JP7784277B2 - Polyisocyanate composition, coating composition, coating film and coated article - Google Patents

Description

The present invention relates to a polyisocyanate composition, a coating composition, a coating film, and a coated article.

Urethane-based coating compositions using aliphatic polyisocyanates as curing agents are widely used as coatings for automobiles, interior and exterior buildings, home appliances, etc., due to the excellent chemical resistance and flexibility of the coating films they produce. Furthermore, coatings obtained from polyisocyanates derived from aliphatic diisocyanates are widely used because they are non-yellowing and have excellent coating film performance, such as weather resistance.

Among them, isocyanurate-type polyisocyanates having isocyanurate groups are known to have excellent coating film properties such as weather resistance (see, for example, Patent Document 1).
Therefore, in recent years, the amount of isocyanurate-type polyisocyanates used in automobile clear coats has also increased due to their excellent coating film properties such as weather resistance and scratch resistance.

At the same time, in order to reduce VOCs, paints for automobile clear coats are becoming more highly solid. To achieve this, lowering the viscosity of both the acrylic polyols and polyisocyanates used is being considered.

To lower the viscosity of polyisocyanates, technologies that incorporate uretdione groups in addition to isocyanurate groups (see, for example, Patent Document 2) and iminooxadiazinedione groups (see, for example, Patent Document 3) are known.

In addition, for high-solids acrylic polyols, efforts are being made to lower the viscosity while increasing the hydroxyl value and glass transition temperature of the polyol in order to maintain the coating film performance after drying.

Japanese Unexamined Patent Publication No. 55-038380 Patent No. 5178200 Patent No. 5112570

When using common isocyanurate-type polyisocyanates, uretdione group-containing polyisocyanates, or iminooxadiazinedione group-containing polyisocyanates in conjunction with the above-mentioned changes in acrylic polyols, the weather resistance and hardness of the coating film obtained from conventional low-solids coatings may decrease due to factors such as insufficient compatibility with the polyol and a decrease in crosslink density.

The present invention was made in consideration of the above circumstances, and provides a polyisocyanate composition that, when combined with a high-solids acrylic polyol to form a coating composition, reduces the amount of volatile organic solvent used, and when formed into a coating film, provides excellent hardness and weather resistance; as well as a coating composition, coating film, and coated article that use the polyisocyanate composition.

That is, the present invention includes the following aspects.
(1) A polyisocyanate composition comprising a polyisocyanate derived from an aliphatic diisocyanate and an alcohol,
The viscosity at 25°C is 600 mPa s or more and 900 mPa s or less,
the molar ratio of the isocyanurate group to the total molar ratio of the isocyanurate group, the urethane group, the allophanate group, the biuret group, the iminooxadiazinedione group, and the uretdione group, expressed as a/(a+b+c+d+e+f)×100, is 65 mol % or more and 95 mol % or less, where a, b, c, d, e, and f are the molar ratios of the isocyanurate group, the urethane group, the allophanate group, the biuret group, the iminooxadiazinedione group, and the uretdione group contained in the polyisocyanate composition, respectively;
the molar ratio of the allophanate groups to the total molar ratio of the isocyanurate groups, the urethane groups, the allophanate groups, the biuret groups, the iminooxadiazinedione groups, and the uretdione groups, represented by c/(a+b+c+d+e+f)×100, is 3 mol % or more and 25 mol % or less,
The content of uretdione dimer relative to the total mass of the polyisocyanate composition is 3.0 mass% or less, and
A polyisocyanate composition having an average number of isocyanate groups of 3.00 or more and 4.00 or less.
(2) The polyisocyanate composition according to (1), wherein the aliphatic diisocyanate is hexamethylene diisocyanate.
(3) The polyisocyanate composition according to (1) or (2), wherein the alcohol includes a monoalcohol and a dialcohol.
(4) The polyisocyanate composition according to any one of (1) to (3), wherein the molar ratio of the urethane groups to the total molar ratio of the isocyanurate groups, the urethane groups, the allophanate groups, the biuret groups, the iminooxadiazinedione groups, and the uretdione groups, expressed as b/(a+b+c+d+e+f)×100, is 2 mol% or more and 8 mol% or less.
(5) A polyisocyanate composition according to any one of (1) to (4),
a high-solids acrylic polyol having a resin hydroxyl value of 150 mgKOH/g or more and a weight average molecular weight of 8,000 or less;
A coating composition comprising:
(6) A coating film obtained by curing the coating composition according to (5).
(7) A coated article having the coating film according to (6).

The polyisocyanate composition of the above embodiment can reduce the amount of volatile organic solvent used when combined with a high-solids acrylic polyol to form a coating composition, and can provide a polyisocyanate composition that exhibits excellent hardness and weather resistance when formed into a coating film. The coating composition of the above embodiment contains the polyisocyanate composition, reduces the amount of volatile organic solvent used, and exhibits excellent hardness and weather resistance when formed into a coating film. The coating film of the above embodiment is formed by curing the coating composition and exhibits excellent hardness and weather resistance. The coated article of the above embodiment has the coating film and exhibits excellent hardness and weather resistance.

The following provides a detailed description of an embodiment of the present invention (hereinafter, sometimes simply referred to as "the present embodiment"). The following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be implemented with appropriate modifications within the scope of its essence.

In this specification, the term "polyisocyanate" refers to a polymer in which a plurality of diisocyanate monomers each having two isocyanate groups (--NCO) are bonded together.
As used herein, the term "polyol" refers to a compound having two or more hydroxy groups (--OH) and a number average molecular weight of more than 300.
In this specification, unless otherwise specified, the term "coating film" refers to a cured product obtained by curing a coating composition. In other words, a coating film is obtained by curing an uncured coating film.

<Polyisocyanate composition>
The polyisocyanate composition of the present embodiment contains a polyisocyanate derived from an aliphatic diisocyanate and an alcohol.

The polyisocyanate composition of the present embodiment satisfies the following conditions.
1) The viscosity at 25°C is 600 mPa·s or more and 900 mPa·s or less;
2) When the molar ratios of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups contained in the polyisocyanate composition are a, b, c, d, e, and f, respectively, the molar ratio of the isocyanurate groups to the total molar ratio of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups, expressed as a/(a+b+c+d+e+f)×100, is 65 mol% or more and 95 mol% or less,
the molar ratio of the allophanate groups to the total molar ratio of the isocyanurate groups, the urethane groups, the allophanate groups, the biuret groups, the iminooxadiazinedione groups, and the uretdione groups, expressed as c/(a+b+c+d+e+f)×100, is 3 mol % or more and 25 mol % or less;
3) The content of uretdione dimer relative to the total mass of the polyisocyanate composition is 3.0 mass% or less;
4) The average number of isocyanate groups is 3.00 or more and 4.00 or less.

The polyisocyanate composition of this embodiment, having the above-described configuration, can reduce the amount of volatile organic solvent used when combined with a high-solids acrylic polyol to form a coating composition, while also producing a coating film with excellent hardness and weather resistance.

Next, the components of the polyisocyanate composition of this embodiment will be described in detail below.

<Polyisocyanate>
The polyisocyanate is derived from an aliphatic diisocyanate and an alcohol, i.e., is the reaction product of an aliphatic diisocyanate and an alcohol.

[Aliphatic diisocyanate]
The aliphatic diisocyanate used in producing the polyisocyanate preferably has 4 to 30 carbon atoms. Examples of such aliphatic diisocyanates include tetramethylene-1,4-diisocyanate, pentamethylene-1,5-diisocyanate, hexamethylene diisocyanate (hereinafter referred to as "HDI"), 2,2,4-trimethyl-hexamethylene-1,6-diisocyanate, and lysine diisocyanate. These aliphatic diisocyanates may be used alone or in combination of two or more. Of these, HDI is preferred because of its ease of industrial availability.

[Other diisocyanates]
As the diisocyanate used in producing the polyisocyanate, in addition to the above-mentioned aliphatic diisocyanates, other diisocyanates such as isophorone diisocyanate (hereinafter referred to as "IPDI") can also be used in combination, if necessary, within a range that does not impair the effects achieved by the polyisocyanate composition of the present embodiment.

[alcohol]
The alcohol used in the production of polyisocyanate is preferably a compound consisting of only carbon, oxygen, and hydrogen, and examples thereof include monoalcohols and dialcohols.

Preferably, the monoalcohol is a straight-chain or branched-chain alcohol having from 1 to 9 carbon atoms, or an alicyclic alcohol. Examples of such monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, n-octanol, n-nonanol, 2-ethylbutanol, 2,2-dimethylhexanol, 2-ethylhexanol, cyclohexanol, methylcyclohexanol, and ethylcyclohexanol. These monoalcohols may be used alone, or two or more may be used in combination.

Examples of dialcohols include 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol. These dialcohols may be used alone or in combination of two or more.

Among these, monoalcohols with 4 to 9 carbon atoms are preferred. Using such monoalcohols can increase the hardness of the resulting coating film.

It is also preferable to use a monoalcohol and a dialcohol in combination. By using a dialcohol, the average number of isocyanate groups can be increased.

The polyisocyanate composition of this embodiment contains an isocyanurate group and an allophanate group, but may also contain a polyisocyanate having an isocyanurate group and an allophanate group in the molecule, or may contain a polyisocyanate having an isocyanurate group in the molecule and a polyisocyanate having an allophanate group in the molecule, or may contain a mixture thereof.

The term "isocyanurate group" refers to a functional group derived from a polyisocyanate consisting of three diisocyanate monomer molecules, and is a group represented by the following formula (I). Furthermore, a polyisocyanate consisting of three diisocyanate monomer molecules, and a compound represented by the following general formula (I-1), is referred to as an isocyanurate trimer or isocyanurate-type polyisocyanate.

In the general formula (I-1), R ¹¹ , R ¹² and R ¹³ are each independently a saturated hydrocarbon group. The number of carbon atoms in the saturated hydrocarbon group for ^{R 11} and R ¹² is preferably from 4 to 30, more preferably from 4 to 16, and even more preferably from 4 to 8. Of these, R ¹¹ , R ¹² and R ¹³ are particularly preferably a hexamethylene group having 6 carbon atoms.

In the polyisocyanate composition of this embodiment, the content of the isocyanurate trimer is not particularly limited, but is preferably 55% by mass or more and 95% by mass or less, and more preferably 60% by mass or more and 95% by mass or less, relative to the total mass of the polyisocyanate composition. When the content of the isocyanurate trimer is equal to or greater than the above-mentioned lower limit, the viscosity of the polyisocyanate composition can be further reduced. On the other hand, when the content of the isocyanurate trimer is equal to or less than the above-mentioned upper limit, the yield of the polyisocyanate composition can be further increased.
The content of the isocyanurate trimer can be measured by gel permeation chromatography (hereinafter sometimes abbreviated as "GPC").

Furthermore, in the polyisocyanate composition of this embodiment, when the molar ratios of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups contained in the polyisocyanate composition are a, b, c, d, e, and f, respectively, the molar ratio of the isocyanurate groups to the total molar ratio of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups, expressed as a/(a+b+c+d+e+f)×100, is 65 mol% or more and 95 mol% or less, preferably 70 mol% or more and 92 mol% or less, and more preferably 75 mol% or more and 90 mol% or less. When the molar ratio of isocyanurate groups is at or above the above lower limit, the weather resistance of the resulting coating film tends to be excellent, and when it is at or below the above upper limit, compatibility with high-solids acrylic polyols is excellent, allowing it to be combined with high-solids acrylic polyols to produce high-solids coatings.

The molar ratio of each functional group, such as an isocyanurate group, can be determined quantitatively by ¹³ C-NMR measurement.
The specific measurement conditions are as follows:

(Measurement conditions)
^13C -NMR device: AVANCE 600 (manufactured by Bruker BioSpin)
Cryoprobe: CP DUL 600S3 C/H-D-05 Z
(Manufactured by Bruker Biospin)
Resonance frequency: 150MHz
Concentration: 60wt/vol%
Shift reference: CDCl ₃ (77 ppm)
Number of accumulations: 10,000 Pulse program: zgpg30 (proton complete decoupling method, waiting time 2 seconds)

(Characteristic peaks (chemical shift values) in polyisocyanate compositions)
Isocyanurate group: 148.5 ppm: integrated value ÷ 3
Urethane group: 156.3 ppm: integrated value ÷ 1
Allophanate group: Around 154 ppm: Integrated value ÷ 1
Buret group: 155.8 ppm: (integral value - allophanate group integral value) ÷ 2
Iminooxadiazinedione group: 137.3 ppm: integrated value divided by 1
Uretdione group: 157.5 ppm: integrated value ÷ 2

The allophanate group has the structure shown in formula (II) below.

In the polyisocyanate composition of the present embodiment, when the molar ratios of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups contained in the polyisocyanate composition are a, b, c, d, e, and f, respectively, the molar ratio of the allophanate groups to the total molar ratio of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups, expressed as c/(a+b+c+d+e+f)×100, is 3 mol% or more and 25 mol% or less, preferably 5 mol% or more and 23 mol% or less, and more preferably 7 mol% or more and 20 mol% or less.
When the molar ratio of allophanate groups is equal to or greater than the above lower limit, the compatibility with high-solid acrylic polyols is excellent, and a high-solid coating material can be obtained by combining with a high-solid acrylic polyol. On the other hand, when the molar ratio of allophanate groups is equal to or less than the above upper limit, the resulting coating film tends to have high coating film hardness.
The molar ratio of allophanate groups can be calculated by quantifying the molar ratio of each functional group using the measurement method described above for the molar ratio of isocyanurate groups.

The polyisocyanate composition of the present embodiment preferably has a urethane group in addition to an isocyanurate group and an allophanate group.
The urethane group is a functional group formed from 1 mole of an NCO group of an aliphatic diisocyanate and 1 mole of an OH group of an alcohol, and has a structure represented by the following formula (III).

In the polyisocyanate composition of the present embodiment, when the molar ratios of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups contained in the polyisocyanate composition are a, b, c, d, e, and f, respectively, the molar ratio of the urethane groups to the total molar ratio of the isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups, expressed as b/(a+b+c+d+e+f)×100, is preferably 2 mol % or more and 8 mol % or less, and more preferably 4 mol % or more and 6 mol % or less.
When the molar ratio of urethane groups is equal to or greater than the above lower limit, the compatibility with high-solid acrylic polyols is excellent, and high-solid coating materials can be obtained by combining with high-solid acrylic polyols. On the other hand, when the molar ratio of urethane groups is equal to or less than the above upper limit, the weather resistance of the resulting coating film tends to be excellent.
The molar ratio of the urethane group can be calculated by quantifying the molar ratio of each functional group using the measurement method described above for the molar ratio of the isocyanurate group.

The polyisocyanate composition of the present embodiment may further have, in addition to the isocyanurate group and allophanate group, one or more functional groups selected from the group consisting of a biuret group, an iminooxadiazinedione group, and a uretdione group.
The biuret group has the structure shown in formula (IV) below.
The iminooxadiazinedione group has the structure shown in formula (V) below.
The uretdione group has a structure represented by the following general formula (VI):
Furthermore, a polyisocyanate consisting of two molecules of aliphatic diisocyanate and represented by the following general formula (VI-1) is called a uretdione dimer or a uretdione-type polyisocyanate.

In the general formula (VI-1), R ⁶¹ and R ⁶² each independently represent a saturated hydrocarbon group. The number of carbon atoms in the saturated hydrocarbon group for ^{R 61} and R ⁶² is preferably from 4 to 30, more preferably from 4 to 16, and even more preferably from 4 to 8. Of these, R ⁶¹ and R ⁶² are particularly preferably hexamethylene groups having 6 carbon atoms.
Furthermore, the polyisocyanate composition of the present embodiment may further have functional groups such as urea groups and carbodiimide groups in addition to the isocyanurate groups and allophanate groups.

In the polyisocyanate composition of the present embodiment, the content of the uretdione dimer is 3.0% by mass or less, preferably 2.8% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less, relative to the total mass of the polyisocyanate composition.
When the content of the uretdione dimer is equal to or less than the upper limit, the average number of isocyanurates can be maintained at a higher level.
The lower limit of the content of the uretdione dimer is not particularly limited, but can be, for example, 0.0 mass % or 1.0 mass %.
The content of uretdione dimer can be measured, for example, by GPC.
Specifically, it is calculated as a number average molecular weight using polystyrene as a standard by GPC under the following measurement conditions.

(Measurement conditions)
Apparatus: "HLC-8120GPC" (product name) manufactured by Tosoh Corporation
Column: Tosoh Corporation "TSKgel Super H1000" (product name) x 1
"TSKgel Super H2000" (product name) x 1
"TSKgel Super H3000" (product name) x 1 Carrier: Tetrahydrofuran (THF)
Detection method: differential refractometer Sample concentration: 5 wt/vol%
Detection method: Parallax refractometer Flow rate: 0.6 mL/min
Column temperature: 40°C

<Method for producing polyisocyanate composition>
The polyisocyanate composition of the present embodiment can be produced by using the above-mentioned aliphatic diisocyanate to carry out a reaction to form an isocyanurate group, an allophanate group, and, as necessary, other functional groups such as a urethane group.

[Method for producing isocyanurate-type polyisocyanate]
The isocyanurate-type polyisocyanate can be obtained by reacting a diisocyanate monomer containing the above-mentioned aliphatic diisocyanate with an isocyanurate catalyst and an alcohol as a co-catalyst.

Examples of isocyanuration catalysts used in the production of isocyanurate-type polyisocyanates include sodium salts, potassium salts, and quaternary ammonium salts of fatty acids.

Examples of fatty acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid. These fatty acids may be linear or branched.

Examples of quaternary ammonium include tetramethylammonium, tetrabutylammonium, butyltrimethylammonium, benzyltrimethylammonium, dibenzyldimethylammonium, and phenyltrimethylammonium.

The amount of isocyanurate catalyst used varies depending on the amounts of co-catalyst and solvent used, but typically, when HDI is used as a raw material for polyisocyanate, it can be 0.001% by mass or more and 0.05% by mass or less relative to the mass of HDI.

As the alcohol promoter, for example, a phenolic hydroxy compound or an alcoholic hydroxy compound can be used, which allows the isocyanurate reaction to proceed more easily.
Examples of the phenolic hydroxy compound include phenol, cresol, and trimethylphenol.
Examples of the alcoholic hydroxy compound include linear alcohols, branched alcohols, cyclic alcohols, and polyhydric alcohols.
Examples of the linear alcohol include methanol, ethanol, propanol, n-butanol, and 1-hexanol.
Examples of branched chain alcohols include isobutanol and 2-ethylhexanol.
Examples of cyclic alcohols include cyclohexanol.
The polyhydric alcohol includes, for example, ethylene glycol.

The amount of alcohol used correlates with the amount of isocyanurate groups present in the polyisocyanate contained in the polyisocyanate composition. When HDI is used as a polyisocyanate raw material, the amount of alcohol used is preferably 500 ppm or more and 30,000 ppm or less by mass relative to HDI. By using an amount of alcohol below the above upper limit, the proportion of isocyanurate groups present in the polyisocyanate contained in the final polyisocyanate composition is maintained at an appropriate level, resulting in better weather resistance and chemical resistance. On the other hand, by using an amount of alcohol above the above lower limit, the reaction rate is maintained at a high level, resulting in better productivity in terms of economic efficiency.

In the production of isocyanurate-type polyisocyanates, the timing of alcohol addition should be such that the alcohol is present in the reaction system during the isocyanuration reaction. Specifically, the alcohol may be added before the isocyanuration reaction, simultaneously with the isocyanuration catalyst, or during the isocyanuration reaction after the addition of the isocyanuration catalyst is complete. The alcohol may be added at any one of these times, or at all of these times. The alcohol may be added all at once or continuously. However, from the perspective of reaction and heat generation control, continuous addition is preferred for alcohol addition during the isocyanuration reaction. From the perspective of economics, bulk addition is preferred for alcohol addition before the isocyanuration reaction.

The isocyanuration reaction temperature is preferably 70°C or lower, and more preferably 30°C to 65°C. By setting the isocyanuration reaction temperature at or below the upper limit, a polyisocyanate with better color can be obtained. On the other hand, by setting the isocyanuration reaction temperature at or above the lower limit, the reaction rate can be maintained at a more appropriate level, resulting in better productivity from an economical perspective.

The reaction time varies depending on the amount of catalyst, the amount and addition method of the alcohol co-catalyst, and the reaction temperature, but can usually be set to between 1 hour and 6 hours.

The decrease in the isocyanate group content (NCO %) that accompanies the progress of isocyanuration can be measured by titration analysis, so the reaction can be stopped when a predetermined NCO % is reached.
The NCO % and viscosity of the isocyanurate polyisocyanate can be freely changed depending on the NCO % at the time of stopping the reaction.

An acidic compound can be used as a reaction terminator. Examples of acidic compounds include hydrochloric acid, phosphoric acid, dimethyl phosphate, diethyl phosphate, dibutyl phosphate, di-2-ethylhexyl phosphate, dicyclohexyl phosphate, p-toluenesulfonic acid, benzenesulfonic acid, alkylbenzenesulfonic acid, acetyl chloride, and benzoyl chloride. Similar compounds to these acidic compounds may also be used.

The amount of reaction terminator used can be 0.5 to 10 times the molar amount, and preferably 1 to 8 times the molar amount, per mole of carboxylic acid in the isocyanuration catalyst. When using a reaction terminator that is soluble in the mixed solution of the diisocyanate monomer raw material and the polyisocyanate produced by the reaction, the amount can be approximately 1 time the molar amount per mole of carboxylic acid in the isocyanuration catalyst. When using an insoluble reaction terminator, the amount can be 2 to 8 times the molar amount per mole of carboxylic acid in the isocyanuration catalyst.

After adding the reaction terminator, heat curing may be performed to complete the termination reaction. If heat curing is performed, the temperature is preferably 80°C or higher and 150°C or lower, more preferably 80°C or higher and 130°C or lower, and even more preferably 90°C or higher and 120°C or lower. By maintaining a temperature at or below the upper limit, it is possible to further suppress the reduction in 1-nylon units in the resulting polyisocyanate component containing isocyanurate-type polyisocyanate, and further to suppress a decrease in color and an increase in viscosity due to the progress of isocyanurate-type polyisocyanate polymerization. By maintaining a temperature at or above the lower limit, it is possible to more quickly grow the salt produced by the termination reaction. Particularly in the case of a combination of a catalyst that forms an insoluble salt and a reaction terminator, it is possible to form more salts of a size that can be filtered out, resulting in better productivity from an economic perspective.

The optimal heat curing time varies depending on the temperature, but can be between 10 and 120 minutes, preferably between 10 and 90 minutes, and more preferably between 10 and 60 minutes. Depending on the temperature, keeping the time below the upper limit can further suppress discoloration and increased viscosity due to further polymerization of the polyisocyanate. On the other hand, keeping the time above the lower limit can ensure more sufficient salt formation and growth, and in the case of insoluble salts, can more easily separate them by filtration.

[Polyisocyanate having allophanate groups]
A polyisocyanate having an allophanate group (allophanate group-containing polyisocyanate) can be obtained by using an aliphatic diisocyanate monomer in combination with an alcohol compound or the like, and by using an allophanate reaction catalyst.

The alcohol compound used in the production of allophanate group-containing polyisocyanates is not limited to the following, but alcohols formed only from carbon, hydrogen, and oxygen are preferred. Furthermore, the alcohol compound preferably has a molecular weight of 200 or less.

Examples of alcohol compounds include monoalcohols and dialcohols.
Examples of the monoalcohol include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, and nonanol.
Examples of the dialcohol include ethylene glycol, 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol.
These alcohol compounds may be used alone or in combination of two or more.
Among these, monoalcohols are preferred as alcohol compounds.

The amount of alcohol compound used is not limited to the following, but the molar ratio of the isocyanate groups of the aliphatic diisocyanate monomer to the hydroxyl groups of the alcohol compound is preferably 10/1 or more and 1000/1 or less, and more preferably 100/1 or more and 1000/1 or less. By using an amount above the above lower limit, a more appropriate average number of isocyanate groups can be ensured in the resulting polyisocyanate.

The allophanatization reaction catalyst includes, but is not limited to, alkyl carboxylates of tin, lead, zinc, bismuth, zirconium, zirconyl, and the like.
Examples of tin alkylcarboxylates (organotin compounds) include tin 2-ethylhexanoate and dibutyltin dilaurate.
Examples of lead alkylcarboxylates (organic lead compounds) include lead 2-ethylhexanoate.
Examples of zinc alkylcarboxylates (organic zinc compounds) include zinc 2-ethylhexanoate.
Examples of the alkyl carboxylate of bismuth include bismuth 2-ethylhexanoate.
Examples of zirconium alkylcarboxylates include zirconium 2-ethylhexanoate.
Examples of zirconyl alkylcarboxylates include zirconyl 2-ethylhexanoate.

When the desired yield is achieved, the allophanation reaction can be stopped by adding an allophanation reaction catalyst deactivator such as phosphoric acid or methyl p-toluenesulfonate.

The amount of the allophanate reaction catalyst used is, by mass ratio relative to the raw material diisocyanate, preferably 10 ppm to 10,000 ppm, more preferably 10 ppm to 1,000 ppm, and even more preferably 10 ppm to 500 ppm.

The lower limit of the reaction temperature for allophanatization is preferably 60° C., more preferably 70° C., even more preferably 80° C., and particularly preferably 90° C. On the other hand, the upper limit of the reaction temperature for allophanatization is preferably 160° C., more preferably 155° C., even more preferably 150° C., and particularly preferably 145° C.
That is, the reaction temperature for allophanation is preferably 60°C or higher and 160°C or lower, more preferably 70°C or higher and 155°C or lower, even more preferably 80°C or higher and 150°C or lower, and particularly preferably 90°C or higher and 145°C or lower.

By keeping the allophanate formation reaction temperature at or below the above upper limit, changes in properties such as coloration of the resulting polyisocyanate can be more effectively prevented.
The lower limit of the reaction time is preferably 0.2 hours, more preferably 0.4 hours, even more preferably 0.6 hours, particularly preferably 0.8 hours, and most preferably 1.0 hour, while the upper limit of the reaction time is preferably 8 hours or less, more preferably 6 hours, even more preferably 4 hours, particularly preferably 3 hours, and most preferably 2 hours.
That is, the reaction time for allophanation is preferably from 0.2 to 8 hours, more preferably from 0.4 to 6 hours, even more preferably from 0.6 to 4 hours, particularly preferably from 0.8 to 3 hours, and most preferably from 1.0 to 2 hours.
By setting the reaction time for allophanation to not less than the above lower limit, it is possible to achieve a lower viscosity, and by setting it to not more than the above upper limit, it is possible to further suppress coloration of the polyisocyanate itself.

The isocyanurate formation catalyst can also be used as an allophanate formation catalyst. When the allophanate formation reaction is carried out using the isocyanurate formation catalyst, an isocyanurate polyisocyanate is also produced at the same time. In particular, from the viewpoint of improving productivity from an economical standpoint, it is preferable to use the isocyanurate formation catalyst as the allophanate formation catalyst to carry out the allophanate formation reaction and the isocyanurate formation reaction.
The isocyanurate formation reaction and the uretdione formation reaction can be carried out sequentially or in parallel.
Furthermore, when an allophanate formation reaction is involved, it is preferable to carry out the isocyanurate formation reaction and the allophanate formation reaction in parallel and then carry out the uretdione formation reaction, since this simplifies the production process.

The allophanatization reaction can be terminated when the desired allophanate group content is reached.

The allophanation reaction can be terminated by adding an acidic compound to the reaction solution, such as, but not limited to, phosphoric acid, acidic phosphate ester, sulfuric acid, hydrochloric acid, or a sulfonic acid compound. This allows the allophanation reaction catalyst to be inactivated by neutralization, thermal decomposition, or chemical decomposition. After the reaction has been terminated, filtration may be performed if necessary.

[Method for producing uretdione-type polyisocyanate]
The uretdione-type polyisocyanate can be obtained by using a uretdione reaction catalyst.

The uretdione-forming reaction catalyst includes, but is not limited to, tertiary phosphines such as trialkylphosphines, tris(dialkylamino)phosphines, and cycloalkylphosphines.
Examples of trialkylphosphines include tri-n-butylphosphine and tri-n-octylphosphine.
Examples of tris(dialkylamino)phosphines include tris-(dimethylamino)phosphine.
Examples of cycloalkylphosphines include cyclohexyl-di-n-hexylphosphine.
Many of these compounds also promote the isocyanuration reaction at the same time, producing an isocyanurate-type polyisocyanate in addition to a uretdione dimer.

When the desired yield is reached, the uretdione formation reaction is stopped by adding a deactivator for the uretdione formation catalyst, such as phosphoric acid or methyl paratoluenesulfonate.

The amount of the uretdione reaction catalyst used is preferably 10 ppm or more and 10,000 ppm or less, more preferably 10 ppm or more and 1,000 ppm or less, and even more preferably 10 ppm or more and 500 ppm or less, by mass ratio relative to the diisocyanate raw material.
The lower limit of the reaction temperature for uretdione formation is preferably 20° C., more preferably 25° C., even more preferably 30° C., and particularly preferably 35° C. On the other hand, the upper limit of the reaction temperature for uretdione formation is preferably 120° C., more preferably 110° C., even more preferably 100° C., and particularly preferably 90° C.
That is, the reaction temperature for uretdione formation is preferably 20°C or higher and 120°C or lower, more preferably 25°C or higher and 110°C or lower, even more preferably 30°C or higher and 100°C or lower, and particularly preferably 35°C or higher and 90°C or lower.
By keeping the reaction temperature for uretdione formation at or below the above upper limit, changes in the properties of the resulting polyisocyanate component, such as coloration, can be more effectively prevented.

Uretodione-type polyisocyanates can also be obtained by heating diisocyanate monomers without using the uretdione reaction catalyst.

When the uretdione reaction catalyst is not used, the lower limit of the heating temperature of the diisocyanate monomer is preferably 120° C., more preferably 130° C., even more preferably 140° C., and particularly preferably 145° C. On the other hand, the upper limit of the heating temperature of the diisocyanate monomer is preferably 180° C., more preferably 175° C., even more preferably 170° C., and particularly preferably 165° C.
That is, the heating temperature of the diisocyanate monomer is preferably 120°C or higher and 180°C or lower, more preferably 130°C or higher and 175°C or lower, even more preferably 140°C or higher and 170°C or lower, and particularly preferably 145°C or higher and 165°C or lower.

When the uretdione formation catalyst is not used, the lower limit of the heating time is preferably 0.2 hours, more preferably 0.4 hours, even more preferably 0.6 hours, particularly preferably 0.8 hours, and most preferably 1.0 hour, while the upper limit of the heating time is preferably 8 hours, more preferably 6 hours, even more preferably 4 hours, particularly preferably 3 hours, and most preferably 2 hours.
That is, the heating time is preferably 0.2 hours or more and 8 hours or less, more preferably 0.4 hours or more and 6 hours or less, even more preferably 0.6 hours or more and 4 hours or less, particularly preferably 0.8 hours or more and 3 hours or less, and most preferably 1.0 hours or more and 2 hours or less.
By setting the heating time to the above lower limit or more, it is possible to achieve a lower viscosity, and by setting it to the above upper limit or less, it is possible to further suppress coloration of the polyisocyanate itself.
When a polyisocyanate component is obtained without using a uretdione formation reaction catalyst, it is preferable to remove the unreacted diisocyanate monomer after the uretdione formation reaction by heating alone and the above-described isocyanurate formation reaction are completed, from the viewpoints of reducing the concentration of unreacted diisocyanate monomer, reducing the rate of change in molecular weight of the obtained polyisocyanate component after storage, and reducing yellowing during high-temperature baking.

[Method for producing polyisocyanate having urethane groups]
Polyisocyanates having urethane groups (urethane group-containing polyisocyanates) can be obtained by using an aliphatic diisocyanate monomer in combination with an alcohol compound or the like, and heating or using a urethanization reaction catalyst.

The alcohol compound used in producing the urethane group-containing polyisocyanate is not particularly limited, but the alcohol compounds described above for the allophanate group-containing polyisocyanate can be used.

The amount of alcohol compound used is not limited to the following, but the molar ratio of the isocyanate groups of the aliphatic diisocyanate monomer to the hydroxyl groups of the alcohol compound is preferably 10/1 or more and 1000/1 or less, and more preferably 100/1 or more and 1000/1 or less. By using an amount above the above lower limit, a more appropriate average number of isocyanate groups can be ensured in the resulting polyisocyanate.

When the urethanization reaction is carried out by heating alone, the lower limit of the reaction temperature is preferably 30° C., more preferably 40° C., and even more preferably 50° C. On the other hand, the upper limit of the urethanization reaction temperature is preferably 120° C., more preferably 100° C., and even more preferably 80° C.
That is, the reaction temperature for urethanization is preferably 30°C or higher and 120°C or lower, more preferably 40°C or higher and 100°C or lower, and even more preferably 50°C or higher and 80°C or lower.

When the urethanization reaction temperature is equal to or higher than the above lower limit, the reaction time can be shortened, and when the temperature is equal to or lower than the above upper limit, changes in the properties such as coloration of the resulting polyisocyanate can be more effectively prevented.
The lower limit of the reaction time is preferably 0.2 hours, more preferably 0.4 hours, even more preferably 0.6 hours, particularly preferably 0.8 hours, and most preferably 1.0 hour, while the upper limit of the reaction time is preferably 8 hours or less, more preferably 6 hours, even more preferably 4 hours, particularly preferably 3 hours, and most preferably 2 hours.
That is, the urethanization reaction time is preferably 0.2 hours or more and 8 hours or less, more preferably 0.4 hours or more and 6 hours or less, even more preferably 0.6 hours or more and 4 hours or less, particularly preferably 0.8 hours or more and 3 hours or less, and most preferably 1.0 hours or more and 2 hours or less.
By setting the urethanization reaction time to the above lower limit or more, it is possible to achieve a lower viscosity, and by setting it to the above upper limit or less, it is possible to further suppress coloration of the polyisocyanate itself.
When a urethane reaction catalyst is used, examples thereof include, but are not limited to, alkyl carboxylates of tin, and tertiary amine compounds.
Examples of tin alkylcarboxylates (organotin compounds) include tin 2-ethylhexanoate and dibutyltin dilaurate.
Examples of the tertiary amine compound include triethylamine, tripropylamine, tributylamine, triphenylamine, dimethylethanolamine, and DABCO.

When the desired yield is achieved, the urethanization reaction can be stopped by adding an allophanation reaction catalyst deactivator such as phosphoric acid or methyl p-toluenesulfonate.

The amount of the urethane reaction catalyst used is preferably 10 ppm or more and 1,000 ppm or less, more preferably 10 ppm or more and 500 ppm or less, and even more preferably 10 ppm or more and 300 ppm or less, by mass ratio relative to the diisocyanate raw material.

When a urethanization reaction catalyst is used, the lower limit of the urethanization reaction temperature is preferably 30° C., more preferably 40° C., and even more preferably 50° C. On the other hand, the upper limit of the urethanization reaction temperature is preferably 90° C., more preferably 80° C., and even more preferably 70° C.
That is, the reaction temperature for urethanization is preferably 30°C or higher and 90°C or lower, more preferably 40°C or higher and 80°C or lower, and even more preferably 50°C or higher and 70°C or lower.

When the urethanization reaction temperature is equal to or higher than the above-mentioned lower limit, the reaction time can be shortened, and when the temperature is equal to or lower than the upper limit, the ratio of urethane groups to allophanate groups can be adjusted, thereby maintaining the ratio of urethane groups and more effectively preventing changes in properties such as coloration.
The lower limit of the reaction time is preferably 0.2 hours, more preferably 0.4 hours, even more preferably 0.6 hours, particularly preferably 0.8 hours, and most preferably 1.0 hour, while the upper limit of the reaction time is preferably 8 hours or less, more preferably 6 hours, even more preferably 4 hours, particularly preferably 3 hours, and most preferably 2 hours.
That is, the urethanization reaction time is preferably 0.2 hours or more and 8 hours or less, more preferably 0.4 hours or more and 6 hours or less, even more preferably 0.6 hours or more and 4 hours or less, particularly preferably 0.8 hours or more and 3 hours or less, and most preferably 1.0 hours or more and 2 hours or less.
By setting the urethanization reaction time to the above lower limit or more, it is possible to achieve a lower viscosity, and by setting it to the above upper limit or less, it is possible to further suppress coloration of the polyisocyanate itself.

Furthermore, when a urethane-formation reaction is involved, it is preferable to carry out the isocyanurate-formation reaction, urethane-formation reaction, and allophanate-formation reaction in parallel, followed by the urethodione-formation reaction, since this simplifies the manufacturing process.

The urethanization reaction can be stopped when the desired urethane group content is reached.

The urethane-forming reaction can be terminated by adding an acidic compound to the reaction solution, such as, but not limited to, phosphoric acid, acidic phosphate ester, sulfuric acid, hydrochloric acid, or a sulfonic acid compound. This allows the urethane-forming reaction catalyst to be inactivated by neutralization, thermal decomposition, or chemical decomposition. After the reaction has been terminated, filtration may be performed if necessary.

[Thin film distillation process and heat treatment process]
The reaction mixture immediately after the reaction has been stopped usually contains unreacted diisocyanate monomers such as HDI, and it is therefore preferable to remove these by a thin film evaporator, extraction or the like.
The thin film distillation process is a process for increasing the efficiency of separation of low boiling components from high boiling components. Specific countermeasures include, for example, reducing the flow rate to extend the residence time, increasing the temperature during distillation, increasing the wiper rotation speed, and increasing the number of distillation cycles, and any of these methods may be selected. Among these, increasing the number of distillation cycles is preferred for the purpose of reducing the thermal history and increasing the separation efficiency. The number of distillation cycles is preferably 1 to 5.

The content of diisocyanate monomer remaining in the polyisocyanate composition is preferably 0.50% by mass or less, more preferably 0.40% by mass or less, even more preferably 0.30% by mass or less, particularly preferably 0.20% by mass or less, and most preferably 0.10% by mass or less.
By keeping the content of the diisocyanate monomer remaining in the polyisocyanate composition at or below the upper limit, the toxicity of the polyisocyanate composition can be further reduced, and safety can be further improved. Furthermore, by keeping the content at or below 0.10 mass%, a coating film with particularly excellent finished appearance can be obtained.

<Characteristics of Polyisocyanate Composition>
[Isocyanate group content]
The lower limit of the isocyanate group content (NCO content) of the polyisocyanate composition of this embodiment is preferably 18.0 mass%, more preferably 19.0 mass%, and even more preferably 20.0 mass%, while the upper limit of the NCO content is preferably 25.0 mass%, more preferably 24.5 mass%, and even more preferably 24.0 mass%.
That is, the NCO content of the polyisocyanate composition (A) is preferably 18.0 mass % or more and 25.0 mass % or less, more preferably 19.0 mass % or more and 24.5 mass % or less, and even more preferably 20.0 mass % or more and 24.0 mass % or less.
When the NCO content is equal to or greater than the lower limit, the physical properties of the resulting coating film, such as hardness, can be improved. On the other hand, when the NCO content is equal to or less than the upper limit, the yield of the polyisocyanate composition can be increased.
The NCO content can be determined by neutralizing the isocyanate groups of the polyisocyanate composition with an excess of 2N amine, followed by back titration with 1N hydrochloric acid.
The NCO content is a value relative to the solid content of the polyisocyanate composition. The solid content of the polyisocyanate component can be determined from the amount remaining when the polyisocyanate composition is heated at 105°C for 3 hours.

[Number average molecular weight]
The lower limit of the number average molecular weight of the solid content of the polyisocyanate composition of the present embodiment is preferably 400, more preferably 450, and even more preferably 500. On the other hand, the upper limit of the number average molecular weight is preferably 1,000, more preferably 900, and even more preferably 800.
That is, the number average molecular weight of the solid content in the polyisocyanate composition is preferably 400 or more and 1,000 or less, more preferably 450 or more and 900 or less, and even more preferably 500 or more and 800 or less.
When the number average molecular weight is equal to or greater than the lower limit, the yield of the polyisocyanate composition tends to be improved. On the other hand, when the number average molecular weight is equal to or less than the upper limit, the compatibility with high-solid acrylic polyol is excellent, and therefore the amount of volatile organic solvent used can be further reduced when the coating composition is prepared in combination with the high-solid acrylic polyol.

[Average number of isocyanate groups]
The average number of isocyanate groups in the polyisocyanate composition of the present embodiment is 3.00 or more and 4.00 or less, preferably 3.01 or more and 3.80 or less, more preferably 3.03 or more and 3.50 or less, and even more preferably 3.05 or more and 3.30 or less.
When the average number of isocyanate groups is equal to or greater than the above lower limit, a coating film with excellent weather resistance can be obtained. On the other hand, when the average number of isocyanate groups is equal to or less than the above upper limit, the viscosity of the polyisocyanate composition becomes low, and the viscosity of the resulting coating composition can be reduced, resulting in a high-solids coating that can be applied even if the solid content is relatively high.

The average number of isocyanate groups (Fn) in the polyisocyanate composition of this embodiment can be calculated using the following formula. In the formula, Mn is the number average molecular weight of the polyisocyanate component, and the NCO content is the content (mass%) of isocyanate groups in the polyisocyanate component.

Fn=(Mn×NCO content×0.01)/42

[viscosity]
The viscosity of the polyisocyanate composition of the present embodiment, measured at 25°C, is 600 mPa·s or more and 900 mPa·s or less, preferably 650 mPa·s or more and 880 mPa·s or less, and more preferably 700 mPa·s or more and 860 mPa·s or less.
When the viscosity is equal to or greater than the above lower limit, the weather resistance of the resulting coating film tends to be excellent. On the other hand, when the viscosity is equal to or less than the above upper limit, the viscosity of the resulting coating composition can be further reduced, resulting in a high-solids coating that can be applied even if the solid content is relatively high.
The viscosity can be measured by using an E-type viscometer (manufactured by Tokimec Co., Ltd.) on a polyisocyanate composition purified to a non-volatile component (solid content) of 99.5% by mass or more. Specifically, the viscosity can be measured by the method described in the examples below.

≪Paint composition≫
The coating composition of the present embodiment is
The polyisocyanate composition;
a high-solids acrylic polyol having a resin hydroxyl value of 150 mgKOH/g or more and a weight average molecular weight of 8,000 or less;
Includes.

By having the above-described configuration, the coating composition of this embodiment reduces the amount of volatile organic solvent used, and when formed into a coating film, it exhibits excellent hardness and weather resistance.

The components of the coating composition of this embodiment are described in detail below.

<High-solids acrylic polyol>
The high-solid acrylic polyol can be obtained, for example, by copolymerizing a (meth)acrylate monomer having one or more active hydrogen-containing groups in one molecule with another monomer copolymerizable with the (meth)acrylate monomer.

Examples of (meth)acrylate monomers having one or more active hydrogen-containing groups per molecule include acrylic acid esters having an active hydrogen-containing group, methacrylic acid esters having an active hydrogen-containing group, (meth)acrylic acid esters having a polyvalent active hydrogen-containing group, monoethers of polyether polyols and (meth)acrylic acid esters having the above-mentioned active hydrogen-containing groups, adducts of glycidyl (meth)acrylate and monobasic acids, and adducts obtained by ring-opening polymerization of lactones with the active hydrogen-containing groups of the above-mentioned (meth)acrylic acid esters having active hydrogen-containing groups. These may be used alone or in combination of two or more.

Examples of acrylic esters having an active hydrogen-containing group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate.

Examples of methacrylic acid esters having an active hydrogen-containing group include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate.

Examples of the (meth)acrylic acid esters having a polyvalent active hydrogen-containing group include (meth)acrylic acid monoesters of triols such as glycerin and trimethylolpropane.

Examples of the polyether polyols include polyethylene glycol, polypropylene glycol, and polybutylene glycol.

Examples of the monobasic acid include acetic acid, propionic acid, and p-tert-butylbenzoic acid.

Examples of lactones include ε-caprolactam and γ-valerolactone.

Other monomers copolymerizable with the above polymerizable monomers include, for example, (meth)acrylic acid esters, unsaturated carboxylic acids, unsaturated amides, vinyl monomers having a hydrolyzable silyl group, and other polymerizable monomers. These may be used alone or in combination of two or more.

Examples of the (meth)acrylic acid esters include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, and glycidyl methacrylate.

Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and itaconic acid.

Examples of unsaturated amides include acrylamide, N-methylolacrylamide, and diacetone acrylamide.

Examples of vinyl monomers having a hydrolyzable silyl group include vinyltrimethoxysilane, vinylmethyldimethoxysilane, and γ-(meth)acrylopropyltrimethoxysilane.

Other polymerizable monomers include, for example, styrene, vinyl toluene, vinyl acetate, acrylonitrile, and dibutyl fumarate.

For example, the polymer can be obtained by solution polymerizing the above-mentioned monomer components in the presence of a known radical polymerization initiator such as a peroxide or azo compound, and then diluting the resultant with an organic solvent, etc., as necessary.

[Hydroxyl value and acid value]
The resin hydroxyl value of the high solid acrylic polyol is 150 mgKOH/g or more, preferably 160 mgKOH/g or more, more preferably 170 mgKOH/g or more, and particularly preferably 180 mgKOH/g or more.
When the resin hydroxyl value is equal to or greater than the above lower limit, the coating film obtained has good coating film performance such as weather resistance.
On the other hand, the upper limit of the hydroxyl value of the resin is not particularly limited, but can be set to, for example, 300 mgKOH/g.
The resin acid value of the high-solid acrylic polyol is preferably 0 mgKOH/g or more and 30 mgKOH/g or less.
The hydroxyl value and acid value can be measured in accordance with JIS K1557.

[Weight average molecular weight]
The weight average molecular weight (Mw) of the high-solid acrylic polyol is 8,000 or less, preferably 7,000 or less, more preferably 6,000 or less, and even more preferably 5,000 or less.
By ensuring that the weight average molecular weight (Mw) is equal to or less than the above upper limit, the viscosity of the resulting coating composition can be further reduced, making it possible to produce a high-solids coating that can be applied even if the solid content is relatively high.
On the other hand, the lower limit of the weight average molecular weight of the high solid acrylic polyol is not particularly limited, and can be, for example, 1,000.
The weight average molecular weight of the high-solid acrylic polyol can be measured, for example, by GPC.
Specifically, it is calculated as a weight average molecular weight based on polystyrene by GPC under the following measurement conditions.

(Measurement conditions)
Apparatus: "HLC-8120GPC" (product name) manufactured by Tosoh Corporation
Column: Tosoh Corporation "TSKgel Super H1000" (product name) x 1
"TSKgel Super H2000" (product name) x 1
"TSKgel Super H3000" (product name) x 1 Carrier: Tetrahydrofuran (THF)
Detection method: differential refractometer Sample concentration: 5 wt/vol%
Detection method: Parallax refractometer Flow rate: 0.6 mL/min
Column temperature: 40°C

[viscosity]
The viscosity of the high-solids acrylic polyol, when diluted with butyl acetate and measured at 25°C in a state where the active ingredient is 65% by mass based on the total mass of the diluted solution, is preferably 100 mPa·s or more and 6,000 mPa·s or less, more preferably 200 mPa·s or more and 5,000 mPa·s or less, and even more preferably 300 mPa·s or more and 4,000 mPa·s or less.
When the viscosity is equal to or greater than the lower limit, the coating film performance such as weather resistance of the obtained coating film tends to be better. On the other hand, when the viscosity is equal to or less than the upper limit, a high-solids coating material can be obtained that can be applied even if the solid content is relatively high.

[NCO/OH]
In the coating composition of this embodiment, the lower limit of the ratio (NCO/OH) of the molar concentration of isocyanate groups (NCO groups) in the polyisocyanate composition to the molar concentration of hydroxyl groups (OH groups) in the high-solids acrylic polyol is preferably 0.8, more preferably 0.9, and even more preferably 1.0, while the upper limit of NCO/OH is preferably 3.0, more preferably 2.0, and even more preferably 1.5.
That is, in the coating composition, the NCO/OH ratio is preferably 0.8 or more and 3.0 or less, more preferably 0.9 or more and 2.0 or less, and even more preferably 1.0 or more and 1.5 or less.
When the NCO/OH ratio is equal to or greater than the lower limit, the coating film obtained can maintain its coating performance better, whereas when the NCO/OH ratio is equal to or less than the upper limit, the hardness of the coating film obtained tends to be better.

<Other polyols>
The coating composition of this embodiment may further contain other polyols in addition to the high-solid acrylic polyol.

The other polyol is a compound having two or more hydroxyl groups in the molecule, and examples include polyester polyol, polyether polyol, polyolefin polyol, and fluorine polyol. However, from the perspective of weather resistance, the content of other polyols other than high-solid acrylic polyol is preferably 20% by mass or less based on the total mass of the polyol component.

[Polyester polyol]
The polyester polyol can be obtained, for example, by subjecting a dibasic acid or a mixture thereof and a polyhydric alcohol or a mixture thereof to a condensation reaction.

Examples of the dibasic acid include succinic acid, adipic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, and other carboxylic acids.
Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, trimethylpentanediol, cyclohexanediol, trimethylolpropane, glycerin, pentaerythritol, 2-methylolpropanediol, and ethoxylated trimethylolpropane.

Specific methods for producing polyester polyol include, for example, mixing the above components and then heating them at a temperature of approximately 160°C or higher and 220°C or lower to carry out a condensation reaction.

Alternatively, a specific example of a method for producing polyester polyol is to obtain polycaprolactones by ring-opening polymerization of lactones such as ε-caprolactone with a polyhydric alcohol, and the resulting polycaprolactones can be used as polyester polyols.

[Polyether polyol]
Examples of polyether polyols include polyether polyols obtained by randomly or block-adding an alkylene oxide or a mixture of alkylene oxides to a polyvalent hydroxy compound or a mixture of alkylene oxides using, for example, a hydroxide, a strong basic catalyst, or a composite metal cyanide complex; polyether polyols obtained by reacting an alkylene oxide with a polyamine compound such as ethylenediamines; and so-called polymer polyols obtained by polymerizing acrylamide or the like using these polyether polyols as a medium.

Examples of the hydroxide include lithium, sodium, and potassium.
Examples of the strong basic catalyst include alcoholates and alkylamines.
Examples of the composite metal cyanide compound complex include metalloporphyrin and zinc hexacyanocobaltate complex.
Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, cyclohexene oxide, and styrene oxide.

Examples of the polyhydric hydroxy compound include diglycerin, ditrimethylolpropane, pentaerythritol, dipentaerythritol, sugar alcohol compounds, monosaccharides, disaccharides, trisaccharides, and tetrasaccharides.
Examples of sugar alcohol compounds include erythritol, D-threitol, L-arabinitol, ribitol, xylitol, sorbitol, mannitol, galactitol, and rhamnitol.
Examples of monosaccharides include arabinose, ribose, xylose, glucose, mannose, galactose, fructose, sorbose, rhamnose, fucose, and ribonucleotides.
Examples of disaccharides include trehalose, sucrose, maltose, cellobiose, gentiobiose, lactose, and melibiose.
Examples of trisaccharides include raffinose, gentianose, and melezitose.
An example of the tetrasaccharide is stachyose.

[Fluoropolyol]
The fluorine polyol is a polyol containing fluorine in the molecule, and examples thereof include copolymers of fluoroolefins, cyclovinyl ethers, hydroxyalkyl vinyl ethers, and monocarboxylic acid vinyl esters, as disclosed in JP-A-57-34107 (Reference 1) and JP-A-61-275311 (Reference 2).

<Other ingredients>
The coating composition of the present embodiment may further contain other components in addition to the polyisocyanate composition and the high-solids acrylic polyol.

Other components include, for example, unsaturated bond-containing compounds, inactive compounds, metal atoms, basic amino compounds, carbon dioxide, halogen atoms, etc. These components may be contained alone or in combination of two or more.

In the coating composition of the present embodiment, the lower limit of the content of other components can be set to 1.0 ppm by mass, 3.0 ppm by mass, 5.0 ppm by mass, or 10 ppm by mass, based on the content of the polyisocyanate composition.
On the other hand, the upper limit of the content of other components may be set to 1.0 × 10 ⁴ ppm by mass, 5.0 × 10 ³ ppm by mass, 3.0 × 10 ³ ppm by mass, or 1.0 × 10 ³ ppm by mass, based on the content of the polyisocyanate composition.
That is, in the coating composition of this embodiment, from the viewpoint of preventing discoloration during long-term storage and improving long-term storage stability, the content of other components can be 1.0 ppm by mass or more and 1.0 × 10 ⁴ ppm by mass or less, 3.0 ppm by mass or more and 5.0 × 10 3 ppm by mass or less, 5.0 ppm by mass or more and 3.0 × 10 ³ ppm by mass or less, or 10 ppm by mass or more and 1.0 × ^{10 3 ppm} by mass or less, based on the content of the polyisocyanate composition.

[Unsaturated bond-containing compound]
The unsaturated bond-containing compound may be a compound in which the unsaturated bond is a carbon-carbon unsaturated bond, a carbon-nitrogen unsaturated bond, or a carbon-oxygen unsaturated bond. From the viewpoint of compound stability, the unsaturated bond is preferably a double bond, more preferably a carbon-carbon double bond (C═C) or a carbon-oxygen double bond (C═O). Furthermore, the carbon atom constituting the compound may be a carbon atom bonded to three or more atoms.
Generally, carbon-carbon double bonds may be carbon-carbon double bonds that constitute aromatic rings, but the unsaturated bonds contained in the unsaturated bond-containing compound in the coating composition do not include carbon-carbon double bonds that constitute aromatic rings.
Examples of compounds having a carbon-oxygen double bond include carbonic acid derivatives, such as urea compounds, carbonate esters, N-unsubstituted carbamic acid esters, and N-substituted carbamic acid esters.

[Inert compound]
The inactive compounds are classified into, for example, Compounds A to G below.
Specifically, hydrocarbon compounds are classified into Compound A and Compound B, ether compounds and sulfide compounds are classified into Compounds C to E below, halogenated hydrocarbon compounds are classified into Compound F below, and silicon-containing hydrocarbon compounds, silicon-containing ether compounds and silicon-containing sulfide compounds are classified into Compound G below. Note that Compounds A to G listed here do not contain unsaturated bonds other than in the aromatic ring, and do not include the compounds having unsaturated bonds described above.
Compound A: A linear, branched or cyclic aliphatic hydrocarbon compound.
Compound B: An aromatic hydrocarbon compound which may be substituted with an aliphatic hydrocarbon group.
Compound C: A compound having an ether structure or a sulfide group and an aliphatic hydrocarbon group, in which the same or different aliphatic hydrocarbon compounds are bonded via the ether structure or the sulfide group.
Compound D: A compound having an ether structure or a sulfide group and an aromatic hydrocarbon group, in which the same or different aromatic hydrocarbon compounds are bonded via the ether structure or the sulfide group.
Compound E: A compound having an ether structure or a sulfide group, an aliphatic hydrocarbon group, and an aromatic hydrocarbon group.
Compound F: a halide in which at least one hydrogen atom constituting an aliphatic hydrocarbon compound or at least one hydrogen atom constituting an aromatic hydrocarbon compound is substituted with a halogen atom.
Compound G: A compound in which some or all of the carbon atoms of the above compounds A to E have been substituted with silicon atoms.

[Metal atom]
The metal atom may exist as a metal ion or as a simple metal atom. It may be one type of metal atom or a combination of multiple types of metal atoms. As the metal atom, a metal atom that can have a valence of 2 to 4 is preferred, and among them, one or more metals selected from iron, cobalt, nickel, zinc, tin, copper, and titanium are more preferred.

[Basic amino compounds]
The basic amino compound is a derivative of ammonia, and examples thereof include compounds in which one hydrogen atom is substituted with an alkyl group or an aryl group (primary), compounds in which two hydrogen atoms are substituted with an alkyl group or an aryl group (secondary), compounds in which all three hydrogen atoms are substituted with an alkyl group or an aryl group (tertiary), etc. Among these, secondary or tertiary amino compounds are preferred as basic amino compounds, and aliphatic amines, aromatic amines, heterocyclic amines, or basic amino acids are more preferred.

[carbon dioxide]
The carbon dioxide may be the amount dissolved in the isocyanate at normal pressure, or may be dissolved in a pressurized vessel. Since the use of carbon dioxide containing moisture may cause hydrolysis of the isocyanate, it is preferable to control the amount of moisture contained in the carbon dioxide as necessary.

[Halogen atom]
From the viewpoint of preventing discoloration, the content of halogen atoms contained in the coating composition is preferably 1.0 × 10 ² ppm by mass or less. The halogen atoms are not particularly limited, but at least one of chlorine atoms and bromine atoms is preferred, and at least one ion or compound selected from the group consisting of chlorine ions, bromine ions, hydrolyzable chlorine and hydrolyzable bromine is more preferred. Examples of hydrolyzable chlorine include carbamoyl chloride compounds in which hydrogen chloride is added to an isocyanate group, and examples of hydrolyzable bromine include carbamoyl bromide compounds in which hydrogen bromide is added to an isocyanate group.

<Melamine-based hardener>
The coating composition of the present embodiment may further contain a melamine-based curing agent, if necessary, in addition to the polyisocyanate composition and the high-solid acrylic polyol.
Examples of melamine-based curing agents include fully alkyl type, methylol type alkyl, and imino group type alkyl.

<Organic solvent>
The coating composition of the present embodiment may further contain an organic solvent in addition to the polyisocyanate composition and the high-solids acrylic polyol. The polyisocyanate composition and the high-solids acrylic polyol may be mixed with the organic solvent in advance before use.

The organic solvent preferably does not have functional groups that react with hydroxyl groups and isocyanate groups. It is also preferable that the organic solvent is compatible with the polyisocyanate composition. Examples of such organic solvents include those commonly used as paint solvents, such as ester compounds, ether compounds, ketone compounds, aromatic compounds, ethylene glycol dialkyl ether compounds, polyethylene glycol dicarboxylate compounds, hydrocarbon solvents, and aromatic solvents.

<Other additives>
In addition to the polyisocyanate composition and high-solids acrylic polyol, the coating composition of the present embodiment may further contain, depending on the purpose and application, various additives used in the relevant technical field, such as a curing-accelerating catalyst, a pigment, a leveling agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a plasticizer, a surfactant, etc., within a range that does not impair the effects achieved by the coating composition of the present embodiment.

Examples of catalysts for accelerating curing include metal salts and tertiary amines.
Examples of metal salts include dibutyltin dilaurate, tin 2-ethylhexanoate, zinc 2-ethylhexanoate, and cobalt salts.
Examples of tertiary amines include triethylamine, pyridine, methylpyridine, benzyldimethylamine, N,N-dimethylcyclohexylamine, N-methylpiperidine, pentamethyldiethylenetriamine, N,N'-endoethylenepiperazine, and N,N'-dimethylpiperazine.

<Method of producing coating composition>
The coating composition of the present embodiment can be obtained by mixing the high-solid acrylic polyol, the polyisocyanate composition, and, if necessary, various additive components, etc., using a known method.

Specifically, first, various additives are added as needed to a high-solids acrylic polyol or its solvent dilution. Next, the polyisocyanate composition is added as a curing agent, and if needed, a solvent is further added to adjust the viscosity. The coating composition can then be obtained by stirring manually or using a stirring device such as a mixer.

<Application>
The coating composition of this embodiment uses a reduced amount of volatile organic solvent and has excellent hardness and weather resistance when formed into a coating film, and is therefore preferably used as a high-solid coating composition. The polyisocyanate composition can also be referred to as a curing agent composition for high-solid coatings, and the base component containing the high-solid acrylic polyol can also be referred to as a base composition for high-solid coatings.

Generally, a high-solids paint composition refers to a paint composition that has a higher paint solids content than conventional paints and a lower amount of volatile organic solvents than conventional paints.

When the coating composition of this embodiment is used as a high-solids coating composition, the amount of volatile organic solvent components, expressed as a mass relative to the total volume of the coating composition, can be less than 435 g/L, and preferably 420 g/L or less. On the other hand, the lower limit of the amount of volatile organic solvent components is not particularly limited, but can be 100 g/L or 200 g/L.
The amount of the volatile organic solvent component can be measured by the following method.
A high-solids acrylic polyol adjusted to 65% solids by weight using butyl acetate and a polyisocyanate composition adjusted to 85% solids by weight using butyl acetate were mixed to achieve an NCO/OH ratio of 1.0. The resulting mixture was then diluted with a thinner prepared by mixing 40 parts by weight of solvent naphtha and 60 parts by weight of butyl acetate. The amount of volatile organic solvents (g/L) in the paint that resulted in a viscosity of 23 seconds using a Ford Cup No. 4 at 23°C was then calculated.

Furthermore, when the coating composition of this embodiment is used as a high-solids coating composition, its viscosity, expressed in seconds using a Ford Cup No. 4 at 23°C, can be 23 seconds or more, preferably 23 seconds or more and 30 seconds or less, more preferably 23 seconds or more and 27 seconds or less, and even more preferably 23 seconds or more and 25 seconds or less.
The viscosity can be measured using the method of JIS K5400.

<Coating film>
The coating film of this embodiment is formed by curing the above coating composition.

The coating film of this embodiment has excellent hardness and weather resistance.

The coating film of this embodiment is obtained by applying the coating composition to the substrate and then drying it.

The drying temperature is not particularly limited, but is preferably 20°C or higher and 160°C or lower, more preferably 30°C or higher and 150°C or lower, and even more preferably 40°C or higher and 140°C or lower.
The drying time is preferably from 1 minute to 120 minutes, more preferably from 5 minutes to 80 minutes, and even more preferably from 10 minutes to 50 minutes.

<Object to be coated>
The substrate to be coated is not particularly limited, and examples thereof include molded articles made by molding materials such as metals (steel plates, surface-treated steel plates, etc.), plastics, wood, inorganic materials, etc. The shape of these molded articles is also not particularly limited, and may be thin articles such as films, sheets, and boards, or thick articles such as cylinders and three-dimensional structures. They may also be hollow articles such as tubes.
The substrate may also be a coating film, such as a coating film prepared by applying and curing a base agent such as a polyol and a curing agent such as a (blocked) polyisocyanate or melamine, or an uncured coating film before curing.

<Application>
The coating film of this embodiment is useful as a primer layer (undercoat layer), intermediate coat layer, or top coat layer for materials such as metals (steel sheets, surface-treated steel sheets, etc.), plastics, wood, inorganic materials, etc. It is also useful as a laminate for imparting cosmetic properties, weather resistance, acid resistance, rust prevention, chipping resistance, etc. to pre-coated metals including rust-resistant steel sheets, automotive paint, etc.

<Painted items>
The coated article of this embodiment is provided with the above-described coating film.

The coated article of this embodiment has excellent hardness and weather resistance due to the coating film.

The coated article of this embodiment has a structure comprising a substrate and a coating film on the substrate. Examples of substrates include those similar to those exemplified above for the coating film.

Hereinafter, the present embodiment will be described in more detail with reference to specific examples and comparative examples, but the present embodiment is not limited in any way by these examples and comparative examples as long as it does not depart from the gist of the present embodiment. In the examples and comparative examples, the physical properties of the polyisocyanate component and the coating film were measured and evaluated as follows. Unless otherwise specified, "parts" and "%" mean "parts by mass" and "% by mass". In the following, Examples 1-1 to 1-4 and Examples 2-1 to 2-5 are referred to as reference examples.

<Method of measuring physical properties>
[Physical Properties 1]
(Viscosity of Polyisocyanate Composition and High Solids Acrylic Polyol)
The viscosity was measured at 25°C using an E-type viscometer (manufactured by Tokimec Co., Ltd.) with a standard rotor (1°34' x R24) at the following rotation speeds:

(rotation speed)
100 rpm (less than 128 mPa·s)
50 rpm (128 mPa·s or more but less than 256 mPa·s)
20 rpm (256 mPa·s or more but less than 640 mPa·s)
10 rpm (for viscosity of 640 mPa·s or more and less than 1280 mPa·s)
5 rpm (for viscosity of 1280 mPa·s or more but less than 2560 mPa·s)
2.5 rpm (for viscosity between 2560 mPa·s and 5120 mPa·s)

[Physical Properties 2]
(Isocyanate group (NCO) content of polyisocyanate composition)
The NCO content (mass %) of the polyisocyanate composition was determined by neutralizing the isocyanate groups in the polyisocyanate composition with an excess of 2N amine and then back titrating with 1N hydrochloric acid.

[Physical Properties 3]
(Average number of isocyanate groups in polyisocyanate composition (Fn))
The Fn of the polyisocyanate composition was determined using the following formula: In the formula, Mn represents the number average molecular weight, and was measured using the method described in "Physical Properties 4" below.

Fn={Mn×(NCO content)×0.01}/42

[Physical Properties 4]
(Number Average Molecular Weight (Mn) and Uretdione Dimer Content of Polyisocyanate Composition)
The number average molecular weight (Mn) and the content of uretdione dimer of the polyisocyanate composition were determined as number average molecular weights based on polystyrene by GPC under the following measurement conditions.

(Measurement conditions)
Apparatus: "HLC-8120GPC" (product name) manufactured by Tosoh Corporation
Column: Tosoh Corporation "TSKgel Super H1000" (product name) x 1
"TSKgel Super H2000" (product name) x 1
"TSKgel Super H3000" (product name) x 1 Carrier: Tetrahydrofuran (THF)
Detection method: differential refractometer Sample concentration: 5 wt/vol%
Detection method: Parallax refractometer Flow rate: 0.6 mL/min
Column temperature: 40°C

[Physical Properties 5]
(molar ratio of each functional group)
The presence of isocyanurate groups and allophanate groups was confirmed by ^13C -NMR measurement using an Avance 600 (trade name) manufactured by Bruker Biospin, and the molar ratios of isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups were quantified by the following method. Next, from the obtained molar ratios, a/(a+b+c+d+e+f)×100, b/(a+b+c+d+e+f)×100, and c/(a+b+c+d+e+f)×100 were calculated, where a, b, c, d, e, and f are the molar ratios of isocyanurate groups, urethane groups, allophanate groups, biuret groups, iminooxadiazinedione groups, and uretdione groups, respectively.
The specific measurement conditions were as follows:

(Measurement conditions)
^13C -NMR device: AVANCE 600 (manufactured by Bruker BioSpin)
Cryoprobe: CP DUL 600S3 C/H-D-05 Z
(Manufactured by Bruker Biospin)
Resonance frequency: 150MHz
Concentration: 60wt/vol%
Shift reference: CDCl ₃ (77 ppm)
Number of accumulations: 10,000 Pulse program: zgpg30 (proton complete decoupling method, waiting time 2 seconds)

(Characteristic peaks (chemical shift values) in polyisocyanate compositions)
Isocyanurate group: 148.5 ppm: integrated value ÷ 3
Urethane group: 156.3 ppm: integrated value ÷ 1
Allophanate group: Around 154 ppm: Integrated value ÷ 1
Buret group: 155.8 ppm: (integral value - allophanate group integral value) ÷ 2
Iminooxadiazinedione group: 137.3 ppm: integrated value divided by 1
Uretdione group: 157.5 ppm: integrated value ÷ 2

[Physical Properties 6]
(Solid content)
The solid content of the acrylic polyol was determined as follows.
First, an aluminum dish with a bottom diameter of 38 mm was precisely weighed. Next, approximately 1 g of the acrylic polyol produced in the Examples and Comparative Examples was placed on the aluminum dish and precisely weighed (W1). Next, the acrylic polyol was adjusted to a uniform thickness. Next, the acrylic polyol placed on the aluminum dish was kept in an oven at 105°C for 1 hour. Next, after the aluminum dish had cooled to room temperature, the acrylic polyol remaining on the aluminum dish was precisely weighed (W2). Next, the solid content (mass%) of the acrylic polyol was calculated using the following formula.

Solid content of acrylic polyol (mass%) = W2/W1 x 100

[Physical Properties 7]
(Hydroxyl value)
The hydroxyl value of the acrylic polyol was measured in accordance with JIS K1557.

[Physical Properties 8]
(Weight average molecular weight)
The weight average molecular weight of the acrylic polyol is a weight average molecular weight based on polystyrene measured by GPC using the following apparatus.

(Measurement conditions)
Apparatus: "HLC-8120GPC" (product name) manufactured by Tosoh Corporation
Column: Tosoh Corporation "TSKgel Super H1000" (product name) x 1
"TSKgel Super H2000" (product name) x 1
"TSKgel Super H3000" (product name) x 1 Carrier: Tetrahydrofuran (THF)
Detection method: differential refractometer Sample concentration: 5 wt/vol%
Detection method: Parallax refractometer Flow rate: 0.6 mL/min
Column temperature: 40°C

[Evaluation 1]
(High solidity test)
A high-solids acrylic polyol adjusted to 65% solids by weight using butyl acetate and a polyisocyanate composition adjusted to 85% solids by weight using butyl acetate were mixed to an NCO/OH ratio of 1.0. The resulting mixture was then diluted with a thinner prepared by mixing 40 parts by weight of solvent naphtha and 60 parts by weight of butyl acetate. The amount of volatile organic solvents (g/L) in the paint that resulted in a viscosity of 23 seconds using a Ford Cup No. 4 at 23°C was then calculated, and the high solids property was evaluated according to the following evaluation criteria.

(Evaluation criteria)
◎: The amount of volatile organic solvent components is less than 435 g/L. ○: The amount of volatile organic solvent components is 435 g or more and less than 450 g/L. ×: The amount of volatile organic solvent components is 450 g/L or more.

[Evaluation 2]
(Coating film hardness (Koenig hardness))
A high-solids acrylic polyol adjusted to a solids content of 65% by mass using butyl acetate and a polyisocyanate composition adjusted to a solids content of 85% by mass using butyl acetate were mixed to an NCO/OH ratio of 1.0, and the mixture was further diluted with a thinner prepared by mixing 40 parts by mass of solvent naphtha and 60 parts by mass of butyl acetate to a viscosity of 23 seconds in a Ford cup No. 4 at 23°C to prepare a coating composition.
The coating composition was then applied to a glass plate so that the dry film thickness was 40 μm, and the plate was left standing for 15 minutes at 23° C. and 50% humidity. The plate was then dried at 140° C. for 30 minutes, and then left standing at 23° C. and 50% relative humidity for 7 days. The Konig hardness of the coated plate was then measured, and the hardness was determined according to the following criteria. The Konig hardness measurement was performed in accordance with ISO 1522.

(Evaluation criteria)
◎: 90 times or more ○: 60 times or more and 89 times or less ×: 59 times or less

[Evaluation 3]
(weather resistance)
A high-solids acrylic polyol adjusted to a solids content of 65% by mass using butyl acetate and a polyisocyanate composition adjusted to a solids content of 85% by mass using butyl acetate were mixed to an NCO/OH ratio of 1.0, and the mixture was diluted with a thinner prepared by mixing 40 parts of solvent naphtha and 60 parts of butyl acetate to a viscosity of 23 seconds in a Ford cup No. 4 at 23°C to prepare a coating liquid.
The coating was then applied using an applicator to a steel plate (JIS G3141, product name: SPCC-SB, treatment method: PF-1077, manufactured by Partec Co., Ltd.) that had been degreased with methyl ethyl ketone, so that the dry film thickness was 40 μm, and the plate was left to stand for 15 minutes at 23°C and a relative humidity of 50%. The plate was then dried at 140°C for 30 minutes and aged for 7 days in an environment at a temperature of 23°C and a relative humidity of 50%, yielding a coating film. The coating film was then subjected to an accelerated weather resistance test under the following conditions.

(Test conditions)
Test equipment: Super Xenon Weather Meter (manufactured by Suga Test Instruments Co., Ltd.)
Illuminance: 180w/ ^m2
1 cycle: 360 minutes (dry: 336 minutes (relative humidity: 50%), wet: 24 minutes)
Test time: 2,000 hours

The gloss at 60° was measured for the coating film immediately after production and for the coating film after the accelerated test using a gloss meter (product name: Micro-Gloss, manufactured by BYK) in accordance with JIS Z8741. The gloss retention was calculated using the following formula. Weather resistance was evaluated from the calculated gloss retention according to the following evaluation criteria.

"Gloss retention (%)" = {100 x (gloss after accelerated testing)} / (initial gloss)

(Evaluation criteria)
◎: Gloss retention is 85% or more. ○: Gloss retention is 70% or more but less than 85%. ×: Gloss retention is less than 70%.

<Production of Polyisocyanate Composition>
[Example 1-1]
(Production of polyisocyanate composition P-a1)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI and 7.0 g of isobutanol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.6% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was then heated to 120°C and maintained at 120°C for 1 hour. The reaction solution was then cooled, filtered to remove precipitate, and purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-a1. The resulting polyisocyanate composition Pa1 had a viscosity of 890 Pa·s (25° C.), an NCO content of 23.4% by weight, and an average number of isocyanate groups of 3.16.

[Example 1-2]
(Production of polyisocyanate composition P-a2)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI and 13.0 g of isobutanol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.6% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was then heated to 110°C and maintained at 110°C for 1 hour. After cooling, the reaction solution was filtered to remove the precipitate, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-a2. The obtained polyisocyanate composition P-a2 had a viscosity of 860 mPa·s (25° C.), an NCO content of 23.3 mass %, and an average number of isocyanate groups of 3.12.

[Examples 1-3]
(Production of polyisocyanate composition P-a3)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI and 17.0 g of isobutanol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.5% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was then heated to 120°C and maintained at 120°C for 1 hour. The reaction solution was then cooled, filtered to remove precipitate, and purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-a3. The obtained polyisocyanate composition P-a3 had a viscosity of 790 mPa·s (25° C.), an NCO content of 23.3 mass %, and an average number of isocyanate groups of 3.16.

[Examples 1-4]
(Production of polyisocyanate composition P-a4)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI and 24.0 g of isobutanol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.6% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was then heated to 110°C and maintained at 110°C for 1 hour. The reaction solution was then cooled, filtered to remove precipitate, and purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-a4. The obtained polyisocyanate composition P-a4 had a viscosity of 710 mPa·s (25° C.), an NCO content of 23.1 mass %, and an average number of isocyanate groups of 3.06.

[Examples 1-5]
(Production of polyisocyanate composition P-a5)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI, 4.0 g of isobutanol, and 5.4 g of 1,3-butanediol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 46.0% by mass, phosphoric acid was added to terminate the reaction. Thereafter, the reaction solution was heated to 120°C and maintained at 120°C for 1 hour. Thereafter, the reaction solution was cooled, filtered to remove precipitate, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-a5. The obtained polyisocyanate composition P-a5 had a viscosity of 720 mPa·s (25° C.), an NCO content of 23.6 mass %, and an average number of isocyanate groups of 3.02.

[Examples 1-6]
(Production of polyisocyanate composition P-a6)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI, 3.0 g of isobutanol, and 6.6 g of 1,3-butanediol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.5% by mass, phosphoric acid was added to terminate the reaction. Thereafter, the reaction solution was heated to 120°C and maintained at 120°C for 1 hour. Thereafter, the reaction solution was cooled, filtered to remove precipitate, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-a6. The resulting polyisocyanate composition Pa6 had a viscosity of 850 mPa·s (25° C.), an NCO content of 22.9 mass %, and an average number of isocyanate groups of 3.20.

[Comparative Example 1-1]
(Production of polyisocyanate composition P-b1)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI was charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.0% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was then heated to 120°C and maintained at 120°C for 1 hour. The reaction solution was then cooled, filtered to remove precipitate, and purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-b1. The obtained polyisocyanate composition P-b1 had a viscosity of 1,030 mPa·s (25° C.), an NCO content of 23.6 mass %, and an average number of isocyanate groups of 3.26.

[Comparative Example 1-2]
(Production of polyisocyanate composition P-b2)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI and 13.0 g of 2-ethyl-1-hexanol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.6% by mass, phosphoric acid was added to terminate the reaction. Thereafter, the reaction solution was heated to 160°C and maintained at 160°C for 1 hour. Thereafter, the reaction solution was cooled, filtered to remove the precipitate, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-b2. The obtained polyisocyanate composition P-b2 had a viscosity of 610 mPa·s (25° C.), an NCO content of 23.1 mass %, and an average number of isocyanate groups of 3.04.

[Comparative Examples 1-3]
(Production of polyisocyanate composition P-b3)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI and 65.0 g of isobutanol were charged. The temperature inside the reactor was maintained at 80°C for 2 hours with stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 43.0% by mass, phosphoric acid was added to terminate the reaction. Thereafter, the reaction solution was heated to 120°C and maintained at 120°C for 1 hour. Thereafter, the reaction solution was cooled, filtered to remove precipitate, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-b3. The obtained polyisocyanate composition P-b3 had a viscosity of 630 mPa·s (25° C.), an NCO content of 22.2 mass %, and an average number of isocyanate groups of 2.90.

[Comparative Examples 1-4]
(Production of polyisocyanate composition P-b1)
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was conditioned with a nitrogen atmosphere, and 6,000 g of HDI, 3.0 g of isobutanol, and 6.6 g of 1,3-butanediol were charged. The temperature inside the reactor was maintained at 70°C for 1 hour while stirring. Next, 2.5 g of a solution prepared by diluting the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to 10% by mass was added, and an isocyanuration reaction was carried out. Next, when the NCO content of the reaction solution reached 45.9% by mass, phosphoric acid was added to terminate the reaction. Thereafter, the reaction solution was heated to 120°C and maintained at 120°C for 1 hour. Thereafter, the reaction solution was cooled, filtered to remove precipitate, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate composition P-b1. The obtained polyisocyanate composition P-b1 had a viscosity of 980 mPa·s (25° C.), an NCO content of 22.7 mass %, and an average number of isocyanate groups of 3.16.

The physical properties of the resulting polyisocyanate composition are shown in the table below. In the table, "iBuOH" means isobutanol, "2EHOH" means 2-ethyl-1-hexanol, and "1,3BG" means 1,3-butanediol.

<Production of acrylic polyol>
[Production Example 1]
(Production of acrylic polyol Ac-a1)
The following monomers and the like were added to a plastic container in advance to prepare a mixed solution.
Monomer components: 15 parts by mass of styrene, 38 parts by mass of n-butyl methacrylate, 15 parts by mass of n-butyl acrylate, 31 parts by mass of 2-hydroxyethyl acrylate, 1 part by mass of acrylic acid. Initiator: 7 parts by mass of tert-butyl peroxy-2-ethylhexanoate (product name: Perbutyl O, manufacturer: NOF Corporation).
Thereafter, a nitrogen atmosphere was created in a four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel, and 28 parts by mass of propylene glycol monomethyl ether acetate (solvent) and 15 parts by mass of solvent naphtha were charged and the temperature was raised to 140°C. The above-described mixed solution was added dropwise from the dropping funnel over 1.5 hours. The mixture was then maintained at 140°C for 1.5 hours and then cooled to obtain acrylic polyol Ac-a1. The obtained acrylic polyol Ac-a1 had a solids content of 65% by mass, a viscosity of 1,300 mPas/25°C, and a resin hydroxyl value of 150 mgKOH/g.

[Production Example 2]
(Production of acrylic polyol Ac-a2)
The following monomers and the like were added to a plastic container in advance to prepare a mixed solution.
Monomer components: 10 parts by mass of styrene, 36 parts by mass of n-butyl methacrylate, 12 parts by mass of n-butyl acrylate, 21 parts by mass of 2-hydroxyethyl acrylate, 20 parts by mass of 4-hydroxybutyl acrylate, 1 part by mass of acrylic acid. Initiator: 12 parts by mass of tert-butyl peroxy-2-ethylhexanoate (product name: Perbutyl O, manufacturer: NOF Corporation).
Thereafter, a nitrogen atmosphere was created in a four-neck flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel, and 28 parts by mass of propylene glycol monomethyl ether acetate (solvent) and 15 parts by mass of solvent naphtha were charged and the temperature was raised to 140°C. The above-described mixed solution was added dropwise from the dropping funnel over 1.5 hours. The mixture was then maintained at 140°C for 1.5 hours and then cooled to obtain acrylic polyol Ac-a2. The obtained acrylic polyol Ac-a2 had a solids content of 65% by mass, a viscosity of 700 mPas/25°C, and a resin hydroxyl value of 180 mgKOH/g.

The physical properties of the resulting acrylic polyol are shown in the table below.

<Production of Coating Composition>
[Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-4]
Except for combining the types of polyisocyanate composition and acrylic polyol as shown in the table below, each coating composition was prepared and evaluated using the methods shown in the above Evaluations 1 to 3. The results are shown in the table below.

As shown in Table 4, coating compositions (Examples 2-1 to 2-7) using polyisocyanate compositions P-a1 to P-a6 (Examples 1-1 to 1-6) with specific physical properties reduced the amount of volatile organic solvent used when combined with a high-solids acrylic polyol to form coating compositions, and the resulting coatings exhibited excellent hardness and weather resistance.

On the other hand, as shown in Table 5,
Polyisocyanate composition P-b1 (Comparative Example 1-1) having a viscosity of more than 900 mPa s and c/(a+b+c+d+e+f)×100 being less than 3 mol%;
Polyisocyanate composition P-b2 (Comparative Example 1-2) in which the content of uretdione dimer is more than 3 mass%, polyisocyanate composition P-b3 (Comparative Example 1-3) in which a/(a+b+c+d+e+f) x 100 is less than 65 mol%, c/(a+b+c+d+e+f) x 100 is more than 25 mol%, and the average number of isocyanate groups is less than 3.00, and polyisocyanate composition P-b4 (Comparative Example 1-4) in which the viscosity is more than 900 mPa s and a/(a+b+c+d+e+f) x 100 is less than 65 mol%,
In the coating compositions using the above (Comparative Examples 2-1 to 2-4), it was not possible to obtain coatings that were good in all respects, including high solidity, hardness, and weather resistance when formed into a coating film.

The polyisocyanate composition of this embodiment can reduce the amount of volatile organic solvent used when combined with a high-solids acrylic polyol to form a coating composition, and can provide a polyisocyanate composition that exhibits excellent hardness and weather resistance when formed into a coating film. The coating composition of this embodiment contains the polyisocyanate composition, reduces the amount of volatile organic solvent used, and exhibits excellent hardness and weather resistance when formed into a coating film. The coating film of this embodiment is formed by curing the coating composition and exhibits excellent hardness and weather resistance. The coated article of this embodiment has the coating film and exhibits excellent hardness and weather resistance.

Claims (5)

A polyisocyanate composition comprising a polyisocyanate derived from an aliphatic diisocyanate and an alcohol,
The viscosity at 25°C is 600 mPa s or more and 900 mPa s or less,
the molar ratio of the isocyanurate group to the total molar ratio of the isocyanurate group, the urethane group, the allophanate group, the biuret group, the iminooxadiazinedione group, and the uretdione group, expressed as a/(a+b+c+d+e+f)×100, is 65 mol % or more and 95 mol % or less, where a, b, c, d, e, and f are the molar ratios of the isocyanurate group, the urethane group, the allophanate group, the biuret group, the iminooxadiazinedione group, and the uretdione group contained in the polyisocyanate composition, respectively;
the molar ratio of the allophanate groups to the total molar ratio of the isocyanurate groups, the urethane groups, the allophanate groups, the biuret groups, the iminooxadiazinedione groups, and the uretdione groups, represented by c/(a+b+c+d+e+f)×100, is 3 mol % or more and 25 mol % or less,
the content of uretdione dimer relative to the total mass of the polyisocyanate composition is 3.0 mass% or less,
the average number of isocyanate groups is 3.00 or more and 4.00 or less,
a molar ratio of the urethane groups to a total molar ratio of the isocyanurate groups, the urethane groups, the allophanate groups, the biuret groups, the iminooxadiazinedione groups, and the uretdione groups, expressed as b/(a+b+c+d+e+f)×100, is 2 mol % or more and 8 mol % or less, and
The alcohol
It is a compound consisting only of carbon, hydrogen and oxygen,
Contains either one or both of a monoalcohol and a dialcohol,
The molecular weight is 200 or less ,
The polyisocyanate composition , wherein the alcohol comprises a monoalcohol and a dialcohol . The polyisocyanate composition according to claim 1, wherein the aliphatic diisocyanate is hexamethylene diisocyanate. The polyisocyanate composition according to claim 1 or 2 ;
a high-solids acrylic polyol having a resin hydroxyl value of 150 mgKOH/g or more and a weight average molecular weight of 8,000 or less;
A coating composition comprising: A coating film obtained by curing the coating composition according to claim 3 . A coated article comprising the coating film of claim 4 .