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Method and device assembly useful for producing molded silicone rubber products from liquid silicone rubber compositions via injection molding
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A technology of silicone rubber and composition, applied in the direction of coating, etc., can solve the problems of unstable injection curing rate, reducing the curing rate of liquid silicone rubber, and quantity imbalance.
Pending Publication Date: 2022-07-08
ELKEM SILICONES USA CORP
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The first problem is related to metering and mixing of off-ramp ratios of the two individual components, which can lead to an imbalance in the amount of silicone hydride crosslinker present in the finished product, resulting in erratic injection cure rates and variable Physical Properties of Cured Parts
The second problem is the need for expensive equipment to pump the two separate mixtures into the metering and mixing unit
A third problem is the presence of a large and specific (non-variable or fixed) amount of inhibitor in component B, which is required to obtain multi-day room temperature working life
[0020] However, lowering the molding temperature in a standard LSR injection molding process would drastically reduce the cure rate of liquid silicone rubber, which is unacceptable as it would have a punitive impact on its economic viability
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Embodiment 1
[0285] Components:
[0286] Control formulation: liquid silicone rubber base composition LSR-4350, Parts A and B, (standard LSR composition), sold by Elkem Silicones USA Corp.
[0287] - Has R 2 HSiO 1 / 2 and type SiO 4 / 2 M of Q siloxy units H Q silicone resin, wherein H is a hydrogen atom and wherein R is a methyl group (wt% of H in SiH = 1.23%).
[0288] Control formulations with different added amounts of MHQ silicone resin were used according to the method of the present invention. A control test was performed without the addition of MHQ silicone resin as a comparative test. Curing was monitored on a moving die rheometer (MDR) at 110°C for 5 minutes using ASTM-D5289. The results are given in Table 1.
[0289]
[0290] Table 1 - Measured properties after adding resin
[0291] The comparative test showed a t90 (90% cure) value of 139s, which was much slower than all tests according to the invention.
Embodiment 2
[0293] a) Crosslinkers tested
[0294] XL1=polyphenyl-(dimethylhydrosiloxy)siloxane hydride terminated, ex Gelest, designation HDP-111, viscosity 50-80 mPa.s, total SiH mmol / g=5.2; formula (M H ) 2+n (T Ph ) n of silicone resins, where M=R 2 HSiO 1 / 2 siloxy units and T Ph =PhSiO 3 / 2 , where H is a hydrogen atom, R is a methyl group, and Ph is a phenyl group.
[0295]
[0296] XL2: copolymer of dimethylsiloxane and methylhydrogensiloxane, partially capped with dimethylhydrogensiloxane groups at both molecular ends (viscosity 18-26 mPa.s; total SiH mmol / g=7.2 (linear crosslinker).
[0297] XL3: with R 2 HSiO 1 / 2 and type SiO 4 / 2 M of Q siloxy units H Q silicone resin, where H is a hydrogen atom and where R is a methyl group, total SiH mmol / g = 7.3 (from Milliken, designation SiVance MQH-8MQ hydride resin).
[0298] XL4: Type M H The branched silicone resin of Q, wherein M H =R 2 HSiO1 / 2 and Q is the molecular formula of SiO 4 / 2 siloxy units of , where H is a...
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Abstract
Methods and device components useful for producing molded silicone rubber products from a liquid silicone rubber composition ("LSR") via injection molding. The method provides a flexible method for producing faster curing silicone rubber products from LSR and allows the use of low curing temperatures in the mold cavity without drastically decreasing the curing rate of the LSR and the physical properties of the molded silicone rubber material produced, the liquid silicone rubber is thus allowed to be overmolded on or on a heat-sensitive substrate. The device assembly allows for faster cycles and the use of precise dosing and mixing units, creating a flexible method for faster production of cured silicone rubber products from liquid silicone rubber (LSR).
Description
[0001] CROSS-REFERENCE TO RELATED APPLICATIONS [0002] This application is an international application under the Patent Cooperation Treaty, and claims priority to US Provisional Application No. 62 / 880,321, filed on July 30, 2019, the contents of which are incorporated herein by reference in their entirety. technical field [0003] The present invention relates to a new method and apparatus assembly that can be used to produce molded silicone rubber products from liquid silicone rubber compositions ("LSR") via injection molding. Background technique [0004] Liquid silicone rubber injection molding apparatus components that use liquid silicone rubber ("LSR") compositions to form molded silicone rubber products have existed for nearly fifty years. LSR compositions that react by addition crosslinking are known in the silicone rubber field. [0005] LSR compositions belong to the category of thermally cured rubbers. One of their characteristic features compared to solid sili...
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