What are the factors that affect sealant curing?

Sealant is often used in our life adhesive, epoxy grouting sealant, acrylic sealant, external wall sealant, joint sealant, door frame sealant, different types of sealant using different application scenarios, while having bonding and sealing effect, adhesive used for sealing referred to as sealant.

1.Factors affecting the curing performance of sealant

(1) Surface dry: the sealant is shaped when it is played, and when it is touched by fingers or other materials, the adhesive will adhere to the fingers or materials. After the sealant is played out, the surface contact water begins to cure the crust, when the skin is formed, and then use the finger or material to contact the surface, there will be no adhesive material adhering to the finger or material. This is called the surface stem. 

(2) table drying time: When the sealant is punched out of the container, the time required to dry it is the table drying time.

(3) Anti-stick: After the sealant is dry, contact the surface with your fingers, although there is no adhesive adhesive on the fingers, you can still feel that there is a certain adhesion between the adhesive surface and the fingers, this phenomenon is called not yet anti-stick. This is the adhesive surface curing reaction has not been fully performed. With the extension of time, it will be further solidified until the surface forms a layer of skin with a certain elasticity and strength, which feels dry with finger contact and has no sense of adhesion, which is called dissticking.

(4) destick time: The sealant starts to time itself from the container, and the time required to destick its surface is the destick time.

(5) Environmental factors: have a significant impact on the curing performance of the sealant. The first is the effect of temperature, the higher the temperature, the faster the curing reaction speed, the phenomenon is that the surface dry, disstick are relatively fast, if the temperature is very low, such as 5°C below, the sealant curing will be very slow. If the temperature is too high, such as more than 40°C, the sealant will dry too fast and inconvenient to use.

(6) Humidity: It also has a significant impact on the curing performance of the sealant, because the sealant curing reaction requires moisture in the air, so too dry weather such as relative humidity below 40°C is unfavorable to the curing of the sealant. But it is not the higher the humidity, the better, because the sealant curing to release volatile small molecules, if the air humidity is too large, small molecules are not easy to volatilize, which is not conducive to sealant curing. Experiments have proved that when the relative humidity is higher than 80°C, the sealant desticking and deep curing will be affected, and sometimes after 2-3 days, the surface of the sealant is still sticky.

2.The main properties of sealant

(1) Appearance: The appearance of the sealant mainly depends on the dispersion of the filler in the base rubber. Filler is a kind of solid powder, after the kneading machine, grinder, planetary machine dispersion, it can be evenly dispersed in the base glue to form a delicate substance, sometimes according to the nature of the filler itself is different, does not exclude the existence of a very small amount of slight fine particles or fine sand, which is acceptable normal phenomenon. If the packing is not well dispersed, there will be a lot of very coarse particles. In addition to the dispersion of the filler, some factors will also affect the appearance of the product, such as mixed particle impurities, crust and so on. These conditions are considered rough in appearance. The observation method of appearance is to directly observe the product from the packaging or to hit the product 1-2g on the white paper, fold the white paper flat and then open the observation, the term is called 'butterfly observation'. Coarse particles should be judged when found.

(2) Hardness: hardness refers to the hardness of the sealant after it is completely cured into the rubber body, which is one of the physical and mechanical properties of the product. Hardness refers to the ability of a material to resist being scratched or pressed into its surface. According to the different hardness measurement methods, hardness expression methods have Brinell hardness, Rockwell hardness, Shore hardness and other methods. Shore A hardness is stipulated by the state. The standard hardness value is detected by the hardness tester according to the national standard method. The hardness of the sealant is high, the surface sealant is rigid, and the elasticity and flexibility are insufficient; Small hardness is the opposite, elasticity and flexibility are good, rigidity is insufficient. Therefore, the sealant is neither the harder the better, nor the softer the better, but according to the actual needs of a certain range of requirements.

(3) Tensile strength: tensile strength is also one of the mechanical properties of the sealant after it is fully cured. Tensile strength is also known as tensile strength, tearing strength, commonly known as tension. The ability of a material to resist damage when subjected to tension. The tensile strength value is also detected according to the method specified in the national standard. Sealant according to the needs of its use is to have a certain strength requirements, especially structural adhesive, is clearly stipulated in the national standard of the minimum value of strength is too poor sealant can not meet the needs of use. However, if you overemphasize the strength of the sealant and ignore the elasticity, it is not enterprising.

(4) Elongation: elongation is the elastic performance of the sealant after complete curing, and also belongs to one of the mechanical properties, which refers to the percentage of the ratio between the total elongation and the original length of the material when stretched. Good elastic sealant will have a larger elongation. As the minimum requirement for elongation, the sealant must meet the requirements of fixed elongation in the national standard.

(5) Tensile modulus and displacement capacity: tensile modulus and displacement capacity are the comprehensive performance of the above mechanical properties. The tensile die scale indicates the strength produced when the sealant is stretched to a certain elongation. Therefore, the representation of the amount of touch is at the same time with the elongation, such as the elongation of 25% when the tensile amount is 0.46Mpa. Displacement capacity is the displacement capacity that the sealant can withstand when the joint displacement is caused by the thermal expansion and cold contraction of the substrate. For example, we say that the sealant has a displacement capacity of +25%, which indicates that the glue seam using the product can withstand the stretching and compression of the original width of 25%, for example, the width of the original glue seam is 12mm, and it can be compressed to a maximum of 9mm and stretched to 15mm. The displacement capacity can be detected by the method of tensile compression cycle or cold tensile hot compression cycle.

(6) Adhesion to the substrate: this is a very important performance in the actual use of sealant, sealant must have good adhesion to the actual use of the substrate to be used. The easy way to test the adhesion is to clean and dry the substrate with an appropriate solvent or detergent, and the sealant is hit on it, and after the sealant has cured (about 3-5 days), peel the sealant by hand to observe the adhesion.

(7) extrudability: This is a project of the construction performance of sealant, which is used to indicate the difficulty of using sealant, and the extrudability of too thick glue is poor, and it is difficult to glue when using. However, if the rubber is too thin simply considering the extrudability, it will affect the thixotropy of the sealant. The extrudability can be determined by the method specified in the national standard.

(8) thixotropy: This is another project of the construction performance of the sealant, thixotropy is the opposite of fluidity, which means that the sealant will only change its shape under a certain pressure, and it can maintain its shape without external force. The determination of droop prescribed by national standards is the judgment of thixotropy of sealant.