Waterproof agent-based carton moistureproof method

Corrugated boxes are used for moisture-proof production. In addition to protecting the packaging from water, it is mainly to prevent the water from infiltrating the box itself. As the carton is wetted by water, the compressive strength and bursting resistance of the box will be greatly reduced, which will seriously affect the quality of the packaging. Corrugated boxes for moisture production, usually coated with waterproof agent to solve. Therefore, according to the effect of the water repellent agent, the manufacturing method of the moisture-proof carton can be divided into: temporary water repellent treatment and permanent water repellent treatment.

Temporary water repellent

Corrugated board has a temporary waterproof function after being treated with a temporary water repellent during the production process. According to the interpretation of JIS Zl537-1989: When the water falls on it for a short time, it is not wetted with water droplets, which can prevent water from penetrating the cardboard. Temporary water repellent treatment cardboard technology has been applied in all major carton factories in China for the past ten years. This water repellent was originally introduced from Japan and its text surface was "water pick-up agent." This type of paint was used on fabric fibers early on and was later used for cardboard processing. Therefore, most tree carton manufacturers use the name of the water picking agent.

Pulling agent is a wax emulsion, the solid content is generally 48% -51%, its most significant feature is that it can be diluted with about 30 times of water in use, and then coated on the surface of the forming corrugated board, through 150 The temperature of about °C is dry, and the surface fiber of the paper has a low surface tension due to the wrapping of vinegar and forms a surface layer that does not wet the water. When it encounters water, the water does not infiltrate on the cardboard, forming a drop of water and falling down, thereby achieving a waterproof effect.

However, the adhesion of the wax to the paper fiber is not good, especially when the water pick-up agent is diluted 30 times, its solid content is only 1.5 to 1.7, and only a thin layer of paper surface fiber is covered with wax. In addition, wax size in wax emulsions is generally larger than that of common polymer emulsions, and it is difficult to penetrate deep into the paper fiber. Simultaneously, the water pick-up agent is generally sensitive to a class of chemicals such as alum, and is often fast on the surface of paper. The emulsion breaks down and precipitates, so most of the wax particles in the puller are only present on a thin layer of paper. Under the effect of external friction, the wax is easily rubbed off, leaving no wax-wrapped fibers, and the waterproof effect is greatly reduced. In order to enhance the adhesion of the wax to the paper fiber, there are often rosin derivatives or carboxylated polymer emulsions in the water pick-up agent, which have good adhesion to the paper fiber and good compatibility with the wax. In this way, their addition promotes the adhesion of the wax to the paper fibers, and at the same time, if the wax is modified, such as oxidation or basification, it also has similar effects and can increase the adhesion of the wax to the paper fibers. However, it must be pointed out that the increase in these measures, the concentration of the water pick-up agent formed at this concentration is still not a waterproof film layer, so when it comes to friction, such as the carton in the handling, stacking process encounters friction, often will Make this waterproof surface useless. This is why a carton coated with a water-repellent agent is defined as a temporary waterproof carton.

Currently, picking agents have been widely used in some carton factories and have become a basic process. This is mainly due to the following four aspects:

Pulling agent price and machine coatability;

The water pick-up agent maintains the true nature of the paper, and is in harmony with the current mainstream of the return to nature;

Pulling agent does not adversely affect the recovery of cartons

The water repellent's water-repellent effect is perfectly adequate for general carton use.

However, it must be pointed out that the cartons used in some special circumstances, such as the need; Dongcai's cartons, need to be stored in a high-humidity environment, cartons, shipping cartons, when using water remover should be cautious. In actual practice, cartons that have been coated with water-drawing agents have been found. After being taken out of the frozen warehouse, the cartons have been deformed, causing economic disputes. Therefore, when recommending what kind of waterproof treatment, customers should fully consider the use environment of the customer's carton.

In addition, different grades of picking agents, their raw materials and preparation process are often different, with some differences in the water ratio, it is very important to use this appropriate water ratio. If the ratio of water is too high, the degree of water withdrawal will be significantly reduced and no waterproof effect will be achieved. When the ratio of water is too low, dark waxy oil spots will often form on the surface of the cardboard and damage the appearance of the cardboard.

Long-term waterproofing agent

The so-called long-lasting moisture-proof method is according to JIS Zl537-1989: "A method that is almost impervious to water even when it is 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 coating can reach the requirement of being in contact with water for a long time and it is almost impervious to water. However, when the paint is applied by hand, if the paint contains a lot of water and the natural drying time is long, it will easily cause collapse or separation of the paper and the corrugated medium. . 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.

Double sparse waterproofing agent

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.

(Chongqing Institute of Packaging Technology Li Peigen)

Source of information: China Packaging News