CA1317399C

CA1317399C - Powdered lacquer, its manufacture and use

Info

Publication number: CA1317399C
Application number: CA000542107A
Authority: CA
Inventors: Jorn-Volker Weiss
Original assignee: Huels AG
Current assignee: Huels AG
Priority date: 1986-07-17
Filing date: 1987-07-15
Publication date: 1993-05-04
Anticipated expiration: 2010-05-04
Also published as: US4788076A; NO873003L; AU588203B2; EP0253101B1; NO873003D0; FI85715C; BR8703719A; AU7573987A; KR880001777A; DE3784396D1; FI85715B; FI873080A0; EP0253101A3; DE3624177A1; EP0253101A2; KR950006070B1; FI873080A; JPS6323977A

Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed are powdered lacquers based on a mixture of epoxide compounds and optionally polyesters as well as salts of primary C4-18 aliphatic and cycloaliphatic-diamines with phosphoric acid and/or sulphuric acid as a hardener. The lacquer also contains 1,4-diazabicyclo[2.2.2]octane. The salts can be prepared using easily available acids and diamines. The lacquers, when hardened, give flat finished coatings.

Description

- 1 - 23443-34~

The invention relates to powdered lacquers based on a mixture of epoxide compounds and salts of inorganic acids with primary diamines as hardeners and optionally polyesters.
There is great need in industry for powdered lacquers of all kinds. This is primarily due to the fact that solvents can be avoided in the application of powdered lacquers, and only small losses occur in use. Powdered lacquers are economical and not environmentally damaging.
Most known lacquers yield glossy finishes. Recently, however, there has been greater interest in flat finishes because they require significantly less cleaning than glossy finishes. In addition, it is often more advantageous to produce flat finishes for safety reasons.
The simplest method of obtaining a flat finish is to admix smaller or larger quantities of fillers, depenZing on the degree of flat effect desired, such as chalk, finely ground silicon dioxide, barium sulfate, or incompatible additives such as wax, or cellulose derivatives. ~owever, these additives result in lacquer films with poor technical characteristics.
German Patentschrift 23 24 696 discloses a method for the manufacture of coverings with a flat finish in which a special hardener - a salt of acyclic amidine with a certain polycarboxylic acid - is used. In fact, due -to its exceptional technical characteristics only this method has been able to succeed in the marketplace. The method has since been improved several times (see German Offenlegungsschrifts 30 26 455, and 30 26 456 and German Patent Application P 35 ll 998.5 of April 2, 1985 , 1 31 73qq "Hardeners for Powdered Covering Agents Based on Epoxy Resins").
Nevertheless, this method has some basic disadvantages.
The required amidines are expensive and not always available in the necessary quantities. It would be desirable if more readily available basic compounds, like straight liquid diamines, could be used in a suitable form as hardeners for epoxide resins. Salts of these amines with usual acids, however, in contrast to the amidine salts, are so stable that under the baking conditions common in the powdered lacquer industry, no adequate hardening of the epoxide resins takes place.
An aqueous coating system obtained through a reaction of a polyol-polyether epoxide with phosphoric acid anhydride is des-cribed in European Patent No. 0 082 196. An aqueous system of this type does not suggest powdered lacquers and would not help in the search for lacquer systems which produce a flat effect.
It is attempted in the present invention to provide a powdered lacquer which is stable in storage and yields a flat finish on hardening using hardeners which are capable of use both with epoxide resins as well as with the so-called hybrid system, i.e. mixed systems of epoxide and polyester resins and which are easy to obtain and manufacture, and are available in practically any quantities desired.
The present invention provides a powdered lacquer which is stablein storage, containing (a) at least one epoxide-containing compound having on the average more than one epoxide group per molecule, (b) a nitrogen-containing salt which is prepared from phosphoric acid or sulfuric ~ 3173~'~

acid and a C4 18 aliphatic or cycloaliphatic primary diamine, and (c) 1,4-diazabicyclo~2.2.2]octane. 'rhe nitrogen-containing salt is used as a hardener and is contained in an amount sufficient to harden the epoxide-containing compound upon baking. 1,4-Diazabicyclo~2.2.2~octane is used as an accelerator and is con~ained in an amount effective to accelerate the hardening of the epoxide-containing compound.
Another aspect of the present invention provides a process for producing the powdered lacquer. This process comprises:
~ i) mixing at least one epoxide-containing compound, a nitrogen-containing salt, and 1,4-diazabicyclo[2.2.2]octane, wherein the nitrogen-containing salt is prepared from phosphoric or sulfuric acld and a C4 18 aliphatic or cycloaliphatic primary diamine; and (ii) extruding the mixture at a temperature between about 160-240C; cooling the extrudate, and grinding the cooled extrudate.
A further aspect of the present invention provides a method for the manufacture of a flat finish coating. This method comprises the steps of:
(a) applying the powdered lacquer to the substrate to coat the substrate; and (b) heating the coa~ed substrate at a temperature about 160-240aC for about 5 35 minutes.

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- 3~ - ~3443-348 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The advantage of the powdered lacquers according to the invention is primarily that one need not rely on special nitrogen-containing compounds and adducts, which first must be synthesized.
Rather one can employ compounds commonly in use which are commercially available.
The expoxide resins used in the present invention have ~-, 131739't more than one epoxide group per molecule on the average. They have a melting point above 40~C. The epoxide resins can be satura-ted or unsaturated, aliphatic, cycloaliphatic, araliphatic or heterocyclic.
~referred epoxide resins include resins made from (i) epoxides of hydrocarbons containing at least two unsaturated bonds, such as vinylcyclohexene; dicyclopentadiene;
1,3-cyclohexadiene; 1,4-cyclododecadiene; cyclododecatriene;
isoprene; 1,5-hexadiene; butadiene; polybutadiene; divinYlbenzene etc;
(ii) epoxy ethers (e.g., glycidyl ethers) of polyvalent alcohols (i.e., polyols), such as ethylene glycol, propylene glycol, butylene glycol, glycerin, pentaerythritol, sorbitol, polyvinyl alcohol and thiodiglycol;
(iii) epoxy ethers (e.g., glycidyl ethers) of polyvalent phenols, such as resorcinol, hydroquinone, bis-(4-hydroxyphenol)-methane, bis-(4-hydroxy-3,5~ichloro~heny~-methane, 1,1-bis-(4-hydroxyphenyl)-ethane, 2,2-kis-(4-hydroxyphenyl)-propane, 2,2-bis-(4-hydroxy-3-methylphenyl)-propane, 2,2-bis-(4-hydroxy-3,5,5-trichlorophenyl~-propane, bis-(4-hydroxyphenyl)-phenylmethane, bis-(4-hydroxyphenyl)-diphenylmethane, bis-(4-hydroxyphenyl)-cyclohexylmethane, 4,4'-dihydroxybiphenyl, 2,2'dihydroxybiphenyl, and (iv) N-containing epoxides, such as N,N-diglycidylaniline, N,~'-dimethyldiglycidyl-4,4'-diaminodiphenylmethane, and trigly-cidylisocyanurate.
Epoxides based on bisphenol A with an epoxide equivalent of 500 to 2,000 and a softening point of 70 to 140~C have proven to be particularly suitable.
Suitable polyesters, added in quantities up to 45%
relative to the weight of the epoxide compounds, include oligo-esters of aliphatic, cycloaliphatic or aromatic polycarboxylic acids with aliphatic or cycloaliphatic diols, wherein each components have from 4 to 18 carbon atoms.
Aliphatic, cycloaliphatic or aromatic dicarboxylic or polycarboxylic acids, on the one hand, and aliphatic or cyclo-aliphatic diols on the other hand, are used to manufacture theoligoesters. The polycarboxylic acids and diols contain from 4 to 18 carbon atoms. ~n the case of diols, individual carbon atoms can also be replaced by oxygen atoms. Oxygen substitution is such that an oxygen atom must be separated in the chain from a hydroxyl group and/or from an additional oxygen atom by at least 2 carbon atoms.
Examples of dicarboxylic acids include l,5-naphthalene-dicarboxylic acid, 4,4'-benzophenone-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, trimethyl adipic acid, azelaic acid, sebacic acid, decanoic acid, dodecanoic acid, fumaric acid, maleic acid and isophthalic acid. Examples of polycarboxcylic acids having three or more carboxyl groups include 1,3,5-benzene-tricarboxylic acid, 1,2,4-benzene tricarboxylic acid, 1,2l3-benzene-tricarboxylic acid, butanetetracarboxylic acid, cyclopent-anetetracarboxylic acid, pyromellitic acid, 1,2,3,4-benzenetetra-carboxylic acid~ 1,2,3,5-benzene-tetracarboxylic acid, and 3,4-dicarboxyl-1,2,3,4-tetrahydronaphthalene-1-succinic acid.

- 6 - ~3443-348 Examples of suitable diols include 1,3-butanediol, 1,4-butanediol; 2,3-butanediol; 1,5-pentanediol; 2,2-dimethyl-1,3-propanediol: 1,6-hexanediol; and 2,5-hexanediol as well as 1,12-dodecanediol.
The carboxyl-group-containing oligoesters have prefer-ably an acid number from about 30 to 150, particularly from 40 to 100. The softening point generally lies in the range from 40 to 110C, and preferably in the range from 60 to 90C. Typically, their average molecular weight lies below 2,500.
The preparation of oligoesters is known (Sorensen and Campbell - "Preparative Methods of Polymer Chemistry," Inter-science Publishers Inc., New York, 1961, pp. 111-127). Generally the manufacture takes place at temperatures up to 200C by conden-sation in the melt. The course of the reaction can be followed by titration of the excess carboxyl groups, so that the end of the reaction can be easily determined.
The amount of the epoxy-containing compound (plus the oligoester if the latter is also employed) in the lacquer compos-ition may vary within a wide range. A preferred amount is up to 90%. When a relatively large amount of pigment or filler is employed, a preferred amount i5 about 30 - 80~ by weight.
Sulfuric acid or phosphoric acid as well as mixtures thereof are used as inorganic acids, with phosphoric acid being preferred.
The primary diamines have an aliphatic or cycloaliphatic structure with 4 to 18 carbon atoms. Particularly suitable are (i) derivatives of cyclohexylamine, containing an additional 1 31 73q9 - 7 - 23443-34~

aliphatic or cycloaliphatic amino group, particularly isophoron-diamine (IPD), and (ii) aliphatic diamines with the basic structure of hexa-methylenediamine, which can also be substituted with one or more lower alkyl groups, particularly 2,2,4- and/or 2,4,4-trimethyl-hexamethylene diamine (TMD).
The manufacture of the salts preferably takes place by reacting the inorganic acids with the above-mentioned diamines in aqueous solution at a temperature of about 50C. The quantity of the acid is adjusted in such a manner that at least one, and preferably at most two acid groups, react with one amino group.
The salt of phosphoric and/or sulfuric acid and the primary diamine is used as a hardener according to the invention.
The amount of the salt may vary depending on various conditions.
A preferred amount is about 2 to 15% relative to the epoxide-containing compound or 1 t 8% relative to the total weight of the formula.
The powdered lacquers according to the invention also contain 1,4-diazabicyclo[2.2.2]octane, preferably in a quantity of 0.2 to 4% relative to the weight of the epoxide-containing com-pound or 0.1 to 2%, relative to the total weight of the formula.
In the manufacture of the powdered coating agents, additional common additives, such as flow enhancers, pigments, dyes, fillers, catalysts, thixotropic agents, and UV and oxidation stabilizers can also be used. The quantity of these additives can vary within a wide range, relative to the quantity of the binding agent. In one preferred embodiment the lacquer composition 1 31 73~

- 8 - 23443-3~8 contains a pigment or filler (such as titanium dioxide) up to about 60% by weight of the composition, more preferably 20 to 60 by weight.
The manufacture of the coating takes place in such a manner that the individual component.s (epoxide resins, hardeners and, if desired, additives) are ground, mixed and extruded at from 90 to 110C. After extrusion, the mixture is cooled and ground to a grain size of less than 100 microns.
The application to the substrate can take place accord-ing to known methods, such as electrostatic powder spraying, whirlsintering or electrostatic whirl sintering.
Subsequently, the applied coating is hardened by baking for 5 to 35 minutes in a temperature range from 160 to 240 C, preferably for 10 to 20 minutes from 180 to 220C.
Any substrate that can withstand the above-mentioned hardening temperatures is suitable for being coated with the powdered coating agents according to the invention, for example metals, glasses, ceramics or plastics.
The coatings manufactured with the aid of the hardeners according to the invention have a uniform structure and a flat finish. According to the testing method of Gardner (at 60) finish grades as low as 14 can be attained. In an unexpected manner, other technical lacquer characteristics remain at a high level.
The technical lacquer characteristics were determined with the aid of the following testing methods:
- Cupping (in mm) according to Erichsen (DIN 53 156) t31739'3 - 9 - 23~43-348 - Ball Impact ~est acco~ding to Gardner (ASTM D 2794) - Grid Test (DIN 53 151) - Finish Degree according to Gardner at 60 (ASTM D 523) Other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof.
EXAMPLES
The manufacture of 200 g of hardener was carried out in a 1 liter 3-neck flask, equipped with a mechanical stirrer, a condenser, a powder funnel and a heating mantle.
The water-soluble polyamines (e.g. IPD, TMD) were dis-solved in 400 ml of completely deionized water. Under stirring, the acids were then added dropwise. Finally, the reaction mixture was stirred for 1 hour at 50C.
The resulting salt was isolated by removing the solvent in a rotary evaporator and the solid residue was subsequently dried under a vacuum at 100C for five hours.
Manufacture of the Powdered Lacq~
The salts used as hardeners were firstground to a very fine powder with the aid of a rapid rotory mill. Subsequently, this powder was roughly mixed with the other powdered lacquer components (epoxide resin and optionally polyester, titanium dioxide, 1,4-diazabicyclo[2.2.2]octane, flow agents in the form of a 10~ master batch, etc.) in a premixer and then extruded in a Buss-cokneader at 100C. The cooled extrudate was ground to a fine powder, whereby the large components greater than 100 microns 13173q9 were separated out with a sieve. The thus-obtained powder was applied to sheet steel in an electrostatic powder spraying system at a voltage of 60 kv and baked in an air drying cabinet at temperatures between 180 and 220C.
The following hardening salts were employed:

No Pol amine/inor anic acid mol ratio Y g 2 TMD/H3PO4 2 : 3 3 TMD/H3po4 3.5 : 1.7 IPD/H3PO4 2 : 3 6 IPD/H3PO4 3 : 2 7 IPD/H3PO4 3 : 2.1 8 TMD/IPD/H3PO4 0.5 : 1.5 : ~.55 9 TMD/IPD/H3PO4 1.5 : 1.5 : 1.7 IPD/H3SO4 1.5 In the manufacture of the powdered lacquers, the following epoxide resins and COOH-group-containing polyester were employed:

1 31 73q~

- 11 - 234~3-348 Epoxide resin 1 (EP 1) EP equi~alent weight 850 - 940 EP-value 0.10 - 0.11 Softening range 80 - 100C

Epoxide resin 2 (EP 2) EP-equivalent weight 730 - 840 EP-value -- 0.12 - 0.13 Softening range 94 - 106 Polyester resln 1(PE 1) Acid number 47 - 57 Glass transition temperature 58C

Epoxide resin 1 is a product of the company Shell A.G., Hamburg, and can be obtained commercially under the name EpikoteX 1004. Epoxide resin 2 is a product of the firm Dow Chemical Co., with designation DER~
663.
Polyester resin 1 is a product of the firm DSM
Resins, Zwolle, Netherlands, with the designation URALAC~ 2228.

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t 3 1 739~3 Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope o the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A powdered lacquer which is stable in storage, comprising:
(a) at least one epoxide-containing compound, having on the average more than one epoxide group per molecule;
(b) a nitrogen-containing salt in an amount effective to harden the epoxide-containing compound upon baking, wherein the salt is prepared from an acid and a base, the acid being selected from the group consisting of phosphoric acid and sulfuric acid and the base being selected from the group consisting of primary C4-18 aliphatic and C4-18 cycloaliphatic C4-18 diamines; and (c) 1,4-diazabicyclo[2.2.2]octane in an amount effective to accelerate the hardening of the epoxide-containing compound.

2. The lacquer of claim 1, wherein the epoxide-containing compound has a melting point above 70°C.

3. The lacquer of claim 1, wherein the epoxide-containing compound is an epoxide resin comprising epoxides selected from the group consisting of epoxides of multiply unsaturated hydrocarbons, epoxy ethers of polyvalent alcohols, epoxy ethers of polyvalent phenols and nitrogen-containing epoxides.

4. The lacquer of claim 1, further comprising a polyester.

5. The lacquer of claim 4, wherein the polyester is present in an amount of up to 45 wt.% relative to the epoxide-containing compound.

6. The lacquer of Claim 4, wherein the polyester is prepared from a polycarboxylic acid and a diol, wherein the polycarboxylic acid is a member selected from the group consisting of C4-18 aliphatic, C4-18 cycloaliphatic and C4-18 aromatic polycarboxylic acids, and wherein the diol is a member selected from the group consisting of C4-18 aliphatic and C4-18 cycloali-phatic diols.

7. The lacquer of Claim 4, wherein the polyester has an acid number about 245-265 and a softening point in the range of 40-110°C.

8. The lacquer of Claim 7, wherein the polyester has an acid number between about 250-260 and a softening point in the range of about 60-90°C.

9. The lacquer of Claim 4, wherein the polyester has an average molecular weight below 2,500.

10. The lacquer of Claim 1, wherein the base is a derivative of cyclohexylamine.

11. The lacquer of Claim 10, wherein the base is isophorone diamine.

12. The lacquer of Claim 1, wherein the base is an alkyl-substituted hexamethylene diamine.

13. The lacquer of Claim 12, wherein the diamine is 2,2,4-trimethylhexamethylene diamine or 2,4,4- trimethylhexamethylene diamine.

14. The lacquer of Claim 1, further comprising additives selected from the group consisting of flow enhances, pigments, dyes, fillers, catalysts, thixotropic agents, UV stabilizers and oxidation stabilizers.

15. The lacquer of Claim 1, wherein the lacquer has a grain size smaller than about 100 micron.

16. A method for the manufacture of a flat finish coating on a substrate, comprising the steps of:
(a) applying the powdered lacquer of claim 1 to the substrate to coat the substrate; and (b) heating the coated substrate at a temperature about 160-240°C for about 5-35 minutes.

17. The method of Claim 16, wherein the heating step is conducted at a temperature about 180-220°C for 10-20 minutes.

18. The method of Claim 16, wherein the applying step is performed by electrostatic powder spraying, whirl sintering, or electrostatic whirl sintering.

19. The method of claim 16, wherein the substrate is a member selected from the group consisting of metals, glasses, ceramics and plastics.

20. A process for producing a storage-stable powdered lacquer which comprises:
(i) mixing at least one epoxide-containing compound, a nitrogen-containing salt in an amount effective to harden the epoxide-containing compound upon baking, and 1,4-diazabicyclo[2.2.2]octane in an amount effective to accelerate the hardening of the epoxide-containing compound, wherein the nitrogen-containing salt is prepared from phosphoric or sulfuric acid and a C4-18 aliphatic or cycloaliphatic primary diamine; and (ii) extruding the mixture at a temperature between about 160-240°C; cooling the extrudate, and grinding the cooled extrudate.

21. The method of claim 20, further comprising adding an additive selected from the group consisting of flow enhancers, pigments, dyes, fillers, catalysts, thixotropic agents, UV
stabilizers and oxidation stabilizers during the mixing step.

- 18a - 23443-348

22. The method of claim 16, wherein the ground extrudate has a grain size less than 100 micron.

23. A storage-stable powdered lacquer, which comprises:
(a) an epoxy resin having a melting point 70 to 140°C and based on an epoxy ether of a polyvalent phenol, the epoxy resin optionally being replaced up to 45% by weight thereof with a carboxyl group-containing oligoester derived from a C4-18 aliphatic, cycloaliphatic or aromatic polycarboxylic acid and a C4-18 aliphatic or cycloaliphatic diol;
(b) 2 to 15% by weight based on the component (a) of a salt prepared from an acid and a base, wherein the acid is phosphoric acid or sulfuric acid and the base is a C4-18 aliphatic or cycloalphatic primary diamine; and (c) 0.2 to 4% by weight based on the component (a) of 1,4-diazabicyclo[2.2.2]octane; and which may further comprise:
(d) up to about 60% by weight based on the lacquer of a pigment or filler.

24. The lacquer of Claim 23, wherein the component (b) is a salt of phosphoric acid and the primary diamine, the molar ratio of the phosphoric acid/the primary diamine being from about 3.5/1.7 to about 2/3.

25. The lacquer of Claim 23, wherein the component (a) is an epoxy resin based on bisphenol A having an epoxide equivalent of 500 to 2,000 and a softening point of 70 to 140°C or a combination thereof with up to 45% by weight (based on the epoxy resin) of the carboxyl group-containing oligoester having an acid number about 30 to 150, a softening point of 40 to 110°C and an average molecular weight below 2,500.

26. The lacquer of Claim 23, 24 or 25, wherein the primary diamine used for producing the component (b) is a derivative of cyclohexylamine containing an additional aliphatic or cyclo-aliphatic amino group.

27. The lacquer of Claim 23, 24 or 25, wherein the primary diamine used for producing the component (b) is an aliphatic diamine having a basic structure of hexamethylenediamine which may be substituted with one or more lower alkyl groups.

28. The lacquer of Claim 23, wherein the primary diamine used for producing the component (b) is isophorondiamine or 2,2,4-or 2,4,4-trimethylhexamethylene diamine.

29. The lacquer of Claim 25, wherein the component (b) is a salt of phosphoric acid and the primary diamine, the molar ratio of the phosphoric acid/the primary diamine being from about 3.5/1.7 to about 2/3.

30. The lacquer of Claim 29, wherein the primary diamine used for producing the component (b) is isophorondiamine or 2,2,4-or 2,4,4-trimethylhexamethylene diamine.

31. The lacquer of Claim 25, 29 or 30, which comprises about 30 to 80% by weight based on the lacquer of the component (a) and 20 to 60% by weight based on the lacquer of titanium dioxide as the pigment.