THE GRADES AND PROPERTIES OF ELASTOSIL® R …

1 THE GRADES AND PROPERTIES OFELASTOSIL R SOLID SILICONE RUBBERCREATING tomorrow S SOLUTIONS22 THE DIFFERENCE BETWEEN STANDARD RUBBER GRADES AND ELASTOSIL R SOLID SILICONE RUBBERIS THE WORD SILICONE. ContentsIntroduction 3 Chemical principles 4 Curing8 GRADES 10 Additives and auxiliaries 28 Primers, adhesives and coatings 32 PROPERTIES Physical 34 Physiological 40 Resistance 42 Service 46 Quality standards48 Subject index 50 WACKER at a glance5133 LUCKILY, SILICONE EXISTS AS RUBBER, TOOELASTOSIL R solid silicone rubbersare synthetic rubbers which differ instructure from conventional R GRADES are based on thechemistry of silicone and share thesame outstanding PROPERTIES . Thesematerials offer a wealth of remarkablefeatures which meet the rubber indus-try s strict requirements in every the following pages, you will finddetailed information about what makesELASTOSIL R solid silicone rubbers1what they are: we explain their chemicalstructure and the resulting PROPERTIES , aswell as how to test and describe those who just want a quick over-view, we have listed the individual ELASTOSIL R GRADES in a table.

2 This will help you to find precisely the information you are looking abbreviation >HTV (for high-temperature vulcanizing)is misleading, since liquid silicone rubbers are also high-temperature-vulcanizing systems. At Wacker Chemie AG,the difference between solid and liquid silicone rubbers is reflected in the trademarks ELASTOSIL R (R = Rubber)und ELASTOSIL LR (LR = Liquid Rubber). We refer to platinum-catalyzed solid silicone rubbers asELASTOSIL R and ELASTOSIL are registered trademarks of Wacker Chemie AG. Wacker Chemie AG is certified to ISO 9001 and EN 14001. The Elastomers Business Unit within WACKER SILICONES is certified to solid and liquid silicone rubbersare made of three components: poly-mers, fillers and additives. RIGHT CHEMISTRYP olymersWhether straight or branched a polymer is a chain of small repeatingunits with the end group X:X- A- A- A- A- A- A- A- X =X - [A] n - X With polyethylene (PE), for example, X isa methyl group (CH3):X - CH2- CH2- CH2- X = X - [CH2] n- XWith silicones, the polymer chains,>siloxanes are formed with Si-O so-called polysiloxane backbone isa chain consisting of silicon and oxygen:- Si - O - Si - O- Si - O-This differs from the carbon backbone of polyethylene (PE):- C- C- C- C- C- C- C-Silicone is part inorganic, part organic.

3 It shares the same Si-O backbone withinorganic materials such as quartz orglass. But, silicones also contain organicgroups which are attached to the SiR2- O - SiR2- O - SiR2- R =Me, Phenyl, VinylThe organic groups on the polysiloxanebackbone may be methyl (Me), vinyl orphenyl groups. The term >polydiorgano-siloxanes is then chains before and after crosslinking without fillersPolymer chains before and with role of fillers in 5 Chemical principlesNamed after the side groupsThe polymers are named after the or-ganic side groups attached to the siliconatom. Each silicon atom has fourchemi-cal bonds, which is why silicone rubbersare often abbreviated with a Q for qua-ternary groups. The polymers present inrubber can vary in structure, withdifferent chain lengths, with or withoutbranching or with a high or low vinylcontent. This, in turn, affects the ultimateproperties of the rubber.>MQIn polydimethylsiloxanes, the organicgroups are methyl groups.

4 They haverelatively little importance as they haveno double bonds and do not react easilywith >crosslinkers (peroxides). Theycan, however, be used as additives, as plasticizers. For further details, see page crosslinking ..>VMQThis compound is similar to polydime-thylsiloxane (MQ), but some of themethyl groups have been replaced withvinyl groups. The double bond is a reac-tive group which is needed for cross-linking. For further details, see page 8.>PVMQIf a small proportion of the methyl groupsin a VMQ is now replaced with phenylgroups, the polymer chain has less tendency to pack closely with adjacentchains at low temperatures than is the case with MQ or VMQ. In the latter cases,such packing causes>embrittlement of the rubber. The chemical structure of>phenylmethyl silicone rubbers helpsthem to retain their flexibility at tempera-tures as low as -80 C. anizationFillers interact with the polymer back-bone and stabilize crosslinking.

5 6 OUR FORMULATORS NEED JUST A FEWSELECT INGREDIENTSF illersA polymer compound crosslinkedwithout the addition of >fillers would notproduce a viable elastomer, and wouldbe useless. This is because the polymerchains do not interact at normal temper-atures, since they are chemically are needed to fill the gaps between the polymers and support thenetwork from within. The type, quantity and composition ofthe filler can vary and this determines toa large extent the PROPERTIES exhibited bythe rubber or elastomer. A distinction ismade between two types of fillers:Reinforcing fillersThese primarily include fumed silicaswith very large BET surface areas (largerthan 100 m2per gram), >WACKER HDK ,for example. Precipitated silicas are alsosometimes added. Even >carbon blackscan provide fillersNonreinforcing fillers are needed forbulking up silicone rubbers, whencompounding. They are also added toattain specific PROPERTIES . Examples ofnonreinforcing fillers are: >Diatomaceous earth: for reducing theprice of compounds >Quartz: for reducing the price andproviding resistance to certain chemi-cals >Carbon blacksAdditivesThe composition of an organic rubberis far more complex than that of a sili-cone rubber primarily due to the additi-ves used.

6 An end formulation for a sili-cone rubber is uncomplicated: it canconsist of just polymers and fillers. And the few remaining>additives canbe counted on one hand:Crosslinking chemicals>Peroxides as well as platinum catalystsystems can be used as crosslinkingchemicals1for solid silicone rubbers. 1 The common generic term >crosslinker is misleadinghere since it is also used to describe short-chain, highlyreactive polymers, which are vital for curing. This is whywe also refer to >catalysts, although this solely applies to platinum catalysts and not peroxides. The latter arealtered by the curing rubbers in fact consist of justa few ingredients. A simple mixture of polymers and fillers suffice for afinal product. This final product needs just a few additives to obtain endless principlesVulcanization accelerators or retarders,often found in organic rubbers, are notused in >plasticizers with a silicone-polymerbase are used. Problems inherent in or-ganic plasticizers such as phthalates arethus rubbers are inherently trans-parent and can be made transparent toopaque in nearly all >colors.

7 For moredetails, see pages 30 organic elastomers, silicones donot require >stabilizers against UV radi-ation or the like. They are inherently veryresistant to extremes of weathering andaging. WACKER offers a range of specialstabilizers for stabilizing against hot air,improving chemical and solvent resis-tance and for avoiding depolymerizationprocesses. For more details, see pages28 additivesSpecial additives are incorporated intosilicone rubbers to optimize the proper-ties required. These can include additivesfor increasing flame retardancy or forimproving the green strength of extrudedgrades. >Special-purpose GRADES canalso be regarded as additives, when theyare mixed with standard GRADES to attainspecific PROPERTIES . For more details, seepages 28 interact with the polymer backboneand stabilize role of fillersPeroxide curing8 ENOUGH TO STRENGTHEN THE SOFTEST COMPOUNDSThe uncured rubber compound is viscous and soft. A solid, elastomericmaterial is obtained by curing, the rubber the rubbers to cure, polysiloxanechains need to bond together with the help of crosslinking is initiated by crosslinkingchemicals, which react with the vinylgroups present in the VMQ and PVMQ polymer chains.

8 The nature of this reac-tion depends to a large extent on thechemicals PROPERTIES : it can be fast orslow, complete or incomplete, more sensitive to temperatures or more resi-lient to external influences. The filler isnot affected by curing. It serves merelyto stabilize the backbone formed are two different>curing proces-ses employed: peroxide curing and plati-num-catalyzed addition curing. A briefexplanation of both is given silicone rubbers1are always platinum catalyzed. For solid siliconerubbers, however, either curing systemcan be employed. WACKER providessuitable crosslinking chemicals for have published a separate brochurecontaining all the platinum-catalyzedELASTOSIL on this subject can be found in our brochure The GRADES and PROPERTIES of ELASTOSIL LR Liquid Silicone Rubber. Reactive group on the polymerH C vinyl double bond is group on the polymerThe vinyl double bond is addition curingHHH C CMeMeSi0Si0 SiMeMeMeA reactive free radical is formed on the OH C positionRRCR OH C position1st stage of the reaction9 CuringReactive groupThe peroxide group produces an oxygen free free radical attaches itself to anotherpolymer chain and forms a bridge.

9 The freeradical chain reaction then of free radicalsHHHHCC HH CCCCRHHRH HTwo polymer chains bond together > cured .Reactive groupThe platinum center has onefree coordination stage of the reactionInteraction with the platinum center activates the double vinyl group crosslinks by transforming the double bond, creating a single bond to a polymer chain; in this case, to acrosslinker molecule containing Si-H groups. The catalystbecomes free and is again available for further C CO Si OMePtRRRRHHH C CO Si OMePtRRRRHHMeOSi OHHH OCCSiMe +HHORRRRPt= Radical position= Low charge density= High charge densityCrosslinking 10 THE ALL-ROUNDERS FROM THE 400 RANGEC rosslinkerAppearanceDensityHardness, Shore A Tensile strengthElongation at breakTear strengthRebound resilienceCompression set (22 h / 175 C)DIN 53 479 ADIN 53 505 DIN 53 504-S1 DIN 53 504-S1 ASTM D 624 BDIN 53 512 DIN 53 517[g/cm3][N/mm2][%][N/mm][%][%] E, C1, 2640 6012 60 Peroxide-curing GRADES and their PROPERTIES Multipurpose GRADES Transparent Shore 20 and 30.

10 Opaque For extrusion and molded articlesBasic characteristicsELASTOSIL R 401/10 ELASTOSIL R 401/20 ELASTOSIL R 401/30 ELASTOSIL R 401/40 ELASTOSIL R 401/50 ELASTOSIL R 401/60 ELASTOSIL R 401/70 ELASTOSIL R 401/80 ELASTOSIL R 401/90 R 401/20 with % Crosslinker Eis only recommended for extrusion Postcured rubbers are suitable forapplication in pharmaceutical andfood-contact sectorsSpecial featuresThese are the advantages of the 400 range: They are all-round products. They are well known and respected. They have been continually developed and are fully optimized. Postcured rubbers are suitable for application in the pharmaceuticaland medical sectors. They can be easily mixed to produce intermediate Shore hardnesses. Individual GRADES are also available in our standard product range1: ELASTOSIL R 401/30 80 S, ELASTOSIL R 402/60 S, ELASTOSIL R 402/75 S and ELASTOSIL R 420/40 70 S. See the special-purpose GRADES on page GRADES can be recognized by the suffix S ELASTOSIL R 401/30 53022 2751 5530 40E, C1, 70031 4050 5515 35E, C1, 1,00025 4045 5515 40 ELASTOSIL R 402/60 ELASTOSIL R 402/65 ELASTOSIL R 402/75 ELASTOSIL R 411/50 ELASTOSIL R 411/55 ELASTOSIL R 411/60 ELASTOSIL R 411/70 ELASTOSIL R 420/30 ELASTOSIL R 420/40 ELASTOSIL R 420/50 ELASTOSIL R 420/60 ELASTOSIL R 420/70 High-green-strength GRADES For extrusion Especially for precision profiles anddimensionally accurate hoses GRADES with good mechanical PROPERTIES between R 401 and R 420 Transparent For extrusion and molded articles High-strength GRADES with high elongation at break Highly transparent For extrusion and molded articlesThis table shows only the minimum and maximum values foreach group of GRADES comprising more than two products.