In the process of controlling “white pollution”, pulp molded products used for industrial product packaging have developed rapidly. According to statistics in 1997, paper products used for industrial product packaging in my country only accounted for about 1% of the total packaging products, while Western developed countries accounted for about 15% of the total. my country has made great progress in replacing wood with paper for industrial product outer packaging and replacing plastic with paper for lining packaging. The types of paper packaging products mainly include honeycomb paperboard pallet series and honeycomb paperboard packaging box series produced by modern electromechanical equipment with recycled kraft paper as the base material, which are used to replace wooden pallets and wooden packaging boxes; paper mold lining products produced by pulp molding machines with scraps of boxboard, waste newspapers, etc. as raw materials, to replace foamed plastic products. However, these paper packaging products, especially paper mold lining packaging products, have the disadvantage of poor strength compared with plastic foam packaging products. In sea transportation and humid environments, paper mold products are easy to absorb moisture and their strength is reduced. Therefore, the enhancement and waterproof and moisture-proof problems of paper packaging products must be solved.
There are four main factors that affect the strength of paper mold packaging products:
① The strength of the fiber itself;
② The bonding strength between fibers;
③ The surface area of fiber bonding;
④ The distribution of bonding bonds.
For the above four factors, the solutions are:
1. In the pulping process, use the medium-consistency long fiber sticky beating method. Medium-consistency beating refers to a beating method carried out in medium-consistency beating equipment under the condition of beating concentration of 4-6%. The long fiber sticky beating method requires to avoid cutting the fiber as much as possible, keep the fiber at a certain length, and carry out high fibrilization, and have good swelling and hydration.
The advantages of this beating method are:
① Less fiber cutting, more distortion, and good finished product strength;
② When the strength of paper products is the same, the pulping degree and water retention value are low, and the dehydration performance is better;
③ The beating time is shortened, the energy consumption is reduced, the equipment performance is improved, and the product cost is reduced. Medium-consistency beating can save 20-30kw ht of absolute dry pulp due to the reduction of concentration and dilution.
2. Disintegration after pulping. At present, most manufacturers only have the pulping process but not the pulping and decomposing process, which makes the finished fiber lack the conditions for increasing the strength part. Although the paper material only takes a few seconds to pass through the decomposing machine, the pulp crushed by the hydraulic pulper is cut, divided and finely fiberized by the decomposing machine, which can not only make the paper product pulp uniform, but also increase the strength of the finished product.
3. Add reinforcing agents to increase the strength of the product; add waterproofing agents to increase the waterproof and moisture-proof properties of the product. There are two ways to enhance paper products with chemical additives, one is internal reinforcing agents and the other is surface reinforcing agents. Internal reinforcing agents are divided into dry reinforcing agents and wet reinforcing agents. Dry reinforcing agents are generally used to enhance the reinforcing agents for pulp molding industrial packaging products. Dry reinforcing agents are fine chemicals used to enhance the bonding between fibers to improve the physical strength of paper products without affecting their wet strength. This type of chemical has an active group with a certain molecular weight. Due to the bonding strength of its own colloidal molecules, it can form hydrogen bonds with the hydroxyl groups of cellulose, which can meet the requirements of paper product enhancement. Common dry strength agents include: cationic starch, anionic starch, amphoteric starch, polyvalent starch and ionic polyacrylamide. Cationic starch and polyvalent starch (including amphoteric starch) are not only good retention and drainage aids, but also good dry strength agents. Its strengthening principle is mainly through the electrostatic attraction between the cationic groups in starch and the negative charges on the fiber surface, which adheres to the fiber surface and adsorbs with the fiber through hydrogen bond bridges, so that the fiber is formed into a network-linked whole, thereby achieving the purpose of improving the strength of paper products. When starch is used as a strength agent, the dosage is generally 1-2% of the dry pulp material. Starch that has not been gelatinized cannot be directly added to the pulp pool.
Starch must be gelatinized and processed into starch paste (dextrin can be purchased if there is no gelatinization condition) before it can be used. The gelatinization method is:
① First add a certain volume of soft water or clean cold water with low hardness into the gelatinization tank, start the agitator (stirring speed is 60-100 rpm), and then slowly add starch to fully disperse the starch. Generally, the gelatinization concentration is 5%, and then steam is passed for direct heating, but the steam pressure should not be too high to prevent the high-temperature steam from degrading the starch. It is better if indirect steam heating can be used. While continuing to stir, heat it to 90-95℃ to make it a gelatinized liquid, and keep it warm at this temperature for about 20 minutes. This step is very critical, and attention should also be paid to incompletely gelatinized starch, because the starch particles are not fully dispersed, which will affect the use effect. However, the insulation time should not be too long, and the temperature should not be too high to prevent starch degradation under the action of high temperature for a long time.
② The starch paste liquid after gelatinization should be diluted in time (concentration is 1-2%). The diluted starch paste liquid is best used up in time. If it needs to be stored for a period of time, it must be kept warm at a temperature of about 65℃, otherwise the starch paste liquid will easily age and stratify, which will affect the use effect.
③ Do not continue to stir the starch paste liquid after gelatinization, especially to prevent high-speed stirring, to prevent the molecular chain of the paste liquid from being sheared and damaged. 5 The gelatinized and diluted paste liquid can be added to the pulping tank. 4. In order to increase the strength and waterproof and moisture-proof problems of paper mold industrial packaging products, add a paperboard water-resistant enhancer after adding starch paste, the amount of which is 5% of the dry weight of starch (it can also be added directly to the starch paste and stirred evenly). Honeycomb paperboard substrates and pulp molded products treated by this processing technology have the advantages of water resistance, moisture resistance, smoothness, firmness, pressure resistance, and impact resistance.
