JP2621222C - - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on a non-magnetic support, and particularly to its durability. The present invention relates to a magnetic recording medium with improved performance. [Summary of the Invention] The present invention relates to a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on a non-magnetic support, wherein a vinyl copolymer having an epoxy group and a tertiary amino group are provided. It is an object of the present invention to provide a magnetic recording medium having excellent durability by using a polyurethane resin having the following as a binder. [Related Art] In recent years, in a magnetic recording medium, for example, a magnetic recording medium for a VTR (video tape recorder), in order to obtain a high reproduction output even when performing short-wavelength recording, magnetic characteristics, electromagnetic conversion characteristics, etc. There is a demand for improvement. As a countermeasure, the magnetic powder is made finer and the magnetic force is increased, and the packing density of the magnetic powder in the magnetic layer, that is, the so-called packing density, tends to be increased. for that reason,
The proportion of the binder in the magnetic coating is very low. Such a magnetic coating film containing a small amount of a binder may cause peeling of the magnetic layer when used as a magnetic recording medium. Need to be raised. For that purpose, it has been proposed to improve the mechanical strength of the magnetic coating by crosslinking the binder in the magnetic coating. As described above, a binder that forms a crosslinked structure by using a compound having an electron beam sensitive bond in a molecule or a hydroxyl group in a molecule as a binder that increases the mechanical strength of a magnetic coating film by forming a crosslinked structure. Which form a crosslinked structure utilizing the reaction between active hydrogen and isocyanate are proposed. However, for example, a binder made of the compound having an electron beam sensitive bond requires a very expensive equipment in order to form a crosslinked structure, and is not practical. On the other hand, in the above-mentioned binder in which active hydrogen of a hydroxyl group reacts with an isocyanate compound or the like to form a crosslinked structure, the reaction is While the actual reaction is Isocyanate reacts with water, and the amino group formed by this reaction It reacts with other isocyanates. Therefore, the -NCO group effective for reacting the isocyanate compound with the hydroxyl group is affected by moisture as shown in the above reaction formula, and the amount of -NCO group contributing to cross-linking is reduced, so that a sufficient cross-linked structure can be formed. Inability to do so results in poor durability. [Problems to be Solved by the Invention] As described above, a cross-linking structure is formed by utilizing a reaction between an isocyanate and a hydroxyl group, or a binder that forms a cross-linking structure by electron beam-sensitive bonding and increases the mechanical strength of a coating film. Binders that form and increase the mechanical strength of the coating film are not practical due to equipment problems, or the reaction itself is easily affected by moisture and does not form a good crosslinked structure. The magnetic recording medium used has a problem that sufficient durability cannot be obtained. Thus, the present invention has been proposed to solve the above-described problems, and provides a binder having a good cross-linked structure without being affected by moisture during the reaction when forming a cross-linked structure, An object of the present invention is to provide a magnetic recording medium having excellent durability. [Means for Solving the Problems] The inventor of the present invention has made extensive efforts to achieve the above-mentioned object, and as a result, has found that a vinyl copolymer having an epoxy group and a polyurethane resin having a tertiary amino group can be used. It has been found that the obtained resin acts as a good binder. The present invention has been proposed based on the above findings, and in a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on a non-magnetic support, the magnetic layer is included in the molecule. It is characterized by containing a vinyl copolymer having an average molecular weight of 400 or less having an epoxy group and a polyurethane resin having a tertiary amino group in a molecule as a binder. In the present invention, a vinyl-based copolymer having an epoxy group used as a binder is mainly composed of a vinyl-based compound, and an epoxy group and a vinyl-based compound introduced to form a cross-linked structure into the vinyl-based compound. It is obtained by copolymerizing a monomer having a copolymerizable double bond. Here, the vinyl compound constituting the vinyl copolymer includes vinyl chloride,
Vinyl acetate, vinyl propionate, vinyl alcohol, methyl vinyl ether,
Vinyl monomers such as isobutyl vinyl ether and cetyl vinyl ether, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) aryl, butyl (meth) acrylate, (meth) acryl Examples include acrylic monomers such as lauryl acid, 2-hydroxypropyl (meth) acrylate, and acrylic acid esters, and vinylidene monomers such as vinylidene chloride and vinylidene fluoride, and one or more of these copolymerized. Can be used. Examples of monomers having a double bond copolymerizable with the vinyl compound and having an epoxy group introduced to form a cross-linked structure include unsaturated monomers such as allyl glycidyl ether and methacryl glycidyl ether. Glycidyl ethers of alcohols, glycidyl acrylates, glycidyl methacrylate, glycidyl-p-vinylbenzoate, methyl glycidyl itaconate, glycidyl ethyl malate, glycidyl vinyl sulfonate, glycidyl esters of unsaturated acids such as glycidyl (meth) allyl sulfonate, Epoxide olefins such as butadiene monooxide, vinylcyclohexene monooxide, and 2-methyl-5,6-epoxyhexene. Further, the vinyl copolymer may be copolymerized with another monomer having a double bond copolymerizable with the vinyl compound in order to improve the properties. Examples of such a monomer include butadiene monomers such as 1,3-butadiene, maleic acid, maleic anhydride, diethyl maleate, butylbenzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, and styrene. , Α-methylstyrene, p-methylstyrene, acrylonitrile, ethylene, propylene and the like. The vinyl copolymer may have an active hydrogen (for example, a hydroxyl group) in the molecule. In this case, an epoxy ring-opened by a catalytic effect of a tertiary amino group in a polyurethane resin described later. By reacting with the group, a crosslinked structure is formed between the vinyl copolymers, and combined with the crosslinked structure composed of the vinyl copolymer and the polyurethane resin, the mechanical strength of the binder can be increased. The amount of the epoxy group contained in the vinyl copolymer is 0.01 to 2.0.
It is preferably about mmol / g. When the amount of the epoxy group is small, the durability is deteriorated, and when the amount is large, it is difficult to form a coating. On the other hand, a polyurethane resin having a tertiary amino group is a polyurethane resin having a tertiary amino group introduced into the polyurethane resin. The polyurethane resin is obtained by a reaction between a polyhydroxy compound and a polyisocyanate. The polyhydroxy compound or polyisocyanate serving as a main component of the resin is a long-chain diol having a molecular weight of about 500 to 5000, and a molecular weight of about 50 to 50.
It is preferable to use 0 short-chain diols and organic diisocyanates. The long-chain diols are roughly classified into, for example, polyester diols, polyether diols, and polyether ester glycols. As the polyester diol, specifically, for example, succinic acid, adipic acid, sebacic acid, aliphatic dicarboxylic acids such as azelaic acid, terephthalic acid, aromatic dicarboxylic acids such as isophthalic acid or lower alcohol esters thereof, ethylene glycol, Polyester diols obtained by reacting with 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexane glycol, diethylene glycol, neopentyl glycol, an ethylene oxide adduct of bisphenol A, or a mixture thereof Or a lactone-based polyester diol obtained by ring-opening polymerization of a lactone such as ε-caprolactone. Examples of the polyether diol include polyethylene glycol, polypropylene ether glycol, polytetramethylene ether glycols, and copolymerized polyether glycols thereof. Examples of the polyetherester glycol include polyester glycols obtained by reacting the above polyalkylene ether glycol as a polyol component with an aliphatic or aromatic dicarboxylic acid. If the molecular weight of this long-chain diol is too small, the resulting polyurethane resin will have too high a urethane group concentration, resulting in poor flexibility of the resin, and poor solubility in solvents, and will be used as a binder for magnetic recording media. It is not so good. Further, when the molecular weight of the long-chain diol is too large, the content of the long-chain diol in the resin becomes too large and the urethane group concentration becomes relatively small, so that the abrasion resistance and heat resistance of the resin decrease. I do. The short-chain diol is, for example, ethylene glycol, propylene glycol, 1,
Aliphatic glycols such as 4-butylene glycol, 1,6-hexane glycol, neopentyl glycol and the like, and aromatic diols such as ethylene oxide adduct or propion oxide adduct of bisphenol A, ethylene oxide adduct of hydroquinone, etc. These can be used alone or in a mixture of various amounts depending on the properties of the resin. Further, glycerin, ethylene oxide adduct of glycerin, 2-methylpropane-1,2,3-triol, 4- [bis (2-hydroxyethyl)]-2-hydroxypentane, 3-methylpentane-1,3, 5-triol, 1,2,6-hexanetriol, 1-
Triols such as bis (2-hydroxyethyl) amino-2-propanol and propionoxide adduct of diethanolamine can be used in combination. As the organic diisocyanate, tetramethylene diisocyanate, aliphatic diisocyanate such as hexamethylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate,
2,6-tolylene diisocyanate, diphenylmethane diisocyanate, 3,3-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4 '-Diisocyanate diphenyl ether, aromatic diisocyanate such as 1,5-naphthalenediisocyanate, 2,4-naphthalenediisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethyl Alicyclic diisocyanates such as cyclohexane, 4,4'-diisocyanatodicyclohexylmethane and isophorone diisocyanate; In the present invention, it is also possible to use a polyurea resin or a polyurethane urea resin in addition to the above polyurethane resin. The above polyurea resin and polyurethane urea resin can be obtained by using a part or all of the organic diisocyanate constituting the polyurethane resin as an organic diamine. In introducing a tertiary amino group into the polyurethane resin, a tertiary amino group-containing polyol shown below may be used as a part of a chain extender, whereby a tertiary amino group is contained in the main chain of the polyurethane resin. An amino group is introduced, resulting in a polyurethane resin having a desired tertiary amino group. Here, the amount of the tertiary amino group contained in the polyurethane resin is preferably 0.01 to 1.0 mmol / g. As the tertiary amino group-containing polyol, for example, And the like. In the present invention, the tertiary amino groups contained in the polyurethane resin are contained in the vinyl copolymer by combining the vinyl copolymer having an epoxy group and the polyurethane resin having the tertiary amino group. Promotes the ring-opening reaction of the epoxy group. Therefore, a crosslinked structure is developed between the vinyl-based copolymer or between the vinyl-based copolymer and the polyurethane resin, and a coating film having excellent durability is obtained. The reaction is shown as follows. Or, (However, R _viny represents a vinyl copolymer, and R _poly represents a polyurethane resin.
Incidentally, the ratio of the vinyl chloride copolymer to the polyurethane resin is preferably about 0.1 to 10 as the vinyl chloride copolymer / polyurethane resin. The binder used in the magnetic recording medium of the present invention may contain a tertiary amine compound alone as a crosslinking accelerator. By using this tertiary amine compound in combination,
The ring opening reaction of the epoxy group contained in the vinyl copolymer can be further promoted. Further, a polyisocyanate is added as a curing agent to the binder used in the magnetic recording medium of the present invention, and the reaction between the polyisocyanate and the hydroxyl group in the vinyl copolymer or the hydroxyl group in the polyurethane resin is utilized. It is also possible to form a cross-linked structure by using the cross-linked structure with an epoxy group, whereby a magnetic coating film having even higher strength can be obtained. The epoxy group-containing vinyl copolymer and the tertiary amino group-containing polyurethane resin described above may be used as a mixture with another binder. As such other binders, those conventionally used as binders for magnetic recording media can be used, and vinyl chloride-vinyl acetate copolymers, vinyl chloride-
Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate -Vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer , Acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer,
Examples include polyester resins, phenol resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, and mixtures thereof. Of these, polyurethane resins, polyester resins, acrylonitrile butadiene copolymers, etc., which are supposed to impart flexibility, are preferred. A hydrophilic polar group may be introduced into the epoxy group-containing vinyl copolymer or the tertiary amino group-containing polyurethane resin or another binder used together for the purpose of further improving dispersibility. Examples of the hydrophilic polar group include -SO ₃ M group, -OS
O ₃ M group, —PO (OM ′) ₂ group, —COOM group, —NG ₃ J group (where M is a hydrogen atom or an alkali metal atom, M ′ is a hydrogen atom, an alkali metal atom or a hydrocarbon atom) , G represents an alkyl group, and J represents a halogen.). In the magnetic recording medium of the present invention, the magnetic layer is formed, for example, by applying a magnetic paint prepared by dispersing a ferromagnetic powder in the above-mentioned binder and dissolving it in an organic solvent to the surface of the non-magnetic support. Here, the material of the non-magnetic support may be any material as long as it is generally used for this type of magnetic recording medium, for example, polyesters such as polyethylene terephthalate, and polyolefins such as polyethylene and polypropylene. , Cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, polyamide, and polyamideimide; paper; aluminum and copper; Examples include metals, light alloys such as aluminum alloys and titanium alloys, ceramics, and single crystal silicon. The form of the non-magnetic support may be any of film, tape, sheet, disk, card, drum and the like. As the ferromagnetic powder used for the magnetic layer, any conventional ferromagnetic powder can be used. Therefore, usable ferromagnetic powders include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, iron nitride and the like. When the ferromagnetic iron oxide particles are represented by the general formula FeOx, the value of X is 1.
33 ≦ X ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1
. 50), magnetite (Fe ₃ O ₄ , X = 1.33) and their solid solutions (FeO
x, 1.33 <X <1.50). Further, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. Cobalt-containing iron oxides are roughly classified into two types: a doped type and an adhered type. As the above-mentioned ferromagnetic chromium dioxide, CrO or a material obtained by adding at least one of Ru, Sn, Te, Sb, Fe, Ti, V, Mn and the like for the purpose of improving coercive force can be used. Examples of the ferromagnetic alloy powder include Fe, Co, Ni, Fe-Co, Fe-Ni, Fe
-Co-Ni, Co-Ni, Fe-Co-B, Fe-Co-Cr-B, Mn-B
i, Mn-Al, Fe-Co-V, etc. can be used, and a metal component such as Al, Si, Ti, Cr, Mn, Cu, Zn or the like may be added thereto for the purpose of improving various characteristics. . Further, in addition to the binder and the ferromagnetic powder, a dispersant, a lubricant, an abrasive, an antistatic agent, a rust inhibitor, and the like may be added to the magnetic layer. The constituent material of the magnetic layer described above is prepared as a magnetic paint by dissolving it in an organic solvent, and is applied on a non-magnetic support. The solvent for the magnetic paint includes acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like. Ketones, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl ether; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; and aromatic carbonization such as benzene, toluene, and xylene Examples include hydrogen, aliphatic hydrocarbons such as hexane and heptane, and chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. [Action] By using an epoxy group-containing vinyl copolymer and a tertiary amino group-containing polyurethane resin in combination, the tertiary amino groups in the polyurethane resin exhibit a catalytic effect,
The ring-opening reaction of the epoxy group of the vinyl copolymer is promoted, and a cross-linking structure is formed between the active hydrogen of the vinyl copolymer or between the epoxy group of the vinyl copolymer and the active hydrogen of the polyurethane resin. Is expressed. Further, the reaction of crosslinking the vinyl copolymers or between the vinyl copolymer and the polyurethane resin by the action of the tertiary amino group proceeds with almost no influence of moisture. Therefore, a binder having a good crosslinked structure and extremely excellent durability can be obtained. EXAMPLES Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples. Table 1 shows the vinyl copolymer used as the binder in this example, and Table 2 shows the polyurethane resin. A magnetic recording medium was produced using the vinyl copolymer shown in Table 1 and the polyurethane resin shown in Table 2 as binders. Example 1 100 parts by weight of ferromagnetic powder (specific surface area 35 m ² / g, gamma iron oxide coated with Co) 12 parts by weight of vinyl copolymer A-1 12 parts by weight of polyurethane resin B-1 12 parts by weight of lubricant (stearic acid) 1 Parts by weight lubricant (butyl stearate) 1 part by weight abrasive (Cr ₂ O ₃ ) 2 parts by weight antistatic agent (carbon) 2 parts by weight methyl ethyl ketone 100 parts by weight methyl isobutyl ketone 60 parts by weight toluene 60 parts by weight After mixing with a ball mill for 24 hours and filtration with a filter, the mixture was applied on a 16 μm-thick polyethylene terephthalate film so that the film thickness after drying was 6 μm. Next, after performing a magnetic field orientation treatment, the film was dried and wound up. After calendering this, it was further heated at 60 ° C. for 24 hours and cut into １ ／ inch width to prepare a sample tape. Examples 2 to 8 In the composition of the magnetic paint, the vinyl copolymer was any of the vinyl copolymers shown in Table 1, and the polyurethane resin was any of the polyurethane resins shown in Table 2. A sample tape was produced in the same manner as in Example 1 except that the type was changed as shown in Table 3. Comparative Examples 1 to 5 In the composition of the magnetic paint, the vinyl copolymer was any of the vinyl copolymers shown in Table 1, and the polyurethane resin was any of the polyurethane resins shown in Table 2. A sample tape was produced in the same manner as in Example 1 except that the type was changed as shown in Table 3. Table 3 shows the types of the vinyl copolymer and the polyurethane resin used in Examples 1 to 8 and Comparative Examples 1 to 5. For each of the obtained sample tapes, the still characteristics and powder drop were measured. In addition, the above-mentioned still characteristic is obtained by recording a video signal of 4.2 MHz on a sample tape,
This was the time required for the reproduction output to attenuate to 50%. The powder drop was evaluated by the deduction method (−10 to 0) by visually observing the powder drop to the head drum, the guide, and the like after running the shuttle 100 times for 60 minutes. The results are shown in Table 4. As is clear from Table 4 above, in each sample tape according to the present invention,
It can be seen that not only the powder drop was small but also the still characteristics were greatly improved. [Effects of the Invention] As is clear from the above description, in the present invention, by using a vinyl copolymer having an epoxy group and a polyurethane resin having a tertiary amino group, the third The ring opening reaction of the epoxy group of the vinyl copolymer is promoted by the action of the tertiary amino group, and a cross-linking reaction occurs between the vinyl copolymers and between the vinyl copolymer and the polyurethane resin, resulting in a bond having excellent mechanical strength. Agent. Further, since this reaction proceeds with little influence of moisture, a binder having very good durability can be obtained. Therefore, by using this binder, it is possible to provide a magnetic recording medium having excellent durability without deteriorating electromagnetic conversion characteristics and the like.

Claims (1)

Claims: 1. A magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on a non-magnetic support, wherein the magnetic layer has an average molecular weight having an epoxy group in a molecule. A magnetic recording medium comprising as a binder a vinyl copolymer of 400 or less and a polyurethane resin having a tertiary amino group in a molecule.