JP7746008B2 - paint composition - Google Patents

Description

The present invention relates to a coating composition.

Polyurethane resins have excellent physical properties such as abrasion resistance, flexibility, flexibility, processability, and adhesiveness, and are also well suited to various processing methods, and are therefore widely used as resin components in coating materials, inks, adhesives, paints, etc. for electronic device components, clothing, furniture, home appliances, daily necessities, construction and civil engineering products, and automotive components, as well as in various molded articles such as films and sheets. Methods for forming these coating films include heat curing and UV curing, and coating films obtained by UV curing in particular have an extremely high crosslink density and therefore excellent coating film physical properties such as chemical resistance.
However, UV-curable coating compositions have problems such as being unsuitable for coating substrates with complex shapes, being difficult to color, and requiring the introduction of a UV irradiation device.

On the other hand, thermosetting paint compositions are paint compositions that are more commonly capable of forming coating films (curing coating films) than UV-curable paint compositions. In the case of coating films formed from commonly used thermosetting paint compositions, the coating film properties, such as chemical resistance, tend to be weaker than those of coating films formed from UV-curable paint compositions.

In recent years, thermosetting coating compositions have been proposed that contain polycarbonate diol as a resin component, which has a more rigid structure than polyether polyols or polyester polyols. However, it has been difficult to achieve the same level of chemical resistance as UV-curable coating compositions.

Patent Document 1 discloses a clearcoat composition that includes at least one hyperbranched dendritic hydroxy-functional polyester having an OH value of 180 to 240 mg KOH/g, and at least one diisocyanate or polyisocyanate, at least one aminoplastic resin, and/or at least one tris(alkoxycarbonylamino)triazine as a crosslinking agent. However, the physical properties and structure of the polyesters that can be used are very limited.

Patent Document 2 discloses a coated body having a coating film that is both excellent in abrasion resistance and chemical resistance by adjusting the coating composition so that the glass transition temperature and Young's modulus fall within a predetermined numerical range.
However, coating films with scratch resistance due to scratch recovery are designed to be soft in order to impart scratch recovery properties, and since they cannot prevent chemicals from penetrating the coating film, it has been difficult to achieve chemical resistance as high as that of UV-curable coating compositions.

Patent No. 6104349 Patent No. 6701582

The present invention provides a coating composition for producing a coating film that has sufficient scratch resistance and adhesion, as well as excellent chemical resistance to ultraviolet absorbers, insect repellents, fragrances, and other substances contained in cosmetics, etc.

The present invention relates to a polyol (a) having a hydroxyl value of 180 or more;
(b) an acrylic polyol not falling under (a); and
Polyisocyanate (c)
A coating composition comprising:
The NCO ratio in the coating composition is 9% by mass or more (based on the total solids in the coating composition),
the dynamic glass transition temperature of the resulting cured coating film is 80°C or higher;
The coating composition is characterized in that the weight average molecular weight (Mw) of the acrylic polyol (b) is 3,000 or more and less than 10,000, and the polyol (a) has at least a portion of a structural unit derived from a trifunctional monomer .
The polyol (a) is preferably a polyester polyol.
The glass transition temperature of the acrylic polyol (b) is preferably 30°C to 100°C.

The coating composition of the present invention is a thermosetting coating composition and can produce a coating film with excellent chemical resistance, etc.

The present invention will be described in detail below.
The coating composition of the present invention is a coating composition containing a polyol (a) having a hydroxyl value of 180 mgKOH/g or more, an acrylic polyol (b) other than (a), and a polyisocyanate (c), characterized in that the NCO ratio in the coating composition is 9 mass% or more (based on the total solids in the coating composition), and the dynamic glass transition temperature of the resulting cured coating film is 80°C or more.

While the NCO ratio in conventional paint compositions has generally been around 2-7% by mass, the present invention limits the NCO ratio to 9% by mass or more, calculated as the total solids in the paint composition, resulting in a paint composition containing an extremely large amount of NCO. The excess NCO increases the glass transition temperature of the paint film, imparting excellent paint film properties such as chemical resistance and moisture-resistant adhesion. Furthermore, because there is an excess of NCO, the remaining NCO reacts with water and other substances on the paint film surface, hardening the surface. This not only improves chemical resistance, but also provides the effect of imparting scratch resistance.

The coating composition of the present invention also contains a polyol (a) with a high hydroxyl value. The use of such a polyol with a high hydroxyl value increases the crosslink density of the coating film and further enhances its chemical resistance.
The coating composition of the present invention will be described in detail below.

(Polyol (a))
The polyol (a) in the present invention has a hydroxyl value of 180 mgKOH/g or more, preferably 220 mgKOH/g or more, more preferably 250 mgKOH/g or more, and preferably 550 mgKOH/g or less.
When the hydroxyl value of the polyol (a) is within this range, a coating film having a high crosslink density can be formed, and improved chemical resistance and good coating film hardness can be achieved.
The hydroxyl value of the polyol (a) can be measured by the neutralization titration method using potassium hydroxide as described in JIS K0070.

The polyol (a) is not particularly limited as long as it satisfies the above range of hydroxyl groups, but it preferably contains at least one branched polymer selected from a dendrimer and a hyperbranched polymer. When the branched polymer contains both a dendrimer and a hyperbranched polymer, a combination of a dendrimer and a hyperbranched polymer having similar terminal substituents is preferred.
It should be noted that a branched polymer is understood to be a polymer that is not crosslinked or is barely crosslinked in the coating composition, and is not unified structurally or molecularly.

A "dendrimer" is a branched polymer in which a branched chain further branches to form a multi-branched structure that spreads outward. For example, a dendrimer has a chemical structure in which branches are regularly repeated from the center of the polymer outward, and can have a spherical three-dimensional structure.

A "hyperbranched polymer" is a structure in which the multiple branched structure described above does not extend radially, but rather in a branched manner in one or more predetermined directions. For example, hyperbranched polymers have a chemical structure similar to that of dendrimers. However, they often lack the highly regular branched structure or highly controlled molecular weight that dendrimers have, and branches may be formed according to a stochastic distribution.
They also often have a broad molecular weight distribution. Because branches can be formed according to a stochastic distribution, they have an overwhelmingly larger number of terminal functional groups than linear polymers. In hyperbranched polymers, the chain lengths of the branches may be of different lengths. Furthermore, the branched structure may have a linear structure and further have functional side groups.

Preferably, the branched polymer is a hyperbranched polymer. Compared to dendrimers, hyperbranched polymers allow for appropriate control of the number and type of terminal functional groups, and also make it easier to control steric hindrance. Therefore, the terminal functional groups of the hyperbranched polymer can be bonded more effectively with the reactive groups of the isocyanate compound than with dendrimers, making it possible to form a coating film that has better coating appearance (e.g., smoothness) and design properties, as well as a well-balanced coating film property such as excellent scratch resistance.

Hyperbranched polymers, based on their skeletal structure, include hyperbranched polycarbonates, hyperbranched polyethers, hyperbranched polyesters, hyperbranched polyphenylenes, hyperbranched polyamides, hyperbranched polyimides, hyperbranched polyamideimides, hyperbranched polysiloxanes, and hyperbranched polycarbosilanes. These hyperbranched polymers also have terminal groups, which may contain at least one functional group containing active hydrogen, such as a hydroxyl group. Such active hydrogen groups can react with isocyanate groups.

As the branched polymer, hyperbranched polyester, hyperbranched polycarbonate, etc. are preferred, and among these, hyperbranched polyester is more preferred.
The hyperbranched polyester has a low viscosity in the paint state and is easy to handle, and the reaction proceeds efficiently when forming a coating film, making it possible to obtain a coating film with the desired coating film properties.
Furthermore, it is particularly preferable that the hyperbranched polyester contains at least a portion of a structural unit derived from a trifunctional monomer.

The acid value of the branched polymer is preferably 5 mgKOH/g or more and 110 mgKOH/g or less, and more preferably 10 mgKOH/g or more and 90 mgKOH/g or less.
By keeping the acid value of the branched polymer within this range, intramolecular crosslinking, such as gelation, within the coating composition can be suppressed. If the acid value exceeds the above range, compatibility with other resins may deteriorate and water resistance may be reduced, while if the acid value is below the above range, the crosslink density may not be increased sufficiently.

The number average molecular weight (Mn) of the branched polymer is, for example, 300 to 2500, such as 400 to 2200, and in some embodiments, 500 to 2000.

The number average molecular weight (Mn) of the branched polymer is a value measured by gel permeation chromatography using HLC-8200 manufactured by Tosoh Corporation. The measurement conditions are as follows.
Column: TSgel Super Multipore HZ-M 3-tube eluent
Tetrahydrofuran Column inlet oven 40°C Flow rate 0.35 ml
Detector: RI standard polystyrene, PS oligomer kit manufactured by Tosoh Corporation

The glass transition temperature (Tg) of the branched polymer is, for example, from -20°C to 70°C, and in one embodiment, from -20 to 50°C.
The glass transition temperature used herein is a value measured using a differential scanning calorimeter (DSC) (thermal analyzer SSC5200 (manufactured by Seiko Electronics)) in the following steps: specifically, a step of increasing the temperature from 20°C to 150°C at a temperature increase rate of 10°C/min (step 1), a step of decreasing the temperature from 150°C to -50°C at a temperature decrease rate of 10°C/min (step 2), and a step of increasing the temperature from -50°C to 150°C at a temperature increase rate of 10°C/min (step 3). The value obtained from the chart during temperature increase in step 3 was taken as the glass transition temperature.

In the coating composition of the present invention, the amount of polyol (a) is preferably 10% by mass or more, and more preferably 20% by mass or more, based on the total solid content of the coating. It is also preferably 40% by mass or less, and more preferably 30% by mass or less. If it is less than 10% by mass, chemical resistance may be insufficient. If it exceeds 40% by mass, moisture resistance, substrate adhesion, etc. may be reduced.

Note that the polyol (a) may be a mixture of two or more types. In that case, the specific value for the polyol (a) mentioned above means a value calculated as a weighted average of the polyols (a) used.

(Acrylic polyol (b))
The coating composition of the present invention further contains an acrylic polyol (b) that does not fall under (a). The acrylic polyol (b) is not particularly limited, but in order to increase the glass transition temperature of the coating film, it is preferable that the acrylic polyol (b) has a high glass transition temperature (Tg), specifically, 10 to 120°C. More preferably, it is 30 to 100°C. If the temperature is less than 10°C, the dynamic Tg of the coating film decreases, which may result in a decrease in chemical resistance. If the temperature exceeds 120°C, the coating viscosity increases, which is undesirable in that it reduces coating workability and the finished appearance.
The glass transition temperature can be measured by a differential scanning calorimeter (DSC) or the like.

More specifically, the acrylic polyol (b) is preferably a copolymer primarily composed of an acrylic monomer. The monomers used in the polymerization of the acrylic polyol (b) are not particularly limited, and examples thereof include ethylenically unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid; ethylenically unsaturated carboxylic acid alkyl ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; alicyclic esters of ethylenically unsaturated carboxylic acids such as cyclohexyl (meth)acrylate and norbornyl (meth)acrylate; monoester monomers of ethylenically unsaturated dicarboxylic acids such as ethyl maleate, butyl maleate, ethyl itaconate, and butyl itaconate; 2-hydroxyethyl (meth)acrylate, acrylic acid Examples of suitable monomer mixtures include hydroxyl-containing ethylenically unsaturated carboxylic acid ester monomers, which are primary hydroxyl-containing monomers such as 4-hydroxybutyl (meth)acrylate and the reaction product of 2-hydroxyethyl (meth)acrylate with ε-caprolactone; hydroxyl-containing ethylenically unsaturated carboxylic acid ester monomers, which are secondary hydroxyl-containing monomers such as 2-hydroxypropyl (meth)acrylate; unsaturated fatty acid glycidyl ester monomers, such as glycidyl acrylate and glycidyl methacrylate; vinyl cyanide monomers, such as (meth)acrylonitrile and α-chloroacrylonitrile; saturated aliphatic carboxylic acid vinyl ester monomers, such as vinyl acetate and vinyl propionate; and styrene-based monomers, such as styrene, α-methylstyrene, and vinyltoluene. The monomer mixtures may contain any of the above monomers alone or in combination of two or more components.

The polymerization method for obtaining the above-mentioned acrylic polyol (b) is not particularly limited, and known methods such as solution polymerization, high-pressure polymerization, and continuous polymerization can be used.

The weight-average molecular weight (Mw) of the acrylic polyol (b) is preferably 3,000 to 20,000. If it is less than 3,000, film performance will decrease, and if it exceeds 20,000, the paint viscosity will increase, and in such a high viscosity state, painting work may become difficult. It is possible to lower the viscosity by using a volatile organic solvent to reduce the proportion of non-volatile components in the paint, but this creates the problem of environmental pollution caused by the organic solvent. The weight-average molecular weight is the number-average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography).

In terms of coating film performance, the hydroxyl value of the above acrylic polyol (b) is preferably 100 to 300 mgKOH/g.

In the coating composition of the present invention, the amount of the acrylic polyol (b) is preferably 10% by mass or more, and more preferably 20% by mass or more, based on the total amount of solids in the coating. It is also preferably 30% by mass or less, and more preferably 25% by mass or less. If it is less than 10% by mass, chemical resistance and substrate adhesion may be insufficient. If it exceeds 30% by mass, coating workability may be reduced.

Note that the acrylic polyol (b) may be a mixture of two or more types. In that case, the specific value for the acrylic polyol (b) mentioned above means a value calculated as a weighted average of the acrylic polyols (b) used.

(Polyisocyanate (C))
The coating composition of the present invention contains a polyisocyanate (C).
The polyisocyanate (C) is not particularly limited as long as it is a compound having two or more isocyanate groups, and examples thereof include aromatic compounds such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate; aliphatic compounds such as hexamethylene diisocyanate; alicyclic compounds such as isophorone diisocyanate; and monomers thereof and polymers such as biuret types, nurate types, and adduct types thereof.

Commercially available examples of the polyisocyanate (C) include Duranate 24A-90PX (NCO: 23.6%, trade name, manufactured by Asahi Kasei Corporation), Sumidur N-3200-90M (trade name, manufactured by Sumitomo Bayer Urethanes Co., Ltd.), Takenate D165N-90X (trade name, manufactured by Mitsui Chemicals, Inc.), Sumidur N-3300, Sumidur N-3500 (all trade names, manufactured by Sumitomo Bayer Urethanes Co., Ltd.), and Duranate 24A-100 (trade name, manufactured by Asahi Kasei Corporation). Blocked isocyanates obtained by blocking these isocyanates can also be used if necessary.

The coating composition of the present invention has an NCO ratio of 9 mass % or more (based on the total solids in the coating composition), i.e., a coating composition containing a much larger amount of NCO than a typical thermosetting coating composition.
The NCO ratio is preferably 9% by mass or more, more preferably 11% by mass or more, and the upper limit is preferably 17% by mass or less, more preferably 15% by mass or less.

Note that the above NCO ratio indicates the mass of NCO functional groups relative to the total solids content in the coating composition.

(catalyst)
The coating composition of the present invention may further contain a catalyst. By including a catalyst, for example, the reaction between the reactive functional group of the branched polymer of the present invention and the isocyanate group of the isocyanate compound can be more selectively promoted, resulting in a coating film with higher surface hardness and scratch resistance. In addition, the coating film can be formed at a lower temperature and/or the curing time of the coating composition can be further shortened. Furthermore, a coating film with excellent heat-resistant color stability and thin-film curing properties can be obtained.

Tin-, zinc-, and bismuth-based catalysts are commonly used as catalysts for active hydrogen and isocyanate.

In addition to the above catalysts, a catalyst can be appropriately selected depending on the branched polymer and isocyanate compound used. In one embodiment, the catalyst is a metal-free organic ionic catalyst. Use of the metal-free organic ionic catalyst can further reduce the burden on the environment. The metal-free organic ionic catalyst is, for example, at least one selected from the group consisting of amines, imidazoles, imidazolines, aromatic group-containing catalysts, and salts thereof.
The term "metal-free organic ionic catalyst" as used herein means a catalyst that forms ions in an organic substance and does not contain either metal atoms or metal ions.

Examples of the imidazoles include 2-methylimidazole, 2-phenylimidazole, 2-ethylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole.
Examples of the imidazolines include 2-ethylimidazoline, 2-phenylimidazoline, and 1-cyanoethyl-2-phenylimidazoline.

The catalyst may also be an aliphatic polycarboxylic acid such as decanedicarboxylic acid, dodecanedicarboxylic acid, or sebacic acid, or an aromatic group-containing catalyst such as benzoic acid or its salts.

The catalyst may be present in an amount of 0.05 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the resin solids content of the coating composition of the present invention.

The coating composition of the present invention may further contain known resins and/or monomers, provided that the effects of the present invention are not impaired. For example, it may contain other acrylic resins, melamine resins, urethane resins, olefin resins, etc., or may contain a combination of two or more of these resins.

(Other ingredients)
The coating composition according to the present disclosure may contain additives such as color pigments, extender pigments, modifiers, leveling agents, dispersants, defoamers, and solvents, as needed, provided that the physical properties of the polyol (a), acrylic polyol (b), and polyisocyanate (c) contained in the coating composition are not impaired. Furthermore, the coating composition preferably contains a viscosity control agent to ensure coating workability. Viscosity control agents that generally exhibit thixotropy can be used. For example, conventionally known viscosity control agents can be used. In one embodiment, the viscosity control agent (rheology control agent) may include at least one of a known microgel, a non-aqueous dispersion type acrylic resin, and an amide resin.

The coating composition of the present invention can be used as a top coat for a multi-layer film. Furthermore, color pigments such as black pigments can be blended, allowing for the formation of a coating film with a single coat, even for designs such as piano black. In contrast, the addition of color pigments to a UV-curable coating composition inhibits curing (film formation), making it impossible to obtain a coating film with sufficient performance.
Thus, the coating composition of the present invention is thermosetting and can provide chemical resistance and the desired appearance. For example, the black pigment may be added by blending a commercially available dispersion paste, or by pre-dispersing the black pigment in the polyol (a) used in the present invention to prepare the coating composition of the present invention.

(Dynamic Glass Transition Temperature)
The coating composition of the present invention has the above-mentioned composition, and the resulting cured coating film has a dynamic glass transition temperature of 80°C or higher. A dynamic glass transition temperature of 80°C or higher is thought to provide good coating film strength and excellent chemical resistance. The dynamic glass transition temperature is more preferably 90°C or higher, and more preferably 120°C or lower.

The dynamic glass transition temperature can be obtained by the same method as that for measuring glass transition temperature by ordinary dynamic viscoelasticity.
First, the coating composition was air sprayed onto a substrate (a PP resin plate) so that the dry film thickness was 30 μm, and after setting for 5 minutes, it was baked and cured for 30 minutes at 80° C. The resulting cured coating film was peeled off and cut to prepare a measurement sample.
Next, the prepared measurement sample is subjected to vibration at a frequency of 11 Hz at a temperature rise rate of 2°C per minute in the temperature range of 30°C to 150°C to measure its viscoelasticity. The ratio (tan δ) of the loss modulus (E") to the storage modulus (E') thus measured is measured, and the dynamic glass transition temperature is determined as the temperature at which tan δ reaches its peak value when the tan δ is plotted against temperature. An example of an apparatus for performing the dynamic viscoelasticity measurement is the Autograph AG-IS (trade name, manufactured by Shimadzu Corporation).

Furthermore, the coating composition of the present invention preferably has a crosslink density of 2.0 (mol/cc) or more in the cured coating film. If the crosslink density is less than 2.0 (mol/cc), chemical resistance may be poor. Furthermore, the crosslink density is preferably 5.0 (mol/cc) or less. If it exceeds 5.0 (mol/cc), the elastic modulus of the coating film may be low, resulting in poor impact resistance.

The crosslink density is a theoretically calculated value obtained by measuring the dynamic viscoelasticity of the cured coating film in the same manner as in the measurement of the dynamic glass transition temperature, and applying the minimum value of the storage modulus in the rubber region to the following theoretical formula for rubber viscoelasticity:
Formula 1: n=E'/3RT
where:
n: crosslinking density (mol/cc)
1/n: Molecular weight between crosslinks (cc/mol)
R: gas constant (8.314 J/K/mol)
T: Absolute temperature (K) when the storage modulus is E'
E': minimum value of storage elastic modulus (Pa)

The coating composition of the present invention can be suitably used as a two-component reactive coating composition. A two-component reactive coating composition is a coating composition in which a base solution and a curing agent solution are prepared and then used to apply the coating.
In the present invention, the base solution and the hardener solution can be prepared by a conventionally known method.

(subject to be coated)
The coating composition of the present invention is suitable for use as exterior materials for everyday items, building materials, fittings, building interiors such as flooring, automobile bodies and automobile parts (e.g., exterior parts, interior parts), home appliances, smart keys, smartphones, laptop computers, etc. Particularly preferred are electrical appliances, electronic device parts, automobiles, and automobile parts.
In particular, since it has excellent chemical resistance to air fresheners, sunscreens, etc., it can be suitably used for automobile interior parts such as navigation systems and shift levers.

For example, when used for automobile interior parts, the composition can be used for various plastic substrates and molded articles thereof, and is preferably used for plastic substrates such as polyolefins such as polypropylene, ABS resins, and polycarbonates, and molded articles thereof, and is particularly preferably used for plastic substrates such as ABS resins and polycarbonates, and molded articles thereof.
If desired, a substrate on which a known coating film such as a primer coating film has been formed may also be used.

(Coating film formation method)
The coating composition of the present invention is a thermosetting coating composition, and therefore can cure (form) a coating film by a simple method. Coating film formation, for example, coating film curing, can be performed more easily without using special equipment such as those used to cure UV-curable resin compositions. Furthermore, despite being a thermosetting coating composition, a coating film can be formed that has a well-balanced coating film properties, such as chemical resistance, scratch resistance, and coating film hardness.

The coating composition of the present invention can be applied by conventional coating methods. It can be applied either by forcing the coating to dry and then curing it, or by applying a primer or undercoat and then applying it wet-on-wet to form a multi-layer coating.

The method for applying the coating composition of the present invention to the substrate is not particularly limited, but preferred methods include spray coating, bell coating, electrostatic coating, etc. Between coating and heating (baking and drying), the composition may be allowed to stand at room temperature for an appropriate period of time to set.

Heating may be carried out at a temperature of 60°C or higher and 120°C or lower, for example, 70°C or higher and 90°C or lower. If the temperature is below 60°C, time is required for curing. If it exceeds 120°C, there is a risk of a large environmental load and of thermal load being placed on the substrate. The curing time varies depending on the curing temperature (heating temperature), but if it is between 70°C and 90°C, it is preferable that the curing time be between 10 and 40 minutes after the material reaches the specified temperature.

Examples of heating devices include drying ovens that use heat sources such as hot air, electricity, gas, and infrared rays. Furthermore, it is preferable to use a drying oven that combines two or more of these heat sources, as this shortens the drying time.

The coating composition of the present invention is preferably applied so that the dry film thickness is 15 to 40 μm. If it is less than 15 μm, the impact resistance and adhesion effects are likely to be insufficient, and if it exceeds 40 μm, popping and sagging may occur. The dry film thickness is more preferably 20 to 35 μm. The dry film thickness can be measured using an SDM-miniR manufactured by SANKO Corporation.

The present invention will be explained below using examples. In the examples, parts and percentages used in describing the blending ratios refer to parts by mass and percentages by mass, unless otherwise specified. The present invention is not limited to the examples described below.

(Production of hydroxyl group-containing acrylic resin b-1)
A reactor equipped with a stirring blade, thermometer, dropping device, temperature control device, nitrogen gas inlet, and cooling tube was charged with 57 parts of butyl acetate, and the temperature was raised to 120 ° C. while stirring and introducing nitrogen gas. Next, a mixture consisting of 1.53 parts of methacrylic acid, 1.68 parts of 2-ethylhexyl acrylate, 61.99 parts of methyl methacrylate, and 34.8 parts of 2-hydroxyethyl methacrylate and a solution obtained by dissolving 6.5 parts of t-butylperoxy-2-ethylhexanate in 5 parts of butyl acetate were added dropwise to the reactor over 3 hours. After completion of the dropwise addition, the mixture was aged for 1 hour, and then a solution obtained by dissolving 0.2 parts of t-butylperoxy-2-ethylhexanate in 5 parts of butyl acetate was added dropwise to the reactor over 1 hour. The mixture was maintained at 120 ° C. for 2 hours while aging to complete the reaction. The nonvolatile content of the resulting hydroxyl-containing resin was 70%, and the weight average molecular weight was 6,500.
Using the same reaction apparatus as in Production Example b-1 and with the same formulation as in Table 1, hydroxyl-containing acrylic resins of Production Examples b-2 and b-3 were obtained by the same procedure. Their property values are also shown in Table 1.

Polyol a-1: XP2488 manufactured by Sumika Covestro Urethane Co., Ltd. Polyol a-2: EQD-1097 manufactured by DIC Corporation Polyol a-3: HPE1265B manufactured by BASF Corporation The hydroxyl value, glass transition temperature (Tg), and number average molecular weight (Mn) of each component are shown in Table 2.

(Isocyanate Compounds)
Polyisocyanate c-1: Nurate type, Desmodur N-3300 manufactured by Covestro Polyisocyanate c-2: Buret type, Duranate 24A-100 manufactured by Asahi Kasei Corporation (catalyst)
Metal catalyst: dibutyltin dilaurate (additive)
Surface conditioner: BYK-310 (manufactured by BYK Corporation)

(Examples 1 to 6, Comparative Examples 1 to 6)
A base solution was prepared according to the formulation shown in Table 3.
The base solution, a polyisocyanate curing agent solution prepared by diluting polyisocyanate with butyl acetate, and T-505HCL thinner (manufactured by Nippon Paint Automotive Coatings Co., Ltd.) were placed in a container and thoroughly stirred with a disperser to obtain a coating composition.

In Table 3, the NCO ratio indicates the mass of NCO functional groups relative to the total solid content in the paint composition. Furthermore, the blending amount indicates the blending amount relative to the total solid content in the paint.

(Formation of coating film)
The resulting coating composition was air sprayed onto a substrate (a black ABS resin plate) to a dry film thickness of 30 μm, allowed to set for 5 minutes, and then baked and cured at 80° C. for 30 minutes to form a cured coating film. The resulting cured coating film was peeled off and cut, and evaluated as described below. The results are shown in Table 3.

The resulting coating films were evaluated based on the following criteria.
(Dynamic Tg of coating film)
The dynamic glass transition temperature of the cured coating film was measured according to the method for measuring the dynamic glass transition temperature described above.

(Adhesion)
A grid of 100 cuts is made on the coating film with a cutter knife at 1 mm intervals, reaching all the way to the substrate, and cellophane tape (manufactured by Nichiban Co., Ltd.) is applied. The tape is rubbed with a finger three times with a force of 2 kgf and then peeled off at a right angle at a speed of 0.5 m/s.
Furthermore, a new tape is applied in the same manner in the perpendicular direction, and the tape is peeled off to count the number of grids that remain unpeeled.
The results are shown in Table 2.

(Moisture-resistant adhesion)
The sample was left in an environment of 50°C and 95% RH for 240 hours, and then the above-described adhesion evaluation was carried out at room temperature. The cuts were made at 2 mm intervals.
The results are shown in Table 2.

(Chemical resistance)
(Chemical resistance tests A and B)
0.1 g of chemical is thinly applied to a 5 cm x 5 cm area of a 6 cm x 6 cm test coating. The test piece is placed in a sealed container and left in an environment of 50 ° C for 24 hours. After that, the chemical is wiped off at room temperature and the state of the coating is compared with the initial state.
(Chemical Resistance Test C)
The air freshener is cut into a triangle with a side length of 5 cm and placed on the coating. The test piece is covered with aluminum foil, a 500 g weight is placed on top, and the test piece is left in an environment of 75°C for 4 hours. After that, the chemical is wiped off at room temperature, and the state of the coating is compared with the initial state.

Test A: Coppertone SPF 50+ PA++++ (Taisho Pharmaceutical)
Test B: Neutrogena SPF 55 PA+++ (Johnson & Johnson)
Test C: Little Tree Royal Pine (manufactured by CAR-FRESHNER)

Criteria for judging the condition of the coating after the test: ○: No traces remain after the test (passed)
△: Slight marks remain, no discoloration, shrinkage or swelling of the coating (passed)
×: Discoloration, shrinkage, and swelling of the coating film (failure)

From the results of the above examples, it is clear that the coating composition of the present invention has good adhesion and moisture-resistant adhesion, and can provide sufficient chemical resistance.

The coating composition of the present invention has excellent chemical resistance and can therefore be suitably used for automobile interior parts such as navigation systems and shift levers.

Claims (3)

a polyol (a) having a hydroxyl value of 180 or more;
(b) an acrylic polyol not falling under (a); and
Polyisocyanate (c)
A coating composition comprising:
The NCO ratio in the coating composition is 9% by mass or more (based on the total solids in the coating composition),
the dynamic glass transition temperature of the resulting cured coating film is 80°C or higher;
The weight average molecular weight (Mw) of the acrylic polyol (b) is 3,000 or more and less than 10,000,
The polyol (a) has at least a portion of a structural unit derived from a trifunctional monomer.
A coating composition characterized by: The coating composition according to claim 1, wherein polyol (a) is a polyester polyol. 3. The coating composition according to claim 1 , wherein the acrylic polyol (b) has a glass transition temperature of 30 to 100°C.