JPS61214129A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce dropouts in repeated traveling by providing a magnetic recording layer having high electric resistance, forming the binder of a backcoat layer with a radiation-curing resin and obtaining the low-resistance backcoat layer. CONSTITUTION:Since barium ferrite itself has a high electric resistance of >=10<16>OMEGA/cm<2> and hence the resistance of a magnetic recording medium is >=10<10>OMEGA/cm, the recording medium is easily covered with dust by electrification and dropouts are easily generated. However, by adjusting the resistance of the backcoat layer to <=10<10>OMEGA/cm<2>, dust is hardly deposited on the magnetic recording layer having >=10<10>OMEGA/cm<2>. Accordingly, dropouts are remarkably reduced, a cinching phenomenon is eliminated and stickiness is also eliminated. Consequently, when a radiation-curing binder is used, dropouts can be prevented, since rear type transfer is not carried out.

Description

[Detailed description of the invention]

Birth Ju111 minutes! The present invention relates to a magnetic recording medium in which ferromagnetic particles are vertically oriented and has a coated magnetic recording layer, in particular, the magnetic recording layer contains hexagonal plate-shaped (hexagonal plate-shaped) barium ferrite magnetic powder,
The present invention relates to a magnetic recording medium in which the back coat layer is made of a specific binder and has a specific electrical resistance. As the days continue to grow, magnetic recording media are used for audio and video. It has become widely used in fields such as computers and magnetic disks, and is expected to be used in fields such as video floppies in the future, but the amount of information recorded on magnetic recording media is also increasing year by year. As a result, magnetic recording media are increasingly required to have higher recording densities. Conventionally, magnetic properties of magnetic recording media such as magnetic tapes have been improved by orienting acicular magnetic powder in the longitudinal direction in the magnetic recording layer. However, although they could provide high output in the low frequency band, they had limitations in high-density recording. Furthermore, recently, a magnetic recording medium has been proposed in which the magnetic powder is flat and uses barium ferrite magnetic powder in the magnetic recording layer, which has an axis of easy magnetization in the perpendicular direction (
JP-A-57-195328). However, although these barium ferrite magnetic powders have good short-wavelength recording characteristics, they have the disadvantage of poor erasing characteristics. Barium ferrite itself has a high electrical resistance of 100/cm2 or more, so if a conductive substance such as carbon black is not used in combination with barium ferrite, the magnetic recording medium may stick to the head, or the coating process etc. During the manufacturing process, sticking occurs on guide rollers, calendar rollers, etc., and in severe cases, discharge noise is generated. Therefore, it is usually considered to use a conductive substance in combination, and carbon black is added to increase its electrical resistance. The current situation is that it is declining. However, as mentioned above, the electrical resistance is high, so although ordinary carbon black can lower the electrical resistance, it is not yet sufficient. Currently, among magnetic recording media, magnetic disks have come to be widely used in the fields of computers and magnetic cameras. Along with this, the amount of information to be recorded on magnetic disks is increasing year by year, and magnetic disks with high density recording capability are increasingly required. As recording density increases, the dropout problem becomes more prominent. That is, in the current recording system using a magnetic head, the spacing loss between the disk or tape and the head is expressed as 54.6 d/in (dB) (d: distance between the disk and head, in: recording wavelength). As can be seen from this equation, in short wavelength recording with high recording density, the rate of output reduction due to spacing is significantly greater than that in long wavelength recording. Therefore, even if a small foreign object is present on the disk or tape, it will be detected as a dropout. What are the possible causes of dropout? Magnetic powder from the coating surface of the magnetic disk, which is caused by deterioration of the coating due to repeated stress, or particles and dust that are generated when the base is scraped off during driving, are electrostatically attached to the base surface. Furthermore, it may be transferred to the coating surface. In order to prevent these problems, some measures have been taken to strengthen the coating film for the former cause, and for the latter cause, the surface of the support opposite to the magnetic surface of the magnetic disk or tape has been improved. (on the back side). Applying a paint made by kneading carbon black or graphite with an organic binder, applying an antistatic agent, etc. to reduce the charging phenomenon of the base, or applying a paint made by kneading silicon oxide etc. with an organic binder, Methods have been devised to increase the strength of the base and reduce the possibility of base wear. Through these processes, the tendency for dropouts to increase due to repeated driving can be significantly suppressed. However, the current level is still not perfect and needs to be further reduced. In order to improve the above-mentioned points, the present inventors conducted further research and found that the magnetic recording layer is made of hexagonal plate-like barium ferrite with a grain size of 0.2 Pm or less and a plate-like ratio of 6 or more. As mentioned above, barium ferrite itself has an electrical resistance of 10Ω/
The electrical resistance of the magnetic recording layer is as high as Cm2 or more, and is 10#Ω/
Although the electromagnetic conversion characteristics become better when cm2 or more, 1
Although various problems arise, the electrical resistance of the magnetic recording layer is
By setting the electrical resistance of the back coat layer to 10/'O/cm2 or less even if it is more than 'Ω/cm2, it becomes surprisingly difficult for dirt and dust to adhere to the magnetic recording layer, and therefore, dropouts are drastically reduced. However, there is no cinching phenomenon and no stickiness, and by using a radiation-curable binder, there is no back mold transfer, so dropouts can be prevented. By setting the ratio within a specific range, the back coat surface becomes tough, increasing durability, eliminating scratches due to the brittle back surface, and further reducing the surface roughness of the back coat layer to below a specific value. The inventors have discovered that this results in no deterioration of electromagnetic conversion characteristics, improved wear resistance, and less curling, and has thus arrived at the present invention. That is, in the present invention, particles with a diameter of 0.2
Pm or less, a magnetic recording layer containing hexagonal plate-like barium ferrite magnetic powder with a platelet ratio of 6 or more, and a back coat layer on the other surface, in which the magnetic recording layer has an electrical resistance of 10"0/ cm2 or more, the binder of the back coat layer is made of a radiation-curable resin, and the electrical resistance thereof is 10''Ω/cm2 or less.Hexagonal crystal system used in the magnetic recording layer. Platy barium ferrite is represented by the chemical formula Ba0.6Fe203, and in addition,
Part of Ba and Fe in this chemical formula are Ti, Cr, Co,
Zn, In, Mn, Cu. Those substituted with metals such as Ge, Nb, Ca, Sr, Pb, and Ni are included. Barium ferrite magnetic powder has a diameter of 0.2 or less. Preferably 0.157-am or less, more preferably 0°1,-& m or less, plate ratio 6 or more, even more preferably 7
That's all. Barium ferrite has a hexagonal plate shape, so it has a greater effect on surface roughness than needle-shaped magnetic powder, and if the diameter is larger than the above or the plate ratio is small, the surface roughness will decrease. Strongly undesirable. When the particle size is in the above range, the vertical component is fully utilized;
Moreover, the surface smoothness of the magnetic layer is improved, noise is sufficiently low, and high-density recording can be achieved. Methods for producing barium ferrite include ceramic method, coprecipitation-firing method, hydrothermal synthesis method, and flux method. There are glass crystallization methods, alkoxide methods, plasma jet methods, etc., and any of these methods can be used. In the present invention, the magnetic recording layer containing barium ferrite magnetic powder has an electric resistance of 1
Very high, over 0 Ω/cm2. Therefore, the electrical resistance of the magnetic recording layer is 10"Ω/cm or more. If the electrical resistance of the magnetic recording layer is 10IO/c
When the magnetic layer is more than m2, dust and flakes are likely to accumulate due to charging, and dropouts are likely to occur.If the electrical resistance of the magnetic layer is lower than 10''/cm2, the above-mentioned phenomenon does not occur. In the back coat layer of the present invention, the binder must be made of a radiation-curable resin. When forming the back surface, if the back surface is formed before the magnetic surface, the unevenness of the back surface will be transferred to the magnetic surface during surface smoothing by calendering after forming the magnetic surface, and the smoothing of the magnetic coating will be difficult. Not enough is done. Therefore, back coating treatment is usually performed on the back surface of the support after a magnetic coating film is formed on the support. Since the backing layer is required to be strong so that dropouts do not increase even when the number of runs is increased, a thermosetting resin is usually used as a binder. In that case, after the backing layer is applied, the tape is wound up and subjected to a heat curing treatment. However, at the time the coating is finished, the hardening reaction has not yet started in the back layer and the coating film is weak. carbon black, graphite. Or the back coating surface containing other inorganic fillers,
It is easy to transfer to the magnetic layer surface on the opposite side where it is in contact,
It was found that this metastasized substance was the cause of dropouts and head clogging. Moreover, it is thought that this phenomenon also occurs in thermoplastic resins. In order to eliminate the above-mentioned problems in the back layer forming process, the present invention uses a coating material in which a radiation-sensitive resin (a resin that hardens when irradiated with radiation) is used as a binder and is mixed with other back coat additives. After the back layer is formed, it is irradiated with radiation from an active energy ray source and then subjected to a curing treatment, or the surface is treated as is and then a hardening treatment is performed to create three-dimensional crosslinking in the back layer, resulting in a strong coating film. After that, the tape is wound up to reduce dropouts caused by the above-mentioned causes. According to this method, the tape is wound up after the crosslinking reaction of the coating film is completed, so even if the back layer is brought into close contact with the magnetic layer by winding, no transition from the back layer to the magnetic layer occurs. More importantly, magnetic disks have the problem of curl. In single-sided magnetic disks, this curling is thought to occur because the mechanical balance between the coating film and the support cannot be maintained. That is, since the Young's modulus of the coating film is greater than the Young's modulus of the support, warpage occurs on the coating film side. Since curl adversely affects head touch and runnability, it is preferable to minimize curl as much as possible.Therefore, a back coating film containing carbon black, graphite, or other inorganic filler is applied to the support opposite to the magnetic layer. It is possible to improve the warping of the disk, which is a problem with head touch and running performance, by providing a mechanical balance between the magnetic surface and the base/back surface. As a result, curls may occur in the winding direction. This causes the base to shrink and promotes curling. However, in the case of electron beam curing, since the curing can be done online, there is no problem with thermal curing, and curling can be advantageously improved. In this way, in a magnetic disk or tape having a magnetic layer containing barium ferrite magnetic powder on one side of the support, a back coat layer is provided on the back side, and a radiation-sensitive curable resin is used as a binder to form a disk. This solves both the warping problem and the dropout problem all at once. The electrical resistance of the back coat layer of the present invention is 10/'
If the electrical resistance of the back coat layer is higher than 10"Q/cm2, frictional electrification will cause sticking during the process, causing sticking of the magnetic layer and back layer, and failure of the incorporation. During the process, adhesion and dust adhesion may occur, causing dropouts.If one side is low, adhesion will not occur.In the case of reel-to-reel type video tapes, audio tapes, etc., the magnetic recording layer may be scraped. However, dropouts occur and other magnetic properties are also significantly deteriorated. In order to reduce the electrical resistance to 10"Q/cm2 or less, inorganic pigments such as 1) conductive carbon black, graphite, and 2) ) As an inorganic filler “C5i02.Ti”
O2, A1203. Cr203, Sic, Cab,
CaC:03, zinc oxide, goethite, PeFa2
03, talc, kaolin, Ca5O, boron nitride, graphite fluoride, molybdenum disulfide, ZnS, etc.
Fine particle pigments (aerosil type, colloidal type) such as: S ic2, Al2O3, T i 02,
ZrO2, Cr2O3, Y2O3, CeO2, Fe
304. Fe2O3, ZrSiO4,5b205.5n
A method of adding 02 or the like is adopted. The particle size of these fine particle pigments is less than 200A, more preferably 150A or less. For example, in the case of 5i02, these fine particle pigments include: ■ Ultrafine particle colloidal solution of silicic anhydride (Snowtex, water-based, methanol silica sol, etc., Nissan Chemical);
Examples include ultrafine particulate anhydrous silica (standard product 100A) (Aerosil, Nippon Aerosil Co., Ltd.) produced by combustion of purified silicon tetrachloride. Further, the ultrafine particle colloidal solution of (1) above, ultrafine aluminum oxide produced by the same vapor phase method as (2), titanium oxide, and the above-mentioned fine particle pigment may be used. The appropriate amount of such inorganic pigment to be used is 20 to 200 parts by weight per 100 parts by weight of the binder for 1), and 10 to 300 parts by weight for 2). The membrane becomes brittle. On the contrary, it has the disadvantage of increasing the number of dropouts. The radiation-curable resin used in the back coat layer of the present invention is one that contains two or more unsaturated double bonds in one molecule that generates radicals and creates a crosslinked structure when exposed to radiation, and it also This is also possible by modifying the plastic resin to make it radiation sensitive. Specific examples of radiation-sensitive modification include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, and allylic double bonds such as diallylphthalate. ,
This method involves introducing into a molecule a group that can be crosslinked or polymerized and dried by radiation irradiation, such as a maleic acid double bond such as maleic acid or a maleic acid derivative. Any unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used. Thermoplastic resins that can be modified into radiation-curable resins are shown below. (1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein Acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, such as VROH, VYNC, VYBGX, VERR, VYE manufactured by UCC
Examples include S, VMCA, VAGH, etc., and radiation sensitivity modification is performed by introducing an acrylic double bond, a maleic acid double bond, or an allylic double bond into this material by the method described below. (2) Saturated polyester resin Saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid, and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1°2 propylene glycol,
1,3 butanediol, dipropylene glycol, 1,
4-butanediol. 1.6 hexanediol, pentaerythritol. Sorbitol, glycerin, neopentyl glycol,
Examples include saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 1,4 cyclohexane dimetatool, or resins obtained by modifying these polyester resins with SO3Na etc. (e.g. Vylon 53S), and these can also be treated similarly. Radiation sensitivity degeneration is performed. (3) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components, and the hydroxyl groups contained in these resins are subjected to radiation-sensitive modification by the method described below. (4) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, epichlorohydrin, and methylepichlorohydrin. For example, Shell Chemical (Epicoat 152, 154, 82)
8゜1001.1004.1007), manufactured by Dow Chemical (D E N431゜D E R732, D E R5
11, DER331), Dainippon Ink ml (Evicron 400, 800), and phenoxy resin manufactured by UCC (PKHA, PKHC,
PKHH), a copolymer of brominated bisphenol A and epichlorohydrin, Dainippon Ink Chemical Industry II (Evicron 145.152.153.1120), and these also include those containing a carboxylic acid group. Radiation sensitivity modification is performed using the epoxy groups contained in these resins. (5) Various cellulose derivatives can be used, but particularly effective ones include nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, acetyl cellulose, etc.
Radiation sensitivity modification is performed using the hydroxyl groups in the resin by the method described below. Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiroacetal resins, Acrylic resins containing at least one type of acrylic ester and methacrylic ester containing hydroxyl groups as a polymerization component are also effective. Furthermore, by blending a thermoplastic nidistomer or a prepolymer with the radiation-sensitive modified thermoplastic resin, an even tougher coating film can be obtained. Furthermore, as described below, it is more effective if these elastomers or prepolymers are similarly modified to be radiation sensitive. Listed below are elastomers or prepolymers that can be combined with the radiation-sensitive resin. (1) The use of polyurethane elastomers or prepolymer polyurethanes is particularly effective in terms of their abrasion resistance and good adhesion to substrate films, such as PET films. Examples of urethane compounds include isocyanates such as 2.4-toluene diisocyanate, 2.6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, P-phenylene diisocyanate, 3.3'-
Dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3
, 3'-dimethylbiphenylene diisocyanate, 4.
4'-biphenylene diisocyanate, hexamethylene diisocyanate. Infron diisocyanate, dicyclohexylmethane diisocyanate, desmodur. Various polyvalent isocyanates such as Desmodur N and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane,
Polyhydric alcohols such as 4-butanediol, 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexane dimetatool, phthalic acid, isophthalic acid, terephthalic acid,
(by condensation polymerization with saturated polybasic acids such as succinic acid, adipic acid, sebacic acid), linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic esters, hydroxyl Polyurethane elastomers and prepolymers made of polycondensates of various polyesters such as methacrylic esters are effective. It is very effective to modify these urethane elastomers to make them radiation sensitive by reacting their terminal isocyanate groups or hydroxyl groups with monomers having acrylic double bonds or allylic double bonds. be. It also includes those containing OH, COOH, etc. as a polar group at the end. (2) Acrylonitrile-butadiene copolymer elastomer Elastomers such as an acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD Retired Resin manufactured by Sinclair Petrochemical Co., Ltd. or Hiker 1432 J manufactured by Nippon Zeon Co., Ltd. are particularly suitable for use in butadiene. It is suitable as an elastomer component whose double bond generates radicals by radiation and is crosslinked and polymerized. (3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Retired Resin R-15 manufactured by Sinclair Petrochemical Co., is particularly suitable in terms of compatibility with thermoplastic resins. R
Since the -15 prepolymer has a hydroxyl group at the molecular end, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the molecular end, making it more advantageous as a binder. In addition, polybutadiene cyclized product 1 CBR- manufactured by Nippon Synthetic Rubber Co., Ltd.
M901 also has excellent properties when combined with thermoplastic resin. Other suitable thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber,
Chlorinated rubber, acrylic rubber, isoprene rubber, and their cyclized products (ClR701 manufactured by Nippon Gosei Rubber) are available, and elastomers such as epoxy modified rubber and internally plasticized saturated linear polyester (Toyobo Vylon $300) can also be treated with the radiation-sensitive modification treatment described below. It can be used effectively by applying Next, an example of radiation-curable polymer synthesis will be explained. a) Synthesis of acrylic modified vinyl chloride vinyl acetate copolymer resin (radiation sensitive modified resin) Partially saponified vinyl chloride vinyl acetate copolymer having OH groups (average degree of polymerization n=500
-) 750 parts, 1250 parts of toluene, and 500 parts of cyclohexanone were placed in a 4-hole flask (No. 51), heated and dissolved, and after raising the temperature to 80°C, 61.4 parts of 2-hydroxyethyl methacrylate adduct x of tolylene diisocyanate was added, and further Tin octylate 0.012 parts, hydroquinone 0
．． 012 parts of the mixture were added and allowed to react at 80°C in a N2 stream until the NGO reaction rate reached 90%. After the reaction is completed, the mixture is cooled and diluted with 1250 parts of methyl ethyl ketone.

[×Production of 2-hydroxyethyl methacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) After heating 348 parts of TDI to 80°C in a 11-hole flask in a N2 stream, 2-ethylene methacrylate 2
60 parts, tin octylate 0.07 parts, hydroquinone 0
．． 05 parts was stirred at 80°C for 3 hours to complete the reaction while controlling the cooling so that the temperature inside the reaction vessel was 80 to 85°C. After the reaction was completed, the reactor was taken out and cooled to obtain TDI 2HEMA in the form of a white paste. b) Synthesis of acrylic modified butyral resin (radiation-sensitive modified resin) 100 parts of butyral resin BM-5 manufactured by Building Blocks Chemical Co., Ltd. was mixed with 191.2 parts of toluene and 71°4 parts of cyclohexanone at 51°C.
Pour 4 pieces into a flask, heat and melt, and after raising the temperature to 80℃, TD.
1 reaction by adding 7.4 parts of 2HEMA adduct × of I, further adding 0.015 parts of tin octylate, and 0.015 parts of hydroquinone, and reacting at 80°C in a N2 stream until the NC○ reaction rate reached 90% or more. After completion, cool and dilute with methyl ethyl ketone. C) Synthesis of acrylic modified saturated polyester resin (radiation-sensitive modified resin) Saturated polyester resin (Vylon RV-200 manufactured by Toyobo Co., Ltd.)
), 100 parts of TDI was dissolved in 116 parts of toluene and 116 parts of methyl ethyl ketone and heated to 80°C.
Add 3.55 parts of Adduct x, tin octylate 0.00
Add 7 parts and 0.007 parts of hydroquinone, and heat at 80°C with N.
2. Let the reaction occur until the NGO reaction rate in the gas flow reaches 90% or more. d) Synthesis of O epoxy resin acrylic modified product (radiation sensitive modified resin) Epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.), 4
After heating and dissolving 00 parts in toluene 50 parts and methyl ethyl ketone 50 parts, N,N-dimethylbenzylamine 0.00
6 parts of hydroquinone and 0.003 parts of hydroquinone were added, the temperature was raised to 80°C, 69 parts of acrylic acid was added dropwise, and the mixture was allowed to react at 80°C until the acid value reached 5 or less. Synthesis of acrylic modified O phenoxy resin (radiation-sensitive modified resin) 600 parts of a phenoxy resin having an OH group (manufactured by PKHSUCC, molecular weight 30,000) and 1800 parts of methyl ethyl ketone were placed in a No. 31 4-tube flask, heated and dissolved, and heated to 80°C. After warming, 6.0 parts of 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate was added,
Furthermore, 0.012 parts of tin octylate and 0.0 parts of hydroquinone.
012 parts of the mixture were added and allowed to react at 80°C in a N2 stream until the NGO reaction rate reached 90%. The molecular weight of this phenoxy modified product is 35,000. There is one double bond per molecule. e) Synthesis of acrylic modified urethane elastomer (radiation-curable elastomer) 250 parts of a diphenylmethane diisocyanate (MDI)-based urethane prepolymer having a terminal isocyanate (Nipporan 3119 manufactured by Nippon Polyurethane), 2HEMA32.
5 parts, 0.07 parts of hydroquinone, 0.07 parts of tin octylate.
Pour 009 parts into a reaction can, heat and melt at 80°C, and then dissolve TDI4.
3.5 parts were added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and the reaction rate was 95% at 80°C after dropping.
Let it react until it reaches the above level. f) Synthesis of acrylic modified polyether-terminated urethane-modified elastomer (radiation-curable elastomer) Polyether PTG-500, 2 manufactured by Nippon Polyurethane Co., Ltd.
50 parts, 2HEMA 32.5 parts, hydroquinone 0.0
07 parts and 0.009 parts of tin octylate were placed in a reaction can.
After heating and dissolving at 80°C, 43.5 parts of TDI was added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and after the dropwise addition was completed, the reaction was allowed to occur at 80°C until the reaction rate reached 95% or more. g) Synthesis of polybutadiene elastomer acrylic modified product (radiation curable nidistomer) Low molecular weight terminal hydroxyl group polybutadiene polybutadiene BD Liqui 2 Toresin R-15,250 manufactured by Sinclair Petrochemical Co.
part, 2HEMA32.5 parts, hydroquinone 0.007 parts
Place 0.009 parts of tin octylate in a reaction vessel, and add 80 parts of tin octylate.
After heating and dissolving 43.5 parts of TDI at ℃, the temperature inside the reaction vessel was 8.
It is added dropwise while cooling to a temperature of 0 to 90°d, and after the completion of the dropping, it is allowed to react at 80°C until a reaction rate of 95% or more is achieved. In addition, some polymers are known to disintegrate when exposed to radiation, while others cause crosslinks between molecules. Polymers that cause crosslinks between molecules include polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyacrylamide, and These include vinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. With such cross-linked polymers, the cross-linking reaction occurs even without the above-mentioned modification, so in addition to the modified products mentioned above, these resins can be used as they are as back coat resins for radiation cross-linking. be. Furthermore, according to this method, even solvent-free resins that do not use solvents can be cured in a short time.
Such resin can be used as a back coat. In addition, as a functional group, alcohol type as a hydroxyl group,
Also included are those containing aromatic, aliphatic, sulfonic acid groups, amine groups, ammonium groups, etc. as phenolic, phosphoric acid, and carboxylic acid groups. Preferred radiation-curable resin compositions are (A) plastic-like compounds having two or more unsaturated double bonds that are curable by radiation and have a molecular weight of 5,000 to 100,000, and (B) curable by radiation. A rubbery compound with a molecular weight of 3,000 to 100,000 that has one or more unsaturated double bonds or does not have radiation curability,
and (C) a compound with a molecular weight of 200 to 3,000 having one or more unsaturated double bonds that is curable by radiation, (A) 20 to 70% by weight, (B) 20 to 80% by weight.
, (C) in a proportion of 10 to 40% by weight. This increases the breaking strength of the coating film, strengthens the VN film, reduces backcoat abrasion, and eliminates the transfer of inorganic filler powder from the backcoat layer to the magnetic layer, resulting in less dropouts and improved rollability. A magnetic recording medium can be obtained which has uniform characteristics in the length direction and is free from curling during curing when wound into a shape. In manufacturing the magnetic recording medium of the present invention, if the organic binder is a thermosetting type, the lubricant in the back coat layer is transferred to the magnetic thin film during the manufacturing process, resulting in an output drop due to unstable running as described above. However, it is undesirable that the image may not appear, or the friction level is still very insufficient, and the ferromagnetic thin film may be removed or destroyed by back-type transfer, which is not desirable. Therefore, it is considered to apply a top coat first. However, they are often easily damaged and inconvenient for operation. Furthermore, in the case of a thermosetting type, there is a problem of a difference in electromagnetic conversion characteristics between the inside and outside of the jumbo roll during thermosetting due to the back-coat surface transition due to curling during curing. On the other hand, in the case of radiation-curable resins, continuous curing is possible due to manufacturing, the curing time is short, dropouts can be prevented because there is no back mold transfer, and in addition, radiation-curing and top coating Processing can be done online, which helps save energy and reduce the number of people involved in manufacturing, leading to cost reductions. In terms of characteristics, in addition to dropouts caused by tight winding during thermosetting, there is no difference in output due to the distance in the length direction of the magnetic tape due to differences in pressure at the inner and outer diameters when wound into a roll. In the radiation-curable resin binder consisting of (A), (B) and (C), (A) alone lacks flexibility, (B) alone lacks elasticity, and (A)
, (B) can be combined to increase the fracture energy, but there is a limit to increasing the brittle energy, and (
Perhaps because of the low hardness of A) and (B) alone, they became sticky under high temperature and humidity, resulting in high static friction. On the other hand, (A)
. By further combining (B) with (C), the crosslinking property increases, the binder has high tensile strength, breaking energy, and brittle energy, and there is no pack coat peeling.
Creates a strong coating film with a high degree of curing. Therefore, when it was stored at a high temperature of 50° C. and 80% for 5 days, no adhesion occurred, the coefficient of friction was low, and no image distortion occurred. This is because the addition of (C) increased the crosslinking properties of the back coat film and increased the degree of curing. By further adding (C) to (A) and (B), (A
) and (B) alone, the (A) component can now be used even if it has a low molecular weight. By introducing component (C) into a plastic-like material made of component (A), the plasticity is improved and the degree of curing is improved, resulting in a coating film with high viscoelasticity and high brittle energy. It is something that In the radiation curable resin binder of the present invention, (A)
If the molecular weight of (B) is less than 5,000 and the molecular weight of (B) is less than 3.500, the coating film will become hard and the back coat will be severely scraped, and the electromagnetic conversion characteristics will also deteriorate.
If it exceeds o, the electromagnetic conversion characteristics will deteriorate due to poor dispersion, and if (B) is radiation curable, the characteristics will deteriorate, resulting in a decrease in strength. For (C), one molecular weight is 3
If it exceeds 0.000°, the crosslinkability will decrease and the strength of the coating will decrease. (A) is 10,000-80,000, (B) is 3,000-80,000. (C) is 200-2,50
The preferred molecular weight range is 0, and (B) is preferably radiation-curable because it increases crosslinking properties and increases coating film strength. The blending ratio of (A), (B), and (C) is as follows: (A) is 20~
70% by weight, preferably 30-70% by weight, (B) is 2
0 to 80% by weight, preferably 20 to 60% by weight, (C)
is 10 to 40% by weight, preferably 10 to 30% by weight. The molecular weights of the compounds (A), (B), and (C) of the present invention are determined by the number average molecular weight measured by the following method. *Measurement of average molecular weight of binder by GPC
El Permeation Chromato
(graphy) is a method that separates molecules in a sample based on their size in a mobile phase. This method performs liquid chromatography by filling a column with a porous gel that acts as a molecular sieve. To calculate the average molecular weight, use polystyrene of known molecular weight as a standard sample and create a calibration curve from its elution time. From this, calculate the average molecular weight in terms of polystyrene. There are molecules with molecular weight Mi in a given high molecular weight substance.
If there are i pieces, the number average molecular weight M n = Z N i M i can be expressed. ΣNi The number of unsaturated double bonds in the compounds (A), (B), and (C) of the present invention is 2 or more, preferably 5 (A) per molecule.
Above, (B) is 1 or more, preferably 5 or more, and (C) is 1
or more, preferably 3 or more. Particularly preferred combinations of the radiation-curable binder composition of the present invention include a vinyl chloride-vinyl acetate copolymer in which the compound (A) is partially saponified, and a vinyl chloride-vinyl acetate copolymer in which a carboxylic acid is introduced. A compound obtained by reacting a compound having an isocyanate group obtained by reacting a polyisocyanate compound with a phenoxy resin, and an acrylic compound or a methacrylic compound having a functional group that is reactive with the isocyanate group,
The compound (B) is a compound obtained by reacting a polyol with an isocyanate compound, or a compound obtained by reacting an acrylic compound or a methacrylic compound having a functional group having monoreactivity with an isocyanate compound or a polyol (polyurethane elastomer), (C) is a polyfunctional (meth)acrylate monomer, oligoester acrylate, or a low molecular weight compound of (B). The active energy rays used for crosslinking the back coat of the present invention include electron beams using a radiation accelerator as a source, Co6
7-ray with 0 as the source, β-ray with 5r90 as the source,
Examples include X-rays or ultraviolet rays using an X-ray generator as a radiation source. In particular, as an irradiation source, it is advantageous to use radiation using a radiation heater from the viewpoints of controlling the absorbed dose, introducing it into the Il manufacturing process line, and shielding ionizing radiation. The radiation characteristics used when curing the back coat layer include an acceleration voltage of 100 to 750 KaV,
It is convenient to use a radiation accelerator of preferably 150 to 300 KeV and irradiate at an absorbed dose of 0.5 to 20 Megaland. When curing the back layer with radiation according to the present invention, a low-dose type radiation accelerator (electrocurtain system) manufactured by Energy Sciences, Inc. in the United States is introduced into the tape coating processing line, and the secondary X-rays inside the accelerated This is extremely advantageous for shielding, etc. Of course, a van de Graaf type accelerator, which has been widely used as a radiation accelerating material, may also be used. In addition, during radiation crosslinking, it is important to irradiate the back coat layer with radiation in an inert gas stream such as N2 gas or He gas. 03 caused by
This is extremely disadvantageous because it prevents radicals generated in the polymer from working advantageously in the crosslinking reaction. Therefore, the atmosphere in the area to be irradiated with active energy rays is N2. It is important to maintain an atmosphere of an inert gas such as He or GO2. For magnetic recording media such as magnetic tapes and other disks and reel-wound media, the back coat layer has an electrical resistance of 10"070 m2 or less and a Young's modulus E' of 200 to 1.
500 kg/mm2, and its surface roughness is required to be R20.0.20 Pm or more at a cutoff of 0°17 mm for reel-wound products. E'(Young's modulus) can be varied depending on the conductive filler, inorganic filler, and back coating resin.1Surface roughness can be varied by changing the particle size and dispersion method of the conductive filler and inorganic filler. can. Note that the dispersion method can be changed depending on the dispersant and the dispersion time per dispersion machine. If E'(Young's modulus) is less than 200 Kg/mm2, the breaking strength will be poor, and in the case of reel-wound products, the back surface will become scratched during endurance running, and the E'(Young's modulus) will be 1500 Kg/mm2.
The above is undesirable because it is too hard and scrapes the magnetic surface. Even with disk type, after coating, the above is undesirable because it gets scratched during process running, winding, and assembly. Also, reel winding is undesirable. The surface roughness of the back coat layer is R20, 0, 20P with a cutoff of 0.17 mm.
If it is more than m, the electromagnetic conversion characteristics will be deteriorated, a cinching phenomenon, scraping of the back coat surface, stickiness will occur, and dropout will also become large. For the magnetic recording layer of the present invention, thermoplastic, thermosetting, or reactive resins conventionally used for magnetic recording media, or mixtures thereof, are used. In particular, radiation-curable resins are preferred. The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 20.
0 to 2,000, such as vinyl chloride-vinyl acetate copolymers (including those with carboxylic acid introduced),
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
(including those with carboxylic acid introduced), vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic 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 (cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether
Acrylic ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. 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, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin, and incyanate. mixtures of prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and It is a mixture of these. Particularly preferred are cellulose resins (nitrified cotton, etc.),
vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Thermosetting resin consisting of a combination of urethane (using hardening agent)
, or from vinyl chloride-vinyl acetate-vinyl alcohol copolymers (including those into which carboxylic acid is introduced), or acrylic-modified vinyl chloride-vinyl acetate-vinyl alcohol copolymers (including those into which carboxylic acid is introduced) and urethane acrylates. It is made of a radiation-curable resin. In addition to the above-mentioned preferred combinations, radiation-curable resins include acrylic double bonds such as acrylic acid, methacrylic acid, or ester compounds thereof, which exhibit radically polymerizable unsaturated double bonds, and diallylphthalate. It is possible to use resins containing or introducing into the molecule of a thermoplastic resin a group that can be crosslinked or polymerized and dried by radiation irradiation, such as an allyl double bond or an unsaturated bond such as maleic acid or a maleic acid derivative. Other binder components that can be used include acrylic acid as a monomer,
Examples include methacrylic acid and acrylamide. As binders with double bonds, various polyesters, polyols, polyurethanes, etc. can be modified with compounds having acrylic double bonds, and polyhydric alcohols and polyhydric carboxylic acids can be added as necessary. Products with various molecular weights can also be produced depending on the method. The above-mentioned radiation-sensitive resins are some of them, and these can also be used in combination. More preferred is (A) having two or more unsaturated double bonds that are curable by radiation. A plastic-like compound with a molecular weight s, ooo ~ 100,000, (B) having one or more unsaturated double bonds that are curable by radiation, or a molecular weight 3,000 ~ too, o that does not have radiation curability. . O rubbery compound, and (C) having one or more unsaturated double bonds that are curable by radiation, with a molecular weight of 200 to
3,000 compounds, (A) 20-70% by weight, (B
) 20 to 80% by weight, and (C) 10 to 40% by weight. The molecular weights of the oligomers and polymers of the compounds (A), CB), and (c) above are based on the number average molecular weight determined by the measuring method described in the section of the back coat layer. When a radiation-curable resin is used, it is preferable because the curing time is short and there is no transfer of fillers or the like on the surface of the back coat to the magnetic layer after one winding. On the other hand, in the case of thermosetting resins, the difference in electromagnetic conversion characteristics between the inside and outside of the jumbo roll during thermosetting becomes a problem because of the back-type transition of the backcoat surface due to curling during curing. As the curing agent for thermosetting resins, all commonly used curing agents can be used, but isocyanate-based curing agents are particularly preferred, and examples thereof include Crisbon 4565.4560 manufactured by Dainippon Ink and Chemicals Co., Ltd. , Coronate manufactured by Nippon Polyurethane Industries, Ltd., and Takenate XL-1007 manufactured by Takeda Pharmaceutical Company Limited. Further, in the magnetic recording layer and back coat layer of the present invention, commonly used inorganic pigments, lubricants, other dispersants, antistatic agents, etc. can be used in accordance with conventional methods. As the inorganic pigment, those mentioned above are used. As the lubricant, silicone oil, fluorine oil, fatty acid, fatty ester, paraffin, liquid paraffin, surfactant, etc. can be used as the lubricant conventionally used in this type of back coat layer, but fatty acids and/or fatty acid esters can be used. It is preferable to use Fatty acids include caprylic acid, capric acid, lauric acid,
myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linuric acid,
Fatty acids with 12 or more carbon atoms such as stearolic acid (RCOO)
H and R are alkyl groups having 11 or more carbon atoms), and fatty acid esters include fatty acid esters consisting of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms; A fatty acid ester consisting of a monobasic fatty acid having 17 or more monobasic fatty acids and a monohydric alcohol having a total of 21 to 23 carbon atoms is used, and an alkali metal or alkali of the fatty acid is used. Metal soaps made of earth metals, lecithin, etc. are used. Silicones are those made by modifying fatty acids. A partially fluorine-modified material is used. The alcohol used is one made of higher alcohol, and the fluorine used is one obtained by electrolytic substitution, telomerization, oligomerization, etc. Among the lubricants, radiation-curable ones are also advantageously used. These are used to suppress back-type transfer to the ferromagnetic thin film.
It has the advantages of preventing dropouts, reducing the difference in output depending on the inner and outer diameters when wound into a roll, and being able to be manufactured online. As radiation-curable lubricants, compounds having a molecular chain exhibiting lubricity and an acrylic double bond in the molecule 5 such as acrylic esters, methacrylic esters, vinyl acetate esters, acrylic amide compounds, and vinyl alcohol esters are used. , methyl vinyl alcohol ester, allyl alcohol ester, glyceride, etc. These lubricants are represented by the structural formula: CH3 CH2=C: HCOOR, CH2= C-G OOR
1CH2=CH-CH2GOOR. CH2=CHC0NHCH20COR1RCOOCH2
-CH=:CH2 etc. 1. ::j, R is a straight chain or branched saturated or unsaturated hydrocarbon group, with a carbon number of 7 or more,
Preferably it is 12 or more and 23 or less, and these can also be fluorine-substituted products. As fluorine substituted substances, Cn Fznt+-, Cn Fzn+t (CH2)+
* (However, m=1 to 5), R CnFznt+S 02 N CH2CH2-1CnF
zntlCH2CH2NHCH2CH2-1CnFzn
-+O-◎-COOCH2CH2-, etc. Preferred specific examples of these radiation-curing lubricants include:
Examples include stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate), glycerin methacrylate (acrylate), glycol methacrylate (acrylate), and silicone methacrylate (acrylate). The backcoat layer, which does not contain lubricant, has a high coefficient of friction, which causes image fluctuations and jitters.In addition, the high coefficient of friction, especially under high-temperature running, tends to cause the magnetic recording layer to be scraped, resulting in single-turn welts. This is likely to occur. Dispersants include organic titanium coupling agents, silane coupling agents, and surfactants; antistatic agents include natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol;
Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids. Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as sulfuric acid or phosphoric esters of amino acids, aminosulfonic acids, and amino alcohols are used. Antistatic agents include conductive fine powder such as carbon black; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; 1) Higher alkylamines, quaternary ammonium salts, and pyridine. Cationic surfactants such as other heterocycles, phosphoniums or sulfoniums; anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, sulfuric ester groups, phosphoric ester groups; amino acids, aminosulfonic acids, amino alcohols Ampholytic activators such as sulfuric acid or phosphoric acid esters are used. Further, the mixing ratio of the barium ferrite magnetic powder and the organic binder is barium/binder=1/1 to 9/1, preferably 271 to 8/1. The amount of other additives can be determined according to conventional methods such as 0.1 to 20 parts by weight. Note that the thickness of the magnetic recording layer and back coat layer of the present invention is generally in the range of 0.1 to 10 pm, respectively. Solvents used for coating the magnetic recording layer and backcoat layer include, for example, ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol-based solvents such as methanol, ethanol, propatool, and butanol; methyl acetate, ethyl acetate, Ester types such as butyl acetate, ethyl lactate, and acetic acid glycol monoethyl ether; Glycol ether types such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; Tar types (aromatic hydrocarbons) such as benzene, toluene, and xylene; Methylene Chlorinated hydrocarbons such as chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, and others such as tetrahydrofuran and dimethylformamide are used. Also, as a non-magnetic base material used in the present invention. Polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, polyimide, polycarbonate, polysulfone, polyethylene naphthalate, aromatic aramid, aromatic polyester, aluminum, glass, etc. are used. It is not limited. Among these, polyester, polyimide, etc. are particularly preferred. The magnetic recording medium of the present invention can be manufactured by a conventional method. For example, a mixed dispersion of magnetic powder, a binder, and other additives is coated on a non-magnetic base material, and while drying, magnetic particles are non-magnetic in a vertically oriented magnetic field. Orient perpendicular to the surface of the magnetic substrate. Immediately thereafter, the binder is cured or crosslinked to obtain a desired magnetic recording medium. Note that the magnetic recording layer can also be provided with an undercoat layer under the magnetic layer. A top coat layer can also be provided if necessary. Permanent magnets, direct current magnetic fields, and alternating current magnetic fields are typically used as orientation methods, and various combinations of these methods are also used, such as vertical and horizontal combinations, permanent magnets or combinations of direct current magnetic fields and alternating current magnetic fields, and mechanical orientation. A wide variety of combinations of the above are used, including mechanical orientation and mechanical orientation. Then, in order to prevent the magnetic particles oriented outside the magnetic field due to the demagnetizing field from becoming disordered and deteriorating their orientation, we dry them in the magnetic field, and to prevent them from being affected by the demagnetizing field. It is necessary to dry it to a certain extent so that the magnetic powder does not move. The present invention will be explained in more detail with reference to examples of dead salmon, but it goes without saying that the present invention is not limited thereto. 1t H-type Part by weight Barium ferrite 120 parts (diameter 0.1P, thickness 0
．． 01P, He 8000 e) Brush-A1203 powder (0,5,-powder) 2 parts Solvent (MEK/Toluene 50150) 100 parts The above composition was mixed in a ball mill for 3 hours to form hexagonal plate barium ferrite. Moisten well. Next, chlorine, vinegar, vinyl alcohol copolymer (containing maleic acid), molecular weight 40.000, 6 parts (solid content equivalent), acrylic double bond-introduced salt, vinyl acetate copolymer (containing maleic acid), molecular weight 20.000, 12 parts (Solid content equivalent) Acrylic double bond introduced polyether urethane elastomer Molecular weight 40
．． 000 9 parts (solid content equivalent) Pentaerythritol triacrylate 3 parts Solvent (MEK/Toluene 5
0150) 200 parts stearic acid
4-part butyl stearate
Mix and dissolve the two parts binder mixture well. This was put into the ball mill that had been subjected to the magnetic powder treatment and mixed and dispersed again for 42 hours. The magnetic paint thus obtained was applied onto a 33P polyester film, vertically oriented while drying on a permanent magnet (3000 Gauss), and then the solvent was dried with an infrared lamp or hot air, and the surface was smoothed. After processing, E
Using an electro-curtain type electron beam accelerator manufactured by SI, the coating film was cured by irradiating the electron beam in an N2 atmosphere under the conditions of acceleration voltage 150 KeV, electrode current 20 mA, and total irradiation dose 5 Mr.ad. I let it happen. When the plate ratio of the hexagonal plate-shaped barium ferrite in the magnetic layer 1 is changed, the degree of vertical orientation changes as shown in FIG. If the plate-like ratio is less than 6, the degree of vertical alignment is poor, and if it is 6 or more, the plate-like ratio becomes large, making it easy to vertically align. In addition, as shown in Table 1, the particle size is 0.1. It is preferable to have a particle size of +-am or less in terms of mold retention, but the particle size is 0 for practical use.
．． Up to 2 parts can be used. Table 1 J1 Rin 1 (Thermosetting magnetic layer) Part by weight Barium ferrite magnetic powder 120 parts (diameter 0.1...
．． , thickness 0.01SP, He 10000 e)
A l 203 powder (0,5,-powder) 2 parts powder (soybean oil refined lecithin) 3 parts solvent (MEK
/toluene 50150) 100 parts The above composition was mixed in a ball mill for 3 hours, and 15 parts of zero-order vinyl chloride vinyl acetate copolymer (Union Carbide Co., Ltd.) was mixed to better wet the hexagonal plate-shaped barium ferrite with the dispersant. A mixture of 15 parts of thermoplastic urethane resin (Nilaporan 3022, manufactured by Nippon Polyurethane Co., Ltd.), 200 parts of solvent (MEK/toluene 50150), and 3 parts of lubricant (higher fatty acid-modified silicone oil) was thoroughly mixed and dissolved. This was placed in the ball mill that had been subjected to the magnetic powder treatment and dispersed again for 42 hours. After dispersion, 5 parts (in terms of solid content) of an isocyanate compound (Desmodur, manufactured by Bayer AG) capable of reacting and crosslinking with the functional groups, mainly hydroxyl groups, of the binder in the magnetic paint were added to the ball milled paint for 20 minutes. Mixing was done. The magnetic paint was applied onto the polyester film of 33)-, vertically oriented while drying on an alternating current magnetic field (3000 Gauss), the solvent was dried with an infrared lamp or hot air, and the surface was smoothed and then heated to 80°C. The roll was kept in an oven for 48 hours to accelerate the crosslinking reaction with the isocyanate. (2) Formation of back coat layer - Quco (thermosetting type) Part by weight Carbon black 30mP 50 Hardening agent Coronate L
20 Lubricant Stearic acid modified silicone 4 Butyl stearate 2 Nitrified cotton 40 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (Made by Block Chemical, S-LEC A) 30 Polyurethane elastomer 30 (B, F Gutdrich, Nisten 5703) mixed Solvent (MIBK/Toluene)
Mix and dissolve the mixture of 250 and 250 thoroughly. This paint was applied onto a polyester film, the solvent was dried using an infrared lamp or hot air, and after surface smoothing treatment, the roll was kept in an oven maintained at 80°C for 48 hours to accelerate the crosslinking reaction by isocyanate. Ta. However, 4 Kuyo, Yu", Fake" - Weight part graphitized carbon black 3400830m, -
50 (A) Acrylic modified chloride, vinegar, vinyl alcohol copolymer Molecular weight 45.000 50 (B) Acrylic modified polyurethane elastomer Molecular weight 20.000
50 stearic acid
Butyl 2 stearate
2 Mixed solvent (MIBK/toluene = 1/1) 300 The above mixture was dispersed in a ball mill for 5 hours, applied to the back side of the polyester film where the magnetic surface was formed to a dry thickness of IP, and electrocurtain type electron beam Using an accelerator, the acceleration voltage was 150 KeV and the electrode current was 10 m.
A. The back coat layer was irradiated with an electron beam in N2 gas at an absorbed dose of 5 M rad. Back coat 2 Parts by weight Carbon black 20 m P50 Acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer (molecular weight 30,000) 40 Acrylic modified polyurethane elastomer molecular weight 20.000 40 Polyfunctional acrylate molecular weight 1.000 20 Stearin Acid 4 Butyl stearate 2 Mixed solvent (MIBK/
Toluene) 250 These were processed and manufactured in the same manner as the back coat layer 1. Bael 22 Upper Summer Yu Weight Part Ca
CO380m P25 Carbon black 30m P25 Acrylic modified vinyl chloride monoacetate vinyl alcohol copolymer
Molecular weight: 30.000 30 Acrylic modified polyurethane elastomer Molecular weight: 50.000
30 Acrylic modified phenoxy resin molecular weight 35.000 20 Polyfunctional acrylate molecular weight 500 20 Stearic acid
4 solvent (MEK/toluene =
1/1) 300 These were treated and manufactured in the same manner as above. Table 2 shows the characteristics of each of these layers. Regarding the magnetic recording medium in which the magnetic layer 1 and the back layer 2 are combined, the ratio of pigment to binder in the back layer is changed, and its E'(Young's modulus), electric resistance, and back surface roughness are adjusted. Tables 3 and 4 show the results of changes in each characteristic. Table 3 is 33. &- base, and Table 4 shows 11. It was applied to a base and evaluated on a deck of 8m/m. Fourth table, 0. From dropout Tables 3 and 4, the electrical resistance of the magnetic layer is 10″O/c1
12 or more, and the back surface has an electrical resistance of 10"O/cII
+2 or less, E' is 200 to 1500 Kg/mm2, and its surface roughness is R20,0,20 with a cutoff of 0.17 mm.
It can be seen that those in the following range (No. 3 to 7) are good over all characteristics. In addition, especially in the case of the disk type, the one without a back layer curled so much that it could not be used, but the one with the back layer had little curl and was not a problem in practical use. Next, magnetic recording media were manufactured by appropriately combining the above magnetic layers 1 and 2 with comparative back layers and back layers 1, 2, and 3, and changing the order of their formation. however. In this case, calendering was performed for each layer formed. The measurement results for each characteristic are shown in Tables 5 and 6. Table 5 shows the results applied to 33P base, and Table 6 shows the results applied to 11P pace. In the table, ■ and ■ indicate the order of formation. Table 5, Table 6 The following can be seen from Tables 5 and 6. In other words, dropout is better when either the magnetic layer or the back layer is of the radiation curing type (A, B) than when both layers are of the thermosetting type (comparative example) because there is no back mold transfer. , which also increases the output. In the case (C) in which the magnetic surface and the back coat surface are radiation-cured, the electromagnetic conversion characteristics are even better. Comparing the groups in the table with the comparative examples, it can be seen that there is no adverse effect due to tight winding, and the difference in electromagnetic conversion characteristics between the outside and inside of the tape wound into a roll is small. This tendency is similar in that C is superior to A and B. Furthermore, in Group C, curing occurs during continuous running, so there is no effect from tight winding. The coating film above contains fatty acids, which reduces friction, and is excellent in that it does not shake the image even when running at high temperatures. Next, the surface roughness of the videotape in Table 5 above was examined. Combination of magnetic layer 1 and back layer 2, base thickness 33)-, barium ferrite grain size 0. Taking the case of O8Pm and plate thickness 0.01P as an example, calculate the surface roughness of the magnetic layer and C/
The relationship between N (dB) is shown in Figure 2. In Figure 2, the videotape is driven at 3.8 m/sec, the center frequency is 7 MHz,
It shows the S/N ratio (relative value) when recording and reproducing using RF signals. As you can see, the surface roughness of the magnetic layer is 06087-
m or less, the S/N ratio can be kept high. The same was true for other combinations. Regarding the above videotape, the surface roughness of the magnetic layer is 0.
08. -m or less, and the surface roughness of the back coat layer is 0.
05-0.6. -m range, the results shown in FIG. 3 were obtained. Furthermore, when I measured the tightness of the winding, it was found that it was 40℃ and 80%RH.
Everything was fine. The above characteristics were measured as follows. 1) Process run 33/- During the process, run 50 guide rollers at a tape speed of 200 m/min to check the scratches on the back surface, the appearance of the jumbo roll, the adhesion on the guide roll, and the adhesion of dust. Examined. 2) Electromagnetic conversion characteristics - Shows the C-8/N ratio (relative value) when recording and reproducing with a video floppy center frequency of 7 MHz and an RF signal. Rotation speed 3600rpm
, the relative speed was 0.6 m/see. ■8 m/m This shows the C-8/N ratio (relative value) when recording and reproducing at a center frequency of 5 MHz on an 8 m/m deck. The relative speed is 3.8 m/see. 3) 8 m/m deck winding configuration Using an 8 m/m deck, fast forward the entire length of the tape, then fast rewind, stop when 50 m remains, and then fast rewind to the end. After that, visually check the winding condition of the tape! I guessed it. The case where there was no gap between the tape layers and the winding condition was good was rated O, and the case where there was a gap between the tape layers was rated X. 4) Scraping of 8 m/m back coat surface Using a commercially available 8 m/m deck, after running it 50 times, the inside of the cassette case was inspected for dirt. O indicates no dirt, and x indicates severe dirt. 5) Based on the measured value at 20°C with a Young's modulus viscoelasticity spectrometer (Iwaki Seisakusho, Toyo Baudouin, Toyo Seikosha). 6) Surface roughness It was determined by the 20-point average method from a chart obtained using Talystep (manufactured by TAYLOR-HOBSON). Cutoff 0017mm, stylus force 0. IX2°5.1- was used. Blood! Introduction L1 The present invention provides a magnetic recording medium having a backcoat layer and a magnetic recording layer containing hexagonal plate-shaped barium ferrite magnetic powder, in which the binder of the backcoat layer is made of a radiation-curable resin, and the electrical resistance is 10/'. 0/cm2 or less, not only does the barium ferrite magnetic powder have good short wavelength recording characteristics, but it also prevents dirt and dust from adhering to it.
There is no back-type transfer, dropouts are reduced, and an excellent magnetic recording medium is obtained with no cinching phenomenon or viscosity.
In the case of magnetic disks, there is no warpage, and in the case of magnetic tapes, the Young's modulus of the back coat layer is 20C)-15.
00 kg/mm2, and by setting the surface roughness of the back coat layer to a cutoff of 0.17 mm and R20 of 0.20 pm or less, the durability of the back coat surface is increased, there is no scratching, and the abrasion resistance is improved. A magnetic tape with excellent electromagnetic conversion characteristics can be obtained. In addition, a vertically oriented magnetic recording medium is less prone to demagnetizing fields than an in-plane oriented recording medium, and is therefore suitable as a magnetic recording medium.One excellent magnetic recording medium of the present invention is a digital audio chip, a floppy disk, It is suitable for high-density recording media such as video floppies.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the platelet ratio and the degree of vertical orientation of barium ferrite, and FIG. 2 is a graph showing the relationship between the surface roughness of the magnetic layer of a magnetic recording medium and C/N. 3
The figure is a graph showing the relationship between back layer surface roughness and C/N.

Claims (2)

[Claims] (1) A magnetic recording layer containing hexagonal plate-shaped barium ferrite magnetic powder with a particle size of 0.2 μm or less and a platelet ratio of 6 or more was provided on one side of a non-magnetic base material, and a back coat layer was provided on the other side. In a magnetic recording medium, the magnetic recording layer has an electrical resistance of 10^1
^0Ω/cm^2 or more, the binder of the back coat layer is made of radiation-curable resin, and its electrical resistance is 10Ω/cm^2 or more.
A magnetic recording medium characterized in that it has a resistance of ^1^0 Ω/cm^2 or less. (2) Back layer has E'(Young's modulus) of 200 to 1500k
g/mm^2, its surface roughness has a cutoff of 0.17mm
Claim 1 in which R20 is 0.20 μm or less
Magnetic recording medium described in Section 1.