FLOW MODIFIERS FOR COATING COMPOSITIONS

Abstract

This invention relates to copolymers AB having moieties derived from vinyl-terminated polysiloxanes A with more than one vinyl group bound to the polysiloxane, and moieties derived from two or more alkyl esters B of an olefinically unsaturated carboxylic acid, wherein at least two different alkyl esters B1 and B2 are used; the alkyl group of the first alkyl ester B1 of an olefinically unsaturated carboxylic acid has from one to five carbon atoms, the alkyl group of the second alkyl ester B2 of an olefinically unsaturated carboxylic acid has from six to thirty carbon atoms, and moieties derived from at least one hydroxyalkyl ester B3 of an olefinically unsaturated carboxylic acid, the ester B3 having at least one hydroxyl group in the alkyl group, and from two to six carbon atoms in the alkyl group, to a process for their preparation, and to a method of use thereof as flow modifiers in coating compositions.

Claims

1. Copolymers AB comprising moieties derived from vinyl-terminated polysiloxanes A with more than one vinyl group bound to the polysiloxane, and moieties derived from two or more alkyl esters B of an olefinically unsaturated carboxylic acid, wherein at least two different alkyl esters are used, the first being referred to as alkyl ester B1, and the second being referred to as alkyl ester B2; wherein the alkyl group of the first alkyl ester B1 of an olefinically unsaturated carboxylic acid has from one to five carbon atoms, and wherein the alkyl group of the second alkyl ester B2 of an olefinically unsaturated carboxylic acid has from six to thirty carbon atoms, and moieties derived from at least one hydroxyalkyl ester B3 of an olefinically unsaturated carboxylic acid, the ester B3 having at least one hydroxyl group in the alkyl group, and from two to six carbon atoms in the alkyl group.

2. The copolymers AB of claim 1 wherein the vinyl-terminated polysiloxanes A have two terminal vinyl groups, and obey the formula I ##STR00002## where R.sup.1 through R.sup.8 are selected, independently from each other, from the group consisting of alkyl groups having from one to eight carbon atoms, aryl groups selected from the group consisting of phenyl and alkylphenyl, the latter having from one to nine carbon atoms in the alkyl group, haloalkyl groups having from one to six carbon atoms where at least one of the hydrogen atoms of the alkyl groups is replaced by a halogen atom selected from the group consisting of F and Cl; and wherein the numbers m and n are independently from each other, zero, or an integer number from 1 to 90, wherein the sum m+n of m and n must be at least 6, and not more than 100.

3. The copolymers AB of claim 2, wherein R.sup.1, R.sup.4, R.sup.5 and R.sup.8 are methyl, R.sup.2 and R.sup.6 are both methyl, and R.sup.3 and R.sup.7 are both ethyl or phenyl, or they are different, and R.sup.3 is methyl while R.sup.7 is 1,1,1-trifluoroprop-3-yl.

4. The copolymers AB of claim 3 wherein n=0.

5. The copolymers AB of claim 4 wherein the value for m is chosen so that the number average molar mass of the divinylpolysiloxane A is from 500 g/mol to 7000 g/mol.

6. The copolymers AB of claim 1, wherein in the alkyl esters B1, the alkyl group having from one to five carbon atoms is selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, and tert-pentyl.

7. The copolymers AB of claim 6 wherein the alkyl esters B1 are selected from the group consisting of ethyl acrylate and n-butylacrylate.

8. The copolymers AB of claim 1, wherein in the alkyl esters B2, the alkyl group having from six to thirty carbon atoms is selected from the group consisting of n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, 2-nonyl, dodecyl, tridecyl, pentadecyl, and octadecyl, including linear and branched isomers of the said alkyl groups.

9. The copolymers AB of claim 8 wherein the alkyl esters B2 are selected from the group consisting of hexylacrylate and 2-ethyl-hexylacrylate.

10. The copolymers AB of claim 1, wherein the hydroxyalkyl esters B3 have at least one hydroxyl group in the alkyl group, and from two to six carbon atoms in the alkyl group, and are selected from the group consisting of hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate including the 3-hydroxypropyl ester, and the isomer mixture of 2-hydroxy-1-propyl (meth)acrylate and 1-hydroxy-2-propyl(meth)acrylate.

11. The copolymers AB of claim 10 wherein the hydroxyalkyl esters B3 are selected from the group consisting of hydroxyethyl acrylate and the isomer mixture of 2-hydroxy-1-propylacrylate and 1-hydroxy-2-propylacrylate.

12. The copolymers AB of claim 1, which comprise the following mass fractions w of repeating units derived from the monomers: for divinyl-terminated polysiloxanes A, w(A) is from 0.5% to 4.5%; for alkyl esters B1, w(B1) is from 30% to 85%; for alkyl esters B2, w(B2) is from 5% to 55%; for hydroxyalkyl esters B3, w(B3) is from 5% to 20%.

13. The copolymers AB of claim 1, having a number average molar mass M.sub.n of from 1.5 kg/mol to 6 kg/mol, and a mass average molar mass M.sub.w of from 2.5 kg/mol to 40 kg/mol, where the numerical values are the polystyrene equivalents as measured by GPC.

14. A method of use of the copolymers AB of claim 1 as flow modifier for coating compositions comprising at least a binder resin, and optionally, one or more of solvents, additives, pigments, colourants, crosslinkers, and catalysts, wherein the copolymer AB is present in the coating composition in a mass fraction of from 0.05% to 5%.

15. Coating compositions comprising the copolymers AB of claim 1.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The vinyl-terminated polysiloxanes A with at least one vinyl group bound to the polysiloxane preferably have two terminal vinyl groups, and further preferably, obey the formula I

##STR00001##

where R.sup.1 through R.sup.8 are selected, independently from each other, from the group consisting of alkyl groups having from one to eight carbon atoms, aryl groups selected from the group consisting of phenyl and alkylphenyl, the latter having from one to nine carbon atoms in the alkyl group, haloalkyl groups having from one to six carbon atoms where at least one of the hydrogen atoms of the alkyl groups is replaced by a halogen atom selected from the group consisting of F and Cl. R.sup.1, R.sup.4, R.sup.5 and R.sup.8 are preferably methyl, R.sup.2 and R.sup.6 are preferably both methyl, and R.sup.3 and R.sup.7 are preferably both ethyl or phenyl, or in another preferred embodiment they are different, and R.sup.3 is methyl while R.sup.7 is 1,1,1-trifluoroprop-3-yl. The numbers m and n are independently from each other, zero, or an integer number from 1 to 90, wherein the sum m+n of m and n must be at least 6, and not more than 100. In a preferred embodiment, m+n is at least 9, and not more than 90. In a further preferred embodiment, m+n is at least 9, and not more than 85. It is also preferred that n is less than m, and more preferred, n=0.

[0020] When using a polysiloxane which has only methyl groups as groups R.sup.1 to R.sup.8, as polysiloxane A, it is particularly preferred to use a value for m so that the number average molar mass of the divinylpolysiloxane A is from 500 g/mol to 7000 g/mol.

[0021] In the alkyl esters B1, the alkyl group has from one to five carbon atoms, and can be selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, and tert-pentyl. The olefinically unsaturated carboxylic acid is preferably acrylic or methacrylic acid. Particularly preferred alkyl esters B1 are ethyl acrylate and n-butylacrylate, especially preferred is ethyl acrylate.

[0022] In the alkyl esters B2, the alkyl group has from six to thirty carbon atoms, and can be selected from the group consisting of n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, 2-nonyl, dodecyl, tridecyl, pentadecyl, and octadecyl, including linear and branched isomers in those cases where these have not been expressly disclosed. The olefinically unsaturated carboxylic acid is preferably acrylic or methacrylic acid. Particularly preferred alkyl esters B2 are hexylacrylate and 2-ethyl-hexylacrylate, especially preferred is 2-ethylhexylacrylate.

[0023] Preferred hydroxyalkyl esters B3 have at least one hydroxyl group in the alkyl group, and from two to six carbon atoms in the alkyl group. The olefinically unsaturated carboxylic acid is preferably acrylic or methacrylic acid. Particularly preferred are hydroxyethyl (meth)-acrylate, hydroxypropyl (meth)acrylate including the 3-hydroxypropyl ester, and the isomer mixture of 2-hydroxy-1-propyl (meth)acrylate and 1-hydroxy-2-propyl(meth)acrylate. Most preferred alkyl esters B3 are hydroxyethyl acrylate and the isomer mixture of 2-hydroxy-1-propylacrylate and 1-hydroxy-2-propylacrylate.

[0024] Preferred copolymers AB according to this invention comprise the following mass fractions w of repeating units derived from the monomers:

for divinyl-terminated polysiloxanes A, w(A) is from 0.5% to 4.5%, particularly preferably, from 1.0% to 4.2%, and especially preferred, from 1.5% to 3.8%;
for alkyl esters B1 of an olefinically unsaturated carboxylic acid wherein the alkyl group has from one to five carbon atoms, w(B1) is from 30% to 85%, particularly preferably, from 35% to 80%, and especially preferred, from 40% to 75%;
for alkyl esters B2 of an olefinically unsaturated carboxylic acid wherein the alkyl group has from six to thirty carbon atoms, w(B2) is from 5% to 55%, particularly preferably, from 6% to 50%, and especially preferred, from 7% to 45%;
for hydroxyalkyl esters B3 of an olefinically unsaturated carboxylic acid wherein the alkyl group has from two to six carbon atoms, w(B3) is from 5% to 20%, particularly preferably, from 7.5% to 18%, and especially preferred, from 10% to 16%.

[0025] All ranges for the different monomers stated here may be combined, paying attention not to exceed 100% for the sum of mass fractions.

[0026] Mass fractions of repeating units in the polymers are calculated by identifying the repeating unit of an olefinically unsaturated monomer —CX.sup.i1X.sup.i2—CX.sup.i3X.sup.i4— for each olefinically unsaturated monomer i having the general formula CX.sup.i1X.sup.i2=CX.sup.i3X.sup.i4, and measuring the average number of these repeating units in the polymer molecules by an appropriate analytical means, in this case preferably by .sup.13C-NMR spectroscopy, and multiplying the number fractions thus obtained by the molar mass of the repeating units which are the same as these of the monomers. When using an analytical tool such as pyrolysis gas chromatography where the signal is mass dependent, mass fractions can be directly calculated from the analytical results after calibration with the pure monomers or copolymers of known composition.

[0027] Combinations of the preferred embodiments for the individual components mentioned herein supra have been found to lead to particularly good results. The best results have been obtained if a particularly preferred choice for component A has been combined with preferred choices, or particularly preferred choices for one or for more of components B1. B2, and B3.

[0028] The addition polymerisation processes which are used and can be used to prepare the copolymers AB of the invention are as follows: [0029] (1) standard radical polymerisation in solution, where the radicals are generated by thermal decomposition preferably of azo compounds, persulfates, or peroxides, by photolysis preferably of metal iodides, metal alkyls, or azo compounds, by ionising radiation, by electrolytical formation of radical anions or radical cations, by redox reactions preferably of hydrogen peroxide or alkyl hydrogen peroxides under iron catalysis, or using ternary initiators such as those based on a metallocene, an initiator such as an acylperoxide, and a diketocarboxylic acid; [0030] (2) controlled radical polymerisation methods which include [0031] (2 a) controlled free-radical polymerisation with xanthogenic esters as transfer agents, as described for example in WO 1998/058974 A1, [0032] (2 b) controlled free-radical polymerisation with dithioesters as transfer agents, as described for example in WO 1998/001478 A1, [0033] (2 c) controlled free-radical polymerisation with dithiocarbamates as transfer agents, as described for example in WO 1999/031 144 A1, [0034] (2 d) atom transfer radical polymerisation (ATRP), using transition metal catalysts, as described for example in WO 1996/030421 A1 or in Chem. Rev. 2001, 101, 2921.

[0035] Polymerisation processes (2 a) and (2 c) are also referred to as RAFT polymerisations.

[0036] An advantage of the monomers and the composition of the copolymers AB used for the flow modifiers in the present invention is that a conventional solution polymerisation using azo or peroxide or peroxy ester initiators can be used to make these copolymers in the desired specifications, which avoids the presence of the sulfur-containing or colour-generating components of the initiators used in the processes according to (2).

[0037] Polymerisation has been made by charging a solution of the vinyl-terminated polysiloxane A in an alcohol solvent, preferably isopropanol, and heating the solution to a temperature between 55° C. and 120° C., preferably under reflux. Two mixtures were added at the same time, one comprising the radical initiator in the same alcohol solvent, and the other comprising a mixture of the monomers B1, B2, and B3, optionally dissolved in the same alcohol solvent. When the reaction is complete, which is checked by determining the concentration of unreacted monomers in the reaction mixture, the reaction mixture is heated to a temperature of between 130° C. and 170° C., and solvent, unreacted monomers and by-products of the decomposition of the radical initiator are removed by distillation under reduced pressure. The copolymer AB can be used as such, or can be purified by solution-precipitation steps, by extraction, or by chromatographic methods as usual.

[0038] The number average molar mass M.sub.n of the copolymers AB of the invention used as flow modifiers is preferably in the range of from 1.5 kg/mol to 6.5 kg/mol, and the mass average molar mass M.sub.w is preferably in the range of from 2.5 kg/mol to 40 kg/mol, measured via gel permeation chromatography, using tetrahydrofuran as solvent, and calibrated with poly-styrene standards. It has to be noted that the values stated for the molar masses of the copolymers are only the equivalent polystyrene molar masses, and do not reflect the actual value for the examined copolymers.

[0039] The copolymers AB according to this invention are used as flow modifiers in coating formulations comprising binder resin, solvents, additives, pigments and colourants etc., including crosslinkers and catalysts if appropriate, in relatively small amounts, corresponding to a mass fraction of flow modifier copolymer in the coating composition, of from 0.05% to 5%, preferably from 0.1% to 3%, and most preferably from 0.2% to 2%.

[0040] The flow modifiers of the invention can be used as solutions, as aqueous emulsions, or in bulk, i. e. undiluted form, depending on the nature of the coating material and the manner of its application.

[0041] In solvent-borne coating materials it is preferred to use flow modifiers whose solvents are similar to those of the coating materials themselves. In radiation-curing systems the flow modifiers are dissolved preferably in corresponding monomers. In powder coating materials preference is given to an undiluted form of the flow modifier, in the form of a master batch, or to a form thereof which is applied to a pulverulent carrier material. These flow modifiers can also be incorporated, as described in German Patent Application DE-A 195 22 475, into wax melts and so converted into free-flowing solid forms. In aqueous powder slurries, the flow modifiers can be added in the form of an aqueous emulsion. These emulsions are prepared in accordance with the prior art with the aid of emulsifiers.

[0042] The invention also relates to coating compositions which comprise the flow modifier in a mass fraction, based on the mass of the coating composition, of from 0.05% to 5%, preferably from 0.1% to 3%, and most preferably from 0.2% to 2%.

[0043] The invention is further illustrated by the following examples.

[0044] Gloss was measured using a micro-TRI-gloss instrument obtained from BYK Gardner GmbH, in accordance with DIN EN ISO 2813.

[0045] Measurement of wave scan and DOI was made with a wave scan dual instrument obtained from BYK Gardner GmbH, in accordance with ASTM E430.

Example 1 Polymerisation of Silicone/Acrylic Hybrid Copolymers

[0046] The polymers were synthesised following always the same procedure described hereunder. The composition of the polymers was varied according to table 1 below.

[0047] A glass reactor having a volume of 500 ml equipped with reflux condenser, stirrer, and two addition funnels was charged with 75 g of isopropanol and the mass of divinyl-poly-dimethylsiloxane indicated in Table 1. The contents were heated to reflux (83° C.), and a mixture of t-amyl per-2-ethylhexanoate in isopropanol as well as a mixture of the monomers ethylacrylate, 2-ethylhexylacrylate and hydroxyethylacrylate were gradually added over five hours. Reaction was then brought to completion by keeping the mixture at 83° C. for one more hour, and finally, residual monomers, solvent and by-products from the decomposition of the radical initiator were removed by distillation under reduced pressure at 160° C.

TABLE-US-00001 TABLE 1 Monomer Composition for Copolymers P1 to P6 P6 (comp. P1 P2 P3 P4 P5 Example) tert-amyl per(2-ethylhexanoate) 4.3 g  4.1 g 4.5 g  4.5 g 3.5 g 3.8 g 2-ethylhexylacrylate 7.3 g 40.0 g 8.5 g 40.0 g 9.5 g 23.6 g  ethylacrylate 70.0 g  43.9 g 70.0 g  38.5 g 70.0 g  60.5 g  hydroxyethylacrylate 15.0 g  10.1 g 15.0 g  15.0 g 15.0 g  7.3 g divinylpolydimethylsiloxane 1000 .sup.(1) 3.4 g  2.0 g 2.0 g 4.8 g divinylpolydimethylsiloxane 4000 .sup.(2) 2.0 g divinylpolydimethylsiloxane 6000 .sup.(3)  2.0 g Divinylpolydimethylsiloxanes used are according to Formula I, with a mass average molar mass of 1 kg/mol .sup.(1), 4 kg/mol .sup.(2) or 6 kg/mol .sup.(3)

Example 2 Two-Pack Clearcoat Coating Compositions

[0048] Two-pack clear-coat compositions have been made, where for part (a), for each of CC0 to CCR, 76.05 g of a solution of a high solids acrylic resin having a hydroxyl value of 140 mg/g in butylacetate, with a mass fraction of resin of 75%, was diluted with 6.73 g each of xylene, of methoxypropyl acetate, and of further butyl acetate, together with the following additives: 0.51 g of a hindered amine light stabiliser (Tinuvin® 292, BASF SE), 1.48 g of a benzotriazole light stabiliser (Tinuvin® 1130, BASF SE),

were completed with additions of flow modifiers as follows, for [0049] part (a) of CC0 (unmodified): no addition [0050] part (a) of CC1: 0.65 g of copolymer P1 of example 1, [0051] part (a) of CC2: 0.65 g of copolymer P2 of example 1, [0052] part (a) of CC3: 0.65 g of copolymer P3 of example 1, [0053] part (a) of CC4: 0.65 g of copolymer P4 of example 1, [0054] part (a) of CC5: 0.65 g of copolymer P5 of example 1, [0055] part (a) of CC6: 0.65 g of copolymer P6 of example 1, [0056] part (a) of CCR (reference): 0.17 g of a commercial levelling additive based on a polyether modified polysiloxane (Additol® VXL 4930, Allnex Austria GmbH), 0.11 g of a commercial acrylic copolymer levelling additive having a hydroxyl value of 40 mg/g (Modaflow® 9200, Allnex Austria GmbH),
with final addition of 1.48 g of a solution of dibutyltin dilaurate in xylene with a mass fraction of the tin salt of 1% (Metatin® 712, The DOW Chemical Company), and 0.1 g of diethyl ethanolamine to each of the portions (a).

[0057] For the crosslinker composition used therefor (part (b)), eight mixtures were prepared, each from 28.18 g of a hexamethylene diisocyanate trimer having a mass fraction of isocyanate groups of 22% (Desmodur® N 3300, Bayer Material Science), 10.75 g of butyl acetate, 2.69 g of an aromatic solvent comprising C.sub.7 to C.sub.10-aromatic compounds having a boiling range of from 150° C. to 180° C. (Solvent Naphtha H), and 0.1 g of xylene isomer mixture.

[0058] The compositions (a) and compositions (b) were mixed separately in a laboratory size blender at 6000 min.sup.−1 for thirty minutes.

Example 3 Preparation of Test Panels

[0059] Cleaned steel panels have been wiped with isopropanol just before spray application. Then a standard solvent borne black auto refinish one-pack spray basecoat was been adjusted to an efflux time of 15 s (DIN-4 cup) by adding appropriate solvents, and applied to one half of the area of each of the cleaned steel panels by spray application at 23° C. and 50% relative humidity. The panels were dried for twenty-four hours at 23° C. and 50% relative humidity. The resulting dry film thickness was approximately 10 μm.

[0060] The clearcoats CC0 to CC6 as well as the reference clearcoat CCR, all of example 2, were mixed by adding one portion each of component (b) to each of the different components (a) in the quantities as detailed in example 2, and the viscosity adjusted to 16 s (DIN-4 cup) by adding butyl acetate. The clearcoats CC0 to CCR then were applied to the entire area of the basecoat covered steel panels by an automatic spray system at 23° C. and 50% relative humidity achieving a constant dry film thickness of 45 μm. The coated panels were flashed off for thirty minutes and then placed into an oven for 30 minutes at 80° C. for forced drying and further stored at 23° C. and 50% relative humidity for five days.

[0061] Then a second layer of clearcoat was applied to the coated panels by casting at a wet film thickness of 150 μm. This second layer of clearcoat was similar to the first one with the exception that the solvents from component (b) have been left out of the formulation. After casting the panels were flashed off for thirty minutes at 23° C. and 50% relative humidity followed by a thirty minutes cure at 80° C. in an oven. Immediately after this cure the first set of cross-cut determination was performed. This test was repeated after one day and after eight days of storage at 23° C. and 50% relative humidity.

Example 4 Quality Test

[0062] The appearance (wavescan, DOI: Distinctness Of Image, gloss) of the clear-coat layer (CC) on the basecoat (BC) for all coated panels as well as the results from the cross-cuts (interlayer adhesion) are given in tables 2 and 3:

TABLE-US-00002 TABLE 2 Wavescan, DOI, Gloss Clear Wave Scan CC on BC Gloss CC on BC Coat Longwave Shortwave DOI 20° 60° 85° CC0 64.1 49.6 65.9 59.70 82.50 89.10 CC1 9.1 1.3 96.5 88.30 93.50 99.00 CC2 25.9 34.2 86.50 89.40 94.10 99.30 CC3 8.3 4.1 96.60 87.50 92.90 99.20 CC4 13.2 29.6 88.5 89.60 93.90 98.40 CC5 26.0 10.0 95.7 88.40 93.80 99.30 CC6 27.1 29.6 85.9 88.10 94.10 98.80 CCR 38.3 30.8 88.4 88.30 93.90 99.30 Longwave and shortwave are both rated on a scale from 0 (best) to 100 (worst), DOI is rated on a scale from 100 (best, like a perfect mirror) to 0 (worst, perfect diffusor). Gloss is also rated on a scale from 100 (best) to 0 (worst).

[0063] The best combination of values was obtained for clearcoats CC1 and CC3.

TABLE-US-00003 TABLE 3 Cross-cut, adhesion BC/CC CC/CC after 8 d after 8 d CC0 0 0 CC1 0 0 CC2 0 1 CC3 0 0 CC4 0 1 CC5 0 0 CC6 0 5 CCR 0 1

[0064] This cross-cut test was performed in accordance with the ASTM D 3359, method A, where “5” means: more than 65% of the paint area removed, “4” means between 35% and 65% of the paint area is removed, and “0” means 0% of the area is removed by pulling off the adhesive tape.

[0065] Clearcoats CC1, CC3 and CC5 show the best results. It is essential that both a good result in the cross-cut test (meaning good interlayer adhesion), and surface quality (high gloss, low waviness) are realised with the same levelling additive. This has been realised with the copolymers AB of the present invention.