How much do you know about a Paper Impregnation Line?

What is a Paper Impregnation Line?

A Paper Impregnation Line, or paper impregnation line, is a process used to resin-impregnate, dry, cut, or rewind rolls of decorative paper, kraft paper, and other materials. The finished product is primarily used for veneer applications on wood-based panels, significantly improving their appearance, physical and chemical properties, and overall mechanical properties. Simply put, it's like giving paper a special "protective layer," enhancing its performance in subsequent use.

How does a Paper Impregnation Line work?

Rolls of base paper to be impregnated are continuously unwound by an unwinder. The glue impregnation line  coats one side of the base paper (also known as back coating). The base paper then absorbs the glue in a glue tank. A metering roller precisely controls the amount of glue applied to ensure even and appropriate levels of glue. The impregnated paper is suspended in airflow through a dryer. The dryer consists of a fan, heat exchanger, ducting, and nozzles, forming an internal circulation system. Air from the fan is sprayed through upper and lower spray boxes, then returned to the fan through the heat exchanger. The staggered arrangement of the nozzles in the upper and lower spray boxes ensures full suspension and contactless drying of the impregnated paper. The temperature of each unit is generally controlled between 110°C and 160°C. Each drying unit is equipped with an exhaust vent to forcibly remove volatile solvents and moisture that escape during the drying process. Some production lines also coat the impregnated paper on one side with glue to increase the glue load and improve the surface properties of the laminated board.

What types of paper impregnation lines are there?

Common types include single-impregnation and double-impregnation lines. These two methods are commonly used to produce the decorative paper and base paper for high-pressure melamine decorative panels (HPL, fireproof panels). The key advantage of the double-impregnation method is that it can use two resins: modified melamine resin or urea-formaldehyde resin for impregnation, followed by a modified melamine resin coating after drying. This method can save 30%-40% of melamine resin, maintain the surface quality of the impregnated paper, adjust the paper's softness, and reduce impregnation costs. Currently, the widely used production line is the double impregnation paper line.

What problems may be encountered during paper impregnation line production?

During the production process, some problems may occur that affect product quality. For example, dried flower problems manifest as white, opaque spots on the product surface. There are many reasons for the occurrence of dried flowers, such as lax inspection of the substrate, uneven surface, deep local depressions, insufficient pressure in the depressions during pressing, affecting the flow of resin; the local pre-curing layer on the surface of the substrate is not sanded clean, resulting in low board density and large resin absorption, insufficient resin during pressing, resulting in poor resin flow on the board surface; the adhesive paper used for pressing is unevenly impregnated with glue during the impregnation process, and the surface paper has glue clumps or uneven glue coating; the hot pressing temperature is too high, the hot pressing pressure is too low, and there are contaminants on the surface of the hot pressing plate; the buffer pad is partially damaged, resulting in excessively high local temperature of the pressing plate; the heat transfer between the steel plate and the pressing plate is uneven; the adhesive paper has been stored for too long, the pre-curing degree is too high, or the pH value of the substrate is too low, affecting the flow of resin; the adhesive paper is impregnated with too much glue, and bubbles appear on the board surface during pressing, etc. There are also issues with wet marking, also known as water marks, which are hazy marks on the product surface. Show-through occurs when the decorative paper film has insufficient coverage, causing defects in the substrate to appear on the board surface. Cracking occurs when irregular cracks appear on the board surface.

Formwork sticking occurs when the board partially or completely sticks to the formwork during the pressing process. Causes include localized damage to the cushion pad, resulting in uneven temperature distribution on the formwork surface and poor demolding, excessive and uneven resin impregnation of the impregnated paper, high residual volatiles in the impregnated paper, excessive moisture content in the substrate, low hot pressing temperature, short hot pressing time, low hot pressing pressure, prolonged storage of the impregnated paper, excessive pre-curing of the impregnated paper, and low pH of the substrate.

Understanding the Paper Impregnation Line helps us better understand the production process of related industrial products and provides a more informed approach to selecting and using these products. With the continuous advancement of technology, we believe the Paper Impregnation Line will continue to be optimized to provide us with more high-quality products.