Application of Wax Additive in Water Base Varnish

Foreword

Polyethylene wax is the most common anti-wearing agent in the printing ink industry, which features better touch and resistance against adhesion, dirt and water. In Water Base Varnish, polyethylene wax exists in four forms: aqueous micronized wax, dispersion, microdispersion and wax emulsion. Aqueous micronized wax has the following advantages: absence of emulsifier and small quantity of additives, and the following disadvantages: high requirements on technical conditions of dispersion in aqueous system and poor convenience. Wax emulsion and wax dispersion then have advantages of convenient use, diversified product specifications and wide choices, and disadvantages of the poor compatibility with aqueous resin system, short shelf life, and unfavorable resistance against high/low temperature during transportation.

In general, the product with an average particle diameter of less than 500nm is wax emulsion, while that of less 100nm is microemulsion; that of more than 500nm is wax dispersion, while that of less than 1um is microdispersion.

Application of Wax Additive in Water Base Varnish

The impact of wax on the abrasion resistance and glossiness of Varnish is closely related to the particle size of wax additives. Wax dispersion of large particle size has better wear resistance and more serious extinction. Main wax dispersion on the market is basically above 5μm in particle diameter, which is generally used in aqueous color inks. Wax emulsion with smaller particle size then has better glossiness, but worse resistance against abrasion, if the same amount is applied. Wax in form of microdispersion is a good balance, which has good wear resistance without compromising the glossiness of aqueous Varnish.

Taking the following three typical products of Nanjing Tianshi New Material Technology Co., Ltd. as an example, we put them into the aqueous Varnish and compare the glossiness and wear resistance.

Test method:

Add wax additive (with a solid content equivalent to 2% of the total ink formulation) to the non-wax Varnish made by a famous producer at 500-600 rpm speed, and paint it on white cardboard printed with red/black/blue offset ink with 200-wire roll. Test after drying.

Glossiness test: Test the glossiness at 60° angle of the red/black/blue area on the test sample with gloss meter, and calculate the average value of 5 spots tested in each area.

Wear resistance test: Conduct a rubbing test with A4 paper on a decolorization tester at a pressure of 4psi and speed of 45RPM, and stop the test when apparent sign of decolorization is shown at the printed surface.

Glossiness test results:

It can be seen from the above table that the emulsion with a particle diameter of 100-200nm does not reduce the glossiness of the Varnish, and the glossiness of the Varnish reduces as the particle size becomes larger.

Wear resistance test results:

According to the above table, as the particle size becomes larger, the wear resistance of the Varnish is greatly improved. This is because the wax particle of a large diameter can protrude more on the surface of the coating film taking shape on the Varnish. In the friction test, the paper first contacts the wax without damaging the coating film, thus improving the wear resistance.

To adapt to the development of water-based gravure printing, some of the wax additives of Nanjing Tianshi have been optimized for better ethanol resistance, to meet the customer’s requirements for rapid drying of the coating film.

Test method: Prepare a 50%-95% alcohol solution, and add 100g alcohol solution of different concentrations to 2g wax emulsion/wax dispersion, and observe whether the emulsion is flocculated.

Conclusion:

Since wax additives of different particle sizes have different properties in water-based inks, they should be selected or compounded according to specific demands. Attention shall be paid the use of it in ethanol, because different wax additives show different ethanol resistance. Instead of common wax additive varieties, aqueous gravure ink producers could also cooperate with wax additive manufacturers to explore the most suitable additive specifications in the new system together.