Adhesive composition and adhesive sheet

Abstract

To provide an adhesive composition which satisfies adhesive properties sufficiently even when the adhesive has a high biomass content and a high usage ratio of biodegradable raw materials, and which exhibits low substrate contamination in a moist heat resistance test and excellent substrate adhesion at low temperatures, and to provide an adhesive sheet using the adhesive composition. [Solution] A pressure-sensitive adhesive composition comprising a hydroxyl group-containing urethane prepolymer (A) which is a reaction product of a polyol (ax) having a number average molecular weight of 1,000 to 45,000, a multifunctional polyol (ay) (excluding polyol (ax)), and a polyisocyanate (az), wherein the polyol (ax) is a copolymer of a monomer mixture containing a monomer (ax'1) having a lactic acid unit and a monomer (ax'2) (excluding lactic acid) having at least one of a lactone unit and an aliphatic hydroxycarboxylic acid unit, and the hydroxyl group-containing urethane prepolymer (A) has a glass transition temperature of -60°C to -10°C.

Description

Technical Field

[0001] Embodiments of the present invention relate to an adhesive composition and an adhesive sheet using the same.

Background Art

[0002] For example, an adhesive that constitutes an adhesive label of a container typically contains a petroleum-derived raw material. The adhesive label may be peeled off from the container after use or discarded in the soil while still attached to the container. In this case, since the decomposition rate of the adhesive that constitutes the adhesive label is extremely slow, the adhesive remains in the soil semi-permanently, and may even cause damage to the ecosystem in the soil. In addition, when a product containing a petroleum-derived raw material is incinerated, carbon dioxide is generated, which is one of the causes of the progression of global warming. For these reasons, in recent years, the use of biodegradable raw materials or raw materials derived from biomass, which are renewable raw materials, has begun to be recommended.

[0003] Among the raw materials of the adhesive composition, polyester polymers using biodegradable raw materials or raw materials derived from biomass are known. Patent Document 1 discloses an adhesive composition containing a biodegradable polyester polymer obtained by copolymerizing lactic acid and caprolactone, a tackifier resin, and an isocyanate curing agent.

[0004] Further, Patent Document 2 discloses an adhesive composition containing a polyester polymer obtained by copolymerizing lactic acid, a dibasic acid, and a glycol component, having a glass transition temperature of -70 to -20°C, a weight average molecular weight of 20,000 to 300,000, and a hydroxyl value of 1 to 100 mgKOH / g.

[0005] However, with the adhesive compositions using the polyester polymers disclosed in Patent Documents 1 and 2, it has been difficult to obtain sufficient adhesive properties. In particular, since the main bonding site of the polymer chain of the polyester polymer is an ester bond and the wettability to the substrate is insufficient, the re-peelability is inadequate. Furthermore, under humid and heat conditions, the polyester polymer undergoes cohesive failure during peeling due to hydrolysis of the ester group, and substrate contamination is likely to occur. Also, the ester bond at the main bonding site has a problem in that the adhesion to the substrate at low temperatures is insufficient and the adhesive strength at low temperatures is low because it enhances the crystallinity of lactic acid.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Thus, in the conventional adhesive compositions containing a polyester polymer using a biodegradable raw material or a biomass-derived raw material which is a renewable raw material, it is difficult to satisfy the adhesive properties and further to fully satisfy these properties such as substrate contaminability in a humid and heat test and substrate adhesion at low temperatures. Therefore, an embodiment of the present invention provides an adhesive composition which uses a biodegradable raw material or a biomass-derived raw material and is excellent in adhesive properties, substrate contaminability, and substrate adhesion at low temperatures.

Means for Solving the Problems

[0008] The present inventors have conducted intensive studies to solve the above problems and completed the present invention. That is, the embodiments of the present invention relate to the following. However, the present invention is not limited to the embodiments described below and includes various embodiments.

[0009] One embodiment of the present invention includes a urethane prepolymer (A) having a hydroxyl group, which is a reaction product of a polyol (ax), a polyfunctional polyol (ay) (excluding the polyol (ax)), and a polyisocyanate (az). The polyol (ax) is a copolymer of a monomer mixture containing a monomer (ax'1) having a lactic acid unit and a monomer (ax'2) having at least one of a lactone unit and an aliphatic hydroxycarboxylic acid unit (excluding lactic acid). The number average molecular weight of the polyol (ax) is 1,000 to 45,000. The urethane prepolymer (A) having a hydroxyl group relates to an adhesive composition having a glass transition temperature of -60°C to -10°C.

[0010] Another embodiment of the present invention relates to an adhesive sheet having a substrate and an adhesive layer formed from the adhesive composition of the above embodiment on at least one surface of the substrate.

Effects of the Invention

[0011] According to the present invention, it is possible to provide an adhesive composition having a high biomass content and a high usage ratio of biodegradable raw materials, which sufficiently satisfies the adhesive properties, is excellent in substrate stainability in a damp heat test, and is also excellent in substrate adhesion at low temperatures. Further, it is possible to provide an adhesive sheet using the above adhesive composition.

Modes for Carrying Out the Invention

[0012] Terms are defined before the description of the present invention. As used herein, the "adhesive sheet" means including a substrate and an adhesive layer made of a cured product of the adhesive composition of the present invention.

[0013] The numerical range specified using "~" in this specification means including the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. Unless otherwise noted, each of the various components described in this specification may be used alone or in combination of two or more thereof independently.

[0014] In this specification, the monomer (ax’1) having a lactic acid unit, the monomer (ax’2) having at least one of a lactone unit and an aliphatic hydroxycarboxylic acid unit, and the other monomer (ax’3) may be abbreviated as monomer (ax’1), monomer (ax’2), and monomer (ax’3), respectively. Further, the urethane prepolymer (A) having a hydroxyl group may be abbreviated as urethane prepolymer (A).

[0015] In this specification, "Mw" is the weight-average molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC) measurement. "Mn" is the number-average molecular weight in terms of polystyrene determined by GPC measurement. These can be measured by the method described in the section of [Examples].

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, the following description is an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents unless it exceeds the gist thereof.

[0017] <1> Pressure-sensitive adhesive composition The pressure-sensitive adhesive composition according to one embodiment of the present invention contains at least a urethane prepolymer (A) having a hydroxyl group. The pressure-sensitive adhesive composition may further contain a curing agent, a tackifier resin, a plasticizer, or other optional components as needed. The pressure-sensitive adhesive composition may further contain a solvent.

[0018] An adhesive composition according to an embodiment of the present invention contains a specific urethane prepolymer (A) having a urethane bond in the molecule, thereby improving the wettability to a substrate and obtaining excellent releasability. Further, in a damp heat test, decomposition of the bonding sites in the polymer is suppressed, so that the substrate stainability is low. Furthermore, since the crystallinity derived from lactic acid in the polymer is suppressed, not only is the adhesive property excellent, but also the adhesion to the substrate at low temperatures is good, and these performances can be satisfied.

[0019] <Urethane prepolymer (A)> The urethane prepolymer (A) is a urethane prepolymer having a hydroxyl group, which is a reaction product of a polyol (ax), a polyfunctional polyol (ay) (excluding the polyol (ax)), and a polyisocyanate (az).

[0020] The above "reaction product" means a reaction product of a polyol (ax), a polyfunctional polyol (ay), and a polyisocyanate (az). The polyol (ax) preferably has two hydroxyl groups in one molecule. Further, the polyfunctional polyol (ay) preferably has two or more hydroxyl groups in one molecule. The polyisocyanate (az) is preferably a bifunctional isocyanate (also referred to as a diisocyanate) having two isocyanate groups in one molecule. The isocyanate groups (isocyanato groups) of the polyisocyanate (az) are used in a molar ratio (NCO / OH) such that they are less than the total number of hydroxyl groups of the polyol (ax) and the polyfunctional polyol (ay). Thereby, the obtained urethane prepolymer becomes a urethane prepolymer having a hydroxyl group.

[0021] The above polyol (ax) is a copolymer of a monomer mixture containing a monomer (ax'1) having a lactic acid unit and a monomer (ax'2) having at least one of a lactone unit and an aliphatic hydroxycarboxylic acid unit (excluding lactic acid). By including the monomer (ax'1) and the monomer (ax'2) in the monomer mixture constituting the above polyol (ax), the glass transition temperature of the urethane prepolymer (A) and the crystallinity derived from lactic acid can be appropriately controlled respectively, and sufficient substrate adhesion and adhesiveness at low temperatures can be obtained.

[0022] The number average molecular weight (Mn) of the above polyol (ax) may be 1,000 to 45,000 or less. When the above Mn is within the above range, urethane bonds can be appropriately introduced. By introducing urethane bonds, the decomposition of the bonding sites in the polymer is suppressed in the damp heat test, and the substrate stainability is reduced. Also, due to the improvement of the cohesive force, the adhesiveness is improved. Furthermore, the wettability is improved and the re-peelability is also improved.

[0023] The glass transition temperature (Tg) of the above urethane prepolymer (A) is -60°C to -10°C. The above Tg is more preferably -50°C to -12°C, and even more preferably -45°C to -15°C. When the glass transition temperature is within the above range, an appropriate cohesive force is obtained by the entanglement of the polymer chains, and sufficient adhesiveness is obtained. Specifically, when the glass transition temperature is adjusted to -60°C or higher, sufficient cohesive force is obtained, and the adhesiveness can be easily increased. Also, when the glass transition temperature is adjusted to -10°C or lower, it is possible to suppress the excessive increase in the cohesive force at low temperatures, and excellent substrate adhesion and excellent adhesive properties at low temperatures can be easily obtained.

[0024] In one embodiment, the urethane prepolymer (A) is a urethane prepolymer having a hydroxyl group, which is a reaction product of a polyol (ax) having a number average molecular weight of 1,000 to 45,000, a polyfunctional polyol (ay) (excluding the polyol (ax)), and a polyisocyanate (az), and has a glass transition temperature of -60°C to -10°C.

[0025] As described above, according to the polyol (ax) having a number average molecular weight of 1,000 to 45,000 and the urethane prepolymer (A) having a glass transition temperature of -60 to -10°C, even when a large amount of the monomer (ax'1) and the monomer (ax'2), which are biomass raw materials or biodegradable raw materials, are used in order to increase the biomass ratio or the usage ratio of biodegradable raw materials, it is possible to easily configure an adhesive composition excellent in each of the substrate contamination property in the wet heat test, the substrate adhesion property at low temperature, and the adhesive property.

[0026] The weight average molecular weight of the urethane prepolymer (A) is preferably 10,000 to 200,000, more preferably 30,000 to 180,000, and still more preferably 40,000 to 150,000. When the weight average molecular weight of the urethane prepolymer (A) is adjusted within the above range, it is possible to impart an aggregating force due to the entanglement of the polymer chains, and it becomes easy to increase the adhesive force. Further, in addition to the improvement of the adhesive force, since it is possible to improve the wettability and the aggregating force due to the urethane bond formed by urethanization, it is preferable because it becomes easier to impart re-peelability and increase the adhesive force. In particular, when the weight average molecular weight is adjusted to 200,000 or less, it is preferable in that it is possible to suppress the decrease in the holding force due to the decrease in the aggregating force.

[0027] Hereinafter, the constituent components of the adhesive composition will be described more specifically. [Polyol (ax)] In one embodiment, the polyol (ax) is obtained by copolymerization of a monomer mixture containing a monomer (ax'1) having a lactic acid unit and at least one of a monomer having a lactone unit and a monomer having an aliphatic hydroxycarboxylic acid unit (however, lactic acid is excluded) (ax'2). The monomer mixture may further contain other monomers (ax'3) as necessary. By appropriately selecting the other monomers (ax'3), it becomes easy to control the molecular weight of the polyol, and it is possible to easily obtain a polyol (ax) having a desired number average molecular weight.

[0028] Based on the total mass of the monomer mixture constituting the polyol (ax), the total content of monomer (ax’1) and monomer (ax’2) is preferably 10 to 99.8% by mass, more preferably 50 to 99.8% by mass, and even more preferably 60 to 99.8% by mass. When the total content is within the above range, it is preferable in that the glass transition temperature of the urethane prepolymer (A) can be easily adjusted to an appropriate range, and the adhesion characteristics can be easily improved.

[0029] When increasing the biomass content or the usage ratio of the biodegradable raw material, it is preferable to increase the content of at least one of monomer (ax’1) and monomer (ax’2) which are biomass raw materials or biodegradable raw materials. In one embodiment, it is particularly preferable that both monomer (ax’1) and monomer (ax’2) are monomers of biomass raw materials or biodegradable raw materials. In other embodiments, in order to increase the biomass content or the usage ratio of the biodegradable raw material, the content of monomer (ax’3) which is a biomass raw material or a biodegradable raw material can also be increased.

[0030] According to the pressure-sensitive adhesive composition of one embodiment of the present invention, even when a large amount of monomer (ax’1) and monomer (ax’2) are used, or when the content of monomer (ax’3) is increased, in order to increase the biomass content or the usage ratio of the biodegradable raw material, it is possible to provide a pressure-sensitive adhesive composition that not only has excellent adhesion characteristics, but also has excellent substrate stainability in a damp heat test and excellent substrate adhesion at low temperatures.

[0031] The ratio (ax’1) / (ax’2) of the content of monomer (ax’1) to the content of monomer (ax’2) in the monomer mixture constituting the polyol (ax) is preferably 10 / 90 to 90 / 10, more preferably 20 / 80 to 80 / 20, and even more preferably 30 / 70 to 70 / 30. In one embodiment, the ratio (ax’1) / (ax’2) is even more preferably 40 / 60 to 60 / 40, and most preferably 50 / 50. By adjusting the ratio (ax’1) / (ax’2) within the above range, even when the biomass content in the adhesive is high and the usage ratio of biodegradable raw materials is high, the desired adhesive properties can be easily obtained.

[0032] The number average molecular weight (Mn) of the polyol (ax) may be 1,000 or more, preferably 2,500 or more. On the other hand, the above Mn may be 45,000 or less, preferably 40,000 or less, more preferably 37,000 or less, and even more preferably 35,000. In one embodiment, the above Mn may be 1,000 to 45,000. The above Mn may preferably be 1,000 to 35,000, and even more preferably 2,500 to 35,000.

[0033] When the above Mn is adjusted within the above range, the wettability and cohesive force due to urethane bonds can be easily controlled. Specifically, when the above Mn is adjusted to 1,000 or more, it is possible to suppress the excessive increase in the number of urethane bonds of the polymer obtained by urethanization. That is, in tests under heating such as heat and humidity resistance, it is possible to suppress the excessive improvement in adhesion due to the rearrangement of urethane groups and the occurrence of cohesive failure, thereby facilitating the improvement of substrate contamination. In addition, when the above Mn is adjusted to 45,000 or less, it is possible to suppress the shortage of urethane bond numbers and the deterioration of heat and humidity resistance and re-peelability.

[0034] In one embodiment, from the viewpoint of easily obtaining more excellent re-peelability, the Mn of the polyol (ax) may exceed 10,000 and be 35,000 or less. The above Mn may more preferably be 11,000 to 30,000, and even more preferably 11,000 to 25,000.

[0035] In other embodiments, the Mn of the polyol (ax) may be 1,000 to 10,000, and more preferably 2,000 to 7,500.

[0036] (Monomer (ax’1)) The monomer (ax’1) having a lactic acid unit only needs to have a lactic acid unit and is not particularly limited. For example, lactic acid monomers (ax’1-1) such as L-lactic acid and D-lactic acid, lactide monomers (ax’1-2) such as L-lactide, D-lactide, DL-lactide, and meso-lactide can be mentioned. By copolymerizing such a monomer (ax’1) having a lactic acid unit with a monomer (ax’2) described later, a urethane prepolymer (A) having desired properties can be obtained. The above-mentioned monomer (ax’1) having a lactic acid unit can be used alone or in combination of two or more.

[0037] In addition, the "lactic acid unit" in this specification means the "-O-CH(CH3)―CO-" unit which is a partial structure of lactic acid. Among the lactic acid monomer (ax’1-1) and the lactide monomer (ax’1-2), the lactide monomer (ax’1-2) is more preferable. From the viewpoint of reactivity, the lactide monomer has excellent copolymerizability and can lower the crystallinity, thereby easily improving the peelability.

[0038] The lactic acid monomer (ax’1-1) and the lactide monomer (ax’1-2) are raw materials derived from biomass and are biodegradable raw materials. Among them, from the viewpoints of reactivity control during polyol production and solubility in solvents, the lactide monomer (ax’1-2) is preferable. The lactide monomer (ax’1-2) contains at least one selected from the group consisting of L-lactide, D-lactide, DL-lactide, and meso-lactide. Here, DL-lactide means an equimolar mixture of L-lactide and D-lactide.

[0039] From the viewpoint of reducing the crystallinity derived from lactic acid and improving the adhesion of the substrate at low temperatures, as the lactide monomer (ax’1-2), a combination of L-lactide and D-lactide, DL-lactide, or meso-lactide is preferable. In particular, from the viewpoints of being amorphous, improving wettability, and further improving peelability, meso-lactide is preferable. When using L-lactide and D-lactide in combination, the weight ratio of L-lactide / D-lactide is preferably from 5 / 95 to 95 / 5, more preferably from 15 / 85 to 85 / 15. By being within this range, the crystallinity of lactic acid in the urethane prepolymer (A) can be lowered, and the adhesion to the substrate at low temperatures can be improved.

[0040] In one embodiment, the monomer (ax'1) having a lactic acid unit preferably contains at least meso-lactide. In one embodiment, the monomer (ax'1) having a lactic acid unit may further contain other lactide forms such as L-lactide, D-lactide, and DL-lactide in addition to meso-lactide. For example, in the production of meso-lactide, lactide forms other than meso-lactide are removed in the purification step. However, in this embodiment, unpurified meso-lactide may be used. That is, at least one of L-lactide, D-lactide, and DL-lactide may be mixed in addition to meso-lactide.

[0041] The content of the monomer (ax'1) is preferably 5 to 92% by mass, more preferably 15 to 70% by mass, based on the total mass of the monomer mixture constituting the polyol (a). When the above content is adjusted within the above range, the glass transition temperature of the urethane prepolymer (A) can be appropriately adjusted, which is preferable in that excellent adhesion to the substrate and excellent adhesive strength at low temperatures can be easily obtained.

[0042] (Monomer (ax'2)) The monomer (ax'2) is a monomer having at least one of a lactone unit and an aliphatic hydroxycarboxylic acid unit. In one embodiment, one kind of monomer or two or more kinds of monomers may be used as the monomer (ax'2). In one embodiment, the monomer (ax’2) may be at least one of a monomer (ax’2-1) having an aliphatic hydroxycarboxylic acid unit (excluding lactic acid) and a monomer (ax’2-2) having a lactone unit. In one embodiment, the monomer (ax’2) preferably contains at least a monomer (ax’2-2) having a lactone unit.

[0043] By copolymerizing these monomers (ax’2) with a monomer (ax’1) having a lactic acid unit, the crystallinity of the lactic acid component in the urethane prepolymer (A) can be reduced, and the glass transition temperature can be adjusted to an appropriate range. As a result, a urethane prepolymer (A) can be obtained that can realize excellent properties such as adhesive strength in the adhesive composition.

[0044] Examples of the monomer (ax’2-1) having an aliphatic hydroxycarboxylic acid unit include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid, and the like. Examples of the monomer (ax’2-2) having a lactone unit include lactones having 3 to 12 carbon atoms. For example, β-propiolactone, β-butyrolactone, δ-valerolactone, ε-caprolactone, enanthrolactone, caprylolactone, laurolactone, and the like can be mentioned.

[0045] Among the monomer (ax’2-1) having an aliphatic hydroxycarboxylic acid unit and the monomer (ax’2-2) having a lactone unit, the monomer (ax’2-2) having a lactone unit is preferred. The monomer (ax’2-2) having a lactone unit is excellent in copolymerizability from the viewpoint of reactivity, and can easily lower the crystallinity of the lactic acid component, so that the re-peelability can be easily improved. Among the monomers (ax’2-2) having a lactone unit, ε-caprolactone or 6-hydroxycaproic acid is preferred from the viewpoint of biodegradability. The above-mentioned monomer (ax’2-2) having a lactone unit may be used alone or in combination of two or more.

[0046] The content rate of the monomer (ax’2) is preferably 5 to 92% by mass, more preferably 18 to 70% by mass, based on the total mass of the monomer mixture constituting the polyol (ax). When the content rate is adjusted within the above range, the glass transition temperature of the urethane prepolymer (A) can be appropriately adjusted, which is preferable in that excellent substrate adhesion at low temperatures and excellent adhesive strength can be easily obtained.

[0047] (Monomer (ax’3)) The monomer (ax’3) is other monomers other than the monomer (ax’1) and the monomer (ax’2), and is not particularly limited as long as it has reactivity with the monomer (ax’1) and the monomer (ax’2). For example, as the monomer (ax’3), polyols such as aliphatic glycols, polyester polyols which are reaction products of aliphatic dibasic acids and glycols, polyether polyols, polybutadiene polyols, and castor oil polyols can be used. When the monomer mixture constituting the polyol (ax) further contains other monomers (ax’3), it becomes easier to lower the crystallinity of the lactic acid component in the urethane prepolymer (A).

[0048] In order to increase the biomass degree or the content rate of the biodegradable raw material, the monomer (ax’3) is also preferably a biomass-derived raw material or a biodegradable raw material. In one embodiment, a polyester polyol can be particularly preferably used as the monomer (ax’3). When a polyester polyol is used, it has excellent compatibility with the monomers (ax’1) and (ax’2), and the copolymerizability is improved, so that the crystallinity of the lactic acid component can be reduced and the re-peeling property can be easily enhanced.

[0049] The aliphatic glycols that can be used as the monomer (ax’3) are not particularly limited. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,5-pentanediol, 2-ethyl-2-butylpropanediol, 1,9-nonanediol, 2-methyloctanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, etc. can be mentioned. In particular, 1,2-propylene glycol and 1,3-propanediol are preferred because they are obtained from biomass-derived raw materials and are biodegradable raw materials. The above aliphatic glycols may be used alone or in combination of two or more.

[0050] The polyester polyol that can be used as the monomer (ax’3) is obtained, for example, by subjecting an aliphatic dibasic acid and an aliphatic glycol to a condensation reaction. The above polyester polyol preferably contains an aliphatic polyester polyol having a hydroxyl group at the terminal and having a COOH / OH molar ratio of less than 1.0. Such an aliphatic polyester polyol is preferable because, unlike aromatic polyester polyols, there are many enzymes in nature that can decompose the aliphatic polyester polyol.

[0051] Examples of the aliphatic dibasic acid include aliphatic and alicyclic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, dodecenyl succinic anhydride, fumaric acid, succinic acid, dodecanedioic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, maleic acid, maleic anhydride, itaconic acid, and citraconic acid. In particular, sebacic acid and succinic acid are preferred because they are obtained from biomass-derived raw materials and are biodegradable raw materials. The above aliphatic dibasic acid may be used alone or in combination of two or more. On the other hand, the aliphatic glycol is as described above.

[0052] In the present invention, an aromatic dibasic acid can be used as a raw material of the polyester polyol as long as the characteristics of the desired adhesive, the biomass degree of the adhesive, and the ratio of the biodegradable raw material in the adhesive are not reduced. The aromatic dibasic acid that can be used is not particularly limited. For example, terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 2,2'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, etc. may be mentioned. These may be used alone or in combination of two or more.

[0053] In the polyester polyol, the smaller the number of carbon atoms in the alkylene chain of the aliphatic dibasic acid used during production, the more the hard segment phase increases in the polymer. As a result, the intrusion of moisture can be effectively prevented, and the tendency is that the wet heat resistance can be easily improved. Also, from the same viewpoint, it is preferable that the alkylene chain of the aliphatic glycol also has a small number of carbon atoms. From such a viewpoint, in one embodiment, the polyester polyol may be, for example, a polymer of an aliphatic dibasic acid having an alkylene chain with 2 to 12 carbon atoms and an aliphatic glycol having a linear or branched alkylene chain with 2 to 10 carbon atoms.

[0054] As the aliphatic dibasic acid, for example, at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid is preferable. Among them, sebacic acid and succinic acid are more preferable, and succinic acid is even more preferable, in combination with being obtained from biomass-derived raw materials and being biodegradable raw materials.

[0055] As the aliphatic glycol, for example, at least one selected from the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2-methyloctanediol is preferable. Among them, 1,2-propylene glycol and 1,3-propanediol are more preferable, and 1,3-propanediol is even more preferable.

[0056] In one embodiment, commercially available products can also be used as the polyester polyol. For example, Kuraray Polyol P-1010 and P-2010 manufactured by Kuraray Co., Ltd. can be mentioned. These are copolymers of adipic acid and 3-methyl-1,5-pentanediol.

[0057] The polyether polyol that can be used as the monomer (ax’3) may be, for example, a reaction product obtained by addition polymerization of one or more oxirane compounds using an active hydrogen-containing compound having two active hydrogens in one molecule as an initiator. Examples of the oxirane compound include alkylene oxides (AO) such as ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO); and tetrahydrofuran (THF). In one embodiment, a commercially available product can also be used as the polyether polyol. For example, "Sun Nix PP-600" (polyoxypropylene glycol) manufactured by Sanyo Chemical Industries, Ltd. can be used.

[0058] The polybutadiene-modified polyol that can be used as the monomer (ax'3) has, for example, two or more hydroxyl group terminals, and may have a 1,2-vinyl site, a 1,4-cis site, a 1,4-trans site, or a structure in which they are hydrogenated, and may be a linear or branched polybutadiene.

[0059] The castor oil polyol that can be used as the monomer (ax'3) may be, for example, a polyol derived from castor oil or a polyol obtained by modifying castor oil.

[0060] Examples of the polyol derived from the castor oil include those in which a part of the ricinoleic acid of this glycerin ester is substituted with oleic acid, those obtained by esterifying ricinoleic acid obtained by saponifying castor oil with a short-chain polyol, and mixtures of these with castor oil, etc., and may be fatty acid ester polyols derived from castor oil.

[0061] Examples of the polyol obtained by modifying the castor oil include vegetable oil-modified polyols, modified polyols having an aromatic skeleton (such as bisphenol A, etc.). The vegetable oil-modified polyol is obtained by substituting a part of the ricinoleic acid of the glycerin ester with higher fatty acids such as linoleic acid, linolenic acid, and oleic acid obtained from other plants such as soybean oil, rapeseed oil, and olive oil.

[0062] Examples of commercially available products of castor oil-derived polyols include "URIC HF-1300, Y-403, HF-2009" manufactured by Ito Seiyu Co., Ltd.

[0063] In one embodiment, the number average molecular weight (Mn) of the monomer (ax’3) is preferably from 50 to 3,000, more preferably from 500 to 2,000. In one embodiment, the Mn of the polyester polyol used as the monomer (ax’3) is preferably from 150 to 3,000, more preferably from 200 to 2,000, and even more preferably from 200 to 800. When the monomer (ax’3) having Mn within the above range is used, since the crystallinity of the component derived from the monomer (ax’3) is low, the crystallinity of the lactic acid component in the urethane prepolymer (A) tends to be easily reduced. As a result, the peelability and the wet heat resistance can be easily enhanced.

[0064] In one embodiment, the monomer mixture constituting the polyol (ax) preferably does not contain a compound having active hydrogen such as a hydroxyl group only at one end and a compound in which an acidic group such as a sulfonate forms a salt, from the viewpoint of obtaining sufficient reactivity in urethanization. Therefore, in one embodiment, the monomer mixture constituting the polyol (ax) preferably consists only of the monomer (ax’1), the monomer (ax’2), and the monomer (ax’3).

[0065] (Method for producing polyol (ax)) The method for producing the polyol (ax) is not particularly limited. The polyol (ax) can be produced by a known polymerization method such as a bulk polymerization method and a solution polymerization method. Examples of the procedure of the production method include the following. (Procedure 1) A method in which a lactic acid body is used as the monomer (ax’1) and an aliphatic hydroxycarboxylic acid body is used as the monomer (ax’2), and these are directly subjected to dehydration polycondensation (for example, the production method shown in USP 5,310,865). (Step 2) A ring-opening polymerization method in which a lactide is used as the monomer (ax’1) and a lactone is used as the monomer (ax’2), and they are melt-polymerized (for example, the production method disclosed in U.S. Patent No. 2,758,987). In this (Step 2), all of the lactide and lactone are ring-opened, and a polyol containing lactic acid units and aliphatic hydroxycarboxylic acid units is obtained. (Step 3) A method for producing a polymer by performing a dehydration polycondensation reaction in the presence of a catalyst using a lactic acid compound and an aliphatic hydroxycarboxylic acid compound, and a method for performing solid-phase polymerization in at least a part of the steps. In addition, in the above (Step 1) to (Step 3), other monomers such as an aliphatic glycol and an aliphatic dibasic acid may be copolymerized to obtain a polyol (ax).

[0066] In the above (Step 1) to (Step 3), the polyol (ax) obtained by copolymerizing the monomer (ax’1-1) of the lactic acid compound and the aliphatic hydroxycarboxylic acid compound (ax’1-1) may have insufficient copolymerizability of the monomer (ax’1-1) of the lactic acid compound and the aliphatic hydroxycarboxylic acid compound (ax’1-1). Therefore, it may be difficult to achieve the desired glass transition temperature and the crystallinity derived from lactic acid in the obtained polyol (ax), and it may be difficult to obtain the desired properties in the urethane prepolymer (A).

[0067] Therefore, the above (Step 2) is more preferable than the method for producing the polyol (ax) by copolymerizing the monomer mixture containing the monomer (ax’1-1) of the lactic acid compound and the aliphatic hydroxycarboxylic acid compound (ax’1-1) according to the above (Step 1). When a monomer mixture containing the monomer (ax’1-2) of the lactide and the monomer (ax’2-2) of the lactone is used to produce the polyol (ax) as in the above (Step 2), it is preferable in that the control of reactivity becomes easy, the copolymerizability is excellent, and the molecular weight increase is easy.

[0068] In the production of the polyol (ax), a catalyst, a solvent, etc. can be used as necessary. The catalyst may be the same as the catalyst exemplified in the production of the urethane prepolymer (A) having a hydroxyl group described later.

[0069] In one embodiment, the content of the monomer (ax'3) may be 0.2% by mass or more and 90% by mass or less based on the total mass of the monomer mixture constituting the polyol (ax). In one embodiment, the content of the monomer (ax'3) is preferably 3 to 90% by mass, more preferably 10 to 70% by mass. For example, in this embodiment, a polyester polyol having a number average molecular weight of 1,000 to 3,000 can be preferably used as the monomer (ax'3).

[0070] In another embodiment, when using a polyester polyol having a number average molecular weight of 200 to 800 as the monomer (ax'3), the content of the monomer (ax'3) is preferably 0.2 to 10% by mass based on the total mass of the monomer mixture constituting the polyol (ax). The above content is more preferably 0.7 to 9.5% by mass, and even more preferably 0.9 to 2.5% by mass.

[0071] When the content of the above monomer (ax'3) is adjusted within the above ranges respectively, the glass transition temperature of the urethane prepolymer (A) can be appropriately adjusted, which is preferable in terms of excellent substrate adhesion at low temperatures and excellent adhesive strength.

[0072] [Polyfunctional polyol (ay)] The polyfunctional polyol (ay) is a compound having two or more hydroxyl groups, preferably a compound having three or more hydroxyl groups. By containing a compound having three or more hydroxyl groups in the polyfunctional polyol (ay), a branched skeleton can be generated in the urethane prepolymer (A) and the cohesive force can be improved, so that initial curability can be imparted. However, the polyfunctional polyol (ay) excludes the polyol (ax).

[0073] The number average molecular weight of the polyfunctional polyol (ay) is preferably from 100 to 5,000, more preferably from 500 to 3,000, and even more preferably from 800 to 2,000. When the number average molecular weight is within this range, a sufficient crosslink density can be obtained by the reaction with the isocyanate curing agent (B), and the holding power is improved.

[0074] As the polyfunctional polyol (ay), an aliphatic polyol, a polyester polyol, a polyether polyol, a polybutadiene polyol, a castor oil polyol, etc. can be used. Among them, an aliphatic polyester polyol is preferable. The polyester polyol is more preferably an aliphatic polyester polyol having three or more hydroxyl groups, which is a reaction product of a polyvalent carboxylic acid and an aliphatic glycol or a reaction product of an aliphatic dibasic acid and an aliphatic polyol. The aliphatic polyester polyol is particularly preferable because many enzymes capable of decomposing them exist in nature.

[0075] Examples of the above polyvalent carboxylic acids include trimellitic acid, pyromellitic acid, benzophenone tetracarboxylic acid, biphenyl tetracarboxylic acid, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), etc. On the other hand, the above aliphatic glycol may be the same as the compounds described in the above description of the monomer (ax’3).

[0076] Examples of the above aliphatic polyols include glycerin, trimethylolpropane, pentaerythritol, etc. On the other hand, the aliphatic dibasic acid may be the same as the compounds described in the above description of the monomer (ax’3).

[0077] In one embodiment, a commercially available product can also be used as the polyfunctional polyol (ay). For example, Sunnex PP-600 manufactured by Sanyo Chemical Industries, Ltd. can be mentioned. This is a polyoxypropylene glycol, which is a copolymer of glycerin, propylene oxide (PO), and ethylene oxide (EO). Also, for example, NISSO-PBGI-3000 manufactured by Nippon Soda Co., Ltd. can be mentioned. This is a polyoxypropylene glycol which is a copolymer of glycerin, propylene oxide (PO), and ethylene oxide (EO). Also, for example, Kuraray Polyol F-1010 manufactured by Kuraray Co., Ltd. can be mentioned. This is a polyester polyol with a three-branched structure which is a copolymer of 3-methyl-1,5-pentanediol, adipic acid, and trimethylolpropane. Furthermore, for example, Placcel 410 manufactured by Daicel Corporation can be mentioned. This is a polyester polyol with a four-branched structure which is a polymer of a tetrafunctional hydroxyl group-containing compound and ε-caprolactone.

[0078] The content of the polyfunctional polyol (ay) is preferably 0.5 to 25% by mass, more preferably 5 to 15% by mass, based on the total mass of the urethane prepolymer (A). When it is 0.5% by mass or more, the branched skeleton is sufficiently formed, the cohesive force is excellent, and the initial curability is further improved. Also, when it is 25% by mass or less, it is preferable because the generation of gelated products or aggregates can be suppressed during the production of the urethane prepolymer (A).

[0079] [Polyisocyanate (az)] Known compounds can be used as the polyisocyanate (az). For example, aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates can be mentioned.

[0080] Examples of aromatic polyisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4''-triphenylmethane triisocyanate, ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate, etc.

[0081] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate, etc.

[0082] Examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatemethyl)cyclohexane, etc.

[0083] In addition, examples of the polyisocyanate include trimethylolpropane adducts, biuret bodies, allophanate bodies, and trimers (the trimers contain an isocyanurate ring) of the above polyisocyanate, and the like.

[0084] As the polyisocyanate (az), 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and the like are preferable. When at least one of these is used, cohesive force due to an appropriate urethane bond can be imparted, and sufficient adhesive properties can be easily obtained.

[0085] In the production of the urethane prepolymer (A), the molar ratio (value of NCO / OH) of the total hydroxyl groups of the polyol (ax) and the polyfunctional polyol (ay) to the isocyanate groups (isocyanato groups) of the polyisocyanate (az) may be 0.1 or more, preferably 0.2 to 0.9, more preferably 0.3 to 0.85, and still more preferably 0.4 to 0.85. It is preferable to adjust the blending ratio of the raw materials so that the above molar ratio (value of NCO / OH) falls within the above range. When the value of NCO / OH approaches 1, gelated products or aggregates may easily occur during the production of the urethane prepolymer (A). Therefore, by adjusting the value of NCO / OH to 0.9 or less, gelation during the production of the urethane prepolymer (A) can be effectively suppressed. When the value of NCO / OH is adjusted to 0.1 or more, it is preferable in that the molecular weight of the obtained urethane prepolymer (A) becomes high and sufficient adhesive properties can be obtained.

[0086] The content of the polyisocyanate (az) may be 0.3 or more based on the total mass of the urethane prepolymer (A) in order to obtain high adhesive strength, preferably 0.5 to 30% by mass, more preferably 0.6 to 20% by mass, and still more preferably 1.0 to 20% by mass.

[0087] [Catalyst] In the production of polyol (ax) or urethane prepolymer (A) having a hydroxyl group, one or more catalysts can be used as necessary. Known compounds can be used as the catalyst. Examples of the catalyst that can be used include tertiary amine compounds and organometallic compounds.

[0088] Examples of the tertiary amine compound include triethylamine, triethylenediamine, and 1,8-diazabicyclo(5,4,0)-undecene-7 (DBU).

[0089] Examples of the organometallic compound include tin-based compounds and non-tin-based compounds. Examples of the tin-based compound include dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin dimaleate, dibutyltin dilaurate (DBTDL), dibutyltin diacetate, dibutyltin sulfide, dioctyltin dilaurate, tributyltin sulfide, tributyltin oxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, tributyltin chloride, tributyltin trichloroacetate, tin 2-ethylhexanoate, and tin 2-ethylhexoate.

[0090] Examples of the non-tin-based compound include titanium-based such as dibutyltitanium dichloride, tetrabutyl titanate, and butoxytitanium trichloride; lead-based such as lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate; iron-based such as iron 2-ethylhexanoate and iron acetylacetonate; cobalt-based such as cobalt benzoate and cobalt 2-ethylhexanoate; zinc-based such as zinc naphthenate and zinc 2-ethylhexanoate; and zirconium-based such as zirconium naphthenate. The type and addition amount of the catalyst can be appropriately adjusted within the range where the reaction proceeds well.

[0091] The amount of the catalyst used is preferably 0.0001 to 1.0 part by mass, more preferably 0.001 to 0.5 part by mass, even more preferably 0.005 to 0.1 part by mass, and even more preferably 0.01 to 0.1 part by mass, based on 100 parts by mass of the total of the components of the polyol (ax) or the urethane prepolymer (A).

[0092] When using a catalyst in the production of the polyol (ax) or the urethane prepolymer (A), the above catalyst may be deactivated. In particular, in the production of the urethane prepolymer (A) having a hydroxyl group, it is preferable to use a deactivated catalyst. As a reaction terminator, for example, acetylacetone or a phosphoric acid compound can be blended. The reaction terminator may be used alone or in combination of two or more.

[0093] [Solvent] In the production of the polyol (ax) and the urethane prepolymer (A), one or more solvents can be used as necessary. Examples of the solvents that can be used include ketone solvents such as acetone and methyl ethyl ketone, ester solvents such as ethyl acetate, hydrocarbon solvents such as toluene and xylene, and ether solvents such as diphenyl ether. In particular, in the production of the urethane prepolymer (A), among the above solvents, ester solvents and hydrocarbon solvents are preferable in terms of solubility and boiling point of the solvent. In one embodiment, the pressure-sensitive adhesive composition may contain the solvent used in the production of the polyol (ax) and the urethane prepolymer (A).

[0094] [Production Method of Urethane Prepolymer (A)] The production method of the urethane prepolymer (A) is not particularly limited. The urethane prepolymer (A) can be produced, for example, by known polymerization methods such as bulk polymerization method and solution polymerization method. Examples of the procedure of the production method include the following. (Step 1) A procedure of using one or more polyisocyanates (az), one or more polyols (ax), a polyfunctional polyol (ay), one or more catalysts as required, and one or more solvents as required, and charging these into a flask all at once. (Step 2) A procedure of charging one or more polyols (ax), a polyfunctional polyol (ay), one or more catalysts as required, and one or more solvents as required into a flask, and dropwise adding one or more polyisocyanates (az) thereto.

[0095] Among these procedures, the above (Step 2) is preferable. In the above (Step 2), by suppressing a local decrease in the reactivity of the polyol (ax), the polyfunctional polyol (ay), and the polyisocyanate (az), and suppressing the reaction of excessive high molecular weight components, the molecular weight distribution can be broadened.

[0096] When using a catalyst, the reaction temperature is preferably less than 100°C, more preferably 85 - 95°C. When the reaction temperature is adjusted to less than 100°C, side reactions other than the urethane reaction can be suppressed, and thus the desired polymer can be easily obtained. When not using a catalyst, the reaction temperature is preferably 100°C or higher, more preferably 110°C or higher.

[0097] <Hardener> The adhesive composition which is one embodiment of the present invention may further contain a hardener. The use of a hardener is preferable in that it can improve the curability of the polymer. As the hardener, for example, an isocyanate hardener (B), an epoxy hardener, a melamine hardener, a carbodiimide hardener, an oxazoline hardener, an aziridine hardener, etc. can be used. In one embodiment, the adhesive composition preferably contains an isocyanate hardener (B). The use of the isocyanate hardener (B) can further improve the initial curability, and is particularly preferable in that sufficient holding power can be easily obtained.

[0098] [Isocyanate hardener (B)] As the isocyanate curing agent (B), known compounds can be used. For example, it may be a compound exemplified as the polyisocyanate (az) which is a raw material of the urethane prepolymer (A) having a hydroxyl group. Specifically, aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, and their trimethylolpropane adducts / biuret bodies / trimers can be used.

[0099] In one embodiment, the pressure-sensitive adhesive composition may further contain an isocyanate curing agent (B) as needed. The content of the isocyanate curing agent (B) is preferably 25 parts by mass or less, more preferably 1.0 to 15 parts by mass, and even more preferably 1.5 to 15 parts by mass with respect to 100 parts by mass of the urethane prepolymer (A). When the content of the isocyanate curing agent (B) is adjusted within the above range, more excellent initial curability can be easily obtained.

[0100] <Tackifying resin> In one embodiment, the pressure-sensitive adhesive composition may further contain a tackifying resin. The use of the tackifying resin is preferable in that it can improve the tack characteristics. As the tackifying resin, for example, rosin-based resins, polyterpene resins, aliphatic hydrocarbon resins, aliphatic petroleum resins, aromatic petroleum resins, alkylphenol formaldehyde resins (oil-based phenolic resins), etc. can be used. Also, the tackifying resin is preferably a resin obtained from biomass-derived raw materials. From such a point, as the tackifying resin, for example, resins such as rosin-based resins or polyterpene resins are preferable.

[0101] The content of the tackifying resin is preferably 2 to 50 parts by mass, more preferably 5 to 40 parts by mass with respect to 100 parts by mass of the urethane prepolymer (A). When the above content is adjusted to 2 parts by mass or more, the desired adhesive properties can be easily obtained due to the effect of adding the tackifier resin. Further, when the above content is adjusted to 50 parts by mass or less, it is preferable in that good compatibility with polymer components such as the urethane prepolymer (A) can be obtained. Therefore, problems such as clouding or whitening can be suppressed in the appearance of the coating liquid or the coating film.

[0102] <Other components> In one embodiment, the pressure-sensitive adhesive composition may further contain common additives in addition to the above components as long as the properties as a pressure-sensitive adhesive are not impaired and biodegradability is not impaired. Examples of additives that can be used include ultraviolet absorbers, light stabilizers, leveling agents, antistatic agents, peeling regulators, fillers, colorants, antioxidants, plasticizers, and surfactants.

[0103] <2>Adhesive sheet Another embodiment of the present invention relates to an adhesive sheet. The adhesive sheet has an adhesive layer formed from the adhesive composition of the above embodiment on at least one surface of the base material. That is, the adhesive sheet has a base material and an adhesive layer provided on one surface of the base material, and the adhesive layer is composed of a cured product of the adhesive composition of the above embodiment. In one embodiment, a release sheet may be provided on the other surface of the adhesive layer not in contact with the base material to prevent foreign matter from adhering. Usually, the adhesive layer is protected by a release sheet until immediately before use.

[0104] The base material may be a flexible sheet or plate material and can be used without limitation. Examples of the base material include plastics, paper, and metal foils, and laminates composed of one or more of these materials. The surface of the base material in contact with the adhesive layer may be subjected to a simple adhesion treatment to improve adhesion. For example, dry treatments such as corona discharge treatment and wet treatments such as application of an anchor coat agent can be applied.

[0105] In one embodiment, examples of the plastic material constituting the base material include ester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); olefin resins such as polyethylene (PE), polypropylene (PP), and cycloolefin polymer (COP); vinyl resins such as polyvinyl chloride; amide resins such as nylon 66; urethane resins (including foams), and the like.

[0106] The thickness of the base material may generally be 10 to 300 μm. When using a polyurethane sheet (including foam) as the base material, the thickness of the base material (sheet) may generally be 20 to 50,000 μm. Paper can also be used as the base material. For example, ordinary paper, coated paper, art paper, and the like can be mentioned. Also, metal foil can be used as the base material. Examples of the metal foil include aluminum foil and copper foil.

[0107] The release sheet may be a release sheet having a known configuration. For example, a release sheet obtained by applying a known release treatment such as a silicone-based release agent to the surface of a sheet-like material such as plastic or paper can be used.

[0108] Examples of the method for manufacturing the pressure-sensitive adhesive sheet include a method in which the pressure-sensitive adhesive composition of the above embodiment is applied to the surface of the base material to form a coating layer, and then the coating layer is dried and cured to form a pressure-sensitive adhesive layer. The heating and drying temperature may generally be 60 to 150°C. The thickness of the pressure-sensitive adhesive layer may generally be 0.1 to 200 μm.

[0109] The coating method may be a known method, and examples thereof include a roll coater method, a comma coater method, a die coater method, a reverse coater method, a silk screen method, and a gravure coater method.

[0110] As another method different from the above method, there is a method in which the pressure-sensitive adhesive composition of the above embodiment is applied to the surface of the release sheet to form a coating layer, then the coating layer is dried and cured to form a pressure-sensitive adhesive layer, and finally a substrate is bonded to the exposed surface of the pressure-sensitive adhesive layer. In this method, when a release sheet is bonded to the pressure-sensitive adhesive layer instead of the substrate, a cast pressure-sensitive adhesive sheet having a structure of release sheet / pressure-sensitive adhesive layer / release sheet can be obtained.

Examples

[0111] Hereinafter, embodiments of the present invention will be described by way of examples. Needless to say, the embodiments of the present invention are not limited to the examples. "Parts" described below means "parts by mass", and "%" means "% by mass". In addition, the blending amounts of the raw materials (excluding solvents) described in the examples and tables below are values in terms of non-volatile content.

[0112] Furthermore, Mw, Mn, and Tg described below are values measured as follows. [Measurement of weight average molecular weight (Mw) and number average molecular weight (Mn)] The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC). The measurement conditions are as follows. Note that both Mw and Mn are values in terms of polystyrene conversion. (Measurement conditions) Apparatus: SHIMADZU Prominence (manufactured by Shimadzu Corporation) Column: Three SHODEX LF-804 (manufactured by Showa Denko KK) columns connected in series Detector: Differential refractive index detector Solvent: Tetrahydrofuran (THF) Flow rate: 0.5 mL / min Solvent temperature: 40 °C Sample concentration: 0.1% Sample injection volume: 100 μL

[0113] [Glass transition temperature (Tg)] A "SSC5200 Disk Station" (manufactured by Seiko Instruments Inc.) was connected to a robotic DSC (Differential Scanning Calorimeter, "RDC220" manufactured by Seiko Instruments Inc.) and used for measurements. Approximately 10 mg of the sample was placed in an aluminum pan, weighed, and set in the differential scanning calorimeter. After holding at a temperature of 100°C for 5 minutes using an aluminum pan of the same type without the sample as a reference, it was rapidly cooled to -120°C using liquid nitrogen. Then, the temperature was raised at a rate of 10°C / min, and the glass transition temperature (Tg, unit: °C) was determined from the obtained DSC chart.

[0114] <1>Raw materials The raw materials shown in the table are as follows. <Polyol (ax)> [Monomer (ax’1)] L-Lactic acid (biomass content 100%, biodegradability 100%) D-Lactic acid (biomass content 100%, biodegradability 100%) L-Lactide (biomass content 100%, biodegradability 100%) D-Lactide (biomass content 100%, biodegradability 100%) DL-Lactide (biomass content 100%, biodegradability 100%) meso-Lactide (biomass content 100%, biodegradability 100%)

[0115] [Monomer (ax’2)] 6-Hydroxycaproic acid (biomass content 0%, biodegradability 100%) ε-Caprolactone (biomass content 0%, biodegradability 100%)

[0116] [Monomer (ax’3)] PD: 1,3-Propanediol, Mn76, number of hydroxyl groups 2, (biomass content 100%, biodegradability 100%) PPG600: Sannix PP-600, polyoxypropylene glycol, Mn600, number of hydroxyl groups 2, manufactured by Sanyo Chemical Industries, Ltd. (biomass content 0%, biodegradability 0%) P-1010: Kuraray Polyol P-1010, 3-methyl-1,5-pentanediol / adipic acid, polyester polyol, Mn 1,000, manufactured by Kuraray Co., Ltd. (biomass content 0%, biodegradability 0%) P-2010: Kuraray Polyol P-2010, 3-methyl-1,5-pentanediol / adipic acid, polyester polyol, Mn 2,000, manufactured by Kuraray Co., Ltd. (biomass content 0%, biodegradability 0%) HF-1300: URIC HF-1300, castor oil polyol, Mn 1,400, hydroxyl number 2, manufactured by Ito Seiyu Co., Ltd. (biomass content 100%, biodegradability 0%) Polyol ax’3-1 to ax’3-3: As described below.

[0117] <Polyfunctional polyol (ay)> P-1010: Kuraray Polyol F-1010, 3-methyl-1,5-pentanediol / adipic acid / trimethylolpropane polyester polyol, Mn 1,000, hydroxyl number 3, manufactured by Kuraray Co., Ltd. (biomass content 0%, biodegradability 0%) GL-600: Sannix PP-600, glycerin / PO / EO, polyoxypropylene glycol, Mn 600, hydroxyl number 3, manufactured by Sanyo Chemical Industries, Ltd. (biomass content 0%, biodegradability 0%) GI3000: NISSO-PBGI-3000, polybutadiene polyol, Mn 3,100, hydroxyl number 2, manufactured by Nippon Soda Co., Ltd. (biomass content 0%, biodegradability 0%) Placcel 410: Polycaprolactone polyol, Mn 1,010, hydroxyl number 4, manufactured by Daicel Corporation (biomass content 0%, biodegradability 100%)

[0118] <Polyisocyanate (az)> IPDI: Isophorone diisocyanate HDI: Hexamethylene diisocyanate XDI: m-Xylene diisocyanate

[0119] <Hardener> [Isocyanate hardener (B)] HDI-TMP: Trimethylolpropane adduct of hexamethylene diisocyanate, Takenate D-160N, manufactured by Mitsui Chemicals, Inc. XDI-TMP: Trimethylolpropane adduct of xylene diisocyanate, Takenate D-110N, manufactured by Mitsui Chemicals, Inc. TDI-Nu: Isocyanurate of tolylene diisocyanate, Takenate D-204, manufactured by Mitsui Chemicals, Inc. [Carbodiimide curing agent] V-09B: Carbodiimide, Carbodilite V-09B, manufactured by Nisshinbo Chemicals, Inc.

[0120] <Adhesion-imparting resin> A-75: Super ester A-75, rosin-based resin, manufactured by Arakawa Chemical Industries, Ltd. (biomass content 92%, biodegradability 0%) D-125: Pencil D-125, rosin-based resin, manufactured by Arakawa Chemical Industries, Ltd. (biomass content 85%, biodegradability 0%)

[0121] In the above raw materials, the biomass content is the mass ratio (mass%) of the biomass-derived raw materials used during production, or the content based on ASTM D6866.

[0122] The biodegradability of the above raw materials was determined based on ISO 17556, ISO 14851, ISO 14852, ISO 15985, ISO 13975, ISO 14853, ISO 14855-1, ISO 14855-2, ISO 18830, ISO 19679, ASTM D7081, ASTM D6691, etc., as well as JIS standards corresponding to ISO standards. When biodegradability was recognized, the biodegradability of the raw material was set to 100%.

[0123] <2> Production example of polyol (ax’3) (Polyol (ax’3-1)) Sebacic acid, which is made from biomass-derived raw materials and is also a biodegradable raw material, was polymerized with 1,3-propanediol to obtain a polyester polyol (ax’3-1) having a number average molecular weight of 1,000. The biomass content of the polyol (ax’3-1) was 100%, and the biodegradability was 100%.

[0124] (Polyol (ax’3-2)) Succinic acid, which is made from biomass-derived raw materials and is also a biodegradable raw material, was polymerized with 1,3-propanediol to obtain a polyester polyol (ax’3-2) having a number average molecular weight of 800. The biomass content of the polyol (ax’3-2) was 100%, and the biodegradability was 100%.

[0125] (Polyol (ax’3-3)) Succinic acid, which is made from biomass-derived raw materials and is also a biodegradable raw material, was polymerized with 1,3-propanediol to obtain a polyester polyol (ax’3-3) having a number average molecular weight of 200. The biomass content of the polyol (ax’3-3) was 100%, and the biodegradability was 100%.

[0126] <3>Production Example of Polyol (ax) (Polyol (ax-1)) 100 parts of L-lactic acid, 35 parts of 6-hydroxycaproic acid, and 0.6 part of tin powder were charged into a reaction vessel equipped with a Dean-Stark trap. These were stirred at 150 °C / 50 mmHg for 3 hours while distilling off water, and then stirred at 150 °C / 30 mmHg for another 2 hours. Next, 210 parts of diphenyl ether was added to this reaction solution, and an azeotropic dehydration reaction was carried out at 150 °C / 35 mmHg. The distilled water and the solvent were separated with a water separator, and only the solvent was returned to the reaction vessel. After 2 hours, it was passed through a column filled with molecular sieve 3A and then returned to the reaction vessel, and the reaction was carried out at 130 °C / 17 mmHg for 10 hours. Thereafter, 6.0 parts of propanediol (PD) was added to the reaction solution, and the reaction was carried out at 130 °C / 17 mmHg for 10 hours to terminate the reaction. To the reaction solution obtained as described above, 440 parts of dehydrated diphenyl ether was added for dilution, and then it was cooled to 40 °C, and the precipitated crystals were filtered. To these crystals, 120 parts of 0.5N-HCl and 120 parts of ethanol were added, and after stirring at 35 °C for 1 hour, it was filtered. The obtained solid was dried at 60 °C / 50 mmHg to obtain polyol (ax-1). The number average molecular weight (Mn) of this polyol (ax-1) was 1,700.

[0127] (Polyol (ax-2, ax-3)) The compounding amounts (parts by mass) were changed as shown in Table 1, and polyols (ax-2, ax-3) were obtained in the same manner as the production of polyol (ax-1). The number average molecular weight (Mn) of the obtained polyols is shown in Table 1.

[0128] (Polyol (ax-4)) Into a reaction vessel equipped with a stirrer, a thermometer, and an outflow cooler, as shown in Table 1, 100 parts of L-lactide, 400 parts of ε-caprolactone, 500 parts of P-1010, and 0.1 part of tin 2-ethylhexanoate as a catalyst were charged. These materials were heated to 170 °C over 5 hours under normal pressure in a nitrogen atmosphere, then reacted for 3 hours, and the water distilled out was removed from the system to carry out a polymerization reaction. Thereafter, while reducing the pressure to 10 mmHg, the remaining unreacted monomers were removed over 3 hours to obtain polyol (ax-4). The number average molecular weight (Mn) of this polyol (ax-4) was 2,000.

[0129] (Polyol (ax-5~ax-55, axc-1~4)) Except that the compounding amounts (parts by mass) were changed as shown in Table 1, polyols (ax-5~ax-55, axc-1~axc-4) were obtained in the same manner as the production of polyol (ax-4). The number average molecular weight (Mn) of the obtained polyols is shown in Table 1.

[0130] In Table 1, the content rate of each monomer is the content rate (mass %) based on the total amount (100 mass %) of the monomer mixture constituting the polyol (ax). Monomer (ax’1) / monomer (ax’2) is the ratio of the content of monomer (ax’1) to the content of monomer (ax’2).

[0131]

Table 1-1

[0132]

Table 1-2

[0133]

Table 1-3

[0134]

Table 1-4

[0135]

Table 1-5

[0136] <4>Production Example of Urethane Prepolymer (A) Having Hydroxyl Group (Urethane Prepolymer (A-1)) 100 parts of polyol (ax-1), 12.1 parts of F-1010, 8.7 parts of HDI, 0.04 part of dioctyltin dilaurate as a catalyst, and toluene were charged into a four-necked flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel in an amount such that the non-volatile content was 60%. These materials were gradually heated to 100 °C and reacted for 5 hours. After confirming that the NCO characteristic absorption (2,270 cm -1 ) in the IR chart had disappeared, it was cooled to 25 °C, 0.08 part of acetylacetone was added, and the reaction was terminated. The weight-average molecular weight (Mw) of the urethane prepolymer (A-1) thus obtained was 50,000, and the glass transition temperature (Tg) was -10°C.

[0137] (Urethane prepolymers (A-2 to A-56, AC-1 to AC-3)) Except for changing the materials and compounding amounts (parts by mass) of the urethane prepolymer (A-1) as shown in Table 2, in the same manner as the production of the urethane prepolymer (A-1), toluene was adjusted so that the non-volatile content became 60%, and urethane prepolymers (A-2 to 56, AC-1 to 3) were obtained respectively. The weight-average molecular weight (Mw) and glass transition temperature (Tg) of the obtained urethane prepolymers are shown in Table 2.

[0138] In Table 2, the value of "NCO / OH" is the molar ratio (NCO / OH) of the isocyanate group (NCO) of the polyisocyanate (ay) and the hydroxyl group (OH) of the polyol (ax) when producing the urethane prepolymer (A) having a hydroxyl group.

[0139] [Table 2-1]

[0140] [Table 2-2]

[0141] [Table 2-3]

[0142] [Table 2-4]

[0143] <5>Production Examples of Adhesive Composition and Adhesive Sheet (Example 1) 100 parts of urethane prepolymer (A-1), 5.0 parts of HDI-TMP as an isocyanate curing agent (B), and ethyl acetate as a solvent were blended so that the non-volatile content was 50%, and the mixture was stirred with a disper to obtain an adhesive composition.

[0144] As a substrate, polyethylene terephthalate (PET) with a thickness of 50 μm ("Lumirror T-60", manufactured by Toray Industries, Inc.) was prepared. Using a comma coater (registered trademark), the previously prepared adhesive composition was coated on the above substrate to form a coating layer. The coating was carried out at a coating speed of 3 m / min and a width of 30 cm so that the thickness after drying was 25 μm. Next, the formed coating layer was dried using a drying oven under the conditions of 100 °C for 1 minute to form an adhesive layer. A commercially available release sheet with a thickness of 38 μm was laminated on this adhesive layer, and further cured for 1 week under the conditions of 23 °C and 50% RH to obtain an adhesive sheet 1.

[0145] (Examples 2 to 82, Comparative Examples 1 to 4) The materials and compounding amounts (parts by mass) of Example 1 were changed as shown in Table 3, and the adhesive compositions and adhesive sheets of Examples 2 to 82 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except for this.

[0146] <6>Characteristic evaluation of the adhesive composition Regarding the adhesive compositions obtained in Examples 1 to 82 and Comparative Examples 1 to 4, the biomass degree and the usage ratio of biodegradable raw materials were calculated according to the following method.

[0147] <Biomass degree of the adhesive> The biomass degree of the adhesive is the mass ratio of the biomass-derived raw materials used in the production of the adhesive to the total mass of the adhesive, and was calculated according to the following calculation formula (1). In addition, each mass is in terms of non-volatile content. The biomass degree is preferably 5% or more, more preferably 10% or more, and even more preferably 25% or more.

[0148] Calculation formula (1): Biomass content of the adhesive (% by mass) = 100 × [Mass of the biomass-derived raw material (g)] / [Total mass of the adhesive (g)]

[0149] <Usage ratio of the biodegradable raw material of the adhesive> The usage ratio of the biodegradable raw material of the adhesive is the mass ratio of the biodegradable raw material used in the production of the adhesive to the total mass of the adhesive, and is calculated according to the following calculation formula (2). Note that each mass is in terms of non-volatile content. The usage ratio is preferably 60% or more.

[0150] Calculation formula (2): Usage ratio of the biodegradable raw material of the adhesive = 100 × [Mass percentage of the biodegradable raw material used] / [100 mass% of the adhesive]

[0151] <7>Characteristic evaluation of the adhesive sheet For the adhesive sheets produced using the adhesive compositions obtained in Examples 1 to 82 and Comparative Examples 1 to 4, various characteristics were evaluated according to the following method. The results are shown in Table 3.

[0152] <Adhesive property> [Peel adhesion strength] The adhesive sheets 1 produced in the examples and comparative examples were cut into pieces with a width of 25 mm and a length of 100 mm and used as samples. This sample was adhered to a stainless steel plate (SUS304) under an atmosphere of 23°C and 50% RH. Then, it was roll-pressed at 2 Kg according to JIS0237 and left for 24 hours under an atmosphere of 23°C and 50% RH. Thereafter, using a tensile tester, the adhesive sheet was peeled from the stainless steel plate at two peeling speeds (180-degree peel), and the appearance such as adhesive residue was compared. The peeling speeds were a low peeling speed (0.3 m / min) and a high peeling speed (30 m / min). The evaluation criteria are as follows. (Evaluation criteria) A: The adhesive sheet could be peeled off without contaminating the SUS plate. Excellent. B: The SUS plate was slightly contaminated. Good. C: The SUS plate was slightly contaminated. Practically acceptable. D: The SUS plate was contaminated. Practically unacceptable.

[0153] [Adhesive force] The pressure-sensitive adhesive sheet 1 produced in the examples and comparative examples was cut into pieces with a width of 25 mm and a length of 100 mm and used as a sample. Then, in an atmosphere of 23°C and 50% RH, in accordance with JIS Z 0237, the release sheet was peeled off from the sample, and the exposed adhesive layer was attached to a polished stainless steel (SUS) plate. It was pressure-bonded once back and forth with a 2 kg roll, and after 24 hours of attachment, using a tensile tester, the adhesive force (N / 25 mm) was measured under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180°. The evaluation criteria are as follows. (Evaluation criteria) A: The adhesive force is 15 N / 25 mm or more. Excellent. B: The adhesive force is 10 N / 25 mm or more and less than 15 N / 25 mm. Good. C: The adhesive force is 5 N / 25 mm or more and less than 10 N / 25 mm. Practically acceptable. D: The adhesive force is less than 5 N / 25 mm. Practically unacceptable.

[0154] [Retention force] The release sheet was peeled off from the pressure-sensitive adhesive sheet 1 produced in the examples and comparative examples, and the exposed part of the adhesive layer (the tip of the pressure-sensitive adhesive sheet, width 25 mm, length 25 mm) was attached to a polished stainless steel (SUS) plate and pressure-bonded once back and forth with a 2 kg roll. Then, a load of 1 kg was applied in an atmosphere of 80°C and held for 70,000 seconds. The evaluation shows the number of seconds when the sample fell from the SUS plate. When the sample did not fall, it shows the number of millimeters by which the adhesive part of the adhesive layer to the SUS plate (the tip of the pressure-sensitive adhesive sheet) shifted downward due to the load. The evaluation criteria are as follows. (Evaluation criteria) A: The displacement of the sample is less than 2 mm. Excellent. B: The displacement of the sample is 2 mm or more and less than 5 mm. Good. C: The displacement of the sample is 5 mm or more and it did not fall. Practically acceptable. D: The sample fell. Practically unacceptable.

[0155] [Initial curability] A polyethylene terephthalate (PET) with a thickness of 50 μm (“Lumirror T-60”, manufactured by Toray Industries, Inc.) was prepared as the base material. Using a comma coater (registered trademark), each pressure-sensitive adhesive composition obtained in the examples and comparative examples was applied onto the base material at a coating speed of 30 m / min and a width of 150 cm so that the thickness after drying would be 25 μm, thereby forming a coating layer. Next, the formed coating layer was dried using a drying oven under the conditions of 100 °C for 1 minute to form a pressure-sensitive adhesive layer. A commercially available release sheet with a thickness of 38 μm was laminated onto this pressure-sensitive adhesive layer, and further cured for 1 week under the conditions of 23 °C and 50% RH to obtain a pressure-sensitive adhesive sheet 2. Regarding this pressure-sensitive adhesive sheet 2, after peeling off the release liner, the state of the surface (coated surface) of the pressure-sensitive adhesive layer was examined by a finger-touch tack test, and the presence or absence of adhesive residue on the finger was evaluated. The evaluation criteria are as follows. (Evaluation Criteria) A: The adhesive did not transfer to the finger. Excellent. B: The adhesive transferred to the finger very slightly. Good. C: The adhesive transferred to the finger slightly. Practically acceptable. D: The adhesive transferred to the finger. Practically unacceptable.

[0156] [Moisture and Heat Resistance] [Base Material Contamination] The pressure-sensitive adhesive sheets 1 manufactured in the examples and comparative examples were cut into samples with a size of 25 mm in width and 100 mm in length and used. This sample was adhered to a stainless steel plate (SUS304) under an atmosphere of 23 °C and 50% RH, and further roll-pressed with a 2 Kg roll in accordance with JIS0237. Then, after leaving it in an atmosphere of 60 °C and 95% RH for 72 hours, the pressure-sensitive adhesive sheet was peeled off, and the surface of the SUS plate after peeling was visually evaluated to evaluate the re-peelability of the pressure-sensitive adhesive layer. The evaluation criteria are as follows. (Evaluation Criteria) A: The SUS plate was not contaminated. Excellent. B: The SUS plate was contaminated very slightly. Good. C: The SUS plate was contaminated slightly. Practically acceptable. D: The SUS plate was contaminated. Practically unacceptable.

[0157] [Low Temperature Resistance] [Adhesion to the substrate] The pressure-sensitive adhesive sheet 1 produced in the examples and comparative examples was cut into a size of 25 mm in width and 100 mm in length to obtain samples. Then, in an atmosphere of -5°C, in accordance with JIS Z 0237, the release sheet was peeled off from the sample, and the exposed adhesive layer was attached to a polished stainless steel plate (SUS304), and further pressure-bonded once back and forth with a 2 kg roll. 24 hours after the attachment, using a tensile tester, the adhesive strength (N / 25 mm) was measured under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180°. The evaluation criteria are as follows. (Evaluation criteria) A: The adhesive strength is 15 N / 25 mm or more. Excellent. B: The adhesive strength is 10 N / 25 mm or more and less than 15 N / 25 mm. Good. C: The adhesive strength is 5 N / 25 mm or more and less than 10 N / 25 mm. Practically acceptable. D: The adhesive strength is less than 5 N / 25 mm. Practically unacceptable.

[0158] [Table 3-1]

[0159] [Table 3-2]

[0160] [Table 3-3]

[0161] As shown in Table 3, the pressure-sensitive adhesive composition (example) of the present invention contains a specific urethane prepolymer (A), so that even when the biomass degree of the pressure-sensitive adhesive and the use ratio of the biodegradable raw material in the pressure-sensitive adhesive are high, the adhesive properties are sufficiently satisfied, and furthermore, it is excellent in the substrate contamination property in the damp heat test, and in addition, it was confirmed that it is also excellent in the adhesion to the substrate at low temperature. In particular, regarding the substrate adhesion at low temperatures, among the lactide forms (ax’1-2), it was confirmed that when L-lactide and D-lactide were used in combination, or when DL-lactide or meso-lactide was used, better substrate adhesion could be obtained. Furthermore, when meso-lactide was used, it was confirmed that particularly excellent results were obtained also for the re-peelability.

[0162] On the other hand, in the pressure-sensitive adhesive compositions of the comparative examples, it was difficult to obtain the desired adhesive properties, the substrate contamination property in the damp heat test, and the substrate adhesion at low temperatures. In Comparative Examples 1 and 2, in the preparation of the polyol (ax), the monomer (ax’1) having a lactic acid unit and the monomer (ax’2) having at least either a lactone unit or an aliphatic hydroxycarboxylic acid unit were not used in combination. Also, in Comparative Example 3, the number average molecular weight of the polyol (ax) was outside the range defined in the present invention. From the above, it can be seen that the pressure-sensitive adhesive composition of the present invention can achieve the desired adhesive properties, the substrate contamination property in the damp heat test, and the substrate adhesion at low temperatures by using the specific urethane prepolymer (A).

Claims

1. A urethane prepolymer (A) having a hydroxyl group, which is a reaction product of a polyol (ax) having a number average molecular weight of 11,000 to 45,000, a polyfunctional polyol (ay) (excluding the polyol (ax)), and a polyisocyanate (az), The polyol (ax) is a copolymer of a monomer mixture containing a monomer (ax'1) having a lactic acid unit and a monomer (ax'2) having at least one of a lactone unit and an aliphatic hydroxycarboxylic acid unit (excluding lactic acid), The urethane prepolymer (A) having a hydroxyl group is an adhesive composition having a glass transition temperature of -60°C to -10°C.

2. The adhesive composition according to claim 1, further comprising an isocyanate curing agent (B).

3. The urethane prepolymer (A) having a hydroxyl group has a weight average molecular weight of 10,000 to 200,000, and the adhesive composition according to claim 1 or 2.

4. Based on the total mass of the monomer mixture constituting the polyol (ax), the total content of the monomer (ax'1) and the monomer (ax'2) is 10 to 99.8% by mass, and the adhesive composition according to any one of claims 1 to 3.

5. The monomer (ax'2) contains at least Meso-lactide, and the adhesive composition according to any one of claims 1 to 4.

6. The monomer mixture constituting the polyol (ax) further contains a monomer (ax'3) capable of reacting with the monomer (ax'1) and the monomer (ax'2), The monomer (ax'3) contains a polyester polyol having a number average molecular weight of 200 to 2,000, and the adhesive composition according to any one of claims 1 to 5.

7. An adhesive sheet having a base material and an adhesive layer formed from the adhesive composition according to any one of claims 1 to 6 provided on at least one surface of the base material.

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