WO1986002652A1

WO1986002652A1 - Ultraviolet curable coating compositions containing ultraviolet curable additive

Info

Publication number: WO1986002652A1
Application number: PCT/US1985/002041
Authority: WO
Inventors: Frank A. Leo; Elias P. Moschovis
Original assignee: Desoto, Inc.
Priority date: 1984-10-22
Filing date: 1985-10-22
Publication date: 1986-05-09

Abstract

Radiation-curable liquid coating compositions which comprise polymerizable ethylenically unsaturated material containing a major weight proportion of preferably liquid polyacrylate or polymethacrylate, preferably containing at least 2.4 acrylate or methacrylate groups per molecule to provide a cured coating which is relatively hard, this composition being substantially free of volatile inert organic solvent, and from 0.1% to 2.5% of a silicone dicarbinol diurethane diacrylate or dimethacrylate in which the carbinol groups are carried by an ethoxylate or propoxylate constituting from 30% to 70% of the silicone. This modification provides improved wetting and surface lubricity while retaining hardness as the silicone diacrylate participates in the radiation cure. The preferred cures are with ultraviolet light, and this requires the presence of a photoinitiator.

Description

ULTRAVIOLET CURABLE COATING COMPOSITIONS

CONTAINING ULTRAVIOLET CURABLE ADDITIVE

DESCRIPTION

Technical Field This invention relates to ultraviolet curable curable coating compositions which are modified to improve the flow, leveling, wetting, mar resistance and flexibility of the coatings. Background Art Liquid ultraviolet curable coatings do not wet substrates well, especially when they do not contain volatile organic solvent, and it is usually . desired to substantially eliminate the use of such solvents in order to minimize pollution, hazard and unnecessary expense. This lack of good wetting of the substrate persists even when the unsaturated coating composition which is used is of low viscosity. As a result, the wet coatings crawl and flow over the substrate is poor, causing all sorts of coating defects like pinholing and orange peel. As a result, liquid radiation curable coatings are modified to include flow control agents which improve the capacity of the coating to wet the substrate.

Many of the common flow modifiers are based on silicones which generally function by spewing to the surface where the concentration of silicone at the surface interferes with the application of further coatings which may be applied for various purposes. Another problem is the mar resistance of the cured coating. Mar resistance is a function of the hardness of the coating in combination with its surface lubricity. The usual silicones plasticize the coating to the extent they remain within it. To the extent the silicone spews to the surface, it provides surface lubricity which enhances mar resistance, though this desired attribute is minimized by the reduction in the hardness of the body of the coating. Moreover, the silicone material at the surface can be removed by contact with an appropriate solvent because it is not reacted into the body of the coating. As a result, solvent wiping or solvent spills can remove the silicone material from the surface of the coating, thus impairing the lubricity of the surface.

It is desired to provide an additive which can be incorporated into liquid radiation-curable coating compositions to improve the capacity of the composition to wet a substrate and thereby minimize crawling and the coating defects associated with poor wetting. It is also desired to provide an agent which will reduce surface friction without being removable by solvent extraction and which will flexibilize the coating without significantly reducing its hardness. Description of Invention

In accordance with this invention, a radiation-curable liquid coating composition comprising polymerizable ethylenically unsaturated material containing a major weight proportion (more than 50%) of a polyacrylate or the corresponding polymethacrylate, which is preferably a liquid, is modified by the addition of from 0.1% to 2.5%, preferably from 0.2% to 1.0%, of a silicone dicarbinol diurethane diacrylate or dimethacrylate in which the carbinol groups are carried by an ethoxylate or propoxylate constituting from 30% to 70% of the silicone. The preferred composition contains polyacrylates or methacrylates having at least 2.4 unsaturated groups per molecule to provide a relatively hard coating after curing with radiation which is preferably ultraviolet radiation.

The preferred coating compositions are substantially free of volatile inert organic solvent, but some of the problems which have been noted persist even when volatile solvent is present, and this is especially true when the proportion of solvent is small.

The terms polyacrylates and polymethacrylates are well known to identify a plurality of acrylic or methacrylic acid ester groups.

The proportion of the silicone polyurethane diacrylate or dimethacrylate is critical because very little is used, and larger amounts are counterproductive because such larger amounts soften the cured coating which is an undesirable effect since hardness is important to obtaining mar resistance.

The crucial component in this invention is a silicone dicarbinol diurethane diacrylate or dimethacrylate, the diacrylate being preferred. These silicone-containing compounds are based on organic polysiloxanes having two substituents having a carbinol-terminal group. The carbinol group is provided by starting with a dihydroxy-ter inated organic polysiloxane and alkoxylating it with ethylene oxide or propylene oxide so that the alkoxylate constitutes from 30% to 70% of the dicarbinol which is produced. The carbinol functionality in the alkoxylate is reacted with an organic diisocyanate, such as 2,4-toluene diisocyanate or isophorone diisocyanate, and also with an hydroxy-functional acrylate or methacrylate, such as 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate, to provide a diacrylate- unctional diurethane derivative of the silicone dicarbinol.

The sequence of the above reactions is known to be variable, it being permissible to react the silicone dicarbinol with excess diisocyanate and then with the hydroxy acrylate, or to prereact the hydroxy acrylate with a molar proportion of the diisocyanate to form an unsaturated monoisocyanate which is reacted with the dicarbinol in a stoichiometric amount based on isocyanate and carbinol functionalities.

The usual organic polysiloxanes which are available in commerce are methyl or phenyl substituted (methyl substitution is preferred and will be used in the examples) and have, a molecular weight in the range of 600 to 10,000. As is known, the valences of the silicon atoms in the polysiloxane carry inert organic substituents, such as methyl and/or phenyl substituents, except for the two hydroxy groups which are ethoxylated to provide the terminal carbinol groups. The initial polysiloxane can be dihydroxy terminated and alkoxylated directly or first prereacted with a monoepoxide, such as propylene oxide or butylene oxide to provide carbinol termination for further alkoxylation. The carbinol groups are then adducted with from 30% to 70%, preferably from 40% to 60%, of ethylene oxide or propylene oxide to form the polyalkoxylates utilized herein after conversion to a urethane acrylate. Referring more particularly to the polymerizable ethylenically unsaturated material including a major weight proportion of liquid polyacrylate or polymethacrylate, radiation curable compounds containing an average of more than 2.4 acrylate or methacrylate groups per molecule are preferred to provide hard cured coatings. It is particularly preferred to employ polyacrylates which are at least approximately tri unctional, such as trimethylol propane triacrylate or pentaerythritol tri- or tetra-acrylate. Acrylate unsaturation is preferred because it provides a more rapid radiation cure, especially when photoinitiators are used to enable an ultraviolet cure. As pointed out in a copending application of one of us, especially hard and mar resistant coatings are obtained using from 70% to 85% of trimethylol propane triacrylate. In that application, from 5% to 15% of a carboxylic acid which contains acrylic or methacrylic acid unsaturation, especially acrylic acid itself, is used to improve adhesion to surfaces having a basic nature, and such carboxyl-functional material is also useful herein.

The acrylation of the p.referred polyacrylate, e.g., trimethylol propane triacrylate, is not usually complete, and the preferred trimethylol propane is acrylated to provide an average of at least 2.4 acrylate groups per molecule, preferably about 2.8 acrylate groups per molecule.

It is preferred to also include in the polyacrylate component from 1% to 12%, preferably 3% to 7%, of an epoxy diacrylate or dimethacrylate, preferably of a diglycidyl ether of a bisphenol in which the molecular weight of the diglycidyl ether is less than about 600, such as about 400 as in the Shell product Epon 828, since this also maximizes hardness and adhesion.

It is also desirable to include up to about 10% of the polymerizable material of a C. to C_g diol diacrylate or dimethacrylate, such as butane diol diacrylate or hexane diol diacrylate, to enhance flexibility without greatly impairing hardness and abrasion resistance, but this is not essential. The corresponding dimethacrylates are also useful. Preferred proportions are from 1% to 6%, and the preferred diacrylate is 1,6-hexanediol diacrylate. Isobornyl acrylate may also be present in small amount to enhance rapid radiation cure, flexibility, and to enhance the liquidity of the composition or one of its components.

The proportions specified throughout this document, including its claims, are by weight, unless otherwise specified. The proportions of polymerizable materials are based on the total weight of polymerizable material.

The photoinitiators are themselves well known and are preferably ketonic in character. It is preferred to employ photoinitiators which comprise benzophenone so that the ultraviolet cure can be carried out in air instead of in a nitrogen or other inert atmosphere. Acetophenone and benzophenone will illustrate ketonic photoinitiators in this well known class. Substituted acetophenones are particularly effective, especially those which are hydroxy-substituted. A large number of substituted acetophenones are disclosed in U. S. Pats. Nos. 4,284,485 and 4,318,791. This invention will be exemplified using the commercial ketonic photoinitiator, Irgacure 184 which is available from Ciba-Geigy (the compound 1-hydroxycyclohexyl phenyl ketone). This compound is a substituted acetophenone. These substituted acetophenones are preferably used in combination with benzophenone to enable rapid and complete cure in an oxygen-containing atmosphere.

The invention is illustrated as follows: Two coating formulations are provided by simply mixing together, with warming to insure dissolution, the components which are tabulated in the table which follows:

TABLE

Exampl e 1 Ex ampl e T

Epoxy diacrylate (1) 6. 0 6. 0

Trimethylol propane triacrylate (2) 74. 0 74. 0

1,6-hexanediol diacrylate 3. 0 3. 0 Acrylic acid 10. 5 - -

Silicone dicarbinol diurethane diacrylate (3) 0. 8 0. 8

Photoinitiator (4) 4. 48 4. 48

Stabilizer (5) 0. 02 0. 02 Benzophenone 1. 2 1. 2

(1) Diglycidyl ether of bisphenol A having a molecular weight of 390 reacted with 2 molar proportions of acrylic acid.

(2) 2.8 acrylate groups per molecule. (3) Dihydroxy- unctional polymethyl polysiloxane polyethoxylated to 50% with ethylene oxide to have a molecular weight of 6000 reacted with one molar proportion of isophorone diisocyanate and one molar proportion of 2-hydroxyethyl acrylate per hydroxy group to provide a silicone diurethane diacrylate (Dow Corning product Q4-3667 may be used as the polysiloxane polyethoxylate) .

(4) 1-hydroxycyclohexyl phenyl ket_.one.

(5) 2,6 di-tert-butyl-4-raethyl phenol The above formulations are sprayed on polystyrene, polycarbonate and dioctyl phthalate-plasticized polyvinyl chloride moldings to provide wet coatings having a thickness of 0.5 mil.

These are cured in air by an ultraviolet exposure of 2.0 Joule/cm2 and the result is hard, abrasion-resistant coatings which are strongly adherent to the plastic surfaces to which they are applied, except the acrylic acid-containing formulation adheres better to the polycarbonate and plasticized polyvinyl chloride, and the formulation - which omits the acrylic acid adheres better to the polystyrene. Variation of the coating thickness from 0.2 mil up to 0.8 mil is permissible while retaining good adhesion. Roll coat application on flat surfaces can also be used with these same formulations.

Claims

WHAT IS CLAIMED IS:

1. A radiation-curable liquid coating composition comprising polymerizable ethylenically unsaturated material containing a major weight proportion of polyacrylate or polymethacrylate, and from 0.1% to 2.5% of a silicone dicarbinol diurethane diacrylate or dimethacrylate in which the carbinol groups are carried by an ethoxylate or propoxylate constituting from 30% to 70% of the silicone.

2. A coating composition as recited in claim 1 in which said polyacrylate or polymethacrylate is liquid.

3. A coating composition as recited in claim 1 in which said composition is substantially free of volatile inert organic solvent.

4. A coating composition as recited in claim 1 in which said coating composition provides a cured coating which is relatively hard.

5. A coating composition as recited in claim 1 in which said silicone dicarbinol diurethane diacrylate is present in an amount of 0.2% to 1.0%.

6. A coating composition as recited in claim 1 in which said silicone compound is a diacrylate which is based on a methyl or phenyl-substituted polysiloxane ethoxylated to from 40% to 60% and having a molecular weight of from 600 to 10,000.

7. A coating composition as recited in claim 1 in which said composition includes photoinitiators which render the composition sensitive to ultraviolet light.

8. A coating composition as recited in claim 7 in which said photoinitiators are ketonic.

9. A coating composition as recited in claim 8 in which said ketonic photoinitiators comprise a substituted acetophenone.

10. A coating composition as recited in claim 9 in which said photoinitiators further comprise benzophenone.

11. A coating composition as recited in claim 10 in which said ketonic photoinitiator is 1-hydroxycyclohexyl phenyl ketone.

12. A coating composition as recited in claim 4 in which said composition includes a major weight proportion of liquid polyacrylates containing an average of at least 2.4 acrylate groups pet molecule to provide said hard coating when cured.

13. A coating composition as recited in claim 12 in which said composition includes from 70% to 85% of trimethylol propane triacrylate, based on the total weight of polymerizable material.

14. A coating composition as recited in claim 13 in which said trimethylol propane has been acrylated to provide an average of about 2.8 acrylate groups per molecule.

15. A coating composition as recited in claim 12 in which said polyacrylates include from 1% to 12% of a diacrylate of a diglycidyl ether of a bisphenol in which the molecular weight of the diglycidyl ether is less than about 600.

16. A coating composition as recited in claim 15 in which said diacrylate of a diglycidyl ether of a bisphenol is present in an amount of from 3% to 7%.

17. A coating composition as recited in claim 12 in which said composition includes up to about 10% of a C. to C_g diol diacrylate.

18. A coating composition as recited in claim 17 in which from 1% to 6%, of 1, 6-hexanediol diacrylate is employed.

19. An ultraviolet-curable liquid coating composition which cures on ultraviolet exposure to form a cured coating which is relatively hard comprising from 70% to 85% of trimethylol propane

5 triacrylate having at least 2.4 acrylate groups per molecule, based on the total weight of polymerizable material, ketonic photoinitiators comprising a substituted acetophenone rendering the composition sensitive to ultraviolet light, said composition

10 being substantially free of volatile inert organic solvent, and being modified by the addition of from 0.2% to 1.0% of a silicone dicarbinol diurethane diacrylate which is based on a methyl or phenyl-substituted polysiloxane ethoxylated to from

15 40% to 60% and having a molecular weight of from 600 to 10,000.

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