Coating composition and floor covering including the composition

Abstract: Floor coverings include a wear layer made from a coat composition including a multifunctional polyurethane (meth)acrylate oligomer. The multifunctional polyurethane is made by reacting a polyisocyanate with a functionality equal or higher than 3, a polyester polyol, and a hydroxyalkyl-(meth)acrylate with a molecular weight of about 116 to about 600. The coating composition preferably includes a reactive (meth)acrylate diluent and a photoinitiator.

Description: The present invention relates to a coating composition including a multifunctional polyurethane (meth)acrylate oligomer and floor coverings made with the coating composition, and more particularly, to radiation-curable coatings which have superior gloss retention, abrasion, gouge and stain resistance surfaces. Coatings as wear layers on floor coverings are designed to provide durability and cleanability to the flooring materials. Durability in this case refers to the ability of the coatings to resist wear and tear. The wear and tear come in two forms: (a) abrasion in micro scales at the very top of the surface that results in changes of gloss and appearance, and (b) deep scratch and gouge damages from soils or other grit particles dragged under foot traffic. Cleanability refers to the ability of the coatings to resist stain and chemical attacks, and maintain their original appearance. The prior art polyurethane-based wear layer compositions provide either gloss retention, stain resistance or gouge, but none of them have all three properties. Consequently, the need exists for performance coatings which have the aforementioned gloss retention, stain, abrasion and gouge resistance for floor coverings. The present invention provides a coating composition comprising the reaction product of a polyisocyanate having 3 to 6 isocyanate functionalities per molecule, an aromatic polyester polyol and a hydroxyalkyl(meth)acrylate with an average molecular weight of about 344 to about 472 and a (meth)acrylate reactive diluent having a molecular weight of at least 200 and less than 2000. The present invention also provides a coating composition comprising a multifunctional polyurethane (meth)acrylate and a (meth)acrylate reactive diluent having a molecular weight of 200 to 2000, the multifunctional polyurethane (meth)acrylate having the following structure: where m = 0, 1 or 2 n = 1 x = Y = R = R' = p = 1, 2 or 3 R" = H or CH 3 R''' = The present invention further provides a floor covering comprising a base layer and wear layer adhered to the base layer, the wear layer comprising a cured coating composition, the coating composition comprising a (meth)acrylate reactive diluent having a molecular weight of about 200 to about 2000 and the reaction product of a polyisocyanate with a functionality of 3 to 6 isocyanate functionalities per molecule, an aromatic polyester polyol, and a hydroxyalkyl(meth)acrylate with a molecular weight of 344 to 472. The oligomer which comprises the coating composition of the present invention is the reaction product of a polyisocyanate with a functionality equal or higher than 3, preferably equal to or higher than 3.5, an aromatic polyester, preferably a phthalate polyester polyol, and a hydroxyalkyl(meth)acrylate with a molecular weight of 344 to 472. The resulting oligomer will be liquid at room temperature, highly branched, and have multi(meth)acrylate functionality. As used herein, term "(meth)acrylate" and its variants mean "acrylate, methacrylate and mixtures thereof." The coating composition may consist essentially of the oligomer. However, the oligomer without a diluent is viscous and difficult to coat. Therefore the coating composition of the present invention preferably includes a diluent. The preferred diluent is a reactive (meth)acrylate diluent. The coating composition may be cured either by electron beam curing or UV curing. The preferred composition includes a photoinitiator and the composition is cured with both electron beam and UV light. It is well known that abrasion resistance and non-yellowing coatings can be obtained from radiation-curable polyurethane (meth)acrylate based on aliphatic diisocyanates such as isophorone diisocyanate (IPDI) or methylene-bis(4-cyclohexylisocyanate) (Bayer Corporation's Desmodur W). However, higher functionality polyisocyanates such as isocyanurate, biuret and allophanate have not been used in the radiation-cured coatings, nor are such uses disclosed in the prior art. Because of their high reactivity, two-component coating systems must be mixed just prior to the application. After the two-components are put together, there is a limited pot-life in which the mixture must be used up before it is rendered useless. It was discovered that reacting isocyanurate trimers such as Bayer's Desmodur N3300 or biurets such as Bayer's Desmodur N100 or N3200 with a long chain hydroxyalkyl(meth)acrylate and an aromatic polyester polyol could produce one-component radiation-curable oligomers which have a long shelf-life. The oligomers would produce radiation-curable coatings of superior stain, gloss retention, abrasion and gouge resistance. Preferred oligomers were prepared by reacting about 0.7 to 1.5 equivalents of Desmodur N-3300 with 1.0 equivalent of a mixture of hydroxyalkyl(meth)acrylate and phthalate polyester polyols (equivalent ratio of hydroxyalkyl(meth)acrylate to polyester polyol greater than about 0.10) to produce a highly branched, multifunctional (meth)acrylate polyurethane product. The product was mixed with acrylate reactive diluents and photoinitiators to form a coating composition. Especially valuable properties were obtained when substantial quantities of high molecular weight, ethoxylated and propoxylated tri(meth)acrylates were the principle reactive diluents. An aromatic polyester polyol is defined as a polyester polyol of acid number of less than about 15, preferably less than 5, comprising the reaction product of an equivalent excess of one or more polyols of equivalent weight less than 150 with at least one aromatic polycarboxylic acid. If the polycarboxylic acid is a phthalic acid derivative the result is a phthalate polyester polyol. Preferably at least 50 equivalent percent of the polycarboxylic acid is isophthalic acid, phthalic acid, terephthalic acid, phthalic anhydride, or dimethyl terephthalate. The preferred multifunctional polyurethane (meth)acrylate of the present invention can be represented by the following Formula 1. where m = 0, 1 or 2 n = 1 x = Y = R = R' = p = 1, 2 or 3 R" = H or CH 3 R''' = The isocyanurates, biurets and allophanates of the present invention can be aliphatic, cycloaliphatic or aromatic such as those prepared from 1,6 hexamethylene diisocyanate (Desmodur H); methylene-bis(4-cyclohexylisocyanate); 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane; 2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylene diisocyanate; toluene diisocyanate; methylenediphenyl diisocyanate; and tetra methylxylene diisocyanate. The preferred polyisocyanates are the trimer isocyanates represented by R in Formula 1 (isocyanurate, biuret and allophanate). The most preferred trimers are those derived from 1,6-hexamethylene diisocyanate which is commercially available as Desmodur N from Bayer Corporation. Suitable hydroxyalkyl(meth)acrylates are the polycaprolactone based hydroxy(meth)acrylate according to the skeletal structures in Formula 2: where R" = H or CH 3 , and p = 2 or 3. The polycaprolactone based hydroxy(meth)acrylates are supplied commercially by Union Carbide as Tone M-100 (molecular weight of about 344) and by San Esters Corporation as Placcel FA and FM series (molecular weights from about 230 to about 472). The preferred oligomer is prepared from Desmodur N-3300, Tone M-100 and a predominantly 1,6-hexylene phthalate polyester polyol. A predominantly 1,6-hexylene phthalate polyester polyol is defined as a phthalate polyester polyol wherein at least 50 equivalent percent of the <150 equivalent weight (eq. wt.) polyol is 1,6-hexanediol and wherein at least 50 equivalent percent of the polycarboxylic acid is phthalic acid or phthalic anhydride. Phthalate polyester polyols suitable for the present invention can be prepared by a procedure similar to example 1 of US Pat. No. 4,138,299 by reacting acids such as isophthalic, terephthalic, phthalic (or phthalic anhydride), adipic, azelaic, and/or sebacic with polyols such as 1,6-hexanediol; trimethylol propane; triethylene glycol; neopentyl glycol; cyclohexane dimethanol; 2-methyl-1,3-propanediol; trihydroxyethylisocyanurate; and glycerol in the presence of a catalyst such as dibutyltin bislauryl mercaptide or stannous oxalate. Suitable (meth)acrylate reactive diluents include, isodecyl (meth)acrylate, isobornyl (meth)acrylate, tetraethylene glycol (meth)acrylate, tripropylene glycol (meth)acrylate, hexanediol di(meth)acrylate, ethoxylate bisphenol-A di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, ethoxylated tripropylene glycol di(meth)acrylate, glyceryl propoxylated tri(meth)acrylate, tris (2-hydroxy ethyl) isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dimethylol propane tri(meth)acrylate dipentaerythritol monohydroxypenta(meth)acrylate, and trimethylol propane tri(meth)acrylate and its ethoxylated and propoxylated analogues of the skeletal structures in Formula 3: or where R" = H, or CH 3 , and q = 0, 1, 2,..., 9 or 10. The preferred (meth)acrylate reactive diluents are the multifunctional acrylates with molecular weights of 200 to 2000. Examples of such are tetraethylene glycol diacrylate with a molecular weight of about 302, ethoxylated bisphenol-A diacrylate with a molecular weight of about 776 (SR602 from Sartomer Company), trihydroxyethyl isocyanurate triacrylate with molecular weight of about 423 (SR368 from Sartomer), trimethylol propane triacrylate with a molecular weight of about 296 (SR351 from Sartomer), and ethoxylated trimethylol propane triacrylates with molecular weights from 400 to 2000 (SR454, SR499, SR502, SR9035, and SR 415 from Sartomer Company and Photomer 4155 and Photomer 4158 from Henkel Corporation). To practice the present invention, it is preferred to employ photoinitiators by themselves or in combinations and/or in combination with photoactivators and photosensitizers. Suitable photoinitiators include benzophenone; 4-methylbenzophenone; benzyl dimethyl ketal; diethoxy acetophenone; benzoin ethers; thioxanthones; 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 from Ciba Corp); 2-hydroxy-2-methyl-1-phenol-propane-1-one; 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-methylpropyl) ketone; 2,4,6-trimethylbenzoyl diphenylphosphine oxide; bis (2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide; 2,2-dimethoxy-2-phenyl acetophenone; 2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone; and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one. A preferred photoinitiator is benzophenone, which may be used in conjunction with other photoinitiators, photoactivators and/or photosensitizers. A preferred combination is about two parts benzophenone per one part of 1-hydroxycyclohexyl phenyl ketone. In addition, other components which may be useful can also be included in the present invention. These include flow additives, free radical inhibitors, thermal stabilizers, light stabilizers, dyes, pigments, optical brighteners, flatting agents, plasticizers, and others as would be obvious to one skilled in the art. In preparing the oligomer of the present invention, a catalyst such as dibutyltin dilaurate may or may not be included to aid the urethane formation between the polyisocyanate and the hydroxy-containing components. However, it is advantageous to prepare the oligomer in a clean vessel free of moisture or water. The vessel is equipped with dry-air blanket and a heating jacket, and has continuous mixing. It is further advantageous to prepare the oligomer in the presence of substantial amounts of the reactive acrylate diluents to help control heat of reactions which may otherwise cause undesired side reactions. The reaction temperature is maintained at about 75°C to about 85°C. Higher temperatures can initiate undesired free radical polymerization. On the other hand, lower temperatures will retard or slow down the NCO/OH reaction. The compositions of the present invention can be applied by brushing, roller, gravure, spin, flow, or curtain coating at room temperature to an elevated temperature of up to about 75°C. The composition of the present invention has an excellent high temperature stability. Prolonged exposure to elevated temperature does not have any adverse effect on its superior properties. The radiation cure is achieved with ultraviolet or electron beam radiation. Although no photoinitiator is required when the composition is cured by electron beam, including a photoinitiator can further enhance the properties of the present invention. The present invention can be readily understood from the examples that follow. However, the following examples are provided to illustrate but not to limit the scope of the present invention. Polyols Used in the Following Illustrative Examples Polyol 1 hydroxyl number = 185, acid number < 0.5 prepared from: 20.0 equivalents of phthalate anhydride 23.8 equivalents of 1,6-hexanediol 6.0 equivalents of glycerine Polyol 2 hydroxyl number = 115, acid number < 0.6 prepared from: 20.0 equivalents of phthalate anhydride 25.75 equivalents of 1,6- hexanediol Polyol 3 hydroxyl number = 315, acid number < 0.6 prepared from: 20.0 equivalents of adipic acid 16.0 equivalents of trimethyl propane 20.0 equivalents of neopentyl glycol Example 1 1. SR351 reactive diluent 16 parts 2. SR499 reactive diluent 10 parts 3. SR502 reactive diluent 10 parts 4. Tone M-100, hydroxyacrylate from Union Carbide 32.58 parts 5. Polyol 1, hydroxyl equivalent weight (eq. wt.) of 303 8.87 parts 6. Desmodur N3300, Bayer's isocyanurate trimer eq. wt. of 195 22.55 parts The above ingredients were mixed in a clean and dry vessel, heated, with stirring and under a trickle of dry air blanket, to 80°C for four hours to react the NCO groups of ingredient 6 to the OH groups of ingredients 4 and 5. Upon cooling to 50°C the following ingredients were added to the vessel with stirring: 7. Irgacure 184 (from Ciba) 1.0 parts 8. Benzophenone 2.0 parts 9. Silwet L7604 0.2 parts This composition had 64% oligomer and 36% reactive diluents, a NCO/OH of 0.933 and a hydroxyacrylate/polyol of 3.24. Viscosity at 25°C of the composition was 14,500 mPa.s (cps). Kept away from actinic light sources, it was stable at room temperature for more than 2 years. At 70°C, it remained in its liquid state for over a 6-month period. The above composition was curtain coated 3-mil thick on a rigid vinyl clad composite tile base. The coating was UV-cured 2 passes under a pair of 200-watt per inch medium pressure mercury lamps at a belt speed which resulted in a total UV dose of 2.32 J/sq cm. Two comparative compositions were prepared, curtain coated on a rigid vinyl clad composite tile base, and UV-cured with the same dose of energy as the composition of the present invention. The two comparative compositions are both used on commercial floor covering. Comparative Composition 1 was similar in composition to Example 1 of US Pat. No. 5,003,026. Comparative Composition 2 was similar in composition to Product B of US Pat. No. 4,421,782. The composition of Example 1 of the present invention and the two comparative compositions were subject to the following performance evaluations: (1) Stain Resistance : Sample specimens were exposed 24 hours to 6 household stains consist of ink, magic marker, hair dye, tincture of iodine, shoe polish, and driveway sealant. The specimens were then cleaned with isopropyl alcohol, soap and water. Stain areas were determined by a colorimeter for LAB color changes before and after exposure to the stains. Colorimeter reading results were reported in ΔE. Higher ΔE indicated poorer staining resistance properties. (2) Gloss Retention : This was an accelerated abrasion resistance test. Sample specimens were laid under a leather clad traffic wheel which traveled in a circular motion. The wheel itself rotated along its own axle. Abrasive soils were applied on top of the specimens while the wheel traveled in the circular motion on top of them. After 90 minute duration, the specimens were determined for their retention of gloss with a gloss meter. Higher gloss retention indicated better abrasion resistance. The results of this test coordinate well with actual gloss loss of the product in the field. (3) Deep Scratch and Gouge Resistance : This was an accelerated test. The test was similar to the gloss retention test except the rotation of the wheel along its axle is at a different speed from its travel in circular motion and a more abrasive mixture of soils was used. The outcomes of the test were rated against a control with known performance. A higher rating indicated a better scratch and gouge resistance property. Example 1 Comparative 1 Comparative 2 Stain resistance 110 260 210 Gloss retention 87 85 45 Gouge resistance 7 3 3 Example 2 The series of formulations in Table 3 were prepared, UV-cured, and tested as in Example 1. Example B is a comparative example. The results which are presented in the bottom of Table 3 showed that polyurethane acrylates, the reaction products of trifunctional isocyanates provided superior gloss retention, stain resistance, abrasion, scratch and gouge resistance. Example 3 The series of formulations in Table 4 were prepared, UV-cured, and tested as in Example 1. Examples N and O are comparative examples. The results are presented at the bottom of Table 4. The results showed superior properties could be obtained from trifunctional isocyanate for the polyurethane acrylates for the present invention. Example I J K L M N O Oligomer Reactants (in % by weight) Desmodur N100 22.25 -- -- -- -- -- -- Desmodur N3200 -- 21.47 -- -- -- -- -- Desmodur N3400 -- -- 23.73 -- -- -- -- Desmodur H -- -- -- -- -- 16.91 -- Desmodur W -- -- -- -- -- -- 31.30 Polyisocyanate A -- -- -- 25.43 -- -- -- Polyisocyanate B -- -- -- -- 23.57 -- -- Polyol 1 8.93 9.10 14.90 8.75 8.61 -- 16.42 Polyol 3 -- -- -- -- -- 11.94 -- Tone M100 32.82 33.43 25.37 29.82 31.82 46.15 37.28 Reactive Diluents (in % by weight) SR351 10.00 10.00 16.00 14.00 16.00 -- -- SR454 -- -- -- -- -- 25.00 -- SR499 13.00 13.00 10.00 10.00 10.00 -- -- SR502 13.00 13.00 10.00 12.00 10.00 -- 25.00 Photoinitiators (in phr) Benzophenone 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Irgacure 184 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Flow Aids (in phr) Silwet L7604 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Oligomer Equivalent Ratio NCO/OH 0.933 0.934 1.000 1.000 1.091 1.000 1.000 Hydroxyacrylate /polyol 3.24 3.24 1.50 3.00 3.26 2.00 2.00 Comparative Properties Stain Resistance, ΔE 210 213 138 194 95 231 192 Gloss Retention, % 89 91 87 81 58 90 79 Gouge Resistance 4 4 7 6 6 3 3 Desmodur N100 is a biuret isocyanate derived from hexamethylene diisocyanate. It has an equivalent weight of 191. Desmodur N3200 is a biuret isocyanate derived from hexamethylene diisocyanate. It has an equivalent weight of 181. Desmodur N3400 is a uretidione isocyanate. It has an equivalent weight of 193. Polyisocyanate A is a mixture of polyisocyanates containing allophanate. It has an equivalent weight of 220. Polyisocyanate B is a partial timer of methyl-bis(4-cyclohexylisocyanate). It has an equivalent weight of 178.7.

Claims: A coating composition comprising the reaction product of a polyisocyanate having 3 to 6 isocyanate functionalities per molecule, an aromatic polyester polyol and a hydroxyalkyl(meth)acrylate with an average molecular weight of 344 to 472 and a (meth)acrylate reactive diluent having a molecular weight of at least 200 and less than 2000. The coating composition of claim 1, wherein the (meth)acrylate diluent is selected from the group consisting of tetraethylene glycol diacrylate, ethoxylated bisphenol-A diacrylate, trihydroxyethyl isocyanurate triacrylate, trimethylol propane triacrylate, and ethoxylated trimethylol propane triacrylate. The coating composition of claim 1, further comprising a photoinitiator. The coating composition of claim 1, wherein the aromatic polyester polyol is a polyester polyol of acid number of less than 15 comprising the reaction product of an equivalent excess of one or more polyols of equivalent weight less than 150 with at least one of the group consisting of a polycarboxylic acid, a polycarboxylic anhydride, and an ester of a polycarboxylic acid, wherein at least 50 equivalent percent of the polycarboxylic acid, polycarboxylic anhydride or ester of a polycarboxylic acid is selected from the group consisting of an aromatic polycarboxylic acid, an aromatic polycarboxylic anhydride, an ester of an aromatic polycarboxylic acid, and mixtures thereof. The coating composition of claim 4 wherein the aromatic polycarboxylic acid, aromatic polycarboxylic anhydride or ester of an aromatic polycarboxylic acid is selected from the group consisting of isophthalic acid, phthalic acid, terephthalic acid, phthalic anhydride, and dimethyl terephthalate. The coating composition of claim 1 wherein the polyisocyanate is selected from the group consisting of an isocyanurate, a biuret and an allophanate. The coating composition of claim 1 wherein the polyisocyanate is selected from the group consisting of those prepared from 1,6 hexamethylene diisocyanate; methylene-bis(4-cyclohexylisocyanate); 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane; 2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylene diisocyanate; toluene diisocyanate; methylenediphenyl diisocyanate; and tetra methylxylene diisocyanate. The coating composition of claim 1 wherein the hydroxyalkyl(meth)acrylate is a polycaprolactone based hydroxy(meth)acrylate having the formula: where R" = H or CH 3 , and p = 2 or 3. The coating composition of claim 1 wherein the polyisocyanate is an isocyanate derived from hexamethyl diisocyanate, the aromatic polyester polyol is a phthalate polyester polyol wherein at least 50 equivalent percent of the polyol is 1,6-hexanediol and at least 50 equivalent percent of the polycarboxylic acid is phthalic acid or phthalatic anhydride, and the hydroxyalkyl(meth)acrylate is a polycaprolactone based hydroxy(meth)acrylate having an average molecular weight of about 344, the isocyanate having an equivalent weight of about 195 and an average isocyanate functionality of about 3.5. The coating composition according to claim 1 comprising a multifunctional polyurethane (meth)acrylate and a (meth)acrylate reactive diluent having a molecular weight of 200 to 2000, the multifunctional polyurethane (meth)acrylate having the following structure: where m = 0, 1 or 2 n = 1 x = Y = R = R' = p = 1, 2 or 3 R" = H or CH 3 R''' = A floor covering comprising a base layer and wear layer adhered to the base layer, the wear layer comprising a cured coating composition, the coating composition comprising a (meth)acrylate reactive diluent having a molecular weight of 200 to 2000 and the reaction product of a polyisocyanate with a functionality of 3 to 6 isocyanate functionalities per molecule, an aromatic polyester polyol, and a hydroxyalkyl(meth)acrylate with a molecular weight of 344 to 472. The floor covering of claim 11, wherein the (meth)acrylate diluent is selected from the group consisting of, isodecyl (meth)acrylate, isobornyl (meth)acrylate, tetraethylene glycol (meth)acrylate, tripropylene glycol (meth)acrylate, hexanediol di(meth)acrylate, ethoxylate bisphenol-A di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, ethoxylated tripropylene glycol di(meth)acrylate, glyceryl propoxylated tri(meth)acrylate, tris (2-hydroxy ethyl) isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dimethylol propane tri(meth)acrylate dipentaerythritol monohydroxypenta(meth)acrylate, and trimethylol propane tri(meth)acrylate and its ethoxylated and propoxylated analogues of the skeletal structure selected from the group consisting of and where R" = H or CH 3 , and q = 0, 1, 2,..., 9 or 10. The floor covering of claim 12, wherein the (meth)acrylate diluent is selected from the group consisting of tetraethylene glycol diacrylate, ethoxylated bisphenol-A diacrylate, trihydroxyethyl isocyanurate triacrylate, trimethylol propane triacrylate, and ethoxylated trimethylol propane triacrylate. The floor covering of claim 11, wherein the coating composition further comprises a photoinitiator.

Inventors: ROSENBERRY ANGELA S, RUPP CLAUDE R, SETTHACHAYANON SONGVIT, ROSENBERRY, ANGELA S., RUPP, CLAUDE R., SETTHACHAYANON, SONGVIT
Applicants: ARMSTRONG WORLD IND INC, ARMSTRONG WORLD INDUSTRIES, INC.
Application year: 1996
Main classification: C08G18
IPC codes: C09D175, C08G18