WO2001094463A1

WO2001094463A1 - Powder coating of epoxy resin, carboxylic acid-terminated polyester, styrene-maleic

Info

Publication number: WO2001094463A1
Application number: PCT/US2001/017671
Authority: WO
Inventors: Jennifer Havard
Original assignee: Sartomer Technology Company, Inc.
Priority date: 2000-06-02
Filing date: 2001-06-01
Publication date: 2001-12-13
Also published as: JP2003535945A; AU2001266639A1

Abstract

The low gloss in a powder coating comprising an epoxy resin, a carboxylic acid-terminated polyester and a styrene-maleic anhydride resin is imparted by the inclusion of a curing catalyst such as an onium compound.

Description

Powder Coating of Epoxy Resin, Carboxylic Acid-Terminated Polyester, Styrene-Maleic

This invention relates to low gloss epoxy-polyester hybrid powder coating paints, particularly to methods for providing such low gloss paints by incorporating a styrene maleic anhydride (ASMA@) resin and a curing catalyst into the powder coating paint formulation.

SMA resins have been used as additives in epoxy-polyester hybrid powder coatings but the necessity of also adding a curing catalyst in order to achieve low gloss has not been previously appreciated. In fact, in a paper on "Gloss and Texture Modification of Thermoset Powder Coatings with new Low Molecular Weight Styrene Maleic Anhydride Copolymers" presented by A. Tedoldi at the Water-Borne, High Solids, and Powder Coatings Symposium on February 9-11, 1994, the author stated that powder coatings based on epoxy/polyester hybrids (containing SMA resin additives) "do not require any type of curing agent; resins react with each other to form binder."

"Low gloss" finishes are also frequently referred to as matt finishes and are generally defined as those finishes which have a gloss of less than 50 percent at a 60 degree angle using conventional test equipment, such as those obtained using a BYK Micro-gloss 60° meter.

Herein provided, among other things, are a low gloss epoxy polyester hybrid powder coating paint formulation containing a styrene maleic anhydride resin and a curing catalyst, the catalyst being adding as a separate component in the paint formulation (in which event it is preferably an onium salt) or as part of as an admixture with the polyester, epoxy or SMA resin, and a method for producing such low gloss paints which comprises incorporating into the paint formulation the styrene maleic anhydride resin and the curing catalyst.

It has now been discovered that incorporating a catalyzing agent into epoxy polyester hybrid powder coating paint formulations along with SMA resin results in low gloss paints. When no catalyst is incorporated, high gloss is observed. While applicant does not wish to be bound by the theory of why this unexpected result occurs, it appears as if the SMA resin participates in the curing of the coating when a curing catalyst is present.

Styrene maleic anhydride resins useful in this invention include styrene-maleic anhydride copolymers and their partial esters. These resins are low molecular weight copolymers of styrene and maleic anhydride, optionally functionalized with an alcohol to provide a partially esterified resin. The anhydride and carboxylic acid groups present in these resins react with epoxy groups when a catalytic agent is incorporated into the paint formulation. In these resins the styrene to maleic anhydride molar ratio isi typically 1:1 to 10:1 (preferably 1:1 to 4: 1), with weight average molecular weights (Mw) in the range of about 500 to 20,000, preferably in the 4,000-10,000 Dalton range. Partial esters can be made from Cl to C30 alcohols, with 10 to 120 percent monoesterification. An example of a useful SMA resin is SMA 3000, a styrene/maleic anhydride resin available from Elf Atochem which has a Mw of 9,500 and a styrene:maleic anhydride ratio of about 3:1.

The catalyst may be incorporated into the paint formulation separately or as an admixture with the polyester, epoxy or SMA resin. These admixtures are available commercially, such as Crylcoat® 7401, a catalyst-containing polyester resin available from UCB Chemical; Albester 2240, a catalyst-containing carboxyl- terminated polyester resin available from McWhorter Teclmo logies; and Urelac P2450 and Urelac P5070, catalyst-containing saturated, carboxylated polyester resins available from DSM Resins. When the catalyst is added separately to the formulation, any compound known to catalyze the reaction between carboxylic acid or anhydride groups and epoxide groups can be used. Examples of such useful curing catalysts include onium compounds such as ethyltriphenylphosphonium acetate, tetraphenylphosphonium iodide, tetraphenylphosphonium acetate-acetic acid complex, phenyltriethylphosponium bromide, tetrabutylammonium acetate, and, preferably, tetrabutylphosphonium bromide, as well as triphenylphosphine and metal complexes such as zinc acetyl acetonate and zinc stearate, amine compounds and their salts, including primary, secondary, tertiary, aliphatic, cycloaliphatic, aromatic and heterocyclic amines, and mixtures thereof.

The paint formulations are typically prepared by (a) mixing about 25 to 50 weight % (preferably 30-35%) of an epoxy resin, about 25 to 50 weight % (preferably 30-35%) of a carboxylic acid-terminated polyester resin, about 1-20 weight % (preferably 3-7%) of the styrene maleic anhydride resin, about 0.5 to 1 weight % of a flow control agent, about 0J to 50 weight % of a pigment, about 0.01 to 5 weight % (preferably OJ-1%) of a catalyst as a separate component or in admixture with the epoxy, polyester, or SMA resin, and, optionally, about 0-40 weight % (preferably 20- produce a well-blended material; and (c) pulverizing and filtering the blended material using a mesh to produce a powder paint.

Useful epoxy resins include epoxy polyethers of polyhydric phenols, the cycloaliphatic epoxide resins, epoxidized novolac resins, epoxidized oils such as epoxidized soybean, cottonseed or linseed oil, and epoxidized phenol formaldehyde resins. Particularly suitable epoxy resins are copolymers of epichlorohydrin with bisphenol A, with epoxy equivalent weight ("EEW") of from 400 to 1000, preferably 600 to 750. Examples of such resins which are commercially available include Epon resin 2002, a solid bisphenol A epichlorohydrin epoxy resin available from Shell and D.E.R. 662UH and D.E.R. 663UH, solid epoxy/bisphenol A resins available from The Dow Chemical Company.

The polyester resins used are functionalized with carboxylic acid groups, and are composed of conventional di- and polyacids, and diols and polyols. Typical examples of the acid component include isophthalic acid, terephthalic acid, 1,4- cyclohexane dicarboxylic acid, phthalic acid, methylterephthalic acid, trimellitic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dimer fatty acid, adipic acid, succinic acid, maleic acid, fumaric acid, benzene- 1,2,4- tricarboxylic acid, pyromellitic acid, trimesic acid or the anhydrides thereof, or hydroxy carboxylic acids such as 12-hydroxystearic acid and -caprolactone. Typical examples of the alcohol component include ethylene glycol, propylene glycol, propane-l,3-diol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, hexane-2,5-diol, neopentyl glycol, isopentyl glycol, bishydroxyethyl terephthalate, hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, glycerol, 2,2,4-trimethylpentane- 1,3-diol, hexane triol, pentaerythritol, sorbitol, trimethylol ethane, trimethylol propane and tris-(2-hydroxyethyl)-isocyanurate.

Care should be taken to balance the amount of epoxy functionality with that of the acidic carboxylic and anhydride groups of the SMA and polyester resins. This balance is normally achieved by incorporating an excess of epoxy groups relative to the number of polyester carboxylic acid groups. This is most easily accomplished by using a so-called 60/40 or 70/30 type polyester resin. These resins were developed for use in high-gloss hybrid powder coatings, where they are normally utilized in a 60/40 or 70/30 weight ratio with the epoxy resin. However, in this invention the use of equivalent weights of the 60/40 or 70/30 polyester resin and an epoxy resin with an epoxy equivalent weight (EEW) of about 700 is preferred, but is not limited to these values. This provides an excess of epoxy groups to react with the SMA Resin. An excess of epoxy groups may also be achieved through the use of a 50/50 type polyester resin by using non-equivalent amounts of epoxy and polyester resin, by incorporating greater than 50 percent epoxy and less than 50 percent polyester resin.

Conventional flow control agents, pigments and fillers can be used. Typical flow control agents include polyacrylates, such as poly-2-ethylhexyl acrylate, finely divided ethyl cellulose, siloxanes, such as dimethyl polysiloxanes, fluorocarbons, or any mixture of the above. A commercially available flow control agent is Resiflow P67, described by the manufacturer, Estron Chemical, as a free-flowing, non-silicone powder based on a liquid oligomer which has been converted into powder by adsorption on a silica-type filler. Suitable pigments include carbon black and other organic dyes, titanium dioxide, iron oxides, zinc oxides, metal hydroxides, sulfides, sulfates, carbonates, silicates, talc, china clays, barytes, or metallic pigments such as aluminum. Suitable fillers include mineral fillers such as inorganic oxide carbonates, sulfates or silicates of a metal of Groups IA, HA, IIIA, IIB, NIB or NIII of the periodic table of elements. Preferred fillers are titanium oxide, calcium carbonate, barium sulfate, calcium silicate, magnesium silicate, strontium silicate, or any combination of the above.

In the examples to follow, the epoxy resins used were Type 3 low viscosity epoxy resins. More specifically, they were epoxies of the epichlorohydrin bisphenol A type having EEWs from about 600 to 750. The polyester resins were carboxylic acid terminated resins, having acid numbers from 15 to 70, preferably from 30-40 mg KOH/g. All gloss readings were performed using a BYK Micro-gloss 60° meter, with an average of 10 readings per panel.

EXAMPLE 1 - Preparation of a low gloss hybrid powder coating using a commercially-available catalyzed polyester resin with a small amount of SMA resin The formulation components were, in parts by weight, 50 parts Epon 2002, 50 parts Crylcoat 7401, 5 parts SMA 3000, 40 parts barium sulfate, 1.2 parts Resiflow P67, 2 parts carbon black and 0.5 part benzoin. These components were mixed by shaking, then passed through a 50 mm twin-screw lab scale extruder. The front section of the extruder was held at 79 °C, the rear section was held at 38 °C, and a screw speed of 400 rpm was used. After extrusion the materials were ground in a hammermill, passed through a 140 mesh screen and spray coated onto metal panels with a film thickness of 2.0 0.2 mils. When coated and baked at 204°C for 10 minutes, a 60° gloss of 22 percent was obtained, indicating a low gloss coating.

EXAMPLES 2 & 3 - Preparation of low gloss hybrid powder coatings using higher levels of SMA resin

Example 1 was repeated using 10 and 20 parts of SMA 3000, respectively. The respective coatings had a 60° gloss of 11% and 16%,

EXAMPLE 4 - Preparation of a hybrid powder coating containing a low level of separately added catalyst Example 2 was repeated except that the formulation contained Albester 2250, a carboxyl-terminated polyester resin which does not contain catalyst, in place of the Crylcoat 7401 and 0.25 part of tetrabutylphosphonium bromide (as curing catalyst). The coating had a 60° gloss of 44%.

EXAMPLE 5 - Preparation of a hybrid powder coating containing a higher level of added catalyst and a non-catalyzed polyester resin

Example 4 was repeated except that the amount of tetrabutylphosphonium bromide catalyst was increased to 0J5 part. The coating had a 60° gloss of 19%.

COMPARATIVE EXAMPLE - Preparation of a hybrid powder coating without any added catalyst, using a non-catalyzed polyester resin Example 4 was repeated except that no catalyst was added. The coating had a 60° gloss of 92%, indicating that a high gloss results when no catalyst is present.

Claims

CLAIMSWhat is claimed is:

1. A low gloss epoxy polyester hybrid powder coating paint formulation containing a styrene maleic anhydride resin and a curing catalyst.

2. A formulation as in Claim 1 wherein the catalyst is part of a pre-catalyzed polyester, epoxy or styrene maleic anhydride resin.

3. A formulation as in Claim 1 wherein the catalyst is tetrabutylphosphonium bromide.

4. A method for producing a low gloss epoxy polyester hybrid powder coating paint which comprises incorporating into the paint formulation a styrene maleic anhydride resin and a curing catalyst.

5. A method as in Claim 4 wherein the catalyst is incorporated as an admixture with the polyester, epoxy or styrene maleic anhydride resin.

6. A method as in Claim 4 wherein the catalyst is tetrabutylphosphonium bromide.