Development of UV Curing Leather Varnish (2)

2 experiments

2.1 Raw materials

Bisphenol A epoxy resin, industrial products; acrylic acid, chemical purity; hydroxyethyl acrylate (HEA), chemical purity; toluene diisocyanate (TDI), chemical purity; anhydride, chemical purity; polypropylene glycol (PPG), chemical purity; Catalysts, polymerization inhibitors, etc. are all industrial grades.

2. 2 Synthesis of Epoxy Acrylate PEA

A glass four-necked flask was used as a reactor, equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen tube, and a constant pressure dropping tube. First, PPG and anhydride were added to the reactor in a stoichiometric ratio, and the catalyst was added. Under nitrogen protection, the temperature was raised to 70-80° C. and the reaction was performed. The acid value was measured every 0.5 h. When the theoretically calculated acid value is reached, epoxy resin is added. A small amount of catalyst was added and the temperature was raised to 80-90°C to continue the reaction. The polymerization inhibitor was added before the acrylic acid was added dropwise, and the reaction was heated at a temperature of 90 to 95°C. When the acid value of the system was less than 5 mgKOH/g, the reaction was stopped and the temperature was lowered.

2. 3 Synthesis of Polyurethane Acrylate PUA

In a four-necked flask equipped with a stirrer, a thermometer, a condenser (reflux), a nitrogen gas pipe, and a constant-pressure dropping funnel, a certain amount of TDI was added. At room temperature, while stirring, PPG was added dropwise. , Warm up to 60 - 50 °C, measure -NCO value once every 0.5h, until -NCO reaches the theoretical calculation value. Add appropriate amount of catalyst and polymerization inhibitor, mix evenly, raise the temperature to between 60 - 70°C, and start adding hydroxyethyl acrylate (HEA) dropwise. During the reaction, the NCO value of the system was measured until after the -NCO value was less than 0.5%, the reaction was stopped and the temperature was lowered.

2. 4 Leather Varnish Formula Test

According to the requirements of high glossiness, good hand feeling, weather resistance and solvent resistance of leather varnish, combined with leather and artificial leather for formula research, find out the best formula, and carry out folding resistance, solvent resistance, glossiness, Measurement of adhesion, cure speed, etc.

2. 5 Analysis and Test Methods

1) Determination of acid value: using KOH ethanol titration method; 2) Determination of epoxy value: use of hydrochloric acid acetone-NaOH standard drop method; 3) Determination of iodine value: Wechsler method; 4)-NCO value determination: Di-n-butylamine-hydrochloric acid standard drop method; 5) Infrared spectrum analysis: Infrared spectrometer FTJR-8300 (Japan) was used for coating measurement on KBr pellets.

3 Results and Discussion

3.1 Synthesis of Flexible Oligomers PEA

The reaction temperature affecting the synthesis was studied. The best data obtained were: 70-80°C in the first step, 80-90°C in the second step, and 90-95°C in the third step; several catalysts were compared in the experiment. The results showed that the three-step reaction selected DMBA with an amount of 0.5% to 1.0%. The above conditions were well repeated, and the structure was determined with the lower FTIR-8300 as the target product.

3.2 Synthesis of flexible oligomer PUA

In the experiment, the main influencing factors of the synthesis reaction: temperature, catalyst, polymerization inhibitor and ratio were tested in condition. The best conditions obtained in the experiment were as follows: the first step reaction temperature was 50~60°C, the second step 80 05%较宜 ~ 90 ° C; the second step should use a catalyst, with dibutyltin laurate is preferred, plus 0.1%; to ethoxy phenol as a polymerization inhibitor, the amount added to the total amount of 0.05% more suitable , Reaction time 1st step 3 ～ 3. 5h, 2nd step 3h; The ratio of each material is more suitable for calculating amount.

3. 3 Formulation test results

After a large number of formulation tests and screening of the major tests, better two formulas were obtained. Formula 1# is suitable for polyurethane artificial leather and Formula 2# is suitable for real leather. Table 1 shows the optimized formula for the top coat of leather, and Table 2 shows the results of its curing properties.

From the test results, the developed UV-cured leather coating satisfies the requirements for the finishing of real leather and artificial leather.

4 Conclusion

Preparation of UV-cured flexible oligomers, after formulation studies, have reached the requirements of UV-cured leather coatings. The performance of the leather varnish synthesized in this experiment has basically reached the technical index of the solvent-based varnish, and it also has the characteristics of no pollution, low energy consumption, etc., showing a good application prospect. The follow-up work will further conduct an experimental study on the brighteners for leather and develop a commercially-available UV-cured leather coating.

Source: Packaging Engineering, Issue 3, 2005

Author: Chen 1,2, Yang Shuangming 2, Peng Xuejun 1,2, Liu Dongxing 1 (1 CSFU; 2 Zhuzhou Institute of Technology.)