Polyvinyl chloride resin composition for powder molding

Abstract: A powder molding composition containing dry-blended polyvinyl chloride resin plasticizer and stabilizer, which is characterized in that there are blended therein 0.05 to 5 parts by weight of carboxylic acid barium salt having a melting point not lower than 250 °C and 0.01 to 5 parts by weight of zinc salt of fatty acid containing 10 or more carbon atoms, per 100 parts by weight said polyvinyl chloride resin. The composition of the invention is of excellent releasability and resistance to mold staining.

Description: This invention relates to a polyvinyl chloride powder molding composition for producing molded articles suited for use in the field of automobiles or the like. There is an increasing demand for interior covering materials of automobiles, such as crash pads, armrests, headrests, console boxes, meter hoods and door trims, which are light in weight and of excellent soft feel and, at the same time, provided with sophisticated embossed or stitched patterns. In recent years, much attention has been focused on powder molding as a method for producing such covering materials. Powder molding methods include fluidized bed coating, electrostatic coating, powder flame spray coating, powder rotational molding, powder slush molding and other techniques. Of these techniques, powder rotational molding and powder slush molding can be most suited for the production of covering materials for automobile interior parts. A powder molding composition can be prepared by dry-blending a polyvinyl chloride resin with plasticizers, stabilizers, pigments, etc., using a blender or high-speed rotating mixer equipped with a heating jacket. In powder molding, a powder composition is fusion-adhered to a mold maintained at a high temperature, and hence the surface of the mold is gradually stained with accumulation of additives or the like as the number of molding shots increases. When the staining of the mold proceeds, the hollows of embossed patterns formed on the interior surface of the mold become shallow because of the accumulation of stains, and covering materials produced using the mold come to assume an undesirable gloss. In general, covering materials of automobiles are designed to have the same color tone as that of accessories and other parts. However, if covering materials so molded assume such an undesirable gloss, their color tone may appear to be different from that of accessories and other parts. This phenomenon significantly impairs the color harmony and quality of automobiles. Where the covering materials are used for crush pads, meter covers or the like, such a gloss can also be detrimental to the safety of drivers of the automobile and of automobiles running on the opposite lane, due to reflection of light. In order to remove the stains, molds are cleaned with alkaline solutions, acid solutions, halogenated hydrocarbon solvents, or the like. Where such chemical cleaning is insufficient in its cleaning effects, molds are cleaned by means of mechanical brushing, whereby alumina powders or glass beads are injected together with air to remove the stains. However, the above cleaning methods are disadvantageous with regard to productivity and cost since the molding operation must be stopped temporarily and a spare mold may be prepared. Where chemical agents are used, special care must be taken over the working environment and waste disposal. In addition, if mechanical brushing is applied repeatedly, the hollows of embossed patters on the interior surface of the mold become shallow, and the life of the mold is shortened. It is therefore highly important from industrial and economical points of view to develop a powder molding composition which is resistant to mold staining and hence does not stain molds in the course of molding. However, a powder molding composition which is resistant to mold staining tends to give poor releasability between the mold and the molded article. Because of this, articles produced from such a composition suffer from deformation and breakage. It is known that the releasability can be improved by applying a release agent, such as silicone compounds or fluorine-containing compounds, to the mold prior to the molding operation. However, this technique is poor in productivity and suffers from the problem that molded products become undesirably glossy due to transfer of the release agent to molded articles. In Japanese Patent Kokai No. 215,845/89 is disclosed a powder molding resin composition having improved properties with regard to resistance to mold staining and releasability. The powder molding composition includes zinc or barium salt of acids selected from aromatic organic acids, naphthenic acids and fatty acids containing 5 to 8 carbon atoms in the alkyl group thereof. However, when the composition is molded in a mold kept at a high temperature, the additive tends to plate-out onto the surface of the mold together with plasticizers since it is highly compatible with plasticizers. Because of this, when molding is carried out repeatedly over a long period, the additive accumulates on the surface of the mold and, as a result, molded articles assume an undesirable gloss. In addition, the composition additionally contains a polyacrylic release agent which tends to accumulate on the mold, thereby forming thermally modified hard stains which are difficult to remove by washing. EP-A-273766 discloses a powder molding composition containing PVC, plasticiser, stabilizer and Ba and Zn carboxylates of melting points above 250°C. The present invention provides a powder molding polyvinyl chloride resin composition prepared by dry-blending the polyvinychloride resin, per 100 parts by weight of the polyvinylchloride resin, 0.05-5 parts by weight of barium carboxylate having a melting point of not lower than 250°C and 0.01-5 parts by weight of zinc salts, plasticizer selected from phthalic acid esters and trimellitic acid esters, and stabilizer selected from magnesium oxide, magnesium hydroxide, hydrotalcites, zinc oxide, barium oxide, calcium oxide and barium phosphate, characterized in that said zinc salts are zinc salts of fatty acid having a carbon atom number of 10 or more. The powder molding composition of the invention shows mold-staining resistance and releasability. Upon powder molding, the powder molding composition is usually fusion-adhered to a mold maintained at a temperature in the range of 180 to 250 °C. When the temperature of the mold is lower than 180 °C, the composition will be fused only to an insufficient degree, and hollows and pin holes will be formed on the surface of molded articles. When the temperature of the mold is more than 250°C, there is undesirable discoloration or decomposition of the molded articles. In the present invention, there are used barium salts of carboxylic acids which have a melting point not lower than 250 °C. Such barium salts improve the mold-staining resistance by preventing undesirable plating-out of plasticizers onto the surface of the mold at the time of molding. As examples of barium salts of carboxylic acids usable in the invention, mention may be made of barium oxalate, barium malonate, barium maleate, barium tartrate, barium benzoate, barium p-t-butylbenzoate, barium succinate, barium glutamate, barium adipate, barium pimelate, barium suberate, barium azelate, barium sebacate, barium malate, barium phthalate, barium isophthalate, barium terephthalate, barium salicylate, barium anthranilate, barium mandelate, and the like. The barium salts of carboxylic acids are used in an amount of 0.05 to 5 parts by weight, preferably 0.1 to 3 parts by weight, per 100 parts by weight of the polyvinyl chloride resin. When the salts are used in an amount less than 0.05 parts by weight, there is insufficient heat resistance at the time of molding, whereas when the salts are used in an amount greater than 5 parts by weight, the molded articles are of undesirably low strength. In the present invention, there are also used zinc salts of fatty acids (hereinafter referred to as "zinc soaps") which contain 10 or more carbon atoms, preferably 10 to 20 carbon atoms. As examples of zinc soaps usable in the invention, mention may be made of zinc caprate, zinc undecylate, zinc laurate, zinc tridecylate, zinc myristate, zinc pentadecylate, zinc palmitate, zinc heptadecylate, zinc stearate, zinc oleate, zinc linoleate, zinc linolenate, zinc ricinoleate, zinc arachinate, and the like. The zinc soaps are used in an amount of 0,01 to 5 parts by weight, preferably 0.01 to 2 part by weight, per 100 parts by weight of the vinyl chloride resin. When the salts are used in an amount less than 0.01 part by weight, the result is insufficient releasing effect. When the zinc soaps are used in an amount greater than 5 parts by weight, there is an undesirable deterioration in mold-staining resistance and thermal stability. Examples of polyvinyl chloride resins usable in the invention include polymers of polyvinyl chloride, and copolymers of vinyl chloride and copolymerizable monomers, such as ethylene, propylene, vinyl acetate, alkyl acrylates and alkyl methacrylates, both of which may be prepared by suspension polymerization, block polymerization or emulsion polymerization. Other examples include graft copolymers prepared by grafting vinyl chloride onto a copolymer of ethylene and vinyl acetate; and mixtures of two or more of the above (co)polymers. However, polyvinyl chloride resins usable in the invention are not limited to these. The plasticizers used in the invention are esters of phthalic acids, such as diisodecyl phthalate, diisoundecyl phthalate and dialkyl phthalates containing 9 to 11 carbon atoms in the alkyl groups thereof; and esters of trimellitic acid, such as trioctyl trimellitate, tri-2-ethylhexyl trimellitate, tridecyl trimellitate and trialkyl trimellitate containing 7 to 11 carbon atoms in the alkyl groups thereof. The composition of the invention additionally includes stabilizer selected from magnesium oxide, magnesium hydroxide, hydrotalcites, zinc oxide, barium oxide, calcium oxide, barium phosphate. It is also possible to use antioxidants, such as phenolic and thioether compounds; UV absorbers, such as hindered amines, phosphites, diketo compounds, salicylic acid esters, benzophenones and triazoles; and others, such as epoxidized soybean oil and an epoxy compound synthesized from bisphenol A and epichlorohydrin. It can be particularly preferable to use a double salt of zinc and barium in combination with hydrotalcite since the use of such a combination brings about an increased heat resistance upon superposition of urethanes. If necessary, the powder molding composition of the invention can contain other additives, such as pigments, fillers, foaming agents, and the like. The quantity of polyvinyl chloride resin (100 parts by weight) in the definition of the invention is based on the total of the weight of the polyvinyl chloride resin added before dry-blending plus that of fine particles of polyvinyl chloride resins which may be added after the completion of dry-blending. As is described hereinabove, there can be obtained by the present invention a powder molding vinyl chloride resin composition which can be of excellent mold-staining resistance and releasability, due to the addition of the particular additives. The present invention will be explained in further detail by examples. It should however be noted that the invention is by no means limited to these. Examples 1 to 5 Into a super-mixer was charged 90 parts by weight of a polyvinyl chloride resin (Sumilit® Sx-8G by Sumitomo Chemical Co,. Ltd.; polymerization degree, 800), and the resin was stirred with heating at a constant rotation speed. When the temperature of the resin reached 80 °C, there were added 70 parts by weight of a plasticizer (diisodecyl phthalate), 2 parts by weight of epoxidized soybean oil, a small quantity of pigment, and stabilizers of the kinds and quantities shown in Table 1, and the resulting mixture was dry-blended. When the temperature of the dry-blend mixture reached 120 °C, cooling was initiated. After the mixture had been cooled to 50°C or below, 10 parts by weight of fine particles of a polyvinyl chloride resin (Sumilit® Px-Q by Sumitomo Chemical Co., Ltd.; polymerization degree, 1,300) was uniformly dispersed thereinto, to obtain a powder molding polyvinyl chloride resin composition. Comparative Example 1 A composition was prepared in the same manner as in Example 1, except that barium octanoate (which is a liquid at room temperature (25 °C)) and zinc octanoate (which contains 8 carbon atoms) were used in quantities shown in Table 1. Comparative Example 2 A composition was prepared in the same manner as in Example 2, except that zinc salt of benzoic acid (which contains 7 carbon atoms) was used instead of zinc laurate. Comparative Example 3 A composition was prepared in the same manner as in Comparative Example 2, except that a polyacrylic acid compound (LS-5, product of Adeka-argus Co., Ltd.) was used as a release agent in the quantity shown in Table 1. Comparative Example 4 A composition was prepared in the same manner as in Example 2, except that zinc salt of octanoic acid (which contains 8 carbon atoms) was used in the quantity shown in Table 1, instead of zinc laurate. Comparative Example 5 A composition was prepared in the same manner as in Example 2, except that zinc laurate was not used. Comparative Example 6 A composition was prepared in the same manner as in Example 5, except that barium maleate and zinc stearate were used in quantities shown in Table 1. Comparative Example 7 A composition was prepared in the same manner as in Example 1, except that barium stearate (melting point, 220 °C) was used in the quantity shown in Table 1, instead of barium oxalate. The compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 7 were evaluated in the following manner. (1) Evaluation of Mold-Staining Resistance An embossed nickel mold of 100 mm x 100 mm x 3 mm (thickness) was heated on an electric hot plate. When the temperature of the mold reached 230 °C, a composition prepared in one of the above examples was sprinkled over the mold and fuse-adhered thereto for 10 seconds. After unfused powder had been removed, the mold was again placed on the hot plate and heated for 30 seconds to complete the fusion. Thereafter, the mold was cooled with water, and the molded article was released. After this procedure had been repeated 800 times, the degree of stain on the mold was observed and evaluated. Results obtained are shown in Table 1. (2) Evaluation of Releasability An embossed nickel mold of 150 mm x 300 mm x 3 mm (thickness) was heated to 230 °C, and a composition prepared in one of the above examples was immediately sprinkled over the mold and fuse-adhered thereto for 10 seconds. After unfused powder had been removed, the mold was placed in a heating furnace maintained at 280 °C and heated for 1 minute to complete the fusion. Thereafter, the mold was cooled to 70 °C, and the molded article was released. This procedure was repeated 10 times. Upon the 10th release operation, the release strength (or peel strength) between the mold and the molded article was determined using a spring scale. Results obtained are shown in Table 1.

Claims: A polyvinyl chloride resin powder molding composition prepared by dry-blending the polyvinychloride resin and, per 100 parts by weight of the polyvinylchloride resin, 0.05-5 parts by weight of barium carboxylate having a melting point not lower than 250°C and 0.01-5 parts by weight of zinc salts, plasticizer selected from phthalic acid esters and trimellitic acid esters, and stabilizer selected from magnesium oxide, magnesium hydroxide, hydrotalcites, zinc oxide, barium oxide, calcium oxide and barium phosphate, characterized in that said zinc salts are zinc salts of a fatty acid having a carbon atom number of 10 or more. A composition according to claim 1 wherein said barium carboxylate is blended in an amount of 0.1 to 3 parts by weight, per 100 parts by weight of said polyvinyl chloride resins. A composition according to claim 1 or 2 wherein said barium carboxylate is at least one member selected from barium oxalate, barium malonate, barium maleate, barium tartrate, barium benzoate, barium p-t-butylbenzoate, barium succinate, barium glutamate, barium adipate, barium pimelate, barium suberate, barium azelate, barium sebacate, barium malate, barium phthalate, barium isophthalate, barium terephthalate, barium salicylate, barium anthranilate and barium mandelate. A composition according to claim 3, wherein said barium carboxylate is at least one member selected from barium oxalate, barium maleate and barium benzoate. A composition according to any preceding claim wherein said zinc fatty acid salt contains from 10 to 20 carbon atoms. A composition according to any preceding claim wherein said zinc fatty acid salt is blended in an amount of 0.01 to 2 parts by weight, per 100 parts by weight of said polyvinyl chloride resins. A compositions according to any preceding claim wherein said zinc fatty acid salt is at least one member selected from zinc carprate, zinc undecylate, zinc laurate, zinc tridecylate, zinc myristate, zinc pentadecylate, zinc palmitate, zinc heptadecylate, zinc stearate, zinc oleate, zinc linoleate, zinc linolenate, zinc recinoleate and zinc arachinate. A composition according to claim 7, wherein said zinc fatty acid salt is at least one member selected from zinc laurate and zinc stearate. The use of a composition according to any preceding claim for powder molding. A product powder molded from a composition according to any of claims 1 to 8.

Inventors: IGARASHI TOSHIO, NAKATSUJI YOSHIHIRO, SHIDA YUU, SHIMIZU HIKARU, WAKATSUKI AKIRA, IGARASHI, TOSHIO, NAKATSUJI, YOSHIHIRO, SHIDA, YUU, SHIMIZU, HIKARU, WAKATSUKI, AKIRA
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1991
Main classification: C08K5
IPC codes: C08K5, C08L27, B29C41, B29L31, B29K27