Thermoplastic resin composition
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thermoplastic resin composition which has an excellent antistatic property and heat resistance. 
     2. Description of the Related Art 
     An acrylic resin is widely used as a molding material having good heat resistance and mechanical properties. 
     While the acrylic resin has a good electrical insulating property, it is easily statically charged so that the surface of a molded article tends to have deteriorated gloss or poor appearance. Thereby, the commercial value of the molded article is greatly reduced. 
     To overcome the above problem, it was proposed to add an antistatic agent to the acrylic resin (see Japanese Patent Kokai Publication No. 197552/1990). 
     Even though the antistatic property may be imparted by the addition of an antistatic agent, the outstanding heat resistance of the acrylic resin may decrease drastically. 
     For this reason, the antistatic agent is used in an amount as small as possible. However, the addition of such a small amount of the antistatic agent may not impart the antistatic property to the acrylic resin satisfactorily and thus a acrylic resin molded article with a satisfactory antistatic property cannot be obtained. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a thermoplastic resin composition having a satisfactory antistatic property together with heat resistance. 
     According to the present invention, there is provided a thermoplastic resin composition comprising (A) 100 parts by weight of a glutarimide copolymer which comprises 5 to 100% by mole of glutarimide units and 95 to 0% by mole of ethylenically α,β-unsaturated monomer units, and (B) 0.3 to 10 parts by weight of an alkali metal alkylsulfonate of the following formula: 
     
         R--SO.sub.3 X                                              (I) 
    
     wherein R represents a C 8  -C 22  alkyl group, and X represents an alkali metal. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The glutarimide unit of the glutarimide copolymer to be used in the present invention may be represented by the following formula: ##STR1## wherein R 1  and R 2  independently represent hydrogen atoms or methyl groups, and R 3  represents a hydrogen atom or a C 1  -C 20  aliphatic, aromatic or alicyclic hydrocarbon group. 
     When R 3  is a hydrogen atom or a methyl group, the composition shows particularly outstanding heat resistance. When R 3  is a cyclohexyl group, the composition has low hygroscopicity. 
     The content of the glutarimide units in the glutarimide copolymer (A) is from 5 to 100% by mole, preferably at least 20% by mole. If the content of the glutarimide units is less than the above lower limit, the composition may not have sufficient heat resistance. 
     Examples of the ethylenically α,β-unsaturated monomer units of the glutarimide copolymer are monomer units derived from, for example, (meth)acrylate esters, (meth)acrylic acid, styrene, α-methylstyrene, vinyltoluene, chlorostyrene, acrylonitrile and so on. 
     Specific examples of the (meth)acrylate esters are methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert.-butyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate unit and so on. 
     These monomer units may be used independently or as a mixture of two or more of them. 
     The content of such monomer units in the glutarimide copolymer is from 95 to 0% by mole. 
     The weight average molecular weight of the glutarimide copolymer is normally from 40,000 to 500,000, preferably from 40,000 to 200,000. 
     If the molecular weight is lower than 40,000, the molded article of the composition will have poor mechanical strength. If it exceeds 500,000, molding workability will suffer. 
     To produce the glutarimide copolymer (A) of the present invention, any of the known methods such as the methods described in Japanese Patent Publication No. 38404/1985 and Japanese Patent Kokai Publication No. 89705/1987 can be used. 
     In one method, a homopolymer or a copolymer comprising (meth)acrylic acid or a (meth)acrylate as the ethylenically α,β-unsaturated monomer unit is heated melted and then an imidizing agent is added, mixed, and reacted to obtain the glutarimide copolymer. 
     Examples of the imidizing agent are ammonia, methylamine, ethylamine, butylamine, hexylamine, octylamine, nonylamine, decylamine, benzylamine, cyclohexylamine, aniline, halogenated aniline, urea, dimethylurea and so on. 
     As the alkali metal alkylsulfonate (B) to be used in the present invention, one having 8 to 22, preferably 12 to 18, carbon atoms in the alkyl group is preferred. When the carbon number is less than 8 or more than 22, the surface of the molded article tends to be sticky. 
     As the alkaline metal, lithium, sodium and potassium are preferred. 
     The resin composition of the present invention comprises 100 parts by weight of the glutarimide copolymer (A) and 0.3 to 10 parts by weight, preferably 0.5 to 8 parts by weight, of the alkali metal alkylsulfonate (B). 
     If the amount of alkali metal alkylsulfonate (B) is less than 0.3 weight part, the composition may not have a sufficient antistatic property. On the other hand, if it exceeds 10 parts by weight, the surface of the molded article will be sticky. 
     In addition to the above components, the resin composition may contain at least one other antistatic agent such as glycerin aliphatic acid esters, aliphatic acid alkylene oxide adducts, glycerin aliphatic acid ester alkylene oxide adducts, alkali metal alkylbenzenesulfonates, polyethyleneglycol-aliphatic acid ester-alkali metal sulfonate and so on. 
     To prepare the composition from the copolymer (A) and the alkali metal alkylsulfonate (B), any of the conventional methods may be used. 
     For example, a method comprising mixing solutions of each of the components and then evaporating off the solvent, or pouring the mixture into a non-solvent to precipitate the product or a method comprising blending the components in a molten state may be employed. To melt and knead the components, a conventional single-screw or twin-screw extruder, or kneader, may be used. Alternatively, direct blending during a melt-processing operation such as injection molding or extrusion molding process can be used also. 
     The thermoplastic resin composition of the present invention may contain known additives, for example, an antioxidant such as a hindered phenol type antioxidant, a phosphorus base antioxidant or a sulfur base antioxidant; an anti-weathering agent such as a ultraviolet-light absorber or a hindered amine type light stabilizer; a lubricant; a flame retardant; a coloring agent; or a pigment. Further, according to the final use of the composition, reinforcing fibers such as glass fibers and so on, and inorganic fillers and so on may be added. 
     The antistatic thermoplastic resin composition of the present invention not only has an outstanding antistatic property, but also improved heat resistance, including thermal deformation temperature. Thus, the thermoplastic resin composition of the present invention can find various applications that utilize its properties such as hoods of lighting equipment exterior displaying materials, and display material for information and guides, and so on. 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     The present invention will be explained further in detail by following Examples, in which parts are by weight unless otherwise indicated. 
     The following test methods were used in the: 
     Thermal deformation temperature 
     The test is conducted with a load of 18.6 kg/cm 2 , according to ASTM D-648. 
     Inherent surface resistivity 
     After conditioning a test sample for 3 days at 23° C. and 50% R.H., the resistivity is measured in the same atmosphere with a Super Insulation meter (Model SM-10E, a product of Toa Denpa Kogyo Kabushikikaisha). 
     Half life of static voltage 
     After conditioning a test sample for 3 days at 23° C. and 50%R.H., a voltage (10 KV) is applied on the test sample with a static onestometer (a product of Shishido Shokai Kabushikikaisha). Then, the applied voltage is reduced to zero, and the time required for the voltage charge to drop down to half of its original value is measured. 
     Surface condition of molded product 
     The condition of the surface of the molded article is examined by touching the surface with the fingers, and evaluated as &#34;Good&#34; or &#34;Bad&#34;. 
     Examples 1-10 and Comparative Examples 1-3 
     Glutarimide copolymer (KAMAX®T-240 manufactured by Rohm &amp; Haas, the content of the glutarimide units =75% by mole) was compounded with various types of metal alkylsulfonates and other antistatic agents in the amounts shown in the following Table and kneaded at 240° C. for 5 minutes at a rotor speed of 100 rpm in a Labo-Plast Mill (a product of Toyo Seiki Seisakusho Kabushikikaisha). 
     The resulting blend was molded using a thermal compression molding device at a molding temperature of 240 ° C. a molding pressure of 150 kg/cm 2  to form a flat plate having a thickness of 3 mm. Test samples were cut out from the plate, and their properties were evaluated. 
     The results are shown in the Table. 
     Comparative Example 4 
     Experiments were carried out in the same manner as in Example 5 except using, as the glutarimide copolymer, a general purpose methacrylate resin (Sumipex-B-MHO, a product of Sumitomo Chemical Co. Ltd.), and the properties were evaluated. 
     The results are shown in the Table. 
     
                                           TABLE                                   
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                            Thermal                                       
                                   Inherent                               
                                           Half life                      
                                                Surface                   
                   Other antistatic                                       
                            deformation                                   
                                   surface of charge                      
                                                condition                 
Alkali metal alkylsulfonate                                               
                   agent    temperature                                   
                                   resistivity                            
                                           voltage                        
                                                of molded                 
Compound (parts)   Compound (parts)                                       
                            (°C.)                                  
                                   (ohm)   (seconds)                      
                                                product                   
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Example                                                                   
No.                                                                       
1    Na 1-decanesulfonate (5)                                             
                   --       115    1.4 × 10.sup.13                  
                                           &gt;120 Good                      
2    Na Cetylsulfonate (0.5)                                              
                   --       109    1.3 × 10.sup.13                  
                                           &gt;120 Good                      
3    Na Cetylsulfonate (1)                                                
                   --       109    2.2 × 10.sup.12                  
                                            41  Good                      
4    Na Cetylsulfonate (2)                                                
                   --       110    3.6 × 10.sup.10                  
                                            1   Good                      
5    Na Cetylsulfonate (5)                                                
                   --       109    1.5 × 10.sup.9                   
                                           &lt;1   Good                      
6    Na Cetylsulfonate (8)                                                
                   --       108    1.1 × 10.sup.9                   
                                           &lt;1   Good                      
7    Na Cetylsulfonate (3)                                                
                   Polyethylene-                                          
                            108    6.7 × 10.sup.11                  
                                            3   Good                      
                   glycol acetate (2)                                     
                   Na sulfonate                                           
8    Na Cetylsulfonate (3)                                                
                   Na lauryl-                                             
                            110    1.8 × 10.sup.10                  
                                           &lt;1   Good                      
                   benzene (2)                                            
                   sulfonate                                              
9    Na Cetylsulfonate (3)                                                
                   Stearic acid (2)                                       
                            106    3.3 × 10.sup.10                  
                                           &lt;1   Good                      
                   monoglyceride                                          
10   Na 1-Octadecylsulfonate (5)                                          
                   --       109    9.5 × 10.sup.11                  
                                            52  Good                      
Comp.                                                                     
Example                                                                   
No.                                                                       
C. 1 Na 1-Hexanesulfonate (5)                                             
                   --       114    1.8 × 10.sup.13                  
                                           &gt;120 Bad                       
C. 2 Na Cetylsulfonate (0.2)                                              
                   --       112     2.0 × 10.sup.14 &lt;               
                                           &gt;120 Good                      
C. 3 Na Cetylsulfonate (15)                                               
                   --       106    7.5 × 10.sup.8                   
                                           &lt;1   Bad                       
C. 4 Na Cetylsulfonate (5)                                                
                   --        81    2.0 × 10.sup.9                   
                                           &lt;1   Good                      
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