Heater and method of forming a heater

A heater includes a heater unit and a holder. The heater unit includes a flat and smooth substrate, a linear heat generator provided on a first surface of the substrate, a plurality of electrodes that supply power to the heat generator, and a protective layer disposed to cover a part of each of the electrodes and the heat generator. A second surface of the substrate is bonded to the holder. The substrate is formed of a transparent material. A plurality of positioning marks for determining the relative positions of the heater unit and the holder are disposed on the first surface of the substrate. The holder has through-holes formed at positions opposite to the positioning marks.

CLAIM OF PRIORITY

This application claims benefit of priority to Japanese Patent Application No. 2014-216010 filed on Oct. 23, 2014, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The present disclosure relates to a heater used as a heat source of a toner fixing device in a copying machine or the like.

2. Description of the Related Art

In recent years, a heater having a linear heat generator, having a low heat capacity, has been used as a heat source of a toner fixing device in a copying machine, an electro-photographic printer, or the like. A toner fixing device in which such a heater is incorporated has the advantage of achieving power saving and a reduction in wait time compared to a toner fixing device employing a heat roller system, a heat plate system, a flash fixing system, an oven fixing system, or the like.

Examples of such heaters include a heating element of a fixing device described in Japanese Unexamined Patent Application Publication No. 2-157886, and a heating element of a fixing device described in Japanese Unexamined Patent Application Publication No. 9-068877.

The heating element820described in Japanese Unexamined Patent Application Publication No. 2-157886 will be described below with reference toFIG. 13.FIG. 13is a plan view showing the configuration of the heating element820.

As shown inFIG. 13, the heating element820includes a heater body821aand a heater body holding member820a. The heater body821aincludes an alumina substrate821, a heat generator822made of silver-palladium (Ag/Pd) that is formed substantially in the center of the surface of the alumina substrate821along the longitudinal direction by screen printing in a linear or band-like shape, and a wear-resistant material such as glass. The temperature of a fixing nip part corresponding to the heat generator822is maintained and controlled at a predetermined fixing temperature. Using a side wall surface820kof a horizontally long slot820bof the heater body holding member820aas a surface reference K, the heater body821ais fitted into the slot820bwith a longitudinal side wall surface821kof the alumina substrate821in close contact with the surface reference K, and is integrally attached to and held by the heater body holding member820a. Owing to the surface reference K, the heat generator822can be positioned.

In the fixing device described in Japanese Unexamined Patent Application Publication No. 9-068877, in order to improve the positional precision, the following structure is discussed. The fixing device911described in Japanese Unexamined Patent Application Publication No. 9-068877 will be described below with reference toFIGS. 14 and 15.FIG. 14is a sectional view showing the schematic configuration of the fixing device911.FIG. 15is a bottom view showing a heater substrate922of the heating element920of the fixing device911.

As shown inFIG. 14, the fixing device911includes a fixing film925, a moving driving means for the fixing film925, the heating element920, and a pressure roller928. The heating element920includes a heater support921and the heater substrate922. The heater substrate922is a flat plate formed of alumina, aluminum nitride, or the like, and is embedded in the heating element920. The heating element920and the pressure roller928are disposed opposite to each other with the fixing film925interposed therebetween. As shown inFIG. 15, the heater substrate922is provided with a heat generator923formed integrally with electrodes931, and marks930for position adjustment of the heat generator. The heat generator923and the marks930for position adjustment of the heat generator are printed patterns formed by collective printing using the same printing plate.

However, if the positional precision of the linear heat generator is low, toner disposed on a recording material cannot be heated appropriately. In the case of the heating element820of the fixing device described in Japanese Unexamined Patent Application Publication No. 2-157886, the positional precision of the heat generator822may be deteriorated owing to the processing variation of the heater body holding member820aand the processing variation of the alumina substrate821. In the case of the fixing device911described in Japanese Unexamined Patent Application Publication No. 9-068877, the heat generator923and the electrodes931are often covered with a protective layer in order to secure durability and insulation thereof. When a protective layer is formed over the marks930for position adjustment of the heat generator, the outlines of the marks930for position adjustment of the heat generator may not be clearly visible. In particular, when the protective layer is formed by screen printing, surface roughness due to a mesh of a printing plate is left on the surface, therefore light is scattered, the outlines of the marks930for position adjustment of the heat generator are not clearly visible, and highly precise positioning is difficult. Therefore, with such a structure of the heat generator, highly precise positioning cannot be performed easily.

SUMMARY

In an aspect of the present invention, a heater includes a heater unit and a holder. The heater unit includes a flat and smooth substrate, a linear heat generator provided on a first surface of the substrate, a plurality of electrodes configured to supply power to the heat generator, and a protective layer disposed to cover a part of each of the electrodes and the heat generator. A second surface of the substrate is bonded to the holder. The holder is attached to an external device. The substrate is formed of a transparent material. A plurality of positioning marks for determining relative positions of the heater unit and the holder are disposed on the first surface. The holder has through-holes formed at positions opposite to the positioning marks.

This configuration makes it possible to observe the positioning marks provided on the first surface of the substrate formed of a transparent material through the through-holes of the holder. In addition, since the substrate is flat and smooth, and the interface between each positioning mark and the substrate is flat and smooth, the positioning marks are clearly visible without being affected by the scattering of light when the positioning marks formed on the first surface of the substrate is viewed from the second surface. The precision of positioning when incorporating the heater into the external device is thereby improved.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

First Embodiment

Embodiments of the present invention will now be described in detail with reference to the drawings. For ease of understanding, dimensions are changed in the drawings.

FIG. 1is a schematic sectional view showing the configuration of an external device100to which a heater1of a first embodiment of the present invention is attached.FIG. 2is an exploded perspective view schematically showing the heater1of the first embodiment of the present invention.FIG. 3is a schematic plan view showing the heater1as viewed from the Z1 direction shown inFIG. 2.FIG. 4is a schematic bottom view illustrating the arrangement of a heating element16, electrodes15, and a protective layer17that are visible through a substrate11when a heater unit10is viewed from the Z2 direction shown inFIG. 2.FIG. 5is a schematic sectional view showing the heater unit10taken along line V-V ofFIG. 4.FIG. 6is a schematic sectional view showing the heater unit10taken along line VI-VI ofFIG. 4.FIG. 7is a schematic plan view showing a holder30as viewed from the Z1 direction shown inFIG. 2.FIG. 8is a schematic bottom view showing the holder30as viewed from the Z2 direction shown inFIG. 2.FIG. 9is a schematic sectional view showing the heater1taken along line IX-IX ofFIG. 3.FIG. 10is a schematic sectional view showing the heater1taken along line X-X ofFIG. 3. In these figures, a connecting part with an external power source is omitted.

As shown inFIG. 1, the heater1of the first embodiment of the present invention is attached for use to the external device100that is a toner fixing device. The external device100includes the heater1, a belt110, and a pressure roller120. As shown inFIGS. 2 and 3, the heater1includes the heater unit10and the holder30. The toner fixing device applies heat and pressure to toner disposed on recording paper, thereby fixing the toner on the recording paper. The external device100is configured such that the belt110moves with the rotation of the pressure roller120. By being pressed against the heater unit10, the belt110is heated, and fixes the toner on the recording paper.

By controlling the heat generation of the heater unit10in a desired state just before the toner disposed on the recording paper is nipped between the pressure roller120and the belt110, power can be saved.

The heater unit10of the heater1is housed in a slot31formed in the holder30, is positioned as described later, and is then fixed. The planar dimension of the slot31is larger than the dimension of the heater unit10so that the position adjustment of the heater unit10can be performed. For example, adhesive is used for fixing the heater unit10, and the Z2 side surface of the heater unit10and the opposite surface of the slot31of the holder30are bonded together with the adhesive. Only part of the heater unit10may be bonded. So, for example, part of the opposite surface along the outer periphery of the heater unit10may be bonded without bonding the central part of the heater unit10. In this case, a recess may be provided in the central part of the slot31so that a space is provided between the central part of the slot31and the Z2 side surface of the heater unit10. In the following description, the Z1 side ofFIG. 2will be referred to as “the upper side,” and the Z2 side ofFIG. 2will be referred to as “the lower side.” This is only for ease of understanding of the description, and “the upper side” and “the lower side” in the following description are different from those in the usage state shown inFIG. 1.

As shown inFIGS. 4 to 6, the heater unit10includes the flat and smooth substrate11, the plurality of electrodes15, the linear heat generator16, the protective layer17, and positioning marks18.

The substrate11is a flat plate-like insulator formed of a transparent material, and has heat resistance. The substrate11is preferably formed of glass.

The electrodes15are conductors formed by firing a conductive coating film patterned by screen printing on a first surface11aof the substrate11. The electrodes15are preferably formed of a highly conductive material such as silver, gold, or copper. The electrodes15include a comb-shaped electrode12and L-shaped electrodes13. The electrodes15are connected to a power source (not shown) at the ends thereof, and supply power supplied from the power source to the heat generator16.

The heat generator16is a resistor that generates heat when supplied with power. The heat generator16has a rectangular shape. The heat generator16is formed by forming a resistor coating film by screen printing on the first surface11aof the substrate11on which the electrodes15are formed, and firing the resistor film. The heat generator16is preferably formed of an electric resistance material such as RuO2 or Ag/Pd.

As shown inFIG. 4, the comb-shaped electrode12includes a comb-shaped electrode12aprovided parallel to the long side of the heat generator16and comb-shaped electrodes12bprovided perpendicularly to the long side of the heat generator16. The comb-shaped electrode12ais disposed a predetermined distance apart from the heat generator16in the Y1 direction of the heat generator16. The comb-shaped electrodes12bare disposed at regular intervals in the longitudinal direction of the heat generator16. The L-shaped electrodes13each include an L-shaped electrode13aprovided parallel to the long side of the heat generator16and an L-shaped electrode13bprovided perpendicularly to the long side of the heat generator16. The L-shaped electrodes13aare disposed apart from the heat generator16in the Y2 direction of the heat generator16. The L-shaped electrodes13bare disposed at regular intervals in the longitudinal direction of the heat generator16between the comb-shaped electrodes12b. In the example shown inFIG. 4, the heat generator16is divided into six parts. However, the present invention is not limited to this, and the heat generator16may be divided into any number of parts.

Thus, current when power is supplied from the power source flows between the comb-shaped electrodes12band the L-shaped electrodes13b, and causes the heat generator16to generate heat. In other words, the heat generating area of the heat generator16is determined by the arrangement of the electrodes15and which of the L-shaped electrodes13bare supplied with power. For example, only part of the heating area can be caused to generate heat according to the width of the recording paper, or according to the area where toner is disposed.

The positioning marks18each include a first positioning mark18aformed in the same step as the heat generator16and a second positioning mark18bformed in the same step as the electrodes15. As shown inFIG. 4, the positioning marks18are disposed apart from the comb-shaped electrodes12band the L-shaped electrode13blocated at both longitudinal ends of the heat generator16, one on each side of the heat generator16. The first positioning mark18aand the second positioning mark18bare provided so as to crisscross in directions parallel to and perpendicular to the longitudinal direction of the heat generator16.

In this embodiment, the step of forming the electrodes15and the second positioning marks18bon the first surface11aof the substrate11is performed, and then, the step of forming the heat generator16and the first positioning marks18ais performed. As shown inFIG. 5, at positions where the electrodes15are formed on the first surface11aof the substrate11, the heat generator16is formed on the upper side (Z1 side) of the electrodes15. As shown inFIG. 6, at positions where the second positioning marks18bare formed, the first positioning marks18aare formed on the upper side (Z1 side) of the second positioning marks18b.

The protective layer17is a thick film of insulator formed by firing a coating film formed of inorganic paste containing particles by screen printing. The protective layer17is formed, for example, of a glass material, and is a thick film containing 0.1 wt % to 30 wt % of hard glass particles having a particle diameter of 0.1 μm to 10 μm. The main component of the protective layer17and the size and amount of particles included in the protective layer17are not limited to this. As shown inFIGS. 5 and 6, the protective layer17is formed on substantially the entire first surface11aof the substrate11so as to cover the electrodes15, the heat generator16, and the positioning marks18. The ends of the electrodes15are exposed from the protective layer17so that they can be electrically connected with the power source (not shown).

Since part of the protective layer17on the heat generator16is heated to a high temperature by the heat generation of the heat generator16, the protective layer17has to be formed of a highly heat-resistant material. In addition, since temperature distribution is produced, the protective layer17preferably has a low thermal expansion coefficient and resistance to thermal stress. Further, since the heater1is attached for use to the external device100that is a toner fixing device as shown inFIG. 1, the protective layer17is preferably has wear resistance in contact with the belt110.

Since, in this embodiment, the protective layer17contains particles, the physical properties of the protective layer17can be modified. For example, in order to improve wear resistance, hard glass particles or alumina particles can be included. By including particles, the thermal expansion coefficient can be adjusted.

Owing to surface roughness caused by a mesh of a printing plate when the protective layer17is formed by screen printing, light is scattered by the surface when the protective layer17is viewed from the Z1 direction, the protective layer17is visually white and opaque, and therefore the positioning marks18are less visible. In the case of the protective layer17formed of inorganic paste containing particles by screen printing, the surface roughness is significant, and the protective layer17is whiter and opaquer.

The holder30is a molding formed by molding synthetic resin. As shown inFIG. 7, the holder30has a slot31formed therein, and through-holes32extending from the bottom surface of the slot31to the lower side (Z2 side) surface of the holder30. As shown inFIG. 8, the holder30further has reference portions33. In this embodiment, the reference portions33are holes (seeFIG. 10).

The heater unit10is bonded into the slot31of the holder30with an adhesive. At this time, positioning can be performed in advance while viewing the positioning marks18of the heater unit10through the through-holes32from the second surface11bside of the substrate11.

Since the first positioning marks18aof the heater unit10are formed in the same step as the heat generator16, the positional relationship with the heat generator16is fixed. Therefore, highly precise positioning relative to the heat generator16is performed by aligning the first positioning marks18awith the reference positions. Since the second positioning marks18bof the heater unit10are formed in the same step as the electrodes15, the positional relationship with the electrodes15is fixed. Since the electrodes15are formed so as to be located at both longitudinal ends of the heat generator16, highly precise positioning relative to the electrodes15is performed by aligning the second positioning marks18bwith the reference positions.

The slot31of the holder30is formed larger than the outline of the heater unit10in plan view shownFIG. 3, and the position of the heater unit10can be fine-tuned in the X1-X2 direction and the Y1-Y2 direction. In addition, the position of the heater unit10can be fine-tuned in the rotation direction within that margin range. Thus, fine tuning is performed such that the first positioning marks18aand the second positioning marks18bviewed through the through-holes32shown inFIGS. 9 and 10are located at desired positions relative to the reference portions33of the holder30, and the relative positions of the heater unit10and the holder30is thereby determined. For example, the reference portions33of the holder30are fixed to a jig, and a worker performs fine tuning such that the heater unit10is located at a predetermined position relative to the reference portions33while observing from the lower side using a microscope. Then, the heater unit10is fixed with adhesive so that the heater unit10is not displaced. Although not shown inFIGS. 9 and 10, the adhesive is applied to the bonding surfaces of the heater unit10and the holder30. In the case where the adhesive is applied to the lower surface of the heater unit10and the upper surface of the holder30, position adjustment is performed, for example, after the adhesive is applied and before the adhesive cures. In the case of a thermosetting adhesive, the adhesive is hardened by heating after the position adjustment, with the heater unit10temporarily fixed so as not to be displaced.

Since the holder30has reference portions33, the heater1of this embodiment can be precisely attached to the external device100. Since the heater unit10is positioned using the reference portions33of the holder30as references, the heat generator16can be highly precisely positioned without performing position adjustment while checking the positions of the heat generator16and the positioning marks18when incorporating the heater1into the external device100. Alternatively, position adjustment may be performed, without using the reference portions33, directly relative to the reference positions of the external device100while viewing the positioning marks18through the through-holes32of the holder30when attaching the heater1to the external device100.

The positioning marks18are formed between the protective layer17and the substrate11. The protective layer17looks white owing to the surface roughness of the upper side (Z1 side) thereof and the particles contained therein. Therefore, the positioning marks18are difficult to check from the upper side (Z1 side). Since the substrate11of the heater1of this embodiment is formed of a transparent material, the positioning marks18can be clearly checked from the second surface11bof the substrate11. Since the through-holes32of the holder30of the heater1of this embodiment are formed at positions coincident with the positioning marks18in plan view, the positioning marks18are visible from the lower side (Z2 side) of the holder30. In addition, since the substrate11is flat and smooth, the positioning marks18looks flat and smooth when the positioning marks18formed on the first surface11aof the substrate11is viewed from the second surface11b. Since the interface between each positioning mark18and the first surface11aof the substrate11is flat and smooth, the outlines of the positioning marks18observed through the through-holes32from the lower side (Z2 side) of the holder30can be clearly distinguished without being affected by the scattering of light or the like. In addition, since the surface roughness of the upper side (Z1 side) of the protective layer17and the particles contained in the protective layer17render the background of the positioning marks18observed from the Z2 side of the holder30white and opaque, the outlines of the positioning marks18are rendered clearer. Therefore, the heater1can be precisely positioned.

The positioning marks18each include a first positioning mark18acorresponding to the position of the heat generator16and a second positioning mark18bcorresponding to the positions of the electrodes15. This configuration makes it possible to more reliably position the heat generator16in the feed direction and the electrodes15in the longitudinal direction.

Advantageous effects of this embodiment will be described below.

The heater1of this embodiment includes a heater unit10and a holder30to be attached to an external device100. The heater unit10includes a flat and smooth substrate11, a linear heat generator16provided on a first surface11aof the substrate11, a plurality of electrodes15that supply power to the heat generator16, and a protective layer17formed so as to cover the heat generator16and the electrodes15. A second surface11bof the substrate11is bonded to the holder30. The substrate11is formed of a transparent material. A plurality of positioning marks18for determining the relative positions of the heater unit10and the holder30are formed on the first surface11aof the substrate11. The holder30has through-holes32formed at positions opposite to the positioning marks18.

This configuration makes it possible to observe the positioning marks18provided on the first surface11aof the substrate11formed of a transparent material through the through-holes32of the holder30. In addition, since the substrate11is flat and smooth, and the interface between each positioning mark18and the substrate11is flat and smooth, the positioning marks18are clearly visible without being affected by the scattering of light when the positioning marks18formed on the first surface11aof the substrate11is viewed from the second surface11b. The precision of positioning when incorporating the heater1into the external device100is thereby improved.

In the heater1of this embodiment, the holder30has reference portions33used as references for attachment to the external device100. This configuration makes it possible to attach the heater1precisely by aligning the positioning marks18with the reference portions33of the holder30in advance and thereby aligning the reference portions33of the holder30with the external device100.

In the heater1of this embodiment, the positioning marks18are formed between the protective layer17and the substrate11. Owing to this configuration, the lower surfaces of the positioning marks18provided on the flat and smooth substrate11are flat and smooth surfaces, and therefore the outlines of the positioning marks18observed from the lower side of the holder30can be clearly distinguished without being affected by the scattering of light or the like. Therefore, the heater1can be precisely positioned.

In the heater1of this embodiment, the positioning marks18each include a first positioning mark18acorresponding to the position of the heat generator16and a second positioning mark18bcorresponding to the positions of the electrodes15. This configuration makes it possible to more reliably position the heat generator16in the feed direction and the electrodes15in the longitudinal direction.

In the heater1of this embodiment, the first positioning marks18aare formed in the same step as the heat generator16, and the second positioning marks18bare formed in the same step as the electrodes15. Owing to this configuration, the positional relationship between the first positioning marks18aand the heat generator16is accurate, and the positional relationship between the second positioning marks18band the electrodes15is accurate, and therefore positioning can be precisely performed.

In the heater1of this embodiment, the protective layer17is a thick film formed by screen printing. Owing to this configuration, surface roughness due to a mesh of a printing plate is left on the protective layer17formed by screen printing, therefore light is scattered, the background of the positioning marks18looks white and opaque when viewed from the second surface11b, and therefore the positioning marks18can be observed more clearly.

In the heater1of this embodiment, the protective layer17contains particles. This configuration renders the protective layer17whiter and opaquer, and therefore the positioning marks18can be observed much more clearly.

In the heater1of this embodiment, the external device100is a toner fixing device. Owing to this configuration, the heat generator16in the toner fixing device can be accurately positioned, and therefore heating efficiency is improved.

Although the heater1of the first embodiment of the present invention has been described specifically, the present invention is not limited to the above-described embodiment, and various changes may be made therein without departing from the spirit of the present invention. The embodiment of the present invention may be modified, for example, as follows, and these are also included in the technical scope of the present invention.

(1) In this embodiment, the protective layer17is the uppermost layer. However, as shown inFIGS. 11 and 12, a heat transfer layer19may be provided on the upper surface of the protective layer17.FIG. 11is a schematic plan view of a heater2of a modification as viewed from the upper side (Z1 side) shown inFIG. 2.FIG. 12is a sectional view at the same position asFIG. 5. The heater2of the modification is the same as the heater1except that the heat transfer layer19is provided on the upper surface of the heater unit10. The heat transfer layer19is formed so as to cover the heat generator16in plan view, in a larger area. The heat transfer layer19is preferably formed of a material having high heat conductivity and high impact resistance. The possibility that the protective layer17is damaged by thermal shock is reduced, and the durability of the heater2is thereby improved.
(2) In this embodiment, the electrodes15are conductive coating films collectively formed by screen printing. However, the electrodes15may be formed in two operations: a screen printing operation to form the comb-shaped electrodes12band the L-shaped electrodes13b, and a screen printing operation to form the comb-shaped electrode12aand the L-shaped electrodes13a. The comb-shaped electrode12aand the L-shaped electrodes13amay be formed in separate screen printing operations. In these cases, the second positioning marks18bmay be collectively formed in the screen printing operation to form the comb-shaped electrodes12band the L-shaped electrodes13b.
(3) In this embodiment, the positioning marks18are formed one on each of the X1 side and the X2 side. However, the positioning marks18may be formed at two locations on the Y1 side and the Y2 side. By performing position adjustment using positioning marks18at a total of four locations, positioning can be performed more precisely. Similarly, the reference portions33of the holder30may be provided at four locations for position adjustment. Although the positioning marks18are formed in a cross shape, the shape of the positioning marks18is not limited to this, and the positioning marks18may have any shape as long as positioning is possible. Similarly, although the reference portions33of the holder30are holes, the present invention is not limited to this, and the reference portions33may be slots or protrusions.