Solvent-free adhesives and laminates

Abstract

The present invention provides a solvent-free adhesive that exhibits rapid rise in adhesive strength and heat seal strength, and suppresses defects in the appearance of the coating film, even in low-temperature and low-humidity environments. Furthermore, it provides a laminate that can be suitably used for packaging material applications using the above solvent-free adhesive. [Solution] A solvent-free adhesive comprising a polyol (A) and a polyisocyanate (B), characterized by satisfying all of the following conditions (1) to (3). (1) The polyol (A) comprises a polyol (a1) with a molecular weight of 200 or less and three or more functionalities. (2) The polyisocyanate (B) comprises an isocyanate-terminated urethane prepolymer (B1), which is a reaction product of a polyol (b1) and an isocyanate compound (b2), and an isocyanate monomer (B2) containing 2,4'-diphenylmethane diisocyanate, wherein the polyol (b1) contains 80% by mass or more of polyether polyol (b1-1) based on the total mass of the polyol (b1). (3) The polyether polyol (b1-1) contains a bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less, and the content of the bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less is 15 to 50% by mass based on the total mass of the polyol (b1).

Description

Technical Field

[0001] Embodiments of the present invention relate to a solventless adhesive and a laminate using the solventless adhesive. More specifically, the present invention relates to a solventless adhesive that can be suitably used for forming a laminate of a plastic film and / or a vapor-deposited film, and a laminate useful as a packaging material for foods, medical products, cosmetics, and the like.

Background Art

[0002] In recent years, due to the strengthening of regulations and considerations for environmental protection and safety, there has been an increasing demand for adhesives for forming laminates used as packaging materials to be solventless. Solventless adhesives (hereinafter referred to as solventless adhesives) are generally designed with formulations using low molecular weight resin components from the perspective of handling properties. Therefore, solventless adhesives tend to have a slower onset of adhesive performance (i.e., a slower rise in adhesive strength and heat seal strength due to the cohesive force of the resin component) compared to solvent-based adhesives, and improvement is desired.

[0003] On the other hand, with the global movement to reduce greenhouse gas emissions, products that are compatible with environmental requirements are desired, and there is also a demand for biomass adhesives using biomass-derived raw materials. In response to such a situation, for example, Patent Document 1 discloses a solventless adhesive containing a polyol (A) and a polyisocyanate (B) and satisfying the following (1) and (2). (1) The polyol (A) contains a polyester polyol (a1), and the content of the polyester polyol (a1) is 30% by mass or more and 70% by mass or less based on the total mass of the polyol (A). (2) The polyol (A) contains castor oil or a castor oil derivative (a2), and the content of the castor oil or the castor oil derivative (a2) is 30% by mass or more and 70% by mass or less based on the total mass of the polyol (A). Patent Document 1 reveals that the above configuration makes it possible to realize a solvent-free adhesive that exhibits rapid rise in adhesive strength and heat seal strength even in low humidity environments, as well as good pot life and excellent handling properties. In the examples, various evaluations were performed on laminates aged in a low humidity environment of 40°C and 20%RH. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-148008 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, when considering use in environments with lower temperatures and humidity, such as winter, it tends to be difficult to obtain sufficiently satisfactory properties with the solvent-free adhesive disclosed in Patent Document 1. Generally, in low-temperature and low-humidity environments, the curing speed of adhesives slows down significantly, which delays the development of adhesive performance such as adhesive strength and heat seal strength, resulting in a significant decrease in production efficiency.

[0006] To improve production efficiency, one possible solution is to accelerate the curing of adhesives in low-temperature and low-humidity environments. However, as the curing speed increases, pot life and handling properties tend to decrease. In other words, there is a trade-off relationship between accelerated curing and pot life and handling properties, making it difficult to strike a balance. Furthermore, from the perspective of accelerating the curing of two-component adhesives consisting of a polyol component and an isocyanate component, methods to increase the reactivity of the isocyanate group (-NCO group) in the isocyanate component can be considered. However, when a highly reactive isocyanate component is used, there is a tendency for the appearance of the coating film (adhesive layer) to be poor. This appearance problem occurs when small bubbles such as carbon dioxide are generated by the reaction of the -NCO group with moisture in the system, and these bubbles then aggregate in the coating film. In laminates obtained by bonding two or more substrates together using an adhesive, the appearance problem of the coating film that is likely to occur during the curing reaction of the adhesive affects the appearance of the laminate, and thus significantly reduces the production efficiency of the laminate. Thus, there is a trade-off relationship between accelerating the curing of the adhesive and the appearance of the coating film, and improvements to balance the two are desired. From these perspectives, there is a need for solvent-free adhesives that can cure well even in low-temperature and low-humidity environments, while also achieving a good balance of desired properties.

[0007] In view of the above circumstances, an embodiment of the present invention provides a solvent-free adhesive that readily exhibits adhesive performance and suppresses defects in the appearance of the coating film, even in low-temperature and low-humidity environments. Another embodiment of the present invention provides a laminate that can be suitably used for packaging materials using the above solvent-free adhesive. [Means for solving the problem]

[0008] One embodiment of the present invention relates to a solvent-free adhesive comprising a polyol (A) and a polyisocyanate (B), characterized in that it satisfies all of the following conditions (1) to (3). (1) The polyol (A) comprises a polyol (a1) with a molecular weight of 200 or less and three or more functionalities. (2) The polyisocyanate (B) comprises an isocyanate-terminated urethane prepolymer (B1), which is a reaction product of a polyol (b1) and an isocyanate compound (b2), and an isocyanate monomer (B2) containing 2,4'-diphenylmethane diisocyanate, wherein the polyol (b1) contains 80% by mass or more of polyether polyol (b1-1) based on the total mass of the polyol (b1). (3) The polyether polyol (b1-1) contains a bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less, and the content of the bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less is 15 to 50% by mass based on the total mass of the polyol (b1). In some embodiments, the polyisocyanate (B) is preferably a reaction mixture obtained by the reaction of a polyol (b1) with an isocyanate compound (b2) containing diphenylmethane diisocyanate. The reaction mixture contains an isocyanate-terminated urethane prepolymer and unreacted diphenylmethane diisocyanate, the unreacted diphenylmethane diisocyanate containing at least 2,4'-diphenylmethane diisocyanate. [Effects of the Invention]

[0009] According to the present invention, a solvent-free adhesive can be provided that readily exhibits adhesive performance and suppresses defects in the appearance of the coating film, even in low-temperature and low-humidity environments. Furthermore, a laminate that can be suitably used for packaging materials can be provided using the above-mentioned solvent-free adhesive. [Modes for carrying out the invention]

[0010] <1> Solvent-free adhesive One embodiment of the present invention relates to a solvent-free adhesive. The solvent-free adhesive of this embodiment comprises a polyol (A) and a polyisocyanate (B), and is characterized by satisfying all of the following (1) to (3). (1) The polyol (A) comprises a polyol (a1) with a molecular weight of 200 or less and three or more functionalities. (2) The polyisocyanate (B) comprises an isocyanate-terminated urethane prepolymer (B1), which is a reaction product of a polyol (b1) and an isocyanate compound (b2), and an isocyanate monomer (B2) containing 2,4'-diphenylmethane diisocyanate, wherein the polyol (b1) contains 80% by mass or more of polyether polyol (b1-1) based on the total mass of the polyol (b1). (3) The polyether polyol (b1-1) contains a bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less, and the content of the bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less is 15 to 50% by mass based on the total mass of the polyol (b1).

[0011] According to the solvent-free adhesive of this embodiment, as described in (1) to (3) above, various desired properties can be easily obtained by combining a specific polyol (A) and a specific polyisocyanate (B). The solvent-free adhesive according to this embodiment is configured as a two-component adhesive. The first component, polyol (A), includes a trifunctional or higher polyol (a1) with a molecular weight of 200 or less. On the other hand, the second component, polyisocyanate (B), includes a reaction product of a polyol (b1) containing a specific amount of a specific polyether polyol (b1-1A) and an isocyanate compound (b2). The above reaction product is a prepolymer containing a urethane bond formed by the reaction of (b1) and (b2) and having an isocyanate group at its terminus. Hereinafter, the above reaction product will be referred to as "urethane bond-containing polyisocyanate," "isocyanate group-terminated urethane prepolymer," or "urethane prepolymer." The above polyisocyanate (B) further includes an isocyanate monomer containing 2,4'-diphenylmethane diisocyanate.

[0012] The solvent-free adhesive of this embodiment undergoes a curing reaction when the polyol (A) and polyisocyanate (B) are mixed at the time of use, and exhibits adhesive performance early even in low-temperature and low-humidity environments. The mechanism by which such effects are obtained is not constrained by theory, but is presumed to be as follows. First, it is generally believed that when an appropriate amount of moisture is present in the environment of use, the water molecules play a supporting role in promoting the curing reaction. Specifically, it is hypothesized that water molecules act on the NCO groups of polyisocyanate molecules to form urethane bonds, and further act on other polyisocyanate molecules to form a three-dimensional cross-linked structure, thereby promoting the progress of the curing reaction with polyols. However, in low-temperature and low-humidity environments, the amount of moisture is low, and the promoting effect of water molecules as described above is reduced, which is thought to slow down the development of adhesive performance.

[0013] In contrast, the solvent-free adhesive of this embodiment has a specific combination of the polyol (A) and the polyisocyanate (B). Furthermore, the polyisocyanate (B) has a composition that includes a specific isocyanate group-terminated urethane prepolymer (B1) and an isocyanate monomer (B2) containing 2,4'-diphenylmethane diisocyanate. It is believed that, due to the above composition, the solvent-free adhesive of this embodiment facilitates the formation of a three-dimensional crosslinked structure from the initial stages of the reaction, even in low-temperature and low-humidity environments, thus facilitating the development of adhesive performance. It is presumed that during the formation of the three-dimensional crosslinked structure, the highly branched, low-molecular-weight prepolymer and polyol in the polyol (A) act as nuclei, and the isocyanate monomer (B2) in the polyisocyanate (B) react preferentially, leading to early molecular entanglement, followed by the reaction of the isocyanate group-terminated urethane prepolymer (B1).

[0014] The following provides a more detailed explanation of each component that makes up the solvent-free adhesive. <Polyol (A)> In the solvent-free adhesive of the present embodiment, the polyol (A) may be any compound having two or more hydroxyl groups, and at least contains a trifunctional or higher polyol (a1) having a molecular weight of 200 or less.

[0015] (Trifunctional or higher polyol (a1)) In the solvent-free adhesive, by using a trifunctional or higher polyol (a1) having a molecular weight of 200 or less as the polyol (A) (hereinafter also referred to as a trifunctional or higher polyol (a1)), the adhesion performance tends to be easily exhibited even under low temperature and low humidity conditions. In this specification, "the manifestation of adhesion performance" means the performance manifested by the progress of the curing reaction between the components constituting the adhesive and the formation of crosslinking bonds. Specifically, it means adhesion performance such as the adhesion strength between substrates in a laminate and the heat seal strength. Also, "the manifestation of adhesion performance becomes easy" means that the time until the adhesion performance is manifested is short (the manifestation of adhesion performance is fast).

[0016] In some embodiments, the molecular weight of the trifunctional or higher polyol (a1) may preferably be a molecular weight of 80 to 200, more preferably 90 to 200. When the molecular weight (Mw) of the trifunctional or higher polyol (a1) is 80 or more, the hydroxyl value of the entire polyol (A) does not become too high, so the increase in viscosity after mixing with the polyisocyanate (B) becomes moderate, and there is a tendency to easily suppress the decrease in coating properties over time. Also, when Mw is 200 or less, the reactivity of the hydroxyl groups of the above trifunctional or higher polyol (a1) is improved, and a three-dimensional structure can be preferentially constructed, and there is a tendency for the manifestation of adhesion performance such as adhesion strength and heat seal strength to be accelerated. [[ID=II]]

[0017] The number of terminal hydroxyl groups of the above trifunctional or higher polyol (a1) is preferably 3 to 5, more preferably 3 to 4, and particularly preferably 3. When the number of the above terminal hydroxyl groups is 5 or less, it becomes easy to appropriately adjust the hydroxyl value of the entire polyol (A). As a result, the increase in viscosity after mixing with the polyisocyanate (B) due to too high hydroxyl groups can be suppressed, and the decrease in coating properties over time can be suppressed.

[0018] Specific examples of the above trifunctional or higher polyol (a1) include, for example, aliphatic polyols such as 1,1,2-trihydroxyethane, trimethylolethane, trimethylolpropane, glycerin, hexanetriol, and pentaerythritol; modified polyether polyols obtained by ring-opening polymerization of the above aliphatic polyols with various cyclic ether bond-containing compounds such as ethylene oxide, propylene oxide, tetrahydrofuran, ethyl glycidyl ether, propyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether, and allyl glycidyl ether; lactone-based polyester polyols obtained by polycondensation reaction of the above aliphatic polyols with various lactones such as ε-caprolactone. Among them, aliphatic polyols are preferred. In some embodiments, the above trifunctional or higher polyol (a1) may be at least one selected from the group consisting of trimethylolpropane, glycerin, and pentaerythritol, and more preferably contains at least trimethylolpropane.

[0019] In the polyol (A), the content of the above trifunctional or higher polyol (a1) may be 0.2% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more, based on the total mass of the polyol (A). Also, the above content may be 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less, and still more preferably 6% by mass or less. When the above content is 0.2% by mass or more, a three-dimensional structure is preferentially constructed, the cohesive force of the coating film of the adhesive increases, and the rise of the adhesive strength and heat seal strength becomes faster. When the above content is 15% by mass or less, the increase in viscosity after mixing with the polyisocyanate (B) becomes gentle, and the decrease in coating property over time can be suppressed. In some embodiments, the above content may preferably be 0.5 to 10% by mass, more preferably 1 to 8% by mass, and still more preferably 2 to 6% by mass.

[0020] (Other polyols) Polyol (A) may further contain one or more polyols other than polyol (a1) (hereinafter referred to as "other polyols"). For example, polyol (A) may further contain three or more functional polyols other than polyol (a1) mentioned above. A specific example of a three or more functional polyol other than polyol (a1) is trifunctional polypropylene glycol (molecular weight 400). Examples of the above-mentioned other polyols include polyester polyols, polycarbonate polyols, polycaprolactone polyols, polyether polyols, polyolefin polyols, acrylic polyols, silicone polyols, castor oil-based polyols, and fluorine-based polyols. One or more of these can be used in combination. In particular, using biomass-derived raw materials such as castor oil-based polyols is preferable because it allows for the construction of a biomass adhesive, providing a solvent-free adhesive that is environmentally friendly.

[0021] In some embodiments, the above-mentioned other polyols may be compounds in which urethane bonds are introduced by reacting a diisocyanate with some of the hydroxyl groups. Specific examples include polyether urethane polyols and polyester urethane polyols. As the diisocyanate used to form the above-mentioned urethane bond, for example, at least one selected from the group consisting of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate can be used.

[0022] In some embodiments, the above-mentioned other polyol may be a compound in which a carboxyl group is introduced by reacting an acid anhydride with some of the hydroxyl groups. The acid anhydride used to form the above compound may be at least one selected from the group consisting of pyromellitic anhydride, mellitic anhydride, trimellitic anhydride, and trimellitic anhydride esters. The trimellitic anhydride ester may be an ester compound obtained by esterifying an alkylene glycol or alkanetriol having 2 to 30 carbon atoms with trimellitic anhydride. Specifically, examples include ethylene glycol bisanehydrotrimellitate and propylene glycol bisanehydrotrimellitate.

[0023] In some embodiments, the polyol (A) preferably further comprises one or more selected from the group consisting of polyether polyol (a2) and polyester polyol (a3), described later, in addition to the polyol (a1). When polyether polyol (a2) and / or polyester polyol (a3) ​​are used, heat resistance and adhesion tend to be easily improved. In particular, when at least polyester polyol (a3) ​​is used, adhesion to substrates such as metal foil or vapor-deposited film tends to be easily improved.

[0024] (Polyether polyol (a2)) The polyether polyol (a2) is any compound having two or more hydroxyl groups and two or more ether bonds in its molecule. These polyether polyols may be used individually or in combination of two or more types. Examples of the polyether polyol (a2) mentioned above include polyalkylene glycols such as polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, and polybutylene glycol; polyethylene glycol / polypropylene glycol block copolymers; and propylene oxide-ethylene oxide random polyethers. Alternatively, an addition polymer obtained by addition polymerization of an oxirane compound such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran to a low molecular weight polyol such as water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, or suicrose may be used as the polyether polyol. Examples of the above-mentioned addition polymers include propylene glycol propylene oxide adducts, glycerol propylene oxide adducts, sorbitol-based propylene oxide adducts, and suocrose-based propylene oxide adducts. The number-average molecular weight (Mn) of the above polyether polyol is preferably 400 or more. In some embodiments, the Mn may be preferably 400 to 4,000, more preferably 400 to 3,000, and even more preferably 400 to 2,000.

[0025] When polyol (A) contains polyether polyol (a2), the leveling properties tend to be good. Based on the total mass of polyol (A), the content of polyether polyol (a2) may be preferably 5 to 40% by mass, more preferably 5 to 20% by mass. In some embodiments, among the polyether polyols (a2), a bifunctional polyether polyol (a2-1) with a number average molecular weight of 500 or less is preferred. Based on the total mass of polyether polyol (a2), the content of polyether polyol (a2-1) is preferably 50% by mass or more, more preferably 80% by mass or more, and may be 100% by mass. From this viewpoint, based on the total mass of polyol (A), the content of polyether polyol (a2-1) is preferably 5 to 40% by mass, more preferably 5 to 20% by mass.

[0026] A bifunctional polyether polyol (a2-1) with a number-average molecular weight of 500 or less can be produced according to methods well known in the art. A specific example is A201 obtained in the examples described later. The above polyether polyol (a2-1) can also be obtained commercially. For example, ADEKA Polyether P-400 manufactured by ADEKA Corporation can be used.

[0027] (Polyester polyol (a3)) Polyester polyols (a3) ​​include, for example, polyester polyols obtained by reacting a carboxyl group component with a hydroxyl group component; and polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, polyvalerolactone, and poly(β-methyl-γ-valerolactone). The carboxyl group component is not particularly limited as long as it is known, and monofunctional carboxylic acids or polycarboxylic acids can be used. Examples of such carboxyl group components include monofunctional carboxylic acids having aromatic rings such as benzoic acid, phenylacetic acid, and 3-phenylpropionic acid; acyclic aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic anhydride, and fumaric acid; alicyclic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, and 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid; anhydrides or ester-forming derivatives of these aliphatic or aromatic dicarboxylic acids; and polybasic acids such as p-hydroxybenzoic acid, p-(2-hydroxyethoxy)benzoic acid, and ester-forming derivatives of these dihydroxycarboxylic acids, and dimer acids. Preferably, it is at least one selected from the group consisting of benzoic acid, adipic acid, sebacic acid, isophthalic acid, and terephthalic acid.

[0028] In particular, from the viewpoint of adhesive performance and heat resistance, the carboxyl group component preferably includes an aromatic carboxyl group component. The aromatic carboxyl group component includes monofunctional aromatic carboxylic acids, bifunctional aromatic dicarboxylic acids, and trifunctional or more aromatic polycarboxylic acids. When considering the total number of moles of carboxyl group components used in the synthesis of polyester polyol (a3), the aromatic carboxyl group component is preferably 25 mol% or more and 60 mol% or less. Particularly preferably 35 mol% or more and 45 mol% or less. A concentration of 25 mol% or more is preferable because it significantly increases the difference between flexibility and rigidity, forming a sea-island structure and improving adhesion and heat resistance. A concentration of 60 mol% or less is preferable because it reduces viscosity and improves appearance and pot life.

[0029] The hydroxyl group component mentioned above is not particularly limited as long as it is a known component, but examples include diols and polyols with three or more functionalities. Examples of the diols include aliphatic diols such as ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3,3'-dimethylolheptane, and 1,4-bis(hydroxymethyl)cyclohesane; ether glycols such as polytetramethylene ether glycol and polyoxyethylene glycol; modified polyetherdiols obtained by ring-opening polymerization of the aliphatic diol with various cyclic ether bond-containing compounds such as ethylene oxide and tetrahydrofuran; lactone-based polyester polyols obtained by polycondensation reactions of the aliphatic diol with various lactones such as lactanoides and ε-caprolactone; and alkylene oxide adducts of bisphenols obtained by adding ethylene oxide or the like to bisphenols such as bisphenol A and bisphenol F. Preferably, it is at least one selected from the group consisting of ethylene glycol, diethylene glycol, 2-methyl-1,3-propanediol, and neopentyl glycol. Examples of the three- or more functional polyols include compounds similar to those previously exemplified as the three- or more functional polyol (a1). However, the molecular weight of the three- or more functional polyol used to prepare polyester polyol (a3) ​​is not particularly limited. The three- or more functional polyol used to prepare polyester polyol (a3) ​​may preferably be an aliphatic polyol, and more preferably trimethylolpropane.

[0030] From the viewpoint of imparting flexibility, polyester polyol (a3) ​​is preferably a polyester polyol using a bifunctional carboxyl group component and / or a bifunctional hydroxyl group component, such as a dicarboxylic acid and a diol. That is, polyester polyol (a3) ​​is preferably a reaction product of a hydroxyl group component containing a diol and a carboxyl group component containing a dicarboxylic acid. Furthermore, the ratio of the total number of moles of hydroxyl groups and carboxyl groups contained in the diol and dicarboxylic acid is preferably 85 mol% or more, based on the total number of moles of hydroxyl groups and carboxyl groups contained in the hydroxyl group component and the carboxyl group component. Particularly preferably it is 90 mol% or more. A ratio of 85 mol% or more is preferable because it suppresses an excessive increase in crosslinking density, prevents a decrease in the degree of freedom of the polymer chain, and exhibits excellent flexibility.

[0031] The ratio of the total number of moles of hydroxyl groups and carboxyl groups contained in the above-mentioned bifunctional raw materials (bifunctional carboxyl group component and bifunctional hydroxyl group component) can be determined according to (i) to (iii) below. (i) Determine the number of moles of carboxyl groups or hydroxyl groups contained in each raw material. Then, (ii) Determine the total number of moles of carboxyl groups and hydroxyl groups contained in all raw materials. Then, (iii) Using the total number of moles determined in (ii) above as a reference, determine the ratio of the total number of moles of carboxyl groups or hydroxyl groups contained in the bifunctional raw materials. In (i) above, the number of moles of carboxyl groups or hydroxyl groups contained in each raw material can be derived by the following formula (1). Formula (1): [Number of moles of functional groups in each raw material] = [Amount of each raw material used (g)] × [Number of functional groups in each raw material] / [Molecular weight of each raw material]

[0032] The reaction equivalent ratio (OH / COOH) between the hydroxyl group of the hydroxyl group component and the carboxyl group of the carboxyl group component used in the synthesis of the polyester polyol is preferably 1.1 or more and 1.5 or less. Particularly preferably it is 1.2 or more and 1.4 or less. A ratio of 1.1 or more is preferable because it increases the cohesive force of the polyester polyol and provides superior adhesive strength. A ratio of 1.5 or less is preferable because it slows down the increase in viscosity after mixing with the polyisocyanate (B) described later and suppresses the deterioration of coating properties over time.

[0033] In some embodiments, the polyester polyol (a3) ​​preferably contains an aliphatic polyester polyol (a3-1). Aliphatic polyester polyol (a3-1) means that both the carboxyl group component and the hydroxyl group component constituting the polyester polyol are the aliphatic compounds described above. When polyol (A) contains an aliphatic polyester polyol, viscosity is reduced and handling properties are improved, which is preferable. For example, it is preferable to use an aliphatic polyester polyol (a3-1) obtained by the reaction of adipic acid with 2-methyl-1,3-propanediol. The reaction equivalent ratio of adipic acid and 2-methyl-1,3-propanediol is as described above. The aliphatic polyester polyol (a3-1) can be produced according to methods well known in the art. A specific example is A101 produced in the example described later.

[0034] In some embodiments, the number-average molecular weight (Mn) of the polyester polyol (a3) ​​may preferably be 500 to 4000, from the viewpoint of achieving both good physical properties and good handling. The above Mn is measured by gel permeation chromatography (GPC) and converted to styrene equivalent. In some embodiments, the Mn of the polyester polyol (a3) ​​may more preferably be 800 to 3000, and even more preferably 1000 to 2000. When the Mn is 1000 or more, the cohesive force is improved, and the rise in adhesive strength under low humidity tends to be faster. On the other hand, when the Mn is 2000 or less, the viscosity after mixing with polyisocyanate (B) can be kept low, so it tends to be easy to obtain a coating film with an excellent appearance after coating with the adhesive. In particular, when the adhesive is applied to a vapor-deposited film (VM film) such as an aluminum (AL) vapor-deposited film, the appearance of the coating film is prone to deterioration. Therefore, when a laminate is formed by applying the adhesive to a vapor-deposited film (VM film) and then bonding it to another substrate, the appearance of the laminate also deteriorates. In contrast, with the adhesive of this embodiment, even when a vapor-deposited film is used as the substrate, a coating film with an excellent appearance can be easily obtained, and a laminate with an even better appearance can be easily obtained. Hereinafter, in this specification, the appearance of a laminate having a structure in which an adhesive layer is formed by coating a vapor-deposited film (VM film) with an adhesive and then laminating another substrate will be referred to as the "VM appearance." In the above laminate, the substrate may have an ink layer (printed layer) as needed. Regarding the VM appearance, in the embodiments described later, the appearance of a laminate obtained by providing an adhesive layer on a VM film such as an AL vapor-deposited CPP film and laminating it with an OPP film having a printed layer is evaluated, but the type of VM film and the structure of the laminate are not limited to the form of the embodiments and may be various forms.

[0035] Based on the total mass of polyol (A), the content of polyester polyol (a3) ​​may preferably be 30 to 90% by mass, more preferably 50 to 90% by mass, and even more preferably 70 to 90% by mass. When the polyester polyol (a3) ​​content is 50% by mass or more, the cohesive strength of the coating film is improved, and the rise in adhesive strength under low humidity conditions is accelerated. On the other hand, when it is 90% by mass or less, the viscosity when compounded with polyisocyanate (B) decreases, and furthermore, the subsequent increase in viscosity becomes more gradual. Based on the total mass of polyester polyol (a3), the content of aliphatic polyester polyol (a3-1) may preferably be 50% by mass or more, more preferably 80% by mass or more, and may also be 100% by mass.

[0036] The hydroxyl value of the polyester polyol (a3) ​​is preferably 30 to 150 mgKOH / g, more preferably 50 to 120 mgKOH / g, and even more preferably 50 to 80 mgKOH / g. When the hydroxyl value is 40 mgKOH / g or higher, the viscosity of the polyester polyol (a1) is reduced, the increase in viscosity after mixing with polyisocyanate (B) becomes gradual, and the deterioration of coating properties over time is suppressed, which is preferable. When it is 150 mgKOH / g or lower, the cohesive force of the polyester polyol (a1) is improved, and the rise in adhesive strength under low humidity conditions becomes faster, which is preferable.

[0037] In some embodiments, the polyester polyol (a3) ​​may be a compound (hereinafter sometimes abbreviated as polyester polyurethane polyol) obtained by reacting a diisocyanate with some of the hydroxyl groups to introduce a urethane bond. Examples of the diisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate.

[0038] Furthermore, in some embodiments, the polyester polyol (a3) ​​may be a compound in which a carboxyl group is introduced by reacting an acid anhydride with some of the hydroxyl groups (hereinafter sometimes abbreviated as acid-modified). Examples of the acid anhydride include pyromellitic anhydride, mellitic anhydride, trimellitic anhydride, and trimellitic anhydride esters. Examples of trimellitic anhydrides include ester compounds obtained by esterifying an alkylene glycol or alkanetriol having 2 to 30 carbon atoms with trimellitic anhydride, and specifically, ethylene glycol bisanehydrotrimellitate, propylene glycol bisanehydrotrimellitate, etc. can be used.

[0039] In some embodiments, the polyol (A) in the solvent-free adhesive preferably comprises the polyol (a1) and other polyols, wherein the other polyol preferably includes at least one selected from the group consisting of polyether polyol (a2) and polyester polyol (a3). Polyol (A) may further contain other polyols to the extent that it does not impair the desired effect. In some embodiments, the polyol (A) may consist only of the polyol (a1) and a polyether polyol (a2) as the other polyol. In some embodiments, the polyol (A) may consist only of the polyol (a1) and a polyester polyol (a3) ​​as the other polyol. In some embodiments, the polyol (A) may consist of the polyol (a1) and a polyether polyol (a2) / polyester polyol (a3) ​​as the other polyol. In the above embodiments, the ratio of polyether polyol (a2) / polyester polyol (a3) ​​may preferably be 10 / 90 to 55 / 45, more preferably 10 / 90 to 40 / 60, and even more preferably 10 / 90 to 30 / 70. In the above embodiments, it is preferable to use a bifunctional polyether polyol (a2-1) having a number average molecular weight of at least 500 or less (substantially, a number average molecular weight of 400 to 500) as the polyether polyol (a2). In some embodiments, the content of the bifunctional polyether polyol (a2-1) may be 0% by mass, but is preferably 50% by mass or more, based on the total mass of the polyether polyol (a2). The above content is more preferably 65% ​​by mass or more, even more preferably 80% by mass or more, and may be 100% by mass. Furthermore, it is preferable to include at least an aliphatic polyester polyol (a3-1) as the polyester polyol (a3).

[0040] While not particularly limited, preferred embodiments of polyol (A) include the following: (I) The polyol (A) above comprises a trifunctional or more polyol (a1) with a molecular weight of 200 or less, a polyether polyol (a2) with a number average molecular weight of 400 to 4000, and a polyester polyol (a3) ​​with a number average molecular weight of 500 to 4000. Preferably, (a2) contains 50% by mass or more of a polyether polyol (a2-1) with a number average molecular weight of 400 to 500. In the above embodiment, based on the total mass of the polyol (A), the content of the trifunctional or more polyol (a1) may be 0.2 to 15% by mass, the content of the polyether polyol (a2) may be 5 to 50% by mass, and the content of the polyester polyol (a3) ​​may be 30 to 96% by mass. The compounds exemplified above can be used as (a1), (a2), and (a3) ​​in appropriate combinations. While not particularly limited, for example, trimethylolpropane, glycerin, or pentaerythritol can be suitably used as the above-mentioned trifunctional polyol (a1). For example, bifunctional polypropylene glycol (ADEKA Corporation, ADEKA Polyether P-400, molecular weight 400) or bifunctional polypropylene glycol (ADEKA Corporation, ADEKA Polyether P-1000, molecular weight 1000) can be suitably used as the above-mentioned polyether polyol (a2). For example, a polyester of 2-methyl-1,3-propanediol and adipic acid (synthesis example A101 produced in the example described later) can be suitably used as the above-mentioned polyester polyol (a3).

[0041] (II) The polyol (A) above comprises a trifunctional or more polyol (a1) with a molecular weight of 200 or less and a polyether polyol (a2) with a number average molecular weight of 400 to 4000. Based on the total mass of the polyol (A), the content of the trifunctional or more polyol (a1) may be 0.2 to 15% by mass, and the content of the polyether polyol (a2) may be 10 to 50% by mass. The compounds exemplified above can be used as (a1) and (a2) in appropriate combinations. Although not particularly limited, trimethylolpropane, glycerin, or pentaerythritol can be suitably used as the trifunctional or more polyol (a1). For example, A201 produced in the example described later can be suitably used as the polyether polyol (a2). Other suitable examples of the above polyether polyol (a2) include, for example, difunctional polypropylene glycol (ADEKA Corporation, ADEKA Polyether P-400, molecular weight 400) and difunctional polypropylene glycol (ADEKA Corporation, ADEKA Polyether P-1000, molecular weight 1000).

[0042] (III) The polyol (A) above comprises a trifunctional or more polyol (a1) with a molecular weight of 200 or less and a polyester polyol (a3) ​​with a number average molecular weight of 500 to 4000. In the above embodiment, the content of the trifunctional or more polyol (a1) is 0.2 to 15% by mass, and the content of the polyester polyol (a3) ​​is 85 to 99.8% by mass, based on the total mass of the polyol (A). For example, trimethylolpropane, glycerin, or pentaerythritol can be suitably used as the trifunctional or more polyol (a1). For example, A101 produced in the example described later can be suitably used as the polyester polyol (a3).

[0043] <Polyisocyanate (B)> In this embodiment, polyisocyanate (B) includes a reaction product of polyol (b1) and isocyanate compound (b2), and a diisocyanate monomer containing 2,4'-diphenylmethane diisocyanate. Polyisocyanate (B) will be described in more detail below.

[0044] (Reaction products) The reaction product of a polyol (b1) and an isocyanate compound (b2) is a compound having a urethane bond formed by the reaction and having two or more isocyanate groups at its termini. In this disclosure, the above reaction product is also referred to as "urethane bond-containing polyisocyanate" or "isocyanate group-terminated urethane prepolymer," and both terms are used synonymously. The reaction product will be described in more detail below.

[0045] (Polyol (b1)) The polyol (b1) used to prepare the above-mentioned urethane bond-containing polyisocyanate comprises at least a polyether polyol (b1-1). Polyol (b1) may further contain polyols other than polyether polyols, such as polyester polyols and trifunctional or higher polyols, as needed. In some embodiments, the urethane bond-containing polyisocyanate preferably contains a reaction product of the polyether polyol and the polyisocyanate (sometimes abbreviated as polyether polyurethane polyisocyanate).

[0046] (Polyether polyol) The above-mentioned polyether polyols may be any compound having two or more hydroxyl groups and two or more ether bonds in their molecule, and may be either a bifunctional polyether polyol or a polyether polyol with three or more functions. These polyether polyols may be used individually or in combination of two or more. Examples of bifunctional polyether polyols include polyalkylene glycols such as polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, and polybutylene glycol; polyethylene glycol / polypropylene glycol block copolymers; and propylene oxide-ethylene oxide random polyethers. Alternatively, an addition polymer obtained by addition polymerization of an oxirane compound such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran to a low molecular weight polyol initiator such as water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, or suocrose may be used as the polyether polyol. Examples of such addition polymers include propylene glycol propylene oxide adducts, glycerol propylene oxide adducts, sorbitol-based propylene oxide adducts, and suocrose-based propylene oxide adducts.

[0047] Examples of polyether polyols with three or more functions include aliphatic polyols such as trimethylolethane, trimethylolpropane, glycerin, hexanetriol, and pentaerythritol; modified polyether polyols obtained by ring-opening polymerization of the aliphatic polyol with various cyclic ether bond-containing compounds such as ethylene oxide, propylene oxide, tetrahydrofuran, ethyl glycidyl ether, propyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether, and allyl glycidyl ether; and lactone-based polyester polyols obtained by polycondensation reactions of the aliphatic polyol with various lactones such as ε-caprolactone.

[0048] From the viewpoint of coating film flexibility and resin compatibility, the number-average molecular weight (Mn) of the polyether polyol (b1-1) is preferably 400 to 2,000. The above polyether polyol (b1-1) may include a bifunctional polyether polyol with an Mn of 400 to 2,000 and / or a trifunctional polyether polyol with an Mn of 400 to 2,000. An Mn of 400 or more is preferable because it increases the flexibility of the polymer chain in the adhesive. An Mn of 2,000 or less is preferable because it improves compatibility with the isocyanate component and facilitates the urethane reaction. Mn is measured by gel permeation chromatography (GPC) and converted to styrene equivalent. In some embodiments, the polyether polyol (b1-1) preferably includes a bifunctional polyether polyol (b1-1A) with a number average molecular weight of 500 or less. The Mn of the above bifunctional polyether polyol (b1-1A) may be 400 to 500. According to the above embodiments, there is a tendency to easily promote the development of adhesive performance.

[0049] The polyol (b1) contains 80% by mass or more of polyether polyol (b1-1) based on the total mass of polyol (b1). The content of polyether polyol (b1-1) is preferably 85% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. Based on the total mass of polyether polyol (b1), the content of bifunctional polyether polyol (b1-1A) with a number average molecular weight of 400 to 500 is preferably 15 to 50% by mass, more preferably 20 to 45% by mass, and even more preferably 25 to 40% by mass. When polyol (b1) contains the above-mentioned bifunctional polyether polyol (b1-1A) within the above range, an improvement in curing speed can be expected after mixing with polyol (A). This makes it easier to promote the development of adhesive properties such as adhesive strength and heat seal strength.

[0050] (Polyester polyol) The polyol (b1) described above may further contain a polyester polyol as needed. The polyester polyol can be any compound having two or more hydroxyl groups and two or more ester bonds in its molecule, and the one described in the section on polyester polyol (a2) above can be used. In particular, it is preferable to include an aliphatic polyester polyol. An aliphatic polyester polyol means that both the carboxyl group component and the hydroxyl group component constituting the polyester polyol are aliphatic compounds. Including such an aliphatic polyester polyol tends to reduce viscosity and easily improve handling properties.

[0051] The above polyester polyol preferably has a number average molecular weight of 500 to 3,000, more preferably 1,000 to 2,000, from the viewpoint of achieving both good initial development of physical properties such as adhesive strength and heat seal strength, and good handling properties. A number average molecular weight of 500 or more is preferable because it improves the cohesive force of the polyester polyol and accelerates the initial development of adhesive strength under low humidity conditions. A number average molecular weight of 3,000 or less is preferable because it slows down the increase in viscosity after mixing with polyol (A) and suppresses the deterioration of coating properties over time.

[0052] The ratio (OH / COOH) of the number of hydroxyl groups in the hydroxyl group component to the number of carboxyl groups in the carboxyl group component used in the synthesis of the above polyester polyol is preferably 1.2 to 2.0, and more preferably 1.2 to 1.5. A ratio of 1.2 or higher is preferable because it improves the cohesive force of the polyester polyol, resulting in a faster rise in adhesive strength even under low humidity conditions. A ratio of 1.5 or lower is preferable because it slows down the increase in viscosity after mixing with polyol (A), suppressing the deterioration of coating properties over time.

[0053] The hydroxyl value of the polyester polyol is preferably 40 to 150 mgKOH / g, and more preferably 60 to 150 mgKOH / g. A value of 40 mgKOH / g or higher is preferable because it reduces the viscosity of the polyester polyol, slows the increase in viscosity after mixing with polyol (A), and suppresses the deterioration of coating properties over time. A value of 150 mgKOH / g or lower is preferable because it improves the cohesive force of polyisocyanate (B) and speeds up the rise of adhesive strength under low humidity conditions. The above-mentioned polyester polyol may be one in which a urethane bond is introduced by reacting a diisocyanate with some of the hydroxyl groups, or it may be one in which a carboxyl group is introduced by reacting an acid anhydride with some of the hydroxyl groups.

[0054] In some embodiments, the content of trifunctional or more polyols in the polyol (b1) may be 35% by mass or less, or 33% by mass or less, based on the total mass of the polyol (b1). In some embodiments, the content may preferably be 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. When the content of trifunctional or more polyols in the polyol (b1) is adjusted to the above range, the number of reaction sites does not become excessive, and it becomes easier to suppress deterioration of the appearance of the laminate. From this viewpoint, the polyol (b1) may consist only of a bifunctional polyol.

[0055] (Polyisocyanate (b2)) The polyisocyanate (b2) used to prepare the urethane bond-containing polyisocyanate may include, for example, one or more selected from the group consisting of aromatic polyisocyanates, aromatic aliphatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and modified versions thereof. The aromatic polyisocyanates, aromatic aliphatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and modified versions thereof are as described above.

[0056] The above polyisocyanate (b2) preferably contains an aromatic polyisocyanate, and more preferably contains diphenylmethane diisocyanate, from the viewpoint of improving the cohesive strength of the adhesive coating film. The diphenylmethane diisocyanate preferably contains 4,4'-diphenylmethane diisocyanate (4,4'-MDI) and 2,4'-diphenylmethane diisocyanate (2,4'-MDI). In some embodiments, the polyisocyanate (b2) preferably contains 4,4'-MDI and 2,4'-MDI in a 50:50 ratio.

[0057] The molar equivalent ratio (moles of NCO groups / moles of OH groups) of the total isocyanate groups of polyisocyanate (b2) to the total hydroxyl groups of polyol (b1) that form the reaction product (urethane prepolymer) of polyol (b1) and polyisocyanate (b2) is preferably 2.5 to 4.5, and more preferably 3.0 to 4.0. A molar equivalent ratio of 2.5 or higher is preferable because it suppresses thickening and improves pot life. A molar equivalent ratio of 4.5 or lower tends to result in a higher molecular weight of the resulting urethane bond-containing polyisocyanate. This is preferable because it promotes the development of adhesive properties such as adhesive strength and heat seal strength.

[0058] The urethane bond concentration of polyisocyanate (B) is preferably 100 to 140 mmol / g, more preferably 110 to 135, and even more preferably 120 to 130. The above urethane bond concentration refers to the value calculated according to the following formula (2). Formula (2): Urethane bond concentration (mmol / g) = [(OH content of polyol component (mass%) ÷ 100) × (ratio of polyol component (mass%) to the total (mass%) of polyol component and polyisocyanate component constituting the urethane prepolymer) ÷ 17 × 1000]

[0059] In some embodiments, the urethane bond-containing polyisocyanate (B1) configured as described above preferably has a number-average molecular weight of 700 to 2000. More preferably, the number-average molecular weight may be 800 to 1600, and even more preferably 900 to 1200. Having a number-average molecular weight of 700 or more tends to facilitate obtaining a long pot life. Having a number-average molecular weight of 2000 or less tends to result in low viscosity, making it easier to obtain a good VM appearance. In this disclosure, the number-average molecular weight was determined by gel permeation chromatography (GPC). The number-average molecular weight of the above-mentioned urethane-bonded polyisocyanate can be adjusted by methods known to those skilled in the art. For example, by blending polyol (b1) and polyisocyanate (b2) so that the ratio of NCO moles to OH moles is as described above, a urethane-bonded polyisocyanate having a desired molecular weight can be easily obtained.

[0060] (Isocyanate monomer (B2)) In the solvent-free adhesive of this embodiment, the polyisocyanate (B) includes, in addition to the urethane bond-containing polyisocyanate (B1), an isocyanate monomer (B2) containing 2,4'-diphenylmethane diisocyanate. Based on the total mass of polyisocyanate (B), the content of urethane bond-containing polyisocyanate (B1) may be preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and even more preferably 50 to 60% by mass. Based on the total mass of polyisocyanate (B), the content of 2,4'-diphenylmethane diisocyanate may be preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and even more preferably 15 to 20% by mass. When polyisocyanate (B) contains 2,4'-diphenylmethane diisocyanate within the above range, it tends to be easier to improve the desired adhesive strength, heat seal strength, and VM appearance.

[0061] In the reaction between polyol (b1) and polyisocyanate (b2) to produce the urethane bond-containing polyisocyanate (B1) described above, the amount of polyisocyanate (b2) used is adjusted so that the number of moles of NCO groups is in excess of the number of moles of OH groups. Therefore, the reaction mixture obtained after the reaction may contain unreacted polyisocyanate in addition to the product, the urethane bond-containing polyisocyanate (B1). As the polyisocyanate (b2), the compounds exemplified above can be used, and among them, diphenylmethane diisocyanate can be preferably used. If an excess amount of diphenylmethane diisocyanate is used during the above reaction, the reaction mixture obtained after the reaction (unpurified reaction product) will contain unreacted diphenylmethane diisocyanate in addition to the urethane bond-containing polyisocyanate (B1). Since diphenylmethane diisocyanate typically contains 4,4'-, 2,4'-, and 2,2'- positional isomers, the remaining diphenylmethane diisocyanate may contain 2,4'-diphenylmethane diisocyanate (MDI).

[0062] Therefore, in some embodiments, the reaction mixture obtained by the reaction of polyol (b1) and polyisocyanate (b2) can be used as polyisocyanate (B) without purification. If necessary, an isocyanate monomer containing 2,4'-MDI may be added to the reaction mixture. In other embodiments, the urethane bond-containing polyisocyanate (B1) obtained by purifying the above reaction mixture may be mixed with the isocyanate monomer (B2) containing 2,4'-MDI and used. As the isocyanate monomer (B2), the compounds described later can be used, but from the viewpoint of reactivity, it is preferable to use diphenylmethane diisocyanate containing 2,4'-MDI and 4,4'-MDI.

[0063] 4,4'-MDI is highly reactive, being approximately 10 times more reactive than 2,4'-MDI. Therefore, when 4,4'-MDI and 2,4'-MDI coexist in a reaction system, 4,4'-MDI will react and be consumed preferentially. For this reason, in some embodiments, the content of 2,4'-MDI can be easily adjusted by using an excess amount of MDI-50 as the polyisocyanate (b2) relative to the polyol (b1). MDI-50 is known as diphenylmethane diisocyanate containing 4,4'-MDI and 2,4'-MDI in a 50:50 mass ratio.

[0064] In polyisocyanate (B), the content of isocyanate monomer (B2) containing 2,4'-MDI is preferably 20 to 70% by mass, more preferably 25 to 55% by mass, and even more preferably 30 to 40% by mass, based on the total mass of polyisocyanate (B). Here, from the viewpoint of reactivity, the molecular weight of the isocyanate monomer is preferably 800 to 2000, more preferably 900 to 1600, and even more preferably 1000 to 1200. Various compounds described later can be used as the above isocyanate monomer, but diisocyanate monomers are preferred, and aromatic diisocyanates are particularly preferred. Diphenylmethane diisocyanate containing 2,4'-MDI and its positional isomer 4,4'-MDI can be suitably used.

[0065] In some embodiments, the polyisocyanate (B) may be a reaction mixture obtained using a polyol (b1) and a diphenylmethane diisocyanate containing 2,4'-MDI and 4,4'-MDI as the polyisocyanate (b2). The reaction mixture contains a urethane bond-containing polyisocyanate (reaction product) and unreacted 2,4'-MDI and 4,4'-MDI as isocyanate monomers. Here, the content of 2,4'-MDI is preferably 10 to 60% by mass, more preferably 20 to 50% by mass, and even more preferably 30 to 40% by mass, based on the total mass of the isocyanate monomers. When the content of 2,4'-MDI in the isocyanate monomers is adjusted to the above range, it becomes easier to improve the balance between the development of adhesive strength and appearance defects.

[0066] In some embodiments, polyisocyanate (B) comprises the urethane bond-containing polyisocyanate (B1) and 2,4'-MDI and 4,4'-MDI, and may further comprise other polyisocyanates (also called other polyisocyanates). The other polyisocyanates may be polyisocyanates known in the art, and may be at least one selected from the group consisting of aromatic polyisocyanates (excluding MDI and poly-MDI described later), aromatic aliphatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and modified versions thereof.

[0067] Examples of aromatic polyisocyanates include aromatic diisocyanates such as carbodiimide-modified diphenylmethane diisocyanate, phenylenediisocyanate, tolylene diisocyanate, and naphthalene diisocyanate; and aromatic polyisocyanates such as polymethylene polyphenyl polyisocyanate.

[0068] Examples of aromatic aliphatic polyisocyanates include 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanate-1-methylethyl)benzene or mixtures thereof, and other aromatic aliphatic diisocyanates.

[0069] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate methyl caproate, lysine diisocyanate, and dimer acid diisocyanate.

[0070] Examples of alicyclic polyisocyanates include alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methyl 2,4-cyclohexane diisocyanate, methyl 2,6-cyclohexane diisocyanate, 1,4-bis(isocyanate methyl)cyclohexane, 1,3-bis(isocyanate methyl)cyclohexane, and norbornene diisocyanate.

[0071] Examples of modified polyisocyanates include allophanate-type modified polyisocyanates, isocyanurate-type modified polyisocyanates, biuret-type modified polyisocyanates, and adduct-type modified polyisocyanates. Alternatively, a polyisocyanate having a urethane bond, which is a reaction product of polyisocyanate and polyol, may be used as a modified polyisocyanate. The polyols that form the modified polyisocyanates mentioned above are not particularly limited, and examples include polyester polyols, polyether polyols, polycarbonate polyols, polycaprolactone polyols, polyolefin polyols, acrylic polyols, silicone polyols, castor oil-based polyols, and fluorine-based polyols.

[0072] The polyisocyanate (B) preferably contains the urethane bond-containing polyisocyanate (B1) and MDI containing 2,4'-MDI and 4,4'-MDI. In some embodiments, the polyisocyanate (B) preferably further contains polymeric MDI. Polymeric MDI (also called crude MDI) is a mixture of monomeric MDI with various isomer content and polynuclear bodies of several structures. That is, polymeric MDI contains an MDI monomer containing at least one selected from the group consisting of 4,4'-MDI, 2,4'-MDI, and 2,2'-MDI, and a polymethylene polyphenylene isocyanate. Polymeric MDI can be obtained commercially. Examples include Wannate PM-200 from Yantai Wanhua and Luplanate from BASF. In some embodiments, the polymeric MDI content may be preferably 1 to 15% by mass, more preferably 3 to 10% by mass, and even more preferably 5 to 7.5% by mass, based on the total mass of polyisocyanate (B).

[0073] In some embodiments, the isocyanate group content in the polyisocyanate (B) may be 8.0% by mass or more, or 8.5% by mass or more. Alternatively, the isocyanate group content may be 20.0% by mass or less, or 19.5% by mass or less. In some embodiments, the isocyanate group content may preferably be in the range of 8.0% by mass to 16.0% by mass, and more preferably in the range of 9.0% by mass to 14.5% by mass. The above isocyanate group content is a value calculated by the method described in the examples below. When the isocyanate group content is within the above range, the crosslinking density is optimized and the adhesive strength is improved, which is preferable.

[0074] In the solvent-free adhesive of this embodiment, the ratio of polyol (A) to polyisocyanate (B) may be 100 / 60 to 100 / 300, preferably 100 / 80 to 100 / 260, more preferably 100 / 90 to 100 / 200, and even more preferably 100 / 100 to 100 / 150. While not particularly limited, in the solvent-free adhesive of this embodiment, the polyol (A) is preferably one of the polyols A301 to A312 described in the examples below. Furthermore, the polyisocyanate (B) is preferably one of the polyisocyanates B101 to B111 described in the examples below. In some embodiments, when polyol A304 and polyisocyanate B104 are combined, excellent results in adhesive strength, heat sealability, and VM appearance can be easily obtained.

[0075] As described above, in the solvent-free adhesive of this embodiment, the combination of a specific polyol (A) and a specific polyisocyanate (B) allows for a rapid rise in physical properties such as cohesive force, adhesive strength, and heat seal strength. Here, "rapid rise in physical properties" means obtaining the desired level of physical properties. In one embodiment, such a rise can be evaluated from the relationship between the storage modulus and loss modulus of the solvent-free adhesive after mixing the polyol (A) and polyisocyanate (B).

[0076] Specifically, it is preferable that the solvent-free adhesive obtained after mixing polyol (A) and polyisocyanate (B) satisfies the following formula (I) within 24 hours. Equation (I): [log(storage modulus) / log(loss modulus)] ≥ 0.9

[0077] In equation (I) above, the storage modulus (Pa) and the loss modulus (Pa) are values ​​measured using a viscoelasticity measuring device under the following conditions: frequency: 5 Hz, stress: 10 Pa, measuring probe: parallel plate (diameter 25 mm), and temperature: 40°C. More specifically, first, a solvent-free adhesive (sample) is prepared by mixing polyol (A) and polyisocyanate (B). Immediately after preparing the sample, it is placed between the parallel plates (25 mm in diameter) of a viscoelasticity measuring device (rheometer). Next, viscoelasticity measurements are performed at a temperature of 40°C, a constant frequency (5 Hz), and a stress (10 Pa) to obtain the values ​​of the storage modulus and loss modulus. The above viscoelasticity measurements are continued, and the time from the start of the measurement until the values ​​of the storage modulus and loss modulus satisfy equation (I) is determined.

[0078] The time required to satisfy the following formula (I) is sufficient if it is 24 hours or less, but more preferably 21 hours or less, and even more preferably 19 hours or less. The shorter the above time, the faster the adhesive performance is achieved. In some embodiments, from the viewpoint of handling, the above time may be preferably 12 hours or more, more preferably 16 hours or more, and even more preferably 18 hours or more.

[0079] <Other ingredients> The solvent-free adhesive of this embodiment may contain components other than polyol (A) and polyisocyanate (B) to satisfy various performance requirements. Such other components may be blended with either polyol (A) or polyisocyanate (B), or they may be blended when mixing polyol (A) and polyisocyanate (B). The other components may be used individually or in combination of two or more.

[0080] (Silane coupling agent) In some embodiments, solvent-free adhesives may contain a silane coupling agent from the viewpoint of improving the adhesive strength to metallic materials such as metal foils and metal vapor-deposited layers. Examples of silane coupling agents include trialksylanes having vinyl groups, such as vinyltriethoxysilane; trialksylanes having amino groups, such as 3-aminopropyltriethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; and trialksylanes having glycidyl groups, such as 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane. The silane coupling agent content is preferably 0.1 to 5% by mass, and more preferably 0.2 to 3% by mass, based on the total mass of the total polyol (A). This range is preferable because it can improve the adhesive strength to the metal foil.

[0081] (Phosphoric acid or phosphoric acid derivatives) In some embodiments, solvent-free adhesives may contain phosphoric acid or a phosphoric acid derivative from the viewpoint of improving the adhesive strength to metallic materials such as metal foils and metal vapor-deposited layers. The phosphoric acid mentioned above can be any phosphoric acid having at least one free oxygen acid, and examples include phosphoric acids such as hypophosphorous acid, phosphorous acid, orthophosphoric acid, and subphosphoric acid; and condensed phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, and ultraphosphoric acid. Furthermore, examples of phosphoric acid derivatives include those obtained by partially esterifying the above-mentioned phosphoric acid with alcohols while retaining at least one free oxygen acid. Examples of such alcohols include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin; and aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglycinol. The content of phosphoric acid or its derivative is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and particularly preferably 0.05 to 1% by mass, based on the mass of the solvent-free adhesive.

[0082] (Leveling agent or defoaming agent) In some embodiments, solvent-free adhesives may contain leveling agents and / or defoaming agents to improve the appearance of the laminate. Examples of leveling agents include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl-containing polydimethylsiloxane, polyether ester-modified hydroxyl-containing polydimethylsiloxane, acrylic copolymers, methacrylic copolymers, polyether-modified polymethylalkylsiloxane, alkyl acrylate copolymers, alkyl methacrylate copolymers, and lecithin. Examples of antifoaming agents include silicone resins, silicone solutions, and copolymers of alkyl vinyl ethers, alkyl acrylates, and alkyl methacrylates.

[0083] (Reaction accelerator) The solvent-free adhesive of this embodiment may contain a reaction accelerator to accelerate the curing reaction. Examples of reaction accelerators include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimalate; tertiary amines such as 1,8-diazabicyclo(5,4,0)undecene-7, 1,5-diazabicyclo(4,3,0)nonene-5, and 6-dibutylamino-1,8-diazabicyclo(5,4,0)undecene-7; and reactive tertiary amines such as triethanolamine.

[0084] (Additives) The solvent-free adhesive of this embodiment may contain various additives, provided that the effects of this embodiment are not impaired. Examples of additives include inorganic fillers such as alumina, mica, talc, aluminum flakes, and glass flakes; layered inorganic compounds; stabilizers (antioxidants, heat stabilizers, UV absorbers, hydrolysis inhibitors, etc.); rust inhibitors; thickeners; plasticizers; antistatic agents; lubricants; antiblocking agents; colorants; fillers; nucleating agents; and catalysts for adjusting the curing reaction.

[0085] <2> Laminate A laminate can be constructed by bonding two or more substrates together using the solvent-free adhesive of this embodiment. Since the solvent-free adhesive of this embodiment forms a cured product when cured under conditions of, for example, 20 to 60°C, it can be used as a material for forming an adhesive layer between substrates. Therefore, one embodiment of the present invention relates to a laminate having a first substrate and a second substrate, with an adhesive layer made of the solvent-free adhesive of this embodiment. The laminate can be manufactured, for example, by applying the solvent-free adhesive to a first sheet-like substrate, then laminating a second sheet-like substrate onto the applied surface, and curing the adhesive layer located between the first and second sheet-like substrates. The amount of solvent-free adhesive applied is preferably 1.0 to 5.0 g / m². 2 More preferably 1.5 to 4.5 g / m 2 The thickness of the laminate may be 10 μm or more, preferably.

[0086] (base material) The substrate constituting the laminate is not particularly limited as long as it is a sheet-shaped substrate (hereinafter referred to as a sheet-like substrate). Examples of sheet-like substrates include conventionally known plastic films, paper, and metal foils, and one of these can be used alone or in combination of two or more. In some embodiments, the first and second substrates in the laminate may each be a sheet-like substrate formed independently using at least one selected from the group consisting of plastics, metals, and non-metallic inorganic materials. In some embodiments, the sheet-like substrate may be a plastic film, a metal foil, or a vapor-deposited film in which a metal vapor-deposited layer or a transparent vapor-deposited layer (an inorganic vapor-deposited layer using non-metallic inorganic materials) is provided on a plastic film. The at least two sheet-like substrates constituting the laminate may be of the same type or different types.

[0087] The above-mentioned plastic film can be a film made of thermoplastic resin or thermosetting resin, and is preferably a film made of thermoplastic resin. Examples of thermoplastic resins include polyolefin, polyester, polyamide, polystyrene, vinyl chloride resin, vinyl acetate resin, ABS resin, acrylic resin, acetal resin, polycarbonate resin, and cellulose-based plastics. The metal constituting the above metal foil may be aluminum (AL), copper, or the like. The metal constituting the metal vapor deposition layer of the above-mentioned metal vapor deposition film may be aluminum (AL) or the like. The inorganic material constituting the inorganic vapor deposition layer of the above-mentioned transparent vapor deposition film may be an inorganic oxide such as silica or alumina.

[0088] The first sheet-like substrate constituting the laminate of this embodiment is preferably a plastic film. Examples of plastic films include those commonly used in packaging materials, such as polyester resin films like polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polylactic acid (PLA); polyolefin resin films like polyethylene (PE) and polypropylene (PP); polystyrene resin films; polyamide resin films like nylon (NY) 6 and poly-p-xylylene adipamide (MXD6 nylon); polycarbonate resin films; polyacrylonitrile resin films; polyimide resin films; and composites of these (e.g., nylon 6 / MXD6 / nylon 6, nylon 6 / ethylene-vinyl alcohol copolymer / nylon 6) or mixtures thereof. Among these, those having mechanical strength and dimensional stability are preferred. In some embodiments, PET, NY, and PP can be suitably used, and PP may be either biaxially oriented polypropylene (OPP) or unoriented polypropylene (CPP). The plastic film preferably has a thickness of 5 to 50 μm, more preferably 10 to 30 μm.

[0089] In some embodiments, the second sheet-like substrate constituting the laminate is preferably a sealant substrate when the second sheet-like substrate becomes the outermost layer of the laminate. Examples of sealant substrates include polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), acid-modified polyethylene, polypropylene (PP), acid-modified polypropylene, copolymerized polypropylene, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-(meth)acrylic acid copolymer, and ionomers. The polypropylene (PP) may be either biaxially oriented polypropylene (OPP) or unoriented polypropylene (CPP). The thickness of the sealant substrate is not particularly limited, but considering processability and heat-sealability for packaging materials, it is preferably 10 to 150 μm, and more preferably 20 to 70 μm. Furthermore, by providing the sealant substrate with bumps and dips with height differences of several μm, properties such as slipperiness and tearability of the packaging material can be imparted.

[0090] Furthermore, in some embodiments, when the second sheet-like substrate is the outermost layer of the laminate, it is preferable that the second sheet-like substrate functions as a barrier layer. A vapor-deposited film can be used to constitute the barrier layer. The vapor-deposited film may be a metal vapor-deposited film or a transparent vapor-deposited film, but a metal vapor-deposited film such as an aluminum vapor-deposited film can be suitably used.

[0091] When the second sheet-like substrate becomes an intermediate layer of the laminate, the second sheet-like substrate can preferably be the aforementioned plastic film, vapor-deposited film, paper, metal foil, etc.

[0092] (Ink layer) The sheet-like substrate may have an ink layer (printed layer) on the substrate, and the ink layer may be in contact with an adhesive layer. The ink layer is a layer that forms any desired printed pattern such as letters, numbers, pictures, figures, symbols, or designs for decoration, indication of contents, indication of expiration date, indication of manufacturer, seller, etc., and to add aesthetic appeal, and may be a solid print layer that is printed across the entire surface. Generally, the ink layer is formed using printing ink containing colorants such as pigments and dyes. Examples of printing inks include oil-based inks, water-based inks, and UV inks. Examples of printing methods include gravure coating, flexo coating, roll coating, bar coating, die coating, curtain coating, spin coating, and inkjet printing. In the printing process, blowing air, heating, vacuum drying, and UV irradiation may be performed as needed. The ink layer preferably has a thickness of 0.1 to 10 μm, more preferably 1 to 5 μm, and even more preferably 1 to 3 μm.

[0093] In the case where the laminate of this embodiment has an ink layer in contact with the adhesive layer, the ink forming the ink layer is not particularly limited. However, even when the ink layer of the laminate of this embodiment is formed using water-based ink, the physical properties such as adhesive strength and heat seal strength can be rapidly developed even in severe low-temperature and low-humidity environments. Generally, water-based ink layers tend to retain more hydroxyl groups than oil-based ink layers. Therefore, when an adhesive is applied to a water-based ink layer, the residual hydroxyl groups consume the isocyanates in the adhesive, inhibiting the urethane reaction that increases the molecular weight of the adhesive. This reduces the cohesive force of the adhesive layer, leading to a slower onset of physical properties such as adhesive strength and heat seal strength. However, by having the adhesive layer using the solvent-free adhesive of this embodiment adjacent to the water-based ink layer, the cohesive force of the adhesive layer can be maintained, and the rise of physical properties such as adhesive strength and heat seal strength can be accelerated even in harsh low-humidity environments.

[0094] As the resin contained in the water-based ink layer, for example, at least one selected from the group consisting of natural resins or synthetic resins of the dissolving type, hydrosol type, or emulsion type, and modified resins thereof, can be used. Examples of the above resins include polyarylamide resins, poly(meth)acrylic acid resins, polyvinyl chloride resins, polyvinyl acetate resins, polyethylene oxide resins, poly-N-vinylpyrrolidone resins, polyurethane resins (two-component curing polyurethane resins), polyurethane urea resins (two-component curing polyurethane urea resins), polyester resins, polyamide resins, amino resins, phenolic resins, synthetic rubber and other synthetic resins; and natural polymers such as polynucleotides, polypeptides, polysaccharides, and natural rubber. One type may be used alone, or two or more types may be used in combination.

[0095] As the poly(meth)acrylic acid resin mentioned above, for example, a copolymer of at least one of the following can be used: (meth)acrylic monomers such as acrylic acid esters, methacrylic acid esters, hydroxylethyl acrylate, and hydroxylethyl methacrylate; nitrile monomers such as acrylonitrile and methacrylicnitrile; amide monomers such as acrylamide and methacrylamide; N-alkoxy-substituted and N-methylol-substituted derivatives of the amide monomers; styrene monomers such as styrene, vinyltoluene, α-methylstyrene, and divinylbenzene; allyl monomers such as diallyl phthalate, allyl glycidyl ether, and triallyl isocyanurate; and monomers having polymerizable double bonds such as vinyl acetate and N-vinylpyrrolidone; and a carboxyl group-containing compound or acid anhydride such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, and itaconic acid.

[0096] Examples of the configuration of the laminate according to this embodiment are given below, but are not limited to these. If the laminate comprises multiple adhesive layers, at least one of the multiple adhesive layers may be an adhesive layer formed from the solvent-free adhesive according to this embodiment. In the following description, OPP represents biaxially oriented polypropylene, CPP represents unoriented polypropylene, and PE represents polyethylene such as LDPE, LLDPE, and HDPE. The ink layer refers to the printing layer formed from a dried or cured film of ink. Transparent vapor deposition refers to a vapor-deposited layer of silica or alumina. • OPP / Ink layer / Adhesive layer / CPP • Ink layer / OPP / Adhesive layer / CPP • OPP / Ink layer / Adhesive layer / AL vapor-deposited CPP • Ink layer / OPP / Adhesive layer / AL vapor-deposited CPP • OPP / Ink layer / Adhesive layer / AL vapor-deposited PET • Ink layer / OPP / Adhesive layer / AL vapor-deposited PET • OPP / Ink layer / Adhesive layer / PE • Ink layer / OPP / Adhesive layer / PE • PET / Ink layer / Adhesive layer / CPP • Ink layer / PET / Adhesive layer / CPP • PET / Ink layer / Adhesive layer / AL vapor deposition CPP • Ink layer / PET / Adhesive layer / AL vapor-deposited CPP • PET / Ink layer / Adhesive layer / AL vapor-deposited PET • Ink layer / PET / Adhesive layer / AL-coated PET ·PET / Ink layer / Adhesive layer / PE • Ink layer / PET / Adhesive layer / PE • NY / Ink layer / Adhesive layer / CPP • Ink layer / NY / Adhesive layer / CPP • NY / Ink layer / Adhesive layer / AL vapor deposition CPP • Ink layer / NY / Adhesive layer / AL vapor deposition CPP • NY / Ink layer / Adhesive layer / AL vapor-deposited PET • Ink layer / NY / Adhesive layer / AL vapor-deposited PET • NY / Ink layer / Adhesive layer / PE • Ink layer / NY / Adhesive layer / PE ·PET / Ink layer / Adhesive layer / NY / Adhesive layer / CPP ·PET / Ink layer / Adhesive layer / NY / Adhesive layer / PE • Transparent vapor-deposited PET / Ink layer / Adhesive layer / NY / Adhesive layer / CPP • Transparent vapor-deposited PET / Ink layer / Adhesive layer / NY / Adhesive layer / PE • PET / Ink layer / Adhesive layer / AL vapor-deposited PET / Adhesive layer / CPP • PET / Ink layer / Adhesive layer / AL vapor-deposited PET / Adhesive layer / PE • NY / Ink layer / Adhesive layer / AL vapor-deposited PET / Adhesive layer / CPP • NY / Ink layer / Adhesive layer / AL vapor-deposited PET / Adhesive layer / PE PET / Ink layer / Adhesive layer / AL vapor-deposited PET / Adhesive layer / NY / Adhesive layer / CPP • PET / Ink layer / Adhesive layer / AL vapor-deposited PET / Adhesive layer / NY / Adhesive layer / PE PET / Ink layer / Adhesive layer / AL / Adhesive layer / CPP PET / Ink layer / Adhesive layer / AL / Adhesive layer / PE PET / Ink layer / Adhesive layer / NY / Adhesive layer / AL / Adhesive layer / CPP PET / Ink layer / Adhesive layer / NY / Adhesive layer / AL / Adhesive layer / PE PET / Ink layer / Adhesive layer / AL / Adhesive layer / NY / Adhesive layer / CPP PET / Ink layer / Adhesive layer / AL / Adhesive layer / NY / Adhesive layer / PE

[0097] The laminate of this embodiment can be suitably used as a packaging material. For example, a packaging bag can be made using the above laminate. Examples of packaging bag forms include two-sided bags, three-sided bags, three-sided bags with zippers, gusseted bags, bottom gusseted bags, stand-up pouches, stand-up zippered bags, two-sided bags, four-sided flat-bottom gusseted bags, side-sealed bags, and bottom-sealed bags.

[0098] In the laminate of this embodiment, the solvent-free adhesive constituting the laminate exhibits rapid development of adhesive performance (reduction in tack) even under low temperature and low humidity conditions. Therefore, subsequent processes such as slitting can be carried out quickly following the manufacturing process of the laminate, easily improving productivity. In some embodiments, the laminate of this embodiment is particularly suitable for use in packaging bags that require molding or heat sealing, among those exemplified above. Furthermore, the laminate constructed using the solvent-free adhesive of this embodiment is also suitable for use in packaging bags distributed in winter or in low temperature and low humidity environments.

[0099] The following are examples of embodiments of the present invention. However, the present invention is not limited to the embodiments described below, but includes various embodiments. <1> A solvent-free adhesive comprising a polyol (A) and a polyisocyanate (B), characterized by satisfying all of the following conditions (1) to (3). (1) The polyol (A) comprises a polyol (a1) with a molecular weight of 200 or less and three or more functionalities. (2) The polyisocyanate (B) comprises a reaction product (B1) of a polyol (b1) and an isocyanate compound (b2), and 2,4'-diphenylmethane diisocyanate, wherein the polyol (b1) contains 80% by mass or more of polyether polyol (b1-1) based on the total mass of the polyol (b1). (3) The polyether polyol (b1-1) contains a bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less, and the content of the bifunctional polyether polyol (b1-1A) having a number average molecular weight of 500 or less is 15 to 50% by mass based on the total mass of the polyol (b1). <2> The storage modulus and loss modulus of the solvent-free adhesive obtained by mixing the polyol (A) and the polyisocyanate (B) satisfy the following formula (I) within 24 hours, <1> Solvent-free adhesive as described above. Equation (I): [log(storage modulus) / log(loss modulus)] ≥ 0.9 [In equation (I) above, the storage modulus (Pa) and loss modulus (Pa) are values ​​measured using a rheometer under the following conditions: frequency: 5 Hz, stress: 10 Pa, measuring probe: parallel plate (diameter 25 mm), and temperature: 40°C.] <3> The polyol (A) contains 5 to 40% by mass of a bifunctional polyether polyol (a2-1) with a number average molecular weight of 500 or less, based on the total mass of polyol (A). <1> or <2> Solvent-free adhesive as described above. <4> The content of the aforementioned bifunctional polyether polyol (b1-1A) with a number average molecular weight of 500 or less is 20 to 40% by mass, based on the total mass of polyol (b1). <1> ~ <3> A solvent-free adhesive as described in any one of the following. <5> The polyol (A) contains 0.5 to 10% by mass of a trifunctional or more polyol (a1) with a molecular weight of 200 or less, based on the total mass of polyol (A), <1> ~ <4> A solvent-free adhesive as described in any one of the following. <6> Based on the total mass of the polyol (b1), the content of trifunctional or more polyols in the polyol (b1) is 25% by mass or less. <1> ~ <5> A solvent-free adhesive as described in any one of the following. <7> The polyisocyanate (B) has a urethane bond concentration of 100 to 140 mmol / g, as described above. <1> ~ <6> A solvent-free adhesive as described in any one of the following. <8> The polyol (A) contains 30 to 90% by mass of polyester polyol (a3) ​​based on the total mass of polyol (A), <1> ~ <7> A solvent-free adhesive as described in any one of the following. <9> The polyisocyanate (B) further contains 1 to 15% by mass of polymeric MDI based on the total mass of the polyisocyanate (B), <1> ~ <8> A solvent-free adhesive as described in any one of the following. <10> the above <1> ~ <9> A laminate comprising at least a first substrate and a second substrate via an adhesive layer formed using a solvent-free adhesive described in any one of the above. <11> The first substrate and the second substrate are each independently formed sheet-like substrates using at least one selected from the group consisting of plastics, metals, and non-metallic inorganic materials. <10> The laminate described above. [Examples]

[0100] The present invention will be described in more detail below with reference to examples. Unless otherwise specified, all "%" and "parts" in the examples and comparative examples are based on mass. The various measurement methods in the following examples are as follows:

[0101] <Number average molecular weight (Mn)> The number-average molecular weight (Mn) of polyether polyols, polyester diols, etc., was determined by gel permeation chromatography (GPC). Molecular weight measurements were performed under the following conditions. (Measurement conditions) Model: TOSOHHLC-8420GPC Column: TSKGELSuperHM-L Solvent: THF Solution outflow rate: 0.6 ml per minute Temperature: 40 °C Detector: Differential refractometer Molecular weight standard: Polystyrene

[0102] <Acid value, hydroxyl value> The acid value and hydroxyl value are expressed in mg of KOH per 1 g of sample. The acid values and hydroxyl values described in the synthesis of various polyols described below are the values obtained according to the following method. The acid value was measured by neutral titration with KOH. The hydroxyl value was measured by acetylation using pyridine and acetic anhydride. Specifically, it is as follows. (Measurement method of hydroxyl value (OHV)) Approximately 1 g of the sample was precisely weighed into a conical flask with a stopper, and 100 mL of a toluene / ethanol (volume ratio: toluene / ethanol = 2 / 1) mixed solution was added and dissolved. Further, 5 mL of an acetylating agent (a solution prepared by dissolving 25 g of acetic anhydride in pyridine to make a volume of 100 mL) was accurately added, and the mixture was stirred for about 1 hour. To this, a phenolphthalein test solution was added as an indicator and held for 30 seconds. Then, it was titrated with a 0.1 N alcoholic potassium hydroxide solution until the solution showed a light pink color. The hydroxyl value was determined by the following formula (3). The hydroxyl value was taken as the value in the dry state of the resin. Formula (3): Hydroxyl value (mgKOH / g) = [{(b - a) × F × 28.25} / S] / (non-volatile content concentration / 100) + D S: Sampling amount of the sample (g) a: Consumption volume of 0.1 N alcoholic potassium hydroxide solution (mL) b: Consumption volume of 0.1 N alcoholic potassium hydroxide solution in the blank experiment (mL) F: Valence of 0.1 N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

[0103] <NCO group content rate (mass%)> The isocyanate (NCO) group content is the amount of isocyanate groups present in the sample (polyisocyanate (B)) expressed as a mass fraction. The NCO group content of polyisocyanates B101 to B115 obtained in synthesis examples B101 to B115 described later was obtained according to the following method. First, each sample was reacted with an excess of dibutylamine in a toluene solution to produce the corresponding urea. Next, back titration was performed using a hydrochloric acid standard solution by indicator titration, and the NCO group content was determined from the measured value. in particular, First, approximately 1 g of the sample was weighed into a 200 mL Erlenmeyer flask, and dissolved in 10 mL of 0.5 N di-n-butylamine toluene solution and 10 mL of toluene. Next, phenolphthalein reagent was added as an indicator, held for 30 seconds, and then titrated with 0.25 N hydrochloric acid solution until the solution turned pale pink. The NCO group content (mass%) was calculated using the following formula (4). Formula (4): NCO (mass%)={(ba)×4.202×F×0.25} / S S: Sample volume (g) a: Amount of 0.25N hydrochloric acid solution consumed (ml) b: Amount of 0.25N hydrochloric acid solution consumed in the blank experiment (ml) F: Titer of 0.25N hydrochloric acid solution

[0104] <Urethane binding concentration> The urethane bond concentration (mmol / g) of polyisocyanate (B) was calculated using the following formula (5). The above urethane bond concentration (mmol / g) is essentially equivalent to the urethane bond concentration (mmol / g) of the urethane prepolymer contained in polyisocyanate (B). Formula (5): Urethane bond concentration (mmol / g) = [(OH content of polyol component (mass%) ÷ 100) × (ratio of polyol component (mass%) to the total (mass%) of polyol component and polyisocyanate component constituting the urethane prepolymer) ÷ 17 × 1000] Here, the "OH content (mass%) of the polyol component" was calculated using the following formula (6). Formula (6): OH content of polyol component (mass%) = Number of functional groups ÷ Molecular weight × 17 ÷ 100

[0105] <1> Preparation of raw materials <Synthesis of various polyols> (Synthesis Example A101) 55.5 parts adipic acid and 44.5 parts 2-methyl-1,3-propanediol were charged into a reaction vessel and heated to 150°C to 240°C while stirring under a nitrogen gas stream to carry out the esterification reaction. When the acid value reached 1.3 (mgKOH / g), the reaction temperature was raised to 200°C, and the pressure inside the reaction vessel was gradually reduced to 1.3 kPa or less for 30 minutes to obtain aliphatic polyester polyol A101 with an acid value of 0.4 (mgKOH / g), a hydroxyl value of 56 (mgKOH / g), and a number average molecular weight of 2,000, having hydroxyl groups at both ends.

[0106] (Synthesis Example A102) Aliphatic polyester polyol A102 was obtained in the same manner as in synthesis example A101, according to the composition shown in Table 1.

[0107] [Table 1]

[0108] (Synthesis Example A201) As shown in Table 2, 30.1 parts of polypropylene glycol with a number average molecular weight of approximately 400 (hereinafter referred to as "PPG-400"), 49.8 parts of polypropylene glycol with a number average molecular weight of approximately 2,000 (hereinafter referred to as "PPG-2000"), 10.0 parts of a triol with a number average molecular weight of approximately 400 obtained by adding polypropylene glycol to glycerin (hereinafter referred to as "PPG-400 trifunctional"), and 10.0 parts of 4,4'-diphenylmethane diisocyanate were charged into a reaction vessel and heated at 90°C to 100°C for 2 hours while stirring under a nitrogen gas stream to carry out the urethane reaction, yielding polyether polyurethane polyol A201 having hydroxyl groups at both ends and a number average molecular weight of 800.

[0109] [Table 2]

[0110] <Preparation of polyol (A)> (Synthesis example A301) 96 parts of A101 and 4 parts of trimethylolpropane (hereinafter referred to as "TMP") were placed in a reaction vessel and heated at 65°C to 75°C for 30 minutes while stirring under a nitrogen gas stream to completely dissolve the TMP and obtain polyol A301.

[0111] (Synthesis examples A302~A313) Polyols A302 to A313 were obtained in the same manner as in synthesis example A301, according to the compositions shown in Table 3.

[0112] [Table 3]

[0113] The details of the raw materials listed in Table 3 are as follows: PPG-400 Trifunctional: Manufactured by ADEKA Corporation, trifunctional polypropylene glycol, molecular weight 400 TMP: Trimethylolpropane, manufactured by Tokyo Chemical Industry Co., Ltd., 3 functional groups, molecular weight 134 PPG-400 bifunctional: Manufactured by ADEKA Corporation, bifunctional polypropylene glycol, molecular weight 400

[0114] <Production of polyisocyanate (B)> (Synthesis Example B101) 9.3 parts of PPG-400, 45.9 parts of PPG-2000, 22.4 parts of 4,4'-MDI, and 22.4 parts of a 50:50 mixture of 4,4'-MDI and 2,4'-MDI (hereinafter referred to as "MDI-50") were charged into a reaction vessel and heated at 90°C to 100°C for 3 hours while stirring under a nitrogen gas stream to carry out the urethane reaction and obtain polyisocyanate B101. Polyisocyanate B101 contained polyether polyurethane polyisocyanate (a prepolymer formed by the above reaction), and the isocyanate group content was 10.9%.

[0115] (Synthesis examples B102~B108) According to the compositions shown in Table 4, polyisocyanates B102 to B108 containing polyether polyurethane polyisocyanate were obtained in the same manner as in synthesis example B101.

[0116] (Synthesis Example B109) 12.7 parts of PPG-400, 7.4 parts of PPG-2000, 4.5 parts of PPG-400 (trifunctional), and 2 parts of TMP were each charged into a reaction vessel and heated at 65°C to 75°C for 30 minutes with stirring under a nitrogen gas stream to completely dissolve the TMP. Then, 36.7 parts of 4,4'-MDI and 36.7 parts of MDI-50 were each charged into the reaction vessel and heated at 90°C to 100°C for 3 hours with stirring under a nitrogen gas stream to carry out the urethane reaction and obtain polyisocyanate B109. Polyisocyanate B109 contained polyether polyurethane polyisocyanate and had an isocyanate group content of 18.6%.

[0117] (Synthesis example B110) The urethane reaction was carried out in the same manner as in Synthesis Example B101, according to the composition shown in Table 4, and then cooled to 75°C. Ten parts of polymeric MDI were added and stirred for 15 minutes to obtain polyisocyanate B110 as a mixture containing polyether polyurethane polyisocyanate and polymeric MDI. The isocyanate group content of polyisocyanate B110 was 17.9%.

[0118] (Synthesis Example B111) According to the composition shown in Table 4, polyisocyanate B111 was obtained as a mixture of polyether polyurethane polyisocyanate and polymeric MDI in the same manner as in synthesis example B110. The isocyanate group content of polyisocyanate B111 was 19.2%.

[0119] (Synthesis Example B112) According to the composition shown in Table 4, polyisocyanate B112 containing polyether polyurethane polyisocyanate was obtained in the same manner as in synthesis example B101. The isocyanate group content of polyisocyanate B112 was 10.6%.

[0120] (Synthesis Example B113) 10.3 parts of PPG-400, 32.1 parts of PPG-2000, 3.2 parts of PPG-300, and 43.1 parts of 4,4'-MDI were each charged into a reaction vessel. The mixture was heated at 90°C to 100°C for 3 hours under a nitrogen gas stream with stirring to carry out the urethane reaction. Then, 15 parts of MDI-50 were added to the reaction mixture obtained to obtain polyisocyanate B113. Polyisocyanate B113 contained polyether polyurethane polyisocyanate, and the isocyanate group content was 10.9%.

[0121] (Synthesis Example B114) According to the composition shown in Table 4, polyisocyanate B114 containing polyether polyurethane polyisocyanate was obtained in the same manner as in synthesis example B113. The isocyanate group content of polyisocyanate B114 was 19.2%.

[0122] (Synthesis examples B115~B118) According to the compositions shown in Table 4, polyisocyanates B115 to B118 containing polyether polyurethane polyisocyanate were obtained in the same manner as in synthesis example B101.

[0123] [Table 4]

[0124] Details of the abbreviations in Table 4 are shown below. <Polyol (b1)> (Polyether polyol) PPG-400 bifunctional: Polypropylene glycol, manufactured by ADEKA Corporation, bifunctional, number average molecular weight 400 PPG-1000 Bifunctional: Polypropylene glycol, manufactured by ADEKA Corporation, bifunctional, number average molecular weight 1000 PPG-2000 bifunctional: Polypropylene glycol, manufactured by ADEKA Corporation, bifunctional, number average molecular weight 2000 PPG-400 Trifunctional: A triol obtained by adding polypropylene glycol to glycerin, manufactured by ADEKA Corporation, trifunctional, number average molecular weight 400, trade name: ADEKA Polyether G-400 PPG-4000 Trifunctional: A triol obtained by adding polypropylene glycol to glycerin, manufactured by ADEKA Corporation, trifunctional, number average molecular weight 4000, trade name: ADEKA Polyether G-4000

[0125] (Polyester polyol) • A101: Aliphatic polyester polyol, bifunctional, number-average molecular weight 2000, prepared using synthesis example A101. • A102: Aliphatic polyester polyol, bifunctional, number-average molecular weight 900, prepared using synthesis example A102.

[0126] (Other polyols) TMP: Trimethylolpropane, manufactured by PERSTORP, 3 functional groups, molecular weight 134 Glycerin: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 3 functional groups, molecular weight 92 • Cantaloupe seed oil: Industrial grade No. 1 cantaloupe seed oil, manufactured by Toyokuni Oil Co., Ltd., functional group number 2.7, molecular weight 1000

[0127] <Isocyanate (b2)> · 4,4'-MDI: 4,4'-diphenylmethane diisocyanate • MDI-50: A mixture of 2,4'-MDI and 4,4'-MDI: A mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate in a 50 / 50 mass ratio. <Post-added polyisocyanate> • MDI-50: A mixture of 2,4'-MDI and 4,4'-MDI: A mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate in a 50 / 50 mass ratio. • Polymeric MDI mixture: Wanate PM-200 from Yantai Wanhua (a mixture of approximately 60% polymeric MDI and 40% 4,4-MDI) • HDI Biuret: Biuret-type polyisocyanate, trimer of 1,6-hexamethylene diisocyanate, manufactured by Asahi Kasei Corporation.

[0128] The compositions of polyisocyanates B101 to B118 obtained according to the formulations described in Table 4 are shown below. [Table 4-1]

[0129] The values ​​listed in the table were obtained in the following way: NCO group content This value was obtained by calculating it according to the method explained earlier. Number average molecular weight of urethane prepolymers These are values ​​obtained by measuring according to the method described earlier. (3) Content of each component The content of urethane prepolymer, 2,4'-MDI, and 4,4'-MDI was obtained by quantitative analysis using liquid chromatography. The measurement conditions are as follows: Column: ODS column Mobile phase: Gradient of aqueous ammonium acetate solution and acetonitrile Detector: UV-Vis absorbance spectrophotometer Detection wavelength: 245nm The total amount of residual MDI monomers listed in the table refers to the sum of unreacted 2,4'-MDI and 4,4'-MDI derived from the MDI used during synthesis and / or MDI monomers added later.

[0130] <2> Manufacturing of adhesives (Example 1) A solvent-free adhesive was obtained by mixing 100 parts of A304, which was previously prepared as polyol (A), and 150 parts of B101, which was previously prepared as polyisocyanate (B), at 40°C. The amount of isocyanate groups to hydroxyl groups (NCO / OH ratio) was 1.7. The NCO / OH ratio was determined as follows. NCO / OH ratio = [Isocyanate group (eq) / Hydroxyl group (eq)] In the formula, "eq" represents the equivalent number. The above isocyanate group (eq) was determined as follows. Isocyanate group (eq) = NCO content (mass%) / (42 × 100) Hydroxyl group (eq.) = Hydroxyl value / 56100 The NCO content (mass%) was determined in accordance with JIS K7301. The hydroxyl value was determined in accordance with JIS K1557-1.

[0131] (Examples 2-22, Comparative Examples 1-5) A solvent-free adhesive was obtained in the same manner as in Example 1, according to the composition shown in Table 5. The mixing ratio was adjusted so that the NCO / OH ratio after compounding was 1.7 to 1.8.

[0132] <3> Evaluation of adhesives The solvent-free adhesives obtained in Examples 1-22 and Comparative Examples 1-5 were subjected to the following measurements to evaluate their respective properties. The results are shown in Table 5. <Viscoelasticity> Viscoelasticity measurements were performed on the adhesive during curing using a rheometer (MCR302, manufactured by Anton Paar), and the storage modulus (Pa) and loss modulus (Pa) were determined. The measurement conditions were as follows: (Measurement conditions) Frequency: 5Hz, Stress: 10Pa, Measuring probe: Parallel plate (25mm diameter), Measurement temperature: 40℃ Measurements were started immediately after preparing the solvent-free adhesive. Using the storage modulus (Pa) and loss modulus (Pa) values ​​obtained from the measurements, the value of [log(storage modulus) / log(loss modulus)] was calculated, and measurements were continued until this value reached 0.9 or higher. The time from the start of measurement until the value of [log(storage modulus) / log(loss modulus)] reached 0.9 or higher was calculated.

[0133] <Adhesive strength> Ink was printed onto a 20 μm thick biaxially oriented polypropylene film (Toyobo's Pylon Film "P2161", hereinafter referred to as OPP) using a gravure proofing machine. More specifically, the ink was printed onto the surface of the OPP to create a grid pattern of plain and inked areas. Printing was performed at a printing speed of 150 m / min. Toyo Ink Co., Ltd.'s LP Bio SX R631 white ink was used. After printing the ink and forming a coating film, it was dried at 70°C to obtain a printed material with a dried ink film (printed layer) on the OPP. The thickness of the printed layer was 1 μm. Next, a solvent-free adhesive was applied to the printed layer of the resulting printed material using a solvent-free laminator at a rate of 2.0 g / m². 2 The coating was applied at a speed of 300 m / min to achieve the desired result. Subsequently, the corona-treated surface of a 25 μm thick CPP film (Toray Industries, Ltd. "FHK2", hereinafter referred to as CPP) and the adhesive-coated surface of the printed material obtained as described above were bonded together, and a 50 m laminate having the structure of OPP / printed layer / adhesive layer / CPP was fabricated by winding it in the longitudinal direction. The wound laminate was placed in an oven at 20°C and 20% RH and left to stand for 24 hours. The adhesive strength of the laminate having the above-described configuration of OPP / printed layer / adhesive layer / CPP was evaluated at a point 20m inward from the outside of the winding. The adhesive strength was evaluated by applying force to the plain area of ​​the printed pattern at a peeling angle of 90° and a peeling speed of 300mm / min to separate the OPP and CPP layers, and according to the following criteria. Better adhesive strength indicates that the adhesive strength will develop more quickly during aging in a low-temperature, low-humidity environment. (Evaluation Criteria) A: Cohesive failure of the OPP has occurred, and it has fully hardened; there is no tackiness on the adhesive surface (very good). B: The adhesive has migrated to either the OPP or CPP surface, and there is no tackiness on the adhesive surface (good). C: The adhesive has migrated to either the OPP or CPP surface, and the adhesive surface has a tacky feel (usable). D: Adhesive remains on both the OPP and CPP surfaces, and the adhesive surface has a tacky feel (unusable).

[0134] <Heat seal strength> Ink was printed onto a 12 μm thick biaxially oriented polyethylene terephthalate film (Toyobo Co., Ltd.'s ester film "E5102", hereinafter referred to as PET) using a gravure proofing machine. More specifically, the ink was printed onto the surface of the PET to create a grid pattern of plain and inked areas. Printing was performed at a printing speed of 150 m / min. Toyo Ink Co., Ltd.'s LP Bio SX R631 white ink was used. After printing the ink and forming a coating film, it was dried at 70°C to obtain a printed material with a dried ink film (printed layer) on the PET. The thickness of the printed layer was 1 μm. Next, a solvent-free adhesive was applied to the printed layer of the resulting printed material using a solvent-free laminator at a rate of 2.0 g / m². 2 The coating was applied at a coating speed of 200 m / min to achieve the desired result. Subsequently, the corona-treated surface of a 50 μm thick LLDPE film (TUX-FCD, manufactured by Tosello Co., Ltd., hereinafter referred to as LLDPE) and the adhesive-coated surface of the printed material obtained as described above were bonded together, and a 50 m laminate having the structure of PET / printed layer / adhesive layer / LLDPE was fabricated by winding it in the longitudinal direction. The wound laminate was placed in an oven at 20°C and 20% RH and left to stand for 24 hours. The heat seal strength of the portion 20 m inward from the outer winding side of the laminate having the structure of PET / printing layer / adhesive layer / LLDPE obtained as described above was evaluated. For the heat seal strength, heat sealing was performed at 150 °C, a pressure of 0.2 bar, and a time of 1.0 second on the non-patterned portion of the printed pattern, and it was cut into a test piece with a width of 15 mm and a length of 300 mm. Based on JIS K6854, using an Instron type tensile tester, in an environment of a temperature of 20 °C and a relative humidity of 65%, force was applied at a peeling speed of 300 mm / min to perform peeling, and the heat seal strength was evaluated according to the following criteria. The test was conducted 5 times, and the most frequent form was adopted. The better the heat seal strength, the faster the heat seal strength is exhibited in the aging under a low temperature and low humidity environment. (Evaluation Criteria) A: The laminated film broke, but the heat seal portion remained unchanged (very good) B: The laminated film did not break, and only the LLDPE film broke (good) C: The laminated film did not break. After the PET / LLDPE between the heat seal portions peeled off, the LLDPE film broke (usable) D: No film break occurred, and the PET / LLDPE between the heat seal portions peeled off (unusable)

[0135] <VM Appearance> A printed matter was produced in the same manner as the printed matter produced for the evaluation of the above adhesion strength. Onto the printing layer of this printed matter, using a solvent-free laminator, a solvent-free adhesive was applied at an application rate of 2.0 g / m 2 at an application speed of 300 m / min. Thereafter, an aluminum (AL) vapor-deposited CPP film with a thickness of 25 μm (manufactured by Toray Industries, Inc. "2203", hereinafter referred to as the AL vapor-deposited surface of VMCPP) and the adhesive-coated surface of the above-obtained printed matter were bonded together to produce 50 m of a laminate having the structure of OPP / printing layer / adhesive layer / VMCPP. The obtained laminate was left standing in an oven at 20 °C and 20% RH for 24 hours. The white printed portion of the outermost layer (outside the winding) of the laminate consisting of the obtained OPP / printed layer / adhesive layer / VMCPP was visually observed. That is, the appearance of the above laminate as seen from the OPP film side (VM appearance) was observed and evaluated according to the following criteria. (Evaluation Criteria) A: No bubbles observed (very good) B: Bubble area is less than 10% (good) C: Area where bubbles are generated is 10% or more but less than 20% (usable) D: Bubble generation area is 20% or more (Not usable)

[0136] [Table 5]

[0137] As shown in Table 5, the solvent-free adhesive of this embodiment obtained good adhesive strength and heat seal strength after 24 hours of aging in a low humidity environment of 20°C and 20%RH, confirming that adhesive strength is easily developed. In particular, a comparison of Example 4, which used TMP as a trifunctional or higher polyol (a1) with a molecular weight of 200 or less, with Examples 19 and 20, which used glycerin or pentaerythritol, shows that the use of TMP makes it easy to improve adhesive strength and heat seal strength during aging in low temperature and low humidity environments.

[0138] Furthermore, as seen in Examples 4 and 13-16, where the amount of trifunctional or higher polyol (a1) with a molecular weight of 200 or less was changed, it can be seen that when the amount of polyol (a1) is 0.5% by mass or more, the adhesive strength and heat seal strength are easily improved, and particularly excellent results are obtained when it is 2% by mass or more. On the other hand, it can be seen that an excellent VM appearance can be easily obtained by adjusting the amount of polyol (a1) to 10% by mass or less. This is thought to be because the reaction rate during curing is moderate (not too fast), which suppresses the reaction with moisture and inhibits the generation of bubbles.

[0139] Furthermore, as seen in Example 4, when the amount of polyol (a1) is 2 to 6% by mass, it is found that the balance between adhesive strength, heat seal strength, and VM appearance is particularly excellent. Also, as seen in Examples 3 to 5, when the amount of bifunctional polyether polyol (b1-1A) with a number average molecular weight of 500 or less is adjusted to 20% by mass or more based on (b1), it is found that the adhesive strength and heat seal strength during aging in low temperature and low humidity environments are easily improved, and the exhibit of adhesive performance is also excellent. On the other hand, when the amount of (b1-1A) is 40% by mass or less, it is found that an excellent VM appearance can be easily obtained.

[0140] Furthermore, in comparison with Examples 8 and 9, improvements in the onset of each property were confirmed in the examples where the urethane bond density of isocyanate (B) was 120 mmol / g or higher. It was found that when the urethane bond density of isocyanate (B) is in the range of 100 to 140 mmol / g, it is easier to achieve both adhesive strength, heat seal strength, and VM appearance. As seen in Examples 10 and 11, it was confirmed that the onset of adhesive performance is also promoted when polymeric MDI is added later. Furthermore, since it is possible to realize an adhesive that satisfies equation (I) within 24 hours and exhibits excellent adhesive strength, heat seal strength, and VM appearance, it is clear that such an adhesive can be used to efficiently carry out the manufacturing of laminates and the like.

Claims

1. A solvent-free adhesive comprising a polyol (A) and a polyisocyanate (B), characterized by satisfying all of the following conditions (1) to (3). (1) The polyol (A) comprises a trifunctional or more polyol (a1) with a molecular weight of 200 or less. (2) The polyisocyanate (B) comprises an isocyanate-terminated urethane prepolymer (B1), which is a reaction product of a polyol (b1) and an isocyanate compound (b2), and an isocyanate monomer (B2) containing 2,4'-diphenylmethane diisocyanate, wherein the polyol (b1) contains 80% by mass or more of polyether polyol (b1-1) based on the total mass of the polyol (b1). (3) The polyether polyol (b1-1) contains a bifunctional polyether polyol (b1-1A) with a number average molecular weight of 500 or less, and the content of the bifunctional polyether polyol (b1-1A) with a number average molecular weight of 500 or less is 15 to 50% by mass based on the total mass of the polyol (b1).

2. The solvent-free adhesive according to claim 1, wherein the storage modulus and loss modulus of the solvent-free adhesive after mixing the polyol (A) and the polyisocyanate (B) satisfy the following formula (I) within 24 hours. Equation (I): [log(storage modulus) / log(loss modulus)] ≥ 0.9 [In the above equation (I), the storage modulus (Pa) and loss modulus (Pa) are values ​​measured using a viscoelasticity measuring device under the following conditions: frequency: 5 Hz, stress: 10 Pa, measuring probe: parallel plate (diameter 25 mm), and temperature: 40°C.]

3. The solvent-free adhesive according to claim 1, wherein the polyol (A) contains 5 to 40% by mass of a bifunctional polyether polyol (a2-1) having a number average molecular weight of 500 or less, based on the total mass of the polyol (A).

4. The solvent-free adhesive according to claim 1, wherein the content of the bifunctional polyether polyol (b1-1A) with a number average molecular weight of 500 or less is 20 to 40% by mass, based on the total mass of the polyol (b1).

5. The solvent-free adhesive according to claim 1, wherein the polyol (A) contains 0.5 to 10% by mass of a trifunctional or more polyol (a1) with a molecular weight of 200 or less, based on the total mass of polyol (A).

6. The solvent-free adhesive according to claim 1, wherein the content of trifunctional or more polyols in the polyol (b1) is 25% by mass or less, based on the total mass of the polyol (b1).

7. The solvent-free adhesive according to claim 1, wherein the polyisocyanate (B) has a urethane bonding concentration of 100 to 140 mmol / g.

8. The solvent-free adhesive according to claim 1, wherein the polyol (A) contains 30 to 90% by mass of polyester polyol (a3) ​​based on the total mass of polyol (A).

9. The solvent-free adhesive according to claim 1, wherein the polyisocyanate (B) further contains 1 to 15% by mass of polymeric MDI based on the total mass of the polyisocyanate (B).

10. The solvent-free adhesive according to claim 1, wherein the content of the isocyanate group-terminated urethane prepolymer (B1) is 30 to 80% by mass, based on the total mass of the polyisocyanate (B).

11. The solvent-free adhesive according to claim 1, wherein the content of 2,4'-diphenylmethane diisocyanate is 15 to 70% by mass, based on the total mass of the isocyanate monomer (B2).

12. The solvent-free adhesive according to claim 1, wherein the number average molecular weight of the isocyanate group-terminated urethane prepolymer (B1) is 800 to 2000.

13. A laminate comprising at least a first substrate and a second substrate via an adhesive layer formed using a solvent-free adhesive according to any one of claims 1 to 12.

14. The laminate according to claim 13, wherein the first substrate and the second substrate are each sheet-like substrates independently formed using at least one selected from the group consisting of plastics, metals, and inorganic materials other than metals.

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