Method of preparing a matte finished vinyl chloride resin article

Abstract: A vinyl chloride resin composition incorporating 0.002-0.02 mol of zinc carboxylate for 100 g of vinyl chloride resin and 0.3-5 mol of a compound having two or more alcoholic hydroxyl groups in one molecule per mol of said zinc carboxylate. This composition yields an article having a good matte-finished surface owing to minute corrugated irregularities formed on the surface.

Description: The present invention relates to production of a matte-finished or surface delustered article of a vinyl chloride resin composition. There is an increasing demand for matte-finished vinyl chloride resin products in such application areas as wall covering, flooring, vehicle interior, electric wires, and daily necessities, where reduced surface gloss, non-glare reflection, dry feel, and quiet appearance are desirable. There are several methods for their matte finishing by (1) physically forming a rough surface, (2) compounding with a special component which gives rise to a rough surface, or (3) coating the surface with dull lacquer. Method (1) involves embossing with finely textured dies, sand blasting, and dusting with fine particles in the course of molding. A disadvantage of mechanical embossing is unsatisfactory matte-finishing which results from the fading out of embossed patterns that takes place after embossing owing to the viscoelastic properties of the material. Another disadvantage of mechanical embossing is that the embossing die becomes contaminated during embossing operations. Sand blasting is applicable only to articles having a hard surface and needs a complex apparatus to confine and recover fine particles. Dusting with fine particles also needs special apparatus for uniform dusting and recovery of fine particles. Method (2) involves blending with a vinyl chloride resin having a different particle diameter, blending with a vinyl chloride resin having a different degree of polymerization, incorporation with a specific polymer other than vinyl chloride resin, partial crosslinking, and incorporation of a large amount of inorganic filler such as calcium carbonate. The first three methods have the disadvantage that molding results depend largely on the molding conditions, no satisfactory matting effect being obtained with a high molding temperature. Incorporation of a large amount of filler has an adverse effect on the physical properties of articles, e.g., decrease in tensile strength. Method (3) is effective in matte finishing but is economically poor in that it needs a special coating material and additional steps for coating and drying. The present invention was completed to address the above-mentioned problems associated with the conventional matte-finishing methods for vinyl chlorodie resin products. DE-A-1241106 describes a vinyl chloride heat stabiliser comprising sorbitol and zinc and calcium salts of fatty acids derived from edible fats and oils. EP-A-0172479 describes a matte film of mixed vinyl chloride polymers containing starch filler and optionally containg zinc salt heat stabiliser. US-A-4134868 discloses a vinyl chloride polymer heat stabiliser comprising metal salt of monocarboxylic acid or substituted phenol with aromatic carboxylic acid partial ester of polyhydric alcohol. US-A-4814369 discloses a PVC floor composition containing polyhydric alcohol, metal salt stabiliser, filler and aromatic carboxylic acid as an anti-water absorption agent. DE-AS-1569372 discloses the use as heat stabiliser for vinyl chloride polymers of a composition comprising nontoxic polyhydric alcohol and magnesium and zinc salts of benzoic acid or fatty acids derived from edible fats and oils. The present invention provides a method of preparing a matte-finished vinyl chloride resin article, which comprises providing a vinyl chloride resin composition containing at least 0.002 mol of zinc carboxylate per 100g of vinyl chloride resin and 0.3n to 5n mol of polyhydric compound comprising fatty acid partial ester having two or more alcoholic hydroxyl groups in one molecule per mol of the zinc carboxylate wherein n is calculated by dividing 3 by the average number of alcoholic hydroxy groups per molecule, the content of alkaline earth metal carboxylate in said composition being less than 0.7 mol per mol of the zinc carboxylate, and the content of each of tin compound, lead compopund and alkali metal carboxylate in said composition being less than 0.3 mol per mol of the zinc carboxylate; molding said composition into an article; and heat-treating the molded article to produce said matte-finished vinyl chloride resin article. The method of the invention can yield molded articles having a good matte-finish surface with minute corrugations; preferred vinyl chloride resin compositions when used in the present invention have the ability to form minute surface irregularities uniformly after molding by means of existing apparatus for the casting, dipping, or coating of plastisols or organosols. The vinyl chloride resin composition used in the present invention is based on a vinyl chloride resin which is a homopolymer of vinyl chloride, or a copolymer of vinyl chloride with comonomer copolymerizable with vinyl chloride, or a mixture thereof. Exemplary comonomers include vinyl acetate, acrylate esters, and methacrylate esters. The vinyl chloride resin used in the present invention is usually produced by emulsion polymerization, microsuspension polymerization, suspension polymerization, or bulk polymerization. It is not specifically limited in particle diameter. Its average diameter usually ranges from 0.1 to 200 µm. One having an average diameter of 0.1-80 µm is preferable, which is used in the form of plastisol or organosol. The zinc carboxylate used in the present invention should preferably be a zinc salt of a monocarboxylic acid having 3-18 carbon atoms. One or more zinc carboxylates may be used. Examples include zinc octanoate, zinc hexanoate, zinc butanoate, zinc propionate, zinc heptanoate, zinc pentanoate, zinc nonanoate, zinc decanoate, zinc 2-ethylhexanoate, zinc laurate, zinc palmitate, and zinc stearate. A zinc salt of a monocarboxylic acid having 6-10 carbon atoms is preferable because it is liquid at normal temperature or readily soluble in common hydrocarbon or carbitol solvents, which facilitates uniform dispersion into the vinyl chloride resin, reducing the amount required for the desired effect. According to the present invention Zn carboxylate is present in an amount of at least 0.002 mol (e.g. 0.002-0.02, preferably 0.0025-0.02)mol per 100 g of vinyl chloride resin. With an amount less than 0.002 mol, the zinc carboxylate does not produce a satisfactory matte-finishing effect. Zinc carboxylate in excess of 0.02 mol does not add to the matte-finishing effect but is wasted. Zinc carboxylate is often used, as a heat stabilizer for vinyl chloride resin, in combination with an alkaline earth metal salt of a carboxylic acid, such as calcium carboxylate and barium carboxylate. The latter, however, is detrimental to the matte-finishing effect which is intended in the present invention, and is therefore used in an amount less than 0.7 mol, preferably less than 0.5 mol, per mol of zinc carboxylate. Other compounds which are detrimental to the matte-finishing effect, like an alkaline earth metal salt of a carboxylic acid, include tin compounds (such as dibutyltin dilaurate and dibutyltin maleate) and lead compounds (such as lead sulfate, lead phosphite, and lead stearate), which are common heat stabilizers for vinyl chloride resin. These tin compounds or lead compounds are used in an amount less than 0.3 mol per mol of zinc carboxylate, if they are to be used in combination with zinc carboxylate. Additional compounds detrimental to the matte-finishing effect include alkali metal carboxylates, which are used in an amount less than 0.3 mol per mol of zinc carboxylate. The compositions used in the invention incorporate said above-mentioned partial esters having 2 or more alcoholic hydroxyl groups per molecule; these are partial esters of polyhydric alcohols and fatty acids (e.g. of 12-18 carbon atoms), preferably selected from sorbitan partial esters (such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monooleate, sorbitan monostearate and sorbitan distearate), glycerin partial esters (such as glycerin monolaurate and glycerin monooleate), condensed glycerin partial esters (such as diglycerin monolaurate, tetraglycerin oleate, hexaglycerin laurate, and decaglycerin laurate), partial esters of a fatty acid with pentaerythritol (such as pentaerythritol monolaurate), condensed pentaerythritol partial esters (such as dipentaerythritol monostearate), trimethylolpropane monoesters (such as trimethylolpropane monostearate), and partial esters of glycerin with a hydroxycarboxylic acid (such as glycerin mono-hydroxystearate). According to the present invention the amount of polyhydric compound present per mol of Zn carboxylate is defined as that sufficient to provide 0.9 - 15 (e.g. 1.5 - 13.5) mol (gm equivalent) of alcoholic hydroxy group; i.e. as n (0.3 - 5) mol, e.g. n (0.5 - 4.5) mol, where n is 3 divided by the average number of alcoholic hydroxy groups per molecule. With an amount less that 0.3 n mol, the polyhydric compound does not produce the desired matte finish; with an amount in excess of 5n mol, it bleeds out of the molded article, resulting in coarse surface irregularities which are detrimental to the finish; moreover, an excess amount leads to higher production cost. The vinyl chloride resin composition used in the present invention may incorporate a variety of additives, such as plasticizer, filler, pigment, stabilizer, and blending resin, which are commonly used for vinyl chloride resins. However, some stabilizers could be detrimental to the matte-finish effect, as mentioned above. For example the vinyl chloride resin composition of the present invention may be in the form of plastisol or organosol which is composed of a vinyl chloride resin and a variety of components. It is processed into film, sheet, leather, and other molded articles by casting, dipping, or coating. The molded articles are finished by heat treatment for gelation. The heat treatment may be accomplished by means of an oven or drying tunnel. This step is important for the matte-finishing effect to fully develop. The matte-finishing effect depends on the heating temperature and heating time. In the case of a small oven, heating is e.g. carried out at 200°C for more than about 40 seconds, at 180°C for more than about 80 seconds, at 160°C for more than about 120 seconds, or at 140°C for more than 160 seconds. Appropriate heating conditions should be selected according to the particular composition. The vinyl chloride resin composition used in the present invention is not specifically limited in its form and molding method. It may take a powder form or pellet form, in addition to plastisol and organosol. The powder or pellet form may be prepared from an extrusion-grade vinyl chloride resin having an average particle diameter of 100-150 µm. Such a composition may undergo calendering, extrusion molding, or injection molding. The resulting molded article will have the matte-finishing surface upon post-heating. For example, a rolled sheet may be heated, with its surface kept at about 200°C for more than 40 seconds, to produce the matte-finish effect. A composition incorporating a blowing agent is also capable of matte finishing in a similar manner. Moreover, a powder composition for fluidized bed coating, electrostatic coating, or cast-sintering is capable of matte finishing. There are no specific restrictions on the method for preparing the vinyl chloride resin composition for the present invention, so long as the resulting composition achieves the desired object of the present invention. For example, it is possible to previously add zinc carboxylate during production of the vinyl chloride resin. The method of the present invention yields molded articles which exhibit a good matte finish effect upon heat treatment after the molding operation. The thus obtained molded articles have a matte-finished surface with reduced gloss, good feel, and non-glare, quiet appearance. The method of the present invention may be applied to wall covering, flooring, leather, sailcloth, vehicle interior, coated steel sheet, coated cotton cloth, coated yarn, tool gripping coat, protective gloves, toys, and daily necessities. The invention will be described in more detail with reference to the following examples. Examples 1 to 9 and Comparative Examples 1 to 3 A plastisol was prepared from the following components by compounding for 15 minutes using a twin-screw stirring mixer. Vinyl chloride resin * 100 g Sumilit® PXNHA (a product of Sumitomo Chemical Co., Ltd.) having an average particle diameter of 1.1 µm. Di-2-ethylhexyl phthalate 65 g Calcium carbonate * 40 g Whiton® SB red (a product of Shiraishi Kogyo Co., Ltd.) Titanium white * 5 g R-820 (a product of Titan Kogyo Co., Ltd.) Zinc octoate * as per Table 1 KV-75A-1, 59% solution (a product of Kyodo Yakuhin Co., Ltd.) Sorbitan monolaurate as per Table 1 The resulting plastisol was cast onto flame-retardant paper to form a 200-µm thick coating using a laboratory knife coater. The coated paper was passed through a tunnel dryer for slight heat treatment so that the coating film was semi-gelled. After cooling, rectangular test pieces were cut out of the coated paper. The test pieces were gelled completely by heating in an oven at 210°C for different periods of time as indicated in Table 1. Finally, the test pieces were evaluated by testing for 60° reflectance (%). The smaller the value of 60° reflectance, the better the matte-finishing effect. The 60° reflectance for practical use should be lower than 30%, preferably lower than 10%. Examples 10 to 15 and Comparative Examples 4 and 5 The same procedure as in Example 7 was repeated except that the sorbitan monolaurate was replaced by other partial ester shown in Table 2. The results are also shown in Table 2. Examples 17 to 20 and Comparative Examples 6 to 8 The same procedure as in Example 6 was repeated except that the zinc octoate was replaced by the zinc carboxylate shown in Table 3. The results are also shown in Table 3. Incidentally, the specimen in Comparative Example 6 gives low reflectance values, but it is not of practical use because of its coarse surface irregularities. Examples 21 to 26 and Comparative Examples 9 to 12 The same procedure as in Example 5 was repeated except that the composition incorporated any of tin stabilizer ("KS-22" made by Kyodo Yakuhin Co., Ltd.), calcium octoate, and potassium octoate as shown in Table 4. The results are also shown in Table 4.

Claims: A method of preparing a matte-finished vinyl chloride resin article, which comprises providing a vinyl chloride resin composition containing at least 0.002 mol of zinc carboxylate per 100g of vinyl chloride resin and 0.3n to 5n mol of polyhydric compound comprising fatty acid partial ester having two or more alcoholic hydroxyl groups in one molecule per mol of the zinc carboxylate wherein n is calculated by dividing 3 by the average number of alcoholic hydroxy groups per molecule, the content of alkaline earth metal carboxylate in said composition being less than 0.7 mol per mol of the zinc carboxylate, and the content of each of tin compound, lead compopund and alkali metal carboxylate in said composition being less than 0.3 mol per mol of the zinc carboxylate; molding said composition into an article; and heat-treating the molded article to produce said matte-finished vinyl chloride resin article. A method according to claim 1 wherein the zinc carboxylate is selected from zinc salts of monocarboxylic acids having 3 to 18 carbon atoms. A method according to claim 1 wherein the zinc carboxylate is selected from zinc salts of monocarboxylic acids having 6 to 10 carbon atoms. A method according to claim 1 wherein the zinc carboxylate is selected from zinc hexanoate, zinc heptanoate, zinc octoate, zinc nonanoate, and zinc decanoate. A method according to any preceding claim wherein the amount of the zinc carboxylate is 0.002 to 0.02 mol per 100g of vinyl chloride resin. A method according to any preceding claim wherein the partial ester is selected from sorbitan partial esters, glycerin partial esters, condensed glycerin partial esters, pentaerythritol partial esters, condensed pentaerythritol partial esters, trimethylolpropane monoesters, and partial esters formed from glycerin and hydroxycarboxylic acids. A method according to claim 6 wherein the partial ester is selected from sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan distearate, sorbitan monooleate, glycerin monolaurate, and diglycerin monolaurate. A method according to any preceding claim wherein the amount of the polyhydric compound is 0.5n to 4.5n mol per mol of the zinc carboxylate where n is calculated by dividing 3 by the average numer of alcoholic hydroxy groups per molecule.

Inventors: MARUYAMA HIROAKI, MITANO TUGIO, YOSHIHARA MASAYUKI, MARUYAMA, HIROAKI, MITANO, TUGIO, YOSHIHARA, MASAYUKI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1992
Main classification: C08K5
IPC codes: C08K5, B29C59, C08L27