Note: Descriptions are shown in the official language in which they were submitted.
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Coating composition comprising hydrolysed wheat proteins
Technical field
The present invention relates to a paper or cardboard coating composition
comprising a modified starch and a hydrolyzed wheat protein, and also to the
method
for obtaining such a composition. The invention also relates to a method for
coating
or brightening paper or cardboard using such a composition, and to the coated
paper
or cardboard thus obtained. Finally, the invention relates to the use of a
hydrolyzed
wheat protein in the replacement of latex in a paper or cardboard coating
composition.
Technical background
Coating is a paper or cardboard finishing step which makes it possible to
confer on a sheet of paper or on a cardboard a certain number of properties,
such as
opacity, gloss or whiteness or else to improve the printability for printing
processes
such as offset printing or photogravure. During this coating step, a
composition
referred to as coating color is applied to the surface of the paper or of the
cardboard.
This composition generally comprises at least one minerai or pigment fluer, at
least
one binder and other additives such as, in particular, dispersants, rheology
modifiers,
lubricants, optical brighteners or antifoams.
The paper industry uses many chemical products, such as surfactants, optical
brighteners, water-resistance agents (ketone resin, anionic latex, etc.), to
give paper
various properties or to simplify the process for obtaining same. Latex,
typically
synthetic latex of styrene-butadiene type, is the binder most widely used. Its
function
is to enable cohesion between the various elements of the composition and to
bind
them to the fibers. Synthetic latex is produced from petroleum resources which
are
by definition non-renewable. In order to reduce the number of chemical
products
used in this industry, and to reduce the consumption of petroleum-derived
products
and also the costs, the replacement of latex in coating colors represents a
potential
market but also a sizeable technical challenge. This is because it is very
difficult to
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maintain the performance levels of a coating color while reducing the
proportion of
synthetic latex used.
Numerous approaches have been tested, including the use of soy proteins
(US 2006/174801). However, these products resulted in the obtaining of
extremely
viscous coating colors or coating colors that have to be used at very low dry
matter
contents (about 38% to 44% DM) in order to compensate for this viscosity or to
ensure dissolving of these products.
The prior art also describes the use of cold-soluble starch in such
compositions; mention may for example be made of international patent
application
WO 08/104574. However, these starches have a tendency to form aggregates
during
the dissolving thereof; they also require the use of a high-shear mixer with
which
most paper manufacturers are not equipped.
Moreover, it should be noted that coating colors are intended to be applied to
the surface of the paper or of the cardboard in very thin layers and at very
high
speed. Their application is carried out by means of a blade or a threaded rod
which
exerts very high shear forces at the surface of the paper. Thus, in the case
of non-
uniformity or of excess viscosity, these shear forces lead not only, at the
level of the
application zone, to turbulences responsible for defects in the deposit,
called
"filaments" or "beads", but also to an increase in the pressure exerted on the
paper,
increasing by the same token the risks of breakage and thus potentially hours
of
production interruption.
In order to solve this technical problem, the prior art proposes coating
compositions which have a low dry matter content. However, the reduction of
the dry
matter of the composition (and thus the increase in the water content) in
order to
reduce the viscosity thereof is not an advantageous solution in the present
application. This is because the coating color has a natural tendency to
transfer into
the sheet of paper ail or some of the water and of the water-soluble parts
that it
contains. This has several consequences, the first of which is the weakening
of the
paper or of the cardboard which, due to the excess water, can lose its
integrity and
can lead to breaking of the paper produced and thus hours of production
interruption.
The second is the loss of gloss of the paper observed following the migration
of the
water-soluble parts of the coating color into the paper. This migration leads
to a third
consequence which is the weakening of the cohesion of the layer of the paper,
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leading to problems during printing. Mention may, for example, be made of
deposits
of fibers or of minerai fillers originating from the coat on the blankets
during offset
printing. The final consequence of this excess water of the coating
composition is the
increase in energy and/or in time required to dry the paper or the cardboard
obtained.
In addition, the advantage of a coating color which has both a high dry matter
content and a low viscosity, beyond the solving of the abovementioned
problems, is
the small amount of coating color that needs to be laid. In addition, a
coating color of
low viscosity would also have the advantage of allowing very-high-speed
coating,
which constitutes a very clear industrial advantage.
Moreover, among the approaches envisioned in the replacement of latex,
none makes it possible to improve or at the very least maintain the pick
resistance
capacities of the paper or cardboard obtained. In point of fact, a strong pick
resistance guarantees preservation of the integrity of the paper or cardboard
when a
force is exerted at its surface and thus a wider use of the latter. This
property is
essential in printing, in particular offset printing where the paper is
subjected to high
stresses at the output of the inking rollers. This is because, in this step,
the film of ink
separates into 2 parts, one remaining on the paper and the other on the
blanket.
During this separation, a normal force is exerted on the paper leading to
picking of
the particles (minerai fillers or fibers) poorly bonded to one another or to
the paper
and the depositing thereof on the blankets. This phenomenon is responsible for
the
fouling of the blankets and can make it necessary for the printer to interrupt
production in order to clean them.
There is therefore currently no coating composition which has both a reduced
latex content beyond what the prior art describes, a very high dry matter
content and
a low viscosity while at the same time conferring a high pick resistance on
the paper
or cardboard obtained.
it is thus the object of the present invention to provide a coating color
corresponding to the needs of the prior art.
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Detailed description of the invention
The invention relates to a paper or cardboard coating composition having
a dry matter content of between 45% and 80%, preferentially 50% and 78%, more
preferentially 55% and 75%, comprising:
= binders which include at least one modified starch and one preferentially
synthetic adhesive,
= a hydrolyzed wheat protein having an average molecular weight of between
7
and 1000 kDa, and
= a minerai
The term "paper or cardboard coating composition" is intended to mean a
composition that is particularly suitable for coating paper or cardboard. It
is an
aqueous formulation conventionally containing water, at least one minerai
filler, one
or more binders and also various additives.
Typically, the composition according to the invention comprises, in parts per
100 parts by weight of minerai fluer:
- 1 to 99 parts of binders, preferentially 1 to 50 parts, more
preferentially 1 to 15
parts, and
- 1 to 50 parts by weight of wheat protein, preferentially 1 to 20 parts,
more
preferentially 1 to 8 parts.
The term "wheat protein" denotes a water-insoluble protein fraction
extracted from wheat four via the wet process and subsequently dried, also
known as
wheat gluten. Typically, wheat proteins having an average molecular weight of
between 7 and 1000 kDa are obtained by hydrolysis according to methods known
well to those skilled in the art [Anfinsen, C.B. Jr. (1965), Advances in
Protein
Chemistry.. y. 20, New York and London, Academic Press]. Typically, the
hydrolysis
may be thermal, acid or enzymatic. Enzymatic hydrolysis is preferred.
A wheat gluten that is particularly suitable for the present invention is
Solprog 508 sold by Tereos Syral.
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Typically, the hydrolyzed wheat protein according to the invention has a
weight-average molecular weight of between 7 and 800 kDa, 5 and 500 kDa or 8
and
100 kDa, preferentially between 9 and 80 kDa, more preferentially between 10
and
70 kDa, even more preferentially between 12 and 50 kDa, even more
preferentially
between 13 and 40 kDa.
The term "binder" is intended to mean a compound having the function of
sticking the particles of minerai fluer (or pigments) to one another and of
maintaining the coat at the surface of the paper.
According to the invention, the composition comprises a binders/wheat
protein ratio of from 1:5 to 5:1, preferentially from 1:3 to 3:1, more
preferentially
1:2 to 2:1.
According to the present invention, the binders are at least one modified
starch and one adhesive such as a synthetic adhesive; typically in a modified
starch/synthetic adhesive ratio of from 1:5 to 5:1, preferentially from 1:3 to
3:1,
more preferentially 1:2 to 2:1.
For the purposes of the present invention, the term "modified starch" is
intended to mean any starch that has been chemically or physically treated.
The molecules of modified starches present in the present invention can
originate from a plant source such as cereals, tubers, roots, vegetables and
fruits.
Thus, the starch(es) can originate from a plant source chosen from corn, peas,
potato,
sweet potato, banana, barley, wheat, rice, oats, sago, tapioca and sorghum.
More particularly, the modification reactions can be carried out for example:
= by pregelatinization by causing the starch granules to burst (for example
drying
and cooking in a drying drum);
= by acid hydrolysis using for example strong acids or by enzymatic
hydrolysis;
= by oxidation using for example strong oxidizing agents resulting in the
introduction of carboxyl groups into the starch molecule and in the
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depolymerization of the starch molecule (for example by treating an aqueous
starch solution with sodium hypochlorite);
= by crosslinking with functional agents capable of reacting with the
hydroxyl
groups of the starch molecules which will thus be bonded to one another (for
example with glyceryl and/or phosphate groups); phosphorus-containing
compounds of monostarch phosphates (of the St-O-P0-(0X)2 type), of distarch
phosphates (of the St-O-P0-(0X)-0-St type) or even of tristarch phosphates (of
the St-O-P0-(0-St)2 type) or mixtures thereof are for example obtained. X
denotes for example alkali or alkaline earth metals;
= by esterification in an alkaline medium for the grafting of functional
groups, in
particular C1-C6 acyl (acetyl), C1-C6 hydroxyalkyl (hydroxyethyl,
hydroxypropyl), carboxymethyl or octenylsuccinic groups. Mention may in
particular be made of sodium carboxymethyl-modified starches;
= by dextrinization, such as for example by a dry-phase treatment of a
native
starch, by the action of heat, in an optionally dry medium, optionally in the
presence of a chemical agent, by the action of heat or a combination of these
various means. Most of these methods, whether they are batchwise or
continuous, call for transformation temperatures higher than 80 C and for the
optional presence of an acid, of an alkaline agent and/or of an oxidizing
agent.
Suitable modified starches comprise, but are flot limited to, pregelatinized
starches, low-viscosity starches (for example, dextrins, hydrolyzed starches,
oxidized
starches), stabilized starches (for example, starch esters, starch ethers),
crosslinked
starches and starches which have received a combination of treatments (for
example
crosslinking and gelatinization treatments) and mixtures thereof.
Dextrins are the preferred modified starches. For the purposes of the present
invention, the term "dextrin" is intended to mean a modified starch obtained
from
native starch by dextrinization; typically, the dextrins according to the
invention are
flot subjected to any other modification, in particular chemical modification.
The
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dextrins that are suitable for the present invention are, for example, white
dextrins,
generally obtained by transformation of starch at temperatures often of
between 100
and 170 C, in the presence of a chemical agent or chemical agents, in
particular of
acid, in relatively high amounts; yellow dextrins, often obtained by
transformation of
starch at higher temperatures, generally of between 170 and 230 C, in the
presence
of a chemical agent or chemical agents, in particular of acid; finally,
dextrins termed
"British Gum" obtained solely by the action of heat, at high temperature,
often above
230 C. A dextrin that is particularly suitable for the present invention is a
wheat-
based dextrin, typically the Mylofilm 214 or Mylofilm 218 dextrin sold by
the
company Tereos Syral.
Typically, in the context of the present invention, the particularly suitable
modified starch has a weight-average molecular weight of between 20 and 300
kDa,
preferentially 30 and 250 kDa, more preferentially between 35 and 233 kDa,
even
more preferentially between 40 and 200 kDa, even more preferentially between
42
and 150 kDa, and/or a viscosity of between 50 and 400 mPa.s (Brookfield, 70 C,
31% DM). The measurement, with a Brookfield viscometer, of the modified
starch,
such as, for example, of a dextrin, is performed in solution and is carried
out on an
RVDV-E model, the measurement is carried out at a speed of 20 rpm with spindle
3.
The measurements are carried out at 70 C. The module is dipped in a
composition of
modified starch in suspension at 31% of dry matter up to the indicator une of
the
spindle; the value is recorded after 10 s of rotation.
The term "average molecular weight" is intended to mean the weight-
average molecular weight.
In the context of the hydrolyzed protein, this average molecular weight is
measured by size exclusion chromatography (SE-11PLC) coupled with a UV
detector
regulated at the wavelength of 214 nm. The size exclusion chromatograph is
equipped with a pump which circulates an eluent composed of a PBS phosphate
buffer (0.1 M Na2HPO4-Nal-12PO4 with 0.1% of SDS) at a flow rate of 0.7 ml/min
in
a TSKG4000SWx1 column. This measurement is expressed in daltons. The
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preparation of a sample can be carried out by dissolving the product studied
in a
phosphate extraction buffer with 1% of SDS, followed by centrifugation to
recover
the supernatant.
In the context of the modified starch and more particularly of dextrin, the
average molecular weight is expressed in daltons and can be determined by
those
skilled in the art by size exclusion chromatography coupled with a detector of
MALLS (Multi Angle Laser Light Scattering) type. The preparation of a sample
can
be carried out by dissolving 50 mg by dry weight of a modified starch and in
particular of dextrin in a solvent consisting of a mixture of 90% (v/v) of
DMSO
(dimethyl sulfoxide) in deionized water containing 0.1% (w/v) of sodium
nitrate.
After stirring overnight, the mixture is preheated for 1 hour at 105 C and
then
centrifuged for 15 min at 5300 g. A volume of 100 ml of the supernatant is
injected
into a size exclusion chromatography apparatus, the mobile phase of which is
for
example composed of a mixture of 90% (v/v) of DMSO (dimethyl sulfoxide) in
deionized water containing 0.1% (w/v) of sodium nitrate, at a flow rate of 0.5
ml/min
and a temperature of 70 C, the columns used preferentially being a combination
in
series of Gram columns. The detector is for example an angle laser such as the
New
Generation 3-angle miniDawn Treos. The calibration is carried out with
Viscotec
P82 Shodex standards. In the context of the present invention, the adhesive is
preferentially synthetic. An example of synthetic adhesive suitable for the
present
invention is a latex, a vinyl acetate, polyvinyl alcohol, sodium
carboxymethylcellulose and hydroxyethylcellulose.
The term "latex" refers to an aqueous dispersion of polymer which
corresponds to a colloidal dispersion of synthetic polymers in an aqueous
phase, i.e.
a dispersion of polymer microparticles in suspension in an aqueous phase,
sometimes
also referred to as polymer suspension or polymer emulsion. Examples of latex
suitable for the present invention are chosen from the group made up of
styrene-
butadiene latexes, polyvinyl alcohol latexes and acrylic copolymer latexes,
preferentially latex of styrene-butadiene type.
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In general in the coating color, the minerai filler introduced is carried in
the
form of an aqueous suspension. Conventionally, this filler is a calcium
carbonate
suspended in water by means of a dispersing agent. Typically, a minerai filler
that is
particularly suitable for a coating composition comprises a sufficient degree
of
whiteness (greater than 80% of the whiteness of barium sulfate at 457 nm), a
particle
size distribution of from 0 to 10 1.1m at most (the average particle size
being between
0.2 and 2 itm) and a minimum degree of agglomeration of the particles. For
example,
the minerai fluer can be chosen from the group made up of calcium carbonates,
coating clay, calcined fine clay, alumina trihydrate, talc and titanium
dioxide.
The term "calcium carbonate" comprises ground calcium carbonate (GCC),
that is to say a calcium carbonate obtained from natural sources, such as
limestone,
marble, calcite or lime. The term "calcium carbonate" also comprises
precipitated
calcium carbonate (PCC), that is to say a synthesized substance, generally
obtained
by precipitation following a reaction of carbon dioxide and calcium hydroxide
(hydrated lime) in an aqueous environment or by precipitation of a source of
calcium
and of carbonate in water.
The composition according to the invention may also comprise other agents
such as one or more dispersing agents. The term "dispersing agent" is intended
to
mean an agent having the function of maintaining the particles of minerai
fluer in a
state of electrostatic dispersion. By way of example, the dispersing agent is
chosen
from the group made up of sodium polyacrylate, tetrasodium polyphosphate,
tetrasodium pyrophosphate, pentasodium tripolyphosphate, sodium tetraphosphate
and sodium silicate.
The composition may also comprise at least one lubricant, typically chosen
from the group made up of sodium stearate, calcium stearate, sulfonated oils,
sulfated
tall ou l fatty acid and polyethylene emulsions.
The composition may also comprise at least one insolubilizing agent chosen
from the group made up of urea resins, melamine resins, glyoxal, zinc
compounds,
formaldehyde and dimethylolurea.
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The invention also relates to a method for producing the composition
according to the invention, comprising the following steps:
- mixing,
with stirring, a minerai rifler and binders which include at least one
modified starch, preferentially a dextrin, and one preferentially synthetic
adhesive, said modified starch preferentially having previously undergone a
cooking step,
- adding,
with stirring, to the mixture obtained, a hydrolyzed wheat protein having
an average molecular weight of between 7 and 1000 kDa, said hydrolyzed wheat
protein preferentially being in a pulverulent form,
- adding water,
with stirring, so as to obtain a composition having a dry matter
content of between 45% and 80%; optionally, the adding of water is carried out
with the minerai fluer and/or the modified starch and/or the hydrolyzed
protein.
Typically, during the method for producing the composition according to the
invention, said modified starch such as in particular a dextrin can be
dissolved in
the water, and can preferentially undergo a cooking step, prior to it being
mixed
with the adhesive. Independently, the minerai tiller can be dissolved
beforehand
in the water before being mixed with the binders.
The invention also relates to a method for coating or brightening paper or
cardboard, said method comprising the steps consisting of
(a) the provision of a composition according to the invention,
(b) the depositing of said composition on a paper or cardboard substrate.
The step of depositing said composition on a paper or cardboard substrate can
be carried out by means of blade coating, pencil coating, a threaded rod, size
press
curtain coating or a film press or any other technique known to those skilled
in the
art. Typically, the depositing step is carried out at a temperature of between
25 and
60 C.
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Typically, said composition is applied to at least one face of said paper or
cardboard substrate in an amount of between 3 g/m2 and 15 g/m2, preferably
between
g/m2 and 10 g/m2.
The invention also relates to a paper or cardboard coated with the
5 composition according to the invention.
The invention also relates to the use of a hydrolyzed wheat protein in the
replacement of latex in a paper or cardboard coating composition, said
hydrolyzed wheat protein preferentially having an average molecular weight of
between 7 and 1000 kDa.
The invention relates to the use of a combination of a hydrolyzed wheat
protein and of a modified starch, and more particularly a dextrin, in the
replacement
of latex, preferentially in a modified starch/wheat protein ratio of 1:5 to
5:1,
preferentially of 1:3 to 3:1, more preferentially 1:2 to 2:1.
Typically, said wheat protein or said combination of wheat protein with a
modified starch, preferentially a dextrin, is used in the replacement of from
1% to
40% of the latex of said composition, preferentially from 10% to 35%, more
preferentially from 15% to 30%.
Although they have distinct meanings, the terms "comprising", "containing"
and "consisting of' have been used interchangeably in the description of the
invention, and can be replaced by one another.
The invention will be understood more clearly on reading the following
examples given only by way of illustration.
Examples
Example 1: Replacement of latex by a modified starch
Production of coating colors:
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Preliminary tests showed that the best results were obtained with a dry matter
content greater than 45% (machinability and energy yield). A clearer
improvement is
observed from 60%. Indeed, an increase in the breaking of the paper when the
coating color is diluted (less than 45% of DM) was noted. Furthermore, an
increase
was noted in the drying time below 60% and even more below 45%, which appears
to be the lowest acceptable dry matter content. Since the paper undergoes a
drying
step after coating, any excess water in the coating color results in an
increase in the
drying times and thus in the production cost. Consequently, the tests were
continued
with coating colors having a dry matter content of 70%.
A coating color was produced according to formulae R1 to R4 of table 1
below.
Calcium Synthetic Dextrin
carbonate binder
RI 100 3.5 3.5
R2 100 3 4
R3 100 2.5 4.5
R4 100 2 5
Table 1: Coating compositions cornprising dextrin as partial replacement for
latex
The recipes are given in number of parts (as is standard practice in
papermaking).
The dextrin (Mylofilm0 214) is a wheat-based dextrin (Mw = 47 kDa,
Wt = 11.6) sold by Tereos Syral. It is first of ail cooked at a concentration
of 35%
dry matter on a jet cooker (Temp. = 130 C, residence time: 3 min), then
diluted to
31%.
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The coating color is produced using a stirrer (IKA type) first of ail by
suspending the calcium carbonate in water at 79.7% (Hydrocarb 90 supplied by
the
company Omya). The synthetic binder (styrene-butadiene DL930 latex from the
company Styron) and also the dextrin dissolved as previously specified are
then
added to the calcium carbonate. The concentration is adjusted with water in
order to
obtain a dry matter content of 70%. The stirring speed is adjusted to 1500
rpm; the
pH is then adjusted to 9. The coating color is thus stirred for 10 min.
The coating colors of table 1 were tested in coating tests.
The viscosity of the coating colors is evaluated before coating of the paper.
Brookfield viscosity
The measurement of the coating color with a Brookfield viscometer is carried
out on an RVDV-E model; the measurement is carried out at a speed of 20 rpm
with
spindle 3. The measurements are carried out at 40 C. The module is dipped in
the
coating color up to the indicator une of the spindle, and the value is
recorded after
10 s of rotation.
Paper coating
The coating color is deposited on the paper in an amount of 6 g/m2 on a
single face using a DT blade coater coating pilot plant allowing drying
combining
infrared radiation and hot air. The coating speed is 20 m/min.
The paper used is an 80 g/m2 thin paper supplied by the company Fedrigoni.
The paper thus coated is then stored in a humidity- and temperature-
conditioned room (50% humidity, 23 C) for 24 h before any test.
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Dry IGT pick resistance
The dry pick measurement is carried out according to the IGT W31 method
(ISO 3783:2006). This measurement makes it possible to evaluate the strength
of the
layer. Indeed, the binders (synthetic or natural such as starch) are used to
maintain
the minerai fillers required for the paper printing properties. If the binding
capacity is
too low, the minerai fillers are picked from the paper during printing and are
deposited on the inking roll, leading to frequent interruptions. The higher
the dry IGT
measurement, the higher the pick resistance of the layer.
Results
The analysis of the characteristics of the paper obtained made it possible to
demonstrate that replacing the latex with dextrin in solution leads to a loss
of the pick
properties (table 2).
Brookfield Dry pick
viscosity (m/s)
(mPa.$)
R1 125 0.45
R2 140 0.40
R3 145 0.37
R4 155 0.19
Table 2: Brookfield viscosity of the coating compositions RI to R4 and pick
properties of the papers obtained
In fact, replacing the latex with dextrin alone does flot make it possible to
maintain the characteristics of the coating and thus leads to a clear decrease
in the
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pick properties of the layer. Thus, dextrin alone does flot make it possible
to
compensate for the reduction in latex in the coating color.
Example 2: Replacement of latex with hydrolyzed soy or wheat proteins
The use of plant proteins as a replacement for latex was evaluated. After
several tests, it was noted that the addition of proteins in addition to the
dextrin
makes it possible to observe better results in the replacement of latex than
those
observed for the dextrin alone, more particularly regarding the dry pick
properties of
the composition obtained. This effect was observed only for hydrolyzed
proteins, not
for native proteins. Thus, nonhydrolyzed wheat gluten, because of its low
solubility,
does flot make it possible to obtain uniform coating colors of acceptable
viscosity,
and even less so the replacement of latex. In order to evaluate the effect of
replacing
the latex with hydrolyzed proteins of various botanical origins, the R1
mixture was
chosen as reference recipe for a coating color.
The coating colors were produced as in example 1 according to the formulae
of table 3 in which the synthetic latex is replaced with proteins in an amount
of 14%
(R5), 30% (R6) and 43% (R7).
Calcium Synthetic Dextrin Protein
carbonate binder
RI 100 3.5 3.5
R5 100 3 3.5 0.5
R6 100 2.5 3.5 1
R7 100 2 3.5 1.5
Table 3: Coating compositions comprising dextrin and proteins as partial
replacement for latex
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In order to reduce the amounts of latex in the coating compositions,
hydrolyzed wheat and soy proteins were tested on the basis of the proportions
provided in table 3.
The proteins tested are the following:
- hydrolyzed wheat proteins having a low molecular weight (Mw = 5.7 kDa),
- hydrolyzed wheat proteins having a medium molecular weight of 15.5 kDa
(Solpro 508 sold by Tereos Syral) and
- hydrolyzed soy protein (Sobind LVL from DuPont).
The proteins are added to the coating color without prior dilution.
The coating color is produced as in example 1, using a stirrer (IKA type), by
suspending the calcium carbonate in water at 79.7% (Hydrocarb 90 supplied by
the
company Omya). The synthetic binder (styrene-butadiene DL930 latex from the
company Styron) and also the dextrin having been dissolved are then added to
the
calcium carbonate as previously specified. In this step, the protein is
incorporated
into the color in solution form or as powder, as appropriate. The
concentration is
adjusted with water in order to obtain a dry matter content of 70%. The
stirring speed
is adjusted to 1500 rpm; the pH is then adjusted to 9. The coating color is
thus stirred
for 10 min.
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Hydrolyzed soy proteins Hydrolyzed wheat proteins
Low molecular weight Medium molecular weight
(Mw = 5.7 kDa) (Mw = 15.5 kDa)
Brookfield Dry pick Brookfield Dry Brookfield Dry
viscosity (m/s) viscosity IGT viscosity IGT
(mPa.$)
RI 125 0.45 125 0.45 125 0.45
R5 254 0.49 128 0.50 147 0.60
R6 636 0.33 218 0.32 168 0.42
R7 853 0.25 230 0.24 182 0.25
Table 4: Brookfield viscosity of the coating compositions in which 14%, 30%
and
43% of latex are replaced with a mixture of dextrins and hydrolyzed proteins
and
pick property of the papers obtained
On reading the results (table 4), it is noted that replacing the latex at more
than 40% with any one of the hydrolyzed proteins tested does flot make it
possible to
maintain the pick resistance characteristics provided by the latex. Only the
partially
hydrolyzed soy and wheat protein hydrolyzates enable a replacement that can
reach
35% (R6).
However, replacing the latex with the hydrolyzed soy protein leads to a clear
increase in the viscosity starting from 14% (R1). This increase is accentuated
at 30%
(R6) and 42% (R7), making the coating composition difficult to use. Such a
viscosity
does flot allow application at the industrial level since it would result in a
considerable increase in pressure during the depositing, leading to
machinability and
paper quality problems.
CA 02975499 2017-07-31
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Conversely, the low-molecular-weight wheat protein hydrolyzates have only
a limited effect on the viscosity of the composition obtained but do flot make
it
possible to compensate for the reduction in latex starting from 30%. Indeed,
at 30%
replacement of the latex, a loss of pick resistance is observed (0.45 of IGT
at 0%
replacement; 0.5 at 14% replacement for 0.30 at 30% replacement).
Among the various hydrolyzed proteins tested, only the partially hydrolyzed
wheat proteins allow a significant increase in pick resistance at 14% latex
replacement (composition R5).
Finally, only the partially hydrolyzed wheat proteins confer a maintaining
both of the pick characteristics and also of the viscosity characteristics.
Indeed, 30%
replacement of the latex (R6) occurs with the pick resistance properties and
also the
viscosity characteristics of the composition obtained being maintained (0.45
m/s for
0 part replaced (R1) compared with 0.42 m/s for 30% replaced (R6)).
In addition, the advantage of the hydrolyzed wheat proteins is that, contrary
to the soy proteins, they are soluble enough to be directly added to the
coating color
and do flot require a prior dilution adding a not insignificant amount of
water and
thus reducing the dry malter content of the coating color, thereby making it
possible
to vary quite freely the dry matter content of the composition.
