Manufacture of moisture-proof carton--moisture protection method (2)

(B) Long-term moisture-proof method

The so-called long-lasting moisture-proof method is a treatment method according to JIS Zl537--1989: "Almost impermeable to water even when exposed to water for a long time."

In China, for a long time, the waterproof treatment of cartons is based on this approach. The carton is hand-painted with a waterproofing agent that is bright, strong, and has good water resistance and does not collapse after brushing. These types of water repellents are often solvent-based (or oily). They are physically detrimental to the operator and cause environmental pollution. They are also unfavorable for the recovery of cartons. They have rarely been used in recent years and replaced by water or emulsions. Waterproof coating.

Aqueous emulsion waterproof paint can reach the requirement of almost water-impermeable contact with water for a long time, but when the paint is applied by hand, if the paint contains a lot of water, the natural drying time is long, and it easily causes collapse or the separation of the paper and the corrugated paper. appear. To solve these problems, we must start from three aspects:

The non-volatile content of the coating is high;

Can add a little non-toxic water-soluble volatile solvents, speed up the rate of evaporation of water;
Change the operation mode of manual brushing and use the method of machine coating and drying for production.

For the existing waterproof coatings, the first two items have actually been adopted, and the third item is difficult to implement with the current paints. Therefore, the drying and molding temperature of corrugated board is generally around 150°C, and some are as high as 180°C. General thermoplastic polymer coatings are already sticky at this temperature, and the cardboard coated with this kind of paint is often caused by hair when passed through a hot plate. Sticky, pull the paper and even pull the surface.

However, a new type of corrugated cardboard waterproof coating can overcome this disadvantage. This coating is a combination of a polymer emulsion and a wax emulsion. The polymer emulsion has good film forming property and water resistance, and the particle size of the emulsion is finer than that of the wax emulsion. After coating, the permeability to paper is stronger than that of the wax emulsion because of its poor compatibility with the wax. After the film is formed, the wax is precipitated from the polymer film, and most of the wax particles that are blocked by the paper fiber float on the surface fiber of the paper. When the corrugated paperboard is shaped into a heating plate, the phenomenon of stickiness on the paper surface is reduced due to the effect of the wax, and the paper surface will not be napped. At the same time, the polymer film will not be scratched under the protection of the wax, so that Cardboard can have a long-lasting waterproof effect. This coating also solves the problem of low efficiency of hand painting. At the same time, due to the presence of wax, it also acts as a matting agent, keeping the cardboard in its true colors. This type of paint is a water emulsion type, and the use of water-based inks for printing does not cause ink sticking. Finally, it must be pointed out that the main resin in this polymer emulsion is easily hydrolyzed by alkali, which is also convenient for paper recycling.

(III) New Moisture Protection Program

A single paperboard waterproof treatment is only one aspect of the widening carton application field. If considered together with water-resistant adhesives, such cartons can be used directly for fresh fruit and vegetables. If the waterproof coating has a certain reinforcing effect, and the application of the reinforcing adhesive, it should be advantageous for those cardboard boxes that are made of recycled cardboard boxes and staple fibers.

With the development of nanotechnology, an ultra-bipolar interface material appears. The structural principle is that the adsorbed gas atoms are stably present on the surface of the nanometer-sized concave surface, and have a stable gas film on the macroscopic surface, so that neither the oil nor the water can directly contact the surface of the material, and thus the material The surface exhibits double sparseness. Paper products, films, etc., treated with super-clear and sparse interface materials, will obtain super-hydrophobic, super-oleophobic effects, which is a revolution in the moisture-proof treatment of cartons.

Author: Lee Bacon Chongqing Institute of Packaging Technology

Corrugated Carton, July 2005 issue