JPH0689425A - Magnetic painnt for magnetic recording medium and manufacture of vertical magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a coating material having a high degree of orientation by imparting prescribed characteristics to the coating material contg. magnetic particles, the surfactant expressed by prescribed formula and electron beam curing resin binder having prescribed characteristics. CONSTITUTION: This coating material is constituted to include the magnetic particles, the surfactant having the structure expressed by the formula and the electron beam curing resin. The concn. of the solid content in the magnetic coating material is specified to >=50wt.% and the apparent viscosity of the magnetic coating material to <=1000cps at a shearing rate = 1sec<-1> . In the formula, R1 , R2 : hydrogen or 1 to 4C lower alkyl groups, R3 : hydroxy lower alkyl group or acetoxy lower alkyl group having carbon atoms 1 to 6, R4 : hydrogen or 1 to 4C lower alkyl group, n: 20 to 40, A<-1> : anion. The electron beam curing resin binder has none of cation functional groups and anion functional groups and have hydrogen bonding energy of >=120J/cm<3> . As a result, the magnetic coating material having the high degree of orientation of >=2.3 in perpendicular orientation ratio and the high surface smoothness is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic coating material suitable for producing a magnetic recording medium, particularly a perpendicular magnetic recording medium, and a method for producing a perpendicular magnetic recording medium using the magnetic coating material.

[0002]

2. Description of the Related Art In manufacturing a magnetic recording medium, the magnetic particles in a magnetic paint applied to a substrate are oriented (orientated) in a certain direction, and the movement of the magnetic particles is carried out without disturbing the orientation. It is necessary to stop (fix the orientation), the orientation is achieved by putting it in the magnetic field while the coating is fluid, and the orientation is fixed by removing the fluidity of the magnetic coating (solidification). To be achieved. However, there is a case where the completed orientation is disturbed and fixed as it is due to the repulsion between the same polarity of magnetic particles and the flow of the solvent in the paint before the fixation after the orientation.

In the currently used video tapes and the like, magnetic recording is performed in the longitudinal direction (parallel to the magnetic surface), so that the magnetic particles are oriented and fixed in the longitudinal direction. In the possible perpendicular magnetic recording system, it is necessary to orient and fix the magnetic particles in the direction perpendicular to the plane of the recording medium. However, it is difficult to fabricate a magnetic recording medium having a high degree of perpendicular orientation suitable for perpendicular magnetic recording because the degree of repulsion between homopolar particles between magnetic particles is large because the arrangement of magnetic materials in perpendicular orientation is unreasonable. Met.

As a means for solving this problem, JP-A-58-222446 and the like use an electron beam-curable resin as a binder to perform vertical alignment of magnetic particles in an alignment magnetic field, and at the same time, use an electron beam. A method is described in which irradiation is carried out to carry out electron beam curing and drying of an electron beam curing resin. Further, in order to obtain sufficient magnetic characteristics, the vertical orientation ratio is 2.
It is known that 3 or more are required, however, these conventional methods only describe using a general surfactant, and do not describe solution viscosity or solid content of paint. . Therefore, it is difficult to achieve a sufficiently high vertical alignment for perpendicular recording only by using these conventional techniques. In addition, as an index of the surface smoothness of the magnetic coating surface, the surface roughness (RMS) is generally 5
It is known that the magnetic properties are good when the thickness is less than nm or the surface gloss is 150% or more.

However, in order to secure the fluidity necessary for orientation, the magnetic coating film used in the vertical alignment treatment still has a considerable amount of solvent remaining, and the coating film in such a state is subjected to electron beam curing treatment. When applied, the reaction of the electron beam curable resin and the evaporation of the solvent due to electron beam irradiation occur, which causes a problem of impairing the surface smoothness of the coating film surface. That is, there is a problem that such evaporation of the solvent occurs rapidly during a short alignment time of 1 second or less, many projections and cracks occur, and the surface smoothness of the coating film surface is significantly impaired.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a high degree of orientation and a high surface smoothness, and is suitable for producing a magnetic recording medium, particularly a perpendicular magnetic recording medium. And a method for manufacturing a perpendicular magnetic recording medium using them.

[0007]

Means for Solving the Problems The present inventor has found out that it is necessary to optimize the fluidity of the coating material as a result of extensive studies in order to realize a high degree of orientation. That is, a high degree of orientation can be achieved by setting the viscosity of the coating solution to be 5000 to 10000 cps under the conditions of a temperature of 25 ° C. and a shear rate of 1 sec ⁻¹ . Further, as a result of various studies on the cause of the lack of the surface smoothness, the following facts were clarified. That is, when electron beam curing is performed simultaneously with the orientation of magnetic particles,
When the coating film drying progresses to the rate-decreasing drying stage, the solvent diffusion in the coating film is rate-determining to the drying speed, the drying of the coating film surface portion progresses, the concentration gradient of the substance in the coating film and the resulting viscosity A gradient is created which forms a coating with very low solvent permeability on the coating surface. Then, in such a state, if the drying is forcibly promoted from the outside by electron beam irradiation, the surface coating is destroyed by evaporation of the solvent inside, and a projection or a crack is generated on the surface.

The present inventor has conducted various studies in order to avoid the above phenomenon and realize high surface smoothness. As a result, the solid content concentration of the coating material, the combination of the surfactant in the coating material and the electron beam curing resin in the coating material are selected. I have found that it needs to be optimized. That is, it has been found that a high surface smoothness can be achieved by using a combination of an interface lubricant and an electron beam curable resin capable of keeping the viscosity of the coating low while keeping the solid content of the coating high. .

Specifically, a surfactant having a high solid content concentration of 50% by weight or more and forming a large volume adsorption layer around the magnetic particles, and strong adsorption (ion adsorption) to the magnetic particles. However, they have found that an electron-curable resin having a surface-active action (dispersion action) may be used in combination.

Accordingly, the present invention is a magnetic coating material for a magnetic recording medium, comprising: (1) magnetic particles; (2) the following formula (I):

[Chemical 2](In the formula, R₁And R₂Is hydrogen or 1 to 4 carbon atoms
Represents a lower alkyl group, R₃Is low with 1 to 6 carbon atoms
Primary alkyl groups, having 1 to 6 carbon atoms in the alkyl portion
Hydroxy lower alkyl group or acetoxy lower alkyl group
R represents a kill group _FourIs hydrogen or a low carbon number of 1 to 4
A primary alkyl group, n is 20-40, and A
^-Is an anion); and (3) having both a cationic functional group and an anionic functional group.
Do not do 120 J / cm ³With the above hydrogen bond energy
An electron beam curable resin binder;
Has a solid content of 50% by weight or more, and a magnetic coating
The apparent viscosity of the material is shear rate = 1 sec^-1At 10,0
Providing a magnetic paint characterized by being less than 00 cps
It

In the present invention, the magnetic coating is applied onto a substrate, and the substrate coated with the magnetic coating is placed in a vertical magnetic field to orient the magnetic particles, and at the same time, the electron beam is irradiated. A method of manufacturing a perpendicular magnetic recording medium, characterized in that a curing treatment of an electron beam curable resin binder is performed.

[0012]

[Detailed Description] In the present invention, as magnetic particles,
Magnetic particles commonly used in magnetic recording media can be used, and examples thereof include barium ferrite, (gamma magnetic iron oxide γ-Fe ₂ O ₃ , cobalt-containing γ-Fe ₂ O ₃ and magnetite iron oxide Fe ₃ O ₄ , Cobalt-containing Fe ₃ O
₄ ), chromium oxide (CrO ₂ ), metallic magnetic iron, etc. can be used.

As the surfactant used in the magnetic coating material of the present invention, the chain of the hydrophobic group (lipophilic group) has a certain length and has a branched structure, and the surface of the magnetic particle is It has been found that the functional group (hydrophilic group) that directly interacts (adsorbs) is a quaternary ammonium salt. In the present invention, the surfactant having the structure represented by the general formula (I) is used as the surfactant satisfying such conditions.

In the present invention, it belongs to the definition of the general formula (I).
Any surfactant that₁Over
And R₂Is a methyl group or an ethyl group, and R₃Is C₂~ C
_FourAlkyl group, hydroxyethyl group (-CH₂CH₂O
H) or acetoxyethyl group (-CH₂CH₂OCOC
H₃) And R_FourIs hydrogen or a methyl group, and n is 2
0-40, and A^-Is acetate, phosphate
Or surfactants that are chloride anions are preferred.
Yes. As an example of such a surfactant, R₁, R ₂as well as
R_FourIs a methyl group, and R₃Is a hydroxyethyl group (-
CH₂CH₂OH), n is 40, and A
^-Is acetate anion (CH₃COO^-) Is the interface
Activators may be mentioned. This surfactant is included in this specification.
Called "E / A".

The amount of this surfactant used is 100
It is 2 to 10 parts by weight, preferably 3 to 7 parts by weight, based on parts by weight. If this amount is too large, the wear resistance of the magnetic layer is reduced, and if it is too small, the viscosity of the coating cannot be sufficiently reduced. The binder resin used in the present invention does not strongly adsorb (ion-adsorb) on the surface of the magnetic particles, but has a nonionic surface-active effect (dispersion ability). Those having no ionic functional group such as an acid group or a carboxylic acid group are preferable.

Therefore, the electron beam curable resin used in the present invention is preferably polyvinyl alcohol having a large number of hydroxyl groups in the molecule, or hydrophilic polyurethane resin having no hydroxyl groups. Examples of such a resin include a polyurethane resin composed of polyethylene glycol / adipic acid / hydrogenated diphenylmethane diisocyanate (MDI), such as NR-2000 (Mitsubishi Rayon), Mu-155 (Mitsubishi Rayon), Desoto 3511F (Nippon Synthetic Rubber). To be

In order to reduce the viscosity of the magnetic coating material, it is desirable to use an electron beam curable resin having a low molecular weight within a range that does not impair the strength of the coating film.
000, preferably 1,000 to 5,000. The most convenient and effective method for quantifying the hydrogen bond energy of the electron beam curing resin is to use "hydrogen bond energy obtained from the solubility parameter (SP)". There are several ways to express this solubility parameter. Among them, the solubility parameter is van
There is a method in which the solubility parameter of a polymer solvent or the like is two-dimensionally expressed by two components, δv caused by der Waals force and δh caused by hydrogen bond [Yuji Harasaki, Basic Science of Coating (Makihara Shoten 198
0)].

That is, δ _Poly ² = δ _Poly v ² + δ _Poly h ² (1): δ _Poly = polymer solubility parameter (SP) δ _Poly v = polymer solubility parameter van d
er Waals force component δ _Poly h = hydrogen bond component of polymer solubility parameter where square of hydrogen bond component of solubility parameter, δ
_Poly h ² corresponds to the hydrogen bond energy (J / cm ³ ) per unit volume of the polymer. Therefore, if the solubility parameter, δ _Poly , of a polymer can be determined, the hydrogen bond energy of the polymer can be quantified by dividing it into the above two components.

On the other hand, the solubility parameter of the solvent can be similarly expressed. That is, δ _Solv ² = δ _Solv v ² + δ _Solv h ² (2): δ _Solv = Solubility parameter of solvent (SP) δ _Solv v = Van der of solubility parameter of solvent
Waals force component δ _Solv h = hydrogen bond component of solubility parameter of solvent

By the way, as for the solubility parameter of the solvent, and the van der Waals force component and the hydrogen bonding force component of the solubility parameter, the literature values are widely known for most of the solvents, and these are also used here. Two or more mixed solvents can be calculated from the literature values of these pure solvents. Solubility parameters of these pure and mixed solvents can be used to create a solubility plot in a two-dimensional plane (see Figure 1). Figure 1
In, the coordinates representing a point on the plot are (x,
y) = (δ _Solv v, δ _Solv h).

Next, regarding the method for obtaining the solubility parameter of the polymer, it is obtained by an experiment as follows with reference to the above-mentioned document. Generally, if the difference between the two solubility parameters of the polymer and the solvent | δ _poly −δ _Solv | is less than a certain value, the polymer is expected to be soluble in the solvent. That is, it is expected that the polymer will dissolve in the solvent when the condition of the following expression (3) is satisfied.

| Δ _poly −δ _Solv | ≦ R (3): R = constant uniquely determined by the polymer. That is, in the solubility plot shown in FIG. 1, the coordinates of the point representing the solubility parameter of the polymer ( δ _poly v, δ
_The solvent and mixed solvent represented by the coordinates of points plotted in a circle of radius = R centering on _poly h) show sufficient solubility for the polymer, and the points outside the circle of radius = R The formula (3) shows that the solvent and mixed solvent represented by the coordinates of do not exhibit sufficient solubility in the polymer.
It is considered that the solvent and mixed solvent represented by the coordinates of points on the circle of radius = R correspond to the critical point in the solubility of the polymer.

Therefore, a "solubility test" is conducted to determine whether a polymer having an unknown solubility parameter is dissolved in any solvent or mixed solvent having a known solubility parameter, and the result is shown in FIG. To plot. In FIG. 1, the results of this solubility test show that when the polymer is dissolved in the solvent (solution is transparent), a circle is marked on the coordinate representing the solubility parameter of the solvent, and when the polymer is not dissolved (polymer is precipitated). , At the coordinates corresponding to the solvent
Is written. Specifically, first, a solvent having a high solubility for the polymer (eg, cyclohexanone, ME
K, toluene, etc.) is found, and a solvent in which the polymer does not dissolve (eg, ethanol, methanol, etc.) is gradually mixed with the solvent, and the point of precipitation (critical point) is found first. The coordinates of the solubility parameter of the mixed solvent of the ratio are plotted as ● in FIG.

In this way, the solubility test is repeated.
Find 3 or more points ● of the boundary points and equidistantly from these points
Find a certain point (■ in FIG. 1). Coordinates of this point =
(Δ _polyv, δ_polyh) is the solubility parameter of the polymer
It represents the starter, from which δ_polyh²Ask for this
The value is taken as the hydrogen bond energy of the polymer.
FIG. 1 shows the binder, NR-2000, used in the present invention.
An example of obtaining the solubility parameter is shown. This
, NR-2000 hydrogen bond energy = 121 J /
cm³Becomes

The amount of the electron beam curable resin is 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic particles. The viscosity of the magnetic coating material of the present invention was measured using a B-type viscometer (manufactured by Tokyo Keiki) at room temperature (25 ° C.) and a shear rate of 1
It is measured under the condition of sec ^-1 , but preferably 5000 to 1
It is 0000 cps. Here, the reason for defining 5000 cps or more is because the molecular weight of the electron beam curable resin is low and the durability of the medium after curing is poor below 100 cps.
The reason why it is defined as 00 cps or less is that if it is exceeded, the fluidity of the coating becomes insufficient and the degree of orientation becomes low.

The other components of the magnetic recording medium of the present invention are the same as those of the conventional magnetic recording medium. For example, abrasives such as alumina, chromium oxide (Cr ₂ O ₃ ), silicon nitride, zirconia; antistatic agents such as carbon black and carbon graphite; fatty acids such as myristic acid, stearic acid, oleic acid; fatty acid esters such as stearin. Lubricants such as isocetyl acid, oleyl oleate, and butyl stearate can be added in conventional amounts.

In producing the magnetic recording medium of the present invention,
First, a magnetic paint is blended and prepared according to a conventional method, and this is applied onto a substrate. This operation can also be performed according to a conventional method. Next, the magnetic particles are oriented by placing the substrate, the surface of which is coated with the magnetic coating material of the present invention, in a vertical magnetic field. During this time, electron beam irradiation is performed to cure the electron beam curable resin. The intensity of the magnetic field and the irradiation intensity of the electron beam differ depending on the type of the electron beam curing resin, etc., but the magnetic field intensity is preferably 4 K gauss or more, and the intensity of the electron beam irradiation is 5 M.
rad or more is preferable.

[0028]

EXAMPLES Next, the present invention will be described more specifically by way of examples. A magnetic paint having the following composition was prepared. Barium ferrite (HEX-6565 manufactured by Toda Kogyo Co., Ltd .; 100 parts by weight BET = 65 m ² / g, Hc = 650 Oe) Surfactant 7 parts by weight Electron beam curable resin 25 parts by weight Abrasive (alumina) 7 parts by weight Antistatic agent (carbon black) 4 parts by weight Fatty acid (myristic acid) 1 part by weight Lubricant (isocetyl stearate) 3 parts by weight Mixed solvent: methyl ethyl ketone / cyclohexanone (9: 1) Solid content concentration: Set according to each experiment (As shown in Table 1).

The above components are uniformly dispersed by a sand mill to form a base film (PET film; E-7 manufactured by Teijin Ltd.).
5) was applied at an optimum speed for each coating composition in the range of 5-20 mpm, followed by a vertical orientation magnetic field of 4 K gauss,
At the electron beam irradiation dose of 5 Mrad, the orientation of the magnetic particles and the curing of the magnetic paint were simultaneously performed. Tables 1 and 2 show the viscosity of the magnetic coating solution and the properties of the obtained magnetic recording medium.

Here, the vertical orientation ratio in Table 1 is measured by a magnetic characteristic measuring device VSM (manufactured by Toei Industry Co., Ltd.), and the surface glossiness is measured by a surface gloss meter gloss meter (manufactured by JEOL Ltd.). It was measured. The surface roughness (RMS) in Table 2 is "TOPO-3D" manufactured by Wako Co.
It is measured by an interferometer.

[0031]

[Table 1]

The symbols in Table 1 have the following meanings. E / A: In FIG. 1, R ₁ = CH ₃ ; R ₂ , R ₃ = CH
₂ CH ₂ OH; R ₄ = CH ₃ ; n = 40; A =
Surfactant used in the present invention which is an acetate anion POC: Polypropylene glycol molecular chain and surfactant having a structure having a phosphate group as a functional group O / A: Oleic acid N / R used as a surfactant : Polyethylene glycol / adipic acid / hydrogenated M
It has a main chain containing DI, the hydrogen bond energy calculated from the solubility parameter = 121 J / cm ³ , the number average molecular weight
2,500 polyurethane resin used in the present invention (NR-2000 / manufactured by Mitsubishi Rayon Co., Ltd.) JSR: electron beam curable resin having -SO ₃ Na as a functional group (Desoto JSR-9514 / manufactured by Japan Synthetic Rubber Co., Ltd.) P / U: Polyurethane resin having a hydrogen bond energy of 90 J / cm ³ obtained from the solubility parameter (TI-7
302 / Made by Sanyo Chemical Co., Ltd.)

[0033]

[Table 2]

[0034]

According to the present invention, a high degree of orientation (vertical orientation ratio 2.
(3 or more) and high surface smoothness (RMS = 5 nm or less, surface glossiness of 150% or more) can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for obtaining a hydrogen bond energy from a solubility parameter, taking an NR-2000 resin as an example.

Claims (7)

[Claims] 1. A magnetic coating material for a magnetic recording medium comprising: (1) magnetic particles; (2) the following formula (I):(In the formula, R₁And R₂Is hydrogen or 1 to 4 carbon atoms
Represents a lower alkyl group, R₃Is low with 1 to 6 carbon atoms
Primary alkyl groups, 1 to 6 carbon atoms in the alkyl group
Having a hydroxy lower alkyl group or acetoxy lower group
R is a group, R_FourIs hydrogen or 1 to 4 carbon atoms
A lower alkyl group, n is 20-40, and
A^-Is an anion); and (3) having both a cationic functional group and an anionic functional group.
Do not do 120 J / cm ³With the above hydrogen bond energy
An electron beam curable resin binder;
Has a solid content of 50% by weight or more, and a magnetic coating
The apparent viscosity of the material is shear rate = 1 sec^-1At 10,0
Magnetic paint characterized by being less than 00 cps. 2. In the formula (I), R ₁ and R ₂ are methyl or ethyl groups, and R ₃ is a C ₂ -C ₄ alkyl group, a hydroxyethyl group (—CH ₂ CH ₂ OH) or acetoxyethyl. a group _{(-CH 2 CH 2 OCOCH 3)} , R 4 is hydrogen or methyl group, n is 20 to 40, and a ^- is acetate, phosphate or chloride anion, according to claim 1 Magnetic paint. 3. The magnetic coating material according to claim 1, wherein the magnetic particles are barium ferrite particles. 4. The magnetic paint according to claim 1, wherein the electron beam curing agent resin is a polyurethane resin. 5. The magnetic particles according to claim 1 are coated on a substrate, and the substrate coated with the magnetic coating is placed in a vertical magnetic field for orientation treatment of the magnetic particles. A method of manufacturing a perpendicular magnetic recording medium, characterized in that the electron beam curable resin is cured by being simultaneously irradiated with an electron beam. 6. The perpendicular magnetic field is 4 K gauss or more,
The method according to claim 5. 7. The method according to claim 5, wherein the intensity of the electron beam irradiation is 5 Mrad or more.