Embossed multi-layer structure

Abstract

To provide an embossment multilayer structure that is obtained by attaching an embossment film having an embossment pattern on both sides and a base material using an adhesive, effectively prevents crushing of embossment during pasting, and effectively prevents delamination between the embossment film and the base material.SOLUTION: The embossment multilayer structure is obtained by attaching an embossment film 1 having an embossment pattern on both sides and a base material 5 using an adhesive, in which an adhesive layer 7 is formed by the adhesive, thickness at a void part distributed at an interface between the embossment film 1 and the adhesive layer 7 is 10 μm or more, and a raised part 7a of the adhesive is formed at a terminal end of the void part.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an embossed multi-layer structure in which a length of embossed film is laminated to a substrate with an adhesive. [Background technology]

[0002] Embossed films having an embossed pattern are widely used for three-dimensional decoration, and for imparting impact resistance and heat insulation properties, and are generally used as multilayer structures laminated on a predetermined substrate.

[0003] A widely known method for forming an embossed pattern on a film is to press a die with convexities on its surface (such as an embossing roller) against the film, thereby lifting up the back surface of the film. This method allows for easy embossing without using special materials.

[0004] The embossed film 1 obtained by such a method has a feature in that convex portions 1a are formed on the outer surface and concave portions 1b corresponding to the convex portions 1a are formed on the back surface, and thus has a morphological feature in that an embossed pattern exists on both sides, as shown in FIG. 1. A substrate is attached to the long embossed film, and the film is cut to an appropriate size depending on the application and used (see FIG. 1(a)). Such an embossed film 1 having an embossed pattern on both sides causes various inconveniences when laminated to a substrate. That is, as shown in FIG. 1(b), when the embossed film 1 is attached to a substrate using an adhesive, the back surface of the embossed film has concave portions 1b (voids) formed corresponding to the convex portions 1a formed on the outer surface, so that the adhesive surface on which the adhesive functions is limited to the flat portions 1c between the concave portions 1b present on the back surface of the embossed film 1. For this reason, the adhesive area becomes extremely narrow, resulting in low adhesive strength and easy delamination. In this case, it is possible to increase the pressure applied during bonding in an attempt to increase the adhesive strength, but in this case the embossed pattern formed on the surface would be crushed, significantly impairing the appearance.

[0005] The reality is that little research has been done on the adhesion problem of such embossed films having embossed patterns on both sides.

[0006] For example, FIG. 1(b) of Patent Document 1 discloses a packaging film (embossed multilayer structure) in which a substrate 1 and a film (second seal layer 3) having an embossed pattern (recesses) are attached with an adhesive (first seal layer 2). However, the embossed film (second seal layer 3) used in this packaging film has an embossed pattern formed on only one side, and the embossed pattern is formed on the back side (adhesive surface) and not on the outer surface. That is, the embossed multilayer structure disclosed in Patent Document 1 does not provide decorative properties due to the embossed film, but does not require suppression of the embossed pattern from being crushed, and therefore the substrate and the embossed film can be firmly heat-pressed with an adhesive between them, increasing the adhesive strength between them and effectively preventing delamination. As can be seen from this, the technology of Patent Document 1 cannot be applied to the attachment of an embossed film having an embossed pattern formed on both sides. In addition, in Patent Document 1, the adhesive (first seal layer 2) penetrates deeply into the recesses forming the embossed pattern, and although the adhesive strength can be ensured, the void ratio of the recessed space formed by the embossed pattern is greatly reduced, and there is a problem in that the advantages of the embossed pattern (thermal insulation, cushioning effect, cost reduction, etc.) are lost.

[0007] Furthermore, Patent Document 2 discloses an embossed multilayer structure (film for pouches) consisting of a front film with an embossed pattern and a back film (substrate film). In this embossed multilayer structure, the front film is an embossed film with an embossed pattern on both sides, and the decorative properties of the embossed pattern are fully utilized. However, after bonding two films (front film and back film) without an embossed pattern, a special embossing process is performed to form an embossed pattern on both sides of the front film. That is, the technology of Patent Document 2 has limitations on the film material, and for example, the front film must have a large elongation and the back film must have a small elongation, and ultimately, this technology cannot be applied to bonding an embossed film with an embossed pattern on both sides to a substrate. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2015-224065 A [Patent Document 2] JP 2020-33108 A Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to provide an embossed multilayer structure which is obtained by bonding an embossed film having an embossed pattern on both sides to a substrate using an adhesive, in which crushing of the embossing during bonding is effectively prevented and delamination between the embossed film and the substrate is effectively prevented. [Means for solving the problem]

[0010] According to the present invention, in an embossed multilayer structure obtained by bonding an embossed film having an embossed pattern formed on both sides thereof and a substrate using an adhesive, The embossed film has a substrate-side surface on its inner surface formed with recesses corresponding to the protrusions of the embossed pattern, and The adhesive layer formed by the adhesive has a thickness of 10 μm or more, and the adhesive layer forms a raised portion around the periphery of a void portion that is formed at the interface between the embossed film and the adhesive layer due to the recess, thereby providing an embossed multilayer structure.

[0011] In the embossed multi-layer structure of the present invention, the following aspects can be suitably adopted. (1) When the width D indicated by a straight line Z perpendicular to a line Y indicating the longitudinal direction in which the recesses extend is at a maximum value in a plane of the embossed film, and the cross-sectional area of ​​the space indicated by the recesses in a side cross section in a vertical plane including the straight line Z is S, the cross-sectional area S' of the voids resulting from the recesses formed between the substrate-side surface and the adhesive layer surface of the embossed film is 50% or more of the cross-sectional area S. (Hereinafter, the proportion (%) of the voids S' expressed as S' / S is referred to as the void ratio.) (2) The adhesive layer is made of polyethylene. (3) The substrate is a film having a heat seal layer (sealant) on the surface opposite to the adhesive layer. (4) The embossed film is used as a heat seal layer (sealant).

[0012] The embossed multilayer structure of the present invention having a heat seal layer can be suitably used for forming a pouch. Effect of the Invention

[0013] The embossed multilayer structure of the present invention has a structure in which an embossed film is attached to a substrate with an adhesive, and is characterized in that the thickness of the adhesive layer formed by the adhesive is 10 μm or more, and a raised portion is formed on the periphery of the gap generated between the embossed film and the adhesive layer (corresponding to the periphery of the joint between the adhesive layer and the embossed film). That is, by making the adhesive layer thicker than a certain degree and forming the raised portion as described above, it is possible to effectively prevent delamination (e.g., peeling at the adhesive interface between the embossed film and the substrate) without crushing the embossed pattern (convex portion) formed on the outer surface of the embossed film. In this configuration, it is also possible to effectively avoid blocking of the recessed space formed on the substrate side surface of the embossed film by the adhesive.

[0014] Therefore, according to the present invention, an embossed film having an embossed pattern formed on both sides can be laminated to various substrates without crushing the embossed pattern, making it possible to make maximum use of the advantages of the embossed pattern, such as three-dimensional decoration, heat insulation, cushioning, and cost reduction. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram for explaining a problem that occurs when an embossed film having embossed patterns formed on both sides is attached to a substrate using an adhesive. [Diagram 2] 1 is a schematic cross-sectional side view of an embossed multi-layer structure of the present invention. [Diagram 3] FIG. 2 is a partial plan view of an embossed film, showing the form of straight lines indicating the width of recesses required for calculating the porosity. [Figure 4] FIG. 2 shows a cross-sectional side view of a recess in an embossed multilayer structure for calculating the porosity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Referring to FIG. 2, the embossed multilayer structure of the present invention has a structure in which an embossed film 1 and a substrate 5 are bonded together with an adhesive layer 7.

[0017] <Embossed film 1> In Fig. 2, as also shown in Fig. 1, the embossed film 1 has an embossed pattern formed on both sides, and is formed by pressing a mold or the like with convex parts formed on its surface against the back surface of the film to push up and float the back surface, so that convex parts 1a are formed on the outer surface side, and on the inner surface side, the parts corresponding to the convex parts 1a become concave parts 1b, forming void parts 3. Also, the flat parts formed between the convex parts 1a (concave parts 1b) are indicated by 1c, as in Fig. 1.

[0018] The shape of the embossed pattern as described above is not particularly limited, and may be, for example, a shape in which the convex portions 1a are formed in a straight line, a curve, a lattice, a dot, or a letter shape, or the interval (pitch) between the convex portions 1a may be made small to form a pattern between the convex portions 1a. The height of the convex portions 1a (concave portions 1b) may be such that the shape can be stably maintained according to the width.

[0019] The embossed film 1 may be made of any thermoplastic resin or thermosetting resin as long as it is capable of forming the above-mentioned embossed pattern, but in general, it is preferable that the film be made of a thermoplastic resin from the viewpoint that the embossed pattern can be easily formed. Examples of such thermoplastic resins include the following: Olefin resins, for example, low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene, cyclic olefin copolymers, etc.; Ethylene-vinyl copolymers, such as ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-vinyl chloride copolymers, etc.; Styrene-based resins, such as polystyrene, acrylonitrile-styrene copolymers, ABS, α-methylstyrene-styrene copolymers, etc.; Vinyl resins, such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymers, polymethyl acrylate, polymethyl methacrylate, etc.; Polyamide resins, such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, etc.; Polyester resins, for example, polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, and copolymer polyesters thereof; Polycarbonate resin; Polyphenylene oxide resin; Biodegradable resins, such as polylactic acid; Of course, blends of these thermoplastic resins can also be used as long as the moldability is not impaired.

[0020] In the present invention, among the above-mentioned thermoplastic resins, olefin resins, polyester resins, and polyamide resins are preferred, and in terms of strength, polyester resins and polyamide resins are particularly preferred, and in terms of heat sealability, olefin resins are optimal. The embossed film 1 may be colored by blending various coloring agents.

[0021] <Base material 5> The substrate 5 may be made of an appropriate material depending on the application requiring three-dimensional decoration by the embossed film 1, and may have a thickness appropriate to the application, and may be, for example, a metal foil such as aluminum foil, paper, or a synthetic resin film, or may have a multilayer structure in which these are laminated. As the synthetic resin used to form this synthetic resin film, a thermoplastic resin that can also be used to form the embossed film 1 described above can be used.

[0022] When this embossed multilayer structure is used as a packaging material, particularly as a pouch, a heat-sealable resin layer can be provided on the outer surface of the base material 5 (the surface opposite to the embossed film 1 and adhesive layer 7), or the embossed film 1 can be formed of a heat-sealable resin. As the heat-sealable resin, an olefin resin such as polypropylene or polyethylene can be used. Furthermore, the surface of the base material 5 (the surface on which the adhesive layer 7 is formed) may be formed of an inorganic vapor deposition film, or the base material 5 may have a multilayer structure including a layer of a gas barrier resin such as an ethylene-vinyl alcohol copolymer.

[0023] Furthermore, when the substrate 5 is a material other than paper, a layer of an anchor coating agent can be provided on the surface of the substrate 5 in order to enhance adhesion with the adhesive layer described below. Typical anchor coating agents include isocyanate compounds, polyethyleneimine, modified polybutadiene, and organic titanate compounds, and the anchor coating layer can be formed by applying a solution of these anchor coating agents in an organic solvent such as methanol or ethyl acetate and drying it.

[0024] <Adhesive layer 7> The adhesive used to form the adhesive layer 7 is a resin material that exhibits good adhesion to the embossed film 1 and the substrate 5. Although polyethylene is usually used, various other materials that exhibit high adhesion to the embossed film 1 and the substrate 5 can be selected. For example, a resin containing a carbonyl group (>C=O) in the main chain or side chain in an amount of 1 to 100 meq / 100 g resin, particularly 10 to 100 meq / 100 g resin, specifically an olefin resin graft-modified with a carboxylic acid such as maleic acid, itaconic acid, or fumaric acid or an anhydride, amide, or ester thereof; an ethylene-acrylic acid copolymer; an ionically cross-linked olefin copolymer; an ethylene-vinyl acetate copolymer; or the like may be used.

[0025] In the present invention, the adhesive layer 7 as described above is applied to the entire surface of the substrate 5, and the embossed film 1 and substrate 5 are bonded together by adhesive layer 7c formed in the portion corresponding to the flat portion 1c between the convex portions 1a (concave portions 1b) of the embossed film 1, and the portion corresponding to the convex portions 1a (concave portions 1b) of the embossed film 1 forms a gap portion 3.

[0026] In this configuration, the adhesive layer 7 has a raised portion 7a on the periphery of the void 3 (or the periphery of the adhesive layer 7c which is the joint). That is, in the central portion 7b facing the void 3, the surface of the adhesive layer 7 is flat, but the periphery (corresponding to the periphery of the adhesive layer 7c which is the joint) is raised. By forming such a raised portion 7a, it is possible to ensure high adhesive strength without crushing the convex portion 1a of the embossed film 1.

[0027] In the present invention, in order to form the above-mentioned raised portion 7a, the thickness d of the adhesive layer 7 (i.e., equivalent to the thickness at the flat central portion 7b) needs to be set to 10 μm or more, particularly 12 μm or more. In other words, if the thickness d of the adhesive layer 7 is thinner than the above range, it becomes difficult to form the raised portion 7a capable of firmly holding the embossed film 1.

[0028] Furthermore, in the present invention, a high void ratio can be ensured by forming the raised portions 7a in the adhesive layer 7. Roughly speaking, this void ratio can be calculated from a side cross section in a vertical plane passing through a straight line Z that indicates the width of the recessed portions 1b when viewed on the plane of the embossed film 1.

[0029] That is, please refer to the plan view of FIG. 3. In FIG. 3, flat portions 1c exist between the recesses 1b (between the protrusions 1a) around the recesses 1b (protrusions 1a). The line Z showing the width of the recesses 1b is the interval D shown by the line Z perpendicular to the line Y showing the longitudinal direction in which the recesses 1b extend, which is the width of the recesses 1b. In FIG. 3(a), the recesses 1b extend in a straight line, but the same applies even if they extend in a curved line as in FIG. 3(b). For example, when the planar shape of the recesses 1b is elliptical, the line showing the minor axis is the line Z, and the minor axis is the width D of the recesses 1b. Also, in FIG. 3(c), when the planar shape of the recesses 1b (protrusions 1a) is circular, the line Z is naturally a line passing through the center O of the circle, and the diameter of the circle corresponds to the width D. In FIG. 3(d), when the planar shape of the recess 1b (protrusion 1a) is square, the line Y indicates the long axis, the line Z perpendicular to the line Y indicates the short axis, and the diagonal corresponds to the width D. Depending on the shape of the embossed pattern, the width of the recesses 1b (protrusions 1a) may not be uniform, with some locations having larger widths and others having smaller widths. In order to eliminate errors due to such variations in width, when the width D reaches its maximum value Dmax, the porosity is calculated from a cross-sectional side view in a vertical plane including the straight line Z at that time. This makes it possible to avoid variations in the porosity due to variations in the width D. For example, when an embossed pattern with a constant width D is formed, the porosity may be measured from a cross-sectional side view in a vertical plane including the straight line Z, regardless of the position of the straight line Z, as long as the straight line Z can indicate the width D.

[0030] The porosity is calculated from a side cross section defined by a vertical plane including the line Z as described above. That is, as shown in Fig. 4(a), the cross-sectional area of ​​the voids 3 originating from the recesses 1b in the side cross section of the embossed film 1 is S, and as shown in Fig. 4(b), the cross-sectional area of ​​the voids 3 originating from the recesses 1b in the side cross section of the embossed film 1 is S', the porosity is expressed as a ratio to the cross-sectional area S, i.e., S' / S, and in the present invention, it can be set to 50% or more, and particularly preferably set in the range of 80 to 90%. This porosity is determined by the size of the raised portion 7a of the adhesive layer, and the larger the porosity, the more the adhesive can be prevented from entering the recesses 1b, and the adhesive raised portion 7a can ensure the adhesion strength of the embossed film 1.

[0031] In the present invention, the embossed film 1 and the substrate 5 are attached by extrusion lamination using the above-mentioned adhesive, and in order to form the above-mentioned raised portion 7a, it is necessary to set the lamination conditions (extrusion temperature, line speed such as extrusion speed, etc.) so that the thickness of the adhesive layer 7 (thickness at 7b) is 10 μm or more, particularly 12 μm or more, depending on the type of adhesive used. Incidentally, although there is no particular limitation, the usual polyethylene (unmodified polyethylene) used as the adhesive is preferably low-density polyethylene, and its MFR is in the range of so-called extrusion grade, for example, about 1 to 50 g / 10 min. Such low-density polyethylene is melt-extruded at a temperature of about 300 to 330° C., and at this time, the molten polyethylene is exposed to air to oxidize the surface, and a polar group is introduced, so that the polyethylene is given adhesiveness and functions as an adhesive. Such polyethylene is melt-extruded onto a predetermined substrate 5, and the embossed film 1 is roll-pressed while maintaining the molten state to obtain an embossed multilayer structure. In such extrusion lamination, the faster the line speed such as the extrusion speed or the smaller the roll pressure, the smaller the protruding portion 7a, the lower the adhesion, and the larger the void ratio (S' / S). The same tendency also occurs when the MFR of the polyethylene used is high. Furthermore, the slower the line speed such as the extrusion speed, the larger the protruding portion 7a, the higher the adhesion, and the smaller the void ratio (S' / S), and the same tendency also occurs when the MFR of the polyethylene used is low. Therefore, a laboratory test should be performed in advance according to the physical properties of the polyethylene used, and the lamination conditions should be set so that the protruding portion 7a of an appropriate size is formed. When using other resins, such as acid-modified olefin resins, as the adhesive, a similar laboratory test should be performed and the lamination conditions should be set.

[0032] In the present invention, the embossed pattern of the embossed film 1 can be firmly attached to the substrate 5 without being crushed, so that the three-dimensional decorative properties, heat insulating properties, and cushioning properties of the embossed film 1 can be utilized for various applications.

[0033] In particular, the embossed multilayer structure of the present invention is preferably made of an olefin resin as the embossed film 1, and the embossed film 1 made of the olefin resin is used as a heat seal resin layer and pasted to produce a pouch. In the pouch thus formed, the unevenness formed in the embossed film 1 is completely crushed at the sealed portion, but the unevenness remains on the inner surface of the pouch (corresponding to the outer surface of the embossed film 1) that comes into contact with the contents, so that the function due to the unevenness can be fully exerted. For example, as described in JP 2020-104888 A, when a wet solid product (a granular or lumpy product such as furikake that is kept in a wet state by impregnation with a seasoning liquid) is filled as the contents, the dischargeability is significantly improved. That is, such a wet solid product is very sticky, so it is difficult to remove from the pouch, and there is a problem that a large amount of the product remains attached to the inner surface of the pouch. However, when the height of the outer convex portions 1a of the embossed film is set to a certain level or more and the minimum distance D between the convex portions 1a (gaps 1b) is set to a certain level or less, an air layer is secured between the inner surface of the pouch (the outer surface of the embossed film 1) and the solid product, making it possible to quickly remove the sticky solid product. EXAMPLES

[0034] In the following experiments, the following embossed films and substrates were used. Embossed film 1; Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) Mixed Polyethylene Film thickness: 40μm Embossed pattern: Diamond-shaped projections and recesses 1b of uniform width D (300 mm) are arranged at regular intervals. I am. (Maximum height of recess 1b: 40 μm) Base material 5; Polyethylene terephthalate (PET) Film thickness: 12μm

[0035] <Adhesive thickness evaluation> The thickness d (see FIG. 2) of the adhesive was measured using an optical microscope with a vertical plane including a straight line indicating the width D of the recess 1b of the embossed film as a cross section.

[0036] <Calculation of void ratio S' / S> The cross-sectional area of ​​the space defined by the recess in the side cross section is S (see FIG. 4(a)), and the cross-sectional area of ​​the void 3 resulting from the recess is S' (see FIG. 4(b)). This was calculated as the ratio (S' / S).

[0037] <Adhesion strength evaluation> The films prepared in the experimental examples described later were cut and torn by hand to check for the presence or absence of delamination. Those that were not delaminated were marked with an ◯, and those that were delaminated were marked with an ×.

[0038] <Experimental Example 1> The embossed film and substrate were laminated by extrusion lamination using polyethylene as an adhesive. An anchor coat material was applied to the substrate immediately prior to the extrusion lamination process. After lamination, the film obtained was subjected to aging treatment, and the thickness of the adhesive was measured, the porosity was calculated, and the adhesion strength was evaluated. The results for N=3 are shown in Table 1.

[0039] <Experimental Example 2> The embossed film and the substrate were dry laminated together using an isocyanate adhesive. The embossed film had a corona treatment applied to the bonding surface. After bonding, the film was aged to measure the thickness of the adhesive, calculate the porosity, and evaluate the adhesion strength. The results for N=2 are shown in Table 1.

[0040] [Table 1]

[0041] From the above results, when high adhesion is obtained by forming the raised portion 7a, a high porosity (S' / S) of about 80 to 90% can be ensured depending on the size of the raised portion. For example, as in Patent Document 1, if the amount of adhesive penetrating into the recesses is increased, adhesion can be ensured, but the porosity (S' / S) will be reduced, and the properties of the embossed film 1 will be impaired. Furthermore, from the above results, it can be seen that when an attempt is made to reduce the size of the raised portion 7a and obtain a larger porosity, adhesion will be impaired and delamination will be more likely to occur. [Explanation of symbols]

[0042] 1: Embossed film 1a: Convex part 1b: Recess 1c: Flat part 3: Voids originating from recesses 5: Base material 7: Adhesive layer 7a: Climbing section 7b: Central part 7c: Flat joint

Claims

1. An embossed multilayer structure in which an embossed film having an embossed pattern formed on both sides and a substrate are extrusion laminated with an adhesive, The embossed film has a substrate-side surface on its inner surface formed with recesses corresponding to the protrusions of the embossed pattern, and the adhesive layer formed by the adhesive has a thickness of 10 μm or more, and the adhesive layer forms a raised portion around a periphery of a gap portion that is formed at an interface between the embossed film and the adhesive layer due to the recess, An embossed multi-layer structure, characterized in that the protrusions of the embossed pattern are not crushed.

2. The embossed multilayer structure according to claim 1, wherein when a width D indicated by a straight line Z perpendicular to a line Y indicating the longitudinal direction in which the recess extends is at a maximum value when viewed in a plane of the embossed film, a cross-sectional area S of the space indicated by the recess in a side cross section in a vertical plane including the straight line Z is defined as S, and a cross-sectional area S' of a gap resulting from the recess formed between the substrate side surface and the adhesive layer surface of the embossed film is 50% or more of the cross-sectional area S.

3. 3. The embossed multi-layer structure according to claim 1, wherein the adhesive layer is made of polyethylene.

4. 4. The embossed multilayer structure according to claim 1, wherein the substrate is a film having a heat seal layer on the surface opposite to the adhesive layer.

5. The embossed multilayer structure according to any one of claims 1 to 3, wherein the embossed film is used as a heat seal layer.

6. A pouch obtained from the embossed multi-layer structure according to claim 4 or 5.

7. A method for producing an embossed multilayer structure obtained by extrusion laminating an embossed film having an embossed pattern formed on both sides and a substrate using an adhesive, comprising: The embossed film has a substrate-side surface on its inner surface formed with recesses corresponding to the protrusions of the embossed pattern, and the adhesive layer formed by the adhesive has a thickness of 10 μm or more, and the adhesive layer forms a raised portion around a periphery of a gap portion that is formed at an interface between the embossed film and the adhesive layer due to the recess, The method for producing an embossed multi-layer structure is characterized in that the convex portions of the embossed pattern are not crushed.

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