JPH05128496A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium and the production method decreased in surface roughness of a magnetic layer and improved in electromagnetic conversion property. CONSTITUTION:When each of flow curve of a magnetic coating material for upper layer forming an upper magnetic layer and a magnetic coating material for under layer, which is adjacent to the upper layer and forms an under magnetic layer, is fitted to a following formula, plural of the magnetic layer are laminated by applying with over layering the magnetic coating material for under layer and for upper layer which are regulated so that difference of exponent n is <=0.1 and difference of coefficient of viscosity K is <1.0. The formula; sigma=Kgamman, where sigma is shearing stress (Pa), gamma is shear rate (S<-1>). The magnetic recording medium is produced by applying the magnetic coating material for upper layer on the magnetic coating material for under layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium and a method for manufacturing the same, and more particularly, to prevent surface roughness of a magnetic layer when a plurality of magnetic layers are formed on a non-magnetic support by multilayer coating. The present invention relates to a magnetic recording medium with improved electromagnetic conversion characteristics and a method for producing a magnetic recording medium with improved electromagnetic conversion characteristics by applying multiple layers of a lower layer magnetic coating material and an upper layer magnetic coating material having a fixed relationship with respect to a flow curve.

[0002]

2. Description of the Related Art In a conventional magnetic recording medium such as a video tape, the depth of a recorded signal differs depending on the type of the signal, so that the magnetic layer is formed by a magnetic layer suitable for each signal. It has been said that a magnetic recording medium having a multilayer structure described above is preferable. It is preferable to manufacture the multi-layered magnetic recording medium by wet-on-wet multi-layer coating, but if there is a difference in liquid physical properties of adjacent paints,
The surface property of the magnetic layer deteriorates, and the running property and electromagnetic conversion characteristics deteriorate.

Various techniques have been developed to solve these problems. For example, Japanese Patent Laid-Open No. 2-1053
Japanese Patent No. 31 discloses a technique for specifying the surface tension of the magnetic paint of each magnetic layer. In this technique, the surface property of the magnetic layer is improved when the type of magnetic powder contained in each magnetic paint is different. Is not enough. Further, in JP-A-2-101627, the type and amount of the binder are specified, but the surface property of the magnetic layer cannot be improved by using the metallic magnetic powder or the hexagonal magnetic powder. .. JP-A-64-863
Japanese Patent Publication No. 21 discloses a technique for specifying the evaporation rate index of the solvent in the magnetic coating in the upper and lower magnetic layers, but this technique causes the solvent to coagulate before it dries due to the strong interaction between the upper and lower magnetic layers. In a system where
It has almost no effect.

The present invention has been made based on the above circumstances. That is, an object of the present invention is to provide a magnetic recording medium having improved electromagnetic conversion characteristics by reliably preventing surface roughness of the magnetic layers when forming a plurality of magnetic layers on a non-magnetic support by multilayer coating. To do.

[0005]

The present invention for solving the above-mentioned problems comprises an upper layer magnetic paint for forming an upper magnetic layer and a lower layer magnetic paint for forming a lower magnetic layer adjacent to the upper layer. The magnetic coating material for the lower layer and the upper layer, which are adjusted so that the difference in the power multiplier n is 0.1 or less and the difference in the viscosity coefficient K is 1.0 or less when the respective flow curves of A magnetic recording medium characterized in that a plurality of magnetic layers are laminated by applying multiple layers of a magnetic coating material on a non-magnetic support. σ = Kγ ⁿ where σ: shear stress (P _a ) γ: shear rate (S ⁻¹ ).

The magnetic recording medium having the above-described structure is manufactured by the manufacturing method of the present invention. In the manufacturing method, a magnetic coating material is coated on a non-magnetic support in multiple layers to produce a magnetic recording medium having multiple magnetic layers. In the method, when the respective flow curves of the upper layer magnetic coating material forming the upper layer magnetic layer and the lower layer magnetic coating layer forming the lower layer magnetic layer adjacent to the upper layer are fitted to the formula of claim 1, ,
It is necessary to apply the upper layer magnetic coating material on the lower layer magnetic coating material which is adjusted so that the difference in the power multiplier n is 0.1 or less and the difference in the viscosity coefficient K is 1.0 or less. A method for manufacturing a characteristic magnetic recording medium.

The present invention will be described in detail below. (I) Magnetic Recording Medium The magnetic recording medium of the present invention is basically a laminated structure in which a plurality of magnetic layers are formed on the surface of a non-magnetic support by multilayer coating. —Nonmagnetic Support— Examples of materials for forming the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and cellulose derivatives such as cellulose triacetate and cellulose diacetate. ,polyamide,
Examples thereof include plastics such as polycarbonate.

The form of the non-magnetic support is not particularly limited, and is mainly tape-like, film-like, sheet-like, card-like,
There are disc shape and drum shape. The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 3 to 100 μm, preferably 5 to 50 μm.
In the case of a disk or card, it is 30 μm-10 m
In the case of a drum shape, it is appropriately selected depending on the recorder or the like.

The non-magnetic support may have a single-layer structure or a multi-layer structure. Further, the non-magnetic support may be subjected to surface treatment such as corona discharge treatment. A back coat layer is preferably provided on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing electrification, and preventing transfer. Further, an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

-Magnetic powder in the upper magnetic layer-The upper magnetic layer contains the magnetic powder, a binder to be described later, and optional components used as appropriate. In the present invention, it is possible to use magnetic powder known in the field of magnetic recording media as the magnetic powder for the upper layer, but barium ferrite magnetic powder is preferable.

Although various kinds of barium ferrite magnetic powder can be used, the barium ferrite magnetic powder preferable for the present invention is Ba-ferrite powder.
Average grain size in which a part of Fe is replaced with at least Co and Zn (height of diagonal line of plate surface of hexagonal ferrite) 4
Ba-ferrite having a plate-like ratio (value obtained by dividing the length of the diagonal line of the hexagonal ferrite plate surface by the plate thickness) of 2.0 to 10.0 and a coercive force (Hc) of 350 to 2,000. Can be mentioned.

The Ba-ferrite powder has a coercive force controlled to an appropriate value by partially substituting Fe for Co, and further partially substituting for Zn, which cannot be obtained only by Co substitution. It is possible to obtain a magnetic recording medium that realizes saturation magnetization and has a high reproduction output and excellent electromagnetic conversion characteristics. Further, by substituting a part of Fe with Nb, it is possible to obtain a magnetic recording medium having a higher reproduction output and excellent in electromagnetic conversion characteristics. Further, in the Ba-ferrite used in the present invention, a part of Fe is T
It may be substituted with a transition metal such as i, In, Mn, Cu, Ge and Sn.

The Ba-ferrite used in the present invention has the general formula BaO.n [(Fe _{1 -m} M _m ) ₂ O ₃ ] (where M represents a substituted metal. M> 0.36 (where Co
+ Zn = 0.08 to 0.3, Co / Zn = 0.5 to 1
0)), n is 5.4 to 6.0, and M
Is preferably a magnetic particle which is a combination of two or more elements having an average number of 3.

In the present invention, the reason why Ba-ferrite preferably has an average particle size, plate ratio and coercive force within the above ranges is as follows. That is, if the average particle size is less than 400 Å, the reproduction output when used as a magnetic recording medium may be insufficient, and conversely, if it exceeds 900 Å, the surface smoothness when used as a magnetic recording medium deteriorates significantly. , The noise level may become too high, and
When the plate ratio is less than 2.0, the perpendicular orientation ratio suitable for high density recording cannot be obtained when the magnetic recording medium is used, and conversely when the plate ratio exceeds 10.0, the magnetic recording medium is not used. If the coercive force is less than 350 Oe, it becomes difficult to hold the recording signal, and if it exceeds 2000 Oe, the head limit is reduced in saturation. This may be difficult to record.

The barium ferrite magnetic powder used in the present invention usually has a saturation magnetization (σ _S ) which is a magnetic characteristic of 6
It is preferably 0 emu / g or more. This is because if the saturation magnetization is less than 60 emu / g, the electromagnetic conversion characteristics may deteriorate. Further in the present invention,
As the recording density increases, the specific surface area by BET method becomes 4
It is desirable to use Ba-ferrite magnetic powder of 0 m ² / g or more.

A preferred specific example of the Ba-ferrite used in the present invention is Co-substituted Ba ferrite [Hc: 1100 Oe, BET: 40 m ² / g, σ
_s : 64, plate ratio: 4]. In addition,
For the specific surface area by the BET method and the measuring method thereof, see “Measurement of powder” (JM Dallas,
ClyorrJr, co-authored by Muta et al .; published by Sangyo Tosho Co., Ltd.)
70-1171 (edited by The Chemical Society of Japan; Maruzen Co., Ltd., published April 30, 1966).

The specific surface area can be measured, for example, by using powder 105
Degassed while being heated at around 13 ° C for 13 minutes to remove those adsorbed on the powder, and then introduce this powder into the measuring device to set the initial pressure of nitrogen to 0.5 kg / m ² .
Measurement is carried out with nitrogen at liquid nitrogen temperature (-105 ° C) for 10 minutes. As the measuring device, for example, a counter soap [made by Yuasa Ionics Co., Ltd.] is used. As a method for producing the hexagonal magnetic powder preferably used in the present invention,
For example, oxides and carbonates of each element necessary for forming the desired Ba-ferrite are melted together with a glass-forming substance such as boric acid, and the resulting melt is rapidly cooled to form glass. Then, the glass is heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass component is removed by heat treatment. A thermal synthesis method, a flux method, an alkoxide method, a plasma jet method or the like can be applied.

-Magnetic Powder in Lower Magnetic Layer-The lower magnetic layer contains magnetic powder, a binder described below, and an optional component used as appropriate. As the magnetic powder for the lower layer, magnetic powder known in the field of magnetic recording media can be used, but cobalt-containing iron oxide-based magnetic powder is preferable. Examples of the cobalt-containing iron oxide-based magnetic powder include Co-containing γ-Fe ₂ O ₃ and Co-coated γ-
Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , Co-deposited Fe ₃ O
₄ , Co-containing magnetic FeO _x (4/3 <x <3/2), and the like. Among these, Co-containing magnetic FeO _x (4/3 <x <3 is preferable for the magnetic recording medium of the present invention.
/ 2) It is a powder.

Specific examples of the cobalt-containing iron oxide magnetic powder preferably used in the lower magnetic layer in the present invention include Co-γFe ₂ O ₃ [Hc: 800 Oe, BET value 50 m ² / g]. it can. In the present invention, a ferromagnetic powder having a specific surface area of 45 m ² / g or more according to the BET method is preferably used according to the higher recording density.

-Binder used for magnetic layer- Examples of the binder used for forming the magnetic layer of the present invention include vinyl chloride resins such as vinyl chloride copolymers, polyurethanes, and polyesters. There are exemplary, these resins are -SO ₃ M, -OSO ₃
It is preferable to include a repeating unit having at least one polar group selected from M, —COOM and —P (═O) (OM ¹ ) ₂ . However, in the above polar group, M
Represents a hydrogen atom or an alkali metal such as Na, K and Li, and M ¹ represents a hydrogen atom, an alkali atom such as Na, K and Li, or an alkyl group.

The above polar group has the function of improving the dispersibility of the magnetic powder, and the content in each resin is usually 0.1 to 8.0 mol%, preferably 0.5 to 6.0 mol%. .. When the content is less than 0.1 mol%, the dispersibility of the magnetic powder is deteriorated, and when the content is more than 8.0 mol%, the magnetic coating may easily gel. The weight average molecular weight of each resin is preferably in the range of 15,000 to 50,000.

The content of the binder in the magnetic layer is usually 5 to 40 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic powder. The binder is not limited to one kind, and two or more kinds can be used in combination. In this case, the ratio of the polyurethane and / or polyester to the vinyl chloride resin is usually 90:10 to 1 by weight.
It is 0:90, preferably 70:30 to 30:70.

The polar group-containing vinyl chloride-based copolymer used as the binder in the present invention is a compound having a hydroxyl group-containing copolymer such as a vinyl chloride-vinyl alcohol copolymer and the following polar group and chlorine atom. It can be synthesized by addition reaction with. Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₃ M, Cl-CH ₂ CO
OM, Cl-CH ₂ -P (= O) (OM ¹ ) _{2 From} these compounds, taking ClCH ₂ CH ₂ SO ₃ Na as an example, the above reaction will be explained as follows.

-[CH ₂ -C (OH) H \ _n- + ClCH ₂ CH ₂ SO ₃ Na →-[CH ₂ C (OCH ₂ CH ₂ SO ₃ Na) H \ _n -Also, polar group-containing vinyl chloride The system copolymer is prepared by charging a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced into a reaction vessel such as an autoclave, and using a general polymerization initiator such as BPO (benzoyl peroxide). Radical polymerization initiator such as AIBN (azobisisobutyronitrile), redox polymerization initiator,
It can be obtained by carrying out a polymerization reaction using a cationic polymerization initiator or the like.

Specific examples of the reactive monomer for introducing sulfonic acid or a salt thereof include vinyl sulfonic acid,
Examples thereof include unsaturated hydrocarbon sulfonic acids such as allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid, and salts thereof. When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid, maleic acid or the like is used, and when introducing a phosphoric acid or a salt thereof, for example, (meth) acrylic acid-2-phosphate ester is used. Good.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so. When introducing an epoxy group, the content of the repeating unit having an epoxy group in the copolymer is preferably 1 to 30 mol%,
20 mol% is more preferable. For example, glycidyl acrylate is preferable as the monomer for introducing the epoxy group.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-57-42427 are cited.
8-108052, 59-8127, 60-1
No. 01161, No. 60-235814, No. 60-23
No. 8306, No. 60-238371, No. 62-121
No. 923, No. 62-146432, No. 62-1464.
No. 33 and the like are described, and these can be used in the present invention.

Next, the synthesis of polyester and polyurethane used in the present invention will be described. Generally, polyesters are obtained by reacting a polyol with a polybasic acid. Using this known method, a polyester (polyol) having a polar group can be synthesized from a polyol and a polybasic acid partially having a polar group. Examples of the polybasic acid having a polar group include 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, and 4 -Dialkyl sulfoisophthalates, dialkyl 3-sulfoisophthalates and their sodium and potassium salts can be mentioned.

Examples of the polyol include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol and propylene glycol.
1,3-butanediol, 1,4-butanediol
1,6-hexanediol, diethylene glycol
And cyclohexane dimethanol.

Incidentally, other polar group-introduced polyesters can also be synthesized by a known method. Next, polyurethane will be described. It results from the reaction of polyols with polyisocyanates. As a polyol,
Generally, a polyester polyol obtained by reacting a polyol with a polybasic acid is used. Therefore, by using a polyester polyol having a polar group as a raw material, a polyurethane having a polar group can be synthesized. Examples of polyisocyanates include diphenylmethane-4-4'-diisocyanate (MD
I), hexamethylene diisocyanate (HMDI),
Examples include tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a polar group and a chlorine atom is also effective. Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₂ M, Cl-CH ₂ COOM
, Cl-CH _2- P (= O) (OM ¹ ) ₂ . Regarding the technology for introducing polar groups into polyurethane,
JP-B-58-41565, JP-A-57-92422
No. 57, No. 57-92423, No. 59-8127, No. 5
No. 9-5423, No. 59-5424, No. 62-121
It is described in Japanese Patent No. 923, etc., and these can be used in the present invention.

In the present invention, the following resins can be used together as a binder in an amount of 20% by weight or less based on the total amount of the binder. The resin has a weight average molecular weight of 10,
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (000 to 200,000). Nitrocellulose), styrene-butadiene copolymer, various synthetic rubber resins, phenol resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic resins, urea formamide resins and the like.

-Arbitrary Component in Magnetic Layer- In the present invention, it is preferable to use an aromatic or aliphatic polyisocyanate as a curing agent in combination with the binder. Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI) and adducts thereof with an active hydrogen compound, and an average molecular weight of 100 to 3,000.
The range of is preferable.

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HMDI) and adducts thereof with an active hydrogen compound, and those having an average molecular weight of 100 to 3000 are preferable, and non-alicyclic polyisocyanates are preferable. Isocyanates and adducts thereof with active hydrogen compounds are preferred. The amount of the aromatic or aliphatic polyisocyanate added is usually 1/20 to 7/10, preferably 1/10 to 1/2, in weight ratio with respect to the binder.

Further, the trade names of the urethane curing agent using diisocyanate as a raw material are as follows.
First, as the trade name of the urethane curing agent that has a urethane bond and uses TDI as a raw material, Mitec GP105A, GP302A; Coronate L, 304
1; Takenate D-102, D-103H, D-10
4; Burnock D750; Sumidule L; AD-30
IPDI (isophorone diisocyanate)
The trade names of the urethane curing agent made from are: Mitec NY210A, NY215A, NY220A; Takenate D-140N; Desmodur Z-4167, Z
There are -4273 and the like, and the brand name of the urethane curing agent made of HMDI (hexamethylene diisocyanate) is Coronate HL, Burnock D-950, and the like, which is a urethane curing agent made of XDI (xylylene diisocyanate). The trade name is Takenate D-
There are 110N and the like, and as a trade name of a urethane curing agent using H ₆ XDI [1,4-cyclohexanebis (methylisocyanate)] as a raw material, Takenate D120N,
Takenate D-123 and the like.

Next, as the trade name of the urethane curing agent of the type having a buret bond and made of HMDI, there are Sumidure N-75 and Desmodur N-7.
5, Duranate 24A100 and the like. Next, as the trade name of the urethane curing agent which is a type having an isocyanurate ring and uses TDI as a raw material, Mitec GP700A, GP750A, GP76
0A, GP770A; Coronate 2030, 2031,
2071; Takenate D-202, D-204, D-2
12, D-215; Sumidule IL, FL; Burnock D-800, etc., and as the trade name of the urethane curing agent using IPDI as a raw material, Desmodur Z-437
No. 0, T-1890, etc., the product name of urethane curing agent made from HMDI is Coronate EH, and the product name of urethane curing agent made from a mixture of TDI and HMDI is Desmodur HL. and so on.

In the present invention, in order to improve the quality of the magnetic layer, additives such as durability improvers, dispersants, lubricants, abrasives, antistatic agents and fillers may be contained as other components. .. Examples of the durability improver include polyisocyanate. Examples of the polyisocyanate include aromatic polyisocyanates such as adducts of TDI and active hydrogen compounds, adducts of HMDI and active hydrogen compounds, and the like. There are aliphatic polyisocyanates. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

As the dispersant, fatty acids having 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid;
Salts of these alkali metals or salts of alkaline earth metals or their amides; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having carboxyl groups and sulfonic acid groups, etc. Can be mentioned.

These dispersants are usually used in the range of 0.5 to 5% by weight based on the ferromagnetic powder. Fatty acids and / or fatty acid esters can be used as lubricants. In this case, the amount of fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the magnetic powder. If the addition amount is less than 0.2% by weight, the running property tends to decrease, and if the addition amount exceeds 10% by weight, the fatty acid tends to exude to the surface of the magnetic layer and the output tends to decrease. The amount of fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder. When the added amount is less than 0.2% by weight,
Still durability is liable to deteriorate, and when it exceeds 10% by weight, fatty acid ester is likely to seep out to the surface of the magnetic layer and output is likely to decrease. When using a fatty acid and a fatty acid ester together to further enhance the lubricating effect, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10.

The fatty acid may be a monobasic acid or a dibasic acid and preferably has 6 to 30 carbon atoms.
The range of -22 is more preferable. Specific examples of fatty acids include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, maleic acid. Acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like can be mentioned.

Specific examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmiate. Tate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2.
-Ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol-mono-butyl ether palmitate, diethylene glycol mono- Butyl ether palmitate and the like.

As the lubricant other than the above fatty acids and fatty acid esters, for example, silicone oil, graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide and the like can be used.

Specific examples of the polishing agent include α-aluminum, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxidation. Examples thereof include zinc, cerium oxide, magnesium oxide, and boron nitride. The abrasive has an average particle size of 0.05 to 0.6.
Those having a thickness of μm are preferable, and those having a thickness of 0.1 to 0.3 μm are more preferable.

As the antistatic agent, carbon black,
Conductive powder such as graphite; cationic surfactant such as quaternary amine; anionic surfactant containing acid group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid;
Examples thereof include amphoteric surfactants such as aminosulfonic acid; natural surfactants such as saponin. The above-mentioned antistatic agent is usually 0.01 to 40% by weight with respect to the binder.
It is added in the range of.

(II) Manufacture of magnetic recording medium The magnetic recording medium of the present invention is not particularly limited in its manufacturing method except that the magnetic layer is coated by a wet-on-wet system, and a known plurality of magnetic recording media can be used. It can be manufactured according to the method used for manufacturing the layer structure type magnetic recording medium. For example, magnetic powder, binder, hardener, dispersant,
A magnetic coating material is prepared by kneading and dispersing a lubricant, an abrasive, an antistatic agent, etc. in a solvent, and then the magnetic coating material is applied to the surface of the non-magnetic support.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol and propanol; esters such as methyl acetate, ethyl acetate and butyl acetate. Cyclic ethers such as tetrahydrofuran and the like; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene can be used.

When kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used. Examples of the kneading / dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a cobol mill, a tron mill, a sand mill, a sand grinder, and a Sqegvar.
Examples thereof include an i attritor, a high speed impeller disperser, a high speed stone mill, a high speed impact mill, a disper, a high speed mixer, a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader and a pressure kneader.

Of the above kneading dispersers, 0.05 to 0.5
Kneading dispersers capable of providing a power consumption load of KW (per 1 kg of magnetic powder) are a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, and a three-roll mill. To coat the magnetic layer on the non-magnetic support, simultaneous multi-layer coating is carried out by the wet-on-wet multi-layer coating method. Specifically, for example, as shown in FIG. 1, first, the film-shaped support 1 delivered from the supply roll 32.
Is an extrusion type extrusion coater 10,
11, the lower layer magnetic coating material and the upper layer magnetic coating material are applied in multiple layers by the wet-on-wet method, and then they pass through the orientation magnet or the vertical orientation magnet 33 and are introduced into the dryer 34, where they are arranged vertically. Blow hot air from the nozzle to dry. Next, the dried support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered and then wound on a winding roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce a magnetic tape for an 8 mm video camera, for example.

In the above method, each coating material is extruded through an in-line mixer (not shown), the coater 10,
11 may be supplied. In the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coater 1
0 and 11 are provided with liquid reservoirs 13 and 14, respectively,
Wet-on-wet coating of paint from each coater. That is, the magnetic coating material for the upper layer is applied in multiple layers immediately after the magnetic coating material for the lower layer is applied (when it is in a non-dried state).

As the solvent to be blended in the above paint or a diluent solvent when the paint is applied, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cenoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
A halogenated hydrocarbon such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more. The magnetic field in the orienting magnet or the vertically orienting magnet is about 20 to 5,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.
It is about 1 to 10 minutes. As the wet-on-wet multilayer coating method, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can also be used. Furthermore, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, etc. can be combined.

In the multi-layer coating by the wet-on-wet method, since the magnetic coating material for the upper layer is coated while the magnetic layer of the lower layer is in a wet state, the surface of the lower layer (that is, the boundary surface with the upper layer) is smooth. In addition, the surface property of the upper layer is improved, and the adhesiveness between the upper and lower layers is improved. As a result, especially for high density recording, the performance required for high output and low noise such as a magnetic tape is satisfied, and film durability is also required for film peeling. It is eliminated, the film strength is improved, and the durability is sufficient. In addition, the wet-on-wet multi-layer coating method can reduce dropout and improve reliability.

-Adjustment of Difference in Liquid Physical Properties between Magnetic Paints-In the present invention, the difference and viscosity of the power multiplier n obtained by fitting the flow curves of the magnetic paints in the adjacent magnetic layers in the following equation at the time of multi-layer coating. It is important to identify the difference in the coefficient K. σ = Kγ ⁿ where σ: shear stress (P _a ) γ: shear rate (S ⁻¹ ).

That is, in the present invention, the difference in n is set to 0.1 or less and the difference in K is set to 1.0 or less. When the difference in n and the difference in K are specified in this way, the surface properties of the magnetic layer are improved and the surface roughness is significantly reduced, so that the electromagnetic conversion characteristics can be improved. On the other hand, if the difference in n exceeds 0.1 or the difference in K exceeds 1.0,
The surface roughness of the magnetic layer becomes remarkable and the electromagnetic conversion characteristics deteriorate, which is not preferable. In order to set the difference of n and the difference of K in a specific range in this way, the types of the magnetic powder, the binder, the solvent, the optional components, and the like, and their compounding amounts may be appropriately selected and adjusted.

-Surface smoothing-After the above-mentioned multi-layer coating, a surface smoothing treatment is usually carried out by calendering, and thereafter, a burnishing treatment or a blade treatment is carried out as required, and slitting is carried out. At this time, the surface smoothing treatment is preferable to achieve the object of the present invention. That is, this surface smoothing treatment is effective to some extent in improving the surface property of the magnetic layer.

In the surface smoothing treatment, temperature, linear pressure, C / s (coating speed) and the like can be mentioned as calendering conditions. In order to achieve the above purpose, the temperature is usually 50 to 120 ° C. and the linear pressure is 5
0 to 400 kg / cm, C / s above 20 to 600 m /
It is preferable to keep the minute.

In the magnetic recording medium of the present invention thus obtained, a plurality of magnetic layers are laminated on a support, and the surface roughness of the magnetic layers is extremely small. Therefore, the magnetic recording medium has high electromagnetic conversion characteristics. For example, it can be suitably used as a video tape.

[0057]

EXAMPLES Examples of the present invention will be shown below. The components, blending ratios, and operation order shown below can be variously changed without changing the gist of the present invention. In addition, all "parts" in the following examples represent parts by weight.

(Examples 1 to 10 and Comparative Examples 1 to 11) Table 1
By kneading the composition shown in a pressure kneader,
Three types of lower layer magnetic coating materials A, B and C having different solid content concentrations were prepared. However, the appropriate amount shown in Table 1 means the power multiplier n and the viscosity coefficient K in the flow curve for each magnetic paint.
Is the amount added so as to be adjusted to the values shown in Table 3.

Further, by kneading the compositions shown in Table 2 with a pressure kneader, three kinds of magnetic paints D, E and F for upper layers having different binder compounding ratios and three kinds of upper layers having different solid content concentrations were used. Magnetic paints G, H and I and a kind of magnetic paint J for the upper layer containing no dispersant (phosphate ester) were prepared.

Next, these magnetic coating materials were simultaneously multilayer coated on a polyethylene terephthalate film having a thickness of 7.5 μm with an extrusion type coating head in a wet state. Magnetic field orientation treatment is performed, followed by drying, and then surface smoothing treatment with a calendar to form a two-layer magnetic layer with an upper layer dry film thickness of 0.3 μm and a lower layer dry film thickness of 2.5 μm. did.

The original fabric thus obtained is slit to 8 m.
A magnetic recording tape for an m video camera was prepared. This 8
For a magnetic recording tape for mm mm video camera, the power multiplier n and the viscosity coefficient K in the flow curve of the magnetic coating material during multi-layer coating were determined as described below, and the surface roughness state, surface roughness (Ra) and The electromagnetic conversion characteristics (S / N) were measured. The results are shown in Table 3. The difference in the power multiplier n between the upper layer magnetic coating material and the lower layer magnetic coating material and the viscosity coefficient K
FIG. 2 shows the relationship with the difference between the two.

<Determination of Power Multiplier n and Viscosity Coefficient K in Flow Curve> Shear stress and shear rate of the magnetic paint were measured using a vibrating viscometer [CJV-2000, manufactured by Chichibu Cement Co., Ltd.]. The obtained shear stress and shear rate were applied to the following equation σ = Kγ ⁿ , where σ: shear stress (P _a ) γ: shear rate (S ⁻¹ ) to determine the power multiplier and the viscosity coefficient K.

<Surface Roughness> It was visually observed using a differential interference microscope, and was evaluated as ◯ when it was fairly smooth, Δ when it was slightly rough, and x when it was considerably rough. <Surface Roughness Ra (nm)> The surface roughness was measured using a tally step roughness meter manufactured by Taylor Hobson. The measurement conditions are: stylus 2.5 x 0.1 μm, needle pressure 2 mg, cut
Off filter 0.33Hz, measurement speed 2.
The reference length was 5 mm / sec and 0.5 mm. In addition, in the roughness curve, unevenness of 0.01 μm or more is cut.

<Electromagnetic conversion characteristics> □ Chroma output, chroma S
/ N, RF output, and Lumi S / N; reference tape [manufactured by Konica Corporation] is expressed as a relative value with 0 dB. For the chroma output, the chroma output at 500 KHz was measured using a VTR deck for measuring the chroma output (unit: d
B). For the chroma S / N, a noise meter (manufactured by Shibasoku) was used, and the S / N difference of the sample at 100% white signal was determined in comparison with the reference tape [manufactured by Konica Corporation]. The RF output was measured at 4 MHz using a VTR deck for measuring RF output (unit: d
B). Lumi S / N uses a noise meter (manufactured by Shibasoku), and in comparison with the standard tape [manufactured by Konica Corporation],
The difference in S / N of the samples in the chroma signal was obtained.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

[Table 3]

[0068]

According to the present invention, it is possible to provide a magnetic recording medium in which the surface roughness of the magnetic layer is reduced and the electromagnetic conversion characteristics are improved, and a manufacturing method thereof.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method of manufacturing a magnetic recording medium of the present invention.

FIG. 2 is a graph showing the relationship between the difference in the power multipliers and the difference in the viscosity coefficients of the respective magnetic paints in the magnetic recording media of Examples and Comparative Examples of the present invention.

Front Page Continuation (72) Inventor Seiichi Tobizawa, Konica Stock Company, 1 Sakura-cho, Hino City, Tokyo (72) Inventor Hajime Takeuchi, 1-cho, Toshiba-cho, Kawasaki-shi, Kanagawa

Claims (2)

[Claims] 1. A power multiplier when the respective flow curves of the upper layer magnetic coating material forming the upper layer magnetic layer and the lower layer magnetic coating layer forming the lower layer magnetic layer adjacent to the upper layer are fitted to the following equations. A plurality of magnetic coating materials for the lower layer and magnetic coating material for the upper layer, which are adjusted so that the difference in n is 0.1 or less and the difference in the viscosity coefficient K is 1.0 or less, are applied in multiple layers on a non-magnetic support. A magnetic recording medium comprising the magnetic layers of 1. σ = Kγ ⁿ where σ: shear stress (P _a ) γ: shear rate (S ⁻¹ ). 2. A method for producing a magnetic recording medium having a multi-layer magnetic layer by applying a multi-layer coating of a magnetic coating on a non-magnetic support, the magnetic coating for an upper layer forming an upper magnetic layer being adjacent to the upper magnetic coating. When the respective flow curves of the lower magnetic coating material for forming the lower magnetic layer are fitted to the formula of claim 1, the difference of the power multiplier n is 0.1 or less, and the difference of the viscosity coefficient K is A method for producing a magnetic recording medium, characterized in that the magnetic coating material for the upper layer is applied onto the magnetic coating material for the lower layer which is adjusted to 1.0 or less.