Abstract:
There is disclosed according to the invention a composition and an article made from the composition. In a preferred embodiment, the composition consists essentially of about 50-99 weight percent of a fluoroelastomer copolymer of tetrafluoroethylene and propylene having the following structure: ##STR1## where x=y, about 0-50 weight percent of a polymer filler, about 1-25 weight percent of dimethyl methyl phosphonate and about 0-15 weight percent of trioctyl phosphate.

Description:
RELATED APPLICATION 
     This application is related to U.S. Ser. No. 682,395 filed even date herewith entitled &#34;A method of Processing a Fluoroelastomer Composition,&#34; which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     This invention relates to the field of fluoroelastomer compositions and articles made therefrom. 
     In a never-ending search for improved materials, attention has been focused on fluoroelastomers because of their inherent chemical inertness. Of course, fluoroelastomers in general are well known. In this regard, see &#34;The Vanderbilt Rubber Handbook,&#34; Robert O. Babbit, R. T. Vanderbilt Co., Inc., pp. 244-253 (1978). Unfortunately, this desirable inherent chemical inertness causes problems of its own. One problem is that blending anything into them is unusually difficult. In certain fluoroelastomers, for example, it is difficult to blend more than 1 or 2% of a processing oil, wax, or lubricant into the material without it bleeding to the surface in a relatively short time. 
     Another problem relates to their processing, in particular blow molding and extrusion. Blow molding and extrusion are, of course, manufacturing processes well known to those skilled in the art. Certain fluoroelastomers cannot be blow molded because they do not knit well at weld lines and can only be extruded with difficulty due to their high molecular weight. In general, rubbers are not blow molded whereas plastics are. Some thermoplastic elastomers can be blow molded but these are considered to be hybrids between rubbers and plastics. 
     A further problem with certain fluoroelastomers is their poor flexibility (i.e., loss of elasticity) at low temperatures. This poor low temperature flexibility excludes these fluoroelastomers from use by the military and oil exploration groups where exposure to extreme cold environments is expected. 
     Two specific fluoroelastomers of interest are VITON® (a product of E. I. du Pont de Nemours and Co., Wilmington, Del.), and AFLAS® (a product of Asahi Glass Co., Ltd., Tokyo, Japan), both of which are known. See, for example, the above &#34;Vanderbilt Rubber Handbook. &#34; In general, VITON is a copolymer of vinylidene fluoride (CH 2  CF 2 ) and hexafluoropropylene (C 3  F 6 ) and AFLAS is a copolymer of tetrafluoroethylene (C 2  F 4 ) and propylene (C 3  H 6 ). 
     Both VITON and AFLAS suffer all of the above problems, to wit, difficulty in processing and loss of elasticity at low temperatures. For example, neither material can be successfully blow molded due to poor knitting at the weld lines. Too, VITON becomes functionally brittle at about -40° C. and AFLAS at about -5°. 
     Attempts have been made to solve the above problems with additives and also by blending with other polymers such as fluorosilicones. Use of additives is discussed, in general, in &#34;Modern Plastics Encyclopedia,&#34; Volume 58, Number 10A, pp. 202-224 (October 1981). At least with respect to VITON and AFLAS, these attempts have largely been unsuccessful. 
     Thus, it is an object of this invention to have an improved fluoroelastomer composition that is processable and is flexible at low temperatures. 
     This and other objects of the invention will become apparent after reference to the following description. 
     BRIEF SUMMARY OF THE INVENTION 
     We have discovered that by the addition of particular amounts of dimethyl methyl phosphonate and trioctyl phosphate, AFLAS compositions can be improved with respect to processibility and low temperature flexibility. Unfortunately, these additives do not produce such efficacious results in VITON. 
     Thus, one aspect of the invention relates to an improved AFLAS composition. A preferred composition consists essentially of about 50-99 weight percent of AFLAS, about 0-50 weight percent of a polymer filler, about 1-25 weight percent of dimethyl methyl phosphonate and about 0-15 weight percent of trioctyl phosphate. 
     Another aspect of the invention relates to a blow moldable and extrudable article made from the improved AFLAS composition. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As previously discussed, AFLAS is known to have poor flexibility at temperatures below about -5° C. It would be desirable to have an AFLAS composition that is flexible down to about -55° C. so as to satisfy military and commercial requirements. 
     AFLAS is also difficult to process because of its inherent chemical inertness. Thus, AFLAS cannot be blow molded because it does not knit well at weld lines. It is also difficult to extrude due to its high molecular weight. Thus, it would be desirable to have an AFLAS composition that is processable. 
     In view of the above, there is disclosed an improved AFLAS composition consisting essentially of about 50-99 weight percent of AFLAS, about 0-50 weight percent of a polymer filler, about 1-25 weight percent of dimethyl methyl phosphate and about 0-15 weight percent of trioctyl phosphate. 
     There is further disclosed another improved AFLAS composition consisting essentially of about 50-99.5 weight percent of AFLAS, about 0-50 weight percent of a polymer filler, about 0-25 weight percent of dimethyl methyl phosphate and about a 0.5-15 weight percent of trioctyl phosphate. 
     The AFLAS is a fluoroelastomer copolymer of tetrafluoroethylene and propylene having the following structure: ##STR2## 
     The dimethyl methyl phosphonate (hereafter DMMP) and the trioctyl phosphate (hereafter TOF) both act as a plasticizer and a process aid. 
     The resultant formulation has improved extrusion characteristics due to its low melt viscosity. No die drool is observed and a smooth surface is produced. Further, the resultant formulation is blow moldable due to the strong knitting now present at the weld lines. 
     The DMMP and the TOF may be added together or separately. When DMMP is added alone or with TOF, there was improved low temperature flexibility at -55° C. without a significant loss of tensile strength. This last result is surprising and unexpected since it is generally known that the addition of plasticizers, while improving flexibility, cause a drastic reduction in tensile strength. 
     It has been found that TOF may be added alone to improve low temperature flexibility and processing characteristics. Unfortunately, TOF also reduces tensile strength. However, if tensile strength is relatively unimportant requirement when compared to low temperature flexibility or processing characteristics, then additions of TOF alone may prove to be beneficial. 
     When DMMP is added alone, it is believed that low temperature flexibility begins to improve when it is added in an amount of at least one weight percent. It has been found, however, that significant benefits accrue when the DMMP is added in amounts of at least 5 weight percent. 
     It is most preferred that DMMP be added in amounts of about 15 to 25 percent. In this range, improvements in low temperature flexibility and processing will be realized without a significant loss in tensile strength. It is, of course, advantageous to add as much DMMP as possible since DMMP is less expensive than AFLAS. However, the maximum amount of DMMP that may be added to about 25 weight percent since any amounts greater than this will cause a drastic dropoff in tensile strength. 
     It is believed that when at least 1/2 weight percent of TOF is added to the composition, without any additions of DMMP, there will be improved low temperature flexibility and processing characteristics without a large loss in tensile strength. 
     If tensile strength is not an important consideration, then it is preferred that TOF be added in amounts of about 5 to 15 weight percent. Beyond about 15 weight percent the composition loses structural integrity. 
     As stated previously, DMMP and TOF may be added together or separately. When added together, tensile strength and low temperature flexibility will be within acceptable limits if the DMMP is present in an amount of about 5 to 15 weight percent and the TOF is present in an amount of about 2 to 5 weight percent. 
     As noted above, the composition may contain about 0 to 50 weight percent of a polymer filler. It is advantageous to add as much filler as possible (without of course detracting from the physical properties of the composition) since the filler material is less expensive than the AFLAS. 
     If the composition is to be heat shrinkable, then it is preferred that the polymer filler be a crystalline polymer such as polyvinylidene fluoride, polyethylene, or polypropylene or even VITON. 
     Further advantages of the invention will become apparent after reference to the following examples. 
    
    
     EXAMPLES 
     A master batch was prepared by blending the following ingredients in a Banbury mixer. All the ingredients are commonly known and available. 
     
                       TABLE 1______________________________________Ingredient             Weight Percent______________________________________AFLAS ® 150E fluoroelastomer                  60.66KYNAR ® 450 hold-out agent                  18.20AEROSIL ® R 972 filler                  18.20STATEX ® 160 black pigment                  0.61carnauba wax process aid                  0.61triallyl isocyanurate crosslinking agent                  0.61TE88XL process aid     0.45sodium stearate process aid                  0.30OMYA ® BSH stabilizer                  0.30IRGANOX ® 1010 antioxidant                  0.06                  100.00______________________________________ 
    
     From the master batch, three formulations were prepared in which various amounts of plasticizers were added. The formulations contained 13 weight percent DMMP, 6.5 weight percent TOF and 6.5 weight percent PLASTOLEIN 9250 (another commercially available plasticizer), respectively. Each of the formulations was extruded. Suitable samples were prepared and then tested for room temperature tensile strength and elongation. The results are summarized in Table 2. 
     
                       TABLE 2______________________________________                   TensileSample Additive         Strength ElongationNo.    w/o              psi      %______________________________________1      13% DMMP         2310     3902      6.5% TOF         1140     4303      6.5% PLASTOLEIN  1160     430______________________________________ 
    
     It can be seen from Table 2 that even though the DMMP is present in the greatest amount, the tensile strength is nevertheless higher than either of the other samples. 
     From the master batch again, 9 formulations as noted in Table 3 were prepared by adding various amounts of TOF, PLASTOLEIN 9250 and DMMP. From each of the 9 formulations, three 6-inch by 75-mil thickness slabs were prepared and then exposed to a beam of electrons for a dose of 5 megarads (Mrads) on each side or a total dose of 10 Mrads. The room temperature tensile strength and elongation were measured. Additionally, each slab was tested for low temperature flexibility by bending the slab around a 3/8-inch mandrel at -55° C. The results of the low temperature flexibility test are reported by number passed to number tested. One set of data was taken with samples prepared on a cold mill and a second set taken with samples prepared on a hot mill. The results are tabulated in Tables 4 and 5 respectively. 
     
                       TABLE 3______________________________________     TOF       PLASTOLEIN  DMMPSample No.     w/o       9250, w/o   w/o______________________________________4         4.35      4.35        4.355         4.55      0           4.556         2.73      0           6.367         0         0           138         1.74      0           11.339         0         1.74        11.3310        0         2.73        6.3611        4.2       0           12.512        0         4.2         12.5______________________________________ 
    
     The results in Tables 4 and 5 are similar with flexibility being somewhat improved in the hot milled samples. This improved flexibility is believed due to better homogeneity of the composition. As can be seen, the compositions containing PLASTOLEIN 9250 did not exhibit an acceptable combination of good tensile strength and good flexibility. Further, the best results were obtained with DMMP alone or DMMP in combination with TOF. 
     
                       TABLE 4______________________________________(Cold Milled)   TensileSample  Strength     ElongationNo.     psi          %         Flexibility______________________________________4        900         420       3/35       1250         400       0/36       1890         370       0/37       3000         380       2/38       2260         370       1/39       1950         380       0/310      1230         280       0/311      1060         280       0/312      1220         340       0/3______________________________________ 
    
     
                       TABLE 5______________________________________(Hot Milled)   TensileSample  Strength     ElongationNo.     psi          %         Flexibility______________________________________4       1120         400       3/35       1800         370       3/36       2190         330       3/37       3180         350       3/38       2250         350       0/39       1740         370       0/310      1730         400       0/311      1730         370       2/312      1700         400       0/3______________________________________ 
    
     A second master batch was prepared in the same manner as before with the following ingredients as shown in Table 7. AFLAS 150P is a cheaper, higher molecular weight version of AFLAS 150E, used in the previous examples. 
     
                       TABLE 7______________________________________Ingredient             Weight Percent______________________________________AFLAS 150P fluoroelastomer                  64.58KYNAR 450 hold-out agent                  19.37AEROSIL R 972 filler   12.92STATEX 160 black pigment                  0.65carnauba wax process aid                  0.65triallyl isocyanurate crosslinking agent                  0.65TE88XL process aid     0.48sodium stearate process aid                  0.32OMYA BSH stabilizer    0.32IRGANOX 1010 antioxidant                  0.06                  100.00______________________________________ 
    
     In this master batch, varying amounts of DMMP were added. Slabs were prepared, beamed to a total dose of 6 Mrads and then tested for room temperature tensile strength and elongation. The results are tabulated in Table 8. 
     
                       TABLE 8______________________________________                 TensileSample  DMMP          Strength ElongationNo.     w/o           psi      %______________________________________13      0             2880     36014      3.13          2600     35015      6.07          2610     37016      8.83          2410     380______________________________________ 
    
     It is apparent from Table 8 that increasing the amount of DMMP does not greatly decrease tensile strength. 
     A final set of samples were prepared to examine the effect of adding DMMP to a composition similar to that of Table 7 except that VITON AHV (a copolymer of vinylidene fluoride and hexafluoropropylene) was substituted for the AFLAS 150P. Six formulations of VITON plus increasing amounts of DMMP were blended and then formed into slabs. Each slab was irradiated to a total based of 5 Mrads. The samples were then tested for tensile strength, elongation, and low temperature (-55° C.) flexibility. The results are tabulated in Table 9. 
     
                       TABLE 9______________________________________           TensileSample DMMP     Strength   ElongationNo.    w/o      psi        %       Flexibility______________________________________17     0        2390       450     0/318     4.76     2190       520     0/319     9.09     1280       560     0/320     13.04     990       460     0/321     16.67     810       500     0/322     20       *          *       *______________________________________ *material had no strength; sample fell apart 
    
     Comparing the results in Table 9 to previous results, it is immediately apparent that the effect of DMMP in VITON stands in marked contrast to the effect of DMMP in AFLAS. Thus, when DMMP is added to VITON, tensile strength is rapidly degraded and flexibility is not improved at all. 
     It is important to understand and appreciate that there is a high degree of specificity required when matching polymeric materials even though AFLAS, DMMP, and TOF are known proven compositions. The fact that DMMP was combined with VITON (a closely related fluoroelastomer compound to AFLAS) to produce a composition with disasterous properties in contrast to the favorable results produced according to the invention amply illustrates the point. 
     It will be obvious to those skilled in the art having regard to this disclosure that other modifications of this invention beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.