In recent years, with the improvement of people's living standards, the requirements for the packaging of goods have become higher and higher. Corrugated cartons as commodity packaging containers can not only ensure the safety of the transportation of goods, but also can play a role in beautifying the goods, increasing the added value, and promoting sales. In particular, various kinds of beautifully-printed moisture-proof vending cartons have appeared on the market in recent years. To a large extent, the quality of the packaging cartons has been improved, and the problems of moisture-susceptibility, mildew, and vulnerability of the cartons have been fundamentally solved. The demand for cartons with waterproof performance is constantly increasing, especially in the packaging applications of vegetables, food, household appliances and industrial products. In particular, the rapid increase in the use of water-resistant cartons for export products has greatly promoted the development of the corrugated box manufacturing industry.
Waterproof cardboard features and waterproof coating
Waterproof paperboard refers to a generic name for paperboard that has the strength to resist water damage to the carton. It is generally coated with a waterproof coating on corrugated board and dried. After the waterproof coating is brushed on the carton and dried quickly, the film has high transparency and good gloss, and the coating is smooth and non-adhesive, which has no effect on the carton printing ink. After the general corrugated carton has been coated with a waterproof coating, the surface of the carton can have enhanced abrasion resistance, scratch resistance, and high strength, and has strong water resistance and good moisture resistance, and can beautify and protect the carton for a long time. effect.
At present, the domestic waterproof coatings mainly include: oil-soluble, alcohol-soluble and water-soluble waterproof coatings. Compared with these three types of waterproof coatings, the water-soluble waterproof coatings have better gloss and moisture resistance than oil-soluble and alcohol-soluble waterproof coatings. Water-soluble carton waterproof coating is usually based on paraffin wax, oxidized polyethylene as the main film-forming substance, and with a dispersant, stabilizer, thickener, brightener, regulator, water and other additives to form a water-based emulsion . Its outstanding advantages are: non-toxic and odorless, good resistance to water penetration, non-flammability, good stability, good adaptability to temperature difference between hot and cold. With the use of safe, low price, excellent waterproof and moisture resistance, easy to use (spray, paint, brush can be) characteristics.
The following table is a technical indicator of a water-soluble carton waterproof coating.
Types of waterproof cardboard
Waterproof cardboard can be roughly divided into three types based on its water resistance:
Water-repellent corrugated cardboard - prevents the penetration of water when it is affected by water for a short time;
Water-resistant paperboard - When the water is soaked for a long time, the strength of the paperboard will not drop much;
Strong water-resistant paperboard - long-term contact with water, but also almost impermeable.
Waterproof board manufacturing method
Hydrophobic Corrugated Cardboard The so-called hydrophobic corrugated paperboard is made by processing the surface of the paperboard when exposed to water for a short time so that the water condenses into water droplets and splashes to prevent the water from immersing. In the papermaking process, in order to increase the water resistance of the base paper, papermaking water repellents may be added into the pulp, or surface sizing may be performed to impart water resistance to the base paper. In the production of linerboards in paper mills, the papermaking water-repellent agent is applied to the surface of the calender of the papermaking machine for coating. In the manufacture of corrugated paperboards, papermaking water-repellent agents are coated on a corrugated board machine with a roll coater, or papermaking water-repellent agents are sprayed on the paperboard surface with a spraying device.
Hydrophobic corrugated cardboard is commonly used for the packaging of vegetables, fruits and aquatic products. According to the different packaging materials and circulation conditions, it is divided into two types: water repellency on the surface and inside of the carton and hydrophobicity on the surface of the box. For example, corrugated cardboard with hydrophobic treatment on the surface of the box will be taken out into the freezer and then taken out after a period of time. Generally, dew will be produced on the surface of the corrugated cardboard. This is because when the cardboard box is taken out of the freezer, the package is cooler than the outside. Just as the cold water is poured into the cup during the summer, the phenomenon of water droplets on the surface of the cup is the same. This is the dew point phenomenon. The dew on the surface of corrugated board can be absorbed by the liner board in a short time, increasing the moisture of the cartons and reducing the strength of the cartons. The use of hydrophobic cardboard can turn dew into water droplets and prevent penetration into the interior, without lowering the strength of the cardboard. However, if it is left outside for a long time or it is repeatedly taken in and out of a freezer, because the hydrophobic treatment is only processed on the surface of the cardboard, the hydrophobic effect is gradually reduced and the water content is increased, and the strength of the corrugated cardboard is reduced after a certain period of time. For consistency. On the other hand, because the surface of the paperboard is subjected to hydrophobic processing, the surface abrasion resistance of the linerboard is greatly increased, which can prevent the carton from rubbing against each other several times during the circulation process, and the paperboard surface is peeled off and paper ends are generated.
Water-resistance corrugated board (water-resisting corrugated board) Water-resistant corrugated board is also referred to as water-repellent corrugated board. This board is in contact with water for a long time and basically does not allow water to pass through. If, on the other hand, water is prevented from immersing, the water resistance of the corrugated board will disappear once water enters it. In the process of bonding corrugated cardboard, a water-resistant waterproof coating is applied to the surface of a sheet of paper by a spray method or a roller coating method, so that the cardboard has a good water resistance. If there is coating on both sides of each sheet, the waterproof performance of the cardboard is better.
A typical method for producing such a corrugated cardboard is a curtain coating method. The so-called curtain cloth method is to make the melted water-proof paint be a curtain-like curtain downwardly, so that the corrugated board (or corrugated cardboard box already printed) passes through, and a method for forming a coating film on the surface of the corrugated board is adopted. Both curtain units can be installed on both sides). The corrugated paperboard manufactured by this method can fully prevent water from immersing into the surface and the processing cost is also low, but it cannot prevent the water from infiltrating through the cross section of the corrugated cardboard. This kind of corrugated cardboard is generally used for packaging aquatic products. In addition to being used for waterproofing, corrugated cardboard has a soft waterproof layer on the surface, and is sometimes used for the packaging of easily bumped furniture, pianos, and precision machinery.
Strong resistance to water-based corrugated board Corrugated board has been treated with water for a long time and the strength has not been reduced so much as a strong water-resistant corrugated board. In other words, paper products have the disadvantage of being weak in water, but strong water-resistance corrugated paperboards are still processed with water resistance after being wetted.
There are two kinds of manufacturing methods. One is a one-time processing method: that is, water resistance is given to the base paper at the papermaking stage; and there is a secondary processing method that is a processing method that imparts water resistance during the manufacturing stage of corrugated cardboard.
The primary processing method is a method in which a water-resistant linerboard and a water-resistance corrugated base paper are used together with a water-resistant adhesive and processed to form a corrugated cardboard. Because of the water resistance of the base paper with water resistance, the water resistance of the base paper is medium, high water resistance and high water resistance. The corrugated board produced is also medium in water resistance and highly resistant to water.
Secondary processing There are two kinds of secondary processing methods, namely coating method and impregnation method.
The coating method is a method in which a roll coater is installed on a corrugated board machine, paraffin is applied to the linerboard and corrugated cardboard, and then bonded. After the corrugated paper is applied to the hot plate, the adhesive is applied to the surface of the corrugated medium after the adhesive is applied to the surface. In order to increase the water resistance of the corrugated board, the corrugated board is also used before the corrugator machine. Spray the waterproof coating on the cut ends.
Impregnation impregnation method is to make the cardboard through the molten waterproof coating dipping tank, so that the waterproof coating soaked the surface of the paper, and then sent the cardboard into the drying section, subjected to hot air heating above 105 °C, so that the cardboard surface adsorption waterproof coating, after cooling, The waterproof coating is fixed on the surface of the board, so that the board has good water resistance. Using the dipping method When the impregnation amount of the waterproof coating reaches 40%-50% of the weight of the used base paper, the strength of the cardboard can be greatly improved, but when used for general linerboard, the color of the cardboard will become black.
Source: People and Packaging
