FIBER REINFORCED THERMOPLASTIC ARTICLES AND PROCESS FOR THE PREPARATION THEREOF

Abstract: Processes for preparing fiber reinforced thermoplastic articles are provided, for example, thermoplastic fibers and reinforcement fibers can be intermingled to produce a com­ posite yarn, which is used to weave a fabric, then the fabric heated to produce a reinforced article. As another example, thermoplastic yarn and reinforcement yarn can be woven together to produce a composite fabric, which, upon heat­ ing, produces a reinforced article.

Description: Background This invention relates to a process for the preparation of fiber reinforced thermoplastic articles. In another aspect, this invention relates to novel fiber reinforced thermoplastic articles. Various methods have been employed to prepare fiber reinforced thermoplastic articles. Each method suffers from drawbacks which prevent the large scale use of the method for the preparation of such articles. Thus, for example, hot melt application of thermoplastic to a reinforcement material is a very energy consuming process since large quantities of thermoplastic resin must be maintained in the melt form during resin application. Solvent application methods introduce the consideration of restricting exposure of both worker and environment to solvents. In addition, considerable process time and energy must be spent driving off excess solvent remaining after resin manipulation is completed. Another problem frequently encountered in the preparation of fiber reinforced thermoplastic articles is the nonuniform contact of thermoplastic resin with reinforcement, thereby resulting in a nonuniform fiber reinforced thermoplastic article. GB-A-2 105 247 discloses a process for making a fiber-reinforced molding by wrapping a core of reinforcing fibers with a thermoplastic yarn and thermal forming the wrapped yarn so that the thermoplastic yarn becomes a polymer matrix around the reinforcing fibers. A substantially untwisted carbon fiber yarn of 3000 filaments and 200 Tex over all count was passed through the hollow spindle of a wrapping machine with 3 monofilaments of PEEK, as the combined core component. This was wrapped with a spiral wrapping of a single monofilament of PEEK, using a twist of 473 turns per meter. Objects of the Invention An object of the invention is an efficient process for the preparation of fiber reinforced thermoplastic articles. Another object of the invention is to provide a hybrid, low-twist yarn and a fabric made thereof for use in the preparation of uniform fiber reinforced thermoplastic articles. These and other objects of the invention will become apparent from the disclosure and claims provided herein. Statement of the Invention In accordance with the invention, a hybrid, low-twist yarn and a fabric made thereof are provided as defined in the claims. A process for the preparation of a fiber reinforced thermoplastic article is also provided as defined in claim 7. I have discovered that fiber reinforced articles can be prepared by weaving thermoplastic fiber together with reinforcing fiber and thereafter melting the thermoplastic whereby intimate contact between the reinforcement material and the thermoplastic "matrix" is achieved. The thermoplastic material used is poly (arylene sulfide). In addition, a hybrid low twist yarn containing individual filaments of thermoplastic material and reinforcement material can be prepared, woven into a fabric or chopped and layed up as a batt of non-woven fibers. Upon melting of the thermoplastic material, intimate contact between the thermoplastic and reinforcement materials results. The product fiber reinforced thermoplastic articles comprising poly (arylene sulfide) are useful in a variety of applications where the chemical properties of the thermoplastic material and the physical integrity imparted by the reinforcement material are required, such as, for example, production of light-weight laminates. Detailed Description of the Invention In accordance with the present invention, a process is provided comprising intermingling at least one fibrous thermoplastic material consisting of poly (arylene sulfide) and at least one fibrous reinforcement material to produce a composite yarn, weaving the composite yarn into a fabric, and heating the fabric to a temperature at least as high as the melting point of the thermoplastic material for a time sufficient to allow intimate contact between the molten thermoplastic material and the fibrous reinforcement material. A process is also provided comprising intermingling at least one fibrous thermoplastic material and at least one fibrous reinforcement material to produce a composite yarn, passing the composite yarn to a staple cutter to produce a composite staple, laying up the composite staple to produce a batt of composite staple and heating the batt of composite staple to a temperature at least as high as the melting point of the thermoplastic material for a time sufficient to allow intimate contact between the molten thermoplastic material and the fibrous reinforcement material. A further process is provided comprising weaving at least one individual filament of PAS with at least one reinforcement yarn to produce a composite fabric and heating the composite fabric to a temperature at least as high as the melting point of the PAS for a time sufficient to allow intimate contact between the molten thermoplastic and the reinforcement yarn. Fiber reinforced thermoplastic articles are prepared in accordance with the above described processes. Thermoplastic Material The term "fiber" as used herein, refers to either staple fibers or continuous fibers employed in making of fabrics. Typical examples of such fibers include those prepared from such thermoplastic materials as polyamides such as polycaprolactam and copolyamides, polyesters such as polyethylene terephthalate and copolyesters, polyacrylonitrile and copolymers of acrylonitrile, vinyl and vinylidene polymers and copolymers, polycarbamates, polyurethanes, polyester-amides, polyolefins such as polypropylene, fluorinated polyolefins, poly(arylene sulfide) compounds such as poly(phenylene sulfide) and mixtures of any two or more thereof. In accordance with the invention, fibers are prepared from poly(arylene sulfide) compounds since the poly(arylene sulfides) have properties which make them suitable for a wide variety of applications. Without being limited thereto, uncured or partially cured poly(arylene sulfide) whether homopolymer, copolymer, terpolymer, or a blend of such polymers, can be used in the practice of the invention. The uncured or partially cured polymer is a polymer the molecular weight of which can be increased by either lengthening a molecular chain or by crosslinking or by combination of both by supplying thereto sufficient energy, such as heat. Suitable poly(arylene sulfide) polymers include, but are not limited to, those described in U.S. 3,354,129. Examples of poly(arylene sulfide) polymers suitable for purpose of the invention include poly(2,4-toluene sulfide), poly(4,4'-biphenylene sulfide) and poly(phenylene sulfide). Because of its availability and desirable properties (such as high chemical resistance, nonflammability, and high strength and hardness) poly(phenylene sulfide) is the presently preferred poly(arylene sulfide). The preferred poly(phenylene sulfide) for use a this invention will have a flow rate of about 75-800 grams/10 minutes, determined according to ASTM D1238 modified to a temperature of 316°C and a total weight of 5.0 Kg and preferably will have a flow rate of about 100-500 grams/10 minutes. Most preferably, the poly(arylene sulfide) compound employed in the practice of the invention will be prepared by the processes described in U.S. 4,282,347 and U.S. 4,350,810, and will have a flow rate of about 160-280 grams/10 minutes. Polymeric material with high flow rates are preferred because intimate contacting between the thermoplastic material and the reinforcement material is most readily achieved with such high flow rate compounds. Reinforcement Any fibrous reinforcement material which will not melt or degrade under the treatment conditions detailed more fully below are suitable for use in the practice use of the present invention. Preferably, reinforcement materials employed in the practice of the invention will have melting points higher than the melting points of the thermoplastic materials employed. Suitable materials include, but are not limited to, glass fibers, carbon fibers, aramid fibers such as, for example, poly(p-phenylene terephthalamide), boron fibers, boron nitride fibers, ceramic fibers, metal fibers, such as for example, iron, nickel, chromium, copper and aluminum, and mixtures of any two or more thereof. Contacting Procedures A wide variety of techniques are suitable for causing the intimate contacting of the fibrous thermoplastic material and at least one fibrous reinforcement material. For example, at least one thermoplastic fiber and at least one reinforcement fiber can be intermingled such as for example by braiding of several fibers together to produce a composite yarn. A yarn with about 100 twists per meter is preferred The composite yarn can then be woven into a fabric which is then ready for further treatment as detailed more fully below. Another means for causing intimate contact of fibrous thermoplastic material and fibrous reinforcement material involves first intermingling at least one thermoplastic fiber and at least one reinforcement fiber as described above to produce a composite yarn. The composite yarn can be then be passed to a staple cutter to produce a composite staple. A composite batt laid up employing the composite staple can then be prepared. Finally, the composite batt can be subjected to further treatment conditions as detailed more fully below. Yet another process for bringing about the intimate contacting of fibrous thermoplastic material and fibrous reinforcement material involves preparing a thermoplastic yarn from the fibrous thermoplastic material and preparing a reinforcement yarn from the fibrous reinforcement material, then weaving together at least one thermoplastic yarn with at least one reinforcement yarn to produce a composite fabric. The composite fabric is then ready for further treatment as detailed more fully below. The ratio of fibrous thermoplastic material to fibrous reinforcement material useful in the practice of the present invention can vary widely. For purposes of guidance, it is suggested that the quantity of fibrous reinforcement material employed constitute about 40 to about 80 wt %, based on the total weight of the resulting fabric. Preferably, the fibrous reinforcement material will be employed in the range of about 55 to about 65 wt.%, based on the total weight of the resulting fabric. Treatment Conditions After the composite fabric or composite batt prepared in accordance with the present invention is formed, the composite materials are subjected to conditions of temperature and pressure for a time sufficient to allow intimate contact between the thermoplastic material and the reinforcement material. Suitable temperatures are at least as high as the melting point of the thermoplastic material, but not so high as to cause significant levels of thermoplastic degradation. By way of example, suitable temperatures for use with poly(phenylene sulfide) are broadly about 285 up to about 350°C. Preferably, temperatures ranging from about 300 up to about 330°C will be employed. While not essential, the use of pressure to aid bringing about the intimate contacting of the thermoplastic material and the reinforcing material is desirable. Broadly, pressures from atmospheric up to about 3.4 MPa (300 psig) are suitable. Higher pressures are not believed to impart any additional benefits and merely increase equipment and operating costs. Preferably, pressures in the range of about 0.34 (50) up to about 1.4 MPa (200 psig) will be employed. The amount of time during which the composite fabric or composite batt is subjected to elevated temperature and pressure is that amount of time necessary to allow the softened or melted thermoplastic material to come into intimate contact with the reinforcement fibers. In addition, it is desirable for the contact time to be sufficient to allow for the escape of any air entrapped in the composite fabric or composite batt to escape form the composite structure. Broadly, contact for about 1 minute up to about 60 minutes is suitable. Preferably, treatment conditions will be maintained for a period of about 5 to about 30 minutes. Most preferably, treatment conditions will be maintained for about 10 up to about 20 minutes, which time period is generally sufficient to ensure intimate contact between the thermoplastic material and the reinforcement fiber without requiring excessive time for the treatment cycle. Example I This example illustrates the preparation of woven carbon-poly(phenylene sulfide) prepregs, i.e., impregnated composite material suitable for lamination and molding application. Two different types of yarn were twisted together: (a) a carbon fiber yarn of 1717 denier containing 3000 filaments, coated with an epoxy sizing, marketed as Thornel Type 300, WYP 30 I/10 by the Carbon Products Division of Union Carbide Corporation, New York, N.Y. and (b) a 850 denier Ryton® poly(phenylene sulfide) (PPS) yarn having a flow rate of 220 ± 60 g/10 min (determined according to ASTM, D1238, modified to a temperature of 316°C and a total weight, including the weight of the piston, of 5.0 kg), containing 200 filaments, marketed under the product designation of XO2 by Phillips Fibers Corporation, Greenville, S.C. A three-ply hybrid yarn was prepared by twisting two plies of the 850 denier PPS fiber yarn and one ply of the 1717 denier carbon fiber yarn at a low twist of 100 twists per meter (2.5 twist per inch) on a commercial twisting machine operated by Phillips Fibers Corporation. The hybrid 3-ply yarn was then used for weaving two fabrics: one having 4 x 4 ends/cm (10 x 10 ends/inch (10 warp ends, 10 fill ends per inch)) and the other-one having a 6.4 x 4 ends/cm (16 x 10 ends/inch) plain weave construction. Weaving was done on a commercial weaving loom operated by Phillips Fibers Corporation. The fabric having the 4 x 4 (10 x 10) construction weighed approximately 3.0 kg/m² (8.8 oz/yd²); it was 2.7 m (3 yards) long and 46 cm (18 inches) wide. The 6.4 x 4 (10 x 16) fabric weighed approximately 3.7 kg/m² (11 oz/yd²); was 1.2 m (1 1/3 yards) long and 46 cm (18 inches) wide. Example II The "prepreg" fabric of Example I prepared from hybrid yarns was laminated by placing from 2 to 10 plies of fabric, cut to a size of about 23 x 25 cm (9" x 10"), in a 23 x 25 cm (9" x 10") metal mold cavity and compressing them at a temperature of about 595°F (313°C) and a pressure of about, 1.4 MPa (200 psi) for 15 minutes. The composite was then removed from the hot press, placed in a second press at room temperature and allowed to cool under 1.4 MPa (200 psi) pressure. The fabric plies were laid up such that the warp yarns of all layers were oriented in the same direction and the fills yarns were oriented at a 90° angle to the warp yarns. Molded composite sheet height ranged from 0.5 mm (0.02 inch) for a 2-ply composite to about 2.0-2.3 mm (0.08-0.09 inches) for a 10-ply composite. Pertinent physical properties of molded composite sheets are listed in Table I. Sample I Sample 2 Number of Plies 10 9 Weave Construction ends/cm (ends/inch) 4 X 4 (10 x 10) 6.4 x 4 (16 x 10) Carbon Fiber Content , weight-% 61 63 Tensile Strenght MPa (psi) 275 (39,900) 277 (40,200) Flexural Strength MPa (psi) 251 (36,500) 254 (36,900) Flexural Modulus MPa (psi) 3.6 x10⁴ (5.3 x 10⁶) 37 (5.4 x 10²) Shear Strength MPa (psi) 22.3 (3,250) 25.8 (3,740) Density , g/cc 1.53-1.56 1.51-1.55

Claims: A hybrid, low twist yarn, comprising a blend of individual continuous filaments of a poly(arylene sulfide) and individual continuous filaments of a fibrous reinforcement, in particular carbon filaments, wherein said reinforcement will not melt or degrade under the conditions of treatment of the low-twist yarn, which include a temperature in the range of 285 to 350°C. A yarn as in claim 1 wherein said filaments of poly(arylene sulfide) are comprised of poly(phenylene sulfide). A yarn as in claim 2 wherein said poly(phenylene sulfide) polymer has a melt flow in the range of from about 75 to 800 grams per ten minutes determined according to ASTM D1238 modified to a temperature of 316°C and a total weight of 5.0 kilograms. A yarn in accordance with one of the preceding claims comprising about 40 to about 80 weight% of said fibrous reinforcement based on total weight of yarn. A yarn in accordance with one of the preceding claims wherein said yarn is twisted about 100 twists per metre (2.5 twists per inch). A fabric containing a hybrid, low-twist yarn as defined in one of the claims 1 to 5. A process for the preparation of a fiber reinforced thermoplastic article, said process comprising: (a) producing an intermediate product from fibrous materials by one of the following procedures (aa) (1) intermingling at least one individual continuous filament of a poly(arylene sulfide) as thermoplastic material and at least one individual filament of a fibrous reinforcement material to produce a composite hybrid, low-twist yarn as defined in one of the claims 1 to 5; (2) weaving said composite yarn into a fabric as said intermediate product; or (bb) (1) intermingling at least one individual continuous filament of a poly(arylene sulfide) as thermoplastic material, and at least one individual filament of a fibrous reinforcement material to produce a composite hybrid, low-twist yarn as defined in of the claims 1 to 5; (2) passing said complete yarn to a staple cutter to produce a composite staple; (3) laying up said composite staple to produce a batt of said composite staple as said intermediate product; or (cc) weaving at least one individual continuous filament of a poly(arylene sulfide) with at least one individual reinforcement yarn of reinforcement material to produce a composite fabric as defined in claim 6; (b) heating said intermediate product to a temperature at least as high as the melting point of said thermoplastic material for a time sufficient to allow intimate contact between said thermoplastic material and said fibrous reinforcement material. A process in accordance with claim 7 wherein said fibrous reinforcement material is selected from the group consisting of: glass, carbon, aramid, boron, boron nitride, ceramic, iron, nickel, chromium, copper, aluminium, and mixtures of any two or more thereof. A process in accordance with claim 7 or 8 wherein said intermingling comprises braiding said fibrous materials to produce said composite yarn. A process in accordance with one of the claims 7 to 9 wherein the weight% of said fibrous reinforcement material is 40 to 80% based on the total weight of said composite yarn. A process in accordance with one of the claims 7 to 10 wherein said heating is carried out at a temperature of 285 to 350° for 1 minute to 60 minutes under sufficient pressure to maintain intimate contact between said thermoplastic material and said reinforcement material. A process in accordance with one of the claims 7 to 11 wherein said batt produced in step (a) (bb) is needle-punched prior to step (b).

Inventors: O'CONNOR, JAMES EDWARD
Applicants: PHILLIPS PETROLEUM COMPANY
Application year: 1985
Main classification: C08J5
IPC codes: B29B15, C08G75, C08J5, D01F6