Abstract:
Disclosed is a fluoroelastomer composition comprising (1) a fluoroelastomer which comprises tetrafluoroethylene, a perfluoro (C 1 -C 5  alkyl vinyl ether) or a perfluoro (C 3 -C 11  (alkoxyalkyl) vinyl ether) and a cyano group-containing perfluorovinyl ether, (2) a hydrotalcite compound, (3) a crosslinking agent and (4) carbon black. The fluoroelastomer composition has excellent metal corrosion inhibition properties, and particularly, this composition generates only small amount of a corrosive material when exposed to high temperatures.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a fluoroelastomer composition, and more particularly to a fluoroelastomer composition having excellent metal corrosion inhibition properties.  
         BACKGROUND OF THE INVENTION  
         [0002]    In Japanese Patent Laid-Open Publication No. 120144/1996, there is described a fluoroelastomer composition comprising a terpolymer of tetrafluoroethylene, a perfluoro (alkyl vinyl ether) and a cyano group-containing perfluorovinyl ether represented by the formula CF 2 =CFO(CF 2 ) n OCF(CF 3 )CN (n: 2-5) and as a crosslinking agent a bis(aminophenyl) compound represented by the following formula:  
                         
 
           [0003]    wherein A is an alkylidene group of 1 to 6 carbon atoms or a perfluoroalkylidene group of 1 to 10 carbon atoms, and X and Y are each a hydroxyl group or an amino group.  
           [0004]    In Japanese Patent Laid-Open Publication No. 31284/1997, there is described a fluoroelastomer composition comprising a terpolymer of tetrafluoroethylene, a perfluoro (alkyl vinyl ether) and a cyano group-containing perfluorovinyl ether and as a crosslinking agent a bisamidoxime compound represented by the following formula:  
                         
 
           [0005]    wherein n is an integer of 1 to 10.  
           [0006]    In this connection, it is preferable to add carbon black to the crosslinking fluoroelastomer compositions, whereby molded articles of the compositions can be enhanced in the mechanical properties.  
           [0007]    Molded products produced from a crosslinking fluoroelastomer composition comprising a terpolymer of tetrafluoroethylene, a perfluoro (C 1 -C 5  alkyl vinyl ether) and a cyano group-containing perfluorovinyl ether, a crosslinking agent and carbon black generally have very excellent heat resistance, solvent resistance and mechanical properties, so that they are used for chemical industry, aerospace industry, semiconductor industry, etc.  
           [0008]    However, when the above fluoroelastomer molded products are in contact with metals, the contact areas of the metals with the molded products are sometimes corroded depending upon the conditions.  
           [0009]    Especially under the high-temperature conditions, the molded products undergo thermal degradation to generate a corrosive material, and the corrosive material sometimes corrodes the metal surfaces.  
           [0010]    To a fluoroelastomer, metallic oxides, such as calcium hydroxide, magnesium oxide, zinc oxide and lead oxide, are generally added in order to inhibit generation of a corrosive material during the processing stage or the practical use.  
           [0011]    However, even if the metallic oxides are added to the fluoroelastomer, corrosion of metals during the practical use cannot be inhibited. Moreover, calcium hydroxide, magnesium oxide and zinc oxide sometimes induce deterioration of solvent resistance such as hot water resistance.  
         OBJECT OF THE INVENTION  
         [0012]    It is an object of the present invention to provide a fluoroelastomer composition having excellent metal corrosion inhibition properties, and more particularly, it is an object of the invention to provide a fluoroelastomer composition which generates only small amount of a corrosive material when it is exposed to high temperatures.  
         SUMMARY OF THE INVENTION  
         [0013]    The fluoroelastomer composition according to the invention comprises:  
           [0014]    (1) a fluoroelastomer comprising:  
           [0015]    (i) tetrafluoroethylene,  
           [0016]    (ii) a perfluoro (C 1 -C 5  alkyl vinyl ether) or a perfluoro (C 3 -C 11  (alkoxyalkyl) vinyl ether), and  
           [0017]    (iii) a cyano group-containing perfluorovinyl ether,  
           [0018]    (2) a hydrotalcite compound,  
           [0019]    (3) a crosslinking agent, and  
           [0020]    (4) carbon black. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    The fluoroelastomer composition according to the invention is described in detail hereinafter.  
         [0022]    The fluoroelastomer for use in the invention is a terpolymer of tetrafluoroethylene, a perfluoro(C 1 -C 5  alkyl vinyl ether) or a perfluoro (C 3 -C 11  (alkoxyalkyl) vinyl ether) and a cyano group-containing perfluorovinyl ether.  
         [0023]    As the fluoroelastomer, preferably used is one obtained by copolymerizing 50 to 75% by mol, preferably 60 to 75% by mol, of the tetrafluoroethylene, 49.8 to 25% by mol, preferably 39.8 to 25% by mol, of the perfluoro (alkyl vinyl ether) or the perfluoro(alkoxyalkyl vinyl ether), and 0.2 to 5% by mol, preferably 0.5 to 2% by mol, of the cyano group-containing perfluorovinyl ether.  
       Perfluoro (C 1 -C 5  alkyl vinyl ether), Perfluoro (C 3 -C 11  (alkoxyalkyl) vinyl ether)  
       [0024]    Examples of the perfluoro (C 1 -C 5  alkyl vinyl ethers) used herein include perfluoro (methyl vinyl ether), perfluoro (ethyl vinyl ether) and perfluoro (propyl vinyl ether). Of these, perfluoro (methyl vinyl ether) is preferably employed.  
         [0025]    Examples of the perfluoro (C 3 -C 11  (alkoxyalkyl) vinyl ethers) include compounds represented by the following formulas. The number of carbon atoms represented by C 3 -C 11  means a sum of carbon atoms in a group bonded to the vinyl ether group (CF 2 =CFO).  
                                                       CF 2 ═CFOCF 2 CF(CF 3 )OC n F 2n+1     (n: 1-5)           CF 2 ═CFO(CF 2 ) 3 OC n F 2n+1     (n: 1-5)           CF 2 ═CFOCF 2 CF(CF 3 )O(CF 2 O) m C n F 2+1     (n: 1-5, m: 1-3)           CF 2 ═CFO(CF 2 ) 2 OC n F 2n+1     (n: 1-5)                      
 
       Cyano group-containing perfluorovinyl ether  
       [0026]    The cyano group-containing perfluorovinyl ether provides crosslinked site unit, and for example, a compound represented by the following formula is employed.  
                                                       CF 2 ═CFO(CF 2 ) n OCF(CF 3 )CN   (n: 2-4)                      
 
         [0027]    Other examples employable in the invention include:  
         [0028]    a compound represented by the following formula:  
                                                       CF 2 ═CFO(CF 2 ) n CN   (n: 2-12)                      
 
         [0029]    (that is described in U.S. Pat. No. 3,546,186);  
         [0030]    a compound represented by the following formula:  
                                                       CF 2 ═CFO(CF 2 CF(CF 3 )O) m (CF 2 ) n CN   (n: 2, m: 1-5)                      
 
         [0031]    (that is described in U.S. Pat. No. 4,138,426);  
         [0032]    a compound represented by the following formula:  
                                                       CF 2 ═CFO(CF 2 CF(CF 3 )O) m (CF 2 ) n CN   (n: 1-4, m: 1-2)                      
 
         [0033]    (that is described in U.S. Pat. No. 4,281,092);  
         [0034]    and  
         [0035]    a compound represented by the following formula:  
                                                       CF 2 ═CFO(CF 2 CF(CF 3 )O) n CF 2 CF(CF 2 )CN   (n: 0-4)                      
 
         [0036]    (that is described in U.S. Pat. No. 3,852,326 and U.S. Pat. No. 3,933,767).  
       Hydrotalcite compound  
       [0037]    The hydrotalcite compound is a compound represented by the formula (Mg) x (R) y (OH) z CO 3 ·nH 2 O (R: Al, Cr or Fe, x: 4-6, y: 2, z: 12-18, n:0-4)  
         [0038]    As the hydrotalcite compound, a compound represented by the formula Mg 4.5 Al 2 (OH) 13 CO 3 ·3.5H 2 O is preferably employed.  
         [0039]    A compound obtained by calcining the above compound to remove water of crystallization is also employable.  
         [0040]    The hydrotalcite compound is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the fluoroelastomer.  
         [0041]    If the amount of the hydrotalcite compound is too small, satisfactory metal corrosion inhibition properties cannot be obtained. If the amount thereof is too large, deterioration of heat resistance of the fluoroelastomer composition is induced.  
       Crosslinking agent  
       [0042]    As the crosslinking agent, a compound represented by the following formula (I) or (II) is employed.  
                         
 
         [0043]    wherein Y is a C 1 -C 6  alkylidene group, a C 1 -C 10  perfluoroalkylidene group, a —SO 2 — group, an —O— group, a —C(=O)— group or a carbon-carbon bond to directly bond two benzene rings, and X is a hydroxyl group or an amino group.  
                         
 
         [0044]    wherein n is an integer of 1 to 10.  
         [0045]    A compound represented by the following formula (III) or (IV) is also employable.  
                         
 
         [0046]    wherein R 2  is H or NH 2 , and n is an integer of 1 to 10.  
         [0047]    For example, there can be mentioned compounds represented by the following formulas.  
                         
 
         [0048]    In the above formulas, n is an integer of 1 to 10.  
                         
 
         [0049]    wherein R 3  is OH or H, and R 4  is H or NH 2 .  
         [0050]    For example, there can be preferably mentioned compounds represented by the following formulas.  
                         
 
       Carbon black  
       [0051]    As the carbon black, carbon black of N-110 to N-990 is employable in the invention, and the carbon black is used in an amount of 1 to 30 parts by weight, preferably 2 to 20 parts by weight, based on 100 parts by weight of the fluoroelastomer.  
         [0052]    To the fluoroelastomer composition containing the above components as essential components, other components such as a processing aid can be appropriately added if necessary.  
         [0053]    The composition can be prepared by, for example, mixing the above components at a temperature of 20 to 100° C., preferably 30 to 80° C., using a two-roll mill.  
         [0054]    The composition can be molded into a desired shape such as a shape of o-ring by means of a compression molding machine or the like. The molding temperature is in the range of 150 to 250° C., preferably 170 to 220° C., and the molding time is in the range of 5 to 60 minutes, preferably 5 to 30 minutes.  
         [0055]    To enhance the properties of the molded article, it is preferable to subject the molded product of the composition to oven vulcanization in an inert atmosphere at a vulcanization temperature of 150 to 320° C., preferably 200 to 300° C., for a vulcanization time of 10 to 50 hours.  
       Effect Of The Invention  
       [0056]    The fluoroelastomer composition of the invention provides a vulcanized molded product having excellent metal corrosion inhibition properties.  
         [0057]    The composition of the invention is favorably applied particularly to uses where the composition is in contact with a metal and is exposed to severe conditions such as temperature conditions of not lower than 150° C.  
         [0058]    The molded product of the composition has excellent chemical resistance, and hence it also exhibits sufficient resistance to severe environment where various conditions such as contact with metals, high temperature and highly reactive liquids complicatedly act on the molded product.  
       EXAMPLE  
     Example 1, Comparative Examples 1-4  
       [0059]    Preparation of composition  
         [0060]    100 Parts by weight of the following fluoroelastomer A, the following crosslinking agent and compounding additives shown in Table 1 were kneaded at a temperature of 40 to 60° C. using a two-roll mill to obtain a composition.  
         [0061]    Fluoroelastomer A  
                                                       Tetrafluoroethylene   68.4% by mol           Perfluoro (methyl vinyl ether)   30.5% by mol           Perfluoro (2-cyano-3,7-dioxa-8-nonene)    1.1% by mol           *Polymer Mooney Viscosity (at 150° C.)   61.1 pts                      
 
         [0062]    Crosslinking agent I  
         [0063]    2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane The composition obtained above was subjected to compression molding to obtain a desired crosslinked product. The crosslinked product was then subjected to oven vulcanization in a nitrogen atmosphere under the following conditions.  
         [0064]    The oven vulcanization was carried out, first, at 90° C. for 4 hours, then with a temperature rise from 90° C. to 204° C. over a period of 6 hours, then at 204° C. for 18 hours, then with a temperature rise from 204° C. to 288° C. over a period of 6 hours, and finally at 288° C. for 18 hours.  
         [0065]    The compounding additives are as follows.  
         [0066]    Hydrotalcite compound: DHT-4A™, available from Kyowa Kagaku  
         [0067]    Calcium hydroxide: Caldic 2000, available from Omi Kagaku  
         [0068]    Magnesium oxide: MgO 150, available from Kyowa Kagaku  
         [0069]    Zinc oxide: Zinc White No. 1, available from Sakai Kagaku  
         [0070]    Carbon black :SAF SEAST 9, available from Tokai Carbon  
         [0071]    The product obtained above was subjected to the following tests.  
         [0072]    Cured product property test  
         [0073]    Hardness: DIN53505  
         [0074]    Tensile test: DIN53503  
         [0075]    Compression set: ASTM D395, Method B (214 O-ring)  
         [0076]    Corrosion test  
         [0077]    Between metal plates (each: 50×50×2 mm), a 214 O-ring was sandwiched, and they were compressed by 3% of the linear diameter of the O-ring.  
         [0078]    The metal plates and the O-ring in the above state were heated in an oven at 250° C. for 70 hours. After the heating, the metal plates were separated from the O-ring, and corrosion of the metal portion formerly sealed with the O-ring was visually observed with the naked eyes.  
         [0079]    The results are set forth in Table 1.  
       Example 2. Comparative Example 5  
       [0080]    Preparation of composition  
         [0081]    100 Parts by weight of the following fluoroelastomer B, the following crosslinking agent and compounding additives shown in Table 2 were kneaded at a temperature of 40 to 60° C. using a two-roll mill to obtain a composition.  
         [0082]    Fluoroelastomer B  
                                                       Tetrafluoroethylene   71.5% by mol           Perfluoro (methyl vinyl ether)   27.7% by mol           Perfluoro (1-cyano-6-oxa-7-octene)    0.8% by mol           *Polymer Mooney Viscosity (at 150° C.)   73.9 pts                      
 
         [0083]    Crosslinking agent II  
         [0084]    2,2,3,3,4,4,5,5-octafluorohexanediamidoxime The composition obtained above was subjected to compression molding to obtain a desired crosslinked product. The crosslinked product was then subjected to oven vulcanization in a nitrogen atmosphere under the following conditions.  
         [0085]    The oven vulcanization was carried out, first, at 90° C. for 4 hours, then with a temperature rise from 90° C. to 204° C. over a period of 6 hours, then at 204° C. for 18 hours, then with a temperature rise from 204° C. to 288° C. over a period of 6 hours, and finally at 288° C. for 18 hours.  
         [0086]    The compounding additives are as follows.  
         [0087]    Hydrotalcite compound: DHT-4A™, available from Kyowa Kagaku  
         [0088]    Zinc oxide: Zinc White No. 1, available from Sakai Kagaku  
         [0089]    Carbon black :SAF SEAST 9, available from Tokai Carbon  
         [0090]    The product obtained above was subjected to the following tests.  
         [0091]    Cured product property test  
         [0092]    Hardness: DIN53505  
         [0093]    Tensile test: DIN53503  
         [0094]    Compression set: ASTM D395, Method B (AS568A214 O-ring)  
         [0095]    Corrosion test  
         [0096]    Between metal plates (each: 50×50×2 mm), a 214 O-ring was sandwiched, and they were compressed by 3% of the cross section of the O-ring.  
         [0097]    The metal plates and the O-ring in the above state were heated in an oven at 250° C. for 70 hours. After the heating, the metal plates were separated from the O-ring, and corrosion of the metal portion sealed with the O-ring was visually observed.  
         [0098]    The results are set forth in Table 2.  
                                                                                                     TABLE 1                                   Comp.   Comp.   Comp.   Comp.               Ex. 1   Ex. 2   Ex. 3   Ex. 4   Ex. 1                                    Fluoroeastomer A (phr)   100   100   100   100   100       Crosslinking agent I   1.4   1.4   1.4   1.4   1.4       (phr)       Zinc oxide (phr)       2       Calcium hydroxide (phr)           2       Magnesium oxide (phr)               2       Hydrotalcite compound                   2       (phr)       Carbon black (phr)   6   6   6   6   6            Molding temperature (° C.)/   220° C./15 min            Molding time (min)                           Properties of molded       products       Hardness (pts)   72   74   75   75   74       Tensile strength (Mpa)   11.8   17.2   15.9   15.0   16.3       Elongation (%)   140   160   150   160   160       Compression set   20   22   27   27   24       (275° C./70 hr) (%)       Metal corrosion test       (SUS304)       250° C./70 hr   DD   CC   AA   AA   AA       295° C./48 hr   DD   CC   BB   BB   AA       Pressure hot water   +0.2   +2.1   +1.7   +1.5   +0.5       immersion test       (200° C./70 hr)       Volume swell (%)                                                  
 
         [0099]    [0099]                                                                             TABLE 2                                   Comparative               Example 5   Example 2                                        Fluoroeastomer B (phr)   100   100           Crosslinking agent II   1.0   1.0           (phr)           Zinc oxide (phr)   2           Hydrotalcite compound       2           (phr)           Carbon black (phr)   6   6                Molding temperature (° C.)/   190° C./15 min                Molding time (min)                   Properties of molded           products           Hardness (pts)   76   77           Tensile strength (Mpa)   23.6   20.7           Elongation (%)   160   190           Compression set   45   50           (275° C./70 hr) (%)           Metal corrosion test           (SUS304)           250° C./70 hr   CC   AA           295° C./48 hr   CC   BB           Pressure hot water   +17.4   +1.9           immersion test           (200° C./70 hr)           Volume swell (%)