JPH0768469B2 - Method for manufacturing magnetic paint - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a magnetic paint used for a magnetic recording medium such as a magnetic tape or a magnetic disk.

(Prior Art) In order to obtain a magnetic recording medium excellent in magnetic characteristics, electromagnetic conversion characteristics, etc., it is important to improve the filling degree of magnetic powder in the magnetic coating material applied to the support. And for this purpose, it is preferable to knead the organic powder solution containing the binder and the magnetic powder in the manufacturing process of the magnetic coating material in a high-concentration state while applying high shearing force. For example, as disclosed in Japanese Unexamined Patent Publication No. 62-41274, it has been devised to meet the above demands by kneading using a twin-screw continuous kneading mixer.

(Problems to be Solved by the Invention) In the manufacturing process of a magnetic coating composition, it is common to add an organic solvent to this kneaded product to dilute it after the above-mentioned kneading, but with a twin-screw continuous kneading mixer. The kneaded mixture has a high viscosity, and even if such a hard kneaded product is diluted at once with a high speed dispersion stirrer (flow jet mixer) as disclosed in the above publication. At the time of dilution, a high shearing force cannot be applied to the kneaded product, and therefore the kneaded product remains as a small lump and a uniform diluted product cannot be obtained. Even if such a diluted product is subjected to a dispersion treatment, the dispersion treatment takes a long time and the level of dispersion reached is low. Therefore, even if the magnetic coating material thus obtained is applied to a support, the magnetic properties are However, it is impossible to obtain a magnetic recording medium having excellent electromagnetic conversion characteristics.

On the other hand, if kneading and dilution are performed using the above-mentioned twin-screw type continuous kneading mixer, the kneaded product is gradually diluted while imparting a certain amount of shearing force to the kneaded product in the form of "dilution kneading" rather than performing dilution at once. It is possible to However, when diluting and kneading, an organic solvent is added, and the viscosity of the kneaded product is lower than that during kneading. Therefore, when diluting and kneading is performed using the usual biaxial continuous kneading mixer used for kneading as it is. Has the following disadvantages. Ie 2
In the axial type continuous kneading mixer, shearing force is applied to the kneaded material in the gap between the pair of blade members and between the blade members and the barrel, but the kneading is properly performed in the gap. When such a dimensional value is set, the above-mentioned gap is too wide to apply a high shearing force to the kneaded product in the diluting kneading in which the kneaded product having a reduced viscosity is handled, and the kneading at the end of the kneading is performed. Since there is a large difference in viscosity between the product and the organic solvent added to it, the kneaded product tends to be released as small lumps, and a short pass phenomenon occurs in which these small lumps pass through the above-mentioned gaps, and therefore a uniform Diluent cannot be obtained. On the contrary, if the gap is narrowed so that the dilution and kneading is properly performed, an excessive load is applied to the blade member during kneading, and smooth kneading cannot be performed.

The present invention has been made in view of the above circumstances, and is a method for producing a magnetic paint capable of obtaining a uniform diluted product by kneading and diluting and kneading using one twin-screw continuous kneading mixer. It is intended to provide a method.

(Means for Solving the Problems) In the method for producing a magnetic coating material according to the present invention, a single twin-screw type continuous kneading / mixing system including a pair of shafts having blade members and a barrel rotatably accommodating these shafts is provided. A method for producing a magnetic coating material using a machine, comprising: kneading an organic solvent solution containing a binder and a magnetic powder in a kneading section located at an upstream portion of the biaxial continuous kneading mixer, Two
In a method for producing a magnetic coating composition in which an organic solvent is added to a kneaded product kneaded in the kneading part in a diluting kneading part located in a downstream part of a shaft type continuous kneading mixer to dilute and knead the kneading product, the kneading is solid. The concentration of the mold component is 65 to 95% by weight, the dilution and kneading is performed at the concentration of the solid component of 30 to 60% by weight, and the blade members of the diluting and kneading section of the twin-screw type continuous kneading mixer and the blade members are The gap between the barrel and the barrel is smaller than the gap in the kneading section of the biaxial continuous kneading mixer.

The “solid content” refers to magnetic powder, binder, non-magnetic powder and other solid materials.

The "kneading" is performed at a solid content concentration of 65 to 95% by weight,
This is defined as the concentration required to obtain a strongly kneaded magnetic coating. That is, in a mixture of magnetic 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, so that sufficient shearing force cannot be obtained during kneading and dispersion is insufficient. Becomes on the other hand,
When the solid content concentration exceeds 95% by weight, the viscosity is too high to obtain a uniform kneaded product. In this case, it is preferable that the solid content concentration is 75 to 90% by weight.

The "diluting and kneading" is performed at a solid content concentration of 30 to 60% by weight. However, when the solid content concentration is less than 30% by weight, the viscosity is too low to sufficiently disperse the solid content. This is because when a highly viscous material having a concentration of more than 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.

If the “gap between the blade members of the dilution kneading section of the twin-screw type continuous kneading mixer and between the blade members and the barrel” is smaller than the gap of the kneading section of the two-axis type continuous kneading mixer, The size is not particularly limited, but it is not limited to 50 of the gap in the kneading part of the twin-screw type continuous kneading mixer.
-80% is preferable. (Function) As shown in the above configuration, the solid content concentration at the time of kneading and diluting kneading is set to a value within a predetermined range, respectively, and the diluting kneading is performed. Since the gaps between the blade members of the dilution kneading section of the shaft type continuous kneading mixer and between the blade members and the barrel are smaller than the gaps of the kneading section of the biaxial type continuous kneading mixer for kneading, the gap is smaller than that at the time of kneading. Even when diluting and kneading a kneaded product whose viscosity has decreased, it is possible to perform dilute kneading while applying high shearing force according to the difference in viscosity, and the kneaded product becomes a small lump and the short pass phenomenon occurs. It can be prevented that a uniform dilution is obtained.

(Effects of the Invention) As described above, according to the present invention, a uniform diluted product can be obtained by kneading and diluting kneading using one twin-screw continuous kneading mixer, and therefore, the dispersion to be performed thereafter is performed. The treatment can be carried out in a short time at a high dispersion level, and by applying the magnetic coating material thus obtained to a support, a magnetic recording medium excellent in magnetic characteristics, electromagnetic conversion characteristics, etc. can be obtained. You can

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

FIG. 1 is a process outline view showing one embodiment of a method for producing a magnetic paint according to the present invention.

The manufacturing process of the magnetic coating material is a kneading step of kneading an organic solvent solution containing a binder with magnetic powder, and an organic solvent is added to the kneaded material obtained in this kneading step to dilute the kneaded material. The magnetic coating material thus obtained is applied to a support, and thereafter, a magnetic recording medium is subjected to a calendering and slitting step. Are being manufactured.

In the kneading step and the diluting step, one twin-screw type continuous kneading mixer 2 is used, kneading is performed in the kneading section 2a, and dilution is performed in the diluting kneading section 2b.

That is, in this biaxial continuous kneading mixer 2, the magnetic powder, the binder and the carbon are charged into the mixing chamber 6 through the charging port 4, and the magnetic powder is bonded through an addition port (not shown) provided in the vicinity of the charging port 4. The organic solvent solution containing the agent is added into the mixing chamber 6, and these are mixed in the kneading section 2a of the mixing chamber 6.
Are kneaded in. Furthermore, 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 predetermined distance from the charging port 4, whereby the above The kneaded product obtained by the kneading is diluted and kneaded (that is, diluted while kneading) in the diluting and kneading section 2b of the mixing chamber 6, and then discharged as a diluted product from the discharge port 8. The mixing chamber 6 is formed in a horizontally long cylindrical shape, and has the above-mentioned charging port 4
The discharge port 8 is provided near both ends of the mixing chamber 6. The path length of the mixing chamber is 0.5-5 m, preferably
It is 0.6 to 4 m.

The mixing chamber 6 has a pair of shafts 10 extending in parallel with each other and spaced apart from each other at a predetermined interval, as shown in the cross section of the kneading section 2a in FIG. And a plurality of paddles 12, which are blade members, fixed to each other and fixed to each other, and a barrel 14 for accommodating the shaft 10 in which these paddles 12 are fixed. Each of the above-mentioned paddles 12 is formed in a rice ball shape of the same size, and
It is fixed to each shaft 10 with a phase difference of 60 °.
Further, a pair of paddles 12 provided on both shafts 10 facing each other are arranged so as to have the same phase. And
The barrel 14 is formed in an eyebrow shape so that a predetermined minute gap d ₁ is formed between the barrel 14 and the tip of each paddle 12.
Has a diaper-shaped outer shape so that a predetermined minute gap d ₂ is formed between the pair of paddles 12 facing each other. The minute gaps d ₁ and d ₂ may have the same size or different sizes, but are set to 0.5 mm ≦ d ₁ ≦ 4 mm and 0.5 mm ≦ d ₂ ≦ 4 mm, respectively. The paddle diameter D of the paddle 12 (that is, the maximum diameter of the rotation trajectory of the paddle 12) D is set to 50 mm ≦ D ≦ 400 mm.

The rotation speed of the paddle 14 is 5 to 200 rpm, preferably 20 to
It is 120 rpm. The peripheral speed is 1 to 50 cm / sec, preferably 2 to 30 cm / sec.

The reason why the minute gaps d ₁ and d ₂ are set to 0.5 mm or more is to prevent the load acting on the paddle 12 and the shaft 10 from becoming excessive and to consider the feasibility in terms of mechanical accuracy. The reason for this is that the kneading is performed while applying a sufficiently high shearing force in order to increase the filling degree of the magnetic powder in the magnetic paint.

The cross-sectional shape of the mixing chamber 6 in the dilution kneading section 2b is substantially the same as that of the kneading section 2a, but differs in the following points. That is, the minute gaps d ₁ and d ₂ in the kneading section 2a shown in FIG.
On the other hand, the gaps d ₁ ′ and d ₂ ′ in the dilution kneading section 2b are
Are set to 0.5d ₁ ≦ d ₁ ′ ≦ 0.8d ₁ and 0.5d ₂ ≦ d ₂ ′ ≦ 0.8d ₂ , respectively.

The fine gaps d ₁ ′ and d ₂ ′ are set to 50 to 80% with respect to the fine gaps d ₁ and d ₂ respectively, because the viscosity of the kneaded product when an organic solvent or the like is added during dilution kneading. However, it is because a sufficiently high shearing force is imparted to the kneaded product with a reduced viscosity, and the kneaded product liberated due to a large difference in viscosity between the kneaded product and the organic solvent, etc. This is to prevent the occurrence of a short pass phenomenon in which small lumps pass through the above-mentioned gap, and the numerical values of 50% and 80% indicate the degree of difference in the viscosity of the kneaded product in the kneading process and the viscosity of the kneaded product in the diluting process. It is set in consideration.

The number of paddles 12 of each shaft 10 is preferably 20 or more for both the kneading section 2a and the diluting kneading section 2b. Further, the paddle number ratio of the kneading section 2a and the dilution kneading section 2b is
6/4 to 3/7 is preferable.

As the blade member, a shallow groove screw or the like may be used instead of the paddle 12.

As shown in FIG. 1, in the dispersion step, a dissolver 16 and a sand grinder 18 arranged in series are used. After the diluent is rapidly stirred by the dissolver 16, the sand grinder 18 performs fine dispersion. ing.

Next, the operation of this embodiment will be described.

In FIG. 1, in the kneading step, a twin-screw type continuous kneading mixer 2 is used.
Kneading is carried out in the kneading section 2a of the above, and the gap d ₂ between the paddles 12 facing each other in the mixing chamber 6 and the gap d ₁ between each paddle 12 and the barrel 14 are set to 0.3 to 2.5 mm. Therefore, the organic solvent solution containing the magnetic powder, the binder, the carbon and the binder is kneaded by being applied with a high shearing force in the above-mentioned gap, and is smooth without applying an excessive load to the paddle 12 and the shaft 10. Will be kneaded into. Therefore, a kneaded product having a high viscosity can be obtained by the above kneading step.

In the diluting step, the diluting kneading section 2b of the twin-screw type continuous kneading mixer 2
While dilution kneading is performed in, the mixing chamber gap d ₂ between the paddles 12 mutually facing each other in the 6 'and the gap d ₁ between each paddle 12 and the barrel 14', the gap d ₂ and kneading portion 2a Since each is set to 50 to 80% with respect to d ₁ , the kneaded product is diluted while being kneaded by being given a high shearing force even though the viscosity of the kneaded product is reduced by adding an organic solvent or the like. Will be done. Further, at this time, the occurrence of a short pass phenomenon in which a small mass of the kneaded material passes through the gap is effectively prevented. Therefore, a uniform diluted product can be obtained by the above-mentioned dilution step.

Since the uniform diluent is supplied to the dispersion step, the dispersion treatment can be performed in a short time at a high dispersion achievement level. Then, the magnetic coating material thus obtained is applied to a support, and thereafter, dried, oriented, subjected to each treatment such as calendar and slit, high packing degree and dispersion degree of the magnetic material, magnetic characteristics, It is possible to obtain a magnetic storage medium having excellent electromagnetic conversion characteristics and the like.

(Examples) Hereinafter, embodiments of the present invention will be specifically described with reference to examples.

Example (1) As a binder resin solution (Y ₁ ), A solution Y ₁ having a resin concentration of 20% was prepared.

As a binder resin solution (Y ₂ ), A solution Y ₂ having a resin concentration of 15% was prepared.

As the kneading process, Co-FeOx (x = 1.48, specific surface area 35 m ² / g major axis length 0.3 μ, HC700
Oe) 100 parts by weight Hydroxyl group-containing vinyl chloride-vinyl acetate copolymer (Electrochemical Co., Ltd., vinyl chloride 1000G) 9.5 parts by weight Carbon black 1 part by weight Binder resin solution (Y ₁ ) 32.5 parts by weight While adding, the gap between the pair of paddles facing each other and the paddle and barrel is 1mm.
With a mixing chamber of 100mm, paddle diameter of 100mm, rotation speed of 30 ~ 120rp
m, the peripheral speed is 5 to 20 cm / sec, and the path length of the kneading part of the mixing chamber is 1
A kneaded material was obtained by continuously performing a kneading process in a kneading section of a twin-screw continuous kneading mixer having a size of m.

Then, as a dilution step, to the mixture 143 parts by weight, the binder resin solution (Y ₂ ) 26.7 parts by weight methyl ethyl ketone 25 parts by weight butyl acetate 25.3 parts by weight The above was continuously added and used in the kneading step. The diameter of the paddle incorporated in the twin-screw continuous kneading / mixing machine is increased by 0.2 mm so that the gap between a pair of opposing paddles is 0.8 mm and the inner diameter of the barrel is reduced by 0.1 mm between the paddle and the barrel. The diluting and kneading treatment was continuously carried out in the diluting and kneading section having a path length of 1 m of the biaxial continuous kneading and mixing machine having a gap of 0.8 mm to obtain a diluted product.

Then, as a dispersion step, myristinic acid 2.0 parts by weight oleic acid 0.5 parts by weight dimethylpolysiloxane 0.2 parts by weight α-Al ₂ O ₃ (average particle size 0.3 μ) 1.0 parts by weight methyl ethyl ketone 35.5 parts by weight with respect to 220 parts by weight of the above diluted product. Parts butyl acetate 36 parts by weight The above materials were mixed, stirred at high speed for 1 hour with a dissolver, and then finely dispersed with a sand grinder. At that time, six sand grinders were continuously connected and the dispersion liquid was sequentially flowed to perform fine dispersion.

At the end of high-speed stirring by the dissolver, and from the first to sixth sand grinders, the dispersions discharged from the respective sand grinders were applied onto the support, oriented and dried to prepare a magnetic recording medium.

The surface glossiness of the magnetic recording medium thus obtained is shown in FIG. 3, and the Br / Bm ratio showing the orientation of the magnetic particles is shown in FIG. 4 as an example of the conventional measuring method for evaluating the dispersity.
As the surface glossiness, the glossiness of the surface of the magnetic layer was measured at a light incident angle of 60 degrees. The indicated values are relative values when the specular gloss of the glass surface having a refractive index of 1.567 is 100%. The measuring instrument used at this time was a digital gloss meter (manufactured by Suga Test Instruments Co., Ltd.).

The dispersion liquid, which had been subjected to the fine dispersion treatment with the sand grinder, was passed through a filter having an average pore diameter of 1.0 μm to prepare a magnetic coating material. The obtained magnetic coating material was applied to the surface of a polyethylene terephthalate support having a thickness of 14 μm using a reverse roll so that the thickness of the magnetic layer after drying was 4.0 μm. Then, the coating film was subjected to an orientation treatment before it was dried, dried and then subjected to a super calendar treatment to obtain a magnetic tape raw fabric. The original magnetic tape thus obtained was measured with a vibration test magnetometer (Toei Kogyo Co., Ltd.) in a magnetic field (Hm) of 3KOe to obtain coercive force (Hc… unit Oersted), maximum magnetic flux density ( The values of Bm ... unit Gauss) and residual magnetic flux density (Br ... unit Gauss) were measured. The result is first
Shown in the table.

Example (2) As a diluting and kneading section of a twin-screw continuous kneading mixer for diluting,
All compositions and treatments were performed under the same conditions as in Example (1) except that a structure having a mixing chamber with a gap of 0.6 mm between a pair of paddles facing each other and between the paddles and barrel was used. It was

Comparative Example (1) As a diluting and kneading section of a twin-screw continuous kneading mixer for diluting,
All the compositions and treatments were performed under the same conditions as in Example (1) except that a structure having a mixing chamber having a gap of 1 mm, which was the same as that used in the kneading step, was used.

Example (3) The biaxial continuous kneading mixer having the structure shown in Table 2 was used in the kneading step and the diluting step, and the solid content concentration was the binder concentration (Y ₁ ), the binder solution ( It was changed as shown in Table 2 by changing the resin concentration of Y ₂ ).
Other than that, the composition and treatment were all performed under the same conditions as in Example (1). The measurement results are shown in the right column of Table 2.

The magnetic paints obtained in Examples (1) and (2) of the present invention are preferred because of high gloss and Br / Bm ratio from the initial dispersion stage. It also shows that the characteristics are more constant and the dispersion efficiency is better than that of the product discharged from the fourth sand grinder. On the other hand, Comparative Example (1)
However, since a uniform diluted product cannot be obtained during the dilution treatment, the gloss and Br / Bm at the initial stage of dispersion are low, and the characteristics as in Examples (1) and (2) can be obtained even if dispersion is repeated with a sand grinder. I can't. Also, looking at the magnetic characteristics of the original magnetic tape, the examples (1) and (2) were found to have Bm, Br, and
Br / Bm is high and preferable. It is considered that this is because a sufficiently high shearing force was applied during the dilution step, the Bm increased, and the degree of dispersion increased, which increased Br / Bm and Br. Further, as is clear from Example (3), it can be seen that the same effect can be obtained by changing the paddle diameter and the gap. Further, regarding the solid content concentration, good results are obtained when kneading is performed at 65 to 95% by weight and dilution kneading is performed at 30 to 60% by weight.

[Brief description of drawings]

FIG. 1 is a process diagram showing one embodiment of a method for producing a magnetic coating material according to the present invention, and FIG. 2 is a cross section of a kneading section of a twin-screw type continuous kneading mixer used in the kneading process. -II sectional drawing, FIGS. 3 and 4 are graphs showing an embodiment of the manufacturing method. 2 …… 2-axis continuous kneading mixer 2a …… Kneading section 2b …… Dilution kneading section 6 …… Mixing chamber 10 …… Shaft 12 …… Paddle (blade member) 14 …… Barrel

Claims (1)

[Claims] 1. A method for producing a magnetic coating material by using a single twin-screw type continuous kneading mixer having a pair of shafts having blade members and a barrel rotatably accommodating these shafts. After kneading an organic solvent solution containing a binder and magnetic powder in a kneading section located in the upstream part of the twin-screw continuous kneading mixer, diluting in the downstream part of the two-screw continuous kneading mixer. In the method for producing a magnetic coating composition in which an organic solvent is added to the kneaded product kneaded in the kneading unit in the kneading unit to dilute and knead the mixture, the kneading is performed at a solid content concentration of 65 to 95% by weight, and the dilute kneading is performed. Is performed at a solid content concentration of 30 to 60% by weight, and the gap between the blade members of the dilution kneading part of the biaxial continuous kneading mixer and between the vane member and the barrel is set to the biaxial continuous kneading mixer. Smaller than the gap in the kneading section of Method for producing a magnetic coating, characterized in that the.