1. What is the reason why the neutral transparent sealant turns yellow?
The yellowing of the neutral transparent sealant is the defect of the sealant itself, which is mainly caused by the crosslinking agent and the tackifier in the neutral sealant. The reason is that these two raw materials have “amine groups”, which are extremely easy to cause. Yellowed. In addition, if the neutral transparent sealant is used together with the acid glass sealant, it may cause the neutral sealant to turn yellow after curing. It may also be caused by the long storage time of the sealant or the reaction between the sealant and the substrate.
2. Why does the neutral porcelain white sealant turn pink? Some sealants turn back to porcelain white one week after curing?
Alcohol-based neutral sealant may have this phenomenon, which is caused by the production of raw material titanium chromium compound. The titanium chromium compound itself is red, and the porcelain white color of the sealant is the color of the titanium dioxide in the sealant. But sealant is organic, and most of the organic chemical reactions are reversible reactions, and there are side reactions. Temperature is exactly the key to causing these reactions. When the temperature is high, a positive reaction will cause the color to change, but after the temperature drops and stabilizes, the reaction proceeds in the reverse direction and restores to its original appearance. If the production technology and formula are well mastered, this phenomenon should be avoided.
3. Why does some transparent glass sealant change porcelain white color after five days after being shot out? The neutral green sealant turns porcelain white color after construction, why?
This should also be a problem in the selection and verification of sealant raw materials. Because some domestic rubbers are added with plasticizers, which are easy to volatile; while some rubbers have more reinforcing fillers, when the plasticizers evaporate, the strips are stretched due to shrinkage, and the filler color appears (all the fillers of neutral rubbers) Itself is white). Various colored sealants are added with pigments to make them into various colors. If there is a problem with the choice of pigments, the color of the sealant will change after construction; or the color sealant is too thin during construction, and the sealant is inherently small in the curing process. The shrinkage will make the color of the sealant lighter. In this case, it is recommended to maintain a certain thickness (above 3mm) when sizing.
4.Some glass sealant has a salt-like granular shape when it is shot out, and some granular shapes will automatically decompose after curing. Why?
This is a matter of choosing the raw material formula of the sealant. Because the cross-linking agent contained in some sealants will crystallize in a low temperature environment, the cross-linking agent will condense in the rubber bottle. After being punched out, you will see the granular shape of salt powder, but it slowly It will melt, so the granular shape will automatically decompose after solidification. This situation has little effect on the quality of the sealant. This situation is mainly due to the relatively large impact of low temperature.
5. Some sealant hits the glass, but the sealant hasn’t dried for 7 days. What is the reason?
This situation mostly occurs in cold weather.
(1) The sealant is too thick and the dry sealant is slow.
(2) The construction environment is affected, and the weather is bad.
(3) The sealant is out of date or there is a problem.
(4) The sealant is soft and does not feel dry.
6. What is the reason for the bubbling sound of some glass sealants when sizing?
There may be three reasons:
(1) The technology is not good enough during the dispensing, and air is mixed into the plastic bottle;
(2) Air is left in the bottle;
(3) It is not 100% silicone sealant. The added filler will react slightly with the PE soft sealant of the glass plastic packaging bottle, causing the plastic bottle to swell and increase. The air remaining in the space penetrates into the sealant. Make it create a gap, it will make a sound of bubbles when sizing. An effective way to overcome this phenomenon is to change to hard bottle packaging and pay attention to the product storage environment (in a cool place below 30°C).
7. Why is there a lot of bubbles when sealant is applied in hot weather, some neutral sealant will appear after curing at the junction of concrete and metal window frame, but some will not? Is it a quality issue? Why hasn’t a similar phenomenon appeared before?
Many brands of neutral sealant have similar phenomena, and it is confirmed by careful testing and repeated experiments that it is not a quality problem of the sealant. Because the neutral sealant has two kinds of alcohol type and ketoxime type, and the methanol contained in the alcohol type sealant will release gas during the curing process (methanol starts to volatilize at about 50 ℃), especially when it is exposed to direct sunlight or high temperature, the reaction is more intense . In addition, concrete and metal window frames are difficult to breathe. In addition, the temperature and humidity are higher in summer, and the curing will be faster. The gas released by the sealant can only escape from the uncured adhesive layer and on the cured adhesive strip. Bubbles of varying sizes will appear. The ketoxime neutral sealant will not release gas during the curing process, and will not produce bubbles. However, the disadvantage of the ketoxime neutral sealant is that once the technology and formula are not handled well, there will be a chance of shrinkage and cracking in the winter during the curing process when it is cold. If the technology is good, the formula will not have this phenomenon.
Similar phenomena did not occur in the past because in the past, construction units used very few silicone sealants in such places, and they generally used acrylic waterproof sealing materials. Therefore, the phenomenon of foaming of silicone neutral sealant is not very common; in recent years In recent years, silicone sealants have been widely used, which greatly improved the quality of the project. However, due to the lack of understanding of the material properties, improper selection of materials caused the sealant to bubble.
To solve such problems, the following points should be paid attention to:
(1) The most prudent way is to do a partial use test first to observe whether it meets the needs of use (generally, the reaction can be seen two or three days after sizing);
(2) To distinguish the use time And the type of substrate, choose the appropriate neutral sealant to use: choose ketoxime type in summer and alcohol type in winter;
(3) Keep the construction surface clean and dry;
(4) Avoid high temperature periods (above 35°C) when sizing in summer. Direct sunlight is generally appropriate in the evening.
8. How to do compatibility test?
Strictly speaking, the compatibility test between the adhesive and the building base material should be carried out by the nationally recognized building material testing department. Of course, the necessary engineering must be the inspection report of the national authoritative testing agency. In order to determine whether to use a certain building material product, the general engineering can provide the substrate to the glass sealant manufacturer for compatibility testing. The test result can be obtained in about 45 days for structural sealant, and 35 days for neutral sealant and acid sealant. The simplest and quickest way is that the user can test the glass sealant on a small amount of substrates. After it is completely cured, observe the surface effect and test its peel strength by hand, so as to simply determine whether the glass sealant product’s adhesion, tension, etc. Meet the needs of use.
9. Why does the acid sealant fall off easily when used on cement?
This is actually one of the most basic problems in the application of glass sealant. Acid sealant produces acetic acid when it is solidified, which will react with the surface of alkaline materials such as cement, marble, granite, etc. to form a chalky substance, which causes it to fall off.
10. Why is the glass sealant applied on the back of the mirror, and after a period of time, mottling or sealant marks appear on the mirror surface?
Mirrors on the market usually have three different back coatings: mercury, sterling silver and copper. Freckles appear on the mirror surface of common mirrors after applying sealant for a period of time. In this case, the user has used acid glass sealant, and acid glass sealant usually reacts with the above materials, causing the mirror surface to see mottling. Therefore, we emphasize that neutral sealant should be used, and neutral sealant is divided into two types: alcohol type and ketoxime type. If the copper base mirror uses ketoxime neutral sealant, the ketoxime will slightly corrode the copper material. After a period of construction, you can see the traces of corrosion on the back sizing part of the mirror. If you switch to alcohol type neutral sealant This phenomenon will not occur. All of the above are improper selection of materials due to the diversity of substrates. Therefore, it is recommended that users do a compatibility test before using the sealant to see if the sealant is compatible with the material. Use appropriate glass sealant products to avoid unnecessary losses.