MOLDING OF MODIFIED POLYPHENYLENE OXIDE RESIN

Abstract: A molding of modified polyphenylene oxide resin comprises a composite of modified polyphenylene oxide containing polyphenylene oxide having structure expressed in the following general formula (I) as a basic skeleton, which resin composite preferably contains a cross linking agent, more preferably phosphoric ester serving as a cross linking agent, while the molding is cross-linked by irradiation to ionizing radiation: where R₁, R₂, R₃ and R₄ represents univalent substituents selected from a group of hydrogen, alkyl group, halogen, alkoxyl group and haloalkoxyl group, and n represents a natural number.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a molding which is obtained by shaping a composite of modified polyphenylene oxide resin into a configuration suitable for use. Description of the Prior Art Modified polyphenylene oxide resin, which is obtained by mixing or grafting thermoplastic resin such as polystyrene into polyphenylene oxide (PPO) such as poly-2,6-dimethylparaphenylene oxide, is widely applied to a material for parts of various electric products or the like, due to its excellence in dimensional stability and electrical property. However, since such modified PPO resin is noncrystalline and inferior in flexibility, strain is left in shaping to easily cause cracking upon contact with a solvent of ketone, a plasticizer for polyvinyl chloride (PVC) or the like. Thus, modified PPO resin cannot be employed in such a field where the same may be brought into contact with such a chemical. For example, an electrical part formed by modified PPO resin may be cracked if the same is in contact with a PVC-covered conductor. Such cracking is caused by a plasticizer added to PVC. The aforementioned problem has generally been solved by a method of introducing crystalline resin such as polyamide into a composite of modified PPO resin to decrease residual strain by relaxing stress applied in crystallization so that no cracking is caused by a solvent, or a method of adding highly flexible elastomer to a composite of modified PPO resin to suppress residual strain. In either method, however, a second component is added in a large amount to sacrifice original electrical property and heat resistance of the modified PPO resin. When crystalline resin is added, such a new problem is caused that the rate of mold shrinkage is increased or a warp or a sink mark is caused by difference in crystallization between parts. US-A- 3 356 761 discloses a composition consisting of a high molecular weight polyphenylene ether and a liquid polymerizable vinyl unsaturated material, which is curable by exposure to a source of radiation. DE-A- 1 694 287 refers to polyphenyleneoxide and modified polyphenyleneoxide films crosslinked by ionizing radiation. JP-A- 61 083 223 discloses a molding of polystyrene modified polyphenyleneoxide and crosslinkable monomer, such as triallyl isocyanurate, which is crosslinked by irradiation with beta- or gamma-rays. SUMMARY OF THE INVENTION An object of the present invention is to provide a molding of a modified PPO resin composite, which can suppress lowering of various characteristics, such as heat resistance, electrical property and flame resistance, of modified PPO resin to the utmost, and prevent cracking caused by contact with a solvent or a plasticizer. A resin molding according to the present invention comprises a composite of modified polyphenylene oxide resin containing polyphenylene oxide having structure expressed in the following general formula (I) as a basic skeleton, said composite of modified polyphenylene oxide resin containing a phosphoric ester having an unsaturated group as a cross linking agent, said molding being crosslinked by ionizing radiation with a dose in the range of 5 to 800 kGy: where R₁, R₂, R₃ and R₄ represent univalent substituents selected from hydrogen, alkyl group, halogen, alkoxyl group and haloalkoxyl group, and n represents a natural number. In relation to the present invention, the term "modified PPO resin" indicates resin which is obtained by mixing or grafting thermoplastic resin such as polystyrene or polyamide into polyphenylene oxide (PPO) such as poly-2,6-dimethylparaphenylene oxide. According to the present invention, resin is cross-linked to provide three-dimensional network structure, so that no cracking is caused by a solvent or the like. Although internal strain of resin is still left in this method, infiltration of the solvent is extremely suppressed in practice by cross linking, whereby cracking can be sufficiently and effectively prevented. According to the present invention, electron beam and gamma rays may be employed as ionizing radiation. The type of ionizing radiation can be arbitrarily selected depending on the configuration of the molding to be irradiated to the same. The radiation dose is within a range of 5 kGy to 800 kGy (0.5 to 80 Mrad). If the radiation dose is smaller than 5 kGy (0.5 Mrad), sufficient cross linking cannot be attained. If the radiation dose is in excess of 800 kGy (80 Mrad), on the other hand, cross linking cannot be attained in a degree proportional to the radiation dose, to lead to a disadvantage in cost. A commercially available product of modified PPO resin of an arbitrary grade can be employed in the present invention. If a sufficient degree of cross linking cannot be attained by simply applying ionizing radiation to such a commercially available product of modified PPO resin a cross linking agent is added to the product of modified PPO resin, thereby to provide a resin composite. Examples of well-known cross linking agents are triallyl cyanurate, triallyl isocyanurate, trimethylol propane trimethacrylate, trimethylol propane triacrylate. If these cross linking agents are added in a large amount, however, original mechanical and electrical properties of the resin itself are reduced while the cost is increased since such a cross linking agent is high-priced. Further, if the radiation dose required for cross linking is increased, the cost is increased to cause a problem in profitability. Particularly when gamma rays are employed, several days are required to merely apply 100 kGy (10 Mrad), and hence it is difficult to use the same in general technique of working a resin molding. Therefore, the inventor has made study on a cross linking agent prepared by a compound having various functional groups to cause cross linking in a small amount of addition and a small radiation dose. It has been recognized through such study that a phosphoric ester having an unsaturated group is particularly suitable for a cross linking agent to be employed in the present invention. The inventor has further discovered that phosphoric ester having unsaturated group can be effectively applied to a cross linking agent as compared with triallyl cyanurate, to attain substantially equivalent cross linking density with a radiation dose of less than half that of triallyl cyanurate. Examples of such phosphoric esters are 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxyethyl acid phosphate, diphenyl-2-methacryloyloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, dibutyl-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxydiethyl phosphate, dioctyl-2-methacryloyloxyethyl phosphate, and dioctyl-2-acryloyloxydiethyl phosphate. Such phosphoric ester having unsaturated group can be employed with another cross linking agent such as triallyl cyanurate, triallyl isocyanurate, trimethylol propane trimethacrylate, and trimethylol propane triacrylate, to attain good cross linking efficiency. The molding of the resin composite according to the present invention can be used with various additives such as a colorant, a stabilizer, a flame retardant, an inorganic filler etc., depending on its use. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a test piece employed for a solvent-cracking resistance test; Fig. 2 is a perspective view showing a state of the test piece set in a frame for the solvent-cracking resistance test; and Fig. 3 is a sectional view showing a state of the test piece set in the frame and dipped in a solvent in the solvent-cracking resistance test. DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with Comparative Examples 1 to 5 and reference examples 1 to 5 shown in Table 1, resin composites were prepared to form test pieces of 40 mm in length, 10 mm in width and 1 mm in thickness. Each test piece was irradiated by electron beam or gamma rays, for measurement of the gel ratio. Each molding thus irradiated by electron beam or gamma rays was extracted in xylene at 130°C for 24 hours, thereby to obtain the gel ratio from the weight of the remainder after extraction. Fig. 1 is a perspective view showing each test piece 1. The test piece 1 irradiated to electron beam or gamma rays was introduced into a frame 2, to be bent by application of stress as shown in Fig. 2. Then the test piece 1 was dipped in methyl ethyl ketone (MEK) for one minute as shown in Fig. 3, to examine whether or not cracking was caused. Table 1 shows the result. As obvious from Table 1, it has been recognized that all of the test pieces according to Comparative Examples 1 to 5 were sufficiently cross-linked with gel ratios of at least 40 %. Further, no cracking was observed after dipping in MEK for one minute. On the other hand, all of the test pieces according to reference examples 1 to 5 were 0 % in gel ratio, and cracked after dipping in MEK. Then, resin composites were prepared in accordance with Examples 6 to 17 at the ratios shown in Table 2, to provide test pieces in the form of sheets of 1 mm in thickness. In Examples 6 to 13, phosphoric ester was employed as a cross linking agent, Examples 14 to 17 are for comparison. Each of the test pieces thus prepared was irradiated to electron beam or gamma rays, for measurement of the gel ratio. Similarly to Comparative Examples 1 to 5, each molding was extracted in xylene at 130°C for 24 hours, thereby to obtain the gel ratio from the weight of the remainder after extraction. Table 2 shows the result. Due to the character of this test, it has been impossible to obtain correct values of the gel ratios indicated as "≦ 30" in Table 2. As obvious from Table 2, all of the test pieces employing phosphoric acid as the cross linking agent were at high gel ratios, to be extremely improved in cross linking efficiency as compared with those employing triallyl cyanurate etc. as a cross linking agent. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: A molding of modified polyphenylene oxide resin comprising a composite of modified polyphenylene oxide resin containing polyphenylene oxide having structure expressed in the following general formula (I) as a basic skeleton, said composite of modified polyphenylene oxide resin containing a phosphoric ester having an unsaturated group as a cross linking agent, said molding being cross-linked by ionizing radiation with a dose in the range of 5 to 800 kGy: where R₁, R₂, R₃ and R₄ represent univalent substituents selected from hydrogen, alkyl group, halogen, alkoxyl group and haloalkoxyl group, and n represents a natural number. A molding of modified polyphenylene oxide resin in accordance with claim 1, wherein said phosphoric ester is at least a single type of phosphoric ester selected from a group of 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxyethyl acid phosphate, diphenyl-2-methacryloyloxyethyl phosphate and diphenyl-2-acryloyloxyethyl phosphate. A molding of modified polyphenylene oxide resin in accordance with claim 1, wherein said ionizing radiation is electron beam. A molding of modified polyphenylene oxide resin in accordance with claim 1, wherein said ionizing radiation is gamma ray. A molding of modified polyphenylene oxide resin in accordance with claim 1, wherein triallyl cyanurate, triallyl isocyanurate, trimethylol propane trimethacrylate or trimethylol propane triacrylate is provided as crosslinking agent.

Inventors: SAKAMOTO, YOSHITO C/O OSAKA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1988
Main classification: C08J3
IPC codes: C08F283, C08J3, C08L71