Blocked isocyanate composition, method for producing the same, curing agent for coating, coating composition, and coating film

Abstract

To provide a blocked isocyanate composition which hardly causes a viscosity change and coloration over time.SOLUTION: A blocked isocyanate composition contains a blocked isocyanate which is a reaction product of a polyisocyanate and a blocking agent or a derivative of the reaction product. The polyisocyanate is a polyisocyanate modified with a tertiary amino alcohol. A ratio of a total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to a total amount of isocyanate groups contained in the polyisocyanate is 0.91-0.99 as a molar ratio. The polyisocyanate contains a C4-6 aliphatic polyisocyanate or a derivative thereof.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a blocked isocyanate composition and a method for producing the same, a curing agent for a paint, a paint composition, and a coating film. [Background technology]

[0002] Polyisocyanates have been known as components of compositions used in paints, etc. For example, polyurethane resin paints in which polyols and polyisocyanates are combined are known to have very good abrasion resistance, chemical resistance, and stain resistance.

[0003] Paints using polyisocyanate as a curing agent are generally two-liquid compositions, in which the main component (e.g., polyol) and polyisocyanate are stored separately and mixed when used for painting. However, once mixed, the paint hardens in a short time, so the pot life is short, and there are problems with workability when painting. In addition, since polyisocyanate easily reacts with water, it was impossible to use the above-mentioned paint in water-based paints such as electrodeposition paints.

[0004] As a method for dealing with these problems, a method is known in which polyisocyanate is inactivated by reacting it with a blocking agent. The blocked isocyanate obtained by this method does not react with the main component (polyol, etc.) at room temperature, but when heated, the blocking agent dissociates, regenerating the isocyanate group, which then reacts with the main component to form a crosslink. Therefore, according to the above method, the pot life is not limited, and it is possible to mix the main component and the curing agent component in advance to form a paint, and it is also possible to apply polyisocyanate to water-based paints.

[0005] Known examples of blocking agents for polyisocyanates include lactam-based blocking agents, oxime-based blocking agents, and phenol-based blocking agents (see Patent Document 1). It is also known that the blocking agent in a blocked polyisocyanate obtained by reacting a polyisocyanate with a tertiary amino alcohol and a blocking agent dissociates at low temperatures (see Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2-620 [Patent Document 2] JP 2016-222891 A Summary of the Invention [Problem to be solved by the invention]

[0007] Depending on the application of the coating film, high transparency and viscosity stability may be required for the coating composition and the blocked isocyanate composition that is a material thereof. However, as a result of investigations by the present inventors, it was found that a blocked isocyanate obtained by reacting a polyisocyanate with a tertiary amino alcohol and an oxime-based blocking agent undergoes coloration and viscosity changes over time.

[0008] An object of one aspect of the present invention is to provide a blocked isocyanate composition that is less likely to undergo coloration and viscosity changes over time. [Means for solving the problem]

[0009] Conventionally, when synthesizing blocked isocyanates, the blocking effect is reduced if free isocyanate groups are present in the blocked isocyanate, so that no free isocyanate groups remain, an equivalent or excess equivalent amount of a blocking agent relative to the polyisocyanate has been used. Surprisingly, the present inventors have found that, contrary to the conventional technical common sense described above, by using an amount of blocking agent less than the equivalent amount relative to the polyisocyanate, it is possible to suppress the occurrence of coloring over time while fully ensuring the blocking effect, and have completed the present invention.

[0010] One aspect of the present invention provides at least the following [1] to [8].

[0011] [1] A method for producing a blocked isocyanate composition, comprising the steps of: The method includes a step of mixing and reacting a polyisocyanate with an oxime-based blocking agent, the ratio of the amount of the oxime-based blocking agent to the amount of the polyisocyanate is 0.91 to 0.99 in terms of equivalent ratio; The method for producing a blocked isocyanate composition, wherein the polyisocyanate contains an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof modified with a tertiary amino alcohol.

[0012] [2] The method for producing a blocked isocyanate composition according to the above-mentioned [1], wherein the ratio of the amount of the oxime-based blocking agent mixed to the amount of the polyisocyanate mixed is 0.91 to 0.95 in terms of equivalent ratio.

[0013] [3] The present invention includes a blocked isocyanate which is a reaction product of a polyisocyanate and a blocking agent or a derivative thereof, a molar ratio of a total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to a total amount of isocyanate groups contained in the polyisocyanate is 0.91 to 0.99; The blocked isocyanate composition, wherein the polyisocyanate comprises an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof, which has been modified with a tertiary amino alcohol.

[0014] [4] The blocked isocyanate composition according to the above item [3], wherein a ratio, in terms of molar ratio, of the total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to the total amount of isocyanate groups contained in the polyisocyanate is 0.91 to 0.95.

[0015] [5] The blocked isocyanate composition according to the above [3] or [4], wherein the blocked isocyanate has a free isocyanate group.

[0016] [6] A coating material curing agent comprising the blocked isocyanate composition according to any one of the above [3] to [5].

[0017] [7] A coating composition comprising a base component and a curing agent component, A coating composition, wherein the curing agent component comprises the blocked isocyanate composition according to any one of the above [3] to [5].

[0018] [8] A coating film comprising a cured product of the coating composition described in [7] above. Effect of the Invention

[0019] According to the present invention, it is possible to provide a blocked isocyanate composition which is unlikely to undergo coloration or change in viscosity over time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, exemplary embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. In this specification, a numerical range indicated using "~" indicates a range including the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In addition, unless specifically stated otherwise, the units of the numerical values ​​before and after "~" are the same. In addition, the upper limit value and the lower limit value described individually can be arbitrarily combined.

[0021] <Method for producing blocked isocyanate composition> One embodiment of the present invention is a method for producing a blocked isocyanate composition, which includes a step of mixing and reacting a polyisocyanate containing an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof modified with a tertiary amino alcohol with an oxime-based blocking agent (hereinafter also referred to as a "blocking step"), and the ratio of the amount of the oxime-based blocking agent mixed to the amount of the polyisocyanate mixed is 0.91 to 0.99 in terms of equivalent ratio. Note that in calculating the above equivalent ratio, the value to two decimal places is rounded off.

[0022] In the above-mentioned production method, the oxime-based blocking agent reacts with the polyisocyanate, thereby blocking the isocyanate groups in the polyisocyanate with the oxime-based blocking agent. The blocked isocyanate composition obtained by the above-mentioned production method contains the blocked isocyanate or its derivative thus produced.

[0023] The blocked isocyanate composition obtained by the above-mentioned production method is a composition that has excellent low-temperature dissociation properties and is unlikely to cause coloration and viscosity change over time (i.e., has excellent coloration resistance and viscosity retention). The reason for this is not clear, but the present inventors speculate as follows. That is, in the conventional method using an equivalent or excess equivalent amount of a blocking agent to a polyisocyanate, unreacted oxime-based blocking agent remains in the blocked isocyanate composition, and the remaining blocking agent is thought to cause coloration and viscosity change due to decomposition over time. On the other hand, in the method of the above-mentioned embodiment, the ratio of the mixed amount of oxime-based blocking agent to the mixed amount of polyisocyanate is 0.99 or less in equivalent ratio, so that no oxime-based blocking agent remains or only a very small amount remains, and it is speculated that the occurrence of coloration and viscosity change over time is suppressed. In addition, since a urethane bond is formed in the reaction between an oxime-based blocking agent and an isocyanate group, it is presumed that the isocyanate group blocked with an oxime-based blocking agent is more stable in the storage temperature range (e.g., 5 to 35°C) than an isocyanate group blocked with other blocking agents (e.g., active methylene-based blocking agents, amine-based blocking agents, etc.), and the blocking agent is less likely to dissociate over time. Therefore, in the above-mentioned production method, by setting the ratio of the amount of oxime-based blocking agent mixed to the amount of polyisocyanate mixed to an equivalent ratio of 0.91 or more, most of the isocyanate groups in the polyisocyanate are maintained in a state blocked with a blocking agent (oxime-based blocking agent) in the storage temperature range, and as a result, the viscosity change over time is suppressed.

[0024] Polyisocyanate is a compound having a plurality of isocyanate groups (two or more). In addition, polyisocyanate includes aliphatic polyisocyanate having 4 to 6 carbon atoms or derivatives thereof modified with tertiary amino alcohol. Note that the polyisocyanate used in the blocking step is a polyisocyanate having no isocyanate groups blocked with a blocking agent.

[0025] Examples of polyisocyanate derivatives include isocyanurates, allophanates, and biuret derivatives. The derivatives may be modified (prepolymerized) using a polyol or the like as a modifying agent. The derivatives may also be modified using a poly(oxyalkylene) glycol monoalkyl ether or the like as a modifying agent. As the polyisocyanate, one type of polyisocyanate may be used alone, or two or more types of polyisocyanates may be used.

[0026] Examples of the aliphatic polyisocyanate having 4 to 6 carbon atoms include hexamethylene diisocyanate, pentamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, and derivatives thereof. Among them, it is more preferable to use hexamethylene diisocyanate or its derivatives from the viewpoint of imparting flexibility to the coating film. As the derivatives of hexamethylene diisocyanate, isocyanurates, allophanates, and biuret compounds are preferably used.

[0027] The tertiary amino alcohol includes a compound represented by the following formula (I).

[0028] [ka]

[0029] In formula (I), R 1 and R 2 each independently represents a monovalent hydrocarbon group having 1 to 8 carbon atoms; R 3 R represents a divalent hydrocarbon group having 1 to 16 carbon atoms. 1 and R 2 may be the same or different from each other.

[0030] R 1 and R 2The monovalent hydrocarbon group represented by the formula (I) may be an aliphatic hydrocarbon group (e.g., an alkyl group or a cycloalkyl group) or an aromatic hydrocarbon group (e.g., an aryl group). When the hydrocarbon group is an aliphatic hydrocarbon group, it may have, for example, 1 to 8 carbon atoms. When the aliphatic hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 1 to 4 or 1 to 2 carbon atoms. When the hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 6 to 16 carbon atoms. When the aromatic hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 6 to 14 or 6 to 12 carbon atoms.

[0031] R 1 and R 2 From the viewpoint of further improving the curability, the monovalent hydrocarbon group represented by the formula (I) is preferably an aliphatic hydrocarbon group, and more preferably an alkyl group. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, and a 2-ethylhexyl group. Among these, a linear alkyl group is preferred, and a linear alkyl group having 1 to 4 carbon atoms (a methyl group, an ethyl group, an n-propyl group, and an n-butyl group) is more preferred.

[0032] R 3 The divalent hydrocarbon group represented by the formula (I) may be an aliphatic hydrocarbon group (e.g., an alkylene group or a cycloalkylene group) or an aromatic hydrocarbon group (e.g., an arylene group). When the hydrocarbon group is an aliphatic hydrocarbon group, it may have, for example, 1 to 16 carbon atoms. When the aliphatic hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 2 to 8 or 2 to 6 carbon atoms. When the hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 6 to 16 carbon atoms. When the aromatic hydrocarbon group is an aromatic hydrocarbon group, it may have, for example, 6 to 14 or 6 to 12 carbon atoms.

[0033] R 3From the viewpoint of further improving the curability, the divalent hydrocarbon group represented by the formula (I) is preferably an aliphatic hydrocarbon group, and more preferably an alkylene group. Specific examples of the alkylene group include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an isobutylene group, a t-butylene group, an n-pentylene group, an n-hexylene group, an n-heptylene group, an n-octylene group, and a 2-ethylhexylene group. Among these, a linear alkylene group is preferred, and a linear alkylene group having 2 to 6 carbon atoms (an ethylene group, an n-propylene group, an n-butylene group, an n-pentylene group, and an n-hexylene group) is more preferred.

[0034] Specific preferred examples of the compound represented by formula (I) include 6-(dimethylamino)-1-hexanol, 2-(dimethylamino)ethanol, 2-(dibutylamino)ethanol, 2-(diethylamino)ethanol, 2-(dipropylamino)ethanol, 2-(diisopropylamino)ethanol, 2-(diisobutylamino)ethanol, 2-(dipentylamino)ethanol, 2-(dihexylamino)ethanol, 2-(dioctylamino)ethanol, and 8-(dimethylamino)-1-octanol.

[0035] The molecular weight of the tertiary amino alcohol is, for example, 80 to 250. From the viewpoint of improving compatibility with polyisocyanate, the molecular weight of the tertiary amino alcohol may be 100 or more or 130 or more. From the viewpoint of further improving curability, the molecular weight of the tertiary amino alcohol may be 230 or less or 200 or less.

[0036] The content of the modified isocyanate group modified with a tertiary amino alcohol may be 0.1 to 30 mass%, or may be 0.5 to 20 mass%, or 1 to 10 mass%, based on the total mass of the compound obtained by dissociating the blocking agent from the modified blocked isocyanate.

[0037] Examples of oxime-based blocking agents include formaldoxime, acetaldoxime, acetoneoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, and cyclohexanone oxime. Among them, methyl ethyl ketoxime has an appropriate vapor pressure and is easy to handle. The oxime-based blocking agents may be used alone or in combination of two or more.

[0038] The above-mentioned equivalent ratio (ratio of the amount of the oxime-based blocking agent mixed to the amount of the polyisocyanate mixed) may be 0.93 or more, 0.95 or more, or 0.97 or more from the viewpoint of further improving the viscosity retention of the blocked isocyanate composition. The above-mentioned equivalent ratio may be 0.98 or less, 0.96 or less, or 0.94 or less from the viewpoint of further improving the coloration resistance of the blocked isocyanate composition. From these viewpoints, the above-mentioned equivalent ratio may be, for example, 0.93 to 0.99, 0.95 to 0.99, or 0.97 to 0.99, or may be 0.91 to 0.98, 0.91 to 0.96, or 0.91 to 0.94. The above-mentioned equivalent ratio can be rephrased as the ratio of the total amount (unit: mol) of the oxime-based blocking agent to the total amount (unit: mol) of the isocyanate groups contained in the polyisocyanate.

[0039] In the blocking step, an organic solvent may be used in addition to the polyisocyanate and the oxime-based blocking agent. That is, the reaction between the polyisocyanate and the oxime-based blocking agent may be carried out in the presence of an organic solvent. Examples of the organic solvent include aromatic solvents such as toluene and xylene, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, and glycol ether solvents such as ethylene glycol monoethyl ether acetate and propylene glycol monomethyl ether acetate. These organic solvents may be used alone or in combination of two or more.

[0040] The polyisocyanate and the oxime-based blocking agent can be mixed and reacted according to the reaction conditions of a normal blocking reaction. The polyisocyanate and the oxime-based blocking agent can be mixed by adding the oxime-based blocking agent to the polyisocyanate (or a solution containing the polyisocyanate and the organic solvent) in multiple batches, as necessary. The reaction between the polyisocyanate and the oxime-based blocking agent can be carried out at room temperature (e.g., 5 to 35°C), or can be carried out while heating the mixed liquid containing the polyisocyanate and the oxime-based blocking agent. Regardless of whether or not heating is performed, the temperature of the mixed liquid during the reaction can be, for example, 20 to 200°C.

[0041] The completion of the reaction between the polyisocyanate and the oxime-based blocking agent can be confirmed by measuring the NCO content (mass concentration) or infrared spectroscopy.

[0042] In the blocking step, in addition to the polyisocyanate and the oxime-based blocking agent, a blocking agent other than the oxime-based blocking agent (hereinafter referred to as "other blocking agent") may be mixed in. That is, the method for producing the blocked isocyanate composition may be a method including a step of mixing and reacting the polyisocyanate, the oxime-based blocking agent, and the other blocking agent.

[0043] As other blocking agents, various blocking agents such as phenol-based, alcohol-based, active methylene-based, mercaptan-based, acid amide-based, acid imide-based, imidazole-based, urea-based, amine-based, imide-based compounds, pyrazole-based, and triazole-based blocking agents can be used. Specific examples of these blocking agents include phenol, cresol, ethylphenol, butylphenol, 2-hydroxypyridine, butyl cellosolve, propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, ethanol, n-butanol, isobutanol, 2-ethylhexanol, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, butyl mercaptan, dodecyl mercaptan, acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam, succinimide, maleimide, imidazole, 2-methylimidazole, urea, thiourea, ethyleneurea, diphenylaniline, aniline, carbazole, ethyleneimine, polyethyleneimine, 3,5-dimethylpyrazole, and 1,2,4-triazole.

[0044] The other blocking agent may be mixed after mixing and reacting the polyisocyanate with the oxime-based blocking agent. That is, the method for producing a blocked isocyanate composition may be a method including a first blocking step of mixing and reacting the polyisocyanate with the oxime-based blocking agent, and a second blocking step of mixing and reacting the reaction product obtained in the first blocking step with the other blocking agent.

[0045] In the blocked isocyanate composition obtained by the above-mentioned production method, a polyisocyanate or blocked isocyanate having an unreacted isocyanate group (free isocyanate group) may be present, and the above-mentioned production method may further include a step of modifying the unreacted isocyanate group (free isocyanate group) by reacting it with a modifying agent such as an active hydrogen group-containing compound (however, tertiary amino alcohols and blocking agents are excluded).

[0046] <Blocked isocyanate composition> Another embodiment of the present invention includes a blocked isocyanate which is a reaction product or a derivative thereof of a polyisocyanate containing an aliphatic polyisocyanate having 4 to 6 carbon atoms modified with a tertiary amino alcohol or a derivative thereof and a blocking agent, In the blocked isocyanate composition, the ratio of the total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to the total amount of isocyanate groups contained in the polyisocyanate is 0.91 to 0.99 in terms of molar ratio.

[0047] The blocked isocyanate composition is, for example, a blocked isocyanate composition obtained by the production method of the embodiment described above, and since the molar ratio is 0.91 to 0.99, it is a composition that is unlikely to undergo coloration or viscosity change over time.

[0048] The blocked isocyanate, which is a reaction product between a polyisocyanate containing an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof modified with a tertiary amino alcohol and a blocking agent, may be, for example, a reaction product between a polyisocyanate and an oxime-based blocking agent. The reaction product has a structure derived from the polyisocyanate and an isocyanate group blocked with an oxime-based blocking agent.

[0049] The blocked isocyanate, which is a reaction product of a polyisocyanate containing an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof modified with a tertiary amino alcohol and a blocking agent, may be a reaction product of a polyisocyanate, an oxime-based blocking agent, and the other blocking agent (a blocking agent other than the oxime-based blocking agent) described above. The reaction product has a structure derived from the polyisocyanate, an isocyanate group blocked with an oxime-based blocking agent, and an isocyanate group blocked with another blocking agent.

[0050] Examples of the polyisocyanate and blocking agent containing an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof modified with a tertiary amino alcohol include those exemplified as the polyisocyanate and blocking agent used in the above-mentioned production method, and preferred examples are also the same. For example, it is more preferable to contain hexamethylene diisocyanate or a derivative thereof. That is, it is more preferable that the blocked isocyanate contains a structure derived from hexamethylene diisocyanate or a derivative thereof. Also, for example, it is preferable that the blocking agent contains methyl ethyl ketoxime. That is, it is preferable that the blocked polyisocyanate has an isocyanate group blocked with methyl ethyl ketoxime.

[0051] The derivative of the reaction product of a polyisocyanate and a blocking agent may be, for example, a modified product obtained by reacting a free isocyanate group in the reaction product of a polyisocyanate and a blocking agent with a modifying agent such as an active hydrogen group-containing compound (excluding tertiary amino alcohols and blocking agents).

[0052] The blocked isocyanate may have a free isocyanate group. When the blocked isocyanate has a free isocyanate group, the curing property of the coating material tends to be improved.

[0053] The molar ratio (the ratio of the total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to the total amount of isocyanate groups contained in the polyisocyanate) may be 0.93 or more, 0.95 or more, or 0.97 or more, from the viewpoint of further improving the viscosity retention of the blocked isocyanate composition. The molar ratio may be 0.98 or less, 0.96 or less, or 0.94 or less, from the viewpoint of further improving the coloration resistance of the blocked isocyanate composition. From these viewpoints, the molar ratio may be, for example, 0.93 to 0.99, 0.95 to 0.99, or 0.97 to 0.99, or may be 0.91 to 0.98, 0.91 to 0.96, or 0.91 to 0.94.

[0054] The content of the blocked isocyanate and its derivative in the blocked isocyanate composition may be, for example, 20 to 99 mass %, 40 to 90 mass %, 50 to 80 mass %, or 70 to 80 mass % based on the total mass of the composition.

[0055] The blocked isocyanate composition may further contain an unreacted polyisocyanate in addition to the blocked isocyanate and its derivative. However, the blocked isocyanate composition preferably does not contain an unreacted blocking agent, and more preferably does not contain an unreacted oxime-based blocking agent. Here, the fact that the blocked isocyanate composition does not contain a blocking agent means that the content of the blocking agent is less than 0.001% by mass based on the total mass of the composition.

[0056] The blocked isocyanate composition may further contain additives such as a dissociation catalyst, a pigment, a dye, a dispersion stabilizer, a viscosity modifier, a leveling agent, an antigelling agent, a light stabilizer, an antioxidant, an ultraviolet absorber, a heat resistance improver, an inorganic or organic filler, a plasticizer, a lubricant, an antistatic agent, and a reinforcing material.

[0057] The content of effective isocyanate groups in the blocked isocyanate composition (hereinafter referred to as "effective NCO content") may be 6 to 28% by mass, 8 to 22% by mass, or 10 to 16% by mass, from the viewpoint of reducing the amount of blocked isocyanate used in the coating material and preventing viscosity changes. Here, the effective isocyanate group means both free isocyanate groups and isocyanate groups blocked (blocked) with a blocking agent. The effective NCO content is the amount of isocyanate groups present in the blocked isocyanate composition that can participate in a crosslinking reaction, expressed in mass% (based on the total mass of the blocked isocyanate composition), and can be determined by measuring the amount of free isocyanate groups in the isocyanate composition obtained by dissociating the blocking agent from the blocked isocyanate. This amount can be determined by reacting the isocyanate groups in the measurement sample (isocyanate composition obtained by dissociating the blocking agent from the blocked isocyanate) with an excess of secondary amine, and then back titrating the unreacted secondary amine with hydrochloric acid.

[0058] The content of free isocyanate groups in the blocked isocyanate composition (hereinafter referred to as "free NCO content") may be 0.1 to 1.5 mass%, or may be 0.1 to 1.0 mass%, or 0.1 to 0.5 mass%, from the viewpoint of further enhancing the curability of the coating material. The free NCO content is the amount of free isocyanate groups present in the blocked isocyanate composition expressed in mass% (based on the total mass of the blocked isocyanate composition). The method for measuring the amount of free isocyanate groups to obtain the free NCO content is the same as the method described above.

[0059] From the viewpoint of handleability, the viscosity of the blocked isocyanate composition at 25° C. may be, for example, 500 to 5000 mPa s, 100 to 10000 mPa s, or 10 to 100000 mPa s. The above viscosity is a value measured using a B-type viscometer.

[0060] The blocked isocyanate composition can be used as a curing agent component of a coating composition. Therefore, the blocked isocyanate composition can also be called a curing agent for coating materials.

[0061] <Paint composition> Another embodiment of the present invention is a coating composition comprising a base component (polyol component) and a curing agent component (polyisocyanate component), in which the curing agent comprises the blocked isocyanate composition of the above embodiment as the curing agent component.

[0062] The coating composition may be a one-liquid type composition in which all of the components are contained in one liquid, or a multi-liquid type composition in which the components are present separately in multiple liquids. The multi-liquid type coating composition may include a first liquid containing a base component and a second liquid containing a curing agent component. In this case, the blocked isocyanate composition of the above embodiment is the second liquid.

[0063] The coating composition contains the blocked isocyanate composition of the embodiment as a curing agent component, so that even if it is a one-part coating, the viscosity is unlikely to change over time. Therefore, problems such as non-uniformity of the main component and the curing agent component, which causes a decrease in performance as a coating, are unlikely to occur. For the same reason, the coating composition can form a coating film with excellent transparency.

[0064] The base agent contains, for example, an active hydrogen group-containing compound. Examples of the active hydrogen group include a hydroxy group and an amino group. The average number of functional groups (average number of active hydrogen groups) of the active hydrogen group-containing compound is 2 or more, and preferably 2 to 50. Examples of the active hydrogen-containing compound having such an average number of functional groups include polyols, polyamines, and amino alcohols.

[0065] The number average molecular weight of the active hydrogen group-containing compound is, for example, 500 to 20,000, and preferably 500 to 10,000. Examples of active hydrogen group-containing compounds having such a number average molecular weight include polyurethane resins, polyamide resins, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, acrylic resins, fluororesins, epoxy resins, and cellulose resins (all of which are resins having active hydrogen groups). Furthermore, in consideration of the coating film performance such as gloss, body feel, hardness, durability, flexibility, and drying property, and cost, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, and acrylic resins are preferred.

[0066] The blending ratio of the polyol component and the blocked isocyanate component in the coating composition may be adjusted based on the ratio of the total amount of effective isocyanate groups in the curing agent component to the total amount of active hydrogen groups in the polyol component. The ratio of the total amount of effective isocyanate groups in the curing agent component to the total amount of active hydrogen groups in the base component is preferably 1 / 9 to 9 / 1, more preferably 2 / 8 to 8 / 2, in molar ratio. When the molar ratio is within the above range, good curability is obtained.

[0067] The coating composition can be used as an automotive topcoat paint, anti-chipping paint, electrodeposition paint, paint for automotive parts, paint for automotive repair, pre-coated metal and rust-proof steel plate for metal products such as home appliances and office equipment, paint for building materials, paint for plastics, adhesive, adhesion promoter, sealant, etc.

[0068] <Coating film> Another embodiment of the present invention is a coating film comprising a cured product of the coating composition of the above embodiment.

[0069] The coating film is formed from the coating composition of the embodiment, and includes a cured product of the coating composition. The coating film can be formed by applying the coating composition to a substrate by a known method and curing the coating film (uncured coating film) made of the coating composition. Examples of known methods include roll coating, curtain flow coating, spray coating, electrostatic coating, bell coating, and electrodeposition coating. The amount of coating composition applied and the thickness of the coating film may be appropriately determined depending on the material of the surface to be coated. The curing conditions (e.g., baking conditions) of the coating film made of the coating composition depend on the type of blocking agent and base agent, but in the case of a blocked isocyanate using methyl ethyl ketoxime, it is sufficiently cured by heating at 150 to 160 ° C for 30 minutes. EXAMPLES

[0070] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0071] <Example 1> In a 1-liter four-neck flask equipped with a stirrer, a thermometer, a cooling tube and a nitrogen seal tube, 520 g of Coronate HXLV (Tosoh Corporation, hexamethylene diisocyanate trimer, NCO content 23.0% by mass) as a polyisocyanate and 11 g of 6-(dimethylamino)-1-hexanol (tertiary amino alcohol: Tokyo Chemical Industry Co., Ltd.) were charged, and the flask was replaced with nitrogen, and the reaction temperature was heated to 80 ° C. while stirring, and the reaction was carried out at the same temperature for 2 hours. After adding 250 g of butyl acetate to the resulting reaction liquid and stirring for 30 minutes, 220 g of methyl ethyl ketoxime (Ube Industries, Ltd.) as an oxime-based blocking agent (equivalent ratio to the mixed amount of polyisocyanate (Coronate HXLV) (ratio R in Table 1) is 0.91), and was charged in three separate portions so that the temperature did not exceed 80 ° C. Thereafter, the mixture was kept at 70° C. and stirred for 2 hours to obtain a blocked isocyanate composition of Example 1.

[0072] The effective NCO content and the free NCO content of the blocked isocyanate composition, which were determined by the following method, were 12.0 mass % and 0.2 mass %, respectively.

[0073] (Calculation of effective NCO content) To the blocked isocyanate composition, an excess amount of secondary amine relative to the isocyanate groups was added, and the mixture was heated at a temperature equal to or higher than the dissociation temperature of the oxime-based blocking agent (e.g., 160°C) for a time period during which the blocking agent is sufficiently dissociated (e.g., 1 hour) to react the free isocyanate groups with the secondary amine, and then the unreacted secondary amine was back-titrated with hydrochloric acid to determine the effective NCO content.

[0074] (Calculation of free NCO content) The isocyanate group in the blocked isocyanate composition was reacted with an excess of secondary amine, and then the unreacted secondary amine was back-titrated with hydrochloric acid to determine the free NCO content.

[0075] <Example 2 and Comparative Examples 1 and 2> The blocked isocyanate compositions of Example 2 and Comparative Examples 1-2 were obtained in the same manner as in Example 1, except that the ratio of the amount of the oxime-based blocking agent (methyl ethyl ketoxime) mixed to the amount of the polyisocyanate (Coronate HXLV) mixed was adjusted to the value (ratio R) shown in Table 1 in terms of equivalent ratio. The effective NCO content and the free NCO content of the blocked isocyanate compositions obtained in Example 2 and Comparative Examples 1-2 were calculated in the same manner as in Example 1. The effective NCO content and the free NCO content of the blocked isocyanate composition obtained in Example 2 were 11.8% by mass and 0.6% by mass, respectively. The effective NCO content and the free NCO content of the blocked isocyanate composition obtained in Comparative Example 1 were 12.2% by mass and 1.8% by mass, respectively. The effective NCO content and the free NCO content of the blocked isocyanate composition obtained in Comparative Example 2 were 11.4% by mass and 0% by mass, respectively.

[0076] <Evaluation> (Color resistance evaluation) The resistance to coloration over time of the blocked isocyanate compositions obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was evaluated by storing the blocked isocyanate compositions at 45°C for 4 weeks, measuring the b* value of the blocked isocyanate composition according to the CIE Lab standard before and after storage, and calculating the rate of change in the b* value (initial b* value and b* value after storage) before and after storage using the following formula. The b* value was measured using a spectrophotometer COH7700 manufactured by Nippon Denshoku Industries Co., Ltd. Change in b* value = b* value after storage - initial b* value The evaluation criteria are as follows: A: Change in b* value is between -2 and 2 B: Change in b* value is 2 or more but less than 3, -3 or more but less than -2 C: Change in b* value is 3 or more and less than -3

[0077] (Evaluation of Viscosity Retention) The viscosity retention of the blocked isocyanate compositions obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was evaluated by storing the blocked isocyanate compositions at 45°C for 4 weeks, measuring the viscosity of the blocked isocyanate compositions before and after storage, and calculating the rate of change in viscosity (initial viscosity and viscosity after storage) before and after storage using the following formula. The viscosity was measured at 25°C using a B-type viscometer. Viscosity change rate (unit: %) = |100 × (viscosity after storage - initial viscosity) / initial viscosity| The evaluation criteria are as follows: A: Viscosity change rate is less than 30% B: Viscosity change rate is 30% or more and less than 60% C: Viscosity change rate is 60% or more

[0078] [Table 1]

Claims

1. A method for producing a blocked isocyanate composition, comprising the steps of: The method includes a step of mixing and reacting a polyisocyanate with an oxime-based blocking agent, the ratio of the amount of the oxime-based blocking agent to the amount of the polyisocyanate is 0.91 to 0.99 in terms of equivalent ratio; The method for producing a blocked isocyanate composition, wherein the polyisocyanate comprises an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof modified with a tertiary amino alcohol.

2. The method for producing a blocked isocyanate composition according to claim 1, wherein the ratio of the amount of the oxime-based blocking agent mixed to the amount of the polyisocyanate mixed is 0.91 to 0.95 in terms of equivalent ratio.

3. The present invention includes a blocked isocyanate which is a reaction product of a polyisocyanate and a blocking agent or a derivative thereof, a molar ratio of a total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to a total amount of isocyanate groups contained in the polyisocyanate is 0.91 to 0.99; The blocked isocyanate composition comprises an aliphatic polyisocyanate having 4 to 6 carbon atoms or a derivative thereof, the polyisocyanate being modified with a tertiary amino alcohol.

4. The blocked isocyanate composition according to claim 3, wherein a ratio of a total amount of isocyanate groups blocked with an oxime-based blocking agent contained in the blocked isocyanate to a total amount of isocyanate groups contained in the polyisocyanate is 0.91 to 0.95 in terms of molar ratio.

5. The blocked isocyanate composition of claim 3 , wherein the blocked isocyanate has free isocyanate groups.

6. A coating material curing agent comprising the blocked isocyanate composition according to any one of claims 3 to 5.

7. A coating composition comprising a base component and a curing agent component, A coating composition, wherein the curing agent component comprises the blocked isocyanate composition according to any one of claims 3 to 5.

8. A coating film comprising a cured product of the coating composition according to claim 7.

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