JPS6352327A - Magnetic material - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder and to improve magnetic characteristics by incorporating coated magnetic powder which is coated with a specific silicone compd. into a magnetic material. CONSTITUTION:This magnetic material contains the magnetic powder coated with the compd. expressed by formula. (In formula, R1 denotes a lower alkyl group or aryl group, R2 denotes a hydrogen atom, alkyl group or aryl group, (a), (b) and (c) denote positive integers including 0.) The existence amt. of the compd. expressed by formula in the entire amt. of the coated powder is about 0.1-20wt%, more preferably 0.2-2.0wt%. The treatment tends to be not enough if the amt. is below 0.1wt% and the flocculation of the powder to each other is liable to arise when the amt. exceeds 20wt%. The dispersibility is thereby improved and the magnetic recording medium having the excellent magnetic characteristics is obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to the improvement of magnetic recording materials used in recording tapes, video tapes, floppy disks, credit cards with magnetic stripes, commuter passes, telephone cards, etc. be.

[Prior Art] Dispersion of magnetic powder in a vehicle plays an important role in the properties of magnetic recording materials. If the dispersion is insufficient, the squareness ratio,
Sensitivity is low, and if the particles are excessively dispersed, the particles will be crushed and the squareness ratio and sensitivity will decrease.

Conventionally, in order to improve dispersibility, magnetic powder has been surface-treated with inorganic or organic substances. Examples of acid salts and organic substances include fatty acids, amines, amides, and silane cuff pulling agents.

y Fe203, Cor Fe203, C
The main problem with rO2 and the like is dispersion, but other problems arise with magnetic iron powder. Magnetic iron powder is used in magnetic tapes that are commercially available as so-called metal tapes, but magnetic iron powder was originally used to make magnetic paint to be applied to tapes, but it did not blend well with paint binder resin, so it was dispersed. This made it difficult to increase the squareness ratio required for magnetic tapes, and there were various difficulties in improving output. Furthermore, magnetic tapes using magnetic iron powder still have the problem of being oxidized again by oxygen and moisture in the air during use, resulting in a decrease in magnetic properties.

Regarding the method of coating a solid surface with a polymer, there are, for example, Japanese Patent Publication Nos. 4028-1982, 4029-1982, 8548-1984, and 15422-1972.

Examples of methods for improving magnetic tapes by attaching polymers or phosphate esters to magnetic powder include JP-A-54
-134753, JP-A-55-15278, JP-A-55-15279, JP-A-55-L5280, JP-A-55-15281, JP-A-55-15282, etc. disclose polymers. A method of attaching is disclosed,
Furthermore, Japanese Patent Application Laid-open No. 102504/1983 discloses a method for attaching a low molecular weight organic substance to magnetic powder.

However, it has been extremely difficult to simultaneously improve dispersibility and provide oxidation resistance when coating magnetic iron powder with a polymer to form a paint.

Furthermore, since the inventions described in the above-mentioned Japanese Patent Laid-Open Nos. 54-15278 to 15282 use water as a dispersion medium, there is a drawback that magnetic iron powder is highly oxidized and deteriorates during treatment.

In the invention of JP-A-55-111105, the improvement in dispersibility is remarkable, but it is still insufficient in terms of FJ+M properties, and the same is true of the invention of JP-A-58-102,504.

Recently, about 0.1μ is used as magnetic iron powder for 3mm video.
However, as the particles become smaller, the dispersibility becomes worse and the deterioration of the tape in the air is accelerated.

[Problems to be solved by the invention] In the conventional technology, many things are processed in a slurry state.
Even when polymerization is carried out in a slurry, the reaction does not necessarily proceed on the surface of the magnetic powder, and polymerization often occurs while the magnetic powder remains entangled in the polymer.

Furthermore, since magnetic powder that is easily oxidized will oxidize even if it is exposed to air, it is desirable to process the magnetic powder immediately after it is synthesized.

As mentioned above, it is important to process magnetic powder quickly and uniformly and to control dispersibility.

In view of these circumstances, the present inventors have conducted intensive research to obtain a magnetic material with excellent magnetic properties. As a result, the present inventors have found that a magnetic material containing powder coated with a specific silicon compound has a magnetic property that satisfies all of the above objectives. Based on this knowledge, the present invention was completed.

[Means for Solving the Problems] That is, the present invention is a magnetic material characterized by containing coated magnetic powder in which magnetic powder is coated with a compound of formula (A).

[RI 5i03] a [RI R2Si
n] b[(R1)3SiO,i] C(A)
λ (wherein R1 is a lower alkyl group or an aryl group, R2
represents a hydrogen atom, an alkyl group, or an aryl group.

a, b and C are positive integers including 0. ) Hereinafter, the configuration of the present invention will be explained in detail.

The powder used in the present invention is usually a magnetic material made of iron (F
eOx 1.33 <
CrXCu, MO% Mns Nis P% Si
s Sn, iron powder containing Zn, CrO2, Ba ferrite, etc. are used.

Further, the powder may be iron, nickel, cobalt, or an oxide thereof coated on mica, but is not limited thereto.

The compound covering the surface is [RI SiO2] a [RI R25i0
3 b[(R1) 3 Sin upper ko C(A
) (in the formula, R represents a lower alkyl group or anol group,
R2 represents a hydrogen atom, an alkyl group or an aryl group. a, b and C are positive integers including 0. )
The molecular weight is preferably 200,000 or more.

If the molecular weight is less than 200,000, it may be difficult to obtain complete coverage and may not exhibit sufficient dispersibility.

Note that the molecular weight can be measured using gel permeation chromatography.

Also, the numerical values of a and b are in the range that satisfies the formula 20≦100a/(a + b)≦100.

It is preferably within 100a/(a + b
) is less than 20, the network structure is small (depending on the solvent, there is a possibility that the silicone coating will fall off).

R2 is a lower alkyl group or an aryl group,
Methyl, ethyl or phenyl groups are preferred, with methyl being particularly preferred.

Note that the ratio of a and b can be calculated using an infrared absorption spectrum.

The amount of the compound of formula (A) in the total amount of the coated powder of the present invention coated with the compound of formula (A) is about 0.1 to
20% by weight, preferably 0.2-2.0% by weight.

If it is less than 0.1% by weight, the treatment tends to be insufficient;
When the amount exceeds 20% by weight, agglomeration of powder particles tends to occur.

Various methods can be used to coat the powder with the compound of formula (A).

For example, powder is dispersed in a solution of organodichlorosilane containing SiH groups, and [RI 5inX] a [RI R25ill b] is applied to the surface of the powder through hydrolysis and crosslinking reactions.

[(R1)35i02] c There is a method of producing a single coating. At this time, the reaction rate can be controlled by adding calcium carbonate.

It can also be produced by dispersing a powder in a solution of silicon represented by formula (B) and then drying it, or it can also be produced by spraying silicon dissolved in a solvent onto a powder and drying it by heating. can.

(In the formula, R1 is a lower alkyl group or an alkyl group, R2
represents a hydrogen atom, an alkyl group, or an aryl group.

a is a positive integer, and b is a positive integer including 0. n is a positive integer and satisfies 3≦n≦100. ) (Hereinafter in the margin) It is also possible to produce the coated powder of the present invention by mixing the powder and the silicone of formula (B) in a ball mill. In addition, in the case of this method, if the numerical value of n in formula (B) exceeds 100, the miscibility between the cyclic silicon and the powder tends to deteriorate, so it is preferably 100 or less.

In addition to cyclic silicone, it is also possible to use linear silicone having terminal groups.

As described above, the powder used in the present invention can be produced using various processing methods, but the simplest and most effective coating method is the following method that utilizes the catalytic activity present on the powder surface. It's a method.

That is, if one or more silicones represented by formula (B) and powder are placed in separate containers and left in a closed system, the formula ( A)
A powder coated with the compound is obtained. In other words, the volatilized silicon reaches the powder and is adsorbed in molecular form on the powder surface. As the atmospheric pressure of the silicon in the closed system decreases due to adsorption, new cyclic silicon evaporates one after another.

Conventionally, it has been thought that heat, a polymerization catalyst, etc. are essential to polymerize silicone oil on the powder surface, but according to the nature of the invention, none of these are necessary. The present inventors have discovered that Si
Polymerization proceeds sufficiently due to the surface activity that generates -0-Si bonds.

The silicon adsorbed on the surface of the powder is successively crosslinked due to the surface activity of the powder, resulting in the formation of a network-like compound of formula (A). When the powder surface is coated with the compound of formula (A) in this manner, the surface active sites on the powder surface are blocked, so that the adsorption, crosslinking reaction, and polymerization are finally stopped, and the coating is completed. Thereafter, by degassing, unreacted silicon is removed and a powder coated with the compound of formula (A) is obtained.

In this method, the silicon represented by formula (B) preferably has a value of 3 to 8.

When n is 9 or more, it becomes difficult to vaporize. Further, it is sufficient that the temperature in the closed system in which the powder and silicone are housed together is 100°C or less. Traditionally, silicone polymerization.

Although it has been believed that a high temperature of around 150°C is required, it has been found that this is not necessary based on the nature of the process. This is because the nature utilizes the activity of the powder surface.

By processing at a temperature of 100°C or lower, it has become possible to process magnetic powders that are susceptible to oxidation and magnetic substances that are sensitive to high temperatures. Of course, if the powder is coated without fear of deterioration, temperature conditions exceeding 100° C. may be used. f
If heating is around 200°C, 100a/(
Even if the value of a + b) increases, it does not exceed the scope of the present invention.

The powder to be treated may be dried in advance or may contain some moisture.

In this way, the above-mentioned vapor phase coating process produces a stable powder by simply leaving the powder and silicon to stand, so it can also remove plastics and metal oxides whose surfaces are coated with magnetic powder. It can easily be further coated with a silicon compound.

As described above, crosslinking between Si-H groups is generated on the powder surface to form a network-structured silicon compound to coat the powder surface, but due to steric hindrance and other reasons, the crosslinking is
Sometimes it's not 00%. Therefore, residual Si--H groups are present, which may become slightly unstable under severe conditions such as in the presence of alkali or acid. An alkene or alkyne is added to the remaining Si--H group to form a Si--C bond to further stabilize the product, and further, by changing the length of the alkyl group, the dispersibility in the vehicle can be adjusted.

The alkene or alkyne may be a hydrocarbon having one or more unsaturated bonds (double bond, triple bond) at any position, preferably at the terminal. Examples include those with low boiling points such as ethylene, propylene, and butene to those with low boiling points such as octene, decene, and octadecene.

If it has an unsaturated bond, it will add to the 5i-H group at that position, so a cyclic structure such as cyclohexane, benzene, naphthalene, etc. may be present at any other position. Also, butadiene, isoprene, etc. having one or more double bonds can also be used.

The addition reaction of alkenes and alkynes to Si-H groups can be carried out in the presence of a catalyst by contacting them in the gas phase or liquid phase at 10°C to 300°C for about 1 hour.

Suitable catalysts include platinum group catalysts and compounds of ruthenium, rhodium, palladium, osmium, iridium, and platinum, with palladium and platinum being particularly good. Palladium-based palladium chloride (■), ammonium chloride tetraamminepalladate (n), palladium oxide (■
), palladium hydroxide (I), etc. Platinum-based platinum chloride (■), tetrachloroplatinic acid (■), platinum chloride (■), hexachloroplatinic acid (■), ammonium hexachloroplatinate (IV) , platinum (II) oxide, platinum hydroxide (■), platinum dioxide (■), platinum oxide (■), platinum disulfide (■), platinum sulfide (■), hexachloroplatinic acid (
rV) acid potassium, etc. In addition, these palladium and platinum compounds have tIJ, -alkyl (n-
1-8) Methyl ammonium chloride and tri-n-
It is also possible to use an organic solvent phase after addition of an alkylamine and ion pair extraction in a water/organic solvent system.

Further, an amine catalyst, ultraviolet T-rays, X-rays, plasma, etc. may be used.

At this time, the addition rate to the 5i-H group can be determined from the absorption of the Si-H group in the infrared absorption spectrum,
When the absorption of Si--H groups disappears, the addition rate becomes 100%.

In the method for producing a magnetic material according to the present invention, a solvent and a vehicle are added to and dispersed in magnetic powder coated with the compound of formula (A), and then a magnetic paint is applied to a resin film and oriented and dried.

As the solvent, toluene, xylene, kerosene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and ethyl acetate can be used, and as the resin binder of the vehicle, vinyl, cellulose, urethane, epoxy, phenoxy, and acrylic resins can be used. etc. can be mentioned.

According to the present invention, as is clear from the Examples described below, the compatibility of the powdered magnetic substance with the resin binder is improved, the dispersibility is improved, and a magnetic recording medium with excellent magnetic properties can be obtained.

〔Example〕

Hereinafter, the present invention will be explained by examples.

Example (1) Treatment of magnetic powder according to the present invention (Example-1
) CO-γ-Fe2031 kg was placed in a closed thermostat,
The mixture was left at 80° C. for 16 hours with 100 g of tetramethylcyclotetrasiloxane placed in another container. Tetramethylcyclotetrasiloxane was then removed from the system and 1
It was dried at 00''C for 4 hours. After drying, the weight was measured to be 1012.6 g, and was coated with 1.26% silicon compound.

(Example-2) 500 g of 160 g of the treated powder obtained in Example-1
isopropatool 3.2 containing 30 g of tetradecene and 32 mg of chloroplatinic acid diluted with isopropatool of 3.2
g was added thereto, and the mixture was allowed to react at room temperature for 16 hours while stirring. Thereafter, it was filtered, washed with ethanol, and dried in a drier at 80° C. for 4 hours to obtain a treated powder.

(2) Preparation of magnetic paint A magnetic paint was prepared by blending the following ingredients and thoroughly kneading them in a paint shaker.

Magnetic powder 80 parts Melting agent *
1 70 parts vehicle * 2 (N
, V, 23.8%) 42 parts *1 <Solvent> Toluene: MI
BK rainbow hexanone = 100: 100:
10*2 Vehicle > VAGH: Urethane elastomer = 100: 100 *Solvent in vehicle is toluene: MIBK: MEK = 1
A 500:00:100:100 container was filled with 600 parts of still beads (3 mm) and dispersed for 15 minutes. After that, 42 parts of vehicle and 100 parts of still beads were added and dispersion was continued for another 120 minutes.

(3) Manufacture of magnetic recording medium The magnetic paint obtained in (2) was applied to a polyester film by a conventional method, oriented and dried to obtain a magnetic recording medium on which a magnetic coating film with a thickness of about 6 μm was formed.

(4) Measurement of squareness ratio Squareness ratio (residual magnetic flux density Br/saturated magnetic flux density Bm) of magnetic recording media using the treated magnetic powder according to the present invention
was measured.

(Evaluation results of Examples 1 and 2) As a result of processing the magnetic powder of Example 1, 100a/(a
+b) is 63%, and the structure of the silicon compound covering the surface is as follows: a is 63%, b is 2
It was 7%.

[CH3SiO2] a [(CH3) H3
iO) bExample in which tetradecene was further added-
The addition rate of silicon compound No. 2 was 100%. Therefore, the structure is [CH35i○3'3 a [(CH3) (C1
4H29) SiOcob, 63% was a and the remaining 27% was b.

(Evaluation of magnetic recording media using Examples-1 and 2) Untreated Cor Fe203, Example-1, Example-
A magnetic recording medium was manufactured using No. 2, and the change in squareness ratio over time was measured depending on the processing time in a measurement magnetic field of 20,000 θe.

(Left space below) As can be seen from the examples, compared to those using untreated magnetic powder, Example-1 has significantly improved magnetic properties, and those with an alkyl group C14 further improve magnetic properties. was seen.

(Example-3) 10 kg of magnetic iron powder was placed in a rotating double cone type reaction tank (made of stainless steel, with heat insulation jacket) having a capacity of 100 N.
After depressurization, nitrogen substitution, and depressurization (20 mm f1 g), 800 g of tetramethyltetrahydrocyclotetrasiloxane was put into a raw material supply tank directly connected to the reaction tank, and reacted at 60° C. for 10 hours.

200 g of the treated magnetic iron powder thus obtained was placed in a 21 Erlenmeyer flask, and 20 mg of tri-n-octylmethylammonium salt of platinum chloride and 20 g of 1-decene were added to it as a catalyst. , J and 500 d of carbon tetrachloride were added, and the mixture was allowed to react at room temperature for 5 hours with stirring. Thereafter, it was washed with chloroform and dried at 50°C. Next, a magnetic coating material was prepared in the same manner as in Example 1, and a magnetic recording medium was manufactured.

[Effects of the Invention] The magnetic material of the present invention is a magnetic material with good magnetic powder dispersion and excellent magnetic properties.

Claims (1)

[Scope of Claims] 1. A magnetic material characterized by containing magnetic powder coated with a compound of formula (A). [R_1SiO_3_/_2]a[R_1R_2SiO
]b[(R_1)_3SiO_1_/_2]a(A)(
In the formula, R_1 represents a lower alkyl group or an aryl group, and R_1 represents a lower alkyl group or an aryl group;
2 represents a hydrogen atom, an alkyl group or an aryl group. a, b and c represent positive integers including 0. 2. The magnetic material according to claim 1, wherein in the compound of formula (A), a and b satisfy the following relational expression 20≦100a/(a+b)≦100. 3. The magnetic material according to claim 1 or 2, wherein the compound of formula (A) has a molecular weight of 200,000 or more. 4 The compound of formula (A) is 0.1 to 20% of the total amount of coated powder
% (weight %). 5 Claims 1 to 4 in which R_2 is a hydrogen atom
The magnetic material described in any of the above. 6. The magnetic material according to claim 1, wherein R_2 is any alkyl group having 2 to 30 carbon atoms. 7. The coating method of coating the powder with the compound of formula (A) is characterized in that the powder is brought into contact with one or more types of cyclic silicones represented by formula (B) and surface polymerized. A magnetic material according to any one of claims 1 to 6. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(B) (In the formula, R_1 is a lower alkyl group or an aryl group, R
_2 represents an alkyl group or an aryl group. a is a positive integer, b is a positive integer including 0, and satisfies the following relational expression a+b=3 to 100 20≦100/(a+b)≦100. ) 8 In the compound of formula (B), a is 0 and b is 3 to 8
The magnetic material according to claim 7, which is any one of the above. 9. The magnetic material according to claim 7 or 8, wherein the powder and the annular silicon represented by formula (B) are brought into contact in a gas phase. 10. The magnetic material according to claim 9, wherein the environmental temperature during gas phase contact is 100° C. or less. 11 Alkene and/or alkyne are further added to the remaining hydrogen atoms on the surface of the coated powder obtained by contacting the powder with one or more cyclic silicones represented by formula (B) and surface polymerizing the powder. 9. The magnetic material according to claim 8, which is hydrosilylated. 12. The magnetic material according to claim 11, wherein the alkene has 2 to 30 carbon atoms. 13. The magnetic material according to claim 12, wherein the double bond of the alkene is in the 1 position.