JPH08286497A - Toner carrier and its production - Google Patents

Abstract

PURPOSE: To carry a large amt. of toner and to prevent scattering of toner of production of a moire pattern by forming a conductive part and lots of separated dielectric parts to form small closed electric fields between the dielectric part and the conductive part on the surface in such a manner that each dielectric part projects from the conductive part. CONSTITUTION: The surface of this toner carrier has a conductive part 15a and lots of separated dielectric parts 16 to form small closed electric fields between the dielectric part and the conductive part 15a. Each dielectric part 16 is formed so as to project from the plane of the conductive part 15a. The dielectric parts 16 are formed like islands on the surface of a conductive base body 15A. The surface of the conductive base body 15A acts as the conductive part 15a for the dielectric parts 16. When the obtd. developing roller 15 is used, clogging of a toner is hardly caused because the dielectric parts 16 are formed in projecting shape, which prevents the toner from scattering. Thus, soiling by the toner in the machine can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner carrier used in a developing device of an image forming apparatus and a manufacturing method thereof.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electronic copying machine, a printer, or a facsimile, which obtains a recorded image by visualizing an electrostatic latent image formed on a latent image carrier as a toner image, an auxiliary is provided if necessary. It is well known in the prior art to employ a developing device that uses a toner to which an agent is externally added, that is, a one-component developer.

In this type of developing device, toner is carried on a toner carrier and conveyed, and an electrostatic latent image formed on the latent image carrier is developed in a developing area where the latent image carrier and the toner carrier face each other. The image is visualized by the toner on the toner carrier.

FIG. 4 shows an example of such a developing device. In the figure, a belt-shaped photosensitive member 1 which is an example of a latent image carrier is driven in the direction of arrow a, and a developing device 2 is provided facing the photosensitive member 1. In the toner container 3 of the developing device 2, a toner 4 to which an auxiliary agent is externally added as needed, that is, a one-component developer is stored.

A developing roller 5 is supported on the front and rear side plates of the toner container 3 with a part thereof exposed from the opening of the container. The roller 5 faces the photoconductor 1 and rotates counterclockwise in the figure. Driven. The developing roller 5 constitutes an example of the structure of the toner carrier, but a toner carrier composed of a developing belt may be used instead of the roller 5. A toner supply roller 6 is supported on the front and rear side plates of the toner container 3, and the roller 6 is rotationally driven counterclockwise, for example, while being in contact with the developing roller 5.

The toner 4 in the toner container 3 is carried to the toner supply roller 6 while being stirred by the agitator 7.
Then, the developing roller 5 is supplied by this roller 6. During this supply, the toner is triboelectrically charged to a predetermined polarity,
It is electrostatically attached to the peripheral surface of the developing roller 5 and is carried by the developing roller 5.

As described above, the toner supplied and carried on the peripheral surface of the developing roller 5 is conveyed by the rotation of the roller 5, leveled by the doctor blade 8, and regulated into a layer having a uniform thickness. Next, this toner is conveyed to the developing area 9 between the photoconductor 1 and the developing roller 5, where it is electrostatically transferred to the electrostatic latent image formed on the photoconductor 1, and the latent image is transferred to the toner image. Is visualized as.

The toner that has passed through the developing area 9 without being used for development is returned to the toner supply roller 6 while being carried by the developing roller 5. The toner image formed on the photoconductor 1 is transferred to a transfer sheet (not shown), and the toner image on the transfer sheet is fixed on the transfer sheet by a fixing device (not shown).

As described above, the developing device using the one-component type developer can simplify the maintenance and control of the device and can reduce the structure of the device as compared with the developing device using the two-component type developer containing the carrier in addition to the toner. The advantage of miniaturization is obtained.

On the other hand, on the other hand, it is difficult to carry a sufficient amount of toner on the toner carrier and convey it to the developing area, and the amount of toner to be used for development is insufficient and the density of the toner image is lowered. May occur.

Therefore, by selectively retaining the electric charge on the surface of the toner carrier, a minute closed electric field (microfield) is formed in the vicinity of the surface of the carrier, and the action of this closed electric field causes the toner carrier to remain on the toner carrier. Various developing devices have been proposed in which a large amount of toner is attached to the toner and the electrostatic latent image is visualized by the toner. According to this developing device,
Due to the action of the minute closed electric field, a sufficient amount of sufficiently charged toner can be carried on the toner carrier, and this can be conveyed to the developing area, so that a high-quality visible image can be formed.

The toner carrier for forming a minute closed electric field includes
There are the following types. (1) A dispersion type in which a conductor substance is dispersed in a dielectric substance, and this mixture is applied onto a conductive substrate (for example, a core metal) to uniformly expose the dielectric portion on the surface. (2) A type in which a conductive material is dispersed in a dielectric material and the dispersed fibers are wound around and melted to evenly disperse the dielectric portion. (3) A knurled type in which vertical and horizontal grid-like grooves are formed in a conductive substrate and a thermosetting resin is embedded in the grooves.

By the way, FIG. 5 shows the developing roller 5, and the roller-shaped conductive substrate (core metal) 5A is made of a conductor made of a metal such as aluminum. By forming the groove of (1) and embedding a dielectric substance made of a thermosetting resin in the groove, the knurl type developing roller of (3) described above is obtained. FIG. 6 is a schematic enlarged cross-sectional view of a part of the developing roller. In the figure, reference numeral 10 indicates
This is a dielectric portion formed by an embedded thermosetting resin, and this dielectric portion 10 is exposed in a dispersed state on the surface of the conductive substrate 5A in a minute width.

The toner 4 carried to the developing roller 5 in contact with the peripheral surface of the toner supplying roller 6 shown in FIG. 4 is supplied to the developing roller 5 while being frictionally charged to a predetermined polarity by friction with the toner supplying roller 6. At this time, the friction with the developing roller 5 causes the toner to be more strongly triboelectrically charged.

At this time, the conductive substrate 5A of the developing roller 5
Is grounded by applying a predetermined bias voltage, and the dielectric portion 10 of the developing roller 5 is triboelectrically charged with a polarity opposite to that of the toner, and a conductive portion (conductive base 5A Since the portion) is exposed, the surface of the developing roller 5 is in a state in which the electric charge having the polarity opposite to that of the toner is selectively applied to the dielectric portion 10. As a result, a closed electric field is formed between the conductive portion and the charged dielectric portion 10 around the conductive portion. That is, a minute closed electric field (microfield) E is formed near the surface of the developing roller 5. The strength of such a closed electric field becomes very strong due to the so-called edge effect or fringing effect, so that the charged toner is strongly attracted to the surface of the dielectric portion 10 and a large amount of toner is difficult to separate on the developing roller 5. Held in.

The toner carried on the developing roller 5 is regulated in layer thickness by the doctor blade 8 (FIG. 4), whereby a toner layer is formed. At this time, the sufficiently charged toner is strongly held on the surface of the developing roller 5 by the minute closed electric field, but the toner having a small amount of charge is removed by the contact pressure with the doctor blade 8, and in the end, it is sufficiently necessary. The toner having a large amount of charge is conveyed to the developing area 9, and the electrostatic latent image is visualized as a toner image by the toner. In this way, the image density of the visible image can be reliably increased.

Here, in the toner carriers of the above-mentioned types (1) and (2), the dispersed conductor substances are released from each other in the dispersion layer, and they do not come into sufficient contact with the conductive substrate. , The micro-field effect is insufficient and it has not been put to practical use so far. The knurled type (3) also has the following problems.

(A) Since vertical and horizontal grid-like grooves are formed in the conductive substrate by grinding at the time of manufacturing the developing roller,
When the completed developing roller is used, grooves having a regular pitch are left, and a moire pattern may be generated on the image depending on the selection of the photosensitive member and the peripheral speed of the developing roller. If it is attempted to suppress this occurrence, the degree of freedom in selecting the peripheral speed of the photosensitive member or the like is limited, or the grating groove pitch is forced to be changed, so that the mechanical design margin is lost. (B) A thermosetting resin is used as a dielectric substance, which is applied on a conductive substrate and then dried and solidified.
Although the surface is polished to form a flat surface, a dent is formed in the dielectric portion before it is completely cured, and toner accumulates in the dent while the image forming operation is performed by the developing roller. , Causing toner scattering.
When the heating temperature is raised and the resin is completely cured and polished, the dielectric portion is less likely to be dented, but the volume resistivity is too large and it is difficult to obtain a good image.

Further, as a manufacturing problem, there are the following problems. (A) When the dielectric substance is coated on the groove of the conductive substrate, it is impossible to pour the resin only into this groove. Therefore, as described above, the resin is applied to the entire surface of the conductive substrate and dried. Although the dielectric part is exposed by polishing from above, the manufacturing process is likely to be complicated because a polishing process is required. (B) In the above process, the resin is poured into the groove, so that air bubbles are often generated, and the partial holding property of the dielectric part is deteriorated, resulting in variation in quality.

[0020]

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner carrier which eliminates the above-mentioned conventional drawbacks and a method for producing the same.

[0021]

In order to achieve the above-mentioned object, the present invention forms a conductive portion and a large number of spaced apart dielectric portions for forming a minute closed electric field between the conductive portions on the surface. The toner carrier is proposed in which each dielectric portion is convex so as to protrude from the surface of the conductive portion.

In this case, in the above structure, the conductive portion is the surface of the conductive substrate, the dielectric portion is the dispersed scattered dielectric portion on the surface of the conductive substrate, and each dielectric portion is rounded. It is advantageous to form a convex shape having

Further, in order to achieve the above-mentioned object, the present invention holds the conductive substrate at a temperature below the melting point of the vapor deposition material to be the dielectric portion and in the vicinity of the melting point, and vacuum-depositing the dielectric portion. A method of manufacturing a toner carrier to be formed is proposed.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic enlarged sectional view showing a part of a toner carrier according to an embodiment of the present invention. In the figure, a developing roller 15 which is an example of the configuration of a toner carrier.
5 has an appearance substantially the same as that of the developing roller 5 shown in FIG. 5, and numeral 15A indicates a roller-shaped conductive base made of a conductive material such as metal, and shown in FIG. It corresponds to the conductive base 5A. The symbol A shown in FIG. 5 is the axial direction of the developing roller 5, and the symbol B is the circumferential direction of the same, but A shown in FIG. 1 also indicates the axial direction of the developing roller 15. FIG. 3 is a diagram schematically showing a part of the surface of the developing roller 15 in a greatly enlarged manner. Also in this figure, A is the axial direction of the developing roller and B is the circumferential direction thereof.

As described above, in the conventional toner carrier, a groove is formed in the conductive substrate and a thermosetting resin is embedded in the groove to form a dielectric portion, and the surface is smoothed as a whole. The developing roller 15 shown in FIGS. 1 and 3 has a shape, but the conductive portion 15a and a large number of spaced apart dielectric portions for forming a minute closed electric field between the conductive portion 15a. 16 are formed on the surface, and each dielectric part 16
Has a convex shape so as to project outward from the surface of the conductive portion. The dielectric part 16 is formed on the surface of the conductive substrate 15A by the manufacturing method described later so as to be dispersed and scattered in an island shape as shown in FIG. With respect to the dielectric portion 16, the ground of the conductive base 15A becomes the conductive portion 15a.

In the developing roller 15 of this embodiment, as described above, the conductive portion 15a is the surface of the conductive substrate 15A, and
The dielectric portions 16 are scattered and scattered on the surface of the conductive substrate 15A, and each of the dielectric portions 16 is formed in a thin and rounded convex shape. Each dielectric part 16
Is formed into a shape of a part of a substantially spherical surface, that is, a substantially dome shape.

The developing roller 15 is also assembled in the developing device as shown in FIG. 4 just like the conventional developing roller, and performs the developing operation in the same manner as described above with reference to FIG. At that time, the conductive substrate 15A of the developing roller 15 is grounded by applying a bias voltage, and the dielectric portion 16 is rubbed with the toner supply roller 6 (FIG. 4) to reverse the charge polarity of the toner. A small closed electric field (see FIG. 6) is formed between the conductive portion 15a and the dielectric portion 16 by being charged with polarity. As a result, a sufficient amount of sufficiently charged toner can be transported to the developing area 9 (FIG. 4),
A high quality toner image can be formed on the photoconductor 1.
Other configurations and operations relating to image formation are the same as those described above, and thus further description will be omitted.

In the conventional developing roller, the dielectric portion is likely to have a recess while the thermosetting resin embedded in the groove of the conductive substrate is cured. Toner accumulates in the recesses to cause clogging, and when the toner carrier is used, the clogging toner scatters around the developing roller and the inside of the machine is soiled with the toner.

According to the developing roller 15 of this example, the dielectric portion 1
Since 6 has a convex shape, clogging of toner and the like is less likely to occur, toner scattering can be suppressed, and contamination by toner inside the apparatus can be prevented.

Further, as shown in FIG. 1, by forming the dielectric portion 16 in a rounded and substantially dome-shaped convex shape, the toner can be smoothly conveyed without being stuck to the dielectric portion 16. The dielectric part 16 will not fall off.

Next, a method of manufacturing the toner carrier including the developing roller having the above-mentioned structure will be described.

The principle of disperse formation of the convex dielectric portion is based on the fact that when vapor molecules of a substance are condensed on a substrate, if the temperature of the substrate is different, the shape of the adhered film is different. It is utilized by appropriately setting the temperature that the adhered film is not a uniform smooth film but a block-shaped aggregated film.

That is, when the temperature of the substrate is set low, the vaporized flying molecules are stacked one after another at the places where they are attached, and have a flat but rugged film quality. On the other hand, when the temperature of the substrate is raised and the temperature of the substrate is set to a temperature equal to or higher than the glass transition temperature of the vaporized flying molecules, the adhering molecules cause migration (movement of the molecules) on the substrate, resulting in smoothness. Form a film.

However, when the temperature of the substrate is further raised and set to a temperature near the melting point of the vaporized flying molecules, the adhered molecules are condensed with each other, and rounded dome-shaped spots are scattered on the substrate surface. However, when the temperature of the substrate is set to be equal to or higher than the melting point, vaporized flying molecules adhering to the substrate drop down from the substrate and fall from the substrate, or depending on the substance, re-evaporation becomes severe and film formation is not performed.

In the method of manufacturing the toner carrier of this example, as described above, when the temperature of the substrate is near the melting point, the adhering molecules are condensed with each other, and rounded almost domed spots are scattered on the substrate surface. It positively uses the phenomenon. This phenomenon is similar to the phenomenon in which water drops adhere to the cooled window glass in spots in a hot and humid room.

Here, the area ratio of the entire dielectric portion 16 to the surface of the conductive substrate 15A shown in FIG. 3 is defined as "coverage ratio". As the area of the dielectric portion 16 increases, the coverage ratio increases. The coverage of the film on the surface of the substrate can be changed by making the radius of the dome-shaped spots different, and the radius can be controlled by making the film thickness of the smooth film different. it can. In the case of the vacuum vapor deposition method, such a thing can be easily realized by adjusting the input amount of the vapor deposition material. The pattern of the dielectric part 16 as shown in FIG. 3 cannot be formed even after the smooth film is once formed and then the substrate is reheated to a temperature equal to or higher than or near the melting point of the vapor deposition material. The reason for this is that once the film is formed, a good coagulation cannot be performed due to the balance of the adhesion between the substrate and the film.

Next, a first embodiment of the method for manufacturing the developing roller 15 will be described.

A holder 12 is rotatably provided inside a vacuum chamber 11 as shown in FIG. 2, and an evaporation material 14 as an evaporation source is provided inside an evaporation tray 13 fixedly installed inside the holder 12.
Is included.

In advance, a cylindrical conductive base 15A made of aluminum and having an outer diameter of 20 mm is attached to the holder 12 so as to rotate integrally with the holder. In addition, nylon 12 (Orgall 2002ES-5NAT manufactured by Nippon Rilsan Co., Ltd.) is placed in the evaporation dish 13 as the vapor deposition material 14.

Basically, the holder 12 is rotated integrally with the conductive substrate 15A while the vapor deposition material 14 and the conductive substrate 15A are heated and held in the vacuum chamber 11.

First, the temperature of the conductive substrate 15A is kept at room temperature (about 30.degree. C.), and while it is rotated at 20 rpm, the amount of the vapor deposition material charged is changed variously, and the vapor deposition material 14 is electrically heated to conduct electricity. Vapor deposition was performed on the conductive substrate 15A, and the thickness of the film formed on the conductive substrate 15A was measured to determine the amount of vapor deposition material input 500 mg / boat segment at which the film thickness becomes 10 μm. That is, make a smooth film in advance,
This film thickness is used as a guide to determine the amount of vapor deposition material to be charged.

Next, the temperature of the conductive substrate 15A is set to 160.degree.
And the substrate was vapor-deposited. The melting point of the above vapor deposition material is 190 ° C. That is, the melting point of the vapor deposition material 14 (190
(° C.) or lower and the temperature is kept at 160 ° C. near the melting point to perform vapor deposition. In this way, the dielectric portion 16 shown in FIGS. 1 and 3 is formed by vacuum evaporation.

The diameter of the dielectric portion 16 (FIG. 3) obtained by this vapor deposition is about 100 μm, the average center-to-center distance (pitch) between the dielectric portions is 110 μm, and the surface area coverage is 8.
The contact angle was 0%, and the dielectric portion 16 was cut vertically, and the contact angle θ (FIG. 1) was measured while observing with a microscope. The contact angle was about 20 °.

Next, a second embodiment of the method for manufacturing the developing roller 15 will be described.

A molecular weight of about 1000 formed by condensation polymerization by mixing and heating a bishydroxy compound and a carbonic acid ester.
Was used as a vapor deposition material, and the temperature of the conductive substrate 15A was maintained at 120 ° C. for vacuum vapor deposition. The melting point of the precursor is 150 ° C.

After cooling, the vacuum condition is broken and the pressure is reduced to 200 in the atmosphere.
A film of polycarbonate that was polymerized and cured by heating to ° C was formed. Although a dome-shaped film with a roundness was formed as it was vapor-deposited, the film was not polymerized, so it had a strong adhesive force and was sticky to the touch. On the other hand, when the film was heated in the atmosphere, the stickiness of the film disappeared, and the shape of the spots and the dispersed distribution state of the almost dome-shaped film were maintained. Although the melting point of the precursor is 150 ° C. as described above, it was still viscous and maintained its surface shape by heating at 200 ° C. before the polymerization.

The diameter of the dielectric portion 16 (FIG. 3), which is formed by the above-described method and is composed of substantially dome-shaped spots, is about 80 μm.
m, the average pitch was 100 μm, and the surface area coverage was 60%. The contact angle θ (Fig. 1) is about 3
It was 0 °. The contact angle θ is preferably as small as possible in order to prevent the toner from entering the valleys between the dielectric portions.

The developing roller 15 having the dielectric portion 16 obtained by the above-described manufacturing method is the A manufactured by Ricoh Co., Ltd.
When incorporated into a D series copying machine and operating this copying machine in the same manner as described above with reference to FIG. 4, the obtained image was evaluated and it was found that moire images did not occur. understood. Further, it was found that the toner was not scattered and an image with better image quality was obtained.

The vapor deposition materials used in the first and second embodiments were used and the temperature of the conductive substrate 15A was kept at room temperature (about 30 ° C.).
The substrate was taken out from the vacuum chamber after cooling, and the taken-out substrate was then heated under atmospheric pressure to the vicinity of the melting point thereof. , A state in which the dielectric part is chained) or a large agglomerated film was formed, so that a film of almost domed material could not be obtained. It is considered that once a smooth film is formed, it cannot be uniformly agglomerated due to the influence of the adhesion with the underlying substance. In any case, if the conductive substrate is not kept at room temperature but is kept at a temperature below the melting point of the vapor deposition material and near the melting point and vapor deposition is not carried out, the dispersion of scattered dots shown in FIG. That is, a uniform dielectric part cannot be obtained. In this way, the temperature of the conductive substrate during vapor deposition is kept below the melting point and in the vicinity thereof, and the deposited material on the conductive substrate is agglomerated in order to form a uniform distribution film of uniform size. It is essential.

In the prior art, vertical and horizontal grid-like grooves were formed on a conductive substrate, and then the resin was uniformly coated, dried and then polished to expose the dielectric portion. The manufacturing method does not require these polishing steps,
The process can be simplified. Further, in the past, when the resin was poured into the groove and the surface of the conductive substrate was coated with the resin, there was a possibility that air bubbles might be generated. There is no partial defect in holding the part. It is possible to suppress variations in quality.

Further, according to the above-mentioned manufacturing method, as described above, since the method of forming the convex portion by aggregation is used, a film having a clean roundness can be formed. In other words, it is possible to produce a toner carrier which is less likely to cause toner accumulation and thus less likely to cause toner scattering. Moreover, the toner can be smoothly conveyed without being caught by the toner on the toner carrier.

Dielectric part 16 configured as a rounded film
Are irregularly distributed on the conductive substrate 15A. That is, when such a developing roller is used, it is possible to prevent a moire pattern from being generated in the image. According to this manufacturing method, it is possible to manufacture a toner carrier in which a moire pattern is unlikely to occur.

Further, the surface coverage of the dielectric portion can be made substantially constant for each toner carrier, and unevenness in the toner carrying capacity can be prevented. Also, instead of vacuum vapor deposition, even if the conductive substrate is exposed to saturated vapor under atmospheric pressure or pressure, it is possible to form an almost dome-like film like condensation of water droplets. The method is advantageous in that the film thickness, and hence the diameter of the substantially dome-shaped film, can be freely changed by controlling the amount of the vapor deposition material used during vapor deposition.

When the particle diameter of the toner is changed or the peripheral speed of the toner carrying member or the photosensitive member is changed, the lattice pitch and the like have been changed in the past in order to adjust the toner conveyance amount. In the manufacturing method described above, the intended purpose can be achieved by changing the amount of vapor deposition material input during vapor deposition and changing the diameter of the almost dome-shaped film. It is possible to easily deal with changes in toner selection conditions.

The rounded, almost dome-shaped film formed by the above-described method can be sufficiently cured in the manufacturing process even if this vapor deposition material is a thermosetting resin, so that it is similar to the conventional type. Changes over time (shape changes, etc.)
It can be used continuously without causing any trouble.

The present invention can also be applied to a belt-shaped toner carrier and a method for manufacturing the same.

[0058]

According to the toner carrier of the first aspect, when the toner carrier is used in an image forming apparatus, the dielectric portions scattered on the conductive substrate are convex, and the toner carrier is Since clogging of the toner is less likely to occur, it is possible to prevent toner from scattering and prevent contamination with toner inside the machine. Further, it is possible to prevent a moire pattern or the like from being generated in the image.

According to the toner carrier of claim 2,
When such a toner carrier is adopted in an image forming apparatus, since the dielectric portion has a rounded and convex shape, the toner does not get caught in the dielectric portion, the toner can be smoothly transported, and the dielectric portion is lacking. It will not fall.

According to the manufacturing method of the third aspect, bubbles are not likely to be generated during the formation of the dielectric portion, so that there is no possibility that a partial defect occurs in holding the dielectric portion and the quality is varied. It can be lost. Further, since the conventional step of polishing the resin coating layer is not required, the manufacturing process can be simplified. Furthermore, it is possible to produce a toner carrier that is less likely to cause moire patterns and toner scattering.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an enlarged part of a developing roller.

FIG. 2 is a sectional view showing an example of a developing roller manufacturing apparatus.

FIG. 3 is a plan view schematically showing an enlarged part of the surface of the developing roller.

FIG. 4 is a schematic sectional view showing an example of a developing device.

FIG. 5 is an external perspective view of a developing roller.

FIG. 6 is an explanatory diagram showing electric lines of force of a minute closed electric field formed near the surface of the developing roller.

[Explanation of symbols]

 14 Vapor Deposition Material 15A Conductive Substrate 15a Conductive Part 16 Dielectric Part

Claims (3)

[Claims] 1. A conductive part and a large number of dielectric parts spaced apart from each other for forming a minute closed electric field between the conductive parts are formed on the surface, and each dielectric part protrudes from the conductive part surface. A toner carrier having a convex shape as described above. 2. The conductive portion is a surface of a conductive substrate, the dielectric portion is a dielectric portion dispersed and scattered on the surface of the conductive substrate, and each dielectric portion is formed into a rounded convex shape. The toner carrier according to claim 1, which is formed. 3. The toner carrier according to claim 1, wherein the conductive substrate is formed at a temperature below the melting point of the vapor deposition material to be the dielectric portion and in the vicinity of the melting point, and the dielectric portion is formed by vacuum vapor deposition. Production method.