JPH0472290B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium with improved surface properties and durability. In recent years, there has been a strong demand for higher density magnetic recording media, and the rapid development of home video tapes in particular has become well known to general consumers. 2-hour format → 6-hour format on VHSVTR,
1 → 2 → 3 → 4.5 time format with BetaformatVTR,
Furthermore, an ultra-compact VTR using 1/4 inch tape
The emergence of "CVC" was largely supported by efforts to increase the density of magnetic tape through subsequent improvements. However, the conventional techniques are no longer able to adequately meet the demand for higher tape densities. In other words, in order to increase the density of a tape, smoothing of the surface of the magnetic layer and presence of magnetic material in a uniformly dispersed state within the magnetic layer are important factors. Merely using techniques such as strengthening conditions or improving magnetic liquid dispersion ability will result in deterioration of the strength and durability of the tape magnetic layer. In addition, carbon black with an average primary particle of about several tens of micrometers is usually mixed into magnetic recording materials mainly for the purpose of preventing static electricity, for example, about 5 to 10% by weight based on the magnetic material. As is well known, since they are finer particles than general pigments, they are difficult to disperse and deteriorate the magnetic dispersibility of the magnetic recording medium and the surface properties of the coating film. If dispersion is strengthened by examining dispersion conditions, the durability of the magnetic layer of the magnetic recording material will deteriorate even if the surface of the coating becomes smooth. The present inventors conducted a detailed study on this point and arrived at the present invention. That is, the present invention improves both the surface properties and the durability of a magnetic recording material at the same time. (a) 1 to 20% by weight of carbon black with an average particle size of 10 mμ or less based on the magnetic material, (b) 0.1 to 3% by weight each of fatty acids and fatty acid esters based on the magnetic material, (c)
An abrasive with a Mohs hardness of 6 or higher is applied to magnetic materials from 1 to 15.
% by weight. The carbon black used in the present invention may have an average primary particle size of approximately 10 mμ or less, such as Royal Spectar manufactured by Columbian Carbon Co., Ltd.
(7mμ) Neo Spectar Mark manufactured by Columbian Carbon
(8mμ) Neo Spectar Mark manufactured by Columbian Carbon
〃 (9mμ) Neo Spectar Mark manufactured by Columbian Carbon Co., Ltd.
〃 (10mμ) Super Spectar manufactured by Columbian Carbon Co., Ltd.
(9 mμ) Superba (11 mμ) manufactured by Columbian Carbon Co., Ltd. is suitable, and by using such fine particles of carbon black, the surface properties of the magnetic recording medium are improved. The amount of carbon black used is preferably 1 to 20% by weight, more preferably 3 to 20% by weight based on the magnetic material.
The content is 15% by weight, more preferably 5 to 10% by weight. As the fatty acid in the present invention, ordinary saturated and unsaturated fatty acids can be used. Specific examples include lauric acid, palmitic acid, myristic acid, stearic acid, behenic acid, and instearic acid. Of course, these may be used in combination if necessary. The fatty acid ester is preferably one consisting of a monobasic fatty acid and a monohydric alcohol, and specific examples include ethyl stearate, butyl stearate, amyl stearate, butyl palmitate, hexyl laurate, butyl laurate, butyl myristate, etc. There is. The amount of fatty acid and fatty acid ester used is preferably 0.1 to 3 wt% each based on 100 wt% of the magnetic material.
More preferably, it is 0.3 to 2 wt%. Fatty acids and fatty acid esters must be used together in order to maintain good durability such as VTR runnability and stale life. The abrasive is effective for durability such as VTR running performance and stale life, and preferably has a Mohs hardness of 6 or higher.General abrasive particles such as Cr ₂ O ₃ , alumina, SiC, Mgo, etc. can be used, and the particle size as
It is preferably 1μ or less, particularly preferably 0.2 to 0.8μ.
The amount used is preferably 1 to 15 wt% based on the magnetic material. As the non-magnetic support, all materials that can be used for normal magnetic recording materials, such as polyethylene terephthalate, triacetylcellulose, polyethylene naphthalate, polyamide, and polyimide, can be used.
Also, it is possible to use a film provided with a back coat layer (on the diamagnetic side) consisting mainly of an Al-deposited polyester film, carbon black and/or other inorganic pigments. As for the surface properties, as shown in the examples, those having a center line average roughness Ra of 0.03μ or less are particularly suitable for the purpose of improving the surface properties of the magnetic recording medium of the present invention. In order to further improve the surface properties of the magnetic recording medium, carbon black may be pre-kneaded together with a magnetic material, a binder and an organic solvent. Similarly to carbon black, the amount of pre-kneading of the magnetic material and binder can be adjusted as necessary. Normally, pre-mixing the entire amount of magnetic material often gives better results, but it is essential to carefully consider the type and amount of the binder and set the pre-mixing conditions. If the focus is only on the surface smoothness of the magnetic layer, it is preferable to add the entire amount of carbon black and pre-knead it, but if the electrical resistance of the magnetic layer surface is required to exceed a certain value, only a portion of the carbon black is added. It is often best to pre-knead the ingredients and add the remaining amount in the subsequent process. More details will be specifically described later in Examples. As the pre-kneading method, it is preferable to use a three-roll mill, a pressure kneader, an open kneader, a Warner kneader, etc., but the method is not limited to these, and almost any method that can be used for kneading ordinary pigments can be applied. As the solvent for pre-kneading, most of the solvents commonly used in magnetic tapes, including acetic esters such as ethyl acetate and butyl acetate, ketones such as MEX, MIBK, and cyclohexanone, can be used. Magnetic materials include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , CrO ₂ , cobalt-added γ-Fe ₂ O ₃ , cobalt-added FeOx.
= 1.33~1.5), Fe-Ni, Fe-Ni
-Metal powders such as Co can be used. As a binder, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, carboxyl group-containing salt-vinyl acetate copolymer, vinyl alcohol-containing salt-vinyl acetate copolymer, polyvinylidene chloride, vinylidene chloride-acrylonitrile copolymer, nitrocellulose Other various cellulose derivatives, acrylonitrile-butadiene rubber, styrene-butadiene rubber, polyester, epoxy resin, polyisocyanate,
Any material that can be used for ordinary magnetic recording materials, such as polyamide, can be used. In addition to fatty acids and fatty acid esters, paraffin, liquid paraffin, silicone oil,
Solid lubricants such as fatty acid-modified silicone, ketone wax, graphite, and MoS ₂ can be used together. If necessary, plasticizers such as DBP (dibutyl phthalate) and TPP (triphenyl phosphate), and dispersants such as lecithin and tenro may be mixed into the magnetic layer. The magnetic recording body of the present invention obtained in this manner has the following advantages. The surface smoothness of the magnetic layer is excellent, resulting in less modulation noise. The tape has excellent durability when repeatedly run on a VTR. Long stale life. Examples of the present invention will be specifically described below. Example 1 Co-added γ-Fe ₂ O ₃ (magnetic material, size 0.4μ×0.04μ)
100% by weight Cr ₂ O ₃ (manufactured by Nippon Kagaku Kogyo, size approximately 0.5μ, Mohs hardness 8-9) 4 Cellulose propionate 13 Nipol 1432J (synthetic rubber manufactured by Nippon Zeon) 2 Coronate L (manufactured by Takeda Pharmaceutical, polyisocyanate)
6 Amyl stearate 1 Stearic acid 1 Butyl acetate/MEK = 1/1 mixed solvent Appropriate amount Neo Spectra Mark (Columbia Carbon carbon black, 9 mμ) 10 After rough dispersion of these compositions except Coronate L using a stirrer The fine dispersion treatment was sufficiently carried out using a sand grinder, and the treatment was stopped immediately before overdispersion occurred. The hardening agent Coronate L was added to the solution using a stirrer and stirred, and the resulting magnetic liquid was adjusted to a viscosity of 60 poise using a mixed solvent, and then filtered through a filter. After that, the above magnetic liquid was applied to a 15μ thick polyethylene terephthalate film (Ra0.033μ) using the reverse method, and the magnetic material was oriented in the coating direction (lengthwise direction) using a solenoid, and then a super calender was used. The surface of the magnetic layer was smoothed at a temperature of 80° C., a linear nip pressure between the rolls of 280 kg/cm, and a speed of 60 m/min. This was cut into 1/2 inch width pieces to obtain a VHS videotape (sample No. 1). Comparative example 1 Co-added iron oxide (magnetic material, size 0.4μ×0.04μ)
100% by weight Cellulose propionate 13 Nipol1432J 2 Coronate L 6 Liquid paraffin 2 Butyl acetate/MEK = 1/1 mixed solvent Appropriate amount Asahi #60 (Asahi Carbon carbon black, size
51 mμ) 10 These compositions were coarsely and finely dispersed in the same manner as in Example 1, the obtained magnetic liquid was made to have a viscosity of 60 poise, and the steps after coating were carried out in the same manner as in Example 1. Sample No. I got .2. Example 2 Samples Nos. 3 to 5 were obtained by changing the type of carbon black to the following in Example 1.

[Table] Example 3 Samples No. 6 to No. 1 in which the amount of carbon black was changed as follows in Example 1, and the others were as in Example 1.
obtained in the same way.

[Table] Comparative Example 2 In Example 1, the type of carbon black was changed to the following, and comparative samples No. 12 to 14 were obtained.

[Table] Comparative Example 3 Comparative samples Nos. 15 to 17 were obtained in the same manner as in Example 1 except that the lubricant "stearic acid and amyl stearate" was replaced with the following.

[Table] Example 4 Samples Nos. 18 to 21 were obtained by replacing stearic acid and amyl stearate with the following in Example 1.

[Table] Example 5 Samples Nos. 22 to 26 were obtained in the same manner as in Example 1 except that the following abrasives were used instead of Cr ₂ O ₃ .

【table】

[Table] Example 6 The following samples were prepared in the same manner as in Example 1, except that a non-magnetic support with a different surface property was used.
Obtained Nos. 27-30.

[Table] Example 7 In Example 1, carbon black was kneaded (ie, pre-kneaded) with the magnetic material, cellulose propionate, and mixed solvent in an open kneader. Cellulose propionate was used as a 20% by weight solution in a mixed solvent. Further, the pre-kneading mixed solvent was gradually added while visually observing the kneading state, and when the load current reached almost the maximum (after 30 minutes in this example), the addition was stopped and the process was continued for another 30 minutes. After pre-kneading, the kneaded product,
Cr ₂ O ₃ , Nipol1432J, stearic acid, and amyl stearate were roughly dispersed together with a mixed solvent using a stirrer. Other steps were carried out in the same manner as in Example 1, and Sample No. 31 was obtained. Example 8 In Example 1, half of the carbon black (2.5% by weight) was kneaded (ie, pre-kneaded) with the magnetic material, cellulose propionate, and mixed solvent in an open kneader. After that, the kneaded product, Cr ₂ O ₃ , Nipol1432J,
Sample No. 32 was obtained in the same manner as in Example 7 except that the residual amount of carbon black (in powder form), stearic acid, and amyl stearate were roughly dispersed together with a mixed solvent. Example 9 In Example 1, carbon black was subjected to an open kneader treatment together with a magnetic material, cellulose propionate (8% by weight), and a mixed solvent. The remaining amount of cellulose propionate (5% by weight) was 20% in the rough dispersion process.
It was added as a wt% solution. Others are Example 7,
Sample No. 33 was obtained in the same manner as in 8. Table 1 shows the evaluation results for samples No. 1 to 33.

【table】

[Table] Sample No. 1 is according to the present invention. Comparing it with Sample No. 2 of the conventional technology, which has a large carbon black size, the tape magnetic layer surface properties (Ra), modulation noise, and VTR 100 pass running properties are It can be seen that sample No. 1 according to the present invention is superior to any characteristic of STILL LIFE. Samples Nos. 3 to 5 are also based on the present invention and have different sizes of carbon particles, but
Ra, modulation noise with fine particles (sample No. 3)
shows a better tendency, and is overall similar to sample No. 1 and outperforms comparative sample No. 2 by a large margin. Samples No. 6 to No. 11 were obtained by changing the amount of carbon black added in Example 1. sample
If the additive amount is as low as 0.5% by weight like No. 6, VTR
The runnability and stale life are insufficient, and if the amount added is as high as 30% by weight as in sample No. 11, it is unfavorable in terms of stale life and modulation noise, and the amount added is preferably in the range of 1 to 20% by weight. Further, Nos. 12 to 14 are samples obtained by changing the carbon black to a conventional size in Example 1 according to the present invention, but both Ra and modulation noise are significantly inferior to those of the present invention. No. 15 is the sample No. 1 with amyl stearate removed, No. 16 is the sample with stearic acid removed,
No. 17 excludes both. No. 15 has insufficient VTR running performance and stale life. No. 16 had a slightly better stale life than No. 15, but was worse in terms of VTR running properties, indicating that both fatty acids and fatty acid esters are essential to the present invention. No. 17 has an extremely short life in both VTR running performance and stale life, which poses a major problem in practical use. Nos. 18 to 21 are Examples according to the present invention, in which the types and amounts of fatty acids and fatty acid esters were changed, but they showed almost the same good results as Sample No. 1. Samples Nos. 22 to 26 are samples in which other abrasives were used in place of Cr ₂ O ₃ in sample No. 1. No. 26, which does not use abrasives, and No. 25, which uses abrasives with a Mohs hardness of 5.5, have poor VTR running performance and stale life, as well as poor modulation noise. This is No.
Both Nos. 26 and 25 had the same Ra as the other Nos. 22 to 24 and 1, and there were scratches and scrapes on the magnetic layer, indicating that the video head was contaminated due to scratches on the tape magnetic layer. It was assumed that
When the head surface was observed under a microscope after the VTR running test, a small amount of brown dirt was observed. It has been shown that abrasives having a Mohs hardness of 6 or more have shown preferable results. Nos. 27 to 30 are samples obtained in the same manner as No. 1 except that the nonmagnetic support was replaced with one of various smoothness. The surface properties of the magnetic layer show a good correspondence with the surface properties of the support, and when smooth supports are used (as you go from No. 27 to No. 30, the smoothness increases), the magnetic layer Ra also becomes smaller. , modulation noise is correspondingly reduced. No. 27 to 30 using a support with Ra of 0.03μ or less
The RA of the non-magnetic support is
A value of 0.030μ or less is more preferable in order to achieve the object of the present invention. Nos. 31 to 33 are carbon blacks subjected to pre-kneading treatment. Sample No. 1 in any case
shows even better Ra, modulation noise than
It can be seen that the pre-kneading treatment is effective in further improving the surface properties, which is the objective of the present invention. Looking at the pre-kneading conditions and results in detail, No. 31, in which the entire amount of carbon black was pre-kneaded, was better than No. 32, in which half of the carbon black was pre-kneaded, but like No. 33, the surface smoothness effect was better. It can be seen that more favorable results can be obtained if the amount of binder (cellulose propionate) during pre-kneading is set more appropriately. In this way, establishing the pre-kneading conditions is extremely important in order to obtain better results. An outline of the above evaluation method is as follows. a Center line average roughness of tape magnetic layer and support surface
Ra: The average roughness of the center line with a cutoff of 0.08 mm was determined using Model SE-3AK manufactured by Kosaka Laboratory. b Modulation noise; 5MHz sine wave signal relative speed
5.8m/sec VHSVTR (HR-
Analyze the output when recording and playing back with the 3600) using a spectrum analyzer, and compare the N (noise) in Figure 1 (with sample No. 2 as the standard).
Expressed in dB. c VTR running performance: VHS system manufactured by Victor Japan
Place the VTR (HR-3600) in a thermo room set at 40℃ and 60% RH, run the tape continuously, and check the number of passes in which running abnormality (tape stickiness) occurs. d Stale life: Set the HR-3600 to the stale state and find the time until the image disappears. The environmental conditions were 5°C, which is harsher than room temperature. FIG. 2 shows modulation noise in a comparative example according to the prior art and several examples according to the present invention. Implementation sample No. 1 according to the present invention is preferable because it has less noise than comparative sample (No. 2) according to the prior art. Sample No. 30 using a smooth support
is even more preferable. Sample No. 26, which did not contain abrasive in Example 1, also had a lot of noise.

[Brief explanation of the drawing]

FIG. 1 is a graph showing a method for evaluating modulation noise of a magnetic recording medium in the present invention, and FIG. 2 is a graph showing modulation noise in the present invention and a comparative example.

Claims (1)

[Scope of Claims] 1. A magnetic recording material comprising a magnetic layer made of a magnetic material and a binder coated on a non-magnetic support, wherein the magnetic layer comprises (a) carbon black having an average particle size of approximately 10 mμ or less; 1 to 20% by weight of the magnetic material, (b) 0.1 to 3% of each of fatty acids and fatty acid esters to the magnetic material, and (c) 1 to 3% of the abrasive with a Mohs hardness of 6 or more to the magnetic material.
~15% by weight, a magnetic recording body characterized by containing. 2. The magnetic recording body according to claim 1, wherein the non-magnetic support has a centerline average roughness Ra of 0.03μ or less. 3. The magnetic recording material according to claim 1, which contains part or all of carbon black by pre-mixing.