PROCESS AND COMPOSITION FOR IMPROVING THE PAINTABILITY OF POLYOLEFINS

Abstract: A process for improving the adhesion of paints and dyes to thermoplastic polyolefin substrates, which comprises the step of mixing and/or compounding with a thermoplastic polyolefin base an epoxy resin having formula (1) wherein each of the X's is independently hydrogen or bromine, n is in average between 0 and 150.

Description: PROCESS AND COMPOSITION FOR IMPROVING THE PAINTABILITY OF POLYOLEFINS Field of the Invention This invention relates to a process for improving the adhesion of paints to plastic compositions based on thermoplastic polyolefin polymers and copolymers such as polypropylene, propylene-ethylene copolymers and the like. It also relates to compositions based on said polymers and copolymers and having improved paintability, to a process for making painted pieces and parts of any kind based on said compositions, as well as to the resulting painted pieces and parts. Background of the Invention In the present art, the automotive industry uses polyolefin substrates and paints them with solvent-based paint systems comprising a primer layer, a urethane-base coat or pigment coat and a clear urethane top coat. An example of such polyolefin substrates to which this invention particularly, but not exclusively, relates is a thermoplastic polyolefin (sometimes briefly indicated as TPO) containing 87-88% of propylene units and 12-13% of ethylene units. The painting process presently used is complex and costly. A typical painting system comprises, e.g., three or four painting booths for priming, applying a base coat in one or two operations and applying the final clear coat. Baking of the primer and at least of the final coat is of course required. The cost of painting is estimated to bet 50% or more of then total cost of the painted component. The art is attempting to improve and simplify the process of painting such substrates. It is highly desirable to improve the adhesion of paints to the substrates without in any way complicating the painting process or rendering it more expensive, and, on the contrary, if possible, by simplifying it. An improved painting system is described by R.A. Ryntz and R.J. Clark in their Report "Toward Achieving a Directly Paintable TPO: Initial Paintability Results", presented at the Second International Conference TPOs in Automotive 95, October 30-31, Novi, Michigan. This system, which is considered a good reference, involves producing compounded TPOs by melt-compounding polypropylene, ethylene-polyethylene rubber, maleated poly(propylene) (MPP) and monofunctional or difunctional poly(etheramines)(PEA). The PEAs are produced by Huntsman Corporation, of Austin, Texas, under the commercial name "Jeffamine". It is stated that only TPO compounded with 20% MPP and 6% difunctional PEA exhibits paint adhesion. It is a purpose of this invention to achieve an improvement on prior art systems in the art of painting thermoplastic polyolefins. It is another purpose of this invention to provide a process that involves no complication or disadvantage with respect to prior art processes, and yet improves the adhesion of the paints to the aforesaid substrates. It is a further purpose of this invention to provide a thermoplastic polyolefin composition to which paints strongly adhere without the need of a primer. Other purposes and advantages of the invention will appear as the description proceeds. Summary of the Invention The invention provides a process for improving the adhesion of paints or dyes to thermoplastic polyolefin (TPO) substrates, in particular polypropylene and ethylene-propylene rubber (EPR or EPDM) as defined in "Plastics and Materials", J.A. Brydsin - 6th edition - British Plastics and Rubber pp. 291-292 and 856, and the like, which comprises the step of mixing and/or compounding with the TPO: a) an unsubstituted or brominated epoxy resin having the formula wherein each of the X's can be, independently of the others, H or Br, which has a molecular weight of at least 340 if all X's are H and of at least 656 if all X's are Br, n being in average between 0 and 150; and b) preferably, a polyolefinic modifier, which is a reactive polyolefin containing carboxylic acid functionality, in particular a maleated polyolefin. Said polyolefinic modifiers are known in the art and used to improve the mechanical properties of polyolefins. They are sometimes called "modified" olefin polymers or copolymers. Therefore, for the sake of clarity, it is specified that the expression "polyolefinic modifiers" and "modified polyolefins", when used in this specification and claims, will have the same meaning. The thermoplastic polyolefin substrates, compounded with the aforesaid epoxy oligomers and, optionally, with the said polyolefinic modifiers, according to the invention, will be called "compounded polyolefins" or "compounded TPO". An example of maleated polyolefin resin usable according to the invention is that manufactured and sold by Uniroyal under the trade name Uniroyal Polybond 3150. Said maleated propylene resin has approximately 0.6% maleic acid functionality. Other modified polyolefin resins, however, can be used according to the invention: for instance, acryhc acid functional polyethylenes or polypropylenes (having approximately 0.1-6% by weight of carboxylic groups). The compounding can be carried out in known ways, e.g. by extruding the components together in one or more passes. The extrudates can then be pelletized and molded or otherwise processed to produce the desired pieces or parts. The invention also provides a composition of matter which comprises: a) a thermoplastic polyolefin (TPO) such as polypropylene, propylene-ethylene copolymers and the like; b) an epoxy resin having the formula set forth above; and, preferably, c) a polyolefinic modifier, as hereinbefore defined. Such a composition of matter can be painted by known techniques, without the application of a primer. Therefore the invention also includes a process for making painted pieces and parts, in particular automobile bumpers and other parts, by compounding a TPO with an epoxy resin, as hereinbefore defined, and preferably, a polyolefinic modifier, making the part to be painted by known methods from the compounded TPO, and painting it without the application of a primer. The invention also includes the painted pieces or parts made by this process. Other thermoplastic polyolefines, besides those mentioned so far, may be chosen from polyethylene (low density polyethylene, hnear low density polyethylene, high density polyethylene), block or random copolymers of polyethylene and polypropylene, including ethylene-propylene rubbers and alike. It should be understood that to such compositions one can add usual plastics additives or modifiers, such as e.g. antioxidants, lubricants, UV/light stabilizers, pigments, flame retardants, antimony trioxide, fillers, foaming agents, glass fiber reinforcement etc.. Detailed Description of Preferred Embodiments In the following preferred embodiments, a TPO was used containing 87-88% of propylene units and 12-13% of ethylene units. The said TPO was compounded with a maleated polyolefin and an epoxy resin. The compounding was executed using a Brabender 42mm, counter-rotating, intermeshing twin-screw extruder, carrying out two passes through the extruder and with temperature profiles that were temperatures compatible with the components compounded into the TPO and which were in general approximately 195-200°C. The extruder was operated at 90 rpm and 3-5 Amps. The compounded TPO extrudates were pelletized. The pellets were compression molded as 1/8" plaques or plates using a heated hydraulic press. Specimen plaques were prepared by molding the pellets between 1/8" thick aluminum plates with a Mylar release film at a temperature of about 390°F. The pellets and the molding plates were preheated in the heated press for 4 minutes before pressing for 2 minutes using 300 psi pressure and cooling in a 55°F press for 2 minutes. The compression molded plaques were cleaned with methanol prior to painting. The control plaques, not prepared according to the invention, viz. consisting of TPO not compounded with a polyolefinic modifier nor with an epoxy oligomer, were primed using a commercial primer, specifically Red Spot LE 16610XM AD PRO primer. These and other Red Spot products are produced by Red Spot Paint and Varnish Co, Inc., of Evansville, Indiana. The primer was allowed to dry for five minutes before it was baked for fifteen minutes at 170°F. Uniroyal Polybond 3150 was used as the modified (maleated) polypropylene resin. As the epoxy resins, having the formula set forth above, were used brominated epoxy resins having the formula set forth hereinbefore, wherein all X's are bromine, manufactured and sold by Dead Sea Bromine Group, under the collective trade designation F-2000. In the embodiments that will be described, several epoxy resins of said series having molecular weights of 700-30,000, were used to show the flexibility of the invention. It has been found that epoxy resin designated as F-2200HM, which contains 48% bromine and has a molecular weight of about 700, gave excellent results, but the other brominated epoxy resins of said series, e.g. those designated as F-2016 and F-2400E, which have higher molecular weights than F-2200HM - 1,600 and 30,000 respectively - gave substantially the same results, when used in the same amounts with the polyolefinic modifier. To the TPO substrates, both those not compounded and conventionally primed, and those compounded according to the invention, a urethane base coat, specifically constituted by Red Spot 317LE21600V Cream White 2K Urethane Base Coat EA16935 was applied and was then air-dried at ambient conditions for 5 minutes followed by a 30 minute post-cure at 170°F. Said base coat was then over-coated with a urethane paint, specifically Red Spot 317LE, with the addition of a catalyst having the trade designation LE9426F. A first set of over-coated samples were dried at ambient conditions for 5 minutes, followed by a 30 minute bake at 170°F. Another set, similarly base-coated and top-coated, were air-dried for 5 minutes but cured at 250°F for 30 minutes. The painted and cured panels were allowed to condition for 72 hours prior to testing. The adhesion of the paint to the TPO was evaluated using the ASTM D3359 Standard Test Method for Measuring Adhesion by Tape Test - Method A (X-Cut). Those specimens that demonstrated good adhesion by said method were then tested by Method B (Lattice Pattern). The aforesaid Method A entailed making an X-shaped cut through the coating to the substrate, applying pressure-sensitive tape over the cut and then removing it. The adhesion of the coating was assessed qualitatively on a scale from 0A to 5A, 5A meaning 100% adhesion, 0A meaning no adhesion. Method B entailed cutting a grid of 6x6 slices spread 1 mm apart through the coating to the substrate. A piece of tape was applied over the grid and was then peeled rapidly away at an angle of 180°. The amount of paint that was moved was evaluated qualitatively on a scale of 0B to 5B, 5B meaning 100% adhesion and 0B meaning no adhesion. The uncompounded TPO substrates, primed with conventional primer, were used as a control versus the other TPO substrates, compounded according to the invention. Masking tape was selected as the pressure-sensitive tape based o its ability to peel the coating baked at 170°F on the control TPO specimen. The 250°F bake appeared to improve the adhesion of the coating, such that the masking tape would no longer peel the coating. The attached Table I illustrates eleven different substrate formulations. For purposes of comparison, one of them contains a PEA commercially known as Jeffamine M-2070, which is a polyoxyalkyleneamine containing primary amino groups attached to the terminals of a polyether backbone and has a molecular weight of about 2000. As stated hereinbefore, the Jeffamines are produced by Huntsman Corporation and are considered a good reference in industry. As epoxy resins, the formulations of the Examples contain those designated as F-2200HM, F-2016 and F-2400E. The amounts of components in Table I are indicated as percentages by weight. Table I: Composition in % by weight Table II shows the results obtained by applying Methods A and B, described above, to the various specimens. Table II: Adhesion properties. 5A - No peeling or removal 4A - Trace peeling or removal along incisions 3A - Jagged removal along incisions up to 1/16" on either side 2A - Jagged removal along most incisions up to 1/8" on either side 1A - Removal from most of the area of the X under the tape 0A - Removal beyond the area of the X 5B - No squares detached 4B - Small flakes of coating are detached at the intersections (<5% of lattice area) 3B - Small flakes of coating are detached along edges and at intersections of cuts (5-15% of lattice area) 2B - The coating flaked along the edges and on parts of the squares (15-35% of lattice area) IB - The coating flaked along the edges of cuts in large ribbons and whole squares have detached (35-65% of lattice area.) The above results show that the adhesion of the paint to the TPO substrates according to the invention is improved with comparison to the adhesion to conventional TPO substrates, even though, according to the invention, the priming step is omitted. They show a remarkable synergy between the modified, e.g. maleated, polyolefin resins, the epoxy oligomer and the TPO base. The most desirable results are obtained with amounts of epoxy oligomer that are as low as 1%, but even lower amounts are operative. On the other hand, it does not appear that there is any critical significance to the molecular weight of said oligomer: low molecular weight ones, such as F-2200HM, give essentially the same results as higher molecular weight ones. It should be noted that the process of this invention can be applied to improve the dyeability of polypropylene fibers and textile products, and the compositions of matter according to the invention can be in the form of fibers and textile products. While embodiments of the invention have been described for purposes of illustration, it will be clear that the invention can be carried into practice with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims.

Claims: CLAIMS 1. Process for improving the adhesion of paints or dyes to thermoplastic polyolefin substrates, which comprises the step of mixing and/or compounding with a thermoplastic polyolefin base an epoxy resin having the formula wherein each of the X's is independently hydrogen or bromine, n is in average between 0 and 150. 2. Process according to claim 1, wherein the thermoplastic polyolefin base is further compounded with a polyolefinic modifier. 3. Process according to claim 2, wherein the polyolefinic modifier is a reactive polyolefin containing carboxyϊic acid functionality. 4. Process according to claim 3, wherein the polyolefinic modifier is a maleated polyolefin. 5. Process according to claim 1, wherein the X's are all hydrogen and the epoxy resin has a molecular weight of at least 340. 6. Process according to claim 1, wherein the X's are all bromine and the epoxy resin has a molecular weight of at least 700. 7. Process according to claim 1, wherein the thermoplastic polyolefin is chosen from among polypropylene and binary propylene-ethylene copolymers. 8. Process according to claim 1, wherein the polyolefinic modifier resin is chosen from among acryhc acid functional polyethylenes or propylenes, having approximately 0.1-6% by weight of carboxylic groups. 9. Process according to claim 1, wherein the polyolefinic modifier resin is used in an amount between 1 and 20%, preferably about 15%, by weight of the thermoplastic polyolefin, and the epoxy resin is a brominated epoxy resin used in an amount of about 0.1 to 20%, preferably about 0.5% to 20%, by weight of the thermoplastic polyolefin. 10. Composition of matter which comprises: a thermoplastic polyolefin base and an epoxy oligomer having the formula wherein each of the X's is independently hydrogen or bromine, n is in average between 0 and 150. 11. Composition of matter according to claim 10, wherein the thermoplastic polyolefin is chosen from among polypropylene and binary propylene- ethylene copolymers. 12. Composition of matter according to claim 10, further comprising a polyolefinic modifier resin. 13. Composition of matter according to claim 12, wherein the polyolefinic modifier is a maleated polypropylene. 14. Composition of matter according to claim 12, wherein the polyolefinic modifier resin is chosen from among acryhc acid functional polyethylenes or propylenes, having approximately 0.1-6% by weight of carboxylic groups. 15. Composition of matter according to claim 10, comprising a thermoplastic polyolefin base, a polyolefinic modifier in an amount of 1% to 20%, preferably about 15%, by weight of said thermoplastic polyolefin, and a brominated epoxy oligomer in an amount of about 0.1 to 20%, preferably of about 0.5% to 20%, by weight of said thermoplastic olefin. 16. Composition of matter according to claim 10, further comprising plastics additives or modifiers. 17. Composition of matter according to claim 16, wherein the plastics addititives or modifiers are selected from the group comprising antioxidants, lubricants, UV/light stabilizers, pigments, flame retardants, antimony trioxide, fillers, foaming agents, glass fiber reinforcement. 18. Process for preparing a thermoplastic polyolefin paint substrate, comprising mixing and/or compounding a thermoplastic polyolefin base with a brominated epoxy oligomer having the formula wherein each of the X's is independently hydrogen or bromine, n is in average between 0 and 150. 19. Process for preparing a thermoplastic polyolefin paint substrate according to claim 18, further comprising mixing and/or compounding the thermoplastic polyolefin and the brominated epoxy ohgomer with polyolefinic modifier. 20. Process for making painted pieces and parts, particularly automobile parts, which comprises preparing a thermoplastic polyolefin substrate according to claims 18 or 19 and applying paint coating thereto without priming. 21. Painted pieces and parts, particularly automobile parts, having a thermoplastic polyolefin paint substrate according to claim 18. 22. Painted pieces and parts, particularly automobile parts, having a thermoplastic polyolefin paint substrate according to claim 18 and a paint coating applied thereto without priming. 23. Process for improving the adhesion of paints to thermoplastic polyolefin substrates, substantially as described and exemplified. 24. Composition of matter, substantially as described and exemplified. 25. Process for preparing a thermoplastic polyolefin paint substrate, substantially as described and exemplified. 26. Process for making painted pieces and parts, particularly automobile parts, substantially as described and exemplified. 27. Painted pieces and parts, particularly automobile parts, substantially as described and exemplified.

Inventors: AGRO SUSAN, REYES JOSE D, AGRO, SUSAN, REYES, JOSE, D.
Applicants: AGRO SUSAN, BROMINE COMPOUNDS LTD, REYES JOSE D, AGRO, SUSAN, BROMINE COMPOUNDS LTD., REYES, JOSE, D.
Application year: 1998
Main classification: C08L23
IPC codes: C08L23, C08L51, C08L63