U.S. patent application number 12/680788 was filed with the patent office on 2011-01-20 for method for controlling deposit formation.
Invention is credited to Jonni Ahlgren, Thorbjorn Ahlskog, Lars-Ola Berts, Juha Rintala, Reetta Strengell.
Application Number | 20110011546 12/680788 |
Document ID | / |
Family ID | 38656760 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110011546 |
Kind Code |
A1 |
Rintala; Juha ; et
al. |
January 20, 2011 |
METHOD FOR CONTROLLING DEPOSIT FORMATION
Abstract
The invention relates to a method for controlling deposit
formation on paper machine rolls, said method comprising applying
at the dry end of a paper machine an aqueous solution of an anionic
or non-ionic polymer on the surface of the paper for preventing the
rolls from being contaminated by stickies and/or other depositable
material from the paper.
Inventors: |
Rintala; Juha; (Vaasa,
FI) ; Berts; Lars-Ola; (Malax, FI) ;
Strengell; Reetta; (Vaasa, FI) ; Ahlskog;
Thorbjorn; (Vaasa, FI) ; Ahlgren; Jonni;
(Espoo, FI) |
Correspondence
Address: |
CANTOR COLBURN LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Family ID: |
38656760 |
Appl. No.: |
12/680788 |
Filed: |
September 30, 2008 |
PCT Filed: |
September 30, 2008 |
PCT NO: |
PCT/FI08/50544 |
371 Date: |
October 8, 2010 |
Current U.S.
Class: |
162/135 |
Current CPC
Class: |
D21H 21/02 20130101;
D21H 17/36 20130101; D21H 17/47 20130101; D21H 23/50 20130101; D21H
17/42 20130101; D21H 17/37 20130101; D21H 17/33 20130101 |
Class at
Publication: |
162/135 |
International
Class: |
D21H 21/02 20060101
D21H021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2007 |
FI |
20070746 |
Claims
1. A method for controlling deposit formation on paper machine
rolls, said method comprising applying at the dry end of a paper
machine an aqueous solution of an anionic or non-ionic polymer on
the surface of the paper for preventing the rolls from being
contaminated by stickies and/or other depositable material from the
paper.
2. The method of claim 1 wherein the paper machine rolls are
calender rolls.
3. The method of claim 2 wherein the calender rolls include thermo
rolls.
4. The method of claim 3 wherein the surface temperature of the
thermo rolls is at least 100.degree. C.
5. The method of claim 1 wherein the anionic polymer comprises a
condensation product of an aromatic sulphonic acid with
formaldehyde.
6. The method of claim 1 wherein the aqueous solution of the
anionic or non-ionic polymer is applied in an amount ranging from
0.001 to 0.5 gram per m.sup.2 of the surface of the paper per side
of the paper calculated as active substance.
7. The method of claim 6 wherein the aqueous solution of the
anionic or non-ionic polymer is applied in an amount ranging from
0.01 to 0.03 gram per m.sup.2 of the surface of the paper
calculated as active substance.
8. The method of claim 1 wherein the aqueous solution of the
anionic or non-ionic polymer is applied on both sides of the
paper.
9. The method of claim 1 wherein the applying is made by
spraying.
10. The method of claim 2 wherein the paper machine is equipped
with a moistening shower or showers downstream of the calender
rolls, said aqueous solution of the anionic or non-ionic polymer
being sprayed by means of said moistening shower(s).
11. The method of claim 5, wherein the condensation product of an
aromatic sulphonic acid with formaldehyde comprises
naphthalenesulphonate formaldehyde condensate.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method for controlling deposit
formation on paper machine rolls, especially calender rolls.
BACKGROUND OF THE INVENTION
[0002] A papermaking process starts with stock preparation where
cellulosic fibers are mixed with water and mineral filler (usually
clay or calcium carbonate). The obtained slurry is delivered by
means of a head box on a forming fabric or press fabric or wire to
form a fibrous web of cellulosic fibers at the forming section of
the paper machine. Then water is drained in the draining section
and the formed web is conducted to the press section including a
series of roll presses where additional water is removed. The web
is then conducted to the drying section of the paper machine where
most of the remaining water is evaporated typically by means of
steam-heated dryer drums. Post drying operations include
calendering where the dry paper product passes between rolls under
pressure, thereby improving the surface smoothness and gloss and
making the caliper/thickness profile more uniform. There are
various calenders such as machine calenders where the rolls usually
are steel rolls and include a heated roll (thermo roll), and
supercalenders that use alternate hard and soft, heated rolls.
[0003] It is well known that pitch can accumulate in papermaking
causing problems. "Pitch" is a term originally used to describe
sticky materials which appear in paper making and originate from
the wood raw material. However, nowadays the term "pitch" also
includes for example ink and adhesive present in recycled paper.
The term "stickies" is also used for such substances. The pitch can
deposit at various points in the paper making system. It can block
fabrics and thus prevent drainage of the web. It can also adhere to
the wires and/or dryer drums causing holes in the paper.
Additionally it can deposit on press rolls or other rolls which
come into direct or indirect contact with the paper material.
[0004] A number of chemicals have been used or proposed to be used
for eliminating the above described problems, especially at the wet
end of the papermaking system.
[0005] EP 0 493 066 A discloses a method for the control of pitch
in pulp or paper making which method comprises applying to the pulp
or paper making equipment which is not in continuous contact with
water a water soluble cationic polymer and a water soluble anionic
polymer. These two polymers are applied separately. It is claimed
that by using this combination of cationic and anionic polymers it
is possible to obtain a coating on the pick up felt, paper forming
wire, press roll and dandy roll which prevents pitch from adhering
to them. The cationic polymer can be polyethylene imine or a
protonated or quaternary ammonium polymer. Preferably the cationic
polymer is derived from an amine and an epihalohydrin or a
dicyandiamide formaldehyde condensate. The anionic polymer can be a
sulphonate or carboxylate. A preferred anionic polymer is lignin
sulphonate or polynaphthalene sulphonate.
[0006] WO 2005/094403 A discloses a paper machine belt conditioning
apparatus and method. In this method, typically in the press
section, a continuously rotating belt on which a fibrous web
travels is sprayed with a conditioning chemical. A number of
conditioning chemicals is proposed including various surfactants,
solvents, acid-based cleaners and alkaline cleaners. The apparatus
may also include a doctor blade.
[0007] WO 97/15646 A discloses a release agent for rolls, such as
press rolls in papermaking. The release agent prevents the
formation of deposits on the surface of the rolls. The release
agent is in the form of a microemulsion which preferably comprises
a deposit preventing component. This component is preferably a
dicyandiamide formaldehyde condensate.
[0008] The paper M. Pohjolainen et al., Paperi ja Puu, Vol. 89, No.
2, 2007, pages 92-94, reports some pilot trials where PCC filled SC
paper were treated on a pilot multi-nip supercalender. Various
chemical solutions were sprayed onto each side of the sheet prior
to calendering. According to this report the spraying of a
starch-based polymer having a concentration of from 3 to 4% in the
spray water, onto the paper can result in minimal deposition of
material on the roll surface.
[0009] Deposit formation on modern calenders, especially on the
thermo rolls is a serious problem. This problem has previously been
solved by mechanical cleaning during production by doctor blades or
by chemical washings during stoppages normally with strong alkaline
solutions. This problem may also appear on other paper machine
rolls, such as heated dryer rolls or drums.
BRIEF DESCRIPTION OF THE INVENTION
[0010] The invention relates to controlling deposit formation on
paper machine rolls by spraying a chemical onto the surface of the
paper. The chemical moves with the paper to the rolls protecting
the same from collecting sticky material from the paper.
DETAILED DESCRIPTION OF THE INVENTION
[0011] According to the invention it has surprisingly been found
that anionic polymers, when sprayed in a small amount in the form
of a diluted aqueous solution on the surface of the paper, worked
perfectly well preventing deposit formation on the rolls. At the
same time paper dusting and linting were significantly reduced.
Also non-ionic polymers work similarly and are useful for this
purpose.
[0012] Thus, according to the invention there is provided a method
for controlling deposit formation on paper machine rolls, said
method comprising applying at the dry end of a paper machine an
aqueous solution of an anionic or non-ionic polymer on the surface
of the paper for preventing the rolls from being contaminated by
stickies and/or other depositable material from the paper.
[0013] "Paper machine" is in this specification meant of include
paper machines having an on-line calender or an off-line calender.
In the latter case the calender is separate from the actual paper
machine. The paper machines also include board machines.
[0014] Said paper machine rolls include calender rolls and dryer
rolls. The paper machine rolls are preferably calender rolls, and
more preferable thermo rolls of calenders, especially of
supercalenders. The surface temperature of thermo rolls is
typically at least 100.degree. C.
[0015] The anionic or non-ionic polymer used in the present
invention is preferably not derived from natural products such as
starch, cellulose or saccharides.
[0016] The anionic and non-ionic polymers should be soluble in
water. Suitable anionic polymers useful in the present invention,
include:
[0017] Lignosulphonates such as sodium lignosulphonate.
[0018] Condensation products of aromatic sulphonic acids with
formalin such as condensed naphtalene sulphonates.
[0019] Dispersing anionic polymers and copolymers polymerized from
anionic monomers, or charged to give an anionic form after
polymerization. Said polymers comprise repeating units with anionic
charges such as carboxylic acids, salts of carboxylic acids,
sulphonic acids, salts of sulphonic acids, and/or mixtures thereof.
Anionic copolymers may be produced by copolymerizing an anionic
monomer with another anionic comonomer, an uncharged comonomer
and/or a cationic comonomer. Anionic monomers may typically include
acrylic acid, methacrylic acid, vinyl sulphonate,
2-acrylamide-2-methylpropanesulphonic acid, styrenesulphonic acid,
or salts thereof and other corresponding monomers. Polymers charged
to give an anionic form only after polymerization include
hydrolyzed polyacrylamides and polymers produced from maleic
anhydride.
[0020] Anionic polymers may also contain different types of charged
repeating units such as phosphates, like ethyleneglycol
methacrylatephosphate, or phosphonic acids or salts thereof, like
vinylphosphonic acid.
[0021] As examples of the anionic polymers described above
following may be mentioned:
poly(meth)acrylates, polyacrylate-maleate, polymaleate,
poly-.alpha.-hydroxyacrylic acid, polyvinylsulphonate,
polystyrenesulphonate, 2-acrylamide-2-methylpropane sulphonate and
polyvinyl phosphonate.
[0022] Suitable non-ionic polymers useful in the present invention
include polyvinyl alcohol, polyvinyl pyrrolidone, polyalkoxy
silanes and polyethoxy alcohols.
[0023] The above mentioned salts of the polymers or monomers are
preferably alkali metal salts, such as sodium or potassium, or
alkaline earth metal salts, such as calcium or magnesium.
[0024] A preferred anionic polymer comprises a condensation product
of an aromatic sulphonic acid with formaldehyde such as
naphthalenesulphonate formaldehyde condensate.
[0025] The aqueous solution of the anionic or non-ionic polymer is
applied in an amount preferably ranging from 0.001 to 0.5 gram per
m.sup.2 of the surface of the paper per side of the paper
calculated as active substance. A more preferred amount ranges from
0.001 to 0.3 gram per m.sup.2, and a still more preferred amount
ranges from 0.01 to 0.03 gram per m.sup.2 of the surface of the
paper calculated as active substance.
[0026] The concentration of the aqueous solution of the anionic or
non-ionic polymer is preferably from 0.01 to 20% by weight, more
preferably from 0.1 to 5% by weight.
[0027] The aqueous solution of the anionic or non-ionic polymer can
be applied on one or both sides of the paper.
[0028] The applying is preferably made by spraying.
[0029] The paper to be calendered is normally moistured and some
paper machines are equipped with a moisturing shower or showers
downstreams of the calender rolls.
[0030] According to a preferred embodiment of the invention the
aqueous solution of the anionic or non-ionic polymer is sprayed by
means of said moisturing shower or showers.
[0031] In respect of dryer rolls the aqueous solution of the
anionic or non-ionic polymer can be applied on the web to be dried
by per se known means, such as by spraying.
[0032] The invention is now described in more detail by means of
examples. In this specification the percentages are % by weight
unless otherwise specified.
Example 1
[0033] Pilot trials were made by using a multi-nip
supercalender.
[0034] The base paper was of mixture of peroxide-bleached
thermo-mechanical pulp and bleached chemical pulp, the base paper
having 51 g/m.sup.2. The filler was kaolin and ground calcium
carbonate and the content thereof was 33-34%.
[0035] The deposit formation on the first thermo roll was
inspected.
[0036] The run parameters of the calender were as follows:
Surface temperature of the first thermo roll: 190.degree. C. Load:
1.sup.st stack 550 kN/m Steaming in 1.sup.st box: 2 g/m.sup.2 Water
amount from moisturing shower before the 1.sup.st nip: 6.5
g/m.sup.2 Speed: 530 m/min
[0037] In the trials following chemicals were tested:
Example 2
Pure Water (Reference)
[0038] In the trial runs precipitation appeared as a yellowish mat
surface/film on the first thermo roll. The deposit was not formed
as bands on the roll but was smooth in the cross direction. Some
loose dusting appeared.
Example 3
A Dicarboxylic Ester in the Form of an Emulsion (Reference)
[0039] This is a commercial product which is used in paper machines
for deposit control, stickies control and wire purification. This
product was diluted to a 2% solution of the commercial product and
on the surface of the paper. As compared to Example 2, this product
resulted in a clearly thinner yellowish, mat layer which was just
detectable. The deposit was not formed as bands on the roll but was
smooth in the cross direction. This product did not have any effect
on dusting.
Example 4
Sodium Naftalenesulphonate Formaldehyde Condensate (Invention)
[0040] This anionic polymer (CAS 36290-04-7) is a chemical which is
typically used at the wet end of paper machines for pitch
control.
[0041] An aqueous 30% solution of this anionic polymer was diluted
to give a 0.3% aqueous solution (as active substance). This
solution was sprayed on the surface of the paper as described above
in the amount of 6.5 g/m.sup.2. Thus, the amount of the anionic
polymer on the paper surface was about 0.02 g/m.sup.2 calculated as
active substance.
[0042] This anionic polymer resulted in that no deposition at all
was formed on the roll. The surface of the roll remained clear and
glossy. Also the dusting was clearly reduced.
Example 5
Dicyandiamide Formaldehyde Condensate (Reference)
[0043] This is a cationic polymer which is a conventional deposit
preventing chemical which is applied directly to the rolls. An
aqueous 30% solution of this cationic polymer was diluted to give a
0.6% aqueous solution (as active substance), and sprayed on the
surface of the paper. This cationic polymer resulted in a thin
smooth, mat layer over the whole thermo roll. Additionally, the
precipitation was accumulated as one narrow (<1.0 cm) yellowish
white band. The band was thin and could be removed by the doctor
blade. As compared to Examples 2, 3 and 4, the dusting was clearly
stronger.
[0044] The above test results from pilot trials show the Example 4
representing the present invention worked perfectly well, whereas
Examples 2, 3 and 5 were not satisfactory.
* * * * *