Silicone compounds and sealants and their application in various branches of industry

ISSN 1995 4212, Polymer Science, Series D. Glues and Sealing Materials, 2010, Vol. 3, No. 4, pp. 244–248. © Pleiades Publishing, Ltd., 2010.Original Russian Text © E.I. Alekseeva, S.R. Nanush’yan, I.Yu. Ruskol, E.V. Sokolyuk, 2010, published in Klei. Germetiki. Tekhnologii, 2010, No. 5, pp. 10–14.244Silicone polymers and materials based on them have found a widest application in all spheres of human activities. Silicone compounds and sealants are used in electronics, micro and optoelectronics,electrical engineering, and in the automotive, avia tion, and construction industries. Within recent years,their application in medicine and even in everyday life has dramatically increased.To design new materials that meet multiaspect needs, modern methods of production that involve nanotechnology are applied. The basic mechanisms of polymerization that are used in the development of formulations of silicone compounds and sealants are (a) the polyaddition reaction and (b) radical polymer ization under ultraviolet irradiation according to the schemes listed below:(a) ≡Si–CH=CH 2 + H–Si ≡≡Si–CH 2–CH 2–Si ≡(b) ≡Si–A–CR=CH 2≡Si–A–CR–CH 2–C R –CH 2–A–Si ≡.The schemes show that polymerization occurs without evolution of byproducts, which makes it pos sible to use these compositions not only as film type or covering materials, but also as potting materials for closed volumes of any configuration.Silicone materials in the cured condition can have different physical states: from the gel and elastomeric state (compounds, sealants, and adhesives of the SIEL brand) to the glassy state (compounds and adhesives ofthe STYK brand). The operating temperatures of the developed materials range from –90 to +350°C. The SIEL 159 305 compound with the glass transition temperature T g = –118°C, which is determined by the differential scanning calorimetry method, exhibits an extremely high freeze resistance surviving up to ⎯90°C.In addition, this compound can also be used at a fairly high positive temperature (up to 200°C for a long term and up to 220°C for a short term). The thermo gravimetric research methods (TGA/DTA) showed that SIEL 159 274 and SIEL 159 275 compounds can operate at temperatures up to 300 and 350°C, respec tively . It is significant that, in the negative range of tem peratures, they also have a higher efficiency than con ventional polydimethylsiloxane polymer compositions.The study of thermal aging processes showed that SIEL and STYK compounds exhibit high thermal sta bility during a long period of time and retain a satisfac tory level of the basic parameters: strength and elonga tion for elastomeric compositions (Fig. 1) and Brinell hardness for glassy materials. Figure 1 shows that an appreciable decrease in these parameters is observed within the first 15 days of thermal aging at 250°C,under which conditions the parameters change only slightly , remaining at a fairly high level.All compounds of the SIEL type have a satisfactory resistance to radiation. However, Table 1 shows that the SIEL 159 275 compound withstands an exposure dose up to 107 rad without significant changes in the physical mechanical and optical properties, which isSilicone Compounds and Sealants and Their Applicationin Various Branches of IndustryE. I. Alekseeva, S. R. Nanush’yan, I. Yu. Ruskol, and E. V. SokolyukState Scientific Center of the Russian Federation, State Research Institute for Chemistry and Technology of Organoelement Compounds, sh. Entuziastov 38, Moscow, 111123 RussiaE mail: eoc@cos.incotrade.ruReceived February 6, 2010Abstract —In this work, we discuss heat and photocurable silicone compounds that have different physical states in the cured condition ranging from the gel and elastomeric state (compounds, sealants, and adhesives of the SIEL brand) to the glassy state (compounds and adhesives of the STYK brand). The operating temper ature range of the developed materials is –90 to +350°C. It is shown that the developed compounds and seal ants exhibit good mechanical and dielectric properties, high heat and freeze resistance, optical and chemical purity , and are biologically inert. There are two and one package formulations of the compounds.Keywords : organosilicon polymer, silicone adhesive, silicone sealant, SIEL compound, STYK adhesive.DOI: 10.1134/S1995421210040076POLYMER SCIENCE Series D V ol. 3 No. 4 2010SILICONE COMPOUNDS AND SEALANTS AND THEIR APPLICATION245apparently explained by the high content of phenyl radicals as a frame of the main siloxane chain.The SIEL 159 305 compound, which contains flu orosiloxane units in the polymer chain, exhibits high values of oil and gasoline resistance. The test results for the films based on this compound are listed in Table 2.Table 2 shows that the films swell only slightly in these environments. The maximum swelling is observed in acetone; however, it fits into the admissible norm, i.e., the decrease in the value of the parameter under study is not more than 20%, which makes it pos sible to recommend this compound as a base for the design of oil and gasoline resistant materials, which are used, e.g., in the oil and gas industry (pumps and other equipment).All of the developed materials have good adhesion to surfaces such as metal, glass, and ceramics. For compounds of the SIEL type, as a rule, a cohesive tearing off takes place. Compounds of the STYK type exhibit a fairly high strength of adhesion bond to steel (τshear at a level of 9–12 MPa), which, as a rule, is pre served in the process of thermal aging at 200–400°C for 14 days.Compounds of the STYK series have a high hard ness (Table 5) and can easily be polished and ground,which predetermines their use as potting and harden ing materials with high optical transmission, which isan important factor for their use in products of fiber optics. In recent years, the interest in these composi tions increases owning to the beginning of the indus trial assimilation of light emitting diodes (LEDs).1SIEL and STYK compounds are produced in both filled and unfilled form. Thus, filled compounds are used as potting and sealing materials. Their properties can vary significantly , ranging from dielectric to con ducting, easy flowing to thixotropic. By selecting a given fillers, one can design materials of almost any color, which is important, e.g., for their use as com pounds for sign writing on keyboards. The main prop erties of produced pigmented compounds are listed in Table 7. It is easy to see that SIEL compounds are characterized by a complex of high physical mechani cal and dielectric properties.Unfilled compositions exhibit a high light trans mission (up to 92–98% in the visible light range) and a variable index of refraction (1.375–1.560), which is of critical importance for using these materials, e.g., as intermediate layers in triplexes of different composi tions and antireflective films for glasses with different refractive indices, etc. The refractive index is con1In LEDs, unlike incandescent lamps or luminescent tubes, electric current is converted directly into light emission, which in theory , can occur almost without losses.1.61.20.80.440302010010060402060L , %σp , MPaTime, days1234Fig. 1. Variation in (1, 2) tensile strength and (3,4)elongation of (1, 3) the SIEL 159 274 compounds and (2,4)SIEL 159 275 compounds under thermal aging (250°C).246POLYMER SCIENCE Series D V ol. 3 No. 4 2010ALEKSEEVA et al.T able 2.Stability of films of SIEL 159 305 compound to oils and solventsLiquid mediumSwelling, wt %Shore hardness A, arb. units, after holding in a liquid medium for 72 hMachine oil 039Methyl alcohol 040Ethylene glycol 139Gasoline 437T oluene 637 Acetone832Note:Shore hardness of film A before testing is 39 arbitrary units.T able 3.Content of microimpurities in SIEL compounds for microelectronicsElement nameContent in compound, wt %Detection limits, wt %Sodium 2 × 10–6 5 × 10–7Magnesium 5 × 10–6 5 × 10–8Aluminum 3 × 10–6 5 × 10–7Calcium 4 × 10–6 1 × 10–7V anadium <1 × 10–7 1 × 10–7Chromium 2 × 10–6 1 × 10–6Manganese 6 × 10–7 1 × 10–7Iron 2 × 10–6 2 × 10–7Nickel 8 × 10–7 1 × 10–7Copper<1 × 10–7 1 × 10–7Uranium and thorium (in total)<1 × 10–61 × 10–6T able 4.Basic properties of heat curable compounds for optic fibers and microelectronics SIEL com pound brand η, MPa s τe , h t c , min σt , MPa L , %Shore hardness A, stand. units V , m/min α, dB/kmOperating temperature range, °C159 305 1.3954000615 3.512030502000–90…+200159 306 1.4264500730 3.012040402500–55…+220159 274 1.4606000630 2.011025303000–70…+230159 275 1.5105000530 1.010*********–80…+250159 4381.37550006201.514012152000–95…+200Note:n is refraction index; η is dynamic viscosity; τe is lifetime at (20 ± 5)°C; t c is curing time; σb is tensile strength at breaking; L is elongation;V is rate of drawing of optic fiber while passing through a draw hole at 280–300°C; and α is radiant energy losses.n D20Table 1.Effect of irradiation on physical mechanical properties of SIEL compounds SIEL compound brand Tensile strength, MPaElongation, %before exposureafter exposure before exposureafter exposure dose 1dose 2dose 1dose 2159–27422.626.324.410010597.0159–27511.416.316.210911392.5Note:Dose 1 is 5.2 × 104 rad; dose 2 is 1.06 × 107 rad.POLYMER SCIENCE Series D V ol. 3 No. 4 2010SILICONE COMPOUNDS AND SEALANTS AND THEIR APPLICATION247T able 6.UV curable SIEL compoundsParameterSIEL compound brandUV 1UV 2UV 3UV 4159 254*Viscosity , cP 200035001000065005000Density , g/cm 3 1.000.98 1.01 1.040.98Refraction index 1.42 1.41 1.43 1.47 1.41T ensile strength, MPa 2.5 2.0 3.5 1.5 3.0Elongation, %1802606060120Shore hardness A, arb. units3530606030 Operating temperature range, °C –60…+200–40…+200–60…+150–60…+150–40…+200Rate of drawing of OF**, m/min 803015012040Water absorption at 25°C for 24 h, %Notes:*Heat curable compound was taken as a basis for comparison.**OF is optical fiber.T able 7.Properties of elastomers for electronics and electrical engineering SIEL brandPhysical formσt , MPa L , %ρv , Ωmtan δE , kV/mm t curing , °COperationrange, °C Note159 190*,**From semitransparent to light green2.01201–3 × 10120.001027160–180–60…+200159 191White4.0901–3 × 10130.000730120–150–60…+200159 254*T ransparent 4.51201–3 × 10140.00052760–150–60…+200159 256**White 2.51001–3 × 10130.000730160–180–60…+220159 360White 2.51201–3 × 10130.006032160–80…+250159 390Black 2.8140120–150–60…+200159 406Gray 2.090120–180–60…+250Heat conducting 159 407Dark gray 3.01001–5 × 10680–150–60…+200Current conducting 159 414Silvery 3.01001–5 × 105150–180–60…+200Current conducting 159 421**White 2.01101–3 × 10110.00127160–180–60…+220Thixotropic 159 440*'' 4.01001–3 × 10130.00102720–100–60…+220159 442**'' 2.01201–3 × 10110.00127140–150–60…+220Thixotropic 159 476T ransparent1.5200–––80–200–60…+200For triplex* There are several modifications of this compound, the viscosity of which is, as a rule, different from the base one given in the table.** Single component compound.Note: In the absence of indication **, the compound has a two package formulation.T able 5.Properties of STYK compoundsParameterCompound brandSTYK 1STYK 2STYK 3STYK 4STYK 5Dynamic viscosity , MPa s 3.5 × 103 3.0 × 103 4.5 × 103 5 × 103 5 × 103Refraction index 1.422 1.402 1.460 1.480 1.520Density , g/cm 31.02 1.08 1.07 1.09 1.13Lifetime at 20°C, h4–64–63–53–53–5Curing temperature, °C/curing time, h 160/3150/3160/3160/4160/4Brinell hardness, HB120401009080Radiant energy losses*, dB/km, maximum 4 × 103 4 × 103 4 × 103 5 × 103 5 × 103Operating temperature range, °C–40…+200–70…+200–60…+200–60…+250–70…+280*In a 100 mm thick layer.248POLYMER SCIENCE Series D V ol. 3 No. 4 2010ALEKSEEVA et al.trolled within the specified range through the intro duction of hetero units in a polydimethylsiloxane matrix, as shown in Fig. 2.High purity silicone compounds of this type hardly contain ionogenic impurities (compounds of Na, K,Ca, Cl, etc.), transition metals (Fe, Ni, Cd, etc.), and radioactive compounds (U, Th, etc.) (Table 3).Depending on the type of device or facility , materials are produced that cure at moderate temperatures (from room temperature to 160°C for 24 h to 30 min,respectively) or under UV irradiation of different intensity at room temperature with duration of a few minutes to a few seconds. Heat curable materials are capable of polymerization in layers with various thick nesses, whereas UV curable materials polymerize in thin layers only (no more than 0.1–0.2 cm). It should be noted that UV curable compositions make it possible to use a stencil screen printing and the selective method of curing.By varying the ratio of ingredients and selecting the appropriate platinum coordination catalyst, we can obtain a silicone composition with a high adhesiveness,which is determined via a standard procedure: a 10 g plummet is placed at the center on the film sur face, the film with a plummet is turned over, and the time of tearing off is recorded. Figure 3 shows the vari ation in time of the adhesiveness versus the operation temperature.The data analysis shows that the composition remains stable over a long period. This material can be advantageously used as an adhesive sealant with high optical purity , as well as in medical technology (special medical tapes). At present, a large series (more than 50items) of materials of the SIEL and STYK types are produced. The basic properties of the developed com pounds are listed in Tables 4–7. These tables show that a wide range of developed silicone compounds gives the possibility to select a material that meets the spec trum of requirements of modern industry , including so called high tech industry .1.501.451.401.35605040302010070Hetero units, mol %123n D20Fig. 2. Control of refractive index of silicone poly mer compositions by introduction of hetero units in a polydimethylsiloxane matrix: (1) methyl trifluoro propyl siloxane units; (2) methyl ethyl siloxane units; and (3) methyl phenyl siloxane units.5.04.54.03.53.0100806040200213A d h e s i v e n e s s *Time, daysFig. 3. Variation in adhesiveness of silicon adhesive compound versus temperature and exposure:(1)room temperature (+25°C); (2) refrigerator (+6°C); and (3) elevated temperature (+40°C).Adhesiveness* is given per unit value.。