Note: Descriptions are shown in the official language in which they were submitted.
CA 02245885 1998-08-13
W097/32074 PCT/GB97/00440
METHOD OF PREPARING A SHEET OF A-LIGNOCELLULOSIC
MATERIAL FOR THE MANUFACTURE OF A FINIS~ED
PRODUCT AND METHOD OF MANUFACTURE OF A
FINISHED PRODUCT
BACKG3~0lJND OF THE ~VENT7iON
This invention relates to a mrthod of y~ al;~g a sheet of a lign~ celllllosic
m~t~ri~l for the m~mlf~r*7re of a ril~l.ch~rl product and to a method of
forming an article or fini.ch~A product from one or more sheets of a
lignorl?lll-lo~;r material so treated.
It is well 7known to ...~....r~ spirally or convolutely wound paper tubing
or angles, the latter ~ ,d to as edge board, from kraft paper. Such
products are most frequently made by first cutting large reels of kraft paper
into reels of li nited widths of from 40mm to 160mm, and then unwinding
the paper from these reels or "biscuits" for multi layer l~min~tiQn, either
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
over a mandrel in the case of spirally wound paper tubing, or across
formers in the case of edge board, the glue between the layers being
generally a water based polyvinyl acetate or alkali silicate. The product
comes off the line continuously and can then be cut to lengths of any size.
The result is a product that is fit for the purposes for which it is presently
m~m~f~c.~lred.
~owever, these basic shapes, i.e. tubular or angular sections, are generally
not suitable for use in other applications such as high pressure pipes,
ventilation pipes, repl~cements for all]minil-m extrusions, as poles or posts
to hold signs, as fencing poles or posts, as irrigation pipes, or for a host of
other applications where the tubular or angular sections are subjected to
greater degree of m~rh~nic~l or other stress. In these cases, the paper from
which the tubular or angular sections are made, must first be modified in
order to provide the required degree of water resistance and m~orh~nic~l
strength.
In the m~nllfactllre of sheet products, i.e boards or panels, from a
lignocellulosic m~tPri~l, it is also nPçes~ry to provide the material with the
required degree of water resistance and me~ nic21 strength.
Natural fibrous materials or lignocellulosic materials are colllylised of hemi
celluloses, celluloses and lignin. During the paper making process, the
lignins are digested out of the composition, leaving ~lh~ ally the celluloses
and heIni celluloses. A change in the moisture content of these rnaterials
results in swelling, as a result of their hydrophilic nature, and thus a loss
in strength. The reason is that the cell wall polymers of the materials
contain hydroxyl or other oxygen cont~ining groups that attract water
through hydrogen bonding. It is the hemi celluloses which are the most
CA 0224~88~ 1998-08-13
W O 97/32074 PCT/GB97/00440
hygroscopic. Water can give rise to further degradation as a result of attack
by micro orsJ~ni~m.c.
It is known to modify lignocellulosic materials chemically. Various classes
of chemical reactions have been used with wood products and these are
esters, acetals and ethers produced inter alia by the use of anhydrides.
Exarnples of documents which teach the use of anhydrides include US
Patent Nos 4 832 987, 5 055 247 and S 064 592.
Examples of documents which teach t~e use of anhydrides to treat a
cellulosic m~tP~i~l to which there is then applied a polymer, are US Patent
No 5 120 776; US Patent No 5 385 754 which teaches a process for
modifying lignocellulosic material by a ch~mif~l treatment method, which
method colllpli~es treating the lignocellulosic material with phthalic
anhydride and a thermnsetting resin selected from phenol form~lclehyde
resins, urea formaldehyde resins and urethane resins and t_en curing the
phth~ tP-l resin treated product so forrned; CA 119:227002; and CA
120: 135905.
However, it is undesirable when preparing an article using a glue bond to
use a material that gives rise to toxic volatiles or that may be toxic in itself.
It is undesirable to have fl~mm~ble solvents present, and in gluing paper
l~min~t~os together that have been ch~mi(~lly modified or re~in~tt-(i, solvent
or water carriers cannot be accommodated in the adhesive composition,
because it is not possible for them subsequently to escape from the
composite.
European Patent 0390536 to Plascon Technologies (Pty) T .imitt~cl teaches the
CA 0224~88~ 1998-08-13
WO 97/32074 PCTIGB97/00440
irnpregnation of spirally wound paper tubing with a thermosetting resin in
an extending liquid. However, it should be noted that the impregnation of
a pre-formed pipe has a number of disadvantages. In the first case. very
little mass of pipe can be fitted into a vacuum/pressure/vacuum
impregnation cylinder and therefore efficiencies are low; the adhesive used
in the pre-winding of the pipe may be inferior for the end purpose, such as
the water based polyvinyl ~-~et~t~s and alkali silicates; and the pre-applied
adhesive mitig~tt~S against the through penetration of the impregnating
composition. The advantage of pre-impregnating narrow reels or biscuits
of paper or other lignocellulosic material is that the volume of the tr~tm~nt
cylinder can be utilised to its m~xim-lnn theoretical extent, and the
subsequent winding of the pre-impregn~tecl material in which the resin may
be in the "B Stage" - in other words, not n~cess~rily fully polymerised,
allows the speci~ic~tion of the hot melt adhesive to be devoid of solvents or
water that could be trapped in the tube composite, and the resins chosen
may cross link with the resin in the paper, forming an intim~t~ bond and a
cohesive whole to the composite.
US Patent No 4 505 778 teaches a paper composition comprising cellulosic
fibres rh~rnic~lly bonded with polyisocyanate sizing resins consisting
essentially of a blend of an aromatic polyisocyanate resin cont~ining from
1 to 10% by weight of an isocyanate t~rmin~tto~l prepolymer having the
forrnula RO(CH2C~IR'O)nCONHX whelcill R is selected from an alkyl
group cont~ining one to four carbon atoms and a polyester con-lenc~tion of
a diacid and a polyether glycol, R' is selected from H or CH3, n is an
integer ranging from 5 to 120, and X is a residue of an alo~ ic di or
polyisocyan~te, and which contains at least one free isocyanate group. The
polyisocyanate composition is applied as an aqueous emulsion tO the
ceilnlo~ic fibres which are then formed into paper. Alternatively, an
CA 0224~885 1998-08-13
aqueous emulsion of the polyisocyanate may be applied to the surface of the
paper af~er its forrnation. It is to be emphasized that the polyisocyanate is
purely used as a sizing resin and that it is always applied in an aqueous
solvent or emulsion.
US-A-5,~80,-097 discloses a laminated product which has an organic polymer
layer on at least one surface of a substrate of cellulosic material impregnated with
polyisocyanate. The isocyanate resin may be dissolved in a suitable miscible
or~anic solvent, preferably one such as propylene carbonate having a high boiling
point and a low flammability and toxicity.
US-A-5-008~359 discloses a method of making a cellulose based polymericmaterial and the products of the invention. A cellulosic substrate is impregnated
with an essentially uncatalysed polyfunctional isocyanate and pressed at elevated
temperature and pressure. The polyisocyanate may be impregnated into the
cellulosic material in either neat form or in solution with a solvent such as
acetone
US-A-3~666.593 teaches a process for making a paper-overlaid panel which
comprises providin . a substrate and at least one layer of kraft paper, applying an
or~anic polyisocyanate resin to the paper, and pressing the layer of paper against
the substrate under closed conditions, whereby the formed carbon dioxide will beentrapped causing internal pressure to impregnate the resin into the paper and into
the substrate and to bond the paper to the substrate. The polyisocyanate resin may
be diluted witn a solvent.
There is therefore a need for products made from lignocellulosic sheets in
which the sheets have first been chemically modified and resinated and
which are then laminated subsequently.
'4A'1E~IGLD ' l
- CA 0224~88~ 1998-08-13
Sl,l\~II\IARY OF THE ~ENTION
According to a first aspect of the invention there is provided a method of
preparing a sheet of a lignocellulosic material for the manufacture of a
finished product, which method includes the steps of:
(a) impregna~ing the sheet of the lignocellulosic material with an
impregnating composition comprising:
(i) a composition for the chemical modification of
the lignocellulosic material comprising a
dicarboxylic anhydride or a tricarboxylic
anhydride selected from the group consisting of
maleic anhydride, phthalic anhydride, succinic
anhydride, tetrahydrophthalic anhydride and
trimellitic anhydride dissolved in a suitable
non-aqueous solvent selected from
dichloromethane and liquid carbondioxide; and
(ii) a composition for resinating the lignocellulosic
material comprising an isocyanate
therrnosetting resin dissolved in a suitable non-
aqueous solvent selected from dichloromethane
and liquid carbondioxide;
(b) removing from the impregnated lignocellulosic material any
excess of the impregnating composition; and
(c) removing the non-aqueous solvent or solvents.
AMEN~ r !- -
CA 0224~88~ 1998-08-13
The sheet of a lignocellulosic material may be for example a sheet of paper,
a sheet of a composite lignocellulosic material, e.g chipboard or fibreboard,
or a shee~ of timber.
The suitable non-aqueous solvent in the chemical modification composition
and the suitable non-aqueous solvent in the resination composition may be
the same or may be different but compatible.
In step (a) the impregnation may be carried out in a suitable
vacuum/pressure/vacuum impregnation apparatus or pressure apparatus.
Alterna~ively. the impregnation may be carried by irrigating a moving web
of the lignocellulosic ma~erial or by immersing the lignocellulosic material
in the impregnating composition, to cause the penetration of the
impregnating composition throughout the lignocellulosic material.
The impregnating composition preferably contains from 0,25 % to 30 %
inclusive, more preferably from 0.25% to 15% inclusive of the anhydride
by weight of the impregnating composition.
As the lignocellulosic material preferably takes up from 50% to 150%
inclusive, more prefcrably from 90% to 110% inclusive of the impregnating
~.~fiE~ ..,v~,.
CA 0224~88~ 1998-08-13
WO 97132074 PCT/GB97100440
composition by weight of the lignocellulosic material before removal of the
solvent, after removal of the solvent the amount of the anhydride in the
lignocellulosic material thus ranges from 0,125 % to 45 % inclnsive by
weight of the lignocellulosic material.
The impregnating composition also includes an isocyanate thermosetting
resin dissolved in a suitable non-aqueous solvent. ~he solvent for the
isocyanate resin is preferably the same as the solvent for the impregnating
composition, which is preferably dichloromethane or liquid carbon dioxide,
but may be a different compatible solvent.
The impregnating composition preferably contains the isocyanate
thermosetting resin in an amount of from 1,5% to 60% inclusive of ~he
isocyanate thermosetting resin by weight of the impregnating composition.
In the impregn~ting composition there may also be incorporated otner
additives such as for example a fire retardant or fire inhibitor, a
bacteriostat, a fungicide, an insecticide, an ultraviolet light absorber or
stabiliser, an anti oxidant, a dye, a hydrophobic agent such as a silicone or
slloxane, or a wax.
In the i~ c~nating composition there may also be incorporated materialsacting as both hydrophobic agents and synergistic binders, chosen from the
group comprising of bitumen, asphalt, coal tar and pitch, and which may
be incorporated in an arnount of from S to 40 % by weight of the
impregn~ting composition.
Step (b) is only carried out if there is any excess of the impregnatingcomposition.
CA 0224~88~ 1998-08-13
WO 97/32~)74 PCT/GB97/00440
According to a second aspect of the invention there is provided a method
of forrning an article from a first sheet of a lignocellulosic material treated
according to steps (a) to (c) above, and a second sheet of a lignocellulosic
material optionally treated according to steps (a) to (c) above, which method
includes the steps of:
(1) locating an adhesive material between the first and second sheets
to adhere the first and second sheets tO each other to ~orm a
layered product; and
(2) subjecting the product of step (1) to conditions suitable to set the
adhesive material to form the article.
According to a third aspect of the invention there is provided a method of
forrning an article from a first sheet of a lignocellulosic material and a
second sheet of a lignocellulosic material both treated according to steps (a)
to (c) above, and a third sheet of a lignocellulosic material optionally treatedaccording to steps (a) to (c) above and sandwiched between the ~Irst and
second sheets, which method inr.1~!drs the steps of:
(1) locating an adhesive material between the first and second sheets
and between the second and third sheets to adhere the first and
second sheets and the second and third sheets to one another to
form a layered product; and
(2) subjecting the product of step (1) to conditions suitable to set the
adhesive m~trri~l to form the article.
One or more fourth sheets of a lignocellulosic material, optionally treated
according to steps (a) to (c) above, may be interposed between either of the
f~rst and second sheets or the second and third sheets, with an adhesive
material being located between each fourth sheet and the adjacent first,
second or third sheet to adhere the fourth sheet or sheets to the first, second
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
or third sheets to form the layered product.
The method of the second aspect of the invention and the method of the
third aspect of the invention may include a further step:
(3) after step (1) and before step (2) passing the layered product
over a former to form the layered product into the shape of the
a;ticle.
In this case the article may be for example a spirally wound tube formed on
a suitable mandrel, or an angle or a channel or a cone section, formed on
a suitably shaped former.
Alternatively, the method of t'ne second aspect of the invention and the
method of the third aspect of the invention may include a further step:
(4) prior to or ~imlllt~n~ously with step (1) shaping one or more of
the sheets of lignocellulosic material to a desired shape, for
example corrugating one or more of the sheets of lignocellulosic
material.
The adhesive material may be a hot melt adhesive applied through a hot
melt a&esive applicator.
~lt(~rn~tively, the adhesive m~t~ri~l may be a film of a thermoplastics
material which is interlayered between two ~ r~ont sheets of the
lignocellulosic m~t~ h Heating of the film of thermoplastics material
causes the film to melt and thus to adhere adjacent sheets of the
lignocellulosic material to each other.
The film of thermoplastics material has preferably either been modified by
irradiation or by fluorination and may be for example a film of
CA 0224~88~ 1998-08-13
WO 97/32074 rCT/GB97/00440
polypropylene or polyethylene or polyvinyl chloride.
Further alternatively, the adhesive material may be a two-component
thermosetting compound in liquid form, which is applied between two
adjacent sheets of the lignocellulosic material, and is subsequently set tO
adhere the sheets to each other.
Further alternatively, the adhesive material may be a combination of anisocyanate prepolymer and a polyol applied between two adjacent sheets of
the lignoce}lulosic material to produce a urethane foam between tWO
adjacent sheets of lignocellulosic material, and to adhere the two a~ e~nt
sheets to each other to form the layered product.
Further ~It~m~tively, the adhesive material may be a combination of a
phenol form~l~lellyde resole resin, a catalyst for the resin, a blowing agent
and an emulsifying agent, applied between two adjacent sheets of the
lignocellulosic material to produce a phenolic foarn between the two
adjacent sheets of lignocellulosic mat.erial, and to adhere the two ~rent
sheets of the lignocellulosic m~t~ri~l to each other to forrn the layered
product.
In step (2) the conditions suitable to set the adhesive material to forrn the
article will depend upon the nature of the adhesive material.
For example, when the adhesive material is a hot melt adhesive, the product
of step (I) will generally be subjected to a temperature of from 60~C to
140~C inclusive for an d~Lopliate length of time, typically up to four
hours, in order to ensure that any resin present in the product is
polymerised andlor crr~s.slink~-
~
CA 0224~88~ 1998-08-13
WO 97/3207~ PCT/GB97/00440
Alternatively, when the adhesive material is a film of a thermoplasticsmaterial, the conditions suitable to set the adhesive material comprise
cooling after heating of the film of thermoplastics material to cause the film
to melt and thus to adhere adiacent sheets of the lignocellulosic material to
each other. Typical heating temperatures are in the range of 180 to 220~C.
.
Further alternatively, when the adhesive material is a two-component
thermosetting compound in liquid form, the conditions in step (2) may be
the application of heat or the like.
Further alternatively, when the adhesive material is a urethane foam or a
phenolic foam, the conditions may be conditions suitable to set the urethane
foam or the phenolic foam to form the article.
According to a fourth aspect of the invention there is provided a method of
ma'King an article from a sheet of a lignocellulosic material treated
according to steps (a) to (c) above, which method includes the steps of:
(A) before or after step (c) passing the sheet through a former to
shape the sheet into the shape of the article;
(B) then if nPce~ry, carrying out step (c) above, i.e. removing the
suitable non-aqueous solvent or solvents; and
(C) then subjecting the product of step (B) to elevated tempeldlu,es
to polymerise and/or cross-link the resin or resins in the product
to form the article.
In step (A) the former may be for example a roller such as a corrugator.
In step (C) the product of step (B) will generally be subjected to a
temperature of from 60~C to 140~C inclusive for an a~p~ .iate length of
CA 02245885 l998-08-l3
WO 97/32074 PCT/GB97/00440
12
time, typically up to four hours, in order to ensure that any resin present in
the product is polymerised and/or cross~ ked.
DI~SCRIPI'ION OF EMBODIMENTS
The first aspect of the invention is a method of preparing a sheet of alignocellulosic material for the m~n7lf~rt~lre of a finished product.
Lignocel}ulosic material refers to any plant material em~n~ring from tne
photosynthetic phenomenon. This inrl~es paper, linen, cotton cloth,
woven hesci~n, and the like.
Thus, the sheet of a lignocellulosic material may be for example a sheet of
paper, a sheet of a composite iign-cellulosic material, e.g chipboard or
fibreboard, or a sheet of timber e.g a pee}ed, sliced or sawn thin section of
timber.
In the first aspect of the invention, the lignocellulosic m~t~ri~l is ch-o,nir~lly
motlifi~cl by impregn~tinp: the lignrcellulosic material with an impregnating
composition comprising a dicarboxylic anhydride such as maleic anhydride,
phthalic anhydride, succinic anhydride, or tetrahydrophthalic anhydride, or
a tricarboxylic anhydride such as trimellitic annydride, dissolved in a
suitable solvent.
The choice of solvent is ~lirt~t~fl by its suitability including toxicity, ease of
h~n-lling, boiling point and evaporative rate, which in turn affect its ease of
recovery from the lignocellulosic material after impregnation, its inertness
and therefore absence of i~ feLG,lce chrmir~lly, fl~mm~bility and danger
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
of explosion, its solvency thereby propag~ting the infusion and intim~t~
wetting of the cellular tissue of the lignocellulosic material, and finally its
ease of recovery e.g by absorption in activated carbon followed by steam
purging and tii~till~tion, or condensation and refrigeration or membrane or
sieve technologies or opt;onally, in the case of liquid carbon dioxide,
allowing escape to the atmosphere. Examples of suitable solvents are
methyl acetate, ethyl acetate, methylethyl }cetone, benzene, trichloroethylene
and dichlorom~th~nP. Dichloromethane is the preferred solvent, because it
is non fl~mm~hle, has a boiling point of approximate'ly 39~ Centigrade and
is relatively inert, and meets the other requirements of the process. In
addition dichlorometnane has the propensity to absorb water as a solute
forming a g8 % azeotrope thereby delldLu~ g the lignocellulosic material and
further proF~g~tin~ the latency of the isocyanates which react with hydroxyl
cont~ining compounds, notably water, to produce urethanes. The high
evaporative rate of dichloromethane also propagates the more rapid
evaporation of residual water.
Another suitable solvent is liquid carbon dioxide
Liquid carbon dioxide is a ~.u~el~liLical fluid solvent mzint~in~l at a
L~lllpeldL~ , of the order of -4~~C, and a ~lcs~ùle of 18 atmospheres.
It is often a waste product from other processes, is non-polluting, is
inexpensive, and meets the other requirements of the non-aqueous solvent.
In order to remove the carbon dioxide solvent from the lignocellulosic
material, ~l~s~.ule is gradually released after the removal of the excess
impregnating composition, and the carbon dioxide is released to the
atmosphere, or recaptured for reuse.
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97100440
When the solvent is removed, the residual carboxylic acid groups have a
dielectric loss factor such that the modified lignocellulosic material is able
to conduct electricity, thereby s-lct~ining an electrostatic field allowing the
sheet of lignocellulosic material to be electrosr~tir~lly powder coated.
The reaction between the anhydride and the lignocellulosic material at
elevated tempt:ld~u,~s in the absence of solvents is an esterif~cation reaction
yielding, as an example, lignocellulosic m~lP~P or phth~l~tP or succinate
with a residue of water. The anhydrides may be ~ ,se~lLed as follows:
CH2 CO HC-CO ~
O O /0
CM2 CO HC-Cl ~/
Succinic Maleic Phthalic
anhydride anhydride anhydride
Other anhydrides such as propionic and butyric anhydride may be esterified
to wood or other lign-cellulosic material. The result of the reaction is
effectively a lignocellulosic polyester, because in the cases of maleic
anhydride, phthalic anhydride and succinic anhydride, a polymerisation
takes place r~ Tting in binding L~ el~ies when the impregnated and dried
material is subjected to heat and ~7les~ , thereby complimenting the
function of the resin used in t_is invention. In the case of maleic
anhydride, the double bond opens allowing cross linking and in the case of
ph~alic anhydride, the ring opens initially, followed by polymerisation.
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
A further notable function of the anhydrides is that they scavenge any
available hydroxyl groups or water, thereby further promoting the latency
of the isocyanates in the impregnating liquor by preventing the reaction of
these isocyanates with hydroxyl groups which would give rise to the
- formation of urethane polymers, and also den~h-ring the lignocellulosic
material during the impregnation process.
A still further function of the anhydrides is that after contact with the
lignocellulosic material and the removal of the solvent, the residual
carboxylic acid groups catalyse the polymerisation of the isocyanates.
The impregnating composition may also include a long chain carboxylic acid
such as a C10 to CS0 monocarboxylic acid, preferably stearic acid,
dissolved in a suitable solvent, such as methyl acetate, ethyl acetate,
methylethyl ketone, benzene, trichloroethylene and dichloromethane.
A number of carboxylic acids may be esterified to wood or other
lignocellulosic materials in the absence of solvents at elevated L~ll.L,eliltures.
Apart from the esterification potential, the long chain carboxylic acids with
a relatively small polar group ~tt~çh~cl, tend to orientate with the polar
group to the hydroxyl groups in the polymers of the lignocellulosic cell
walls, with the long carbon chain ori~nt:~te~l toward water ingress, thereby
irnposing hydrophobicity.
The impregn~ting composition preferably contains from 0,25% to 30%
inclusive, more preferably from 0,25% to 15% inclusive of the anhydride
by weight of the impregnating composition.
The impregnating composition also contains an isocyanate thermosetting
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97/00440
resin dissolved in a suitable non-aqueous solvent.
Isocyanates are compounds cont~ ining the group - N = C = O and are
characterised by the general follnula:
R(NCO)~.
wherein x is variable and denotes the number of NCO groups, and R
denotes a suitable group.
Exarnples of organic isocyanates include aromatic isocyanates such as m-
and p-phenylenediisocyanate, toluene-2,4- and 2,6-diisocyanates,
diphenylmethane-4, 4 ' diisocyanate, diphenylmethane-2 ,4-diisocyanate,
chlorophenylene-2,4-diisocyanate, diphenylene-4,4'-diisocyanate,
4,4'diisocyanate-3,3'dimethyldiphenyl, 3-methyldiphenylmethane4,4'-
diisocyanate and diphenyletherdiisocyanate and 2,4,6-triisocyanatotoluene
and 2,4,4'-triisocyanatodiphenylether. There may be present mixtures of
isocyanates for example a mixture of toluene diisocyanate isomer such as
the comrnercially available l~Pi~Lul~s of 2,4- and 2,6-isomers and also the
ix lule of di and higher polyisocyates produced by phosgenation of
aniIinefforrn~kltohyde con-l~nc~t~s. Such mixtures are well-known in the art
and include the crude phosgenation products cont~ining lll~x.Lulc:S of
methylene bridged polyphenylpolyisocyanates including diisocyanate,
triisocyanate and higher polyisocyanal~:s together with any phosgenation by-
products.
Preferred compositions are those wherein the isocyanate is an aromatic
diisocyanate or polyisocyanate of higher functionality in particular crude
mixtures of methylene bridged polyphenylpolyiso~;y~llates cont~ining
diisocyanate, triisocyanate and higher fi~n-~.tiQn~lity polyisocyanates. The
methylene bridged polyphenylpolyisocyallates are well-known in the art and
-
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97/1)0440
are sometimf s referred to as polymeric methylene bridged
polyphenyldiisocyanate (MDI) having an isocyanate functionality ranging
from 2,5-3 and other products somelimes referred to as crude MDI having
higher functionality. They are prepared by phosgenation of corresponding
mixtures of polyamines obtained by condensation of aniline and
formaldehyde.
Specific examples of suitable isocyanates are those having an (NCO) content
p~ ge preferably excee~linP 20%, more preferably excee~iinP 25%.
These isocyanates promote latency or reduced reactivity because of the high
number of NCO groups, and provide the m~ximl7m capacity for hydroxyl
bonding. Examples are De~m~ r VKS or Desm~ r VK by Bayer, which
are solvent free nlL~Lul~;s of aromatic polyisocyanates such as diphenyl
m,oth~n~-4,4 di-isocyanate and polymeric matter. These and similar are
among those referred to as MDIs in the industry. A further description
used is a di-isocyanate-diphenyl meth~n~o, further examples being Suprasec
DNR-5005, which is a polymeric MDI, or Suprasec 2020 which is a
monomeric MDI with available NCO percentages of 30,7% and 29% and
which are polymeric MDI with standard functionality and monomeric MDI
respectively. The Suprasec resins are supplied by ICI. A further example
of a crude MDI is Voronate M 229 by Dow Chemir~l Co~ ally.
Further suitable di-isocyanates are the toluene di-isocyanates with the
alternative names tolylene di-isocyanate or toluylene di-isocyanate with the
abbreviation TDI, such as De~m~ lr ~75 by Bayer.
A further example of the principle of wood esterification is the use of ethyl
- isocyanate which reacts with hydroxyl groups to form ethyl carbamate
(ure~lalle) according to the formula:
-
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
C2H5NCO ~ H.O ~ NH~COOC~H5
The isocyanate resins are fully soluble in dicnlorometnane and react with the
hydroxyl groups on the cellulose and hemi cellulose molecules of the
lignocellulosic material to form a wood ester. In this way they form a
rhtomi~ ~l bond adhesion ratner than a cohesive adhesion. They are therefore
effec~ive in contributing not only to a reduction in water sensitivity but also
to superior binding. In addition, tney scavenge any carboxyl groups which
are residual from the carboxylic acid derived from the anhydride. The
isocyanate resins lend themselves to synergistic binding of composites and
to the propagation of superior ~lecl~ r~l properties by a two way linkage
with the residue of the anhydrides and tne hydroxyl groups on the
lignocellulosic material itself.
'rhe solvent may be any suitable solvent and is preferably dichlorom~-th~nP
or liquid carbon dioxide, the isocyanate thermosetting resin being dissolved
in the solvent at a concentration of from 1,5% to 60% by weight, more
preferably at a concentration of from 2,5 to 50 % by weight of the
impregnating composition.
After the tre~tment of the lignocellulosic material with the illlp~egll;.~
composition and after removal of excess impregnating composition, if any,
tne solvent or solvents are recovered for reuse. The isocyanate
t'nermosetting resin is left on and in the lignocellulosic material eitner in a
latent condition or more generally in a partially polymerised condition as a
result of the temperatures reached during and after the solvent removal
stage, ready for subsequent complete polymerisation when sub~ected to the
app,opliate conditions of heat and optionally pressure.
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
19
This may occur, for exarnple, in step (~) of the methods which form the
second and third aspects of the invention.
The lignocellulosic material may be impregnated with the impregnating
composition in any suitable manner. An example o~ one method of
impregnation is set out below.
The lignocellulosic sheet material ~in the form of paper), cut into narrow
rolls of from 40rnm to 160mm in width and fli~m~?ters of up to 11/2 metres,
may be impregnated by placing them in an impregnation cylinder or
autoclave. The cylinder is then sealed and subjected to a vacuum. This
e~h~ tc all air from the lignocellulosic material and from between the
windings in the rolls. The vacuum line is isolated and the impregnating
liquor is c~cc~ rl into the cylinder until full. Pressure is now exerted
either hydraulically or p..~ul..,.~ lly to ensure through irnpregnation
ullirolll'ly throughout the mass of the material. The cylinder is drained and
the charge is subjected to a post vacuum in order to remove all excess
impregn~ting li~uor which is also returned to its receptacle. The charge is
now subjected to intlucerl heat, in order rapidly to evaporate the solvent.
The heat induction may be by heating coils around the cylinder or
ely by the introduction of hot air circ TI~3ting around the charge
serving both to convey heat and to carry the rapidly evaporating solvent, or
by microwave or by any combination. The solvent laden air passes from
the cylinder, over con~l~on~ti-)n coils onto which the solvent condenses and
thence again past the heating elements, and back into the cylinder on a
closed loop. Mer1~ni~l colll~l~,s~ion may also be used to further facilitate
con-l~n~tion. As the process of the recovery of solvents nears completion,
the residual air is then preferably passed through activated carbon or
through a membrane in order to "polish" the emitted air to conform to
CA 0224~88~ 1998-08-13
WO 97/32074 PCTIGB97/00440
emission standards.
In the case of carbon dioxide, controlled pressure release is followed by the
heating of the charge to induce completion of the chemical reaction.
Where the lignocellulosic sheet material is to be impregnated and then
shaped before the recovery of the solvent, it may optionally be immersed
in the impregnating composition, then withdrawn to allow drainage,
followed by shaping, followed by solvent recovery, followed by heating, to
induce resin polymerisation or cross-linl~ing as the case may be.
In step (a) there may also be incorporated in the impregn~ting composition
other additives such as for example a fire l~LaldallL such as
hr~rlllorophthalic anhydride, or a fire inhibitor, a bacteriostat, a fungicide,
an insecticide, an ultraviolet light stabiliser or absorber, an anti-oxidant, a
hydrophobic agent such as a silicone or siloxane, a carboxylic acid or an oil
or a dye.
In particular the impregnating composition may also contain a light fast dye
in an amount of from 0,005% to 0,5% inclusive of the light fast dye by
weight of the impregn~t;ng composition.
A dye is generally used to colour light coloured soft woods such as forexample a light coloured col~rc:lvus wood such as pine. Preferably, the dye
has a light f~tn~s~ of 6 or greater in the light stability range of from O to
8. Examples of suitable dyes are those by Sandoz sold under the brand
name Clariant Savinyl.
In step (a) there may also be included in the impregnating composition other
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
additives for the purpose of imposing hydrophobic proper~ies as well as
synergistic binding, chosen from the group comprising bitumen, asphalt,
coal tar and pitch. The bitumen is preferably one with a softening
temperature in excess of 90~C and a penetration index of 10 or lower.
These biLulllells are preferably those that have been blown and may be
modified with styrene butadiene styrene block copolymer and the like, to
improve their behaviour in weather exposure.
The second aspect of the invention is a method of forming an article from
a first sheet of a lignocellulosic material treated according to steps (a) to (c)
above, and a second sheet of a lignocellulosic material optionally treated
according to steps (a) to (c) above, which rnethod includes the steps of
locating an adhesive material between the first and second sheets to adhere
the first and second sheets to each other to form a layered product, and
subjecting the product to conditions suitable to set the adhesive material to
form the article.
The third aspect of the invention is a method of forming an article from a
first sheet and a second sheet of a lignocellulosic material both treated
according to steps (a) to (c~ above, and a third sheet of a lignocellulosic
material optionally treated according to steps (a) to (c) above, and
sandwiched between the first and second sheets, which method includes the
steps of locating an adhesive material between the first and second sheets
and between the second and third sheets to adhere the first and second
sheets and the second and third sheets to one another to form a layered
product, and subjecting the product to conditions suitable to set the adhesive
material to form the article.
In addition, one or more fourth sheets of a lignocellulosic material
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
optionally treated according to steps ~a~ to ~c) above may be interposed
between the first and second sheets or the second and third sheets in the
methods described above.
The method of the second aspect of the invention and the method of the
third aspect of the invention may include a further step:
(3) after step (1~ and before step (2) passing the layered product
over a former to form the layered product into the shape of the
article
In this case the article may be for example a spirally wound tube formed on
a suitable mandrel7 or an angle or a channel or a cone section, formed on
a suitably shaped former.
.AltPrn~fively, the method of the second aspect of the invention and the
method of the third aspect of the invention may include a further step:
(4) prior to or .simlllt~n~ously with step (1) shaping one or more of
the sheets of lignocellulosic material to a desired shape, for
example corrugating one or more of the sheets of lignocellulosic
material.
~;or example, one or more of the sheets of lignocellulosic material, treated
according to steps (a) to (c) of the method of the first aspect of the
invention may be colTugated before being sub3ected to the method of the
second aspect of the invention or the method of the third aspect of the
i.lve~ on.
In addition, corrugation of one or more of the sheets of lignocellulosic
material may occur simll~t~neously with the application of the adhesive
CA 0224~88~ 1998-08-13
WO 97132074 PCT/GB97/~)0440
material between the various sheets of lignocellulosic material.
The adhesive material may be a hot melt adhesive applied through a hot
melt adhesive applicator in the form of a ribbon or film. Generally, the hot
melt adhesive is applied at temperatures of the order of 180 ~ C . The
adhesive may consist of a hard resin with, for example, an ethylene vinyl
acetate copolymer and a hard wax. An example of a hot melt adhesive is
Henkel Technomelt TU 2210 with a melt viscosity of 600 centipoise at
160~C.
An example of the use of a hot melt adhesive for the production of spirally
wound tubing is given below and includes the steps of:
(i) placing two or more reels or "biscuits" of treated lignocellulosic
material on carriers, winding the sheet m~t~riz~l from the reels
through a hot melt adhesive applicator m~-hin~, whereby one
surface of the lignocellulosic material has applied to it a ribbon
or a film of hot melt adhesive. The hot melt a&esive is applied
at telllp~ldLul.,s of the order of 150~C. The adhesive may
consist of a hard resin with, for example, an ethylene vinyl
acetate copolymer and a hard wax. Application rate is a film
weight of 20 to 70g per m~ of lamina surface;
(ii) winding the treated strips of lignocellulosic material onto a
mandrel whilst being pressed by high tensile moving belts which
bring Cur-ces~ive plys into intim~tP contact with each other at
high pressure before the hot melt adhesive solidifies by cooling,
to form a spirally wound tube, the tube having ply numbers of
from 3 to 40 or more, and being wound continuously;
(iii) finally cutting the tube formed to whatever d~loyliate length is
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97/00440
24
required;
(iv) applying to the formed tube, coatings or liners chosen from the
group comprising liquid spray applied coatings, centrifically casl
lining, extruded lining and resin modified fibre windings, or
over placement of thin walled metal, plaster or inorganic
material tubing or liner placement of such material or both.
.Altern~3fively, the adhesive material may be a film of a thermoplastics
material which is interlayered between two adjacent sheets of the
lignocelluIosic material. Heating of the film of thermoplastics material
causes the film to melt and thus to adhere adjacent sheets of the
lignocellulosic material together.
The film of thermoplastics material has preferably eit_er been modified by
irr~ tion or by fluorination and is preferably a polypropylene film in the
latter case (fluorination) or a polyethylene film in the former case
(irradiation).
In this regard, the poly~roE,ylene film may have a weight in the region of
50g/m~, which film has high team7~ ,Lll and puncture r~ t~nre~ excellent
rçci~t~nre to }ow telllpelaLulc:s, is dimen~ion~lly stable under varying
atmospheric hllmi~liti~, and is sealable by heat. The film also has low
vapour permeability, is water repellant, is resistant to oils or greases, is
physiologically h~rmles.~, is neutral in odour and taste, and is ~,3i.7~ to
acids and aL~alis and to tropical conditions. It also has high merh~nic~l
strengths and as a part of the reslllting product contributes to much
i ~ u~lovt:d merh~nic~l properties .
An example of a suitable polypropylene film is Trespaphan GND by
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
~Ioechst.
The film may also be l~min~t~l to the sheets of lignocellulosic material
using one or two component adhesives which are solvent free. Seal
temperature is typically about 140~C. Typical suitable film thicknesses are
from 20 microns to 150 microns.
As a further alternative, the film of a thermoplastics material may be a ~llm
of polyvinyl chloride, of typical thickn~?s~ of 50 to 200 microns and which
has optionally been modified by irradiation or fluorination to propagate
adhesion.
The film of a thermoplastics material is preferably modified by irradiation
or fluorination in order to propagate cross linking and adhesion to the
lignocellulosic material.
In the case of irradiation, the thickn.o~.~ of the film may be between S and
3 000 microns. The thermoplastic film or sheet is made through the
conversion of a suitable thermoplastic polymeric starting material, modified
with ionising radiation prior to conversion to the film or sheet. The
ionising radiation employed can be produced either by a suitable radio
active isotope, such as cobalt - 60, or a suitable electron beam accelerator
which gelleldtes ellelgeLic electrons with an energy of 50 keV to 10 MeV.
The absorbed radiation dose applied to the thermoplastic polymeric starting
material may be of the order of 4 to 150 kGy, and conventional electron
beam accelerators or gamma irradiators can be employed for this purpose.
In the case of fluorination, the pre made film is fluorinated with fluorine gas
preferably diluted with either oxygen or nitrogen or other gas, up to the
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97/00440
26
level of 99%. Fluorine is a very strong oxidising agent and the process of
fluorination induces the bonding of reactive groups to the polymer which in
turn induces adhesion.
In both cases, the morlific~tion of the thermoplastic material irnproves the
properties of the interlayer film for the purposes of the invention.
After the film has been located between two ~ ce~t sheets of the
lignocellulosic material to form the layered product. the layered product
may be passed over a former at which point the film of the thermoplastics
material is heated by for example radiofrequency or infrared or microwave
heating, and thus melts or softens sufficiently to adhere the two ~ ent
sheets to each other to form the layered product. In this case, the
conditions in step (2) will be the subseq~ltont cooling of the product.
In an ~ re, the film of the tnermoplastics material may be flamed just
before making contact with the lignocellulosic material, again to adhere two
adjacent sheets of the lignocellulosic m~t~r;~l to each other.
The use of a film of a therrnoplastics material as an adhesive m~t~ri~l has
a number of advantages, in~ in~ the fact that such a film is impervious to
water7 and it imposes a ~nghnpss and rP~i~iPnfe on the product thereby
imposing the advantages of a polymer film on the advantages of a resin~t.~d
lignocellulosic material. For example, rec-ict~n~e to hail damage or other
impact is improved.
As another ~ItPrn~tive7 the adhesive material in step (1) may be a two-component thermosetting compound in liquid form which may be applied
for example tnrough suitable mixer application heads. In this case, the
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97/00440
conditions in step (2) may be the application of heat or the like.
An example is 25 % Suprasec 5005 by ICI with 75 % by weight of a suitable
polyol compound such as 1003 by Industrial Urethanes of South Africa.
Further ~ltrrn~tiveLy, there is applied a combination of an isocyanate
prepolymer and a polyol between each pair of adjacent sheets to form a
u~ alle foam between the ~dj~cent sheets and to adhere the two or more
sheets to one another to forrn a layered product.
The t~,vo components, i.e the isocyanate prepolymer and the polyol may be
mixed and then applied to the sheets by a fixed or traversing spray device.
Thereafter the adjacent sheets are l~min~t~-l to each other and the layered
product is then optionally passed over or between a former to form the
layered product into the shape of the article, whereafter the product is
subjected to conditions suitable to set the urethane foam to form the article.
For example, the combination may be ~lmini.~trred to a moving sheet of
paper in an automatic l~ i.".l;~g line by head mixing the components in a
fixed or traversing spray device, such that the generation of the interlayer
foam is very rapidly achieved, foaming between the sheets of paper, which
then traverse between calibrating or forming surfaces to deterrnine the final
thickness and/or shape of the product, during which time the urethane foam
adheres to the sheets of paper such that on exiting the calibrating or forming
surfaces, the product is of a ul~lro.,ll thi~knr5.c and a stable con.~ trnry,
,. rçci.ctinsg warping, and which can then be cut to a~lo~liate length and/or
width. An example of such a m~rhinr is an isobaric double belt continuous
press by Hymmen Tnt.orn~tional of Bielefeld, Germany
CA 0224=.88=. 1998-08-13
W O 97/32074 PCT/GB97/00440
28
The isocyanate prepolymer is preferably an MDI, being an isocyanate
compound cont~ining the group-N=C=O, as described above.
The polyol may be a hydroxyl terrnin~fe-l polyetner or a hydroxyl
terrnin~t.ocl polyester. The polyethers are typically made by the addition of
~Ik~lin~ oxide, e.g. propylene oxide to alcohol or amines which are usually
called starters or initiators. The polymerisation of the ~ik~linP oxide occurs
either with basic or acid catalysis, usually with basic catalysis. In order to
achieve the correct reactivities, the polyethers or polyesters contain a
suitable mixture of secondary hydroxyl end groups and pl~llaly hydroxyl
end groups.
A typical combination for use in the method of the invention is 50% of
Suprasec 5005 by ICI, mixed with 50 % of polyol 826 by Industrial
Urethanes of South Africa. Typical de~siti~s of the foam produced by this
combhlatioll are from 35-lSOkg/m3, more preferably from 40 to 90kg/m3.
An example is a ceiling board co~ li'.hlg 250g/m2 high buL~ chip recycled
paper on either side of a foam core. The paper is modified with 15%
Suprasec 5005 by ICI and 6% maleic anhydride on the weight of the paper
and has a nominal thickn~os5 of 0,5mm per sheet with an interlayer of 6mm
of foam between the sheets, this foam having a density of 40g/mm
thickn~s~/m2 The MDI foam may optionally be based upon Suprasec 5005
by ICI 50% and Polyol 826 by Industrial Urethanes, South Africa, or a
phenolic closed cell foam, or Cellobond K in situ pourable by l3P Ch~rnic~ls
Ltd., UK.
The lllcLhalle foarn serves not only to separate the sheets of lignocellulosic
material but also securely to bond the sheets to one another. This bond may
CA 02245885 1998-08-13
WO 97/32074 PCT/GB97/00440
be further propagated by the cross-linking of the urethane foam with free
carboxylic acid groups and NCO groups in the modified lignocellulosic
material.
In another ~lr~rn~tive a combination comprising a phenol forrnaldehyde
resole resin, a catalyst for the resin, a blowing agent and an emulsifying
agent, is applied between each pair of adjacent sheets to form a phenolic
foam between the ~ renf sheets and to adhere the two or more sheets to
one another to form a layered product.
The combination of components may be applied to the sheets of
lignocellulosic material as described above.
The components of the composition which produce the phenolic foam
gellelate heat as a function of the commerlrement of conll~n~tion under the
action of the acid catalyst. As this commences, the vaporisation of the
blowing agent takes place and further heat induction may be inllic~t~cl in
order to form the cured foam as quickly as possible.
The advantage of a phenolic foam is that it does not support combustion, it
is rigid, it is dimensionally stable, it is relatively water resi~t~nt
An example of an ap~ L~ phenolic ~oam is Cellobond K by BP
Ch~omi~ Ltd., of the UK. Cellobond in situ is a pourable foam system
used in combination with BP catalysts and suitable flowing agents, which
forms a high quality in~ul~tin~ closed cell foam with exceptional thermal
properties 0,020 Wn~K and excellent fire pluL,el~ies with good adhesion to
the m~dified li~nocellulosic outer lamina.
7r! ~
-- CA 0224~88~ 1998-08-13
Each foam system has its own advantages, but in each case the chemically
modified and resinated lignocellulosic product is light, strong, rigid, stable
and economic to produce.
The conditions in s~ep ~2), suitable to set the adhesive material to form the
article, will generally also be conditions suitable to cause complete
polymerisation of Ihe isocyanate resin in the lignocellulosic material. These
conditions generally include heat and optionally also pressure. For
example ~ the layered product produced in step ( 1 ) may be compressed
and/or he~led in a suitable press at temperatures of between 120~C and
250~C inclusive, preferably in the range of 180~C to 220~C inclusive, and
at pressures of from 1 96-19 61 MPa (2 to 20 kg/cm2) inclusive.
A suitable press is for example a double belt l~min~ting press.
These condi~ions will cause complete polymerisation of the isocyanate resin
in the li~nocellulosic material.
Before the first step of the method of forming an article from two or more
sheets of a lignocellulosic material treated or optionally treated according
to steps (a) to (c) above. there may be applied to one or more surfaces of
the sheets of lignocellulosic material a powder coating.
Alternatively, the product produced by the method of forrning an article as
described above, may have a sheet or sheets of polypropylene or
polyethylene film, which may have been printed, pigmented, coated or
modified by fluorination, adhered to one or more surfaces of the product,
to prevent humidity uptake in use.
~IIEN~)ED StlEET
CA 0224~88~ 1998-08-13
WO 97/32074 PCT/GB97/00440
~urther alternatively, one or more surfaces of the product may have applied
thereto a clear coating. Such a coating may be applied by roller with
intermr~ tr s~n-linsr and ultraviolet light cure. Successive coatings may be
applied until the ~oy~iate degree of build and beauty is imposed.
When the product produced is a llat product, it may be for example a board
for use in the building industry as a flooring board or as a p~nr.lling
board, or as a board used for construction or for the m~m-f~rfllre of
ru~ e or the like.
Examples of such boards include:
(1) a board co~ ,lisillg two sheets of lignocellulosic material with
a foam core between them. The sheets of lignocellulosic
material may be kraft paper treating according to steps (a) to (c)
above, and the foam may be an MDI foam, or a phenolic closed
cell foam.
~2) a board as described in paragraph (1) above, but having two
sheets of lignocellulosic material adhered to each other on either
side of the foam core.
(3) a board Co~ liSil~g 2, 3 or 4 sheets of lignocellulosic material,
one or more of the sheets having been treated to according to
steps (a) to (c) above, the sheets being adhered to one another
with a hot melt a&esive or with a two-component adhesive, or
with a film of a thermoplastics material. Again the sheets of
lignocellulosic material may be paper, e.g kraft paper, or thin
sheets of timber, or a combination thereof.
CA 0224588C7 1998-08-13
WO 97/32074 PCT/GB97/00440
(4) a board as in paragraph (3) above, wherein the lignocellulosic
material is paper and the sheets are corrugated.
(S) a board as in paragraph (4) above, sandwiched between two or
more sheets of lignocellulosic material treated according to steps
(a) to (c) above.
When the product is the shaped product, it may be for example spirally
wound paper tubing, or an angle or channel section or the like.
The third aspect of the invention is a process of making an article from a
sheet of a lignocellulosic material treated by steps (a) to (c) above.
This method includes the step of forming the sheet into a shape such as a
corrugated board either by ~lcs..illg or by rolling, and thereafter, if
n~ce~.S~ry, removing the suitable non-aqueous solvent from tne impregnated
and shaped sheet. Thereafter the irnpregnated and shaped sheet of
lignocellulosic material is subjected to an elevated temperature to induce the
polymerisation andlor cross-linking of tne resin in the article.
