CA2102788C

CA2102788C - Thermosetting powder coating compositions

Info

Publication number: CA2102788C
Application number: CA002102788A
Authority: CA
Inventors: Lawrence Lester Bott; Max Eugene Helvey
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1991-06-05
Filing date: 1992-06-02
Publication date: 1997-03-25
Anticipated expiration: 2012-06-02
Also published as: ES2114941T3; EP0587757A1; EP0587757B1; KR100235268B1; WO1992021727A1; DE69224744D1; KR940701429A; US5244944A; ATE163963T1; DK0587757T3; DE69224744T2; JPH06508172A

Abstract

Provided are thermosetting powder coating composi-tions which contain a quaternary ammonium salt or hydroxide having at least one substituent of eight carbons or more and one lower alkyl group. Such quaternary ammonium salts or hydroxides were found to catalyze the curing or cross-linking reaction at lower temperatures in such compositions than previously possible.

Description

~VO 92/21727 ' 2 1 ~,~ 7 8 ~ Pcr/Us92~048s0 .r.rl~ s~ I LlNG POWDER COAI~ING CONPOSITIONS
Field of the Invention This invention belongs to the field of powder coat--ings. Nore particularly, thi5 invention relates to a novel class of cross--linking catalysts and thermosetting powder co~ting compositions containing aid catalysts.
Bacl.u~ ou,.~ of the Invention Plastic materials used in the manufacture of powder coatings ~re classif ied broadly as either thenDosetting or thermoplastic. In the application of thermoplastic powder coatings, heat is applied to the coating on the ~ubstrate to ~elt the particles of the powder coating and thereby permit the particles to f low tog~ther and f orm a sr,ooth coating .
~hermosetting coatings, when co~pared to coatings derived from thermopl~stic compositions, generally are tougher, ~ore resistant to solvents and detergents, have better adhesion to metal ~ubstrates and do not soften when exposed to elevated temperatures. However, the curing of thermosetting coatings ~as created problems in 2S obtaining co~tings which have, in ~ddition to the above-~tated desirable characteri~tics, good ~moothness and ~lexibility. Coatings prepared from thermosetting powder compositions, upon the application of heat, r.ay cure or ~et prior to forming a l;~ooth coating, resulting 30 in a relatively rough finish referred to as an "orange peel" surface. Such a coating ~urface or fini~h lacks the gloss and luster of coatings typically obtained from thermoplastic compositions. The "orange pcel" Lurface problem has caused thermosetting coatings to bc applied from organic ~olvent ~ystems which are inherently _ _ _ _ _ _ _ _ _ _ ... _ _ . _ . _ _ .. .. .. _ _ _ _ _ _ _ _ .

~` 2~0~788 undesirable because o~ the environmental and sa3~ety problems that may be occasioned by the evaporation of the solvent system. Solvent--based coating compositions also suffer from the disadvantage of relatively poor 5 percent utilization, i . e ., in some modes of application, only 60 percent or less of the solvent--based coating composition being applied contacts the article or substrate being coated. Thus, a substantial portion of solvent--based coatings can be wasted since that portion lO which does not contact the article or substrate being coated obviously cannot be reclaimed.
- In addition to exhibiting good gloss, impact strength and resistance to solvents and rh~m;c~lq, coatings derived from l-hl ~-etting coating compositions 15 must possess good to PYr~ t f leYibility . For e~cample, good flexibility is egsential for powder coating compositions used to coat sheet (coil) steel which is destined to be formed or shaped into articles used in the manu~acture of various household"appliances 20 and automobiles wherein the sheet metal is fle~ed or bent at various angles.
Further, research interest in powder coating compositions has shifted to lower and lower curing parameters. We have dis~uvo:Led a new class of cross--25 linking catalysts which, when utiliz~d with certain resins and cross--linkers, effect heretofore unachievable levels of cure ( i . e ., cross--linking) at temperatures as low as 115C.
French Patent No. 2, 457, 884 describes powder 30 coating compositions containing csrtain guaternary ammonium c _ ' as curing catalysts.
AuslegeschriiX 2,541,635 describes powder coating compositions using certain . i11m _ ,_ 'e as curing accelerators .
_ _ _ _ _ _ _ _ ~ 21~788 -- 2a -~ rv of thP Tnv~nt iOn The present invention provides thermosettinq powder coating compositions which utilize certain quaternary 5 ammoniu~ salts or hydroxides as cross--linkinq catalysts.
With this new class of cross--linkiny catalysts, an ~WO 92/21727 2 ~ ~ 2 788 PCI/Us92/048so effective curing of the coating composition may be achieved at temperatures as low as 115C. Thus, this invention allows for powder coatings to be applied and cured with significantly less energy expended in the 5 case of coatings applications on metals, as well as ~llowing for the effective coating of various thermo--plzstic or thermosettiny resin compositions which would ordinarily be unsuitable for use with conventional thermosetting powder coating compositions.
Detailed DescrimtiQn of the InventiQn The present invention provides a thermosetting powder coating composition comprising (I) a curable polymer;
(II) a cross--linking compound or a polymer reactive with component (I); and (III) a quaternary ammonium ~alt or hydroxide having ~t least one hydrocarbyl radical of at least eight carbon atoms in length and at least one lower alkyl group.
Prefer2bly, the curable polymer component (I) is chosen from the known resins used in the powder coating art which have epoxy, carboxy, hydroxy, or anhydride functional groups which can be reacted with known cross-30 linking c~ u.lds to provide cured coatings.
Preferred epoxy functional resins generally have amolecular weight of about 300 to about 4000, and have ~pproximately . 05 to about . 99, epoxy groups per lOOg of resin(i.e., 100-2000 weight per epoxy (WPE)). Such 35 resins ~re widely known and are commercially - available _ _ under the EPON0 trademark of the Shell Chemical Company, the Araldite0 trademark of CIBA~eigy, and D.E.R. resins of the Dow Chemical Company.
Curable polymers (I) which have carboxy functional groups include polyesters . Such polyesters pref erably have a molecular weight of about 500 to about 5000 and an acid number of about 35--~5. Commercially available examples of such resins include 6Alftalat AN 720, 721, 722, 744, 758, and 0Alftalat*AN 9970 and 9983 resins available from Hoechst Celanese.
Curable polymers (I) which have free hydroxy groups also include the polyesters and acrylics. Hydroxy--functional polyesters and acrylic polymers preferably have a hydroxyl number from about 30 to about 60 (mg KOH/g polymer).
The polyesters as described herein may be produced using well--known polycondensation procedures employing an excess of glycol (or acid) to obtain a polymer having the specified hydroxyl (or carboxyl) number. The glycol residues of the polyester component may be derived from a wide variety and number of aliphatic, alicyclic and alicyclic--aromatic glycols or diols containing from 2 to about lO carbon atoms. Examples of such glycols include ethylene glycol, propylene glycol, 1,3--propanediol, 2,4--dimethyl--2--ethylhexane--1, 3--diol, 2, 2--dimethyl--1, 3--propanediol, 2--ethyl--2--butyl--1, 3--propanediol, 2--ethyl--2--isobutyl--1, 3--propanediol, 1, 3--butanediol, 1, 4--butane-diol, 1, 5--pentanediol, 1, 6--hexanediol, thiodiethanol, 1, 2--, 1, 3-- and 1, 4--cyclohexanedimethanol, 2, 2, 4, 4--3o tetramethyl--1,3--cyclobutanediol, 1,4--xylylenediol and the like.
The dicarboxylic acid constituent of the polyesters may be derived from various aliphatic, ~licyclic, aliphatic--alicyclic and aromatic dicarboxylic acids containing about 4 to lO carbon atoms or ester--forming *~rademark .
A

... ... . . .

21 0278~

derivatives thereof such as dialkyl ester and~or anhydrides. Succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic, 1,3-- and 1,4--cyclohexanedicarboxylic, phthalic, isophthalic and terephthalic are representative of the dicarboxylic acids from which the diacid residues of the amorphous polyester may be derived . A minor amount , e . g., up to 10 mole percent, of the glycol and~or diacid residues may be replaced with branching agents, e.g., tri--functional residues derived from trimethylolethane, trimethylolpropane and trimellitic anhydride.
The preferred polyesters of the composition provided by this invention have a Tg greater than 55C, and an inherent viscosity of about 0 .15 to 0 . 4 . The polyester component (I) preferably is comprised of (1) diacid residues of which at least 50 mole percent are terephthalic acid residues, t2) glycol residues of which at least 50 mole percent 2re derived from 2, 2--dimethyl--1,3--propanediol (neopentyl glycol) and (3) up to 10 mole percent, based on the total moles of (2) and ( 3 ), of trimethylolpropane residues . These pref erred hydroxyl functional polyesters are commerciall-y avail--able, e.g., under the names AZS*50 Resin, Rucote* 107 and Cargill*Resin 3000, and~or can be prepared according to the procedures described in l~.S. Patent Nos. 3,296,211, 3,842,021, 4,124,570 and 4,264,751, and Published Japanese Patent Applications (Rokai) 73--05,89s and 73--26,292. The most preferred polyester consists essentially of terephthalic acid residues, 2,2--dimethyl--1,3--propanediol residues and up to 10 mole percent, based on the total moles of 2,2--dimethyl--1, 3--propanediol residues, of trimethylolpropane residues, and possesses a Tg of about 500 to 65C, a hydroxyl number of about 35 to 60, an acid number of *Trademark ~3L
_ _ . . .. ....

-

2 1 02788 less than 10 and an inherent viscosity of about 0.1 to 0.25.
The acrylic polymer component (I) is preferably a polymer or resin prepared by polymerization of a hydro~yl--beariny monomer such as hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, hydroxypropyl acrylate, hydLo~y~ro~yl methacrylate, hycllu,-yb-lL~
acrylate, hydroxylbutyl methacrylate and the like optionally polymerized with other monomers such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, styrene, vinyl acetate, and the like. The ratio of reagents and molecular weights of the resulting acrylic polymer are preferably chosen 50 as to give polymers with an average functionality (the number o~ OH groups per molecule) greater than or equal to 2. Commercially--avail~ble curable hydroxy--functional acrylic polymers include Joncryl*800, Joncryl* 500, and Neocryl* LE--800.
Polymeric binders (I) which have epoxy groups can also be resins comprised of residues of glycid~l methacrylate(GMA) and~or glycidyl acrylate. Such resins generally have a number average n~olecular weight of about 500 to about 5000, and a weight average molecular weight of about 1000 to about 10,000. In a preferred embodiment of the present invention, Co~rQn~rt (I) is a glycidyl methacrylate resin containing from about 5 to about 40 weight percent GMA residues, having a number average molecular weight of about 1000 to about 3000, and a weight average molecular weight of ~bout 2000 to about 8000. Commercially--available resins include those available from Mitsui Toatsu Chemicals, Inc., available under the trademark Almatex0 PD*6100, PD 6300, *Trademark . _ .. _ . , ... _ _ _ . _ _ _ .

PD 7110, PD 1210, PD ?310, PD 1610, and PD 1~00.
Further examples of such resins include those described in U.S. Patent Nos. 4,042t645; 4,091,024; 4,346,144; and 4,499,239.
The quaternary ammonium salt or hydroxide is preferably a compound of Formula (A) -- +
1 _2 3_ wherein R, R~, R2, and R3 are independently C~--C25 alkyl or alkenyl or C~--C25 substituted alkyl or alkenyl or R and R~
are taken together to form a 5 or 6 r hpred carbocyclic or heterocyclic ring, provided that at least one of R, R~, R2 or R3 i5 a hydrocarbyl radical containing at least eight carbon atoms and one is a lower alkyl group; X is chloro, bromo, fluoro, hydroxide, acetate, or so~-2; n is 1 when X is chloro, bromo, fluoro, hydroxide or acetate, and n is 2 when X is so~-2.
In the above Formula (A), the term Cl--C25 substituted alkyl is a C~s alkyl group substituted by one or more hydroxy, methoxy, or quaternary ammoniuw groups (A) as defined above. In the l~tter case, the quaternary aDonium salt or hydroxide compound of Formula (A) will have 2 or more quaternary S~mmonium groups .
Many of the compounds of Formula ~A) are coDercially available from A}~Z0 Corporation under the trademarks Arquad0, Ethoquad~ and Duoquad$~
As noted above, R and R~ may be taken together to form a ring system with the nitrogen atom to which they are bonded. For example, the quaternary ammonium *Trademark , .. .
, .

21~ ~88 WO 92121727 , PCr/US92/0485 compound of Formula (A) may be an imidazolinium compound, e . g ., 5 C 7H $--C~ j -- Cl ~
~ 5 and C17H35-~_i + 2 cI
H3C CH2--CH2 N(CH3)3_ Other examples of quaternary ammonium compounds are illustrated by the following Table tl):
32 B3 a~
methyl ethyl octyl octyl Cl' ethyl methyl , octyl nonyl Cl' methyl ethyl octyl decyl Cl methyl methyl octyl nonyl Cl' 4 o methyl ethyl octyl dodecyl Cl methyl ethyl decyl decyl Cl' methyl ethyl octyl octyl ~ 8r ethyl methyl octyl n~yl Br methyl ethyl octyl decyl Br 4 5 methyl methyl octyl nonyl Br methyl ethyl octyl dodecyl Br' methyl ethyl decyl decyl ~3r methyl ethyl octyl octyl OH
ethyl methyl octyl nonyl OH
50methyl ethyl octyl decyl OH
methyl methyl octyl nonyl OH
methyl ethyl octyl dodecyl OH

2 1 0278~
.
_ g methyl ethyl decyl decyl - OH
methyl methyl dodecyl dodecyl Br methyl methyl dodecyl dodecyl Cl methyl methyl octadecyl octadecyl Br 5 methy- methyl octadecyl octadecyl Cl-The various cross--linking compounds suitable for use in the present invention (II) are well--known to one of ordinary skill in the art of powder coatings. For 10 example, with carboxy functional resins, cross--linking compounds with epoxy groups can be utilized. Likewise, with an epoxy functional resin, an anhydride type cross--linking compound can be used. Further, with hydroxy--functional resins, blocked isocyanates can be used. As 15 will be shown below, a carboxy functional resin may be blended with an epoxy resin and, optionally, in the presence of another epoxy functional compound such as triglycidyl isocyanurate, and cured.
~ xamples of anhydride type cross--linking compounds 20 include trimellitic anhydride, benzophenone tetra--carboxylic dianhydride, pyromellitic dianhydride, tetrahydrophthalic anhydride, and the like.
In general, carboxy-functional cross--link-ing agents 2re C3--C30 alkyl, alkenyl, or alkynyl cc,.ll~u.lllds with two 25 or more carboxylic acid functional groups. Preferred carboxy-functional cross--linking compounds can be described by the formula H20C--[ (CH2)D]--C02H~
wherein n is an integer of 1--10. Examples of such carboxy-functional cross--linking agents include polycarboxy alkyl ~ .ou,,ds such as dodecanedioic acid, azelaic acid, adipic acid, 1,6--hexanedioic acid, .

succinic acid, pimelic acid, ~ebacic acid, and the like.
Other examples of carboxy--type cross--linking compounds include maleic acid, citric acid, itaconic acid, aconitic acid, and the like.
l~he blocked polyisocyanate compounds of the compositions of this invention are known compounds and can be obtained from commercial sources or may be prepared according to published procedures. Upon being heated to cure coatings of the compositions, the compounds become unblocked and the isocyanate groups react with hydroxy groups present on the amorphous polyester to cross--link the polymer chains and thus cure the compositions to form tough coatings. Examples of the blocked polyisocyanate cross--linking component include those which are based on isophorone diisocyanate blocked with i--caprolactam, commercially available as 8uls 1530*and Cargill 2400,* or toluene 2,4--diisocyanate blocked with ~--caprolactam, commercially available as Cargill 2450,* and phenol--blocked hexamethylene diiso--2 0 cyanate .
The most readily--available, and thus the preferred, blocked polyisocyan2te cross--linking agents or compounds are those commonly referred to as ~--caprolactam--blocked isophorone diisocyanate, e.g., those described in U.S.
Patent Nos. 3,822,240, 4,150,211 and 4,212,962.
However, the products marketed as ~--caprolactam--blocked isophorone diiso--cyanate may consist primarily of the blocked, difunctional, monomeric isophorone diisocyanate, i.e., a mixture of the cis and trans isomers o~ 3--isocyanato--methyl--3,5,5--trimethylcyclohexylisocyanate, the blocked, difunctional dimer thereof, the blocked, trifunctional trimer thereof or a mixture of the monomeric, dimeric and~or trimeric forms. For example, the blocked poly--isocyanate ~ a used as the cross--linking agent may *Trademæk ~1~2788~
~WO Y2/21727 PCr/US92/04850 be a mixture consisting primarily of the ~--caprolactam--blocked, difunctional, monomeric isophorone diisocyanate and the ~--caprolacta~blocked, trifunctional trin~er of isophorone diisocyanate. The description herein of the cross--linking ~gents as "polyisocyanates" refers to cu,l,uuu-.ds which contain at least two isocyanato yroups which are blocked with, i.e., reacted with, another compound, e.g., ~--caprolactam. The reaction of the isocyanato groups with the blocking ~~ _ ' is reversible at elevated temperatures, e.g., normally about 150C, and above, at which temperature the isocyan~to groups are available to react with the hydroxyl groups present on the free hydroxy groups of the polyester to f orm urethane linkages .
Alternatively, the blocked isocyanate may be a cross-linking effective amount of an adduct of the 1,3-diazetidine--2, 4--dione dimer of isophorone diisocyanate and a diol having the structure 2 5 OCN--R1~X--R1--NH--C~R2~C--NH--Rl~X--Rl--NCO
wherein Rl is a divalent 1--methylene--1, 3, 3-trimethyl--5--cyclohexyl radical , i . e ., a radical having the structure CH
4 o CH3'! ~ ,!
CH ~ ~CH
4s R2 is a div~lent aliphatic, cycloaliph~tic, araliphatic or Aromatic residue of a diol; and X is a 1, 3--diazetidine-2, 4--dionediyl radical, i . e ., a radical having the structure _~ _ 1 ~ç~N
o wherein the ratio of NCO to OH groups in the fonr.a--tion of the adduct is about 1: 0 . 5 to 1: 0 . 9, the mole ratio of diazetidinedione to diol is from 2 :1 to 6: 5, the content of free isocyanate groups in the adduct is not greater than 8 weight percent and the adduct has a molecular weight of about 500 to 4000 and a melting point of about 70 to 130C.
The adducts of the 1,3--diazetidine-2,4--dione dimer of isophorone diisocyanate and a diol are prepared according to the procedures described in U. S. Patent 4, 413, 079, by reacting the diazetidine dimer of isophorone diisocyanate, preferably free of isocyanurate trimers of isc~phorone diisocyanate, with diols in a ratio of reactants which gives as isocyanto:hydroxyl ratio of about 1:0.5 to l:O.9, preferably 1:0.6 to 1:0.8. The adduct preferabl~
has a molecular weight of 1450 to 2800 and a melting point of about 85 to 120C. The preferred diol reactant is 1, 4--butanediol. Such an adduct is commercially available under the name Huls*BF1540.
The amount of the blocked diisocyanate cross--linking compound present in the compositions of this invention can be varied d~r~ on several factors such as those mentioned hereinabove relative to the amount of components (I) and (II~ which are utilized.
Typically, the amount of cross--linking compound which * Trademark WO 92/21727 2 1 Q ~ 7 8 8 Pcr/US92/048s0 will effectively cross--link the polymers to produce coatings having a good combination of properties is in the range of about 5 to 30 weight percent, preferably 15 to 25 weight percent, based on the total weight of 5 components (I) and (II).
As a further aspect of the present invention, there is provided an improved method for curing a thermo--setting coating composition, said composition comprising (I) a curable polymer; and (II) a cross--linking compound or a polymer reactive with component (I);
the im~r~vl t comprising (a) contacting said composition with a guaternary ammonium salt or hydroxide having at least one hydrocarbyl radical of at least eight carbon atoms in length and one lower alkyl group to f orm a r,ixture;
(b) applying said mixture to a substrate;
followed by (c) heating said substrate to a temperature su~f icient to cure the resulting coating .
As noted above, it is possible to cure ~ome 30 systems, namely epoxy--anhydride functional, at tempera--tures as low as 115C. In this regard, the criterion chosen herein to determine whetber a coating has achieved a sufficient "cure" is merely whether the coating will pass a standard methyl ethyl ketone (MEI~) 35 rub test, i.e., 50 double rubs with no breakdown of the _ 21 0278~

curéd film. No special procedures are necessary when utilizing the compositions of the present invention or when practicing the method of the present invention other tkan the utilization of the quaternary ammonium 5 salt or hydroxide catalyst.
As used herein, the term "hydrocarbyl radical"
preferably refers to a hydrocarbon which is either 6traight or branched, optionally substituted by one or more groups and optionally containing one or more 10 heteroatoms.
The term "lower alkyl" preferably refers to a straight or branched alkyl chain of one to six carbon atoms, most preferably an alkyl chain of one to three carbon atoms in length, i . e., methyl, ethyl, and propyl .
The powder coating compositions of this invention may be prepared from the compositions described herein by dry--mixing and then r,elt--blending cr~-rone~t (I) and the cross--linking compound, the cross--linking catalyst (III~, along with other additives commonly us~d in 20 powder coatings, and then grinding the solidified blend to a particle size, e.g., an average particle size in the range of about 10 to 300 microns, suitable for producing powder coatings. For example, the ingredients of the powder coating composition may be dry blended and 25 then melt blended in a Brabender*extruder at 90 to 130C, granulated and finally ground. The melt blending should be carried out at a temperature sufficiently low to prevent the unblocking of the polyisocyanate cross--linking compound and thus avoiding premature cross--30 linking.
Typical of the additives which may be present in the powder coating compositions include benzoin, flow aids or flow control agents which aid the formation of a smooth, glossy surface, stabilizers, pigments and dyes.
* Trademark .

2 1 0278~

The powder coating compositions preferably contain ~ flow aid, also referred to as flow control or leveling agents, to enhance the surface appearance of cured coatings of the powder coating compositions . Such f low 5 aids typically comprise acrylic polymers and are avail--able from several suppliers, e.g., Modaflow*from Monsanto Company 2nd Acronal*from BASF. Other flow control ~gents which may be used include Modarez*!~FP
nvailable from Synthron, EX 486 available from Troy 10 Chemical, BYK 360P available from BYK Mallinkrodt and Perenol F--30--P available from ~ienkel. An example of one specific flow aid is an acrylic polymer having a molecular weight of about 17, 000 and containing 60 mole percent 2--ethylhexyl methacrylate residues and about 4 0 15 mole percent ethyl acrylate residues. The amount of flow aid present may preferably be in the r2nge of about O . 5 to 4 . O weight percent, based on the total weight of the resin component, and the cross--linking agent.
The powder coating compositions may be deposited on 2~ various metallic and non--metallic (e.g., thermoplastic or thermoset composite) substrates by known techniques for powder deposition such as by means of a po~der gun, by electrostatic deposition or by deposition from a fluidized bed. In fluidized bed sintering, a preheated 25 article is immersed into a suspension of the powder coating in air. The particle size of the powder coating composition normally is in the range of 60 to 300 microns. The powder is maintained in suspension by passing air through a porous bottom of the fluidized bed 30 chamber. The articles to be coated are preheated to about 250 to 400F tabout 121 to 205C) and then brought into contact with the fluidized bed of ~he powder coating composition. The contact time depends on the thickness of the coating that is to be produced and 35 typically is from 1 to 12 seconds. The temperature of * Trademark A

210~788 ~- -W09V21727 ~ US92~a4850 the substrate being coated causes the powder to ~low and thus fuse together to form a smooth, uniform, continuous, uncratered coating. The temperature of the preheated 2rticle also effects cross--linking of the coating composition and results in the formation of a tough coating having a good combination of properties.
Coatings having a thickness between 200 and 500 microns may be produced by this method.
The compositions also may be 2pplied using an electrostatic process wherein a powder coating composi-tion having a particle size of less than 100 microns, preferably about 15 to 50 microns, is blown by means of compressed air into an applicator in which it i~ charged with a voltage of 30 to 100 kV by high-voltage direct current. The charged particles then are sprayed onto the grounded article to be coated to which the particles adhere due to the electrical charge thereof. The coated article is heated to melt and cure the powder particles.
Coatings of 40 to 120 microns thickness may be obtained.
Another method of applying the powder coating compositions is the electrostatic f luidized bed process which is a combination of the two methods de cribed above. For example, ~nnular or partially annu~ar electrodes are mounted in the air feed to a fIuidized bed so as to produce an electrostatic charge ~uch as ~o to loO kV. ~he article to be coated, either heated, e.g., 250 to 400DF, or cold, is exposed briefly to the fluidized powder. The coated article then can be heate~
to effect cross--linking if the article wa~ not preheate~
to a temperature sufficiently high to cure the coating upon contact of the coating particles with the article.
The powder coating compositions of this invention may be used to coat articles of v~rious shapes and si2es constructed of heat--resistance materials such e5 glass, ceramic and various metal materials. The compositions ... ..

~ 210278~

are especially useful for producing coatings on articles constructed of metals and metal alloys, partlcularly 6teel articles. As noted above, since the compositionS
provi~ed by the present invention cure at a te~peratureS
5 of as low as 115C, it is also possible to coat many thermoplastic and ther~osetting resin compositions with the compositions of the present invention.
Further examples of formulation methods, additives, and methods of powder coating application may be found 10 in tJser's Guide to Powder Coatinq, 2nd Ed., Emery Miller, editor, Society of Manufacturing Engineers, Dearborn, (1987).
The compositions and coatings of this inven-tion are further illustrated by the following examples.
15 The inherent viscosities (I.V.; dl~g? referred to herein were measured at 25DC using 0.5 g polymer per 100 mL of a 601vent consisting of 60 parts by weight phenol and 40 parts by weight tetrachloroethane. Acid and hydroxyl numbers were determined by titration and are reported 20 herein as mg of KOH consumed for each gram of polymer.
The glass transition temperatures (Tg) and the melting temperatures (Tm) were determined by differential scanning calorimetery (DSC) on the second heating cycle at a scanning rate of 20C per minute after the sample 25 has been heated to melt and quenched to below the Tg of the polymer. Tg values are reported as the midpoint of the transition and Tm at peaks of transitions.
EXPERIMENTA~ S~CTION
In the examples which follow, the ingredients of the powder coating compositions were charged to a Henschel*mixer and premixed to a uniform preblend, melt--blended in a twin screw extruder, ground to a powder in 35 a micro--bantam mill with nitrogen assist and classif ied *Trademark ~102788 WO 92/21727 PCr/US92/0~8S0~
~ ., through a 200 ~esh rotary screener. The p~rticle size of the f inished product thus produced had an average size of approximately 3 0 microns .
The powder coating compositions were subsequently 5 ~pplied by electrostatic spray process with a Ransburg corona type gun to 22 X 3 . 9 X . 03 inch steel panels .
This application process yielded f ilms that were controlled between 1.5 and 2.0 mils.
The curing process was conducted by heating the o panel with 2pplied powder on a beated yradient oven for 5 minutes. The gradient oven is r,anufactured by the 3yk Gardner Company (Cat. l~o. 2617). The 3--function option was chosen to effect cure on each panel. The objective of the test was to determine the lowest temperature at 15 which these powder coating compositions were found to be in an adequate cured state as determined by a methyl ethyl ketone (MEX) solvent rub test.
A cotton towel soaked in MEK was attached to a 13 ounce ball peen ha=mer for the purpose of rlaintaining 2~ consistent pressure on the film when tested. The individual test was concluded with either of the following situations: (a) at less than 50 double rubs of M~R, fil~ wears away to substrate, or (b) film withstands 50 double rubs of NEK. The following cure 25 rating scale was used to determine whether or not films were adequately cross--linked to show cure for each temperature:
.

21 027a~

Cure Ratinq #l.Full Cure -- no sur~ace mar and no gloss reduced .
#2 Full Cure -- minimal mar with some gloss reduced .
~3 Ade~uate Cure -- surface ~ar with no color transfer #4 Partial Cure -- f ilm 50ftens with 50 double rubs, with some color tr2nsf er ~5 Under Cure -- film softens to bare metal at less than 50 double rubs.
.

The powder coating compositions of this invention are further illustrated by the following examples:
Example 1 -- (Epoxy~Anhydride) _ ~
Epon* 2002~ 1000 1000 BTDA7 170 ; 170 Resiflow P--673 12 ~ 12 Ro3o974 . 8 . 8 YLo22885 .1 6.7 Lomicron *1067 229 229 ARQUAD* 218--100~ 0 15 35 ~Registered Trademark Curing of the above formulations in Example 1 was c2rried out by the aforementioned procedure and exhibited the following cure scale ratings:

Cure Temperature Examined, Cure Ratinq F
5o. A B
5 ~under cure) 325 (30*~ 210 (10 4 (partial cure) 330 230 2 (full cure) 350 250 1 (full cure) 375 270 *No . of IIER double rubs bef ore breaking through to substrate .

ExalDple 2 -- ~Epoxy/Amine) A
Epon* 2002~ 1000. 0 looo . 0 Dicyandiamide9 45 . 0 45. 0 30Resiflow P--673 12.0 1~2.0 Ult 5008' 1.4 1.4 R_9006 647 . 0 647 . 0 ARQUAD* 218--lOOPI -- 15 . 0

3 5 *Registered Trademark Curing of the powder coating compositions in Example 2 was carried out as in Example 1 to determine the following cure scale ratings:

., 21 0278~

Cure Temperature Examined, Cure Ra t i nq F
5 ~ ~ ~
5 (under cure) 330 tl5*) 325 (30*)

4 tpartial cure) 350 (48*) 2 (full cure) 370 350

5 *No . of I~EK double rubs bef ore breaking through to substrate .
0 ~xample 3 -- (Epoxy~Polyester) A ~ C
AN744~ 500 500 500 25Epon* 2002~ 500 500 500 Resif low P--673 12 12 12 ~llt 50C8~ * 1. 1 1 . 1 1. 1 R--960a 573.5 573.5 573.5 ARQUAD* 218--lOOP~ -- 15. 0 -~ --30DDARI~ -- -- 15. 0 *Registered Trademark Curing of the powder coating compositions in 35 Example 3 was carried out as in Example 1 to determine the following cure scale ratings:

- 2~2~8~
W092/21727 PCr/US92/04850 Cure Temperature F'Y:~m i n~
Cure R~tin~ F
5 ~ A ~ 5~
5 (under cure) 305 ~6*) 265 (20*) 275 (40*) 4 (partial cure) 345 275 280 3 (adeguate cure) 375 290 305 5 *~o. of ~EK double rubs before breaking through to 6ubstrate .
0 Exa~Dle 4 -- (Polyester~TGIC) k 1~ C
Ur~lac* p5000l3 1000 1000 lOOo 25Araldite* PT81014 75 75 75 Benzoin~s 12 . 9 12 . 9 12 . 9 Resif low P--673 12 . 9 12 . 9 12 . 9 R960~ 618 . 6 618 . 6 618 . 6 ARQUAD~t 218--lOOP -- 12 . 9 3 0 DDA~ 12 . 9 *Registered Trademark Curing of the powder coating compositions in 35 Example 4 was carried out as in Example 1 to determine the following cure scale ratings:

Cure Temperature Examined, Cure Ratinq F
No. _ ~ _ ~ (under cure~ 305 (6*) 265 (20*) 265 (10*) 4 (partial cure) 345 275 275 3 tadequate cure) 375 290 290 2 (full cure) -- 30s 305 *No. of ~ER double rubs before breaking through to substrate .

Example S -- (AcrylicXPolycarboxylic Acid) ç

. a Almatex* PD76101~ 1000 1000 1000 Dodecanedioic Acidl7 204 . 8 Z04 . 8 204 . 8 EX4861~ * 18 18 18 Benzoin~5 6 6 6 ARQUAD* 218--looPI -- 14 . 5 DDAHI2 _ _ 14 . 5 *Registered Trademark Curing of the powder coating compositions in Example 5 was carried out as in Example 1 to determine the following cure scale ratings:
--2~Q~7~8 WO g2121727 PCr/US92/0485û~

Cure Temperature Examine~, Cure Ratir~ F
5 No. ,a ~ ~
5 (under cure) ~ 280 (25*) 265 (45*) 250 (30*) 4 (partial cure) 310 280 265 3 (adequate cure) 325 295 295 2 (full cure) -- -- 310 15 1 (full cure) -- 325 325 ~tNo. of 15EX double rubs before breakirlg through to 20 substrate.

2~ 02788 ExAmr~le 6 -- (Hydroxyl Polyester~310cked I~ocyanate) 5 ~ , A ~ Ç
Rucote* 10419 1000 1000 1000 Carqill* 30-24002 538 538 538 Araldite* GT70142~ 76.8 76.8 76.8 Resiflow*P--673 24.6 24.6 24.6 -BK5099 1.1 1.1 1.1 Ult* 5008~ 2 . 2 2 . 2 2 . 2 Benzoin's 24 . 6 24 . 6 24 . 6 R9742l 5.2 5.2 5.2 15 Zinc stearatel3 1. 8 1. 8 1. 8 Irganox* 10102~ 3 . 4 3 . 4 3 . 4 Premier 209025 76.8 76.8 76.8 R9605 828 . 0 828 . 0 828 . O
ARQUAD* 218--lOOP~ -- 38 . 8 20 DDAHI2 -- -- 38.8 *Registered Trademark _i Cure Temperature F~m i r~d 25 Cure Ratinq F
No. ,~
30 5 (under cure) 330 (10*) 305 (8*) 305 (42*) 3 (adequate cure) 345 330 330 2 (~ull cure) 360 360 360 *No. of MEK double rubs be~ore breaking through to 40 substrate.

WO 92~21727 PCr/US92/048~0 FY~mnle 7 -- (Carboxyl Polyester~Glycidyl MethAcrylate Acrylic ) Uralac} P36602~ 1000 1000 Almatex* PD76101C ~24 724 Do~le~ne~}ioic Acidl7 86.2 86.2 Resiflow P--673 20.8 20.8 10Ult 50081 . g . g R960C 466.2 466.2 ARQUAD* 218--lOOPI -- 25. 9 15 *Registered Trademark Curing of the powder compositions in Example 7 was carried out in the ~ame manner as in Example 1 to determine the ~ollowing cure ~cale ratings:
2 0 Cure Temperature PY:~m; ned, ~ure Ratinq CF
2 5 No . _ E~
4 ~p~rtial cure) 270 210 3 (adequate cure) -- 230 302 (full cure) 290 270 ., `~WO92/21727 2~ 0~ 7~8 PCriUS9i/0485o INGREDIE~T REFERENCES
1~ Bisphenol--A Epoxy Resin -- Shell Oh~mic~l 2) Benzophenone Tetracarboxylic Dianhydride -- ALLCO
Chemica 1 3 ) Flow Control -- Estron Chemical, Inc .
4) Red Iron Oxide -- Pfizer Pigments 5) Yellow Iron Oxide -- Pfizer Pigments

6) Titanium Dioxide -- DuPont

7) Barytes -- Whittaker, Clark, and Daniels

8) Dioctadecyldimethy1 Ammonium Chloride --~czo Chemical

9) Dicyandiamide -- SKW Chemicals, Inc.

10) Ultramarine Blue -- Whittaker, Clark, and Daniels

11) Car~oxyl Polyester -- American Hoechst

12) Dioctadecyldimethyl Ammonium Hydroxide --L. L. Bott and Associates

13) Carboxyl Polyester -- DS~ Corp.

14 ) Triglycidyl Isocyanurate -- CIBA GEIGY
35 15) Benzoin -- GCA Corp.
16) Glycidyl Methacrylate ~crylic Resin -- Mitsui Toatsu 40 17) Polycarboxylic Acid -- DuPont 18) Flow Control Agent -- Troy Chemical 19) Hydroxy Polyester -- Ruco Polymer Corp.
20) Isophorone Diisocyanate (E--Caprolactam Blocked) -- Cargill 21) Bisphenol--A Epoxy Resin -- CIBA GEIGY
22) Hydrophobic Silica -- Degussa Corp.
.

0~788 WO 92/21727 ~ PCI/IJS92/04850~, 23) Zinc Stearate --Witco Corp.
24 ) Antioxidant -- CIBA GEIGY
5 25) Barytes -- Microminer~ls Inc.
26) Carboxyl Polyester Resin -- DSM Resins .. . _

Claims

We Claim:

1. A thermosetting powder coating composition comprising (I) a curable polymer;
(II) a cross-linking compound or a polymer reactive with component (I); and (III) a quaternary ammonium salt or hydroxide selected from a list consisting of dioctadecyldimethyl ammonium hydroxide, diocta-decyldimethyl ammonium chloride, dioctadecyldiethyl ammonium hydroxide, dioctadecyldiethyl ammonium chloride, dioctadecyl-dipropyl ammonium hydroxide, and dioctadecyldipropyl ammonium chloride.

2. The thermosetting powder coating composition of Claim 1, wherein the quaternary ammonium salt is dioctadecyldimethyl ammonium hydroxide or chloride.

3. A thermosetting powder coating composition comprising (I) an epoxy-functional resin having a molecular weight of about 300 to about 4000, and having approximately 0.05 to about 0.99, epoxy groups per 100g of resin;

(II) a carboxy or anhydride functional cross-linking compound;

(III) a quaternary ammonium salt or hydroxide selected from a list consisting of dioctadecyldimethyl ammonium hydroxide, dioctadecyldimethyl ammonium chloride, dioctadecyldiethyl ammonium hydroxide, dioctadecyldiethyl ammonium chloride, dioctadecyldipropyl ammonium hydroxide, and dioctadecyldipropyl ammonium chloride.

4. The thermosetting powder coating composition of Claim 3, wherein the cross-linking compound is a C3-C30 alkyl, alkenyl, or alkynyl compound having at least two carboxylic acid groups.

5. The thermosetting powder coating composition of Claim 3, wherein the cross-linking compound is selected from a list consisting of adipic acid, dodecanedioic acid, maleic acid, citric acid, sebacic acid, itaconic acid, pimelic acid, aconitic acid, succinic acid, 1,6-hexanedioic acid, and azelaic acid.

6. The thermosetting powder coating composition of Claim 3, wherein the cross-linking compound is selected from a list consisting of trimellitic anhydride, benzophenone tetracarboxylic anhydride, pyromellitic dianhydride, and tetrahydrophthalic anhydride.

7. The thermosetting powder coating composition of Claim 3 or 6, wherein the quaternary ammonium salt is dioctadecyldimethyl ammonium hydroxide or chloride.

8. A thermosetting powder coating composition comprising (I) a carboxy-functional polyester or acrylic polymer;

(II) an epoxy functional polymer or cross-linking agent; and (III) a quaternary ammonium salt or hydroxide selected from a list consisting of dioctadecyldimethyl ammonium hydroxide, dioctadecyldimethyl ammonium chloride, dioctadecyldiethyl ammonium hydroxide, dioctadecyldiethyl ammonium chloride, dioctadecyldipropyl ammonium hydroxide, and dioctadecyldipropyl ammonium chloride.

9. The thermosetting powder coating composition of Claim 8, wherein the epoxy-functional cross-linking compound is triglycidyl isocyanurate.

10. The thermosetting powder coating composition of Claim 8, wherein the acrylic resin is a glycidyl methacrylate resin having a number average molecular weight of about 500 to about 5000 and a weight average molecular weight of about 1000 to about 10,000.

11. The thermosetting powder coating composition of Claim 8, wherein the epoxy-functional resin has a molecular weight of about 300 to about 4000, and having approximately 0.05 to about 0.99, epoxy groups per 100g of resin.

12. The thermosetting powder coating composition of Claim 8, wherein the quaternary ammonium salt is dioctadecyldimethyl ammonium hydroxide or chloride.

13. The thermosetting powder coating composition comprising (I) a hydroxy-functional polyester or acrylic polymer;

(II) a blocked polyisocyanate cross-linking agent; and (III) a quaternary ammonium salt or hydroxide selected from a list consisting of dioctadecyldimethyl ammonium hydroxide, dioctadecyldimethyl ammonium chloride, dioctadecyldiethyl ammonium hydroxide, dioctadecyldiethyl ammonium chloride, dioctadecyldipropyl ammonium hydroxide, and dioctadecyldipropyl ammonium chloride.

14. The thermosetting powder coating composition of Claim 13, wherein the quaternary ammonium salt is dioctadecyldimethyl ammonium hydroxide or chloride.

15. The thermosetting powder coating composition of Claim 13, wherein the blocked polyisocyanate cross-linking agent is an -caprolactam-blocked poly-isocyanate.

16. The thermosetting powder coating composition of Claim 15, wherein the blocked polyisocyanate -caprolactam-blocked toluene-2,4-diisocyanate or -caprolactam-blocked isophorone diisocyanate.

17. A thermosetting powder coating composition comprising (I) an epoxy-functional acrylic polymer;
(II) a polycarboxylic acid cross-linking compound; and (III) a quaternary ammonium salt or hydroxide selected from a list consisting of dioctadecyldimethyl ammonium hydroxide, dioctadecyldimethyl ammonium chloride, dioctadecyldiethyl ammonium hydroxide, didodecyldiethyl ammonium chloride, dioctadecyldipropyl ammonium hydroxide, and dioctadecyldipropyl ammonium chloride.

18. The thermosetting powder coating composition of Claim 17, wherein the cross-linking compound is a C3-C30 alkyl, alkenyl, or alkynyl compound having at least two carboxylic acid groups.

19. The thermosetting powder coating composition of Claim 17, wherein the carboxy-functional cross-linking compounds have the formula H2OC-[(CH2)n]-CO2H, wherein n is an integer of 1-10.

20. The thermosetting powder coating composition of Claim 17, wherein the cross-linking compound is selected from a list consisting of adipic acid, dodecanedioic acid, maleic acid, citric acid, sebacic acid, itaconic acid, pimelic acid, aconitic acid, succinic acid, 1,6-hexanedioic acid, and azeleic acid.

21. The thermosetting powder coating composition of Claim 17, wherein the acrylic resin is a glycidyl methacrylate resin having a number average molecular weight of about 500 to about 5000 and a weight average molecular weight of about 1000 to about 10,000.

22. The thermosetting powder coating composition of Claim 17, wherein the quaternary ammonium salt is dioctadecyldimethyl ammonium hydroxide or chloride.

23. A shaped or formed article coated with the cured thermosetting powder coating composition of Claims 1, 3, 8, 13 or 17.

24. An improved method for curing a thermosetting coating composition, said composition comprising (I) a curable polymer; and (II) a cross-linking compound or a polymer reactive with component (I);

the improvement comprising (a) contacting said composition with a quaternary ammonium salt or hydroxide selected from a list consisting of dioctadecyldimethyl ammonium hydroxide, dioctadecyldimethyl ammonium chloride, dioctadecyldiethyl ammonium hydroxide, didodecyldiethyl ammonium chloride, dioctadecyldipropyl ammonium hydroxide, and dioctadecyldipropyl ammonium chloride;

(b) applying said mixture to a substrate;
followed by (c) heating said substrate to a temperature sufficient to cure the resulting coating.