Note: Descriptions are shown in the official language in which they were submitted.
- 217016g
METHOD OF CONTROLLING THE SURFACE PROPERTIES OF
SURFACES lN A PAPER MACHlNE AND USE OF THE METHOD lN THE
SURFACE TREATMENT OF SURFACES IN A PAPER MACHINE
BACKGROUND OF THE INVENTlON
The present invention relates to a method of controlling the surface properties of surfaces
in a paper m~r.hin~ by treating the surfaces with a surface treatment material to achieve desired
surface properties.
Paper machines or similar equipment (including boxboard machines and pulp
5 sheeting/drying machines, for instance) and various paper finishing machines have a plurality
of different surfaces on which special requirements are set with regard to their surface
properties such as desired degree of friction, predetermined surface energy, self-cleaning
property, good web separation properties and wear resistance. Surfaces typically prone to
accumulate debris are, e.g., dryer cylinders, web guide rolls, sizing press rolls and their
10 surroun~ingc. Special surface property requirements (besides self-cleaning) are also placed on,
e.g., the center rolls of the press sections, sizing press rolls, composite rolls, different glide
surfaces, doctor blades, etc.
One of the specific areas considered problematic today is the porous facings of rolls and
similar machine components. Such porous facings particularly include thermally-sprayed paper
15 machine roll facings which generally are made as ceramic, metal or cermet facings. Porosity
is a factor affecting the facing-substrate combination and can impair its corrosion resistance,
the wear resistance of the facing layer, the mechanical strength of the facing layer and the
adhesion between the facing and the substrate material. The requirements set for, e.g.,
thermally-sprayed roll facings are widely varying. The facing must have good wear resistance,
20 high strength of facing, corrosion resistance, certain desirable friction qualities, debris repellent
property, etc. However, a thermally-sprayed surface alone does not usually provide these
characteristics or combinations thereof.
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Rather, the surface properties must be modified as desired by various surface treatment
compounds. For instance, the ceramic-covered center roll of the paper machine press section
is assumed to permit the separation of the paper web from the roll surface as optimally as
possible in terms of the paper-making process. To achieve the desired characteristics
S particularly for such a porous facing, the facing must, in a great number of cases, be treated
with a special sealant or surface treatment compound whose purpose is to modify and control
the surface properties in the desired manner improving, e.g., its surface energy specification,
debris repellent property or a similar characteristic.
The use of a surface treatment compound can vastly improve the surface properties. For
10 surface treatment of porous surfaces, such an organic liquid compound with suitable viscosity
has been used that can be impregnated into the pores of the facing and then cured by a suitable
method after the impregnation step. Conventionally, the organic surface treatment compounds
have been selected from the group cont~ining, e.g., different polymers such as epoxy resins,
phenol resins, polyester resins, vinyl ester resins, various types of organic waxes and similar
15 compounds. The processing temperature of such surface treatment compounds is typically in
the order of 80-100 C. However, surface treatment compounds do not always function in the
desired fashion. Therefore, a need has arisen to modify the properties of the surface treatment
compound in a desired fashion. For instance, the conventional organic sealant compounds used
in surface treatment compounds have been found to increase, among other things, the adherence
20 of the web on the surface of a sealed roll and to increase the wear of doctor blades as compared
with a roll whose surface has not been sealed nor subjected to surface treatment. A factor
contributing to this has been the sealing of the roll surface pores caused by the surface treatment
compound. Then, the sealing of the roll surface alters the thickness of the moisture layer
rem~ining between the web and the roll surface, whereby the separation of the web from the
25 roll surface is impaired.
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SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel method of controlling the
surface properties of surfaces in a paper machine.
It is a further object of the present invention to modify surface treatment compound
characteristics so as to achieve a desired effect. To this end, the invention is principally
characterized in that the surfaces are treated with a liquid surface treatment compound whose
characteristics are controlled by modifying the backbone polymer chain of the surface treatment
compound by halogenated macrooligomers, diols, triols, thiols and/or other polyols.
The invention offers si~nifi~nt benefits over conventional methods particularly in
situations in which it is desirable to avoid soiling of surfaces, or the adherence of debris on
surfaces. Other advantages include improving and aiding the flow of fluids along surfaces
and/or improving the separation of a paper web or similar material from a surface, particularly
from the surface of a roll. Particularly in such rolls or similar surfaces covered by a porous
facing, the treatment according to the invention with a surface treatment compound also
improves the strength and corrosion resistance properties of the facing.
In the method of the invention, the surface treatment compound has a general corrosion
resistance improving effect in cases where the surface treatment compound is applied directly
onto a metal surface. Such metal surface objects include the flow surfaces of headboxes, pipings
and similar machine elements. Also the treatment of, e.g., metal-faced rolls and cylinders, and
composite-material rolls with the surface treatment compound of the inventioll can reduce the
surface energy of such rolls, thus improving the separation of the web from the roll. A
composite roll is fabricated from, e.g., carbon fiber and epoxy resin using, e.g., filament
winding techniques. It is an extremely light, yet sufficiently strong and stiff roll for paper
machines. Such rolls are presently used, for example, as a web tension measuring roll whose
surface is required to stay free of debris and possess good web separation properties. Otller
benefits and characteristics of the present invention will be evident from the exemplifying
embodiments of the invention described in greater detail below.
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DETAn ~n DESCRIPTION OF THE INVENTION
The surface energy and chemically reactive groups of a surface treatment compound such
as a sealant compound intended for sealing porous facings have a crucial effect on, among other
5 things, the adherence of paper web to the surface treatment compound. If the surface energy
of a solidified surface treatment compound or similar sealant can be lowered, the adhesion work
required to separate the web from the surface treatment compound decreases, whereby the
separation of the web from the roll surface is eased. Simultaneously, the probability of the
formation of hydrogen bonds between the roll surface and the web is reduced. This example
10 is given here to elucidate the factors related to roll facings and their treatment with surface
treatment compounds. A feasible method of reducing the surface energy of a surface treatment
compound is to artificially add halogen atoms to the polymer structure of the surface treatment
compou~d. Halogen atoms in the polymer structure have an extremely electronegative role and
thus can lower the surface energy. As a result, in the rolls the adherence of the web to the roll
15 surface is reduced. In this text, the term halogen particularly refers to fluorine, although other
halogens such as iodine or bromine, for instance, can be used.
In conventional methods halogens or halogen compounds are introduced into the surface
treatment compound in the form of discrete particles having a particle size sufficiently small
with regard to, e.g., the pore size of a porous facing. When the halogen species used is
20 fluorine, for instance, it is embedded in the surface treatment compound as separate particles
of a fluorinated polymer. However, such a particle compounding method has several
shortcomings. First, the particles separate in the liquid polymer phase. Second, desired efrect
on the properties of the surface treatment compound camlot be obtained even at elevated particle
concentrations. Third, compounding with particles also increases the viscosity of the liquid
25 polymer resulting in inferior impregnation of the facing pores by the particles, for example.
Lastly, compounding with particles may impair the mechanical properties of the surface
treatment compound.
The goal of the invention is achieved by modifying the chemical structure of the surface
treatment compound by, e.g., halogenated macrooligomers, halogenated diols, halogenated
30 triols, halogenated thiols and/or other halogenated polyols. Accordingly, if the halogell is
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fluorine, the chemical structure of a liquid organic surface treatment compound, for instance,
can be modified by adding fluorinated macrooligomers or diols to the backbone polymer of the
treatment compound. Problems involved with particle compounding can be avoided througll tllc
use fluorinated compounds, whereby also significant improvements are achieved in the
S properties of the surface treatment compound.
In the case the halogen species are brought into backbone of the surface treatment
compound in the form of separate halogenated (e.g., fluorinated) polymer particles, they can
be either in the dry form of separate particles or dispersed in a liquid carrier of low surface
energy, whereby the particles are blended in the carrier medium with the surface treatment
10 compound. The carrier can be a hydrocarbon or similar compound suited for the purpose. Prior
to the curing of the surface treatment compound, the carrier is removed by a suitable heat
treatment. By varying the amount of particles embedded in the surface treatment compound
matrix, the adhesion characteristics of the surface with, e.g., a paper web can be modified.
However, a problem arises from the addition of halogenated particles in the surface treatment
15 compound matrix. Namely, the particles tend to enrich on the thin top layer of the facing,
whereby a majority of the particles will be ground away if the facing need to be finished by
sanding. Here, a significant portion of the advantageous web release property of the halogenated
(fluorinated) polymer particles will be lost. Moreover, the amount of halogenated particles in
the surface treatment compound must be relatively high, whereby the surface treatment
20 compound becomes balsam-like and its penetration into the facing pores is hindered in situations
where the surface treatment compound is used for sealing the pores of a facing.
As mentioned above, the chemical structure of the surface treatment compound canby altered by modifying the backbone polymer chain by, e.g., halogenated macrooligomers,
diols or the like. For instance, if the surface treatment compound is intended for sealing a
25 porous facing and when the surface treatment compound used is an epoxy resin-based
surface treatment compound, the modification of such an epoxy-resin based surface
treatment compound by fluorinated macrooligomers is based on the reaction of reactive
(mono- or bifunctional) ends of the polymer chain of fluorinated macrooligomers witll the
epoxy group of the resin. As noted above, fluorine is mentioned as only an advantageous
30 alternative of the available halogens. Other usable halogens are iodine and bromine, for
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instance. Further, the surface treatment compound need not be limited to an epoxy resin or
an epoxy-resin-based surface treatment compound alone, but rather, almost any
thermosetting or thermoplastic polymer can be used in the surface treatment compound.
Examples of suitable base materials for the surface treatment compound include epoxy
S resins, phenolic resins, polyester resins, vinylester resins, acrylate resins, methacrylate
resins, organic waxes and similar compounds, and copolymers and terpolymers of these. In
the exemplifying embodiment the macrooligomers usually exhibit poor solubility in the
epoxy matrix, whereby the oligomers are initially converted into so-called adducts with
different anhydrides, and then actual prepolymers are made from the adducts through a
10 chain extension reaction. These prepolymers exhibit good solubility in the base epoxy matrix
and are capable of reacting with the epoxy groups of the resin. Hence, the base resins can
be cured into solid, homogeneous structures having a predetermined/desired content of
fluorine atoms. The fluorine atoms may occur in the form of different CFX groups in the
linear part of the polymer chain, or alternatively, as side groups. Then, the surface energy
15 of the facing drops to a value of 15-20 mN/m.
The surface treatment compound may also include inorganic surface treatment
compounds of suitable viscosity such as phosphates and silicates, for instance.
The above-described exemplifying embodiment is particularly suited for use of the
surface treatment compound as the sealant of a porous roll facing. This is because the
20 surface energy of fluorine-modified surface treatment compound is lower, whereby tlle
adhesion work holding the web against the roll surface decreases and the separation of the
web from the roll surface is eased. Additionally, the corrosion tolerance, heat resistance and
mechanical properties of lnodified epoxy-based sealant compounds are improved. While the
above-described exemplifying embodiments are related to the use of fluorine and fluorinated
25 macrooligomers or diols, a final note must be made that fluorine can be replaced by other
halogenated compounds including at least those of iodine and bromine. Moreover, epoxy
resin as the base polymer matrix can be replaced by any other polymer whose halogenation
results in structures of lower surface energy. Such alternative base polymers are listed in the
description of the invention above.
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For those versed in the art it is obvious that the invention is not limited by the
exemplifying embodiments described above, but rather, can be varied within the scope and
inventive spirit of the annexed claims.
