Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-07-07
2001-04-03
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S074000, C525S078000, C525S079000, C525S080000, C525S088000, C525S191000, C525S216000, C525S221000, C525S222000, C525S223000, C525S224000, C525S226000, C525S227000, C525S240000, C525S241000
Reexamination Certificate
active
06211290
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
The research and development leading to the subject matter disclosed herein was not federally sponsored.
BACKGROUND OF THE INVENTION
This invention relates to modified polyolefins, especially a class of polyolefins useful as engineering thermoplastics that are known as “thermoplastic olefin” polymers, or “TPOs”.
Vehicle manufacturers are increasingly looking to engineering thermoplastic materials as a lightweight, cost-effective replacement for metal and other polymer materials in many applications such as body panels, bumpers, doors, interior trim, etc. In addition to being lightweight and relatively low in cost, engineering thermoplastics provide increased design flexibility, favorable thermal and mechanical performance, and are recyclable.
One common class of engineering thermoplastics is thermoplastic polyolefins (TPOs). TPOs are blends of a polypropylene and an elastomer such as an ethylene-propylene copolymer, and often contain other additives such as fillers and pigments.
Polyolefins, generally, and TPOs, in particular, are nonpolar materials. Because they are nonpolar, many paints and adhesives do not adhere well to TPOs, because those paints and adhesives tend to be polar materials. Accordingly, it has been necessary to treat TPO parts prior to painting or gluing in order to increase the adhesion of the paint or of the adhesive to the TPO.
Treatments to enhance adhesion to TPOs fall into two main types. The first type is a surface treatment, which comes in several forms. The surface can be oxidized to increase its polarity, such as by a plasma treatment, corona discharge or surface etching. Another form of surface treatment is to apply a thin layer of a water- or solvent-based adhesion promoter or primer to the surface of the TPO. However, these surface treatments tend to significantly increase the cost of using TPO parts.
The second main type of TPO treatment involves modifying the TPO matrix itself so that when a part is molded from the TPO resin, no additional treatment steps are needed for adequate adhesion to coatings or adhesives. This second approach generally involves incorporating chemicals having polar groups into the TPO. A common approach involves the use of a modified polyolefin additive that has polar groups grafted onto a polyolefin backbone. One way of doing this is to graft or copolymerize an unsaturated anhydride and/or unsaturated ester compound into a polyolefin to form a somewhat polar additive. The additive is then blended into a TPO, thereby increasing its polarity and improving its adhesion to coatings and adhesives. This approach is described, for example, in U.S. Pat. No. 3,873,643 to Wu et al., U.S. Pat. No. 3,856,889 to McConnell, U.S. Pat. No. 3,882,194 to Krebaum et al., U.S. Pat. No. 4,298,712 to Machonis et al., and DeVito et al., J. Polym. Sci., Polym. Chem. Edit. 2; 1335p (1984). Unfortunately, it has been found that TPOs modified with additives of this type often do not have sufficient adhesion to coatings and adhesives.
A variation of the foregoing approach is described by R. Ryntz et al., “Toward Achieving Directly Paintable TPO: Initial Paintability Studies”, TPOs in Automotive, Executive Conference Management, Ann Arbor, Mich., (October 1995) and in U.S. Pat. Nos. 5,179,164 and 5,783,630 to Evans et al. In this approach, a modifier is prepared by grafting unsaturated anhydride, ester or acid monomers onto a polypropylene backbone, and reacting that grafted material with a polyetheramine. The modifier is then blended with a TPO to improve its paintability. Unfortunately, the approach suffers from the drawbacks of using relatively expensive aminated polyethers as raw materials. In addition, the modified polypropylene is often prepared in situ by feeding polypropylene, grafted polypropylene and polyetheramine into an extruder. This may lead to some problems with inconsistency in the product and volatilization of the amine in the extruder.
It would be desirable to provide an efficient means for improving the adhesion of polyolefins, and TPOs in particular, with a minimal adverse impact on its desirable physical properties.
SUMMARY OF THE INVENTION
In one aspect, this invention is a modified polyolefin comprising a blend of a polyolefin polymer and an adhesion-promoting additive that is compatible with said polyolefin, wherein the adhesion-promoting additive contains a polyolefin backbone with at least one pendant polar chain structure having at least one ester linkage and at least one hydroxyl or oxirane moiety, said pendant polar chain structure having a molecular weight of at least about 200 daltons.
The modified polyolefin of this invention exhibits improved adhesion to a variety of coatings and adhesives, and as such can be, for example, formed into automotive body parts that are more easily painted or glued than are parts made from the polyolefin polymer alone. These modified polyolefins can be molded into parts that can be easily coated or glued using a variety of coatings or adhesives, with minimal surface preparation and without additional treatment to improve adhesion. In addition, the modified polyolefin will usually have physical properties that are quite similar to those of the polyolefin alone.
In a second aspect, this invention is an organic polymer having a polyolefin backbone and at least one pendant polar chain structure having at least one ester linkage and at least one hydroxyl or oxirane moiety, the pendant polar chain structure having a molecular weight of at least about 200 daltons. This polymer can be blended into a polyolefin to form a modified polyolefin having improved paintability and adhesion to a variety of types of adhesives.
In a third aspect this invention is a method comprising:
(a) reacting a functionalized polyolefin having at least one carboxylic acid, carboxylic acid anhydride or carboxylic acid ester group with a compound having at least two hydroxyl and/or oxirane groups to form an adhesion-promoting additive having a polyolefin backbone and at least one pendant polar chain structure of at least 200 molecular weight that contains at least one ester group and at least one hydroxyl or oxirane group and
(b) blending the adhesion-promoting additive from step (a) with a polyolefin resin in which the adhesion-promoting additive is compatible, in proportions such that the adhesion-promoting additive constitutes about 5 to about 50 weight-% of the blend.
DETAILED DESCRIPTION OF THE INVENTION
In this invention, a modified polyolefin having improved adhesion to a variety of coatings and adhesives is prepared by blending the polyolefin with a certain adhesion-promoting additive. The adhesion-promoting additive is compatible with the polyolefin and has a polyolefin backbone with at least one pendant polar chain structure. The pendant polar chain structure contains an ester linkage and at least one hydroxyl or oxirane moiety. In this invention, a pendant chain structure is considered as “polar” if it contains at least one ester group and at least one hydroxyl or oxirane group. The pendant polar chain structure is preferably linked to the polyolefin backbone through the ester group. The pendant polar chain structure has a weight of at least about 200 daltons.
The polyolefin backbone of the adhesion-promoting additive is generally polyethylene, polypropylene, a polymer of a C
4
-C
8
alpha-olefin, a block or random copolymer of ethylene with propylene and/or a C
4
-C
8
alpha-olefin, or a block or random copolymer of propylene and a C
4
-C
8
alpha-olefin. The composition of the polyolefin backbone of the adhesion-promoting additive is advantageously selected so that the adhesion-promoting additive is compatible with the polyolefin resin to be modified. Thus, for example, in the preferred embodiment in which the polyolefin to be modified is polypropylene, the polyolefin backbone of the adhesion-promoting additive is preferably polypropylene or a random or block copolymer containing a major amount (at least 50% by weight) of polymerized propylene.
Hailat Mohammad
Xiao Han Xiong
Gary C. Cohn PLLC
GX Associates, Inc
Nutter Nathan M.
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