Knowing whether silicone can self-adhere is of great significance to you. Because this directly affects your product selection plan, helps you avoid the risk of adhesive failure, and ensures stable product quality and efficient project implementation.
This article provides you with professional guidance about silicone adhesion from several dimensions including influencing factors, different application schemes, and testing methods.
Will Silicone Stick to Silicone?
When using silicone, you should judge the self-adhesive property based on the curing state: uncured or partially cured silicone can chemically crosslink with additional uncured silicone during the curing process.
However, cured silicone mostly cannot self-adhere. If you want to achieve bonding, you need to apply a primer or adjust the formula. There is also special self-bonding silicone, which relies on an exclusive formula design. Even after curing, it can still achieve self-adhesion.
What Is Self-Adhesive Silicone?
This type of silicone undergoes formulation treatment and is equipped with reactive groups. After complete curing, it can achieve self-adhesion.
Typical Applications
Silicone, due to its self-adhesive property, is widely used in the following applications. You can refer to the following information:
- Insulation protection for coils of electric motors and generators
- Suitable for insulation treatment of connection parts of coils and ends of stator coils
- Can perform on-site molding repair for damaged insulation areas of motor coils
Factors Affecting the Self-adhesion of Silicone
Degree of Cure
The degree of cure of the silicone directly affects the bonding effect between the silicone pieces. Unvulcanized silicone can bond normally. For ordinary fully vulcanized silicone, the molecular structure is stable and it is difficult to achieve mutual bonding.
Formulation Design
When choosing silicone, you should pay attention to the formula. If anti-sticking additives and internal lubricants are added to the silicone product, it will directly reduce the self-adhesion property of the silicone itself and affect the subsequent bonding performance.
Surface Cleanliness
The cleanliness of the surface is of utmost importance. Before use, make sure the surface of the silicone is clean. If the surface is not clean, the sealant cannot adhere firmly.
For instance, impurities such as release agents, oil stains, and dust can hinder the bonding of silicone molecules, directly suppressing the bonding effect and resulting in insufficient adhesion.
Surface Roughness
Although a smooth surface can reduce pseudo-adhesion, slight surface roughening may improve mechanical interlocking and increase bonding performance. Therefore, surface roughness is also an important factor affecting the self-adhesion of silicone. When using silicone, please keep this in mind.
Ambient Humidity
Excessive humidity may disrupt surface preparation, lower adhesion consistency, hinder molecular bonding, and thus compromise overall bonding performance. Therefore, you need to control the humidity of the usage environment to avoid the negative impact caused by overly humid conditions.
Silicone Type
There are various types of silicone materials, such as room-temperature vulcanizing (RTV), high-temperature vulcanizing (HTV), and liquid silicone rubber (LSR). Moreover, the molecular characteristics of different types of silicone vary, resulting in significant differences in adhesion performance.
To illustrate with a specific example: acetoxy-cure silicone and neutral curing silicone. Since acetoxy-cure silicone releases acetic acid, which causes platinum poisoning and inhibits addition-cure platinum catalysts. On the other hand, neutral curing silicone is more versatile and compatible, and can be adapted to various substrates, including other types of silicone.
How to Prevent Cured Silicone Products from Mutual Sticking?
When you are storing, transporting silicone gaskets, silicone pads, silicone tubes and other finished products, you may encounter adhesion problems. These can be solved by the following solutions:
Surface Treatment
If you choose a surface treatment method, it is recommended to apply a fluorine-based coating or lubricant to the silicone products to enhance the surface smoothness. However, considering the cost and process of applying the fluorine-based coating, this method is more suitable for high-end products.
Formulation Adjustment
During your mass production process, you can start by looking at the formula and add anti-adhesion additives such as CoatOSil™ 7602 to prevent adhesion from the very beginning.
Physical Isolation
If you want it to be more convenient, you can find a simple and universal method. You can use PET isolation film, non-woven fabric or talcum powder for physical isolation.
For precision or large-sized products, we recommend individual packaging per piece and adding padding paper between layers to effectively prevent the problem of adhesion during transportation and storage.
How to Achieve Permanent Silicone-to-Silicone Bonding?
4 Technical Solutions
When bonding multi-layer silicone products or silicone composite parts of different hardness or colors, you can choose from the following 4 technical solutions:
Using Primer
The first option is to use a dedicated silicone primer, such as Wacker G 791. This approach has moderate difficulty and cost, and it is suitable for large-scale industrial sealing component production.
Self-Adhesive Silicone Raw Material
The second option is to use self-adhesive silicone material, which eliminates the need for an additional primer. The process is simple, but the cost of the raw materials is relatively high. This option is suitable for those who aim for high production efficiency and want to manufacture food-grade multi-layer silicone products.
Partial Cure and Over‑Molding
The third method is to use the partial cure + over-molding process. When curing the first layer of silicone, you directly inject the second layer. This can achieve lower costs, but the process is quite challenging.
If your factory already has a good grasp of the core molding process or if the production structure of the double-layer composite silicone parts is simple, this method is suitable.
Plasma Treatment
The fourth method is plasma treatment. This approach achieves bonding by activating the surface, resulting in excellent bonding results. However, it is more challenging and costly. It is suitable for your brand, which is positioned to pursue the highest quality and is centered on creating environmentally friendly and compliant products.
Additional Recommendations
Apart from choosing a technical solution that suits your business, you also need to pay attention to the following details:
Allow Adequate Curing Time
The curing time of silicone adhesives is usually longer than that of other adhesives. You can follow the curing time instructions provided by the supplier. Do not apply pressure to your product before the adhesive has fully cured.
Moreover, the curing time of each adhesive varies, typically ranging from 24 hours to several days. Therefore, you need to reasonably reserve the curing period according to the actual product.
Avoid Excessive Movement During Curing
Because silicone has inherent flexibility, but if you move it excessively during the curing process, it will directly reduce the bonding effect. During the glue curing stage, please keep the bonding surface stable and do not bend, twist, or otherwise manipulate the silicone.
Consider Temperature and Humidity
Because temperature and humidity directly affect the curing process of the silicone adhesive. If the temperature in your working environment is low or the humidity is too high, the curing time will be prolonged accordingly.
Therefore, you need to control the environmental conditions to ensure that the environmental parameters are suitable for the normal curing of the adhesive.
Test Methods for Evaluating Whether Silicone Sticks to Silicone
Standard Test Method
Silicone is often used as a sealant due to its excellent resistance to weathering and aging, as well as its elasticity. You can test its self-adhesiveness using the methods listed in the table below:
| Test Standard / Method | Applicable Object | Description |
| ASTM D903 | Silicone-to-Silicone Peel Strength | Standard 180° peel test for flexible materials |
| Thin-Specimen Peel Test Method | Silicone Sealant | Improved version to reduce cohesive failure of sealant |
| Thin-Specimen Lap Shear Method | Silicone Sealant | Newly proposed alternative solution |
| Accelerated Aging Adhesion Test | Silicone Sealant-Substrate System | Applies both mechanical and environmental stresses simultaneously |
Simplified Enterprise-Level Test Method
The simple enterprise-level peeling method is suitable for the testing of your silicone sheet. First, stack the two silicone samples according to the corresponding pressure, temperature and time parameters, and complete the pressing process.
Then, cool the samples to room temperature. Next, perform the peeling operation on the samples manually or using a force gauge, and record the peeling force value and the failure mode. This will clearly indicate whether it is interface failure or cohesive failure, thereby determining the bonding performance between the silicone samples.
The rating criteria can be referred to as follows:
- Level 0: Completely non-sticky. Separates easily upon gentle touch.
- Level 1: Slightly adhered. Can be easily separated without residue.
- Level 2: Moderately adhered. Requires forceful separation.
- Level 3: Clearly adhered. The surface is damaged after separation.
- Level 4: Fully bonded; substrate fails before bond line.
Failure Mode Identification
The failure mode identification is of vital importance for product quality control and research and development optimization. Through it, you can precisely identify the root cause of the bonding problems and provide an effective basis for formula adjustment and process improvement.
| Failure Mode | Description | Implication |
| Interfacial Failure | Clean separation at the bonding surface | Insufficient surface treatment or formulation issues |
| Cohesive Failure | Fracture of the silicone material itself | Bonding strength exceeds material strength, indicating good adhesion performance |
| Mixed Failure | Partial interfacial failure + partial cohesive failure | Moderate bonding performance; acceptable but not optimal |
FAQ
Why Does Cured Silicone Not Stick?
Because the surface activity of fully cured silicone is very low. Moreover, silicone is a non-porous material with a low surface energy, and the interaction force with other materials is weak, which is insufficient to form a firm bond.
How to Improve Silicone Surface Cleanliness Without Affecting Its Self-Adhesiveness?
You can clean the surface with solvents or alcohol-based cleaners to remove residues such as dirt and oil. Afterwards, it is best to sand the silicone surface with sandpaper to enhance the adhesion. Make sure the surface is completely dry.
What Adhesive Is Best for Bonding Silicone to Silicone?
Silicone-based adhesives, such as RTV silicone or specialized silicone sealants, are the preferred options for inter-silicone bonding. These adhesives can penetrate deeply into the surface of the silicone substrate, achieving a stable and firm bonding effect, and are suitable for meeting the high bonding requirements between silicone materials.
Can Cyanoacrylate Adhesives Bond Silicone To Silicone?
The cyanoacrylate adhesive needs to be paired with a special silicone primer to achieve effective bonding between silicone. If you do not use the primer, problems such as poor surface wetting and insufficient adhesion will occur, resulting in the failure of the bonding and inability to achieve the desired bonding effect.
What Factors Should Be Considered When Selecting a Silicone Bonding Solution?
You should take into account factors such as production scale, efficiency, bonding strength, substrate, and temperature resistance requirements. In particular, when choosing adhesives for addition-cure silicone and condensation-cure silicone, be cautious as cross-use may lead to curing failure.
Final Thoughts
Legensilico is a silicone manufacturer in China with over 20 years of experience, and it can provide various customized silicone services. If you want to learn more about the self-adhesive properties of silicone, please feel free to contact us at any time. We look forward to cooperating with you.
