absorbing and flex-resistant film according to any one of claims 1 to 7 , characterized in that the number of pinholes generated after 1,000 flexes in a Gelbo flex test in accordance with ASTM F392 is 0 or more and 7 or less. The highly moisture-absorbent and flexible film according to any one of claims 1 to 8 , characterized in that the impact strength in an impact breaking test in accordance with ASTM D3420 Standard Test Method for Pendulum Impact Resistance of Plastic Films is 1.5 J or more and 3 J or less. A highly moisture-absorbent and flexible packaging material produced using the highly moisture-absorbent and flexible film according to any one of claims 1 to 9 . A highly moisture-absorbent and flexible packaging product, which is packaged with the highly moisture-absorbent and flexible packaging material according to claim 10 .

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