JP2581095C - - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly, to a binder contained in a magnetic layer formed on a non-magnetic support. It is related to the improvement of. [Summary of the Invention] The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the binder constituting the magnetic layer is in a molecule. By using a vinyl chloride copolymer containing a —COOM group (where M represents hydrogen) and a quaternary ammonium salt, the dispersibility of the magnetic powder and the surface properties of the magnetic layer can be improved and obtained. It is intended to improve the durability, magnetic characteristics, electromagnetic conversion characteristics, etc. of the magnetic recording medium. [Related Art] In recent years, in a magnetic recording medium, particularly 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,
There is a need for improved electromagnetic conversion characteristics. 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 is increased.
There is a strong tendency to increase the so-called packing density. On the other hand, as binders for magnetic recording media conventionally used, vinyl chloride-vinyl acetate copolymers, vinyl chloride-propionic acid copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, etc. A vinyl-based binder may be used. However, when the above-mentioned vinyl chloride-based binder is used, the flexibility of the magnetic layer is insufficient, so that it is necessary to add a large amount of a plasticizer or use a large amount of a soft resin in combination. For this reason, in the former case, there are problems such as blooming and a decrease in the durability of the magnetic layer, and in the latter case, the dispersibility of the ferromagnetic powder is deteriorated, or in the case of high temperature and high humidity. There is a problem in running performance. Furthermore, with the increase in the specific surface area due to the micronization of the magnetic powder as described above and the increase in the cohesive force due to the high magnetic force, satisfactory dispersibility and surface properties cannot be obtained with the above-mentioned binder, and the packing of the magnetic powder It is also difficult to increase the density. Therefore, durability, magnetic characteristics, and electromagnetic conversion characteristics were also insufficient.
Alternatively, for example, a method of using a surfactant as a dispersant has been considered. In this case, since the surfactant is a low molecule, the presence of the surfactant in the magnetic layer causes a powder. Problems such as mechanical strength such as blooming due to dropping and aging and durability are caused. Under such circumstances, a binder capable of further improving such properties has been demanded,
Attempts have been made to introduce hydrophilic polar groups into the side chains of various binder resins. However, as described above, the binder into which a hydrophilic polar group is introduced has a certain effect in improving the dispersibility as compared with a conventional binder into which a polar group is not introduced, but the ultrafine magnetic particles The performance with respect to the powder and the magnetic powder having a high magnetization was insufficient. [Problems to be Solved by the Invention] As described above, further improvement of the binder is demanded in view of the dispersing performance with respect to the ultrafine magnetic powder and the physical properties of the coating film. Therefore, the present invention has been proposed to solve the above-mentioned drawbacks in the technical field, and provides a binder resin having excellent dispersibility in magnetic powder and physical properties of a coating film, and has excellent durability and magnetic properties. It is an object to provide a magnetic recording medium having good electromagnetic conversion characteristics. [Means for Solving the Problems] The inventors of the present invention have conducted intensive studies over a long period of time to achieve the object described above, and as a result, have found that a —COOM group (provided that a polar group is present on the side chain of the vinyl chloride copolymer) , M represents hydrogen.) And the introduction of a quaternary ammonium salt have been found to exhibit high affinity for magnetic powder, and have completed the present invention. That is, the magnetic recording medium according to the present invention is a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the binder has -CO in a molecule.
It contains an OM group (where M represents hydrogen) at a ratio of 0.2 to 1.0 mol% and contains a vinyl chloride copolymer having a quaternary ammonium salt. is there. The vinyl chloride-based copolymer used as a binder of the magnetic layer in the present invention is obtained by introducing a polar group into a side chain of a copolymer mainly composed of vinyl chloride, and has a general formula (Where X is a monomer having a vinyl group copolymerizable with vinyl chloride,
Y is a monomer having a vinyl group copolymerizable with vinyl chloride and a -COOM group,
Z represents a monomer having a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt. Further, i, j, k, and l each represent a degree of polymerization. ). In the above general formula, each component of the compound is described for convenience so as to be sequentially and regularly arranged, except for the case shown in the above general formula, each component is regularly arranged by a fixed ratio. Obviously, they may be arranged repeatedly or randomly. Here, the polymerization degree (i + j + k + 1) of the vinyl chloride copolymer is 100 ≦ (i
+ J + k + 1) ≦ 1000. If this value is less than 100, the durability of the obtained coating film will be deteriorated, and if it exceeds 1000, the solubility in a solvent will be deteriorated and it will be difficult to prepare a coating. Further, the ratio of the vinyl chloride component contained in the vinyl chloride copolymer is as follows:
It is preferably 30 to 95 mol%. If the vinyl chloride component is less than 30% by mole, the durability deteriorates. On the other hand, if it exceeds 95% by mole, thermal deterioration becomes remarkable, which is not preferable. When a monomer X having a vinyl group copolymerizable with vinyl chloride is added, its ratio is preferably 5 to 70 mol%. This is copolymerized for improving the physical properties of the coating film. Next, the monomers Y and Z are preferably introduced in a total amount of 0.05 to 5 mol%. Among them, particularly, the monomer Y is desirably in the range of 0.05 to 3 mol%, and if it is less than 0.05 mol%, the dispersibility is deteriorated, and if it is more than 3 mol%, the viscosity of the coating material is increased and the handleability is lowered. Further, the content of the monomer Z is desirably 0.05 mol% or more. By introducing the quaternary ammonium salt by copolymerizing the monomer Z, the dispersibility can be further improved without causing a problem of the paint viscosity. Next, the monomers X, Y, and Z will be described in order. First, examples of the monomer X copolymerizable with vinyl chloride include vinylidene chloride, vinyl acetate, vinyl alcohol, maleic acid, maleic anhydride, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, vinyl propionate, and the like. No. By selecting and copolymerizing one or more of these monomers, the solubility in a solvent, the flexibility of a coating film, the dispersibility of a ferromagnetic powder, the cross-linkability with a curing agent such as isocyanate, etc. are controlled to some extent. can do. Next, the monomer Y can be introduced by the following methods A and B, roughly classified into a case where the monomer contains a -COOM group from the beginning and a case where the monomer is modified later. A. A method of copolymerizing a monomer Y having a vinyl group copolymerizable with vinyl chloride and a -COOM group with vinyl chloride. The monomer Y has an acryl group or a methacryl group in the molecule and has a -COOM group, and specific examples thereof are shown below. (However, the M is hydrogen or an alkali metal wherein, R _B is a divalent hydrocarbon group having 2 to 4 carbon atoms, R _C represents respectively a divalent hydrocarbon group.) B. The functional group introduced into the terminal or side chain of the vinyl chloride copolymer is -COOM
A method of modifying with a compound having a group. This method can be further divided into the following two methods depending on the type of the functional group previously introduced into the vinyl chloride copolymer. (B-1) A method in which a monomer having an active hydrogen and a vinyl group copolymerizable with vinyl chloride is copolymerized with vinyl chloride, and then modified with a compound having a group capable of reacting with active hydrogen and a -COOM group. . Examples of the monomer having the active hydrogen and a vinyl group copolymerizable with vinyl chloride include, for example, (Wherein, X represents hydrogen or a methyl group) and vinyl alcohol. Further, as the compound having a group capable of reacting with active hydrogen and a -COOM group,
For example: i) ClCH ₂ -COOM ii) O = C = NCH ₂ -COOM (Wherein, M represents hydrogen or an alkali metal). (B-2) After copolymerizing a monomer having a vinyl group copolymerizable with vinyl chloride and a group capable of reacting with active hydrogen in the molecule with vinyl chloride, it has active hydrogen and a -COOM group in the molecule. A method of denaturing with a compound. Examples of the monomer having a vinyl group copolymerizable with vinyl chloride and a group capable of reacting with active hydrogen in the molecule include, for example, (Wherein, X represents hydrogen or a methyl group). Examples of the compound having the active hydrogen and the -COOM group include, for example, (Wherein, M represents hydrogen or an alkali metal). Finally, the monomer Z is roughly classified into a case where the quaternary ammonium salt is contained from the beginning and a case where the monomer is introduced later, and can be introduced by the following methods C and D. C. A method in which a monomer Z having a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt is copolymerized with vinyl chloride. The monomer Z having a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt can be synthesized by an ordinary method, for example, by the following method. (Where R represents an alkyl group having 1 to 4 carbon atoms, R _m represents a divalent hydrocarbon group, R _n represents a hydrogen atom or a methyl group, and X represents Cl, Br, or I, respectively. .
) In particular, And the like. D. A method in which a functional group introduced into a terminal or a side chain of a vinyl chloride copolymer is modified with a compound having a quaternary ammonium salt. (D-1) After a monomer having a vinyl group copolymerizable with vinyl chloride and an active hydrogen group in the molecule is copolymerized with vinyl chloride, a group capable of reacting with active hydrogen and a quaternary ammonium salt are added in the molecule. A method of denaturing with a compound having the above. Examples of the monomer having a vinyl group copolymerizable with vinyl chloride and an active hydrogen group in the molecule include, for example, (Wherein, R ′ represents hydrogen or a methyl group). Examples of the compound having a group capable of reacting with the active hydrogen and a quaternary ammonium salt in the molecule include, for example, (Wherein, R represents an alkyl group having 1 to 4 carbon atoms, and X represents Cl, Br, and I, respectively). These compounds can be easily prepared by reacting, for example, a diisocyanate compound with the compound having active hydrogen and a quaternary ammonium salt synthesized according to the formulas (1) and (2) in the above method C. Synthesized. (D-2) After a monomer having a vinyl group copolymerizable with vinyl chloride and a group capable of reacting with active hydrogen in the molecule is copolymerized with vinyl chloride, an active hydrogen group and a quaternary ammonium salt are added in the molecule. A method of denaturing with a compound having the above. Examples of the monomer having a vinyl group copolymerizable with vinyl chloride and a group capable of reacting with active hydrogen in the molecule include, for example, (Wherein, R ′ represents hydrogen or a methyl group). The compound having the above-described active hydrogen group and a quaternary ammonium salt in a molecule, for _{example, i) HO (CH 2)} 2 N + (R) 3 · X - ii) HO (CH 2) 3 N + ^{_{(R) 3 · X - (}} . However, the formula in which R is an alkyl group having 1 to 4 carbon atoms, X is Cl, Br, respectively representing I) and the like, in the previous method C (1) It is easily synthesized by the reaction shown in the formula and the formula (2). The above is an essential element of the binder used in the present invention, but it may be used by mixing with another binder. As the binder, those conventionally used as binders for magnetic recording media can be used, and vinyl chloride-vinyl acetate copolymer, 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, methacrylate-
Vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer Polymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenolic resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin or a mixture thereof No. Of these, polyurethane resins, polyester resins, acrylonitrile butadiene copolymers, etc., which are supposed to impart flexibility, are preferred. In addition, if a trifunctional isocyanate compound or a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate is used in combination as a crosslinking agent, durability and the like can be further improved. In any case, the combined introduction amount of the polar group -COOM group and the quaternary ammonium salt in these binders is preferably 0.001 to 1.0 mmol / g of the binder, more preferably 0.01 to 0.5 mmol. Millimoles. Among these, the content of the -COOM group is preferably 0.01 to 0.5 mmol. When the amount is lower than the above range, the dispersibility is deteriorated. Gets worse. The quaternary ammonium salt is preferably at least 0.001 mmol. 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, as the ferromagnetic powder used in the magnetic layer, any conventional ferromagnetic powder can be used, such as ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, and hexagonal barium ferrite fine particles. , Iron nitride and the like. When the ferromagnetic iron oxide particles are represented by the general formula FeO _x , 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 (FeOx, 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 ferromagnetic chromium dioxide, CrO ₂ or a material to which at least one of Ru, Sn, Te, Sb, Fe, Ti, V, and Mn is added 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-
Bi, Mn-Al, Fe-Co-V, etc. can be used, and even if a metal component such as Al, Si, Ti, Cr, Mn, Cu, Zn or the like is added thereto for the purpose of improving various characteristics. Good. 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. As these dispersants, lubricants, abrasives, antistatic agents, and rust preventives, any conventionally known ones can be used. The constituent material of the above-mentioned magnetic layer is dissolved in an organic solvent to prepare a magnetic paint, which is applied to a non-magnetic support. The solvent of the magnetic paint includes ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. A solvent, an ester solvent such as methyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether, etc., and a glycol dimethyl ether magnetic paint are prepared and applied on a non-magnetic support. Ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl ether; glycol dimethyl ether, glycol monoethyl ether; dioxane Glycol ether solvents, aromatic hydrocarbon solvents such as benzene, toluene and xylene, aliphatic hydrocarbon solvents such as hexane and heptane, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. An organic chlorine compound-based solvent is exemplified. Further, nonmagnetic supports on which the magnetic material is coated include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, and polyvinyl chloride. And vinyl-based resins such as polyvinylidene chloride and plastics such as polycarbonate, polyimide and polyamide-imide. The form of the nonmagnetic support may be any of a film, a tape, a disk, a card, a drum, and the like. Alternatively, as the nonmagnetic support, light alloys such as aluminum alloys and titanium alloys, polystyrene, ABS
A so-called hard disk may be formed using a thermoplastic resin such as a resin, ceramics such as alumina glass, single crystal silicon, or the like. In this case, it is preferable that the surface of the support is hardened by, for example, providing a Ni-P plating layer or performing alumite treatment in advance. In addition, the vinyl chloride copolymer containing the above-mentioned -COOM group and quaternary ammonium salt can be used as a binder for a back coat layer, an undercoat layer and the like. [Action] As described above, by using a vinyl chloride copolymer having a -COOM group, which is a polar group in the molecule, and a quaternary ammonium salt as the binder, the affinity for the magnetic powder is greatly improved. . Therefore, good decomposability can be expected even when ultrafine magnetic powder or magnetic powder having a large amount of magnetization is used. EXAMPLES Hereinafter, specific examples of the present invention will be described. First, a binder was prepared. That is, the following a and b are used as a monomer Y containing a maleic acid, a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt as a monomer Y containing a -COOM group. ^{_{b) CH 2 = CHN + (}} CH 3) 3 Br - and select, by changing the type and proportion of these monomers shown in Table 1, were prepared binder A or binder G. For comparison, binders I to VI not containing either one or both of monomer Y and monomer Z were also prepared. Example 1 Using the binder A described above, a magnetic coating composition was prepared according to the following composition. 100 parts by weight of Co-coated γ-Fe ₂ O ₃ (specific surface area 35 m ² / g) Binder A 12 parts by weight Polyurethane resin N-2304 (binder) 8 parts by weight Dimethyl silicone oil (lubricant) 1 part by weight Lecithin ( Dispersant) 1 part by weight Cr ₂ O ₃ (abrasive) 2 parts by weight Methyl ethyl ketone 100 parts by weight Methyl isobutyl ketone 50 parts by weight Toluene 50 parts by weight The above composition was mixed for 48 hours by a ball mill and filtered with a 3 μm filter. ,
2.5 parts by weight of a curing agent (manufactured by Bayer, Desmodur L) were added, mixed for 30 minutes, and applied to a 14 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. Further, after performing a super calender treatment, the sample tape was cut into a 1/2 inch width. Example 2 A sample tape was prepared in the same manner as in Example 1 except that the binder B was used instead of the binder A. Example 3 A sample tape was prepared in the same manner as in Example 1 except that the binder C was used instead of the binder A. Example 4 A sample tape was produced in the same manner as in Example 1 except that the binder D was used instead of the binder A. Example 5 A sample tape was produced in the same manner as in Example 1 except that the binder E was used instead of the binder A. Comparative Example A A sample tape was prepared in the same manner as in Example 1 except that the binder F was used instead of the binder A. Example 6 A sample tape was produced in the same manner as in Example 1 except that the binder G was used instead of the binder A. Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that the binder I was used instead of the binder A. Comparative Example 2 A sample tape was prepared in the same manner as in Example 1 except that Binder II was used instead of Binder A. Comparative Example 3 A sample tape was prepared in the same manner as in Example 1 except that binder III was used instead of binder A. Comparative Example 4 A sample tape was produced in the same manner as in Example 1 except that the binder IV was used instead of the binder A. Comparative Example 5 A sample tape was produced in the same manner as in Example 1, except that the binder V was used instead of the binder A. Comparative Example 6 A sample tape was prepared in the same manner as in Example 1 except that the binder VI was used instead of the binder A. For each sample tape obtained, paint viscosity, surface gloss, powder drop,
Still properties were measured. The surface gloss was measured by measuring the reflectance at an incident angle of 75 ° and a reflection angle of 75 ° using a gloss meter. The amount of powder falling was evaluated by the deduction method (the greater the absolute value, the more powder falling) by visually observing the amount of powder falling onto the head drum, guide, etc. after 100 times of the 60-minute shuttle. The still characteristic is 4.2 MHz for the sample tape.
Was recorded, and the time until the playback output attenuated to 50% was set. Second result
It is shown in the table. Table 2 shows that the use of a vinyl chloride copolymer having both a -COOM group and a quaternary ammonium salt as a binder as a binder improves the surface gloss and powder drop and improves the still characteristics. It can be seen that it is greatly improved. As far as the still properties are concerned, Comparative Example 3 also gives good results, but the paint viscosity is too high and the coatability is poor. Here, when the introduction rate of the monomer Z is increased while the introduction rate of the monomer Y is kept constant, there is a tendency that the viscosity of the coating material slightly decreases, and the surface gloss, powder dropout, and still characteristics tend to be improved (Examples 1 to 3). ). Further, the monomer Y
When the rate of introduction of the compound was increased, the viscosity of the coating material was increased, and there was a tendency that the powder falling and the still characteristics were improved (Examples 4, 5 and Comparative Example A). On the other hand, in the comparative example, good results cannot be obtained even if either the monomer Y or the monomer Z is missing. When only the monomer Y is missing (Comparative Examples 4 to 6), the powder falling and the still properties are inferior, and when only the monomer Z is missing (Comparative Example 2).
In Comparative Example 3), the powder drop was improved, but the paint viscosity was significantly increased. In the case where both are missing (Comparative Example 1), all of the characteristics are significantly inferior. [Effects of the Invention] As is clear from the above description, in the present invention, a vinyl chloride copolymer having a -COOM group and a quaternary ammonium salt as a polar group in the molecule is used as a binder for the magnetic layer. Therefore, the affinity for the magnetic powder is high, and the dispersibility is good even when a magnetic powder that has been made into ultrafine particles or a magnetic powder having a large amount of magnetization is used. Therefore, the durability and surface properties of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely excellent.

Claims (1)

Claims: In a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a nonmagnetic support, the binder has a -COOM group in a molecule (where M is Represents hydrogen) from 0.2 to
A magnetic recording medium containing a vinyl chloride copolymer having a quaternary ammonium salt content of 1.0 mol%.