JPS60125922A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has high S/N and is free from scintillation and chipping of a back coat layer by providing the back coat layer consisting of pigments having specific particle sizes and hardnesses on the rear surface of a base. CONSTITUTION:A magnetic layer which is formed by dispersing ferromagnetic metallic or alloy powder into a resin binder or a magnetic layer which is a thin ferromagnetic metal or alloy film layer and has >=1,000 Oe coercive force and <=0.08mum surface roughness is provided on the front surface of a plastic film base body. A back coat layer formed by dispersing particles consisting of two kinds of inorg. pigments having 2-4 and 5-7 Mohs' hardnesses and 0.04- 0.5mum average particle sizes in a thermosetting resin binder is provided on the rear surface of the base body. The intended magnetic recording medium is obtd. by such constitution. CaCO3, ZnO, MgCO3, etc. are adequate as the inorg. pigment having 2-4 MOhs' hardness and TiO2, alpha-Fe2O3, MgO, SiO2, SnO2, ZrO2, etc. are suitable as the inorg. pigment having 5-7 Mohs' hardness.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and particularly to a high-density magnetic recording medium having excellent physical properties and electromagnetic conversion characteristics.

Background of the Invention Examples of ferromagnetic powders conventionally used as magnetic recording media include γ-Fe 203 and Co-containing γ-Fe.
2es, , Fe5Oa, CO-containing Fe s○4, C
There was rO2 etc. However, the magnetic properties of these ferromagnetic powders, such as coercive force and maximum residual magnetic flux density, are insufficient for high-sensitivity, high-density recording. is not very suitable.

As the requirements for magnetic recording media become stricter, ferromagnetic powders with characteristics suitable for high-density recording have been developed or proposed.

Such magnetic powders include Fe, Co, Fe-Co
,F'e-C.

Examples include metals or alloys such as -Nl, Co-Ni, and alloys of these with AI, Cr, 3i, etc. A magnetic recording layer using such an alloy powder must have a high coercive force and a high residual magnetic flux density for the purpose of high-density recording, and in order for the magnetic powder to meet these standards, various manufacturing methods or Alloy composition must be selected.

The present inventor manufactured magnetic recording media using various alloy powders, and the specific surface area measured by the BET method was 4 am/g.
The coercive force of the magnetic layer is t o o o Oe or more, and the surface roughness of magnetic non-magnetic (20 point average value in the pre-step method manufactured by TAYLOR-HOBSON Co., Ltd., cutoff 0.17 m, needle force 21%l) , needle Q, and lx25μ were used (the same applies hereafter). , 08 μm or less, it has been found that a magnetic recording medium with a sufficiently low noise level and suitable for high-density short-wavelength recording can be obtained.

On the other hand, magnetic recording media in which a ferromagnetic metal thin film is adhered to a plastic base are also used for the purpose of similar high-density recording.

Electroplating, chemical plating, vacuum deposition, sputtering,
When a method such as ion blating is used, the ferromagnetic metal thin film formed is 100% metal or alloy, so it can have a high recording density. However, when a ferromagnetic metal thin film is formed by the above method, the surface roughness can be reduced to about α01 μm, but on the other hand, the surface condition of the support strongly influences the surface condition of the ferromagnetic thin film and affects the electromagnetic conversion characteristics.

Moreover, in all of these magnetic recording media, the thickness of the plastic film base made of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, etc. as a support tends to become thinner and thinner, and at present, the thickness of the plastic film base of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, etc. is becoming thinner and thinner. It is being considered.

If the base becomes thin, the media becomes too soft and friction increases, causing it to stop running. Therefore, it became necessary to strengthen the pace and improve running performance. Conventionally, a dog coat is sometimes applied to the magnetic surface as a means of improving running performance, but in this case, problems arise because the lubricant on the top coat surface is not permanent, or it may stick when stored at high temperatures. Become. In addition, since the surface roughness of the magnetic surface has become better, when a top coat is applied, sticking occurs due to the tightness of the winding, which is undesirable.

Conventionally, it has been widely practiced to apply a back coat layer instead of a top coat to prevent poor running, irregular winding, insufficient strength, etc.

Disadvantages of the Prior Art However, the performance of conventional magnetic tapes provided with back coat layers is not necessarily satisfactory, and the following problems have been pointed out.

(a) Decrease in S/H due to application of back coat (mouth')! :l) Occurrence of cinching phenomenon due to air being involved (c) Scraping of the back coat layer (d) Damage to the tape during loading or unloading operation with long-term magnetic tape (e) Defective tape winding Object of the present invention The present invention solves the above-mentioned conventional technical problems, and
/N is high, and it prevents shinching phenomenon, abrasion of the back coat layer, tape damage during loading or unloading operations, etc., and also does not cause the tape to fly out or become disordered during high-speed winding. The purpose is to provide a medium.

Summary of the Invention In order to achieve the above object, the present invention provides a magnetic layer or a ferromagnetic metal or alloy thin film layer in which the above-mentioned ferromagnetic metal or alloy powder is dispersed in a resin binder on the surface of a plastic film substrate. A magnetic layer with a coercive force of 1000 Qe or more and a surface roughness of 008 μm or less is provided on the back surface of the substrate, and an average particle size of two inorganic pigments with a Mohs hardness of 2 to 4 and 5 to 7 is 0.04 to 05 μm. The present invention provides a magnetic recording medium characterized in that it is provided with a back coat layer in which particles of the present invention are dispersed in a thermosetting resin binder.

When the magnetic layer is of a metal or alloy powder dispersion type, it is preferable that the magnetic powder has a specific surface area of 48 m27 g or more by the BET method because the S/N of the recording medium is improved. However, if it is too thick, the magnetic powder will not be well dispersed in the binder resin, and the effect will be saturated. The surface roughness of this type of magnetic layer is preferably 0.08 μm or less, thereby making it possible to improve the recording sensitivity at short wavelengths.

In the case of a metal or alloy thin film type magnetic layer, a surface roughness of 0.08 μm or less can be easily achieved, and a surface roughness of about 0.08 μm is also possible.

Conventionally, various inorganic pigments have been proposed as fillers for backcoat layers. However, it is difficult to properly convey the type, hardness, particle size, or shape of the inorganic pigment to be filled, which not only impairs the effectiveness of the bank coat layer but also adversely affects its properties. There were other problems.

For example, when using CaCO5 with an average particle size of 0.04 μm or less, which is well known as a filler for the back coat layer, dispersion in the binder becomes difficult unless the particle size is appropriately selected. If the backcoat layer is formed with insufficient dispersion, the backcoat layer will have unevenness, and when the magnetic tag is wound overlappingly, the unevenness will be transferred to the magnetic recording layer, resulting in a deterioration of the S/N ratio. Moreover, since the particles of CaCO5 are soft, the repeated running durability is poor, and the back coat layer is scraped and white powder is generated. Generation of a large amount of white powder is undesirable because it can lead to malfunction of video, tape, and recorders.

In addition, when an inorganic pigment with a relatively large average particle size is used as a filler for the back coat, the surface irregularities of the bank coat layer become large, and when the magnetic tape is wound in layers, the irregularities of the back coat layer become larger than the magnetic recording layer. transcribed into S
/N decreases, so this is not appropriate.

As a result of intensive research on inorganic pigments used as fillers in bank coat layers, the present inventors found that particles selected from inorganic pigments with an average particle size of 004 to 05 μm and a Mohs hardness of 2 to 4; It has been found that a mixture of particles selected from inorganic pigments having α of 04 to 05 μm and a Mohs hardness of 5 to 7 and dispersed in a binder is suitable as a filler for the bank coat layer.

The inorganic pigments having an average particle size of [11.02 to 0.5 μm and a Mohs hardness of 2 to 4 include CaC'C)3,
ZnQ, MgCO3, etc. are suitable. Inorganic pigments with an average particle size of 01 to 0.9 μm and a Mohs hardness of 5 to 7 include TiO2, α-F'e 20s, MgO
1St02, SnOZrO2, etc. are suitable. In the present invention, S these inorganic pigment particles having different Mohs hardnesses are mixed in a weight ratio of 1:9 to 5:5, and this mixture is mixed with a binder in a weight ratio of 4. :1 to 1:1
Disperse and knead at a ratio of 03 to 1.
Back coat to give a surface roughness of 5 μm and a surface roughness of 0.05 to 0.6 μIn. The magnetic tape backcoated in this manner can overcome all of the above-mentioned conventional drawbacks.

That is, in the present invention, since the average particle size of the inorganic pigment to be filled is selected to be an appropriate particle size of 0.04 to 0.05 μm, the dispersibility is improved and a back coat layer having an appropriate surface roughness is formed. can get.

Therefore, the S/N ratio is improved and at the same time, the occurrence of one-sinching is prevented.

In addition, since hard inorganic pigment particles with a Mohs hardness of 5 to 7 and soft inorganic pigment particles with a Mohs hardness of 2 to 4 are mixed, the hardness of the bank coat layer can be appropriately controlled, giving it appropriate flexibility. A bank coat layer having the following characteristics and excellent reinforcing effect can be obtained. This eliminates magnetic tape flying out and winding irregularities during high-speed winding, prevents damage to the magnetic tape during loading and unloading, and eliminates back coat scraping due to contact with VTR and video cassette guides. The generation of white powder is prevented.

As the binder constituting the back coat layer, any binder made of thermosetting resin conventionally used in magnetic recording media can be used. In particular, nitrocellulose, urethane, vinyl chloride/vinyl acetate copolymers (including those with carboxylic acids such as maleic acid introduced), vinyl chloride/vinyl acetate/vinyl alcohol copolymers (including those with carboxylic acids such as maleic acid introduced), vinyl chloride/vinyl alcohol copolymers (including those with carboxylic acids such as maleic acid introduced), binders or urethanes containing incyanates, vinyl chloride/vinyl acetate copolymers (including those with carboxylic acids introduced), (same as above) and incyanate-containing binders are suitable for dispersing the pigments mentioned above.

If the ratio of filler to binder is less than 1:1, it will cause adhesion to the magnetic recording layer and is not suitable.

Also, if the amount of filler is greater than 4:Ma, the running friction will increase, which is not appropriate. That is, the ratio of filler to binder is 4
:1 to 1:1 is suitable.

It is desirable that the thickness of the back coat layer be as thin as possible, but if it is too thin, it will not be possible to obtain a sufficient reinforcing effect.
Approximately 3 to 1.5 μm is appropriate. In addition, if the surface roughness R2o of the back coat layer is less than 0.6 μm, the unevenness on the surface of the back coat layer will be transferred to the magnetic recording layer, resulting in a decrease in S/N, and if it is smoother than 0.05 μm, the friction will increase and the running speed will increase. Surface roughness is 0.05~
A range of 0.6 μm is suitable.

Furthermore, in order to reduce the friction of the back coat layer and improve running properties, silicone oil, fluorine oil, fatty acid,
Fatty acid esters, paraffin, liquid paraffin, surfactants, etc. can be used, but it is particularly preferable to use fatty acids and/or fatty acid esters. Examples of fatty acids include fatty acids with 12 or more carbon atoms (RC0OH, R is an alkyl group having 11 or more carbon atoms), and the fatty acid esters include monobasic fatty acids having 12 to 16 carbon atoms and 3 carbon atoms.
Fatty acid esters consisting of ~12 monohydric alcohols, monobasic fatty acids having 17 or more carbon atoms, and monohydric alcohols having 21 to 23 carbon atoms in total with the carbon number of the fatty acid Fatty acid esters and the like are used.

When using a dispersed magnetic layer, examples of magnetic alloys that can satisfy the above characteristics include Co, Fe-Co, and Fe-Co-
4Ji, Co-Ni, etc., and also Cr, A
A fine powder to which I, 81, etc. is added is used. These are fine powders obtained by wet reduction of metal salts with a reducing agent such as BI3, fine powders obtained by coating the iron oxide surface with a Si compound and then dry-drying in H2 gas, or fine powders obtained by evaporating alloys in low-pressure argon. powder, etc., with an axial ratio of 1:5 to 1:10, and a residual magnetic flux density Br = 2. Of] 0~3, D D
It is of D Gauss and satisfies the above conditions of coercive force and surface strength.

The alloy magnetic powder can be made into a magnetic paint using various binders, but thermosetting resin binders and electron beam curing binders are generally preferred, and other additives such as dispersants, lubricants, Antistatic agents can be used according to conventional methods. Since magnetic powder with a BET surface area ratio of 48 m27 g is used, if there is a problem with dispersibility, a surfactant, an organic titanium coupling agent, a silane coupling agent, etc. may be used as a dispersant. As a binder, vinyl chloride/vinyl acetate/vinyl alcohol co-N polymer, vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl alcohol copolymer, (all of which may have a carboxylic acid such as maleic acid introduced) ) A binder made of polyurethane prepolymer and polyisocyanate, a binder further added with nitrocellulose, other known thermosetting binders, or acrylic double bonds or maleic double bonds that are sensitive to ionization energy. A radiation-curable binder contained as a resin base can be used.

According to the usual method, the alloy magnetic powder is mixed with a binder, a specified solvent, and various additives to form a magnetic coating, which is applied to a substrate such as a polyester base, and then thermally cured or electron beam cured to form a magnetic film. Super calendering is performed, a back layer is formed in the same manner, and the entire surface is supercalendered to give a predetermined surface roughness.

In the case of metal or alloy thin film magnetic layers, the ferromagnetic material can be selected from the same powder materials as described above and can be manufactured by the methods described above.

Examples of the present invention will be described below along with comparative examples.

magnetic layer 1 Various alloy powders were produced by wet reduction method.

These consist of acicular particles with an axial ratio (minor axis/long axis) of 115 to 1/10, a residual magnetic flux density of 2000 to 3000 Gauss, a coercive force of 1000 to 20000, and a BET surface area ratio of 45
~70 m2/9. These magnetic powders were mixed in the following mixing ratio in a conventional manner.

Parts by weight: Fe-Co-Ni alloy powder 100 Myristic acid 2 Sorbitan tristearate 2 60 parts by weight of polyisocyanate (Desmodur L manufactured by Bayer AG) was added to this mixture to make a magnetic paint, which was applied to a polyester film in a thickness of 65μ. , dried and calendered. Thereafter, a heat curing reaction was carried out at 80°C for 48 hours.

By adjusting the calendering conditions, various surface roughnesses of 002 to 012 μm were obtained.

Magnetic Layer 2 Arsenic Layer 1 Using the same magnetic powder as in Layer 1, a mixture of the following formulation was made.

Part by weight Fe-Co-Ni alloy powder 100 This mixture was applied to a polyester film in a thickness of 35 μm, dried, calendered, and cured with an electron beam.

The surface roughness was set to 002 to 012 μm by adjusting the calendering conditions.

Magnetic Layer 3 The magnetic layer used was a diagonally evaporated alloy magnetic film of 130% cobal and 20% nickel deposited on the surface of a polyethylene terephthalate film to a thickness of about 1500 nm using a vacuum evaporation method. The surface roughness was 0.01 μm.

EXAMPLE A Barafco-1 layer was formed on the back side of the above polyester film substrate on which magnetic layers 1, 2 and 6 were formed by washing and shaving as described below.

Next, each of the compositions in Table 1 was thoroughly kneaded and dispersed in a ball mill, and then coated on the back surface of the six types of substrates with a thickness of 10 μm, heated and cured, and calendered. ~505 samples were created. In addition,
In Table 1, the country of the 4n product is X1fE IJJ pigment i
It represents the M amount ratio to the oo part.

Further, the average particle size of the inorganic pigment Ca Co 3 in Sample 1o is 0.02 μm, and the average particle size of the inorganic pigments in Samples 1 to 4 are all 0.04 to 0.5 μm.

Thereafter, it was cut into 1/2 inch width and assembled into a VHS video cassette, and the electromagnetic characteristics, cinching, back coat scraping, scratches during loading or unloading, and winding irregularities were determined by 1 flN. The measurement results are shown in W2 (using 8 layers 1), λ3 (using magnetic layer 2), and Table 4 (using magnetic layer 3). In Tables 1 to 4, samples 1 to 8 are examples of the present invention,
Samples 9 and 10 are comparative examples. The surface roughness of all the magnetic layers of the samples in Table 2.3 is 0.08 μm or less, and that of the bank coat layer is \Q, 6 μm or less.

Table 1 Table 2 Table 3 Table 4 The relationship between the surface roughness of the puncture coat layer and the surface roughness of the magnetic surface was investigated for each sample of magnetic layer 1.2.
It became a diagram. Therefore, in Tables 2 to 4, the surface roughness was selected to be 06 μm or less and 008 μm or less, respectively. Further, regarding the magnetic layer 1.2, the relationship between the surface area of the metal powder and S/H was investigated, and it was confirmed that 48 m2/g or more is preferable. Table 2
As is clear from 4 to 4, comparative sample 9, which used only TiO2 particles as the inorganic pigment, had relatively good characteristics such as color S/N, scintching, bank coat scraping, and scratches during loading and unloading. ,
The winding disorder of the magnetic tape is likely to occur. In addition, as an inorganic pigment, CaC03 has a small average particle size of 0.02 μm.
Comparative sample 10, which uses only particles, does not cause winding irregularities in the magnetic tape, but is inferior in color S/N, cinching, and bank coat scraping, and has large scratches during loading or unloading.

On the other hand, Samples 1 to 8, which are Examples of the present invention, have better color S/N and are less likely to cause cinching than Comparative Samples 9 and 10. Furthermore, there is no abrasion of the back coat, there is very little damage to the magnetic tape during loading or unloading, and there is no occurrence of magnetic current (tape winding disorder).

Effects of the Invention As described above, the present invention provides a magnetic recording medium having a magnetic recording layer on the surface of a support and a bank coat layer on the back surface, in which the back coat layer has an average particle size of 0.
．． Particles selected from inorganic pigments with a Mohs hardness of 0.04 to 0.5 μm and an average particle size of 0.04 to 0.5 μm.
Particles selected from inorganic pigments with a Mohs hardness of 5 to 7 m are dispersed in a binder, so the S/N is high and there is no scinting phenomenon or scraping of the bank coat layer. It is also possible to provide a bank coat type magnetic recording medium that can prevent tape damage during loading or unloading operations, and that does not cause popping out or winding irregularities during high-speed winding.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the surface roughness of the bank coated surface and Y-8/N. -,1 Name of agent Motohiro Kurauchi1■1 /-1-ゝ-1

Claims (3)

[Claims] (1) A magnetic recording medium consisting of a magnetic layer in which ferromagnetic alloy powder is dispersed in a resin binder or a ferromagnetic metal thin film layer coated on a plastic base is heated at 10°C.
It has a coercive force of 00Qe or more and a surface roughness of α08μm or less, and the back surface of the base has an average particle size of o.
, o first particles selected from inorganic pigments having a diameter of 4 to 15 μm and a Mohs hardness of 2 to 4, and an average particle size of 0.04 to 4.
A magnetic recording medium comprising a back coat layer in which second particles selected from inorganic pigments having a diameter of 0.5 μm and a Mohs hardness of 5 to 7 are dispersed in a thermosetting binder. (2) First particle kI Ca LOs, ZnO, MgCO
3. The magnetic recording medium according to item 1 above, which is selected from ZnCO3. (3) 83; 2 particles &'L 'I' + 02, α-F
e2o3,)”e504. MgO1sho2, SnQ
2. The magnetic recording medium according to item 1 or 2, which is selected from ZrO2.