The problem of two-component thin-layer curing is a common phenomenon. There are two main reasons for this: 1. During the sizing process, when the strip is thin, the crosslinking agent in the colloid is easy to volatilize, causing cross-linking. Insufficient agent; 2. Due to the small amount of catalyst used in the two-component silicone gum, the content of the colloidal catalyst is lower after scraping, resulting in the phenomenon that the catalytic reaction cannot stick back.There are two main methods to solve this problem: 1. Increase the content of the cross-linking agent; 2. Use a cross-linking agent with a lower activity and a larger molecular weight, which can reduce the volatility and increase the content of the catalyst.
The choice of silane coupling agent in silicone rubber has a relatively large effect on the performance of the rubber.
Deacidified silicone rubber: The coupling agent used in acidic rubber is relatively small. Currently, it is mainly D-11 di-tert-butoxydiacetoxysilane, which can improve the adhesion of acidic rubber to metals.
Deoxime type silicone glue: The commonly used silane coupling agents of ketoxime type are LT-550, LT-560 and LT-792. Among them, LT-550 and LT-792 can improve the adhesiveness and storage stability of glue. LT-792 has better adhesion than LT-550, and LT-550 is better than LT-792 in terms of storage stability and yellowing resistance. LT-560 can improve the curing strength and curing speed of the glue, but excessive addition of coupling agent will affect the storage stability and yellowing resistance of the silicone glue.
Dealcoholic silicone adhesive: silane coupling agents commonly used in alcohol type are LT-171, LT-550, LT-560 and LT-792. Among them, LT-550 and LT-792 can improve the adhesiveness of the adhesive and reduce the storage stability of the adhesive, and at the same time easily cause yellowing of the adhesive; 171 and 560 can improve the curing speed and storage stability of the adhesive, but the The improvement is limited.
It is not necessary to use them at the same time, but they are often used together in actual use. This is mainly because methyl tributanone oxime silane and vinyl tributanone oxime silane can each play a complementary role in the gum. Their respective advantages and disadvantages are as follows:
Methyl tributanone oxime silane
Vinyl tributanone oxime silane
1, Not easy to yellow
2, Low price
1, Fast curing speed
2, Not easy to crack
、固化速度慢 1.Slow curing speed
、易黄变 1 , easy yellowing
、价格高 2.High price
Tetrabutanone oxime silane is solid at normal temperature. Mixed deoxime type cross-linking agents are all mixed products of tetrabutanone oxime silane. When the temperature is low, tetrabutanone will appear due to solubility problems. The phenomenon that the oxime silane is precipitated as a powder.
The mixed deoxime type cross-linking agent has the phenomenon of precipitation of tetrabutanone oxime silane. The tetrabutanone oxime silane must be heated before it can be used.
There are many reasons for the poor storage stability of dealcoholized silicone gums, but there are two main reasons:
1. Methanol produced during storage of silicone glue will cause alkoxy capping on 107 glue, and finally cause 107 glue to lose its reactivity.
2. Titanium complex is easy to react or lose its catalytic activity during storage due to its high reactivity.
There are two main reasons for the bubbling phenomenon of alcoholic silicone glue.
1. External reasons: due to construction conditions, the main reason is that the temperature difference is too large or the construction surface temperature is too high.
2. Internal reasons: dealcoholic silicone glue is caused by itself, because dealcoholic rubber releases methanol during curing, and the boiling point of methanol is low, so when the construction surface temperature is too high, the released methanol cannot be timely and effective The volatilization will vaporize inside the colloid and form bulging and bubble phenomenon.
The easy bubbling of dealcoholized silicone glue has not been completely solved. According to the product vulcanization incentive, the common methods in the industry for reducing or reducing bubbling are:
1, The amount of cross-linking agent is controlled because the more the cross-linking agent is added, the greater the amount of methanol released and the easier it is to bubbling.
2, Reduce the colloid surface drying time to allow the released methanol to have sufficient time to volatilize.
3. Using methanol absorbent, no good absorbent has been found.
4. Avoid exposure during construction.
The main reason for the production of odor caused by acid gum is caused by the release of a large amount of acetic acid after the reaction between methyltriacetoxysilane and 107 gum during the production process. Therefore, when using acidic cross-linking agents, workers must use labor protection articles, such as protective glasses, masks and gloves. The acidic cross-linking agent itself is non-toxic, and is mainly irritating to the skin and respiratory mucosa. Doing a good job of protection will not cause any harm to the human body.