JPS61142530A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide high-speed winding adaptability and to decrease the fluctuation of audio output by incorporating carbon black into a back layer and specifying the ratio of nonmagnetic powder and total binder as well as the voids of the back layer. CONSTITUTION:The back layer of a magnetic recording medium of which the back layer contains the nonmagnetic powder dispersed in the binder contains the carbon black having 0.1-1mu average single particle size. The ratio of the nonmagnetic powder and total binder of the back layer is 300/100-40/100 and the voids of the back layer are 30-50%. There is, for example, a thermoplastic polyurethane elastomer as the binder of the back layer. There are titanium dioxide, etc. as the nonmagnetic powder which is used for the purpose of controlling the surface roughness, voids and electric resistance of the back layer. The amt. of the nonmagnetic powder to be used is preferably 40-300pts.wt. by 100pts.wt. the binder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more particularly, to enhancement of the sensitivity of a magnetic recording layer (hereinafter referred to as a magnetic layer) and support for achieving these characteristics. The present invention relates to a magnetic recording medium in which a pack layer is provided on the other side of the body having a magnetic layer.

[Conventional technology]

In recent years, magnetic recording has been required to have higher sensitivity. Higher sensitivity enables higher image quality, better sound quality, and higher density recording, and these can be achieved by improving the magnetic recording/reproducing deck, the recording method for magnetic recording media, and improving and improving magnetic recording media.

High sensitivity in magnetic recording media can be achieved by increasing the signal part of the signal-to-noise ratio and reducing the noise part, and the former is specifically achieved by making the ferromagnetic powder even finer and shape anisotropy. This can be achieved by increasing the residual magnetic flux density and coercive force of the magnetic recording medium by manipulating the magnetic flux density and the arrangement of single magnetic domains in the fine powder bed.

On the other hand, there are various factors that can be used to reduce the latter noise portion, including smoothing the magnetic layer and controlling the charging characteristics of the magnetic recording medium.

However, such a smooth magnetic recording medium is likely to be unrolled in an orderly manner during winding and unwinding, resulting in irregular winding.

When such a magnetic recording medium is used, the tape runnability is poor and the output fluctuates due to tension fluctuations. Furthermore, deformation and damage to the magnetic recording medium are likely to occur. In order to avoid this drawback, a magnetic recording tape has been proposed in which a pack layer is provided on the surface of the support opposite to the magnetic recording layer.

It has also been proposed to provide a back layer to control charging characteristics, maintain running durability, and maintain an appropriate coefficient of friction.
It is known in Japanese Patent Application Laid-open No. 111828, Japanese Patent Application Publication No. 50-61202, Japanese Patent Application Publication No. 52-102004, Japanese Patent Application Publication No. 52-96505, and Japanese Patent Application Publication No. 59-116.930.

[Problem that the invention seeks to solve]

However, even with these technologies, it is extremely difficult to obtain a highly sensitive magnetic recording medium with running durability, and the main reasons for this are: 1) Improving (smoothing) the surface properties of the magnetic recording medium Although the spacing loss between the magnetic recording and reproducing head is reduced and the 8-N ratio is increased, running durability is deteriorated and the coefficient of friction is increased, resulting in irregular winding phenomenon and falling off of the magnetic layer and back layer. . Furthermore, when a magnetic recording medium that has been smoothed too much is run repeatedly, the cut surface deforms into a seaweed-like shape, increasing audio output fluctuations. 2) When the surface of the back layer is roughened to improve running durability, the rough surface of the pack layer is transferred to the magnetic layer, resulting in a decrease in the signal-to-noise ratio of the magnetic layer. 3) Improving the surface properties of the magnetic layer for high sensitivity (high s, "N")
The surface properties of the back layer are also improved, and the suitability for high-speed winding of the magnetic recording medium on the deck is eliminated. 4) The number of dropouts of the magnetic recording medium increases due to repeated running.

An object of the present invention is to prevent the coefficient of friction of a magnetic recording medium from increasing.
The objective is to provide a magnetic recording medium with good running durability.

Another object of the present invention is to provide a puncture layer that does not impair the 87N characteristics of a magnetic recording medium.

Another object of the present invention is to provide a backing layer that prevents random winding of a magnetic recording medium at high speeds and reduces audio fluctuations.

[Means for resolving the gap @]

As a result of various studies, the present inventors found that the back layer contains carbon black with an average single particle diameter of (11 to 1 μm), and the ratio of the nonmagnetic powder in the back layer to the total binder is 300 μm.
/100 to 40/100 and the porosity of the back layer is 30 to 50. It has been found that the above objectives can be achieved, and the present invention has been achieved.

That is, the present invention provides a magnetic recording medium that has a magnetic layer on one side of a support and a back layer on the other side, and the back layer includes nonmagnetic powder dispersed in a binder. Contains carbon black, and the ratio of the non-magnetic powder of the back layer to the total binder is 300/1 G G ~ 40/1
00 and the back layer has a porosity of 30 to 511116.

In the present invention, the magnetic layer is not particularly limited, and any of the coating type, vapor deposition type, etc. used in conventional audio tapes, video tapes, memory tapes, etc. can be used. .

As the support, materials used in conventional magnetic recording media such as those mentioned above can be used, and wood materials include, for example, polyesters, polyolefins, cellulose derivatives, vinyl resins, and other plastics. , paper laminated with non-magnetic metals, alloys, polyolefins, etc. can also be used.

The manufacturing method for such magnetic recording media was published in the Special Publication Publication No. 56-26.
It is described in No. 890, etc.

As described above, the feature of the present invention lies in the use of a special back layer within the magnetic recording medium, so the back layer will be described in detail below.

The carbon black used in the back layer of the present invention has an average particle size classified by the carbon black industry as α.
1-1p IL T, (Medium Therma
lλF, T, (Fine Thermal) and 7 Arness Carbon's M, T, or F', 'I
', is equivalent. Commercial products of these carbon blacks include HTC S20 (Nichi 11 Kagaku) and Sehacal 7'.
lLT, (Separco), 71 per ml 99 G (7
-Bar), Leben M, T, P, (Colombian)
, Thermax P-33, etc. These carbon
Black is characterized by having a nitrogen adsorption method specific surface area of less than 25 m''/2, and a relatively undeveloped carbon black structure called stracture.

The back layer in the present invention is formed by dispersing non-magnetic powder in a binder, and contains at least polyisocyanate as the binder.

Examples of the polyisocyanate include 2,4-tolylene diiso7ane), 1,6-hexamethylene diiso7ane, and triisocyanate (for example, Coronate IJm manufactured by Nippon Polyurethane Industries, Ltd.).

As the binder for the back layer of the present invention, in addition to the polyisocyanate described above, materials generally used as binders for magnetic recording media can be used.

Examples of these include, for example, thermoplastic polyurethane elastomers. These are also available as commercial products.

Namely, organic dibasic acids such as 7-talic acid, adipic acid, dimerized sulfuric acid, maleic acid, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, O/'J alcohols, or trimethylol. Polyester polyols obtained by reaction with polyhydric alcohols such as propane, hexanetriol, glycerin, trimethylolethane, and pentaerythritol (t), 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, metaxylylene diin Polyester polyurethane resins and polyether polyurethane resins urethanized with polyisocyanate compounds such as cyanate, and those having a zero ring in the molecular skeleton represented by general formula (1) are used.

[+0-R-00(!-R"-00+-0ROOONH
-R”-NHOO-) [Formula 13, where m is an integer of 5 to 100, R is a hydroxyalkyl group having 1 to 4 carbon atoms or an alicyclic ring having at least two hydroxyalkoxyl groups having 1 to 4 carbon atoms When divalent H3 or +04 is introduced by a group or an aromatic compound, n is an integer from 4 to 6.

The molecular weight of these is preferably from s,ooo to 50QOOO, preferably from IQ, 000 to 200,000. Regarding these polyurethanes, Japanese Patent Application Laid-Open No. 55-12
It is described in Publication No. 2234.

The properties of these binders used in the back layer of the present invention are as follows: 100% modulus is 150 to 9/cW? It is preferable to use the following resin in an amount of 50 to 95% by weight of the total binder amount.

Particularly preferred is a 100% modulus of 120 9/α
2 or less. 100% modulus is 150ky/m”
A representative example of the following resins is Dkai-480.
5 (100% modulus = 50 Yuichi or less), DN-
4806 (100ψ), D N -4850 (120
kg/lar”), N2302 (25-40 disorders/-)
, N2304 (15-30 kg/cy?) (all manufactured by Nippon Polyurethane), etc.

The reason why a resin with a 100% modulus of 150 k4I/- or less is required at 50 to 95 times is to reduce scratches caused by dust with the guide thread, and it is thought that it mainly absorbs the impact of dust. It will be done. At the same time, the back layer needs to be strong, and we designed this by using a fast-curing and hard polyisocyanate to create a well-balanced coating.

In particular, it is desirable to use polyincyanate in an amount of 5 to 40 times the total weight of the binder.

Generally, excessive dispersion force is required for mixing carbon black and a binder, so that the structure of carbon black is usually destroyed. However, if the mixture is not sufficiently mixed, there will be a problem of powder missing in the coating layer. However, the structure is also 7? , MT, FT, and FT equivalent carbon have good miscibility with the binder and do not cause an increase in the surface electrical resistance of the coating film as the dispersion progresses. Further, these carbon blacks can provide a coating film with an appropriate roughness and strength, and can provide a magnetic recording medium with excellent running durability and high S/H.

In addition, the surface roughness of the magnetic surface and pack surface of a magnetic recording medium is determined by focusing on the structure of the back layer.In order to improve durability, the binder, carbon black, and inorganic powder must be well wetted and dense. This is very important. Considering the back layer to be dense, it is necessary that there are few voids or pores in the back layer from the viewpoint of structural strength. If there are many voids, force acts on the puncture layer, and a portion of the void tends to become a core of stress concentration, causing the back layer to break from that location and cause cracks, cracks, etc. In order to prevent such shearing and dusting, the present inventors have studied and found that it is a good idea to use a resin with a 100% modulus of 150 kg/cnt" or less at 50 to 95% by weight of the total binder. Also, carbon fiber such as MT, FT, etc.
The coating film obtained when mixed with black etc. does not become hard,
It has been found that due to its elasticity and good affinity, there is very little powder build-up.

It is desirable to carefully select the type and form of the filler in the back layer so as not to affect the magnetic layer.

Examples of the non-magnetic powder dispersed in the back layer of the present invention include titanium dioxide, graphite, tungsten disulfide, molybdenum disulfide, boron nitride, silicon dioxide, calcium carbonate, aluminum oxide, and iron oxide (Fe2O2).
, magnesium oxide, zinc oxide, calcium oxide, titanium oxide, Merck, bentonite, barium sulfate, carbon fluoride, boron nitride, zeolite, magnesium carbonate,
Examples include barium carbonate, chromium oxide, silicon carbide, silicon terraride, zirconium silicate, benzoguanamine resin, cesium oxide, beryllium oxide, and the like.

These non-magnetic powders improve the surface roughness of the back layer.

Used for purposes such as adjusting porosity and electrical resistance.

The amount of these nonmagnetic powders used is preferably 40 to 300 parts by weight per 100 parts by weight of the binder.

In the present invention, the above-mentioned non-magnetic powder is used,
Particular attention must be paid to size, hardness and form. As for the size, the average particle diameter is (101 to (15
The μ hardness is preferably 2 < Mohs hardness, preferably 2 to 8, especially 3 to 7.
is desirable. Fillers that meet these conditions include:
Specific examples include calcium carbonate, talc, barium sulfate, and graphite.

As mentioned above, the thickness is more preferably 1.0 to 50 .mu.m in order to provide a back layer with less transfer to the magnetic layer so as not to impair the S/N characteristics of the magnetic recording medium.

Furthermore, in order to provide a back layer in which the irregularities of the back layer are not reflected on the magnetic layer, it is preferable to keep the surface roughness of the puncture layer low. As a result of intensive research by the present inventors, we found that when the surface roughness of the magnetic layer is 102μ or less, the surface roughness iRa of the back layer is preferably 0.05μ or less [ It has been found that good results can be obtained by keeping the LO below 4μ.

For this reason, as mentioned above, it is desirable that the size of the filler in the back layer be as small as possible within a range that maintains the winding properties, but at the same time it has been found that the roughness of the back layer has a large effect.

The method for calculating the porosity in the present invention is shown below.

Engraving of the details table (no changes to the contents) That is, a method of injecting mercury (Hg) was used.

Clydre orr, Jr., ``Gowder Technology'' (Clydre orr, Jr.) focused on the property that liquids such as Hg, which have a large wetting angle with objects, do not easily enter pores or voids unless pressure is applied. 'PowderT
technology”), 3, 117 (j 96
The 9-gap characteristics were investigated using the method shown in 9/70).

When mercury is injected into the voids in the gap layer provided in a magnetic recording medium using this method, does the volume into which mercury is injected (void volume) increase as the pressure increases? At a certain pressure (for example, 1000 KP/C11), the volume does not increase and reaches an unreasonable saturation value. This value is calculated as the pore volume of the Notoku layer (
cc).

Based on these facts, the porosity (%) is defined as follows.

・Apparent volume of the Gutsuku layer = Tape width x Length x Thickness of the Tsuku layer 0
OERBA ) mercury intrusion method bosimeter (Merc
Ury Pressure Porosimeter M
OD-200) etc. are used.

When the surface of a magnetic recording medium is roughened, its suitability for high-speed recording generally improves, but the RF specific output S/N deteriorates. Also, porosity i50%
If the thickness is made larger, the suitability for high-speed winding will be improved, but the strength of the coating film itself of the elastic backing layer of the present invention is weak, and the durability during rolling is poor.

Also, if the porosity is lower than 30, the escape of air which makes the magnetic recording medium suitable for high-speed winding will be lost, so air will be drawn in and the winding shape of the magnetic recording medium will be poor. , edge damage occurs due to protrusion.

For this reason, the present invention is characterized by a porosity value of 30% to 50%, and in order to obtain such a porosity,
As mentioned above, a binder and non-magnetic powder containing carbon black of at least 01 to 1 μm are kneaded together with a suitable solvent, and the mixture is coated on the surface of the support opposite to the magnetic layer as a back layer and dried. If desired, it can be obtained by calendering.

Next, examples of the present invention will be described. “Part” in Examples
IIi indicates "parts by weight".

Example 1 The following composition was thoroughly kneaded in a T-ball mill, 20 parts of Ato, Tesmodor T, +-75 (trade name of a polyisocyanate compound manufactured by Inil Co., Ltd.) was added, and the mixture was uniformly mixed and dispersed to form a magnetic paint. Don't create.

(Japan Polyurethane) Graphite (5bet 200 m”/t)
5 parts oleic acid
Part 2 Squalene
15 parts Octyl laurate 3 parts Lauric rR 3 parts Butyl acetate 660 parts Methyl ethyl keto 7 330 parts This magnetic paint was applied to the surface of a polyethylene terephthalate substrate, oriented, dried and calendered.

A pack solution of the following composition was mixed with a ball mill to adjust the crosstalk, and 5 parts of Tesmodur R, +-75 (Polyisocyanate manufactured by Bayer AG) was added, and in order to mix and disperse uniformly, it was applied to the side of the polyester substrate opposite to the magnetic layer. After drying, the film was coated to a thickness of 2 μm and dried.

Niboran-2304 (manufactured by Nippon Polyurethane) 34
Saran resin (manufactured by Dow Chemical) 12
Parts Methyl Ethyl Keto 7 Parts Cyclohexanone This tape was slit into 1 inch width to create a mirror finish using a calendar to prepare a sample No. 1.

Comparative Example 1 The sample of Example 1 was subjected to a linear pressure of 300 kC9/cm,
It was calendered at 100°C to have a porosity of 25 inches.

ζn was designated as sample number 2.

Comparative Example 2 The carbon black in the pack coat composition of Example 10 was replaced with 50,100 parts of Asahi +, and the pack liquid was applied forcefully.

Let's call this sample number 3.

Comparative Example 3 Among the pack liquid composition of Example 1, 1 carbon black was added.
A sample was prepared by replacing 7 parts with the pack solution and designated as sample number 4.

Example 2 A pack liquid was prepared by changing the pack liquid composition of Example 1 to 25 parts of carbon black, and a sample was prepared.
Sample number 5.

Comparative Example 4 Of the pack liquid composition of Example 1, 2 carbon black
A pack solution was prepared by replacing part 011 to prepare a sample, and this was designated as sample number 6.

Table 1 Traveling speed when FiPLAY is shown in Table 1 14.9 tn
/ minute as a reference, winding tests were carried out repeatedly at 20 times, 30 times, 40 times, and 50 times the RKW) hourly speed, and if the degree of winding stage misalignment on the end face was 1 or more times, Δ, 0.1 for less than 1m+ 11 days or more
Less than W was marked as ○. Also, PLAY with R11W at 50x speed
After repeating 100 times, record a 10x2 sine wave signal on the sample with the specified bias at a level 104E lower than the specified input level, and read the maximum value of the output fluctuation of the playback output level.

The combination of carbon black, P/B, and porosity is considered to be a factor that influences each other, but at high speed t'
For a suitability, the rough surface provided by the carbon blank and the voids through which the air escapes during winding are required, and the P/B to maintain the voids S is 40/100 to 300/10.
It turns out that 0 is a good thing.

[Effects of the Invention] It can be seen that when the present invention is used, there is less variation in the audio output due to suitability for high-speed winding.

Agent Patent Attorney (8107) Kiyoshi Sasaki 0 inventors in Ogimachi, Odawara City Hideaki Ko Xie 0 inventors in Ogimachi, Odawara City 1) Tokoro Sakae - 2-1 Ogimachi, Odawara City, Fuji Photo Film Co., Ltd. 2-1 Fuji Photo Film Co., Ltd. 2-1 Fuji Photo Film Co., Ltd. Procedural Amendment April q, 1985 Patent Application No. 262694, filed in 1988 2, Title of invention Magnetic recording medium 3, Make amendments Relationship with the case: Patent applicant name (520) Fuji Photo Film Co., Ltd. Kasumigaseki Building Post Office PO Box No. 49 Eikou Patent Office Telephone (sag-9601 (representative) 6,
Number of inventions increased by amendment 0 7. Specification clearly improved with the type stamp (black) to be amended (page 14) 8. Contents of amendment

Claims (1)

[Claims] A magnetic recording medium comprising a magnetic layer on one side of a non-magnetic support and a packed layer on the other side, wherein the packed layer contains carbon black with an average single particle diameter of 0.1 to 1 μm, and non-magnetic powder and total binder ratio is 300/100 to 40/1
00, and the pack layer has a porosity of 30 to 50%.