COMPOSITION

Abstract: A storage stable, room-temperature curable coating composition for wood finishing is described which is based on a cross-linking system which does not give rise to formaldehyde emission and which comprises, in one or more organic solvents whereof at least one is a monofunctional alcohol, polymers containing active hydrogen; compounds functionalized from carbonyl containing compounds which compounds are hydrates and/or acetals of mono-, di- and/or polyaldehydes containing at least 2 carbon atoms as such or/and modified with hydrogen functional binders selected from polyesters, cellulose derivatives, acrylics or modified polyesters; and a catalyst selected from strong acids and salts thereof or alkalis.

Description: COMPOSITION The present invention relates to coating compositions with no or extremely low-formaldehyde emission for use in lacquers and paints, especially in wood finishing without giving rise to additional yellowing from the crosslin ing agent. PRIOR ART Increasing concern regarding the formaldehyde emission during either the curing process or long term emission by wood coated surfaces has initiated the development of formaldehyde free systems. Acid curing systems are defined as crosslinkable laquers which contain as reactive crosslinker an amino resin melamine/- urea/guanidine-formaldehyde type which gives rise to formaldehyde emission. All acid curing systems as defined above give rise to formaldehyde emission when drying at a level of 0.1-0.2 mg/100 g wet laquer according to the NIF-method (cf. Article No. 3-82 (November 1982) from Scandinavian Paint and Printing Ink Research Institute), a value which is interesting from the point of view of safety regulations. Different approaches have been made to improve the quality of the amino resins to comply with the request of a low formaldehyde emission during the curing process as well as the long term emission. Different systems have previously been proposed, viz. acetalated acrylic resin crosslinked with a polyhydroxy containing monomer which is described in US 4,663,410, and EP 0 201 693 polyhydroxylated resin based on polyvinylalcohol and polyvinylacetate which is sprayed with a second component containing a diacetal which is described in US 4,655,841 a polyhydroxypolymer, a hexaalkoxy methylolmelamine and a polyacetal and acid catalyst, which is described in US patent 5,155,170. Furthermore, it is usual to use polyurethane based system compri¬ sing a crosslinker such as high molecular weight polyisocyanate in combination with hydroxy functional polyesters or polyacryla- tes as an alternative in formaldehyde free system. However, the presence of free isocyanate groups give rise to environmentally dangerous products by handling and exposure and as well as when destroying residual products. Attempts to reduce the formaldehyde emission from lacquers comprise inter alia the use of additives reacting with formalde¬ hyde such as ethyleneurea, peroxides, organic sulphites, alkyl- acetone modified resins, cf..eg. EP 0043036.., which reduce the emission to about 0.1 mg m . The emission values in this specification and claims have been determined according to The European Standard prepared by the Technical Committee CEN/TC 112. The present invention relates to coating compositions with low formaldehyde emission below the normal background emission and at most is about 0.005 mg m . The coating compositions according to the invention are based on essentially formaldehyde free crosslinking system comprising, in one or more organic solvents whereof at least one is a monofunctional alcohol, polymers containing active hydrogen, compounds functionalized from carbonyl containing compounds and a catalyst selected from strong acids and salts thereof or alkalis. The present invention more specifically relates to a storage stable, room-temperature curable coating composition for wood finishing based on a crosslinking system which does not give rise to formaldehyde emission and which comprises, in one or more organic solvents whereof at least one is a monofunctional alcohol, polymers containing active hydrogen; compounds func¬ tionalized from carbonyl containing compounds, which compounds are hydrates and/or acetals of mono-, di- and/or polyaldehydes containing at least two carbon atoms as such or/and modified with hydrogen functional binders selected from polyesters, cellulose derivatives, acrylics, or modified polyesters; and a catalyst selected from strong acids and salts thereof or alkalis. The crosslinking system according to the present invention comprises the reaction between hydrogen active groups and carbonyl functionalized groups in a activ equiv./equiv. in the range of 0.3-2, preferably 1-1.2. The polymers containing active hydrogen comprise: 1 - hydroxyl groups -OH 2 - primary and secondary amino groups -NR^, -NH and/or amidogroups -C0-NH- 3 - acetylacetone groups -CH2-C-CH2-C-CH3 0 0 or enolisable aldehyde groups The essential formaldehyde free crosslinking system according to the present invention contains compounds functionalized from carbonyl containing compounds in the form of semiacetal, acetal, semiketal, ketal and/or hydrated groups. In this specification and in the claims the expression compound functionalized from a carbonyl containing compound refers to all these types of carbonyl derivatives. As the third component in the crosslinking system according to the present invention catalysts such as strong acids are used, e.g. pTSA, H2S0 4 , H PO4 and derivatives, HC1 or strong basic solutions as LiOH, NaOH, KOH in protic solvents such as methanol, ethanol, propylalcohol, i-propylalcohol, butanol, i-butanol, methoxypropanol, glycols, or similar and mixtures thereof. The hydroxy functional polymers with active hydrogen which can be used in the crosslinking system according to the present invention includes such polymers as: 1 ) conventional cellulose derivatives such as nitrocellulose containing approximatively 2-5 hydroxyl groups/kg and nitrogen at a level of 10-12.5% - cellulose acetobutyrate with at least one hydroxyl group per unit anhydro glucose. - cellulose acetopropionate with at least one hydroxyl group per unit anhydro glucose. - cellulose ethers, methyl or ethyl, with at least one hydroxyl group per unit anhydro glucose. 2) hydroxy functional oil-free polyester with a hydroxy func¬ tionality in the range of 25 mg KOH/g up to 950 mg KOH/6, suitably 35 mg KOH/g up to 650 mg KOH/g - hydroxy functional polyesters modified with either vegetable or animal or synthetic fatty acids with a hydroxy functionality of 25 mg KOH/g up to 800 mg KOH/g, suitably 35 mg KOH/g up to 260 mg KOH/g, - acryl or vinyl polymers and/or copolymers with a hydroxy functionality of 25 mg KOH/g up to 1275 mg KOH/g, preferably 25- 200 mg KOH/g, - oxirane-free epoxy resins containing hydroxy functional groups having a molecular weight of 800-6000, as such, and/or as epoxy esters with fatty vegetable oils and/or aminoadducts, - hydroxy functional aldehyde and/or ketone resins with a melting point of 75-170°C and an average hydroxy functionality between 50 and 110 mg KOH/g, - sulfonamide resins with a melting point in the range of 40- 100°C, preferably 35-65°C and acid number less than 1 mg KOH/g. Rosin derivatives esterfied with polyols like glycerol, penthae- rythritol having a melting point of 90-130°C. 3) Polymers containing amino/amido groups obtained by condensa¬ tion of dimer fatty acids with diamines and/or by blocking in part or completely the hydroxy/carboxy functionality of the previously described polymers with mono- or/and di-isocyanate compounds such as phenylisocyana e, cyclohexylisocyanate, TDI, MDI etc. 4) Polymers containing acetyl acetone functional groups and/or enolisable aldehyde groups obtained by condensation of the hydroxy functional polymers as described as above with t- butylacetylacetone and/or i-butyraldehyde, ethanal, propanal etc, glyoxal, succinic aldehyde, glutaric aldehyde etc. Such polymers as described above having hydroxy functionality and/or amino/amido functionality and/or acetylacetone or enolisable aldehyde groups are used to crosslink with carbonyl funtional compounds containing at least one carbonyl group presented as hydrates or acetals or ketals. Examples of typical reactions involved in this crosslinking process used in the present invention are illustrated in reaction schemes 1)-4) wherein the general formula of the carbonyl derivative is: ■ 0 . 0 - R R n where R = H, -C n H2 n+] _; n = 1, 2 ... 8 R χ = H, -C n H 2n+1 , -(CH 2 ) n -CH 2 OR 3 , CH 3 - (CH 2 ) n -CH 2 -CH—(-CH 2 ) n -COOR 3 , -C 6 H 4 -CO-0-R 3 , n = l, 2, ... 8, R = polymer backbone, polyester type. R 2 = H, -C n H 2n+1 , -(CH 2 ) n -0-R 4 R4 = polymer backbone of acryl type, n = 1, 2 ... 8. R SUBSTITUTE SHE Typical examples of R are alkyl chains with 1-6 C-atoms, preferably 2-4 C-atoms. R, R^, R2, n are defined as above. The compound functionalized from a carbonyl containing compound shall contain at least 2 carbon atoms and at least one group functionalized from carbonyl selected so that the boiling point of the carbonyl derivative is at least 21°C. The highest derivative in the series is a polyacetal which has a maximum carbonyl functionality of 450 mg KOH/g and a molecular weight of 20 000. One of the components of the organic solvents to be used must always be a monofunctional alcohol. Other components of the solvent mixture if several organic solvents are used can be selected from esters, alcohols, aromatic hydrocarbons and glycol ethers. The molar ratio between the monofunctional alcohol and the acetal and/or ketal functionality skall be in the range of from 2:1 to 10:1. The catalysts used in the composition according to the present invention are strong acids or alkalis in accordance with the desired network polymer and/or the starting point formulation, i.e. the functional groups involved in the curing process. The acid catalyst shall be used in such an amount that equiv. H + /equiv.C=0 is at most 0.2, preferably 0.001-0.05 (suitably about 0.02). In the formulations it is suitable to use H active (from binder) to C=0 ( from carbonyl derivatives) in such amounts that the ratio in the sealer lacquer from 0.3 to 1, preferably 0.6-0.8 and in the top lacquer from 0.5 to 2.0, preferably 0.8-1.2. In a suitable embodiment of the coating composition according to the present invention it also combines a condensation reaction between a polyacetal reactive compound and a hydrogen active oligomer selected from polymers modified with unsaturated fatty acids of vegetable, animal and synthetic origin capable to crosslink through an airdrying mechanism catalyzed by metal ions such as Co, Fe, Mn, Zr, Pb at a level of 0.01-0.1% based on non¬ volatile content of composition. In another suitable embodiment of the coating composition according to the present invention the composition comprises a crosslinking system based on solvent borne cellulose derivates, acetal functionalized where the active species are stabilized by means of a strong acid which is also a catalyst in further reaction with H-functional polymers whereby improved resistance against discolouration is obtained. The composition of the present invention may be modified by the addition of additives and ingredients which normally are added to paint and lacquer compositions such as conventional amount of fillers, pigments, reinforcing agents, mar, slip and flow control agents, flattening agents, levelling agents etc, selected so as to be compatible with the system. The compositions of the present invention can be applied to wood, plastic and metal substrates as such or in combination with other sealers or top coats. The composition according to the present invention has an emitted formaldehyde level within 24 hours of less than 0.01 mg m , experimentally detected less than 0.005 mg m . A cured sealer made by the composition according to the present invention provides a coating surface which is not dissolved by any usual top layer used in the wood finishing industry. The carbonyl derivatives used in the composition according to the present invention are liquids at room temperature and have a boiling temperature higher than 60°C. The composition according to the present invention provides a high built finishing on wood surfaces and has a nonvolatile content of about 30-50% at room temperature and at application viscosity. The finished coating according to the present invention exhibits very good properties that impart recoatability, sandability, stain and chemical resistance without any aldehyde emission caused by the coating, all of which properties mean that the coating composition according to the present invention is a superior alternative to both classic acid curing systems and polyurethane systems not least for environmental reasons. The following comparison with an acid curing system according to the prior art and a polyurethane based system according to the prior art which is presented below clearly shows that the composition according to the present invention must be regarded as an important advance in the paint industry. The tests carried out gave the following results: Acid curing Polyurethane Coating sys¬ system based system tem accor¬ ding to the present in¬ vention Butyl acetate re¬ O.K. Bad O.K. sistance 1 hour after application Hardness O.K. Bad O.K. Recoatability 1 O.K. Bad O.K. hour after appli¬ cation at room temperature Formaldehyde More than Less than Less than emission 24 hours 0.3 mg m~ 3 0.005 mg m ~3 0.005 mg m "3 after application The constituents of the composition of the present invention are blended together with methods conventional within the paint and lacquer industry. The invention is illustrated by means of the following examples wherein examples 1-3 describes the preparation of crosslinkers and examples 4-14 describe the preparation of lacquers with the use of different crosslinking systems in accordance with the present invention. Example 1 A carbonyl functional derivate in acetal form is produced by using a reactor equipped with a reflux condenser, agitator and heating mantel by blending: la lb lc Id Glyoxal 80% 40 40 40 40 Ethanol 59.5 - n-Propanol - 59.5 - i-Propanol - - 59.5 - i-Butanol - - - 59.5 NaOH SolutiolON 0.5 0.5 Water 0.5 - 0.5 The mixture is maintained at 54-56°C in order to obtain a clear yellow pale solution. Example 2 A polycarbonyl functional derivate in acetal form is produced in a reactor as above by using a formulation as such: 2a 2b 2c Ethanol 59.5 59.5 59.5 Alkyd 70% in ethanol 20 talloil 39% phtalic anhydride 30% OH ~ 170 mg KOH/g Alkyd 75% in butyl acetate 20 talloil 52% phtalic anhydride 27% OH ~ 165 - 180 mg KOH/g Acrylic polymer 60% in butyl acetate 20 (styrene, acrylic monomers, methylolated acrylamide) OH - 160 mg KOH/g Glyoxal 80% 20 20 20 Water 0.5 0.5 0.5 The mixture is maintained at 54-56°C to obtain a pale yellow clear solution. Example 3 In a reactor equipped with an agitator, reflux condenser, phase separator, heating mantle an acetal condensation product is produced according to the formulation 3a 3b 3c Glyoxal 870 40% in water Glutaraldehyde - 1030 300 50% in water Ethylene urea 86 Melamine 126 126 pTSA solution 1 1 0.1N The mixture is maintained at 52-54°C until the solution is waterclear. Butanol 608 - 111 Ethanol - 1290 The mixture is heated at 80-110°C to distill the water in order to obtain a polyfunctional*acetal. Examples 4-13 The following lacquers were produced according to the instant invention using conventional blending and agitation methods. All these systems involve chemical reactions such as these previously described catalysed by acids or in certain cases by alkalis. The coating compositions were applied on wood or glass panels by means of an applicator in a thickness of between 80 and 150 μm wet and dried 24 h at room temperature. Example 4 Parts by weight Butyl acetate 15 Ethyl acetate 5.5 Ethanol 6,798 Nitrocellulose, 65% 8,959 (11.1% N) Alkyd resin 70% in Butyl Acetate 53.23 (OH - 170 mg KOH/g oil 50% oil type - tall oil) Flattening agent (silica) 2.5 Glyoxal (40% in water) 7.715 Levelling agent (silicone type) 0.298 Catalyst 2-ethylhexyl acid phosphate 0.223 Ethanol 4.750 Butyl acetate 5.018 The lacquer has Nonvolatile content ~ 50% Kδnig hardness after 24 h ~ 100 aldehyde emission after 24 h less than 0.0005 mg m -3 pot life at 23.3°C more than 72 h Nonvolatile content ~ 32% at spraying viscosity Example 5 Butyl acetate 17.857 Ethyl acetate 10 Ethanol 5 Acrylic resin 60% in 16.194 Butyl Acetate (OH - 160 mg KOH/g) Alkyd resin 75% in Butyl Acetate 39.349 oil 45% non yellowing phtalic anhydride 33% pentaerythritol Flattening agent (silica Acetal derivate such as in 8.5 example Id Levelling agent (silicone type) 0.1 Catalyst Ethanol 9.8 H 3 P0 4 0.2 The lacquer has a pot life at 23.3°C more than 72 h aldehyde emission after 24 h less than 0.003 mg m -3 nonvolatile content at 28-30% spraying viscosity Konig hardness ~ 80 Example 6 Ethanol 14.8 Nitrocellulose (11,1% N) 12.9 Alkyd resin 75% in Butyl Acetate 32.64 NH - 40 mg KOH/g OH ~ 110 mg KOH/g oil length 44% Flattening agent (silica) 1.5 Butyl acetate 28.106 Ethyl acetate 9.9 pToluene Sulphonic Acid 0.054 Levelling agent (silicon derivate) 0.1 Crosslinking agent Acetal derivate such as ex. la 10 The lacquer has a pot life at 23.3°C more than 72 h aldehyde emission after 24 h less than 0.005 mg m -3 Kόnig hardness - 80 nonvolatile content at spraying viscosity 28-30% Example 7 Butyl acetate 15.198 Ethyl acetate 5 Ethanol 6.498 Nitrocellulose (10.8% N) 8.954 Oil free polyester 65% in Butyl Acetate 53.23 acetylacetone functionality 2.2/mole OH - 85 mg KOH/g Flattening agent (wax polyethylene type) 2 2,2 dimethoxyethanal 60% 7.705 Glutaraldehyde 50% 1.31 Levelling agent (silicone derivate) 0.1 Catalyst NaOH 0.01 Ethanol 9.99 The lacquer has a pot life at 23.3°C more than 48 h aldehyde emission after 24 h less than 0.01 mg m~ nonvolatile content of spraying viscosity 35-40% KOnig hardness 70-80 Example 8 Ethanol 5.4 Alkyd resin 70% ethanol 70 oil length 39% OH - 5% Flattening agent (silica) 2.5 Carbonyl derivate such as in ex. 3b 22 Levelling agent (silicone type) 0.1 The lacquer obtained is hardened at room temperature with a catalyst consisting of Ethanol 9.8 p.Toluene Sulphonic Acid 0.2 Aldehyde emission after 24 h is less than 0.005 mg m -3 Example 9 Epoxy ester 55% in Butyl Acetate 72.7 40% dehydrated castor oil 60% Epoxy resin MW - 1000 - 1100 Flattening agent (silica) 1.2 Carbonyl derivate such as in ex. I d 8 Ethyl Acetate 18 Levelling agent (silicon oil) 0.1 Catalyst Ethanol 9.8 p. oluene Sulphonic Acid 0.2 The lacquer has a potlife at 23,3°C more than 48 h Aldehyde emission after 24 h less than 0.004 mg m -3 Example 10 Butyl acetate 27.-! Ethyl acetate 5 Nitrocellulose (10.8% N) 8 Oil free polyester 55 65% in Butyl Acetate acetylacetone functionality 2.5/mole OH - 80 mg KOH/g Flattening agent (silica) 2 Pentanedione 2.5 Levelling agent (silicone derivate) 0.1 Catalyst NaOH 0.01 Ethanol 9.99 Pot life/23.3°C > 48 h Aldehyde emission after 24 h < 0.005 mg m "3 Nonvolatile content at spraying viscosity - 35% Example 11 Dendrimer (dendritic macromolecule) (polyester type) Nonvolatile 100% Viscosity 1200 m PaS OH - 160 mg KOH/g modified with caprylic/caprinic acid 80 Carbonyl derivate (ex. 2c) 18 Flattening agent (silica) 1.8 Levelling agent 0.2 Catalyst Ethanol 9.8 pTSA 0.2 pot life > 1 week Aldehyde emission after 24 h less thai ,-3 Example 12 Butyl acetate 3.39 Ethyl acetate 15 Ethanol 10 Nitrocellulose 65% (ethanol soluble) 3.9 Alkyd resin 70% in Butyl Acetate 54.23 (OH - 170 mg KOH/g oil 50% oil type - mixture of vegetable oils) Flattening agent 2.8 Acetal derivate such as in ex. l a 10.4 Co octoate (6% Co) 0.18 Levelling agent 0.1 Catalyst Ethanol 9.8 p. oluene Sulphonic Acid 0.2 Kόnig hardness after 24 h - 100 Aldehyde emission after 24 h less than 0.005 mg m ~3 Pot life at 23.3°C more than 72 h Nonvolatile content at spraying viscosity - 37% Example 13 Nitrocellulose (11.1% N) 7.370 Tix agent (silica type) 0.500 Flattening agent (silica type) 2.3 Flattening agent (polyamide wax) 0.3 Alkyd resin (70% in Butyl Acetate 60.3 (OH - 170 mg KOH/g oil length ~ 50% oil type ~ tall oil) Levelling agent 0.15 Butyl Acetate 28.78 Co drier (6% Co) 0.3 Crosslinking formulation Nitrocellulose (11.1% N) 2.777 Carbonyl derivate such as example 1 d 11.556 Butyl Acetate 5.000 Butanol 0.167 p-Toluene Sulphonic Acid 0.5 Konig hardness after 24 h - 100 Aldehyde emission after 24 h less than 0.005 mg m ° Pot life at 23.3°C more than 72 h Nonvolatile content - 37% at spraying viscosity

Claims: CLAIMS 1. A storage stable, room-temperature curable coating composi- tion preferably, but not exclusively, for wood finishing, based on a crosslinking system which does not give rise to formaldehyde emission and which comprises, in one or more organic solvents, whereof at least one is a monofunctional alcohol, polymers containing active hydrogen; compounds functionalized from carbonyl containing compounds which are hydrates and/or acetals of mono-, di- and/or polyaldehydes containings at least two carbon atoms as such or/and modified with hydrogen functional binders selected from polyesters, cellulose derivatives, acrylics, or modified polyesters; and a catalyst selected from strong acids and salts thereof or alkalis. 2. A coating composition according to claim 1, which does not give rise to any kind of aldehyde during the drying process when the carbonyl derivate used is an acetal functionalized carbonyl group. 3. A coating composition according to any of the preceding claims, in which the crosslinking system comprises an equivalent of active hydrogen per equivalent functionalized carbonyl group in the range of 0.3-2, preferably 1.0-1.2. 4. A coating composition according to claim 1 and claim 3, characterized in that the compound functionalized from a carbonyl containing compound is derived from a di- or polyfunctional aldehyde or ketone having a boiling point of at least 21°C, optionally dissolved as a solution in water or in a low molecular weight, monofunctional alcohol. 5. A coating composition according to claim 1, characterized in that the molar ratio between the monofunctional alcohol and the acetal and/or ketal functionality shall be in the range of from 2:1 to 10:1. 6. A coating composition according to claim 4, characterized in that the low molecular weight monofunctional alcohol is selected from the group ethanol, propanol, isopropanol, butanol, isobuta- nol and sec. butanol. 7. A coating composition according to any of the preceding claims characterized in that it as polymer with active hydrogen includes one or several polymers selected from polyesters, oil modified polyesters, aldehyde resins, acrylic homo-polymers and copolymers, oxirane free epoxy resins and/or derivatives, cellulose derivatives containing hydrogen active groups, preferably selected from hydroxyl groups, amino groups, amido groups, acetylacetone groups or any mixture thereof. 8. A coating composition according to any of the preceding claims characterized in that the catalyst is a strong acid, preferably selected from HC1, H 3 P0 4 , phosphoric acid alkyl derivative, H 2 S0 4 , alkyl or aryl sulfonates, sulphonic acid, p- toluensulphonic acid and any sulphonic acid derivative or a salt thereof. 9. A coating composition according to claim 1, characterized in that the catalyst is a strong base such as NaOH, KOH, LiOH and alcoholates thereof. 10. A coating composition according to any of the preceding claims characterized in that it comprises an activator such as water added to the system as such or as humid solvent in the range of 0.2-2.5 mole water/equivalent acetal and/or ketal, preferably in the range of 0.5-1.2. 11. A coating composition according to any of the preceding claims characterized in that it also combines a condensation reaction between a polyacetal reactive compound and a hydrogen active oligomer selected from polymers modified with unsaturated fatty acids of vegetable, animal and synthetic origin capable to crosslink through an airdrying mechanism catalyzed by metal ions such as Co, Fe, Mn, Zr, Pb at a level of 0.01-0.1% based on non¬ volatile content of composition. 12. A coating composition according to claim 1, characterized in that the crosslinking agent is a polyacetal and/or -ketal functionalised compound obtained by a condensation reaction between a dialdehyde and an oligomer with polyhydroxy func¬ tionality in which the ratio between dialdehyde and OH equivalent is at least 1 mole dialdehyde to 1 hydroxy functional group, thereby forming pendant acetal groups. 13. A coating composition according to any of the preceding claims which has a high nonvolatile content of about 30-50% at application viscosity, a long pot life and gives a crosslinked product with excellent sandability and recoatability.

Inventors: MANEA MIRCEA MIHAI, MANEA, MIRCEA, MIHAI
Applicants: BECKER ACROMA AB
Application year: 1995
Main classification: C09D167
IPC codes: C08G12, C09D167