JP7387067B1 - Rubber magnets and refrigerator door gaskets - Google Patents

Abstract

A rubber magnet according to the present disclosure includes a group of hexagonal ferrite particles that is a collection of a plurality of hexagonal ferrite particles, and a holding material that holds the group of hexagonal ferrite particles, and a holding material that holds the group of hexagonal ferrite particles and the holding material. When the rubber magnet is divided into three parts in the thickness direction, the part that includes the surface of the rubber magnet is defined as the surface part, and when the rubber magnet is divided into three parts in the thickness direction. In this case, when the part sandwiched between the surface parts is defined as the center part, and the surface part including the surface on the magnetized side of the surface parts is defined as the magnetized side surface part, the magnetized side surface part The degree of c-plane orientation of the hexagonal ferrite particle group present is greater than the degree of c-plane orientation of the hexagonal ferrite particle group present in the central portion.

Description

The present disclosure relates to a rubber magnet with improved magnetic force, and a door packing for a refrigerator equipped with the rubber magnet.

Permanent magnets using hard magnetic materials are used in a wide range of fields such as home appliances, audio equipment, and OA equipment, and have become an indispensable material for electrical products. Among them, rubber magnets, which are formed by mixing a group of hard magnetic particles, which are particles of a plurality of hard magnetic particles, and a holding material such as a resin binder that holds the group of hard magnetic particles, have excellent workability. It can be relatively easily molded into sheet shapes, elongated shapes, etc. For this reason, the uses of rubber magnets are expanding. For example, in refrigerators, long rubber magnets are used in the door packing. This refrigerator door packing is used to improve the airtightness of the door using the magnetic attraction force of the rubber magnet. For this reason, rubber magnets used in refrigerator door packings are required to have a certain level of high magnetic force. However, rubber magnets contain a non-magnetic holding material as a component in order to improve moldability. For this reason, it is difficult for rubber magnets to obtain high magnetic force compared to sintered magnets made of only hard magnetic material.

Therefore, conventionally, rubber magnets with improved magnetic force have been proposed (see Patent Document 1). Specifically, the rubber magnet described in Patent Document 1 is manufactured by melting a mixture of hard magnetic particles and a holding material into a cavity of an injection mold having one or more cavities to which an orienting magnetic field is applied. It is injected and molded inside. At this time, in the rubber magnet described in Patent Document 1, the injection rate of the molten mixture is set to 15 cm ³ /s or more per cavity, and the rise time of the injection rate is set to 0.01 seconds or less. Eject inside. According to Patent Document 1, by molding the mixture of the hard magnetic particles and the holding material in this way, the variation in surface magnetic flux density is 10% or less and the orientation index of the hard magnetic particles is 3.0. It is said that the above rubber magnet can be obtained.

Patent No. 4069714

When manufacturing a rubber magnet, a mixture of hard magnetic particles and a holding material is molded, and then a magnetic field is applied to the molded product to magnetize it and form magnetic poles on the molded product. Complete. Here, in the rubber magnet described in Patent Document 1, the molded product obtained by molding the mixture of the hard magnetic particles and the holding material is such that the hard magnetic particles at each position in the thickness direction of the rubber magnet are The degree of orientation becomes approximately uniform. When magnetizing such a molded product by applying a magnetic field, a very strong magnetic field is required for magnetization. For this reason, when applying a magnetic field to magnetize such a molded product, a large yoke is required for magnetization, making it difficult to magnetize, for example, making it difficult to magnetize in a complicated pattern. It goes up. In other words, conventional rubber magnets with improved magnetic force have a problem in that the degree of difficulty in magnetizing them increases.

The present disclosure has been made to solve the above-mentioned problems, and a first object thereof is to provide a rubber magnet that has both improved magnetic force and ease of magnetization. A second object of the present disclosure is to provide a refrigerator door packing including such a rubber magnet .

A rubber magnet according to the present disclosure includes a hexagonal ferrite particle group that is a collection of a plurality of hexagonal ferrite particles, and a holding material that holds the hexagonal ferrite particle group, and includes a holding material that holds the hexagonal ferrite particle group and the holding material. When the rubber magnet is divided into three parts in the thickness direction, the part that includes the surface of the rubber magnet is defined as the surface part, and when the rubber magnet is divided into three parts in the thickness direction. If the part sandwiched between the surface parts is the center part, and the surface part including the surface on the magnetized side of the surface part is the magnetized side surface part, then the magnetized side surface part The degree of c-plane orientation of the hexagonal ferrite particle group present in the center portion is greater than the degree of c-plane orientation of the hexagonal ferrite particle group present in the central portion, and the hexagonal ferrite particle group is The particles include first particles and second particles having a larger particle size than the first particles, and the degree of c-plane orientation of the hexagonal ferrite particle group in the magnetized side surface portion calculated by the Lotgering method is 0. .2 or more, and the c-plane orientation degree of the hexagonal ferrite particle group in the central portion calculated by the Lotgering method is 0.12 or less .

Moreover, the refrigerator door packing according to the present disclosure includes the rubber magnet according to the present disclosure .

In the rubber magnet according to the present disclosure, the c-plane orientation degree of the hexagonal ferrite particle group existing in the magnetized side surface portion is greater than the c-plane orientation degree of the hexagonal ferrite particle group existing in the central portion. , it is possible to achieve both improvement in magnetic force and ease of magnetization.

FIG. 2 is a schematic cross-sectional view of the rubber magnet according to the first embodiment, cut along the thickness direction of the rubber magnet. FIG. 3 is a schematic cross-sectional view of another example of the rubber magnet according to the first embodiment, cut along the thickness direction of the rubber magnet. FIG. 3 is a diagram for explaining the effect of the rubber magnet according to the first embodiment. FIG. 3 is a diagram for explaining the effect of the rubber magnet according to the first embodiment. FIG. 3 is a diagram for explaining the effect of the rubber magnet according to the first embodiment. FIG. 3 is a diagram for explaining the effect of the rubber magnet according to the first embodiment. FIG. 3 is a schematic diagram for explaining an example of arrangement of magnetic poles of a rubber magnet according to the first embodiment. FIG. 3 is a schematic diagram for explaining an example of arrangement of magnetic poles of a rubber magnet according to the first embodiment. FIG. 7 is a schematic diagram showing a refrigerator door packing according to the second embodiment. FIG. 2 is a schematic diagram for explaining the range that the magnetic force of a rubber magnet magnetized with a multipolar magnetization structure can reach. FIG. 2 is a schematic diagram for explaining the range that the magnetic force of a rubber magnet magnetized with a multipolar magnetization structure can reach.

Embodiment 1.
FIG. 1 is a schematic cross-sectional view of the rubber magnet according to the first embodiment, cut along the thickness direction of the rubber magnet. Specifically, in FIG. 1, the vertical direction of the paper surface is the thickness direction of the rubber magnet 1.
The rubber magnet 1 according to the first embodiment includes a hexagonal ferrite particle group 20 that is a collection of a plurality of hexagonal ferrite particles 21, and a holding material 10 that holds the hexagonal ferrite particle group 20. The rubber magnet 1 is formed by mixing the hexagonal ferrite particle group 20 and the holding material 10. Further, in the rubber magnet 1 according to the first embodiment, the degree of orientation of the hexagonal ferrite particle group 20 at each position in the thickness direction of the rubber magnet 1 is as shown in FIG.

Specifically, when the rubber magnet 1 is divided into three parts in the thickness direction, the part including the surface 2 of the rubber magnet 1 is defined as the surface part 3. That is, the rubber magnet 1 has a surface portion 3 including the surface 2 on the upper side of the paper and a surface portion 3 including the surface 2 on the lower side of the paper. Furthermore, when the rubber magnet 1 is divided into three parts in the thickness direction, the part sandwiched between the surface parts 3 is defined as the central part 4. Further, among the surface portions 3, the surface portion 3 including the magnetized side surface 2 is referred to as a magnetized side surface portion 3a. As will be described later, the rubber magnet 1 according to the first embodiment is magnetized at least from the surface 2 side on the upper side of the paper. Therefore, in the first embodiment, the surface portion 3 including the surface 2 on the upper side of the paper becomes the magnetized side surface portion 3a.

When defined in this way, in the rubber magnet 1 according to the first embodiment, the hexagonal ferrite grains 20 present in the magnetized side surface portion 3a are such that each hexagonal ferrite grain 21 is relatively oriented in one direction. The situation is as follows. Furthermore, in the rubber magnet 1 according to the first embodiment, the hexagonal ferrite particle group 20 present in the central portion 4 is different from the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a. The orientation of the ferrite particles 21 is small, and each hexagonal ferrite particle 21 is arranged in a relatively random posture. In other words, in the rubber magnet 1 according to the first embodiment, the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is higher than that of the hexagonal ferrite particle group 20 present in the central portion 4. The degree of orientation of the c-plane is greater than that of the c-plane orientation. More specifically, in the rubber magnet 1 according to the first embodiment, the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is smaller than the hexagonal ferrite particle group 20 present in the central portion 4. , there are many hexagonal ferrite particles 21 whose c-planes are nearly parallel to the surface 2. In other words, in the rubber magnet 1 according to the first embodiment, the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a has a hexagonal ferrite particle group 20 that is present in the center portion 4. The degree of orientation of the c-plane of the ferrite particles 21 in the direction along the surface 2 is increased.

In the first embodiment, considering the possibility of magnetization from the surface 2 side on the lower side of the paper, the c of the hexagonal ferrite particle group 20 present in the surface portion 3 including the surface 2 on the lower side of the paper The degree of plane orientation is also greater than the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the central portion 4.

Here, in the rubber magnet 1 shown in FIG. 1, in one sheet formed by mixing the hexagonal ferrite particle group 20 and the holding material 10, the hexagonal ferrite particle group is arranged in the thickness direction of the rubber magnet 1. The degree of c-plane orientation of 20 was varied. However, the rubber magnet 1 shown in FIG. 1 is an example of the rubber magnet 1 according to the first embodiment. If the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is greater than the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the central portion 4, this embodiment The rubber magnet 1 according to Embodiment 1 is not limited to the configuration shown in FIG. For example, the rubber magnet 1 according to the first embodiment may be configured as shown in FIG. 2, which will be described later.

FIG. 2 is a schematic cross-sectional view of another example of the rubber magnet according to the first embodiment, cut along the thickness direction of the rubber magnet. In FIG. 2, the vertical direction of the paper surface is the thickness direction of the rubber magnet 1.
The rubber magnet 1 shown in FIG. 2 is constructed by laminating a plurality of sheets formed by mixing a hexagonal ferrite particle group 20 and a holding material 10. Furthermore, within each sheet, the degree of c-plane orientation of the hexagonal ferrite particle group 20 is uniform. Furthermore, the degree of c-plane orientation of the hexagonal ferrite particle group 20 differs from sheet to sheet. If the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is greater than the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the central portion 4, as shown in FIG. The rubber magnet 1 according to the first embodiment may be configured as follows. Note that at this time, the thickness of each sheet and the number of sheets to be laminated are not particularly limited.

As in the rubber magnet 1 according to the first embodiment, the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is determined by the c-plane orientation of the hexagonal ferrite particle group 20 present in the central portion 4. By making the degree of orientation larger than the degree of orientation, it is possible to obtain a rubber magnet that can achieve both improved magnetic force and ease of magnetization. Hereinafter, the reason why the rubber magnet 1 according to the first embodiment can obtain this effect will be explained.

3 to 6 are diagrams for explaining the effects of the rubber magnet according to the first embodiment. Specifically, FIGS. 3 and 4 are schematic cross-sectional views of the rubber magnet 201 cut in the thickness direction of the rubber magnet 201 for explaining the effects of the rubber magnet 1 according to the first embodiment. Further, FIGS. 5 and 6 are schematic cross-sectional views for explaining the magnetization depth 5 of the rubber magnet 201. In FIGS. 3 to 6, the vertical direction of the paper surface corresponds to the thickness direction of the rubber magnet 201. It should be noted that the rubber magnet 201 is different from the rubber magnet 1 according to the first embodiment. Furthermore, in FIGS. 3 to 6, when describing the rubber magnet 201, the same components as the rubber magnet 1 according to the first embodiment are given the same reference numerals as the rubber magnet 1 according to the first embodiment. ing.

The hexagonal ferrite particles 21 have a plate-like particle shape and have magnetic anisotropy in the in-plane direction and the thickness direction of the plate-like particle. For this reason, when each hexagonal ferrite particle 21 is held by the holding material 10 such that the thickness direction of the hexagonal ferrite particle 21 is along the thickness direction of the rubber magnet 201 like the rubber magnet 201 shown in FIG. The magnetic force in the thickness direction of the magnet 201 becomes stronger. However, since a very strong magnetic field is required to magnetize the hexagonal ferrite particles 21, which are plate-shaped particles, in the thickness direction, magnetization becomes difficult. In particular, when magnetizing from the surface 2 of the rubber magnet 201, it becomes difficult to magnetize the central part of the rubber magnet 201 in the thickness direction because the distance from the yoke, which is the source of the magnetic field during magnetization, is long. There is a tendency to For this reason, when the rubber magnet 201 is magnetized from the surface 2 using a yoke, the central part of the rubber magnet 201 in the thickness direction is not magnetized, and as shown in FIG. The magnetization depth 5 may become shallow. Furthermore, if the magnetization depth 5 in the thickness direction of the rubber magnet 201 is shallow, an excessive demagnetizing field is generated in the thickness direction of the rubber magnet 201, resulting in an effective magnetic force in the thickness direction of the rubber magnet 201. may cause a decrease in

On the other hand, when each hexagonal ferrite particle 21 is held by the holding material 10 so that the orientation of each hexagonal ferrite particle 21 is relatively random, as in the rubber magnet 201 shown in FIG. becomes easier. Therefore, when the rubber magnet 201 is magnetized from the surface 2, it is relatively easy to increase the magnetization depth 5 in the thickness direction of the rubber magnet 201, as shown in FIG. However, since each hexagonal ferrite particle 21 is oriented in a random direction, the magnetic force in the thickness direction of the rubber magnet 201 does not improve much.

Therefore, as a result of intensive research aimed at realizing a rubber magnet that can achieve both improved magnetic force and ease of magnetization, the inventors arrived at the configuration of the rubber magnet 1 according to the first embodiment.

Specifically, since the magnetized side surface portion 3a is located near the yoke during magnetization, a strong magnetic field is likely to be applied thereto. Therefore, the magnetized side surface portion 3a prioritizes increasing the magnetic force in the thickness direction of the rubber magnet 1, and is relatively easily magnetized even if the degree of c-plane orientation of the hexagonal ferrite particle group 20 is increased. be able to. In addition, since the magnetized side surface portion 3a has a high degree of c-plane orientation of the hexagonal ferrite particle group 20, the magnetic force in the thickness direction of the rubber magnet 1 can be improved.

On the other hand, when magnetizing the central portion 4 of the rubber magnet 1, the distance from the yoke becomes long, making it difficult to apply a strong magnetic field. For this reason, in the central portion 4, priority is given to facilitating magnetization, and the degree of c-plane orientation of the hexagonal ferrite particle group 20 is made relatively small. Therefore, when the rubber magnet 1 according to the first embodiment is magnetized from the surface 2 of the rubber magnet 1, the magnetization depth 5 in the thickness direction of the rubber magnet 1 becomes deep as shown in FIG. Therefore, the rubber magnet 1 according to the first embodiment can suppress the demagnetizing field generated in the thickness direction of the rubber magnet 1, and can improve the effective magnetic force in the thickness direction of the rubber magnet 1. In this way, the rubber magnet 1 according to the first embodiment can achieve ease of magnetization of the rubber magnet 1 and improvement in magnetic force in the thickness direction. That is, the rubber magnet 1 according to the first embodiment can achieve both improved magnetic force and ease of magnetization.

The hexagonal ferrite particles 21 included in the rubber magnet 1 according to the first embodiment are not particularly limited as long as they can be dispersed in the holding material 10 and generate spontaneous magnetization when magnetized. For example, as the hexagonal ferrite particles 21, particles such as M-type hexagonal ferrite, W-type hexagonal ferrite, Z-type hexagonal ferrite, and Y-type hexagonal ferrite can be used. M-type hexagonal ferrite can be expressed as BaFe ₁₂ O ₁₉ or SrFe ₁₂ O ₁₉ in chemical formula. W-type hexagonal ferrite can be expressed as BaFe ₁₈ O ₂₇ or SrFe ₁₈ O ₂₇ in chemical formula. Z-type hexagonal ferrite can be represented by the chemical formula Ba ₃ Co ₂ Fe ₂₄ O ₄₁ or Sr ₃ Co ₂ Fe ₂₄ O ₄₁ . Y-type hexagonal ferrite can be represented by the chemical formula BaZnFe ₁₂ O ₂₂ .

Note that, for example, the hexagonal ferrite particles 21 may be a mixture of particles of a plurality of ferrites among these ferrites. Further, for example, the hexagonal ferrite particles 21 may be particles of hexagonal ferrite having a composition in which some of the metal elements of the above-mentioned hexagonal ferrite are replaced with transition metal elements. The metal elements of the hexagonal ferrite mentioned above are Ba, Sr, and Fe.

When a rubber magnet is used in a refrigerator door packing, it is necessary to maintain stable magnetic force over a long period of time. However, metal hard magnetic materials may oxidize during long-term use, resulting in deterioration of their magnetic properties. For this reason, the hexagonal ferrite particles 21 are preferably oxide ferrite particles. Among the above, M-type hexagonal ferrite, which has large crystal magnetic anisotropy and excellent magnetic force, is particularly suitable as the hexagonal ferrite particles 21.

Moreover, it is preferable that the hexagonal ferrite particle group 20 includes first particles and second particles having a larger particle size than the first particles as the hexagonal ferrite particles 21. The first particles are, for example, particles with a particle size of 1 μm or less. The second particles are, for example, particles with a particle size of 5 μm or more. When the particle size of the hexagonal ferrite particles 21 increases, the hexagonal ferrite particles 21 tend to become plate-shaped particles with a large aspect ratio. Therefore, as the particle size of the hexagonal ferrite particles 21 increases, it becomes easier to control the orientation of the hexagonal ferrite particles 21 dispersed in the holding material 10. Therefore, by including the second particles in the hexagonal ferrite particle group 20, it becomes easier to realize the structure of the rubber magnet 1 according to the first embodiment. Furthermore, since the hexagonal ferrite particle group 20 includes hexagonal ferrite particles 21 having different particle sizes, the filling property of the hexagonal ferrite particles 21 into the holding material 10 is improved, and the hexagonal ferrite particles 21 into the holding material 10 are It becomes possible to increase the filling rate.

The particle size of the hexagonal ferrite particles 21 can be determined, for example, by measuring particle size distribution using a laser diffraction scattering method. Specifically, the rubber magnet 1 is heat-treated in an air atmosphere at a temperature of 500° C. to 800° C. for about 5 hours to 10 hours using an electric furnace to incinerate it. The particle size of the hexagonal ferrite particles 21 can be determined by using the hexagonal ferrite particles 21 thus obtained as a sample and measuring the particle size distribution of this sample by a laser diffraction scattering method.

Further, the content of the hexagonal ferrite particle group 20 in the rubber magnet 1 according to the first embodiment is preferably 70 wt% or more and 95 wt% or less. By setting the content of the hexagonal ferrite particle group 20 of the rubber magnet 1 in this way, each hexagonal ferrite particle 21 of the hexagonal ferrite particle group 20 mixed in the holding material 10 can be dispersed in the holding material 10. This is because it is easy and the workability when manufacturing the rubber magnet 1 is improved. Further, by setting the content of the hexagonal ferrite particle group 20 of the rubber magnet 1 in this manner, the magnetic performance of the rubber magnet 1 is also improved. In particular, in order to more easily obtain the above-mentioned effects, it is more preferable that the content of the hexagonal ferrite particle group 20 in the rubber magnet 1 is 75 wt% or more and 90 wt% or less.

Note that if the content of the hexagonal ferrite particle group 20 in the rubber magnet 1 is less than 70 wt%, the magnetic force when magnetized will be weak, resulting in insufficient adhesion when the rubber magnet 1 is used for door packing. There are cases where On the other hand, if the content of the hexagonal ferrite particles 20 in the rubber magnet 1 exceeds 95 wt%, it becomes difficult to disperse each hexagonal ferrite particle 21 in the holding material 10, making it difficult to mold the rubber magnet 1, etc. , the workability when manufacturing the rubber magnet 1 may be reduced.

The holding material 10 of the rubber magnet 1 according to the first embodiment is not particularly limited as long as it can hold the hexagonal ferrite particle group 20, but from the viewpoint of moldability of the rubber magnet 1, a thermoplastic resin is preferable. For example, as the holding material 10, ethylene, propylene, chlorinated polyethylene, butadiene, isoprene, styrene, methacrylic acid, acrylic acid, methacrylic ester, acrylic ester, vinyl chloride, tetrafluoroethylene, acrylonitrile, maleic anhydride, and A polymer of one monomer selected from the group consisting of vinyl acetate can be used. For example, as the holding material 10, ethylene, propylene, chlorinated polyethylene, butadiene, isoprene, styrene, methacrylic acid, acrylic acid, methacrylic ester, acrylic ester, vinyl chloride, tetrafluoroethylene, acrylonitrile, maleic anhydride, etc. , and vinyl acetate can be used. For example, as the holding material 10, polyphenylene ether, chlorinated polyethylene, silicone resin, polyamide, polyimide, polycarbonate, polyester, polyacetal, polyphenylene sulfide, polyethylene glycol, polyetherimide, polyketone, polyether ether ketone, polyether sulfone can be used. , polyarylate, etc. can also be used. Further, the holding material 10 may contain additives such as a coupling material and a flame retardant within a range that does not impede the desired magnetic performance.

The degree of c-plane orientation of the hexagonal ferrite particle group 20 in the rubber magnet 1 can be evaluated by the Lotgering method described below using X-ray diffraction.

The degree of c-plane orientation f of the hexagonal ferrite particle group 20 in the Lotgering method is determined by the reference peak intensity P0 obtained from a non-oriented sample of the hexagonal ferrite particle group 20 and the peak intensity obtained from an oriented sample of the hexagonal ferrite particle group 20. It is calculated using Equation (1) using P.
f=(P-P0)/(1-P0)...(1)

The reference peak intensity P0 is calculated using the measured value of the X-ray diffraction intensity I0 obtained from the non-oriented sample of the hexagonal ferrite particle group 20. As shown in equation (2), the reference peak intensity P0 is the crystal orientation of the non-oriented sample of the hexagonal ferrite particle group 20 relative to the sum of the diffraction intensities I0 (hkl) obtained in the non-oriented sample of the hexagonal ferrite particle group 20. It is expressed as a ratio of the sum of the diffraction intensities I0 (xyz) obtained on the plane (xyz).
P0=ΣI0(xyz)/ΣI0(hkl)...(2)
Note that the reference peak intensity P0 in calculating the degree of c-plane orientation f of the hexagonal ferrite particle group 20 can be set to P=0.05.

The peak intensity P is calculated using the measured value of the X-ray diffraction intensity I obtained from the oriented sample of the hexagonal ferrite particle group 20. Assuming that the crystal orientation plane of the rubber magnet 1 is the (00l) plane, the peak intensity P is, as shown in equation (3), relative to the sum of the diffraction intensities I (hkl) obtained from the oriented sample of the hexagonal ferrite particle group 20. It is expressed as a percentage of the total diffraction intensity I (00l) obtained on the crystal orientation plane (00l) of the oriented sample of the hexagonal ferrite particle group 20.
P=ΣI(00l)/ΣI(hkl)...(3)

That is, by performing X-ray diffraction of the magnetized side surface portion 3a in a plane perpendicular to the thickness direction of the rubber magnet 1, the degree of c-plane orientation f of the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is determined. can be calculated using the Lotgering method. Furthermore, by performing X-ray diffraction on the central portion 4 in a plane perpendicular to the thickness direction of the rubber magnet 1, the degree of c-plane orientation f of the hexagonal ferrite particle group 20 present in the central portion 4 is calculated by the Lotgering method. can do.

Here, as described above, in the rubber magnet 1 according to the first embodiment, the degree of c-plane orientation of the hexagonal ferrite particle group 20 present in the magnetized side surface portion 3a is the hexagonal ferrite grain group present in the central portion 4. The degree of c-plane orientation may be greater than the degree of c-plane orientation of the particle group 20. However, from the viewpoint of ease of manufacturing the rubber magnet 1 and magnetic performance when the rubber magnet 1 is used as a door packing, the hexagonal crystal of the magnetized side surface portion 3a and the center portion 4 calculated by the Lotgering method is The c-plane orientation degree f of the ferrite particle group 20 preferably has the following value. Specifically, in the rubber magnet 1 according to the first embodiment, the degree of c-plane orientation f of the hexagonal ferrite particle group 20 of the magnetized side surface portion 3a calculated by the Lotgering method is 0.2 or more, and the Lotgering It is preferable that the degree of c-plane orientation f of the hexagonal ferrite particle group 20 in the central portion 4 calculated by the method is 0.12 or less. Further, from the above-mentioned viewpoint, in the rubber magnet 1 according to the first embodiment, the degree of c-plane orientation f of the hexagonal ferrite particle group 20 of the magnetized side surface portion 3a calculated by the Lotgering method is 0.3 or more. It is more preferable that the degree of c-plane orientation f of the hexagonal ferrite particle group 20 in the central portion 4 calculated by the Lotgering method is 0.1 or less.

By the way, the rubber magnet 1 is made by molding a mixture of hexagonal ferrite particles 20 and a holding material 10 into a prescribed shape as shown in FIG. , completed by forming magnetic poles. At this time, the rubber magnet 1 may be magnetized from both surfaces 2 sides, but it is preferable that it is magnetized only from one surface 2 side. That is, it is preferable that the rubber magnet 1 has a magnetic pole formed only on one surface 2 side. In the rubber magnet 1 configured in this way, the manufacturing of the rubber magnet 1 becomes easy, and the manufacturing cost of the rubber magnet 1 can be reduced. An example of the arrangement of magnetic poles formed on the rubber magnet 1 will be described below with reference to FIGS. 7 and 8.

7 and 8 are schematic diagrams for explaining an example of the arrangement of magnetic poles of the rubber magnet according to the first embodiment. Note that in FIGS. 7 and 8, the vertical direction of the paper surface is the thickness direction of the rubber magnet 1.
The rubber magnet 1 is magnetized on at least one surface 2 side with a multipolar magnetized structure 6 in which S poles and N poles are alternately formed along the surface 2, for example, as shown in FIG. You can. Further, the rubber magnet 1 may be magnetized on at least one surface 2 side, for example, with a unipolar magnetized structure 7 in which only one magnetic pole is formed, as shown in FIG. At this time, it is preferable that the rubber magnet 1 is magnetized with a multipolar magnetization structure 6. This is because the rubber magnet 1 magnetized with the multi-pole magnetized structure 6 can obtain strong magnetic force and can exhibit stable adhesion when used as a door packing. On the other hand, the rubber magnet 1 magnetized with the unipolar magnetization structure 7 may lack magnetic force to be used as a door packing. However, the rubber magnet 1 that is magnetized with a single-pole magnetization structure 7 has a simpler yoke structure than the rubber magnet 1 that is magnetized with a multi-pole magnetization structure 6. , the manufacturing cost of the yoke can be reduced.

Next, an example of a method for manufacturing the rubber magnet 1 according to the first embodiment will be described.
First, the hexagonal ferrite particle group 20 is mixed with the heated and melted holding material 10, and the hexagonal ferrite particle group 20 is dispersed within the holding material 10 to form a mixture. The method of mixing the holding material 10 and the hexagonal ferrite particle group 20 is not particularly limited, and can be carried out according to a method known in the technical field. As a mixing method, for example, the holding material 10 and the hexagonal ferrite particle group 20 are mixed using a single-screw or multi-screw extruder. Further, the holding material 10 and the hexagonal ferrite particle group 20 may be mixed using, for example, a Banbury mixer, a roller, a co-kneader, a blast mill, a Prabender Blautograph, or the like. Moreover, when mixing the holding material 10 and the hexagonal ferrite particle group 20, the above-mentioned apparatus may be operated batchwise or continuously. Further, for example, the holding material 10 and the hexagonal ferrite particle group 20 may be mixed by a method other than mixing the hexagonal ferrite particle group 20 with the molten holding material 10. For example, the pellet-shaped holding material 10 and the hexagonal ferrite particle group 20 may be mixed together, the mixed material may be used as a molding resin, and the mixture may be melted and kneaded in a heating cylinder of a molding machine. That is, the mixture of the holding material 10 and the hexagonal ferrite particle group 20 may be made by so-called mold blending.

Next, the mixture of the holding material 10 and the hexagonal ferrite particle group 20 is heated to a temperature at which the holding material 10 melts to melt it, and is molded into a prescribed shape. Examples of the molding method include extrusion molding, roll molding, and uniaxial press molding. Through these molding methods, the orientation of the hexagonal ferrite particle group 20 near the surface 2 of the rubber magnet 1 becomes large, and the orientation of the hexagonal ferrite particle group 20 near the center of the rubber magnet 1 tends to become small. The molding conditions such as the molding speed and press pressure during molding may be adjusted as appropriate depending on the shape of the rubber magnet 1, the thickness of the rubber magnet 1, the particle size of the hexagonal ferrite particles 21, and the like. Moreover, the shape of the rubber magnet 1 may be any shape as long as it is suitable for use as a rubber magnet. For example, when the rubber magnet 1 is used as a door packing, the shape of the rubber magnet 1 is preferably a sheet shape. Furthermore, a crushing process can be provided before heating and melting the mixture of the holding material 10 and the hexagonal ferrite particle group 20. The crushing treatment is preferable because it improves workability when heating and melting the mixture of the holding material 10 and the hexagonal ferrite particle group 20.

In addition, when manufacturing the rubber magnet 1 with the laminated structure as shown in FIG. A large sheet is produced, for example, by the steps described above. By bonding these sheets together, a rubber magnet 1 having a laminated structure as shown in FIG. 2 can be manufactured. The method of bonding the sheets together is not particularly limited. As a method for bonding the sheets together, for example, a method of thermocompression bonding, a method of bonding with an adhesive, a method of fixing with an adhesive tape, etc. can be used.

Next, using a magnetizing device, the mixture of the holding material 10 molded into a prescribed shape and the hexagonal ferrite particle group 20 is given a strength that reaches the saturation point of the maximum magnetic flux density of the hexagonal ferrite particles 21. By applying a magnetic field of , the mixture formed into a specified shape is magnetized. Thereby, the rubber magnet 1 is completed. The method of magnetizing the mixture is not particularly limited, and the mixture can be magnetized according to methods known in the technical field. For example, the mixture can be magnetized by a static magnetic field generation method using a DC electromagnet, a pulsed magnetic field generation method using a capacitor type magnetizer, or the like. Furthermore, when a mixture is magnetized with multiple poles on one side, a yoke made by winding an electric wire around an iron core can be used to magnetize the mixture. At this time, the shape of the yoke may be adjusted as appropriate depending on the desired shape and magnetization pitch of the rubber magnet 1.

At the end of the first embodiment, some examples and comparative examples of the rubber magnet 1 according to the first embodiment will be introduced to show the effects of the rubber magnet 1 according to the first embodiment. It should be noted here that the rubber magnet according to the present disclosure is not limited to the following examples and comparative examples.

In the following Examples and Comparative Examples, the M-type hexagonal ferrite particles are hexagonal ferrite particles 21, No. A～No. Four types of hexagonal ferrite particle groups 20 of D were used. Specifically, a bulk body of M-type hexagonal ferrite was pulverized using known methods such as coarse pulverization using an attritor and fine pulverization using a ball mill to produce hexagonal ferrite particle groups 20. At this time, by changing the grinding conditions, No. A～No. Four types of hexagonal ferrite particle groups 20 of D were manufactured. Moreover, the content ratio of the first particles and the second particles in the hexagonal ferrite particle group 20 was determined by the above-mentioned laser diffraction scattering method. Note that hexagonal ferrite particles 21 with a particle size of 1 μm or less were used as the first particles. Further, hexagonal ferrite particles 21 having a particle size of 5 μm or more were used as second particles. Manufactured No. A～No. Table 1 shows the characteristics of the four types of hexagonal ferrite particle groups 20 of D.

[Example 1]
As the holding material 10, chlorinated polyethylene resin was used. In addition, 100 parts by mass of the holding material 10 was added to No. 900 parts by mass of hexagonal ferrite particle group 20 of C was added and mixed at a temperature of 180° C. to obtain a mixture of retaining material 10 and hexagonal ferrite particle group 20. In this case, the content of the hexagonal ferrite particle group 20 in the rubber magnet 1 is 90 wt%. Next, this mixture was crushed into pieces about several cm in size using a crusher, and molded into a sheet shape with a thickness of 6 mm at a temperature of 180° C. using a twin-screw extruder equipped with rollers. At this time, the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a is 0.26, and the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the central portion 4 is 0.12. , the extrusion speed was adjusted. Next, the rubber magnet 1 according to Example 1 was obtained by subjecting one side of the molded sheet to single-sided multipole magnetization using a magnetizing device equipped with a yoke with a magnetization pitch of 5 mm.

[Example 2]
The extrusion speed was adjusted such that the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a was 0.15, and the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the central portion 4 was 0.08. adjusted. The other conditions were the same as in Example 1 to obtain a rubber magnet 1 according to Example 2.

[Example 3]
The extrusion speed was adjusted so that the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a was 0.35, and the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4 was 0.21. adjusted. The other conditions were the same as in Example 1 to obtain the rubber magnet 1 according to Example 3.

[Example 4]
No. 1 was added to 100 parts by mass of the holding material 10. 900 parts by mass of hexagonal ferrite particle group 20 of A was added. The extrusion speed was adjusted such that the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a was 0.16, and the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4 was 0.07. adjusted. The other conditions were the same as in Example 1 to obtain a rubber magnet 1 according to Example 4.

[Example 5]
No. 1 was added to 100 parts by mass of the holding material 10. 900 parts by mass of hexagonal ferrite particle group 20 of B was added. The extrusion speed was adjusted so that the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a was 0.23, and the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4 was 0.11. adjusted. The other conditions were the same as in Example 1 to obtain a rubber magnet 1 according to Example 5.

[Example 6]
No. 1 was added to 100 parts by mass of the holding material 10. 900 parts by mass of hexagonal ferrite particle group 20 of D was added. The extrusion speed was adjusted such that the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a was 0.41, and the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the central portion 4 was 0.33. adjusted. The other conditions were the same as in Example 1 to obtain a rubber magnet 1 according to Example 6.

[Comparative example 1]
A first sheet with a thickness of 2 mm in which the degree of c-plane orientation of the hexagonal ferrite particle group 20 is 0.28, and a second sheet with a thickness of 2 mm in which the degree of c-plane orientation of the hexagonal ferrite particle group 20 is 0.06. Created. Then, the first sheet was stacked with two second sheets such that they were sandwiched between them, and a rubber magnet according to Comparative Example 1 was obtained. That is, in the rubber magnet according to Comparative Example 1, the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a is 0.06, and the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the central portion 4 is 0.06. The degree is 0.28. Other conditions of the rubber magnet 1 according to Comparative Example 1 are the same as those in Example 1.

[Comparative example 2]
No. 1 was added to 100 parts by mass of the holding material 10. 900 parts by mass of the hexagonal ferrite particle group 20 of D was added, and the extrusion speed was adjusted so that the degree of c-plane orientation of the hexagonal ferrite particle group 20 became 0.65 uniformly in the thickness direction. Thereafter, pressure was applied in the thickness direction using a uniaxial press to obtain a rubber magnet according to Comparative Example 2. That is, in the rubber magnet according to Comparative Example 2, the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a and the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4 are 0.65. It becomes. Other conditions of the rubber magnet 1 according to Comparative Example 2 are the same as those in Example 6.

[Comparative example 3]
No. 1 was added to 100 parts by mass of the holding material 10. 900 parts by mass of the hexagonal ferrite particle group 20 of A was added, and a thick plate with a thickness of 20 mm was molded so that the degree of c-plane orientation of the hexagonal ferrite particle group 20 was 0.06 uniformly in the thickness direction. Thereafter, a rubber magnet according to Comparative Example 3 was obtained by molding the thick plate to a thickness of 6 mm by grinding. That is, in the rubber magnet according to Comparative Example 3, the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a and the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4 are 0.06. It becomes. Other conditions of the rubber magnet 1 according to Comparative Example 3 are the same as those in Example 4.

In each of the rubber magnets 1 according to Examples 1 to 6 and the rubber magnets according to Comparative Examples 1 to 3, the magnetization depth 5 in the thickness direction of the rubber magnet and the magnetic flux density were evaluated. The evaluation results are shown in Table 2. In Table 2, the magnetization depth 5 of each of the rubber magnets 1 according to Examples 1 to 6 and the rubber magnets according to Comparative Examples 1 to 3 is the same as that of the rubber magnet 1 according to Example 1. It is shown as a ratio of magnetization depth, which is a relative value with magnetic depth 5 as a reference. For example, the ratio of the magnetization depths of the rubber magnet 1 according to Example 2 is calculated by dividing the magnetization depth 5 of the rubber magnet 1 according to Example 2 by the magnetization depth 5 of the rubber magnet 1 according to Example 1. The value is as follows. Furthermore, in Table 2, the magnetic flux densities of the rubber magnets 1 according to Examples 1 to 6 and the rubber magnets according to Comparative Examples 1 to 3 are based on the magnetic flux density of the rubber magnet 1 according to Example 1. It is expressed as a ratio of magnetic flux density, which is a relative value to . For example, the ratio of the magnetic flux densities of the rubber magnet 1 according to the second embodiment is a value obtained by dividing the magnetic flux density of the rubber magnet 1 according to the second embodiment by the magnetic flux density of the rubber magnet 1 according to the first embodiment.

As shown in Table 2, the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a is greater than the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4. It can be seen that the rubber magnets 1 according to Examples 1 to 6 have a large magnetization depth ratio and are easy to magnetize. Furthermore, it can be seen that the rubber magnets 1 according to Examples 1 to 6 have large magnetic flux density ratios and have high magnetic force. Furthermore, the c-plane orientation degree of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a is 0.2 or more, and the c-plane orientation degree of the hexagonal ferrite particle group 20 in the central portion 4 is 0.12 or less. The rubber magnets 1 according to Examples 1 and 5 are greatly superior in both the magnetization depth ratio and the magnetic flux density ratio.

On the other hand, in the rubber magnet according to Comparative Example 1, in which the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a is small, and the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the central portion 4 is large, The ratio of magnetization depth and the ratio of magnetic flux density are significantly reduced. Also, in the rubber magnet according to Comparative Example 2 in which the degree of c-plane orientation of the hexagonal ferrite particle group 20 in the magnetized side surface portion 3a and the central portion 4 is similarly large, the ratio of the magnetization depth and the ratio of the magnetic flux density It can be seen that this has decreased significantly. Furthermore, in Comparative Example 3 in which the degree of c-plane orientation of the hexagonal ferrite grain group 20 in the magnetized side surface portion 3a and the center portion 4 is similarly small, the ratio of the magnetization depth shows a large value; It can be seen that the ratio of magnetic flux density is small and the magnetic force is small.

As described above, the rubber magnet 1 according to the first embodiment includes a hexagonal ferrite particle group 20 that is a collection of a plurality of hexagonal ferrite particles 21, and a holding material 10 that holds the hexagonal ferrite particle group 20. This is a rubber magnet formed by mixing a group of crystalline ferrite particles 20 and a holding material 10. Here, when the rubber magnet 1 is divided into three parts in the thickness direction, the part including the surface 2 of the rubber magnet 1 is defined as a surface part 3. When the rubber magnet 1 is divided into three parts in the thickness direction, the part sandwiched between the surface parts 3 is defined as a central part 4. Among the surface portions 3, the surface portion 3 including the magnetized surface 2 is referred to as a magnetized side surface portion 3a. When defined in this way, in the rubber magnet 1 according to the first embodiment, the degree of c-plane orientation of the hexagonal ferrite grain group 20 present in the magnetized side surface portion 3a is equal to the degree of c-plane orientation of the hexagonal ferrite grains present in the central portion 4. The degree of c-plane orientation is greater than that of the ferrite particle group 20.

The rubber magnet 1 according to the first embodiment configured in this manner can achieve both improvement in magnetic force and ease of magnetization, as described above.

Embodiment 2.
In the second embodiment, a refrigerator door packing 100 including the rubber magnet 1 shown in the first embodiment will be described. Note that matters not mentioned in the second embodiment are the same as those in the first embodiment.

FIG. 9 is a schematic diagram showing a refrigerator door packing according to the second embodiment.
A refrigerator door packing 100 according to the second embodiment includes a rubber magnet 1 magnetized with a multipolar magnetization structure 6. The refrigerator door packing 100 is used to improve the sealing performance of a refrigerator door. For example, the refrigerator door packing 100 is attached to a portion of the refrigerator door that faces the periphery of the opening of the storage compartment. In a state where the door closes the opening of the storage room, the refrigerator door packing 100 sticks to the metal parts disposed at the opposing position, thereby improving the airtightness of the refrigerator door. Since the refrigerator door packing 100 according to the second embodiment includes the rubber magnet 1 magnetized with the multipolar magnetization structure 6, the high magnetic force improves the airtightness of the refrigerator door.

Here, in the refrigerator door packing 100, it is preferable that a non-magnetic resin layer 30 is laminated on the surface 2 included in the magnetized side surface portion 3a. Thereby, it is possible to suppress the formation of a gap between the metal component to which the refrigerator door packing 100 sticks and the refrigerator door packing 100, thereby further improving the airtightness of the refrigerator door. Further, when a non-magnetic resin layer 30 is laminated on the surface of the magnetized side surface portion 3a, it is more preferable that the hardness of the resin layer 30 is lower than the hardness of the rubber magnet 1. This makes it more difficult for a gap to be formed between the metal component to which the refrigerator door packing 100 is attached and the refrigerator door packing 100, thereby further improving the airtightness of the refrigerator door. Note that the resin layer 30 may also have the functions of other parts. For example, conventional refrigerators include a resin part called a gasket for attaching door packing to the refrigerator door. The resin layer 30 may constitute at least a portion of this gasket.

Further, when the refrigerator door packing 100 includes the resin layer 30, the thickness of the resin layer 30 is preferably as follows.

FIGS. 10 and 11 are schematic diagrams for explaining the range that the magnetic force of a rubber magnet magnetized with a multi-pole magnetization structure can reach.
As shown in FIGS. 10 and 11, in the rubber magnet 1 magnetized with the multipolar magnetization structure 6, S poles and N poles are alternately formed at a pitch d. At this time, as can be seen from the lines of magnetic force 9 shown in FIG. 10, when the pitch d is large, the distance that the magnetic force reaches from the surface 2 of the rubber magnet 1 becomes long. On the other hand, as can be seen from the lines of magnetic force 9 shown in FIG. 11, when the pitch d is small, the distance that the magnetic force reaches from the surface 2 of the rubber magnet 1 becomes short. Therefore, when the refrigerator door packing 100 includes the resin layer 30, if the resin layer 30 is excessively thick with respect to the pitch d, the magnetic force of the rubber magnet 1 may not reach the metal parts to which the rubber magnet 1 sticks. becomes. That is, if the resin layer 30 is too thick with respect to the pitch d, the adhesion force due to the magnetic force of the rubber magnet 1 is not exerted, so the refrigerator door packing 100 may not function as a door packing.

Therefore, when the refrigerator door packing 100 includes the resin layer 30, it is preferable that 0<t≦d/5, where t is the thickness of the resin layer 30. Moreover, when the refrigerator door packing 100 includes the resin layer 30, it is more preferable that the thickness t of the resin layer 30 satisfies 0<t≦d/7. By setting the thickness of the resin layer 30 in this way, the resin layer 30 does not become excessively thick with respect to the pitch d, and the adhesion force due to the magnetic force required for the refrigerator door packing 100 can be effectively exhibited. can.

In addition, it is preferable that the pitch d of the rubber magnet 1 magnetized by the multipolar magnetized structure 6 is 2 mm or more and 8 mm or less. Moreover, it is more preferable that the pitch d of the rubber magnet 1 magnetized by the multipolar magnetized structure 6 is 3 mm or more and 6 mm or less. This is because if the pitch d is less than 2 mm, the coil constituting the yoke used for magnetization becomes too small, making it difficult to apply the magnetic field necessary for magnetization. Further, if the pitch d exceeds 8 mm, the pitch d is too wide and the magnetic force of the rubber magnet 1 may decrease.

As described above, since the refrigerator door packing 100 according to the second embodiment includes the rubber magnet 1 that has both high magnetic force and ease of magnetization, the refrigerator door packing has excellent sealing performance.

1 Rubber magnet, 2 Surface, 3 Surface portion, 3a Magnetized side surface portion, 4 Center portion, 5 Magnetized depth, 6 Multipolar magnetized structure, 7 Unipolar magnetized structure, 9 Lines of magnetic force, 10 Holding material, 20 Hexagonal ferrite particle group, 21 Hexagonal ferrite particle, 30 Resin layer, 100 Refrigerator door packing, 201 Rubber magnet.

Claims (7)

A hexagonal ferrite particle group that is a collection of multiple hexagonal ferrite particles,
a holding material that holds the hexagonal ferrite particle group;
Equipped with
A rubber magnet formed by mixing the hexagonal ferrite particle group and the holding material,
When the rubber magnet is divided into three parts in the thickness direction, the part including the surface of the rubber magnet is defined as the surface part,
When the rubber magnet is divided into three parts in the thickness direction, the part sandwiched between the surface parts is the central part,
Among the surface portions, when the surface portion including the surface on the magnetized side is defined as the magnetized side surface portion,
The degree of c-plane orientation of the hexagonal ferrite particle group present in the magnetized side surface portion is greater than the degree of c-plane orientation of the hexagonal ferrite particle group present in the central portion,
The hexagonal ferrite particle group includes, as the hexagonal ferrite particles, first particles and second particles having a larger particle size than the first particles,
The degree of c-plane orientation of the hexagonal ferrite particle group in the magnetized side surface portion calculated by the Lotgering method is 0.2 or more,
A rubber magnet, wherein the degree of c-plane orientation of the hexagonal ferrite grain group in the central portion calculated by the Lotgering method is 0.12 or less. The rubber magnet according to claim 1, wherein the content of the hexagonal ferrite particles is 70 wt% or more and 95 wt% or less. The rubber magnet according to claim 1 or 2, wherein the rubber magnet is magnetized only from the surface side of one side. The rubber magnet according to claim 1 or 2, wherein the rubber magnet is magnetized in a multi-polar magnetized structure in which south poles and north poles are alternately formed along the surface. A refrigerator door packing comprising the rubber magnet according to claim 4. The refrigerator door packing according to claim 5, wherein a non-magnetic resin layer is laminated on the surface included in the magnetized side surface portion. The S poles and the N poles are alternately formed with a pitch d,
When the thickness of the resin layer is t,
0<t≦d/5
The refrigerator door packing according to claim 6.

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