HIGH PRESSURE LAMINATE PROCESS

The different stages the resin is taken through subjected to the effects of heat and pressure are as follows:

Superficial Film Formation

Air bags created between the plate and the resin film are compressed and forced to penetrate the film and the celluosic material own pores through the action of the melted resin which flows due to pressure. Water and formaldehyde formed during the condensation process do not vaporize by pressing because the pressure is higher than their vapor pressure.

Resin flow in the sheet, necessary to form a closed surface, which reflects the pressing plates surface, is determined to a large extent by how pressure behaves and its relationship with temperature in an appropriate amount of time, and it all depends on resin condensation degree which provides its ability to flow. When pressure, temperature and time in which this is achieved are not adequate, flow can be inhibited and this could result in final laminates having porous and permeable covers.

Pressure also depends on the density of the substrate used. Higher pressures are conductive to resin flow, specifically when polished plates are used. In this case a slight variation in pressure will result in opaque stains on a glossy surface.

Melted resin flow time and viscosity (which depends on the degree of condensation, reactivity and temperature) must be regulated in such manner that bubbles migrate freely before the melted resin hardens and the surface is definitively conformed. If flow time is too long it will cause a resin deficiency on the surface. The resulting resin cover will not cover adequately the cellulose fibers.

Homogeneous Plastic Cover

There are also air bubbles inside the papers resin layer. If such bubbles are maintained they can create optical interfaces resulting in glossy areas of visible turgidity in the final product. The papers structure resist resin flow, therefore, it is recommended that the internal resin flow time is prolonged (or shortened) in accordance to the flow of the resin on the surface in order to achieve an evening sealing on both areas. Reticulation reaction which begins at a temperature range of110-120 degrees C (depending on the process and the resin) concludes the flow process. At approximately 80 degrees C, the resin starts to melt and form a closed surface. As temperature continues to rise, the resin on the inside of the film starts to flow. Fusion continues until reticulation begins.

Hardening Stage

Reticulation reaction depends, among other things, on the concentration of radicals available for resin reticulation. Reticulation ratio is initially fast, then it asymptomatically decreases as reticulation goes on. In order to achieve economically viable hardening times an excess of radicals are added (adding acid-donor substances to the impregnation mixture) in order to accelerate the chemical reaction until technological properties such as hardness, resistance to abrasion and chemical stability are achieved.

If the resin layer has an excessive amount of radicals an overcoming of the resin layer will occur (excessive hardening), then it is possible that the reticulation bonding density is so big that paper fibers are not able to reduce tensions which create cracking on the design’s surface. In this case the problem can be avoided in the final product by reducing pressing time or temperature in order to achieve balance again. On the other hand, if the amount of radicals is reduced, stability to chemical reactives and the synthetic resins hardness will diminish. For a given resin, hardening time and pressing temperature will determine the degree of reticulation and, therefore, the superficial films mechanical and chemical properties. By modifying resins and using special hardening agents it is possible to guarantee greater reticulation times with the proper curing degree.

Cooling

During high pressure lamination process, cooling takes place under pressure, water vapor condenses and tension exerted on the conformed sheets will disappear. The results will be a smooth surface with high glossy potential, which will depend on the plate or mold.

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