ADHESIVE

Abstract

An adhesive 50 contains a bisphenol-F resin 51, a curing agent 53 for the bisphenol-F resin 51, and magnetic powder 52. The volume ratio of the magnetic powder 52 to the adhesive 50 is 35 vol% or less. The number-mean molecular weight of the bisphenol-F resin 51 is 312 to 360 g / mol.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to an adhesive. 2. Description of the state of the art

[0002] A coil component disclosed in Japanese Unexamined Patent Application No. 2021-190633 includes a core. The core includes a winding core and two flanges. The winding core is shaped like a quadrangular prism. One of the two flanges is connected to one side of the winding core, and the other flange is connected to the other side of the winding core. Each flange protrudes outward from the winding core in a direction perpendicular to the central axis of the winding core. The core is made of a magnetic material. The coil component also includes a top plate. The top plate has a substantially rectangular, planar shape. The top plate is connected to the core such that the two flanges therebetween are connected like a bridge. The coil component contains an adhesive. The adhesive is located between the top plate and the core and bonds the top plate and core together. The adhesive contains magnetic powder. PRESENTATION OF THE INVENTION

[0003] The adhesive for the coil component described in the above-mentioned publication contains magnetic powder, so its permeability is higher than that of an adhesive without magnetic powder. However, the larger the proportion of magnetic powder in an adhesive, the higher the viscosity of the adhesive. If the viscosity of the adhesive is too high, when the adhesive is applied to a top plate, for example, using a stencil, the adhesive may become thread-like or fibrous between the stencil and the top plate. In other words, the increased viscosity of an adhesive makes it difficult to handle the adhesive during application. Therefore, it is desirable to provide an adhesive that ensures sufficiently high permeability and is also simple and easy to handle during the manufacture of a component to which the adhesive is applied.

[0004] To solve the above-described problem, one aspect of the present invention provides an adhesive containing a bisphenol F resin, a curing agent for the bisphenol F resin, and magnetic powder. The volume ratio of the magnetic powder to the adhesive is 35 vol% or less. The number-average molecular weight of the bisphenol F resin is 312 to 360 g / mol.

[0005] With the configuration described above, the adhesive can ensure sufficiently high permeability and is also simple and easy to handle when manufacturing a component to which the adhesive is applied. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a coil component; Fig. 2 is an exploded perspective view of the coil component; Fig.3 is a schematic view of an adhesive in an uncured state; Fig. 4 is a graph showing the test results of a thread formation stop time; and Fig. Figure 5 is a graph showing the test results of the thread formation stop time. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] An embodiment of a coil component containing an adhesive is described below with reference to the drawings. For a better understanding of the embodiment, the elements in the drawings may be enlarged. The proportions of the elements in one drawing may differ from those in another drawing or from those of the actual elements. (coil component)

[0007] As in Fig.1, a coil component 10 includes a drum core 10C serving as a first core and a top plate 10F serving as a second core.

[0008] The drum core 10C includes a winding core 11. The winding core 11 is shaped like a quadrangular prism with a central axis line 11C. A cross-section of the winding core 11 perpendicular to the central axis line 11C has a rectangular shape. In this embodiment, the term "rectangular shape" includes an approximately rectangular shape with four sides, for example, a rectangle with chamfered corners. Examples of the material of the winding core 11 include alumina, Ni-Zn ferrite, synthetic resin, and a mixture of these materials. In this embodiment, the material of the winding core 11 is Ni-Zn ferrite, which is a type of magnetic material.

[0009] A specific axis perpendicular to the central axis line 11C of the winding core 11 is set as a first axis X. In the embodiment, the first axis X is parallel to the two short sides of the winding core 11 when the winding core 11 is viewed in a direction along the central axis line 11C. An axis perpendicular to both the first axis X and the central axis line 11C is set as a second axis Y. In the embodiment, the second axis Y is parallel to the two long sides of the winding core 11 when the winding core 11 is viewed in a direction along the central axis line 11C. An axis parallel to the central axis line 11C is set as a third axis Z. One of the directions along the first axis X is set to a first positive direction X1, while the opposite direction to the first positive direction X1 is set to a first negative direction X2.Similarly, one of the directions along the second Y axis is set to a second positive direction Y1, while the opposite direction of the second positive direction Y1 is set to a second negative direction Y2. One of the directions along the third Z axis is set to a third positive direction Z1, while the opposite direction of the third positive direction Z1 is set to a third negative direction Z2.

[0010] As in Fig.1, the drum core 10C includes two flanges 20: one flange 20 is connected to one side of the winding core 11, and the other flange 20 is connected to the other side of the winding core 11, as viewed in the direction of the central axis line 11C. Specifically, the two flanges 20 are a first flange 21 and a second flange 22. The first flange 21 is connected to a first end of the winding core 11, which is the end of the third positive direction Z1. The first flange 21 has a flat, substantially quadrangular, planar shape. The thickness direction of the first flange 21 is a direction along the third axis Z. When the first flange 21 is viewed in a direction along the third axis Z, the individual sides of the first flange 21 are substantially parallel to the individual sides of the winding core 11.The first flange 21 protrudes outwardly with respect to the outer surfaces of the winding core 11 in the direction along the first axis X and the direction along the second axis Y. That is, when the first flange 21 is viewed in the direction along the third axis Z, the first flange 21 protrudes approximately 360 degrees with respect to the outer surfaces of the winding core 11.

[0011] The first flange 21 has a first cavity 21A. The first cavity 21A is recessed with respect to the end surface of the first flange 21 in the first positive direction X1. The first cavity 21A is located in the center of the first flange 21 in the direction of the second axis Y. The first cavity 21A is open on both sides of the first flange 21 in the direction of the third axis Z. In this configuration, the end surface of the first flange 21 is divided into two sections in the first positive direction X1, with the first cavity 21A located between them.

[0012] The second flange 22 is connected to a second end of the winding core 11, which is the end of the third negative direction Z2. The shape of the second flange 22 is plane-symmetrical to that of the first flange 21. That is, the second flange 22 has a substantially quadrangular, planar shape. The second flange 22 protrudes outwardly from the outer surfaces of the winding core 11 in the direction along the first axis X and in the direction along the second axis Y. That is, when the second flange 22 is viewed in the direction along the third axis Z, the second flange 22 protrudes 360 degrees from the outer surfaces of the winding core 11. The second flange 22 has a second recess 22A similar to the first recess 21A of the first flange 21. The material of the first and second flanges 21 and 22 is Ni-Zn ferrite, the same material as the winding core 11.That is, the drum core 10C is made of a magnetic material. The first and second flanges 21 and 22 are formed integrally with the winding core 11.

[0013] The upper plate 10F has a flat, rectangular, and planar shape. The thickness direction of the upper plate 10F is a direction along the first axis X. The long sides of the upper plate 10F are parallel to the third axis Z. The short sides of the upper plate 10F are parallel to the second axis Y. The upper plate 10F is located in the first negative direction X2 with respect to the drum core 10C. The upper plate 10F is bonded to the surface of the first flange 21 facing the first negative direction X2 and is also bonded to the surface of the second flange 22 facing the first negative direction X2. That is, the upper plate 10F is bonded to the drum core 10C to connect the first and second flanges 21 and 22 therebetween like a bridge. The material of the upper plate 10F is the same as the material of the winding core 11.That is, the upper plate 10F is made of Ni-Zn ferrite, a type of magnetic material. The upper plate 10F, together with the drum core 10C, forms a closed magnetic path. In the embodiment, the upper plate 10F, around which wires, discussed later, are not directly wound, and elements of the drum core 10C, such as the flanges 20, around which the wires are not wound, are also considered to be a core or part of the core.

[0014] The coil component 10 contains an adhesive 50. The adhesive 50 is located between the drum core 10C and the top plate 10F. That is, the adhesive 50 bonds the drum core 10C and the top plate 10F to each other. In this embodiment, the drum core 10C and the top plate 10F directly contact the adhesive 50. In other words, the top plate 10F is bonded to the two flanges 20 via the adhesive 50. The details of the adhesive 50 will be discussed later.

[0015] The coil component 10 includes four external electrodes 30. Specifically, the coil component 10 includes a first electrode 31, a second electrode 32, a third electrode 33, and a fourth electrode 34. Of the outer surfaces of the first flange 21, the first electrode 31 is located on the end surface facing the first positive direction X1. Among the outer surfaces of the first flange 21, the first electrode 31 is also located in the second positive direction Y1 with respect to the central axis line 11C. Specifically, the first electrode 31 is located in the second positive direction Y1 with respect to the first cavity 21A.

[0016] Of the outer surfaces of the first flange 21, the second electrode 32 is located on the end surface positioned in the first positive direction X1. Among the outer surfaces of the first flange 21, the second electrode 32 is also arranged in the second negative direction Y2 with respect to the central axis line 11C. Specifically, the second electrode 32 is arranged in the second negative direction Y2 with respect to the first cavity 21A.

[0017] Of the outer surfaces of the second flange 22, the third electrode 33 is located on the end surface positioned in the first positive direction X1. Among the outer surfaces of the second flange 22, the third electrode 33 is also located in the second positive direction Y1 with respect to the central axis line 11C. Specifically, the third electrode 33 is located in the second positive direction Y1 with respect to the second cavity 22A.

[0018] Of the outer surfaces of the second flange 22, the fourth electrode 34 is located on the end surface positioned in the first positive direction X1. Among the outer surfaces of the second flange 22, the fourth electrode 34 is also arranged in the second negative direction Y2 with respect to the central axis line 11C. Specifically, the fourth electrode 34 is located in the second negative direction Y2 with respect to the second cavity 22A.

[0019] The outer electrode 30 has a metal layer and a plated layer, which are not shown. The material of the metal layer is silver. The metal layer is formed on the outer surface of the first and second flanges 21 and 22. The plated layer is composed of three layers. The plated layer is formed of copper, nickel, and tin layers deposited in this order on the surface of the metal layer. The end surface of the coil component 10 located in the first positive direction X1 serves as a mounting surface at the time of mounting the coil component 10 on a substrate.

[0020] As in Fig. 1, the coil component 10 comprises a first wire 41 and a second wire 42. The first and second wires 41 and 42 are wound around the winding core 11 of the drum core 10C.

[0021] The first wire 41 includes a copper wire and an insulating coating (not shown). The insulating coating covers the outer surface of the copper wire. The first wire 41 is substantially circular in a cross-section perpendicular to the extension direction of the first wire 41. The configuration of the second wire 42 is the same as that of the first wire 41. That is, the second wire 42 includes a copper wire and an insulating layer. Fig. 1, the first wire 41 is represented by a dot pattern.

[0022] A first end 41A of the first wire 41 is connected to the first electrode 31. A second end 41B of the first wire 41 is connected to the third electrode 33. The first and second ends 41A and 41B are thermally pressure-connected to the corresponding outer electrodes 30.

[0023] When the first wire 41 is viewed in the third negative direction Z2, it is wound around the winding core 11 in a clockwise direction from the first end 41A to the second end 41B.

[0024] A first end 42A of the second wire 42 is connected to the second electrode 32. A second end 42B of the second wire 42 is connected to the fourth electrode 34. The first and second ends 42A and 42B are thermally pressure-connected to the respective electrodes.

[0025] When viewed in the third negative direction Z2, the second wire 42 is wound clockwise around the winding core 11 from the first end 42A to the second end 42B. That is, the second wire 42 is wound in the same direction as the first wire 41. The second wire 42 is wound around the winding core 11 on the outside of the first wire 41. (Adhesive)

[0026] As in Fig.As shown in Figure 2, the adhesive 50 covers the entire surface of the first flange 21 facing the first negative direction X2. The adhesive 50 bonds the first flange 21 and the upper plate 10F together without any gap. Likewise, the adhesive 50 covers the entire surface of the second flange 22 facing the first negative direction X2. The adhesive 50 bonds the second flange 22 and the upper plate 10F together without any gap. That is, the upper plate 10F is bonded to the two flanges 20.

[0027] As in Fig. 3, the adhesive 50 contains a bisphenol F resin 51, magnetic powder 52, a curing agent 53, a curing accelerator 54, a silane coupling agent 55 and a dispersing agent 56. The Fig. The adhesive 50 shown in Figure 3 is in a not yet cured state. Fig.3, only some magnetic powders 52 and only a part of the curing agent 53 and the curing accelerator 54 are provided with reference numbers.

[0028] Specifically, the adhesive 50 is prepared as follows. First, the bisphenol F resin 51, the curing agent 53, the curing accelerator 54, the silane coupling agent 55, the dispersant 56, and the magnetic powder 52 are mixed with a kneader (model type: HIVIS MIX (registered trademark) 2P-03 (manufactured by PRIMIX Corporation)) at 30 rpm for five minutes. Then, the resulting mixture is kneaded with a dispersing machine (model type: EXAKT 80E (manufactured by Nagase Screen Printing Research Co., Ltd.)) at a pitch of 6 µm and 230 rpm. As a result, the uncured adhesive 50 was prepared.

[0029] In the embodiment, the bisphenol F resin 51 is a bisphenol F epoxy resin, and more specifically, it is CAS No. 9003-36-5. In this embodiment, the resin is referred to collectively as bisphenol F resin 51, regardless of whether it is a monomer or a polymer.

[0030] The number-average molecular weight of bisphenol F resin 51 is 312 g / mol. The number-average molecular weight of bisphenol F resin 51 can be any value within a range of 312 to 360 g / mol. The number-average molecular weight can be measured using GPC (model type: HLC-8120GPC (manufactured by Tosoh Techno-System Inc.)). GPC stands for gel permeation chromatography. For measurements using this instrument, the column temperature was set to 40°C, and tetrahydrofuran was used as the solvent. The flow rate of a solution including the solvent was set to 1.0 mL / min. Monodisperse polystyrene was used as the standard sample.

[0031] In the embodiment, the volume ratio of the bisphenol F resin 51 to the adhesive 50 is 54.5 vol%, and more preferably 54.4 to 68.7 vol%. "Volume ratio of the bisphenol F resin 51 to the adhesive 50" is the proportion of the volume of the bisphenol F resin 51 to the total volume of the uncured adhesive 50, which is expressed as a percentage.

[0032] In the embodiment, the magnetic powders 52 are nickel powders, specifically, CAS No. 7440-02-0. The magnetic powders 52 contain particles with particle sizes ranging from 0.1 to 3.0 µm. The volume ratio between the magnetic powders 52 and the adhesive 50 is 35 vol% or less. In this embodiment, the volume ratio between the magnetic powders 52 and the adhesive 50 is 35 vol%. The volume ratio between the magnetic powders 52 and the adhesive 50 may be 35 vol% or less, preferably 20 to 35 vol%.

[0033] In the particle size distribution of the magnetic powder 52, the average particle size (D50) is 0.8 to 2.5 µm.

[0034] For example, the average particle size (D50) of the magnetic powder 52 is calculated as follows. First, samples of the magnetic powder 52 are selected using a scanning electron microscope to obtain the particle size distribution. Then, in the particle size distribution, the frequency of each particle size is accumulated in order from the smallest to the largest particle size, and the particle size whose accumulated value is 50% is set as the average particle size (D50).

[0035] The curing agent 53 is that for the bisphenol F resin 51. In the present embodiment, the curing agent 53 is dicyandiamide, and more specifically, it is CAS No. 461-58-5. The volume ratio of the curing agent 53 to the adhesive 50 is 4.36 vol%, and is preferably in a range of 4.36 to 5.49 vol%.

[0036] The curing accelerator 54 is that for the bisphenol F resin 51. In the embodiment, the curing accelerator 54 is an amine adduct, and more specifically, it is CAS No. 134091-75-1. The volume ratio of the curing accelerator 54 to the adhesive 50 is 2.73 vol%, and preferably ranges from 2.72 to 3.43 vol%.

[0037] The dispersant 56 is used to disperse the magnetic powder 52 in the adhesive 50. In the embodiment, the dispersant 56 is a carboxyl group-containing polymer-modified substance, particularly a carboxyl group-containing polymer-modified substance with an acid value of 55 mgKOH / g. The volume ratio of the dispersant 56 to the adhesive 50 is 3.1 vol% and is preferably in a range of 2.18 to 3.13 vol%.

[0038] In the embodiment, the silane coupling agent 55 is glycidoxypropyltrimethoxysilane, and in particular, it is CAS No. 253-83-8. The volume ratio of the silane coupling agent 55 to the adhesive 50 is 0.3 vol% and is preferably in the range of 0.24 to 0.35 vol%. (Properties of the adhesive)

[0039] The glass transition temperature of the adhesive 50 in the cured state is 125°C or higher. The glass transition temperature of the adhesive 50 was measured as follows. First, the bisphenol F resin 51, the curing agent 53, the curing accelerator 54, the silane coupling agent 55, the dispersant 56, and the magnetic powder 52 were mixed and then fired at a temperature of 150°C for three hours. This prepared a specimen for the cured adhesion test. The specimen had a length of 20 mm, a width of 10 mm, and a thickness of 1.5 mm. The short sides of the adhesion test specimen were mounted on a viscoelasticity tester (model type: DMS7100 (manufactured by Hitachi High-Tech Corporation)), and the elastic modulus was measured. During the measurements, the temperature was increased while a sine wave with a frequency of 1 Hz acted on the test specimen.The temperature increase occurred at a rate of 5°C / min. The temperature range was between 25°C and 280°C. The transition of the specimen's elastic modulus was then measured as a function of the temperature increase, and the inflection point was set to the glass transition temperature.

[0040] The bond strength of the cured adhesive 50 is 10 MPa or more. The bond strength of the adhesive 50 was measured as follows. First, the bisphenol F resin 51, the curing agent 53, the curing accelerator 54, the dispersant 56, the silane coupling agent 55, and the magnetic powder 52 were mixed to form the uncured adhesive 50. Then, the uncured adhesive 50 was applied to a space of 5 × 5 square millimeters between two alumina substrates. That is, the bond strength of the adhesive 50 to 25 square millimeters was measured. Then, the two alumina substrates coated with the uncured adhesive 50 were baked at a temperature of 150°C for three hours. Thus, a test specimen in the cured state was prepared.Then, one alumina substrate and the other alumina substrate were bonded to an autograph (model type: AG XD Plus (manufactured by Shimadzu Corporation)), and tensile tests were conducted. In this case, the tensile bond strength was measured as the adhesion strength. During the test, the tensile speed was 20 mm / min. The bond strength of the adhesive was determined as the stress at the fracture of the specimen. During the test, the temperature was 23°C and the relative humidity was 50%. (Continuous printability of the adhesive)

[0041] Four samples of the adhesive 50 were prepared by varying the number-average molecular weight of the bisphenol F resin 51, and the stringing stop time of each sample was measured. Except for the number-average molecular weight of the bisphenol F resin 51, other conditions were the same for the four samples. The volume ratios of the magnetic powders 52 in the four samples were all 35% by volume. The volume ratio of the magnetic powders 52 is the same as that of the uncured adhesive 50. The stringing stop time is the time that elapses when the uncured adhesive 50 is applied to a substrate with a squeegee using a screen printer and the squeegee is removed from the substrate until the adhesive 50, which is in a filamentous or fibrous state between the squeegee and the substrate, is separated from the squeegee.For the stringing stop time measurements, the screen printer conditions were set as follows: printing speed was 60 mm / s, air pressure was 0.2 MPa, back pressure was 0.125 MPa, and the pitch was 1 mm. Continuous printing was performed 100 times under these conditions, and the stringing stop times for the first, twenty-fifth, fiftieth, and hundredth prints were measured. The average of the stringing stop time was taken as the representative value.

[0042] The number-average molecular weights of the bisphenol F resin 51 in the four samples were determined as follows: the first sample was 312 g / mol, which corresponds to that of the embodiment; the second sample was 340 g / mol; the third sample was 360 g / mol; and the fourth sample was 380 g / mol. These four samples correspond to the first, second, and third examples and a first comparative example in Table 1 shown below.

[0043] As from Fig. As can be seen in Figure 4, the thread formation stop times of the four samples are as follows: the first sample is 11 seconds, the second sample 12 seconds, the third sample 20 seconds, and the fourth sample 80 seconds. Fig.4 shows that the larger the number-average molecular weight of the bisphenol F resin 51 in the adhesive 50, the longer the stringing stop time becomes, and the sharp increase occurs when the number-average molecular weight of the bisphenol F resin 51 exceeds 360 g / mol. That is, the inflection point of the stringing stop time with respect to an increase in the number-average molecular weight is around 360 g / mol. When the adhesive 50 is applied with a screen printer, as the stringing stop time increases, the waiting time in a state where the squeegee is separated from the substrate becomes longer, thereby deteriorating continuous printability. Therefore, it is noted that the number-average molecular weight of the bisphenol F resin 51 in the adhesive 50 is preferably 360 g / mol or less to enable easy handling of the adhesive 50.

[0044] Five samples of the adhesive 50 were formed by varying the volume ratio of the magnetic powders 52, and the stringing stop time of each sample was measured. Except for the volume ratio of the magnetic powders 52, other conditions were the same for the five samples. The number-average molecular weights of the bisphenol F resin 51 in the five samples were all 340 g / mol. The definition of the stringing stop time is as described above. The volume ratios of the magnetic powders 52 in the five samples were set as follows: the first sample was 20 vol%, the second sample was 25 vol%, the third sample was 30 vol%, the fourth sample was 35 vol%, and the fifth sample was 40 vol%. The volume ratio of the magnetic powders 52 is the same as that of the uncured adhesive 50. These five samples correspond to the fourth, fifth, sixth, and second examples, as well as a second comparative example in Table 1 shown below.

[0045] As from Fig. As can be seen in Figure 5, the thread formation stop times of the five samples are as follows: the first sample is 10 seconds, the second sample is 10 seconds, the third sample is 11 seconds, the fourth sample is 12 seconds, and the fifth sample is 80 seconds. Fig. 5 that the threading stop time increases abruptly when the volume ratio of the magnetic powder 52 to the adhesive 50 exceeds 35 vol%. That is, the inflection point of the threading stop time with respect to an increase in the volume ratio of the magnetic powder 52 is approximately 35 vol%. Therefore, it is noted that the volume ratio of the magnetic powder 52 to the adhesive 50 is preferably 35 vol% or less in view of ease of handling of the adhesive 50. (Comparison test)

[0046] The adhesives of the first to ninth examples and those of the first and second comparative examples listed in Table 1 and Table 2 below were prepared. Then, the properties of the uncured adhesives and those of the cured adhesives of these examples and the comparative examples were examined. In the adhesives of the first to ninth examples and the first and second comparative examples, the synthetic resin is a bisphenol F epoxy resin. In the adhesives of the first to sixth examples and the first and second comparative examples, the average particle size (D50) of the magnetic powder 52 is 0.8 µm. The adhesives of the first to ninth examples and the first and second comparative examples each contain the magnetic powder 52, the curing agent 53, the curing accelerator 54, the silane coupling agent 55, and the dispersing agent 56. (First to sixth examples)

[0047] The results of the comparison test for the first to sixth examples and the first and second comparison examples are explained below. Table 1 material Properties (uncured) Properties (cured) resin Number average molecular weight [g / mol] Volume fraction of the magnetic powder [Vol%] Viscosity [Pa-s] Thread formation stop time [s] Test results [≤20] Permeability Glass transition temperature [°C] Adhesive strength [MPa] First example Bisphenol F epoxy resin 312 35 1833 11 OK 2,5 125 14 Second example Bisphenol F epoxy resin 340 35 2528 12 OK 2,5 125 14 Third example Bisphenol F epoxy resin 360 35 3223 20 OK 2,5 125 14 Fourth example Bisphenol F epoxy resin 340 20 283 10 OK 1,7 125 14 Fifth example Bisphenol F epoxy resin 340 25 567 10 OK 2,0 125 14 Sixth example Bisphenol F epoxy resin 340 30 1143 11 OK 2,2 125 14 First comparison example Bisphenol F epoxy resin 380 35 3760 80 NG 2,5 125 14 Second comparison example Bisphenol F epoxy resin 340 40 4507 80 NG 2,9 125 14

[0048] As shown in Table 1, the properties of the adhesive of the first example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 312 g / mol; the volume ratio of the magnetic powder 52 is 35 vol%; the viscosity of the adhesive in the uncured state is 1833 Pa-s; the permeability of the adhesive in the cured state is 2.5; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0049] The viscosity was measured using a rotational rheometer (model type: MCR302 (Anton Paar GmbH)). A conical plate with a diameter φ of 25 mm was used for the measurements, the rotation mode was set to flow curve, and the shear rate was set to 0.01 s -1 and the temperature in the experiment was set to 25°C.

[0050] The permeability was measured as follows. First, the bisphenol F resin 51, the curing agent 53, the curing accelerator 54, the dispersant 56, the silane coupling agent 55, and the magnetic powder 52 were mixed to form the uncured adhesive 50. Then, the uncured adhesive 50 was baked at a temperature of 85°C for one hour to form the semi-cured adhesive 50. Subsequently, the semi-cured adhesive 50 was filled into a mold with an outer diameter φ of 16 mm and an inner diameter φ of 10 mm and pressed for 15 minutes using a small hot-pressing machine (model type: H300-15 (manufacturer: AS ONE Corporation)) at a pressure of 4 MPa and a heating temperature of 150°C. As a result, a toroidal core was formed. The complex permeability of the toroid core was measured using an impedance analyzer (model type: E4991A (manufactured by Keysight Technologies)) at 10 MHz.The real part of the complex permeability was determined as the permeability. The test temperature was 25°C.

[0051] The properties of the adhesive of the second example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 35 vol%; the viscosity of the adhesive in the uncured state is 2528 Pas; the permeability of the adhesive in the cured state is 2.5; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0052] The properties of the adhesive of the third example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 360 g / mol; the volume ratio of the magnetic powder 52 is 35 vol%; the viscosity of the adhesive in the uncured state is 3223 Pas; the permeability of the adhesive in the cured state is 2.5; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0053] The properties of the adhesive of the fourth example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 20 vol%; the viscosity of the adhesive in the uncured state is 283 Pas; the permeability of the adhesive in the cured state is 1.7; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0054] The properties of the adhesive of the fifth example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 25 vol%; the viscosity of the adhesive in the uncured state is 567 Pas; the permeability of the adhesive in the cured state is 2.0; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0055] The properties of the adhesive of the sixth example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 30 vol%; the viscosity of the adhesive in the uncured state is 1143 Pas; the permeability of the adhesive in the cured state is 2.2; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0056] The properties of the adhesive of the first comparative example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 380 g / mol; the volume ratio of the magnetic powder 52 is 35 vol%; the viscosity of the adhesive in the uncured state is 3760 Pa-s; the permeability of the adhesive in the cured state is 2.5; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0057] The properties of the adhesive of the second comparative example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 40 vol%; the viscosity of the adhesive in the uncured state is 4507 Pa-s; the permeability of the adhesive in the cured state is 2.9; the glass transition temperature of the adhesive in the cured state is 125°C; and the bond strength of the adhesive in the cured state is 14 MPa.

[0058] The results of the threading stop time in the comparison test are as follows: the first example is 11 seconds; the second example is 12 seconds; the third example is 20 seconds; the fourth example is 10 seconds; the fifth example is 10 seconds; the sixth example is 11 seconds; the first comparison example is 80 seconds; and the second comparison example is 80 seconds.

[0059] In the "Test Results" field of "Properties (Uncured)" in Table 1 and Table 2, "OK" means that the stringing stop time is 20 seconds or less, while "NG" means that the stringing stop time is longer than 20 seconds. The value used in the test results is determined by whether the adhesive 50, which is stringy and does not peel off from the squeegee, can adhere to a material other than a printing medium.

[0060] The test results of the first to sixth examples and the first comparative example show that when the number-average molecular weight of the bisphenol F resin 51 is large, the stringing stop time tends to become long. That is, when the number-average molecular weight of the bisphenol F resin 51 exceeds 360 g / mol, as in the measurement results of the stringing stop time using the four samples described above, the rate of increase in the stringing stop time suddenly becomes high. In other words, it is noted that the number-average molecular weight of the bisphenol F resin 51 in the adhesive 50 is preferably 360 g / mol or less.

[0061] The test results of the first to sixth examples and the second comparative example show that when the volume ratio of the magnetic powder 52 is high, the threading stop time tends to become long. That is, when the volume ratio of the magnetic powder 52 exceeds 35 vol%, as in the measurement results of the threading stop time using the five samples described above, the rate of increase in the threading stop time suddenly becomes high. In other words, it can be said that the volume ratio of the magnetic powder 52 is preferably 35 vol%.

[0062] For the adhesive of the third example, whose viscosity is 3223 Pa·s, the stringing stop time is 20 seconds. For the adhesive of the first comparative example, whose viscosity is 3760 Pa·s, the stringing stop time is 80 seconds. It can therefore be seen that the inflection point for the transition of the stringing stop time with respect to an increase in viscosity can be estimated at 3223 to 3760 Pa·s, i.e., approximately 3500 Pa·s. Therefore, it is noted that the viscosity of the adhesive, for example, is preferably 3500 Pa·s or less.

[0063] The permeability of the adhesives in the cured state is greater than 1.7 in all examples 1 to 6. If the permeability of an adhesive exceeds 1.7, that adhesive can be practically used as the adhesive 50 for bonding the drum core 10C and the top plate 10F of the coil component 10. That is, the permeability of each of the adhesives in the first to sixth examples is sufficient for the adhesive 50 of the coil component 10. (Second, third and seventh to ninth examples)

[0064] The results of the comparison test for the second, third, and seventh to ninth examples are explained below. Table 2 material Properties (uncured) resin Number average molecular weight [g / mol] Volume fraction of magnetic powder [Vol%] Average particle size (D50) [µm] Viscosity [Pa-s] Thread formation stop time [s] Test results [≤20] Second example Bisphenol F epoxy resin 340 35 0,8 2528 11 OK Third example Bisphenol F epoxy resin 360 35 0,8 3223 20 OK Seventh example Bisphenol F epoxy resin 340 35 0,5 2911 16 OK Eighth example Bisphenol F epoxy resin 360 35 1,5 1820 11 OK Ninth example Bisphenol F epoxy resin 340 25 2,5 1137 11 OK

[0065] As shown in Table 2, the adhesive of the second example is the adhesive of the second example described above. That is, the average particle size (D50) of the magnetic powder 52 in this adhesive is 0.8 µm. The adhesive of the third example is the adhesive of the third example described above. That is, the average particle size (D50) of the magnetic powder 52 in this adhesive is 0.8 µm.

[0066] The properties of the adhesive of the seventh example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 35 vol%; the average particle size (D50) of the magnetic powder 52 is 0.5 µm; and the viscosity of the adhesive in the uncured state is 2911 Pa·s.

[0067] The properties of the adhesive of the eighth example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 360 g / mol; the volume ratio of the magnetic powder 52 is 35 vol%; the average particle size (D50) of the magnetic powder 52 is 1.5 µm; and the viscosity of the adhesive in the uncured state is 1820 Pa-s.

[0068] The properties of the adhesive of the ninth example are as follows: the number-average molecular weight of the bisphenol F resin 51 is 340 g / mol; the volume ratio of the magnetic powder 52 is 25 vol%; the average particle size (D50) of the magnetic powder 52 is 2.5 µm; and the viscosity of the adhesive in the uncured state is 1137 Pa·s.

[0069] The results of the thread formation stop time in the comparison test are as follows: the seventh example is 16 seconds, the eighth example is 11 seconds, and the ninth example is 11 seconds.

[0070] The test results of the second, third, and seventh to ninth examples show that when the average particle size (D50) of the magnetic powder 52 is in a range of 0.8 to 2.5 μm, the stringing stop time is 20 seconds or shorter, and that the smaller the average particle size (D50) of the magnetic powder 52 in the adhesive 50, the higher the viscosity tends to be. Therefore, it is noted that the average particle size (D50) of the magnetic powder 52 is preferably 0.8 μm or larger. (Advantages of the embodiment)

[0071] (1) In this embodiment, the adhesive 50 contains the magnetic powders 52 and therefore has a higher permeability than the adhesive without the magnetic powders 52. The larger the number-average molecular weight of the bisphenol F resin 51 in the adhesive 50, the higher the viscosity of the adhesive 50 tends to be. Examples of the number-average molecular weight of a typical commercially available bisphenol F epoxy resin are about 3300 g / mol and about 5500 g / mol. In contrast, the number-average molecular weight of the bisphenol F resin 51 in this embodiment is 312 to 360 g / mol, which is much smaller than that of a typical bisphenol F resin. Using the bisphenol F resin 51 with a number-average molecular weight in this range can cause an increase in the viscosity of the adhesive 50.

[0072] Likewise, the viscosity of the adhesive 50 tends to increase as the volume ratio of the magnetic powder 52 to the adhesive 50 increases. In the present embodiment, the volume ratio of the magnetic powder 52 to the adhesive 50 is 35 vol% or less. Using magnetic powder 52 with such a volume ratio can control an increase in the viscosity of the adhesive 50.

[0073] With the configurations described above, the adhesive 50 can ensure sufficiently high permeability to be used as an adhesive for the coil component 10, and is also simple and easy to handle in the manufacture of the coil component 10. Among other things, the use of the adhesive 50 of the embodiment can reduce the stringing stop time when the uncured adhesive 50 is applied to the top plate 10F of the coil component 10 with a screen printer. That is, the adhesive 50 is also desirable in terms of continuous printability.

[0074] (2) In the embodiment, the volume ratio of the magnetic powder 52 to the adhesive 50 is 20 vol% or more. With this volume ratio, the adhesive 50 to be applied to the coil component 10 achieves a desired permeability.

[0075] (3) In the embodiment, the adhesive 50 contains the silane coupling agent 55. The use of the silane coupling agent 55 can improve the adhesive strength of the adhesive 50. Specifically, in the embodiment, the adhesive 50 is disposed between the drum core 10C and the top plate 10F, and the silane coupling agent 55 is useful for bonding such inorganic materials.

[0076] (4) In this embodiment, the adhesive 50 contains the dispersant 56. The use of the dispersant 56 can make it difficult for the magnetic powders 52 to aggregate. For this reason, even if the volume ratio of the magnetic powders 52 is high to a certain extent, the magnetic powders 52 are less likely to aggregate.

[0077] (5) In this embodiment, the glass transition temperature of the adhesive 50 is 125°C or higher. This can improve the heat resistance of the adhesive 50. For this reason, the reliability of the coil component 10 is less affected even when used in a high-temperature environment, for example.

[0078] (6) In this embodiment, the average particle size (D50) of the magnetic powder 52 is 0.8 μm or more. The smaller the average particle size (D50) of the magnetic powder 52 in the adhesive 50, the higher the viscosity tends to be. The results of the comparative test described above show that using magnetic powder 52 with an average particle size (D50) of 0.8 μm or more can regulate an increase in the threading stop time.

[0079] (7) In this embodiment, the average particle size (D50) of the magnetic powders 52 is 2.5 μm or less. If the average particle size (D50) of the magnetic powders 52 is larger, the magnetic powders 52 tend to collide with each other in the adhesive 50. That is, depending on the shape of a part to be coated with the adhesive 50, the magnetic powders 52 may not match the shape of that part and may become uneven in the adhesive 50. When using magnetic powders 52 with an average particle size (D50) within the range described above, these problems are less likely to occur.

[0080] (8) In the embodiment, the bonding strength of the adhesive 50 per 25 square millimeters with respect to alumina is 10 MPa or more. By using the adhesive 50 with such bonding strength, sufficient bonding strength of the coil component 10 is also achieved.

[0081] (9) In the embodiment, the coil member 10 has a closed magnetic path formed by the flanges 20 and the upper plate 10F. The use of the adhesive 50 of the embodiment to bond the flanges 20 and the upper plate 10F, which form a closed magnetic path, is desirable to improve the characteristics of the coil member 10 as a whole. (Modified examples)

[0082] The above-described embodiment and the following modified examples can be combined and implemented as appropriate, provided that the resulting configurations do not become technically inconsistent. (Modified examples of coil components)

[0083] The shape of the winding core 11 is not limited to the example in the embodiment. The shape of the winding core 11 may be, for example, a cylinder or a polygonal prism other than a quadrilateral prism.

[0084] The configuration of the drum core 10C is not limited to the example in the embodiment. For example, if the first electrode 31 and the second electrode 32 are separated from each other, and the third electrode 33 and the fourth electrode 34 are separated from each other, the provision of the first cavity 21A and the second cavity 22A for the drum core 10C may be omitted.

[0085] The material and shape of the external electrodes 30 are not limited to the examples mentioned in the embodiment. In one example, the material of the plated layer of the external electrodes 30 may be an alloy of tin and nickel, for example. In another example, the coating of the external electrodes 30 may be omitted. In this case, a region where a conductive metal layer is exposed may be used as the external electrode 30.

[0086] The coil component 10 may include at least one wire. If the coil component 10 includes a wire, any number of external electrodes 30 may be provided if one external electrode 30 is arranged on the first flange 21 and one external electrode 30 is arranged on the second flange 22.

[0087] The configuration of the coil component 10 is not limited to that formed by the drum core 10C and the top plate 10F. The coil component 10 can be configured in any manner as long as it includes a first core around which a wire is wound and a second core bonded to the first core via the adhesive 50, and the first core and the second core are bonded to each other by the adhesive 50. (Modified examples of the adhesive)

[0088] The adhesive 50 can be applied to a component other than the coil component 10. Preferably, the adhesive 50 is applied to an electronic component having a core made of a magnetic material.

[0089] The type of curing agent 53 contained in the adhesive 50 is not limited to the example in the embodiment. Any type of curing agent compatible with the bisphenol F resin 51 can be used.

[0090] The volume ratio between the magnetic powders 52 and the adhesive 50 can be any value of 35 volume percent or less. That is, the volume ratio of the magnetic powders 52 to the adhesive 50 can be less than 20 volume percent. The volume ratio of the magnetic powders 52 is adjusted so that a desirable permeability can be achieved in a coil component 10 to which the adhesive 50 is applied.

[0091] The number average molecular weight of the bisphenol F resin 51 in the adhesive 50 can be any value in the range of 312 to 360 g / mol.

[0092] The silane coupling agent 55, the dispersant 56, and the curing accelerator 54 may be omitted from the adhesive 50. The types of the silane coupling agent 55, the dispersant 56, and the curing accelerator 54 are not limited to the examples in the embodiment.

[0093] The glass transition temperature of the cured adhesive 50 may be lower than 125 °C. The desirable glass transition temperature can be determined depending on the intended use of the adhesive 50.

[0094] The average particle size (D50) of the magnetic powder 52 in the adhesive 50 can be less than 0.8 µm or greater than 2.5 µm. A desirable value for the average particle size (D50) can be set so that the adhesive 50 can be handled appropriately.

[0095] The bond strength of the cured adhesive 50 per 25 square millimeters to aluminum oxide may be less than 10 MPa. Preferably, the bond strength of the adhesive 50 is within a range that allows the top plate 10F and the drum core 10C to be adequately bonded together.

Claims

[1] Adhesive comprising: a bisphenol F resin; a curing agent for the bisphenol F resin; and magnetic powder, wherein the volume ratio between the magnetic powder and the adhesive is 35 vol% or less, and wherein the number average molecular weight of the bisphenol F resin is 312 to 360 g / mol. [2] The adhesive according to claim 1, wherein the volume ratio of the magnetic powder to the adhesive is 20 vol% or more. [3] Adhesive according to claim 1 or 2, further comprising: a silane coupling agent. [4] Adhesive according to any one of claims 1 to 3, further comprising: a dispersant for dispersing the magnetic powder. [5] The adhesive according to any one of claims 1 to 4, wherein the average particle size (D50) of the magnetic powder is 0.8 µm or more. [6] The adhesive according to any one of claims 1 to 5, wherein the average particle size (D50) of the magnetic powder is 2.5 µm or less. [7] Adhesive according to any one of claims 1 to 6, wherein the glass transition temperature of the adhesive in the cured state is 125 °C or more. [8] An adhesive according to any one of claims 1 to 7, wherein the adhesive strength of the adhesive in the cured state per 25 square millimeters in terms of aluminum oxide is 10 MPa or more.

Images