JP2024050017A - Laminate - Google Patents

Abstract

[Problem] To provide a laminate with excellent shape retention. [Solution] A laminate 100 comprising a paper base material 10, a first resin layer 20 containing a first biodegradable resin provided on one surface 11 of the paper base material, and a second resin layer 30 containing a second biodegradable resin provided on the surface of the first resin layer opposite the paper base material 10 side, wherein the first biodegradable resin is a biodegradable resin other than cellulose acetate, and the second biodegradable resin is the cellulose acetate. [Selected Figure] Figure 1

Description

The present invention relates to a laminate.

In recent years, biodegradable resins have been researched to reduce the environmental impact of plastic waste processing. Biodegradable resins have the property of eventually being decomposed into carbon dioxide and water by the action of microorganisms, and circulate back into nature. Furthermore, paper products have attracted attention because they can be decomposed after disposal, and laminated materials in which paper and biodegradable resin are layered have been proposed.

For example, Patent Document 1 discloses a laminated packaging material in which at least two layers, an aliphatic/aromatic copolymer polyester resin layer with good adhesion to paper and a sealing layer, are laminated by a co-extrusion method with the aliphatic/aromatic copolymer polyester resin layer on the paper layer side. The aliphatic/aromatic copolymer polyester resin layer is a biodegradable copolymer polyester resin layer of three components, terephthalic acid/adipic acid/1,4-butanediol. The sealing layer is made of a biodegradable resin made of polylactic acid, polybutylene succinate, or a starch/polycaprolactone mixture, or a blend resin in which 10-50% by weight of the aliphatic/aromatic copolymer polyester resin is kneaded with 90-50% by weight of a biodegradable resin made of polylactic acid, polybutylene succinate, or a starch/polycaprolactone mixture.

JP 2004-098321 A

In some cases, a laminate in which a biodegradable resin is laminated is embossed, for example, to give the surface of the laminate an uneven pattern or to impart a desired function. However, the laminated packaging material described in Patent Document 1 does not take into consideration the application of embossing, nor does it take into consideration the shape retention that would result from embossing.

Generally, biodegradable resins tend to have low heat resistance. For this reason, for example, when an embossed product (hereinafter, an embossed product obtained by embossing a laminated material in which a paper base material and a biodegradable resin are laminated) is produced by embossing a laminate material, if the embossed laminate is exposed to a high-temperature environment, there is a concern that the uneven shape imparted by the embossing will not be maintained and will be restored to some extent.

The object of the present invention is to provide a laminate in which a biodegradable resin is laminated onto a paper substrate, which has excellent shape retention even when the laminate is left in a high-temperature environment after being embossed.

[1] A paper base material,
A first resin layer including a first biodegradable resin provided on one surface of the paper base material;
a second resin layer including a second biodegradable resin provided on a surface of the first resin layer opposite to the paper substrate;
Equipped with
the first biodegradable resin is a biodegradable resin other than cellulose acetate,
The second biodegradable resin is cellulose acetate.
Laminate.

[2] The laminate according to [1],
The thickness of the second resin layer is 2 μm or more and 20 μm or less.
Laminate.

[3] The laminate according to [1] or [2],
The acetylation degree of the cellulose acetate is 50% or more and 62% or less.
Laminate.

[4] The laminate according to any one of [1] to [3],
The cellulose acetate has a total degree of acetyl substitution of 2.3 or more and 2.6 or less.
Laminate.

[5] The laminate according to any one of [1] to [4],
The second resin layer is a resin layer formed by coating a coating liquid in which the cellulose acetate is dissolved in an organic solvent.
Laminate.

[6] The laminate according to any one of [1] to [5],
The first biodegradable resin is at least one biodegradable resin selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polyethylene terephthalate succinate, polyglycolic acid, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate);
Laminate.

[7] The laminate according to any one of [1] to [6],
The thickness of the first resin layer is 20 μm or more and 300 μm or less.
Laminate.

According to one aspect of the present invention, a laminate in which a biodegradable resin is laminated onto a paper substrate can be provided that has excellent shape retention even when the laminate is left in a high-temperature environment after being embossed.

FIG. 1 is a schematic cross-sectional view showing an example of a laminate according to an embodiment of the present invention.

The following describes a preferred embodiment of the laminate, which is an example of the present invention.

<Laminate>
The laminate according to the present embodiment comprises a paper substrate, a first resin layer containing a first biodegradable resin provided on one side of the paper substrate, and a second resin layer containing a second biodegradable resin provided on the side of the first resin layer opposite to the paper substrate side, wherein the first biodegradable resin is a biodegradable resin other than cellulose acetate, and the second biodegradable resin is the cellulose acetate.

The laminate according to this embodiment has the above-mentioned configuration, and thus has the characteristic that a laminate having excellent shape retention can be obtained even when the embossed laminate is left in a high-temperature environment. Although the reason is unclear, it is presumed that the above-mentioned shape retention can be obtained because cellulose acetate has higher heat resistance than biodegradable resins other than cellulose acetate.

The laminate according to this embodiment will be described with reference to the drawings. The laminate 100 shown in FIG. 1 includes a paper base material 10, a first resin layer 20 provided on one side of the paper base material 10 (first main surface 11 of the paper base material 10), and a second resin layer 30 provided on the side of the first resin layer 20 opposite the paper base material 10 side (main surface 21 of the first resin layer 20), and the paper base material 10, the first resin layer 20, and the second resin layer 30 are sequentially laminated in this order from the paper base material 10 toward the second resin layer 30. The first resin layer 20 and the second resin layer 30 are not provided on the second main surface 13 of the paper base material 10, and the second main surface 13 of the paper base material 10 is exposed. The first resin layer 20 contains a first biodegradable resin, and the first biodegradable resin is a biodegradable resin other than cellulose acetate. The second resin layer 30 contains a second biodegradable resin, and the second biodegradable resin is cellulose acetate. When embossing is performed on the laminate 100, for example, the main surface 31 of the second resin layer 30 is given an uneven shape by embossing. Here, the main surface refers to the largest surface of the paper base material, the first resin layer, or the second resin layer, and refers to the surface facing the thickness direction (i.e., the stacking direction of each layer).

Although an example of the laminate according to this embodiment has been described above with reference to FIG. 1, the laminate according to this embodiment is not limited to this. The laminate according to this embodiment may adopt various forms as long as it has the above-mentioned configuration.

(Paper base material)
The paper substrate is not particularly limited as long as it can support the first resin layer described below. Examples of the paper substrate include kraft paper, glassine paper, uncoated paper (e.g., fine paper, medium-quality paper, and thin paper), and coated paper (e.g., art paper, clay-coated paper, and cast-coated paper).

In this specification, the coated paper comprises a base paper mainly composed of pulp fibers and a pigment coating layer provided on the base paper. The base paper is obtained by a known method, for example, by adding the desired additives to pulp fibers as the main component. The pigment coating layer is provided on the base paper by a known method. The pigment coating layer may have a single layer structure or a multilayer structure. The pigment coating layer contains, for example, an adhesive such as a water-based resin in a range of 2 parts by mass or more and 50 parts by mass or less per 100 parts by mass of one or more pigments such as calcium carbonate, kaolin, clay, talc, satin white, titanium oxide, and plastic pigment.

The basis weight of the paper substrate is not particularly limited, and is preferably, for example, 30 g/m ² or more, and more preferably, 40 g/m ² or more. The basis weight of the paper substrate is preferably, for example, 300 g/m ² or less, and more preferably, 200 g/m ² or less. The thickness of the paper substrate is not particularly limited, and is preferably, for example, 5 μm or more, and more preferably, 10 μm or more. The thickness of the paper substrate is preferably, for example, 300 μm or less, and more preferably, 200 μm or less.

When the paper substrate is a coated paper, the thickness of the base paper is preferably 50 μm or more, and more preferably 100 μm or more. The thickness of the base paper is preferably 250 μm or less, and more preferably 200 μm or less. The thickness of the pigment coating layer is preferably 5 μm or more, and more preferably 10 μm or more. The thickness of the pigment coating layer is preferably 40 μm or less, and more preferably 30 μm or less.

(First Resin Layer)
The first resin layer is not particularly limited in the type of biodegradable resin as long as it contains a biodegradable resin other than cellulose acetate as the first biodegradable resin. The biodegradable resin other than cellulose acetate is preferably at least one biodegradable resin selected from the group consisting of, for example, polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polyethylene terephthalate succinate, polyglycolic acid, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Among these, the biodegradable resin other than cellulose acetate is more preferably one or more of polylactic acid, polybutylene succinate, polybutylene succinate adipate, and polybutylene adipate terephthalate, and even more preferably one or more of polybutylene succinate adipate and polybutylene adipate terephthalate.

The thickness of the first resin layer is not particularly limited, and is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more, from the viewpoint of film-forming properties. The thickness of the first resin layer is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. If the thickness of the first resin layer is 300 μm or less, for example, curling is easily suppressed.

In addition to the first biodegradable resin, the first resin layer may contain other components such as additives as necessary. Examples of additives include crystallization nucleating agents, plasticizers, hydrolysis inhibitors, antioxidants, ultraviolet absorbers, colorants, and fillers. These additives may be used alone or in combination of two or more.

(Second Resin Layer)
The second resin layer contains cellulose acetate as the second biodegradable resin. The second resin layer may contain only cellulose acetate as the second biodegradable resin.

The thickness of the second resin layer is not particularly limited. From the viewpoint of superior shape retention when the embossed laminate is left in a high-temperature environment, the thickness of the second resin layer is, for example, preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 4 μm or more. The thickness of the second resin layer is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. If the thickness of the second resin layer is 20 μm or less, for example, curling is easily suppressed.

From the viewpoint of easily obtaining biodegradability, it is preferable that the acetylation degree of cellulose acetate is 50% or more. The acetylation degree of cellulose acetate may be 52% or more, 53% or more, or 54% or more. From the viewpoint of easily obtaining biodegradability, it is preferable that the acetylation degree of cellulose acetate is 62% or less.

The acetylation degree of cellulose acetate can be measured in accordance with the acetylation degree measurement method of ASTM D-817-91 (test method for cellulose acetate, etc.).

From the viewpoint of easily obtaining biodegradability, the total degree of substitution of acetyl groups in cellulose acetate is preferably 2.3 or more, and more preferably 2.4 or more. From the viewpoint of easily obtaining biodegradability, the total degree of substitution of acetyl groups in cellulose acetate is preferably 2.6 or less, and more preferably 2.5 or less.

The total degree of acetyl substitution of cellulose acetate can be calculated from the acetylation degree of cellulose acetate by the following formula (F1).
DS = 162.14 × AV / (6005.2 - AV × 42.037) ... (F1)
In formula (F1), DS represents the total degree of acetyl substitution, and AV represents the degree of acetylation (%).

In addition, it is preferable that the 6% viscosity of the cellulose acetate (viscosity when diluted to 6%) at 25±1°C is 50 mPa·s or more and 200 mPa·s or less. The 6% viscosity can be measured, for example, by dissolving 3 g of a dry sample in 39.9 g of a 95% aqueous acetone solution to give a solution with a concentration of 6 wt/vol% (mass/volume%) using an Ostwald viscometer.

The melting point of cellulose acetate is preferably 230°C or higher and 300°C or lower. The melting point of cellulose acetate can be measured, for example, according to the method specified in JIS K7121:1987.

The viscosity of a solution containing cellulose acetate, such as the coating solution of the second resin layer-forming composition described below, can be measured, for example, according to the method specified in JIS K7117-1:1999.

The second resin layer may be (i) a resin layer formed by melt extrusion of cellulose acetate, or (ii) a resin layer formed by coating with a coating liquid in which cellulose acetate is dissolved in an organic solvent. From the viewpoint of ease of forming the second resin layer and adhesion to the paper substrate, it is preferable that the second resin layer is a resin layer formed by coating with a coating liquid in which cellulose acetate is dissolved in an organic solvent (coating liquid of the composition for forming the second resin layer).

In addition to the second biodegradable resin, the second resin layer may contain other components such as additives (e.g., plasticizers) as necessary, as long as the effects of this embodiment are not impaired.

(Method for manufacturing laminate)
The method for producing the laminate according to the present embodiment is not particularly limited. An example of a preferred method for producing the laminate according to the present embodiment includes, for example, a step of preparing a paper substrate, a step of providing a first resin layer containing a first biodegradable resin on one side of the paper substrate, and a step of providing a second resin layer containing a second biodegradable resin on the side opposite to the paper substrate side of the first resin layer, wherein the first biodegradable resin is a biodegradable resin other than cellulose acetate, and the second biodegradable resin is the cellulose acetate.

The paper base material preparation process can be carried out by preparing the paper base material described above.

The step of providing the first resin layer is not particularly limited as long as the first resin layer containing the biodegradable resin described above in the first resin layer can be provided on one side of the paper substrate. Examples of the method of providing the first resin layer on the paper substrate include (1) a method of providing the layer by a melt extrusion method or the like, and (2) a method of providing a resin film of the first biodegradable resin on the paper substrate via an adhesive, a primer, or both, after obtaining the resin film by a casting method or the like. In the step of providing the first resin layer, various surface treatments such as heating or corona discharge treatment may be performed on the surface of the paper substrate on which the first resin layer is to be provided in order to increase adhesion to the paper substrate.

The step of providing the second resin layer is not particularly limited as long as the second resin layer containing cellulose acetate can be provided on the surface opposite to the paper substrate side of the first resin layer provided on the paper substrate. For example, a method of providing the second resin layer on the first resin layer includes a method of coating the first resin with a coating liquid of a composition for forming a second resin layer, in which a material for forming a second resin layer containing cellulose acetate as a second biodegradable resin is dissolved in an organic solvent. The coating liquid of the composition for forming the second resin layer is coated on the first resin and then dried to form the second resin layer. In the step of providing the second resin layer, various surface treatments such as heating or corona discharge treatment may be performed on the surface of the first resin layer in order to increase adhesion with the first resin layer.

The organic solvent for dissolving cellulose acetate is not particularly limited, and examples thereof include ketones (acetone, cyclohexanone, methyl ethyl ketone (MEK), etc.), ethers (diethyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, etc.), amides (dimethylformamide, etc.), and esters (ethyl acetate, butyl acetate, etc.). These organic solvents may be used alone or in combination of two or more. Among these organic solvents, from the viewpoint of ease of dissolving cellulose acetate, at least one selected from the group consisting of ethyl methyl ketone, dimethylformamide, and cyclohexanone is preferable.

The viscosity of the coating liquid of the composition for forming the second resin layer at 25°C is preferably 20 mPa·s or more and 2000 mPa·s or less. If the viscosity is within the above range, it is easy to form the second resin layer using the coating liquid. This viscosity can be measured, for example, in accordance with the method specified in JIS K7117-1:1999. There are no particular limitations on the non-volatile content concentration in the coating liquid of the composition for forming the second resin layer, so long as the viscosity at 25°C can be adjusted to be within the above range.

Examples of the method for coating the coating liquid of the composition for forming the second resin layer on the first resin layer include, for example, a bar coating method, a knife coating method, a roll knife coating method, a roll coating method, a blade coating method, a die coating method, a curtain coating method, and a gravure coating method. The coating amount of the coating liquid of the composition for forming the second resin layer is preferably, for example, an amount that results in a thickness of the second resin layer after drying in the range of 2 μm or more and 20 μm or less. When the second resin layer is a layer consisting of only cellulose acetate, the coating amount of the coating liquid of the composition for forming the second resin layer is not particularly limited, and may be, for example, 3 g/m ² or more and 30 g/m ² or less.

By performing the above steps, the laminate according to this embodiment is obtained.

In order to impart functionality to the laminate according to this embodiment, the laminate obtained in the above step can be embossed. The embossing process, for example, involves pressing the laminate by sandwiching it between an embossing roll having a concave-convex shape and a pressure roll. When embossing the laminate according to this embodiment, it is preferable to sandwich the laminate between the embossing roll and the pressure roll so that the second resin layer side of the laminate faces the embossing roll. In this case, the concave-convex shape of the embossing roll is brought into contact with the second resin layer provided on the laminate, thereby transferring the concave-convex shape to the second resin layer.

The processing conditions for embossing are not particularly limited, and examples thereof include the following conditions.
The heating temperature for the embossing is preferably 100° C. or more and 200° C. or less, and more preferably 120° C. or more and 180° C. or less. The pressure for the embossing is preferably 1 MPa or more and 50 MPa or less, and more preferably 5 MPa or more and 30 MPa or less. The heating time for the embossing is preferably 1 second or more and 2 minutes or less, and more preferably 5 seconds or more and 1 minute or less.

(Applications of the laminate)
The laminate according to the present embodiment is excellent in shape retention, because the embossed shape is easily maintained even when the embossed laminate is left in a high-temperature environment (for example, 60° C. or higher and 140° C. or lower). Therefore, the laminate according to the present embodiment can be applied to applications in which decorativeness is imparted by embossing, and applications in which a desired function is imparted. The laminate according to the present embodiment is useful, for example, specifically, for applications such as food containers that can be heated in a microwave oven.

The present invention is not limited to the above-described embodiment. The present invention may include modifications and improvements within the scope of the invention.

The following examples are provided, but the present invention is not limited to these examples.

The following raw materials were prepared as raw materials for producing the laminates of each Example and Comparative Example.

(Paper base material)
P-1: High-quality paper (manufactured by Nippon Paper Industries Co., Ltd., npi high-quality, basis weight 64 g/m ² )

(First biodegradable resin)
PBS-1: Polybutylene succinate (Mitsubishi Chemical Corporation, FORZEAS DM9B01)
PBS-2: Polybutylene succinate (Mitsubishi Chemical Corporation, FORZEAS ZM9B02)
PBAT-1: Polybutylene adipate terephthalate (manufactured by BASF, Ecoflex C1200)

(Second biodegradable resin)
CA-1: Cellulose acetate having an acetylation degree of 55% (total degree of acetyl substitution of 2.4) (manufactured by Daicel Corporation, L-20)

Example 1
Polybutylene succinate (PBS-1) was used as the first biodegradable resin. PBS-1 was heated and melted at 190 ° C., and the melted PBS-1 was extruded from a T-die onto the surface of fine paper (P-1), forming a first resin layer with a thickness of 100 μm on one side of the fine paper. Next, the surface of this first resin layer was coated with a coating liquid (viscosity at 25 ° C. 1200 mPa · s) of a composition for forming a second resin layer prepared by dissolving cellulose acetate (CA-1) in methyl ethyl ketone, and then dried at 120 ° C. for 1 minute to form a second resin layer with a thickness of 5 μm, and the laminate of Example 1 was obtained.

Example 2
A laminate of Example 2 was obtained in the same manner as in Example 1, except that the first biodegradable resin was changed according to Table 1.

Example 3
A laminate of Example 3 was obtained in the same manner as in Example 1, except that the first biodegradable resin was changed according to Table 1.

<Comparative Example 1>
A laminate of Comparative Example 1 was obtained in the same manner as in Example 1, except that the second resin layer was not provided.

<Comparative Example 2>
A laminate of Comparative Example 2 was obtained in the same manner as in Example 3, except that the second resin layer was not provided.

[Evaluation of shape retention]
The surface on which the resin layer of the laminate obtained in each of the above examples (the first resin layer and the second resin layer in each of the examples, and the first resin layer in the comparative example) was formed was sequentially overlapped with the uneven surface of an embossing material (material: stainless steel, arithmetic mean surface roughness Ra: 5.0 μm, dimensions: 100 mm × 100 mm, thickness: 3 mm), and embossing was performed by performing heat pressing and cooling using a hot press machine under conditions of a heating temperature of 130°C, a pressing pressure of 10 MPa, a heating time of 10 seconds, and a cooling time (left at room temperature) of 2 minutes.

The embossed laminate obtained by embossing the laminate was placed in a thermostatic chamber at 140°C for 5 minutes for heat treatment, and the shape retention was confirmed by visually checking the change in appearance of the embossed laminate before heat treatment and the embossed laminate after heat treatment, using the following evaluation criteria.

(Evaluation criteria)
A: No change F: Disappearance of uneven shape

The shape retention of the embossed laminate was evaluated by measuring the arithmetic mean surface roughness Ra of the embossed surface of each of the embossed laminates before and after the heat treatment. The arithmetic mean surface roughness Ra was measured in accordance with JIS B0601:2001 using a contact surface roughness meter (SV3000S4, manufactured by Mitutoyo Corporation).

The above results show that the laminates of the Examples, which are provided with a second resin layer containing a second biodegradable resin that is cellulose acetate, have superior shape retention, even when left in a high-temperature environment after embossing, compared to the laminates of the Comparative Examples, which are not provided with the second resin layer.

10...paper substrate, 11...first main surface (first main surface of the paper substrate), 13...second main surface (second main surface of the paper substrate), 20...first resin layer, 21...main surface (main surface of the first resin layer 20), 30...second resin layer, 31...main surface (main surface of the second resin layer 30), 100...laminate.

Claims (7)

A paper substrate;
A first resin layer including a first biodegradable resin provided on one surface of the paper base material;
a second resin layer including a second biodegradable resin provided on a surface of the first resin layer opposite to the paper substrate;
Equipped with
the first biodegradable resin is a biodegradable resin other than cellulose acetate,
The second biodegradable resin is cellulose acetate.
Laminate. The laminate according to claim 1 ,
The thickness of the second resin layer is 2 μm or more and 20 μm or less.
Laminate. The laminate according to claim 1 or 2,
The acetylation degree of the cellulose acetate is 50% or more and 62% or less.
Laminate. The laminate according to claim 1 or 2,
The cellulose acetate has a total degree of acetyl substitution of 2.3 or more and 2.6 or less.
Laminate. The laminate according to claim 1 or 2,
The second resin layer is a resin layer formed by coating a coating liquid in which the cellulose acetate is dissolved in an organic solvent.
Laminate. The laminate according to claim 1 or 2,
The first biodegradable resin is at least one biodegradable resin selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polyethylene terephthalate succinate, polyglycolic acid, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate);
Laminate. The laminate according to claim 1 or 2,
The thickness of the first resin layer is 20 μm or more and 300 μm or less.
Laminate.

Images