Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/12—Polysiloxanes containing silicon bound to hydrogen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/20—Polysiloxanes containing silicon bound to unsaturated aliphatic groups

Definitions

• the present invention relates to the technical field of addition-curing silicone rubbers, in particular to the technical field of addition-curing silicone rubber compounds.
• WO 2013137473A discloses a silicone rubber composition for medical tubing.
• Table 1 and Table 2 therein disclose several examples containing methyl vinyl gums, hydroxyl-terminated silicone oils, fumed silicas, vinyl silicone oils and hydrogen silicone oils, wherein the vinyl silicone oil (b2) contains 10 wt%vinyl groups and the weight ratio of Si-H groups in the formulation to all vinyl groups in the composition is between 2.0 and 3.5.
• the composition is heated at 120°C for 10 minutes to obtain a product having a suitable hardness of about 70.
• CN103665885B discloses a high tear resistant silicone rubber composition containing 100 parts of methyl vinyl gum, hydroxy silicone oil and fumed silica, from 4 to 6 parts of vinyl silicone oil and from 3 to 7 parts of hydrogen silicone oil, wherein the vinyl silicone oil has a vinyl content of from 5 to 10%, and the hydrogen silicone oil has a hydrogen content of from 0.5 to 3%. Since the unit of the above-mentioned functional group contents is not disclosed, and may be vinyl weight ratio or the vinyl mole fraction, it is not possible to make relevant calculations.
• the invention discloses a polysiloxane composition which has good prolonged curing behavior, and elastomers obtained after the first curing and post-curing processes have a high hardness and are suitable for manufacturing various kinds of silicone rubber parts with complicated shapes, high mechanical strength and stable properties.
• the polysiloxane composition herein is a compound formulated with polyorganosiloxanes having a linear high polymer (consisting of 5,000 to 10,000 siloxane units) as gum and a crosslinking agent (e.g. a hydrogen silicone oil) added with a reinforcing filler filler (be composed of silicas) , an extender (including calcium carbonate, talc, silica powder, diatomaceous earth, titanium dioxide, iron oxide, etc) , a structural control agent and various property-improving additives. When used, it is added with a hydrosilylation catalyst before heated and cured to form a polysiloxane elastomer. In the course of processing, a roll mill is often used for compounding before curing and molding processes, which relates to the technical field of silicone rubber compounds.
• a crosslinking agent e.g. a hydrogen silicone oil
• a reinforcing filler filler filler be composed of silicas
• an extender including calcium carbonate
• Si-H/Vi*weight ratio is between 1.5 and 3.5, preferably between 1.9 and 2.8, and it refers to the weight ratio of the hydrosilyl groups (Si-H) of the hydrogen silicone oils to the vinyl groups (Vi*) of (b) multi-vinyl siloxanes, wherein Vi*does not include the vinyl groups of (a) vinyl siloxane gums.
• R is independently selected from among C1-C4 alkyl groups, preferably methyl and R 1 is independently selected from among C1-C4 alkenyl groups, preferably vinyl; R can be the same or different, R 1 can be the same or different; n and m are integer greater than or equal to 0; and
• m/ (n+m+2) 2-100%, preferably 3-50%, more preferably 5-40%, and most preferably 10-30%;
• the viscosity of the multi-vinyl siloxanes is less than or equal to 8,000 mPa. s, preferably less than or equal to 5,000 mPa. s, more preferably less than or equal to 1, 500 mPa. s.
• the multi-vinyl siloxanes are selected from the group being composed of a tetramethyldivinyldisiloxane and multi-vinyl silicone oils having a viscosity of between 50 and 5,000 mPa. s, wherein the vinyl content of the multi-vinyl silicone oils is between 0.1 and 20 mmol/g, preferably between 0.5 and 15 mmol/g, and more preferably between 1 and 10 mmol/g.
• composition as mentioned above comprising
• silica (s) used in an amount of from 20 to 40 wt%, preferably from 25 to 35 wt%, and/or
• inhibitor (s) preferably 1-ethynyl-cyclohexanol,
• hydrosilylation catalyst preferably Karstedt’s catalyst, chloroplatinic acid and chloroplatinic acid-tetramethyltetravinylcyclotetrasiloxane complex, wherein the concentration of Pt atoms in the composition is from 3 to 100 ppm,
• composition as mentioned above, wherein the hydrogen silicone oil has an Si-H content of between 1 and 10 mmol/g, preferably between 4 and 8 mmol/g.
• composition as mentioned above wherein the vinyl siloxane gum has a weight average molecular weight (Mw) of between 100,000 g/mol and 1,000,000 g/mol and a vinyl mole fraction of between 0.01 and 1%, preferably between 0.05 and 0.5 %, more preferably between 0.05 and 0.34%.
• Mw weight average molecular weight
• a vinyl fraction of 0.01% corresponds to about 1 methylvinylsiloxane segment per 10,000 siloxane units in the copolymer.
• composition as mentioned above, wherein the weight ratio of hydrophilic fumed silica to hydrophobic fumed silica is (6 to 1) : 1, preferably (1.5 to 1) : 1.
• composition as mentioned above further comprising (g) a hydroxypolysiloxane in an amount of from 4 to 15 wt%, based on 100 wt%of the total composition.
• composition as mentioned above further comprising (h) one or more methylsiloxane gums, the weight ratio of which to (a) the vinyl siloxane gums is between 0.01 and 0.5.
• composition as mentioned above wherein (e) the inhibitor and (f) the hydrosilylation catalyst are stored in separate packages, and preferably (e) the inhibitor and (d) the hydrogen silicone oil are stored in one package.
• a method for preparing silicone rubber elastomers comprising the steps of
• step (ii) Post-curing: the elastomer obtained in step (i) is heated at 180-220°C for 2-6 hours.
• step (ii) the elastomer obtained in step (i) is further subjected to force while being heated to deform.
• step (i) and step (ii) are greater than or equal to 5 mins, preferably greater than or equal to 15 mins, more preferably greater than or equal to 30 mins.
• the time gap between 2 steps helps realize a relative robust production process.
• a silicone rubber elastomer characterized in that it is obtained sequentially from steps (i) and (ii) of the above preparation method, and exhibits a Shore A hardness change of between 8 and 15, preferably between 8 and 11.
• the elastomer mentioned above characterized in that it is obtained from step (i) of the above preparation method, and has a Shore A hardness of between 55 and 70, preferably between 60 and 65.
• the polysiloxane composition herein is first cured by heating at 110-180°C for 5-20 minutes, preferably at 115°C for 10 minutes, at 120°C for 10 minutes, ; and the first curing can specifically be adjusted according to the thickness of cured rubber products.
• Post-curing is done by heating at 180-220°C for 2-6 hours, preferably at 200°C for 4 hours. During the post-curing process, a force can be applied to deform the elastomer.
• the prolonged curing behavior of the silicone rubber composition herein means the ability of the post-cured silicone rubber elastomer to retain its deformation after the removal of the force, which was applied for a while with a mold or a jig or a tool having a specific shape to deform the silicone rubber elastomer (sheet, tube, bar, etc. ) obtained from the first curing.
• Certain silicone compositions were first cured and then post-cured to form an elastomer exhibiting a Shore A hardness change of between 8 and 15, preferably between 8 and 11, and the elastomer from the first curing had a tensile strength greater than or equal to 6 N/mm 2 . It could retain its deformation after the force was removed at the end of the post-curing process. The prolonged curing behavior of these silicone compositions was evaluated “good” .
• Certain silicone compositions were first cured and then post-cured to form an elastomer exhibiting a Shore A hardness change of greater than 15, or the elastomer from the first curing had a tensile strength of less than 6 N/mm 2 .
• These elastomers had poor mechanical properties and could not be used as molded parts such as pipes, sheets and bars in the fields of health care, automotive, electric power, industry, electronics, electrical appliances and the like.
• the prolonged curing behavior of these silicone compositions was evaluated “poor” .
• Certain silicone compositions were first cured and then post-cured to form an elastomer that exhibited a Shore A hardness change of between 5 and 6 and could partially retain its deformation after the force was removed at the end of the post-curing process.
• the prolonged curing behavior of these silicone compositions was evaluated “not good” .
• the vinyl siloxane gum herein is a methyl vinyl silicone rubber gum and/or a methyl phenyl vinyl siloxane gum.
• methyl vinyl silicone rubber gum and methyl phenyl vinyl silicone rubber gum see Heat-Vulcanizing Silicone Rubber, Huang Wenrun, Sichuan Science and Technology Press 2009, Edition 1, Sections 3.1.2 and 3.1.3.
• methyl siloxane gum herein refers to dimethyl silicone rubber gum.
• Section 3.1.1 of the above book See Section 3.1.1 of the above book.
• the hydrogen silicone oil herein refers to a linear organopolysiloxane containing 3 or more Si-H bonds in its molecules, including Me 3 SiO (MeHSiO) a (Me2SiO) b SiMe 3 , HMe 2 Si (MeHSiO) a (Me 2 SiO) b SiMe 2 H and Me 3 SiO (MeHSiO) a SiMe 3 , where Me stands for methyl, a and b are positive integers and their viscosities range from 5 to 150 mPa. s.
• the hydroxypolysiloxane herein includes ⁇ , ⁇ -dihydroxypolydimethylsiloxane having a low degree of polymerization, linear methylsiloxane oligomers with multi-hydroxy groups, siloxane oligomers with hydroxyl side groups and phenyl and hydroxyl containing siloxane oligomer, as described in detail in Sections 5.2.1, 5.2.2, 5.2.3 and 5.2.4 of the above book; and preference is given to the ⁇ , ⁇ -dihydroxy polydimethylsiloxane having a low degree of polymerization and a viscosity of between 30 and 500 mPa. s, preferably between 30 and 120 mPa. s., as measured at 25°C according to DIN 53019-1-2008.
• Tetramethyldivinyldisiloxane a multi-vinyl siloxane, having a vinyl content of 26 wt%, i.e. 9.6 mmol/g;
• Multi-vinyl silicone oil 2 a multi-vinyl siloxane having a viscosity of 1000 to 3,000 mm 2 /sas measured at 25°C according to DIN 53019-1-2008, a vinyl content of 3.3 wt%, a vinyl chloride content of 1.15 mmol/g, a vinyl content of 9.4% (vinyl molar fraction of 9.4%corresponds to about 9.4 methylvinyl siloxane units per 100 siloxane units in the copolymer) ;
• Hydroxyl-terminated silicone oil an ⁇ , ⁇ -dihydroxy polydimethylsiloxane having a low degree of polymerization and a viscosity of 100 mPa ⁇ sas measured according to DIN 53019-1-2008;
• Hydrophilic fumed silica 1 a hydrophilic pyrogenic silica having a BET surface area of 300 m 2 /g,
• Hydrophobic fumed silica 2 a hydrophobic pyrogenic silica having a BET surface area of 300 m 2 /g,
• Hydrophobic fumed silica 3 a hydrophobic pyrogenic silica having a BET surface area of 200m 2 /g,
• Hydrogen silicone oil a linear polysiloxane with Si-H side groups, having a hydrogen content of 5 mmol/g and a viscosity of 50-100 mPa. sas measured at 25°C according to DIN 53019.
• the Karstedt’s catalyst allow a Pt atom concentration of about 4 ppm in each of the compositions.
• the inhibitor is 1-ethynylcyclohexanol, the concentration of which is about 340 ppm in each of the compositions.
• the weight ratio of Component A to Component B can be adjusted within a range of 100: (1-2) as needed.
• the method for preparing the polysiloxane composition in the present invention is as follows:
• Each of the ingredients of Component A in Table 1 is added to a kneader using a shear mixing apparatus (for example, a kneader or a closed kneading apparatus) at room temperature, sheared and mixed until uniform to obtain the composition of Component A.
• a shear mixing apparatus for example, a kneader or a closed kneading apparatus
• Specific methods can be referred to in Heat-Vulcanizing Silicone Rubber, Huang Wenrun, Sichuan Science and Technology Press 2009, First Edition, Section 6.1, where instructions for the basic preparation process can be found.
• the components can be processed on a roll mill or kneader (re-milling is optional depending on the creep hardening degree of the composition) .
• Component A can be continuously spread on the roll, Component B is added and mixed for more than 15 cycles to obtain a polysiloxane compound composition.
• compositions of the examples and comparative examples obtained by the above preparation method are processed using a mold/extruder/roll mill and first cured and then post-cured to form a silicone rubber elastomer. During the post-curing process, a force is applied to the elastomer to maintain its target deformation.
• the compositions are first cured at 115°C for 10 minutes, and then post-cured at 200°C for 4 hours using compress molding. It is relevant to first cured at 250°C for 1-2 minutes and post-cured at 200°C for 4 hours using extrusion molding.
• the instructions for the curing and molding process in Section 6.3 of the above book can also be referred to.
• the mechanical properties of the silicone rubber elastomers including test hardness, tensile strength, 100%modulus, elongation at break and tear strength, are tested separately according to DIN 53505 A, DIN 53479, DIN 53504 S1 and ASTM D624B after the first curing and post-curing processes (Table 2) .
• Ex. 1-1, Ex. 2-2 and Ex. 3-3 are examples of the present invention, and the rest are comparative examples. It can be seen from these examples that, when the Si-H content remains the same, changing the amount and type of multi-vinyl siloxanes (i.e., adjusting vinyl (Vi*) content in the multi-vinyl siloxanes) can greatly affect the prolonged curing behavior of the polysiloxane compositions.
• the Si-H/Vi*weight ratio also changes as the content of the Vi*in the multi-vinyl siloxanes varies, and any small change in the ratio greatly affects the addition-curing degree of the compositions during the first curing process.
• Ex. 1-2 shows that the elastomer, obtained from the first curing, has poor mechanical properties with a tensile strength of only 0.8 N/mm 2 , and, after post-curing, has a hardness of no more than 62, well below the theoretical hardness of 70. This silicone rubber elastomer cannot be used as a molded part/article.
• Ex. 1-3 shows that the hardness and tensile strength of the elastomer after the first curing are lower than those of Ex. 1-2, which indicates that the silicone rubber elastomer in this example has a lower curing degree after the first curing and post-curing processes.
• Ex. 3-2 shows that the silicone rubber elastomer obtained from the first curing has a hardness of 66, and exhibits a hardness change of 6, which indicates that the elastomer has a too high degree of curing in this example and can even retain only a small amount of deformation formed during the post-curing process.
• the composition of Ex. 3-2 has “not good” prolonged curing behavior.
• compositions of Ex. 1-1, Ex. 2-2 and Ex. 3-3 are first cured and then post-cured to form elastomers exhibiting a suitable Shore A hardness change of between 8 and 11. This indicates that these compositions have good prolonged curing behavior, allow a variety of stable deformation in the post-curing stage, and is therefore suitable for the manufacture of complex shapes of silicone rubber parts. And the elastomers obtained by the first curing of these compositions have a tensile strength greater than 6.5 N/mm 2 , indicating a high mechanical strength and good properties of silicone rubber parts.
• the composition of Ex. 2-2 is first cured and then post-cured to form an elastomer having a tensile strength that increases from 6.9 N/mm 2 to 8.6 N/mm 2 , indicating very stable mechanical properties.
• the composition is first cured to form an elastomer having a tear strength of as high as 53.2 N/mm and excellent properties.

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