Plastic and rubber bonding parts can combine the sealing properties of rubber and the rigidity of plastic. This rubber to plastic bonding design can achieve advantages such as good performance and lightweight.
The rubber bonding(overmolding) process forms a strong bond between the rubber and plastic through the vulcanization process. However, due to the significant differences in the physical and chemical properties of rubber and plastic, material selection on both plastic and rubber and product design adapting for vulcanization process have to be considered during development phrase .
Material Selection
Rubber vulcanization temperatures typically range from 120°C to 180°C, which means the plastic materials used for overmolding must have a heat deflection temperature higher than 120°C. Below are the heat deflection temperatures of several commonly used plastic materials:（Adding glass or carbon fibers significantly increases HDT. For instance, glass-reinforced PP can achieve 120-140°C）
Heat Deflection Temperatures of Common Thermoplastics
| aterial | HDT (°C) | Notes |
| Polyethylene (PE) | 50-80 | LDPE has a lower HDT, while HDPE is higher. |
| Polypropylene (PP) | 80-110 | Higher crystallinity than PE, better heat resistance. |
| Polystyrene (PS) | 70-100 | Rigid PS has a higher HDT but is more brittle. |
| ABS Resin | 85-100 | HDT varies depending on the rubber and styrene ratio. |
| Polyvinyl Chloride (PVC) | 50-70 | Rigid PVC has a higher HDT, while plasticized PVC is lower. |
| Polymethyl Methacrylate (PMMA) | 95-110 | Also known as acrylic, with excellent transparency and weather resistance. |
| Polyamide (PA, Nylon) | 100-190 | HDT depends on the type (e.g., PA6, PA66). |
| Polyethylene Terephthalate (PET) | 70-75 | Low crystallinity results in lower HDT; glass-fiber reinforced PET can reach up to ~200°C. |
| Polycarbonate (PC) | 120-140 | A transparent material with excellent toughness and heat resistance. |
| Polyoxymethylene (POM) | 100-120 | Offers excellent self-lubricating properties and wear resistance. |
| Polyphenylene Ether (PPO) | 140-170 | High heat resistance but limited processability. |
| Polyimide (PI) | >250 | Exceptional heat resistance, used in advanced engineering applications. |
| Polyether Ether Ketone (PEEK) | 240-290 | Outstanding heat and chemical resistance. |
| Polytetrafluoroethylene (PTFE) | 55-120 | HDT is less common; continuous service temperature reaches around 260°C. |
| Polyphenylene Sulfide (PPS) | 230-270 | High heat resistance and excellent dimensional stability; glass-fiber reinforced grades can reach higher values. |
| Polyphthalamide (PPA) | 280-300 | Superior high-temperature and chemical resistance, ideal for high-performance applications. |
Surface Treatment
Low surface energy plastics (such as PP, PE) require special surface modifications (e.g., plasma treatment, surface activation) to improve bonding performance.
Additionally, specific primers or activators can be used to enhance bonding between rubber and plastic materials.
Rubber Material Selection
The choice of rubber material should be based on the medium it will be exposed to. For example:
- Coolants: EPDM (Ethylene Propylene Diene Monomer) is suitable for coolant applications due to its excellent resistance to heat and water.
- Chemical Solvents: FKM (Fluoroelastomer) is recommended for chemical solvent resistance due to its high chemical stability and temperature resistance.
- Oils: FKM or HNBR (Hydrogenated Nitrile Butadiene Rubber) are ideal for oil-resistant applications due to their high resistance to oil, fuel, and lubricants.
Design Of Plasct Rubber Bonding Product
The design of the Plasct Rubber Bonding should consider the plastic shrinkage, thermal expansion, and the stress distribution during the vulcanization process. Here are some design suggestions:
1. Avoid large flat bonding surfaces
- Problem: Large, flat bonding surfaces may cause warping or delamination due to shrinkage of the plastic during the rubber vulcanization process, affecting adhesive strength.
- Optimization Suggestion:
- Add protrusions or grooves to create mechanical interlocking.
- Use segmented bonding designs to reduce the surface area of a single bond.
2. Avoid significant thickness variations in plastic walls
- Problem: Variations in plastic wall thickness can cause uneven cooling and shrinkage of the plastic during rubber vulcanization. It will lead to warping or internal stresses, which affect overall structure and dimensional accuracy.
- Optimization Suggestion:
- Maintain a uniform wall thickness in plastic components and avoid areas with excessive thickness.
- Add ribs or transition fillets on plastic part to reduce stress concentration.
3. Avoid sharp edges and right-angle transitions on plastic part
- Problem: Sharp edges can cause stress concentration during heating, leading to cracks, while right-angle transitions amplify the shrinkage differences between plastic and rubber.
- Optimization Suggestion:
- Use rounded corners or fillets to smooth transitions and reduce stress.
- Ensure smooth shapes at bonding interfaces to avoid stress concentration.
Please contact us,OBT Rubber Seal,for customized rubber plastic bonding solutions according to your applications. Our application engineer could support for material selection and our suggestions on product design.
In some case, we can launch FEA analysis in order to simulate the deformation of rubber under different loads, temperatures, and environmental conditions.
