LAMINATING AND PRESSING
What is Lamination?
It is the process during which final polymerization and
binding of impregnated sheets to the substrate or particle board
are carried out.
Low Pressure Lamination Types
Slow Cycle. In this cycle a multi-openings hydraulic press is
used. After polymerizing the material through high temperature,
it remains under pressure until it is cooled. That is, the
multi-openings press opens after completing the materials curing
and cooling processes. The complete cycle lasts approximately 10
to 15 minutes.
The typical slow cycle pressing program is as
follows:
1. When the press has been opened, impregnated material is
rapidly fed into it placed on the particle board.
2. The press is closed at high speed and pressure is immediately
set. Pressure used is approximately 30 to 50 kg/cm squared. The
heating system reaches pressing temperature, which ranges from
130 to 140 degrees C. Heating time depends on the films
temperature; The higher the temperature is, the shortest pressing
time will be, and visa versa, the lower the temperature is the
longer the pressing time will be. Although plates higher
temperatures result in faster pressing cycles, applying
temperatures that are too high is not recommended because
controlling pressing becomes more critical.
3. Final cooling of curing is reached at a 50-60 degree C
temperature. The multi-openings process requires intensive
cooling, carefully defined, in order to take out the board a
great amount of heat accumulated and doing it fast enough to
avoid contraction of the melanimic resin.
4. Finally, the already pressed panel is refined, that is, excess
impregnated papers is eliminated and it is then inspected with
machines which allow an adequate resin flow.
Short Cycle
Short cycle, as we know it, was developed from experiments on
resin modification and on changing several process conditions.
This is how it was possible to get to a lamination in which resin
polymerization in a single opening press kept at constant
temperature is carried out, while presses material cooling is
carried out outside of the press. Today, pressing times depend
more on the mechanical speed at which material is handled than on
the speed of resin curing. In fact, these systems reach a 70
second total cycle, 40 seconds of which are pressing time. There
is no difference between particle boards used in this cycle and
those in the slow cycle, but it is important to consider some
factors in order to make sure lamination results are high
quality:
· Boards density must not be lower than 650 kg/m squares. Lower
densities may cause compression during pressing and therefore a
loss in thickness.
· Surface must be homogeneous, free of fine splinters or fibers,
closed and pore free
· Tolerance in all of the boards thickness and in one in regards
to the other must not exceed +/- 0.15mm..
The short cycle process is as follows:
The sheets and the board are put together manually. A belt
conveyor then puts this material in a preheated press and returns
to the initial work cycle position. The press is immediately
closed and reticulation is carried out by applying pressure and
heat.
Once the pressing time is over, the press is opened and the hot
finished panel is discharged from the press. Finally, the panel
goes through inspection and packi9ng. During the short cycle
process the resins surface is cooled outside the press. This
becomes possible because the board has absorbed very little heat
during the short curing time and is rapidly dissipated outside
the press, which stops the reticulation process.
Plates
Pressing plates provide the panels surface finish. The plates
surfaces must be prepared so they can be easily separated from
the panel once the cycle is over. Chromium plated brass plates or
chromium steel plates are always used as pressing plates. the
resins surface will reflect the plates surface which will be
glossy or textured.
There are three finishing options for the high
and low pressure laminates.
1. For glossy finish the range is 100+/-10 gloss units
2. For textured finish we use LC-19 that has between 7.5+/-.15
gloss units.
3. Plate’s texturized finish for 0.91 by 3.05 plates has a
range of 12.5 to 20.6 gloss units. Gloss from 24.5 to 38 can be
found in exceptionally few plates. In this size, 42.3% of plates
checked are between 12 to 16 gloss units. In 1.22 by 2.44 plates
we find a gloss range of 8.0 to 20.0 gloss units. In this size,
57.3% of plates checked are between 12 and 16 gloss units.
