GB1592205A - Reinforced thermoplastic compositions of polyester resins and glass fibers in combination with fine ground mica - Google Patents

Description

(54) REINFORCED THERMOPLASTIC COMPOSITIONS OF POLYESTER RESINS AND GLASS FIBERS IN COMBINATION WITH FINE GROUND MICA (71) We, GENERAL ELECTRIC COMPANY, a corporation organised and existing under the laws of the State of New York, United States of America, of 1 River Road; Schenectady 12305, New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to glass reinforced molding compositions which have improved heat distortion resistance and warp resistance in the molded article.More particularly, it pertains to compositions comprising a polyblend of poly(1,4-butylene terephthalate) resin and poly(ethylene terephthalate), resin, and as a reinforcement therefor, glass fibbers combined with finely ground mica.

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 petal., U.S. 2,465,319 and in Pengilly, U.S. 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 injection moldable compositions. Poly(1,4-butylene terephthalate), because of its very rapid crystallization from the melt, is uniquely useful as a component in such compositions. Workpieces molded from such polyester resins, in comparison with other thermoplastics, offer a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction.

Our co-pending British Patent Application No. 50646/77 (Serial No. 1592204) discloses polyester compositions, e.g. poly(1,4-butylene terephthalate) or poly(ethylene terephthalate) which can be molded to articles having good resistance to warpage or heat distortion when they are filled with talc or mica, as well as glass fibres.

It has now been discovered that superior polyblends of poly(1,4-butylene terephthalate) resin and poly(ethylene terephthalate) resin are obtained upon reinforcement with fibrous glass, in combination with finely divided mica. The compositions of the invention possess less inherent warpage in the molded article and good moldability when compared with compositions of glass fiber reinforced polyblends of polyester resins. The improved resistance to heat distortion and decrease in warpage is achieved without any appreciable decrease in other mechanical properties, such as notched Izod impact strength, tensile strength and modulus. The flexural strength is improved.

According to this invention, there is provided a thermoplastic molding composition which comprises an intimate mixture of: (a) a poly(1,4-butylene terephthalate) resin; (b) a poly(ethylene terephthalate) resin; c) a reinforcing amount of glass fibers; and (d) particulate mica having a particle size of less than 325 mesh, in an amount sufficient to improve the deflection temperature under load.

The reinforced thermoplastic composition according to the invention are useful for molding, e.g., injection molding, compression molding, and transfer molding.

The mica suitable for this invention as component (d) can be obtained from a number of commercial sources.

Nearly all will pass through a 325 mesh U. S. standard sieve. Water ground mica is suitable. A source for this is English Mica Co., Stamford, Connecticut 06905, U.S.A.

The polyester resins of the compositions of this invention are available commercially or can be prepared by known techniques such as by the alcoholysis of esters of terephthalic acid with ethylene glycol or 1,4-butanediol and subsequent polymerization, by heating the glycols with the free acids or with halide derivatives thereof, and similar processes. These are described in U.S. Patents No. 2,465,319 and 3,047,539, and elsewhere.

Illustratively, these high molecular weight polyesters will have an intrinsic viscosity of at least 0.4 deciliters/gram and preferably, at least 0.8 deciliters/gram, as measured in a 60:40 phenol/tetrachloroethane mixture at 30"C.

In preferred embodiments component (a) comprises from 1 to 99 parts by weight, and component (b) comprises from 99 to 1 parts by weight per 100 parts by weight of the total resinous components in the composition.

The filamentous glass to be employed as component (c) in the present compositions is well known to those skilled in the art, and is widely available from a number of manufacturers. For compositions ultimately to be employed for electrical uses, it is preferred to use fibrous glass filaments comprised of lime-aluminum borosilicate glass that is relatively soda free. This is known as "E" glass. However, other glasses are useful where electrical properties are not so important, e.g., the low soda glass known as "C" glass. The filaments are made by standard processes, e.g., by steam or air blowing, flame blowing and mechanical pulling. The preferred filaments for plastics reinforcement are made by mechanical pulling. The filament diameters range from 0.00012 to 0.00075 inch, but this is not critical to the present invention.

The length of the glass filaments and whether or not they are bundled into fibers and the fibers bundled in turn to yarns, ropes or rovings, or woven into mats, are also not critical to the invention. However, in preparing the molding compositions, it is convenient to use the filamentous glass in the form of chopped strands of from one-eighth to 2 inches long. In articles molded from the compositions, on the other hand, even shorter lengths will be encountered because, during compounding, considerable fragmentation will occur. This is desirable, however, because the best properties are exhibited by thermoplastic injection molded articles in which the filament lengths lie between 0.00005 and 0.125 (one-eighth) inch.

In general, best properties will be obtained if the reinforcing agent combination comprises from at least 1 part by weight and, preferably, from 1 to 60 parts by weight, based on 100 parts of the combined weights of components (a), (b), (c) and (d).

In the most preferred compositions, the glass fibers (c) comprise from 1 to 10 parts by weight, and the mica component (d) comprises from 15 to 30 parts by weight per 100 parts by weight of components (a), (b), (c) and (d).

The compositions of this invention can include, in addition to the reinforcement combination, other ingredients, such as dyes, pigments, stabilizers, plasticizers, flame retardants, and drip retardants, added for their conventionally employed purposes.

Illustrative flame retardant additives are disclosed in U. S. Patents No. 3,833,685; 3,341,154; 3,915,926 and 3,671,487. Other flame retardants are disclosed in U. S. Patents No. 3,681,281; 3,557,053 and 3,830,771 and U. K. Patent No. 1,358,080.

The compositions of this invention can be prepared by a number of procedures. In one way, the glass fibers and mica are put into an extrusion compounder with the resinous components to produce molding pellets. The reinforcement is dispersed in a matrix of the resin in the process. In another procedure, the glass fiber (c) and mica (d) are mixed with the resins (a) and (b) by dry blending, then either fluxed on a mill and comminuted, or they are extruded and chopped. The glass fibers and mica can also be mixed with the resins and directly molded, e.g., by injection or transfer molding techniques.

It is always important that all of the ingredients: resin, reinforcement, and any optional conventional additives, be as free from water as possible.

In addition, compounding should be carried out to ensure that the residence time in the machine is short; the temperature is carefully controlled; the friction heat is utilized; and an intimate blend between the resin and the reinforcement is obtained.

Although it is not essential, best results are obtained if the ingredients are precompounded, pelletized and then molded. Pre-compounding can be carried out in conventional equipment. For example, after carefully pre-drying the polyester and the reinforcing agent composition, e.g., under vacuum at 100"C. for 12 hours, a single screw extruder is fed with a dry blend of the ingredients, the screw employed having a long transition section to ensure proper melting. On the other hand, a twin screw extrusion machine, e.g., a Werner & Pfleiderer machine, can be fed with resins and additives at the feed port and reinforcement down stream. In either case, a generally suitable machine temperature will be 450 to 4600F.

The pre-compounded composition can be extruded and cut up into molding compounds such as conventional granules, pellets, by standard techniques.

The composition can be molded in any equipment conventionally used for glass-filled thermoplastic compositions, e.g., a Newbury type injection molding machine with conventional cylinder temperatures,-e.g., 525"F. and conventional mold temperatures, e.-g., 1500F.

The following example illustrates the invention.

Example A dry blend of poly(1,4-butylene terephthalate), intrinsic viscosity 0.8 dl/g., melt viscosity 1700 poise, poly (ethylene terephthalate), intrinsic viscosity 0.62 dl/g., 1/8" glass fibers (Owens Corning 419), finely divided mica, Ferro 904 antioxidant ("Ferro" is a Registered Trade Mark) are compounded and extruded at 5250F. in an extruder.The extrudate is pelletized and injection molded at 525"F. (mold temperature 1300F.). The formulations and physical properties obtained are shown in the following table: TABLE Physical properties Ingredients (parts by weight) 1 1A* poly(1,4-butylene terephthalate) 45.5 45.5 poly ethylene terephthalate) 30.5 30.5 fibrous glass reinforcement 1/8 inch 4 4 mica, < 325 mesh 20 talc - 20 antioxidant 0.05 0.05 Properties Heat Deflection Temp., "F 264 psi 321 287 Warp:As molded, mm. 0 0 After 30 min. at 350"F., mm. 1.5 7 Notched Izod impact, ft.lbs./in. 0.54 0.56 Unnotched Izod impact, ft.lbs./in. 6.9 6.7 Tensile strength, psi 11,000 10,000 Flexural modulus, psi 886,000 775,000 Flexural strength, psi 20,000 17,000 * control - talc product designated EMTAL 500.

The composition of this invention is injection molded into a large part with only slight warpage. In contrast thereto, an identical part molded from the control sample (1A*) would have a significantly increased warpage. Only by such expensive expedients as treating the talc with a coupling agent is it possible to approach the superior resistance to heat deflection, warp resistance, flexural strength and modulus shown by the composition of this invention.

WHAT WE CLAIM IS: 1. A thermoplastic molding composition which comprises an intimate mixture of: (a) a poly(1,4-butylene terephthalate) resin; (b) a poly(ethylene terephthalate) resin; (c) a reinforcing amount of glass fibers; and (d) particulate mica having a particle size of less than 325 mesh, in an amount sufficient to improve the deflection temperature under load.

2. A composition as claimed in Claim 1 wherein the component (a) comprises from 1 to 99 parts by weight and component (b) comprises from 99 to 1 parts by weight per 100 parts by weight of the total resinous components in the composition.

3. A composition as claimed in Claim 1 or 2 wherein components (c) and (d) are present in a total amount of at least 1 part by weight per 100 parts by weight of the combined components (a), (b), (c) and (d).

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. The pre-compounded composition can be extruded and cut up into molding compounds such as conventional granules, pellets, by standard techniques. The composition can be molded in any equipment conventionally used for glass-filled thermoplastic compositions, e.g., a Newbury type injection molding machine with conventional cylinder temperatures,-e.g., 525"F. and conventional mold temperatures, e.-g., 1500F. The following example illustrates the invention. Example A dry blend of poly(1,4-butylene terephthalate), intrinsic viscosity 0.8 dl/g., melt viscosity 1700 poise, poly (ethylene terephthalate), intrinsic viscosity 0.62 dl/g., 1/8" glass fibers (Owens Corning 419), finely divided mica, Ferro 904 antioxidant ("Ferro" is a Registered Trade Mark) are compounded and extruded at 5250F. in an extruder.The extrudate is pelletized and injection molded at 525"F. (mold temperature 1300F.). The formulations and physical properties obtained are shown in the following table: TABLE Physical properties Ingredients (parts by weight) 1 1A* poly(1,4-butylene terephthalate) 45.5 45.5 poly ethylene terephthalate) 30.5 30.5 fibrous glass reinforcement

1/8 inch 4 4 mica, < 325 mesh 20 talc - 20 antioxidant 0.05 0.05 Properties Heat Deflection Temp., "F 264 psi 321 287 Warp:As molded, mm. 0 0 After 30 min. at 350"F., mm. 1.5 7 Notched Izod impact, ft.lbs./in. 0.54 0.56 Unnotched Izod impact, ft.lbs./in. 6.9 6.7 Tensile strength, psi 11,000 10,000 Flexural modulus, psi 886,000 775,000 Flexural strength, psi 20,000 17,000 * control - talc product designated EMTAL 500.

The composition of this invention is injection molded into a large part with only slight warpage. In contrast thereto, an identical part molded from the control sample (1A*) would have a significantly increased warpage. Only by such expensive expedients as treating the talc with a coupling agent is it possible to approach the superior resistance to heat deflection, warp resistance, flexural strength and modulus shown by the composition of this invention.

WHAT WE CLAIM IS: 1. A thermoplastic molding composition which comprises an intimate mixture of: (a) a poly(1,4-butylene terephthalate) resin; (b) a poly(ethylene terephthalate) resin; (c) a reinforcing amount of glass fibers; and (d) particulate mica having a particle size of less than 325 mesh, in an amount sufficient to improve the deflection temperature under load.

2. A composition as claimed in Claim 1 wherein the component (a) comprises from 1 to 99 parts by weight and component (b) comprises from 99 to 1 parts by weight per 100 parts by weight of the total resinous components in the composition.

3. A composition as claimed in Claim 1 or 2 wherein components (c) and (d) are present in a total amount of at least 1 part by weight per 100 parts by weight of the combined components (a), (b), (c) and (d).

4. A composition as claimed in Claim 3 wherein the total amount of components (c) and

(d) is from 1 to 60 parts by weight, per 100 parts by weight of the combined components (a), (b), (c) and (d).

5. A composition as claimed in any preceding Claim wherein the glass fiber (c) comprises from 1 to 10 parts by weight and the mica component (d) comprises from 15 to 30 parts by weight, per 100 parts by weight of components (a), (b), (c), and (d).

6. A composition as claimed in Claim 1 substantially as hereinbefore described with reference to the Example.