METHOD FOR PREPARING INORGANIC FOAMED MATERIALS

Abstract: A method for preparing an inorganic foamed material, characterized by kneading an inorganic filler with vinyl chloride resin, zinc oxide, a foaming agent and a plasticizer in order to obtain a compound, and themally foaming said com­ pound in a mold.

Description: The present invention relates to a method for preparing inorganic foamed materials. The foamed materials having closed cells are lightweight and excellent in heat insulating properties, therefore they are widely utilized as heat insulating materials for a variety of apparatuses and buildings. Of these materials, vinyl chloride resin foamed materials are particularly excellent in chemical resistance, mechanical strength and the like and are thus now extensively used. However, these vinyl chloride resin foamed materials, though being fire retardant, are not incombustible. Further, they are relatively weak in heat and have the fault that if put in a high-temperature atmosphere, they will contract their volumes, and the other faul that particularly if brought into contact with a flame, they will generate a poisonous gas. In view of such a fact, the foamed material has now been developed which can be prepared by mixing the inorganic powder with the vinyl chloride resin and foaming the resulting mixture. Such a development contemplates adding, to the features of the above-mentioned organic foamed material i.e. the lightweight and the heat insulating properties, the characteristic that if heated, the material will less contract its volume; the characteristic that when brought into contact with a flame, it will render the hydrogen chloride gas nontoxic; and the other characteristic that it is made more fire retardant. As such inorganic filler-containing foamed materials, there are known, for example, a material which is obtained by mixing the inorganic filler including water of crystallization in its molecules with the vinyl chloride resin and heating the resulting mixture to generate water vapor and to thereby cause a foaming; and a material which is obtained by kneading the vinyl chloride resin, the inorganic filler and a solvent in a sealed kneader while heating, adding thereto a solvent including liquefied butane, and carrying out a thermal foaming in a mold. In the former case of these foamed materials, however, when a great deal of inorganic filler is mixed therewith, its uniform dispersion and foaming cannot be accomplished, and a so-called venting phenomenon will occur, with the result that any satisfactory foamed material cannot be obtained. For this reason, it is impossible to blend 25% or more of the inorganic filler therewith. Further, in the latter case of the above-mentioned materials, 40% or more of the inorganic filler can be blended therewith subject to adding the liquefied butane or the like thereto in order to premit a kneading and to thereby cause them to gel, whereby the apparently satisfactory foamed material can be obtained. In this case, however, at least 25% of more of the vinyl chloride resin are required to obtain such a foamed material. Therefore, it is difficult to restrain the generation of the harmful gas at the time of exposing the material to a flame, and to render the material incombustible. Further, the thus obtained material is disadvantageously poor in wokability, shape stability and the like. The inventors of the present case have conducted researches with the intention of overcoming the above-mentioned problems and drawbacks, and as a result, they have succeeded in obtaining an excellent foamed material by employing the inorganic filler as a base material, adding thereto the vinyl chloride resin, the zinc oxide, a foaming agent and a plasticizer and kneading them, and carrying out a thermal foaming, even when it includes a great deal of the inorganic filler. The thus obtained foamed material is incombustible and lightweight, and has sufficient heat insulating properties, water resistance, sound absorbing qualities, mechanical strength and the like. In this foamed material, the coating film of the vinyl chloride resin of the components is uniformed and strengthened by the added zinc oxide, therefore a press molding by means of a re-heating treatment after curing as well as a molding on a curing step after a foaming can very easily and successfully be accomplished. As a result, the present invention has now succeeded. The gist of the present invention resides in a method for preparing an inorganic foamed material, characterized by kneading an inorganic filler with vinyl chloride resin, zinc oxide, a foaming agent and a plasticizer in order to obtain a compound, and thermally foaming said compound in a mold. Further, an effective blending proportion in the abovementioned method is 50 to 80 parts by weight of the inorganic filler, 5 to 15 parts by weight of the vinyl chloride resin, and 15 to 35 parts by weight of the zinc oxide. The inorganic fillers used in the method for preparing the foamed material according to the present invention are hydroxides, carbonates, sulfates, silicates and the like of calcium, magnesium, aluminum and the like, as well as their compounds, they each having water of crystallization. Examples of them include calcium hydroxide Ca(OH)2, magnesium hydroxide Mg(OH)2, aluminum hydroxide A1(OH)3, calcium carbonate CaCO3, magnesium carbonate MgCO3, calcium silicate (3CaO SiO2and Ca2 SiO3), magnesium silicate (Mg2SiO4, MgSiO3, Mg3Si401l H2O, and 2MgO.3Si02.nH2O) and aluminum silicate (Al2SiO3, A14(SiO4)3.5H2 O and 3A12O3.2Si02) as well as asbestos, talc, bentonite and clay. They can be employed alone or in the form of a mixture of two or more kinds thereof. A particle size of each filler is a significant factor to determine an oil absorption of the plasticizer, but depends preferably on each kind of material. For example, in the case of the talc Mg3H2(Si03)4), its particle size is preferably such that its 90% or more pass through a 150-mesh sieve, so as to improve its dispersion. In the case of the calcium carbonate, its particle size is preferably distributed within the range of 70 to 200 meshes so that it may be reacted with chlorine generated by the combustion of the vinyl chloride resin in order to render the chlorine non-toxic and so that the adhesion between the vinyl chloride resin and the plasticizer may be improved. Further, with regard to the aluminum hydroxide which serves to enhance incombustibility, its suitable particle size is 300 meshes or less. A blending proportion of the inorganic filler and the vinyl chloride resin can be 50 to 80 parts by weight of the former with respect to 5 to 15 parts by weight of the latter, preferably 70 parts by weight of the former with respect to 8 parts by weight of the latter. If the content of the vinyl chloride resin is less than indicated above, any sufficient foaming will scarcely be accomplished, and any satisfactory mechanical strength will not be obtained, so that the manufactured material will be brittle. In contrast, if the content of the vinyl chloride resin is more than indicated above, it will be difficult to obtain the foamed material having a good non-combustibility and heat resistance which are aimed by the present invention. Further, the vinyl chloride resin is preferably a so-called paste resin which has such a particle size that its particles all pass through a 325-mesh sieve and in which the particles are suitably distributed so as to keep up a close relation between the oil absorption of the plasticizer and the inorganic filler. Further, the zinc oxide may be employed in a proportion of 15 to 35 parts by weight, preferably 25 parts by weight or so based on 50 to 80 parts by weight of the inorganic filler and 5 to 15 parts by weight of the vinyl chloride resin. This zinc oxide functions as a catalyst and serves to permit a uniform and stable foaming behavior of the mixture in which the inorganic filler and small amounts of the vinyl chloride resin are blended, with the result that the mechanical strength of the foamed material, the working properties of a press molding under re-heating and the like can be improved to a remarkable degree It would be considered that this fact results from the mechanism that a dechlorination reaction is brought about in the molecules of the vinyl chloride resin by the zinc oxide to produce zinc chloride, and a combination of each two free radicals of the dechlorinated vinyl chloride resin or an addition of the free radicals to double bonds in other molecular chains causes a crosslinking reaction to occur. As a result, the strength and the viscosity of the vinyl chloride resin are improved. Moreover, even when extremely small amounts of the vinyl chloride resin are added to the inorganic filler, a sufficient foaming constitution can be obtained, and the foamed material can be prepared which has a great mechanical strenth and which can facilitate a press molding operation under re-heating. Of the above-mentioned fillers, hydroxides such as the magnesium hydroxide and the aluminum hydroxide as well as the compounds having water of crystallization are decomposed by virtue of the applied heat and are reacted with the chlorine generated by the combustion of the vinyl chloride resin in order to change into chlorides and water. In consequence, a combustion temperature affected by the vinyl chloride resin will be lowered and the incombustibility of the prepared material will thus be improved. The generated chlorine gas is converted into chlorides such as aluminum chloride and magnesium chloride by the reaction in order to be rendered nontoxic, and these chlorides are not decomposed any more by the combustion temperature. When the hydroxide or the compound including water of crystallization is included in the inorganic filler in amounts of 15 to 35 parts by weight based on its whole weight, the foamed material can be made incombustible. As the foaming agents, there can be employed DPT (dinitrosopentamethylenetetramine), AC (azodicarbonamide), AIB (azobisisobutyronitrile) and the like which are organic foaming agents; sodium bicarbonate, ammnonium chloride and the like which are inorganic foaming agents, and Freon and the like which are gaseous. As the plasticizers, there can be employed aromatic temporary plasticizers such as toluene and the like as well as incombustible plasticizers such as paraffin chlorldes. The aforementioned foaming agent can be properly used in a proportion of 10 to 16 parts by weight based on 100 parts by weight of the inorganic filler, the vinyl chloride resin and the zinc oxide, and the plasticizer can be used in a proportion of 50 parts by weight or so based on the same. Further, in the foamed material regarding the present invention, there may be included a thermal stabilizer, an ultraviolet absorber, an antioxidant, a fire retardant, a reinforcing filler, an incombustible dye and pigment, an antistatic agent, a fungicide and other suitably necessary additives, in addition to the above-mentioned essential components. The foamed material can be prepared in accordance with the present invention as follows: The inorganic material such as calcium carbonate, talc, asbestos or the like, the vinyl chloride resin and the foaming agent are placed in a mixer in the aforementioned proportion and are mixed with each other. Then, 50 parts by weight of the total weight of the placticizer are added to the resulting mixed powder, and a kneading operation is carried out by the use of a suitable kneader or the like at its low-speed rotation at ordinary temperature and at ordinary pressure. Further, the hydroxide such as aluminum hydroxide or the incombustibility improving filler which includes water of crystallization is added to the resulting compound in the aforementioned proportion, and a kneading operation is carried out again. To the compound is further added the remaining 50 parts by weight of the plasticizer in order to obtain the paste compound. Afterward, heat is applied to a mold including the compound therein at least up to a temperature at which the used foaming agent is decomposed or vaporized, and up to a temperature at which the vinyl chloride resin is caused to gel. As a result, the vinyl chloride resin is dissolved in the solvent (plasticizer), and the fine particles of the inorganic filler are throughout wrapped in the dissolved resin, whereby the resin adheres to the fine particles and connects them to each other adhesively. At this time, the vinyl chloride resin reacts with the zinc oxide to heighten the viscosity and the strength of its coating films embracing the fine particles. Therefore, even though the amount of the vinyl chloride resin is small, the fine particles of the inorganic filler are completely wrapped in the resin, and the fine particles adhere to each other and take a gel state. After the foaming agent has been decomposed or vaporized under this gelation, the heating operation is stopped, and cooling is then carried out while the mold is kept closed. After a while, the mold is opened to release the presssure therein. Immediately, the contents in the mold thereby bring about a primary foaming, so that its volume is increased two to five times. Then, the primarily foamed material is heated in a warm air circulating device such as an oven in order to bring about a secondary foaming. As a result, the volume of the material is finally increased 4 to 30 times as much as its original, thereby obtaining the desired foamed product. According to the present invention, even if the amount of the vinyl chloride resin is extremely small, the added zinc oxide permits the viscosity of the coating film to increase and the film itself to strengthen. Generally, when the content of the inorganic filler is approximately 909, a thermal plasticity will be lost. With regard to the foamed material prepared in accordance with the present invention, however, its complete thermal plasticity can still remain. Thus, the uncured foamed material which is the aimed product can very easily be sliced, if necessary, in some pieces each having a desired size. Further, the soft uncured foamed material can easily be deformed in accordance with a shape of a selected specific mold only by putting it on the mold and can be then cured. Accordingly, the molding of the material into, e.g., a wavelike shape can easily be accomplished. Moreover, the foamed material which has once been molded into a shape such as a plate can easily be plasticized due to the improvement properties of the vinyl chloride resin by reheating it afterward. Therefore, the foamed material has the highly characteristic property that a heating press molding and a post-forming can be carried out. Since composed of the inorganic filler as the main component and the closed cells, the foamed material obtained through the present invention is lightweight, and has heat insulating properties, sound absorbing qualities and water resistance, and is excellent in mechanical strength and dimensional stability. Additionally, the foamed material is particularly incombustible, therefore it can widely be utilized as a building material, an interior material for a car, a constitutional material for a device, an electrical insulating material and an electromagnet shielding material as well as a heat insulating material, without any additional treatment, or after coloring has been accomplished by previously adding thereto an incombustible pigment or dyestuff, or by applying it to the outer surface of the foamed material. Further, even when exposed to a high temperature, for example, at a fire, the generated hydrogen chloride gas will be extremely small, therefore there is little danger of the generation of the poisonous gas. Furthermore, in the manufacturing method according to the present invention, if the temporary plasticizer is used, the hard foamed material can be obtained; if the plasticizer, which still remains even after the foaming, is utilized, the soft foamed material can be obtained. Now, the present invention will be described in reference to an example as follows: EMI12.1 <tb> Calcium <SEP> carbonate <SEP> 24 <SEP> parts <SEP> by <SEP> weigh <tb> Talc <SEP> 15 <tb> Aluminum <SEP> hydroxide <SEP> 20 <SEP> l <SEP> <SEP> 100 <tb> <SEP> parts <tb> Asbestos <SEP> 3 <SEP> " <SEP> <SEP> by <tb> <SEP> weight <tb> Viny <SEP> chloride <SEP> resin <SEP> 12 <tb> Zinc <SEP> oxide <SEP> 26 <tb> D? (dinitrosopenta methylenetetramine) 10 Sodium bicarbonate 3 1I Toluene 40 A blend of the aforementioned composition was kneaded at ordinary temperature for about 50 minutes to prepare a paste compound. The prepared compound was fed to a transfer mold, and the mold was airtightly closed so as not to allow a gas to leak. Then, heating was stepwise carried out toward a foaming temperature of the foaming agent and a dissolving temperature of the vinyl chloride resin up to about 170 C. Afterward, the mold was cooled slowly up to room temperature and was then opened, whereby the foamed molded material brought about a primary foaming, thereby increasing Its volume about twofold. This foamed material was then sliced in pieces each having a thickness of 50 mm, and they were put in an oven and were allowed to stand for 8 hours for the sake of a free foaming. With regard to the thus obtained secondary foamed material, a foam swelling ratio was about 8 times as much as its original, a spesific gravity was 0.1778, and a water absorption was 2.34 g/100 cm (the size of each sample was 70 x 70 x 10 mm at 220C and RH of 50%). Further, a 40 x 40 x 50-mm sample of the secondary foamed article, i.e. the foamed material obtained by the present invention was heated in the oven at a temperature of 7500C for 20 minutes in accordance with a JIS fire retardant testing method (JISA 1321). As a result, the combustion temperature of the sample fell once to 6600C after about 15 seconds, reached a maximum level of 7650C after 4 minutes, and got to a constant level of 7500C after 10 minutes. The reason why the combustion temperature fell once at the early stage is that the hydroxyl groups of the aluminum hydroxide in the inorganic filler were thermally decomposed and absorbed the combustion heat of the vinyl chloride resin. By virtue of this phenomenon, a temperature rise of the sample was restrained on the whole, and a standard value regulated was satisfied. Furthermore, when a 220 x 220 x 15-mm example was heated for 10 minutes, a temperature curve of its exhaust gas showed, for 3 minutes at an early stage, 20 to 400C lower values than on a standard temperature curve, and after that, it indicated values substantially comparable to the standard curve. Moreover, with regard to smoke amounts, according to results of a prescribed measurement, its smoke coefficient per unit area was 12 CA at maximum. Other dangerous factors at a fire, e.g., deformation, dissolution and cracks did not occur, any harmful gas to human beings was not generated, and after the heating was over, the remaining flame was also extinguished.

Claims: What is claimed is: (1) A method for preparing an inorganic foamed material, characterized by kneading an inorganic filler with vinyl chloride resin, zinc oxide, a foaming agent and a plasticizer in order to obtain a compound, and thermally foaming said compound in a mold. (2) A method for preparing an inorganic foamed material according to Claim 1 wherein 50 to 80 parts by weight of said inorganic filler, 5 to 15 parts by weight of said vinyl chloride resin and 15 to 35 parts by weight of said zinc oxide are mixed. (3) A method for preparing an inorganic foamed material according to Claim 1 wherein said inorganic filler is at least one selected from the group consisting of hydroxides, carbonates, sulfates and silicates of calcium, magnesium and aluminum, their compounds each having water of crystallization, and asbestos, talc, bentonite and clay. (4) A method for preparing a foamed material according to Claim 1 wherein said inorganic filler includes a hydroxide such as magnesium hydroxide or aluminum hydroxide, or its compound having water of crystallization.

Inventors: ASAMI, TSUTOMU, KASAHARA, KANESUKE
Applicants: FUJI KASEI KOGYO KK
Application year: 1984
Main classification: C04B26
IPC codes: C04B26, C04B38