Polyvinyl Chloride Resin Composition for Powder Molding

1. Mixed trimellitate plasticizers:

TABLE 1 shows the mixed trimellitate plasticizers which were employed in Examples of this invention and Comparative Examples.

The distribution of the alkyl groups in each of plasticizers A to I was determined by programed-temperature gas chromatography.

These mixed trimellitate plasticizers may be prepared by reacting trimellitic anhydride with a mixture of alcohols having a composition corresponding to the alkyl groups, their mol % and straight chain ratio desired in the resulting trimellitate mixture, the reaction proceeding substantially stoichiometrically.

More specifically the particular mixed trimellitate plasticizers indicated in the above TABLE 1 were prepared as follows:

To a reaction vessel (50 liters volume) equipped with a stirrer and a jacket for circulation of pressurized steam there were charged 9600 g (50 mol) of trimellitic anhydride, 1275 g (12.5 mol) of n-hexyl alcohol, 4930 g (42.5 mol) of n-heptyl alcohol, 11700 g (90 mol) of n-octyl alcohol, 1080 g (7.5 mol) of n-nonyl alcohol, 95 g (0.5% based on total alcohols) of p-toluene sulfonic acid and 3000 g of benzene (as water entrainer). The mixture was reacted at 120.degree. C. for 8 hours. Then the reaction product was added with 1000 g of 4% aqueous solution of sodium hydroxide for the neutralization and then washed three times with 15 liters of distilled water. Benzene was distilled off by distillation under atmospheric pressure and then the product was subjected to distillation under reduced pressure to obtain 16.4 kg (yield 58%) of a mixed trimellitate having a composition corresponding to the Plasticizer A shown in TABLE 1.

The same procedures were repeated except that the kinds and amounts of alcohols were varied to obtain the Plasticizers B to I indicated in TABLE 1.

2. Items and methods of evaluation:

The resin composition of this invention was evaluated with respect to the following items:

(1) Powder flowability:

A sample of each powder resin composition in the amount of 100 ml was placed in the funnel of a bulk specific gravity measuring device conforming to the specifications of JIS-K-6721. The counting of time (seconds) was started when the sample began to drop upon removal of a damper, and was terminated when all of the sample finished dropping. The results of Examples 1 to 6 are shown in TABLE 2, and those of Comparative Examples 1 to 8 in TABLE 3. The shortness of the time is a measure of good flowability.

(2) Moldability:

A sample of each powder resin composition in the amount of 500 g was scattered on a 300 mm square embossed nickel plate used as a mold and heated to a temperature of 220.degree. C. in an oven having an atmosphere temperature of 300.degree. C., and was allowed to undergo fusion. After 10 seconds, the unfused powder was discharged from the oven and the embossed plate with the fused powder thereon was heated for 40 seconds in the oven having an atmosphere temperature of 300.degree. C. After it had been cooled, a molded sheet was released from the mold. The molded sheets which had been obtained had an average thickness of about 1 mm. The moldability of each composition was judged from the weight of the sheet which had been molded from it. A sheet molded from a composition of low moldability had a heavy weight, since the unfused powder could not satisfactorily be discharged, but a considerably large amount thereof remained on the sheet.

Moreover, the rear surface of each molded sheet was examined for the evaluation of each composition for moldability in accordance with the following criteria:

o: All of the powder had been uniformly fused without leaving any unfused portion;

o-.DELTA.: A portion remained unfused (not more than about 5%);

.DELTA.: A considerable portion remained unfused (about 5 to 30%);

.DELTA.-x: A large portion remained unfused (about 30 to 50%), giving a partly uneven surface;

x: A very large portion remained unfused (more than about 50%), giving a wholly uneven surface.

The results of Examples 1 to 6 are shown in TABLE 2, and those of Comparative Examples 1 to 8 in TABLE 3.

(3) Heat resistance:

Each of the molded sheets which had been obtained from the moldability tests as described at (2) above was placed with its embossed surface down in a 300 mm square aluminum supporting frame having a thickness of 10 mm and mounted on a foaming stand formed from an aluminum plate. A total of 153 g consisting of 100 parts by weight of a polyol mixture comprising a polyol composed mainly of a propylene and ethylene oxide adduct of glycerin, water, triethanolamine and triethylenediamine, and 50 parts by weight of polymeric MDI containing 30.5% of NCO was injected into the frame to produce a urethane foam bonded intimately to the rear surface of the molded sheet. The urethane laminated on the sheet had a thickness of 9 mm and a foam density of 0.16 g/cm.sup.3. The urethane-laminated sheet was formed into specimens each measuring 70 mm by 150 mm. Three specimens were placed in a Geer oven having an atmosphere temperature of 110.degree. C. so that they might be taken out every 400 hours, and were subjected to up to 1200 hours of thermal discoloration and deterioration tests.

The results of the thermal discoloration tests are shown by the grades of a gray scale. The results of the thermal deterioration tests are shown by the elongation (%) at rupture which was determined by a tensile testing machine in which a sample formed by a #1 dumbbell from the molded sheet separated from the specimen which had been taken out of the Geer oven upon expiration of a given length of time was pulled at a constant rate of 200 mm per minute at an ambient temperature of 23.degree. C. The results of Examples 1 to 6 are shown in TABLE 2, and those of Comparative Examples 1 to 8 in TABLE 3.

(4) Low temperature resistance:

Each of the urethane-laminated sheets which had been prepared for the heat resistance tests as described at (3) above was cut into 100 mm square specimens. Each specimen was cooled to a temperature of -40.degree. C. and was immediately subjected to a low-temperature impact test conducted by employing a Dupont impact tester and dropping a weight of 500 g from various levels of height. The maximum height from which the weight could be dropped without breaking any of three specimens of each sheet was adopted as a measure indicating its low temperature resistance. The results of Examples 1 to 6 are shown in TABLE 2, and those of Comparative Examples 1 to 8 in TABLE 3.

The invention will now be described with reference to the examples which are not intended for limiting the scope of this invention.

(1) Preparation of resin compositions for powder molding:

A supermixer having a capacity of 20 liters was charged with 1.8 kg of a polyvinyl chloride resin produced by an ordinary method of suspension polymerization and having an average polymerization degree of 800 [Sumilit (registered trademark) SX-8G; product of Sumitomo Chemical Co., Ltd.]. The mixer was rotated at a constant speed to stir the resin, and when the resin had reached a temperature of 80.degree. C., the mixer was charged with a plasticizer, a stabilizer, a pigment and epoxidized soybean oil, so that dry blending might be started.

The plasticizer and the amount thereof which were employed in each of Examples 1 to 6 are shown in TABLE 2, while those employed in each of Comparative Examples 1 to 8 are shown in TABLE 3. The stabilizer was a mixture of 14 g of barium oxalate, 12 g of zinc oxalate, and 20 g of a perchlorate salt of hydrotalcite. The pigment was a gray pigment produced by Sumika Color Co., Ltd. and was employed in the amount of 80 g. The epoxidized soybean oil was a product of Adeka Argus known as 0-130P and was employed in the amount of 80 g. When the dry blended product had reached a temperature of 122.degree. C., the supply of steam for heating was discontinued, and when dry blending had been completed, the supply of cooling water was started. When the dry blended product had been cooled to a temperature not exceeding 50.degree. C., 200 g of fine particles of a paste polyvinyl chloride resin [Sumilit (registered trademark) PxQL product of Sumitomo Chemical Co., Ltd.]were uniformly Scattered on the dry blended product, whereby a powder resin composition was obtained.

Each of the powder resin compositions which had been obtained was evaluated for flowability, moldability, heat resistance and low-temperature resistance by the methods as hereinabove described. The results are shown in TABLES 2 and 3.

All of the compositions according to Examples 1 to 6 were good in flowability and moldability, and all of the molded products thereof were good in heat and low-temperature resistances.

The sheets molded from the compositions of Comparative Examples 1 and 6 were low in heat resistance. The compositions of Comparative Examples 2, 3, 4, 7 and 8 were all low in flowability and moldability. The sheet molded from the composition of Comparative Example 5 was poor in low-temperature resistance.