WO2025115885A1 - Coating composition and coated article - Google Patents

Abstract

Provided is a coating composition including (i) an organopolysiloxane composed of the ratio of units represented in formula (1): (R¹ ₃SiO_1/2)_a(R² ₂SiO)_b(R³ ₁SiO_3/2)_c(SiO₂)_d(OR⁴)_e (where R¹-R³ represent alkyl groups or the like that may be substituted with a hydrogen atom, one or more hydroxy groups, or the like, and that may have an ether bond, with at least a portion of the same being an alkyl group or the like that is substituted with a hydroxy group and that may have an ether bond, R⁴ represents a hydrogen atom or an alkyl group, and a is 0-0.5, b is 0-0.5, c is 0.2-1.0, d is 0-0.5, e is 0-3.0, and a+b+c+d=1 is satisfied), and (ii) an inorganic filler.

Description

Coating compositions and coated articles

The present invention relates to a coating composition and a coated article, and more specifically to a flame-retardant coating composition and a coated article for use on wood substrates.

In recent years, the use of wood in buildings has been promoted from the perspective of carbon fixation and effective use of domestic resources. However, wood is a flammable base material, and its use in applications requiring flame retardancy is greatly restricted.
In this context, various techniques for imparting flame retardancy to wood are being investigated.

For example, in Patent Document 1, wood is successfully imparted with flame retardancy by impregnating it with a high concentration of a flame retardant such as boric acid. However, this system has the problem that the flame retardant adsorbed on the wood dissolves or deliquesces due to moisture in the air, greatly impairing the aesthetic appearance.

Patent Document 2 reports that it is possible to prevent chemical leaching by impregnating wood with a boron compound and then coating the wood surface with a siloxane compound. However, when this method is used, there have been reported cases where the boron compound dissolves due to the moisture contained in the wood itself, causing efflorescence at the interface between the coating film and the wood. In addition, this method requires many steps, such as impregnation with a flame retardant, drying, and surface painting, which inevitably increases manufacturing costs.

Patent Document 3 reports a technology that imparts flame retardancy to wood without impregnating it with a flame retardant by coating the wood surface with a primer component whose main component is silica, and then coating water glass on top of that. However, water glass has a known problem of low hardening and water resistance, and can react with wood and discolor, leaving many challenges to overcome before it can be put into practical use.

In addition, when coating the surface of wood, some of the coating liquid is absorbed into the wood, causing powder additives such as pigments and fillers to segregate on the surface, which can lead to poor appearance such as efflorescence and discoloration. This type of poor appearance is particularly likely to occur around knots where the fibers are sparse. Normally, an undercoat layer called a sealer is applied to prevent the paint from being absorbed into the wood, but sealer paints generally contain organic polymers to improve film-forming properties, which can worsen the fire retardancy of the wood.

Patent No. 3538194 Patent No. 4367640 JP 2018-115294 A

The present invention was made in consideration of the above circumstances, and aims to provide a coating composition that maintains the appearance of wood, such as the grain, while also imparting excellent flame retardancy and moisture resistance, and a coated article using the same.

As a result of extensive research into achieving the above objective, the inventors discovered that the above objective could be achieved by using a coating composition containing a specific hydroxyl-modified organopolysiloxane and an inorganic filler, and thus completed the present invention.

That is, the present invention provides
1. (i) 100 parts by mass of an organopolysiloxane having a unit ratio represented by the following formula (1): (R ¹ ₃ SiO _1/2 ) _a (R ² ₂ SiO) _b (R ³ ₁ SiO _3/2 ) _c (SiO ₂ ) _d (OR ⁴ ) _e (1)
(In the formula, R ¹ , R ² and R ³ each independently represent a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms which may be substituted with one or more amino groups, hydroxy groups, epoxy groups, acid anhydride groups, maleimide groups, vinyl groups, allyl groups, acrylic groups, methacrylic groups, or heterocyclic groups and which may have an ether bond, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms which may have an ether bond, but at least a part of R ¹ , R ² and R ³ is an alkyl group having 1 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, an aryl group having 6 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, or an aralkyl group having 7 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, Each of ⁴ independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, a is 0 to 0.5, b is 0 to 0.5, c is 0.2 to 1.0, d is 0 to 0.5, and e is a number that satisfies 0 to 3.0, and a+b+c+d=1.
(ii) a coating composition containing an inorganic filler: 100 to 900 parts by mass;
2. The coating composition according to 1, wherein the total number of hydroxy groups contained in R ¹ , R ² and R ³ is 50 mol % or more based on the total number of silicon atoms in the formula (1).
3. The coating composition according to 1 or 2, wherein the inorganic filler (ii) comprises one or more selected from silica, alumina, and phyllosilicate;
4. The coating composition according to any one of 1 to 3, further comprising (iii) 10 to 300 parts by mass of one or more flame retardants selected from phosphorus-based, boron-based, magnesium-based, aluminum-based, nitrogen-based, antimony-based and halogen-based compounds per 100 parts by mass of component (i);
5. The coating composition according to 4, wherein the ratio of the total mass of the component (ii) and the component (iii) to the mass of the component (i), [(ii)+(iii)]/(i), is 2.0 to 9.0.
6. A cured product of the coating composition according to any one of 1 to 5.
7. A coated article having a coating layer made of a coating composition according to any one of 1 to 5, directly or via one or more other layers, on at least a portion of the surface of a wood substrate.
8. A coated article having, on at least a portion of the surface of a wood substrate, an undercoat layer formed of a coating film of the coating composition according to any one of 1 to 5, and a topcoat layer formed of a coating film of a topcoat coating composition containing the following components (A), (B), and (C):
(A) Organopolysiloxane having a unit ratio represented by the following formula (2): 100 parts by mass
(R ⁵ ₃ SiO _1/2 ) _f (R ⁶ ₂ SiO) _g (R ⁷ ₁ SiO _3/2 ) _h (SiO ₂ ) _i (OR ⁸ ) _j (2)
(In the formula, R ⁵ , R ⁶ and R ⁷ each independently represent a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms or an aralkyl group having 7 to 20 carbon atoms, which may be substituted with one or more amino groups, hydroxy groups, epoxy groups, acid anhydride groups, maleimide groups, vinyl groups, allyl groups, acrylic groups, methacrylic groups or heterocyclic groups, and at least a part of R ⁵ , R ⁶ and R ⁷ is an alkyl group having 1 to 20 carbon atoms substituted with an amino group, an aryl group having 6 to 20 carbon atoms substituted with an amino group, or an aralkyl group having 7 to 20 carbon atoms substituted with an amino group, and R Each of ⁸ independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, f is 0 to 0.5, g is 0 to 0.5, h is 0.2 to 1.0, i is 0 to 0.5, and j is a number that satisfies 0 to 3.0, and f+g+h+i=1.
(B) one or more flame retardants selected from phosphorus-based, boron-based, magnesium-based, aluminum-based, nitrogen-based, antimony-based, and halogen-based compounds: 50 to 300 parts by mass (C) inorganic filler: 25 to 150 parts by mass 9. The present invention provides a coated article according to claim ⁸ , wherein the coating amount of the undercoat layer is 0.01 to 0.50 kg/m2 relative to the wood substrate, and the coating amount of the topcoat layer is 0.1 to 2.0 kg/ ^m2 relative to the wood substrate.

When the paint composition of the present invention is used as an undercoat paint for wood substrates, the organopolysiloxane and inorganic filler effectively cover the gaps between the wood fibers, thereby improving moisture resistance, and by suppressing absorption of the topcoat paint into the surface of the wood substrate, deterioration of appearance such as whitening around knots can be suppressed.
Furthermore, by combining with a topcoat layer containing an organopolysiloxane, a flame retardant, and an inorganic filler, the coating film becomes ceramic upon combustion, forming a fire-resistant layer and/or a heat-insulating layer, thereby preventing the wood substrate from burning.
Due to these effects, the present invention makes it possible to provide a coated article that maintains the appearance of a wood substrate, such as the wood grain, which has been considered difficult to achieve in the past, and that is excellent in flame retardancy and moisture resistance.
The coating composition of the present invention can impart flame retardancy to a wooden substrate by coating the surface of the wooden substrate, and can impart flame retardancy to the wooden substrate more easily than the conventional method of impregnating a flame retardant. In addition, it can also be applied on-site to impart flame retardancy, which is expected to greatly expand the freedom of design and/or construction of wooden buildings.

The present invention will be specifically described below.
[1] Coating Composition The coating composition of the present invention contains the following components (i) and (ii):
(i) an organopolysiloxane having a unit ratio represented by the following formula (1); and (ii) an inorganic filler.

(i) Organopolysiloxane Component (i) is an organopolysiloxane composed of units in the ratio represented by the following formula (1): In formula (1), unless otherwise specified, units represented by ( ^R13SiO1 _{/ 2} ) are called M units, units represented by ( ^R22SiO ) are called D units, units represented by ( ^R3SiO3 _{/2 )} are called T units, and units represented by ( _SiO2 ) are called Q units.

(R ¹ ₃ SiO _1/2 ) _a (R ² ₂ SiO) _b (R ³ ₁ SiO _3/2 ) _c (SiO ₂ ) _d (OR ⁴ ) _e (1)

In formula (1), R ¹ , R ² and R ³ each independently represent a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms which may be substituted with one or more amino groups, hydroxy groups, epoxy groups, acid anhydride groups, maleimide groups, vinyl groups, allyl groups, acrylic groups, methacrylic groups, or heterocyclic groups and which may have an ether bond, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms which may have an ether bond, and at least a part of R ¹ , R ² and R ³ is an alkyl group having 1 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, an aryl group having 6 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, or an aralkyl group having 7 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond.

The alkyl group having 1 to 20 carbon atoms may be linear, branched or cyclic, and specific examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-decyl, cyclopentyl and cyclohexyl groups, with the methyl or ethyl group being preferred from the viewpoint of increasing the flame retardancy of the coating composition.
Examples of the aryl group having 6 to 20 carbon atoms include a phenyl group and a naphthyl group.
Examples of the aralkyl group having 7 to 20 carbon atoms include benzyl and phenethyl groups.
Heterocyclic groups include piperidinyl, pyridinyl, pyrrolyl, thienyl groups, and the like.

As described above, in formula (1), at least a part of R ¹ , R ² and R ³ is an alkyl group having 1 to 20 carbon atoms and substituted with a hydroxy group and optionally having an ether bond, an aryl group having 6 to 20 carbon atoms and substituted with a hydroxy group and optionally having an ether bond, or an aralkyl group having 7 to 20 carbon atoms and substituted with a hydroxy group and optionally having an ether bond. Preferred examples of such a group substituted with a hydroxy group include a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 2,3-dihydroxypropyl group, a 3,4-dihydroxybutyl group, a β-(3,4-dihydroxycyclohexyl)ethyl group, and a group represented by the following formula (3):

（式中、波線を付した線は結合手を表す。）

(In the formula, the wavy line represents a bond.)

Taking into consideration the solubility of component (i) in water, the affinity with the inorganic filler component and the substrate, and the like, the total number of hydroxy groups contained in R ¹ , R ² and R ³ is preferably 50 mol % or more, more preferably 80 mol % or more, and even more preferably 100 mol % or more, of the total number of silicon atoms in formula (1).

Among R ¹ , R ² and R ³ , the substituents other than the groups substituted with hydroxyl groups are preferably methyl or ethyl groups, which have a small number of carbon atoms in the combustible alkyl chain, and more preferably methyl groups.

In formula (1), each R ⁴ independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.
Specific examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, and n-octyl groups.
Among these, from the viewpoint of flame retardancy of the coating composition, ^R4 is preferably a hydrogen atom.

a is a number that ranges from 0 to 0.5, b is a number that ranges from 0 to 0.5, c is a number that ranges from 0.2 to 1.0, and d is a number that ranges from 0 to 0.5 and satisfies a+b+c+d=1.
The character e is a number from 0 to 3.0, and from the viewpoint of the water solubility of the organopolysiloxane, is preferably a number from 0.1 to 2.0. If e exceeds 3.0, the film-forming properties of the coating composition and the moisture resistance of the coating film may deteriorate.

The organopolysiloxane of component (i) has undergone a certain degree of condensation, which facilitates network formation and allows it to be easily fixed to the substrate. In addition, it has fewer alkoxy groups, which are a source of flammable gas, compared to monomer components (such as silane coupling agents) that do not contain siloxane bonds (Si-O-Si bonds), which gives it the advantage of less loss of flame retardancy.

The amount of the monomer component not containing a siloxane bond is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and even more preferably 1% by mass or less, based on the organopolysiloxane of component (i).
The ratio of the monomer component not containing a siloxane bond to the organopolysiloxane component can be determined from the signal and integral ratio in the ^29Si -NMR (nuclear magnetic resonance) spectrum. In the case of a trifunctional siloxane (T unit), for example, in ^29Si -NMR, the number of silicon atoms forming the siloxane bond can be determined by examining the ratio of (T0) to (T3) shown below. The detection magnetic field is generally higher in the order of T3>T2>T1>T0, so the T0 component is a silicon atom derived from the silane coupling agent, and the rest are silicon atoms derived from the siloxane, and the ratio of the monomer (silane coupling agent) component to the organopolysiloxane component can be determined from the ratio of the integral values of each peak.

（式中、Ｒは、有機基を表し、Ｘは、水素原子または有機基を表す。）

(In the formula, R represents an organic group, and X represents a hydrogen atom or an organic group.)

The organopolysiloxane of component (i) can be produced by hydrolysis and condensation of the monomer components of each structural unit in the presence of an acid or base catalyst. In addition, by carrying out a deprotection reaction of the protected hydroxyl groups as necessary, it is possible to produce organopolysiloxanes having alkyl groups, aryl groups, aralkyl groups, etc. substituted with hydroxyl groups.

Examples of monomers with Q units include tetramethoxysilane, tetraethoxysilane, tetra(n-propoxy)silane, tetra(i-propoxy)silane, tetra(n-butoxy)silane, alkali silicate, and activated silicic acid obtained by cation exchange of alkali silicate.

Examples of monomers of T units include methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltriisopropoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3 ,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-chloropropyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, perfluorooctylethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, γ-isocyanatepropyltrimethoxysilane, γ-isocyanatepropyltriethoxysilane, and the like.
Among these, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, etc. can be converted into hydroxy group-substituted products by an ester exchange reaction with water, and γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc. can be converted into diol products by reacting the epoxy ring with water, and are therefore preferred because they improve the solubility of the siloxane in water and the affinity with wood and inorganic filler components.

Examples of monomers of D units include dimethyldimethoxysilane, dimethyldiethoxysilane, methylethyldimethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, diisopropyldimethoxysilane, phenylmethyldimethoxysilane, vinylmethyldimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane.
Among these, taking into consideration the solubility of the resulting siloxane in water and the affinity with wood and flame retardant components, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, and the like can be converted into hydroxy group-substituted products by an ester exchange reaction with water, and γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, and the like can be converted into diol forms by reacting the epoxy ring with water, which are preferred because they improve the solubility of the siloxane in water and the affinity with wood and inorganic filler components.

Examples of monomers of M units include trimethylmethoxysilane, trimethylethoxysilane, triethylmethoxysilane, n-propyldimethylmethoxysilane, n-propyldiethylmethoxysilane, isopropyldimethylmethoxysilane, isopropyldiethylmethoxysilane, propyldimethylethoxysilane, n-butyldimethylmethoxysilane, n-butyldimethylethoxysilane, n-hexyldimethylmethoxysilane, n-hexyldimethylethoxysilane, n-pentyldimethylmethoxysilane, n-pentyldimethylethoxysilane, n-hexyldimethylmethoxysilane, and n-hexyldimethylmethoxysilane. Examples of the silane include dimethylethoxysilane, n-decyldimethylmethoxysilane, n-decyldimethylethoxysilane, trimethylsilanol, triethylsilanol, n-propyldimethylsilanol, n-propyldiethylsilanol, isopropyldimethylsilanol, isopropyldiethylsilanol, propyldimethylsilanol, n-butyldimethylsilanol, n-hexyldimethylsilanol, n-pentyldimethylsilanol, n-decyldimethylsilanol, γ-aminopropyldimethylmethoxysilane, and N-(2-aminoethyl)-3-aminopropyldimethylmethoxysilane.
Among these, taking into consideration the solubility of the resulting organopolysiloxane in water and the affinity with the substrate and flame retardant components, γ-methacryloxypropyldimethylmethoxysilane, γ-methacryloxypropyldimethylethoxysilane, and the like can be converted into hydroxy group-substituted products by an ester exchange reaction with water, while γ-glycidoxypropyldimethylmethoxysilane, γ-glycidoxypropyldimethylethoxysilane, β-(3,4-epoxycyclohexyl)ethyldimethylmethoxysilane, and the like can be converted into diol products by reacting the epoxy ring with water, and are therefore preferred because they improve the solubility of the siloxane in water and the affinity with wood and inorganic filler components.

Since the M units and D units have two or more Si-C bonds and are easily combustible, the content of M units and D units among all the structural units in the organopolysiloxane of component (i) is each 50 mol % or less.
That is, in the above formula (1), a is a number from 0 to 0.5, preferably a number from 0 to 0.2, and more preferably a number from 0 to 0.1.
Furthermore, b is a number from 0 to 0.5, preferably a number from 0 to 0.2, and more preferably a number from 0 to 0.1.

T units have one Si-C bond and are less flammable than D and M units, and therefore, by containing 20 mol % or more of T units among all the structural units in the organopolysiloxane of component (i), good flame retardancy is achieved.
That is, in the above formula (1), c is a number from 0.2 to 1.0, preferably a number from 0.5 to 1.0, and more preferably a number from 0.6 to 1.0.

Q units do not contain Si-C bonds and have low flammability, and are effective in preventing a decrease in flame retardancy due to combustion resulting from Si-C bonds. On the other hand, Q units have many cross-linking points and are highly reactive, so from the standpoint of compatibility with flame retardant components and film-forming properties, the Q units are in the range of 0 to 50 mol % of all constituent units in the organopolysiloxane of component (i), i.e., d is a number from 0 to 0.5, with 0 to 0.4 being preferred.

The ratio of each constitutional unit in component (i) can be confirmed by a known method using, for example, the ratio of chemical shifts and integral values of ²⁹ Si-NMR signals.

The content of component (i) is preferably 5 to 50% by mass, more preferably 10 to 30% by mass, based on the total solid content in the coating composition. When it is 5% by mass or more, the film-forming property and transparency of the coating film are good. When it is 50% by mass or less, the flame retardancy of the coating film and the effect of suppressing poor appearance around knots of the wood substrate are good.
The component (i) may be used alone or in combination of two or more types.

(ii) Inorganic Filler As the inorganic filler of the component (ii), a known general inorganic filler can be used. Examples of the inorganic filler include inorganic fillers containing a Group 13 element, a Group 14 element (excluding carbon), a first series transition element, a second series transition element, a third series transition element, a lanthanoid, etc.
Examples of inorganic fillers containing a Group 13 element include oxides derived from aluminum, boron, indium, etc., and among these, alumina is preferred.
Examples of inorganic fillers containing a Group 14 element (excluding carbon) include oxides and salts derived from silicon, tin, etc., with silica being preferred.
Examples of inorganic fillers containing a first series transition element include oxides derived from titanium, manganese, zinc, etc., and these oxides can also be used as light absorbing materials of specific wavelengths.
Inorganic fillers containing second series transition elements include oxides derived from yttrium, zirconium, etc., and these oxides can also be used as light absorbing and fluorescent materials of specific wavelengths.
Examples of inorganic fillers containing third series transition elements include oxides derived from hafnium, tantalum, and the like.
Examples of inorganic fillers containing lanthanoids include oxides derived from lanthanum, cerium, praseodymium, neodymium, terbium, dysprosium, ytterbium, etc., and these oxides can also be used as light absorbing and fluorescent materials of specific wavelengths.
Furthermore, a compound formed by combining two or more of these via a chemical bond can also be used.

There are no particular limitations on the shape of the inorganic filler, and inorganic fillers of various shapes, such as spherical, hollow spherical, porous, plate-like, needle-like, and fibrous, can be used.

In particular, the inorganic filler used in the present invention is preferably an inorganic oxide or silicate containing elements such as silicon, boron, or aluminum that becomes ceramic when burned and forms a fire-resistant or heat-insulating layer, such as silica, alumina, or phyllosilicates. In particular, it is preferable to use a silicon oxide-containing filler such as silica in combination with a phyllosilicate such as clay, as this provides better flame retardancy and suppresses poor appearance around the knots.

In particular, as the inorganic filler used in the present invention, it is preferable to use silica particles with an average particle size calculated based on the BET specific surface area of 15 to 100 nm, and it is more preferable to use silica particles with an average particle size of 20 to 80 nm. If the average particle size is 15 nm or more, the coating film will have excellent film-forming properties, and if it is 100 nm or less, the coating film will have excellent transparency.

The amount of component (ii) is 100 to 900 parts by mass, and more preferably 200 to 800 parts by mass, per 100 parts by mass of the organopolysiloxane of component (i). At 100 parts by mass or more, the flame retardancy of the coating film is improved. For example, when the coating composition of the present invention is used as an undercoat layer on a wooden substrate and a topcoat layer is formed on top of it, the undercoat layer is formed so that the inorganic filler fills the grain of the surface of the wooden substrate, thereby suppressing absorption of the topcoat paint and suppressing the occurrence of poor appearance around knots. At 900 parts by mass or less, the coating film has good film-forming properties, and the transparency of the coated article and the effect of suppressing poor appearance around knots are good. Also, component (ii) may be used alone or in combination of two or more types.

(iii) Flame Retardant The coating composition of the present invention may contain, as component (iii), one or more flame retardants selected from phosphorus-based, boron-based, magnesium-based, aluminum-based, nitrogen-based, antimony-based and halogen-based compounds.
Examples of phosphorus-based compounds include organic phosphorus compounds, phosphoric acid, phosphoric acid esters, and phosphates, and specific examples thereof include diammonium hydrogen phosphate, ammonium dihydrogen phosphate, diguanidine phosphate, ammonium polyphosphate, hydrophobized ammonium polyphosphate, guanylurea phosphate, carbamate polyphosphate, and melamine phosphate.
Examples of boron compounds include organic boron compounds, boric acid, borax, boron oxide, borate esters, and borates.
Examples of magnesium compounds include magnesium hydroxide and magnesium oxide.
An example of the aluminum compound is aluminum hydroxide.
Examples of the nitrogen-based compound include ammonium sulfate, ammonium carbonate, ammonium hydrogen carbonate, and melamine cyanurate.
An example of an antimony compound is antimony trioxide.
An example of the halogen-based compound is zinc chloride.

Among these, phosphorus-based compounds and boron-based compounds are preferred as flame retardants for use in the coating composition of the present invention, as they provide good transparency and flame retardancy of the coated article, and good effect in suppressing poor appearance around knots in wood.
Specific examples of suitable usable compounds include diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium polyphosphate, boric acid, borax, and boron oxide.

When component (iii) is used, the blending amount is preferably 10 to 300 parts by mass, and more preferably 50 to 200 parts by mass, per 100 parts by mass of the organopolysiloxane of component (i) above, from the viewpoints of flame retardancy, film formability, transparency, and moisture resistance of the coating film.
The component (iii) may be used alone or in combination of two or more types.

In the coating composition of the present invention, the ratio of the total mass of the above-mentioned components (ii) and (iii) to the mass of the above-mentioned component (i), [(ii)+(iii)]/(i), is preferably 1.0 to 10.0, more preferably 2.0 to 9.0, and even more preferably 3.0 to 8.0. When the above ratio is 1.0 or more, the flame retardancy is good, and when it is 10.0 or less, the moisture resistance, film-forming property, and transparency of the coating film are good.

(iv) Solvent The coating composition of the present invention may contain a solvent in addition to the above components (i) to (iii). The solvent is not particularly limited, but alcohol or water is preferred, and water is more preferred from the viewpoints of environmental conservation and easy availability.

When water is used as the solvent, specifically, fresh water such as tap water, industrial water, well water, natural water, rainwater, distilled water, and ion-exchanged water can be used, with ion-exchanged water being particularly preferred. Ion-exchanged water can be produced using a pure water production device (for example, Organo Corporation, product name "FW-10," Merck Millipore, product name "Direct-QUV3," etc.).

When a solvent is used, the amount is preferably 20-98% by mass, more preferably 70-95% by mass, of the entire composition. When the solvent is present in an amount of 20% by mass or more of the entire composition, the fluidity and workability of the paint are improved, and when the solvent is present in an amount of 98% by mass or less of the entire composition, the concentration of the active ingredients in the paint is high, making it easier to thicken the coating film.

(v) Curing catalyst The coating composition of the present invention may contain a curing catalyst for the purpose of promoting the curing reaction. The type, mixing amount, and addition method of the curing catalyst may be selected from known methods and conditions according to the type of composition.
In particular, when the coating composition contains a component that cures by a chemical reaction in the presence of a catalyst, the coating composition preferably contains a curing catalyst. Examples of the curing catalyst include basic compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methylate, sodium propionate, potassium propionate, sodium acetate, potassium acetate, sodium formate, potassium formate, trimethylbenzylammonium hydroxide, tetramethylammonium hydroxide, tetramethylammonium acetate, n-hexylamine, tributylamine, diazabicycloundecene (DBU), and dicyandiamide; metal-containing compounds such as tetraisopropyl titanate, tetrabutyl titanate, titanium acetylacetonate, aluminum triisobutoxide, aluminum triisopropoxide, tris(acetylacetonate)aluminum, diisopropoxy(ethylacetoacetate)aluminum, aluminum perchlorate, aluminum chloride, cobalt octylate, cobalt acetylacetonate, iron acetylacetonate, tin acetylacetonate, dibutyltin octylate, and dibutyltin laurate; and acidic compounds such as p-toluenesulfonic acid and trichloroacetic acid.
Among these, particularly preferred are sodium propionate, sodium acetate, sodium formate, trimethylbenzylammonium hydroxide, tetramethylammonium hydroxide, tris(acetylacetonato)aluminum, diisopropoxy(ethylacetoacetate)aluminum, and the like. In particular, metal-containing compounds such as aluminum-based catalysts, titanium-based catalysts, and tin-based catalysts containing organic ligands are preferred.

The coating composition of the present invention may contain additives that exert additional effects to the extent that they do not impair the effects of the present invention. Examples of additives include leveling agents. As the leveling agent, for example, well-known common leveling agents such as acrylic, vinyl, silicone, and fluorine-based leveling agents can be used. Among these, silicone-based leveling agents having a siloxane structure in the main chain are preferred from the viewpoint of increasing the flame retardancy of the coated article.

Additives other than the leveling agent include ultraviolet absorbers, anti-termite agents, antioxidants, dyes, pigments, etc., and these additives may be used alone or in combination of two or more types.

In the coating composition of the present invention, the total content of the above components (i) to (iii) relative to the total solid content is preferably 70 mass% or more, more preferably 80 mass% or more, and most preferably 90 mass% or more.

The coating composition of the present invention can be produced by mixing the above components (i) and (ii), and, if necessary, the components (iii), (iv), (v) and other components. The mixing method for each component may be appropriately selected from known methods and is not particularly limited. For example, a mixer, a shaking device, an ultrasonic homogenizer, a high-pressure homogenizer, a bead mill, a ball mill, or the like can be used as the device used for mixing.
For the purpose of accelerating the dissolution or dispersion of each component, the mixing operation may be carried out under heating within a range that does not impair the effects of the present invention.

[2] Cured product and coated article A cured product (cured film) can be obtained by curing the coating composition of the present invention. For example, a flame-retardant coated article can be obtained by applying the coating composition of the present invention directly or via one or more other layers to at least a portion of the surface of a wood substrate to be flame-retarded, and then curing the composition to form a coating film (coating layer).
After the coating composition of the present invention has been applied to the surface of a wood substrate, a coating film may be formed by merely drying the composition without curing the composition by crosslinking the organopolysiloxane of component (i) above.

The coating composition of the present invention can also be suitably used as a coating composition for an undercoat layer on a wooden substrate. A flame-retardant coated article can be obtained by forming a topcoat layer on the surface of a wooden substrate, the topcoat layer being a coating film obtained by applying, drying, and, if necessary, curing a coating composition for a topcoat layer that contains a flame retardant, via an undercoat layer consisting of a coating film obtained by applying, drying, and, if necessary, curing the coating composition of the present invention.

In this case, the coating layer having the above undercoat layer and topcoat layer may be formed on a part of the substrate surface or on the entire surface. For example, in the case of a plate-shaped substrate, the coating layer may be formed on at least one surface.

(1) Wood Substrate Examples of wood substrates include wood materials such as lumber, logs, plywood, laminated veneer lumber (LVL), laminated timber, cross laminated timber (CLT), high strength engineered wood lumber (LSL), laminated veneer board (LVB), laminated veneer sandwich (LVS), parallel strand lumber (PSL), medium density fiberboard (MDF), structural panels (oriented strand board (OSB)), particle board, and fiberboard.
In particular, building materials such as lumber, laminated lumber, and CLT-type base materials are suitable.

Furthermore, these wood substrates and wood substrates whose surfaces have been treated, specifically wood substrates that have been treated with chemical conversion coating, corona discharge treatment, plasma treatment, or acid or alkaline liquid, can also be used.

Furthermore, the surface of a wood substrate on which other functional layers have already been formed may be coated with the coating composition of the present invention.
Other functional layers include an anti-rust layer, a gas barrier layer, a waterproof layer, a heat ray shielding layer, etc., and one or more of these layers may be formed in advance on the wood substrate.

(2) Undercoat Layer The undercoat layer can be formed by applying the coating composition of the present invention described above to at least a part of the surface of the wood substrate, followed by drying and, if necessary, curing.

The conditions for applying and drying the coating composition of the present invention to a wood substrate may be appropriately set depending on the type and shape of the wood substrate. Specific conditions may be appropriately selected from known conditions.

The method for applying the coating composition may be appropriately selected from known techniques, and various coating methods such as brush coating, spraying, immersion, flow coating, roll coating, curtain coating, spin coating, and knife coating can be used.
The coating composition of the present invention is, for example, a composition capable of forming a film at about 0 to 40°C, preferably about 5 to 35°C, and more preferably capable of forming a film at 25°C after 24 hours.
For the purpose of shortening the curing time, heating may be performed within a temperature range that does not adversely affect the substrate, etc.

(3) Topcoat layer The topcoat layer can be formed by applying a coating composition for topcoat layer on the undercoat layer, drying and curing as necessary. The topcoat layer is preferably formed from a coating composition for topcoat layer containing the following components (A) to (C) from the viewpoints of moisture resistance, flame retardancy and coating film transparency.
(A) an organopolysiloxane having a unit ratio represented by the following formula (2); (B) a flame retardant; and (C) an inorganic filler.

Component (A) is an organopolysiloxane composed of units in the ratio represented by formula (2) below: In formula (2), unless otherwise specified, units represented by ( ^R53SiO1 _/2 ) are called M units, units represented by ( _R62SiO ) are called D units, units represented by ^{( R7SiO3} _{/ 2} ) are called T units, and units represented by ( _SiO2 ) are called Q units.

(R ⁵ ₃ SiO _1/2 ) _f (R ⁶ ₂ SiO) _g (R ⁷ ₁ SiO _3/2 ) _h (SiO ₂ ) _i (OR ⁸ ) _j (2)

In formula (2), R ⁵ , R ⁶ and R ⁷ each independently represent a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms, which may be substituted with one or more amino groups, hydroxy groups, epoxy groups, acid anhydride groups, maleimide groups, vinyl groups, allyl groups, acrylic groups, methacrylic groups, or heterocyclic groups, and at least a part of R ⁵ , R ⁶ and R ⁷ is an alkyl group having 1 to 20 carbon atoms substituted with an amino group, an aryl group having 6 to 20 carbon atoms substituted with an amino group, or an aralkyl group having 7 to 20 carbon atoms substituted with an amino group.

The alkyl group having 1 to 20 carbon atoms may be linear, branched or cyclic, and specific examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-decyl, cyclopentyl and cyclohexyl groups, with the methyl or ethyl group being preferred from the viewpoint of increasing the flame retardancy of the coating composition.
Examples of the aryl group having 6 to 20 carbon atoms include phenyl and naphthyl.
Examples of the aralkyl group having 7 to 20 carbon atoms include benzyl and phenethyl groups.
Heterocyclic groups include piperidinyl, pyridinyl, pyrrolyl, thienyl groups, and the like.

As described above, in formula (2), at least a part of R ⁵ , R ⁶ and R ⁷ is an alkyl group having 1 to 20 carbon atoms substituted with an amino group, an aryl group having 6 to 20 carbon atoms substituted with an amino group, or an aralkyl group having 7 to 20 carbon atoms substituted with an amino group. As such a group substituted with an amino group, a γ-aminopropyl group or an N-(2-aminoethyl)-3-aminopropyl group is preferable.
Taking into consideration the solubility of component (A) in water and the affinity with the flame retardant component and the substrate, among R ⁵ , R ⁶ and R ⁷ , the total number of alkyl groups having 1 to 20 carbon atoms and substituted with amino groups, aryl groups having 6 to 20 carbon atoms and substituted with amino groups, or aralkyl groups having 7 to 20 carbon atoms and substituted with amino groups is preferably 50 mol % or more, more preferably 55 mol % or more, and even more preferably 60 mol % or more, relative to the total number of silicon atoms in formula (2).

Among R ⁵ , R ⁶ and R ⁷ , the substituents other than the groups substituted with amino groups are preferably methyl or ethyl groups, which have a small number of carbon atoms in the combustible alkyl chain, and more preferably methyl groups.

In formula (2), each R ⁸ independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.
Specific examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, and n-octyl groups.
Among these, from the viewpoint of flame retardancy of the coating composition, R ⁸ is preferably a hydrogen atom.

f is a number ranging from 0 to 0.5, g is a number ranging from 0 to 0.5, h is a number ranging from 0.2 to 1.0, i is a number ranging from 0 to 0.5, and f+g+h+i=1.
j is a number from 0 to 3.0, and from the viewpoint of the water solubility of the organopolysiloxane, is preferably a number from 0.1 to 2.0. If j exceeds 3.0, the film-forming properties of the coating composition and the moisture resistance of the coating film may deteriorate.

The organopolysiloxane of component (A) has undergone a certain degree of condensation, which facilitates network formation and allows it to be easily fixed to the substrate. In addition, it has fewer alkoxy groups, which are a source of flammable gas, compared to monomer components (such as silane coupling agents) that do not contain siloxane bonds (Si-O-Si bonds), which gives it the advantage of less loss of flame retardancy.

The amount of the monomer component not containing a siloxane bond is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and even more preferably 1% by mass or less, based on the organopolysiloxane of component (A).
The ratio of the monomer component not containing a siloxane bond to the organopolysiloxane component can be determined from the signal and integral ratio in a ²⁹ Si-NMR (nuclear magnetic resonance) spectrum.

The organopolysiloxane of component (A) can be produced by hydrolysis and condensation of the monomer components of each structural unit in the presence of an acid or base catalyst.

Examples of monomers with Q units include tetramethoxysilane, tetraethoxysilane, tetra(n-propoxy)silane, tetra(i-propoxy)silane, tetra(n-butoxy)silane, alkali silicate, and activated silicic acid obtained by cation exchange of alkali silicate.

Examples of monomers of T units include methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltriisopropoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3 ,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-chloropropyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, perfluorooctylethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, γ-isocyanatepropyltrimethoxysilane, γ-isocyanatepropyltriethoxysilane, and the like.
Among these, taking into consideration the solubility of the resulting siloxane in water, the affinity with wood and flame retardant components, and the like, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, γ-isocyanatepropyltrimethoxysilane, γ-isocyanatepropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane are preferred, and γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltriethoxysilane are more preferred.

Examples of monomers of D units include dimethyldimethoxysilane, dimethyldiethoxysilane, methylethyldimethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, diisopropyldimethoxysilane, phenylmethyldimethoxysilane, vinylmethyldimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane.
Among these, γ-aminopropylmethyldiethoxysilane and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane are preferred, taking into consideration the solubility of the resulting siloxane in water and the affinity with wood and flame retardant components.

Examples of monomers of M units include trimethylmethoxysilane, trimethylethoxysilane, triethylmethoxysilane, n-propyldimethylmethoxysilane, n-propyldiethylmethoxysilane, isopropyldimethylmethoxysilane, isopropyldiethylmethoxysilane, isopropyldimethylethoxysilane, n-butyldimethylmethoxysilane, n-butyldimethylethoxysilane, n-hexyldimethylmethoxysilane, n-hexyldimethylethoxysilane, n-pentyldimethylmethoxysilane, n-pentyldimethylethoxysilane, and n-hexyldimethylmethoxysilane. Examples of the silanol include silane, n-hexyldimethylethoxysilane, n-decyldimethylmethoxysilane, n-decyldimethylethoxysilane, trimethylsilanol, triethylsilanol, n-propyldimethylsilanol, n-propyldiethylsilanol, isopropyldimethylsilanol, isopropyldiethylsilanol, n-butyldimethylsilanol, n-hexyldimethylsilanol, n-pentyldimethylsilanol, n-decyldimethylsilanol, γ-aminopropyldimethylmethoxysilane, and N-(2-aminoethyl)-3-aminopropyldimethylmethoxysilane.
Among these, γ-aminopropyldimethylmethoxysilane and N-(2-aminoethyl)-3-aminopropyldimethylmethoxysilane are preferred, taking into consideration the solubility in water of the resulting organopolysiloxane and the affinity with the substrate and flame retardant components.

Since the M units and D units have two or more Si-C bonds and are easily combustible, it is preferable that the content of M units and D units among all the structural units in the organopolysiloxane of component (A) be no more than 50 mol % each.
That is, in the above formula (2), f is preferably a number from 0 to 0.5, more preferably a number from 0 to 0.2, and even more preferably a number from 0 to 0.1.
Furthermore, g is preferably a number from 0 to 0.5, more preferably a number from 0 to 0.2, and even more preferably a number from 0 to 0.1.

T units have one Si-C bond and are less flammable than D and M units, and therefore, by containing 20 mol % or more of T units among all the structural units in the organopolysiloxane of component (A), good flame retardancy is achieved.
That is, in the above formula (2), h is preferably a number from 0.2 to 1.0, more preferably a number from 0.5 to 1.0, and even more preferably a number from 0.6 to 1.0.

Q units do not contain Si-C bonds and have low flammability, and are effective in suppressing the decrease in flame retardancy caused by combustion resulting from Si-C bonds. On the other hand, Q units have many cross-linking points and are highly reactive, so from the viewpoint of compatibility with flame retardant components and film-forming properties, the Q units are preferably in the range of 0 to 50 mol % of all constituent units in the organopolysiloxane of component (A); that is, i is preferably a number from 0 to 0.5, more preferably a number from 0.1 to 0.4, and even more preferably a number from 0.3 to 0.4.

The ratio of the structural units in component (A) can be confirmed by a known method that uses, for example, the ratio of the chemical shift and integral value of the ²⁹ Si-NMR signal.

The content of component (A) is preferably 5 to 60% by mass, more preferably 10 to 40% by mass, based on the total amount of the coating composition for the topcoat layer. When the content is 5% by mass or more, the film-forming property, transparency, and moisture resistance of the coating film are improved. When the content is 60% by mass or less, the flame retardancy of the coating film is improved.
The component (A) may be used alone or in combination of two or more types.

(B) Flame Retardant Component (B) is one or more flame retardants selected from phosphorus-, boron-, magnesium-, aluminum-, nitrogen-, antimony- and halogen-based compounds.
Examples of phosphorus-based compounds include organic phosphorus compounds, phosphoric acid, phosphoric acid esters, and phosphates, and specific examples thereof include diammonium hydrogen phosphate, ammonium dihydrogen phosphate, diguanidine phosphate, ammonium polyphosphate, hydrophobized ammonium polyphosphate, guanylurea phosphate, carbamate polyphosphate, and melamine phosphate.
Examples of boron compounds include organic boron compounds, boric acid, borax, boron oxide, borate esters, and borates.
Examples of magnesium compounds include magnesium hydroxide and magnesium oxide.
An example of the aluminum compound is aluminum hydroxide.
Examples of the nitrogen-based compound include ammonium sulfate, ammonium carbonate, ammonium hydrogen carbonate, and melamine cyanurate.
An example of an antimony compound is antimony trioxide.
An example of the halogen-based compound is zinc chloride.

Among these, phosphorus-based compounds and boron-based compounds are preferred as flame retardants for use in the coating composition for the topcoat layer, and it is particularly preferred to use phosphates and polyphosphates, which form a carbonized layer in a short period of time and are therefore likely to ensure flame retardant performance.
In particular, it is preferable to use a water-soluble phosphate and/or polyphosphate in combination with a water-insoluble phosphate and/or polyphosphate, since this further improves the flame retardancy and moisture resistance of the coating film without impairing the transparency of the coating film.

The amount of component (B) blended is preferably 50 to 300 parts by weight, and particularly preferably 75 to 250 parts by weight, per 100 parts by weight of the organopolysiloxane of component (A) above. If the amount is less than 50 parts by weight, the flame retardancy of the coating film may be insufficient, whereas if the amount exceeds 300 parts by weight, the film-forming properties, transparency, and moisture resistance of the coating film may be poor.
The component (B) may be used alone or in combination of two or more types.

(C) Inorganic Filler As the inorganic filler of component (C), a known general inorganic filler can be used, and examples thereof include inorganic fillers containing a Group 13 element, a Group 14 element (excluding carbon), a first series transition element, a second series transition element, a third series transition element, a lanthanoid, etc.
Examples of inorganic fillers containing a Group 13 element include oxides derived from aluminum, boron, indium, etc., and among these, alumina is preferred.
Examples of inorganic fillers containing a Group 14 element (excluding carbon) include oxides and salts derived from silicon, tin, etc., with silica being preferred.
Examples of inorganic fillers containing a first series transition element include oxides derived from titanium, manganese, zinc, etc., and these oxides can also be used as light absorbing materials of specific wavelengths.
Inorganic fillers containing second series transition elements include oxides derived from yttrium, zirconium, etc., and these oxides can also be used as light absorbing and fluorescent materials of specific wavelengths.
Examples of inorganic fillers containing third series transition elements include oxides derived from hafnium, tantalum, and the like.
Examples of inorganic fillers containing lanthanoids include oxides derived from lanthanum, cerium, praseodymium, neodymium, terbium, dysprosium, ytterbium, etc., and these oxides can also be used as light absorbing and fluorescent materials of specific wavelengths.
Furthermore, a compound formed by combining two or more of these via a chemical bond can also be used.

There are no particular limitations on the shape of the inorganic filler, and inorganic fillers of various shapes, such as spherical, hollow spherical, porous, plate-like, needle-like, and fibrous shapes, can be used. Among these, fibrous inorganic fillers are preferred because they are highly effective in suppressing cracks in the ceramic layer that form after combustion and have particularly good flame retardancy.

In particular, as the inorganic filler used in the coating composition for the topcoat layer, it is preferable to use inorganic oxides or silicates containing elements such as silicon, boron, and aluminum, which become ceramic when burned and form a fire-resistant layer or a heat-insulating layer. In particular, it is preferable to use a silicon oxide-containing filler such as silica or glass fiber in combination with a phyllosilicate such as clay, as this provides better flame retardancy.

The blending amount of component (C) is preferably 25 to 150 parts by mass, and particularly preferably 50 to 150 parts by mass, per 100 parts by mass of the organopolysiloxane of component (A) above. If it is less than 25 parts by mass, the flame retardancy of the coating film may be insufficient, whereas if it exceeds 150 parts by mass, the film-forming properties and transparency of the coating film may be poor.
The component (C) may be used alone or in combination of two or more types.

In the coating composition for the topcoat layer, the ratio of the total mass of the above-mentioned components (B) and (C) to the mass of the above-mentioned component (A), [(B)+(C)]/(A), is preferably 1.0 to 4.5, more preferably 1.2 to 4.0, and even more preferably 1.5 to 2.5. When the ratio is 1.0 or more, the flame retardancy is good, and when it is 4.5 or less, the moisture resistance, film-forming properties, and transparency of the coating film are good.

(D) Leveling Agent The coating composition for the topcoat layer may contain a component derived from (D) a leveling agent.
As the leveling agent, for example, known common leveling agents such as acrylic, vinyl, silicone, fluorine-based leveling agents, etc. Among these, silicone-based leveling agents having a siloxane structure in the main chain are preferred from the viewpoint of enhancing the flame retardancy of the coating composition.

When component (D) is used, the blending amount thereof is preferably 1 to 10 parts by mass, and more preferably 3 to 6 parts by mass, per 100 parts by mass of the organopolysiloxane of component (A) above. Within such a range, it is possible to obtain a topcoat layer that has excellent film-forming properties while maintaining flame retardancy and transparency.
The component (D) may be used alone or in combination of two or more types.

(E) Solvent The coating composition for the topcoat layer may contain a solvent in addition to the above components.
The solvent is not particularly limited, but alcohol or water is preferable, and water is more preferable from the viewpoints of environmental protection and availability.

When water is used as the solvent, specifically, fresh water such as tap water, industrial water, well water, natural water, rainwater, distilled water, and ion-exchanged water can be used, with ion-exchanged water being particularly preferred. Ion-exchanged water can be produced using a pure water production device (for example, Organo Corporation, product name "FW-10," Merck Millipore, product name "Direct-QUV3," etc.).

When a solvent is used, the amount is preferably 20 to 80% by mass, more preferably 30 to 60% by mass, based on the total paint composition for the topcoat layer. When the solvent is present in an amount of 20% by mass or more based on the total composition, the fluidity and workability of the paint are improved, and when the solvent is present in an amount of 80% by mass or less based on the total composition, the concentration of the active ingredients in the paint is high, making it easier to thicken the coating film.

The coating composition for the topcoat layer may contain a curing catalyst for the purpose of accelerating the curing reaction. The type, mixing amount, and addition method of the curing catalyst may be determined by known methods and conditions according to the type of composition. Specifically, the examples of component (v) above may be used.

The coating composition for the topcoat layer may contain additives that exert additional effects, provided that the effects of the present invention are not impaired.
Examples of additives include ultraviolet absorbents, anti-termite agents, antioxidants, dyes, pigments, etc., and these additives may be used alone or in combination of two or more kinds.

The total content of the above components (A) to (C) relative to the total solid content of the topcoat layer coating composition is preferably 70% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more.

The coating composition for the topcoat layer can be produced by mixing the above-mentioned components (A) to (C), and, if necessary, the components (D), (E) and other components. The method for mixing the components may be appropriately selected from known methods and is not particularly limited. For example, a mixer, a shaking device, an ultrasonic homogenizer, a high-pressure homogenizer, a bead mill, a ball mill, or the like can be used as the device used for mixing.
For the purpose of accelerating the dissolution or dispersion of each component, the mixing operation may be carried out under heating within a range that does not impair the effects of the present invention.

The conditions for applying the coating composition for the topcoat layer onto the undercoat layer and drying to form the topcoat layer may be appropriately set depending on the type and shape of the wood substrate, and the specific conditions may be appropriately selected from known conditions.

The coating method may be appropriately selected from known techniques, and various coating methods such as brush coating, spraying, dipping, flow coating, roll coating, curtain coating, spin coating, and knife coating can be used.
The coating composition for the top coat layer is a composition capable of forming a film at about 0 to 40°C, preferably about 5 to 35°C, and more preferably capable of forming a film at 25°C after 24 hours.
For the purpose of shortening the curing time, heating may be performed within a temperature range that does not adversely affect the substrate, etc.

The coating weight of the undercoat layer and the topcoat layer is not particularly limited, but the undercoat layer is preferably coated so as to be 0.01 to 0.50 kg/m ² relative to the substrate, and more preferably 0.01 to 0.10 kg/m ^2. Within this range, the flame retardancy is good, and the effect of suppressing poor appearance around the knots is better.
The topcoat layer is preferably applied to the substrate at a weight of 0.1 to 2.0 kg/ ^m2 , and more preferably at a weight of 0.2 to 1.0 kg/ ^m2 . This range provides good flame retardancy and coating appearance. In order to achieve a coating weight within the above range, the coating composition may be applied to the substrate at a weight of the solid content within the above range.

The coated article of the present invention may be coated with one or more layers, such as a hard coat layer, an anti-rust layer, a gas barrier layer, a waterproof layer, a heat shielding layer, an antifouling layer, a photocatalyst layer, an antistatic layer, etc., on the surface on which the topcoat layer is formed or on the opposite surface. Materials constituting these layers include alkyd resins, acrylic resins, urethane resins, acrylic silicone resins, fluororesins, silicone resins, epoxy resins, vinylidene chloride copolymer resins, vinyl chloride resins, etc. (whether water-based or solvent-based). The above layers can be applied as a coating liquid, or laminated as a pre-formed film by bonding with an adhesive or the like.

The present invention will be explained in more detail below with reference to synthesis examples, comparative synthesis examples, working examples, and comparative examples, but the present invention is not limited to these examples.

[1] Preparation of coating composition for undercoat layer [Examples 1 to 8, Comparative Examples 1 to 6]
Coating compositions for undercoat layer were prepared by mixing the following components in the amounts shown in Tables 1 and 2. Note that the active ingredient concentration in Tables 1 and 2 refers to the total of the solid content of the blended amounts of component (i), comparative component, component (ii-1), component (ii-2), component (ii-3), and component (iii-1), the blended amount of component (ii-4), and the blended amount of component (iii-2) in 100 parts by mass of the coating composition, and the active ingredient mass ratio in Tables 1 and 2 is the value calculated by converting the mass ratio of each component based on the solid content, with component (i) set to 100.

（式中、波線を付した線は結合手を表す。） (i) Component (i-1): 30% by weight aqueous solution of hydroxyl-containing organopolysiloxane (in the above formula (1), a=0, b=0, c=1.0, d=0, e=0.7, R ³ =methyl group, group represented by the following formula (3), R ⁴ =hydrogen atom, hydroxyl group substitution amount (relative to total silicon atoms)=200 mol%)

(In the formula, the wavy line represents a bond.)

[Comparative ingredients]
(i'-2): Aqueous dispersion of acrylic resin produced in Comparative Synthesis Example 1 below

[Comparative Synthesis Example 1]
A five-neck flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping device, and a nitrogen inlet tube was charged with 200 parts by mass of ion-exchanged water and 6.0 parts by mass of a non-reactive emulsifier (Hitenol NF0825: anionic, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and while replacing the atmosphere inside the flask with nitrogen, the temperature was raised to 80° C., after which 1.0 part by mass of potassium persulfate was added, and then a mixture of 190 parts by mass of methyl methacrylate, 250 parts by mass of butyl acrylate, 10 parts by mass of acrylic acid, 220 parts by mass of ion-exchanged water, and 30.0 parts by mass of the non-reactive emulsifier, which had been previously mixed and stirred in a separate container, was continuously added dropwise over 3.5 hours. Thereafter, the mixture was aged at 80° C. for 2 hours while continuing stirring, and then a mixture of 2.7 parts by mass of ion-exchanged water and 0.3 parts by mass of a 70% by mass aqueous solution of tert-butyl hydroperoxide was added to the reactor, and then a mixture of 9.7 parts by mass of ion-exchanged water and 0.3 parts by mass of sodium erythorbate was continuously dropped over 5 minutes. Thereafter, the mixture was aged at 80° C. for 2 hours while continuing stirring, and after cooling to room temperature, 4.0 parts by mass of a 25% by mass aqueous ammonia solution was added to adjust the pH to 9.0, and an aqueous dispersion of acrylic resin i'-2 was obtained. The content of the acrylic resin in the dispersion was 49.8% by mass, and the volume average particle size of the emulsion was 144 nm.

(ii) Component ii-1: Snowtex OL (20% by mass silica aqueous dispersion, particle size 45 nm, manufactured by Nissan Chemical Industries, Ltd.)
ii-2: Snowtex O40 (40% by weight silica water dispersion, particle size 22 nm, manufactured by Nissan Chemical Industries, Ltd.)
ii-3: Alumina sol 520-A (20% by mass alumina water dispersion,
(Nissan Chemical Co., Ltd.)
ii-4: BENTONE-EW NA (Hectorite clay, Ele
Mentis Specialties, Inc. (manufactured by)

(iii) Component iii-1: Nonene W2-50 (50% by mass of phosphorus-nitrogen flame retardant)
Aqueous solution, manufactured by Maruzen Yuka Kogyo Co., Ltd.)
iii-2: Boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[Evaluation of paint stability]
The stability of the undercoat paint composition was visually evaluated according to the following criteria. In this case, the sedimentation of the water-insoluble flame retardant component or filler component, which is originally solid, over time was not judged to be a deterioration in paint stability as long as the composition could be used without problems if shaken. The results are shown in Tables 1 and 2.
〇: When the components are mixed, no gelation or solid precipitation occurs and the liquid remains. ×: When the components are mixed, gelation or solid precipitation occurs.

[2] Preparation of coating composition for topcoat layer [Synthesis Example 1]
A 30% by weight aqueous solution of an amino group-containing organopolysiloxane (A-1, in the above formula (2), f=0, g=0, h=0.7, i=0.3, j=0.7, R ⁷ =methyl group, N-(2-aminoethyl)-3-aminopropyl group, R ⁸ = hydrogen atom, amine substitution amount (relative to total silicon atoms) = 61 mol%) 56.0 g, Nonnen W2-50 (B-1, 50 mass% aqueous solution of phosphorus-nitrogen flame retardant, manufactured by Maruzen Yuka Kogyo Co., Ltd.) 16.7 g, Taien K (B-2, water-insoluble ammonium polyphosphate powder, manufactured by Pacific Industrial Co., Ltd.) 13.6 g, EPH80M-01N (C-1, glass fiber, manufactured by Nippon Electric Glass Co., Ltd.) 12.7 g), BYK3450 (leveling agent, polyether-modified polydimethylsiloxane, manufactured by BYK Japan Co., Ltd.) 0.9 g were mixed to prepare a water-based coating composition. The solid content ratio of each component in the solution was 100 parts by mass of component (A), 131 parts by mass of component (B), and 76 parts by mass of component (C).

[3] Preparation of coated wood and its evaluation The undercoat paints of Examples 1 to 8 and Comparative Examples 2 to 6 were applied to knot-containing cedar wood (air-dry specific gravity 0.27 to 0.49) cut to 300 mm x 300 mm x 20 mm and dried at 115 ° C for 24 hours, so that the coating amount of the solid content was about 0.01 to 0.02 kg / m ² , and air-dried for 2 hours. Next, the topcoat paint obtained in the above Synthesis Example 1 was applied to the wood so that the coating amount of the solid content was about 0.38 kg / m ² , and the wood was aged at a temperature of 21 to 25 ° C and a relative humidity of 45 to 55% RH until a constant mass was reached. Note that, for Comparative Example 1, the undercoat paint was not applied, and the topcoat paint obtained in the above Synthesis Example 1 was applied to the wood so that the coating amount of the solid content was about 0.38 kg / m ² , and the wood was aged at a temperature of 21 to 25 ° C and a relative humidity of 45 to 55% RH until a constant mass was reached.
The following tests were carried out on the prepared coated cedar wood (coated wood).

(1) Appearance of the coating film The appearance of the coating film around the knots of the cedar wood was visually evaluated according to the following criteria. The results are shown in Table 1.
○: The paint film around the knots is transparent and the wood grain can be seen.
×: White turbidity occurs in the coating film around the knots.
(2) Moisture resistance Each piece of wood was subjected to five cycles of wet-drying at 40°C, 90% RH (24 hours) followed by air drying at 60°C (24 hours), and then cooled at 20°C, 60% RH for 24 hours. The condition of the coating surface was then observed and visually evaluated according to the following criteria. The results are shown in Table 1.
◯: No whitening, deliquescence, discoloration, etc. was observed. ×: Whitening, deliquescence, discoloration, etc. was observed. (3) Flame retardancy A cone calorimeter test (ISO-5660-1) was conducted on each piece of wood with a radiant heat intensity of 50 kW/ ^m2 , and the flame retardancy was evaluated according to the following criteria.
⊚: When the amount of heat generated when heated for 10 minutes is 6 (MJ/ ^m2 ) or less; ◯: When the amount of heat generated when heated for 10 minutes is 8 (MJ/ ^m2 ) or less; ×: When the amount of heat generated when heated for 10 minutes is more than 8 (MJ/ ^m2 ) and/or the coating expands and comes into contact with the device (igniter).

＊：膨張した塗膜が装置に接触

*: Expanded coating film comes into contact with the device

As shown in Table 1, the coated articles of Examples 1 to 8, which have an undercoat layer made of a coating of a paint composition that satisfies the requirements of the present invention, and a topcoat layer containing a siloxane compound, a flame retardant, and an inorganic filler, have good coating appearance and moisture resistance, suppress whitening around knots, and generate little heat during combustion, demonstrating flame retardancy that meets the standards for semi-noncombustible wood.
From the above, it is believed that by providing an undercoat layer consisting of a coating of a paint composition that satisfies the requirements of the present invention, the gaps between the wood fibers are filled, the penetration of the topcoat paint into the wood is suppressed, and a uniform topcoat layer can be formed, thereby suppressing whitening.In addition, it is possible to form a sturdy ceramic layer during combustion, and the fire resistance and insulating effects of these layers greatly improve the flame retardancy of the wood.
On the other hand, as shown in Table 2, in Comparative Example 1, which did not have an undercoat layer, whitening occurred around the knots. In Comparative Examples 2 and 3, in which the amount of inorganic filler added was insufficient, the flame retardancy was poor. In Comparative Example 4, in which the amount of inorganic filler added was excessive, the undercoat layer was not sufficiently formed, the flame retardancy was poor, and whitening occurred around the knots.
In addition, in Comparative Examples 5 and 6, in which an undercoat layer not containing a siloxane structure was provided, the amount of flammable organic components increased, causing intense combustion, resulting in a deterioration in flame retardancy and expansion of the coating film.

Claims (9)

(i) 100 parts by mass of an organopolysiloxane having a unit ratio represented by the following formula (1): (R ¹ ₃ SiO _1/2 ) _a (R ² ₂ SiO) _b (R ³ ₁ SiO _3/2 ) _c (SiO ₂ ) _d (OR ⁴ ) _e (1)
(In the formula, R ¹ , R ² and R ³ each independently represent a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms which may be substituted with one or more amino groups, hydroxy groups, epoxy groups, acid anhydride groups, maleimide groups, vinyl groups, allyl groups, acrylic groups, methacrylic groups, or heterocyclic groups and which may have an ether bond, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms which may have an ether bond, but at least a part of R ¹ , R ² and R ³ is an alkyl group having 1 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, an aryl group having 6 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, or an aralkyl group having 7 to 20 carbon atoms which is substituted with a hydroxy group and which may have an ether bond, Each of ⁴ independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, a is 0 to 0.5, b is 0 to 0.5, c is 0.2 to 1.0, d is 0 to 0.5, and e is a number that satisfies 0 to 3.0, and a+b+c+d=1.
(ii) A coating composition comprising an inorganic filler: 100 to 900 parts by mass. 2. The coating composition according to claim 1, wherein the total number of hydroxy groups contained in R ¹ , R ² and R ³ is 50 mol % or more based on the total number of silicon atoms in formula (1). The coating composition according to claim 1 or 2, wherein the inorganic filler (ii) comprises one or more selected from silica, alumina, and phyllosilicates. The coating composition according to any one of claims 1 to 3 further comprises (iii) 10 to 300 parts by mass of one or more flame retardants selected from phosphorus-, boron-, magnesium-, aluminum-, nitrogen-, antimony-, and halogen-based compounds per 100 parts by mass of component (i). The coating composition according to claim 4, wherein the ratio of the total mass of the components (ii) and (iii) to the mass of the component (i), [(ii)+(iii)]/(i), is 2.0 to 9.0. A cured product of the coating composition according to any one of claims 1 to 5. A coated article having a coating layer formed of a coating film of the coating composition according to any one of claims 1 to 5, either directly or via one or more other layers, on at least a portion of the surface of a wood substrate. A coated article having, on at least a portion of the surface of a wood substrate, an undercoat layer formed of a coating film of the coating composition according to any one of claims 1 to 5, and a topcoat layer formed of a coating film of a topcoat coating composition containing the following components (A), (B), and (C):
(A) Organopolysiloxane having a unit ratio represented by the following formula (2): 100 parts by mass
(R ⁵ ₃ SiO _1/2 ) _f (R ⁶ ₂ SiO) _g (R ⁷ ₁ SiO _3/2 ) _h (SiO ₂ ) _i (OR ⁸ ) _j (2)
(In the formula, R ⁵ , R ⁶ and R ⁷ each independently represent a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms or an aralkyl group having 7 to 20 carbon atoms, which may be substituted with one or more amino groups, hydroxy groups, epoxy groups, acid anhydride groups, maleimide groups, vinyl groups, allyl groups, acrylic groups, methacrylic groups or heterocyclic groups, and at least a part of R ⁵ , R ⁶ and R ⁷ is an alkyl group having 1 to 20 carbon atoms substituted with an amino group, an aryl group having 6 to 20 carbon atoms substituted with an amino group, or an aralkyl group having 7 to 20 carbon atoms substituted with an amino group, and R Each of ⁸ independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, f is 0 to 0.5, g is 0 to 0.5, h is 0.2 to 1.0, i is 0 to 0.5, and j is a number that satisfies 0 to 3.0, and f+g+h+i=1.
(B) One or more flame retardants selected from phosphorus-based, boron-based, magnesium-based, aluminum-based, nitrogen-based, antimony-based and halogen-based compounds: 50 to 300 parts by mass (C) Inorganic filler: 25 to 150 parts by mass 9. The coated article according to claim 8, wherein the coating amount of the undercoat layer is 0.01 to 0.50 kg/ ^m2 of the wood substrate, and the coating amount of the topcoat layer is 0.1 to 2.0 kg/ ^m2 of the wood substrate.