Radiation polymerizable waterborne soft-feel coatings

Abstract

A soft-feel radiation polymerizable aqueous coating composition comprising: (i) an aqueous polyurethane dispersion having radiation polymerizable ethylenic unsaturation and which is substantially free of groups reactive with hydroxyl functionality under conditions of radiation polymerization; and (ii) an aqueous polyurethane polyol which is substantially free of polymerizable ethylenic unsaturation and which is unreactive with the aqueous polyurethane dispersion (i) under conditions of radiation polymerization; (iii) a photoinitiator; and (iv) water;
and wherein the coating composition is free of external crosslinkers reactive with the polyurethane polyol.

Claims

1. A radiation polymerizable aqueous coating composition consisting essentially of: (i) an aqueous polyurethane dispersion having radiation polymerizable ethylenic unsaturation and which is substantially free of groups reactive with hydroxyl functionality under conditions of radiation polymerization; and (ii) an aqueous polyurethane polyol having a Tg between 35 and 45 C. and a hydroxyl value of 10 to 20, and which is substantially free of polymerizable ethylenic unsaturation and which is unreactive with the aqueous polyurethane dispersion (i) under conditions of radiation polymerization; (iii) a photoinitiator; and (iv) water; wherein the radiation polymerization is high energy radiation having wavelength less than 4000 Angstroms; wherein the weight solids ratio is 19 to 30 weight percent of the ethylenically unsaturated polyurethane dispersion relative to the total weight solids of the aqueous polyurethane polyol and the ethylenically unsaturated polyurethane dispersion; and wherein the coating composition has no intentionally added crosslinkers reactive with the polyurethane polyol, and wherein curing the coating composition forms a soft-feel texture after polymerization by treatment with an effective amount of actinic radiation.

2. The composition of claim 1 wherein the composition is substantially free of ethylenically unsaturated monomers.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) This invention relates to single component water reducible radiation polymerizable coatings which cure to a film having excellent adhesion, solvent and mar resistance while maintaining a favorable tactile soft-feel.

(2) The coatings involve the combination of: (i) an aqueous polyurethane dispersion (PUD) having radiation polymerizable ethylenic unsaturation and which is substantially free of groups reactive with hydroxyl functionality under conditions of high energy radiation polymerization; and (ii) an aqueous dispersion of a polyurethane polyol (PUD) which is substantially free of polymerizable unsaturation, and which is unreactive with the aqueous polyurethane dispersion (i) under conditions of high energy radiation polymerization; and (iii) a photoinitiator.

(3) The coatings can be conveniently cured by exposure to actinic radiation having a wavelength less than about 4000 Angstroms, such as ultraviolet and electron beam radiation.

(4) As used herein, the term, substantially free of, means that element, other than to the extent it may be incidentally present in any raw material, is not intentionally present or intentionally added.

(5) As used herein, the term conditions of high energy radiation polymerization means typical reaction conditions within the industry for the high energy cure of polymers and at temperatures not exceeding those normally involved in flashing off solvents.

(6) Additionally, radiation polymerizable PUD acrylates having good adhesion to plastics and good chemical resistance are known, but they often fail to have acceptable soft-feel properties.

(7) The water reducible compositions of this invention provide stable coatings having excellent adhesion, favorable soft-feel properties and excellent hardness and solvent resistance and protection for plastic and other substrates.

(8) In one embodiment, the radiation polymerizable aqueous coating compositions of this invention comprise: (i) an aqueous polyurethane dispersion having radiation polymerizable ethylenic unsaturation and which is substantially free of groups reactive with hydroxyl functionality under conditions of radiation polymerization; and (ii) an aqueous polyurethane polyol dispersion which is substantially free of polymerizable ethylenic unsaturation and which is unreactive with the aqueous polyurethane dispersion (i) under conditions of radiation polymerization; (iii) a photoinitiator; and (iv) water;
and wherein the coating composition is substantially free of external crosslinkers reactive with active hydrogen.

(9) In another embodiment, the present invention is directed to a method for improving the adhesion, solvent and mar resistance of a soft-feel coating composition that comprises the combination of: (i) an aqueous polyurethane dispersion (PUD) having radiation polymerizable ethylenic unsaturation and which is substantially free of groups reactive with hydroxyl functionality under conditions of high energy radiation polymerization; and (ii) an aqueous dispersion of a polyurethane polyol (PUD) which is substantially free of polymerizable unsaturation, and which is unreactive with the aqueous polyurethane dispersion (i) under conditions of high energy radiation polymerization; and (iii) a photoinitiator.
The coatings can be conveniently cured by exposure to actinic radiation having a wavelength less than about 4000 Angstroms, such as ultraviolet and electron beam radiation.

(10) The weight solids ratio of the aqueous polyurethane dispersion having radiation polymerizable ethylenic unsaturation and the aqueous polyurethane polyol can be varied widely to obtain the desired soft-feel. In some embodiments the aqueous polyurethane dispersion having radiation polymerizable ethylenic unsaturation will be present at a level of weight solids such that the weight percent solids of the unsaturated PUD will be at least about 16% of the total combined weight solids of the unsaturated PUD and the polyol PUD. For many applications, it will be present at a level up to about 50% and for many applications will be at a range of about 16 to about 35%.

(11) The coatings of this invention provide sufficient hardness and chemical resistance based upon the high energy cure alone and the coatings will be free of external crosslinkers such as isocyanates, ureas, melamines etc. that would be reactive with hydroxyl groups or other active hydrogen groups.

1. Aqueous Polyurethane Dispersion Having Radiation Polymerizable Ethylenic Unsaturation

(12) Ethylenically unsaturated aqueous polyurethane dispersions are well known in the art and are widely commercially available. The polyurethanes typically contain pendent unsaturation groups and will have water-dispersibility assisting groups such as anionic, cationic, or hydrophilic groups to provide water dispersibility.

(13) In one representative method of preparation, an aqueous polyurethane dispersion can be obtained by the reaction of one or more isocyanates and one or more active hydrogen containing compounds such as alcohols, amines, polyols or polyamides. The active hydrogen containing groups can also contain ionic groupssuch as acid functionality, for example from hydroxy functional carboxylic acids such as dimethylolpropanoic acid, malic acid and the like. Non-ionic groups such as polyethylene oxide groups can also be incorporated to provide water miscibility.

(14) Representative commercially available unsaturated polyurethane dispersions include Ucecoat 7200 form Cytec, Bayhydrol UV XP 2689/1 from Bayer Material Science, and Neorad R-1500.

2. Polyurethane Polyol

(15) Similarly, hydroxy functional water reducible polyurethane dispersions are well known in the art. In one embodiment of this invention, it is useful to utilize polyurethane polyols of relatively low hydroxyl value, generally less than about 25, and for some embodiments between 10 and 20. The polyurethane polyol will have a Tg of at least about 30 C. For many embodiments, the Tg of the polyol will be less than about 60 C. and sometimes less than 50 C. For some embodiments the Tg will be in a range between 35 and 45 C.

(16) The hydroxy functional polyurethane dispersions can be prepared by any method known in the art. One representative method is by the reaction of one or more isocyanates and a stoichiometric excess of one or more polyols. Ionic groupssuch as acid functionality, for example can be incorporated by the use of from hydroxy functional carboxylic acids such as dimethylolpropanoic acid, malic acid and the like. Non-ionic groups such as polyethylene oxide groups can also be incorporated to provide water miscibility.

3. Additional Materials

(17) The coatings of this invention can also incorporate other materials known in the art. If desired, water miscible organic solvents, typically less than 20%, and often less than 10% by weight of the coating composition, can be added. Generally these solvents should be low boiling alcohols, ethers or similar materials that will evaporate quickly from the film once it is applied to minimize flash off time. Flow agents, light stabilizers, dispersants and pigments (if they do not adversely affect the high energy cure) can also be added.

(18) Water miscible unsaturated monomers and oligomer could be added to the compositions of this invention, but for some embodiments, such as those where the monomers might chemically attack or haze the substrate, or when it is desired to minimize exposure to monomers they can be excluded. In a useful embodiment, the compositions are free of unsaturated monomers.

(19) Typically, the coatings will also contain an effective catalytic amount, usually about 0.1 to about 8% by weight of the polymerizable compounds, of a free radical polymerization initiator, such as a photoinitiator, to facilitate cure of the coating after application. Typical photoinitiators include benzophenone. Michler's ketone, diethoxyacetophenone, 2-chlorothioxanthone, hydroxy-alkyl phenones, and other materials known in the art.

(20) The compositions of this invention can be conveniently applied by any conventional method, such as spray, curtain coating, etc. to a substrate, allowed a short flash time (possibly at temperatures ranging up to about 60 C.) and then cured by exposure to high energy radiation. High energy radiation typically has a wavelength less than about 4,000 Angstroms such as electron beam or ultraviolet light radiation. The exposure need only be long enough to provide the desired amount of cure. The time required for cure depends on the intensity of the incident radiation, but typically sufficient cure can be obtained in one minute or less. Typical doses of ultraviolet radiation range from about 5 to about 150 feet/minute/lamp while useful doses of electron beam radiation range from about 0.5 to about 15 megarads.

(21) It would also be possible to cure the coatings of the invention by any other free radical initiator, e.g. visible light initiators such as taught in U.S. Pat. No. 3,650,699 or 4,071,424 or by subjecting the coatings to heat in the presence of a heat sensitive free radical initiator. Although these methods may be useful, they are not preferred for most embodiments because the thermal initiators are undesirable for heat-sensitive substrates and are less energy efficient than curing by exposure to radiation, and the visible light initiators often require special handling to avoid premature polymerization.

(22) As used herein, unless otherwise stated, the term parts means parts by weight and percentages are percent by weight.

Example 1

(23) A model coating formula containing a hydroxy functional polyurethane dispersion was prepared by combining materials in the order shown below:

(24) TABLE-US-00001 Parts Raw Material by Weight hydroxy functional polyurethane 719.23 dispersion.sup.1 defoamer.sup.2 0.84 water 50.09 sodium nitrate 1.17 dipropylene glycol methyl ether 16.72 (DPM) 2-butoxyethoxyethanol 25.09 defoamer 1.67 surfactant.sup.3 0.84 UV stabilizer.sup.4 1.09 dimethylethanolamine 1.67 associative thickness.sup.5 7.19 water 16.73 defoamer 0.84 .sup.1Commercially supplied polyurethane dispersion having a Tg of 41 C., and an OH # of 18. Supplied at 38.4% NVM in a 93/7 mix of water/dipropylene glycol dimethyl ether .sup.2Tego.sup. Foamex.sup. 805 .sup.3Byk.sup. 346 .sup.4Tinuvin.sup. 292 .sup.5Rheovis.sup. PU 1214 from BASF

Example 2

(25) A Pre-Mix of 99 parts of a commercially available UV curable ethylenically unsaturated polyurethane dispersion, Bayhydrol UV XP 2689/1, (42% NVM in water) commercially available from Bayer Material Science) and 1 part Irgacure 500 (1/1 blend of benzophenone and 1-hydroxy-cyclohexyl-phenyl-ketone commercially available from BASF) was prepared. This premix was then blended at various levels with the coating of Example 1 to produce the Examples below. The individual formulas were spray applied at about a 0.6 mil dry film thickness to ABS plastic and to Q-Steel panels, allowed to flash for 20 minutes at 140 F. (60 C.), and cured by exposure to a mercury vapor UV lamp. All gave acceptable adhesion to the ABS plastic. Solvent resistance was measured by 50 rubs with isopropyl alcohol. Hardness was measured as pencil hardness on the Q-Steel panels. The Solid ratio is the weight percent solids of the ethylenically unsaturated PUD divided by the total weight solids of the hydroxy functional PUD and the ethylenically unsaturated PUD combined.

(26) TABLE-US-00002 Parts Parts Example Pre- Solvent Hard- Solid Example 1 Mix Resistance ness Feel ratio 2 100 5 severe HB velvety 5.7% burnish 3 100 10 severe HB velvety 10.8% burnish 4 100 15 severe H velvety 15.4% burnish 5 100 20 moderate HB velvety 19.5% burnish 6 100 25 moderate HB silky 23.3% burnish 7 100 30 moderate H silky 26.7% burnish 8 100 35 moderate HB silky 29.8% burnish

(27) The modification levels above about 16% provide acceptable burnish resistance, adhesion and soft-feel. By comparison, a 2-component formula using Example 1 crosslinked with a commercially available polyisocyanate still exhibited severe burnishing from isopropyl alcohol.

(28) While this invention has been described by a specific number of embodiments, it is obvious that other variations and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.