silicone elastomers.

by:Keyuan     2020-07-02
Silicone rubber is widely used in almost every industry for its wide range of unique and valuable properties.
Due to the physical and mechanical properties of the materials that limit the application and environment of their use, the versatility and reliability of silicone make it an ideal candidate for many designs under harsh conditions.
Silicone is manufactured in a variety of physical forms, and the three main types are fluid, resin and elastomer.
They are also formulated into lotions, oils and gels.
In addition, these polymers may be reactive (
Triggered by moisture, heat, or radiation)or non-reactive.
Although silicones appear in different physical forms, they have many common properties.
These include excellent thermal and oxidation stability, high chemical and biological inertia, excellent weather-
Good electrical insulation performance.
It is precisely because of the unique chemical properties of silica gel that these materials show amazing properties and properties, because the inherent versatility of this chemistry makes it easy to change the molecular structure or formula composition, the performance of the product is often contradictory.
For example, some silicone compositions act as adhesives, while others are mold release agents.
Silicone liquids can be used as Defoamer or as new foam materials.
They can be soft sponge-like elastic materials or rigid coatings similar to glass.
In addition, silicone can be conductive or insulated.
The chemical structure of silicone polymers is different from that of organic polymers, and silicone has excellent stability and inertia in demanding environments.
Although organic polymers have molecular skeletons of carbon atoms, silicon polymers have skeletons of alternating silicon atoms and oxygen atoms. The silicon-oxygen bond -
Found at other high temperatures.
Wear-resistant materials such as sand, ceramics and glass
Is the main reason for the high content of silicone
Temperature resistance.
The silicone chain is not the backbone of the carbon atom, it can go through oxidation and break of the product chain, but is oxidized and stable because it is already in the highest oxidation state.
In addition, the attack on ozone by silica gel linkage is immune (
Because there\'s no carbon-
Carbon unsaturated)and UV light (
Because it is transparent to UV).
Silicon atoms in silicon
The oxygen backbone is an organic lateral base that changes properties and provides a reaction site for other molecules.
Changes in these side bases can give different properties to silicone polymers such as flexibility, radiation, heat and fuel resistance.
Silicone in the three families of silicone-
Fluid, resin and elastic materials
Rubber is particularly important for design engineers because they meet the requirements that organic rubber does not meet.
Silicone rubber is based on highmolecular-
Weight linear polymer.
Through the curing process, the silicone polymer with appropriate molecular weight is crossed
Associated with increasing polymer molecular weight and providing elastic properties.
The catalyst controls the rate of the curing process.
When the link, Long
Chain compounds create a flexible network that is elastic, but physically weak, compared to organic polymers.
In order to increase the strength, the reinforced filler is added.
In order to obtain other required properties, additives such as antioxidants, adhesion enhancing agents and pigments can also be added.
There are three types of solid silicone rubber: Chamber-temperature-vulcanizing (RTV)products; liquid-injection-Molding products; and heat-cured-
Rubber products (
Listed in order of increasing tensile strength).
In addition, it can also be from the heat-cured and room-temperature-
Vulcanization process.
RTV elastic adhesive and sealant chamber-temperature-
Silicone sulfide is the most elastic of the three series of elastic materials.
Based on the middle
They are commonly used as adhesives, sealant and filling agents.
Compared with structural adhesives such as epoxy resin and acrylic acid, the cured polymer has medium strength, but has a softer and more flexible adhesive advantage.
There are two forms of RTV silicone for use: one is-
Component adhesive/sealant and double-
Component products.
Most rtv offers no primerless bonding to a variety of substrates, such as metal, glass, ceramics, some plastic and concrete, for sealing and bonding purposes.
They can also be used for molding and packaging applications.
Processing of uncured RTV products as liquid or paste-
Such as a mixture of polymers, fillers, additives, curing agents and catalysts. With one-
Since exposure to atmospheric water vapor activates the reaction of the cured polymer, the mixture is packaged to prevent moisture.
Curing at room temperature (hence the name)
Although the curing time depends on both moisture and temperature.
Usually, the higher the humidity and/or temperature, the faster the curing speed is.
The time required to fully cure also depends on the composition of the mixture (
Whether it\'s vinegar-based oxygen, alcohol-based oxygen or amine
Curing chemistry, for example)
And the thickness of the silicone layer.
For example, 1/8-
The inch of the oxygen-
The Cure RTV adhesive/sealant will be within approximately 24 hours [77]degrees]F and 50% RH. Two-
The component RTVs does not require moisture to trigger curing.
In contrast, curing begins after the mixing of the two components, one of which is composed of or contains a catalyst.
For some products, the curing can be accelerated by adding heat.
The two components of the product, from easy foaming to paste, vary in viscosity
Like the material, provided in a separate package.
They can replace one-
Component products when longer working hours are required, thicker parts are cured, or faster curing times are required. Some two-
Component RTVs can be cured in 10 minutes.
The chemical structure of RTVs gives these polymers excellent resistance to extreme temperature properties.
For example, in the aviation industry, their high
Temperature stability enables them to be used as washers and seals on aircraft doors and windows.
Rtv is ideal for use as automotive transmission and engine seals where hydraulic or lubrication fluids and high
Operating temperature causes most organic rubber to fail.
Their thermal insulation properties enable them to adhere and separate the two substrates that must be maintained at significantly different temperatures.
For example, RTV silicone acts as an adhesive and sealant between the inside and outside housing of the refrigerator.
As an electrical insulator, RTV silicone can connect two metal components to prevent electrical corrosion between them.
In electrical and electronic components, RTVs can easily coat and connect irregular parts or connections;
In many cases, a satisfactory bond can be formed without the need for primer.
The bending and elongation properties of cured RTV silicone adhesives, sealant and gels allow them to differ significantly from flexible substrates or with heat-
Extended features.
The silicone can move with the substrate while maintaining the adhesion. Also, good gap-
Filling properties make them useful when connecting substrates of different shapes or textures.
Silicone rtv is also inert in biology, chemistry and the environment.
In medical applications, they are used to make prosthesis and catheter, to pack pacemakers and to make dental molds.
Their ability to resist chemical and environmental attacks is extremely important in building applications.
The weather resistance and solar, ozone and water resistance of silicone make their service life much better than organic rubber in a wider temperature range.
To better adhere to many standard panel materials, including glass, ceramics, these sealant do not require primer
Coated metal and some types of aluminum and stainless steel. Liquid-injection-
Molded elastic liquid-injection-
Molded silicone in the middle of the strength between RTVs and heat
Cured silicone rubber, formed in a process similar to thermoplastic injection molding.
This process combines the advantages of thermoplastic molding
Speed, precision and design flexibility
With its unique physical performance --
Silicone rubber.
Therefore, liquidinjection-
Molded silicone is replacing heat-
Cured silicone rubber and/or traditional organic elastomer processed by compression or injection molding.
Processing liquid-injection-
Molded silicone based on two
RTV composition of components modified to heat-curing systems.
An inhibitor was added to the RTV mixture that only released the catalyst at high temperatures.
This suppressed product produces a mixture of long pot life (72-96 hours)
For easier handling and mixing, fast curing is also allowed.
The molding process adapts the basic principle of injection molding to the processing of hot-solid elastic materials.
Use heating and pressure like compression molding.
But it doesn\'t take a few steps, it\'s a closed, whole, one-step process.
Fresh mixed liquid silicone pump directly into the molding equipment from the container, and inject heat into the molding equipment. mold cavities.
Curing is almost unstable at a typical molding temperature (150-200[degrees]C/302-392[degrees]F).
Parts can be used as soon as they pop up from the mold, as they usually do not require Postmold curing.
Due to the relatively low molding pressure ,(
About 1,500 psi)
, Fast curing rate, no need to trim flash or excess rubber from the finished part, speed up and simplify production.
Due to the excellent temperature stability of silicone, liquid-injection-
In some industries, molded products have replaced materials such as flexible polyurethane, flexible PVC and neoprene.
Liquid, for example-injection-
In automotive applications, molded products are used as engine block seals and spark plug boots.
In addition, because they are easy to process and cost-effective, they replace silicone hot curing rubber as connector seals, temperature probes and pipes in electrical and electrical applications.
Purity and product consistency are important in te healthcare.
Since the molding process is carried out in a closed system, the minimum contamination of the product can be ensured.
In addition, silicone is inert in biology and environment.
Toxic, very durable in demanding environments. Liquid-injection-
Molded products are also commonly used in building applications where their weather resistance makes them ideal materials for a variety of products. Heat-
Hot curing rubber compoundcured rubber (HCR)
The product is the oldest and most widely used silicone rubber.
They provide the highest strength and physical properties of any silicone rubber that can be extruded, molded or coated on the fabric.
Extruded and molded parts are used as oven washers and wire sheaths on a flat surfaceiron cords.
HCRs are also used to manufacture conduit tubes, shunt and bend joints, and coated tape.
Unlike RTVs, most HCRs processing is based on highmolecular-weight-polymer gums.
Consistency of uncured-
The rubber mixture ranges from tough putty to hard, deformed plastic.
Silicone before use-Rubber mixture (
Chewing gum, filling, additives)
Being catalytic and fresh;
That is to say, adding catalyst, fresh mixture through water-
The cooled rubber mill turns it into a smooth continuous sheet.
These easy-to-process sheets are now processed directly.
The silicone rubber compound mixed fresh is usually 100-180[degrees]C (212-356[degrees]F)and 800-
1,500 psi, complete the conditions of hot curing in a few minutes.
In the manufacture of insulated wires, rods, tubes and other similar products, the silicone mixture is extruded through standard rubber
Extrusion equipment.
Use HCRs dispersed in aromatic solvents to coat a glass cloth or other fabric.
The fabric is soaked.
Apply to the dispersion and then dry and solidify in the heated tower.
This cloth can also be pressed with a soft silicone material and cured without dispersion in the solvent.
This process leads to flexible products of paper or tape for packing parts of heavy-duty motors, large cables and connectors.
One of the most important uses of applying HCRs is in the electrical industry, where they provide insulation for wires and cables.
For power cables, especially underground cables, HCRs will dissipate heat and increase current
Carrying capacity.
They are also used to manufacture silicone rubber tape for large cables, irregular shape conductors, and insulation of joints and terminals.
In addition, HCRs is used in the automotive industry and in the automotive industry, HCRs has excellent chemical resistance to hot ethylene glycol, diesel and engines
Clean solvents and their electrical, thermal properties and flexibility
Make them perform better on organic rubber.
In the aviation industry, HCRs is valued for its resistance to pressure and extreme temperature.
Foam silicone rubber may be based on HCR or RTV formulations.
The earliest foam product silicone sponge is made of heat-cured rubber.
Cast silicone sponge material-in-
Used to make molded parts or places that are laminated on foil or fabric.
These materials have the highest mechanical properties of any foam silicone product;
However, their processing is more complex and they are relatively heavy and expensive compared to the newer silicone foam. Newer RTV-
Silicone-based foam is usually used for thermal insulation or electrical insulation, but also for light weight-
The weight of molded parts.
They can be continuous cas sheets, or they can be used as a freely blown compound.
They provide greater density reduction and versatility in design and manufacture, replacing silicone sponges in applications where high performance and weight are critical and where mechanical strength requirements are low.
The latest generation of RTV silicone foam combines the best of previous foam silicone technology.
With mechanical strength close to silicone rubber sponge, design and processing versatility of RTV foam, and excellent heat resistance and inherent flame retardant properties, these products begin to replace flexible organic foam such as polyurethane.
Given the government\'s increasingly stringent standards for the flammable, smoke and toxicity of materials used in public building and transportation applications, their performance is particularly important.
The processing process of silicone rubber sponge is done by softening the rubber, first mixing the chemical cleaning agent with the uncured silicone rubber in the form of mother material in the mill.
Next, heat the mixture, which breaks down the foaming agent (
Make it a bubble)
At the same time, it makes rubber vulcanization.
When the rubber begins to solidify around the rising bubble, the cell structure is formed.
Sponge may be formed by freedom. blowing (
Paper squeezed or pressed)
Or blow (
For thicker parts or parts that have to maintain more stringent dimensional tolerances).
For the grade of silicone rubber used, a foamer needs to be selected and best suited to the specific processing method selected.
It is said that some grades of silicone rubber have better results than other grades of silicone rubber.
The density of the resulting sponge product will vary with the molding time and temperature, the number and type of blow molding agent used, and the degree of limitations applied during blow molding and cross moldinglinking phase.
RTV silicone foam is based on two
A component liquid system capable of curing at room temperature.
Uncured products are supplied as curing agents and base compounds that start to crossLink when mixing.
Without any external reagent, the silicone foam will bubble.
Instead, hydrogen is released as a by-product
A product of curing reaction used in foam materials.
It takes only two minutes to fully bubble at high temperatures.
The treatment of foam mixture is very simple;
It can be sprayed, cast, co-extruded or molded.
The molding process can occur in thermoplastic injection molding-
There is a forming machine for curing with a cooling barrel and a heating mold.
The foam can also be processed using compression molding as it will quickly solidify at room temperature.
Standard equipment for spray systems, solvents-borne.
These foam can also be high using standard lamination technology-
Performance of composite fabric. The just-
The catalytic material is continuously transmitted between the fabric roll and the release paper and then passed through the oven.
Foam forms a good No primerless bond with most fabrics such as wool/nylon blends, as well as fiberglass and foil.
In construction and construction applications, silicone foam is currently used as a fire/smoke-proof barrier, especially around wires and cables.
In addition, because the foam is easy to repair, their low mechanical properties are advantageous in this application.
Their light weight, heat resistance and flame resistance make these materials a great choice for fabric backing.
Here they can be used for heat and moisture transfer is a problem where organic foam does not meet the performance requirements.
Silicone foam in the automotive market-
Coated Fabrics are considered for their thermal insulation and acoustic shielding properties.
Aluminum foil and silicone foam composites can be used to shield plastic gas tanks located near the hot exhaust system.
This composite can also minimize possible vibration
Associated noise in the body pillar.
In addition, silicone
Foam pad, and silicone-
Composite fabric, can reduce the heat radiation from the catalytic converter up to the passenger compartment.
Superior flame-
Flame resistance makes silicone foam an ideal material for high safety considerations such as construction and public transportation.
They can be used as flames-
Backing of flame retardant carpet with added insulation and flame retardant
Flame retardant properties of curtains.
Conclusion silicone rubber-
Whether it\'s solid or foam, whether it\'s RTV adhesive/sealant, liquid-injection-
Molded rubber or hot-
Rubber Products
Provide designers with many of the performance, design and manufacturing advantages that organic competitors cannot offer.
Elastic silicone provides excellent thermal, chemical and oxidation stability in most environments.
In fact, their reliability and long-term
Even in harsh environments, the term performance retention enables them to be used for applications that do not even take into account organic polymers.
Now, improvements in chemistry and processing enable these versatile materials to penetrate into more diverse applications in almost every industry. Dr. R.
Custom message
Chat Online 编辑模式下无法使用
Chat Online inputting...