Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DEFINITION OF T~E INVENTION
The object of the presente invention is to
develop an adhesive composition for obtaining a product of best
quality which can compete in the international market. More
speciafically, the invention relates to an adhesive composition
comprising isocyanate-phenolformaldehyde-tannin useful for
manufacturing plywoods for exterior applications, not only with
wood small tulips but with Pinus radiata as well.
Plywood is a product which has been produced
for many centuries. Originally it was produced by artisans
preparing furniture from veneers of very expensive timbers to
save on the amount of wood which was used. They only used
adhesives of animal or vegetal origin as these were the only
available ones. Since the beginning of this century plywood has
been produced industrially due to its exceptional strength to
weight ratio. At first casein, an animal derived protein, was
used as the only adhesive, but from the 1930's the introduction
of synthetic resins, namely urea-formaldehyde (UF) adhesives for
interior applications and phenol-formaldehyde (PF) adhesives for
exterior and marine-grade applications, revolutionized plywood
manufacture. The use of synthetic resins allowed the
manufacture of plywood always of consistant quality, at
affordable prices, and as a consequence of this a great expansion
of its worldwide production capacity ensued, expansion which
continued well after the end of the second world war.
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At present PF resins dominate the worldwide
market for the production of exterior and marine grade plywood.
One of the problems presented however by PF resins is that a
variety of formulations are employed due to the very different
types of wood used for veneers. PF resins furthermore have
some serious limitations. They are not able for instance (i)
to bond consistently well veneers of higher moisture content
(8~ to 12~), (ii) to bond equally well with the same
formulation medium density veneers and high density veneers
(0.6 to 0.8 Kg/ m3 into structural plywood and to accomplish
all the above with lower adhesive spread levels. A resin of
any nature or composition which is capable of overcoming all
the defects of PF resins listed above, while still maintaining
their excellent performance, would indeed be a great step
forward in adhesives for exterior and marine grade plywood.
Diisocyanates, in particular polymeric MDI, have
been introduced in the wood industry for almost 15 years.
These materials can produce excellent results when used as
adhesives for particulate products but have been widely
recognized as totally unusable for plywood. This is due to
their low viscosity which makes these resins migrate from the
glue-line into the veneers before and particularly during
plywood hot-pressing operations, completely starving the glue-
line of adhesive and leading to joints of very poor strength.
A composite resin containing MDI which would be capable of
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utilizing the great strength capabilities of MDI, but capable
to also bonding plywood would become as succesfull in the field
of plywood manufacture as MDI is succesfull today in bonding
wood particle products.
Tannin-formaldehyde resins have been another set
of adhesives which has been used commercially, in certain
countries, during the last 20 years. Their exterior durability
and their performance is similar and often superior to that of
PF resins, to which they resemble due to the phenolic nature of
polyflavonoid condensed tannins obtained from the bark and wood
of certain trees. Up to now however, only mimosa (wattle),
quebracho and chestnut tannins have been used commercially for
plywood adhesives application. While they perform well on
softwoods, they perform poorly on the higher densities hardwood
veneers. Furthermore their limited worldwide production, not
more than 150,000 Tons per year has severely limited their
ability to make serious quantitative inroads in the worldwide
PF wood adhesives market which is reputed to be of up to 5
million Tons yearly. The only tannin which could be produced
in such large scale is that obtainable from the bark of pine
trees. Pine trees are the most common forestry crop worldwide
and thus great amounts of waste pine bark are available. This
could be the source of considerable amounts of pine tannin.
Unfortunately pine tannins are reputed to be not easily
amenable to the formulation of wood adhesives as some of the
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other tannins mentioned above and no present successfull
industrial use is at present recorded.
The preparation thus of a composite adhesive system
using in bulk the characteristics of MDI, of pine tannins and
of PF resins to overcome at the industrial level most of the
problems listed for the three materials when used singly is
then a great step forward in the formulation industrial
plywood adhesives.
The composition according to the invention
lo comprises:
a) 121 parts by weight of phenolic resin:
b) 5 to 121 parts by weight of isocyanate;
c) 1 to 30 parts by weight of pine tannin, quebracho, mimose
or combinations thereof;
d) 1 to 15 parts by weight of paraformaldehyde or
formaldehyde solutions in water;
e) 1 to S0 parts by weight of water, and
f) wood flour or other filling comprising inorganic and/or
organic materials commonly used in the veneer industry, in a
Zo sufficient amount to provide the composition with the desired
viscosity.
The phenolic resin preferably may be prepared from
44.98% phenol, 26.30% paraformaldehyde, 19.19% water/methanol
and 9.57% soda, but any phenolic resin can be used.
Taking into account the main components of the
a t
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operates can be explained as follows: the isocyanate reacts
with the phenolic resin each one of these two components
fortifying and partly hardening the other; the isocyanate
groups react with the phenolic hydroxyl groups as well as with
the methylol hydroxy groups of the phenol-formaldehyde resin.
The tannin functions as an accelerator of the reaction and must
be used in lesser amount in order to maintain this role in the
compositions; it works as an accelerator because it reacts with
the reactive methylol groups of the phenol-formaldehyde resin
and, therefore, it is also a hardener and cross-linker of the
phenol-formaldehyde resin; it acts as an accelerator because it
is also a phenolic material, but containing natural phenols of
a type ten times more reactive than the phenol-formaldehyde
resin. The overall balance of hardener would be deficient for
obtaining a hard gel and, therefore, an extra amount of
paraformaldehyde is added. This compound is mainly a hardener
and hardening aid for the tannin accelerator, as the other two
polymers can be polymerized and hardened with themselves (in
the case of the phenol-formaldehyde resin) or slowly with the
water of the system (in the case of isocyanate).
Summarizing: the isocyanate reacts with the
phenol-formaldehyde resin, with the tannin, with the water and,
probably, with the paraformaldehyde; the phenol-formaldhyde
resin reacts with the isocyanate, with the tannin and with the
paraformaldehyde; and the tanning reacts with the isocyanate,
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with the phenol-formaldehyde resin and with the para-
formaldehyde.
The compositions of the invention can be used in the
manufacture of plywood and show excellent results with
different timber specied operating in the same manner with all
types of wood (hardwood and softwood), something which is not
achieved with the phenol-formaldehyde resins.
Furthermore, the composition is highly resis to
small tulips (wood) penetration and has a good flow
10 viscosities upto 5000 cps, something which is not possible
known compositions.
The following example are presented in order to
illustrate the invention without limiting its scope.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a diagram giving the average shear
srtength values of laboratory plywood panels according to the
invention and to din standard.
Fig. 2 is a diagram giving the average shear
strength of pilot plant plywood panels according to the
invention.
Fig. 3 is a diagram giving the average shear
strength of dry industrial scale plywood panels bonded with
five different compositions numbered 1, 2, 3, 4 and 8 on
different types of wood veneers.
Fig. 4 is a diagram giving the average shear
strength of wet industrial scale plywood panels bonded with
compositions 1, 2, 3, 4 and 8 on different types of wood
30 veneers.
Fig. 5 is a diagram giving the adhesive values of
dry industrial scale plywood panels bonded with compositions
1, 2, 3, 4 and 8 on different types of wood veneers.
Fig. 6 is a diagram giving the adhesive values of
wet industrial scale plywood panels bonded with compositions
1, 2, 3, 4 and 8 on different types of wood veneers.
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6a
Fig. 7 is a diagram giving the average tensile
strengths for dry wood.
Fig. 8 is a diagram giving the average wood failure
in dry wood tensile strength.
Fig. 9 is a diagram giving the average tensile
strengths for wet wood.
Fig. 10 is a diagram giving the average wood failure
in wet wood tensile strengths.
EXAMPLE
Adhesive compositions 1, 2 and 3 were prepared
comprising the compounds shown in Table 1:
TA~LE I
I ~ 1(2) 2 3
P~ ~ LIC ~IN 121 P,P. 121 121
ISX~U~ATE (MDI) ~0 27.5 15
PINE TANNIN 10 7.5 10
PA~DE~E 1 6.75
WOOD F1~ 10(1) 10 20
WATER 17 17 34
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Plywoods were prepared using~ sjtions 1, 2 and 3, with
the following working conditions:
Woods: Tulips of Tepa, coigue, ulmo and pine
Small tulip moisture: 8 - 10%
Small tulip thickness: 2.1 and 3.6 mm.
Adhesive charge: 200 g/m2 (for glue-line)
Previous Press Time: 6'30"
Press Time: 14'
Press Temperature: 120~C
Press pressure: 11 Kg/cm
COMPARATIVE EXAMPLE
Assays were performed in order to obtain the
average values of the adhesion percentages (APA standard) and
shear (DIN Standard) with the plywoods obtained with adhesive
compositions 1, 2 and 3 of the Example according to the
invention and with plywoods manufactured with other adhesives
according to the following table:
TABLE 2
PLYWOOD ADHESIVE
A COMPOSITION 1
B NESTE-OY PHENOLIC, FINLAND
C OXIQUIM PHENOLIC, CHILE
D CIBA-GEIGY PHENOLIC, ENGLAND
E COMPOSITION 2
F COMPOSITION 3
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The DIN standard ~nds a shear which is 1 N/mm
or higher and the APA standard demands an adhesive average of
80% or more.
All the plywoods have shear values which are
higher than 1 N/mm , as can be seen from Figure 1 and only
plywoods A and E, manufactured with compositions 1 and 2 of the
invention, respectively, achieved the APA standard, as can be
seen from Figure 2.
PILOT PLANT ASSAY
Assays were performed in order to measure the
shear and adhesive values in plywoods manufactured in the pilot
plant using compositions 2 and 3 of the Example according to
the invention. results are shown in tabla 3 and are
graphically presented in Figures 3 and 4.
TABLE 3
PLYWOOD SHEAR (N/mm2) ADHESION (%)
1 (a) 4.34 94.50
1' (b) 4.34 97.00
1 II (c) 3.89 96.00
1 III (d) 3.70 100.00
1,5 (e) 3.53 77.50 ***
1,5 (f) 4.34 96.00
1.5 II (g) 4.31 88.00
1.5 III(h) 3.67 92.00
2 (i) 3.42 60.00 ***
2' (j) 3.46 98.50
2 II (k) 3.95 95.00
2 III (1) 3.14 89.00
*** : NOT APPROVED BY THE STANDARD.
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It can be noted that the shear resistance results are
all higher than 3N/mm2, thus largely exceeding the DIN
standard. The adhesive values are high and with the exception
of the boards, they exceed the 85% of adhesiveness and
therefore the average of the boards may be accepted according
to the APA standard.
INDUSTRIAL ASSAY 1
For this industrial assay compositions 1 and 2 of the
Example according to the invention were applied to pine, tepa,
coigue and "olivillo" small tulips under the conditions
specified in Table 4.
TABLE 4
PROCESS CONDITIONS
ASSAY o~OSITION PRESS. P~ESS. PRESS C ~ GE PRESS. OPEN
TEMP . TI1~3 PRESSU~E ( * ) 2 TIME TIME
( oc) (MIN) (Kg/cm ) (Kg/cm ) (MIN) (MIN)
01 1 125 16 11 480 7 100
02 1 125 16 11 480 7 30
03 1 125 12 11 400 7 30
04 1 125 16 11 400 7 70
06 2 125 16 11 400 7 3 5
07 2 125 16 11 360 7 35
08 2 125 16 11 360 7 35
AT 2 GLUE LINES.
The shear resistance values and adhesive values for
the plywoods are summarized in Table 5 and are plotted in
Figures 5 and 6.
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TABLE S
SUMMARY OF PROPERTIES
PLYWOOD SHEAR (N/mm2) ADHESION
1,1 (m) 1.90 92.54
1,11 (n) 1.97 91.51
1,70 (o) 1.36 87.72
1,100 (p) 1.65 72.33
2,1 (q) 1.42 88.42
2,11 (r) 1.35 91.00
3,1 (s) 1.33 91.94
3,11 (t) 1.29 93.25
4,1 (u) 1.46 90.33
4,11 (v) 1.53 91.67
4,70 (w) 1.54 89.67
6,1 (x) 1.59 83.17
6,11 (y) 1.65 90.76
7,1 (z) 1.48 84.04
7,11 (A) 1.97 88.00
8,1 (B) 1.87 84,92
8,11 (C) 1.55 90.33
8,70 (d) 1.52 73.56
SIDE S 1.53 85.75
SIDE I 1.63 86.52
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It can be seen from the graphs that the shear values
for all the plywoods are higher than 1 N/mm2 thus fulfilling
the DIN standard and that the adhesive values are high with 84%
of the boards assayed showing over 80% adhesion, thus achieving
the APA standard. No unplyed probes or having 0% adhesion were
found.
INDUSTRIAL ASSAY 2
For this industrial assay, composition 1 of the
example according to the invention was applied to tepa, coigue,
ulmo, olivillo and pine small tulips with thicknesses of 1.5,
2.2 and 4.0 mm.
The operating conditions are specified in Tabla 6.
TABLA 6
PROCESS CONDITIONS
ITEM VALUE
Small tulip moisture (%) 8 - 10
Adhesive charge (gJm2) 200
Previous Press Time (Min) 6
Press Time (Min) 18
Press Temperature (~C) 125
Press Pressure (Kg/cm ) 11
Previous Press Pressure (Kg/cm2) 10
Open Time (Min) 30 - 45
~ By glue - line.
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The shear strength and wood failure values are
summarized in Tables 7, 8, 9 and 10 and are plotted in figures
7, 8, 9 and 10.
As can be seen from the tables and graphs, the
moisture of the boards as well as the adherence with vacuum-
pressure as well as with boiling water and heat resistance,
fulfill the corresponding standard.
TABLE 7
PLYWOOD ~OISTURE
PLYWOOD MOISTURE
N~ %
01 9.1
02 9.7
03 9.5
04 9.1
08 9-7
The plywood moisture corresponds to average of
f ive probes per plywood .
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TABLE 8
TRACTION SHEAR ASSAY - VACUUM-PRESSURE
PLYWOOD PROBE TENSILE STRENGTH WOOD FAILURE
N~ N~ KGF CM %
1 P 24.7 100
2 P 18.8 90
1 3 P 25.1 90
1 T 30.9 90
2 T 30.6 100
1 P 11.2 95
2 P 12.3 80
2 3 P 15.2 85
1 T 18.9 90
2 T 17.0 95
1 P 18.0 25
2 P 17.5 90
3 3 p 10.8 95
1 T 16.0 95
2 T 34.7 100
1 P 25.2 90
2 P 14.6 90
4 3 P 10.8 60
1 T 26.7 95
2 T 16.0 90
1 P 16.0 95
2 P 15.0 70
8 3 P 14.0 90
1 T 32.3 100
2 T 29.7 100
P means stress of the sheet parallel to the direction of the
load and T, the transverse one.
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TABLE 9
TRACTION SHEAR ASSAY, BOILING WATER IMMERSION
PLYWOOD PROBE TENSILE STR~NGTH WOOD FAILURE
N~ N~ KGF/CM %
1 P 12.2 100
2 P 13.7 100
1 3 P 13.7 100
1 T 15.8 100
2 T 19.9 95
1 P 9.5 100
2 P 17.9 100
2 3 P 14.0 100
1 T 26.0 95
2 T 15.6 90
1 P 16.4 90
2 P 16.0 90
3 3 P 20.0 80
1 T 26.4 100
2 T 26.9 100
1 P 12.6 100
2 P 9.3 100
4 3 P 22.4 85
1 T 32.0 100
2 T 27.5 100
1 P 16.9 70
2 P 7.3 100
8 3 P 27.5 100
1 T 15.4 90
2 T 25.7 100
P means, tress of the sheet paralel to the direction fo the
load and T, the transverse one.
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TABLE 10
~EAT RESISTANCE ASSAY
PLYWOOD AFTER FLAME
N~ EXPOSURE
01 N.F.
02 N.F.
03 N.F.
04 N.F.
08 N.F.
N.F.: Without failure.
