Neoprene rubber adhesive preparation method

1 Introduction The preparation of neoprene adhesives has been in China for several decades. There are nearly 1,000 manufacturers of large and small neoprene adhesives, and the annual output is nearly 200kt. Better quality and lower cost of neoprene adhesives are the goals pursued by each neoprene adhesive manufacturer during these decades. The preparation method and process of the neoprene adhesive have a great influence on its performance and production cost, and it is one of the keys to the production technology of the neoprene adhesive.
2 Preparation of neoprene adhesive
2.1 Mixing method The mixing method is the most common method of preparation. The method is to muffle the chloroprene rubber on a cold start and degrade the polymer chain of the polymer through shear force. According to the three phase characteristics of the neoprene rubber in the elastic state (temperature> 93 °C), the compound is mixed into the raw rubber on the mixing machine. The order of addition is first magnesium oxide, then antioxidant, and finally zinc oxide. In order to increase the speed of the sol, the compound often needs to be cut into small pieces and added to the sol kettle. The stirrer of the sol kettle is frame-type or anchor-type stirrer. When the rotation speed is 60-80 rpm, the compounded rubber is dissolved in the solvent for 16-20 hours to obtain an adhesive. According to the process requirements, magnesium oxide can also be pre-reacted with the 2402 resin, and then the rubber compound is dissolved therein with stirring. Depending on the season, the sol kettle can be heated or cooled.
2.2 Direct sol method The direct sol method is also the method used by more manufacturers. In this method, small pieces of neoprene rubber raw material and compounding agent are directly dissolved and mixed in a sol-pot (stirring or frame-stirred stirrer with rotation speed of 60-80 rpm) for 24-32 h to obtain a product. Compared with the kneading method, this method is economical because it does not require the input of the kneading equipment and the operating expenses and manual operation costs of the non-kneading equipment. However, adding the dry compounding agent directly to the solvent or the glue solution may result in some fillers not being wetted by the solvent and not well dispersed. On the one hand, small particles of filler particles will appear in the adhesive; on the other hand, in the storage of the adhesive, a phenomenon of sedimentation will occur in a short time. At this point, the dry complex and the solvent should be dispersed in a special equipment (such as a ball mill) and then added to the glue solution. Therefore, this method is also called a "slurry method." Magnesium oxide and the resin can also be chelated pre-reacted and then mixed.
2.3 High shear direct sol method The high shear direct sol method was adopted in some coastal areas such as Guangzhou, but it has not been understood, recognized and promoted in other areas. The equipment of this method features a sol kettle with an aspect ratio of 1.5-2:1, a ratio between the diameter of the drum and the stirrer of 1:0.6-0.9, a rotational speed of the stirrer of about 1000 rpm, and a propeller type or disc. Different technical parameters for conventional Sol Solders such as turbines. The process is characterized by the shear force of the high speed mixer, which degrades the polymer chain of the polymer and achieves the plasticization of the neoprene on the plasticizer. The heat released during the high speed stirring process accelerates the dissolution of the neoprene rubber. The compounding agent such as magnesium oxide is well dispersed under the action of a high-speed stirring motion. The entire process only takes 3-5h, the product obtained is even and stable, and the viscosity is between the mixing method and the direct sol method. Since there is no input for mixing equipment and the cost of operation and manual operation of non-mixing equipment, coupled with short operating time, high production efficiency, lower operating costs and labor costs, the mixer is more economical. Magnesium oxide and the resin can also be chelated pre-reacted and then mixed. For adhesive-type, high-crystalline chloroprene rubber, due to various aspects of the production process, some of the polymers are branched and cross-linking occurs, that is, the gel fraction increases, resulting in high product Mooney values. (such as part of the high Mooney CR 244 III, CR 244 processing products, etc.).

Mixing method can not be used as a raw material for such products, one is the glue is not easy to grasp the time easy to glue, and the second adhesive appearance is darker. The direct sol method also cannot use such products as raw materials, otherwise the insoluble gel will seriously affect the product quality. However, the heat generated by the high-shear direct sol method causes the polymer to crystallize, and the high-shear force causes the polymer to degrade and dissolve, and the viscosity of the adhesive can be controlled by the stirring time, so that the product quality reaches a predetermined value. High-shear sol method can be used for raw materials that cannot be used in the direct sol process. The excess heat generated during the high shear sol process should be given a cooling treatment.
The comparison of the above three methods is shown in Table 1.

3 Necessity of promotion of high-shear direct sol method According to the National Standard of “Limiting Adhesives for Indoor Decoration Material Hazardous Substances” (GB18583 2001), the amount of benzene, toluene, or xylene in chloroprene rubber adhesives is ≤ 20%. The use of toluene or ethyl acetate or acetone, gasoline, cyclohexane, n-hexane and other binary or more complex solvents for the dissolution of chloroprene rubber than the original binary mixture of benzene or benzene and gasoline There are many differences.

The specific differences are:
1. Toluene as a good solvent for chloroprene rubber ≤ 20%, sol longer time;
2. The adhesive solution viscosity becomes smaller;
3. The adhesive's stability deteriorates;
4. Increase in production costs.
Combining with Table 1, it can be seen that the preparation of chloroprene rubber adhesives by the high shear direct sol process is the best process.
4 Conclusion High-shear direct sol method not only maintains the kneading method to make the neoprene rubber adhesive fluidity, the coating surface is smooth, with a good dispersing agent, storage stability and other characteristics, but also to maintain a direct sol method to make neoprene adhesive The appearance of lighter color, higher product solution viscosity, more economical production costs, etc.; itself also brings high production efficiency, lower operating costs and labor costs, can digest the mixing method and direct sol method can not be used quality times Low-cost raw materials (such as part of the high Mooney CR 244 III, CR 244 treatment, etc.) produce higher-quality products with more significant economic benefits. Therefore, it is worthwhile for each neoprene rubber adhesive manufacturer to attach great importance to and adopt it.