Laminate, method for manufacturing the same, and packaging bag

Abstract

To provide a laminate having sufficiently high adhesive strength between a first substrate and a second substrate, a method for manufacturing the same, and a packaging bag using the laminate. [Solution] A method for manufacturing a laminate, comprising the steps of: (A) printing an aqueous ink onto the surface of a first substrate to form an ink layer; (B) applying a coating solution made by mixing at least a polyester polyol and a polyisocyanate (excluding the biuret form of hexamethylene diisocyanate) and the biuret form of hexamethylene diisocyanate to the surface of the ink layer opposite to the first substrate to form an adhesive layer; and (C) laminating a second substrate on the surface of the adhesive layer opposite to the ink layer, wherein the 100% modulus of the adhesive constituting the adhesive layer at 25°C is 0.1 to 2.5 MPa.

Description

Technical Field

[0001] The present disclosure relates to a laminate, a method for manufacturing the same, and a packaging bag.

Background Art

[0002] Conventionally, as a packaging material used for a packaging bag (for example, a flexible packaging bag) that undergoes heat treatment or heat and pressure treatment such as boiling treatment or retort treatment, a laminate having a laminated structure made of a material that has properties such as storage stability of the contents, heat resistance, pressure resistance, durability (strength) against external stress, and printability while considering cost-effectiveness is used.

[0003] In the field of packaging materials, efforts are being made to reduce VOC (volatile organic compounds). That is, for the formation of an ink layer such as characters, patterns, and designs, a conversion is being made from oil-based ink containing a solvent (such as toluene and methyl ethyl ketone), which is a volatile organic compound (VOC), to water-based ink that does not contain a solvent. Since water-based ink does not contain an organic solvent that is a VOC, it has the advantage of improving the production site environment and solving the problem of residual organic solvents in the laminate. For example, Patent Document 1 discloses a laminated material for heat-sterilization packaging using water-based ink.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional manufacturing of laminates used in flexible packaging bags that undergo heat treatment or heat-pressure treatment, when an ink layer is formed using water-based ink, delamination is likely to occur between the ink layer and the layer in contact with it (e.g., the adhesive layer). When delamination occurs, problems such as deterioration of the ink layer surface, reduction of barrier properties, and an increased risk of bag rupture can occur, making it difficult to adequately perform the heat treatment or heat-pressure treatment required for sterilization of the flexible packaging bag.

[0006] In response to this, Patent Document 1 proposes providing a specific laminating adhesive layer. However, our own investigations have revealed that the adhesive strength between the ink layer and the laminating adhesive layer is not sufficient with the method described in Patent Document 1.

[0007] This disclosure is made in view of the above circumstances and aims to provide a laminate having sufficiently high adhesive strength between a first substrate and a second substrate, a method for manufacturing the same, and a packaging bag using the laminate. [Means for solving the problem]

[0008] Until now, studies to improve the adhesive strength of adhesives to ink layers have focused on increasing the chemical affinity between the adhesive and the ink layer (for example, the chemical affinity between the materials used in the ink layer and the materials used in the adhesive layer). On the other hand, the inventors of this invention focused on the physical properties of the adhesive. In the process, they discovered that the adhesive strength between the ink layer and the adhesive layer is improved when the 100% modulus of the adhesive at 25°C is 2.5 MPa or less, leading to this disclosure.

[0009] The method for manufacturing a laminate according to this disclosure includes the steps of: (A) printing an aqueous ink onto the surface of a first substrate to form an ink layer; (B) applying a coating solution made by mixing at least a polyester polyol and a polyisocyanate (excluding biuret of hexamethylene diisocyanate) and a biuret of hexamethylene diisocyanate to the surface of the ink layer opposite to the first substrate to form an adhesive layer; and (C) laminating a second substrate onto the surface of the adhesive layer opposite to the ink layer, wherein the 100% modulus of the adhesive constituting the adhesive layer at 25°C is 0.1 to 2.5 MPa.

[0010] According to the above manufacturing method, a laminate with sufficiently high adhesive strength (peel strength) between the first substrate and the second substrate can be obtained. The reason for this effect is not clear, but the inventors speculate as follows.

[0011] Normally, the ink layer formed by printing with water-based ink contains through-pores within which gaps between pigments form a continuous mesh-like structure. Therefore, when the coating liquid is applied in process (B), the coating liquid penetrates into the ink layer to fill the above-mentioned through-pores, and a mesh-like structure made of adhesive is formed within the ink layer. In conventional laminates, the adhesive does not have sufficient flexibility, so the mesh structure of the adhesive is easily broken, and it is thought that the adhesive that penetrates into the ink layer does not particularly contribute to improving the adhesion between the ink layer and the adhesive layer. On the other hand, in the above manufacturing method, since the 100% modulus of the adhesive at 25°C is 0.1 to 2.5 MPa, it is thought that the mesh structure of the adhesive in the ink layer does not break under stress, improving the stress-following ability of the adhesive layer. Therefore, it is inferred that the adhesive strength between the ink layer and the adhesive layer becomes sufficiently high, and as a result, the adhesive strength between the first substrate and the second substrate becomes sufficiently high.

[0012] In step (A) above, water-based ink may be printed by flexographic printing. When an ink layer is formed using water-based ink for flexographic printing with flexographic printing, the above-mentioned improvement in adhesive strength tends to be significantly observed. The reason for this is presumed to be as follows.

[0013] Flexographic printing, which uses relief plates, is said to have inferior color reproduction compared to gravure printing, which uses intaglio plates, because it uses less ink to adhere to the substrate. Therefore, water-based inks used in flexographic printing tend to contain high concentrations of pigment to improve color reproduction. When flexographic printing is performed using such water-based inks, voids between pigments are more easily formed within the ink layer, and the adhesive network structure formed within the ink layer becomes denser. This is presumed to significantly improve the adhesive strength between the ink layer and the adhesive layer through the mechanism described above.

[0014] The mass ratio of the above-mentioned polyester polyol to the above-mentioned polyisocyanate may be 2:1 to 9:1. In this case, the 100% modulus of the adhesive can be easily set to the above range.

[0015] The amount of the biuret compound of the hexamethylene diisocyanate described above may be 30 parts by mass or more per 100 parts by mass of the polyisocyanate described above. In this case, the 100% modulus of the adhesive can be easily set to the above range.

[0016] The laminate according to this disclosure has a laminated structure in which a first substrate, an ink layer, an adhesive layer, and a second substrate are arranged in this order, and the adhesive layer consists of an adhesive containing a polyester polyol, a polyisocyanate (excluding the biuret form of hexamethylene diisocyanate), and a urethane compound which is a reaction product of the biuret form of hexamethylene diisocyanate, and the 100% modulus of the adhesive at 25°C is 0.1 to 2.5 MPa.

[0017] The above laminate has sufficiently high adhesive strength (peel strength) between the first substrate and the second substrate. The peel strength between the first substrate and the second substrate in the above laminate at 25°C is, for example, 1.0 N / 15 mm or more.

[0018] The laminate may further include a sealant layer on the side of the second substrate opposite to the adhesive layer side.

[0019] The above-mentioned first base material and / or the above-mentioned second base material may include a barrier layer.

[0020] The packaging bag according to the present disclosure is formed by bag-making the above laminate.

[0021] According to the above packaging bag, it is possible to suppress the occurrence of problems such as deterioration of the surface of the ink layer, reduction of barrier properties, and increase in the risk of bag breakage due to peeling between the ink layer and the adhesive layer. Also, it becomes easy to sufficiently perform the heat treatment or heat and pressure treatment of the flexible packaging bag required for the sterilization treatment.

Effect of the Invention

[0022] An object of the present disclosure is to provide a laminate having a sufficiently high adhesive strength between a first base material and a second base material, a method for manufacturing the same, and a packaging bag using the laminate.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an embodiment of the laminate according to the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an embodiment of the method for manufacturing the laminate shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view schematically showing another embodiment of the laminate according to the present disclosure. [Figure 4] FIG. 4 is a plan view schematically showing an embodiment of the packaging bag using the laminate according to the present disclosure.

Modes for Carrying Out the Invention

[0024] In this specification, the numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples. Also, the individually described upper limit values and lower limit values can be arbitrarily combined.

[0025] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments described below. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. The dimensional ratios in the drawings are not limited to those shown.

[0026] <Laminate> Figure 1 is a schematic cross-sectional view showing a laminate according to one embodiment. The laminate 10 shown in Figure 1 is in the form of a sheet and comprises a first substrate 1, an ink layer 2, an adhesive layer 3, and a second substrate 4A. The ink layer 2 contains a pigment 2a. The adhesive layer 3 consists of an adhesive containing a urethane compound which is a reaction product of a polyester polyol, a polyisocyanate (excluding the biuret form of hexamethylene diisocyanate; hereinafter also referred to as "polyisocyanate (A)"), and the biuret form of hexamethylene diisocyanate (hereinafter also referred to as "polyisocyanate (B)"). Here, the reaction product of polyester polyol, polyisocyanate (A), and polyisocyanate (B) means at least the product obtained by reacting polyester polyol, polyisocyanate (A), and polyisocyanate (B).

[0027] The 100% modulus of the above adhesive at 25°C is 0.1 to 2.5 MPa. Here, the 100% modulus represents the tensile stress when the elongation of the test specimen is 100%. The above 100% modulus is a value measured in accordance with JIS K 7161 and is a physical property value specific to the adhesive. Specifically, it can be measured by the method described in the examples. An adhesive with a 100% modulus of 2.5 MPa or less can be said to be a flexible adhesive that easily expands and contracts when external stress is applied. On the other hand, an adhesive with a 100% modulus of 0.1 MPa or more can be said to have sufficient hardness as an adhesive.

[0028] In this embodiment, the laminate 10 has sufficiently high adhesive strength (peel strength) between the ink layer 2 and the adhesive layer 3, and sufficiently high adhesive strength (peel strength) between the first substrate 1 and the second substrate 4A, because the adhesive constituting the adhesive layer 3 has such physical properties. Specifically, for example, the peel strength between the first substrate 1 and the second substrate 4A at 25°C is 1.0 N / 15 mm or more. Laminate 10 having such peel strength is less likely to delaminate between the ink layer 2 and the adhesive layer 3 even when subjected to heat treatment or heat-pressure treatment. Therefore, laminate 10 is suitably used as a packaging material for packaging bags (e.g., flexible packaging bags) that undergo heat treatment or heat-pressure treatment such as boiling or retorting. Note that the peel strength between the first substrate 1 and the second substrate 4A at 25°C is a value measured in accordance with JIS K 6854, and can be measured specifically by the method described in the examples.

[0029] From the standpoint of superior adhesive strength, the 100% modulus of the adhesive at 25°C may be 2.3 MPa or less, 2.1 MPa or less, or 1.9 MPa or less. The lower limit of the 100% modulus of the adhesive at 25°C is sufficient if it is 0.1 MPa or higher, but if higher hardness is required, it may be 1.0 MPa or higher.

[0030] The 100% modulus of an adhesive can be adjusted by factors such as the type and amount of components used in the adhesive (e.g., polyester polyol, polyisocyanate (A), polyisocyanate (B)). For example, a high amount of polyester polyol results in a higher molecular weight and a higher 100% modulus, while a low amount of polyester polyol tends to result in a lower 100% modulus. Similarly, a high amount of polyisocyanate (B) tends to result in a lower 100% modulus, while a low amount of polyisocyanate (B) tends to result in a higher 100% modulus. Based on these tendencies, a person skilled in the art can easily produce an adhesive with a 100% modulus of 0.1 to 2.5 MPa at 25°C.

[0031] Specifically, for example, if the blending mass ratio of polyester polyol to polyisocyanate (A) is 2:1 to 9:1, the 100% modulus of the adhesive tends to fall within the above range. From this viewpoint, the blending mass ratio of polyester polyol to polyisocyanate (A) is preferably 2:1 to 9:1, but may also be 5:1 to 9:1, 7:1 to 9:1, 7.5:1 to 8.5:1, or 7.7:1 to 8.2:1. Note that the above blending mass ratio is the blending mass ratio of the solid content.

[0032] Furthermore, as will be described later, if the polyisocyanate (A) includes a modified form of hexamethylene diisocyanate, the 100% modulus of the adhesive tends to fall within the above range when the blending mass ratio of polyester polyol to polyisocyanate other than the modified form of hexamethylene diisocyanate is 2:1 to 9:1. From this viewpoint, the blending mass ratio of polyester polyol to polyisocyanate other than the modified form is preferably 2:1 to 9:1, but may also be 5:1 to 9:1, 7:1 to 9:1, 7.5:1 to 8.5:1, or 7.7:1 to 8.2:1. Note that the above blending mass ratios are the blending mass ratios of solid content.

[0033] Furthermore, for example, if the amount of polyisocyanate (B) is 30 parts by mass or more per 100 parts by mass of polyisocyanate (A), the 100% modulus of the adhesive is likely to fall within the above range. From this viewpoint, the amount of polyisocyanate (B) is preferably 30 parts by mass or more per 100 parts by mass of polyisocyanate (A), and may be 40 parts by mass or more, or 50 parts by mass or more. From the viewpoint of cost and preventing deactivation by reaction with moisture in the air, the amount of polyisocyanate (B) may be 200 parts by mass or less per 100 parts by mass of polyisocyanate (A). Note that the above amounts refer to the solid content.

[0034] Furthermore, as will be described later, if polyisocyanate (A) contains a modified hexamethylene diisocyanate, the 100% modulus of the adhesive tends to fall within the above range if the amount of the modified hexamethylene diisocyanate (including polyisocyanate (B)) is 30 parts by mass or more per 100 parts by mass of polyisocyanates other than the modified hexamethylene diisocyanate. From this viewpoint, the amount of the modified hexamethylene diisocyanate is preferably 30 parts by mass or more per 100 parts by mass of polyisocyanates other than the modified hexamethylene diisocyanate, and may be 40 parts by mass or more or 50 parts by mass or more. From the viewpoint of cost and preventing deactivation by reaction with moisture in the air, the amount of the modified hexamethylene diisocyanate may be 200 parts by mass or less per 100 parts by mass of polyisocyanates other than the modified hexamethylene diisocyanate. Furthermore, the content of the biuret form of hexamethylene diisocyanate in the modified hexamethylene diisocyanate may be 50% by mass or more. Also, the above blending amounts refer to the solid content.

[0035] (First substrate) The first substrate 1 is, for example, a resin film. The first substrate 1 may be a resin film composed of resins such as polyester resin, polyamide resin, polyaramid resin, polypropylene resin, polyvinyl chloride resin, polystyrene resin, polycarbonate resin, polyacetal resin, and fluororesin. The first substrate 1 may be an unstretched resin film, or a resin film stretched uniaxially or biaxially. Specifically, the first substrate may be a polyethylene terephthalate (PET) resin film, a biaxially oriented polypropylene (OPP) resin film, or a biaxially oriented nylon (ONy polyamide resin) film.

[0036] The thickness of the first base material 1 (e.g., resin film) may be such that it satisfies the strength, rigidity, etc. required for heat and pressure treatment, and may be, for example, 10 μm to 100 μm or 12 μm to 50 μm. If the thickness of the first base material 1 is 100 μm or less, the flexible packaging bag will be easier to tear by hand when opened, and manufacturing costs can be reduced. If the thickness of the first base material 1 is 10 μm or more, sufficient strength, rigidity, etc. can be easily obtained.

[0037] (Ink layer) The ink layer 2 is in contact with the first substrate 1 and the adhesive layer 3. The ink layer 2 is, for example, an aqueous ink layer formed by printing an aqueous ink containing a pigment 2a and a binder resin (also called a "vehicle") onto the first substrate.

[0038] Pigment 2a may be an inorganic or organic pigment. Examples of inorganic pigments include titanium dioxide (white pigment), carbon black (ink pigment), barium sulfate, calcium carbonate, and other extender pigments. Examples of organic pigments include azo pigments, phthalocyanine pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, and underglaze lake pigments. The average primary particle size of pigment 2a is, for example, 0.3 to 1.0 μm. Here, the average primary particle size of pigment 2a is a value measured by laser diffraction.

[0039] Pigment 2a may be one type of pigment or multiple types of pigments. For example, ink layer 2 may contain multiple pigments of different colors, or multiple pigments of different particle sizes.

[0040] The pigment content 2a may be 40 to 75% by mass, based on the total mass of the ink layer 2. When the pigment content 2a is 40% by mass or more, excellent color development is easily obtained, and the effect of improving adhesive strength tends to be significant. Also, when the pigment content 2a is 75% by mass or less, delamination between the ink layer 2 and the adhesive layer 3 tends to be less likely to occur. From the viewpoint of achieving an even higher level of both excellent color development and suppression of delamination, the pigment content 2a may be, for example, 45 to 75% by mass or 50 to 70% by mass, based on the total mass of the ink layer 2.

[0041] The binder resin contained in ink layer 2 is, for example, a water-based binder resin. Examples of water-based binder resins include water-soluble binder resins, emulsion-type binder resins, and colloidal dispersion-type binder resins. Among these, when a water-soluble binder resin is used, the dispersion stability of the ink, the adhesion of the ink layer, and the strength of the ink layer tend to be good. Examples of water-soluble binder resins include natural resin-based casein resin and shellac resin, synthetic resin-based rosin-modified maleic acid resin, styrene-maleic acid resin, styrene-acrylic acid resin, styrene-maleic acid-acrylic acid resin, acrylic acid-acrylic acid ester resin, acrylic resin, polyester resin, as well as water-soluble polyamide resin and water-soluble polyurethane resin. From the viewpoint of obtaining a more significant improvement in adhesive strength, the water-based binder resin may be a resin that does not have a urethane skeleton. As the water-soluble binder resin, a resin with no acid value or a low acid value may be used as the main component, from the viewpoint of improving the dispersion stability of the ink, the adhesion of the ink layer, and the strength of the ink layer, and a resin with a high acid value may be used in combination with this resin. The content of the water-based binder resin may be, for example, 25-60% by mass, 25-55% by mass, or 30-50% by mass, based on the total mass of the ink layer 2.

[0042] The ink layer 2 may contain auxiliary agents such as dispersants, plasticizers, waxes, lubricants, and defoamers. Examples of plasticizers include dioctyl terephthalate. Examples of waxes include polyethylene and polypropylene. Examples of lubricants include calcium carbonate, barium sulfate, and clay. Examples of defoamers include silicone-based and hydrocarbon-based defoamers.

[0043] Some of the ink solvent (e.g., water or hydrophilic solvent contained in the water-based ink) may remain in the ink layer 2, but the solvent content (e.g., water or hydrophilic solvent) is, for example, 1% by mass or less based on the total mass of the ink layer 2. Examples of hydrophilic solvents include alcohol-based solvents such as methanol, ethanol, propanol, and butanol.

[0044] Water-based inks may contain basic compounds such as ammonia, trimethylamine, sodium hydroxide, and potassium hydroxide to improve the solubility and dispersibility of the resin in the solvent, and these components may also be included in ink layer 2.

[0045] The ink layer 2 has, for example, a network of continuous through-pores. The adhesive constituting the adhesive layer 3 may seep into the ink layer 2 from the ends of the through-pores present on the surface of the ink layer 2, so that at least a portion of the through-pores may be filled with the adhesive. The through-pores in the ink layer 2 are formed, for example, by the continuous gaps between pigments 2a that are formed when the pigments 2a contained in the ink layer 2 come into contact with each other. Therefore, by adjusting the content of pigments 2a, the size of the through-pores, the volume ratio of the through-pores to the ink layer 2, etc., can be adjusted. The thickness of the ink layer 2 is, for example, 0.3 to 2.5 μm.

[0046] In Figure 1, the ink layer 2 is shown as a single layer, but the ink layer 2 may have a multilayer structure of two or more layers. For example, the ink layer 2 may be a two-layer ink layer obtained by forming a first ink layer containing a pigment with relatively small particle size on the surface of the first substrate 1, and then forming a second ink layer containing a pigment with relatively large particle size (e.g., white pigment) on the surface of this first ink layer. When the laminate includes a second ink layer containing a white pigment, the color development of the first ink layer tends to be improved.

[0047] (adhesive layer) The adhesive layer 3 is interposed between the ink layer 2 and the second substrate 4A, bonding these layers together. The adhesive constituting the adhesive layer 3 contains a polyester polyol and a urethane compound which is a reaction product of polyisocyanate (A) and polyisocyanate (B).

[0048] A polyester polyol is a compound having two or more hydroxyl groups and whose main skeleton has a polyester structure. The polyester structure may also be a polyester polyurethane structure. That is, a polyester polyol may also be a polyester urethane polyol. In addition to the polyester and polyurethane structures, a polyester polyol may further have a polyether structure. Specific examples of polyester polyols include polyadipate polyols and polycaprolactone diols. A polyester polyol may be a single polyester polyol or a combination of two or more polyester polyols.

[0049] Commercially available polyester polyols may be used. Examples of commercially available polyester polyols include Takelac A525 (product name, "Takelac" is a registered trademark (hereinafter the same)) manufactured by Mitsui Chemicals, Inc., and DIC Dry LX-747 manufactured by DIC Corporation.

[0050] Polyisocyanate (A) is a compound having two or more isocyanate groups (excluding the biuret form of hexamethylene diisocyanate). Polyisocyanate (A) may be an aromatic compound or an aliphatic compound. Polyisocyanate (A) may be a low molecular weight compound or a high molecular weight compound. Polyisocyanate (A) may be a single polyisocyanate or a combination of two or more polyisocyanates.

[0051] Specific examples of polyisocyanates (A) include phenyl isocyanate, isophorone diisocyanate, tetramethylene diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate (metaxylylene diisocyanate and paraxylylene diisocyanate), and hydrogenated xylylene diisocyanate, as well as modified forms (multimers, adducts, etc.) of these polyisocyanates. Specific examples of modified polyisocyanates include isocyanurates, uretdiones, and adducts thereof (e.g., polyhydric alcohol adducts such as TMP).

[0052] Polyisocyanate (A) may contain a modified form of hexamethylene diisocyanate (excluding the biuret form), but in this case, it is preferable that polyisocyanate (A) further contains polyisocyanates other than modified forms of hexamethylene diisocyanate. Examples of polyisocyanates other than modified forms of hexamethylene diisocyanate include phenyl isocyanate, isophorone diisocyanate, tetramethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate and hydrogenated xylylene diisocyanate, and modified forms of these polyisocyanates (multimers, adducts, etc.). The amount of polyisocyanates other than modified hexamethylene diisocyanate contained in polyisocyanate (A) may be 50% by mass or more, and may be 70% by mass or more, or 90% by mass or more, based on the total mass of polyisocyanate (A). The amount of polyisocyanates other than hexamethylene diisocyanate contained in polyisocyanate (A) may be less than 100% by mass, and may be 95% by mass or less, or 90% by mass or less, based on the total mass of polyisocyanate (A).

[0053] Commercially available polyisocyanates (A) may be used as the supply material. Examples of commercially available products include Takenate A52 (trade name, "Takenate" is a registered trademark (hereinafter the same)) manufactured by Mitsui Chemicals, Inc., and KX-75 manufactured by DIC Corporation.

[0054] The urethane compound (compound having urethane bonds) contained in adhesive layer 3 may include polyols other than polyester polyols as constituent components (reactive components for obtaining the reactant), as long as they do not hinder the effect of improving adhesive strength. That is, adhesive layer 3 may contain a urethane compound which is a reaction product of polyester polyol, a polyol other than polyester polyol, polyisocyanate (A), and polyisocyanate (B). Examples of polyols other than polyester polyols include polyoxypropylene polyol, polyether polyol, polyether polyols such as polyoxytetramethylene glycol, polycarbonate polyol, polybutadiene polyol, and hydrocarbon polyols such as polyacrylate polyol.

[0055] The urethane compound content in the adhesive layer 3 may be, for example, 60% by mass or more, 75% by mass or more, or 90% by mass or more, based on the total mass of the adhesive layer 3. The adhesive layer 3 may consist substantially of only a urethane compound. The urethane compound content in the adhesive layer 3 may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total mass of the adhesive layer 3.

[0056] The adhesive layer 3 may further contain additives such as dispersants, defoamers, leveling agents, stabilizers, fillers, lubricants, and waxes, in addition to the urethane compound mentioned above. The adhesive layer 3 may contain some of the solvent (diluent, etc.) that was contained in the coating liquid for forming the adhesive layer, but the solvent content should be, for example, 1% by mass or less based on the total mass of the adhesive layer 3. Examples of solvents include ethyl acetate and methyl ethyl ketone.

[0057] The thickness of the adhesive layer 3 is, for example, 0.5 to 5.0 μm. Note that the thickness of the adhesive layer 3 refers to the shortest distance from the surface on the ink layer 2 side to the surface on the opposite side of the ink layer 2, and does not include the thickness of the area in the ink layer 2 into which the adhesive has permeated.

[0058] (Second substrate) The second substrate 4A is, for example, a resin film. An example of a resin film may be the resin film described above as an example of the first substrate 1.

[0059] The thickness of the second base material 4A (e.g., resin film) may be such that it satisfies the strength, rigidity, etc. required for heat and pressure treatment, and may be, for example, 10 μm to 100 μm or 12 μm to 50 μm. If the thickness of the second base material is 100 μm or less, the flexible packaging bag will be easier to tear by hand when opened, and manufacturing costs can be reduced. If the thickness of the second base material is 10 μm or more, sufficient strength, rigidity, etc. can be easily obtained.

[0060] The thickness (total thickness) of the laminate 10 may be, for example, 20 to 300 μm.

[0061] <Method for manufacturing laminates> Next, a method for manufacturing the laminate 10 will be described using Figure 2. Figure 2 is a schematic cross-sectional view showing one embodiment of the method for manufacturing the laminate 10. The method for manufacturing the laminate 10 includes the steps of: (A) (see Figure 2(a)) printing an aqueous ink onto the surface of the first substrate 1 to form an ink layer 2; (B) (see Figure 2(b)) applying a coating liquid for forming an adhesive layer to the surface of the ink layer 2 opposite to the first substrate 1 to form an adhesive layer 3; and (C) (see Figure 2(c)) laminating the second substrate 4A onto the surface of the adhesive layer 3 opposite to the ink layer 2.

[0062] The water-based ink contains, for example, the pigment 2a and binder resin described above. The solvent (dispersion medium) of the water-based ink is water or the hydrophilic solvent described above. The pigment is dispersed in the solvent, and the binder resin is dissolved or dispersed in the solvent. The solvent content in the water-based ink is, for example, 40 to 80% by mass based on the total mass of the water-based ink.

[0063] The water-based ink may further contain the above-mentioned auxiliary agents and basic compounds as components that may be included in the ink layer 2.

[0064] Water-based ink printing can be carried out by known methods such as gravure printing, flexographic printing, and inkjet printing. In step (A), an ink layer may be formed by solid printing, or by pattern printing of characters, figures, symbols, pictures, or other desired patterns. Alternatively, after forming a first ink layer by solid printing, a second ink layer may be formed by pattern printing of a desired pattern on the first ink layer.

[0065] The coating solution for forming the adhesive layer is made by mixing at least the polyester polyol, polyisocyanate (A), and polyisocyanate (B) described above. The coating solution can be prepared, for example, by mixing the polyester polyol, polyisocyanate (A), and polyisocyanate (B) all at once.

[0066] The coating solution can also be prepared, for example, by mixing a polyester polyol with a polyisocyanate other than the biuret form of hexamethylene diisocyanate to obtain a mixture, and then adding the biuret form of hexamethylene diisocyanate (polyisocyanate (B)) to the mixture and mixing. In this case, when adding polyisocyanate (B) to the mixture, other polyisocyanates other than the biuret form of hexamethylene diisocyanate may also be added. For example, a mixture containing the biuret form of hexamethylene diisocyanate as the main component (for example, 50% by mass or more) may be added to the mixture. The mixture may be, for example, a mixture (HDI mixture) containing the biuret form of hexamethylene diisocyanate, and at least one selected from the group consisting of the isocyanurate and uretdione forms of hexamethylene diisocyanate and their adducts. When using an HDI mixture, the polyisocyanate other than the biuret form of hexamethylene diisocyanate used in preparing the mixture may be a polyisocyanate other than a modified form of hexamethylene diisocyanate.

[0067] The coating liquid for forming the adhesive layer may be a solvent-free adhesive composition that does not contain solvents, from the viewpoint of reducing VOCs, but it may also contain solvents. For example, if components such as polyester polyol, polyisocyanate (A), and polyisocyanate (B) used in the preparation of the coating liquid are provided in a diluted state with a solvent (i.e., as a solution), the coating liquid will contain the solvent (diluent) of these solutions. The solvent may be one of the solvents mentioned above as a component that can be included in the adhesive layer 3.

[0068] The coating liquid for forming the adhesive layer may contain, for example, a polyester polyol, polyisocyanate (A), and polyisocyanate (B), but may also contain a reactant (urethane compound) formed by the reaction of some of these.

[0069] When preparing the coating solution for forming the adhesive layer, components other than polyester polyol, polyisocyanate (A), and polyisocyanate (B) (for example, the additives and solvents mentioned above as components that may be included in the adhesive layer 3) may be incorporated.

[0070] Conventional methods known as the following can be used for coating the coating solution: the commonly used casting method, dipping method, roll coating method, gravure coating method, screen printing method, reverse coating method, spray coating method, kit coating method, die coating method, metering bar coating method, chamber doctor combined coating method, curtain coating method, etc.

[0071] If the coating liquid contains a solvent, a drying treatment may be performed after coating to remove the solvent and dry the coating film. The drying of the coating film may be carried out at, for example, 25 to 120°C.

[0072] Although a laminate and its manufacturing method according to one embodiment have been described above, the laminate according to this disclosure is not limited to the above embodiment.

[0073] Figure 3 is a schematic cross-sectional view showing a laminate according to another embodiment. In the laminate 20 according to the other embodiment, the second substrate 4B includes a base film 5 such as the resin film described above and a barrier layer (gas barrier layer) 6 provided on the base film 5, and includes a sealant layer 7 on the surface of the second substrate 4B opposite to the adhesive layer 3 side. Except for these points, the configuration of the laminate 20 is the same as the configuration of the laminate 10.

[0074] In the laminate 20, the barrier layer 6 is in contact with the adhesive layer 3. The barrier layer 6 includes, for example, an inorganic thin film layer 6a and a gas barrier coating layer 6b provided on the surface of the inorganic thin film layer 6a facing the adhesive layer 3.

[0075] The inorganic thin film layer 6a is formed, for example, by depositing a metal, or an oxide, nitride, or oxide nitride of silicon (e.g., by vacuum deposition). Specifically, the material for the inorganic thin film layer 6a can be a metal such as aluminum, titanium, copper, indium, or tin, or an oxide thereof (alumina, etc.), or silicon, silicon oxide, or even a nitride or oxide nitride of metal or silicon. The inorganic thin film layer 6a may be a thin film layer containing multiple of these metals. In particular, inorganic thin film layers containing oxides, nitrides, or oxide nitrides of aluminum, titanium, copper, indium, or silicon tend to have excellent transparency and barrier properties, and among them, inorganic thin film layers containing oxides or oxide nitrides of silicon tend to have even higher barrier properties.

[0076] For forming the inorganic thin film layer 6a, vacuum deposition methods (resistance-heated vacuum deposition, electron beam-heated vacuum deposition, induction-heated vacuum deposition), sputtering methods (reactive sputtering, dual magnetron sputtering), and PECVD methods (with various plasma generation methods including DC (Direct Current), RF (Radio Frequency), MF (Middle Frequency), DC pulse, RF pulse, and DC+RF superposition) can be used. The method for forming the inorganic thin film layer 6a can be appropriately selected depending on the purpose and application. For example, sputtering may be selected from the viewpoint of film homogeneity, while vacuum deposition may be selected from the viewpoint of cost.

[0077] The thickness of the inorganic thin film layer 6a may be, for example, 5 nm or more, or 100 nm or less. When the thickness of the inorganic thin film layer 6a is 5 nm or more, good barrier properties are easily obtained, and when it is 100 nm or less, crack generation is suppressed, the decrease in water vapor and oxygen barrier properties is small, and costs can be reduced due to reduced material usage and shortened formation time.

[0078] As the inorganic thin film layer 6a, a metal foil such as aluminum foil may be used. In this case, the thickness of the metal foil may be 6 to 9 μm.

[0079] The gas barrier coating layer 6b can be formed by applying a coating solution containing, for example, polar compounds such as polyvinyl alcohol, polyvinylpyrrolidone, and ethylene vinyl alcohol, chlorine-containing compounds such as polyvinylidene chloride, and compounds containing Si atoms, Ti atoms, Al atoms, and Zr atoms onto an inorganic thin film layer, drying, and curing it. By laminating the gas barrier coating layer 6b, it is possible to prevent various secondary damages in subsequent processes and to provide high barrier properties.

[0080] The sealant layer 7 is composed of a resin that can be melted and fused together by heat, for example. The resins constituting the sealant layer may be polyolefin resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, polyethylene, polypropylene, etc., or acid-modified polyolefin resins obtained by modifying these with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, etc. The resins constituting the sealant layer may be one type or two or more types.

[0081] The thickness of the sealant layer 7 may be, for example, 5 to 300 μm, or 10 to 100 μm.

[0082] The sealant layer 7 can be formed by applying a coating liquid containing the resin using conventionally known methods such as dipping, roll coating, screen printing, or spraying. Alternatively, it can be formed by attaching a film or sheet made of the resin.

[0083] The laminate 20 described above includes a second substrate 4B which contains a substrate film 5 and a barrier layer 6. However, the second substrate does not necessarily have to contain a substrate film and may consist only of a barrier layer. Alternatively, the first substrate may also contain a barrier layer. In this case, the first substrate may or may not contain a substrate film. The barrier layer may be included in either the first substrate or the second substrate, or in both. Furthermore, a primer layer may be provided between the substrate film 5 and the barrier layer 6.

[0084] <Packaging bag> Figure 4 is a schematic plan view showing one embodiment of a packaging bag using a laminate 10 (a packaging bag made by forming a bag from the laminate 10). The packaging bag 30 shown in Figure 4 is processed into a bag shape by heat sealing three sides L1, L2, and L3. After placing the contents into the opening 30a which is not heat-sealed, the packaging bag 30 can be sealed by heat-sealing the opening 30a as well. However, the form of the packaging bag is not limited to this. Other examples of packaging bags include pillow packaging, three-side seal packaging, and gusset packaging. [Examples]

[0085] The present disclosure will be described below based on examples and comparative examples. However, the present invention is not limited to the following examples.

[0086] <Example 1> (Manufacturing of laminates) [Process (A)] As the first substrate, a barrier film (manufactured by Toppan Printing Co., Ltd., product name: GL-ARH) with a thickness of 12 μm and a polyethylene terephthalate resin film as the base film was prepared. A water-based ink for flexographic printing (manufactured by DIC Corporation, product name: XS-911) was printed onto the surface of the first substrate by flexographic printing to form an ink layer with a thickness of 0.3 μm.

[0087] [Process (B)] A mixture was prepared by blending Takelac A525, a polyester polyol manufactured by Mitsui Chemicals, Inc., and Takenate A52, a polyisocyanate manufactured by Mitsui Chemicals, Inc., in a mass ratio (solid content ratio) of 7.9:1. The ratio (NCO / OH) of the total number of moles of hydroxyl groups in the polyester polyol (Takelac A525) to the total number of moles of isocyanate groups in the polyisocyanate (Takenate A52) was set to 1.3. Subsequently, an HDI mixture (containing 50% or more biuret form of hexamethylene diisocyanate) as the main component, was added in 40 parts by mass per 100 parts by mass of polyisocyanate and mixed to prepare a coating solution for forming an adhesive layer.

[0088] Next, the adhesive-forming coating liquid obtained above was applied to the surface of the ink layer formed in step (A) by a roll coating method and dried to form an adhesive layer with a thickness of 3.3 μm. The coating amount in the dry state was 3.0 g / m². 2 That was the case.

[0089] [Process (C)] A 15 μm thick biaxially oriented nylon film (manufactured by Unitika Ltd., product name: Emblem) was laminated onto the adhesive layer formed in step (B) as a second substrate.

[0090] [Process (D)] On the second substrate laminated in process (C), a 60 μm thick axially oriented polypropylene film (manufactured by Toray Industries, Inc., product name: Pyrene ZK207) was laminated as a sealant layer by dry lamination. After lamination, the laminate of Example 1 was obtained by curing at 50°C for 72 hours.

[0091] (Making packaging bags) Two sheets measuring 140 mm in length and 180 mm in width were cut from the laminate. These sheets were overlapped so that the sealant layers were in contact with each other, and the three edges were sealed by heat sealing to create a bag-shaped packaging container (packaging bag) as shown in Figure 4. Heat sealing was performed by heating the three edges at 160°C for 1 second using a 10 mm wide sealing bar.

[0092] <Example 2, Comparative Examples 1-2> In step (B), the laminates and packaging bags of Example 2 and Comparative Examples 1-2 were prepared in the same manner as in Example 1, except that the proportions of polyester polyol (Takelac A525), polyisocyanate (Takenate A52), and HDI mixture were changed as shown in Table 1 when preparing the coating solution for forming the adhesive layer.

[0093] <Evaluation of the physical properties of adhesives> In accordance with JIS K 7161, the 100% modulus of the adhesives used in the manufacture of the laminates in Examples 1-2 and Comparative Examples 1-2 was measured. Specifically, the adhesive forming solution prepared in step (B) above was used to form a film on release paper using a doctor blade, dried at room temperature for 24 hours under a nitrogen atmosphere to remove the solvent, and then cured at 60°C for 6 days to form a cured film (film thickness 40-50 μm), and strip-shaped test pieces (samples) with a width of 5 mm were prepared. Using the obtained test pieces, the tensile stress in the longitudinal direction of the test piece was measured at 24°C and a tensile speed of 300 mm / min, and the tensile stress (100% modulus) when the test piece was 100% elongated was determined.

[0094] <Evaluation of adhesive strength and delamination> Test specimens with a width of 15 mm were cut from the laminates of Examples 1-2 and Comparative Examples 1-2. Using a tensile testing machine, the initial adhesive strength of the laminate (adhesion strength between the first substrate and the second substrate) was measured at room temperature (20°C, 30% RH) in accordance with JIS K 6854. The results are shown in Table 1.

[0095] Next, 100 ml of water was poured into the top opening of the packaging bags of Examples 1-2 and Comparative Examples 1-2. The opening (top) was then heat-sealed under the same conditions as when the packaging bags were made. The appearance of the sealed packaging bags was visually inspected to check for delamination. Bags without delamination were marked "○ (good)," and those with delamination were marked "× (bad)." The results are shown in Table 1.

[0096] Next, the sealed packaging bags were retorted in hot water at 121°C for 30 minutes. A 15 mm wide test piece was cut from the retorted packaging bag, and the laminate strength after retorting was measured in the same manner as the initial laminate strength. The appearance of the retorted packaging bags was also visually inspected to check for delamination. Bags without delamination were marked "○ (good)," and those with delamination were marked "× (poor)." The results are shown in Table 1.

[0097] [Table 1]

[0098] 1...First substrate, 2...Ink layer, 2a...Pigment, 3...Adhesive layer, 4A, 4B...Second substrate, 5...Substrate film, 6...Barrier layer, 7...Sealant layer, 10, 20...Laminate, 30...Packaging bag.

Claims

1. Step (A) involves printing an ink layer onto the surface of a first substrate using an aqueous ink, Step (B) involves applying a coating solution, which is a mixture of at least a polyester polyol and a polyisocyanate (excluding the biuret form of hexamethylene diisocyanate) and the biuret form of hexamethylene diisocyanate, to the surface of the ink layer opposite to the first substrate, thereby forming an adhesive layer. The step (C) includes laminating a second substrate on the side of the adhesive layer opposite to the side of the ink layer, A method for manufacturing a laminate, wherein the 100% modulus of the adhesive constituting the adhesive layer is 0.1 to 2.5 MPa at 25°C.

2. The method for manufacturing a laminate according to claim 1, wherein in step (A), the aqueous ink is printed by flexographic printing.

3. The method for producing a laminate according to claim 1 or 2, wherein the blending mass ratio of the polyester polyol and the polyisocyanate is 2:1 to 9:

1.

4. A method for producing a laminate according to any one of claims 1 to 3, wherein the amount of the biuret form of the hexamethylene diisocyanate is 30 parts by mass or more per 100 parts by mass of the amount of the polyisocyanate.

5. It has a laminated structure in which a first substrate, an ink layer, an adhesive layer, and a second substrate are arranged in this order. The adhesive layer comprises an adhesive containing a polyester polyol, a polyisocyanate (excluding the biuret form of hexamethylene diisocyanate), and a urethane compound which is a reaction product of the biuret form of hexamethylene diisocyanate. A laminate in which the adhesive has a 100% modulus of 0.1 to 2.5 MPa at 25°C.

6. The laminate according to claim 5, wherein the peel strength between the first substrate and the second substrate at 25°C is 1.0 N / 15 mm or more.

7. The laminate according to claim 5 or 6, further comprising a sealant layer on the surface of the second substrate opposite to the adhesive layer side.

8. The laminate according to any one of claims 5 to 7, wherein the first substrate and / or the second substrate includes a barrier layer.

9. A packaging bag made by forming a bag from the laminate according to any one of claims 5 to 8.

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