Polyisocyanate composition and cured film

Abstract

To provide a polyisocyanate composition that is cured alone to give a cured film having a good appearance and high hydrolyzability.SOLUTION: A polyisocyanate composition contains a polyisocyanate derived from a diisocyanate and a polyester polyol, wherein a molar ratio NCO / OH in a reaction between an isocyanate group of the diisocyanate and a hydroxy group of the polyester polyol is 3.0 or more, wherein the content of an aliphatic diisocyanate with respect to a total mass of the diisocyanate is 10 mass% or more and 100 mass% or less, wherein the polyisocyanate composition is substantially free of unreacted diisocyanates, wherein an isocyanate group content of the polyisocyanate composition with respect to a total mass of the polyisocyanate composition is 1.0 mass% or more and 5.9 mass% or less, and wherein the polyester polyol is composed of a dicarboxylic acid unit having 8 or fewer carbon atoms and a polyol unit.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyisocyanate composition and a cured film. [Background Art]

[0002] In recent years, there has been an increasing demand for degradable resins with low environmental impact, and there is also a demand for degradability for polyisocyanates. However, since high-performance urethane compositions are excellent in durability and hydrolysis resistance, they may remain intact without being decomposed even when released into the environment. In order to impart degradability to high-performance urethane compositions, the first step is to subdivide the resin particles by hydrolysis.

[0003] For example, Patent Document 1 discloses a polyisocyanate obtained by adding a diisocyanate to a polyester polyol containing succinic acid as a carboxylic acid and triethylene glycol as an alcohol as essential components. [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent No. 5263644 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, Patent Document 1 does not specifically verify the appearance of a cured film obtained by curing the resulting polyisocyanate alone. In addition, the polyisocyanate described in Patent Document 1 has a high isocyanate group content of 6 mass% or more and 11 mass% or less, leaving room for improvement in degradability. Therefore, in order to further improve degradability, there is a demand for a polyisocyanate that has a large ester content and a low isocyanate group content.

[0006] The present invention has been made in view of the above circumstances, and provides a polyisocyanate composition that has excellent appearance when a cured film is obtained by curing the polyisocyanate composition alone, and also has excellent hydrolysis resistance. [Means for solving the problem]

[0007] In other words, the present invention includes the following embodiments. (1) A polyisocyanate composition comprising a diisocyanate and a polyisocyanate derived from a polyester polyol, The molar ratio NCO / OH during the reaction between the isocyanate group of the diisocyanate and the hydroxyl group of the polyester polyol is 3.0 or higher. The content of aliphatic diisocyanate relative to the total mass of the diisocyanate is 10% by mass or more and 100% by mass or less. It contains virtually no unreacted diisocyanates. The isocyanate group content of the polyisocyanate composition is 1.0% by mass or more and 5.9% by mass or less, relative to the total mass of the polyisocyanate composition. The polyester polyol is a polyisocyanate composition composed of dicarboxylic acid units having 8 or fewer carbon atoms and polyol units. (2) The polyisocyanate composition according to (1), wherein the number average molecular weight of the polyester polyol is 1000 or more and 4000 or less. (3) The polyisocyanate composition according to (1) or (2), wherein the average number of hydroxyl groups in the polyester polyol is 2.0 or more and 4.0 or less. (4) The polyester polyol is composed of aliphatic dicarboxylic acid units having 8 or fewer carbon atoms and aliphatic polyol units, the polyisocyanate composition according to any one of (1) to (3). (5) The polyisocyanate composition according to any one of (1) to (4), wherein the molar ratio NCO / OH during the reaction between the isocyanate group of the diisocyanate and the hydroxyl group of the polyester polyol is 5.5 or more and 20 or less. (6) A polyisocyanate composition according to any one of (1) to (5), which is a curing agent for a paint composition or a resin composition. (7) A cured film obtained by curing a polyisocyanate composition described in any one of (1) to (5) in the presence of a catalyst. [Effects of the Invention]

[0008] According to the polyisocyanate composition of the above embodiment, it is possible to provide a polyisocyanate composition that has excellent appearance and hydrolysis resistance when a cured film is obtained by curing the polyisocyanate composition alone. The cured film of the above embodiment is obtained by curing the polyisocyanate composition alone and has excellent appearance and hydrolysis resistance. [Modes for carrying out the invention]

[0009] The following describes in detail an embodiment for carrying out the present invention (hereinafter referred to as "this embodiment"), but the present invention is not limited thereto, and various modifications are possible without departing from its essence.

[0010] In this specification, "polyol" means a compound having two or more hydroxyl groups (-OH) in one molecule. Furthermore, in this specification, "polyisocyanate" means a reaction product in which multiple monomer compounds having two or more isocyanate groups (-NCO) are bonded together. Furthermore, unless otherwise specified in this specification, "(meth)acrylic" encompasses methacrylic and acrylic, and "(meth)acrylate" encompasses methacrylate and acrylate.

[0011] Polyisocyanate Composition The polyisocyanate composition of this embodiment includes a diisocyanate and a polyisocyanate derived from a polyester polyol.

[0012] The isocyanate group content of the polyisocyanate composition, in a state substantially free of solvents and diisocyanates, is preferably 1.0% to 5.9% by mass, more preferably 1.5% to 5.8% by mass, more preferably 2.0% to 5.7% by mass, even more preferably 2.5% to 5.6% by mass, and particularly preferably 3.0% to 5.5% by mass. By ensuring the isocyanate group content is above the lower limit, the hardness of the cured film can be sufficiently achieved. On the other hand, by ensuring the content is below the upper limit, the cured film exhibits excellent hydrolysis resistance. The NCO group content can be determined, for example, by reacting the isocyanate groups of a polyisocyanate composition with an excess amine (such as dibutylamine) and then back-titrating the remaining amine with an acid such as hydrochloric acid.

[0013] Polyester polyols are composed of dicarboxylic acid units with 8 or fewer carbon atoms and polyol units.

[0014] The polyisocyanate composition of this embodiment, having the above configuration, exhibits excellent appearance and hydrolysis resistance when a cured film is obtained by curing the polyisocyanate composition alone.

[0015] Next, each component constituting the polyisocyanate composition of this embodiment will be described in detail below.

[0016] <Polyisocyanate> The polyisocyanate contained in the polyisocyanate composition of this embodiment is derived from diisocyanate and polyester polyol, that is, it is a reaction product of diisocyanate and polyester polyol.

[0017] The polyisocyanate may have at least one structure selected from the group consisting of an allophanate structure, a uretdione structure, an iminooxadiazinedione structure, an isocyanurate structure, a urea structure, a urethane structure, and a biuret structure. Among these, it is preferable for the polyisocyanate to have at least one structure selected from the group consisting of a urethane structure, an allophanate structure, a biuret structure, a urea structure, and an isocyanurate group, and it is more preferable for the polyisocyanate to contain a urethane structure.

[0018] [Diisocyanate] Diisocyanate is a general term for compounds containing two isocyanate groups. The diisocyanate used in the polyisocyanate composition of the present embodiment includes an aliphatic diisocyanate.

[0019] Examples of the aliphatic diisocyanate include, but are not limited to, 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, ethyl (2,6-diisocyanato)hexanoate, 1,6-diisocyanatohexane (hereinafter sometimes abbreviated as "HDI"), 1,9-diisocyanatononane, 1,12-diisocyanatododecane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, and the like. One of these aliphatic diisocyanates may be used alone, or two or more thereof may be used in combination. Among these, HDI is preferable as the diisocyanate.

[0020] The above diisocyanate may further contain an isocyanate monomer as shown below, as long as it does not impair the effects exerted by the polyisocyanate composition of the present embodiment. (1) Aromatic diisocyanates such as diphenylmethane-4,4'-diisocyanate (MDI), 1,5-naphthalene diisocyanate, tolylene diisocyanate (TDI), xylylene diisocyanate, m-tetramethylxylylene diisocyanate (TMXDI), and the like. (2) Triisocyanates such as 4-isocyanate methyl-1,8-octamethylene diisocyanate (hereinafter sometimes referred to as "NTI"), 1,3,6-hexamethylene triisocyanate (hereinafter sometimes referred to as "HTI"), bis(2-isocyanatoethyl)2-isocyanatoglutarate (hereinafter sometimes referred to as "GTI"), and lysine triisocyanate (hereinafter sometimes referred to as "LTI"). (3) Alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (hereinafter sometimes abbreviated as "hydrogenated XDI"), 1,3- or 1,4-diisocyanatocyclohexane, 3,5,5-trimethyl1-isocyanato-3-(isocyanatomethyl)cyclohexane (hereinafter sometimes abbreviated as "IPDI"), 4-4'-diisocyanato-dicyclohexylmethane (hereinafter sometimes abbreviated as "hydrogenated MDI"), and 2,5- or 2,6-diisocyanatomethylnorbornane.

[0021] The content of aliphatic diisocyanate relative to the total mass of the diisocyanate is 10% by mass or more and 100% by mass or less, and preferably 50% by mass or more and 100% by mass or less. When the content of aliphatic diisocyanate is within the above range, the appearance of the coating film tends to be good.

[0022] The polyisocyanate composition of this embodiment does not contain substantially unreacted diisocyanate. Because the polyisocyanate composition does not contain substantially unreacted diisocyanate, the cured film obtained by curing the polyisocyanate composition alone has excellent appearance and excellent hydrolysis resistance.

[0023] In this specification, "substantially free of unreacted diisocyanate" means that the concentration of unreacted diisocyanate present in the polyisocyanate composition is 2.0% by mass or less, preferably 1.0% by mass or less, and more preferably 0.7% by mass or less. A method for obtaining a polyisocyanate composition that is substantially free of unreacted diisocyanate includes, for example, a method of separating unreacted diisocyanate from the composition obtained after the production of the polyisocyanate. A method for purifying the polyisocyanate composition by separating unreacted diisocyanate and solvent is not particularly limited, but examples include thin-film distillation and solvent extraction. If the polyisocyanate composition is not purified, the concentration of unreacted diisocyanate present in the polyisocyanate composition tends to exceed 2.0% by mass.

[0024] [Polyester polyol] Polyester polyols are composed of dicarboxylic acid units having 8 or fewer carbon atoms and polyol units. In other words, they are derived from dicarboxylic acids having 8 or fewer carbon atoms and polyols. By having dicarboxylic acids having 8 or fewer carbon atoms as constituent units, polyester polyols can have an excellent appearance when cured and good hydrolysis resistance.

[0025] In dicarboxylic acids with 8 or fewer carbon atoms, the number of carbon atoms refers to the number of carbon atoms constituting the dicarboxylic acid, excluding the two carbon atoms contained in the two carboxyl groups. The lower limit of the number of carbon atoms is not particularly limited, but for example, it can be 1 or more, and is preferably 2 or more.

[0026] Examples of dicarboxylic acids having 8 or fewer carbon atoms include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, phthalic acid, isophthalic acid, terephthalic acid, and 1,4-cyclohexanedicarboxylic acid. Among these, aliphatic dicarboxylic acids having 8 or fewer carbon atoms are preferred, with succinic acid or adipic acid being more preferred.

[0027] The polyol constituting the polyester polyol is not particularly limited, but for example, a polyol having a molecular weight of 50 to 500 can be used. Examples of polyols include ethylene glycol, propylene glycol, diethylene glycol, 1,3-butylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, trimethylpentanediol, cyclohexanediol, trimethylolpropane, glycerin, pentaerythritol, 2-methylolpropanediol, and ethoxylated trimethylolpropane. Among these, aliphatic polyols are preferred.

[0028] Preferred polyester polyols include, for example, those composed of aliphatic dicarboxylic acid units having 8 or fewer carbon atoms and aliphatic polyol units.

[0029] Polyester polyols may be synthesized or commercially available. Polyester polyols are obtained by a condensation reaction between a mixture of the above-mentioned polyols and a mixture of the above-mentioned dicarboxylic acids, either individually or in a mixture of two or more.

[0030] Examples of commercially available polyester polyols include "Polylite® OD-X-106" and "Polylite® OD-X-2518," both manufactured by DIC Corporation.

[0031] The number-average molecular weight of the polyester polyol is preferably between 1000 and 4000, more preferably between 1500 and 3500, and even more preferably between 2000 and 3000. Having a number-average molecular weight of the polyester polyol above the lower limit improves the hydrolysis properties of the polyisocyanate composition. On the other hand, having a number-average molecular weight below the upper limit further suppresses the thickening of the polyisocyanate composition. The number-average molecular weight of polyester polyols can be calculated using gel permeation chromatography (GPC) based on polystyrene.

[0032] The average number of hydroxyl groups in the polyester polyol is preferably 2.0 to 4.0, more preferably 2.0 to 3.0, and even more preferably 2.4 to 2.9. Having an average number of hydroxyl groups above the lower limit of the polyester polyol improves the crosslinking properties of the polyisocyanate composition, resulting in superior coating performance. Conversely, having an average number below the upper limit of the polyisocyanate composition improves its flexibility.

[0033] The average number of hydroxyl groups (average number of OH groups) of a polyester polyol can be determined, for example, by the following formula.

[0034] "Average number of OH groups" = {(number-average molecular weight of polyester polyol) × OH% × 0.01} / 17

[0035] Note that "OH%" represents the hydroxyl group content (mass%). The hydroxyl value can be measured by potentiometric titration, and the hydroxyl group equivalent can be calculated using the following formula before determining the hydroxyl group content.

[0036] "Hydroxyl equivalent" = (56.1 × 1000) / (Hydroxyl value) "Hydroxyl group content (mass%)" = 100 x 17 / (hydroxyl group equivalent)

[0037] <Method for producing polyisocyanate composition> Polyisocyanates are obtained by reacting the above-mentioned diisocyanate with the above-mentioned polyester polyol.

[0038] The amount of polyester polyol blended can be, for example, 50 parts by mass or more and 100 parts by mass or 53 parts by mass or 90 parts by mass or 55 parts by mass or 80 parts by mass per 100 parts by mass of diisocyanate.

[0039] During the reaction, the molar ratio of isocyanate groups of the diisocyanate to the hydroxyl groups of the polyester polyol (molar ratio of isocyanate groups / hydroxyl groups) (NCO / OH) is 3.0 or higher. When the above molar ratio is above the above lower limit, the amount of unreacted diisocyanate monomer remaining can be effectively reduced, and a polyisocyanate composition with excellent coating appearance and hydrolysis properties can be obtained. The upper limit of the above molar ratio is not particularly limited, but it can be 40 or less. From the viewpoint of further increasing the curing speed of the coating film, the above molar ratio is preferably 4.0 to 35, more preferably 4.5 to 30, more preferably 5.0 to 23, and even more preferably 5.5 to 20.

[0040] The reaction between polyester polyol and diisocyanate is carried out as follows. The reaction temperature is usually between room temperature (around 23°C) and 200°C, and preferably between 60°C and 120°C. A reaction temperature above the lower limit shortens the reaction time, while a temperature below the upper limit helps to avoid undesirable side reactions that increase the viscosity of the polyisocyanate, and also helps to avoid discoloration of the resulting polyisocyanate.

[0041] The reaction may be carried out without a solvent, or with any solvent that is inert to the isocyanate group. Furthermore, if necessary, a known catalyst may be used to accelerate the reaction between the isocyanate group and the hydroxyl group.

[0042] <Application> The polyisocyanate composition of this embodiment yields a cured film with excellent appearance and hydrolysis properties, and can therefore be used as a raw material for paint compositions, resin compositions, ink compositions, particulate compositions, adhesive compositions, sealants, films, foams, plastic materials, etc., where the above performance is required. In particular, it is preferably used as a curing agent for paint compositions or resin compositions.

[0043] ≪Cured film≫ The cured film of this embodiment is obtained by curing the above-described polyisocyanate composition in the presence of a catalyst.

[0044] The cured film of this embodiment has excellent appearance and hydrolysis properties.

[0045] The cured film of this embodiment can be produced, for example, by diluting or dissolving the polyisocyanate composition described above with a solvent as needed, adding a catalyst, coating it onto a substrate using a coater or the like, drying it as needed, and curing it with heat.

[0046] The catalysts used are not particularly limited, but examples include those listed in (a) to (f) below. These may be used individually or in combination. (a) Organotin compounds such as tin octanoate, tin 2-ethyl-1-hexanoate, tin ethylcaproate, tin laurate, tin palmitate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dimalate, dibutyltin dilaurate, dioctyltin diacetate, and dioctyltin dilaurate. (b) Organic zinc compounds such as zinc chloride, zinc octanoate, zinc 2-ethyl-1-hexanoate, zinc 2-ethylcaproate, zinc stearate, zinc naphthenate, and zinc acetylacetone. (c) Organic titanium compounds. (d) Organic zirconium compounds. (e) Tertiary amines such as triethylamine, tributylamine, N,N-diisopropylethylamine, and N,N-dimethylethanolamine. (f) Diamines such as triethylenediamine, tetramethylethylenediamine, and 1,4-diazabicyclo[2.2.2]octane. [Examples]

[0047] The embodiment will be described in more detail below based on examples and comparative examples, but the embodiment is not limited in any way by the following examples.

[0048] <Test Items> The polyester polyol used as the raw material, as well as the polyisocyanate compositions produced in the examples and comparative examples, were subjected to measurement and evaluation of their physical properties according to the methods described below.

[0049] [Physical Properties 1] (Isocyanate group content) First, 2 g to 3 g of the sample was accurately weighed into a flask (Wg). Next, 20 mL of toluene was added and the sample was dissolved. Then, 20 mL of a 2 N toluene solution of di-n-butylamine was added and mixed, and the mixture was left at room temperature for 15 minutes. Next, 70 mL of isopropyl alcohol was added and mixed. This solution was then titrated with a 1 N hydrochloric acid solution (factor F) on an indicator. The obtained titration value was defined as V2 mL. Next, the titration value obtained without the polyisocyanate sample was defined as V1 mL. Then, the isocyanate group content (NCO%) (mass%) of the polyisocyanate composition was calculated from the following formula.

[0050] Isocyanate group content (mass%) = (V1-V2)×F×42 / (W×1000)×100

[0051] [Physical Properties 2] (number average molecular weight) The number-average molecular weight is the number-average molecular weight and weight-average molecular weight relative to polystyrene, measured by gel permeation chromatography (GPC) using the following apparatus.

[0052] (Measurement conditions) Equipment: HLC-802A, manufactured by Tosoh Corporation Column: Tosoh Corporation, G1000HXL x 1 G2000HXL x 1 G3000HXL x 1 Carrier: Tetrahydrofuran Detection method: Differential refractometer

[0053] [Physical Properties 3] (Average number of hydroxyl groups) The average number of hydroxyl groups (average number of OH groups) in polyester polyols was determined by the following formula.

[0054] "Average number of OH groups" = {(number-average molecular weight of polyester polyol) × OH% × 0.01} / 17

[0055] In the above formula, the "number-average molecular weight of the polyester polyol" is the value calculated in "Physical Properties 2" above. Also, "OH%" represents the hydroxyl group content (mass%), and the hydroxyl value was measured by potentiometric titration, and the hydroxyl group equivalent was calculated using the following formula, after which the hydroxyl group content was calculated.

[0056] "Hydroxyl equivalent" = (56.1 × 1000) / (Hydroxyl value) "Hydroxyl group content (mass%)" = 100 x 17 / (hydroxyl group equivalent)

[0057] [Physical Properties 4] (Content of aliphatic diisocyanates relative to the total mass of diisocyanates (mass%)) The weight ratio of aliphatic diisocyanates to the total amount of diisocyanates is: 13 The measurement was performed using the 1C-NMR method as follows. As an example, the measurement method for a polyisocyanate composition containing HDI as an aliphatic diisocyanate and IPDI as an alicyclic diisocyanate is as follows.

[0058] The polyisocyanate composition was dissolved in deuterium chloroform at a concentration of 20% by mass (after dissolution, 0.03% by mass of tetramethylsilane was added to the polyisocyanate composition). The chemical shift standard was set to 0 ppm for the signal of the carbon of the methyl group of tetramethylsilane. The measurement was performed using a quantitative mode called the NNE method. Under these measurement conditions, the signals of the carbons of the two types of methyl groups emanating from the cyclohexane ring of the IPDI constituent unit were observed around 31.5–32.5 ppm and around 27.0–28.0 ppm. The carbons at positions 2–5 of the hexamethylene chain of the HDI constituent unit were observed around 26.0–27.0 ppm, around 27.0–28.0 ppm, around 29.0–30.0 ppm, and around 31.0–31.5 ppm. Therefore, the molar ratio (HDI / IPDI) and mass ratio (HDI mass / IPDI mass) of the constituent units of HDI to the constituent units of IPDI were calculated using the following formulas.

[0059] 1. The area of ​​the signal originating from the constituent units of IPDI around 31.5-32.5 ppm was set to 1.0, and the area of ​​each signal was converted accordingly.

[0060] 2. HDI / IPDI was calculated using the following formula. HDI / IPDI ={(Area of ​​signal around 26.0~27.0 ppm + Area of ​​signal around 27.0~28.0 ppm + Area of ​​signal around 29.0~30.0 ppm + Area of ​​signal around 31.0~31.5 ppm) / (Area corresponding to the signal of one carbon atom of the methyl group emanating from the cyclohexane ring, a constituent unit of IPDI, observed around 27.0~28.0 ppm)} / 4

[0061] 3. The HDI mass / IPDI mass ratio was calculated using the following formula. HDI mass / IPDI mass = (HDI / IPDI)×(168 / 222)

[0062] [Physical Properties 5] (Concentration of unreacted diisocyanate monomer) The peak area percentage corresponding to the molecular weight of the unreacted diisocyanate obtained by the GPC measurement (for example, 168 for HDI) was expressed as the mass concentration of the unreacted diisocyanate monomer in the polyisocyanate composition.

[0063] [Preparation of hardened film] Each polyisocyanate composition was diluted with butyl acetate to a solid content of 57% by mass. Then, 3000 ppm by mass of dibutyltin dilaurate (DBT, manufactured by Nitto Chemical Co., Ltd., trade name "Neostan U-100"), a tin catalyst, was added relative to the solid content to prepare a diluted solution. Subsequently, the diluted solution was applied to a glass plate to a dry film thickness of 30 μm, and the plate was kept at 23°C and 50% RH for 7 days to obtain a cured film.

[0064] <Evaluation Method> [Rating 1] (Coating film curing speed) After applying the above diluted solution to a glass plate to a dry film thickness of 30 μm, the curing properties of the coating film after one day in an environment of 23°C and 50% RH were determined by touch and the presence or absence of sagging of the coating film, and the coating film curing speed was evaluated according to the following evaluation criteria.

[0065] (Evaluation Criteria) ○: No tackiness and no paint film dripping. △: Has tack and no paint film drips. ×: Has tackiness and paint film is dripping.

[0066] [Rating 2] (exterior) The appearance of the obtained cured film was visually observed and evaluated according to the following evaluation criteria.

[0067] (Evaluation Criteria) ○: Transparent uniform ×: Turbidity present

[0068] [Rating 3] (hydrolyzable) 0.1 g of the obtained cured film was weighed out and kept in ion-exchanged water at 60°C for 14 days. After removal and drying, the remaining amount of coating film was weighed out. The percentage obtained by dividing the remaining amount of coating film after immersion by the weight before immersion was calculated as the survival rate (mass%) and evaluated according to the following evaluation criteria.

[0069] (Evaluation Criteria) ○: Remaining percentage less than 96% by mass ×: Survival rate 96% by mass or more

[0070] <Synthesis of polyester polyols> [Synthesis Example 1] (Synthesis of polyester polyol A-3) In a flask equipped with a stirring rod, temperature sensor, and rectification tube, 40 g of 1,3-butylene glycol, 170 g of 1,6-hexanediol, 220 g of neopentyl glycol, 83 g of 2-ethyl-1,3-hexanediol, and 590 g of adipic acid (4 carbon atoms) were charged. Dry nitrogen was introduced into the flask, and the mixture was heated between 180°C and 210°C while stirring to carry out the esterification reaction. The reaction was stopped when the acid value fell below 0.5 mg KOH / g, yielding polyester polyol A-3 with a number-average molecular weight of 2,100, a hydroxyl value of 60 mg KOH / g, and an average number of hydroxyl functional groups of 2.1.

[0071] [Synthesis Example 2] (Synthesis of polyester polyol A-4) In a flask equipped with a stirring rod, temperature sensor, and rectification tube, 160 g of 1,3-butylene glycol, 250 g of 1,6-hexanediol, 227 g of 2-ethyl-1,3-hexanediol, and 575 g of succinic acid (2 carbon atoms) were charged. Dry nitrogen was introduced into the flask, and the mixture was heated between 180°C and 210°C while stirring to carry out the esterification reaction. The reaction was stopped when the acid value fell below 0.5 mg KOH / g, yielding polyester polyol A-4 with a number-average molecular weight of 2,300, a hydroxyl value of 60 mg KOH / g, and an average number of hydroxyl functional groups of 2.4.

[0072] [Synthesis Example 3] (Synthesis of polyester polyol A-5) In a flask equipped with a stirring rod, temperature sensor, and rectification tube, 100 g of 1,3-butylene glycol, 150 g of 1,6-hexanediol, 160 g of 2-ethyl-1,3-hexanediol, and 600 g of sebacic acid (8 carbon atoms) were charged. Dry nitrogen was introduced into the flask, and the mixture was heated between 180°C and 210°C while stirring to carry out the esterification reaction. The reaction was stopped when the acid value fell to 0.5 mg KOH / g or less, yielding polyester polyol A-5 with a number-average molecular weight of 2,000, a hydroxyl value of 60 mg KOH / g, and an average number of hydroxyl functional groups of 2.0.

[0073] [Synthesis Example 4] (Synthesis of polyester polyol A-6) In a flask equipped with a stirring rod, temperature sensor, and rectification tube, 100 g of 1,3-butylene glycol, 140 g of 1,6-hexanediol, 150 g of 2-ethyl-1,3-hexanediol, and 650 g of dodecanedioic acid (C10) were charged. Dry nitrogen was introduced into the flask, and the mixture was heated between 180°C and 210°C while stirring to carry out the esterification reaction. The reaction was stopped when the acid value fell below 0.5 mg KOH / g, yielding polyester polyol A-6 with a number-average molecular weight of 2,000, a hydroxyl value of 60 mg KOH / g, and an average number of hydroxyl functional groups of 2.0.

[0074] <Production of polyisocyanate compositions> [Example 1] (Manufacturing of polyisocyanate composition PA-a1) A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was placed under a nitrogen atmosphere. 1000 g of hexamethylene diisocyanate (HDI) and 746 g of polyester polyol (DIC Corporation, trade name "Polylite® OD-X-106", containing adipic acid units, number average molecular weight 2,400, average number of hydroxyl groups 2.6) were charged into the flask, and the reactor temperature was maintained at 100°C under stirring to allow the urethane reaction to proceed. After filtering the reaction solution, unreacted HDI was removed using a thin-film evaporator to obtain polyisocyanate composition PA-a1. The obtained PA-a1 had an NCO content of 3.9% by mass and a residual HDI content of 0.7% by mass.

[0075] [Examples 2-7 and Comparative Examples 1-4] (Production of polyisocyanate compositions PA-a2 to PA-a7 and PA-b1 to PA-b4) Each polyisocyanate composition was obtained using the same method as in Example 1, except that the type and amount of polyester polyol were as shown in the table below.

[0076] [Example 8] (Manufacturing of polyisocyanate composition PA-a8) A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was placed under a nitrogen atmosphere. 510 g of HDI, 490 g of isophorone diisocyanate (IPDI), and 437 g of polyester polyol A-4 were charged into the flask, and the reactor temperature was maintained at 100°C under stirring to allow the urethane reaction to proceed. After filtering the reaction solution, unreacted HDI was removed using a thin-film evaporator to obtain polyisocyanate composition PA-a8. The obtained PA-a8 had an NCO content of 4.0% by mass, a residual HDI content of 0.4% by mass, and a residual IPDI content of 0.4% by mass.

[0077] [Example 9 and Comparative Example 5] (Production of polyisocyanate compositions PA-a9 and PA-b5) Each polyisocyanate composition was obtained using the same method as in Example 8, except that the amounts of HDI and IPDI used, and the types and amounts of polyester polyols were as shown in the table below.

[0078] [Comparative Example 6] (Manufacturing of polyisocyanate composition PA-b6) A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was placed under a nitrogen atmosphere. 1000 g of HDI and 50 g of polycaprolactone polyol (manufactured by Daicel Corporation, trade name "Praxel® 303", number average molecular weight 300, average number of hydroxyl functional groups 3.0) were charged, and the reactor temperature was maintained at 90°C for 1 hour under stirring to carry out the urethane reaction. After that, the reactor temperature was maintained at 60°C, and the isocyanuration catalyst tetramethylammonium caproate was added. When the yield reached 54% by mass, phosphoric acid was added to stop the reaction. After filtering the reaction solution, unreacted HDI was removed using a thin-film evaporator to obtain the polyisocyanate composition PA-b6. The NCO content of the obtained PA-b6 was 19.2% by mass, and the residual HDI content was 0.7% by mass.

[0079] The evaluation results for the cured films prepared using the polyisocyanate compositions obtained in the examples and comparative examples are shown in Table 1 below. In Table 1, the types of polyester polyols are as follows:

[0080] (Polyester polyol) A-1: Manufactured by DIC Corporation, product name "Polylight (registered trademark) OD-X-106", contains adipic acid units, number average molecular weight 2,400, average number of hydroxyl groups 2.6 A-2: Manufactured by DIC Corporation, product name "Polylight (registered trademark) OD-X-2518", contains adipic acid units, number average molecular weight 3,000, average number of hydroxyl groups 2.9 A-3: Product synthesized in Synthesis Example 1, containing adipic acid units, number-average molecular weight 2,100, average number of hydroxyl groups 2.1 A-4: Product synthesized in Synthesis Example 2, containing succinic acid units, number-average molecular weight 2,300, average number of hydroxyl groups 2.4 A-5: Synthesized product from Synthesis Example 3, containing sebacic acid units, number-average molecular weight 2,000, average number of hydroxyl group functional groups 2.0 A-6: Synthesized product from Synthesis Example 4, containing dodecanedioic acid units, number-average molecular weight 2,000, average number of hydroxyl groups 2.0 A-7: Manufactured by Kawasaki Chemical Industries, Ltd., product name "Maximol (registered trademark) SDK-145", contains succinic acid units, number average molecular weight 1,250, average number of hydroxyl groups 2.0 A-8: Manufactured by Daicel Corporation, product name "Plaxel (registered trademark) 303", number average molecular weight 300, average number of hydroxyl groups 3.0

[0081] [Table 1]

[0082] [Table 2]

[0083] As shown in Tables 1 and 2, polyisocyanate compositions PA-a1 to PA-a9 (Examples 1 to 9), which contain aliphatic diisocyanates and polyisocyanates derived from polyester polyols having a specific structure, have an NCO content of 3.9% to 5.3% by mass, a molar ratio NCO / OH of 3.0 or more during the reaction between the isocyanate groups of the isocyanate and the hydroxyl groups of the polyester polyol, have an aliphatic diisocyanate content of 10% to 100% by mass relative to the total mass of diisocyanates, and have an unreacted diisocyanate content of 2.0% by mass or less, exhibited excellent curing speed of the coating film, as well as excellent appearance and hydrolysis resistance of the cured film.

[0084] On the other hand, polyisocyanate composition PA-b1 (Comparative Example 1), which had an NCO content of more than 5.9% by mass, exhibited good hydrolysis properties when formed into a cured film, but had a poor appearance. In the polyisocyanate composition PA-b2 (Comparative Example 2), in which the number of carbon atoms in the dicarboxylic acid unit exceeds 8, the curing speed of the coating film and the appearance of the cured film were good, but the hydrolysis resistance was poor. In polyisocyanate composition PA-b3 (Comparative Example 3), which contained more than 2.0% by mass of unreacted diisocyanate, the curing speed of the coating film, as well as the appearance and hydrolysis resistance of the cured film, were all poor. Polyisocyanate composition PA-b4 (Comparative Example 4), in which the molar ratio NCO / OH during the reaction between the isocyanate group of the isocyanate and the hydroxyl group of the polyester polyol was less than 3.0 and the content of unreacted diisocyanate was more than 2.0% by mass, exhibited poor curing speed of the coating film, as well as poor appearance and hydrolysis resistance of the cured film. In polyisocyanate composition PA-b5 (Comparative Example 5), in which the aliphatic diisocyanate content relative to the total mass of diisocyanate was less than 10% by mass, the curing speed of the coating film and the hydrolysis resistance of the cured film were good, but the appearance was poor. In polyisocyanate composition PA-b6 (Comparative Example 6), which contains a polyisocyanate using a polycaprolactone polyol instead of a polyester polyol having a specific structure, and has an NCO content of more than 5.9% by mass, the curing speed of the coating film and the appearance of the cured film were good, but the hydrolysis resistance was poor. [Industrial applicability]

[0085] The polyisocyanate composition of this embodiment provides a polyisocyanate composition that exhibits excellent appearance and hydrolysis resistance when cured as a cured film by curing the polyisocyanate composition alone.

Claims

1. A polyisocyanate composition comprising a diisocyanate and a polyisocyanate derived from a polyester polyol, The molar ratio NCO / OH during the reaction between the isocyanate group of the diisocyanate and the hydroxyl group of the polyester polyol is 3.0 or higher. The content of aliphatic diisocyanate relative to the total mass of the diisocyanate is 10% by mass or more and 100% by mass or less. It contains virtually no unreacted diisocyanates. The isocyanate group content of the polyisocyanate composition is 1.0% by mass or more and 5.7% by mass or less, relative to the total mass of the polyisocyanate composition. The aforementioned polyester polyol is composed of dicarboxylic acid units having 8 or fewer carbon atoms and polyol units. The aforementioned polyester polyol is obtained by a condensation reaction. Polyisocyanate composition for single-stage curing.

2. The polyisocyanate composition according to claim 1, wherein the number average molecular weight of the polyester polyol is 1,000 or more and 4,000 or less.

3. The polyisocyanate composition according to claim 1 or 2, wherein the average number of hydroxyl groups in the polyester polyol is 2.0 or more and 4.0 or less.

4. The polyisocyanate composition according to claim 1 or 2, wherein the polyester polyol is composed of aliphatic dicarboxylic acid units having 8 or fewer carbon atoms and aliphatic polyol units.

5. The polyisocyanate composition according to claim 1 or 2, wherein the molar ratio NCO / OH during the reaction between the isocyanate group of the diisocyanate and the hydroxyl group of the polyester polyol is 5.5 or more and 20 or less.

6. A cured film obtained by curing only the polyisocyanate composition according to claim 1 or 2 in the presence of a catalyst.

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