Melamine resin impregnated paper stick mdf production quality control.

Melamine resin impregnated paper stick mdf panel production quality control.

Melamine resin impregnated paper stick mdf board artificial manufacturing board (referred to as melamine stick mdf plywood) with its production of less material, low energy consumption, less process, low cost advantages, as well as colorful appearance, the surface has “certain wear resistance, heat resistance, pollution resistance, easy to clean and other functions, Is rapidly to the office and people’s life used furniture, vehicle building, construction, shipbuilding, interior decoration and other materials industry expansion, and has occupied a considerable market share. According to the count, the market share of melamine-impregnated paper appropriate mdf  in Europe 1980 (refers to the ratio of all veneer artificial manufacturing board) is 8%, rose to 18% in 1995, is expected to grow in the next 10 years potential strength is very big, so melamine-impregnated paper stick mdf by more and more attention.

Based on several years’ practice, the quality control of melamine impregnated paper pasted mdf  was discussed. Quality control of production process

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1.1 Paper quality and impregnation Process In order to ensure the quality of impregnated paper, high quality decorative base paper must be used. No matter what kind of paper should be used after entering/passing the test, failing must not flow into the production line. In the process of impregnation, strict operation in accordance with the requirements of the process, every half an hour to sample inspection, to ensure that the amount of glue in 130% ~ 150%, volatile content of 6% ~ 7%, pre-curing degree ≤ 65% of the technical requirements; Impregnated and dried adhesive paper should be immediately wrapped with molecular compound plastic film and sealed with adhesive strip; Stored in the temperature of 20-25℃, humidity 55%-65%, installed in air-conditioned storage room, storage time should not exceed 3 months; Make the duration to take the principle of open with use, once the unused paper should be immediately sealed and sent to the warehouse storage, to prevent moisture absorption caused by adhesive paper bonding together and can not be used, resulting in unnecessary loss.

1.2 Substrate quality Veneer The substrate of artificial manufactured board is usually medium density fibreboard and particleboard. For particleboard, according to the different customers to purchase, but the particleboard products must be pressed to meet the requirements of GB/T4897-92 grade A.

The quality requirements of the base material:

(1) the surface is smooth and clean, not allowed to have water stains, oil stains, effective size can not have edge, gnawing phenomenon;

(2) The thickness deviation of the plate should not exceed ± 0.2mm, and the sanding is uniform, sand leakage is not allowed;

(3) The sheet water cut rate should be controlled within the range of 6%-10%. Because particleboard is purchased, the change of environment can cause the change of moisture content of board. If the moisture content is high, it may lead to blasting and stratification in the veneer process. If the moisture content is low, or the content of the volatile content of the soaked paper is low, it may cause the surface of the hot pressing can not be well wetted and paperboard stratification phenomenon. Therefore, in the production process, it is necessary to observe at any time and remove the failing base material in time.

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1.3 Hot pressing process the three elements of hot pressing process are interdependent and mutually restricted, and need to be unified analysis and adjustment in process adjustment. The three factors have different effects on the pasted plywood, and the hot pressing temperature mainly catalyzes the chemical reaction of the impregnated resin, that is, accelerates the curing. According to the practical requirements of production and the author’s experience, the temperature of hot pressing plate is more suitable at 145 ~ 165℃. The high temperature helps the demoulding after pressing, and can shorten the same period of hot pressing and improve the output, but the high temperature makes the resin too late to uniformly flow, that is, curing, resulting in tiny pores on the surface. According to the data of inspection of quality of artificial manufacturing board of paper of impregnate film of whole country 1998, ever had quite a number of enterprises to achieve the purpose of raising output, through the process of raising hot pressing temperature to shorten hot pressing, the result causes board surface to rebound easily and not smooth.

It seems to increase output, but in fact it is at the cost of the quality of the sacrificed products, and it also has an impact on the manufacturers of regular products. Suitable pressure can ensure a good combination between the base material and impregnated paper, under the action of appropriate temperature and pressure, the resin in the impregnated paper is fused and solidified to form a closed, compact surface, but also can make the surface of the base material is not quiet and small pores can be filled. In general, the pressure is generally 2.0 ~ 3 OMPa, in the premise of not affecting the quality of the product, should be as low pressure as possible, so that the equipment, the service life of hydraulic oil, the underlying structure of the substrate are beneficial; But too low pressure affects the bond strength and resin flow ability of the substrate and impregnated paper.

Therefore, in actual production, the unit pressure should be adjusted appropriately for the new and old of different substrates and cushions. The length of hot pressing time depends on the curing speed and hot pressing temperature of the impregnated resin, generally in the 40 ~ 50s is better.

Too long time will cause excessive resin curing, off the due elasticity, easy to cause cracks or internal stress to the product, so that it appears cracks and warping in the subsequent processing process; If the time is too short, the resin curing is not sufficient, it is easy to produce sticky plate phenomenon, and affect the physical and chemical function of the product surface, affecting the durability of the product.

Different materials require different time, the degree of curing should be tested on the surface of each new product, then adjust the hot pressing parameters according to the results of the test. In addition, in the process of operation, the movement of impregnated paper needs to be careful to avoid damage; Do not wear dirty gloves to operate; Group blank pass in such as invention board surface is not clean to be cleaned up in time; Substrate feed should be carefully checked, such as invention board surface has big shavings, lack of Angle, damage, sand mark and other defects, should be timely removed, refused to use;

The pressure roller of the paving machine, the big suction cup of discharging material, the small suction cup of stacking classification, and the conveying roller should be cleaned regularly to prevent the suction plate imprint and dust on the surface of the plate, which may lead to the product reduction.

2. Analysis of common problems and measures to solve them.

2.1 Sticking plate phenomenon Sticking plate refers to the plate is partially or completely stuck to the plate in the process of hot pressing.

The reasons are as follows:

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

(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 not suitable or uneven coating;

(5) Slab positioning is not accurate during hot pressing. Sticky plate phenomenon occurs around the plate, which is because the edge temperature is low, and it may be that the position of the slab in the press deviates from the person. Check item by item to find out the real cause of the sticky plate, timely treatment to complete, reduce the loss. Production of adhesive board is due to incomplete curing of adhesive, therefore, the appropriate increase of temperature or extension of hot pressing time is to deal with the completion of this kind of problem.

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2.2 Plate warping 1 from the Angle of hot pressing, plate warping is because the temperature difference between the upper and lower pressing plate is too large, resulting in the process of pressing the substrate on both sides of the film paper curing speed is not synchronous, plate bending to the solid fast side to.

(1)The author thinks that the temperature difference between upper and lower pressing plate should be 3-5 higher than that of lower pressing plate.

(2) from the material itself, village wood used two layer impregnation paper machine can not be the same will lead to plate warpage. Warping is inevitable if the base material is single-sided sticker. From the production point of view, through the process of using the same impregnated paper or adjust the temperature difference between the upper and lower pressure plate, to ensure that the plate does not produce warpage.

(3) Incorrect stacking points of hot-pressed products is another main reason for plate warpage. The way to complete the treatment is to use even and straight pads or pallets to store hot-pressed melamine impregnated paper pasted mdfs. To sum up, to produce high quality products, we must choose excellent impregnated paper and substrate, reasonable processing technology; This also need to operate, inspection personnel to work together, present problems should be timely feedback, only in this way, to ensure stable product quality, occupy a larger market.The processing should be completed in time to reduce the loss. The production of adhesive plate is due to incomplete curing of adhesives, therefore, the appropriate increase in temperature or extended hot pressure time is an effective key to deal with the completion of such problems. 

2.3 Plate warping

(1) from the perspective of thermal pressure analysis, plate warping is because the temperature difference between the upper and lower pressure plate is too large, resulting in the pressure of the substrate on both sides of the film paper curing speed is out of sync, the plate bends to the side of the solid 17 fast. The author thinks that the temperature difference of the upper and lower pressure plate should be 3 to 5 higher than the upper pressure plate temperature. 

(2) From the material itself, the two layers of impregnated paper machine used in the village can also cause the plate to warp. If a substrate single-sided sticker is used, warping is an inevitable result. From a production point of view, the same impregnated paper can be used through the process or adjust the appropriate temperature difference of the upper and lower pressure plate to ensure that the plate does not produce warping. 

(3) Incorrect stacking of products after hot pressure is another major reason for the plate to produce warping, the treatment is done by using uniform, straight mat wood or tray storage hot-pressed melamine impregnated paper sticker plywood.  To sum up, in order to produce high-quality products, we must choose excellent impregnated paper and substrates, reasonable processing technology.

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