GB1564717A

GB1564717A - Aqueous baking finishes containing as binder a polybutadiene oil

Info

Publication number: GB1564717A
Application number: GB5273076A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1975-12-20
Filing date: 1976-12-17
Publication date: 1980-04-10
Also published as: FR2335530B1; FR2335530A1; DE2557562A1; DE2557562C2

Description

(54) AQUEOUS BAKING FINISHES CONTAINING AS BINDER A MODIFIED POLYBUTADIENE OIL (71) We, BASF AKTIENGESELL SCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to aqueous baking finishes, especially for cathodic electrocoating, which contain modified polybuta diene oils which carry sulfonium groups.

The use of certain modified polybutadiene oils which carry carboxyl groups as binders for aqueous baking finishes, especially for anionic electrocoating finishes, has been disclosed. These finishes are distinguished by high elasticity and good adhesion to the subetrate and to other finishes. The advantage of cationic electrocoating finishes over anionic electrocoating finishes is that during electrolysis the binder cannot suffer oxidative damage, and that no metal ions go into solution.

German Laid-Open Application DOS 2,236,910 discloses cationic electrocoating finishes in which the binder consists of watersoluble polyelectrolytes containing sulfonium groups. These binders are polymeric aromatic compounds containing methylene groups and carrying sulfonium groups, which demand a rather complicated method of manufacture.

Cationic binders based on polybutadiene are not disclosed.

It would be desirable to provide electrocoating finishes which exhibit high stability in the coating bath and give coatings which possess high elasticity, good adhesion and good chemical resistance, and which provide the coated metals with good corrosion protection.

The present invention provides an aqueous baking finish which contains as binder modified polybutadiene oil having a molecular weight of from 500 to 10,000 and carrying sulfonium groups.

The sulfonium groups preferably have the general formula

where R is alkylene of 2 to 8 carbon atoms and R' is alkyl of I to 6 carbon atoms, hydroxyalkyl of 2 to 6 carbon atoms, aminoalkyl of 2 to 6 carbon atoms or a CH2n bridge, where n is from 0 to 6, to another polybutadiene molecule.

In a preferred process for the manufacture of the present modified polybutadiene oils, a polybutadiene oil and a mercaptan or hydrogen sulfide are subjected to an addition reaction, in a first stage, and the resulting thioether is alkylated, in a second stage, with a 1,2-epoxide in the presence of an acid.

The starting materials are polybutadiene oils which have a molecular weight of from 500 to 10,000, preferably from 1,000 to 5,000. The viscosity of the oils is preferably from 5 to 2,000 poise (at 25"C). Particularly advantageous results are obtained by employing polybutadienes with relatively high 1,2-vinyl contents, i.e. if more than 10%, preferably more than 20% and especially more than 40%, of the double bonds have the 1,2-configuration. If the reaction with the mercaptan or hydrogen sulfide is catalyzed with strong acids, e.g. perchloric acid or boron trifluoride, addition at double bonds in the chain also takes place, so that polybutadienes with a low 1,2-content can also be used. The polybutadienes can carry terminal hydroxyl groups or amino groups.

In the first stage, the polybutadiene oils are subjected to an addition reaction with mercaptans. The latter are preferably mercaptoalkanols of 2 to 6 carbon atoms, e.g.

mercaptoethanol, mercaptopropanol or mercaptobutanol. However, alkylmercaptans of 1 to 6 carbon atoms, e.g. methylmercaptan, ethylmercaptan or butylmercaptan, or aminoalkylenemercaptans of 2 to 6 carbon atoms, can also be employed. Hydrogen sulfide or dimercaptans, e.g. ethylenedithiol, can also be used. In these cases, linkage of two poly butadiene chains results.

The ratio of polybutadiene oil to mercaptan is preferably so chosen that an average of from 2 to 50%, preferably from 5 to 20%, of the double bonds of the polybutadiene is saturated by sulfonium groups. The reaction can be carried out with the undiluted re actants or in the presence of a solvent, e.g.

dioxane, glacial acetic acid, dimethylform amide or ethylene glycol monoethyl ether, in the presence or absence of an acid catalyst, at from 10 to 1500C, preferably from 20 to 100"C.

The resulting thioether is then converted to the sulfonium compound by alkylation with a 1,2-epoxide in the presence of an acid. Pre ferred 1,2-epoxides are monoepoxides of 1 to 8 carbon atoms, e.g. ethylene oxide, pro pylene oxide, butylene oxide, glycidol or styrene oxide; however, diepoxides, e.g. reac tion products of bisphenol A with epichloro hydrin, can also be employed. From 0.5 to 2, and preferably about one, epoxide group is employed per thio group. The reaction is car ried out in the presence of an acid, and in particular an oxygen-containing acid, e.g.

formic acid, acetic acid, carbonic acid, sul furic acid, lactic acid or boric acid may be used, amongst which acetic acid and carbonic acid are preferred. In general, from 0.5 to 1.5 protons are present per thio group; prefer ably, a very slight excess is used. If carbonic acid is used, a substantial excess of carbon dioxide can be passed into the reaction mix ture and can subsequently again be removed by heating the solution, if appropriate under reduced pressure. In this way, electrocoating baths which have a neutral or even slightly alkaline reaction can be produced. The alkyl ation can also be carried out in organic sol vents. As a rule it is advantageous to add small amounts of water. The reaction tem perature is in general from 10 to 1000 C, pre ferably from 20 to 500 C.

The binders are diluted with water, prefer ably to a solids content of from 5 to 20%.

They can be mixed with the additives con ventionally employed in coating processes, e.g. further binders, crosslinking agents, pig ments, fillers, flow control agents, catalysts or plasticizers. Suitable crosslinking agents are those with functional groups which react with the hydroxyl groups of the sulfonium com pound, e.g. completely blocked polyiso cyanates, melamine/formaldehyde or phenol formaldehyde condensates, acrylate resins, epoxy resins or polyesters. Blocked polyisocyanates are preferred, and in particular toluylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate or reaction products of 1 mole of ethylene glycol with 2 moles of isophorone diisocyanate may be used.Suitable yocking agents are lactams, such as e-capro- lacLam, phenol, cresols, maleate esters, malonate esters, glycols or imidazoles. Highly reactive, more highly condensed melamine/ formaldehyde resins, e.g. butanol-etherified resins, may also be used.

The binders may be used for coating metals, wood or plastics, employing conventional methods such as spraying, dipping, brushing or casting. Electrocoating is the preferred method. The use of weak acids, especially acetic acid, lactic acid or carbonic acid is particularly advantageous, since the electrocoating baths can be operated at a weakly acid to weakly alkaline pH. The preferred pH is from 4 to 8, especially from 5 to 7. The use of carbonic acid at a neutral pH has the advantage that the coating equipment does not corrode and furthermore the air extraction and baking equipment does not suffer corrosion from acid decomposition products. Baking may be carried out under conventional conditions at from 80 to 220"C, preferably from 120 to 2000 C.

It is a particular advantage of the binders that malodorous products are eliminated in small amounts only, if at all, during baking.

The coatings obtained have good elasticity and excellent resistance to solvents, detergents and corrosive alkaline liquors. The binders are therefore particularly suitable for coating automotive components and household equipment.

EXAMPLES.

A) Manufacture of the addition product of polybutadiene oil and mercaptan.

1. 675 g of a polybutadiene oil with terminal hydroxyl groups, which has a molecular weight of about 1,300, a viscosity of 650 poise at 25"C and a hydroxyl number of 65 mg of KOH/g, and in which 85% of the double bonds are in the 1,2-vinyl configuration, are dissolved in 245 g of dioxane in a 2 liter four-neck round fiask equipped with a stirrer, reflux condenser, dropping funnel and internal thermometer, whilst stirring the mixture and passing nitrogen through it. A solution of 78 g of mercaptoethanol and 78 g of dioxane is added dropwise from a dropping funnel, at room temperature, in the course of 30 minutes whilst stirring; during the addition the temperature rises from 22"C to 37"C. When all has been added, the mixture is additionally stirred for 90 minutes at 70"C.

The solids content is 69.3% by weight and the content of chemically bonded sulfur is 4.15% by weight (based on solids); this corresponds to a conversion of 98%.

2. The procedure described in Example 1 is followed except that a polybutadiene oil is employed which has a molecular weight of about 1,000 and a viscosity of 22 poise and in which 45% of the double bonds are in the 1,2-vinyl configuration, 15% in the 1,4-transconfiguration, 5% in the 1,4-cis-configuration and 35% in a cydized (saturated) form.

1,000 g of this polybutadiene oil are dissolved.

in 171 g of dioxane and a solution of 156 g of mercaptoethanol, 156 g of dioxane and 98 g of glacial acetic acid is added dropwise.

After completion of the addition, the mixture is stirred for a further 90 minutes at 80"C and a colorless solution having a solids content of 75% by weight, corresponding to 100% conversion, is obtained. If no glacial acetic acid is added, the conversion is about 75%.

3. The procedure described in Example 2 is followed, but the polybutadiene used has a molecular weight of about 950 and a viscosity of 3 poise, whilst 40% of its double bonds are 1,2-vinyl structures and 60% have the 1,4-configuration.

4. The procedure described in Example 2 is followed, but the polybutadiene used has a molecular weight of about 1,500 and a viscosity of 7 poise, whilst 20% of its double bonds are 1,2-vinyl structures and 80% have the I ,4-configuration.

5. (Comparative Example).

The procedure described in Example 2 is followed, but the polybutadiene used has a molecular weight of about 1,500 and a viscosity of I poise, whilst 1% of the double bonds have the 1,2-vinyl structure. No reaction occurs under the stated reaction conditions.

B) Manufacture of the sulfonium salt.

6. 44 g of ethylene oxide gas are passed, whilst stirring, into the solution of the polybutadiene-thioether prepared according to Example 1. At the same time, 120 g of 50% by weight strength aqueous acetic acid are added dropwise. After completion of the addition, the mixture is stirred for one hour at room temperature. A colorless solution is obtained, which leaves a residue of 59.5% by weight on baking (2 hours at 1250C). On dilution with deionized water to 10% by weight solids content, a translucent solution having a bluish opalescence, a pH of 5.5 and a specific conductivity of 750 S/cm is obtained.

7. 88 g of ethylene oxide gas are passed into the solution prepared according to Example 2, and at the same time 124 g of 50% by weight strength aqueous acetic acid are added dropwise. A yellowish solution which leaves a residue of 66% by weight on baking is obtained. On dilution with water to 10% by weight solids content, a whitish, turbid dispersion which has a pH of 5.2 and a he conductivity of 620 S/cm is obtained.

C) Production of coatings.

8. The sulfonium salt produced according to Example 6 and water were mixed with melamine resins in various ratios, and the mixtures were coated as aqueous baking finishes onto phosphatized steel sheets to give a wet film thickness of about 100 pm and baked for 20 minutes at 1700 C. The melamine resins used were: Melamine resin I: a highly etherified, solvent-free hexamethoxymethylmelamine.

Melamine resin II: a butanol-etherified, medium - reactive melamine/formaldehyde condensate (dissolved in butanol/xylene), having a flow time (measured with the DIN cup No. 4 at 200 C) of from 60 to 80 seconds, and having a miscibility with gasoline greater than 1:3.

Melamine resin III: an isobutanol-etherified, highly reactive melamine/formaldehyde resin (dissolved in isobutanol), which has a cup flow time of from 360 to 440 seconds and a miscibility with gasoline greater than 1:1.5.

The properties are listed in Table 1.

9. The sulfonium salt produced according to Example 6 and water were mixed with blocked diisocyanates in various ratios, and the mixtures were coated as aqueous baking finishes onto phosphatized steel sheets and baked for 20 minutes at 170"C. The blocked diisocyanates used were: Diisocyanate I: isophorone diisocyanate blocked with diethyl malonate.

Diisocyanate II: 4,4-dicyclohexylmethane diisocyanate blocked with phenol.

The properties are listed in Table 2.

10. 134 g of the solution of the sulfonium salt described in Example 6, 36.5 g of melamine resin II (55% by weight strength in butanoljxylene) and 40 g of titanium dioxide were mixed, stirred with 500 g of deionized water and milled for 16 hours in a glass bottle on a roll stand, after having added 300 g of poreclain balls of 0.5 cm diameter to the mixture. The aqueous pigmented finish obtained was decanted and made up to 1 iiter with deionized water. A finish with a 15% by weight solids content is obtained. Phosphatized steel sheets were cathodically elec- trocoated with this finish at a voltage of 200 V for 2 minutes, and were then rinsed with water and baked for t0 minutes at L90"C.

The coating exhibited the following properties: Erichsen cupping test (DIN 53,156): > 10 Pendulum hardness (DIN 53,157). 52 seconds Gardner reverse impact (ASTM D 279469): 120 in-Ib Salt spray test 1 mm (after ten (ASTM B 117-64): days) TABLE 1 Composition in % by weight Properties Sulfonium Melamine resins Levelling Pendulum hardness Impact Experiment salt I II III 1) DIN 53,157 ASTM D 2794-69 a 100 - - - 0-1 17 (seconds) > 160 (in-1b) b 90 10 - - 1 119 (seconds) > 160 (in-1b) c 80 20 - - 1 147 (seconds) > 160 (in-1b) d 70 30 - - 1-2 102 (seconds) > 160 (in-1b) e 90 - 10 - 1 21 (seconds) > 160 (in-1b) f 70 - 30 - 1-2 139 (seconds) 80 (in-1b) g 90 - - 10 1 32 (seconds) > 160 (in-1b) h 70 - - 30 1-2 115 (seconds) 80 (in-1b) 1) The levelling was rated as follows: from 0 = very good to 5 = poor.

TABLE 2 Properties Composition Pendulum Salt spray test Sulfonium Blocked isocyan ate hardness Impact (240 h) ASTM Experiment salt I II Levelling (seconds) (in-1b) B 117-64 (mm) a 90 10 2 15 160 0-1 b 70 30 1 34 160 0-1 c 50 50 1 70 160 0-1 d 70 30 0 17 160 0-1 e 50 50 1 83 160 3

Claims

WHAT WE CLAIM IS:

1. An aqueous baking finish which contains as binder a modified polybutadiene oil having a molecular weight of from 500 to 10,000 and carrying sulfonium groups.

2. An aqueous baking finish as claimed in claim l, wherein the modified polybutadiene oil carries sulfonium groups of the general formula

where R is alkylene of 2 to 8 carbon atoms and R' is alkyl of 1 to 6 carbon atoms, hydroxyalkyl of 2 to 6 carbon atoms, aminoalkyl of 2 to 6 carbon atoms or a C,,H2,1 bridge, where n is from 0 to 6, to another polybutadiene molecule.

3. An aqueous baking finish as claimed in claim 1 or 2, wherein the modified polybutadiene oil is derived from a polybutadiene in which more than 10% of the double bonds have the 1,2-configuration.

4. An aqueous baking finish as claimed in claim 1 or 2, wherein the modified polybutadiene oil has been prepared by a process in which a polybutadiene oil having a molecular weight of from 500 to 10,000 and having more than 10% of its double bonds in the 1,2-vinyl configuration is subjected, in a first stage, to an addition reaction with a mercaptan or hydrogen sulfide, and the resulting thioether is alkylated, in a second stage, with a 1,2epoxide in the presence of an acid.

5. An aqueous baking finish as claimed in claim 1, 2 or 4, wherein the modified polybutadiene oil is derived from a polybutadiene in which more than 20% of the double bonds have the 1,2-configuration.

6. An aqueous baking finish as claimed in claim 1, 2 or 4, wherein the modified polybutadiene oil is derived from a polybutadiene in which more than 40% of the double bonds have the 1,2-configuration.

7. An aqueous baking finish as claimed in any of claims 1 to 5, wherein sulfonium groups have been added onto an average of from 2 to 50% of the double bonds of the polybutadiene.

8. An aqueous baking finish as claimed in any of claims 1 to 7, which contains from 5 to 20% by weight binder solids in water.

9. An aqueous baking finish as claimed in claim 1 and substantially as described in any of the foregoing Examples 6 to 10.

10. A method of coating an article which comprises applying to the article a coating of an aqueous baking finish as claimed in any of claims 1 to 9 and baking the coated article.

11. A method as claimed in claim 10 wherein the coating is applied by cathodic electrocoating.

12. A method as claimed in claim 11 wherein an electrocoating bath having a pH of from 5 to 7 is used.

13. A method as claimed in claim 11 or 12 wherein a crosslinking agent is present.

14. A method as claimed in claim 13 wherein the crosslinking agent is a blocked polyisocyanate.

15. A method as claimed in claim 13 wherein the crosslinking agent is a melamine/ formaldehyde or phenol/formaldehyde condensate.

16. Articles coated with coatings obtained from finishes as claimed in any of claims 1 to 9 or obtained by a method as claimed in any of claims 10 to 15.