High-temperature TPE is based on silicone. (Close-Up).

Automotive engineers are becoming converts to thermoplastic elastomers as alternatives to thermoset rubbers, but they've found that TPEs can't go everywhere rubber can--particularly under the hood. For these applications, they need elastomeric thermoplastics that can survive long-term exposure to temperatures as high as 150 C (302 F) and ones that can take a combination of heat and contact with automotive fuels. To satisfy these needs, Dow Corning Corp., Midland, Mich., has come out with a family of TPEs based on vulcanized silicone rubber particles dispersed in a variety of engineering-thermoplastic matrixes. Dow Corning is a global leader in silanes and silicones, but its experience in thermoplastics to date has been only with silicone-based additives.

Dow Corning calls its new family TPSiV (thermoplastic silicone vulcanizate) and has sampled it to 30-40 selected customers in automotive and other industries. This pre-launch phase will last through the summer, during which time Dow Corning plans to sample 10-15 more customers. Kevin Murphy, portfolio leader for thermoplastics, expects to make TPSiV widely available in October.

At that time, the company will have captive capacity for making TPSiV through its acquisition in April of Multibase SA of France. Multibase compounds its own lines of TPEs. Dow Corning plans to produce TPSiV under the Multibase name in France and at Multibase's U.S. operation in Copley, Ohio.

Not like other TPEs

The new family uses three different thermoplastic matrixes--nylon, polyester, and an unidentified proprietary resin. For the time being, company sources will not be more specific about these polymer vehicles for the dispersed silicone rubber phase. The nylon and polyester versions are said to have particularly good chemical resistance to automotive fluids. They also have a higher hardness range of 40 Shore D to 60D. Grades based on the unidentified vehicle are softer (40-50A to 60-70A) and have a silky, leather-like feel, which customers say is unlike that of other TPEs. They also show excellent resistance to automotive oils, glycols, and diesel fuels.

These materials can be injection and blow molded and extruded. (Predrying is necessary.) They are said to offer low compression and tensile set at elevated temperatures (in some cases, further improved by post-curing). Their broad colorability includes "appliance white," which reportedly is difficult to achieve with other TPEs whose oils or plasticizers cause yellowing.

Dow Corning foresees applications in automotive tubing, air ducts, CVJ boots, and jackets for brake hoses and fuel lines. Other possibilities are wire and cable, chemical-resistant industrial tubing and conveyor belts, and seals and diaphragms. In addition, the TPSiV family is said to offer inherently good adhesion to a broad spectrum of engineering thermoplastics. Combined with their leather-like feel, that suggests premium soft-touch applications in areas like consumer electronics and cosmetics packaging.

For the most part, TPSiV will not compete with existing TPEs but with thermoset rubbers such as epichlorohydrin (ECO) types. Commercial pricing is expected to be in the range of $4.55 to $6.80/lb.

NEED TO KNOW MORE?

Multibase, Inc., Copley, Ohio

www.dowcornig.com/plastics

[phone]

NEW SILICONE VULCANIZATE TPEs

                  TPSiV      TPSiV       TPSiV             TPSiV
                  X1120      X1180       X2100             X3000-50A

TP Matrix         Nylon      Nylon       Polyester         Proprietary
Processing        Injection  Inj., Ext.  Inj., Ext., Blow  Injection
Color             Natural    Black       Nat. to White     Nat. to White
Specif. Grav.     1.11       1.09        1.173             1.118
Tens. Str., MPa   31         24          13.2              7.1
Tens. Str., MPa-
@100% Strain      25         19          10.9              --
Ult. Elong., %    182        207         201               473
Flex. Mod., MPa   254        319         231.5             --
Shore Hardness    59D        52D         46D               52A
Tear Str., Die C
N/mm              126        107         72.4              23.5
Compress. Set, %
22 hr @ 23 c      46         70          46.4              13.7
Brittle Temp., C  <-45       <-45        --                --
Dielect. Str. @
100 Hz, kV/mm     21.4       22.4        20                19
Dielect. Const.
@ 100 Hz          4.64       4.04        2.9               4.37

                  TPSiV
                  X3000-60A

TP Matrix         Proprietary
Processing        Injection
Color             Nat. to White
Specif. Grav.     1.206
Tens. Str., MPa   13
Tens. Str., MPa-
@100% Strain      --
Ult. Elong., %    814
Flex. Mod., MPa   --
Shore Hardness    62A
Tear Str., Die C
N/mm              43.9
Compress. Set, %
22 hr @ 23 c      25.3
Brittle Temp., C  --
Dielect. Str. @
100 Hz, kV/mm     --
Dielect. Const.
@ 100 Hz          --