In the packaging of goods, some require that the corrugated boxes be waterproof, rust-proof, fresh-keeping, and flame-retardant. These are not available in ordinary corrugated boards, and therefore require further processing.
(a) waterproof corrugated cardboard in the high temperature environment of the packaged goods or the product itself, the water content is too high, the use of ordinary corrugated board will significantly reduce the compressive strength of the carton, high moisture is the corrugated board flat compressive strength, edge pressure intensity is particularly obvious .
According to the requirements of the use of different methods to improve the waterproof performance of corrugated board, the main products are hydrophobic corrugated cardboard and water-resistant corrugated cardboard.
1, hydrophobic corrugated cardboard, also known as water repellent corrugated cardboard, short-term exposure to water, after processing the surface of the cardboard, so that the water into the water droplets splash open to prevent water infiltration into the interior of the cardboard.
Processing Method Generally, the processing method of hydrophobic corrugated cardboard is to perform coating processing. Commonly used coatings include hydrophobic agents such as paraffin wax, organic silicon, and varnish. Varnish viscosity is low, but permeability is good, but too much penetration into the paper will reduce the hydrophobic effect. Therefore, it is better to brush a starch slurry on the surface of the cardboard before painting the varnish, and then apply the varnish after drying to form a film. In addition, the addition of a suitable amount of water-resistant additives, such as urea-formaldehyde resin, melamine-formaldehyde resin, and polyvinyl butyral, can improve the water resistance of the coating. The waterproof coating can be applied directly to the surface of the corrugated cardboard during processing.
The paraffin wax is applied to both surfaces of the corrugated board, and the corrugated core is spray-coated, so that a corrugated cardboard with higher hydrophobicity can be obtained. The patent name is M/R corrugated cardboard.
The hydrophobic corrugated paperboard is suitable for packaging dry powdered articles, especially powders that are easily agglomerated after absorbing water, and is also suitable for packaging goods that often enter and leave the cold storage. After being taken out of a cold storage, condensation on the wall of the box is easy, and ordinary corrugated cardboard can be quickly absorbed. The reduction of the compressive strength causes the carton to be crushed without stacking pressure, and the cardboard after hydrophobic processing will not significantly reduce the compressive strength before dew evaporation, and can effectively protect the goods.
2, water-blocking corrugated board, also known as waterproof or retaining water corrugated board, the surface of a long time with water almost impermeable, but can not be immersed in water, or lose waterproof performance, the results are similar to ordinary corrugated board, which is mainly with it Process related.
Method of processing Water-blocking corrugated cardboard commonly used curtain coating method, the molten synthetic resin or paraffin mixture from the hopper mouth in the form of film-like flow down, coated on the horizontal running corrugated board, the cardboard surface to form a layer of resin film or film , with good water retention performance. If necessary, cover the membrane once again on the other side to obtain double-sided waterproof performance.
Uses Water-blocking corrugated cardboard is used for packaging salted products, frozen foods, and fruits and vegetables. Since corrugated cardboard has a soft paraffin layer, it is also suitable for packaging high-gloss finish furniture, pianos, safes, and precision machines. Wait.
3, water-resistant corrugated board long after the water does not significantly reduce the strength of the corrugated board is called water-resistant corrugated board. There are two types of equipment and processes for the production of water-resistant corrugated board. Its processing principle is similar to that of dipping.
(1) Impregnating liquid: It is made of paraffin or chloroprene synthetic rubber, polyphenylene butadiene, chloroprene, polyhydrosiloxane, chromium difluoroacetate, and the like.
(2) Immersion wax: The automatic paper feeding machine continuously feeds the corrugated board into a paraffin wax bath at a temperature of 90 to 100° C. The immersion time is 5 to 10 seconds. It is adjusted according to the quantitative and number of layers of the paperboard, so that the wax liquid penetrates the corrugated cardboard as a degree. .
(3) Heat Bake: The corrugated cardboard removed from the wax bath removes the excess wax liquid, and then slowly moves in a hot drying room at 110-130°C to further penetrate the wax liquid into the interior of the paperboard while allowing the excess wax liquid to flow away.
(4) Cooling: The dipping wax paper removed from the hot air chamber is forced to cool at room temperature to solidify the wax liquid.
After the above processing, the corrugated board has good water resistance. The instrument can be used to measure its water resistance. The so-called water resistance is to corrugated board into the water (20 ± 2 °C tap water) 30MM, soak 1h, and then test the degree of rupture and side pressure strength, the required residual strength should not be less than the standard strength (before water) 75%.
Water-resistant corrugated cartons are used to ship live fish, seafood and a very high-water content class of goods.
After waterproof processing, the corrugated cardboard not only has good waterproof and moisture resistance, but also has improved compressive strength. Table 1-16 lists the relative compressive strength properties of several types of waterproof corrugated cardboard and ordinary corrugated board under different conditions.
Table 1-16 Comparison of compressive strength of waterproof corrugated cardboard
Variety normal 20°C, 65% rh high humidity 40°C, 95% rh watering 100MM/h, last 3h Ordinary corrugated cardboard 100 40 21 Hydrophobic corrugated cardboard 105 70 35 M/R corrugated cardboard 118 89 98 Single-sided curtain-covered cardboard 106 75 56 double-sided curtain covering 112 82 60 impregnated cardboard 180 110 150 double-sided covering 200 140 170
