Annals of Warsaw University of Life Sciences - SGGW
Forestry and Wood Technology № 83, 2013: 268-270
(Ann. WULS - SGGW, For. and Wood Technol. 83, 2013)
A method of improving the surface of HDF
DANUTA NICEWICZ, SŁAWOMIR MONDER
Faculty of Wood Technology, Warsaw University of Life Sciences – SGGW
Abstract: A method of improving the surface of HDF. In order to lower the roughness of HDF boards, the
surface of fiber mats was coated with a coating mixture. The mixture was composed of an organic filler, binding
component and water. Applying the mixture in an optimal amount (40g/m2) allowed to substantially lower the
roughness and swelling of boards in relation to roughness and swelling of raw boards.
Keywords: HDF, coating mixture
INTRODUCTION
In Poland the majority of wood based panels is produced for the needs of furniture
manufacture. These boards, apart from the properties indicated in the subject standards,
should be characterized by additional features, such as surface layer tearing resistance, joiners
binding force, surface quality. Surface quality is important in these boards, surfaces of which
are finishing, including lacquer coating or printing. The quality of surface of boards is
evaluated through surface roughness, water surface absorption or toluene surface absorption.
The required "smoothness" of the board surface is achieved by appropriate grinding of
the wood material used in the production of boards, the use of appropriate technological
parameters (mainly during pressing of mats), sanding of surface of produced boards.
However, thin plates (HDF) are not sanded. Therefore, sought are other methods of
"smoothing" of their surfaces.
In the paper industry, one method of surface finishing of paper products is the
application of special coatings. Coating pastes are typically aqueous mixtures of pigments and
binding agents (Sobczak 2003, Gruber i in. 2006, Drzewińska, Stanisławska 2007, Sień,
Möller 2010, Glittenberg 2010).
This paper proposes the use of similar substances for the surface of HDF. Coating
mixture was prepared according to our own recipe. It was applied as a thin layer to the
surfaces of formed mats, in order to fill the space between fibers. Attempts were made to
determine the composition of the mixture so that the ingredients do not affect the reduction of
mechanical properties of boards, or increase their thickness swelling.
MATERIALS AND METHODS
Pulp from pine wood, obtained in industrial conditions was applied in the production
of HDF. Melamine-urea-formaldehyde was added as an adhesive in the amount of 13,5% in
relation to absolutely dry fibers. The boards with a target density of 880 kg/m3 and thickness
of 3 mm were produced in laboratory conditions. Resin was sprayed onto fibers in a
laboratory blender. The blended fibers were manually formed into mats using a wooden
frame. To the surfaces of the mats was applied mechanically a layer of coating mixture in an
amount of 40-55 g/m2, depending on the variant of produced boards. The mixture contained
an organic filler, a binding component and water. The different variants of produced boards
differed in amount of applied mixture and the temperature of mat pressing (see Table 1).
The mats were pre-pressed in the platens press at room temperature, and then in hot-
press at 180oC, at a pressure 2,5 MPa for 60 or 90s. Physical and mechanical properties of
268
boards were tested according to the PN-EN 622-5/2010 standard and additionally surface
roughness Mitutoyo SJ-201 was performed. Significance of results was evaluated using the
Student’s t-test.
Tab. 1 Amounts of coating mixture on the surfaces
of boards and mat pressing time
Variant Mixture Time
(g/m2) (s)
0 0,0 60
I 55 60
II 60 90
III 39 90
RESULTS AND DISCUSION
Board properties were presented in Table 2.
Tab. 2. Properties of raw HDF and with applied coating mixture
Variant MOR SD MOE SD IB SD TS SD RA SD
(N/mm2) (N/mm2) N/mm2) (N/mm2) (N/mm2) (N/mm2) (%) (%) (μm) (μm)
„O” 48 8.3 5060 815 1.2 0.3 13.2 3.4 9.13 0.7
I 47 7.2 4990 739 1.0 0.4 15.4 4.7 3.87 0.5
II 50 4.6 5510 648 1.1 0.4 12.6 4.6 2.05 0.7
III 51 4.5 5590 567 1.2 0.2 7.1 1.9 1.72 0.4
The data in Table 2 shows that the application of the coating mixture to the surface of
fiber mats can favorably affect the properties of the HDF. It depends on the amount of applied
mixture and used pressing time. Boards of variant I had slightly lower mechanical properties
and higher swelling as compared to the plates of variant "0" (no coating agent). These
changes were minuscule and statistically insignificant. This decrease of properties was
probably due to the additional water, which was applied to the surface of mats with the
coating mixture.
In variant II the amount of coating mixture was only marginally increased (from 55 to
2
60 g/m ), but the press time was extended (from 60 to 90 seconds) in order to remove excess
water. Then all of the tested board properties were improved, both in relation to the properties
of the panels made in variants "0" and I. Furthermore, in variant III, the amount of applied
coating mixture was reduced (to 40g/m2), maintaining the long mat pressing time. This
optimization process allowed to obtain boards with the best properties. In variant III the
mechanical properties of boards have increased, although the increase was not statistically
significant, but the swelling of boards decreased significantly (from 13 to 7%).
The most favorable results were obtained for the surface roughness. While the
roughness of the boards of variant "0" was 9.13 μm, in the boards of variant III it decreased to
1.72 μm. On the one hand it must be admitted that the roughness of the boards of variant "0"
was relatively high, compared to the roughness of the boards produced in industrial
conditions. However, in the laboratory, in shelf presses one does not produce such a smooth
board surface as in continuous operation presses. On the other hand, it is worth noting that the
proposed method of applying the mixture to the mats is simple, in the coating mixture readily
available, environmentally friendly materials are used, and the results were interesting
enough, that the research will be continued.
269
CONCLUSIONS
1. Applying of the coating mixture to the surface of fiber mats influence the
improvement of HDF properties.
2. The optimal amount of coating mixture should be 40 g/m2 of board surface.
3. the use of the coating mixture in the optimal amount allows to obtain the board
roughness at a level of 1.7 μm and swelling at a level of 7%.
REFERENCES
1. DRZEWIŃSKA E., STANISŁAWSKA A. 2007: Postęp w papierach i tekturach
powlekanych. Przegląd Papierniczy 4:225-229.
2. GLITTENBERG D. 2010: Powlekanie na prasach powlekających – czego można się
spodziewać po skrobiach modyfikowanych? Przegląd Papierniczy 6:333-337.
3. GRUBER E., HANDARTO V., GEISMANN V., WOLL K.L. 2006: Przydatność
fragmentaryzowanej skrobi jako środka wiążącego w mieszankach pigmentowych
(Potential of fragmented starch as binder/co-binder in coating colour formulations).
Przegląd Papierniczy 1:23-27.
4. SIEŃ D., MÖLLER K. 2010: Technologia zaklejania powierzchniowego. Przegląd
Papierniczy 6:331-333.
5. SOBCZAK M. 2003:Wpływ objętościowego stężenia pigmentu na zdolności kryjące
powłok i papierów powlekanych. Przegląd Papierniczy 1:21-28.
6. PN-EN 622-5:2010 - Fibreboards - Specifications - Part 5: Requirements for dry
process boards (MDF).
7. EN 382-1: 2001 Fibreboards – Determination of surface absorption – Part 1: Test
method for dry process fibreboards.
8. EN 382-2: 2001 Fibreboards – Determination of surface absorption – Part 2: Test
method for hardboards.
Streszczenie: Sposób ulepszenia powierzchni HDF. W celu ulepszenia powierzchni HDF,
podczas ich produkcji, na powierzchnie kobierców włóknistych nanoszono cienką warstwą
mieszaniną powlekającą w ilości 40 -55 g/m2. Mieszanina składała się z wypełniacza
organicznego, składnika wiążącego i wody. Stosując mieszaninę w optymalnej ilości (40g/m2)
i odpowiedni czas prasowania kobierców (90 s) uzyskano znaczne zmniejszenie
chropowatości powierzchni płyt (z 9,13 do 1,72 μm) i spęcznienia z 17,2 do 7,1%.
Corresponding authors:
Danuta Nicewicz, Sławomir Monder
Faculty of Wood Technology,
Warsaw University of Life Sciences– SGGW,
02-776 Warsaw,
Nowoursynowska str. 159,
Poland
e-mail: danuta_nicewicz@sggw.pl
e-mail: slawomir_monder@sggw.pl
270
