JPH03295022A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent traveling property and durability for a long time by specifying the mol.wt. of lubricants used for an uppermost magnetic layer and for a lowest magnetic layer. CONSTITUTION:A lubricant having >=500mol.wt. is added to the uppermost magnetic layer, while a lubricant having a mol.wt. smaller by >=100 than that of the lubricant used for the uppermost layer is added to the lower magnetic layer. The obtd. magnetic recording medium thus formed has excellent electromagnetic conversion characteristics, traveling property and durability. Especially, it shows excellent still durability even in an environment of extremely low temp. of -10 deg.C, and the effect above mentioned can be maintained for a long time.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a magnetic recording medium for high-density recording with a multilayer structure having at least two magnetic layers, and in particular to a magnetic recording medium with excellent running properties and durability. Regarding.

(Prior Art and Section 8) Generally, magnetic recording tapes such as audio tapes and video tapes are prepared by adding ferromagnetic powder to a binder 784. It is manufactured by coating a magnetic coating material dispersed in a magnetic coating material on a non-magnetic support (for example, polyethylene terephthalate (PET) E) and drying it.

In recent years, video tapes have been required to have higher density recording, and magnetic tapes with better electromagnetic conversion characteristics are required. For this reason, it has been attempted to change the magnetic layer from a single-layer structure to a multi-layer structure to improve electromagnetic conversion characteristics. Efforts have been made to improve long wavelength audio characteristics and to improve short wavelength video characteristics by using high coercive force (Hc) ferromagnetic powder in the top magnetic layer.

In this way, when the magnetic layer has a multilayer structure for high-density recording, the thickness loss is generally reduced by using finer grained magnetic material in the topmost magnetic layer and reducing the thickness of the magnetic layer. However, efforts are being made to improve the electromagnetic conversion characteristics. Further, reducing the thickness of the uppermost magnetic layer is advantageous in terms of cost.

However, when the thickness of the uppermost magnetic layer is reduced, the amount of lubricant and the amount of abrasive added to the uppermost layer are regulated, resulting in a disadvantage that the running properties and durability of the magnetic tape are reduced. Furthermore, there is a drawback that the running properties and durability of the magnetic tape are reduced due to a decrease in the strength of the magnetic layer due to the finer particles of the magnetic material used in the uppermost magnetic layer and a smoothing of the surface of the magnetic layer.

In addition, a bank coat layer is provided on the side opposite to the magnetic layer side of the support in order to improve running properties, prevent static electricity, and ensure light transmittance. There is a drawback that the lubricant in the uppermost layer of the magnetic layer is transferred to the hack layer due to contact while the tape is being wound up, reducing the amount of lubricant in the uppermost layer of the magnetic layer and deteriorating durability.

As a countermeasure for these drawbacks, for example, Japanese Patent Application Laid-Open No. 63-944
Publication No. 31 states that runnability and durability can be improved by making the amount of lubricant used in the magnetic layer smaller in the uppermost layer than in the lower layer. However, the results were not completely satisfactory in terms of both runnability and durability, and further improvements were desired.

Furthermore, among the usage conditions of a videotape, durability of the magnetic layer (still durability) is particularly required when producing still images in a still state, but the multilayer structure reduces the film strength of the uppermost N magnetic layer. This still durability was a particular problem in video tapes, and improvements were desired.

In Japanese Patent Application No. 63-227376, the lubricant used in the magnetic layer is a fatty acid ester, and the uppermost layer and lower layer each contain a specific fatty acid ester having a different structure (in particular, the uppermost layer contains an alcohol having an alkyl ether moiety and a fatty acid). It is said that the use of esters) can improve both running performance and still durability.

It is true that this method can considerably improve still durability, but at very low temperatures such as -10°C;
Still durability in the field was still insufficient, and improvements were desired.

In other words, recently, as consumer VTRs have become smaller and more popular, and their use outdoors has increased, the conditions for using video tapes have also changed over a wide range of environmental conditions, including use at low temperatures and use at high temperatures. has become required. Therefore, in addition to excellent running performance and durability under a wide range of environmental conditions, excellent still durability is also required.

However, as mentioned above, when multilayering is used to improve electromagnetic conversion characteristics and the thickness of the top layer of the magnetic layer is thinned, the amount of lubricant in the top layer is regulated, and especially at low temperatures, the amount of lubricant supplied from the bottom layer is also limited. As a result, still durability tends to deteriorate. In particular, the still durability deteriorates significantly under harsh environmental conditions such as -10°C, and improvement thereof has been desired.

Therefore, an object of the present invention is to provide a novel magnetic recording medium having a plurality of magnetic layers, which has excellent electromagnetic conversion characteristics, and has improved running properties and durability.

Another object of the present invention is to provide a new magnetic recording medium with improved still durability at low temperatures.

Furthermore, another object of the present invention is to provide a novel magnetic recording medium that has excellent running properties and durability for a long period of time.

(Means for Solving the Problems) The present inventors have discovered a product that has excellent electromagnetic conversion characteristics, has excellent running properties,
As a result of extensive research into magnetic recording media with excellent durability and further excellent still durability at low temperatures, it was discovered that these objectives could be achieved by the following magnetic recording media, and the present invention was completed.

That is, in a magnetic recording medium having at least two or more magnetic layers mainly containing ferromagnetic powder and a binder on a non-magnetic support, the uppermost magnetic layer has a molecular weight of 500.
This magnetic recording medium is characterized in that it contains the lubricant described above, and the lower magnetic layer contains a lubricant whose molecular weight is 100 or more smaller than the molecular weight of the uppermost layer lubricant.

As described above, in conventional magnetic recording media, the magnetic layers have a multilayer structure and the thickness of the uppermost magnetic layer is thinned in order to improve electromagnetic conversion characteristics.

Furthermore, additives such as lubricants and abrasives are used in the magnetic layer to improve running performance and durability, but if the amount of additives is increased to improve these effects, the electromagnetic characteristics described above deteriorate. Therefore, it is necessary to use the additive in the uppermost magnetic layer within a range that does not impair the electromagnetic conversion characteristics. However, as long as the additives are used within a range that does not impair the electromagnetic conversion characteristics, no significant improvement in running durability could be expected. Therefore, it has been difficult to achieve both excellent electromagnetic conversion characteristics and excellent running durability with conventional multilayer magnetic recording media.

As a result of intensive studies by the present inventors, it was found that the amount of lubricant present on the surface has a large effect as an important physical property in order to obtain a magnetic recording medium with a multilayer structure that can achieve both running durability and electromagnetic conversion characteristics. I understand.

Generally speaking, the larger the amount of lubricant added, the larger the amount of lubricant present on the surface, but as mentioned above, if the amount added is large, the electromagnetic characteristics may be adversely affected. In addition, if the amount of addition is increased, the magnetic layer becomes plasticized, resulting in a decrease in film strength.

For this reason, we considered how to reduce the amount of lubricant added to optimize the amount present on the surface, and found that we could control the amount of lubricant present on the surface by selecting the molecular weight of the lubricant used in the multilayer magnetic layer. They discovered what could be done and completed the present invention. Specifically, by selecting the molecular weight of the lubricant used for the uppermost magnetic layer to be 500 or more, and the molecular weight of the lubricant used for the lower magnetic layer so that it is 100 or more smaller than the molecular weight of the lubricant for the uppermost layer. I was able to achieve it.

If the magnetic layer has a single-layer structure, the amount of surface lubricant can be controlled to some extent by the amount of lubricant added, but if the magnetic layer has a multi-layer structure, the amount of surface lubricant cannot be controlled just by adding the amounts of the upper and lower layers of the magnetic layer. Control■Cannot be done. This is because the composition of the upper and lower layers of a typical sheet is different, and in particular, the uppermost magnetic layer uses finer particles of magnetic material than the lower layer and uses as much non-magnetic powder as possible to place emphasis on electromagnetic conversion characteristics. In most cases, the composition is different from the lower layer because the body is reduced. When the compositions differ in this way, the adsorption behavior of the lubricant to the magnetic material and the non-magnetic material differs, and therefore, there is a large difference in the behavior of the lubricant in the film between the two layers. For this reason, the amount present on the surface cannot be controlled by the amount added in a single layer as in the case of a single layer. As a result of investigation into a method for controlling the amount of surface lubricant in a magnetic recording medium having a plurality of magnetic layers, the molecular weight of the lubricant, which is a feature of the present invention, was arrived at.

The following may be the reason why the amount of surface lubrication ifQ was able to be controlled by the molecular weight of the lubricant. In other words, by using a lubricant with a relatively large molecular weight in the top layer, even a small amount can improve durability such as still durability, prevent deterioration of the film quality and electromagnetic conversion characteristics of the top magnetic layer, and also prevent the lower layer from deteriorating the film quality and electromagnetic conversion characteristics. It is presumed that by adding a lubricant with a relatively small molecular weight that easily migrates to the top layer, it was possible to maintain the running durability effect by compensating for the lubricant consumption in the top layer.

It has also been found that lubricants with a relatively large molecular weight have poor sliding properties within the deck, and that a lubricant with a relatively small molecular weight is required in order to obtain excellent running properties.

As described above, in the magnetic layer B of the multilayer structure, the molecular weights of the lubricants used in the uppermost layer and the lower layer are selected as in the present invention, and the film quality and electromagnetic conversion characteristics of the magnetic layer are determined to be the same. However, it was possible to obtain a magnetic recording medium with excellent durability such as still durability and running performance.

The present invention will be explained in detail below.

The magnetic recording medium of the present invention has at least two or more multilayered magnetic layers. The plurality of magnetic layers may have a two-layer structure of an upper layer and a lower layer, a three-layer structure of an upper layer, a middle layer, and a lower layer, or a multilayer structure of three or more layers.

In the multilayered magnetic layer of the present invention, the magnetic layer farthest from the support is hereinafter referred to as the "top magnetic layer" or "top layer", and the magnetic layer closer to the support than the top magnetic layer All are collectively referred to as the "lower magnetic layer" or "lower layer." In particular, the lower magnetic layer closest to the support is referred to as the "lowest magnetic layer" or "bottom layer."

In the magnetic recording medium of the present invention, a nonmagnetic intermediate layer may be provided between the plurality of magnetic layers. Furthermore, an undercoat layer may be provided between the lowermost magnetic layer and the support.

The uppermost magnetic layer of the present invention contains a lubricant having a molecular weight of 500 or more, more preferably a lubricant having a molecular weight of 500 to 700.

In the present invention, the molecular weight used for the uppermost magnetic layer is 5.
The lubricant having a molecular weight of 500 or more is preferably a fatty acid ester having a molecular weight of 500 or more.

Specific examples of fatty acid esters with a molecular weight of 500 or more used in the uppermost magnetic layer include the following.

Esul Molecule 1 Oleyl Balmitate 506 Isocetyl Isostearate 508 Isocetyl Stearate
508 Oleyl oleate
532 Oleyl stearate
534 Oleyl isostearate
534 Stearyl isostearate
536 Isostearyl isostearate 536
Eicosenyl isostearate 590 Isotetracosyl stearate 620 Isotetracosyl behenate 670 Diglyceride oleate 648 In the present invention, the lower magnetic layer has a molecular weight 100% lower than the molecular weight of the lubricant used for the uppermost layer.
Contains a lubricant with a low molecular weight. In the present invention, it is essential that the molecular weight of the lubricant used in the lower layer is smaller than the molecular weight of the lubricant used in the uppermost layer, and the difference therebetween is 100 or more; however, the molecular weight of the lubricant used in the lower layer is is not particularly limited, and may be 500 or more. For example, when a lubricant with a molecular weight of 600 or more is used in the uppermost layer, a lubricant with a molecular weight of 500 or more may be used as long as the difference is at least 100 or more.

However, since the lubricant easily migrates from the lower layer to the uppermost layer, the molecular weight of the lubricant used in the lower layer is preferably relatively small, more preferably 500 or less, and even more preferably 450 or less.

Most preferably it is 250-400.

In the present invention, the lower magnetic layer is preferably the lowermost magnetic layer.

Examples of these lubricants used in the lower magnetic layer include fatty acid esters, fatty acids, fatty acid amides, etc., and fatty acid esters are more preferred.

Specific examples of fatty acid esters with a molecular weight of 500 or less that are preferably used in the lower magnetic layer include the following.

Esul Molecule l Isopropyl myristate 270 Isobutyl myristate Butyl oleate Butyl stearate Butyl myristate Isooctyl stearate 5ec-Butyl stearate Isoamyl stearate Amyl palmitate Isooctyl palmitate Octyl stearate Hequinrustearate Butyl stearin Butquin acid ethyl stearate isooctyl stearate octyl palmitate decyl stearate denur laurate isocetyl stearate isodenol stearate bunal diethylene glycol 428 oleyl laurate 450 isotridecyl stearate 452 isocetyl myristate 452 stearyl laurate
452 Butyltriethylene glycol stearate 474 Isocetyl valmitate 480 In a magnetic layer having a multilayer structure, the amount of lubricant added to the top layer has a large effect on running durability and still durability. Therefore, in the uppermost magnetic layer of the present invention, the amount of lubricant added is preferably 5 parts by weight or less per 100 parts by weight of the ferromagnetic powder.

Particularly preferably 0.5 to 4 parts by weight.

The amount of lubricant added in the lower layer is not particularly limited;
The usual amount of lubricant added to the lower magnetic layer of a multilayer structure can also be applied to the present invention. For example, the amount is 0.1 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder of the lower magnetic layer.

In the uppermost magnetic layer of the present invention, a lubricant such as a fatty acid or a fatty acid amide may be used in combination with the fatty acid ester having a molecular weight of 500 or more, within a range that does not impair the effects of the present invention.

Examples of ferromagnetic powders used in the plurality of magnetic layers include ferromagnetic iron oxide powder, cobalt-coated ferromagnetic iron oxide powder, ferromagnetic chromium dioxide fine powder, ferromagnetic metal powder, and barium ferrite.

The ferromagnetic powder is usually acicular, and the acicular ratio is preferably 2/1 to 20/1 (particularly preferably 5/1).
~20/1) and has an average length (major axis length) of 0.1 to 2.0 tm.

The shape of the ferromagnetic powder is not limited to a needle shape, and commonly used shapes such as a rice grain shape and a plate shape can be used.

As the ferromagnetic powder, use a ferromagnetic powder with a long axis length of 0.3p or less and a crystallite size of 300 Å or less by chi-ray diffraction (preferably a long axis length of 0.2- or less and a crystallite size of 200 Å or less). It is particularly preferable.

When using ferromagnetic metal powder, 75% by weight or more (preferably 80% by weight or more) of the metal content of the ferromagnetic metal powder is a ferromagnetic metal or alloy (e.g., Fe, Co,
Ni, Fe-Co, Fe Ni, Co
Ni, Fe-Co-N1) whose major axis is 1.0
- The following particles are preferred.

The coercive force (Hc) of these ferromagnetic powders is 350 to 5000
0e is preferable, 600 to 25,000e is more preferable, and 800 to 20,000e is particularly preferable. If it is smaller than 3500e, the output in the short wavelength range will decrease, and if it is smaller than 50000e
If it is larger than this, normal hent recording cannot be performed, which is not preferable.

In the multilayered magnetic layer of the present invention, the ferromagnetic powder used for the uppermost magnetic layer has a specific surface area of 30 rd/g or more and a crystallite size of 300 Å or less as determined by the BET method.
Ferromagnetic powder having a coercive force of 600 to 10,000 e is preferred. In addition, the ferromagnetic powder used for the lower magnetic layer is as follows:
The specific surface area measured by BET method is 40 rI'r/g or less, the crystallite size is 210 Å or more, and the coercive force is 500 to 800.
0e ferromagnetic powder is preferred.

Also, the binder used in the magnetic layer has a softening temperature of 150
°C or less, the average molecular weight is 10,000 to 300,000, and the degree of polymerization is about 50 to 1,000, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid Ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, meccrylic acid ester styrene copolymer, urethane elastomer , nylon-silicon resin, nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (e.g., cellulose acetate butyrate, cellulose diacetate) , cellulose triacetate, cellulose propylene chloride, nitrocellulose, etc.), styrene-butanoene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and these A mixture of etc. is used.

Particularly preferred is one 503M group in the molecule, -COOM
Vinyl chloride copolymers, polyurethane resins, and polyester resins having the following are preferred. As the functional group, a hydrophilic group is particularly preferred.

Here, M represents hydrogen or an alkali metal (Li, Na, K, etc.), and -' represents hydrogen or an alkali metal (Li, Na, K, etc.).
K, etc.) or a hydrocarbon group.

Regarding resins having these functional groups, Japanese Patent Application Laid-Open No. 59-8
No. 127, Kaikai No. 57-44227, Kaikai No. 57-924
No. 22, No. 57-92423, Inter-office No. 59-4030
Those listed in No. 2 etc. can be used.

A vinyl chloride copolymer containing an epoxy group in addition to the above-mentioned functional groups can also be used (JP-A-62-146432).

A preferred combination of binders is a combination of a vinyl chloride copolymer containing the above-mentioned functional groups and polyurethane. Examples of polyurethane include polyester polyurethane, polyether polyurethane, polyester ether polyurethane, polycaprolactone polyurethane,
Polycarbonate polyurethanes are preferred, particularly polyurethanes having the aforementioned functional groups.

Specific examples of hydrophilic group-containing binders include -COOH group-containing polyurethane (TIM-3005 manufactured by Sanyo Chemical Co., Ltd.), S
O3Na-containing polyurethane (FIR-83 manufactured by Toyobo ■)
00, UR-8600), -COOH group-containing vinyl chloride vinyl acetate copolymer (400X110 manufactured by Nippon Zeon ■)
A), -5O3Na-containing polyester (Vylon 530, manufactured by Toyobo Co., Ltd.), SO, Na-containing vinyl chloride/vinyl acetate copolymer (MR-110, manufactured by Nippon Zeon ■), and the like. The content of hydrophilic groups is 1-10000 equivalents/lo6
A range of gr is preferred.

Further, the molecular weight is preferably 3,000 to 200,000.

The above thermoplastic resins are preferably used in combination with a curing agent.

As the curing agent, epoxypolyamide, epoxypolycarboxylic acid, polyimine, and polyisonene 1- are used. Polyisonoanate is particularly preferred, with -11
, tri-, and tetrason-amorphous selected from aliphatic, aromatic, or alicyclic compounds having two or more of , c, and 0 groups. These isonor 2-ates include ethanediiisonoanate, butane diisocyanate,
Hexane diisono-7-ate, 2.2-dimethylpentanedi-iso7-ate, 2.2.4-)limethylbentane-iso-7-ate, decane-iso-7-ate, ωω-diisocyanate 1-- 1 3-dimethylhenthol, ω,
ω-diisocyasutoh-12-methylnochlorohexane,
ω5 ω'-diisonoanato 1,4-diethylhenzole, ω ω diisonoar 7-to 1,5-trimethylnaphthalene, ω, ω'-diisonoacea 2-tone n-propylbiphenyl/mu 1, 3-phenylenediisonore 2-
F, amethylhenzole-2,4-diisonoanate, 1,3-methylhenzole-26-physosoanoate, naphthalene-14-diisocyanate, 1,1'-nonaphthyl-2,2'noisonoanate, biphenyl-2
4'-diisocyanate, 3,3'-dimethylhyphenyl 4.4-diisonoanate, diphenylmethane 4.
4'-diisonoanate, 2,2'-tumethyldiphenylmethane-4,4'-diisonoanate, 3,3'-
Dimethoxydiphenylmethane 4,4'-diisonoanate, 4,4'-diethoquinonophenylmethane-4,4
'-diisono-7-ate, 1-methylhenzole-2,4
6-Doliisonoanate, 1.3.5-trimethylhenthol-2,4,6-triisonoanate, diphenylmethane-2,4,4'-triisonoanate, triphenylmethane-4,4' , 4″-triisonoanate, tolylene diisonoanate, 1,5 naphthylene diisonoanate, etc.;
or an addition product of these isonorate 7-ates and a divalent or trivalent polyalcohol. These are, for example, addition products of trimethylfiroban and tolylene diisonate or xamethylene diisonate.

These curing agents are used in an amount of 10 to 6 parts by weight per 10 parts by weight of the binder.
It is used in an amount within the range of 0 parts by weight.

Commercially available trade names of these polyisocyanates include Coronate and Coronate HL.

Coronate 2030, Coronate 2031, Mirio Spear
To Ml+, Millionate MTL (manufactured by Nippon Polyurethane ■), Take name - To D-102, Take non-) D-110, Take Daiichi To D-200, Takenate D-202 (manufactured by Takeda Pharmaceutical ■), Desmodor , Desmodule IL, Desmodule N, Desmodule Anal (manufactured by Sumitomo Bayer)
These can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, Evokin resin,
Polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and These include mixtures of diisocyanate prepolymers, mixtures of voluster polyol and polyisonoanate, urea formaldehyde resins, mixtures of low molecular weight glycol/high molecular weight diol/triphenylmethane triisocyanate, polyamine resins, and mixtures thereof.

These binders may be used alone or in combination;
Other additives may be added. The mixing ratio of the ferromagnetic fine powder and the binder is in the range of 5 to 300 parts by weight per 100 parts by weight of the ferromagnetic fine powder.

The binders for the upper and lower magnetic layers preferably have good compatibility. If the compatibility is poor, the adhesion between the upper layer and the lower layer may deteriorate, or the interface may be disturbed, resulting in poor surface properties, which is not preferable.

The coating thickness (after drying) of the uppermost magnetic layer is preferably 2.5 mm or less, more preferably 0.1 to 2.0 mm, more preferably 0.1 to 1 mm.
．． 0 prisoners are particularly preferred.

If the coating thickness of the top layer exceeds 2.51II11, the output in the short wavelength range will decrease due to thickness loss, which is not preferable.

Moreover, if it is less than 0.1-, the effect of multilayering will be small,
This is not preferable because the noise improvement effect is lost.

The coating thickness of the lower magnetic layer (after drying) is thicker than the coating thickness of the uppermost magnetic layer, preferably 0.5- or more, and particularly preferably 14 or more.

Examples of materials forming the non-magnetic support include Bossester resins, polyolefin resins, cellulose derivatives,
Examples include polycarbonate resins, polyimide resins, and polyamideimide resins. In addition, depending on the purpose, non-magnetic metals such as aluminum, copper, tin and zinc, or non-magnetic metals containing these, plastics coated with metals such as aluminum, and polyolefins are coated or laminated. Paper materials such as paper can also be used. There are no particular restrictions on the shape of the nonmagnetic support, but notebook-shaped ones are usually used. However, the nonmagnetic support may be in the form of a film, tape, disk, cart, or matram.

When a notebook-shaped non-magnetic support is used, it generally has a thickness within the range of 5 to 100 mm.

Abrasives 7" include alumina, silicon carbide, titanium oxide,
Materials having a Mohs hardness of 5 or more, such as magnoum oxide, silicon nitride, silicon oxide, and zirconia, can be used, and the particle size is preferably 10 or less, particularly preferably 05 or less.

In the magnetic layer of the present invention, other additives may include, for example,
Dispersants, antistatic side (carbon bra, surfactant side, etc.), antioxidants, etc. can be used.

The specific compounds and amounts of these additives used in ordinary magnetic recording media can also be applied to the present invention.

On the other hand, a bank coat layer may be formed on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is provided.

There are no particular restrictions on the binder used to form the bank layer (including known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof that have been conventionally used as binders for magnetic recording media). can be used.

The thermoplastic resin has a softening temperature of 150°C or less,
Those with an average molecular weight of about 10,000 to 300,000, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic ester Vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-silicon resin , nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (e.g., cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose- propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amine resins, and various synthetic rubber-based thermoplastic resins.

In addition, the above-mentioned thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and the molecular weight becomes extremely large when heated after coating and drying, such as phenol resin, Phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, Mixtures of methacrylate copolymers and neutral prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate, polyamine resins, and these Examples include mixtures.

Furthermore, these binders may have other functional groups known per se, among which -
503M, -3OZM, -COOM, -NO3, -N'
At least one functional group selected from the group consisting of R, OH, phosphoric acid group, and phosphoric ester group (where M represents a hydrogen atom or an alkali metal atom, and R represents a lower alkyl group having IO or less carbon atoms) ) is preferred. These functional groups contain IXl0-'~l per gram of resin.
It is preferable that the amount of Xl0-'' equivalent is contained.

The above-mentioned binder preferably has a glass transition temperature Tg of 40°C or higher, particularly 60°C or higher.

The above binder further includes a compound having two or more isocyanate groups! III! 1 (polyisocyanate) may be contained. As such polyisocyanate,
For example, tolylene diisocyanate, 4,4'-diphenylmethane diisonoanate, hexamethylene diisocyanate, quinlylene diisocyanate, naphthylene diisocyanate,
Isocyanates such as 15-diisonoabbut, O-)/raynone diisonoate, isophorone diisonoate, triphenylmethane triisocyanate, reaction products of these isocyanates and polyalcohols, and , and polyisonoanates produced by condensation of these isocyanates. The above-mentioned polyisocyanates are, for example, from Nippon Polyurethane ■,
Coro Daiichi Toshi, Corobut HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate M
From Takeda Pharmaceutical ■, Takenate D-102, Takenate D-11ON, Takenate D-200, Takenate D-202, from Resident Bayer ■, Desmodule Upper 1 Desmono Ale IL, Desmodule N, Desmodule H It is sold under product names such as.

In the present invention, an inorganic powder is used in the hack layer together with a binder. Examples of the inorganic powder include abrasives, carbon black, calcium carbonate, and the like described in the magnetic layer.
Examples include molybdenum disulfide.

The blending ratio of the binder and the inorganic powder in the hack layer of the magnetic recording medium of the present invention is II! Preferably, the amount of binder is 40 to 200 parts by weight, particularly 50 to 130 parts by weight, per 100 parts by weight of powder. If the blending ratio of the binder is less than the above range, the running durability of the magnetic recording medium will deteriorate, and if it is more than the above range, the packing density of the inorganic V powder will be low, so that the bank layer of the magnetic recording medium There is a tendency that the desired surface electrical resistance cannot be obtained or that the coefficient of friction tends to increase.

The thickness of the hack layer is preferably 1.5 or less, more preferably 0.5 to 1.0. The thickness of the back layer is 1.
51! If it exceeds m, the running properties of the tape will become unstable.

Methods for forming a magnetic layer on a nonmagnetic support are already well known, and the magnetic layer of the magnetic recording medium of the present invention can also be formed on the surface of the support by basically the same procedure.

That is, the ferromagnetic powder, binder, lubricant, and optionally other additives and organic solvent are mixed and dispersed to prepare a magnetic paint.

A magnetic layer is formed by applying this magnetic paint to the surface of the support and then drying and curing it.

Here, since the magnetic recording medium of the present invention has at least two or more magnetic layers, in order to form these plural magnetic layers on a non-magnetic support, a plurality of magnetic paints are applied in a wet state in layers. In the present invention, a method of applying magnetic paint in multiple layers in a wet state is preferred.
In other words, the wet-on-wet coating method is a so-called sequential coating method in which one layer is first coated and then the next layer is coated on top of it as soon as possible in a wet state, and the other is a method in which multiple layers are simultaneously coated using an extrusion coating method. It refers to the method etc.

When preparing the above-mentioned magnetic paint, conventional techniques known per se can be used for the solvent, the dispersion kneading method and device, the method and device for applying the coating liquid to the support, and the like.

A magnetic layer coated on a non-magnetic support is usually subjected to a treatment for orienting the ferromagnetic powder in the magnetic layer, that is, a magnetic field orientation treatment, and then dried. Furthermore, after the resin component is cured to form a cured product, usually by heating or the like, a surface smoothing treatment can be performed if desired. The magnetic recording medium that has been subjected to surface smoothing treatment is then subjected to blade treatment if desired, and then cut into a predetermined shape.

The method of forming a hack layer on the surface of a nonmagnetic support opposite to the surface on which the magnetic layer is formed is already known, and the bank layer of the magnetic recording medium of the present invention can also be formed on the surface of the support by basically the same operation. can do. That is, for example, a coating solution is prepared in which the inorganic powder, the binder component, and other optional additives are dispersed or dissolved in an organic solvent, and this coating solution is applied to the surface of the support, and then dried. A hack layer is formed by evaporating the solvent and curing the binder component.

When preparing the above-mentioned coating liquid, conventional techniques known per se can be used for the organic 7 medium, the dispersion kneading method and apparatus, the method and apparatus for applying the coating liquid to the support, and the like.

Incidentally, either the attachment of the magnetic layer or the attachment of the hack layer to the support may be carried out first, or they may be carried out simultaneously.

(Effects of the Invention) According to the present invention, the magnetic layer has a multilayer structure, a lubricant having a molecular weight of 500 or more is added to the uppermost magnetic layer, and a lubricant having a molecular weight of 100 or more than the uppermost layer lubricant is added to the lower magnetic layer. Magnetic recording media to which a small amount of lubricant is added have extremely superior electromagnetic characteristics, runnability, and durability compared to conventional magnetic recording media with single-layer or multi-layer structures. In particular, -1
It showed excellent still durability even under extremely low environmental conditions of 0°C, and showed the remarkable advantage of being able to maintain these effects for a long period of time.

(Examples) Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to the following Examples. In the following examples, "parts" indicate "parts by weight."

[Formulation for lower layer]

Ferromagnetic powder ioo part (Co
-Doped 7 FeOx (x = 1.45) major axis length 0
．． 3-1 Crystallite size 400, He 6000e) Vinyl chloride/vinyl acetate/vinyl alcohol 92:2:6 copolymer 15 parts (degree of polymerization 400) Polyester polyurethane (NM=50,000) 5 parts Desmodur L-75 6.7 parts (75% solution of isotourmy 4-based curing agent) Conductive carbon (particle size 7 mμ) 2 parts Lubricant
(See Table-1) Methyl ethyl ketone
250 parts (formulation for top layer) 100 parts of ferromagnetic powder (C
o-doped T-FeO8 (x = 1.45) major axis length 0.
2-1 Crystallite size 300 people, Hc 8500e) Vinyl chloride/vinyl acetate/vinyl alcohol 92:2:6 copolymer 15 parts (degree of polymerization 400) Polyester polyurethane (NM=50,000) 5 parts Desmodur L-75 6.7 parts (75% solution of isocyanate curing agent) Conductive carbon (particle size 7 mμ) 0.2 parts Lubricant (see Table 1) α-Alumina 2 parts Methyl ethyl ketone 250 parts [Hack layer formulation] Carbon black 100 parts Nitrocellulose 25 parts Urethane resin and Tuboran 2301, 15 parts manufactured by Nippon Polyurethane (trade name) Polyisonoanate (made by Coro Daiichi, 40 parts manufactured by Nippon Polyurethane (trade name)) Methyl ethyl ketone 480 parts The above formulation for the lower layer The respective compositions of the formulation for the uppermost layer were dispersed and kneaded to prepare respective magnetic paints.

Using an extrusion type coating method with two slits in one head, the bottom layer was 411 m and the top layer was 1.5 m.
After oriented and drying the magnetic layer, the above bank layer was applied, dried and calendered, and each section was slit to a width of 2 inches. (Sample Nos. 1 to 18) were obtained.

The performance of each videotape sample produced was evaluated by the following method.

■Magnetic conversion characteristics (Y-S/N, C-5/N) Y-5/
N is the S/N ratio at 5 MHz, manufactured by Fuji Photo Film 5)
IG tape was compared in OdB.

C-3/N was compared based on the S/N ratio at 0.75 MHz and 5FIG tape manufactured by Fuji Photo Film as OdB.

Measuring device: HR-0555 video deck manufactured by Victor KK Japan was used.

■Running durability T-120 (120
A videotape of 1 minute length) was run on a VH3 type VTR, and a test was repeated to run the entire length, and the number of runs until the prerecorded signal no longer appeared on the monitor due to head clogging was measured.

■Still durability - Durability was examined in steel mode under the condition of 10°C.

■Friction coefficient Under environmental conditions of 43°C and 170%RH, the magnetic layer surface of the obtained videotape and the stainless steel pole were connected under 50g of tension (
TI), and the tension (T2) required to run the videotape at a speed of 3.3 cm/sec was measured under these conditions by making contact at a wrapping angle of 180°. Based on this measured value, the friction coefficient μ of the videotape was determined using the following calculation formula.

μ=1/π・An(Tz/T+) The friction coefficient measured in this way is called the initial friction coefficient μm.

Further, using a video tape that had been run 100 times using a VH5 type video tape recorder, the coefficient of friction μ was determined in the same manner as above. This is called the repeated friction coefficient μ2.

The results are shown in Table-2.

From the results in Table 2, the video tapes obtained in each example show superior performance in electromagnetic conversion characteristics, running durability, and still durability compared to the video tapes obtained in each comparative example. That is clear.

177-

Claims (4)

[Claims] (1) In a magnetic recording medium having at least two or more magnetic layers mainly containing ferromagnetic powder and a binder on a non-magnetic support, the uppermost magnetic layer contains a lubricant with a molecular weight of 500 or more. , and a magnetic recording medium characterized in that the lower magnetic layer contains a lubricant whose molecular weight is 100 or more smaller than the molecular weight of the uppermost layer lubricant. (2) The magnetic recording medium according to claim 1, wherein the amount of lubricant added to the uppermost magnetic layer is 5 parts by weight or less per 100 parts by weight of the ferromagnetic powder. (3) The magnetic recording medium according to claim 1 or 2, wherein the lubricant in the uppermost layer is a fatty acid ester. (4) The magnetic recording medium according to claim 1, wherein the lower magnetic layer is a lowermost magnetic layer.