EP0610355A1

EP0610355A1 - Polymeric powder coating compositions comprising low molecular weight polyethylene polyols

Info

Publication number: EP0610355A1
Application number: EP92922813A
Authority: EP
Inventors: Donald Francis Loar
Original assignee: AlliedSignal Inc
Current assignee: Honeywell International Inc
Priority date: 1991-10-29
Filing date: 1992-10-28
Publication date: 1994-08-17
Also published as: WO1993009188A1; JPH07500858A

Abstract

Compositions de revêtement en poudre polymère dotées de propriétés physiques améliorées, comprenant une meilleure résistance aux chocs, un plus grand pouvoir adhésif, ainsi que d'autres propriétés. Ces compositions sont constituées (a) d'une résine de revêtement en poudre polymère; (b) d'au moins un copolymère d'éthylène de faible poids moléculaire, présentant un degré de saponification égal à 25 % au moins; (c) d'un autre composant sélectionné dans le groupe constitué d'agents catalyseurs, d'agents régulateurs d'écoulement, d'agents colorants, d'agents de charge, et d'adjuvants de traitement. Le rapport pondéral entre (a) et (b) est compris dans la plage 0,01 % - 20 % à 99,99 % - 80 %. Ces compositions peuvent être appliquées sur des articles par des techniques classiques. On décrit également de procédés de production de ces compositions de revêtement, ainsi que des articles revêtus de ces compositions.Polymer powder coating compositions with improved physical properties, including improved impact resistance, greater adhesive strength, and other properties. These compositions consist of (a) a polymeric powder coating resin; (b) at least one low molecular weight ethylene copolymer having a degree of saponification equal to at least 25%; (c) another component selected from the group consisting of catalyzing agents, flow control agents, coloring agents, bulking agents, and processing aids. The weight ratio between (a) and (b) is in the range of 0.01% - 20% to 99.99% - 80%. These compositions can be applied to articles by conventional techniques. Also disclosed are methods of making these coating compositions, as well as articles coated with these compositions.

Description

POLYMERIC POWDER COATING COMPOSITIONS COMPRISING LOW MOLECULAR WEIGHT POLYETHYLENE POLYOLS

Field of the Invention

The present invention relates to polymeric powder coating compositions. More particularly, the present invention relates to polymeric powder coating compositions which comprise a low molecular weight polyethylene copolymer or polyethylene terpolymer.

10

DESCRIPTION OF THE PRIOR ART Powder coating compositions find wide use in the production of articles which require that a sheet, rod, tube, wire, or other structure need be imparted with a 15 coating of a polymeric material. For example, it may be desired that a continuous pipe be provided with an exterior jacket of a polymeric material so to provide particular benefits which may include resistance to corrosive effects in the environment, improvements in 20 the appearance thereof, or electrical or thermal insulation thereof. Alternately, it may be desired that a continuous rod like structure, or wire type structure be provided with an exterior jacketing of a polymeric materials. Generally, such articles are 25 provided with a powder coating composition by causing an uncrosslinked/uncured composition in a fine \ particulate form to be adhered to the exterior surf ce of the item desirably to be coated and thereafter « causing the crosslinking/curing of the composition by

30 any of a variety of means which may include exposure to elevated temperatures, infrared radiation, or other effective means. Accordingly, the art includes various teachings directed towards polymeric powder compositions.

U.S. Patent 4,009,224 to Warnken describes a stable free-flowing epoxy resin powder which fuses to and cures upon striking an object which has been preheated to the curing temperature of the composition so to provide a tough protective coating. The compositions includes 3-30 party of a copolymer of 2- 50% vinyl acetate and 5-75% ethylene per 100 parts of the epoxy resin.

A paper entitled "Developments in Thermoplastic Powders" by G.E. Barrett published in the proceedings of the 4th International Plastics Powder Coating Conference, London, UK, 5th and 6th of March 1974 describes properties, applications techniques and perfomrance of various thermoplastic powders used in protective coatings applications.

An article indexed in the Chemical Abstracts 98:73886b titled "Properties of crosslinked coatings from modivied ethylene-vinyl acetate polymer" in Plast. Massy 1983, Vol. (1) , 56 described compositions which include a partially saponified ethylene-vinyl acetate copolymer powder useful with a caprolactam-blocked aromatic polyisocyanante crosslinking agent which coatings with good physical properties.

U.S. Patent 4,552,920 provides co postions useful as surface coatings which contain an epoxide resin and a mixture of polymeric carboxylic acids compounds.

Japanese Patent 56050941 of 8 May 1981 assigned to Sumitomo Chemical KK is directed to a resin coating composition which is comprised essentially of: (a) a modified ethylene-vinyl acetate copolymer, (b) a maleic anhydriede-styrene low polymer and (c) an epoxy resin containing at least two epoxy groups in one molecule therof. The weight ratios of the three constituents (a) : (b) : (c) is reported to be in the range of 100:1- 40:5-20.

Whereas there and other polymeric powder coating compositions are known to the art, generally such 5 coatings described herein consist either substantially in large part of an olefin copolymer, or are comprised essentially of a mixture of various olefinic copolymers.

Whereas such provide useful compositions, there

10 yet remains a real and continuing need in the art for further improved polymeric coating compositions which comprise only minor amounts of any olefinic material, such as an olefinic copolymer and/or terpolymer, and which provide good adhesivity to surfaces both during

15 the coating operation and in subsequent use. Further, there remains a continuing need in the art for further improvements in coatings and in coating compositions, as well as in production processes therefor and in articles comprising the same which feature good

20 physical properties, including good adhesion to the substrate material upon which the coating is applied and ultimately rests. It is these and to other objects of the present invention is directed.

In one aspect, the present invention provides an

25 improved polymeric powder coating composition which comprises a crosslinkable or curable polymeric resin material and further includes a saponified low molecular weight copolymer or terpolymer of ethylene which has a degree of saponification in excess of 25%,

30 preferably about 50% or greater.

In other aspects of the present invention, there are provided improved polymer powder compositions which includes a conventional crosslinkable or otherwise curable polymeric resin material and which further

35. includes a saponified low molecular weight copolymer terpolymer of ethylene which has a degree of saponification of at least about 25% wherein the polymeric powder composition exhibits improved physical properties over the polymeric resin material without the inclusion of the ethylene copolymer or ethylene . terpolymer.

In a further aspect of the present invention, there is provided a process for providing an improved polymeric powder coating to an article which comprises the process step of: a) melt blending a crosslinkable or otherwise curable conventional polymeric resin material with a low molecular weight ethylene copolymer or terpolymer which has a degree of saponification of about 25% or more, preferably about 50% or more wherein the weight ratio of the conventional polymeric resin to the low molecular weight ethylene copolymer is in the range of 0.01%-20% to 99.99%-80% respectively.

In other aspects of the present invention, there is provided an article which includes a polymeric coating wherein said polymeric coating comprises at least one conventional crosslinkable or otherwise curable polymeric resin material and which further includes a saponified low molecular weight ethylene copolymer or terpolymer which has a degree of saponification of about 25% or more, preferably 50% or more and wherein the coating composition exhibits improved physical properties including improved flexibility and improved impact resistance as compared to a like polymeric coating composition which does not comprise the ethylene copolymers or terpolymers.

These and other aspects of the present invention will become more apparent in light of the foregoing detailed description. DETAILED DESCRIPTION OF THE INVENTION The present invention provides improved polymeric powder coating compositions which comprises as essential constituents one or more conventional polymeric powder coating resin and further include at least one low molecular weight ethylene copolymer having a degree of saponification of about 25% or more, preferably about 50% or more wherein the weight ratio of the conventional polymeric powder coating resin to the low molecular weight ethylene copolymer is in the range of 0.01%-20% to 99.99%-80% respectively. Preferably, the relative weight ratios of these respective compostions is in the range of 0.01%-15% to 99.99%-85%. The inventive polymeric powder coating compositions may further include conventional constituents and additives as are customarily known and in use in the polymer powder coating art. Further, it is contemplated that certain terpoly ers may be used as the copolymer as described immediately preceeding and are to be considered as interchangeably with the copolymers as described above as well as in the following.

Polymeric powder coating compositions which may be used in the compositions according to the present invention include at least one conventional crosslinkable or otherwise curable polymeric powder coating resin. Such coating resins which may be used and are presently known to the art include, but are not limited to: epoxy coating resins, polyester coating resins, acrylic coating resins, as well as others. More particularly, conventional polymeric powder coating resins may include polyisocyanate crosslinked polyester coating resins, triglycidyl isocyanurate crosslinked polyester coating resins, polyester epoxy "hybrid"-type coating resins, triglycidyl isocyanurate crosslinked acrylic-type coating resins, polyisocyanate crosslinked acrylic-type coating resins, hydroxy alkylamine crosslinked polyester coating resins, hydroxy alkylamine crosslinked acrylic coating resins, a ine crosslinked epoxy coating materials, anhydride crosslinked epoxy coating resins, tetramethoxymethyl glcoluril crosslinked acrylics or polyesters, and uretdione crosslinked polyester-type coating resins. The crosslinking resins may be either aromatic or aliphatic, as well as either blocked or unblocked materials, and for example, include polyisocyanate-type materials blocked with caprolactam and methyl ethyl ketone.

The low molecular weight copolymers and terpolymers of ethylene which find use in accordance with the present invention include at least partially hydrolized (interchangeably referred to as "saponified") ethylene vinyl acetate copolymers (and terpolymers) which have a number-average molecular weight of up to about 3000, and are preferably ethylene vinyl acetate copolymers having a number-average molecular weight not in excess of about 2700. The degree hydrolysis of the copolymer is at least about 35%, but is preferred to be at least about 50% saponified, with particular preferred embodiments having a degree of saponification of at least about 90% and is preferably in the range of about 90% - 100% saponified. The ethylene vinyl acetate copolymers generally comprise at least about 10% and preferably about 13% by weight vinyl acetate and correspondingly about 90% and preferably about 87% by weight of low molecular weight polyethylene. In certain preferred embodiments the weight percentages of vinyl acetate is about 26%, and the corresponding weight percentage of the low molecular weight polyethylene is about 74%. The ethylene vinyl acetate copolymers which find use in accordance with the present teaching may be produced by conventional process, or may be a obtained commercially as a vinyl acetate copolymer and then at least partially hydrolized in accordance with conventional techniques, or in the alternative may be commercially obtained as partially hydrolized vinyl acetate copolymers. One such conventional process which may be used is by cocondensing appropriate stochiometric quantities of a low molecular weight polyethylene with vinyl acetate in the presence of a catalyst and a chain terminating agent to produce a copolymer product. Subsequently the copolymer product may be hydrolized to an appropriate degree in conjunction with a stochiometric amount of at least one hydroxide, such as sodium hydroxide or potassium hydroxide. One commercial source is from the A-C® Performance Additives Division of Allied-Signal Inc. under the trade designation ACtol(tm) . Low molecular weight terpolymers of ethylene which find use in accordance with the present invention include at least partially hydrolized ethylene vinyl acetate terpolymers which have an number-average molecular weight of up to about 3000, and are preferably ethylene vinyl acetate copolymers having a number-average molecular weight not in excess of about 2700. Preferably, the ethylene vinyl acetate terpolymer further include a copoly erized third constituent which may be one or more selected from the group which includes: styrene, methacrylic acid, 2- ethylhexylacrylate, ethyl aerylate, butyl acrylate, α- methylstyrene, glycidyl acrylate, acrylonitrile and methacrylamide, and is most preferably acrylic acid. The ethylene vinyl acetate terpolymers have relative weight percentages of the three constituents which comprise the terpolymer in the relative ranges of 60- 99% ethylene, 1-40% vinyl acetate, 0-39% of the third constituent; preferably the relative weight percentages of the three constituents are 75-99% ethylene, 1-25% vinyl acetate, 0-24% of the third constituent. The ethylene vinyl acetate copolymers (and terpolymers) useful in conjuction with the present invention comprise one or more of the following functional groups: hydroxyl, ester, carboxyl. Further, it is preferred that the ethylene vinyl acetate copolymers (and terpolymers) have a hydroxyl number in excess of 50, and preferably have a hydroxyl number of about 75 and greater. The hydroxyl number may be determined by conventional techniques by titrating a sample with sodium hydroxide.

In forming the compositions according to the instant invention, one or more of the low molecular weight ethylene vinyl acetate copolymers and/or terpolymers may be used. Further constituents which may ind use in the improved polymer coating compositions according to the present invention include catalyzing agents, flow control agents, coloring agents such as pigments or dyes, fillers, processing aids such as silica, catalysts, matting agents, and other conventional processing aids and other conventional additives.

Conventional organic and inorganic pigments which may be included in the compositions of the present invention include such as carbon black, ultra marine blue, dyes based on phthalocyanide, titanium dioxide, cadmium sulfide, cadmium sulfide selenide, nigrosine as well as others. Generally, such conventional pigments are included to comprise up to about 50 weight percent or less of the total composition, and are included in amounts to comprise preferably 30 weight percent or less.

Conventional flow control agents may be utilized and such flow control agents include hexyl acrylates. Fillers conventionally used in powder coating . compositions may be incorporated into the composition of the present invention and include both organic and inorganic type fillers. By way of example inorganic fillers which may be used include asbestos, calcium silicate, calcium metasilicate, aluminum silicate, amorphous silica, precipitated silica, fumed silica, magnesium carbonate, kaolin, dolomite, chalk, feldspar, mica, barium sulfate, calcium carbonate, as well as others fillers not denoted here. Conventional catalyzing agents (which are known to the art and sometimes referred to as "accellerators") known to improve the crosslinking and/or curing of the polymeric powder coating resin material may be incorporated in the compositions according to the present invention. Generally, these catalyzing agents lower the required temperature in applications wherein the coating composition is crosslinked or cured by exposure to heat and/or reduce the time interval at an elevated temperature at which the coated article need be exposed. Such conventional catalysts include, but are not limited to, stannous octoate, dibutyl tin dilaurdeate, dibutyl tin diacetate.

Conventional materials which are used to control the surface appearance of the polymeric coating include matting agents which limit the surface gloss. Such matting agent materials include waxes, silicas, polytetrafluoroethylene, as well as other conventional materials not particularly denoted here.

Processing aids which improve the processability, and in the formation of the polymeric coating may be included in the compositions. By way of example, silica is known to the art as a processing aid useful in improving the free-flow characteristics of the particulate polymeric powder coating composition. A further conventional processing aid includes benzoin, which is known to reduce pinhole formation during the crosslinking and/or curing or the polymeric constituents in the coating composition. Further conventional processing aids not particularly denoted here may be incorporated in the compositions according to the present invention.

In the formulation of the improved polymer powder coating compositions of the present invention, it is to be understood that the low molecular weight ethylene copolymers (and terpolymers) as described above are useful in partially substituting the amount of a conventional polymeric powder coating resin in a conventional polymeric powder coating composition; improvements in physical characteristics including improvements in impact strength, flexibility and interfacial adhesion are expected as compared to a like composition where no substitution has been made.

In determining the amount of the conventional polymeric powder coating resin which is to be substituted by the low molecular weight polyethylene copolymers taught herein, it will be clearly understood by the skilled practitioner that conventional experimental techniques wherein various amounts of the low molecular weight ethylene copolymers are incorporated into conventional polymer powder coating compositions and the resultant physical properties of the cured/crosslinked composition are subsequently evaluated is a very useful method for determining the optimum amount of substitution of low molecular weight ethylene copolymers within any conventional polymer powder coating composition. From such a determination, the optimal degree of substitution for a desired set of physical properties may be particularly evaluated. Preferably, the amount of low molecular weight polyethylene copolymers are substituted for an amount of conventional polymeric powder coating resin such that the weight ratio of the conventional polymeric powder coating resin to the low molecular weight ethylene copolymer is in the range of 0.01%-20% to 99.99%-80% respectively. Preferably, the relative weight ratios of these respective compostions is in the range of 0.01%-15% to 99.99%-85%.

The inventor has also noted that in certain polymeric powder coating compositions as taught in the present specification necessitates that the amount of the conventional catalyzing agent used in the composition may need to be increased if it is desired that increased rates of crosslinking/curing of the composition is desired. It has been observed that with the use of low molecular weight copolymers which have higher equivalent weights (which are a function of the hydroxyl number) , lesser amounts of the conventional catalyzing agent need be added to the compositions. Such increases may be determined experimentally by routine evaluative techniques, but it is not expected that more than about a 35% by weight increase in the amount of the conventional catalyzing agent will be necessitated.

The improved polymer powder coating compositions according to the present invention may be used in forming polymeric coatings on articles in accordance with conventional techniques.

In an exemplary conventional process, the constituents of the composition are measured out and blended in a suitable apparatus and subsequently the blended constituents are provided to the throat of a kneader or extruder apparatus which heats and plastificates the blended constituents into a mass which mass is subsequently extruded into any desired form.

Extruded strands, films, ribbons, (or the like) which are then chopped, ground, or otherwise comminuted into a fine powder wherein the particulates which form the powder have a size of about 200 microns or less, preferably 120 microns and less.

In a process described above wherein a single or twin extruder is used to plastificate the blended constituents, it is to be recognized that the temperature of the extruder barrel be suf iciently high so to insure that the polymer be melted; preferably it is preferred that the initial zone of the extruder following the feed inlet be at a temperature of at least 5° to 10"C above the melting point of the polymer so to insure the rapid melting of the same. The powder composition may be applied to the surface of an article in any conventional manner known to the art.

One such manner utilizes a corona discharge gun wherein the powder is imparted with a negative electrostatic charge and wherein the article is grounded, and the negatively charged powdered particles are then propelled at the grounded surf ce where the attraction of the oppositedly charged particles induces their retention at the surface. Subsequently, the coated surface is the placed in a oven at a elevated temperature and for a sufficient time to ensure the crosslinking and/or curing of the polymeric powder coating resin materials within the powder coating composition or in the alternative other crosslinking or curing means such as the utilization of infrared waves are contemplated.

In a further manner useful as an alternative production process utilizes a fluidized bed. In such process, the surface upon which the polymeric powder is to be imparted is heated and placed in a chamber proximate the fluidized bed from wherein the particles are blown and due to electrostatic attractive forces and/or the rapid action of the heated article in melting the powder, are collected upon the surface and fused.

In a third alternative manner of production known to the practitioner as "tribocharging" , an electrostatic charge generated by frictional forces is imparted to the polymeric powder coating to be deposited. Then due to electrostatic forces, the powder then is attracted to the surface and thereupon retained during a subsequent curing and/or crosslinking step, usually via exposure to an elevated temperature in an oven.

Each of these conventional powder deposition methods which are useful in providing a layer of the polymeric powder coating to the surface is subsequently crosslinked and/or cured so to fuse the particles and to form a continuous polymeric coating. Such may be accomplished in several manners as is conventionally known to the art.

In one popular manner, the surface or article which has a polymeric powder coating retain thereupon due to electrostatic and/or other forces is introduced to a dry circulating air oven wherein the surface is retained at an elevated temperature for a sufficient time so to effect an acceptable degree of curing and/or crosslinking. In a second alternative method, articles and/or surfaces are provided with a polymeric powder coating and then subjected to exposure to electromagnetic radiation, particularly in the infrared spectra region. Such exposure to infrared frequencies causes the curing and/or crosslinking of the polymeric constituents of the polymeric powder coating composition on the surface to fuse into a continuous layer.

The articles or surfaces which are provided with polymeric powder coating according to the present invention may be used in the construction of a broad range of useful items. For example, wherein a cold rolled steel sheet or panel is provided with a cured/crosslinked powder coating in accordance with the teaching herein, the same may be used to fabricate articles which include, but are not limited, to furniture, cabinets, shelving, partition panels, panels for use in automotive, aerospace and aeronautical applications, containers, boxes, fencing, housing and containers for electro and/or mechanical apparatus such as electro components, mechanical components, pipes, wires, cables, including the formation of one or more layers on a pipe and/or wire or cable construction, as well as other items not particularly denoted here. An advantageous feature of the present invention is best realized in the post formation of a flat sheet or panel i.e., such as that formed of a coated cold rolled steel panel by bending or otherwise deforming the same, such as would be realized in bending the panel to a 90^* or greater angle. As is appreciated by the practitioners in the art, such an action would cause extreme stress within the metal and most particularly in the polymeric coating at the line of the bend which within polymeric coating. Advantageously, the compositions of the present invention are known to the particularly resistant to breaking or rupturing at such stress locations due to observed increased flexibility of the coating. Such is particularly beneficial wherein the final appearance of the formed item or article is of concern and further provides the assurance of a continuous thermoplastic layer which ensures that the underlined sheet panel or other material is isolated from potentially corrosive effects in the environment of use.

The compositions of the present invention also feature improvements in impact resistance as compared to like compositions which do not comprise the polyethylene copolymers or polyethylene terpolymers as is taught herein.

The invention is more easily understood by reference to specific embodiments which are representative examples according to the teachings of the instant invention. It must be understood however, that the specific embodiments discussed herein are provided only for the purpose of illustration, and not by way of limitation, and it is to be further understood that the invention my be practiced otherwise than specifically described and yet be within the inventive scope.

XA P ES In the following examples of compositions according to comparative examples and those in accordance with the present invention, the following general production process was used.

The constituents of the respective composition were weighed out and introduced to a blender wherein they were dry blended to form a well mixed dry particulate blend which was essentially homogeneous. Subsequently, the dry particulate blend was provided to the inlet throat of a Haake twin screw extruder having two standard duty mixing screws. The temperature profile across the extruder was set as follows: zone 1, 85"C; zone 2 , 115*C; zone 3, 115'C. The throat was . water cooled and the die temperature was set at about 110"C. The screws rotated at a speed of approximately 40 rpm.

The extruded formulation exiting the die was cooled, and subsequently comminuted to a fine powder through a 140 mesh sieve. The particle size of the powder was not in excess of about 106 microns.

The fine powder of the respective ormulation was then provided to a Ransberg type 706 cup gun operated at 70 kV, which was used to spray cold rolled steel panels so to provide a dry film thickness of 2.0-2.5 mils. The panels were then baked at a temperature of 182°C for 30 minutes to cure the panels.

The panels were evaluated in accordance with conventional test protocols which included the following: Pencil Hardness according to the the Standard Test Method for Film Harness by Pencil Test, ASTM D 3363 (1980) ; Adhesion according to the Standard Test Method for Measuring Adhesion by Tape Test, ASTM D 3359 (1987); Impact Resistance according to the

Standard Test Method for Resistance of Organic Coatings to the Effects of Rapid Deformation (Impact) , ASTM D 2794 (1984) ; Flexibility according to the Standard Method for Coating Flexibility of Prepainted Sheet, ASTM D 4145 (1983); Gloss according to the Standard

Method for Specular Gloss, ASTM D 523 (1985) ; Overbake Resitance in accordance with the Standard Test Method for Yellowness Index of Plastics, ASTM D 1925 (1977) , as well as resitance to softening to organic solvents by "double rubbing" a respective sample with methyl ethyl ketone ("MEK") to evaluate if the respective sample exhibited softening.

All testing was performed on the cold rolled steel sheet as indicated except that impact resistance was evaluated for all compostions on 22 guage steel treated with a conventional pretreatment agent, "Bonderite® 901" which is commercially available from the Henkel Corp.

Certain of the formulations were also evaluated for recoatability wherein a formulation was sprayed onto cold rolled steel sheet panels and baked at 182°C and withdrawn at intervals of 10, 20 and 30 minutes. All of the withdrawn panels were allowed to cool to room temperature and then provided with a further coat of the same formulation used to provide the first coat and then reintroduced into the oven and rebaked for a further 30 minutes at 182^βC to ensure crosslinking/curing of the subsequent coat. The panels were then removed and allowed to cool to room temperature; the coatings were then crosshatched to evaluate the interlayer adhesion. In all tested samples, no loss of adhesion of the formulation to the substrate panel or between the coats was observed.

Comparative Fvam le c A conventional unfilled formulation comprising 404 g of a conventional polyester resin having hydroxyl functionality, "Cargill 3000"; 88 g of a conventional curing agent effective when used with the polyester resin, "Cargill 2400" believed to be a caprolactam blocked polyisocyanate material, 5 g of a conventional flow control agent, "Modaflow Powder III" from Monsanto, and 246 g of a commercially available titanium dioxide constituent "R900" from the E.I. du Pont de Nemours Co. was mixed, extruded, comminuted to a fine powder, sprayed onto substrate panels and cured as outlined above.

The panels bearing the substrate according to the formulation Cl was evaluated in accordance with the test protocols described; test results are provided -on Table 1.

TABLE 1

Example: C1 C2

Impact Resistance*: Gardner Impact, In-lbs units

Flexibility**: (T Bend)

Gloss: 60 degrees, initial

Overbake Resistance* +: units of deKa(YI)

MEK Resistance + + : evaluated with 100 double rubs

Esarøφle 1 A formulation according to the present invention utilizing the constituents described in conjunction with the preceeding Comparative Example was formulated and included 351 g of Cargill 3000 polyester resin, 100 g of the effective curing agent Cargill 2400, 39 g of a hydroxyl unctional group containing low molecular weight ethylene vinyl acetate copolymer having a number-average molecular weight of about 2400, a hydroxyl number in the range of 130-170, and an equivalent weight of 330-430 and comprised of about 26% by weight vinyl acetate which was subsequently saponified to a degree of about 90-100% herein identified as the "E copolymer" as well as 5 g of the conventional flow control agent, "Modaflow Powder III" from Monsanto, and 246 g of the commercially available titanium dioxide constituent "R900". The constituents were mixed, extruded, comminuted to a fine powder, sprayed onto substrate panels, cured and tested as outlined above. Results of the testing is presented on Table 1.

The unfilled composition according to the present example was evaluated for interfacial adhesion in accordance with the protocol outlined above. The interfacial adhesion between the composition and the panel as well as between the composition layers was was observed to be excellent indicating that good recoatability of a panel or article may be realized with the inventive compositions. Testing results according are provided on Table 2.

Adhesion *: per ASTM D3359

Comparative Example C2 A illed formulation according to the prior art comprised 358 g of Cargill 3000, 78 g of Cargill 2400, 4.5 g of Modaflow Powder III, 216 g of the commercially available titanium dioxide constituent "R900". As filler agents, the composition further comprised 91 g of Blanc Fixe commercially available as Sachtleben Blame Fixe "F", and a conventional finely comminuted silica filler, "Cabot TS-530" available from the Cabot Corp.

The constituents were mixed, extruded, comminuted to a fine powder, sprayed onto substrate panels, cured and tested as outlined above. Results of the testing is presented on Table 1.

Exam le ? A filled formulation according to the present invention comprised 333 g of Cargill 3000, 85 g of Cargill 2400, 4.5 g of Modaflow Powder III, 216 g of the commercially available titanium dioxide constituent "R900", 91 g of Blanc Fixe commercially available as Sachtleben Blanc Fixe "F", and 4.5 g of the finely comminuted silica filler, "Cabot TS-530" available from the Cabot Corp. The composition further comprised 18 grams of the at least partially saponified ethylene vinyl acetate copolymer identified as the "E copolymer" and more fully described in Example 1 above.

The filled composition according to the present example was evaluated for interfacial adhesion in accordance with the protocol outlined above. The interfacial adhesion between the composition and the panel as well as between the composition layers was was observed to be excellent indicating that good recoatability of a panel or article may be realized with the inventive compositions. Test results are. provided on Table 2.

Example 3

A further filled formulation according to the present invention comprised 324 g of Cargill 3000, 89 g of Cargill 2400, 4.5 g of Modaflow Powder III, 216 g of the commercially available titanium dioxide constituent "R900", 91 g of Blanc Fixe commercially available as Sachtleben Blanc Fixe "F", and 4.5 g of the finely comminuted silica filler, "Cabot TS-530" available from the Cabot Corp.

The composition further comprised 26 grams of the at least partially saponified ethylene vinyl acetate copolymer identified as the "E copolymer" and more fully described in Example 1 above. The constituents were mixed, extruded, comminuted to a fine powder, sprayed onto substrate panels, cured and tested as outlined above. Results of the testing is presented on Table 1.

The compositions of the present invention provide high impact resistant polymeric coating compositions which feature excellent interfacial adhesion between the coating and the substrate as well as good interfacial adhesion between plural layers of the coating, and good flexibility of the coating upon the substrate.

It will be appreciated that the instant specifications and examples set forth herein are by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention, whose limitations are bounded only by the appendant claims.

Claims

Claims I Claim:

1. A polymeric powder coating composition which comprises: (a) polymeric powder coating resin,

(b) at least one low molecular weight ethylene copolymer having a degree of saponification of at least 25%,

(c) a further constituent selected from the group consisting of catalyzing agents, flow control agents, coloring agents, fillers, processing aids, wherein the weight ratio of (a) to (b) is in the range of 0.01%-20% to 99.99%-80%.

2. A polymeric powder coating composition according to claim 1 wherein the weight ratio of (a) to (b) is in the range of 0.01%-15% to 99.99%-85%.

3. A polymeric powder coating composition according to claim 1 wherein the degree of saponification of the low molecular weight ethylene copolymer is at least 50%.

4. A polymeric powder coating composition according to claim 3 wherein the degree of saponification of the low molecular weight ethylene copolymer is at least 90%.

5. A polymeric powder coating compostion according to claim 1 wherein the at least one low molecular weight ethylene copolymer is an ethylene vinyl acetate copolymer having a number average molecular weight not in excess of 3000.

6. A polymeric powder coating compostion according to claim 1 wherein the at least one low molecular weight ethylene copolymer is a an ethylene vinyl acetate terpolymer which further includes a copolymerized constituent selected from the group consisting of: acrylic acid, styrene, methacrylic acid, 2- ethylhexylacrylate, ethyl acrylate, butyl acrylate, α- methylstyrene, glycidyl acrylate, acrylonitrile and methacrylamide and, having a number average molecular weight not in excess of 3000.

7. A polymeric powder coating composition according to claim 6 wherein the low molecular weight ethylene vinyl acetate terpolymer is a low molecular weight ethylene vinyl acetate acrylic acid terpolymer having a number average molecular weight not in excess of 3000.

8. A polymeric powder coating composition exhibiting improved physical properties according to claim 1.

9. A process for providing an article with a polymeric powder coating having improved physical properties which includes the process steps of: (a) melt blending the composition according to claim 1, and forming a comminuted powder therefrom, and

(b) coating an article with the comminuted powder, and

(c) curing the powder so to form a polymeric coating on the article.

10. An article which comprises at least one polymeric layer formed of the polymeric powder coating composition according to claim 1.