STRUCTURAL ADHESIVE

Poor Adhesion or Detachment

This is the most critical failure issue for structural adhesives, typically manifesting as separation between the adhesive and the substrate, or internal splitting of the adhesive itself.

* Main Causes:

1. Inadequate Substrate Surface Preparation: Dust, oil, moisture, or rust on the surface severely hinder the adhesion between the adhesive and the substrate.

2. Substrate with Poor Bonding Characteristics: Materials such as PP (polypropylene) and PE (polyethylene) have low surface tension, making it difficult for ordinary structural adhesives to achieve effective adhesion.

3. Lack of Primer Application: Certain metals (such as aluminum profiles) or porous surfaces require a specialized primer to enhance adhesion and water resistance.

4. Insufficient Curing Time: Structural adhesives require sufficient time to fully cure (typically 7 days for single-component adhesives and more than 3 days for two-component adhesives). Premature stress can lead to adhesive failure.

* Solutions:

1. Thoroughly Clean the Substrate: Use a specialized cleaner (such as alcohol or acetone) to thoroughly remove oil and dust from the surface and ensure the surface is completely dry.

2. Conduct compatibility and adhesion tests: Before large-area application, test on a small sample to confirm the adhesive's compatibility with the substrate.

3. Use primer correctly: Apply primer evenly to the specific substrate according to the manufacturer's instructions.

4. Ensure sufficient curing time: After application, allow the substrate to stand in the specified temperature and humidity environment until it is fully cured before use.

Abnormal Curing (Slow Curing, No Curing, or Skin Formation)

Symptoms include the adhesive taking a long time to dry, the surface drying but the interior remaining soft, or a hardened skin appearing on the surface upon application.

* Main Causes:

1. Inadequate Ambient Temperature and Humidity: Low temperature or humidity (for moisture-curing single-component adhesives) significantly prolongs curing time.

2. Incorrect Two-Component Ratio: Inaccurate mixing ratio of components A and B prevents the chemical reaction from proceeding properly.

3. Expired Product or Uneven Mixing: Using expired adhesive, or uneven mixing of the two-component adhesive during application (resulting in a "speckled" appearance).

* Solutions:

1. Control the Application Environment: Apply adhesive within the temperature and humidity range specified by the manufacturer (generally recommended between 5℃ and 40℃). In low winter temperatures, extend the curing time or preheat the substrate.

2. Calibrate the Application Equipment: Regularly check the mixing ratio and mixer of the two-component adhesive applicator to ensure even dispensing and accurate ratios.

3. Check the expiration date: Do not use expired structural adhesive. Use it up as soon as possible after opening and seal it for safekeeping.

Epoxy Structural Adhesive Crystallization (Thickening, Granulation)

This is very common in epoxy structural adhesives during winter and spring. It manifests as the adhesive becoming cloudy, developing granules, or thickening and becoming difficult to extrude.

* Main Cause: Epoxy resins have high purity, and in low-temperature environments (especially with large day-night temperature differences in winter and spring), the molecular structure easily forms "crystal nuclei" and crystallizes rapidly.

* Solution:

* Water Bath Heating (Most Effective): Place the sealed adhesive container in warm water at 50℃-60℃ and heat in one direction until the crystals completely melt and the adhesive returns to a transparent and uniform state. The performance of the structural adhesive is not affected after heating and it can be used normally.

Air bubbles or pinholes in the adhesive

The dispensed adhesive is not dense, contains air bubbles, or has pinhole-like pores on the bonding surface.

* Main causes:

1. Air introduced during two-component container change: Air was not completely purged from the pressure plate when changing A/B component adhesive containers.

2. Damp substrate surface: Moisture inside the substrate evaporates during curing, forming air bubbles.

3. Excessive dispensing speed: Aggressive application forces air into the adhesive.

* Solutions:

1. Standardize container change procedures: Always purge air from the pipes and pressure plate when changing containers on a two-component adhesive dispenser.

2. Ensure substrate dryness: Confirm the substrate moisture content meets requirements before application; extend drying time in humid environments.

3.Apply adhesive smoothly: Maintain a uniform dispensing speed and avoid violent vibrations.

Construction Safety and Health Issues

* Potential Risks: Uncured structural adhesives may contain volatile organic compounds (VOCs), which may irritate the skin or eyes upon direct contact.

* Solutions:

1. Personal Protective Equipment: Wear rubber gloves and goggles during construction, and a respirator if necessary.

2. Maintain Good Ventilation: Especially when working indoors or in confined spaces, ensure good air circulation to accelerate the dissipation of harmful gases.

3. Handling Accidental Contact: If adhesive gets on skin, do not peel it off forcefully. Soak the skin in warm water and then repeatedly rub it off with cooking oil or hand cream.