Silicone sealants are now widely used in the field of building curtain walls. With the development of the past two decades, the application of silicone sealants has involved curtain walls, doors and windows, automobiles, roads and bridges, new energy, electronic appliances, aerospace, power and environmental protection. and many other fields. Silicone sealants lead the adhesive industry by virtue of their excellent weather resistance, wide temperature range, suitable physical and mechanical strength, and long service life.

Silicone glue is a kind of adhesive, and good adhesion is essential. However, in the actual use process, the problem of poor adhesion occasionally occurs. Below we analyze the reasons for the poor adhesion of silicone sealants

1. Is the product selection correct

Nowadays, silicone sealants have been involved in many fields, and there will be many application points in different application fields. Silicone sealants are divided into acid-type adhesives, alcohol-type adhesives and oxime-type adhesives in terms of reaction types. The advantages of acid-type adhesives are fast surface drying and deep curing, but acetic acid molecules will be released during the curing process, which has a strong taste and will corrode some substrates, such as concrete and metal; the advantages of alcohol-type adhesives are that Neutral curing, the released ethanol molecules are non-toxic to the body, and can be bonded to a wide range of substrates. The disadvantage is that deep curing is not as good as acid glue; the advantage of oxime glue is that it is neutral curing, deep curing is faster than alcohol glue, and it can be Bonding substrates are also very broad, but will corrode copper-based substances.

Different types of silicone sealants have different chemical systems and different ways of forming bonds. In order to form a good bond, appropriate products must be selected.

l2. Is it a special substrate?

With the rapid development of the material industry, many new materials are widely available, a silicone sealant cannot guarantee good adhesion to all substrates; even the same substrate, different surface treatments will make silicone The bonding effect of ketone sealant is different; even the same processing method, the bonding effect of materials from different manufacturers is very different. Against this background, there is a strong demand for adhesion testing before silicone sealants are used in order to select suitable products, cleaning agents and primers.

3. Is it cleaned according to the cleaning process?

The two-cloth cleaning method involves first wiping with a cotton cloth dampened with solvent, and then wiping with a second, clean cloth. Note that a white, clean, soft, lint-free cotton cloth should be used during the process.

Thoroughly remove any loose residue from the surface of the substrate.

lPour some solvent of the appropriate cleaning grade on the cotton cloth. Organic solvents are best packaged in squeezable (solvent resistant) plastic bottles. Do not immerse the cotton cloth directly in the container of solvent, as the dust on the cotton cloth will contaminate the solvent.

Wipe the surface of the substrate vigorously, checking the rag to see if surface dirt has been removed. Wipe with a clean area of ​​the cotton cloth in turn until no dirt is absorbed on the cloth.

Immediately thereafter, use another completely clean cotton cloth to dry the substrate of solvent and residue. Before evaporating, the organic solvent must be dried with a dry cotton cloth, otherwise the cleaning effect will be reduced. Some porous materials may have a little residual solvent on the surface of the substrate. In this case, the backing material and sealant must be installed after the surface substrate is dry.

Isopropyl alcohol and methyl ethyl ketone are soluble in water, so they are very suitable for use in winter, and it can effectively remove condensation and frost on the surface of the substrate. Toluene and xylene are insoluble in water, so they are more suitable for summer use.

Note: Do not touch the surface after cleaning to check if the surface is dry.

4. Is the primer applied correctly?

The role of the primer is to promote the adhesion of the sealant to the substrate, and the correct use of the primer helps to create a strong and continuous bond on surfaces that are otherwise difficult to bond. Before using the primer, the surface of the substrate should be dry and clean; use a clean, lint-free cotton cloth to apply a thin and even layer of primer to the interface surface. Use a brush for difficult to apply or rough surfaces. Excessive use of primer; silicone sealant should be applied after primer is completely dry.

5. Is the glue filling full?

The silicone sealant needs to be filled with glue at the designed interface, and the width and thickness can meet the interface design requirements to achieve the expected performance requirements. At the same time, it is also necessary to use a scraper to fully contact the glue and the substrate to form an effective bond. The correct sizing should be uniform and continuous gluing, and then modify it with a scraper within the operable time range. When modifying, force should be exerted to make the colloid have good contact with the surface to be bonded of the substrate.

6. Is the maintenance time sufficient?

It is stipulated in "GB 16776-2005 Silicone Structural Sealant for Construction" that the two-component silicone structural sealant needs to be cured for 14 days under standard test conditions (temperature 23℃±2℃, humidity 50%±5%). One-component silicone structural sealant needs to be cured for 21 days under standard test conditions (temperature 23℃±2℃, humidity 50%±5%). The properties of the silicone sealant are manifested after it is completely cured, and the bond is gradually formed during the curing period. The adhesion test should also be carried out after the curing period. In addition, it should be noted that the 21 days and 14 days mentioned above for the single and double components are the curing period under the standard test conditions. If the temperature is low or the humidity is low, the curing period should be appropriately extended.

Through the inspection from product selection → special substrate → cleaning → primer → gluing → maintenance process, most of the problems of poor adhesion can be solved. However, some special situations cannot be ruled out. At this time, you can contact the technicians of the silicone sealant manufacturer for analysis and solutions.