Do you want to learn more about the impact of different production processes on the accuracy of silicone products? What is the process of customizing silicone products? This article will help you understand the manufacturing process of silicone products to help you better choose silicone manufacturers and customize silicone products.
What Is Silicone?
Silicone is the collective name for a class of polymers whose skeleton consists of silicon and oxygen atoms with organic groups, such as methyl groups, attached to the side. It includes silicone resin, silicone oil, etc., but people often refer to silicone rubber.
Because of its good weather resistance, temperature adaptability, chemical compatibility, and other characteristics, whether it is daily consumer products such as cell phone cases, medical equipment, or even the aerospace field, you can see the applications of silicone materials.
How Is Silicone Made?
Step 1: From Quartz Sand to Silicon Metal
The industrial raw material for silicone is silicon metal, which in turn comes from quartz sand. Unlike sand that you can find in parks, the quartz sand that can be used to make industrial silicon metal is of high purity and has fewer impurities. Raw materials used to produce food-grade, medical-grade, and high-transparency silicones for optical instruments must meet more stringent impurity content requirements.
When quartz sand is heated to high temperatures above 1800°C, the oxygen atoms it carries in its molecules are taken away by materials such as coke. After cooling and other treatments, they are transformed into purer, industrially produced silicon metals.
Next, these silicon metals are ground into a finer powder, ready for the next step in production.
Step 2: Mixing Silicon Powder and Chloromethane
The fine silicon powder obtained from grinding is mixed with chloromethane and reacts at high temperatures and in the presence of a catalyst to form methylchlorosilane. Dimethyl dichlorosilane is primarily utilized in the silicone manufacturing process.
Since this step results in a mixture of chemicals, the manufacturer also needs to go through a distillation step to separate out the various components.
Step 3: Hydrolysis and Condensation
If the previous steps in the production process were used to obtain small building blocks for the construction of silicones, from now on, these blocks will be used to assemble a strip of building blocks. Dimethyldichlorosilane is reacted with water and subsequently condensed to form polysiloxanes (DMC). At this point, the strips are still relatively short and need to undergo the next step to become longer.
Step 4: Polymerization
DMC is further reacted in the presence of a catalyst to form high molecular weight linear polysiloxanes. You may have heard of “Silicone Rubber Gum”, which is composed of these chemicals. It is not yet a flexible elastomer, but only after vulcanization and molding steps can it become a truly usable silicone product.
Step 5: Mixing
Before the formal vulcanization and molding steps, additives and fillers such as silica, structuring control agents, and other additives are placed into the raw rubber in a mixer to allow them to mix well. Their homogeneity affects silicone longevity, clarity, and a number of other indicators, and can be somewhat of a reflection of the technology of the manufacturer you choose.
The chemicals added in this step can have an impact on the physical strength, heat resistance, and more of the silicone rubber to meet different needs. Carbon black and titanium dioxide may be added to silicone rubber used in industrial manufacturing, while safer fillers and additives are used in food and medical-grade silicone rubber, and avoid the use of PFAS and BPA.
If you want to learn more about the composition of silicone, you can read What Is Silicone Made Of? How Compositions Affect Safety and Performance.
Vulcanization and Molding Process
Injection Molding
Different types of silicone rubber are vulcanized and molded using different processes as needed. For liquid silicone rubber (LSR), which is often used in food production and medical applications, the liquid silicone rubber injection molding(LIM) is the more common choice.
Where safety is more important, liquid silicone rubber is typically vulcanized with platinum vulcanization systems that are free of harmful byproducts. At high temperatures, liquid silicone rubber with a vulcanizing agent is injected into the mold and cured into a silicone rubber product with a specific shape.
Due to its low viscosity and good flowability, liquid silicone rubber can easily fill every detail within the mold to produce parts with fine or complex structures. If you are looking for a more suitable production process for your fine silicone rubber bristles or all-in-one parts, then LIM is a smarter choice.
It maximizes precision and allows for high-volume production and customization with less material loss.
Silicone overmolding is a special injection molding process that is used to produce the toothbrush handles and car keys you normally see. It can add a soft-touch surface to a wide range of materials, such as metal and PC, greatly improving the comfort and safety of your products.
Like injection molding, overmolding can achieve ultra-thin results, making it ideal for making lightweight wraps around the surfaces of electronic watches.
Compression Molding
For high-temperature vulcanized silicone rubber(HTV/HCR), the use of peroxide vulcanizing agent and silicone compression molding is more common. Although less safe than platinum vulcanization systems, peroxide vulcanization systems are more cost-effective and a good choice for industrial applications.
Unlike liquid silicone rubber, silicone rubbers using compression molding don’t flow well. They rely on the high temperatures and pressures of the machine to change shape. Molding is able to accommodate both softer and harder materials. One of its major drawbacks is that it can’t process delicate parts like injection molding can, and simple shapes are where it’s at. Gaskets, buttons,s and O-rings can be produced using this process.
Transfer Molding
Silicone transfer molding is similar to injection molding and compression molding in its simplicity and ability to mass-produce high-precision parts. In the transfer molding process, the silicone material is first heated in a transfer chamber and then pressurized by a plunger to fill the mold.
Because of process limitations, transfer molding is not suitable for silicone rubber that is too viscous or tends to cure quickly at high temperatures. It can also not be used to produce too large silicone products.
Transfer molding is ideal for electrical connectors with metal inserts, as it has less impact on the contents and is less likely to cause them to deform. This type of molding is also often chosen for waterproof earphone plugs.
Extrusion Molding
The process of silicone extrusion is similar to squeezing cream from a piping bag, where the shape of the extruded silicone rubber depends on the shape of the “piping nozzle”. The difference is that silicone rubber extrusion lasts a long time, and the silicone material is continuously extruded by the rotating screw inside. For this reason, it is generally used for long products with a stable cross-section, such as silicone hoses or insulation for electrical wires.
In addition, the products that can be produced are not limited to simple shapes such as pipes, but by changing the type of mold, grooves, and special-shaped seals are possible. And it costs much less to produce extruded molds.
It is also flexible to mix and combine colors of silicone rubber inside, like a laminating bag, and finally get multifunctional products. After being extruded into a fixed shape, these silicone rubbers can be cured at high temperatures by UV irradiation, hot air irradiation, and other methods.
Extrusion molding produces products with a uniform texture, and quality consistency is an advantage of this process.
Calendering
If extrusion molding is like squeezing cream through a laminating nozzle, silicone calendering is like rolling out dough with a rolling pin. Unvulcanized silicone rubber material is passed through a set of steel rollers and then crushed into a sheet or film. By adjusting the rollers, silicone rubber products can be made with different thicknesses, textures, and smoothness.
These products can also be combined with a variety of materials such as metal and fabric to make composite products. Composite baking mats made by calender molding have rigid glass fibers on the inside, and a smooth silicone surface with anti-adhesive properties on the outside, and the thickness error is also very small.
In addition to being able to produce continuously, it is not so strict in terms of material requirements, and the calendering process can be used even if the silicone material is sticky before vulcanization.
Secondary Vulcanization
In addition to the vulcanization and molding steps, some silicone products undergo an additional secondary vulcanization step. The secondary vulcanization is intended to eliminate odors created during the first vulcanization process, make it safer, or improve physical properties.
For this reason, silicone products vulcanized with peroxides that produce harmful volatiles, some medical-grade silicone rubbers, and O-rings used for seals often undergo a secondary vulcanization. Silicone rubber products used in high-temperature environments and for electrical insulation also undergo a secondary vulcanization, which can effectively enhance their performance.
Similar to the first vulcanization, these silicone products are placed at high temperatures, allowing the molecules that would otherwise combine with each other to form a three-dimensional lattice structure to bond more tightly. However, secondary vulcanization often results in a higher cost for your silicone product.
Room temperature vulcanized silicone rubber (RTV) is an exception to this rule, as it is capable of complete cure at room temperature and generally doesn’t require secondary vulcanization. In rare cases, it can be heated slightly to achieve similar results.
Quality Inspection of Silicone Products after Manufacturing
To ensure quality, after the silicone products are manufactured, the silicone manufacturers will conduct quality tests on them. These tests cover the appearance, tensile strength, hardness, safety, and other aspects of silicone products. Here are the tests that most silicone products undergo:
- Appearance Inspection:Check if the silicone product still has imperfections such as burrs, bubbles, cracks after treatment, and if the size, shape, surface texture, and color are within the tolerance range.
- Hardness Test:Use the indenter to test the hardness of the product, and the result shows whether the Shore A is as expected.
- Tensile Test: Test the tensile strength and elongation at break of the product to check whether the elasticity is enough.
- Compression Set Test:Test whether silicone products can return well to their original shape after being subjected to external forces.
- Tear Strength Test: Test the tear resistance of silicone products, which is important for seals.
Depending on the use of the product, the manufacturer may also perform the following tests on the product:
- FDA/LFGB:For food contact silicone rubber, such as silicone rubber spatulas and silicone rubber straws, manufacturers should conduct comprehensive safety testing in accordance with the FDA or the more stringent LFGB safety standards for the extraction or release of hazardous substances when in contact with different chemicals.
- ISO 10993: Medical-grade silicone rubber used in medical devices and tools needs to pass the allergenicity and cytotoxicity tests specified in ISO 10993 to ensure that it is odorless and does not cause harmful effects.
- Fourier Transform Infrared Spectroscopy (FTIR): Infrared spectroscopy is used to analyze the composition of the material to avoid the introduction of impurities.
- Thermal Properties:Place silicone products that need to work at high temperatures, such as oven seals and silicone piping, at high temperatures to test for changes in their properties.
- Airtightness Test: Check if the silicone waterproof parts or seals will leak water and air.
- Flame Retardant Test:Check whether the silicone can meet UL94v-0.
- Conductivity Electrical Conductivity: Test electrical conductivity and resistivity.
Custom Silicone Products: How Silicone Products Are Manufactured to Meet the Needs
The silicone manufacturing process is not the same if you intend to customize silicone instead of purchasing an existing product.
Confirm Requirements
First of all, you should provide the manufacturer with as many details about the customized product as possible. It’s important to know exactly what the silicone product will be used for, as this will help the manufacturer assist you in adjusting the product based on their experience to make it the most cost-effective and achieve the best results.
Indicators such as size, color, and hardness are also essential. If you are able to provide 2D or 3D drawings or samples of the silicone product, it will greatly enhance the speed of customization. If there are no detailed drawings, then a manufacturer with specialized engineers will work with you on the design.
Engineers will assess your requirements, confirm whether it is possible, and give some plans. After your confirmation, the manufacturer will give a quotation accordingly.
Mold Making
The manufacturer will start manufacturing molds based on the previously confirmed plans. The molds used to produce samples are manufactured and adjusted through CNC, EDM, and other processes.
Prototype and Confirmation
The samples are manufactured soon after the mold production is completed. You will need to check each value of the sample to ensure that it meets the needs. The manufacturer may provide test reports for some indicators such as safety.
If you are not satisfied with some parts of the sample, the manufacturer will make adjustments and reconfirm.
Mass Manufacturing
After receiving your confirmation, the manufacturer will proceed with mass production, quality testing, packaging, and transportation based on the samples. Then you can wait at home for the silicone products meeting your requirements to be delivered to the specified location.
FAQ
What Are the Raw Materials for Silicone?
The raw materials for silicones are silicon metal, chloromethane, silica, additives and fillers. And silicon metal is derived from quartz sand. Depending on the type of silicone and the application, the specific ingredients in it are adjusted.
What Types of Silicone Rubber Are There?
The three main types of silicone rubber are high-temperature vulcanized silicone rubber (HTV/HCR), room-temperature vulcanized silicone rubber (RTV), and liquid silicone rubber (LSR).
Depending on the safety level, they can be further categorized into industrial-grade silicone rubber, food-grade silicone rubber, and medical-grade silicone rubber. There are also specialty silicone rubbers like conductive silicone rubber and high-temperature-resistant silicone rubber.
A Simple Guide to Silicone Rubber Types and Applications shows more details about the types of silicone rubber.
Are Any Harmful Substances Added to Silicone During the Production Process?
During the manufacturing process of silicones for general and industrial use, additives and fillers that are used to improve the properties of the silicone but are harmful to the human body, such as talc, PFAS, industrial colors, etc., may be added.
You don’t have to worry about the presence of such substances in FDA or LFGB-compliant food-grade silicones or ISO 10993-tested medical-grade silicones, because they have been tested accordingly. They have been tested accordingly. As long as the instructions are followed, they don’t release harmful substances even at high temperatures, and they are virtually immune to silicone allergies.
Recommended reading: Is Silicone Toxic: Silicone Safety Guide.
What Aspects of Silicone Products Can Be Customized?
Generally speaking, the shape, size, color, and surface texture of silicone products can be customized, and you can also have a silicone product with your company’s logo. Food-grade and medical-grade silicone will have fewer color options than regular silicone because of safety concerns.
Its hardness, density, transparency, electrical conductivity, temperature adaptation range, and other properties can also be controlled by adjusting the formula and production process. You can also choose to combine silicone with other materials or add special effect coatings to the surface.
What’s the Difference between Liquid Silicone Rubber(LSR) and High-temperature Vulcanized Silicone Rubber(HCR) Manufacturing Processes?
LSR and HTV use different polymerization processes, with HTV using intermittent polymerization techniques to obtain more complex molecules and LSR using continuous polymerization.
LSR generally uses an injection molding process, while HTV will use compression molding, transfer molding and other molding processes.
In terms of the type of vulcanization, LSR generally uses a platinum vulcanization system, whereas HTV uses a peroxide system, so HTV requires a secondary vulcanization.
Final Thoughts
Standardized production process and strict quality inspection are very important to ensure the quality of each batch of silicone products.
As a manufacturer of silicone products with more than 20 years of experience, Legensilico specializes in silicone compounding, injection molding, and many other key silicone production processes, providing a wide range of silicone products with stable quality and customized services. If you are still looking for a reliable partner, please contact us!
