Cross-frame-corrugated joint structure

Abstract

To provide a beam-vertical member joint structure, which is essential for wooden buildings, and has excellent earthquake resistance and durability against major earthquakes, for example, earthquakes of magnitude 6 or more. [Solution] A cross member-vertical member joint structure in a rectangular frame consisting of upper and lower wooden cross members and wooden vertical members, which are columns sandwiched between these cross members, or in the joint structure of a frame body with wooden diagonal members arranged between them, in which the surfaces of the vertical member joints and the surfaces of the cross members have a polyurethane resin layer that, after hardening, has a tensile strength of 30 MPa or more and a tensile elongation of 100% or more.

Description

[Technical Field]

[0001] The present invention relates to a cross member-vertical member joint structure, and more particularly to a cross member-vertical member joint structure that is essential for wooden buildings with excellent earthquake resistance and durability. [Background technology]

[0002] In wooden buildings, the foundations, pillars, beams, girders, etc. are made of wood. The joints between pillars and beams or girders are the parts that are subjected to extremely strong forces when the building is exposed to earthquakes or strong winds. Therefore, the strength of these joints can determine whether or not a wooden building will collapse.

[0003] Conventional methods of reinforcing such areas include using metal or carbon fiber reinforced plastic (CFRP) to reinforce the joints between horizontal members such as beams and vertical members such as pillars, specifically the traditional construction method of connecting wood with joints and nails to construct the framework of a building (joint metal joint reinforcement method), and metal construction methods that use metal joint members.

[0004] In addition, diagonal members such as diagonal braces and braces are sometimes used as reinforcing materials for a rectangular frame consisting of upper and lower horizontal members that serve as the foundation or beams, and vertical members that are columns sandwiched between these horizontal members.In this case, connecting fittings (diagonal brace connecting fittings) are used on both ends of the diagonal braces and the frame, so that they do not easily come apart from each other.

[0005] However, metal and CFRP parts are fixed to wood using nails, screws, bolts, nuts, etc., and there are issues such as the wood shrinking as it dries and shrinks, and the nails, screws, bolts, nuts, etc. loosening due to repeated micro-vibrations, reducing the reinforcing effect over time.

[0006] Furthermore, wooden buildings are also being required to have sufficient earthquake resistance and durability to withstand the large earthquakes of magnitude 6 or higher that are expected in the future. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-19393 [Patent Document 2] Japanese Patent Application Laid-Open No. 2024-158098 [Patent Document 3] WO 2024 / 194971 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a beam-vertical member joint structure, which is essential for wooden buildings, that has excellent earthquake resistance and durability against major earthquakes, for example, earthquakes of magnitude 6 or higher. [Means for solving the problem]

[0009] The object of the present invention is to provide a joint structure of a rectangular frame consisting of wooden upper and lower horizontal members and wooden vertical members sandwiched between these horizontal members, in which a polyurethane resin layer having a tensile strength of 30 MPa or more and a tensile elongation of 100% or more is provided on the surface of the vertical member joint and the surface of the horizontal member. Between the wood surface and the urethane resin layer, a primer layer is provided, which is a urethane prepolymer made of polytetramethylene glycol-containing polyol and polyisocyanate, and at least a part of which contains a reaction product of an isocyanate group and an amino group-containing silane coupling agent. This is achieved by using a crossbeam-vertical beam joint structure. [Effects of the Invention]

[0010] The horizontal member-vertical member joint structure according to the present invention has a polyurethane resin layer on the surface of the horizontal member and on the surface of the vertical member joint, which has a tensile strength of 30 MPa or more and a tensile elongation of 100% or more after hardening, thereby enhancing the joint strength of the joint between the horizontal member and the vertical member, and thereby achieving the excellent effect of significantly improving the wall factor. Note that the wall factor is an index used mainly in wooden and steel-framed buildings to evaluate the earthquake resistance and wind resistance of a building, indicating how well a wall can withstand horizontal forces such as earthquakes and wind, and is an index relative to a standard shear wall (wall factor = 1.0) (Patent Document 1, paragraphs

[0063] to

[0064] ). [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a front view showing a frame body having a cross member-vertical member joint structure at four locations in Example 1. [Figure 2] FIG. 10 is a front view showing a frame body having a cross member-vertical member joint structure at four locations in Example 2. [Figure 3] FIG. 10 is a front view showing a frame body having a cross member-vertical member joint structure at four locations in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] The crossbeam-vertical member joint structure of the present invention has a crossbeam-vertical member joint structure in which a wooden crossbeam is joined to a wooden vertical member joint, and the surface of the vertical member joint and the surface of the crossbeam have a coating layer made of polyurethane resin with a tensile strength of 30 MPa or more after hardening and a tensile elongation of 100% or more, for example 300% or more.

[0013] Polyurethane resins that achieve a tensile strength of 30 MPa or more and a tensile elongation of 100% or more after curing include those that primarily contain urethane prepolymers as the resin component. Such urethane prepolymers have terminal isocyanate groups synthesized from polyols and polyisocyanates, with the polyols primarily being polycarbonate polyols and / or polytetramethylene glycols, preferably in an amount of 40% by mass or more, and more preferably 50% by mass or more.

[0014] Examples of polycarbonate polyols include those obtained by reacting at least one aliphatic polyhydric alcohol, such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, diethylene glycol, or cyclohexanedimethylol, with a dialkylene carbonate or dialkyl carbonate, such as diethylene carbonate, dimethyl carbonate, or diethyl carbonate, in which the alkylene or dialkyl group has 2 to 10 carbon atoms. Such polycarbonate polyols preferably have a number average molecular weight Mn of 500 to 3000, and commercially available products such as ETERNACOLL UH-50, UH-100, UH-200, UH-300, PH-50, PH-100, PH-200, PH-300, UC-100, and UM-90U manufactured by UBE, and Nipporan 981, 980R, 982R, 965, 963, 964, and 968 manufactured by Tosoh can be used as they are.

[0015] Polytetramethylene glycol can be used with a molecular weight of 250 to 3000. If the molecular weight is smaller than this, the tensile strength will be high but the tensile elongation will be low, while if the molecular weight is larger than this, the tensile strength will be low but the tensile elongation will tend to be high.

[0016] The polyisocyanate may be an aliphatic, aromatic or alicyclic polyisocyanate. Examples of such isocyanates include MDI (diphenylmethane diisocyanate), hydrogenated MDI, 1,5-naphthalene diisocyanate, tolylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, tetramethylxylene diisocyanate (TMXDI), 1,8-diisocyanatomethyloctane, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, bicycloheptane triisocyanate, and derivatives thereof such as modified products (biuret, allophanate, isocyanurate), and trimethylolpropane adducts, and from the viewpoint of weather resistance, aliphatic polyisocyanates such as isophorone diisocyanate and derivatives thereof are preferred. The use of aromatic isocyanates increases the strength but reduces the stability of the one-component formulation, whereas the use of aliphatic isocyanates improves the stability of the one-component formulation.

[0017] Other polyols can be used to adjust physical properties, provided that the tensile strength of the cured product is not impaired, specifically, in a proportion of less than 60% by weight of the total polyols. Using more than 60% by weight of other polyols is undesirable because it can make it difficult to achieve both tensile strength and tensile elongation. Examples of such other polyols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,3-butanediol, 1,4-butanediol, 4,4'-dihydroxyphenylpropane, 4,4'-dihydroxyphenylmethane, pentaerythritol propylene oxide, ethylene oxide, butylene oxide, styrene oxide, tetramethylene glycol, polyoxypropylene polyol, polyester polyol, and acrylic polyol, with polyester polyol and acrylic polyol being preferred.

[0018] The polyester polyol used is one obtained by dehydration condensation of a dibasic acid and a polyhydric alcohol, or by ring-opening polymerization of ε-caprolactone using a polyhydric alcohol as an initiator, and preferably has a number average molecular weight Mn of 300 to 3,000. In practice, various polyester polyols can be used, such as commercially available products such as the Polylite series manufactured by DIC and the Nipporan series manufactured by Tosoh.

[0019] Examples of acrylic polyols include homopolymers or copolymers of (meth)acrylic monomers having hydroxyl groups, and copolymers of (meth)acrylic monomers having hydroxyl groups with other monomers having polymerizable unsaturated bonds. Preferably, the acrylic polyols used have an average of 2 to 8 hydroxyl groups per molecule.

[0020] Examples of (meth)acrylic monomers having a hydroxyl group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, as well as triol (meth)acrylic acid monoesters such as glycerin (meth)acrylic acid monoester and trimethylolpropane (meth)acrylic acid monoester. These may be used alone or in combination of two or more.

[0021] The glass transition temperature of the acrylic polyol is not particularly limited, and generally, an acrylic polyol having a glass transition temperature of -70 to 60°C can be used. Taking into consideration the viscosity of the urethane prepolymer and the physical properties of the cured product, an acrylic polyol having a hydroxyl value of 50 to 150 mgKOH / g is preferably used. If the hydroxyl value is less than 50 mgKOH / g, the strength and weather resistance of the cured product tend to decrease, while if it exceeds 150 mgKOH / g, the viscosity of the prepolymer increases, which can cause problems in prepolymer production.

[0022] In order to control the curing property of the one-component moisture-curable urethane resin composition or to suppress foaming during curing, a moisture-curable latent curing agent is preferably further added. Specifically, an oxazolidine having a hydroxyl group, such as 2-isopropyl-3-(2-hydroxyethyl)oxazolidine, is added during the synthesis of the urethane prepolymer, or a hydroxyl-containing oxazolidine is reacted with a polyisocyanate in advance and then added.

[0023] Examples of such polyurethane resins include isocyanate group-containing urethane prepolymers, which are reaction products of a polyol, preferably consisting of an acrylic polyol and polytetramethylene glycol or polycarbonate polyol, with an aliphatic polyisocyanate, in which the equivalent ratio of hydroxyl group-containing oxazolidine to isocyanate groups in the reaction product of the polyol and the aliphatic polyisocyanate (hydroxyl groups of the hydroxyl group-containing oxazolidine / isocyanate groups) is 0.05 to 0.55, and which contain oxazolidine groups at least in part (Patent Documents 2 and 3).

[0024] Examples of solvents include aromatic hydrocarbons such as toluene, xylene, Solvent Naphtha 100, and Solvent Naphtha 150; hydrogenated high-boiling aromatic solvents such as Swaclean 150; carbonate solvents such as dimethyl carbonate, diethyl carbonate, and ethylene carbonate; and ethers such as diethyl ether, dimethyl ether, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monobutyl ether acetate, triethylene glycol monobutyl ether acetate, and propylene glycol monomethyl ether acetate. These may be used alone or in combination of two or more. The amount of solvent used in the one-component moisture-curable urethane resin composition is 20 to 60% by mass, from the viewpoints of ensuring coating thickness and workability.

[0025] Furthermore, other additives include antioxidants, ultraviolet absorbers, pigments, thixotropic agents, anti-sagging agents, matting agents, fillers, etc., which may be used as appropriate.

[0026] Prior to forming the urethane resin coating, Vertical members A primer layer is formed on the surfaces of the joints and the cross members. Polytetramethylene glycol-containing polyol Polyisocyanate and A urethane prepolymer consisting of At least a part of which is a reaction product of an isocyanate group and an amino group-containing silane coupling agent A primer containing the above-mentioned prepolymer is used. By forming a primer layer using such a urethane-based prepolymer, it is possible to control the penetration of the urethane resin into the wood and to achieve sufficient adhesion between the wood and the urethane resin layer. Here, the polytetramethylene glycol preferably has a molecular weight of about 200 to 1000. Note that, while primers typically comprise a binder resin, an isocyanate compound, a silane coupling agent, and a solvent, using a primer with such a composition does not provide sufficient adhesion between the wood and the urethane resin layer.

[0027] The structure of the joint between the horizontal member and the vertical member will be explained with reference to Figures 1 to 3. From the viewpoint of wall magnification, the horizontal member-vertical member joint structure is preferably composed of upper and lower horizontal members 1, 1' which serve as foundations or beams, and columns which are vertical members 2 sandwiched between these horizontal members, and the horizontal members are joined to the vertical member joints of a structure which preferably uses diagonal members 3, 3' such as braces or rafters as reinforcing members. Here, the frame joint is generally joined at a right angle, but it may also be at an acute or obtuse angle.

[0028] The urethane resin layer 4 is formed on the surfaces of the vertical member connections and the surfaces of the cross members where the vertical member connections abut, on at least two, preferably three, and more preferably four, surfaces where these contact, generally to a thickness of about 1.5 to 4 mm, preferably about 2 to 4 mm after drying. Furthermore, in the case of frames with diagonal members, the urethane resin layer 4 is provided not only on the surfaces of the horizontal members and vertical member connections, but also on the surfaces of the diagonal members that contact the vertical members or cross members, further increasing the joint strength of the cross member-vertical member joints. The urethane resin can be applied to the surfaces of the horizontal members, vertical member connection surfaces, and diagonal members by spraying (spray gun), brushing, roll coating, spatula, or other methods.

[0029] In this case, in order to further increase the strength of the cross member-vertical member joints, a reinforcing fabric 5 can be preferably disposed in at least a part or all of the urethane resin layer. Examples of reinforcing fabrics include synthetic long fiber woven fabric, synthetic long fiber nonwoven fabric, glass fiber woven fabric, and glass fiber nonwoven fabric, and from the viewpoint of increasing the strength of the urethane resin layer, glass fiber woven fabric is preferably used. [Example]

[0030] Next, the present invention will be described with reference to examples.

[0031] Synthesis Example (1) 80.0 g of polytetramethylene glycol (PTMG2000, manufactured by Mitsubishi Chemical Corporation, with a hydroxyl value of 56 mg KOH / g), 20.0 g of acrylic polyol (ARUFON UH-2041, manufactured by Toa Gosei Co., Ltd., with a hydroxyl value of 120 mg KOH / g), and 7.0 g of diisononyl adipate (DINA) were placed in a 500 ml separable flask equipped with a stirring blade, and the mixture was dried under reduced pressure at 100°C for 4 hours. After cooling, 2.1 g of hydroxyethyl acrylate, 50.8 g of isophorone diisocyanate, 90 g of naphthenic solvent (Maruzen Petrochemicals Swaclean 150) and 0.01 g of dibutyl dilaurate were added, and the temperature was gradually raised to 80°C under a nitrogen atmosphere. After reacting at 80°C for 2 hours, 13.0 g of 2-isopropyl-3-(2-hydroxyethyl)oxazolidine was added and reacted at the same temperature for 1 hour, yielding 262.9 g of one-component moisture-curing polyurethane resin A.

[0032] (2) One-component moisture-curing polyurethane resin A 262.9g Dimethyl carbonate 10g Octanoic acid 0.03g Fumed silica (Evonik ACEMATT3300 10g) ;Secondary particle diameter D50 9.5μm) Amido wax (Kusumoto Chemical Products Disparlon 6650) 6g UV absorber (Ciba-Geigy UV1164) 4g Light stabilizer (HALS292) 4g Hardener 32.1g [2-Isopropyl-3-(2-hydroxyethyl)oxazolidine an adduct of 2 moles of methylisocyanate with 1 mole of hexamethylene diisocyanate; Molecular weight 486.68] The above mixture was thoroughly stirred to obtain a transparent one-component moisture-curable urethane resin composition (viscosity of 2470 mPa·S at 23°C using an E-type viscometer at 5 rpm).

[0033] The one-component moisture-curable resin composition obtained in (2) was used to measure the tensile strength and tensile elongation, and the tensile strength was 44.3 MPa and the tensile elongation was 350%. Tensile test: One-component moisture-curing material is cured at 23°C and 50% RH for 2 weeks, and the thickness A 0.3 mm sheet was prepared, and test pieces were obtained based on No. 4 dumbbells. Tensile strength and tensile elongation measurements were carried out at a speed of 500 mm / min.

[0034] Example 1 The rectangular frame consisted of a lower horizontal member (120 x 120 x 1710 mm) that served as the base, an upper horizontal member (210 x 120 x 1710 mm) that served as a beam, and two vertical members (120 x 120 x 2570 mm) that served as columns located 340 to 460 mm from the ends of the lower horizontal member and the upper horizontal member (210 x 120 x 1710 mm) that served as columns. A primer was applied to an area of ​​approximately 120 x 300 mm on all 16 surfaces at eight L-shaped locations where the horizontal and vertical members met at right angles, and after drying, a 120 x 600 mm polyester fiber sheet (JUU-CE, an Aica Industrial product) made of glass fiber was placed on top of the primer layer on each surface. A urethane resin composition was then applied using a 20 mm long-haired microfiber, roller, rubber spatula, and plastic spatula to a thickness of 2 to 4 mm after drying, and the composition was allowed to dry to form a urethane resin layer (Fig. 1). The primer used here was a reaction mixture of 175 g of polytetramethylene glycol with a molecular weight of 2000 (Mitsubishi Chemical product #2000), 75 g of polytetramethylene glycol with a molecular weight of 250 (Mitsubishi Chemical product #250), 200.0 g of aromatic solvent (Shin-Nihon Kagaku product R100), 82.5 g of isophorone diisocyanate, and 0.3 g of dibutyl dilaurate, which was further reacted with 3.0 g of 3-aminopropyltriethoxysilane.

[0035] Example 2 The rectangular frame consisted of a lower horizontal member (120 x 120 x 1710 mm) that served as the base, an upper horizontal member (210 x 120 x 1710 mm) that served as a beam, and two vertical members (120 x 120 x 2570 mm) that served as columns located 340 to 460 mm from the ends of the lower and upper horizontal members. Two diagonal members (38 x 89 x 2690 mm) were used as reinforcement for the frame. As in Example 1, a primer was applied to the surfaces of the frame where the horizontal members, vertical members, and diagonal members meet, up to a point approximately 30 mm from the point where they meet, and then dried. After this, a urethane resin composition was applied to a thickness of 2 to 4 mm after drying, and this was then dried to form a urethane resin layer (Figure 2).

[0036] Example 3 Using a frame with the diagonal members used in Example 2, a primer was applied to the surfaces of the cross members, vertical members, and diagonal members where they joined, as in Example 2. Then, a glass fiber fabric measuring 360 mm wide and 510 mm long was used at the joint between the lower cross member and vertical member, and a glass fiber fabric measuring 360 mm wide and 865 mm long was used at the joint between the upper cross member and vertical member, and these were arranged to cover the four outer periphery surfaces in the longitudinal direction of each member, including the diagonal member. Next, a urethane resin composition was applied and dried using the same method as in Example 1 to a thickness of 2 to 4 mm after drying, forming a urethane resin layer (Figure 3).

[0037] Comparative Example 1 In Example 1, the urethane resin layer was not formed.

[0038] Comparative Example 2 In Example 2, the urethane resin layer was not formed.

[0039] Comparative Example 3 In Example 3, a coating material (Mitsui Chemicals Industrial Products Swale AR-100: tensile strength: 24 MPa, tensile elongation: 200%) was used in place of the urethane resin composition.

[0040] Loading tests were carried out using the frames obtained in the above examples and comparative examples, and the wall factor was calculated. Loading test: The allowable stress of a wooden frame house is measured against a test specimen placed inside a reaction frame. Design Method (2001 edition): Review of the Japan Housing and Wood Technology Center (foundation) In accordance with the evaluation procedure manual, a 20t jack was used to repeatedly load the structure. The rule of repetition is that the apparent shear deformation angle is 1 / 450, 1 / 300, After three cycles of loading in the order of 1 / 200, 1 / 150, 1 / 100, 1 / 75, and 1 / 50 rad Loading was carried out up to 1 / 15 [rad].

[0041] The results obtained are shown in the following table. table Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Wall magnification 0.56 5.55 6.00 0.11 3.97 4.62

[0042] From the above results, the following can be said: (1) The frame body with urethane resin layers on two sides of the glass fiber fabric had a wall strength five times higher than that without the urethane resin layer (Example 1 - Comparative Example 1). This achieved a strength equivalent to the general wall strength of mud walls, which is 0.5 to 1.0 times. (2) In the case of a frame body having diagonal members, the wall ratio was improved by about 1.4 times by forming a urethane resin layer on four sides (Example 2 - Comparative Example 2). (3) The frame body has diagonal members, and by forming a urethane resin layer with a reinforcing fabric on all four sides, the wall ratio was improved by 1.5 times (Example 3 - Comparative Example 2). (4) Even if a layer with low tensile strength is provided, the desired wall ratio of 5 times or more cannot be achieved (Comparative Example 3). [Explanation of symbols]

[0043] 1,1' beam 2,2' vertical members 3,3' Diagonal 4 Polyurethane resin layer 5 Reinforcement fabric 10 Frame

Claims

1. A cross member-vertical member joint structure in which the joint structure of a rectangular frame body is composed of upper and lower wooden cross members and wooden vertical members, which are columns sandwiched between these cross members, has a polyurethane resin layer on the surface of the vertical member joint and the surface of the cross members, which has a tensile strength of 30 MPa or more and a tensile elongation of 100% or more after hardening, and between the wood surface and the urethane resin layer is provided a primer layer consisting of a urethane prepolymer made from polytetramethylene glycol-containing polyol and polyisocyanate, at least a portion of which contains a reaction product of an isocyanate group and an amino group-containing silane coupling agent.

2. A beam-vertical member joint structure in which the joint structure of a rectangular frame is composed of upper and lower wooden cross members and wooden vertical members (pillars) sandwiched between these cross members, with wooden diagonal members arranged in the joint section, and the surfaces of the vertical member joints, the surfaces of the cross members, and the diagonal members have a polyurethane resin layer with a tensile strength of 30 MPa or more and a tensile elongation of 100% or more after hardening, and between the wood surface and the urethane resin layer is provided a primer layer consisting of a urethane prepolymer made from polytetramethylene glycol-containing polyol and polyisocyanate, at least a portion of which contains a reaction product of an isocyanate group and an amino group-containing silane coupling agent.

3. A crossbeam-vertical member joint structure according to claim 1 or 2, wherein the amino group silane coupling agent is 3-aminopropyltriethoxysilane.

4. 3. A beam-vertical member joint structure according to claim 1, wherein a reinforcing fabric is disposed between the surface of the wood and the polyurethane resin layer.

5. 3. A crossbeam-vertical member joint structure according to claim 1 or 2, wherein the polyurethane resin layer is a reaction product of a polyol consisting of acrylic polyol and polytetramethylene glycol or polycarbonate polyol with an aliphatic polyisocyanate, in which the equivalent ratio of hydroxyl group-containing oxazolidine to isocyanate groups in the reaction product of the polyol and the aliphatic polyisocyanate (hydroxyl group / isocyanate group of the hydroxyl group-containing oxazolidine) is 0.05 to 0.55, and the cured product is an isocyanate group-containing urethane prepolymer having oxazolidine groups in at least a portion thereof.

6. 2. A beam-vertical member joint structure according to claim 1, wherein the urethane resin layer is formed on at least two surfaces of the vertical member joint surface and the horizontal member surface where the vertical member joint abuts.

7. A horizontal member-vertical member joint structure as described in claim 2, wherein the urethane resin layer is formed on at least two surfaces where these contact: the surface of the vertical member joint, the surface of the horizontal member where the vertical member joint abuts, and the surface of the diagonal member where the vertical member joint or the surface of the horizontal member abuts.

8. An isocyanate group-containing urethane prepolymer used in the polyurethane resin layer of a crossbeam-vertical member joint structure according to claim 1 or 2, wherein the polyol consisting of acrylic polyol and polytetramethylene glycol or polycarbonate polyol and aliphatic polyisocyanate are reaction products in which the equivalent ratio of hydroxyl group-containing oxazolidine to isocyanate groups in the reaction product of the polyol and aliphatic polyisocyanate (hydroxyl group / isocyanate group of the hydroxyl group-containing oxazolidine) is 0.05 to 0.55, and at least a portion of it contains oxazolidine groups.

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