Polyurethane Adhesive Polyester Production Technology for Shoes

As an important intermediate for the synthesis of polyurethane (PU), the structure and quality of hydroxyl-containing compounds not only affect the production process but also determine the performance of the product. Polyurethane adhesives for footwear have very high requirements in terms of adhesive strength, tackiness and temperature resistance, and polycrystalline butylene adipate diol (abbreviated as polyester) with high crystallinity should be used as the softener in its molecular chain. segment.

The current production process of polyester mainly includes vacuum dehydration and nitrogen high-temperature dehydration. The reaction temperature of vacuum dehydration and nitrogen high temperature dehydration is above 245°C. Long time high temperature and vacuum reaction not only require high equipment, but also may cause product molecular weight distribution, color, etc. due to side reactions such as cyclic etherification and oxidation. It has an adverse effect. In the course of the research on the solution-synthesized polyurethane shoe adhesive, we repeated the trial and gradually enlarged the 1000 litre reactor. We found that using relatively mild reaction conditions to produce the polyester, the process is not only simple and easy to control, but also the product quality. Can fully meet the requirements of the solution method to produce polyurethane shoe glue.

1 Experimental section

1.1 Equipment

1000l stainless steel reactor (oil bath electric heating, homemade anchor stirrer, 87rpm), 50l oil-water separator, tube condenser, vacuum pump.

1.2 Raw materials

Adipic acid, 1,4-butanediol, and toluene are domestic industrial products. Stannous hydrate is a chemically pure reagent, and A reagent is self-made.

1.3 Process

438kg of adipic acid, 306-310kg of 1,4-butanediol, and an appropriate amount of (<0.1%) A reagent were added to the reaction vessel, weakly passing through N2. The temperature of the material was controlled below 140°C for 5 hours, and the amount of water discharged exceeded the theoretical limit. 55% of the amount. The hot bath temperature rose to 200°C as soon as possible and remained constant thereafter. When the material temperature reached 180 ~ 190 °C, add 25kg toluene reflux water. 2h after sampling the acid value, acid value is lower than 14mgKOH / g, add 65g of stannic chloride hydrate, 4h after the acid value dropped to 4mgKOH / g or less, decompression, 0.01 ~ 0.02MPa pressure reaction 0.5 ~ 1h. After cooling, the material was discharged to obtain 621 kg of a white waxy product in a yield of 83.2% (theoretical value: 85.5%), an acid value of <1 mgKOH/g, and a hydroxyl value of 45 to 60 mgKOH/g.

1.4 Acid Test Method

Take 1 ~ 2g polyester, dissolved in 20ml 1:1 benzene - ethanol solution, 0.1NKOH standard solution was dropped until the phenolphthalein indicator was reddish.

2 Results and Discussion

2.1 Low temperature reaction and high temperature reaction

Since the K value of the equilibrium constant of the esterification reaction is only 4 to 10, it is very necessary for the high temperature to proceed smoothly. The data show that the same reaction time, under the premise of ensuring 55% of the effluent, the reaction temperature in the low temperature phase is low, then the high temperature reaction time in the later period is short; the same reaction temperature, low temperature reaction time is better. This is mainly due to the fact that 1,4-butanediol has obvious cyclic etherification above 140°C. The boiling point of tetrahydrofuran (THF) is much lower than the boiling point of water. If the low temperature phase can not use the reaction speed, the side reaction is low. Advantageous conditions are to make the material fully and evenly oligomerized. The greater the amount of free butanediol, the higher the loss of butanediol caused by the etherification and evaporation of the high-temperature stage. As a result, not only the molecular weight of the polyester polyol is high, but also The wide distribution range affects the use effect, and more importantly, the acid value is difficult to fall in the later period of the reaction, and the reaction time at the high temperature stage has to be greatly increased. This will not only reduce the production efficiency, but may also cause yellowing due to the side reactions such as decarboxylation, cracking, and oxidation. In severe cases, the product may be scrapped.

2.2 Atmospheric and vacuum reactions

In the polymerization reaction, especially in the later stage of the reaction, the viscosity of the system is large, and it is necessary to discharge the small-molecular byproducts and excess raw materials by means of reduced pressure. At 200°C, the pressure is in the range of 0.01 to 0.02 MPa and the acid value is 4 mgKOH/g. The evacuation time is only 0.5 to 1.5 hours. If the temperature rises, the vacuum increases, or the decompression time increases, the initial acid value may be higher. Because the equipment is difficult to seal, the degree of vacuum is difficult to arbitrarily increase, but increasing the temperature or prolonging the reaction time is very easy to cause yellowing, so the initial acid value should not be too high. Generally, the acid value is difficult to fall at room temperature below 4.0, and even if it drops below 2.0, it must be decompressed and evacuated for more than 0.5 hours. The advantage of this process is self-evident compared to the process conditions of 6-8h, 0.01MPa, and 220-240°C.

2.3 Effect of acid-alcohol ratio on the process

Generally, the acid-to-alcohol ratio is 1:1.10 to 1.13. Due to the fact that the raw materials purchased in the market are in terms of purity, taking into account the requirement for the hydroxyl value, it is necessary to adopt an acid-to-alcohol ratio of 1:1.13 to 1.15. The increase of the proportion of alcohol and the process also have a certain relationship, the higher proportion of alcohol can greatly reduce the late reaction time, especially in the early reaction temperature is low, especially when the reaction time is longer. A slight excess of alcohol can be recovered during evacuation and does not have a significant effect on the hydroxyl value of the product within a certain range.

2.4 Catalysis and Water Reagents

With the increase of the viscosity of the material, the effluent at the later stage of the reaction is gradually difficult and the reaction speed is obviously slowed down. To reduce the acid value to 15 mgKOH/g, which can effectively function as a catalyst for hydration of stannous chloride, we added a small amount of toluene to the weak refluxing water at the later stage, and the effect was very good.

3 Conclusion

It can be seen from the above discussion that the synthesis of the polyester polyol does not need to be performed at a high temperature higher than 220° C., nor does it need to be performed under a high vacuum for a long time. As long as an adequate low-temperature stage is added and a water-carrying agent is added, a high-quality polyester that is suitable for use in a solution-synthetic polyurethane shoe adhesive can be easily and efficiently synthesized.

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