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THE GRADES AND PROPERTIES OFELASTOSIL® LR LIQUID SILICONE RUBBER

CREATING TOMORROW’S SOLUTIONS

2

PERHAPS THE MOST USEFUL PROPERTYOF ELASTOSIL® LR LIQUID SILICONERUBBER IS THE LOW UNIT COST OF THECURED RUBBER PRODUCTS

ContentsIntroduction 3Chemical Principles 4Curing 6Grades 8Additives and auxiliaries 18Properties – Overview 22

– Physical Properties 24– Physiological Properties 30– Resistance 32– Oil-bleeding behavior 36Service 38Quality standards 40Subject index 42WACKER at a glance 43

3

FORTUNATELY, SILICONES ALSO COMEIN THE FORM OF LIQUID SILICONE RUBBER

With ELASTOSIL® LR liquid silicone rubbers, you save on unit costs, withoutcompromising on good properties.These high-temperature-vulcanizing rubbers have a very low viscosity andcan be processed like thermoplasticswith ultra-modern manufacturing equip-ment. And they have all the good properties of silicones.

ELASTOSIL® LR liquid silicone rubbers1

are delivered as two-part, ready-to-usesystems and are cured through platinum-catalyzed addition.

Unlike peroxide curing, no undesirableby-products are released. The result is ahighly elastic, three-dimensional networkwith outstanding mechanical, electricaland optical properties.

With the help of this brochure, we wouldlike to provide you with more detailedinformation on these properties: What isthe chemistry behind them, and how arethey tested? Furthermore, for those whowould simply like a quick overview, wehave listed the individual ELASTOSIL® LRgrades in a table for your convenience.

1 The difference between solid and liquid silicone rubbersis reflected in the trademarks ELASTOSIL® R (R = rubber)and ELASTOSIL® LR (LR = liquid rubber).

WACKER and ELASTOSIL® are registered trademarks of Wacker-Chemie GmbH. Wacker-Chemie GmbH is certified to ISO 9001 and EN 14001. The Elastomers Business Unitwithin WACKER SILICONES is certified to ISO/TS.

4

ELASTOSIL® LR liquid silicone rubbersconsist of polymers, fillers, crosslink-ing chemicals and, where necessary,further additives. Nothing more.

LESS IS MORE

PolymersAs with quartz and glass, the backbone ofa > polymer is the > silicon-oxygen bond.However, > methyl and > vinyl groupshave been incorporated into the otherwiserigid structure of the three-dimensionalquartz lattice. This produces linear VMQpolymer chains that are characteristic of liquid silicone rubbers.

> VMQ polymers are highly versatile. By varying the vinyl-group density ofpolydiorganylsiloxanes, it is possible tooptimally control the crosslinking densityof the fully cured rubber and hence its properties.

Fillers> Fillers are needed to strengthen thefully cured rubbers. Most often, > fumedsilicas with BET surface areas of > 100 m2/gare used. For example >WACKER HDK®.

> Precipitated silicas, > inert fillers suchas > quartz or > diatomaceous earth,

as well as specialty grades of carbonblack can also be added. The remarkablevariety of formulations means there is an equally broad range of applications.

CrosslinkersLiquid rubbers are two-part systems.Component A contains an added plat-inum catalyst, and component B con-tains added methylhydrogensiloxane as > crosslinker and a higher alcohol as inhibitor. The two components are not mixed until the processing stage.

Curing takes place by means of a plat-inum-catalyzed hydrosilylation reaction in which the methylhydrogensiloxanesadd across the vinyl groups in the poly-mer. Reactivity is controlled by the con-centration of > catalyst and > inhibitor.

Linear VMQ polymer chain

CH3 CH = CH2 CH3 CH3

H3C Si 0 Si 0 Si 0 Si CH3

CH3 CH3 xCH3 y

CH3 y >> x

5

Chemical principles

ELASTOSIL® LR liquid silicone rubber is supplied as a ready-to-usetwo-part mix.

6

CURED IN A FLASH

The uncured rubber compound is viscous and soft. A solid, elastomericmaterial is obtained by curing, i.e.crosslinking, the rubber compound.And in this case, curing takes place in a flash.

The platinum catalyst is so fast that itgoes through several catalyst cyclesduring curing.

In a flash!> Platinum-catalyzed addition curing is much faster than peroxide curing, be-cause, unlike peroxide curing, it involvesjust a single reaction: the addition of Si-H across the double bonds of thevinyl groups. The platinum catalyst alsoreduces the activation energy, therebyensuring that the reaction occurs morereadily.

The > peroxide reaction, on the otherhand, comprises several partial reactions.In the first, an unstable molecule (peroxide)has to be cleaved to obtain the highlyreactive free radicals that induce thecrosslinking reaction in the second. Thefree radicals first add across the doublebonds. This produces a new free radical,triggering a chain reaction that termi-nates when crosslinking has occurred at all the double bonds. Once initiated,this kind of radical reaction runs itscourse very quickly and non-selectively,giving rise to undesirable by-products.

Liquid silicone rubbers cure when themethylhydrogensiloxanes bond with thesilicone polymer. The Si-H groups of thecrosslinker molecules add across thedouble bonds of the silicone polymer’svinyl groups. This reaction is activated by platinum catalysts.

The reaction will even take place at roomtemperature, though very slowly. But atelevated temperatures it is very fast. The specific advantage of this type ofcrosslinking is that no undesirable by-products whatsoever are formed.

The filler is not affected by curing. It servesmerely to stabilize the backbone formedduring curing.

7

Curing

The route taken by a platinum catalyst during curing

CATALYSTPolymer

Elastomer

Complexing

Crosslinkerπ-complex

Platinum

Silicon

Carbon

Hydrogen

Oxidative additionPt 0 Pt +IIMigration

Reductive eliminationPt +II Pt 0

σ-complex

8

THE STANDARD GRADES

These are the advantages of the standard grades:– They are all-round products.– They have been continually improved

and are fully optimized.– Postcured rubbers are suitable for

application in the medical-technical,food-contact and pharmaceutical sectors.

Appearance

Density

Viscosity of the mix AB (0.9 s–1)

Hardness, Shore A

Tensile strength

Elongation strength

Tear strength

Rebound resilience

Compression set (postcured 6 h/200 °C)

Dielectric strength (1-mm sheet)

Volume resistivity

Dielectric constant 50 Hz

Dissipation factor 50 Hz (tan δ)

Limiting oxygen index (LOI)

DIN 53 479 A

DIN 53 505

DIN 53 504-S1

DIN 53 504-S1

ASTM D 624 B

DIN 53 512

DIN 53 517

VDE 0303

VDE 0303

VDE 0303

VDE 0303

[g/cm3]

[mPa · s]

[N/mm2]

[%]

[N/mm]

[%]

[%]

[kV/mm]

[Ω · cm]

[%]

Transparent

1.08–1.19

100,000–3,000,000

15–78

3.0–10.0

300–700

9–35

44–65

10–25

23

5 · 1015

3.1

30 · 10–4

27

ELASTOSIL® LR liquid silicone rubbers and their properties

Special characteristics

ELASTOSIL® LR 3003/10








– High mechanical strength

9

Grades

Transparent

1.17–1.19

200,000–3,000,000

20–70

7.0–10.0

300–700

15–35

45–65

10–25

23

5 · 1015

3.1

30 · 10–4

27

Transparent

1.10–1.14

600,000–1,600,000

30–60

8.5–9.8

450–750

30–45

45–60

18–30

23

5 · 1015

3.1

30 · 10–4

27











– High mechanical strength– Fast curing– Short cycle time

– High tear strength – For articles subjected to intensive, dynamic stress– Masks and pacifiers

This table shows only the minimum and maximum values foreach group of grades comprising more than two products.For more precise information, please ask for the individualproduct data sheets.

10

THE NON-POSTCURING GRADES

Appearance

Density


Hardness, Shore A

Tensile strength

Elongation at break

Tear strength

Rebound resilience

Compression set (non-postcured)


Volume resistivity




DIN 53 479 A

DIN 53 505

DIN 53 504-S1

DIN 53 504-S1

ASTM D 624 B

DIN 53 512

DIN 53 517

VDE 0303

VDE 0303

VDE 0303

VDE 0303

[g/cm3]

[mPa · s]

[N/mm2]

[%]

[N/mm]

[%]

[%]

[kV/mm]

[Ω · cm]

[%]

Transparent

1.08–1.15

100,000–2,000,000

20–70

3.5–9.5

350–600

12–25

60–65

10–22

28

1 · 1016

2.5

30 · 10–4

27


– Very short curing time– Excellent compression set,

even without postcuring









These are the advantages of the non-postcuring grades:– They do not need postcuring.– They have especially low compression sets.– They are ideal for technical applications.

11

Grades

Beige

1.29–1.34

400,000–1,800,000

50–70

6.0–7.0

230–430

15–18

57–60

17–25

23

5 · 1015

3.1

30 · 10–4

–

Beige

1.30–1,34

500,000–600,000

50–70

6.7

370

18

60

40

23

5 · 1015

3.1

30 · 10–4

–

Opaque

1.12

1,500,000

50–60

4.5

300

12

65

22

23

5 · 1015

3,1

30 · 10–4

27




ELASTOSIL® LR 3015/70 ELASTOSIL® LR 3023/50


– Oil resistant– Short curing time

– Oil resistant– Short curing time– Nonabrasive

– Coolant resistant– Very short curing time


12

THE SELF-LUBRICATING GRADES

Appearance

Density


Hardness, Shore A

Tensile strength

Elongation at break

Tear strength

Rebound resilience

Compression set (non-postcured)

DIN 53 479 A

DIN 53 505

DIN 53 504-S1

DIN 53 504-S1

ASTM D 624 B

DIN 53 512

DIN 53 517

[g/cm3]

[mPa · s]

[N/mm2]

[%]

[N/mm]

[%]

[%]



These are the advantages of the self-lubricatinggrades:– They are oil bleeding.– They do not need postcuring.– They have low compression sets.– They are ideal for technical applications.

13

Grades


Opaque

1.12–1.15

1,700,000–2,400.000

40–60

7.5–11.0

500–650

15–35

55–65

15–20

Opaque

1.09–1.12

800,000–1,200,000

20–30

6.5–7.5

800–900

10–20

45–50

19–24







– Slight oil-bleeding – Considerable oil-bleeding

Opaque

1.11–1.14

1,000,000–1,700,000

30–50

7,5–8,5

500–700

15–35

50–55

15–20





– Oil-bleeding

14

THE SELF-ADHESIVE GRADES

Appearance

Density


Hardness, Shore A

Tensile strength

Elongation at break

Tear strength

Rebound resilience

Compression set (non-postcured)1

DIN 53 479 A

DIN 53 505

DIN 53 504-S1

DIN 53 504-S1

ASTM D 624 B

DIN 53 512

DIN 53 517

[g/cm3]

[mPa · s]

[N/mm2]

[%]

[N/mm]

[%]

[%]

Transparent

1.07–1.16

800,000–3,800,000

10–60

1.5–10.5

600–750

5–25

40–60

20–25

Transparent

1.13 / 1.15

1,800,000 / 2,300,000

40 / 50

9.5 / 10.0

600 / 750

20 / 22

55 / 58

20 / 25




– Standard grades – Postcured rubberscomply to BfR and FDA

– Short curing time







These are the advantages of the self-adhesive grades:– They are completeley new.– They adhere to many thermoplastics.– They adhere to many thermosets.– They adhere to many elastomers.– They adhere to many metals.– They do not adhere to case-hardened steel molds.– They can be processed via coinjection molding.– They are ideal for hard/soft composites.– Further details are given in the brochure

“Self-Adhesive ELASTOSIL® Silicone Rubber Grades”

1 Measured after conditioning: 22 h/125 °C

15

Grades

Opaque

1.10 / 1.12

1,000,000 / 1,600,000

30 / 40

8.0 / 9.5

700 / 750

13 / 20

50 / 55

20 / 20

Opaque

1.3

1,000,000

60

5.5

300

14

65

20




– Self-adhesive– Slight oil-bleeding

– Improved coolant resistance


Beige

1.33

900,000

70

5.2

320

14

60

25

Transparent

1.10

1,000,000

50

9.5

500

55

55

20


– Improved oil resistance

– Non-abrasive

– Improved tear strength– Postcured rubbers are BfR and

FDA-compliant


16

THE SPECIAL-PURPOSE GRADES

Appearance

Density


Hardness, Shore A

Tensile strength

Elongation at break

Tear strength

Rebound resilience

Compression set (postcured 6 h/200 °C)


Volume resistivity




DIN 53 479 A

DIN 53 505

DIN 53 504-S1

DIN 53 504-S1

ASTM D 624 B

DIN 53 512

DIN 53 517

VDE 0303

VDE 0303

VDE 0303

VDE 0303

[g/cm3]

[mPa · s]

[N/mm2]

[%]

[N/mm]

[%]

[%]

[kV/mm]

[Ω · cm]

[%]

Dark gray

1.36

310,000

55

5.7

350

15

50

40

27

5 · 1015

3.2

100 · 10–4

35


– Flame retardant– Corresponds to UL 94 VO

with a layer thickness of 0.8 mm



These are the advantages of the special-purpose grades:– They are specialized for particular

applications.– All necessary additives are already

included.

New series:– ELASTOSIL® LR 3060 and 3065:

with improved surface properties– ELASTOSIL® LR 3900 and 3905:

fluoro-silicone

17

Grades

Black

1.15

1,600,000

60

9.0

400

30

65

20

32

2 · 1016

2.7

13 · 10–4

27

Highly transparent

1.05

120,000

60

8,0

300

13

65

50

23

5 · 1015

3.1

30 · 10–4

27

Black

1.12

5,000,000

50

4.5

350

12

50

25

–

11

–

–

–

ELASTOSIL® LR 3094/60 ELASTOSIL® LR 3153 ELASTOSIL® LR 3162

– Very short curing time– Excellent compression set

even without postcuring– Thermally stabilized

– Long pot life – Fast Curing – Primerless adhesion

to textiles

– Electrically conductive


18

THE SIXTEEN BEST ALTERNATIVES TOPLAIN GRAY

Ivory 1014 + +Yellow 1016 + +3

Reddish brown 2001 + +Orange 2004 + –Dark red 3000 + +3

Iron oxide red 3013 + +Ulramarine blue 5002 + +Dark blue 5010 + +Pale Blue 5015 + –Green 6010 + +Gray 7000 + –Jet black 9005 + +White aluminum silver 9006 + +White 9010 + +Black 9011 – –Ice blue – + +

ELASTOSIL® Pigment Pastes FL

1 The RAL numbers in the table are only guide values.2 See the “Food” section on page 31.3 For additions up to max. 1 %

Name of color Similar to RAL1 BfR 2 FDA2 Color

We do not guarantee conformity to the above-mentionedregulations, since the requirements can change. For thelatest data please ask our Technical Service.

19

Additives and auxiliaries

With ELASTOSIL® LR liquid siliconerubbers, you can produce anything inthe color of your choice. Becausewith ELASTOSIL® Pigment Pastes FL,you can color your rubber blends however you like.

ELASTOSIL® Pigment Pastes FL are avail-able in 16 ready-to-use standard colors.So, practically all > RAL colors can beblended by simply mixing the pigmentpastes in the required proportions.

The > pigments are incorporated homo-geneously in a static or dynamic mixer.

The pasty pigment is metered as thethird component via the pigment line in concentrations of 0.3 % to 5 %depending on the desired hiding power.However, the concentration shouldalways be kept as low as possible.

For more information on this subject,please ask for our data sheet on ELASTOSIL® Pigment Pastes FL.

Please note:If you would like to increase the hot-air resistance of your cured rubber, you canadd 3 to 4 % of ELASTOSIL® PigmentPaste FL 1014, ELASTOSIL® PigmentPaste FL 3013 or ELASTOSIL® PigmentPaste FL 9005 to your rubber blend.

20

PRIMERS AND COATINGSUNDER AND OVER

Primers and > adhesives are neces-sary to improve the adhesion orbonding of silicones to any substrate. This substrate may be a metal part, a plastic or even another silicone.

Coatings and overmoldings are neces-sary to achieve certain surfaces onsilicones or for coating with silicones.Occasionally, coatings can also beused as primers or adhesives.

Primers and adhesivesPrimer G 790Used e.g. for preliminary priming to pre-vent corrosion when bonding metal andsilicone parts using room-temperature-vulcanizing, one-part systems (RTV-1adhesives)

Primer G 795These > primers are only partially suitablefor applications with ELASTOSIL® LRliquid silicone rubbers. They primarily serveto promote adhesion of room-temperature-vulcanizing, two-part systems (RTV-2) toaluminum, plywood, etc.

ELASTOSIL® LR 3153 A + 6 % Crosslinker W Primer for crosslinked polyethylene surfaces and textiles.

ELASTOSIL® LR 3112 A+BThis two-part adhesive is used in a ratioof 99 : 1 at higher temperatures to bondsilicones to silicones.

Coatings and overmoldingsELASTOSIL® RD 3151This dispersion with excellent adhesionto textiles as well as silicones and cross-linked polyethylene surfaces is used for > coating. Its special characteristicsinclude a dry hand and excellent abra-sion resistance.

ELASTOSIL® LR 3153A > coatings dispersion with excellentadhesion to textile fibers such as textile-braided cables as well as crosslinkedpolyethylene surfaces. One special characteristic is that it can also be used as an adhesive for silicones to thesematerials.

21

Additives and auxiliaries

The correct choice of primer determineshow a composite part performs.

22

OUR TESTERS ONLY BELIEVE WHATTHEY CAN MEASURE

The compression set of silicone rubber,unlike that of organic rubbers, is measuredunder extreme conditions. At 175 °C to beprecise

23

Properties

ELASTOSIL® LR liquid silicone rubbershave all the useful properties charac-teristic of silicones. These propertiesand their measuring methods are dis-cussed in more detail on the followingpages.

If you would like to test certain propertiesyourself, you can easily produce bubble-free ELASTOSIL® LR liquid silicone rubber> test slabs in the laboratory.– Blend both components in a mixer and

then deaerate in an exsiccator undervacuum

– Pour an excess of the molding com-pound (about 20 % excess) into, orspread it onto, a cold, conventionaltest-slab mold

– Close the mold and cure for 5 minutesat 165 °C and 240 bar. Any bubblesintroduced during mixing will be forcedout

– Punch out the test specimens to de-termine the relevant product properties

What you get from ELASTOSIL® LRELASTOSIL® LR liquid silicone rubbersoffer not only outstanding product quali-ty for the finished > cured rubbers, butalso noteworthy processing advantages:– They are easy to handle, cure very

quickly and require almost no post-processing. They therefore increaseyour production output and reduce unit costs.

– They contain neither toxic nor aggres-sive substances. Special handling precautions are therefore not required.However, you should always ensurethat your production rooms are wellventilated.

– During the addition curing of ELASTOSIL® LR liquid silicone rubbers,no crosslinker by-products are released.This reduces pollution and in manycases, saves postcuring.

What your product gets from ELASTOSIL® LR– Heat stability up to 180 °C– Heat stability up to 250 °C with the

help of special additives– Low-temperature flexibility down to

-50 °C– Constant mechanical and electrical

properties over a wide temperaturerange

– Good weathering, UV and aging resistance

– Outstanding electrical properties– Especially good insulation– Safe burning properties thanks to

nontoxic combustion– Excellent physiological compatibility– Pigmentable in nearly every color– High transparency– Excellent environmental compatibility

24

THE HARDNESS TEST IS JUST ONEOF OUR EASIEST EXERCISES

Density> Density is determined by the buoyancymethod (DIN 53 479 A). Liquid siliconecompound with fumed or precipitated silicahave a density of 1.05 to 1.22 g/cm3. If inert fillers are used additionally, densi-ties up to 1.45 g/cm3 can be achieved.This corresponds to a compound withapproximately 75 % quartz flour, forexample. Greater amounts of fillers andconsequently higher densities are notcommon in silicone rubbers, as themechanical strength of the rubber is then inadequate for most applications.

Rubbers with a high specific gravity areused in particular for seals which comeinto contact with fluids, since the highamount of extending filler reduces theincrease in volume of the rubber when in contact with swelling media.

HardnessThe > hardness of silicone rubber ismeasured in > “Shore A” as described in DIN 53 505 and in some cases in > “IHRD” units1 according to DIN 53 519,as well. The hardness of ELASTOSIL® LRliquid silicone rubber parts usually rangesfrom 10 to 80 Shore A.

Tensile strength and elongation at breakUltimate > tensile strength and > elonga-tion at break are tested as described inDIN 53 504. An S1 dumbbell is employedto test ELASTOSIL® LR liquid siliconerubber compounds. Slightly differentvalues are obtained if the tests are per-formed using the smaller S2 or S3 testspecimens. This must be taken intoaccount when defining specifications.

The tensile strength of different ELASTOSIL® LR liquid silicone rubbercompounds generally varies between 5 and 11 N/mm2. Elongation at breakvaries between 100 and 900 %.

Tear strengthVarious methods are commonly used to determine the > tear strength.ELASTOSIL® LR liquid silicone rubbercompounds are measured mainly on thebasis of ASTM D 624 B (> Crescent).Depending on the application, the testmethods in accordance with ISO 34-1Method B-b (> Graves) and ISO 34-1Method A (> Trousers) are also used.

In accordance with ASTM D 624 B, thetear strength of different ELASTOSIL® LRcompounds ranges from 5 to 45 N/mm.

Compression set> Compression set is tested on ELASTOSIL® LR liquid silicone rubbertest specimens as described in DIN 53 517.2 The test is usually conductedafter conditioning at 175 °C for a periodof over 22 hours. Self-adhesive gradesare tested after conditioning at 125 °Cfor over 22 hours. Curing was carriedout for five minutes at 165 °C and post-curing for four hours at 200 °C in allcases. Non-postcuring and self-adhesivegrades were not postcured.

1 Hardness measurements to DIN 53 505 in Shore A andIHRD values are not always identical.

2 It could also be tested in conformity with ASTM D 395.

WACKER maintains a high-tech labor-atory to manage the huge volume of quality tests necessary each day.Thus we are always able to test whether products satisfy the specificrequirements of our customers.

25

Physical properties

Rebound resilience> Rebound resilience characterizes the“snap” of rubber. In conformity with DIN53 512, it is measured using a 12-mmthick test specimen and is determinedas the ratio of the rebound of a pendu-lum to its original height. Typical valuesof ELASTOSIL® LR test specimens varyfrom 20 % to 70 %.

Properties at different temperaturesThe hardness, tensile strength, elonga-tion at break and tear strength of elasto-mers are usually determined at temper-atures of around 23 °C to 25 °C. Theseproperties vary along with the > measure-ment temperature. Care should be takento condition the test slabs as laid downin the specifications.

The automatic and precise determinationof key data is an integral part ofWACKER's routine quality control.

26

A LIGHTER IS ALL YOU NEED FOR THEFLAME-RETARDANCY TEST

Fire behaviorThe > autogenous ignition temperatureof ELASTOSIL® LR cured liquid rubbersis approx. 430 °C. The flash point isapprox. 750 °C. When silicone rubberburns, it forms a white ash of silicon dioxide. The gases emitted are not cor-rosive. Special additives can be used to achieve self-extinguishing properties.Such compounds are generally termed“flame retardant.”

The standard ASTM D 2863 (Determin-ation of LOI = Limiting Oxygen Index) orthe > fire standards laid down by Under-writer Laboratories (UL 94) are preferablyused to measure > flame retardancy.

The LOI values of flame-retardant grades,e.g. ELASTOSIL® LR 3001/55, rangefrom 27 % to 35 %.

UL 94 V-1 or UL 94 HB is achievedwithout difficulty; the standard UL 94 V-O can be met using special gradesand/or additives.

Coefficient of linear thermal expansionThe > coefficient of linear thermal expan-sion of ELASTOSIL® LR liquid siliconerubber grades is directly dependent onthe specific gravity of the compound.The lower it is, the higher the density ofthe rubber used. Typical values vary inthe range 2 · 10–4 · K–1 to 4 · 10–4 · K–1.This general guideline is not, however,without exception. Particularly proces-sing conditions and the composition ofthe rubber influence the dimensions ofthe finished parts. Preliminary trialsshould always be carried out for preci-sion parts.

The coefficient of linear thermal expan-sion of tool steel amounts to approx. 1.5 · 10–6 · K–1. This difference causes > shrinkage of the finished parts and isalso affected to a great extent by pro-cessing parameters such as the moldtemperature, injection pressure andpostcuring conditions.

Silicone rubber can easily be madeflame-retardant. And if the materialdoes catch fire, it forms a white, ceramifying silicon dioxide ash thatacts as an insulator. This remarkableproperty is particularly useful for safety cables.

27

Physical properties

Thermal conductivityThe > thermal conductivity of siliconerubber again depends on the type andamount of fillers used. The average at 100 °C amounts to approx. 0.2 Wm–1 · K–1 to 0.3 Wm–1 · K–1.

Special thermally conductive com-pounds achieve values of approx. 0.8 to 1.2 Wm–1 · K–1, by the proceduregiven in DIN 52 612.

Specific heatValues of approx. 1.25 kJ · kg–1 · K–1 aretypical for the > specific heat, measuredaccording to DIN 52 612.

Gas permeabilityUnlike other elastomers, silicone rubberhas a very high > gas permeability. Itspermeability to air at 25 °C, for example,is 30 times that of natural rubber and400 times that of butyl rubber. The gaspermeability of silicone rubber increaseswith temperature.

The permeability/temperature curve isless steep for ELASTOSIL® LR compoundsthan for organic elastomers. The differ-ences between synthetic and siliconerubbers at high temperatures are thusless marked.

Gas permeability can be measured accord-ing to DIN 53 536. The absolute air per-meabilities of a 50 Shore A grade are570 and 1,330 cm3 (NTP) · mm · m–2 · h–1

· bar –1 at 20 °C and 80 °C respectively.This corresponds to the rate, in cm3/hour,at which air permeates a membrane of 1 m2 area and 1 mm thickness at a pressure difference of 1 bar across themembrane.

Special formulations enable you to meeteven the toughest fire-behavior demands,as in this UL test.

Air 100

Steam 190

Oxygen 170

Nitrogen 80

Carbon dioxide 1,000

Ethylene 390

Gas Relative permeability at 20 °C

Gas permeability

28

ELECTRIFYING SILICONES

Silicone rubber is chemically relatedto inorganic insulators. As a result, ithas a variety of outstanding electricalproperties with practically universalapplication possibilities in electricalengineering.

ELASTOSIL® LR liquid silicone rubbersare ideal for applications in the electricalindustry. The electrical properties de-scribed in this section are almost com-pletely independent of temperature inthe range from -50 °C to +200 °C. They change only negligibly even whenELASTOSIL® LR is subjected to hightemperatures for long periods.

Dissipation factorThe test for > dissipation factor is carriedout in conformity with VDE 0303. Tan δranges from 30 · 10-4 to 250 · 10-4 as afunction of the frequency and the fillersused.

Dielectric strength> Dielectric strength is tested in accord-ance with VDE 0303. The various gradesof ELASTOSIL® LR liquid silicone rubberhave dielectric strengths which varyfrom approx. 18 to 20 kV/mm.

Dielectric constantThe > dielectric constant ε is measuredas set forth in DIN 53 482 and VDE0303. Silicone rubbers generally havevalues of ε = 2.7 to 3.3 (measurementsbeing carried out at 25 °C and 50 Hz).These characteristic values can be maxi-mized by using suitable fillers. For in-stance, rubber grades with ε = approx.150 are used for the refractive field con-trol of cable terminals.

Tracking resistanceThe > tracking resistance of special-pur-pose grades reaches 3.5 kV/6 h (mea-sured according to VDE 0441 or ASTM D2303). Under these conditions standardgrades withstand only 10 to 30 minutes.

Arc resistanceWhen measured in accordance with VDE 0441, the > arc resistance is approx.80 – 100 seconds. Special-purpose grades used as insulators in high-voltageapplications can achieve resistancetimes of up to approx. 420 seconds.

Surface resistance> Surface resistance is measured inaccordance with VDE 0303. Values forinsulating ELASTOSIL® LR compoundstypically vary from 1012 to 1013 Ω.

Volume resistivityInsulating silicone rubbers exhibit a > volume resistivity of approx. 1015 to1016 Ω · cm (in accordance with VDE0303). Electrically conductive rubberparts can be made of rubbers whichcontain special-purpose grades of > carbon black. Such components have a volume resistivity which varies from 2 to 150 Ω · cm (e.g. ELASTOSIL® LR3162).

The temperature dependence of thevolume resistivity is much more pro-nounced in addition-curing systems.Temperature dependence is more evi-dent at high initial values than at lowconductivities. Special-purpose com-pounds can achieve volume resistivityvalues of 4 · 10–3 Ω · cm (in EMI/EMP applications).

29

Physical properties

Silicone rubbers have a broad range ofapplications in the electrical industry. Thisinvolves not only different types of tests,but also a variety of specialized instru-ments.

30

OUR PRODUCTS COMPLY WITH ALLSAFETY REGULATIONS

The use of silicone rubber articles inthe food and pharmaceutical indus-tries is regulated by the state accord-ing to regulations drawn up by publicauthorities.

WACKER healthcare guidelinesThese guidelines relate to the use of silicone products in the manufacture ofmedical devices.

We do not supply products for long-termimplants that remain for more than 30days in the human body.

Our products should not be used for thefollowing applications:– Cosmetic reconstruction (e.g. plastic

surgery, prosthetic devices)– Devices for gynecological or obstetric

applications (e.g. cervical caps, tampons)except for diagnosis and monitoringand surgical instruments

– Contraceptive devices (e.g. condoms,condom lubricants, intrauterine devices,cervical caps)

– Direct injection including the use of sili-cone fluids in applications where theycan be introduced directly into tissues,body cavities or blood (e.g. syringelubricants, intraocular fluids)

PharmaceuticalsGermany– „Gummiteile“ – Transfusion, Infusion,

Injektion, DIN 58 367– „Infusionsgeräte“ – Infusion, Transfu-

sion, DIN 58 362

USA– „Biological Tests – Plastics“, United

States Pharmacopoeia

France– „Silicone élastomère réticulé à chaud“,

french Pharmacopoeia

Europe– „Silicone Elastomers for Closures

and Tubing“, European PharmacopoeiaPA/PH/Exp. 3/T (82) 57 DefinitiveJanuary 22, 1985

– Commission Directive 93/11/EEC„Release of N-nitrosamines and N-nitrosable substances from elasto-mer or rubber tests and soothers“,(1993)

31

Physiological properties

The non-toxicity of silicone rubbers makesthem perfect for food-related applications.

Food contactGermany– BfR XV, Teil A, „Silicone“, 182.

Mitteilung BGBl. 32, 211 (1989)– BfR IX, Teil A, „Farbmittel zum Ein-

färben von Kunststoffen und anderenPolymeren für Bedarfsgegenstände“,178. Mitteilung BGBl. 31, 363 (1988)

– „Kennzeichnung von Bedarfsgegen-ständen im Sinne des Lebensmittel-gesetzes“, DIN 7 725

– KTW-Empfehlung, BGBl. 28, Nr. 12(1985)

– The following ELASTOSIL® LR gradeswere tested: ELASTOSIL® LR 3003/XXand ELASTOSIL® LR 3004/XX

USA– “Rubber Articles Intended for Repeated

Use in Contact with Food,” FDA Codeof Federal Regulation, § 177.2600

France– “Décrets et Circulaires du Ministère de

l’Agriculture,” Brochure No. 1227

United Kingdom– BS 6920 (WRAS)– The following ELASTOSIL® LR grades

were tested: ELASTOSIL® LR 3003/XXand ELASTOSIL® LR 3004/XX

32

WE USE BOILING WATER, TOO, BUT THERE’S SILICONE RUBBER IN IT

The hydrophobic character of the silicones bestows silicone rubber withexcellent resistance to boiling water.In general, silicones are known fortheir outstanding high temperatureresistance.

WaterSilicone rubber is very stable to boiling> water. Its hydrophobic character preventsthe penetration of water, so that the in-crease in volume remains less than 1 %,even after prolonged immersion. Conse-quently, the insulating effect of silicone rubber cables, for instance, is fully retained.

SteamThe behavior of different ELASTOSIL® LRcompounds in > steam is not uniform.Highly flexible rubber grades – those withhigh rebound resilience and low com-pression set – usually perform better.Steam sterilization at 120 °C or 130 °Ccan be carried out repeatedly with virtu-ally all grades.

Hot airSilicone rubber articles remain flexibleeven when exposed to extreme tempera-tures. When it comes to > hot-air resist-ance, they thus surpass most organicelastomers, whose polymers are derivedfrom the carbon-carbon bond, which isless thermally stable.

> Oxidative degradationAt high temperatures (approx. 180 °Cand above), the organic substituents aresplit off from the silicon atoms to formfree radicals, thus creating additionalcrosslinks between polymer chains. This> oxidative degradation, an irreversiblechemical process, becomes evident in aloss of weight, which is accompanied byshrinkage of rubber parts combined withincreasing embrittlement. This in turnmeans an increase in hardness, but adecrease in tensile strength, elongationat break and tear strength. The processcan be retarded, although not stoppedcompletely, by adding carbon black.

Oxidative and hydrolytic degradation

CH3

Si 0

CH3

Oxidative degradation

Hydrolytic degradation

33

Resistance

On the other hand, the overall increasein crosslinking density under sustainedhigher temperatures has a positive effecton resilience and compression set. Thisalso explains why the insulating propertyof silicone rubber at high temperaturesremains virtually constant for prolongedperiods: the rubber’s insulating proper-ties are comparable to those of quartz.

Hydrolytic degradationIn the initial phase of oxidative degrada-tion, a parallel reaction, > hydrolytic deg-radation, occurs at high temperatures(200 °C and higher). Traces of moistureor the hydroxyl groups in the fillers orplasticizers present in the rubber causethe polymer chains to hydrolyze. Theeffect is a softening of the material.

Atmospheric oxygen inhibits this reaction.The excellent stability of silicone rubberat high temperatures only applies in thepresence of sufficient oxygen. This prop-erty of silicone rubber must always betaken into account in the design of sealsand gaskets.

As the test shows, silicone rubber's reliable properties remain fully intact even after the cured rubber products have been boiled for a long time.

34

ELASTOSIL® LR liquid silicone rubber isdurable in hot acids or alkalis, too.

SOME OF OUR TEST SPECIMENS AREOLDER THAN THEIR TESTERS

35

Resistance

ChemicalsThe > chemical resistance of curedELASTOSIL® LR liquid silicone rubbergrades depends to a large extent on thecrosslinking density and the type of fillerused. In general, it can be said that resistance to chemical attack is in directcorrelation to the amount of filler in therubber. For this reason, high-density rubber compounds should be used inswelling media.

Aqueous solutions of weak acids, alkalisor salts hardly attack silicone rubber. Dilute acids and alkalis can be used attemperatures of 70 to 80 °C to cleanpipes and tubing in the food industry, forexample. Acids at higher concentrationshaving oxidizing properties (e.g. sulfuricor nitric acid) destroy silicone rubber.

Polar liquids (short-chain alcohols, espe-cially polyhydric ones, low molecularweight ketones) cause hardly any swell-ing of silicone rubber. Therefore, sealsand gaskets of ELASTOSIL® LR com-pounds can be readily used in appropri-ate applications.

Nonpolar liquids (linear or cyclic hydro-carbons, aliphatic or aromatic mineraloils, gasoline etc.) cause severe swelling.They can only be used to a limitedextent. Processors must set prioritieshere, especially as organic elastomersresistant to swelling often have unsatis-factory heat resistance.

WeatheringEven after years of exposure to > weather-ing, there is virtually no change in theproperties of silicone rubber parts.ELASTOSIL® LR compounds, unlikeorganic elastomers, require no additionaladditives to improve their resistance to weathering. In an industrial climate test in accordance with DIN 50 018 –SFW 2.0 S (2 l sulfur dioxide) specialcompounds1 reach 1.5 million cycleswithout changes in the surface.

RadiationThe resistance to high-energy > radia-tion and hot-air resistance of siliconerubber is superior to most elastomers.

The effects of radiation are comparableto the consequences of exposure to hightemperatures. VMQ rubbers can absorb aradiation dosage of approx. 40–50 Mrad.This reduces elongation at break by upto 50 %.2 The > sterilization of siliconerubber articles by > gamma radiation, often employed in the field of medicine,does not, however, impair their quality.

If silicone rubber is exposed to radiationat elevated temperatures, its chemicaland mechanical resistance drops con-siderably. At 180 °C, the maximum permissible dose amounts to approx. 10 Mrad for VMQ grades. These limitsdrop, however, if the silicone rubber isexposed to radiation at dosages belowthe limits. In this case, the crosslinkingefficiency of the radiation is also higher.

1 This applies to ELASTOSIL® LR 3003/50, for example.2 These values relate to a 2-mm thick test specimen that

was irradiated at room temperature and with a dose of 2 Mrad/h.

Obtaining a desired test result is oftenjust one side of the coin. In manycases, it is important to maintain acertain property over a lengthy period.Our customers can rest assured thatproduct properties are stable.

36

WHY SOME GRADES BLEED OIL

Specialty silicone fluids are added toself-lubricating ELASTOSIL® LR liquidsilicone rubbers. These silicone fluidsare homogeneously distributed in the rubber, but are incompatible withthe fully cured rubber – leading to“oil-bleeding.”

> Methylphenyl silicone fluids consist ofmethylphenylsiloxy units combined withstatistically distributed dimethylsiloxygroups. Their incompatibility is due tothe fact that some of the methyl groupsare replaced by phenyl groups. Incor-poration of phenyl groups into the poly-diorganylsiloxane chain causes a strongintermolecular interaction that results inhigh viscosity with a comparatively lowmolecular weight. This viscosity increaseis also shown in the thixotropic behaviorof the self-lubricating liquid silicones, par-ticularly as their viscosity, with the samehardness, is about twice that of standardproducts without addition of oil.

The cause of the strong intermolecularinteractions lies in the different electroniceffects of methyl and phenyl groups: for example inductive and resonanceeffects.

In physical terms, the incompatibility ofsilicone fluid in the rubber is due to thedifferences in chemical potential betweenthe system’s liquid and solid phases.This potential gradient causes a passivemigration of the > silicone fluid.

The > oil-bleeding or > diffusive proper-ties of oil-bleeding grades depends onthe following parameters:– Temperature– Viscosity– Particle cross-section or size– Pressure

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Oil-

blee

ding

rat

e [w

eigh

t %

]

10 Time [d]

Oil-bleeding properties of ELASTOSIL® LR 3844/50

20 30 40 50 60

–20 °C +25 °C +50 °C

37

Oil-bleeding behavior

Methylphenyl silicone fluids

CH3 CH3

(CH3)3Si 0 Si 0 Si 0 Si(CH3)3

C6H5 m CH3 n

Some care is necessaryFluctuations in the oil-bleeding behaviorof silicone rubber articles may lead toconsiderable difficulties, particularly whenweather packs or cable bush pads aremanufactured in automatic processes.This is why it is essential to take accountof certain dependencies when self-lubricating liquid silicone rubbers areprocessed.

Crosslinking densityThe interparticle distance depends onthe crosslinking density in the siliconerubber. And this in turn can be controlledby various processing parameters:– By the curing conditions:

injection pressure, molding temperatureand heating time

– By the hardness of the rubber:filler and crosslinker content

– By the color:the incorporated pigment

By means of a special rubber blend and an appropriate processing windowemploying modern technology, it is easy to maintain a constant crosslinkingdensity.

PressureApart from the > oil content of the rubbercompound, the pressure depends on thearticle’s design and on the storage con-ditions. Small moldings, in particular, areoften tightly packed in plastic bags andstored for a fairly long time. Silicone fluidmay easily escape under such conditions.

Storage timeThe oil content on the surface of siliconerubber articles is not only influenced by temperature and pressure, but alsoby the storage duration. Therefore, it isessential to ensure optimum storage conditions.

TemperatureThe storage temperature affects the rateof the diffusion process substantially.This is because at higher temperaturesdiffusion occurs much more quickly thanat low temperatures (see illustration).Seasonal temperature fluctuations cantherefore influence oil-bleeding proper-ties. Especially as the fully cured rubberarticles are not stored in a conditionedstate. Although in winter a silicone rubberarticle gives the impression that it doesnot bleed oil, in summer a comparablearticle may be considerably wetted withsilicone fluid.

38

COOPERATION MEANS GETTING TOGETHER ONCE IN A WHILE

Even though you can find out about ourproduct range by reading our brochures,visiting our website or calling us at any time,in some situations, nothing can beat a personal meeting.

39

Service

Although this is the age of communi-cation, meeting in person is becomingincreasingly rare. Yet the quickest wayto solve certain problems is often forpeople to meet up briefly. Our techni-cal support staff know our productsand their related properties. But theyalso know your production processesand what these processes require.They can therefore offer you expertadvice – on site if necessary.

It is quite obvious that the more infor-mation you receive, the smoother yourmachinery will run. We strive to ensurethat our complete product portfolio isvery easy to understand. Our goal is toprovide you with the information youneed quickly and easily – through ourbrochures, our hotline or the internet.

However, our most important informationmedium will continue to be personal dia-log with our customers. This is the bestway for us to find out about your par-ticular needs and to develop individual solutions to problems not dealt with inany of our brochures. Ask us. We’ll beglad to help: Your rubber fabricator busi-ness team.

How to stay well informedPlease ask about our brochures or visitour web site at www.wacker.com orwww.wacker-silicones.com. Our website offers you a source of quick referen-ce, plus the option to search and down-load specific information around theclock.– Processing ELASTOSIL® LR Liquid

Silicone Rubber– ELASTOSIL® Products According to

Application– All ELASTOSIL® Product Data Sheets

at a Glance– Self-Adhesive ELASTOSIL® Silicone

Rubber Grades– Platinum-Catalyzed Addition Curing

with ELASTOSIL® R plus– ELASTOSIL® Is Everything You Want

A general summary of WACKER’scomplete ELASTOSIL® silicone rubberrange

40

YOU NOW KNOW OUR TEST RESULTSHERE ARE OUR QUALITY STANDARDS

General DIN ASTM BS ISO

Silicone rubber (uncured) DIN ASTM BS ISO

Silicone rubber (cured) DIN ASTM BS ISO

Units 1 301 E 380 1000-1382

Definitions 53 501 D 1566 4632/1

TR 8461

Classification of elastomers 78 078 D 2000 1629

Rubber, nomenclature, categories 1 629 D 1418

Grouping of high-polymeric materials

according to temperature dependency 7 724

Classification for automotive applications D 2000 4632/1

Storage, cleaning 7 716 2230

Tolerances 7 715 3302

Factory certificate 50 049

Quality control 9000

9004

Statistical evaluation 53 598 D 3488

Mooney viscosity 53 523 D 1646 289

Vulcanization characteristics 53 529 D 2084 667

Extrudability D 2230

Preparation of test specimens 53 502 D 3182 903-A36 DP 2214

D 3183 4661

Density 53 479 D 792 903-A1 1183, 2781

Hardness Shore A, IRHD 53 505 D 2240 903-A26 868

53 519 D 1415

Tensile strength, elongation at break 53 504 D 412 903-A2 37

Tension set 53 518 D 412 903-A5 2285

Tear strength ISO 34-1 D 624 903-A3 34

Rebound resilience 53 512 D 1054 903-A8 4662

Compression set 53 517 D 395 903-A6 1653-815

Dynamic torsion test 53 445 903-A31 4663

41

Quality standards

Behavior at low temperatures 53 545 D 3847 903-A13 1432

53 548 D 797 903-A25 812

53 546 D 1053

D 746

D 2137

Electrical properties DIN-VDE 0 303 D 149, 150 903-C1 TO C5

D 257

Tracking resistance DIN-VDE 0 441 D 2303

Arc resistance DIN-VDE 0 441 D 495

Flame resistance: 4589

oxygen index D 2863 2782

construction materials and components 4 102 476

Abrasion 53 516 D 1630 903-A9 4649

Gas permeability 53 536 903-A17 1399, 2782

Flexometer test 53 533 903-A50

Flexing endurance test 53 522 D 813 903-A10, 903-A11 132, 133

D 430

Determination of adhesion to metal 52 531 D 429 903-A21 813, 814

Siloxane content of HTV

silicone elastomers 53 621/10

Pyrolysis residue of silicone

rubber products 53 587

Accelerated aging 53 508 D 573 903-A19 188, 1826

Temperature-time limits 53 446

Water vapor permeability 53 122

Effects of liquids, vapors and gases 53 521 D 471 903-A16 1817

Testing in a saturated atmosphere (Kesternich test) 50 018

Weathering resistance outdoors or in equipment 53 386 D 518 4892

53 387

Resistance to ozone cracking 53 509 D 3395 903-A23 1431

D 518, 1171

Resistance to ionizing radiation D 1672

Flexible cellular materials D 1056

Heat-shrinkable tubing D 2671

Silicone rubber (cured) DIN ASTM BS ISO

42

WHERE TO FIND YOUR KEYWORD INTHE TEXT

> Adhesives (20)> Arc resistance (28)> Autogenous ignition temperature (26)> Carbon black (28)> Catalyst (4)> Chemical resistance (35)> Coating (20)> Coatings dispersion (20)> Coefficient of linear thermal

expansion (26)> Compression set (24)> Crescent (24)> Crosslinker (4)> Cured rubbers (23)> Density (24)> Diatomaceous earth (4)> Dielectric constant (28)> Dielectric strength (28)> Diffusive properties (36)> Dissipation factor (28)> Elongation at break (24)> Fillers (4)> Fire standards (26)> Flame retardancy (26)> Fumed silicas (4)> Gamma radiation (35)> Gas permeability (27)> Graves (24)> Hardness (24)> Hot-air resistance (32)> Hydrolytic degradation (33)> Inert fillers (4)> Inhibitor (4)

> IHRD (24)> Measurement temperature (25)> Methyl groups (4)> Methylphenyl silicone fluids (36)> Oil-bleeding properties (36)> Oil content (37)> Oxidative degradation (32)> Peroxide reaction (6)> Pigments (19)> Platinum-catalyzed addition curing (6)> Polymer (4)> Precipitated silicas (4)> Primers (20)> Quartz (4)> Radiation (35)> RAL colors (19)> Rebound resilience (25)> Shore A (24)> Shrinkage (26)> Silicone fluid (36)> Silicon-oxygen bond (4)> Specific heat (27)> Steam (32)> Sterilization (35)> Surface resistance (28)> Tear strength (24)> Tensile strength (24)> Test slabs (23)> Thermal conductivity (27)> Tracking resistance (28)> Trousers (24)> Vinyl groups (4)> VMQ polymers (4)

> Volume resistivity (28)> WACKER HDK® (4)> Water (32)> Weathering (35)

We extend thanks to Starlim for theirkind assistance with the photographsin this brochure.

WACKER AT A GLANCE

WACKER SILICONESis a leading supplier of complete silicone-based solutions that comprise products, services and conceptual approaches. As a provider of solutions, the business divi-sion helps customers press ahead with innovations, exploit global markets fully, and optimize business processes to reduce overall costs and boost productiv-ity. Silicones are the basis for products offering 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 and paper, cosmetics, consumer care and textiles, to mechanical engineering and metal processing.

WACKER POLYMERSis the global leader for high-quality bind-ers and polymer additives. This business division’s activities encompass construc-tion chemicals and functional polymers for lacquers, surface coatings and other industrial applications, as well as basic chemicals, i. e. acetyls. Products such as dispersible polymer powders, disper-sions, solid resins, powder binders and surface coating resins from WACKER POLYMERS are used in the construction, automotive, paper and adhesives industries, as well as by manufacturers of printing inks and industrial coatings.

WACKER FINE CHEMICALSAs an expert in organic synthesis, silanes and biotechnology, WACKER FINE CHEMICALS supplies innovative biotech products and catalog chemicals for life-science and consumer-care customers worldwide. Its product portfolio includes cyclodextrins and cysteine, organic intermediates and acetyl acetone. A key

specialty is the contract manufacturing of pharmaceutical proteins via microbial systems.

WACKER POLYSILICONhas been producing hyperpure silicon for the semiconductor and photovoltaics industries for over 50 years. As one of the largest global manufacturers of polycrys-talline silicon, WACKER POLYSILICON supplies leading wafer and solar-cell manufacturers.

Siltronicis one of the world’s leading producers of hyperpure silicon wafers, supplying many major chip manufacturers. Siltronic devel-ops and produces wafers up to 300 mm in diameter at facilities in Europe, the USA, Asia and Japan. Silicon wafers form the basis of state-of-the-art micro and nanoelectronics used, for example, in computers, telecommunications, motor vehicles, medical technology, consumer electronics and control systems.

WACKERis a technology leader in the chemical and semiconductor industries and a worldwide innovation partner to cus-tomers in many key global sectors. With around 14,700 employees, WACKER generated sales of € 3.34 billion in 2006. Germany accounted for 20 % of sales, Europe (excluding Germany) for 28 %, the Americas for 20 % and Asia-Pacific, including the rest of the world, for 32 %. Headquartered in Munich, Germany, WACKER has some 20 production sites worldwide and a global network of over 100 sales offices.With R&D spending at 5 % of sales in 2006, WACKER is among the world’s most research-intensive chemical companies.

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www.wacker.com

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