Liquid silica gel has excellent transparency, tear strength, resilience, yellow resistance, thermal stability, water resistance, good air permeability, heat resistance aging and weather resistance, while the viscosity is moderate, good liquidity, easy to operate, high transparency products.
Recent development of liquid silicone rubber applications
In recent years, liquid rubber injection molding method (LIMS), namely liquid silicone rubber injection molding has been widely popularized. Recently, this method has become a widely concerned molding method because of its advantages of short time automatic molding and composite molding with plastics. The following is an introduction to the latest trends of liquid silicone rubber injection molding and the materials suitable for this molding method.
1. Liquid injection molding of silicone rubber
Liquid silicone rubber injection molding method started in the 1970s gradually popularized, now, as a silicon rubber molding method has been recognized, first of all, the widely used LIMS method is described.
To explain LIMS(liquid silicone rubber injection molding) in a sentence, is to pump the addition of the solidified liquid silicone rubber into the injection molding machine, solidified in the model. From the difference of the process flow and curing reaction between the two methods,
There are several advantages of LIMS:
(1) Manpower saving: Continuous automation of material conveying, metering, mixing, injection and other processes to reduce power consumption.
(2) Can improve production efficiency: through rapid curing to seek to shorten the molding cycle.
(3) Can improve product quality: no reaction byproduct is generated and no impurities are mixed.
(4) Suitable for composite molding: Due to the good fluidity of the material, low forming pressure, and wide curing temperature range, it can also be used for composite molding in addition to the embedment molding.
2. The latest technical trends of LIMS
Not only is the transition from the pure mixing type with the above advantages to the LIMS method under way, but the following two directions are being actively developed recently.
(1) Automatic molding: no flash, no runner, automatic stripping
As for the fully automated forming process, people have studied the injection machine, mold, material and other aspects. It not only saves manpower in process operation, but also reduces material cost because it does not produce useless solidified material. From the perspective of taking environmental protection into account, this method also attracts people's attention. For the molding of micro products such as the automobile skeleton oil seal, the molding cycle (from injection to the next injection) is required to be within 10s, which can be completed in a very short time.
(2) Composite forming: clamping piece forming, binary forming
Because the form of crosslinking reaction is additive curing, it can be formed at relatively low temperature. As there is no by-product formation such as peroxide decomposition residues in the crosslinking reaction, there is no need to overdo the secondary vulcanization in principle. Therefore, the whole can be formed with resin, through the coating material for Mosaic, so that the sealing part and the skeleton part into a whole of binary molding has also begun to popularize.
Silicone rubber has excellent properties (heat resistance, plug resistance, weather resistance, electrical insulation, flame retardant, etc.). Because of these properties, it is possible to make environmentally friendly molding based on fully automatic molding, with integral molding of metals and organic resins. In addition, the material itself is transparent and colorable, so its application range involves many fields, such as (computer, mobile phone, etc.) keys, milk bottle nipple, (copier, printer, etc.) cots, pipe joint seal, oil seal and other auto parts, TV picture tube anode cap, diving supplies, etc.
3. Materials for automatic molding without rubber edge/runner
In recent years, in the injection molding of liquid silicone rubber, a so-called no rubber edge, no flow molding method began to be popular. This is a molding method that does not produce useless solidification and does not require secondary processing, that is, it is a molding method that does not have injection port, flow path (even if there is no solidification), and does not produce waste rubber edge. In order to implement this molding method, the structure of the model and the finish of the parting surface, and the measuring and discharging precision of the injection machine must meet the requirements, even in terms of the material, it must be difficult to generate waste edge material. As shown in FIG. 2(omitted), after the mold cavity is filled with too much adhesive, or due to the thermal expansion of silicone rubber and other factors, the adhesive flows into the parting surface, and becomes a waste adhesive edge after curing. If design of parting face gets some strictness, waste glue edge is generated hard, but at the same time, air also is not easy to discharge, become the reason that contains bubble in finished product then.
Compared with the materials previously used, the curing curve of this material is in a state of rapid transition (from the beginning of curing to the end of curing time is very short). By selecting the appropriate injection conditions for this type of material, that is, before the material fills the cavity, curing has not begun, the material flows well, and when the material fills the cavity, curing immediately ends, even if there is residual pressure, the material will not flow to the parting surface, to prevent the formation of waste glue edge.