Silicone pressure-sensitive adhesives as a class of silicone polymers as the core of functional adhesive materials, its value is not only reflected in the basic adhesion performance but also in its ability to withstand extreme environments and material science level of designability. How is Silicone PSA leading the industry change?
Silicone PSA has significant advantages: its temperature resistance is excellent, can be in -65 ℃ to 300 ℃ under extreme temperatures to maintain stability, suitable for high-temperature electronic equipment and low-temperature environments. Strong weather resistance, high resistance to UV, ozone, and other environmental factors, and long outdoor service life. Excellent chemical stability, resistant to a wide range of acids, alkalis, and solvents. In addition, good adhesive strength with light pressure to difficult-to-bond materials such as PTFE, and good exhaust performance in the bonding process to ensure tight bonding.
The following five aspects of silicone pressure-sensitive adhesive technology innovation and application areas:
- What is the composition of silicone PSA?
- What are the properties of silicone PSA?
- What are the application scenarios of silicone PSA?
- What is the technology innovation direction of Silicone PSA?
- How to improve the performance of silicone PSA?
1. What is the composition of silicone PSA?
The silicone pressure-sensitive adhesive formulation system is essentially a silicone resin and silicone rubber micro-phase regulation results, its performance advantages from the synergistic effect of the two:
(1) Silicone resin (MQ resin):
MQ resin consists of monofunctional (M unit, R3SiO1/2) and tetrafunctional (Q unit, SiO4/2) structure, through the hydrolysis polycondensation reaction to form a three-dimensional network skeleton. Among them, the organic groups (e.g., methyl, phenyl) in the M-unit can regulate the polarity of the resin, while the Q-unit determines the cross-linking density. For example, in high-temperature adhesive formulations, phenyl instead of methyl can enhance heat resistance (glass transition temperature Tg increased to more than 200 ℃), and increasing the proportion of Q unit can enhance the anchoring force on the metal substrate.
(2) Silicone Rubber (PDMS):
The long-chain linear structure of polydimethylsiloxane (PDMS) (molecular weight usually 500,000-1,000,000) gives the system flexibility. The energy storage modulus (G') of the colloid can be precisely controlled by adjusting the mass ratio of PDMS to MQ resin (typical range 1:1 to 4:1). For example, when the percentage of PDMS is increased, G' decreases from 10^5 Pa to the 10^4 Pa level, and the colloid shifts from hard bonding to soft cushioning characteristics, which is suitable for shock-absorbing bonding in vibration environments.
(3) Crosslinking system:
Platinum-catalyzed addition curing (Hydrosilylation) is currently the mainstream process, which achieves controlled cross-linking through the quantitative reaction between the Si-H bond and vinyl. Compared with traditional peroxide curing, the platinum-catalyzed system without by-product release, is especially suitable for medical or optical-grade adhesives. For example, a medical dressing adhesive using a delayed platinum catalyst, at room temperature to maintain a liquid state to facilitate coating, warming to 80 ℃ after 10 minutes to complete curing, to avoid high-temperature damage to the heat-sensitive substrate.
Add particle size distribution optimized aluminum nitride (AlN, thermal conductivity 320 W/m-K) or surface-modified alumina (thermal conductivity 30 W/m-K), which can make the thermal conductive adhesive thermal resistance down to less than 0.5 ℃-cm²/W. For conductive adhesive, silver-coated copper powder (particle size 5-10μm, loaded with 60-70wt%) can be maintained in the volume resistivity <0.01 Ω-cm at the same time, the cost control in the pure silver filler 1/3.
2. What are the features of Silicone PSA?
(1) High temperature resistance:
Silicone-oxygen bond (Si-O) bond energy is as high as 452 kJ/mol, much higher than the C-C bond (347 kJ/mol), which is the root of heat resistance. Take a typical electronic grade silicone pressure-sensitive adhesive as an example, after aging at 250 ℃ for 1000 hours, its 180 ℃ peel strength retention rate is still more than 80%, while the acrylate adhesive in this condition has been completely carbonized and failed. More notably, the introduction of heat-resistant additives (such as cerium oxide), can capture the free radicals generated at high temperatures, the thermal decomposition temperature from 300 ℃ to 450 ℃, to meet the aerospace engine compartment cable fixing needs.
(2) Chemical inertness:
The methyl group of the PDMS molecular chain forms a dense hydrophobic layer, which can effectively block the penetration of polar solvents. Test data show that after 24 hours of immersion in concentrated sulfuric acid (98%), the thickness of the adhesive layer expands by <5%, while acrylate adhesive expands by more than 200%. In addition, the UV absorption peak of the siloxane network is located in the short-wave region (<250nm), which is much lower than the UV intensity of the solar spectrum on the ground (280-400nm), so the outdoor service life can reach more than 20 years, which is more than 3 times higher than the weathering performance of polyurethane adhesive.
(3) Electrical performance:
At 10GHz high frequency, the dielectric constant (ε) of silicone pressure-sensitive adhesive is stable at 2.8-3.2, and the loss factor (tanδ) is <0.002, which is a characteristic that makes it an ideal choice for the encapsulation of 5G millimeter-wave antenna modules. For example, a base station antenna manufacturer used a customized silicone adhesive film instead of traditional epoxy resin to reduce signal transmission loss from 0.15 dB/cm to 0.03 dB/cm, while solving the interface cracking problem caused by the coefficient of thermal expansion (CTE) mismatch.
(4) Biocompatibility:
The key to passing the ISO 10993-5 cytotoxicity test is to control the residual amount of low molecular weight siloxane cyclic (D4-D6). The advanced process uses molecular distillation to reduce the D4 content from the conventional 500 ppm to less than 50 ppm and reduces protein adsorption by surface grafting polyethylene glycol (PEG) chain segments. A pacemaker fixation tape was tested by 30-day in vivo implantation, and the level of inflammatory response was grade 0 (no irritation), while the traditional acrylate tape was grade 2 (moderate irritation).
XJY-301 Silicone Pressure Sensitive Adhesive
It is made from the specific structure of silicone resin and high molecular weight polydimethylsiloxane in conjunction with organic adhesives for specific scenario conditions.
Compared with natural rubber, it is characterized by heat resistance, high stability, good electrical insulation, good transparency, high peel adhesion, and chemical resistance. In industrial product processing, electronic processing, optical materials, health care and mica tape, splicing tape, protective film, and other fields PSA properties have a wide range of applications.
3. What are the application scenarios of silicone PSA?
3.1 Electrical and electronic industry:
Flexible circuit board (FPC) fixation:
In the folding screen phone, the hinge area FPC needs to withstand more than 200,000 times of dynamic bending. By optimizing the modulus gradient design, the silicone pressure-sensitive adhesive adopts a low-modulus adhesive (G'=5×10^4 Pa) in the bending area to absorb stress, and a high-modulus adhesive (G'=2×10^5 Pa) at the fixed end to prevent creep, which has successfully reduced the failure rate from the initial 15% to less than 0.3%. In terms of cost, although the unit price of organic silicone is three times higher than that of acrylate adhesive, the overall BOM cost dropped by 12% due to the reduction in the use of structural components such as shields.
(2) Chip thermal interface materials:
Take a GPU chip as an example, the use of boron nitride-filled silicone thermal conductivity adhesive (12 W/m-K) to replace the traditional silicone grease, the interface thermal resistance from 0.8 ℃ - cm ² / W down to 0.3 ℃ - cm ² / W, the chip junction temperature down 18 ℃, the same power consumption under the same arithmetic power reduced by 7%. More noteworthy is that its thixotropic properties allow the thickness of the adhesive layer to be controlled at 50±5μm under vertical installation conditions, avoiding the uneven thickness problem caused by the mobility of traditional phase change materials.
(3) Electromagnetic shielding applications:
5G base station shielding cover requires surface impedance <0.1 Ω/sq and long-term salt spray corrosion resistance. Through the silver nanowires (diameter 50nm, aspect ratio > 1000) and silicone resin composite, the development of both conductive and flexible adhesive film. In a coastal base station test, after 2000 hours of salt spray test, the shielding effectiveness is still maintained above 60dB, while the conductive epoxy resin coating due to silver migration led to the effectiveness of the attenuation to 40 dB.
3.2 Medical and health field
(1) Medical dressing innovation:
Traditional hydrocolloid dressings face the problem of viscosity loss after exudate absorption. By introducing microporous structure (pore size 20-50μm), the new organic silica gel maintains air permeability (MVTR>2000 g/m²/day) while realizing directional fluid management - the upper layer of hydrophobic silica gel blocks bacterial invasion, and the lower hydrophilic modified layer guides the lateral diffusion of exudate, which extends the adherence maintenance time from 3 days to 7 days. to 7 days. Clinical data shows that the chronic wound healing cycle is shortened by 30% and dressing change frequency is reduced by 50%.
(2) Wearable medical devices:
Continuous glucose monitoring (CGM) sensors require the colloid to maintain an adhesion force of >1 N/cm even under sweat immersion. By constructing a bionic micropillar array structure (100 μm in diameter and 200 μm in height), the wet adhesion of the organic silica gel is increased to 80% of the dry state, and a “controlled failure” mode is adopted when peeling off to avoid damaging the epidermis. A product test shows that in the sweaty conditions of sports, 14 14-day shedding rate <2%, while the traditional medical acrylic adhesive shedding rate of 15%.
(3) Transdermal drug delivery system:
Taking fentanyl patch as an example, organic silica gel is used as a drug reservoir cum controlled release layer, and its three-dimensional network structure can accurately adjust the molecular diffusion coefficient. By adjusting the cross-linking density, the 72-hour drug release fluctuation rate is narrowed from ± 25% to ± 8%, and the smoothness of blood drug concentration is significantly improved, reducing the incidence of side effects.
4. What is the technology innovation direction of Silicone PSA?
(1) Material formulation optimization
Functionalized filler composite: through the addition of graphene, boron nitride, and other nanomaterials, the development of high thermal conductivity (> 10W/m-K), conductive or electromagnetic shielding type pressure-sensitive adhesive;
Environmentally friendly solvent system: development of water-based or UV-curable silicone pressure-sensitive adhesives to reduce VOC emissions;
Dynamic reversible bonding: based on reversible chemical bonds such as Diels-Alder, to achieve multiple bonding of the adhesive layer and non-destructive peeling.
(2) Technological innovation
Precision coating technology: ultra-thin coating (<10μm) and patterned coating to meet the needs of miniaturized electronic devices;
On-line inspection system: combined with AI vision to detect defects in the adhesive layer and improve production yield;
3D printing technology: develop silicone pressure-sensitive adhesive pastes suitable for extrusion 3D printing to expand the bonding scenarios of complex structures.
(3) Emerging application field
Flexible electronics: for folding screen cell phone hinge area bonding and stretchable circuit package;
Space exploration: radiation-resistant pressure-sensitive adhesive in the application of satellite solar panels;
Bionic medical devices: skin-like modulus of elasticity of the pressure-sensitive adhesive for bionic prosthetic interface.
5. How to make silicone PSA performance better?
Silicone pressure-sensitive adhesive in the traditional acrylate or rubber-based pressure-sensitive adhesive is difficult to meet the high-end scene, silicone pressure-sensitive adhesive by virtue of the unique physicochemical properties given by the silicone main chain has become a precision electronics, medical and health care, new energy vehicles and other fields of the “invisible guardian”. How to improve the competitiveness of products?
XJY Silicones is one of the leading silicone MQ resin and VMQ silicone manufacturers in China, with more than 30 years of R&D and manufacturing experience in the silicone industry, as well as more than 15 related patents and technical support. Our silicone raw material products can meet the needs of the pressure-sensitive adhesive field and support the provision of diversified customized solutions.
