Note: Descriptions are shown in the official language in which they were submitted.
~ D42-36
BIAXIALLY STRESSED FLUORINATED POLYMER ROLL COVER
AND METHOD FOR 21AKING SAME
BACKGROUND OF THE INVENTION
A) Field of the Invention
This invention relates to the installation of a
heat shrinkable polymer roll cover over the'lateral
area of a process roll. The invention further relates
to the heat shrinkable sleeve and the process roller
covered with the sleeve.
B) Histor~ of the Prior Art
Process rollers or rolls are used in industry
to press, roll or convey sheet or laminar materials.
Examples of such rolls are nip rolls for the production
of plastic sheets and films, paper machine dryer drums
used in the production of paper and textile dyeing and
drying drums used in the production of textiles.
Originally, such process rolls had a metallic
surface. These surfaces were sometimes covered with a
polymer film to obtain better corrosion resistance or
better abrasion resistance. In addition, such metallic
surfaces are now known to have high surface energy
characteristics which frequently causes the material
being processed to stick to the roll. In most processes,
such sticking or adhesion cannot be tolerated.
In order to reduce the surface energy of such
process rolls, the rolls were frequently covered with
a fluorinated polymer as soon as such polymers became
available for such applications.
One of the better methods for covering such rolls
in the prior art consisted of placing the roll within
a radially elongated fluorinated polymer sleeve which
was then heat shrunk to provide a tight fitting roll
cover.
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Such covers, however, continued to have serlous
problems since, especially in large rollers, the
cover expanded in the axial direction when the roll
was heated thus causing uneven roller surface char-
acteristics. Furthermore, especially in larger rolIers,
the sleeve was able to move on the roller, par-
ticularly at high temperatures, which also caused
uneven roller surface characteristics.
In order to avoid axial elongation when it was
required to heat a roller, the sleeves were axially
stretched at the time of application of the sleeve
to the roller. Such axial stretching at the time
of applying the sleeve to the roller made the appli-
cation of the sleeve exceedingly difficult and re-
quired complicated processes and apparatus. Examples
of such processes and apparatus to axially stretch
a sleeve during application to a roller are disclosed
in U. S. Patents 3,426,119 and 3,749,621. Furthermore,
such sleeves continued to be free to move on the roller
thus creating uneven surface characteristics.
In order to prevent such movement, various ad-
hesives were tried which, while being somewhat success-
ful at low temperatures, were not completely successful
at high processing temperatures such as those encountered
in paper drying. Certain adhesives were, for example,
tried and were found to become brittle at high temperatures,
i.e., above about 150C, and were found to have insufficient
adhesion to the fluorinated polymer sleeve.
U. S. Patent 3,481,805 discloses that a silicone
resin adhesive could be used when the inside surface of
a sleeve was preliminarily etched to aid the adhesive.
The patent does not, however, disclose the axial stretch-
ing of the sleeve during its application to a roller.
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Furthermore, the silicone resin adhesive was still in-
sufficiently adherent to a fluorinated polymer sleeve
to prevent the sleeve from moving under high temperature
conditions.
As a result of the foregoing disadvantages, no com-
mercially available prior art fluoropolymer covered
roller was able to operate for an extended period at
temperatures in excess of 120C.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with this invention, there is therefore
provided a polymer sleeve for a prism which is usually a
cylinder such as a process roller, which can be readily
applied to the cylinder, a process for applying this
sleeve to the prism, eg., a cylinder which prevents
movement of the sleeve upon the cylinder even at tem-
peratures as high as 260C (500F) and a combined prism
and sleeve manufactured in accordance with the process.
The cylinder is usually a process roller, having
its lateral area covered with the biaxially heat
shrunken polymer sleeve wherein the sleeve is preferably
adhesively bound to the lateral surface of the cylinder
with a high temperature elastomeric adhesive which is
desirably a polydimethylsiloxane. The novel sleeve is
biaxially stretched beyond its room temperature elastic
limit. The interior surface of the sleeve is desirably
slightly abraded, eg. with 0~ steel wool or with a very
fine abrasive, eg. 600 grit or smaller, and etched with a
composition selected from the group consisting of
sodium dissolved in liquid ammonia; sodium dissolved
in a mixture of naphthalene and tetrahydrofuran; and
molten sodium hydroxide. The method for covering the
lateral area of a cylinder with a heat shrinkable
polymer sleeve comprises placing the biaxially heat
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shrinkable sleeve over the lateral area of a cylinder
and biaxially heat shrinking the sleeve into a tight
fitting relationship with the cylinder by applying heat
to the sleeve. The sleeve is selected so that at least
1%, preferably 2% and most preferably at least 3% re-
sidual biaxial stress remains in the sleeve after heat
shrinking. Desirably, a silicone adhesive is applied
between the lateral surface of the cylinder and the
interior surface of the sleeve and the interior surface
0 i9 desirably slightly abraded and etched as previously
described.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an end perspective view of a roller
covered with a fluorocarbon polymer roll cover in
accordance with the invention.
Figure 2 is a cross sectional view of the roller
shown in Figure 1 taken along line 2-2 of Figure 1.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, there is pro-
vided a prism such as a cylinder having its lateralarea covered with a biaxially heat shrunken polymer,
preferably a fluoropolymer, sleeve.
"Prism" as used herein means any prism having from
three to an infinite number of sides, i.e., a cylinder.
The circumference of the prism need not be completely
uniform along its entire length but for a tight sleeve
fit should generally not have a circumference which
- varies by ove~ 1007a~d th~ pJ-iS~ s~uld n~t have axial
concave portions which are greater than 50~ of the radius
of the prism. The prism should have no radial concave
portions for a tight sleeve fit. Whenever "cylinder"
is used herein, it is to be understood that other prisms
can be substituted for a cylinder.
"Lateral Area" as used herein means the surface
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area of 8 prism such as a cyllnder excluding the end
surface areas.
"Sleeve" as used herein means a tube formed
from a flexlble polymeric material which has a wall
thickness which is thin relative to the overall tube
diameter, eg. usually not thicker than about 0.01
times the overall diameter. Relatively thicker walls
can be used when very small diameter cylinders are
being covered. Examples of such cylinders are small
tubes such as 1/8 inch diameter heat exchange conduit.
The prism is almost always a cylinder which is usually
a process roller such as those encountered in plastic
film, paper, and textile industries. The cylinder or .
roller can be made of any suitable material such as
natural rubber, silicone rubber, steel or combinations
thereof such as rubber covered steel.
"Axial" as used herein means along the longitudinal
axis of the sleeve or cylinder.
"Biaxially" as used herein means along both the
axial and radial axes of the cylinder or sleeve or in
directions perpendicular to each other along the surface
of the flexible plastic material from which the sleeve
is manufactured.
The polymer from which the sleeve is manufactured
may be any flexible polymer which can be used at tem-
peratures of about 100C or above and which can be bi-
axially stretched beyond its room temperature elastic
limit yet biaxially shrink upon the application of heat.
The polymer is usually an alkene polymer such as poly-
ethylene, polypropylene and substituted polyethylenesand polypropylenes such as polyvinyl chloride, chloro-
vinylidene and polytetrafluoroethylene. The thickness
of the sleeve is usually from about 0.001 to about
0.5 cm., and most frequently from about 0.025 to about
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0.25 cm. for most applications. The polymer should
have low surface energy to prevent material being
processed, such as polyethylene film, textiles or
paper, from sticking to the roller. Examples of
suitable fluorinated polymers are polytetrafluoro-
ethylene (PTFE), fluorinated ethylene-propy~lene
- copolymer (FEP) and perfluoroalkoxy fluoroalkane
polymers (PFA).
PFA and PTFE are particularly good under tem-
perature conditionq as high as 260C whereas FEP i8a melt processable material which is suitable for
use at temperatures as high as 200C.
The interior surface of the sleeve is desirably
adhesively bound to the lateral surface of the cy-
linder to prevent movement of the sleeve about
the cylinder while the cylinder is in use. The
adhesive should be a high temperature elastomeric
adhesive; i.e., an adhesive stable at use temperatures
without becoming brittle and without losing its ad-
hesive properties. Examples of such adhesives areusually specific adhesives selected for their pro-
perties which comprise a polymer selected from poly-
sufones, silicones, polyurethanes, and silicone
and fluorine modified epoxies. The most preferred
adhesive is a silicone elastomer adhesive which is
preferably a polydimethylsiloxane since such an
adhesive is able to bind the fluorinated polymer
sleeve to the cylinder yet function at a temperature
as high as 260C without becoming brittle or de-
composing. An example of a suitable polydimethyl-
siloxane silicone elastomer adhesive is a polydi-
methylsiloxane with pendant hydroxy groups available
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from Dow Corning Corporation under the designation RTV
140. Similar adhesives are also available from General
Electric Company.
Another very desirable adhesive is a silicone
elastomer adhesive comprising a chain which contains
polydimethylsiloxane, alkane and phenylmethylsilane
groups. Such an adhesive is available from Dow Corning
under the designation 96-083 and is cured by means of
a catalyst comprising platinum. This adhesive is
particularly desirable, not only due to its performance
at high temperatures but due to its ability to cure
without emitting undesirable gases or vapors. The
RT~ 140 type adhesive has been found to emit gases
or vapors which can cause bubbling under the sleeve.
It has, however, been unexpectedly found that very
- small holes or perforations can be placed in a pro-
cess roller sleeve to permit venting of such gases
without causing surface imperfections in material
which is subsequently processed by the roller. The
size of the holes can be up to about 4 mm for certain
applications but desirably should have a diameter of
from about 0.1 to about 0.5 millimeters. The distance
or interval between holes should be from about 0.1 to
about 5 cms.
- In order to further enhance the adhesion of the
sleeve to the lateral surfac~ of the cylinder, the in-
ternal surface of the sleeve is desirably etched. The
etching composition is usually selected from a com-
position comprising sodium dissolved in liquid ammonia;
a composition comprising sodium dissolved in tetra-
hydrofuran and napthalene; and a composition com-
prising molten alkali metal hydroxide such as sodium
hydroxide.
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Adhesion is even further enhanced if prior to
etching the interior surface of the sleeve is slightly
abraded with very fine steel wool or about 600 grit
or finer and preferably 1,000 grit or finer polish-
ing abrasive such as silicon carbide or alumina. The
abrasive is preferably a loose abrasive powder or steel
wool but may be a coated or bonded abrasive product.
The method in accordance with the invention com-
. prises placing the biaxially heat shrinkable sleeve
10 over a cylinder and biaxially shrinking the sleeve into
a tight fitting relationship with the cylinder by
applying heat to the sleeve. As previously discussed,
the cylinder is usually a process roller. Any suitable
means for placing the sleeve over the cylinder may be
used. The sleeve may be preformed and slipped over
the cylinder or a biaxially stretched heat shrinkable
polymer sheet may be wrapped over the lateral surface
of the cylinder and seamed to form a sleeve. Heat i8
i then applied to shrink the sleeve. After shrinking,
usually at least 1% and preferably at least 3% butusually less than 25% residual biaxial stress remains
in the sleeve at operating temperature and pressure,
that is, the sleeve would further contract the addi-
itional percentage in both the axial and radial
directions at operating temperature if it were not
restrained by the cylinder.
The biaxially heat shrinkable fluorinated polymer
sleeve, again as previousl.y discussed, is manufactured
from a polymer, preferably a fluorinated polymer, which
can be biaxially stretched beyond its room temperature
elastic limits yet biaxially shrink upon the application
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of heat. The sleeve has a finished thickness of from
about 0.05 to about 0.15 centimeters for most appli-
cations. The sleeve is prepared by biaxially expand-
ing a smaller sleeve or the film from which it is made,
in both the radial and axial directions beyond its room
temperature elastic limits. That is, at room temperature
it retains a dimension larger than its unexpanded di-
mension for a sufficient time to slip the sleeve over the
roll. For ease of processing, such expansion may take
place at an elevated temperature, eg., about 100C,
followed by cooling of the sleeve to room temperature.
Once it was determined, in accordance with this invention,
that biaxial expansion of the sleeve was desirable,
numerous methods for obtaining such biaxial expansion
become apparent to those skilled in the art.
In one embodiment for obtaining such biaxial stretch-
ing or expansion, end plugs are installed in two ends of
a piece of fluoropolymer tubing such as FEP tubing and
tightly banding the tubing to the plug to prevent loss
of air and slippage. The plugs are connected in the
center by means of a pipe that can be extended such
as a hydraulic ram. The assembly is then place'd in
a sizing pipe of a larger diameter. The assembly is
then heated as with application of steam inside the
sizing pipe and on the outside of the inserted assem-
bly to a temperature of about 105C . The tubing is
then extended axially by lengthing the pipe between the
end plugs and circumferentially or radially by air pres-
sure inside the tubing applied through one of the plugs.
The tube is thereby distended to the length of the
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pipe between the end plugs and radially to the inside
diameter of the sizing pipe. The sleeve is then
cooled thus producing a roll cover which becomes
smaller in circumference and shorter in length when
subsequently heated to a temperature of above about
110~C.
Other methods and apparatus for biaxially stretch-
ing the sleeve beyond its room temperature elastic limits
are possible. For example, a formed tube or sleeve can
be drawn over a tapered mandrel to stretch it radially,
i.e., to lengthen the radius as well as the circumference,
and the force applied against the friction to pull it
over the mandrel would be used to stretch it axially.
It is also possible to biaxially stretch a polymer film
before it is made into a sleeve. For example, a film
could be biaxially calendered or could be placed in or on
an expandable frame or rack and pulled in biaxial di~
rections. Similarly, a finished tube or sleeve can be
placed in or on an expandable frame or rack or calender-
~' 20 ed in biaxial directions. The film or sleeve in or on a
frame or rack can be gripped at its edges by clamps
attached to the frame or rack or the film or sleeve
be wrapped around the frame or rack, eg., pipes which
are then separated. A particularly desirable method for
biaxially stretching a sleev~ or tube is to radially ex-
pand it with a compressed gas within a retaining tube
which can be readily adjusted to different diameters,
eg., a screen or canvas which is rolled at its edges to
change the diameter of a cylinder formed by the screen
or canvas, while axially stretching the sleeve by any
suitable means. When the tube or sleeve is radially ex-
panded with compressed air or other gas, it is desirable
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1~.3~68
to expand the end~ of the sleeve or tube first, eg.,
by end calendering or placing an expandable sphere with-
in each end and blowing up the spheres with compresged
air. Another method for biaxially stretching or ex-
pandlng a film or sleeve is to hammer the film or sleeve,
eg., with a reciprocating hammer on one surface of the
film or sleeve and an anvil on the opposing surface of
the film or sleeve. The area struck by the hammer should
be small relative to the total surface of the film or
sleeve and the film or sleeve should move relative to
the hammer and anvil so that essentially the entire film
or sleeve i9 struck between the hammer and anvil.
Many other possibilities for biaxially distend-
ing or expanding the sleeve beyond its cold tem-
perature biaxial elastic limits can be envisioned by
those skilled in the art.
Further, in accordance with the invention, and
as previously discussed with respect to the resulting
cylinder, the adhesive can be applied between the
cylinder such as a roller and the interior surface of
the sleeve. The adhesive may be applied by any suitable
method as by brushing the adhesive on the cylinder before
applying the sleeve or by injecting adhesive beneath the
sleeve with a long hyperdermic type needle after the
sleeve is applied to and shrunken upon the cylinder.
The sleeve, as previously discussed, may be
slightly abraded and etched to further enhance a &esion
of the sleeve to the lateral surface or area of the
cylinder such as a process roller. Another method for
increasing adhesion is by applying colloidal silica
to the internal surface of the sleeve, i.e., the sur-
face facing the cylinder and heating the silica coated
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surface before using the adhesive.
The resulting process roller is provided with a
polymer sleeve, desirably a fluorinated polymer sleeve,
which has a smooth surface and which does not move
about the lateral surface or area of the roller at tem-
peratures above 150C, as high as 200C and even as high
as 260C when appropriate fluorinated polymer sleeves and
silicone elastomer adhesives are used.
Referring now to the drawings, Figure 1 shows an
end perspective view of a cylinder 10 having a
lateral area 12 covered with a biaxially heat shrunk-
en fluorinated polymer sleeve 14. As best seen in
Figure 2, sleeve 14 is secured to lateral area 12
by means of a silicone adhesive 16. Desirably, the
interior surface 18 of sleeve 14 is slightly abraded
and etched prior to securing sleeve 14 to lateral
area 12 by means of adhesive 16.
The following examples are provided to more fully
illustrate and not limit the invention. Unless other-
wise indicated, all parts and percentages are by weight.EXAMPLE I
An FEP polymer film having a thickness of about
0.5 millimeters is slightly abraded on onè side with
00 steel wool and etched with a composition comprising
11.8 weight percent metallic sodium dissolved in 8 mix-
ture of 11.8 weight percent napthalene and 78.4 weight
percent tetrahydrofuran. The film is then formed into a
sleeve in accordance with methods well known to those
skilled in the art. The resulting seam is then abraded
with 00 steel wool and etched with the composition com-
prising sodium dissolved in a mixture of napthalene and
tetrahydrofuran. The sleeve is formed so that it has an
inside diameter of about 54 centimeters and a length of
1~.3~
- about 163 centimeters. The sleeve is then biaxially
stretched by plugging the ends wlth aluminum plugs
and banding the ends of the sleeves to the plugs.
Compressed air is forced into the sleeve through one
of the plugs at a pressure of about 2.45 kilograms
per square centimeter. The plugs are simultaneously
pulled in opposite directions with a force of about
1000 kilograms over and above the force being applied
against the plugs by the compressed air. The resulting
sleeve has an inside diameter of about 61 centimeters and
a length of about 178 centimeters. The sleeve is then
slid over a steam heated textile drying drum having an
outside diameter of about 58 centimeters and a lateral
surface length of about 152 centimeters.,
Each end of the sleeve is then heated to a tem-
perature of about 95C and banded to the end of the
cylinder. The entire sleeve is then heated to about
120C to shrink the sleeve into a tight fitting re-
lationship with the cylinder. The cylinder and sleeve
are then cooled to room temperature. About 158 grams
of Dow Corning 96-083 adhesive is then injected be-
neath the sleeve along the length of the cylinder
at several locations using a hyperdermic type syringe.
The adhesive is then uniformly spread beneath the sleeve
by moving a rubber squeegee about the external surface of
the sleeve. The resulting sieeve and cylinder are then
cured at 160C.
The cylinder and sleeve are then placed into
textile drying service at a temperature of 165C.
After a period of 18 months, the sleeve continues to
have a ~mooth wrinkle-free appearance.
EXAMPLE II
The procedure of Example I is repeated except
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that the cylinder is a heating roll utilized for
laminating plastic underlayment for carpet. The
drum has an outside diameter of 40 centimeters and
a length-of about 221 centimeters. The inside di-
ameter of the unstretched sleeve is about 37 cen-
timeters-and the length of the unstretched sleeve is
238 centimeters. The stretched sleeve has an inside
diameter of about 42 centimeters and a length of
258 centimeters.
The finished roll and sleeve are utilized to
laminate plastic to foam at a temperature of about
230 DC . After a time period of 4 months, the sleeve
has a smooth wrinkle-free appearance.
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