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Publication numberUS3629549 A
Publication typeGrant
Publication dateDec 21, 1971
Filing dateDec 29, 1969
Priority dateDec 29, 1969
Also published asCA918729A, CA918729A1, DE2064842A1
Publication numberUS 3629549 A, US 3629549A, US-A-3629549, US3629549 A, US3629549A
InventorsSvendsen John A
Original AssigneeMinnesota Mining & Mfg
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Heating device
US 3629549 A
Abstract  available in
Images(1)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent Inventor John A. Svendsen St. Paul, Minn. Appl. No. 888,412 Filed Dec. 29, 1969 Patented Dec. 21, 1971 Assignee Minnesota Mining and Manufacturing Company St. Paul, Minn.

HEATING DEVICE 10 Claims, I Drawing Fig.

U.S.Cl 219/216, 165/185, 21 /388, 219/469 Int. Cl 1105b 1/00 Field of Search 219/216,

388, 469-471; 100/93 P, 93 RP; 356/651, 65.2; 355 9, 1 1; 156/583; 263/6; 165/185 Primary Examiner-C L. Albritton A!lorneyl(inney, Alexander, Sell, Steldt & Delahunt ABSTRACT: A heating device for producing graphic images on sheet material. The device includes a novel travels platen that provides an even amount of heat over the whole heating surface of the heating platen. The heating platen includes a heat source, an exterior heat conductive plate having on one side a heating surface adapted to contact and conduct heat to sheet material, and a sheetlike spacer between the heat source and exterior heat-conductive plate that conducts heat more rapidly along its length than through its thickness and thereby spreads heat from the heat source as it travels to the exterior heat-conductive plate.

PATENIH] nan-21 m lNVliN'l ()R. JOHN A. aS I END SEN mawa A 7' TORNE Y8 HEATING DEVICE BACKGROUND OF THE INVENTION Several processes for forming images on sheet material require heat-either applied to the sheet material itself to develop a latent image or applied to sheet assemblies of the sheet material and either the original or an intermediate sheet to transfer the image to the sheet material. One generally useful device for providing the necessary heat comprises a heating platen in the form of an arcuate heated shoe and a pressure platen in the form of a rotatable cylindrical drive roll against which the shoe is pressed. The arcuate heated shoe comprises a thin arcuate heat-conductive plate having a thin heating blanket-formed from a grid of electric conductors in an insulating sheath-bonded to the back side of the plate. On its front side the heat-conductive plate is provided with a heating surface adapted to contact the sheet material or sheet assemblies.

While the described device is useful to rapidly provide heat to sheet material or sheet assemblies, the heat provided has sometimes been found to vary over the heating surface of the heating platen. This nonuniformity of heat can be traced to the fact that the heat from the heating blanket originates in finite, separated electric conductors, and to the fact that at junctions of conductors, and in places where the insulation of the heating blanket is thinner than in other places, the heating blanket develops hot spots. Since the intensity of an image formed on sheet material may be dependent on the amount of heat reaching the sheet material or sheet assembly, an image that is uneven in intensity sometimes is produced. This uneven intensity sometimes lessens the quality of a copy of printed matter by making portions difficult to read or even unintellegible. But uneven intensity is especially critical and intolerable when continuous-tone images are being produced. In order for an image to have continuous-tone quality, the intensity of the image" must be essentially uniform over its whole area, and prior art heating platens as described above have not reliably provided the needed degree of uniformity of heat over their heating surface.

SUMMARY OF THE INVENTION The present invention provides a heating device having a novel heating platen that is capable of evenly heating the whole area of sheet material or sheet assemblies placed against the platen. This new heating platen comprises as a laminate structure (a) an exterior heat-conductive plate having on one side a heating surface adapted to contact and conduct heat to the sheet material or sheet assembly, (b) a heat source substantially coextensive with and parallel to the heating surface of the exterior heat-conductive plate, and (c) a sheetlike spacer between the exterior heat-conductive plate and heat source in position to conduct heat between the heat source and the exterior heat-conductive plate. The spacer is made from a material such as paper that causes the spacer to conduct heat more rapidly along its length than through its thickness. The result is that heat from hot areas of the heat source is spread as it travels to the heating surface of the platen, whereupon the heat becomes evenly distributed over the whole area of the heating surface.

A heating device of this invention further includes a pressure platen that presses sheet material against the heating surface of the heating platen. Preferably, the pressing surface of the pressure platen is covered with a self-sustaining resilient foam to prevent drainage of heat through the pressure platen and to provide a uniform pressure against the heating surface of the heating platen. Heating devices of the present invention, with their uniform application of heat and uniform pressure against the heating surface provide continuous-tone images of high quality.

DESCRIPTION OF THE DRAWING The drawing is a partial section through an illustrative heating device of this invention.

DETAILED DESCRIPTION The illustrative heating device 10 of the invention shown in the drawing comprises an arcuate heating platen 11 and a rotatable cylindrical drive roll 12 that draws sheet material between it and the heating platen and serves as a pressure platen pressing the sheet material against the heating platen. The heating platen 11 includes several different elements as a laminate structure. A base heat-conductive plate 15 has a heat source in the form of a heating blanket l6 bonded over its back surface. The heating blanket 16 comprises a grid of electric conductors l7 sheathed in an organic electrical insulating material 18. Fibrous heat insulation 19 and an exterior housing 20 cover the heating blanket to conserve heat and protect users against contact with the hot blanket. The illustrative heating platen is completed by a sheetlike heat-spreading spacer 22 and an exterior heat-conductive plate 23, with the heat-spreading spacer sandwiched between the base and exterior heat-conductive plates.

The heat-spreading spacer can be made from several different materials that conduct heat more rapidly along their length than through their thickness. In general, the spacer should conduct heat at least twice as fast along its length as through its thickness. Paper, which is formed from fibers that lie in the plane of the paper, is a preferred material since it is inexpensive and quite excellent in spreading capabilities-it often conducts heat five or six times faster along its length than through its thickness. Alternatives to paper include thin sheets of mica paper or asbestos, and less desirably, waffleconfigured thin metal foils and very fine wires screens. While spreading heat, the spacer must still conduct heat rather rapidly between the heating blanket and the exterior heating plate to provide sufficient heat to overcome the heat withdrawn by sheet material passed over the heating surface. The heat-conductive base and exterior plates typically conduct heat more rapidly than the spacer and are usually a metal such as aluminum, brass, or copper.

The cylindrical drive roll 12 of the embodiment of the invention illustrated in the drawing includes a preferably heatinsulative central tube 25 covered with a layer 26 of selfsustaining resilient foam. Instead of being covered with a selfsustaining foam, the pressure platen may be covered with a layer of flocking or furlike fabrics. The foam, such as a polyurethane foam, is preferred principally because it provides the most uniform pressure on sheet material, thus avoiding mottle patterns and other kinds of uneven development. In addition, foam is a better and more uniform insulator, and it develops the greatest drive force on sheet material. When a copy sheet 27 is drawn into the heating device in the direction of the arrow 28, the layer of resilient foam 26 collapses somewhat to accommodate the copy sheet.

The exterior heating surface 230 of the heat-conductive plate 23 is a low-friction, low-adherence surface with respect to the surface of sheet material passed over it. Preferably the surface 230 is covered with a low-friction material such as polytetrafluoroethylene. Some sensitized sheet material is best developed when a functional layer of image-forming material on the sheet material is directly against the heating surface of the heating platen, and a polytetrafluoroethylene coating has been found to provide a good contact surface against the image-forming coating on such sheet material.

Prior art, arcuate heating platens generally comprise a structure like that shown in the drawing except that they do not have the spacer 22 and exterior plate 23. Such prior art heating platens may be conveniently modified in the fleld by feeding between a drive roll such as the drive roll 12 and existing heating platen a sandwich of paper or other heat-spreading spacer and heat conductive smooth-surfaced plate. The added plate desirably has some means like a curved end flange such as the flange 23b on plate 23 which catches on the existing structure and prevents the sandwich from being completely fed through the device.

Instead of taking the form of an arcuate shoe such as shown in the drawing, heating platens of the invention also comprise a heated rotatable cylindrical roll, in which case the pressure platen is usually an arcuate shoe. Heating platens of the invention also have a flat or gently convexly curved heating surface, in which case they may be used with pressure platens that have a cooperating structure or with pressure platens in the form of rollers that are drawn across the heating surface of the heating platen.

Although the embodiment of the invention illustrated in the drawing includes a base heat-conductive plate to which the heating blanket is attached, heating platens of the invention also are formed by omitting the base heat-conductive plate and directly attaching the heating blanket to a heat-spreading spacer. In such a device it may be desirable to increase the thickness of the exterior heat-conductive plate to accomplish a greater heat spreading by that plate.

As an example of the invention, a heating platen such as illustrated in the drawing was formed using as the base heatconductive plate a sheet of aluminum 35 mils thick, on one side of which a heating blanket that comprised a network of nichrome resistance heating wires encased in silicone rubber was attached. A sheet of photographic base paper, 6% mils thick, was disposed between the base heat-conductive plate and an exterior heat-conductive aluminum plate that was 32 mils thick. On the exterior surface of the exterior heatconductive plate was a coating 0.7-mil-thick of polytetrafluoroethylene. The drive roll comprised a EPA-inchdiameter tube of paper-filled phenolic resin having a wallthickness of one-eighth inch and covered with a ,fi-inch-thick layer of polyurethane foam.

lclaim:

l. A heating device for producing graphic images on sheet material comprising 1. a heating platen that comprises as a laminate structure (a) an exterior heat-conductive plate having on one side a heating surface adapted to contact and conduct heat to the sheet material, (b) a heating blanket that is on the other side of the exterior heat-conductive plate and is substantially coextensive with and parallel to the heating surface of the exterior heat-conductive plate, and (c) a sheetlike spacer between the exterior heat-conductive plate and heating blanket in position to conduct heat between the heating blanket and the exterior heat-conductive plate, the spacer conducting heat more rapidly along its length than through its thickness; and

2. a pressure platen adapted to press sheet material toward the heating surface of the exterior heat conductive plate.

2. A heating device of claim 1 in which the sheetlike spacer is a fibrous paper.

3. A heating device of claim 1 in which the surface of the pressure platen that presses against the sheet material is covered with a uniform layer of self-sustaining resilient foam.

4. A heating device of claim 1 in which the heating platen is arcuate and the pressure platen is a rotatable cylindrical roll that mates within the concave arc of the heating platen.

5. A heating device of claim I in which the heating platen further includes a base heat-conductive plate between the spacer and the heating blanket.

6. A heating device of claim 1 in which a low-friction lowadherence coating covers the heating surface of the exterior heat-conductive plate.

7. A heating device for producing graphic images on sheet material comprising 1. an arcuate heating platen that comprises as a laminate structure (a) an arcuate base heat-conductive metal plate, (b) an arcuate exterior heat-conductive metal plate having on one side a smooth heating surface covered with a low-friction coating and adapted to contact and conduct heat to sheet material, (c) a heating blanket comprising a grid of electric conductors sheathed in electrically insulative organic polymeric material, the blanket being bonded to the convexly curved surface of the base heat-conductive plate and positioned substantially coextensive with and parallel to the heating surface of the exterior heat-conductive plate, (d) heating insulation covering the nonbonded surface of the heating blanket, and (e) a sheetlike spacer between the base and exterior heatconductive plates and in position to conduct heat from the base heat-conductive plate to the exterior heat-conductive plate, the spacer conducting heat more rapidly along its length than through its thickness; and

2. a rotatable drive roll that mates within the arc of the heating platen, is covered over its exterior surface with a layer of resilient heat-insulative material, and is adapted to press sheet material toward the heating surface of the exterior heat-conductive plate.

8. A heating device of claim 7 in which the sheetlike spacer is a fibrous paper.

9. A heating device of claim 7 in which the resilient heat-insulative material covering the drive roll is a resilient selfsustaining foam.

10. A heating device of claim 7 in which the spacer and exterior heat-conductive plate are not attached to the base heatconductive plate and are removable from between the base heat-conductive plate and the cylindrical roll.

t i i i

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2644151 *Jul 29, 1948Jun 30, 1953SealDry mounting press with timing signals
US3243579 *Aug 1, 1963Mar 29, 1966Frederick Post CoThermal developer
US3291466 *Sep 30, 1964Dec 13, 1966Xerox CorpXerographic fixing device
US3469077 *Sep 3, 1963Sep 23, 1969Minnesota Mining & MfgHeating device
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3725639 *Mar 23, 1972Apr 3, 1973Eastman Kodak CoThermal processor
US3741651 *Oct 12, 1971Jun 26, 1973Matsushita Electric Ind Co LtdRecording device
US3757662 *Jan 8, 1971Sep 11, 1973Ingels FApparatus for thermic development of heat-sensitive paper
US3932103 *Jan 31, 1974Jan 13, 1976Reynolds Metals CompanyDie for extruding plastic film
US3991483 *Apr 21, 1975Nov 16, 1976Canon Kabushiki KaishaPhotographic copying apparatus
US4013871 *Apr 15, 1975Mar 22, 1977Ricoh Co., Ltd.Image fixing roll for electrophotography
US4021523 *Oct 22, 1975May 3, 1977Reynolds Metals CompanyMethod of extruding plastic film
US4167771 *Jun 16, 1977Sep 11, 1979International Business Machines CorporationThermal interface adapter for a conduction cooling module
US4317026 *Mar 25, 1980Feb 23, 1982Hoechst AktiengesellschaftDeveloping chamber
US4322158 *Jan 30, 1980Mar 30, 1982Micron CorporationThermal film development apparatus
US5352863 *Apr 3, 1992Oct 4, 1994Minnesota Mining And Manufacturing CompanyFlat bed thermophotographic film processor
US5406930 *Aug 10, 1993Apr 18, 1995Atd CorporationOutdoor cooking device
US5408071 *May 19, 1993Apr 18, 1995Atd CorporationElectric heater with heat distributing means comprising stacked foil layers
US5665257 *Oct 23, 1995Sep 9, 1997Minnesota Mining And Manufacturing CompanyFlat bed thermophotographic film processor
US5800905 *Sep 19, 1995Sep 1, 1998Atd CorporationPad including heat sink and thermal insulation area
US5849388 *Feb 2, 1996Dec 15, 1998Imation Corp.Article, apparatus and method for cooling a thermally processed material
US5869806 *Feb 2, 1996Feb 9, 1999Imation Corp.Apparatus and method for thermally processing an imaging material employing means for bending the imaging material during thermal processing
US5869807 *Feb 2, 1996Feb 9, 1999Imation Corp.Apparatus and method for thermally processing an imaging material employing improved heating means
US5895592 *Sep 3, 1997Apr 20, 1999Imation Corp.Apparatus and method for thermally processing an imaging material employing a system for reducing fogging on the imaging material during thermal processing
US5946025 *Sep 29, 1997Aug 31, 1999Imation Corp.Thermal drum processor assembly with roller mounting assembly for a laser imaging device
US5986238 *Dec 19, 1996Nov 16, 1999Imation CorporationApparatus and method for thermally processing an imaging material employing means for reducing fogging on the imaging material during thermal processing
US6007971 *Oct 9, 1997Dec 28, 1999Minnesota Mining And ManufacturingApparatus, system, and method for processing photothermographic elements
US6041516 *Sep 29, 1998Mar 28, 2000Minnesota Mining & ManufacturingArticle, apparatus and method for cooling a thermally processed material
US6091480 *Jul 17, 1997Jul 18, 20003M Innovative Properties CompanyFilm removal mechanism for use with a thermal drum processor system
US6137087 *Dec 24, 1998Oct 24, 2000Brother Kogyo Kabushiki KaishaThermal roller for thermal fixing device
US6276356Jul 9, 1999Aug 21, 2001Atd CorporationPortable gas grill
US6342689 *Apr 14, 2000Jan 29, 2002Fuji Photo Film Co., Ltd.Heat developing method for heat developable image recording material
US6479221Sep 30, 1999Nov 12, 2002Fuji Photo Film Co., Ltd.Heat-developable image-recording material and method of developing the same
US6704197 *May 1, 2002Mar 9, 2004Denso CorporationElectronic unit having desired heat radiation properties
US7317468Jan 5, 2005Jan 8, 2008Carestream Health, Inc.Thermal processor employing drum and flatbed technologies
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EP1045284A1 *Apr 14, 2000Oct 18, 2000Fuji Photo Film Co., Ltd.Heat developing method for heat developable image recording material
Classifications
U.S. Classification219/216, 219/388, 219/469, 165/185
International ClassificationG03B27/02, G03B27/30, G03D13/00
Cooperative ClassificationG03B27/306, G03D13/002
European ClassificationG03D13/00D, G03B27/30H