JPH03107183A - Fixing device, heat roll therefor and recorder - Google Patents

Abstract

PURPOSE:To stably perform printing with sufficient fixing strength by setting the thickness of a surface layer applied to the core metal surface of a heat roll and the thickness of a core metal to specific ones. CONSTITUTION:This fixing device is provided with the heat roll 6 and a backup roll 7 pairing with the heat roll 6. A nip part 23 fixing toner 27 onto a recording sheet 2 passing by the facing part of the rolls 6 and 7 is provided on the facing part. The heat roll 6 is provided with the hollow core metal 24, a heater lamp 30 disposed inside the core metal 24, and the surface layer applied to the surface of the core metal 24. The thickness of the surface layer 25 is set to a specific value or less; this value is determined by the square root of a product between the thermal diffusivity of the surface layer material and the nipping time when a sheet 2 passes by the nip part 23. The thickness of the core metal 24 is set to a specific value or more; this value is determined by the square root of a product between the heat diffusivity of the core metal material and the one rotation of the core metal.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a recording device using an electrophotographic method such as a printer, a copier, or a facsimile, and particularly to recording a toner image formed on the surface of a recording medium. The present invention relates to a fixing device for fixing to a body.

[Conventional technology]

Conventional fusing systems have at least a heat roll and a backup roll. Note that in this specification, the heat roll may be referred to as HR, and the backup roll may be referred to as BR. In addition, in a fusing system where both the HR and BH rolls are sometimes referred to as a fusing roller pair, HR is heated,
Bring HR and BR into contact and rotate. At this time, the roll to be driven is either one or both of HR and BR. A contact surface is formed by the contact between HR and BR.

This surface is called the nip. The recording paper having the unfixed toner image passes through the nip portion while being sandwiched between the HR and BR. At that time, the unfixed toner is heated by HR and melted after passing through the nip.

It solidifies and sticks to the recording paper. This series of operations is called fixation.

In the fixing system, at least the adhesion strength of the toner to the recording paper after fixing is good, and the fixed image cannot be rubbed or rubbed.
It is desirable that toner peeling does not occur even when folded. In this specification, the fixing strength is referred to as fixing strength.

However, in conventional fixing systems, when the rotational speed of the pair of fixing rollers is high, it is difficult to obtain sufficient fixing strength with only the pair of fixing rollers. In this case, even if the fixing system is not improved, the fixing strength can be improved by increasing the meltability of the toner. However, increasing the meltability of the toner shortens the shelf life of the toner. At the same time, development stability deteriorates, causing fog to occur in one image, or in severe cases, toner blocks inside the developing machine, making printing impossible. Furthermore, toner from the developing machine scatters outside the developing machine and adheres to a conveyance device, etc., causing erroneous printing on recording paper.

In severe cases, the friction coefficient of the conveyance device decreases, causing the inability to convey and affecting the entire recording system. Therefore, it is necessary to obtain sufficient fixing strength under toner conditions that do not cause such problems. Therefore, Photographic Science and Engineering 27 (19
1983) pages 19 to 25 (Photograph
ic 5science and engineering
27. (1983) PP19-25),
A preheating plate (preheater) may be installed just in front of the pair of fixing rollers in the recording paper conveyance direction to supplementarily heat the recording paper and unfixed toner from the back side of the printing surface of the recording paper.

HR has a structure in which the surface of a metal core, which is a hollow cylinder, is coated with a non-adhesive heat-resistant material such as fluorocarbon resin or silicone rubber, and the center of the cylinder has a structure such as a halogen lamp. The most common type has a structure in which a heating element is installed. In the Suijin Jllll book, this non-adhesive coating is referred to as a surface layer. The surface layer is provided to reduce the occurrence of a toner offset phenomenon in which toner adheres to the HR surface when toner passes through the nip portion. The heating element is on the back surface of HR or
It operates based on a detection signal from a temperature sensor that detects the temperature near the surface.

Furthermore, Japanese Patent Application Laid-Open No. 57-100459 describes the following. Fluorine resin is a poor conductor of heat, so after the heating element is brought into a heating state, the surface of the HR coat is heated to a specified temperature (
In order to shorten the time until the temperature reaches 150°C to 200°C, it is desirable to reduce the thickness of the fluorocarbon resin film. The film thickness is preferably 20 μm or less as measured from the tip of the convex portion of the unevenness of the facing layer of the fluorocarbon resin film to the surface of the film.

In addition, JP-A No. 60-213974 states the following: Due to the poor thermal conductivity of the heat-resistant resin of the 9 surface layer, it is difficult for the thermal energy from the 5 heating element to be transmitted to the back surface of the HR, resulting in poor thermal response. This has the disadvantage that heat loss is large, and when the thickness of the surface layer is about 40 μm to 50 μm, the temperature difference between the heating element and the back surface of the HR is 20° C. to 25° C.
It was also ℃. Therefore, by making continuous copies etc.
When a large amount of heat is suddenly taken away from the back surface, the amount of heat supplied from the heating element becomes temporarily insufficient, resulting in a drop in the temperature of the HR peripheral surface, which causes fixing failure. there were. In addition, if a large amount of heat is taken away from the center of the back surface of the HR and the surface temperature of the center temporarily decreases, such as when making a series of small-sized copies with a narrow width, the heating element Since the temperature of the HR is increased and the amount of heat supplied to the circumferential surface of the HR is increased, the surface temperature at both ends of the HR increases significantly, exceeding the heat-resistant temperature of the heat-resistant resin layer and shortening its lifespan. There have been drawbacks such as a toner offset phenomenon occurring at both ends of the paper if the image quality is significantly reduced, or if a large size copy with a wide width is made after successively making small size copies. In order to eliminate and improve the above-mentioned drawbacks, the thickness of the heat-resistant resin layer is made to be approximately 20 μm to 30 μm, thereby improving the thermal response of HR, improving fixing performance, and preventing toner offset phenomena. It can be prevented. Also, the temperature difference between the heating element and the HR surface is 1
The temperature can be lowered by 0°C to 15°C, and even when making small-sized copies with a narrow width, the temperature drop at the center of the HR cloth surface is small, and since the set temperature of the heater itself is lower than before, the temperature at both ends of the HR The temperature rise is also significantly smaller. Furthermore, the heat response of HR is improved, and a high-precision temperature control device is not required, and inexpensive control is sufficient, thereby reducing the cost of the fixing device.

[Problem to be solved by the invention]

Among the above-mentioned conventional techniques, the apparatus that uses a preheating plate and rotates a pair of fixing rollers at high speed to perform fixing has a problem in that the fixing system including the preheating plate becomes large. In addition, since the preheating plate needs to heat the recording paper from the non-printing side, it is not possible to install the preheating plate in the case of a high-speed double-sided printing recording system that may not have a non-printing side. Can not. Therefore, when the fixing system is used in the recording system for high-speed printing without the preheating plate, there is a problem that sufficient fixing strength cannot be obtained.

In addition, with the conventional technology that reduces the thickness of the surface layer made of fluororesin without using a preheating plate, there is no problem when the number of sheets is small, but when printing a large number of sheets continuously, the thickness of the surface layer is reduced. By making it thinner, the amount of heat transferred from the underlying core metal to the surface layer increases, so when continuous fusing is performed, the HR core metal temperature will drop rapidly, and the HR surface temperature will also drop accordingly, making it impossible to achieve sufficient fusing. There was a problem that strength could not be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and a heater roll for the fixing device that do not use a preheating plate and do not reduce fixing strength even when continuous fixing is performed.

Another object of the present invention is to provide a recording device that can stably realize printing with sufficient fixing strength.

[Means to solve the problem]

In order to achieve the above object, a fixing device according to the present invention includes a heat roll and a backup roll paired with the heat roll, and a nip in which the toner is fixed to the recording paper passing through the opposing portion of both rolls. a separation device that separates the recording paper that has come out of the nip portion and is in close contact with the heat roll surface from the heat roll surface; and a cleaning device that removes toner transferred from the recording paper to the heat roll. In the fixing device, the heat roll includes a hollow cylindrical core metal, a heat source disposed inside the core metal, and a surface layer provided on the surface of the core metal,
The thickness of this surface layer is determined by the square root of the product of the thermal diffusivity of the surface layer material and the nip time during which the paper passes through the nip portion, and the thickness of the cored metal is determined by the thickness of the cored metal. The thickness is determined by the square root of the product of the thermal diffusivity of the material and one rotation period of the core metal. Here, the material of the first surface layer is a fluororesin, and the thickness of the surface layer is preferably 40 μm or less. Further, the core metal material is aluminum, and the thickness of the core metal is preferably 61'1I11 or more.

In the fixing device, it is preferable that the first separating device is a separating claw disposed with a gap from the surface of the heat roll. Here, the gap is preferably set to be less than the thickness of the recording paper, and furthermore, the gap is preferably formed variably depending on the thickness of the recording paper. Further, the separating claw is preferably made of metal and has a fluororesin layer provided on its surface. Also,
It is preferable that a gas outlet is provided at the end of the separating claw on the heat roll side to cause gas to flow out and separate the recording paper from the heat roll by the airflow.

In the fixing device, the cleaning device supports a wiping band that is moved from the feed roller toward the take-up roller and slides on the surface of the heat roller, and a sliding portion of the wiping band with the heat roller. The wiping strip is made of heat-resistant synthetic paper and has a thickness of approximately 5 μm or less. Further, the support member is arranged to be inclined so that the separated liquid supply part is in an upward position, and a pressing member for pressing the wiping band against the heat roll is provided at the inclined lower end of the support member. The one that is given is good. Further, the wiping strip preferably contains a resin having an affinity for the toner, and the resin is preferably transparent. Further, the support member is provided with a weir that suppresses the flow of the separated liquid, and the weir is located above the pressing member and below the separated liquid supply position, which is the main position where the separated liquid is absorbed into the wiping band. Things are good. Preferably, a pre-wiping device is provided at a position upstream of the position where the wiping band of the heat roller slides on the heat roller. Here, the pre-wiping strip of the pre-wiping device is preferably wound onto the wiping strip take-up roller so as to overlap the wiping strip, and furthermore, the pre-wiping strip is made of heat-resistant synthetic paper. What becomes is good.

A heat roll for a fixing device according to the present invention includes a hollow cylindrical core metal and a surface layer provided on the surface of the core metal, wherein the thickness of the surface layer is: The thickness of the core metal is determined by the square root of the product of the thermal diffusivity of the surface layer material and the nip time during which the paper passes through the nip portion, and the thickness of the core metal is determined by the thermal diffusivity of the core metal material and the nip time. The thickness is determined by the square root of the product of one rotation period of the core metal or more. Here, the surface layer material is a fluororesin, the thickness of the surface layer is preferably 4 μm or less, the core metal material is aluminum, and the core metal thickness is preferably 6 ann or more.

The recording device according to the present invention includes a developing station that forms an unfixed toner image on a fed recording paper, a heat roll, and a backup roll that pairs with the heat roll, and the rollers are placed opposite each other. A nip section is provided in the section for fixing toner on the recording paper sent from the development station and passing through the nip section, and a separation section for separating the recording paper that has come out of the nip section and is in close contact with the heat roll surface from the heat roll surface. In the recording device, the heat roll of the fixing device includes a hollow cylindrical core metal and a cleaning device for removing toner transferred from the recording paper to the P1-roll. It includes a heat source disposed inside the core metal and a surface layer provided on the surface of the core metal, and the thickness of this surface M is determined by the thermal diffusivity of the surface layer material and the nip portion of the paper. The thickness of the core metal is determined by the square root of the product of the nip time during which the core metal passes, and the thickness of the core metal is determined by the square root of the product of the thermal diffusivity of the core metal material and one rotation period of the core metal. This is the structure described above. Here, in the heat roll of the fixing device, the surface layer material is fluororesin, the thickness of the surface layer is formed to be 40 μm or less, the core material is aluminum, and the core metal thickness is 6 μm.
It is preferable to have an IIN of 11 or more.

[Effect]

Making the HR surface layer thinner acts to increase the amount of heat supplied to the surface layer from the metal core during the time the paper passes through the nip. As a result, the amount of heat flowing into the toner from the surface layer increases, so that the fixing strength can be improved. At that time, the temperature of the core metal decreases, but by setting the core metal thickness optimally, the heat capacity of the core metal can be increased and temperature fluctuations can be minimized, so continuous printing can be performed semi-permanently. Even when fixing is performed, sufficient fixing strength can be stably maintained.

According to the thinning of the HR surface layer in the fixing system of the present invention, the amount of heat supplied to the toner increases, thereby improving thermal responsiveness. This effect, if only the surface layer is made thinner, has the effect of increasing the temperature drop of the HR and shortens the ON-OFF time interval in controlling one heating element. Therefore, a highly accurate temperature control device is required.

However, in the present invention, as mentioned above, the thickness of the core metal has been optimized to compensate for the drawbacks associated with the thinning of the surface layer.
Does not require high-precision temperature control equipment.

〔Example〕

<Embodiment 1> An embodiment of the present invention will be described below with reference to FIGS. 1 to 10. FIG. 1 is a sectional view showing the printing process of a double-sided recording apparatus equipped with a fixing device of the present invention. Here, 1 is a paper feed hopper, 2 is a recording paper, 3 is a developing station, 4 is the first side of the recording paper, 5 is a fixing device, 6 is a heat roll, and 7
is a backup roll, 8 is a separating claw, 9 is an inverter roll, 10 is a paper discharge stacker, 11 is a return conveyance path, 12 is a reversing stacker, 13 is a merging conveyance path, 14 is a merging section, IS
is the second side of the recording paper, 20 is the photoreceptor, 21 is the developing machine, 22
is a transcription machine. In the present invention, the fixing device 5 employs a heat roll fixing configuration using a heat roll 6 and a backup roll.

The recording paper 2 stored in the paper feed hopper 1 is conveyed to a development station 3 consisting of at least a photoreceptor 20, a developing machine 21, and a transfer machine 22, where unfixed L and toner are deposited on the first surface of the recording paper 2. An image is created. Next, the recording paper 2 with the unfixed toner image is conveyed to the fixing device 5, where it is heated so that the toner image on the first side 4 is fixed and fixed to the recording paper 2. After fixing on the first side 4, the recording paper 2
The water reaches a diverting section formed by the separation claw 8, and when the second side printing mode is set, the fluid is diverted upward there and then conveyed to the inverter roll 9 side. The separation claw 8 divides the flow by switching its position up and down.

In this figure, the position of the separation claw 8 is drawn downward.

In this case, the flow is diverted to the inverter roll 9 side. When the separation claw 8 is positioned upward, the flow is diverted to the paper discharge stacker 10 side. Next, the recording paper 2 is sent to the return conveyance path 11 by the inverter roller 9.The 8 recording paper 2 is loaded onto the reversing stacker 12, and before the next recording paper 2 reaches the reversing stacker 12. Then, the paper is discharged to the merging conveyance path 13 and reaches the merging section 14 . Confluence part 1
4, the recording paper 2 rides on the same transport path on which it was placed when it was first discharged from the paper feed hopper 1, and reaches the development station 3 again. At this time, the first surface 4 printed earlier is facing upward. Therefore, in this case, an unfixed toner image is formed on the second surface 15 of the recording paper 2 at the developing station 3. Next, in the same way as when fixing to the first surface 4, the second surface 1 is fixed.
5 fixing is performed. At this time, the separation claw 8 is switched to the upper position, and the recording paper 2 is printed on both the first and second sides and is discharged to the paper discharge stacker 1o. The basic operation and configuration of a double-sided recording device has been described above, focusing on the movement of a single sheet of recording paper. In reality, this operation is performed continuously. Further, when printing only on the first side, when the recording paper 2 reaches the separation claw 8 for the first time, the one-separation claw 8 is positioned upward, and the paper is ejected to the paper ejection stacker 10 as it is.

FIG. 2 is a sectional view of the fixing device of the present invention.

23 is a nip portion, 24 is a core metal, 25 is a surface layer, 26 is a silicone rubber layer, 27 is a toner, 28 is a separation device, 29 is a cleaning device, 30 is a heater lamp serving as a heat source, and 31 is a pressing force. The heat roll 6 consists of a core metal 24 which is a hollow cylinder made of aluminum and a surface layer 25 made of Teflon provided on the surface of the metal core 24, and a heater lamp 3 in the center thereof.
0 (halogen lamp) is placed. The backup roll 7 is composed of an aluminum cylinder and a silicone rubber layer 26 on the outside thereof. The heat roll 6 and the backup roll 7 face each other under a pressing force 31, and their contact surfaces are formed by elastic deformation of the silicone rubber layer 26. This contact surface is called a nip portion 23. The recording paper 2 on which the unfixed toner 27 has been formed in the form of an image is passed through the nip 23 between the heated heat roll 6 and the bank-and-roll 7, so that the toner 7 is melted and recorded. It sticks to paper 2. This process is called fixation. The separating device 28 is used to separate the recording paper 2 that is in close contact with the surface of the heat roll 6 at the nip portion 23 from the heat roll 6 .

In this embodiment, a non-contact peeling method is used, which will be described in detail later. Most of the toner 27 is fused to the recording paper 2 at the nip portion, but some toner 27 is also transferred to the heat roll 6 . A cleaning device 29 is provided because the toner 27 transferred to the heat roll 6 may be retransferred to the recording paper 2 to which it is next fixed, resulting in erroneous printing. The cleaning device 29 has the function of wiping off the toner 27 transferred to the heat roll 6. This will also be explained in detail later.

In the fixing device of this embodiment, the diameter of both the heat roll 6 and the backup roll 7 is 1001001 mm, and the time required for one point of the paper to pass through the nip portion (slip time) is 14 m5, as shown in Figures 1 and 2. Thus, in the fixing device of this embodiment, the toner 27 is heated only by the nip portion 23 formed between the heat roll 6 and the backup roll 7. To achieve this objective, it is necessary to increase the amount of heat flowing into the toner 27 from the heat roll 6. Therefore, the heat flow mechanism inside the heat roll 6 during fixing was determined.

For the study, an unsteady temperature distribution calculation using the finite element method was used. FIG. 3 is a diagram showing the model used for calculation.

Aluminum core bar 24, Teflon surface layer 25, toner 2
7. It is a four-layer one-dimensional model consisting of two recording sheets (sheets). Although the names of specific substances have been listed for convenience, the substances shown here are defined by the thermal conductivity and thermal diffusivity shown in FIG. Therefore, it does not essentially specify a substance. For example, if materials have the same thermal conductivity and thermal diffusivity, the calculation results obtained will be the same even if the types of materials are different.

Here, unsteady temperature distribution calculation using the finite element method will be explained. The heat conduction equation expressed by the following equation was solved using the finite element method.

Here, T indicates temperature, t indicates time, and X indicates position.

In the finite element method, the solution is obtained at a temperature defined by position and time. Specifically, it is displayed as a time step (time) and a temperature at a node (position). A general-purpose program is used for calculations.

For the temperatures displayed in this specification, the solution obtained by the above finite element method calculation was used as is. The heat flux is the value obtained by dividing the difference between the temperature at the interface and the temperature at the next node by the distance between the nodes, multiplied by the thermal conductivity.

To explain the heat flux flowing into the toner from the surface layer as an example, the temperature and position of the interface between the surface layer and the toner are T and X, respectively, and the temperature and position of the node closest to the interface in the toner are T,,X.

shall be. Furthermore, when the thermal conductivity of the toner is λ and the heat flux is q, the heat flux is defined by the following equation.

In the actual calculation, 2 μm was used for x, −X.

FIG. 4 is a diagram showing the relationship between the surface layer thickness and the heat roll (HR) surface temperature at the nip portion during fixing, which was determined by the above calculation. The parameter is the time after the paper is nipped at the front end of the nip. Therefore, 1 ms indicates the early stage of the nip time, 4 ms and 7+as indicate the middle stage, and 14 m5 indicates the late stage. Displays the displayed HR humidity temperature and the set temperature before fixing. The reason why the HR surface temperature at each time is lower than the HR set temperature (190° C.) is that heat is absorbed by the paper as soon as it is caught in the nip. The fact that the thinner the HR surface layer is, the higher the HR surface temperature is indicates that heat is supplied to the surface layer from the core bar of the inner layer more quickly when the thickness is thinner. As described above, the thinner the surface layer is, the more the surface temperature increases regardless of the hour. Usually, when the pre-fixing temperature of HR is increased by 10° C., the fixing strength is improved by 5 to 10%. Considering this point, by making the surface layer thinner,
It is expected to improve fixing strength.

Next, we will try to determine the optimal surface layer thickness by examining the heat transport mechanism. Figure 5 shows the surface layer thickness and H determined by the above calculation.
FIG. 3 is a diagram showing the relationship between heat flux (inflow heat amount per unit time and unit area) from R to toner. Parameters, etc. are the same as in FIG. 4. As the surface layer becomes thinner, the heat flux from the surface layer to the toner tends to increase, and the heat flux from the surface layer to the toner tends to increase. In II8, the surface layer thickness increases sharply below 20 μm. Moreover, at 4 ms and 7 ms, which are the middle stages of the nip time, the surface layer thickness increases sharply below 30 μm. Note that the reason why the value of the heat flux decreases as a whole as time passes is because the temperature difference between the toner and the surface layer gradually decreases.

We attempted to further clarify this phenomenon.

FIG. 6 is a diagram showing the relationship between the surface layer thickness determined by the above calculation and the heat flux from the aluminum core metal to the surface layer. Parameters, etc. are the same as in FIG. 4. The thinner the surface layer is, the greater the amount of heat that flows into the surface layer from the aluminum core metal. This tendency is particularly remarkable at the beginning of the nip time (1 ms).

It can be seen that at this time, the range where the surface layer is thick (40 to 50 μm) is close to an adiabatic state. Thereafter, the heat flux gradually increases with the passage of time, but in the range where the surface layer is thin (10~
30 μm), the absolute value is low. The boundary between the thin and thick surface layer exists at a surface layer thickness of about 40 μm,
The change in heat flux with respect to the surface layer thickness is also discontinuous beyond 40 μm. The reason for this is that in areas where the surface layer is thin, the effect of the heat flux on the toner due to fixing generated on the HR coat surface is likely to reach the aluminum core metal during the nip time, whereas in areas where the surface layer is thick, the effect is difficult to reach, and the boundary between This is because the surface layer has a thickness of 40 μm. This is synonymous with the fact that in a range where the surface layer thickness is 40 μm or less, heat supply from the aluminum core metal is large during the nip time, and in a thicker range, heat supply from the aluminum core metal is small. The reason why the amount of heat flowing into the toner increases below a specific surface layer thickness (20 μm for L is, 30 μm for 4 ms and 7 ms) in FIG. 5 can be understood from this result.

From the above results, it can be expected that the fixing strength will be greatly improved in a range where the amount of heat flowing from the aluminum core metal during the nip time is large (surface layer thickness of about 40 μm or less). therefore,
The thickness of the surface layer is preferably within this range (40 μm or less). Preferably, in the middle of the nip time, the heat flux from the surface layer to the toner is large (surface layer thickness 30 μm or less).
is good.

Furthermore, preferably, at the beginning of the nip time, the heat flux from the surface layer to the toner is large (surface layer thickness 20
μm or less) is better.

In order to confirm this calculation result, an experiment was conducted under the same conditions as the calculation. FIG. 7 is a diagram showing the relationship between HR pre-fixing temperature (HR humidity temperature and fixing strength) under conditions of surface layer thicknesses of 20 μm and 40 μm.Fixing strength is shown by tape peel strength.Tape peel strength is An adhesive tape was applied to the fixed image and then peeled off, and adhesion was defined as the ratio of the reflection density of the image before and after peeling off.Therefore, the larger the value, the higher the fixing strength.Figure 8 shows the HR
FIG. 3 is a diagram showing the relationship between surface layer thickness and fixing strength using pre-fixing temperature (HR humidity temperature) as a parameter. The smaller the surface layer thickness is, the greater the tape isolation strength is.

For convenience, the thickness of the surface layer has been specifically shown using Teflon as an example of the material of the surface layer, but the calculation results corresponding to the above-mentioned FIGS. 4 to 6 are obtained for other materials with different thermal diffusivities for the surface layer. are shown in FIGS. 9 to 14. Figures 9 to 11
The figure shows that the thermal diffusivity of the surface layer is 6.41 x 10-”rr?
/s material and the core metal is AQ, and Figures 12 to 14 show that the thermal diffusivity of the surface layer is 2.85X10'''''
This is a case where the material is m/s and the core metal is AQ. The same conclusions as those shown in FIGS. 4 to 6 can be basically obtained from these calculation results.

Furthermore, from these examples, generally speaking, the range where the amount of heat flowing from the core metal is large (40 μm or less for Teflon) is Q.
□, the thermal diffusivity of the surface layer material is a5, and the nip time is t.
If n, then Q1=pTr7-(1). Further, let Q2 be the range in which the heat flux from one surface layer to the toner is large (30 μm or less for Teflon) in the middle of the nip time.

There is a tendency that Q2 = Yug 4 " = - (2). Furthermore, at the beginning of the nip time, the heat flux from the surface layer to the toner is large (20μ for Teflon).
m or less) is Q, there is a tendency that Q□=upper Gπ 2°−(3). When equations (1) to (3) are calculated using the thermal diffusivity of Teflon shown in FIG. 3, the results are shown to be in good agreement with the calculation results shown in FIGS. 5 and 6. This is an example of -grain amount in formulas (1) to (3), but similar results can be obtained using other substances. Therefore, it can be said that a surface layer thickness of 1 is good, and more preferably a thickness of T or less.

By the way, the HR core metal has the function of being supplied with heat from a heater pump, temporarily storing it in the core metal, and supplying the heat as necessary fixing energy to the surface layer. In other words, it is a secondary heat source.

Since the HR of the present invention having the surface layer thickness described above has a large amount of heat flowing from the core metal in the nip, the temperature at the interface between the core metal and the surface layer is stable when the core metal is used as a secondary heat source. It is necessary to increase the quality. That is, if the temperature at the interface is unstable, the recording paper is fixed once.

When fixing 2 or 3 sheets in a row, it is possible to fix the first sheet, but it is impossible to fix subsequent sheets, or it is possible to fix a limited number of sheets, but only tens or tens of thousands of sheets. Semi-permanent establishment becomes impossible.

Next, we investigated the temperature stability at the interface between the core metal and the surface layer. For the study, unsteady temperature distribution calculations using the finite element method were used, as in the case above. 15th
The figure shows the model used for calculation. This is a two-dimensional model in which an aluminum core metal 24 and a Teflon surface layer 25 are laminated in a donut shape. To simulate the rotation of HR, H
A heat flux was generated sequentially from the surface of the R cloth to the outside.

This corresponds to the amount of heat required for fixing. In this calculation, this range is 210 m, that is, the horizontal direction of A4 size paper is used. The thermophysical property values used are the same as those shown in FIG. Similar to FIG. 3, in the above description, the names of specific substances are mentioned for convenience, but the substances are defined by thermal conductivity and thermal diffusivity, and the names of the substances are not specified.

Figure 16 shows the difference (temperature (descent). Here, the time required from fixing the first page to immediately before fixing the second page at the circumferential position corresponding to the heat flow generation time O is called a fixing cycle. Further, expressed in terms of the phenomenon, the fixing cycle can be said to be the time required from when the leading edge of the recording paper contacts the HR until the position on the HR where the leading edge of the recording paper contacted next meets the recording paper. Therefore, when the circumferential length of HR is shorter than the length of the paper in the conveyance direction, the fixing period is equal to the rotation period of HR. Even in the opposite case, that is, when the circumferential length of the HR is longer than the length of the paper in the conveyance direction, the minimum value of the fixing period is equal to the rotation period, so the present invention is defined by this rotation period. In this calculation, the paper feeding period is equal to the time required for one rotation of the HR, that is, the rotation period. The thicker the aluminum core, the lower the temperature drop and the greater the stability.

Further, the temperature drop becomes approximately constant when the thickness of the core metal is 6 mm.

The reason for this is that the influence of heat flow due to fixing generated on the surface of the HR coat is 6 + 1 m inside the aluminum core in one rotation period.
It extends to ++. Therefore, the thickness of the core metal is 6
Above m, the temperature drop becomes approximately constant. From this result, the thickness of the aluminum core metal is preferably 6 mm or more. Under these conditions, a temperature drop of approximately 0.8°C occurs per page, so the control width for temperature fluctuations during continuous paper feeding is set to 10°C.
℃, it will be possible to print up to about 12 pages without turning on the heater lamp 30. That is, during these 12 pages, heat may be supplied from the heater lamp 30 to the core metal, which is a secondary heat source. At this time, the problem is how to quickly supply heat to the point having a thickness of 6I. If the core metal thickness is made thicker than this, it will take time for the heat from the heater lamp 30 to propagate to the 6nn point in the aluminum core metal. That is, the aluminum core metal acts as a thermal resistance in transmitting the heat from the heater lamp 30 to the 6 m point.

If the thickness of the aluminum core metal is 6m, the time is O
becomes. Therefore, the thickness of the aluminum core metal is more preferably 6+am.

The above explanation has been given using a specific material (aluminum) and conditions as an example for convenience, but more generally, if the thermal diffusivity of the core metal material is am and the rotation period is tp, the effect of heat flow due to fixing is 1 rotation. The thickness L of the core metal over the period is L = 67G...(4
). When formula (4) is calculated using the thermal diffusivity of aluminum shown in FIG. 3, the following is obtained, which agrees well with the calculation result shown in FIG. 16. This is an example of -grain amount in equation (4), but similar results can be obtained using other substances. Figure 17 shows the core metal made of SUS C.
This is a diagram corresponding to the above-mentioned FIG. 16 in which the same calculation was performed in place of the thermal diffusivity (4.44×10-”rrf/S). Therefore, the thickness of the core metal is preferably 67G or more, and preferably,
FTG is good.

According to the present embodiment described above, there is an effect that high fixing strength can be stably obtained even with semi-permanent continuous feeding without requiring supplementary preheating using only the heat roll and the backup roll.

<Example 2> Another embodiment will be described below with reference to FIG.

FIG. 2 is a sectional view of the fixing device of the present invention as described in the first embodiment. A separating device 28 is used to separate the paper from the HR and is commonly referred to as a separating claw. In the fixing device of the first embodiment, the surface layer 25 is thin as described above, so when the one-separation device 28 is brought into contact with the HR 6, there is a risk of damaging the surface layer 25.

Even if the HR6 is not damaged, the parts in contact with the separation device 28 will rapidly wear out, significantly shortening the lifespan of the HR6. Because of this problem, in this embodiment, the separation device 28 and the HR
A gap was provided between the surface of 8. The gap is set to be less than or equal to the thickness of the recording paper 2 to be printed in order to completely separate the recording paper.

According to the present embodiment described above, since a gap is provided between the separation device 28 and the HR6, the HR by the separation device 28 is
There is no decrease in the lifespan of HR6 due to wear of HR6.

<Example 3> A modification of Example 2 will be described below with reference to FIGS. 2 and 1. The gap between HR6 and separation device 28 shown in FIG.
The gap is set to be equal to or less than the thickness of the recording paper 2, but since this recording apparatus sometimes prints thin paper with a thickness of 80 μm as the recording paper 2, the gap is set to be equal to or less than 80 μm. If such a small gap is set, eccentricity of HR6 may occur.

There is a possibility that separation table M28 and HR6 will come into contact with each other.

In order to reduce the probability of such occurrence, in this embodiment, the gap is widened when printing on thick paper. In order to perform this gap control, this recording apparatus is equipped with a recording paper thickness detection device 50 in the paper feed hopper 1 as shown in FIG.
Based on the detection signal, the gap between the separation device 28 and the HR 6 is set by a control signal from the gap control section 51. According to this embodiment described above, the HR6
As a result, when the thickness of the recording paper is thick, the gap between the separation device 28 and the separation device 28 can be set, which reduces the probability of contact between the separation device 28 and the HR6, and extends the life of the HR6. It can be extended.

<Example 4> Hereinafter, other examples will be described using FIG. 2. In Examples 2 and 3, the separation device 28 due to the eccentricity of HR6, etc.
There is a slight risk of contact with HR6.

In this embodiment, the gap between the separating device 28 and the HR 6 is set so as to have a margin for deviations in dimensions over time such as eccentricity of the HR 6, regardless of the thickness of the recording paper 2. Specifically, the gap was set to 1 m. Furthermore, in order to eliminate poor separation of the recording paper 2, the airflow along the surface of the HR 6 is removed by the separation claw 28 at the moment the front end of the recording paper 2 passes through the nip portion 23.
A gas spout 52 is provided in the separating claw so that the gas is generated from the protrusion side.

This airflow fans the front edge of the recording paper 2, causing the HR
Make sure to separate it from 6. According to this embodiment described above,
Since there is a sufficient gap between the HR 6 and the separating device 28, the life of the HR 6 is not reduced, and since separation is performed using air flow, the recording paper 2 can be reliably separated from the HR 6.

<Example 5> The separation device 28 of Examples 2 to 4 described above is made of metal with high processing accuracy in order to maintain a constant gap between it and the HR6. In Examples 2 to 4, aluminum is used. In this case, the toner melted during fixing is removed from the separating device 28.
There is a risk that this adhered toner will be re-transferred to the paper on which it is printed later, leading to erroneous printing. In this embodiment, in order to eliminate this problem, a fluororesin layer 53 having high releasability from the toner is provided on the surface of the separation device 128.

According to this embodiment described above, since the fluororesin layer 53 is provided on the surface of the separation device 28, toner does not adhere to the separation device 28, and as a result, there is no occurrence of printing errors due to retransfer.

<Embodiment 6> Next, another embodiment will be described using FIG. 18 and FIG. 19. FIG. 18 shows the temperature distribution inside the toner and recording paper at the exit of the nip section 23 as a solid line when fixing is performed using BH6 and BH3 described in Example 1, and shows a fixing device with a preheater that achieves the same fixing strength. FIG. 3 is a diagram showing the temperature distribution inside the toner and the recording paper at the exit of the nip portion with broken lines when fixing is performed using the toner (conventional example). As shown in FIG. 18, the temperature gradient inside the toner according to the present invention is larger than that of the conventional example. That is, when obtaining the same fixing strength, the fixing device of the present invention has a temperature gradient close to HR6 compared to the conventional example. The temperature on the toner surface is high, and conversely, the temperature at the interface between the toner and the paper is low. This phenomenon occurs because, in the fixing device of the present invention, a large amount of heat is supplied to the toner during the nip time.

When such a temperature distribution is present, the distribution of melt physical properties such as melt viscosity inside the toner becomes large, and the toner layer tends to crack vertically during the nip time. This causes the offset phenomenon mentioned above to occur. In addition, since the offset phenomenon generally occurs at high temperatures (hot offset) and at low temperatures (cold offset), it can be interpreted that the non-offset temperature range for the offset phenomenon is narrow. As described above, in the fixing device of the above embodiment, the offset phenomenon tends to occur, and as a result, the amount of toner transferred onto the HR (hereinafter referred to as offset toner) increases, so the ability of the cleaning device to wipe off the toner increases. It is necessary to increase

FIG. 19 is a sectional view of a cleaning device according to another embodiment of the present invention. 32 is a main wick, 33 is a wiping band serving as an auxiliary wick, 34 is a separation liquid supply port, 35 is a delivery roller, and 36 is a take-up roller. Separated liquid is supplied to the main wick 32 from the separated liquid supply port 34 in order to improve the releasability of the toner and BH6. Silicone oil is used as the separation liquid. The separated liquid permeates into the wiping band 33 through the main wick 32, and the BH6
applied to the surface of The wiping band 33 has the function of applying the separation liquid to the BH6 and wiping off the offset toner at the same time. The wiping band 33 moves from the delivery roller 35 toward the take-up roller 36 in a direction opposite to the rotational direction of the HR 6. The wiped offset toner accumulates on the wiping surface of the wiping band 33. When the amount of offset toner increases, the wiping band 33
Offset toner is retransferred from to BH6. In order to prevent this retransfer, the wiping band 33 is constantly moved to renew the contact surface (wiping surface) between the wiping band 33 and the BH6. The moving speed of the wiping band 33 is such that the wiping band 33 moves faster than the retransfer occurs.
is set so that it is away from the wiping surface. The structure and operation of the cleaning device described above are similar to those described in Japanese Utility Model Publication No. 63-50669. Wiping of this type of wiping device $
33 is generally made of felt with a thickness of about II.

In the fixing device of the present invention, since the amount of offset toner is large, retransfer of the offset toner to BH6 is likely to occur. Therefore, it is necessary to increase the moving speed of the wiping band 33. Therefore, when the above-mentioned felt is used for the wiping band 33, there is a problem that the wiping band 33 ends winding up quickly. Normally, when the wiping band 33 is wound up, it is replaced with a new wiping band 33.

In other words, is the above problem wiped away? The problem is that the F33 replacement cycle is fast. In order to solve the above problem, if the length of the felt to be wound in the -th turn is increased, the feed roller 35
, and the take-up roller 36 are enlarged, causing problems in that mounting becomes difficult. As a means to solve these problems all at once, in this embodiment, a thin heat-resistant synthetic paper is used for the wiping band 33. The thickness of heat-resistant synthetic paper is approximately 50μ
m or less. Therefore, the length of the auxiliary wick 33 is increased to increase the winding speed. According to this embodiment, sufficient wiping performance can be obtained and the diameter of the feed roller 352 and take-up roller 36 can be made small. , sufficient wiping performance can be obtained, and the cleaning device can be downsized.

<Example 7> Other embodiments will be described using FIG. 20.

FIG. 20 is a sectional view of a cleaning device according to another embodiment of the present invention. 37 is a wiping band, and 38 is a pressing member.

39 is a separation liquid supply device, and 40 is a support member.

In this embodiment, there is only one wiping band 37, and the wiping band 3
7 moves against the rotational direction of HR6.

The moving speed is determined in the same manner as in the sixth embodiment based on the condition that retransfer of the offset toner to the HR6 does not occur. In this cleaning device, the support member 4o is installed so as to be inclined with respect to the direction of gravity (downward).

As a result, the one separated liquid flows downward after being discharged from the separated liquid supply port 34, and is supplied from the separated liquid supply position 39 to the surface of the HR6. Silicone oil is used as the separation liquid. The pressing member 38 presses the wiping band 37 against the HR6. This position becomes the main wiping position for offset toner. That is, the wiping band 37 acts as a wiping band at the separation liquid supply position 39, but acts as a wiping member at the position sandwiched between the pressing member 38 and HR6 (wiping position). In the separation liquid supply bag W39, since less offset toner adheres to the wiping band 37, there is less resistance to the separation liquid supply, and smooth supply is possible.

Moreover, while the wiping band 37 moves from the separation supply position 39 to the wiping position, most of the separated liquid that has soaked into the wiping band 37 is
The separated liquid transfers to R6 or evaporates, and at the wiping position, almost no separated liquid permeates into the wiping band 37. This effect is very effective in achieving both the supply of the separation liquid and the wiping, since the separation liquid has the effect of reducing the wiping performance due to its releasability.

In this embodiment, felt is used for the wiping band 37, and the felt is impregnated with the same type of transparent resin as the toner. The inventors have confirmed that when there is no infiltration of the same type of resin as the toner, the wiped off-set toner stays on the felt and rarely infiltrates into the inside of the felt. By impregnating the felt with a resin that has an affinity for the offset toner, the wiped off offset toner can be infiltrated into the inside of the felt.

This U improves the ability of the wiping band 37 to retain the offset toner after wiping, and it is possible to prevent the offset toner from being retransferred to the HR 6 without increasing the moving speed of the wiping band 37. According to this embodiment, since the separation liquid supply position and the wiping position are separated, the separation liquid supply is smooth and the wiping performance is also high. Furthermore, since the wiping band 37 contains a resin that has an affinity for toner, it has a high ability to retain offset toner, and the offset toner can be recycled to HR6 without increasing the moving speed of the wiping band 37. Transfer can be prevented. Therefore, sufficient cleaning performance can be obtained as the cleaning device for the fixing device of the first embodiment.

<Example 8> A modification of the seventh embodiment will be explained using FIG. 21.

FIG. 21 is a sectional view of a cleaning device according to a modification of the seventh embodiment of the present invention. 41 is a separated liquid damming part.

The structure is the same as in Example 7 except for the installation of the separated liquid damming part 41. In Example 7, when the supply of separated liquid becomes excessive, the remaining separated liquid that is not supplied to the HR 6 at the separated liquid supply position 39 may flow to the position of the pressing member 38, which may reduce the wiping performance. Ta. In order to stop this outflow, a separated liquid dam 41 is installed. According to this embodiment, the separation liquid supply and wiping functions are completely separated, and even if excessive separation liquid supply occurs, the wiping performance will not be degraded.

<Example 9> Other embodiments will be described using FIG. 22.

FIG. 22 is a sectional view of a cleaning device according to another embodiment of the present invention. When the fixing device of Example 1 is used and toner that tends to cause offset is used, there are cases where it is difficult to completely wipe off the offset toner even if the wiping devices of Examples 6 to 8 are used. do. This embodiment shows a wiping device used in this case. 42 is a pre-wiping roller;
44 is a second delivery roller, 43 is heat-resistant synthetic paper, and a pre-wiping device 45 is formed by these. Other symbols and the like are the same as in Example 7. In this embodiment, the wiping band 37 and the heat-resistant synthetic paper 43 are simultaneously wound around the winding roller 36. The same felt as in Example 7 is used for the wiping band 37. The heat-resistant synthetic paper 43 has a thickness of about 50 μm, and has approximately the same length as the wiping band 37. In this case, the second delivery roller can be made smaller as shown. The heat-resistant synthetic paper 43 passes from the second delivery roller 44 around the outer periphery of the pre-wiping roller 42 and reaches the take-up roller 36. The pre-wiping roller 42 is rotatable and is subjected to a certain load toward the center of the HR6. In this example,
When the pre-wiping roller 42 and the HR 6 are brought into direct contact, the surface pressure generated on the contact surface is set to be 1 kg/#.

Most of the offset toner generated in the nip section of the fixing device of Example 1 is wiped off by the heat-resistant synthetic paper 43, and the offset toner that was wiped off is also removed by the wiping device described in Example 7 of the wiping band 37. wiped off. According to the present embodiment of the present invention described above.

With two wiping members, heat-resistant synthetic paper 43 and wiping band 37,
Since offset toner can be wiped off, sufficient wiping performance can be ensured even if toner that is easily offset is used. Although the use of two or more wiping members has the disadvantage of increasing the size of the device, according to this embodiment of the present invention,
Since felt and heat-resistant synthetic paper are used together, and the take-up roller is integrated, this problem does not occur.

〔Effect of the invention〕

According to the fixing device and the heat roll for the same according to the present invention, by specifying the thickness of the surface layer of the heat roll and the thickness of the core metal, a large amount of heat flows from the core metal to the surface layer during the nip time. Therefore, it is effective to obtain high fixing strength.

Further, according to the recording device of the present invention, the thickness of the core bar is more affected by the heat flow on the heat roll surface generated during fixing in one paper feeding cycle, so semi-permanent continuous paper feeding is possible. It also has the effect of stably achieving high fixing strength.

The separating device in the fixing device according to the present invention can reduce the risk of damage caused by forming the surface layer of the heat roll thin. Furthermore, by using the cleaning device in the fixing device according to the present invention, it is possible to reduce the offset phenomenon caused by the easy transfer of heat from the core metal to the surface of the heat roll.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a double-sided recording device equipped with a fixing device according to the present invention, FIG. 2 is a cross-sectional view of a fixing device according to the present invention, FIG. 3 is a diagram showing a model used for calculation, and FIG. 5 is a diagram showing the relationship between the surface layer thickness and the HR surface temperature at the nip portion, and FIG. 5 is a diagram showing the relationship between the surface layer thickness and the heat flux to the toner.
Figure 6 is a diagram showing the relationship between surface layer thickness and heat flux to the surface layer, Figure 7 is a diagram showing the relationship between HR humidity and temperature fixing strength, and Figure 8 is a diagram showing the relationship between surface layer thickness and fixing strength. , FIG. 9 corresponds to FIG. 4 according to another embodiment, FIG. 10 corresponds to FIG. 5 according to another embodiment, and FIG. 11 corresponds to FIG. 6 according to another embodiment. 12 corresponds to FIG. 4 according to another embodiment, FIG. 13 corresponds to FIG. 5 according to another embodiment, and FIG. 14 corresponds to FIG. 6 according to another embodiment. Figure 15 is a diagram showing the model used for calculation, Figure 16 is a diagram showing the model used for calculation.
The figure shows the relationship between core metal thickness and temperature drop, Figure 17 is a diagram corresponding to Figure 16 according to another embodiment, and Figure 18 is a diagram showing the temperature distribution inside the toner and recording paper at the nip exit. , FIG. 19 is a sectional view showing a cleaning device portion of another embodiment of the present invention, FIG. 20 is a sectional view showing a cleaning device portion of another embodiment of the present invention, and FIG. 21 is a sectional view showing a cleaning device portion of another embodiment of the present invention. FIG. 22 is a cross-sectional view showing a cleaning device portion according to another embodiment of the present invention. 2... Recording paper, 6... Heat roll, 7... Backup roll, 23... Nip portion, 24... Core metal, 25... Surface layer, 26... Silicone rubber layer, 27... Toner 28...
- Separation device, 29... Cleaning device, 3o... Heater lamp, 33... Wiping band. 34... Separated liquid supply port, 35... Delivery roller, 36
... Winding roller, 37... Wiping band, 38... Pressing member, 39... Separated liquid supply position, 40... Supporting member, 41... Separated liquid damming part, 42... . . . Pre-wiping roller, 43 . . . Heat-resistant synthetic paper, 44 . . . Second delivery roller.

Claims (1)

[Scope of Claims] 1. A heat roll and a backup roll paired with the heat roll are provided, and a nip portion for fixing the toner to the recording paper passing therethrough is provided in the opposing portion of both rolls, and the In the fixing device, the fixing device includes a separation device that separates the recording paper that has come out of the nip portion and is in close contact with the heat roll surface from the heat roll surface, and a cleaning device that removes toner transferred from the recording paper to the heat roll. The heat roll includes a hollow cylindrical core metal, a heat source disposed inside the core metal, and a surface layer provided on the surface of the core metal, and the thickness of this surface layer is equal to the thickness of the surface layer. The thickness of the core metal is determined by the square root of the product of the thermal diffusivity of the material and the nip time during which the paper passes through the nip portion, and the thickness of the core metal is determined by the thermal diffusivity of the material and the nip time of the paper. A fixing device characterized in that the fixing device is formed to have a thickness greater than or equal to the square root of the product of one rotation period. 2. The fixing device according to claim 1, wherein the surface layer material is a fluororesin, and the thickness of the surface layer is 40 μm or less. 3. The fixing device according to claim 2, wherein the core material is aluminum, and the thickness of the core is 6 mm or more. 4. The fixing device according to claim 1, wherein the separating device is a separating claw disposed with a gap from the surface of the heat roll. 5. The fixing device according to claim 4, wherein the gap is set to be equal to or less than the thickness of the recording paper. 6. The fixing device according to claim 4, wherein the gap is formed variably according to the thickness of the recording paper. 7. The fixing device according to claim 4, wherein the separation claw is made of metal and a fluororesin layer is provided on the surface thereof. 8. The fixing device according to claim 4, wherein a gas jet port is provided at the end of the separating claw on the side of the heat roll to cause gas to flow out and separate the recording paper from the heat roll by the air flow. 9. In claim 1, the cleaning device comprises a wiping band that is moved from the feed roller toward the take-up roller and slides on the surface of the heat roller, and a sliding portion of the wiping band with the heat roller. The wiping strip is made of heat-resistant synthetic paper and has a thickness of about 100 ml. A fixing device formed with a thickness of 50 μm or less. 10. In claim 9, the support member is arranged to be inclined so that the separated liquid supply part is in the upper position, and a pressing member for pressing the wiping band against the heat roll is provided at the inclined lower end of the support member. Fixing device. 11. The fixing device according to claim 9, wherein the wiping band contains a resin having affinity with the toner. 12. The fixing device according to claim 11, wherein the resin is transparent. 13. In claim 10, the support member is provided with a weir that suppresses the flow of the separated liquid, and the weir is located above the pressing member, and the separated liquid supply is the main position where the separated liquid is absorbed into the wiping band. The fixing device is below the position. 14. The fixing device according to claim 9, wherein a pre-wiping device is provided at a position upstream from a position where the wiping band of the heat roller slides with the heat roller. 15. The fixing device according to claim 14, wherein the pre-wiping band of the pre-wiping device is wound around the wiping band take-up roller so as to be overlapped with the wiping band. 16. The fixing device according to claim 15, wherein the pre-wiping band is made of heat-resistant synthetic paper. 17. A heat roll for a fixing device comprising a hollow cylindrical core metal and a surface layer provided on the surface of the core metal,
The thickness of the surface layer is determined by the square root of the product of the thermal diffusivity of the surface layer material and the nip time during which the paper passes through the nip portion, and the thickness of the core metal is determined by the thickness of the core metal. A heat roll for a fixing device, characterized in that the heat roll is formed to have a thickness equal to or greater than the square root of the product of the thermal diffusivity of a gold material and one rotation period of the core metal. 18. In claim 17, the surface layer material is a fluororesin, the surface layer has a thickness of 40 μm or less, the core material is aluminum, and the core has a thickness of 6 mm or more. Heat roll for fixing device. 19. A developing station that forms an unfixed toner image on the fed recording paper, a heat roll, and a backup roll paired with the heat roll, and a portion opposite to these rolls from the developing station. A nip section is provided for fixing the toner on the recording paper that is fed and passes through the nip section, and a separation device that separates the recording paper that has come out of the nip section and is in close contact with the heat roll surface from the heat roll surface; A recording device including a fixing device having a cleaning device for removing toner transferred from recording paper, wherein the heat roll of the fixing device includes a hollow cylindrical core metal and a core metal disposed inside the core metal. and a surface layer provided on the surface of the core bar, the thickness of the surface layer being the product of the thermal diffusivity of the surface layer material and the nip time during which the paper passes through the nip portion. The core metal is formed to have a thickness equal to or less than the square root, and the thickness of the core metal is greater than or equal to the square root of the product of the thermal diffusivity of the core metal material and one rotation period of the core metal. Characteristic recording device. 20. In claim 19, in the heat roll of the fixing device, the surface layer material is a fluororesin, the thickness of the surface layer is formed to be 40 μm or less, the core material is aluminum, and the core material has a thickness of 40 μm or less. is a recording device formed to be 6 mm or more.