A Comprehensive Analysis of Liquid Silicone-Encapsulated PC Injection Molding Technology: Process, Problems, and Solutions (Part 2)

Keywords: Liquid silicone encapsulation of PC, LSR injection molding, liquid silicone overmolding, silicone overmolding, injection molding process, LSR encapsulation of PC injection molding process

IV. Common Problems and Solutions

4.1 Poor Adhesion

Causes: Oil, dust, and other contaminants on the PC surface affect the contact and reaction between the primer or self-adhesive LSR and the PC surface; insufficient surface treatment, such as too short a plasma treatment time, too low a power, or uneven application and insufficient drying of the primer, results in insufficient surface energy enhancement, preventing effective chemical bonding or physical adsorption; mismatched process parameters such as temperature and pressure during injection molding affect the curing reaction and bonding effect between the LSR and PC.

Solution: Before surface treatment, add a rigorous surface cleaning process, using organic solvents such as alcohol and acetone to wipe the PC surface to ensure it is free of oil, dust, and other contaminants; optimize surface treatment process parameters, rationally adjusting the power and time of plasma treatment or the concentration and drying conditions of the primer, based on material characteristics and product requirements; comprehensively optimize injection molding process parameters, determining the optimal temperature, pressure, injection speed, and other parameters through experiments and simulation analysis to ensure good bonding between LSR and PC under suitable conditions.

4.2 PC Cracking

Causes: Inadequate product design, with structural defects such as sharp corners and uneven wall thickness, easily leads to stress concentration during injection molding, causing cracking of the PC substrate; improper PC injection molding process parameter settings, such as excessively high injection pressure, excessively long holding time, and excessively rapid cooling rate, can generate significant residual stress within the PC, causing cracking during subsequent processing or use; quality problems with the PC material itself, such as uneven molecular weight distribution or the presence of impurities, can also reduce its crack resistance.

Solutions: During the product design phase, adhere to the principle of avoiding stress concentration, optimize product structure design, and adopt design methods such as rounded corners and uniform wall thickness; precisely control the PC injection molding process, reducing the generation of residual stress inside the PC by adjusting parameters such as injection pressure, holding time, and cooling rate; if necessary, add an annealing process after PC injection molding, heating the product to an appropriate temperature and holding it for a certain time, then slowly cooling it to eliminate internal residual stress; select reliable PC raw materials and conduct strict quality testing on the raw materials to ensure their performance meets requirements.

4.3 LSR Flash

Causes: Insufficient mold precision, gaps, wear, or deformation at the parting surface cause LSR to overflow from the gaps during injection molding, forming flash; excessive injection pressure causes the LSR to flow too quickly within the mold, easily breaking through the mold's sealing boundaries and generating flash; an unreasonable mold venting system design prevents timely gas discharge during injection molding, leading to increased pressure within the cavity and causing LSR to overflow and form flash.

Solutions: Improve mold manufacturing precision and quality; regularly maintain and service molds, check the fit of parting surfaces, and promptly repair or replace worn or deformed mold components; optimize injection pressure control by determining the appropriate injection pressure range through testing and data analysis, and employ pressure curve control technology to dynamically adjust the injection pressure during the injection molding process based on actual conditions; improve the mold venting system design by rationally setting the position, size, and number of venting grooves to ensure smooth gas discharge from the mold, reduce cavity pressure, and minimize flash.

V. Quality Control Standards

5.1 Testing Items

Adhesive Strength: Use tensile testing to determine the adhesive strength between LSR and PC, requiring an adhesive strength ≥1.5MPa to ensure that the product will not delaminate during use.

Sealing Performance: Based on the specific application requirements of the product, test the product's sealing performance using methods such as airtightness and watertightness testing to ensure that the product meets waterproof, dustproof, and gas leakage prevention requirements.

Durability: The product undergoes high and low temperature cycling tests to simulate the temperature variations it might encounter during actual use. The number of tests is generally no less than 50 cycles. The product should show no significant performance degradation after testing, and its appearance should be free of defects such as cracks or deformation, to verify its long-term reliability and stability.

Appearance Quality: The product's appearance quality is evaluated through visual inspection and optical microscopy. The product surface should be free of defects such as burrs, bubbles, impurities, and scratches, and the color should be uniform and consistent, meeting design requirements.

5.2 Testing Methods

Tensile Testing Machine: Used for bond strength testing. The prepared test sample is mounted on the tensile testing machine and stretched at a certain tensile speed. The maximum tensile force at failure is recorded, and the bond strength is calculated based on the bonded area of ​​the sample.

Air Tightness Testing Machine: The product's air tightness is tested using either the differential pressure method or the direct pressure method. The differential pressure method determines whether there is a leak by comparing the pressure difference between the test product and a standard part; the direct pressure method detects leaks by directly measuring changes in the internal pressure of the product. Test pressure and holding time are set according to the product's sealing requirements.

High and Low Temperature Test Chamber: Used for high and low temperature cycling tests. The product is placed in the chamber and cycled according to the set temperature curve. The temperature range is generally -40℃ to 125℃. Heating/cooling rates, holding time, and other parameters can be adjusted according to product standards.

Optical Microscope: Used to observe the product's interface bonding and surface micro-defects. After appropriate treatment of the product's cross-section or surface, it is placed under an optical microscope for observation. The magnification is selected as needed, generally 50-500x. Product quality is assessed by observing the tightness of the interface bonding and the presence of defects such as gaps and holes.

VI. Application Areas

6.1 Consumer Electronics

Smartphone Casing: Combining the high strength and impact resistance of PC with the anti-slip, shock-absorbing, and wear-resistant properties of LSR, it provides comprehensive protection for smartphones while improving user comfort and tactile feel.

Smartwatch Straps: Utilizing the softness, elasticity, and excellent biocompatibility of LSR, these straps are perfectly integrated with PC cases to create comfortable, wrist-hugging smartwatch straps that are waterproof and dustproof.

Earphone Protective Covers: Earphone protective covers made from LSR-encapsulated PC through injection molding effectively protect headphones from impacts and scratches, while providing excellent sound insulation and noise reduction. Their soft material does not put pressure on the ears.

6.2 Automotive Components

Sealing Components: Such as automotive headlight seals and door/window sealing strips, LSR's superior sealing and aging resistance effectively prevent dust, rain, and moisture from entering the vehicle's interior, protecting automotive electronic equipment and components from corrosion and improving the overall performance and reliability of the vehicle.

6.3 Medical Devices

Surgical Instrument Handles: LSR-encapsulated PC injection molding technology provides surgical instrument handles with a non-slip, easy-to-clean surface. The high strength of PC ensures the structural stability of the handles, meeting medical and hygiene standards and effectively reducing the risk of errors during surgical procedures.

Equipment Seals: In medical equipment such as MRI scanners, ultrasound diagnostic instruments, and blood glucose meters, the use of LSR-encased PC seals ensures the sealing and stability of the internal environment, preventing dust, moisture, and other impurities from entering the equipment and affecting its normal operation and detection accuracy. It also meets the stringent requirements of medical equipment for material biocompatibility and sterilization resistance.

VII. Technological Development Trends

7.1 Self-Adhesive LSR Materials

Developing self-adhesive LSR materials with higher adhesive performance will further reduce or completely eliminate surface treatment processes, simplify production processes, lower production costs, and improve product quality and production efficiency. The development of self-adhesive LSR materials will move towards greater environmental friendliness, efficiency, and stability, meeting the ever-increasing material performance and process requirements of different industries.

7.2 Smart Manufacturing

Introducing advanced sensor technology, automated control technology, and data analysis algorithms will enable real-time monitoring and precise adjustment of the injection molding process. Intelligent manufacturing systems can automatically collect and analyze process parameters such as temperature, pressure, and time, and adjust production parameters in a timely manner according to preset quality standards to ensure product quality consistency and stability, while improving production efficiency and reducing scrap rates.

7.3 Microforming Technology

With the increasing demand for miniaturized products in industries such as electronics and medical, microforming technology will be more widely used in the field of liquid silicone encapsulation of PC injection molding. Microforming technology enables high-precision injection molding of tiny components, meeting the development needs of products in terms of miniaturization, lightweighting, and integration, and providing technical support for the manufacture of high-performance microelectronic devices and medical device components.