U.S. patent application number 10/098744 was filed with the patent office on 2003-04-03 for polytetrafluoroethylene film and manufacture of same.
Invention is credited to Kikukawa, Hiroyasu, Oyama, Shinro.
Application Number | 20030062644 10/098744 |
Document ID | / |
Family ID | 18935397 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030062644 |
Kind Code |
A1 |
Oyama, Shinro ; et
al. |
April 3, 2003 |
Polytetrafluoroethylene film and manufacture of same
Abstract
Polytetrafluoroethylene thin film comprising a thin film of
polytetrafluoroethylene having thickness of .ltoreq.20 .mu.m;
surface roughness (Ra) of .ltoreq.0.1 .mu.m; tensile strength of
.gtoreq.80 N/mm.sup.2; and light beam transmittance of .gtoreq.80%
for light of 500 nm wavelength. A process for manufacture of
polytetrafluoroethylene film comprising compressing porous
polytetrafluoroethylene film at a temperature above the melting
point of the film, followed by cooling to a temperature below the
melting point of the film while continuing to apply pressure.
Inventors: |
Oyama, Shinro; (Okayama-shi,
JP) ; Kikukawa, Hiroyasu; (Okayama-shi, JP) |
Correspondence
Address: |
W. L. Gore & Associates, Inc.
551 Paper Mill Road
P.O. Box 9206
Newark
DE
19714-9206
US
|
Family ID: |
18935397 |
Appl. No.: |
10/098744 |
Filed: |
March 15, 2002 |
Current U.S.
Class: |
264/41 ; 264/320;
264/322; 428/141; 428/220; 428/422 |
Current CPC
Class: |
G03G 15/2057 20130101;
C08J 2327/18 20130101; Y10T 428/31544 20150401; B29K 2027/18
20130101; B29L 2007/008 20130101; Y10T 428/265 20150115; B29K
2105/04 20130101; B29C 55/18 20130101; Y10T 428/24355 20150115;
B29C 43/003 20130101; B29C 43/22 20130101; Y10T 428/1352 20150115;
B32B 27/28 20130101; C08J 5/18 20130101 |
Class at
Publication: |
264/41 ; 428/422;
428/220; 428/141; 264/320; 264/322 |
International
Class: |
D06N 007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2001 |
JP |
01-78842 |
Claims
1. In an electrophotographic device, including a fixing belt and a
fixing apparatus, the improvement wherein at least one of the
fixing roll, the fixing belt, and the fixing apparatus comprises a
thin film of polytetrafluoroethylene having thickness of .ltoreq.20
.mu.m; surface roughness (Ra) of .ltoreq.0.1 .mu.m; tensile
strength of .gtoreq.80 N/mm.sup.2; and light beam transmittance of
.gtoreq.80% for light of 500 nm wavelength.
2. The electrophotographic device according to claim 1 wherein
porosity of said thin film is .ltoreq.10%.
3. A process for manufacture of polytetrafluoroethylene film
comprising the steps of compressing porous polytetrafluoroethylene
film at a temperature below the melting point of said film,
followed by compression at a temperature above the melting point of
said film.
4. A process for manufacture of polytetrafluoroethylene film
comprising the steps of compressing porous polytetrafluoroethylene
film while subjecting it to a temperature above the melting point
of said film, followed by cooling to a temperature below the
melting point of said film while continuing to apply pressure.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to thin film and thick film of
polytetrafluoroethylene (PTFE); to processes for manufacture
thereof; to a fixing roll and fixing belt employing the thin film;
and to fixing apparatus employing the fixing roll or fixing
belt.
[0002] The usual method for production of polytetrafluoroethylene
(PTFE) film is the skiving process, which involves preforming PTFE
molding powder into a hollow cylinder profile; sintering; and then
shaving films from the resultant preform.
[0003] However, the conventional process has a number of drawbacks,
such as the following.
[0004] (1) There is a tendency for microvoids to form.
[0005] (2) It is difficult to produce thicknesses below 50
.mu.m.
[0006] (3) The material has a milky opacity, giving it low light
beam transmittance in the visible region (light beam transmittance
of light of the 500 nm wavelength is .ltoreq.20%).
[0007] (4) It is difficult to produce a smooth [film] having
surface roughness (Ra) of .ltoreq.0.1 .mu.m.
[0008] (5) Tensile strength is low (20-50 N/mm.sup.2).
[0009] Unexamined Patent Application 56-24431 discloses a process
for modifying PTFE by subjecting skived PTFE film to a softening
process at 327-450.degree. C., and stretching the film by a ratio
of 1.1-6.0 at a temperature of 150-400.degree. C. during or after
the [softening] process.
[0010] While this process affords PTFE films with thicknesses of
.ltoreq.50 .mu.m and high strength (maximum tensile strength of
about 160 N/mm.sup.2), it has the following drawbacks.
[0011] (1) It is not possible to completely eliminate
microvoids.
[0012] (2) It is difficult to produce thicknesses below 20 .mu.m,
and there is significant irregularity in thickness.
[0013] (3) Light beam transmittance in the visible region is low
(light beam transmittance of light of the 500 nm wavelength is
.ltoreq.60%).
[0014] (4) It is difficult to reduce surface roughness (Ra) to
below 0.1 .mu.m.
[0015] Unexamined Patent Application 9-278927 discloses a PTFE film
casting process that involves applying a PTFE dispersion onto the
surface of a thin film of an organic solvent-soluble
fluororesin--formed on a substrate--, and then drying it; fusing or
sintering at a temperature above the PTFE melting point; and then
immersing it, together with the substrate, in an organic solvent
that dissolved the organic solvent-soluble fluororesin, to separate
the PTFE film.
[0016] With this method, it is possible to produce smooth-surfaced
PTFE films with thicknesses of .ltoreq.10 .mu.m, but nevertheless
there are the following drawbacks:
[0017] (1) The resultant films have low tensile strength (about
20-40 N/mm.sup.2).
[0018] (2) The resultant films have a fair degree of milky opacity,
such that light beam transmittance in the visible region is low
(light beam transmittance of light of the 500 nm wavelength is
about 50-70%).
[0019] (3) It is difficult to produce thicknesses of more than 10
.mu.m with a single application of PTFE dispersion, and thus
several applications are needed to produce films of greater
thickness.
[0020] Unexamined Patent Application 53-55380 discloses a PTFE
manufacturing process that involves subjecting PTFE film to
stretching along at least two axes, with the stretch ratio along
each axis being from 2 to 4, to obtain an expanded film. The
expanded film is then calendered with calender rolls held at a
temperature below the PTFE melting point (327.degree. C.) until
specific gravity reaches .gtoreq.2.1.
[0021] While this process gives PTFE films that are thin and have
high tensile strength, the fact that calendering is carried out at
temperatures below the PTFE melting point, and that the PTFE film
shrinks by several percent after passing through the calender
rolls, results in the following drawbacks.
[0022] (1) It is difficult to reduce surface roughness (Ra) to
below 0.1 .mu.m.
[0023] (2) The resultant film has a milky opacity such that light
beam transmittance in the visible region is low (light beam
transmittance of light of the 500 nm wavelength is about
60-70%).
[0024] (3) Thickness is irregular.
[0025] In electrophotography fixing roll applications (such as in
electrophotographic devices such as printers and copiers), a PFA
tube is typically used as the release surface layer for the elastic
roll, as described in Denshi Shashin Gakkai Shi, Vol. 33, No. 1
(1994). For reasons relating to the fabrication process, it is
difficult to produce PFA tubes that are less than 25 .mu.m in
thickness, and moreover the poor wear resistance means that
adequate service life is not achieved with thinner materials. For
this reason, fixing rolls that use PFA tubes less than 25 .mu.m in
thickness as the surface layer are not currently practical. On the
other hand, if the surface release layer is too thick, the effects
of the underlying elastic layer are lost, so that the surface
release layer loses its ability to conform to contours on the paper
surface during the process of fixing the toner onto the paper,
resulting in uneven application of pressure to the toner and
consequent deterioration in image quality. To avoid losing the
effects of the elastic layer due to a thick surface release layer,
it is necessary to increase the thickness of the elastic layer, but
this creates the problem of requiring a significant amount of heat
to bring the temperature of the surface release layer up to the
temperature at which fixing becomes possible. For fixing belts as
well, the use of a PFA tube surface layer results in a
deterioration in image quality, for the same reasons as with fixing
rolls. Fixing belts typically use a coated surface layer of
fluororesin (such as PTFE or PFA), but adequate service life cannot
be assured due to the low wear resistance.
[0026] Unexamined Patent Application 60-186883 teaches the use of a
porous film of polytetrafluoroethylene rendered void-free at least
in its surface layer, as the surface layer for a fixing roll.
However, as this method renders the porous polytetrafluoroethylene
film void-free by compressing it between rolls, the surface of the
resultant surface layer is not very smooth, and does not readily go
below surface roughness (Ra) of 1.0 .mu.m. As a result, toner
release tends to be poor, and uneven application of pressure to the
toner causes deterioration in image quality.
[0027] The invention has the following objects:
[0028] (1) To provide PTFE film that is free from voids; has a
highly smooth surface; is either thick or thin; and is highly
transparent; and a process for manufacture thereof.
[0029] (2) To provide a fixing roll and a fixing belt having a thin
fluororesin surface layer with thickness of .ltoreq.20 .mu.m; that
offer extended service life and high image quality; and that allow
fixing to be carried out with less heat; and to provide a fixing
apparatus employing this fixing roll or fixing belt.
[0030] The present invention was perfected as a result of extensive
research directed to achieving these aims.
[0031] Specifically, the invention provides an electrophotographic
device comprising a fixing roll, a fixing belt, and a fixing
apparatus made from a polytetrafluoroethylene film, as well as a
process therefore, described hereinbelow,
[0032] (1) Polytetrafluoroethylene thin film comprising a thin film
of polytetrafluoroethylene having thickness of .ltoreq.20 .mu.m;
surface roughness (Ra) of .ltoreq.0.1 .mu.m; tensile strength of
.gtoreq.80 N/mm.sup.2; and light beam transmittance of .gtoreq.80%
for light of 500 nm wavelength.
[0033] (2) Polytetrafluoroethylene thin film according to (1)
wherein porosity is .ltoreq.10%.
[0034] (3) A fixing roll employing as the surface layer
polytetrafluoroethylene thin film according to (1) or (2).
[0035] (4) A fixing belt employing as the surface layer
polytetrafluoroethylene thin film according to (1) or (2).
[0036] (5) A fixing apparatus employing the fixing roll according
to (3)
[0037] (6) A fixing apparatus employing the fixing belt according
to (4).
[0038] (7) A process for manufacture of polytetrafluoroethylene
film comprising a film of polytetrafluoroethylene and having light
beam transmittance of .gtoreq.80% for light of 500 nm
wavelength.
[0039] (8) A process for manufacture of polytetrafluoroethylene
film [comprising the step of] compressing porous
polytetrafluoroethylene film at a temperature below the melting
point of said film, followed by compression at a temperature above
the melting point of said film.
[0040] (9) A process for manufacture of polytetrafluoroethylene
film [comprising the step of] compressing porous
polytetrafluoroethylene film while subjecting it to a temperature
above the melting point of said film, followed by cooling to a
temperature below the melting point of said film while continuing
to apply pressure.
[0041] The material for producing the PTFE film herein is porous
PTFE film. This porous PTFE film may consist of expanded or
unexpanded porous PTFE films of types known in the art; however,
expanded PTFE (ePTFE) film is preferred owing to the high strength
of the resultant PTFE film.
[0042] The ePTFE film herein is produced from a molded article of
paste--prepared by mixing fine powder of PTFE with a molding
aid--by eliminating the molding aid from the molding, expanding it
at high temperature at a high rate of speed, and then optionally
sintering; where the material is uniaxially expanded, nodes (folded
crystals) form narrow "islands" at a right angle to the stretching
direction, these nodes being interconnected by fibrils (linear
bundles of molecules produced by folded crystals breaking up and
being drawn out) oriented in the stretching direction. The result
is a fibrous texture in which spaces between fibrils or defined by
fibrils and nodes serve as pores. Where the material is biaxially
expanded, the result is a "spider web" texture in which fibrils
extend radially between island-like nodes that interconnect the
fibrils, and containing numerous spaces defined by the fibrils and
nodes.
[0043] The ePTFE film material herein may be either uniaxially
expanded ePTFE or biaxially expanded ePTFE, with biaxially expanded
ePTFE being preferred. Since biaxially expanded ePTFE has been
stretched along two axes, anisotropy is lower than for uniaxially
expanded ePTFE, and the resultant PTFE film has high strength in
both the TD and MD.
[0044] ePTFE film used as the film material herein will preferably
have porosity of from 10 to 95%, and preferably from 40 to 90%; and
thickness of from 5 to 500 .mu.m, and preferably from 5 to 200
.mu.m. The TD stretch ratio is 100-1000% and preferably 150-800%;
the MD stretch ratio is 100-1000%, and preferably 150-800%. The
ratio of tensile strength in the machine direction and transverse
direction of the film (product film) herein can be manipulated via
the TD and MD stretch ratios of the film material. Where, for
example, the product film is produced from ePTFE film material
having a TD stretch ratio of 400% and an MD stretch ratio of 200%,
tensile strength along the axis corresponding to the TD of the film
material will be approximately twice tensile strength along the
axis corresponding to the MD of the film material.
[0045] The PTFE film herein is manufactured by first subjecting the
ePTFE film to a first compression process in which it is compressed
(pressed) at a temperature below the melting point, to produce a
calendered film. Compression temperature is not particularly
critical provided it is below the PTFE melting point; temperature
is low, typically .gtoreq.1.degree. C., and preferably
.gtoreq.100.degree. C. Where compression temperature is above the
melting point there will be significant shrinkage of the product
film. Compression parameters are selected such that resultant film
porosity is .ltoreq.50%, preferably .ltoreq.20%, and ideally
.ltoreq.10%. Compressing force, expressed as planar pressure, is
typically 0.5-60 N/mm.sup.2, and preferably 1-50 N/mm.sup.2.
Compressing apparatus selection is not critical provided the
apparatus is capable of compressing the film; preferred apparatuses
are those in which the film is compressed as it passes between
rolls or belts, such as a calender roll apparatus or belt press
apparatus. Where a calender roll apparatus or belt press apparatus
is employed, air present within the ePTFE film or between ePTFE
film layers is readily pressed out from the ePTFE film as the film
is passed through the rollers or belts, thus giving a product film
that is free from voids and wrinkles.
[0046] Product film thickness will depend in part upon the desired
thickness and the porosity of the film material, but is usually
from 3 to 500 .mu.m, and preferably from 5 to 200 .mu.m.
[0047] The calendered film from the first compression process is
then subjected to a second compression process in which it is
compressed (pressed) at a temperature above the PTFE melting point.
Compression temperature is not particularly critical provided it is
above the PTFE melting point; temperature is high, typically from 1
to 100.degree. C., and preferably from 20 to 80.degree. C., above
melting. Heating the ePTFE film to a temperature above melting
allows a smoother surface to be imparted to the product film. In
preferred practice, compression temperature will be dropped to a
temperature below melting at the point in time at which pressure is
released. Where pressure is released [with the material] above the
melting point, the product film will experience appreciable
shrinkage and be susceptible to wrinkling. Compression parameters
are selected such that resultant film porosity is .ltoreq.10%, and
preferably .ltoreq.1%. Compressing force, expressed as planar
pressure, is typically 0.1-100 N/mm.sup.2, and preferably about
1-30 N/mm.sup.2. Compressing apparatus selection is not critical
provided the apparatus is capable of nipping and compressing the
film; preferred apparatuses are a belt press or hot press unit
capable of applying desired temperature and pressure for a
predetermined duration.
[0048] The product film herein may be manufactured in a single pass
where the apparatus is capable of heating the film material to a
temperature above the PTFE melting point, and then cooling it to a
temperature below the PTFE melting point while maintaining
pressure. With such a process, there is substantially no shrinkage
of the product film, since despite the fact that the ePTFE film is
brought to a temperature above the PTFE melting point at the outset
of the compression process, it is cooled to a temperature below
melting prior to releasing the pressure applied to the ePTFE
film.
[0049] Where, for example, a belt press unit is employed, the ePTFE
film is brought to a temperature above the PTFE melting point while
compressed between the belts, and then cooled to a temperature
below melting, the resultant product film will have negligible
shrinkage. This method also enables continuous production of
product film.
[0050] The thin film of PTFE herein has thickness of .ltoreq.20
.mu.m and smooth surfaces. Thickness is 0.1-20 .mu.m, preferably
1-20 .mu.m; and surface roughness (Ra) is .ltoreq.0.1 .mu.m, and
preferably .ltoreq.0.05 .mu.m. The thin film herein has exceptional
tensile strength; tensile strength is ordinarily .gtoreq.80
N/mm.sup.2, and preferably 100 N/mm.sup.2.
[0051] The thin film of PTFE herein has exceptional light beam
transmittance; transmittance of light of 500 nm wavelength is
.gtoreq.80%, and preferably .gtoreq.90%.
[0052] In the first compression process herein, compression may be
carried out in two or more stages in order to minimize voids in the
resultant film. In the second compression process, where a hot
press is employed to heat and compress the film, smooth,
heat-resistant film may be interposed between the hot press plates
and the film when compressing it with hot press plates. Or, where a
belt press unit is employed, thermal compression may be carried out
with a smooth, heat-resistant film interposed between the metal
belts and the film. Films serviceable for this purpose include
polyimide film, e.g. UPILEX 20S (ex Ube Kosan). With this method,
the product film may be imparted with surface roughness (Ra) about
equal to the surface roughness (Ra) of the heat-resistant film, and
is effective in cases where a high degree of surface smoothness
cannot be imparted to the hot press plate or metal belts.
[0053] The process herein readily gives transparent thin films of
20 .mu.m or thinner, an accomplishment difficult where conventional
processes are used. As an example, ePTFE film 50 .mu.m thick with
80% porosity can be subjected to compression with calender rolls
(at roll temperature of 70.degree. C.) to reduce porosity to 2% and
thickness to 14 .mu.m; and then to pressing in a press unit at
press plate temperature of 320-400.degree. C., pressure of 10.0
N/mm.sup.2, a feed rate of 0.5-2.0 m/min, and press time of 1 to 4
min. to produce a film of 0% porosity and 12 .mu.m thickness.
Subjecting film 9 .mu.m thick with 85% porosity to a similar
process gives a film of 0% porosity and 2 .mu.m thickness. Surface
roughness (Ra) of film herein is determined either by the surface
roughness (Ra) of the press plates--where hot pressing with hot
press plates is conducted is the second compression process--or by
the surface roughness (Ra) of the heat-resistant film--where the
calendered film from the first compression process is sandwiched
between heat-resistant films and compressed by hot press plates.
Where, for example, hot pressing is performed with highly polished
press plates having surface roughness (Ra) of .ltoreq.0.1 .mu.m,
the resultant film will have surface roughness (Ra) of .ltoreq.0.1
.mu.m. Similarly, where the calendered film from the first
compression process is sandwiched between polyimide film (UPILEX
20S, Ra=0.01 .mu.m), the resultant film will have surface roughness
(Ra) of about 0.1 .mu.m.
[0054] The invention is not limited to thin film, and may be used
to give thicker transparent film as well. In this process, film
material is compressed in a first compression process and then
compressed in a second compression process, in the manner described
earlier. However, the film material here--while having the same
general qualities as the film material described earlier--will be
thicker, e.g., thicker than 400 .mu.m, and usually 400 .mu.m to 1
mm. The film material may consist of a single film, or of a
laminate composed of 2 to 6, preferably 2 to 4, laminated
layers.
[0055] Transparent product film of thickness exceeding 20 .mu.m,
and preferably 25-100 .mu.m in thickness, can be produced from such
thick film materials. According to the invention, laminate film
having total thickness of 450 .mu.m--composed of three layers of
ePTFE film each having 70% porosity and 150 .mu.m thickness--can be
made into film having 0% porosity and 50 .mu.m thickness, and
having excellent transparency and surface gloss. The product film
will have light beam transmittance of .gtoreq.80% and preferably
.gtoreq.85%, and porosity of .ltoreq.10% and preferably .ltoreq.2%.
Surface roughness is typically .ltoreq.0.1 m and preferably
.ltoreq.0.5 .mu.m. The high transparency and tensile strength of
such PTFE film makes it suitable as a heat-, weather-, chemical-
and wear resistant release film for applications such as protective
film for construction applications.
[0056] The use of ePTFE film of high tensile strength herein gives
product film endowed with high tensile strength. For example, the
use herein of ePTFE film having tensile strength of 10-100
N/mm.sup.2 will give product film having tensile strength of 50-200
N/mm.sup.2. Conventional skived PTFE film typically has tensile
strength of 20-50 N/mm.sup.2, while cast PTFE film typically has
tensile strength of about 20-40 N/mm.sup.2; compared to these
conventional PTFE films, the product film herein has extremely high
tensile strength.
[0057] Turning now to a more detailed description of the PTFE film
(product film) herein, film porosity is from 0 to 5%, and scanning
electron microscope (SEM) examination of the surface (at
50-2000.times. magnification) shows no visible voids, pinholes or
fibril structures. When the film is sliced with a microtome and the
cut surface examined by SEM, no voids, pinholes or fibril
structures are observed. Examination of the film appearance with
the naked eye shows it have uniform transparency, free of milky
opacity or striations produced by residual voids, pinholes, and
fibril structures.
[0058] The PTFE film herein has extremely high transparency and
cosmetic appearance. Conventional PTFE film does not have such high
transparency.
[0059] As noted, the PTFE film herein is thin and endowed with
outstanding transparency and tensile strength, making it suitable
for a variety of applications. It is particularly useful as a
surface film for fixing rolls or fixing belts of the sort commonly
used to date in electrophotography systems. Used as a surface layer
film for a fixing roll, the PTFE thin film herein gives a fixing
roll having good heat- and chemical resistance, release properties,
wear resistance and long service life. As it is a simple matter to
produce a surface layer having thickness of .ltoreq.20
.mu.m--difficult to accomplish to date--there can be obtained a
fixing roll giving high image quality, and capable of fixing with
less heat. Where a fixing roll has a thin release surface layer,
the effects of the underlying elastic layer are more readily
expressed, and this not only gives higher imaging quality, but also
allows the elastic layer to be made thinner, so that fixing can be
accomplished with less heat. The PTFE thin film herein is superior
to PFA in terms of heat resistance, wear resistance, release
properties, and affinity to release oils, giving a fixing roll with
extended service life, high imaging quality, and fixing with less
heat.
[0060] For fixing belts as well, the use of the PTFE thin film
herein as the release surface layer affords longer service life and
higher imaging quality than does a PFA surface layer. While fixing
belts typically have a fluororesin coating layer, the PTFE thin
film herein has better wear resistance than a fluororesin coating
layer, giving the fixing belt a longer service life and higher.
[0061] According to the invention, a fixing apparatus having a
fixing roll or fixing belt can produce better imaging quality than
a conventional fixing apparatus when the fixing roll or fixing belt
herein is used as the fixing roll or fixing belt thereof.
EXAMPLES
[0062] A fuller understanding of the invention is provided through
the following examples.
Example 1
[0063] ePTFE film (porosity 80%, thickness 100 .mu.m) was
compressed in a calender roll unit (roll temperature 70.degree. C.,
linear pressure 8 N/mm.sup.2, feed speed 6.0 m/min) to produce a
milky film of 5% porosity and 14 .mu.m thick. The milky film was
sandwiched between two sheets of polyimide film (UPILEX 20S ex Ube
Kosan) and subjected to hot pressing in a hot pressing unit at a
press plate temperature of 400.degree. C. and planar pressure of 10
N/mm.sup.2, which yielded dense PTFE film with 0% porosity, 12
.mu.m thickness, high transparency, and a glossy surface.
Example 2
[0064] ePTFE film (porosity 80%, thickness 100 .mu.m) was
sandwiched between two sheets of polyimide film (UPILEX 20S ex Ube
Kosan) and compressed in a double-belt press unit (roll temperature
at point of initial compression 395.degree. C., roll temperature at
point of release of pressure 100.degree. C., linear pressure 6
N/mm.sup.2, feed speed 1 m/min), which yielded dense PTFE film with
0% porosity, 12 .mu.m thickness, high transparency, and a glossy
surface.
Example 3
[0065] Following the procedure in Example 1, ePTFE film (porosity
80%, thickness 50 .mu.m) was used to produce dense PTFE film with
0% porosity, 6 .mu.m thickness, high transparency, and a glossy
surface.
Example 4
[0066] Following the procedure in Example 1, ePTFE film (porosity
80%, thickness 30 .mu.m) was used to produce dense PTFE film with
0% porosity, 4 .mu.m thickness, high transparency, and a glossy
surface.
Example 5
[0067] Following the procedure in Example 1, ePTFE film (porosity
90%, thickness 7 .mu.m) was used to produce dense PTFE film with 0%
porosity, 0.5 .mu.m thickness, high transparency, and a glossy
surface.
Example 6
[0068] Three layers of ePTFE film (porosity 70%, thickness 150
.mu.m) were stacked to give a film laminate with total thickness of
450 .mu.m, which was compressed in a calender roll unit in the
manner of Example 1. The compressed film laminate was sandwiched
between two highly-polished press plates, compressed using a hot
press (press plate temperature 400.degree. C., planar pressure 15
N/mm.sup.2), and held for 15 minutes at this same temperature and
pressure. Press plate temperature was then gradually brought back
down to 25.degree. C. over a 45-minute period, while continuing to
apply pressure. This procedure yielded dense PTFE film with 0%
porosity, 50 .mu.m thickness, high transparency, and a glossy
surface.
[0069] SEM examination of the transparent, glossy dense PTFE films
obtained in Examples 1-6 revealed no pinholes, voids or fibril
structures.
[0070] Measurements of surface roughness (Ra) of the transparent,
glossy dense PTFE films obtained in Examples 1-6 gave values of
less than 0.05 .mu.m in each case.
[0071] Comparison 1
[0072] Production of Skived PTFE Film
[0073] A fine molding powder of PTFE (mean particle size 35 .mu.m)
was preformed in a hollow cylindrical mold under molding pressure
of 17.2 N/mm.sup.2, to give a hollow cylindrical perform 250 mm in
diameter and 300 mm high. The preform was removed from the mold,
placed in an electric oven, and sintered for 15 hours at
370.degree. C. The sintered article was cooled in the furnace to
give a molding. The molding was lathed to produce skived PTFE film
50 .mu.m thick.
[0074] Comparison 2
[0075] Production of PTFE Film by PTFE Dispersion Application
[0076] A 20% solution of PTFE/vinylidene fluoride copolymer resin
in acetone was applied to polyimide film, dried, and baked at
130.degree. C. to produce a 1 .mu.m layer. A PTFE dispersion was
applied over the fluororesin layer, dried, and sintered at
360.degree. C. to produce a layer 3 .mu.m thick. The process of
applying, drying and sintering the PTFE dispersion was repeated
twice to produce a layer of total [thickness] of 5 .mu.m. [The
film], together with the polyimide film base, was immersed in
acetone to completely dissolve the PTFE/vinylidene fluoride
copolymer resin, yielding a PTFE film 5 .mu.m thick.
Example 7
[0077] The dense PTFE film prepared in Example 3 was subjected to
corona discharge treatment along an edge thereof, and then
thermally fused into a tube. The tube inside wall was impregnated
with a 25.degree. C. Na/naphthalene complex salt solution (trade
name TETRA H ex Junkosha), and sequentially immersed in methanol,
water, and again in methanol (10 seconds each time). Air was jetted
onto the inside and outside surfaces to dry them. A primer (trade
name DY39-051 ex Toray-Dow Corning) was applied to the inside of
the tube, which was then arranged within a roll mold (35 mm inside
diameter). An aluminum core (outside diameter 31 mm, barrel length
320 mm) was inserted through the center and held there while
injecting silicone rubber between the tube and aluminum core. After
thermal curing for 30 minutes at 150.degree. C., secondary
vulcanization was conducted at 200.degree. C. for 4 hours, yielding
a fixing roll with a surface layer of dense PTFE film.
[0078] Comparison 3
[0079] A fixing roll having a PFA surface layer was produced
analogously to Example 7, except for using a tube of PFA 25 .mu.m
thick (STM ex Gunze).
Example 8
[0080] A fixing roll with a surface layer of dense PTFE film was
produced analogously to Example 7, except that the outside diameter
of the aluminum core inserted to the roll mold was 33 mm.
[0081] Comparison 4
[0082] A fixing roll having a PFA surface layer was produced
analogously to Example 7, except for using a tube of PFA 30 .mu.m
thick (STM ex Gunze).
Example 9
[0083] Polyamide varnish (U VARNISH S ex Ube Kosan) was applied
onto a hollow cylindrical core of stainless steel (25 mm outside
diameter), and the hollow cylindrical core was passed through a die
(26 mm inside diameter) to produce a polyimide varnish coating film
on the hollow cylindrical core. After baking for 30 minutes at
300.degree. C., the hollow cylindrical core was withdrawn to give a
polyimide tube 50 .mu.m thick, with a 25 mm outside diameter and
250 mm length. The outside surface of the polyimide tube was
subjected to a corona discharge process, and an adhesive for rubber
(DY39-012 ex Toray-Dow Corning) was applied to a thickness of
approximately 2 .mu.m. A stainless steel core was then inserted
into the bore of the polyimide. Separately, a dense PTFE film
tube--treated on its inside wall with 25.degree. C. Na/naphthalene
complex salt solution as in Example 7--was inserted into a
stainless steel hollow cylinder of 26.5 mm inside diameter. The
polyimide tube-sheathed stainless steel core was inserted into this
stainless steel hollow cylindrical mold, and the entire assembly
was placed in a vulcanization mold. Liquid rubber (LSRSE6744 ex
Toray-Dow Corning) was then injected into the gap between the dense
PTFE film layer and the stainless steel core, and vulcanized. After
vulcanization the assembly, together with the hollow cylindrical
mold, was removed from the vulcanization mold, and the hollow
cylindrical mold was slipped off to give a fixing belt having a
surface layer of dense PTFE.
[0084] Comparison 5
[0085] A fixing belt having a PFA surface layer was produced
analogously to Example 8, except for using a tube of PFA 30 .mu.m
thick (STM ex Gunze).
[0086] Comparison 6
[0087] The surface of a polyimide tube prepared as in Example 9 was
subjected to corona discharge treatment, after which an adhesive
for rubber (DY39-012 ex Toray-Dow Corning) was applied thereto to a
thickness of approximately 2 .mu.m, and dried. A PFA resin
dispersion (855-104 ex Dupont) was sprayed on and baked for 30
minutes at 380.degree. C. to produce a fixing belt with a
fluororesin coating layer.
[0088] The dense PTFE films of the above Examples and Comparisons
were evaluated as follows. Results are tabulated in Table 1.
[0089] (1) Porosity: using the equation below, calculated from
apparent density (.quadrature.) measured in accordance with
apparent density measurement described in JIS K 6885.
porosity (%)=(2.2-.quadrature.)/2.2.times.100 (a)
[0090] (2) Thickness: measured with a 1/1000 mm dial thickness
gauge (ex Technolock) without any load apart from the body spring
load.
[0091] (3) Surface roughness (Ra): measured in accordance with JIS
B 0601.
[0092] (4) Tensile strength: measured in accordance with JIS K
7127. Test pieces were #2 test pieces, testing speed was 50
mm/min.
[0093] (5) Light beam transmittance: transmittance of visible light
(500 mm wavelength) was measured with a spectrophotometer (Uv-240
ex Shimadzu Seisakusho).
[0094] (6) SEM examination: surface and cross section were examined
at 50-2000.times. magnification with an SEM (S-3500N ex
Hitachi).
1 TABLE 1 Tensile Thick- strength 500 nm Porosity ness Roughness
(N/mm2) Transmittance SEM (%) (.mu.m) Ra (.mu.m) MD TD (%)
Examination Ex. 1 0 12 0.010 105 105 90 no voids, fibrils, pinholes
Ex. 2 0 12 0.009 110 110 90 no voids, fibrils, pinholes Ex. 3 0 6
0.010 150 130 90 no voids, fibrils, pinholes Ex. 4 0 4 0.009 120
130 90 no voids, fibrils, pinholes Ex. 5 0 0.5 0.009 200 160 90 no
voids, fibrils, pinholes Ex. 6 0 50 0.009 100 100 88 no voids,
fibrils, pinholes Cmp. 3 50 0.200 50 40 10 striations on 1 surface
Cmp. 3 5 0.150 30 24 60 no voids, fibrils, 2 pinholes
[0095] From Table 1 it will be apparent that dense PTFE films
according to the invention are free from voids, thin, have little
surface roughness, and good strength and transparency.
[0096] The fixing rolls of the above Examples and Comparisons were
evaluated as follows. Results are tabulated in Table 2.
[0097] (1) Wear resistance (service life): the fixing roll was
installed in a printer, and after printing 50,000 pages the portion
contacted by the separating claw was inspected for wear damage.
Wear resistance was determined by removing the film surface layer
from the fixing roll and measuring the depth (maximum) of the worn
portion of the film surface with a surface roughness gauge (SV-600
ex Mitsutoyo).
[0098] (2) Image quality: solid images were output and inspected
for image quality with the naked eye.
[0099] (3) Heat required for fixing: a halogen lamp heater was
installed inside the fixing roll, and with fixing roll surface
temperature at 25.degree. C., halogen lamp heater was switched on.
The time required for fixing roll surface temperature to reach
150.degree. C.--a temperature level at which fixing is
possible--was measured.
2 TABLE 2 Worn portion depth Warm-up time (max)(.mu.m) Image
quality (sec) Example 7 3.0 no irregularity 120 in solid image
Example 8 3.5 no irregularity 60 in solid image Comparison 3 6.5
some irregularity 150 in solid image Comparison 4 7.1 no
irregularity 70 in solid image
[0100] From Table 2 it will be apparent that the fixing roll herein
has excellent wear resistance, uniform imaging, and short fixing
roller warm-up time.
[0101] The fixing belts of the above Examples and Comparisons were
evaluated as follows. Results are tabulated in Table 3.
[0102] (1) Wear resistance (service life): the fixing belt was
installed in a printer, and after printing 50,000 pages, the
portion contacted by the separating claw was inspected with the
naked eye for wear damage.
[0103] (2) Image quality: solid images were output and inspected
for image quality with the naked eye.
3 TABLE 3 Wear by separation claw after 50,000 pages Image
evaluation Example 9 negligible no irregularity in solid image
Comparison 5 significant some irregularity in solid image
Comparison 6 significant irregularity in solid image
[0104] From Table 3 it will be apparent that the fixing belt herein
has excellent wear resistance and uniform imaging.
[0105] The dense PTFE films of the above Examples and a PFA tube
(STM ex Gunze, 30 .mu.m thick) were evaluated as follows. Results
are tabulated in Table 4.
[0106] (1) Release: Teflon adhesive tape (#5490 ex 3M, 2.54 cm
width) was cut to a length of 10 cm and applied to the sample film.
Using a tensile tester (TG-200N ex Ninebea), Teflon adhesive
tape/sample film peel strength was measured. Peel strength is
average stress over a distance of 10-40 mm from initial peeling
location at a peeling speed of 50 mm/min.
4 TABLE 4 Peel strength (N/2.54 cm) Example 1 1.9 Example 2 1.8 PFA
tube (STM ex Gunze, 30 .mu.m thick) 2.8
[0107] From Table 4 it will be apparent that dense PTFE according
to the invention has better release than conventional PFA
tubing.
[0108] The dense PTFE films of the above Examples and a PFA tube
(STM ex Gunze, 30 .mu.m thick) were evaluated as follows. Results
are tabulated in Table 5.
[0109] (1) Wetting by silicone oil: under conditions of 22.degree.
C., 30% humidity, the angle of contact of dimethylsilicone oil
(KF-96-300 cs ex Shin-Etsu Chemical) vis--vis the sample film was
measured with a contact angle measuring unit (CA-D ex Kyowa Kaimen
Kagaku).
5 TABLE 5 Dimethylsilicone oil (KF-96-300 cs) contact angle
(.degree.) Example 2 34.5 PFA tube (STM ex Gunze, 30 .mu.m thick)
41.0
[0110] From Table 5 it will be apparent that dense PTFE according
to the invention has better dimethylsilicone oil wetting than
conventional PFA tubing.
* * * * *