Abstract:
A synthetic chloroprene rubber adhesive composition which contains carboxylated synthetic chloroprene rubber for the main ingredient thereof and further contains chlorinated polypropylene and/or a chlorinated polypropylene derivatives. The adhesive composition can strongly bond various components to polypropylene used for a speaker frame, etc. unlike conventional synthetic chloroprene rubber adhesives which have insufficient adhesion strength in this application.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a synthetic chloroprene rubber adhesive composition, and, more particularly, the invention relates to a synthetic chloroprene rubber adhesive composition for bonding components, at least one of which is formed with polypropylene, and a process for producing a speaker by using the adhesive composition. 
     BACKGROUND OF THE INVENTION 
     Conventionally, a chrome plated steel plate is used for a speaker frame, and various speaker components are bonded to the speaker frame by using an adhesive. 
     A vibration plate (hereinafter referred to as a cone) is bonded to the speaker frame via an edge. 
     When the edge is formed with a compression molded foamed urethane or an ethylene-vinyl-acetate-copolymer to increase mechanical strength, a water base synthetic chloroprene rubber adhesive or a water base SBR (styrene-butadiene-copolymer-rubber) adhesive are used for bonding the edge to the frame because those edge materials are soluble or swelled in a solvent based adhesive. 
     On the other hand, when the edge is formed with a kind of rubber such as natural SBR, EPDM (ethylene-propylene-diene-rubber) or the like, a solvent base synthetic chloroprene rubber adhesive, a water base synthetic chloroprene rubber adhesive, a solvent base SBR adhesive or a water base SBR adhesive is used. 
     In general, the adhesive is selected taking adhesion, influence on the materials, cost and production efficiency into account. 
     When the cone is directly bonded to the speaker frame the adhesive is selected in the same manner as described above in general. 
     When a damper is bonded to the speaker frame, a solvent base synthetic chloroprene rubber adhesive is generally used because the damper is formed with phenol-resin-impregnated cloth. 
     For bonding a top plate to the speaker frame, a solvent base synthetic chloroprene rubber adhesive is generally used because the top plate is formed with a metal plate. 
     In recent years, however, from the viewpoint of recycling for the protection of environment and for decreasing the weight of a speaker, polypropylene has come to be used for the speaker frame. In this case, the conventional adhesives described above have not sufficient adhesion to the polypropylene speaker frame, i.e., the conventional adhesives have not sufficient bonding strength for producing a speaker having a polypropylene frame. 
     The present invention aims to provide a synthetic chloroprene rubber adhesive composition that is superior in bonding various components to the components formed with polypropylene as described above, also aims to provide a process for producing a speaker by using the adhesive composition. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a synthetic chloroprene rubber adhesive composition which contains carboxylated synthetic chloroprene rubber for the main ingredient thereof and further contains chlorinated polypropylene and/or chlorinated polypropylene derivatives. 
     The above adhesive composition shows improvement in adhesion and durability against heat compared with conventional adhesives in bonding various components to polypropylene, which is resulted from the synergistic effect of carboxylated synthetic chloroprene rubber selected from the varieties of synthetic chloroprene rubber and a kind of chlorinated polypropylene, i.e., chlorinated polypropylene and/or the derivative thereof, which are(is) used for the additive(s) of the adhesive composition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a cross sectional view of a speaker the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following are descriptions of a synthetic chloroprene rubber adhesive composition in the present invention and a process for producing a speaker using the same. 
     First, the structure of the speaker, which is described in the background of the invention, is described hereinafter in more detail, referring to  FIG. 1 . 
     A cone  2  which is formed with resin impregnated natural pulp or the like is bonded to a speaker frame  1  which is formed by molding polypropylene, via an edge  3  which is formed with compression molded foamed urethane or an ethylene-vinyl-acetate-copolymer to increase mechanical strength. The edge  3  is formed with a kind of rubber such as natural SBR, EPDM or the like also. The inner annular end of the cone  2  is bonded to a voice coil  4 . 
     The outer annular end of a damper  5  which is formed with resin impregnated cloth is bonded to the speaker frame  1 , and, the inner annular end of the damper  5  is bonded to the voice coil  4 . 
     A ring-shaped top plate  6  which is bonded to the bottom of the speaker frame  1 , a ring-shaped magnet  7  and a bottom plate  8  having a center pole compose a magnetic circuit  9 . In a gap between the center pole of the bottom plate  8  and the top plate  6 , a magnetic gap  9   a  is formed. The coiled portion of the voice coil  4  is movably inserted into the gap. 
     An adhesive  10 , which is a synthetic chloroprene rubber adhesive composition containing carboxylated synthetic chloroprene rubber for the main ingredient thereof and further containing chlorinated polypropylene, is applied between the speaker frame  1  and the other speaker component parts such as the edge  3 , the damper  5 , the top plate  6 , etc. respectively for tenaciously bonding between the speaker frame  1  formed with polypropylene and the other speaker components. 
     In a speaker in which the edge  3  is not used, the adhesive  10  is applied between the cone  2  and the speaker frame  1  for bonding between these. 
     Next, a synthetic chloroprene rubber adhesive composition, which is used for bonding various speaker components to the speaker frame formed with polypropylene, is described hereinafter referring to Table 1. 
     In Table 1, test examples 2 through 4 show adhesive compositions in the exemplary embodiment of the present invention, and test example 1 shows an adhesive composition in a conventional synthetic chloroprene rubber adhesive. 
     
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 (PHR) 
               
             
          
           
               
                   
                 Test example 
               
             
          
           
               
                 Ingredient 
                 1 
                 2 
                 3 
                 4 
               
               
                   
               
             
          
           
               
                 Neoprene AD (synthetic chloroprene rubber 
                 100 
                   
                   
                   
               
               
                 used as adhesive in general) 
               
               
                 Neoprene AF (carboxylated synthetic 
                   
                 100 
                 100 
                 100 
               
               
                 chloroprene rubber) 
               
               
                 BHT (antioxidant) 
                 2 
                 2 
                 2 
                 2 
               
               
                 Zinc oxide 
                 5 
                 5 
                 5 
                 5 
               
               
                 Magnesium oxide 
                 8 
                 8 
                 8 
                 8 
               
               
                 tert-Butylphenol resin 
                 60 
                 60 
                 60 
                 60 
               
               
                 Terpene-phenol resin 
                 10 
                 10 
                 10 
                 10 
               
               
                 Chlorinated polypropylene 
                 20 
                 20 
                   
                 10 
               
               
                 Hydroxyethyl-acrylate-grafted 
                   
                   
                 20 
                 20 
               
               
                 chlorinated polypropylene 
               
               
                 Organic solvent composed of toluene (4), 
                 465 
                 465 
                 465 
                 455 
               
               
                 ethyl acetate (3) and normal hexane (3) 
               
               
                   
               
             
          
         
       
     
     The adhesive compositions of the test examples in Table 1 are prepared in such a manner that the necessary volume of the organic solvent is poured into a vessel, then tert-butylphenol resin and terpene-phenol resin are put into the same vessel and these are dissolved under room temperature. In the other process, synthetic chloroprene rubber, antioxidant, zinc oxide and magnesium oxide are kneaded using a roll mill, then the kneaded lump is cut to small pieces, then these are put into the above vessel. Then, stirring is performed on the materials in the vessel for 8 to 10 hours under room temperature until all of these dissolve completely. 
     Then additive(s) such as chlorinated polypropylene and/or the like are/is put into the vessel, and the additive(s) are/is dissolved by stirring under the temperature of 20–40° C. Thus the adhesive compositions of Table 1 are obtained. The viscosity of the adhesive compositions is adjustable by changing the volume of the organic solvent. 
     Table 2 shows the test results of the adhesion strength of the adhesive compositions of the test examples 1 through 4 of Table 1 under the conditions of (a) after 48 hours under normal condition, (b) after heat aging and (c) under high temperature. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 (N/25 mm) 
               
             
          
           
               
                   
                 adhesion strength 
                   
               
               
                   
                 (180° peeling off) 
               
             
          
           
               
                 Test condition 
                 1 
                 2 
                 3 
                 4 
                 Test method 
               
               
                   
               
               
                 Adhesion after 48 hours 
                 25 
                 35 
                 42 
                 39 
                 JIS K6854 
               
               
                 under normal condition 
               
               
                 Adhesion after heat aging 
                 18 
                 42 
                 45 
                 45 
                 JIS K6854 
               
               
                 (70° C. × 96 hours) 
               
               
                 Adhesion under high 
                 20 
                 30 
                 35 
                 32 
                 JIS K6854 
               
               
                 temperature (80° C.) 
               
               
                   
               
             
          
         
       
     
     The test pieces used in the test are a polypropylene plate and a polypropylene film, and, 150 grams per square meter of the respective adhesive compositions of Table 1 is applied by using a brush on the respective bonding surfaces. After keeping 15 minutes in the room of temperature 23° C. and humidity 60%, the two test pieces are put together and pressed by a hand roller for bonding between these. 
     The adhesive composition of the test example 1 of Table 2, in which the conventionally and generally used synthetic chloroprene rubber is used, shows the lowest adhesion comparing with the adhesive compositions of the other test examples in all test conditions of normal condition, heat aging and high temperature. 
     On the other hand, the test examples of 2 through 4 of Table 2, in which the carboxylated synthetic chloroprene rubber is used for the adhesive compositions, show higher values of adhesion strength in all test conditions of normal condition, heat aging and high temperature. The test example 3, in which only hydroxyethyl-acrylate-grafted chlorinated polypropylene is added to the additive, shows the highest adhesion strength in all of the test conditions. 
     Table 3 shows the basic composition of the synthetic chloroprene rubber adhesive composition of the present invention, which is obtained from the above test results. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 (PHR) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Carboxylated synthetic chloroprene rubber 
                 100  
               
               
                 Antioxidant 
                 2 
               
               
                 Magnesium oxide 
                 8 
               
               
                 Zinc oxide 
                 5 
               
               
                 Reinforcing resin 
                 10–100 
               
               
                 Tackifier 
                 0–10 
               
               
                 Inorganic filler 
                 0–10 
               
               
                 Chlorinated polypropylene, or, Acrylic-monomer-and- 
               
               
                 methacrylic-monomer-grafted chlorinated polypropylene 
                 1–30 
               
               
                 Organic solvent 
                 as required 
               
               
                   
               
             
          
         
       
     
     The above composition is an example and not limited thereto. For example, the volume of the antioxidant, magnesium oxide, zinc oxide and organic solvent can be adjusted according to necessity. 
     INDUSTRIAL APPLICABILITY 
     As described above, the synthetic chloroprene rubber adhesive composition of the present invention uses carboxylated synthetic chloroprene rubber selected from the varieties of synthetic chloroprene rubber, also uses a kind of chlorinated polypropylene, i.e., chlorinated polypropylene and/or the derivative thereof for the additive(s) of the adhesive composition, which creates a synergistic effect for increasing adhesion to the polypropylene and durability against heat. Further details of the effects are as follows: 
     (1) When the chlorinated polypropylene derivative is acrylic-monomer-and-methacrylic-monomer-grafted chlorinated polypropylene, and, when the volume of the chlorinated polypropylene and/or the chlorinated polypropylene derivative contained in the adhesive composition is adjusted to be 1–30 parts by weight per 100 parts in weight of carboxylated synthetic chloroprene rubber, an adhesive composition having a high temperature adhesion strength without loosing a good adhesion to the polypropylene, can be obtained. 
     (2) In a process for producing a speaker having a speaker frame formed with polypropylene, a process for producing a speaker which results in a good adhesion and superior durability against heat can be obtained. In which process, various speaker components are bonded to the speaker frame using the synthetic chloroprene rubber adhesive composition containing carboxylated synthetic chloroprene rubber for the main ingredient thereof and further containing chlorinated polypropylene and/or a chlorinated polypropylene derivative. The good adhesion and superior durability against heat is resulted by using carboxylated synthetic chloroprene rubber for the main ingredient and chlorinated polypropylene and/or a chlorinated polypropylene derivative for the additive(s) of the adhesive composition. 
     (3) When the chlorinated polypropylene derivative is acrylic-monomer-and-methacrylic-monomer-grafted chlorinated polypropylene and when the volume of the chlorinated polypropylene and/or the chlorinated polypropylene derivative contained in the adhesive composition is adjusted to be 1–30 parts by weight 100 parts in weight of carboxylated synthetic chloroprene rubber, a process for producing a speaker, in which various speaker components are more strongly bonded under high temperature to the speaker frame formed with polypropylene, can be obtained.