Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
1
As originally filed
Manufacturing a papery article
Description
The present invention relates to a process for manufacturing papery articles,
such as
paper, card and board, comprising the addition of methanesulfonic acid (MSA)
to an
aqueous composition comprising at least one fiber stock to set the pH.
The present invention further relates to the use of methanesulfonic acid in
the
manufacture of a papery article, more particularly for setting the pH of an
aqueous
composition comprising at least one fiber stock in the paper/board machine
approach
flow.
Paper and papery article for the purposes of the present invention refer to
sheetlike
articles manufactured from fibers, more particularly from chemically or
mechanically
uncovered vegetable fibers, which are formed by dewatering a fiber stock
suspension
using at least one wire screen usually under addition of fillers and further
additives.
The manufacture of papery articles on state of the art paper/board machines
generally
comprises the dewatering of a fiber stock suspension, for example a chemical
pulp,
mechanical pulp and/or waste paper suspension, on at least one moving wire
screen to
form a paper web. The term paper or board machine typically subsumes the
following
assemblies: approach flow system, head box, wire section, press section, dry
end, size
press (surface sizing), film press, smoothing cylinder, smoothing system,
online
calender, online coating assembly and windup. Often, the manufacture of papery
articles comprises downstream steps of surface treatment (e.g., calendering,
coating)
and comprises finishing (e.g., roll cutting, format cutting, packing). A
general
description of the process steps and equipment parts involved in the
manufacture of
papery articles is described for example in "Papiermacher Taschenbuch, 8th
edition, Dr.
Curt Haefner-Verlag GmbH, Heidelberg".
The approach flow system is where the fiber stock suspension is made machine-
ready
for the subsequent sheet forming in the wire section. It is where, for
example, the
final/compensatory beating of the fiber stock is carried out, the stock
amounts and
stock densities are regulated, and also the regulation of the flow rates is
carried out.
Within the approach flow system, it is also possible for the metered addition
of fillers,
process chemicals and/or performance chemicals to take place. The approach
flow
system is generally held to include all equipment parts and pipework between
the
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
2
mixing and machine chest and the head box of the paper/board machine. The
approach flow system of the paper/board machine is generally also where the pH
of the
fiber stock suspension is set.
In the head box, the fiber suspension having a stock density of generally less
than
1.4% is applied to at least one moving endless wire screen (machine wire). In
the
subsequent wire section as it is known, the fiber stock suspension is drained
to a stock
density of about 12 to 24% (augmented by application of vacuum or pressure for
example) and the fibers become interfelted together to form a still wet
fibrous web
(sheet formation). This fibrous web is removed from the wire using a pickup
felt (felt
band) for example, and passes into the subsequent wet presses where the stock
density is further increased to about 50%.
Thereafter, the fibrous web is generally dried in the dryer section using
drying
cylinders. For certain end uses, the paper can then be subjected to further
processing
steps (e.g., smoothing, coating, calendering).
The fiber stock suspensions used for paper or board manufacture, in addition
to fibers,
usually comprise fillers, more particularly inorganic fillers such as calcium
carbonate,
kaolin, titanium dioxide, barium sulfate and multiple process and/or
performance
chemicals, for example sizing agents to increase the hydrophilicity and
printability of
the paper, and also, for example, retention aids, drainage aids, dyes, optical
brighteners, wet strength agents, dry strength enhancers, defoamers, biocide.
Possible fiber stocks for the manufacture of papery articles are generally
primary fiber
stocks and also secondary fiber stocks. Primary fiber stocks used are more
particularly
wood-free fiber stocks, more particularly chemical pulps such as sulfate pulp
(SA) (also
known as kraft pulp), sulfate semi-pulp, sulfite pulp (SI) of hard- and/or
softwoods.
However, wood-containing fiber stocks, more particularly mechanical pulps such
as
groundwood (HS) (also known as stone groundwood SGW), pressurized groundwood
(PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemical
thermal mechanical pulp (CTMP) and thermomechanical pulp with caustic-peroxide
pretreatment (BCTMP) may also be used. Secondary fiber stocks include various
waste paper varieties recycled into paper/board and card production, and also
deinked
pulp (DIP). DIP is produced by a waste paper recovery process in which a large
proportion of the printing ink is removed from the fiber stock suspension. In
the
deinking process, the slurried, defibered waste paper is commonly admixed with
caustic, water glass, complexing agent, surfactant and hydrogen peroxide. The
printing
inks detach from the fiber surface and are removed from the fiber stock
suspension by
flotation.
CA 02825337 2013-07-22
BASF SE PF0000071212
BPB/BPE
=
3
Chemical pulp, such as goundwood, pressurized groundwood, TMP, RMP, but also
chemical pulp are typically bleached in the course of production and/or before
use. A
distinction is generally made between oxidative and reductive bleaching
stages,
although these bleaching stages are often combined into bleaching sequences.
Bleaching frequently comprises a treatment with hydrogen peroxide under
alkaline
conditions. When the bleaching process concludes with an alkaline stage, it is
generally necessary for the fiber stock suspension to be acidified. In order
to establish
the pH necessary for paper production, it is therefore generally necessary to
add an
acid to regulate the pH.
Depending on the pH of the fiber stock suspension used for paper formation, a
general
distinction is niade between the conventional acidic process (pH in the range
from 4.5
to 6.8) comprising generally the addition of acidic aluminum salts and the
neutral
process in the pH range from 6.8 to 10.8. In the ideal case of a neutral
process, the pH
is adjusted to a value between 7.0 to 7.5. In recent decades, the neutral
process has
become more and more established, particularly because it enables calcium
carbonate
(CaCO3) to be used as a filler, for example in the form of ground calcium
carbonate
(GCC) or precipitated calcium carbonate (PCC).
Fiber stock suspension pH is of decisive importance for paper production and
has a
direct influence on paper/board machine runnability. A high pH leads to
increased
swelling of the fibers and impedes fiber stock suspension drainage. Accurate
and
reliable pH setting further contributes to preserving the whiteness of the
papery articles
and to preventing yellowing by alkalis. The choice of suitable acids for
setting the pH as
part of the manufacture of papery articles is very limited. Owing to the
requirements of
availability, price and stability, a person skilled in the art chooses from a
very limited
number of acids suitable for paper production. The use of phosphoric acid, or
of a
combination of phosphoric acid and phosphonates, or the use of carbon dioxide
for pH
setting is described in the prior art. It is further known to use sulfuric
acid and/or
bisulfite to set the pH in paper production. It has also been written that the
pH of a fiber
stock suspension can be adjusted by adding an electrolyte, such as aluminum
sulfate,
aluminum nitrate, polyaluminum chloride (PAC) and aluminum hydroxide chloride.
The WO 98/56988 document describes a process for stabilizing the pH of a pulp
suspension for paper production using a combination of an alkali metal
hydroxide and
carbon dioxide.
The US 2010/0175839 document describes a multi-stage process for adjusting the
pH
of a cellulosic pulp suspension wherein the pulp is treated at least twice
with carbon
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
4
dioxide and at least once with a strong acid, e.g., sulfuric acid, sulfurous
acid or
bisulfite, and wherein a step for carbonate removal is included.
The WO 2009/003770 document discloses a process for making paper wherein a
fiber
stock suspension comprising a mechanical pulp is subjected to an acid-base
treatment
to avoid reducing the brightness. In the process, the fiber stock suspension
is treated
initially with a strong acid, more particularly sulfuric acid, sulfurous acid,
hydrochloric
acid and bisulfite, and then with a weak base (e.g., an alkali metal
bicarbonate or alkali
metal carbonate).
The prior art use of phosphoric acid and phosphonates results in increased
formation
and deposition of calcium phosphates in various parts of the paper machine.
The
paper/board machine thus has to be increasingly idled to allow for cleaning.
Many state of the art paper machines operate at very high speeds of up to 1800
meters
per minute and outputs of up to 1000 t of paper per 24 h to increase the
production of
paper/card. Paper/board machine idling and the increased production of broke
are
therefore the decisive factors for the efficiency and economics of the
production
process.
Furthermore, phosphorus compounds pollute the wastewater cleaning facilities
of
paper mills which, unlike communal water treatment facilities, generally have
no
phosphorus-eliminating stage.
One particular problem with using carbon dioxide for pH regulation of fiber
stock
suspensions is the outgassing of carbon dioxide in the wire water circuit and
also the
attendant fluctuations in the pH. In addition, metering the gaseous additive
carbon
dioxide requires costlier metering devices.
It is an object of the present invention to provide a pH-regulating additive,
more
particularly an acid, for fiber stock suspensions in paper production, and/or
an
improved process for paper production. The process should firstly meet all
wastewater-
relevant and environmental requirements as well as provide for an efficient,
simple and
inexpensive operation. Simple metering, minimal introduction of additional
salt content
into the wire water/wastewater of the paper machine and also good drainage
behavior
of the fiber stock suspension should be ensured for instance.
We have found that, surprisingly, adding methanesulfonic acid (MSA) is a
particularly
effective way to adjust the pH of fiber stock suspensions in papermaking.
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
Methanesutfonic acid has a pKa value of about -0.6 and so is a strong or very
strong
acid. Methanesulfonic acid is generally non-oxidizing and is marked by heat
and
hydrolysis resistance in particular. Methanesulfonates are used in washing and
cleaning compositions for example. Methanesulfonic acid is further used in
acidic
5 electroplating solutions for metal coatings.
The present application is directed to a process for manufacturing a papery
article,
such as paper, card and board, comprising the steps of:
a) providing an aqueous composition comprising at least one fiber stock;
b) adding methanesulfonic acid to the aqueous composition comprising at least
one fiber stock to adjust the pH;
c) draining the aqueous composition comprising at least one fiber stock.
The use of methanesulfonic acid is associated with the following advantages in
particular:
Methanesulfonic acid is readily biodegradable and is halogen-free and thus
reduces the burden on the wastewater treatment of the production process.
Moreover, no or distinctly less phosphorus/phosphate ends up in the wastewater
of the paper/board machine.
There is less, if any, formation of deposits of calcium phosphate, for
example, in
the parts of the paper/board machine.
Owing to the high acid constant of methanesulfonic acid, comparatively low
quantities need to be added. The salt burden of process waters in papermaking
can accordingly be reduced.
Economic viability/efficiency of the manufacturing process is improved.
Methanesulfonic acid is colorless, odorless and available in high purity,
hence
there is no alien impact on the manufacturing system (process water,
wastewater, circuit water, papery articles). Therefore, methanesulfonic acid
is
particularly suitable for use in the manufacture of papery articles (packaging
materials for example) which are used in the food sector.
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
6
Methanesulfonic acid has high thermal stability, a low vapor pressure,
hydrolysis
resistance and unlimited miscibility with water, hence handling and metering
are
simple.
Methanesulfonic acid is halogen-free and has minimal corrosivity compared with
sulfuric acid for example.
The use of methanesulfonic acid is thus able to provide a distinct improvement
in the
economics of manufacturing papery articles.
Paper and papery article for the purposes of the present invention refer to
sheetlike
articles manufactured from fibers, more particularly from chemically or
mechanically
uncovered vegetable fibers, which are formed by dewatering a fiber stock
suspension
using at least one wire screen usually under addition of fillers and further
additives.
Additives are generally distinguished into process chemicals (e.g., biocides,
deaerators, retention aids) and performance chemicals (e.g., dyes, optical
brighteners,
wet strength agents). Paper and papery articles for the purposes of the
present
invention are more particularly graphic papers, office communications papers,
packaging papers, hygiene papers and specialty papers. Graphic papers for the
purposes of the invention are all papers used for printing in flexographic
printing,
letterpress, offset printing or gravure printing for example, e.g., news
print. Office
communication papers are writing, printing and copying papers, for example
photoprint
and digital printing papers. Packaging papers are papers, card and board for
packaging
purposes, for example corrugated fiberboard. Hygiene papers for the purposes
of the
invention are papers of high specific volume and high absorbency, which are
typically
used in the sanitary or kitchen sector or in the industrial sector. The term
specialty
papers identifies papers and paperboards for specific technical uses, for
example
decor papers and filter papers.
Papery articles can be classified, according to their mass per unit area, as
paper, card
or board. According to German standard specification DIN 6730, a mass per unit
area
of not more than 225 g/m2 is indicative of paper and above 225 g/m2 of board.
Papery
articles having a mass per unit area in the range from 7 to 150 g/m2 are often
also
referred to as paper, in the range from 150 to 600 g/m2 as cardboard and from
600 g/m2 as paperboard. Cardboard and paperboard typically consist of multiple
layers.
The present invention more particularly provides a process as described above,
wherein the step of draining the aqueous composition (step c) results in the
formation
of a fibrous web which is pressed and/or dried in one or more further process
steps.
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
7
The aqueous composition more particularly is a suspension (slurry) of a fiber
stock in
water. The aqueous composition may comprise further dissolved, colloidally
dissolved
or solid constituents. The constituents in question are more particularly
known to a
person skilled in the art and used/generated in the course of manufacturing
papery
articles.
The fiber stock can be more particularly selected from:
= chemical pulp (ZS), such as sulfate pulp (SA) (also called kraft pulp),
sulfate
semichemical pulp, sulfite pulp (SI);
= mechanical pulp, such as groundwood (HS) (also called stone groundwood
SGW), pressurized groundwood (PGW), refiner mechanical pulp (RMP),
thermomechanical pulp (TMP), chemical thermomechanical pulp (CTMP),
thermomechanical pulp with caustic/peroxide pretreatment (BCTMP);
= secondary fiber stock, such as waste paper (AP) and deinked pulp (DIP).
Fiber stocks used can be more particularly the above-described bleached and/or
unbleached pulps and/or fiber stocks from hard- or softwoods. Preference is
given to
using beech sulfite pulp and/or long fiber sulfate pulp.
More particularly, the aqueous composition comprises at least one fiber stock
selected
from the group consisting of sulfate pulp (SA), sulfate semi-pulp, sulfite
pulp (SI),
groundwood (HS), pressurized groundwood (PGW), refiner mechanical pulp (RMP),
thermomechanical pulp (TMP), chemical thermomechanical pulp (CTMP),
thermomechanical pulp with caustic/peroxide pretreatment (BCTMP), waste paper
(AP)
and deinked waste pulp (DIP).
In a preferred embodiment, the fiber stock used is at least one secondary
fiber stock,
more particularly waste paper and/or deinked pulp (DIP).
More preferably, the aqueous composition comprises at least one fiber stock
which has
been alkali-oxidatively bleached.
Preferably, the aqueous composition comprising at least one fiber stock has a
stock
density in the range from 0.01 to 5%, preferably in the range from 0.1 to 5%
and more
preferably in the range from 0.2 to 1.4%.
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
8
The stock density of an aqueous composition comprising at least one fiber
stock (fiber
stock suspension) is the percentage of the dry mass of the filterable solids
in the
composition relative to the mass of the entire composition. Commonly, the dry
mass is
reported as absolute dry mass or as dry mass on drying under standard
conditions
(oven dry, otro). The determination of the stock density of fiber stock
suspensions is
described in DIN 54359 (EN ISO 4119) for example.
By further constituents, the aqueous composition may comprise at least one
customary
additive (process and performance chemicals) known to a person skilled in the
art. The
additive may be selected from:
process chemicals, such as
= electrolyte, for example aluminum sulfate, aluminum nitrate,
polyaluminum chloride (PAC), aluminum hydroxide chloride, inorganic
precipitants
= organic precipitant
= biocide (e.g., slime control agent)
= deaerator
= defoamer
= dispersant
= adsorbent (e.g., talc)
= fixative (e.g., short-chain cationic polymers)
= retention aid (e.g., long-chain anionic and cationic polymers, also
partially crosslinked)
= drainage accelerant
and performance chemicals, such as
= dye
= optical brightener
= internal sizing agent (resin size, AKD, ASA, polymer size)
= surface sizing agent
= wet strength agent
= dry strength enhancer
= internal wet web strength polymer (IWWS)
More particularly, the aqueous composition additionally comprises at least one
further
additive selected from the group consisting of aluminum sulfate, aluminum
nitrate,
polyaluminum chloride (PAC), aluminum hydroxide chloride, organic precipitant,
biocide, deaerator, defoamer, dispersant, adsorbent, fixative, retention aid,
drainage
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
9
accelerant, dye, optical brightener, internal sizing agent, wet strength
agent, dry
strength enhancer and internal wet web strength polymer (IWWS).
Preferably, the aqueous composition additionally comprises at least one
inorganic filler
selected from the group consisting of ground calcium carbonate (GCC),
precipitated
calcium carbonate (PCC), kaolin, titanium dioxide and barium sulfate,
preferably
selected from the group consisting of ground calcium carbonate (GCC) and
precipitated calcium carbonate (FCC).
Adjusting the pH of an aqueous composition comprising at least one fiber stock
is more
particularly effected by adding methanesulfonic acid until the desired pH
value or the
desired pH range is reached. A person skilled in the art is familiar with
common
methods of pH control. The amount of methanesulfonic acid added depends on the
type of the aqueous composition comprising at least one fiber stock and its
original pH
and also the desired pH target value.
Adjusting the pH of the aqueous composition comprising at least one fiber
stock can be
effected by adding a mixture of acids comprising methanesulfonic acid. It is
further
conceivable to use a mixture of methanesulfonic acid and carbon dioxide, or a
mixture
of acids comprising methanesulfonic acid and carbon dioxide. More
particularly,
methanesulfonic acid is added as sole acid to adjust and/or stabilize the pH.
It is further
conceivable to adjust/regulate the pH of the aqueous composition by
additionally
adding a base known to a person skilled in the art.
The present invention provides more particularly a process for manufacturing a
papery
article as described above, wherein the pH of the aqueous composition
comprising at
least one fiber stock is adjusted to a value in the range from 4 to 11, more
particularly
in the range from 4.5 to 6.8 and more particularly in the range from 6.8 to
10.8.
When the process of the present invention relates to a process for
manufacturing a
papery article using the acidic method, it is particularly a pH in the range
from 4.5 to 6.8
which is set by adding methanesulfonic acid. When the process of the present
invention relates to a process for manufacturing a papery article using the so-
called
neutral method (usually with use of calcium carbonate as filler), the pH of
the aqueous
composition comprising at least one fiber stock is preferably adjusted to a
range from
6.8 to 10.8 and more particularly from 7.0 to 7.5.
The process described in the present application for manufacturing a papery
article
may comprise further common process steps of paper/board production, for
example
steps in stock preparation comprising dispersing, sorting, beating of the
fiber stock,
CA 02825337 2013-07-22
BASF SE PF0000071212 BPB/BPE
steps downstream of drying, such as calendering, coating, cutting, and also
steps
concerning finishing.
The addition of methanesulfonic acid to the aqueous composition comprising at
least
5 one fiber stock can take place at one or more different process sections
of the
manufacturing process of the papery article. More particularly, the addition
of
methanesulfonic acid to the aqueous composition comprising at least one fiber
stock
takes place in a paper machine approach flow.
10 The approach flow system for the purposes of the present invention is
generally held to
include all equipment parts and pipework between the mixing and machine chest
and
the head box of the paper/board machine. The approach flow system is where the
fiber
stock suspension is made machine-ready for the subsequent sheet forming in the
wire
section. It is where, for example, the final/compensatory beating of the fiber
stock is
carried out, the stock amounts and stock densities are regulated, and also the
regulation of the flow rates is carried out. The approach flow system of the
paper/board
machine is where more particularly the aqueous composition comprising at least
one
fiber stock (fiber stock suspension) is uniformly diluted from about 3 to 5%
stock
density (thick stock) to about 0.2 to 1.4% stock density. In addition, the
fiber stock
suspension can be cleaned of fiber bundles, sand, plastics, etc. This is done
more
particularly in the so-called stock fine screening via centrifugal, pressure
and/or
vibration screeners for example. The approach flow system is also where
fillers,
process chemicals and/or performance chemicals can be added. The approach flow
system of the paper/board machine is generally also where the pH of the fiber
stock
suspension is set.
It is particularly preferable for the addition of methanesulfonic acid for
adjusting the pH
to take place before, after and/or during the stock fine screening of the
aqueous
composition comprising at least one fiber stock. Stock fine screening is more
particularly effected using common screening assemblies, for example
centrifugal,
pressure and/or vibration screeners. It is preferable to add methanesulfonic
acid before
the last screening assembly before the head box.
The process of the present invention can generally be used for manufacturing
any
papery articles known to a person skilled in the art. The process of the
present
invention relates more particularly to the manufacture of a papery article
selected from
graphic paper, office communication paper, packaging paper, card, board,
hygiene
paper and specialty paper, preferably a process for manufacturing a graphic
paper or
an office communication paper. In a preferred embodiment, the invention
provides a
CA 02825337 2013-07-22
BASF SE PF0000071212
BPB/BPE
, .
11
process for manufacturing a papery article wherein the papery article is a
packaging
material for the food sector.
The present application is further directed to the use of methanesulfonic acid
in the
manufacture of a papery article.
More particularly, the use which the present invention provides for
methanesulfonic
acid in the manufacture of a papery article comprises adjusting the pH of an
aqueous
composition comprising at least one fiber stock.
More particularly, the present invention provides for the use of
methanesulfonic acid in
the manufacture of papery articles on industrially common paper and/or board
machines. Preferably, the use of methanesulfonic acid comprises adjusting the
pH of
an aqueous composition comprising at least one fiber stock in a paper and/or
board
machine approach flow. The methanesulfonic acid may be more preferably used
before
the head box.
More particularly, the present invention provides for the use of
methanesulfonic acid in
the manufacture of a papery article selected from graphic paper, office
communication
paper, packaging paper, board, card, hygiene paper and specialty paper, more
particularly a packaging material for the food sector.
