HK1019890B - Paint stabiliser - Google Patents

Description

Method for stabilizing coating

The invention relates to the use of photoreactive, UV-absorbing piperidine compounds and mixtures of such piperidine compounds and at least one UV absorber as light stabilizers in coatings, preferably automotive coatings.

The invention also provides a method of stabilizing a coating against degradation of polymeric substances present in the coating by the action of atmospheric oxygen, heat and/or UV light, and the coating itself stabilized by this method.

The action of atmospheric oxygen, moisture, and especially UV light in the coating results in degradation of the polymer in the coating. This degradation is manifested, for example, by cracking, loss of weight, discoloration, delamination, and blistering. It is known to delay this process in coatings with suitable stabilizers. Known coating compositions therefore often comprise a mixture of a VU absorber and a sterically hindered amine (HALS: hindered amine light stabilizer). These compounds of the HALS type are known to react as radical scavengers and are therefore generally used to stabilize polymeric substrates.

It has now been found that specific, sterically hindered amines of the formula (A) are particularly suitable as light stabilizers for coatings, in particular for automotive coatings, alone or in combination with UV absorbers or mixtures of different UV absorbers. Wherein said compound of formula (A) is photoreactive and absorbs UV light.

The present invention therefore provides the use of a piperidine compound of the formula (a) (hereinafter HALS a) to enhance the photostability of a coating.Another embodiment of the present invention relates to the use of a mixture of such photoreactive, UV absorbing piperidine compounds and at least one UV absorber selected from the group consisting of 2-hydroxyphenylbenzotriazoles (1), 2-hydroxyphenyltriazines (2), 2-hydroxybenzophenones (3), ethanediamides (4) and cinnamic acid derivatives (5) as light stabilizers in coatings.

Suitable 2-hydroxyphenylbenzotriazoles correspond to the formula (1a) or (1b),wherein, in the compound of formula 1(a),

R₁are hydrogen atoms, alkyl groups having from 1 to 24 carbon atoms, preferably alkyl groups having from 1 to 20 carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl, octyl, nonyl, undecyl, tetradecyl, hexadecyl, octadecyl, nonadecyl and eicosyl, and the corresponding branched isomers, or phenylalkyl groups having from 1 to 4 carbon atoms in the alkyl moiety, in particular benzyl.

R₂Are hydrogen atoms, halogen atoms, in particular chlorine and bromine atoms, alkyl radicals having 1 to 18 carbon atoms or phenylalkyl radicals having 1 to 4 carbon atoms in the alkyl moiety, in particular benzyl, alpha-methylbenzyl, cumyl.

R₃Is a hydrogen atom, a chlorine atom or an alkyl radical having 1 to 4 carbon atoms, especially methyl, butyl, R₁And R₂At least one is not a hydrogen atom, and wherein, in the compound of formula (1b),

t is a hydrogen atom or an alkyl radical having 1 to 6 carbon atoms, in particular methyl and butyl,

T₁is hydrogen, chlorine or an alkyl radical having 1 to 4 carbon atoms, in particular methyl,

n is 1 or 2, and

if n is 1, T₂Is chlorine or of the formula-OT₃A group, and if n is 2, T₂Is of the formula-O-T₉-O-group, wherein

T₃Is a hydrogen atom, an alkyl group of 1 to 18 carbon atoms optionally substituted with 1 to 3 hydroxyl groups, an alkyl group of 3 to 18 carbon atoms containing one or more oxygen atoms in the middle and optionally substituted with hydroxyl groups, an alkenyl group of 2 to 18 carbon atoms optionally substituted with hydroxyl groups (suitable alkenyl groups are represented by R₁Alkyl in the definition), phenylalkyl having 1 to 4 carbon atoms in the alkyl moiety, in particular benzyl, phenylethyl, cumyl, alpha-methylbenzyl or is of the formula-CH₂CH(OH)-T₇The radical(s) is (are),

T₇is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms or a phenyl group,

T₉is alkylene having 2 to 8 carbon atoms, alkenylene having 4 to 8 carbon atoms, cyclohexylene or alkylene having 2 to 18 carbon atoms which contains in the middle one or more oxygen atoms, where the alkylene or alkenylene radicals may also be branched.

Suitable 2-hydroxyphenyltriazines correspond to the formula (2):wherein

u is a number of 1 or 2,

r is an integer of 1 to 3,

Y₁independently of one another, is a hydrogen atom, a hydroxyl group, a halomethyl group, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 18 carbon atoms or a halogen atom,

if u is 1, then Y₂Is an alkyl group having 1 to 18 carbon atoms, or a substituted hydroxyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a halogen atom, -COOH, -COOY₈、-CONH₂、-CONHY₉、-CONY₉Y₁₀-CH and/or-OCOY₁₁Substituted alkyl, or alkyl having 4 to 20 carbon atoms which is interrupted by one or more oxygen atoms and is optionally substituted by hydroxyl or alkoxy having 1 to 12 carbon atoms, or alkenyl having 3 to 6 carbon atoms, or glycidyl, or phenylalkyl having 1 to 5 carbon atoms in the alkyl moiety and unsubstituted or substituted by hydroxyl, chlorine and/or methyl, or-COY₁₂or-SO₂Y₁₃Or is or

If u is 2, then Y₂Is alkylene having 2 to 16 carbon atoms, alkenylene having 4 to 12 carbon atoms, xylylene, alkylene having 3 to 20 carbon atoms which has one or more oxygen atoms in the middle and/or is substituted by hydroxyl, or is-CH₂CH-(OH)CH₂-O-Y₁₅-OCH₂CH(OH)CH₂Or is- (CH)₂)_m-CO₂-Y₁₈-OCO-(CH₂)_mWherein m is 1, 2 or 3,

Y₈is an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 3 to 18 carbon atoms, an alkyl group having 3 to 20 carbon atoms which is interrupted by one or more oxygen atoms and/or which is substituted by hydroxyl, or is a glycidyl group or a phenylalkyl group having 1 to 5 carbon atoms in the alkyl moiety,

Y₉and Y₁₀Independently of one another, is alkyl having 1 to 12 carbon atoms, alkoxyalkyl having 3 to 12 carbon atoms, dialkylaminoalkyl having 4 to 16 carbon atoms or cycloalkyl having 5 to 12 carbon atoms,

Y₁₁is an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms or a phenyl group,

Y₁₂is alkyl having 1 to 18 carbon atoms, alkenyl having 2 to 18 carbon atoms, phenyl, alkoxy having 1 to 12 carbon atoms, phenoxy, alkylamino having 1 to 12 carbon atoms or phenylamino,

Y₁₃is an alkyl group having 1 to 18 carbon atoms, a phenyl group, an alkylphenyl group having 1 to 8 carbon atoms in the alkyl moiety,

Y₁₅is an alkylene, phenylene or-phenylene-M-phenylene radical having 2 to 20 carbon atoms, in which M is-O-, -S-, -SO₂-、-CH₂or-C (CH)₃)₂-, and

Y₁₈is an alkylene group having 2 to 10 carbon atoms or an alkylene group having 4 to 20 carbon atoms with one or more oxygen atoms in the middle.

Suitable 2-hydroxybenzophenones correspond to the formula (3):wherein

v is an integer of 1 to 3,

w is 1 or 2, and

z is independently of each other a hydrogen atom, a halogen atom, a hydroxyl group or an alkoxy group having 1 to 12 carbon atoms.

Suitable oxalanilides correspond to formula (4):wherein

x is an integer of 1 to 3,

y is 1 or 2, and

l are each independently of the other H, alkyl having 1 to 20 carbon atoms, hydroxyl or alkoxy having 1 to 20 carbon atoms. In this formula, the substituents L are preferably in the ortho and/or para positions.

Examples of alkyl, alkoxy, phenylalkyl, alkylene, alkenylene, alkoxyalkyl and cycloalkyl radicals and also alkylthio, oxaalkylene or azoalkylene radicals in the compounds of the formulae (2), (3), (4) and (5) can be taken from the above.

Suitable cinnamic acid derivatives correspond to the formula (5):wherein

n is an integer of 1 to 4,

U₁is H, alkyl, hydroxy, alkoxy, NH₂NH alkyl, N-dialkyl,

U₂is H, alkyl, aryl, alkyl-substituted aryl, alkoxyaryl, p-hydroxyaryl, p-aminoaryl,

U₃is H, CN, COOU₆，

U₄: if n is 1, then U₄Is an alkyl group (normal, iso, cyclic) containing from 1 to 20 carbon atoms with or without one or more oxygen atoms in the middle,

if n is 2, then U₄Is a compound containing 1 to 20 carbon atoms and containing or not containing one or more oxygen atoms in the middleAlkyl (normal, iso, cyclic),

if n is 3, then U₄Being the radical of triols, such as trimethylolpropane, glycerol,

if n is 4, then U₄Is a radical of a tetraol such as pentaerythritol,

U₅is a hydrogen atom or a substituent such as U₁Preferably, an alkoxy group,

U₆is an alkyl group (normal, iso, cyclic) having 1 to 20 carbon atoms.

The formulae (1 ｃA), (1b), (2), (3), (4) and (5) are known per se and are described, together with their preparation, for example in EP-A-0323408, EP-A-0057160, EP-A-0434608, US-A-4619956, DE-A-3135810, GB-A-1336391 and EP-A-0322557.

Particular preference is given to UV absorbers which correspond to the formulae UVA-1 to UVA-11 below.UVA-1 UVA-2 UVA-3 UVA-4 UVA-5 UVA-6 UVA-7 UVA-8 UVA-9 UVA-10 UVA-11

The invention also relates to a process for stabilizing coatings against degradation by the action of heat and light of polymers present in the coatings, characterized in that a piperidine compound of the formula A or a mixture of this piperidine compound and at least one UV absorber selected from the group consisting of 2-hydroxyphenylbenzotriazoles, 2-hydroxyphenyltriazines, 2-hydroxybenzophenones, oxalamides and cinnamic acid derivatives, is added in solid or dissolved form and in an amount sufficient to stabilize the coating to be stabilized and is incorporated into the coating or coating composition by conventional methods known per se. The total amount of light stabilizer chosen and the mixing ratio of HALS A to UV absorber depend on the properties of the coating composition and the need to prolong its stability. In general, the total amount of light stabilizers is from 0.2 to 5% by weight, preferably from 0.5 to 1.5% by weight, based on the solids content of the coating. The mixing ratio of HALS A to UV stabilizer depends on the nature of the coating, the required stability and the nature of the UV absorber used. Thus, it may vary between 10: 1 and 1: 10. Typical mixing ratios are from 4: 1 to 1: 4, preferably from 3: 1 to 1: 3. For example, in polyurethane coatings, the mixtures recommended according to the invention consist of 2 parts of piperidine compound of the formula A and 1 part of UV absorber, whereas for coatings based on vulcanizable acrylic resins, a ratio of HALS A to UV absorber of, for example, 1 to 3 is used in order to achieve the results according to the invention. The individual components of the synergistic mixture can be added individually or in the form of a mixture to the corresponding coating composition. In the case of two-layer application, this addition can be in the primer or in the topcoat. The top coat preferably contains the light stabilizers according to the invention. Other additives which are customary and do not impair the protective action of the light stabilizers used according to the invention may also be added to the coating compositions.

The light stabilizers of the invention are preferably used in powder form, liquid form or liquid formulations, which can be introduced into the liquid application system volumetrically, rapidly and in precise amounts.

The coating composition of the present invention may contain any desired type of coating, such as pigmented or unpigmented coatings or metallic effect (metallic) coatings. They may comprise organic solvents or may be solvent-free or may be aqueous coatings.

Examples of coatings containing specific binders are as follows:

1. alkyd, acrylate, polyester, epoxy or melamine resins or mixtures of these resins based on cold or hot crosslinking, with or without addition of an acid curing catalyst;

2. two-component polyurethane coatings based on hydroxyl-containing acrylate, polyester or polyether resins and on aliphatic or aromatic polyisocyanates;

3. one-component polyurethane coatings based on blocked polyisocyanates which are not blocked during baking;

4. two-component coatings based on (poly) ketimines and on aliphatic or aromatic polyisocyanates;

5. two-component coatings based on (poly) ketimines and on unsaturated acrylic resins or polyacetoacetate resins or methacrylamidoglycolate methyl esters;

6. two-component coatings based on carboxyl-or amino-containing polyacrylates and polyepoxides;

7. two-component coatings based on acrylic resins containing anhydride groups and on polyhydroxy or polyamino components;

8. two-component coatings based on (poly) oxazolidines and on acrylate resins containing anhydride groups or on unsaturated acrylic resins or aliphatic or aromatic polyisocyanates.

9. Two-component coatings based on unsaturated polyacrylates and polymalonates.

10. Thermoplastic polyacrylate coatings based on thermoplastic acrylic resins or externally crosslinked acrylic resins in combination with etherified melamine resins.

11. Coating system based on silicone-modified acrylic resins.

12. Coating system based on fluorine modified acrylic resins.

The coating may also be a radiation curable coating. In this case, the binder consists of monomeric or oligomeric compounds containing olefinic double bonds, which are converted into the form of crosslinked, high molecular weight substances by irradiation with actinic light or electron beams. In this case, it is usually a mixture comprising these compounds.

The coating can be applied as a one-layer or two-layer coating system, the stabilizers of the invention preferably being added to the pigment-free top coat.

The coating can be applied to a substrate (metal, plastic, wood, etc.) by conventional techniques, for example, by brushing, spraying, flow application, dipping, or electrolysis. Particularly preferably, the composition of the present invention is a coating for electric power tools. Examples of suitable coating systems and adhesives are described, for example, in US-A-4314933, 4344876, 4426471, 4426472 and 4429077.

The invention also relates to the coating of surfaces and to the applied films obtainable by vulcanization.

The invention also provides coatings which are photostable with the compound HALS A or with a mixture of the compound HALS A and a UV absorber.

The following examples illustrate the invention, all parts and percentages being by weight unless otherwise indicated.

The tables below show the content of the light stabilizers according to the invention per se incorporated in the resin component (% pure light stabilizer, i.e. active substance, based in each case on the solids content of the coating, i.e. resin and hardener). Hardener B was blended into this mixture.

Examples 1-4 high solids polyurethane coatings (2C HS PU coatings) in 2-component. Resin component FQ 95-0104 and hardener component SC 29-0160 are both supplied by BASF.

Clear is applied to the spray viscosity and sprayed onto the pretreated substrate (coil coated aluminum plate, silver metal base application [ aqueous, silver mooney (mooney silver) XSC 2431 WCA, Bollig and Kemper) with xylene adjustment, vented at room temperature for about 1 hour, and then oven dried at 140 ℃ for 30 minutes (pmt: peak metal temperature). The thickness of the transparent dry film applied is thus 40 to 50 μm.

Accelerated weathering of the samples was carried out in a Xenon weather meter (CI 35, from Atlas; CAM 180); the 20 ℃ gloss (DIN 67530) was measured and used to calculate the residual gloss (%) relative to the initial value.

Examples 5 and 6 were carried out in a two-component medium-solid polyurethane coating (2C MS-PU coating). Resin component 5 K.53.058 and hardener component 8 K.71.037 were obtained from Akzo Nobel Coatings.

Clear is adjusted with xylene to spray viscosity and sprayed onto the pretreated substrate (silver metal base application [ light grey MS 612 VR modified polyester/melamine, solvent containing, Akzo Nobel ]), vented at room temperature for about 1 hour, and then oven dried at 80 ℃ for 30 minutes (pmt: peak metal temperature). The thickness of the transparent dry film applied was 40 to 45 μm.

In example 5, samples were subjected to accelerated weathering in a UVCON instrument (ASTMG 53-93: 8 hours at 70 ℃ under light, 4 hours in the dark/condensation at 50 ℃); the 20 ℃ gloss (DIN 67530) was measured and used to calculate the residual gloss (%) relative to the initial value. The yellowing was also determined colorimetrically (determination of the b values according to the CIELAB standard and calculation of the Δ b values relative to the initial values).

In example 6, the samples were accelerated weathered in a Xenon weather meter (WOM Ci 65; CAM 7/DIN 53231A); the 20 ℃ gloss (DIN 67530) was determined and used to calculate the residual gloss (%) relative to the initial value.

In a comparative example, the following prior art HALS compounds were used, which are non-photoreactive and do not absorb UV light:

HALS 1: tinuvin (RTM)292, a commercial product available from Ciba-Geigy, Switzerland

HALS 4: sanduvor (RTM)3055, a commercial product available from Clariant, Switzerland

Example 1

LALS conjugate with oxalanilide UV absorbers:

serial number	HALS	UV absorbers	20 ℃ gloss after 4000 hours	Residual gloss after 4000 hours (%)
					1	Is free of	Is free of	15(3000h，z*)	17(3000h，z*)
2	0.6％HALS 1	0.6％UVA 9	20	24
					3	0.6％HALS 4	0.6％UVA 9	19	22
4	0.6％HALS A	0.6％UVA 9	33	39
					5	0.6％HALS 1	0.6％UVA 10	24	28
6	0.6％HALS 4	0.6％UVA 10	21	25
					7	0.6％HALS A	0.6％UVA 10	27	32

^*) z-destroyed

Reference numerals 4 and 7 are examples of the present invention.

Example 2

LALS combination with benzotriazole UV absorbers:

serial number	HALS	UV absorbers	20 ℃ gloss after 4000 hours	Residual gloss after 4000 hours (%)
					1	Is free of	Is free of	15(3000h，z*)	17(3000h，z*)
2	0.6％HALS1	0.6％UVA 2	41	48
					3	0.6％HALS4	0.6％UVA 2	29	34
4	0.6％HALSA	0.6％UVA 2	59	69
					5	0.6％HALS1	0.6％UVA 3	32	38
6	0.6％HALS4	0.6％UVA 3	21	25
					7	0.6％HALSA	0.6％UVA 3	39	46
8	0.6％HALS1	0.6％UVA 5	49	58
					9	0.6％HALS4	0.6％UVA 5	29	34
10	0.6％HALSA	0.6％UVA 5	65	76

^*) z-destroyed

Reference numerals 4, 7 and 10 are examples of the present invention.

Example 3

LALS conjugate with ortho-hydroxyphenyltriazine UV absorber:

serial number	HALS	UV absorbers	20 ℃ gloss after 4000 hours	Residual gloss after 4000 hours (%)
					1	Is free of	Is free of	15(3000h，z*)	17(3000h，z*)
2	0.6％HALS 1	0.6％UVA 6	59	69
					3	0.6％HALS 4	0.6％UVA 6	59	69
4	0.6％HALS A	0.6％UVA 6	63	74
					5	0.6％HALS 1	0.6％UVA 7	68	80
6	0.6％HALS 4	0.6％UVA 7	65	76
					7	0.6％HALS A	0.6％UVA 7	68	80

^*) z-destroyed

Reference numerals 4 and 7 are examples of the present invention.

In examples 1 to 3, the samples stabilized with HALS A show greater stability to weathering than the samples containing the same amount of HALS which do not absorb UV light and are not photoreactive.

Example 4

Serial number	Hals	UV absorbers	20 ℃ gloss after 4500 hours	Residual gloss after 4500 hours (%)
					1	Is free of	Is free of
2	0.8％HALS1	1.2％UVA 1		20
					3	0.8％HALS1	1.2％UVA 6		65
4	0.8％HALSA	1.2％UVA 1		75
					5	0.8％HALSA	1.2％UVA 6		78
6	2.0％HALSA	Is free of		81

Surprisingly, it is clear that the effect of the UV absorbing HALS a itself is equal to or even greater than the effect of the prior art UV absorber and sterically hindered amine combination which is neither photoreactive nor absorbs UV light, if concentrations corresponding to the combination are used.

Example 5

Serial number	HALS	UV absorbers	20 ℃ gloss after 1750 hours	Residual gloss after 1750 hours (%)	Δb*
						1	Is free of	Is free of	Is broken down
2	0.3％HALS1	0.3％UVA8	71	79	4.2
						3	0.3％HALS4	0.3％UVA8	78	87	4.9
4	0.3％HALSA	0.3％UVA8	83	92	3.7
						5	0.3％HALS1	0.3％UVA11	46	51	6.2
6	0.3％HALS4	0.3％UVA11	57	63	5.9
						7	0.3％HALSA	0.3％UVA11	62	69	5.1

Example 6

Serial number	HALS	UV absorbers	20 ℃ gloss after 2000 hours	Residual gloss after 2000 hours (%)
					1	Is free of	Is free of	33	36
2	0.3％HALS1	0.3％UVA9	52	58
					3	0.3％HALS4	0.3％UVA9	65	72
4	0.3％HALSA	0.3％UVA9	68	76
					5	0.3％HALS1	0.3％UVA8	71	79
6	0.3％HALS4	0.3％UVA8	74	82
					7	0.3％HALSA	0.3％UVA8	77	85
8	03.％HALS1	0.3％UVA11	51	57
					9	0.3％HALS4	0.3％UVA11	55	61
10	0.3％HALSA	0.3％UVA11	61	68

The excellent effect of the combination of the UV absorbers of the invention with HALS A is also evident in these examples. Furthermore, the yellowing tendency of these binders expressed as Δ b values is significantly improved (see example 5).

Claims (8)

1. Use of a mixture of a piperidine compound of the formula (A) and at least one UV absorber selected from the group consisting of 2-hydroxyphenylbenzotriazoles, 2-hydroxyphenyltriazines, 2-hydroxybenzophenones, oxalanilides and cinnamic acid derivatives as stabilizers against the action of heat and/or UV light on coatings,

2. use according to claim 1, characterized in that the ratio of piperidine compound of formula (a) to UV absorber is from 10: 1 to 1: 10.

3. Use according to claim 2, characterized in that the ratio of piperidine compound of formula (a) to UV absorber is from 4: 1 to 1: 4.

4. Use according to claim 3, characterized in that the ratio of piperidine compound of formula (A) to UV absorber is from 3: 1 to 1: 3.

5. A process for stabilizing coatings against degradation by atmospheric oxygen, moisture, heat and/or UV light of polymers present in the coatings, characterized in that a mixture of a piperidine compound of the formula (A) according to claim 1 and at least one UV absorber is added to the coating to be stabilized in an amount of from 0.2 to 5% by weight, based on the solids content of the coating.

6. The process as claimed in claim 5, wherein the mixture of piperidine compounds of the formula (A) and at least one UV absorber as claimed in claim 1 is added to the coating material to be stabilized in an amount of from 0.5 to 1.5% by weight, based on the solids content of the coating material.

7. Stable automotive coatings containing 0.2 to 5% by weight, based on the solids content of the coating, of a mixture of piperidine compounds of the formula (A) according to claim 1 and at least one UV absorber.

8. The automotive coating of claim 7, wherein a mixture of the piperidine compound of formula (a) according to claim 1 and at least one UV absorber is present in an amount of from 0.5 to 1.5% by weight, based on the solids content of the coating.