Factors affecting the performance of wet-curing polyurethane adhesives |
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| Reading Volume： 【 264 】 | Time： 【 2023-05-09 】 | |
| 1. The polyether polyols used in the preparation of wet-set polyurethane adhesives include poly(propylene oxide) glycols and triols, poly(tetrahydrofuran) glycols, copolyether glycols and triols, etc. Commonly used polyesters are polyadipic acid-alkyl glycols and triols, etc. The molecular weight of these zwitterionic polyols is usually between 500 and 3000. Polyether polyol type prepolymer has low viscosity and low cost. Polyester-type polyurethane prepolymer viscosity is larger, but the adhesive strength of the adhesive made than polyether type is better, some prepolymer using polyester and polyether mixed system as polyol raw materials. 2. Most of the one-component wet-curing adhesives for a long period of time, can be cured at room temperature, because of the water as a curing agent, so the relative humidity of the air required at least 40% or more, the shortest curing time required 0.5-1h, the longest to tens of hours, such as to achieve the degree of surface non-stick. Therefore, it is usually necessary to use clamps to fix the bonded parts. The bonding area should not be too large, so as to avoid incomplete curing in the middle of the adhesive layer. Some wet-curing polyurethane adhesives in the application of glue, using humidifier or water to solve the problem of long curing time. 3. wet-curing polyurethane adhesives in the isocyanate group (NCO) content has a greater impact on the performance of the adhesive. In general, the NCO content is low, the molecular weight of the prepolymer is high, the viscosity of the adhesive is large, the storage period, the applicable period and the curing time of the adhesive is short. When the viscosity is too large, it is necessary to add solvent or plasticizer for dilution to make it reach the suitable sizing viscosity. high NCO content, the viscosity of the adhesive is small, solvent-free one-component adhesive can be made, the storage period and curing time is relatively long. Wet-curing polyurethane adhesive NCO content is usually between 2%-10%. 4. The amount of glue coating layer to affect the curing time. The thin coating layer, the curing time is short. In the bonding of very dry materials or coated with a large amount of glue, the amount of water as a curing agent is relatively inadequate, or not easy to penetrate the inside of the adhesive layer, it takes a long time to fully cured, and some even cured incomplete. Improve the curing temperature, conducive to water to participate in the reaction, shorten the curing time. When the water content of the sticky material is too high, the air humidity is larger, the NCO content of the adhesive is higher, and the curing temperature is higher, the adhesive cures faster. In this case, it is easy to produce more carbon dioxide, and the adhesive layer produces foam, reducing the bonding strength. |
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