JP2016082149A - Magnetic sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sheet which has a satisfactory magnetically-attracting property, and which is superior in rust prevention, low in cost, and easy to handle its material.SOLUTION: A magnetic sheet 10 comprises: a magnetic layer 12 including a soft magnetic material and a binder; a surface resin layer 14 provided on a surface of the magnetic layer 12; and an adhesion layer 16 provided on a backside of the magnetic layer 12. The soft magnetic material consists of a soft ferrite of which the particle diameter is 1-10 μm. In the magnetic layer 12, the filling rate of the soft ferrite is 40-80 vol.%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic sheet.

  For example, a magnetic sheet having a non-magnetized ferromagnetic layer is used in a wide range of applications such as installing a whiteboard on an existing wall surface. Specifically, for example, a flexible magnetic sheet is known in which a white vinyl chloride film is provided on the surface of a ferromagnetic layer made of a plastic plate or iron foil containing iron powder. By installing the magnetic sheet on the wall surface with an adhesive, etc., it is possible to magnetize magnetic articles such as magnets on the surface, and it can be used as a whiteboard on which characters etc. can be written or erased with a whiteboard marker .

As a magnetic sheet, for example, a magnetic material such as a metal powder such as iron powder and a synthetic resin material such as vinyl chloride are kneaded into a sheet, and rust-proof galvanizing is applied. There is known a technique using an iron foil (Patent Document 1).
By using metal powder such as iron powder for the magnetic sheet, excellent magnetic adsorption characteristics can be obtained.

JP 2010-262130 A

  However, a magnetic sheet using iron powder has a problem that rust is generated, and cost is likely to increase. Moreover, iron powder with a small particle size is difficult to handle as a material. The iron foil that has been subjected to the rust prevention treatment is somewhat suppressed in the generation of rust, but has a problem that it is difficult to handle because it is a hard material.

  An object of the present invention is to provide a magnetic sheet having sufficient magnetic adsorption properties, excellent rust prevention, low cost, and easy material handling.

  The magnetic sheet of the present invention is a magnetic sheet having a magnetic layer containing a soft magnetic material and a binder, wherein the soft magnetic material is composed only of soft ferrite, and the particle diameter of the soft ferrite is 1 to 10 μm. It is characterized by that.

In the magnetic sheet of the present invention, it is preferable that the filling rate of the soft ferrite in the magnetic layer is 40 to 80% by volume.
The soft ferrite is preferably a Mn—Zn soft ferrite.

  The magnetic sheet of the present invention has sufficient magnetic adsorption characteristics, is excellent in rust prevention, is low in cost, and is easy to handle materials.

It is sectional drawing which showed an example of the magnetic sheet of this invention. It is sectional drawing which showed the other example of the magnetic sheet of this invention.

[First Embodiment]
FIG. 1 is a cross-sectional view of a magnetic sheet 10 which is an example of the magnetic sheet of the present invention.
The magnetic sheet 10 of the present embodiment is a flexible sheet having a magnetic layer 12, a surface resin layer 14 provided on the surface of the magnetic layer 12, and an adhesive layer 16 provided on the back surface of the magnetic layer 12. It is.

(Magnetic layer)
The magnetic layer 12 is a layer containing a soft magnetic material and a binder.

<Soft magnetic material>
In the magnetic sheet 10, the soft magnetic material contained in the magnetic layer 12 is made only of soft ferrite. Thereby, generation | occurrence | production of rust in the magnetic sheet 10 is suppressed. In addition, the cost is lower than when iron powder is used for the soft magnetic material, and handling of the material is facilitated.

Examples of the soft ferrite include Mn—Zn soft ferrite, Ni—Zn soft ferrite, and Mg—Zn soft ferrite. Among these, Mn—Zn soft ferrite is preferable in terms of initial permeability and cost. In terms of magnetic adsorption characteristics, Ni—Zn soft ferrite is preferable.
The soft ferrite contained in the magnetic layer 12 may be one type or two or more types.

The magnetic layer 12 is preferably filled with particulate soft ferrite.
The particle diameter of the soft ferrite is 1 to 10 μm, and preferably 2 to 5 μm. If the particle diameter of the soft ferrite is not less than the lower limit value, it can be kneaded into the binder with a high filling rate. If the soft ferrite particle size is less than or equal to the upper limit value, the dimensional stability and appearance of the sheet can be kept good even if the filling rate of soft ferrite is increased, so that magnetic adsorption characteristics, dimensional stability and appearance are compatible. It is easy to obtain a magnetic sheet.

The particle diameter of soft ferrite is measured by the following procedure.
An object to be measured (soft ferrite powder) is put into an organic liquid such as water or ethanol, and a dispersion is prepared by applying a dispersion treatment for about 2 minutes in a state where an ultrasonic wave of about 35 kHz to 40 kHz is applied. The amount of the particulate matter in the dispersion is such that the laser transmittance of the dispersion (ratio of the output light quantity to the incident light quantity) is 70% to 95%. Next, the dispersion liquid is subjected to a microtrack particle size analyzer, and the particle diameters (D1, D2, D3...) Of the individual granular materials by the scattering of laser light, and the number (N1, N2, N3,. (The particle diameter (D) of each granular material is automatically measured as a sphere equivalent diameter for each granular material having various shapes according to a microtrack particle size analyzer). From the number (N) of individual particles present in the field of view and each particle size (D), the average particle size is calculated by the following formula (1).
Average particle diameter = (ΣND ³ / ΣN) ^1/3 (1)

The filling rate of soft ferrite in the magnetic layer 12 is preferably 40 to 80% by volume, and more preferably 50 to 70% by volume. If the filling rate of the soft ferrite is equal to or higher than the lower limit value, a magnetic sheet excellent in magnetic adsorption characteristics can be easily obtained even if the magnetic layer does not contain iron powder. If the filling rate of the soft ferrite is equal to or less than the upper limit value, the moldability is good.
The filling rate of soft ferrite in the magnetic layer is the ratio of the total volume of soft ferrite to the total volume of the magnetic layer.

<Binder>
As a binder, the well-known binder used for the magnetic layer of a magnetic sheet can be used, For example, rubber | gum (natural rubber, synthetic rubbers, such as acrylic rubber), resin (chlorinated polyethylene etc.), etc. are mentioned.
The binder contained in the magnetic layer 12 may be one type or two or more types.

  20-60 volume% is preferable and, as for content of the binder in the magnetic layer 12 (100 volume%), 30-50 volume% is more preferable. If content of the said binder is more than a lower limit, sheeting will become easy. When the content of the binder is not more than the upper limit value, a magnetic sheet having excellent magnetic adsorption characteristics can be easily obtained.

The magnetic layer 12 may contain an additive as long as the effects of the present invention are not impaired.
Examples of the additive include an ultraviolet absorber, a light stabilizer, an antioxidant, a plasticizer, a colorant, a lubricant, and a processing aid.
An additive may be used individually by 1 type and may use 2 or more types together.

  The thickness of the magnetic layer 12 is preferably 0.1 to 1 mm, and more preferably 0.2 to 0.8 mm. If the thickness of the magnetic layer 12 is equal to or greater than the lower limit value, the magnet can be attracted with a sufficient attracting force. If the thickness of the magnetic layer 12 is less than or equal to the upper limit value, construction on the wall surface or the like is facilitated.

(Surface resin layer)
Examples of the material for forming the surface resin layer 14 include polyvinyl chloride, fluororesin, polyethylene terephthalate, and polypropylene. Among these, polyvinyl chloride is preferable in terms of easy coloring with a pigment or the like, and polyethylene terephthalate or fluororesin is preferably selected in terms of ease of erasing the marker ink by an eraser.
For example, when the magnetic sheet 10 is used as a white board, a pigment (titanium oxide, zinc oxide, etc.) is blended with the surface resin layer 14 to make it white.

  The thickness of the surface resin layer 14 is preferably 0.1 to 0.5 mm, and more preferably 0.1 to 0.3 mm. If the thickness of the surface resin layer 14 is equal to or greater than the lower limit value, the color of the magnetic layer can be sufficiently concealed. If the thickness of the surface resin layer 14 is equal to or less than the upper limit value, it is difficult to inhibit the magnet's attractive force.

  If possible, the magnetic layer 12 and the surface resin layer 14 may be bonded by heat lamination or extrusion lamination, and an adhesive or pressure-sensitive adhesive may be applied. It can select suitably according to the kind of each layer.

(Adhesive layer)
As a material for forming the adhesive layer 16 used for providing the magnetic sheet 10 on an existing wall surface, door, window, furniture, or the like, for example, when a magnetic sheet is temporarily used, a re-peelable adhesive, surface And a sucker sheet made of an elastomer having minute recesses and / or minute projections such as an annular shape and a polygonal shape.

  0.1-3 mm is preferable and, as for the thickness of the contact bonding layer 16, 0.5-2 mm is more preferable. If the thickness of the adhesive layer 16 is not less than the lower limit value, the magnetic sheet 10 can be stably attached to the wall surface or the like. If the thickness of the adhesive layer 16 is less than or equal to the upper limit value, the magnetic sheet 10 can be easily handled and space is saved.

  5-30 are preferable and, as for the magnetic permeability of the magnetic sheet 10, 10-25 are more preferable. If the magnetic permeability of the magnetic sheet 10 is within the above range, the magnetic adsorption characteristics are excellent.

(Production method)
The manufacturing method of the magnetic sheet 10 is not specifically limited, A well-known method is employable except using only a soft ferrite as a soft magnetic material. For example, the method shown below is mentioned.
A composition obtained by mixing soft ferrite, which is a soft magnetic material, and a binder is kneaded, pulverized, formed into a sheet by roll rolling, and then magnetized by a magnetizing device to form the magnetic layer 12. A resin sheet (polyvinyl chloride sheet or the like) for forming the surface resin layer 14 is laminated on the surface of the obtained magnetic layer 12 by a dry lamination method, and a sucker sheet is laminated on the back side of the magnetic layer 12 by a dry lamination method. The magnetic layer 10 is formed by forming the adhesive layer 16.

[Second Embodiment]
FIG. 2 is a cross-sectional view of a magnetic sheet 20 which is another embodiment of the magnetic sheet of the present invention.
The magnetic sheet 20 of the present embodiment is a flexible sheet having a magnetic layer 22, a surface resin layer 24 provided on the surface of the magnetic layer 22, and a backing layer 26 provided on the back surface of the magnetic layer 22. It is.
The magnetic layer 22 can be the same as the magnetic layer 12 described above.

(Surface resin layer)
The surface resin layer 24 includes a surface layer 241 and a decorative layer 242. A decorative layer 242 is provided on the magnetic layer 22, and a surface layer 241 is provided on the decorative layer 242.
Examples of the material for forming the surface layer 241 include polyvinyl chloride, fluororesin, polyethylene terephthalate, and polypropylene. Especially, it is preferable to select from a polyethylene terephthalate and a fluororesin from the point of the ease of erasing the marker ink by an eraser. At least a portion of the surface layer 241 is transparent so that the cosmetic layer 242 can be visually sensed through the surface layer 241.

  The thickness of the surface layer 241 is preferably 0.01 to 0.5 mm, and more preferably 0.02 to 0.2 mm. If the thickness of the surface layer 241 is not less than the lower limit value, the surface smoothness is good. If the thickness of the surface layer 241 is equal to or less than the upper limit value, it is difficult to inhibit the magnet's attractive force.

Examples of the material for forming the decorative layer 242 include polyvinyl chloride, polyester, and polypropylene. Of these, polyvinyl chloride is preferred from the viewpoint of easy coloring with a pigment or the like.
For example, when the magnetic sheet 20 is used as a white board, a pigment (titanium oxide, zinc oxide, etc.) is blended with the decorative layer 242 to make it white.

  The thickness of the decorative layer 242 is preferably 0.05 to 0.5 mm, and more preferably 0.1 to 0.3 mm. If the thickness of the decorative layer 242 is equal to or greater than the lower limit value, the color of the magnetic layer can be sufficiently concealed. If the thickness of the decorative layer 242 is less than or equal to the upper limit value, it is difficult to inhibit the magnet's attractive force.

  For example, when the magnetic sheet 20 is used as a projector screen, the surface of the surface layer 241 may be provided with irregularities with high light reflectance. Such a surface resin layer 24 is commercially available, for example, as a “writing sheet” (manufactured by General).

The surface resin layer 24 may contain an additive as long as the effects of the present invention are not impaired.
Examples of the additive include an ultraviolet absorber, a light stabilizer, an antioxidant, a plasticizer, a colorant, a lubricant, and a processing aid.
An additive may be used individually by 1 type and may use 2 or more types together.

If possible, the surface layer 241 and the decorative layer 242 may be bonded by heat lamination or extrusion lamination, and an adhesive may be applied. It can select suitably according to the kind of layer to adhere | attach.
1-10 micrometers is preferable and, as for the thickness of an adhesive agent, 3-7 micrometers is more preferable. If the thickness of the adhesive is not less than the lower limit value, the surface layer 241 and the decorative layer 242 can be stably bonded. If the thickness of the adhesive is not more than the upper limit value, the magnetic attractive force is not hindered.

  If possible, the magnetic layer 22 and the surface resin layer 24 may be bonded by heat lamination or extrusion lamination, and an adhesive or a pressure-sensitive adhesive may be applied. It can select suitably according to the kind of each layer.

(Backing layer)
The backing layer 26 is provided on the back side of the magnetic layer 22 for the purpose of easiness in handling the magnetic sheet 20, applicability to a wall surface, improvement of tactile sensation after wall surface installation, and the like. The backing layer 26 is made of, for example, a mat, a woven fabric, a knitted fabric, a nonwoven fabric, or the like made of a flame-retardant or non-flammable fiber such as a flame-retardant polyester fiber, glass fiber, or carbon fiber.

  By providing the backing layer 26, when the magnetic sheet 20 is provided on the wall surface, if the underlying wall surface is a wood board or plaster board, an inexpensive starch-based adhesive that does not contain organic solvents or formalin causing sick house syndrome can be obtained. It can be used. Even when the wall surface base is a metal plate, it is possible to select a rubber-based adhesive that is inexpensive and easily available when the magnetic sheet 20 is provided on the wall surface. Moreover, since the wall surface after installing the magnetic sheet 20 has appropriate elasticity, when using the magnetic sheet 20 as a white board, an effect that the hand is not easily fatigued can be obtained.

  The thickness of the backing layer 26 is preferably 1 to 10 mm, and more preferably 3 to 7 mm. If the thickness of the backing layer 26 is equal to or greater than the lower limit value, the magnetic sheet 10 can be stably attached to the wall surface or the like. If the thickness of the backing layer 26 is equal to or less than the upper limit value, it is easy to handle.

  Adhesion between the backing layer 26 and the surface resin layer 24 may be thermal lamination or extrusion lamination if possible, and an adhesive or a pressure-sensitive adhesive may be applied. It can select suitably according to the kind of each layer.

[Function and effect]
The magnetic sheet of the present invention described above has sufficient magnetic adsorption characteristics.
In addition, since the magnetic sheet of the present invention uses only soft ferrite as the soft magnetic material, it is excellent in rust prevention as compared with the case where iron powder is used as the soft magnetic material. In addition, since no iron powder is used, the cost is low and the material is easy to handle.

The magnetic sheet of the present invention is not limited to the magnetic sheet 10 described above.
For example, the magnetic sheet of the present invention is a magnetic sheet that does not have an adhesive layer on the back surface of the magnetic layer when it is attached to a wall surface with an adhesive on the site, or attached to a wall surface with screws, double-sided tape, etc. May be.
The magnetic sheet of the present invention may be a magnetic sheet that does not have a surface resin layer on the surface of the magnetic layer.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Rust prevention evaluation]
A sample was cut from a magnetic sheet into a 5 cm × 5 cm square. This sample was left in an atmosphere of a temperature of 60 ° C. and a relative humidity of 90% RH for 1 week, and the state of the sample thereafter was visually confirmed to evaluate the rust prevention property of the magnetic sheet.
Evaluation was performed according to the following criteria.
○: Rust does not occur.
X: Generation | occurrence | production of rust is seen.

[Permeability]
A plurality of magnetic sheets were punched into a ring shape having an outer diameter of 20 mm and an inner diameter of 9 mm, and the punched ones were laminated to a thickness of about 10 mm to obtain an annular body. The enamel wire was wound around the annular body for 30 turns, and both ends of the enamel wire were connected to an LCR meter (E4980A, manufactured by Agilent), and the effective self-inductance of the toroidal coil was measured. The frequency during measurement was 100 kHz. Then, the effective permeability μ _e was obtained from the following equation.
μ _e = πDL / (n ² Aμ ₀ )
D: Average diameter of the annular body = (outer diameter + inner diameter) / 2
L: Toroidal coil inductance (measured value)
n: Number of turns = 30
A: Cross-sectional area of annular body = (outer diameter−inner diameter) × t / 2
t: height of the annular body (thickness)
μ ₀ = 4π × 10 ⁻⁷ (H / m)

[Example 1]
Mixing and kneading 63 volume% of Mn—Zn soft ferrite A (particle size 2 μm) which is a soft magnetic material and 37 volume% of chlorinated polyethylene (made by Showa Denko KK, chlorine content 32 mass%) as a binder After pulverizing, roll rolling was performed to obtain a magnetic sheet consisting only of a magnetic layer having a thickness of 0.5 mm.

[Example 2]
Except for mixing 63% by volume of Mn—Zn soft ferrite B (particle size 5 μm) as a soft magnetic material and 37% by volume of chlorinated polyethylene (made by Showa Denko KK, chlorine content 32% by mass) as a binder, A magnetic sheet was obtained in the same manner as in Example 1.

[Example 3]
Except for mixing 75% by volume of Mn—Zn soft ferrite B (particle diameter 5 μm) as a soft magnetic material and 25% by volume of chlorinated polyethylene (made by Showa Denko KK, chlorine content 32% by mass) as a binder, A magnetic sheet was obtained in the same manner as in Example 1.

[Comparative Example 1]
As a soft magnetic material, Mn-Zn soft ferrite A (particle size 2 μm) 60% by volume, iron powder 5% by volume, and chlorinated polyethylene (made by Showa Denko Co., Ltd., chlorine content 32% by mass) 35% by volume A magnetic sheet was obtained in the same manner as in Example 1 except that was mixed.

[Comparative Example 2]
Except for mixing 60% by volume of Mn—Zn-based soft ferrite C (particle size 15 μm) as a soft magnetic material and 40% by volume of chlorinated polyethylene (made by Showa Denko KK, chlorine content 32% by mass) as a binder, An attempt was made to obtain a magnetic sheet in the same manner as in Example 1, but it was broken by its own weight and could not be made into a sheet.
The evaluation results of Examples and Comparative Examples are shown in Table 1.

As shown in Table 1, the magnetic sheets of Examples 1 to 3 using only Mn-Zn soft ferrite as a soft magnetic material have high magnetic permeability and sufficient magnetic adsorption characteristics, and also the occurrence of rust. It was excellent in rust prevention. In Example 3, the magnetic permeability was particularly high, but the mass and bending elasticity were large, and the sheet was relatively difficult to handle.
On the other hand, although the magnetic sheet of Comparative Example 1 using iron powder in addition to Mn—Zn soft ferrite as a soft magnetic material had sufficient magnetic adsorption characteristics, rust was observed.

DESCRIPTION OF SYMBOLS 10 Magnetic sheet 12 Magnetic layer 14 Surface resin layer 16 Adhesive layer

Claims (3)

A magnetic sheet having a magnetic layer containing a soft magnetic material and a binder,
The soft magnetic material consists only of soft ferrite,
A magnetic sheet, wherein the soft ferrite has a particle size of 1 to 10 μm.   The magnetic sheet according to claim 1, wherein a filling rate of soft ferrite in the magnetic layer is 40 to 80% by volume.   The magnetic sheet according to claim 1 or 2, wherein the soft ferrite is a Mn-Zn soft ferrite.

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