JPH0453028A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve magnetic characteristics by predispersing ferromagnetic powder specified in crystallite size and adsorbed moisture to specific values and a binder together with a solvent by using a twin shaft type continuous kneading and mixing machine, then adding an additive to the dispersion and applying a magnetic coating liquid on a nonmagnetic base after mixing and dispersing. CONSTITUTION:The ferromagnetic powder of <=400Angstrom crystallite size controlled in moisture to <0.8 wt.% and the binder are charge from a feed port 4 into a mixing chamber 6 and are predispersed by using the twin shaft type continuous kneading and mixing machine. The additive is in succession added to the dispersion and the dispersion is mixed and dispersed, by which the dispersion state of a high degree is obtd. in a short period of time in spite of the continuous treatment. A high degree of brightness and Br/Bm are attained in a short period of time as the dispersibility is improved. Further, a vinyl chloride resin contg. a functional group and more particularly substituent, such as OH type or amino group, and a rubber resin are used. The predispersing stage which is the 1st stage is executed by kneading and dilute kneading at a prescribed solid concn. The dispersibility is improved in this way and the brightness and Br/Bm are obtd. at a high degree in a short period of time.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a magnetic recording medium, and in particular to a method for manufacturing a magnetic recording medium in which ferromagnetic powder is well dispersed and 1 has excellent magnetic conversion characteristics. Regarding the manufacturing method.

(Prior art) Coated magnetic recording media are made by dispersing ferromagnetic powder in a binder, coating it on a non-magnetic support, and subjecting it to magnetic field orientation, smoothing, etc., if necessary. Manufactured by.

In recent years, magnetic recording media (hereinafter sometimes referred to as magnetic tapes) are required to have advanced characteristics, and various improvements have been made. One of these properties is excellent electromagnetic conversion properties. As a means to improve the electromagnetic characteristics of coated magnetic tapes, we improved the filling layer of the magnetic layer coated on the non-magnetic support, and also used ferromagnetic powder with small particle size and large specific surface area. It is important to improve the /N ratio. To achieve this, it is necessary to knead a solvent solution containing a binder and ferromagnetic powder in the manufacturing process of magnetic paint to give a high shearing elasticity in a highly concentrated state, and to increase the degree of filling of the applied magnetic layer. It is required to increase the magnetic flux, uniformly disperse the ferromagnetic powder in the binder, and smooth the surface of the applied magnetic layer.

For this reason, conventionally, as disclosed in Japanese Patent Application Laid-open No. 60-187931, dyeing moisture of ferromagnetic powder has been reduced to 0. S
Efforts have been made to meet the above requirements by kneading 9iJ magnetic powder whose humidity has been adjusted to Nt% or more with a binder using various kneaders.

However, the adsorption of ferromagnetic powder as disclosed in the above-mentioned publication does not provide the desired properties even when the moisture is adjusted to 0.8 wt% and kneaded with a continuous kneader. #A was moistened to a moisture content of 1.5@t% and kneaded using a continuous kneader, but the properties were even worse, making it impossible to obtain a magnetic recording medium with excellent magnetic conversion properties.

In addition, in order to improve the filling degree of ferromagnetic powder in the magnetic coating material applied to the support, it is necessary to use a coating agent containing a binder that is carried out in the manufacturing process of the magnetic coating material. It is preferable to knead the solvent solution and the ferromagnetic powder in a highly concentrated state while applying a high shearing force.
As disclosed in Japanese Patent No. 1274, an attempt has been made to meet the above requirements by performing kneading using a twin-screw continuous kneading mixer.

In the manufacturing process of magnetic paint, after the above-mentioned kneading, the kneaded product is usually diluted by adding an organic solvent to it, but the kneaded product kneaded with a twin-screw continuous mixer has a high viscosity. Therefore, even if such hard mixed materials are diluted all at once using a high-speed dispersion mixer (flow jet mixer) as disclosed in the above publication, there will be a high degree of high concentration in the mixed material during dilution. It is not possible to apply shearing force, and as a result, the kneaded material remains in small clumps, making it impossible to obtain a uniform dilution. Since the processing time is long and the level of dispersion achieved is low, even if the magnetic paint obtained in this way is applied to a support, the magnetic properties are... A magnetic recording medium with excellent magnetic conversion characteristics etc. cannot be obtained.

The inventors of the present invention have conducted repeated studies to improve this problem, and have found that when kneading ferromagnetic powder with a crystallite size of 400 Å or less with a binder in a twin-screw continuous mixer (continuous kneader), , contrary to the method disclosed in JP-A-60187931, the water content of the ferromagnetic powder was reduced to 0.8w.
The inventors have discovered that sufficient crosstalk and dispersion can be achieved by reducing the amount to t% or less, leading to the present invention. This is a feature of a continuous kneader, in which ferromagnetic powder and binder are continuously fed into a fixed subtable, and the ferromagnetic powder and binder are kneaded in the tank and discharged as mixed materials after a certain period of time. If there is a lot of moisture in the ferromagnetic powder during the kneading process, crosstalk between the ferromagnetic powder and binder will not start from the beginning in the tank, and the more moisture in the ferromagnetic powder, the more crosstalk will occur in the middle of the tank or at the rear of the tank. As a result, the ferromagnetic powder and the binder are not sufficiently mixed and are discharged. When the moisture content of the ferromagnetic powder is sufficiently low, the ferromagnetic powder and the binder are sufficiently mixed together from the beginning in the bath.

That is, when cross-crossing is performed in a continuous kneader, it has been found that by reducing the adsorbed moisture of the ferromagnetic powder to 0.8 wt% or less, sufficient cross-crossing and dispersion can be achieved and a desired magnetic recording medium can be obtained. reached. Furthermore, it was discovered that good mixing and dispersion can be achieved in the next mixing and dispersing step by dividing the pre-dispersion step into two, a mixing step and a dilution mixing step, and making a difference in solid content concentration, leading to the present invention.

(Objective of the Invention) An object of the present invention is to provide a method for manufacturing a magnetic recording medium that has a high degree of filling of ferromagnetic powder, good dispersibility, and excellent magnetic properties.

(Structure of the Invention) That is, the above object of the present invention is to obtain crystallites with a crystallite size of 400 Å.
In the following, ferromagnetic powder with adsorbed moisture adjusted to less than 0.8 wt% and a binder are used together with a solvent, a pair of shafts each having a blade member, and a barrel that rotatably accommodates these shafts. The first step is pre-dispersion using a mixer, the second step is to add additives and mix and disperse, and the third step is to apply the dispersed magnetic coating liquid onto the magnetic support. This can be achieved by a method of manufacturing a magnetic recording medium characterized by including the steps of.

More preferably, this can be achieved by a method for producing a magnetic recording medium, characterized in that the no-inder used in the first step is a functional vinyl chloride resin and a rubber resin.

More preferably, the above-mentioned object of the present invention is such that the first pre-dispersion step includes a kneading step carried out at a solid content concentration of 65 to 95% by weight, and further a dilution kneading step carried out at a solid content concentration of 30 to 60% by weight. This can be achieved by a method for manufacturing a magnetic recording medium characterized by the following.

That is, in the present invention, when ferromagnetic powder of fine particles with a crystallite size of 4.00 Å or less is kneaded using a twin-screw continuous kneading mixer (hereinafter also referred to as a twin-screw continuous kneader),
Unlike the case of an oven kneader, it has to be processed and discharged in a short time, so we found that if the water content is lower than Q, 3wt%, it will be more easily absorbed into the binder in a short time, and dispersion will be better. Ta. Maven;--
In the case of goo, kneading takes time, so the higher the moisture content, the better the result.However, in the case of a twin-screw continuous kneading mixer, there are unique factors due to the continuous kneading process. Seem.

The functional groups contained in the binder are effective in dispersing the ferromagnetic powder, but in the case of a twin-screw continuous kneading mixer, the lower the water content, the faster the binder will blend in with the binder, resulting in a better dispersion effect. , the functional groups contained in the binder are also OH
Groups such as amino groups, which are not very acidic, have a low affinity with water, and a good dispersion effect can be obtained. Preferably, in the first pre-dispersion step, the kneading is carried out at a solid dispersion degree of 65 to 65.
Knead vigorously at 95% by weight, and reduce the solids concentration to 3 in the dilution kneading process.
Smooth dilution can be achieved by using 0 to 601j% by weight, and when combined with fine ferromagnetic powder that has a water content of less than 0.8wt% and little adsorbed water, the dispersibility is significantly improved, and the glossiness and High values of Br/Bm are achieved in a short time.

The ferromagnetic powder used in the first step in the present invention includes rFezes, Fe5Oa, Co-rFe
In addition to Ox (4/3≦X≦3/2), alloy fine powder whose main component is iron, metamorphosed barum ferrite, metamorphosed strontium ferrite, etc. are used. The shape of these ferromagnetic powders can be needle-like, granular, dice-like, wood-like, or plate-like.

The crystallite size of these ferromagnetic powders is 400 Å or less, preferably 270 to 400 Å, particularly preferably 290 Å.
It is possible to provide a ferromagnetic powder with a water content within the range of the present invention, which is from 0 to 390 people, without using any particularly new techniques. This is also possible, for example, in the process of making cobalt-doped ferromagnetic iron oxide. That is, this can be achieved by coating the iron oxide magnetic powder with a cobalt compound, then washing it with water, filtering it, and drying it by controlling the moisture content in the drying process. Alternatively, this can be achieved by providing a w1 wet process as a post process. In addition, the water content in the present invention refers to that measured using the principle of water measurement by the Karl Fischer method, and the adsorbed water content of the ferromagnetic powder is preferably Q, 8 wt % or less, particularly preferably 0. 2at%~Q, 7+mt% is good, 0.2w
If it is less than t%, there will be no change in characteristics, and it will take time to dry in the humidity conditioning process, which will increase costs, which is not preferable.

In addition, the functional groups of the vinyl chloride vinyl acetate resin used in the first step include hydroxyl group, carboxyl group, epoxy group, phosphoric acid group, sulfonic acid group, amino group, sulfonic acid metal base, sulfuric ester group (metal salt ), (-OH, -COO
M, -3OsM.

O20,M--P=O(OM) -NH,,0-P=
O(OM), M is hydrogen or an alkali metal, etc. Particularly preferred are those that are not strongly acidic such as 10H1-NH2, and these can be used alone or in combination. Rubber resins used in conjunction with functional group-containing vinyl chloride vinyl acetate resin include polyurethane rubber (polyurethane resin), styrene butadiene rubber, butadiene rubber, isoprene rubber, chloroprene rubber, isobutylene rubber,
These are resins such as isoprene rubber, acrylonitrile butadiene rubber, acrylic rubber, and epichlorohydrin rubber.

Among these rubber-based resins, polyurethane rubber (polyurethane resin) is particularly preferred, and among these rubber-based resins,
The above-mentioned functional groups may be included.

The continuous kneader used in the first process is a horizontal closed-type mixer, with two pumping shafts lined up in a two-part barrel, each with a specially shaped feeding screw. The two shafts, which have a built-in paddle for cross-conducting lines, rotate in the same direction at a constant speed. Raw materials supplied from one end of the barrel are fed into the closed trough by a screw, kneaded, diluted, and pre-dispersed by paddles in the mixing area, and then discharged from the other end of the barrel. The cross section of the paddle is triangular, and there are three types of paddles: a ``flat paddle'' for kneading, a ``helical paddle'' for mixing and feeding, and a ``reverse helical paddle'' for reverse feeding. The kneading mechanism consists of (1) compression and elongation of the material in the axial direction caused by the way the paddles are assembled, (2) compression and elongation of the material in the cross-sectional direction perpendicular to the axis caused by the rotation of the paddles, and (3) compression and elongation of the material between the paddles and the barrel, and between the paddles. The shear applied to the material between the two is the main one. This continuous kneader is described in "Mixing Cross-Circulation Technology" published by Nikkan Kogyo Shimbun.

In the present invention, the additives used in the second step include dispersants, lubricants, stabilizers, abrasives, antistatic agents, and the like.

Dispersants include caprylic acid, capric acid, lauric acid,
Fatty acids with 12 to 18 carbon atoms (R, C0OH,
R1 is an alkyl having 11 to 17 carbon atoms; a metal soap consisting of the alkali gold IK (Li, Na, etc.) or alkaline earth gold [(Mg, Ca, Ba) of the above fatty acid; Compounds containing fluorine; fatty acid amides; aliphatic amines; higher alcohols; polyalkylene oxide alkyl phosphates; alkyl phosphates; alkyl borates; class ammonium salts; known pigment dispersants and surfactants such as lecithin can be used.

These dispersants are used in an amount of 0.00 parts by weight per 100 parts by weight of ferromagnetic powder.
1 to 10 parts by weight are used, preferably 0.5 to 5 parts by weight.

As the lubricant, the aforementioned fatty acids; higher alcohols;
Fatty acid ester consisting of a monobasic fatty acid having 12 to 20 carbon atoms such as butyl stearate and sorbitan oleate and a monohydric or polyhydric alcohol having 3 to 20 carbon atoms;
Silicone oils such as dimethylpolysiloxane and methylphenylpolysiloxane; fatty acid-modified silicone compounds; fluoroalkylpolysiloxanes; mineral oils - animal and vegetable oils;
In addition to olefin low polymers and α-olefin low polymers, known lubricants such as graphite fine powder, molybdenum disulfide fine powder, Teflon fine powder, and lubricants for plastics can be used.

These lubricants are 0.0% per 100 parts by weight of ferromagnetic powder.
1 to 10 parts by weight, preferably 0.5 to 5 parts by weight are used.

Stabilizers include organic tin compounds such as dibutyltin dilaurate; alkaline earth metal soaps of fatty acids; epoxy compounds such as epoxidized oils; organic phosphite benzophenone compounds; benzotriazole compounds; phenolic antioxidants, etc. Stabilizers for plastics, UV inhibitors for plastics, antioxidants for plastics, etc. are used.

Materials commonly used as abrasives include α-alumina,
silicon carbide chromium oxide, corundum, artificial corundum,
Diamonds, synthetic diamonds, garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm. These abrasives contain 0 parts by weight per 100 parts by weight of ferromagnetic powder.
．． 1 to 20 parts by weight are used, preferably 0.5 to 5 parts by weight.

As antistatic agents, in addition to carbon, natural surfactants such as saponin; alkylene oxide type, glycerin type,
Nonionic surfactants such as glycidol; cationic surfactants such as higher alkyl amines, quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, Anionic surfactants containing acidic groups such as phosphate ester groups; amphoteric surfactants such as sulfuric acid or sulfuric esters of amino acids, aminosulfonic acids, and amino alcohols are used.

These additives may not be added before dispersion, but may be added at the end of dispersion or at the coating stage, if necessary. In the present invention, polyisocyanate is used in the second step if necessary. Polyisocyanate-1 is a reaction product of 3 moles of diisocyanate such as tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate-F and 1 mole of trimethylolpropane, or a pureed atact compound of 3 moles of hexamethylene diisocyanate. , an isocyanurate adduct compound of 3 moles of tolylene diisocyanate and 2 moles of hexamethylene diisocyanate, a polymer compound of diphenylmethane diisocyanate, and isophorone diisocyanate.

These compounds are available from Nippon Polyurethane KK as "Coronate", "Coronate HLJ", "Coronate 203", and "Coronate 203".
0J, [Millionate MRJ, [Millionate MTLJ]
"Desmodule 1., J.

Takenate D-102J, Takenate D-1 from Takeda Pharmaceutical Co., Ltd. under the trade names of "Desmodule N", "Desmodule ILj", "Desmodule HLJ", etc.
1ONJ, rTakenate D202, etc., respectively.

Amount of binder used in the present invention (for example, total amount of vinyl chloride copolymer, rubber resin, and polyisocyanate)
It is preferable to use 10-10 parts by weight, particularly preferably 15 to 40 parts by weight, per 100 parts by weight of the ferromagnetic powder.

The solvent used in the present invention is, for example, an organic solvent that dissolves the vinyl chloride copolymer and the rubber resin, and has a boiling point of 50°C or more and 200°C or less. Particularly preferred are those having a boiling point of 80°C or higher and 160°C or lower. Furthermore, when using polyisocyanate, it is necessary to use one that does not have active hydrogen groups.

The solvents may be used alone or in combination. When used in combination, for example, a solvent that does not dissolve the vinyl chloride copolymer and the rubber resin may be used.

Examples of these organic solvents include alcohols such as ethanol, n-propanol, isopropanol, n-butanol, methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone, acetate esters such as ethyl acetate and butyl acetate, and hydrocarbons such as toluene and xylene can be used.

Other examples include cellosolves, chlorinated hydrocarbons, nitrated hydrocarbons, and formamides.

The mixing and dispersion performed in the second step of the present invention can be performed using conventionally known dispersing machines, such as a ball mill, an attritor sand grinder, an impeller mill, a dissolver, a flow jet mixer, etc., and any of these may be used alone or in combination. A sand grinder is particularly preferred.

Regarding dispersion machines, please refer to "Introduction to Dispersion Technology" published by Nikkan Kogyo Shimbun.
is described in detail.

Furthermore, for details on the method of applying the kneaded and dispersed magnetic coating liquid onto the magnetic material as the third step, please refer to Japanese Patent Laid-Open No. 52
-108804, 54-21805, 54-4
It is described in Publication No. 6011 and the like.

To explain in more detail the method for producing magnetic paint according to the present invention, the step of dispersing before the first step includes
This kneading is carried out after kneading the ferromagnetic powder and the Il-containing solvent solution containing the binder using a twin-screw continuous kneading mixer equipped with a pair of shafts and a barrel rotatably housing these shafts. In the method for producing a magnetic paint, the kneaded product is diluted and kneaded by adding an Il-containing solvent to the kneaded product, using ferromagnetic powder that has been conditioned in humidity, and the kneading is performed at a solid content concentration of 65 to 95.
L7 is preferably carried out at a solid content concentration of 30 to 60% by weight.

The above-mentioned "solid content" refers to ferromagnetic powder, binder, non-magnetic powder, and other surface-type materials.The above-mentioned "kneading" is performed at a solid content concentration of 65 to 95% by weight, but this It is defined as the concentration necessary to obtain a kneaded magnetic paint. In other words, in the case of a mixture of ferromagnetic powder, binder, etc. in which the solid content concentration of the kneaded product is less than 65% by weight, the viscosity of the mixture is too low and sufficient shear force cannot be obtained during kneading, resulting in poor dispersion. It becomes insufficient.

On the other hand, if the solid content concentration exceeds 95% by weight, the viscosity is too high and a uniform mixed material cannot be obtained. In this case, the solid content concentration is preferably 75 to 90% by weight.

The above-mentioned "dilution crosstalk" is carried out at a solid content concentration of 30 to 60% by weight, but this is because if the solid content concentration is less than 30% by weight, the viscosity is too low and sufficient dispersion cannot be achieved. This is because when a highly viscous material with a concentration of 60% by weight is diluted and kneaded, the dispersion efficiency is poor and it is difficult to obtain a uniform dispersion. In this case, the solid content concentration is preferably 40 to 55% by weight.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a process outline diagram showing one embodiment of the magnetic paint creativity method according to the present invention.

The manufacturing process for pre-dispersion of magnetic paint involves kneading an organic solvent solution containing a binder with ferromagnetic powder. It consists of a dilution step in which the kneaded material is diluted, and a second mixing and dispersion step in which the diluted material obtained in this dilution step is subjected to a dispersion treatment, and the magnetic paint obtained in this way is applied to a support, Thereafter, a magnetic recording medium is manufactured by going through a calendering and slitting process.

A twin-screw continuous kneading mixer 2 is used in the above-mentioned kneading process and dilution process, and kneading is performed in the kneading part 2a, and dilution is performed in the dilution mixing part 2b.

That is, in this twin-screw type continuous kneading mixer 2, ferromagnetic powder and binder are introduced into the mixing chamber 6 through the input port 4, and the ferromagnetic powder and binder are combined through the addition port (not shown) provided near the input port 4. An organic solvent solution containing the agent is added into the mixing chamber 6, and these are added to the kneading section 2 of the mixing chamber 6.
Kneaded in a. Further, an organic solvent solution containing a binder and an organic solvent are added into the mixing chamber 6 for dilution from an addition port (not shown) provided at a heated position a predetermined distance from the input port 4, and as a result, The mixed material obtained by the above-mentioned kneading is diluted and kneaded (that is, diluted while kneading) in the dilution mixing section 2b of the mixing chamber 6, and then is discharged from the discharge port 8 as a diluted material. The mixing chamber 6 is formed into a horizontally long cylindrical shape, and the input port 4 and the discharge port 8 are provided near both ends of the mixing chamber 6. The path length of the mixing chamber 6 is 0.5 to 5 m, preferably 0.6 to 4 m.

As shown in the cross section of the kneading section 2a in FIG. It consists of a plurality of paddles 12, which are blade members, which are superposed and fixed on top of each other, and a barrel 14 which accommodates a shaft 10 to which these paddles 12 are fixed. Each of the paddles 12 is shaped like a rice ball and has the same size, and is fixed to each shaft 10 with a phase difference of 606. Further, a pair of mutually opposing paddles 12 provided on both shafts 10 are arranged so as to be in the same phase. Then, the barrel 14 includes each barrel 1
Each paddle 12 is formed into a cocoon shape so that a predetermined minute gap d is formed between the pair of paddles 12 facing each other. The outer shape of the rice ball is set so that The minute gaps d and d may have the same size or different sizes, but each has the following conditions: 0.5 mm≦d 1 ≦4 mm, 0. 51≦
d2 ≦ 4 mm, and the diameter D of each paddle 12 (that is, the maximum diameter of the rotation locus of the paddle 12) is 50 snow-≦ D ≦ 4. Preferably, it is set to OO-Seal.

The rotation speed of the paddle 14 is 5 to 200 rpm, preferably 20 to 1.20 rpm. Circumferential speed is 1~5 Q
cs/sec, preferably 2-30 cm/
See.

The reason why the minute distances Ha + and dt are set to 0.5- or more is to prevent the load acting on the paddle 12 and shaft 10 from becoming excessive, and to take into consideration the feasibility in terms of mechanical accuracy. The reason for setting the ferromagnetic powder to be 4 or less is to knead while applying a sufficiently high shearing force to increase the degree of filling of the ferromagnetic powder in the magnetic paint.

The cross-sectional shape of the mixing chamber 6 in the dilution kneading section 2b is the same as that of the above-mentioned kneading section 2a, but may be different as follows.
That is, the minute gap d in the kneading section 2a shown in FIG.
1 and d, the gaps dI' and d,' in the dilution crosstalk section 2b are 0.5d, ≦dl, respectively.
'≦0.8d, , 0°5az≦d, '≦0.8d.

It is preferable that it is set to .

The reason why the micro gaps dI' and d,' are set to 50% to 80% of the micro gaps d and dt, respectively, is that during dilution and kneading, a certain amount of solvent is added and the viscosity of the kneaded product is reduced. However, this is to apply a sufficiently high shearing force to the mixed material whose viscosity has decreased, and also to apply a sufficiently high shearing force to the mixed material whose viscosity has decreased. This is to prevent the occurrence of a short bath phenomenon in which small lumps pass through the gap, and the values of 50% and 80% take into account the degree of difference in the viscosity of the kneaded material in the kneading process and the viscosity of the kneaded product in the dilution process. It was set as follows.

The number of paddles 12 of each shaft 10 is
It is preferable that the number of sheets is 20 or more in both the dilution kneading section 2b and the dilution kneading section 2b. Further, the ratio of the number of paddles between the crosstalk section 2a and the dilution crosstalk section 2b is preferably 6/4 to 3/7.

Note that a shallow groove screw or the like may be used instead of the paddle 12 as the blade member.

As shown in FIG. 1, a dissolver 16 and a sand grinder 18 arranged in series are used in the mixing and dispersion process, and after the diluted material is stirred at high speed by the dissolver 16, it is finely dispersed by the sand grinder 18. It has become.

Next, the effect of this implementation S will be explained.

In Figure 1, the twin-screw type continuous kneading mixer II is used in the mixing process.
Mixing occurs in the kneading section 2a of No. 2, but the gap d between the paddles 12 facing each other in the mixing chamber 6
2 and the gap d1 between each paddle 12 and barrel 14
is set to 0.3 to 2.5 mm, so the ISl containing ferromagnetic powder, binder, carbon, and binder
The solvent solution is kneaded while being subjected to a high shearing force in the above-mentioned gap, and is kneaded smoothly without applying an excessive load to the paddle 12, shaft 10, etc. Therefore, a high viscosity mixed material can be obtained through the above-mentioned kneading step.

In the dilution process, the dilution crosstalk section 2 of the two-shaft continuous crosstalk mixer 2
Although dilution and crosstalk is performed in b, the gaps d,' between the mutually opposing paddles 12 in the mixing chamber 6, and the gaps d,' between each paddle 12 and barrel 14 are as follows:
Since the gaps d and d of the kneading section 2a are each set to 50 to 80%, the mixed material is subjected to high shear even though its viscosity is reduced due to the addition of an organic solvent, etc. The mixture is diluted while being kneaded by applying force. Further, at this time, the occurrence of a short bath phenomenon in which small lumps of the kneaded material pass through the gap is also effectively prevented. Therefore, a uniform dilution can be obtained by the above dilution step. Since the uniform diluent and addition side are supplied to the second mixing and dispersing step, the dispersion process can be performed in a short time and at a high level of dispersion. The magnetic paint obtained in this way is applied to a support, and then subjected to various treatments such as drying, orientation, calendering, and slitting, to achieve magnetic properties with high filling and dispersion of ferromagnetic powder. , a magnetic recording medium with excellent electromagnetic conversion characteristics etc. can be obtained.

(Effect of the invention) The present invention uses a two-wheeled continuous kneading mixer to
By performing pre-dispersion using ferromagnetic powder with a crystallite size of 400 Å or less and controlling the humidity to less than 8 ut%, and then adding the additive side and mixing and dispersing, it can be processed in a short time even when continuously processed. A highly dispersed state can be obtained. And due to improved dispersibility, high gloss, B r /
B m is achieved within a short time. Furthermore, functional groups, especially O
By using a vinyl chloride resin containing substituents such as H-type or amino groups, and a rubber resin, and further performing cross-mixing and dilution kneading at a predetermined solid content concentration in the first step, the pre-dispersion step. , improved dispersibility, gloss, Br/Bm
can be obtained to a high degree in a short time.

(Example) Hereinafter, embodiments of the present invention will be specifically described using Examples.

Example (11) As a binder resin solution (Yl), a solution Y1 with a hydroxyl group-containing vinyl chloride acid-resistant vinyl chloride [butyl acetate 40 parts by weight and a resin concentration of 20%] was prepared.

As a binder solution (Y2), a solution Y2 containing 30 parts by weight of r-polyurethane resin solution (30 parts by weight of butyl acetate and a resin concentration of 15%) was prepared.

As the first step, Co-7FeOx ioo parts by weight (x
, = 1.45, crystallite size 350 people, HC7000e
, moisture 0.4% by weight) Hydroxyl group-containing vinyl chloride vinyl acetate copolymer (MPR-TA) 9. 5 parts by weight Carbon blank 1 part by weight α-alumina 1 part by weight Binder resin solution (Yi) 32.5 parts by weight While continuously adding the above, a pair of paddles facing each other were provided in the barrel. A kneaded product was obtained through continuous processing in the mixing section of a two-wheeled continuous kneader machine having a mixing chamber. Next, as a pre-dispersion treatment, 26.7 parts by weight of binder resin solution (Y2), 25 parts by weight of methyl ethyl ketone, and 143 parts by weight of the above kneaded material, butyl acetate.
25.3 parts by weight While continuously adding the above materials, a pre-dispersion was obtained by carrying out dilution and kneading treatment in the dilution and kneading section of the two-wheeled continuous kneader used in the kneading process. Next, as a second step, to 220 parts by weight of the above pre-dispersion, 2.0 parts by weight of myristic acid, 0.5 parts by weight of oleic acid, 0.2 parts by weight of dimethylpolysiloxane,
．． 3μ) 1.0 parts by weight Methyl ethyl ketone 35.5 parts by weight Butyl acetate 36 parts by weight The above materials were mixed, stirred at high speed for 1 hour using a dissolver, and then finely dispersed using a sand grinder. At that time, the dispersion liquid was sequentially passed through six sand grinders to achieve fine dispersion.

At the end of high-speed stirring by the dissolver, the dispersion liquid discharged from each sand grinder from the first to the sixth sand grinder is applied onto the support, and the orientation and
It was dried to produce a magnetic recording medium.

FIG. 3 shows the surface glossiness of the magnetic recording medium thus obtained, and FIG. 4 shows the B r /B m ratio, which indicates the orientation of magnetic particles, as an example of a measuring method for evaluating the degree of dispersion.

The dispersion liquid that had been subjected to the fine dispersion treatment using the sand grinder was filtered using a filter having an average pore size of 1.0 μm to prepare a magnetic paint. Then, an orientation treatment was performed while the coating film was not yet applied, and after drying, a supercalender treatment was performed to obtain an original magnetic tape.

Table 1 shows the magnetic properties of the obtained magnetic recording medium.

Example (2) Same conditions as Example (1) except that the water content of the magnetic material used in the 11th kneading was changed from 0.4% by weight to 0.8% by weight. I went there.

Comparative Example (1) Example (1) and Example (1) except that the moisture content of the magnetic material used during kneading in the first step was changed from 0.4% to 1.2%. It was conducted under the same conditions.

Comparative Example (2) Same as Example (1) except that the water content of the magnetic material used during kneading in the first step was changed from 0.4% by weight to 1.6% by weight. I went for sex.

Table 1 According to the embodiment of the present invention, Example (1), (214 m
Therefore, the magnetic paint obtained has glossiness and B from the initial stage of dispersion.
It has a high r/Bm ratio, which is preferable.6 It also shows that the characteristics are more constant than the product discharged from the fourth land grinder, and the dispersion efficiency is better.

On the other hand, in Comparative Example (1), the kneading in the first step was not carried out for 1 minute, so a uniform pre-dispersion could not be obtained, and the gloss and B r / B m at the initial stage of dispersion were low, and the ginodo grinder Even if the dispersion is repeated, the characteristics as in Examples (1) and (2) cannot be obtained. In Comparative Example (2), the first I' culm was hardly kneaded and a high shearing force was applied to the magnetic material during the kneading process, causing the i↑-shaped granules to break, resulting in B r / Bm becomes low and satisfactory characteristics such as those of the embodiments cannot be obtained. Furthermore, when looking at the magnetic properties of the raw magnetic chive fabric, it can be seen that Hc is low.

On the other hand, in Examples (1) and (2), when looking at the magnetic properties of the original magnetic tape, compared to the comparative example, Bm, Br, Br/Br
It is preferable that n is high. This is because the water content of the magnetic material is low, so kneading is carried out at ~) minutes, and as Bm increases, the degree of dispersion also increases, and as a result, B r / B m also increases.
I think that the price has also increased.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the method for producing magnetic paint according to the present invention.
A process diagram showing the process. Figure 2 shows a cross section of the kneading and dilution kneading section of the twin-screw continuous kneader used in the first step, taken from n-n in Figure 1.
Line sectional view. 3 and 4 are graphs showing an example of the manufacturing method. 2... Two-wheel continuous kneader 2a... Kneading section 2b... Dilution kneading section 4... Raw material input port 6... Mixing chamber 8... Outlet] 0...・Shaft 12... Paddle (blade member) 14... Barrel

Claims (3)

[Claims] (1) The crystallite size is 400 Å or less, and the adsorbed moisture is 0.
Pre-dispersion of ferromagnetic powder and binder with a moisture content of less than 8 wt%, together with a solvent, is carried out using a two-shaft continuous kneading mixer equipped with a pair of shafts having blade members and a barrel that rotatably accommodates these shafts. A magnetic recording medium comprising a first step of adding additives, a second step of mixing and dispersing the additives, and a third step of applying the dispersed magnetic coating liquid onto a non-magnetic support. manufacturing method. (2) The method for manufacturing a magnetic recording medium according to claim 1, wherein the binder used in the first step is a functional group-containing vinyl chloride resin and a rubber resin. (3) The first step of pre-dispersion is a solid content concentration of 65 to 9.
The kneading step is carried out at 5% by weight, and the solid content concentration is further increased from 30 to 60% by weight.
2. The method for producing a magnetic recording medium according to claim 1, further comprising a dilution and kneading step carried out in % by weight.