Note: Descriptions are shown in the official language in which they were submitted.
PF 70633 CA 02794340 2012-09-24
Use of synthetic adhesives for producing corrugated cardboard
Description
The present invention relates to the use of synthetic adhesives based on
aqueous
dispersions having a high solids content of certain, selected synthetic,
dispersed
copolymers in the manufacture of corrugated fiberboard at relatively low
temperatures
of below 95 C and high lineal speeds of at least 150 m/min, and also to a
corresponding process for manufacturing corrugated fiberboard.
Corrugated fiberboard is one of the most widely used forms of packaging in the
world.
It includes at least one corrugated sheet of paper, which is adhered to flat
sheets of
paper, the linerboards. Corrugated fiberboard frequently consists of three
plies. Two
outer, planar layers of paper and a corrugated ply adhered therebetween. There
are
also corrugated fiberboards having two or three corrugated plies and
altogether 5 or,
respectively, 7 layers. The manufacture of corrugated fiberboard is costly,
inconvenient
and associated with high raw-material and energy requirements. In the
conventional
manufacturing process, the raw paper is heated and hot steam is used to
moisten it.
This gives it the requisite elasticity and makes it formable. To form it into
the corrugated
pattern, the heated and moistened sheet of paper is corrugated between two
heated
fluted rolls under heat and pressure. Temperatures of 180 C or higher are
customary
here. The still hot tips of the flutes are coated with a heated starch-based
glue and
adhered to the linerboard under light pressure. The starch-based glue is
heated to
temperatures above the gelatinization point of starch (60-64 C). Frequently,
the
linerboard is also preheated in order that the requisite temperature above the
gelatinization point of starch may be ensured for the duration of the adhering
operation
until the onset of sufficient adherence between the sheets of paper.
CA 1071085 describes a process for manufacturing corrugated fiberboard wherein
heating the linerboard may be advantageous, but is not absolutely necessary. A
vinyl
acetate homopolymer is used in combination with a crosslinker. Although the
adhesive
formulation itself does not have to be heated, the corrugating is effected by
heating
with steam at a temperature of 149 C (300 F) and by using rolls heated to 99 C
(210 F), and so the subsequent adhering takes place at elevated temperature.
DE 2347145 describes an adhesive composition for manufacturing corrugated
fiberboard in the form of an aqueous dispersion comprising mineral particles
and
polymeric particles composed of styrene-butadiene copolymers. A piece of
prefabricated corrugated paper has adhered to it, in a batch process, at room
temperature, a liner paper during a setting time of 15 s. Such long setting
times are
unsuitable for continuous processes. Accordingly, the adhesive composition is
called
particularly useful for cases where a delay time has to be maintained between
application of the adhesive composition and the pressing together of the
layers coated
PF 70633 CA 02794340 2012-09-24
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with adhesive composition, for example in the manufacture of large bags or
sacks of
paper.
DE 2243687 describes an adhesive composition for manufacturing corrugated
fiberboard in the form of an aqueous dispersion comprising certain, selected
synthetic
polymers in combination with certain, selected mineral particles. The problem
underlying the invention of DE 2243687 was that of providing an adhesive
composition
which is produced and applied at minimally elevated temperatures, but is used
on
customary machines for manufacturing corrugated fiberboard. As the adhesive
composition produced and applied at minimally elevated temperatures comes into
contact with the corrugated sheet and the previously heated or warmed liner
layer, the
temperature of the adhesive composition also becomes elevated. To manufacture
the
corrugation, the corrugated paper was treated with steam and the fluted rolls
are
heated to about 180 C for corrugation duty. DE 3042850 describes a so-called
cold-
hardening adhesive for the manufacture of corrugated fiberboard. The adhesive
is
applied at high temperatures and gels on cooling. The adhesive consists
essentially of
water-dissolved polyvinyl alcohol, a filler and a water-soluble boron
compound.
DE 1594231 describes a heat-activatable adhesive for manufacturing corrugated
fiberboard. The adhesive comprises water-dissolved polyvinyl alcohol,
suspended clay,
a titanium oxalate complex and ammonium bicarbonate. EP 0181579 describes a
process for manufacturing corrugated fiberboard wherein an adhesive
composition is
heated at 60 to 95 C and is applied to the tips of the flutes of the sheet
corrugated in a
conventional manner, i.e., at high temperatures. The adhesive composition
comprises
polyvinyl alcohol in aqueous solution. WO 06/086754 describes an applicator
for
aqueous adhesive compositions in the manufacture of corrugated and laminated
board
whereby less adhesive than otherwise customary can be used. The substrate used
for
applying the adhesive is a corrugated fiberboard which already includes a
corrugated
sheet produced in a conventional manner, i.e., at high temperatures, and a
first
linerboard adhered thereto, and to which a second linerboard is adhered. The
adhesive
for adhering the second linerboard is heated to, for example, about 38 C or 43
C
(100 F or, respectively 110 F) or applied to heated substrate.
It is an object of the present invention to provide an adhesive for an energy-
efficient,
economical manufacture of corrugated fiberboard whereby good adhering is made
possible at comparatively low temperatures and high speeds and, more
particularly, the
selected composition of adhesive displays very rapid setting and also a very
high initial
tackiness at low temperatures. Moreover, the adhesive should impact the
recyclability
of the corrugated fiberboard only minimally, if at all.
The present invention accordingly provides for the use of synthetic adhesives
in the
manufacture of corrugated fiberboard wherein the corrugated fiberboard
includes at
least one corrugated sheet of paper and at least one flat linerboard and the
corrugation
PF 70633 CA 02794340 2012-09-24
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of the corrugated sheet of paper is produced at paper temperatures below 95 C
and at
a lineal speed of above 150 m/min,
= wherein in a continuous operation immediately after production of the
corrugation
of the corrugated sheet of paper a corrugated board adhesive, which is
preferably
unheated, is applied to the corrugated sheet of paper and the corrugated sheet
of
paper is adhered to at least one first linerboard;
= wherein the corrugated board adhesive used is an aqueous adhesive dispersion
having a solids content of preferably more than 40% by weight based on at
least
one synthetic, dispersed polymer selected from the group consisting of
acrylate
copolymers, copolymers of vinyl aromatics and conjugated aliphatic dienes and
vinyl acetate-alkylene copolymers,
= wherein the synthetic, dispersed polymers have glass transition temperatures
which are above 20 C and below the surface temperature of the corrugated sheet
of paper to which they are applied.
The corrugated board adhesive used is an aqueous adhesive dispersion based on
at
least one synthetic, dispersed polymer. The solids content is preferably more
than 40%
by weight and more preferably more than 50% by weight, for example in the
range from
50% to 60% by weight. The pH of the adhesive dispersion is preferably set to
above
pH 3.7, more particularly to a pH between 4 and 8.
The glass transition temperature Tg of the dispersed polymers is above 20 C,
preferably not less than 25 C, and is below the surface temperature of the
corrugated
sheet of paper, i.e., when the corrugation of the corrugated sheet of paper is
produced
at a temperature of less than 95 C, a polymer having a Tg of, for example,
less than
95 C is used. When the corrugation of the corrugated sheet of paper is
produced at a
temperature of less than 90 C, a polymer having a Tg of, for example, less
than 90 C
is used, and so on. The glass transition temperature Tg of the polymer
dispersed in the
aqueous adhesive formulation is preferably less than 60 C or less than 55 C.
Preferably, the glass transition temperature is in the range from above +20 C
or not
less than +25 C to not more than +70 C or not more than +60 C or in the range
from
not less than +25 C to not more than +55 C.
Glass transition temperature T9 is to be understood as referring to the glass
transition
temperature limit to which the glass transition temperature tends with
increasing
molecular weight, according to G. Kanig (Kolloid-Zeitschrift & Zeitschrift for
Polymere,
vol. 190, page 1, equation 1). Glass transition temperature can be determined
by
Differential Scanning Calorimetry (ASTM D 3418-08, "midpoint temperature"). By
purposive variation of monomer type and quantity, a person skilled in the art
is able
according to the present invention to prepare aqueous polymeric compositions
the
polymers of which have a glass transition temperature in the desired range.
Orientation
is possible by means of the Fox equation. According to Fox (T.G. Fox, Bull.
Am. Phys.
PF 70633 CA 02794340 2012-09-24
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Soc. 1956 [Ser. 111 1, page 123 and according to Ullmann's Encyclopadie der
technischen Chemie, vol. 19, page 18, 4th edition, Verlag Chemie, Weinheim,
1980),
the glass transition temperature of at most slightly crosslinked copolymers is
given to a
good approximation by:
1/Tg = x'/Tg1 + x2/Tg2 + .... xn/Tgn,
where x1, x2, .... xn are the mass fractions of the monomers 1, 2, .... n and
Tg1, T92, ....
Tgn are the glass transition temperatures in degrees kelvin of the polymers
constructed
of just one of the monomers 1, 2, .... n at a time. The Tg values are known
for the
homopolymers of most monomers and listed for example in Ullmann's Ecyclopedia
of
Industrial Chemistry, vol. 5, Vol. A21, page 169, VCH Weinheim, 1992; further
sources
for glass transition temperatures of homopolymers are for example J. Brandrup,
E.H. Immergut, Polymer Handbook, 1st Ed., J. Wiley, New York 1966, 2"d Ed. J.
Wiley,
New York 1975, and 3,d Ed. J. Wiley, New York 1989.
The minimum processing temperature of the corrugated board adhesive is
preferably
less than 80 C or not more than 60 C and is for example in the range from 5 to
60 C.
The minimum processing temperature is that temperature at which the corrugated
board adhesive is sufficiently fluid for application to the sheet of paper,
more
particularly, has a viscosity of less than 7000 mPa s or less than 5000 mPa s,
for
example in the range from 2000 to 5000 mPa s. The viscosity of the adhesive
dispersion directly prior to application is preferably less than 7000 mPa s or
less than
6000 mPa s, for example in the range from 2000 to 5000 mPa s. Viscosities can
be
measured in a Brookfield viscometer (RVT spindle 5, 10 revolutions per minute)
at the
application temperature (20 C for example). The viscosity of the adhesive
dispersion at
60 C is preferably less than 7000 mPa s or less than 5000 mPa s, for example
in the
range from 2000 to 5000 mPa s. The viscosity of the adhesive dispersion at 20
C is
more preferably less than 7000 mPa s or less than 5000 mPa s, for example in
the
range from 2000 to 5000 mPa s.
The dispersed synthetic polymers used in the process of the present invention
are
selected from the group consisting of acrylate copolymers, copolymers of
vinylaromatics and conjugated aliphatic dienes and vinyl acetate-alkylene
copolymers.
They are obtainable by free-radical polymerization of ethylenically
unsaturated
compounds (monomers).
Acrylate copolymers useful for the present invention are copolymers formed
from at
least two different (meth)acrylic esters. Hereinafter the notation
"(meth)acrylic" is used
as an abbreviation for "acrylic or methacrylic". The acrylate copolymers
consist of
(meth)acrylic esters, preferably C,-C20-alkyl (meth)acrylates, preferably to
an extent of
at least 60% by weight or to an extent of at least 80% by weight, more
preferably to an
extent of at least 90% by weight or to an extent of at least 95% by weight and
up to
100% by weight. Suitable (meth)acrylate monomers are for example alkyl
PF 70633 CA 02794340 2012-09-24
(meth)acrylates having a C1-C20-alkyl radical. Preference is given to C1- to
C1o-alkyl
acrylates and Cl- to C1o-alkyl methacrylates, more particularly C1- to C8-
alkyl acrylates
and methacrylates. Very particular preference is given to methyl acrylate,
methyl
methacrylate, ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, octyl
acrylate, 2-
5 ethylhexyl acrylate and 2-propylheptyl acrylate and also mixtures thereof.
More
particularly, mixtures of three or more alkyl (meth)acrylates are suitable.
In addition to the principal monomers, the polymers to be used according to
the present
invention may comprise further monomers, for example monomers having
carboxylic
acid, sulfonic acid or phosphonic acid groups. Carboxylic acid groups are
preferred.
Acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid may
be
mentioned by way of example. The acid monomer content of the polymer can be
for
example in the range from 0 to 10% by weight and more particularly in the
range from
0.05% to 5% by weight, based on the polymer. The acid groups can be present in
the
form of their salts. Further monomers also include for example hydroxyl-
containing
monomers, more particularly C1-C1o hydroxyalkyl (meth)acrylates or
(meth)acrylamide.
Useful further monomers further include phenyloxyethyl glycol
mono(meth)acrylate,
glycidyl (meth)acrylate, aminoalkyl (meth)acrylates such as, for example, 2-
aminoethyl
(meth)acrylate. Alkyl groups preferably have from 1 to 20 carbon atoms.
Crosslinking
monomers may also be mentioned as further monomers. The further monomers are
generally used in minor amounts, their proportion in total being preferably
below 10%
by weight, more particularly below 5% by weight.
In one embodiment, the dispersed polymer of the adhesive formulation is a
vinyl
acetate-alkylene copolymer. Vinyl acetate-alkylene copolymers are copolymers
formed
from vinyl acetate and at least one alkylene, preferably at least one C2- to
C8-alkylene
such as, for example, ethylene and/or propylene.
Copolymers formed from vinylaromatics and conjugated aliphatic dienes are for
example copolymers formed from
(a) 19.9 to 80 parts by weight of at least one vinylaromatic compound,
(b) 19.9 to 80 parts by weight of at least one conjugated aliphatic diene,
(c) 0.1 to 15 parts by weight of at least one ethylenically unsaturated acid,
and
(d) 0 to 20 parts by weight of at least one other monoethylenically
unsaturated
monomer.
Vinylaromatic compounds are, for example, styrene, a-methylstyrene and/or
vinyltoluene. Of this group of monomers, styrene is preferred. 100 parts by
weight of
the total monomer mixtures used in the polymerization comprise for example
from 19.9
to 80 parts by weight and preferably from 25 to 70 parts by weight of at least
one
vinylaromatic.
PF 70633 CA 02794340 2012-09-24
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Conjugated aliphatic dienes are for example 1,3-butadiene, isoprene, 1,3-
pentadiene,
1,3-dimethylbutadiene and cyclopentadiene. Of this group of monomers, it is
1,3-butadiene and/or isoprene which are preferably used. 100 parts by weight
of the
monomer mixtures used in total in the emulsion polymerization comprise for
example
from 19.9 to 80 parts by weight, preferably from 25 to 70 parts by weight and
more
particularly from 25 to 60 parts by weight of at least one conjugated
aliphatic diene.
Ethylenically unsaturated acids are for example ethylenically unsaturated
carboxylic
acids, ethylenically unsaturated sulfonic acids and vinylphosphonic acid. As
ethylenically unsaturated carboxylic acids it is preferable to use alpha,beta-
monoethylenically unsaturated mono- and dicarboxylic acids having from 3 to 6
carbon
atoms in the molecule. Examples thereof are acrylic acid, methacrylic acid,
maleic acid,
fumaric acid, crotonic acid, vinylacetic acid and vinyllactic acid. Examples
of useful
ethylenically unsaturated sulfonic acids are vinylsulfonic acid,
styrenesulfonic acid,
acrylamidomethylpropanesulfonic acid, sulfopropyl acrylate and sulfopropyl
methacrylate. Monomers comprising acid groups can be used in the
polymerization in
the form of the free acids and also partially or completely neutralized with
alkali metal
hydroxide solutions or with ammonia or with an ammonium base. Preference is
given
to using aqueous sodium hydroxide solution, aqueous potassium hydroxide
solution or
ammonia as neutralizing agent. 100 parts by weight of the monomer mixtures
used in
the emulsion polymerization comprise for example from 0.1 to 15 parts by
weight,
preferably 0.1 to 8 parts by weight and usually from 1 to 5 parts by weight of
at least
one ethylenically unsaturated acid monomer.
Other monoethylenically unsaturated monomers are for example ethylenically
unsaturated carbonitriles such as, more particularly, acrylonitrile and
methacrylonitrile,
ethylenically unsaturated carboxamides such as, more particularly, acrylamide
and
methacrylamide, vinyl esters of saturated C1- to C18 carboxylic acids,
preferably vinyl
acetate, and also esters of acrylic acid and of methacrylic acid with
monohydric C1- to
C18 alcohols such as methyl acrylate, methyl methacrylate, ethyl acrylate,
ethyl
methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate,
isopropyl
methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate,
isobutyl
methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate,
tert-butyl
methacrylate, pentyl acrylates, pentyl methacrylates, 2-ethylhexyl acrylate, 2-
ethylhexyl
methacrylate, allyl esters of saturated carboxylic acids, vinyl ethers, vinyl
ketones,
dialkyl esters of ethylenically unsaturated carboxylic acids, N-
vinylpyrrolidone,
N-vinylpyrrolidine, N-vinylformamide, N,N-dialkylaminoalkylacrylamides,
N,N-dialkylaminoalkylmethacrylamides, N,N-dialkylaminoalkyl acrylates,
N,N-dialkylaminoalkyl methacrylates, vinyl chloride and vinylidene chloride.
This group
of monomers is optionally used for modifying the polymers. 100 parts by weight
of the
monomer mixtures used in the emulsion polymerization comprise for example from
0 to
CA 02794340 2012-09-24
PF 70633
7
20 parts by weight or from 0.1 to 15 parts by weight and more particularly
from 0.1 to
parts by weight of at least one other monoethylenically unsaturated monomer.
It is particularly preferable for the synthetic, dispersed polymers to be
selected from the
5 group consisting of acrylate copolymers of at least two different C,- to C8-
alkyl
(meth)acrylates, styrene-butadiene copolymers and vinyl acetate-ethylene
copolymers.
The polymers may be prepared by emulsion polymerization. To achieve
particularly
high solids contents, for example of more than 55% by weight, a bi- or
polymodal
10 particle size should be aimed for, since otherwise the viscosity becomes
too high and
the dispersion is more difficult to handle. The production of a new generation
of
particles can be effected for example by adding seed, by adding excess
quantities of
emulsifier or by adding miniemulsions. A further advantage associated with low
viscosity at high solids content is the improved coating behavior at high
solids contents.
In a further embodiment, the adhesive dispersion comprises an aqueous
polymeric
dispersion of polymers obtainable by free-radical polymerization of
unsaturated
monomers (especially the ones mentioned above) and comprising in added form at
least one starch degradation product obtainable by hydrolysis in aqueous
phase. The
starch degradation product preferably has a weight average molecular weight Mw
in
the range from 2500 to 25 000. Such polymeric dispersions are described in
EP 0 536 597.
In a further embodiment, the adhesive dispersion comprises an aqueous
polymeric
dispersion based on copolymers formed from vinylaromatics and conjugated
aliphatic
dienes wherein the dispersed particles have an average particle size in the
range from
80 to 150 nm and are obtainable by free-radically initiated emulsion
copolymerization of
(a) 19.9 to 80 parts by weight of at least one vinylaromatic compound,
(b) 19.9 to 80 parts by weight of at least one conjugated aliphatic diene,
(c) 0.1 to 15 parts by weight of at least one ethylenically unsaturated acid,
and
(d) 0 to 20 parts by weight of at least one other monoethylenically
unsaturated
monomer,
wherein the sum total of the parts by weight of the monomers (a), (b), (c) and
(d) is
always 100, in an aqueous medium in the presence of at least one degraded
starch
having an intrinsic viscosity q; of less than 0.07 dl/g using at least 0.9% by
weight,
based on total monomers used, of initiators selected from peroxodisulfates,
peroxosulfates, azo initiators, organic peroxides, organic hydroperoxides and
hydrogen
peroxide, by initially charging at least 30% by weight of the initiators
together with the
degraded starch in the aqueous medium and metering the monomers and the rest
of
the initiators into this initial charge under polymerization conditions.
PF 70633 CA 02794340 2012-09-24
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In another embodiment of the adhesive dispersion, starches are present in
addition to
the dispersed synthetic polymers, preferably degraded starches and
specifically
amylopectin starch types, for example Amflora starch. The starch can be mixed
into
the final dispersion or else be used as a protective colloid in the making of
the
dispersion.
The size distribution of the dispersion particles in the adhesive dispersion
can be
monomodal, bimodal or multimodal. In the case of a monomodal particle size
distribution, the average particle size of the polymer particles dispersed in
the aqueous
dispersion is preferably less than 400 nm and more particularly less than 250
nm. It is
particularly preferable for the average particle size to be between 140 and
250 nm.
Average particle size here is understood as meaning the d50 value of the
particle size
distribution, i.e., 50% by weight of the total mass of all the particles have
a smaller
particle diameter than the d5o value. The particle size distribution can be
determined in
a known manner using an analytical ultracentrifuge (W. Machtle,
Makromolekulare
Chemie 185 (1984), page 1025 - 1039). In the case of a bi- or multimodal
particle size
distribution, the particle size can be up to 1000 nm.
The adhesive dispersion can consist exclusively of the dispersed polymer and
the
optional starch. However, the adhesive dispersion may also additionally
comprise
further added substances, for example flow control agents, thickeners,
preferably
associative thickeners, defoamers, wetters or tackifiers. Tackifiers are
tackifying resins
and known for example from Adhesive Age, July 1987, pages 19-23 or Polym.
Mater.
Sci. Eng. 61 (1989), pages 588-592. To improve its wetting of surfaces, the
adhesive
dispersion may comprise particularly wetting assistants, for example fatty
alcohol
ethoxylates, alkylphenol ethoxylates, nonylphenol ethoxylates,
polyoxyethylene/
polyoxypropylenes or sodium dodecylsulfonates. The amount of added substances
is
generally in the range from 0.05 to 5 parts by weight and more particularly in
the range
from 0.1 to 3 parts by weight per 100 parts by weight of polymer (solid).
Tackifiers are
for example natural resins, such as rosins and their disproportionation or
isomerization,
polymerization, dimerization, hydrogenation derivatives. These can be present
in their
salt form (with, for example, mono- or polyvalent counterions (cations)) or
preferably in
their esterified form. Alcohols used for esterification can be mono- or
polyhydric.
Examples are methanol, ethanediol, diethylene glycol, triethylene glycol,
1,2,3-propanethiol, pentaerythritol. It is further possible to use hydrocarbon
resins, for
example coumarone-indene resins, polyterpene resins, hydrocarbon resins based
on
unsaturated CH compounds, such as butadiene, pentene, methylbutene, isoprene,
piperylene, divinylmethane, pentadiene, cyclopentene, cyclopentadiene, cyclo-
hexadiene, styrene, a-methylstyrene, vinyltoluene. Tackifiers used
increasingly also
include polyacrylates having a low molecular weight. The weight average
molecular
weight M,v of these polyacrylates is preferably below 30 000. The
polyacrylates
preferably consist of C1-C8 alkyl (meth)acrylates to an extent of at least 60%
by weight
CA 02794340 2012-09-24
PF 70633
9
and more particularly at least 80% by weight. Preferred tackifiers are natural
or
chemically modified rosins. Rosins consist predominantly of abietic acid or
abietic acid
derivatives. Tackifiers can simply be added to the polymeric dispersion. For
this, the
tackifiers themselves are preferably present in the form of an aqueous
dispersion. The
weight quantity of the tackifiers is preferably in the range from 5 to 100
parts by weight
and more preferably in the range from 10 to 50 parts by weight, based on 100
parts by
weight of polymer (solid/solid).
In one embodiment, adhesive dispersion further comprises inorganic fillers.
The level of
inorganic fillers is preferably in the range from 1 % to 90% by weight and
more
preferably in the range from 5% to 80% by weight, or from 20% to 80% by weight
or
from 40% to 70% by weight, based on the solids content.
Suitable fillers are for example calcium carbonate and also calcium sulfate,
calcium
aluminate sulfate, barium sulfate, magnesium carbonate, of which carbonate
pigments
and more particularly calcium carbonate are preferred. The calcium carbonate
may be
natural ground calcium carbonate (GCC), precipitated calcium carbonate (PCC),
lime
or chalk. Suitable calcium carbonate pigments are available for example as
Covercarb 60, Hydrocarb 60 or Hydrocarb 90 ME. Suitable fillers further
include,
for example, silicas, aluminas, aluminum hydrate, silciates, titanium dioxide,
zinc oxide,
kaolin, argillaceous earth, talcum or silicon dioxide. Suitable fillers are
for example
available as Capim MP 50 (clay), Hydragloss 90 (clay), Amazon Plus Slurry
(kaolin)
or Talcum C10.
Corrugated fiberboard is produced by means of a corrugating operation.
Corrugating is
effected by passing an uncorrugated sheet of paper as corrugatable medium
through a
corrugator wherein one or more suitably shaped rolls (two fluted rolls for
example)
endow the medium with a corrugated profile. To achieve optimal corrugation,
the
corrugatable material can be pretreated with steam or heated/warmed by means
of
other media. However, a maximum temperature of 95 C and preferably of 90 C is
not
exceeded in the process. The temperatures used in the corrugating operation
are
preferably in the range from 40 to 90 C and more preferably in the range from
40 to
60 C. The paper is heated to improve its formability for corrugation. The
adhesive itself
need not necessarily be heated since it can even be filmed without heating in
one
preferred embodiment. For superior filming of the adhesive, however, the step
of
coating the corrugated fiberboard with the adhesive can optionally be followed
by
heating with a source of radiation such as IR radiators for example, or the
sheet of
paper can be diverted via a heated roll.
Corrugation and the directly subsequent adhering to the first linerboard takes
place in a
continuous operation. The lineal speed of the sheets of paper is preferably
more than
PF 70633 CA 02794340 2012-09-24
150 m/min, particularly more than 200 m/min, more than 250 m/min or more than
300 m/min.
Immediately thereafter, the tips of the flutes of the corrugated medium have
corrugated
5 board adhesive applied to them and a flat sheet of paper is applied as a
linerboard
(liner paper) under light pressure to that side of the medium which bears the
adhesive
in order that a one-face corrugated fiberboard may be produced. Subsequently,
additional adhesive can be applied to the unadhered side of the corrugated
sheet of
paper to adhere a further linerboard, leading to the production of single-wall
standard
10 corrugated fiberboard. Multi-wall corrugated fiberboards are obtainable by
bonding a
succession of one-face boards to each other, followed by a final application
of a
linerboard.
The adhesive can be applied in a conventional manner using a system of rolls
of which
one roll bears a film of adhesive. As the corrugated material revolves around
this roll,
the film of adhesive becomes applied to the ribbed side (tips of the flutes)
of the
corrugated material. The adhesive, however, can also be applied by means of
other
suitable devices, for example with nozzles, slotted dies or similar.
The amount of adhesive applied is preferably in the range from 2 to 15 g/m2
and more
particularly in the range from 3 to 7 g/m2, based on the solids content and
the total area
of the corrugated material. The tips of the corrugated material may have 15 to
25 g/m2
applied to them, for example, depending on the geometry.
The corrugated board adhesive need not be warmed prior to application. It is
accordingly preferable to apply unheated corrugated board adhesive to the
corrugated
sheet of paper, i.e., the adhesive is not heated by a separate source of heat
prior to
application, and has a temperature of preferably not more than 25 C.
Optionally,
however, slight heating of the adhesive to temperatures of, for example, more
than
25 C to 50 C or to 40 C is also possible.
The present invention also provides a process for manufacturing corrugated
fiberboard
wherein the corrugated fiberboard includes at least one corrugated sheet of
paper and
at least one flat linerboard and the corrugation of the corrugated sheet of
paper is
produced at paper temperatures below 95 C and at a lineal speed of above 150
m/min
= wherein in a continuous operation immediately after production of the
corrugation
of the corrugated sheet of paper a preferably unheated corrugated board
adhesive
is applied to the corrugated sheet of paper and the corrugated sheet of paper
is
adhered to at least one first linerboard;
= wherein the corrugated board adhesive used is one of the aqueous adhesive
dispersions described in more detail above.
= CA 02794340 2012-09-24
PF 70633
11
The adhesive used according to the present invention allows good recyclability
on the
part of the corrugated fiberboard. For recyclability to be good a rating of 4
or better is
required in the test described in the examples. In this test, a corrugated
paper is coated
with the adhesive of the present invention and laminated with a liner paper.
The
laminate obtained is dried and fiberized in a repulper. Subsequently, the pulp
thus
produced is used to produce a sheet of paper and this sheet of paper is
visually
inspected for specks and visible contraries.
It has been determined that particularly good recyclability can be achieved
when in
addition to the glass transition temperature being in the claimed range the
synthetic,
dispersed polymers are constructed to at least 3% by weight, preferably from
4% to
15% by weight, based on the sum of all monomers, of hydrophilic comonomers.
Hydrophilic comonomers are monomers having hydrophilic groups. Hydrophilic
groups
are for example acid groups and also amino groups, ammonium groups, hydroxyl
groups or polyethylene oxide groups having at least two ethylene oxide units.
Hydrophilic monomers are for example ethylenically unsaturated acid monomers,
ethylenically unsaturated amine monomers and ethylenically unsaturated
monomers
having polyethylene oxide groups, of which ethylenically unsaturated acid
monomers
are preferred.
Ethylenically unsaturated acid monomers are for example ethylenically
unsaturated
carboxylic acids, ethylenically unsaturated sulfonic acids and vinylphosphonic
acid. As
ethylenically unsaturated carboxylic acids it is preferable to use alpha,beta-
monoethylenically unsaturated mono- and dicarboxylic acids having from 3 to 6
carbon
atoms in the molecule. Examples thereof are acrylic acid, methacrylic acid,
itaconic
acid, maleic acid, fumaric acid, crotonic acid, vinylacetic acid and
vinyllactic acid.
Examples of useful ethylenically unsaturated sulfonic acids are vinylsulfonic
acid,
styrenesulfonic acid, acrylamidomethylpropanesulfonic acid, sulfopropyl
acrylate and
sulfopropyl methacrylate. Monomers comprising acid groups can be used in the
polymerization in the form of the free acids and also partially or completely
neutralized
with alkali metal hydroxide solutions or with ammonia or with an ammonium
base.
Preference is given to using aqueous sodium hydroxide solution, aqueous
potassium
hydroxide solution or ammonia as neutralizing agent. Acrylic acid, methacrylic
acid and
itaconic acid are particularly preferred.
Amine monomers are for example aminoalkyl (meth)acrylates such as, for
example,
2-aminoethyl (meth)acrylate, monoalkylaminoalkyl (meth)acrylates,
dialkylaminoalkyl
(meth)acrylates, aminoaIkyl(meth)acrylamides,
monoalkylaminoalkyl(meth)acrylamides
and dialkylaminoalkyl(meth)acrylamides. Alkyl groups preferably have from 1 to
20 carbon atoms. The amino-containing monomers can be present in the form of
the
free amino groups and also after partial or complete conversion, with acids or
quaternizing agents, into ammonium groups.
= PF 70633 CA 02794340 2012-09-24
12
Hydrophilic comonomers having hydroxyl groups are, for example, C2-C8
hydroxyalkyl
esters of acrylic acid or of methacrylic acid.
Hydrophilic comonomers having polyethylene glycol groups are for example those
of
the general formula
H2C=CR1-COO-(EO)n-(PO)m-R2
where R1 is hydrogen or methyl, n is at least two, preferably from 6 to 100 or
from 10 to
40, m is from zero to 50, preferably from zero to 20, EO is an ethylene oxide
group
(-CH2-CH2-O-), PO is a propylene oxide group (-CH2-CH(CH3)-O-) and R2 is
hydrogen
or a C1-C3o alkyl group or a C1-C3o alkaryl group, wherein n is preferably not
less than
m and n+m is preferably from 6 to 100 or from 10 to 40.
The corrugated board adhesives used according to the present invention and/or
the
process of the present invention have the following advantages over existing
processes:
The adhesives provide for a more energy-efficient, economical manufacture of
corrugated fiberboard than conventional starch-based adhesives. The adhesives
of the
present invention provide good adhering at comparatively low temperatures and
high
lineal speeds, with particularly the selected compositions of adhesive
providing very
rapid setting and also a very high initial tack at low temperatures. The
adhesive does
not impair the recyclability of the corrugated fiberboard.
Examples
Unless the context suggests otherwise, percentages are always by weight. A
reported
content is based on the content in aqueous solution or dispersion.
Inventive example 1
Copolymer formed from 39.5 parts by weight of n-butyl acrylate, 56.5 parts by
weight of
styrene, 4 parts by weight of methacrylic acid, emulsion polymerized in water
in the
presence of 0.1 part by weight of tert-dodecyl mercaptan, 1.2 parts by weight
of
Disponil FES 27 emulsifier, 0.25 part by weight of Dowfax 2A1 emulsifier, 0.6
part by
weight of sodium persulfate (initiator).
Solids content: 49%, pH 6.2, Tg +41 C
Inventive example 2
Copolymer formed from 43 parts by weight of n-butyl acrylate, 52 parts by
weight of
styrene, 5 parts by weight of acrylic acid, emulsion polymerized in water in
the
presence of 0.5 part by weight of tert-dodecyl mercaptan, 0.9 part by weight
of
Disponil FES 27 emulsifier, 0.6 part by weight of sodium persulfate
(initiator).
Solids content: 54%, pH 4.0, Tg +31 C
CA 02794340 2012-09-24
PF 70633
13
Inventive example 3
Copolymer formed from 38 parts by weight of n-butyl acrylate, 55 parts by
weight of
styrene, 5 parts by weight of vinyl acetates, 2 parts by weight of acrylic
acid, emulsion
polymerized in water in the presence of 0.1 part by weight of tert-dodecyl
mercaptan,
1.2 parts by weight of Disponil FES 27 emulsifier, 0.25 part by weight of
Dowfax 2A1
emulsifier, 0.6 part by weight of sodium persulfate (initiator).
Solids content: 49%. pH 4Ø Tg +35 C
Inventive example 4
Copolymer formed from 42 parts by weight of n-butyl acrylate, 48 parts by
weight of
styrene, 5 parts by weight of vinyl acetate, 5 parts by weight of acrylic
acid, emulsion
polymerized in water in the presence of 0.5 part by weight of tert-dodecyl
mercaptan,
0.9 part by weight of Disponil FES 27, 0.6 parts by weight of sodium
persulfate.
Solids content: 52%, pH 4.0, Tg +28 C
Inventive example 5
Copolymer formed from 36 parts by weight of n-butyl acrylate, 62 parts by
weight of
styrene, 2 parts by weight of acrylic acid, emulsion polymerized in water in
the
presence of 0.1 part by weight of tert-dodecyl mercaptan, 1.2 parts by weight
of
Disponil FES 27 emulsifier, 0.25 part by weight of Dowfax 2A1 emulsifier, 0.6
part by
weight of sodium persulfate (initiator).
Solids content: 49%, pH 4.1, Tg +43 C
Inventive example 6
Copolymer formed from 33 parts by weight of 2-propylheptyl acrylate, 62 parts
by
weight of styrene, 5 parts by weight of acrylic acid, emulsion polymerized in
water in
the presence of 0.5 part by weight of tert-dodecyl mercaptan, 0.9 part by
weight of
Disponil FES 27, 0.6 part by weight of sodium persulfate.
Solids content: 54%, pH 4.7, Tg +37 C
Inventive example 7
Copolymer formed from 49.5 parts by weight of n-butyl acrylate, 48.5 parts by
weight of
styrene, 2 parts by weight of acrylic acid, emulsion polymerized in water in
the
presence of 0.1 part by weight of tert-dodecyl mercaptan, 1.2 parts by weight
of
Disponil FES 27 emulsifier, 0.25 part by weight of Dowfax 2A1 emulsifier, 0.6
part by
weight of sodium persulfate (initiator).
Solids content: 49%, pH 4.0, Tg +44 C
Inventive example 8
Copolymer formed from 60.5 parts by weight of styrene, 28.0 parts by weight of
butadiene, 11 parts by weight of acrylic acid; 0.5 part by weight of itaconic
acid;
PF 70633 CA 02794340 2012-09-24
14
emulsion polymerized in water in the presence of 1.1 parts by weight of tert-
dodecyl
mercaptan, 0.5 part by weight of Disponil FES 27, 0.9 part by weight of
sodium
persulfate.
Solids content: 52%, pH 5.4, Tg +38.2 C
Inventive example 9
Copolymer formed from 56.5 parts by weight of styrene, 32 parts by weight of
butadiene, 11 parts by weight of acrylic acid, 0.5 part by weight of itaconic
acid,
emulsion polymerized in water in the presence of 1.1 parts by weight of tert-
dodecyl
mercaptan, 0.5 part by weight of Disponil FES 27, 0.9 part by weight of
sodium
persulfate.
Solids content: 50%, pH 5.5, Tg +30 C
Inventive example 10
Copolymer formed from 56.5 parts by weight of styrene, 32.0 parts by weight of
butadiene, 11 parts by weight of acrylic acid; 0.5 part by weight of itaconic
acid,
emulsion polymerized in water in the presence of 1.1 parts by weight of tert-
dodecyl
mercaptan, 0.5 part by weight of Lumiten I-SC, 0.9 part by weight of sodium
persulfate.
Solids content: 52%, pH 5.6, Tg +26.3 C
Inventive example 11
Copolymer formed from 65.5 parts by weight of styrene, 23 parts by weight of
butadiene, 11 parts by weight of acrylic acid; 0.5 part by weight of itaconic
acid;
emulsion polymerized in water in the presence of 1.1 parts by weight of tert-
dodecyl
mercaptan, 0.5 part by weight of Disponil FES 27, 0.9 part by weight of
sodium
persulfate.
Solids content: 49%, pH 5.3, Tg +53 C
Inventive example 12
The copolymer dispersion of inventive example 2 was admixed with Precarb 100
calcium carbonate in a ratio of 77:23 (solid/solid) for the same total solids
content, i.e.,
some of the polymer was replaced by calcium carbonate.
Solids content: 54%, pH 6.5
Comparative example V1
Copolymer formed from 52 parts by weight of n-butyl acrylate, 38 parts by
weight of
styrene, 10 parts by weight of acrylic acid, emulsion polymerized in water in
the
presence of 0.5 part by weight of tert-dodecyl mercaptan, 1.2 parts by weight
of
Disponil FES 27, 0.25 part by weight of Dowfax 2 Al, 0.6 part by weight of
sodium
persulfate.
Solids content: 49%, pH 3.5, Tg +17 C
PF 70633 CA 02794340 2012-09-24
Comparative example V2
Copolymer formed from 41 parts by weight of ethyl acrylate, 57 parts by weight
of
styrene, 2 parts by weight of acrylic acid, emulsion polymerized in water in
the
presence of 0.1 part by weight of tert-dodecyl mercaptan, 1.2 parts by weight
of
5 Disponil FES 27, 0.25 part by weight of Dowfax 2 Al, 0.6 part by weight of
sodium
persulfate.
Solids content: 49%, pH 4.6, Tg +57 C
Comparative example V3
10 Copolymer formed from 64.5 parts by weight of styrene, 35 parts by weight
of
butadiene, 0.5 part by weight of itaconic acid; emulsion polymerized in water
in the
presence of 1.1 parts by weight of tert-dodecyl mercaptan, 0.5 part by weight
of
Disponil FES 27, 0.9 part by weight of sodium persulfate.
Solids content: 51%, pH 11.6, Tg +10 C
Performance tests
Wet grab:
To evaluate wet grab, a corrugated paper having a basis weight of 105 g/m2 is
blade
coated at 55 C with an approximately 1 mm layer of adhesive. Almost at the
same time
as the coating, a liner paper (test liner 3) is laminated onto the wet
adhesive. Directly
after wet lamination, a stopwatch is started and the bonded assembly is slowly
pulled
apart. What is measured is the time to a significant fiber pullout becoming
visible. The
shorter the time to fiber pullout, the better the wet grab. At a value of less
than 10 s, it
can be assumed that the wet-bonded assembly is sufficiently firm on a
production scale
machine even at a production speed of more than 300 m/min not to come apart in
the
machine at a change of direction roll for example.
Recyclability:
A corrugated paper having a basis weight of 105 g/m2 is coated with 5 g/m2 (20
pm
doctor blade) of the adhesive to be tested and wet laminated with a test liner
3. After
the laminate thus produced has dried at 90 C for 5 min, the laminate is
fiberized in a
repulper for 30 min. Subsequently, the pulp thus produced is used to produce a
sheet
of paper and this sheet of paper is visually inspected for specks and visible
contraries.
On a scale from 1 to 10, a weighting of 1 means "no visible specks/no visible
contraries" and a weighting of 10 means "very many visible specks/very many
contraries". When rated 4 or better, such a material is believed to be readily
recyclable
in the customary recycling operations.
= PF 70633 CA 02794340 2012-09-24
16
Example Acid content Tg Wet grab Recycling test
of polymer of polymer
1 4 wt% 41 C 6 s 2
2 5wt% 31 C 4s 3
3 2 wt% 35 C 4 s 2
4 5 wt% 28 C 4 s 3
2 wt% 43 C 7 s 2
6 5 wt% 37 C 4 s 2
7 2 wt% 44 C 5 s 2
8 11 wt% 38 C 4 s 2
9 11.5 wt% 30 C 5 s 2
11 wt% 26 C 4 s 2
11 11.5wt% 53 C 4s 2
12 5wt% 31 C 4s 3
V1 10wt% 17 C 6s 9
V2 2wt% 57 C >60s 2
V3 0.5 wt% 10 C 3 s 9
