1.1 Paper quality and impregnation process
To ensure the quality of impregnated film paper, high-quality decorative base paper must be used. No matter what kind of paper, it should be used after passing the inspection at the time of entry. Unqualified ones must not flow into the production line. During the impregnation process, the operation should be carried out strictly in accordance with the process requirements, and sampling and inspection should be carried out every half an hour to ensure that the amount of glue is 130% to 150%, the volatile content is 6% to 7%, and the pre-curing degree is ≤ 65%. The film paper after impregnation and drying should be immediately wrapped with plastic film and sealed with adhesive strips; stored in a warehouse with a temperature of 20-25℃, a humidity of 55% to 65%, and air conditioning installed. The storage time should not exceed 3 doors; when using, the principle of opening as you use it should be adopted. The paper that cannot be used at one time should be sealed immediately and sent to the warehouse for storage to prevent moisture absorption from causing the film paper to stick together and become unusable, causing unnecessary losses.
1.2 Substrate quality
The substrate of veneer artificial board is commonly medium-density fiberboard and particleboard. For particleboard, it should be purchased from outside according to the different requirements of customers, but the particleboard products must meet the requirements of GB/T4897-92 first-class products.
Quality requirements for substrates:
(1) The board surface should be flat and clean, no water stains or oil stains are allowed, and no slipping or biting can occur within the effective size;
(2) The thickness deviation of the board should not exceed ±0.2mm, and the sanding should be uniform, and no sand leakage is allowed;
(3) The moisture content of the board should be controlled within the range of 6%-10%. Since particleboard is mostly purchased from outside, changes in the environment may cause changes in the moisture content of the board. If the moisture content is too high, it may cause blasting and delamination during the veneer process; if the moisture content is too low, or the volatile content of the impregnated paper is too low, it may cause the surface to not be well wetted during hot pressing, resulting in cardboard delamination. Therefore, during the production process, it is necessary to observe and remove unqualified substrates in a timely manner.
1.3 Hot Pressing Process
The three elements of hot pressing process are interdependent and mutually restrictive, and need to be analyzed and adjusted uniformly when adjusting the process. The three factors have different effects on the veneer board. The hot pressing temperature mainly catalyzes the chemical reaction of the impregnated resin, that is, accelerates the curing. According to the actual production requirements and the author's experience, the temperature of the hot pressing plate is more suitable at 145-165℃. High temperature is conducive to demoulding after pressing, and can shorten the hot pressing period and increase production. However, too high temperature prevents the resin from flowing evenly and curing, resulting in tiny pores on the board surface. According to the national quality inspection data of impregnated film paper veneer artificial boards in 1998, a considerable number of enterprises have increased the hot pressing temperature to shorten the hot pressing time in order to increase production, resulting in the board surface being easy to rebound and not smooth. It seems that the output has been increased, but in fact it is at the expense of product quality, and it also has an impact on the manufacturers of regular products.
Appropriate pressure can ensure a good combination between the substrate and the impregnated paper. Under the action of appropriate temperature and pressure, the resin in the impregnated paper melts and solidifies to form a closed and dense surface, and can also fill the unevenness and tiny pores on the surface of the substrate. Usually, the pressure is generally 2.0~3.OMPa. Under the premise of not affecting the quality of the product, the lowest pressure should be used as much as possible, which is beneficial to the service life of the equipment, hydraulic oil, and the internal structure of the substrate; but too low pressure affects the bonding strength between the substrate and the impregnated paper and the resin flow ability. Therefore, in actual production, the unit pressure should be appropriately adjusted according to the newness and oldness of different substrates and cushions.
The length of the hot pressing time depends on the curing speed and hot pressing temperature of the impregnated resin, which is generally 40~50s. Too long a time will cause the resin to cure excessively and lose its due elasticity, which is easy to cause cracks or internal stress to the product, causing it to crack and warp in the subsequent processing; too short a time will cause the resin to cure insufficiently, which is easy to cause sticking to the board, and affect the physical and chemical properties of the product surface and the durability of the product. Different materials require different times. The curing degree of each new product should be tested, and then the hot pressing parameters should be adjusted according to the test results.
In addition, during the operation, the impregnated paper should be moved carefully to avoid damage; it is not allowed to operate with dirty gloves; if the board surface is found to be unclean during the assembly process, it should be cleaned in time; the substrate should be carefully checked when feeding, if the board surface is found to have large shavings, missing corners, damage, sand marks and other defects, it should be removed in time and refused to use; the pressure roller of the paving machine, the large suction cup for discharging, the small suction cup for stacking and grading, and each conveying roller should be cleaned regularly to prevent suction cup marks and dust on the board surface, which may lead to product degradation.