New regulations for water-based transparent coatings for wood

Abstract

This invention has been made in view of the above circumstances, and the water-based transparent coating for wood of the present invention does not discolor, crack, stain due to moisture absorption, or grow mold even after long-term weather resistance testing, and provides a water-based resin transparent coating for wood that not only maintains its appearance but also sustains the original scent of wood when it was newly built, which is a characteristic of wood. [Solution] A water-based transparent paint for wood was developed by using a water-based urethane emulsion resin as the base material and applying it in three stages: a primer layer (U), an intermediate layer (T), and a topcoat layer (W), with each layer having added functionality.

Description

Technical Field

[0001] The present invention relates to an aqueous transparent paint for wood.

Background Art

[0002] In recent years, the number of buildings and structures using wood has increased, and as the requirements for people's living environment are changing, the demand for wood is gradually increasing. Traditional Japanese buildings using hinoki, cedar, pine, zelkova, etc. are highly evaluated worldwide. Recently, the construction of log houses has also become popular. Wooden benches, playground equipment, etc. have also diversified. Furthermore, the production of laminated wood based on forest resource protection has increased, and since it can be used as a strong structural material, it has attracted attention from architectural designers. Each function of wood protection has been investigated through respective acceleration tests, but there is a demand for a film-forming paint that can maintain the color tone and beautiful wood grain of wood, especially when used as an external member for a long time. For this purpose, it is most appropriate to conduct a comprehensive exposure test, which is particularly important for wood. Therefore, exposure tests were repeatedly conducted on the coast of Chikura, Chiba Prefecture, where the solar radiation and rainfall are high, and an aqueous transparent paint for wood was developed over approximately ten years.

Prior Art Documents

[0003] Conventionally, wood has the property of changing color to a wet color when water penetrates. In addition, wood has moisture absorption and desorption properties, and the wood itself has elasticity that repeats expansion and contraction. Although the elasticity of wood is not large in terms of the ratio of the expansion and contraction length, it always repeats expansion and contraction. Although the coating film formed from conventional wood paints can follow the expansion and contraction of wood, there is a risk of fine cracks occurring in the coating film due to repeated long-term expansion and contraction. When cracks occur, there is a problem that the wood coated with the conventional wood paint may change color to a wet color due to water penetrating through these cracks. In order to solve such problems, the following methods have been proposed as aqueous wood paints due to environmental issues. [Patent Document 1] proposes a water-based paint mixture of fluorine emulsion, UV absorber, and pigment. However, although it has sufficiently good weather resistance, fluorine resin emulsion is expensive, and it is difficult to achieve a thick, full-bodied appearance when applied to wood. While transparency is ensured by controlling the amount of inorganic pigment added, there are drawbacks such as a narrow range of transparency. [Patent Document 2] proposes coating wood using urethane resin. However, this paint is mainly for concrete formwork plywood applications and is characterized by its alkali resistance and surface gloss, and is not a weather-resistant paint for building applications. [Patent Document 3] proposes a method of impregnating wood with a mixture of vegetable oil dispersed in water with an emulsifier, rather than using conventional film-forming paints. However, vegetable oils have low molecular weight, and the impregnation method does not offer much weather resistance. Furthermore, because it is not a film-forming method, the concentration of UV absorbers is low, and it is easily washed away by water, resulting in poor durability. [Patent Document 4] proposes a solvent-based paint using acrylic resin and a solvent with a flash point of 70°C to 200°C or lower. Recently, water-based types have become desirable from an environmental perspective, so water-based types are preferred. [Patent Document 5] proposes a method in which a UV absorber and a light stabilizer are impregnated into wood, and then a fluorine-based water repellent is applied on top of it. Although weather resistance is good, there are problems with long-term water repellency because the coated wood surface is a thin film (15 μm or less). [Patent Document 6] proposes a method in which colloidal silica dispersed in alcohol is treated with a silane coupling agent as a primer, and then a solvent-type acrylic urethane resin containing an ultraviolet absorber is applied; however, all of these are solvent-type resins. [Patent Document 7] proposes a method of curing a solvent-based composite resin, which is a mixture of nanosilica / silicone oligomer and an alkoxy-containing acrylic resin, with a tin catalyst. However, this method is not water-based and raises environmental concerns. [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-137445 [Patent Document 2] Japanese Patent Publication No. 1990-189322 [Patent Document 3] Japanese Patent Publication No. 2008-297413 [Patent Document 4] Japanese Patent Publication No. 2009-51986 [Patent Document 5] Japanese Patent Publication No. 2018-176500 [Patent Document 6] Japanese Patent Publication No. 2022-100051 [Patent Document 7] Japanese Patent Publication No. 2024-64267 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention has been made in view of the above circumstances, and aims to develop a water-based transparent resin coating for wood that, even after long-term weather resistance testing, does not show discoloration, cracking, staining due to moisture absorption, or mold growth, and not only maintains its appearance but also sustains the original scent of wood, which is a characteristic of newly built wood. [Means for solving the problem]

[0006] The inventors diligently conducted research to achieve the above objectives and, as a result, discovered that by using a water-based urethane emulsion resin as the base for a water-based transparent coating for wood, and applying it in three stages—a primer layer (U), an intermediate layer (T), and a topcoat layer (W)—with added functionality to each layer, it is possible to prevent discoloration, cracking, staining due to moisture absorption, mold growth, and maintain the scent of new wood over time, thus leading to the present invention. [Modes for carrying out the invention]

[0007] The above-mentioned aqueous resin emulsion (a) is not particularly limited, but acrylic resin emulsions, vinyl resin emulsions, rubber emulsions, urethane resin emulsions, silicone-modified emulsions, fluorine-modified emulsions, silicone resin emulsions, and organic-inorganic hybrid emulsions can be used. Wood is susceptible to deterioration from light, temperature, humidity, and moisture, and also expands and contracts significantly. Therefore, an emulsion that adheres to the wood while maintaining good adhesion and is easy to design is desirable. From this perspective, acrylic resin emulsions and urethane resin emulsions are easy to handle. Among these, urethane resin has more rubber elasticity than acrylic resin emulsion, making it easier to ensure adhesion. The urethane resin emulsion can be synthesized as follows.

[0008] The aqueous urethane resin emulsion (a) in claim 2 is synthesized by a general method. Specifically, it is obtained by dispersing a urethane prepolymer having residual isocyanate groups, obtained by reacting a compound having carboxyl groups and / or sulfonic acid groups and two or more hydroxyl groups, a compound having two or more isocyanate groups, and a compound having two or more hydroxyl groups in water, and then performing a chain extension reaction with a compound having two or more amino groups.

[0009] More specifically, compounds having a carboxyl group and / or a sulfonic acid group, and having two or more hydroxyl groups, include polybasic acids such as 2,2-dimethylol lactic acid, 2,2-dimethylol propionic acid, 2,2-dimethylol butanoic acid, 2,2-dimethylol butyric acid, 2,2-dimethylol valerate adipic acid, azelaic acid, sebacic acid, terephthalic acid, succinic anhydride, maleic anhydride, fumaric acid, and trimellitic anhydride. As compounds having both a hydroxyl group and a sulfonic acid group in the molecule, for example, hydroxysulfonic acids such as 2-hydroxyethanesulfonic acid and 3-hydroxypropanesulfonic acid are included.

[0010] Compounds having two or more hydroxyl groups include 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 1,4-cyclohexanedimethanol, trimethylolpropane, and glycerin.

[0011] Compounds having two or more isocyanate groups include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated toluene diisocyanate, tetramethylene xylylene diisocyanate, and all conventionally used aromatic, aliphatic, and alicyclic isocyanates, either alone or in mixtures, such as biuretized or isocyanurated derivatives of these isocyanates. However, tolylene diisocyanate and diphenylmethane diisocyanate are preferred in terms of low cost and heat resistance.

[0012] Compounds having two or more amino groups that undergo chain extension reactions in water include ethylenediamine, propylenediamine, diethylenetriamine, hexylenediamine, triethylenetetramine, tetraethylenepentamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, and hydrogenated diphenylmethanediamine.

[0013] It is preferable that the particle size of the aqueous urethane resin emulsion (a) in claim 2 is in the range of 20 nm to 200 nm. This is because wood has conduits that absorb water, and preventing water intrusion by blocking these conduits is important for improving durability. If the particle size is 20 nm or less, it is small enough to penetrate the conduits of wood, but the water resistance of the aqueous urethane resin emulsion decreases, and performance cannot be obtained. If it is 200 nm or more, it is difficult to penetrate the conduits of wood, the anchoring property of the coating film to the wood decreases, and peeling of the coating film due to moisture is likely to occur, making it difficult to obtain durability. Also, especially at the ends of the wood, it is necessary to make them R-shaped to maintain the coating amount. When painting, the surface is sanded or sandpapered. The coarseness of the sandpaper is preferably #120 to #240.

[0014] The undercoat layer (U) in claim 3 is a paint obtained by mixing an aqueous resin emulsion (a), tannin (b), and a fungicide (c). Tannin (b) is a complex aromatic compound having phenolic hydroxy groups. It not only has an antiseptic function but also functions such as improving adhesion to wood, antibacterial, water repellent, and ant termite, being derived from plants. As types of tannin, there are condensed tannins in which compounds having a flavanol skeleton are polymerized, and those in which aromatic compounds such as gallic acid and ellagic acid are ester-bonded with glucose, etc. The tannin used in the present invention includes mimosa, mangrove bark as condensed tannins, and chestnut obtained from oak wood, kuri wood, etc. as ester-based tannins, but is not necessarily limited thereto.

[0015] In the undercoat layer (U), the ratio of (a) to (b) is used at a weight ratio of 98 to 80:2 to 20 wt%, but if tannin (b) is 2% or less, the adhesion to wood and the antiseptic effect decrease. On the other hand, if it is 20% or more, the film-forming property of the coating film decreases and the water resistance decreases. Preferably, 5% to 10% is desirable.

[0016] The ratio of the aqueous resin emulsion (a) + tannin (b) to the mold inhibitor (c) in Claim 3 is preferably 99.9 - 99:0.1 - 1% by weight. If the mold inhibitor is less than 0.1%, the persistence of the mold inhibitor will decrease. On the other hand, if it is 1% or more, it will lead to an increase in cost. In particular, as a wood preservative, if a wood preservative containing a fungicide, a preservative, and an insecticide is applied in advance, deterioration of the woody substrate can be suppressed, and a method for further improving the durability of wooden members can also be achieved. In addition, by suppressing mold and corrosion of the woody substrate, the aesthetics of wooden members can also be maintained. These may be used alone or in combination of two or more depending on the purpose. The fungicide, preservative, and insecticide can be added to the paint composition, but it is more effective to form a paint film with the paint composition after directly applying it to the woody substrate.

[0017] As the mold inhibitor, for example, mold inhibitors such as triazine-based, morpholine-based, thiazoline-based, iodine-based, and aromatic amine-based can be used. Examples of the mold inhibitor include PROXEL KL2 manufactured by Ark Surda Japan Co., Ltd., ACTICIDELG and ACTICIDEMBS manufactured by Soge Japan Co., Ltd. As the preservative, known ones can be used. For example, organic iodine-based compounds, triazole-based compounds, etc. can be used. These compounds can be used alone or in combination of two or more compounds. As the insecticide, known ones can be used. For example, organophosphorus-based compounds, carbamate-based compounds, pyrethroid-based compounds, phenylpyrazole-based compounds, phenylpyrazole-based compounds, etc. can be used. These compounds can be used alone or in combination of two or more compounds. The undercoat layer (U) can exhibit adhesion to wood and mold resistance.

[0018] The intermediate coating layer (T) of claim 4 is intended for weather resistance and mold resistance, and in particular, weather resistance and mold resistance can be maintained by ensuring a film thickness of 10 μm to 150 μm. Specifically, the intermediate coating layer (T) is a mixture of an aqueous resin emulsion (a), an ultraviolet absorber (d), a light stabilizer (e), and an antifungal agent (c), and is used in a weight ratio of 99 to 95:1 to 5% by weight of (a) to (d) + (e). Below 1%, discoloration and deterioration of the coating film due to ultraviolet light will occur over the long term, and above 5%, further increases will not only not improve the effect but will also increase costs. As the UV absorber (d), for example, UV absorbers such as benzophenone-based, benzotriazole-based, and triazine-based UV absorbers can be used. Examples of UV absorbers include TINUVIN384, TINUVIN400, TINUVIN571, TINUVIN900, and TINUVIN1130 manufactured by BASF Japan Ltd.

[0019] Specific UV absorbers include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, (2'-hydroxy-5'-tert-octylphenyl)benzotriazole, and 2,2'-methylenebis[6-( [2H-benzotriazol-2-yl)-4-tert-octylphenol], 6-(2-benzotriazolyl)-4-tert-octyl-6'-tert-butyl-4'-methyl-2,2'-methylenebisphenol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1, Examples include benzotriazole-based UV absorbers such as 3,3-tetramethylbutyl)phenol, 2-methylenebis[6-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol], 2-(2H-benzotriazole-2-yl)-p-cresol, and 2-(5-chloro-2H-benzotriazole-2-yl)-6-tert-butyl-4-methylphenol; triazine-based UV absorbers such as 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol and 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine; benzophenone-based UV absorbers such as [2-hydroxy-4-(octyloxy)phenyl](phenyl)methanone; benzoate-based UV absorbers; iron oxides; and titanium dioxide. These can be used as is, or diluted with water, alcohol, organic solvents, etc.Of these, it is preferable to use an oil-soluble UV absorber, and more preferably to use a triazine-based UV absorber, such as the reaction product with 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl)-5-hydroxyphenyl, tooxirane (C10-C16 mainly C12-C13 alkyloxy)methyl]oxirane, benzenepropanoic acid·3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy·C7-9 side chain and linear alkyl ester, 2,4,6-tris(2-hydroxy-4- It is most preferable to use hexyloxy-3-methylphenyl)-1,3,5-triazine. In particular, the reaction product with 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl)-5-hydroxyphenyl,tooxirane ((C10-C16 mainly C12-C13 alkyloxy)methyl)oxirane and the benzenepropanoic acid·3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy·C7-9 side chain and linear alkyl ester are colorless and transparent, resulting in the least change in appearance when applied to wood. Inorganic UV absorbers such as titanium dioxide, zinc oxide, and cerium oxide can be used. It is preferable to use the UV absorber together with a light stabilizer (for example, TINUVIN123 or TINUVIN770 manufactured by BASF Japan Ltd.).

[0020] Examples of the light stabilizer (e) include bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(2, Examples of hindered amine-based light stabilizers include 2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1-undecanoxy-2,2,6,6-tetramethylpiperidine-4-yl) carbonate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, and bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate. These can be used as is or diluted with water, alcohol, organic solvents, etc. Of these, it is preferable to use an oil-soluble light stabilizer, and more preferably to use a sebacate hindered amine-based light stabilizer such as bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate or methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate. In addition, hindered amine-based light stabilizers (HALS) are commonly used as light stabilizers and are additives that are excellent at suppressing photodegradation of polymers and especially at preventing surface degradation. Examples of such light stabilizers include BASF's Tinuvin (trade name), Adekastab LA72, Adekastab LA82 (all trade names, manufactured by ADEKA Corporation), HOSTAVIN3051-2DISP, HOSTAVIN3070DISP (all trade names, manufactured by Clariant Chemicals Co., Ltd.).

[0021] In claim 4, the ratio of aqueous resin emulsion (a) + ultraviolet absorber (d) + light stabilizer (e) to antifungal agent (c) is 99.9 to 99:0.1 to 1% by weight. Furthermore, it is used with a dry coating thickness in the range of 10 μm to 150 μm. At thicknesses of 10 μm or less, paint film degradation is more likely to occur in long-term weather resistance tests, while at thicknesses of 150 μm or more, the drying time during painting increases, leading to higher costs. The intermediate coat layer (T) is specifically designed to create a paint film with improved weather resistance and mold resistance.

[0022] The topcoat layer (W) in claim 5 is intended to maintain aesthetic appeal and durability by using a matting agent and a fungicide for the purpose of achieving a matte finish. Calcium carbonate and silica are used as matting agents.

[0023] Other additives that can be added include pigments, adhesion aids, penetrating agents, film-forming aids, wetting agents, matting agents, viscosity modifiers, defoaming agents, antioxidants, leveling agents, fragrances, and other additives commonly found in paints.

[0024] As the aforementioned pigments, inorganic coloring pigments such as titanium dioxide, zinc oxide, lead yellow, zinc oxide, yellow iron oxide, red iron oxide, carbon black, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, and cobalt blue can be used; organic coloring pigments such as azo pigments, diketopyrrolopyrrole pigments, benzimidazolon pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, isoindolinone pigments, surene pigments, perylene pigments, perinone pigments, and dioxane pigments; and extender pigments such as talc, clay, and calcium carbonate can be used.

[0025] As adhesion aids, for example, silane coupling agents, titanium-based coupling agents, and aluminum-based coupling agents can be used. From the viewpoint of adhesion and storage stability of the paint, it is preferable to use a silane coupling agent. Examples of silane coupling agents include KBM-403, KBM-503, KBM-803, and KBM-903 manufactured by Shin-Etsu Chemical Co., Ltd.

[0026] Wood contains oil and has a fine porous structure, making it prone to repelling water-based paints. For example, the contact angle of water on wood is approximately 80°, while the contact angle of oil is only about 30°. As a result, poor adhesion may occur if the surface wettability is poor. Therefore, it is preferable for water-based paints to contain a penetrating agent that improves wettability to wood. As a penetrating agent, surfactants such as polyoxyethylene alkyl ethers like Emulgen 1108 (HLB value 13.5) manufactured by Kao Corporation, and sodium dialkyl sulfosuccinates like Perex OT-P manufactured by Kao Corporation can be used. When using a nonionic surfactant as a penetrating agent, it is preferable to use a nonionic surfactant with an HLB value of 13 or more and less than 15. Penetrating agents have an SP value of 8 (cal / cm²) from the perspective of adhesion. 3 )0.5 or more 13(cal / cm 3 It is preferable to use it in combination with a solvent of 0.5% or less, and it is particularly preferable to use it in combination with ethanol.

[0027] To form a coating on the surface of a wood substrate using a paint composition, it is necessary to round the edges of the wood, especially before painting, to maintain paint adhesion. When painting, the surface is sanded or sandpapered. The coarseness of the sandpaper should preferably be between #120 and #240. Afterward, the paint composition is applied to the wood substrate and allowed to dry and harden. The application method is not particularly limited, but it can be applied using commonly used painting tools or machines such as rollers, brushes, air sprayers, air guns, airless sprayers, or airless guns.

[0028] Next, Table 1 shows the comparative tests, including examples and comparative examples. 1 (Poor evaluation) ⇒ 5 (Good evaluation) Adhesion: Cellophane tape adhesion test (grid test) Evaluation 1: (50 / 100 or less) ⇒ Evaluation 5: (90 / 100 or more) Water resistance: 1-week immersion test at room temperature. Evaluation 1: (Whitening) ⇒ Evaluation 5: (No whitening) Weather resistance: Xenon lamp weather resistance test: Rating 1 (change after 200 hours) ⇒ Rating 5 (no problems after 1000 hours) Mold resistance: JIS Z 2911 "Testing of general industrial products (wood and bamboo products) and testing of paints" Spray 0.5 mL of mixed spore suspension evenly onto the test specimen, cover the petri dish, and place it in a constant temperature incubator at 26±2°C and 80-85% humidity for 4 weeks. Evaluation 1: The area of ​​mycelial growth observed in the inoculated portion of the sample or test piece exceeds 2 / 3 of the total area. ⇒ Evaluation 5: No mycelial growth is observed in the inoculated portion of the sample or test piece. Crackability: Surface condition after 1 year of outdoor exposure. Rating 1: Cracks are visible. ⇒ Rating 5: No problems at all. Discoloration: Color change after 1 year of outdoor exposure. Rating 1: Significant discoloration. ⇒ Rating 5: No discoloration at all. [Table 1]

Claims

1. A novel water-based transparent paint for wood, characterized by its application in three layers: a primer layer (U), an intermediate layer (T), and a topcoat layer (W) as needed, using a water-based resin emulsion (a). The primer layer (U) uses a water-based resin emulsion mixed with tannin (b) and an antifungal agent (c). The intermediate layer (T) uses a water-based resin emulsion (a) mixed with an ultraviolet absorber (d), a light stabilizer (e), and an antifungal agent (c). The topcoat layer (W) uses a water-based resin emulsion (a) mixed with a matting agent (e) and an antifungal agent (c).

2. A novel water-based transparent paint for wood, characterized in that the above-mentioned water-based resin emulsion (a) uses a water-based urethane resin emulsion and has a particle size of 20 nm to 200 nm, as described in claim 1.

3. The novel water-based transparent paint for wood according to claims 1 and 2, characterized in that the undercoat layer (U) is a mixture of a water-based resin emulsion (a), tannin (b), and antifungal agent (c), in which the ratio of (a) to (b) is 98 to 80:2 to 20% by weight, and the ratio of (a) + (b) to (c) is 99.9 to 99:0.1 to 1% by weight.

4. The novel water-based transparent paint for wood according to claims 1 to 3, characterized in that the intermediate coat layer (T) is a mixture of a water-based resin emulsion (a), an ultraviolet absorber (d), a light stabilizer (e), and an antifungal agent (c), in which the ratio of (a) to (d) + (e) is 99 to 95:1 to 5% by weight, the ratio of (a) + (d) + (e) to (c) is 99.9 to 99:0.1 to 1% by weight, and the dry film thickness is in the range of 10 μm to 150 μm.

5. The new water-based transparent paint for wood according to claims 1 to 4, characterized in that the topcoat layer (W) is a mixture of a water-based resin emulsion (a), a matting agent (f), and a fungicide (c), with the ratio of (a) to (f) being 98-90:2-10% by weight, and the ratio of (a) + (f) to (c) being 99.9-99:0.1-1% by weight.

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