JP5193769B2 - Method for producing polyurethane water dispersion for wood paint - Google Patents

Description

  The present invention relates to a method for producing a polyurethane-based aqueous dispersion for wood paint. More specifically, the present invention can form a film that is hardly discolored, particularly yellowed, and has excellent water resistance, solvent resistance, and moist heat resistance when used as a main component of a wood coating. The present invention relates to a method for producing a polyurethane-based aqueous dispersion for wood paint.

  Conventionally, various polyurethane-based aqueous dispersions in which an isocyanate-terminated prepolymer produced using a polyol such as a castor oil-based polyol is dispersed in water have been proposed and used as a main component of a paint or the like. For example, an aqueous urethanized alkyd resin dispersion containing a reaction product of a polyol compound such as an unsaturated fatty acid ester polyol, an organic diisocyanate compound, and a dialkyl monohydroxyalkanoic acid as an essential component is known (for example, Patent Documents). 1). In addition, active hydrogen is added to an isocyanate-terminated prepolymer obtained by reacting a polyisocyanate compound, a castor oil-based polyol compound, a compound having a hydrophilic group other than a hydroxyl group in the molecule and having two or more hydroxyl groups. A urethane-based aqueous composition obtained by reacting a compound having two or more compounds to cause a chain extension reaction is known (for example, see Patent Document 2).

JP 7-166130 A JP 2000-273138 A

  As described above, various urethane-based aqueous dispersions used as paints and the like are known. However, although many organic diisocyanate compounds are exemplified in Patent Document 1, no attention is paid to selecting a specific organic diisocyanate compound in relation to discoloration of the film. Further, in the examples, tolylene diisocyanate which is easily discolored is used, and isophorone diisocyanate is also used, but even this diisocyanate has a problem of discoloration when a specific polyol is not used. Furthermore, in Patent Document 2, there is no description about using dehydrated castor oil as a polyol raw material and curing the coating film by oxidative polymerization, and no attention is paid to discoloration of the coating film.

  The present invention has been made in view of the above-described conventional situation, and when used as a main component of a wood paint, an isocyanate-terminated prepolymer (hereinafter referred to as “prepolymer”) contained after being applied to wood. For wood coatings that are oxidatively polymerized and cross-linked to form a film that is resistant to discoloration, particularly yellowing, and that has excellent water resistance, solvent resistance, and moist heat resistance. It is an object of the present invention to provide a method for producing a polyurethane-based water dispersion (hereinafter sometimes abbreviated as “water dispersion”).

The present invention is as follows.
1. A reaction product of dehydrated castor oil and / or dehydrated castor oil fatty acid and a tetrafunctional or higher polyol, and the total of the dehydrated castor oil and / or dehydrated castor oil fatty acid and the tetrafunctional or higher polyol is 100. In the case of mass%, the tetrafunctional or higher polyol is 5 to 40 mass% of a polyol (A) having a dehydrated castor oil fatty acid skeleton, at least two hydroxyl groups, and at least one carboxyl group. And a diisocyanate compound (B) having 2 or 3 cyclohexyl groups are reacted to form an isocyanate-terminated prepolymer, and then a reaction solution in which the isocyanate-terminated prepolymer is dissolved and water. A method for producing a polyurethane-based aqueous dispersion for wood paint, which comprises mixing.
2. 1. The iodine value of the polyol (A) is 80 to 130. The manufacturing method of the polyurethane-type water dispersion for wood coatings as described in any one of .
3. At the same time as or after the mixing of the reaction solution and the water, carbodiimide is added to the mixed solution, and when the solid content in the mixed solution is 100 parts by mass, the carbodiimide is 0. The above 1. which is 3 to 3.0 parts by mass. Or 2. The manufacturing method of the polyurethane-type water dispersion for wood coatings as described in any one of.
4). Above 1. To 3. A polyurethane-based aqueous dispersion for wood coatings produced by the method for producing a polyurethane-based aqueous dispersion for wood coatings according to any one of the above.

According to the method for producing a polyurethane-based water dispersion for wood paints of the present invention, an aqueous dispersion containing an isocyanate-terminated prepolymer capable of forming a film having sufficient hardness by easily curing the coating film by oxidative polymerization. The body can be manufactured efficiently. In addition, when conventional polyols derived from vegetable oils such as linseed oil and soybean oil are used, discoloration tends to occur. However, in the production method of the present invention, discoloration is sufficiently achieved by using a polyol (A) having a specific structure. Can be suppressed. Furthermore, by using the polyol (A) while having a one-component type, a film having excellent water resistance and solvent resistance as well as sufficient heat-and-moisture resistance, etc., as in the case of the conventional two-component paint. An aqueous dispersion containing an isocyanate-terminated prepolymer that can be formed can be efficiently produced.
Also, the polyol (A) is a reaction product of dehydrated castor oil and / or dehydrated castor oil fatty acid and a tetrafunctional or higher functional polyol, and the dehydrated castor oil and / or dehydrated castor oil fatty acid and the tetrafunctional when the total 100 mass% of the above polyols, for the tetra- or higher-functional polyol is from 5 to 40 wt%, and a polyisocyanate compound (B), in a diisocyanate compound having two cyclohexyl there therefore, easier to react them, the prepolymer can be readily produced.
Furthermore, when the polyol (A) has an iodine value of 80 to 130, a film having sufficient hardness and the like can be formed when used as a paint for wood.
Moreover, carbodiimide is 0.3-3, when carbodiimide is added to a liquid mixture simultaneously with mixing a reaction liquid and water or after mixing, and the solid content contained in a liquid mixture is 100 mass parts. In the case of 0.0 part by mass, crosslinking is promoted by carbodiimide, and a film can be formed more easily.

The present invention will be described in detail below.
The method for producing a polyurethane-based aqueous dispersion for wood paint according to the present invention is a reaction product of dehydrated castor oil and / or dehydrated castor oil fatty acid and a tetra- or higher functional polyol, and dehydrated castor oil and / or dehydrated castor oil. When the total of the fatty acid and the tetrafunctional or higher functional polyol is 100% by mass, the tetrafunctional or higher functional polyol is 5 to 40% by mass of the polyol (A) having a dehydrated castor oil fatty acid skeleton, and at least two A hydrophilic compound having a hydroxyl group, at least one carboxyl group, and a diisocyanate compound (B) having 2 or 3 cyclohexyl groups are reacted to form an isocyanate-terminated prepolymer, and then an isocyanate-terminated prepolymer. The reaction solution in which the prepolymer is dissolved is mixed with water.

[1] Polyol (A) having a dehydrated castor oil fatty acid skeleton
The “polyol (A) having a dehydrated castor oil fatty acid skeleton” can be produced by transesterification or esterification of dehydrated castor oil, dehydrated castor oil fatty acid and the like with a tetrafunctional or higher functional polyol. Although the specific method is not particularly limited, for example, dehydrated castor oil and / or dehydrated castor oil fatty acid, a tetrafunctional or higher functional polyol and a catalyst are charged into a reaction vessel equipped with a stirrer, a cooler and the like, and stirred while heating. And can be made to react. The reaction atmosphere is preferably an inert atmosphere such as a nitrogen gas atmosphere or an inert gas atmosphere such as an argon gas atmosphere. The reaction temperature and reaction time are not particularly limited, but the reaction temperature is preferably 190 to 250 ° C, particularly 200 to 240 ° C, and the reaction time is preferably 2 to 10 hours, particularly 2.5 to 8 hours. .

  Dehydrated castor oil is a compound in which a hydroxyl group of ricinoleic acid that constitutes castor oil is dehydrated and converted into a double bond by extracting together with hydrogen bonded to adjacent carbon by a catalyst. Since ricinoleic acid has a hydroxyl group at the 9-position and a double bond at the 12-position, the double bond produced by the dehydration reaction may be conjugated with other double bonds or not conjugated. In some cases, dehydrated castor oil contains a mixture of conjugated and non-conjugated systems. Dehydrated castor oil fatty acid is a compound obtained by hydrolyzing dehydrated castor oil and removing glycerin.

  Examples of the tetrafunctional or higher functional polyol include pentaerythritol, ditrimethylolpropane, diglycerin, dipentaerythritol, sorbitol, and shulksol. Of these, tetrafunctional polyols are preferable, and pentaerythritol is frequently used. Only one tetrafunctional or higher functional polyol may be used, or two or more polyols may be used in combination. Also, polyols having different numbers of functional groups can be used in combination.

The blending ratio of the dehydrated castor oil and / or dehydrated castor oil fatty acid and the tetrafunctional or higher polyol is when the total of the dehydrated castor oil and / or dehydrated castor oil fatty acid and the tetrafunctional or higher polyol is 100% by mass. The tetrafunctional or higher functional polyol is 5 to 40% by mass. The tetrafunctional or higher polyol is a tetrafunctional or higher polyol (M ₁ mol) and dehydrated castor oil and / or dehydrated castor oil fatty acid (M ₂ mol. When used in combination, the total amount). It is preferable to set the blending amount so that the molar ratio (M ₁ / M ₂ ) is 0.40 to 1.00, particularly 0.45 to 0.90. If this molar ratio (M ₁ / M ₂ ) is 0.40 to 1.00, a polyol (A) slightly exceeding bifunctionality can be easily synthesized. In the transesterification / esterification reaction of dehydrated castor oil and / or dehydrated castor oil fatty acid with a tetra- or higher functional polyol, castor oil or the like can be used in combination as another polyol. The blending amount of the other polyol is preferably 50% by mass or less when the total amount of the polyol is 100% by mass. If it exceeds 50% by mass, the effect of oxidative polymerization crosslinking by dehydrated castor oil and / or dehydrated castor oil fatty acid is undesirably reduced.

  As a catalyst, the catalyst generally used for transesterification / esterification reaction can be used. Examples of the catalyst include sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, potassium tert-butoxide, tetraethoxy titanium, tetrabutoxy titanium and other alkoxide catalysts, various oxide catalysts, various hydroxides. Examples thereof include catalysts and various dialkyltin compound catalysts.

  Although the iodine value of a polyol (A) is not specifically limited, It is preferable that it is 80-130, especially 85-125. When the iodine value is 80 to 130, the prepolymer is sufficiently oxidatively polymerized, and it is possible to form a film having excellent water resistance and solvent resistance, and sufficient moisture and heat resistance. The acid value is usually 1.5 mgKOH / g or less, particularly 1.2 mgKOH / g or less. Furthermore, the hydroxyl value is 100 to 200 mgKOH / g, particularly 100 to 170 mgKOH / g. The viscosity measured at 25 ° C. is 200 to 600 mPa · s, particularly 250 to 550 mPa · s. When this viscosity is too high, it can be adjusted by increasing the mass ratio of the organic solvent during the production of the prepolymer.

[2] Formation of Isocyanate-Terminated Prepolymer The “hydrophilic compound” has at least two hydroxyl groups and at least one carboxyl group. This hydrophilic compound can react with the polyisocyanate compound together with the polyol (A) during the production of the isocyanate-terminated prepolymer to produce a prepolymer having a carboxyl group. Examples of the hydrophilic compound include dimethylol alkanoic acids such as dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, and dimethylolnonanoic acid. Only one hydrophilic compound may be used, or two or more hydrophilic compounds may be used in combination.

Above-mentioned "di isocyanate compound (B)" is in terms of suppressing the discoloration of the coating, di- isocyanate compound having two or three cyclohexyl (B) is used. As the di-isocyanate compound (B), 4,4' hydrogenation product of diphenylmethane diisocyanate (MDI), tolidine diisocyanate hydrogenated product, triphenylmethane diisocyanate hydrogenation product, triphenylmethane triisocyanate hydrogenates Etc. Of these, diisocyanate compounds having two cyclohexyl groups, such as hydrogenated MDI, are preferred. Also, this way, by having two or three cyclohexyl group, di-isocyanate compound to one chromatic cyclohexyl, for example, than when using isophorone diisocyanate, to improve the solvent resistance of the film it can. Furthermore, when it is not a hydrogenated product, for example, MDI is used, the reactivity is too high, and before the particulate prepolymer is dispersed in water, the reaction proceeds too much to become a resinous state, resulting in water dispersion. You may not be able to make a body. Di isocyanate compound (B) may be used singly or in combination of two or more kinds.

  Further, when the prepolymer is produced, the polyol (A) and other polyol (however, excluding the above-mentioned “hydrophilic compound”) can be used in combination as the polyol. The other polyol is not particularly limited, For example, (1) short of ethylene glycol, propylene glycol, 1,4-butanediol, 3-methylpentanediol, 1,6 hexanediol, diethylene glycol, neopentyl glycol, glycerin, bisphenol A, trimethylolpropane, pentaerythritol, etc. Long chain polyols such as chain polyols and dimer acid diols, (2) ethylene oxide and / or propylene oxide adducts of the short chain polyols of (1) above, polyether polyols such as polytetramethylene glycol, (3) adipic acid , Ma It is obtained by reacting a polybasic acid such as acid, sebacic acid, azelaic acid, phthalic acid, terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic acid and the short-chain polyol of (1) by a known method. Polyester polyols such as polyester polyols and lactone polyester polyols obtained by ring-opening polymerization such as caprolactone, and (4) synthesized by dealcoholization reaction of the short-chain polyol of (1) above with diethyl carbonate, dimethyl carbonate, etc. Polycarbonate polyol, (5) Polyolefin polyol such as polybutadiene polyol, polyisoprene polyol, etc. These other polyols may be used alone or in combination of two or more.

The blending ratios of the polyol (A) (total amount of polyol when other polyols are used in combination), the hydrophilic compound and the polyisocyanate compound (B) at the time of prepolymer generation are not particularly limited, The ratio (M ₃ / M ₄ ) of the hydrophilic compound (M ₃ mmol) and the total amount of polyol (A) or polyol (M ₄ g) is 0.25 to 0.60. In particular, the blending amount is preferably 0.30 to 0.50. When this ratio (M ₃ / M ₄ ) is 0.25 to 0.60, a required amount of carboxyl groups can be introduced into the prepolymer. Moreover, it is preferable that the isocyanate index showing the amount ratio of a polyol (A) or the total amount of a polyol and a polyisocyanate compound (B) is 1.10-2.00, especially 1.20-1.70. .

  Catalysts used to produce the prepolymer include metal catalysts such as dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dimaleate, lead octenoate, and amine catalysts such as triethylamine, triethylenediamine, and dimethylaminoethanol. Can be mentioned. Only one type of catalyst may be used, two or more types may be used in combination, and a metal catalyst and an amine catalyst may be used in combination.

  The prepolymer can be produced without using an organic solvent, or can be produced using an organic solvent as a medium. When an organic solvent is used, this organic solvent can dissolve and generate a polyol (A), a hydrophilic compound, a polyisocyanate compound (B) and the like at a temperature of room temperature (for example, 25 to 35 ° C.) or higher. There is no particular limitation as long as the prepolymer can be dissolved at a temperature of room temperature (for example, 25 to 35 ° C.) or higher. The organic solvent is preferably a solvent that is inert to the urethanization reaction and has a high affinity with water, and ketones such as methyl ethyl ketone, acetone, and methyl isobutyl ketone, and N-methylpyrrolidone, dimethylacetamide, dimethylformamide, tetrahydrofuran, and the like. Among them, ketones having sufficient dissolving power and low boiling point, particularly methyl ethyl ketone is preferable. In addition, a solvent having a boiling point higher than that of water, such as N-methylpyrrolidone, cannot be distilled off under the conditions for distilling off a normal organic solvent, and remains after being applied to a substrate as a wood paint. However, since it also functions as a binder such as prepolymer particles and a film-forming aid, it is preferable to use them in combination. The usage-amount of an organic solvent can be made into the range of 10-100 mass parts, when a prepolymer is 100 mass parts.

  Further, the content of the terminal isocyanate group of the prepolymer is not particularly limited, but when the prepolymer is 100% by mass, the content is 1.5 to 5.5% by mass, particularly 2.0 to 4.5% by mass. be able to. The content of the terminal isocyanate group is preferably set in consideration of required physical properties such as polishing properties, hardness, gloss, and chemical resistance.

[3] Aqueous dispersion and aqueous dispersion composition A water dispersion can be obtained by mixing the reaction liquid prepared as described above and having the prepolymer dissolved therein and water. Moreover, the organic solvent whose boiling point is higher than that of water usually remains in the aqueous dispersion.
The “water” is not particularly limited, but it is preferable to use high-purity water such as distilled water, ion-exchanged water, or pure water. A method of mixing the reaction solution and water is not particularly limited, but a method of adding water as droplets to the reaction solution is preferable to mixing with a large amount of water at a time. If it is the method of dripping, a prepolymer can be more uniformly disperse | distributed to water and it can be set as a more homogeneous water dispersion.

  Moreover, it is preferable to add the neutralizing agent for neutralizing the carboxyl group introduce | transduced into the prepolymer to a reaction liquid before mixing a reaction liquid and water. As the neutralizing agent, amines are preferable and tertiary amines are more preferable because they do not remain in the coating after the coating is cured. The tertiary amine is not particularly limited, and examples thereof include aliphatic tertiary amines such as trimethylamine, triethylamine, tri-n-propylamine and tri-n-butylamine, and N, N-dimethylaniline, N, N- Aromatic tertiary amines such as diethylaniline can be used. Only one tertiary amine may be used, or two or more tertiary amines may be used in combination. By this neutralization, the hydrophilicity of the prepolymer is improved and a more homogeneous aqueous dispersion can be obtained.

  The tertiary amine used as the neutralizing agent is preferably equimolar with the carboxyl group introduced into the prepolymer, whereby the hydrophilicity of the prepolymer is further improved and the prepolymer particles are more uniformly dispersed. It can be an aqueous dispersion.

  Furthermore, it is preferable to add a chain extender to the mixed solution at the same time as or after mixing the reaction solution and water. Moreover, when an organic solvent is used for the production | generation of a prepolymer, it is more preferable to add a chain extender before distillation of an organic solvent. As the chain extender, a compound having two or more active hydrogens that react with an isocyanate group can be used. Examples thereof include diamines such as ethylenediamine, propylenediamine, isophoronediamine, piperazine, and phenylenediamine, and trifunctional or more polyamines. It is done. By this chain extension, the prepolymer molecule is bonded and chain extended, and the terminal of the chain extended molecule becomes an amino group or a hydroxyl group. Thereby, when the molecular terminal remains an isocyanate group, the reaction of the prepolymer that reacts with water can be suppressed, and the aqueous dispersion can be stabilized.

The usage-amount of the diamine used as a chain extender can be set based on the equivalent ratio with the isocyanate group content of the prepolymer measured by chemical analysis. The diamine is equivalent in which the ratio (M ₅ / M ₆ ) of the amino group equivalent (referred to as M ₅ ) of the diamine and the isocyanate group equivalent (referred to as M ₆ ) of the prepolymer is 0.5 to 1.0. The ratio is preferably used. The reaction conditions for the chain extension reaction are not particularly limited, but the reaction temperature is preferably 30 to 60 ° C. and the reaction time is preferably 30 minutes to 4 hours.

  The mass ratio of the component derived from dehydrated castor oil and / or dehydrated castor oil fatty acid in the chain-extended prepolymer to the total amount of the prepolymer is not particularly limited, but dehydration is performed when the total amount of the prepolymer is 100% by mass. The component derived from castor oil or the like is preferably 20 to 60% by mass. If the mass ratio of this component is 20 to 60% by mass, a coating having sufficient hardness and the like can be obtained after the prepolymer is easily oxidized and polymerized after the wood coating containing the aqueous dispersion is applied to the substrate. Can be formed.

  Moreover, it is preferable to add a carbodiimide compound to the mixed solution after the prepolymer is neutralized and chain-extended. Although this carbodiimide compound will not be specifically limited if it is a compound which has a carbodiimide group in a molecule | numerator, It is more preferable that it is a water-soluble carbodiimide compound. Therefore, a more preferable carbodiimide compound includes a compound obtained by polymerizing a diisocyanate compound by a carbon dioxide condensation reaction and then capping the terminal isocyanate group with an organic compound having a hydrophilic group having reactivity such as a hydroxyl group. it can. Specific examples include compounds such as the Carbodilite series manufactured by Nisshinbo Industries. This product is a water-soluble type and has a solid content of about 40% by mass. The addition amount of the carbodiimide compound is not particularly limited, but is preferably 0.3 to 3.0 parts by mass when the solid content contained in the mixed liquid (aqueous dispersion) is 100 parts by mass.

  The above-mentioned “polyurethane aqueous dispersion for wood coatings” can be blended with various additives as necessary to obtain an aqueous dispersion composition. Examples of the additive include (1) plasticizers such as diethyl phthalate, dibutyl phthalate, and dibutyl adipate, (2) tackifying resins such as rosin, terpene resin, and coumarone resin, and (3) calcium carbonate and silica. In addition to inorganic fillers such as clay, talc and carbon black, (4) stabilizers such as antioxidants, UV absorbers and UV inhibitors, oxidation polymerization accelerators, flame retardants, antifungal agents, rust prevention Various additives such as an agent may be mentioned.

  The specific production method and production conditions of the aqueous dispersion are not particularly limited. For example, an organic solvent, a polyol (A), a hydrophilic compound, and a catalyst are charged into a reaction vessel equipped with a stirrer, a cooler, and the like. After the dissolution, the polyisocyanate compound (B) is charged, and these are stirred while being heated and reacted to form a prepolymer, and then the reaction solution and water are mixed. When an organic solvent is used, the method for distilling off the organic solvent is not particularly limited, and the temperature is preferably set according to the boiling point of the organic solvent. Moreover, although it may distill off under reduced pressure and it may distill off under normal pressure, it is preferable to distill off under reduced pressure. If the solvent is distilled off under reduced pressure, the set temperature can be lowered, and the organic solvent can be efficiently distilled off in a short time without applying unnecessary heat to the prepolymer.

  The atmosphere during the production may be an inert atmosphere or an air atmosphere, but it is preferable to react in an inert atmosphere such as a nitrogen gas atmosphere or an inert gas atmosphere such as an argon gas atmosphere. Further, the reaction temperature and reaction time at the time of producing the prepolymer are not particularly limited, but the reaction temperature is preferably 60 to 100 ° C., particularly preferably 70 to 90 ° C., and the reaction time is 4 to 10 hours, particularly 5.5 to It is preferably 8.5 hours.

  The mass ratio of dehydrated castor oil and / or dehydrated castor oil fatty acid to the total amount of raw materials such as dehydrated castor oil used for the production of the chain-extended prepolymer is not particularly limited, but when the total amount of raw materials is 100% by mass It is preferable that it is 20-60 mass%, especially 25-55 mass%. If the mass ratio of dehydrated castor oil or the like is 25 to 60% by mass, the prepolymer is easily subjected to oxidative polymerization and has sufficient hardness and the like after applying the wood coating material containing the aqueous dispersion to the substrate. A film can be formed.

[5] Wood paints A polyurethane-based water dispersion for wood paints produced by the method of the present invention, and an aqueous dispersion composition in which various additives are blended with these, various additives for use as paints, etc. Can be used as a paint for wood.

  The aqueous dispersion preferably has a viscosity measured at 25 ° C. of 10 to 200 mPa · s, particularly 15 to 170 mPa · s. When the viscosity is within this range, the wood paint is easy to handle and the paint is easy to prepare. Further, the hydrogen ion exponent (pH) of the aqueous dispersion is preferably 7.0 to 9.0, particularly preferably 7.0 to 8.5. If it is pH of this range, it will be stable as a polyurethane-type water dispersion. Further, the nonvolatile content in the aqueous dispersion is preferably 25 to 60% by mass, particularly 30 to 55% by mass, when the aqueous dispersion is 100% by mass. If the non-volatile content is within this range, the viscosity is low and the resin content of the paint is sufficient. Even in the case of an aqueous dispersion composition, the viscosity, pH, and non-volatile content are preferably in the same ranges as those of the aqueous dispersion described above, whereby the same effects can be achieved.

  Various additives are blended in the water dispersion produced by the method of the present invention and the wood coating material mainly composed of the water dispersion composition. Examples of the additive include (1) (a) polymethylsiloxane to which polypropylene glycol is added, silicon-based polymethylsiloxane, polyphenylmethylsiloxane and the like, (b) ether-based such as polyvinyl isobutyl ether, and (c) acrylic such as polyisobutyl acrylate. (2) (a) propylene glycol, esterified vegetable oil fatty acid, cellosolve such as cellosolve acetate, butylcellosolve, butylcellosolve acetate, (b) texanol, (c) glycol ether such as polypropylene glycol monomethyl ether, etc. (3) (a) Silicon type such as dimethylpolysiloxane, ether type such as polyvinyl isobutyl ether, (b) acrylic type antifoaming agent such as polylauryl methacrylate, (4) carbon Black, red iron, calcium carbonate, Prussian blue, zinc white, inorganic pigments such as red lead, and azo, anthraquinone, organic phthalocyanine pigments such as, include various additives such. Each of these various additives may be used alone or in combination of two or more. The total amount of these additives is 5 to 25% by mass, particularly 10 to 20% by mass, when the prepolymer is 100% by mass. In other words, the prepolymer is preferably 75 to 95% by mass, particularly 80 to 90% by mass.

  The method of applying the wood coating to the substrate is not particularly limited, and is applied by brush coating, roller coating, spray coating, gravure coating, reverse roll coating, air knife coating, bar coating, curtain roll coating, dip coating, rod coating, doctor blade. It can apply | coat by various application methods, such as a coat | court. Also, after applying the wood paint to the base material, the method of drying and curing the coating film to form a film is not particularly limited, but it is allowed to stand at a predetermined temperature for a required time in an air atmosphere to evaporate water, When a chain-extended prepolymer is used by oxidative polymerization and a carbodiimide compound, it can be polymerized and cured together with polymerization by this compound. The temperature and time are not particularly limited, but it is preferably a low temperature and a long time rather than a high temperature and a short time, the temperature is preferably 30 to 60 ° C., particularly 35 to 50 ° C., and the time is the temperature and the prepolymer. Although depending on the reactivity of the above, it is preferably 48 to 288 hours, particularly preferably 96 to 240 hours.

Hereinafter, the present invention will be described specifically by way of examples.
[1] Synthesis of dehydrated castor oil In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube, reflux condenser and distiller, 1000 g (0.93 mol) of castor oil, 4.0 g of sodium hydrogen sulfate and water were added. 4.0 g was added, the pressure was gradually reduced to 5 mmHg, and the temperature was raised to 240 ° C. While maintaining the temperature, the mixture was stirred for 3 hours to cause dehydration reaction, and the reaction water was distilled out of the system. After completion of the reaction, the reaction mixture was cooled to 100 ° C. or lower, and 3.0 g of sodium hydrogen carbonate and 10 g of water were added to neutralize the catalyst. The pressure was reduced again to remove moisture, and then the neutralized salt was removed. The obtained dehydrated castor oil had an acid value of 3.0 mgKOH / g, a hydroxyl value of 10 mgKOH / g, and a viscosity at 25 ° C. of 150 mPa · s.

[2] Synthesis of polyol Synthesis example 1
In a reactor equipped with a stirrer, a thermometer, a nitrogen inlet tube and a reflux condenser, 1500 g (1.66 mol) of dehydrated castor oil, 113 g (0.83 mol) of pentaerythritol, and a 28% by mass methanol solution of sodium methoxide 2.4 g was added, and the mixture was stirred at 220 ° C. for 3 hours under a nitrogen stream to react. Then, it cooled to 100 degrees C or less, added 1.3g of 75 mass% aqueous solution of phosphoric acid, and neutralized and removed the catalyst. The obtained castor oil-based polyol had an iodine value of 123, an acid value of 1.0 mgKOH / g, a hydroxyl value of 129 mgKOH / g, and a viscosity at 25 ° C. of 500 mPa · s (hereinafter referred to as “polyol A-1”). In Tables 1 and 2, it is expressed as “polyol A-1”.)

Synthesis example 2
Synthetic Example 1 except that 1200 g (1.33 mol) of dehydrated castor oil was used, and 400 g (0.73 mol) of a propylene oxide adduct of pentaerythritol (hydroxyl value: 410 mgKOH / g) was used instead of pentaerythritol. A castor oil-based polyol was produced in the same manner. The obtained castor oil-based polyol had an iodine value of 99, an acid value of 1.0 mgKOH / g, a hydroxyl value of 111 mgKOH / g, and a viscosity at 25 ° C. of 300 mPa · s (hereinafter referred to as “polyol A-2”). In Tables 1 and 2, it is expressed as “polyol A-2”.)

Synthesis example 3
A castor oil-based polyol was produced in the same manner as in Synthesis Example 2, except that 1040 g (1.16 mol) of dehydrated castor oil and 560 g (1.02 mol) of a propylene oxide adduct of pentaerythritol were used. The iodine value of the resulting castor oil-based polyol was 86, the acid value was 1.0 mgKOH / g, the hydroxyl value was 147 mgKOH / g, and the viscosity at 25 ° C. was 400 mPa · s (hereinafter referred to as “polyol A-3”). In Tables 1, 2, and 3, it is also expressed as “polyol A-3”.)

Synthesis example 4
In the same manner as in Synthesis Example 1, except that 960 g (1.07 mol) of dehydrated castor oil was used and 96 g (0.71 mol) of pentaerythritol and 544 g (0.58 mol) of castor oil were used as polyols. An oil-based polyol was produced. The resulting castor oil-based polyol had an iodine value of 106, an acid value of 1.0 mgKOH / g, a hydroxyl value of 154 mgKOH / g, and a viscosity at 25 ° C. of 500 mPa · s (hereinafter referred to as “polyol A-4”). In Tables 1 and 2, it is expressed as “polyol A-4”.)

Synthesis example 5
In a reactor equipped with a stirrer, a thermometer, a nitrogen introduction tube and a water sampling tube, a reflux condenser, 590 g (2 mol) of dehydrated castor oil fatty acid, 138 g (0.25 mol) of propylene oxide adduct of pentaerythritol, triisopropyl titanate 0 .2 g was added and stirred at 220 ° C. for 6 hours under a nitrogen stream, and 36 g of reaction water was distilled to react, then cooled to 100 ° C. or lower and dehydrated under reduced pressure. The iodine value of the resulting castor oil-based polyol was 118, the acid value was 1.0 mgKOH / g, the hydroxyl value was 101 mgKOH / g, and the viscosity at 25 ° C. was 500 mPa · s (hereinafter referred to as “polyol A-5”). In Tables 1 and 2, “Polyol A-5” is also used.)

Comparative Synthesis Example 1
A castor oil-based polyol was produced in the same manner as in Synthesis Example 1, except that 1500 g (1.66 mol) of linseed oil was used instead of dehydrated castor oil and 113 g (0.83 mol) of pentaerythritol was used. The resulting castor oil-based polyol had an iodine value of 166, an acid value of 1.0 mgKOH / g, a hydroxyl value of 116 mgKOH / g, and a viscosity at 25 ° C. of 500 mPa · s (hereinafter referred to as “polyol B”. Tables 1 and 3 also indicate “polyol B”.)
The iodine value, acid value, hydroxyl value, and viscosity at 25 ° C. of the polyols (A-1 to 5 and B) of Synthesis Examples 1 to 4 and Comparative Synthesis Example 1 are described in Table 1.
The iodine value was measured according to JIS K 0070-6. The acid value was measured according to JIS K 0070-3. Furthermore, the hydroxyl value was measured according to JIS K 0070-7. The viscosity was measured according to JIS K 8803-8.

[2] Production of polyurethane-based aqueous dispersion for wood coating Example 1
In a reactor equipped with a stirrer, a thermometer, a nitrogen inlet tube and a reflux condenser, 110 g of polyol A-1, 80 g of MEK, 10.9 g of DMBA, 20 g of NMP, and 0.06 g of DBTDL were charged and dissolved. 68.3 g of HMDI was charged, and then the temperature was raised and reacted at 80 ° C. for 7 hours to give an isocyanate-terminated prepolymer (having 2.6% by mass of isocyanate groups when the prepolymer is 100% by mass). A containing reaction solution was obtained. Then, 6.7g of TEA was added to this reaction liquid at 40 degreeC, and it neutralized. Next, 420 g of ion-exchanged water containing 6.0 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then 3.9 g of carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Industries, Inc.) was added. Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Example 2
Into a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 554 g of polyol A-2, 300 g of MEK, 61 g of DMPA, 61 g of NMP, and 0.15 g of DBTDL are charged, and after dissolution, HMDI is added. 328 g was charged, then heated, reacted at 80 ° C. for 7 hours, and a reaction liquid containing an isocyanate-terminated prepolymer (having 2.9 mass% isocyanate group when the prepolymer was 100 mass%). Got. Thereafter, 46 g of TEA was added to the reaction solution at 40 ° C. to neutralize it. Next, 2020 g of ion-exchanged water containing 46.0 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then 19.8 g of carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Industries, Inc.) was added. Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Example 3
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 83.6 g of polyol A-3, 20.8 g of SA / MPD, 60 g of MEK, 11.6 g of DMPA, 28 g of NMP, and DOTDL 0.04 g was added, and after dissolution, 65.6 g of HMDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours to obtain an isocyanate-terminated prepolymer (2.3 when the prepolymer was 100% by mass). A reaction liquid containing a mass% isocyanate group) was obtained. Thereafter, at 40 ° C., 8.7 g of TEA was added to the reaction solution for neutralization. Next, 370 g of ion-exchanged water containing 6.8 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then 3.8 g of carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Industries, Inc.) was added. Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Example 4
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 113.6 g of polyol A-4, 63 g of MEK, 12.6 g of DMPA, 30 g of NMP, and 0.06 g of DBTDL are charged and dissolved. Thereafter, 82.0 g of HMDI was charged, and then the temperature was raised and reacted at 80 ° C. for 7 hours to have an isocyanate-terminated prepolymer (having 2.9% by mass of isocyanate groups when the prepolymer was 100% by mass). ) Containing was obtained. Thereafter, at 40 ° C., 9.5 g of TEA was added to the reaction solution for neutralization. Next, 490 g of ion-exchanged water containing 12 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then 4.4 g of a carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Co., Ltd.) was added, Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Example 5
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 132.1 g of polyol A-5, 9.3 g of AP-2, 60 g of MEK, 14.0 g of DMPA, 30 g of NMP, and DBTDL 0.06 g was added, and after dissolution, 85.0 g of HMDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours to obtain an isocyanate-terminated prepolymer (2.6% when the prepolymer was 100% by mass). A reaction liquid containing a mass% isocyanate group) was obtained. Thereafter, at 40 ° C., 9.5 g of TEA was added to the reaction solution for neutralization. Next, 440 g of ion-exchanged water containing 5.1 g of piperazine was dropped to cause chain extension reaction and phase inversion, and then 4.8 g of carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Industries, Inc.) was added. Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Example 6
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 77.0 g of polyol A-1, 4.5 g of 1,4-BD, 60 g of MEK, 9.0 g of DMBA, 23 g of NMP, And 0.06 g of DBTDL were added, and after dissolution, 70.9 g of HMDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours to give an isocyanate-terminated prepolymer (3% when the prepolymer was 100% by mass). The reaction liquid containing 6 mass% isocyanate group) was obtained. Thereafter, 4.9 g of TEA was added to the reaction solution at 40 ° C. to neutralize it. Next, 340 g of ion-exchanged water containing 6.0 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then 3.3 g of carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Industries, Inc.) was added. Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Example 7
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 70.5 g of polyol A-1, 4.3 g of 1,4-BD, 4.4 g of AP-2, 60 g of MEK, DMPA 7.8 g, 17 g of NMP, and 0.06 g of DBTDL were added. After dissolution, 73.5 g of HMDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours to obtain an isocyanate-terminated prepolymer (prepolymer of 100 A reaction liquid containing 4.2% by mass of isocyanate groups when the mass% was obtained) was obtained. Thereafter, at 40 ° C., 4.7 g of TEA was added to the reaction solution for neutralization. Next, 380 g of ion-exchanged water containing 4.0 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then 3.2 g of carbodiimide compound (trade name “Carbodilite SV-02” manufactured by Nisshinbo Industries, Inc.) was added. Thereafter, the mixture was sufficiently stirred to make it uniform, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint.

Comparative Example 1
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 492 g (0.246 mol) of AA / HG, 300 g of MEK, 36.4 g of DMBA, 50 g of NMP, and 0.08 g of DBTDL are charged. After dissolution, 210 g of HMDI was charged, and then the temperature was raised and reacted at 80 ° C. for 7 hours to give an isocyanate-terminated prepolymer (having 3.7% by mass of isocyanate groups when the prepolymer was taken as 100% by mass). .) Was obtained. Thereafter, 24.8 g of TEA was added to the reaction solution at 40 ° C. to neutralize it. Next, 1200 g of ion-exchanged water containing 23.5 g of IPDA was added dropwise to cause chain extension reaction and phase inversion, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint. did.

Comparative Example 2
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, AA / IPA 200 g (0.10 mol), TMP 3 g, MEK 150 g, DMPA 39.0 g, NMP 30 g, and DBTDL 0.06 g was added, and after dissolution, 184 g of HMDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours to obtain an isocyanate-terminated prepolymer (4.2 mass% when the prepolymer was 100 mass%). A reaction solution containing an isocyanate group) was obtained. Thereafter, at 40 ° C., 32 g of TEA was added to the reaction solution for neutralization. Next, 800 g of ion-exchanged water containing 10 g of EDA was added dropwise to cause chain extension reaction and phase inversion, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood coating.

Comparative Example 3
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, polyol B is 80.6 g, 1,4-BD is 4.7 g, MEK is 60 g, DMBA is 9.5 g, NMP is 23 g, and DBTDL. 0.06 g was added, and after dissolution, 70.9 g of HMDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours to obtain an isocyanate-terminated prepolymer (3.6% when the prepolymer was 100% by mass). A reaction liquid containing a mass% isocyanate group) was obtained. Thereafter, at 40 ° C., 5.2 g of TEA was added to the reaction solution for neutralization. Next, 340 g of ion-exchanged water containing 6.0 g of IPDA was dropped to cause chain extension reaction and phase inversion, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint. did.

Comparative Example 4
A general-purpose soybean oil-based polyurethane aqueous dispersion (commercially available product) was used.

Comparative Example 5
In a reactor equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, 83.6 g of polyol A-3, 20.8 g of SA / MPD, 60 g of MEK, 11.6 g of DMBA, 23 g of NMP, and DOTDL 0.04 g was added, and after dissolution, 55.6 g of IPDI was added, and then the temperature was raised and reacted at 80 ° C. for 7 hours. A reaction liquid containing a mass% isocyanate group) was obtained. Thereafter, at 40 ° C., 8.7 g of TEA was added to the reaction solution for neutralization. Next, 370 g of ion-exchanged water containing 6.8 g of IPDA was added dropwise to cause chain extension reaction and phase inversion, and then MEK was distilled off at 50 ° C. under reduced pressure to produce a polyurethane-based aqueous dispersion for wood paint. did.

In addition, the meaning of the abbreviation in an Example and a comparative example is as follows.
DMPA; dimethylolpropionic acid DMBA; dimethylolbutanoic acid MEK; methyl ethyl ketone NMP; N-methylpyrrolidone DBTDL; dibutyltin dilaurate DOTDL; dioctyltin dilaurate HMDI; hydrogenated product of MDI IPDI; isophorone diisocyanate TEA; Ethylenediamine TMP; trimethylolpropane 1,4-BD; 1,4-butanediol AP-2; propylene oxide 2-mol adduct of bisphenol A SA / MPD; polyester which is a reaction product of sebacic acid and 3-methylpentanediol Polyol (weight average molecular weight; 3500, hydroxyl value; 34 mgKOH / g)
AA / HG: polyester polyol which is a reaction product of adipic acid and hexanediol (weight average molecular weight: 2000, hydroxyl value: 56 mgKOH / g)
AA / IPA = 1/1 (molar ratio) / HG; polyester polyol which is a reaction product of adipic acid and isophthalic acid (1/1 by molar ratio) and hexanediol (weight average molecular weight; 2000, hydroxyl value; 56 mgKOH / g)

The viscosity, pH, non-volatile content, and dehydrated castor oil content of the polyurethane-based aqueous dispersions for wood coatings of Examples 1 to 7 and Comparative Examples 1 to 5 are described in Tables 2 and 3, respectively.
The viscosity was measured according to JIS K 8803-8. The pH was measured with “pH meter F-22” manufactured by Horiba. Further, the nonvolatile content (abbreviated as “NV” in Tables 2 and 3) was calculated as the volatile residue when heated at 125 ° C. for 3 hours in accordance with JIS K 0067-2-3.
Non-volatile content (%) = [(total weight after heating−weight of container) / (total weight before heating−weight of container)] × 100
The “mass ratio of dehydrated castor oil” in Tables 2 and 3 is the mass ratio of dehydrated castor oil when the total amount of raw materials used for the production of the chain-extended prepolymer is 100 mass%. .
Mass ratio (%) of dehydrated castor oil = (mass of dehydrated castor oil / total mass of raw materials) × 100

[3] Preparation of respective formulations for coating and film production Nonvolatiles of polyurethane-based aqueous dispersions for wood paints of Examples 1 to 7 and Comparative Examples 1 to 5 (abbreviated as “PUD” in Table 4). The minute amount (abbreviated as “NV” in Table 4) was adjusted to 30% by mass, and this water dispersion, leveling agent (trade name “Additol XW395” manufactured by Cytec Co., Ltd.), film-forming aid (Dow Chemical) Nippon Shokubai Co., Ltd., trade name “Dawanol DPM”) and ion-exchanged water were blended so as to have the respective compositions for coating and film production shown in Table 4, and used for the production of test pieces.

[4] Performance Evaluation (1) Evaluation of Coating Film Using the polyurethane-based aqueous dispersions for wood paints of Examples 1 to 7 and Comparative Examples 1 to 5 on one surface of a base material of Lauan plywood having a length of 200 mm and a width of 150 mm. The paint blended so as to have the composition shown in Table 4 was applied four times, and the coating amount was adjusted to 4.0 to 6.0 g at a time to form a coating film. Each application interval was 6 hours or more (6 to 10 hours), and the first to third layers were dried at an ambient temperature (25 ° C.). The layers 1 to 3 were polished with No. 240 sandpaper before the upper layer was applied. On the other hand, the uppermost layer, that is, the fourth layer was not polished and was cured at 40 ° C. for 1 week for evaluation.
In addition, the polishability at the time of the above polishing was visually evaluated. Evaluation criteria are: ○: Sandpaper is not clogged and is good, Δ: Clogging is slightly observed, but polishing is possible.

The performance of the film formed on the surface of the substrate as in (1) above was evaluated.
(A) Yellowing; Coloring of the film was visually observed when 30 days had elapsed after curing. The evaluation criteria are ○: good without any discoloration, Δ: slightly discolored to yellow, ×: discolored yellow.
(B) Pencil hardness; evaluated according to JIS K 5600-5-4.
(C) Glossiness: 60 ° specular glossiness was evaluated according to JIS K 5600-4-7 using a model “IG-331” manufactured by HORIBA, Ltd.
(D) Spot test (chemical resistance): In accordance with JIS K 5600-6-1 [Method 3 (Drip method)], the liquid shown in Table 5 is dropped onto the film, and the test surface is coated to prevent excessive evaporation. After covering with a cap and allowing to stand for 24 hours, the state of the test surface was visually observed. Evaluation criteria: ○: Drop marks are not visually recognized and good, Δ: Drop marks are visually recognized and slightly infiltrated with the liquid, X: Wrinkles are observed on the dropping surface, and the liquid is invaded .
Na ₂ CO ₃ , acetic acid and EtOH (ethanol) are all aqueous solutions. The detergent is a product name “Joy” manufactured by P & G, and the lacquer thinner is a product defined in JIS K 5538.
(E) Moisture and heat resistance; boiling water is put into a circular stainless steel container having a bottom surface of 100 mm in diameter, and this container is allowed to stand on the surface of the film on which water has been cast. After 30 minutes, the container is removed and the surface of the film is removed. Was visually observed. The evaluation criteria are ○: the standing trace is not visually recognized and good, and Δ: the standing trace is visually recognized and is slightly affected by humidity and heat.
The evaluation results of (a) to (e) are shown in Table 5 above.

  According to the results of Table 5, when the polyurethane-based aqueous dispersions for wood paints of Examples 1 to 7 were used, there were no problems with polishing, yellowing and heat-and-moisture resistance, sufficient hardness, and gloss. Is 81 or more, which is excellent. Moreover, although chemical resistance (solvent resistance) with respect to ethanol and lacquer thinner may be a little low, it turns out that it has sufficient chemical resistance generally. On the other hand, when using the polyurethane-based aqueous dispersions for wood paints of Comparative Examples 1 to 5, there are no significant problems in chemical resistance against abrasiveness, acetic acid and detergent, but there are items that are greatly inferior in other evaluations. I understand that. In particular, in Comparative Example 4 using a general-purpose soybean oil-based polyurethane aqueous dispersion, yellowing is severe in Comparative Example 3 using a polyol synthesized using linseed oil which is a dry oil instead of dehydrated castor oil. Moreover, although the polyol synthesize | combined using dehydrated castor oil is used, it turns out that it is inferior to solvent resistance in the comparative example 5 using the isocyclohexylone diisocyanate with one cyclohexyl group.

(2) Evaluation of film Using the compound for film preparation blended so as to have the composition shown in Table 4 using the polyurethane-based aqueous dispersions for wood paints of Examples 1 to 7 and Comparative Examples 1 to 5, the film was made of metal. A film having a thickness of 300 μm was produced by pouring into a mold of 100 mm, and a test piece having a length of 100 mm and a width of 30 mm was cut out from the film, and this test piece was immersed in warm water at 40 ° C. and adhered to the surface after 48 hours. The water was wiped off with gauze, the weight change rate was calculated, and the appearance was visually evaluated.
Weight change rate (%) = [(weight after immersion−weight before immersion) / weight before immersion] × 100
The results are listed in Table 6.

  According to the results of Table 6, when using the polyurethane-based aqueous dispersion for wood paints of Examples 1 to 7, the weight change rate is + 2.4% or less, that is, the weight increase rate is 2.4% or less. In addition, the water absorption is extremely low, and the appearance is only slightly turbid, indicating that there is no problem at all. On the other hand, when the polyurethane-based aqueous dispersion for wood paints of Comparative Examples 1 to 5 is used, Comparative Examples 1 to 2 and 4 to 5 have a large weight increase rate. Then, the rate of weight increase is extremely large, which is a problem. In Comparative Example 3, there is no problem in the weight increase rate and the appearance, but the yellowing is inferior, which is a problem.

  INDUSTRIAL APPLICABILITY The present invention can be used in various applications such as wooden floors, walls, ceilings, furniture, and the like that are made of wood and need to be coated with a paint to form a film in order to improve aesthetics.

Claims (4)

A reaction product of dehydrated castor oil and / or dehydrated castor oil fatty acid and a tetrafunctional or higher polyol, and the total of the dehydrated castor oil and / or dehydrated castor oil fatty acid and the tetrafunctional or higher polyol is 100. In the case of mass%, the tetrafunctional or higher polyol is 5 to 40 mass% of a polyol (A) having a dehydrated castor oil fatty acid skeleton, at least two hydroxyl groups, and at least one carboxyl group. And a diisocyanate compound (B) having 2 or 3 cyclohexyl groups are reacted to form an isocyanate-terminated prepolymer, and then a reaction solution in which the isocyanate-terminated prepolymer is dissolved and water. A method for producing a polyurethane-based aqueous dispersion for wood paint, which comprises mixing. The method for producing a polyurethane-based aqueous dispersion for wood paint according to claim 1, wherein the iodine value of the polyol (A) is 80 to 130. At the same time as or after the mixing of the reaction solution and the water, carbodiimide is added to the mixed solution, and when the solid content in the mixed solution is 100 parts by mass, the carbodiimide is 0. It is 3-3.0 mass parts, The manufacturing method of the polyurethane-type water dispersion for wood paints of Claim 1 or 2 . A polyurethane-based aqueous dispersion for wood coatings produced by the method for producing a polyurethane-based aqueous dispersion for wood coatings according to any one of claims 1 to 3 .