KR101514107B1 - Urethane Prepolymer - Google Patents

Abstract

[PROBLEMS] To provide a urethane prepolymer having a moisture-curable property which exhibits elasticity and is excellent in moisture permeability without being infiltrated into a substrate when it is applied to a porous substrate at room temperature.
[Solution]
A urethane prepolymer obtained by reacting a polyether polyol, a polyester polyol and a polyisocyanate in an NCO / OH equivalent ratio of 1.1 to 3.0 and then containing 0.01 to 5% by mass of an amine-based curing accelerator, wherein the polyether polyol / Wherein the main component of the polyether polyol is a polytetramethylene glycol-polyethylene glycol copolymer or polypropylene glycol, and the weight ratio of the urethane prepolymer is 95/5 to 75/25.

Description

Urethane prepolymer < RTI ID = 0.0 >

The present invention relates to a urethane prepolymer useful as an adhesive, and more particularly to a urethane prepolymer having fluidity at room temperature and curing while being foamed by moisture and having excellent moisture permeability, a urethane prepolymer coating method, And an adhesive composed of the urethane prepolymer.

The urethane prepolymer is used for an adhesive, a paint and a sealing material, and in particular, a moisture-curing urethane prepolymer can be used as a single solution because it is cured with moisture in the air. In order to obtain the adhesive strength, many of the resins are solid at room temperature in the structure, and they have been diluted with a solvent or heated and melted by a melter or the like to form a liquid phase. Further, at the time of coating a porous substrate such as a fiber, the urethane prepolymer penetrates into the inside of the substrate until curing, so that tactile feeling and elasticity of the porous substrate are impaired and the adhesive strength is lowered when used for an adhesive. In addition, when the coating film is poor in the moisture permeability and the materials having poor moisture permeability are laminated with each other, a method such as dot bonding has been used to impart moisture permeability, but there has been a problem that the bonding strength is insufficient.

Under these circumstances, Japanese Patent Application Laid-Open No. 61-141777 (hereinafter referred to as Patent Document 1) discloses a urethane prepolymer obtained by reacting polytetramethylene glycol with 4,4'-diphenylmethane diisocyanate , It has been proposed that an urethane prepolymer satisfying all the quality properties required for an adhesive such as moisture permeability, foaming property and hydrolysis resistance is not sufficient in addition to the resin property, I could not.

Japanese Patent Application Laid-Open No. 61-141777

Accordingly, an object of the present invention is to solve the above-described drawbacks, and it is an object of the present invention to solve the above-mentioned drawbacks, and to provide a curable coating composition which exhibits elasticity without being infiltrated into a base material even when it is liquid at room temperature and applied to a porous base material, And an excellent moisture-curable urethane prepolymer.

The inventors of the present invention have conducted intensive studies in order to solve the above problems of the present invention. As a result, they have found that by using a specific polyether polyol component and a specific proportion of a polyether polyol, a polyester polyol and a specific curing accelerator The present inventors have derived the present invention on the basis of the finding that the urethane prepolymer obtained can solve the above problems.

Thus, according to the present invention, the following (1) to (6) are provided.

(1) A urethane prepolymer obtained by reacting a polyether polyol, a polyester polyol and a polyisocyanate at an NCO / OH equivalent ratio of 1.1 to 3.0 and then containing 0.01 to 5% by mass of an amine curing accelerator, wherein the polyether polyol / Urethane prepolymer in which the mass ratio of ester polyol is 95/5 to 75/25 and the main component of polyether polyol is polytetramethylene glycol-polyethylene glycol copolymer or polypropylene glycol.

(2) The urethane prepolymer according to the above (1), wherein the number average molecular weight of the polyether polyol is 500 to 3000 and the number average molecular weight of the polyester polyol is 300 to 3000.

(3) The urethane prepolymer described in the above (1) or (2), wherein the polyester polyol is an aliphatic polyester polyol.

(4) The urethane prepolymer according to any one of (1) to (3), wherein the viscosity is 20,000 dPa · S / 25 ° C. or lower.

(5) A process for coating a urethane prepolymer, wherein the urethane prepolymer described in any one of (1) to (4) above is cured while being foamed by moisture.

(6) An adhesive comprising the urethane prepolymer according to any one of (1) to (4).

The urethane prepolymer of the present invention exhibits excellent performance as an adhesive for laminating a moisture permeable substrate since the urethane prepolymer of the present invention is easy to handle since it is liquid at room temperature and the cured product has moisture permeability. In addition, as an adhesive such as a fiber, it is required to have hydrolysis resistance by washing, and also has a certain durability.

In addition, by adding an amine-based curing accelerator, it is possible to exhibit initial strength without foaming immediately after coating and being absorbed into a substrate upon coating on a porous substrate.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The polyether polyol used as the synthetic component of the urethane prepolymer according to the present invention is a copolymer of polytetramethylene glycol and polyethylene glycol or polypropylene glycol.

When a polyether polyol other than the polyether polyol is used, there arises a problem that the urethane prepolymer becomes solid at room temperature or the hydrolysis resistance and moisture permeability of the obtained film become low.

The ratio of polytetramethylene glycol to polyethylene glycol in the copolymer of polytetramethylene glycol and polyethylene glycol may be in the range of 80/20 to 20/80 by mass ratio of polytetramethylene glycol / polyethylene glycol, The mass ratio is in the range of 70/30 to 30/70.

The number average molecular weight of the polyether polyol is preferably 500 to 3000, more preferably 800 to 2,500. When the number average molecular weight is less than 500, the moisture permeability of the cured coating deteriorates. On the other hand, when the number average molecular weight exceeds 3,000, the adhesion to the porous substrate decreases.

The polyether polyols may be used alone or in combination of two or more.

The polyester polyol used as the synthetic component of the urethane prepolymer according to the present invention is not particularly limited, but is preferably a bifunctional, and more preferably an aliphatic polyester polyol. Examples of the acid component of the aliphatic polyester polyol include dibasic acids such as succinic acid, adipic acid, sebacic acid and azelaic acid. Examples of the alcohol component include ethylene glycol, 1,2-propanediol, n-propanediol, Butanediol, 1,4-butanediol, 1,6-hexanediol, and the like.

The molecular weight of the polyester polyol is preferably 300 to 3000 as the number average molecular weight. If the number average molecular weight is less than 300, the adhesion to the porous substrate decreases. When the number average molecular weight exceeds 3000, the flowability of the prepolymer at room temperature is deteriorated.

The polyester polyols may be used alone or in combination of two or more.

The ratio of the polyether polyol to the polyester polyol is 95/5 to 75/25, and preferably 90/10 to 80/20 in terms of the mass ratio of the polyether polyol / polyester polyol. When the mass ratio of the polyether polyol / polyester polyol is more than 95/5, the bonding strength with the porous substrate is lowered, which is not preferable. When the mass ratio of the polyether polyol / polyester polyol is less than 75/25, the moisture permeability and the hydrolysis resistance are lowered.

The polyisocyanate used as the synthetic component of the urethane prepolymer of the present invention is not particularly limited, but a bifunctional polyisocyanate is preferable. Specific examples of polyisocyanates include tolylene diisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4- Butene-1,3-phenylene diisocyanate, 2,4-diisocyanate-diphenyl ether, mesitylene diisocyanate, 4,4'-methylene bis (phenyl isocyanate), dureylene diisocyanate, 1,5-naphthalene diisocyanate , Benzidine diisocyanate, o-nitrobenzidine diisocyanate, 4,4-diisocyanate dibenzyl, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,10-decamethylene diisocyanate, 4-cyclohexylene diisocyanate, xylylene diisocyanate, 4,4-methylene bis (cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate Anate, and the like.

In addition, a low-molecular polyol may be used as long as the effect of the present invention is not impaired.

The ratio of polyol to polyisocyanate is 1.1 to 3.0 in NCO / OH equivalent ratio. If the NCO / OH equivalence ratio is less than 1.1, the strength of the cured film after adhesion tends to be lowered, and the adhesive strength is lowered. On the other hand, if the NCO / OH equivalent ratio exceeds 3.0, the cured film strength after bonding becomes hard, Which is undesirable.

The curing accelerator used as a blending component for the urethane prepolymer according to the present invention is preferably an amine curing accelerator. The curing accelerator other than the amine curing accelerator is not preferable because it lacks the foamability of the cured coating.

Specific examples of the amine-based curing accelerator include triethylamine, triethylenediamine, tetramethyl-1,3-butanediamine, ethylmorpholine, diazabicyclo-undecene, and diazabicyclo- nonenene.

The amount of the amine-based curing accelerator to be added is 0.01 to 5% by mass, preferably 0.1 to 2% by mass, based on the urethane prepolymer. If the addition amount is less than 0.01% by mass, the foamability of the cured coating is insufficient. If the addition amount is more than 5.0% by mass, the pot life is shortened and the workability is deteriorated.

The viscosity of the urethane prepolymer according to the present invention is preferably 20,000 dPa 占 퐏 / 25 占 폚 or lower. Preferably 10,000 dPa 占 퐏 / 25 占 폚 or less, and particularly preferably 3,000 dPa 占 퐏 / 25 占 폚 or less. When the liquid is in a liquid state, the lower limit is not particularly limited, but it is particularly preferably at least 50 dPa · s / 25 ° C. On the other hand, when the viscosity is higher than 20,000 dPa · s / 25 ° C, the workability is not preferable.

When the urethane prepolymer of the present invention is applied to a substrate, it is cured while generating carbon dioxide by moisture in the air. The urethane prepolymer does not penetrate into the interior of the porous substrate when it is coated on the porous substrate. Therefore, when the porous substrate is used as an adhesive without deteriorating tactility and elasticity of the substrate, a necessary amount of urethane prepolymer is present on the substrate surface Therefore, there is no decrease in adhesion due to insufficient application amount.

The urethane prepolymer of the present invention is useful for paints, sealing materials, etc. in addition to adhesives.

The adhesive composed of the urethane prepolymer according to the present invention occupies a major area as one of uses of the urethane prepolymer, and the specificity of the urethane prepolymer according to the present invention is demonstrated.

That is, the urethane prepolymer is obtained by reacting a polyether polyol, a polyester polyol and a polyisocyanate at an NCO / OH equivalence ratio of 1.1 to 3.0 and then containing 0.01 to 5% by mass of an amine curing accelerator. The polyether polyol / Wherein the weight ratio of the polyester polyol is 95/5 to 75/25, and the main component of the polyether polyol is a copolymer of polytetramethylene glycol and polyethylene glycol or polypropylene glycol. The urethane prepolymer has a predetermined viscosity And has a liquid state at an environmental temperature (room temperature). Therefore, a solvent-free adhesive can be provided without further solvent for use as an adhesive.

The quality characteristics such as adhesive strength required as an adhesive are all satisfied as shown in Examples described later.

On the other hand, various additives such as fillers, plasticizers, stabilizers and the like may be added as desired in order to be used as an adhesive.

[Example]

Next, the present invention will be described in more detail with reference to examples and comparative examples. Above all, the present invention is not limited by the embodiments and the like.

On the other hand, numerical values in the Examples and Comparative Examples are based on mass.

The number average molecular weight of the urethane prepolymer, the polyether polyol and the polyester polyol used in the production of the urethane prepolymer according to the present invention was measured by GPC.

[Example 1]

610 parts of polypropylene glycol (number average molecular weight 2,000, OH valence 56) and 2 parts of 1,4-butanediol and adipic acid were added to a glass reaction vessel of 2 liters equipped with a stirrer, a thermometer and a gas inlet, (Number-average molecular weight: 500, OH value: 235) were charged, dehydrated by heating and decompression, and nitrogen gas was introduced thereinto to an internal temperature of 90 to 100 ° C. 234 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been melted and heated was added, and the mixture was reacted at 100 ° C for 2 hours with stirring. After completion of the reaction, the mixture was cooled to 40 캜 or lower, and 3.0 parts of an amine-based curing accelerator (1,8-diazabicyclo (5,4,0) -undecene) was added thereto.

The viscosity of the obtained urethane prepolymer was 950 dPa-s / 25 캜. Its NCO / OH equivalent ratio is 1.54.

[Example 2]

588 parts of a bifunctional polyether polyol (copolymerized polyether polyol of polytetramethylene glycol and polyethylene glycol, number average molecular weight 1,800, OH of 62) and 1, 2, and 3 parts of a 1 liter glass reaction vessel equipped with a stirrer, a thermometer, 159 parts of a bifunctional polyester diol (number-average molecular weight 500, OH of 235) composed of 4-butanediol and adipic acid was placed, dehydrated by heating and decompression, and then nitrogen gas was introduced to adjust the internal temperature to 90 to 100 占 폚. 176 parts of 2,4-tolylene diisocyanate was added, and the mixture was reacted at 100 DEG C for 2 hours with stirring. After completion of the reaction, the mixture was cooled to 40 캜 or lower, and 3.0 parts of an amine-based curing accelerator (1,8-diazabicyclo (5,4,0) -undecene) was added thereto.

The viscosity of the obtained urethane prepolymer was 1,050 dPa-s / 25 ° C. Its NCO / OH equivalent ratio is 1.57.

[Example 3]

797 parts of polypropylene glycol (number average molecular weight: 2,000, OH: 56) (797 parts) in a 2-liter glass reaction vessel equipped with a stirrer, a thermometer and a gas inlet and a bifunctional polyester diol Average molecular weight: 2,000, OH: 56) was added, and the mixture was dehydrated by heating and decompression, and then nitrogen gas was introduced to adjust the internal temperature to 90 to 100 캜. 157 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been melted and melted was placed, and the mixture was reacted at 100 ° C for 2 hours with stirring. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 2.8 parts of an amine-based curing accelerator (1,5-diazabicyclo (4,3,0) -nonene-5) was added and stirred and mixed.

The viscosity of the obtained urethane prepolymer was 2,020 dPa-s / 25 ° C. Its NCO / OH equivalent ratio is 1.50.

[Example 4]

In a 2 liter glass reaction vessel equipped with a stirrer, a thermometer and a gas inlet, 671 parts of polypropylene glycol (number average molecular weight: 2,000, OH: 56) and 2 parts of a bifunctional polyester diol composed of 1,4-butanediol and adipic acid Molecular weight: 2,000, OH: 56), dehydrated by heating under reduced pressure, and then dried nitrogen gas was introduced to return to normal pressure, and the inner temperature was adjusted to 90 to 100 캜. 157 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been molten and melted was added, and the mixture was reacted at 100 ° C for 2 hours with stirring. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 2.8 parts of an amine-based curing accelerator (1,5-diazabicyclo (4,3,0) -nonene-5) was added and stirred and mixed.

The viscosity of the obtained urethane prepolymer was 2,340 dPa-s / 25 캜. Its NCO / OH equivalent ratio is 1.50.

[Example 5]

In a 2 liter glass reaction vessel equipped with a stirrer, a thermometer and a gas inlet, 629 parts of polypropylene glycol (number average molecular weight: 2,000, OH: 56), and bifunctional polyester diol composed of 1,4-butanediol and adipic acid Molecular weight: 2,000, OH: 56), dehydrated by heating and decompression, and then dried nitrogen gas was introduced to return to normal pressure, and the inner temperature was adjusted to 90 to 105 占 폚. 157 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been melted and melted was added, and the mixture was reacted at 100 ° C for 3 hours with stirring. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 2.8 parts of an amine-based curing accelerator (1,5-diazabicyclo (4,3,0) -nonene-5) was added and stirred and mixed.

The viscosity of the obtained urethane prepolymer was 2,650 dPa-s / 25 캜. Its NCO / OH equivalent ratio is 1.49.

[Comparative Example 1]

620 parts of polyethylene glycol (number average molecular weight: 2,000, OH: 56) and 2 parts of 1,4-butanediol and adipic acid were added to a 2 liter reaction vessel equipped with a stirrer, a thermometer and a gas inlet, 500, and OH: 235) were charged, dehydrated by heating and decompression, and then nitrogen gas was introduced to adjust the internal temperature to 90 to 100 캜. 232 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been molten and melted was added, and the mixture was reacted at 100 ° C for 2 hours with stirring. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 3.0 parts of an amine-based curing accelerator (1,8-diazabicyclo (5,4,0) -undecene) was added to the mixture.

The obtained urethane prepolymer was solid at 25 占 폚, and was 150 dPa-s / 100 占 폚.

Its NCO / OH equivalent ratio is 1.53.

[Comparative Example 2]

610 parts of polypropylene glycol (number average molecular weight: 2,000, OH: 56) and 2 parts of 1,4-butanediol and adipic acid and a bifunctional polyester diol (number average Molecular weight: 500, OH: 235) was added, and the mixture was dehydrated by heating and decompression, and then nitrogen gas was introduced to adjust the internal temperature to 90 to 100 deg. 234 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been melted and heated was added, and the mixture was reacted at 100 ° C for 2 hours with stirring. After completion of the reaction, the reaction product was cooled to 40 ° C or lower and then discharged.

The urethane prepolymer obtained was 900 dPa-s at 25 占 폚. Its NCO / OH equivalent ratio is 1.54.

[Comparative Example 3]

678 parts of bifunctional polyether polyol (copolymerized polyether polyol of polytetramethylene glycol and polyethylene glycol, number average molecular weight 1,800, OH of 62) was placed in a 2 liter glass reaction vessel equipped with a stirrer, a thermometer and a gas inlet, After decompression and dehydration treatment, nitrogen gas is introduced and the internal temperature is adjusted to 90 to 100 캜. To which 102 parts of 2,4-tolylene diisocyanate was added, followed by stirring at an internal temperature of 90 to 100 DEG C for 3 hours. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 3.0 parts of an amine-based curing accelerator (1,8-diazabicyclo (5,4,0) -undecene) was added to the mixture.

The urethane prepolymer obtained was 340 dPa-s at 25 占 폚. Its NCO / OH equivalent ratio is 1.56.

[Comparative Example 4]

In a 2-liter reaction vessel made of glass provided with a stirrer, a thermometer and a gas inlet, 420 parts of polypropylene glycol (number average molecular weight 2,000, OH 56) and 2 parts of polyester diol having 1,4-butanediol and adipic acid Molecular weight: 500, OH: 235), dehydrated by heating and decompression, and then introduced with nitrogen gas to an internal temperature of 90 to 100 캜. 298 parts of 4,4'-methylenebis (phenylisocyanate) which had been preheated and melted was added, and the mixture was reacted at 90 to 100 ° C for 2 hours with stirring. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 3.0 parts of an amine-based curing accelerator (1,5-diazabicyclo (4,3,0) -nonene-5) was added and stirred and mixed.

The urethane prepolymer obtained was 940 dPa-s at 25 占 폚. Its NCO / OH equivalent ratio is 1.55.

[Comparative Example 5]

616 parts of polytetramethylene glycol (number average molecular weight: 2,000, OH: 55) was added to a 2 liter glass reaction vessel equipped with a stirrer, a thermometer and a gas inlet, and a bifunctional polyester diol consisting of 1,4-butanediol and adipic acid Average molecular weight: 500, OH: 235) were charged, dehydrated by heating and decompression, dried nitrogen gas was introduced, and the internal temperature was returned to 90 to 100 캜 while returning to normal pressure. 235 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been melted and heated was added, and the mixture was reacted at 100 ° C for 2.5 hours with stirring. After completion of the reaction, the mixture was cooled to 40 占 폚 or lower and 3.0 parts of an amine-based curing accelerator (1,8-diazabicyclo (5,4,0) -undecene) was added and stirred and mixed.

The urethane prepolymer obtained was a solid at 25 占 폚 and was 630 dPa-s / 100 占 폚. Its NCO / OH equivalent ratio is 1.55.

[Comparative Example 6]

610 parts of polypropylene glycol (number average molecular weight: 2,000, OH: 56) and 2 parts of 1,4-butanediol and adipic acid and a bifunctional polyester diol (number average Molecular weight: 500, OH: 235) was added, and the mixture was dehydrated by heating and decompression, and then nitrogen gas was introduced to adjust the internal temperature to 90 to 100 deg. 234 parts of 4,4'-methylene bis (phenyl isocyanate) which had previously been melted and heated was added, and the mixture was reacted at 100 ° C for 2 hours with stirring. After the completion of the reaction, the mixture was cooled to 40 캜 or lower, and 3.0 parts of a zinc-based curing accelerator (octyl zinc) was added, stirred and mixed and taken out.

The viscosity of the obtained urethane prepolymer was 990 dPa-s / 25 캜. Its NCO / OH equivalent ratio is 1.54.

The following measurements were carried out in order to evaluate the urethane prepolymers obtained in Examples 1 to 5 and Comparative Examples 1 to 6.

[Resin] The viscosity at 25 캜 and 100 캜 was measured. (In accordance with JIS K 7117)

[Foamability] The urethane prepolymer was applied onto the PET to a thickness of 100 microns, and the appearance of the cross section of the film after the film was left in a thermostatic chamber at a temperature of 40 캜 and a humidity of 60% for 24 hours was evaluated.

○: Identify a uniform foam layer

X: The foam layer was not confirmed

[Water vapor permeability test] The urethane prepolymer was coated on the release paper and allowed to stand in a thermostatic chamber at a temperature of 40 DEG C and a humidity of 60% for 168 hours and peeled to obtain a film having a thickness of 100 microns. The moisture permeability of these films was measured in accordance with JIS L1099A-1.

[Hydrolysis resistance] The urethane prepolymer was coated on the release paper and allowed to stand in a thermostatic chamber at a temperature of 40 DEG C and a humidity of 60% for 168 hours and peeled to obtain a film having a thickness of 100 microns. These films were allowed to stand for 4 weeks under the conditions of a temperature of 70 캜 and a humidity of 95%, and then subjected to a hydrolysis test. The films were compared with the film properties before the test (modulus after 100% elongation).

○: retention ratio 80% or more

△: Less than 80% retention ratio 50% or more

X: Less than 50% retention rate

[Adhesive strength (Peel strength [N / 25 mm])]: Composition: PET / woven fabric

Urethane prepolymer was coated on a PET film at 100 microns and immediately bonded with a cotton cloth and pressed with a 1 kg roller. Positive pressure was applied for 7 days under conditions of a temperature of 40 캜 and a humidity of 60%, and then a rectangular sample of 25 mm in width was prepared , And tensile adhesive strength was measured at a speed of 300 mm / min.

The compounding ratios of the respective urethane prepolymers in the above-mentioned Examples and Comparative Examples and the evaluation results of the performance thereof are summarized in Table-1.

As is apparent from the results of Examples and Comparative Examples, as described above, the urethane prepolymer according to the present invention can satisfy all of required quality properties such as adhesive strength, resin property, moisture permeability, foaming property and hydrolysis resistance .

INDUSTRIAL APPLICABILITY The urethane prepolymer according to the present invention can be used in various fields such as adhesives, paints, and sealing materials, and is useful as an industrially applicable material.

Claims (9)

A urethane prepolymer obtained by reacting a polyether polyol, a polyester polyol and a polyisocyanate in an NCO / OH equivalent ratio of 1.1 to 3.0 and then containing 0.01 to 5% by mass of an amine-based curing accelerator, wherein the polyether polyol / Wherein the weight ratio of the urethane prepolymer is 95/5 to 75/25, and the main component of the polyether polyol is a polytetramethylene glycol-polyethylene glycol copolymer. The urethane prepolymer according to claim 1, wherein the number average molecular weight of the polyether polyol is 500 to 3000 and the number average molecular weight of the polyester polyol is 300 to 3000. The urethane prepolymer according to claim 1, wherein the polyester polyol is an aliphatic polyester polyol. The urethane prepolymer according to claim 1, having a viscosity of 20,000 dPa · s / 25 ° C or less. The urethane prepolymer according to claim 4, having a viscosity of 3,000 dPa · s / 25 ° C. or less and 50 dPa · s / 25 ° C. or more. The method according to claim 1, wherein the amine curing accelerator is selected from the group consisting of triethylamine, triethylenediamine, tetramethyl-1,3-butanediamine, ethylmorpholine, diazabicyclo-undecene and diazabicyclo- A urethane prepolymer which is at least one kind of amine compound. The urethane prepolymer according to claim 6, wherein the amine-based curing accelerator is at least one kind of curing accelerator selected from the group consisting of diazabicyclo undecene and diazabicyclo- none nene. A process for coating a urethane prepolymer, which comprises curing the urethane prepolymer according to any one of claims 1 to 7 while foaming it with moisture. An adhesive comprising the urethane prepolymer according to any one of claims 1 to 6.