TWI894158B - Moisture-curing polyurethane hot-melt resin composition - Google Patents

Abstract

The problem to be solved by the present invention is to provide a moisture-curing polyurethane hot-melt resin composition having excellent low viscosity, initial adhesive strength, flexibility, coating suitability, and hydrolysis resistance. The present invention provides a moisture-curing polyurethane hot-melt resin composition comprising a urethane prepolymer (i) having an isocyanate group, which is prepared from a polyol (A) and a polyisocyanate (B). The moisture-curing polyurethane hot-melt resin composition is characterized in that the polyol (A) comprises a polyester polyol (a1) prepared from adipic acid, a polyether polyol (a2), and an aromatic polyester polyol (a3), and the total amount of the polyester polyol (a1) and the polyether polyol (a2) used is greater than the amount of the aromatic polyester polyol (a3) used.

Description

Moisture-curing polyurethane hot-melt resin composition

The present invention relates to a moisture-curing polyurethane hot-melt resin composition.

Because moisture-curing polyurethane hot-melt adhesives are solvent-free, they are currently being researched as environmentally friendly adhesives, primarily for fiber bonding and building material lamination, and are widely used within the industry.

Moisture-curing polyurethane adhesives develop their ultimate bond strength through moisture curing of the isocyanate groups in their main urethane prepolymer. However, high initial bond strength is required even immediately after application when bonding various substrates.

To achieve high initial adhesive strength, large amounts of crystalline polyester polyols are typically used (see, for example, Patent Document 1). However, this method has been criticized for its high viscosity, making coating difficult, and for the resulting hardened film, which can reduce the feel in applications requiring softness, such as fiber. Furthermore, the use of large amounts of polyester polyols can impair hydrolysis resistance, leading to its current lack of widespread use.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2011-190309

The problem to be solved by this invention is to provide a moisture-curing polyurethane hot-melt resin composition with low viscosity, excellent initial adhesive strength, flexibility, coating adaptability, and hydrolysis resistance.

The present invention provides a moisture-curing polyurethane hot-melt resin composition comprising a urethane prepolymer (i) having an isocyanate group, which is prepared from a polyol (A) and a polyisocyanate (B). The moisture-curing polyurethane hot-melt resin composition is characterized in that the polyol (A) comprises a polyester polyol (a1) prepared from adipic acid, a polyether polyol (a2), and an aromatic polyester polyol (a3), and the total amount of the polyester polyol (a1) and the polyether polyol (a2) used is greater than the amount of the aromatic polyester polyol (a3).

The moisture-curing polyurethane hot-melt resin composition of the present invention exhibits excellent low viscosity, initial adhesive strength, flexibility, coating suitability, and hydrolysis resistance. Therefore, the moisture-curing polyurethane hot-melt resin composition of the present invention is particularly suitable for fiber applications.

The moisture-curing polyurethane hot-melt resin composition of the present invention comprises a urethane prepolymer (i) having an isocyanate group, which is made from a polyol (A) containing a specific polyol and a polyisocyanate (B).

The polyol (A) contains polyester polyol (a1) made from adipic acid, polyether polyol (a2), and aromatic polyester polyol (a3).

The polyester polyol (a1) is an essential component for achieving excellent initial adhesive strength and softness. For example, a reaction product of a polybasic acid including adipic acid and a compound having two or more hydroxyl groups can be used.

Examples of polybasic acids other than adipic acid include aliphatic polybasic acids such as succinic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedioic acid, dodecanedioic acid, eicosanedioic acid, liconic acid, itaconic acid, liconic anhydride, and itaconic anhydride; and alicyclic polybasic acids such as 1,4-cyclohexanedicarboxylic acid. These polybasic acids may be used alone or in combination. The amount of adipic acid used in the polybasic acid is preferably 50% by mass or greater, more preferably 70% by mass or greater, further preferably 80% by mass or greater, and particularly preferably 90% by mass or greater.

As the compound having two or more hydroxyl groups, for example, ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3- Aliphatic compounds such as propylene glycol, 2,2-diethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2,4-diethyl-1,5-pentanediol, trihydroxymethylethane, trihydroxymethylpropane, and pentaerythritol; and alicyclic compounds such as cyclopentanediol, cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, and alkylene oxide adducts of these compounds. These compounds may be used alone or in combination of two or more. Among these, aliphatic compounds and/or alicyclic compounds are preferred in terms of achieving even better initial adhesive strength and softness. More preferred is the use of one or more compounds selected from the group consisting of ethylene glycol, 1,4-butanediol, diethylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, and 2,4-diethyl-1,5-pentanediol.

The number average molecular weight of the polyester polyol (a1) is preferably less than 2,800, more preferably 300 to 2,500, and even more preferably 600 to 2,200, in order to achieve even better initial adhesive strength and softness. The number average molecular weight of the polyester polyol (a1) is the value measured by gel permeation chromatography (GPC).

The content of the polyester polyol (a1) in the polyol (A) is preferably 5% to 80% by mass, more preferably 10% to 75% by mass, and even more preferably 15% to 70% by mass, in order to achieve even better initial adhesion strength, coating suitability, and softness.

The polyether polyol (a2) is an essential component for achieving excellent low viscosity, flexibility, and hydrolysis resistance. Examples of polyether polyols (a2) include polyoxyalkylene polyols, which are produced by ring-opening polymerization of cyclic ethers such as alkylene oxides using one or more compounds having two or more active hydrogen atoms as initiators.

The cyclic ether preferably has 2 to 10 carbon atoms, more preferably 2 to 6, and even more preferably 2 to 4. The hydrogen atoms in the cyclic ether may be substituted with halogen atoms. The cyclic ether may be one or more of the following: ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, epichlorohydrin, tetrahydrofuran, alkylated tetrahydrofuran, etc.

As the initiator, one or more initiators may be used, for example, compounds having two active hydrogen atoms such as ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and water; and compounds having three or more active hydrogen atoms such as glycerol, diglycerol, trihydroxymethylethane, trihydroxymethylpropane, hexanetriol, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, pentaerythritol, and sugars.

As the polyether polyol (a2), polyoxypropylene glycol and/or polytetramethylene glycol are preferably used, and polyoxypropylene glycol is more preferred in terms of achieving further excellent low viscosity, softness, coating suitability, and hydrolysis resistance.

The number average molecular weight of the polyether polyol (a2) is preferably less than 2,800, more preferably 300-2,500, and even more preferably 600-2,200, in order to achieve even better low viscosity, softness, coating suitability, and hydrolysis resistance. The number average molecular weight of the polyether polyol (a2) is the value measured by gel permeation chromatography (GPC).

The content of the polyether polyol (a2) in the polyol (A) is preferably 5% to 80% by mass, more preferably 10% to 75% by mass, and even more preferably 15% to 70% by mass, in order to achieve even better low viscosity, softness, and hydrolysis resistance.

The aromatic polyester polyol (a3) is an essential component for achieving excellent initial adhesive strength and softness. Examples of the aromatic polyester polyol (a3) include reaction products of a compound having a hydroxyl group and a polybasic acid including an aromatic polybasic acid; reaction products of an aromatic compound having two or more hydroxyl groups and a polybasic acid; and reaction products of an aromatic compound having two or more hydroxyl groups and a polybasic acid including an aromatic polybasic acid.

As the compound having a hydroxyl group, for example, ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, Aliphatic compounds such as ethanol, 2,2-diethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2,4-diethyl-1,5-pentanediol, trihydroxymethylethane, trihydroxymethylpropane, and pentaerythritol; and alicyclic compounds such as cyclopentanediol, cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, and alkylene oxide adducts thereof. These compounds may be used alone or in combination of two or more.

Examples of aromatic compounds with two or more hydroxyl groups include bisphenol A, bisphenol F, and their alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) adducts. These compounds can be used alone or in combination. Of these, alkylene oxide adducts of bisphenol A are preferred for achieving superior initial adhesive strength and softness. The molar amount of the added alkylene oxide is preferably in the range of 1 mol to 10 mol.

Examples of the aromatic polybasic acid include phthalic acid, isophthalic acid, terephthalic acid, and phthalic anhydride. Other polybasic acids include oxalic acid, malonic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, and 1,12-dodecanedicarboxylic acid. These polybasic acids may be used alone or in combination. To achieve even greater initial adhesive strength and flexibility, it is preferred to use one or more compounds selected from the group consisting of phthalic acid, isophthalic acid, terephthalic acid, and phthalic anhydride.

Other polyacids that can be used include succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedioic acid, dodecanedioic acid, eicosanedioic acid, liconic acid, itaconic acid, liconic anhydride, and itaconic anhydride.

The number average molecular weight of the aromatic polyester polyol (a3) is preferably less than 2,800, more preferably 300 to 2,500, and even more preferably 600 to 2,200, in order to achieve even better initial adhesive strength and softness. The number average molecular weight of the aromatic polyester polyol (a3) is a value measured by gel permeation chromatography (GPC).

The content of the aromatic polyester polyol (a3) in the polyol (A) is preferably 1% to 49% by mass, more preferably 4% to 47% by mass, and even more preferably 8% to 45% by mass, in order to achieve even better initial adhesive strength, softness, and coating suitability.

Furthermore, in order to fully satisfy the objectives of the present invention, the total amount of the polyester polyol (a1) and the polyether polyol (a2) must be greater than the amount of the aromatic polyester polyol (a3). The ratio of the total amount of the polyester polyol (a1) and the polyether polyol (a2) to the amount of the aromatic polyester polyol (a3) [((a1) + (a2)) / (a3)] is preferably in the range of 99/1 to 51/49, more preferably in the range of 95/5 to 53/47, and even more preferably in the range of 90/10 to 55/45.

The mass ratio of the polyester polyol (a1) to the polyether polyol (a2) [(a1)/(a2)] is preferably in the range of 90/10 to 10/90, more preferably in the range of 85/15 to 15/85, and even more preferably in the range of 80/20 to 20/80.

As the polyol (A), in addition to the polyols (a1) to (a3), other polyols may be used as needed.

As the other polyols, for example, polyester polyols other than (a1) and (a3), polycarbonate polyols, polyacrylic polyols, polybutadiene polyols, hydrogenated polybutadiene polyols, etc. can be used. These polyols can be used alone or in combination of two or more.

The total amount of the polyester polyol (a1), the polyether polyol (a2), and the aromatic polyester polyol (a3) in the polyol (A) is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more.

As the polyisocyanate (B), for example, aromatic polyisocyanates such as polymethylene polyphenyl polyisocyanate, diphenylmethane diisocyanate, carbodiimide-modified diphenylmethane diisocyanate isocyanate, phenylene diisocyanate, toluene diisocyanate, and naphthalene diisocyanate; and aliphatic or cycloaliphatic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate can be used. Among these, aromatic polyisocyanates are preferred, and diphenylmethane diisocyanate is more preferred, in terms of achieving further superior reactivity and ultimate strength.

In order to achieve even better bonding strength, the amount of the polyisocyanate (B) used in the raw material of the urethane prepolymer (i) is preferably in the range of 5% to 60% by mass, and more preferably in the range of 15% to 50% by mass.

The urethane prepolymer (i) is obtained by reacting the polyol (A) with the polyisocyanate (B), and has isocyanate groups at the polymer terminals or within the molecule that can react with moisture in the air or in the frame or adherend to which the urethane prepolymer is applied to form a crosslinked structure.

The urethane prepolymer (i) can be produced, for example, by dropwise adding the polyol (A) to a reaction vessel containing the polyisocyanate (B), followed by heating and reacting under conditions such that the isocyanate groups of the polyisocyanate (B) are in excess relative to the hydroxyl groups of the polyol (A).

The urethane bond content of the urethane prepolymer (i) is preferably in the range of 0.5 mol/kg to 3 mol/kg, more preferably in the range of 0.9 mol/kg to 2.7 mol/kg, and even more preferably in the range of 1.1 mol/kg to 2.4 mol/kg, in order to achieve further excellent initial adhesive strength, flexibility, and low viscosity.

When producing the urethane prepolymer (i), the equivalent ratio ([isocyanate group/hydroxy group]) of the isocyanate group of the polyisocyanate (B) to the hydroxyl group of the polyol (A) is preferably in the range of 1.1 to 1.5, and more preferably in the range of 1.15 to 1.45, in order to achieve further improved initial adhesive strength, flexibility, and low viscosity.

The isocyanate group content (hereinafter abbreviated as "NCO%") of the urethane prepolymer (i) is preferably in the range of 1% to 4% by mass, and more preferably in the range of 1.2% to 3.5% by mass, in order to achieve further improved initial adhesive strength, flexibility, and low viscosity. The NCO% of the urethane prepolymer (i) refers to the value measured by potentiometric titration in accordance with Japanese Industrial Standards (JIS) K1603-1:2007.

The moisture-curing polyurethane hot-melt resin composition of the present invention may contain other additives as needed in addition to the urethane prepolymer (i).

Examples of the other additives include antioxidants, adhesion promoters, plasticizers, stabilizers, fillers, dyes, pigments, fluorescent brighteners, silane coupling agents, and waxes. These additives may be used alone or in combination of two or more.

As a method for obtaining a cured film of the moisture-curing polyurethane hot-melt resin composition, for example, the following method can be cited: the moisture-curing polyurethane hot-melt resin composition is melted at 50°C to 130°C, then applied to a substrate, and moisture-cured.

As the substrate, for example, acrylic resin, urethane resin, silicone resin, epoxy resin, fluorine resin, polystyrene resin, polyester resin, polysulfone resin, polyarylate resin, polyvinyl chloride resin, polyvinylidene chloride, cycloolefin resin, polyolefin resin, polyimide resin, alicyclic polyimide resin, cellulose resin, polycarbonate (PC), polybutylene terephthalate (PBT), modified polyphenylene ether (PPE), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyimide resin, alicyclic polyimide resin, cellulose resin, polycarbonate (PC), polybutylene terephthalate (PBT), modified polyphenylene ether (PPE), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, polyvinyl chloride resin, Resin films such as polytetraphthalate (PET), lactic acid polymer, acrylonitrile-butadiene-styrene (ABS), and acrylonitrile-styrene (AS); wood substrates such as medium-density fiberboard (MDF), plywood, and particle board; and fiber substrates such as nonwovens, woven fabrics, and knitted fabrics. These substrates may also be treated with electrosurgery, plasma treatment, or primer, as needed.

Examples of methods for applying the moisture-curing polyurethane hot-melt resin composition include methods using a roll coater, a spray coater, a T-die coater, a knife coater, or a notched wheel coater.

After application, the final adhesive strength can be achieved by aging the surface for 0.5 to 3 days at a temperature of 20°C to 80°C and a relative humidity of 50% to 90%.

In order to achieve even better initial adhesive strength, the moisture-curing polyurethane hot-melt resin composition of the present invention preferably has a storage modulus (G') of melt viscoelasticity at 20°C before curing of 0.1 MPa or greater, preferably within the range of 0.2 MPa to 1,000 MPa, and even more preferably within the range of 0.3 MPa to 500 MPa.

The storage modulus (G') refers to the storage modulus (G') at 20°C obtained by melting a moisture-curing polyurethane hot-melt resin composition at 110°C for 1 hour, taking a 10 ml sample, placing it on the parallel plates of a melt viscoelasticity measuring apparatus ("MCR-302" manufactured by Anton Paar), and measuring the melt viscoelasticity at a cooling rate of 1°C/min and a frequency of 1 Hz from 110°C to 10°C.

In order to achieve even better flexibility, the Young's modulus of the hardened film of the present invention is preferably 20 MPa or less, more preferably in the range of 0.5 MPa to 15 MPa, and even more preferably in the range of 1 MPa to 10 MPa.

The Young's modulus is expressed as follows: a moisture-curing polyurethane hot-melt resin composition was melted at 110°C for 1 hour, and then applied to a release-treated polyethylene terephthalate substrate using a knife coater to a film thickness of 100 μm after curing. The film was left for 3 days to obtain a cured film. The cured film was peeled off from the release PET and punched using a No. 2 dumbbell. The resulting specimen was used as a test piece. A tensile test was performed on this specimen using a Tensilon tensile testing machine ("RTM-100" manufactured by Orientec Co., Ltd.) at 25°C and a crosshead speed of 200 mm/min. The value was measured based on the origin of the graph and the stress at an elongation of 2.5%.

As described above, the moisture-curing polyurethane hot-melt resin composition of the present invention exhibits excellent low viscosity, initial adhesive strength, flexibility, coating suitability, and hydrolysis resistance. Therefore, the moisture-curing polyurethane hot-melt resin composition of the present invention is particularly suitable for fiber applications.

[Example]

The present invention is further described below through examples.

[Example 1]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 35 parts by mass of an aliphatic polyester polyol (obtained by reacting butanediol and adipic acid, number-average molecular weight: 1,000, hereinafter referred to as "BG/AA"), 35 parts by mass of polyoxypropylene glycol (number-average molecular weight: 1,000, hereinafter referred to as "PPG"), and 30 parts by mass of an aromatic polyester polyol (obtained by reacting neopentyl glycol and phthalic acid, number-average molecular weight: 1,000, hereinafter referred to as "NPG/PA1000") were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture until the moisture content was below 0.05% by mass.

The temperature inside the container was then cooled to 60°C, followed by the addition of 33 parts by mass of 4,4'-diphenylmethane diisocyanate (hereinafter referred to as "MDI"). The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant. This yielded a urethane prepolymer (i-1) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-1) had an NCO% of 1.7% by mass, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Example 2]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 25 parts by mass of BG/AA, 50 parts by mass of PPG, and 25 parts by mass of NPG/PA1000 were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

Next, 33 parts by mass of MDI was added, the temperature was raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-2) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-2) had an NCO% of 1.7% by mass, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Example 3]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 35 parts by mass of an aliphatic polyester polyol (obtained by reacting neopentyl glycol and adipic acid, number-average molecular weight: 1,000, hereinafter referred to as "NPG/AA"), 35 parts by mass of PPG, and 30 parts by mass of an aromatic polyester polyol (obtained by reacting a 6-mole adduct of bisphenol A with propylene oxide and sebacic acid, number-average molecular weight: 1,000, hereinafter referred to as "BISA6PO/SEBA") were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture until the moisture content was below 0.05% by mass.

The temperature inside the container was then cooled to 60°C, followed by the addition of 33 parts by mass of MDI. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant. This yielded a urethane prepolymer (i-3) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-3) had an NCO% of 1.7% by mass, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Example 4]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 20 parts by mass of NPG/AA, 40 parts by mass of PPG, and 40 parts by mass of BISA6PO/SEBA were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

The container was then cooled to 60°C, and 33 parts by weight of MDI was added. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-4) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-4) had an NCO% of 1.7% by weight, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Example 5]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 55 parts by mass of NPG/AA, 30 parts by mass of PPG, and 15 parts by mass of NPG/PA1000 were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

The container was then cooled to 60°C, and 33 parts by weight of MDI was added. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant. This yielded a urethane prepolymer (i-5) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-5) had an NCO% of 1.7% by weight, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Example 6]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 30 parts by mass of an aliphatic polyester polyol (obtained by reacting diethylene glycol and adipic acid, number-average molecular weight: 1000, hereinafter referred to as "DEG/AA"), 30 parts by mass of PPG, and 40 parts by mass of an aromatic polyester polyol (obtained by reacting neopentyl glycol and o-phthalic acid, number-average molecular weight: 2,000, hereinafter referred to as "NPG/PA2000") were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture until the moisture content was below 0.05% by mass.

The temperature inside the container was then cooled to 60°C, followed by the addition of 28 parts by mass of MDI. The temperature was then raised to 110°C and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-6) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-6) had an NCO% of 1.8% by mass, a urethane bond content of 1.25 mol/kg, and an [NCO/OH] ratio of 1.40 during synthesis.

[Example 7]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 20 parts by mass of DEG/AA, 50 parts by mass of PPG, and 30 parts by mass of an aromatic polyester polyol (obtained by reacting ethylene glycol and o-phthalic acid, number-average molecular weight: 600, hereinafter referred to as "EG/PA600") were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

The container was then cooled to 60°C, and 38 parts by weight of MDI was added. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-7) containing isocyanate groups, thereby obtaining a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-7) had an NCO% of 1.6% by weight, a urethane bond weight of 1.74 mol/kg, and an [NCO/OH] ratio of 1.27 during synthesis.

[Comparative example 1]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 15 parts by mass of BG/AA, 15 parts by mass of PPG, and 70 parts by mass of NPG/PA were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

The container was then cooled to 60°C, and 35 parts by weight of MDI was added. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-R1) containing isocyanate groups, thereby producing a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-R1) had an NCO% of 2.2% by weight, a urethane bond weight of 1.48 mol/kg, and an [NCO/OH] ratio of 1.40 during synthesis.

[Comparative example 2]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 70 parts by mass of PPG and 30 parts by mass of NPG/PA1000 were placed and heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

The container was then cooled to 60°C, and 33 parts by weight of MDI was added. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-R2) containing isocyanate groups, thereby producing a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-R2) had an NCO% of 1.7% by weight, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Comparative example 3]

In a four-necked flask equipped with a thermometer, stirrer, inert gas inlet, and reflux cooler, 70 parts by mass of BG/AA and 30 parts by mass of NPG/PA1000 were placed. The mixture was heated under reduced pressure at 90°C to dehydrate the mixture to a moisture content of less than 0.05% by mass.

The container was then cooled to 60°C, and 33 parts by weight of MDI was added. The temperature was then raised to 110°C, and the reaction was allowed to proceed for approximately 3 hours until the isocyanate group content reached a constant level. This yielded a urethane prepolymer (i-R3) containing isocyanate groups, thereby producing a moisture-curing polyurethane hot-melt resin composition. The urethane prepolymer (i-R3) had an NCO% of 1.7% by weight, a urethane bond weight of 1.50 mol/kg, and an [NCO/OH] ratio of 1.32 during synthesis.

[Determination of number average molecular weight]

In the Examples and Comparative Examples, the number average molecular weight of polyols, etc., represents the value measured by gel permeation chromatography (GPC) under the following conditions.

Measuring device: High-speed GPC device (HLC-8220GPC manufactured by Tosoh Corporation)

Column: Use the following columns manufactured by Tosoh Co., Ltd. by connecting them in series.

TSKgel G5000 (7.8mm I.D. x 30cm) x 1

TSKgel G4000 (7.8mm I.D. x 30cm) x 1

TSKgel G3000 (7.8mm I.D. x 30cm) x 1

TSKgel G2000 (7.8mm I.D. x 30cm) x 1

Detector: RI (differential refractometer)

Column temperature: 40°C

Solvent: Tetrahydrofuran (THF)

Flow rate: 1.0 mL/min

Injection volume: 100 μL (sample concentration 0.4 mass% tetrahydrofuran solution)

Standard sample: The following standard polystyrene is used to prepare the standard curve.

(Standard polystyrene)

"TSKgel Standard Polystyrene A-500" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene A-1000" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene A-2500" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene A-5000" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-2" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-4" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-10" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-20" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-40" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-80" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-128" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-288" manufactured by Tosoh Corporation

"TSKgel Standard Polystyrene F-550" manufactured by Tosoh Corporation

[Viscosity measurement method]

The moisture-curing polyurethane hot-melt resin compositions obtained in the Examples and Comparative Examples were melted at 120°C for 1 hour. A 1 ml sample was then taken and the melt viscosity was measured using a cone-plate viscometer (40P cone, rotor speed: 50 rpm). Low viscosity was evaluated as follows.

"○": Less than 30,000 mPa.s

"×": 30,000 mPa.s or above

[Method for measuring initial bonding strength]

The moisture-curing polyurethane hot-melt resin compositions obtained in the Examples and Comparative Examples were each melted at 120°C for 1 hour. Using an applicator, the adhesive was applied to a polyethylene terephthalate sheet to a thickness of 100 μm. The polyethylene terephthalate sheet was then laminated onto the coated layer and press-bonded using a press roll. Five minutes after the press-bonding, the bond strength (N/25 mm) was measured using a Shimadzu Corporation precision universal testing machine, the "AG-10NX." Initial bond strength was evaluated as follows.

"○": Adhesion strength is 15 (N/25mm) or above.

"×": The continuous strength is less than 15 (N/25mm).

[Evaluation method of softness]

The moisture-curing polyurethane hot-melt resin compositions obtained in the Examples and Comparative Examples were melted at 110°C for 1 hour and then applied to a polyester nonwoven fabric using a knife coater to a film thickness of 100 μm after curing. The film was then left to stand for 3 days to form a cured film. The softness of the film was evaluated based on its touch as follows.

「○」: Very soft and supple.

"×": Gives a hard impression.

[Evaluation method of coating adaptability]

The moisture-curing polyurethane hot-melt resin compositions obtained in the Examples and Comparative Examples were melted at 110°C for 1 hour and then applied to a polyethylene terephthalate sheet using an applicator to a thickness of 100 μm. The coating compatibility was evaluated as follows.

"○": Uneven coating, with few streaks.

"×": Uneven application with many streaks.

[Evaluation method for hydrolysis resistance]

The moisture-curing polyurethane hot-melt resin compositions obtained in the Examples and Comparative Examples were melted at 110°C for 1 hour and then applied to a release paper using an applicator to a thickness of 100 μm. The films were then allowed to stand for 3 days to form cured films. The resulting cured films were then cured at 70°C and 95% humidity for 3 weeks. The tensile strength of the films was measured before and after curing using an "Autograph AG-I" manufactured by Shimadzu Corporation in accordance with JIS-K7312 (1996). Post-curing values of 50 or greater relative to the pre-curing value of 100 were rated "○" and values less than 50 were rated "×."

[Table 1]

It can be seen that the moisture-curing polyurethane hot-melt resin composition of the present invention has excellent low viscosity, initial adhesive strength, flexibility, coating suitability, and hydrolysis resistance.

On the other hand, Comparative Example 1 uses an amount of aromatic polyester polyol that exceeds the range specified in the present invention, resulting in low viscosity, poor softness, and poor coating compatibility.

Comparative Example 2 does not use polyester polyol (a1), and its coating compatibility is poor.

Comparative Example 3 does not use polyether polyol (a2), and the hydrolysis resistance is poor.

Claims (5)

A moisture-curing polyurethane hot-melt resin composition comprises a urethane prepolymer (i) having an isocyanate group, which is made of a polyol (A) and a polyisocyanate (B). The moisture-curing polyurethane hot-melt resin composition is characterized in that: the polyol (A) comprises a polyester polyol (a1) made of adipic acid, a polyether polyol (a2) and an aromatic polyester polyol (a3), and in the polyol (A), the content of the polyester polyol (a1) is in the range of 5% by mass to 80% by mass, the content of the polyether polyol (a2) is in the range of 5% by mass to 80% by mass, and the content of the aromatic polyester polyol (a3) is in the range of 10% by mass to 15% by mass. The amount of the polyester polyol (a1) and the polyether polyol (a2) used in the present invention is in the range of 1% by mass to 49% by mass. The total amount of the polyester polyol (a1) and the polyether polyol (a2) used is greater than the amount of the aromatic polyester polyol (a3). The polyether polyol (a2) is a polyether polyol prepared by ring-opening polymerization of one or more compounds having two or more active hydrogen atoms as initiators with one or more compounds selected from the group consisting of propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, epichlorohydrin, tetrahydrofuran, and alkylated tetrahydrofuran. The urethane bond weight of the urethane prepolymer (i) is in the range of 1.1 mol/kg to 2.4 mol/kg. The moisture-curing polyurethane hot-melt resin composition according to claim 1, wherein the molar ratio [NCO/OH] of the polyol (A) to the polyisocyanate (B) is in the range of 1.1 to 1.5. The moisture-curing polyurethane hot-melt resin composition according to claim 1 or claim 2, wherein the isocyanate group content of the urethane prepolymer (i) is in the range of 1% by mass to 4% by mass. The moisture-curing polyurethane hot-melt resin composition according to claim 1 or claim 2, wherein the polyether polyol (a2) is polyoxypropylene glycol and/or polytetramethylene glycol. The moisture-curing polyurethane hot-melt resin composition according to claim 1 or claim 2, wherein the aromatic polyester polyol (a3) is a reaction product of a reactant composed of an aliphatic compound or alicyclic compound having a hydroxyl group and an aromatic polybasic acid, or a reaction product of a reactant composed of an aromatic compound having two or more hydroxyl groups and an aromatic polybasic acid.