Radiant fuser for xerographic reproducing apparatus

Abstract

Apparatus for heat fixing toner images electrostatically adhered to copy paper. The apparatus is characterized by the provision of plural radiant energy sources capable of fusing low density as well as high density images in an efficient manner. In order to prevent physical contact of the radiant energy sources by the copy paper, a shield is provided which is transparent to energy in the wave length bands required for fusing high and low density images.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to electrostatographic copying apparatus and, more particularly, to radiant energy apparatus for fixing toner images to a support member.

In the process of electrostatography, latent electrostatic images are formed on a support member, for example, plain paper with the subsequent rendering of the latent images visible by the application of electroscopic marking particles, commonly referred to as toner. The toner or powder images so formed vary in density in accordance with the magnitude of electrostatic charges forming the individual images. The toner images can be fixed directly upon the support member on which they are formed or they may be transferred to another support member with subsequent fixing of the images thereto.

Fixing of toner images can be accomplished by various methods one of which is by the employment of thermal energy. In order to permanently fix or fuse toner images onto a support member by means of thermal energy it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner coalesce and become tacky or melt. This action causes the toner to be absorbed to some extent into the fibers of the paper. Thereafter as the toner cools, solidification of the toner material occurs causing it to be firmly bonded to the support member. In the process of electrostatography, the use of thermal energy for fixing toner images is old and well known.

One approach to thermal fusing of toner images onto a support member is to pass the support with the toner images thereon past a source of radiant energy such that the image bearing side of the support is opposite the source of radiation while the reverse side thereof is moved in contact with a heated platen. In the foregoing arrangement, for reasons understood by those skilled in the art, the radiant energy source is so constructed and functions such that it radiates energy at short wave lengths (i.e., 0.5-2.0 microns) which satisfactorily fuses high density images by means of the energy being directly absorbed by the toner. The heated platen provides thermal energy for elevating the temperature of the copy paper so that the paper does not act as a heat sink which would rob the toner images of heat provided by the radiant source. While the foregoing arrangement has been found to operate satisfactorily, it is possible for the low density images not to be fused satisfactorily due to either, the lack of intimate contact between the reverse side of the paper and the platen or the platen not being at the proper fusing temperature when the copy paper passes thereover. Moreover, in a duplex mode of operation the heated platen which operates above the softening point of the toner causes offsetting of toner to the platen.

Accordingly, it is the primary object of this invention to provide a new and improved electrostatographic apparatus.

It is a more particular object of this invention to provide a new and improved radiant fuser for use in a xerographic reproducing apparatus.

Another object of this invention is to provide, in a radiant fuser, a shield disposed between the radiant energy source and image support member which shield is transparent to substantially all the energy emitted from the source whereby high and low density images are fused by radiant energy.

BRIEF SUMMARY OF THE INVENTION

Briefly, the above-cited objects are accomplished by the provision of a radiant fuser having two sources of radiant energy. The peak power of one of the sources is concentrated at wave lengths on the order of 0.5-2.0 microns while the peak power of the other is concentrated at wave lengths greater than 2 microns.

In order to prevent physical contacting of the radiant energy sources by the copy paper, a shield is supported intermediate the source and the copy paper. The shield, unlike prior art devices is transparent to substantially all energy wave lengths emitted from the sources.

In one embodiment of the invention the radiation sources comprise a quartz lamp which emits the short wave length energy and a reflector which absorbs energy emitted from the quartz lamp and re-radiates long wave length energy for heating the copy paper to thereby fuse the lower density images. As will be appreciated, the short wave length energy is directly absorbed by the toner images having a high density of toner particles.

In another embodiment of the invention, a resistance heater operating at a much lower surface temperature than the quartz lamp it is substituted for the reflector.

Other objects and advantages of the invention will become apparent in view of the detailed description to follow when read in conjunction with the accompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a reproducing apparatus incorporating the invention;

FIG. 2 illustrates a sectional view in elevation of a radiant fuser incorporated in the apparatus of FIG. 1;

FIG. 3 illustrates a modified embodiment of the radiant fuser illustrated in FIG. 2; and

FIG. 4 is a perspective view of a shield and support therefore incorporated in the fuser of FIGS. 2 and 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown by way of example an automatic xerographic reproducing machine 1 which incorporates the improved fusing apparatus 15 of the present invention. The reproducing machine 1 depicted in FIG. 1 illustrates the various components utilized therein for producing copies from an original. Although the fusing apparatus 15 of the present invention is particularly well adapted for use in an automatic xerographic reproducing machine 1, it should become evident from the following description that it is equally well suited for use in a wide variety of machines where an image is fused to a sheet of final support material and it is not necessarily limited in its application to the particular embodiment shown herein.

The reproducing machine 1 illustrated in FIG. 1 employs an image recording drum-like member 10 the outer periphery of which is coated with a suitable photoconductive material 11. One type of suitable photoconductive material is disclosed in U.S. Pat. No. 2,970,906 issued to Bixby in 1961. The drum 10 is suitably journaled for rotation within a machine frame (not shown) by means of a shaft 12 and rotates in the direction indicated by arrow 13, to bring the image retaining surface thereon past a plurality of xerographic processing stations. Suitable drive means (not shown) are provided to power and coordinate the motion of the various cooperating machine components whereby a faithful reproduction of the original input scene information is recorded upon a sheet 14 of final support material such as paper or the like.

Since the practice of xerography is well-known in the art, the various processing stations for producing a copy of an original are herein represented in FIG. 1 as blocks A to E. Initially, the drum 10 moves photoconductive surface 11 through charging station A. At charging station A an electrostatic charge is placed uniformly over the photoconductive surface 11 of the drum 10 preparatory to imaging. The charging may be provided by a corona generating device of a type described in U.S. Pat. No. 2,836,725 issued to Vyverberg in 1958.

Thereafter, the drum 10 is rotated to exposure station B where the charged photoconductive surface 11 is exposed to a light image of the original input scene information, whereby the charge is selectively dissipated in the light exposed regions to record the original input scene in the form of a latent electrostatic image. A suitable exposure system may be of the type described in U.S. patent application Ser. No. 259,181 filed June 2, 1972.

After exposure, drum 10 rotates the electrostatic latent image recorded on the photoconductive surface 11 to development station C wherein a conventional developer mix is applied to the photoconductive surface 11 of the drum 10 rendering the latent image visible. A suitable development station is disclosed in U.S. patent application Ser. No. 199,481 filed Nov. 17, 1971. The application describes a magnetic brush development system utilizing magnetizable developer mix having carrier granules and toner colorant. The developer mix is continuously brought through a directional flux field to form a brush thereof. The electrostatic latent image recorded on photoconductive surface 11 is developed by bringing the brush of developer mix into contact therewith.

The developed image on the photoconductive surface 11 is then brought into contact with a sheet 14 of final support material within a transfer station D and the toner image is transferred from the photoconductive surface 11 to the contacting side of the final support sheet 14. The final support material may be paper, plastic, etc., as desired. After the toner image has been transferred to the sheet of final support material 14, the sheet with the image thereon is advanced to a fuser assembly 15, which fixes the transferred powdered image thereto. After the fusing process, the sheet 14 is advanced through a snuffing apparatus 2 then by rolls 16 to a catch tray 17 for subsequent removal therefrom by the machine operator.

Although a preponderence of the toner powder is transferred to the final support material 14, invariably some residual toner remains on the photoconductive surface 11 after the transfer of the toner powder image to the final support material 14. The residual toner particles remaining on the photoconductive surface 11 after the transfer operation are removed from the drum 10 as it moves through cleaning station E. Here the residual toner particles are first brought under the influence of a cleaning corona generating device (not shown) adapted to neutralize the electrostatic charge remaining on the toner particles. The neutralized toner particles are then mechanically cleaned from the photoconductive surface 11 by conventional means as for example the use of a resiliently biased knife blade as set forth in U.S. Pat. No. 3,660,863 issued to Gerbasi in 1972.

If desired, in accordance with the invention, the sheets 14 of final support material processed in the automatic xerographic reproducing device can be stored in the machine within a removable paper cassette 18. A suitable paper cassette is set forth in U.S. patent application Ser. No. 208,138 filed Dec. 15, 1971.

The reproducing apparatus in accordance with this invention can also have the capability of accepting and processing copy sheets 14 of varying lengths. The length of the copy sheet 14, of course, being dictated by the size of the original input scene or information recorded on the photconductive surface 11. To this end the paper cassette 18 is preferably provided with an adjustable feature whereby sheets of varying length and width can be conveniently accommodated. In operation the cassette 18 is filled with a stack of final support material 19 of pre-selected size and the cassette 18 is inserted into the machine by sliding along a base plate (now shown) which guides the cassette into operable relationship with a pair of feed rollers 20. When properly positioned in communication with the feed rollers 20, the top sheet of the stack 19 is separated and forwarded from the stack 19 into the transfer station D by means of registration rolls 21.

It is believed that the foregoing description is sufficient for purposes of the present application to illustrate the general operation of the automatic xerographic reproducing machine 1 which can embody the teachings of the present invention.

Referring now to FIG. 2, that portion of the reproducing machine 1 of FIG. 1 embodying the fusing apparatus 15 of this invention is shown in greater detail. The image bearing sheet 14 after passing through the transfer station D of FIG. 1 upon separation from the photoconductive surface 11 is allowed to fall into contact with a vacuum belt transport system 22 which conveys the sheet directly to the fusing station 15.

The fusing station 15 comprises a radiant type fuser. The fusing station 15 comprises a heated platen 30 mounted to engage the non-image bearing side of the copy sheet 14 which moves in sliding contact therewith as it is transported through the fusing zone. The heated platen 30 is designed so that an efficient heat flow is established between the platen and the copy sheet 14 to raise the temperature of the sheet rapidly to a level somewhat below the sheet's scorch temperature. By controlling the temperature of the sheet 14 in this manner the ability of the sheet to act as a heat sink during image fixing is minimized.

The radiant energy for fusing is provided by an infrared quartz lamp 31 which is mounted in a reflector assembly 32 in opposing relationship to the heated platen 30 and in a position to thermally communicate with the image side of the copy sheet 14. The operating temperature of the lamp is on the order of 2400.degree.K. Preferably the spectral output of the lamp 31 is within a range at which the imaging material which may be toner for a xerographic machine 1 is highly absorptive and at which the support material 14 which may be paper is relatively non-absorptive. As a result, the toner images are rapidly raised to the desired fusing temperature while the support sheet 14 remains at a relatively lower temperature. A forced air cooling chamber 33 is provided about the backside of the reflector assembly 32 to cool the fuser 15 in operation.

A heating element 34 is provided in the platen 30 to maintain it at the desired temperature during standby periods. When the quartz lamp 31 is operated the preheat element is disconnected and the platen 30 receives its heat input directly from the quartz lamp.

The reflector assembly 32 is so constructed that it both reflects the short wave length energy emitted from the quartz lamp 31 and absorbs the long wave length energy with the subsequent reradiation thereof, the temperature of the reflector being on the order of 1000.degree.K. To this end the reflector 32 is a low mass construction and an air insulating barrier is provided between the reflector and the cooling chamber 33. The re-radiated long wave length energy is effective to raise the temperature of the paper 14 to thereby assist the heating element 34 in providing the energy necessary for fusing low density images. It will be appreciated that the reflected short wave length energy is absorbed by the high density images to thereby effect fusing thereof.

A shield assembly 50 as best illustrated in FIG. 4 is provided to preclude physical contacting of the quartz lamp 31 and the reflector 32 by the copy paper 14. The assembly 50 comprises a radiant energy transparent film 51 which has a thickness on the order of 5 mils. Typical materials which are useful as a film such as 51 are tetrafluoroethylene, flourinated ethylene-propylene and polyimide polymers. The film 51 is attached to a pair of frame or support members 52 and 53 the former of which is provided with a pair of pins 54 which are received in recesses or bores 55 of the frame member 53. This arrangement allows relative movement of the frame members by virtue of a pair of bias members in the form of coil springs 56. Temperature variations of the film will cause it to sag, consequently, the specific construction of the shield assembly provides for a constant planar orientation of the film over the operating temperatures of the fuser 15.

The frame members each have a flange 57 which is received in one of a pair of opposed recesses 58 provided in the reflector assembly 32. The space between the bottoms of the recesses 58 is such as to allow for relative movement of the frame members in a horizontal direction.

In the modified embodiment of the fuser assembly 15, illustrated in FIG. 3, the source of long wave length radiation is provided by means of a resistance heater 59 operated at a temperature on the order of 1000.degree.K which may be fabricated from any suitable material, for example, nicrom wire.

While the invention has been described with respect to two preferred embodiments it will be apparent that certain modifications and changes can be made without departing from the spirit and the scope of the invention and it is therefore intended that the foregoing disclosure be limited only by the claims appended hereto.

Claims

What is claimed is:

1. Apparatus for heat fusing toner images to a substrate on which they are supported, said apparatus comprising:

a first source of radiant energy capable of emitting energy having wave lengths on the order of 0.5-2.0 microns;

a second source of radiant energy capable of emitting energy having wave lengths over 2.0 microns;

means for transporting said substrate past said sources of radiant energy such that said toner images are directly exposed to said radiant sources;

means interposed between said radiant sources and said substrate, said interposed means being substantially transparent to the energy emitted from both of said energy sources;

said first source comprising a quartz lamp and said second source comprising a resistance heating element having an operating temperature substantially less than said first source; and

expansible means for mounting said means interposed between said radiant sources and said substrate in a substantially planar orientation regardless of the temperature thereof.

2. Apparatus according to claim 1, wherein said expansible means is supported by depending flanges of reflector means associated with said energy sources.

3. Apparatus according to claim 1, wherein said means interposed between said radiant sources and said substrate comprises a shield of polyimide film approximately 5 mils thick.

4. Apparatus according to claim 1, wherein said means interposed between said radiant sources and said substrate comprises a shield of polytetrafluoroethylene film on the order 5 mils in thickness.