JPH0715741B2 - Magnetic recording medium - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic card, and a magnetic disk.

B. 2. Description of the Related Art In recent years, magnetic recording media have been further developed in application and product development on the other side, and electromagnetic conversion characteristics, physical properties, and other characteristics far superior to those in the past have been required. Therefore, various studies and improvements have been made on the binder in the magnetic material.

Conventionally, as a binder for magnetic recording media, cellulose derivatives, vinyl chloride-vinyl acetate copolymers, polyurethane resins, acrylic resins and their copolymers, vinylidene chloride and its copolymers, epoxy resins, phenoxy resins, polyesters. Etc. are used alone or in combination of several kinds of components. Among them, a typical example is a combination of a polyurethane resin and a vinyl chloride-vinyl acetate copolymer.

The conventionally known urethane resin used for such magnetic layers and the like is synthesized from a polymer diol, a diisocyanate, a chain extender, and a crosslinking agent (which is used as necessary).
Examples of the polymer diol include polyester diol obtained from adipic acid and butane diol, polyether diol and polycarbonate diol, and diphenylmethane diisocyanate and the like can be used as the diisocyanate. The chain extender may be ethylene glycol, butanediol or the like, and the crosslinking agent may be polyols, polyamines or the like.

However, even though such a general urethane resin is excellent in flexibility, it lacks in hardness, so that the mechanical strength of the magnetic recording medium is poor against sliding contact with a guide pin or a magnetic head. In addition, there are problems in terms of runnability and powder falling. For example, when a polyester type urethane resin and polyvinylidene chloride or a vinyl chloride-vinyl acetate copolymer are used, there are problems particularly in heat resistance and still image stability. Further, since such urethane resin tends to have adhesiveness, unstable running called stick-slip is likely to occur in the case of a video tape, and as shown in FIG. 8, the average surface roughness of the magnetic layer is (Ra-mag) is especially 0.014μm
If it is below, jitter increases and running instability becomes significant. Therefore, the surface of the magnetic layer may be roughened for traveling stability, but this is rather inconvenient because the output is rather lowered.

In recent years, with the increase in density and S / N of magnetic materials, especially recording media for video and computers, the particles of magnetic powder used have become smaller. For example, the surface area per unit weight is VH.
S or magnetic powder BET surface area 19~28m ² / g class magnetic tape standard grade beta system is used, the magnetic powder of 30 to 40 m ² / g class is used in the super-high grade class. Also, 45-50 m ² / g in professional grade
Class flour is used.

Generally, the S / N ratio of a magnetic recording medium is said to be proportional to the square root of the number of particles of the magnetic substance in the recording material related to recording / reproducing. The smaller the magnetic material, the more advantageous the S / N is.
However, since the surface area of the particles increases in inverse proportion to the square of the particle diameter, it becomes difficult to disperse the particles as the particle diameter decreases, and the dispersion stability deteriorates. As the magnetic powder becomes finer and has a higher magnetic force, the cohesive force of individual particles becomes stronger, and as a result, a high reproduction output for short wavelength recording and a good S / N ratio are obtained.
The dispersibility and surface smoothness necessary for obtaining the ratio cannot be sufficiently satisfied. In addition, since such a recording medium violently makes sliding contact with the magnetic head during recording and reproduction, the magnetic coating film is abraded by repeated use, and the magnetic powder contained in the coating film tends to fall off, which is an undesirable result of clogging of the magnetic head. Give rise to.

Usually, in dispersing the magnetic powder, a dispersant sufficient to coat the surface of the magnetic powder particles should be sufficient, but in reality, sufficient dispersibility and stability cannot be obtained. A considerable excess of dispersant has been added.
The dispersant that is not adsorbed by the magnetic powder mixes with the binder resin as a binder in the coating film to plasticize the magnetic layer or hinder the curing of the binder resin, and therefore the mechanical strength of the magnetic layer, especially Young's modulus. Is significantly reduced. Recently, there is a tendency to reduce the total thickness of the tape by using a thin base film as the tape is recorded for a long time. However, since the stiffness of the tape is proportional to the cube of the tape thickness, it is necessary to reduce the thickness. As a result, the waist becomes significantly weaker, which deteriorates the running characteristics of the thin tape and the head touch of the tape, thus leading to deterioration of the S / N ratio. In order to maintain mechanical properties associated with the reduction in thickness, particularly the rigidity of the tape, a super-stretched base film is used and the Young's modulus of the magnetic layer is increased. Therefore, the decrease in the Young's modulus of the magnetic layer due to an excessive amount of dispersant and other low molecular weight additives significantly deteriorates the mechanical properties of the thin tape.

Therefore, the viscosity distribution of the magnetic powder is adjusted to improve the dispersibility of the magnetic powder in the binder, or a surfactant is used as the dispersant, or a hydrophilic group in the binder, for example, a hydroxyl group, There has been proposed a method of modifying by introducing a phospho group, a sulfo group, a carboxy group or the like to improve the characteristics.

For example, by introducing a sulfonic acid metal salt residue into a polyester resin, JP-A-56-74824 and JP-A-56-74827 disclose that surface smoothness (gloss) and adhesion to a support are improved. 56-13519, 56-74826, 56-74
No. 828, No. 56-74829 and the like disclose dispersibility and improvement of filling properties related to interfacial tension. The sulfonic acid metal group-introduced polyester resin, polyurethane resin, nitrocellulose, vinyl chloride-vinyl acetate resin, etc. There have been many proposals for binder compositions by combining the above.

Further, since vinyl chloride resins have high mechanical strength, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers or vinyl chloride-vinyl acetate-vinyl alcohol- Maleic anhydride copolymers and the like are prized.

The modification of the vinyl chloride resin with a sulfonic acid metal salt residue is disclosed in JP-A-57-44227. First, a vinyl chloride resin containing an OH group and, for example, a chlorine atom and a sulfone in a molecule. Dehydrochlorination is carried out with a compound containing an acid metal salt residue to obtain a modified vinyl chloride resin having a sulfonic acid metal salt residue introduced therein.

As for the vinyl chloride copolymer containing free sulfo group (-SO ₃ H), there is a place where disclosed in JP-A-58-108032.

However, studies on such fine particles of magnetic powder, high magnetic force and improvement of their dispersibility, filling property, surface smoothness, etc.,
Other problems have arisen with the improvement. That is, the higher density and higher S / N of the magnetic powder in the magnetic layer, on the other hand, leads to a decrease in the mechanical strength of the coating film, and there are many problems regarding running stability and running durability when taped. Is left. For example, when the tape is repeatedly run in a normal state, the edge of the tape may be broken, the tape may be deformed into a wakame shape, or powder may fall off. Such deterioration and failure of running durability are particularly noticeable under conditions of high temperature and high humidity, and are accompanied by deterioration of skew characteristics, jitter, output, S / N and the like.

C. Object of the invention The object of the present invention is very excellent in running durability, excellent running durability even under high temperature and high humidity, electromagnetic conversion characteristics are well maintained, the mechanical strength of the magnetic coating film is large,
Moreover, the adhesion between the magnetic coating film and the support is good, the dispersibility of the magnetic powder in the total magnetic field is good, and high density packing is possible, and the running stability is excellent and the skew characteristics, jitter, and output characteristics are good. It is an object of the present invention to provide a magnetic recording medium having excellent S / N ratio and the like.

D. Structure of the invention and its action and effect The present invention is a vinyl chloride resin having a negative group, the breaking strength is 550kg / cm ² or more, 800kg / cm ² or less, and 100%
The present invention relates to a magnetic recording medium having a magnetic layer containing a urethane resin having a stress of 100 kg / cm ² or more during elongation.

In the present invention, the inclusion of the urethane resin in the magnetic layer has an important meaning. That is, the first
Compared with the characteristics of the conventional soft urethane resin as illustrated by the curve a in the figure, since urethane resin having a small elongation to stress is used, the urethane resin is provided with appropriate hardness and the elongation to stress is Since the range is limited, the flexibility and the binding force of the binder resin can be appropriately provided. As a result, the mechanical strength of the magnetic layer (magnetic coating film) and the magnetic recording medium is increased, the running durability is greatly improved, and damage such as abrasion during sliding contact of the magnetic head and powder drop are greatly reduced. The running performance is remarkably improved. In particular
Magnetic tapes for VTRs can prevent edge breakage and tape deformation, significantly improve running stability and running durability, and hold the control track near the edge to exert its function well. . This allows
Improves skew characteristics, jitter, output characteristics, and S / N ratio.

Further, since the urethane resin of the present invention has appropriate flexibility due to the above limitation, the adhesiveness between the magnetic coating film and the support (or the underlayer) becomes good. Further, by the presence of the urethane resin of the present invention, it is possible to prevent stickiness and decrease in stiffness (stiffness), which are disadvantages when only the soft urethane resin is used, to suppress the tackiness, and to strengthen the rigidity of the medium. The magnetic layer can be easily calendered.

Further, since the urethane resin of the present invention has higher heat resistance than conventional ones, good running durability, running stability, electromagnetic conversion characteristics are maintained even when used under high temperature and high humidity, and it is suitable for severe operating conditions. It is possible to provide a magnetic recording medium that is highly practical and durable.
In particular, it is necessary to stop the tape running during still playback of the video tape and slide the video head on the same surface of the video tape at a rate of 60 times / second to maintain this state for two hours or more. No significant output reduction or dropout increase is allowed during this still time. When still, due to continuous rubbing by the video head,
It is known that the temperature of the tape surface can reach 80-100 ° C. That is, according to the present invention, it is possible to effectively deal with such severe use conditions as described above.

That is, in the present invention, it is important to limit the mechanical properties of the urethane resin to the above range, and thereby it is possible to sufficiently exhibit the above effects.

Further, in the present invention, since the vinyl chloride resin having a negative group is contained in the magnetic layer, the mechanical strength of the magnetic layer is large, the dispersibility of the magnetic powder is improved, and the surface of the magnetic layer is improved. The smoothness is good, and the stains on the calendar rolls are reduced. As a result, high density filling of the magnetic powder becomes possible, and a high level of electromagnetic conversion characteristics can be obtained. Moreover, even with such high density packing of magnetic powder, since the urethane resin as described above is contained in the magnetic layer, there is an increase in tape edge breakage, deformation, powder drop, etc. as described in the prior art section. Can be prevented, and good running stability and running durability can be maintained even under conditions of high temperature and high humidity.

The physical properties of the polyurethane resin are such that the breaking strength is 580 kg / cm.
² or more and 700 kg / cm ² or less is more preferable, and 10
The stress at 0% elongation is more preferably 150 kg / cm ² or more and 300 kg / cm ² or less.

Among the urethane resins, those having a yield point YP as exemplified by the curve b in FIG. 1 are particularly preferable. Such a urethane resin has a very small elongation when stress is applied up to the yield point YP, and is therefore particularly suitable for imparting an appropriate hardness to the magnetic layer, and after the yield point YP. Shows the property of elongating with an increase in stress without causing breakage. Therefore, the flexibility and binding force as a binder resin can be appropriately imparted. The above-mentioned yield point YP is also important for the performance of urethane resin and is preferably 50-600 kg / cm.
^2, and more preferably it is desirable to present the yield point stress range of 100~560kg / cm ² (in the example of FIG. 1 about 290 kg / cm ^2). When the yield point is in the range of 50 kg / cm ² or more, it is possible to prevent the resin from becoming too soft, and when it is 600 kg / cm ² or less, it is possible to prevent the resin from becoming brittle even if it becomes hard. Further, the urethane resin having this yield point is also good in terms of dispersibility, and the durability of the magnetic layer is improved.

The urethane resin having a yield point preferably has a cyclic hydrocarbon residue in the molecule in order to exhibit the above excellent performance. The cyclic hydrocarbon residue is preferably a saturated cyclic hydrocarbon residue, which includes a divalent or monovalent cyclopentyl group, a cyclohexyl group or the like, or a derivative thereof (for example, a substituted alkyl group such as a methyl group, And a halogen substitution product such as a chlorine atom). These saturated cyclic hydrocarbon residues are desirable from the viewpoint of imparting an appropriate hardness to the urethane resin and the availability of raw materials. Further, the bonding position of this cyclic hydrocarbon residue is preferably in the main chain of the urethane resin molecule, but it may be bonded to its side chain. Further, by changing the amount of the constituent component having a cyclic hydrocarbon residue in the urethane resin,
A urethane resin having an arbitrary glass transition point (Tg) can be obtained, and Tg is −30 ° C. to 100 ° C., preferably 0 ° C.
~ 90 ℃. When Tg is -30 ° C or higher, the resin strength is prevented from being lowered (Tg <-30 ° C), and
If the temperature is 100 ° C. or lower, the film can be prevented from becoming brittle and brittle more than necessary.

Furthermore, it was confirmed that the average surface roughness (Ra-mag) of the magnetic layer and the chroma S / N using the urethane resin having the above-mentioned yield point as a binder resin have a strong correlation as shown in FIG. (However, the data in Fig. 2 is Ra-ma
It is expressed as a relative value when the chroma S / N of the medium with g of 0.020 μm is 0 dB). According to this, by setting Ra-mag to 0.020 μm or less, the chroma S / N becomes large and the chroma S / N changes in inverse proportion to the value of Ra-mag. Therefore, Ra-mag is preferably 0.020 μm or less, and 0.01
If it is 6 μm or less, it is more preferable, and if it is 0.014 μm or less, it is extremely suitable for high-fidelity, high-grade, high-resolution, master tape, etc. which require high quality. If Ra-mag is made too small, running characteristics are likely to become unstable, such as image distortion, so the lower limit is preferably 0.005 μm.

Similar results were obtained when the urethane resin according to the present invention having no yield point was used.

To realize Ra-mag in the above range, the amount of the dispersant used when forming the magnetic layer is preferably 0.5 to 6% by weight. If the amount of the dispersant is out of this range and the amount of the dispersant is too small, the surface roughness of the magnetic layer may increase as described above due to poor dispersion.
It becomes difficult to achieve a small value of ≦ 0.020 μm within a predetermined range, and when the dispersant is too much, bleed-out of the dispersant from the magnetic layer easily occurs.

In this case, in the present invention, since the vinyl chloride resin having a negative group is used as the binder, the dispersibility of the magnetic powder and the surface smoothness of the magnetic layer are improved, and the Ra-
It is advantageous to realize mag. Further, since the binder itself has a dispersing effect in this way, the amount of the dispersant can be reduced, the bleed-out of the dispersant described above and the plasticization of the magnetic layer can be prevented, and the mechanical strength of the magnetic coating film can be reduced. Is advantageous in improving.

Further, the urethane resin used in the present invention (not limited to those having a yield point) has a lower adhesiveness as compared with the conventional urethane resin, so that, for example, in the case of a video tape, the running becomes stable and the jitter value is Can be kept smaller than Therefore, for example, Ra-mag of the magnetic layer is 0.0
Even if it is 14 μm or less, the running performance does not become unstable,
Moreover, there is an advantage that a high output can be maintained.

The above-mentioned "average surface roughness" is measured as follows. That is, using the measurement value at the center line roughness of the cutoff value 0.25 mm of the rough curve shown in JIS-B0601 item 5, the measuring device is made by Kosaka Laboratory, three-dimensional roughness measuring device SE-3FK Was used.

In the present invention, the urethane resin contained in the magnetic layer can be synthesized by reacting a polyol with a polyisocyanate. As usable polyols, organic dibasic acids such as phthalic acid, adipic acid, dimerized linoleic acid and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol and diethylene glycol or trimethylolpropane, hexanetriol, By reaction with polyhydric alcohols such as glycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol or any two or more polyols selected from these glycols and polyhydric alcohols Synthesized polyester polyol; or s-
Caprolactam, α-methyl-1-caprolactam, s
Examples include lactone-based polyester polyols synthesized from lactams such as -methyl-s-caprolactam and γ-butyrolactam; and polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide and the like.

These polyols are reacted with an isocyanate compound such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and metaxylylene diisocyanate, whereby urethanized polyester polyurethane and polyether polyurethane are synthesized. These urethane resins according to the invention are usually produced mainly by the reaction of polyisocyanates and polyols and are also in the form of polyurethanes or urethane prepolymers containing free isocyanate groups and / or hydroxyl groups or of their reactivity. It may have no terminal group (for example, in the form of urethane elastomer).

Since methods for producing polyurethanes, urethane prepolymers, urethane elastomers, curing cross-linking methods and the like are known, detailed description thereof will be omitted.

The hardness of the urethane resin described above can be controlled by variously changing the components and / or the manufacturing method thereof, and thus the urethane resin according to the present invention can be manufactured.
That is, in order to reduce the hardness of the urethane resin, multiple kinds of polyester polyol components are randomly present in the molecule, or as the isocyanate, one having a chain-like aliphatic hydrocarbon group between the isocyanate groups is used. To increase the hardness of the urethane resin, use the same type of polyol, or increase the amount of isocyanate added, use an isocyanate that easily crystallizes, or use an isocyanate having a benzene ring in the molecule. There is a method such as using.

The urethane resin having a yield point can be synthesized by reacting a polyol with a polyisocyanate.
At this time, in order to introduce the cyclic hydrocarbon residue, the following methods (1) to (4) can be adopted.

(1) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as the polyhydric alcohol which is a raw material of a polyol (for example, a polymer diol).

(2) A method of using a dicarboxylic acid having a cyclic hydrocarbon residue in advance as the organic dibasic acid (dicarboxylic acid) as a raw material of the polyol.

(3) A method of using the polyhydric alcohol and dicarboxylic acid according to the above (1) and (2) as a raw material for the polyol.

(4) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as a chain extender, in combination with any of the above (1) to (3) or alone.

For example, as a synthetic method for obtaining the urethane resin, 1,4
-Di-hydroxymethylcyclohexane Adipic acid _{(HOOC- (CH 2) 4 -COOH} ) and a polyester polyol obtained from methylene - bis - phenyl isocyanate There is a method of urethane-forming with. In this case, the chain extender may be the above-mentioned 1,4-di-hydroxymethylcyclohexane or other diol (for example, butane-1,4-diol).

As the polyhydric alcohol having a cyclic hydrocarbon residue in advance, those having a cyclohexyl group in the molecular difference of the ethylene glycol structure can be used as described above. Alcohols or glycols thereof, or those having a cyclic hydrocarbon residue in the structure can be used. Further, examples of the dibasic acid include phthalic acid, dimerized linoleic acid, maleic acid, and the like, or those having a cyclic hydrocarbon residue in the molecule thereof. Instead of the above polyols, lactone polyester polyols synthesized from lactams such as s-caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, γ-butyrolactam; or ethylene oxide, butylene oxide, etc. Polyether polyols and the like synthesized from may also be used.

These polyols are used as a raw material for urethane resins in the same manner as the above-mentioned ordinary polyols, and in the form of urethane resins or urethane prepolymers containing a free isocyanate group and / or a hydroxyl group, or in the form of these reactive end groups. It may not be contained (for example, in the form of urethane elastomer).

Further, the usable difference extender may be the polyhydric alcohol exemplified above (which may or may not have a cyclic hydrocarbon residue in the molecule).

It should be noted that the urethane resin having the above-mentioned yield point and the one not having the yield point may be used together in the magnetic layer, and those having different physical properties may be used together. Further, a soft urethane resin or a hard urethane resin may be appropriately used together with the urethane resin according to the present invention.

The vinyl chloride resin according to the present invention can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer having a negative group, and optionally another copolymerizable monomer. Since this copolymer is produced by vinyl synthesis, it is easy to synthesize, and various copolymerization components can be selected, and the characteristics of the copolymer can be optimally adjusted.

Examples of the negative group include one or more selected from a strong acid residue containing sulfur, an acid residue containing phosphorus, a carboxyl group or a hydroxyl group, or salts thereof.

Among the above, as a strong acid residue containing sulfur, a sulfonic acid residue is easily available and there are many kinds. Moreover, a phosphoric acid residue is mentioned as an acid residue containing phosphorus. Examples of these salts include alkali metal salts (particularly preferably sodium, potassium and lithium) and ammonium salts. Among the above alkali metal salts, potassium salt is particularly preferable in terms of solubility, reactivity, yield and the like.

Examples of the above-mentioned copolymerizable monomer having a sulfonate as a negative group include CH ₂ ═CHSO ₃ M, CH ₂ ═CHCH ₂ SO ₃ M, CH ₂ ═C (CH ₃ ) CH ₂ SO ₃ M, CH _{2 = CHCH 2 OCOCH (CH 2 COOR} ) SO 3 M, CH 2 = CHCH 2 OCH 2 CH (OH) CH 2 SO 3 M, CH 2 = C (CH 3) COOC 2 H 4 SO 3 M, CH 2 = CHCOOC ₄ H ₈ SO ₃ M, CH ₂ = CHCONHC (CH ₃ ) ₂ CH ₂ SO ₃ M, and the like.

As the copolymerizable monomer having a phosphate or the like, CH ₂ ═CHCH ₂ OCH ₂ CH (OH) CH ₂ —O—PO ₃ MY ¹ , CH ₂ ═CHCONHC (CH ₃ ) ₂ CH ₂ —O— PO ₃ MY ² , CH ₂ = CHCH ₂ O (CH ₂ CH ₂ O) mPO ₂ MX ^{2 In the} above, M is H, an ammonium group or an alkali metal, R is an alkyl group having 1 to 20 carbon atoms, and Y ¹ is M or CH. _{2 = CHCH 2 OCH 2 CH (} OH) CH 2 -, Y 2 is M or _{^{CH 2 = CHCONHC (CH 3)}} 2 CH 2 -, X 1 is Or OM, X ² is _{CH 2 = CHCH 2 O (CH} 2 CH 2 O) m- or OM. N is 1
-100 and m are positive numbers of 1-100.

Those having a carboxyl group or a salt thereof are particularly preferable from the viewpoint of improving durability, and as the salt, an alkali metal salt or an ammonium salt is particularly preferable. In this case, those having a salt of a carboxyl group are more preferable in terms of dispersibility of magnetic powder and the like.

Then, each copolymer containing a copolymerizable monomer having each of these groups (hereinafter referred to as a monomer unit A) as a component is used as a magnetic layer to form each magnetic recording medium, and the squareness ratio (Bm / Br) was used, a copolymer having a carboxyl group as a salt was used, but the squareness ratio tends to be improved. This is because when -COOH is made into a salt, it does not dissolve in the solvent when dispersed in a solvent, and therefore the copolymer adsorbed on the magnetic powder is difficult to desorb and the copolymer itself becomes more hydrophilic. it is conceivable that.

The above-mentioned copolymer used in the present invention can be produced by copolymerizing the above-mentioned respective starting materials. For example, by synthesizing a copolymer of maleic anhydride and vinyl chloride, and hydrolyzing this copolymer to open the maleic anhydride portion, ammonia is allowed to act on the resulting carboxyl group to effect the reaction as described above. All the carboxyl groups in the monomer unit A are ammonium chloride. However, in this case, a portion of the maleic anhydride portion which does not ring-open during the hydrolysis may remain, and at this time, the maleic anhydride portion is ring-opened by the action of the above-mentioned ammonia so that a part of the carboxyl group of the monomer unit A is released. Is amidated, and the other carboxyl group is ammonium-salt-ized into a so-called half-amide state, or the maleic anhydride moiety may be left as it is without ring-opening due to the action of ammonia. The degree of ring opening of the maleic anhydride moiety (thus the degree of ammonium chloride of the carboxyl group in the monomer unit A) can be controlled by the degree of hydrolysis described above. Further, the solubility of the copolymer in water can be controlled by the ratio of the half amidation or the maleic anhydride moiety described above. The obtained copolymer is analyzed and identified by, for example, GC / Mass.

As the negative group contained in the vinyl chloride resin of the present invention,
The use of a salt such as a metal salt is considered to be more advantageous in obtaining a magnetic layer having retention stability of a magnetic coating material, coatability, and excellent properties aimed at by the present invention. That is, when the urethane resin is contained in the magnetic layer, a polyfunctional isocyanate curing agent is added to the magnetic layer to carry out a crosslinking (curing) reaction.

As the copolymerizable monomer to be copolymerized as necessary, there are known polymerizable monomers, for example, various vinyl esters, vinylidene chloride, vinylidene fluoride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various Acrylic acid ester, methacrylic acid ester, itaconic acid ester, ethylene, propylene, isobutene, butadiene, isoprene, various vinyl ethers, aryl ethers, aryl esters, acrylamide, methacrylamide, maleic acid,
Maleic acid ester, styrene, α-methylstyrene,
P-methyl styrene etc. are illustrated.

These copolymers, in addition to the purpose of improving the solubility of the resin while adjusting the compatibility and softening point of the resin of the present invention and other resins when mixed, other characteristics of the coating film and coating It is appropriately selected depending on the needs of process improvement and the like.

The binder according to the present invention is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization and bulk polymerization. In any method, if necessary, a molecular weight regulator, a polymerization initiator,
Known techniques such as divided addition or continuous addition of monomers can be applied.

Examples of the polymerization initiator used for producing the resin include lauroyl peroxide, benzoyl peroxide,
3,5,5-Trimethylhexanoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, t-butyl-peroxypiparate, t- Organic peroxides such as butylperoxy neodecanoate; 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 4,4'-azobis-4- Azo compounds such as cyanovaleric acid; inorganic peroxides such as ammonium persulfate, potassium persulfate and ammonium perphosphate.

As the suspension stabilizer, for example, polyvinyl alcohol,
Partially saponified polyvinyl acetate, cellulose derivatives such as methyl cellulose, hydroxypropyl cellulose, 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. The above-mentioned polymerization initiator, vinyl chloride and other monomers, suspending agents, emulsifiers, molecular weight modifiers, etc. may be added to the polymerization system at once at the start of polymerization, or may be added separately during polymerization. You can also

The amount of the negative group-containing monomer in the binder used in the present invention is preferably 0.01 to 30 mol%. When the amount of the negative group-containing monomer is too large, the solubility in the solvent is poor and gelation is likely to occur. If the amount of the negative group-containing monomer is too small, the desired characteristics cannot be obtained.

By selecting the amount of the negative group-containing monomer and the type of the negative group, it is possible to appropriately control both the hydrophilic property and the hydrophobic property of the copolymer, that is, HLB (Hydrophile Lipophile Balance).

The average degree of polymerization of the vinyl chloride-based copolymer is particularly preferably from 100 to 600, and if it is within this range, the magnetic layer or the like does not easily become sticky and the dispersibility is kept good. . This vinyl chloride-based copolymer may be partially hydrolyzed.

The compounding ratio of the vinyl chloride copolymer according to the present invention and the urethane resin (the total of both is 100 parts by weight) is as follows.
The vinyl chloride copolymer according to the present invention is preferably 90 to 10 parts by weight, more preferably 80 to 20 parts by weight. If the compounding ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film remarkably deteriorates, and the adhesion to the support also deteriorates. Further, if the above-mentioned mixing ratio is less than 10 parts by weight, the magnetic powder is likely to fall off.

In addition to the urethane resin as the binder resin and the vinyl chloride copolymer having a negative group, a vinyl chloride copolymer (ordinary one) and / or a phenoxy resin having strong mechanical strength may be used together. it can.

The phenoxy resin that can be used is a polymer obtained by polymerization of bisphenol A and epichlorohydrin, and is represented by the following general formula.

For example, there are PKHC, PKHH, PKHT manufactured by Union Carbide.

Further, as a vinyl chloride-based copolymer having no usable negative group, There is something represented by. in this case, The molar ratios derived from 1 and m in the above are 95 to 50 mol% for the former unit and 5 to 50 mol% for the latter unit. X represents a monomer residue capable of copolymerizing with vinyl chloride and is selected from various known copolymerizable monomers (various vinyl esters, etc.) described in the description of the vinyl chloride copolymer having a negative group. Represents one or two or more types. The degree of polymerization represented by (l + m) is preferably 100 to 600. When the degree of polymerization is less than 100, the magnetic layer or the like tends to be tacky, and when it exceeds 600, the dispersibility deteriorates. The vinyl chloride copolymer may be partially hydrolyzed. As a vinyl chloride copolymer,
Preferred is a copolymer containing vinyl chloride-vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate-based copolymer"). Examples of vinyl chloride-vinyl acetate-based copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, and vinyl chloride-vinyl acetate-based copolymers. Among them, the partially hydrolyzed copolymer is preferable.
Specific examples of the above vinyl chloride-vinyl acetate copolymer, Union Carbide's "VAGH", "VYHH",
"VMCH", Sekisui Chemical Co., Ltd. "ESREC A""ESRECA-5","ESRECC","ESRECM", Denki Vinyl Industry Co., Ltd. "Denka Vinyl 1000"
G "," Denka vinyl 1000W ", etc. can be used.

In addition to the above, it is possible to use a fibrin resin as a binder resin, which includes cellulose ether,
Cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. As the cellulose ether, methyl cellulose, ethyl cellulose or the like can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate or the like can be used. As the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose or the like can be used. Of these fibrin-based resins, nitrocellulose is preferred.

As the binder resin of the layer constituting the magnetic recording medium of the present invention, a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam irradiation curable resin may be used in addition to those described above.

The thermoplastic resin has a softening temperature of 150 ° C. or lower, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 200 to 2,000, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer. , Vinyl chloride-acrylonitrile copolymer, acrylic acid ester-acrylonitrile copolymer, acrylic acid ester-vinylidene chloride copolymer, acrylic acid ester-styrene copolymer, methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester- Vinylidene copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-
Acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, various The synthetic rubber-based thermoplastic resin and the mixture thereof are used.

Further, the thermoplastic resin or reactive resin has a molecular weight of about 200,000 or less in the state of a coating liquid, and the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of methacrylate copolymer and diisocyanate prepolymer. , A mixture of polyester polyol and polyisocyanate, a urea formaldehyde resin, a mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, a polyamine resin, and mixtures thereof.

As the electron beam irradiation curable resin, an unsaturated prepolymer,
Examples thereof include maleic anhydride type, urethane acrylic type, polyester acrylic type and the like.

The resin is _{-SO 3 M -, - OSO 3} M, -COOM, -PO (O
It may be a resin containing a hydrophilic polar group such as M ′) ₂ (where M is hydrogen, an ammonium group or an alkali metal, M ′ is a hydrogen, an ammonium group, an alkali metal or a hydrocarbon residue).

Further, the durability can be improved by adding a polyisocyanate curing agent to the magnetic paint. Examples of such a polyisocyanate curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), Desmodur L (manufactured by Bayer), and the like. Three
Any of functional isocyanates, urethane prepolymers having isocyanate groups at both ends, which have been conventionally used as a curing agent, and polyisocyanates usable as a curing agent can be used. The amount of the polyisocyanate-based curing agent used is 5 to 80 parts by weight based on the total amount of the binder.

Further, usable curing accelerators include acetylacetone chain salt, dibutyltin dilaurate, oleic acid, DABCO.
(1,4-diazabicyclo-2,2,2-octane), amines (eg tri (dimethylamino) phenylmethane), iron chloride, piperazine compounds and the like can be mentioned.

When using a curing accelerator, the addition amount should be 0.5-2 of the curing agent.
5% by weight is preferable, but if it is less than 0.5% by weight, the promoting effect is poor, and if it exceeds 25% by weight, bleeding out to the surface of the layer tends to occur. Further, it is preferable to be 1.0 to 10% by weight with respect to the binder.

FIG. 3 shows an example of a magnetic recording medium according to the present invention, for example, a magnetic tape, in which a magnetic layer 2 is provided on a support 1 and a BC layer 3 is provided on the opposite surface. .
In FIG. 4, the underlayer 4 is provided between the support 1 and the magnetic layer 2 in the configuration of FIG.

FIG. 5 shows another magnetic recording medium.
An OC layer (overcoat layer) 5 is provided on the magnetic layer 2 of the medium shown in the figure. The urethane resin according to the present invention can be used as the binder resin of the OC layer 5. This OC
The layer 5 is provided in order to protect the magnetic layer 2 from damage or the like, and for that reason, it is necessary that the lubricity is sufficient. OC layer 5
Surface roughness is Ra ≦ 0.01μm, R especially in relation to color S / N
It is preferable that max ≦ 0.13 μm. In this case, it is desirable that the surface roughness of the support 1 is Ra ≦ 0.01 μm and Rmax ≦ 0.13 μm, and the support 1 is smooth.

FIG. 6 shows a magnetic recording medium configured as a magnetic disk, in which the same magnetic layer 2 and OC layer 5 as described above are provided on both surfaces of the support 1.

Even in the medium as shown in FIGS. 5 and 6, the subbing layer 4 may be provided as shown in FIG.

The specific surface area in the magnetic layer of the magnetic recording medium is 35 m ² / gr as a BET value.
By using the above-mentioned magnetic powder (more preferably 38 m ² / gr or more), high density magnetic recording and high S / N ratio are possible, and high level electromagnetic conversion characteristics can be obtained. Moreover, in the magnetic recording medium of the present invention, since the urethane resin and the vinyl chloride resin having a negative group are used, the running durability is remarkably improved while maintaining the electromagnetic conversion characteristics at a high level. It is possible to exert an effect. This point has been described above.

If the specific surface area of the magnetic powder is unnecessarily large, dispersion failure will occur, so it is desirable to set the upper limit to 100 m ² / gr. In the above, the “BET value” means a surface area per unit weight, and is a physical quantity different from the average particle diameter, for example, even if the average particle diameter is the same, a large specific surface area, Some have a small surface area. To measure the specific surface area, first, for example, magnetic powder at around 250 ° C for 30-6
Degas while heating for 0 minutes to remove those adsorbed on the powder, then introduce into the measuring device, set the initial pressure of nitrogen to 0.5 kg / m ^2, and use liquid nitrogen with nitrogen. Adsorption measurement is performed at temperature (-195 ° C) (generally called BET method for measuring specific surface area. For details, see J. Ame. Chem. Soc. 6 ).
0 309 (1938)). As a measuring device for this specific surface area (BET value), a "powder and particle measuring device (cantersoap)" jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. can be used. For a general explanation of specific surface area and how to measure it, see "Measurement of powders" (J.
M.DALLAVALLE, CLYDEORR Jr, co-authored by Benda et al .; published by Sangyo Tosho Co., Ltd.)
(Applied edition, pages 1170 to 1171, edited by The Chemical Society of Japan, published by Maruzen Co., Ltd. on April 30, 1966) (Note that in the above “Chemical Handbook”, the specific surface area is simply the surface area (m ² / gr), but it is the same as the specific surface area in this specification.).

As the magnetic powder used for the magnetic layer, particularly as the ferromagnetic powder, γ
-Fe ₂ O _3, Co-containing _{γ-Fe 2 O 3, Fe} 3 O 4, Co -containing Fe ₃ O ₄ and the like iron oxide magnetic powder: Fe, Ni, Co, Fe -Ni-Co alloy, Fe-Ni- Al
Alloy, Fe-Al-Co alloy, Fe-Al-Co-Ni alloy, Fe-Al-
Ni-P alloy, Fe-Ni-Cr alloy, Co-Ni alloy, etc., Fe, Ni,
Metal magnetic powder containing Co as a main component: various ferromagnetic powders such as CrO ₂ are included.

In the magnetic recording medium of the present invention, the magnetic layer or BC layer may optionally contain additives such as non-magnetic particles, dispersants, lubricants, antistatic agents and the like.

In the present invention, the non-magnetic particles usable for the magnetic layer or BC layer include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum hydroxide, chromium oxide, silicon carbide, Calcium carbide, α-Fe ₂ O ₃ , calcium sulfate, boron nitride,
Zinc fluoride, molybdenum dioxide, molybdenum disulfide, barite powder, precipitated barium sulfate, precipitated carbonate coal, white powder, talc, kaolin, coal stone powder, lithobon, lead white, carbon black, graphite, yellow lead, zinc yellow, cadmium yellow ,
One kind or two or more kinds selected from melamine resin, guanamine resin and the like can be used, but it is not limited thereto.

Carbon black that can be used in the magnetic layer or the BC layer is preferably one having conductivity, for example, Conductex 975 (specific surface area 250 m ² / g, manufactured by Columbia Carbon Co.,
Particle size 24mμ), Conductex 900 (specific surface area 120m ² /
g, particle size 27mμ), Cabot Vulc
an) XC-72 (specific surface area 254 m ² / g, particle size 30 mμ), Raven
There are 1040, 420, and # 44 manufactured by Mitsubishi Kasei. Carbon black for shading may be used together, for example, Raven 2000 (specific surface area 190 m ² / g, particle size 18 m manufactured by Columbia Carbon Co., Ltd.
μ), 2100, 1170, 1000, # 100 manufactured by Mitsubishi Kasei Corporation,
# 75, # 40, # 35, # 30, etc. can be used. Carbon black should have a particle size of 20 to 30 mμ, preferably 21 to 29 mμ, but if its oil absorption is 90 ml (DBP) / 100 g or more, it easily takes a structure structure and exhibits higher conductivity. Desirable in terms.

The non-magnetic particles (abrasive) that can be used in the magnetic layer include
Alumina (preferably α-Al ₂ O ₃ ), silicon carbide, chromium oxide, silicon nitride, titanium oxide, α-iron oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite) ) And the like, but of course, other materials may be used, and alloys may be used regardless of the type of inorganic or organic. The content of the non-magnetic particles is preferably 20 parts by weight or less, more preferably 2 parts by weight to 10 parts by weight, based on 100 parts by weight of the magnetic powder.

The non-magnetic particles as described above preferably have a Mohs hardness of 5 or more, and more preferably 6 or more. The average particle size of the non-magnetic particles is 0.6 μm or less (further, 0.1 to 0.3 μm).
Within the range of m), good electromagnetic conversion characteristics can be maintained.

Dispersants that can be used include metal salts of fatty acids, alkali metal fatty acids (Li, Na, K, etc.) or alkaline earth metals; fatty acid amides; lecithin; trialkylpolyolefinoxy quaternary ammonium salts (where alkyl is 1 carbon atom).
Up to 5 olefins such as ethylene and propylene). In addition to this, higher alcohols with 12 or more carbon atoms,
And sulfuric acid ester, alkyl sulfate, phosphoric acid ester, phosphoric acid ester having CH ₂ —CH ₂ —On, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, known surfactants and salts thereof, and negative an organic group (e.g. -COOH, -PO ₃ H, -SO
₃ H, —SO ₂ NH—, and salts of polymer dispersants having these). These dispersants may be used alone or in combination of two or more. When using these dispersants in the magnetic layer is preferably added in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the magnetic powder, when used in the backcoat layer relative to 100 parts by weight of the binder resin. It is preferable to add it in the range of 2 to 20 parts by weight.

Lubricants that can be used include dialkyl polysiloxanes (where alkyl has 1 to 5 carbon atoms), COOR (R = H or C ₁
Dialkyl polysiloxane modified with an alkyl group) in C _20, shea alkoxy polysiloxane (alkoxy has from 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has from 1 to 5 carbon atoms, alkoxy having a carbon number of 1 ~ 4 pieces), phenyl polysiloxane, fluoroalkyl polysiloxane (where alkyl has 1 to 5 carbon atoms), etc., silicon oil; graphite, etc. conductive fine powder; molybdenum disulfide, tungsten disulfide, etc. inorganic fine powder;
Plastic fine powder of polyethylene, polypropylene, polyethylene-vinyl chloride copolymer, polytetrafluoroethylene, etc .; α-olefin polymer; unsaturated aliphatic hydrocarbon that is liquid at room temperature (n-olefin double bond is a terminal carbon Examples thereof include bonded compounds, carbon atoms of about 20); fluorocarbons, higher fatty acids such as lauric acid, myristic acid, stearic acid and behenic acid; and fatty acid esters. These lubricants may be used alone or in combination of two or more. These lubricants are preferably added in a proportion of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

As the antistatic agent that can be used, conductive fine powder such as carbon black and carbon black graft polymer;
Natural surfactants such as saponins; alkylene oxide-based, glycerin-based, glycidol-based, etc. nonionic surfactants; higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, cations such as phosphoniums Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester, phosphoric acid ester group; amphoteric active agents such as amino acid, aminosulfonic acid, sulfuric acid or phosphoric acid ester of aminoalcohol Etc. are used. The conductive fine powder is 0.2 to 20 parts by weight with respect to 100 parts by weight of the magnetic powder, the surfactant is
It is added in the range of 0.1 to 10 parts by weight. You may add these surfactant individually or in mixture. Although these are used as antistatic agents, they are sometimes used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and coating aid.

In addition, the following may be used as an additive. Phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, dinchloromate, calcium chromate, strontium chromate, etc. can be used, but especially dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine phosphate, cyclohexyl ammonium carbonate, The use of hexamethylenediamine carbonate, propylenediamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate and the like (inorganic acid salt or organic acid salt of amine, amide or imide) improves the rust preventive effect. These are used in the range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic fine powder.

Further, the constituent material of the magnetic layer is mixed with an organic solvent to prepare a magnetic paint, which is coated on a support. The solvent of the magnetic paint is a ketone (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone). , Alcohol (eg methanol, ethanol, propanol, butanol), ester (eg methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether), glycol ether (eg ethylene glycol monoethyl ether, ethylene glycol diethyl ether, Dioxane), aromatic hydrocarbons (eg benzene, toluene, xylene), aliphatic hydrocarbons (eg hexane, heptane), nitropropane and the like.
The support to which this magnetic coating is applied is polyester (for example, polyethylene terephthalate, polyethylene-2,6-naphthalate), polyolefin (for example, polyethylene,
Polypropylene), cellulose derivative (eg, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate), polycarbonate, polyvinyl chloride, polyimide, polyamide, polyhydrazide, metal (eg, aluminum, copper), paper, etc. Can consist of

E. EXAMPLES Hereinafter, the present invention will be described with reference to specific examples. The components, ratios, operation sequences and the like shown below can be variously modified without departing from the spirit of the present invention. In the following examples, all "parts" represent "parts by weight".

After dispersing each component shown in FIG.
After filtering with a μm filter, 5 parts of polyfunctional isocyanate was added, coated on a support to a thickness of 5 μm, supercalendered, and slit into 1/2 inch width to obtain each video tape of FIG. (Corresponding to the numbers of Examples and Comparative Examples). However, the numerical values after the second column in FIG. 7 represent parts by weight, “actual” after the second column represents an example, and “ratio” represents a comparative example.

Here, polyurethanes A to G and vinyl chloride copolymers A to C in FIG. 7 are as follows.

Polyurethane A: Yield point 350 kg / cm ² , Breaking strength 560 kg / cm ² ,
Stress at 100% elongation 120 kg / cm ² .

Polyurethane B: Yield point 540 kg / cm ² , Breaking strength 550 kg / cm ² ,
Stress at 100% elongation 380kg / cm ² .

Polyurethane C: Breaking strength 660 kg / cm ² , stress at 100% elongation 200 kg / cm ² .

Polyurethane D: Estan 5701 (manufactured by Goodrich).

Polyurethane E: stress at the time of the breaking strength of 530kg / cm ^2, 100% elongation 90kg / cm ^2.

Polyurethane F: breaking strength 850 kg / cm ² , stress at 100% elongation 410 kg / cm ² .

Vinyl chloride copolymers A to C were synthesized as follows.

The following composition was charged into a reaction vessel and replaced with N ₂ to cause a reaction.

Methyl isobutyl ketone 86 parts by weight Methyl acetate 280 〃 Vinyl chloride 150 〃 Vinyl acetate 50 〃 CH ₂ ＝ CHCH ₂ OCOCH (SO ₃ K) -CH ₂ COOC ₈ H ₁₇ 6 parts by weight Diisopropyl peroxydicarbonate (polymerization initiator) 2 Parts by weight The above formulation composition was heated to 53 ° C. with stirring, and 9 methyl isobutyl ketone was added to the polymerization initiator 1 in the formulation.
After 15 hours, the mixture was cooled to 30 ° C., the residual vinyl chloride was recovered, and further recovered under reduced pressure. In this way, solid content 32%, viscosity 70 cp
480 parts by weight of a copolymer solution of s (25 ° C) was obtained. This is the seventh
It was designated as copolymer A in the figure.

In the same manner as described above, copolymers B and C shown in FIG. 7 were prepared using copolymerizable monomers containing the following metal salt residues of phosphoric acid or carboxylic acid.

Monomers of the copolymer _{B: CH 2 = CHCH 2 OCH} 2 CH (OH) CH 2 -OP 3 MY 1 Copolymer C Monomers: For each of the above magnetic tapes, we measured various characteristics,
The results are shown in Fig. 7. These measuring methods are as follows.

Chroma S / N: Measured with a color video noise meter "Shibasoku 925 D / 1".

Rumi S / N: Same as above.

RF output: We measured the RF output at 4MHz using a VTR deck for measuring RF output, and showed a value that was lower than the original output after 100 times of playback.

(Unit: dB) Still image life: Indicates the time until the still image decreases by 2 dB in minutes.
The larger the value, the higher the durability and wear resistance of the magnetic recording medium.

Skew: A video recording of color bar signals on a magnetic tape was run under high temperature and high humidity of 30 ° C and 80% relative humidity by a video deck, and when the number of running times reached 100, the switching point on the monitor screen The image distortion is measured and is expressed in μs.

Jitter (μsec): Measured with a VTR jitter meter manufactured by Meguro Electrics Corporation. Measurement conditions are 25 ℃, relative humidity 90%
Is.

However, chroma S / N, Lumi S / N, and RF output are relative values when the value of ratio -3 is 0 dB for actual -1 to 7 and ratio -1, 2 and for actual -8 and 9. Is a relative value when the value of ratio -4 is 0 dB.

From the results shown in FIG. 7, it is understood that the performance of the magnetic tape is remarkably improved by including the vinyl chloride resin having a negative group in the magnetic layer and the urethane resin according to the present invention. That is, according to the present invention, it is understood that the running durability of the magnetic tape, running durability under high temperature and high humidity, electromagnetic conversion characteristics, skew characteristics, jitter, output characteristics, and S / N ratio are all improved.

[Brief description of drawings]

1 to 7 show an embodiment of the present invention, wherein FIG. 1 is a graph showing the stress-elongation ratio relationship of urethane resin, and FIG. 2 is the chroma due to the average surface roughness of the magnetic layer. Graphs showing changes in S / N, FIGS. 3, 4, 5, and 6 are partially enlarged cross-sectional views showing examples of magnetic recording media, and FIG. 7 is a magnetic paint of each magnetic tape. It is a figure which shows a component and a characteristic. FIG. 8 is a graph showing changes in the jitter value depending on the average surface roughness of the magnetic layer. In the reference numerals shown in the drawings, 1 ... Non-magnetic support 2 ... Magnetic layer 3 ... Backcoat layer 4 ... Undercoat layer 5 ... Overcoat layer.

Claims (1)

[Claims] 1. A vinyl chloride resin having a negative group, a breaking strength of 550 kg / cm ² or more and 800 kg / cm ² or less, and 100.
A magnetic recording medium containing a urethane resin having a stress of 100 kg / cm ² or more at% elongation in a magnetic layer.