NO783953L - ACID, WATER-BASED, THERMOUSING POLYMER COATING - Google Patents

Description

The invention relates to organic coating preparations.

The invention specifically relates to new storage-stable, acidic, water-based, thermosetting coating preparations which contain certain glycoluril derivatives as cross-linking agents.

Organic surface varnishes have been known for a number of years.

Coatings of natural materials, such as linseed oil, have gradually been replaced by synthetic polymer materials. These later materials have usually been dissolved in organic solvents and deposited on the substrate and then dried or burned in to produce the coating on the substrate. However, these coatings were not as hard or as resistant to chemicals (solvents, acids, etc.) as could be desired. Consequently, coating preparations have been developed which comprise cross-linking polymer material in combination with cross-linking agents, these preparations by heat treatment on metal or other types of surfaces, for example wood, plastic or textile surfaces, treated the polymer material to a heat-cured state so that a hard, chemically resistant coating.

In recent times, the organic solvent systems have, for ecological reasons, been largely replaced by aqueous systems comprising an aqueous dispersion of the mixed materials.

The cross-linking agents that have been used so far do not fulfill all the desired requirements, especially from an ecological point of view. The existing cross-linking agents which are based on melamine, guanamines, for example benzoguanamine, urea, etc., thus require the presence of a base, for example a water-soluble organic amine, to provide stable coating preparations. Thus, the coating materials in their normally acidic state are unstable and tend to gelatinize within a short time, i.e. several days.

In accordance with the present invention, it has emerged that a certain class of cross-linking agents which are based on glycoluril can be used for stable water-containing, acidic coating preparations whereby no addition of amine is necessary to stabilize these preparations. With the use of the glycoluril-based cross-linking agents, the water-based preparations are thus less polluting for the environment

and also use less energy as they are cross-linked at lower temperatures than the preparations that use the melamine

and urea-based preparations containing the amine.

It is generally accepted in this field that the alkoxynethyl groups in amino crosslinking agents which are based on melamine, benzoguanamine and urea, under acidic conditions hydrolyze to the N-methylol group and then undergo demethylolation and self-condensation. Because of this, coating preparations that utilize this type of cross-linking agent gel on storage within just a few days. In accordance with the present invention, however, it has now emerged that coating preparations which utilize amino crosslinking agents based on glycoluril are very stable under acidic conditions.

The polymer component used in the preparations according to the present invention are water-dispersible, non-gelled polymer materials which are also stable under acidic conditions. These polymers can either be non-ionic, for example polyether polyols, polyester polyols and polyurethane polyols, or they can be anionic, for example acrylic or vinyl polymers, prepared by emulsion polymerization using non-ionic or anionic surfactants. The pH value for such emulsions must be below 7 and preferably not above 5, and they are stable under these conditions.

The polymer materials contain reactive groups, for example one or more carboxyl groups, alcoholic hydroxyl groups or amide groups, whereby the amount of said groups present in the polymer material is usually from approx. 0.5

to 25% by weight thereof.

The polyols suitable for the coating preparations according to the invention are reaction products of ethylene oxide with bis-phenol-A (2,2-bis(p-hydroxyphenyl)propane) and hydrogenated bis-phenol-A. Also useful are block copolymers of ethylene oxide, propylene oxide, polyethylene glycol and polypropylene glycol. These polyols are non-ionic and are stable under acidic conditions.

The polymer materials include from approx. 50 to 98% by weight, based on the total weight thereof and the glycoluril cross-linking agent in the coating preparation.

Polymer materials which are not suitable for the preparations according to the invention are polymers which are substantially water-insoluble but become water-soluble or dispersible in the presence of alkali or an organic amine, for example the polymers currently used in electroplating preparations and most aqueous coatings. Water-dispersible cationic polymers and acrylic emulsions containing cationic emulsifiers are. nor suitable for coating preparations according to the invention.

The glycoluril-based cross-linking agents which are applicable in connection with the invention include non-alkylated glycoluril/formaldehyde resins, partially alkylated glycoluril/formaldehyde resins and fully alkylated glycoluril/formaldehyde resins, whereby the alkyl groups contain 1-4 carbon atoms. These glycoluril compounds or resins correspond to the general formula

where n is an integer from 1-4, m is an integer from 0 to 2 and each R is, independently of one another, hydrogen or an alkyl group of 1-4 carbon atoms. The -(CH20R), -H and -CH2 groups are thus bound to the individual N atoms in the glycoluril ring whereby at least one and up to 4 of the nitrogen atoms have a (-CH2OR) group bound to them. The -CH2 group is a bridging group that connects to another glycoluril ring similar to that shown in parentheses. \

The glycoluril derivatives may contain from 1 to 4 methylol groups or they may contain from 1 to 4 alkoxymethyl groups or any combination of from 1 to 4 methylol groups and alkoxymethyl groups. When there is only one methylol group or only one alkoxymethyl group, then at least one methylene bridge must be present.

Among the glycoluril derivatives that can be used as cross-linking agents in the preparations according to the invention are dimethylol glycoluril, trimethylol glycoluril, tetramethylol glycoluril. monomethyl ether of dimethylol glycoluril, dimethyl ether of dimethylol glycoluril, trimethyl ether of tetramethylol glycoluril, tetramethyl ether of tetramethylol glycoluril, tetrakisethoxymethyl glycoluril, etc. If desired, mixed ethers can be used, for example diethyl, dimethyl ethers of tetramethylol glycoluril. The cross-linking agents can also be used individually or in combination, although it is usually preferred to use them individually. The amount of glycoluril derivative used in the preparations according to the invention can be varied between approx. 2 and approx. 50% by weight,

calculated on the total dry weight of the glycoluril derivative and the water-dispersible, non-gelled, non-self-crosslinking polymeric material. However, it is preferred to use the glycoluril derivative on a weight% basis varying between approx. 10 and 40%.

It will therefore obviously be present in the preparation between approx. 50 and approx. 98% by weight of the non-self-crosslinking polymer material and preferably between approx. 60 and 90% by weight of said polymer material.

An essential component of the preparations according to the invention is an acid catalyst. This catalyst is used in an amount that varies from approx. 0.05 to approx. 5.0% by weight, based on the total solids weight of the polymer material and the glycoluril cross-linking agent, although the preferred amount is from about

0.1 to 2.5%. Among the preferred acid catalysts that can be used in the preparations according to the invention are: trismethyl-sulfonylmethane, p-toluenesulfonic acid, n-dodecylbenzenesulfonic acid, naphthalenesulfonic acid, etc. The catalytic activity for an acid can even be developed in the coating preparations according to the invention by incorporating sulfonic acid groups in the polymeric material. This can be achieved by copolymerizing from approx. 0.1 to approx. 5.0% (based on the total monomer weight) of such a monomer as 2-sulfoethyl methacrylate, styrenesulfonic acid, etc. It is also possible to use alkyl esters of phosphoric acid or alkylphosphonic acids as acid catalyst in the coating preparations according to the invention.

Weaker organic acids, for example formic acid, acetic acid, phthalic acid and the like, can be used, but are not preferred as they are not effective in promoting the cross-linking reaction at temperatures below 175°C for a reasonable period of time,

for example less than approx. 30 minutes.

Inorganic acids, such as nitric acid, sulfuric acid, phosphoric acid, hydrohalogen acids, Lewis acids, etc. can also be used.

In what follows, the invention will be illustrated by means of examples.

Preparation of tetramethylol glycoluril

To a three-necked flask fitted with a stirrer, thermometer and condenser was added 688 parts (10 mol) of aqueous formaldehyde (44%), and the pH was adjusted to 8.7 with 22 parts of 0.5n NaOH- solution. To this was added 284 parts (2 mol) of glycoluril at 40°C. During the reaction, the temperature was allowed to rise to 55°C. At this stage, most of the glycoluril went into solution. After approx. After 15 minutes the pH was adjusted to 8.0 with 5 parts of 0.5N NaOH. A clear pale yellow solution was obtained.

The clear solution was distilled at 50°C under reduced pressure to remove water, until the contents of the flask amounted to approx. 640

parts. The syrupy mass in the flask was poured into 800 parts methanol. The white crystalline precipitate was filtered and dried. The total yield of tetramethylol glycoluril was 483 parts (92% yield) and melting point 132-136°C.

Preparation of tetrabutoxymethyl glycoluril

To a suitably equipped three-necked flask was added 1000 parts (13.5 moles) of n-butanol and 7.0 parts of concentrated nitric acid and 20 parts of water. To this mixture was added 200 parts of tetramethylol glycoluril (0.76 mol), and the reaction mixture was stirred at 40°C for 2 hours. The reaction mixture became a clear solution. It was then distilled at reduced pressure between 45 and 50°C to remove the butanol/water azeotrope mixture. After 260 parts of n-butanol/water mixture had been removed, 260 parts of n-butanol were added to the clear solution, and the reaction temperature was lowered to 2<L>2-25°C. The solution was neutralized with 10% caustic to pH 9-10', followed by removal of n-butanol under reduced pressure. The remainder was filtered with filter aid. The resulting water white syrupy mass had a Gardner-Holdt viscosity Y-Z (25°C). Solid pan substances (pan solids). was 95% (2 hours at 105°C) and solid foil substances (foil solids) were 97% (45 minutes at 45°C). Gel phase chromatography shows that the product was 85% monomer.' NMR

for the product confirms that the structure for the monomer is tetrabutoxymethylglycoluril.

Preparation of partially methylated glycoluril

Add 950 to a suitably equipped wooden flask

parts (30 moles) of methanol and 40 parts of concentrated hydrochloric acid. 262 parts (1 mol of tetramethylol glycoluril) are added to this mixture, and the reaction mixture is stirred at 25-30°C. During approx. 15-20 minutes, all tetramethylol glycoluril goes into solution.

After half an hour, the reaction mixture is neutralized with 140

parts sodium bicarbonate and 20 parts sodium carbonate at 22-23°C. The pH value after neutralization is approx. 8. The salt is filtered off. The filtrate is concentrated at 60°C under reduced pressure. The dividend

of the syrupy product after filtering the salt is 290 parts, which is diluted to 90% solids with "Cellosolve". The product's properties are as follows: foil solids = 91.4% pan solids = 82.2%; Gardner Holdt viscosity (25°C) = Z^. IR analysis of the product shows that the methylated product has a significant amount of unreacted methylol groups.

Preparation of methylated ethylated glycoluril

180 parts of formalin (44%) adjusted to pH 7.5-8.0 and 85.2 parts of glycoluril are added to a suitably equipped wooden flask. The mixture is heated to 80°C until it becomes clear. The clear solution is cooled to 60°C, and the pH value is adjusted to 7.5. The clear, pale yellow solution is concentrated by distilling off 80 parts of water under reduced pressure. To the resulting syrupy mass in the flask is added 96 parts methanol and 3.6

parts 70% nitric acid. The reaction mixture is kept at 55°C for 30 minutes and then cooled to 25°C. To this mixture are added approximately 8.5 parts of a 20% caustic solution to neutralize the reaction mixture. The unreacted methanol and residual water is removed from the mixture at 100°C under reduced pressure. To the resulting syrupy mass are added 83 parts ethanol and 2.4 parts 70% nitric acid. The reaction mixture is kept at 70°C for 30 minutes with constant stirring. The mixture is cooled .

neutralized iried 20% caustic and concentrated, under reduced pressure to remove unreacted ethanol and water formed during the reaction. The resulting product, methylated ethylated tetramethylol glycoluril, is then filtered. The clear, viscous product is diluted with 10 parts of n-butanol to 95% solids. Based on NMR analysis, the proportion of -.methoxymethyl- to ethoxymethyl groups in the product compound is 2, 2-1,8.

Paint recipes

Example 1

A clear, water-based coating was prepared by mixing 30 parts of a commercially available diol, a reaction product of 1 mole of bisphenol-A (2,2-bis(p-hydroxyphenyl)propane), and 6 moles of ethylene oxide, 35 parts of 60 100% solution of tetramethylol glycoluril, 5 parts ethanol and 0.5 part 40% solution of p-toluenesulfonic acid in isopropanol. The aqueous coating composition had a pH value. of 1.9 5 and a Gardner-Holdt<y>viscosity of K-L after "24 hours. When this coating preparation was aged at 55°C for 17 days, the viscosity was N. Films were cast on aluminum plates and -<y>arm treated at 93°C and 121°C respectively for 20 minutes.The film properties were as follows:

Comparative example 1( a)

A clear, water-based coating was prepared by mixing 30 parts of the diol from example 1, 20 parts of hexamethoxymethylmelamine, 19 parts of water, 5 parts of ethanol and 0.5 part of 40% p-toluenesulfonic acid in isopropanol . The aqueous coating composition had a pH of 2.75 and a Gardner-Holdt viscosity of E-F after 24 hours. When the coating composition was aged at 55°C

for 7 days, it gelled. The film that was cast from the non-gelled original preparation on aluminum plates was burned in at 93°C resp. 121°C for 20 minutes. The film properties. was as follows:

Comparative example 1( b)

A clear, water-based coating was prepared by mixing 30 parts of the diol from example 1, 20 parts of a methylated urea/formaldehyde resin, 15 parts of water, 5 parts of ethanol, 0.5 parts of a 40% solution of p-toluenesulfonic acid in isopropanol . The aqueous coating composition had a pH of 2.9 and a Gardner-Holdt viscosity of B-C after 24 hours. When the coating composition was aged at 55°C for 17 days, it gelled. The films that were cast from the non-gelled original preparation on aluminum plates were burned in at 93°C resp. 121°C for 20 minutes, the film properties were as follows:

From the above two comparison examples appear

it is very clear that coating preparations containing jnelamine or urea-based cross-linking agents have very limited storage resistance under acidic conditions, while the glycoluril-based preparation is very stable and has good storage resistance.

The stabilities of the coating preparations which were prepared with the diol according to example 1 and different contents of tetramethylol glycoluril and the like. preparations with hexamethoxymethyl-' melamine and methylated urea/formaldehyde resins are shown on

the accompanying drawing. The drawing thus shows curves for viscosity (in centipoise) as a function of time (in 24 hours) for preparations A, B, C and D containing 20, 30, 40 resp. 50% tetramethylol glycoluril and before preparations E, F and G also for preparation H which contains 40% of the methylated urea/formaldehyde resin. It appears that the tetramethylol glycoluril-based coatings show a certain increase in viscosity from the beginning and then remain fairly constant for an unlimited time (curves A,

B, C and D). In the case of the melamine resin, however, the viscosity rises very quickly; and the preparations gel in: the course of several days (curves E, F and G), The coating containing urea^

the resin becomes, in that it is stable for approx. 2 weeks, in hay

degree viscous at this point and gels (curve H) r

Example 2

A clear, water-based coating was prepared by mixing 126 parts of the diol from example 1, 56.8 parts methylated ethylated tetramethylol glycoluril, 3.6 parts 70% n-dodecylbenzenesulfonic acid solution in isopropanol, 9 parts ethanol and 0.1 part surfactant silicone compound. The pH value of the preparation was 1, and the Gardner-Holdt viscosity was N. After storage i.

At 1 week at 55°C the coating composition had a pH of 1.0 and a Gardner-Holdt viscosity of W-X. A 0.0 25 mm film on aluminum

plates cured at 125°C for 2 minutes had a pencil hardness of 2B-B and a MEK double rub resistance of 200. The same coating preparation, stored for 3 weeks at 55°C, had a pH of 2.5 and a Gardn er-Holdt viscosity of X-Y .The cured film of 0.025 mm thickness under the same conditions had pencil hardness 2B-B and more than 200+ MEK double rubbing resistance.

Example 3

A coating preparation similar to that according to Example 2 was prepared, but 108 parts of the same diol and 75f8 parts

of the same cross-linking agent. was applied. The pH value of the preparation was 1, and a Gardner^Holdt^ viscosity of N-O was obtained. The films were cast on aluminum plates and cured

125°C for 20 minutes'. The 0.0 25 mm thick film had a pencil hardness of H-2H and a MEK double rub resistance of more than 200+. After aging for 3 weeks at 55°C, the coating preparation had a pH value of 2.4 and a Gardner-Holdt viscosity of Z., - Z^. Films cast on aluminum foil of the aged preparation were cured at 125°C for 20 minutes. The 0.0 25 mm thick film had a pencil hardness of F-H and a MEK double rub resistance of

more than 200+.

Example 4

An unpigmented coating preparation was prepared by mixing 320 parts of a commercially available crosslinkable, aqueous, acidic acrylic emulsion containing hydroxyl groups with approx. 40% solution of p-toluenesulfonic acid in isopropanol. The aqueous coating composition had a pH value of 2.1 and a. Brookfield site of 215 cP.

Films cast on aluminum sheets were cured at 100°C and 125°C for 20 minutes. The film properties were as follows:

The properties of films cast on aluminum plates after aging the preparation for 3 weeks at 55°C were as follows:

The aged coating composition had a pH-<y>erdi. of 2.9 and a Brookfield viscosity of 375 cP,

Claims (6)

1. Stable, acidic, water-based, thermosetting polymer coating composition, characterized in that it comprises (1) a polymeric material selected from (a) a nonionic polyether polyol, polyester polyol or polyurethane polyol and (b) an anionic polymer of an acrylic - or vinyl monomer prepared by the emulsion process using a nonionic or anionic surfactant, (2) a glycoluril compound or mixture of glycoluril compounds corresponding to the general formula wherein n is an integer from 1 to 4, m is an integer from 0 to 2 and each R is, independently, a hydrogen atom or an alkyl group of 1-4 carbon atoms, and (3) an acid catalyst; whereby the proportions of said polymer material in the preparation are from approx. 50 to 98% and consequently from approx. 2 to 50% of said glycoluril based on the total weight of the two in the preparation and the proportion of catalyst present is from approx. 0.05 to 5.0% based on the total weight of the polymer material and the glycoluril compound. 2. Preparation as stated in claim 1, characterized in that the polymer material is a diol which forms the reaction product of 1 mole part bisphenol-A and approx. 6 mole parts of ethylene oxide. 3. Preparation as stated in claim 1, characterized in that the polymer material is an aqueous, acidic emulsion polymer. 4. Preparation as stated in any one of claims 1 to 3, characterized in that the glycoluril compound is tetramethylol glycoluril. 5. Preparation as specified in any of the claims 1 to 4, characterized in that the glycoluril compound is methylated ethylated tetramethylol glycoluril. 6. Preparation as stated in any one of claims 1 to 5, characterized in that the acid catalyst is p-toluenesulfonic acid.