GB2025430A - Method for reducing electrostatic charging on shaped articles of polyvinyl chloride resins - Google Patents

Abstract

The method comprises the steps of (a) blending a surface active agent with the polyvinyl chloride resin prior to fabrication of the resin into a shaped article, (b) fabricating the resin admixed with the surface active agent into a shaped article, and (c) subjecting the shaped article to a treatment with low temperature gas plasma.

Description

SPECIFICATION Method for reducing electrostatic charging on shaped articles of polyvinyl chloride resins The present invention relates to a method for reducing electrostatic charging -on the surface of shaped articles of polyvinyl chloride resins.

As is well known, polyvinyl chloride resins belong to one of the most important classes of thermoplastic synthetic resins and shaped articles of the resin are widely employed in various applications.

One of the difficulties encountered in the use of shaped articles of polyvinyl chloride-based synthetic resins is the tendency to become charged with static electricity which in turn results in a rapid loss of the attractive appearance of the articles due to the adhesion or attraction of dust as well as in an unpleasant and sometimes dangerous effect to the human body such as an electric shock caused by the electrostatic charges accumulated on the surface.

Various attempts have been made hitherto to reduce the accumulation of static electricity on the surfaces of shaped articles of polyvinyl chloride resins including application of an antistatic agent on the surfaces and incorporation of an antistatic agent into the resin composition prior to fabrication of the resin composition into shaped articles. The former method of coating can give an instantaneous effect but is disadvantageous because of poor durability of its effectiveness and because of the sticky feel of the surfaces which possibly leads to blocking of the shaped articles. The latter method is, on the other hand, better than the former method as regards durability of the antistatic effect but the effectiveness is usually insufficient due to the limited amount of the antistatic agent incorporated in the shaped articles.

When the amount of the antistatic agent is increased with a view to obtaining a sufficient antistatic effect, the surfaces of the shaped articles become sticky due to the bleeding of.the antistatic agent leading to blocking of the shaped articles in addition to the problems of decreased heat resistance, poor workability and coloring and accelerated staining of the surfaces.

On the other hand, an attempt has been made to reduce the static electricity on the surfaces of shaped articles of polyvinyl chloride resins by the treatment of the surface with low temperature gas plasma whereby the affinity of the surface with water can be enhanced but the antistatic effect obtained by this method is not always satisfactory, especially, as regards durability.

It was therefore desirable to provide a novel method for reducing the static electricity on the surfaces of a shaped article of a polyvinyl chloride resin.

The method of the present invention, established as a result of the extensive investigations undertaken by the inventors, comprises the steps of (a) blending a surface active agent with the polyvinyl chloride resin prior to fabrication of the resin into a shaped article, (b) fabricating the polyvinyl chloride resin admixed with the surface active agent into a shaped article, and (c) subjecting the shaped article to a treatment with low temperature gas plasma.

The antistatic effect obtained by the above method is very durable laSting for a long period of time even with an amount of the surface active agent in the shaped article as small as 0.003 to 3 parts by weight per 1 00 parts by weight of the polyvinyl chloride resin.

The polyvinyl chloride resins used in the above step (a) are not particularly limited to certain specific types of polyvinyl chloride resins and include homopolymers of vinyl chloride of various average degrees of polymerization as well as copolymers of vinyl chloride with one or more of copolymerizable comonomers insofar as the main component, say, 50 % by weight or more, of the copolymer is vinyl chloride.The comonomers copolymerizable with vinyl chloride are well known in the art and are exemplified by vinyl esters such as vinyl acetate, vinyl ethers such as vinyl ethyl ether, acrylic and methacrylic acids and esters thereof, maleic and fumaric acids and esters thereof, maieic anhydride, aromatic vinyl compounds such as styrene, vinylidene halides such as vinylidene chloride, acrylonitrile, methacrylonitrile, olefins such as ethylene and propylene, and the like.

In step (a) of the method, a surface active agent is blended with the polyvinyl chloride resin. The type of surface active agent is not critical. The surface active agents include cationic, anionic, nonionic and amphoteric surface active agents, among which the most preferred are cafionic surface active agents as they have greater effectiveness than the surface active agents of the other types.

The cationic surface active agents are classified into primary amine salts, secondary amine salts, tertiary amine salts, quaternary amine salts, pyridinium salts and the like and the anionic surface active agents are exemplified by sulfonated oils, metal soaps, sulfonated ester oils, sulfonated amide oils, sulfuric acid esters of olefins, sulfuric acid esters of aliphatic alcohols, ester salts of alkylsulfuric acids, aliphatic acid ethylsulfonates, alkylsulfonates, alkylnaphthalene sulfonates, alkylbenzene sulfonates, reaction products of naphthalensulfonic acid and formalin, sulfonates of succinic acid esters, salts of phosphoric acid esters and the like.

The nonionic surface active agents include aliphatic carboxylic acid esters of polyvalent alcohols, addition products of ethylene oxides with aliphatic alcohols, addition products of ethylene oxide with aliphatic carboxylic acids, addition products of ethylene oxide with aliphatic amines or aliphatic amides, addition products of ethylene oxide with alkyl phenols, addition products of ethylene oxide with alkyl naphthols, addition products of ethylene oxide with partial carboxylic acid esters of polyvalent alcohols polyethyleneglycols and the like and the amphoteric surface active agents include those of carboxylic acid type, e.g. betaine derivatives, sulfuric acid esters salts, e.g. sulfuric acid esters of hydroxyethylimidazoline, those of sulphonic acid type, e.g. taurine condensation type succinic acid esters and imidazolinesulfonic acids, and-the like.

These surface active agents may be blended with the polyvinyl chloride resin in an amount from 0.003 to 3 parts by weight or, preferably, from 0.03 to 1 part by weight per 100 parts by weight of the resin. When the amount is smaller than the above given range, the antistatic effect exhibited by the plasma treatment in the subsequent step (c) is insufficient while larger amounts of the surface active agent than the above given range may have adverse effects on the properties of the shaped articles in addition to increased staining of the surface of the articles.

The polyvinyl chloride resin composition prepared in stap (a) above of the method may contain, in addition to the surface active agent, various kinds of additives conventionally admixed in polyvinyl chloride resin compositions to be fabricated into shaped articles with no particular disadvantages to the desired antistatic effect in the shaped articles. Those optional additives include plasticizers, stabilizers, fillers, anti-oxidants, ultraviolet light absorbers, antistatic agents other than surface active agents antifogging agents, pigments, dyestuffs, crosslinking aids and the like. Further, several types of rubbery elastomers may be incorporated into the resin composition to improve the mechanical properties of the shaped articles if the amount thereof is not excessively large, say, less than 50 parts by weight per 100 parts by weight of the polyvinyl chloride resin.

It is convenient if the above named additives are blended with the resin simultaneously with the surface active agent but it is possible to blend these additives with the resin either prior to or after the blending fo the surface agent. Blending of the surface active agent as well as the other optional additives with the polyvinyl chloride resin may be carried out in a conventional blending machine such as a roller mill and the like, preferably, at an elevated temperature.

The polyvinyl chloride resin composition thus obtained is then fabricated into a shaped article in step (b) of the method. The techniques of fabrication are not critical and conventional methods can be applied according to the shape of the desired article and the moldability of the resin composition; they include extrusion molding, injection molding, calendering, inflation, vacuum forming, blow molding, compression molding and the like. The shapes of the articles are also not critical although articles with complicated shapes, for example, with concavity may require specific elaboration in order to ensure uniform treatment with low temperature plasma in the subsequent step (c) of the method.

The shaped article obtained in the above step (b) of the method is then subjected to a treatment with low temperature plasma. Low temperature plasma is well known in the art as a gaseous atmosphere full of electrically charged species where the temperature of the gaseous atmosphere is not excessively high in comparison with the ambient temperature irrespective of the energy of the charged species per se. Low temperature plasma is produced mainly by glow discharge in a gaseous atmosphere at a pressure in the range from 0.001 to 10 Torr where the frequency of the electric power supply is not critical ranging from direct current to microwave region. In particular, a frequency of the so-called high frequency region is recommended due to the availability of generator apparatuses and the possibility of obtaining stable plasma discharge.For example, a frequency of 13.56 MHz or 27.12 MHz is recommended since these frequencies are relatively free from statutory regulations for radio waves.

The shapes and arrangement of the electrodes are not critical insofar as a stable plasma discharge can be ensured within the space in which the surface of the shaped article is treated, i.e. exposed to the plasma atmosphere. Thus, a pair of inside electrodes, a pair of exterior electrodes and a coiled electrode may be usEd according to particular types of the apparatuses for plasma generation. The electrodes may be connected to the high frequency generator either by capacitive coupiing or inductive coupling.

The intensity or power density of the low temperature plasma and the time required for the plasma treatment are interrelated parameters but extreme difficulties are encountered in explicitly defining the power density of low temperature plasma due to the very complicated nature of the plasma atmosphere which is presently not understood. Therefore, the best approach is to say that the time for the plasma treatment is determined by a careful preparatory experiment in which several parameters including the electric power supplied are selected according to the specific purpose. With the power density obtained in most of the currently available apparatuses for plasma generation, a time from a few seconds to several tens of minutes is usually sufficient for obtaining the objective antistatic effect of the invention.

In any case, it is a least requirement that the surface of the shaped articles never undergoes thermal degradation by the heat evolved in the discharge.

The other parameters to be taken into consideration in the plasma treatment are the kind of gaseous constituents and the pressure of the gaseous atmosphere. The pressure of the gaseous atmosphere within the apparatus for plasma generation should be maintained in a range from 0.001 to 10 Torr or, preferably, from 0.01 to 1.0 Torr in order to ensure stability of the plasma discharge.

The gas filling the atmosphere under the above specified pressure is either inorganic or organic as exemplified by helium, neon, argon, nitrogen, nitrous oxide, nitrogen dioxide, oxygen, air, carbon monoxide, carbon dioxide, hydrogen, halogens, e.g. chlorine, and halogen compounds, e.g. hydrogen chloride, as well as olefins, e.g. ethylene and propylene, halogenated hydrocarbons, e.g. fluorocarbons, aromatic hydrocarbons, e.g. benzene, heterocyclic organic compounds, e.g. pyridine, organosilanes and the like. Among the above named gases, the inorganic gases are preferred to the organic ones due to the absence of coloration on the surface of the plasma-treated articles and formation of a powdery polymerized matter.In particular, helium, argon, carbon monoxide, carbon dioxide and hydrogen, especially, carbon monoxide, are preferred because of their higher efficiency (due to an unknown mechanism). These gases are used either singly or as a mixture of two or more and, when a mixed gas is used, it is recommended that one of the components is carbon monoxide.

In accordance with the method of the present invention, a good antistatic effect is obtained in the shaped articles of polyvinyl chloride resins with small amounts of the surface active agent owing, presumably, to the synergistic effect with the treatment with low temperature plasma. In addition, the antistatic effect obtained by the method of the invention is very advantageous as regards as durability and, along with the antistatic effect, the shaped articles obtained by the method are imparted with excelient anti-fogging property, resistance against staining, printability, workability and appearance.

The following are Exampies to illustrate the present invention in further detail, in which parts are all expressed in parts by weight.

EXAMPLE 1. (Experiments No. 1 and No. 2) A resin composition was prepared by intimately blending 100 parts of a homopolymeric polyvinyl chloride resin having an average degree of polymerization of about 1,300 (TK-1 300, a trade name of Shin-Etsu Chemical Co., Japan), 2 parts of calcuim stearate, 2 parts of zinc stearate and 0.2 part of a cationic surface active agent stearamidopropyldimethyl-,B-hydroxyethylamrnonium nitrate (Catanac SN, a trade name of American Cyanamid Co.) on a roller mill at 1 80 C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 1 mm thickness.

A 10 cm by 10 cm pieces of the prepared sheet was placed on a lower electrode of 20 cm diameter facing an upper electrode at a distance of 3 cm in an apparatus for plasma generation and low temperature plasma was generated by a high frequency power supply of 50 watts at a frequency of 13,56 MHz for 10 minutes while the pressure in the appatatus was maintained at 0.2 Torr by passing argon gas with simultaneous evacuation by means of vacuum pump.

The resin sheet thus treated with low temperature plasma on a surface as well as the sheet without the plama treatment were subjected to the tests of the distance of cigarette ash attraction, electric surface resistivity, voltage by frictional charging and contact angle of water to give the results set out in Table 1 below (Experiment No. 1). The distance of cigarette ash attraction was determined by measuring the largest distance between cigarette ash and the sample sheet rubbed ten times with a cotton cloth, at which the cigarette ash was attracted by the charged sample sheet at 250C in an atmosphere of 60 % relative humidity. The voltage induced by frictional charging was determined by use of a rotary static tester made by Kowa Shokai Co., Japan, with a cotton cloth under the conditions of 200 g load, 750 r.p.m. and 30 seconds.Table 1 also gives the data obtained with the same sheet before the piama treatment (Experiment No. 2).

EXAMPLE 2. (Experiments No. 3 to No. 6) A resin composition was prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 1, 1.5 parts of cadmium stearate, 0.5 part of barium stearate and 0.1 part of a cationic surface active agent (New Elegan A, a trade name by Nippon Oil and Fats Co., Ltd., Japan) on a roller mill at 1 800C for 10 minutes and the resin composition was fabricated by press molding at 1850C into a sheet of 1 mm thickness.

The thus prepared resin sheet was subjected to treatment wifh low temperature plasma in the same manner as in Example 1 except that the pressure of the argon atmosphere and the high frequency power supplied to the electrodes were 0.35 Torr and 75 watts, respectively, and the properties of the thus plasma-treated sheet were measured in the same manner as in Example 1 to give the results set out in Table 1 (Experiment No. 3). Table 1 also summarizes the data obtained with the same data sheet before the plasma treatment (Experiment No. 4) as well as with the sheets prepared with a resin composition of the same formulation as above excepting the omission of the cationic surface active agent before and after the plasma treatment (Experiments No. 5 and No. 6).

EXAMPLE 3. (Experiments No. 7 and No. 8) A resin composition was prepared by intimately blending 100 parts of a 88:12 by weight copolymeric resin of vinyl chloride and vinyl acetate (SC-4O0, a trade name by Shin-Etsu Chemical Co., Japan), 1.5 parts of cadmuim stearate, 0.5 part of barium stearate and 0.3 part of a cationic surface active agent (Denon 310, a trade name by Marubishi Yuka Co., Japan) on a roller mill at 1 80 C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 1 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the same manner as in Example 1 except that the atmosphere. was air instead of argon and the pressure was 0.3 Torr and this plasma-treated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experiment No. 7). The same sheet before the plasma treatment was tested in the same manner and the results are also shown in the same table (Experiment No. 8).

EXAMPLE 4. (Experiments No. 9 and No. 10) A resin composition was prepared by intimately blending 100 parts of a homopoiymeric polyvinyl chloride resin having an average degree of polymerization of about 1,000 (TK-1 000, a trade name of Shin-Etsu Chemical Co., Japan), 2 parts of calcium stearate, 2 parts of zinc stearate and 0.3 part of an anionic surface active agent sodium dodecylbenzene sulfonate (Neopelex F-60, a trade name of Kao Atlas Co., Japan) in a roller mill at 1 8O0C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the same manner as in Example 1 except that the pressure of the argon atmosphere was 0.3 Torr and this plasma-treated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experiment No. 9). The table also gives the data obtained with the same sheet before the plasma treatment (Experiment No. 1 0).

EXAMPLE 5. (Experiments No. 11 to No. 14) A resin composition was prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 4, 1.5 parts of cadmium stearate, 0.5 part of barium stearate and 0.2 part of an anionic surface active agent, a normal paraffin sulfonate (TB-i 60, a trade name of Matsumoto Yushi Co., Japan) on a roller mill at 1 8O0C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the same manner as in Example 1 except that the plasma gas was a 90:10 by volume mixed gas of argon and carbon monoxide instead of pure argon and that the high frequency power supplied to the electrodes and the time of the plasma treatment were 100 watts and 5 minutes, respectively and this plasmatreated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experiment No. 11). The table also gives the data obtained with the same sheet before the plasma treatment (Experiment No. 1 2) as well as with the sheets prepared with a resin composition of the same formulation excepting the omission of the anionic surface active agent before and after the plasma treatment (Experiments No. 13 and No. 14).

EXAMPLE 6. (Experiments No. 1 5 and No. 16).

A resin composition was prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 4, 2 parts of calcium stearate, 2 parts of zinc stearate and 0.5 part of a nonionic surface active agent which is a block copolymer of oxyethylene and oxypropylene units (Emulgen PP-250, a trade name of Kao Atlas Co., Japan) on a roller mill at 1 800C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the same manner as in Example 1 and this plasma-treated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experiment No. 1 5). The table also gives the data obtained with the same sheet before the plasma treatment (Experiment No 16).

EXAMPLE 7. (Experiments No. 17 and No. 18).

A resin composition was prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 4, 1.5 parts of cadmium stearate, 0.5 parts of barium stearate and 0.3 part of a nonionic surface active agent (Denon 1886, a trade name of Marubishi Yuka Kogyo Co., Japan on a roller mill at 1 800.C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the same manner as in Example 1 except that the plasma gas was a 80:20 by volume mixed gas of argon and carbon monoxide and that the pressure of the gas, the high frequency power supplied to the electrodes and the time of the plasma treatment were 0.1 Torr, 100 watts and 5 minutes, respectively, and this plasma-treated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experment No. 17). The table also gives the data obtained with the same sheet before the plasma treament (Experiment No. 18).

EXAMPLE 8. (Experiments No. 19 and No. 20) A resin composition was prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 4, 2 parts of calcium stearate, 2 parts of zinc stearate and 0.3 part of an amphoteric surface active agent (Chemistat 4005, a trade name of Sanyo Chemical Industries, Ltd., Japan) on a roller mill at 1 800C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the sme manner is in Example 1 except that the pressure of the argon atmosphere was 0.3 Torr and this plasmatreated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experiment No. 19). The table also gives the data obtained with the same sheet before the plasma treatment (Experment No. 20).

EXAMPLE 9. (Experiments No. 21 and No. 22) A resin composition was prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 4, 1.5 parts of cadmium stearate, 0.5 part of barium stearate and 0.2 part of an amphoteric surface active agent (Reostat 923, a trade name of The Lion Fat and Oil Co., Ltd., Japan) on a roller mill at 1 800C for 10 minutes and the resin composition was fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheet was subjected to treatment with low temperature plasma in the same manner as in Example 5 and this plasma-treated sheet was subjected to the same tests as in Example 1 to give the results set out in Table 1 (Experiment No. 21). The table also gives the data obtained with the same sheet before the plasma treatment (Experiment No. 22).

EXAMPLE 10.

Three kinds of resin compositions were prepared by intimately blending 100 parts of the same polyvinyl chloride resin as used in Example 4, 2 parts of calcium stearate, 2 parts of zinc stearate and 0.2 part of a cationic surface active agent (Ameet 105, a trade name of Kao Atlas Co., Japan), an anionic surface active agent (Neopelex F-60, a trade name of Kao Atlas Co.) or a nonionic surface active agent (Emulgen PP-250, a trade name of Kao Atlas Co.) on a roller mill at 1 800C for 10 minutes and the resin compositions were each fabricated by press molding at 1 850C into a sheet of 0.5 mm thickness.

The thus prepared sheets were each subjected to treatment with low temperature plasma in the same manner as in Example 1 except that the pressure of the argon atmosphere was 0.4 Torr and these plasma-treated sheets were subjected to the tests of the distance of cigarette ash attraction, voltage by frictional charging and contact angle of water in the same manner as in Example 1 directly after the plasma treatment or after storage of 3 months or 6 months to give the results set out in Table 2 below.

Table 1

Distance of Surface Voltage by Contact Exp. cigarette ash resistivity frictional angle of No. attraction, cm ohm charging, volt water 1 0 3.3 x 10 350 43 2 3 7.8 x 10 2800 71 3 0 6.0 x 1010 100 33 4 2 7 x 10 2500 65 5 2 3 x1011 720 36" 6 5 1.8 x 1015 3200 90" 7 0 2.3x1010 230 46" 8 1 1.8 x 1012 2100 58" 9 0 2.5x1011 230 21" 10 4 8.3 x 1013 3200 65" 11 0 5 x1010 210 32" 12 2 8 x 1012 1800 66" 13 3 4 x 1011 930 39 14 5 1.8 x 1015 3200 90 15 0 4.6 x 10 530 28 16 3 2.1 x 1014 3500 73 17 0 8 x 1010 620 38 18 3 8 x 1012 2800 63" 19 0 2.1 x 1011 250 23" 20 4 2.8 x 1013 2500 62" 21 0 8 x1010 310 30" 22 2.5 1;1:x1012 2200 65" Table 2

Type of Distance of Voltage by Contact suface Period of cigarette ash frictional angle of active agent storage attraction, cm charging, volt water Initial 0 180 350 Cationic 3 months 0 250 40" 6 months 0 350 49' Initial 0 270 20" Anionic 3 months 0 380 25" 6 months 1 500 40" Initial 0 400 28" Non ionic 3 months 1 600 37" .6 months 3 820 45"

Claims (7)

1. A method for reducing static elecricity on the surface of a shaped article of a polyvinyl chloride resin which comprises the steps of (a) blending a surface active agent with a polyvinyl chloride resin prior to the fabrication of the polyvinyl chloride resin into a shaped article, (b) fabricating the polyvinyl chloride resin admixed with the surface active agent into a shaped article, and (c) subjecting the shaped article to a treatment with low temperature gas plasma.

2. The method as claimed: in claim 1 wherein the surface active agent is a cationic surface active agent.

3. The method as claimed in claim 1 or 2 wherein the amount of the surface active agent is in the range from 0.03 to 3 parts by weight per 100 parts by weight of the polyvinyl chloride resin.

4. The method as claimed in claim 1, 2 or 3 wherein the pressure of the gas for the low temperature plasma is in the range from 0.001 to 1 Torr.

5. The method as claimed in any preceding claim wherein the gas for the low temperature plasma is carbon monoxide or a mixed gas containing carbon monoxide.

6. The method as claimed in claim 1, substantially as described in any preceding claim.

7. A shaped article when treated by the method of any preceding claim.