Note: Descriptions are shown in the official language in which they were submitted.
18 Background and Summary of the Invention
19 The present invention relates to the xero-
graphic process step of fusing toner to support material
21 by a dry release hot roll contact fuser.
22 In the xerographic process a toned visual
23 image is transferred to a copy medium, for example
24 a sheet of copy paper, at a transfer station. The
toner is usually a pigmented thermoplastic resin.
26 ,The individual toner particles'are formulated such
27 that they will soften under heat. When soft, they
28 firmly stick to the surface of the copy pap2r. In
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1 order to fuse the toned copy paper it is nece~sary
2 to heat the toner to a relatively hiyh temperature,
3 usually in excess of 200 F. One method of so heating
4 the toner is by a hot roll contact fuser. The hot
roll fuser operates to pass the toned copy sheet
6 through a fusing nip formed by a heated and driyen
7 fuser roll, and a backup roll. This step o contact
8 fusing usually produces a tendency for th~ toned
9 side of the copy paper to adhere to the surface of
the hot roll. If the sheet o~ copy paper should
11 adhere to the hot roll, a-paper jam or roll~wrap
12 occurs.
13 Prior hot roll fusers may be of the WQt
14 release type wherein a release liquid such as sil$cone
oil is supplied to the fusing nip to enhance release
- 16 of the toned paper sheet from the fuser rolls. Such
17 hot roll fusers generally use a thick, soft elastomer
18 coating on the metal core of the backup roll and
19 a thin elastomer coating on the metal core of the
hot roll. ~len the two rolls are force-biased toward
21 each other, to form a fusing nip, an axial depression,
22 also called a footprint, i5 formed in the backup -
23 roll. The prior art has been constructed in this
24 manner to enable the use of a thin elastomer coating
on the hot roll, thereby preventing exc~ssive hot
26 roll surface temperature excursion between the standby
27 condition and the ~using condition. The use of silicone
~ 28 oil i5 costly, and tends to coa-t the paper with oil.
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1 It has been proposed that the thick deformable
elastomer coating be placed on the hot roll, and
3 that the backup roll be provided with a ~igid surfac~,
4 such ~l~t the closing of the fusing nip ~esults in
a footprin-t deformation into the hot roll's thick,
6 soft coating. An advantage of such a structure is
7 that the nip configuration of the deformable hot
8 roll provides a contour which is shaped such as
9 to aid in the release of the toned side o~ the sheet
from the hot roll. The shape of this nip is such
11 that the paper is literally pushed away from the
12 hot roll upon exit from the nip, thereby tending
13 to overcome the tendency of the hot toned sheet to
14 stick to the hot roll's surface.
lS With this type of fuser, it is necessary
16 that the hot roll's metal core be maintained at
17 a temperature which is higher than the optimum fusing
18 temperature. This is true since a copy run involving
19 a number of sheets rèquires that sufficient heat
be supplied through khis relatively thick heat insulator
- 21 to prevent the fusing nip temperature from drooping
22 to a temperature below the optimum fusing temperature.
23 However, the use of the hot roll's thick elastomer
24 coating allows the hot roll's fusing surface to achi~ve
unduly high temperatures, substantially above the
26 optirnum fusing temperature, when in a standby~condition,
27 due to the ~act that this thick elastomer coating,
28 ~which is a good heat insulator~ approache~ the tempera-
29 ture o~ the hot roll's metallic core.
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1 The fusing nip temperature is critical.
2 If the temperature is too low, the toner will not
3 fuse, whereas too high a fusing temperature tends
4 to cause the toner side of the sheet to stick to
the hot roll. This narrow temperature window pla~es
6 many restrictions on the construction of a hot roll
7 fuser.
8 The present invention successfully overcomes
9 these problems in,a dry release hot roll fuser who~e
hot roll is coated with a thick deformable elastomer
11 by providing early closure of the hot roll 1 5 fu~ing
12 nip. Thus, even though the external surface of the
13 elastomer coating may elevate to an unduly high tempera-
14 ture during a,standby period, the early closure of
the fusing nip causes this external surface to be
16 cooled, much as it would be cooled by the ~using
17 of sheets. By the time the first sheet to be fused
18 arrives at the fusing nip, the temperature at the
19 fusing nip has lowered to the vicinity of the optimum
fusing temperature and adequate fusing occurs without
.
21 relea~se failure.
22 As a further feature of the present invention,~
23 the rigid backup roll is constructed and arranged
24 to be generally equal to the cooling ef~ect of a-
sheet to be fused.
26 ' The foregoing,and o~her features and advanta-
27 ges o~ the,invention will be apparent from the follo~ing
28 more particular description of a preferred embodiment
.
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1 of the invention, as illustrated in the acco~panying
2 drawing.
3 Brief Description of the Drawing
4 FIGURE 1 is a schematic view of a xerogr~phic
copying apparatus incorporating the present invention;
6 FIGURE 2 is a side view of the fu~ing nip
7 portion of FIG~RE l's hot dry release roll fuser; ~nd
8 FIGURE 3 is a time-temperature graph which
9- plots the fusing nip temperature profile achieved
by operation of the present invention~ For comparlson,
11 the broken line curve of FIGURE 3 plots an exemplary
12 fusing nip temperature profile wherein the early
13 roll closing feature of the present invention is
14- not used.
Description of the Preferred Embodi~ent
16 FIGURE 1 is a schematic view of a xerographic
17 copying apparatus incorporating thé present invention.
18 In this device a scanning mirror system 10 and a
19 moving lens 11 move in synchronism with the rotation
of photoconductor drum 12 to place a latent image
21 of an original document 13 onto the drum's surface.
22 As is well known, prior to imaging at 14 the drum
23 is charged by corona 15. After imaging, the drum's
24 latent image is developed by magnetic brush d~veloper
16. Thereafter the drum's toned visible image is
26 transferred to a sheet of copy paper at transfer
27 station 17 by operation of transfer corona 18. Sheet
28 detach means l9 operates to cause the now-toned sheet
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to leave the surface of the drum and to follow sheet path 20, adjacent
vacuum conveyor 21 on ;ts way to dry release hot roll fuser assembly 22.
After fusing, the finished copy sheet follows sheet path 23 and is deposited
in tray 24. After transfer, the drum is cleaned as it passes cleanin~
station 25.
The apparatus o~ FIGURE 1 includes a copy sheet supply bin 26.
This supply bin includes a bidirectionally movable elevator which supports
the bottom sheet of the stack. While this structure is well known to those
of skill in the art, an exemplary structure is described in the IBM
TECHNICAL DISCLOSURE BULLETIN of August 1974, at pages 670 and 671. The
bin is operable to feed the top sheet of the stack to sheet discharge path
27. This sheet then travels down sheet path 28 to be momentarily stopped
at gate 29. When the leading edge of the drum's toned image arrives at
the vicinity of the gate, the gate is opened to allow the sheet to progress
into transfer station 17 in exact registry with the drum's image. An
exemplary means of picking the top sheet from the bin is described in the
IBM TECHNICAL DISCLOSURE BULLETIN of February 1974, at pages 2966 and 2967.
The apparatus of FIGURE 1 includes control logic 30 which is
operable to program or time the operation of the various mechanisms within
the copying appanatus of FIGURE 1.
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Registered Trade Mark
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1 Tlle present inventiorl provides an lmproved
2 dry release hot roll fuser to inhibit the toned side
3 of the copy sheet from adhering to hot roll 31, as
4 this sheet is pressed into ~he hot roll by backup
roll 32,
; 6 The fusing nip formed by rolls 31 and 32
7 is preferably opened and closed by control loglc
8 30, as thls logic is controlled by a drum position
- 9 sensing means, not shown, which responds to the posi-
tion of drum 12 and effects opening and closing of
11 the nip by means of a control system, not shown.
12 An exemplary mechanism for effecting the opening
13 and closing of this nip is shown in the IBM TECHNICAL
:14 DISCLOSURE BULLETIN of May 1973, at page 3644.
With the exception of the early closing
.
16 feature of the present lnvention, it is desirable
17 that the fusing nip be closed only.when paper is
18 between the rolls. Thus, it is desirable to open
19 the fusing nip during the inter-sheet gap~ which
; ~ 20 may exist between adjacent sheets to be fused, and
,
21 to close the nip when the next sheet.arrives. In
22 the alternative, the sheet velocity may be reduced
23 in the fuser, to ellminate this inter-sheet gap,
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24 in the manner described in U. S. Patent 3,794,417,
issued to J. A. Machmer.
26 FIGURE 2 discloses FIGURE l's hot roll
27 fuser 22 in detail. Hot roll 31 is an aluminum cylinder
28 having a thick, de~ormable silicone elastom~r outer
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1 layer 33. A pair of insulating end walls are fitt~d
2 into cylinder 31 at each end and support bearings
3 which, in turn, support the cylinder for rotation
4 about i-ts longitudinal axis. A conventional tungst~n
filament infrared heating lamp is located along this
6 axis. A reflective end plate may be carried within
7 the cylinder at each end to improve the axial uniformity
8 of heat reception by the cylinder from the lamp.
9 The inner surface of cylinder 31 may be colored black
to improve its radiant energy absorption characteristic.
11 Backup roll 32 is constructed and arrangéd
12 to simulate the cooling effect of the sheets to be
13 fused. Specifically, this roll may be a polished
14 cromlum plated steel roll, or may be made of a tubular
aluminum extruslon having a relatively heavy cylindrical
16 wall section ànd, for example, a smooth outer surface
17 of polytetrafluoroethelene.
18 As shown in FIGURE 2, the deformable outer
19 surface 33 layer o~ heated roll 31 is indented by
backup roll 32 to produce at the exit of fusing nip
21 33 a curvature tending to separate paper copy she~t
22 34 from the surface of heated roll 50.
23 The thick, deformabIe outer surface 33
24 of the hot roll is preferably an elastomeric heat
insulating layer. An example of such a material
26 is a ~ilicone elastomer,,such as the silicone rubber
27 material manufactured and sold by General Electric
28 Corporation, deslgnated as RTV-60. ~ preferred dry
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l release hot roll fuser is described in United States
2 Patent 3, 848, 305, issued to P. D. Jachimiak.
3 The hot roll's metal tube or core i5 main-
4 tained at a controlled temperature by a temperature
sensing and control means, not shown. An exemplary
6 means for accomplishing this result is described
7 in the IBM TECHNICAL DISCLOSURE BULLETIN of October
8 1972, at page 1587. A temperature sensor, not shown,
9 operates to sense the temperature of the outer surface
of this metal tube. Since layer 33 is a good heat
- ll insulator, the temperature of this outer surface
12 is maintained above the optimum fusing temper~ture
13 during a standby period--i.e. when the fusing nip
.
14 is open.
With reference to FIGURE 3, an exemplary
16 control temperatuxe ls seen to be 375 F. Thus,
17 during standby periods the outer surface of layer
18 33 achieves this high temperature. At time zero
19 control logic 30 of FIGURF. 1 is enabled to begin
a copy run. The temperature profile plotted in FIGURE
21 3 assures a standby period long enough fox the outer
22 surface of layer 33 to assume the same temperature
23 aS the hot roll's inner tube, namely 375. As the
24 copy process continues, and at approximately 1.5
seconds into the proces~, control logic 30 operates
26 to close the fusing nip. This is indicated a~ point
27 35 on the curve. From this time until approximately
~8 the 2.5-second time the hot roll and the backup roll
.
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1 are in fusing engagement with no sheet interposed
2 be~ween them. As a result of the cooling effect
3 provided by the backup roll, the fusing temperature
4. drops rapidly, following curve 36. At ~7 the first
sheet arrives to be fused, and the temperature of
6 the fusing nip has now been cooled approximately
7 to the optimum fusing temperature, namely 340.
8 The backup roll used in FIGURE 3 has a
9 cooling effect somewhat greater than the sheets to
be fused. A preferred feature is that the backup
.11 roll must cool the hot roll at least as well as sheets
12 to be fused.
13 For comparison, dotted line 38 plot~ the
14 fusing temperature of a hot roll, having a thick.
deformable elastomeric heat insulating coating when
16 early closure o~ the fusing nip is not provided.
17 In this case, at least the first sheet is subjected
18 to an average fusing temperature o about 370, and
19 sticking to the hot roll is likely.to occur.
Preferably, the hot roll and backup roll
21 may be constructed to have diameters in the range
22 of from 1 to 5 inchesi the deformable elastomeric .
23 heat insulating coating on the hot roll may have
24 a-thickness in the range of from .02 to .06 inch;.
and the surface velocity of the rolls is such as
26. to achieve a sheet velocity, through the fusing nip,
27 of from 10 to 30 inches per second. As a result,
28 the fusing nip preferably has a width in the range
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1 of from .1 to .4 inch, measured in the direction
2 of roll rotation.
3 While the invention has been particularly
4 shown and described with reference to a preferred
embodiment thereof, it will be understood by those
6 skilled ln the art that various changes in form and
7 details may be made therein without departing from
8 the spirit and scope of the invention.
9 What is claimed is:
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