Low-smoke noise insulating material

Abstract: Fillers comprising a composition in which 50 to 90 wt.% or iron oxides and 10 to 30 wt.% of silica are contained, at least 50 wt.% of the iron oxides being present in the form of iron oxide silicate, and the content of alkali metal oxides or alkaline earth metal oxides is 10 wt.% or less in total, are suitable as fillers for the fabrication of noise insulating materials. Noise insulating materials obtained by using said fillers are excellent in flexibility and processibility and moreover are large in surface density, thus exhibiting excellent noise insulating ability.

Description: This invention relates to low-smoke noise insulating materials formed by blending fillers having chemical compositions suitable for those for the fabrication of noise insulating materials with synthetic resin binders. Description of the Prior Art: There have been known to date a variety of noise insulating materials for the prevention of external noise from entering an enclosure and of sound from emitting from an enclosure and again of sound absorbing materials for weakening the reflection of sound off surfaces, e.g. bounding an enclosure. These noise insulating materials are processed into sheets and applied or adhered to the floors or walls of automobiles, rail road cars and buildings or are widely used for the fabrication of composite materials by sticking them together with steel plates, nonwoven fabrics, concrete panels or wood plates. In order to enhance noise insulating effects of these composite materials, it is desirable to incorporate a filler of high density in as large an amount as possible in a unit weight of a resin. A noise insulating material with high noise insulating effects requires blending of a greater proportion of a filler having a large specific weight with a binding material of superb processibility, according to the following mass law of sound insulation: TL = a x log mf + b wherein TL is a noise transmission loss (dB), m is a surface density (kg/m²), f is a frequency (Hz) and "a" and "b" are constants. However, fillers, when used for the fabrication of noise insulating materials, can not be incorporated in binders in large amounts and also can not impart flexibility to the noise insulating materials, if they fail to obtain proper combination with binders. In addition, such problems are raised that upon molding and processing the blended materials what is called a plate-out phenomenon occurs seriously and the surface finish of the products is thereby degraded. In this connection, a sound proof material has recently been proposed, in which a vinyl chloride resin containing a plasticizer is combined and blended with iron oxides by-produced in the steel making process (Japanese Patent Laid-Open No. 34064/1982). In this disclosure, it is emphasized that the iron oxides are excellent in adhesive property with vinyl chloride resins. The oxide-base filler has the following composition and hence contains a lot of CaO. However, the sound proof material is poorly released from the surface of a production roll upon its fabrication and also takes a prolonged period of time for gelation so that the mechanical properties of the resulting sheets are not deemed satisfactory. Currently known noise insulating materials employ, as a binder, natural rubber, synthetic rubber, rubber adhesives, polyethylene, polypropylene, polyvinyl chloride, synthetic resin adhesives and asphalt and, as a filler, lead powder, lead compounds, iron powder, iron oxide slag and barytes (barium sulfate), all of which have large specific gravities. Lead powder and lead compounds are favorable in view of their large specific gravities, but they are expensive and, upon combustion, are liable to evolve toxic dust gases which contain lead oxides. Iron powder is disadvantageous in that it produces rust and thus deteriorates the appearance of the product significantly. Iron oxide slag is inexpensive, but it contains calcium oxide in considerable amounts so that its specific gravity is low as compared with those of the foregoings. Further, iron oxide slag involves problems in that when kneaded into a thermoplastic resin, it adheres to the surface of a production roll seriously and thus is deficient in processibility. There have been known to date many noise insulating materials which are fabricated by mixing inorganic powder in a resin and then molding the resultant resin composition. For example, Japanese Patent Publication No. 25375/1983 discloses a resin composition obtained by mixing powder of iron or an iron compound in a mixture of a vinyl chloride resin and a methacrylic resin. Japanese Patent Laid-Open No. 62361/1977 discloses incorporating a filler, the specific gravity of which is 4 or higher, in the above-described combination of the resins and teaches that the resultant composition has excellent mechanical strength and moldability. In addition, Japanese Patent Publication No. 21052/1980 discloses a noise insulating material, which makes combined use of an ethylene-vinyl acetate copolymer, especially, an ethylene-vinyl acetate copolymer containing 10 to 28 wt.% of vinyl acetate and an ethylene-propylene base synthetic rubber, and also teaches its good moldability. As noise insulating materials imparted with flame retardancy in addition to noise insulating property and flexibility, reference may be had to Japanese Patent Publication No. 32951/1982 and Japanese Patent Laid-Open Nos. 127254/1985 and 127341/1985 which disclose noise insulating materials composed of a PVC-base resin in combination with Sb₂O₃ tricresyl phosphate and chlorinated paraffin respectively. Recently, we have also proposed a filler composed of iron oxide and silicon oxide as essential components and also containing basic components such as CaO and MgO in amounts limited below their respective prescribed levels, as well as a noise insulating material obtained by kneading the filler with a vinyl chloride resin and molding the resultant resin composition (Japanese Patent Laid-Open Nos. 56732/1986 and 33887/1987). Further, for noise insulating materials to be used as building materials for interior finish of buildings and hotels, it is important for them to have sufficient fire protective abilities, or in other words, to be fire retardant and not to evolve toxic gases and black smoke in any quantity when a fire takes place. Summary of the Invention: An object of the present invention is to provide a noise insulating material having good flexibility and fire retarding properties which comprises a filler which can be intimately blended with a specified synthetic resin used as a binder, is well-processible, has a high specific gravity, and thus is suitable for the fabrication of noise insulating materials, excellent in flexibility and mechanical strength, the binder being composed of a specified synthetic resin. Some ways of carrying out the present invention in all its aspects will now be described in detail by way of example. According to the present invention there is provided a low-smoke noise insulating material formed by blending 400 to 1,500 parts by weight of a filler in which 50 to 90 wt.% of iron oxides and 10 to 30 wt.% of silica are contained, 50 wt.% or more of the iron oxides being contributed by iron oxide silicates (calculated as iron oxides), and the content of alkali metal oxides or alkaline earth metal oxides in 10 wt.% or less in total, to 100 parts by weight of an ethylene-vinyl acetate copolymer. Detailed Description: A filler for use in fabricating noise insulating materials in the practice of the present invention may be characterized by containing the following chemical composition. The filler comprises a chemical composition in which 50 to 90 wt.% of iron oxides and 10 to 30 wt.% of silica are contained as principal constituents, all or a greater part of the iron oxides and the silica being present in the form of iron oxide silicate (2FeO·SiO₂: iron (II) ortho-silicate), and the content of alkali metal oxides or alkaline earth metal oxides should be 10 wt.% or less in total. No particular limitations are imposed on the composition of the remaining portion. The iron oxides in the above-described composition may include various forms of iron oxide such as FeO, Fe₂O₃, Fe₃O₄, FeO·Fe₂O₃, nFeO·SiO₂ and nFeO·Fe₂O₃·SiO₂ (n is an integer of 1, 2 or 3). Of these forms of iron oxide, that in the form of iron oxide silicate is excellent particularly in adhesive property with resins used as a binder. Further, iron oxides present in the form of nFeO·SiO₂ and nFeO·Fe₂O₃·SiO₂ are favorable in uniform dispersibility of the granules into the above-described resins as compared with those in which iron oxide granules and SiO₂ granules are simply mixed by mechanical means, and thus are especially adequate as the filler. Therefore, for the fillers being described, it is important that a greater part of the constituents, i.e., iron oxides and silica, are present in the form of iron oxide silicate. It is hence favorable that 50 wt.% or more, preferably 70 wt.% or more, or more preferably 80 wt.% or more of the iron oxides are present in the form of nFeO·SiO₂ and nFeO·Fe₂O₃·SiO₂ in which n represents an integer of 1, 2 or 3. If the content of the iron oxides in the whole filler is 50 wt.% or less, the noise insulating material obtained by using said filler fails to exhibit sufficient noise insulating effects. Since the silica itself in the filler has a low bulk density of about 0.3 to 1, it does not serve to improve the surface density of a noise insulating material in which the filler is used. However, the presence of silica can increase the amount of iron oxides to be filled markedly and shows an effect of improving the surface smoothness of the noise insulating materials. Accordingly, in order to increase the amount of iron oxides incorporated in a noise insulating material, it is preferable to allow silica to be present in the filler in an amount of at least 10 wt.%. However, as described above, since silica itself is low in density, its presence in the filler in large amounts unfavourably results in the suppression of the amount of the filler to be incorporated at high densities. Preferably, the amount of silica in the filler should therefore be at most 30 wt.%. Further, it is preferable for the filler to contain alkali metal oxides or alkaline earth metal oxides such as Na₂O, MgO and CaO in a smaller amount. it is therefore preferably to restict their total amounts to 10 wt.% or less, preferably to 7 Wt.% or less, or particularly to 5 wt.% or less. Incidentally, in the case of a noise insulating material employing a filler in which these oxides are present, they are responsible for the plateout phenomenon occurred on the metal surface of a roll used for the fabrication of the material and also for the delay in gelation. These phenomena become serious as the amounts of the oxides are increased. As those satisfying the above-described specific chemical composition of the filler may be mentioned what is called iron concentrate slag which is obtained by: adding silicon dioxide and oxygen to a matte obtained from an autogenous-blast furnace in a copper refining process for its silicification and oxidation in a converter to form a slag; subjecting the slag to electromagnetic separation; subjecting the resulting slag to ore floatation to separate copper concentrates from iron concentrate slag; and subjecting the latter to dehydration. Specifically, the slag contains about 50 to 80 wt.% of 2FeO·SiO₂ (40 to 50 wt.% as FeO and 15 to 30 wt.% as SiO₂), 10 to 30 wt.% of Fe₃O₄, 5 wt.% of Fe₂O₃ and 5 wt.% or less of MnO as principal components, but contains practically no CaO. Further, the slag is composed of crushed particles which have undergone ore floatation and have particle sizes of about 30 µ. It has a bulk density of 3 to 4 and a true specific gravity of 4.5 to 5.5 so that it is suitable for use as a filler in accordance with the present invention. In order to use the iron concentrate slag as the filler, it should be borne in mind that the slag be dried to reduce its water content to 2 wt.% or less, preferably to 1 wt.% or less, or particularly to 0.5 wt.% or less. It is because the slag containing a larger amount of water is responsible for the foaming occurring in the course of fabricating a composite material when it is used as a filler of the material. A noise insulating material according to the present invention obtained by utilizing the characteristics of a filler will be described hereunder. A noise insulating material according to the present invention is obtained by kneading the filler with a specified synthetic resin as a binder and forming and processing the resulting mixture. The filler to be used for this purpose is composed of granules with sizes of e.g. 200-mesh through or preferably 250-mesh through and is mixed with a binder in a blending proportion of 400 to 2,000, preferably 400 to 1,500 parts by weight of the filler to 100 parts by weight of the binder. The mixture is heated to a temperature of about 100 to 150°C and then kneaded intimately by means of a Banbury mixer, mixing roll or similar mixers. The binder used for fabricating the noise insulating materials of the invention is an ethylene-vinyl acetate resin. Exemplary blending proportions of the filler and the binder in a noise insulation material according to the present invention are illustrated below. In the present invention, however, an organic flame retardant containing red phosphorus, antimony oxide or a halogen may be blended to the mixture of filler and binder for the purpose of improving the flexibility, fire retardancy and low-smoke property of the resulting noise insulating material. A blending example in a noise insulating material is as follows: The noise insulating material according to the present invention has a smoke-preventive ability and has 400 to 1,500 parts by weight of a filler blended with 100 parts by weight of an ethylene-vinyl acetate copolymer as the binder. Further, to impart fire retardant property as well as smoke-preventive ability to a noise insulating material, the following blending proportion should be chosen. Namely, 400 to 1,500 parts by weight of a filler and 5 to 50 parts by weight of a red phosphorus powder are blended to 100 parts by weight of an ethylene-vinyl acetate copolymer. Alternatively, 400 to 1,500 parts by weight of a filler, 20 to 100 parts by weight of an organic flame retardant containing a halogen and 5 to 50 parts by weight of antimony trioxide are blended to 100 parts by weight of an ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer used as a binder in each of the above blending examples has superb affinity for the aforesaid filler of the present invention. Consequently, it is possible to fill the filler in the copolymer upto 1,500 parts by weight per 100 parts by weight of the copolymer. This also makes it possible to increase the specific gravity of the resulting insulating material to 3.4 kg/m² per millimeter of its thickness while permitting the material to retain its flexibility and mechanical strength. Further, use of the aforesaid resin causes no evolution of toxic gases upon a fire and also permits a significant reduction in the emission of black smoke. The ethylene-vinyl acetate copolymer used herein contains vinyl acetate in an amount in the range of 15 to 70 wt.% or preferably 30 to 60 wt.%, more preferably 35 to 60 wt.%. If the vinyl acetate content is below 15 wt.%, it becomes impossible to incorporate the filler to a high degree so that the resulting noise insulating material is lowered in specific gravity and becomes deficient in noise insulating ability. On the other hand, any contents greater than 70 wt.% will unfavorably degrade the mechanical strength of the resulting noise insulating material. The amount of the filler to be blended is in the range of 400 to 1,500 parts by weight or preferably 600 to 1,200 parts by weight based on 100 parts by weight of the ethylene-vinyl acetate copolymer. If the amount of the filler to be blended is less than 400 parts by weight, the resulting noise insulating material will not have increased specific gravity and will be deficient in noise insulating ability. On the contrary, any amounts greater than 1,500 parts by weight will unfavorably lead to poor processibility in kneading and cause the resulting noise insulating material to lack flexibility and reduce its mechanical strength. The amount to be blended of the red phosphorus powder, which is used to impart fire retarding property to the noise insulating material, is in the range of 5 to 50 parts by weight or preferably 10 to 30 parts by weight relative to 100 parts by weight of the ethylene-vinyl acetate copolymer. If the amount of the red phosphorus powder to be blended is below 5 parts by weight, the resultant noise insulating material will not have sufficient fire retarding property. Conversely, any amounts in excess of 50 parts by weight will not improve the fire retarding property any further due to saturation and renders the noise insulating material uneconomical in view of its cost. Further, the processibility and mechanical strength of the material will unfavorably be degraded. The halogen-containing organic flame retardant useful in the practice of the present invention includes chlorinated paraffin, decabromodiphenyl ether and tetrabromobisphenol A. They may be used singly or in combination. The amount of the halogen-containing flame retardant to be blended is in the range of 20 to 100 parts by weight or preferably 30 to 60 parts by weight based on 100 parts by weight of the ethylene-vinyl acetate copolymer. If its amount to be blended is less than 20 parts by weight, the resulting noise insulating material will not be imparted with sufficient fire resistative ability. On the other hand, when the amount exceeds 100 parts by weight, the resulting noise insulating material will not be improved any further in fire retarding property due to saturation and is uneconomical from the stand point of cost. Further, it will unfavorably be lowered in mechanical strength and processability. No particular limitations are imposed on the antimony trioxide used, so far as it is of a water-insoluble white powder and prepared in accordance with the processes known in the art. The product will not be affected by the granular state of the trioxide nor by its shape. The amount of the antimony trioxide to be blended is in the range of 5 to 50 parts by weight or preferably 10 to 30 parts by weight per 100 parts by weight of the ethylene-vinyl acetate resin. If the amount of the antimony trioxide to be blended is less than 5 parts by weight, the resulting noise insulating material will be insufficient in fire retarding property. On the contrary, any amounts in excess of 50 parts by weight will not improve its fire retarding property any further due to saturation and render the resulting noise insulating material uneconomical in view of cost. The fillers according to the present invention described in detail are superior in affinity for the resin used as a binder. Even if incorporated in a given amount of a resin at its high blending proportion, one can obtain a noise insulating material provided with excellent flexibility and mechanical strength. Further, the noise insulating material with the above-described fillers contained has such a high specific gravity that its weight per 1 mm of thickness times 1 m² of area amounts to 3.4 kg and moreover is excellent in fire retarding property. The present invention will now be illustrated still more specifically with reference to the following examples. Example 1 and Comparative Example 1: Filler F-1 shown in Table 1 and each of the ethylene-vinyl acetate copolymers with the blending proportions give in Table 2 were kneaded with each other in a 6-inch ovenroll at a temperature of 150 - 160°C for 20 minutes, thereby preparing each sheet with a width of 300 mm and a thickness of about 1 mm. The following properties of each of the sheets obtained were examined and the results are also shown in Table 2. Specific gravity: represented by kg/mm (thickness) x m² (area). Since a noise insulating material is largely dependent on the density of the material, the noise insulating property was evaluated by the specific gravity of the material. The larger the specific gravity, the greater is the noise insulating property. Flexibility: A test piece with a size of 30 mm x 70 mm x 1 mm was stamped out from each of the sheets prepared. The test piece was bent by 180 degrees to examine its flexibility. ○ mark: those neither cracked nor broken ▵ mark: those cracked but not broken X mark: those cracked and broken Processibility: While each of the blended compositions in Example and Comparative Example was being kneaded in a 6-inch ovenroll at 150 to 160°C for 20 minutes, its adhering nature round the roll or stickiness thereto was examined and evaluated. ○ mark: well-processible ▵ mark: somewhat poorly-processible X mark: poorly-processible Smoke concentration: The prepared sheet was heat-pressed for 5 minutes at 160°C and 180 kg/cm² to form a sheet with a thickness of 0.5 mm. Using this sheet, the smoke concentration was determined in accordance with the non-flaming method, a testing method for smoke concentration described in ASTM-E662 (1979). As can be seen in Table 2, it is obvious that Samples Nos. 20, 21 and 22, which were fabricated by using ethylene-vinyl acetate copolymers with a vinyl acetate content of 45 wt.% or 60 wt.% in accordance with the present invention, are superior in flexibility and processibility in spite of their high specific gravities. On the other hand, Sample No. 26 which was fabricated by using a vinyl chloride resin has considerable flexibility and processibility, but produces smoke at high concentrations. Example 2 and Comparative Example 2: Noise insulating sheets comprising the compositions of Sample Nos. 20, 21 and 22 given in the above Table 2 added with SbO₃ and decabromodiphenyl ether were fabricated. The fire resistative property of the resulting sheets was measured by the method described below. The results are shown in Table 3. Fire retarding property: A test piece with a size of 15 mm x 70 mm x 1 mm was stamped out from the sheet prepared. The test piece was maintained horizontal and a Bunsen burner was ignited in such a way that the tip (top end) of the flame with a length of 15 mm reached the under surface of the test piece. Upon removal of the flame after 15 seconds, it was examined whether or not the test piece burned further. As seen in Table 3, it is obvious that the addition of SbO₃ and decabromodiphenyl ether enables the resulting sheets to improve their fire retarding ability significantly. In other words, taking these results jointly with those of Table 2 into consideration, it can be understood that noise insulating materials which have high specific gravities, possess flexibility and are excellent in smoke-preventive property and fire resistative ability can be fabricated with good processibility by using ethylene-vinyl acetate resins as a binder, filling the fillers of the present invention into the resins, and blending specific amounts of SbO₃ and halogen-containing organic flame retardants to the resulting compositions.

Claims: A low-smoke noise insulating material formed by blending 400 to 1,500 parts by weight of a filler in which 50 to 90 wt.% of iron oxides and 10 to 30 wt.% of silica are contained, 50 wt.% or more of the iron oxides being contributed by iron oxide silicates (calculated as iron oxides), and the content of alkali metal oxides or alkaline earth metal oxides is 10 wt.% or less in total, to 100 parts by weight of an ethylene-vinyl acetate copolymer. A low-smoke noise insulating material as claimed in Claim 1, which is formed by further blending 5 to 50 parts by weight of red phosphorus based on 100 parts by weight of the ethylene-vinyl acetate copolymer to add fire-retardant property. A low-smoke noise insulating material as claimed in Claim 1, which is formed by further blending 20 to 100 parts by weight of a halogen-containing organic flame retardant and 5 to 50 parts by weight of antimony trioxide based on 100 parts by weight of the ethylene-vinyl acetate copolymer to add fire-retardant property. The low-smoke noise insulating material as claimed in any one of Claims 1 to 3 wherein the ethylene-vinyl acetate copolymer contains 15 to 70 parts by weight of vinyl acetate. The low-smoke noise insulating material as claimed in any one of Claims 1 to 3 wherein the ethylene-vinyl acetate copolymer contains 35 to 60 parts by weight of vinyl acetate. The low-smoke noise insulating material as claimed in Claim 3 wherein the halogen-containing organic flame retardant is one or more halogen-containing organic flame retardants selected from the group consisting of chlorinated paraffin, decabromodiphenyl ether and tetrabromobisphenol A.

Inventors: FUJIO NOBUHIRO, NEGISI ISAO, NISHIZAKI TOSHIO, TSURUMARU HIDEKAZU, YAMASAKI TAKESHI, FUJIO, NOBUHIRO, NEGISI, ISAO, NISHIZAKI, TOSHIO, TSURUMARU, HIDEKAZU, YAMASAKI, TAKESHI
Applicants: NIPPON MINING CO, NIPPON MINING & METALS COMPANY, LIMITED
Application year: 1987
Main classification: C08K3
IPC codes: C08K3