Curing and Influencing Factors of Two-component Polyurethane Adhesives

Curing of two-component polyurethane adhesive

Usually through the main agent (mostly hydroxyl-containing binary compounds) and curing agents (mostly isocyanate-containing ternary compounds) cross-linked reaction into the network to achieve the purpose of curing. In general, the curing agent should be used in an excessive amount, and the molar ratio is about 1.5 times that of the main agent.

The purpose of a proper excess of curing agent: adequate cross-linking facilitates the heat and media resistance of the glue; increases the curing temperature; and counteracts the effect of moisture. However, the excessive amount of curing agent can not be excessive, otherwise it will cause the softness of the film to decrease; the adhesive strength decreases (especially for non-polar film materials); the adhesive layer at the heat sealing place has been destroyed. If the curing agent is not sufficient, the lack of strength will result in insufficient strength and the cohesive strength will be low; when the heat is applied, the adhesive strength will drastically decrease and wrinkles or delamination will occur easily.

The effect of humidity (moisture), temperature, etc. on curing

1 Effect of moisture on curing

1) For moisture-curing polyurethane adhesives, the absolute humidity must be maintained during use in order for the adhesive to obtain sufficient moisture to ensure complete cure.

2) For two-component polyurethane adhesives, too much moisture will consume too much of the curing agent (isocyanate groups), unbalance the ratio, affect the curing effect, and affect the high temperature resistance and media resistance of the adhesive layer. Sex.

2. Effect of ethanol on curing

When the content of ethanol in the solvent is low, a small amount of curing agent is consumed, which reduces the cross-linking density (increases the free branching) and affects the resistance to heat and medium. At higher levels, the curing agent is consumed in large amounts, resulting in incomplete curing. Therefore, we must choose moisture at work. Low-ethanol solvent, and prevent secondary pollution during storage and use.

3. Effect of temperature on curing

Polyurethane adhesives can be cured at room temperature, but they take longer to cure and can increase the temperature for shorter cure times (this can also be achieved by adding a catalyst). Raising the temperature is also beneficial to the softening of the initial adhesive, enhancing the wetting of the adherend surface and increasing the contact points between the molecules. However, if the temperature is too high and the curing is too fast, the stress will not be easily released and the strength of the adhesive will be weakened later.

Factors affecting the performance of adhesives in the production process

In addition to the relevant influencing factors in the process, various factors may cause different properties of the adhesive during the adhesive production process, and require special attention.

1) Different raw materials, different product performance; the same raw materials, ratio, process operating conditions, product performance is also different.

2) The compound adhesives are mostly polyester type or polyester-polyether type. In order to facilitate the adjustment and control of the adhesive quality, the main manufacturers all synthesize polyesters themselves. The performance of the final product obtained using raw materials from different manufacturers is also different.

Therefore, even if the same brand of products from different manufacturers will have performance differences, the products of manufacturers with stable quality should generally be used.

Author; / Beijing Wanfu Da Fine Chemical Co., Ltd. Zhao Weijiang

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