Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1992-07-27
2001-04-10
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S141000, C524S504000, C523S201000, C525S067000
Reexamination Certificate
active
06214910
ABSTRACT:
The present invention relates to flexible thermoplastic polyester compositions. More particularly, it relates to thermoplastic extrusion and molding compositions having a flexural modulus of less than 140,000 psi, which are capable of being formed into flexible hoses, tubings, wire coatings, cable jackets, and in film or sheet form, for use as automobile bumper and seat covers and the like.
High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described, inter alia, in Whinfield, et al, U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539, incorporated herein by reference. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
With the development of molecular weight control, the use of nucleating agents and two-step molding cycles, poly(ethylene terephthalate) has become an important constituent of injector moldable compositions. Poly(1,4-butylene terephthalate), because of its very rapid crystallization from the melt, is uniquely useful as a component in molding resins. Work-pieces molded from such polyester resins, alone or combined with reinforcement, in comparison with other thermoplastics, offer a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction.
Stable polyblends of poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) can be molded into useful unreinforced and reinforced articles. See Fox and Wambach, U.S. Pat. No. 3,953,394, incorporated herein by reference.
In U.S. Pat. No. 3,218,372 to Okamura et al, it is disclosed that aromatic polycarbonate resins may be blended with poly)alkylene terephthalate) resins over a wide range of proportions to form useful molding compositions having an improved combination of properties over either the polycarbonate or the polyester resins alone.
In general, the above-described compositions based on the poly)alkylene terephthalate) resins have a useful balance of physical properties, as reported in the
Modern Plastics Encyclopedia
1982-1983. The compositions exhibit good electrical properties, e.g., the dielectric strength of poly(1,4-butylene terephthalate) ranges from about 420-550 volts/mil. The compositions exhibit good solvent resistance to such solvents as leaded and unleaded gasoline. The poly(alkylene terephthalates) possess only moderate impact resistance, e.g., the notched Izod impact strength of poly(1,4-butylene terephthalate) (PBT) is within the 0.8-1.0 ft-lbs./in. range and for poly(ethylene terephthalate) (PET) within the 0.25-0.65 ft-lbs/in. range. Aromatic polycarbonates exhibit relatively high impact resistance having notched Izod impact strengths in the 10.0-16.0 ft-lbs/in. range, and blending aromatic polycarbonates with poly)alkylene terephthalates) is known to effectively increase the impact strength of the latter.
Poly(alkylene terephthalate) homopolymers, resin blends based on mixtures of these polyesters, and mixtures of poly(alkylene terephthalates) with aromatic polycarbonates, are also known to exhibit relatively high stiffness, e.g., each is characterized by a high flexural modulus of above about 300,000 psi. More particularly, the flexural modulus of PBT at room temperature is about 330,000-350,000 psi; of PET about 340,000-360,000 psi and of aromatic polycarbonate above about 340,000 psi. Compositions exhibiting this high a flexural modulus are too stiff to be considered flexible; and as such, are generally unsuitable for forming articles which are required to have a high degree of flexibility, such as hoses, tubings, cable jacketing and the like.
On the other hand, thermoplastic compositions having a flexural modulus of less than about 140,000 psi, preferably less than about 120,000 psi and especially preferably less than about 100,000 psi, exhibit sufficient flexibility for use in forming flexible tubings, cable jacketing, or flexible fibers or sheets, for use in automobile bumper covers and the like.
In the past, efforts have been made to render polyesters and polyester resin compositions more flexible. More particularly, in one method, certain plasticizer compounds are added to the polyester resin composition to effectively decrease the glass transition temperature of the composition. The glass transition temperature of a polymer resin or resin composition is that temperature below which the resin or composition is in a glass-like brittle state. Above the glass transition temperature, the resin or composition exhibits greater resilience, flexibility and impact strength.
Plasticizers are generally high boiling organic liquids or low melting solids that exert varying degrees of solvating action on resins. A plasticizer's softening action usually is attributed to its ability to reduce the intermolecular attractive forces between the polymer molecules in a resin or resin system. More particularly, plasticizers are believed to work in two different ways. The first involves reaction between the plasticizer and certain reactive groups on the polymer molecule which is operative to reduce attractive forces between the resin molecules by reducing or nullifying dipole—dipole interactions, hydrogen bonding or other forces between molecules of the resin composition. In this manner, for example, the dipoles of the polymer molecules are no longer available to attract adjacent polymer molecules.
In accordance with another theory, plasticizers are believed to impart a softening effect on polymer compositions by a simple dilution effect. In this instance, attractive forces between polymer molecules are reduced by increased separation.
Generally, the plasticizer compounds which are employed with polyester resin compositions include low and medium molecular weight esters representing the reaction products of acids or acid anhydrides and alcohols. The acids may be cyclic, such as ortho-, iso- or terephthalic, benzoic, trimellitic and the like, or they may be linear, e.g., adipic, azelaic, sebacic, phosphoric and the like. The alcohol constituent may be monohydric, such as 2-ethylhexanol, isodecanol, butanol, isononyl, mixed alkyl, etc., or polyhydric, for example, ethylene glycol, propylene glycol, pentaerythritol, and the like. Other suitable plasticizers have included toluene sulfonamides. and N-alkyl-substituted toluene sulfonamides. Although these plasticizer compounds have been effective at reducing random brittleness in poly)alkylene terephthalate) resin compositions, in order to obtain a polyester compositon having a flexural modulus of less than about 140,000 psi such large quantitites of the plasticizer must be added, that other beneficial properties of the polyester are lost. Moreover, toxicity problems and volatility problems associated with these plasticizers have rendered their use less desirable for most end use applications. More particularly, known plasticizer compounds have a tendency to migrate to the surface of the polymer composition and thereafter volatilize from the surface, liberating potentially toxic gases, which may be harmful if the gases are emitted into the interior of an automobile, for example, and elsewhere. Furthermore, the migration and volatility of most known plasticizers leads to a decrease in flexibility with respect to time, such that the flexible service lives of polyester compositions containing these plasticizers is generally, undesirably short.
In copending application Ser. No. 290,879, filed Aug. 7, 1981, which is a continuation of U.S. Pat. No. 762,325 filed Dec. 20, 1976 certain block copolyesters are described which are formed from polyesters and polyester diols. More particularly, the block copolyesters are derived from terminally-reactive pre-formed blocks of poly(1,4-butylene terephthalate) and from terminally reactive pre-formed blocks of an aromatic/aliphatic or aliphatic polyester. The blocks in the copolyester are connected end-to-end by ester linkages. Examples of these block copolyesters include poly(1,4-butylene terephthalate)-co-poly(hexylen
General Electric Company
Short Patricia A.
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