JP2024098240A - Adhesive composition, adhesive resin layer, and laminate - Google Patents

Abstract

To provide an adhesive composition that has good wettability on substrates and can rapidly form an adhesive layer being an adhesive resin layer excellent in heat resistance and adhesion to these substrates.SOLUTION: An adhesive composition contains a polyurethane resin A having a terminal hydroxyl group, a polyurethane resin B having a terminal isocyanate group, and an organic solvent, where the polyurethane resin A has a constitutional unit derived from a polyol (a) represented by Formula (1) and the polyurethane resin B has a constitutional unit derived from a polyol (c) represented by Formula (2), with the mass ratio (a)/(c) of the polyol (a) to the polyol (c) between 70/30 to 30/70. (In the formulas, n represents a number at which the average molecular weight of the polyol (a) is 400 to 3,000, and m represents a number at which the average molecular weight of the polyol (c) is 300 to 2,000.)SELECTED DRAWING: None

Description

The present invention relates to an adhesive composition, an adhesive resin layer, and a laminate.

Polyurethane resin is usually a resin obtained by reacting a high molecular weight polyol with a polyisocyanate, and then reacting it with a chain extender if necessary. By changing the type and combination of each component, it is possible to give the resin a variety of properties, including adhesiveness. However, since the components that make up polyurethane resin, such as the polyol, are mainly derived from petroleum resources, there is a demand for improvements that take into account the impact on the environment.

Adhesives used to manufacture various laminates in the industrial materials field are required to have properties such as high adhesion, heat resistance, and suitability for high-speed lamination processing. Polyether-based polyurethane resins are useful resins for use in adhesives with such properties. Meanwhile, biomass, a renewable organic resource derived from living organisms, has been attracting attention in recent years as a non-exhaustible industrial resource.

As related technologies, for example, a two-component curing adhesive composition has been proposed that uses polyether urethane polyol, which is made from plant-derived polytetramethylene ether glycol (biomass PTMG), as the main component (Patent Document 1). In addition, a packaging material has been proposed that contains a biomass-derived component as part of its constituent materials, and that has an adhesive layer that contains a cured product of polyether polyol, which is a reaction product of a polyfunctional alcohol and a polyfunctional carboxylic acid (Patent Document 2). Furthermore, a polyurethane has been proposed that is obtained using a polyether polyol containing 1,3-propanediol units and is used as a constituent material for films and fibers (Patent Document 3).

Patent No. 6587584 JP 2019-142041 A JP 2008-274205 A

However, the adhesive strength of the adhesive layer formed with the adhesive composition proposed in Patent Document 1 was prone to decrease under heating conditions. For this reason, when used as an adhesive to form an adhesive layer disposed between layers of a laminated product, for example, there was an issue that the layers tended to peel off when heated, such as during boiling sterilization, which is known as "delamination."

In addition, while the adhesive layer of the packaging material proposed in Patent Document 2 is useful from the viewpoint of increasing the biomass content, there is room for improvement in terms of properties such as heat resistance. Furthermore, the polyurethane proposed in Patent Document 3 is not primarily used as an adhesive, so it cannot be said that it is sufficient in terms of heat resistance as well as adhesion.

The present invention has been made in consideration of the problems associated with the conventional technology, and its object is to provide an adhesive composition that has good wettability with respect to substrates such as various olefins and metals, and that can rapidly form an adhesive layer that is an adhesive resin layer that has excellent adhesion to these substrates and excellent heat resistance, and that can also be made of biomass materials as part of its constituent materials. Another object of the present invention is to provide an adhesive resin layer and a laminate that use this adhesive composition.

That is, according to the present invention, there is provided an adhesive composition as shown below.
[1] An adhesive composition comprising a polyurethane resin A having a hydroxyl group at its terminal, a polyurethane resin B having an isocyanate group at its terminal, and an organic solvent, wherein the polyurethane resin A has a structural unit derived from a polyol (a) represented by the following formula (1), a structural unit derived from a chain extender (b), and a structural unit derived from an aromatic diisocyanate, the polyurethane resin B has a structural unit derived from a polyol (c) represented by the following formula (2), the chain extender (b) comprises a triol compound (b1) and a polyol compound (b2) other than the triol compound (b1), and the mass ratio of the polyol (a) to the polyol (c) is (a)/(c)=70/30 to 30/70.

（前記式（１）中、ｎは、前記ポリオール（ａ）の数平均分子量が４００～３，０００となる数を示し、前記式（２）中、ｍは、ポリオール（ｃ）数平均分子量が３００～２，０００となる数を示す）

(In the formula (1), n represents a number such that the number average molecular weight of the polyol (a) is 400 to 3,000, and in the formula (2), m represents a number such that the number average molecular weight of the polyol (c) is 300 to 2,000.)

[2] The adhesive composition according to [1], wherein the ratio of the content of the polyurethane resin B to the content of the polyurethane resin A is a molar ratio of isocyanate groups (NCO) in the polyurethane resin B to hydroxyl groups (OH) in the polyurethane resin A, NCO/OH, of 1.05 or more.
[3] The adhesive composition according to [1] or [2], wherein the hydroxyl value of the polyurethane resin A is 5.0 to 40.0 mgKOH/g, and the isocyanate group content of the polyurethane resin B is 3.2 to 5.1%.
[4] The adhesive composition according to any one of [1] to [3], wherein the polyol compound (b2) has a hydroxyl value of 200 to 1,200 mgKOH/g, and the ratio ((a)/(b)) of the average hydroxyl value (mgKOH/g) of the polyol (a) to the average hydroxyl value (mgKOH/g) of the chain extender (b) is 0.15 to 0.70.
[5] The adhesive composition according to any one of [1] to [4], wherein the polyol compound (b2) is at least one selected from the group consisting of a compound obtained by ring-opening addition of 1 mole of an acid anhydride to 1 mole of a trifunctional polyol, dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, dimethylolheptanoic acid, dimethyloloctanoic acid, and dimethylolnonanoic acid.
[6] The adhesive composition according to any one of [1] to [5], wherein the polyurethane resin A has a biomass degree of 10 mass% or more.

Furthermore, according to the present invention, there are provided an adhesive resin layer and a laminate as described below.
[7] An adhesive resin layer which is a coating and drying product of the adhesive composition according to any one of [1] to [6] above.
[8] A laminate comprising a first substrate, a second substrate, and the adhesive resin layer described in [7] above, which is disposed between the first substrate and the second substrate, wherein the second substrate is a plastic film, a metal-vapor-deposited film, or a metal foil.

According to the present invention, it is possible to provide an adhesive composition that has good wettability with respect to substrates such as various olefins and metals, can rapidly form an adhesive layer that is an adhesive resin layer that has excellent adhesion to these substrates and excellent heat resistance, and can also use biomass materials as part of the constituent materials. In addition, according to the present invention, it is possible to provide an adhesive resin layer and a laminate that use this adhesive composition.

<Adhesive Composition>
Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to the following embodiment. One embodiment of the adhesive composition of the present invention is an adhesive composition containing a polyurethane resin A having a hydroxyl group at a terminal, a polyurethane resin B having an isocyanate group at a terminal, and an organic solvent. The polyurethane resin A has a structural unit derived from a specific polyol (a), a structural unit derived from a chain extender (b), and a structural unit derived from an aromatic diisocyanate. The polyurethane resin B has a structural unit derived from a specific polyol (c). The chain extender (b) includes a triol compound (b1) and a polyol compound (b2) other than the triol compound. The mass ratio of the polyol (a) to the polyol (c) is (a)/(c)=70/30 to 30/70.

(Polyurethane resin A)
The polyurethane resin A is a component that can function as a main component of the adhesive composition of the present embodiment, and is a urethane resin having a hydroxyl group (OH group) at its terminal. The polyurethane resin A has a structural unit derived from a specific polyol (a), a structural unit derived from a chain extender (b), and a structural unit derived from an aromatic diisocyanate.

[Polyol (a)]
Polyol (a) (hereinafter, also referred to as "polyoxytrimethylene glycol" or "PO3G") is represented by the following formula (1). As shown in the following formula (1), polyol (a) does not have a secondary hydroxyl group, so it has good reactivity with isocyanate groups (high NCO decay rate), and is expected to shorten aging. In addition, it has good adhesion not only to metals but also to olefins.

（式（１）中、ｎは、ポリオール（ａ）の数平均分子量が４００～３，０００となる数を示す）

(In formula (1), n represents a number that provides the number average molecular weight of polyol (a) of 400 to 3,000.)

As the PO3G, plant-derived PO3G can be used. The number average molecular weight of the PO3G is 400 to 3,000, and preferably 600 to 2,000. If the number average molecular weight of the PO3G is less than 400, the adhesive performance of the adhesive composition decreases. On the other hand, if the number average molecular weight of the PO3G is more than 3,000, the heat resistance of the adhesive layer (adhesive resin layer) formed decreases.

[Other polyols]
The polyurethane resin A may have a structural unit derived from a polyol (other polyol) other than the above-mentioned polyol (a) (PO3G). As the other polyol, a petroleum-derived polyol or a plant-derived polyol can be used. As the petroleum-derived polyol, polypropylene ether triol, polyethylene ether glycol, polytetramethylene ether glycol, adipic acid-based polyester polyol, phthalic acid-based polyester polyol, polycaprolactone polyol, polycarbonate polyol, polyolefin polyol, and acrylic polyol can be mentioned. As the plant-derived polyol, sebacic acid-based polyol, succinic acid-based polyol, glutaric acid-based polyol, and dimer acid-based polyol, which are plant-derived raw materials, can be mentioned.

[Chain extender (b)]
The chain extender (b) includes a triol compound (b1) and a polyol compound (b2) other than the triol compound (b1). By using a polyurethane resin A having a structural unit derived from the chain extender (b) using the triol compound (b1) and the polyol compound (b2) in combination, an adhesive composition having excellent heat resistance and improved adhesion to various substrates such as metal foils, metal-deposited plastic films, and transparent plastic films deposited with silica, alumina, etc. can be obtained. The mass ratio of the triol compound (b1) to the polyol compound (b2) is preferably (b1)/(b2)=1/99 to 20/80, more preferably 3/97 to 10/90.

The triol compound (b1) is a polyfunctional alcohol having three hydroxyl groups in its molecule. Examples of the triol compound (b1) include glycerin, triol-type polypropylene glycol, trimethylolpropane, triethanolamine, and triethylolpropane.

As the polyol compound (b2), a dihydroxycarboxylic acid compound having an acid value of 80 to 600 mgKOH/g can be used. By using such a dihydroxycarboxylic acid compound as the polyol compound (b2), metal adhesion can be improved. Specific examples of the dihydroxycarboxylic acid compound include a compound in which 1 mole of an acid anhydride is ring-opened and added to 1 mole of a trifunctional polyol such as a trifunctional polyester polyol or a trifunctional polyether polyol, dimethylol propionic acid, dimethylol butanoic acid, dimethylol pentanoic acid, dimethylol heptanoic acid, dimethylol octanoic acid, and dimethylol nonanoic acid. The number average molecular weight of the trifunctional polyol is usually 150 to 500, and preferably 200 to 400.

The chain extender (b) may contain other polyfunctional alcohols in addition to the triol compound (b1) and the polyol compound (b2). As the other polyfunctional alcohols, it is possible to use polyfunctional alcohols derived from petroleum and aliphatic polyfunctional alcohols derived from plants. As the polyfunctional alcohols derived from petroleum, there can be mentioned compounds having two or more, preferably two to eight, hydroxyl groups in one molecule. As such polyhydric alcohols, there can be mentioned ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,6-hexanediol, neopentyl glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,9-nonanediol.

Examples of plant-derived aliphatic polyfunctional alcohols include 1,3-propanediol, 1,4-butanediol, and ethylene glycol. Plant-derived 1,3-propanediol can be produced from glycerol via 3-hydroxypropylaldehyde by a fermentation method that decomposes plant resources (e.g., corn). When producing 1,3-propanediol by a biomethod such as a fermentation method, useful by-products such as lactic acid can be obtained and production costs can be kept low, unlike when 1,3-propanediol is produced by the EO production method. 1,4-butanediol can be produced by hydrogenating succinic acid obtained by fermenting glycol produced from plant resources. Ethylene glycol can also be produced, for example, from bioethanol obtained by a conventional method via ethylene.

The hydroxyl value of the polyol compound (b2) is preferably 200 to 1,200 mgKOH/g, and more preferably 230 to 1,000 mgKOH/g. The ratio ((a)/(b)) of the average hydroxyl value (mgKOH/g) of the polyol (a) to the average hydroxyl value (mgKOH/g) of the chain extender (b) is preferably 0.15 to 0.70, and more preferably 0.30 to 0.50. This makes it possible to obtain an adhesive composition with an excellent balance between wettability to substrates such as various olefins and metals, and heat resistance.

[Aromatic diisocyanates]
By using polyurethane resin A having a structural unit derived from aromatic diisocyanate, it is possible to obtain an adhesive composition having improved adhesion to various substrates and heat resistance. If an aliphatic diisocyanate is used instead of an aromatic isocyanate, the adhesive composition does not exhibit an appropriate hardness, and the adhesiveness to a substrate made of polypropylene or the like is insufficient. As the aromatic diisocyanate, a petroleum-derived aromatic diisocyanate can be used. Examples of aromatic diisocyanates include toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, a toluene-2,4-diisocyanate/toluene-2,6-diisocyanate=80/20 mixture, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate diphenyl ether, 4,4'-diphenylmethane diisocyanate, jurylene diisocyanate, xylylene diisocyanate, 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, and 4,4'-diisocyanate dibenzyl.

Polyurethane resin A can be obtained by a copolymer urethane reaction of components including polyol (a) (PO3G), chain extender (b), and aromatic diisocyanate. In particular, it is preferable to carry out the reaction so that the molar ratio of the isocyanate group (NCO) in the aromatic diisocyanate to the total of the hydroxyl group (OH) in polyol (a) and the hydroxyl group (OH) in chain extender (b) is NCO/OH = 0.6 to 0.99, and it is even more preferable to carry out the reaction so that NCO/OH = 0.7 to 0.99. If the value of NCO/OH is less than 0.6, the adhesive strength and heat resistance of the adhesive composition may be slightly reduced. On the other hand, if the value of NCO/OH is more than 0.99, it may be difficult to introduce a sufficient amount of hydroxyl groups to the terminal of polyurethane resin A.

At the end of the copolymerized urethane reaction, a compound having two or more hydroxyl groups of the same type as the chain extender (b) can be reacted as a reaction terminator to ensure stability of the solution viscosity over time.

The hydroxyl value of polyurethane resin A is preferably 5.0 to 40.0 mgKOH/g, and more preferably 7.5 to 25.0 mgKOH/g. If the hydroxyl value of polyurethane resin A is less than 5.0 mgKOH/g, the wettability may decrease slightly. On the other hand, if the hydroxyl value of polyurethane resin A is more than 40.0 mgKOH/g, the adhesive strength of the laminate film may decrease slightly.

As described above, the polyurethane resin A used in the adhesive composition of the present embodiment can use a plant-derived compound as at least a part of the constituent material. Therefore, the biomass degree of the polyurethane resin A can be preferably 10 mass% or more, more preferably 20 mass% or more, and particularly preferably 30 mass% or more. Therefore, the adhesive composition of the present embodiment containing the polyurethane resin A having a biomass degree of 10 mass% or more is an environmentally friendly material in line with the idea of carbon neutrality, and can contribute to reducing _CO2 emissions.

(Polyurethane resin B)
The polyurethane resin B is a component capable of functioning as a curing agent that reacts with the main component of the adhesive composition of the present embodiment to cure the composition, and is a urethane resin having an isocyanate group (NCO group) at its terminal. The polyurethane resin B has a structural unit derived from a specific polyol (c).

[Polyol (c)]
Polyol (c) (hereinafter also referred to as "polypropylene glycol") is represented by the following formula (2). The number average molecular weight of polyol (c) is 300 to 2,000, and preferably 400 to 1,000. If the number average molecular weight of polyol (c) is less than 300, the adhesive performance of the adhesive composition decreases. On the other hand, if the number average molecular weight of polyol (c) is more than 2,000, the heat resistance of the formed adhesive layer (adhesive resin layer) decreases.

（式（２）中、ｍは、ポリオール（ｃ）の数平均分子量が３００～２，０００となる数を示す）

(In formula (2), m represents a number that provides a number average molecular weight of the polyol (c) of 300 to 2,000.)

[Other polyols]
The polyurethane resin B may have a structural unit derived from a polyol (other polyol) other than the above-mentioned polyol (c) (polypropylene glycol). Examples of the other polyol include the same polyols as those that can be used in the polyurethane resin A.

[Chain extender]
The polyurethane resin B can be obtained, for example, by subjecting a component containing the above-mentioned polyol (c), a chain extender, and a diisocyanate to a copolymer urethane reaction. As the chain extender, the same one as the "other polyfunctional alcohol" that can be used in producing the above-mentioned polyurethane resin A can be used. Among them, it is preferable to use a diol having a branched alkyl side chain, such as 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, or 2-butyl-2-ethyl-1,3-propanediol, as the chain extender, since the adhesive strength, including the initial adhesive strength, can be further improved.

As a chain extender, a triol compound can also be used. As the triol compound, the triol compound (b1) used in producing the polyurethane resin A described above and a diol having a branched alkyl side chain are preferable, and the triol compound (b1) is particularly preferable.

The amount of chain extender used is preferably 0.05 to 2 moles, and more preferably 0.1 to 1.5 moles, per mole of polyol (c). By using a chain extender within the above range per mole of polyol (c), an adhesive composition with superior adhesive strength and heat resistance can be obtained.

[Diisocyanate]
As the diisocyanate, the same aromatic diisocyanate as that used in producing the polyurethane resin A described above can be used.

Polyurethane resin B can be obtained, for example, by reacting components containing polyol (c), a chain extender, and a diisocyanate to produce a urethane copolymer. In particular, it is preferable to react so that the molar ratio of the isocyanate group (NCO) in the diisocyanate to the sum of the hydroxyl group (OH) in polyol (c) and the hydroxyl group (OH) in the chain extender is NCO/OH = 1.01 to 2.0, and it is even more preferable to react so that NCO/OH = 1.1 to 1.5. If the value of NCO/OH is more than 2.0, the amount of free diisocyanate may be large. On the other hand, if the value of NCO/OH is less than 1.01, it may be difficult to introduce a sufficient amount of isocyanate groups to the ends of polyurethane resin B.

The isocyanate group (NCO group) content of polyurethane resin B is preferably 3.2 to 5.1%, and more preferably 3.5 to 4.9%. By setting the isocyanate group content of polyurethane resin B within the above range, the heat resistance and adhesive performance can be further improved. The isocyanate group (NCO group) content of polyurethane resin B is a value measured in accordance with JIS K1603.

(Organic solvent)
As the organic solvent, ethyl acetate, butyl acetate, ethyl lactate, butyl lactate, methyl ethyl ketone, etc. can be used. Among them, the use of organic solvents derived from plant raw materials is preferable because it can contribute to reducing _CO2 emissions. As the organic solvents derived from plant raw materials, ethyl acetate, butyl acetate, ethyl lactate, butyl lactate, etc. can be mentioned.

(Adhesive Composition)
The adhesive composition of the present embodiment can be used as a two-component curing adhesive in which, for example, polyurethane resin A, which is a base agent, and polyurethane resin B, which is a curing agent, are mixed and reacted at the time of use. The mass ratio of polyol (a) to polyol (c) is preferably (a)/(c)=70/30 to 30/70, and more preferably 60/40 to 40/60. By setting the mass ratio ((a)/(c)) of polyol (a) to polyol (c) within the above range, the adhesive performance with olefin, metal adhesion, and heat resistance can be further improved.

The ratio of the content of polyurethane resin B to the content of polyurethane resin A is the molar ratio of isocyanate groups (NCO) in polyurethane resin B to hydroxyl groups (OH) in polyurethane resin A, and is preferably NCO/OH = 1.05 or more, and more preferably NCO/OH = 2.00 or more when considering the consumption of isocyanate groups due to moisture. Furthermore, when considering the improvement of adhesive properties due to the high dimensionality of allophanate bonds, it is particularly preferable that NCO/OH = 2.50 to 10.0. If the NCO/OH value is less than 1.05, poor curing may occur easily and adhesion to olefins may be easily reduced.

The adhesive composition of this embodiment is useful as an adhesive for forming an adhesive layer used in manufacturing a laminate in which sheets (substrates) made of various materials are laminated and bonded together via an adhesive layer (adhesive resin layer). In particular, since it is possible to form an adhesive resin layer that has excellent adhesion to various substrates and excellent heat resistance, it is suitable as an adhesive for high-speed lamination.

The adhesive composition of this embodiment preferably further contains a curing catalyst. By including a curing catalyst, the heat resistance of the adhesive resin layer (adhesive layer) to be formed can be further improved. As the curing catalyst, a metal catalyst, an amine catalyst, or the like can be used.

The adhesive composition of the present embodiment preferably further contains at least one of an aromatic polyfunctional isocyanate compound having a biuret structure, an isocyanurate structure, or a trimethylolpropane adduct structure and an aliphatic polyfunctional isocyanate compound. By further containing such an isocyanate compound, the heat resistance of the adhesive resin layer (adhesive layer) to be formed can be further improved.

The adhesive composition of this embodiment may further contain various known additives, such as a reaction catalyst used during urethane elongation, a silane coupling agent for improving adhesion, a titanate coupling agent, an aluminate coupling agent, an epoxy resin, a phenoxy resin, a styrene-maleic anhydride copolymer resin, a butyral resin, an acrylic resin, an antifoaming agent, a leveling agent, an ultraviolet absorber, and an antioxidant, as necessary.

<Adhesive Resin Layer, Laminate>
One embodiment of the adhesive resin layer of the present invention is a coating and drying product of the adhesive composition described above. The adhesive resin layer of this embodiment can be formed, for example, by applying the adhesive composition to the surface of various substrates and drying the coating layer formed. The adhesive resin layer of this embodiment thus formed has excellent adhesion and heat resistance to substrates such as various olefins and metals. Therefore, the adhesive resin layer of this embodiment is useful as an adhesive layer when laminating and bonding various substrates such as sheets and films together.

In addition, one embodiment of the laminate of the present invention comprises a first substrate, a second substrate, and the above-mentioned adhesive resin layer disposed between the first substrate and the second substrate. The second substrate is a plastic film, a metal-deposited film, or a metal foil. The adhesive resin layer disposed between the first substrate and the second substrate is a coating and drying product of the above-mentioned adhesive composition, and therefore has excellent adhesion to substrates such as various olefins and metals, and excellent heat resistance. For this reason, the laminate of this embodiment is not susceptible to delamination even when heated by boiling sterilization or the like. Therefore, the laminate of this embodiment is useful as a material for constructing high-speed laminated products such as retort pouches that are expected to be used under heated conditions. Furthermore, by using the first substrate and the second substrate formed from raw materials derived from plants, a more environmentally friendly laminate can be obtained.

The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. Note that "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

<Preparing materials>
The materials shown in Table 1 were prepared.

<Synthesis of Polyurethane Resin A (1)>
(Synthesis Example A-1)
380 parts of POL3, 101.5 parts of a dihydroxycarboxylic acid compound obtained by ring-opening addition of 1 mole of phthalic anhydride to 1 mole of polypropylene ether triol having a number average molecular weight of 300 (product name "MN-F300", manufactured by Dainichiseika Chemicals Co., Ltd., hydroxyl value 250 mg KOH / g, acid value 125 mg KOH / g) (MN-F300), 3.37 parts of trimethylolpropane (TMP, hydroxyl value: 837 mg KOH / g), 111 parts of tolylene diisocyanate (TDI), and 270.9 parts of ethyl acetate (EA) were placed in a synthesis vessel. An appropriate amount of stannous octylate was added while stirring the contents, and the mixture was reacted at 90 ° C. for 5 hours to obtain a solution of polyurethane resin A-1 (non-volatile content 70%). The biomass degree (%) of polyurethane resin A-1 was 63.8%. The biomass degree is the content (mass %) of the biomass component in the solid content of the polyurethane resin A.

(Synthesis Example A-2)
1,000 parts of POL3, 89.4 parts of MN-F300, 8.92 parts of TMP, 347 parts of TDI, and 531 parts of EA were placed in a synthesis vessel. An appropriate amount of stannous octylate was added while stirring the contents, and the mixture was reacted at 90°C for 3 hours to obtain a solution of a urethane prepolymer. 85.3 parts of 1,4-butanediol (1,4-BD), 37 parts of diethylene glycol (DEG), and 8.98 parts of 2-methyl-1,3-propanediol (2-MPG) were added, and the mixture was reacted at 90°C for 1 hour with stirring to obtain a solution of polyurethane resin A-2 (70% non-volatile content).

(Synthesis examples A-3 to 7)
Solutions of polyurethane resins A-3 to A-7 (non-volatile content 70%) were obtained in the same manner as in Synthesis Example A-1 described above, except that the types and amounts of each component shown in the upper row of Table 2 were used.

<Synthesis of Polyurethane Resin B (1)>
(Synthesis Example B-1)
174 parts of TDI, 100 parts of POL5, and 250 parts of POL7 were placed in a synthesis vessel. The contents were reacted at 90° C. for 2 hours while stirring, and then 250 parts of diphenylmethane diisocyanate (MDI), 100 parts of POL5, and 250 parts of POL7 were added and reacted at 90° C. for 1 hour while stirring. 22.3 parts of TMP were further added, and then reacted at 90° C. for 1 hour while stirring. 287 parts of EA were added to dilute the mixture, and a solution of polyurethane resin B-1 (non-volatile content 80%) was obtained. The NCO content (%) of polyurethane resin B-1 was 4.4%. NCO% is a value measured in accordance with JIS K1603.

(Synthesis Example B-2)
A solution of polyurethane resin B-2 (non-volatile content 75%) was obtained in the same manner as in Synthesis Example B-1 described above, except that the types and amounts of each component shown in the upper row of Table 2 were used.

<Synthesis of Polyurethane Resin C>
(Synthesis Example C-1)
600 parts of POL7, 161 parts of MN-F300, 5.35 parts of TMP, and 177 parts of TDI were placed in a synthesis vessel. An appropriate amount of stannous octoate was added while stirring the contents, and the mixture was reacted at 90° C. for 5 hours. 428 parts of EA was added to dilute the mixture, and a solution of polyurethane resin C-1 (75% non-volatile content) with a hydroxyl value of 9.7 mgKOH/g was obtained.

<Synthesis of Polyurethane Resin A (2)>
(Synthesis examples A-8 to 13)
Solutions of polyurethane resins A-8 to A-13 (non-volatile content 70%) were obtained in the same manner as in Synthesis Example A-1, except that the types and amounts of each component shown in Table 3 were used.

<Synthesis of Polyurethane Resin B (2)>
(Synthesis Example B-3)
62.5 parts of TDI, 210 parts of MDI, 600 parts of POL7, and 16.1 parts of TMP were placed in a synthesis vessel. The contents were reacted at 90° C. for 5 hours with stirring, and then 222 parts of EA were added to dilute the mixture, thereby obtaining a solution of polyurethane resin B-3 (non-volatile content 80%).

<Preparation of Adhesive Composition>
(Examples 1 to 8, Comparative Examples 1 to 7)
The prepared polyurethane resin solutions were blended in the combination shown in Table 4 to prepare a two-component curing adhesive composition. Specifically, polyurethane resin A was used as the main component, polyurethane resin B was used as the curing agent, and the respective solutions were blended so that the molar ratio (NCO/OH (molar ratio)) of the isocyanate group (NCO) in polyurethane resin B to the hydroxyl group (OH) in polyurethane resin A was the value shown in Table 4. EA was then added to dilute the mixture, and an adhesive composition with a solid content of 30% was prepared.

<Evaluation>
The prepared adhesive compositions were subjected to evaluations of (1) adhesive strength test (PP adhesion), (2) adhesive strength test (metal adhesion), (3) heat resistance, (4) NCO decay rate, and (5) wettability. The results are shown in Table 5.

(1) Adhesion strength test (PP adhesion)
The prepared adhesive composition was applied to a stretched polypropylene film (corona-treated, thickness 25 μm) so that the solid resin content was 3.0 g/m ² -dry. After drying the dilution solvent using a dryer, an unstretched polypropylene film (corona-treated, thickness 30 μm) was placed and laminated through a nip roll (nip temperature 40° C., roll pressure 3 MPa). Then, aging was performed for 2 days at 40° C. to obtain a laminate film. A 15 mm wide test piece cut out from the obtained laminate film was used as an evaluation sample. For this evaluation sample, a tensile tester (model name "EZ-S", manufactured by Shimadzu Corporation) was used to measure the T-peel strength (N/15 mm) at a tensile speed of 300 mm/min under an environment of 25° C. and 65% RH, and the PP adhesion was evaluated according to the following evaluation criteria.
⊚: T-peel strength was 2.3 N/15 mm or more.
◯: The T-peel strength was 1.9 N/15 mm or more and less than 2.3 N/15 mm.
Δ: The T-peel strength was 1.7 N/15 mm or more and less than 1.9 N/15 mm.
×: The T-peel strength was less than 1.7 N/15 mm.

(2) Adhesion strength test (metal adhesion)
The prepared adhesive composition was applied to a stretched polypropylene film (corona-treated, thickness 25 μm) so that the solid resin content was 3.0 g/m ² -dry. After drying the dilution solvent using a dryer, a metal-deposited unstretched polypropylene film (corona-treated, thickness 30 μm) was placed on it and laminated through a nip roll (nip temperature 40° C., roll pressure 3 MPa). Then, the laminate film was aged at 40° C. for 2 days to obtain a laminate film. A 15 mm wide test piece cut out from the obtained laminate film was used as an evaluation sample. For this evaluation sample, a tensile tester (model name "EZ-S", manufactured by Shimadzu Corporation) was used to measure the T-peel strength (N/15 mm) at a tensile speed of 300 mm/min under an environment of 25° C. and 65% RH, and the metal adhesion was evaluated according to the following evaluation criteria.
⊚: T-peel strength was 0.9 N/15 mm or more.
◯: The T-peel strength was 0.5 N/15 mm or more and less than 0.9 N/15 mm.
×: The T-peel strength was less than 0.5 N/15 mm.

(3) Heat resistance The prepared adhesive composition was applied to a stretched nylon film (corona-treated, thickness 15 μm) so that the solid resin content was 3.0 g/m ² -dry. After drying the dilution solvent using a dryer, an unstretched polyethylene sealant film (corona-treated, thickness 50 μm) was placed and laminated through a nip roll (nip temperature 40° C., roll pressure 3 MPa). Then, aging was performed for 2 days at 40° C. to obtain a laminate film. The unstretched polyethylene sealant film sides of the obtained laminate films were placed face to face, and a 1 cm wide seal bar was used to make a three-sided sealed bag under sealing conditions of 160° C., 0.1 MPa, and 1 second to prepare a sample bag with an inner side of 8 cm x 12.5 cm. 100 g of water was filled into the sample bag through the filling port, and the filling port was sealed to prepare 10 sample bags filled with the contents. A heat resistance test was conducted by boiling sterilization of the content-filled sample bags at 98° C. for 30 minutes using a sterilization tester (model "SR-240", manufactured by Tommy Seiko Co., Ltd.). After the heat resistance test, the state of lifting due to peeling in the laminate film constituting the sample bag was visually observed, and the heat resistance was evaluated according to the following evaluation criteria.
◯: No floating was observed in any of the 10 bags.
×: Floating was observed in one or more of the ten bags.

(4) NCO decay rate The prepared adhesive composition was applied to a stretched polypropylene film (corona-treated, thickness 25 μm) so that the solid resin content was 3.0 g/m ² -dry. After drying the dilution solvent using a dryer, a stretched polypropylene film (corona-treated, thickness 25 μm) was placed and laminated through a nip roll (nip temperature 40° C., roll pressure 3 MPa) to obtain a laminate film. While aging the obtained laminate film under conditions of 40° C. and 5% RH, IR measurement was performed over time using a Fourier transform infrared spectrophotometer (product name "FT/IR-4600", manufactured by JASCO Corporation), and the NCO decay rate was calculated from the peak of the isocyanate group (near 2,260 cm ⁻² ). After performing IR measurement for up to 80 hours under conditions of 40° C. and 5% RH, the film was left for 3 days under conditions of 25° C. and 65% RH to completely cure. The NCO decay rate was calculated for each elapsed time, with the NCO decay rate in a completely cured state taken as the standard (100%), and the NCO decay rate was evaluated according to the following evaluation criteria. The higher the NCO decay rate, the shorter the curing time after bonding to the substrate, and therefore the time required for aging can be shortened.
⊚: NCO decay rate after 24 hours was 81% or more.
◯: The NCO decay rate after 24 hours was 65% or more and less than 81%.
x: The NCO decay rate after 24 hours was less than 65%.

(5) Wettability If the fluidity of the adhesive composition or the wettability to the substrate is not very good, the roll-to-roll processing conditions result in instantaneous thermocompression bonding, which tends to cause air bubble entrapment defects. The wettability of the adhesive composition was evaluated by checking the presence or absence of appearance defects after lamination using the following procedure. The prepared adhesive composition was applied to a stretched polypropylene film (corona-treated, thickness 25 μm) so that the solid resin content was 3.0 g/m ² -dry. After drying the dilution solvent using a dryer, a stretched polypropylene film (corona-treated, thickness 25 μm) was placed on it and laminated through a nip roll (nip temperature 40° C., roll pressure 3 MPa) to obtain a laminate film. The appearance of the obtained laminate film was observed, and the wettability was evaluated according to the evaluation criteria shown below.
◯: No air bubble entrapment defects were observed.
×: Air bubble entrapment defects were observed.

The adhesive composition of the present invention is useful as a material for forming adhesive layers that constitute various laminates. In addition, because it has high wettability to substrates, it is expected that a small amount of coating will suffice.

Claims (8)

The polyurethane resin A contains a hydroxyl group at its terminal, a polyurethane resin B contains an isocyanate group at its terminal, and an organic solvent;
The polyurethane resin A has a structural unit derived from a polyol (a) represented by the following formula (1), a structural unit derived from a chain extender (b), and a structural unit derived from an aromatic diisocyanate,
The polyurethane resin B has a structural unit derived from a polyol (c) represented by the following formula (2),
the chain extender (b) comprises a triol compound (b1) and a polyol compound (b2) other than the triol compound (b1);
The adhesive composition, wherein the mass ratio of the polyol (a) to the polyol (c) is (a)/(c)=70/30 to 30/70.

(In the formula (1), n represents a number such that the number average molecular weight of the polyol (a) is 400 to 3,000, and in the formula (2), m represents a number such that the number average molecular weight of the polyol (c) is 300 to 2,000.) The adhesive composition according to claim 1, wherein the ratio of the content of the polyurethane resin B to the content of the polyurethane resin A is a molar ratio of the isocyanate groups (NCO) in the polyurethane resin B to the hydroxyl groups (OH) in the polyurethane resin A, NCO/OH = 1.05 or more. The hydroxyl value of the polyurethane resin A is 5.0 to 40.0 mgKOH/g,
2. The adhesive composition according to claim 1, wherein the polyurethane resin B has an isocyanate group content of 3.2 to 5.1%. The hydroxyl value of the polyol compound (b2) is 200 to 1,200 mgKOH/g;
The adhesive composition according to any one of claims 1 to 3, wherein a ratio ((a)/(b)) of the average hydroxyl value (mg KOH/g) of the polyol (a) to the average hydroxyl value (mg KOH/g) of the chain extender (b) is 0.15 to 0.70. The adhesive composition according to any one of claims 1 to 3, wherein the polyol compound (b2) is at least one selected from the group consisting of a compound obtained by ring-opening addition of 1 mole of an acid anhydride to 1 mole of a trifunctional polyol, dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, dimethylolheptanoic acid, dimethyloloctanoic acid, and dimethylolnonanoic acid. The adhesive composition according to any one of claims 1 to 3, wherein the biomass content of the polyurethane resin A is 10% by mass or more. An adhesive resin layer that is a coating and drying product of the adhesive composition according to any one of claims 1 to 3. A first substrate, a second substrate, and the adhesive resin layer according to claim 7 disposed between the first substrate and the second substrate,
The laminate, wherein the second substrate is a plastic film, a metallized film, or a metal foil.