Silicone adhesive is widely used in numerous fields such as electronics, automotive, and construction due to its excellent properties like high and low temperature resistance, electrical insulation, and weather resistance. However, during actual use, the problem of uneven surfaces after the curing of silicone adhesive occurs frequently. This not only affects the appearance quality of products but may also have an adverse impact on their performance and service life. Therefore, it is of great practical significance to deeply explore the reasons for the uneven surface of silicone adhesive after curing and find effective ways to avoid and solve this problem.

II. Reasons for the Uneven Surface of Silicone Adhesive after Curing

(1) Characteristics of the Adhesive Itself

• Poor Thixotropy: The thixotropy of silicone adhesive refers to the property that its viscosity decreases when subjected to shear force and gradually recovers after the shear force stops. If the thixotropy is poor, during the glue - applying process, the adhesive cannot well adapt to the shape of the adhered object's surface. It is prone to piling up or sagging, resulting in an uneven surface after curing. For example, when applying glue on a vertical surface, an adhesive with poor thixotropy may flow downward due to gravity, forming an uneven - thickness adhesive layer.
• Content of Volatile Components: If the adhesive contains a large amount of volatile components, during the curing process, the volatilization of these components will form tiny pores in the adhesive layer. When the distribution of these pores is uneven, it will cause the surface to be uneven. Especially for some silicone adhesives containing organic solvents, the volatilization problem is more prominent when curing in a high - temperature or poorly - ventilated environment.

(2) Glue - applying Process Factors

• Improper Glue - applying Method: Different glue - applying methods have a significant impact on the uniformity of the adhesive layer. For example, during manual brushing, due to differences in operation techniques, it is difficult to ensure that the thickness of each brushing is consistent, and it is easy to have local areas that are too thick or too thin. When spraying, if the pressure, distance, and angle of the spray gun are not properly controlled, it will also lead to uneven distribution of the adhesive. For instance, if the spray gun is too close to the adhered object, it will cause local adhesive to pile up; if it is too far away, it may result in poor atomization of the adhesive and uneven drop points.
• Inaccurate Control of Glue - applying Amount: An excessive amount of glue applied will lead to a too - thick adhesive layer. Under the action of gravity and curing shrinkage, it is likely to cause sagging and an uneven surface. Conversely, if the amount of glue applied is too small, it may not be able to completely cover the surface of the adhered object, resulting in glue leakage or insufficient local thickness. In some automated glue - applying equipment, if the metering system is not accurate enough, it will lead to unstable glue - applying amounts.
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