U.S. patent application number 12/041360 was filed with the patent office on 2008-07-03 for oriented strand boards.
This patent application is currently assigned to DSM IP ASSETS B.V.. Invention is credited to Rudolphus Antonius Theodorus Maria Benthem, Van, Lars EVERS, Jose Guadalupe Gomez Bueso, Jozef Maria Johannes Mattheij, Jacobus Adriaan Antonius Vermeulen.
Application Number | 20080160303 12/041360 |
Document ID | / |
Family ID | 33555954 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080160303 |
Kind Code |
A1 |
EVERS; Lars ; et
al. |
July 3, 2008 |
ORIENTED STRAND BOARDS
Abstract
Oriented strand board (OSB), comprising a core layer and two
face layers, whereby the face layers comprise an adhesive
composition, wherein the adhesive composition in at least one of
the face layers comprises a resin composition comprising melamine,
formaldehyde, optionally urea and aromatic hydroxyl compounds,
wherein the molar ratio of melamine to formaldehyde is 1:0.84.0,
the molar ratio of melamine to urea is 1:0-2.0 and the molar ratio
of melamine to aromatic hydroxyl compounds is 1:0-2.0. In a
preferred embodiment, both the face layers and the core layer
comprise the said adhesive composition. The OSB's according to the
invention can meet the OSB/3 and even the OSB/4 requirements in the
EN 300 standards.
Inventors: |
EVERS; Lars; (Sittard,
NL) ; Benthem, Van; Rudolphus Antonius Theodorus Maria;
(Limbricht, NL) ; Mattheij; Jozef Maria Johannes;
(Sittard, NL) ; Gomez Bueso; Jose Guadalupe;
(Oslo, NO) ; Vermeulen; Jacobus Adriaan Antonius;
(Geleen, NL) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DSM IP ASSETS B.V.
DYNEA OY
|
Family ID: |
33555954 |
Appl. No.: |
12/041360 |
Filed: |
March 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10561942 |
Dec 22, 2005 |
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PCT/NL2004/000456 |
Jun 28, 2004 |
|
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12041360 |
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60558142 |
Apr 1, 2004 |
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Current U.S.
Class: |
428/375 ;
156/296; 156/62.2 |
Current CPC
Class: |
B32B 2307/514 20130101;
B32B 2317/16 20130101; B32B 21/14 20130101; B32B 7/12 20130101;
B32B 21/02 20130101; Y10T 428/2933 20150115; C08G 12/38 20130101;
B27N 3/002 20130101; Y10T 428/249939 20150401; Y10T 428/249925
20150401; B27N 3/04 20130101; C09J 161/28 20130101 |
Class at
Publication: |
428/375 ;
156/62.2; 156/296 |
International
Class: |
B27N 3/00 20060101
B27N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2003 |
EP |
03077077.0 |
Aug 18, 2003 |
EP |
03102564.6 |
Claims
1. Oriented strand board (OSB), comprising a core layer and two
face layers, whereby at least the core layer comprises an adhesive
composition, wherein the adhesive composition in the core layer
comprises a resin composition comprising melamine, formaldehyde,
optionally urea and optionally an aromatic hydroxyl compound, and
wherein the molar ratio of melamine to formaldehyde is 1:0.8-1:9,
the molar ratio of melamine to urea is 1:0-1:6, and the molar ratio
of melamine to aromatic hydroxyl compound is 1:0-1:2.
2. Oriented strand board according to claim 1, wherein the resin in
the adhesive composition of the core layer has a molar ratio of
melamine to formaldehyde of 1:0.8-1:4 and a molar ratio of melamine
to urea of 1:0-1:2.
3. Oriented strand board according to claim 1, wherein the amount
of resin in the core layer is 2.5-8 wt % dry resin/dry wood.
4. Oriented strand board according to claim 1, wherein the amount
of urea in the core layer is 0-0.025 kg/kg core layer.
5. Oriented strand board according to claim 1, wherein the OSB has
a thickness swell lower than 15 or 12% according to the OSB/3 or
OSB/4 standard, respectively.
6. Oriented strand board according to claim 1, wherein the OSB has
an internal bond value after boiling according to the OS/3 or OSB/4
standard.
7. Process for the preparation of an oriented strand board (OSB),
comprising the steps of: a) preparing an adhesive composition
comprising a resin composition comprising melamine, formaldehyde,
optionally urea and an aromatic hydroxyl compound, wherein the
molar ratio of melamine to formaldehyde is 1:0.8-1:9, the molar
ratio of melamine to urea is 1:0-1:6 and the molar ratio of
melamine to aromatic hydroxyl compound is 1:0-2.0; b) treating wood
strands with the adhesive composition; c) scattering
adhesive-treated wood strands for a face layer, a core layer on top
of the face layer, and again a face layer on top of the core layer,
whereby the wood strands of at least the core layer were treated
with the adhesive composition prepared in a); d) pressing the wood
strands, whereby the adhesive composition is at least partially
cured, to form an OSB.
8. Process according to claim 7, wherein the resin composition as
used in step a) has a molar ratio of melamine to formaldehyde of
1:0.8-1:4, and a molar ratio of melamine to urea of 1:0-1:2.
9. Process according to claim 7, wherein the wood strands of the
face layers and of the core layer were treated with an adhesive
composition as prepared in step a).
Description
[0001] This application is a divisional of copending U.S.
application Ser. No. 10/561,942 filed on Dec. 22, 2005, which is
the US national phase of Internal application PCT/NL2004/000456
filed Jun. 28, 2004 which designated the US and claims benefit of
EP 03077077.0 filed Jun. 30, 2003 and EP 03102564.8 filed Aug. 18,
2003 and U.S. Provisional Application Ser. No. 60/558,142 filed
Apr. 1, 2004, the entire content of each being expressly
incorporated hereinto by reference.
[0002] The invention is directed to an Oriented Strand Board (OSB),
comprising a core layer and two face layers, whereby at least the
face layers comprise an adhesive composition.
[0003] The oriented strand boards that are commercially prepared at
the moment comprise a core layer of wood strands combined with an
adhesive composition, covered by two face layers of wood strands
combined with an other adhesive composition. The strands in the OSB
typically have the following dimensions; length between 5 and 150
mm, width between 1 and 50 mm and thickness between 0.1 and 2 mm.
The core can form between 10 and 90 wt. % of the OSB, preferably
between 40 and 70% of the OSB. The adhesive composition in core
layer of the known OSB comprises 2-8 wt % (dry resin/dry wood) of a
polymeric methylene diphenyl diisocyanate (pMDI) or a phenol
formaldehyde (PF) resin. The adhesive composition in the face
layers comprises a melamine-urea-formalydehyde (MUF) resin, and may
also comprise a small amount of phenol or a phenol formaldehyde
resin or pMDI resin with a release agent added thereto. The face
layers have a resin content of typically 9-12 wt % dry resin/dry
wood for MUF and typically 2-6 wt % dry resin/dry wood for PF. As
is common practice, the adhesives in a prepared OSB are at least
partially cured, preferably fully cured. These known OSB's can meet
the requirements of OSB/3 or OSB/4 in the EN 300 standards.
[0004] It is a disadvantage of the known OSB's that a relatively
high amount of resin is necessary, in particular in the face
layers, in order to ensure that the OSB/3 or OSB/4 standards are
met.
[0005] It is the objective of the present invention to overcome
said disadvantage.
[0006] Said objective is achieved in that that the adhesive
composition in at least one of the Face layers comprises a resin
composition comprising melamine, formaldehyde, optionally urea and
optionally an aromatic hydroxyl compound, wherein the molar ratio
of melamine to formaldehyde is 1:0.8-1:4.0, the molar ratio of
melamine to urea is 1:0-1:2.0 and the molar ratio of melamine to
aromatic hydroxyl compounds is 1:0-1:2.0. Preferably, the adhesive
composition in both face layers comprises a resin according to the
invention.
[0007] An advantage of the OSB according to the invention is that
an OSB meeting the OSB/3 or OSB/4 standards can be made with a
lower amount of resin in the face layers when the known type of
resin for this application is used. By application of the resin as
defined above for the preparation of at least one of the face
layers of the OSB the amount of resin that has to be used for the
face layer to make an OSB that meets the OSB/3 or OSB/4 standards
can be reduced to as little as between 2.5-8 wt % dry resin/dry
wood. As a result of this the cost price of the OSB will be lower
than for a known OSB as described above. Alternatively, if the OSB
according to the invention comprises the same amount of resin in at
least one face layer, it will show superior properties compared to
the known OSB, in particular relating to internal bond strength and
swelling after contact with boiling water.
[0008] An OSB according to the invention means a prepared OSB; as
is known, this means that any resins and/or adhesive compositions
have been at least partially cured. Preferably, they have been
cured fully.
[0009] The resin composition according to the invention comprises
melamine and formaldehyde. The melamine and formaldehyde are
present in the resin composition in a molar ratio of 1:0.8-1:4.0;
preferably, the said molar melamine:formaldehyde ratio lies between
1:0.85 and 1:3.5, more preferably, the said ratio lies between
1:0.9 and 1:3.25; even more preferably, the said ratio lies between
1:1.0 and 1:3.0; in particular, the said ratio lies between 1:1.05
and 1:2.8; most preferably, the said ratio lies between 1:1.1 and
1:2.6. As is commonly known, resins are cured in order to achieve
their final properties. The wording `resin` in the present
invention relates to the resin in both uncured condition as well as
in partially or fully cured condition in the end product, when it
is part of a prepared OSB.
[0010] The resin is normally made by mixing dry melamine powder
with an aqueous solution of formaldehyde. This solution having a
formaldehyde concentration of for instance 30-55 wt % of
formaldehyde.
[0011] Further the resin composition can contain urea and/or
aromatic hydroxyl compounds.
[0012] When urea is present in the resin composition the molar
ratio of melamine to urea is 1:0-2.0; preferably, the said molar
melamine:urea ratio lies between 1:0.05 and 1:1.8, more preferably
between 1:0.1 and 1:1.6, in particular between 1:0.15 and 1:1.4 or
between 1:0.25 and 1:1.2. It was found, surprisingly, that the
presence of some urea in the resin composition according to the
invention has a beneficial effect on the end properties of the OSB
according to the invention, even though urea as such is generally
regarded as leading to inferior properties in comparison to
melamine. In a preferred embodiment, therefore, the molar
melamine:urea ratio in the resin lies between 1:0.25 and 1:0.9.
When an aromatic hydroxyl compound is present in the resin
composition the molar ratio of melamine to aromatic hydroxyl
compound is 1:0-2.0, preferably 1:0.05-1.0.
[0013] Examples of aromatic hydroxyl compounds are resorcinol,
hydrochinon or bisphenol A. Preferably however phenol is used as
the aromatic hydroxyl compound.
[0014] The urea can be introduced in the resin composition by
adding solid urea or by adding a urea solution in water and mixing
it with the melamine and the formaldehyde solution. Also an aqueous
solution of formaldehyde and urea can be used in combination with
the melamine powder.
[0015] Phenol can be added as such when the resin composition is
prepared or as a formaldehyde/phenol precondensate.
[0016] In a preferred embodiment of the OSB according to the
invention at least one face layer does not comprise a polymeric
methylene diphenyl diisocyanate (pMDI) resin; more preferably,
neither of the face layers comprises a pMDI resin. In another
preferred embodiment according to the invention, the core layer
does not comprise a pMDI resin. Still more preferably, the OSB as a
whole does not comprise a pMDI resin. This has the advantage that
the OSB can be prepared more quickly, since aminoplast-containing
adhesive compositions typically have a higher cure speed than
pMDI-based adhesive compositions.
[0017] A non-limiting indication of the preparation of the resin
that is used for preparing the OSB according to the invention is as
follows: the components that make up the resin composition are
added to each other and mixed at a temperature of 20 to 40.degree.
C. Thereafter the temperature is raised to a temperature between 70
and 100.degree. C. The pH-value of the mixture is preferably
between 7.0 and 10.0. Under these conditions the mixture reacts,
i.e. condensation taking place, until the viscosity of the resin
composition is between 10 and 1000 mPas, preferably between 200 and
900 mPas. Thereafter the resin composition is cooled to
20-75.degree. C., preferably to room temperature The pH of the
cooled resin composition will typically be between 7 and 10.
[0018] Another non-limiting indication of a method for preparation
of the resin composition that is part of the OSB according to the
invention is a method that comprises stepwise dosing of the
components. For example, urea can be added during or after the
condensation.
[0019] To adjust the pH of the resin composition the normal
additives to create alkaline conditions can be used, like alkali or
earth alkalihydroxydes, preferably in the form of their aqueous
solutions, tertiary amines, like for instance tributylamine or
triethylamine, or tertiary alkanolamines, like for instance
triethanolamine and methyidiethanolamine.
[0020] The viscosity of the aqueous resin composition is typically
at 20.degree. C. 10-900 mPas and has a solids content of between 50
and 80%.
[0021] The products can usually be stored for a couple of weeks at
20.degree. C. As is known, small amounts of other additives can
also be added to the resin.
[0022] The resin composition according to the invention has
surprisingly good properties when applied as the resin in the face
layers of oriented strand board (OSB). A process thereto is
described below.
[0023] To be applied in a face layer, the resin is usually mixed
with a catalyst or hardener, whereby an adhesive composition is
formed. As a hardener for instance ammonium sulphate is commonly
used, in an amount of up to 5 wt % dry hardener/dry resin. However,
other hardeners can also be used; for instance ammonium chloride or
ammonium nitrate. The adhesive composition according to the
invention may optionally comprise one or more other resins. During
the preparation of the adhesive composition also waxes can be
applied; this is commonly done in order to enhance the moisture
resistance of the OSB. In a preferred embodiment of the OSB
according to the invention, the three molar ratios as given above
for the resin as comprised within the adhesive composition
(melamine to formaldehyde, melamine to urea and melamine to
aromatic hydroxyl compound) also apply to the adhesive composition
as a whole. Preferably, the adhesive composition does not comprise
any other resins than the resin composition as indicated above.
[0024] After addition of the catalyst the adhesive composition is
normally used within a time frame of a few hours in the production
of an OSB; the adhesive composition is sprayed on the wood strands
to coat the wood strands with it. The wood strands usually have a
length between 5 and 200 mm, preferably between 20 and 150 mm, more
preferably between 40 and 140 mm, in particular between 60 and 130
mm and most preferably between 80 and 120 mm. The wood strands
usually have a width between 1 and 60 mm, preferably between 5 and
50 mm, more preferably between 10 and 40 mm, in particular between
14 and 30 mm and most preferably between 18 and 25 mm. The wood
strands usually have a thickness lying between 0.1 and 2 mm,
preferably between 0.2 and 1.5 mm, more preferably between 0.3 and
1.2 mm, in particular between 0.4 mm and 1 mm, most preferably
between 0.5 and 0.8 mm. The adhesive composition is cured/hardened
upon heating, thereby binding the wood strands to each other.
Heating and curing/hardening takes place when pressing the final
OSB material.
[0025] The process for the production of an OSB is known in
general, and described in for instance: "Holzwerkstoffe und Leime,
M. Dunky and P. Niemz, p 133-135, Springer-Verlag, 2002" and in
"Taschenbuch der Spanplatten Technik, Deppe & Ernst, p 258-266,
1991, DRW Verlag".
[0026] A method of making the oriented strand boards according to
the invention comprises spraying the adhesive composition according
to the invention onto the wood strands for at least one of the face
layers of the OSB, preferably in both face layers. In order to
achieve a quality according to the OSB/3 or OSB/4 standard, the
amount of resin in the said face layer or layers can be 2.5 to 8 wt
% dry resinidry wood. Preferably, the amount of resin in the face
layer or layers is at least 2.75%, more preferably at least 3.0%;
this has the advantage that with increasing amount of resin, the
properties of the OSB also increase; in particular, the amount of
resin in the face layer or layers is at least 3.25%, most
preferably at least 3.5 wt. % dry resinidry wood. In order to
ensure that the OSB according to the invention remains cost
competitive, it is preferred that the amount of resin in the face
layer or layers is at most 7.5%, more preferably at most 7.0%, in
particular at most 6.5% and most preferable at most 6 wt. % dry
resinidry wood The core material is prepared by coating wood
strands. Usually, the wood strands in the core layer are smaller
than the wood strands in the face layers. In the known OSB's, the
coating (also referred to as treating) of the wood strands is
typically done with adhesive compositions essentially consisting of
polymeric methylene diphenyl diisocyanate (pMDI) or phenol
formaldehyde (PF) resins. In the OSB according to the invention,
this may also be done. In a preferred embodiment of the OSB
according to the invention, however, the wood strands of the core
layer comprise an adhesive composition comprising a resin
composition comprising mainly or even consisting essentially
of--melamine, formaldehyde, optionally urea and optionally an
aromatic hydroxyl compound. The resin in the adhesive composition
in the core layer preferably has a molar ratio of melamine to
formaldehyde of 1:08-1:9, a molar ratio of melamine to urea of
1:0-1:6, and a molar ratio of melamine to aromatic hydroxyl
compound of 1:0-1:2. More preferably, the resin in the adhesive
composition in the core layer has a molar ratio of melamine to
formaldehyde of 1:0.8-1:4 and a molar ratio of melamine to urea of
1:0.1-1:1.5. This has the advantage that, as in the face layers, a
lower amount of adhesive composition may be used in the core layer
compared to the known adhesive compositions based on pMDI or pure
PF resins while still achieving the desired end properties such as
the properties as required in the OSB/3 or OSB/4 standard. in this
embodiment, the OSB according to the invention preferably does not
comprise any pMDI (uncured, partically cured or fully cured).
Preferably, the molar ratios as given also apply to the adhesive
composition as a whole, whereby the adhesive composition preferably
does not comprise any other resins.
[0027] The resin composition as used in the adhesive composition
according to the invention has a solids content. As is known to the
skilled person, the solids content of a resin is determined by
putting a small amount of resin (eg., 1 or 2 grams) in an oven at
120.degree. C. during 2 hours. The solids content is defined as the
relative weight of the remaining material, and is expressed as
percentage of the weight of the resin as put in the oven. In a
preferred embodiment of the process according to the invention, the
resin composition as used in treating the wood strands of the core
layer has a solids content of at least 60% or 62%. More preferably,
the solids content is at least 64% or 66%. As the solids content
rises, the amount of water that is introduced into the core layer
is reduced. Since this water should be removed during the
subsequent pressing step, it is beneficial that as little water as
possible is introduced. In particular, therefore, the solids
content of the resin is at least 68%. Most preferably, the solids
content is at least 70%. As the solids content rises, so does the
viscosity of the resin. Practice has shown that it is beneficial
for achieving a smooth distribution of the adhesive composition
over the wood strands if the solids content of the resin remains
below 80%, more preferably below 78%, in particular below 76% and
most preferably below 75%, Preferably, the viscosity of the
adhesive composition lies between 700 and 900 mPa.s; as indicated
earlier, the viscosity of the adhesive composition is also
influenced by the degree of condensation that has taken place.
[0028] The use of a resin composition comprising melamine,
formaldehyde, optionally urea and optionally an aromatic hydroxyl
compound in adhesive composition of the core layer of an OSB
is--aside from considerations relating to the face
layers--beneficial in itself. The invention therefore also relates
to an OSB, comprising a core layer and two face layers, whereby at
least the core layer comprises an adhesive composition, wherein the
adhesive composition in the core layer comprises a resin
composition comprising melamine, formaldehyde, optionally urea and
optionally an aromatic hydroxyl compound, wherein the molar ratio
of melamine to formaldehyde is 1:0.8-1:9, the molar ratio of
melamine to urea is 1:0-1:6, and the molar ratio of melamine to
aromatic hydroxyl compound is 1:0-1:2. Preferably, the resin in the
adhesive composition of the core layer has a molar ratio of
melamine to formaldehyde of 1:0.8-1:4 and a molar ratio of melamine
to urea of 1:0.1-1:2. The amount of resin in the core layer is in
this aspect of the invention as given above. Preferably, therefore,
the amount of urea in the core layer is 0-0.025 kg/kg core layer,
more preferably 0.005-0.015 kg of urea per kg core layer. The
solids content of the resin used for the core layer is preferably
within the limits as given above.
[0029] The face layers of this OSB according to the invention may
comprise the known adhesive compositions, i.e. comprising a
pMDI-based resin or a PF resin. Preferably, however, at least one
face layer--and preferably both face layers--comprise adhesive
compositions whereby the resins comprise--or even consist
essentially of--the compounds as described above according to the
invention. Preferably, the same adhesive composition is used for
both the face layers as well as for the core layer. This has the
advantage that only one type of resin and adhesive composition has
to be handled for the preparation of the OSB.
[0030] An OS is typically prepared by first scattering--while
usually achieving an orientation--the face layer material,
thereafter the core layer material and then again a layer of face
layer material, followed by hot pressing this to an OSB. During the
hot pressing curing takes place. The pressing can be continuous or
batch wise. In the core layer and the face layers wood strands of
different size and orientation can be used. Typically, the wood
strands in the core layer have smaller dimension(s) and less
orientation than the wood strands in the face layers.
[0031] As described here, an OSB has three layers--a core and two
face layers. It is also known that an OSB having 4 or more layers
may be prepared, for instance by introducing at least one layer
between the core and at least one face layer. Preferably within the
context of the present invention, all layers that are not face
layers are regarded--and treated according the invention--as core
layer.
[0032] Typical known press conditions are 1-7 MPa, 150-270.degree.
C. during 3-12 sec/mm, preferably 5-10 sec/mm. As is known to those
skilled in the art, press times are given in seconds per mm of OBS
thickness.
[0033] In summary, a process for the preparation of an oriented
strand board (OSB) according to the invention preferably comprises
the following steps: [0034] a) preparing an adhesive composition
comprising a resin composition comprising melamine, formaldehyde,
optionally urea and aromatic hydroxyl compounds, wherein the molar
ratio of melamine to formaldehyde is 1:0.8-4.0, the molar ratio of
melamine to urea is 1:0-2.0 and the molar ratio of melamine to
aromatic hydroxyl compounds is 1:0-2.0, [0035] b) treating wood
strands with the adhesive composition; [0036] c) scattering
adhesive-treated wood strands for a face layer, a core layer on top
of the face layer, and again a face layer on top of the core layer,
whereby the wood strands of at least one face layer were treated
with the adhesive composition prepared in a); [0037] d) pressing
the wood strands, whereby the adhesive composition is at least
partially cured, to form an OSB.
[0038] Preferably, the wood strands of both of the face layers are
treated with an adhesive composition as prepared in step a).
Preferably, the resin in the adhesive composition as prepared in
step a) has a solids content lying between 67% and 77%, more
preferably between 70% and 75%. Preferably, the core layer is also
treated with an adhesive composition as prepared in step a).
[0039] The OSB's according to the invention may comprise an amount
of urea--typically for the most part in bonded form--in at least of
face layer. This amount can be expressed as the number of kilograms
of urea per kg of face layer. Preferably, at least one face layer
of the finished OSB according to the invention comprises an amount
of urea of 0.001-0.025 kg/kg face layer, more preferably
0.005-0.015 kg/kg face layer. The amount of urea in the face layer
can be determined with known methods such as for instance Raman
spectroscopy or solid state NMR. The reference to urea in an OSB
face layer within the context of the present invention means urea
as such and in bonded form in a resin. Preferably, the urea content
of the core layer is also within the range as given above.
[0040] The finished OSB according to the invention can meet the
requirements for an OSB/3 or OSB/4 material as are laid down in the
EN 300 requirements. Typical requirements herein are the
requirements for thickness swelling and internal bond after
boiling.
[0041] The thickness swelling is determined according to EN 317 and
must be lower than 15 or 12% for an OSB meeting the OSB/3 or OSB/4
standard, respectively. The internal bond after boiling is
determined according to EN 321 and EN 319. The minimum values
differ with the OSB thickness and are:
TABLE-US-00001 Internal bond (N/mm.sup.2) OSB thickness (mm) OSB/3
OSB/4 6-<10 >0.15 >0.17 10-<18 >0.13 >0.15
18-<25 >0.12 >0.13
[0042] The invention is elucidated further by means of the
following examples.
EXAMPLE I
Resin Preparation
[0043] A solution of a 50 wt. % solution of formaldehyde in water
and a phenol formaldehyde precondensate were added to each other
and stirred. The mixture was adjusted with NaOH to a pH of 9
Melamine was added at room temperature.
[0044] Thereafter the temperature was raised to 90.degree. C.
Dissolution of the melamine and condensation takes place until the
water tolerance was 1.5-2. The water tolerance was determined at
20.degree. C.
[0045] Thereafter the mixture was cooled. At 60.degree. C. the urea
was added and thereafter the mixture was cooled further to room
temperature during stirring.
[0046] The resin composition contained per mol of melamine: 2.2 mol
formaldehyde; 0.26 mol urea and 0.16 mol phenol.
[0047] The resin properties were: [0048] Viscosity 300 mPas (at
20.degree. C.), [0049] pH=10, [0050] Solid content=62.5%, [0051]
Gel time=50 sec., [0052] Water tolerance=1.5
OSB Preparation
[0053] The adhesive composition for the two face layers of the OSB
was made by adding ammonium sulphate as hardener to the resin, and
1 wt. % (based on the `wet` resin) of a wax emulsion. Then the
adhesive composition was sprayed onto the wood strands.
[0054] The face layer for the OSB contained 5.8% dry resin/dry wood
and 1% dry hardener/dry resin.
[0055] The adhesive composition for the core layer was also sprayed
on the wood strands. The core layer for the OSB contained 3.0% dry
pMDI/dry wood. Thereafter an OSB was made by scattering a layer of
the wood strands for the face layer, than scattering a layer of
wood strands for the core layer and thereafter again scattering a
layer of wood strands for the second face layer.
[0056] The weight ratio core layer to face layers was 50/50. The
OSB was pressed with a press factor of 9.4 sec/mm, an average
temperature of 235.degree. C. and a pressure of 5 MPa.
[0057] An OSB was made with a thickness of 22 mm having a thickness
swell of 8.9% and an internal bond value after boiling of 0.155
N/mm.sup.2.
EXAMPLE II
[0058] With the same method as described for example I an OSB was
made with a thickness of 18 mm. For this OSB the face layer
contained 6.0% dry resin/dry wood and 1.5% dry hardener/dry
resin.
[0059] The OSB was pressed with a press factor of 9.2 sec/mm, an
average temperature of 235.degree. C. and a pressure of 5 MPa.
[0060] An OSB was made with a thickness swell of 11.0% and an
internal bond value after boiling of 0.15 N/mm.sup.2.
COMPARATIVE EXPERIMENT
Resin Preparation
[0061] A solution of a 50 wt. % solution of formaldehyde in water
and a phenol formaldehyde precondensate were added to each other
and stirred. The mixture was adjusted with NaOH to a pH of 9.
Melamine was added at room temperature.
[0062] Thereafter the temperature was raised to 90.degree. C.
During this phase, when the temperature had reached 82.degree. C.,
urea was added. Dissolution of the melamine (and urea), and
condensation took place until the water tolerance was 3. The water
tolerance was determined at 20.degree. C. During condensation, the
pH was kept at 9 by addition of NaOH; when water tolerance of 3 was
reached, the pH was raised to 10. Thereafter the mixture was cooled
to room temperature.
[0063] The resin composition contained per mol of melamine: 4.17
mol formaldehyde, 2.27 mol urea and 0.2 mol phenol.
[0064] The resin properties were: [0065] Viscosity 300 mPas (at
20.degree. C.), [0066] pH=10, [0067] Solid content=62.5%, [0068]
Gel time=50 sec., [0069] Water tolerance=3
OSB Preparation
[0070] The adhesive composition for the two face layers of the OSB
was made by adding ammonium sulphate as hardener to the resin, and
1 wt. % (based on the `wet` resin) of a wax emulsion. Then the
adhesive composition was sprayed onto the wood strands.
[0071] The face layer for the OSB contained 11 wt. % dry resin/dry
wood and 1% dry hardener/dry resin.
[0072] The adhesive composition for the core layer was also sprayed
on the wood strands. The core layer for the OSB contained 3.0% dry
pMDI/dry wood. Thereafter an OSB was made by scattering a layer of
the wood strands for the face layer, than scattering a layer of
wood strands for the core layer and thereafter again scattering a
layer of wood strands for the second face layer.
[0073] The weight ratio core layer to face layers was 50/50. The
OSB was pressed with a press factor of 9.4 sec/mm, an average
temperature of 235.degree. C. and a pressure of 5 MPa.
[0074] An OSB was made with a thickness of 22 mm having a thickness
swell of 10% and an internal bond value after boiling of 0.14
N/mm.sup.2.
EXAMPLE III
Preparation of Resin A--Resin for Face Layer
[0075] The same resin as prepared in Example I was used.
Preparation of Resin B--Resin for Core Layer
[0076] A solution of a 50 wt. % solution of formaldehyde in water
and a phenol formaldehyde precondensate were added to each other
and stirred. The mixture was adjusted with NaOH to a pH of 9.
Melamine was added at room temperature.
[0077] Thereafter the temperature was raised to 90.degree. C.
During this phase, when the temperature had reached 82.degree. C.,
urea was added. Dissolution of the melamine (and urea), and
condensation took place until the water tolerance was 3. The water
tolerance was determined at 20.degree. C. During condensation, the
pH was kept at 9 by addition of NaOH; when water tolerance of 3 was
reached, the pH was raised to 10. Thereafter the mixture was cooled
to room temperature.
[0078] The resin composition contained per mol of melamine: 2.6 mol
formaldehyde; 0.9 mol urea and 0.16 mol phenol.
[0079] The resin properties were: [0080] Viscosity 300 mPas (at
20.degree. C.), [0081] pH=9.6, [0082] Solid content=62%, [0083] Gel
time=55 sec., [0084] Water tolerance=1
OSB Preparation
[0085] The adhesive composition for the two face layers of the OSB
was made by adding ammonium sulphate as hardener to resin A, and 1
wt. % (based on the `wet` resin) of a wax emulsion. Then the
adhesive composition was sprayed onto the wood strands.
[0086] The face layer for the OSB contained 5.8% dry resin/dry wood
and 1% dry hardener/dry resin.
[0087] The adhesive composition for the core layer of the OSB was
made by adding ammonium nitrate as hardener to resin B, and 1 wt. %
(based on the `wet` resin) of a wax emulsion. Then the adhesive
composition was sprayed onto the wood strands.
[0088] The core layer of the OSB contained 4% dry resin/dry wood
and 2% dry hardener/dry resin.
[0089] Thereafter an OSB was made by scattering a layer of the wood
strands for the face layer, than scattering a layer of wood strands
for the core layer and thereafter again scattering a layer of wood
strands for the second face layer.
[0090] The weight ratio core layer to face layers was 50/50. The
OSB was pressed with a press factor of 8 sec/mm, an average
temperature of 200.degree. C. and a pressure of 5 MPa.
[0091] An OSB was made with a thickness of 16 mm having an internal
bond value after boiling of 0.13 N/mm.sup.2.
EXAMPLE IV
Preparation of Resin A--Resin for Face/Layer
[0092] The same resin A as prepared in Example III was used.
Preparation of Resin B--Resin for Core Layer
[0093] The same resin B as prepared in Example III was used.
OSB Preparation
[0094] The adhesive compositions and the 16 mm OSB were prepared in
the same fashion as in example III, except that the core layer
contained 5% dry resin/dry wood. The internal bond value after
boiling of the OSB was 0.25 N/mm.sup.2.
Additional Data
[0095] The OSB's as prepared in Example II and Example IV were
stripped completely of their face layers. Subsequently, the
internal bond value after boiling of the core layers as such was
measured. Both core layers had a value of 0.25 N/mm.sup.2.
[0096] As is evident from Example I and the comparative experiment,
the OSB according to the invention has a much lower amount of
aminoplast resin in the face layers than the OSB prepared with an
aminoplast resin known for this purpose, and yet the properties of
OSB according to the invention are at least as good as those of the
known OSB. Examples II, III and IV demonstrate that also thinner
OSB's can be made according to the invention, showing satisfactory
properties--also when both the face layers and the core layer
comprise an adhesive prepared according to the invention from an
aminoplast resin. The additional data, moreover, shows that it is
beneficial when the adhesive composition in both the face layers
and the core layer comprises or even consists essentially of an
adhesive prepared according to the invention from an aminoplast
resin, since this results in an OSB having a higher internal bond
value.
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