JP7616967B2 - Flexible packaging materials and recycling methods - Google Patents

Description

The present invention relates to packaging films used to form packaging materials such as pouch containers.

Traditionally, a variety of products such as food, cosmetics, and medicines have been distributed packaged in various packaging materials. Among these packaging materials, soft packaging materials such as pouch containers and pillowcase packaging bags are made from flexible packaging films. The packaging films that form soft packaging materials usually use laminates in which two or more base layers made of different materials are laminated together.

JP 2007-062786 A JP 2003-084670 A

The above-mentioned packaging film has a base layer made of different materials, so it is difficult to recycle it as a raw material unless it is separated into each base layer. Patent Document 1 (JP 2007-062786 A) discloses an easily peelable food packaging paper that has a paper layer and a non-paper layer made of a resin film or a metal film attached to the paper layer with wax. The paper layer and the non-paper layer of this packaging paper can be separated by picking up either the paper layer or the non-paper layer and peeling it off from the other. However, the method of peeling and separating by hand requires a lot of time and labor for recycling. Patent Document 2 discloses a plastic label in which a display printing ink layer is formed on a base film via an alkaline aqueous solution soluble coating layer in order to peel the display printing ink layer from the base film. However, such document 2 does not disclose the separation of two base layers made of different materials.

The objective of the present disclosure is to provide a packaging film in which at least two base layers made of different materials are laminated, in which each base layer can be easily separated, making the packaging film easy to recycle, and a pouch container using this film.

The packaging film disclosed herein is a packaging film in which at least two base layers made of different materials are laminated, and includes two adjacent base layers and a solvent-soluble intervening layer disposed between the two adjacent base layers, the intervening layer being a layer that allows the two base layers to be separated by immersion in a solvent. With this packaging film, the two base layers can be easily separated by immersion in an appropriate solvent, and thus a packaging film that is easily recyclable can be provided.

In the preferred packaging film of the present disclosure, the intervening layer is at least one of water-soluble and alkali-soluble.

In the preferred packaging film of the present disclosure, the intervening layer contains an acrylic acid copolymer resin.

In the preferred packaging film of the present disclosure, the intervening layer has an acid value of 40 mg-KOH/g or more and 150 mg-KOH/g or less.

The preferred packaging film of the present disclosure has a printed ink layer formed on at least one substrate layer.

In a preferred packaging film of the present disclosure, one of the two adjacent substrate layers is a resin layer, and the other substrate layer is a metal thin film layer or a resin layer.

The pouch container of the present disclosure is formed using any one of the packaging films described above. With this pouch container, the two base layers can be easily separated, making it possible to provide a pouch container that is easily recyclable.

The packaging film of the present disclosure can be easily separated into two base layers made of different materials by immersing it in an appropriate solvent. The packaging film of the present disclosure, which can be separated into different materials, and the pouch containers using the same can be easily recycled.

FIG. 1 is a plan view in which a portion of the packaging film is omitted. FIG. 2 is a cross-sectional view showing an example of a first laminate structure of a packaging film. FIG. 3 is a cross-sectional view showing another example of the first laminate structure of the packaging film. FIG. 4 is a cross-sectional view showing another example of the first laminate structure of the packaging film. FIG. 5 is a cross-sectional view showing another example of the first laminated structure of the packaging film. FIG. 6 is a cross-sectional view showing another example of the second laminated structure of the packaging film. FIG. 7 is a cross-sectional view showing another example of the second laminated structure of the packaging film. FIG. 8 is a cross-sectional view showing another example of the second laminated structure of the packaging film. FIG. 9 is a cross-sectional view showing another example of the second laminated structure of the packaging film. FIG. 10 is a cross-sectional view showing another example of the third laminated structure of the packaging film. FIG. 11 is a cross-sectional view showing another example of the third laminated structure of the packaging film. FIG. 12 is a cross-sectional view showing another example of the third laminated structure of the packaging film. FIG. 13 is a cross-sectional view showing another example of the third laminated structure of the packaging film. FIG. 14 is a cross-sectional view of a packaging film having two substrate layers with a pre-adhesive layer disposed adjacent an interposer layer. FIG. 15 is a cross-sectional view of a packaging film having three substrate layers with a pre-adhesive layer disposed adjacent an interposer layer. FIG. 16 is a cross-sectional view of a packaging film having four substrate layers with a pre-adhesive layer disposed adjacent an interposer layer. FIG. 17 is a perspective view showing an example of a pouch container formed using a packaging film. FIG. 18 is a perspective view showing an example of a pillow packaging bag formed using a packaging film.

The following describes the embodiments of the present disclosure with reference to the drawings. In this specification, the terms may be prefixed with "first," "second," "third," etc., but the "first," etc. are added only to distinguish the terms and do not have any special meaning such as order or superiority. In this specification, a numerical range represented by "lower limit X to upper limit Y" means a range from lower limit X to upper limit Y. When a plurality of numerical ranges are separately described, it is assumed that an arbitrary lower limit and an arbitrary upper limit can be selected to set "an arbitrary lower limit to an arbitrary upper limit." The dimensions, scale, and shapes of the layers and members shown in each figure may differ from the actual ones. In addition, the surface of the packaging film is the upper surface of the packaging film shown in each figure, and the back surface of the packaging film is the lower surface of the packaging film shown in each figure. In addition, the surface of each layer is the upper surface of each layer shown in each figure, and the back surface of each layer is the lower surface of each layer shown in each figure.

<Overview of packaging film>
The packaging film of the present disclosure is a packaging film in which at least two base layers made of different materials are laminated. Specifically, the packaging film of the present disclosure is a laminate including at least two adjacent base layers and an intervening layer disposed between the two base layers. The two base layers are made of different materials. The intervening layer is intervened between the two base layers adjacent in the thickness direction. The intervening layer is a layer that is solvent-soluble and allows the two base layers to be separated by immersion in a solvent. Solvent-soluble refers to the property of dissolving in a solvent.

In this way, the intervening layer is a layer that allows two adjacent base layers to be separated when the packaging film is immersed in an appropriate solvent. However, when not immersed in a solvent (when not immersed in a solvent), the two adjacent base layers do not separate. In other words, when not immersed in a solvent, the packaging film is a laminate in which the adhesive state of each layer, such as the base layer and intervening layer, is maintained to such an extent that they cannot be easily peeled apart by human force. Note that adhesion refers to a state in which two layers are bonded together by physical and/or chemical forces, and are bonded in such a way that the layers cannot be easily peeled apart by human force.

The packaging film may have at least two adjacent substrate layers, and may have three or more substrate layers. When the packaging film has three or more substrate layers, it is preferable that the above-mentioned intervening layer is provided between each of two adjacent substrate layers. In addition, in the packaging film, at least one substrate layer selected from the multiple substrate layers (at least two substrate layers) may have a printing ink layer formed thereon, if necessary.

The printed ink layer is made of a solidified ink film formed by directly printing a known ink onto a substrate layer or the like using a known printing method. The printed ink layer is firmly adhered to the surface on which it is formed. The printed ink layer may be colored or uncolored (colorless and transparent). A colored printed ink layer may be opaque or colored and transparent. In the substrate layer on which the printed ink layer is formed, the intervening layer may be disposed between the printed ink layer and the substrate layer, or may be disposed between the substrate layer on which the printed ink layer is formed and the substrate layer adjacent thereto.

In this specification, transparent means colorless transparent or colored transparent. "Transparent" refers to a state in which a number (12 point size) printed on white paper in black ink is placed 1 cm away from the back side of the layer to be measured, and the number can be discerned from the front side through the layer to be measured. "Opaque" refers to a state in which a number placed on the back side under the same conditions as above cannot be seen from the front side (a state in which the number cannot be recognized).

Transparency (colorless transparent or colored transparent) can be expressed, for example, using total light transmittance. Transparency (colorless transparent or colored transparent) means, for example, a total light transmittance of 70% or more, preferably 80% or more, and more preferably 90% or more. However, the total light transmittance refers to a value measured by a measurement method conforming to JIS K 7361:1997 (Test method for total light transmittance of plastic transparent materials) for a transparent measurement object. Note that, if the substrate layer, intervening layer, or printing ink layer itself cannot be used as the measurement object, the measurement object is one in which they are provided on a support film having a total light transmittance of 90% or more as measured according to the JIS standard.

The base layer, intervening layer, and printing ink layer are all layered, but the base layer differs from the intervening layer and printing ink layer in that it can form a layer by itself. In other words, the base layer can maintain a layered structure by itself, while the intervening layer and printing ink layer form a layer while attached to the base layer (they form a layer by being supported by the base layer), but are very fragile by themselves and can break with even a slight force, making it impossible to maintain a layered structure.

The packaging film is flexible. The packaging film may be transparent or opaque as a whole. The packaging film may have heat shrinkability, but preferably has no substantial heat shrinkability. Heat shrinkability refers to the property of shrinking when heated to a desired temperature (e.g., 70°C to 90°C).

The shape of the packaging film in plan view is a long strip, as shown in FIG. 1. The long strip refers to a generally rectangular shape in plan view, in which the longitudinal length is sufficiently longer than the lateral length, and for example, the longitudinal length is at least three times, preferably at least five times, the lateral length. Specific dimensions of the long strip include, for example, a lateral length of 100 mm to 3000 mm and a longitudinal length of 2 m to 500 m. The long strip packaging film is usually wound into a roll for storage and transportation, and is cut into a desired shape when preparing packaging material. However, the packaging film of the present disclosure is not limited to a long strip, and may be formed into a sheet-like shape in plan view (not shown). Examples of the sheet-like shape include a generally rectangular shape in plan view, a generally polygonal shape in plan view such as a generally triangular shape or a generally hexagonal shape, and a generally circular shape in plan view.

<Example of laminated structure of packaging film>
Next, several laminated structures of the packaging film of the present disclosure will be illustrated. Figures 2 to 5 are cross-sectional views showing examples of a first laminated structure of the packaging film. In Figures 2 to 5, the packaging film 1 has two substrate layers (for convenience, referred to as a first substrate layer 21 and a second substrate layer 22) laminated together. The first substrate layer 21 and the second substrate layer 22 are substrate layers made of different materials.

Specifically, the packaging film 1 in FIG. 2 is laminated in this order from the surface side (upper side in the figure) with the first base material layer 21, the intervening layer 3, and the second base material layer 22. The packaging film 1 in FIG. 3 is laminated in this order from the surface side with the first base material layer 21, the colored printing ink layer 41, the intervening layer 3, and the second base material layer 22. The packaging film 1 in FIG. 4 is laminated in this order from the surface side with the first base material layer 21, the intervening layer 3, the colored printing ink layer 41, and the second base material layer 22. The packaging film 1 in FIG. 5 is laminated in this order from the surface side with the colorless and transparent printing ink layer 42, the first base material layer 21, the intervening layer 3, and the second base material layer 22.

The packaging film 1 in which the colored printing ink layer 41 is formed between the first base material layer 21 and the second base material layer 22 may have, for example, the following configuration:
(A) In order to make the color of the colored printed ink layer 41 visible from the front side of the packaging film 1, each layer (e.g., the first base material layer 21 in FIG. 3 , the first base material layer 21 and the intermediate layer 3 in FIG. 4 ) arranged on the front side of the colored printed ink layer 41 is transparent, and each layer arranged on the back side of the colored printed ink layer 41 is transparent or opaque;
(B) In order to enable the color of the colored printed ink layer 41 to be visible from the back side of the packaging film 1, each layer arranged on the back side of the colored printed ink layer 41 (e.g., the second base material layer 22 and the intervening layer 3 in Figure 3, and the second base material layer 22 in Figure 4) is transparent, and each layer arranged on the front side of the colored printed ink layer 41 is transparent or opaque.

The colored printing ink layer 41 is not limited to being formed between the first substrate layer 21 and the second substrate layer 22, but may be formed on the surface of the first substrate layer 21 (in this case, for example, even if the first substrate layer 21 etc. is opaque, the color can be seen from the surface side), or may be formed on the back surface of the second substrate layer 22 (in this case, even if the second substrate layer 22 etc. is opaque, the color can be seen from the back surface side). The colored printing ink layer 41 may be formed between the substrate layers, and on the surface of the first substrate layer 21 or/and the back surface of the second substrate layer 22. The colorless and transparent printing ink layer 42 is not limited to being formed on the surface of the first substrate layer 21, but may be formed between the first substrate layer 21 and the second substrate layer 22, or/and on the back surface of the second substrate layer 22.

Figures 6 to 9 are cross-sectional views showing an example of the second laminated structure of the packaging film. In Figures 6 to 9, the packaging film 1 has three laminated substrate layers (for convenience, referred to as a first substrate layer 21, a second substrate layer 22, and a third substrate layer 23). In these packaging films 1, there are two sets of two adjacent substrate layers, and at least one set of two adjacent substrate layers is a substrate layer made of a different material, and preferably, the two sets of two adjacent substrate layers are substrate layers made of a different material.

Specifically, the packaging film 1 in FIG. 6 is laminated in the following order from the surface side: the first substrate layer 21, the intermediate layer 3, the third substrate layer 23, the intermediate layer 3, and the second substrate layer 22. In this example, the first substrate layer 21 and the third substrate layer 23 are adjacent substrate layers, and the third substrate layer 23 and the second substrate layer 22 are adjacent substrate layers. For example, it is preferable that the first substrate layer 21, the second substrate layer 22, and the third substrate layer 23 are all made of different materials. The packaging film 1 in FIG. 7 is laminated in the following order from the surface side: the first substrate layer 21, the colored printing ink layer 41, the intermediate layer 3, the third substrate layer 23, the intermediate layer 3, and the second substrate layer 22. The packaging film 1 in Fig. 8 is laminated in this order from the surface side, with the first substrate layer 21, the intervening layer 3, the colored printed ink layer 41, the third substrate layer 23, the intervening layer 3, and the second substrate layer 22. The packaging film 1 in Fig. 9 is laminated in this order from the surface side, with the colorless and transparent printed ink layer 42, the first substrate layer 21, the intervening layer 3, the third substrate layer 23, the intervening layer 3, and the second substrate layer 22.

The packaging film 1 in which the colored printing ink layer 41 is formed between the first base material layer 21 and the third base material layer 23 may have a configuration such as (A) or (B) below:
(A) In order to make the color of the colored printed ink layer 41 visible from the front side of the packaging film 1, each layer arranged on the front side of the colored printed ink layer 41 is transparent, and each layer arranged on the back side of the colored printed ink layer 41 is transparent or opaque;
(B) In order to enable the color of the colored printed ink layer 41 to be visible from the back side of the packaging film 1, each layer arranged on the back side of the colored printed ink layer 41 is transparent, and each layer arranged on the front side of the colored printed ink layer 41 is transparent or opaque.

The colored printing ink layer 41 is not limited to being formed between the first substrate layer 21 and the third substrate layer 23, but may be formed between the third substrate layer 23 and the second substrate layer 22. In the packaging film 1 having three substrate layers, the colored printing ink layer 41 may be formed on the surface of the first substrate layer 21, or on the back surface of the second substrate layer 22, or between the substrate layers, and on the surface of the first substrate layer 21 and/or the back surface of the second substrate layer 22, as in the packaging film 1 having the above two substrate layers. In addition, the colorless and transparent printing ink layer 42 is not limited to being formed on the surface of the first substrate layer 21, but may be formed between the substrate layers or/and on the back surface of the second substrate layer 22.

Figures 10 to 13 are cross-sectional views showing an example of the third laminated structure of the packaging film. In Figures 10 to 13, the packaging film 1 has four laminated substrate layers (for convenience, referred to as the first substrate layer 21, the second substrate layer 22, the third substrate layer 23, and the fourth substrate layer 24). In the four laminated substrate layers, there are three pairs of two adjacent substrate layers, and at least one pair of adjacent substrate layers is made of substrate layers made of different materials, and preferably, the three pairs of adjacent substrate layers are made of substrate layers made of different materials.

Specifically, the packaging film 1 in FIG. 10 is laminated in the following order from the surface side: a first substrate layer 21, an intervening layer 3, a third substrate layer 23, an intervening layer 3, a fourth substrate layer 24, an intervening layer 3, and a second substrate layer 22. In this example, the first substrate layer 21 and the third substrate layer 23 are two substrate layers adjacent to each other, the third substrate layer 23 and the fourth substrate layer 24 are two substrate layers adjacent to each other, and the fourth substrate layer 24 and the second substrate layer 22 are two substrate layers adjacent to each other. For example, it is preferable that the first substrate layer 21, the second substrate layer 22, the third substrate layer 23, and the fourth substrate layer 24 are all made of different materials. In the packaging film 1 of FIG. 11, the first base material layer 21, the colored printing ink layer 41, the intermediate layer 3, the third base material layer 23, the intermediate layer 3, the fourth base material layer 24, the intermediate layer 3, and the second base material layer 22 are laminated in this order from the surface side. In the packaging film 1 of FIG. 12, the first base material layer 21, the intermediate layer 3, the colored printing ink layer 41, the third base material layer 23, the intermediate layer 3, the fourth base material layer 24, the intermediate layer 3, and the second base material layer 22 are laminated in this order from the surface side. In the packaging film 1 of FIG. 13, the colorless and transparent printing ink layer 42, the first base material layer 21, the intermediate layer 3, the third base material layer 23, the intermediate layer 3, the fourth base material layer 24, the intermediate layer 3, and the second base material layer 22 are laminated in this order from the surface side.

The packaging film 1 in which the colored printing ink layer 41 is formed between the first base material layer 21 and the third base material layer 23 may have a configuration such as (A) or (B) below:
(A) In order to make the color of the colored printed ink layer 41 visible from the front side of the packaging film 1, each layer arranged on the front side of the colored printed ink layer 41 is transparent, and each layer arranged on the back side of the colored printed ink layer 41 is transparent or opaque;
(B) In order to enable the color of the colored printed ink layer 41 to be visible from the back side of the packaging film 1, each layer arranged on the back side of the colored printed ink layer 41 is transparent, and each layer arranged on the front side of the colored printed ink layer 41 is transparent or opaque.

The colored printing ink layer 41 is not limited to being formed between the first substrate layer 21 and the third substrate layer 23, but may be formed between the third substrate layer 23 and the fourth substrate layer 24, or/and between the fourth substrate layer 24 and the second substrate layer 22. In the packaging film 1 having four substrate layers, similar to the packaging film 1 having the above two substrate layers, the colored printing ink layer 41 may be formed on the surface of the first substrate layer 21, or on the back surface of the second substrate layer 22, or between the substrate layers, and on the surface of the first substrate layer 21 or/and the back surface of the second substrate layer 22. In addition, the colorless and transparent printing ink layer 42 is not limited to being formed on the surface of the first substrate layer 21, but may be formed between the substrate layers, or/and on the back surface of the second substrate layer 22.

Figures 14 to 16 are cross-sectional views showing an example of a configuration in which a preliminary adhesive layer that complements an intervening layer is provided between adjacent base material layers of a packaging film. Specifically, Figure 14 is a cross-sectional view of a packaging film having two base material layers, in which a preliminary adhesive layer is provided in contact with the intervening layer. Figure 15 is a cross-sectional view of a packaging film having three base material layers, in which a preliminary adhesive layer is provided in contact with the intervening layer. Figure 16 is a cross-sectional view of a packaging film having four base material layers, in which a preliminary adhesive layer is provided in contact with the intervening layer.

If the intervening layer does not adhere or does not adhere well to the base layer or to the printed ink layer formed on the base layer, a preliminary adhesive layer 5 is provided between the intervening layer and the base layer and/or between the intervening layer and the printed ink layer formed on the base layer as necessary. In all of Figures 14 to 16, the preliminary adhesive layer 5 is provided between the printed ink layer 41 formed on the first base layer 21 and the intervening layer 3, but this is not limited to this and the preliminary adhesive layer 5 may be provided between any suitable layers. Furthermore, the preliminary adhesive layer 5 is not limited to one layer and may be provided between several layers.

Although not specifically shown, the arrangement of the preliminary adhesive layer 5 may be implemented in packaging films 1 in which five or more base material layers are laminated. As with the packaging film having five or more base material layers, as long as the packaging film has at least two base material layers in which two adjacent base material layers are made of different materials and an intervening layer is provided between the layers, as described above.

<Intervening layer>
The intermediate layer is soluble in a solvent and is disposed between adjacent substrate layers. For example, the intermediate layer is between two adjacent substrate layers, and is directly adhered to the back surface of one substrate layer and the front surface of the other substrate layer, thereby binding the two substrate layers. This embodiment is shown, for example, in Fig. 2, Fig. 5, Fig. 6, and Fig. 9. For example, the intermediate layer is between two adjacent substrate layers, and is directly adhered to the back surface (or front surface) of the printed ink layer of one substrate layer on which the printed ink layer is formed and the front surface (or back surface) of the other substrate layer, thereby binding the two substrate layers via the printed ink layer. This embodiment is shown, for example, in Fig. 3, Fig. 4, Fig. 7, and Fig. 8. For example, the intervening layer is between two adjacent substrate layers and is directly adhered to the back (or front) side of the printed ink layer of one substrate layer on which a printed ink layer is formed and to the front (or back) side of the printed ink layer of the other substrate layer on which a printed ink layer is formed, binding both substrate layers via the one and the other printed ink layers.

In addition, when it is difficult for the intervening layer to adhere directly to the front or back surface of the base layer or the printed ink layer due to the material of the base layer or the printed ink layer, the above-mentioned preliminary adhesive layer is provided as appropriate. As described above, the preliminary adhesive layer is provided between the intervening layer and the base layer and/or between the intervening layer and the printed ink layer. In this case, the preliminary adhesive layer and the intervening layer work together to bind two adjacent base layers.

The solvent-soluble intervening layer has at least one property selected from, for example, water solubility, alkali solubility, organic solvent solubility, etc., and preferably has at least one of water solubility and alkali solubility. The solvent-soluble intervening layer contains a solvent-soluble polymer as a main component. The intervening layer may contain components other than the main component, the solvent-soluble polymer, and such components include known additives, residual solvents, etc.

Here, in this specification, the main component of a layer refers to the component (weight ratio) that is the largest among the components contained in that layer. For example, the main component is contained in an amount of 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more, when the entire layer is taken as 100% by weight.

Because the intervening layer contains a solvent-soluble polymer as a main component, when the packaging film is immersed in a solvent, the solvent-soluble polymer in the intervening layer dissolves into the solvent from between the substrate layers. This causes the intervening layer to gradually lose or lose its function of binding between layers or its function of binding between substrate layers in cooperation with the preliminary adhesive layer. Therefore, two substrates adjacent to each other with the intervening layer in between can be easily separated.

A solvent-soluble polymer is a polymer that is soluble in a specific solvent. Examples of solvent-soluble polymers include water-soluble polymers, alkali-soluble polymers, and organic solvent-soluble polymers. Preferably, at least one of a water-soluble polymer and an alkali-soluble polymer is used. An intervening layer that is mainly composed of a water-soluble polymer has water solubility, and an intervening layer that is mainly composed of an alkali-soluble polymer has alkali solubility.

A water-soluble polymer is a polymer that is soluble in water or an aqueous solvent at room temperature and normal pressure, for example, a polymer with a solubility in water of 1 (g/100 g) or more at 23°C and 1 atmosphere, preferably a polymer with a solubility of 5 (g/100 g) or more. In addition, it is preferable for the water-soluble polymer to have improved solubility in water heated to an appropriate temperature. Examples of heating temperatures include 50°C to 100°C.

The water-soluble polymer is not particularly limited, and examples thereof include synthetic resins and natural polymers. Examples of synthetic resins include polyvinyl alcohol-based resins such as polyvinyl alcohol and modified polyvinyl alcohol, polyvinyl acetate-based resins, cellulose-based resins, acrylic resins, polyacrylamide-based resins, polyethylene oxide-based resins, polyurethane-based resins, and amino-based resins. Examples of natural polymers include polysaccharides such as starch and polypeptides, glue, casein, and natural rubber. These may be used alone or in combination of two or more.

An aqueous solvent is a mixed solvent containing water and a hydrophilic solvent. A hydrophilic solvent is a solvent that can be dissolved uniformly in water. Examples of hydrophilic solvents include alcohols such as methanol, glycols such as ethylene glycol, cellosolves such as methyl cellosolve, and esters such as ethyl acetate.

An alkali-soluble polymer is a polymer that is soluble in an alkaline aqueous solution at room temperature and normal pressure, for example, a polymer with a solubility of 1 (g/100g) or more in an alkaline aqueous solution (aqueous sodium hydroxide solution with a concentration of 1.5% by weight) at 23°C and 1 atmosphere, preferably a polymer with a solubility of 5 (g/100g) or more. In addition, it is preferable that the alkali-soluble polymer has improved solubility in the alkaline aqueous solution heated to an appropriate temperature. Examples of heating temperatures include 50°C to 100°C.

The alkali-soluble polymer is not particularly limited, and examples thereof include copolymers of one or more unsaturated carboxylic acids and one or more compounds having a polymerizable unsaturated group. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, and itaconic acid. Examples of compounds having a polymerizable unsaturated group include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate; hydroxyl group-containing polymerizable unsaturated compounds such as hydroxyethyl acrylate and hydroxyethyl methacrylate; cyano group-containing polymerizable unsaturated compounds such as acrylonitrile and methacrylonitrile; amide group-containing polymerizable unsaturated compounds such as acrylamide, methacrylamide, N-alkoxyacrylamide, N-alkoxymethacrylamide, N-methylolacrylamide, and N-methylolacrylamide; styrene-based compounds such as styrene, vinyltoluene, α-methylstyrene, and divinylbenzene; olefins such as ethylene; allyl group-containing compounds such as diallyl phthalate, allyl glycidyl ether, and triallyl isocyanurate; vinyl esters such as vinyl acetate; and N-vinylpyrrolidone.

In particular, alkali-soluble polymers mainly composed of styrene-maleic anhydride resins having an acid value of 50 to 300 (mg-KOH/g), rosin-maleic acid resins having an acid value of 50 to 300 (mg-KOH/g), and acrylic acid copolymer resins having an acid value of 50 to 300 (mg-KOH/g) are preferred.

As the styrene-maleic anhydride resin, a known styrene-maleic anhydride resin can be used. For example, suitable styrene-maleic anhydride resins include known styrene-maleic anhydride copolymers, which are copolymers of styrene and maleic anhydride, and modified products of the styrene-maleic anhydride copolymers (e.g., partially esterified products). In the styrene-maleic anhydride copolymer, in addition to styrene, styrene compounds such as α-methylstyrene can be used as the styrene.

The rosin-maleic acid resin may be a known rosin-maleic acid resin. For example, a suitable rosin-maleic acid resin may be an ester obtained by condensing an addition reaction product of rosin and maleic anhydride (e.g., an addition product of a tribasic acid) with a polyhydric alcohol (e.g., glycerin).

An acrylic acid copolymer resin is a resin that has acrylic acid and/or methacrylic acid as the main repeating unit and further has a copolymerizable monomer that can be copolymerized with the acrylic acid and/or methacrylic acid. It is preferable that the total ratio of the acrylic acid and/or methacrylic acid and the copolymerizable monomer in the acrylic acid copolymer resin is 60 mol% or more.

Examples of copolymerizable monomers include (meth)acrylic acid alkyl esters (preferably lower alkyl esters of (meth)acrylic acid) such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and t-butyl (meth)acrylate; hydroxyl group-containing (meth)acrylates such as hydroxyethyl (meth)acrylate; glycidyl group-containing (meth)acrylates such as glycidyl (meth)acrylate; and N,N'-dimethyl (meth)acrylamide. , (meth)acrylamides such as N,N'-diethyl(meth)acrylamide; amino group-containing (meth)acrylates such as dimethylaminoethyl(meth)acrylate; styrenes such as styrene, vinyl toluene, α-methylstyrene; vinyl esters such as vinyl acetate and vinyl propionate; vinyl halides such as vinyl chloride; vinyl ethers such as methyl vinyl ether; carboxyl group-containing vinyls such as itaconic acid and maleic anhydride [excluding (meth)acrylic acid]; cyano group-containing vinyls such as acrylonitrile and methacrylonitrile; olefins and dienes such as ethylene and propylene. The copolymerizable monomers can be used alone or in combination of two or more.

The intermediate layer preferably has an acid value of 40 to 150 (mg-KOH/g). For example, if the intermediate layer is mainly composed of an acrylic acid copolymer resin, and the acrylic acid copolymer resin is a mixed resin of two types of acrylic acid copolymer resins, the acid value of the intermediate layer will be different from the acid value of each of the two acrylic acid copolymer resins. Also, if the intermediate layer contains a resin having an acid value other than the main resin, the acid value of the intermediate layer will be different from the acid value of the main resin. The acid value of the intermediate layer varies depending on the acid value of each of the resins contained and the content ratio of each. The acid value of the intermediate layer can be confirmed, for example, by measuring the acid value of the resin composition that constitutes the intermediate layer.

In addition, it is preferable that the intervening layer further contains a vinyl chloride-vinyl acetate copolymer in addition to the resin that is the main component described above. In this case, the adhesion of the intervening layer to other layers can be improved, and the design of the packaging film can be improved.

The content of the vinyl chloride-vinyl acetate copolymer in the intervening layer is preferably 1 to 10% by weight, and more preferably 2 to 5% by weight, when the entire intervening layer is taken as 100% by weight. If the weight percentage is less than 1, the further improvement in adhesion tends to be insufficient, and if it exceeds 10, the viscosity of the intervening layer tends to be too high, making handling difficult. The vinyl chloride-vinyl acetate copolymer preferably has an Mn (number average molecular weight) of 10,000 to 40,000, and more preferably has an Mn of 15,000 to 35,000. In this case, the improvement in adhesion becomes significant.

The intervening layer of the present disclosure is preferably a layer formed from a resin composition having an acrylic acid copolymer resin as a main component and an apparent acid value of 40 to 150 (mg-KOH/g). It is further preferable that the intervening layer contains a vinyl chloride-vinyl acetate copolymer. In this case, the acrylic acid copolymer resin may be a mixed resin of two or more kinds of acrylic acid copolymer resins.

The alkali-soluble polymer may be one described in Patent Document 2 (JP Patent Publication No. 2003-084670). As an intermediate layer containing an alkali-soluble polymer that can be used in the present disclosure, the alkali-soluble coating layer described in Patent Document 2 is described in this specification, and the description of Patent Document 2 is omitted in this specification due to space limitations. However, this specification is intended to incorporate at least the description of [0011] to [0032] of Patent Document 2 as it is. The alkali-soluble coating layer described in Patent Document 2 is preferably used as an intermediate layer between the printing ink layer and the substrate layer of the present disclosure.

The thickness of the intervening layer is not particularly limited and is, for example, 0.5 μm to 20 μm, and preferably 1 μm to 15 μm.

<Preliminary adhesive layer>
The preliminary adhesive layer is provided between the intermediate layer and the base layer, or/and between the intermediate layer and the printing ink layer, as necessary. The preliminary adhesive layer is not particularly limited as long as it can bond the two layers between which it is interposed, and a known adhesive can be used. For example, the preliminary adhesive layer can be a so-called dry lamination adhesive such as a solvent volatilization type adhesive, a solventless adhesive, an anchor coating agent, or the like.

<Base layer>
Examples of the substrate layer include a resin layer, a metal thin film layer, a nonwoven fabric layer, and a paper layer. Examples of the resin layer include those containing a known resin as a main component. Examples of the resin include polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polylactic acid; polyolefin-based resins such as polyethylene and polypropylene; polyamide-based resins such as 6-nylon and 66-nylon; polystyrene-based resins such as polystyrene; polycarbonate-based resins; nitrile-based resins such as polyacrylonitrile; imide-based resins such as polyimide; vinyl chloride-based resins such as polyvinyl chloride and polyvinylidene chloride; and acrylate-based resins such as polymethyl methacrylate. The thickness of the resin layer is not particularly limited, and is, for example, 10 μm to 200 μm, and preferably 10 μm to 100 μm. The resin layer is usually a non-foamed layer, but may be foamed.

Examples of the metal thin film layer include aluminum foil and copper foil. The thickness of the metal thin film layer is not particularly limited and is, for example, 5 μm to 30 μm. Examples of the nonwoven fabric layer include nonwoven fabrics prepared in a sheet shape by a bonding method, a needle punching method, a spunbonding method, a meltblowing method, etc. Examples of the fibers include polyester fibers; polyolefin fibers such as polypropylene and polyethylene; rayon fibers; polyamide fibers such as nylon; and natural fibers. The basis weight of the nonwoven fabric is not particularly limited and is, for example, 10 to 100 g/m ^2. Examples of the paper layer include plain paper and fine paper.

The polyvinylidene chloride resin layer and the metal thin film layer have gas barrier properties. By using a base layer with such gas barrier properties, gas barrier properties can be imparted to the packaging film. In addition, low-density polyethylene layers, ethylene-propylene copolymer layers, ethylene-olefin copolymer layers, and the like have sealant properties (thermal welding properties). By using a base layer with such sealant properties (for example, a base layer that constitutes the backmost surface of a laminate), sealant properties can be imparted to the packaging film.

Furthermore, polyester resin layers such as polyethylene terephthalate and polyamide resin layers such as nylon have superior heat resistance compared to sealant properties. Therefore, by using a base layer having such heat resistance (for example, a base layer constituting the outermost surface of a laminate), heat resistance can be imparted to the packaging film. In addition, foamed resin layers, nonwoven fabric layers, etc. have heat insulating properties. By using a base layer having such heat insulating properties, heat insulating properties can be imparted to the packaging film.

As described above, the two adjacent base layers on which the intervening layer is provided are made of different materials. Here, two base layers made of different materials refer to those made with different materials as the main components, and two base layers made of the same material refer to those made with the same material as the main component.

For example, examples of substrate layers made of different materials include combinations of a resin layer and a metal thin film layer (resin and metal are different materials), a resin layer and a paper layer (resin and pulp are different materials), and a metal thin film layer and a paper layer (metal and pulp are different materials).

In addition, in the resin layer, resin layers that have different resins as their main components are in a relationship of substrate layers made of different materials. Similarly, in the metal thin film layer, metal thin film layers that have different metals as their main components are in a relationship of substrate layers made of different materials, and in the nonwoven fabric layer, nonwoven fabric layers that have different fibers as their main components are in a relationship of substrate layers made of different materials.

For example, a resin layer whose main component is polyethylene terephthalate and a resin layer whose main component is polyethylene are two base layers made of different resins and different materials. A metal thin film layer whose main component is aluminum (aluminum foil) and a metal thin film layer whose main component is copper (copper foil) are two base layers made of different metals and different materials. A nonwoven fabric layer whose main component is rayon fiber and a nonwoven fabric layer whose main component is nylon are two base layers made of different fibers and different materials.

On the other hand, a resin layer whose main component is polyethylene terephthalate and a nonwoven fabric whose main component is polyethylene terephthalate fibers are two base material layers that are made of the same material and have the same main component resin.

In the packaging film 1 having two base layers shown in Figures 2 to 5, for example, any resin layer is used as the first base layer 21, which is the base layer on the front side, and a resin layer made of a different resin material is used as the second base layer 22, which is the base layer on the back side, and a solvent-soluble intermediate layer 3 is provided between them.

In the packaging film 1 having three substrate layers shown in Figures 6 to 9, for example, any resin layer is used as the first substrate layer 21, which is the substrate layer on the front side, a resin layer made of a different resin material is used as the third substrate layer 23, which is the intermediate substrate layer, and a resin layer made of a different resin material is used as the second substrate layer 22, which is the substrate layer on the back side, and an intermediate layer 3 having solvent solubility is provided between the first substrate layer 21 and the third substrate layer 23, and between the third substrate layer 23 and the second substrate layer 22.

The third substrate layer 23 may be a metal thin film layer, a nonwoven fabric layer, or a paper layer. The first substrate layer 21 and the third substrate layer 23 may be substrate layers made of the same material, or the third substrate layer 23 and the second substrate layer 22 may be substrate layers made of the same material. In this way, in a packaging film 1 including two adjacent substrate layers made of the same material, a solvent-soluble intermediate layer 3 may be provided between the two substrate layers made of the same material, or such an intermediate layer may not be provided.

When the packaging film 1 having the three base material layers shown in Figs. 6 to 9 is used as a pouch film for forming a pouch container, it can be configured, for example, as follows.
A first base material layer 21 having heat resistance, such as a polyester-based resin layer or a polyamide-based resin layer such as nylon;
a third substrate layer 23 having gas barrier properties, such as a polyvinylidene chloride resin layer or a metal thin film layer;
A second base material layer 22 having sealant properties, such as a low-density polyethylene layer or an ethylene-propylene copolymer layer.

In the packaging film 1 having four substrate layers shown in Figures 10 to 13, for example, any resin layer is used as the first substrate layer 21, which is the substrate layer on the front side; a metal thin film layer is used as the third substrate layer 23, which is the intermediate substrate layer; any resin layer is used as the fourth substrate layer 24; and a resin layer made of a different resin material is used as the second substrate layer 22, which is the substrate layer on the back side; and solvent-soluble intermediate layers 3 are provided between the first substrate layer 21 and the third substrate layer 23, between the third substrate layer 23 and the fourth substrate layer 24, and between the fourth substrate layer 24 and the second substrate layer 22.

The third substrate layer 23 may be a resin layer, a nonwoven fabric layer, or a paper layer, or the fourth substrate layer 24 may be a metal thin film layer, a nonwoven fabric layer, or a paper layer. The first substrate layer 21 and the third substrate layer 23 may be substrate layers made of the same material, or the third substrate layer 23 and the fourth substrate layer 24 may be substrate layers made of the same material, or the fourth substrate layer 24 and the second substrate layer 22 may be substrate layers made of the same material. In this way, in a packaging film 1 including two adjacent substrate layers made of the same material, a solvent-soluble intermediate layer 3 may be provided between the two substrate layers made of the same material, or such an intermediate layer may not be provided.

When the packaging film 1 having the four base material layers shown in Figs. 10 to 13 is used as a pouch film for forming a pouch container, it can be configured, for example, as follows.
A first base material layer 21 having heat resistance, such as a polyester-based resin layer or a polyamide-based resin layer such as nylon;
a third substrate layer 23 having gas barrier properties, such as a polyvinylidene chloride resin layer or a metal thin film layer;
a fourth base material layer 24 having heat resistance, such as a polyester-based resin layer or a polyamide-based resin layer such as nylon;
A second base material layer 22 having sealant properties, such as a low-density polyethylene layer or an ethylene-propylene copolymer layer.

<Wrapping film manufacturing method>
The packaging film is obtained by laminating the respective base layers with an intervening layer interposed therebetween. For example, a solution of a solvent-soluble polymer dissolved in a suitable solvent is applied to the joining surface of one or both of the two adjacent base layers to form an uncured intervening layer, and then the solvent is removed by drying or the like. As a result, the solvent-soluble intervening layer bonds the two adjacent base layers.

The method of applying the solution containing the solvent-soluble polymer is not particularly limited, and examples thereof include a conventionally known printing method and a coating method using an appropriate coater. The concentration of the solution containing the solvent-soluble polymer is not particularly limited, and the concentration may be adjusted to provide an appropriate viscosity according to the application method.

<Applications of packaging film>
The packaging film of the present disclosure can be generally used as a known packaging material (including tack labels, etc.), and is used, for example, by processing it into a soft packaging material. The soft packaging material is a soft packaging material that wraps various items. The soft packaging material formed using the packaging film of the present disclosure is preferably one that wraps an item in a sealed state, and representative examples of such soft packaging materials include pouch containers and pillow packaging bags.

Figure 17 is a perspective view showing an example of a pouch container formed using a packaging film. Figure 18 is a perspective view showing an example of a pillow packaging bag formed using a packaging film. It is preferable that the packaging film forming the pouch container A1, the pillow packaging bag A2, etc. uses a base material layer having sealant properties as the base material layer on the backmost surface (the surface facing the internal space of the container and packaging bag).

The packaging film of the present disclosure has an intermediate layer between two base layers made of different materials, which is solvent-soluble and allows the two base layers to be separated by immersion in a solvent. By immersing such a packaging film in an appropriate solvent, the intermediate layer dissolves, allowing the base layers made of different materials to be easily separated.

For example, when a water-soluble intermediate layer is used in a packaging film, water penetrates into the intermediate layer from the end face of the intermediate layer by immersing the packaging film in water or an aqueous solvent, and the adhesive strength of the intermediate layer gradually decreases or disappears. This allows two base layers made of different materials to be easily separated. For example, when a packaging film uses an intermediate layer that is alkali-soluble, alkali penetrates into the intermediate layer from the end face of the intermediate layer by immersing the packaging film in an aqueous alkali solution, and the adhesive strength of the intermediate layer gradually decreases or disappears. This allows two base layers made of different materials to be easily separated. This allows the packaging film to be separated into individual materials, making it easy to recycle the packaging film.

In another aspect, the present disclosure provides a method for separating a packaging film having a solvent-soluble intervening layer between two adjacent substrate layers made of different materials by immersing the film in an appropriate solvent. As is clear from the examples below, the intervening layer can separate the two substrate layers at the latest 24 hours after immersion in the solvent.

The packaging film processed into the soft packaging material such as the above-mentioned pouch container can be immersed in an appropriate solvent while still in the form of the soft packaging material, and the two adjacent base layers can be separated via the intervening layer. Preferably, the soft packaging material can be cut into small pieces as desired, allowing for faster separation. The smaller the area of the pieces, the shorter the time required for separation. The packaging film of the present disclosure has an intervening layer that allows the two base layers to be separated without any particular load at the latest 24 hours after immersion in a solvent when cut into small pieces of, for example, 60 square centimeters.

The following describes examples and comparative examples to further explain this disclosure. However, this disclosure is not limited to the following examples.

[Example 1]
A water-soluble polymer (Nichigo G Polymer, product name: "Nichigo G Polymer") aqueous solution (polymer concentration: 10% by weight) was applied to the back surface of a 12 μm-thick biaxially stretched polyethylene terephthalate film (manufactured by Toyobo Co., Ltd. under the trade name "E5100") to a thickness of about 3 μm using a gravure printing method to form a first intervening layer. Then, a 7 μm-thick aluminum foil (manufactured by Toyo Aluminum Co., Ltd. under the trade name "General Foil") was laminated and bonded to the first intervening layer. Furthermore, a water-soluble polymer aqueous solution was applied to the back surface of the aluminum foil to a thickness of about 3 μm using a gravure printing method to form a second intervening layer. Then, a low-density polyethylene film (manufactured by Toyobo Co., Ltd. under the trade name "L4102") having a thickness of 80 μm was laminated and bonded to the second intervening layer to form a laminate. Then, the entire laminate was dried with hot air at about 80 ° C. This resulted in the production of a packaging film having a laminated structure, from the surface side, of a polyethylene terephthalate resin layer/a water-soluble first intermediate layer approximately 3 μm thick/aluminum thin film layer/a water-soluble second intermediate layer approximately 3 μm thick/polyethylene resin layer.

The packaging film of Example 1 was cut into strips 15 mm wide to obtain test pieces, and the 180° peel strength of the test pieces was measured. As a result, the 180° peel strength of the test pieces was 4.0 N/15 mm, which was a sufficient adhesion strength. The peel strength was measured at a peel speed of 200 mm/min using a tensile tester (manufactured by Shimadzu Corporation under the trade name "Autograph") at a peel speed of 200 mm/min. In the above measurement, the peel strength when the polyethylene terephthalate resin layer was peeled from the laminate and the peel strength when the polyethylene resin layer was peeled from the laminate were measured, but since both showed the above values, only one value was recorded. The same applies below.

Next, the packaging film of Example 1 was cut into pieces measuring 60 mm x 100 mm in length x width to prepare several identical sample pieces, which were then immersed in tap water at room temperature and left at room temperature (23°C). After immersion, one sample piece was removed every 20 minutes to check the peelability between the layers.

As a result, after 6 hours, the aluminum thin film layer and the polyethylene resin layer peeled off without any resistance. After 24 hours, the polyethylene terephthalate resin layer and the aluminum thin film layer peeled off without any resistance.

[Example 2]
15 parts by weight of styrene-maleic anhydride resin (acid value: 270 mg-KOH/g) (product name "SMA17352P" manufactured by Kawahara Oil Chemical Co., Ltd.), 4 parts by weight of acrylic resin (acid value: 4 mg-KOH/g, glass transition temperature: 47°C) (product name "UH2011" manufactured by Toa Gosei Co., Ltd.), and 1 part by weight of cellulose derivative (product name "CAB-381-0.5" manufactured by Eastman Chemical Japan Co., Ltd.) were dissolved in a mixed solvent of 50 parts by weight of ethyl acetate and 30 parts by weight of isopropyl alcohol to obtain a uniform resin liquid (coating agent). Of the coating agents, the styrene-maleic anhydride resin is an alkali-soluble polymer. The apparent acid value of this coating agent is 203 mg-KOH/g.

This coating agent was applied to the back of a 15 μm-thick nylon film (manufactured by Unitika Ltd. under the trade name "Emblem ON") in a solid manner using gravure printing, and then dried with hot air at about 80°C to form an intervening layer. Next, white ink (manufactured by Toyo Ink Co., Ltd. under the trade name "Rio Alpha S") was solid-printed to a thickness of about 1 μm on the back of this intervening layer using gravure printing. After that, dry laminating adhesive (manufactured by DIC Graphics Corporation under the trade name "LX500") was solid-printed to a thickness of about 3 μm on the back of the printed ink layer using gravure printing, and the solvent components were volatilized to dry the adhesive so that it could be adhered, and a 70 μm-thick polyethylene film (manufactured by Tamapoly Corporation under the trade name "SE620") was laminated and bonded. This produced a packaging film consisting of, from the surface side, a nylon resin layer, an alkali-soluble intermediate layer with a thickness of approximately 1 μm, a printing ink layer, an adhesive layer, and a polyethylene resin layer.

When the peel strength of the packaging film of Example 2 was measured in the same manner as in Example 1, the 180° peel strength was 4.0 N/15 mm, indicating sufficient adhesion.

Next, the packaging film of Example 2 was cut to a size of 60 mm x 100 mm to prepare one sample piece. This sample piece was immersed in a 1.5% by weight aqueous solution of sodium hydroxide at 85°C, and while maintaining that temperature, it was stirred briefly and the nylon layer and polyethylene layer were observed for peeling every 20 minutes.

As a result, the nylon layer and the polyethylene layer were separated 24 hours after the start of immersion.

[Example 3]
An acrylic acid copolymer resin having an acid value of 63 (mg-KOH/g) was prepared by mixing an acrylic acid copolymer resin (acid value: 50 mg-KOH/g) (manufactured by Mitsubishi Rayon Co., Ltd. under the trade name "DIANAL LR-1941") and an acrylic acid copolymer resin (acid value: 85 mg-KOH/g) (manufactured by BASF under the trade name "JONCRYL JDX3000").

Next, 33 parts by weight of the acrylic acid copolymer resin (acid value: 63 mg-KOH/g) and 3 parts by weight of a cellulose derivative (manufactured by Corea CNC under the trade name "RS-1sec", solid content 70 parts by weight) were dissolved in a mixed solvent of 44 parts by weight of ethyl acetate and 20 parts by weight of isopropyl alcohol to obtain a uniform resin liquid (coating agent). Of the coating agent, the acrylic acid copolymer resin is an alkali-soluble polymer. The apparent acid value of this coating agent is 57 mg-KOH/g.

A packaging film was produced in the same manner as in Example 1, except that the coating agent prepared as described above was used instead of the water-soluble polymer in Example 1, and a 15 μm-thick nylon film (trade name "EMBLEM ON" manufactured by Unitika Ltd.) was used instead of the aluminum foil. The produced packaging film has a laminated structure of, from the surface side, a polyethylene terephthalate resin layer/an alkali-soluble first intermediate layer having a thickness of about 2 μm/a nylon resin layer having a thickness of about 15 μm/an alkali-soluble second intermediate layer having a thickness of about 2 μm/a polyethylene resin layer.

When the peel strength of the packaging film of Example 3 was measured using the same method as in Example 1, the 180° peel strength was 4.0 N/15 mm, indicating sufficient adhesion strength.

Next, the packaging film of Example 3 was cut to a length x width of 60 mm x 100 mm to prepare several identical sample pieces, which were then immersed in a 1.5% by weight aqueous solution of sodium hydroxide at 85°C and stirred briefly while maintaining that temperature. After every 20 minutes, one sample piece was removed and the peelability between the layers was checked.

As a result, 20 minutes after the start of immersion, the nylon resin layer and the polyethylene resin layer peeled off without any resistance. Similarly, 20 minutes after the start of immersion, the polyethylene terephthalate resin layer and the nylon resin layer peeled off without any resistance.

[Example 4]
A packaging film was produced in the same manner as in Example 3, except that 1 part by weight of a vinyl chloride-vinyl acetate copolymer (trade name "SOLVIN TA5R" manufactured by Nissin Chemical Industry Co., Ltd.) was added to the coating agent of Example 3, and the amount of isopropyl alcohol blended was 19 parts by weight. The apparent acid value of this coating agent was 56 mg-KOH/g.

When the peel strength of the packaging film of Example 4 was measured in the same manner as in Example 1, the 180° peel strength was 4.5 N/15 mm, indicating sufficient adhesion strength.

Next, the packaging film of Example 4 was cut into pieces measuring 60 mm x 100 mm to prepare several identical sample pieces. These sample pieces were then immersed in a 1.5% by weight aqueous solution of sodium hydroxide at 85°C, and while maintaining that temperature, simple stirring was continued. After every 20 minutes, one sample piece was removed and the peelability between each layer was confirmed.

As a result, 20 minutes after the start of immersion, the nylon resin layer and the polyethylene resin layer peeled off without any resistance. Similarly, 20 minutes after the start of immersion, the polyethylene terephthalate resin layer and the nylon resin layer peeled off without any resistance. In addition, when the packaging film was visually observed before immersion, it was found that the laminate structure was highly uniform and had excellent design.

[Example 5]
Using the coating agent prepared in Example 3, a packaging film was produced in the same manner as in Example 2. The produced packaging film had a laminated structure of, from the surface side, a nylon resin layer/an alkali-soluble intermediate layer having a thickness of about 1 μm/a printing ink layer/an adhesive layer/a polyethylene resin layer.

When the peel strength of the packaging film of Example 5 was measured in the same manner as in Example 1, the 180° peel strength was 4.0 N/15 mm, indicating sufficient adhesion.

Next, the packaging film of Example 5 was cut to a size of 60 mm x 100 mm to prepare one sample piece. This sample piece was immersed in a 1.5% by weight aqueous solution of sodium hydroxide at 85°C, and while maintaining that temperature, it was stirred briefly and the state of peeling between the nylon layer and the polyethylene layer was observed every 20 minutes.

As a result, the nylon layer and the polyethylene layer were separated 20 minutes after the start of immersion.

[Example 6]
Using the coating agent prepared in Example 4, a packaging film was produced in the same manner as in Example 2. The produced packaging film had a laminated structure of, from the surface side, a nylon resin layer/an alkali-soluble intermediate layer having a thickness of about 1 μm/a printing ink layer/an adhesive layer/a polyethylene resin layer.

When the peel strength of the packaging film of Example 6 was measured in the same manner as in Example 1, the 180° peel strength was 4.5 N/15 mm, indicating sufficient adhesion.

Next, the packaging film of Example 6 was cut to a size of 60 mm x 100 mm to prepare one sample piece. This sample piece was immersed in a 1.5% by weight aqueous solution of sodium hydroxide at 85°C, and while maintaining that temperature, it was stirred briefly and the state of peeling between the nylon layer and the polyethylene layer was observed every 20 minutes.

As a result, 20 minutes after the start of immersion, the nylon layer and the polyethylene layer had separated. Furthermore, visual inspection of the packaging film before immersion revealed that the laminated structure was highly uniform and had excellent design.

[Comparative Example]
A packaging film was prepared in the same manner as in Example 2, except that no coating agent was applied (no alkali-soluble intervening layer was formed), with a nylon resin layer/printed ink layer/adhesive layer/polyethylene resin layer in that order from the surface side.

The packaging film of the comparative example was also measured for peel strength using the same method as in Example 1, and found to have a 180° peel strength of 4.0 N/15 mm, indicating sufficient adhesion strength. The packaging film of the comparative example was also immersed in a 1.5% by weight aqueous sodium hydroxide solution at 85°C in the same manner as in Example 2, and the state of peeling between the layers was observed. As a result, no separation of the nylon layer and the polyethylene layer was observed even after 24 hours.

1 Packaging film 21, 22, 23, 24 Base material layer 3 Intervening layer 41, 42 Printing ink layer

Claims (6)

A flexible packaging material for sealingly packaging an article,
The packaging film is made of a laminate including a first base material layer, an intermediate layer, a printing ink layer, and a second base material layer made of a different material from the first base material layer, laminated in this order;
The intermediate layer is a layer that enables two base layers made of different materials to be separated by immersion in a solvent,
the second base layer is a resin layer having a sealant property on the back surface of the packaging film,
the resin layer having a sealant property is a low-density polyethylene layer or an ethylene-propylene copolymer layer,
The first base layer is an outermost surface of the packaging film and is made of a polyester-based resin layer or a polyamide-based resin layer,
the intermediate layer is alkali-soluble and contains a first acrylic acid copolymer resin and a second acrylic acid copolymer resin;
The soft packaging material, wherein the apparent acid value of the intermediate layer is 40 mg-KOH/g or more and 150 mg-KOH/g or less. A third base material layer made of a material different from both the first base material layer and the second base material layer is further provided between the printing ink layer and the second base material layer,
the third base layer is a layer having a gas barrier property,
Further comprising a second intermediate layer between the second base layer and the third base layer;
the second intermediate layer is a layer that enables two base layers made of different materials to be separated by immersion in a solvent;
the second intermediate layer is alkali-soluble and contains the first acrylic acid copolymer resin and the second acrylic acid copolymer resin,
2. The flexible packaging material according to claim 1, wherein the apparent acid value of the second intermediate layer is 40 mg-KOH/g or more and 150 mg-KOH/g or less. A flexible packaging material for sealingly packaging an article,
A packaging film is provided which is a laminate in which a first base material layer, a printing ink layer, an intervening layer, and a second base material layer made of a different material from the first base material layer are laminated in this order,
The intermediate layer is a layer that enables two base layers made of different materials to be separated by immersion in a solvent,
the second base layer is a resin layer having a sealant property on the back surface of the packaging film,
the resin layer having a sealant property is a low-density polyethylene layer or an ethylene-propylene copolymer layer,
The first base layer is an outermost surface of the packaging film and is made of a polyester-based resin layer or a polyamide-based resin layer,
the intermediate layer is alkali-soluble and contains a first acrylic acid copolymer resin and a second acrylic acid copolymer resin;
The soft packaging material, wherein the apparent acid value of the intermediate layer is 40 mg-KOH/g or more and 150 mg-KOH/g or less. a third base material layer between the intermediate layer and the second base material layer, the third base material layer being made of a material different from both the first base material layer and the second base material layer;
the third base layer is a layer having a gas barrier property,
Further comprising a second intermediate layer between the second base layer and the third base layer;
the second intermediate layer is a layer that enables two base layers made of different materials to be separated by immersion in a solvent;
the second intermediate layer is alkali-soluble and contains the first acrylic acid copolymer resin and the second acrylic acid copolymer resin,
4. The flexible packaging material according to claim 3, wherein the apparent acid value of the second intermediate layer is 40 mg-KOH/g or more and 150 mg-KOH/g or less. A method for recycling the flexible packaging material according to claim 1 or 2, comprising the steps of:
A recycling method comprising the step of treating the packaging film with an alkali to separate the first base material layer and the second base material layer and to separate the printing ink layer from the first base material layer. A method for recycling the flexible packaging material according to claim 3 or 4, comprising the steps of:
A recycling method comprising the step of treating the packaging film with an alkali to separate the first base material layer and the second base material layer and to separate the printing ink layer from the second base material layer.