JP7843185B2 - Polyurethane resin-forming composition for in-mold coating, in-mold coating agent set, coating film, and in-mold coating method - Google Patents

Description

This invention relates to a polyurethane resin-forming composition for in-mold coating, an in-mold coating agent set, a coating film, and an in-mold coating method.

Compositions that form polyurethane resins are widely used as coating agents. While polyether polyols and polyester polyols have traditionally been used as reaction raw materials for polyurethane resins in general coating applications, polycarbonate polyols are increasingly being used in coating applications for plastic molded products used in automotive interior and exterior parts, etc., to provide high durability and other advantages (see, for example, Patent Document 1).

In recent years, in-mold coating has attracted attention as a method for coating the surface of plastic molded products, etc., from the perspective of reducing environmental impact (see, for example, Patent Document 2). In-mold coating is a method in which a coating agent is injected into a mold, such as a die, while the substrate is placed inside the mold, and the coating agent reacts to form a coating film on the surface of the substrate. In this method, the mold used to form the substrate can be used as the mold for coating, making it possible to coat the surface of the substrate in fewer steps compared to conventional coating methods, and reducing the amount of waste and energy consumption associated with coating.

Japanese Patent Publication No. 2014-201680 Japanese Patent Publication No. 2005-074896

Traditionally, solvents have been used to ensure the fluidity of paints. However, in in-mold painting, the use of solvents is restricted because the mold is a sealed space, thus preventing defects in paint film formation due to air bubbles, etc. Therefore, ensuring the fluidity of the paint is difficult in in-mold painting, and coupled with the constricted nature of the mold, the paint film is prone to appearance defects such as wrinkles, streaks, unevenness, defects (shorts), and discoloration. Furthermore, while high transparency is required for paint films formed for decorative purposes, forming a highly transparent paint film in in-mold painting is not always easy.

Several aspects of the present invention aim to provide a polyurethane resin-forming composition capable of forming a coating film with good film-forming properties and excellent transparency in an in-mold coating method, an in-mold coating agent set for providing the composition, a coating film formed from the composition, and an in-mold coating method using the composition.

Some aspects of the present invention provide the following [1] to [10].

[1] A polyurethane resin-forming composition for in-mold coating, comprising a non-aromatic polyisocyanate (A) that is liquid at 25°C and a polycarbonate polyol (B) that is liquid at 25°C, wherein the hydroxyl value of the polycarbonate polyol (B) is 100 to 400 mg KOH/g.

[2] The composition according to [1], wherein the non-aromatic polyisocyanate (A) comprises at least one selected from the group consisting of isocyanurate derivatives of aliphatic diisocyanates and allophanate derivatives of aliphatic diisocyanates.

[3] The composition according to [1] or [2], wherein the polycarbonate polyol (B) comprises, as monomer units, at least one selected from the group consisting of 1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-1,8-octanediol, and a linear glycol having 3 to 6 carbon atoms.

[4] The composition according to [1] or [2], wherein the polycarbonate polyol (B) contains at least two linear glycols having 3 to 6 carbon atoms as monomer units.

[5] The composition according to any one of [1] to [4], wherein the polycarbonate polyol (B) contains trimethylolpropane as a monomer unit.

[6] The composition according to any one of [1] to [5], further comprising a polyol (C) with a molecular weight of less than 200.

[7] The composition according to [6], wherein the polyol (C) comprises at least one selected from the group consisting of 1,3-butanediol and trimethylolpropane.

[8] A mold coating agent set for preparing the composition described in any of [1] to [7], comprising: a first agent containing the non-aromatic polyisocyanate (A); and a second agent containing the polycarbonate polyol (B).

[9] A coating film comprising a reaction product of any of the compositions described in [1] to [7].

[10] A mold coating method comprising: preparing a substrate and a mold in which the substrate is placed; injecting a composition described in any of [1] to [7] into the mold and applying the composition to the surface of the substrate; and reacting the composition to form a coating film on the surface of the substrate.

According to several aspects of the present invention, it is possible to provide a polyurethane resin-forming composition capable of forming a coating film with good film-forming properties and excellent transparency in an in-mold coating method, an in-mold coating agent set for providing the composition, a coating film formed from the composition, and an in-mold coating method using the composition.

This is a schematic diagram illustrating one embodiment of the in-mold coating method of the present invention.

The following describes several embodiments of the present invention. However, the present invention is not limited in any way to the embodiments described below.

In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. Unless otherwise specified, the units of the numbers before and after "~" are the same. In numerical ranges described in stages within this specification, the upper or lower limit of one stage may be replaced with the upper or lower limit of another stage. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values shown in the examples. Also, the upper and lower limits described individually can be combined in any way. The materials exemplified below may be used individually or in combination of two or more, unless otherwise specified. The content of each component in a composition, if multiple substances corresponding to each component exist in the composition, means the total amount of those multiple substances present in the composition, unless otherwise specified.

<Polyurethane resin-forming composition>
One embodiment of the present invention relates to a polyurethane resin-forming composition (hereinafter simply referred to as "the composition") comprising a non-aromatic polyisocyanate (A) that is liquid at 25°C (hereinafter also referred to as "component (A)") and a polycarbonate polyol (B) that is liquid at 25°C (hereinafter also referred to as "component (B)"), wherein the hydroxyl value of the polycarbonate polyol (B) is 100 to 400 mg KOH/g. Here, "polyurethane resin-forming property" means that the composition has the property of being able to form a polyurethane resin through the reaction of the components contained in the composition (i.e., the reaction of at least component (A) and component (B)).

The above composition, containing component (A) and component (B), exhibits excellent film-forming properties in in-mold coating. Specifically, even when coating is performed using the in-mold coating method, the above composition allows for the formation of a coating film with suppressed appearance defects such as wrinkles, streaks, unevenness, defects (shorts), and discoloration. Therefore, the above composition is suitably used as a polyurethane resin-forming composition (in-mold coating agent) for in-mold coating. In particular, the above composition exhibits excellent film-forming properties even at low temperatures (for example, when in-mold coating is performed under conditions where the temperature of the composition from two-component mixing to injection into the mold is 30°C or lower, and the mold temperature is 85°C or lower), making it suitable for coating substrates with low heat resistance. Furthermore, by using, for example, an isocyanurate of an aliphatic diisocyanate as component (A), it is possible to achieve both excellent film-forming properties in low-temperature in-mold coating and rapid low-temperature curing properties (for example, rapid curing at 85°C or lower), thereby increasing production efficiency in coating substrates with low heat resistance.

Furthermore, the above composition can form a coating film with excellent transparency. In particular, because the above composition has good coating film formation properties in in-mold painting at low temperatures, it can suppress discoloration and clouding of the coating film caused by painting in a high-temperature sealed section, and can form a coating film with excellent transparency in in-mold painting.

Furthermore, since the above composition contains a polycarbonate polyol as component (B), it is easy to obtain a coating film with sufficiently high mechanical properties (hardness, tensile elongation, tensile strength, and tear strength) using this composition.

The polyurethane resin-forming composition may further contain, in addition to components (A) and (B), a polyol (C) with a molecular weight of less than 200 (hereinafter also referred to as "component (C)") and a catalyst (D) (hereinafter also referred to as "component (D)"), and may also contain other components. The components that may be included in the polyurethane resin-forming composition are described below.

[Component (A)]
Component (A) is a non-aromatic polyisocyanate that is liquid at 25°C. In this specification, "non-aromatic polyisocyanate" means a compound that does not have an aromatic ring and has multiple isocyanate groups. Furthermore, "liquid at 25°C" means that when heated to 80°C or higher, then left to stand at 25°C for 24 hours, and then tilted, at least slight fluidity can be observed visually.

Examples of non-aromatic polyisocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and their modified forms. Examples of modified forms include isocyanurate modified forms, allophanate modified forms, biuret modified forms, urethane modified forms, urea modified forms, carbodiimide modified forms, uretonimine modified forms, and uretdione modified forms.

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methylpentane-1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate, lysine diisocyanate, trioxyethylene diisocyanate, ethylene diisocyanate, trimethylene diisocyanate, octamethylene diisocyanate, nonamethylene diisocyanate, 2,2'-dimethylpentane diisocyanate, 2,2,4-trimethylhexane diisocyanate, decamethylene diisocyanate, butene diisocyanate, 1,3-butadiene-1,4-diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate. Examples include ethylene diisocyanate, 1,6,11-undecane triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,8-diisocyanate-4-isocyanate methyl octane, 2,5,7-trimethyl-1,8-diisocyanate-5-isocyanate methyl octane, bis(isocyanate ethyl) carbonate, bis(isocyanate ethyl) ether, 1,4-butylene glycol dipropyl ether-α,α'-diisocyanate, lysine diisocyanate methyl ester, 2-isocyanate ethyl-2,6-diisocyanate hexanoate, and 2-isocyanate propyl-2,6-diisocyanate hexanoate. These may be used individually or in combination of two or more.

Examples of alicyclic polyisocyanates include isophorone diisocyanate, cyclohexyl diisocyanate, bis(isocyanate-methyl)cyclohexane, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, dicyclohexyldimethylmethane diisocyanate, 2,2'-dimethyldicyclohexylmethane diisocyanate, bis(4-isocyanate-n-butylidene)pentaerythritol, and hydrogenated dimer acid diisocyanate. , 2-isocyanatemethyl-3-(3-isocyanatetopropyl)-5-isocyanatemethyl-bicyclo[2.2.1]-heptane, 2-isocyanatemethyl-3-(3-isocyanatetopropyl)-6-isocyanatemethyl-bicyclo[2.2.1]-heptane, 2-isocyanatemethyl-2-(3-isocyanatetopropyl)-5-isocyanatemethyl-bicyclo[2.2.1]-heptane, 2-isocyanatemethyl-2-(3-isocyanatepropyl (L)-6-isocyanatemethyl-bicyclo[2.2.1]-heptane,2-isocyanatemethyl-3-(3-isocyanatetopropyl)-5-(2-isocyanateethyl)-bicyclo-[2.2.1]-heptane,2-isocyanatemethyl-3-(3-isocyanatetopropyl)-6-(2-isocyanateethyl)-bicyclo-[2.2.1]-heptane,2-isocyanatemethyl-2-(3-isocyanatetopropyl)-5-(2-isocyanateethyl) Examples include bicyclo-[2.2.1]-heptane, 2-isocyanatemethyl-2-(3-isocyanatepropyl)-6-(2-isocyanateethyl)-bicyclo-[2.2.1]-heptane, 2,5-bis(isocyanatemethyl)-bicyclo[2.2.1]-heptane, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate. These may be used individually or in combination of two or more.

Among the polyisocyanates described above, when component (A) includes at least one selected from the group consisting of isocyanurate and allophanate derivatives of aliphatic diisocyanates, the balance between film formation during in-mold coating (e.g., film formation during in-mold coating at low temperatures) and curability (e.g., rapid curing at low temperatures) tends to be improved. In particular, when component (A) includes an isocyanurate-modified aliphatic diisocyanate, curability (e.g., rapid curing at low temperatures) tends to be improved, and when component (A) includes an allophanate-modified aliphatic diisocyanate, film formation during in-mold coating (e.g., film formation during in-mold coating at low temperatures) tends to be improved. From these viewpoints, the above-mentioned isocyanurate-modified derivative and the above-mentioned allophanate-modified derivative may be used in combination.

The content of the isocyanurate modified product in component (A) may be 10% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, or 90% by mass or more; it may be 100% by mass or less, 90% by mass or less, 70% by mass or less, 50% by mass or less, 30% by mass or less, or 10% by mass or less; and it may be 0 to 100% by mass, 10 to 90% by mass, or 30 to 70% by mass. Note that the above content is based on the total mass of component (A).

The content of the allophanate modifier in component (A) may be 10% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, or 90% by mass or more; it may be 100% by mass or less, 90% by mass or less, 70% by mass or less, 50% by mass or less, 30% by mass or less, or 10% by mass or less; and it may be 0 to 100% by mass, 10 to 90% by mass, or 30 to 70% by mass. Note that the above content is based on the total mass of component (A).

The NCO content of component (A) may be 10 to 40% by mass, and may also be 15 to 35% by mass or 19 to 30% by mass. When the NCO content of component (A) is 10% by mass or more, the coating film tends to have higher hardness. When the NCO content of component (A) is 40% by mass or less, the coating film tends to exhibit good self-healing properties. The above content is based on the total mass of component (A).

In this specification, the NCO content is the value measured by the method described in JIS K1603-1 (Test Method for Aromatic Isocyanates in Polyurethane Raw Materials).

(A) The content of component may be, for example, 20 to 90% by mass, 30 to 80% by mass, or 40 to 70% by mass, based on the total mass of the composition.

[(B) Component]
Component (B) is a polycarbonate polyol that is liquid at 25°C. The polycarbonate polyol has multiple hydroxyl groups (-OH) and multiple carbonate groups (-OCOO-). The polycarbonate polyol is, for example, a reaction product of a polyol component and a carbonate component, and contains the polyol component and the carbonate component as monomer units. From the viewpoint of obtaining better transparency, the polycarbonate polyol may be a non-aromatic polycarbonate polyol that does not have an aromatic ring (e.g., a benzene ring).

The polyol component preferably contains glycol. Glycol is a compound having a structure in which one hydroxyl group is substituted on each of two carbon atoms of a chain aliphatic hydrocarbon or a cyclic aliphatic hydrocarbon. Examples of glycols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, and 1,16-he Examples include linear glycols such as xadecanediol, 1,18-octadecanediol, and 1,20-eicosanediol, and branched glycols such as 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, 2-methyl-1,8-octanediol, and 1,12-octadecanediol. When the polyol component contains some of these glycols individually or in specific combinations of several glycols, the polycarbonate polyol is liquid at 25.

Polycarbonate polyols tend to become liquid at 25°C the lower the crystallinity of the polyol component. Furthermore, polycarbonate polyols become liquid at 25°C when two or more polyols are used in combination, and even more so when three or more polyols are used in combination. Also, when two or more polyols are used in combination, the smaller the ratio (mass ratio) of the linear single component, the more likely the polycarbonate polyol is to become liquid at 25°C. For example, when two linear glycols are used in combination, the closer the ratio (mass ratio) of the two glycols is to 1:1, the more likely the polycarbonate polyol is to become liquid at 25°C. Additionally, when two or more polyols are used in combination, the presence of polyols with short carbon chains (e.g., polyols with 6 or fewer carbon atoms) and/or branched polyols further increases the likelihood of the polycarbonate polyol becoming liquid at 25°C.

For example, if the polyol component contains at least one selected from the group consisting of 1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-1,8-octanediol, and a linear glycol having 3 to 6 carbon atoms (i.e., if the polycarbonate polyol contains at least one selected from the group consisting of 1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-1,8-octanediol, and a linear glycol having 3 to 6 carbon atoms as monomer units), the polycarbonate polyol tends to become liquid at 25°C.

Furthermore, for example, if the polyol component contains at least two linear glycols having 3 to 6 carbon atoms (i.e., if the polycarbonate polyol contains at least two linear glycols having 3 to 6 carbon atoms as monomer units), the polycarbonate polyol tends to become liquid at 25°C.

The polyol component may include a polyol having three or more hydroxyl groups, from the viewpoint of further improving the mechanical properties of the coating film and forming a harder coating film. The polyol having three or more hydroxyl groups may be at least one selected from the group consisting of 1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-1,8-octanediol, and/or used in combination with a linear glycol having 3 to 6 carbon atoms. The polyol having three or more hydroxyl groups is, for example, a non-aromatic polyol that does not have an aromatic ring. Specific examples of polyols having three or more hydroxyl groups include trimethylolethane, trimethylolpropane, 2-hydroxy-2-methyl-1,4-butanediol, glycerin, ditrimethylolethane, ditrimethylolpropane, diglycerin, pentaerythritol, xylitol, dipentaerythritol, sorbitol, and 1,3,5-tris(hydroxymethyl)benzene.

The content of polyols having three or more hydroxyl groups in the polyol component may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, from the viewpoint of further improving the mechanical properties of the coating film. From the viewpoint of composition compatibility and further improving the self-healing properties of the coating film, it may be 45% by mass or less, 35% by mass or less, or 30% by mass or less. From these viewpoints, the content of polyols having three or more hydroxyl groups may be 5 to 45% by mass, 10 to 35% by mass, or 15 to 30% by mass. Note that the above content is based on the total mass of the polyol component.

The carbonate component can be any compound capable of condensing with a polyol to produce a polycarbonate polyol. Examples of carbonate components include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, and dipropyl carbonate; alkylene carbonates such as ethylene carbonate and propylene carbonate; and diaryl carbonates such as diphenyl carbonate, dinaphthyl carbonate, diantryl carbonate, diphenanthryl carbonate, diindanyl carbonate, and bistetrahydronaphthyl carbonate. These may be used individually or in combination of two or more.

Polycarbonate polyols may be reaction products obtained by reacting the reaction product of a polyol component and a carbonate component, or a polyol component and a carbonate component, with another reaction component (e.g., a polyester polyol), for example, in the presence of a catalyst. When the other component is a polyester polyol, the polycarbonate polyol can be called a polyester polycarbonate polyol. A polyester polycarbonate polyol contains the above-mentioned polyol component and carbonate component as monomer units, and also contains an ester skeleton derived from the polyester polyol.

Other reactants include, for example, cyclic esters such as ε-caprolactone and polycaprolactone oligomers. These may be used individually or in combination of two or more. The amount of other reactants may be, for example, 0 to 40 parts by mass, 5 to 35 parts by mass, or 10 to 30 parts by mass per 100 parts by mass of polycarbonate polyol.

The hydroxyl value of component (B) is 100 to 400 mg KOH/g. Having the hydroxyl value of component (B) within this range enhances the low-temperature processability of the composition, enabling the formation of a coating film with reduced appearance defects in the in-mold coating method. From the viewpoint of further enhancing the low-temperature processability of the composition, improving its compatibility, and further improving coating film formation, the hydroxyl value of component (B) may be 150 mg KOH/g or higher or 200 mg KOH/g or higher. From the viewpoint of forming a coating film with superior mechanical properties, the hydroxyl value of component (B) may be 380 mg KOH/g or lower or 350 mg KOH/g or lower.

In this specification, hydroxyl value refers to the number of milligrams (mg) of potassium hydroxide equivalent to hydroxyl groups in 1 g of sample, and is measured in accordance with JIS K1557-1.

The molecular weight of component (B) is, for example, 200 or more. From the viewpoint of obtaining a coating film with superior mechanical properties, the molecular weight of component (B) may be 300 or more, 400 or more, or 450 or more. From the viewpoint of further improving the low-temperature processability of the composition, increasing the compatibility of the composition, and further improving coating film formation, the molecular weight of component (B) may be 1100 or less, 1000 or less, or 800 or less. From these viewpoints, the molecular weight of component (B) may be 200 to 1100, 300 to 1000, or 400 to 800.

In this specification, molecular weight refers to the molecular weight measured using gel permeation chromatography (for example, the converted molecular weight using a polycarbonate diol composed of 1,6-hexanediol as a calibration curve), but it can also be calculated from the hydroxyl value and the number of hydroxyl groups (theoretical value).

The above component (B) can be obtained, for example, by reacting a polyol component and a carbonate component under a catalyst such as tetrabutoxytitanium. The reaction may be carried out under a nitrogen atmosphere in a reaction apparatus equipped with a stirrer, thermometer, heating device, and distillation column. Specifically, for example, under a nitrogen atmosphere, the temperature can be gradually increased to 190°C while distilling off ethanol, and then the pressure can be gradually reduced to 0.5 kPa or less. The reaction can then be carried out at a pressure of 0.5 kPa or less for 4 hours or more to obtain component (B) as a reaction product of the polyol component and the carbonate component. The mixing ratio of each component may be adjusted as appropriate, for example, from the viewpoint of hydroxyl value.

(B) The content of component may be, for example, 10 to 80% by mass, 20 to 70% by mass, or 30 to 60% by mass, based on the total mass of the composition.

[(C) Component]
Component (C) is a polyol with a molecular weight of less than 200 (excluding polyols that fall under component (B)). The molecular weight of component (C) may be, for example, 50 or more and less than 200, and may be 60 to 180 or 70 to 150.

Component (C) may be a diol or a polyol having three or more hydroxyl groups. Component (C) preferably contains a diol and/or a triol. When component (C) contains a diol, a coating film with superior self-healing properties is more easily obtained, and the compatibility of the composition is improved, as well as the film-forming properties are enhanced by lower viscosity. When component (C) contains a triol, a coating film with superior mechanical properties is more easily obtained. From the viewpoint of achieving a higher level of balance between the self-healing and mechanical properties of the coating film, it is preferable that component (C) contains both a diol and a triol.

Examples of diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, dimethylolheptane, diethylene glycol, dipropylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, and dimerdiol. Among these, 1,3-butanediol is preferred. The above diols can be used individually or in combination of two or more.

The diol content may be 1 to 15% by mass, 3 to 12% by mass, or 5 to 10% by mass, based on the total mass of the composition, from the viewpoint of obtaining a coating film with superior self-healing properties, improving the compatibility of the composition, and further enhancing coating film formation by lowering viscosity.

Examples of triols include trimethylolethane, trimethylolpropane, 2-hydroxy-2-methyl-1,4-butanediol, glycerin, ditrimethylolethane, ditrimethylolpropane, diglycerin, and pentaerythritol. Among these, trimethylolpropane is preferred. The above triols can be used individually or in combination of two or more.

The triol content may be 3 to 20% by mass, 4 to 15% by mass, or 5 to 10% by mass, based on the total mass of the composition, from the viewpoint of facilitating the formation of a harder coating film and obtaining a coating film with superior mechanical properties.

(C) The content of component C may be 30% by mass or less, 25% by mass or less, or 20% by mass or less, based on the total mass of the composition, from the viewpoint of suppressing a decrease in self-healing properties and curing properties.

[(D) Component]
Component (D) is a catalyst for forming urethane resin. Examples of component (D) include organotin compounds such as dioctyl tin dilaurate, dibutyl tin dilaurate, dibutyl tin dioctoate, and tin 2-ethylhexanoate; iron compounds such as iron acetylacetonate and iron chloride; lithium compounds such as lithium acetylacetonate; lead compounds such as lead octoate; bismuth compounds such as bismuth octoate; and tertiary amine catalysts such as triethylamine and triethylenediamine.

The content of component (D) may be, for example, 0.001 to 1.000% by mass, based on the total mass of the composition.

[Other ingredients]
Other components include, for example, antioxidants such as 2,6-di-tert-butyl-4-methylphenol, ultraviolet absorbers, pigments, dyes, solvents, flame retardants, hydrolysis inhibitors, lubricants, plasticizers, fillers, antistatic agents, dispersants, storage stabilizers, thickeners, and internal release agents.

The composition may further contain isocyanate group-containing compounds other than component (A) as other components. However, from the viewpoint of obtaining better transparency, it is preferable that the composition does not contain isocyanate group-containing compounds having aromatic rings (e.g., aromatic polyisocyanates). The content of isocyanate group-containing compounds having aromatic rings is preferably 5% by mass or less, and more preferably 0% by mass, based on the total mass of the composition.

The composition may further contain hydroxyl group-containing compounds other than components (B) and (C). However, from the viewpoint of obtaining better transparency, it is preferable that the composition does not contain hydroxyl group-containing compounds having aromatic rings (e.g., aromatic polyols). The content of hydroxyl group-containing compounds having aromatic rings is preferably 5% by mass or less, and more preferably 0% by mass, based on the total mass of the composition.

The ratio of moles of isocyanate groups in the isocyanate group-containing compound to moles of hydroxyl groups in the hydroxyl group-containing compound (NCO/OH equivalent) in the composition may be 0.8 or higher, and may be 0.9 or higher or 1.0 or higher, from the viewpoint of suppressing excess hydroxyl groups and further improving the durability and mechanical properties of the coating film. The NCO/OH equivalent may be 1.3 or lower, and may be 1.2 or lower or 1.1 or lower, from the viewpoint of suppressing excess isocyanate groups and further improving the durability and mechanical properties of the coating film. The NCO/OH equivalent may be 0.8 to 1.3, 0.9 to 1.2, or 1.0 to 1.1, from the above viewpoint.

The composition may contain volatile organic compounds (VOCs), but from the viewpoint of suppressing the occurrence of defects in the appearance of the coating film due to the volatilization of VOCs within the mold, the content of VOCs in the composition is preferably 5% by mass or less, and more preferably 1% by mass or less, based on the total mass of the composition. The lower limit of the VOC content is 0% by mass. Note that VOCs refer to organic compounds with a boiling point of 150°C or less at 1 atm.

The compositions described above may form a polyurethane resin with a urethane group concentration of 1 to 5 mmol/g. Here, urethane group concentration refers to the number of moles of urethane groups (-NHCOO-) contained in the polyurethane resin, based on the total mass of the formed polyurethane resin. Therefore, the urethane group concentration can be calculated from the content of the active hydrogen group-containing compound and the isocyanate group-containing compound. Compositions forming a polyurethane resin with a urethane group concentration of 1 mmol/g or more tend to yield coatings with superior mechanical properties. Compositions forming a polyurethane resin with a urethane group concentration of 5 mmol/g or less tend to exhibit excellent compatibility and curability. From the viewpoint of obtaining coatings with even better mechanical properties, the above urethane group concentration may be 1.5 mmol/g or more or 4.5 mmol/g or more, and from the viewpoint of further improving the compatibility and curability of the composition, it may be 4 mmol/g or less or 2 mmol/g or less.

<In-mold coating agent set>
Another embodiment of the present invention relates to an in-mold coating agent set for preparing the composition of the above embodiment. The in-mold coating agent set comprises a first agent containing component (A) and a second agent containing component (B).

The in-mold coating agent set may further comprise other agents containing components other than those described in (A) and (B). The components other than those described in (A) and (B) contained in the above composition may be incorporated into the first agent, the second agent, or other agents. However, component (C) is preferably incorporated into the second agent, component (D) is preferably incorporated into either the first or second agent, isocyanate group-containing compounds other than component (A) are preferably incorporated into the first agent, and hydroxyl group-containing compounds other than component (B) are preferably incorporated into the second agent.

The first and second agents may be prepared so that the above composition is obtained by mixing them, or they may be prepared so that the above composition is obtained by mixing the first agent, the second agent, and other agents other than the first and second agents.

The viscosity of the first component at 25°C may be 1 to 15,000 mPa·s, and may also be 5 to 1,000 mPa·s or 10 to 5,000 mPa·s. When the viscosity of the first component at 25°C is within the above range, a composition (coating agent) with even better film-forming properties is more likely to be obtained.

The viscosity of the second component at 25°C may be 1 to 15,000 mPa·s, and may also be 5 to 1,000 mPa·s or 10 to 5,000 mPa·s. When the viscosity of the second component at 25°C is within the above range, a composition (coating agent) with even better film-forming properties is more likely to be obtained.

In this specification, viscosity at 25°C is the value measured using a B-type viscometer.

When using the in-mold coating set, for example, the first agent, the second agent, and any other agents used may be mixed so that the NCO/OH equivalent falls within the range described above.

<Coating film>
Another embodiment of the present invention relates to a coating film comprising a reaction product (e.g., a cured product) of the composition of the above embodiment. The reaction product of the composition is obtained by the reaction of components contained in the composition and comprises a polyurethane resin produced by the reaction of component (A), component (B), and optionally other components (e.g., component (C)). The coating film may contain some of the components contained in the composition (e.g., unreacted components).

The thickness of the coating film is, for example, 1 to 10,000 μm, and may also be 5 to 5,000 μm or 10 to 1,000 μm.

The coating film may be provided on a substrate such as a plastic molded product and constitute a part of a component including the substrate (for example, an interior part of an automobile). That is, as another embodiment, the present invention provides a component comprising a substrate and the above-mentioned coating film provided on the substrate.

<In-mold painting method>
Another embodiment of the present invention relates to an in-mold coating method comprising: preparing a substrate and a mold in which the substrate is placed; injecting the composition of the above embodiment into the mold and applying the composition to the surface of the substrate; and reacting the composition to form a coating film on the surface of the substrate. According to this method, the coating film of the above embodiment can be obtained. The in-mold coating method of this embodiment will now be described with reference to Figure 1.

Figure 1 is a schematic diagram illustrating one embodiment of an in-mold coating method. In this embodiment, a substrate 1 and a mold 2 in which the substrate 1 is placed are first prepared (see Figure 1(a)).

The base material 1 is, for example, a molded body (plastic molded product) made from a plastic material. Examples of plastic materials include acrylic polyol resin, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene phthalate resin, polystyrene resin, AS resin, ABS resin, polycarbonate-ABS resin, 6-nylon resin, 6,6-nylon resin, MXD6 nylon resin, polyvinyl chloride resin, polyvinyl alcohol resin, polyurethane resin, phenolic resin, melamine resin, polyacetal resin, chlorinated polyolefin resin, polyolefin resin, polyamide resin, polyetheretherketone resin, polyphenylene sulfide resin, NBR resin, chloroprene resin, SBR resin, SEBS resin, and combinations thereof. The surface of the molded body may be subjected to surface treatment such as corona discharge treatment. Other coatings that can serve as intermediate layers may be formed on the surface of the molded body.

Mold 2 has a gap 2a for forming a coating film between the inner wall of mold 2 and the substrate 1, an opening 2b for injecting the coating agent, and a flow path 2c for supplying the coating agent from the opening 2b to the gap 2a. Mold 2 may be the same mold used for molding the substrate 1, and may have an internal structure identical in shape to the target substrate 1. In this case, for example, after injecting a plastic material heated and melted in an injection cylinder into mold 2, cooling and pressurizing to mold the substrate 1, the clamping force may be reduced, or the gap between the resulting molded product (substrate) and the inner wall of the mold may be slightly opened to provide a gap 2a for forming a coating film between the substrate 1 and mold 2.

Next, the composition 6 (urethane resin-forming composition for in-mold coating) of the above embodiment is prepared by supplying the first agent 3 and the second agent 4 into the tank 5 and mixing them. The composition 6 is then injected into the mold 2 to coat the surface 1a of the substrate 1 (see Figure 1(b)). During the preparation of composition 6, the first agent 3 and the second agent 4 may be heated to ensure more uniform mixing. Furthermore, during the injection of composition 6, composition 6 and the mold 2 may be heated to an extent that does not significantly increase the viscosity of composition 6. However, the temperature of composition 6 during injection is preferably 30°C or lower, and the temperature of the mold 2 during injection is preferably 85°C or lower.

Next, by reacting with composition 6, a coating film 7 (e.g., a cured film) containing the reaction products of composition 6 is formed on the surface of the substrate 1 (see Figure 1(c)). The reaction of composition 6 may be carried out by injecting composition 6 into a heated mold. The heating temperature should not exceed the heat resistance of the substrate; from the viewpoint of coating film formation, it may be 50 to 150°C, or 50 to 85°C. To allow the reaction of composition 6 to proceed more sufficiently, the coating film may be heated again after removing the substrate from the mold.

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

<Synthesis and Evaluation of Polycarbonate Polyols>
(Synthesis Example 1)
In a reaction apparatus equipped with a stirrer, thermometer, heating device, and distillation column, 792 g of 3-methyl-1,5-pentanediol (MPD) and 88 g of 1,6-hexanediol (1,6-HG) were charged as the polyol component (mixture of polyols), 638 g of diethyl carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was charged as the carbonate component, and 0.05 g of tetrabutyl titanate was charged as a reaction catalyst. The temperature inside the apparatus was gradually increased to 190°C under a nitrogen stream. When the distillation of ethanol slowed down and the top temperature of the distillation column fell below 50°C, the temperature inside the apparatus was kept at 190°C and the pressure was gradually reduced to 0.1 kPa. The reaction was continued at a pressure of 0.1 kPa for a further 5 hours to distill off the ethanol. This synthesized the polycarbonate polyol of Synthesis Example 1.

(Synthesis examples 2-6, 10-12)
Polycarbonate polyols for Synthesis Examples 2-6 and 10-12 were synthesized in the same manner as Synthesis Example 1, except that the polyols shown in Tables 1-2 were used as polyol components in the mass ratios (unit: parts by mass) shown in Tables 1-2, and the amounts of polyol components and carbonate components were adjusted to achieve the desired hydroxyl value.

(Synthesis Example 7)
In a reaction apparatus equipped with a stirrer, thermometer, heating device, and distillation column, 695 g of 1,3-butanediol and 345 g of trimethylolpropane (TMP) were charged as the polyol component (mixture of polyols), 911 g of diethyl carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was charged as the carbonate component, and 0.1 g of lithium acetylacetonate (manufactured by Sigma-Aldrich) was charged as a reaction catalyst. The temperature inside the apparatus was gradually increased to 150°C under a nitrogen stream. When the distillation of ethanol slowed and the temperature at the top of the distillation column fell below 50°C, the temperature inside the apparatus was kept at 150°C and the pressure was gradually reduced to 2 kPa. The reaction was continued at a pressure of 2 kPa for a further 5 hours to distill off the ethanol. This synthesized the polycarbonate polyol of Synthesis Example 7.

(Synthesis examples 8-9)
Polycarbonate polyols for Synthesis Examples 8 and 9 were synthesized in the same manner as in Synthesis Example 7, except that the polyols shown in Table 2 were used as polyol components in the mass ratios (unit: parts by mass) shown in Table 2, and the amounts of polyol components and carbonate components were adjusted to achieve the desired hydroxyl value.

(Synthesis Example 13)
In a reaction apparatus equipped with a stirrer, thermometer, heating device, and condenser, 660 g of the polycarbonate polyol obtained in Synthesis Example 12, 20 g of Praxel 210 (polycaprolactone diol, manufactured by Daicel Corporation), 320 g of Praxel 305 (polycaprolactone triol, manufactured by Daicel Corporation), and 0.03 g of potassium bicarbonate were mixed. The resulting mixture was heated at atmospheric pressure at 120-190°C (120°C initially, 190°C towards the end) and reacted under a nitrogen atmosphere at a flow rate of 50 ml/min for 3 hours. Furthermore, the pressure in the flask was reduced to 267 kPa at a reaction temperature of 190°C and the reaction was continued for another 5 hours. This synthesized the polycarbonate polyol (polyester polycarbonate polyol) of Synthesis Example 13.

(Condition assessment)
The polycarbonate polyols obtained in Synthesis Examples 1 to 13 were heated to 100°C, placed in transparent glass bottles, and left to stand at 25°C for 24 hours. The state of the polycarbonate polyols at 25°C after standing was then evaluated. Specifically, the fluidity of the polycarbonate polyols after standing was visually observed when tilted. If there was even slight fluidity, it was judged to be liquid, and if there was no fluidity, it was judged to be solid. The evaluation results are shown in Tables 1 to 3.

(Hydroxyl value measurement)
The hydroxyl values of the polycarbonate polyols obtained in Synthesis Examples 1 to 13 were evaluated using an acetylation reagent in accordance with JIS K1557-1. The molecular weight of the polycarbonate polyols was also calculated based on the hydroxyl values. The results are shown in Tables 1 to 3.

(molecular weight measurement)
The molecular weight of the polycarbonate polyol was calculated based on the number of hydroxyl groups (theoretical values) and the hydroxyl value. The results are shown in Tables 1 and 2.

The details of the materials (polyol components) shown in Tables 1 to 3 are as follows.
1,3-BG: 1,3-butylene glycol (1,3-butanediol, manufactured by Tokyo Chemical Industry Co., Ltd.)
1,5-PG: 1,5-propylene glycol (1,5-pentanediol, manufactured by Tokyo Chemical Industry Co., Ltd.)
• MPD: 3-methyl-1,5-pentanediol (manufactured by Kuraray Co., Ltd.)
• 1,6-HG: 1,6-hexylene glycol (1,6-hexanediol, manufactured by Tokyo Chemical Industry Co., Ltd.)
MOD: 2-methyl-1,8-octanediol, 1,9-ND: 1,9-nonanediol, TMP: trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.)
- PCP12: Polycarbonate polyol obtained in Synthesis Example 12. ND-15 (trade names) manufactured by Kuraray Co., Ltd. was used as the 1,9-ND source and MOD source.

<Examples 1-22 and Comparative Examples 1-3>
Compositions for Examples 1 to 22 and Comparative Examples 1 to 3 were prepared using the components shown in Tables 4 to 6 in the amounts shown in Tables 4 to 6. Molded articles (test pieces) containing polyurethane resin were then prepared and evaluated using these compositions. The compositions were prepared using a first agent consisting of component (a) (polyisocyanate) and a second agent consisting of component (b) (polycarbonate polyol), component (c) (polyol with a molecular weight of less than 200) and component (d) (catalyst). However, in Comparative Example 1, which used the polycarbonate polyol obtained in Synthesis Example 10, the second agent was solid, and it was not possible to prepare a composition usable for injection molding, so Comparative Example 1 was not evaluated. In all examples and comparative examples, the first agent was liquid at 25°C.

The viscosities of the first and second components at 25°C, measured using a B-type viscometer, are shown in Tables 4 to 6, respectively. In Comparative Example 2, the compatibility of the polyols was poor, making it impossible to calculate the viscosity of the second component; therefore, the viscosity of the second component in Comparative Example 2 is not shown. In Tables 4 to 6, the NCO/OH equivalent represents the ratio of the number of moles of isocyanate groups in the isocyanate group-containing compound to the number of moles of hydroxyl groups in the hydroxyl group-containing compound contained in the composition. The urethane group concentration in Tables 4 to 6 is the theoretical value of the urethane group concentration in the urethane resin of the obtained coating film, calculated from the blending amounts of the active hydrogen group-containing compound (components (b) and (c)) and the isocyanate group-containing compound (component (a)). The specific method for preparing and evaluating the molded article is described below.

(Evaluation of film formation properties by in-mold coating method)
Using injection molding, heated and molten ABS resin was injected into a mold at 80°C, and the mold pressure was maintained for 40 seconds while it cooled to obtain an ABS resin molded product that would serve as the base material. The first and second components, which had been thoroughly degassed under reduced pressure, were thoroughly mixed in a sealed space to prevent air bubbles from entering, ensuring a nearly uniform composition. Next, the mold was opened to create a 500 μm gap between the base material surface and the mold, and the composition obtained from the mixing process was injected between the base material and the mold. The temperature of the composition at injection was 20°C, and the mold temperature was 80°C. After injection, the mold temperature was maintained at 80°C for 150 seconds to allow the composition to react and harden, forming a coating film (hardened film) on the surface of the base material. After demolding the base material from the mold, the appearance of the formed coating film was inspected, and the coating film formation performance was evaluated based on the presence or absence of wrinkles, streaks, unevenness, defects (shorts), discoloration, etc. If wrinkles, streaks, unevenness, defects, discoloration, etc., were observed in the coating film, the coating film formation performance was considered insufficient (evaluation C). If none of these were observed, the coating film formation performance was considered good (evaluation A). If only minor defects were observed, the evaluation was B. The results are shown in Tables 4 to 6.

(Transparency assessment)
The transparency of the coating film was evaluated by the total light transmittance and haze of test specimens prepared using the method described below.

The first and second components were thoroughly mixed under room temperature conditions to obtain a substantially homogeneous composition, and then degassed under reduced pressure. Next, the resulting composition was poured into a mold and heated at 100°C for 30 minutes to 1 hour to react and cure, yielding a 0.5 mm thick flat molded body (test piece A) and a 2 mm thick flat molded body (test piece B).

The total light transmittance of test specimen A obtained above was measured using a spectrophotometer/haze meter (COH7700) manufactured by Nippon Denshoku Industries Co., Ltd. The results are shown in Tables 4 to 6.

The haze of test specimen A obtained above was measured using a spectrophotometer (COH7700) manufactured by Nippon Denshoku Industries Co., Ltd. The results are shown in Tables 4 to 6.

A material was evaluated as having excellent transparency if its total light transmittance was 90% or higher and its haze was 1% or less.

(Self-healing ability assessment)
Under conditions of 23°C and 50% RH, the surface of test specimen B was scratched by rubbing it with a brass wire brush. The degree of scratch repair was observed visually, and the time it took for the scratches to completely heal was measured. Self-healing properties were evaluated according to the following criteria. A rating of A, B, or C indicated good self-healing properties. The results are shown in Tables 4 to 6.
[Evaluation Criteria]
A: The wound disappeared within 1 minute of being made. B: The wound disappeared within 10 minutes of being made. C: The wound disappeared within 24 hours of being made. D: The wound did not disappear even after 24 hours had passed.

(Mechanical property evaluation)
The mechanical properties of the coating film were evaluated by measuring the hardness, tensile elongation, tensile strength, and tear strength of test specimens prepared using the method described below.

The first and second components were thoroughly mixed under room temperature to obtain a substantially homogeneous composition, and then degassed under reduced pressure. Next, the resulting composition was poured into a mold and heated at 100°C for 30 minutes to 1 hour to allow the composition to react and harden. This method yielded cylindrical (Φ30 mm × 13 mm) molded bodies (test piece C), dumbbell-shaped (test piece D), and angle-shaped molded bodies (test piece E).

The hardness of test specimen C obtained above was measured using Asker rubber hardness testers type D and A. The results are shown in Tables 4 to 6.

The tensile elongation and tensile strength of test specimen D obtained above were measured using a tensile testing machine (Autocom universal tester AC-10kN-C, manufactured by TSE Corporation) in accordance with JIS K 6251. The test speed was set to 500 mm/min. The results are shown in Tables 4 to 6.

The tear strength of test specimen E obtained above was measured using a tensile testing machine (Autocom universal testing machine AC-10kN-C, manufactured by TSE Corporation) in accordance with JIS K 6251. The test speed was set to 500 mm/min. The results are shown in Tables 4 to 6.

(Evaluation of low-temperature rapid curing properties)
The shear viscoelasticity of the composition immediately after preparation was measured at 80°C using a rheometer (HAAKE MARS 60, Thermo Fisher Scientific Co., Ltd.) at a frequency of 1 Hz, and the low-temperature rapid curing properties were evaluated according to the following evaluation criteria. The results are shown in Tables 4 to 6.
[Evaluation Criteria]
- A: The storage modulus (G') reached ^10⁵ Pa within 200 seconds from the start of measurement. - B: The storage modulus (G') reached ^10⁵ Pa within 300 seconds after 200 seconds from the start of measurement. - C: The storage modulus (G') reached ^10⁵ Pa within 400 seconds after 300 seconds from the start of measurement. - D: The storage modulus (G') did not reach ^10⁵ Pa within 400 seconds from the start of measurement.

Details of each ingredient in Tables 4 to 6 are as follows:
(a) Component C-HXLV: Isocyanurate modified form of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name: Coronate HXLV ("Coronate" is a registered trademark, the same applies hereinafter), NCO content 23.4% by mass)
• C-2770: Allophanate modified hexamethylene diisocyanate (manufactured by Tosoh Corporation, product name: Coronate 2770 ("Coronate" is a registered trademark), NCO content 19.4% by mass)
• C-2094: Urethane-modified hexamethylene diisocyanate (manufactured by Tosoh Corporation, product name: Coronate 2094 ("Coronate" is a registered trademark), NCO content 16.1% by mass)
Hydrogenated MDI (dicyclohexylmethane diisocyanate), NCO content 32.0% by mass
MR-200: Aromatic isocyanate (polymeric MDI), NCO content 31.0% by mass
(b) Components - Synthesis Examples 1-11 and 13: Polycarbonate polyols synthesized in Synthesis Examples 1-11 and 13. (c) Component - TMP: Trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.)
1,3-BG: 1,3-butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.)
(d) Ingredients: DOTDL: Dioctyl tin dilaurate (manufactured by Kishida Chemical Co., Ltd.)

1...Substrate, 2...Mold, 3...First agent, 4...Second agent, 6...Urethane resin forming composition for in-mold coating, 7...Coating film.

Claims (9)

It comprises a non-aromatic polyisocyanate (A) that is liquid at 25°C and a polycarbonate polyol (B) that is liquid at 25°C.
The hydroxyl value of the aforementioned polycarbonate polyol (B) is 100 to 400 mg KOH/g.
The polycarbonate polyol (B) contains, as monomer units, at least one selected from the group consisting of 1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-1,8-octanediol, and a linear glycol having 3 to 6 carbon atoms.
A polyurethane resin-forming composition for in-mold coating, wherein the aromatic polyol content is 5% by mass or less based on the total mass of the composition . The composition according to claim 1, wherein the non-aromatic polyisocyanate (A) comprises at least one selected from the group consisting of isocyanurate derivatives of aliphatic diisocyanates and allophanate derivatives of aliphatic diisocyanates. The composition according to claim 1, wherein the polycarbonate polyol (B) contains at least two types of linear glycols having 3 to 6 carbon atoms as monomer units. The composition according to claim 1, wherein the polycarbonate polyol (B) contains trimethylolpropane as a monomer unit. The composition according to any one of claims 1 to 4 , further comprising a polyol (C) with a molecular weight of less than 200. The composition according to claim 5 , wherein the polyol (C) comprises at least one selected from the group consisting of 1,3-butanediol and trimethylolpropane. A set of in-mold coating agents for preparing the composition according to any one of claims 1 to 4 ,
An in-mold coating agent set comprising a first agent containing the non-aromatic polyisocyanate (A) and a second agent containing the polycarbonate polyol (B). A coating film comprising a reaction product of the composition according to any one of claims 1 to 4 . A method for in-mold coating, comprising: preparing a substrate and a mold in which the substrate is placed; injecting a composition according to any one of claims 1 to 4 into the mold and applying the composition to the surface of the substrate; and reacting the composition to form a coating film on the surface of the substrate.