EP0643742A1

EP0643742A1 - Paintable polyethylenes

Info

Publication number: EP0643742A1
Application number: EP93914397A
Authority: EP
Inventors: Yuh-Chin Hwang
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1992-06-05
Filing date: 1993-06-04
Publication date: 1995-03-22
Also published as: JPH07507590A; WO1993025617A2; CA2137283A1; WO1993025617A3

Abstract

Paintable, thermoplastic polymer blends are prepared from (A) at least about 50 weight percent polyethylene, for example, high density polyethylene (HDPE), grafted with at least about 0.01 weight percent of an unsaturated organic compound, for example, maleic anhydride, and (B) a thermoplastic polymer containing polar groups, for example, a polyurethane or a polyester. Optionally, the grafted polyethylene of (A) can be diluted with an ungrated polyethylene, for example, ungrafted HDPE. These blends can be molded into various structural components, for example, automobile parts, and can be painted without the use of either a primer or a preliminary surface treatment, for example, chemical etching. The polyethylene blends also demonstrate excellent adhesion to various rigid polyurethane foams.

Description

PAINTABLE POLYETHYLENES

This invention relates to functionalized polyethylenes. In one aspect, the invention relates to polyethylenes grafted with an unsaturated organic compound containing at least one double bond and at least one functional acid group, for example, maleic anhydride, while in another aspect, the invention relates to the high compatibility of these functionalized polyethylenes with various thermoplastic polymers containing a polar group. In one embodiment, the invention relates to articles molded from blends of functionalized polyethylenes and such polymers that can be painted without a surface pretreatment or a special primer while in another embodiment, the invention relates to laminates of functionalized polyethylenes and certain polyurethane foams that demonstrate near perfect adhesion to one another.

Because of their light weight, durability, low cost and other desirable properties, thermoplastic polyolefins (TPO's) have steadily grown in use as a material of construction for a large array of consumer goods. For example, the automotive industry uses these materials in a variety of interior and exterior parts, while household appliance manufacturers employ TPO's in everything from support structures to decorative facia.

While TPO's have many desirable properties, they also have certain undesirable properties not the least of which is their reluctance to accept a paint or decorative print. TPO's are, by definition, hydrocarbon polymers, typically a polyethylene, polypropylene or an ethylene-propylene rubber, and as such, are nonpolar. Most paints are polar, and thus require a surface with some degree of polarity before they can adhere to it with any degree of desirable fastness. This problem has been addressed, with varying degrees of success, in a number of different ways.

One relatively common solution is to apply a primer to the TPO.

Primers are, typically compositions containing a halogenated polyolefin and an aromatic solvent, for example, a chlorinated polypropylene and toluene. hile primers are generally recognized as effective, they are expensive and their application is an extra step in the finishing of the TPO article.

Another method of enhancing the paintability of a TPO surface is to subject the surface to a physical or chemical etching, or irradiating the surface with a plasma. While generally effective, these methods are more complex in nature than the application of a primer, and thus more difficult to control in terms of quality and consistency from part to part. In addition, these techniques are generally more expensive than the simple application of a primer.

Yet another technique, and one that continues to grow in use, is to modify the physical and/or chemical properties of the TPO either by blending it with other thermoplastic polymers, or by incorporating into it one or more polar groups, or both. For example, USP 4,946,896 to Mitsuno et al. teaches a paintable TPO comprising 20-80 weight percent polypropylene; 5-38 weight percent of an ethylene copolymer consisting of ethylene, an ester unit of either alkyl acrylate or methacrylate, and an unsaturated dicarboxylic acid anhydride; and 5-70 weight percent ethylene- propylene rubber. USP 4,888,391 to Domine et al. teaches a paintable polyolefin composition comprising a blend of a polyolefin as the continuous phase with an ethylene/acrylate/acrylic acid terpolymer as the discontinuous phase. Yet another teaching is USP 4,945,005 to Aleckner, Jr. et al. which teaches paintable TPO's comprising 2-25 weight percent of a copolymer of an ethylenically unsaturated carboxylic acid and ethylene; 3-50 weight percent of an ethylene-alpha-olefin copolymer; optionally a crystalline homopolymer or copolymer of propylene; 5-50 weight percent of an inorganic filler; and 10-35 weight percent of a polyethylene or a copolymer of ethylene and an alpha-olefin. These and other modified TPO compositions all demonstrate some degree of efficacy, but none are completely satisfactory with respect to such considerations as ease of formulation and cost. According to this invention, a paintable thermoplastic composition comprises:

A. At least about 50 weight percent polyethylene grafted with at least about 0.01 weight percent, based on the weight of the polyethylene, of an unsaturated organic compound containing at least one double bond and at least one functional acid group; and

B. At least one thermoplastic polymer containing polar groups.

Preferably, the polyethylene is a high density polyethylene, and it comprises at least about 80 weight percent of the composition. The thermoplastic polymer is preferably a nylon or polyurethane. In one embodiment of this invention, the compositions are molded into various articles, for example, automobile parts, while in another embodiment, the grafted polyethylene (g-PE) is laminated to a polyurethane foam. In yet another embodiment, the g-PE is blended with and demonstrates excellent adhesion to other materials, such as wood, metal and latex paints. The paintable thermoplastic compositipns of this invention can receive and hold paint without the use of a primer or preparatory surface treatment, as can many of the g-PE/other material blends.

Any ethylene polymer or copolymer that can be grafted with an unsaturated organic compound containing at least one double bond and at least one functional acid group can be used in this invention. Ethylene polymers and copolymers fall into two broad categories, those prepared with a free radical initiator at high temperature and high pressure, and those prepared with a coordination catalyst at high temperature and relatively low pressure. The former are generally known as low density polyethylenes (LDPE) and are characterized by branched chains of polymerized monomer units pendant from the polymer backbone. LDPE polymers generally have a density between 0.910 and 0.935 g/cc. Ethylene polymers and copolymers prepared by the use of a coordination catalyst, such as a Ziegler or Phillips catalyst, are generally known as linear polymers because of the substantial absence of branch chains of polymerized monomer units pendant from the backbone. High density polyethylene (HDPE), generally having a density of 0.941 to 0.965 g/cc, is typically a homopolymer of ethylene, and it contains relatively few side branch chains relative to the various linear copolymers of ethylene and an α-olefin. HDPE is well known, commercially available in various grades, and is useful in this invention.

Linear copolymers of ethylene and at least one alpha-olefin of 3 to 12 carbon atoms, preferably of 4 to 8 carbon atoms, are also well known, commercially available and useful in this invention. As is well known in the art, the density of a linear ethylene/alpha-olefin copolymer is a function of both the length of the alpha-olefin and the amount of such monomer in the copolymer relative to the amount of ethylene, the greater the length of the alpha-olefin and the greater the amount of alpha-olefin present, the lower the density of the copolymer. Linear low density polyethylene (LLDPE) is typically a copolymer of ethylene and an alpha- olefin of 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms (for example, 1-butene, 1-octene, etc.), that has sufficient alpha-olefin content to reduce the density of the copolymer to that of LDPE. When the copolymer contains even more alpha-olefin, the density will drop below about 0.91 g/cc and these copolymers are known as ultra low density polyethylene (ULDPE) or very low density polyethylene (VLDPE) . The densities of these linear polymers generally range from 0.87 to 0.91 g/cc.

Both the materials made by the free radical catalysts and the coordination catalysts are well known in the art, as are their methods of preparation. Relevant discussions of both these materials and their methods of preparation are found in USP 4,950,541 and the patents to which it refers, all of which are incorporated herein by reference. HDPE is the preferred polyethylene for use in grafting in this invention. Preferably, the HDPE for grafting has a melt index of about 10-25 g/10 min, and a density of about 0.95 - 0.965 g/cm³. Any unsaturated organic compound containing at least one double bond and at least one functional acid group that will graft to a polyethylene polymer or copolymer as described above can be used in the practice of this invention. Preferably, the compound to be grafted onto the polymeric chain contains a double bond conjugated with the double bond of an acyl group, and preferably the compound has a moderate tendency to polymerize to yield polymers of relatively high molecular weight and which readily undergo chain transfer reactions. Typical of such compounds are the acids and anhydrides, if any, of maleic, fumaric, acrylic, methacrylic, itaconic, crotonic, alpha-methyl crotonic, cinnamic. Maleic anhydride is the preferred unsaturated organic compound containing at least one double bond and at least one functional acid group.

The unsaturated organic compound content of the grafted polymer is at least about 0.01 weight percent, and preferably at least about 0.05 weight percent. The maximum amount of unsaturated organic compound content can vary to convenience, but typically it does not exceed about 5 weight percent, preferably it does not exceed about 2 weight percent, and more preferably it does not exceed about 1 weight percent.

The unsaturated organic compound can be grafted to the polymer by any known technique, such as those taught in USP 3,236,917 which is incorporated herein by reference. For example, the polymer is introduced into a two-roll mixer and mixed at a temperature of 60 C until a relatively homogeneous mixture is obtained. A free radical initiator, such as benzoyl peroxide, is added along with the unsaturated compound and the components are mixed at 30 C until the grafting is completed.

An alternative and preferred method of grafting is taught in USP 4,950,541, the disclosure of which is incorporated herein by reference, by using a twin-screw devolatilizing extruder as the mixing apparatus. The polymer and unsaturated organic compound are mixed and reacted within the extruder at temperatures at which the reactants are molten in the presence of a free radical initiator. Preferably, the unsaturated organic compound is injected into a zone maintained under pressure within the extruder. In one embodiment of this invention, the g-PE is blended with any thermoplastic polymer containing a polar group, for example, a carboxyl or hydroxyl group, and then molded into a shaped article. These polymers include copolymers of ethylene and acrylic acid (EAA) , ethylene and carbon monoxide (ECO) , polyamides, epoxies, polyurethanes, polyesters and various polyolefins containing polar groups. These thermoplastic polymers are sufficiently compatible with the g-PE such that the blend of the two does not separate either during or subsequent to mixing. The molecular weights of these materials can vary widely but for compression molding, typically the thermoplastic polymers used in this embodiment have a melt index (I2, measured according to ASTM D-1238, condition 190 C/2.16 kg) between 0.01 and 3,000, preferably between 0.1 and 300. For injection molding, the melt index is typically between 0.05 and 1200, preferably between 0.5 and 100.

The g-PE comprises at least about 50 weight percent , preferably at least about 70 weight percent and more preferably at least about 80 weight percent, of the g-PE/thermoplastic blend. Preferably only one thermoplastic polymer is blended with the g-PE, although blends of two or more compatible thermoplastic polymers and the g-PE can be prepared if desired. Polyurethanes and polyesters are the preferred thermoplastic polymers.

The g-PE and the thermoplastic polymer are mixed with one another in any conventional manner that ensures the creation of a relatively homogeneous blend. If the blend is molded into a finished article by extrusion, the g-PE and thermoplastic polymer are typically introduced into the extruder separately and mixed within it prior to extrusion. If the blend is molded by a compression or injection technique, then the two components are first well mixed by any conventional means, for example, roller mill, agitator, etc., and then introduced as a homogeneous mass into the mold. While the surfaces of the mold or die heads can be constructed of any material, conventionally stainless steel, preferably these surfaces are constructed of or coated with a polyester or polytr.ter film, such as Mylar® (manufactured by the E. I. Du Pont de Nemours & Company) . Articles shaped under relatively low shear conditions, for example, by compression molding, demonstrate better paint adhesion than articles shaped under relatively high shear conditions, for example, injection molding.

In another embodiment of this invention, the g-PE is laminated to a polyurethane (PU) foam. PU foam has many different uses, and one of particular interest is as an insulation material. For example, rigid PU is presently used as an insulation material in refrigerator cabinets, usually laminated to a terpolymer of acrylonitrile-butadiene-styrene (ABS) . However, the traditional blowing agents for rigid PU foam are chlorofluorocarbons which are currently believed to be a threat to the ozone layer. New blowing agents are under development and these include the hydrochlorofluorocarbons, but these attack and dissolve the ABS liner and this in turn causes poor interfacial adhesion between the liner and the PU foam.

The g-PE's of this invention demonstrate excellent adhesion to PU foams prepared with a hydrochlorofluorocarbon blowing agent. Accordingly, laminates of ABS and PU foams made from the new blowing agents are readily constructed without detriment to the interfacial adhesion between the two by either blending the ABS with the g-PE prior to lamination with the PU foam, by using the g-PE as an adhesion layer between the two or by substituting the g-PE for the ABS entirely.

The g-PE can also be used as a binder to form melt blends with wood fibers, for example, cedar fibers. These blends differ from polymer impregnated wood, and demonstrate excellent dimensional stability and water-resistant properties. Their appearance is that of wood but the surface is not wetted by water, that is, water beads on the surface. These blends also accept and retain paint well.

In another embodiment of this invention, the grafted polyolefin or g-PE is "let-down" or diluted with virgin polyolefin or another g-PE prior to its use as a blend component or adhesive. For example, after the g-PE has been prepared as described in USP 4,950,541, it is then back-blended in an extruder with virgin polyethylene to a predetermined dilution. Let- down or dilution ratios will vary with the ultimate application of the g- PE, but weight ratios between 1:10 and 10:1 are typical.

The following examples are illustrative of certain specific embodiments of this invention. All parts and percentages are by weight unless otherwise noted.

EXAMPLES

Ex. 1-42 and Controls C-l to C-42: Automotive Paint Adhesion Tests

Sample Preparation

In all samples save one (Ex. 39), the grafted polyethylene was a high density polyethylene grafted with maleic anhydride (expressed as HDPE.g.MAH) according to the procedure described in USP 4,950,541. The grafted polyethylene and thermoplastic polymer were then fed into a Werner and Pfleiderer ZSK-30 twin-screw extruder operated at about 210 C. The blends were made in one pass.

Injection molded samples were prepared using a 50 ton Negri-Bossi Injection Molder operated with a ,barrel temperature between 200 and 250 C, a barrel pressure of 40 bars, cooling mold temperature of 85 F (29.4 C) , and a residence time in the cooling mold of about 12 seconds. Compression molded samples were prepared using a Drake Press (Model #45-062) operated with a press platen temperature of about 190 C, a press pressure of 27.7 psi (190.85 kP) for five minutes and then 83.1 psi (572.56 kP)for one minute, and a cooling rate of about 15 C per minute. Unless indicated to the contrary, the surfaces of the compression mold and die heads were made of stainless steel. The samples were formed into 6" x 6" x 3/4" plaques.

Paint Adhesion Test Protocols

After the samples were washed, they were painted with one of two automotive paint formulations. The paint that was cured at 180 F

(82.2 C)was a two-component polyurethane paint system combining white paint and isocyanate (for example, 317LE19747-SRA white paint and Durethane™ LE 800 series sold by PPG Industries, Inc.), while the paint that was cured at 250 F (121.1 C) was a one-component (that is, heat cured melamine formaldehyde cross-linked systems) polyurethane or polyester paint system. Each plaque was given a single top coat (no primer) , and baked for 40 minutes.

Initial paint adhesion was determined using the Crosshatch and tape peel test of ASTM D3359-87 and the dime scrape test of GM-9506-P. If these tests were successfully passed, then the samples were subjected to immersion in a water bath of 100 F (37.8 C) according to GM-4466-P. Each sample was then inspected for blisters and wrinkles. If this test was passed, then the samples were subjected to a second series of the Crosshatch and tape peel and dime scrape tests.

Table 1A reports the results of these tests for the samples prepared by injection molding. Table IB reports the results of these tests for the samples prepared by compression molding. Table IC reports the legend for Tables 1A and IB.

TABLE 1A

SUMMARY OF AUTOMOTIVE PAINT ADHESION TESTS FOR SAMPLES MADE BY INJECTION MOLDING

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SUBSTITUTE SHEET TABLE 1A (Continued)

SUMMARY OF AUTOMOTIVE PAINT ADHESION TESTS F R AMPLE MADE BY INE Η N M L IN

-10a-

SUBSTITUTE SHEET TABLE IB

SUMMARY OF AUTOMOTIVE PAINT ADHESION TESTS FOR SAMPLES MADE BY COMPRESSION MOLDING

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SUBSTITUTE SHEET TABLE IB (Continued)

SUMMARY OF AUTOMOTIVE PAINT ADHESION TESTS FOR SAMPLES MADE BY COMPRRSSION MOLDING

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SUBSTITUTE SHEET TABLE IC

LEGEND FOR COMPOSITION OF TABLES 1A AND IB

HDPE: High Density Polyethylene

MAH: Maleic Anhydride

MI: Melt Index

PE: Polyethylene

(v=2,5) Velocity reading of injection molding, for two different molding conditions, for example, 2 and 5, respectively

(v=0.2-1.6) Velocity reading of injection molding for many different conditions are from 0.2 to 1.6

Molding temperature in injection molding is 100 F (37.8 C) Melting temperature in injection molding is 430 F (221.1 C) Mylar film installed on steel molding surfaces

Fiberglass 919 by CertainTeed

Fiberglass 930 by CertainTeed

Fiberglass 93B by CertainTeed

Fiberglass 93X by CertainTeed

Ultra Low Density Polyethylene manufactured by The Dow

Chemical Company

Crystalline Polyamide Dow epoxy resin 667 Copolymer of ethylene and acrylic acid Ediylene/acrylic acid copolymer having 10 percent acid and a melt index of 2 which was grafted with 1 percent MAH ethylene carbon monoxide copolymer (weight 10 percent mono- oxide)

Exxelor. Exxelor VA 1830 ethylene/propylene copolymer grafted with MAH and sold by Exxon HDG: HDPE grafted with MAH

SUBSTITUTE SHEET TABLE IC (Continued)

LEGEND FOR COMPOSITION OF TABLES 1 A AND IB

HDG.01: HDPE 10062 which was grafted with about 1.5 weight percent MAH; the grafted product had a MI of about lg/10 min

HDG.02: HDPE 25355 grafted widi about 1.5 weight percent MAH; the grafted product had a MI of about 2.5g/10 min

HDG.04: EUιylene/1-propene copolymer having a MI of about 25 g/10 min and a density of about 0.955 g/cm³ which was grafted with about 1.5 weight percent MAH; the grafted product had a MI of about 2.5 g/10 min

HDPE 25355: Ethylene/1-octene copolymer having a MI of about 25 g/10 min and a density of about 0.955 g cm³

HDPE 10062: PE homopolymer having a MI of about lOg/10 min and a density of about 0.962 g/cm³

Dowlex® 2047: Ethylene/ 1-octene copolymer made by The Dow Chemical

Company having a MI of about 2.3g/10 min and a density of about 0.917 g/cm³

LLG: Dowlex® 2047 grafted widi about 1 percent by weight MAH Nylon: Capron 8207 by Allied-Signal

P1410: Primacor® 1410 is an ethylene/acrylic acid copolymer made by

The Dow Chemical Company having a MI of about 0.5 g/10 min and about 10 weight percent acrylic acid content

P5980: Primacor® 5980 is an ethylene/acrylic acid copolymer made by

The Dow Chemical Company having a MI of about 300 g/10 min and about 20 weight percent acrylic acid content Polyester Dow Research Material Polyester TB900502RU1

Polyol: Jeffamine® M-2005 made by Texaco Talc: Microtuff® 1000 by Pfizer

TPU: Thermoplastic Polyureύiane made by The Dow Chemical

Company and trademarked Pellethane

TPU-80A: PELLETHANE® 2102-80A TPU-90A: PELLETHANE® 2102-90A C: Indicates a comparative example; not an example of the invention

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SUBSTITUTE SHEET Results and Conclusions In Tables 1A and IB, column 1 reports the composition of each of the blends. The legend for these compositions is reported in Table IC. Column 2 reports the nature of the paint by curing temperature; column 3 the actual curing oven temperature; and column 4 the test results.

In column 4,

"4" means that the painted plaque passed the Crosshatch and dime scrape tests in both the initial test and after the water immersion test;

"3" means that the painted plaque passed both initial tests but failed either the Crosshatch or dime scrape test after the water immersion test;

"2" means that the painted plaque passed both initial tests but failed both the Crosshatch and dime scrape tests after the water immersion test;

"1" means that the painted plaque failed one of the initial Crosshatch or dime scrape tests; and

"0" means that the painted plaque failed both initial tests.

Molding conditions directly influence the surface properties and thus the paintability of the plaques. Compression molding equipment heat the samples from the free surfaces to the bulk. Injection molding equipment, after melting the pellets, cool the moldings from the free surface to the bulk. The pressure of the two moldings are also different as is the shear ratio. For a PE having a MI of 10 g/10 min, the shear ratio for injection molding is about 2000-5000/sec. The effects of these two different thermal and mechanical histories can be seen in the results reported in Tables 1A and IB. For example, C-l, prepared by injection molding, reports only marginal paint adhesion while Ex. 26, prepared by compression molding, reports essentially perfect adhesion.

-15- The effect of the molding surface on the paintability of the plaque is seen in a comparison of C-24 with Ex. 7, and of Ex.11-12 with C-34. In the first comparison (between injection molded samples) , the plaque of Ex. 7 outperformed the plaque of C-24 even though both failed to demonstrate an acceptable level of paint adhesion. The Crosshatch and tape peel test has scores that range from 0 to 5B, and any score below 3B fails the test. The plaque of Ex. 7 scored a 2B, but the plaque of C-24 scored a 0. These results show that the Mylar surface imparted some improvement to the paint adhesion properties of the plaque.

Similar effects in compression molded plaques are reported in Ex. 11-12 and C-34, but here the results are more marked. Ex. 11-12 report essentially perfect adhesion, while C-34 (prepared with a Teflon® - coated mold surface) reports virtually no adhesion.

Examples 1-6 report acceptable paint adhesion results on plaques made by injection molding. Controls 1-27 report unacceptable paint adhesion results, and most, if not all, of this can be attributed to the method of fabrication (injection molding) . Similar compositions, as shown above, made by compression molding techniques demonstrate acceptable paint adhesion properties.

Examples 8-42 show that plaques made from a wide variety of compositions demonstrate excellent paint adhesion properties when made by compression molding. These compositions include simple g-PE diluted or let down with LLDPE (Ex. 8-9) or HDPE (Ex. 10), g-PE itself (Ex. 11-12), and blended with various thermoplastic polymers or simply fillers, for example, polyamide (Ex. 16-17), epoxy (Ex. 18-19), nylon (Ex. 26), fiberglass (Ex. 13-14), talc (Ex. 29-30), etc.

Controls 28-29, 31-33, and 35-42 show the effect of using an ungrafted polyethylene, alone or blended with various thermoplastic polymers or fillers.

-16- Ex. 42a and 42b: Additional Automotive Paint Adhesion Tests

In both Examples, a one to one blend of HDE.04 and P1410 (see legend of Table IC) was prepared, 6.5" x 2.5" x 0.075" plaques of the blend were made by injection molding, the plaques painted with a white top coat (no promoter, no primer) of the two-component polyurethane system described in Ex. 1-42, and then tested, all by the procedures described for Ex. 1-42. Perfect paint adhesion was achieved in both examples.

Ex. 43-44 and Cntrls C-43 to C-45: Adhesion of Polyethylene to Rigid

Polyurethane Foam

Sample Preparation

The rigid polyurethane foam was an appliance polyether polyol/PMDI based formulation of The Dow Chemical Company utilizing two different hydrochlorofluorocarbon blowing agents. Final in-place foam densities were in the range of 2.1 (33.64 kg/m³)to 2.2 lb/ft³ (35.24 kg/m³) inorder to assure freeze stability of the foam samples. These samples were prepared utilizing a Brett mold which is standard industry equipment for determining the flow characteristics of rigid polyurethane foams. The polyethylene panels were mounted in the bottom, middle and top of the Brett mold for foaming such that the effects of variations in foam density and texture could be assessed. The results of the adhesion tests are reported in Table 2.

^■17- TABLE 2 U

Results

The legend for the various compositions is in Table IC. "Pass" indicates perfect adhesion, that is, under stress the polyurethane foam fails before the interface between the foam and the g-PE. "Fail" indicates imperfect adhesion, that is, under stress the interface between the foam and the g-PE fails before the foam. As the results of Table 2 report, g-PE demonstrates excellent adhesion properties to polyurethane foams prepared with hydrochlorofluorocarbon blowing agents, while the ungrafted polyethylene did not. C-45 demonstrates that the g-PE is preferably present is certain minimum amounts.

Ex. 45-46 and Cntrls C-46 and C-47 : Polyethylene/Wood Fiber Blends

Sample Preparation

Polyethylene and cedar fiber melt blends were made on a Haake 90 system operated at 190 degrees C and 60 rpm for 5 minutes. The Haake was heated to the run temperature, and then the polyethylene was added and allowed to melt with blending. The cedar fibers were then added and melt blended for 5 minutes. The melt blends were then extruded into sample sizes suitable for testing, the results of which are reported in Table 3. LDPE 723 is a branched PE homopolymer made by The Dow Chemical Company having a MI of about 8 g/10 min and a density of about 0.916 g/cm³.

-18- TABLE 3

TENSILE STRENGTH AND PAIN ADHESION OF CEDAR-FIBER/POLYETHYLENE BLENDS

Part A. Using Raw Cedar Fiber and Virgin Polyethylenes

Ex./ Tensile Elongation Density Control (kpsi) (percent) (g/cc)

C-46* 0.61 (4,202.9 kP) 1 1.034

45** 1.94 (13,366.6 kP) 1 1.033 Part B. Using Refined Cedar Fiber and Virgin Polyethylene

Ex./ Tensile Elongation Density Control (kpsi) (percent) (g/cc)

C-47* 0.75 (5,167.5 kP) 1 1.059

46** 1.72 (11,850.8 kP) 1 1.059

* 50 percent fiber + 50 percent LDPE 723 ** 50 percent fiber + 40 percent LDPE 723 + 10 percent HDG.04

Results

As reported in Table 3, the presence of g-PE in the blend significantly increases the tensile strength of the composite without adversely impacting its elongation and density properties. The effect is present in composites of both raw and refined wood fibers.

Although the invention has been described in detail by the preceding examples, such detail is for the purpose of illustration only and is not to be construed as a limitation upon the invention. Many variations can be made upon the preceding examples without departing from the spirit and scope of the following claims.

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Claims

CLAIMS 1. A paintable, thermoplastic composition comprising:

A. at least about 50 weight percent of a polyethylene polymer grafted with at least about 0.01 weight percent, based on the weight of the polyethylene of an unsaturated organic compound containing at least one^' double bond and at least one functional acid group; and

_^α B. at least one thermoplastic polymer containing polar groups.

2. The composition of Claim 1 in which the unsaturated organic compound is maleic anhydride.

3. The composition of Claim 2 in which the polyethylene polymer i-s high density polyethylene.

4. The composition of Claim 3 in which the polyethylene polymer comprises at least about 70 weight percent by weight of the composition.

5. The composition of Claim 4 in which the polyethylene polymer is grafted with at least about 0,.1 weight percent of maleic anhydride.

6. The composition of Claim 5 in which the thermoplastic polymer is at least one of a polyurethane, polyester, epoxy, polyamide, and a polyolefin containing polar groups.

7. A paintable, thermoplastic composition comprising:

A. At least about 50 weight percent of a polyethylene blend consisting essentially of (1) at least about 10 weight percent of a polyethylene polymer grafted with at least about 0.01 weight percent of an unsaturated organic compound containing at least one double bond and at least one functional acid group, and (2) an ungrafted polyethylene polymer; and

-20- B. At least one thermoplastic polymer containing polar groups .

8. The composition of Claim 7 in which the unsaturated organic compound is maleic anhydride.

9. The composition of Claim 8 in which the polyethylene polymer grafted with the unsaturated organic compound is high density polyethylene.

10. The composition of Claim 9 in which the ungrafted polyethylene polymer is high density polyethylene.

11. The composition of Claim 10 in which the polyethylene blend is prepared by a process comprising:

A. melting an ethylene polymer by heating and shearing the polymer in an extruder;

B. injecting the maleic anhydride and a free radical initiator into a chamber of the extruder filled with the ethylene polymer;

C. mixing the ethylene polymer and maleic anhydride in the extruder for sufficient time to graft the maleic anhydride to the polymer;

D. extruding and collecting the product of step (C) ;

E. blending the collected product of step (C) with additional ethylene polymer by shearing a mixture of both in an extruder; and

F. extruding and collecting the blend of step (E) .

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12. An article molded from the paintable, thermoplastic composition of Claim 1.

13. An article molded from the paintable, thermoplastic composition of Claim 7.

14. An automobile part made from the paintable, thermoplastic composition of Claim 1.

15. An automobile part made from the paintable, thermoplastic composition of Claim 7.

16. A process of making a paintable, thermoplastic, compression molded article from a thermoplastic composition comprising:

B. at least one thermoplastic polymer containing polar groups;

the process comprising:

a. contacting the thermoplastic composition with a polyester mold surface;

b. applying heat and pressure to the thermoplastic composition such that it takes the shape of the mold surface;

c . removing the heat and pressure of Step (b) from the thermoplastic composition; and

-22- d. removing the shaped thermoplastic composition of Step (c) from the mold surface.

17. The process of Claim 16 in which the unsaturated organic compound is maleic anhydride.

18. The process of Claim 17 in which the polyethylene polymer grafted with the unsaturated organic compound is high density polyethylene.

19. The process of Claim 18 in which the ungrafted polyethylene polymer is high density polyethylene.

20. The process of Claim 19 in which the polyester mold surface is polyethylene terephthalate.

21. A laminate comprising a first layer comprising a polyethylene blend consisting essentially of (i) at least about 15 percent of a polyethylene polymer grafted with at least about 0.01 weight percent of an unsaturated organic compound containing at least one double bond and at least one functional acid group, and (ii) an ungrafted polyethylene polymer, the first layer joined to a second layer comprising a polyurethane foam.

22. The laminate of Claim 21 in which the polyethylene polymer grafted with the unsaturated organic compound is high density polyethylene, and the unsaturated organic compound is maleic anhydride.

23. The laminate of Claim 22 in which the ungrafted polyethylene polymer is linear low density polyethylene.

24. The laminate of Claim 23 in which the polyethylene blend of the first layer is admixed with ABS rubber.

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