HK1116127B - Method for reducing face checking of a wood product - Google Patents

Description

Method for reducing surface cracking of wood products

The present invention relates to a method for reducing surface cracking of wood products by applying to at least a portion of the wood product a composition comprising a (meth) acrylate moiety and a pigment, wherein the cured coating has a Tg of less than 55 ℃.

Background information

Wood products are needed and used in many industries, such as furniture, flooring, mills, and cabinets. Wood products, such as those made from wood, veneer, and wood composites, typically contain more than one bottom layer and may include, for example, multiple plies. In the case of veneers, a thin sheet of wood is applied over a wood or wood composite product such as plywood or medium density fiberboard ("mdf"). Thus, it is often desirable to use veneer and other wood composites because it can give the appearance of solid wood without cost. However, thin layers of wood often crack or "crack," especially when exposed to cycles of heat and cold. Cracking of the sheet also occurs due to moisture, etc.; similarly, solid wood can crack upon exposure to environmental conditions. There is a need for methods of reducing, if not eliminating, cracking (i.e., "surface cracking") on the surface of wood products.

Summary of The Invention

The present invention relates to a method of reducing surface cracking of wood products comprising applying to at least a portion of the wood product a composition comprising a (meth) acrylate moiety and a pigment, wherein the coating, when cured, has a Tg of less than 55 ℃. Wood products treated according to the present method are also within the scope of the present invention.

Detailed Description

The present invention relates to a method of reducing surface cracks in wood products comprising applying to at least a portion of the wood product a composition comprising a (meth) acrylate moiety and a pigment, wherein the coating, when cured, has a glass transition temperature ("Tg") of less than 55 ℃. In certain embodiments, the Tg can be 35 ℃ or less. The term "wood product" as used herein refers to any product comprising wood and may include solid wood, hardwood, or products having at least two plies, the outermost ply being wood. Examples of such products include veneers, composites, and plywood. "surface cracking" means cracking or splitting that occurs at the surface of a wood product, and may or may not extend to different depths below the surface of the wood product and/or may not extend above the surface with or without splitting.

The compositions used in the present methods comprise (meth) acrylate moieties. The term "(meth) acrylate moiety" herein refers to any compound having at least one (meth) acrylate functional group. "(meth) acrylate" refers to both (meth) acrylate and acrylate. Any (meth) acrylate moiety can be used so long as it imparts the desired flexibility to the coating composition. Examples include carbamates of (meth) acrylates such as those commercially available from Bayer, such as the ROSKYDAL product series by Bayer (ROSKYDAL LS2298), Sartomer Company Inc. (CN966J75, or CN981), or UCB Chemicals, Inc. (EBECRYL230, EBECRYL8402, or EBECRYL 8804). The urethane (meth) acrylate may be aromatic or aliphatic. Other suitable (meth) acrylate moieties include (meth) acrylated epoxy resins, (meth) acrylated polyesters, (meth) acrylated amines, methacrylated acrylic resins, and/or mixtures of the foregoing. Combinations of individual (meth) acrylate moieties may also be used. In certain embodiments, at least one (meth) acrylate moiety has a functionality greater than two and in certain embodiments at least two (meth) acrylate moieties are used, at least one of which has a functionality greater than two (meth) acrylates.

The coating composition further comprises a pigment (sometimes also referred to as "filler" in the formulation). Suitable pigments/fillers include, for example, silica, inorganic oxides, calcium carbonate, amino silicates, zinc oxide, titanium dioxide, and the like. The pigment may or may not impart opacity, depending on the needs of the user. In certain embodiments, a relatively high weight percentage of pigment is used; that is, the pigment is between 20 and 60 weight percent, with weight percent based on the total weight of solids in the composition. Surprisingly, the coating compositions of these embodiments retain the flexibility needed to reduce, if not eliminate, surface cracking of the wood product; generally, high-charge systems (i.e., systems having weight percentages within this range) are relatively inflexible. "reducing" and similar terms as used with respect to cracking refer to reducing the size of the cracks and/or reducing the number of cracks.

The use of pigments/fillers in the present compositions allows the desired viscosity to be obtained. The viscosity of the coating may be such that it can be pushed or "packed" into the grains and/or pores of the wood. The viscosity of the coating can be, for example, 10,000-75,000 centipoise ("cPs"), such as 10,000-50,000cPs, 20,000-50,000cPs, 20, 00-40,000cPs, or about 30,000+/-5,000cPs, as measured with a Brookfield viscometer, such as a model RVT viscometer, using spindle 7 at 50RPM and 25 ℃. It will be appreciated that the viscosity of the coatings used in these embodiments is not as thick as, for example, putty, but is thicker than formulations that do not use pigments/fillers.

The coating of the present invention may further comprise one or more diluents. Suitable diluents include, for example, glycerol propoxylate triacrylate, propoxylated neopentyl diacrylate, 1, 6-hexanediol diacrylate, isodecyl (meth) acrylate, isobornyl (meth) acrylate, dodecyl (meth) acrylate, 2-phenoxyethyl acrylate, ethylene glycol di (meth) acrylate, 1, 3-butanediol di (meth) acrylate, 1, 4-butanediol diacrylate, 2, 3-dimethylpropyl 1, 3-diacrylate, 1, 6-hexanediol di (meth) acrylate, dipropylene glycol di (meth) acrylate, ethoxylated hexanediol dimethacrylate, propoxylated hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, alkoxylated neopentyl glycol di (meth) acrylate, and mixtures thereof, Hexanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, thiodiethylene glycol diacrylate, 1, 3-propanediol dimethacrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropyl tetra (meth) acrylate, glycerol propoxylate tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, and tetraethylene glycol di (meth) acrylate, including mixtures thereof. These diluents may be added, for example, to reduce or adjust the viscosity of the coating. In one embodiment, the coating comprises a (meth) acrylate moiety having a functionality of a (meth) acrylate greater than two, and a diluent having a functionality of a (meth) acrylate less than two.

The coatings used in accordance with the present invention may further comprise a variety of other art-standard additives. Examples include initiators, defoamers, wetting agents, inhibitors, thermoplastic resins, colorants, dyes, surfactants, and the like. When the coating is cured by means of actinic radiation, for example UV light, suitable photoinitiators include, for example, benzyl, benzoin methyl ether, benzoin isobutyl ether benzophenon, acetophenone, benzophenone, 4 ' -dichlorobenzophenone, 4 ' -bis (N, N ' -dimethylamino) benzophenone, diethoxyacetophenone, fluorones, initiators of the H-Nu series, such as those from the Spectra Group Ltd, 2-hydroxy-2-methyl-1-phen-1-one, 1-hydroxycyclohexylphenyl ketone, 2-isopropylthioxanthone (2-isopropylthioxanthone), alpha-aminoalkylphenones, such as 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1-butanone, methyl ethyl ketone, methyl ketone, Acylphosphine oxides such as 2, 6-dimethylbenzoyldiphenylphosphine oxide, 2, 4, 6-trimethylbenzoyldiphenylphosphine oxide, bis (2, 4, 6-trimethylbenzoyl) phenylphosphine oxide, 2, 6-dichlorobenzoyl-diphenylphosphine oxide, and 2, 6-dimethoxybenzoyldiphenylphosphine oxide, bisacylphosphine oxides such as bis (2, 6-dimethoxybenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, bis (2, 6-dimethylbenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, bis (2, 4, 6-trimethylbenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, and bis (2, 6-dichlorobenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, and mixtures thereof. The coating may be cured by any crosslinking mechanism, such as thermal crosslinking. Suitable thermal initiators include peroxides and amines. When used, these other additives are generally present in the composition in an amount up to 30 weight percent, the weight percent being based on the total weight of solids in the formulation. The composition may be water-based, solvent-based, or 100% solids.

The coating composition may be prepared by any method known in the art. For example, the liquid component can be added to the tank with stirring; the powder is then added, followed by any other desired additives. Stirring may continue until the mixture is substantially homogeneous, and, in certain embodiments, until the mixture has a Hegman grind fineness of 2 to 7.

For coating products having a desired viscosity, e.g., pumped, poured, etc., they may be applied to the wood product by any method standard in the art. A roll paint filling machine is a particularly suitable application method.

The coating is typically applied in an amount of 0.5 to 5mils, e.g., 1 to 2mils, wet film thickness.

In certain embodiments, the wood product may be colored prior to treatment according to the methods of the present invention. For example, the colorant may be applied first and cured or dried. The coatings described herein may then be applied to these stained wood products, typically to fill the pores and impart a smooth, fully filled appearance to the final product; the present coatings may then be cured, sanded and/or other coatings, such as decorative and/or protective coatings, applied to the wood product. Typically, the protective layer comprises a wear resistant layer, a sandable sealing layer and/or a top layer. The present coatings may also be applied to uncolored and/or otherwise treated wood products, and/or may be used with other coatings, layers, and/or treatments.

The invention further relates to wood products treated according to the method. In certain embodiments, wood products treated in accordance with the present invention can withstand 10 cycles of cold and heat, e.g., up to 20 cycles, with little or no surface cracking. In certain embodiments, wood products treated according to the present method having a treated "face" of 40+/-5 square inches may have 5 or fewer cracks of 2 inches or less after 10 cycles of cold and heat. One "cold-heat cycle" refers to exposing the wood product to 120 ° f for 1 hour, to-5 ° f for 1 hour, and to room temperature for 15 minutes.

The coatings used in the present invention are sufficiently flexible to expand and contract with wood upon exposure to various environmental conditions, such as moisture, heat, cold, and the like. As noted above, the cured coating has a Tg of less than 55 deg.C, for example 35 deg.C or less, where the Tg is determined by dynamic mechanical analysis ("DMA") of the free film according to methods standard in the art.

Certain embodiments of the present invention specifically exclude the use of compositions comprising both hydrophilic polymers and reactive monomers. Other embodiments specifically exclude the use of urethane acrylate oligomers and/or reactive polyesters with urea groups. It will be understood that the composition used in accordance with the present invention is not the term "stain" as used in the art, which is used in low viscosity form and is commonly used to color wood products.

Unless otherwise specifically indicated, all numbers such as those expressing values, ranges, amounts or percentages used herein may be read as if prefaced by the word "about", even if the term does not expressly appear. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. Plural encompasses singular and vice versa. For example, while the invention is described in terms of "a" (meth) acrylate and "a" pigment, more than one (meth) acrylate and/or more than one pigment may also be used. Also, as used herein, the term "polymer" is meant to refer to prepolymers, oligomers and homopolymers as well as copolymers; the prefix "poly" refers to two or more.

Examples

The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Example 1

The "flexible" fillers according to the invention were tested against the other two commercially available fillers. All wood products tested were Southern Red Oak sheets with stain, filler, high abrasion sealer, sandable sealer and topcoat applied thereto. On one of the wood products with flexible filler according to the invention and the other wood products with commercially available "non-flexible" filler, a coating commercially available from PPG Industries, inc; all coatings were identical for both test wood products except for the filler. The third wood product was coated with the product supplied by Chemcraft. Each system was tested using 2 plates, each approximately 40+/-5in². The results were obtained by visual observation and reported as the average of two panels. Ten cycles of cooling and heating were performed, and the results were as follows。

TABLE 1

Filler material	Results	Note
			R1596Z-8	2 cracks, length up to 1 inch	R1596Z-8 is commercially available from PPG Industries, Inc., and comprises urethane acrylate and about 36 wt% filler
R1340Z-8	20 cracks and length varied from 1 to 3 inches	R1340Z-8 is commercially available from PPG Industries, Inc., and comprises an acrylic epoxy resin, a reactive polyester, and about 25 wt% filler. The product is sold as a filling and is not considered to be a "pliable" filling.
			Chemcraft	35 cracks and the length varies from 0.5 to 3 inches	Commercially available from Chemcraft filer.

Example 2

The Southern Red Oak sheets were subjected to the above test, and the results are shown below.

TABLE 2

Filler material	Results
		R1596Z-8	2 cracks are all raised without splitting
R1340Z-8	At most 10 cracks, most bulges and 3 splits open

Example 3

The Southern Red Oak sheets were subjected to the above test using two fillers within the scope of the present invention, and the results are as follows.

TABLE 3

Filler material	Results	Note
			R1596Z-8	Less than 1 inch of cracking at 8, 1 inch of cracking at 2
R1623Z-8	Up to 5 cracks of between 0.5 and 2 inches	R1623Z-8 is commercially available from PPG Industries and comprises an acrylated polyester and an acrylated amine and an acrylic epoxy resin, and about 50 wt% filler.

Example 4

Three fillers as shown in table 4 were used to test the Tg of the free film, measured using the DMA method under the following parameters of a TAInstruments 2980 unit.

The method comprises the following steps: free film

Amplitude: 20 micron

Frequency: 1Hz

Heating rate: 3 ℃ per minute

Sample size: about 15X 6.5X 0.050 mm

TABLE 4

Sample (I)	Tg(℃)
		R1340Z-8	55
R1623Z-8	35
		R1596Z-8	33

Although detailed embodiments of the present invention have been described above for illustrative purposes, it will be apparent to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims (14)

1. A method of reducing surface cracking of a wood product comprising:

(a) filling the grains and/or pores of the wood with a composition comprising a (meth) acrylate moiety and a pigment, the composition having a viscosity of 10,000-,

(b) curing the composition to provide a cured composition having a Tg of less than 55 ℃,

wherein the wood product comprises at least two plies, the at least two plies comprising an outermost ply comprising wood.

2. The method of claim 1, wherein the (meth) acrylate moiety comprises a urethane acrylate.

3. The method of claim 2, wherein the urethane acrylate is aliphatic.

4. The method of claim 2, wherein the urethane acrylate is aromatic.

5. The method of claim 1, wherein the composition comprises at least two (meth) acrylate moieties, at least one of which has a (meth) acrylate functionality greater than two.

6. The method of claim 1, wherein the composition comprises a (meth) acrylated epoxy resin, a (meth) acrylated polyester, and a (meth) acrylated amine.

7. The method of claim 1, wherein the weight percent of pigment in the composition is from 20 to 60 weight percent, the weight percent based on the total weight of solids in the composition.

8. The method of claim 1 wherein the composition has a viscosity of 10,000-50,000 cPs.

9. The method of claim 1 wherein the composition has a viscosity of 20,000-40,000 cPs.

10. The method of claim 1, wherein the composition has a viscosity of 30,000+/-5,000 cPs.

11. The method according to claim 1, wherein the wood product has been stained prior to application of the composition comprising the (meth) acrylate moiety and the pigment.

12. The method of claim 1, wherein the Tg of the cured composition is 35 ℃ or less.

13. The method of claim 1, wherein the (meth) acrylate moiety has a (meth) acrylate functionality greater than two.

14. The method of claim 13, wherein the composition further comprises a diluent having a (meth) acrylate functionality of less than two.