THERMOPLASTIC RESIN COMPOSITION FOR MOLDING

Abstract: A thermoplastic resin composition comprises a crystal­ line thermoplastic resin, a reinforcing fiber, a flaky filler and polycarbonate and is suitable for molding.

Description: This invention relates to a thermoplastic resin composition which is low in deformation degree when molded and has excellent mechanical properties, in particular, impact resistance. Though crystalline thermoplastic resins are generally used per se as engineering plastics to be molded into machine parts for various purposes, they are used in the form of a composition containing reinforcing material such as glass fibers in the field requiring high mechanical strength or rigidity. However, a composition containing reinforcing fibers such as glass fibers is in general remarkably anisotropic and has the drawback of causing deformation of moldings during molding or annealing, though it has high mechanical strength and rigidity. Such deformation is particularly significant in resins of high crystallization degree, such as polyacetal and polybutylene terephthalate, or those of which crystallization is facilitated by annealing, such as polyethylene terephthalate. Therefore, the applicability of these resins as molding materials must be judged mainly on the basis of the balance between the mechanical properties such as impact resistance or rigidity and deformation, in addition to the chemical and thermal properties according to the purpose of use of the compound. This balance is particularly important when the resin is used as material for moldings of which dimensional accuracy is required, for example, substrate and cases. It is extremely difficult to improve the mechanical properties such as rigidity or impact resistance of moldings while suppressing the deformation thereof and, particularly, in the case of a crystalline thermoplastic resin, the manufacture of products having a high dimensional accuracy is nearly impossible. Australian patent No. 522 577 discloses a composition which comprises a thermoplastic resin, reinforcing fibers and flaky fillers and teaches that the composition is fairly satisfactory. But the disclosed composition is not yet sufficient when it is used for molding. US-A-4352907 discloses blends comprising for example, 92,5 parts of polyethyleneterephthalate, 2,5 parts of an aromatic polycarbonate 30% of fiberglass and 0,5% talc. FR-A-2374368 discloses blends containing polybutyleneterephthalate, fiberglass, polycarbonate and talc. US-A-4123415 discloses reinforced thermoplastic compositions comprising a high molecular weight polyester resin and glass fibers having an average diameter of 0,0005 inches. The composition may also contain a polycarbonate resin. DE-A-2811795 discloses thermoplastic resins containing reinforcing fibers and plate-like fillers. It is the object of the present invention to provide a thermoplastic resin composition having a reduced deformation degree and an improved impact resistance. Said object is achieved by a thermoplastic resin composition having a reduced deformation degree and an improved impact resistance when molded which comprises 1) a crystalline thermoplastic resin and (a) a reinforcing fiber having a staple length not greater than 1 mm and a ratio of length to diameter in the range of from 5 to 1000, said fiber being present in a concentration in the range of from 1 to 60 weight percent; (b) a flaky filler having an average diameter in the range of from 100 to 1000 um, an average thickness in the range of from 0.1 to 10 um and a diameter/thickness ratio in the range of from 4 to 400, said filler being present in a concentration in the range of from 1 to 59 weight percent; and (c) a polycarbonate in a concentration in the range of from 1 to 50 weight percent, all based on the total quantity of the resin composition, and 2) an organic high molecular substance selected from ethylene/carboxylate ester copolymers and metallic salts thereof, polyacrylate resins and segment type thermoplastic copolyesters in a concentration of from 5 to 40 weight percent of said crystalline thermoplastic resin. The crystalline thermoplastic resin used in this invention is an organic high molecular substance which has a crystalline structure at least partly in a solid state, such as, polyacetal (homo- or copolymer); polyalkylene terephthalate, e.g., polybutylene terephthalate, polypropylene terephthalate, or polyethylene terephthalate, and copolymers or mixtures thereof; or various polyamides. These crystalline resins are per se suitable for functional parts in respect of their chemical and thermal properties, but often insufficient when used as molding materials, mechanical strength and dimensional accuracy both of which are important factors, owing to a large degree of deformation during molding or annealing. However, a composition containing additional constituents as described below exhibits particularly high effects and provides a satisfactory function for the purpose. The reinforcing fibers used in this invention ininclude inorganic fibers such as glass fibers, carbon fibers, graphite fibers, metallic fibers, silicon carbide fiber, asbestos, wollastonite or fibrous potassium titanate, whiskers, and various organic fibers. The reinforcing material is preferably glass fiber, but various materials can be used in various ways according to the purpose such as reinforcement of mechanical properties, impartment of electric conductivity, improvement in frictional characteristics, or increase in fire-proofness. These reinforcing fibers may be used alone or as a mixture thereof. According to this invention, the length/diameter ratio of the reinforcing fibers to be incorporated in the resin is within the range of from 5 to 1,000, in particular, from 10 to 100. For example, a glass fiber with a diameter of about 10 µm preferably has an average length ranging from 100 to 1,000 µm. Excessively long fibers degrade the moldability of the composition to be produced and, therefore, the staple length is preferably not larger than 1 mm. The quantity of the reinforcing fiber to be added ranges from 1 to 60% by weight of the total quantity of the resin composition, being appropriately determined according to the use, and is particularly from 2 to 30%. The flaky fillers used in this invention include, for example mica (for example, muscovite, phlogopite or sericite), glass flakes, talc or metallic foil, among which glass flakes are particularly desirable. The proportion of the flaky fillers to be added ranges from 1 to 59% by weight of the total quantity of the resin composition, particularly from 2 to 40% by weight. These flaky fillers may be used alone or as a mixture thereof. The addition of flaky substances is effective for preventing deformation of the composition even when used alone, but is more effective when used in combination with fibrous additives for maintaining high mechanical properties, particularly, tensile strength and impact resistance as well as possessing high dimensional accuracy and low warpage as disclosed in the above Australian patent No. 522 577. However, since an excessive quantity of additives degrades the moldability of the resin composition, a practical upper limit of the total quantity of the flaky and fibrous additives is 60% by weight of the composition, preferably 30 to 50%. To reduce the deformation degree of the moldings, the diameter (the average length in the direction of spreading) of the flaky substance is preferably 40 µm or longer and the thickness thereof is from 0.1 to 10 µm, particularly from 1 to 5 µm The diameter/thickness ratio is from 4 to 400 and most desirably from 30 to 400. Flaky substances which are low in diameters or diameter/thickness ratios exhibit a deformation preventive effect to a low degree only, whereas those which are too high tend to undesirably degrade the moldability of the composition. Above all, as regards glass flakes, thicknesses thereof range preferably from 2 to 5 µm and diameters (lengths in the direction of spreading) are from 100 to 1,000 µm in average. Though these flaky fillers and reinforcing fibers may be incorporated without any particular treatment, they are capable of increasing the mechanical strength further when used after their surfaces have been treated with an appropriate surface-treating agent to improve the affinity and adhesiveness to synthetic resins. As surface-treating agents, various kinds of known ones may be used and there can be mentioned, for example, silanes, titanates, and epoxy compounds. A characteristic of this invention is that a polycarbonate is incorporated therein, which provides synergistic effects for preventing deformation and warpage of the composition of the present invention as well as for improving the mechanical properties of said composition. The polycarbonate used in this invention is of a bisphenol type and obtained, for example, by the reaction of a bisphenol with a carbonate or with phosgene in the presence of an alkali. This polycarbonate is desired to have a high degree of fluidity and the quantity thereof to be added is preferably within the range of from 1 to 50% by weight of the total quantity of the resin composition, preferably from 2 to 25%, because the addition of too large a quantity of polycarbonate degrades the heat resistance of the composition. The composition according to this invention is easily prepared by conventional methods of preparing reinforced resins or filler-containing resins. Any of the following methods is applicable, for example: a first method in which pellets to be used in this invention are prepared by mixing and extruding various additives using an extruder and then molded; a second method in which pellets containing different constituents from each other are blended together prior to moIding and a composition containing constituents according to this invention is obtained after molding; and a third method in which every constituent is directly fed into the molding machine. The composition according to this invention is used after organic high molecular substances are added thereto for adjusting or modifying the physical properties thereof according to the field of use of this composition. The organic high molecular substances are ethylene/carboxylate ester copolymers and metallic salts thereof, such as an ethylene/vinyl acetate copolymer, an ethylene/alkyl acrylate copolymer, and sodium salt of an ethylene/methacrylic acid copolymer; as well as a modifier comprising a polyacrylate resin, and a modifier comprising a segment type thermoplastic copolyester. The modifier is one in which the polyacrylate resin contains a unit derived from C₁ - C₆ alkyl acrylates, and the polyacrylate comprises a multistage copolymer having a rubber-like first stage and a final thermoplastic hard stage. A preferred multi-stage copolymer is, for example, butyl acrylate/butylene diacrylate/allyl methacylate. The modifier comprising a segment type thermoplastic copolyester comprises a large number of repeating long-chain and short-chain ester units which are connected with each other through a head-to-tail bonding, the long-chain ester unit being represented by the following formula (I): and the short-chain having the following formula (II): In formulae (I) and (II), X represents a bivalent residue obtained by removing terminal hydroxy groups from polyalkylene oxide glycol having a melting point of not higher than about 60°C, a molecular weight of from about 400 to 4,000, and a carbon/oxygen ratio of from about 2.5 to 4.3; R represents a bivalent residue obtained by removing carboxyl groups from a dicarboxylic acid having a molecular weight of not larger than about 300; and Y denotes a bivalent residue obtained by removing hydroxyl groups from a diol having a molecular weight of not larger than about 250. These organic high molecular substances can be used alone or as a mixture of two or more of them according to the purpose. The quantity of these substances to be added is from 5 to 40% by weight of the crystalline thermoplastic resin. The composition according to this invention may be endowed with required properties according to the purpose of use by addition of known antistatic agents, coloring agents, lubricants, mold release agents, nucleating agents, stabilizers, fire-resistant agents, or surfactants. The following examples illustrate the invention. Examples 1 to 3 and Comparative Examples 1 to 12: A composition was prepared by mixing polybutylene terephthalate (Duranex made by Polyplastics Co., Ltd.) with glass fibers, glass flakes (average diameter of 600 µm), and polycarbonate at the rate as shown in Table 1, and extruding the mixture into pellets by means of a 40 m/m uniaxial extruder. Then, test pieces were molded of said pellets by a molding machine for measurement of the deformation degree, tensile strength, and impact resistance. On the other hand, other examples for comparison which are devoid of polycarbonate or of any one of glass fiber and glass flake or an organic high molecular substance were measured with respect to the same items as above. The results of these measurements are shown in Table 1. For measurement of the deformation degrees, flat test pieces, 120 mm square (2 mm thick), were prepared and the most severely deformed part of the test piece was measured as a representative of the deformation degree. The quantity is denoted in terms of percent by weight against the total quantity of the composition. Among the above examples, Examples 1 to 3 which specific high molecular substances were added, were able to give moldings which are low in the deformation degree and have an increased impact resistance. By using these resins, a high impact resistance can be obtained even if the quantity of glass fibers to be added is reduced, so that a further advantage of attaining reduction in the deformation degree is obtained.

Claims: A thermoplastic resin composition having a reduced deformation degree and an improved impact resistance when molded which comprises 1) a crystalline thermoplastic resin and (a) a reinforcing fiber having a staple length not greater than 1 mm and a ratio of length to diameter in the range of from 5 to 1000, said fiber being present in a concentration in the range of from 1 to 60 weight percent; (b) a flaky filler having an average diameter in the range of from 100 to 1000 µm, an average thickness in the range of from 0.1 to 10 µm and a diameter/thickness ratio in the range of from 4 to 400, said filler being present in a concentration in the range of from 1 to 59 weight percent; and (c) a polycarbonate in a concentration in the range of from 1 to 50 weight percent, all based on the total quantity of the resin composition, and 2) an organic high molecular substance selected from ethylene/carboxylate ester copolymers and metallic salts thereof, polyacrylate resins and segment type thermoplastic copolyesters in a concentration of from 5 to 40 weight percent of said crystalline thermoplastic resin. The thermoplastic resin composition of claim 1 wherein the total content of said reinforcing fiber and said flaky filler is not more than 60 weight percent. The thermoplastic resin composition of claim 1 or 2, wherein said reinforcing fiber is present in a concentration of from 2 to 30 weight percent. The thermoplastic resin composition of any of claims 1 to 3, wherein said flaky filler is present in a concentration of from 2 to 40 weight percent. The thermoplastic resin composition of any of claims 1 to 4, wherein the total content of said reinforcing fiber and said flaky filler is in the range of from 30 to 50 weight percent. The thermoplastic resin composition of any of claims 1 to 5, wherein said polycarbonate is present in a concentration of from 2 to 25 weight percent. The thermoplastic resin composition of any of claims 1 to 6 wherein the crystalline thermoplastic resin is polybutylene terephthalate resin. The thermoplastic resin composition of any of claims 1 to 7, wherein the flaky filler is glass. The thermoplastic resin composition of any of claims 1 to 8, in which said reinforcing fiber is a fiber selected from the group consisting of glass, carbon, graphite, metals, silicon carbide, asbestos, wollastonite, potassium titanate and organic fibers.

Inventors: KASUGA, TAKUZO, TAKAHASHI, KATSUHIKO
Applicants: POLYPLASTICS CO. LTD.
Application year: 1984
Main classification: C08L69
IPC codes: C08K7, C08L67, C08L69, C08L59, C08L101, C08J5, C08L77