JP2011221259A - Insulation film composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation film composition which is capable of forming an insulation film having a further superior withstand voltage characteristic.SOLUTION: Thick film insulation paste having glass as its principal element includes alumina powder with its aspect ratio of 1.2 or less, produced using CVD; therefore, voltage which an insulation film, obtained from the thick film insulation paste, can withstand can be increased. Especially, when the alumina powder has an aspect ratio of 1.1 or less and is significantly spherical, a denser insulation film can be obtained as the result of burning, since protrusions come to be rarely caused to the insulation film and high dispersibility is obtained when preparing the thick film insulation paste, so that the density of the film is increased at the time of printing and desiccation.

Description

  The present invention relates to an insulating film composition suitable for forming an insulating film provided for the purpose of protecting an electrode on a substrate, particularly an insulating film such as a fixing heater of a copying machine.

  For example, in a copying machine of a type in which a toner image is transferred to a paper or the like and fixed, the transferred toner is melted and applied to the paper or the like by being heated and pressurized in the fixing device. It is fixed. The fixing device includes a fixing heater for heating the paper or the like, and a pressure roller for feeding the paper or the like toward the fixing heater in one direction. 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 on the outer peripheral surface of a cylindrical insulating substrate. In addition, an insulating film is formed for the purpose of protecting a conductor film such as an electrode provided on the surface, an electronic component, and the like.

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

  By the way, in order to obtain high reliability in the insulating film as described above, it is desired that the withstand voltage is as high as possible and that dielectric breakdown does not easily occur. On the other hand, a glass paste having a higher withstand voltage by replacing 5-45 wt% of the glass powder with alumina powder has been proposed (see, for example, Patent Document 1). This glass paste tends to have a low withstand voltage 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 purpose is to increase the withstand voltage. However, the insulating film produced from the glass paste has a low withstand voltage, and further improvement has been desired.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide an insulating film composition capable of forming an insulating film having a higher withstand voltage.

  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. It contains 1.2 or less alumina powder.

  In this way, since the insulating film composition containing glass as a main component contains the alumina powder, the withstand voltage of the insulating film formed from the insulating film composition is increased. At this time, since the aspect ratio of the alumina powder is as small as 1.2 or less and close to a sphere, an insulating film having a higher withstand voltage can be obtained.

  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, the higher the withstand voltage and the smaller the variation. That is, it is preferable that the alumina powder is closer to a spherical shape.

  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. For this reason, since low-cost crushed alumina, which is advantageous in terms of manufacturing cost, was used, the aspect ratio was large, so the variation in withstand voltage was large, and it was considered that 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 this resin composition has a low thermal conductivity, an 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.

  Here, preferably, the aspect ratio of the alumina powder is 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.

  Preferably, the alumina powder is manufactured using a chemical vapor deposition (CVD) method. By using the CVD method, it is possible to easily produce a fine spherical alumina powder with a small aspect ratio and a small variation in particle size, so that an insulating film composition that can form an insulating film with higher withstand voltage and smaller variation A thing is obtained. 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. The production method of alumina powder with a small aspect ratio is not limited to the CVD method, but a liquid phase method or a method of processing a crushed powder can be considered. However, according to the CVD method as described above, a powder with little variation is produced at low cost. It is preferable because it is possible.

  Preferably, the alumina powder has an average particle diameter D50 of 5 (μm) or less. Depending on the film thickness of the insulating film to be formed, if the average particle size is 5 (μm) or less, the projections that cause problems in insulating film applications such as fixing heaters and circuit boards are unlikely to occur. The minimum voltage is also sufficiently high.

  Preferably, the alumina powder has an average particle diameter D50 of 0.3 (μm) or more. In order to suppress aggregation of the alumina powder to be added and obtain high dispersibility, the average particle size is preferably set to 0.3 (μm) or more.

  Preferably, the alumina powder is added in a range of 30 to 70 (wt%) with respect to the glass powder. If it is kept at 70 (wt%) or less, the film surface after baking is sufficiently suppressed with the addition of alumina powder, so that an insulating film with higher surface smoothness can be obtained. Further, if it is 30 (wt%) or more, the thermal conductivity is sufficiently high. From the same viewpoint, the amount of alumina powder added is more preferably in the range of 40 to 60 (wt%).

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. Since the insulating film composition of the present invention has a high withstand voltage when the alumina powder having a low aspect ratio is added as described above, it is suitable for an insulating film of a fixing heater to which a high voltage is applied.

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 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. 4 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.

  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. .

  In any of the applications shown in FIGS. 1 to 3, since the insulating films 22, 36, and 42 contain alumina powder having higher thermal conductivity than glass, thermal conductivity is also improved. Therefore, it has the characteristic which is excellent also in heat dissipation.

  For the insulating films 22, 36, 42, for example, a thick film insulating paste, that is, an insulating film composition in which glass powder and filler are dispersed in a vehicle is prepared, and this is used as the resistance heating element layers 20, 34 and the conductor film. It is formed by applying on a suitable coating method such as dipping or screen printing on 46 and the like, followed by baking treatment.

  4 and 5 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. 4 and 5 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. 4, when a fine alumina powder having an average particle size of 0.8 (μm) is used, an insulating film having 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. 5, 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.

  In short, according to the present embodiment, the thick film insulating paste mainly composed of glass contains alumina powder having an aspect ratio of 1.2 or less manufactured by CVD, and thus formed from the thick film insulating paste. The withstand voltage of the insulating film is 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 in the insulating film and the thick film insulating paste is prepared. In this case, 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.

  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.

Claims (2)

An insulating film composition mainly composed of glass used for forming an insulating film on the surface of a predetermined substrate,
An insulating film composition comprising an alumina powder having an aspect ratio of 1.2 or less.   The insulating film composition according to claim 1, wherein the alumina powder is manufactured using a chemical vapor deposition method.