Poor water and moisture resistance has always been a flaw criticized by the market for corrugated boxes. Especially in recent years, the scale of the cold chain packaging market for fresh fruits, vegetables, medicines, etc. has grown larger and larger, and the corrugated packaging industry urgently needs to fundamentally solve the problem of cartons packaging easily collapsed when damp.
01, heavy sizing box board paper
In the papermaking process of boxboard paper, heavy sizing is applied to the surface of the boxboard paper to ensure that water droplets will not penetrate within 5 minutes of the surface. Usually, a large amount of water-resistant additives are added to the starch paste, such as urea-formaldehyde resin, melamine formaldehyde resin, polyvinyl butyral, etc. However, the cost of the water-resistant agent is relatively high, and in the production process of corrugated cardboard, it is easy to cause problems such as opening of corrugated cardboard.
02, coated paper
Laminated paper is a composite material that coats plastic particles on the surface of the paper by a casting machine. Its main features are oil resistance, water resistance (relative), and heat sealing. However, due to the high cost, it is not conducive to widespread use in the packaging industry.
03, hydrophobic corrugated cardboard
Refers to the process of coating low surface energy substances such as polylactic acid (PLA), polyolefin, polycarbonate, polyamide, polyester, molten paraffin, etc. on the surface of cardboard tissue to change the surface roughness and surface morphology of the material. When the water-repellent corrugated cardboard is exposed to water, it forms a state of water droplets on the lotus leaf. The water turns into water droplets and slides down without seeping into the interior of the cardboard. The cost is very low, and it is suitable for packaging dry powder items, especially powders that are easy to agglomerate after absorbing water. It is also suitable for packaging products that often enter and exit the cold storage, and it is easy to condense on the wall of the box after being taken out of the cold storage. The paperboard after hydrophobic processing will not significantly reduce the compressive strength before the dewdrop evaporates, and can effectively protect the goods.
04. Anti-corrugated (corrugated) cardboard
Also known as waterproof or water-repellent corrugated cardboard, its surface is almost impermeable to water for a long time, but it cannot be immersed in water, otherwise it will lose waterproof performance. Waterproof corrugated cardboard is commonly used curtain coating method, the molten synthetic resin or paraffin wax mixture is coated on the surface of corrugated cardboard to form a layer of resin film or wax film. If necessary, double-sided coating is also possible.
Corrugated cardboard is mostly used for packaging salted products, frozen food and fruits and vegetables. Because the surface of corrugated cardboard has a soft paraffin layer, it is also suitable for packaging high-finish furniture, pianos, safes and precision machines .
05 、 Water-resistant corrugated cardboard
Corrugated board paper whose strength does not decrease significantly after being immersed in water for a long time is called water-resistant corrugated board. There are two kinds of equipment and processes for the production of water-resistant corrugated board. Its processing principle is similar to the impregnation process. Water-resistant corrugated cardboard can be measured with instruments to measure its water resistance. The so-called water resistance is to immerse the corrugated cardboard in water (20 ± 2 ℃ tap water) at 30mm, soak for 1h, and then test its burst resistance and edge pressure strength. The required residual strength should not be less than 75% of the standard strength (before immersion).
Water-resistant corrugated boxes are used to ship live fish, seafood and a class of commodities with extremely high water content. However, the recycling of such cartons is difficult, and the EU has restricted their use.
06 、 Coated corrugated box
Glazing is a common process of post-printing processing of packaging products. After the surface of the product is coated by glazing, the printed products can be enhanced in water resistance, light resistance, friction resistance and pollution resistance. At the same time, the surface brightness of the product can also be improved, so that The grade of the product has been greatly improved.
The glazing process of corrugated boxes is usually after pre-printing and glazing the facial paper, then laminating into corrugated cardboard, and then die-cutting into cardboard boxes. It can also be coated directly on the surface of corrugated cardboard, but the waterproof effect is not good, and it may also damage the carton's compression resistance.
07. Surface coated corrugated box
Laminating is the process of covering the surface of printed products with polypropylene and other plastic films, and using adhesives to heat and press them together. The coating process is divided into two types: pre-coated film and coated film. After the color box is covered with film, the surface is bright, resistant to rubbing, and has a certain waterproof effect, and the folding box is not easy to crack. However, the recycling of products is difficult, and countries such as the United States and Europe have restricted its use.
08 、 Aluminum coated kraft paperboard
Japan Toyo Steel Co., Ltd. has developed a pure iron foil with a thickness of 0.02mm ~ 0.05mm, which is galvanized, nickel or tin rust-proofed, and is extruded together with kraft paper and polyethylene film to form a composite paperboard. Waterproof, moisture-proof, and can also shield electromagnetic waves, antistatic, especially suitable for the packaging of aquatic products, fruits and vegetables, electronic instruments, semiconductor devices and electromechanical products. The aluminum-coated PVC film is combined with kraft paper to make a carton, which also has waterproof and moisture-proof functions.
09, corrugated paste added water resistant carton
In the production process of corrugated cardboard, adding appropriate amount of polymer (also known as crosslinking agent or bridging agent) to the starch binder, the polymer will replace the hydroxyl group in the starch molecule, so that the corrugated paste line has a better Waterproof and moisture proof effect. When the carton enters cold storage or humid environment, it can prevent the carton from collapsing due to moisture absorption and emulsification of the corrugated paste line.
As for the products that are often promoted, they can improve the adhesion effect of cardboard and improve the stability of adhesion.
10. Carton vents to prevent moisture
For products such as beer that have heat when packaged, a certain amount of hot steam formed in the box after packing may be absorbed by the carton, and then the compressive strength decreases. To deal with these situations, it is a common practice to punch two vent holes with a diameter of 18 mm at appropriate positions on the side labels of the carton.