PROCESS FOR COVERING PARTICLE BOARD

PROCEDE DE REVETEMENT D'UN PANNEAU DE PARTICULES

English Abstract

The process comprises impregnation of first sheets of
paper with a first aqueous resin having a solids content of
30-60 % of urea-melamine-formaldehyde resin; from 4-10 % of a
plasticizer; a surfactant wetting agent; a catalyst, and a
mould stripping agent; impregnation of second sheets of paper
with a second aqueous resin having a solids content of from
30-60 % of urea-melamine-formaldehyde resin; 0-8 % of a
plasticizer; a surfactant wetting agent; a catalyst and a
mould stripping agent, this impregnation until the sheets
have a resin solids content of 30-60 % and a volatiles
content of 5-7 %; forming an ensemble with a first sheet of
paper, a second sheet of paper, a board, a second sheet of
paper and a first sheet of paper; and pressing the ensemble,
the press surface being at a temperature ranging from 130 to
180 °C

Claims

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The embodiments of the invention, in which an exclusive
property or privilege is claimed are defined as follows:
1.- A process for covering particle board, particularly
board having a thickness of from 10 to 40 mm, and having two
main opposite surface layers of a surface density in excess
of 800 kg/cu.m. and a face strength ranging from 8 to 12
kg/sq.cm, said covering comprising, for each surface, a first
sheet of paper in contact with the layer and a second sheet
of paper applied over said first sheet, said process compris-
ing a pressing step, characterized in that it comprises the
following steps: (A) providing first sheets of paper weighing
between 60 and 180 g/sq.m.; (B) providing a first aqueous
resin with a solids content of 30 to 60 wt% of urea-mela-
mine-formaldehyde resin of low degree of condensation; from 4
to 10 wt% of a plasticizer from the family of the
sulphonamides or the polyglycols; from 0.3 to 1 wt% of a
wetting agent of the family of the surfactants; from 0.5 to 3
wt% of an acid catalyst; and from 0.5 to 1 wt% of a mould
stripping agent; (C) impregnating said first sheets with said
aqueous resin, until said first sheets have a resin solids
content of 45 to 60 wt% and a volatiles content of 5 to 7
wt%; (D) providing second sheets of paper; (E) providing a
second aqueous resin having a solids content of from 30 to 60
wt% of urea-melamine-formaldehyde resin of low degree of
condensation, from 0 to 8 wt% of a plasticizer from the
family of the sulphonamides or the polyglycols; from 0.1 to 1
wt% of a wetting agent of the family of the surfactants;
from 0.2 to 2 wt% of an acid catalyst; and from 0.1 to 1 wt%
of a mould stripping agent; (F) impregnating said second
sheets with said second aqueous resin, until said second
sheets have a resin solids content of 30 to 60 wt% and a
volatiles content of 5 to 7 wt%; (G) forming an ensemble
comprising successively a first sheet of paper, a second
sheet of paper, a board, a second sheet of paper and a first
sheet of paper; and (H) pressing said ensemble, applying a
specific pressure ranging from 20 to 30 kg/sq.cm, the press
surface being in contact with the ensemble at a temperature
ranging from 130 to 180 °C, for a period of time ranging from
30 to 80 seconds.

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2.- The process of claim 1, characterized in that said
second sheets have a weight ranging from 60 to 180 g/sq.m.
3.- The process of claim 1 or claim 2, characterized in
that said plasticizer is o-p-toluene sulphonamide or diethyl-
ene glycol.
4.- The process of any one of claims 1 to 3, charac-
terized in that said wetting agent is an alkyl nonyl phenol.
5.- The process of any one of claims 1 to 4, charac-
terized in that said acid catalyst is an acid hydrolysis
organic acid salt.
6.- The process of any one of claims 1 to 5, charac-
terized in that said mould stripping agent is an aqueous
silicone emulsion.

Description

A PROCESS FOR COVERING PARTICLE BOARD
.
D E S C R I P T I O N
The invention relates to a process for covering particle
board, particularly board having a thickness of from 10 to 40
mm, and having two main opposite surface layers of a surface
density in excess of 800 kg/cu.m. and a face strength
ranging from 8 to 12 kg/sq.cm, said covering comprising, for
each surface, a first sheet of paper in contact with the
layer and a second sheet of paper applied over said first
sheet, said process comprising a pressing step. The "face
strength" is determined according to the European Norm 311,
entitled "Surface soundness".
In other words, the invention concerns a covering of
particle board with paper impregnated with a modified amino-
plastic resin; the covering is produced in a short cycle
medium pressure pressing line.
The invention seeks to provide a process in which the
covered board is suitable to be subjected to a post-forming
process in which the covering paper may be curved, with an
- appropriate device, over the edge of the board, with a mini-
mum radius of curvature of 4 mm and without cracks being
formed in the covered board surface.
This aim is achieved with a process of the type referred
to at the beginning which is characterized in that it com-
prises the following steps: (A) providing first sheets of
paper weighing between 60 and 180 g/sq.m.; (B) providing a
first aqueous resin with a solids content of 30 to 60 wt% of
urea-melamine-formaldehyde resin of low degree of condensa-
tion; from 4 to 10 wt% of a plasticizer from the family of
the sulphonamides or the polyglycols; from 0.3 to 1 wt% of a
wetting agent of the group formed by surfactants; from 0.5 to
3 wt% of an acid catalyst; and from 0.5 to 1 wt% of a mould
stripping agent; (C) impregnating said first sheets with said
aqueous resin, until said first sheets have a resin solids
content of 45 to 60 wt% and a volatiles content of 5 to 7
wt%; (D) providing second sheets of paper; (E) providing a
second aqueous resin having a solids content of from 30 to

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60 wt% of urea-melamine-formaldehyde resin of low degree of
- condensation, from O to 8 wt% of a plasticizer from the
family of the sulphonamides or the polyglycols; from 0.1 to 1
wt% of a wetting agent of the family of the surfactants;
from 0.2 to 2 wt% of an acid catalyst; and from 0.1 to 1 wt%
of a mould stripping agent; (F) impregnating said second
sheets with said second aqueous resin, until said second
sheets have a resin solids content of 30 to 60 wt% and a
volatiles content of 5 to 7 wt%; (G) forming an ensemble
comprising successively a first sheet of paper, a second
sheet of paper, a board, a second sheet of paper and a first
sheet of paper; and (H) pressing said ensemble, applying a
specific pressure ranging from 20 to 30 kg/sq.cm, the press
surface being in contact with the ensemble at a temperature
ranging from 130 to 180 C, for a period of time ranging from
30 to 80 seconds.
Said plasticizer is preferably o-p-toluene sulphonamide
or diethylene glycol; said wetting agent is an alkyl nonyl
phenol; said acid catalyst is an acid hydrolysis organic acid
salt and said mould stripping agent is an aqueous silicone
emulsion.
The invention provides advantages over the ptesent tech-
niques of post-formable board coverings.
One advantage lies in directly obtaining, in a single
operation, a post-formable product by application of impreg-
nated paper to the board in a short cycle, medium pressure
press, instead of having to manufacture first an impregnated
paper covering in a long cycle high pressure press and then
adhere said covering to a base board in another press.
Another advantage obtained from the invention is that a
-post-formable product is obtained by a paper covering having
a much lower overall weight than that used in the long cycle
high pressure coverings and with the usé of aminoplastic
resins instead of phenolic resins.
As stated above, the product of the present invention is
obtained by covering a particle board of appropriate surface
properties, specifically the density of its surface layer,
and the face strength.
The covering must comprise four sheets of impregnated

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paper per board, two on each side, with the sheets which are
applied directly on the board surfaces being different from
the outer ones applied over the former.
The sheets of paper applied directly to the board must
weigh from 60 to 180 grams per square metre and must be
impregnated with a urea-melamine-formaldehyde resin of low
degree of condensation, but having a long shelf life, modi-
fied with plasticizers from the families of the polyglycols
and the sulphonamides.
The outer sheets of paper applied over the previous
ones, are the usual decorative papers in all kinds of high
and low pressure, long and short cycle coverings, but for
this application they must be impregnated with a urea-mela-
mine-formaldehyde resin of low degree of condensation, but
having a long shelf life, modified with plasticizers from
the families of the polyglycols and of the sulphonamides.
The postformable covering of the present invention is
produced in a short cycle, medium pressure press by applica-
tion of an appropriate pressure and temperature to the
ensemble formed by a particle board between four impregnated
papers as described above, two on one side and the other two
on the other side, the papers in contact with the board
being different from the outer papers.
Hereinafter, without any limitative effect, there are
described examples of the process of the invention.
EXAMPLE 1
A wood particle board, having a surface layer density of
910 kg per cu.m. and a face strength of 12 kg/sq.cm., is
placed between four impregnated papers, two on each side, of
the following properties:
Papers in contact with the lower and upper surfaces of
the board: paper of 132 g/sq.m. impregnated with resin such
that the resin solids content of the impregnated paper is 58
wt% and the volatiles content is 7%. For impregnation, an
aqueous resin having a solids content of 42% of urea-mela-
mine-formaldehyde resin of low degree of condensation, with
9.5% of ortho-para-toluene sulphonamide as plasticizer, 0.9%
of octyl nonyl phenol as wetting agent and 2.2% of para-tolu-
ene sulphonic acid ammonium salt was used-

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,~ 4
External decorated papers: paper of 72 g/sq.m. impreg-
- nated with resin such that the resin solids content of the
impregnated paper is 58 wt% and the volatiles content is 7%.
For impregnation, an aqueous resin having a solids content of
48% of urea-melamine-formaldehyde resin of low degree of
condensation, with 0.9% of octyl nonyl phenol as wetting
agent, 1.5% of para-toluene sulphonic acid ammonium salt and
0.6% of M-75 mould stripping agent was used.
The ensemble formed by the board and the four papers is
subjected to a pressing operation in a medium pressure, short
cycle installation, applying a specific pressure of 25
kg/sq.m and a temperature of the press surface in contact
with the ensemble of 140C, for a period of 60 seconds.
EXAMPLE 2
15A wood particle board, having a surface layer density of
820 kg per cu.m. and a face strength of 10 kg/sq.cm., is
placed between four impregnated papers, two on each side, of
the following properties:
Papers in contact with the lower and upper surfaces of
the board: paper of 160 g/sq.m. impregnated with resin such
that the resin solids content of the impregnated paper is 50
wt% and the volatiles content is 6%. For impregnation, an
aqueous resin having a solids content of 35% of melamine-
formaldehyde resin of low degree of condensation, with 6.0%
of diethylene glycol as plasticizer, 2.2% of octyl nonyl
phenol as wetting agent and 1.2% of para-toluene sulphonic
acid ammonium salt was used.
External decorated papers: paper of 120 g/sq.m. impreg-
nated with resin such that the resin solids content of the
impregnated paper is 51 wt% and the volatiles content is 6%.
For impregnation, an aqueous resin having a solids content of
40% of melamine-formaldehyde resin of low degree of condensa-
tion, with 2.0% of octyl nonyl phenol as wetting agent, 1.0%
of para-toluene sulphonic acid ammonium salt and 1.5% of M-75
mould stripping agent was used.
The ensemble formed by the board and the four papers is
subjected to a pressing operation in a medium pressure, short
cycle installation applying a specific pressure of 25 kg/sq.m
and a temperature of the press surface in contact with the

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ensemble of 145C, for a period of 70 seconds.