JP4993408B2 - Polyurethane resin for decorative sheet primer and primer for decorative sheet using the same - Google Patents

Description

  The present invention relates to a polyurethane-based primer for a decorative sheet used as an interior material or a fitting for a building such as a house, a furniture fixture, a housing equipment or an exterior material for home appliances, and more specifically, for example, A polyurethane primer for a decorative sheet excellent in durability including water resistance and moisture resistance, particularly suitable for a portion exposed to water (cold water or hot water) or moisture (water vapor) such as a bathroom or kitchen It is.

  Conventionally, as a decorative sheet for decorative steel sheets used for, for example, the exterior of an electric refrigerator or the interior of a unit bath, on a base sheet made of an opaque colored polyolefin resin film or the like, a pattern layer by printing or the like is used. A decorative sheet formed by laminating a transparent thermoplastic resin layer made of an axially stretched polyester resin film or the like is widely used (Patent Documents 1 to 3, etc.).

Japanese Unexamined Patent Publication No. 63-280627 Japanese Patent Laid-Open No. 10-166499 JP-A-10-258488

  However, in the decorative sheet using the conventional adhesive system, the bathroom interior that becomes hot and humid due to the hot water of the bathtub or the hot water of the shower, the scattering of the hot water of the tap water or the water heater, the steam from the boiling pot, In kitchens exposed to hot water that has been spilled over, around windows that condensate on the surface when cold, and in the vicinity of the outer wall, peeling at the laminated interface and swelling of the decorative surface may occur.

  In such a case, a primer is generally used to improve the adhesion. For example, Patent Document 4 proposes a two-component curable urethane resin of acrylic polyol and polyisocyanate as a primer. Patent Document 5 proposes an acrylic-polyester urethane copolymer obtained by extending a chain with a diamine to a prepolymer obtained by reacting acrylic polyol, polyester polyol, and diisocyanate.

JP-A-2005-313411 JP 2001-260109 A

  However, these primers did not sufficiently satisfy the moisture resistance under more severe conditions (for example, boiling test).

  According to the present invention, it is possible to provide a polyurethane resin for a primer for a decorative sheet that is particularly required to have moisture resistance, such as a wallpaper for water, and a primer for a decorative sheet using the same.

  The present invention is a primer for a decorative sheet excellent in durability including water resistance and moisture resistance, particularly suitable for a part exposed to water (cold water or hot water) or moisture (water vapor) such as a bathroom or a kitchen. The purpose of the present invention is to provide a polyurethane resin and a primer for a decorative sheet using the same.

  As a result of repeated studies in order to solve such problems, the inventors have found that the following polyurethane resin for a decorative sheet primer and a primer for a decorative sheet using the same solve the above problems, thereby completing the present invention.

  That is, this invention is shown by the following (1)-(4).

(1) A polyurethane resin for a primer of a decorative sheet obtained by reacting the following (A) to (G), wherein the polyurethane resin has a crosslinking point content derived from (D) of 0.01 to 0.1 mmol. / G of polyurethane resin for primer of decorative sheet.
(A) Acrylic polyol having a number average molecular weight of 1,000 to 30,000 (B) Polycarbonate polyol having a number average molecular weight of 500 to 3,000 (C) Low molecular diol having a molecular weight of less than 500 (D) Low molecular triol having a molecular weight of less than 500 (E) Organic diisocyanate (F) Low molecular diamine having a molecular weight of less than 500 (G) Amino alcohol having a molecular weight of less than 500

(2) (C) Low molecular diol, (E) Organic diisocyanate, and (F) Low molecular diamine are compounds having a cyclic structure. resin.

(3) The polyurethane resin for a primer of a decorative sheet according to (1) or (2), wherein the low molecular triol (D) is trimethylolpropane.

(4) A decorative sheet comprising 1 to 20 parts by mass of a polyisocyanate curing agent (each in terms of solid content) based on 100 parts by mass of the polyurethane resin of any one of (1) to (3). Primer.

  The present invention provides a primer for a decorative sheet obtained by reacting (A) to (G) described later, and having a crosslinking point content derived from (D) of 0.01 to 0.1 mmol / g. Polyurethane resin. When the crosslinking point content is too small, the moisture resistance, moist heat resistance and the like are insufficient. When there is too much content of a crosslinking point, resin itself will become easy to gelatinize at the time of manufacture.

  The (A) acrylic polyol used in the present invention is obtained by a polymerization reaction of an unsaturated double bond-containing compound (acrylic monomer). The polymerization reaction is usually a radical polymerization reaction. As this acrylic monomer, acrylic acid esters such as alkyl acrylate, cycloalkyl acrylate, phenyl acrylate, benzyl acrylate, glycidyl acrylate, alkyl methacrylate, cycloalkyl methacrylate, phenyl methacrylate, benzyl methacrylate, Methacrylic esters such as glycidyl methacrylate, vinyl ester compounds such as vinyl acetate and vinyl propionate, vinyl alkyl ethers such as vinyl methyl ether, vinyl cyclohexyl ether, vinyl phenyl ether, vinyl benzyl ether, vinyl glycidyl ether and other vinyl ethers Compounds, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, ethylene such as styrene, vinyltoluene and α-methylstyrene Unsaturated double bond-containing aromatic compounds, maleic acid diesters such as dialkyl maleate, fumaric acid diesters such as dialkyl fumarate, itaconic acid diesters such as dimethyl itaconate, and dialkyls such as N, N-dimethylacrylamide Ε-caprolactone of acrylamides, heterocyclic vinyl compounds such as N-vinylpyrrolidone, 2-vinylpyridine, etc., 2-hydroxyethyl acrylate, hydroxypropyl acrylate, polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, 2-hydroxyethyl acrylate Adducts, β-methyl-valerolactone adducts of 2-hydroxyethyl acrylate, acrylates such as glycerol monoacrylate, glycerol diacrylate, 2-hydroxy Ethyl methacrylate, hydroxypropyl methacrylate, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, ε-caprolactone adduct of 2-hydroxyethyl methacrylate, β-methyl-valerolactone adduct of 2-hydroxyethyl methacrylate, glycerol monomethacrylate, glycerol di Examples include methacrylates such as methacrylate, allyl compounds such as allyl alcohol, glycerol monoallyl ether, and glycerol diallyl ether. The acrylic polyol used in the present invention includes a hydroxyl group-containing acrylic monomer selected from 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate, and an alkyl acrylate and alkyl methacrylate (particularly preferably methyl acrylate and methyl methacrylate). It is preferable to use an acrylic monomer selected from

  The content of the (A) acrylic polyol decorative sheet used in the present invention with respect to the polyurethane resin for primer is 20 to 80% by mass, more preferably 20 to 50% by mass in terms of solid content. When the acrylic polyol content is less than the lower limit, the weather resistance and the like of the obtained primer are deteriorated.

  Examples of (B) polycarbonate polyol used in the present invention include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 2-ethyl-4-butyl-1, 3-propanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, dimer acid diol, ethylene oxide or propylene oxide adduct of bisphenol A, bis (β -Hydroxyethyl) benzene, xylyl It is obtained from dealcoholization reaction or dephenol reaction of one or more kinds of low molecular polyols such as ethylene glycol, glycerin, trimethylolpropane, pentaerythritol and low molecular carbonates such as ethylene carbonate, diethyl carbonate and diphenyl carbonate. is there. In the present invention, a preferred polycarbonate polyol is a polycarbonate polyol obtained from a low molecular diol having 2 to 10 carbon atoms, and a polycarbonate polyol derived from 1,6-hexanediol is particularly preferred because it is most readily available.

  In addition, polymer polyols other than the above (A) acrylic polyol and (B) polycarbonate polyol can be used as necessary. This polymer polyol has a number average molecular weight of 500 to 3,000. For example, polyester polyol, polyamide ester polyol, polyether polyol, polyether ester polyol, polyolefin polyol, animal and plant polyol, dimer acid polyol, hydrogen Additive dimer acid type polyol etc. are mentioned. In addition, epoxy resin, polyamide resin, polyester resin, acrylic resin, rosin resin, urea resin as long as the number average molecular weight is 500 to 3,000 and the molecule has one or more active hydrogen groups on average. Further, active hydrogen group-containing resins such as melamine resin, phenol resin, coumarone resin, and polyvinyl alcohol can also be used.

  The (C) low molecular weight diol preferred in the present invention is a compound having a molecular weight of less than 500, preferably 300 or less, and having two alcoholic hydroxyl groups in one molecule. Specifically, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 2-ethyl-4-butyl-1,3-propanediol, diethylene glycol, diethylene glycol Propylene glycol, neopentyl glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, dimer acid diol, ethylene oxide or propylene oxide adduct of bisphenol A, bis (β-hydroxyethyl) benzene, xylylene Glycol and the like. In the present invention, an alicyclic diol that has good solubility and can impart durability is preferable, and cyclohexane-1,4-diol and cyclohexane-1,4-dimethanol are particularly preferable.

  The low molecular weight triol (D) used in the present invention is a compound having a molecular weight of less than 500, preferably 300 or less, and having three alcoholic hydroxyl groups in one molecule. Specific examples include glycerin, trimethylolpropane, hexanetriol and the like. (C) When low molecular triol is not used, the water resistance and heat-and-moisture resistance of the resulting primer are significantly reduced. In the present invention, in order to efficiently introduce a crosslinked structure into the resin skeleton, trimethylolpropane in which all hydroxyl groups are primary hydroxyl groups having high reactivity is preferable.

  The organic diisocyanate (E) used in the present invention includes tetramethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, decamethylene diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, and the like. Aliphatic diisocyanates such as aliphatic diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tetramethylxylylene diisocyanate, cyclohexyl diisocyanate, 2,4-tolylene diisocyanate, 2, , 6-Tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmeta Diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, o-xylylene diisocyanate, m-xylylene diisocyanate, p- Xylylene diisocyanate, tetramethyl xylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'- Fragrances such as dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate Diisocyanates, mixtures of two or more of these, urethane modified products of these organic diisocyanates, allophanate modified products, urea modified products, biuret modified products, uretdione modified products, uretoimine modified products, isocyanurate modified products, carbodiimide modified products, etc. Can be mentioned. The organic diisocyanate (D) preferred in the present invention is an alicyclic diisocyanate which has a low possibility of gelation during production and is excellent in weather resistance and mechanical strength of the resin, and isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate are particularly preferred.

  The low molecular diamine (F) used in the present invention has a molecular weight of less than 500, specifically, aliphatic diamines such as tetramethylene diamine, hexamethylene diamine and dodecyl diamine, isophorone diamine, hydrogenated diphenylmethane diamine and hydrogenated xylylene. Examples thereof include alicyclic diamines such as range amine, aromatic diamines such as tolylene diamine, and diphenylmethane diamine. In the present invention, isophoronediamine is preferred in consideration of the solubility and mechanical strength of the resulting resin.

  The (G) amino alcohol used in the present invention is used to adjust the (number average) molecular weight of the resin during the production of the polyurethane resin for the primer of the decorative sheet, and is introduced at the end of the polyurethane resin skeleton. Is done. This (G) amino alcohol is a compound having a molecular weight of less than 500 and having a hydroxyl group and a primary and / or secondary amino group in one molecule. Specific examples include monoethanolamine, diethanolamine, monopropanolamine, dipropanolamine and the like.

  The synthetic method in the polyurethane resin for primer of the decorative sheet of the present invention comprises (A) acrylic polyol, (B) polycarbonate polyol, (C) low molecular diol, (D) low molecular triol, and (E) organic diisocyanate. The isocyanate group-containing prepolymer is reacted to obtain an isocyanate group-containing prepolymer, and then this prepolymer is chain-extended with (F) a low molecular diamine and (G) amino alcohol until the predetermined molecular weight is reached. Method (prepolymer method).

  As a reaction catalyst in the prepolymerization reaction, a known so-called urethanization catalyst can be used. Specific examples thereof include organic metal compounds such as dibutyltin dilaurate and dioctyltin dilaurate, organic amines such as triethylenediamine and triethylamine, and salts thereof.

  The reaction apparatus for the polyurethane resin used in the present invention may be any apparatus as long as the above reaction can be achieved, and examples thereof include a mixing kneading apparatus such as a reaction kettle or kneader equipped with a stirrer, a uniaxial or multiaxial extrusion reaction apparatus. It is done. A preferred synthesis method of the polyurethane resin in the present invention is a prepolymer method in a solution.

  The prepolymer method in solution will be described in more detail. In producing a polyurethane resin, first, (A) acrylic polyol, (B) polycarbonate polyol, and (C) low-molecular triol are dissolved in an organic solvent such as a ketone or ester having no active hydrogen group or a hydrocarbon.

  Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents such as pentane, hexane, and octane, alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane, and methylcyclohexane, acetone , Ketone solvents such as methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, ether solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, Cellosolve solvents such as propylene glycol dimethyl ether and propylene glycol monomethyl ether acetate, monobasic acid ester solvents such as ethyl acetate and butyl acetate Dimethyl adipate, dimethyl succinate, dibasic esters such as dioctyl phthalate, dimethyl formamide, dimethyl acetamide, not particularly limited as long as it is inactive to the isocyanate group, such as N- methylpyrrolidone. Also, an alcohol solvent such as isopropanol can be used as a diluting solvent in the reaction between the isocyanate group and the amino group or after the completion of the reaction. In the present invention, it is preferable not to use toluene because toluene is likely to remain on the olefin base material.

  (D) Organic diisocyanate is added to the above polyol solution, and after adding a urethanization catalyst as necessary, the reaction temperature is 30 to 100 ° C., preferably 50 to 80 ° C., and reacted for several hours to contain an isocyanate group. A urethane prepolymer solution is synthesized. At this time, the isocyanate group / hydroxyl molar ratio (R value) is preferably 1.1 to 2.5, and particularly preferably 1.1 to 2.0.

  When the R value is less than 1.1, the durability and blocking resistance of the finally obtained polyurethane-based primer are lowered. Moreover, when R value exceeds 2.5, the solubility to a solvent and adhesiveness of a polyurethane resin fall.

  (E) Low molecular diamine and (F) amino alcohol are added to the isocyanate group-containing urethane prepolymer solution thus obtained, and a chain extension reaction is carried out. By reacting at a reaction temperature of 30 to 80 ° C., preferably 30 to 50 ° C., until the isocyanate group disappears, a desired polyurethane resin solution is obtained.

  The number average molecular weight of the polyurethane resin is measured by a gel permeation chromatography (GPC) method using a polystyrene calibration curve, preferably 5,000 to 100,000, and particularly preferably 8,000 to 50,000. When the number average molecular weight is less than 5,000, the durability is lowered. When the number average molecular weight exceeds 100,000, the fluidity is poor and the workability is poor.

  In the polyurethane resin for primer of the decorative sheet of the present invention, the above-mentioned polyurethane resin is added to pigments, dyes, thixotropic agents, flame retardants, antioxidants, ultraviolet absorbers, antifoaming agents, thickeners, dispersants, surfactants. Additives such as agents, fungicides, antibacterial agents, preservatives, catalysts, fillers, etc. and auxiliary binders such as nitrified cotton can be used.

  The decorative sheet primer of the present invention is obtained by blending a polyisocyanate curing agent with the above-described polyurethane resin for a decorative sheet primer.

  The addition amount of the polyisocyanate curing agent is 1 to 20 parts by mass with respect to 100 parts by mass of the polyurethane resin (in terms of each solid content). When there are too few compound amounts of a polyisocyanate hardening | curing agent, the physical property improvement of the film obtained is not seen. In addition, when the amount of the curing agent is too large, the curing agent molecules are simply bonded without cross-linking the polyurethane molecules as the main agent, so that the physical properties are hardly improved. Examples of the polyisocyanate curing agent include products of Nippon Polyurethane Industry Co., Ltd., hexamethylene diisocyanate-modified coronate (registered trademark) HX, coronate HL, tolylene diisocyanate-modified coronate L, coronate 2030, coronate 2031 and the like. These may be used alone or in combination.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In the following examples and comparative examples, “parts” and “%” mean “parts by mass” and “% by mass”, respectively.

Example 1
[Manufacture of polyurethane resin]
In a reaction vessel equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, AC-1 is 429.1 parts, PC-1 is 306.5 parts, CHDM is 4.4 parts, and TMP is 2.1 parts. Charged and mixed uniformly. Thereafter, 50.1 parts of IPDI and 39.4 parts of H ₁₂ MDI were added, and 0.03 part of DOTDL was added as a urethanization catalyst, and the mixture was reacted with stirring at 80 ° C. for 4 hours under a nitrogen stream. An isocyanate group-terminated urethane prepolymer solution having a group content of 0.387 mmol / g was obtained. Thereafter, 910 parts of MEK and 23 parts of MIBK were added to make uniform, and an amine mixed solution consisting of 210 parts of IPA, 21.9 parts of IPDA, and 3.9 parts of MEA was charged in advance to carry out chain extension reaction at 40 ° C. For 1 hour to obtain a polyurethane resin solution PU-3. PU-3 had a solid content of 30.0% and a viscosity of 680 mPa · s.

Examples 2-3 and Comparative Examples 1-3
Polyurethane resins PU-1 to 2 and 4 to 5 were obtained using the same raw materials and the same reaction vessel and procedure as in Example 1 with the preparation shown in Table 1. Since Comparative Example 3 (PU-6) gelled during the chain extension reaction, subsequent evaluation could not be performed.

Examples 2-3, Comparative Examples 1-3, Table 1 AC-1: MIBK solution of copolymerized acrylic polyol of MMA and HEMA
Hydroxyl value = 5.6 mg KOH / g (solid content)
Solid content = 40%
Number average molecular weight = 20,000
* MMA: Methyl methacrylate
HEMA: 2-hydroxyethyl methacrylate
MIBK: methyl isobutyl ketone PC-1: polycarbonate diol obtained from 1,6-HD and DEC
Number average molecular weight = 2,000
* 1,6-HD: 1,6-hexanediol
DEC: diethyl carbonate TMP: trimethylolpropane IPDI: isophorone diisocyanate H ₁₂ MDI: hydrogenated diphenylmethane diisocyanate DOTDL: dioctyltin dilaurate MEK: methyl ethyl ketone MIBK: methyl isobutyl ketone IPA: isopropanol IPDA: isophorone diamine MEA: monoethanolamine

[Primer evaluation]
Example 4
Primer evaluation was performed using PU-3 as the main agent. Coronate (registered trademark) HX was used as the curing agent. The compounding ratio of main agent / curing agent was main agent / curing agent = 100 / 3.8 (each in terms of solid content). The adhesion, blocking resistance, and weather resistance (with / without boiling) of the primer were evaluated.
Coronate HX: product of Nippon Polyurethane Industry Co., Ltd. Isocyanurate-modified polyisocyanate of hexamethylene diisocyanate * Boiling conditions: Put a coating sample (see below) in boiling water for 20 minutes and boil.

(1) Adhesion The primer obtained by blending the main agent / curing agent is applied to the discharge-treated surface of the discharge-treated surface of a 15 μm thick corona discharge-treated stretched polyethylene terephthalate (hereinafter abbreviated as PET) film with a bar coater. After coating and heating at 70 ° C. for 30 seconds and aging at room temperature for 1 day, an adhesive cellophane tape was applied to the coated surface, and this was rapidly peeled off. Moreover, the coating sample obtained similarly was evaluated after boiling on the above-mentioned conditions.
In addition, a primer is applied to PET in the same procedure as described above, heated at 70 ° C. for 30 seconds, and then aged at room temperature for 1 day, and then an acrylic electron beam curable resin is applied to the primer application surface, and 5 Mrad. After being irradiated with an electron beam for 1 second, it was cut into a grid pattern with a cutter-knife on an acrylic electron beam curable resin-coated surface with or without boiling, and an adhesive cellophane tape was attached and peeled off rapidly.
Primer coating amount: 3 g / m ^{2 for} resin
Electron beam curable resin coating amount: 5 g / m ^{2 in} resin content
Evaluation A: The film was not peeled off at all.
A: 80% to 100% of the film remained.
Δ: 50% to 80% of the film remained.
X: Only 50% or less of the film remained.

(2) Blocking resistance A primer was applied to the discharge-treated surface of a PET film in the same manner as described above, and after aging at 40 ° C. for 7 days, it was layered on the surface and back and blocked at 50 ° C. and 80 RH% for 24 hours. Blocking resistance was evaluated by applying a load of 0.5 MPa with a tester. Moreover, the coating sample obtained similarly was evaluated after boiling on the above-mentioned conditions.
Primer coating amount: 3 g / m ^{2 for} resin
Evaluation (circle): It peels without resistance at the time of peeling, and a film does not fall off.
(Triangle | delta): The resistance at the time of peeling is a little large, and the fall of a film is seen somewhat.
X: The resistance at the time of peeling is large, and the fall of the film is observed.

(3) Weather resistance A primer was applied to the discharge-treated surface of a PET film in the same manner as described above, aged at 40 ° C. for 7 days, allowed to stand at room temperature for 1 day, and then QUV manufactured by Q-PANEL. After setting in a testing machine and repeating the following cycle 10 times, an adhesive cellophane tape was affixed to the coated surface, and this was peeled off rapidly. Moreover, the coating sample obtained similarly was evaluated after boiling on the above-mentioned conditions.
1 cycle condition with QUV tester:
70 ° C. × 8 hours (Dry) + 50 ° C. × 4 hours (Wet)
Irradiation energy: 0.59 (W / m ² / nm)
Primer coating amount: 3 g / m ^{2 for} resin
Evaluation ○: The film remained 80% to 100%.
Δ: 50% to 80% of the film remained.
X: Only 50% or less of the film remained.

Examples 5-6, Comparative Examples 4-5
Primer evaluation was performed in the same manner as in Example 4. The compounding ratio of the main agent / curing agent was the same as in Example 4.

Table 2 shows that the primer of the present invention has particularly good adhesion after boiling, and that the blocking resistance and weather resistance are greatly improved. On the other hand, in the comparative example, the blocking resistance and the weather resistance showed the same performance as the primer of the present invention, but the adhesion after boiling was particularly poor.

Claims (4)

A polyurethane resin for a primer of a decorative sheet obtained by reacting the following (A) to (G), wherein the content of crosslinking points derived from (D) in the polyurethane resin is 0.01 to 0.1 mmol / g A polyurethane resin for a primer of a decorative sheet, characterized by being.
(A) Acrylic polyol having a number average molecular weight of 1,000 to 30,000 (B) Polycarbonate polyol having a number average molecular weight of 500 to 3,000 (C) Low molecular diol having a molecular weight of less than 500 (D) Low molecular triol having a molecular weight of less than 500 (E) Organic diisocyanate (F) Low molecular diamine having a molecular weight of less than 500 (G) Amino alcohol having a molecular weight of less than 500   The polyurethane resin for a primer for a decorative sheet according to claim 1, wherein (C) the low molecular diol, (E) the organic diisocyanate, and (F) the low molecular diamine are compounds having a cyclic structure.   3. The polyurethane resin for a primer for a decorative sheet according to claim 1 or 2, wherein the low molecular triol (D) is trimethylolpropane. A primer for a decorative sheet, further comprising using 1 to 20 parts by mass of a polyisocyanate curing agent (each in terms of solid content) based on 100 parts by mass of the polyurethane resin according to any one of claims 1 to 3. .