Resin composition for impregnating wood substrates and resin-impregnated wood substrates

Abstract

To provide a resin composition with which it is possible to manufacture a resin-impregnated woody base material that is excellent in adhesion to a cured coating film, water resistance, and weather resistance while being excellent in curability in the interior of wood.SOLUTION: A resin composition of the invention is used for impregnation into a woody base material, and includes (A) isocyanate (meth)acrylate, (B) nitrogen-containing mono function (meth)acrylate monomer (except (A) component), and (C) a photoinitiator.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition used for impregnation of wood-based substrates. The present invention also relates to a wood-based substrate impregnated with the resin composition. [Background technology]

[0002] In recent years, the use of wood has been expanding due to increased housing demand resulting from teleworking during the COVID-19 pandemic, policies promoting the use of domestically produced timber, and international efforts toward the SDGs. Wood is used not only as interior material but also as exterior material exposed to the outdoors (building exterior walls, decks, balconies, fences, window frames, wooden doors, etc.).

[0003] When wood is used as exterior material exposed to the outdoors, it is often painted. The main purpose of outdoor painting is to protect the wood surface from weather-related deterioration caused by natural elements such as sunlight, wind and rain, dew and frost, temperature changes, and humidity, as well as from surface contaminants such as mold, and to maintain its aesthetic appearance. In Japan, wood protective coatings that provide a semi-transparent finish that does not easily impair the wood's texture are widely used. Wood protective coatings are broadly classified into two types: those that impregnate the wood to make the coating film less noticeable (impregnation type) and those that form a coating film on the surface (film-forming type). In the impregnation type, fine cracks and peeling occur uniformly dispersed, and the coating film gradually disappears from the surface as if weathered. For example, Patent Documents 1 to 3 disclose resin compositions of the wood impregnation type. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-055719 [Patent Document 2] Japanese Patent Publication No. 2007-326313 [Patent Document 3] Special Publication No. 2008-540160 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The inventors of this invention have found that when wood with a conventional coating is exposed to the outdoors, deterioration easily leads to paint peeling and whitening, and this is particularly pronounced near the end grain. When exposed to the outdoors, ultraviolet rays from sunlight and moisture from rain synergistically accelerate the deterioration of the wood and coating compared to indoor environments. In particular, the area near the end grain of wood is susceptible to the above effects because moisture easily penetrates through tracheids and vessels depending on the tree species. Therefore, by impregnating the wood substrate with an impregnation-type resin composition, it is expected that the penetration of moisture into the wood surface, especially the surface near the end grain, will be prevented, leading to the suppression of deterioration and improvement of the durability of the wood substrate. However, when impregnating the wood substrate with an impregnation-type resin composition, a drying process using solvents, etc., is required, which presents the challenge of needing to shorten the work efficiency. On the other hand, when conventional UV-curing paints are impregnated into the wood substrate, ultraviolet rays do not reach the inside of the wood, resulting in areas where curing does not proceed sufficiently, which presents the challenge of low weather resistance and insufficient suppression of whitening of the wood substrate.

[0006] Therefore, the present invention aims to provide a resin composition that can produce a resin-impregnated wood substrate that exhibits excellent curing properties within the wood, as well as excellent adhesion to the cured coating film, water resistance, and weather resistance. [Means for solving the problem]

[0007] As a result of diligent research, the inventors of the present invention have found that the above problems can be solved by including (A) isocyanate (meth)acrylate, (B) nitrogen-containing monofunctional (meth)acrylate monomer (excluding component (A)), and (C) a photopolymerization initiator in a resin composition for impregnating wood substrates. The present invention was completed based on this finding.

[0008] In other words, the present invention provides the following invention. [1] A resin composition used for impregnation into a wood substrate, (A) Isocyanate (meth)acrylate and (B) Nitrogen-containing monofunctional (meth)acrylate monomers (excluding component (A)) (C) Photopolymerization initiator and A resin composition containing the following: [2] The resin composition according to [1], wherein the content of (A) isocyanate (meth)acrylate is 20% by mass or more and 70% by mass or less based on 100% by mass of the solid content of the resin composition. [3] The resin composition according to [1] or [2], wherein the (A) isocyanate (meth)acrylate is an oligomer or polymer. [4] The resin composition according to any one of [1] to [3], wherein the (A) isocyanate (meth)acrylate has an isocyanate content of 10% or more if it has one or more but less than two (meth)acrylate groups in one molecule, and an isocyanate content of 3% or more if it has two or more (meth)acrylate groups in one molecule. [5] The resin composition according to any one of [1] to [4], wherein the (B) nitrogen-containing monofunctional (meth)acrylate monomer comprises (meth)acryloylmorpholine. [6] The resin composition according to any one of [1] to [5], wherein the content of the nitrogen-containing monofunctional (meth)acrylate monomer (B) is 5% by mass or more and 75% by mass or less based on 100% by mass of the solid content of the resin composition. [7] The resin composition according to any one of [1] to [6], wherein the content of the (C) photopolymerization initiator is 1% by mass or more and 15% by mass or less based on 1000 mass of the solid content of the resin composition. [8] A resin composition according to any one of [1] to [7], wherein the viscosity (KU value) at 25°C is 49 or more and 80 or less. [9] A solvent-free resin composition as described in any of [1] to [8].

[10] A wood substrate impregnated with any of the resin compositions described in [1] to [9].

[11] The wood substrate according to

[10] , having a hardened coating on its surface. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a resin composition that can produce a resin-impregnated wood substrate that exhibits excellent curing properties within the wood, as well as excellent adhesion to the cured coating film, water resistance, and weather resistance. Furthermore, according to the present invention, it is also possible to provide a resin-impregnated wood substrate that combines excellent adhesion, water resistance, and weather resistance with the characteristics of UV curing, thereby enabling efficient continuous coating lines from impregnation coating to laminated film coating. [Modes for carrying out the invention]

[0010] The present invention will be described in more detail below. In this specification, "(meth)acrylate" refers to acrylate and methacrylate, and "(meth)acryloyl" refers to acryloyl and methacryloyl. Furthermore, "solids" refers to the resin composition excluding volatile components such as organic solvents.

[0011] <Resin composition> The resin composition according to the present invention comprises at least (A) isocyanate (meth)acrylate, (B) nitrogen-containing monofunctional (meth)acrylate monomer (excluding component (A)), and (C) a photopolymerization initiator. The resin composition according to the present invention may further contain other (meth)acrylate monomers (excluding components (A) and (B)). Because the resin composition according to the present invention contains the above components, the curing reaction proceeds not only by ultraviolet irradiation but also by moisture (such as humidity in the air). In other words, the resin composition according to the present invention is a so-called dual-cure type. Therefore, the resin composition according to the present invention exhibits excellent curability even inside wood where the curing reaction by ultraviolet irradiation is difficult to proceed, and can therefore be suitably used for impregnation into wood substrates. By using such a resin composition, it is possible to manufacture a resin-impregnated wood substrate with excellent adhesion to the cured coating film, water resistance, and weather resistance.

[0012] The viscosity (KU value) of the resin composition according to the present invention at 25°C is preferably 49 or more and 80 or less, more preferably 49 or more and 70 or less. If the viscosity (KU value) of the resin composition according to the present invention at 25°C is within the above numerical range, impregnation into the woody base material becomes easy. Note that the viscosity (KU value) of the resin composition according to the present invention at 25°C is the value measured with a Stormer viscometer under the conditions described in JIS K 5600-2-2.

[0013] Hereinafter, each component of the resin composition according to the present invention will be described in detail.

[0014] ((A) Isocyanate (meth)acrylate) The isocyanate (meth)acrylate contained in the resin composition according to the present invention (hereinafter also referred to as component (A)) has an isocyanate group (-N=C=O) and an acryloyl group (CH2=CHCO-) and / or a methacryloyl group (CH2=C(CH3)-CO-). Isocyanate (meth)acrylate is a dual-cure type because the isocyanate group contributes to the curing reaction (formation of urea bond) by moisture (such as moisture in the air), and the (meth)acryloyl group contributes to the curing reaction by ultraviolet irradiation. By using such isocyanate (meth)acrylate, it has excellent curability even inside wood where the curing reaction by ultraviolet irradiation hardly progresses, and thus can be suitably used for impregnation into the woody base material. By using such a resin composition, it is possible to produce a resin-impregnated woody base material excellent in adhesion to the cured coating film, water resistance, and weather resistance.

[0015] When an isocyanate (meth)acrylate has one or more but less than two (meth)acrylate groups in one molecule, the isocyanate content is preferably 10% or more, more preferably 12% or more, preferably 25% or less, and more preferably 20% or less. Furthermore, when an isocyanate (meth)acrylate has two or more (meth)acrylate groups in one molecule, the isocyanate content is preferably 3% or more, more preferably 5% or more, preferably 25% or less, and more preferably 20% or less. If the isocyanate content of the isocyanate (meth)acrylate is within the above numerical range, the curing reaction (formation of urea bonds) due to moisture (such as humidity in the air) proceeds more easily. The isocyanate content of isocyanate (meth)acrylate is expressed as the mass ratio of isocyanate groups (-NCO: Mw=42) to the total mass, and can be calculated using the method specified in the following Japanese Industrial Standard JIS K 1603-1 Test Method for Aromatic Isocyanates in Polyurethane Raw Materials.

[0016] As the isocyanate (meth)acrylate, any monomer, oligomer, or polymer can be used. As the isocyanate (meth)acrylate, for example, a compound having one isocyanate group and one polymerizable unsaturated group can be used. As a compound having one isocyanate group and one polymerizable unsaturated group, for example, isocyanate methyl (meth)acrylate, isocyanate ethyl (meth)acrylate, isocyanate propyl (meth)acrylate, isocyanate butyl (meth)acrylate, isocyanate octyl (meth)acrylate, p-methacryloxy-α,α'-dimethylbenzyl isocyanate, m-acryloxy-α,α'-dimethylbenzyl isocyanate, and other isocyanate alkyl group (meth)acrylates, m- or p-isopropenyl- Examples of reaction products include α,α'-dimethylbenzyl isocyanate, 2-methacryloyloxyethyl isocyanate, 2-acryloyloxyethyl isocyanate, and reaction products of 1 mole of hydroxyalkyl (meth)acrylate and 1 mole of diisocyanate compound. Specifically, examples include compounds obtained by equimolar addition reactions of compounds having two (differently reactive) isocyanate groups, such as isophorone diisocyanate, with hydroxyl group-containing polymerizable unsaturated monomers such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

[0017] Examples of compounds having two or more isocyanate groups or unsaturated groups include compounds obtained by reacting some of the isocyanate groups of a polyisocyanate compound having three or more isocyanate groups with a hydroxyl group-containing polymerizable unsaturated compound; and compounds obtained by reacting some or all of the carbodiimide groups of a carbodiimide group-containing isocyanate compound with a carboxyl group-containing polymerizable unsaturated compound.

[0018] Furthermore, as isocyanate (meth)acrylate, it may be obtained, for example, by reacting a polyisocyanate with a hydroxyl group-containing (meth)acrylate, or by reacting a polyisocyanate with a hydroxyl group-containing (meth)acrylate and, if necessary, other monomers.

[0019] The polyisocyanate described above is not limited to a specific number of carbon atoms as long as it does not impair the effects of the present invention. For example, linear or branched isocyanate group-containing hydrocarbons, isocyanate group-containing cyclic hydrocarbons, and isocyanate group-containing aromatic hydrocarbons with a total carbon number of 4 to 20, preferably 6 to 15 carbon atoms, can be used.

[0020] Specifically, examples include, but are not limited to, linear hydrocarbons containing isocyanate groups such as tetramethylene diisocyanate and hexamethylene diisocyanate; branched hydrocarbons containing isocyanate groups such as 2,2,4-trimethylhexamethylene diisocyanate; cyclic hydrocarbons containing isocyanate groups such as isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated toluene diisocyanate; and aromatic hydrocarbons containing diisocyanate groups such as p-phenylene diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, 1,3-xylene diisocyanate, dianisidine diisocyanate, tetramethylxylene diisocyanate, 1,5-naphthalene diisocyanate, tolylene diisocyanate, and 4,4-diphenylmethane diisocyanate.

[0021] The above polyisocyanates may be modified with adducts, allophanates, isocyanurates, etc. Examples of adduct-modified polyisocyanates include hexamethylene diisocyanate modified with trimethylolpropane. Examples of allophanate-modified polyisocyanates include allophanate-modified hexamethylene diisocyanate. Examples of isocyanurate-modified polyisocyanates include isocyanurate-modified toluene diisocyanate. In addition, polyfunctional isocyanates such as dimethyltriphenylmethanetetraisocyanate, triphenylmethanetriisocyanate, and isocyanate group-containing acrylates may be used as polyisocyanates other than those mentioned above. Such polyisocyanates may be used individually or in combination of two or more.

[0022] As the hydroxyl group-containing (meth)acrylate mentioned above, a (meth)acrylate having at least one hydroxyl group, preferably 1 to 5, can be used. Furthermore, the number of carbon atoms in such a hydroxyl group-containing (meth)acrylate is not limited as long as it does not impair the effects of the present invention, but it is preferable that it has hydrocarbon moieties with 2 to 20 carbon atoms. Here, the hydrocarbon moiety refers to an organic group having a linear or branched aliphatic hydrocarbon group, alicyclic hydrocarbon group, or aromatic hydrocarbon group, and the aliphatic hydrocarbon group or alicyclic hydrocarbon group may be saturated or unsaturated. In addition, some of the hydrocarbon moieties may contain ether bonds (COC bonds).

[0023] Specifically, examples include, but are not limited to, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, hydroxyhexyl (meth)acrylate, 3-hydroxy-3-chloropropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, glycidol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, and dipentaerythritol di(meth)acrylate. Such hydroxyl group-containing (meth)acrylates may be used individually or in combination of two or more types.

[0024] Other monomers mentioned above include known monomers other than the hydroxyl group-containing (meth)acrylates mentioned above, such as monomers or oligomers having one or more (meth)acryloyl groups.

[0025] (A) Commercially available isocyanate (meth)acrylates can be used. Examples include Laromer LR-9000 from BASF Ltd, and EBECRYL 4150 and EBECRYL 4250 from Daicel Ornex Co., Ltd.

[0026] (A) The isocyanate (meth)acrylate content is preferably 20% to 70% by mass, more preferably 25% to 65% by mass, and even more preferably 27% to 60% by mass, based on 100% by mass of the solid content of the resin composition. If the isocyanate (meth)acrylate content is within the above range, the resin composition can produce a resin-impregnated wood substrate that has excellent curing properties within the wood, as well as excellent adhesion to the cured coating film, water resistance, and weather resistance.

[0027] ((B) Nitrogen-containing monofunctional (meth)acrylate monomer) (B) Examples of nitrogen-containing monofunctional (meth)acrylate monomers (excluding component (A)) include (meth)acryloylmorpholine, acrylamide, and N-vinylformamide. Among these, (meth)acryloylmorpholine is preferred from the viewpoint of impregnation, adhesion to wood, and weather resistance.

[0028] (B) The content of nitrogen-containing monofunctional (meth)acrylate monomer is preferably 5% to 75% by mass, more preferably 7% to 72% by mass, and even more preferably 9% to 70% by mass, based on 100% by mass of the solid content of the resin composition. (B) If the content of nitrogen-containing monofunctional (meth)acrylate monomer is within the above range, the resin composition can produce a resin-impregnated wood substrate that has excellent curing properties within the wood, as well as excellent adhesion to the cured coating film, water resistance, and weather resistance.

[0029] ((C) Photopolymerization initiator) (C) The photopolymerization initiator is not particularly limited, and conventionally known photopolymerization initiators for UV curing can be used. Examples of photopolymerization initiators include acylphosphine oxide-based photopolymerization initiators, alkylphenone-based photopolymerization initiators, benzoylformate-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, oxime ester-based photopolymerization initiators, and benzophenone-based polymerization initiators. These photopolymerization initiators may be used individually or in combination of two or more.

[0030] Examples of acylphosphine oxide-based photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of alkylphenone-based photopolymerization initiators include 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexylphenyl ketone, 2,2-dimethyl-2-phenylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 1-[4-(2-hydroxyethoxyl)phenyl]-2-hydroxymethylpropanone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, and 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone. Examples of benzoylformate-based photopolymerization initiators include methylbenzoylformate. Examples of thioxanthone-based photopolymerization initiators include isopropylthioxanthone. Examples of oxime ester-based photopolymerization initiators include 1,2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyl oxime)] and ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-,1-(O-acetyl oxime). Examples of benzophenone-based photopolymerization initiators include benzophenone, 4-chlorobenzophenone, and 4,4′-diaminobenzophenone.

[0031] (C) The content of the photopolymerization initiator is preferably 1% to 15% by mass, more preferably 2% to 12% by mass, and more preferably 3% to 10% by mass, based on 100% by mass of the solid content of the resin composition. If the content of the photopolymerization initiator is within the above numerical range, the curability of the resin composition will be good.

[0032] (Other (meth)acrylates) The resin composition according to the present invention may contain other (meth)acrylates other than components (A) and (B), as long as the effects of the present invention are not impaired. The other (meth)acrylates are not particularly limited, but for example, it is preferable to use a polyfunctional (meth)acrylate monomer. The number of functional groups of the polyfunctional (meth)acrylate monomer is preferably 2 to 6 functional groups.

[0033] Examples of (meth)acrylate monomers with two to six functionalities include alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol diacrylate and neopentyl glycol di(meth)acrylate; diethylene glycol di(meth)acrylate, tri- Polyoxyalkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate and polytetramethylene glycol di(meth)acrylate; halogen-substituted alkylene glycol di(meth)acrylates such as tetrafluoroethylene glycol di(meth)acrylate; trimethylolpropane di( Di(meth)acrylates of aliphatic polyols such as meth)acrylate, ditrimethylolpropane di(meth)acrylate, and pentaerythritol di(meth)acrylate; di(meth)acrylates of hydrogenated dicyclopentadienyl di(meth)acrylate and tricyclodecanedimethanol di(meth)acrylate; di(meth)acrylates of hydrogenated dicyclopentadiene or tricyclodecanedialkanol such as hydrogenated dicyclopentadienyl di(meth)acrylate and tricyclodecanedimethanol di(meth)acrylate; and dioxaneglycols such as 1,3-dioxane-2,5-diyl di(meth)acrylate (also known as dioxaneglycol di(meth)acrylate). These include di(meth)acrylates of dioxanedialkanols; di(meth)acrylates of alkylene oxide adducts of bisphenol A or bisphenol F, such as bisphenol A ethylene oxide adduct diacrylates and bisphenol F ethylene oxide adduct diacrylates; epoxy di(meth)acrylates of bisphenol A or bisphenol F, such as acrylic acid adducts of bisphenol A diglycidyl ether and acrylic acid adducts of bisphenol F diglycidyl ether; and silicone di(meth)acrylates.Di(meth)acrylate of neopentyl glycol hydroxypivalate; 2,2-bis[4-(meth)acryloyloxyethoxyethoxyphenyl]propane; 2,2-bis[4-(meth)acryloyloxyethoxyethoxycyclohexyl]propane; di(meth)acrylate of 2-(2-hydroxy-1,1-dimethylethyl)-5-ethyl-5-hydroxymethyl-1,3-dioxane;Tris(hydroxyethyl)isocyanurate di(meth)acrylate, glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, EO-added trimethylolpropane tri(meth)acrylate, PO-added trimethylolpropane tri(meth)acrylate (PO portion n=2), PO-added trimethylolpropane tri(meth)acrylate (PO portion n=3), glycerin PO-added tri(meth)acrylate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen terephthalate, PO-added glycol tri(meth)acrylate, tris(meth)acryloyloxyethyl phosphate Examples include phosphate, pentaerythritol tri(meth)acrylate, EO-added pentaerythritol tri(meth)acrylate, tris((meth)acryloxyethyl) isocyanurate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkoxy-modified dipentaerythritol hexa(meth)acrylate, EO-added pentaerythritol tetra(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, polycaprolactone-modified dipentaerythritol hexa(meth)acrylate, alkylene oxide-modified dipentaerythritol polyfunctional (meth)acrylate, etc. These (meth)acrylate monomers may also be modified monomers obtained by silicone modification, fluorine modification, etc. These polyfunctional (meth)acrylate monomers may be used individually or in combination of two or more.

[0034] The content of other (meth)acrylates can be adjusted as appropriate depending on the content of components (A) and (B). The content of other (meth)acrylates is preferably 1% to 60% by mass, and preferably 5% to 55% by mass, based on 100% by mass of the solid content of the resin composition. If the content of other (meth)acrylates is within the above range, the resin composition can produce a resin-impregnated wood substrate that has excellent curing properties within the wood, as well as excellent adhesion to the cured coating film, water resistance, and weather resistance.

[0035] (Other ingredients) In addition to the above-mentioned components, the resin composition according to the present invention may further, as necessary, contain polymerization inhibitors, organic solvents (non-reactive diluents), defoaming agents, settling inhibitors, leveling agents, dispersants, heat stabilizers, ultraviolet absorbers, light stabilizers, antifouling enhancers, substrate adhesion enhancers, photosensitizers, antistatic agents, scratch resistant agents, antifungal agents, antibacterial agents, antiviral agents, matting agents, silane coupling agents, plasticizers, etc., to the extent that they do not impair the objectives of the present invention.

[0036] The resin composition according to the present invention may be either a solvent-type resin composition diluted with an organic solvent (non-reactive diluent) such as a thinner that does not contain alcohols, or a solvent-free resin composition that does not require dilution with an organic solvent. However, a solvent-free resin composition is preferred because it does not leave any residue of volatile organic compounds (VOCs), thus having no impact on the human body and offering excellent environmental compatibility. Furthermore, since a drying process is not required for a solvent-free resin composition, production efficiency in industrial applications can be improved.

[0037] (Method for preparing resin composition) The resin composition according to the present invention is obtained by mixing and stirring the above components using conventionally known devices such as mixers, dispersers, and stirrers. Examples of such devices include dispersers, mixing and dispersing mills, mortar mixers, rolls, paint shakers, and homogenizers.

[0038] [Wood base material] The wood substrate according to the present invention is impregnated with the above-mentioned resin composition. The wood substrate according to the present invention may further have a cured coating on its surface. By impregnating with the above-mentioned resin composition, a resin-impregnated wood substrate with excellent adhesion to the cured coating, water resistance, and weather resistance can be manufactured.

[0039] (wood base material) Examples of wood-based substrates include wood flooring, wall materials, ceiling materials, plywood, solid wood, hardboard, and particleboard. While there are no specific limitations on the thickness of the wood-based substrate, it is typically around 1 to 50 mm.

[0040] (cured coating) The paint composition that forms the cured coating film is not particularly limited, and conventionally known paint compositions can be used. The cured coating film may be applied to the entire surface of one side of the substrate, to only a part of one side, or to both sides of the wood substrate. When applied to only a part, the form of the cured coating film is not particularly limited, and any form can be adopted without particular restriction, such as a sea-island-like sea section or island section, a grid pattern, a mosaic pattern, etc. Furthermore, the cured coating film may be formed in multiple layers using a primer, an intermediate coat, a topcoat, etc.

[0041] The thickness of the cured coating film is not particularly limited, but from the viewpoint of drying properties, curing properties, adhesion, water resistance, and weather resistance, it is usually 1 to 200 μm, preferably 3 to 150 μm, and more preferably 5 to 100 μm. In this invention, the thickness of the cured coating film refers to the thickness of the cured coating film when its cross-section is observed with an optical microscope or a scanning electron microscope (SEM). When forming a coating film of such thickness, the desired thickness may be formed in a single coat, or it may be formed in multiple coats.

[0042] <Method for manufacturing wood-based materials> The method for producing a wood-based substrate according to the present invention includes the step of impregnating the wood-based substrate with the above-mentioned resin composition. The method for producing a wood-based substrate according to the present invention may further include the step of forming a hardened coating film on the surface of the wood-based substrate after resin impregnation.

[0043] (Impregnation process) The method of impregnating the resin composition is not particularly limited, and any conventionally known impregnation method can be selected. Examples of impregnation methods include natural impregnation and vacuum-pressure impregnation. Natural impregnation is a method in which the resin composition is applied to or immersed in a wood substrate, and then left to stand until impregnation is complete. Vacuum-pressure impregnation is a method in which the wood substrate is placed in a sealed tank, the tank is depressurized, the resin composition is injected into the tank, and then the tank is repeatedly pressurized and depressurized to impregnate the wood substrate with the resin composition.

[0044] (cured coating film formation process) In the cured coating film formation process, a cured coating film can be formed by applying the coating composition to the surface of the wood substrate after resin impregnation, and then curing the coating surface. The method of applying the coating composition is not particularly limited, and conventionally known application methods can be selected. For example, coating machines such as bar coaters, gravure coaters, roll coaters (natural roll coaters and reverse roll coaters, etc.), curtain flow coaters, air knife coaters, spin coaters, and blade coaters can be used. Among these, the application method using a roll coater is preferred from the viewpoint of workability and productivity. It is preferable that the coating film thickness after curing and drying is within the range of the film thickness of the cured coating film.

[0045] The curing method is not particularly limited, and any conventionally known curing method can be selected. For example, a curing method may involve curing the coated surface of a wood substrate by irradiating it with ultraviolet light. From the viewpoint of the curability of the paint composition, the amount of ultraviolet light irradiated is preferably 100 to 3,000 mJ / cm². 2 And more preferably 100 to 2,000 mJ / cm² 2 And more preferably 100 to 1,000 mJ / cm² 2 That is the case. [Examples]

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0047] First, the following raw materials were prepared for the preparation of the resin composition. • Isocyanate (meth)acrylate 1 ((meth)acrylate group count: 2, isocyanate content: 14.75%, manufactured by BASF, product name: Laromer LR9000) • Isocyanate (meth)acrylate 2 ((meth)acrylate group count: 1, isocyanate content: 12.8%, manufactured by Daicel Ornex Co., Ltd., product name: EBECRYL 4150) • Isocyanate (meth)acrylate 3 ((meth)acrylate group count: 3-4, isocyanate content: 5%, manufactured by Daicel Ornex Co., Ltd., product name: EBECRYL 4250) • Urethane (meth)acrylate ((meth)acrylate group count: 2, isocyanate content: 0%, manufactured by Ohtake Akishin Chemical Co., Ltd., product name: UV-831) • Polyisocyanate (isocyanate content: 21.25%, manufactured by Tosoh Corporation, product name: Coronate HX) • Nitrogen-containing monofunctional (meth)acrylate monomer (acryloylmorpholine, manufactured by KJ Chemicals Co., Ltd., product name: ACMO) • Nitrogen-free monofunctional (meth)acrylate monomer (phenoxy polyethylene glycol acrylate, manufactured by Kyoeisha Chemical Co., Ltd., product name: P-200A) • Trifunctional (meth)acrylate monomer (trimethylolpropane EO-modified triacrylate (TMP(EO)3TA), manufactured by KPX Green Chemical Co., Ltd., product name: KOMERATE-T033) • Trifunctional / tetrafunctional (meth)acrylate monomer (pentaerythritol (tri / tetra)acrylate (PETA), manufactured by KPX Green Chemical Co., Ltd., product name: KOMERATE-T001L) • Photopolymerization initiator 1 (2-hydroxy-2-methylpropiophenone, manufactured by Chemfine International, Inc., trade name: HYCURE 1173) • Photopolymerization initiator 2 (2,4,6-trimethylbenzoyldiphenylphosphine oxide, manufactured by Chitec Technology Co., Ltd., trade name: CHIVACURE TPO) • Polymerization inhibitor (p-dihydroxybenzene, manufactured by Ube Industries, Ltd., trade name: Hydroquinone)

[0048] [Examples 1-7, Comparative Examples 1-3] <Preparation of resin composition> According to the formulations shown in Table 1, each raw material was uniformly mixed and stirred using a disperser to obtain a solvent-free resin composition.

[0049] <Viscosity of resin composition> The viscosity of the resin composition prepared above at 25°C was measured using a Stormer viscometer (manufactured by Taiyu Kikai Co., Ltd., product name: Stormer viscometer) under the conditions of JIS K 5600-2-2. The measurement results are shown in Table 1.

[0050] <Preparation of resin-impregnated wood substrate 1> Cypress plywood (2mm thick) was prepared as the wood base material. Next, approximately 10g / shaku of the resin compositions of Examples 1-3 and Comparative Examples 1-3 were applied to the wood base material using a sponge roll coater. 2 The material was coated and allowed to impregnate for approximately one hour. Afterward, the remaining resin composition on the surface was removed with a spatula, and the material was cured using a UV irradiation device to obtain a resin-impregnated wood substrate. A UV POWER PUCK II UV irradiator was used, and the following values ​​were obtained at wavelength A (320-390 nm). • For an 80W mercury lamp, the emission level is 330 mJ / cm². 2 80W gallium lamp: 220mJ / cm² 2

[0051] Next, a general ultraviolet-curing paint (manufactured by Chugoku Marine Paints Ltd., product name: Aurex) was applied to the obtained resin-impregnated wood substrate using a roll coater in the order of (1) to (6) below. (1) Perform intermediate polishing with #400 grit sandpaper. (2) Apply the Oracal primer and cure it by ultraviolet irradiation (100 mJ / cm 2 ). (3) Apply the Oracal intermediate coat paint and cure it by ultraviolet irradiation (100 mJ / cm 2 ). (4) Conduct intermediate grinding with abrasive paper #400. (5) Apply the Oracal intermediate coat paint (second time) and cure it by ultraviolet irradiation (100 mJ / cm 2 ). (6) Apply the Oracal topcoat paint and cure it by ultraviolet irradiation (400 mJ / cm 2 ).

[0052] In addition, a sample in which an ultraviolet-curing paint (Oracal) was applied in the same manner as above except that the woody base material (Japanese cypress sawn board plywood) was not impregnated with resin was used as Comparative Example 4.

[0053] <Preparation of Resin-Impregnated Woody Base Material 2> A resin-impregnated woody base material was obtained by impregnating a woody base material with the resin compositions of Examples 4 to 7 and curing them in the same manner as in <Preparation of Resin-Impregnated Woody Base Material 1>, except that Japanese cypress solid wood (15 mm thick) was used instead of Japanese cypress sawn board plywood as the woody base material. Subsequently, using the obtained resin-impregnated woody base material, a general ultraviolet-curing paint (manufactured by China Paint Co., Ltd., trade name: Oracal) was applied in the order of (1) to (6) above using a roll coater.

[0054] In addition, a sample in which an ultraviolet-curing paint (Oracal) was applied in the same manner as above except that the woody base material (Japanese cypress solid wood) was not impregnated with resin was used as Comparative Example 5.

[0055] <Evaluation of Resin-Impregnated Woody Base Material after Formation of Cured Coating Film> (Adhesion) The adhesion of the resin-impregnated wood substrates after curing, obtained in the above-described <Preparation of Resin-Impregnated Wood Substrate 1> and <Preparation of Resin-Impregnated Wood Substrate 2>, was evaluated using the following method. Specifically, in accordance with the grid test method described in JIS K 5600-5-6, test pieces were prepared by making 1 mm wide, 100 square (10 squares x 10 squares) scratches on the cured coating of the resin-impregnated wood substrate with a cutter to create a grid pattern. Next, cellophane tape (registered trademark) (product name, manufactured by Nichiban Co., Ltd.) was attached to the test piece. Then, the cellophane tape (registered trademark) was quickly peeled off by pulling it diagonally upward at a 45-degree angle to the grid pattern. The number of remaining coatings in the grid pattern was counted, and this number of coatings was used as an indicator of adhesion, which was evaluated according to the following criteria. The evaluation results are shown in Table 2. [Evaluation Criteria] ○: No peeling occurred at all. (Remaining paint film count: 100 / 100) △: Slight peeling was observed. (Remaining paint film count: 90 or more but less than 100 / 100) ×: There was a lot of peeling. (Less than 90 remaining paint layers out of 100)

[0056] (water resistance) The resin-impregnated wood substrates obtained in the above-described <Preparation of Resin-Impregnated Wood Substrate 1> and <Preparation of Resin-Impregnated Wood Substrate 2>, after the formation of the cured coating film, were evaluated for water resistance using the following method. Specifically, the resin-impregnated wood substrates were subjected to two water resistance tests (immersion in 60°C hot water for 1 hour, followed by drying in a 60°C dryer for 2 hours). Subsequently, the adhesion of the resin-impregnated wood substrates after the two water resistance tests was evaluated using the same method as described above. The evaluation results are shown in Table 2.

[0057] (Weather resistance: outdoor) Using the resin-impregnated wood substrate obtained in <Preparation of Resin-Impregnated Wood Substrate 1> above, a test specimen measuring 10 cm wide x 15 cm long was prepared. The specimen was then placed on an outdoor exposure platform and left for 6 months. Afterward, the whitening and paint peeling conditions of the surface and cut surface (end grain) of the specimen were visually evaluated according to the following criteria. The evaluation results are shown in Table 2. The percentage of whitening at the end grain was also measured and is shown in Table 2. [Evaluation Criteria (Whitening)] ◎: No bleaching was observed. ○: The extent of whitening was less than 10% of the entire surface or the total length of the end grain, and was not noticeable. △: The whitening area was 10% to less than 50% of the entire surface or the entire end grain, and was noticeable. ×: The whitening covered more than 50% of the entire surface or the entire end grain, making it very noticeable. [Evaluation Criteria (Paint Film Peeling)] ○: No peeling of the coating was observed. △: Some paint peeling occurred. ×: Most of the paint film peeled off.

[0058] (Weather resistance: accelerated testing) Using the resin-impregnated wood substrate after curing the coating obtained in <Preparation of Resin-Impregnated Wood Substrate 2> above, a test specimen measuring 7.5 cm wide x 7.5 cm long was prepared. Subsequently, the test specimen was placed on an indoor exposure stand, and a 400-hour irradiation test (equivalent to a 5-month outdoor exposure test) was performed using a weathering tester (Suga Test Instruments Co., Ltd., Xenon Weather Meter X75). After that, the whitening and coating peeling conditions of the surface and cut surface (end grain) of the test specimen were visually evaluated according to the above criteria, in the same manner as for the weathering test outdoors. The evaluation results are shown in Table 2. In addition, the percentage of whitening at the end grain was measured and is shown in Table 2.

[0059] [Table 1]

[0060] [Table 2]

Claims

1. A resin composition used for impregnation into wood-based substrates, (A) Isocyanate (meth)acrylate and (B) Nitrogen-containing monofunctional (meth)acrylate monomers (excluding component (A)) (C) Photopolymerization initiator and Includes, The (A) isocyanate (meth)acrylate is a resin composition in which the isocyanate content is 10% or more when it has one or more but less than two (meth)acrylate groups in one molecule, and the isocyanate content is 3% or more when it has two or more (meth)acrylate groups in one molecule.

2. The resin composition according to claim 1, wherein the content of (A) isocyanate (meth)acrylate is 20% by mass or more and 70% by mass or less based on 100% by mass of the solid content of the resin composition.

3. The resin composition according to claim 1, wherein the (A) isocyanate (meth)acrylate is an oligomer or polymer.

4. The resin composition according to claim 1, wherein the (A) isocyanate (meth)acrylate has an isocyanate content of 10% to 25% when it has one or more but less than two (meth)acrylate groups in one molecule, and an isocyanate content of 3% to 25% when it has two or more (meth)acrylate groups in one molecule.

5. The resin composition according to claim 1, wherein the (B) nitrogen-containing monofunctional (meth)acrylate monomer comprises (meth)acryloylmorpholine.

6. The resin composition according to claim 1, wherein the content of the nitrogen-containing monofunctional (meth)acrylate monomer (B) is 5% by mass or more and 75% by mass or less based on 100% by mass of the solid content of the resin composition.

7. The resin composition according to claim 1, wherein the content of (C) the photopolymerization initiator is 1% by mass or more and 15% by mass or less based on 100% by mass of the solid content of the resin composition.

8. The resin composition according to claim 1, wherein the viscosity (KU value) at 25°C is 49 or more and 80 or less.

9. The resin composition according to claim 1, which is solvent-free.

10. A wood substrate impregnated with the resin composition according to any one of claims 1 to 9.

11. The wood substrate according to claim 10, having a cured coating film on its surface.

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