JPH1139637A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which hardly causes contamination of calender rolls in a calendering process, and which has high productivity, excellent electromagnetic conversion characteristics and durability. SOLUTION: This medium consists of a supporting body and plural coating films containing vinyl chloride copolymers formed on at least one surface of the supporting body. At least one layer of the plural coating films is a magnetic layer. The vinyl chloride copolymers contain hydroxyl groups. The content Xt (wt.%) of hydroxyl groups in the vinyl chloride copolymers in the outermost coating layer among the plural coating films most distant from the supporting body, and the content Xb (wt.%) of hydroxyl groups in the vinyl chloride copolymers in a coating film nearer to the supporting body than the outermost coating film satisfy the relation of 0.1<Xb<=Xt<1.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art For example, a coating type magnetic recording medium such as a magnetic tape is prepared by kneading a magnetic paint obtained by kneading a magnetic powder, a binder, a curing agent, various other additives and a solvent with a base film such as a polyester film. In general, the support has a magnetic layer formed by coating and curing on one surface side. If necessary, a coating material obtained by kneading carbon black, a binder, other various additives and a solvent is applied to the other surface of the support (the side opposite to the side on which the magnetic layer is provided). By applying, a so-called back layer is provided. Further, there is also known a structure in which a so-called intermediate layer (undercoat layer) is provided between the magnetic layer and the support.

Various proposals have been made for components of the magnetic layer and the intermediate layer in these magnetic recording media since ancient times. In particular, many proposals have been made for a binder which is a component of the magnetic layer and the intermediate layer. Among them, proposals using a vinyl chloride resin as a binder are disclosed in JP-A-59-40320 and JP-A-59-81.
No. 27, JP-A-60-121514, JP-A-2-209972, JP-A-5-62154, JP-A-8-339527, and the like.

[0004]

However, even a magnetic recording medium using the above-mentioned vinyl chloride resin as a binder for a coating film has not been satisfactory in electromagnetic conversion characteristics and durability. In addition, there was a problem that the calendar roll was stained during the calendering process and the productivity was low.

Accordingly, a first object of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and durability. A second problem to be solved by the present invention is to provide a magnetic recording medium having high productivity, in which a calendar roll is unlikely to be stained during calendar processing.

[0006]

The first and second objects are to provide a support and a plurality of coating films containing a vinyl chloride copolymer laminated on at least one surface of the support. In a magnetic recording medium comprising, at least one of the plurality of coating films is a magnetic layer, the vinyl chloride copolymer is a vinyl chloride copolymer having a hydroxyl group,
Among the plurality of coating films, the hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the outermost coating film on the farthest side from the support, and the support from the outermost coating film And the hydroxyl group content Xb (wt%) in the vinyl chloride copolymer in the coating film on the side close to is 0.1 <Xb ≦
The problem is solved by a magnetic recording medium characterized by satisfying Xt <1.5.

[0007] In particular, the plurality of coating films can be solved by a magnetic recording medium which is cured by using an isocyanate-based curing agent. That is, as a binder of a coating film in a coating type magnetic recording medium in which two or more layers are laminated, the hydroxyl group content Xt (wt) in the vinyl chloride copolymer in the outermost coating film farthest from the support is considered. %) And the hydroxyl group content Xb (wt%) in the vinyl chloride copolymer in the coating film closer to the support than the outermost coating film,
By selecting a material that satisfies 0.1 <Xb ≦ Xt <1.5, the durability of the coating film becomes high, the dropout hardly occurs, and the electromagnetic conversion characteristics are improved.

In the present invention, the values of the hydroxyl group contents Xt and Xb in the vinyl chloride-based copolymer are determined by dissolving 10 g of the vinyl chloride-based copolymer in 50 ml of tetrahydrofuran and using this solution to obtain a 40 μm-thick film. A film was prepared and the hydroxyl group contents Xt and Xb (wt%) were determined from the absorption of methylene and OH using an infrared absorption spectrometer.

In the present invention, the thickness of the outermost coating film is 0.05 to 0.5 μm (a more preferred lower limit is 0.1 μm).
m. A more preferred upper limit is 0.3 μm, and a still more preferred upper limit is 0.2 μm. The thickness of the coating on the side closer to the support than the outermost coating is 0.5 to 3.0 μm (particularly,
1.0 to 2.0 μm). That is,
The thickness of the outermost coating film using a vinyl chloride copolymer having a hydroxyl group content of a specific value Xt as a binder or a vinyl chloride copolymer having a hydroxyl group content of a specific value Xb as a binder By setting the thickness of the coating film below the outermost layer used as described above, the rigidity becomes favorable, the durability is further improved, and the electromagnetic conversion characteristics are further improved.

The proportion of the vinyl chloride copolymer in the coating film is 5 to 20% by weight, and the curing agent used for curing the coating film is 1 to 100 parts by weight of the vinyl chloride copolymer.
It is preferably from 0 to 15 parts by weight. By doing so, the rigidity becomes favorable, the durability is further improved, and the electromagnetic conversion characteristics are further improved. Particularly, the curing agent used for curing the coating film is the vinyl chloride copolymer 10
In addition to 5 to 40 parts by weight per 0 parts by weight, the proportion Z wt% of the aliphatic isocyanate curing agent Z and the proportion Y wt% of the aromatic isocyanate curing agent Y are Y ≦ 1.3Z. By satisfying them, the durability is further improved and the electromagnetic conversion characteristics are further improved. In addition, during calendering, stains on the calender roll were further reduced.

The content of alumina contained in each coating film is preferably 1 to 20 wt% (particularly, 5 to 15 wt%). That is, when the content of alumina is 1 to 20
This is because the effect of improving the electromagnetic conversion characteristics and the durability is further enhanced when the content is set to wt%. The magnetic layer is preferably in the outermost layer farthest from the support. By doing so, spacing loss with the magnetic head can be reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A magnetic recording medium according to the present invention comprises a support, and a plurality of coating films containing a vinyl chloride copolymer laminated on at least one surface of the support. In the magnetic recording medium, at least one of the plurality of coating films is a magnetic layer, and the vinyl chloride-based copolymer is a vinyl chloride-based copolymer having a hydroxyl group. The hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the outermost layer coating film furthest from the support and the coating film closer to the support than the outermost coating film And the hydroxyl group content Xb (wt%) in the vinyl chloride copolymer is 0.1 <Xb ≦ Xt <
It satisfies 1.5. Further, in a magnetic recording medium comprising a support and a plurality of coating films containing a vinyl chloride-based copolymer laminated on the support, the plurality of coating films include an isocyanate-based curing agent. Cured, at least one of the plurality of coating films is a magnetic layer,
The vinyl chloride-based copolymer is a vinyl chloride-based copolymer having a hydroxyl group, and the vinyl chloride-based copolymer in the outermost coating film on the farthest side from the support in the plurality of coating films. The hydroxyl group content Xt (wt%) and the hydroxyl group content Xb (wt%) of the vinyl chloride copolymer in the coating film closer to the support than the outermost coating film are 0.1%. 1 <Xb ≦ Xt <1.5.
Further, in a magnetic recording medium comprising a support and a plurality of coating films containing a vinyl chloride copolymer laminated on the support, each of the coating films contains alumina,
At least one of the plurality of coating films is a magnetic layer, and the vinyl chloride-based copolymer is a vinyl chloride-based copolymer having a hydroxyl group, and is the farthest from the support among the plurality of coating films. The hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the outermost layer coating film on the side and the vinyl chloride copolymer content in the coating film closer to the support than the outermost layer coating film were determined. Hydroxyl content in polymer Xb (wt%)
Satisfies 0.1 <Xb ≦ Xt <1.5, and among the plurality of coating films, the outermost coating film farthest from the support is cured by using an aromatic isocyanate curing agent. The coating film on the side closer to the support than the coating film of the outermost layer is cured by using an aliphatic isocyanate curing agent, and the aromatic coating used for 100 parts by weight of the coating film of the outermost layer is used. Percentage of Y part by weight of isocyanate curing agent Ywt%
And the ratio Z wt% of Z parts by weight of the aliphatic isocyanate curing agent used to 100 parts by weight of the coating film cured by using the aliphatic isocyanate curing agent is Y ≦ 1.3.
Z is satisfied. The thickness of the outermost coating film is 0.
05 to 0.5 μm (a more preferred lower limit is 0.1 μm.
A more preferred upper limit is 0.3 μm, and a still more preferred upper limit is 0.2 μm. The thickness of the coating on the side closer to the support than the outermost coating is 0.5 to 3.0 μm (particularly, 1.
0 to 2.0 μm). The ratio of the vinyl chloride copolymer in the coating film is 5 to 20% by weight, and the curing agent used for curing the coating film is 5 to 40 parts by weight based on 100 parts by weight of the vinyl chloride copolymer. is there. In particular, the curing agent used for curing the coating film not only satisfies the requirement of 5 to 40 parts by weight based on 100 parts by weight of the vinyl chloride copolymer, but also the proportion of the aliphatic isocyanate curing agent Z parts by weight Zwt%. And the ratio Y wt% of the Y part by weight of the aromatic isocyanate curing agent satisfies Y ≦ 1.3Z. Alumina contained in each coating film has a content of 1 to 20 wt% (particularly, 5 to 15 wt%).
It is.

Hereinafter, the present invention will be described in detail. The support used in the magnetic recording medium of the present invention may be magnetic or non-magnetic, but is generally non-magnetic. As such a support, for example, polyeletin terephthalate (PET), polyethylene-
Polyesters such as 2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, and vinyl such as polyvinyl chloride and polyvinylidene chloride Plastics such as resin, polycarbonate, polyimide, and polyamideimide, paper,
Papers such as baryta or paper coated or laminated with α-polyolefins having 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylene-butene copolymer can also be used. In addition, metals such as Al alloys and ceramics such as glass and porcelain are also used. These nonmagnetic supports may be transparent or opaque depending on the purpose of use. The thickness of the support varies depending on the application, but is 3 to
10 μm.

A magnetic layer (coating type magnetic layer) is provided on one side of the support. That is, a magnetic layer having a thickness of 0.05 to 0.5 μm after drying and curing is provided by applying a magnetic paint to one surface of the support. Here, the thickness of the magnetic layer after drying and curing is 0.05 to 0.5 μm.
m is too thin, it is difficult to apply uniformly,
In addition, the output is reduced, the rigidity is also reduced, and the head touch (the degree of contact between the magnetic head and the magnetic recording medium) is reduced. Conversely, if the thickness is too large, the thickness loss increases and the high frequency range increases. This is because the output in the above case is lowered and the overwrite characteristics are lowered. In addition, more preferably, the thickness after drying and curing is 0.1 to 0.3 μm, and more preferably 0.1 μm to
It is 0.2 μm, especially 0.1 μm to 0.15 μm.

As the magnetic powder contained in the magnetic layer, a known magnetic powder is appropriately used. For example, ferromagnetic metal (including alloy) powder is used. The ferromagnetic metal powder has a metal content of 75% by weight or more and a metal content of 80% by weight.
Or more is at least one ferromagnetic metal (eg,
Fe, Co, Ni, Fe-Co, Fe-Ni, Co-N
i, Fe-Co-Ni), and 20% by weight or less of metal content, preferably 0.5 to 5% by weight of Al, S
i, S, Sc, Ti, V, Cr, Mn, Cu, Zn,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Hy, Pb, Bi, La,
It may have a composition such as Ce, Pr, Nd, B, and P. This ferromagnetic metal powder has a major axis of 0.05 to
Preferably, the particles are 0.2 μm. Its needle ratio is 3
It is preferably from 10 to 10. The coercive force is 1500-2
Those which are 500 Oe are preferred. In addition to the above magnetic powder, a hexagonal ferrite magnetic powder can also be used. This ferrite magnetic powder has a plate diameter of 0.02 to 0.02.
It is preferably 0.2 μm. Its plate ratio is 2
It is preferably from 10 to 10. The coercive force is 1500-2
Those which are 500 Oe are preferred. In addition, an oxide-based magnetic powder can be used.

The magnetic powder is subjected to a surface treatment, if necessary, to improve the dispersibility of the magnetic powder in the magnetic paint. For example, "Characterization of Powder
Surfaces (Academic Press) ". Further, a silane coupling treatment, a titanium coupling treatment, an alumina coupling treatment, or the like can be performed. Also, resin coating can be performed.

The magnetic layer contains an abrasive in addition to the magnetic powder. As an abrasive, alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum,
Diamond, artificial diamond, garnet, emery
(Main components: Conrad and magnetite). In the present invention, it is preferable to use alumina. In particular, it is preferable to use alumina powder having a particle size of 0.05 to 0.5 μm (particularly, 0.1 to 0.3 μm). Incidentally, an abrasive other than alumina may be used in combination. The abrasive may be subjected to the surface treatment described above for the magnetic powder in order to improve dispersibility. The abrasive is added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the magnetic layer (100 parts by weight after the magnetic paint is applied, dried and cured).

The magnetic layer contains, in addition to the above components, antistatic agents, lubricants, dispersants and the like as additives usually used in this field. Examples of antistatic agents include conductive fine powders such as carbon black and titanium monoxide, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin and glycidol, higher alkylamines, and quaternary. Ammonium salts, pyridine and other heterocycles, cationic surfactants such as phosphonium or sulfonium, carboxylic acids, sulfonic acids, phosphoric acids, sulfate groups, anionic surfactants containing acidic groups such as phosphate groups, amino acids, amino acids Examples include amphoteric activators such as sulfonic acids and sulfuric acid or phosphoric acid esters of amino alcohol. Such an antistatic agent is added in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the magnetic powder. The above surfactants may be added alone or as a mixture. Some of them are used as antistatic agents, but sometimes they are used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and application aids.

As the lubricant, for example, dialkyl polysiloxane (alkyl group has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy group has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl group has 1 to 5 carbon atoms, the alkoxy group has 1 to 4 carbon atoms),
Silicone oils such as phenylpolysiloxane and fluoroalkylpolysiloxane (the alkyl group has 1 to 5 carbon atoms); conductive fine powders such as graphite; inorganic fine powders such as molybdenum disulfide and tungsten disulfide; polyethylene, polypropylene, and polyethylene -Vinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene, α-olefin polymer, unsaturated aliphatic hydrocarbon liquid at room temperature, monobasic aliphatic having 12 to 20 carbon atoms and 3 carbon atoms Fatty acid esters composed of up to 12 monohydric alcohols, fluorocarbons and the like. Some of the following dispersants exhibit a function as a lubricant, and these may be used. These lubricants are added in the range of 0.1 to 15 parts by weight based on 100 parts by weight of the magnetic powder.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms (R ₁ COOH, R ₁ is an alkyl or alkenyl group having 11 to 17 carbon atoms), and alkali metals of the above fatty acids (Li, Na, K, etc.). ) Or alkaline earth metals (Mg,
Ca, Ba, etc.), a fluorine-containing compound of the fatty acid ester, an amide of the fatty acid,
Examples thereof include polyalkylene oxide alkyl phosphates, lecithin, and trialkyl polyolefin oxy quaternary ammonium salts (alkyl has 1 to 5 carbon atoms, and olefins include ethylene and propylene). In addition, there are also higher alcohols having 12 or more carbon atoms, sulfates, and the like. These dispersants are used in an amount of 1 to 100 parts by weight of the magnetic powder.
It can be added in a range of 0 parts by weight or less.

Further, in addition to the above components, a rust preventive or a fungicide may be added. As the fungicide, for example, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate, and the like can be used, and in particular, dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine Phosphate, cyclohexyl ammonium carbonate, hexamethylene diamine carbonate,
The use of a vaporizable rust inhibitor (an inorganic acid salt or an organic acid salt of an amine, an amide or an imide) such as propylene diamine stearate, guanidine carbonate, triethanolamine nitrite, and morpholine stearate improves the rust prevention effect.

Examples of fungicides include saltyl anilide, bis (tributyltin) oxide, mercury phenyloleate, copper naphthenate, zinc naphthenate, mercury naphthenate, pentachlorophenol, trichlorophenol,
Examples thereof include p-dinitrophenol, sorbic acid, butyl p-oxybenzoate, and dihydroacetoic acid. A binder is used to form a coating type magnetic layer. In particular, the total amount of the magnetic layer after coating, drying and curing is 100
In terms of parts by weight, 5 to 20 parts by weight, especially 10 to 15 parts by weight of a binder is used. As the binder, a vinyl chloride copolymer having a hydroxyl group is used as an essential component. Examples of such a hydroxyl group-containing vinyl chloride copolymer include vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinyl alcohol copolymer, vinyl chloride-vinyl acetate-
Examples thereof include a vinyl alcohol copolymer and a vinyl chloride-vinylidene chloride copolymer. The hydroxyl group content Xt (wt%) in the hydroxyl group-containing vinyl chloride copolymer
Is used that satisfies 0.1 <Xt <1.5.
In the present invention, the hydroxyl group content Xt (wt%) is 0.1%.
Although a hydroxyl group-containing vinyl chloride copolymer satisfying <Xt <1.5 is necessarily used, other resins, for example, a thermoplastic resin such as polyurethane, a thermosetting resin, or a reactive resin can also be used in combination.

A hardener is used to form a coating type magnetic layer. This curing agent is preferably an isocyanate-based curing agent. In particular, aromatic isocyanates are preferred. Examples of the aromatic isocyanate include a TMP adduct type and an isocyanurate ring type. Of course, it is not limited to these. The amount of the isocyanate (aromatic isocyanate) to be used is 0.1 to 2.0 parts by weight based on 100 parts by weight of the outermost coating film (magnetic layer after application, drying, and curing) cured using the isocyanate.
0 parts by weight. In particular, it is 0.5 to 1.8 parts by weight.

In the present invention, the number of magnetic layers is not limited to one, but may be two or more. When there are two or more layers, the above-mentioned binder and curing agent are used for the upper magnetic layer, that is, the outermost (uppermost) magnetic layer farthest from the support. The magnetic layer below the outermost (uppermost) magnetic layer conforms to the later-described intermediate layer. Although the thickness of the magnetic layer is described above, in the case where there are two or more magnetic layers, the thickness of the outermost (uppermost) magnetic layer (the thickness after drying and curing)
Is preferably 0.05 to 0.5 μm. And
Thickness of the magnetic layer below the outermost layer (top layer) (thickness of the lower magnetic layer when there are two magnetic layers; outermost layer (top layer) when there are three or more magnetic layers) Is preferable to be 0.5 to 3.0 μm. still,
When the number of magnetic layers is one, it is as described above.

A non-magnetic or magnetic intermediate layer (undercoat layer) is provided between the support and the magnetic layer, if necessary. Since the intermediate layer is of a coating type, it contains a binder as in the case of the magnetic layer. As a binder used for the intermediate layer, a vinyl chloride copolymer having a hydroxyl group is used as an essential component. The above-mentioned thing is used for such a hydroxyl group-containing vinyl chloride copolymer. The hydroxyl group content Xb (wt%) in the hydroxyl group-containing vinyl chloride copolymer is 0.1 <Xb <1.5, Xb ≦ Xt.
Those satisfying are used. In the present invention, the hydroxyl group content Xb (wt%) is 0.1 <Xb <1.5, Xb ≦ X
Although a hydroxyl group-containing vinyl chloride copolymer satisfying t is always used, other resins, for example, a thermoplastic resin such as polyurethane, a thermosetting resin, or a reactive resin may be used in combination. The amount of the hydroxyl group-containing vinyl chloride copolymer having a hydroxyl group content of Xb is 5 to 5 parts by weight when the total amount of the intermediate layer (the intermediate layer after coating, drying and curing) is 100 parts by weight.
20 parts by weight, especially 10 to 15 parts by weight.

To form the coating type intermediate layer, a curing agent is used. This curing agent is preferably an isocyanate-based curing agent. In particular, aliphatic isocyanates are preferred. Examples of the aliphatic isocyanate include a TMP adduct type, an isocyanurate ring type, and a burette type. Of course, it is not limited to these. The amount of the isocyanate (aliphatic isocyanate) to be used is 0.08 to 8.0 parts by weight based on 100 parts by weight of the coating film (the magnetic layer after coating, drying and curing) of the intermediate layer cured using the isocyanate. Department. In particular, 0.4-
4.0 parts by weight. Further, the aromatic isocyanate curing agent used for 100 parts by weight of the outermost layer coating film (the coating film after coating, drying and curing) using the aromatic isocyanate is Y parts by weight, and the aliphatic isocyanate is used. When the aliphatic isocyanate curing agent used is 100 parts by weight based on 100 parts by weight of the coated film (coated, dried, and cured film), it is defined to satisfy Y ≦ 1.3Z.

In the present invention, the number of intermediate layers is not limited to one, but may be two or more. The thickness of the intermediate layer (the thickness after drying and curing) is preferably 0.5 to 3.0 μm. When the intermediate layer is composed of two or more layers, the total thickness (thickness after drying and curing) is 0.5 to 3.0 μm, and each thickness (thickness after drying and curing). Is 2.0 μm
It is preferable to set the following.

The intermediate layer also contains the same abrasive as the magnetic layer. Alumina is preferably used as the polishing agent. In particular, the particle size is 0.05 to 0.5 μm (particularly 0.1 to 0.5 μm).
3 μm) of alumina powder is used. Incidentally, an abrasive other than alumina may be used in combination. The abrasive may be subjected to the surface treatment described above for the magnetic powder in order to improve dispersibility. The abrasive is added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the intermediate layer (100 parts by weight after the coating of the intermediate layer is applied, dried and cured).

In addition, appropriate components are included. For example,
Titanium oxide, zinc oxide, calcium oxide, magnesium oxide, cerium oxide, tin dioxide, non-magnetic chromium oxide,
Metal oxide powder such as non-magnetic iron oxide, carbon black, graphite, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, tungsten disulfide, molybdenum disulfide, boron nitride, silicon dioxide, silicon carbide, corundum, artificial diamond , Garnet, garnet,
Silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite,
Synthetic or natural resin powder may be included. Among them, nonmagnetic iron oxide and carbon black are preferable. Iron oxide has a needle ratio of 3 to 10 and a major axis of 0.0
Those having a thickness of 5 to 0.2 μm are preferred. Carbon black has a primary particle size of 5 to 150 nm and a BET specific surface area of 1
^{2 to} 1000 m ² / g, DBP oil absorption 40 to 300 m
1/100 g of carbon black is preferred. 100 parts by weight of the intermediate layer (the coating of the intermediate layer is applied, dried,
It is preferably added so as to be 30 to 90 parts by weight based on 100 parts by weight after curing. Carbon black is preferably added in an amount of 5 to 30 parts by weight based on 100 parts by weight of the intermediate layer (100 parts by weight after the coating of the intermediate layer is applied, dried and cured).

In addition, a lubricant and a dispersant are contained. When the intermediate layer has magnetism, the intermediate layer contains a powder having magnetism. Any magnetic powder may be used. On the other surface side of the support, a so-called back layer is provided as necessary. The back layer is generally non-magnetic. However, the magnetic recording medium may have such a magnetic property that it cannot be used for recording and reproduction. For example, the back layer is made of a magnetic powder having a high magnetic permeability (for example,
Spherical magnetite with a diameter of 0.005 to 0.2 μm)
May be contained. The back layer has a thickness after drying of 0.1 to 5 μm (particularly 0.2 to 3 μm) by applying a paint having a desired component on the other surface of the support.
Provided. Here, the thickness of the back layer after drying is 0.1
0.1 to 5 μm (particularly 0.2 to 3 μm)
If the thickness is less than μm, uniform coating is difficult, and
This is because the Young's modulus of the back layer is small, so that the back layer cannot have appropriate rigidity, and the head touch is reduced.

The back layer contains carbon black. The content of carbon black is 100 parts by weight of the back layer (10 parts after the coating of the back layer is applied, dried and cured).
0 parts by weight) to 30 to 70 parts by weight, especially 40 to 60 parts by weight.
Parts by weight, more preferably 45 to 55 parts by weight. Carbon black has, for example, a primary particle size of 5 to 150 nm, and B
Carbon black having an ET specific surface area of 12 to 1000 m ² / g and a DBP oil absorption of 40 to 300 ml / 100 g.

In addition, the same lubricants and dispersants as described for the magnetic layer and the intermediate layer may be used, if necessary.
Since the back layer is of the coating type, it contains the same binder as described above. The amount of the binder is
30 to 70 parts by weight, especially 4 parts by weight, per 100 parts by weight (100 parts by weight after the coating of the back layer is applied, dried and cured)
0 to 60 parts by weight.

Further, a curing agent is used. In particular, a curing agent such as an aromatic isocyanate or an aliphatic isocyanate is used. The amount of the curing agent is 100 parts by weight of the back layer (100 parts after the coating of the back layer is applied, dried and cured).
Parts by weight). To form the above-mentioned coating type magnetic layer, intermediate layer, and back layer, a paint for the magnetic layer (magnetic paint), a paint for the intermediate layer (intermediate paint), and a paint for the back layer (back paint) are prepared. You. This is a paint in which each component is dissolved in a solvent.

Solvents used in the production of paints include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, and ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol monoethyl ether such as glycol acetate. Solvents, glycol ether solvents such as ether, glycol dimethyl ether, glycol monoethyl ether and dioxane; tar (aromatic hydrocarbon) solvents such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride Chlorinated hydrocarbon solvents such as chloroform, ethylene chlorohydrin and dichlorobenzene can be appropriately selected and used.

The magnetic powder, binder resin, lubricant and the like are kneaded to form a coating. In kneading, all the above-mentioned components are simultaneously or individually placed in a kneading machine. . In particular, the curing agent is added just before the application. In kneading and dispersing the paint, various kneading machines, for example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand glider, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper, A kneader, a high-speed mixer, a homogenizer, an ultrasonic disperser or the like is used.

Any method may be used for applying the magnetic paint, the intermediate paint, and the back paint on the support. For example, a gravure method, a reverse method, an extrusion method and the like can be mentioned, but other methods are also possible. The magnetic layer and the intermediate layer may be formed by simultaneous multilayer coating. The coating head used for coating may be any type.

Then, the above paint is applied on a support,
A coating type magnetic recording medium is obtained by orientation and curing. Curing of the coating film is, for example, 40 to 100 ° C.
This is performed by supplying hot air heated to the temperature. The degree of curing of the coating film is controlled by controlling the temperature and the supply amount. Either the magnetic paint or the back paint may be applied first.

A magnetic recording medium can be obtained by performing a surface smoothing treatment as necessary or cutting the material into a desired shape. For calendering the magnetic coating film, a super calendering method is used in which a metal roll and a cotton roll, a synthetic resin (for example, nylon, polyurethane, etc.) roll, and a metal roll and a metal roll are passed between two rolls.

Hereinafter, a specific example will be described.

[0040]

Example 1 [Components of Magnetic Coating] 100 parts by weight of ferromagnetic metal powder (major axis length 0.075 μm, needle ratio 4, coercive force Hc2300 Oe, saturation magnetization 140 emu / g, BET specific surface area 50 m ² / g) Powder (AKP50 manufactured by Sumitomo Chemical Co., Ltd., average particle size: 0.3 μm) 7 parts by weight Vinyl chloride copolymer (hydroxyl content Xt = 0.5 wt%) 10 parts by weight Polyester polyurethane (UR8300 manufactured by Toyobo) 5 parts by weight Carbon black (Conductex SC, manufactured by Columbia Chemicals Company, average primary particle size: 0.02 μm) 0.3 part by weight Aromatic isocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) 2 parts by weight 1 part by weight butyl stearate 2 parts by weight myristic acid Parts methyl ethyl ketone 100 parts by weight toluene 50 parts by weight Cyclohexanone 100 parts by weight of the magnetic coating material, the components except the curing agent in a sand mill 6
After kneading and dispersing for an hour, it was prepared by adding an aromatic isocyanate.

[Ingredient of Intermediate Paint] α iron oxide (major axis length 0.15 μm, needle ratio 7) 100 parts by weight Alumina powder (AKP50 manufactured by Sumitomo Chemical Co., Ltd., average particle size 0.3 μm) 5 parts by weight carbon black (Conductex SC manufactured by Columbia Chemicals Company, average primary particle size: 0.02 μm) 10 parts by weight Vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) 10 parts by weight Polyester polyurethane (UR8300 manufactured by Toyobo Co., Ltd.) 5 Parts by weight Aliphatic isocyanate (Coronate HX manufactured by Nippon Polyurethane Industry Co., Ltd.) 4 parts by weight Butyl stearate 1 part by weight Myristic acid 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 50 parts by weight Cyclohexanone 100 parts by weight 6 in a sand mill
After kneading and dispersing for an hour, it was prepared by adding an aliphatic isocyanate.

[Components of Back Coating] 100 parts by weight of carbon black (Raven 1255 manufactured by Columbian Chemicals Company) 5 parts by weight of alumina powder (AKP50 manufactured by Sumitomo Chemical Co., Ltd.) 5 parts by weight Vinyl chloride copolymer (MR110 manufactured by Zeon Corporation) 15 5 parts by weight Polyester polyurethane (UR8300 manufactured by Toyobo) 5 parts by weight Aromatic isocyanate (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) 5 parts by weight 1 part by weight butyl stearate 1 part by weight myristic acid 1 part by weight methyl ethyl ketone 360 parts by weight toluene 240 parts by weight cyclohexanone 120 parts by weight The back coating composition was prepared by kneading and dispersing the above components except a curing agent in a sand mill for 6 hours, and then adding an aromatic isocyanate.

[Magnetic Tape] The intermediate paint and the magnetic paint were applied on one surface of a PET film having a thickness of 6 μm by a simultaneous multilayer coating method. The thickness is such that the dried intermediate layer has a thickness of 1.5 μm and the magnetic layer provided on the intermediate layer has a dried thickness of 0.2 μm. Then, before the magnetic coating film has been dried, the magnetic coating film is passed through a magnetic field of 5,000 Oe to perform a magnetic field orientation treatment.
Hot air at 0 ° C. was passed through a drying furnace supplied at a rate of 15 m / sec for 30 seconds to dry.

Next, the above-mentioned back coating was applied so that the thickness after drying became 0.5 μm, and passed through a hot-air drying oven at 90 ° C. to be dried. Thereafter, calendering was performed under the conditions of a roll surface temperature of 90 ° C. and a roll linear pressure of 300 kg / cm. 8mm of raw material obtained as above
By slitting to width, a magnetic tape for 8 mm VTR was obtained.

The hydroxyl group contents Xt and Xb of the vinyl chloride copolymer used in the magnetic layer and the intermediate layer in this embodiment were calculated by the above-described method. The ratio Y of the aromatic isocyanate curing agent Y part by weight used to 100 parts by weight of the coating film of the outermost layer (magnetic layer) in this embodiment is 2 / (100+
7 + 10 + 5 + 0.3 + 2 + 1 + 2) × 100 = 1.6
%, and the content of the abrasive (alumina powder) in the outermost layer (magnetic layer) was 7 / (100 + 7 + 10 + 5 +
0.3 + 2 + 1 + 2) × 100 = 5.5 wt%.

The ratio Z of the aliphatic isocyanate curing agent used to 100 parts by weight of the coating film of the intermediate layer is 4 parts by weight.
/ (100 + 5 + 10 + 10 + 5 + 4 + 1 + 2) × 10
0 = 2.9 wt%, and the content of the abrasive (alumina powder) in the intermediate layer was 5 / (100 + 5 + 10 + 10 +
5 + 4 + 1 + 2) × 100 = 3.6 wt%. Solvents such as methyl ethyl ketone, toluene and cyclohexanone volatilize in the calculation of Y, Z and the like in the magnetic layer and the intermediate layer, and therefore do not enter the denominator.

[0047]

EXAMPLE 2 Instead of the vinyl chloride copolymer (hydroxyl content Xt = 0.5 wt%) in the magnetic paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xt = 0.8).
wt%), except that the method of Example 1 was used.

[0048]

Example 3 Instead of the vinyl chloride copolymer (hydroxyl content Xt = 0.5 wt%) in the magnetic paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xt = 1.1) was used.
wt%), except that the method of Example 1 was used.

[0049]

EXAMPLE 4 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xb = 0.4) was used.
wt%), except that the method of Example 1 was used.

[0050]

Embodiment 5 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xb = 0.3) was used.
wt%), except that the method of Example 1 was used.

[0051]

Comparative Example 1 Instead of the vinyl chloride copolymer (hydroxyl content Xt = 0.5 wt%) in the magnetic paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xt = 1.5) was used.
wt%), and instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint, a vinyl chloride copolymer (hydroxyl content Xb = 0.8 wt)
%), Except that%) was used.

[0052]

Comparative Example 2 Instead of the vinyl chloride-based copolymer (hydroxyl content Xt = 0.5 wt%) in the magnetic paint in Example 1, a vinyl chloride-based copolymer (hydroxyl content Xt = 1.7) was used.
wt%), and instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint, a vinyl chloride copolymer (hydroxyl content Xb = 0.8 wt)
%), Except that%) was used.

[0053]

Comparative Example 3 Instead of the vinyl chloride copolymer (hydroxyl content Xt = 0.5 wt%) in the magnetic paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xt = 1.9).
wt%), and instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint, a vinyl chloride copolymer (hydroxyl content Xb = 0.8 wt)
%), Except that%) was used.

[0054]

Comparative Example 4 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xb = 0.1) was used.
wt%), except that the method of Example 1 was used.

[0055]

Comparative Example 5 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 2, a vinyl chloride copolymer (hydroxyl content Xb = 0.1) was used.
wt%), except that the method of Example 2 was used.

[0056]

Comparative Example 6 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 3, a vinyl chloride copolymer (hydroxyl content Xb = 0.1) was used.
wt%), except that the method of Example 3 was used.

[0057]

Comparative Example 7 Instead of the vinyl chloride-based copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 1, a vinyl chloride-based copolymer (hydroxyl content Xb = 0.8) was used.
wt%), except that the method of Example 1 was used.

[0058]

Comparative Example 8 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xb = 1.1) was used.
wt%), except that the method of Example 1 was used.

[0059]

Comparative Example 9 Instead of the vinyl chloride copolymer (hydroxyl content Xb = 0.5 wt%) in the intermediate paint in Example 1, a vinyl chloride copolymer (hydroxyl content Xb = 1.4).
wt%), except that the method of Example 1 was used.

[0060]

[Characteristics] The magnetic tape obtained in each of the above examples was examined for electromagnetic conversion characteristics, dropout, durability, and stains on a calendar roll during calendering. The results are shown in Table 1 below. The electromagnetic conversion characteristics were 0.49 µm, 0.9 by modifying a commercially available Hi8 video deck.
This is a reproduction of a recording signal having a wavelength of 8 μm.

The dropout is obtained by modifying a commercially available Hi8 video deck, reproducing a recorded signal having a wavelength of 0.49 μm, and counting the number of dropouts. The durability is 23 ° C, 59% using a commercially available Hi8 video deck.
In this figure, the vehicle repeatedly travels in an atmosphere of RH and the number of repetitions until the traveling stops is examined. Calendar stains
The metal roll in the calendering device was visually observed and indicated by the presence or absence of dirt.

Table 1 Electromagnetic Conversion Characteristics (%) Dropout Durability Calendar Dirt 0.98 μm 0.49 μm (pcs / 10000 trk) (number of times) Example 1 120 120 2500 1100 None Example 2 120 110 2500 1300 None Example 3 120 110 3000 1500 None Example 4 110 100 3000 1500 None Example 5 110 100 3000 1500 None Comparative Example 1 90 90 6000 1700 Yes Comparative Example 2 80 70 8000 1700 Yes Comparative Example 3 70 60 9000 1900 Yes Comparative Example 4 120 300 provided Comparative Example 5 120 110 2000 500 provided Comparative Example 6 120 110 2500 600 provided Comparative Example 7 90 80 9000 1000 provided Comparative Example 8 90 80 8000 1200 provided Comparative Example 9 80 70 8 According to Table 1, a vinyl chloride copolymer having a hydroxyl group is used as a binder for the intermediate layer and the magnetic layer of the coating type magnetic recording medium in which the intermediate layer and the magnetic layer are laminated, and the upper layer is used. The hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the magnetic layer and the hydroxyl group content Xb (wt%) in the vinyl chloride copolymer in the lower interlayer are
Since 0.1 <Xb ≦ Xt <1.5 was satisfied,
The electromagnetic conversion characteristics are excellent, the dropout hardly occurs, and the durability is high. In addition, the calendar roll is hardly stained during the calendar processing. Therefore, productivity is high.

Further, the intermediate layer and the magnetic layer each contain alumina powder, an aliphatic isocyanate curing agent is used for forming the intermediate layer, and an aromatic isocyanate curing agent is used for forming the magnetic layer. The proportion of the aliphatic isocyanate curing agent used Z in the layer and the proportion of the aromatic isocyanate curing agent used Y in the magnetic layer are Y ≦ 1.3Z.
Is satisfied, electromagnetic conversion characteristics are excellent, dropout hardly occurs, and durability is high. In addition, the calendar roll is hardly stained during the calendar processing. Therefore, productivity is high.

On the other hand, a vinyl chloride copolymer having a hydroxyl group was used as a binder for the intermediate layer and the magnetic layer.
In addition, the hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the upper magnetic layer and the hydroxyl group content Xb (wt%) in the vinyl chloride copolymer in the lower intermediate layer
Satisfies 0.1 <Xb ≦ Xt, but 1.5 ≦
In the case of Xt, as shown in Comparative Examples 1, 2, and 3, the electromagnetic conversion characteristics are low and the dropout is large.

Further, a vinyl chloride copolymer having a hydroxyl group is used as a binder for the intermediate layer and the magnetic layer, and the hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the upper magnetic layer is as follows: The hydroxyl group content Xb (wt%) in the vinyl chloride copolymer in the lower intermediate layer is represented by Xb
Even if Xb <1.5 is satisfied, when Xb≤0.1, the durability is low as shown in Comparative Examples 4, 5, and 6.

Further, a vinyl chloride copolymer having a hydroxyl group is used as a binder for the intermediate layer and the magnetic layer, and the hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the upper magnetic layer is: The hydroxyl group content Xb (wt%) in the vinyl chloride copolymer in the lower intermediate layer is 0.1%.
Even if 1 <Xb <1.5 and 0.1 <Xt <1.5 are satisfied, when Xb> Xt, as shown in Comparative Examples 7, 8, and 9, the electromagnetic conversion characteristics are low, and There are many dropouts.

[0067]

As described above, in a magnetic recording medium provided with a plurality of coating films containing a vinyl chloride copolymer laminated on a support, the vinyl chloride copolymer has a hydroxyl group. Wherein the hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the outermost layer coating film furthest from the support of the plurality of coating films, and the outermost layer coating film The hydroxyl group content Xb (wt.) Of the vinyl chloride copolymer in the coating film closer to the support
%) Is set to satisfy 0.1 <Xb ≦ Xt <1.5, so that the electromagnetic conversion characteristics are excellent, the dropout hardly occurs, and the durability is high. . In addition, since the calendar roll is not easily stained during the calendar processing, the productivity is high.

Claims (5)

[Claims] 1. A magnetic recording medium comprising: a support; and a plurality of coating films containing a vinyl chloride-based copolymer laminated on at least one surface of the support. At least one of them is a magnetic layer, the vinyl chloride-based copolymer is a vinyl chloride-based copolymer having a hydroxyl group, and of the outermost layer on the farthest side from the support in the plurality of coating films. The hydroxyl group content Xt (wt%) in the vinyl chloride copolymer in the coating film and the hydroxyl group content in the vinyl chloride copolymer in the coating film closer to the support than the outermost coating film When the amount Xb (wt%) is 0.1 <Xb ≦
A magnetic recording medium satisfying Xt <1.5. 2. The magnetic recording medium according to claim 1, wherein the plurality of coating films are cured using an isocyanate-based curing agent. 3. The thickness of the outermost coating film is 0.05 to 0.5.
3. The magnetic recording medium according to claim 1, wherein the thickness of the coating film on the side closer to the support than the outermost coating film is 0.5 to 3.0 [mu] m. 4. The ratio of the vinyl chloride copolymer in the coating film is 5 to 20% by weight, and the curing agent used for curing the coating film is 5 to 20 parts by weight based on 100 parts by weight of the vinyl chloride copolymer.
4. The composition according to claim 1, wherein the amount is 40 parts by weight.
Any magnetic recording medium. 5. The magnetic recording medium according to claim 1, wherein the outermost layer farthest from the support is a magnetic layer.