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Analysis of Common Issues with Traditional Adhesives (Part 2)

Release time:

2025-04-15 01:15

Analysis of Common Issues with Traditional Adhesives (Part 2)
Analysis of Common Issues with Traditional Adhesives (Part 2)

In the application of traditional adhesives, rough adhesive layers are the second most common issue after sticky adhesive layers. This manifests directly as an uneven adhesive surface with particles or bubbles present, severely affecting bonding strength and the aesthetic appeal of the product. This article explores the issue of rough adhesive layers and provides technical improvement directions for the industry.

I. Typical manifestations of a rough adhesive layer

The intuitive characteristic of a rough adhesive layer is that the surface of the cured adhesive exhibits an uneven, granular texture or bubble-like defects. This phenomenon not only degrades the aesthetic quality of the product but also reduces the bonding area and causes stress concentration, ultimately leading to bond failure.

1. Uneven surface: The adhesive layer exhibits localized bulges or depressions, creating noticeable texture or an uneven feel.

2. Particle Residue: The surface of the adhesive layer is scattered with particulate matter, which may be incompletely dissolved fillers, impurities, or precipitates from the curing agent.

3. Bubble marks: Circular or elliptical voids are present in the adhesive layer, with clear edges; the interiors may contain residual air or volatile solvents.

II. Analysis of the Causes of Roughness in the Adhesive Layer

1. Inconsistent mixing of the adhesive components

(1) Insufficient mechanical mixing: During manual mixing, localized unmixed areas are prone to occur, resulting in uneven distribution of the curing agent, diluent, or filler.

(2) Incorrect mixing sequence: Some adhesives require the main agent and additive to be mixed first, followed by the addition of the curing agent. An incorrect sequence may lead to abnormal reactions.

(3) Improper stirring speed and duration: If the stirring speed is too high or the stirring time is too short, the filler cannot be adequately dispersed, leading to particle agglomeration.

2. Abnormal adhesive quality

(1) Improper storage conditions: When adhesives are exposed for prolonged periods to high temperatures, high humidity, or light, their molecular chains may break and active functional groups may lose their effectiveness.

(2) Overuse beyond the shelf life: Adhesives that have exceeded their expiration date may experience a decline in performance and could exhibit layering, sedimentation, or gelation. Additionally, if an adhesive is mixed but not used promptly, some of its components may undergo premature reactions, leading to gel formation or particle aggregation.

3. Poor component compatibility

(1) Mismatch between the curing agent and the main agent: Components of adhesives from different brands or models may exhibit chemical reaction conflicts, leading to abnormal structures in the cured product. This could result in phase separation between the resin and the curing agent, as well as between the filler and the matrix.

(2) The filler is incompatible with the matrix resin: If the filler particle size is too large or its surface treatment is inadequate, it will have weak bonding strength with the matrix resin and is prone to exudation.

(3) Particle Size and Dosage of Fillers: If the particle size of the filler exceeds the dispersing capacity of the adhesive system, it can lead to particle agglomeration. Alternatively, if the amount of filler added surpasses the adhesive’s load-bearing capacity, stress concentration points may form, triggering cracking or delamination.

4. Influence of environmental factors

(1) Low-temperature curing inhibition: The curing reaction of adhesives is temperature-dependent. In low-temperature environments, molecular motion slows down, reducing the reaction rate and causing the adhesive to become excessively viscous, with poor flowability. This can easily lead to entrapment of air bubbles or incomplete curing.

(2) Hindered solvent evaporation: At low temperatures, the solvent evaporates slowly, leaving behind residual solvents that can form bubbles or voids.

(3) Moisture involvement in the reaction: Excessive humidity can cause the adhesive layer to absorb moisture on its surface before curing, leading to the formation of bubbles or whitening during curing, or the creation of pores after the moisture has evaporated. In high-humidity environments, moisture can penetrate the adhesive layer and react with active groups such as isocyanates, generating carbon dioxide bubbles.

III. Summary

In summary, the issue of roughness in adhesive layers—a common challenge in the application of traditional adhesives—is caused by a variety of complex factors, including formulation processes, adhesive quality, component compatibility, and environmental conditions. The existence of this problem not only weakens bonding strength and reduces the overall performance and aesthetic appeal of products but also poses a potential threat to their long-term reliability. Therefore, a thorough understanding of the causes of adhesive-layer roughness and effective control measures are crucial for enhancing the performance of adhesive applications and ensuring product quality.

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