HALOGEN-FREE FIRE-RETARDANT SYNTHETIC RESIN COMPOSITION

Abstract: A halogen-free self-extinguishing, fire-retardant synthetic resin compsn. is predp. by adding 0.5-15 pts. (by wt.) of synthetic silicate (silicic acid hydrate or hydrated silica) to 100 pts. of a mixt. of one or more thermoplastic synthetic resins (70-30 pts.) and magnesium or aluminium hydroxide (30-70 pts.) The metal hydroxide has an ave. particle dia. of 0.1-10 microns.

Description: Technical Field The present invention is applicable to the field of preparing a synthetic resin composition of a flame resisting material. The expression "flame resisting" as used herein means that the criteria of the Test No. 302 of the Federal Motor Vehicle Safety Standards (USA) and/or the criteria V-1 of the Underwriters Laboratories Test (UL)94 are fulfilled. Background Art Recently, a wide variety of flame resisting synthetic resin compositions have been developed with the purpose of ensuring the safety against a fire. Among them, flame resisting sysnthetic resin compositions not containing halogen, phosphorus or antimony trioxide, i.e., so-called non-toxic flame resisting synthetic resin compositions of a halogen-free type are given special attention. Generally, such a flame resisting synthetic resin composition of a halogen-free type contains an inorganic filler such as aluminum hydroxide or magnesium hydroxide. Further, the amount of the inorganic filler required to obtain sufficiently high flame resisting effect is generally 30 to 70% by weight based on the composition. However, a synthetic resin composition containing an inorganic filler in such a high content does not generally exhibit well-balanced strength, so that it is brittle and poor in processability. Further, some synthetic resin compositions containing such a flame resistant filler alone do not exhibit sufficient flame resistance. Thus the simultaneous addition of such a filler and carbon black has been attempted with the purpose of overcoming these problems (see Japanese Patent Publication No.10898/1982). The simultaneous addition thereof is known to impart high flame resistance to a synthetic resin, even when the amount of a flame resistant filler is relatively small. However, the halogen-free flame resisting compositions thus prepared are all black, so that they can not be applied to the fields wherein color discrimination is necessitated or the fields wherein importance is attached to appearance, i.e., the fields wherein the use of a black material is unfavorable (for example, wall covering material). Disclosure of Invention An object of the present invention is to provide, without using carbon black, a halogen-free flame resisting synthetic resin composition. Thus making it widely appliable to the field wherein a color-discriminable flame resisting composition must be used. In addition to fields wherein importance is attached to appearance, for example, wall covering material. From Japanese laid open patent application No. 212247/1982 halogen-free flame retardant resin compositions are known which are used in the crass-linked structural form, comprising aluminium-hydroxide having an average particle diameter smaller than 10 µm and either amorphous silica or carbon black having an average secondary particle diameter smaller than 10 µm. It is said that cross-linking can be effected by the aid of a chemical crosslinking agent, like an organic peroxide, or by irradiation e.g. with electron rays. Furthermore it was known from Japanese laid-open patent application No. 117237/1983 to incorporate hard clay having an average particle diameter smaller than 10 µm and amorphous silica having an average secondary particle diameter smaller than 10 µm and/or carbon black, optionally together with aluminium hydroxide having an average particle diameter smaller than 10 µm into a resin composition. Such compositions are said to have good flame-retardant properties. The present invention relates to a halogen-free and flame resisting resin composition . This is obtained by adding 0,5 to 15 parts by weight of a synthetic amorphous silicate containing 40 to 70 % by weight of silicon dioxide and 10 to 45% by weight of magnesium oxide and calcium oxide to 100 parts by weight of a mixture comprising 70 to 30 parts by weight of a thermoplastic synthetic resin and 30 to 70 parts by weight of magnesium hydroxide having an average particle size of 0,1 to 10 µm. Best Mode for Carrying Out the Invention (Synthetic resin) The synthetic resin to be used in the present invention may be any one as far as it is thermoplastic, and examples thereof include crystalline polyolefins such as polyethylene, ethylene-vinyl acetate copolymer (abbreviated to "EVA"), ethylene-ethyl acrylate copolymer (abbreviated to "EEA"), ethylene-methyl methacrylate copolymer (abbreviated to "EMMA") and polypropylene (abbreviated to "PP"), polystyrene, polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer (abbreviated to "ABS"), nylon-6 and nylon-6,6. It is preferred from the viewpoint of the strength of the resulting composition that the resin have a melt index of 0.2 to 10.0. (Inorganic flame retardant) The inorganic flame retardant to be used in the present invention is magnesium hydroxide having a particle size of 0.1 to 10µm. According to the present invention, such a flame resistant filler may be added in an amount of 30 to 70% by weight based on the composition to thereby impart flame resistant effect to the resin. (Synthetic silicate) The amorphous synthetic silicate to be used in the present invention may be any one containing 40 to 70% by weight of SiO₂ as a major component and 10 to 45% by weight of MgO and CaO as secondary component Particularly, a synthetic silicate containing 50 to 60% by weight of SiO₂ and 12 to 30% by weight of MgO and CaO and having an ignition loss of 10 to 30% by weight is preferred. (Other additives) Although the composition according to the present invention essentially comprises a thermoplastic synthetic resin, an inorganic flame retardant as described above and a synthetic silicate, it may contain an antioxidant or lubricant for the purpose of enhancing the stability of the composition at processing, or a titanate or silane coupling agent for the purpose of enhancing the adhesion of the filler to the matrix in an arbitrary amount in addition to the above essential components without affecting the effect of the present invention. Further, the composition of the present invention may also contain an organic or inorganic pigment such as carbon black, azotype pigment, cyanine blue, cyanine green, iron oxide red or titanium oxide for the purpose of coloring. (Function of the Invention) The amorphous synthetic silicate is added to a halogen-free flame resisting synthetic resin composition containing an inorganic flame retardant as described above, thereby imparting a special flame resistant effect to the composition due to the flame resistant properties of the silicate itself and the steric flame resistant network formed in the composition. Thus substantially utilizing the generation of water by the decomposition of the inorganic flame retardant and the endothermic effect thereby. (Preparation of the composition of the present invention) The halogen-free flame resisting synthetic resin composition according to the present invention may be prepared by using a master batch comprising a thermoplastic synthetic resin, an inorganic, retardant as described above, synthetic calcium silicate and other additives or by mixing these components each in such an amount as to give its end-use concentration and kneading the obtained mixture by an ordinary means such as single-screw type extruder, twin-screw type extruder, roll mill or Banbury mixer. Further, the synthetic silicate may be preliminarily added as such to the other components to obtain the composition of the present invention. Alternatively, a master batch comprising the synthetic silicate and a synthetic resin may be added to a composition comprising a synthetic resin and an inorganic flame retardant as described above to thereby obtain the composition of the present invention. (Evaluation of the invention) The evaluation of the composition according to the present invention is carried out as follows: Namely, when a thermoplastic resin other than polystyrene or ABS was used, the resin, an inorganic flame retardant and other additives were mixed and the obtained mixture was kneaded in a 75 l. Banbury mixer and processed with a mixing roll to obtain a sheet having a thickness of 3mm. This sheet was reprocessed with a rectangular pelletizer to obtain a rectangular pellet having a length of each side of about 3mm. This rectangular pellet was repelletized with a 70 ⊘ extruder of a vent type at 150°C to obtain a cylindrical pellet. This cylindrical pellet was used as a sample. The cylindrical pellet was examined for oxygen index according to JIS K-7201. Further, the pellet was molded into a sheet having a thickness of 200µm with a T-die sheet molding machine to determine the combustion rate of the sheet with a flammability tester of FMVSS-302 (Federal Motor Vehicle Safety Standards, USA, Test No.302: flammability of interior materials). When polystyrene or ABS was used as the thermoplastic synthetic resin, the resulting composition was molded with an injection machine in an amount of 99,22 g (3,5 ounce) into a test bar according to the vertical flame test of UL-94 (Underwriter Laboratories, USA: flammability of plastic material) and the test bar was further molded into a test piece having a thickness of 3.175 mm. This test piece was used as a sample for the vertical flame test. (Examples and Comparative Examples) The present invention will be described in more detail by referring to the following Examples and Comparative Examples. The components constituting the composition of each Example or Comparative Example will be described, with the proviso that the amounts thereof used are shown in parts by weight and the comparative results of the compositions are shown in Tables 1 to 3. Example 1 low-density polyethylene (YUKARON HE-30 mfd. by Mitsubishi Petrochemical Co., Ltd., MI:0.3) 60.0 parts magnesium hydroxide (KISUMA 5B mfd. by Kyowa Chemicals Co., Ltd., average particle size:0.8µm) 40.0 parts synthetic silicate (SILMOS-T mfd. by Shiraishi Industrial Co., Ltd., SiO₂ content:60%) 3.0 parts total 103.0 parts Example 2 low-density polyethylene (the same as that used in Example 1) 55.0 parts magnesium hydroxide (the same as that used in Example 1) 45.0 parts synthetic silicate (the same as that used in Example 1) 3.0 parts total 103.0 parts Example 3 low-density polyethylene (the same as that used in Example 1) 50.0 parts magnesium hydroxide (the same as that used in Example 1) 50.0 parts synthetic silicate (the same as that used in Example 1) 1.5 parts total 101.5 parts Example 4 low-density polyethylene (the same as that used in Example 1) 50.0 parts magnesium hydroxide (the same as that used in Example 1) 50.0 parts synthetic silicate (the same as that used in Example 1) 3.0 parts total 103.0 parts Example 5 straight-chain low-density polyethylen (ULTZEX 3520F mfd. by Mitsui Petrochemical Industries, Ltd. MI:2.1) 50.0 parts magnesium hydroxide (KX-4S mfd. by Asahi Glass Co., Ltd., average particle size:0.6µm) 50.0 parts synthetic silicate (SILMOS-T mfd. by Shiraishi Industrial Co., Ltd., SiO₂ content:60% 3.0 parts total 103.0 parts Example 6 low-density polyethylene (YUKARON HZ-30, the same as that used in Example 1) 50.0 parts magnesium hydroxide (KISUMA 5B, the same as that used in Example 1) 50.0 parts synthetic silicate (SILMOS-T, the same as that used in Example 1) 7.0 parts total 107.0 parts Example 7 polystyrene (STYRON 470 mfd. by Asahi Chemical Industry Co., Ltd., MI:4.0) 50.0 parts magnesium hydroxide (KISUMA 5B, the same as that used in Example 1) 50.0 parts synthetic silicate (SILMOS-T, the same as that used in Example 1) 3.0 parts total 103.0 parts Example 8 ABS (DENKA OF mfd. by Denki Kagaku Kogyo K.K.) 50.0 parts magnesium hydroxide (KISUMA 5B, the same as that used in Example 1) 50.0 parts synthetic silicate (SILMOS-T, the same as that used in Example 1) 3.0 parts total 103.0 parts Comparative Example 1 low-density polyethylene (YUKARON HZ-30 mfd. by Mitsubishi Petrochemical Co., Ltd., MI:0.3) 60.0 parts magnesium hydroxide (KISUMA 5B mfd. by Kyowa Chemicals Co., Ltd., average particle size:0.8µm) 40.0 parts total 100.0 parts Comparative Example 2 low-density polyethylene (the same as that used in Comparative Example 1) 55.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 45.0 parts total 100.0 parts Comparative Example 3 low-density polyethylene (the same as that used in Comparative Example 1) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts total 100.0 parts Comparative Example 4 straight-chain low-density polyethylene (ULTZEX 2020L mfd. by Mitsui Petrochemical Industries, Ltd., MI:2.1) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts total 100.0 parts Comparative Example 5 high-density polyethylene (HIZEX 3300F mfd. by Mitsui Petrochemical Industries, Ltd., MI:0.9) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts total 100.0 parts Comparative Example 6 low-density polyethylene (the same as that used in Comparative Example 1) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts crystalline silica (TOKUSIL U mfd. by Tokuyama Soda Co., Ltd., SiO₂ content:95%) 3.0 parts total 103.0 parts Comparative Example 7 low-density polyethylene (the same as that used in Comparative Example 1) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts mica (Mica #300 mfd. by Repco, average particle size:2µm) 3.0 parts total 103.0 parts Comparative Example 8 low-density polyethylene (the same as that used in Comparative Example 1) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts calcium magnesium carbonate (Pigment white 18A mfd. by Shiraishi Industrial Co., Ltd., average particle size:1µm) 3.0 parts total 103.0 parts Comparative Example 9 low-density polyethylene (the same as that used in Comparative Example 1) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts carbon black (Mitsubishi MB#30 mfd. by Mitsubishi Chemical Industries, Ltd.) 3.0 parts total 103.0 parts Comparative Example 10 polystyrene (STYRON 470 mfd. by Asahi Chemical Industry Co., Ltd., MI:4.0) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts total 100.0 parts Comparative Example 11 ABS (DENKA OF mfd. by Denki Kagaku Kogyo K.K.) 50.0 parts magnesium hydroxide (the same as that used in Comparative Example 1) 50.0 parts total 100.0 parts Results of Examples using crystalline olefin No. Synthetic resin Flame resistant filler Additive Oxygen index combustion rate(mm/min) Ex. 1 60.0 LDPE 40.0 Mg(OH)₂ 3.0 SILMOS-T 24.0 68.0 Ex. 2 55.0 LDPE 45.0 Mg(OH)₂ 3.0 SILMOS-T 27.0 46.0 Ex. 3 50.0 LDPE 50.0 Mg(OH)₂ 1.5 SILMOS-T 29.2 o Ex. 4 50.0 LDPE 50.0 Mg(OH)₂ 3.0 SILMOS-T 30.4 o Ex. 5 50.0 LDPE 50.0 Mg(OH)₂ 3.0 SILMOS-T 30.2 o Ex. 6 50.0 LDPE 50.0 Mg(OH)₂ 7.0 SILMOS-T 30.0 o Results of Comparative Examples using crystalline olefin No. Synthetic resin Flame resistant filler Additive Oxygen index Combustion rate(mm/min) Comp. Ex. 1 60.0 LDPE 40.0 Mg(OH)₂ - 22.4 180.0 Comp. Ex. 2 55.0 LDPE 45.0 Mg(OH)₂ - 24.2 78.0 Comp. Ex. 3 50.0 LDPE 50.0 Mg(OH)₂ - 25.2 76.0 Comp. Ex. 4 50.0 LDPE 50.0 Mg(OH)₂ - 24.8 84.0 Comp. Ex. 5 50.0 HDPE 50.0 Mg(OH)₂ - 25.4 80.0 Comp. Ex. 6 50.0 LDPE 50.0 Mg(OH)₂ 3.0 crystalline silica 25.6 67.0 Comp. Ex. 7 50.0 LDPE 50.0 Mg(OH)₂ 3.0 mica 25.2 73.0 Comp. Ex. 8 50.0 LDPE 50.0 Mg(OH)₂ 3.0 carbonate 25.0 81.0 Comp. Ex. 9 50.0 LDPE 50.0 Mg(OH)₂ 3.0 carbon black 29.4 o (note) LDPE refers to low-density polyethylene, HDPE refers to high-density polyethylene and EVA refers to ethylene-vinyl acetate copolymer. The symbol "o" in the column of combustion rate means that the test sheet or test piece did not burn up to the mark, i.e., that the test sheet or test piece was self-fire extinguishable. Examples and Comparative Examples using styrenic resin No. Synthetic resin Flame resistant filler Additive Oxygen index UL 94 3.175 mm Ex.7 50.0 PS 50.0 Mg(OH)₂ 3.0 SILMOS-T 29.0 V-1 Ex.8 50.0 ABS 50.0 Mg(OH)₂ 3.0 SILMOS-T 29.4 V-1 Comp. Ex. 10 50.0 PS 50.0 Mg(OH)₂ - 26.0 HB Comp. Ex. 11 50.0 ABS 50.0 Mg(OH)₂ - 25.6 HB (note) PS refers to polystyrene. "V-1" means that the flame of the test piece guttered out within 30 seconds after contacting the test piece with flame. "HB" means that the test piece did not burn up to the mark in the horizontal flame test, though the test piece did not fit the vertical flame test. Industrial Applicability According to the present invention, a white semi-translucent synthetic resin composition which is highly flame resistant and does not generate any toxic substance can be obtained, though such a composition can not be obtained according to the prior art. The flame resisting synthetic resin composition of the present invention will be able to be used in a wide field requiring color discrimination, for example, floor materials of a nuclear power station.

Claims: A halogen-free flame resisting (fulfilling the criteria of the Test No. 302 of the Federal Motor Vehicle Safety Standards (U.S.A) and/or the criteria V-1 of the Underwriters Laboratories Test (UL 94)) synthetic resin composition obtained by adding 0,5 to 15 parts by weight of synthetic amorphous silicate containing 40 to 70 percent by weight of silicon dioxide and 10 to 45 percent by weight of magnesium oxide and calcium oxide to 100 parts by weight of a mixture comprising 70 to 30 parts by weight of at least one thermoplastic synthetic resin and 30 to 70 parts by weight of magnesium hydroxide having an average particle size of 0,1 to 10 µm.

Inventors: NODA MITSUO, SAITO NOBUO, NODA, MITSUO, SAITO, NOBUO
Applicants: DAINICHISEIKA COLOR CHEM, DAINICHISEIKA COLOR & CHEMICALS MFG. CO. LTD.
Application year: 1987
Main classification: C08L101
IPC codes: C08K3, C08L101