JPH02141925A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a back coating layer which is small in coefft. of dynamic friction and does not generate medium damages after repetitive traveling by separately kneading two kinds of carbon blacks which are different in grain size and inorg. particles, then mixing the same to prepare a coating compd. for the back coating layer. CONSTITUTION:Two kinds of the carbon blacks having 20 to 40mum and 50 to 100mum average primary grain sizes are respectively mixed with the binder to prepare kneaded materials 1 and 2. The inorg. powder is kneaded with the binder, separately therefrom, to prepare a kneaded material 3. These kneaded materials 1, 2 and 3 are mixed and dispersed to prepare the coating compd. for the back coating BC layer. This coating compd. is applied on the back layer of the base. The BC layer which is uniformly dispersed without generating the flocculated particles, etc., is obtd. in this way. In addition, the coefft. of dynamic friction is lowered and the generation of the tape damages, etc., after the repetitive traveling is obviated by the uniform dispersion of the carbon black and the inorg. powder.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method of manufacturing a magnetic recording medium such as a magnetic tape.

BACKGROUND OF THE INVENTION Generally, magnetic recording media are manufactured by coating a support with a magnetic paint containing magnetic powder, a binder resin, and the like, and drying the coating. In the magnetic recording medium produced in this way, in order to improve the running properties and stability of the winding form (in the case of tape) of the medium, a baraf coat is placed on the back surface of the support opposite to the magnetic layer. f (hereinafter sometimes referred to as BC layer) may be provided. For example, regarding the provision of a BC layer, there are
There are descriptions in various publications such as No.-2415.

When carbon black is added to the BC layer, inorganic powder (
For example, compared to those to which Zn0) is added, it has an antistatic effect, a light shielding effect, and a roughening effect due to carbon black particles. However, carbon black has poor dispersibility in paints partly because of its small particle size, and tends to form aggregated particles in the BC layer. These aggregated particles cause unevenness in the magnetic layer when the tape is wound, and since the bonding force with the binder is not strong, they tend to peel off and cause dropouts.

Furthermore, in order to improve running properties, the use of inorganic particles and carbon black in combination is described in JP-A-59-210534, JP-A No. 6G-25022, JP-A No. 60-25023, etc. There is. However, since inorganic particles and carbon black are kneaded together with a binder and dispersed, the inorganic particles and carbon black inherently have different dispersibility, and the dispersibility of carbon black is poor as described above. Therefore, the dispersibility has not been improved at all.

In order to improve this dispersibility, the dispersion process is divided into two steps, and inorganic particles and carbon black are dispersed in separate steps, as disclosed in JP-A-52-40304 (after dispersion of carbon black, inorganic particles are dispersed in the same system). ),
It is disclosed in Japanese Patent No. 59-201220 (dispersing carbon black in the same system after dispersing inorganic particles). However, since both are dispersed in the same system, that is, the first additive is kneaded with the binder and then the next additive is added to this kneaded mixture, the dispersibility of one of them is inevitable. The object of the present invention is to obtain a back coat layer which has a small coefficient of dynamic friction and does not cause damage to the medium after repeated running, has excellent uniform dispersibility, and has a surface area of the back coat layer. It is an object of the present invention to provide a method for producing a medium that can reduce the roughness, does not transfer the roughness of the back coat layer to the magnetic layer, and has good chroma S/N characteristics.

21 Structure of the invention and its effects, that is, the present invention comprises a first kneaded product obtained by kneading carbon black with an average primary particle size of 20 to 40 mμ with a binder;
A back coat layer is formed by mixing a second kneaded product made by kneading carbon black with an average primary particle size of 50 to 100 mμ with a binder, and a third kneaded product made by kneading an inorganic powder with a binder. The present invention relates to a method for producing a magnetic recording medium in which a coating material for a back coat layer is prepared and the coating material for a back coat layer is applied to the back surface of a support.

According to the present invention, in order to separately knead carbon black and inorganic powder (inorganic particles), which inherently have different dispersibility, the carbon black and inorganic powder are dispersed under the most suitable conditions during each kneading process. However, since two types of carbon black with different average primary particle sizes are mixed separately with a binder, the dispersion of each is also improved. This can be done under the most suitable conditions. Therefore, the paint for the BC layer can be prepared by kneading each additive in a well-dispersed state.
C layer can be obtained, dropout can be reduced, and B
The surface roughness of the C layer is made appropriately fine, and the roughness of the BC layer is not transferred to the magnetic layer. Moreover, the uniform dispersion of carbon black and inorganic powder makes it possible to lower the coefficient of dynamic friction, lower the tape's tensile strength, and improve runnability (particularly to prevent damage to the tape after repeated runs).

In the present invention, while the above-mentioned carbon black provides the surface properties of the BC layer, the latter can impart appropriate roughness or unevenness to the surface to achieve running stability of the medium. In this case, the former carbon black (hereinafter referred to as carbon black A) having a small particle size generally tends to cause agglomeration and tends to be insufficiently dispersed, but this can be overcome by the method of the present invention. However, if the average primary particle size of the former carbon black is less than 20 mμ, it will be too fine and difficult to disperse, and if it exceeds 40 mμ, it will be too large and the effect of adding the same carbon black will be insufficient and the surface will become rough. The primary particle size should be between 20 and 40 mμ. It is further preferable that this particle size range is 20 to 30 mμ. In addition, if the average primary particle size of the latter carbon black, which has a large particle size (this is referred to as carbon black), is less than 50 mμ, the effect of its addition will be insufficient;
Moreover, if it exceeds 100 mμ, it is too large and transfer (transfer of irregularities to the magnetic layer when wound or stacked) is more likely to occur, so the average primary particle size should be 50 to 100 mμ. This particle size range is preferably 70 to 100 mμ.

Note that the above-mentioned "average primary particle size" is a value obtained by measuring the particle size one by one using an electron microscope immediately after the particles are produced, and dividing the sum of these measured values by the number of particles measured.

The method according to the invention is carried out, for example, as shown in FIG. That is, carbon black A and carbon black were kneaded with a binder (binder) to prepare kneaded products 1 and 2, and separately, an inorganic powder was kneaded with a binder (binder) to produce kneaded product 3. do. These kneaded products may be prepared at the same time or at different times. Then, these kneaded products 1, 2, and 3 are mixed and dispersed to prepare a paint for the back coat layer, and this is applied to the back surface of the support.

Alternatively, as shown in FIG. 2, a kneaded product 1.2 is prepared by kneading carbon black A and carbon black with a binder (binder), and separately, inorganic powder is kneaded with a binder (binder). A kneaded product 3 is prepared by kneading. These kneaded products may be prepared at the same time or at different times. These kneaded products are then dispersed, and the respective dispersions are then mixed with each other to prepare a paint for the back coat layer, which is applied to the back surface of the support.

In the above, various kneaders (continuous kneader, open kneader, pressure kneader, etc.) and roll mills (two-roll mill, three-roll mill, etc.) can be used as the kneading means. In addition, as a dispersion means, a ball mill,
A sand mill etc. can be used. Then, the dispersed paint can be supplied to a coating means (gravure roll coater, reverse roll coater, extrusion coater, etc.) after passing through an in-line mixer or the like.

In the composition of the above-mentioned back coat layer paint, the inorganic powders include titanium oxide, calcium oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Fe,
O, talc, kaolin, calcium sulfate, barium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably zinc oxide, calcium carbonate, barium sulfate. Zinc oxide has particularly good dispersibility, but its average particle size is 0.5 to 1.0 μm.
It is preferable that These non-magnetic inorganic powders are BC
If it is included in the layer coating material, the surface of the BC layer can be appropriately roughened (matted) to improve the surface properties and the running properties of the medium, and it is also possible to obtain a sufficient hardness of BCH. In addition to the above-mentioned effects, the carbon black contained in the BC layer imparts conductivity to the BC layer, thereby providing an antistatic effect. Therefore, the combined use of carbon black and non-magnetic inorganic powder is advantageous since it is possible to obtain both the effects of improving surface properties (stabilizing running properties) and improving conductivity.

However, the surface roughness of the BC layer is such that the average roughness or height (Ra) of the center line of the surface irregularities is 0.005 to 0.1 μm, preferably 0.030 μm or less, and the maximum roughness (Rma
x) is preferably 0.05 to 0.40 ura. Regarding Ra, in order to improve the chroma S/N,
It can be seen that it is desirable to set the value to ≦0.030 u ts.

If the Ra or RmaxO value is too small, running stability and tape winding appearance will be insufficient, and if it is too large, B
Transfer from the C layer to the magnetic layer (at the same time as tape winding) occurs, making the surface even rougher. In addition, a lubricant may be added to the paint for the BC layer, and examples of such lubricants include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 2 carbon atoms (for example, stearin A fatty acid ester consisting of a monohydric alcohol having 13 to 26 carbon atoms and the like can also be used.

The thickness of the BC layer after coating and drying is 0.1 to 3.0 microns, preferably 1.5 microns or less.

In addition, examples of the binder resin used in the paint for the BC layer include urethane resin, vinyl chloride-vinyl acetate copolymer,
Vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral,
Cellulose derivatives (cellulose acetate butyrate,
cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.),
Styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin,
Examples include acrylic reactive resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

The above resins are 505M and C00M.

-PO(OM'')z (where M and M' are hydrogen, alkali metals such as lithium, potassium, and sodium, or substituted or unsubstituted hydrocarbon residues) and a resin containing a hydrophilic polar group. It is better to do so.

In particular, it is preferable to use a urethane resin, and also to use a vinyl chloride copolymer, an epoxy resin (especially a phenoxy resin), a polyester resin, or a nitrocellulose resin (hereinafter referred to as other resins). It is better.

In this case, the blending ratio of the urethane resin and the other resin is 90 to 10 parts by weight, more preferably 80 to 10 parts by weight.
Preferably, the amount is 20 parts by weight. If the above-mentioned blending ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film is significantly deteriorated, and the adhesion to the support also deteriorates. Further, if the above-mentioned blending ratio is less than 10 parts by weight, the magnetic powder tends to fall off.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate curing agent to the magnetic paint containing the binder resin.

In the above composition, the amount of carbon black A in the kneaded material 1 is preferably 20 to 70 parts by weight, and 30 to 60 parts by weight.
Parts by weight are even better. In the kneaded product 2, the amount of carbon black is preferably 60 to 10 parts by weight, more preferably 50 to 20 parts by weight. The amount of inorganic powder in kneaded material 3 is 5
-30 parts by weight is good, and 10-20 parts by weight is even better. B
Their content ratio in the C layer is carbon black A: force-
Bomb black B: inorganic powder = 5:4:2 (weight ratio) is preferable.

A magnetic recording medium manufactured by the method according to the present invention has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, as shown in FIG.
This is a configuration in which the above-mentioned BCC 50 is provided on the opposite side. Further, as shown in FIG. 4, an overcoat layer (QC layer) is formed on the magnetic layer 2 of the magnetic recording medium of FIG.
4 may be provided.

Further, the magnetic recording media shown in FIGS. 3 and 4 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may be provided with no undercoat layer. (the same applies hereinafter), or the support may be subjected to corona discharge treatment.

As the magnetic powder, especially the ferromagnetic powder, used for the magnetic layer 2 shown in FIGS. 3 and 4, for example, γ-Fez 03
, Go-containing IF ez Os , C'-deposited 7-Fe
,O,,Fe50. , Co-containing Fe, O,, Co-deposited F
There are inspection material magnetic powders such as e, 04, CrO□. Also,
Metal magnetic powder may also be used in combination, and usable metal magnetic powders include Fe, Ni, Co, Fe-Af series, Fe
-Aj! -Ni series, Fe-Al! -Co-based, Fe-Af
-Zn series, Fe-Nf-Co series, Fe-Mn-Zn series,
Fe-Ni system, Fe-Ni-Al! , system, Fe-Ni-
Zn-based, Fe-Co-Ni-Cr-based, Fe-Co-N1
-P-based, Co--Ni-based, and ferromagnetic powders such as metal magnetic powders containing Fe, Ni, Go, etc. as main components.

Among them, Fe-based metal magnetic powders containing 80atn+% or more have excellent electrical properties, and are particularly good in terms of corrosion resistance and dispersibility, such as Fe-Al, Fe-A1-Ni, Fe-Aj! -Zn,
Fe-A1. -CoSFe-NiSFe-Ni-Al,
Fe-Ni-Zn type metal magnetic powders are preferred; additives for these metal magnetic materials include Si, Cu, Z
Elements such as n, Al, P, Mn, Cr, etc. or compounds thereof may be included, and hexagonal ferrite such as papalium ferrite and iron nitride are also used.

In addition to the magnetic powder described above and the same binder resin as the BC layer, the magnetic layer 2 may contain fatty acids and/or fatty acid esters such as myristic acid and butyl stearate as lubricants.

Thereby, while exhibiting the respective features of both, it is possible to offset the defects that occur when used alone, improve the lubrication effect, and improve still image durability, running stability, S/N ratio, etc. In addition to fatty acids and fatty acid esters, other lubricants (for example, silicone oil, carboxylic acid modification, ester modification, etc.) may be added to the magnetic layer. In addition to the above-mentioned lubricants, the magnetic layer may also contain known dispersants (for example, powdered lecithin), abrasives (for example, fused alumina), antistatic agents (for example, carbon black), and the like.

Solvents that can be used in the paints for the BC layer and magnetic layer include ketones (e.g. methyl ethyl ketone), ethers (e.g. diethyl ether), esters (e.g. ethyl acetate), aromatic solvents (e.g. methanol). ), and these can be used alone or in combination.

E, Example More specific examples will be described below.

The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" represent parts by weight.

l　bi　　6　1■ A magnetic paint having the following composition was prepared.

Go-containing 7 FezOz Too much polyurethane 8 parts (Nistan 5701 manufactured by Gutdrich) Vinyl chloride-vinyl acetate copolymer 12 parts (U, C, C, manufactured by VAGH) Powdered lecithin 2 parts Alumina 7 parts Myristic acid
0.5 part butyl stearate
0.5 part methyl ethyl ketone
72 parts toluene 5
0 parts cyclohexanone 40 parts Carbon black 2 parts (Conductex 975) This composition was sufficiently stirred and mixed in a ball mill, and then polyfunctional isocyanate (Coronet, manufactured by Nippon Polyurethane Co., Ltd.) L was added.
) was added thereto, and then filtered through a filter with an average pore size of 1 μm. The obtained magnetic paint was applied to the surface of a polyethylene terephthalate base having a thickness of 12 μm to a dry thickness of 5 μm.

On the other hand, kneaded products 1, 2, 3, and 4, which were to be used as back coat paints and had the following compositions, were prepared using Ni-Goo.

(Margin below) Table Next, as shown in Table 2 below, kneaded products 1, 2, and 3, which were kneaded separately, were mixed and dispersed in a ball mill for 10 hours (Example 1). The kneaded product 4 was directly dispersed in a ball mill for 10 hours (Comparative Example 1).

(Hereinafter, blank spaces) Table Each dispersion was used as a paint for the BC layer, and was applied to the surface opposite the magnetic layer to a dry thickness of 0.4 .mu.m.

Comparison 1 In Comparative Example 1, the following composition was directly dispersed in a ball mill for 20 hours as a paint for the BC layer.

(Left below) This dispersion was used as a paint for the BC layer, and was applied to the surface opposite to the magnetic layer to a dry thickness of 0.4 μm.

Comparison ■ Knee 1 In Comparative Example 1, when inorganic particles of the same diameter were added after first adding carbon black A and then kneading (Comparative Example 3), conversely, after first adding inorganic particles and kneading, A case (Comparative Example 4) in which carbon black A and carbon black were added to the same diameter was carried out and applied as a paint for the BC layer in the same manner as above. A wide magnetic film having a magnetic layer and a BC layer of a predetermined thickness was obtained as described above, and this was wound up. This film was cut to a width of η inches to obtain each videotape.

The following measurements were performed on each of these tapes.

RF output fluctuation: RF ratio output fluctuation range after 200 playbacks.

(Unit: dB) Chroma S/N: RF at 4MH2 using a VTR deck for RF output measurement
The specific output was measured and the value after 200 reproductions is shown.

(Unit: dB) Back coat scraped, tape damage: Judgment was made visually after running 200 times.

Coefficient of dynamic friction: Measure the tape tension at the inlet and outlet of the head cylinder. Coefficient of glabellar friction: At 23°C and 160% RH, using the same device as used for measuring the coefficient of dynamic friction, the input rotor tension is set to 20 g, and the diameter is 62
Wrap the sample tape around a nm stainless steel drum with the magnetic layer facing up, and wrap the sample tape 180° on top of it, with the BC side facing 0.
．． It was run at a speed of 2 cm/sec, and the rotensidin released from behind was measured and calculated from the above formula.

The results of measuring the performance of the tape obtained as described above are shown in Table 4 below.

(See margin below, continued on next page) These results show that the tape performance is significantly improved by manufacturing the magnetic tape based on the present invention.

That is, by separately kneading carbon black and inorganic particles and then mixing them to form a paint for BCJ'i, each additive (filler) can be optimally dispersed. On the other hand, if each additive is added at the same time, or if they are added one after the other with the same diameter, the dispersion conditions for one of them will deteriorate, which will adversely affect the tape performance.

2 Carbon black A used in Example 1
When the daily average primary particle size was varied as shown in Table 5 below, the average primary particle size of carbon black A was 20~20.
40 mμ, the average primary particle size of carbon black B is 50 ~
It turns out that it should be 100 mμ.

(Margin below)

[Brief explanation of the drawing]

The drawings illustrate the present invention, and FIGS. 1 and 2 are schematic flowcharts showing the main steps of a method for manufacturing a magnetic recording medium, and FIGS. 3 and 4 each illustrate an example of a magnetic recording medium. In each cross-sectional view, the symbols shown in the drawings are: 1...Nonmagnetic support 2...Magnetic layer 3...Barfcoat )1 (BC layer)4・
...... Overcoat layer (OC layer). Agent Patent Attorney Hiroshi Osaka

Claims (1)

[Claims] 1. A first kneaded product made by kneading carbon black with an average primary particle size of 20 to 40 mμ with a binder, and a second kneaded product made by kneading carbon black with an average primary particle size of 50 to 100 mμ with a binder. A magnetic recording method in which a back coat layer paint is prepared by mixing the kneaded product and a third kneaded product made by kneading an inorganic powder with a binder, and this back coat layer paint is applied to the back surface of a support. Method of manufacturing media.