A PROCESS FOR THE PREPARATION OF AN ANTISTATIC RESIN COMPOSITION AND AN ANTISTATIC RESIN COMPOSITION PREPARED BY THE SAME

Abstract: This invention provides a process for preparing an antistatic resin composition comprising mixing and stirring a mixture of alkali metal alkylsulfonate and polyalkylene glycol to obtain a liquid mixture of the antistatic agents, which is fed into an extruder in a proper amount to homogeneously blend with a melted resin and to continuously extrude. This invention also provides an antistatic resin composition prepared thereby and a use of the composition as a master batch.

Description: A process for the preparation of an antistatic resin composition and an antistatic resin composition prepared by the same TECHNICAL FIELD The present invention relates to a process for the preparation of an antistatic resin composition and an antistatic resin composition prepared thereby. Particularly, the present invention relates to a process for the preparation of an antistatic resin composition which comprises mixing and stirring a mixture of an anionic antistatic agent such as an alkali metal alkylsulfonate and a noniomc antistatic agent such as polyalkylene glycol including polyethylene glycol to obtain a liquid mixture of the antistatic agents, said liquid mixture being fed into an extruder at a suitable amount to uniformly blend with a melted resin such as PMMA (polymethyl methacrylate) and to be continuously extruded; and an antistatic resin composition prepared thereby. BACKGROUND ART In general, plastics are used for the production of various articles not only due to its light weight, gorgeous colors and good quality, but also due to its good insulating properties. However, the insulating property of plastics occasionally causes the generation of static electricity which would be an obstacle for using plastics to produce certain articles . Although reasons of the generation of the static electricity in plastics have not been clearly revealed, generally the static electricity arises due to surface contact such as friction, and m particular, it has been known that insulator such as plastics can be easily charged with friction. The phenomenon of the static electricity shortens the life of electrical/elctronical products and causes any danger to workers and m the work place. Trerefore, it is desirable to develop new plastic materials m wr ch the generation of static electricity is prevented or decreased. Hitherto, to decrease the generation of the static electricity m plastics, three methods r-ave been proposed as follows: a method of surface coating wnerem the surface of a plastic article is coated by spraying or by dipping said article into with a solution of an antistatic agent; a method of melt-blendmg wherein plastic materials are melt-blended with an antistatic agent; and a method of copolymerization wherein a hydrophilic monomer is copolymerized or grafted into the resin. The surface-coating method has advantages that it is easy to impart tne antistatic property to resins and the process to impart the antistatic property is convenient; however, said method has disadvantages that it is difficult to be applied to large articles because such articles need a large dipping bath. Further, the surface-coating method also has a disadvantage that the coated antistatic agent layer may be eliminated to loss the antistatic property; as such, due to additional processes of coating, the cost of the method becomes high. The copolymerization method can ser>ι-permanently provide resins with antistatic properties and can be used to produce antistatic articles only by molding the antistatic resin composition. However, this method has disadvantages that it is difficult to produce various articles according to various applications. Further, due to its low thermal resistance of the antistatic resin composition, products can be produced by injection molding and it is difficult to produce articles by extrusion. The melt-blendmg method has a good flexibility but has disadvantages such that it is very difficult to find out optimum process conditions such as a processing temperature, a composition ratio, shapes of the resin and antistatic agents, and compatibility) . Nevertheless, the melt-blending method is now commonly used and the process of the present invention is based on the melt-blending method. In the melt-blending method, resins are melt-blended with an antistatic agent and extruded at a temperature of between 210 °C and 250 °C or injected at a temperature of between 190 °C and 210 °C. Thus, the antistatic agent used in the melt- blending method, especially by extrusion should have good thermal stability. As antistatic agents which can be used to remove or decrease the generation of statistic electricity, they can be classified into two types, one being external coating type which is used in the surface coating method and another being internal incorporating type which is used in the melt-blending method. Alternatively, antistatic agents can be classified according to natural properties into thee types, being respectively cationic antistatic agent type such as compounds containing a quaternary ammonium salt in its molecular, anionic antistatic agent type such as phosphates and sulfonates, and nonionic antistatic agent type such as polyalkylene glycol. In general, the cationic antistatic agent type is most antistatic, but has the worse thermal stability and thus it cannot be used for the melt-blending method. The nonionic antistatic agent type is most thermal stable, but is least worse antistatic; thus to impart any antistatic ability to a resin, a large amount of the antistatic agent should be added to the resin, for example in an amount of more than 10 parts by weight based on the weight of the resin. As such, the physical properties of the resulted antistatic resin composition and articles prepared therefrom are deteriorated. The anionic antistatic agent type has a good balance of good antistatic property and good thermal stability. However, while the cationic or nonionic antistatic agents can De prepared m liquid or powder form, tne anionic antistatic agents are generally prepared in paste or solidified form. Such anionic antistatic agents thus would be difficult to be quantitatively supplied with a common liquid pump or a powder feeder and would be difficult to be intimately blended with resins m an extruder. Meanwhile, porous powdery resins such as PVC (polyv yl chloride) can be easily mixed and extruded with an antistatic agent in a form of powder, liquid, paste or granule regardless of the melting viscosity and thermal stability of the resm. Similarly, since some non-porous resins such as PE (polyethylene) and PP (polypropylene) , which are generally prepared in the form of pellet or granule have a relatively low melting viscosity and good thermal stability, the resm can be easily mixed and extruded with an antistatic agent in th form of powder, liquid, paste or granule. However, some non-porous resins which have low thermal stability and high melting viscosity, such as PMMA (polymethyl methacrylate) , can be mixed and extruded with an antistatic agent m the form of powder, liquid or granule, but cannot be well mixed eith antistatic agents in paste or solidified form. As described above, anionic antistatic agents are good in view of the antistatic ability, however since they are prepared mainly in the form of paste or solid anionic antistatic agents are difficult to be quantitatively supplied, further viscous paste sticks on the extruder wall so as to render the uniform blending difficult. Moreover, the blended amount of the agents is thus difficult to be estimated. In case where the anionic antistatic agents in the past or solidified form are heated so as to be used n liquid form, problems may be arise due to the thermal decomposition of the agents. Further, viscosity of the agents may not be decreased sufficiently such that the agent cannot be supplied with a liquid pump. In particular, sodium alkylsulfonate, an anionic antistatic agent, changes its color to olack when heateα and its viscosity does not decrease much, tnerefore, it is nearly impossible to use a sulfonate type antistatic agent sucn as sodium alk lsulfonate alone. There are commercially available anionic agents which have been suitablly processed after or during the preparation which are in the form of liquid or powder not the solidified form or paste. However, articles produced by using such anionic antistatic agents of the liquid or powder form, do not have a satisfactory antistatic property. Further, the supply and variety of such commercially available liquid or powdery form anionic antistatic agents are limited and it is thus difficult to produce a variety of products according to various applications. Most prior art compositions having antistatic properties are produced by a method m which a resm and an antistatic agent are dry-blended in a mixer such as Henshel mixer. However, m such method, the antistatic agent added sticks to the wall of the mixer and thereby the incorporation of the exact amount of the agent into the resm is difficult and non- porous resm such as PMMA cannot well absorb the agent. Therefore, it is difficult to apply such method on real production and it is difficult to incorporate a large amount of the antistatic agent to prepare a master batch. The present invention aims at to provide a new process for the preparation of an antistatic resm composition by melting-blending PMMA which is non-porous and has a relative high melting viscosity with an anionic antistatic agent which has a good antistatic ability. As discussed, such anionic antistatic agent is usually obtained in paste or solidified form which makes the meltmg-blendmg difficult. The inventor of the present invention found surprisingly that when an anionic antistatic agent which is obtained m paste or solidified form is mixed with a nonionic antistatic agent which is in liquid form to prepare a liquid mixture, this liquid mixture can be fed by using a common liquid pump or feeder, further, it was found that tne liquid mixture thus obtained and fed can be uniformly melt-olended and extruded with a non-porous resm such as PMMA. Still Further, the inventor of tne present invention also found that, according to the new method, a large amount of the anionic antistatic agent can be incorporated into the resm by melt-blendmg to give an antistatic resm composition which can be used as a master batch. DISCLOSURE OF INVENTION Therefore, a first object of the present invention is to provide a process for the preparation of an antistatic resm composition, which process comprises mixing and stirring an anionic antistatic agent such as alkali metal alkylsulfonate with a nonionic antistatic agent such as polyalkylene glycol to obtain a liquid mixture of the antistatic agents, said liquid mixture is fed into an extruder at a suitable amount to be uniformly blended with a melted resm to be continuously extruded. According to the present invention, the above-mentioned anionic antistatic agent, which is generally obtained m paste or solidified form, is used directly without any additional process to make them a liquid or powder form. Examples of the anionic antistatic agent include phosphates and sulfonates, preferably an alkali metal alkylsulfonates, more preferably sodium dodecylsulfonate . Examples of the above-mentioned nonionic antistatic agent include polyalkylene glycol such as polyethylene glycol and polypropylene glycol, preferably polyethylene glycol. The molecular weight thereof is preferably between 100 and 500. The mixing ratio of the anionic antistatic agent and the nonionic antistatic agent is such that they can be mixed without separation to form a liquid phase or a phase which can be pumped with a liquid pump. The ratio is generally between 1:1 to 1:9 oy weight. In addition, it is preferable that the liquid mixture of the anionic and nonionic agents nas a viscosity of about 500 cps . There is no special restriction as to the nature of the resins which can be used for the process of the present invention. For the purposes of the process of the present invention, a commonly known non-porous resm, particularly in pellet form is advantageously used. Especially, PMMA can be used. A second object of the present invention is to provide an antistatic resm composition which can be prepared by the process of the present invention. The antistatic resm composition thus prepared can contain an amount of 0.5 to 10 °_ by weight of the antistatic agent based on the total weight of the composition. In general, the amount of the antistatic agent in the composition is preferably about 1 to 3 % by weight. An antistatic resm composition of the present invention in which the content of the antistatic agents is relatively high, for example from 10 to 20 % by weight, can be used as a master batch, which can then be mixed or melt-blended with a resm which does not contains the antistatic agents m an appropriate ratio to give an antistatic resm composition having a relative low content of the antistatic agents, for example 1 to 3 by weight. The preparation of such master batch can enable the mass production of antistatic resm composition. Therefore, a third object of the present invention is to provide a method for using a master batch which is an antistatic resm composition having a relatively high content of the antistatic agent and can be prepared be the process of the present invention. As such, the present invention provides a solution to prior art problem which are due to the using only one type of antistatic agents. Tne present invention provides a synergistic antistatic effect by using as a liquid mixture Doth an anionic antistatic agent such as alkali metal alkylsulfonate and a nonionic antistatic agent such as polyethylene or polypropylene. There is no particular restriction as to the method of mixing the anionic antistatic agent and the nonionic antistatic agent. Preferably, they are mixed at a temperature of 30 to 100 °C under stirring. When the temperature is below 30 °C, they cannot be well mixed and may be separated and when the temperature is above 100 °C, a foam and/or color change m the mixture may occur. As discussed earlier, as the nonionic antistatic agent, polyethylene glycol, especially polyethylene glycol having the molecular weight of 100 to 500 can be used. As the anionic antistatic agent, alkali metal alkylsulfonates can be used. In this regard, polyethylene glycol as a nonionic antistatic agent generally has a better thermal stability but the less antistatic ability than a cationic or anionic antistatic agent. When used alone, m order to impart antistatic ability, more than 10 parts by weight of polyalkylene glycol (nonionic antistatic agent) should be added, which is more than 5 times of the amount (0.2 to 2 parts by weight) of other type antistatic agents. However, if such a large amount of polyethylene glycol is added to the resm, the surface of the resulted res or products becomes slick and its thermal resistance is deteriorated. On the other hand, alkali metal alkylsulfonate as an anionic antistatic agent has a good balance of antistatic ability and thermal stability, but is obtained in paste or solidified form having high viscosity. Further, alkali metal alkylsulfonate may change the colour of the resm to black, and thus when used alone with PMMA which is transparent, there is a high probability that the colour of the resm composition wi l l change . The present invention, however, provides a novel method which produces continuously an uniform resin composition with antistatic property can be continuously prepared by mixing polyethylene glycol and alkali metal alkylsulfonate to prepare a liquid mixture; said liquid mixture is quantitatively introduced into the barrel of an extruder with a liquid pump to be blended or mixed with a nonporous pellet or granular resin such as PMMA and to be extruded, According to an variant of the present invention, the composition can be naturally used for an injection molding. The antistatic resin composition thus prepared shows an excellent antistatic effect with no significant deterioration in its physical properties such as impact strength, flexible strength, elastic modulus and tensile strength. Thus it can be useful as raw material for the production of various articles in which an antistatic property is needed. BEST MODE FOR CARRYING OUT THE INVENTION Below, the present invention is illustrated by examples and comparative examples, which do not limit the scope of the invention . Examples 1 to 3 and Comparative Examples 1 to 3 Preparation of resin composition and test piece Sodium dodecylsulfonate as an anionic antistatic agent and polyethylene glycol (Mw=400) as a nonionic antistatic agent are mixed and stirred in a bath preheated to a temperature of 50 °C to 200 °C in a weight ratio described in below Table 1 to prepare a liquid mixture. When the viscosity of the mixture reaches about 500 cps the mixture is quantitatively introduced at a ratio shown in Table 1 with a liquid pump into an extruder to be blended with 100 parts by weight of PMMA. During the introduction, the temperature of the mixture is maintained between 80 to 90 °C to maintain tne flowability of the mixture of the agents. The blended mixture is continuously extruded by the extruder into sheet, pellet, granule or the like. Test A sheet prepared by a Bravender Single Extruder T-Die is cut in a size of a width of 5 cm and a length of 5 cm, which is conditioned at 23 °C and 50> RH m accordance with ASTM D 618-61. By using the prepared sheet as test piece, the surface resistance is determined m accordance with ASTM D 257 by using a surface resistance measuring equipment (Ultra Resistance Meter, Adventest, Japan) . The result is shown m Table 1. Table 1 Example 4 By the same procedure as Example 1, a master batch is prepared except that the content of the antistatic agents is 15 parts by weight based on the total weight of the antistatic resm composition. 8.2 and 28.7 parts by weight of the master batch is respectively blended w th 100 parts by weight of PMMA to prepare antistatic resm compositions having 1 and 3 parts by weight of the antistatic agents, respectively. The compositions thus obtained is extruded into sheets. The surface resistance ( Q. /square) of the sheets thus prepared is 2.0xl0 : and l.lxl0 :: , respectively. INDUSTRIAL APPLICABILITY According to the present invention an antistatic resin composition having a good balance of the antistatic property and thermal stability can be economically and conveniently prepared by melt-blending a resin such as PMMA with a liquid mixture of an anionic antistatic agent such as alkali metal alkylsulfonate and a nonionic antistatic agent such as polyethylen glycol.

Claims: WHAT IS CLAIMED : 1. A process for the preparation of an antistatic resm composition, which comprises mixing an anionic antistatic agent such as an alkali metal alkylsulfonate and a nonionic antistatic agent such as a polyalkylene glycol under stirring to prepare a liquid mixture of the antistatic agents, feeding the mixture into an extruder in a suitable amount to be uniformly blended with a melted resm to be extruded them. 2. The process according to claim 1, wherein the melted resm is PMMA (polymethyl methacrylate) . 3. The process according to claim 1, wnerem the polyalkylene glycol is a polyethylene glycol. 4. The process according to claim 1, 2 or 3, wherein the resm is in pellet form. 5. The process according to claim 1, 2 or 3, wherein alkali metal alkylsulfonate and polyalkylene glycol is mixed m a weight ratio of between 1:1 and 1:8-9. 6. An antistatic resin composition prepared by a process according to any one of claims 1 to 5. 7. Use of the antistatic resm composition according to claim 6 as master batch. 8. A composition of antistatic agents comprising an alkali metal alkylsulfonate and a polyalkylene glycol, wherein the alkali metal alkylsulfonate and the polyalkylene glycol is mixed m a weight ratio of between 1:1 and 1:8-9.

Inventors: PARK CHAN DONG, PARK, CHAN, DONG
Applicants: ATOCHEM ELF SA, ELF ATOCHEM KOREA LTD, PARK CHAN DONG, ELF ATOCHEM KOREA, LTD., ELF ATOCHEM S.A., PARK, CHAN, DONG
Application year: 1998
Main classification: C09K3
IPC codes: C08J3, C08K5, C08L33, C08L101, C09K3