US3853552A

US3853552A - Method of fixing a toner by heating in electrophotographic duplication

Info

Publication number: US3853552A
Application number: US00310155A
Authority: US
Inventors: R Namika
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1971-12-03
Filing date: 1972-11-28
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10
Also published as: JPS4862438A; DE2257536B2; DE2257536A1; GB1409755A; JPS5637549B2

Abstract

A method whereby a toner is fixed in the fixing step of electrophotographic duplication by heating at a temperature in a range from its secondary transition point to its melting point.

Description

a I ,1 1111111 tatna 16111 1 1 1 1 hiamiita e6. 10, 1974 METHOD OF FIXING A TONER BY 3,256,002 6/1966 Hudson 118/60 HEATHNG 1N nmcmornoroomrmc h st 3 ancoc DUPLICATKON 3,682,738 8/1972 Smith 117/21 X [75] Inventor: Ryochi Namika, Tokyo, Japan 3,698,314 10/1972 Grier 117/21 X 3,716,018 2/1973 Ohta et a1. 118/60 X [73] Assrgnee: Rrcoh (30., Ltd., Tokyo, Japan [22] Filed: Nov. 28, 11972 Primary Examiner-Ro1and E. Martin, Jr. [21] Appl' (L155 Attorney, Agent, or Firm-Cooper, Dunham, Clark,

Griffin & Moran [30] Foreign Application Priority Data Dec. 3, 1971 Japan 1. 46-98059 52 IU.S.1C1. 96/1 R, 96/1 so, 117/21, [57] ABSTRACT 118/59, 118/60, 118/DIG. .l [51] im. C1 G03g 13/20 A method whereby a toner is fixed in the fixing step of [58] Field of Search 96/1 R, 1 SD, 1.4; 117/21; electrophoto'graphic duplication by heating at a tem- 1 18/59, 60, DIG. 1 perature in a range from its secondary transition point to its melting point. [56] References Cited UNITED STATES P S 10 Claims, 2 Drawing Figures 2,870,312 1/1959 Westervelt 96/1 R X PATENTEb- I 3.853.552

VISCOELASTiCITY s i Tg Tr Tm TEMPERATURE METHOD OF FIXING A TONER BY HEATING IN ELECTROPIIOTOGRAPHIC DUPLICATION BACKGROUND OF THE INVENTION This invention relates to methods of fixing a toner by heating in electrographic duplication, and more particularly it is concerned with a method of fixing a toner adhering to a sheet of recording paper by heating at a temperature in a range from its secondary transition point to its melting point.

In one method of electrographic duplication known in the art, an electrostatic latent image of an original is formed on a sheet of recording paper, a toner is caused to adhere electrically to the electrostatic latent image, and the toner is fixed on the recording paper by heating. In this method of fixing a toner on the recording paper by heating, it has hitherto been customary to pass the recording paper on which an electrostatic latent imageis formed between a pair of rollers which are heated, so that the toner is melted by the heat of the rollers and fixed on the recording paper.

This method of heating a toner by means of rollers to fix the same on recording paper has a disadvantage in that the offset phenomenon occurs or the molten toner adheres to the peripheral surfaces of the rollers and tends to adhere to and soil the sheets of recording paper which follow the preceding sheet of recording paper in movement between the rollers, thereby producing duplicates of the original which are unacceptable.

Proposals have been made to obviate this disadvantage of the prior art by providing each of the rollers with a coat of the type to which a toner does not readily adhere or applying to the rollers a liquid capable of preventing adhesion of a toner to the rollers. However, these proposals are not economical because they require complex and costly devices.

SUMMARY OF THE INVENTION This invention has as its object the provision of a method of fixing a toner by heating in electrophotographic duplication whereby the toner adhering to a copy sheet such as a sheet of recording paper is fixed on the sheet by heating at a temperature in a range from its secondary transition point to its melting point.

In a specific sense, the invention contemplates the steps of depositing a resinous toner on an image portion of a copy sheet and heating the toner to a temperature in a range between its secondary transition point and its melting point, for fixing the toner, while bringing the toner on the copy sheet into contact with a surface (e.g., a roller surface) for aiding in fixing the toner. The heating and surface-contacting steps may, for example, comprise passing the copy sheet between a pair of rollers while heating at least one of the rollers for transfer of heat to the toner to raise the toner temperature into the stated range. The rollers mayact to apply pressure to the toner on the copy sheet to aid in fixing the toner thereon. The temperature of the toner, during contact of the toner with the surface of a roller, does not exceed the stated range, for preventing transfer of toner by offset onto the roller surface. Unexpectedly, it is found that heating of the toner to a temperature within the stated range effectively fixes the toner on the sheet, even though the toner is not heated above its melting point as in prior practice; and that fixing is thereby accomplished without offset, i.e., without pick-up of toner by the rollers.

According to the present invention, there is provided a method of fixing a toner by heating in electrographic duplication which permits fixing of the toner on the recording paper to be accomplished by means of a simple inexpensive device without the fear of soiling the next following sheets of recording paper by the occurrence of the offset phenomenon and without requiring to provide the rollers with a protective coat or applying a liquid to the rollers.

Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. ll is a diagram showing the characteristics of a toner in explanation of the behavior of the toner; and

FIG. 2 is a sectional view of one form of apparatus adapted to carry the method according to this invention into practice.

DESCRIPTION OF A PREFERRED EMBODIMENT In electrophotographic duplication, an electrostatic latent image of an original is formed on a sheet of recording paper, a toner is caused electrically to adhere to the electrostatic latent image, and the toner is fixed on the recording paper by heating. Generally, a toner mainly consists of a thermoplastic resin and carbon, and a plasticizer and other materials are added to reduce the melting point of the toner to a range from 45 to 120C. i

Thus, a resin accounts for about to percent of the toner, so that the behavior of the toner is governed by the properties of the resin it contains. Accordingly, toners behave much the same as high molecular compounds.

FIG. I is a graph on which viscoelasticity is plotted against temperature in explanation of the behavior of a high molecular compound. It will be seen that the compound is converted from powder form into a glass transformation zone A at a secondary transition point at a first temperature Tg, from the glass transformation zone into a rubbery zone B at a higher temperature Tr, and from the rubbery zone into a fluid zone C at a still higher temperature Tm (the melting point temperature as the heating temperature rises. Generally, Tg is about one half to one third of Tm.

A range in the neighborhood of the secondary transition point is the softening temperature range for a high molecular compound or toner. When heated to near this range, a high molecular compound or toner shows a marked change rapidly, and a change in temperature of 5 to 10C results in its modulus of elasticity increasing thousandfold, with the toner becoming as resilient as rubber. The particles of the toner rarely undergo transformation at Tg; the toner tends to show visco elasticity and fluidity and the particles tend to be fused between Tr and Tm; and the particles become fluid beyond Tm. It will thus be seen that, by heating the toner in a range from Tg to Tm, it is possible to fix the toner without the occurrence of the offset phenomenon. This invention resides in fixing the toner by heating at a temperature in a range from Tg to Tm.

Heating softens the surfaces of the toner particles and causes the particles to start being fused. Application of a suitable pressure to the toner particles at this time quickens the fusion of particles and at the same time causes the particles to begin to be bonded to one another as soon as they begin to soften.

When the toner adhering to a sheet of recording paper is fixed on the sheet by heating with heating rollers, it is not necessary to raise the temperature of the toner to the fluid zone in which the offset phenomenon occurs. It is quite natural that whether the offset phenomenon occurs depends greatly on the material of the heating rollers when the temperature of the toner draws near to or slightly invades the fluid zone. It has been ascertained by experiments that when the material used for the heating roller tends to cause the offset phenomenon to occur, the offset phenomenon occurs even if the temperature of the toner is slightly lower than the fluid zone temperature range, and that when the roller material is such that it seldom causes the offset phenomenon to occur, the offset phenomenon does not occur even if the temperature of the toner is in the fluid zone temperature zone.

When oil for preventing the offset phenomenon was applied to heating rollers made of metal and fixing of a toner image was carried out by heating the toner to a temperature above its melting point, it was impossible to prevent the occurrence of the offset phenomenon. It appears that the oil layer has no boundary lubricating effect if the layer has a thickness in a range from 10* to millimeter. If the oil layer is made to have a sufficiently large thickness to effect fluid lubrication satisfactorily, it may be possible to prevent the occurrence of the offset phenomenon. However, it is generally impossible to provide a layer of such great thickness at a temperature above the melting point of the toner. Even if it is possible, the provision of such layer is not desirable because it may stain the recording paper.

The coefficient of viscosity of the toner is in a range of 10 to 10 P when its temperature is in a softening temperature range near the secondary transition point, so that the toner will become fluid in 1 to 10 seconds in this temperature range. For practical purposes, if sheets are fed to the heating rollers at a rate of 10 centimeters per second and the heating rollers are brought into contact with each sheet for a distance of 5 millimeters, the toner will be in contact with the heating rollers for 0.05 second. This makes it necessary to raise the surface temperature of the heating rollers above the secondary transition point temperature. When the toner is heated quickly, it will not become fluid because of time lag unless it is heated at a temperature higher than its melting point. Thus, when fixing of the toner is carried out at high speed, the offset phenomenon will not occur even if the temperature is set at a level near Tm.

If the temperature is set at a level below the secondary transition point, the toner will adhere to the heating rollers owing to frictional charging taking place between the heating rollers and toner. That is, the toner particles are prevented from becoming viscous and the toner is attracted to the heating rollers with a greater force than it is attracted to the recording paper, so that the toner adheres to the rollers and the offset phenomenon occurs.

Fixing of the toner to the recording paper may be completed by virtue of the heat accumulated in the paper and the pressure applied to the paper after the recording paper has passed between the heating rollers. This is the case when the temperature for fixing the toner is set at a level near the secondary transition point. The temperature of the recording paper will be 50 to C about one second after it has passed between the heating rollers. The temperature for fixing the toner may also vary depending on the thickness of the recording paper.

In view of the foregoing, it has been found that it is advantageous to heat the toner on the recording paper at a temperature in a range from its secondary transition point to its melting point by means of heating rollers. This invention is based on this finding. Examples of the invention will now be described with reference to FIG. 2 which shows one embodiment of apparatus adapted to carry the invention into practice.

in FIG. 2 there is shown a pair of heating rollers 1 and 2 maintained in engagement with each other. The heating roller 11 consists of a heat resisting cylindrical roller 3 and a heater 5 disposed coaxially in the roller 3 while the heating roller 2 consists of a heat resisting cylindrical roller 4 and a heater 6 disposed coaxially in the roller 4, the

rollers

3 and 4 being adapted to be driven by means for rotation individually or with the heaters 5 and 6.

A sheet of recording paper 8 to which a toner 7 adheres was fed between the pair of rollers l and 2 at a rate of 10 centimeters per second, and at the same time pressure was applied by pressing means between the heating rollers l and 2 so that a pressure of 5 kg might be applied to the recording paper 8 which is of A4 size according to the Japanese standards. When the surfaces of heating rollers 1 and 2 were heated to to C, the toner was fixed perfectly to the recording paper without causing the offset phenomenon to occur and a fixed image of high quality was produced. In this example, the secondary transition point of the toner was 50C.

When an attempt was made to fix a toner whose secondary transition point is 70C to a sheet of recording paper by heating the surfaces of heating rollers to to 180C, no offset phenomenon occurred. When the surfaces of heating rollers were heated to to 225C in fixing a toner having its secondary transition point at 100C to a sheet of recording paper, no offset phenomenon occurred.

In the apparatus described above for carrying the method according to this invention into practice, one

of the two rollers may be a heating roller and the other roller may be an ordinary roller having no heater therein. The heating rollers may be constructed such that each of them comprises a follower roller having a heater built therein, and a main roller which is heated by the heat emanating from the heater in the follower roller. The heating rollers may be heater by heaters from outside the rollers instead of from inside the rollers. An endless belt trained over a pair of rollers may sheet of recording paper between a pair of heating rol lers, said sheet of recording paper having a toner adhering to one surface thereof and coming into contact with one of said rollers, while heating the toner to a temperature in a range from its secondary transition point to its melting point so as to fix the toner on the recording paper, the temperature of said toner not being raised to the fluid zone, said one roller having a surface subject to pick-up of toner by offset.

2. A method of fixing a toner by heating in electrophotography comprising the steps of passing a sheet of recording paper between a heating roller and a rotary member maintained in engagement with each other and rotated in opposite directions, said sheet of recording paper having a toner adhering thereto and the toner adhering surface of the recording paper being brought into contact with the periphery of the heating roller, while heating the toner to a temperature in a range from its secondary transition point to its melting point, the temperature of said toner not being raised to the fluid zone.

3. A method as set forth in claim 2 further comprising the step of applying pressure to the toner-bearing paper between the heating roller and the rotary member.

4. In electrographic duplicating procedure, the steps of a. depositing a resinous toner adherently on an image portion of a paper copy sheet, said toner having a secondary transition point at a first temperature and a melting point at a second and higher temperature, and

b. heating said toner on said copy sheet to a temperature in a range between said first and second temperatures for fixing the toner, while 0. bringing said toner on said copy sheet into contact with a surface subject to pick-up of toner by offset, while pressing said sheet against said surface for applying pressure to the toner on the copy sheet to aid in fixing said toner, the temperature of said toner being not higher than said range throughout contact of the toner with said surface for preventing offset of toner from the copy sheet to the surface, and said temperature of said toner not being raised to the fluid zone.

5. Procedure according to claim 4, wherein the step of heating said toner comprises heating said surface for transfer of heat therefrom to said toner and said copy sheet for raising the temperature of the toner into said range.

6. Procedure according to claim 4, wherein said surface is a moving surface, and wherein the copy sheet is advanced during contact with said surface such that the portions of said surface and said copy sheet in mutual contact are moving with a common velocity in a common direction.

7. Procedure according to claim 6, wherein said copy sheet is advanced between a pair of rollers, said surface being a surface of one of said rollers.

8. Procedure according to claim 7, wherein the setp of heating said toner comprises heating at least one of said rollers for transfer of heat therefrom to said toner and said copy sheet for raising the temperature of the toner into said range.

9. Procedure according to claim 7, wherein said copy sheet is pressed between said rollers for applying pressure to the toner on the copy sheet to aid in fixing said toner.

10. In electrographic duplicating procedure, the steps of a. depositing a resinous toner adherently on an electrostatic image on a paper copy sheet, said toner having a secondary transition point at a first temperature and a melting point at a second and higher temperature, and

b. advancing the copy sheet between a pair of rollers,

the toner being in contact with a surface of one of the rollers, said one roller having a metal surface, while, heating at least one of the rollers for transfer of heat to the toner and the copy sheet to raise the toner temperature to a range between said first and second temperatures, for fixing said toner, the toner temperature being maintained not greater than said second temperature throughout contact of the toner with said roller surface for preventing offset of toner from said copy sheet to said roller surface, said temperature of said toner not being raised to the fluid zone, and while d. pressing said copy sheet between said rollers for applying pressure to the heated toner on the copy sheet to aid in fixing the toner.

I UNWE STATES mm OFFME CERHTfiATE @F @QEEQTON Patent No. 53,552 Dated December 10, 1974 Ifivent Ryoichi Namiki It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Correct name of inventor:

Title page, heading, line change "Namika" to read Namiki '7;

Title page, after "[75] Inventor:" change "Ryochi Namike'Y to read Signed and sealed this 11th day of'March 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C MASON Commissioner of Patents Attesting Officer and Trademarks

Claims

1. A METHOD OF FIXING A TONER BY HEATING IN ELECTROGRAPHIC DUPLICATION COMPRISING THE STEPS OF PASSING A SHEET OF RECORDING PAPER BETWEEN A PAIR OF HEATING ROLLERS, SAID SHEET OF RECORDING PAPER HAVING A TONER ADHERING TO ONE SURFACE THEREOF AND COMING INTO CONTACT WITH ONE OF SAID ROLLERS, WHILE HEATING THE TONER TO A TEMPERATURE IN A RANGE FROM ITS SECONDARY TRANSITION POINT TO ITS MELTING POINT SO AS TO FIX THE TONER ON THE RECORDING PAPER, THE TEMPERATURE OF SAID TONER NOT BEING RAISED TO THE FLUID ZONE, SAID ONE ROLLER HAVING A SURFACE SUBJECT TO PICK-UP OF TONER BY OFFSET.

4. In electrographic duplicating procedure, the steps of a. depositing a resinous toner adherently on an image portiOn of a paper copy sheet, said toner having a secondary transition point at a first temperature and a melting point at a second and higher temperature, and b. heating said toner on said copy sheet to a temperature in a range between said first and second temperatures for fixing the toner, while c. bringing said toner on said copy sheet into contact with a surface subject to pick-up of toner by offset, while pressing said sheet against said surface for applying pressure to the toner on the copy sheet to aid in fixing said toner, the temperature of said toner being not higher than said range throughout contact of the toner with said surface for preventing offset of toner from the copy sheet to the surface, and said temperature of said toner not being raised to the fluid zone.

10. In electrographic duplicating procedure, the steps of a. depositing a resinous toner adherently on an electrostatic image on a paper copy sheet, said toner having a secondary transition point at a first temperature and a melting point at a second and higher temperature, and b. advancing the copy sheet between a pair of rollers, the toner being in contact with a surface of one of the rollers, said one roller having a metal surface, while, c. heating at least one of the rollers for transfer of heat to the toner and the copy sheet to raise the toner temperature to a range between said first and second temperatures, for fixing said toner, the toner temperature being maintained not greater than said second temperature throughout contact of the toner with said roller surface for preventing offset of toner from said copy sheet to said roller surface, said temperature of said toner not being raised to the fluid zone, and while d. pressing said copy sheet between said rollers for applying pressure to the heated toner on the copy sheet to aid in fixing the toner.