Sealant performance and judgment method
Main properties of sealant

(1) Appearance: The appearance of the sealant mainly depends on the dispersion of the filler in the base rubber. The filler is a solid powder. After being dispersed by a kneader, a grinder or a planetary machine, it can be uniformly dispersed in the base rubber to form a fine paste. Sometimes, depending on the nature of the filler itself, the presence of the pole is not excluded. A small amount of fine fine or fine sand is acceptable as normal. If the filler is not well dispersed, many very coarse particles will appear. In addition to the dispersion of the filler, other factors may also affect the appearance of the product, such as the incorporation of particulate impurities, crusts and the like. These situations are considered to be rough. The appearance of the observation method is to take the product out of the package and directly observe it, or put the product on 1-2g on white paper, and fold the white paper to open and observe it. The term is called "butterfly observation". When coarse particles are found, the coarse particles should be judged.

(2) Hardness: Hardness refers to the hardness of the sealant after it has completely cured into a rubber body, and it is one of the physical and mechanical properties of the product. Hardness refers to the ability of a material to resist the scoring or pressing of an attempted substance into its surface. According to the method of measuring the hardness, the hardness is expressed by various methods such as Brinell hardness, Rockwell hardness, and Shore hardness. The state specifies Shaw A hardness. The standard hardness value is measured by a hardness tester prepared 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. The hardness is small, the elasticity and flexibility are good, and the rigidity is insufficient. Therefore, the sealant is neither as hard as possible, nor as soft as possible, but has a certain range of requirements according to actual needs.

(3) Tensile strength: Tensile strength is also one of the mechanical properties after the sealant is completely cured. Tensile strength, also known as tensile strength, tear strength, commonly known as tensile force. Refers to the ability of a material to resist damage when subjected to tension. Tensile strength values are also detected by methods specified by national standards. According to the needs of its use, the sealant has certain strength requirements, especially the structural adhesive. The minimum value of the strength is clearly specified in the national standard. The sealant with too weak strength cannot meet the needs of use. However, it is also inadmissible to over-emphasize the strength of the sealant while ignoring the elasticity.

(4) Elongation: Elongation is the elastic behavior of the sealant after it is fully cured. It is also one of the mechanical properties and refers to the ratio of the ratio of the total elongation to the original length of the material during stretching. A good elastic sealant will have a large elongation. As a minimum requirement for elongation, the sealant must meet the requirements of the national standard for the elongation performance.

(5) Tensile modulus and displacement capacity. Tensile modulus and displacement capacity are the combined performance of several of the above mechanical properties. The tensile modulus characterizes the strength produced when the sealant is stretched to a certain elongation. Therefore, the method of expressing the amount of the touch is at the same time as the elongation, for example, when the elongation is 25%, the tensile amount is 0.46 MPa. The displacement capability is the ability of the sealant to withstand the displacement of the seal due to the expansion and contraction of the substrate. For example, we say that the sealant has a displacement capacity of ±25%, which means that the seam with this product can withstand 25% of the original stretch and compression. For example, the original seam width is 12mm, it can be compressed up to 9mm, stretching To 15mm. The displacement capacity can be detected by a tensile compression cycle or a cold drawn hot pressure cycle.

(6) Adhesion to the substrate. This is an important property in the actual use of the sealant. The sealant must have good adhesion to the actual substrate to be used. A convenient way to verify the adhesion is to clean and dry the substrate with a suitable solvent or detergent, and place the sealant on it. After the sealant is cured (about 3-5 days), peel off the sealant by hand. Observe the bonding.

(7) Extrusion: This is a project of the construction performance of the sealant. It is used to indicate the difficulty of the sealant when it is used. The extrusion of the too thick glue is poor, and it is very laborious to use the glue. However, if the glue is made too thin considering the extrudability alone, it will affect the thixotropy of the sealant. Extrusion can be measured by the method specified by national standards.

(8) Thixotropy: This is another item of sealant construction performance. Thixotropy is the opposite of fluidity. It means that the sealant will change its shape only when a certain pressure is applied. If there is no external force, it can maintain its shape. Shape without flowing. The determination of the sag specified in the national standard is the judgment of the thixotropy of the sealant.

(9) Curing properties
The one-component sealant is packaged in a container that is stable and will cure when exposed to air and exposed to air. This is a chemical reaction process. The sealant is originally a paste. After contact with air, the base glue, cross-linking agent and catalyst in the sealant react with the moisture in the air. The result of this chemical reaction is This paste gradually becomes an elastic solid, which is the curing of the sealant. After the sealant is punched out, since the first contact with moisture is the surface of the sealant, the first surface is cured. After the surface is solidified, the water penetrates from the solidified surface, and the inner layer is cured. The sealant is gradually cured from the inside and the inside of the watch. The longer the time, the thicker the cure. The thicker the sealant is, the longer it takes to fully cure. For example, a 10mm thick glue usually takes more than a week to fully cure.

Two-component sealant is carried out by chemical reaction between components A and B. The A and B components are sealed and stored separately. Once the components A and B are mixed, they begin to react, so the components A and B should be used immediately after mixing. The two-component curing reaction does not require the participation of moisture in the air, so its curing is carried out simultaneously with the interior and the surface. The complete curing time is independent of the thickness of the glue, so the reaction is not related to whether or not it is in contact with air, as long as A, The components B are mixed together and solidified even in a sealed state.

The following are a few concepts of sealant curing properties:

Dry surface: The sealant is creamy when it is punched out. When it is touched with a finger or other material, the compound will adhere to the finger or material. After the sealant is punched out, the surface contacts the moisture to start to solidify the crust. When the skin is formed, and then the finger or material is used to contact the surface, no glue will adhere to the finger or material. This is called the stem.

Dry time: When the sealant is shot from the container, the time required for the surface to dry is the dry time.

Detackification: After the sealant is dry, touch the surface with your fingers. Although there is no glue attached to the finger, you can still feel a certain adhesion between the surface of the glue and the finger. This phenomenon is called No sticky. This is that the curing reaction of the rubber surface has not yet been fully demonstrated. As time goes on, it will cure further until the surface forms a layer of skin with a certain elasticity and strength. It feels dry with finger contact and has no sticky feeling. We call it tack free.

Tack free time: The time required for the sealant to start from the container and the time it takes to tackify the surface is the tack free time.

Simple judgment method of sealant performance

The sealant is punched out of the rubber bottle into a strip, and the following properties can be tested or simply judged during the process of marking the glue and the strip.
(1) Extrusion: The extrudability of the glue can be initially felt by the difficulty of the glue.

(2) Curing performance: After the rubber strip is printed, the dry time, the tack free time and the complete curing time can be determined to det

(5) Strength, Elasticity, and Elongation: Pulling the fully cured strip allows for relative judgment of strength, elasticity, and elongation. Attention must be paid to this experiment: we usually put the strip on the paper. After peeling off the strip from the paper, a layer of paper is often stuck on the strip. If the strip is pulled, the paper is not Elastic, one pull will tear, and the strip stuck on the paper will tear open a hole. Because the silicone sealant is generally low in tear strength, the stress generated by stretching will concentrate on tearing. Cracks, it is easy to pull the strip from here, affecting observation and judgment. The correct way is to put the strip on the plastic film, and pull the strip to judge the performance after the strip is completely cured.ermine whether the curing performance is normal.

(3) Thixotropy: After the rubber strip is shot, the horizontal placement is not deformed, and the surface sealant is thixotropic. If there is a phenomenon of rogue deformation, it indicates that the thixotropy is not good.

(4) Hardness: After the strip is fully cured (generally about 1-2 days), it can be felt by pressing the strip with a finger. This method can compare the hardness relatively.