Paper impregnation

Paper impregnation

To attain attractive and durable surfaces for furniture and flooring particleboards and MDF are usually thermo-fused with printed or solid color paper. Such décor-paper is saturated with melamine and urea resins in specially designed impregnation treaters.

Usually, such treaters have two sections, one to fill the core and the second to coat the surface. Both sections consist of an application unit, and a drying stage. This process requires that the resin be uniformly distributed within the paper core and on its surface. This is achieved by careful adjustment of the resin viscosity and line speed, and through the obligatory use of specially designed additives. After drying the impregnated papers can be stored for several months before being hot-pressed onto boards. During hot-pressing or thermo-fusing the resin in the paper softens sufficiently to bond with the substrate. Subsequently the resin cures to become a very hard and durable solid that protects the décor paper. Release agents support the clean separation of the laminated board from the press plate. Curing speed and completion is determined by the right choice of catalysts. All additives and catalysts are added to the resin prior to the impregnation process.

 

Impregnation resin

Impregnation resins for décor-paper consist of either melamine-formaldehyde (MF) or urea-formaldehyde (UF) pre-polymers in aqueous solution. Such resins are living chemicals with a limited shelf life of 1-3 weeks. Prior to use the resins are blended with water to adjust the viscosity, and at the same time catalysts and additives are added. In a typical two-stage impregnation process the paper core is first impregnated with a UF resin to fill all the voids to accomplish good internal tear strength. After the drying of the core resin the surfaces are coated in a second step with the MF resin thereby achieving superior surface characteristics such as hardness, scratch resistance, and vivid colors. After the MF resin is dried likewise the paper can be cut to size and stored for several months before laminated onto particleboards and MDF for furniture and flooring.

 

additives within the impregnation process

In order to effectively saturate the core of décor-paper and to coat its surface impregnation resins require several chemical additives and catalysts (hardener). Very important is the uniform distribution of the resins within and on the paper, which generally is achieved with wetting agents. Turbulences in the resin bath and on the coater often lead to foam generation. It is therefore very important that wetting agents are designed to prevent the formation of stable foams. The quality of the surface is enhanced through film forming additives that permit a smooth and bubble free drying process. Clean release of the cured paper laminate from the press without accumulation of residues on the press plates is essential for a cost efficient process. Specially designed release agents are thusly needed to minimize the need for long plate cleaning.

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