JP7782108B2 - Moisture-curing resin sheet, vehicle part, vehicle, and method for manufacturing vehicle and vehicle part - Google Patents

Description

The present invention relates to moisture-curing resin sheets, vehicle parts, vehicles, and methods for manufacturing vehicles and vehicle parts.

Conventionally, various products such as furniture, steel plates, and vehicle bodies have been painted to impart functions such as design, durability, weather resistance, and scratch resistance. Painting is generally performed by spraying with air or electrostatic force. In view of the loss that occurs during painting, the _CO2 emitted from factories, and the large-scale capital investment required for spray painting, replacement with decorative techniques using resin films has recently been considered.

Decoration technology is a technique that achieves high functionality and design by applying a resin film (decorative film) printed with letters or patterns in white, black, or colored ink to an adherend to add decoration. For example, a thermosetting resin sheet containing a thermosetting resin and a curing agent is known to be used as a decorative film. After being attached to the adherend, the thermosetting resin sheet is heated to harden it, allowing it to coat the adherend with high adhesive strength.

However, since thermosetting resin sheets require heating after lamination, they may not be applicable to some types of adherends. For this reason, the use of moisture-curing resin sheets as decorative films has been considered.
Generally, moisture-curing urethane resins are widely used as moisture-curing resins, as disclosed in, for example, Patent Document 1. It is also known that an acrylic skeleton is introduced into a urethane prepolymer used in a moisture-curing urethane resin, as disclosed in, for example, Patent Document 2.

Patent No. 7363124 Patent No. 6584382

Incidentally, decorative resin sheets (resin layers) are sometimes laminated on a transfer layer to facilitate easier attachment to the adherend, and then attached to the adherend. In this case, if the transfer layer of the resin sheet attached to the adherend is peeled off before curing and the resin is allowed to cure in an exposed state, foreign matter may adhere to the resin or the resin may become scratched. Furthermore, if the transfer layer is peeled off in an uncured state, stick-slip may occur, resulting in streaks, or the resin may adhere to the transfer layer, causing a rough surface. Therefore, to maintain a smooth surface for the resin layer, it is desirable to allow the resin to cure with the transfer layer still attached.

However, according to the inventors' investigations, it was found that when a decorative resin sheet is made of urethane resin, which is a common moisture-curing resin, and is cured with the transfer layer still attached, gases such as carbon dioxide that are generated during curing do not escape, and air bubbles remain in the coating film after curing, causing surface roughness.
Furthermore, the resin composition disclosed in Patent Document 2 is a coating-type hot-melt resin composition, and it is difficult to apply it to decorative resin sheets.

Therefore, the objective of the present invention is to provide a moisture-curing resin sheet that can form a coating with good surface condition by suppressing the generation of bubbles during curing.

As a result of extensive investigation, the present inventors have found that the above-mentioned problems can be solved by incorporating a (meth)acrylic resin having an isocyanate group into a moisture-curable resin sheet having a transfer layer and a moisture-curable resin layer, and have completed the present invention as described below. That is, the present invention provides the following [1] to [12].
[1] A moisture-curable resin sheet comprising a transfer layer and a resin layer containing a (meth)acrylic resin (A) having an isocyanate group.
[2] The moisture-curable resin sheet according to the above [1], wherein the weight average molecular weight of the (meth)acrylic resin (A) is 10,000 or more and 500,000 or less.
[3] The moisture-curable resin sheet according to the above [1] or [2], further containing a compound (B) having two or more isocyanate groups other than the (meth)acrylic resin (A).
[4] The moisture-curable resin sheet according to the above [3], wherein the compound (B) has a molecular weight of 1000 or less.
[5] The moisture-curing resin sheet according to any one of [1] to [4], wherein the content of the (meth)acrylic resin (A) in the resin layer is 30% by mass or more.
[6] The moisture-curable resin sheet according to any one of [1] to [5] above, wherein the (meth)acrylic resin (A) has an isocyanate group in a side chain.
[7] The moisture-curing resin sheet according to any one of [1] to [6], wherein the isocyanate group content in the (meth)acrylic resin (A) is 0.5% by mass or more and 15% by mass or less.
[8] The moisture-curing resin sheet according to any one of [1] to [7] above, wherein the resin layer contains a pigment.
[9] A vehicle part having a coating formed from the moisture-curing resin sheet according to any one of [1] to [8] above.
[10] A vehicle having a coating formed from the moisture-curing resin sheet according to any one of [1] to [8] above.
[11] A vehicle manufacturing method comprising a step of painting using the moisture-curing resin sheet according to any one of [1] to [8] above.
[12] A method for manufacturing a vehicle part, comprising a step of painting using the moisture-curing resin sheet according to any one of [1] to [8] above.

The present invention provides a moisture-curing resin sheet that suppresses the generation of bubbles during curing, thereby forming a coating with a good surface condition.

1 is a schematic cross-sectional view showing one embodiment of a moisture-curable resin sheet. 1 is a schematic cross-sectional view showing one embodiment of a moisture-curable resin sheet.

<Moisture-curing resin sheet>
Hereinafter, the moisture-curing resin sheet of the present invention will be described with reference to an embodiment. As shown in Figures 1 and 2, the moisture-curing resin sheet 10 includes a resin layer 11 and a transfer layer 12, with the transfer layer 12 laminated on one side of the resin layer 11. The moisture-curing resin sheet 10 may be composed of the resin layer 11 and the transfer layer 12 as shown in Figure 1, but may also include a release layer 13 as shown in Figure 2, and the release layer 13 may be laminated on the side of the resin layer 11 opposite to the side on which the transfer layer 12 is provided. Hereinafter, each component of the moisture-curing resin sheet will be described in detail.

[Resin layer]
The resin layer of the present invention contains a (meth)acrylic resin (A) having an isocyanate group. By containing the (meth)acrylic resin (A) having an isocyanate group, the resin layer suppresses the generation of bubbles during curing, even when the transfer layer is cured in a laminated state. This prevents surface roughening during curing, and a cured layer with a good surface condition can be formed. While the underlying mechanism is unclear, it is presumed that the (meth)acrylic resin (A) having an isocyanate group suppresses gas generation even when moisture curing progresses, or generates gas in a manner that prevents the formation of bubbles, thereby preventing surface roughening during curing. It is presumed that the generation of gas during curing is suppressed due to the polarity of the ester group of the (meth)acrylic resin, which has the ability to adsorb water and carbon dioxide to a certain extent and gradually releases the gas after adsorption.

((Meth)acrylic resin (A))
The (meth)acrylic resin (A) is a moisture-curable resin having moisture-curing properties due to the inclusion of an isocyanate group. The (meth)acrylic resin (A) preferably has an isocyanate group in a side chain. The (meth)acrylic resin (A) may also preferably have two or more isocyanate groups in one molecule.
The (meth)acrylic resin (A) is not particularly limited as long as it has an isocyanate group, but it is preferable to use a (meth)acrylate having an isocyanate group as a raw material. Therefore, the (meth)acrylic resin (A) is preferably a polymer containing a structural unit derived from a (meth)acrylate having an isocyanate group. By having a structural unit derived from a (meth)acrylate having an isocyanate group, the (meth)acrylic resin (A) has an isocyanate group, and the isocyanate group is positioned close to the main chain, so the molecular arrangement after curing becomes relatively regular and the curability is good. Therefore, it is easy to improve the hardness of the resin layer after curing while improving the surface condition.

The (meth)acrylate having an isocyanate group used as a raw material may have a (meth)acrylate-derived portion of the compound constituting the main chain of the polymer, and an isocyanate group located in a side chain of the polymer. A single molecule of the (meth)acrylic resin (A) may contain a plurality of isocyanate groups in the side chain. The (meth)acrylic resin (A) may have an isocyanate group at its terminal, but need not have an isocyanate group at its terminal.
In this specification, the term "(meth)acrylate" is used to mean either or both of acrylate and methacrylate, and the same applies to other similar terms.

The (meth)acrylic resin (A) is a polymer obtained by polymerizing a (meth)acrylate-containing monomer (a). It may have a (meth)acrylate-derived structural unit in its main chain. However, it is preferably a polymer obtained by polymerizing a monomer (a) containing an isocyanate group-containing (meth)acrylate, and more preferably a polymer obtained by polymerizing a monomer (a) containing an isocyanate group-containing (meth)acrylate and an alkyl (meth)acrylate. The use of an alkyl (meth)acrylate can impart adhesiveness to the resin layer before curing. Furthermore, the monomer (a) may further contain a monomer (other monomer) other than an isocyanate group-containing (meth)acrylate and an alkyl (meth)acrylate.

Examples of (meth)acrylates containing an isocyanate group include isocyanatoalkyl (meth)acrylates such as 2-isocyanatoethyl (meth)acrylate, 4-isocyanatobutyl (meth)acrylate, and 6-isocyanatohexyl (meth)acrylate, as well as 2-(2-isocyanatoethoxy)ethyl (meth)acrylate and 1,1-bis(acryloyloxymethyl)ethyl isocyanate. Of these, isocyanatoalkyl (meth)acrylates are preferred. The number of carbon atoms in the alkyl group in the isocyanatoalkyl (meth)acrylate is not particularly limited, but is, for example, approximately 1 to 10, and preferably 2 to 4.

Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl group containing approximately 1 to 18 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, isomyristyl (meth)acrylate, and stearyl (meth)acrylate. From the viewpoint of imparting adhesive strength before curing to the resin layer, the alkyl(meth)acrylate is preferably an alkyl(meth)acrylate in which the alkyl group has 1 to 12 carbon atoms. Furthermore, from the viewpoint of improving adhesive strength before curing, the alkyl(meth)acrylate more preferably contains an alkyl(meth)acrylate in which the alkyl group has 3 to 10 carbon atoms.

Other monomers besides (meth)acrylates and alkyl (meth)acrylates having an isocyanate group include alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate, (meth)acrylates having an aromatic ring such as benzyl (meth)acrylate and phenoxydiethylene glycol (meth)acrylate, styrene-based monomers such as styrene, α-methylstyrene, α-ethylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-ethoxystyrene, p-chlorostyrene, m-chlorostyrene, and o-chlorostyrene, and vinyl monomers having a vinyl ester group such as vinyl acetate and vinyl propionate.

The amount of the (meth)acrylate having an isocyanate group used in the monomer (a) constituting the (meth)acrylic resin (A) is preferably 2 mol % or more and 40 mol % or less, more preferably 5 mol % or more and 30 mol % or less, and even more preferably 8 mol % or more and 25 mol % or less.
By using the (meth)acrylate having an isocyanate group in an amount within the above range, it is possible to easily suppress the generation of bubbles during curing, even when the transfer layer is cured in a state where it is laminated on a resin layer, and it is also possible to easily achieve a good balance between the adhesive strength before curing, the adhesive strength after curing, and the hardness after curing.

The amount of alkyl (meth)acrylate used in the above monomer (a) is preferably 50 mol% or more and 98 mol% or less, more preferably 65 mol% or more and 95 mol% or less, and even more preferably 70 mol% or more and 92 mol% or less. By using an amount of alkyl (meth)acrylate equal to or greater than the above lower limit, flexibility is increased and adhesive strength before curing is easily improved. By using an amount equal to or less than the upper limit, it is easier to incorporate a certain amount of isocyanate groups, which makes it easier to improve adhesive strength and hardness after curing.

In order to increase flexibility and improve adhesive strength before curing, it is particularly preferable that the alkyl (meth)acrylate in monomer (a) contains an alkyl acrylate having 3 to 10 carbon atoms in the alkyl group. However, the amount of alkyl acrylate in monomer (a) having 3 to 10 carbon atoms used is preferably 30 mol% or more and 98 mol% or less, more preferably 35 mol% or more and 95 mol% or less, and even more preferably 40 mol% or more and 90 mol% or less.

The weight-average molecular weight of the (meth)acrylic resin (A) is preferably 10,000 or more and 500,000 or less. By keeping the weight-average molecular weight of the (meth)acrylic resin (A) within this range, it becomes easier to achieve a good balance of the coatability, curability, adhesion, extensibility, etc. of the resin layer. The weight-average molecular weight of the (meth)acrylic resin (A) is more preferably 20,000 or more and 300,000 or less, and even more preferably 40,000 or more and 100,000 or less. In this specification, the weight-average molecular weight is measured by gel permeation chromatography (GPC) and is calculated as a value converted into standard polystyrene.

The isocyanate group content in the (meth)acrylic resin (A) is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 8% by mass or less. When it is 0.5% by mass or more, crosslinking is at a certain level or more, the hardness becomes appropriate, and deterioration of solvent resistance, etc. can be prevented. Furthermore, when it is 15% by mass or less, it does not become too hard and is less likely to crack, and deterioration of storage stability can also be prevented.
The isocyanate group content referred to here is the proportion of the mass of NCO molecules (molecular weight 42) to the total mass of the (meth)acrylic resin (A), and can be determined, for example, by potentiometric titration in accordance with JIS K 1603-1. That is, the sample and di-n-butylamine are mixed and reacted, and the remaining di-n-butylamine is subjected to potentiometric titration with a hydrochloric acid standard solution, thereby determining the NCO content.

The content of (meth)acrylic resin (A) in the resin layer may be, for example, 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. By ensuring that the content of (meth)acrylic resin (A) is at least a certain amount, the surface condition of the resin layer is improved, while the adhesive strength before curing, the hardness of the resin layer after curing, and the adhesion to the substrate are easily increased. The content of (meth)acrylic resin (A) in the resin layer may be up to 100% by mass, but from the perspective of including a certain amount or more of other components such as compound (B), it is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

(Compound (B))
The moisture-curable resin sheet preferably further contains a compound (B) (polyisocyanate compound) having an isocyanate group. By containing the compound (B), the moisture-curable resin sheet can increase the hardness of the resin layer after curing, and therefore can improve the mechanical strength and scratch resistance of the resin layer after curing. The compound (B) preferably has two or more isocyanate groups. In addition, the compound (B) is preferably a compound other than the above-mentioned (meth)acrylic resin (A) and does not contain a polyacrylic skeleton.

Examples of compound (B) include polyisocyanates such as aliphatic diisocyanate compounds such as hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, lysine diisocyanate, norbornane diisocyanate, isophorone diisocyanate (IPDI), xylylene diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), hydrogenated diphenylmethane diisocyanate, cyclohexane diisocyanate, bis(isocyanatomethyl)cyclohexane, and dicyclohexylmethane diisocyanate, and aromatic diisocyanate compounds such as 4,4-diphenylmethane diisocyanate, tolylene diisocyanate, and naphthalene-1,5-diisocyanate.

The compound (B) may be a modified product obtained by polymerizing the above-mentioned polyisocyanate, such as polymeric MDI, or may be a polyol-modified product (adduct) of a polyisocyanate such as a trimethylolpropane adduct of a polyisocyanate, a biuret of a polyisocyanate, an allophanate of a polyisocyanate, an isocyanurate of a polyisocyanate, or a condensate thereof, etc. Specific preferred examples include HDI adduct, HDI biuret, HDI allophanate, HDI isocyanurate, H6XDI isocyanurate, IPDI isocyanurate, IPDI adduct, etc.
As the compound (B), it is preferable to select one that is flexible and has high adhesive strength in an uncured state. From this viewpoint, an aliphatic polyisocyanate or a modified product thereof is preferable, and among these, an adduct, biuret, allophanate, or isocyanurate of an aliphatic polyisocyanate is more preferable, and an adduct, biuret, allophanate, or isocyanurate of HDI or IPDI is even more preferable.
The compound (B) may be used alone or in combination of two or more.

The molecular weight of compound (B) is not particularly limited, but is preferably 1000 or less. By reducing the molecular weight of compound (B), the adhesive strength of the resin layer before curing and the adhesion to the adherend after curing can be increased. The molecular weight of compound (B) is preferably 800 or less, more preferably 700 or less. The molecular weight of compound (B) is not particularly limited, but may be, for example, 160 or more, preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more.
The molecular weight of the compound (B) is calculated from the structural formula. When two or more compounds (B) are used in combination, the molecular weight means the weight average molecular weight.

When compound (B) is used, the content of compound (B) in the resin layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, based on 100 parts by mass of the total of (meth)acrylic resin (A) and compound (B). By ensuring that the content of compound (B) is at least a certain amount, the hardness of the resin layer after curing tends to be increased. Furthermore, the content of compound (B) may be, for example, 80 parts by mass or less, but is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less. By ensuring that the content of compound (B) is at most a certain value, the surface condition of the resin layer is improved, while the adhesive strength of the resin layer before curing and the adhesion of the resin layer after curing tend to be improved.

(Moisture cure accelerating catalyst)
The resin layer may contain a moisture-cure-accelerating catalyst that accelerates the moisture-cure reaction. By using the moisture-cure-accelerating catalyst, the resin layer has better moisture-cure properties, and the hardness of the resin layer and adhesive strength after curing can be easily increased. Furthermore, even when the outside temperature is low, such as in winter, the resin layer can be properly cured by leaving it in the air.
Specific examples of moisture-cure-accelerating catalysts include amine compounds, metal catalysts, etc. Examples of amine compounds include compounds having a morpholine skeleton such as di(methylmorpholino)diethyl ether, 4-morpholinopropylmorpholine, and 2,2'-dimorpholinodiethyl ether, dimethylamino group-containing amine compounds having two dimethylamino groups such as bis(2-dimethylaminoethyl)ether and 1,2-bis(dimethylamino)ethane, triethylamine, 1,4-diazabicyclo[2.2.2]octane, and 2,6,7-trimethyl-1,4-diazabicyclo[2.2.2]octane.
Examples of the metal catalyst include tin compounds such as di-n-butyltin dilaurate, di-n-butyltin diacetate, and tin octoate; zinc compounds such as zinc octoate and zinc naphthenate; and other metal compounds such as zirconium tetraacetylacetonate, copper naphthenate, and cobalt naphthenate.
The content of the moisture-cure-accelerating catalyst in the resin layer is preferably 0.001 parts by mass or more and 5 parts by mass or less, more preferably 0.01 parts by mass or more and 3.5 parts by mass or less, and even more preferably 0.02 parts by mass or more and 2 parts by mass or less, relative to 100 parts by mass of the total amount of the (meth)acrylic resin (A) and the compound (B).

(Surface conditioner)
The resin layer may contain a surface conditioner. The surface conditioner adjusts the surface tension and improves wettability. Examples of the surface conditioner include silicone acrylic copolymers, silicones, polyacrylates, and fluorine-based agents. By incorporating a surface conditioner into the resin layer, the wettability of the resin layer can be improved, thereby improving the peel strength to the adherend. Furthermore, the smoothness and slipperiness of the surface can be adjusted, thereby improving scratch resistance.
The content of the surface conditioner in the resin layer is preferably 0.01 parts by mass or more and 3 parts by mass or less, more preferably 0.05 parts by mass or more and 2 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the total amount of the (meth)acrylic resin (A) and the compound (B).

(Coloring agent)
The resin layer may be used, for example, to protect or beautify the adherend. Therefore, the resin layer may contain a colorant to form a colored layer. The colorant may be a pigment, a dye, or a luster material. Among these, pigments are preferred.
Examples of pigments used in the colorant include, but are not limited to, metal oxide pigments such as titanium oxide and iron oxide; inorganic pigments such as carbon black, clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white; and organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, vat pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, indanthrone pigments, dioxane pigments, and indigo pigments.
As the dye, known dyes can be used, and examples thereof include azo dyes, anthraquinone dyes, indigoid dyes, and stilbene dyes.
The lustrous material is a compound that can impart lustrous properties to the resin layer and can impart the property of exhibiting gloss when observed from multiple directions. Examples of the lustrous material include, but are not limited to, compounds in which a titanium oxide layer is provided on the surface of natural mica, synthetic mica, alumina flakes, glass flakes, etc.
The content of the colorant in the resin layer is not particularly limited, but is preferably about 0.05% by mass to 15% by mass, more preferably 0.1% by mass to 12% by mass, and even more preferably 0.3% by mass to 8% by mass.

The resin layer may also be a clear layer that does not substantially contain a colorant. The clear layer is a transparent layer that is transparent enough that the color of the colored layer can be seen from the outside through the clear layer; for example, it may have a transmittance of 80% or more for light with a wavelength of 450 nm. The clear layer is preferably a resin layer that does not contain a colorant, but may contain a small amount of colorant as long as it does not impair its function. The content of colorant in the clear layer is not particularly limited, but may be, for example, 0 to 2% by mass, preferably 0 to 0.5% by mass, and more preferably 0 to 0.1% by mass.

The resin layer may also be used to provide functions other than protecting or beautifying the adherend, for example, as a heat-shielding coating. In this case, it is preferable that the coating formed by the resin layer functions as a heat-shielding coating, in which case the resin layer should contain a heat-shielding agent to form a heat-shielding layer. Furthermore, by providing the resin layer with surface irregularities, it is possible to impart surface properties such as matte or grained finishes. Other functions such as rust prevention, mildew prevention, heat insulation, and antistatic properties can also be achieved by incorporating components appropriate for the purpose (e.g., rust inhibitors, mildew inhibitors, antistatic agents, etc.) into the resin layer.

The resin layer may contain components other than those described above, for example, additives other than those listed above. Examples of additives include plasticizers, inorganic fillers other than colorants and heat-shielding agents, dispersants, antioxidants, antioxidants, and ultraviolet absorbers. The resin layer may also contain resin components other than the components (A) and (B) listed above, as long as the effects of the present invention are not impaired.

The resin layer may consist of a single layer, or may have a multi-layer structure of two or more layers, but a single-layer structure is preferred. A single-layer structure makes it easier to manufacture the resin layer. Furthermore, a multi-layer structure allows various functions to be imparted to the coating formed from the resin layer. When the resin layer has a multi-layer structure, it is sufficient for the entire resin layer to contain the above-mentioned components in the above-mentioned amounts, but it is preferable for each layer to be a resin layer as described above. In the case of a multi-layer structure, the composition of each layer may be the same or different, but is usually different from each other.

In the case of a multi-layer structure, the resin layer may include, for example, at least one of a colored layer containing a colorant and a clear layer substantially free of a colorant, but preferably includes a colored layer and a clear layer. When a colored layer and a clear layer are included, the clear layer and the colored layer are preferably arranged in this order from the transfer layer side. With this layer structure, when the moisture-curing resin sheet is attached to an adherend, the colored layer and the clear layer are arranged in this order from the adherend side.
As described above, the resin layer has a colored layer, which allows the adherend to be colored by the coating formed by the resin layer. Furthermore, by providing a clear layer in addition to the resin layer, the colored layer can be protected and glossy.
The colored layer in the multilayer structure may have a colorant content within the above range, and the clear layer may also have a colorant content within the above range.

Of course, if the resin layer has a multi-layer structure, it is not limited to a two-layer structure consisting of a clear layer and a colored layer, and various laminate structures are possible. A three-layer or more structure may be formed by providing two or more colored layers and one or more clear layers, or the clear layer may be omitted and the structure may consist of two colored layers. Two or more clear layers may also be provided. A heat-shielding layer or the like may be provided between the clear layer and the colored layer, resulting in a three-layer or more structure.

The thickness of the resin layer is not particularly limited, but is, for example, about 5 μm to 1000 μm, preferably 15 μm to 500 μm, and more preferably 20 μm to 200 μm. Note that the thickness of the resin layer refers to the total thickness of the resin layer when the resin layer has a multilayer structure.
When a colored layer and a clear layer are provided on the resin layer, the thickness of the colored layer is not particularly limited, but is, for example, 5 μm to 500 μm, preferably 10 μm to 100 μm, and more preferably 15 μm to 50 μm. The thickness of the clear layer is not particularly limited, but is, for example, 5 μm to 500 μm, preferably 10 μm to 100 μm, and more preferably 15 μm to 50 μm.

(Transfer layer)
The transfer layer is a member that protects the resin layer from scratches and adhesion of foreign matter, and also serves as a support when attaching the resin layer to an adherend. The transfer layer is preferably formed from a resin film. The resin used in the resin film is preferably a thermoplastic resin, but may be a resin other than a thermoplastic resin. Specific examples of resins used in the resin film include polyolefin resins such as cyclic polyolefin resins, polyethylene resins, and polypropylene resins, ethylene vinyl acetate copolymer resins, polyester resins such as polybutylene terephthalate, polyamide resins, acrylonitrile butadiene styrene resins, polycarbonate resins, acrylic resins, fluororesins, vinyl chloride resins, polymethylpentene resins, and tetrafluoroethylene resins.

The resin film constituting the transfer layer may be a single-layer film consisting of one single layer, or may be a multilayer film consisting of two or more layers. Furthermore, in the resin film constituting the transfer layer, the resin contained in the resin film may be used alone, or two or more types may be used in combination. When two or more types of resins are used in combination, a multilayer film may be formed by using different types of resins in each layer. Furthermore, a single-layer film may be formed by mixing two or more types of resins, or one or more layers in a multilayer film may be formed by mixing two or more types of resins.
The resin film used for the transfer layer may be a stretched resin film or a non-stretched resin film.

The transfer layer may have at least one surface that has been release-treated with a release agent such as a silicone-based release agent or a fluorine-based release agent. If the transfer layer is release-treated, it is preferable that the release-treated surface constitutes the surface on the resin layer side. The release treatment of the transfer layer makes it easier to peel it from the resin layer. However, the transfer layer does not need to be release-treated as long as it can be peeled from the resin layer.

The thickness of the transfer layer is not particularly limited, but is, for example, 10 μm or more and 1000 μm or less, preferably 30 μm or more and 700 μm or less, and more preferably 50 μm or more and 500 μm or less. If the thickness of the transfer layer is within the above range, the transfer layer can be given a certain level of strength and flexibility.

(Release layer)
The release layer is a member that protects the resin layer from scratches and foreign matter adhesion. The release layer is preferably formed from a resin film. The resin used in the resin film for the release layer is preferably a thermoplastic resin, but may be a resin other than a thermoplastic resin. Specific examples of the resin used in the resin film for the release layer are the same as those listed for the resin used in the transfer layer. The resin used in the release layer and the resin used in the transfer layer may be the same or different.

The resin film forming the release layer may be a single-layer film consisting of one single layer, or may be a multilayer film consisting of two or more layers. Furthermore, in the resin film constituting the release layer, the resin contained in the resin film may be used alone, or two or more types may be used in combination. When two or more types of resins are used in combination, different types of resins may be used in each layer to form a multilayer film. Furthermore, a single-layer film may be formed by mixing two or more types of resins, or one or more layers in a multilayer film may be formed.
The resin film used for the release layer may be a stretched resin film or a non-stretched resin film.

The release layer may have at least one surface that has been release-treated with a release agent such as a silicone-based release agent or a fluorine-based release agent. When the release layer is release-treated, it is preferable that the release-treated surface constitutes the surface on the resin layer side. The release layer is easily released from the resin layer by being release-treated. However, the release layer does not need to be release-treated as long as it can be released from the resin layer.
The thickness of the release layer is not particularly limited, but is, for example, 10 μm or more and 1000 μm or less, preferably 30 μm or more and 700 μm or less, and more preferably 50 μm or more and 500 μm or less.

(Method for manufacturing moisture-curing resin sheet)
The manufacturing method of the moisture-curing resin sheet is not particularly limited, but can be manufactured by a known method. For example, a moisture-curing resin composition is prepared, and the prepared moisture-curing resin composition is applied to a transfer layer and dried as necessary to form a resin layer. The moisture-curing resin composition may contain a (meth)acrylic resin (A), but may optionally contain a compound (B), a surface conditioner, a moisture-cure accelerating catalyst, a colorant, or other components. The details and contents of each component in the moisture-curing resin composition are as described above for the resin layer. However, if the content standard is a resin layer, the solid content excluding the volatile content of the moisture-curing resin composition instead of the resin layer may be used as the content standard.

In addition, when the moisture-curable resin sheet has a release layer, the moisture-curable resin composition may be applied to the release layer and dried as necessary to form a resin layer, and a transfer layer may be further laminated to the resin layer formed on the resulting release layer to obtain a moisture-curable resin sheet. When applying the curable resin composition to the transfer layer or release layer, the curable resin composition may be appropriately diluted with a solvent or the like. Examples of solvents include ethyl acetate, butyl acetate, and toluene. The solvent may be, for example, the solvent used in producing the (meth)acrylic resin (A).

Moreover, when the resin layer is multilayered, it may be formed by sequentially forming and laminating each layer. For example, when a clear layer and a colored layer are provided, the clear layer and the colored layer may be laminated in this order on the transfer layer. Furthermore, when the moisture-curing resin sheet has a release layer, the moisture-curing resin sheet may be obtained by laminating one or more resin layers formed on the release layer with one or more resin layers formed on the transfer layer. In the case of a multilayered structure, as described above, it is preferable that each layer is made of a moisture-curing resin composition containing each of the above-mentioned components in the above-mentioned content. The formulation of each layer may be the same or different, but is usually different from each other.
The resin layer is preferably formed in a low humidity environment so as not to accelerate curing due to moisture absorption.

[Painting method]
The moisture-curable resin sheet of the present invention can be used as a coating sheet by laminating it to an adherend and then curing the resin layer to form a coating made of the cured resin layer on the surface of the adherend.

Hereinafter, one embodiment of a coating method for forming a coating on an adherend using the moisture-curing resin sheet of the present invention will be described in detail. The coating method according to one embodiment of the present invention includes the following first and second steps.
First step: A step of attaching a moisture-curable resin sheet to an adherend. Second step: A step of curing the moisture-curable resin sheet.

(1st step)
The first step is a step of attaching a moisture-curable resin sheet to an adherend.
Before being attached to an adherend, the moisture-curing resin sheet may have a release layer laminated on the surface of the resin layer opposite to the surface on which the transfer layer is provided. When a release layer is laminated, the moisture-curing resin sheet may be attached to the adherend by peeling the release layer from the resin layer to expose the resin layer. The method for peeling the release layer is not particularly limited, and may be peeled off using a peeling device or by hand. Of course, the release layer may be omitted from the moisture-curing resin sheet.

In this process, the moisture-curable resin sheet with the exposed resin layer is attached to the adherend so that the resin layer is in contact with the adherend. There are no particular limitations on how the moisture-curable resin sheet is attached to the adherend; it may be attached by hand or using a laminating device. Because the resin layer is made of a moisture-curable resin composition and is in its pre-cured state when attached, it is easy to ensure a certain degree of flexibility. Therefore, the resin layer adheres appropriately to the adherend and can be temporarily fixed to the adherend with appropriate adhesive strength.

Moisture-curing resin sheets can also be attached using the so-called water lamination method. Water lamination is preferably performed by first applying water to the adherend, laminating the moisture-curing resin sheet to the water-coated surface, and then using a squeegee or similar tool to push out the water between the moisture-curing resin sheet and the adherend. This pushes out any air bubbles or bubbles that may have been present between the moisture-curing resin sheet and the adherend along with the water, allowing the moisture-curing resin sheet to be neatly attached to the adherend. The water applied to the adherend may be water alone, or additives such as surfactants or organic solvents may be added as appropriate.

The moisture-curing resin sheet may be preformed by vacuum forming, press forming, compressed air forming, or the like, and may be shaped to have a shape corresponding to the shape of the adherend, and the shaped moisture-curing resin sheet may be attached to the adherend. When the moisture-curing resin sheet has a release layer, preforming may be performed before the release layer is peeled off from the resin layer, or after the release layer is peeled off from the resin layer. By performing preforming, even if the adherend has a complex shape, the moisture-curing resin sheet can be easily attached by adhering it to the adherend. Among the above, preforming is preferably performed by vacuum forming. Preforming may be performed by pressing the coated sheet against a jig or mold by vacuum forming, and stretching the moisture-curing resin sheet using the jig or mold to form it into a shape corresponding to the surface shape of the adherend.
Here, the vacuum forming is preferably TOM forming. TOM stands for "Three Dimension Overlay Method," and when TOM forming is applied, it is possible to form a complex shape.

(Second process)
The second step is a step performed after the first step, and is a step of curing the resin layer of the moisture-curable resin sheet. In this step, the resin layer is preferably cured to an extent that it can be used as a coating. The curing of the resin layer is not particularly limited as long as it is cured by moisture, but is usually left at room temperature or a temperature close to it (e.g., 0 to 45 ° C, preferably 5 to 30 ° C) in the atmosphere or in a humidified environment (e.g., in an environment of 50% RH or higher). The time left in the atmosphere or in a humidified environment is not particularly limited, but is, for example, about 1 hour to 2 weeks, preferably about 1 day to 1 week.
The moisture-curable resin sheet of the present invention can be cured simply by being left in the atmosphere, so the resin layer can be cured industrially without the need for large-scale equipment. Furthermore, even when the adherend is large and difficult to heat, or when the adherend has low heat resistance, the resin layer can be cured appropriately.

The coating method of the present invention may further include a step of peeling the transfer layer from the resin layer. The transfer layer may be peeled off using a peeling device or manually. The transfer layer may be peeled off before, after, or during the second step described above, but is preferably peeled off after the resin layer has cured to a certain extent. Therefore, it is preferable to peel off the transfer layer after leaving it in the atmosphere for a certain period of time (e.g., one hour or more, preferably one day or more). Once the resin layer has cured to a certain extent, the uncured or undercured resin layer is prevented from being exposed to the outside, thereby preventing dust and scratches from adhering to the uncured resin layer. Furthermore, peeling the transfer layer off of a resin layer that has cured to a certain extent also prevents scratches on the resin layer during peeling.

The moisture-curing resin sheet may be attached to various adherends to form a coating. The adherend to which the moisture-curing resin sheet can be attached is not particularly limited, and examples thereof include vehicle interior materials such as automobile interior materials and interior materials for transportation equipment other than automobiles, vehicle exterior materials such as automobile exterior materials and exterior materials for transportation equipment other than automobiles, vehicle parts, exterior materials for heavy machinery, ships, aircraft, etc., exterior walls or roofing materials for houses and buildings, bridges, steel frames, plants, wind power generation blades, electrical appliances, and miscellaneous goods.
Among these, it is preferable to use it on vehicles and vehicle parts, and in particular, it is preferable to use vehicle exterior materials such as exterior materials for transportation equipment other than automobiles as the adherend. The vehicle exterior material is preferably the exterior of the vehicle body, but may also be a hood, roof, door panel, bumper, fuel filler panel, trunk lid, rear gate, etc. When attached to a vehicle exterior material, the moisture-curing resin sheet may be attached to an exterior material attached to the vehicle body, or may be attached to an exterior material before being attached to the vehicle body.
The material of the adherend is not particularly limited, but may be any of resin materials, inorganic materials such as ceramics, and metal materials such as steel, with metal materials such as steel being preferred.
Furthermore, a base layer or the like may be appropriately formed on the surface of the adherend to which the moisture-curable resin sheet is attached.

The present invention also provides a method for manufacturing a vehicle and a method for manufacturing a vehicle part. The method for manufacturing a vehicle or vehicle part of the present invention includes a step of painting using the moisture-curing resin sheet of the present invention. In the painting step, the vehicle or vehicle part may be painted using the method described above for the painting method.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.
The measurement and evaluation methods in the present examples are as follows.

(1) Evaluation of adhesive strength before curing A moisture-curing resin sheet was cut into a width of 1 inch (2.54 cm), and the PET film constituting the release layer was peeled off. The sheet was then attached to a coated plate (SPCC-SD urethane coated test piece, manufactured by Standard Test Piece Co., Ltd.) using a squeegee. The adhesive strength (N/inch) of the attached film was measured by a 180° peel test at 25°C and a pulling speed of 30 mm/sec.

(2) Air bubble generation After cutting the moisture-curing resin sheet film into 5 cm squares, the PET film constituting the release layer was peeled off, and the film was then attached to the same coated plate as in (1) by water lamination. The attached test piece was left in an environment of 25 ° C. and 70% RH for 5 days with the PET film constituting the transfer layer still attached, to moisture-cure the resin layer. After moisture curing, it was visually confirmed whether or not the PET film had lifted due to gas generation. A test piece in which bubbles or peeling occurred over the entire surface of the transfer layer due to gas generation was rated as "C", a test piece in which bubbles were partially generated was rated as "B", and a test piece in which there was no peeling or bubbles was rated as "A".

(3) Pencil Hardness In the same manner as in (2) above, the resin layer was adhered to a steel plate and moisture-cured, and then the PET film constituting the transfer layer was peeled off, and the pencil hardness of the exposed surface of the resin layer was measured in accordance with JIS K 5600-5-4.

(4) Cross-cut test evaluation: After the resin layer was bonded to a steel plate and moisture-cured in the same manner as in (2) above, the PET film constituting the transfer layer was peeled off. The resin layer was subjected to a cross-cut test in accordance with JIS K 5600-5-6 and evaluated according to the following criteria.
<Evaluation criteria>
A: Test results are classified as 0 to 2
B: Test results are classified as 3 or higher

(Production Example 1)
A 1 L glass reaction vessel equipped with a stirrer, thermometer, and condenser was charged with 20 g of methyl methacrylate (hereinafter referred to as "MMA"), 77 g of butyl acrylate (hereinafter referred to as "BA"), 31 g of 2-isocyanatoethyl methacrylate (trade name "Karenz MOI" (manufactured by Resonac Corporation, hereinafter referred to as "MOI"), 2.0 g of 2,2'-azobis-2,4-dimethylvaleronitrile (manufactured by Wako Pure Chemical Industries, Ltd., trade name "V-65", hereinafter referred to as "V-65"), and 200 g of ethyl acetate (hereinafter referred to as "EA"), and the contents were uniformly dissolved at room temperature. While stirring the contents of the flask, the internal temperature was raised to 60°C under a nitrogen atmosphere, and solution polymerization was carried out over 6 hours to obtain a solution (solids content 40% by mass) of acrylic resin (A-1) having isocyanate groups in the side chains. The weight-average molecular weight of the resulting acrylic resin (A-1) was 80,000. The monomers constituting the acrylic resin (A-1) were 20 mol % MMA, 60 mol % BA, and 20 mol % MOI, and the isocyanate group content (NCO content) of the resulting acrylic resin (A-1) was 7.0 mass %.

(Production Example 2)
A 1 L glass reaction vessel equipped with a stirrer, thermometer, and condenser was charged with 44 g of MMA, 56 g of BA, 18.5 g of MOI, 2.0 g of V-65, and 200 g of EA, and the contents were dissolved uniformly at room temperature. While stirring the contents of the flask, the internal temperature was raised to 60 ° C. under a nitrogen atmosphere, and solution polymerization was carried out over 6 hours to obtain a solution of acrylic resin (A-2) having an isocyanate group in the side chain (solid content 38% by mass). The weight average molecular weight of the obtained polymer was 70,000. The monomers constituting the acrylic resin (A-2) were 44 mol% MMA, 44 mol% BA, and 12 mol% MOI. The isocyanate group content of the obtained acrylic resin (A-2) was 4.6% by mass.

(Production Example 3)
A solution of acrylic resin (A-3) (solid content 38% by mass) was obtained in the same manner as in Production Example 2, except that the amount of initiator V-65 was changed to 3.0 g. The weight-average molecular weight of the obtained polymer was 30,000. The monomers constituting the acrylic resin (A-3) were 44 mol % MMA, 44 mol % BA, and 12 mol % MOI, and the isocyanate group content of the acrylic resin (A-3) was 4.6 mol %.

(Production Example 4)
A solution of acrylic resin (A-4) (solid content 38% by mass) was obtained in the same manner as in Production Example 2, except that the amount of initiator V-65 in Production Example 2 was changed to 0.5 g. The weight-average molecular weight of the obtained polymer was 250,000. The monomers constituting the acrylic resin (A-4) were 44 mol % MMA, 44 mol % BA, and 12 mol % MOI, and the isocyanate group content of the acrylic resin (A-4) was 4.6 mol %.

(Production Example 5)
A solution of acrylic resin (A-5) (solid content 38% by mass) was obtained in the same manner as in Production Example 2, except that the amounts of methyl methacrylate (hereinafter referred to as "MMA"), butyl acrylate (hereinafter referred to as "BA"), and 2-isocyanatoethyl methacrylate (trade name "Karenz MOI" (manufactured by Resonac Corporation; hereinafter referred to as "MOI") were changed to 10 g, 64 g, and 64 g, respectively. The weight-average molecular weight of the obtained polymer was 50,000. The monomers constituting the acrylic resin (A-5) were 10 mol % MMA, 50 mol % BA, and 40 mol % MOI, and the isocyanate group content of the acrylic resin (A-5) was 11.9 mol %.

(Production Example 6)
A solution of acrylic resin (A-6) (solid content 38% by mass) was obtained in the same manner as in Production Example 2, except that the amounts of methyl methacrylate (hereinafter referred to as "MMA"), butyl acrylate (hereinafter referred to as "BA"), and 2-isocyanatoethyl methacrylate (trade name "Karenz MOI" (manufactured by Resonac Corporation; hereinafter referred to as "MOI") were changed to 37 g, 77 g, and 4.7 g, respectively. The weight-average molecular weight of the obtained polymer was 80,000. The monomers constituting the acrylic resin (A-6) were 37 mol % MMA, 60 mol % BA, and 3 mol % MOI, and the isocyanate group content of the acrylic resin (A-6) was 0.9 mol %.

The components used in the resin layer other than the (meth)acrylic resin were as follows:
Urethane prepolymer: Trade name "Takenate M-605N", manufactured by Mitsui Chemicals, Inc. Polyisocyanate (1): Trade name "Desmodur N3200A", manufactured by Covestro, HDI biuret, molecular weight 479
Polyisocyanate (2): Trade name "Takenate D-140N", manufactured by Mitsui Chemicals, Inc., isophorone diisocyanate adduct, molecular weight 801
Surface conditioner: trade name "BYK-378", manufactured by BYK Corporation Catalyst: moisture curing accelerator catalyst, 2,2'-dimorpholinodiethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., reagent)
Pigment: "NSP-UP 841B" manufactured by Nihon Bix Co., Ltd., effective pigment concentration = 9% by mass, solid content (NV) = 24% by mass

Example 1
To the solution of (meth)acrylic resin (A-1) obtained in Production Example 1 (100 parts by mass of (meth)acrylic resin (A-1) based on solids), 0.2 parts by mass of a surface conditioner was added to prepare a solution of a moisture-curable resin composition. The obtained solution of the moisture-curable resin composition was applied to a 50 μm thick release-treated PET film (manufactured by Nakamoto Pax Co., Ltd., trade name "NS-50B") as a release layer in a dry bench (dew point -50 ° C.) with a doctor knife so that the thickness of the coating after drying would be 50 μm. Then, the solution was heated on a hot plate at 100 ° C. for 5 minutes to dry the solvent and form a resin layer. A release-treated PET film (manufactured by Nakamoto Pax Co., Ltd., trade name "NS-50C") as a transfer layer was laminated on the obtained resin layer and then stored in a moisture-proof bag.

(Examples 2 to 9, Comparative Example 1)
The same procedure as in Example 1 was carried out, except that the components were blended as shown in Table 1 to prepare a moisture-curable resin composition.

*The content of each component in Table 1 is based on solid content.
*The amount of active ingredient in the pigment is the value in Table 1 multiplied by 9/24.

In Examples 1 to 9, by using a (meth)acrylic resin having an isocyanate group as the moisture-curing resin, it was possible to suppress the generation of bubbles even when the transfer layer was left laminated and the moisture-curing was carried out, and a coating with a good surface condition was formed.
In contrast, in Comparative Example 1, in which urethane resin was used as the moisture-curing resin, when moisture curing was carried out while the transfer layer was still laminated, the generation of air bubbles could not be suppressed and a coating with a good surface condition could not be obtained.

Claims (12)

A moisture-curing resin sheet comprising a transfer layer and a resin layer containing a (meth)acrylic resin (A) having an isocyanate group. The moisture-curable resin sheet according to claim 1, wherein the weight-average molecular weight of the (meth)acrylic resin (A) is 10,000 or more and 500,000 or less. The moisture-curable resin sheet according to claim 1 or 2, further comprising a compound (B) having two or more isocyanate groups other than the (meth)acrylic resin (A). The moisture-curable resin sheet according to claim 3, wherein the compound (B) has a molecular weight of 1,000 or less. The moisture-curable resin sheet according to claim 1 or 2 , wherein the content of the (meth)acrylic resin (A) in the resin layer is 30% by mass or more. The moisture-curable resin sheet according to claim 1 or 2 , wherein the (meth)acrylic resin (A) has an isocyanate group in a side chain. The moisture-curable resin sheet according to claim 1 or 2 , wherein the isocyanate group content in the (meth)acrylic resin (A) is 0.5% by mass or more and 15% by mass or less. The moisture-curable resin sheet according to claim 1 or 2 , wherein the resin layer contains a pigment. A vehicle part having a coating formed from the moisture-curable resin sheet according to claim 1 or 2 . A vehicle having a coating formed from the moisture-curing resin sheet according to claim 1 or 2 . A method for manufacturing a vehicle, comprising a step of painting using the moisture-curing resin sheet according to claim 1 or 2 . A method for manufacturing a vehicle part, comprising a step of painting using the moisture-curing resin sheet according to claim 1 or 2 .