JP3480579B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art A back coat layer is provided on the back surface side of the magnetic layer of various magnetic tapes in order to improve its running property, durability and storage property. Conventionally, as a back coat resin, a thermosetting type resin in which nitrocellulose and urethane resin are used in combination and which is crosslinked with polyisocyanate is used. This is because the nitrocellulose / urethane system has high rigidity and has a high blocking preventing effect between the magnetic layer and the back coat layer under high temperature and high humidity.

However, this nitrocellulose / urethane type thermosetting back coat layer has a poor dispersibility of carbon black or the like to be added due to an antistatic effect and the like, and the surface becomes rough. The surface of the magnetic layer becomes rough due to transfer to the layer side, winding tightness, etc., and especially in the digital audio tape recorder (DA
When high density magnetic recording such as T) is performed, the error rate becomes large. In order to eliminate such inconvenience, it is conceivable to use an electron beam curing type back coat layer. If an electron beam curing type back coat is performed, in-line curing can be performed after coating, which is extremely advantageous in mass production.

However, if nitrocellulose is modified to be sensitive to an electron beam, it may be decomposed upon irradiation with an electron beam, and it is very difficult to handle. Therefore, if an electron beam curable vinyl chloride resin is used instead of nitrocellulose, its rigidity is low. To increase the rigidity, the content ratio of vinyl chloride resin should be increased, but if the ratio of vinyl chloride resin is increased, the coating becomes brittle this time, it becomes easy to scrape when the tape is running, and the error rate due to powder falling is increased. It will increase.

[0005]

The main object of the present invention is, firstly, to use an electron beam curable binder of a novel combination of polar group-containing electron beam curable resins, whereby the dispersibility is high and calendar processing is performed. (EN) A magnetic recording medium having good properties, excellent electromagnetic conversion characteristics, and having a small error rate even when performing high-density digital recording. Secondly, the main object of the present invention is to provide a magnetic recording medium having a backcoat layer having high rigidity, less powder falling, and a small error rate even when high density digital recording is performed.

[0006]

These objects are achieved by the present invention described in (1) to (8) below. (1) A back coat layer is provided on one surface of a non-magnetic support, and a magnetic layer in which ferromagnetic fine powder is dispersed in a binder is provided on the other surface, and the back coat layer is made of carbon black. An electron beam curable resin contained is applied and cured by electron beam. The resin comprises an electron beam curable vinyl chloride resin having a sulfur-containing polar group and a phosphorus-containing polar group. An electron beam curable urethane resin having, wherein the binder of the magnetic layer is an electron beam curable resin coated and electron beam cured, and the resin contains a sulfur-containing polar group. Electron beam curable vinyl chloride resin having, and electron beam curable urethane resin having a phosphorus-containing polar group, the electron beam curable chloride having a sulfur-containing polar group of the back coat layer and the magnetic layer. Vinyl resin contains sulfur A hydroxyl group of a raw material vinyl chloride resin having a polar group and a hydroxyl group, which is subjected to electron beam modification by a monomer having an ethylenically unsaturated double bond and an isocyanate group and having no urethane bond in the molecule. The magnetic recording medium in which the ethylenically unsaturated double bond is bonded to the vinyl chloride resin skeleton through one urethane bond. (2) The magnetic recording medium according to (1), wherein the electron beam-curable vinyl chloride resin having a sulfur-containing polar group in the back coat layer and the magnetic layer has an acryl group or a methacryl group as an ethylenically unsaturated bond. (3) The sulfur-containing polar group of the electron beam-curable vinyl chloride resin having the sulfur-containing polar group of the back coat layer and the magnetic layer is -SO ₄ Y and / or -SO ₃ Y.
(Here, Y is an alkali metal.) The magnetic recording medium according to (1) or (2) above. (4) the back coat layer and -SO ₄ Y and -SO ₃ Y of the electron beam curable vinyl chloride resin having a sulfur-containing polar group of the magnetic layer, respectively -SO ₄ K and -SO ₃ K The magnetic recording medium according to (4) above. (5) The phosphorus-containing polar group of the electron beam curable urethane resin having the phosphorus-containing polar group of the back coat layer and the magnetic layer is one or more of the groups represented by the following chemical formula (4) to (1) to ( The magnetic recording medium according to any one of 4).

[0007]

[Chemical 4]

(Here, Y is H or an alkali metal.) (6) The electron beam curable urethane resin having a phosphorus-containing polar group in the back coat layer and the magnetic layer is represented by the following compound as a phosphorus-containing polar group. The magnetic recording medium according to any one of (1) to (5) above, which comprises a group represented by 5.

[0009]

[Chemical 5]

(7) The electron beam curable urethane resin having a phosphorus-containing polar group in the back coat layer and the magnetic layer is a raw material urethane resin obtained by using a monomer having any of the groups shown in the following chemical formula 6. The magnetic recording medium according to the above (6), which is obtained by denatured by electron beam.

[0011]

[Chemical 6]

(Here, Y is H or an alkali metal.) (8) The back coat layer and the magnetic layer have an electron beam curable vinyl chloride resin having a sulfur-containing polar group and a phosphorus-containing polar group. The magnetic recording medium according to any one of the above (1) to (7), wherein the content ratio with respect to the electron beam curable urethane resin is 70:30 to 90:10 by weight.

[0013]

Specific Structure The specific structure of the present invention will be described in detail below.

The magnetic recording medium of the present invention preferably has a magnetic layer coating film on one surface of a non-magnetic substrate made of various resins such as polyester, and a back coat layer on the other surface. The back coat layer is formed by applying a coating composition containing an electron beam curable resin and curing it with an electron beam. Then, as the electron beam curable resin, an electron beam curable vinyl chloride resin is used.

The vinyl chloride resin as the resin skeleton of the electron beam curable resin preferably has a vinyl chloride content of 60 to 100% by weight, particularly 60 to 95% by weight. Examples of such vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-
Although there are vinyl alcohol-glycidyl (meth) acrylate copolymers and the like, a copolymer of vinyl chloride and a monomer having an epoxy group is particularly preferable. The average degree of polymerization is preferably about 100 to 900.

The vinyl chloride resin has an unsaturated double bond, and as the unsaturated double bond, an acrylic group CH ₂ ═CH—COO— or a methacryl group CH ₂ ═.
Preferably contains CHCH ₃ COO-. It is preferable that the average number of the (meth) acrylic groups is 1 to 20, preferably 2 to 10 in the molecule. Further, it is preferable that the (meth) acrylic group is bonded to the vinyl chloride resin skeleton through one urethane bond.

Such an electron beam-curable vinyl chloride resin has a sulfur-containing polar group. As a result, the dispersibility of carbon black or the like is improved, and an even better backcoat layer can be obtained. The sulfur (S) containing a polar group, in particular -SO ₄ Y and / or -SO ₃ Y is _preferably, -SO 4 Y, in -SO ₃ Y, Y is is an alkali metal, with Y = K, - SO ₄ K, -SO ₃ K
Is particularly preferable. These -SO ₄ Y, -SO
₃ Y may be either one or both, and when both are included, the ratio is arbitrary. Further, these S-containing polar groups are preferably contained in the molecule as S atoms in an amount of 0.01 to 10% by weight, particularly 0.1 to 5% by weight.

In order to obtain such an electron beam-curable vinyl chloride resin, the following is preferable. That is, first, a raw material vinyl chloride resin having an S-containing polar group and further containing a hydroxyl group is prepared. The number of hydroxyl groups of this raw material vinyl chloride resin is 3 to 60 in one molecule.
, Preferably 2 to 30, and as the polar group, if necessary, in addition to the S-containing polar group, a group represented by the following chemical formula 7, a —COOY group (Y is H or an alkali metal),
N (R) ₂ group, -N ⁺ (R) ₃ · Z ⁻ [wherein, R is an alkyl group or a hydrogen atom, and Z is halogen. ], Etc. can also be contained.

[0019]

[Chemical 7]

As such a raw material vinyl chloride resin, especially, JP-A-60-238371 and JP-A-60-1
No. 01161, No. 60-235814, No. 6
Those disclosed in 0-238306 and 60-238309 are suitable. This is a radical-generating radical having a strong acid radical containing S, such as ammonium persulfate and potassium persulfate, in addition to vinyl chloride, a monomer having an epoxy group, and optionally another monomer copolymerizable therewith. It is obtained by polymerizing in the presence of an agent. The amount of the radical generator used is usually 0.3 to 9.
It is 0% by weight, preferably 1.0 to 5.0% by weight. More specifically, since many radical generators having a strong acid radical containing S are water-soluble, emulsion polymerization, suspension polymerization using alcohol such as methanol as a polymerization medium, or solution using ketones as a solvent. Polymerization is preferred.

At this time, in addition to the radical generator having a strong acid group containing S, it is also possible to use a radical generator usually used for polymerization of vinyl chloride. Examples of these radical generators include lauroyl peroxide, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and di-2-ethoxy. Ethyl peroxydicarbonate, t-butyl-peroxypiperate,
Organic peroxides such as t-butyl peroxy neodecanoate: 2,2'-azobisisobutyronitrile, 2,2 '
-Azobis-2,4-dimethylpareronitrile, 4,
Examples thereof include azo compounds such as 4'-azobis-4-cyanoparellic acid. It is also possible to combine a reducing agent such as sodium formaldehyde sulfoxylate, sodium sulfite, or sodium thiosulfate with a radical generator having a strong acid radical.

Examples of the suspension stabilizer include polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose, polyvinyl pyrrolidone, polyacrylamide, maleic acid-styrene copolymer, Examples thereof include synthetic polymeric substances such as maleic acid-methyl vinyl ether copolymer and maleic acid-vinyl acetate copolymer, and natural polymeric substances such as starch and gelatin. Examples of the emulsifier include anionic emulsifiers such as sodium alkylbenzene sulfonate and sodium lauryl sulfate, and nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene sorbitan fatty acid partial ester. If necessary, a molecular weight modifier such as trichloroethylene or thioglycol can be used.

Further, examples of the monomer having an epoxy group include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-P-vinylbenzoate and methylglycidyl. Glycidyl esters of unsaturated acids such as itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth) allyl sulfonate, butadiene monooxide, vinyl cyclohexene monooxide, epoxides such as 2-methyl-5,6-epoxyhexene Examples thereof include olefins. This monomer is generally used in a range such that the amount of epoxy groups in the copolymer is 0.5% by weight or more.

In addition to vinyl chloride and a monomer having an epoxy group, examples of a monomer which can be optionally used include vinyl acetate, vinyl propionate and other carboxylic acid vinyl esters: methyl vinyl ether, isobutyl. Vinyl ethers such as vinyl ether and cetyl vinyl ether: vinylidene chloride, vinylidene fluoride and the like: diethyl maleate, butylbenzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth) acrylate, (meth) Unsaturated carboxylic acid esters such as ethyl acrylate, lauryl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate: olefins such as ethylene and propylene: unsaturated nitriles such as (meth) acrylonitrile.

The raw material resin thus obtained has an average degree of polymerization of 100 to 900, preferably 200 to 500,
The content of vinyl chloride is 60% by weight or more. Incidentally, such a raw material resin is commercially available as MR-110 from Nippon Zeon Co., Ltd., for example.

Such a raw material vinyl chloride resin is then subjected to electron beam modification. To perform electron beam modification,
A monomer having one or more ethylenically unsaturated double bonds and one isocyanate group in one molecule and having no urethane bond in the molecule is used. Examples of such a monomer include 2-isocyanatoethyl (meth) acrylate. When the distance between the isocyanate group and the acrylic group becomes short as in this molecule, and only one urethane bond exists between the molecule and the resin main chain, extremely favorable results are obtained.

As a method for modifying a thermosetting vinyl chloride resin into an electron beam curing type, a compound having a (meth) acryl group and a carboxylic acid anhydride or a carboxylic acid is added to a resin having a hydroxyl group or a carboxylic acid group. A method of reacting and ester-modifying, and tolylene diisocyanate (TD
I) and 2-hydroxyethyl (meth) acrylate (2
The urethane modification in which a reaction product (adduct) with (-HEMA) is reacted is well known. However, the ester modification makes the coating film brittle. Further, the surface property is deteriorated by the urethane modification by the above adduct. If 2-isocyanatoethylmethacrylate is used, it will not become brittle even if the content ratio of the vinyl chloride resin is increased, and the dispersibility,
A coating film having excellent surface properties can be obtained. Adduct TDI-2-H of the above isocyanate and acrylate
Since EMA already has a urethane bond in the molecule, two urethane bonds are present in the branched molecular chain having an acrylic double bond at the end. Then, the presence of the urethane bond, the long chain length, and the dispersibility are reduced. However, since isocyanate ethyl methacrylate does not have a urethane bond in the molecule, only one urethane bond exists in the branched molecular chain and the branched chain is short, so that the dispersibility or the like does not decrease. Moreover, since urethane bonds are present in the main chain of the molecule, the coating film will not become brittle even if the proportion of the vinyl chloride resin is increased.

An ethylenically unsaturated double bond is introduced by a urethane bond by a reaction between a raw material vinyl chloride resin polymer (A) having a hydroxyl group and an S-containing polar group and a monomer (B). The electron beam curability can be freely designed by the molar ratio of the vinyl chloride copolymer (A) having a group and the monomer (B). However, as described above, if the urethane bond concentration is too high, the dispersibility will decrease. Therefore, if the dispersibility and curability are balanced, 1 to 20, preferably 2 to 10 monomers (B) are reacted per 1 molecule of vinyl chloride copolymer (A) having a hydroxyl group and other polar groups. Dispersive,
A radiation curable resin having excellent curability can be obtained.

The reaction of the vinyl chloride-based copolymer (A) having a hydroxyl group and other polar groups with the monomer (B) is
If necessary, a vinyl chloride copolymer having a hydroxyl group and other polar groups is dissolved in a known organic solvent that does not participate in the reaction, a known urethanization reaction catalyst is used, and a known radical polymerization inhibitor such as hydroquinone is used. Used at a reaction temperature of 60 ° C. or lower. Such a modified product is commercially available from Toyobo Co., Ltd. as TB-0246 or by Nippon Zeon Co., Ltd. as MR-301.

An electron beam curable urethane resin is used in combination with such an electron beam curable vinyl chloride resin. This improves dispersibility and backcoat quality. The electron beam curable urethane resin contains a phosphorus-containing polar group. As the phosphorus-containing polar group, one or more of the groups represented by the following chemical formula 8 (Y is H or an alkali metal) is preferable, and among these, Y is particularly preferably Na, and among these polar groups, the following chemical formula 9 Contains only the groups shown, or
Those containing as a main component a group represented by the following chemical formula 9 are preferable. It is preferable that these P-containing polar groups are contained as P atoms in the molecule in an amount of 0.01 to 10% by weight, particularly 0.02 to 3% by weight. These may be present in the main chain of the skeleton resin or in the branches. This allows
Dispersibility is improved.

[0031]

[Chemical 8]

[0032]

[Chemical 9]

The resin skeleton for bonding the P-containing polar group is an electron beam curable urethane resin. That is, a P-containing electron beam curable resin having at least one acrylic double bond in the molecule and reacted with at least one of the P compounds described below, wherein the acrylic double bond-containing compound and the urethane bond are included. It is a polyurethane acrylate resin that is bonded via.

The acrylic double bond referred to here is a residue (acryloyl group or methacryloyl group) of acrylic acid, acrylic acid ester, acrylic acid amide, methacrylic acid, methacrylic acid ester, methacrylic acid amide and the like.
Say. Examples of the acrylic double bond-containing compound (A) include mono (meth) acrylates of glycols such as ethylene glycol, diethylene glycol and hexamethylene glycol, and mono (meth) acrylates of triol compounds such as trimethylolpropane, glycerin and trimethylolethane. Also preferred are hydroxy group-containing acrylic compounds such as mono (meth) acrylate, di (meth) acrylate and tri (meth) acrylate of a tetravalent or higher valent polyol such as di (meth) acrylate, pentaerythritol and dipentaerythritol. is there. It is necessary that at least one, preferably 2 to 20 of these acrylic double bonds are present in the binder molecule.

The polyurethane acrylate resin is generally obtained by reacting a hydroxy group-containing resin (B ') and a hydroxyl group-containing acrylic compound (A') with a polyisocyanate-containing compound (C '). Examples of the hydroxyl group-containing resin include polyalkylene glycols such as polyethylene glycol, polybutylene glycol and polypropylene glycol, alkylene oxide adducts of bisphenol A, various glycols, and polyester polyol (B ') having a hydroxyl group at the molecular chain end. To be Among these, a polyurethane acrylate resin obtained by using the polyester polyol (B ') as one component is preferable.

Examples of the carboxylic acid component of the polyester polyol (B ') include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, p- (hydroxyethoxy). Aromatic oxycarboxylic acids such as benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fatty acid dicarboxylic acids such as dodecanedicarboxylic acid, fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, hexahydrophthalic acid, etc. Examples include unsaturated fatty acids and alicyclic dicarboxylic acids, trimellitic acid, trimesic acid, and tricarboxylic acids such as pyromellitic acid, and tetracarboxylic acids.

As the glycol component of the polyester polyol (B '), ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-putanediol, 1,5-pentanediol, 1,6-hexanediol, Neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct such as bisphenol A and propylene oxide adduct, hydrogenated bisphenol Examples thereof include ethylene oxide and propylene oxide adducts of A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination.
Other examples of the polyester polyol include lactone-based polyester diol chains obtained by ring-opening polymerization of lactones such as caprolactone.

The polyisocyanate (C ') used is 2,4-tolylene diisocyanate, 2,6-
Tolylene diisocyanate, p-phenylene diisocyanate, biphenyl methane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate,
2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,
4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5'-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methyl Diisocyanate compounds such as cyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate cyclohexylmethane and isophorone diisocyanate, or trimers of 2,4-tolylene diisocyanate of 7 mol% or less of all isocyanate groups, Triisocyanate compounds such as trimer of hexamethylene diisocyanate may be mentioned.

The phosphorus (P) compound used in the polyurethane acrylate resin used is represented by the following chemical formulas 10 to 1
It is preferable that it is the P compound shown by 4.

[0040]

[Chemical 10]

[0041]

[Chemical 11]

[0042]

[Chemical 12]

[0043]

[Chemical 13]

[0044]

[Chemical formula 14]

In the above, X ₁ and X ₂ represent ester-forming functional groups. R ₁ preferably has 3 to ₁ carbon atoms
A trivalent hydrocarbon group of 0, R ₂ preferably has 1 carbon atom
~ 12 alkyl groups, cycloalkyl groups, aryl groups,
It is preferably an alkoxy group having 1 to 12 carbon atoms, a cycloalkoxy group or an aryloxy group. The aryl group and aryloxy group may have a halogen atom, a hydroxy group, -OM '(M' is an alkali metal) or an amino group bonded thereto. R ₃ and R ₄ are preferably an alkylene group having 1 to 12 carbon atoms, a cycloalkylene group, an arylene group, a group represented by the following formula: — (CH ₂ OR ₅ ) _m (R ₅ is 1 to 12 carbon atoms. Represents an alkylene group, a cycloalkylene group or an arylene group, and m can take any numerical value of 1 to 4). Y represents an alkali metal atom, hydrogen, a monovalent hydrocarbon group, or an amino group, and Na is particularly preferable. Specific examples of these are shown in Chemical Formulas 15 to 51 below.

[0046]

[Chemical 15]

[0047]

[Chemical 16]

[0048]

[Chemical 17]

[0049]

[Chemical 18]

[0050]

[Chemical 19]

[0051]

[Chemical 20]

[0052]

[Chemical 21]

[0053]

[Chemical formula 22]

[0054]

[Chemical formula 23]

[0055]

[Chemical formula 24]

[0056]

[Chemical 25]

[0057]

[Chemical formula 26]

[0058]

[Chemical 27]

[0059]

[Chemical 28]

[0060]

[Chemical 29]

[0061]

[Chemical 30]

[0062]

[Chemical 31]

[0063]

[Chemical 32]

[0064]

[Chemical 33]

[0065]

[Chemical 34]

[0066]

[Chemical 35]

[0067]

[Chemical 36]

[0068]

[Chemical 37]

[0069]

[Chemical 38]

[0070]

[Chemical Formula 39]

[0071]

[Chemical 40]

[0072]

[Chemical 41]

[0073]

[Chemical 42]

[0074]

[Chemical 43]

[0075]

[Chemical 44]

[0076]

[0077]

[0078]

[Chemical 47]

[0079]

[Chemical 48]

[0080]

[Chemical 49]

[0081]

[Chemical 50]

[0082]

These P compounds can be reacted in various processes. For example, it can be used as one component when producing a raw material resin for polyester polyol (B ′) and polyalkylene glycol.
Especially when producing the polyester polyol (B ′),
The above-mentioned P compound can be added and reacted at any stage before the completion of the polymerization of the polyester polyol (B '). Moreover, these P compounds can be used as one component of the raw material of a polyurethane acrylate resin.
For example, a polyurethane acrylate resin can be produced by directly reacting a phosphorus compound having a hydroxy group with an isocyanate compound (C '), a polyester polyol (B') or an acrylate compound (A ').

Such an electron beam-curable urethane resin is prepared by a known method from the acrylic double bond-containing compound (A).
It is obtained by reacting a specific phosphorus compound and / or a raw material containing a raw material resin reacted with the specific phosphorus compound in a solvent or in the absence of a solvent. The molecular weight of the obtained resin is preferably 500 to 100,000. Incidentally, these manufacturing methods are disclosed in JP-A-62-43830, JP-A-61-77134 and JP-A-62-40615.
No. 62-195720 and the like. Also, these are TB-02 from Toyobo Co., Ltd.
It is marketed as 42.

The vinyl chloride resin containing the S-containing polar group and the urethane resin containing the P-containing polar group are
It is preferable that the weight mixing ratio is 7: 3 to 9: 1. Within this range, the backcoat quality is extremely high. In addition to these resins, various known resins may be contained in the range of 20% by weight or less of the whole.

An electron beam is used to cure such a resin, and its irradiation dose is preferably 1 to 10 Mrad, more preferably 3 to 7 Mrad, and its irradiation energy (accelerating voltage) is 1
It is better to set it to 00 kV or more. The electron beam irradiation is preferably performed after coating and drying and before winding, but it may be performed after winding.

The backcoat layer preferably contains 2 to 50% by weight of various carbon blacks. The solvent of the coating composition for the back coat is not particularly limited, and various solvents such as methyl ethyl ketone, methyl isobutyl ketone, acetone, cyclohexanone, and other ketone-based solvents, and toluene and other aromatic-based solvents may be selected according to the purpose. There is no particular limitation on the content of the solvent in the coating composition.

The coating composition contains α-Fe ₂ O ₃ and α-Al ₂ O _{3 in} order to enhance the mechanical strength of the back coat layer.
, Cr ₂ O ₃ , TiO ₂ , SiC, etc. are preferably contained. Content is 0.5-10% by weight
The degree. In addition, a fatty acid, a fatty acid ester, a surfactant such as silicone oil, a lubricant, and various other additives may be added to the coating composition, if necessary.

The thickness of the back coat layer is generally 0.1 to 10.
It is about 3 μm. When applying the back coat layer, after applying the coating composition by a known method, the surface may be smoothed, and then dried and cured. Usually, a magnetic layer is formed after forming the back coat layer.

The magnetic layer can be cured in-line,
At that time, in order to obtain a magnetic recording medium having high dispersibility, good calendar processability, excellent electromagnetic conversion characteristics, and a small error rate even when performing high-density digital recording, an electron beam curable magnetic layer is used. A magnetic coating material containing a ferromagnetic fine powder and an electron beam curable resin is applied onto a coating film, that is, a substrate, and cured by an electron beam.

As the electron beam curable resin to be used, in particular, an electron beam curable vinyl chloride resin having the same sulfur-containing polar group as described above and an electron beam curable urethane resin having a phosphorus-containing polar group are used. Combined. And it is preferable that the amount ratio is also within the above range.

As the ferromagnetic fine powder used, any of those used in ordinary magnetic recording media can be used. For example, γ
Iron oxide particles such as -Fe ₂ O _3, Co-containing γ-Fe ₂ O
₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ , barium ferrite, strontium ferrite, and other oxide fine powders, and known ferromagnetic metal fine powders such as Fe, Co, Ni, and their alloy fine powders are available. Can be used. Further, the ferromagnetic powder used is usually in the form of needles or particles, and is selected depending on the use as a magnetic recording medium. However, the binder of the present invention is particularly effective in improving the dispersibility of the magnetic metal powder.

The solvent for the magnetic paint is not particularly limited, and methyl ethyl ketone, methyl isobutyl ketone, acetone,
Various solvents such as a ketone system such as cyclohexanone and an aromatic system such as toluene may be selected according to the purpose. The content of the solvent in the magnetic paint is not particularly limited, but the ferromagnetic fine powder 1
About 100 to 1000 parts by weight is preferable with respect to 00 parts by weight.

In order to enhance the mechanical strength of the magnetic layer, α-Al ₂ O ₃ , Cr ₂ O ₃ , TiO ₂ , and
It is preferable to contain inorganic fine particles such as SiC and α-Fe ₂ O ₃ . If necessary, a surfactant such as fatty acid, fatty acid ester and silicone oil, a lubricant, and various other additives may be added to the magnetic paint. The thickness of the magnetic layer is generally about 0.1 to 5 μm. In applying the magnetic layer, after applying the magnetic coating material by a known method, orientation in a magnetic field or mechanical orientation is performed, followed by drying and surface smoothing treatment, and curing. A base layer and the like may be provided as necessary. The curing conditions may be set within the above range.

[0095]

EXAMPLES Specific examples of the present invention will be described below together with comparative examples.

Example 1 A magnetic tape for DAT having a back coat layer and a magnetic layer was prepared as follows.
The numerical values of the composition are parts by weight.

Back coat layer carbon black (particle size 0.02 μm / BET 220 m ² / g) 100 carbon black (particle size 0.34 μm / BET 8 m ² / g) 5 abrasive (α-alumina / particle size 0.2 μm / α) Conversion rate 85%) 1 Electron beam curable vinyl chloride resin (TB-0246 in MEK 30% solution) 300 Electron beam curable urethane (TB-0242 in MEK 35% solution) 70 Methyl ethyl ketone (MEK) 200 Toluene 200

The above composition was placed in a ball mill and dispersed for 15 hours, then the following composition was added and further dispersed for 3 hours to prepare a back coat paint.

[0099]     Butyl stearate 1     MEK 500     Toluene 500

This back coat paint was applied to a polyester film having a thickness of 10 μm, and the coating film thus formed was subjected to an accelerating voltage of 150 kV, an electrode current of 10 mA and an absorbed dose of 5 Mr using an electron curtain type electron beam accelerator.
It is cured by irradiation with an electron beam in ad, N ₂ gas and has a thickness of 0.5μ.
A back coat layer of m 2 was prepared.

Magnetic Layer Metal Magnetic Powder (Specific Surface Area 50 m ² / g · Hc: 1500 Oe · σs: 120 emu / g) 100 Abrasive (α-alumina / α-conversion rate 65% / particle size 0.2 μm) 10 Carbon Black ( Particle size 0.34 μm BET8 m ² / g) 5 Electron beam curable vinyl chloride resin (TB-0246 MEK 20% solution) 80 Electron beam curable urethane resin (TB-0242 MEK 30% solution) 13 MEK 50 Toluene Fifty

The above composition was placed in a sand mill and dispersed for 13 hours, then the following composition was added and further dispersed for 2 hours to prepare a magnetic coating composition.

[0103]     Stearic acid 2     Butyl stearate 2     MEK 100     Toluene 100

This magnetic coating is applied to the opposite side of the support provided with the back coat layer to form a magnetic layer, magnetic field orientation is performed, drying and calendering are performed, and then an electron beam is applied under the same conditions as above. This magnetic layer is irradiated and cured to a thickness of 3 μm
To form a magnetic layer, and a magnetic tape for DAT was obtained.

In the above description, TB-0246 and TB-0242 are electron beam curable (EBC) sulfur-containing polar group (S) -containing vinyl chloride resin (VC) and phosphorus-containing resin manufactured by Toyobo Co., Ltd., respectively. It is a polar group (P) -containing urethane resin (U). These are those having the chemical structures described above as the most preferred ones:

[0106]   TB-0246     Vinyl chloride-epoxy-containing monomer copolymer     Average degree of polymerization 310     Epoxy content 3% by weight     Use potassium persulfate     S content 0.6% by weight     Using 2-isocyanatoethylmethacrylate (hereinafter MOI), Japan Acrylic modified MR-110 manufactured by Zeon Corporation     Acrylic content 6 mol / 1 mol   TB-0242     Hydroxy-containing acrylic compound-phosphonic acid group-containing phosphorus compound-hydroxy Containing polyester polyol     Average molecular weight 23,000     P content 0.2% by weight     Acrylic content 8 mol / 1 mol

Comparative Example 1 As the vinyl chloride resin for the back coat layer, an acrylic-modified (urethane-modified) MR-110 manufactured by Nippon Zeon Co., Ltd. was used. For urethane modification, an adduct (THA) of tolylene diisocyanate and 2-hydroxyethyl methacrylate was used. The acrylic content is 10 mol / 1 mol.

Comparative Example 2 MR-11 was used as a vinyl chloride resin for the back coat layer.
A product obtained by acryl-modifying 0 by ester modification was used. For the ester modification, maleic anhydride and glycidyl methacrylate were used, and the acrylic content was 8 mol / 1.
Mole.

Comparative Example 3 The vinyl chloride resin in the back coat layer was changed to nitrocellulose, and the urethane resin was changed to a thermosetting (TS) urethane resin (U) having a sulfur (S) -containing polar group (weight ratio). Are the same 4: 6). This TSU (S) is a urethane resin composed of a phthalic acid type polyester polyol having a molecular weight of 23,000 and diphenylmethane diisocyanate, and contains 0.005% by weight of SO ₃ Na. As the cross-linking agent, Nippon Polyurethane Coronate L was used.

Each of the obtained tapes was RD with a length of 60 m.
Built in half for AT, blocking, powder drop, B
ER and surface roughness were measured. Regarding the powder drop, the dirt on the guide pin after running was visually judged and evaluated by ○ and ×. When measuring blocking, the length is 1m.
Fix one end of the sample tape to a glass tube with a diameter of 36 mm,
Suspend a weight of 110 g on the other end, slowly rotate the glass tube and wind it up properly so that the magnetic surface is on the inside, then fix it so that the tension can be maintained and remove the weight. , Relative humidity 80 ± 5% 4
Saved for hours. After that, leave it in the test environment condition for 24 hours, attach a weight of 10 g to the end of the tape, slowly rewind, and observe the degree of peeling or adhesion between layers,
It was evaluated by ○ and ×.

Regarding the block error rate BER (random), first, a 1 kHz sine wave, which is 3 dB lower by the full scale level, is applied to any part of the tape under test by L and R.
Recorded on both channels. During reproduction, the number of C1 error blocks was counted every second, and the ratio to the number of decoded blocks per second was calculated. The measurement was performed continuously for 6 minutes or more only in the main area, and the average value was used as the measured value. The results are shown in Table 1.

[0112]

[Table 1]

In Table 1, the powder drop and BER in the case of the ester modification of Comparative Example 2 are poor because the back coat layer is brittle. Further, the reason that the BER and the surface roughness in the case of the urethane (THA) modification of Comparative Example 1 are poor is that the paint is poorly dispersed. Further, the reason why the BER of the thermosetting of Comparative Example 3 is bad is that the transfer at the time of thermosetting in the roll state (the rough surface of the backcoat layer roughens the surface of the magnetic layer in contact).

Comparative Example 4 The electron beam curable resin for the magnetic layer was changed to TB-0246 [EBCV].
C (S)] only.

Comparative Example 5 The electron beam curable resin for the magnetic layer was changed to TB-0242 [EBCU].
(P)] only.

Comparative Example 6 EBCVC (COOH) 8 was used as the electron beam curable resin for the magnetic layer.
It was set to 0 + EBCU (COOH) 13. EBCVC (C
OOH) and EBCU (COOH) are the following COOH-containing electron beam-curable vinyl chloride resins and C, respectively.
It is an electron beam curable urethane resin containing OOH.

[0117]   EBCVC (COOH)     Vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer     Average degree of polymerization 400     COOH content 1% by weight     Acrylic content 10 mol / 1 mol   EBCU (COOH)     Hydroxy-containing acrylic compound-carboxy-containing compound-hydroxy-containing     Polyester polyol-diphenylmethane diisocyanate     Average molecular weight 25,000     COOH content 1% by weight     Acrylic content 6 mol / 1 mol

Comparative Examples 7 and 8 The above-mentioned various EBCVCs and EBCUs were combined with the same VC: U amount ratio to obtain electron beam curable resins.

Comparative Example 9 EBCVC and EBCU were used as thermosetting (TS) vinyl chloride resin [TSVC (S)] and urethane resin [TS].
U (S)]. The volume ratio of VC: U is the same. In this case, TSVC (S) is TB-02 of EBCUC (S).
MR-110 manufactured by Nippon Zeon Co., Ltd. before modification of No. 46. Further, TSU (S) is a urethane resin consisting of phthalic acid based polyester polyol and diphenylmethane diisocyanate having a molecular weight of 23,000, SO ₃
It contains 0.005% of Na. As a cross-linking agent, Coronate L manufactured by Nippon Polyurethane Co., Ltd. was used.

The surface gloss of each of the obtained tapes (gloss 60
Degree), electromagnetic conversion characteristics (deck: Sony DTC-1000
ES, Reference: Sony RSD-1079), BE
R (block error rate, deck: Sharp RX-X
100) and surface roughness Ra (taly step).

Among these, the electromagnetic conversion characteristics are those of Sony R-DAT deck DTC- which is modified to allow RF input / output.
It was measured at 1000 ES under the following conditions.

[0122] Mode: Normal track mode Tape speed: 8.15mm / s Measuring track: Positive azimuth track

For the electromagnetic conversion characteristics, the following reference tape was used as a reference. Reference tape: Sony RSD-1079

The measurement was carried out after the tape was bulk demagnetized.
The input signal was a square wave, and the fundamental frequency of the output signal was measured using a spectrum analyzer. Regarding the block error rate (BER), 60 ° C 90% R
The amount of change in BER after storage for 5 days under the condition of H was measured. The results are shown in Table 2.

[0125]

[Table 2]

From the results shown in Table 2, the effect of the present invention is clear.

[0127]

According to the present invention, rigidity and dispersibility are improved, surface smoothness is improved, and powder falling and blocking are prevented. In addition, the error rate is reduced in high density digital recording. Furthermore, the storage stability is also good.

Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI C09D 5/23 C09D 5/23 G11B 5/735 G11B 5/735 (72) Inventor Yasushi Ishikawa 1-13-1 Nihonbashi, Chuo-ku, Tokyo DK Inc. (72) Inventor Hideki Sasaki 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Inc. (72) Inventor Yasushi Takasugi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Inc. (56) References JP-A-63-104219 (JP, A) JP-A-61-39224 (JP, A) JP-A-61-59621 (JP, A) JP-A-6-131651 (JP, A) Kai 62-287418 (JP, A)

Claims (8)

(57) [Claims] 1. A nonmagnetic support has a backcoat layer on one surface thereof, and a magnetic layer having ferromagnetic fine powder dispersed in a binder on the other surface thereof, wherein the backcoat layer is carbon. An electron beam curable resin containing black is applied and cured by electron beam. The resin is an electron beam curable vinyl chloride resin having a sulfur-containing polar group and a phosphorus-containing polar resin. An electron beam curable urethane resin having a group is contained, and the binder of the magnetic layer is obtained by applying an electron beam curable resin and subjecting the resin to electron beam curing. Electron beam curable vinyl chloride resin having a group, and electron beam curable urethane resin having a phosphorus-containing polar group, the electron beam curable having a sulfur-containing polar group of the back coat layer and the magnetic layer Vinyl chloride resin A raw material vinyl chloride resin having a sulfur-containing polar group and a hydroxyl group, the hydroxyl group of which is modified by electron beam with a monomer having an ethylenically unsaturated double bond and an isocyanate group and having no urethane bond in the molecule. The magnetic recording medium in which the ethylenically unsaturated double bond is bonded to the vinyl chloride resin skeleton through one urethane bond. 2. The magnetic recording medium according to claim 1, wherein the electron beam-curable vinyl chloride resin having a polar group containing sulfur in the back coat layer and the magnetic layer has an acryl group or a methacryl group as an ethylenically unsaturated bond. . 3. The sulfur-containing polar group of the electron beam-curable vinyl chloride resin having the sulfur-containing polar group of the back coat layer and the magnetic layer is —SO ₄ Y and / or —SO.
The magnetic recording medium according to claim 1, which is ₃ Y (where Y is an alkali metal). 4. The —SO ₄ Y and —SO ₃ Y of the electron beam-curable vinyl chloride resin having the sulfur-containing polar group in the back coat layer and the magnetic layer are respectively —SO.
The magnetic recording medium according to claim 4, which is ₄ K or -SO ₃ K. 5. The phosphorus-containing polar group of the electron beam curable urethane resin having the phosphorus-containing polar group of the back coat layer and the magnetic layer is one or more of the groups represented by the following chemical formula 1. 4. The magnetic recording medium according to any one of 4 above. [Chemical 1] (Here, Y is H or an alkali metal.) 6. The electron beam curable urethane resin having a phosphorus-containing polar group in the back coat layer and the magnetic layer contains a group represented by the following chemical formula 2 as a phosphorus-containing polar group. Magnetic recording medium. [Chemical 2] 7. The electron beam curable urethane resin having a phosphorus-containing polar group in the back coat layer and the magnetic layer is a raw material urethane resin obtained by using a monomer having any of the groups shown in the following chemical formula 3. 7. The magnetic recording medium according to claim 6, which has been modified by electron beam. [Chemical 3] (Here, Y is H or an alkali metal.) 8. The content ratios of the electron beam-curable vinyl chloride resin having a sulfur-containing polar group and the electron beam-curable urethane resin having a phosphorus-containing polar group in the back coat layer and the magnetic layer are respectively 70:30 to 90: by weight ratio
10. The magnetic recording medium according to claim 1, which is 10.