Melamine board production process and matters needing attention

melamine faced mdf board has the advantages of less production materials, low energy consumption, fewer procedures, and low cost, as well as beautiful appearance and a certain degree of wear resistance on the surface. The properties of heat resistance, pollution resistance, and ease of cleaning are rapidly expanding into the material industries such as public and civil furniture, vehicle manufacturing, construction, shipbuilding, and interior decoration, and have occupied a considerable market share. According to statistics, the market share of mdf with melamine finish in Europe in 1980 (referring to the proportion of all veneer wood-based panels) was 8%, which rose to 18% in 1995. It is expected that the growth potential in the next 10 years is still quite right. Therefore, 3mm melamine faced mdf have received more and more attention.

1. Quality control of production process

1.1 Paper quality and impregnation process

In order to ensure the quality of impregnated film paper, the calculation formula of hardware processing cost must use high-quality decorative base paper. No matter what kind of paper, it should be used after passing the inspection when entering the mdf factory, and the unqualified paper must not flow into the production line. During the dipping process, strictly follow the process requirements, take samples and inspect once every half an hour to ensure that the amount of glue is 130%-150%, the volatile content is 6%-7%, and the pre-curing degree is less than 65%. The dried adhesive film and paper should be packaged with plastic film immediately, and sealed with adhesive tape; stored in a warehouse with air-conditioning at 20-25℃, humidity 55%-65%, and the storage time should not exceed 3 Purpose: Adopt the principle of open as you use it when you use it. A piece of unused paper should be sealed immediately and sent to the warehouse for storage to prevent moisture absorption and cause the adhesive film to stick together and become unusable.

medium density fiberboard and particleboard are commonly used as the base material of veneer wood-based panels. For particleboard, it is purchased 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 the substrate:

(1) The surface of the board is flat and clean, no water or oil stains are allowed, and there can be no edge slipping, head gnawing, etc. within the effective size;

(2) The thickness deviation of the plate 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 can 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 low, it may cause the surface to not be well wetted during hot pressing. Delamination of cardboard. Therefore, in the production process, it is necessary to observe at any time and remove unqualified substrates in time.

1.2 Hot pressing process

The three elements of the hot pressing process are interdependent and restrict each other, so unified analysis and adjustment are required when the process is adjusted. The three factors have different effects on the veneer. The hot pressing temperature is mainly to catalyze the chemical reaction of the impregnated resin, that is, to accelerate the curing. According to the actual requirements of production. Generally, the temperature of the hot pressing plate is 145~165℃. High temperature is conducive to demolding after pressing, and can shorten the hot pressing cycle and increase output. However, too high temperature makes the resin harden before it can flow uniformly, resulting in tiny pores on the board surface. According to the national statistics on the quality of impregnated adhesive-film paper veneer wood-based panels in 1998, a considerable number of companies used to increase the heat-pressing temperature to shorten the heat-pressing time in order to achieve the purpose of increasing the output. As a result, the board surface was easy to rebound and not smooth. 

Appropriate pressure can ensure a good bond between the substrate and the impregnated paper. Under the action of appropriate temperature and pressure, the resin in the impregnated paper will melt and solidify to form a closed and dense surface. It can also make the surface of the substrate uneven. The flat and tiny pores are filled. Normally, the pressure is generally 2.0-3.0mpa. The pressure should be as low as possible without affecting the quality of the product. This is beneficial to the service life of the equipment, hydraulic oil, and the internal structure of the substrate; but too low pressure affects the bond 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 of different substrates and cushions.

The length of the hot pressing time depends on the curing speed of the impregnating resin and the hot pressing temperature, generally 40-50s is appropriate. Too long time will cause the resin to over cure and lose its due elasticity, which will easily cause cracks or internal stress to the product, which will cause cracks and warpage in the subsequent processing; if the time is too short, the resin will not be cured enough, and it is easy to produce sticky boards. Affect the product surface physical and chemical properties, also affect the durability of the product. Different materials require different time. In addition, during the operation, the impregnated paper must 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 must be cleaned up in time; Check the materials carefully when the substrate is imported . If large shavings, missing corners, breakages, sand marks and other defects are found on the board surface, they should be removed in time refusal to use; the pressure roller of the paving machine, the large suction cup for discharging, the small suction cup for stacking, etc, and each conveying roller must be cleaned regularly to prevent the suction cup marks and dust on the board surface from causing product degradation.

2. Analysis of common problems and solutions

2.1 Sticky pad phenomenon

Sticky pad refers to the part or all of the board is glued to the pad during the hot pressing process. The reasons are as follows:

(1) The hot pressing time is short, or the temperature of the hot pressing plate is low or partially low, so that the resin is not cured completely;

(2) The moisture content of the substrate is too high;

(3) The amount of glue on the impregnated paper is too large, and the volatile content is too high;

(4) The surface of the steel plate is not clean, the type of release agent is inappropriate or the coating is uneven;

(5) Inaccurate positioning of the slab during hot pressing. The sticking phenomenon mostly occurs around the board, which is due to the low temperature of the edge, or it may be caused by the excessive deviation of the position of the slab in the press. Therefore, appropriately increasing the temperature or prolonging the hot pressing time is an effective way to solve such problems.

a. From the perspective of hot pressing, the warpage of the sheet is due to the excessive temperature difference between the upper and lower pressing plates. During the pressing process, the curing speed of the adhesive film paper on both sides of the substrate is not synchronized, and the sheet is bent to a fast curing. Caused by one side. The suitable temperature difference between the upper and lower platens should be that the temperature of the upper platen is 3-5°C higher than that of the lower platen.

b. From the perspective of the material itself, the different properties of the two layers of impregnated paper used in the substrate will also cause the board to warp. If a substrate single-sided sticker is used, warpage is an inevitable result. From a production point of view, the same impregnated paper can be used or the appropriate temperature difference between the upper and lower platens can be adjusted to ensure that the plates are not deformed.

c. The incorrect stacking method of the finished board product after hot pressing is another main reason for the warpage of the board. The solution is to use a uniform and flat stow or a tray to store the hot pressed melamine faced boards.

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