JPH06195679A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To decrease production of chips by constituting a nonmagnetic supporting body of >=70wt.% aromatic polyamide and controlling to form projections of >=0.54mum height on the principal surface of the supporting body to <=50 particles/100cm<2>. CONSTITUTION:A magnetic layer 2 containing a magnetic powder, binder, etc., is formed on the one surface of a nonmagnetic supporting body 1 consisting of aromatic polyamide. On the other surface of the supporting body, a back coating layer 3 essentially consisting of a binder and nonmagnetic powder such as carbon black is formed. In the process of forming the aromatic polyamide film, surface roughness of the casting surface of a stainless belt used is controlled by degree of buffing, and the surface of the film is measured a surface roughness meter to obtain the number of projections of >=0.54mum height. The number of projections of projections of >=0.54mum height on the surface of the nonmagnetic supporting body where the back coating layer 3 is formed is controlled to <=50 particles/100mm<2>. Thus, both of dropout and head clogging characteristics are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and a manufacturing method thereof.

[0002]

2. Description of the Related Art A magnetic recording medium, for example, a magnetic tape, can be manufactured through a process of applying a magnetic paint containing a magnetic powder and a binder as main components on a non-magnetic support (base film).

So far, PET (polyethylene terephthalate) has been used as a material for a non-magnetic support for magnetic tape.
And PEN (polyethylene naphthalate) are used. However, in order to lengthen the magnetic tape and record for a long time, the non-magnetic support was thinned (especially 8.4μ in total tape thickness).
m or less), the elastic modulus of PET or PEN becomes insufficient, the hit waveform against the head is bad, the output is likely to decrease, and the edge damage of the tape increases. This has become a problem in tapes for data cartridges, which back up the hard disks as the capacities of the hard disks increase in recent years.

Therefore, as a non-magnetic support, a high elastic modulus material (Young's modulus of 600 kg / mm ² or more, for example, 1000 kg / mm ² )
It has become necessary to use aromatic polyamide and the like.

The support of such an aromatic polyamide is P
It is necessary to form a film by a melt film-forming method instead of the melt film-forming method when forming a film of a support of ET or PEN. That is,
An aromatic polyamide solution is uniformly cast from a die onto a surface-polished rotary stainless belt (endless),
The solvent is evaporated and the film is formed by stretching, washing and the like.

However, the surface property of the stainless steel belt to be used is very important because of the dissolution film formation method, and the surface property of the aromatic polyamide after film formation is greatly influenced by the surface property of the belt. That is, all the defects on the surface of the stainless belt are transferred to the polyamide film surface on the belt side.

Up to now, the surface of the stainless belt has been polished and used with a considerable degree of accuracy. However, when a magnetic tape is produced using an aromatic polyamide film formed by this, the surface of the film on the belt side. Not only when the magnetic layer was formed on the disk, but even when the back coat layer was formed, the head clog and the dropout level were very bad.

That is, since the defect of the belt is directly transferred to the film surface, a large number of large protrusions are formed on the film surface, and surface protrusions are also formed on the magnetic layer provided thereon, which increases dropout. Cause of.
Also in the case of the back coat layer, the protrusions generated on the surface are scraped during traveling, and the scraps are transferred to the magnetic surface, resulting in dropouts and clogging of the magnetic head gap (head clog).
Will occur.

Even when the polyamide is formed by coating on the die surface instead of the belt, a magnetic tape having a large error rate can be formed by providing a magnetic layer on the surface in contact with the die surface.

[0010]

Therefore, as a result of various investigations, the present inventor has found that in a magnetic tape using an aromatic polyamide as a main component as a non-magnetic support, the surface of its main surface (especially the back surface). The inventors have found that the aforementioned drawbacks can be reduced or eliminated by controlling the sex within a specific range, and have reached the present invention.

Therefore, an object of the present invention is to provide a magnetic recording medium capable of reducing or substantially eliminating dropout and head clog while making the most of the characteristics of aromatic polyamide having a high elastic modulus, and a method for producing the same. Especially.

[0012]

That is, according to the invention of claim 1, in a magnetic recording medium in which a magnetic layer is formed on a non-magnetic support, 70% by weight of the constituent components of the non-magnetic support is provided.
A magnetic recording medium characterized by comprising the above-mentioned aromatic polyamides and having 50/100 cm ² or less projections having a height of 0.54 μm or more on a predetermined main surface of the non-magnetic support. It is related.

In this magnetic recording medium, a part of the aromatic nucleus of the aromatic polyamide is substituted with a halogen group (especially chlorine atom), and the aromatic polyamide is composed of polyparaphenylene terephthalamide. Is desirable.

In the invention according to claim 5, the nonmagnetic support is cast on the mold surface to form a film, and the nonmagnetic support is backed on the main surface on the mold surface side. The present invention relates to a magnetic recording medium in which a coat layer is formed and a magnetic layer is formed on the other main surface opposite to the back coat layer.

The magnetic recording medium of the present invention is particularly suitable for thinning, and is advantageous when the total thickness is 8.4 μm or less.

The invention described in claim 7 is the same as claim 1.
In manufacturing the magnetic recording medium according to claim 1, the constituent material of the non-magnetic support is cast on a rotary belt having heat resistance and solvent resistance, and the protrusions according to claim 1 are provided on the rotary belt side. The present invention relates to a method for producing a magnetic recording medium, which comprises forming a film on a non-magnetic support existing on the main surface of

Further, the invention described in claim 8 is the same as claim 1.
Alternatively, in manufacturing the magnetic recording medium described in 5, the magnetic recording medium is manufactured by coating the constituent material of the non-magnetic support on a film having heat resistance and solvent resistance to form the non-magnetic support. It relates to the method.

The present inventor uses the aromatic polyamides for the non-magnetic support, especially when the surface protrusions of the aromatic polyamide film caused by the transfer of the defects on the surface of the rotary belt such as the stainless belt during the film formation are formed. Of which, the height is 0.
By controlling the number of protrusions of 54 μm (2 rings of Newton ring: the second ring of Newton rings and observed as interference fringes due to light of wavelength 5400Å) to 50 pieces / 100 cm ² or less, a non-magnetic support A magnetic recording medium such as a magnetic tape with good dropout and head clog characteristics can be created by improving the surface properties of the upper magnetic layer and reducing large protrusions on the back coat layer to reduce the amount of shavings. Found.

In producing such a magnetic recording medium, the surface property (surface roughness) of the rotary belt is polished by buffing or the like so that the protrusions on the non-magnetic support surface on the belt surface side meet the above-mentioned conditions. Can be controlled down.

The present inventor, when using an aromatic polyamide as a non-magnetic support, forms a back coat layer on the principal surface having the above-mentioned protrusions and a magnetic layer on the opposite principal surface. Then, it was found that the effect of the present invention can be fully exerted, and in particular, if a magnetic layer is provided on the surface not in contact with the above-mentioned film-forming film, a magnetic recording medium with less dropout can be obtained. It was

In the present invention, when the ratio of the above aromatic polyamides to the constituent components of the non-magnetic support is less than 70% by weight, the amount is too small and the elastic modulus of the non-magnetic support becomes insufficient, The above effects cannot be obtained.

When halogen is substituted or introduced into the aromatic nucleus of this aromatic polyamide, the humidity expansion in the predetermined direction (especially longitudinal direction) of the non-magnetic support becomes small.

In particular, the proportion of halogen is preferably 17 to 38% by weight of aromatic polyamides. Within this range, the coefficient of humidity expansion of the non-magnetic support is as small as 1.5 × 10 ^-5 or less, and the influence of humidity changes. It is possible to produce a magnetic tape that is hard to receive. The smaller this humidity expansion coefficient is, the better. If the proportion of halogen groups is less than 17% by weight, the expansion due to humidity change will be large, and if it exceeds 38% by weight, the Young's modulus of the non-magnetic support tends to decrease due to the deterioration of the physical properties of the aromatic polyamides. Here, the humidity expansion coefficient is obtained by calculating the ratio of the amount of expansion due to humidity to the initial length with respect to the change in relative humidity, and for example, using TTMA manufactured by Rigaku Denki Co., Ltd.
It can be measured at 25 ℃ and humidity of 30 to 90% RH.

Examples of the aromatic polyamides used in the present invention include those having the following general formula I or II as a basic skeleton.

[0025]

[Chemical 1]

[Chemical 2] [In the above formulas, a and b are integers, R ¹ , R ² , R ³
Is a hydrocarbon group containing an aromatic group and may contain halogen such as chlorine atom. Of the above general formula I, the following polyparaphenylene terephthalamide (PPTA) or a halogen-substituted derivative thereof is preferable.

[Chemical 3]

Specific examples of the aromatic polyamides having the general skeletons of the general formulas I and II are as follows.

[Chemical 4]

[Chemical 5]

The above-mentioned aromatic polyamides can be generally produced by the following method. That is, para-phenylenediamine halide (aromatic nucleus substituted with halogen), para-phenylenediamine, terephthalic acid halide (halogen substituted aromatic nucleus or acid halide of terephthalic acid), etc. are blended appropriately, and polar Obtained by polycondensation in an organic solvent.

As the usable solvent, polar amide solvents such as dimethylformamide, dimethylacetamide and N-methylpyrrolidone are used. Further, an inorganic base such as lithium hydroxide or calcium hydroxide is added, if necessary, in order to neutralize hydrogen halide generated during polycondensation.

To prepare the above-mentioned non-magnetic support containing aromatic polyamide as a main component, for example, as shown in FIG. 2, the aromatic polyamide solution 11 is cast as it is from the nozzle 12 onto the casting surface 13 and dried. A dry method or a dry-wet method is used in which the solvent is heated and dried by 14 (for example, hot air method), and washed and stretched if necessary.

For casting, a metal belt 13 (or film) having heat resistance and solvent resistance, capable of polishing the surface, and driven to rotate between rollers 15-16 is used. To dry the solvent, air is used. Alternatively, a heated gas such as nitrogen may be circulated. The above belt or film is made of stainless steel,
Ceramics, glass, etc. can be used.

The non-magnetic support thus produced may be a blend of one or more of the above aromatic polyamides, or a blend with another polymer (for example, aromatic polyimide), or necessary additives. May be contained. However, the amount of aromatic polyamide must be 70% by weight or more.

In the magnetic recording medium of the present invention, a magnetic layer is formed on the above-mentioned non-magnetic support. In this case, for example, magnetic powder is dispersed in a binder and ethers are added depending on the kind of the binder. A magnetic paint is prepared by kneading with an organic solvent selected from ketones, aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, etc., and this magnetic paint is applied to the surface of a non-magnetic support, dried, and calendered. To do.

As the magnetic powder used in the present invention, any conventionally known magnetic powder can be used. It is possible to use oxide magnetic powders, which include
For example, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Co-deposited γ-Fe
₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-deposited Fe ₃ O ₄ , CrO _{2 and the} like can be mentioned. Further, hexagonal ferrite such as barium ferrite, iron carbide such as Fe ₅ C ₂ and iron nitride can also be used.

The metal magnetic powder that can be used includes
For example, Fe, Co, Ni, Fe-Co, Fe-Ni, Fe-Co-Ni, Co
-Ni, Fe-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn-Al,
Fe-Co-V and the like can be mentioned, and further, metal components such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added for the purpose of improving these various characteristics. Further, hexagonal ferrite such as barium ferrite and iron nitride can be used.

As the binder, a modified or non-modified vinyl chloride resin, a polyurethane resin (including polyester polyurethane and polycarbonate polyurethane) or a polyester resin can be used or mixed, and a fibrin resin, A phenoxy resin or a thermoplastic resin having a specific usage system, a thermosetting resin, a reactive resin, an electron beam irradiation curable resin, or the like may be used in combination. The group to be introduced for the above modification, -SO ₃ M that attained a dispersibility improvement of the magnetic _{powder, -OSO 3 M, -COOM, -PO} (OM ') may be ₂ or the like (M is Na Alkali metal atom such as, M'is the same alkali metal atom or alkyl group).

As the usable fibrin resin, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

Further, it is preferable to add a curing agent to such a binder in order to further improve durability. As this curing agent, a polyfunctional isocyanate can be used, and particularly tolylene diisocyanate (T
The DI) system is preferred. The addition amount of the curing agent is preferably 5 to 30% by weight based on the total amount of the binder.

In the magnetic recording medium of the present invention,
In addition to the above-mentioned binder and magnetic powder, myristic acid, a dispersant such as lecithin, a lubricant such as stearic acid ester, an abrasive such as alumina, an antistatic agent such as carbon black, an anticorrosive agent, and the like, if necessary. May be added. As the dispersant, the lubricant, the antistatic agent and the rust preventive, any conventionally known material can be used, and the dispersant is not limited at all.

An intermediate layer or an undercoat layer may be provided on the surface of the non-magnetic support in order to improve the adhesiveness of the magnetic layer.

Further, on the surface of the non-magnetic support opposite to the magnetic layer, a non-magnetic powder (eg silica, carbon black) and a binder (similar to those described above) are used to improve the running property of the medium. Can be provided.) Can be provided.

FIG. 1 shows an example (magnetic tape for video) of the magnetic recording medium of the present invention. That is, the magnetic layer 2 containing magnetic powder, a binder and the like is provided on one surface (the surface opposite to the casting surface) of the non-magnetic support 1 made of the aromatic polyamide. Also,
On the other surface (the surface on the casting surface side described above), there is a back coat layer 3 mainly composed of non-magnetic powder such as carbon black and the above-mentioned binder.

The present invention is applicable not only to a coating type medium in which a magnetic layer is formed by coating as described above, but also to a medium such as a vapor deposition type continuous magnetic thin film in which a magnetic layer is formed by vapor deposition of a magnetic material. Can also be applied.

[0043]

EXAMPLES The present invention will be described below with reference to specific examples, but the present invention is not limited to the following examples.

Examples 1 to 6 and Comparative Examples 1 and 2 Raw materials having the following compositions were prepared. Magnetic coating composition: Magnetic powder: Fe-based metal magnetic powder (specific surface area BET value = 50 m ² / g: manufactured by Kanto Denka Kogyo Co., Ltd.) 100 parts by weight Binder: Polyester (Vylon 53S manufactured by Toyobo Co., Ltd.) 10 parts by weight Polyurethane (Nippon Polyurethane) Kogyo Co., Ltd. N-2304) 12 parts by weight Abrasive: Alumina (E-550 manufactured by Norton) 6.5 parts by weight Dispersant: Stearylamine 1.5 parts by weight Lubricant: Butyl stearate 2.5 parts by weight Solvent: Methyl ethyl ketone 140 parts by weight Toluene 100 parts by weight

After mixing the raw materials having the above composition with a sand grind mill for 6 hours and filtering, a curing agent:
3.5 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the surface of the aromatic polyamide film (thickness 6 μm) formed on the opposite side of the stainless steel belt as described below.
It was applied to a thickness of μm, dried, and calendered and cured. Then, a back coat layer coating composition having the following composition was dispersed in a sand grind mill for 4 hours, filtered, and added with 3 parts by weight of a curing agent (same as above), and then applied to the surface opposite to the magnetic surface (stainless belt side surface). It was applied, dried and cured to a thickness of μm.

Backcoat layer coating composition: Carbon black (R-1255 manufactured by Colombian Carbon Co., Ltd.) 98 parts by weight Spherical silica (manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd .: particle size 0.3 μm) 2 parts by weight Binder: Polyurethane (Nippon Polyurethane Industry Co., Ltd.) N-3109) 30 parts by weight Polyurethane (N-5033 manufactured by Nippon Polyurethane Industry Co., Ltd.) 20 parts by weight Dispersant: Phosphate ester 0.5 parts by weight Lubricant: Heptyl stearate 1 part by weight Solvent: Methyl ethyl ketone 350 parts by weight Toluene 130 Parts by weight

Next, the film wound into a roll is unrolled, slit into a width of 8 mm, assembled in a cassette, and Hi-
Evaluation was carried out using an 8 (high band 8 mm) deck, and the results are shown in Table 1 below.

In the above, as a raw material for the aromatic polyamide film, 2-chloro-p-phenylenediamine,
Solution polymerization (condensation polymerization) was carried out in an N-methylpyrrolidone solution using 2-chloroterephthaloyl chloride. The obtained polymer solution was uniformly cast on a stainless belt from a die, and a film having a thickness of 4 μm was prepared through the steps of heating and drying, washing and stretching. This film forming process is, for example,
According to Japanese Patent Publication No. 51463.

In each of the examples shown below, corresponding tapes were obtained by using the same raw material and method, but only the polishing level of the stainless belt at the time of forming the aromatic polyamide film was changed. That is, in each example, the surface roughness of the casting surface of the stainless belt used was controlled by the degree of buffing.

The evaluation was performed as follows. Number of protrusions: The film surface is measured with a surface roughness meter, and the height is 0.54.
The number of protrusions of μm or more was determined.

Dropout: A dropout counter was used, and an average value per minute was obtained with one dropout being an output that has dropped for 16 μsec or more and has been lowered by 16 dB.

Head clog: When the tape was repeatedly run, the occurrence of head clogging (clog) was observed, and the number of passes in which clog occurred was evaluated.

[0053]

From these results, according to the present invention, the number of protrusions of 0.54 μm or more on the non-magnetic support surface on the back coat layer side was determined.
It can be seen that the dropout and head clog characteristics are improved by suppressing the number to 50/100 cm ² or less.

Example 7, Comparative Example 3 Raw materials having the following compositions were prepared. Magnetic coating composition: Metal (Fe) magnetic powder (specific surface area 50 m ² / g) 100 parts by weight Polyester polyurethane (Nipporan N-2304 manufactured by Nippon Polyurethane Co.) 8 parts by weight Vinyl chloride-vinyl acetate copolymer (VAGH manufactured by Union Carbide) ) 8 parts by weight Carbon black (Asahi # 50 Asahi Carbon Co., Ltd.) 4 parts by weight Alumina (Sumitomo Chemical Co., Ltd. AKP-50) 8 parts by weight Butyl stearate 2 parts by weight Methyl ethyl ketone 150 parts by weight Toluene 70 parts by weight

The above materials were mixed and dispersed in a sand mill for 4 hours to prepare a magnetic coating material. At the time of coating, 3 parts by weight of curing agent Coronate L was added.

On the other hand, an aromatic polyamide solution of PPTA was applied on the mold surface of a stainless film and dried to form an aromatic polyamide film having a thickness of 6 μm. Then, the magnetic coating composition was applied to the surface not in contact with the mold surface film so that the layer thickness was 1.5 μm, calendering was performed, and the back coating composition below was applied to the opposite surface ( Example 7).

Coating composition for back coat layer: Carbon black (Asahi # 50 Asahi # 50) 100 parts by weight Polyester polyurethane (Nippon Polyurethane Nipporan N-2304) 100 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight

The above materials were mixed and dispersed in a ball mill for 24 hours, and 20 parts by weight of curing agent Coronate L was added at the time of coating. The back coat layer coating material was applied to a thickness of 0.7 μm and left in an oven at 60 ° C. for 20 hours. Then, it was slit into a width of 8 mm and incorporated into a shell for data 8 mm.

On the other hand, contrary to Example 7, a magnetic layer was coated on the surface in contact with the mold surface film, the back coat layer was coated on the surface on the opposite side, and a tape was prepared in the same manner as in the other cases. (Comparative example 3).

Next, the block error rate (BER) of the magnetic tapes produced in Example 7 and Comparative Example 3 was measured as follows. The results are shown in Table 2 below. Drive used: EXB-8500 (manufactured by EXABYTE) Measurement procedure: 1. Write data over 32000 blocks. 2. Rewind and return to the original position. 3. Read the written data of 32000 blocks. 4. Rewind and return to the original position. This is 32000 when the block error rate is E%.
Of the blocks, 320xE blocks indicate that writing or reading could not be done normally.

[0062]

As is clear from this result, when the magnetic layer is formed on the surface opposite to the mold surface film according to the present invention, a magnetic recording medium having a small error rate can be obtained.

[0064]

As described above, according to the present invention, the projections having a height of 0.54 μm or more existing on the predetermined main surface of the non-magnetic support are 50 or more.
Since it is controlled to 100 pieces / 100 cm ² or less, the surface properties of the magnetic layer on the non-magnetic support are improved, and large protrusions are reduced in the back coat layer, reducing the amount of shavings and resulting in dropout. It is possible to create a magnetic recording medium such as a magnetic tape having good head clog characteristics.

Further, since the back coat layer is formed on the main surface on the die surface side and the magnetic layer is formed on the main surface on the opposite side when the non-magnetic support is formed into a film, the effect of the present invention is achieved. Can be demonstrated for
In particular, dropouts can be reduced.

Moreover, even if the medium is made thin, the elastic modulus is satisfied because the non-magnetic support is made of aromatic polyamides, and the hit waveform and edge damage level are improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one structural example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic view of an apparatus for forming a film on a non-magnetic support of the magnetic recording medium.

[Explanation of symbols]

 1 ... Non-magnetic support 2 ... Magnetic layer 3 ... Back coat layer 11 ... Aromatic polyamide solution 12 ... Nozzle (base) 13 ... Stainless belt 14 ... Dryer

Claims (8)

[Claims] 1. A magnetic recording medium having a magnetic layer formed on a non-magnetic support, wherein 70% by weight or more of the constituent components of the non-magnetic support are aromatic polyamides, and
A magnetic recording medium characterized in that projections having a height of 0.54 μm or more are present at 50/100 cm ² or less on a predetermined main surface of the non-magnetic support. 2. The magnetic recording medium according to claim 1, wherein a part of the aromatic nucleus of the aromatic polyamide is substituted with a halogen group. 3. The halogen group is a chlorine atom, 2.
The magnetic recording medium described in 1. 4. The magnetic recording medium according to claim 1, wherein the aromatic polyamide comprises polyparaphenylene terephthalamide. 5. A back coat layer is formed on the main surface of the non-magnetic support, which is formed by casting a constituent material of the non-magnetic support on the mold surface, and the back surface is formed. A magnetic recording medium having a magnetic layer formed on the other main surface opposite to the layer. 6. The total thickness is not more than 8.4 μm.
5. The magnetic recording medium described in any one of 5. 7. A magnetic recording medium according to claim 1, wherein the constituent material of the non-magnetic support is cast on a rotary belt having heat resistance and solvent resistance. A method for producing a magnetic recording medium, wherein a film of the non-magnetic support having the above-mentioned protrusions on the main surface of the rotary belt is formed. 8. When manufacturing the magnetic recording medium according to claim 1 or 5, the non-magnetic support is manufactured by coating the constituent material of the non-magnetic support on a film having heat resistance and solvent resistance. A method of manufacturing a magnetic recording medium having a film.