DE69412007T2 - Heating element and image heating device using this element - Google Patents

Description

Background of the invention Field of the invention

The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer or the like, and more particularly to a heating element and an image heating device capable of heating an unfixed image.

Relevant state of the art

An image heating device using a fixed heating element and a thin film sliding on the heating element as shown in Fig. 51 is proposed, for example, in U.S. Patent No. 5,149,941. In Fig. 51, there are shown a heater 500, a film 505 sliding on the heater 500, a drive roller 506 for driving the film 505, a driven roller 507, and a pressure roller 508 in contact with the heater 500 with the film 505 interposed therebetween. The heater 500 is provided with a substrate 501, a resistance layer 502 provided on the substrate 501 and generating heat by supplying electric current; with an insulating protective layer 503 to protect the resistance layer 502, and with a support frame 504 to support the aforesaid components.

Thermal fixation of an unfixed image is achieved by transferring heat from the heater through the insulating protective layer on the film and a sliding contact surface of the film. However, due to the sliding contact between the insulating protective layer and the film, noticeable abrasion of the film generally occurs when the total distance of a sliding movement reaches about 60 km. The resulting abraded powder is deposited unevenly on the roller for driving the film. As a result, the drive speed for the film is irregular, so that the fixation of the unfixed image also becomes uneven.

Summary of the invention

It is an object of the present invention to provide a heating element provided with a protective layer which is excellent in sliding performance against a film and an image heating device.

Another object of this invention is to provide an image heating device equipped with a film which is excellent in sliding performance against a heating element.

A still further object of this invention is to provide a heating element and an image heating device which are provided with a protective layer which is excellent in sliding properties and thermal conductivity.

Still further objects of this invention will become more fully apparent from the following description.

The objects are achieved by the heating element defined in claim 1 and by the image heating device defined in claim 17.

Short description of the drawings

Fig. 1 is a plan view of a heating device of this invention on the side of its heat generating resistor;

Fig. 2 is a plan view of a heater of this invention from the rear thereof;

Fig. 3 is a sectional view of a fixing device using the heating device embodying the present invention;

Figs. 4A to 4E are partial sectional views of a heating device embodying this invention;

Fig. 5 is an illustration of an apparatus used in the production of a hard carbon layer in an embodiment of this invention;

Fig. 6 is a sectional view of a fixing device using the heating device of this invention in another embodiment;

Fig. 7 is an illustration of an apparatus used for producing a hard carbon layer in another embodiment of this invention;

Fig. 8 is an illustration of an apparatus used in producing a hard carbon layer in still another embodiment of this invention;

Figs. 9 and 10 are sectional views of a fixing device using heaters of still other embodiments of this invention;

Figs. 11A to 11E are partial sectional views of the heating device of another embodiment of this invention;

Fig. 12 is an illustration of an apparatus used in producing a DLC film in another embodiment of this invention;

Fig. 13 is an illustration of an apparatus used in producing an a-C:H film in another embodiment of this invention;

Fig. 14 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Figs. 15A to 15E are partial sectional views of the heating device of another embodiment of this invention;

Figs. 16 to 18 are sectional views of a fixing device using the heating device of still further embodiments of the present invention;

Figs. 19A to 19E are partial sectional views of the heating device of another embodiment of the present invention;

Fig. 20 is an illustration of an apparatus used in producing a DLC film in another embodiment of this invention;

Fig. 21 is an illustration of an apparatus used in producing an a-C:H film in another embodiment of this invention;

Figs. 22 and 23 are sectional views of a fixing device using the heating device of still other embodiments of this invention;

Figs. 24A to 24E are partial sectional views of the heating device of another embodiment of the present invention;

Fig. 25 is an illustration of an apparatus used in the production of a DLC film in another embodiment of this invention;

Fig. 26 is an illustration of an apparatus used in producing an a-C:H film in another embodiment of this invention;

Fig. 27A is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Fig. 27B is a graph showing the relationship between the amount of metal added in this invention and the friction coefficient;

Figs. 28A to 28E are partial cross-sectional views of the heating device of another embodiment of this invention;

Fig. 29 is an illustration of an apparatus used in producing a DLC film in another embodiment of this invention;

Fig. 30 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Figs. 31 and 32 are diagrams showing an apparatus used in producing an a-C:H film in other embodiments of this invention;

Fig. 33 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Figs. 34A to 34E are partial sectional views of the heating device of another embodiment of this invention;

Fig. 35 is an illustration of an apparatus used in producing a DLC film in another embodiment of this invention;

Fig. 36 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Fig. 37 is an illustration of an apparatus used in producing an a-C:H film in another embodiment of the present invention;

Fig. 38 is an illustration of an apparatus used in fluorinating an a-C:H film in another embodiment of the present invention;

Fig. 39 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Fig. 40 is a diagram showing the Raman spectrum of diamond crystals of this invention;

Fig. 41 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Figs. 42A to 42F are partial sectional views of the heating device of another embodiment of this invention;

Fig. 43 is an illustration of an apparatus used in the production of diamonds in another embodiment of this invention;

Fig. 44 is an illustration of an apparatus used in the production of diamonds in another embodiment of this invention;

Fig. 45 is a sectional view of a fixing device using the heating device of still another embodiment of this invention;

Figs. 46A to 46E are partial sectional views of the heating device of another embodiment of this invention;

Fig. 47 is an illustration of an apparatus used in producing a DLC film in another embodiment of this invention;

Fig. 48 is an illustration of an apparatus used in producing an a-C:H film in another embodiment of the present invention;

Fig. 49 is an illustration of an apparatus used in producing a hard carbon layer in another embodiment of this invention;

Fig. 50 is an illustration of an apparatus used in ashing a hard carbon layer in another embodiment of the present invention;

Fig. 51 is an illustration of a conventional fixing device.

Detailed description of the preferred embodiments

The present invention is described using preferred embodiments shown in the accompanying drawings.

A heating device of this invention is shown in Figs. 1 and 2, as viewed from the heat generating resistor side and the back side (substrate side), respectively.

According to Figs. 1 and 2, the heating device 1 is provided with a narrow, electrically insulating substrate 2 of high heat resistance and low heat capacity, with an electrically heat generating element 3 formed as a narrow, straight strip on a surface (front side) of the substrate 2 along its longitudinal direction in the middle of its width, with electrode terminals (terminals) 4 and 5 formed on the surface of the substrate at both ends of the heat generating resistor, with an electrically insulating protective layer 6 made of, for example, glass and supporting the heat generating resistor de surface of the substrate 2, and with a temperature sensor 7, e.g. a thermistor, formed on the other surface (back surface) of the substrate 2. The substrate 2 consists of, for example, a ceramic plate, e.g. of Al₂O₃, AlN or SiC, a width of 10 mm, a thickness of 1 mm and a length of 240 mm. The heat generating resistor 3 is a patterned layer of Ag/Pd (silver-palladium alloy), RuO₂ or Ta₂N which is deposited by screen printing followed by sintering in air and which has, for example, a thickness of 10 µm and a width of 1 mm. The electrode terminals 4, 5 are patterned layers of, for example, Ag which is deposited by screen printing to a thickness of 10 µm followed by sintering in air. The electrodes 4, 5 are connected to wires for electrical energy supply by a connector (not shown).

In order to maintain and control the temperature at the fixing surface of the heater 1, the heat generating resistor 3 is arranged in cross section at the approximate center of the width of a fixing clamping gap 15. The heater 1 is in contact with a sliding film on the side of its electrically insulating protective layer 6. A voltage is applied between the electrode terminals 4, 5 of the heat generating resistor 3 from an alternating current source 12a to heat the heat generating resistor 3, thereby raising the temperature of the heater 1.

The temperature of the heater 1 is detected by the temperature sensor 7 arranged on the back of the substrate, and the detected information is fed back to a power supply control circuit to control the power supply from the AC power source 12a to the heat generating resistor 3 so that the heater is maintained at a predetermined temperature. The temperature sensor 7 of the heater is arranged at a position on the back of the substrate corresponding to the position of the best heating effect on the Fixing surface, ie in the position of the heat generating resistor 3 on the front side of the substrate.

First, the formation of a hard carbon layer according to the present invention on the insulating protective layer or the heat generating resistor of the heater will be explained.

The hard carbon layer of this invention has a macroscopically amorphous structure, consists of carbon atoms of sp², sp³ bonds and is almost free of hydrogen, less than 1 atomic % if it is present. The density of the hard carbon layer is in a range larger than that of graphite (2.26 g/cm³) and smaller than that of diamond (3.51 g/cm³). Also, the physical properties of the hard carbon layer are represented by, for example, a hardness of 2000-5000 kg/mm², a friction coefficient u < 0.2 and an electrical resistance (volume resistivity) of 10⁵-10¹¹ Ωcm.

The hard carbon layer to be used in the present invention can be formed by, for example, plasma sputtering, ion beam sputtering, ion beam evaporation, ion beam mixing, ion plating, by a complex ion beam, by ion implantation, arc discharge or laser evaporation. The solid carbon source to be used in these methods may be graphite or glassy carbon of high purity. When carbon-containing gas, e.g., a hydrocarbon such as methane, ethane, propane, ethylene, benzene or acetylene; a halogenated hydrocarbon such as methylene chloride, carbon tetrachloride, chloroform or trichloroethane; an alcohol such as methyl alcohol or ethyl alcohol; a ketone such as (CH₃)₂CO or (C₆H₅)₂CO; or CO or CO₂ is used as a gaseous carbon source, it is used as a carbon ion beam after mass separation. A source material gas can also be used to control the ion beam. support, He, N₂, H₂, O₂, H₂O, Ar, Ne, Kr or Xe.

The thickness of the hard carbon layer to be formed on the insulating protective layer or on the heat generating resistor of the heater may be within a range of several nanometers to several tens of microns, preferably several tens of nanometers to several microns, because a layer thinner than several nanometers cannot provide sufficient lubrication or insulation, while a layer thicker than several tens of microns can easily be peeled off from the substrate by the tension of the film. In the case of direct layer formation on the heat generating resistor, a layer of high electrical resistance is required to ensure sufficient insulation. In the case of formation on the film, a thickness of several to several hundred nanometers is preferable, because a thickness less than several nanometers cannot provide sufficient lubrication, while a thickness greater than several hundred nanometers can result in peeling off of the carbon layer from the plastic film or in curling of the plastic film due to the tension in the carbon layer. If the plastic film still curls within the above-mentioned preferred thickness range of the carbon layer, the hard carbon layer can be formed on both sides of the plastic film.

The density of the hard carbon layer is, as stated above, placed between that of graphite and that of diamond, but practically it must be equal to or higher than 2.0 g/cm³. A layer whose density is less than 2.0 g/cm³ is of low hardness, low electrical resistance and low adhesion strength due to an increased proportion of the sp²-bonded (graphite) component, and is not suitable as the lubricating protective layer of the present invention.

The lubricating protective layer of this invention can be formed not only on the insulating protective layer or the heat generating resistor of the heater or the plastic film, but also on a heating element holder that comes into contact with the plastic film, thereby improving the sliding performance between the heater and the film.

The present invention is to improve the abrasion resistance and the sliding performance between the heater and the film by forming a hard carbon layer as a lubricating protective layer by gas synthesis on the insulating protective layer or the heat generating resistor of the heater which comes into contact with the plastic film or on the plastic film, thereby prolonging the life of the heater.

In the following, specific embodiments of this invention will be explained with reference to the accompanying drawings.

[Embodiment 1]

Fig. 3 is an enlarged partial sectional view of a heat fixing apparatus using a heating device embodying the present invention, wherein a heating element 1 is supported by a heating element support 9 with a heat insulating heating element holder 8 interposed therebetween. In the heating element 1, a ceramic substrate 2, a heat generating resistor 3 made of Ag/Pd, a glassy insulating protective layer 6, a hard carbon layer 18 formed on the insulating protective layer 6, and a temperature sensor 7 are provided. A heat-resistant film 10 is made of, for example, polyimide with a thickness of about 40 µm and is formed as an endless belt or an elongated sheet. A rotating pressure roller 11 serves as a pressing member for pressing the film toward the heating element 1. The film 10 rotates or moves at a predetermined speed in a direction indicated by an arrow in contact with the edges of the heater holder 8 while sliding on a surface of the heater 1 in close contact with the surface of the heater by a driving member (not shown) or by the rotating force of the pressure roller 11. The heat generating resistor 3 is electrically operated to heat the heater to a predetermined temperature, and a recording material 16 carrying an unfixed toner image 17 on the side of the film 10 is introduced into a fixing nip 15 which is in the state that the film 10 is moved. In this way, the recording material 16 is held in contact with the film 10 and passes through the fixing nip 15 together with the film 10. During the passage, heat energy is imparted to the recording material 16 across the film 10 from the heater 1 to fuse the unfixed toner image 17 to the recording material 16.

4A to 4E are schematic sectional views of the heating device of the first embodiment, showing Cu made electrode terminals 4 and 5, a heater holder 8, an electrode tab 12, AuSi solder 13 and a wire conductor 14.

The heating element of the present embodiment was manufactured by first applying Ag/Pd paste by screen printing on an Al₂O₃ substrate 2, followed by firing in air. The heat generating resistor 3 was trimmed to a desired resistance value after its resistance value was measured. Then, Cu paste was applied by screen printing, and the electrode terminals 4, 5 were formed by firing under controlled oxygen partial pressure (Fig. 4A). Thereafter, the insulating protective layer 6 was formed by applying silicate glass with a low softening point by screen printing, followed by firing in air (Fig. 4B). Thereafter, a hard carbon layer 18 with a thickness of 500 nm was formed by DC sputtering (Fig. 4C). Fig. 5 is a schematic 1. Schematic representation of a DC magnetron sputtering apparatus used for the formation of the hard carbon film. Herein, a vacuum chamber 40, a substrate 41, a graphite target 42 with a purity of 99.99%, a gas supply system 43, a DC power source 44 and an evacuation system 45 are shown. After the vacuum chamber was evacuated to 1 x 10-7 Torr, Ar was introduced from the gas supply system to a pressure of 0.9 Pa. The substrate was kept at room temperature, and a discharge power of 50 W and a substrate-target distance of 40 mm were applied. Before the film formation, pre-sputtering was carried out at 300 W for 20 minutes. When a film formed under the same conditions was analyzed by HFS (hydrogen forward scattering spectrometry), a hydrogen concentration was equal to 0 atomic %. The film hardness measured by a thin film hardness meter was 2200 kg/mm2 in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. The friction coefficient was 0.10 when measured in air at a relative humidity of 45% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as the pin with a load of 2.2 N and a sliding speed of 0.04 m/s. The density measured by RBS (Rutherford backscattering spectrometry) was 2.8 g/cm'.

Then, the electrode tab 12 made of a copper alloy and the ceramic substrate 2 were soldered with AuSi solder 13 (Fig. 4C). Then, the wire conductor 14 was pressure-connected to the electrode tab 12 and the heating element was adhered to the heating element holder 8 (Fig. 4D and 4E). When manufacturing the heater 1, the surface of the electrode terminals 4, 5 were provided with Au quick plating to improve the wettability with the solder, thereby achieving constant reliability for the connection. Instead of a copper alloy, the electrode tab can also be made of Covar, 42 alloy or phosphor bronze. The Solder preferably has a melting point of at least 250ºC and can be AuGe or AuSn instead of AuSi. Furthermore, soldering could be carried out in a more stable manner by quickly plating the Cu electrode terminals with Au, Ni or Au/Ni to prevent oxidation and contamination until soldering. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

The heat fixing device thus manufactured was free from the generation of abraded powder by the friction between the heater and the plastic film and is thus able to maintain a stable sliding behavior over a long period of time.

[Embodiment 2]

Fig. 6 is an enlarged partial sectional view of a heat fixing device using a heating element embodying the present invention, wherein the same components as those in Fig. 3 are designated by the same reference numerals and will not be further explained hereinafter. In Fig. 6, a recess G and a hard carbon layer 18 are shown.

A recess G of 350 mm x 2 mm x 12 µm for forming the heat generating resistor was mechanically formed on an Al₂O₃ substrate similar to Embodiment 1. Ag/Pd paste of 11 µm thickness was screen printed into the recess, followed by firing in air. After measuring the resistance value, the heat generating resistor 3 was trimmed to a desired resistance value. Then, the substrate was placed in a sputtering apparatus (not shown), and a W (tungsten) layer 3a of 1 µm thickness was formed on the resistor layer to prevent mutual diffusion of Ag/Pd and C. Then, a dual ion beam sputtering apparatus shown in Fig. 7 was used to form a hard carbon layer having a thickness of 600 nm was formed. Fig. 7 shows a vacuum chamber 20, a sputtering ion source 21, an auxiliary ion source 22, a graphite target 23, a substrate 24, a gas supply system 25 and a vacuum system 26. After the vacuum chamber was evacuated to 1 x 10-7 Torr, Ar was introduced at 20 sccm (cm³/min at standard condition) from the gas supply system to the sputtering ion source and the auxiliary ion source to a pressure of 4 x 10. 4 . The graphite target was sputtered by the ion sputtering source with an Ar ion beam having an ion energy of 1 keV and an ion current density of 4 mA/cm2, and at the same time the substrate was irradiated by the auxiliary ion source with an Ar ion beam having an ion energy of 200 eV and an ion current density of 0.1 mA/cm2. The film hardness measured by a thin film hardness meter as in Embodiment 1 was 2500 kg/mm2 in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. The friction coefficient was 0.08 when measured in air at a relative humidity of 50% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as a pin with a load of 1.0 N and a sliding speed of 0.04 m/s. The density measured by RBS (Rutherford backscattering spectrometry) was 2.6 g/cm3, and the hydrogen concentration of the film measured by HFS (hydrogen forward scattering spectrometry) was less than 1 atomic %. Then, the heater was completed by connecting the electrode tabs and wire leads to the electrode terminals and adhering them to the heater holder as in Embodiment 1.

The heat fixing of the recording material was carried out using a heat fixing device equipped with the heating element thus obtained as in Embodiment 1. As a result, stable fixing ability and constant durability as in Embodiment 1 were obtained.

[Embodiment 3]

A hard carbon layer was formed as a lubricating protective layer on the insulating protective layer in a similar manner to Embodiment 1. Fig. 8 is a schematic diagram of a DC magnetron sputtering apparatus used in Embodiment 1 to which an auxiliary ion source was added. Here, a vacuum chamber 30, an auxiliary ion source 31, an ionization chamber 32, a gas supply system 33, an ion beam extraction electrode 34, a substrate 35, a graphite target 36, a vacuum system 37, and a DC power source 38 are shown. After the vacuum chamber was evacuated to 1 × 10'7 Torr, Ar was introduced from the gas supply system to the vacuum chamber and the auxiliary ion source at 100 sccm and 35 sccm, respectively, to a pressure of 6 × 10-2 Pa. Graphite was sputtered with a discharge power of 1 kW, and the substrate was simultaneously irradiated with an Ar ion beam with an ion energy of 300 eV and an ion current density of 0.2 mA/cm2 from the auxiliary ion source, so that a hard carbon layer with a thickness of 500 nm was produced.

The film hardness measured by the thin film hardness meter as in Embodiment 1 was 2700 kg/mm2 in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. When measured in air at a relative humidity of 45% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as the pin with a load of 1.0 N and a sliding speed of 0.04 m/s, the friction coefficient was 0.07. The density evaluated by RBS (Rutherford backscattering spectrometry) was 2.8 g/cm3, and the hydrogen concentration in the film measured by HFS (hydrogen forward scattering spectrometry) was less than 1 atomic %. The heating device was then completed by connecting the electrode tabs and wire conductors to the electrode terminals and creating an adhesive connection to the heating element holder.

The heat fixing of the recording material was carried out using a heat fixing device equipped with the heating element thus obtained in the same manner as in Embodiment 1. As a result, stable fixing ability and durability were obtained as in Embodiment 1.

[Embodiment 4]

A hard carbon film having a thickness of 450 nm was formed on the insulating protective layer of the heater under the same conditions as in Embodiment 1 except that the ion current density of the Ar ion beam from the auxiliary ion beam source was set at 0.2 mA/cm2 and the ion energy was varied within a range of 0-500 eV. Samples 1-4 of the heaters thus prepared were subjected to evaluation of hydrogen concentration, film thickness, film hardness, electrical resistance (volume resistivity) and friction coefficient. The results obtained are summarized in Table 1. The hydrogen concentration was measured by HFS, the density by RBS, the hardness by the thin film hardness meter, the electrical resistance by the four-point method and the friction coefficient under the same conditions as in Embodiment 3. Table 1

A heat fixing device equipped with the heating element thus obtained was used for heat fixing the recording material as in Embodiment 1. Samples 1 to 3 show stable fixing performance and durability as in Embodiment 1, but sample 4 shows slight layer peeling with an increase in the number of fixing times.

[Embodiment 5]

Under the same conditions as in Embodiment 1, a hard carbon layer having a thickness of 50 nm was formed on both surfaces 10a of a polyimide film as shown in Fig. 9. Also, in a similar manner, a hard carbon layer having a thickness of 200 nm was formed on a part 8a of the heater holder that comes into contact with the plastic film.

A heat fixing device using the heater and film thus obtained was subjected to heat fixing of the recording material as in Embodiment 1 and exhibited stable fixing performance and durability as in Embodiment 1.

In the following, a production according to the present invention of a hydrogenated amorphous carbon layer (hereinafter referred to as a-C:H layer) or a diamond-like carbon layer (hereinafter referred to as DLC layer) having high electrical insulation property, high thermal conductivity, high hardness and low friction coefficient on the heating element or its insulating protective layer by gas synthesis will be explained.

The a-C:H layer or DLC layer of the present invention is characterized by a thermal conductivity of 200-600 W/m-K, an electrical resistance (volume resistivity) of 10⁸-10¹¹ Ωcm and a hardness of 2000-5000 kg/mm².

The a-C:H film or DLC film to be used in this invention can be formed by, for example, microwave plasma CVD, DC plasma CVD, high frequency plasma CVD, magnetic field microwave plasma CVD, ion beam sputtering, ion beam evaporation or reactive plasma sputtering. Examples of the carbonaceous raw material gas to be used in these methods include hydrocarbons such as methane, ethane, propane, ethylene, benzene and acetylene; halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform and trichloroethane; alcohols such as methyl alcohol and ethyl alcohol; ketones such as (CH3)2CO and (C6H5)2CO; and gases such as CO and CO2; and mixtures of these with other gases such as N₂, H₂, O₂, H₂O and Ar.

The aC:H layer or the DLC layer contains hydrogen in several tens of atomic % in the layer. The properties of the layer change significantly with the hydrogen content. For example, an aC:H layer containing hydrogen at 50 atomic % or higher is a transparent polymer-like layer with a wide optical band gap, high electrical resistance, high thermal conductivity, but low hardness. On the other hand, an aC:H layer containing hydrogen at 10-40 atomic % is characterized by high thermal conductivity, high insulating capacity, and high hardness, having a Vickers hardness as high as 2000-5000 kg/mm2, an electrical resistance exceeding 10⁸Ωcm, a thermal conductivity exceeding 200 W/m·K, and a friction coefficient less than 0.2. It is believed that these properties are due to the sp3 bonds present in the layer in a proportion of 40-70%. Therefore, the aC:H layer or the DLC layer containing 10⁻⁴ atomic % of hydrogen should be used for the protective layer of the present invention. It is also difficult to clearly distinguish the aC:H layer from the DLC layer. Both layers are macroscopically amorphous, contain hydrogen in the layer, consist of sp²- and sp³-bonded carbon and have similar physical properties as explained above. The DLC layer in this invention has the crystal structure of diamond microscopically, e.g. a diffraction pattern specified as diamond in the electron beam diffraction analysis.

On the above-mentioned insulating ceramic substrate, e.g. made of Al₂O₃, AlN or SiC, the heat generating resistor is formed, for example, by sputtering, and after the resistance value is measured, it is trimmed to a desired resistance value if necessary. Then, electrode terminals are formed in a similar manner by sputtering Au, Ag or Cu. Then, the insulating protective layer made of, for example, lead silicate glass of a low softening point is formed on the heat generating resistor and the electrode terminals by screen printing followed by firing. The heating element is manufactured by forming a protective layer made of an a-C:H layer or a DLC layer on the insulating protective layer. The thickness of the a-C:H or DLC layer should be in a range capable of guaranteeing mechanical strength and friction coefficient for protecting the heating element against the fixing pressure when the heating device is used, and may be in a range from several nanometers to several tens of microns, preferably from several tens of nanometers to several microns. The formation of the heat generating resistor and the electrode terminals is not limited to a PVD method such as sputtering, vacuum evaporation or ion plating, but may also be achieved by a CVD method, plating or screen printing. Thereafter, the heating element is completed by attaching the electrode contact tabs to the electrode terminals, for example by soldering, then by connecting the wire conductors to the electrode contact tabs and by making the adhesive connection of the heating element to the heating element holder.

The present invention uses an a-C:H or DLC layer formed by gas synthesis as the protective layer for the heating element to improve the abrasion resistance and sliding properties of the heating element protective layer, thereby extending the service life of the heating element.

[Embodiment 6]

Fig. 10 is an enlarged partial sectional view of a heat fixing apparatus using the heater embodying the present invention, wherein a heater 1 is supported by a heater support 9 with the interposition of a heat insulating heater holder.

The heating device 1 is equipped with a ceramic substrate 2, an Ag/Pd heat generating resistor 3, an insulating glass protective layer 6, a protective layer 18a consisting of a DLC layer and a temperature sensor 7. A heat-resistant film 10 consists, for example, of polyimide with a thickness of about 40 µm and is designed as an endless belt or an elongated material web. A rotating pressure roller 11 serves as a pressure element to press the film towards the heating element 1. The film 10 rotates or moves at a predetermined speed in a direction indicated by an arrow in contact with the surface of the heating element 1 on which it slides by a driving member (not shown) or by the rotating force of the pressure roller 11. The heat generating resistor 3 is electrically operated to heat the heating element to a predetermined temperature, and a recording material 16 carrying an unfixed toner image 17 on the side of the film 10 is introduced into the fixing nip 15 in the state that the film 10 is moved. Thus, the recording material 16 is kept in contact with the film 10 and passes through the fixing nip together with the film 10. During the passage, heat energy is imparted to the recording material 16 via the film 10 from the heating element 1 to fix the unfixed toner image 10 to the recording material 16 by melting. 11A to 11E are schematic sectional views of the heater of Embodiment 6, showing electrode terminals 4 and 5 made of Cu, a heater holder 8, an electrode tab 12, AuSi solder 13, and a wire conductor 14.

The heating element of the present embodiment was manufactured by first applying Ag/Pd paste by screen printing on an Al₂O₃ substrate 2. After measuring the resistance value, the heat generating resistor 3 was trimmed to a desired resistance value. Then, Cu paste was applied by screen printing, and the electrode terminals 4, 5 were fired by firing under a controlled oxygen partial pressure (Fig. 11A). Then, the insulating protective layer 6 was formed by applying a lead silicate glass with a low softening point by screen printing, followed by firing in air (Fig. 11B). Then, a DLC layer 18a with a thickness of 200 nm was formed by ECR plasma CUD. Fig. 12 is a schematic diagram of an ECR plasma CUD apparatus used for forming the DLC layer. Fig. 12 shows a cavity resonator type plasma chamber 50; a gas supply system 51, a microwave introduction window 52, a microwave guide tube 53, a magnet 54, a microwave oscillator 55, a substrate and a support 56 therefor, a vacuum chamber 57 and a vacuum system 58. After electrode formation, the substrate was mounted on the substrate support and the vacuum chamber was evacuated to 1 x 10-7 Torr. Then, C6H6 at 31 sccm and H2 at 14 sccm were introduced from the gas supply system to a pressure of 3.3 x 10-4 Torr and plasma was generated by introducing a 2.45 GHz microwave at 1.2 kW into the plasma chamber. In this state, an external magnetic field was induced by the magnet to create ECR conditions of 1600 gauss at the insertion window, 875 gauss at the cavity exit and 700 gauss at the substrate position. The DLC layer was deposited by applying a voltage of -500 V to the substrate through a (not shown) DC power source. The hardness of the DLC layer measured by the thin film hardness meter was 3000 kg/mm2 in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. When measured in air with a relative humidity of 45%, using a ball (5 mm in diameter) of a bearing steel as the pin with a load of 2.2 N and a displacement speed of 0.04 m/s, the friction coefficient was 0.08 - 0.09.

Then, the electrode tab 12 made of copper alloy and the ceramic substrate 2 were soldered with AuSi solder 13 (Fig. 11C). Then, the wire conductor 14 was held in contact with the electrode tab 12 (Fig. 11D), and the heater 1 was adhered to the heater holder 8 (Fig. 11E). In the manufacture of the heater 1, the surfaces of the electrode tabs 4, 5 were given Au flash plating to improve the wettability with the solder so that a stable reliability for the connection is achieved. The electrode tab may be formed of Covar, 42 alloy or phosphor bronze instead of copper alloy. The solder preferably has a melting point of at least 250°C and may also be made of AuGe or AuSn instead of AuSi. Furthermore, soldering could be achieved in a more stable manner by quickly coating the Cu electrode terminals with Au, Ni or Au/Ni to prevent oxidation and contamination until soldering. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

The heater thus manufactured was able to efficiently supply the recording material with heat generated by electric energy and to realize a stable heater performance without thermal or electrical deterioration of the components of the heater. In particular, the improvement in the abrasion resistance and sliding performance of the heater protective layer resulted in more than double Lifespan compared to conventional lifespan.

[Embodiment 7]

On a ceramic substrate, as in Embodiment 6, Au was sputtered to a thickness of 10 µm as the heat generating resistor 3. After the resistance value was measured, the resistor was trimmed to a desired resistance value. Then, Cu was sputtered to form the electrode terminals 4, 5. The insulating glass protective layer 6 was formed thereon, and an a-C:H layer 18b was formed thereon. Fig. 13 is a schematic diagram of an ion beam evaporation apparatus used in the formation of the a-C:H layer. Therein, a vacuum chamber 60, an ion beam source 61, an ionization chamber 62, a gas supply system 63, an ion beam exhaust electrode 64, a substrate 65, a substrate holder 66, and a vacuum system 67 are shown. After the electrode formation, the substrate was placed on the substrate holder and the vacuum chamber was evacuated to 1 x 10 7 Torr. Then, CH 4 at 16 sccm and H 2 at 31 sccm were introduced from the gas supply system and the gas pressure was controlled to 3.2 x 10 4 Torr to generate plasma in the plasma chamber. The substrate was irradiated with an ion beam extracted with a voltage of 1 kV applied to the extraction electrode, whereby an a-C:H layer with a thickness of 1 µm was formed at a predetermined position on the insulating glass protective layer. An a-C:H layer prepared in the same manner showed a hydrogen content of 30 atomic % by HFS (hydrogen forward scattering spectrometry). The film hardness and frictional resistance measured in the same manner as in Embodiment 6 were 2500 kg/mm2 and 0.07, respectively. Then, the heating element was completed in the same manner as in Embodiment 6 by connecting the electrode tabs and the wire conductors and making the adhesive bond to the heating element holder.

When heat-fixing the recording material as in Embodiment 6, this heating element could achieve stable fixation as in Embodiment 6.

In the preceding embodiments, the a-C:H or the DLC layer can be formed directly on the resistor 3 without the insulating protective layer 6.

An embodiment of the present invention is explained below, wherein a recess for forming the heat generating resistor is machined in advance on a ceramic substrate, then the heat generating resistor is formed so as not to protrude from the surface of the ceramic substrate, and an a-C:H or DLC layer having high electrical insulation, high thermal conductivity, high hardness and low friction coefficient is formed thereon by gas synthesis as the insulating protective layer.

A recess for forming the heat generating resistor is machined on the above-mentioned ceramic substrate made of, for example, Al₂O₃, AlN or SiC. Specifically, a peelable film or a resist material is formed on the entire surface of a ceramic substrate having a dimension of 350 mm x 350 mm, and a recess corresponding to the heat generating resistor layer, for example, having a dimension of 2 mm x 350 mm x 10 µm, is machined at a predetermined position. The heat generating resistor is formed in the recess by a PUD method such as sputtering, and, if necessary, trimmed to a desired resistance value after the resistance value is measured. The formation is carried out so that the heat generating resistor layer protrudes not more than 2 µm from the surface of the ceramic substrate. If it protrudes more than 2 µm, the aC:H or DLC layer inevitably becomes thicker to obtain sufficient step coverage and causes peeling. After the film or resist material attached to the ceramic substrate are removed, the electrode terminals are formed by sputtering Au, Ag or Cu. Then, an aC:H or a DLC layer is formed on the heat generating resistor to complete the heater substrate. The thickness of the aC:H or the DLC layer should be in a range capable of ensuring mechanical strength and a friction coefficient for protecting the heater against the fixing pressure in the application of the heater, and may be in a range from several nanometers to several tens of microns, preferably from several tens of nanometers to several microns. The formation of the heat generating resistor and the electrode terminals is not limited to a PUD method such as sputtering, vacuum evaporation or ion plating, but can also be achieved by a CVD method, by plating or by screen printing. Then, the heater of this invention is completed by mounting the electrode tabs on the electrode terminals of each heater, capping them to a desired size by, for example, soldering, and then connecting the wire leads to the electrode tabs by pressure and adhesively bonding the heater to the heater support. It is also possible to improve the sliding performance of the heater and the film by similarly forming an aC:H layer or a DLC layer on a part of the heater support that comes into contact with the film.

The present invention thus uses a gas-synthesized a-C:H or DLC layer as the protective layer for the heating element, thereby improving the abrasion resistance and sliding behavior between the heating element and the film and extending the service life of the heating device.

[Embodiment 8]

Fig. 14 is an enlarged partial sectional view of a heat fixing device embodying the present invention. embodying heating element is used. A heating element 1 is carried by a heating element carrier 9 via a heat-insulating heating element holder 8. A heat-resistant film 10 consists for example of polyimide with a thickness of about 40 µm and is designed as an endless belt or as an elongated material web. A rotating pressure roller 11 serves as the pressure member to press the film onto the heating element 1. The film 10 rotates or moves at a predetermined speed in a direction indicated by an arrow in contact with the edges of the heater holder 8 and the front surface of the heater 1 while sliding thereon by a driving member (not shown) or by the rotational force of the pressure roller 11. The heat generating resistor 3 is electrically operated to heat the heater to a predetermined temperature, and a recording material 16 carrying an unfixed toner image thereon on the side of the film 10 is introduced into a fixing nip 15 in the state that the film 10 is moved. In this way, the recording material 16 is held in contact with the film 10 and passes through the fixing nip together with the film 10. During the passage, heat energy is imparted from the heater 1 across the film 10 to the recording material 16 to fix the unfixed toner image to the recording material 16 by melting.

15A to 15E are schematic sectional views of Embodiment 8, showing a heater 1, a ceramic substrate 2, an Ag/Pd heat generating resistor 3, Cu electrode terminals 4 and 5, a protective layer 18a made of a DLC film, a heater holder 8, an electrode tab 12, an AuSi solder 13, and a wire lead 14.

In this embodiment, a recess G with a dimension of 350 mm · 2 mm · 12 um was first mechanically formed on a substrate to form the heat generating resistor made of Al₂O₃, and the heat generating resistor 3 was formed in the recess by applying Ag/Pd paste by screen printing, followed by firing in air, and was trimmed to a desired resistance value after measuring the resistance value. In this state, the surface of the heat generating resistor layer is in agreement with the surface of the ceramic substrate 2. Then, Cu paste was applied by screen printing, and by firing under controlled oxygen partial pressure, the electrode terminals 4, 5 were formed (Fig. 15A). Thereupon, the DLC layer 18a serving as the insulating protective layer was formed. The DLC layer was formed by the apparatus shown in Fig. 12.

Then, the electrode tab 12 made of a copper alloy and the ceramic substrate 2 were soldered using AuSi solder 13 (Fig. 15C). Then, the wire conductor 14 was held in contact with the electrode tab 12 (Fig. 15D), and the adhesive connection for the heating element 1 to the heating element holder 8 was made (Fig. 15E). In the manufacture of the heating element 1, the surfaces of the electrode terminals 4, 5 were given a quick Au coating to improve the wettability with the solder so that a consistently reliable connection can be achieved. The electrode tab can also be made of Covar, 42 alloy or phosphor bronze instead of a copper alloy. The solder preferably has a melting point of at least 250°C and can also consist of AuGe or AuSn instead of AuSi. Furthermore, soldering could be achieved in a more stable manner by quickly plating the Cu electrode terminals with Au, Ni or Au/Ni to prevent oxidation and contamination until soldering. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

The heating device created in this way was able to heat the recording material efficiently with electrical energy generated heat and to produce a stable heating performance without thermal or electrical deterioration of the components of the heater. In particular, it was free from the generation of abraded powder caused by friction between the heater and the film and could maintain a stable sliding performance.

[Embodiment 9]

Fig. 16 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention. The constructions of the components are the same as those of Fig. 14.

As in Embodiment 8, a recess for forming the heat generating resistor was mechanically machined on a ceramic substrate. The heat generating resistor was formed in the recess by sputtering Au with a thickness of 10 µm and a W (tungsten) layer 3a with a thickness of 50 nm. The recess for forming the heat generating resistor was designed as in Embodiment 8, and the W layer was formed to prevent the mutual diffusion of Au and C. After measuring the resistance value, the heat generating resistor was trimmed to a desired resistance value. Then, the electrode terminal 4 was formed by Cu sputtering, and an a-C:H layer 18b serving as the insulating protective layer was formed thereon.

The aC:H layer 18b was formed by the apparatus shown in Fig. 13. After the electrode formation, the substrate was placed on the substrate holder and the vacuum chamber was evacuated to 1 x 10-7 Torr. Then, CH4 at 12 sccm and H2 at 25 sccm were introduced from the gas supply system with the gas pressure controlled to 2.8 x 10-4 Torr to generate a plasma in the plasma chamber. The substrate was irradiated with an electron beam extracted by a voltage of 0.75 kV applied to the extraction electrode, whereby an aC:H layer having a thickness of 400 nm was formed at a predetermined position on the heat generating resistor. An aC:H layer prepared in the same manner showed a hydrogen content of 27 atomic % by HFS (hydrogen forward scattering spectrometry). Also, the layer hardness and frictional resistance measured in the same manner as in Embodiment 6 were 2500 kg/mm² and 0.07, respectively. The heating device was then completed by connecting the electrode tabs and the wire conductors to the electrode terminals and adhesively bonding the heating element to the heating element holder.

When heat-fixing the recording material as in Embodiment 8, the thus-manufactured heating device showed stable fixing ability and durability as in Embodiment 6.

[Embodiment 10]

Fig. 17 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention. The structures of the components are the same as those shown in Fig. 14.

The heat generating resistor layer was formed in a similar manner as in Embodiment 8 to have a thickness of about 10 µm. The depth of the recess for forming the heat generating resistor was made to be 12 µm. After the electrode terminal 4 was formed as in Embodiment 8, lead silicate glass with a low softening point was screen-printed onto the recess containing the heat generating resistor and fired in air to form an insulating protective layer 6' having a thickness of about 2 µm. Then, a DLC layer 18a was formed on the entire surface of the heater element by the same method or conditions as in Embodiment 8.

Then, the electrode tabs and the wire leads were connected to the electrode terminals as in Embodiment 8, and the substrate was adhered to the heater holder carrying a DLC layer having a thickness of 60 nm in the area of contact with the foil as in Embodiment 9, to complete the heater.

When the recording material was heat-fixed as in Embodiment 8, the heating element thus obtained exhibited stable fixing ability and stable durability as in Embodiment 8.

An embodiment of this invention is explained below, wherein a hydrogenated amorphous carbon layer (a-C:H layer) or a DLC layer having a high hardness and a low friction coefficient is formed by gas synthesis on the surface of the film in sliding contact with the heating element.

An aC:H or a DLC layer is formed by the above-mentioned method on a surface of a heat-resistant film, e.g. made of polyimide, which is made as an endless belt or an elongated sheet of material, which comes into contact with the heating element. The thickness of the aC:H or the DLC layer is preferably within a range of several nanometers to several hundred nanometers, because a thickness less than several nanometers cannot provide sufficient lubricating performance, while a thickness greater than several hundred nanometers results in peeling of the layer from the plastic film or in the layer curling due to the tension in the layer. The plastic film can be curled even if the layer is in the above-mentioned preferred thickness range. In this case, the aC:H or the DLC layer can be formed on both sides of the plastic film. The sliding behavior between the heating element and the plastic film can be further improved by designing the aC:H or The DLC layer can also be improved on the insulating protective layer of the heating element or on the heating element holder, which come into contact with the plastic film.

Thus, the present invention serves to form an a-C:H or a DLC layer as a lubricating protective layer by gas synthesis on the surface of the plastic film which is in sliding contact with the heating element, so that the abrasion resistance and sliding property between the heating element and the plastic film are improved and the service life of the heating element is prolonged.

[Embodiment 11]

Fig. 18 is an enlarged partial sectional view of a heat fixing apparatus using the heating element embodying the present invention, in which a heating element 1 is supported by a heating element support 9 with the interposition of a heat-insulating heating element holder 8. A heat-resistant film 10 is made of, for example, polyimide with a thickness of about 40 µm and is formed into an endless belt or an elongated sheet. A rotating pressure roller 11 serves as the pressing member for pressing the film onto the heating element 1. The film 10 revolves or moves at a predetermined speed in a direction indicated by an arrow in contact with the edges of the heating element holder 8 and the surface of the heating element 1 on which it slides, by means of a driving member (not shown) or by means of the rotational force of the pressure roller 11. The heat generating resistor 3 is electrically operated to heat the heating element to a predetermined temperature, and a recording material 16 carrying an unfixed toner image 17 thereon on the side of the film 10 is introduced into a fixing nip 15 in the state that the film 10 is moved. In this way, the recording material 16 is kept in contact with the film 10 and passes through the fixing nip together with the film 10. In the course of the passage, heat is transferred from the heating element 1 via the Film 10 imparts heat energy to the recording material 16 in order to fix the unfixed toner image 17 to the recording material 16 by melting.

19A to 19E are schematic sectional views of the heating device of Embodiment 11, showing a heating element 1, an insulating substrate made of, for example, ceramics, an Ag/Pd heat generating resistor 3, a Cu electrode terminal 4, an insulating glass protective layer 6, a heating element holder 8, an electrode tab 12, an AuSi solder 13, and a wire conductor 14.

In the heating element of this invention, Ag/Pd paste was first screen-printed on an Al₂O₃ substrate and fired in air to form the heat generating resistor 3, which was then trimmed to a desired resistance value after measuring the resistance value. Cu paste was then screen-printed and the electrode terminal 4 was formed by firing under a controlled oxygen partial pressure. Then, lead silicate glass with a low softening point was screen-printed and fired in air to form the insulating protective layer.

Then the electrode contact lug 12 made of a copper alloy and the ceramic substrate 2 were soldered with AuSi solder 13. The wire conductor 14 was then held in contact with the electrode contact lug 12 and the adhesive connection of the heating element to the heating element holder 8 was made. During the manufacture of the heating element 1, the surface of the electrode terminal 4 was provided with an Au quick coating in order to improve the wettability with the solder and to achieve a constant reliability for the connection. The electrode terminal lug can also be made of Covar, 42 alloy or phosphor bronze instead of a copper alloy. The solder preferably has a melting point of at least 250ºC and can also consist of AuGe or AuSn instead of AuSi. Furthermore, a Soldering can be achieved in a more stable manner by applying a quick coating of Au, Ni or Au/NI to the Cu electrode terminals to prevent oxidation and contamination until soldering. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

Fig. 20 is a schematic diagram of an ECR plasma CUD apparatus used in forming the DLC layer 118a (Fig. 18) on the polyimide film 10. Therein, a cavity resonator type plasma chamber 70, a gas supply system 71, a microwave introduction window 72, a microwave guide tube 73, a magnet 74, a microwave oscillator 75, a mechanism 76 for feeding and winding a film under a constant tension and a constant speed, a vacuum chamber 77, a vacuum system 78, and an enclosure 79 for defining the film formation region are shown. After the vacuum chamber was evacuated to 1 x 10-7 Torr, C6H6 at 40 sccm and H2 were introduced into the plasma chamber 70. at 25 sccm from the gas supply system to a pressure of 4.0 10 4 Torr, and a plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz at 1.0 kW. In this state, an external magnetic field was induced by the magnet to realize the ECR conditions of 1200 gauss at the insertion window, 875 gauss at the exit of the cavity resonator, and 700 gauss at the position of the substrate. The DLC layer 118a shown in Fig. 18 was formed by applying a voltage of -500 U from a DC power source (not shown) to the substrate to a thickness of 70 nm. The hardness of the DLC layer measured by the thin film hardness meter was 2500 kg/mm2 in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. When a measurement was carried out in air with a relative humidity of 50%, using a ball (5 mm in diameter) of a bearing steel (SUJ2) as the pin with a load of 2.2 N and a displacement speed of 0.04 m/s, the friction coefficient was 0.10. In the above-mentioned operation, the speed of motion was speed of the film was 1 m/min. and the layer formation speed was 0.5 nm/sec.

The heat fixing device thus prepared was free from the generation of abraded powder resulting from the friction between the heating element and the plastic film and was able to maintain a stable sliding behavior over a prolonged period of time.

[Embodiment 12]

An a-C:H layer was formed as a lubricating protective layer on the plastic film as in Embodiment 11. Fig. 21 is a schematic diagram of an ion beam vapor deposition (IBD) apparatus used in forming the a-C:H layer. Fig. 21 shows a vacuum chamber 80, ion beam sources 81, ionization chambers 82, gas supply systems 83, ion beam exhaust electrodes 84, a substrate 85, a mechanism 86 for feeding and winding a film under a constant tension and a constant speed, a vacuum system 87, and shrouds 88 for confining the film forming region. A pair of ion beam sources 81 are provided in positions opposite to each other with respect to the plastic film. After the vacuum chamber is heated to 1 x 10-7 Torr, CH4 at 12 sccm and H2 at 25 sccm were introduced from the gas supply system to a pressure of 2.5 x 10-4 Torr to generate a plasma in the plasma chamber. The plastic film was irradiated on both sides thereof with ion beams extracted by a voltage of 0.8 kW applied to the extraction electrodes, thereby forming a-C:H layers with a thickness of 60 nm on both surfaces of the plastic film. In the HFS analysis, the a-C:H layer showed a hydrogen content of 27 atomic %. Also, the film hardness and friction coefficient, measured as in Embodiment 6, were 3000 kg/mm2 and 0.12, respectively.

A heat fixing device equipped with a plastic film prepared as described above showed stable fixing performance and durability as in Embodiment 11 when heat fixing the recording material as in Embodiment 6.

[Embodiment 13]

Fig. 22 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention, showing an additional DLC layer 119. The other components are the same as those in Fig. 18.

A DLC layer 118 was formed on a polyimide film having a thickness of 65 nm in the same manner as in Embodiment 11. Also, a DLC layer 119 having a thickness of 200 nm was formed on the insulating protective layer 6 provided on the heat generating resistance layer of the heater in Embodiment 11 and on a part of the heater holder 8 that comes into contact with the plastic film.

A heat fixing device using the plastic film and heater thus prepared provided stable fixing performance and durability as in Embodiment 11 in heat fixing the recording material in the same manner as in Embodiment 11.

The a-C:H layer or the DLC layer may also be provided only on the heating element or the heating element holder. Hereinafter, an embodiment of the present invention is explained, according to which a hydrogenated amorphous carbon layer (a-C:H layer) produced by gas synthesis or a diamond-like carbon layer (DLC layer) of high electrical insulation, high thermal conductivity, high hardness and low friction coefficient is used as a protective layer of the heater.

The a-C:H layer or the DLC layer of this invention is characterized by a thermal conductivity of 200-600 W/m·K, an electrical resistance (volume resistivity) of 10⁸ to 10¹¹ Ωcm and a hardness of 2000-5000 kg/mm².

The a-C:H or DLC layer to be used in the present invention can be formed by, for example, microwave CUD, DC plasma CUD, RF plasma CUD, magnetic field microwave plasma CVD, ion beam sputtering, ion beam evaporation or reactive plasma sputtering. Examples of the carbonaceous raw material gas to be used in these methods include hydrocarbons such as methane, ethane, propane, ethylene, benzene and acetylene; halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform and trichloroethane; alcohols such as methyl alcohol and ethyl alcohol; ketones such as (CH3)2CO and (C6H5)2CO; and gases such as CO and CO2. and mixtures of these with other gases such as N₂, H₂, O₂, H₂O and Ar.

The aC:H or DLC film contains hydrogen in several tens of atomic % in the film, and the properties of the film change significantly with the hydrogen content. For example, an aC:H film containing hydrogen in 50 atomic % or more is a transparent polymer-like film which has a wide optical band gap, high electrical resistance, but low hardness and high thermal conductivity. On the other hand, an aC:H film containing hydrogen in 15-35 atomic % is characterized by high thermal conductivity, high insulating property and high hardness with a Vickers hardness as high as 2000-5000 kg/mm2, an electrical resistance exceeding 10% qcm, a thermal conductivity exceeding 200 W/mK and a friction coefficient less than 0.2. These properties are believed to be attributable to the sp3 bonds present in a proportion of 40-70% in the film. Consequently, for the The protective layer of this invention may be the aC:H layer or the DLC layer with a hydrogen content of 15-35 atomic %.

On the above-mentioned insulating ceramic substrate, e.g., made of Al2O3, AlN or SiC, the heat generating resistor is formed by a PVD method such as sputtering and, if necessary, trimmed to a desired resistance value after measuring the resistance value. Thereafter, the electrode terminals are similarly formed by sputtering Au, Ag or Cu. The heater substrate is then manufactured by forming the protective layer consisting of an a-C:H or a DLC layer. The thickness of the a-C:H or DLC layer should be in a range capable of ensuring sufficient insulation in use of the heater and mechanical strength for protecting the heater against the fixing pressure, and may be within a range of several microns to several hundred microns, preferably several microns to several tens of microns. The formation of the heat generating resistor and the electrode terminals is not limited to a PUD method such as sputtering, vacuum evaporation or ion plating, but can also be achieved by a CVD method, plating or screen printing. After that, the heater device is completed by attaching the electrode contact tabs such as by soldering, then connecting the wire leads to the electrode contact tabs and making the tack connection of the heating element substrate to the heating element holder.

The present invention thus uses an a-C:H layer or DLC layer produced by gas synthesis as the protective layer for the heating element, so that the thermal performance of the heating element is improved, its energy consumption is reduced and a heating element excellent in abrasion resistance and sliding behavior is realized.

[Embodiment 14]

Fig. 23 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention. A heating element 1 is supported by a heating element support β with the interposition of a heat-insulating heating element holder 8. A heat-resistant film 10 is made of, for example, polyimide with a thickness of about 40 µm and is formed as an endless belt or an elongated sheet. A rotating pressure roller 11 serves as a pressing member to press the film against the heating element 1. The film 10 rotates at a predetermined speed in a direction indicated by an arrow or moves at the predetermined speed in that direction in contact with the surface of the heating element 1 while sliding thereon by a drive means (not shown) or by the rotational force of the pressure roller 1. The heat generating resistor 3 is electrically operated to heat the heating element to a predetermined temperature, and a recording material 16 having an unfixed toner image 17 thereon on the side of the film 10 is introduced into a nip 15 in the state of movement of the film 10. Thus, the recording material 16 is held in contact with the film 10 and passes through the fixing clamping gap together with the film 10. During the passage, heat energy is imparted to the recording material 16 via the film 10 from the heating element 1 in order to fix the unfixed toner image 17 to the recording material 16 by melting it.

24A to 24E are schematic sectional views of Embodiment 14, showing a heater 1, a ceramic substrate 2, an Ag/Pd heat generating resistor 3, Cu electrode terminals 4 and 5, a protective layer 6 made of a DLC film, a heater holder 8, an electrode tab 12, an AuSi solder 13, and a wire lead 14.

In this embodiment, Ag/Pd paste was first screen-printed at a predetermined location on an Al₂O₃ substrate and sintered in air to form the heat generating resistor 3, which was then trimmed to a desired resistance value based on the measurement of the resistance value. Cu paste was then screen-printed and the electrode terminal 4 was formed by sintering under a controlled oxygen partial pressure (Fig. 24A). Then, a DLC film was formed as the insulating protective film (Fig. 24B). Fig. 25 is a schematic diagram of an ECR plasma CVD apparatus used in forming the DLC film. Herein, a cavity resonator type plasma chamber 90, a gas supply system 91, a microwave introduction window 92, a microwave guide tube 93, a magnet 94, a microwave oscillator 95, a substrate holder 96 with a substrate, a vacuum chamber 97, and a vacuum system 98 are shown. After the electrode formation, the substrate was attached to the substrate holder, and the vacuum chamber was evacuated to 1 x 10-7 Torr. Then, C6H6 at 30 sccm and H2 at 15 sccm were introduced from the gas supply system to a pressure of 3.4 x 10-4 Torr, and a plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz at 1 kW. In this state, an external magnetic field was induced by the magnet to establish ECR conditions of 1500 gauss at the insertion window, 875 gauss at the cavity resonator outlet, and 700 gauss at the substrate position. Further, a voltage of -500 V was applied to the substrate by a DC power source (not shown) and the DLC layer with a thickness of 10 µm was formed. The thermal conductivity of the DLC layer, measured by an AC photothermoconstantometer, was 400 W/m-K. Also, the electrical resistance was 2 × 10¹¹ Ωcm.

Subsequently, the copper alloy electrode tab 12 and the ceramic substrate 2 were soldered with AuSi solder 13 (Fig. 24C). The wire conductor 14 was then held in contact with the electrode tab 12 (Fig. 24D) and the Heating element substrate is adhered to the heating element holder (Fig. 24E). In the manufacture of the heating element 1, the surface of the electrode terminal 4 is given a Au flash plating to improve the wettability with the solder, thereby achieving a stable reliability for a connection. Instead of a copper alloy, the electrode tab may be formed of Covar, 42 alloy or phosphor bronze. The solder preferably has a melting point of at least 250°C and may be made of AuGe or AuSn instead of AuSi. Furthermore, soldering could be achieved in a more stable manner by flash plating the Cu electrode terminals with Au, Ni or Au/Ni to prevent oxidation and contamination until soldering. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

The heater manufactured in this way is capable of efficiently supplying the recording material with the heat generated by electric power and can realize constant performance without thermal deterioration of the heater components.

[Embodiment 15]

In a similar manner to Embodiment 14, a heat generating resistor 3 was formed on a ceramic substrate by sequentially sputtering Ti of 20 nm and Au of 10 µm and then trimmed to a desired resistance value in accordance with the resistance value measurement. Then, electrode terminals 4, 5 were fabricated by Cu sputtering. Then, an a-C:H layer was formed as the insulating protective layer. Fig. 26 is a schematic diagram of an ion beam evaporation (IDB) apparatus used in forming the a-C:H layer. Fig. 26 shows a vacuum chamber 200, an ion beam source 201, an ionization chamber 202, a gas supply system 203, an ion beam extraction electrode 204, a substrate 205, a substrate holder 206 and a vacuum system 207.

After the electrode formation, the substrate was attached to the substrate holder and the vacuum chamber was evacuated to 1 x 10-7 Torr. Then, CH4 at 15 sccm and H2 at 30 sccm were introduced from the gas supply system to a pressure of 3.1 x 10-4 to generate a plasma in the plasma chamber. The substrate was irradiated with an ion beam extracted by a voltage of 0.7 kV applied to the extraction electrode, whereby an a-C:H film with a thickness of 15 µm was formed at a predetermined position on the heat generating resistor. A film prepared in the same manner showed a hydrogen content of 25 atomic % by HFS analysis. Also, the thermal conductivity and electrical resistance, measured as in Embodiment 14, were 250 W/m·K·and 2·10¹¹ Ωcm, respectively. The heating element was then completed by connecting the electrode contact tabs and the wire leads to the electrode terminals and by making the adhesive connection to the heating element holder as in Embodiment 14.

When heat-fixing the recording material as in Embodiment 14, the heating element thus manufactured showed a stable fixing ability as in Embodiment 14.

An embodiment of this invention is explained below, wherein an a-C:H layer or DLC layer containing a metallic element is formed on the insulating protective layer or the heat generating resistor of the heating element by gas synthesis.

The a-C:H or DLC layer of this invention is characterized by a thermal conductivity of 200-600 W/m·K, an electrical resistance (resistivity) of 10⁸-10¹¹ Ωcm and a hardness of 2000-5000 kg/mm².

The aC: H or DLC layer to be used in the present invention can be deposited, for example, by microwave Plasma CVD, direct current plasma CVD, high frequency plasma CVD, magnetic field microwave plasma CUD, ion beam sputtering, ion beam evaporation or reactive plasma sputtering. Examples of the carbonaceous raw material gas to be used in these methods include hydrocarbons such as methane, ethane, propane, ethylene, benzene and acetylene; halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform and trichloroethane; alcohols such as methyl alcohol and ethyl alcohol; ketones such as (CH₃)₂CO and (C₆H₅)₂CO; and gases such as CO and CO₂, and mixtures of these with other gases such as N₂, H₂, O₂, H₂O and Ar. Also, a solid carbon source such as graphite or glassy carbon of high purity may be used. An element to be added to the aC:H layer or the DLC layer such as Ta, W, Mo, Nb, Ti, Cr, Fe, B or Si may be supplied from a solid metal, a semiconductor or from organometallic gas, silane gas, higher silane gas, diborane gas or higher boron gas containing such a metal.

The aC:H or DLC layer contains hydrogen at several tens of atomic % in the layer, and the properties of the layer change remarkably with the hydrogen content. For example, an aC:H layer containing hydrogen at 50 atomic % or higher is a transparent polymer-like layer that has a wide optical band gap, high electrical resistance, but low hardness and high thermal conductivity. On the other hand, an aC:H layer containing hydrogen at 10-45 atomic % is characterized by high thermal conductivity, high insulating capacity and high hardness with a Vickers hardness as high as 2000-5000 kg/mm2, an electrical resistance exceeding 10⁸Ωcm, a thermal conductivity exceeding 200 W/m K, and a friction coefficient less than 0.2. It is believed that these properties are due to the sp³ bonds present in the layer in a proportion of 40-70%. Consequently, for the protective layer of this invention, the aC: H or DLC layer should be coated with a water hydrogen content of 10⁻⁴⁴ atomic % can be used. It is also difficult to clearly distinguish the aC:H layer from the DLC layer. Both layers are macroscopically amorphous, contain hydrogen in the layer, consist of sp² and sp³ bonded carbon and have similar physical properties as explained above. The DLC layer in the present invention microscopically has the crystal structure of diamond, e.g. a diffraction pattern specified as diamond in the electron beam diffraction analysis.

The friction coefficient of the a-C:H layer or the DLC layer is as low as 0.02 in vacuum or in a dry nitrogen atmosphere, but it tends to increase as the relative humidity increases. In the ordinary state, the friction coefficient is lower than 0.2, but it becomes worse under a higher relative humidity or with an increase in the distance of sliding. On the other hand, the friction coefficient of the a-C:H layer or the DLC layer containing Ta, W, Mo, Nb, Ti, Cr, Fe, B or Si according to this invention remains constant regardless of the humidity or the distance of sliding. The concentration of such an element in the layer should not exceed 30 atomic % because a proportion exceeding 30 atomic % not only increases the friction coefficient compared with the case without adding such an element but also deteriorates the layer hardness. In particular, an element concentration of 10-20 atomic % which minimizes the friction coefficient is preferred. Fig. 27B shows the relationship between the element concentration and the friction coefficient. Also, the addition of the above-mentioned element can increase the adhesion strength to the substrate.

The metal-containing aC:H or DLC layer is formed on the insulating protective layer or the heat generating resistor of the heating element by the above-mentioned methods. The thickness of such aC:H or DLC layer should be in the range of several nanometers to several tens of microns, preferably The thickness of the layer should be between several tens of nanometers and several microns, for example, because a thickness of less than a few nanometers cannot provide sufficient lubrication or insulation, while a thickness exceeding a few tens of microns may result in the layer peeling off from the substrate due to the layer stress. In the case of direct layer formation on the heat generating resistor, the element to be added and its amount should be selected to ensure sufficient insulation (to achieve a desired electrical resistance).

The following explains the method of adding a metal element to the a-C:H or DLC layer in the case of DC magnetron sputtering, for example. Reactive sputtering is carried out by using a target of a metal element to be added (e.g., Ta) and mixing a carbon-containing gas (e.g., C₂H₂) and sputtering inert gas (noble gas, e.g., Ar or nitrogen) in an appropriate ratio. In this process, a DC plasma is generated by introducing a power of several hundred W to several kW from a DC power source and applying an appropriate bias voltage to the substrate. The concentration of the element to be added is controlled by the flow rate ratio of the reaction gas and the sputtering gas. The concentration can be made higher by increasing the flow rate of the sputtering gas.

The sliding performance between the heating element and the plastic film can be further improved by forming the lubricating protective layer of this invention not only on the insulating protective layer or the heat generating resistor of the heating element but also on the plastic film that comes into contact with the heating element and/or the heating element holder.

Thus, the present invention serves to form a metal element-containing aC:H layer or DLC layer by gas syn these as the lubricating protective layer on the insulating protective layer or on the heat generating resistor of the heating element which is in sliding contact with the plastic film, so that the abrasion resistance and the sliding behavior between the heating element and the plastic film are improved and the service life of the heating element is extended.

[Embodiment 16]

Fig. 27A is an enlarged partial sectional view of a heat fixing device using the heating device of this invention, in which a heating element 1 is supported by a heating element support 9 via a heat insulating heating element holder 8. A heat-resistant film 10 is made of, for example, polyimide with a thickness of about 40 µm and is formed as an endless belt or an elongated sheet. A rotating pressure roller 11 serves as a pressing member for pressing the film onto the heating element 1. The film is circulated or moved by a driving member (not shown) or by the rotating force of the pressure roller 11 at a predetermined speed in a direction indicated by an arrow, in contact with the edges of the heating element holder 8 and the surface of the heating element 1 on which it slides. The heat generating resistor 3 is electrically operated to heat the heating element to a predetermined temperature, and a recording material 16 carrying an unfixed toner image thereon on the side of the film 10 is introduced into a fixing nip 15 in the state of movement of the film 10. In this way, the recording material 16 is kept in contact with the film 10 and passes through the fixing nip 15 together with the film 10. During the passage, heat energy is imparted to the recording material 16 via the film 10 from the heating element 1 to fix the unfixed toner image 17 to the recording material by fusing.

Figs. 28A to 28E are schematic sectional views of Embodiment 16 and show a heating element 1, a ceramic micro substrate 2, an Ag/Pd heat generating resistor 3, Cu electrode terminals 4 and 5, an insulating glass protective layer 6, a DLC layer 120 containing a metal element, a heating element holder 8, an electrode contact tab 12, AuSi solder 13 and a wire conductor 14.

In this embodiment, first, Ag/Pd paste was screen-printed on an Al2O3 substrate and fired in air to form the heat generating resistor 3, which was then trimmed to a desired resistance value based on the measurement of the resistance value. Cu paste was screen-printed thereon, and the electrode terminals 4, 5 were formed by firing under a controlled oxygen partial pressure (Fig. 28A). Then, the insulating protective layer was formed by applying a low-softening point lead silicate glass by screen-printing, followed by firing in air. Subsequently, a DLC layer containing Ta with a thickness of 400 nm was formed by ECR plasma CVD (Fig. 28C). Fig. 29 is a schematic diagram of an ECR plasma CVD apparatus used in forming the DLC layer. Fig. 29 shows a cavity resonator type plasma chamber 210, a gas supply system 211, a microwave introduction window 212, a microwave guide tube 213, a magnet 214, a microwave oscillator 215, a substrate 216, a vacuum chamber 217, a vacuum system 218, and a Ta target 219 having a purity of 99.99%. After the vacuum chamber was evacuated to 1 x 10-7 Torr, C2H2 of 40 sccm, H2 of 20 sccm, and Ar of 120 sccm were introduced from the gas supply system to a pressure of 2.0 x 10-3 Torr, and a plasma was generated by introducing a microwave of 2.45 GHz of 1.0 kW into the plasma chamber. In this state, an external magnetic field was formed by means of the magnet to establish the ECR conditions of 1200 gauss at the insertion window, 875 gauss at the Ta target 219 at the cavity outlet and 600 gauss at the substrate position. Also, a DC power source (not shown) was used to generate a Voltage of -500 U was applied to the substrate, and the DLC film 120 shown in Fig. 28C was formed. A film prepared in a similar manner showed a hydrogen content of 20 atomic % by HFS (hydrogen forward scattering) analysis. Also, the Ta concentration in the film analyzed by EPMA was 10 atomic %. The hardness of the film measured by the thin film hardness meter was 2000 kg/mm² in Vickers hardness. The friction properties of the film were evaluated by the pin-on-plate method. The friction coefficient was 0.06 in a measurement conducted in air with a relative humidity of 60% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as a pin with a load of 2.2 N and a displacement speed of 0.04 ms.

Subsequently, the electrode tab 12 made of a copper alloy and the ceramic substrate 2 were soldered with AuSi solder 13 (Fig. 28D). Then, the wire conductor 14 was kept in contact with the electrode tab 12 and the heater substrate was adhered to the heater holder 8 (Fig. 28E). In the manufacture of the heater 1, the surface of the electrode terminals 4, 5 was provided with an Au quick plating to improve the wettability with the solder so that a constant reliability for the connection is achieved. Instead of a copper alloy, the electrode tab can also be made of Covar, 42 alloy or phosphor bronze. The solder preferably has a melting point of at least 250°C and can also be made of AuGe or AuSn instead of AuSi. Furthermore, soldering could be achieved in a more stable manner by quickly plating the Cu electrode terminals with Au, Ni or Au/Ni to prevent oxidation and contamination until the soldering process. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

The heat fixing device produced in this way was free from the generation of abraded powder resulting from the friction between the heating element and the plastic film and was able to maintain stable sliding behavior over a long period of time.

[Embodiment 17]

A recess of 350 mm x 2 mm x 12 µm was mechanically machined on an Al₂O₃ substrate as in Embodiment 16 to form the heat generating resistor layer. In this recess, Ag/Pd paste of 11 µm thickness was screen printed and sintered in air to prepare the heat generating resistor 3, which was then trimmed to a desired resistance based on the resistance value measurement. The substrate was then placed in a sputtering device (not shown), and a W (tungsten) layer 3a of 1 µm thickness was formed on the resistor layer to prevent mutual diffusion of Ag/Pd and C. Then, an aC:H layer containing Si was formed in the ECR plasma CVD apparatus shown in Fig. 29 and used in Embodiment 16 but without the target 219. After the vacuum chamber was evacuated to 1 x 10-7 Torr, C6H6 of 25 sccm, H2 of 15 sccm and SiH4 of 10 sccm were introduced from the gas supply system to a pressure of 3.6 x 10-4 Torr, and plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz of 1.2 kW. In this state, an external magnetic field was induced by the magnet to establish the ECR conditions of 1500 gauss at the insertion window, 875 gauss at the cavity outlet, and 650 gauss at the substrate position. Also, a voltage of -700 V was applied to the exhaust electrode (not shown) provided at the cavity outlet, and an aC₁-xSix:H layer having a thickness of 400 nm was formed. The range of x was 0 ≤ x ≤ 0.4 because an x value exceeding 0.4 increases the SiC component in the layer and thus increases the friction coefficient beyond 0.2. Fig. 30 is an enlarged fragmentary view. A sectional view of a heat fixing device using the heating element embodying the present invention. The hardness of the film measured by the thin film hardness meter was 2500 kg/mm² in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. When measured in air at a relative humidity of 50% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as the pin with a load of 2.2 N and a displacement speed of 0.04 m/s, the friction coefficient was 0.05. The hydrogen content in the film measured by the HFS (hydrogen forward scattering) analysis was 25 atomic %.

A heat fixing device equipped with the heating element thus prepared exhibited stable fixing performance and durability as in Embodiment 16 in the heat fixing of the recording material performed in the same manner as in Embodiment 16.

[Embodiment 18]

An aC:H layer was formed as the lubricating protective layer on the insulating protective layer in a manner similar to Embodiment 17. Fig. 31 is a schematic diagram of an ion beam deposition (IBD) apparatus used in forming the aC:H layer. Fig. 31 shows a vacuum chamber 220, an ion beam source 221, an ionization chamber 222, a gas supply system 223, an ion beam exhaust electrode 224, a substrate 225, an electron gun 226, and a vacuum system 227. After the vacuum chamber was evacuated to 1 x 10-7 Torr, CH4 of 15 sccm and H2 of 35 sccm were supplied from the gas supply system to a pressure of 3.8 x 10-4 Torr. Torr was introduced, which generated a plasma in the plasma chamber. The substrate was irradiated with an ion beam extracted by a voltage of 0.8 kV, which was applied to the extraction electrode. At the same time, the metal to be added was extracted by means of the electron catapult 226. The metal added was Ta, W, Mo, Nb, Cr, Fe, B or Si, and the total film thickness was 450 nm. Samples 1-9 of the heating elements thus prepared and a sample 10 using an undoped aC:H film were subjected to measurements of hydrogen content, metal content, film hardness and friction coefficient. The results obtained are summarized in Table 2. The hydrogen content was measured by HFS analysis, the metal concentration by EPMA, the film hardness by the thin film hardness meter and the friction coefficient under the same conditions as in Embodiment 17. Table 2

Thermal fixing devices equipped with the heating elements thus prepared were used in thermally fixing the recording material as in Embodiment 16. Samples 1 to 9 show stable fixing performance and durability as in Embodiment 16, but Sample 10 shows some generation of powder rubbed off from the layer with the increase in the number of fixing operations.

[Embodiment 19]

A heater provided with the insulating protective layer as in Embodiment 16 was placed in a DC magnetron sputtering apparatus shown in Fig. 32. Fig. 32 shows a vacuum chamber 230; , a substrate 231, a target 232, a gas supply system 233, a DC power source 234 and a vacuum system 235. The target was made of Ta having a purity of 99.9%. After the vacuum chamber was evacuated to 1 x 10-7 Torr, C2H2 and Ar were introduced from the gas supply system and an aC:H layer containing Ta was formed to a thickness of 400 nm while the C2H2/Ar flow ratio was varied within a range of 0-60%. In this process, a gas pressure of 0.4 Pa, a substrate temperature equal to room temperature, a discharge power of 2 kW and a substrate-target distance of 70 mm were used. Samples 11-15 of the heaters thus prepared were subjected to measurement of hydrogen content, element content, film hardness and friction coefficient, and the results obtained are summarized in Table 3. The hydrogen content was measured by HFS analysis, the element content by EPMA, the film hardness by the thin film hardness meter and the friction coefficient under the same conditions as in Embodiment 17. Table 3

Heat fixing devices equipped with the heating elements thus prepared were used in thermally fixing the recording material as in Embodiment 16. Samples 11 to 13 show stable fixing performance and durability as in Embodiment 16, but Samples 14 and 15 show some generation of powder rubbed off from the plastic film with an increase in the number of fixing operations.

An embodiment of this invention is explained below, wherein a fluorine-containing a-C:H layer or DLC layer is formed by gas synthesis on the insulating protective layer or on the heat generating resistor of the heater or on the plastic film.

The formation method and starting materials for the a-C:H or DLC layer used in the present embodiment are the same as those in the previous embodiments, but if necessary, the addition of an element such as Ta or W by an organometallic gas may be omitted.

The friction coefficient of the a-C:H or DLC layer is as low as 0.02 in a vacuum or dry nitrogen atmosphere, but it tends to increase as the relative humidity increases. The friction coefficient is less than 0.2 in the normal state, but it increases as the relative humidity increases or the distance of sliding becomes longer.

On the other hand, the fluorine-containing a-C:H or DLC layer according to the present invention exhibits a constant friction coefficient regardless of the humidity or the distance of sliding motion. The concentration of fluorine in the layer should not exceed 30 atomic % because a content exceeding 30 atomic % deteriorates the properties inherent in the a-C:H or DLC layer. In particular, a loss in the layer hardness will result, and the adhesion to the substrate will also be deteriorated.

The reason for the constant friction coefficient of the fluorine-containing a-C:H or DLC layer regardless of the environmental conditions (especially humidity) or the use condition (length of a sliding motion) is still unclear, but it is believed that the floating bonds present in the a-C:H or DLC layer are reduced by breaking off by fluorine atoms, thereby stabilizing the layer against the environmental conditions or the use condition.

The fluorine-containing aC:H or DLC layer is formed on the insulating protective layer or the heat generating resistor of the heater or on the plastic film by the above-mentioned methods. The thickness of this aC:H or DLC layer should be within a range of several nanometers to several tens of microns, preferably several tens of nanometers to several microns, in the case of formation on the insulating protective layer or the heat generating resistor, because a thickness of less than several nanometers does not can provide sufficient lubricity or insulation, while a thickness greater than several tens of microns tends to cause peeling of the layer from the substrate as a result of stress in the layer. In the case of direct formation on the heat generating resistor, it is necessary to ensure sufficient insulation (to achieve a desired electrical resistance). On the other hand, in the case of layer formation on the plastic film, a range of several to several hundred nanometers is preferred because a thickness less than several nanometers cannot provide sufficient lubricity, while a thickness greater than several hundred nanometers results in peeling of the layer from the plastic film or curling of the plastic film due to stress in the layer. If curling of the plastic film itself occurs within the above-mentioned preferred thickness range, the layer can be formed on both surfaces of the plastic film.

In the above-mentioned film formation methods, fluorine can be added to the a-C:H or DLC film by, for example, using a fluorine-containing gas such as CF4 or C6H6-mFm (m = 0 to 6) as the raw material gas or by exposing the a-C:H or DLC film to the plasma of a fluorine-containing gas such as CF4, thereby fluorinating the surface of that film, or by implanting fluorine ions.

The sliding behavior between the heating element and the plastic film can be further improved by forming the lubricating protective layer of this invention not only on the heating element or on the heating element holder that comes into contact with the plastic film, but also on the said plastic film that is in sliding contact with the heating element.

The present invention thus produces as the lubricating protective layer a fluorine-containing aC:H or DLC layer by means of gas synthesis on the insulating protective layer or the heat generation resistance of the heater, which come into sliding contact with the plastic film, thereby improving the abrasion resistance and sliding behavior between the heater and the plastic film and extending the service life of the heater.

[Embodiment 20]

Fig. 33 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention, wherein the heating element 1 is supported by a heating element support 9 with the interposition of a heat insulating heating element holder 8. A heat-resistant film 10 is made of, for example, polyimide with a thickness of about 40 µm and is formed as an endless belt or an elongated sheet. A rotating pressure roller 11 serves as a pressing member for pressing this film toward the heating element 1. By means of a drive member (not shown) or by the rotating force of the pressure roller 11, the film 10 makes a revolution or movement at a predetermined speed in a direction indicated by an arrow in contact with the edges of the heating element holder 8 and with the surface of the heating element 1, while sliding thereon. The heat generating resistor 3 is electrically operated to heat the heating element to a predetermined temperature, and a recording material 16 carrying an unfixed toner image 17 thereon on the side of the film 10 is introduced into a fixing nip 15 in the state that the film 10 is moved. In this way, the recording material 16 is kept in contact with the film 10 and passes through the fixing nip together with the film 10. During the passage, heat energy from the heating element 1 is imparted to the recording material 16 via the film 10 to fix the unfixed toner image 17 to the recording material 16 by melting it.

Figs. 34A to 34E are schematic sectional views of the heating element of Embodiment 20, wherein a heating element 1, a ceramic substrate 2, an Ag/Pd heat generating resistor 3, a Cu electrode terminal 4, an insulating glass protective layer 6, a fluorine-containing DLC layer 121, a heater holder 8, an electrode contact tab 12, an AuSi solder 13 and a wire conductor 14 are shown.

In the heater of this embodiment, Ag/Pd paste was first screen-printed on an Al₂O₃ substrate and fired in air to form the heat generating resistor, which was then trimmed to a desired resistance value based on a measurement of the resistance value.

Cu paste was applied thereon by screen printing, and the electrode terminals 4, 5 were formed by firing under a controlled partial pressure of oxygen. Then, the insulating protective layer was formed by applying a lead silicate glass with a low softening point by screen printing, followed by sintering in air. Thereon, a fluorine-containing DLC layer 121 with a thickness of 800 nm was formed by ECR plasma CVD. Fig. 35 is a schematic representation of an ECR plasma CVD apparatus used in forming the DLC layer. There are shown a cavity resonator type plasma chamber 250, a gas supply system 251, a microwave introduction window 252, a microwave guide tube 253, a magnet 254, a microwave oscillator 255, a substrate 256, a vacuum chamber 257 and a vacuum system 258. After the vacuum chamber was evacuated to 1 x 10-7 Torr, C2H2 at 30 sccm, CF4 at 10 sccm and H2 at 20 sccm were introduced from the gas supply system to a pressure of 2.0 x 10-3 Torr and a plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz at 1.0 kW. In this state, an external magnetic field was induced by the magnet to establish the ECR conditions of 1200 gauss at the insertion window, 875 gauss at the cavity outlet and 600 gauss at the substrate position. Furthermore, a voltage of -500 V was applied to the substrate, and the fluorine-containing DLC film 121 shown in Fig. 34C was formed. A film prepared in the same manner showed a hydrogen content of 20 atomic % by HFS (hydrogen forward scattering analysis). Also, the fluorine concentration measured by RBS (Rutherford back scattering spectroscopy) was 10 atomic %. The hardness of the film measured by the thin film hardness meter was 2500 kg/mm² in Vickers hardness. The friction properties were evaluated by the pin-on-plate method. When measured in air with a relative humidity of 50% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as a pin with a load of 1.5 N and a displacement speed of 0.04 m/s, the friction coefficient was 0.05. Subsequently, the electrode tab 12 made of a copper alloy and the ceramic substrate 2 were soldered by means of an AuSi solder 13. The wire conductor 14 was then held in contact with the electrode tab 12 and the heater substrate was adhered to the heater support 8. In the manufacture of the heater 1, the surfaces of the electrode terminals 4, 5 were given a quick Au plating to improve the wettability with the solder and thereby achieve a stable reliability for the connection. Instead of a copper alloy, the electrode tab may also be formed of Covar, 42 alloy or phosphor bronze. The solder preferably has a melting point of at least 250°C and may be made of AuGe or AuSn instead of AuSi. The soldering could also be achieved in a more stable manner by giving the Cu electrode terminals a quick Au, Ni or Au/Ni plating to prevent oxidation and contamination until the soldering process. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

The heat fixing device thus manufactured was free from generation of abraded powder resulting from friction between the heating element and the plastic film and could maintain stable sliding performance over a prolonged period of time.

[Embodiment 21]

A recess having a dimension of 350 mm x 2 mm x 12 µm was mechanically machined on an Al₂O₃ substrate similar to that of Embodiment 20 to form the heat generating resistor layer. Ag/Pd paste having a thickness of 11 µm was placed in this recess by screen printing and fired in air to form a heat generating resistor 3, which was then trimmed to a desired resistance value based on the measurement of the resistance value. The substrate was then set in a sputtering device (not shown), and a W (tungsten) layer 3a having a thickness of 1 µm was formed on the resistor layer to prevent mutual diffusion of Ag/Pd and C. Then, a fluorine-containing aC:H layer was formed in the ECR plasma CVD apparatus shown in Fig. 35 as in Embodiment 20. After the vacuum chamber was evacuated to 1 × 10 Torr, C6H5F at 25 sccm and H2 at 15 sccm were introduced from the gas supply system to a pressure of 3.6 × 10-4 Torr, and a plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz at 1.2 kW. In this state, an external magnetic field was formed by the magnet to establish the ECR conditions of 1500 gauss at the insertion window, 875 gauss at the outlet of the cavity resonator, and 650 gauss at the position of the substrate. Also, a voltage of -700 U was applied to an exhaust electrode (grid) (not shown) provided at the exit of the cavity resonator, and the aC:HF layer was formed to a thickness of 1000 nm. Then, a heating element sample 1 was prepared by connecting the electrode tabs and the wire leads to the electrode terminals and adhesively bonding them to the heating element holder in the same manner as in Embodiment 20. Fig. 36 is an enlarged partial sectional view of a heat fixing device using the heating element embodying this invention. Samples 2 and 3 were prepared under the same conditions except that the Raw material gas was replaced by C₆H₃F₃ and C₆F₆, respectively. These test pieces were subjected to measurement of hydrogen content, fluorine content, film hardness and friction coefficient, and the results obtained are summarized in Table 4. The hydrogen content was measured by the HFS analysis, the fluorine content by the RBS analysis, the film hardness by the thin film hardness meter and the friction coefficient under the same conditions as in Embodiment 20. Table 4

Thermal fixing devices equipped with the heating elements thus prepared were subjected to thermal fixing of the recording material as in Embodiment 20. Samples 1 and 2 showed stable fixing performance and durability as in Embodiment 20, but in Sample 3, slight layer peeling developed with the increase in the number of fixing operations.

[Embodiment 22]

An aC:H layer was formed on the insulating protective layer as the lubricating protective layer as in Embodiment 20. Fig. 37 is a schematic diagram of an ion beam vapor deposition (IBD) apparatus used in forming the aC:H layer. Fig. 37 shows a vacuum chamber 260, an ion beam source 261, an ionization chamber 262, a gas supply system 263, an ion beam exhaust electrode 264, a substrate 265 and a vacuum system 266. After the vacuum chamber was evacuated to 1 x 10-7 Torr, CH4 at 15 sccm and H2 at 35 sccm were introduced from the gas supply system to a pressure of 3.0 x 10-4 Torr to generate a plasma in the plasma chamber. The substrate was irradiated with an ion beam which was exhausted by applying a voltage of 0.7 kV to the exhaust electrode, and the aC:H layer was formed to a thickness of 400 nm. The substrate was then set in an RF plasma CVD apparatus shown in Fig. 38. Fig. 38 shows a vacuum chamber 270, a gas supply system 271, an electrode 272, a substrate 273, a vacuum system 274 and an RF power source 275. After the vacuum chamber was evacuated to 1 x 10-7 Torr, CF4 was introduced from the gas supply system at 100 sccm to a pressure of 3.0 x 10-2 Torr, and RF plasma was generated by introducing a power of 1.5 kW from the RF power source. The substrate bearing the aC:H layer was exposed to the RF plasma, thereby fluorinating the surface of the layer. The layer showed a hydrogen content of 30 atomic percent, a fluorine content of 5 atomic percent, a layer hardness of 2500 kg/mm2 and a friction coefficient of 0.05. The fluorine concentration in the film decreased from the surface toward the substrate. The methods and conditions of this measurement were the same as in Embodiment 14. Then, the heater was completed by connecting the electrode tabs and the wire leads to the electrode terminals and making the adhesive bond to the heater holder in the same manner as in Embodiment 20.

A heat fixing device equipped with the heating element thus prepared was applied to the thermal fixation of the recording material in the same manner as in Embodiment 20, and stable fixing performance and stable durability were achieved as in Embodiment 20.

[Embodiment 23]

In a similar manner to Embodiment 22, a-C:H layers were formed with a thickness of 450 nm on the insulating protective layer, with a thickness of 550 nm on the heater holder in contact with the plastic film, and with a thickness of 30 nm on the plastic film. Then, the heater, the heater holder, and the plastic film each carrying the a-C:H layer thereon were set in the RF plasma CVD apparatus shown in Fig. 38 in the same manner as Embodiment 22, and the surface of the a-C:H layers was fluorinated. Fig. 39 is an enlarged partial sectional view of a heat fixing device sending the heater embodying the present invention.

A thermal fixing device equipped with the heating element thus prepared was applied to thermally fix the recording material as in Embodiment 20, and stable fixing performance and durability as in Embodiment 20 were obtained.

In the following, an embodiment is explained which uses a diamond layer produced by gas synthesis with a high electrical insulation capacity, a high thermal conductivity, a high hardness and a low friction coefficient as the protective layer of the heating element.

The diamond crystals of this invention are characterized by a thermal conductivity of 600-2100 W/m K, an electrical resistivity (volume resistivity) of 10¹⁰-10¹⁶ Ωcm and a hardness of 10,000 kgf/mm².

The substrate for forming the diamond layer of the present invention is preferably made of a material that is suitable for producing diamond crystals and allows mechanical grinding and etching. Examples of such a Materials include Si, Ta, Mo, W, SiC, WC, SiO₂, Al₂O₃ and Si₃N₄.

The gas synthesis of diamond crystals to be used in the present invention can be achieved, for example, by a filament CVD, microwave plasma CVD, DC plasma CVD, RF plasma CVD, magnetic field microwave plasma CVD or a flame combustion method. Examples of the carbonaceous raw material gas include hydrocarbons such as methane, ethane, propane, ethylene, benzene and acetylene; halogenated hydrocarbons such as methylene chloride, carbon tetrachloride, chloroform and trichloroethane; alcohols such as methyl alcohol and ethyl alcohol; ketones such as (CH3)2CO and (C6H5)2CO; gases such as CO and CO2; as well as mixtures of these with other gases such as N₂, H₂, O₂, H₂O or Ar.

For example, in the case of a microwave CVD method using hydrogen and methane as the raw material gas, the synthesis of diamond crystals is carried out with a methane gas concentration of 0.1-1.0%, a substrate temperature of 600-900ºC, a gas pressure of 1.33-26.6 kPa and a total gas flow rate of 100-1000 ml/min. The production conditions of diamond crystals are variable according to the synthesis method.

The diamond crystals mentioned in this invention are those which can be identified as the diamond crystals by, for example, X-ray diffraction, electron beam diffraction or Raman spectroscopy. For example, as shown in Fig. 40, Raman spectroscopy shows a sharp, high diamond peak at about 1333 cm⁻¹ and weak, broad peaks resulting from the diamond-free carbon component at about 1360 and 1550 cm⁻¹. The thermal conductivity of the diamond crystals depends largely on the crystallinity of the diamond and becomes higher as the crystallinity becomes higher and the impurity becomes lower. Consequently, diamond crystals which have the broad peaks at about 1360 and 1550 cm⁻¹ in the Raman spectrum is preferred. When the ratio of diamonds and amorphous carbon is expressed by the intensity ratio (I₁₅₅�0/I₁₃₃₃) of the peak of amorphous carbon (broad peak around 1550 cm⁻¹) and the peak of diamonds (1333 cm⁻¹) in the Raman spectrum, a range of 0 ≤ I₁₅₅�0/I₁₃₃₃ ≤ 1 is preferred. Above the upper limit of this range, the crystallinity of diamonds is deteriorated and the thermal conductivity is worsened. Also, the crystallinity of diamonds is remarkably correlated with the type and concentration of the raw material gases used in film formation. For example, in the methane-hydrogen system, a reduced methane concentration improves the crystallinity with an increase in thermal conductivity. In the methane-hydrogen-oxygen system, a diamond film with satisfactory crystallinity can be obtained by selecting the carbon-oxygen atomic ratio as 0/C = 0.8. Satisfactory diamond crystallinity realizes the aforementioned diamond physical properties, thereby realizing high insulating capacity in addition to high thermal conductivity.

The thickness of the diamond layer should be selected so as to ensure a mechanical strength capable of protecting the heating element against the fixing pressure as well as providing sufficient insulation during use of the heating element, and is generally within a range of several to several thousand microns, preferably from several tens to several hundred microns.

After a diamond coating or layer is formed on the above-mentioned substrate, the heat generating resistor is formed by a PVD method such as sputtering and, if necessary, trimmed to a desired resistance value based on the resistance value measurement. The electrode terminals are formed in a similar manner by sputtering Au, Ag or Cu. Then, a ceramic cal paste (an adhesive) is applied to the diamond layer, the heat generating resistor and the electrode terminals by screen printing, and an insulating substrate is attached thereto and bonded thereto by firing. The heat generating resistor and the electrode terminals can be formed not only by a PVD method such as sputtering, vacuum evaporation or ion plating but also by CVD, electroplating or screen printing. Then, the substrate for diamond layer formation is removed by mechanical grinding or chemical etching. The surface of the diamond layer showing the polycrystalline nature has a larger surface roughness as the crystallinity increases, and it is generally in a range of several thousand angstroms to several microns in Rmax. However, the surface roughness of the diamond layer after substrate removal is equal to that of the substrate used for diamond layer formation, so that the surface roughness of a covering layer can be made equal to or less than several hundred angstroms in Rmax. The heating element of the present invention is then completed by attaching the electrode contact tabs to the electrode terminals, for example by killing, then pressing the wire conductors to the electrode contact tabs and adhesively bonding the heating element substrate to the heating element mount.

The present invention thus uses a diamond layer obtained by gas synthesis as the protective layer of the heating element, thereby improving the thermal performance of the heating element, reducing its energy consumption and realizing a heating element excellent in abrasion resistance and sliding behavior.

[Embodiment 24]

Fig. 41 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention, wherein a heating element 1 is supported on a heater support 9 through the interposition of a heat-insulating heater support 8. A heat-resistant film 10 is made of, for example, polyimide and has a thickness of about 40 µm and is formed as an endless belt or an elongated sheet. A rotating pressure roller 11 serves as a pressing member for pressing said film toward the heater 1. The film 10 rotates or moves at a predetermined speed in a direction indicated by an arrow in contact with the front surface of the heater 1 while sliding thereon by a driving member (not shown) or by the rotating force of the pressure roller 11. The heat generating resistor 3 is electrically operated to heat the heater to a predetermined temperature, and a recording material 16 having an unfixed toner image 17 thereon on the side of the film 10 is introduced into a fixing nip 15 in the state of movement of the film 10. In this way, the recording material 16 is held in contact with the film 10 and passes through the fixing clamping gap together with the film 10. During the passage, heat energy is imparted to the recording material 16 from the heating element 1 via the film 10 in order to fix the unfixed toner image 17 to the recording material 16 by melting it.

42A to 42F are schematic sectional views of the 24th embodiment, showing a heating element 1, a ceramic substrate 2, an Ag/Pd heat generating resistor 3, a Cu electrode terminal 4, a substrate 5 made of, for example, Si for diamond film formation, a protective layer 6 made of a polycrystalline diamond film, a heating element holder 8, an electrode tab 12, AuSi solder 13, and a wire conductor 14.

In this embodiment, a polycrystalline diamond layer 6 was first formed on the Si substrate 5 for diamond layer formation (Fig. 42A). On the Si substrate, areas which were not subjected to diamond layer formation were were covered in advance by a resist material. This substrate was immersed in an alcoholic dispersion of diamond abrasive particles of 15 to 30 µm and subjected to a scarring treatment by means of an ultrasonic oscillator, after which the covering resist material was removed. The said substrate was then subjected to formation of the diamond layer in a filament CVD apparatus shown in Fig. 43. Fig. 43 shows a quartz reaction tube 270, an electric furnace 271, a tantalum filament 272, a substrate 273, a raw gas material inlet 274 connected to gas containers, gas flow regulators and valves (not shown), and a gas outlet 275 connected to a mechanical booster pump, a rotary pump and a valve (not shown). After the substrate was placed in the apparatus and the interior was evacuated by the vacuum pump (not shown), methane at 1 ml/min and hydrogen at 999 ml/min were introduced from the gas containers (not shown) into the quartz reaction tube, and the pressure therein was controlled to 6.0 Pa by a regulating valve (not shown). The inside of the reaction tube was heated to 900°C by the electric furnace, the filament was heated to 2100°C, and the diamond film was formed in 20 hours to a thickness of 40 µm. According to the observation under a scanning electron microscope (SEM), the obtained diamond film was a polycrystalline film with clear side faces. Raman spectroscopy showed a sharp diamond peak around 1333 cm-1, and the intensity ratio of the amorphous carbon peak to the diamond peak was I₁₅₅₀/I₁₃₃₃ ≤ 0.1. Also, a diamond film prepared under the same conditions showed a thermal conductivity of 900 W/m·K as measured by the radiation cooling method.

On the diamond layer, the heat generation resistor was formed by successively sputtering Ti to a thickness of 200 Å and Au to a thickness of 10 µm, and based on the resistance measurement, it was set to a desired resistance value. Then, the electrode terminal 4 was formed by Cu sputtering. Alumina paste (adhesive) was applied thereon and an alumina substrate was applied and integrated by firing (Fig. 42B). Then, the Si substrate was removed by mechanical lapping and a Si etchant (e.g. HF/HNO₃/CH₃COOH) (Fig. 42C).

In the heating element or insulating substrate with the Si substrate removed, the electrode terminal 4, the electrode tab 12 made of a copper alloy and the ceramic substrate 2 were soldered and fused together with the solder 13 made of AuSi by heating above the melting point (370°C) of the solder (Fig. 42D). The wire conductor 14 was then pressed onto the electrode tab 12 thus attached (Fig. 42E), and the heating element 1 was bonded to the heating element holder 8 (Fig. 42F). In the manufacture of the heating element 1, the surface of the electrode terminal 4 was given an Au quick coating to improve the wettability with the solder and thereby achieve constant reliability in the connection. The electrode tab may be made of Covar, 42 alloy or phosphor bronze instead of copper alloy. The solder preferably has a melting point of at least 250ºC and may be made of AuGe or AuSn instead of AuSi. Furthermore, soldering could be achieved in a more stable manner by providing the Cu electrode terminal with a quick coating of Au, Ni or AuJNi to prevent surface oxidation of the Cu electrode terminal until soldering and to provide the terminal with chemical resistance when the Si substrate is removed. The Ni layer serves to prevent excessive diffusion of Gu into the solder.

The heating element produced in this way was able to efficiently supply the recording material with the heat generated by electrical energy supply and was able to achieve a stable achieve optimal heating element performance without thermal deterioration of the heating element components.

[Embodiment 25]

In a similar manner to Embodiment 24, a polycrystalline diamond film was formed on a Si substrate. Fig. 44 is a schematic diagram of a microwave plasma CVD apparatus used in the formation of the diamond film, and shows a quartz reaction tube 286, a Si substrate 287, a raw gas material supply system 288, a microwave source 289, a microwave guide tube 280, and a vacuum system 281.

After a Si substrate subjected to the scarring treatment with diamond abrasive particles was placed in the apparatus shown in Fig. 44, the interior was evacuated by means of the vacuum system 281, and carbon monoxide at a rate of 25 ml/min and hydrogen at a rate of 375 ml/min were introduced into the quartz reaction tube from the gas supply system. The pressure in the reaction tube was controlled to 5.3 kPa by the regulating valve, and with a microwave output of 4 kW supplied from the microwave source 289 and a substrate temperature of 900°C, the diamond layer with a thickness of 150 µm was synthesized in ten hours. A similarly synthetically produced diamond layer was a polycrystalline layer with clear side surfaces in SEM observation and showed a thermal conductivity of 1500 W/m-K in the radiation cooling process.

The heat generating resistor 3 was formed on the diamond layer at a predetermined position by applying Ag/Pd paste by screen printing, and it was trimmed to a desired resistance value if necessary based on the resistance value measurement. Then, the electrode terminal 4 was formed by applying Cu paste by screen printing. Then, aluminum oxide paste (adhesive agent) was applied. and then an alumina ceramic substrate 2 was applied and bonded by sintering. Then, the heater substrate was prepared by removing the Si substrate in the same manner as in Embodiment 24. The heater was completed by connecting the electrode tabs and lead wires to the electrode terminals and bonding to the heater holder. The heater thus obtained could achieve a stable fixing operation as in Embodiment 24 in thermally fixing the recording material as in Embodiment 24.

In the foregoing embodiments, the formation of a carbon layer on the protective layer, the resistance layer or the plastic film has been explained, but under certain circumstances or conditions in use, the carbon layer thus formed may be locally peeled off or damaged so that the heat fixing device may no longer be usable for the fixing operations.

The present invention also serves to eliminate the above-mentioned disadvantage by regenerating the locally peeled or damaged lubricating carbon protective layer on the heating element or on the plastic film, thereby providing a heat fixing device with a high durability (long life) and at a low cost.

Above all, according to this invention, the above-mentioned disadvantage can be eliminated by removing the carbon layer having a high hardness and a low friction coefficient formed as a lubricating protective layer on the insulating protective layer or the heat generating resistor of the heating element or on the plastic film by means of ashing (an oxidation treatment) and forming a carbon layer again.

The carbon layer of the present invention is a hydrogenated amorphous carbon layer (a-C:H layer), a diamond-like carbon layer (DLC layer) or a hard carbon layer. Also included is an a-C:H layer or a DLC layer containing at least one of the following elements: Ta, W, Mo, Nb, Ti, Cr, Fe, B, Si and fluorine. The a-C:H and DLC layers are characterized by certain physical properties, for example, represented by a thermal conductivity of 200-600 W/m·K, an electrical resistance (volume resistivity) of 10⁸-10¹¹ Ωcm, a hardness of 2000-5000 kg/mm² and a friction coefficient of less than 0.2. Also, the hard carbon layer is characterized by certain physical properties, for example, represented by a thermal conductivity of 200-600 W/m·K, an electrical resistance (volume resistivity) of 10⁸-10¹¹ Ωcm, a hardness of 2000-5000 kg/mm² and a friction coefficient of less than 0.2. B. can be represented by a hardness of 2000-5000 kg/mm², a friction coefficient u < 0.2 and an electrical resistivity (specific volume resistance) of 10⁵-10¹¹ Ω cm.

The oxidation can be achieved, for example, by microwave plasma CVD, DC plasma CVD, RF plasma CVD, magnetic field microwave plasma CVD, ion beam sputtering, ion beam evaporation or ion beam plating, which are used in the production of the above-mentioned a-C:H film, DLC film or hard carbon film. In these methods, oxygen is used as the reaction gas to generate an oxygen plasma or an oxygen ion beam to which the carbon film is exposed, thereby ashing (deoxidizing and removing) the carbon film. The reaction gas can be a mixture of oxygen with H₂, N₂, air, Ar or CF₄. Also, after the oxidation, the substrate can be etched with plasma or with an ion beam of H₂, N₂, air or CF₄. The ashing state can be perceived by monitoring the plasma in the ashing process using a spectroscopic method and thus the end point of the ashing process can be determined.

The lubricating protective layer of the heating element or plastic film is then reconditioned by re-forming the carbon layer using the layer formation process explained above. The ashing and reconditioning can be carried out sequentially in the same device or a washing step with an organic solvent is added after the ashing.

[Embodiment 26]

Fig. 45 is an enlarged partial sectional view of a heat fixing device using the heating element embodying the present invention, and this heating element 1 is supported by a heating element support 9 with the interposition of a heat insulating heating element holder 8. A heat-resistant film 10 is made of, for example, polyimide with a thickness of about 40 µm and is formed as an endless belt or an elongated sheet. A rotating pressure roller 11 serves as a pressing member for pressing the above-mentioned film toward the heating element 1. The film 10 rotates or moves at a predetermined speed in a direction indicated by an arrow in contact with the edges of the heater holder 8 and the front surface of the heater 1 on which it slides by a drive member (not shown) or by the rotational force of the pressure roller 11. The heat generating resistor 3 is electrically operated to heat the heater to a predetermined temperature, and a recording material 16 carrying an unfixed toner image 17 thereon on the side of the film 10 is introduced into a fixing nip 15 in the state of movement of the film 10. Thus, the recording material 16 is kept in contact with the film 10 and passes through the fixing nip together with the film 10. During the run, heat is imparted to the recording material 16 via the film 10 by the heating element 1 in order to fix the unfixed toner image 17 to the recording material by melting it.

46A to 46E are schematic sectional views of the heater of Embodiment 26, showing a heater 1, a ceramic substrate 2, an Ag/Pd heat generating resistor 3, Cu electrode terminals 4 and 5, an insulating glass protective layer 6, a DLC layer 122 containing a metal element, a heater holder 8, an electrode tab 12, AuSi solder 13, and a wire conductor 14. In the heater of this embodiment, Ag/Pd paste was first screen-printed on an Al₂O₃ substrate and then fired in air to form the heat generating resistor 3, which was then trimmed to a desired resistance value based on the resistance value measurement. Cu paste was then applied by screen printing, and the electrode terminals 4, 5 were formed by firing under a controlled oxygen partial pressure (Fig. 46A). Then, the insulating protective layer was formed by applying a lead silicate glass with a low softening point by screen printing, followed by firing in air (Fig. 46B). Then, a DLC layer 122 with a thickness of 400 nm was formed by ECR plasma CVD (Fig. 46C). Fig. 47 is a schematic diagram of an ECR plasma CVD apparatus used in the formation of the DLC film, and shows a cavity resonator type plasma chamber 290, a gas supply system 291, a microwave introduction window 292, a microwave guide tube 293, a magnet 294, a microwave oscillator 295, a substrate 296, a vacuum chamber 297, and a vacuum system 298. In a similar manner, a DLC film containing Si at 10 atomic % and a DLC film containing fluorine at 10 atomic % were formed to a thickness of 400 nm. The hydrogen content, Si content, fluorine content, film hardness and friction resistance of these DLC films were evaluated by HFS (hydrogen forward scattering spectrometry), EPMA, RBS (Rutherford back scattering spectrometry), a thin film hardness meter and a pin-on-plate method, respectively. The friction coefficient was measured in air with a relative humidity of 25% using a ball (5 mm in diameter) of a bearing steel (SUJ2) as a pin with a load of 1.2 N and a displacement speed of 0.04 m/s. The results obtained are summarized in Table 5. Table 5

Subsequently, the electrode tab 12 made of a copper alloy and the ceramic substrate 2 were soldered with the AuSi solder 13 (Fig. 46C). Then, the wire conductor 14 was held in contact with the electrode tab 12 and the heater substrate was made to adhere to the heater holder 8 (Figs. 46D and 46E). In the manufacture of the heater 1, the surfaces of the electrode terminals 4, 5 were given a quick Au coating to improve the wettability with the solder and thereby achieve a connection of constant reliability. The electrode tab may be made of Covar, 42 alloy or phosphor bronze instead of a copper alloy. The solder preferably has a melting point of at least 250°C and may be made of AuGe or AuSn instead of AuSi. Furthermore, soldering could be achieved in a more stable manner by flash plating the Cu electrode terminals with Au, Ni or Au/Ni to prevent oxidation and contamination until the soldering process. The Ni layer serves to prevent excessive diffusion of Cu into the solder.

A heat fixing device equipped with the heating element thus prepared was used in the continuous fixing of 300,000 unfixed images, and Local peeling was observed in each of the above-mentioned heating elements. Therefore, the regeneration of the heating element was carried out in the following manner.

After the heater was placed in the ECR plasma CVD apparatus used in the formation of the carbon layer, the vacuum chamber was evacuated to 1 x 10-7 Torr, and O2 was introduced in an amount of 100 sccm from the gas supply system to a pressure of 3 x 10-3 Torr. Then, an oxygen plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz with 1.0 kW. In this state, an external magnetic field was induced by the magnet to establish the ECR conditions of 1500 gauss at the insertion window, 875 gauss at the outlet of the cavity resonator, and 650 gauss at the position of the substrate. Under these conditions, ashing of the carbon layer was carried out on the insulating protective layer. The end point of ashing was monitored by the change in time of the intensity of ultraviolet light at 297.7 nm emitted by the electronically excited CO in the plasma using plasma emission spectroscopy. During the ashing process, the electrodes were masked to prevent oxidation.

After completion of ashing, the heater was taken out and subjected to DLC film formation using the same method and conditions as explained above. The hydrogen content, Si content, fluorine content, film hardness and friction coefficient in the regenerated DLC film were the same as those in the film before regeneration. The heat fixing device equipped with the heater thus regenerated showed stable fixing performance and durability equal to those before regeneration. Similar tests on the DLC film containing Ta, W, Mo, Nb, Ti, Cr, Fe or B produced similar results to those in the case of the DLC film containing Si.

[Embodiment 27]

To form the heat generating resistor layer, a recess of 350 mm x 2 mm x 12 µm was mechanically machined on an Al₂O₃ substrate similar to Embodiment 26. Ag/Pd paste of 11 µm thickness was screen printed into the recess and fired in air to form the heat generating resistor 3, which was then trimmed to a desired resistance value based on the resistance value measurement. Then, the substrate was set in a sputtering device (not shown), and a W (tungsten) layer 3a of 1 µm thickness was formed on the resistor layer to prevent mutual diffusion of Ag/Pd and C. In this, an a-C:H layer having a thickness of 500 nm was formed in an ion beam deposition (IBD) apparatus shown in Fig. 48. Fig. 48 shows a vacuum chamber 300, an ion beam source 301, an ionization chamber 302, a gas supply system 303, an ion beam exhaust electrode 304, a substrate 305, and a vacuum system 306. After the vacuum chamber was evacuated to 1 x 10-7 Torr, CH4 at 15 sccm and H2 at 30 sccm were introduced from the gas supply system to a pressure of 3.0 x 10-4 Torr to generate a plasma in the plasma chamber. By irradiating the substrate with an ion beam which was sucked by applying 0.8 kV to the suction electrode, an a-C:H layer was formed. The hydrogen content in the a-C:H layer, measured by HFS analysis, was 30 atomic %. Also, the layer hardness and friction coefficient, measured as in Embodiment 26, were 3000 kg/mm2 and 0.11, respectively.

A heat fixing device equipped with the heating element thus obtained developed local peeling when thermally fixing the recording material in the same manner as in Embodiment 26, and the heating element was regenerated in the following manner. After the heating element was used in the IBD device shown in Fig. 48 After the heating element was placed in a vacuum chamber, the vacuum chamber was evacuated to 1 x 10-7 Torr, and O2 was introduced from the gas supply system at 30 sccm to a pressure of 3 x 10-4 Torr, thereby generating an oxygen plasma in the plasma chamber. The carbon layer on the heater was ashed by irradiating it with an oxygen ion beam which was exhausted by applying a voltage of 0.5 kV to the exhaust electrode. Following the ashing, Ar was introduced from the gas supply system at 30 sccm to a pressure of 3 x 10-4 Torr, and the heat generating resistor layer and the ceramic substrate were etched by 5 nm with an Ar ion beam exhausted at a voltage of 0.5 kV. After the etching, the aC:H layer was reformed in the same manner as explained above. The regenerated aC:H layer was of the same quality as that before regeneration. The thermal fixing device equipped with the regenerated heater showed stable fixing performance and durability equal to those before regeneration in thermally fixing the recording material.

[Embodiment 28]

An aC:H layer containing Si was formed on a polyimide film having a thickness of 25 nm by using the ECR plasma CVD apparatus shown in Fig. 47, which was additionally provided with an exhaust electrode (grid) at the outlet of the cavity resonator. After the vacuum chamber was evacuated to 1 x 10-7 Torr, C6H6 at 30 sccm, H2 at 15 sccm and SiH4 at 10 sccm were introduced from the gas supply system to a pressure of 4.1 x 10-4 Torr, and a plasma was generated in the plasma chamber by introducing a microwave of 2.45 GHz at 1.5 kW. In this state, an external magnetic field was formed by means of the magnet to establish the ECR conditions of 1200 gauss at the insertion window, 875 gauss at the cavity resonator outlet and 650 gauss at the substrate position. Also, a voltage of -500 V was applied to the suction electrode (not shown) provided at the cavity resonator outlet to suck an ion beam, so that a layer having the composition a-C1-xSix:H was formed, wherein x was in a range of 0 ≤ · ≤ 0.4. When evaluated the same as in Embodiment 26, the obtained layer showed a layer hardness of 2500 kg/mm², a friction coefficient of 0.05, a hydrogen content of 20 atomic % and a Si content of 15 atomic %.

In the thermal fixation of the recording material similar to that of Embodiment 26, the thermal fixation device equipped with the thus obtained layer developed local peeling, and therefore the layer was regenerated in the following manner. After the polyimide film was placed in the ECR plasma CVD apparatus, the vacuum chamber was evacuated to 1 x 10-7 Torr, and O2 was introduced from the gas supply system at 10 sccm to a pressure of 3.0 x 10-3 Torr to generate an oxygen plasma in the plasma chamber. Ashing was carried out by irradiating the layer with oxygen plasma without applying a voltage to the exhaust electrode. After ashing, CF4 was added. at 30 sccm from the gas supply system to a pressure of 3 x 10-4 Torr, and the film was etched to 5 nm by the CF4 plasma irradiation. Then, the a-C1-xSix:H film was again formed by the method and conditions same as those explained previously. The regenerated film was of the same quality as the film before regeneration. The thermal fixing device equipped with this regenerated film showed stable fixing performance and durability in thermally fixing the recording material equal to those before regeneration.

[Embodiment 29]

In the same manner as in Embodiment 26, a hard carbon layer having a thickness of 300 nm was formed on the insulating protective layer as a lubricating protective layer. Fig. 49 is a schematic representation of a process used in the formation of the hard carbon layer. current magnetron sputtering apparatus and shows a vacuum chamber 310, a substrate 311, a graphite target 312 with a purity of 99.99%, a gas supply system 313, a DC power source 314 and a vacuum system 315. After the vacuum chamber was evacuated to 1 x 10-7 Torr, Ar was introduced from the gas supply system to a pressure of 0.9 Pa. In this process, the conditions of a substrate temperature at room temperature, a discharge power of 50 W and a substrate-target distance of 50 mm were used. Before film formation, the target was pre-sputtered for 20 minutes at 300 W. With the evaluations as in Embodiment 26, the obtained layer showed a layer hardness of 2100 kg/mm², a friction coefficient of 0.12 and a density of 2.8 g/cm³.

When the recording material was thermally fixed as in Embodiment 26, the thermal fixing device equipped with the heating element thus obtained developed local peeling, and therefore the heating element was regenerated in the following manner. The heating element was set in an RF plasma CVD apparatus shown in Fig. 50, which comprises a vacuum chamber 320, a gas supply system 321, an electrode 322, a substrate 323, a vacuum system 324 and an RF power source 325. After the vacuum chamber was evacuated to 1 x 10-7 Torr, O2 at 80 sccm and CF4 were supplied from the gas supply system. at 20 sccm to a pressure of 3.0 x 10-2 Torr, and an RF plasma was generated by introducing electric power of 1 kW from the RF power source. By exposing the heating element carrying the hard carbon layer to the said RF plasma, ashing was carried out. Then, by the same method and conditions as those previously explained, the hard carbon layer was regenerated. The regenerated layer was the same in quality as that before regeneration. The heat fixing device equipped with the heating element thus regenerated showed a stable fi Fixing performance is equal to that before regeneration during thermal fixation of the recording material.

Although the present invention has been explained by its preferred embodiments, this invention is in no way limited to these embodiments and is subject to various modifications within the scope of the appended claims.

Claims (35)

1. A heating element comprising: - an insulating substrate; - a resistive layer provided on said insulating substrate and capable of generating heat by supplying an electric current; and - a protective layer to protect the said resistive layer; - characterized in that - the protective layer mentioned contains at least on its surface a hard carbon layer, a hydrogenated, amorphous carbon layer or a diamond structure layer. 2. A heating element according to claim 1, characterized in that said hard carbon layer has a hydrogen concentration in the layer of less than 1 atomic % and a density of not less than 2.0 g/cm³. 3. A heating element according to claim 1, characterized in that the said diamond structure layer is a diamond-like carbon layer. 4. A heating element according to claim 1, characterized in that said hydrogenated amorphous carbon layer contains a metal. 5. A heating element according to claim 4, characterized in that the said metal is Ta, W, Mo, Nb, Ti, Cr, Fe, B or Si, the concentration of which in the layer is less than 30 atomic %. 6. A heating element according to claim 1, characterized in that said hydrogenated amorphous carbon layer contains fluorine. 7. A heating element according to claim 6, characterized in that the concentration of said fluorine in the layer is less than 3.0 atomic %. 8. A heating element according to claim 3, characterized in that said diamond-like carbon layer contains a metal. 9. A heating element according to claim 8, characterized in that the said metal is Ta, W, Mo, Mb, Ti, Cr, Fe, B or Si, the concentration of which in the layer is less than 30 atomic %. 10. A heating element according to claim 3, characterized in that said diamond-like carbon layer contains fluorine. 11. A heating element according to claim 10, characterized in that the concentration of said fluorine in the layer is less than 30 atomic %. 12. A heating element according to claim 1, characterized in that the said diamond structure layer is produced by means of gas synthesis. 13. A heating element according to claim 1, characterized in that the said protective layer consists entirely of a hard carbon layer, a hydrogenated amorphous carbon layer or a diamond structure layer. 14. A heating element according to claim 1, characterized in that said insulating substrate is provided with a recess and said resistive layer is formed in said recess. 15. A heating element according to claim 1, characterized in that said hard carbon layer or said hydrogenated amorphous carbon layer is removable by an oxidation treatment. 16. A heating element according to claim 3, characterized in that said diamond-like carbon layer is removable by an oxidation treatment. 17. An image heating device comprising: - a heating element; and - a film, one surface of which slides over said heating element and the other surface of which is in contact with an image on a recording material; - in which the image on the recording material is heated by the heat supplied by said heating element through said foil; - characterized in that - a hard carbon layer, a hydrogenated amorphous carbon layer or a diamond structure layer is present on a sliding part between said heating element and said foil. 18. An image heating device according to claim 17, characterized in that said heating element comprises an insulating substrate and a resistive layer provided on said insulating substrate and capable of generating heat by supplying electric current, and that said hard carbon layer, hydrogenated amorphous carbon layer or diamond structure layer is formed on said resistive layer. 19. An image heating device according to claim 17, characterized in that said heating element comprises an insulating substrate, a resistive layer provided on said insulating substrate and capable of generating heat by supplying electric current, and a protective layer to protect said resistance layer, and that said hard carbon layer, the hydrogenated amorphous carbon layer or the diamond structure layer is formed on said resistance layer. 20. An image heating device according to claim 17, characterized in that said hard carbon layer, the hydrogenated amorphous carbon layer or the diamond structure layer is provided on said film. 21. An image heating device according to claim 17, characterized in that said hard carbon layer has a hydrogen concentration in the layer of less than 1 atomic % and a density of not less than 2.0 g/cm³. 22. An image heating device according to claim 17, characterized in that said diamond structure layer is a diamond-like carbon layer. 23. An image heating device according to claim 17, characterized in that said hydrogenated amorphous carbon layer contains a metal. 24. An image heating device according to claim 23, characterized in that said metal is Ta, W, Mo, Nb, Ti, Cr, Fe, B or Si, the concentration of which in the layer is less than 30 atomic %. 25. An image heating device according to claim 17, characterized in that said hydrogenated amorphous carbon layer contains fluorine. 26. An image heating device according to claim 25, characterized in that the concentration of said fluorine in the layer is less than 30 atomic %. 27. An image heating device according to claim 22, characterized in that said diamond-like carbon layer contains a metal. 28. An image heating device according to claim 27, characterized in that said metal is Ta, W, Mo, Nb, Ti, Cr. Fe, B or Si, the concentration of which in the layer is less than 30 atomic %. 29. An image heating device according to claim 22, characterized in that said diamond-like carbon layer contains fluorine. 30. An image heating device according to claim 29, characterized in that the concentration of said fluorine in the layer is less than 30 atomic %. 31. An image heating device according to claim 17, characterized in that said diamond structure layer is produced by means of gas synthesis. 32. An image heating device according to claim 18, characterized in that said insulating substrate is provided with a recess and said resistive layer is formed in said recess. 33. An image heating device according to claim 19, characterized in that said insulating substrate is provided with a recess and said resistive layer is formed in said recess. 34. An image heating device according to claim 17, characterized in that said hard carbon layer or said hydrogenated amorphous carbon layer is removable by an oxidation treatment. 35. An image heating device according to claim 22, characterized in that said diamond-like carbon layer is removable by an oxidation treatment.