Silicone Resins Used in Mica Products

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Mica products come in two varieties: hard and soft. For hard mica sheets, we recommend our LR-152 and LR-608 methyl silicone resins. For soft mica paper, which is a composite of mica paper and other materials, such as fiberglass cloth and fiberglass paper, which requires a soft, dry finish, we recommend LR-922. For motor impregnation, we use methylphenyl silicone resins, which are heat-resistant. LR-162 and LR-163 are recommended.

The key differences in choosing silicone resins for hard and soft mica sheets lie in the type of crosslinker and the final form of the resin.

Features	Rigid mica sheet	Soft mica sheet
Recommended Resin Type	Methylphenyl silicone resin	Methyl silicone resin
Crosslinker Type	Mainly uses catalysts such as organotin to achieve condensation-type crosslinking, releasing byproducts during the curing process.	Must use a platinum catalyst to achieve addition-type crosslinking, resulting in a curing process with no byproducts and low shrinkage.
Cured Form	This three-dimensional network thermosetting resin is hard, insoluble, and infusible.	Linearly or lightly crosslinked thermoplastic elastomers maintain softness and compressibility.
Key Properties	It exhibits extremely high mechanical strength, rigidity, and dimensional stability at high temperatures.	Remains flexible, elastic, and tear-resistant even at high temperatures.
Common Applications	It is suitable for rigid mica sheets, mica tubes, mica special-shaped parts, and high-strength support components in electric heating equipment.	Suitable for use as insulation in soft mica sheets, mica tapes, mica foils, and flexible heating films.

Detailed Analysis and Recommendations

1. Rigid Mica Plate

After being formed under high temperature and high pressure, rigid mica plate resembles a hard wooden board and is used for insulation applications requiring high mechanical strength.

* Recommended Resin: Methylphenyl Silicone Resin

* Why?

* High Heat Resistance: The introduction of the phenyl group significantly improves the resin's thermal stability, oxidation resistance, and high-temperature resistance (typically reaching H-grade 180°C or higher).

* High Mechanical Strength: The phenyl group increases the rigidity of the molecular chain and the intermolecular forces, giving the cured resin higher hardness, flexural strength, and compressive strength—precisely required for rigid board applications.

* Good Compatibility: It exhibits excellent wettability and adhesion to mica sheets and mica paper.

* Good Toughness: Compared to pure methyl silicone resin, methylphenyl silicone resin is less brittle after curing and can withstand certain impacts without cracking.

* Curing Process: A condensation-type curing system (catalysts such as organotin) is typically used. During heating and pressure, the active groups (such as Si-OH) in the resin undergo a condensation reaction, releasing small molecules (such as ethanol or water), forming a dense three-dimensional cross-linked network structure, thus becoming rigid.

2. Flexible Mica Plate

Flexible mica plate, also known as soft mica plate, maintains flexibility and rollability like leather or cardboard after curing, making it suitable for applications requiring bending and wrapping.

* Recommended Resin: Methyl silicone resin (typically the base polymer for addition-type (platinum-cured) liquid silicone rubber)

* Why?

* Maintaining Flexibility: Pure methyl silicone resin chains are inherently flexible. More importantly, an addition-type cure method must be used.

* Byproduct-Free Curing: The addition reaction is catalyzed by a platinum catalyst. The crosslinker containing silicon-hydrogen bonds (Si-H) reacts with the polysiloxane containing vinyl groups (Vi), producing no small molecule byproducts. This ensures a uniform, defect-free curing process, resulting in a low-density crosslinked network, which preserves the material's elasticity and softness.

* Deep Processability: The cured product can be reheated to soften (thermoplastic behavior), facilitating subsequent deep processing such as stamping and winding without cracking.

* Tear Resistance: Its excellent elasticity allows it to rebound after being subjected to external forces, resulting in superior tear resistance compared to rigid boards.

* Key Differences: You may see both types called "methyl silicone resin," but those used for flexible boards are always cured via an addition reaction, while traditional methyl (phenyl) silicone resins used for rigid boards are cured via a condensation reaction. The crosslinking method is crucial to their hardness or softness.

Recommendations

1. Choose condensation for rigid boards and addition for soft boards: This is the most important selection principle.

* Rigid boards: Look for high-temperature-curing methyl phenyl silicone resins (condensation-type). Silicone resins used in "rigid mica boards" require high hardness and strength.

* Soft boards: Look for addition-type methyl silicone resins (the base for liquid silicone rubber). Silicone resins are used for "soft mica sheets/mica tapes" and are required to maintain flexibility at high temperatures and be free of volatiles.

2. Detailed description of the application (mica sheet), molding process (temperature, pressure, time), and required final product properties (rigid or soft) is required before we can recommend the most suitable resin type and matching catalyst/crosslinker.

3. Performance Balance: Sometimes, to achieve a certain balance of flexibility and strength, methylphenyl silicone resins are combined with specialized curing systems to create "semi-rigid" or specialized sheet materials. However, this requires specialized formulation tuning.

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