CA2167667A1

CA2167667A1 - A binder mixture and its use in two-component coating compositions

Info

Publication number: CA2167667A1
Application number: CA002167667A
Authority: CA
Inventors: Wieland Hovestadt; Gerhard Ruttmann; Rainer Rettig
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1995-01-24
Filing date: 1996-01-19
Publication date: 1996-07-25
Also published as: ES2147868T3; EP0733656A3; DE19502086A1; JPH08239626A; DE59605020D1; ATE192172T1; EP0733656B1; EP0733656A2

Abstract

The present invention relates to a solvent-free binder composition for preparing hard coatings which contains a) a polyisocyanate component having an NCO content of 10 to 35 wt.% and containing one or more organic polyisocyanates and b) a hydroxy-functional polyacrylate component having a hydroxyl group content of 10.1 to 20 wt.% and a viscosity at 23C of 200 to 20,000 mPa.s, wherein components a) and b) are present in an amount sufficient to provide an NCO/OH equivalent ratio of 0.5:1 to 2.0:1.
The present invention also relates to the use of this binder mixture as the binder in solvent-free two-component polyurethane coating and sealing compositions.

Description

Mo4326 LeA 30,873 US
A BINDER MIXTURE AND ITS USE IN
TWO-COMPONENT COATING COMPOSITIONS
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a new binder mixture containing a polyisocyanate component and a hydroxy-functional polyacrylate component which is suitable for producing solvent-free coatings, and to the use of the binder mixture in solvent-free coating and sealing compositions.
Description of the Prior Art Two-component polyurethane coating compositions containing lacquer polyisocyanates and hydroxy-functional polyacrylates are known (see, e.g., Glasurit, Lacke und Farben, 11th ed., page 66 et seq., Curt R.
Vincentz Verlag, Hannover 1984). They are characterized by their outstanding resistance to light, weathering and chemicals, and in this regard are superior to two-component polyurethane coating compositions based on polyethers or polyesters.
For ecological reasons, solvent emissions during the application of coating compositicns should be kept as low as possible. Therefore, even though many solids-rich systems have been recently developed, there is still a need for solvent-free compositions.
Light-resistant, hard, solvent-free two-component polyurethane coating and sealing compositions based on aliphatic polyisocyanates and polyether polyols and polyester polyols are used mainly in the field of floor, ceiling and roof coatings. These coatings are deficient with respect to resistance to weathering and chemicals. The relatively high hydrophilicity is also a disadvantage because it causes a relatively high degree of absorption of water by the polyols during storage, processing and curing. The water absorbed, in particular from the atmosphere, ,_ Mo4326 -2-reacts with polyisocyanates to form polyureas and carbon dioxide.
Because of the formation of carbon dioxide, it is not possible to prepare bubble-free coatings without taking complicated precautions (e.g., drying the polyols before processing them either by a vacuum treatment or by 5 adding water-absorbing substances to the binder mixture).
EP-A-0,580,054 describes low-viscosity, solvent-free, ester-modified polyacrylate resins which according to the general description have an OH content of 2 to 10 wt.% and a viscosity at 23C of 250 to 80,000 mPa.s. The compounds are prepared by polymerizing the 10 monomers in a mixture of lactones and polyhydric alcohols. The specifically described polyhydroxyl compounds have an OH content of less than 6 wt.%. Although binders containing these polyacrylate polyols and aliphatic polyisocyanates can be used for the production of coatings which have improved resistance to saponification, weathering and 15 chemicals when compared to the corresponding coatings based on polyester polyols or polyether polyols, the hardness of the coatings is frequently not sufficient to satisfy the requirements of the construction industry.
Therefore, an object of the invention is to provide new binder 20 compositions which can be used for the production of solvent-free coating compositions and which can be cured to give hard coatings that do not have the specified disadvantages of the prior art.
This object may be achieved with the binder mixtures according to the invention described in more detail below. The ability to achieve this 25 object is surprising because it could not have been expected that the polyacrylate polyols used, despite their high concentration of OH groups, would have the hydrophobicity required for low-bubble curing of the often thickly applied coating and sealing compositions. Rather the evolution of carbon dioxide and an associated increase in bubble formation would -Mo4326 8 have been expected, due to the reaction between isocyanate groups and moisture.
SUMMARY OF THE INVENTION
The present invention relates to a solvent-free binder composition 5 for preparing hard coatings which contains a) a polyisocyanate component having an NCO content of 10 to 35 wt.% and containing one or more organic polyisocyanates and b) a hydroxy-functional polyacrylate component having a hydroxyl group content of 10.1 to 20 wt.% and a viscosity at 23C of 200 to 20,000 mPa.s, wherein components a) and b) are present in an amount sufficient to provide an NCO/OH equivalent ratio of 0.5:1 to 2.0:1.
The present invention also relates to the use of this binder mixture as the binder in solvent-free two-component polyurethane coating and sealing compositions.
DETAILED DESCRIPTION OF THE INVENTION
The polyisocyanate component a) has an average NCO
functionality of more than 2, preferably 2.5 to 6 and more preferably 2.8 to 4; an NCO content of 10 to 35, preferably 15 to 25, wt.%; and a concentration of distillable diisocyanates (i.e., free monomer content) of less than 0.7, preferably less than 0.5 wt.%. Component a) is selected from lacquer polyisocyanates having biuret, urethane, allophanate, isocyanurate and/or uretdione groups and preferably aliphatically and/or cylcoaliphatically bound isocyanate groups. The production of these lacquer polyisocyanates is performed by the known modification reactions of simple organic diisocyanates, as described, for example, in DE-OS
1,595,273, DE-OS 3,700,209 and DE-OS 3,900,053; EP-A-0,330,966, EP-A-0,259,233, EP-A-0,377,177, EP-A-0,496,208, EP-A-0,524,501; and US-PS 4,358,171.

21676~7 Mo4326 4 Suitable diisocyanates for preparing lacquer polyisocyanates include 1,4-diisocyanatobutane, 1,6-diisocyanatohexane (HDI), 1,5-diisocyanato-2,2-dimethylpentane. 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanato-5 methylcyclohexane (IPDI), 1-isocyanato-1-methyl4-(3)-isocyanatomethyl-cyclohexane, 1,3-diisocyanato-6-methyl-cyclohexane, bis-(4-isocyanatocyclohexyl)methane, 1,10-diisocyanatodecane, 1,12-diisocyanatododecane, cyclohexane-1,3- and -1,4-diisocyanate and mixtures thereof. Preferred lacquer polyisocyanates are those prepared 0 from HDI or IPDI or mixtures of HDI and IPDI.
Polyol component b) has a hydroxyl group content of 10.1 to 20, preferably 11 to 17.5 and more preferably 11 to 15 wt.%; and a viscosity at 23C of 200 to 20,000, preferably 1000 to 10,000 mPa.s. Component b) is preferably selected from polyacrylate polyols which have been 15 prepared by the radical polymerization of b1) 100 parts by weight of a mixture of olefinically unsaturated monomers, at least 5 % of which are monomers having alcoholic hydroxyl groups, in the presence of b2) 20 to 200 parts by weight of an alcohol component selected from polyhydric alcohols having a molecular weight of 62 to 1000, and b3) 0 to 100 parts by weight of cyclic compounds which, in the presence of initiator compounds containing alcoholic hydroxyl groups, are capable of a ring-opening polymerization reaction.
Monomers b1) are selected from olefinically unsaturated compounds having a molecular weight of 53 to 400, preferably 80 to 220.
Examples include alkyl esters or cycloalkyl esters of acrylic acid or methacrylic acid having 1 to 18, preferably 1 to 8 carbon atoms in the alkyl or cycloalkyl group, such as methyl, ethyl, n-propyl, n-butyl, 30 isopropyl, isobutyl, t-butyl, the isomeric pentyl, hexyl, octyl, dodecyl, Mo4326 5 hexadecyl or octadecyl esters of the acids mentioned; acetoacetoxyethyl methacrylate; acrylonitrile; vinyl ether; methacrylonitrile; vinyl acetate;
styrene or vinyl toluene; and hydroxyalkyl esters of a"~-unsaturated carboxylic acids, in particular of acrylic acid or methacrylic acid having 2 5 to 12, preferably 2 to 6 carbon atoms in the hydroxyalkyl group, such as 2-hydroxyethyl acrylate, the isomeric hydroxypropyl acrylates obtained by the addition of 1 mole of propylene oxide to 1 mole of acrylic acid, 2-, 3-and 4-hydroxybutyl acrylate, the isomeric hydroxyhexyl acrylates and the methacrylates corresponding to these acrylates.
Also suitable are hydroxy-functional monomers which have been modified or chain-extended with ethylene, propylene and/or butylene oxide to a maximum molecular weight of 376. In addition, carboxyl group containing, unsaturated monomers such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, semi-esters of maleic and fumaric acid and mixtures of these and other monomers are suitable.
With respect to the total amount of olefinically unsaturated monomers b1), the hydroxyl group-containing monomers are used in an amount of at least 5 wt.%, preferably at least 15 wt.% and more preferably at least 30 wt.%.
Alcohol component b2) is selected from polyhydric alcohols having a molecular weight of 62 to 1000, preferably 62 to 286. Examples include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, tripropylene glycol, 1,3-propane diol, 2-methyl-propane diol, 1,2-butane diol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, 2,2-dimethyl-1,3-propane diol, 1,6-hexane diol, 2,5-hexane diol, 2-ethyl-2-methyl-1,3-propane diol, 3,3-dimethyl-1,2-butane diol, 2-methyl-2,4-pentane diol, 2,2-diethyl-1,3-propane diol, octane diol, 2-ethyl-1,3-hexane diol, decane diol, dodecane diol, hexadecane diol, octadecane diol, cylcohexane diol, glycerine, 1,1,1-tris-(hydroxymethyl)-propane, 1,2,6-hexane triol and mixtures of these. Diols or mixtures of diols which are liquid at room -Mo4326 -6-temperature and have a boiling point above the polymerization temperature, such as 1,3-butanediol or 2-ethyl-1,3-hexanediol are preferred, in particular 2-ethyl-1,3-hexanediol or mixtures with this diol.
Also suitable as component b2) are polyhydric alcohols having ether 5 groups and molecular weights in the previously disclosed range which may be obtained in known manner by the alkoxylation of the previously disclosed polyhydric alcohols that do not contain ether groups with ethylene oxide and/or propylene oxide.
Cyclic compound b3), which may optionally be used during 10 preparation of hydroxy-functional component b), is selected from compounds having a molecular weight of 72 to 439, which in the presence of initiator compounds containing alcoholic hydroxyl groups, are capable of a ring-opening polymerization reaction. Examples of these cyclic compounds are lactones such as ,B-propiolactone, ,~-butyrolactone, 15 ~-butyrolactone, y-valerolactone, pivalolactone and -caprolactone;
substituted lactones such as methyl, ethyl, propyl, dodecyl -caprolactone, dialkyl lactones, trialkyl lactones, cyclohexyl -caprolactone, phenyl -caprolactone, methoxy -caprolactone and ethoxy -capro-lactone; cyclic carbonates such as ethylene carbonate, 20 propylene carbonate and neopentylglycol carbonate; epoxides such as 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, glycidyl esters of versatic acid; and mixtures of these cyclic compounds. Lactones are preferably used, in particular -caprolactone.
When preparing polyacrylate component b) for the binder mixture 25 according to the invention, components b1), b2) and optionally b3) are used at a molar ratio within the previously disclosed ranges so that the OH content of the resulting polyacrylate polyols is within the previously disclosed amounts. Preferably, 40 to 140 parts by weight of component b2) and 0 to 60, in particular 10 to 60, parts by weight of component b3) 30 are used per 100 parts by weight of b1).

Mo4326 -7-Polyacrylate component b) is prepared by radical polymerization in known manner as described, for example, in EP-A-0,580,054. In general at least 50 wt.% of component b2) and/or optionally at least 50 wt.% of component b3) are initially introduced into the reaction vessel and heated 5 to the reaction temperature of 80 to 220C, preferably 120 to 190C.
Then monomer mixture b1), optionally additional amounts of components b2) and b3) and a polymerization initiator are added. When addition is complete, the reaction temperature is kept constant, with stirring, until the reaction is terminated.
Suitable polymerization initiators include dibenzoyl peroxide, di-tert.-butyl peroxide, dilauryl peroxide, dicumyl peroxide, didecanoyl peroxide, tert.-butyl peroxy-2-ethyl hexanoate, butyl peroxybenzoate and azo compounds such as 2,2'-azobis-(2,4-dimethyl-valeronitrile), 2,2'-azobis-(isobutyronitrile), 2,2'-azobis-(2,3-dimethylbutyronitrile) and 1,1'-1 5 azobis-(1-cyclohexanenitrile).
When preparing polyacrylate component b) for the binder mixture according to the invention, molecular weight regulating substances, such as n-dodecyl mercaptan or tert.-dodecyl mercaptan, may optionally be incorporated in amounts of up to 10 wt.%, based on the total weight of 20 reaction mixture.
Catalysts for the ring-opening polymerization reaction of component b3) may also be added in amounts of up to 0.8 wt.%, based on the total weight of reaction mixture. Suitable catalysts include Lewis acids or organic metal compounds such as boron trifluoride etherate, 25 tetrabutyl titanate, zinc chloride, zinc acetate, tin dioctoate, dibutyltin oxide and mixtures thereof.
The type and proportion by weight of components b1), b2) and optionally b3), the amount of polymerization initiator and the polymerization temperature are selected such that the viscosity of 30 polyacrylate component b) is within the previously disclosed ranges. All 2167667 .
Mo4326 -8-data on viscosity in connection with component b) refers to the viscositydetermined at 23C in accordance with DIN 53019 in a Contrave rotational viscometer.
In addition to polyacrylate component b), which is essential to the 5 invention, other hydroxyl group possessing binder components c) may also be present in the binder mixture according to the invention.
Examples include polyester, polycarbonate or polyether resins known from lacquer technology. Polyacrylate polyols, which do not correspond to the definition of component b), may also be incorporated as an 10 additional polyhydroxyl component c). In accordance with the present invention the binder mixture may contain up to 50 wt.%, based on the total weight of components b) and c), of polyhydroxyl compounds c).
Preferably, polyhydroxyl compounds c) are not present in the binder mixture according to the invention.
To prepare the coating compositions according to the invention, components a) and b) and optionally c) are mixed with each other in amounts sufficient to provide an NCO/OH equivalent ratio of 0.5:1 to 2.0:1, preferably 0.8:1 to 1.5:1. Either before, during or after thoroughly mixing individual components a), b) and optionally c), known additives 20 from coating technology may optionally be added. Examples of these additives include flow control agents (such as those based on cellulose esters or oligoalkyl acrylates), pigments and fillers, viscosity controlling additives (such as bentonite and silicates), matting agents (such as silica, aluminum silicates and high molecular weight waxes) and catalysts for 25 the cross-linking reaction (such as dibutyltin oxide or dimethylbenzyl-am ine).
The coating and sealing compositions made from the binder mixture according to the invention are suitable in particular as solvent-free, weather-resistant, yellowing-resistant, hard coatings in the building 30 industry, in particular for ceiling, roof and floor coatings.

2167~67 -Mo4326 -9-The following examples are intended to explain the invention in more detail without, however, restricting it. All data in "%" is based on weight.
EXAMPLES
5 Lacquer PolYisocyanate A
An isocyanurate group-containing polyisocyanate based on 1,6-diisocyanatohexane and having an NCO content of 21.8 % and a viscosity of 3250 mPa.s at 23C (Desmodur N 3300, available from Bayer AG, Leverkusen).
10 Lacquer polyisocyanate B
A biuret group-containing polyisocyanate based on 1,6-diisocyanatohexane and having an NCO content of 23.0 % and a viscosity of 2750 mPa.s at 23C (Desmodur N 3200, available from Bayer AG, Leverkusen).
15 Examples 1 - 7 - General procedure for preparing the polyacrylate polyols set forth in Table 1 Components from part I were heated to polymerization temperature in a reaction vessel with stirring. Part ll was continuously added over a period of 3 hours and simultaneously part lll was 20 continuously added over a period of 3.5 hours. After a further 3 hours at the same temperature, the product was cooled to room temperature. The composition of Parts I to lll, the polymerization temperatures, and the OH
content and viscosity of the products are set forth in Table 1.

Example 1 2 3 4 5 6 7' Part 12-ethyl-1,3-hexanediol (g) 935 595 456 456 433 neopentylglycol (g) 170 153 1,3-butanediol 170 442 100 -caprolactone (g) 209 209 252 289 403 Part llmethyl methacrylate (g) 68 n-butyl methacrylate (g) 150 2-ethylhexyl acrylate (g) 323 72 n-butyl acrylate (g) 225 250 182 267 238 styrene (g) 225 340 216 216 207 238 2-hydroxyethyl methacrylate (g) 258 374 321 406 296 340 hydroxypropyl methacrylate(2) (g) 205 Part llldi-tert-butyl peroxide (g) 57 68 78 78 75 85 60 polymerization temperature C 165 180 165 165 165 165 160 OH content % 14.8 11.0 11.7 11.8 11.2 12.0 5.8 Viscosity (23C) mPas 3200 8700 3950 4700 1980 4480 3100 21676~7 -Mo4326 -11-1) Comparison example in accordance with Example 9 of EP-A
0,580,054 (U.S. Patent 5,442,421) 2) Addition product of 1 mole of propylene oxide and 1 mole of methacrylic acid 5 Examples 8 - 13 General procedure for preparing the binder mixtures and their use.
The compositions and final Shore D hardnesses are given in Table 2.
0.1 wt.% of dibutyltin oxide were added to the lacquer polyisocyanate and the polyacrylatepolyol and homogeneously mixed.
10 The binder mixture was applied to a test plate in a layer thickness of 5 mm.
The final Shore D hardness was determined after 3 days at 50C
or after 14 days at room temperature. The coatings exhibited very good resistance to light, weather and saponification.

15Example 8 9 10 11 12 13 Lacquer B A A A B B
polyisocyanate Amount 153 9 124 g 132 g 133 g 116 g 124 g Polyacrylate 1 2 3 4 5 6 20polyol Amount 100 9 100 9 100 9 100 9 100 9 100 9 NCO/OH ratio by 1:1 1:1 1:1 1:1 1:1 1:1 -equivalents Final shore D 65 61 68 74 55 77 25hardness 21~7667 Mo4326 -1 2-Example 14 (not according to the invention) 0.16 g of dibutyltin oxide were added to 65 9 of lacquer polyisocyanate A and 100 9 of the polyacrylate polyol from example 7 (NCO/OH equivalent ratio 1:1) and the components were homogeneously 5 mixed. The binder mixture was applied to a test plate in a layer thickness of 5 mm.
After 14 days at room temperature the coating exhibited only adequate resistance to saponification and had a final Shore D hardness of 22.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims

1. A solvent-free binder composition for preparing hard coatings consisting essentially of a) a polyisocyanate component having an NCO content of 10 to 35 wt.% and containing one or more organic polyisocyanates and b) a hydroxy-functional polyacrylate component having a hydroxyl group content of 10.1 to 20 wt.% and a viscosity at 23°C of 200 to 20,000 mPa.s, wherein components a) and b) are present in an amount sufficient to provide an NCO/OH equivalent ratio of 0.5:1 to 2.0:1.

2. The binder mixture of Claim 1 wherein polyisocyanate component a) has an average NCO functionality of 2.5 to 6 and consists essentially of one or more polyisocyanates having (cyclo)aliphatically bound isocyanate groups and containing biuret, urethane, allophanate, isocyanurate and/or uretdione groups.

3. The binder mixture of Claim 1 wherein polyacrylate component b) has a hydroxyl group content of 11.0 to 17.5 wt.% and a viscosity at 23°C of 1000 to 10,000 mPas.

4. The binder mixture of Claim 2 wherein polyacrylate component b) has a hydroxyl group content of 11.0 to 17.5 wt.% and a viscosity at 23°C of 1000 to 10,000 mPas.

5. A solvent-free binder composition for preparing hard coatings consisting essentially of a) a polyisocyanate component having an NCO content of 10 to 35 wt.% and containing one or more organic polyisocyanates and b) a hydroxy-functional polyacrylate component which has a hydroxyl group content of 10.1 to 20 wt.% and a viscosity at 23°C of 200 to 20,000 mPa.s and consists of one or more polyacrylate resins prepared by radical polymerization of b1) 100 parts by weight of a mixture of olefinically unsaturated monomers, at least 5 % of which are monomers having alcoholic hydroxyl groups, in the presence of b2) 20 to 200 parts by weight of an alcohol component consisting of one or more polyhydric alcohols having a molecular weight of 62 to 1000 and b3) 0 to 100 parts by weight of cyclic compounds which, in the presence of initiator compounds containing alcoholic hydroxyl groups, are capable of a ring-opening polymerization reaction, wherein components a) and b) are present in an amount sufficient to provide an NCO/OH equivalent ratio of 0.5:1 to 2.0:1.

6. The binder mixture of Claim 5 wherein polyisocyanate component a) has an average NCO functionality of 2.5 to 6 and consists essentially of one or more polyisocyanates having (cyclo)aliphatically bound isocyanate groups and containing biuret, urethane, allophanate, isocyanurate and/or uretdione groups.

7. The binder mixture of Claim 5 wherein polyacrylate component b) has a hydroxyl group content of 11.0 to 17.5 wt.% and a viscosity at 23°C of 1000 to 10,000 mPas.

8. The binder mixture of Claim 6 wherein polyacrylate component b) has a hydroxyl group content of 11.0 to 17.5 wt.% and a viscosity at 23°C of 1000 to 10,000 mPas.

9. The binder mixture of Claim 5 wherein alcohol component b2) consists of one or more diols which are liquid at room temperature and have a boiling point above the polymerization temperature.

10. The binder mixture of Claim 6 wherein alcohol component b2) consists of one or more diols which are liquid at room temperature and have a boiling point above the polymerization temperature.

11. The binder mixture of Claim 7 wherein alcohol component b2) consists of one or more diols which are liquid at room temperature and have a boiling point above the polymerization temperature.

12. The binder mixture of Claim 8 wherein alcohol component b2) consists of one or more diols which are liquid at room temperature and have a boiling point above the polymerization temperature.

13. The binder mixture of Claim 9 wherein at least 65 wt.% of alcohol component b2) consists of 2-ethyl-1,3-hexanediol.

14. The binder mixture of Claim 10 wherein at least 65 wt.% of alcohol component b2) consists of 2-ethyl-1,3-hexanediol.

15. The binder mixture of Claim 11 wherein at least 65 wt.% of alcohol component b2) consists of 2-ethyl-1,3-hexanediol.

16. The binder mixture of Claim 12 wherein at least 65 wt.% of alcohol component b2) consists of 2-ethyl-1,3-hexanediol.

17. A solvent-free, two-component polyurethane coating or sealing composition containing as binder the binder mixture of Claim 1.