Key words: emulsion adhesive; modified vinyl acetate emulsion; bonding strength; drying speed; paper tube adhesive for paper tubes in China is generally based on white glue, while white glue has low bonding strength and slow drying speed. Other disadvantages. However, with the rapid development of China's chemical fiber (filament), man-made plastic films and adhesive tapes in recent years, a large number of new adhesives for paper tube packaging are needed. This kind of paper tube, especially chemical fiber FDY tube, has high requirements for paper adhesive due to its fast rotation speed. At present, the decisive factors of the general roll tube speed in China are mainly the quality of the paper and the quality of the adhesive. It is required that the adhesive not only has good initial tackiness, high adhesive strength, but also must be fast-drying, otherwise it cannot enter the next process. In order to meet these requirements, the general practice is to increase the solid content and add some 107 glue in the paper glue to improve the initial viscosity and drying speed, but this must increase the cost of the product, and the effect is not good.
To this end, we adopted the process of copolymerization followed by cross-linking. By adding suitable additives, the original white rubber was modified to meet the requirements of good initial tackiness, high bonding strength, and fast drying speed.
1 Experimental part 1.1 Raw material base glue: polyvinyl alcohol (PVA), EVA emulsion, acrylic acid and vinyl acetate (VAC).
Additives: catalysts, emulsifiers, cross-linkers, plasticizers, fillers, etc.
1.2 Experimental method A certain amount of EVA emulsion, PVA and emulsifier were added to a four-necked flask with electric stirring, reflux condenser and thermometer, mixed and dissolved. Then VAC, acrylic acid and catalyst were added for copolymerization, and the water bath was used to control the reaction temperature. After the polymerization reaction is completed, a cross-linking agent is added to perform the cross-linking reaction. Finally, the filler and plasticizer were added and stirred for 0.5 h.
1.3 Determination of the main technical indicators Solid content: evaporation residue (gravimetric method);
Viscosity: measured with a NDJ-I rotary viscometer at a constant temperature of 25 °C;
MFT: Measured with a QMB minimum film-forming temperature meter;
pH: Determined with a precision pH paper.
2 Results and discussion 2.1 Effect of reaction temperature The fixed copolymerization reaction time was 5 h and the cross-linking reaction time was 3 h. The effect of different reaction temperatures on product performance was examined. The results are shown in Table 1.
Table 1 Effect of Reaction Temperature on Product Performance
* Emulsion diluted to a concentration of 43% was applied to the paper. The two layers of paper were bonded at room temperature, rolled with a rubber roller, and immediately peeled off (approximately 100 mm/min). Determine the time the material was destroyed or the extent of damage on the surface of the material.
The experimental results show that the reaction temperature has a great influence on the viscosity and initial viscosity of the product. The temperature is low and the reaction is incomplete. The product has low viscosity and poor initial viscosity. The temperature is too high and the polymer backbone is too soft, which can affect the viscosity. Therefore, it is appropriate to control the reaction in the range of 65-70°C.
2.2 Effect of reaction time The reaction temperature was fixed within the range of 65-70°C. The different copolymerization reaction time (fixed cross-linking reaction time was 3 h) and different cross-linking reaction time (fixed copolymerization reaction time was 5.5 h) were compared to the performance of the product. Impact conditions, results are shown in Table 2 and Table 3.
Table 2 Effect of copolymerization reaction time on product performance
Table 3 Effect of cross-linking reaction time on product performance
It can be seen that the reaction time has a great influence on the viscosity and initial viscosity of the product. As the reaction time increases, the reaction tends to be complete. Therefore, after 5.5 hours of copolymerization, the change in viscosity was not significant. After 2.5 hours of crosslinking reaction, the viscosity became stable. Considering the need of production operation and production capacity, the copolymerization reaction time was 5.5 hours and the cross-linking reaction time was 2.5 hours.
2.3 Selection of Additives The use of suitable additives can not only reduce the cost of the product, increase the solid content of the product, but also increase the drying speed. However, if it is not properly selected, it will not only increase the drying speed but also cause precipitation, which will affect the product performance. For this reason, we have selected dozens of tests among dozens of additives and screened several additives with good dispersibility and ability to react with the binder, and determined the amount of them (all base gums are used as the calculation basis).
(1) Emulsifier: It plays a better role in the stability of the base rubber and the dispersion effect of the filler. We use dodecane
Other
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