Two-Part Silicone Adhesive Viscosity Control
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Solution Overview
Problem
Silicone rubber compositions curing by hydrosilylation face issues with hydrogen gas generation due to alkaline impurities and viscosity imbalances, leading to difficulties in storage stability and homogeneous mixing, which affect the final physical properties and adhesion of the silicone rubber.
Innovation Solution
A two-part silicone rubber adhesive system is developed, where one part contains diorganopolysiloxane, calcium carbonate powder treated with a paraffin compound, and a hydrosilylation catalyst, while the other part includes an organopolysiloxane with hydrogen atoms, allowing for stable storage and homogeneous mixing at a 1:1 volume ratio, ensuring designed physical properties and adhesion post-curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If calcium carbonate powder is incorporated into the silicone rubber composition, then the composition exhibits good adhesion to silicone rubber, but hydrogen gas is generated during storage due to reaction between alkaline impurities and the curing agent
Solution Approach 1:
A silane coupling agent is introduced as an intermediary substance that coats the calcium carbonate powder surface. This coupling agent acts as a barrier between the alkaline impurities in the calcium carbonate and the organopolysiloxane curing agent, preventing harmful chemical reactions while allowing the calcium carbonate to maintain its adhesion-promoting function. The coupling agent mediates the interaction between the filler and the base polymer, eliminating the harmful effect of hydrogen gas generation.
2Stability of the object's composition
If the two-part composition is prepared with balanced viscosity by incorporating surface treated calcium carbonate powder in the curing agent part, then the composition can be stored separately, but strong thixotropy develops during storage and homogeneous mixing becomes difficult
Solution Approach 1:
The viscosity parameters of the two parts are carefully adjusted and balanced. The composition containing the curing agent is formulated to have a viscosity that, when mixed with the other composition in a 1:1 volume ratio, results in optimal mixing characteristics. This parameter optimization ensures that the thixotropic effects are minimized and homogeneous mixing can be achieved effectively by static mixers during the mixing process.
3Stability of the object's composition
If the two-part adhesive is prepared with great difference in viscosity between the two parts, then the compositions can be stored separately, but homogeneous mixing at equivalent volume ratio becomes difficult
Solution Approach 1:
The viscosity of each part is independently controlled and optimized. The composition containing the curing agent is formulated with specific viscosity characteristics that complement the other composition. By adjusting the viscosity parameters of both parts, the system achieves a balance where the compositions can be stored separately with good stability but can also be easily mixed in a 1:1 volume ratio to achieve homogeneous mixing.
4Stability of the object's composition
If the viscosity of the composition containing the curing agent is increased to balance the two parts, then separate storage is enabled, but the mixing homogeneity and final physical properties deteriorate
Solution Approach 1:
The viscosity of the curing agent composition is optimized to a specific range that enables separate storage while maintaining good mixing characteristics. This viscosity parameter is carefully controlled to prevent excessive thixotropy and ensure that when the two parts are mixed in a 1:1 volume ratio, homogeneous mixing is achieved and the final silicone rubber exhibits the desired physical properties.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The two-part system maintains reduced viscosity changes during storage, enabling homogeneous mixing and achieving the desired physical properties and adhesion of the silicone rubber, suitable for applications like air bag adhesives or seals.
Implementation Method 1
a calcium carbonate powder having its surface treated with a paraffin compound
Implementation Method 2
an organopolysiloxane having at least two hydrogen atoms bonded to the silicon atom per molecule
Implementation Method 3
a catalytic amount of a hydrosilylation catalyst
Data Source
AI summary
A two part adhesive for a silicone rubber which cures by addition reaction is provided. This adhesive containing a calcium carbonate powder cures by hydrosilylation, and this adhesive experiences reduced viscosity change in the long term storage. Accordingly, this adhesive can be homogeneously mixed to realize the designed physical properties of the silicone rubber as well as good adhesion to the silicone rubber. This adhesive contains (A) an alkenyl group-containing diorganopolysiloxane; (B) an organohydrogenpolysiloxane; (C) a calcium carbonate powder having its surface treated with a paraffin compound; (D) an inorganic powder of a member selected from quartz, aluminum hydroxide, diatomaceous earth, alumina, titanium dioxide, zinc oxide, iron oxide, magnesium carbonate, and carbon black; and (E) a hydrosilylation catalyst. Of the two parts, the composition (I) contains the components (A), (C), (E), and optionally (D) without (B), and the composition (II) contains the components (A), (B), and (D) without (C) and (E), and these compositions (I) and (II) cures when they are mixed at room temperature.