Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-06-29
2002-02-12
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S292400, C264S210100, C264S290500, C264S210500
Reexamination Certificate
active
06346325
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fiber-reinforced composite encased in a thermoplastic, which is useful in the fabrication of large plastic parts such as automotive parts and window profiles.
At present, most automotive bumper systems consist of three basic components, a bumper beam, a bumper absorber, and a cover or facia. The bumper beam is usually metal, typically steel, since steel has the necessary strength and stiffness required for impact resistance and energy absorption. Unfortunately, steel has the disadvantage of being heavy and not easily formable to the complex shapes required to fit the styling of a car.
An alternative to steel is an injection or blow molded thermoplastic material, which is contoured to provide the facia support function. As noted in U.S. Pat. No. 5,799,991 (Glance), although this system eliminates the discrete bumper absorber, it suffers from being expensive and from having excessive impact rebound, rather than absorption during impact. Therefore, the bumper systems of the prior art fail to provide an effective, low cost, low space-consuming, and lighter weight solution to the bumper requirement problem.
Window frame profiles are typically made from wood, polyvinyl chloride, or aluminum. Although wood is rigid and aesthetically pleasing, it requires much maintenance, is inconsistent, and has availability limitations. PVC requires little or no maintenance and is readily available and consistent, but has a low modulus and high coefficient of linear thermal expansion (CLTE). Its application in window frame profiles is therefore limited to domestic windows. Aluminum, on the other hand, has a relatively low CLTE and high modulus, but it is also very thermally conductive, and requires elaborate systems to create thermal breaks to prevent significant heat loss.
In view of the deficiencies in the art, it would be desirable to discover a material that is strong and light-weight, one that has high energy absorption and high modulus, as well as low CLTE and low thermal conductivity, and one that is easy to style and shape.
SUMMARY OF THE INVENTION
The present invention addresses a need in the art by providing an encased article comprising a) a thermoplastic polyurethane composite that is reinforced with fibers that extend through the length of the composite and are at least 100 mm long; and b) a thermoplastic resin encasing the fiber-reinforced composite.
In a second aspect, the present invention is a process for preparing an encased fiber-reinforced rigid thermoplastic polyurethane composite comprising the steps of drawing a fiber bundle continuously through a melt obtained by heating a rigid thermoplastic polyurethane that contains a hydrolytically- and thermally-stable catalyst to a temperature sufficient to depolymerize the thermoplastic polyurethane; impregnating the drawn fiber bundle with the depolymerized thermoplastic polyurethane to form a composite melt; shaping the composite melt into an article; then encasing the article with a thermoplastic resin.
The present invention addresses a problem in the art by providing an overmolded fiber reinforced thermoplastic polyurethane composite that provides a light-weight and compact part suitable for a variety of applications that require very high strength, stiffness, and exceptional impact, together with complex shape.
DETAILED DESCRIPTION OF THE INVENTION
The overmolded composite of the present invention can be prepared by encasing in a thermoplastic resin a fiber-reinforced composite containing a depolymerizable and repolymerizable thermoplastic polymer (DRTP). As disclosed in U.S. Pat. No. 5,891,560 (Edwards et al.), which teachings are incorporated herein by reference, the DRTP is a thermoplastic polymer that depolymerizes upon heating and repolymerizes upon cooling.
The DRTP contains the following structural unit:
where Z is S or O, preferably O, and Z′ is S, O, N-alkyl or NH, preferably O or NH, more preferably O. Preferred DRTPs are thermoplastic polyurethanes and thermoplastic polyureas, preferably thermoplastic polyurethanes (TPUs).
The DRTP is a single- or two-phase polymer that can be prepared by the reaction of approximately stoichiometric amounts of: a) a diisocyanate or a diisothiocyanate, preferably a diisocyanate; b) a low molecular weight compound (not more than 300 Daltons) having two active hydrogen groups; and c) optionally, a high molecular weight compound (molecular weight generally in the range of from about 500 to about 8000 Daltons) with two active hydrogen groups. The low molecular weight compound, in combination with the diisocyanate or diisothiocyanate, contributes to what is known as the “hard segment content”, and the high molecular weight compound, in combination with the diisocyanate or diisothiocyanate, contributes to what is known as the “soft segment content”.
As used herein, the term “active hydrogen group” refers to a group that reacts with an isocyanate or isothiocyanate group as shown:
where Z and Z′ are as previously defined, and R and R′ are connecting groups, which may be aliphatic, aromatic, or cycloaliphatic, or combinations thereof.
The compound with two active hydrogens may be a diol, a diamine, a dithiol, a hydroxy-amine, a thiol-arnine, or a hydroxy-thiol, preferably a diol.
The DRTP may be soft or rigid, and is preferably rigid. Soft DRTP, preferably soft TPUs (STPUs) are characterized by having a Shore A hardness of not more than 95 or a glass transition temperature (T
g
) of not more than 25° C. Rigid DRTPs, preferably rigid thermoplastic polyurethanes (RTPUs) are characterized by having T
g
of not less than 50° C. and typically have a hard segment content of at least 75 percent, more preferably at least 85 percent, and most preferably at least 90 percent. The disclosure and preparation of RTPUs is described, for example, by Goldwasser et al. in U.S. Pat. No. 4,376,834, which teachings are incorporated herein by reference. Such RTPUs are commercially available under the trade name ISOPLAS™ engineering thermoplastic polyurethanes (a trademark of The Dow Chemical Company).
Preferred diisocyanates include aromatic, aliphatic, and cycloaliphatic diisocyanates and combinations thereof. Representative examples of these preferred diisocyanates can be found in U.S. Pat. Nos. 4,385,133; 4,522,975; and 5,167,899, which teachings are incorporated herein by reference. Preferred diisocyanates include 4,4′-diisocyanatodiphenylmethane, p-phenylene diisocyanate, 1,3-bis(isocyanatomethyl)-cyclohexane, 1,4-diisocyanato-cyclohexane, hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3′-dimethyl-4,4′-biphenyl diisocyanate, 4,4′-diisocyanato-dicyclohexylmethane, and 2,4-toluene diisocyanate. More preferred are 4,4′-diisocyanato-dicyclohexylmethane and 4,4′-diisocyanato-diphenylmethane. Most preferred is 4,4′-diisocyanatodiphenylmethane.
Preferred low molecular weight compounds having two active hydrogen groups are ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, neopental glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-(bishydroxyethyl)-hydroquinone, 2,2-bis(&bgr;-hydroxy-4-ethoxyphenyl)propane (i.e., ethoxylated bisphenol A), and mixtures thereof. More preferred chain extenders are 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tripropylene glycol, and mixtures thereof.
The DRTP may optionally contain structural units formed from a high molecular weight compound having two active hydrogen groups, which is preferably a glycol having a molecular weight in the range of preferably not less than about 750, more preferably not less than about 1000, and most preferably not less than about 1500; and preferably not more than about 6000, and more preferably not more than about 5000. These high molecular weight glycol units constitute a sufficiently low fraction of the DRTP, preferably the RTPU, such that the T
g
o
D'Hooghe Edward Louis
Edwards Christopher Michael
Dixon Merrick
The Dow Chemical Company
Willis Reid S.
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