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Factors affecting the properties of moisture cured polyurethane adhesives

Reading Volume：【 142 】

Time：【 2023-03-03 】

1. Polyether polyols used to prepare wet set polyurethane adhesive include polypropylene oxide glycol and triol, Polytetrahydrofuran glycol, copolyether glycol and triol, etc. Commonly used polyester includes poly (Adipic acid) - alkyl glycol and triol. These oligomeric polyols typically have molecular weights between 500 and 3000. Polyether polyol type prepolymers have low viscosity and low cost. Polyester type polyurethane prepolymers have a higher viscosity, but the adhesive strength of the adhesive is better than that of polyether type. Some prepolymers use a mixed system of polyester and polyether as polyol raw materials.

2. Most single component moisture curing adhesives have a longer shelf life and can be cured at room temperature. Due to the use of water as the curing agent, it is required that the relative humidity of the air be at least 40% or above, and the curing time should be at least 0.5-1 hours, or even tens of hours, in order to achieve surface non adhesion. Therefore, it is usually necessary to use fixtures to secure the adhesive components. The bonding area should not be too large to avoid incomplete solidification in the middle of the adhesive layer. Some moisture cured polyurethane adhesives use humidifiers or water to solve the problem of long curing time when applying.

3.The content of isocyanate group (NCO) in moisture cured polyurethane adhesive has a significant impact on the performance of the adhesive. Generally, if the NCO content is low and the molecular weight of the prepolymer is high, the viscosity of the adhesive is high, and the storage, shelf life, and curing time of the adhesive are short. When the viscosity is too high, a solvent or plasticizer needs to be added for dilution to achieve the appropriate sizing viscosity. If the NCO content is high, the viscosity of the adhesive is low, and solvent-free single component adhesives can be prepared, with a relatively long storage and curing time. The NCO content in moisture cured polyurethane adhesives is usually between 2% and 10%.

4.The amount of adhesive applied to the adhesive layer should affect the curing time. If the adhesive layer is thin, the curing time is short. In situations where the bonding of very dry materials or a large amount of adhesive is applied, the amount of water used as a curing agent is relatively insufficient or difficult to penetrate into the interior of the adhesive layer, and it takes a long time to fully cure, and some even cure incompletely. Increasing the curing temperature is beneficial for water to participate in the reaction and shorten the curing time. When the moisture content of the adhesive material is too high, the air humidity is high, the NCO content in the adhesive is high, and the curing temperature is high, the adhesive cures quickly. In this case, it is easy to produce more carbon dioxide, which will make the adhesive layer produce foam and reduce the adhesive strength.

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