UV curable white coating composition and article

Abstract

The present invention relates to a UV-curable white coating composition, comprising: (a) at least one (meth)acrylate polymer; (b) at least one reactive diluent; (c) titanium dioxide and magnesium oxide; and (d) at least one acylphosphine oxide; wherein the content of magnesium oxide is at least 10% by weight relative to the total weight of the UV-curable white coating composition. The present invention also relates to an article comprising a coating formed from the white coating composition.

Description

Technical Field

[0001] The present invention relates to a UV-curable white coating composition and also to an article comprising a coating formed from the white coating composition. Background Art

[0002] Wood products, including wooden furniture, are the most commonly used products in production and life, and are mainly made of wooden substrates. As is known, wooden substrates have advantages that other materials cannot match, such as special textures and natural colors. However, wooden substrates inevitably have complex organizational structures, uneven materials, multiple pores, swelling and shrinking when exposed to water, and contain such characteristics as grease, tannins and other colored impurities, and are not an ideal industrial material.

[0003] Therefore, the research on wood paint that can provide a protective layer for wooden substrates is particularly interesting. In recent years, white furniture has been very popular among market consumers. Most white wood paints are cured by UV light sources. The existing UV-curable white wood paints are limited by factors such as coating amount, and it is difficult to achieve a high whiteness value.

[0004] Therefore, there is still a need in the art of wood coatings for UV-curable white coating compositions that can provide higher whiteness. Summary of the invention

[0005] In one aspect, the present invention provides a UV-curable white coating composition comprising:

[0006] (a) at least one (meth)acrylate polymer;

[0007] (b) at least one reactive diluent;

[0008] (c) titanium dioxide and magnesium oxide; and

[0009] (d) at least one acylphosphine oxide;

[0010] Wherein, the content of magnesium oxide is at least 10 wt % relative to the total weight of the UV-curable white coating composition.

[0011] In an embodiment of the present invention, the content of magnesium oxide is up to 50 wt % relative to the total weight of the UV-curable white coating composition.

[0012] In an embodiment of the present invention, the sum of the amounts of titanium dioxide and magnesium oxide used is 40 wt % to 65 wt % relative to the total weight of the UV-curable white coating composition.

[0013] In another aspect, the present invention provides a UV-curable white coating composition, wherein, relative to the total weight of the UV-curable white coating composition, the UV-curable white coating composition comprises:

[0014] (a) 15 to 30% by weight of at least one (meth)acrylate polymer;

[0015] (b) 10-30% by weight of at least one reactive diluent;

[0016] (c) 40-65 wt % titanium dioxide and magnesium oxide;

[0017] (d) 1 to 5 weight percent of at least one acylphosphine oxide; and

[0018] (e) 0.1-5 wt % of additional additives, wherein the additional additives include dispersants, thickeners, defoamers, bactericides or any combination thereof.

[0019] The invention relates to a sealing coating formed by the two-component water-based wood sealing primer according to the present invention.

[0020] In an embodiment of the present invention, the L value of the coating formed by curing the UV-curable white coating composition of the present invention on BYK white coating test card paper is at least 97.

[0021] In addition, the present invention also provides an article, comprising: a substrate partially or fully coated with the UV-curable white coating composition according to the present invention.

[0022] Thus, the present invention also relates to the use of magnesium oxide for improving the whiteness of a coating formed from the UV-curable white coating composition according to the present invention.

[0023] The inventors surprisingly found that adding magnesium oxide to a conventional UV-curable white coating composition can significantly improve the whiteness of the cured coating, even better than a white coating composition using only titanium dioxide.

[0024] Titanium dioxide (TiO2) is the most common white pigment used in coatings. However, in order to achieve a certain whiteness, the coating must contain at least a large amount of titanium dioxide, and such a pigment content is close to or even exceeds the maximum pigment content allowed in the coating formulation. In contrast, the present invention innovatively adds magnesium oxide to a UV-curable white coating composition, and combines it with titanium dioxide commonly used in coating compositions, significantly improving the whiteness of the cured coating at the same pigment content, obtaining a whiteness (L value) of 97.3 or even above 97.5, which has never been recognized before the present invention.

[0025] The details of one or more embodiments of the invention are set forth in the description which follows. Other features, objects, and advantages of the invention will become apparent from the description and claims.

[0026] definition

[0027] As used herein, "a", "an", "the", "at least one" and "one or more" and the absence of quantifiers are used interchangeably. Thus, for example, a component containing "an" additive can be interpreted to mean that the component contains "one or more" additives.

[0028] Where a composition is described as comprising or including specific components, it is contemplated that optional components not contemplated by the present invention are not excluded from the composition, and that the composition may consist of or be composed of the contemplated components; or where a method is described as comprising or including specific process steps, it is contemplated that optional process steps not contemplated by the present invention are not excluded from the method, and that the method may consist of or be composed of the contemplated process steps.

[0029] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0030] As used herein, "acrylate" is a general term for esters of acrylic acid and its homologues, such as methyl acrylate, ethyl acrylate, methyl 2-methacrylate, and ethyl 2-methacrylate, etc. Therefore, unless otherwise specified, "acrylate" includes both acrylate and methacrylate.

[0031] When used in the context of a substrate, the term "major surface" is the surface formed by a certain length and a certain width dimension of the substrate for providing decoration.

[0032] As used herein, the term "topcoat" refers to a coating composition that can be applied over a primer and dried, crosslinked or otherwise hardened to form a decorative or protective outermost finish layer. Further, such topcoats are capable of withstanding long-term outdoor exposure without showing visible unsatisfactory degradation.

[0033] When used in the context of "applying ...on a coating layer", the term "on" includes applying one paint or coating composition directly or indirectly on another coating layer.

[0034] When appearing in this description and claims, the terms "comprises" and "includes" and variations thereof do not have a limiting meaning.

[0035] In this application, numerical ranges defined by endpoints include all values ​​within the range, for example, a range of 1 to 5 includes values ​​of 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. Moreover, the disclosed numerical ranges include all subset ranges within the broader range, for example, a range of 1 to 5 includes subranges of 1 to 4, 1.5 to 4.5, 1 to 2, etc.

[0036] The terms "preferred" and "preferably" refer to embodiments of the present invention that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. In addition, the recitation of one or more preferred embodiments does not mean that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present invention. DETAILED DESCRIPTION

[0037] In one aspect, an embodiment of the present invention provides a UV-curable white coating composition, comprising:

[0038] (a) at least one (meth)acrylate polymer;

[0039] (b) at least one reactive diluent;

[0040] (c) titanium dioxide and magnesium oxide; and

[0041] (d) at least one acylphosphine oxide;

[0042] Wherein, the content of magnesium oxide is at least 10 wt % relative to the total weight of the UV-curable white coating composition.

[0043] (a) (Meth)acrylate polymer

[0044] The UV-curable white coating composition according to an embodiment of the present invention includes at least one (meth)acrylate polymer as a film-forming resin.

[0045] The at least one (meth)acrylate polymer includes at least one of epoxy (meth)acrylate, polyurethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and acrylate copolymer.

[0046] The epoxy (meth) acrylate polymer is an addition product of an epoxy resin and an unsaturated carboxylic acid (e.g., acrylic acid, methacrylic acid), including epoxy (meth) acrylate of bisphenol A epoxy resin, epoxy (meth) acrylate of phenol or cresol-novolac epoxy resin, or (meth) acrylate of diglycidyl ether.

[0047] The polyurethane (meth) acrylate polymer is a reaction product obtained by reacting a hydroxyl-containing (meth) acrylate with a reaction product of a polyol and an organic polyisocyanate. The hydroxyl-containing (meth) acrylate is a hydroxyalkyl (meth) acrylate, such as 2-hydroxyethyl (meth) acrylate or 2-hydroxypropyl (meth) acrylate. The polyol includes ethylene glycol, propylene glycol or butylene glycol, etc. The organic polyisocyanate includes toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate.

[0048] The polyester (meth) acrylate polymer is a dehydration condensation product of polyester polyol and (meth) acrylic acid. The polyester polyol is a reaction product of a polyol and a dibasic acid, wherein the polyol includes ethylene glycol, polypropylene glycol, 1,6-hexanediol or trimethylolpropane, etc., and the dibasic acid includes adipic acid, succinic acid, phthalic acid, hexahydrophthalic acid or terephthalic acid, etc.

[0049] The polyether (meth)acrylate polymer is a polyalkylene glycol di(meth)acrylate, such as polyethylene glycol di(meth)acrylate or polypropylene glycol di(meth)acrylate.

[0050] The acrylic ester copolymer is a type of polymer obtained by free radical polymerization of monomers such as (meth)acrylic acid, (meth)acrylate and styrene under the action of a peroxide initiator (for example, benzoyl peroxide).

[0051] The (meth)acrylate polymer is present in an amount of 15 to 30 wt %, preferably 15 to 25 wt %, based on the total weight of the UV-curable white coating composition.

[0052] (b) Reactive diluent

[0053] Reactive diluents include (meth)acrylic monomers. Examples of monofunctional (meth)acrylic monomers include, but are not limited to, butylene glycol mono(meth)acrylate, cyclohexyl(meth)acrylate, dicyclopentanyl(meth)acrylate, dicyclopentenyl(meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, caprolactone-modified 2-hydroxyethyl(meth)acrylate, isobornyl(meth)acrylate, lauryl(meth)acrylate, acryloylmorpholine, N-vinylcaprolactam, nonylphenoxypolyethylene glycol(meth)acrylate, nonylphenoxypolypropylene glycol(meth)acrylate, phenoxyethyl(meth)acrylate, phenoxyhydroxypropyl(meth)acrylate, phenoxydiglycol(meth)acrylate, polyethylene glycol(meth)acrylate, polypropylene glycol(meth)acrylate, and tetrahydrofurfuryl(meth)acrylate, and the like.

[0054] The multifunctional (meth)acrylic monomers include, but are not limited to, 1,4-butanediol di(meth)acrylate, dicyclopentyl di(meth)acrylate, ethylene glycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, di(meth)acrylate, trimethylolpropane tri(meth)acrylate and its alkoxylates, tetraethylene glycol tri(acryloyloxyethyl)isocyanurate, caprolactone-modified tri(acryloyloxyethyl)isocyanurate, tri(methacryloyloxyethyl)isocyanurate, and tricyclodecane dimethanol di(meth)acrylate, etc.

[0055] These monofunctional (meth)acrylic monomers and polyfunctional (meth)acrylic monomers may be used alone or in combination of two or more monomers, or the monofunctional and polyfunctional monomers may be used in combination.

[0056] As a component used in combination, a monofunctional (meth)acrylic monomer is preferably used for viscosity adjustment and / or physical property adjustment. In a specific application, an alicyclic (meth)acrylate compound such as isobornyl acrylate is preferred.

[0057] In a preferred embodiment according to the present invention, the reactive diluent is selected from at least one of dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, hexanediol di(meth)acrylate, (ethoxylated) trimethylolpropane tri(meth)acrylate, (propoxylated) trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate and isobornyl(meth)acrylate.

[0058] The reactive diluent is present in an amount of 10 to 40 wt %, preferably 10 to 30 wt %, more preferably 15 to 20 wt %, based on the total weight of the UV-curable white coating composition.

[0059] (c) Titanium dioxide and magnesium oxide

[0060] Based on the total weight of the UV-curable white coating composition, magnesium oxide is present in an amount of at least 10 wt %, preferably at least 20 wt %, more preferably at least 30 wt %. Based on the total weight of the UV-curable white coating composition, magnesium oxide is present in an amount of up to 50 wt %, preferably up to 45 wt %, more preferably up to 40 wt %. Thus, based on the total weight of the UV-curable white coating composition, the content of magnesium oxide is 10 wt % to 50 wt %.

[0061] Based on the total weight of the UV-curable white coating composition, the titanium dioxide is present in an amount of at least 20% by weight, preferably at least 25% by weight, and more preferably at least 30% by weight. Based on the total weight of the UV-curable white coating composition, the magnesium oxide is present in an amount of up to 45% by weight, preferably up to 40% by weight, more preferably up to 35% by weight, and preferably up to 30% by weight. Thus, based on the total weight of the UV-curable white coating composition, the content of titanium dioxide is 20% to 45% by weight, preferably 20% to 40% by weight.

[0062] In a preferred embodiment according to the present invention, the sum of the amounts of titanium dioxide and magnesium oxide used is 40 to 65 wt %, preferably 40 to 60 wt %, and more preferably 45 to 55 wt %, based on the total weight of the UV-curable white coating composition.

[0063] Titanium dioxide, also known as titanium dioxide (TiO2), is a commonly used white pigment in UV-curable white coating compositions. However, in order to achieve a certain whiteness, the coating must contain at least a large amount of titanium dioxide, and such a pigment content is close to or even exceeds the maximum pigment content allowed in the coating formulation. In contrast, the present invention innovatively adds magnesium oxide to the UV-curable white coating composition, and combines it with the titanium dioxide commonly used in the coating composition, which significantly improves the whiteness of the cured coating at the same pigment content, and even obtains a whiteness (L value) of 97.3 or even above 97.5, which has never been recognized before the present invention.

[0064] Without wishing to be bound by any theoretical limitations, the inventors speculate that the addition of magnesium oxide may be because magnesium oxide and titanium dioxide of different particle sizes effectively block the light penetration, improving the hiding power of the overall coating and achieving the effect of improving whiteness; in addition, magnesium oxide has a lighter specific gravity than titanium dioxide, and during the film-forming process, magnesium oxide migrates to the surface of the white topcoat, improving the overall whiteness. Therefore, less pigment is needed to achieve the same "hiding" ability and obtain a higher whiteness value.

[0065] Magnesium oxide is a commercially available product in the form of white powder with a particle size D50 of less than 100 nm.

[0066] (d) at least one acylphosphine oxide

[0067] In an embodiment of the present invention, the UV-curable white coating composition comprises an acylphosphine oxide having significant absorption under light radiation in the range of 340-420 nm as a photoinitiator. As a typical cleavage-type photoinitiator, the maximum absorption peak of the acylphosphine oxide is in the range of 340-420 nm, and can effectively absorb ultraviolet light.

[0068] The acylphosphine oxide includes a monoacylphosphine oxide, a bisacylphosphine oxide or a combination thereof. The bisacylphosphine oxide may be a compound of formula (I):

[0069]

[0070] Among them, Ar 1 ,Ar 2 and Ar 3 Each of them is independently a substituted or unsubstituted C6-C18 aryl or C1-C6 alkyl.

[0071] The structure of monoacylphosphine oxide is similar to that of bisacylphosphine oxide, except that only one acyl group is directly attached to phosphorus. As an example, the monoacylphosphine oxide may be a compound of formula (II) (Lucirin TPO-L):

[0072]

[0073] Acylphosphine oxides suitable for use in the present invention include, but are not limited to, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO, commercially available from BASF), ethyl 2,4,6-trimethylbenzoylphenylphosphonate (Lucirin TPO-L, commercially available from BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE 819, commercially available from BASF), or any combination thereof.

[0074] Currently, the most successful commercial acylphosphine oxides are IRGACURE 819 and Lucirin TPO, which can absorb ultraviolet light at 385-410nm.

[0075] The acylphosphine oxide is present in an amount of 1 to 8 wt %, preferably 1 to 5 wt %, more preferably 2 to 5 wt %, based on the total weight of the UV-curable white coating composition.

[0076] In one embodiment of the present invention, the UV-curable white coating composition further comprises an α-hydroxyl photoinitiator, such as an α-hydroxyketone photoinitiator. In the context of the present invention, "α-hydroxyketone" refers to a class of organic compounds containing a hydroxyl group and a ketone group in the same molecule, and the hydroxyl group is at the α-position of the ketone group.

[0077] According to the present invention, the α-hydroxy ketone includes α-hydroxycyclohexyl phenyl ketone (photoinitiator I-184), 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone (photoinitiator D-1173), or any combination thereof.

[0078] The inventors of the present invention surprisingly found that when ultraviolet light is used as the radiation source for radiation curing, the combination of an α-hydroxyl photoinitiator and an acylphosphine oxide can achieve effective surface curing and deep curing.

[0079] The UV-curable white coating composition of the present invention may optionally include additional additives commonly used in coating compositions, which additives do not adversely affect the coating composition or the cured coating obtained therefrom. Suitable additives include, for example, those reagents that can improve the processing properties or manufacturing properties of the composition, enhance the aesthetics of the composition, or improve the specific functional properties or characteristics (such as adhesion to substrate) of the coating composition or the cured composition obtained therefrom. The additives that may be included are, for example, carriers, film-forming aids, cosolvents, fillers, anti-migration aids, antibacterial agents, chain extenders, lubricants, wetting agents, biocides, plasticizers, defoamers, waxes, antioxidants, corrosion inhibitors, flow control agents, thixotropic agents, dispersants, adhesion promoters, UV stabilizers, thickeners, defoamers, pH regulators, or combinations thereof. The content of each optional component is sufficient to achieve the purpose it is intended to achieve, but preferably, such content does not adversely affect the coating composition or the cured coating obtained therefrom. In a preferred embodiment of the present invention, suitable additional additives include thickeners, surfactants, defoamers, bactericides, mildewicides, or any combination thereof.

[0080] The content of the additional additive is in the range of about 0 to about 10 weight %, preferably in the range of about 0.1 to about 5 weight %, and more preferably in the range of about 0.1 to about 1 weight %, relative to the total weight of the UV-curable white coating composition. In one embodiment of the present invention, the UV-curable white coating composition comprises, relative to the total weight of the UV-curable white coating composition, 0.1 to about 10 weight % of the additional additive. Specifically, the amount of the additional additive included in the UV-curable white coating composition is, relative to the total weight of the UV-curable white coating composition, from about 0.2 weight %, about 0.3 weight %, about 0.4 weight %, about 0.6 weight %, about 0.7 weight %, about 0.8 weight % or about 0.9 weight % to about 9.0 weight %, about 7.0 weight %, about 6.0 weight %, about 5.0 weight %, about 4.0 weight %, about 2.0 weight % or about 1.0 weight %.

[0081] In one embodiment of the present invention, the UV-curable white coating composition comprises, relative to the total weight of the UV-curable white coating composition,

[0082] (a) 15 to 30% by weight of at least one (meth)acrylate polymer;

[0083] (b) 10-30% by weight of at least one reactive diluent;

[0084] (c) 40-60 wt % of titanium dioxide and magnesium oxide;

[0085] (d) 1 to 5 weight percent of a mixture of at least one acylphosphine oxide; and

[0086] (e) 0.1-5 wt % of additional additives, wherein the additional additives include dispersants, thickeners, defoamers, bactericides or any combination thereof.

[0087] Suitable dispersants may include anionic dispersants, cationic dispersants, nonionic dispersants, amphoteric dispersants, or any combination thereof. All types of dispersants are commercially available products.

[0088] In a preferred embodiment, the UV-curable white coating composition may contain about 0.1 wt % to about 3 wt %, preferably about 0.2 wt % to about 2 wt % of a dispersant, relative to the total weight of the UV-curable white coating composition. Specifically, the amount of dispersant contained in the UV-curable white coating composition is from about 0.2 wt %, about 0.3 wt %, about 0.4 wt %, about 0.5 wt %, about 0.6 wt % to about 2.5 wt %, about 2.0 wt % or about 1.5 wt %, relative to the total weight of the UV-curable white coating composition.

[0089] Suitable thickeners include cellulose ether thickeners, alkali swellable thickeners, polyurethane thickeners, hydrophobically modified polyurethane thickeners or any combination thereof, preferably hydrophobically modified polyurethane thickeners. All types of thickeners are commercially available commodities. For example, as an example of cellulose ether thickeners, methyl hydroxyethyl cellulose ether thickener HMHEC Plus 330 purchased from Aqualon Company of the United States can be used. As an example of alkali swellable thickeners, TT935 purchased from Rohm & Haas Company of the United States can be used. As an example of hydrophobically modified polyurethane thickeners, RM-8W.

[0090] In a preferred embodiment, the UV-curable white coating composition comprises about 0.1 wt % to about 2 wt %, preferably about 0.4 wt % to about 1.0 wt % of a thickener, relative to the total weight of the UV-curable white coating composition. Specifically, the amount of thickener included in the UV-curable white coating composition is from about 0.2 wt %, about 0.3 wt %, about 0.4 wt %, about 0.5 wt %, about 0.6 wt %, about 0.7 wt %, about 0.8 wt % or about 0.9 wt % to about 2.0 wt %, about 1.5 wt %, about 1.0 wt %, relative to the total weight of the UV-curable white coating composition.

[0091] The leveling agent is an agent that can promote the film-forming resin to form a flat, smooth and uniform coating during the film-forming process. Suitable leveling agents include polysiloxane leveling agents, polyacrylic leveling agents or any combination thereof. As an example of a commercially available leveling agent, BYK420 purchased from BYK Company of Germany can be used.

[0092] Suitable defoamers include organosiloxane defoamers, grease defoamers, polyether defoamers, polyether-modified organosilicon defoamers, or any combination thereof. All types of defoamers are commercially available commodities. As an example of organosiloxane defoamers, BYK8820 purchased from German BYK can be used. As an example of grease defoamers, DF 6007 purchased from Dongguan Defeng can be used.

[0093] In a preferred embodiment, the UV-curable white coating composition comprises about 0.1 wt % to about 1 wt %, preferably about 0.2 wt % to about 0.8 wt % of a defoamer relative to the total weight of the UV-curable white coating composition. Specifically, the amount of defoamer included in the UV-curable white coating composition is from about 0.1 wt %, about 0.2 wt %, 0.3 wt %, about 0.4 wt %, about 0.5 wt % or about 0.6 wt % to about 1.0 wt %, about 0.9 wt % or about 0.8 wt %, relative to the total weight of the UV-curable white coating composition.

[0094] Suitable wetting agents include silicone wetting agents, acetylenic diol wetting agents or combinations thereof. All types of wetting agents are commercially available. As an example of silicone wetting agents, BYK 346 from BYK, Germany, can be used.

[0095] In a preferred embodiment, the UV-curable white coating composition comprises about 0.1 wt % to about 2 wt %, preferably about 0.4 wt % to about 1.0 wt % of a wetting agent, relative to the total weight of the UV-curable white coating composition. Specifically, the amount of the wetting agent included in the UV-curable white coating composition is from about 0.2 wt %, about 0.3 wt %, about 0.4 wt %, about 0.5 wt %, about 0.6 wt %, about 0.7 wt %, about 0.8 wt % or about 0.9 wt % to about 2.0 wt %, about 1.5 wt %, about 1.0 wt %, relative to the total weight of the UV-curable white coating composition.

[0096] The content of each optional component is sufficient to achieve its intended purpose, but preferably, such content does not adversely affect the UV-curable white coating composition or the cured coating obtained therefrom. According to certain embodiments of the present invention, the total amount of additional additives is in the range of about 0 wt % to about 20 wt %, preferably in the range of about 0.1 wt % to about 5 wt %, relative to the total weight of the UV-curable white coating composition.

[0097] The UV-curable white coating composition according to the present invention is curable when irradiated with ultraviolet light.

[0098] In the present invention, the preparation of the UV-curable white coating composition can be carried out by a method commonly used in the art.

[0099] According to the present invention, the UV-curable white coating composition can be applied by conventional coating methods known to those skilled in the art, including dip coating, spin coating, spray coating, curtain coating, brush coating, roller coating, and other coating methods known in the art.

[0100] The UV-curable white coating composition according to the present invention can undergo photopolymerization when applied to a surface of a substrate and irradiated with ultraviolet light, thereby providing a cured coating on the surface of the substrate.

[0101] Due to the above-mentioned specific composition, the curing efficiency of the UV-curable white coating composition according to the present invention is high. After curing, the UV-curable white coating composition according to the present invention can provide good surface curing properties. Compared with conventional UV-curable white coating composition, the UV-curable white coating composition according to the present invention after curing, obtains comparable, even more excellent whiteness and yellowing resistance coating.

[0102] In an embodiment of the present invention, the L value of the coating formed by curing the UV-curable white coating composition on BYK white coating test card is at least 97, preferably at least 97.3, more preferably at least 97.5, even more preferably at least 97.7, and most preferably at least 98.

[0103] The coating formed by curing the UV-curable white coating composition according to the present invention on BYK white coating test card paper has a color difference value of ΔE<2.0 and Δb<1.5 with the BYK white coating test card paper. The color difference value test is described in detail in the example part.

[0104] Therefore, the UV-curable white coating composition according to the present invention can be used as a topcoat or a primer, preferably as a topcoat.

[0105] Therefore, the present invention also provides an article, which comprises a substrate partially or completely coated with the UV-curable white coating composition according to the present invention. A person skilled in the art will select and determine a suitable material as the substrate according to actual needs.

[0106] The substrate may be a non-heat-sensitive substrate, such as glass, ceramic, fiber, cement board or metal (such as aluminum, copper or steel), or a heat-sensitive substrate.

[0107] Suitable heat-sensitive substrates include wood substrates, for example solid wood, such as: hardwood, softwood, plywood; veneer, particle board, low-density fiberboard, medium-density fiberboard and high-density fiberboard, OSB (oriented structural board), wood laminate, chipboard and other substrates in which wood is an important component, such as metal foil-coated wooden substrates, composite wood flooring, plastic-modified wood, plastic substrates or wood-plastic composites (WPC); substrates with cellulose fibers, such as cardboard or paper substrates.

[0108] As the wooden substrate for making wooden products, any suitable wooden substrate known in the art can be used. In the present application, term "wooden substrate" refers to any cellulose / lignin material derived from the hard, fibrous structural organization in the stem and root of trees or other woody plants. Timber includes, for example, hardwood and softwood timber directly cut from trees, and engineered wood composites made of wood strips, wood chips, wood fiber or wood veneer. The example of wood composite includes but is not limited to plywood, oriented strand board (OSB), medium density fiberboard (MDF), particle board etc.

[0109] As exemplary wood substrates, one or more of quercetin, chestnut, oak, red chestnut, tea, eucalyptus, Douglas fir, Japanese cedar, American cypress, Japanese red pine, Japanese cypress, water walnut, black walnut, maple, Japanese beech, Japanese paulownia, birch, sal, magnolia, ash, teak, oak, catalpa, camphor, fir, oak, and rubber wood can be used.

[0110] According to certain embodiments of the present invention, the wood substrate has at least one, preferably two, major surfaces that are opposite to each other.

[0111] According to certain embodiments of the present invention, the articles thus obtained can be used in the following applications, including, but not limited to: household furniture, such as tables, chairs, cabinets, etc.; bedroom and bathroom furniture; office furniture; custom furniture, such as school and children's furniture, hospital furniture, restaurant and hotel furniture, kitchen cabinets and furniture; panels for interior design; indoor and outdoor windows and doors; indoor and outdoor window frames and door frames; outdoor and indoor wainscoting and wood flooring.

[0112] The inventors surprisingly found that adding magnesium oxide to a conventional UV-curable white coating composition can significantly improve the whiteness of the cured coating, even better than a white coating composition using only titanium dioxide.

[0113] Therefore, the present invention also relates to the use of magnesium oxide in improving the whiteness of a coating formed from the UV-curable white coating composition according to the present invention, wherein the L value of the coating formed by curing the UV-curable white coating composition on a BYK white coating test card is at least 97.3, preferably at least 97.5, more preferably at least 97.7, and most preferably at least 98.

[0114] The following examples more specifically describe the disclosure of the present invention, which are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available and can be used directly without further treatment.

[0115] Example

[0116] Test Method

[0117] Adhesion

[0118] Adhesion testing is performed to evaluate the adhesion of the coating to the coated substrate. The adhesion test is performed according to ASTM D 3359 - Test Method B. Adhesion is generally rated on a scale of 0-5B, with 5B indicating optimal adhesion.

[0119] Whiteness (L value)

[0120] Use the American RDS No. 7 wire rod coater to scrape UV-curing white paint on BYK white paper card, with a coating amount of 15-20g / m 2 , cured with UV lamp (gallium lamp), curing energy 700-1000mJ / cm 2. , and then use X-rite colorimeter (model CI-64) to test the whiteness value.

[0121] Characterization of yellowing resistance

[0122] On BYK white film test card, apply UV-curable white coating composition with a coating amount of 15-20 g / m 2 ; Cured under UV light (gallium lamp), curing energy is 700-100mJ / cm 2After curing, use a colorimeter to test and calculate (the formula is as follows) the color difference between the coated area and the original white cardboard.

[0123] △E=[(△L*) 2 +(△a*) 2 +(△b*) 2 ] 1 / 2

[0124] Where ΔL = L sample - L standard (brightness difference); Δa = a sample - a standard (red / green difference); Δb = b sample - b standard (yellow / blue difference).

[0125] △E represents the magnitude of total color difference;

[0126] A large △L indicates whiteness, and a small △L indicates blackness.

[0127] A large △a indicates a reddish color, and a small △a indicates a greenish color.

[0128] A larger △b indicates a yellowish color, and a smaller △L indicates a bluish color.

[0129] Characterization of solvent resistance

[0130] Resistance to solvents (such as methyl ethyl ketone or alcohol) is performed to evaluate the "cure" or crosslinking of the coating. This test is performed as described in ASTM D 5402 93. The integrity of the coating is determined after a certain number of double-sided rubs (i.e., a back and forth motion) (usually 50 times). Solvent resistance is usually rated on a scale of 0-5, where 5 = coating is intact with no scratches (best), 4 = coating scratches are barely noticeable, 3 = coating scratches can be clearly identified, 2-1 = coating gloss is lost due to scratches, and 0 = coating peels off to the substrate (worst).

[0131] Material

[0132] The materials used are listed in Table 1 below.

[0133] Table 1: Materials used and related information

[0134] Product Name describe HDDA Hexanediol diacrylate TPO 2,4,6-Trimethylbenzoyldiphenylphosphine oxide TPO-L Ethyl 2,4,6-trimethylbenzoylphenylphosphonate 819 Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide 1173 2-Hydroxy-2-methyl-1-phenyl-1-propanone ZL-914 Polyester acrylic resin TPGDA Tripropylene glycol diacrylate BYK-55 Dispersants Tego 920 Defoaming agent

[0135] The components were mixed according to the amounts shown in Table 2 to obtain a UV-curable white coating composition.

[0136] The coating composition thus formed was applied as a topcoat on a log-colored cherry veneer MDF board (the board was pre-rolled with a UV-specific white primer and polished with 400-mesh sandpaper) to form a 15-micron coating. The coating thus formed was then UV-cured. The ultraviolet lamp (gallium lamp) used was purchased from Shenzhen Renwei Optoelectronics Co., Ltd., which emitted light with a wavelength of 280-380 nm and a power of 4500-5000 mW / cm 2 .

[0137] The properties of the cured coatings were measured according to the methods listed in the Test Methods and the results are shown in Table 2.

[0138] Table 2

[0139]

[0140] It can be seen from the above results that the UV-curable white coating composition according to the present invention has a high whiteness and excellent yellowing resistance. The present invention innovatively adds magnesium oxide to the UV-curable white coating composition, and combines it with titanium dioxide commonly used in coating compositions, significantly improving the whiteness of the cured coating at the same pigment content, obtaining a whiteness (L value) of 97.3 or even above 97.5, which has never been recognized before the present invention.

[0141] Although the invention has been described with reference to a number of embodiments and examples, a person skilled in the art, based on the present disclosure, will recognize that other embodiments can be designed without departing from the scope and spirit of the invention.

Claims

1. A UV-curable white coating composition comprising: (a) 15-30 wt. % of at least one (meth)acrylate polymer; (b) 10-30% by weight of at least one reactive diluent; (c) 40-65 wt % titanium dioxide and magnesium oxide; (d) 1 to 5 wt. % of at least one acylphosphine oxide; and (e) 0.1-5 wt % of additional additives, wherein the additional additives include dispersants, thickeners, defoamers, bactericides or any combination thereof; in, The content of magnesium oxide is at least 10 wt % relative to the total weight of the UV-curable white coating composition; Wherein, the content of titanium dioxide is 20 wt % to 45 wt % relative to the total weight of the UV-curable white coating composition.

2. The UV-curable white coating composition according to claim 1, wherein The content of magnesium oxide is up to 50 wt % relative to the total weight of the UV-curable white coating composition.

3. A UV-curable white coating composition according to any one of claims 1 to 2, wherein The (meth)acrylate polymer is selected from at least one of epoxy (meth)acrylate, polyurethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and acrylate copolymer.

4. A UV-curable white coating composition according to any one of claims 1 to 2, wherein The reactive diluent is selected from at least one of dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, hexanediol di(meth)acrylate, (ethoxylated) trimethylolpropane tri(meth)acrylate, (propoxylated) trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and isobornyl(meth)acrylate.

5. A UV-curable white coating composition according to any one of claims 1 to 2, wherein The acylphosphine oxide includes monoacylphosphine oxide, bisacylphosphine oxide or a combination thereof.

6. A UV-curable white coating composition according to any one of claims 1 to 2, wherein The acylphosphine oxide includes 2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, or any combination thereof.

7. The UV-curable white coating composition according to any one of claims 1 to 2, further comprising at least one α-hydroxy type photoinitiator.

8. The UV-curable white coating composition according to any one of claims 1 to 2, which is used as a topcoat or a primer.

9. A UV-curable white coating composition according to any one of claims 1 to 2, wherein The coating formed by curing the UV-curable white coating composition on BYK white coating test card paper has an L value of at least 97.

10. An article comprising a substrate partially or fully coated with the UV-curable white coating composition according to any one of claims 1 to 9.

11. The article of claim 10, wherein: The substrate is wood.

12. Use of magnesium oxide for improving the whiteness of a coating formed from the UV-curable white coating composition according to any one of claims 1 to 9.

13. The use according to claim 12, wherein The L value of the coating formed by curing the UV-curable white coating composition on BYK white coating test card is at least 97.

3.

14. The use according to claim 12, wherein The L value of the coating formed by curing the UV-curable white coating composition on BYK white coating test card paper is at least 97.5.

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