JP2013043797A - Insulating film composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulating film composition for forming an insulating film or a protective layer (hereinafter called as an insulating film or the like) which is much higher in a withstand voltage, wear resistance, heat conductivity, and scratch resistance.SOLUTION: Since alumina powder is contained in thick film insulating paste with glass as a main component, it is possible to obtain an insulating film of a fixing heater or an insulating film which is suitable for the protective layer of a thermal print head, and high in hardness, high in wear resistance or scratch resistance, and high in heat conductivity and high voltage resistance. Since the aspect ratio of the alumina powder is as small as 1.2 or lower, it is possible to obtain packing density, and to further increase the improvement effect of the hardness of the insulating film or the like. Since the volume percentage of the alumina powder is as large as 25(%) or higher, it is possible to further increase the improvement effect of the hardness or heat conductivity of the insulating film or the like, and since the volume percentage is kept in 60(%) or lower, it is possible to obtain the strong insulating film or the like.

Description

  The present invention provides an insulating film provided for the purpose of protecting an electrode and a resistance heating element provided on a substrate, particularly a protective layer covering an insulating film of a fixing heater of a copying machine or a heating element of a thermal print head. The present invention relates to an insulating film composition suitable for formation.

  For example, in a copying machine of a type in which a toner image is transferred and fixed on a printed material such as paper, the transferred toner is melted by applying pressure while the printed material is heated in the fixing device. It can be fixed on paper. The fixing device includes a fixing heater for heating the printed material and a pressure roller for feeding the printed material in one direction while pressing the printed material toward the fixing heater. As one type of such a fixing device, a fixing heater is formed in a long plate shape, and a fixing film made of a heat-resistant resin that is rotated with the rotation is provided between the pressure roller and the fixing device. There is one that has been reduced in size and reduced its heat capacity.

  In the fixing heater, for example, a resistance heating element layer made of an Ag / Pd alloy or the like is provided on the surface of a flat substrate made of glass, ceramics, or the like by an appropriate method such as printing or transfer. The resistance heating element layer is connected, for example, to electrode terminals made of Ag or the like at both ends thereof, and the surface thereof is covered with an insulating film containing glass as a main component. Such an insulating film is not limited to a flat fixing heater, but is also provided on a fixing roller having a resistance heating element layer provided on the outer peripheral surface of a cylindrical insulating substrate.

  In a thermal printer, an image is formed on a recording sheet by heating the recording sheet while feeding the recording sheet in one direction. In the type using the thermal recording paper, when heated, the thermal dye in the thermal layer provided on the thermal recording paper is colored to form an image. Further, in the type using the thermal transfer ink ribbon, the ink melted or sublimated by heating is transferred onto the recording paper to form an image. In this case, plain paper is used as the recording paper. The printing unit includes a thermal print head for heating the thermal recording paper and the thermal transfer ink ribbon, and a pressure roller for feeding the recording paper in one direction while pressing the recording paper toward the thermal print head. Yes. This thermal print head has a basic structure in which, for example, a line-shaped resistance heating element provided on one surface of a ceramic substrate via a heat storage layer is covered with a protective layer.

  The insulating film or the protective layer as described above is formed for the purpose of protecting a conductor film such as an electrode provided on the surface of the circuit board or an electronic component, for example, also on a circuit board.

JP 10-338543 A Japanese Patent Laid-Open No. 11-147711 JP 2001-226117 A JP-A-10-193659 Japanese Patent Laid-Open No. 04-073163

  By the way, the insulating film of the fixing heater and the protective layer of the thermal print head as described above have a high thermal conductivity so that the generated heat is efficiently transmitted to the printing material, and a high hardness and resistance. It is required to have high wear resistance and scratch resistance, and are difficult to be worn and scratched even when rubbed against a printing material. In addition, the insulating film of the fixing heater is required to have a high withstand voltage as much as possible and to prevent dielectric breakdown easily in order to obtain high reliability. Also, the thermal conductivity and withstand voltage must be as high as possible in the insulating film of the circuit board in order to easily dissipate the heat generated from the electronic components or to prevent the protective function from being lost due to dielectric breakdown. It is desired.

  For example, in supermarket registers and portable thermal printers, thin film thermal print heads are the mainstream, but in the thin film type, a protective layer is generally formed by sputtering. This is because when the protective layer is formed of glass paste, thermal conductivity, wear resistance, and scratch resistance are insufficient. However, since the manufacturing cost increases when the sputtering method is used, it is desired to improve these characteristics with a glass paste. In portable printers, it is particularly desirable that batteries (including rechargeable batteries) have good durability. However, if the thermal conductivity of the protective layer is low, it is difficult to achieve both quality such as print density and battery durability. Become.

  In response to the above requirements, glass pastes have been proposed for use in fixing heaters and thick film resistor cover coats that have increased withstand voltage by replacing 5 to 45 wt% of the glass powder with alumina powder. (For example, see Patent Document 1). When using a low softening point glass that can form a dense film at a relatively low firing temperature of 900 (° C.) or less, the withstand voltage tends to be low, whereas the above glass paste has a high withstand voltage without increasing the film thickness. The purpose is to increase. However, the insulating film produced from the glass paste has a low withstand voltage, and further improvement has been desired.

  In addition, when forming a smooth wear-resistant overcoat layer (that is, a protective layer) on the surface of various electronic components such as thin film transistors and thermal print heads, spherical inorganic particles having an average particle size of 0.1 (μm) or less are fired. It has been proposed to mix with metal organics that sometimes form glass (see, for example, Patent Document 5). This protective layer forming technique is intended to satisfy the wear resistance and smoothness required for the protective layer without using an expensive thin film technique such as sputtering. However, the protective layer using the mixture as described above still does not have sufficient wear resistance, and further improvement has been demanded.

  The present invention has been made against the background described above, and its purpose is to provide an insulating film or protective layer (hereinafter referred to as insulating film) having higher withstand voltage, wear resistance, thermal conductivity, and scratch resistance. Etc.) is provided.

In order to achieve such an object, the gist of the present invention is an insulating film composition mainly composed of glass used for forming an insulating film on the surface of a predetermined substrate, and having an aspect ratio. The volume ratio x (%) and the average particle size y (μm) of the alumina powder of 1.2 or less in the entire insulating film composition are included in a range satisfying the following relational expression (1).
0.09exp (9.8 / (60−x)) + 0.24 ≦ y ≦ 7
(However, 25 ≦ x <60) (1)

  In this way, since the insulating film composition mainly composed of glass contains alumina powder, the insulating film composition is applied to the insulating film of the fixing heater of the copying machine and the protective layer of the thermal print head. An insulating film having high hardness, high wear resistance and scratch resistance, and high thermal conductivity and withstand voltage can be obtained. At this time, since the aspect ratio of the alumina powder is as small as 1.2 or less and is nearly spherical, a high packing density can be easily obtained at the time of film formation. Enhanced. Moreover, since the volume ratio x of the alumina powder is sufficiently large as 25 (%) or more, the effect of improving the hardness, thermal conductivity, etc. of the insulating film and the like due to the inclusion of the alumina powder is further enhanced, and the volume ratio x is Since it is kept below 60 (%), a strong insulating film or the like can be obtained. The average particle size y of the alumina powder satisfies the above formula (1) and is 0.09exp (9.8 / (60−x)) + 0.24 (μm) or more, that is, 0.35 (μm) or more. The alumina particles are sufficiently prevented from falling off from the film or the like, and as a result, higher scratch resistance is obtained. In addition, since the average particle size y is kept at 7 (μm) or less, the unevenness of the film surface is sufficiently small even if the thickness of the insulating film to be formed is sufficiently thin, for example, 10 (μm) or less. Thus, an insulating film having sufficiently high smoothness can be obtained even by baking.

  In the present application, the “aspect ratio” is the ratio of the major axis / minor axis of the particle, and the value becomes closer to 1 as the particle becomes closer to a sphere. The smaller the aspect ratio is, the closer to the spherical shape and the higher the packing density, so that the effect of adding alumina powder is further enhanced. For example, the smaller the aspect ratio, the higher the withstand voltage of the formed insulating film or the like and the smaller the variation. As the aspect ratio becomes smaller, the protrusions on the surface of the insulating film to be formed become smaller or less likely to occur, so that the smoothness of the film surface improves. This seems to contribute to the improvement of the withstand voltage. In addition, as the aspect ratio decreases, the particle filling property in the film after coating and drying improves, so that there is an advantage that variation in characteristics between films or in the film is suppressed in the formed insulating film or the like. In the present application, the “average particle diameter” is an average value measured using an electron microscope (SEM) photograph of alumina powder. Specifically, for example, two fields of view are arbitrarily photographed with an electron microscope at 10000 times or 5000 times, and five particles of an average size are visually selected from the particles of the entire photograph, and the diameter of the particles is selected. Is measured, and this is taken as the particle size of the particle, and the average of a total of 10 particles in 5 fields of view is taken as the average particle size.

  As described above, the hardness, thermal conductivity, and withstand voltage of the insulating film formed by mixing alumina powder having an aspect ratio of 1.2 or less are sufficiently improved. Therefore, if this condition is satisfied, the volume ratio x and the average particle diameter y of the alumina powder are not particularly limited. However, by controlling the volume ratio x and the average particle diameter y, each of the above characteristics can be further improved.

  First, the volume ratio x is preferably in the range of 25 to 60 (%). In order to sufficiently obtain the effect of adding the alumina powder, that is, the effect of improving the above-described characteristics, the volume ratio x is preferably sufficiently large, and preferably 25 (%) or more. When the formed insulating film or the like is rubbed with paper or the like to scrape the glass in the insulating film or the like, the alumina particles are exposed. If the volume ratio x is sufficiently large, the effect of suppressing wear of the insulating film or the like by the exposed alumina particles can be sufficiently obtained, so that wear resistance and scratch resistance are further improved. That is, the service life of a thermal printer or the like is also improved. Moreover, since the thermal conductivity of alumina powder is higher than that of glass, the effect of improving the thermal conductivity is also increased. A sufficiently high responsiveness can be obtained by sufficiently increasing the thermal conductivity. Higher responsiveness has the advantage that the start-up of the printer is accelerated and the printing speed is increased, so that waste of electricity is reduced and energy is saved. Further, since the scratch resistance is further improved, the insulating film or the like is hardly scratched, and printing defects due to the scratch are suppressed. On the other hand, as the amount of alumina powder increases, the insulating film formed with a relatively small amount of glass as a binder becomes fragile, and the gap between particles increases and the compactness also decreases. In order to obtain a sufficiently high density and a sufficiently high surface smoothness (that is, to obtain a sufficient smoothness) and a sufficient film strength, the volume ratio x is preferably sufficiently small, It is preferable that it is less than 60 (%). When the volume ratio x is excessively high, the denseness is suddenly lost, and particularly when the volume ratio x is 60% or more, the unevenness of the surface of the formed insulating film or the like becomes remarkably large and the practicality is inferior. The range of the volume ratio x corresponds to approximately 30 to 65 (%) in terms of weight percentage.

  Further, according to the equation (1), when the volume ratio x is the lower limit value 25 (%), the average particle size y becomes the lower limit value 0.35 (μm). Accordingly, the average particle size y is preferably a value within the range of 0.35 ≦ y ≦ 7 (μm). In order to sufficiently obtain the effect of improving the above characteristics, the average particle size y is preferably sufficiently large, and more preferably 0.37 (μm) or more. By making the average particle size sufficiently large, when the glass is scraped and the alumina particles are exposed as described above, the alumina particles are less likely to fall off, so the wear resistance and scratch resistance are sufficiently high. Enhanced. Moreover, agglomeration of the alumina powder is suppressed and high dispersibility is obtained. On the other hand, as the average particle size y increases, surface irregularities of the formed insulating film and the like are more likely to occur, and the film strength decreases due to the relatively small amount of glass. It is preferably sufficiently small, and is preferably 7 (μm) or less.

  Further, the alumina powder to be added preferably satisfies the above formula (1), but in this formula (1), the lower limit of the average particle size y increases as the volume ratio x increases. That is, alumina powder having a fine average particle size y can be used in a region where the volume ratio x is small, but it is necessary to use alumina powder having a large average particle size y in a region where the volume ratio x is large. For example, in the region where the volume ratio x is about 55 (%) or less, an alumina powder having an average particle size y of about 1.5 (μm) can be used. growing. As described above, the smaller the average particle size y, the easier the alumina particles fall off. However, when the volume ratio x is small, it is considered that the change in physical properties of the insulating film is small even if the volume ratio x falls off.

  The method for producing the alumina powder is not particularly limited, but a vapor phase method such as CVD, a liquid phase method such as a sol-gel method, that is, a wet method, or a high temperature spraying method is preferable. According to these production methods, a fine alumina powder having a small particle diameter variation and a small aspect ratio close to a sphere can be easily obtained. Moreover, since the alumina powder produced by these methods has a smooth particle surface, there is an advantage that the printing paper is hardly damaged and the printing quality is further improved. As a method for producing alumina powder, a method of synthesizing by an appropriate method and then crushing it to a desired size is well known, but since such a crushing alumina has a large aspect ratio, a high packing density is obtained. In addition, since the film formed is difficult to be porous and a sharp edge is present on the particle surface, the alumina powder obtained by the above gas phase method or the like is preferable. In the CVD method, for example, aluminum powder synthesized by hydrolyzing aluminum alkoxide is jetted together with a halogen gas such as chlorine to be vapor-phase grown to obtain alumina powder. In addition, the above high temperature spraying method is, for example, spraying alumina powder obtained by the Bayer method into a high temperature flame, or spraying aluminum hydroxide powder or slurry thereof into the flame, and capturing the fine powder obtained at high temperature. (See, for example, Japanese Patent Laid-Open No. 2001-019425).

  Incidentally, the addition of alumina powder to an insulating film composition containing glass as a main component is conventionally known as described above (see Patent Document 1), and such insulation. The film composition is commercially available. However, in these insulating film compositions known to date, no particular consideration has been given to the physical properties of the alumina powder to be added. Therefore, since cheap crushed alumina, which is advantageous in terms of manufacturing cost, was used, the aspect ratio is large, so that withstand voltage, wear resistance, thermal conductivity, and scratch resistance are all insufficient, or It seems that the variation was large and the reliability was lacking.

  Further, it has been proposed to add alumina powder as a filler in a resin composition for forming an insulating film for protecting a conductor film, an electronic component or the like on a circuit board (see Patent Documents 2 and 3). .). Since these resin compositions have low thermal conductivity of the resin, alumina powder is added for the purpose of improving the resin composition. Therefore, the alumina powder is added to the insulating film composition as in the present invention, but the main component is different and the purpose of adding the alumina powder is completely different.

  Further, in a thermal print head having a heat storage layer between a substrate and a heating resistor layer, it has been proposed to use a mixture of resin and inorganic material particles having a Vickers hardness of 400 or more as the heat storage layer (for example, (See Patent Document 4). When this heat storage layer is made of glass, the thermal responsiveness becomes insufficient. On the other hand, if it is made of a resin having excellent thermal responsiveness such as polyimide, the heat resistance and mechanical strength are insufficient. The purpose is to improve the mechanical strength. Examples of the inorganic material particles include silica, alumina, silicon nitride, silicon carbide, titanium carbide, titanium nitride, and boron nitride, and that the particle diameter is preferably a true sphere. In the above technique, alumina powder or the like is added to the insulating film composition as in Patent Documents 2 and 3, but the main component is different and the purpose of adding the alumina powder is completely different.

  Further, in the mixture of Patent Document 5, inorganic particles such as alumina are mixed with glass. However, since extremely fine inorganic fine particles are used to obtain surface smoothness, handling thereof becomes difficult. Yes. Moreover, only a mixture of glass fine particles and a metal organic material is shown as a specific example. When alumina is used as an inorganic particle, what particle size is used and how it is used is completely touched. Absent.

  Here, preferably, in the insulating film composition, the volume ratio x (%) of the alumina powder is in a range of 35 ≦ x ≦ 55. In this way, an insulating film having higher thermal conductivity and hardness and smaller surface irregularities can be obtained.

  Preferably, the insulating film composition has an average particle size y (μm) of the alumina powder of 5 (μm) or less. In this way, an insulating film with even smaller surface irregularities can be obtained. Depending on the thickness of the insulating film to be formed, if the average particle size y is 5 (μm) or less, protrusions that cause problems in fixing heaters, thermal print heads, circuit board insulating films, etc. will occur. In addition, the minimum withstand voltage is sufficiently high.

  In addition, the alumina powder may be used in combination of two or more different average particle diameters. In this way, since the smoothness of the surface of the formed insulating film and the like is improved by entering the small-sized particles between the large-sized particles, the surface of the paper or the like when the surface is rubbed with paper or the like is improved. The occurrence of scratches on the surface is further suppressed. The alumina powder to be mixed is preferably selected from a range of, for example, an average particle size of 0.35 to 7.0 (μm).

  Preferably, the alumina powder has an aspect ratio of 1.1 or less. In this way, since the alumina powder becomes more spherical, protrusions are less likely to occur in the fired insulating film. In addition, when the insulating film composition paste is prepared and the screen printing method is used when forming the insulating film, the dispersibility of the paste is improved because alumina powder having a more spherical shape is used. There is an advantage that the density of the film after drying is further increased and a denser insulating film can be obtained after firing.

In the present invention, the glass as the main component of the insulating film is not particularly limited, and may be lead glass or lead-free glass. Examples of the lead glass include PbO—SiO ₂ —ZnO glass and PbO—SiO ₂ —B ₂ O ₃ glass. Lead-free glass includes SiO ₂ -B ₂ O ₃ -ZnO glass, SiO ₂ -B ₂ O ₃ -ZnO-Al ₂ O ₃ glass, Bi ₂ O ₃ -B ₂ O ₃ glass, etc. It is done. In any case, in addition to the above components, an alkali metal oxide, an alkaline earth oxide, or the like can be appropriately contained.

  Preferably, the insulating film composition of the present invention is for forming an insulating film covering a resistance heating element layer formed on the surface of a fixing heater used for fixing toner in a copying machine or the like. The insulating film composition of the present invention can obtain an insulating film having a high withstand voltage by adding alumina powder having a low aspect ratio as described above, so that insulation of a fixing heater to which a high voltage is applied is obtained. Suitable for membranes.

  Preferably, the insulating film composition of the present invention is used for a protective layer of a thermal print head. As described above, the insulating film composition of the present invention has a sufficiently high film hardness because the low-aspect-ratio alumina powder is contained in the volume ratio x and the average particle diameter y satisfying the above formula (1). In addition, since an insulating film having excellent thermal conductivity and surface smoothness can be obtained, it is suitable for a protective layer of a thermal print head that is required to satisfy hardness, thermal conductivity, and surface smoothness at the same time.

1 is a diagram schematically illustrating a cross-sectional configuration of a main part of a fixing device provided with a fixing heater in which an insulating film is formed with an insulating film composition according to an embodiment of the present invention. It is a figure which shows typically the cross-sectional structure of the other fixing heater which formed the insulating film with the insulating film composition of one Example of this invention. It is a figure which shows typically the cross-section of the circuit board which formed the insulating film with the insulating film composition of one Example of this invention. It is a figure which shows typically the principal part cross-section structure of the printing part of the thermal printer provided with the thermal print head which formed the protective layer with the insulating film composition of one Example of this invention. It is a figure which shows the withstand voltage characteristic of the insulating film formed from the insulating film composition of one Example of this invention which added the alumina powder of the low aspect ratio with that of the comparative example which added the alumina powder of the high aspect ratio. It is a figure which shows the withstand voltage characteristic of the insulating film using the alumina powder different from what was shown in FIG. 5 in the Example and the comparative example. It is an electron micrograph which shows an example of the alumina powder of a high aspect ratio. It is an electron micrograph which shows the other example of the alumina powder of a high aspect ratio. 2 is an electron micrograph showing an example of low aspect ratio alumina powder. It is an electron micrograph which shows the other example of the alumina powder of a low aspect ratio. It is an example of the surface micrograph of scratch evaluation "(circle)". It is an example of the surface micrograph of scratch evaluation "(triangle | delta)". It is an example of the surface micrograph of scratch evaluation "x". It is the figure which put together the suitable range of the relationship between an alumina volume ratio and an alumina particle size based on the characteristic evaluation result as a protective layer of a thermal print head. It is a surface micrograph of an example of the sample for evaluation. It is a surface micrograph of another example of the sample for evaluation. It is a surface micrograph of another example of the sample for evaluation. It is a surface micrograph of another example of the sample for evaluation. It is a surface micrograph of another example of the sample for evaluation. It is a surface micrograph of another example of the sample for evaluation. It is a surface micrograph of another example of the sample for evaluation. It is a surface micrograph in the case of using crushed alumina having a particle size of 5 (μm). It is a surface micrograph in the case of using crushed alumina having a particle size of 3 (μm).

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a cross-sectional view schematically showing a main configuration of a fixing device of a copying machine provided with a fixing heater 10 according to an embodiment of the present invention. In FIG. 1, the fixing device includes a fixing heater 10 fixed to the lower end portion of a base 12, a substantially cylindrical fixing film 14 disposed around the fixing heater 10, and a pressure roller 16 below the fixing film 14. It is provided so as to be rotatable around an axis.

  The fixing heater 10 includes a flat plate-like base material 18 made of a ceramic material such as alumina and extending in a direction perpendicular to the paper surface, a resistance heating element layer 20 provided in an appropriate pattern on one surface thereof, and a resistance thereof. The base material 18 is fixed in a state of being embedded in a recess provided in the base 12.

  The resistance heating element layer 20 is made of, for example, an Ag / Pd alloy or the like, and has an appropriate pattern such as a straight line from one end side to the other end side of the substrate 18 so as to obtain a heat generation amount necessary for toner fixing. Provided in the shape pattern, the bent pattern, or the like. It should be noted that a pair of electrodes (not shown) are provided at both ends in the longitudinal direction of the base material 18 so as to be exposed from the insulating film 22, and the resistance heating element layer 20 has both ends at the pair of electrodes. It is connected.

The insulating film 22 is made of, for example, SiO ₂ —B ₂ O ₃ —ZnO-based glass and a filler, and is provided with a thickness within a range of about 10 to 50 (μm), for example. . The above glass is composed of, for example, network components SiO ₂ , B ₂ O ₃ and ZnO in total 73 (mol%), intermediate network component Al ₂ O ₃ 4 (mol%), and a modified oxide component. It has a composition containing certain BaO and SrO in a total proportion of 23 (mol%). The glass has a softening point of about 690 (° C.) and a coefficient of thermal expansion of about 67 (%).

  The filler is made of alumina powder having an aspect ratio of 1.2 or less, for example, about 1.07, and an average particle size of about 0.8 (μm), and is contained in the insulating film 22 at a ratio of about 45 (wt%). It is. This filler is added for the purpose of increasing the withstand voltage of the insulating film 22. The alumina powder is produced by, for example, spraying aluminum hydroxide synthesized by hydrolyzing aluminum alkoxide together with chlorine gas and performing vapor phase growth. It is fine and has a small aspect ratio.

  The pressure roller 16 is made of, for example, a silicone rubber 26 fixed to the outer peripheral surface of an aluminum cylinder 24, and the aluminum cylinder 24 is rotatably supported by a bearing device (not shown). The pressure roller 16 is pressed against the fixing heater 10 through the fixing film 14 in the use state.

  In the fixing device configured as described above, when the recording paper 28 or the like on which the toner is transferred by a transfer device (not shown) is fed, the recording paper 28 is added between the fixing heater 10 and the pressure roller 16 via the fixing film 14. The resin contained in the toner is melted at the same time as being pressed, and the toner is fixed on the recording paper 28 or the like. At this time, since the fixing film 14 is rotated in accordance with the rotation of the pressure roller 16, the surface of the fixing heater 10, that is, the surface of the insulating film 22 is rubbed with the fixing film 14. Since the insulating film 22 has a high withstand voltage, even if static electricity is generated by this, the insulating film 22 has a characteristic that dielectric breakdown does not easily occur.

  That is, since the insulating film 22 includes the alumina powder having a small aspect ratio as described above, the average withstand voltage is sufficiently high, for example, 120 (V / μm) or more, and the variation is ± 10 ( %) And has an excellent withstand voltage characteristic that is sufficiently small. Therefore, since the withstand voltage is sufficiently high, dielectric breakdown due to static electricity generated during use of the copying machine is unlikely to occur. In addition, since the variation in withstand voltage is small, there is an advantage that the fixing heater 10 having a desired withstand voltage characteristic can be manufactured with a high yield.

  FIG. 2 schematically shows a cross-sectional structure of a cylindrical fixing heater 30 of another embodiment used in the copying machine in place of the fixing heater 10 and the fixing film 14. The fixing heater 30 includes a cylindrical base material 32, a resistance heating element layer 34 fixed to the outer peripheral surface thereof, and an insulating film 36 covering the resistance heating element layer 34.

The substrate 32 is made of, for example, SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ hard glass. This hard glass contains a small amount of an alkali metal oxide or an alkaline earth metal oxide in addition to the above components.

  The resistance heating element layer 34 is provided in an appropriate shape such as a linear pattern or a spiral pattern using an Ag / Pd alloy or the like, like the resistance heating element layer 20. The insulating film 36 is configured in the same manner as the insulating film 22. Even in such a fixing heater, a high voltage is applied to the resistance heating element layer 34 when used, and the recording paper 28 and the pressure roller 16 rub against each other. Since the insulating film 36 has an excellent withstand voltage characteristic like the fixing heater 10, there is an advantage that the fixing heater 30 having an excellent withstand voltage can be manufactured with a high yield.

  Further, the glass constituting the insulating films 22 and 36 having such an excellent withstand voltage characteristic is not limited to the fixing heaters 10 and 30 described above, and other applications that require high withstand voltage and high reliability, for example, The thick film hybrid IC as shown in FIG. 3 and other insulating films 42 of the circuit board 40 are also used.

  In FIG. 3, a circuit board 40 is formed by forming a conductor film 46 on one surface of a substrate 44 made of alumina or the like and mounting an electronic component 48 such as an IC or a chip resistor, and covering them with an insulating film 42. The conductor film 46 is made of a thick film conductor material such as Ag or Ag / Pd, for example, and the electronic component 48 is fixed to the conductor film 46 using solder or the like. Even in such an application, according to the insulating film 42 of the present embodiment containing the low-aspect-ratio alumina powder as a filler, a sufficiently high withstand voltage can be obtained, so that there is an advantage that the reliability of the circuit board 40 can be improved. .

  FIG. 4 is a cross-sectional view schematically showing a main configuration of a printing unit of a thermal printer provided with a thermal print head 50 which is still another application example of the insulating film composition. In the thermal printer, a thermal print head 50 is fixed to a frame, a casing, or the like (not shown), and a pressure roller 52 is provided above the shaft so as to be able to rotate about its axis.

  The thermal print head 50 includes a heat storage layer 56, a resistance heating element layer 58, a pair of electrode layers 60 and 60, and a protective layer 62, which are sequentially laminated on one surface of a substrate 54 made of alumina or the like. The substrate 54 is fixed to a frame or a housing (not shown). The heat storage layer 56 is made of, for example, glaze glass, and is provided in a belt shape extending along a direction perpendicular to the paper surface with a uniform cross section shown in FIG. 4, for example. The length dimension of the heat storage layer 56 is determined according to the width dimension of the recording paper 64 to be printed by the thermal printer, and the width dimension is determined in consideration of the printing speed, printing accuracy, and the like.

  Further, the resistance heating element layer 58 is made of, for example, ruthenium oxide so that a heat generation amount necessary for coloring the thermal dye of the thermal recording paper or melting or sublimating the ink of the thermal transfer ink ribbon can be obtained. These are provided with appropriate thickness dimensions and patterns. Further, since the resistance heating element layer 58 is provided on the heat storage layer 56, the portion located on the heat storage layer 56 forms a protrusion. The electrode layers 60, 60 are made of a conductive material such as Al, for example, and are formed on the resistance heating element layer 58 so as to be energized from both the left and right sides in FIG. The distance between the electrode layers 60 and 60 on the resistance heating element layer 58 is appropriately determined so that an appropriate amount of heat generation can be obtained.

  The protective layer 62 is made of, for example, glass and filler, and is provided with a thickness dimension of 10 (μm) or less, for example, about 7 to 8 (μm). Although the said glass is not specifically limited and various things can be used, For example, they are lead glass, bismuth glass, and zinc glass, for example.

  The filler is made of spherical alumina powder having an aspect ratio of 1.2 or less, for example, about 1.04 to 1.15 and an average particle size of about 0.35 to 5 (μm). %) Volume ratio. This filler is added for the purpose of improving the thermal conductivity, surface smoothness, and hardness of the protective layer 62. Since alumina has a higher thermal conductivity than glass, the thermal conductivity is increased according to the amount of the alumina added, and the protective layer 62 excellent in thermal response and heat dissipation can be obtained. Such an effect can be similarly obtained in any of the applications shown in FIGS.

  The alumina powder is produced by, for example, spraying aluminum hydroxide synthesized by hydrolyzing aluminum alkoxide together with chlorine gas and performing vapor phase growth. And has a small aspect ratio. In addition, it is particularly preferable to use the alumina powder produced by such a CVD method. For example, a similar alumina powder can be obtained by a liquid phase method such as a sol-gel method or a high temperature spraying method.

  The pressure roller 52 is similar to the pressure roller 16 in that a rubber layer 68 made of silicone rubber or the like is fixed to the outer peripheral surface of a metal cylinder 66 made of aluminum or the like. The metal cylinder 66 is pivotally supported so as to be capable of rotating about an axis perpendicular to the paper surface. The pressure roller 52 is pressed against the protective layer 62 of the thermal print head 50, in particular, the protruding portion in the use state, and when the recording paper 64 is fed from the left side, for example, The recording paper 64 is pressed between the thermal print head 50 and the pressure roller 52 and simultaneously heated according to the heating pattern of the thermal print head 50, and the recording paper 64 is heated by coloring of a thermal dye or melting of ink. Is printed.

  At this time, in the thermal print head 50, the surface of the protective layer 62 is rubbed with the recording paper 64. However, since the protective layer 62 has high surface smoothness as described above, it is difficult to damage the recording paper 64. There is an advantage that paper dust does not easily occur. Moreover, since the high thermal conductivity provides high energy efficiency, there is an advantage that the battery can be held while increasing the print density even when incorporated in a portable terminal. Further, since it is high in hardness, it is difficult to cause abrasion due to the recording paper 64, and thus there is an advantage that it is excellent in durability.

  The insulating films 22, 36, 42 and the protective layer 62 as described above are prepared by, for example, preparing a thick film insulating paste, that is, an insulating film composition in which glass powder and filler are dispersed in a vehicle. 34, the conductor film 46, the electrode layers 60, 60 and the like are applied by using an appropriate application method such as dipping or screen printing, and are subjected to a baking treatment.

  5 and 6 show the results of evaluating the withstand voltage of the insulating film formed as described above by changing the aspect ratio and the particle size of the alumina powder added as a filler. The characteristics of the alumina powder used and the mixing ratio with glass are shown in Tables 1 and 2. In Tables 1 and 2, “high aspect ratio alumina” is a comparative example, and “low aspect ratio alumina” is an example. Alumina A shown in Table 1 has a fine average particle diameter (D50) of 0.8 (μm), and alumina B shown in Table 2 has a relatively large average particle diameter of around 4 (μm). The particle diameter is a value measured by a laser diffraction method. Electron micrographs of these four types of alumina are shown in FIGS. The glass: alumina mixing ratio (wt%) of the thick film insulating paste using fine powdered alumina A was 55:45, and that using alumina B was 50:50. In each sample, an insulating film was formed under the same conditions except that the alumina powder added as a filler had different aspect ratios, particle sizes, and mixing ratios.

  The withstand voltage characteristics shown in FIGS. 5 and 6 are as follows. For example, a thick film conductor is printed on a flat alumina substrate to form a lower electrode, and each thick film insulating paste is applied thereon by thick film screen printing. After forming an insulating film by baking, Cu tape is pasted on the insulating film to form the upper electrode, and an AC voltage is applied between the upper and lower electrodes using a test device, and dielectric breakdown occurs at each applied voltage. Evaluation was made by measuring the number (cumulative value). The number of samples is 36 for each specification. In this evaluation, the applied voltage was increased by 0.1 (V), and the voltage when dielectric breakdown occurred was taken as the measured value. As the test apparatus, TOS-5051 manufactured by KIKUSUI was used. The voltage shown in the graph is an effective value.

  In FIG. 5, when fine alumina powder with an average particle size of 0.8 (μm) is used, an insulating film with a film thickness of about 22 (μm) can be formed. In the present embodiment, a withstand voltage of about 2.4 to 3.1 (kV), that is, about 109 to 141 (V / μm) is obtained. On the other hand, in the comparative example using alumina having a high aspect ratio, the withstand voltage is about 1.7 to 2.1 (kV), that is, about 77 to 95 (V / μm). In terms of the average value and variation per unit thickness, in the example, the average value is about 120 (V / μm) and the variation is about 22 (V / μm), whereas in the comparative example, the average value is The variation is about 18 (V / μm) at about 84 (V / μm). Although the variation is about the same, the example using the low aspect ratio alumina powder as the filler is 30 (V / μm) or more at the minimum value and the average value compared with the comparative example using the high aspect ratio filler. It has improved.

  In FIG. 6, when a relatively large alumina powder having an average particle size of about 4 (μm) is used, an insulating film having a thickness of about 33 (μm) can be formed. In the embodiment using alumina, a withstand voltage of about 1.3 to 2.4 (kV), that is, about 39 to 73 (V / μm) can be obtained. On the other hand, in the comparative example using the high aspect ratio alumina, the withstand voltage is about 0.4 to 1.5 (kV), that is, about 12 to 45 (V / μm). Looking at the average value and variation per unit thickness, in the example, the average value is about 62 (V / μm) and the variation is about 34 (V / μm), whereas in the comparative example, the average value is The variation is about 33 (V / μm) at about 27 (V / μm). Although the variation is about the same, in the example using the low aspect ratio alumina powder as the filler, the minimum value and the average value are around 30 (V / μm) compared to the comparative example using the high aspect ratio filler. It has improved.

  The high aspect ratio alumina B is a generally used crushed alumina, and the high aspect ratio alumina A is, for example, further pulverized, and has an aspect ratio as large as about 2. In contrast, the low aspect ratio aluminas A and B have a small aspect ratio of about 1. According to the above evaluation results, it is clear that the withstand voltage is remarkably improved when the low-aspect-ratio alumina powder is used as the filler as compared with the case where the high-aspect-ratio alumina powder is used as the filler.

  The average aspect ratios listed in Tables 1 and 2 above are determined by measuring the major axis dimension and minor axis dimension by arbitrarily selecting an appropriate number of particles in an electron micrograph, for example, about 10 particles per field of view. The average value was calculated by measuring the aspect ratio (major axis dimension / minor axis dimension) of the particles. The high aspect ratio alumina A varied in the aspect ratio of, for example, 1.38 to 2.25, and the average value was 1.75. Further, the high aspect ratio alumina B varied in the aspect ratio range of 1.21 to 3.33, and the average value was 2.31. Further, the low aspect ratio alumina A varied in the range of 1.00 to 1.13, and the average value was 1.07. Further, the low aspect ratio alumina B varied in the aspect ratio range of 1.00 to 1.08, and the average value was 1.04. High aspect ratio alumina not only has a large average aspect ratio, but also has a large variation.

  According to the evaluation results described above, the thick film insulation paste mainly composed of the glass of this example contains alumina powder having an aspect ratio of 1.2 or less manufactured by CVD. It is clear that the withstand voltage of the insulating film formed from the paste can be increased.

  In particular, in this example, both the low aspect ratio aluminas A and B have an aspect ratio of 1.1 or less and are closer to a spherical shape, so that it is difficult for protrusions to occur on the insulating film and the thick film insulating paste is prepared. Since high dispersibility is obtained, the density of the film is increased during printing and drying, and there is an advantage that a denser insulating film can be obtained after firing.

  Table 3 below shows the denseness of the protective layer 62 formed by variously changing the content and particle size of the alumina powder in order to determine the suitability as a thick film insulating paste for forming the protective layer 62. The results of evaluating the properties and scratch properties are summarized. The denseness was judged based on the continuity of the glass by observing the surface and cross section of the formed glass film with an electron microscope. “○” indicates that the continuity of the glass is maintained (= highly dense), “△” indicates that the void is recognized but has a degree of denseness that can be used as the protective layer 62, and the continuity of the glass is Those not retained, that is, those in which the existence of independent particles were recognized were evaluated as “x” (= low density). The scratch property was judged on the basis of the ease of scratching and the ease of dropping off alumina particles by rubbing the glass film surface with # 180 abrasive paper. “◯” indicates that a slight scratch is slightly generated, “×” indicates that a scratch easily enters or alumina particles easily fall off, and “Δ” indicates an intermediate between these. All of these evaluations were performed on the surface (ie, as-fired) as it was fired. For reference of evaluation criteria for scratch properties, surface micrographs of “◯”, “Δ”, and “×” are shown in FIGS.

  According to the above evaluation results, when the addition amount of alumina powder is 9.5 (vol%), the denseness is sufficient for all the average particle sizes evaluated, and 25 to 45 (vol. %), Sufficient results were obtained with an average particle size of 0.5 (μm) or more. With an addition amount of 50 (vol%), a denseness that can be used with an average particle diameter of 0.5 (μm) or more was obtained, and a sufficient denseness was obtained with an average particle diameter of 0.7 (μm) or more. With an addition amount of 55 (vol%), a denseness that can be used with an average particle diameter of 1.5 (μm) or more was obtained, and a sufficient denseness was obtained with an average particle diameter of 3 (μm) or more. With an addition amount of 57 (vol%), sufficient denseness was obtained with an average particle size of 5 (μm), and a usable fineness was obtained with an average particle size of 3 (μm) or more. With an addition amount of 60 (vol%), it was not possible to obtain a dense enough to be used.

  As for the scratch property, when the alumina powder is 9.5 (vol%), the scratch property is insufficient for all particle sizes, and the addition effect of the alumina powder does not appear, but when the added amount is 25 (vol%), 0.5% With a particle size of (μm) or more, scratch properties that can be used are obtained. When the addition amount is 35 (vol%), sufficient scratch properties can be obtained with a particle size of 0.5 (μm) or more. With an addition amount of 50 (vol%), scratch properties that can be used with a particle size of 0.5 (μm) or more can be obtained, and sufficient scratch properties can be obtained with a particle size of 0.7 (μm) or more. Further, with an addition amount of 55 (vol%), sufficient scratch properties can be obtained with a particle size of 0.7 (μm) or more. With an addition amount of 57 (vol%), a scratch property that can be used with a particle size of 3 (μm) or more can be obtained. Sufficient scratch properties could not be obtained with an addition amount of 60 (vol%). That is, when the addition amount is increased, a tendency to decrease the scratch property at a small average particle diameter is observed, and when the addition amount is 60 (vol%) or more, good scratch property cannot be obtained.

  FIG. 14 shows that based on the above evaluation results, both of the denseness and the scratch property are “◯” when “◯”, at least one is “△”, and at least one is “×”. It is the figure which showed the suitable range by making a thing "x". It can be used at an alumina volume ratio of 25 (vol%) and an alumina particle size of 7 (μm) or less, and the upper limit of the volume ratio and the lower limit of the particle size are shown by the curves in the figure. The range surrounded by the three straight lines and the curve in the figure is a range where good fineness and scratching can be obtained, and the line is a boundary between good and bad, that is, not sufficient but usable conditions. The equation of the curve is the above equation (1).

  Of the data shown in Table 3 and FIG. 14, for example, a micrograph of the surface of the glass film when the alumina volume ratio is 45 (%) and the alumina average particle size is 1.5 (μm) is shown in FIG. It can be seen that an extremely dense glass film can be obtained even under such conditions of volume ratio and average particle diameter. Although the photographs are omitted, the average particle diameter is different when the average particle size is 0.5 (μm) to 3 (μm), and the same result is obtained when the volume ratio is 25 (%). When the volume ratio is 45 (%) and the average particle size is 0.3 (μm), as shown in FIG. 16, voids are conspicuous on the film surface, and both the denseness and the scratch property become insufficient. With this volume ratio, when the particle size is smaller than 0.5 (μm), the denseness is abruptly lost. When the volume ratio is 50 (%), if the average particle diameter is 0.7 (μm) or more, sufficient denseness can be obtained as shown in FIG. 17, but 0.5 (μm) is shown in FIG. As a result, the results are slightly inferior.

  Further, when the volume ratio is 55 (%), those having an average particle diameter of 5 (μm) are sufficiently dense although unevenness is conspicuous as shown in FIG. However, when the volume ratio is about this level, as described above, when the average particle size is small, the denseness tends to be impaired. For example, in the sample of 55 (%)-0.7 (μm) as shown in FIG. Inadequate results in terms of compactness. On the other hand, when it is 60 (%) or more, as shown in a photograph of a sample of 3 (μm) as shown in FIG.

  Although not shown in the above Table 3 and FIG. 14 and the like, when the average particle diameter of alumina is 7 (μm) or more, the surface of the protective layer 62 becomes thin and the unevenness of the surface becomes large. If the thickness is increased, the thermal efficiency is inferior, so the effect of adding alumina powder is impaired. In addition, since spherical particles of 7 (μm) or more are expensive, their utility value is low. The thickness of the protective layer 62 is preferably thin in terms of thermal efficiency, and needs to be 10 (μm) or less, and is usually about 7 to 8 (μm). When the average particle diameter of alumina is 5 (μm) or more, considering the particle size distribution, particles of about 7 to 8 (μm) are included, and it is difficult to make the film thickness 10 (μm) or less. Therefore, the average particle diameter of alumina is more preferably 5 (μm) or less.

  Further, as described above, the alumina powder added to the protective layer 62 may be one having an average particle size in the range of 0.35 to 7 (μm). It can also be determined according to the application. For example, in applications where durability is important, such as for supermarket resistors, it is preferable to use coarse particles that have high wear resistance and that alumina particles are less likely to fall off. On the other hand, in applications where the fineness of printing is important, such as medical use, durability is slightly sacrificed, but it is preferable to use fine particles.

  As shown in Table 3, in Examples using spherical particles produced by the CVD method, protection with excellent denseness and scratch properties can be achieved by appropriately selecting the relationship between the alumina volume ratio and the average particle size. Although the layer 62 can be obtained, if crushed alumina is used, the denseness can be obtained to some extent, but the scratch property is inferior, so that it cannot be used for the protective layer 62. 22 and 23 show surface micrographs of glass films having a volume ratio of 55 (%) for each of average particle diameters 5 (μm) and 3 (μm) when crushed alumina is used. When crushed alumina is used, the reduction in denseness is particularly remarkable at a high content. This result is thought to be due to the fact that the aspect ratio of crushed alumina is extremely large. Moreover, when the protective layer 62 is formed using crushed alumina, there is a problem that the recording paper 64 is damaged by the edges of the alumina particles.

  As described above, according to this embodiment, since the thick film insulating paste mainly composed of glass contains alumina powder, the insulating film 22 of the fixing heater 10 of the copying machine and the thermal print head. It is suitable for 50 protective layers 62, and it is possible to obtain an insulating film having high hardness and high wear resistance and scratch resistance and high thermal conductivity and withstand voltage. At this time, since the aspect ratio of the alumina powder is as small as 1.2 or less and is nearly spherical, a high packing density can be easily obtained at the time of film formation. Enhanced. Further, since the volume ratio of the alumina powder is sufficiently large as 25 (%) or more, the improvement effect of the hardness and thermal conductivity of the insulating film and the like due to the inclusion of the alumina powder is further enhanced, and the volume ratio is 60 ( %), It is possible to obtain a strong insulating film or the like. In addition, since the average particle diameter of the alumina powder satisfies the above formula (1) and is 0.35 (μm) or more, the alumina particles are sufficiently prevented from falling off from the formed insulating film, etc. Scratch property is obtained. In addition, since the average particle size is kept at 7 (μm) or less, the unevenness of the film surface is sufficiently small even if the thickness of the insulating film to be formed is sufficiently thin, for example, 10 (μm) or less. An insulating film having sufficiently high smoothness can be obtained even by firing.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

10 fixing heater, 12 base, 14 fixing film, 16 pressure roller, 18 base material, 20 resistance heating element layer, 22 insulating film, 24 aluminum cylinder, 26 silicone rubber, 28 recording paper, 30 fixing heater, 32 base Material, 34 Resistance heating element layer, 36 Insulating film, 40 Circuit board, 42 Insulating film, 44 Substrate, 46 Conductor film, 48 Electronic component, 50 Thermal print head, 52 Pressure roller, 54 Substrate, 56 Thermal storage layer, 58 Resistance Heating element layer, 60, 60 electrode layer, 62 protective layer, 64 recording paper, 66 metal cylinder, 68 rubber layer

Claims (3)

An insulating film composition mainly composed of glass used for forming an insulating film on the surface of a predetermined substrate,
An insulating film comprising alumina powder having an aspect ratio of 1.2 or less in a range where the volume ratio x (%) and the average particle size y (μm) in the whole insulating film composition satisfy the following relational expression (1): Composition.
0.09exp (9.8 / (60−x)) + 0.24 ≦ y ≦ 7
(However, 25 ≦ x <60) (1)   The insulating film composition according to claim 1, wherein the volume ratio x (%) is in a range of 35 ≦ x ≦ 55.   The insulating film composition according to claim 1 or 2, wherein the average particle size y (µm) is 5 (µm) or less.