Powder coating compositions and coated substrates with multilayered coatings

Curable powder clear coating composition and coated substrate with multilayered coatings have as the predominant film-forming polymer in the coating at least one epoxy acrylic copolymer in an amount from 60 to 99.99 percent by weight and 10 to 40 percent by weight of a polycarboxylic acid crosslinking agent. The percentages by weight are based on solids of the curable coating composition. A single predominant film-forming epoxy acrylic copolymer has a number average molecular weight in the range of about 1000 to 5500; a calculated Tg in the range of 50 to 85.degree. C.; epoxy content in the range of 35 to 85, and a styrene content resulting from an amount of styrene monomer in the range of up to about 25 weight percent based on the weight percent of the monomers to form the copolymer. The blend of epoxy acrylic copolymer has one polymer which is the single epoxy acrylic copolymer or one having a number average molecular weight in the range of about 1000 to about 10,000, a calculated Tg in the range of about 40.degree. C. to 85.degree. C., and an epoxy content from 40 to 60 weight percent of the total weight of the monomers to prepare the epoxy acrylic copolymer. The other polymer of the blend has a number average molecular weight in the range of about 500 to about 3000, a calculated Tg in the range of about 35.degree. C. to about 125.degree. C., and an epoxy content from glycidyl functional ethylenically unsaturated monomer that is higher than that of the first epoxy functional acrylic copolymer of the blend and in the range of about 50 to about 100.

FIELD OF THE INVENTION
 The present invention relates to curable thermosetting powder coating
 compositions for clear coats of a multilayered coating composite on
 substrates. The composite has at least a base coat layer with a clear coat
 layer over the base coat layer. Additionally, the composite can have a
 primer coating layer beneath the base coat layer. Such powder clear coat
 layers and multilayer coating composites are useful in painting motor
 vehicles.
 Solid particulate coating formulations referred to in the industry as
 "powder coatings" are finding increasing use in painting metal substrates
 both as primer coatings and as top or clear coats of the base coat and
 clear coat composite coatings. The automotive industry provides corrosion
 protection and decorative appearance for motor vehicles by multilayered
 paint composites on the various types of surfaces of motor vehicles. The
 finishing layers of this composite usually include the popular base coat
 clear coat composites. The base coat is a pigmented layer and the clear
 coat is a nonpigmented or only slightly pigmented layer that is applied
 separately to the base coat and cured to some degree with the base coat.
 To provide improved coating composites for motor vehicles, the industry is
 seeking solutions to the problem of abrasive chipping of the paint from
 the action of road dirt and debris, like sand and gravel, that may strike
 areas of the vehicle such as the hood and lower portions of the vehicle
 such as rocker panels. These strikes can be with considerable impact
 velocity to result in unaesthetic chipping of the clear coat which can
 expose one or more underlying layers of the multilayered coating
 composite, which can also contribute to rusting.
 Chipping in a multilayered coating composite can involve several failure
 mechanisms such as adhesive failure between layers of the multilayered
 composite or cohesive failure within a layer. To obtain good protection
 against chipping damage, the main underlying layers of the multilayered
 composite should have good intercoat or interlayer adhesion. Typically,
 clear coats which are generally the outermost layer of the multilayered
 coating composite typically assist in providing the properties of good
 appearance and environmental protection from etch, scratch and UV
 degradation along with good intercoat adhesion with the base coat.
 The powder clear coats are becoming more widely used for their advantages
 in application from their lower organic solvent emissions. These coatings
 typically have very low levels of volatile solvents, i.e., on the order of
 two percent or slightly higher but generally much less than other paint
 systems. Generally, powder coating manufacturers have focused on the
 appearance, protection, and processability features of powder coatings to
 extract the environmental benefits of these coatings rather than any
 contribution of these coatings to chip resistance of the multilayered
 coating composite.
 For instance, U.S. Pat. Nos. 5,270,391 and 5,407,706 show thermosetting
 curable powder coatings having epoxy functional acrylic copolymers in
 blends where the powders have good storage stability and give coatings
 with good appearance properties. The resin blends are of either a high
 softening point glycidyl-containing acrylic with a low softening point
 glycidyl-containing acrylic, or of different viscosities.
 It is an object of the present invention to provide a clear coating
 composition which contributes to improved chip resistance of the
 multilayered coating composite of which the clear coat is a part without a
 detrimental effect on the appearance properties of the coating. Another
 object of the present invention is to provide improved stability of the
 powder and outstanding durability of the clear coat.
 SUMMARY OF THE INVENTION
 In accordance with the present invention, a curable thermosetting powder
 clear coating composition is provided for a clear coat of a base coat and
 clear coat composite coating with improved chip resistance. This is
 accomplished by the curable clear coating composition having: I) as the
 predominant film-forming polymer of the powder coating at least one epoxy
 functional acrylic polymer or copolymer (hereinafter referred to as "epoxy
 acrylic polymer"), and (II) polycarboxylic acid crosslinking agent where
 the ratio of epoxy functionality of (I) to acid functionality of (II) is
 about 1:0.6 to 1.4. Generally, the amount of the at least one particulate
 film-forming epoxy acrylic polymer is from about 60 to about 99.99 percent
 by weight based on the solids of the curable clear powder coating
 composition. Generally, the amount of the polycarboxylic acid crosslinking
 agent is in the range of about 10 to about 40 weight percent based on the
 weight of solids of the curable clear powder coating composition.
 When a single epoxy acrylic polymer is the predominant film-forming
 polymer, the polymer has a number average molecular weight ("Mn") range, a
 range of glass transition temperature (Tg), and a range of epoxy content
 all as shown in Table A below. When a blend of more than one epoxy acrylic
 polymer is the predominant film-forming polymer of the curable clear
 coating composition, two of the epoxy acrylic polymers in the blend have
 the Mn, Tg, and epoxy content of one and the other epoxy acrylic polymers
 are as shown in Table A as "A" and "B".
 TABLE A
 Mn (grams) Tg .degree. C. Epoxy Content.sup.2
 Single Epoxy about 1000 about 30 to about 35 to 85
 Acrylic to about 60.degree. C. as measured or
 Polymer 5500 50 to 85.degree. C..sup.1
 Blend of A) about about 40 to about 85.sup.1 40-60
 Epoxy Acrylic 1000 to
 Polymers about 10,000
 B) about 500 about 35 to about 125.sup.1 50-100
 to about
 3000
 .sup.1 As calculated by the Acrylic Glass Transition Temperature Analyzer
 from Rohm and Haas Company which is based on the Fox equation.
 .sup.2 (GMA) As weight percent of the monomers to prepare the epoxy acrylic
 polymer.
 In the blend, two epoxy acrylic polymers have relatively low molecular
 weights and one polymer has a higher epoxy content within the higher range
 shown in Table A. If the epoxy acrylic polymer B of Table A has the epoxy
 content of 50 weight percent, the epoxy acrylic polymer A has a lower
 epoxy content within the range of 40 to almost 50. Also, when the higher
 epoxy content epoxy acrylic polymer has an epoxy content from 50 to 60,
 the epoxy content of the lower epoxy content epoxy acrylic polymer is in
 the range from 40 up to almost the value of epoxy content for the higher
 epoxy content epoxy acrylic polymer. Of course, with the epoxy content of
 greater than 60 for the higher epoxy content epoxy acrylic polymer, the
 epoxy content for the lower epoxy content epoxy acrylic polymer is in the
 range of from about 40 to 60. Also, the higher epoxy content epoxy acrylic
 polymer usually has the lower molecular weight between the two polymers
 "A" and "B" in the blend. Generally, the ratio of the low epoxy content
 polymer to the higher epoxy content polymer is in the range of 90:10 to
 10:90.
 The one or more epoxy acrylic polymers typically are formed by addition
 polymerization under free radical initiated conditions from at least the
 following: (i) about 20 to about 100 percent by weight of the total
 monomers of a glycidyl functional copolymerizable ethylenically
 unsaturated monomer; and (ii) up to about 65 percent by weight of one or
 more copolymerizable ethylenically unsaturated monomer or mixture of
 monomers. The exact amount of each monomer (i) and (ii) depends on the
 desired epoxy content for the epoxy acrylic polymer and on whether one or
 a blend of the epoxy acrylic polymers is used as the predominant
 film-forming polymer for the powder coating composition. With a single
 polymer the particular amounts of (i) and (ii) are from about 35 to about
 85 percent by weight of (i) and about 15 to 65 percent by weight of (ii)
 monomers. The monomers of (ii) that are free of glycidyl functionality are
 of a type and in an effective amount with the other monomers to yield the
 desired Tg for the epoxy acrylic polymer. The percents by weight for the
 monomers of (i) and (ii) are based on the total weight of (i) and (ii)
 monomers for each polymer of the blend. As with the single epoxy acrylic
 polymer, the epoxy acrylic polymers of the blend have amounts of (i) and
 (ii) that vary according to the desired values of the parameters of Table
 A for each of the polymers of the blend.
 Also, the epoxy acrylic polymer as a single epoxy acrylic polymer or in the
 blend can have the addition type of polymerization residue of styrene. For
 the single epoxy acrylic polymer, this can be resulting from an amount of
 styrene monomer in one or more of the (ii) monomers of up 25 weight
 percent of the total monomers used to prepare the epoxy acrylic polymer.
 For the epoxy acrylic polymers in the blend, the amount of styrene can be
 that resulting from an amount of styrene monomer in one or more of the
 (ii) monomers of up to about 39 weight percent of the total monomers used
 to prepare the epoxy acrylic polymers of the blend. In the blend, the
 polymer with the lower epoxy content generally has less than 25 weight
 percent of such a polymerization residue from styrene based on the total
 monomers used to prepare that epoxy acrylic polymer.
 Another aspect of the invention is a multilayered coating composite on a
 substrate which includes a primer layer, base coat layer and powder clear
 coat layer, where the latter has as a film-forming polymer of at least one
 low molecular weight epoxy acrylic polymer. This epoxy acrylic polymer or
 blend of epoxy acrylic polymers has the Mn, Tg, and epoxy content as shown
 in the aforementioned ranges of Table A. The multilayered coating
 composite on substrates like those with electrodeposited primer coatings
 over prepared metallic surfaces has improved adhesion between the base
 coat and the adjacent primer layer.
 DETAILED DESCRIPTION OF THE INVENTION
 In the following discussion, unless explicitly stated otherwise, the ranges
 of amounts, molecular weights, ratios, temperatures, time, and reaction
 conditions and the like usually can be varied to a degree from about the
 lower stated number to about the higher stated number of each specific
 range. By the term "film-forming", it is meant that 1) the particulate
 polymeric material of a powder coating upon melting and curing at elevated
 temperature or 2) the polymeric material dispersed or solubilized in a
 solvent or carrier upon drying or evaporation of the solvent or carrier
 and curing of the polymeric material forms a self-supporting continuous
 film on at least a horizontal surface. Also by the term "powder", it is
 meant a particulate, finely divided solid polymeric material generally
 having a particle size of 0.005 to 100 microns. The terms "epoxy content"
 refer to a determination through the determination of epoxide equivalent
 weight in non-aqueous resins and their solutions by differential titration
 with perchloric acid using crystal violet as an indicator. An
 epoxy-containing sample is dissolved in glacial acetic acid and titrated
 against a standard solution of (0.1N) perchloric acid in glacial acetic
 acid in the presence of tetraethylammonium bromide, using crystal violet
 as indicator. This potentiometric titration with perchloric acid
 determines the base content of the polyepoxide. The mass in grams of
 sample containing one mole of unreacted epoxide functionality is
 determined by reaction of the epoxide with hydrobromic acid. The
 hydrobromic acid is generated in situ by the reaction of
 tetraethylammonium bromide with perchloric acid. A second sample of the
 polyepoxide is mixed with excess tetraethylammonium bromide and titrated
 with 0.1N perchloric acid to a green endpoint that persists for at least
 30 seconds, and total epoxide and amine equivalents are calculated from
 these titrations, and the epoxide equivalent weight is calculated as the
 difference. The epoxy content is the epoxy equivalent weight divided by
 the molecular weight of the polyepoxide sample.
 For the film-forming polymeric epoxy acrylic polymer for the predominant
 film-forming polymer of the curable powder coating, whether as the single
 polymer or the blend, the Tg's of Table A can generally be calculated by
 any method known to those skilled in the art. The Tg of the copolymer
 contributes to the stability of the powder coating composition. Generally,
 the higher the Tg of the polymer, the better the stability of the coating.
 The Tg is described in PRINCIPLES OF POLYMER CHEMISTRY (1953), Cornell
 University Press. The Tg can actually be measured or it can be calculated
 as described by Fox in Bull. Amer. Physics Soc., 1, 3 page 123 (1956). The
 Tg of the high Tg monomers mentioned herein refers to the calculated value
 of the homopolymer made from the monomer calculated as described above by
 Fox. For example, the Tg of methylmethacrylate monomer is 221.degree. F.
 (105.degree. C.) and that of styrene monomer is 212.degree. F.
 (100.degree. C.). The Tg of the copolymer from these monomers and the
 glycidyl-containing monomer in appropriate amounts is typically between
 30.degree. C. and 60.degree. C., and more preferably between 35.degree. C.
 and 55.degree. C. The actual measured values for Tg are obtainable by
 differential scanning calorimetry (DSC) usually at a rate of heating of
 18.degree. F. (10.degree. C.) per minute, where the Tg is taken at the
 first inflection point. Also, the Tg can be measured experimentally by
 using a penetrometer such as a DuPont 940 Thermomedian Analyzer or
 comparable equipment from Perkin-Elmer Corporation. The Tg of the polymers
 as used herein for this invention refers to the calculated values in
 accordance with the Fox equation as part of the tables of the "Acrylic
 Glass Transition Temperature Analyzer" from Rohm and Haas Company, unless
 otherwise indicated.
 The epoxy acrylic polymer can be prepared by copolymerizing a glycidyl
 functional ethylenically unsaturated monomer (i), typically a glycidyl
 functional acrylic monomer, such as glycidyl acrylate or glycidyl
 methacrylate ("glycidyl (meth)acrylate"), with (ii) an ethylenically
 unsaturated monomer or mixture of monomers free of glycidyl functionality.
 Preferably in the practice of the invention where the polymer is the
 single main film-forming polymer of the coating composition, the glycidyl
 functional monomer (i) can be copolymerized with one or more (ii) monomers
 having a Tg greater than 200.degree. F. (93.degree. C.). Preferably, the
 measured Tg for the single epoxy acrylic polymer is 30.degree. C. to
 60.degree. C. The high Tg monomer can assist in preventing caking and
 instability problems associated with powder coatings. Suitable monomers
 free of glycidyl functionality include methylmethacrylate and methacrylic
 acid ester or acrylic acid ester ("(meth)acrylic acid ester") having an
 alicyclic hydrocarbon group having 5 to 22 carbon atoms, more suitably 5
 to 10 carbon atoms in the ester portion. Suitable examples include:
 cyclopentyl methacrylate, cyclohexyl methacrylate,
 methylcyclohexyl-methacrylate, trimethylcyclohexyl methacrylate,
 norbornylmethacrylate, norbornylmethyl methacrylate, isobornyl
 methacrylate and the like. The amount of styrene on a weight percent basis
 of the total monomers for the single type epoxy acrylic polymer is
 preferably up to about 20 weight percent of the total monomers. When
 styrene is absent from the epoxy copolymer, it is preferred to have at
 least one of the aforementioned high Tg ethylenically unsaturated monomers
 as monomers to prepare the epoxy acrylic polymer. Also, other
 ethylenically unsaturated monomers can be used in the preparation of the
 one or more epoxy acrylic polymers such as hydroxyalkylacrylates and
 hydroxyalkylmethacrylates such as hydroxypropylacrylate,
 hydroxypropylmethacrylate, and hydroxybutylacrylate.
 The epoxy acrylic polymer can be prepared by traditional free radical
 initiated polymerization techniques using suitable catalysts which include
 organic peroxides and azo-type compounds and chain transfer agents such as
 alpha-methyl styrene dimer and tertiary dodecyl mercaptan. The preparation
 of the epoxy copolymer as an epoxy-containing acrylic polymer may be
 conducted as disclosed in U.S. Pat. No. 4,650,718 (column 1, line 61
 through column 3, line 40 and column 4, line 55 through column 9, line
 15), incorporated herein by reference. The preparation of the epoxy
 acrylic polymer utilized as the single copolymer for the main film-forming
 polymer of the powder composition usually has amounts of the (i) and (ii)
 monomers in the following ranges. Preferably, this polymer has: (i) 35 to
 65 percent by weight of the glycidyl functional monomer and (ii) 35 to 65
 percent by weight of one or more copolymerizable ethylenically unsaturated
 monomers free of glycidyl functionality. Most preferably, the (ii) monomer
 is methylmethacrylate or trimethylcyclohexyl methacrylate. In addition to
 the (i) and (ii) monomers, the epoxy acrylic polymer can also have from 5
 to 20 percent by weight, based on weight of the total monomers for the
 polymer, of one or more additional copolymerizable monomers different from
 the (i) and (ii) monomers, like butylmethacrylate. Although other
 ethylenically unsaturated monomers can be present in the epoxy acrylic
 polymer, the percentages by weight of the aforementioned monomers
 including any styrene preferably are based on the total weight of (i), and
 (ii) monomers, to achieve a total of 100 percent.
 In addition to the aforementioned Mn, the single type of epoxy acrylic
 polymer preferably has a weight average molecular weight typically between
 about 1000 and 5500 and most preferably about 2000 to about 4000 and a
 peak molecular weight in the range of 2000 to 5500. Also, the single type
 of epoxy acrylic polymer preferably has the aforelisted epoxy content so
 that there is from 3.0 to 5.9 moles of glycidyl functional ethylenically
 unsaturated monomer per kilogram of epoxy functional copolymer, more
 suitably between 3.5 and 5.1 moles of glycidyl functional monomer per
 kilogram of epoxy copolymer.
 When the predominant film-forming polymer of the powder coating is a blend
 of the epoxy acrylic polymers, as is preferred, the lower epoxy content
 polymer can have a peak molecular weight in the range of 4500 to 8000 and
 a measured Tg of 40.degree. C. to 60.degree. C. The higher epoxy content
 polymer can have a peak molecular weight of 2000 to 4500 and a measured Tg
 in the range of 40.degree. C. to 60.degree. C. The blend preferably has a
 range from around 25 to 75 to 75 to 25 of the two aforementioned epoxy
 acrylic polymers where the preferred molecular weight range, Tg range,
 epoxy equivalent weight and epoxy content are as shown in Table B.
 TABLE B
 Epoxy
 Equivalent
 Mn (grams) Tg .degree. C. Weight Epoxy Content
 A) 1000 to 3000 50 to 85 (calculated) 240-350 50
 30 to 60 (measured)
 B) 800 to 2000 35 to 120 (calculated) 142-285 90
 about 0 to about 40
 The epoxy acrylic polymers for the blend are preferably two epoxy
 copolymers that are prepared in a similar manner as the single epoxy
 acrylic polymer. The blend has a total styrene content for the two or more
 epoxy acrylic polymers, based on the weight of the total epoxy acrylic
 polymers, of from 0 up to about 39 weight percent taking into
 consideration both epoxy acrylic polymers. This means that one of the
 epoxy acrylic polymers in the blend may have a styrene content greater
 than these ranges, but when considering the lower styrene content of the
 other epoxy acrylic polymer in the blend and the ratios of each epoxy
 acrylic polymer in the blend, the blend preferably does not have a styrene
 content greater than the aforementioned range. The amounts of the (i) and
 (ii) monomers for one of the epoxy acrylic polymers in the blend are
 preferably the same as those for the single type of epoxy acrylic polymer.
 While the other epoxy acrylic polymer in the blend has amounts of the (i)
 and (ii) monomers preferably in the range to result in the higher epoxy
 content and the preferred Tg and molecular weight as aforelisted in Table
 B.
 The polyacid crosslinking agent in the film-forming resinous material is in
 amounts of about 10 to 90, preferably 25 to 75 percent by weight based on
 total weight of resin solids in the powder coating composition. The
 polyacid crosslinking agent has a high average acid functionality. More
 specifically, the polyacid crosslinking agent on average contains more
 than two acid groups per molecule, more preferably three or more, and most
 preferably four or more, such acid groups being reactive with the
 polyepoxide to form a crosslinked coating as indicated by its resistance
 to organic solvent. The parameter of greater than two acid groups per
 molecule is intended to encompass mixtures of polyacid crosslinking agents
 in which difunctional curing agents are mixed with tri- or higher
 functionality polyacid crosslinking agents. Polyacid crosslinking agent
 mixtures including up to about 50 percent of a difunctional curing agent
 with a trifunctional curing agent are suitable. Higher percentages of
 difunctional materials can be used if the remainder of the curing agent
 mixture is higher than trifunctional or if the polyacid crosslinking agent
 mixture is used with a highly functional polyepoxide component. The acid
 functionality is preferably carboxylic acid, although acids such as
 phosphorus-based acid may be used. Preferably, the polyacid crosslinking
 agent is a carboxylic acid terminated material having, on average, greater
 than two carboxylic acid groups per molecule. Among the polyacid
 crosslinking agents which may be used are carboxylic acid group-containing
 polymers such as acrylic polymers, polyesters, and polyurethanes;
 oligomers such as ester group-containing oligomers, which are preferred;
 and monomers. Suitable art-recognized polyacid crosslinking agents include
 those described in U.S. Pat. No. 4,650,718 to Simpson et al. (column 1,
 line 61 through column 3, line 40 and column 4, line 55 through column 9,
 line 15); U.S. Pat. No. 4,681,811 to Simpson et al. (column 1, line 63
 through column 10, line 65); U.S. Pat. No. 4,703,101 to Singer et al.
 (column 3, line 26 to column 6, line 5); U.S. Pat. No. 4,804,581 to Pettit
 et al. (column 5, line 12 through column 7, line 34); and U.S. Pat. No.
 5,407,707 to Simeone et al. (column 3, line 50 through column 4, line 10),
 which are hereby incorporated by reference.
 Preferably, the polycarboxylic acid is a crystalline material, more
 preferably a crystalline aliphatic material containing from 4 to 20 carbon
 atoms. Examples of suitable acids include adipic, succinic, sebacic,
 azelaic and dodecanedioic acid. In addition, carboxylic acid functional
 polyesters may be used to crosslink the powder coating composition. Low
 molecular weight polyesters and half-acid esters can be used which are
 based on the condensation of aliphatic polyols with aliphatic and/or
 aromatic polycarboxylic acids or anhydrides, or the reaction of aliphatic
 polyols and aliphatic and/or aromatic anhydrides, respectively. Examples
 of suitable aliphatic polyols include ethylene glycol, propylene glycol,
 butylene glycol, 1,6-hexanediol, trimethylol propane, di-trimethylol
 propane, neopentyl glycol, 1,4-cyclohexanedimethanol, pentaerythritol and
 the like. The polycarboxylic acids and anhydrides may include those
 mentioned above, as well as terephthalic acid, isophthalic acid, phthalic
 acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic
 anhydride, hexahydrophthalic acid, methyltetrahexahydrophthalic anhydride,
 alkylhexahydrophthalic anhydride, chlorendic anhydride and the like.
 Mixtures of the polycarboxylic acids, anhydrides, and polyols may also be
 used.
 The use of aliphatic crystalline dicarboxylic acids is preferred, and in
 particular, dodecanedioic acid is most preferred. The advantage of these
 crystalline crosslinkers, particularly at the higher levels, is that
 generally they are incompatible with the epoxy functional copolymer
 providing for a more stable powder coating composition. However, when the
 powder coating composition is melted, the polyacid crosslinking agent is
 compatible and soluble in the acrylic copolymer acting somewhat as a
 diluent allowing for improved flow and appearance.
 The powder coating composition is prepared by combining approximately 60 to
 90 percent by weight of the epoxy copolymer with about 10 to 40 percent by
 weight, based on total weight of the powder coating of a polycarboxylic
 acid crosslinking agent. When the epoxy copolymer is in an amount in the
 lower portion of the aforementioned range, minor amounts of other
 film-forming polymers known to those skilled in the art to be useful in
 powder coating can be used.
 Typically, a suitable range of epoxy copolymer to polycarboxylic acid
 crosslinking agent can be between 70 to 85, more preferably 70 to 80
 percent by weight epoxy copolymer and between 15 to 30, more preferably 20
 to 30 percent by weight polycarboxylic acid crosslinking agent, based on
 total weight of the powder coating. Also, it is preferred that the
 equivalent ratio of the reactants present in the powder composition of the
 present invention is adjusted such that for each equivalent of epoxy there
 are around 0.3 to around 3.0, preferably 0.75 to 1.5 equivalents of
 carboxyl (anhydride, if present, is considered monofunctional).
 The powder coating composition may also contain additional materials as
 known to those skilled in the art. For example, an anhydride for improved
 cure response and copolymer of an alpha olefin and olefinically
 unsaturated anhydride for improved humidity resistance of the cured
 coating can be used.
 Additionally, polymer or copolymer flow control or flow modifying agents
 known to those skilled in the art can be used in the powder coating of the
 present invention. Suitable examples and amounts are shown in U.S. Pat.
 No. 5,212,245 (columns 2-4). Also, commercially available flow control
 polymers and copolymers can be used such as Modaflow (or Resiflow) flow
 additives, available from Monsanto Chemical Company of St. Louis, Mo. and
 the like. Generally, the weight average molecular weight of the copolymer
 flow control agents can range from about 1000 to 40,000, preferably 1000
 to 15,000. Generally, the glass transition temperature (Tg) of the
 copolymer is less than 10.degree. C. and preferably less than 0.degree. C.
 and most preferably in the range of -60.degree. C. to -10.degree. C. The
 Tg can be calculated and measured in the aforedescribed manner. The Tg of
 the copolymer is not limiting of its performance as a flow additive but
 Tg's greater than 10.degree. C. are not preferred because of decreased
 flow on coating application. A suitable amount of the flow control agent
 can be in the range of from about 0.01 to about 10 percent by weight based
 on total resin solids for the curable powder composition. With the
 preferred powder coating, the weight percent is of the total resins of the
 particulate film-forming polymer and flow modifier. Preferably, the flow
 control copolymer will be included in the powder coating composition in
 amounts of 0.1 to 3 percent by weight, more preferably from about 0.5 to
 about 2 percent by weight for clear coat applications. The preferred flow
 modifier is that from Troy as shown in the examples.
 The thermosetting powder coating compositions of the invention can
 optionally include other materials such as pigments, fillers, light
 stabilizers and antioxidants such as those shown in U.S. Pat. No.
 5,407,707, hereby incorporated by reference. Nonexclusive examples of
 light stabilizers include those shown in the Examples herein and others
 such as CGL 1545 hydroxyphenyl triazine ultraviolet absorber available
 from Ciba-Geigy Limited, Basel, Switzerland.
 Although the powder coating composition is preferably a clear coat for a
 base coat and clear coat composite, one or more pigments can be included
 in the coating composition. Their amounts would range from 1 to 50 percent
 by weight based on total weight of the composition if color is desired for
 the resultant coating. Suitable pigments include, for example, titanium
 dioxide, ultramarine blue, phthalocyanine blue, phthalocyanine green,
 carbon black, graphite fibrils, black iron oxide, chromium green oxide,
 ferride yellow and quindo red.
 Anti-popping agents can be added to the composition to allow any volatile
 material to escape from the film during baking. Benzoin is a commonly
 preferred anti-popping agent useful in effective amount to retard popping
 of the coating. When used benzoin is generally present in amounts of from
 about 0.5 to 3.0 percent by weight based on total weight of the powder
 coating composition.
 In addition, the powder coating composition may include fumed silica or the
 like to reduce caking of the powder during storage. An example of a fumed
 silica is sold by Cabot Corporation under the trademark CAB-O-SIL. The
 fumed silica is present in amounts ranging from 0.1 to 1 percent by weight
 based on total weight of the powder coating formulation.
 The thermosetting powder coating compositions are prepared by melt blending
 the ingredients. This can be accomplished by first blending the
 ingredients in a high shear mixer such as a planetary mixture, and then
 melt blending in an extruder from about 80.degree. C. to about 130.degree.
 C. The extrudate is then cooled and pulverized into a particulate blend.
 Such a particulate mixture can be applied preferably by spraying
 techniques. The thermosetting powder coating compositions of the invention
 can be applied as clearcoats in color-plus-clear or basecoat, clearcoat
 composite coatings.
 The powder coating composition and preferably the particulate thermosetting
 powder coating composition can be applied directly to a substrate of, for
 example, metal such as steel or aluminum. Most preferably, the powder
 coating is a clearcoat for application over or with any basecoat
 formulations known to those skilled in the art such as water-borne
 basecoats.
 The film-forming composition of the base coat in the color-plus-clear
 system can be any of the compositions useful in coatings applications,
 particularly automotive applications. The film-forming composition of the
 base coat comprises a film-forming resinous binder and a pigment to act as
 the colorant. Particularly useful resinous binders are acrylic polymers,
 polyesters, including alkyds, and polyurethanes.
 The base coat compositions may be solventborne or waterborne. Waterborne
 base coats in color-plus-clear compositions are disclosed in U.S. Pat. No.
 4,403,003; EP 0038127; EP 0206615; EP 0502934; EP 0260447; EP 0281936; EP
 0228003; and EP 0355433 and the resinous compositions used in preparing
 these base coats can be used in the practice of this invention. Also,
 waterborne polyurethanes such as those prepared in accordance with U.S.
 Pat. No. 4,147,679 can be used as the resinous binder in the base coat.
 Further, waterborne coatings such as those described in U.S. Pat. No.
 5,071,904 can be used as the base coat. Additional examples of such base
 coats include those solvent-borne and water-borne film-forming resinous
 materials that include one or more pigments such as those available from
 PPG Industries, Inc., Pittsburgh, Pa., U.S.A.
 The base coat contains pigments to give it color. Compositions containing
 metallic flake pigmentation are useful for the production of so-called
 "glamour metallic" finishes chiefly upon the surface of automobile bodies.
 Suitable metallic pigments include in particular aluminum flake, copper
 bronze flake and metal oxide coated mica.
 Besides the metallic pigments, the base coating compositions of the present
 invention may contain non-metallic color pigments conventionally used in
 surface coatings including inorganic pigments such as titanium dioxide,
 iron oxide, chromium oxide, lead chromate, and carbon black, and organic
 pigments such as phthalocyanine blue and phthalocyanine green. In general,
 the pigment is incorporated into the coating composition in amounts of
 about 1 to 80 percent by weight based on weight of coating solids. The
 metallic pigment is employed in amounts of about 0.5 to 25 percent by
 weight based on weight of coating solids.
 If desired, the base coat composition may contain additional materials well
 known in the art of formulated surface coatings. These would include
 surfactants, flow control agents, thixotropic agents, fillers,
 anti-gassing agents, organic cosolvents, catalysts, and other customary
 auxiliaries. These materials can constitute up to 40 percent by weight of
 the total weight of the coating composition.
 The base coating compositions can be applied to various substrates to which
 they adhere including wood, metals, glass, and plastic. The compositions
 can be applied by conventional means including brushing, dipping, flow
 coating, spraying and the like, but they are most often applied by
 spraying. The usual spray techniques and equipment for air spraying and
 electrostatic spraying and either manual or automatic methods can be used.
 During application of the base coat composition to the substrate, a film of
 the base coat is formed on the substrate. Typically, the base coat
 thickness will be about 0.01 to 5 mils (0.254 to 127 microns), preferably
 0.1 to 2 mils (2.54 to 50.8 microns) and most preferably 5 to 30 microns
 in thickness.
 After application of the base coat to the substrate, a film is formed on
 the surface of the substrate by driving solvent, i.e., organic solvent or
 water, out of the base coat film by heating or by an air drying period.
 Preferably, the heating will only be for a short period of time,
 sufficient to ensure that the clear coat can be applied to the base coat
 without the former dissolving the base coat composition, yet insufficient
 to fully cure the basecoat. Suitable drying conditions will depend on the
 particular base coat composition and on the ambient humidity with certain
 waterborne compositions, but in general a drying time of from about 1 to
 15 minutes at a temperature of about 80-250.degree. F. (20-121.degree. C.)
 is adequate. At the same time, the base coat film is adequately wetted by
 the clear coat composition so that satisfactory intercoat adhesion is
 obtained. Also, more than one base coat and multiple clear coats may be
 applied to develop the optimum appearance. Usually between coats, the
 previously applied coat is flashed, that is, exposed to ambient conditions
 for about 1 to 20 minutes.
 Application of the powder coating of the present invention can be by
 spraying, and in the case of a metal substrate, by electrostatic spraying
 which is preferred, or by the use of a fluidized bed. The powder coating
 powder can be applied in a single sweep or in several passes to provide a
 film having a thickness after cure of from 1 to 15, preferably 1 to 6 mils
 (25.4 to 381 usually 25.4 to 152 microns). After application of the
 coating composition such as the preferred powder coating, the powder
 coating substrate is baked at a temperature sufficient to cure the
 coating, typically at about 250.degree. F. to about 400.degree. F.
 (121.degree. C. to 204.degree. C.) for about 1 to 60 minutes, and
 preferably at about 275.degree. F. to 350.degree. F. (135.degree. C. to
 177.degree. C.) for about 10 to 30 minutes.
 While the powder coating composition can be applied directly upon bare
 metal, that is, upon untreated, unprimed steel or upon pretreated, i.e.,
 phosphatized unprimed steel, in one embodiment of the invention the powder
 coating composition is applied to a metal substrate having a thin layer of
 electrodeposited primer coating. The electrodeposited primer coating upon
 the metal substrate can be, for example, a cathodic electrodeposition
 primer composition such as those available from PPG Industries, Inc. under
 the UNI-PRIME trademark. In one aspect of the present invention, it is
 contemplated that the powder coating composition can be applied directly
 upon at least a portion of an uncured electrodeposited primer coating, for
 example, the electrodeposited primer coating deposited over an automotive
 or truck body and thereafter both the electrodeposited primer coating and
 powder coating as a primer coating can be co-cured by heating at a
 temperature between 275.degree. F. to 350.degree. F. (135.degree. C. to
 177.degree. C.) for about 10 to 30 minutes.
 As another aspect of the present invention, the aforementioned powder
 coating with the epoxy acrylic polymer as a single predominant
 film-forming polymer or as the blend of epoxy acrylic polymers is the
 clear unpigmented, or only slightly pigmented without interfering
 pigments, clear coat in a multilayered coating composite on substrates
 like those mentioned above. The multilayered coating composite can have
 one or more primer coats which can be any primer coating known to those
 skilled in the art and a basecoat for a basecoat plus clearcoat composite.
 For instance, the primer coat can be an electrodeposited primer coat of a
 cationic epoxy amine adduct cured with a polyisocyanate curing agent alone
 or with solvent-borne primers. The basecoat can be any known to those
 skilled in the art like those noted above. In addition to the at least one
 epoxy acrylic polymer for the powder clear coat, other acrylic polymers
 and copolymers can be used as long as their Mn or weight average ("Mw")
 molecular weight is in a range similar to the aforementioned and
 hereinafter mentioned ranges for the epoxy acrylic polymer. This use is as
 the predominant film-forming polymer as the aforedescribed epoxy acrylic
 polymer for the powder clear coat. These acrylic polymers and copolymers
 can have other functional groups with abstractable hydrogen such as
 hydroxyl, carboxyl, and amino and suitable noninterfering mixtures
 thereof.

EXAMPLES
 The following examples show the preparation of powder coating compositions
 and polymers utilized in the thermosetting powder coating compositions of
 the present invention. All of the amounts are in parts by weight as grams
 of the actual component used in preparing the powder coating formulation.
 Polymer Synthesis Examples
 Examples A through I show the preparation of various polymer compositions,
 differing in styrene content, Tg (high and low) and molecular weight (Mw),
 which were used to prepare powder coating compositions of the present
 invention shown below in Examples 1 through 12.
 Examples A-I
 The ingredients of Examples A through I are listed below in Table I. The
 polymers of each example were prepared using the following procedure.
 An initial solvent portion was charged into a four-neck flask, which served
 as the reaction vessel, and which was equipped with a thermocouple, a
 reflux condenser and a stirrer. The initial solvent charge was heated to
 reflux under a nitrogen gas blanket. A "first initiator mixture" is
 prepared in a separate premix flask. Also, the monomer mixture is prepared
 in a separate second premix flask. The first initiator mixture and the
 monomer mixture are simultaneously added dropwise from separate addition
 funnels into the reaction vessel over a period of time of 3 hours while
 maintaining the reaction at reflux and under a nitrogen gas blanket. After
 the completion of the additions, the reaction mixture was held at reflux
 for 30 minutes. After this period of time, a "second initiator mixture",
 which is premixed, was added by the addition funnel to the reaction vessel
 and the reaction was then held at reflux under the nitrogen blanket for
 one hour. After this period of time, a "third initiator mixture", which
 was premixed, is added by the addition funnel to the reaction vessel and
 the reaction was then held at reflux under the nitrogen blanket for one
 hour after which the reaction mixture was cooled. The reaction mixture was
 then vacuum stripped to remove volatile components. The reaction mixture
 was analyzed for solids content, and weight average molecular weight as
 determined by gel permeation chromatography using a polystyrene standard.
 TABLE I
 Ingredients A B C D E F G
 H I
 Initial Charge:
 Xylene 502.2 500.3 500.3 0 0 1093.5 1447.8
 482.6 482.6
 Butyl acetate 0 0 0 1093.5 1093.5 0 0
 0 0
 Monomer Mixture:
 Glycidyl methacrylate 1050 1045.7 1045.7 2300 2300 2300
 3632.4 1210.8 1210.8
 Butyl methacrylate 105 209.1 104.6 460 460 460 0
 0 0
 Methyl methacrylate 630 732.0 732.0 1610 1610 1610 0
 0 0
 Styrene 315 104.6 209.1 230 230 230 0
 0 201.8
 Butyl acrylate 0 0 0 0 0 0 0
 0 201.8
 Trimethylcyclohexyl 0 0 0 0 0 0
 2421.6 807.2 403.6
 methacrylate
 First Initiator Mixture:
 Xylene 360 359.1 359.1 0 0 790.1 1039.2
 346.4 346.4
 Butyl acetate 0 0 0 790.1 790.1 0 0
 0 0
 Lupersol 555.sup.1 181 209.1 209.1 460 230 613.3 0
 0 0
 Vazo-67.sup.2 0 0 0 0 0 0 302.4
 100.8 100.8
 Second Initiator
 Mixture:
 Xylene 18.9 18.7 18.7 0 0 40.7 54
 18 18
 Butyl acetate 0 0 0 40.7 40.7 0 0
 0 0
 Lupersol 555 14.5 14.0 14.0 30.7 30.7 30.7 0
 0 0
 Vazo-67 0 0 0 0 0 0 24.6
 8.2 8.2
 Third Initiator
 Mixture:
 Xylene 18.9 18.7 18.7 0 0 40.7 54
 18 18
 Butyl acetate 0 0 0 40.7 40.7 0 0
 0 0
 Lupersol 555 14.5 14.0 14.0 30.7 30.7 30.7 0
 0 0
 Vazo-67 0 0 0 0 0 0 24.6
 8.2 8.2
 % Styrene (on 15 5 10 5 5 5 0
 0 10
 monomers)
 Mw 4530 4264 3757 5446 10,505 -- --
 4479 4657
 Mn 1700 1600 1500 1900 2400 1300 2000
 2300 1800
 Tg in degrees C. 43 36 35 40 51 29 34
 52 30
 .sup.1 t-Amyl peroxyacetate commercially available from Elf Atochem North
 America, Inc.
 .sup.2 2,2'-Azobis(2-methylbutyronitrile), available from E. I. DuPont de
 Nemours and Co.
 Powder Coating Composition Examples
 Each formulation in the examples below in Tables II and III are shown in
 amounts of parts by weight which are the grams of the actual component
 used in the formulation and each formulation was processed in the
 following manner. The components were blended in a Henschel Blender for 30
 to 60 seconds. The mixtures were then extruded through a Werner & Pfleider
 co-rotating twin screw extruder at a temperature of 100.degree. C. to
 130.degree. C. The extruded material was then ground and classified to a
 particle size of 17 to 27 microns using and ACM1 Grinder (Air Classifying
 Mill from Micron Powder Systems, Summit, N.J.). The finished powders were
 electrostatically sprayed onto test panels and evaluated for appearance
 and chip resistance. The results are tabulated below in Table IV.
 Examples 1 through 12 show powder coating compositions of the present
 invention. Examples 1 to 3 show powder compositions with a variation in
 styrene content of the polymer while holding polymer Mw approximately
 constant (Example 1: 15% styrene content, 4530 Mw; Example 2: 5% styrene,
 4264 Mw; Example 3: 10% styrene, 3757 Mw). Examples 2, 4 and 5 show powder
 compositions with a constant polymer composition (50% glycidyl
 methacrylate, 5% styrene, 10% butyl methacrylate, 35% methyl methacrylate)
 and varying Mw (Ex. 2: 4264 Mw; Ex. 4: 5446 Mw; Ex. 5: 10,505 Mw). The Mw
 of Example 5 is outside the scope of this invention and is considered a
 comparative example. Examples 6 through 10 show powder compositions made
 from blends of polymers having varying Mw and Tg.
 TABLE II
 Ingredient 1 2 3 4 5 6 7 8 9 10
 Polymer of 717.4 0 0 0 0 0 0 0 0 0
 Example A
 Polymer of 0 717.4 0 0 0 538.0 0 0 0 217.4
 Example B
 Polymer of 0 0 717.4 0 0 0 0 0 0 0
 Example C
 Polymer of 0 0 0 717.4 0 0 0 0 0 0
 Example D
 Polymer of 0 0 0 0 717.4 0 0 0 0 0
 Example E
 Polymer of 0 0 0 0 0 179.3 226.4 226.0 208.2 0
 Example F
 Polymer of 0 0 0 0 0 0 0 0 624.7 0
 Example G
 PD-9060.sup.1 0 0 0 0 0 0 0 677.8 0 0
 PD-3402.sup.2 0 0 0 0 0 0 679.2 0 0 652.9
 VXL-1381.sup.3 0 0 0 0 0 0 0 0 0 258.6
 DDDA.sup.4 282.6 282.6 282.6 282.6 282.6 282.7 294.4 296.4 367.1 70.8
 EX 570.sup.5 13.2 13.2 13.2 13.2 13.2 13.6 15.8 15.8 15.8 15.6
 Benzoin 2.2 2.2 2.2 2.2 2.2 2.2 2.6 2.6 2.6 2.6
 Wax C.sup.6 6.6 6.6 6.6 6.6 6.6 6.6 7.9 7.9 7.9 7.8
 PR-31.sup.7 22.0 22.0 22.0 22.0 22.0 22.0 26.4 26.4 26.4 26.0
 TINUVIN 900.sup.8 22.0 22.0 22.0 22.0 22.0 22.0 26.4 26.4 26.4
 26.0
 GCA-1.sup.9 22.0 22.0 22.0 22.0 22.0 22.0 26.4 26.4 26.4 26.0
 Methyl 11.0 11.0 11.0 11.0 11.0 11.0 13.2 13.2 13.2 0
 dicocoamine
 FOOTNOTES FOR TABLE II
 .sup.1 PD 9060, glycidyl containing polymer having a Tg of 44.degree. C.,
 commercially available from Anderson Development, Inc. made in accordance
 with U.S. Pat. No. 4,042,645.
 .sup.2 PD 3402, glycidyl containing polymer having a Tg of 52.degree. C.,
 commercially available from Anderson Development, Inc.
 .sup.3 ADDITOL VXL 1381 anhydride crosslinker commercially available from
 Hoechst-Celanese.
 .sup.4 Dodecanedioic Acid.
 .sup.5 TROY EX 570, amide modified polyester oligomer commercially
 available from TROY Corporation.
 .sup.6 Wax C Micro Powder, a fatty acid amide (ethylene bis-stearoylamide),
 commercially available from Hoechst-Celanese.
 .sup.7 Sanduvor PR-31 Powder, hindered amine light stabilizer containing
 propanedioic acid,
 [(4-methoxyphenyl)-methylene]-,bis(1,2,2,6,6-pentamethyl-4-piperdivinyl)es
 ter, commercially available from Clariant Corporation.
 .sup.8 TINUVIN 900 (2-(3',5'-bis(1-methyl-1-phenylethyl)-2'-hydroxyphenyl)
 benzotriazole), an ultraviolet light stabilizer available from Ciba-Geigy
 Corp.
 .sup.9 GCA-1, an anti-yellowing agent commercially available from Sanko
 Chemical Corp.
 TABLE III
 Ingredient 11 12
 Polymer of Example H 501.5 334.3
 Polymer of Example I 167.2 334.3
 DDDA 246.3 246.3
 Benzoin 7.0 7.0
 TINUVIN 144.sup.1 20.0 20.0
 TINUVIN 900 20.0 20.0
 GCA-1 20.0 20.0
 Liquid Modaflow.sup.2 8.0 8.0
 Methyl dicocoamine 2.5 2.5
 Triphenyl Tin Hydroxide.sup.3 7.5 7.5
 .sup.1 TINUVIN 144
 (2-tert-butyl-2-(4-hydroxy-3,5-di-tert-butylbenzyl)[bis(methyl-2,2,6,6,-te
 tramethyl-4-piperidinyl)]dipropionate), an ultraviolet light stabilizer
 available from Ciba-Geigy Corp.
 .sup.2 Modaflow, flow control additive, commercially available from
 Monsanto.
 .sup.3 Commercially available from Elf Atochem North America.
 The clear coat compositions of Examples 1 through 12 were prepared for
 testing as follows. For Monochip testing, test panels coated with
 electrocoat primer, commercially available from PPG Industries, Inc. as
 ED-5000, were first primed to a film thickness of about 1.1 to 1.3 mils
 (28 to 33.mu.) with an automotive solvent-borne black primer commercially
 available from Mehnert & Veek, Germany, then baked for 20 minutes at
 320.degree. F. The test panels were then basecoated, by spray application
 to a film thickness of about 0.6 mils ( 15.2.mu.), with an oxford green
 waterborne base coat, commercially available from BASF, Germany. The
 basecoated panels were then flash baked for 10 minutes at 176.degree. F.
 (80.degree. C.) before electrostatically spray applying each powder clear
 coat composition of Examples 1 to 12. The powder coated panels were then
 cured for 30 minutes at 285.degree. F. (140.degree. C.). The dry film
 thickness (DFT) of the powder clear was targeted for 2.3 to 3.5 mils (58
 to 89.mu.).
 For appearance evaluations, each powder was electrostatically sprayed to a
 film thickness of 2.3 to 3.5 mils directly onto test panels coated with a
 smooth black electrocoat paint, commercially available from PPG
 Industries, Inc. as ED5051, and then cure for 30 minutes at 285.degree. F.
 (140.degree. C.). The test panels were then tested for chip resistance
 using the Monochip test described below, and appearance using 20.degree.
 gloss, haze, and DOI as criteria. The results are tabulated in Table IV.
 TABLE IV
 MONOCHIP** Appearance Over Black
 Initial -20.degree. C. ED 5051
 EXAMPLE mm Mode mm Mode 20.degree. Gloss* Haze* DOI*
 1 Ac C VG A 96 18 93
 2 G C VG C 83 24 97
 3 Ac C VG C 84 18 97
 4 VG M M A 84 22 92
 5 G M M A 83 31 85
 6 M C VG A 86 17 90
 7 Ac C G C 86 13 89
 8 Ac C VG A 86 18 93
 9 M C VG A 83 22 88
 10 M C VG M 88 18 93
 11 M C -- -- 81 19 97
 12 M C -- -- 79 25 96
 *Appearance Properties: 20.degree. Gloss and Haze were measured by a BYK
 Gardner Haze - Gloss Meter. Higher numbers for gloss indicate better
 performance and lower numbers for Haze indicate better performance. Haze
 numbers over 30 are considered unacceptable. Distinction of Image (DOI)
 was measured by a Hunter Lab's Dorigon II where higher numbers indicate
 better performance.
 **Monochip Test: The test panels were chipped with the use of a Byk-Gardner
 Mono-chip Tester. This machine uses an air driven piston to impact the
 test panel with a small steel mallet shaped like a screw-driver head. The
 pressure used was 43 psi (3 bar). Three impacts were run at ambient
 conditions, then the test panel was placed in a freezer at -20.degree. C.
 and allowed to equilibrate. Within one minute after removing the test
 panel from the freezer, the panel was impacted three more
 # times in the Byk-Gardner Mono-chip Tester. Next the panels were tape
 tested by covering the impact zone of the panel with Tesa 4651 tape from
 Beiersdorf AG, Hamburg, Germany, and then removing the tape from the test
 panel in one rapid pull. The "Mode" of failure or loss of adhesion of the
 coating after tape testing is designated "C" for cohesive failure when
 there is a loss of adhesion between layers of coating, "A" for adhesive
 failure when there is loss of
 # adhesion to the metal substrate, and "M" for mixed adhesive and cohesive
 failures. A cohesive failure mode is preferred over an adhesive failure
 mode. The rating is the average width of paint loss from the impact areas
 measured in millimeters. Ac is acceptable which is generally 3.0 to 3.5
 mm, M is marginal which is generally 4.0 to 5.5 mm, G is good which is
 generally 2.5 to 3.0 mm, and VG is very good which is generally 2.0 to 2.5
 mm.