1. What are high modulus and low modulus?

High modulus - for sealant with displacement capacity of ± 20% and ± 25%, if its tensile modulus at 23 ℃ and - 20C is > 0.4MPa or > 0.6MPa respectively, the sealant is of high modulus.

Low modulus - for sealant with displacement capacity of + 20% and + 25%, its tensile modulus at 23 ℃ and - 20 ℃ is < 0.4MPa and < 0.6MPa respectively (these two conditions shall be met at the same time), then the sealant is of low modulus.

2. Heat resistance of silicone sealant

Silicone rubber is a silicone polymer with silicon oxygen bond as the main chain. It has good high and low temperature resistance, insulation and physiological properties. Among them, high temperature resistance is one of the important properties of silicone rubber. It is widely used in printing industry, electronics, electrical appliances, automobile and aerospace.

Continuous working temperature and service life of silicone rubber:

150 ℃ 15000 hours

200 ℃ 7500 hours

250 ℃ 2000 hours

316 ℃ 20-100 hours

3. Deep curing of silicone sealant is slow.

Firstly, the objective conditions of sizing have a great impact on the deep curing speed, such as construction environment, temperature and humidity

Too low temperature and too high humidity will significantly slow down the deep curing (especially alcohol based adhesive). In addition, the ventilation at the construction site will also affect the deep curing if the air circulation is not smooth. In addition, the design of adhesive joint also has a great impact on the deep curing. When the width depth ratio of adhesive joint is inappropriate or the depth is too deep, the deep curing will be slow; In general, the deep curing is slightly slow, which will not affect the actual engineering use without quality problems (such as blistering, internal non curing, etc.). The curing period of the test piece specified in the national standard is 21 days, and the tested test piece is equivalent to the sizing thickness in the actual engineering, that is to say, the complete curing time recognized in the national standard takes 21 days, while the actual curing speed reflected by us is far less than 21 days (generally, it is reflected as slow drying if it exceeds 5-7 days): in addition, we believe that too fast curing of sealant is not good for long-term use, because too fast curing is not conducive to releasing the stress caused by temperature during curing, and there are hidden dangers. For example, the curing time of concrete is limited, and if it is too fast, it will lead to stress concentration and cracking.

4.  Apply silicone glass glue to the back of a mirror. After a period of time, the mirror will show spots or traces of glue?

Mirrors on the market usually have three different back coatings: Mercury, Sterling Silver and copper. Common mirror spots appear on the mirror after sizing for a period of time. This situation should be that the user uses acid glass glue, which usually reacts with the above materials, resulting in spots on the mirror. Therefore, we emphasize that neutral glue should be selected, and neutral glue can be divided into alcohol type and ketoxime type. If ketoxime type neutral glue is selected for the mirror on the copper bottom, ketoxime will corrode the copper material. After construction for a period of time, the mirror can see traces of corrosion at the sizing position behind the mirror, one by one. If alcohol type neutral glue is used, this phenomenon will not occur. The above are due to the improper material selection caused by the diversity of substrates. Therefore, it is recommended that users should conduct a compatibility test before using the glue to see whether the glue is compatible with the material. Select appropriate glass adhesive products to avoid unnecessary losses.

5. The color of neutral silicone glue becomes lighter after construction.

This should also be the quality problem of silicone glue, which belongs to the problem of raw material selection and verification. Because some domestic adhesives are added with plasticizer (mainly white oil), they are volatile; while some adhesives are added with more CC powder. When the plasticizer volatilizes, the rubber strip is stretched due to shrinkage to show the filler color (CC powder itself is white): various color adhesives add pigments to make them become various colors. If there is a problem in pigment selection, the color of the silicone sealant will change after construction; Or the color sealant is too thin during construction, and the inherent small shrinkage of the sealant during curing will make the glue color lighter. In this case, it is recommended to maintain a certain thickness (more than 2mm) during sizing.