HPL kraft paper ,decorative paper,Overlay paper Assembling and build-up

HPL kraft paper ,decorative paper,Overlay paper Assembling and build-up

The impregnation (treating) of papers

Kraft paper and decor paper are delivered in large rolls. In continuous horizontal “treaters” (i.e.

impregnation machines) the paper is unwound, immersed into the resin bath, saturated with resin

and then dried. The dry paper, filled with still reactive resin, is cut to sheets of the desired length or

wound up again and stored in conditioned rooms for later use.

Assembling and build-up

The treated papers are collected from stock and assembled in clean, dust free rooms to build the

right order in the desired colour, size, thickness and backing:

Typical build-up of a compact laminate

Single sided laminates are always produced “back to back”, using a release paper. Release papers

(i.e. coated special papers) or foils are applied to avoid sticking of laminates together in the press.

In case of multi-opening-presses (multi-daylight-presses) the assembling must be repeated many

times to fill the press. Presses with up to 45 openings are in use. Every opening is filled with up to 24

single sided laminates (usually 0.5 – 1.9 mm thick) or at least with one compact laminate (usually 2

to 20 mm thick).

The high pressure process

Multi-daylight presses are loaded at room temperature, closed, set under hydraulic pressure (5 – 8

MPa) and heated up to more than 120 °C. The heat causes a liquefying process of the melamine-

and phenolic resins. At high pressure the liquid resins are pressed between and into the cellulosic

fibres – the density increases followed by the completion of the chemical reaction (polycondensation),

called “curing”. That forms a homogenous rigid, completely cross-linked network in the form of the

sheet. The result is a non-porous laminate, which will not melt.

The cellulose fibres reinforce the laminate. They are chemically bonded and fully integrated into the

new compound. The structure of the surface (high gloss, matt, textured etc.) is formed by the press

plate (or templates) pressed against the liquefied and afterwards cured melamine layer.

After curing is completed, the laminates is cooled down under pressure to release any tensions.

The complete press cycle may take up to 100 min. depending on press load and max. temperature.

Another production method utilizes continuous presses, where endless strips of treated paper are

pressed between two steel belts. Depending on the thickness of the laminate (usually 0.5 – 1.0 mm)

and the length of the line, speed varies between 8 and 25 m/min.

Trimming, Sanding, Inspection

The laminates are unloaded from the press, and any release material is stripped off. The length and

width of the laminate are cut to the required size. Single sided laminates are sanded on the back to

improve gluing.

After surface and quality inspection for defects the laminates are labelled, packed and stored for

further disposition.

Fabrication of HPL elements and compact sheets

Single-sided laminates are usually glued to substrates (e.g. chipboard, MDF etc.) to obtain

composite elements.

Edging strips may be applied or the laminate may be postformed (e.g. for kitchen worktops).

Compact laminates are cut to size, and fittings are attached to make them ready to be installed as

lockers, cubicles, partition-walls, etc.

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