Note: Descriptions are shown in the official language in which they were submitted.
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ADHESIVE SYSTEM
The present invention relates to an adhesive system and a method of producing
a wood based product.
Introduction
Formaldehyde based resins such as phenol-formaldehyde resin, melamine-
formaldehyde resin and urea-formaldehyde resin are widely used as binders in
the
production of wood based products. Examples of such wood based products are
composite products comprising layers glued together such as plywood, laminated
flooring
products and veneered products used in, e.g., furniture. Further examples are
board
products such as particle-, chip- and fibreboards wherein wood chips and/or
fibres,
together with a binder, are pressed to form a board.
Upon curing a formaldehyde based resin, formaldehyde may be released both
during the manufacture of the wood based product and also later during use of
the
product. Formaldehyde emission to indoor air is a major concern since many
years for
health reasons.
There is an increasing demand for formaldehyde-free wood adhesives which
give sufficient bond strength and overall end-product quality making them
suitable as
alternatives to prior art adhesives containing formaldehyde based resins.
Water resistance and bond strength are generally important properties
reflecting
quality for the wood based products. Generally there exist specific quality
parameters
required for meeting an established standard for a specific end-product. For
example, a
particle board needs to meet certain standards in terms of, e.g., internal
bonding,
thickness swelling and water absorption, while a laminated flooring product
needs to
meet certain standards in terms of, e.g., delamination.
Protein based adhesives were used in the production of plywood many decades
ago but were replaced by formaldehyde based resins due to their superior
performance.
Recently, there have been proposed different types of protein-based adhesives.
WO
2005/113700 Al, US 2004/0037906 and US 2004/0089418 disclose adhesive
compositions based on soy protein. A further example of a protein based
adhesive is
disclosed in Li et al., "Soy-based adhesives with 1,3-dichloro-2-propanol as a
curing
agent", Wood and Fiber Science, 36(2), 2004, pp. 186-194. US 2002/0005251
discloses
an adhesive based on soy protein isolate. US 2005/0166796 discloses an
adhesive
composition comprising soy protein isolate. US 6,790,271 and US 2005/0234156
disclose
adhesive compositions comprising soy protein isolate used for forming a
particle board.
Mori et al., "A honeymoon-type adhesive for wood products...", J. of applied
polymer
science, Vol. 91, 2966-2972 (2004) discloses acetoacetylated polyvinyl alcohol
in wood
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adhesives but not in combination with any protein. US 4,350,788, US 4,687,809
and US
2005/0197441 Al disclose the use of acetoacetylated polyvinyl alcohol in wood
adhesives but not in combination with any protein.
There is still a need for an alternative protein based wood adhesive which
gives
high bond strength and high product quality.
Accordingly, the present invention provides a protein based adhesive
composition which gives excellent gluing strength and product quality in terms
of, e.g.
water resistance. Also, a method of producing wood based products is provided.
The invention
The present invention provides an adhesive system comprising a protein and
one or more polymers (P) containing acetoacetoxy groups.
By "adhesive system" is herein meant a combination of two or more components
which forms, and functions as, a wood adhesive. In the term "adhesive" is
herein also
included the term "binder".
The present invention also relates to a method of producing a wood based
product comprising providing an adhesive system, comprising a protein one or
more
polymers (P) containing acetoacetoxy groups onto one or more pieces of a wood-
based
material and joining the pieces with one or more further pieces of a material,
preferably
wood based material.
The weight ratio protein to one or more polymers (P) is suitably from about
1:2 to
about 100:1, preferably from about 1:1 to about 100:1, more preferably from
about 1:1 to
about 20:1, most preferably from about 2:1 to about 10:1.
In one embodiment the adhesive system comprises an adhesive composition.
The adhesive composition suitably comprises from about 1 to about 99 weight %
of protein, preferably from about 3 to about 75 weight %, most preferably from
about 5 to
about 50 weight %.
The adhesive composition suitably comprises from about 0.1 to about 99 weight
% of the one or more polymers (P), preferably from about 1 to about 80 weight
%, more
preferably 2 to about 50 weight %, even more preferably from about 2 to about
25 weight
%, most preferably from about 5 to about 15 weight %.
The solids content in the adhesive composition is suitably from about 10 to
about
95 weight %, preferably from about 20 to about 75 weight %, most preferably
from about
30 to about 50 weight %.
In one embodiment the adhesive system comprises the protein and the one or
more polymers (P) as separate components which preferably remain separated
until their
actual use in the gluing process. The separate components of the adhesive
system may
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also be mixed a short time before the actual use in the gluing process,
thereby forming an
adhesive composition of the present invention. By "short time" is herein
suitably meant
less than about 1 hour, preferably less than about 30 minutes, most preferably
less than
about 15 minutes.
In one embodiment of the method of the invention, the adhesive system is
applied onto one or more pieces of a wood-based material as separate
components,
wherein one component comprises the protein and a further component comprises
the
one or more polymers (P).
The component comprising protein may comprise a protein solution or
dispersion, or comprise the protein as a dry material. The protein solution or
dispersion is
preferably aqueous. The component comprising the one or more polymers (P) is
suitably
a solution or dispersion, preferably an aqueous solution or dispersion, or as
a solid
material. As a separate component of the adhesive system, the polymer (P) is
suitably
present in an aqueous composition comprising from about 0.1 to about 99 weight
% of
polymer (P), preferably from about 1 to about 80 weight %, more preferably
from about 2
to about 50 weight %, even more preferably from about 2 to about 25 weight %,
most
preferably from about 3 to about 15 weight %.
When provided as separate components of the adhesive system onto the one or
more pieces of wood-based material, there is preferably a sequential
application of
components of the adhesive system comprising a first component applied and a
second
component applied.
In one embodiment of the method of the invention, the first component applied
comprises a protein, either as a solution or dispersion, or as a dry material,
and the
second component applied comprises a solution or dispersion of the one or more
polymers (P).
In one embodiment of the method of the invention, the first component applied
comprises a solution or dispersion of the one or more polymers (P) and the
second
component applied comprises a protein, either as a solution or dispersion, or
as a dry
material.
In one embodiment of the method of the invention, the first component applied
comprises the one or more polymers (P) as a solid material and the second
component
applied comprises a protein, either as a solution or dispersion, or as a dry
material.
In one embodiment of the method of the invention, a mixture of the one or more
polymers (P) as a solid material and a protein as a dry material is applied.
In one embodiment of the method of the invention, the first applied component
being a solution or dispersion is dried after application before the second
component is
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applied. In this case, the first applied component is preferably a solution or
dispersion of
the one or more polymers (P).
Examples of suitable proteins are native proteins, i.e. unmodified proteins,
and
modified proteins, originating from, e.g., milk (casein), soy, potato, corn,
wheat, rice, peas
etc.. Examples of suitable soy protein products include soy protein
concentrate, soy meal,
soy protein hydrolysate and soy protein isolate. Preferably, the protein is a
soy protein
isolate (SPI). The protein is suitably provided for use in the present
invention in the form
of a product such as a protein meal or a protein isolate. The protein content
in the protein
meal or protein isolate is suitably from about 30 to about 100 weight %,
preferably from
about 50 to about 100 weight %, most preferably from about 70 to about 100
weight %.
An aqueous composition comprising 12 weight % of the protein has suitably a
viscosity (Brookfield, 12 rpm, spindle 4, at 20 C) of from about 500 to about
5.000.000
mPa*s, preferably from about 1.000 to about 2.000.000 mPa*s, more preferably
from
about 50.000 to about 1.500.000 mPa*s. most preferably from about 100.000 to
about
1.000.000 mPa*s.
The one or more polymers (P) have suitably a weight average molecular weight
of from about 1.000 to about 5.000.000 g/mol, preferably from about 10.000 to
about
2000.000 g/mol.
The content of acetoacetoxy groups in the one or more polymers (P) is suitably
from about 0.05 to about 50 mole%, preferably from about 1 to about 30 mole %,
most
preferably from about 5 to about 20 mole%.
The one or more polymers (P) preferably comprises acetoacetylated polyvinyl
alcohol (AAPVA).
The adhesive system suitably further comprises one or more polymers (P1)
containing amine or amide groups, preferably as a separate component or as
mixed with
the protein component. The amide groups are preferably pendant amide groups.
By the term "amide groups" is herein included formamide groups.
The one or more polymers (P1) preferably comprise primary amine groups or
formamide groups. Preferably the one or more polymers (P1) comprises
polyvinylamine,
polyvinylformamide, poly(vinylalcohol-co-vinylamine), poly(vinylalcohol-co-
vinylformamide), polyallyl amine, polyethylene imine or polyamidoamine. Most
preferably
the one or more polymers (P1) comprises polyvinylamine or polyethylene imine.
The one or more polymers (P1) suitably have a weight average molecular weight
of from about 1.000 to about 5.000.000 g/mol, preferably from about 10.000 to
about
2000.000 g/mol.
As a separate component of the adhesive system, the polymer (P1) is suitably
present in an aqueous composition comprising from about 0.1 to about 99 weight
% of
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polymer (P1), preferably from about 1 to about 80 weight, more preferably from
about 2 to
about 50 weight %, even more preferably from about 2 to about 25 weight %,
most
preferably from about 3 to about 15 weight %.
The aqueous composition comprising the one or more polymers (P1) may further
5 comprise inorganic- or organic salts. A part of the one or more polymers
(P1) may be
ionically charged, preferably cationically charged. The amount of negative
counter-ions of
the salts in the aqueous composition is suitably from 0 to about 50 weight %,
preferably
from about 1 to about 30 weight %, most preferably from about 2 to about 20
weight %.
The one or more components of the adhesive system comprising protein,
polymer (P) and optionally polymer (P1) respectively, or the adhesive
composition
comprising protein and polymer, and optionally polymer (P1), may further
comprise
additives and fillers such as kaolin.
In one embodiment of the method the adhesive composition is dried after
application and later activated by adding water or an aqueous composition
comprising the
one or more polymers (P) or an aqueous composition comprising one or more
polymers
(P1).
In one embodiment the adhesive system comprises the protein, the one or more
polymers (P) and the one or more polymers (P1) as separate components which
remain
separated until their actual use in the gluing process. The separate
components of the
adhesive system may also be mixed a short time before the actual use in the
gluing
process, thereby forming an adhesive composition of the present invention. By
"short
time" is herein suitably meant less than about 1 hour, preferably less than
about 30
minutes, most preferably less than about 15 minutes.
In one embodiment of the method of the invention, the adhesive system is
applied onto one or more pieces of a wood-based material as separate
components,
wherein one component comprises the protein, a further component comprises the
one or
more polymers (P), and a further component comprises the one or more polymers
(P1).
The component comprising protein may comprise a protein solution or
dispersion, or
comprise the protein as a dry material. The component comprising the one or
more
polymers (P) is suitably a solution or dispersion. The component comprising
the one or
more polymers (P1) is suitably a solution or dispersion.
In one embodiment of the method a first component applied comprises a solution
or dispersion of the protein and the one or more polymers (P), which is dried
before
application of a second component which comprises a solution or dispersion of
the one or
more polymers (P1).
In one embodiment of the method a first component applied comprises a solution
or dispersion of the protein and the one or more polymers (P1), which is dried
before
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application of a second component which comprises a solution or dispersion of
the one or
more polymers (P).
In one embodiment of the method a first component applied comprises a solution
or dispersion of the one or more polymers (P), which is dried before
application of a
second component which comprises a solution or dispersion of the protein and
the one or
more polymers (P1).
In one embodiment of the method a first component applied comprises a solution
or dispersion of the one or more polymers (P1), which is dried before
application of a
second component which comprises a solution or dispersion of the protein and
the one or
more polymers (P).
The amount of protein and one or more polymers (P) and the optional one or
more polymers (P1) in the adhesive composition suitably make up at least 75
weight % of
components having a molecular weight equal to or above 1000 g/mole, also
suitably from
about 75 to about 100 weight %, preferably at least 85 weight %, also
preferably from
about 85 to about 100 weight %, most preferably at least 95 weight %, also
most
preferably from about 95 to about 100 weight %.
The invention further relates to the use of the adhesive system according to
the
invention for gluing pieces of wood based materials forming a wood based
product.
In one embodiment of the present invention, the pieces of wood based material
are sheets or lamellas. In this case, the wood based product is suitably a
laminated
flooring material, veneered flooring, a veneered furniture material, plywood,
a wall panel,
a roofing panel or a laminated beam.
In one embodiment of the present invention, the pieces of wood based material
are wood chips or wood particles, such as chips, shavings, flakes, sawdust or
any similar
finely divided wood based material. In this case the wood based product is
suitably a
chip-, particle-, or fibreboard, or oriented strand board.
The moisture content of the wood particles to be used in the present invention
is
suitably from about 0 to about 20 weight %, preferably from about 1 to about
10 weight
%, more preferably from about 1.5 to about 5 weight %.
The weight ratio wood particles to adhesive system, calculated as dry weight,
is
suitably from about 100:1 to about 1:1, preferably from about 50:1 to about
2:1, more
preferably from about 30:1 to about 2.5:1, most preferably from about 15:1 to
about 3:1.
The method according to the invention suitably comprises the steps of
contacting
one or more pieces of wood based material with the adhesive system according
to the
invention, pressing and thereby joining pieces of wood based material with
further wood
based material. The pressing suitably takes place at an elevated temperature.
The wood
based material can be any type and form of wood based material such as chips,
fibres,
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sheets, laminas, veneers, pieces etc. The method suitably comprises
application of the
adhesive composition according to the invention onto a surface of the wood
based
material followed by pressing. The pressing temperature depends on which wood
based
product intended to be manufactured but is suitably from about 50 to about 250
C and
preferably from about 70 to about 200 C. For particle-, chip-, and fibreboard
products, the
pressing temperature is preferably from about 100 to about 225 C, most
preferably from
about 150 to about 200 C. For laminated products, such as plywood, laminated
flooring
or veneered flooring products, the pressing temperature is preferably from
about 70 to
about 175 C, most preferably from about 90 to about 160 C.
The pressing time and pressing temperature are linked so that lower pressing
temperatures generally require longer pressing times. The wood based product
to be
produced does also determine suitable pressing temperatures and pressing
times. The
pressing time is suitably at least about 10 s , also suitably from about 10 s
to about 60
minutes, preferably at least about 30 s, also preferably from about 30 s to
about 30
minutes, most preferably at least about 1 minute, also preferably from about 1
to about 15
minutes.
In one embodiment of the method, when manufacturing laminated products, the
method suitably comprises application of the adhesive composition according to
the
invention onto a surface so that the glue joint will comprise an originally
applied amount
of from about 0.1 to about 500 g/m2. The applied amount depends on the product
to be
produced: for compression moulded veneers it is preferably from about 50 to
about 200
g/m2, for laminated flooring material it is preferably from about 100 to about
160 g/m2. The
suitable upper limit also depends on which type of wood based material that is
applied
with the solution. The adhesive composition may be applied on one or both of
the
surfaces to be joined. If applied on both surfaces, the sum of the amounts
applied on
each surface will correspond to the preferred amounts for the whole glue joint
specified.
In another embodiment of the method, when manufacturing laminated products,
the method suitably comprises application of the adhesive system according to
the
invention as separate components of the protein and the one or more polymers
(P) onto a
surface. Suitably, both the protein and polymer (P) are applied as aqueous
compositions.
Alternatively, the protein and the one or more polymers (P) can be applied
onto separate
surfaces intended to be joined. The total amount of applied adhesive system
onto the one
or both surfaces is such that the glue joint will comprise an originally
applied amount of
from about 0.1 to about 500 g/m2. The applied amount depends on the product to
be
produced: for compression moulded veneers it is preferably from about 50 to
about 200
g/m2, for laminated flooring material it is preferably from about 100 to about
160 g/m2. The
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suitable upper limit also depends on which type of wood based material that is
applied
with the solution.
In another embodiment of the method, when manufacturing particle-, chip-, or
fibre boards and similar products, the method suitably comprises application
of the
adhesive system according to the invention as separate components of the
protein and
the one or more polymers (P) onto the wood chips.
When applied separately, in the manufacturing of particle-, chip-, or fibre
boards
and similar products, the protein can be applied in dry form or as present in
an aqueous
composition. Preferably, the protein is applied in dry form. The one or more
polymers (P)
can be applied as a solid or as an aqueous composition. The one or more
polymers (P)
are preferably first added to the chips followed by addition of the protein.
In one embodiment, in the manufacturing of particle-, chip-, or fibre boards
and
similar products, the one or more polymers (P) are applied as an aqueous
composition
followed by the addition of protein in dry form.
In one embodiment, in the manufacturing of particle-, chip-, or fibre boards
and
similar products, the one or more polymers (P) are applied as a solid
simultaneously with
the protein in dry form.
The present invention also relates to a wood based product obtainable by the
method of producing a wood based product.
The wood based product is suitably a particle-, chip-, or fibreboard product.
Alternatively, the wood based product is suitably a laminated products, such
as plywood,
laminated flooring or veneered flooring product.
A particle-, chip-, or fibreboard product made according to the invention
suitably
has a content of protein from about 1 to about 20 weight %, preferably from
about 3 to
about 15 weight %, calculated as dry weight.
A particle-, chip-, or fibreboard product made according to the invention
suitably
has a content of the polymer comprising acetoacetoxy groups of from about 0.5
to about
10 weight %, preferably from about 1 to about 5 weight %, calculated as dry
weight.
The invention is further illustrated by means of the following non-limiting
examples. Parts and percentages relate to parts by weight respectively percent
by
weight, unless otherwise stated.
Examples
Example 1:
Veneered products were made by applying different compositions onto a 15x15
cm different particle boards followed by drying for 5 days. The dried adhesive
layers were
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then remoistened followed by veneering a layer of 0.6 mm beech onto the
boards. The
assemblies were pressed during 1 minute at 130 C. The fiber tear (chisel) was
tested.
The compositions tested were:
1) 14 g soy protein isolate (SPI) (Supro 500E from Solae), 100 ml water.
2) 8 g soy protein isolate (SPI) (Supro 500E from Solae), 50 g acetoacetylated
polyvinyl
alcohol solution (AAPVA) (Gohsefimer Z-220 from Nippon Gohsei) (5 wt%),
3) 8 g soy protein isolate (SPI) (Supro 500E from Solae), 50 g acetoacetylated
polyvinyl
alcohol solution (AAPVA) (Gohsefimer Z-220 from Nippon Gohsei) (10 wt%).
Table 1.
First applied Amount first Remoistening Fiber tear (%)
component applied
Warm Cold
SPI 2.7 g 1 g water 20-30 -5
SPI 2.7 g 1 g AAPVA 50-60 50-60
(12 wt%)
SPI + AAPVA 3.7 g 1.4 g water -90 -30
(5 wt%)
SPI + AAPVA 3.7 g 1.4 g water 100 100
(10 wt%)
SPI + AAPVA 3.7 g 1.1 g 100 100
(10 wt%) polyvinylamine
(11 wt%)
Example 2:
A particle board was manufactured by mixing 864 g wood chips, having a
moisture content of 2 weight %, with 205 g of an aqueous solution of about 11
weight %
acetoacetylated polyvinyl alcohol (AAPVA) (Gohsefimer Z-220 from Nippon
Gohsei),
followed by mixing in about 85 g of a soy protein isolate (SPI) (Prisolate
601 EM from
Food Partner). The SPI had a protein content of >90 weight % and a dry content
of 94
weight %. The chips mixture was formed into a sheet of 30x30 cm and pressed at
185 C
for three minutes and pressed into a board of 16 mm thickness. The sequence of
pressure was 160 kg/cm2 during 30 s, 40 kg/ cm2 during 2.5 min and no pressure
during
the last 30 s. The tensile strength (internal bond, IB), thickness swelling
(TSW) and water
absorption (ABS) were measured.
A further particle board was manufactured in the same way as previously by
mixing 994 g wood chips, having a moisture content of 2 weight %, with about
85 g of a
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soy protein isolate (Supro 500E from Solae). The SPI had a protein content of
>90
weight % and a dry content of 94 weight %. The tensile strength (internal
bond, IB) was
measured.
Table 2.
Wood Protein Protein AAPVA Moisture IB TSW ABS
chips (g) (11%), (g) content (kPa) 24 h 24 h
(g) before (%) (%)
pressing
(%)
864 SPI 85.3 205 14.6 490 30.2 93.7
994 SPI 79.6 - 7.8 10 * *
5 * not measured
Example 3:
Particle boards were manufactured in a smaller scale by mixing 50.7 g wood
chips respectively, having a moisture content of 2 weight %, with 1 g of
acetoacetylated
10 polyvinyl alcohol (AAPVA) (Gohsefimer Z-220 from Nippon Gohsei), present
as an
aqueous solution of about 16.5 weight %, followed by mixing in soy protein
isolate (SPI)
(Supro 500E from Solae) in various amounts. The SPI had a protein content of
>90
weight % and a dry content of 94 weight %. A reference with no SPI and a
reference with
no AAPVA was also prepared. The chips mixtures were pressed into boards of 10
mm
thickness. The pressing was made at 9 kg/cm2 at 180-185 C during 5 minutes.
The
internal bond strength (IB) was measured by gluing pieces of 5 x 5 cm onto two
metal
blocks and tearing them apart.
Table 3.
Amount protein Amount AAPVA IB
(SPI) (g) (kPa)
(g)
- 1 127
0.2 1 222
0.5 1 359
2 1 480
5 1 322
5 - 176
