Normal Temperature-Curable Hard Coat Composition for Plastics
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Solution Overview
Problem
Current hard coat compositions for plastics are either difficult to apply outdoors due to heat curing requirements or result in insufficient hardness when used on soft substrates, and existing normal temperature-curable solutions face challenges with film thickness and substrate depression.
Innovation Solution
A normal temperature-curable hard coat composition comprising a polysilazane compound with Si—H bonds and an alkoxysilane compound, with a specific ratio of Si—H bonds to alkoxy groups, along with a condensation curing catalyst, to achieve excellent workability and surface hardness on plastics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If perhydropolysilazane is used to achieve normal temperature curing and high hardness, then curing temperature is reduced and hardness is improved, but film thickness is limited to approximately 1 μm or less due to large curing shrinkage
Solution Approach 1:
The patent uses a composite system combining perhydropolysilazane (for normal temperature curing capability) with organopolysilazane containing organic groups (to reduce curing shrinkage). This composite approach allows the coating to cure at normal temperature while achieving greater film thickness by reducing the volume shrinkage that limits perhydropolysilazane alone.
Solution Approach 2:
The patent modifies the chemical structure of polysilazane by introducing organic groups (methyl, ethyl, propyl groups) to change the curing shrinkage parameter. This structural modification reduces the shrinkage during curing, enabling film thickness to exceed 1 μm while maintaining normal temperature curing capability.
2Volume of moving object
If organic polysilazane with organic groups is used to reduce curing shrinkage and increase film thickness, then film thickness is improved, but curing at normal temperature becomes difficult and requires relatively low temperature curing which results in insufficient hardness
Solution Approach 1:
The patent merges two types of polysilazane: perhydropolysilazane (which provides normal temperature curing and high hardness) and organopolysilazane (which reduces curing shrinkage). By combining these complementary materials, the patent achieves both adequate film thickness and sufficient hardness that neither component could achieve alone.
Solution Approach 2:
The patent creates different functional zones within the coating system: perhydropolysilazane provides the hard, crosslinked network structure for hardness, while organopolysilazane provides the reduced shrinkage characteristic for thickness. Each component contributes its specific local quality to the overall coating performance.
3Strength
If heat curing step is used to achieve high hardness coating, then surface hardness is improved, but outdoor construction becomes difficult and unrealistic
Solution Approach 1:
The patent uses perhydropolysilazane which can cure at normal temperature through self-service mechanism without requiring external heat curing equipment or facilities. This makes outdoor construction feasible as the coating can cure in ambient conditions, eliminating the need for controlled heat curing environments.
4Strength
If CVD method is used to form dense silica top coat layer to improve hardness, then surface hardness is improved, but productivity decreases and high temperature of several hundred °C is required making outdoor coating unrealistic
Solution Approach 1:
The patent replaces the CVD mechanical/thermal process (which requires high temperature equipment and batch production) with a chemical solution-based coating method using polysilazane composition. This substitution enables normal temperature curing, continuous processing, and outdoor application while achieving comparable or superior hardness through chemical crosslinking.
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 composition effectively cures at normal temperatures, improves surface hardness of plastics, and provides excellent workability for outdoor applications, making it a suitable alternative to glass while maintaining transparency.
Implementation Method 1
Perhydropolysilazane, which turns to silica glass completely after curing
Implementation Method 2
an alkoxysilane compound
Implementation Method 3
along with a condensation curing catalyst
Data Source
AI summary
The present invention is a normal temperature-curable hard coat composition containing at least (A) a polysilazane compound having structures shown by the following formula (1) and (B) an alkoxysilane compound. The ratio of [a] the number of Si—H bonds in the polysilazane compound and [b] the number of alkoxy groups in the alkoxysilane compound is in a range of [b]/[a]=1.5 to 3. The present invention provides the normal temperature-curable hard coat composition which has excellent workability on outdoors, cures at normal temperature, improves surface hardness of plastic materials, and is used as an alternative material to glass.