ELASTOSIL SILICONE RUBBER FOR THE APPLIANCE INDUSTRY · silicone rubber from WACKER offers almost...
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ELASTOSIL ® SILICONE RUBBER FOR THE APPLIANCE INDUSTRY CREATING TOMORROW’S SOLUTIONS
Transcript of ELASTOSIL SILICONE RUBBER FOR THE APPLIANCE INDUSTRY · silicone rubber from WACKER offers almost...
ELASTOSIL® SILICONE RUBBER FOR THEAPPLIANCE INDUSTRY
CREATING TOMORROW’S SOLUTIONS
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GOOD TO KNOW: THE DEVELOPMENT POTENTIAL OFELASTOSIL® SILICONE RUBBER OPENSUP NEW OPPORTUNITIES FOR THEAPPLIANCE INDUSTRY
Where to find whatIntroduction and contents 3Applications 4Properties 6Which is the right silicone system? 8Condensation and addition-curing 10RTV-1 and RTV-2 systemsLiquid silicone rubber grades 14Foams and more 16Wacker Chemie AG 18
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INNOVATIONS THROUGH DIALOG
Innovations are daily business. At least in the domestic appliance industry. Theever higher demands in this sector haveresulted in products that meet the high-est technical standards. Paradoxically,as quality requirements become stricter,cost pressures become greater. Productshave to become even better, and theirproduction processes even more effi-cient and economical. Production meth-ods today hardly have time to get estab-lished before they are superseded bynew technologies. The challenges facingproduct developers, engineers, applica-tions technologists and cost controllersare huge.
With more than 50 years’ experience in silicone technology and with itsabove-average commitment to R&D,WACKER has long been a driving forcefor progress in this sector.
ELASTOSIL® is a registered trademark of Wacker Chemie AG.
Here, dialog among experts is essential,because creating a never-ending streamof new and compelling solutions tailoredprecisely to the needs of the marketrequires thorough knowledge of produc-tion processes and material require-ments. We develop many of our solu-tions in direct collaboration with ourcustomers.
Innovations are daily business. At least at WACKER. Take advantage of theexpertise of our service engineers, and ask them about the extensiveresearch facilities in our company. Our pilot plant can develop new prod-ucts and test prototype series at anytime, under realistic conditions and onstate-of-the-art production lines.
Let’s tackle it together.Preferably right away.
You can always rely on WACKER’s extensivetechnical support service.
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Thanks to its wide variety of out-standing properties, ELASTOSIL®
silicone rubber from WACKER offersalmost unlimited applications in thedomestic appliance industry. Theproduct has become indispensablefor the production of state-of-the-artirons, cookers, baking trays andmolds, as well as solar collectors.
The following properties make ELASTOSIL®
silicone rubber the ideal choice fornumerous applications in the applianceindustry:
– Excellent high-temperature resistance– Very good adhesion to many sub-
strates– Gas and water-vapor permeability– Very good chemical resistance– Excellent radiation resistance – Environmental compatibility– Low order of toxicity– Outstanding electrical properties
IronsELASTOSIL® silicone rubber has manypotential applications in a steam iron.Components exposed to high-tempera-ture water and steam have to be bondedtogether or sealed at various points:
The entire interface between the die-caststeam chamber and the riveted lid has tobe sealed.
High-quality steam irons have a stainlesssteel or ceramic sole plate which makesironing much easier. This sole plate isbonded to the steam chamber with athin layer of silicone adhesive.
The tubular heating elements integratedin the steam chamber are also sealed attheir ends and thus protected from mois-ture with a drop of very low-viscosity silicone.
In all these applications, ELASTOSIL®
silicone rubber excels on account of itsexcellent adhesion, heat resistance andtailored rheological properties.
CookersThe main use of ELASTOSIL® siliconerubber in cookers is to bond the ovendoor and the cooktop, since it is herethat the materials used must withstandthe highest temperatures.
An oven door is basically a compositeassembly of different materials, such asglass, steel, enamel and polyurethaneand epoxy-based paint. For some ofthese materials, only an adhesive canprovide a secure and cosmeticallyacceptable bond.
The fabrication of cooktops involvesbonding the glass sheet to a frame ofsteel, aluminum or coated profiles.Besides long-term resistance to heatand cleaning agents, it is important forthe adhesive to have finely tuned rheo-logical properties. This allows the cook-top to meet the aesthetic requirementsplaced on an exposed adhesive joint.
Solar collectorsHighly transparent potting compoundsthat permit maximum transmission ofsunlight are used to embed crystallinesilicon wafers behind plates of glass orplastic.
On account of its exceptionally highresistance to weathering and extremetemperatures, ELASTOSIL® silicone rub-ber is used to bond the metal frame tothe plates and to seal the joint.
Baking trays and moldsOutstanding release properties and hot-air resistance make ELASTOSIL® siliconerubber ideal for coating baking trays andmolds. You no longer need to greasetrays or molds prior to baking. Nothingsticks and nothing burns.
A MATERIAL’S POTENTIAL APPLICATIONSALWAYS DEPEND ON ITS PROPERTIES
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ELASTOSIL® grades for these applica-tions are physiologically compatible andconform to guidelines of the FDA andGermany’s Institute for Risk Assessment(BfR).
And moreOther established uses of ELASTOSIL®
rubber grades in the domestic applianceindustry, which we hope will inspire youto join us in developing new, tailor-madesolutions, include:
– Seals for dishwashers and washingmachines
– Electric kettles– Bonding of coffee jugs
WACKER silicone rubber grades providereliable sealing and bonding. Over periodsof several years in the case of solar cellsand hot-water collectors.
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QUALITY IS THE PROPERTY THAT SUMSUP ALL THE OTHER PROPERTIES
Thanks to their many excellent proper-ties, ELASTOSIL® silicone elastomersare ideal for use in high-quality adhe-sives and coatings. In the domesticappliance industry, they are used wherever one or more of these proper-ties are essential.
Resistance to extreme temperaturesAmong the outstanding properties of sili-cones is their resistance to extreme tem-peratures. While no other elastomerscan be used at temperatures above 150 °C, silicone rubbers can withstandcontinuous service at temperatures up to 180 °C. Special grades even retaintheir elasticity for 1,000 to 2,000 hoursat 250 °C, and withstand peak tempera-tures of up to 300 °C.
Adhesive propertiesSilicone rubber adheres without a primerto a wide variety of substrates. Thisapplies especially to the self-adhesivegrades. In certain cases, however, it isadvisable to prime the substrate. Our G 790 primer is an almost universal prob-lem solver in this respect. It will producegood adhesion to siliceous and oxidicsurfaces. With plastics and painted sur-faces, adhesion should be tested on acase-to-case basis.
Gas and water-vapor permeabilityAt room temperature, the gas permeabil-ity of silicone rubber is about ten timeshigher than that of natural rubber; at100 –150 °C, however, it is approximatelythe same as that of natural rubber. Undernormal conditions, silicone rubber cancontain about 15– 20 % by volume ofdissolved air.
Chemical resistanceSilicone rubber is resistant to aqueoussolutions, dilute acids and bases, andsolvents. It may swell in organic solventssuch as ketones, esters and hydrocar-bons, but it will not break down. Curedsilicone rubber can only be removed bycomplete degradation with an agentsuch as concentrated sulfuric acid oralcoholic lye.
Radiation resistanceSilicone rubber withstands high doses of electromagnetic radiation in the micro-wave-to-UV range. This explains thewide variety of applications it enjoys,from microwave ovens to solar collectors.
Environmental compatibilityThe basic structure of silicone polymersis similar to that of quartz. Cured siliconerubber is therefore ecologically compati-ble and has a low order of toxicity. It canbe disposed of along with householdgarbage.
Thermal conductivityThe thermal conductivity of most siliconeelastomers is of the order of 0.15–0.25 WK–1 m–1 at room temperature. Special,highly filled grades can reach values upto 2.5 W K–1 m –1.
Electrical propertiesThe electrical properties of silicone rub-ber are comparable to those of otherinsulating materials at room temperature.However, silicone rubber has the advan-tage that these properties remain virtual-ly constant over a temperature rangefrom –45 to +180 °C. The fact that theirinsulation resistance, dielectric strengthand loss factor are practically unalteredby high temperatures is important inmany applications. They are also virtuallyunchanged after immersion in water,which is an important advantage forapplications such as steam irons.
Optical propertiesThe color and appearance of siliconerubber is determined by the fillers usedin the respective compound. In the visi-ble spectral range (400–760 nm), thinlayers of unfilled materials are almost100 % transparent. They only become
opaque in the UV range below 200 nm.Their refractive index nD
25 is between1.410 and 1.404.
Storage stabilityDepending on the grade, ELASTOSIL®
silicone rubber from WACKER has ashelf life of up to 12 months if stored inthe tightly closed original containers at 5 to 30 °C. If the material is kept beyondthe recommended shelf life, it is not nec-essarily unusable, but a quality checkshould be performed on the propertiesrelevant to the application. Practical tests are performed on all products
in the applications technology lab.
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THE RIGHT SILICONE SYSTEM FORYOUR PRODUCTION PROCESS
WACKER offers various ELASTOSIL®
silicone rubber systems for the appli-ance industry. The processing proper-ties of these silicones often differconsiderably, which makes it impor-tant to set the right priorities whenchoosing the system best suited toyour individual production require-ments. Discuss the options with yourWACKER technical support consultant.
Every application defines a range ofmaterial properties that limits the choiceof suitable silicone rubber. In the appli-ance industry, resistance to extremelyhigh temperatures and good adhesion ofthe elastomer are often essential prop-erties.
Which product is best suited to yourapplication will depend on the technicali-ties of your production process. A fullyautomated mass production process
with short cycle times places differentrequirements on the silicone rubber than a short-run batch process does. WACKER offers various silicone sys-tems, the processing parameters ofwhich may differ significantly irrespec-tive of the properties of the cured rub-ber. These parameters are especiallythe pot life, processing technology, cur-ing rate and temperature, whether thesilicone system is a one or two-part sys-tem, and whether it is available in thedesired quantity.
Curing [%]
1 2 3 Time [d]
RTV-2 RTV-1
Curing of a 10-mm silicone layer
4 5 6 7 8 9 10
100
90
80
70
60
50
40
30
20
10
0
A 10-mm test specimen of RTV-1 rubbertakes about a week to cure. An identicaltest specimen of RTV-2 rubber takes only a few minutes.
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Fas
t cu
rin
g >
>
Easy processing >>
• Two-part systems that cure at room tempera-ture. Special metering and mixing equipmentis needed to process them.
• Fast curing in the order of minutes is possibleif elevated temperatures or a suitable catalystare used.
RTV-2 silicones
• Heat-curing one-part systems that only cure at high tem-peratures. They can be processed with simple meteringequipment.
• Fast vulcanization within a few minutes
One-part silicones
• One-part systems that cure at room temperature. They canbe processed with simple metering equipment, and can evenbe applied manually.
• Since they need atmospheric moisture to cure, they hardenslowly from the outside inwards.
RTV-1 silicones
Products and their production requirements
The goal is often the same. The variousWACKER rubber systems only point todifferent ways of reaching it.
In the past, RTV-1 silicones were pre-ferred, because they are particularly easyto process.
In some circumstances, this is still thecase: for example, with a discontinuousproduction process and if relatively longcuring times are tolerated. If these condi-tions do not apply, WACKER also offersfaster curing alternatives: RTV-2 siliconesand heat-curing one-part systems.
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WE OFFER ONE OR TWO-PART, CONDENSATION OR ADDITION-CURING SYSTEMS
The key to successful visible gaskets is a perfectly adjusted material flow frombeginning to end.
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ELASTOSIL® silicone elastomers forthe domestic appliance industry aregrouped under four different curingsystems: condensation-curing oneand two-part systems and addition-curing one and two-part systems. The various systems offer differentprocessing advantages.
Condensation-curing RTV-1 siliconeelastomersELASTOSIL® RTV-1 silicone elastomersare one-part systems that cure at roomtemperature. They owe their popularityto the outstanding properties of thecured products and their ease of pro-cessing, requiring minimum investment.
To cure, RTV-1 silicone elastomers needmoisture. The rate of curing of these sili-cones is limited by the rate of diffusion,typically about 1–2 mm per day.
RTV-1 silicone rubber grades are classi-fied according to the by-products thatsplit off during curing: acetic acid, amine,oxime or alcohol-curing systems.
Thanks to their ease of processing,ELASTOSIL® RTV-1 silicone elastomersare popular for applications involvingonly thin layers and tolerable curingtimes. However, these silicones some-times require lengthy postcuring, whichis not reconcilable with the short cycletimes required of modern mass produc-tion. In such cases, fast-curing systemsare needed.
The advantages at a glance
– Very easy processing– Low capital investment– Very good adhesion to a large variety
of substrates
Condensation-curing RTV-2 siliconeelastomersThe two components of the self-adhe-sive, condensation-curing ELASTOSIL®
RTV-2 silicone elastomers are typicallymixed in a ratio of 8 : 1 to 12 : 1. As thesystem cures, alcohol is eliminated [Fig. 1].
The following silicone rubber gradeswere developed for mass production, inwhich interruptions to production mustbe kept to an absolute minimum: ELASTOSIL® RT 771, ELASTOSIL® RT772 and ELASTOSIL® RT 778 [Fig. 2].
Our condensation-curing RTV-2 siliconeelastomers typically have a pot life ofabout 10 minutes and take 70 minutesto set. The ultimate mechanical strengthis reached after about 6 hours. Thesetimes can be varied within limits by vary-ing the ratio of main component to cata-lyst. To ensure reliable processing, how-ever, the pot life should not be less than2 minutes.
It is not usual to accelerate curing byincreasing the temperature. On the con-trary, the temperature should not exceed90 °C until the product has cured com-pletely, as the silicone rubber could otherwise be destroyed.
The advantages at a glance
– Rapid curing at room temperature,even of thick layers
– Very good adhesion to a large varietyof substrates
– Outstanding heat resistance
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Structural formula of condensation curing Addition-curing RTV-2 silicone elastomersAddition-curing ELASTOSIL® RTV-2 sili-cone elastomers cure via a completelydifferent mechanism from that of con-densation-curing systems: when the twocomponents are mixed, the polymer, aplatinum catalyst and the curing agentare brought into contact with each other.Unlike the condensation-curing RTV-2silicone elastomers, the curing rate iscontrolled by the temperature and notthe mixing ratio. No by-products areformed during curing [Fig. 3].
Our transparent, crystal-clear, addition-curing RTV-2 silicone elastomers ELASTOSIL® RT 601 and SilGel® 612 are used in many potting applications.
The advantages at a glance
– Rapid curing, even in combination withlong pot life
– Reaction accelerated by raising thetemperature
– Flowable and non-sag grades available
Si
CH3 CH3
CH3 CH3 CH3
CH3 CH3
O
CH3
Si Si SiOH
ROH + ROH
ROO
O
O
OSi SiO
OR HO O O~~
~ ~
Si
Si O OSi
CH3
CH3
Si O
Sn catalyst
O
O
O
CH3
CH3
Polymer chain end Polymer chain endCuring agent
+ +
30
25
20
15
10
5
0
Pot life [min]
8 12 14
RT 771 RT 772 RT 778
Typical pot lives as a function of mixing ratios
Parts RT 77x to onepart catalyst10
Fig. 1
Fig. 2
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Time [min]
140 150 160 170 180 200
RT 705
The influence of temperature on the curing time of ELASTOSIL® RT 705
Structural formula of addition curing One-part, heat-curing silicone elastomersOne-part, heat-curing ELASTOSIL®
silicone elastomers comprise the samecomponents as the addition-curing RTV-2 silicone elastomers. Consequent-ly, they cure by the same chemical reac-tion. They are preferable to the two-partaddition-curing silicones if the purchaseof two-part metering equipment is notpossible for technical or financial rea-sons. Their principal advantage is thatthey can be processed without the needfor complicated mixing equipment, mak-ing them suitable for both long-run massproduction and for short-run production.
We have developed special grades, suchas ELASTOSIL® RT 705, for adhesivebonding applications.
The curing reaction can be acceleratedas required by increasing the tempera-ture. Even with pot lives as long as 6 months, curing times can be as shortas 30 min at 140 °C or 2 min at 200 °C.The only limit on curing temperature isthe heat resistance of the substrate tobe bonded [Fig. 4].
The curing temperature should be atleast 120 °C.
The advantages at a glance
– Low capital investment– Suitable for short production runs– Long pot lives and short curing times – Reaction accelerated by increasing the
temperature– Flowable, non-sag grades available
Pt catalyst
CH3 CH3
CH3
CH3
CH3
CH3
CH3
O H2C = CH
CH3
Si Si Si
Si
CH = CH2 H
H
O O+ +O
O
O
OSi SiCH3
CH3
~ ~
~~
~
CH3
CH3
CH3
CH3
CHCH2 OOSi Si ~
CH3 CH3
CH3
O
H
CH3
Si Si CH CH2O~
H
Si
Si
O
O
O
CH3
CH3
~~
~
Polymer chain end Polymer chain end
Curing agent
30
25
20
15
10
5
0
Temperature [°C]
Fig. 3
Fig. 4
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ATTRACTIVE AND PRACTICAL: COMBINATIONS OF RUBBER AND PLASTICS
The ELASTOSIL® LR family of self-adhesive liquid silicone elastomers isone of the latest accomplishments ofWACKER product research. Thesesilicones can be molded in a singleoperation together with plastics toproduce multicomponent articles.The resulting time and cost savingsare huge.
Mass-produced injection-molded prod-ucts, such as gaskets and valves, areused in a wide variety of products by the domestic appliance industry.
The self-adhesive ELASTOSIL® LR liquidsilicone rubber grades can be combinedwith polymers such as polyamide or poly-ester in a single operation to producemulticomponent articles.
Our self-adhesive ELASTOSIL® LR 3070and ELASTOSIL® LR 3071 liquid siliconeswere developed specifically for the massproduction of molded multicomponentarticles.
There are two technologies available forprocessing these silicones, the one-shotprocess and the two-shot process:
In the one-shot process, the article ismolded in a single operation in a two-component injection-molding machinewith two cores. In the two-shot process,the thermoplastic part is molded first in a thermoplastics injection-moldingmachine. While still hot, the part is transferred by gantry robot to the sili-cone mold of an LSR injection-moldingmachine, where it is overmolded.
The advantages at a glance
– Fast and economic production of high-volume parts
– Similar cycle times for processing thermoplastics and liquid silicone rubber
– Consistently good mechanical proper-ties displayed by the composite
– Scrap-free and flash-free production of liquid silicone rubber
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Silicone rubber is readily processed by injection molding, resulting in high productivity.
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WE OFFER MORE
As one of the world’s major siliconeproducers, WACKER supplies sili-cones in all their forms. We can onlygive a brief outline of other productgroups here, with selected examples.For more detailed information, pleaseask us for the appropriate specialbrochure. Or discuss your productrequirements with your WACKERtechnical consultant, who will be glad to assist you in finding the bestsolution to your specific problem.
Silicone foamsELASTOSIL® SC 870 is a two-part, addi-tion-curing silicone foam. The product isideal for applications that require a low-density, highly compressible sealing orfilling material, especially where organicfoams cannot be used because of hightemperatures.
ELASTOSIL® SC 870 silicone foam formsa predominantly closed cell structurethat confers excellent mechanical prop-erties on the foam.
Process parameters such as air contentand type of mixer have a significanteffect on the quality of the foam. In ourpilot metering plant, we can performtests to find out the right processingconditions for a particular case.
The advantages at a glance
– Silicone foam has the high heat resistance and chemical resistance of silicone rubber
– Rapid curing when heated– Foaming without ozone-depleting
blowing agents– High compressibility – Low compression set – Quickly becomes tack-free, even at
room temperature
Heat-curing ELASTOSIL® R und LRsilicone elastomers Heat-curing silicone rubber is processedefficiently by injection molding and extru-sion to manufacture valves, gaskets,cables and the like for use in manydomestic appliances. Aside from thewide range of standard grades, we alsooffer special grades with exceptionalsteam resistance for use in cookers, etc.
Silicone fluidsSilicone fluids are used as heat transfermedia and in temperature sensors,where they are able to withstand tem-peratures from –60 °C to +350 °C.
Silicone resinsSilicone resins are used together withmetal oxides as heat-resistant fillingmaterials in tubular heating elements.
Microporous insulation materialThanks to its good radiation absorption,WDS® microporous insulation materialfrom WACKER is superior to all otherthermal insulation materials at high tem-peratures. Thus relatively thin insulationlayers suffice for high-temperature insu-lation of radiant heaters.
Special grades for electronic applicationsModern electrical appliances almostalways incorporate electronics. WACKERoffers a special range of high-purity sili-cones that effectively screen electroniccomponents against external influencesthroughout their service life.
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RTV-2 silicone rubber grades are preferredfor sealing glass ceramic cooktops. Foams made of other materials cannotwithstand the high temperatures in thelong term.
WACKERAT A GLANCE
WACKER SILICONESis a leading supplier of complete silicone-based solutions that comprise products,services and conceptual approaches. Asa provider of solutions, the business divi-sion helps customers press ahead withinnovations, exploit global markets fully,and optimize business processes toreduce overall costs and boost productiv-ity. Silicones are the basis for productsoffering highly diverse properties for vir-tually unlimited fields of application, rang-ing from the automotive, construction,chemical, electrical engineering and elec-tronics industries, through pulp andpaper, cosmetics, consumer care andtextiles, to mechanical engineering andmetal processing.
WACKER POLYMERSis the global leader for high-quality bind-ers and polymer additives. This businessdivision’s activities encompass construc-tion chemicals and functional polymersfor lacquers, surface coatings and otherindustrial applications, as well as basicchemicals, i. e. acetyls. Products such as dispersible polymer powders, disper-sions, solid resins, powder binders andsurface coating resins from WACKERPOLYMERS are used in the construction,automotive, paper and adhesivesindustries, as well as by manufacturers of printing inks and industrial coatings.
WACKER FINE CHEMICALSis an expert in organic synthesis, silanechemistry and biotechnology, providingtailored solutions for its customers in the life sciences and consumer careindustries. The range of innovativeproducts includes complex organicintermediates, organosilanes, chiralproducts, cyclodextrins and amino acids.
With its comprehensive expertise,WACKER FINE CHEMICALS is a preferredpartner for highly challenging custom-manufacturing projects in the fields ofchemistry and biotechnology.
WACKER POLYSILICONhas been producing hyperpure silicon forthe semiconductor and photovoltaicsindustries for over 50 years. As one of thelargest global manufacturers of polycrys-talline silicon, WACKER POLYSILICONsupplies leading wafer and solar-cellmanufacturers.
Siltronicis one of the world’s leading producers ofhyperpure silicon wafers, supplying manymajor chip manufacturers. Siltronic devel-ops and produces wafers up to 300 mm in diameter at facilities in Europe, theUSA, Asia and Japan. Silicon wafers formthe basis of state-of-the-art micro andnanoelectronics used, for example, incomputers, telecommunications, motorvehicles, medical technology, consumerelectronics and control systems.
WACKERis a technological leader in the chemi-cal and electrochemical industries anda worldwide innovation partner to cus-tomers in many key global sectors.With around 14,400 employees,WACKER generated sales of EUR 2.76billion in 2005. Germany accounted for 21% of sales, Europe (excludingGermany) for 31%, the Americas for22 % and Asia-Pacific, including the rest of the world, for 26 %. Headquartered in Munich, Germany,WACKER has some 20 productionsites worldwide and a global networkof over 100 sales offices.With R&D spending at 5.3 % of sales in 2005, WACKER is among the world’smost research-intensive chemicalcompanies.
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CREATING TOMORROW’S SOLUTIONS
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