JP3365872B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium in which a magnetic coating liquid in which a ferromagnetic powder is dispersed in a binder is provided on a support, and in particular, it has excellent magnetic properties such as running durability and electromagnetic conversion characteristics. Recording medium

[0002]

2. Description of the Related Art Conventionally, magnetic recording media having a magnetic layer in which a ferromagnetic powder is dispersed in a binder provided on a non-magnetic support have been widely used for magnetic recording and reproduction. Generally, when the magnetic recording medium as described above is used for, for example, a video tape or the like, the occurrence of dropout is observed, and as a cause thereof, abrasion of the magnetic layer during running generated from the magnetic recording medium itself, or scratching Examples thereof include generation and generation of dust from the outside of the magnetic recording medium, etc. to the magnetic layer.

As a measure against the former, means such as adding an abrasive to the magnetic layer to improve the running stability of the tape, or increasing the glass transition temperature (Tg) of the binder in the magnetic layer to increase the film strength of the magnetic layer. Has been taken. On the other hand, the latter is mainly due to the charging property of the magnetic recording medium, and is electrified by friction between the tapes or the tape and other substances while the tape is running, and the generated electrostatic charge attracts dust and the like in the air. It is considered. In order to prevent this, measures such as adding carbon black or a conductive polymer to the magnetic layer to lower the surface electric resistance Rs of the magnetic recording medium are taken.

However, the conventional means for preventing the abrasion of the magnetic recording medium as described above is still insufficient, and the dropout due to the occurrence of scratches during running still occurs, and the above-mentioned conventional ones. The means for preventing the adhesion of dust and the like on the magnetic recording medium has been carried out by adding a conductive substance such as carbon black to the magnetic layer to increase the conductivity of the magnetic recording medium and release the charged electric charge. Antistatic is not sufficient only by such means, and if the amount of filler such as carbon black is increased in order to further increase the conductivity, not only the running property of the tape is deteriorated but also the filling rate of the ferromagnetic powder is increased. There is a problem such as deterioration of the recording / reproducing characteristics. The latter problem also occurs when an abrasive is added in order to improve the running stability.

A magnetic head, especially a metal tape for business use.
In such a case, frictional heat is generated by sliding on the magnetic head, and the temperature rises to 100 ° C. or higher for a short time. This is a problem especially for commercial use because the sliding speed is high. In this case, if the heat resistance of the binder is low, there is a problem in that it melts on the surface of the magnetic layer and fluidizes to deteriorate durability. As mentioned above, especially for products using metal for business use, the number of revolutions is large, the tape area is large, the tape is long, and the sliding area is large, so the amount of deposits tends to increase, while the dropout is for ordinary consumer use. There is a problem that it is not accepted even if there is a dropout even if there is a higher demand level than the product of.

Therefore, various attempts have been made to improve the characteristics of the binder that disperses the ferromagnetic powder to solve the above problems. For example, Japanese Patent Application Laid-Open No. 61-104325 (hereinafter referred to as A1) discloses aromatic polyether /
Disclosed polyurethane of polyester polyol, improved compatibility with vinyl chloride, heat resistance, moisture resistance, hydrolysis resistance,
It aims to provide a magnetic recording medium having excellent durability.

Further, Japanese Patent Application Laid-Open No. 62-121922 (hereinafter referred to as A2) discloses polyurethane of aromatic polyether / polyester polyol, epoxy and SO.
_It discloses that a binder made of ₃ M-containing vinyl chloride is disclosed and that the same effect as that of the above-mentioned A1 publication can be obtained. Further, JP-A-3-201211 (hereinafter referred to as "B") discloses a polyurethane having a blocking property of polyether polyurethane and polyester polyurethane, which is said to improve dispersibility, hydrolysis resistance and adhesion. There is.

Further, Japanese Unexamined Patent Publication No. 60-32113 (hereinafter referred to as C) discloses a compound (curing agent) having an active hydrogen-containing binder and an isocyanurate skeleton, and has heat resistance, water resistance and sliding resistance. It is said that it improves the mobility, the solvent solubility, the compatibility with the binder, the surface property of the magnetic layer and the like. Further, Japanese Patent Application Laid-Open No. 62-241128 (hereinafter referred to as D) discloses a binder containing an isocyanurate-based polyisocyanate curing agent, which improves scratches, scrapes, dropout due to triboelectrification, and the like. It states that the combined use with black is more effective.

Further, JP-A-62-298921 (hereinafter referred to as E) discloses SO ₃ M containing an aromatic polyisocyanate and an isocyanurate type polyisocyanate.
The disclosed polyurethane is disclosed to provide a magnetic recording medium having good compatibility with two polyisocyanates, improved durability, and low friction. JP-A-5-31446
Japanese Unexamined Patent Publication No. 4 (hereinafter, Japanese Unexamined Patent Publication No. F) discloses a binder containing a polyisocyanate curing agent containing an isocyanurate ring, and improves durability in a wide temperature range, head clogs, and abrasion.

By the way, polyether polyurethane is P
When EG (polyethylene glycol), PPG (polypropylene glycol), PTMG (polytetramethylene glycol) or the like is used as a long-chain polyol raw material, a binder having excellent hydrolysis resistance can be obtained. However, it has the drawback of low thermal deformation temperature (Tg) and low mechanical strength. B
The publication discloses a polyurethane using a polyether polyol and a polyester polyol as a long-chain polyol, but this polyester polyol uses an aliphatic polyester polyol and has insufficient Tg and mechanical strength. Needed improvement. The publication B is mainly intended to improve the hydrolysis resistance of polyurethane, and as it is, it does not satisfy the overall characteristics as a magnetic recording medium and cannot be used.

A1 and A2 are polyurethanes using a long-chain diol obtained by esterifying a polyether polyol with an aromatic dicarboxylic acid in order to improve the heat resistance and Tg of the polyether urethane. The polyether part has a blocking property, but the polyester part does not have a blocking property. Although this method improves heat resistance and Tg,
The elongation at break became small, and the brittleness disadvantageously occurred, and the durability of the magnetic recording medium was not exhibited and it was insufficient for practical use. That is, since the magnetic layer becomes brittle, the magnetic layer is likely to be sloppy (peeled or dropped) from the edge portion of the tape during VTR running, and powder is likely to be generated to cause DO (dropout). The magnetic layer tape is used in the slit process.
Cracks are generated in the edge portion, powder is easily dropped, and DO easily occurs.

Accordingly, it has been desired to use a polyurethane that can remedy this drawback. Each of the C, D, E, and F publications contains a polyisocyanate having an isocyanurate ring in the molecule as a curing agent, and it is possible to obtain coating film mechanical properties with high heat resistance and small temperature dependence. ,
Durability can be improved. However, the drawback of this type of curing agent is that the curing speed is fast and a hard coating film is formed immediately after the magnetic layer is applied, resulting in poor calendar formability, low smoothness and low magnetic powder filling degree. I couldn't do it. In particular, a curing agent having a high molecular weight cures more rapidly, and a coating film having a high curability and an extremely high mechanical strength can be obtained, but there is a problem that the smoothness further decreases. Therefore, this curing agent could not be applied to a magnetic recording medium having an extremely high recording density.

That is, a binder that solves these problems is desired.

[0014]

The objects of the present invention are as follows. A magnetic recording medium having excellent durability is provided. Provided is a magnetic recording medium having excellent long-term storage stability. Provided is a magnetic recording medium which has a good head contact and an excellent electromagnetic conversion characteristic. A magnetic recording medium having excellent smoothness and electromagnetic conversion characteristics. Provided is a magnetic recording medium which is free from calendar stains and has excellent productivity. Provided is a magnetic recording medium that has a small increase in DO during initial use, repeated use, and storage, and has a low error rate in digital recording. System with a rotating head at high speed (digital β
The present invention provides a magnetic recording medium having excellent durability even with a cam, D2, D3, etc. system). (EN) Provided is a magnetic recording medium which does not generate cracks at an edge portion during slitting, has good durability, and has a small dropout (DO).

[0015]

An object of the present invention is to provide a magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder resin and a hardener on a non-magnetic support, and a polyether polyol as the binder resin. and comprises a polyurethane derived from a polyester polyol, wherein the number-average molecular weight is seen containing a polyisocyanate of less than 1000 or 5000 as the curing agent, NCO content of the polyisocyanate
Of 3 to 35% by weight can be achieved.

The present invention is a binder in which a specific polyurethane (binder resin) and polyisocyanate (curing agent) are combined (refers to a binder resin and a curing agent).
Is used to obtain a magnetic layer which is extremely smooth and has a high packing density of ferromagnetic powder, and which has extremely high electromagnetic conversion characteristics and at the same time has high durability. It is considered that this is because the adsorption increases the interfacial force between the ferromagnetic powder and the binder and also increases the mechanical strength of the binder, which dramatically increases the durability. Further, the curing agent of the present invention having a relatively high molecular weight has a very dense and thermally stable crosslinked structure, whereby the durability can be remarkably improved.

To increase the mechanical strength of the binder, a high T
It is conceivable to use a resin of g or an isocyanurate type curing agent for polyester urethane, but with these methods, calender-formability is low and a smooth magnetic layer cannot be obtained, and further the physical properties of the coating film are There was a problem that it became very brittle, cracks were easily formed at the edge of the tape, and powder fell off, resulting in many dropouts.

By combining the polyurethane of the present invention and the curing agent, these problems can be solved all at once. That is, the polyurethane of the present invention has a high Tg, but has a low Tg polyether portion in a block form, so that it has excellent fluidity, has a high Tg polyester segment, and has a curing agent with a high molecular weight. Nevertheless, the smoothing treatment makes it possible to obtain a smooth magnetic layer surface that is easy to flow and has high electromagnetic conversion characteristics.

Further, it has been found that the head contact is extremely improved as an unexpected effect. In particular, there is a strong demand to reduce the total thickness of the tape in order to increase the volume recording density, and therefore, a tape having a magnetic layer provided on an extremely thin support is required. In this case, the contact between the recording / reproducing head and the tape often deteriorates. When the polyurethane of the present invention and the curing agent were combined, the head contact was very good probably because it had appropriate flexibility and rigidity, and very favorable characteristics could be exhibited for a magnetic recording medium for high density recording.

Further, according to the present invention, the electromagnetic conversion characteristics are excellent,
In addition, a magnetic recording medium having excellent repeatability, less dropout, and good tape storability was obtained.
Further, the durability of stills and the like has been dramatically improved by the present invention. Further, the present invention has good storage stability. In the case of polyester urethane, the problems of storability and hydrolyzability were also improved by the polyurethane of the present application, and the still durability after storage was improved. In the prior art, the polyether urethane, which had only good hydrolysis resistance but could not withstand practical use for high recording density applications, was the first to achieve both durability and storability enough for practical use by the present application.

Further, it was possible to improve the stain on the head after running. The above-mentioned publication A is a urethane of polyester obtained by esterifying polyester polyol,
The polyurethane of the present application is a polyurethane having a blocking property in both the polyether part and the polyester part. That is, when the polyurethane of the present application is made into a polyurethane by using a polyether polyol component having a low Tg and a polyester polyol component having a high Tg, even if the property of each component is changed to polyurethane, it is maintained as it is, and a different Tg corresponding to each component is obtained. A polyurethane having is produced.

In the present invention, this Tg appears to be 2 or more. For example, a low Tg polyether polyol and a high Tg polyester polyol generally have low compatibility, and even after being made into a polyurethane, they are microphase-separated into a soft and easily spreadable phase with a low Tg and a hard phase with a high Tg in the coating film.
This can be understood by examining the temperature dependence of the dynamic viscoelasticity, because the peaks of loss elastic modulus (E ″) and tan δ that reflect the glass transition appear in two places. A large elongation can be achieved in a soft phase while maintaining the strength.When polyurethane is formed in a state where a soft polyether part and a hard polyester part are mixed in a long-chain polyol as in Japanese Patent Publication No. A, a substantially uniform phase is obtained. Its physical properties are hardness, Tg, and elongation have intermediate properties, that is, the higher Tg, the more brittle it becomes, and the hardness,
It is impossible to achieve both high Tg and large elongation. Therefore, when this resin is used as a binder, the publication No. A has insufficient durability, but the present invention remarkably improves the durability.

In the polyurethane of the present invention, it is considered that the highly fluid polyether component forms a micro phase,
Calender-High moldability, fast curing rate as in the present invention, extremely smooth even when combined with a hard curing agent, the polyisocyanate of the present invention, to obtain a magnetic layer having a high filling degree of a magnetic material and a high surface smoothness. I found out that The curing agent of the present invention has not only a high molecular weight and a high curability as compared with the conventional curing agent, but also an effect of entanglement with the binder resin molecular chain, so that the mechanical strength is extremely high, the flexibility is high and the durability is high. Form an excellent magnetic layer.

The magnetic tape in which the polyurethane of the present invention and the curing agent are combined has appropriate flexibility and rigidity, and it is very likely to hit the head and to obtain high output and high electromagnetic conversion characteristics. Due to such characteristic properties, heat resistance,
Rotating video head rotates at higher speeds (3600, 5400, 720) than storage tackiness resistance, running durability, (especially VHS, 8 mm VTR (1800 rpm / minute for improving magnetic recording density).
High-definition V with 0, 9000 revolutions / minute, and more)
The running durability in the next recording system of TR and digital VTR) was improved.

Since the magnetic layer has high flexibility, cracks at the edge portion at the time of slitting are improved, DO is reduced, and increase in DO during traveling can be improved. The following can be enumerated as the embodiments of the polyurethane used in the present invention. Any one or more groups selected from SO ₃ M, PO ₃ M ₂ and COOM (M is a metal or ammonium) is usually used in an amount of 1 × 10 ⁻⁵ to 2 × 10.
^-4 eq / g included. The yield stress is usually 2 kg / mm ² or more, preferably 2.8.
The breaking elongation at -8 kg / mm ² is usually 100% or more, preferably 200-800%. Breaking stress is usually 1 to 1
It is 5 Kg / cm ² , preferably ² to 10 Kg / cm ² .

The Tg of the polyester of the present invention is 2
In some cases, the lower one (low Tg) is usually 0 ° C. or lower, preferably −5 ° C. or lower, and more preferably −10 to −40.
The higher one (high Tg) at 40 ° C. is usually 40 ° C. or higher, preferably 50 to 120 ° C., more preferably 60 to 100.
℃. When Tg is 3 or more, whether to use two different polyester polyol components and one polyether polyol component, or one polyester polyol component and two different polyether polyol components. ,do it. The same applies when Tg is 4 or more.

The Tg of the polyester of the present invention is 20.
A film having a thickness of μm is formed, and the peak temperature of E ″ is set using Vibron (manufactured by Orientec Co.). 3 or more OH groups per molecule, preferably 4 to 1
Including two. If the number is less than 3, the curability will be low and the durability will be poor. Examples of the polyether polyol structure include the following.

Composition: PPG (polypropylene glycol), PTMG (polytetramethylene glycol), P
EG (polyethylene glycol), BPA (bisphenol A) to which PO (propylene oxide) and / or EO (ethylene oxide) are added, and a mixture thereof. PPG and PTMG are preferred. Tg: 0 ° C or lower, preferably -10 to -60 ° C Molecular weight: usually 400 to 10,000, preferably 50
0-5000, more preferably 800-3000 The proportion of polyether polyol in the polyurethane is
Usually, 3 to 80% by weight, preferably 5 to 70% by weight,
More preferably, it is 10 to 50% by weight. If the ratio is too small, the effect becomes small. If it is too large, the mechanical strength is lowered and the durability is lowered. The composition of the polyester polyol preferably contains a monomer having a cyclic structure (aromatic or alicyclic) and a monomer having a branched structure. Specifically, as the acid component,
Isophthalic acid (iPA), terephthalic acid, etc.,
Neopentyl glycol (NP) is used as the alcohol component.
G), cyclohexanedimethanol (CHM), cyclohexanediol, bisphenol A, hydrogenated bisphenol A and the like are preferable. The molecular weight of the polyester polyol is usually 400 to 10,000, preferably 5
It is from 00 to 5000, and more preferably from 800 to 3000. Known low molecular weight diols such as chain extenders used for polyurethane may be used. A polyurethane having a branched structure may be formed by using a trifunctional or higher functional alcohol such as trimethylolpropane in combination. Examples of diisocyanates used for polyurethane include T
The weight average molecular weight of the polyurethane, which is preferably aromatic or alicyclic diisocyanate such as DI, MDI, IPDI and hydrogenated MDI, is usually 20,000 to 20.
10,000, preferably 30,000 to 100,000.

Next, the embodiments of the polyisocyanate of the present invention will be listed. The number average molecular weight is 1,000 or more and less than 5000, preferably 1500 to less than 3000, and more preferably 180.
It is 0 to 2500, and preferably has an isocyanurate ring (hereinafter referred to as an isocyanurate type curing agent). If it is too small, the curability and durability will be poor. If it is too large, the viscosity of the coating solution becomes high and it becomes difficult to apply the coating solution, so that the smoothness of the magnetic layer is deteriorated and the electromagnetic conversion characteristics are deteriorated. Molecular structure A. TDI (tolylene diisocyanate), MDI (diphenylmethane diisocyanate), IPDI (isophorone diisocyanate), HDI (hexamethylene diisocyanate), XDI (xylylene diisocyanate),
Diisocyanate compounds such as hydrogenated XDI.

Preferably, an oligomer of one or more selected from these diisocyanate compounds, for example,
Trimer, pentamer, heptamer, 9mer ..., (2n + 1) mer (n = 1 or more integer), and a mixture thereof, in which the number average molecular weight is isocyanurate type curing. For agents, ie TDI, usually 3 to 15 mers, preferably 5
~ 11-mer. In particular, those derived from aromatic diisocyanates such as TDI and MDI have a high curing speed and a high coating strength. Those in which the NCO group is directly attached to the aromatic ring are preferable because of their high curability.

For example, the structure of the oligomer having an isocyanurate ring of TDI is as shown below.

[0032]

[Chemical 1]

Further, a modified product obtained by reacting the above-mentioned multimer with a low-molecular diol or diamine and having a molecular weight within the above range is also used. Diamines are preferred because they have a high reaction rate and are not easily modified. Low molecular weight diols include ethylene glycol, propylene glycol, 1,3-propanediol, butanediol, pentanediol,
Hexanediol, neopentyl glycol, 3-methylpentanediol, and other aliphatic glycols, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and other polyalkylene glycols, cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc. Alicyclic glycols, bisphenol A, aromatic diols such as alkylene oxide adducts of bisphenol A, and polyester polyols containing polycaprolactone and the like having a relatively low molecular weight of less than 1,000 can also be used.

Of these, preferred diols are neopentyl glycol, cyclohexanedimethanol, hydrogenated bisphenol A, and ethylene oxide adduct of bisphenol A. B. Modified MDI of Polymeric MDI with the following structure (number average molecular weight is usually
250-800, preferably 300-700, more preferably 350-600) is reacted with the above diol or diamine to give a number average molecular weight of 1,000 or more and 5,000.
Less than.

[0035]

[Chemical 2]

The present invention, as a polyisocyanate, is preferably the above-mentioned A. Alternatively, B. Alternatively, a mixture of these is used. The NCO content of the polyisocyanate of the present invention is usually 3 to 35% by weight, and if it is less than this, the curability is low and the durability is lowered. If it is too high, the pot life will be short. The NCO content is preferably 5 to 20% by weight.

In addition to the above-mentioned binders, the binder of the present invention is a conventionally known binder resin in an amount of usually 10 to 80% by weight with respect to the total amount of binders within a range that is not useful or adversely affecting the achievement of the object of the present invention. It can be used in combination within a range. Among these known resins, vinyl chloride resin is preferable. As the binder composition, vinyl chloride resin: polyurethane: polyisocyanate (weight ratio) is usually 80 to 10:80 to 10:
50-10, preferably 70-20: 70-20: 4
0 to 20, more preferably 60 to 30:60 to 3
0:35 to 25.

If the proportion of the vinyl chloride resin is too large, it becomes brittle, and if it is too small, the dispersibility deteriorates. Examples of the vinyl chloride resin include those of the following embodiments. Polymerization degree is 200 to 1000, more preferably 250 to
500 things. As polar groups, COOM, SO ₃ M, OSO ₃ M, PO (OM) ₂ , OPO
(OM) ₂ (where M is as defined above), tertiary amine, and quaternary ammonium salt are preferred. The polar group amount is preferably 1 × 10 ⁻⁵ to 1 × 10 ⁻³ eq / g.

If it exceeds this range, the viscosity is high and the dispersibility is lowered. If it is too small, the dispersibility will decrease. When it contains an epoxy group, it is preferably from 1 × 10 ⁻⁴ to
5 × 10 ⁻³ eq / g, more preferably 5 × 10 ⁻⁴ to 2 × 1
It is 0 ^-3 eq / g. Examples of the monomer copolymerizable with vinyl chloride include (meth) acrylic acid alkyl ester, carboxylic acid vinyl ester, allyl ether, styrene, glycidyl (meth) acrylate, and other vinyl monomers.

The ferromagnetic powder used in the magnetic layer of the magnetic recording medium of the present invention is not particularly limited, and ferromagnetic metal powder or plate-like hexagonal ferrite powder can be used. When the ferromagnetic powder is a ferromagnetic metal powder, its particle size desirably has a specific surface area of 50 m ² / g or more, and preferably 55-55.
The crystallite size of 65 m ² / g and determined by X-ray diffractometry is usually 100 to 250 Å, preferably 12
It is 0 to 180Å. If the specific surface area is too small, it is not possible to sufficiently cope with high density recording, and even if it is too large, it is not possible to disperse sufficiently and a magnetic layer having a smooth surface cannot be formed and it is not possible to cope with high density recording either. . on the other hand,
In the case of plate-like hexagonal ferrite powder, the specific surface area is 25 to 7
0 m ² / g, the plate ratio is 2 to 15, and the particle length is 0.
It is from 02 to 1.0 μm.

For the same reason as the ferromagnetic metal powder, if the particle size is too large or too small, high density recording becomes difficult. The ferromagnetic metal powder preferably contains at least Fe, and specifically, Fe, Fe-Co, Fe-N.
It is a simple metal or an alloy mainly composed of i or Fe-Ni-Co. The Co content is usually 8 to 40 atom%, preferably 10 to 35 atom%. Furthermore, a small amount of C
A metal such as r, Ni, Mn, Zn, Sr, or Nd may be included.

In order to increase the recording density of the magnetic recording medium of the present invention, it is necessary that the particle size is small as described above, and at the same time, the saturation magnetization is usually 10 as a magnetic characteristic.
0 to 200 emu / g, preferably 120 to 150 e
mu / g. The coercive force is usually 1500O
e (oersted) or more, preferably 1700 to 25
It is 00 Oe. The axial ratio (long axis length / short axis length) of the particles is usually 1.5 to 10, preferably 2 to 7.

To further improve the characteristics, B,
Non-metals such as C, Al, Si and P may be added. Usually, an oxide layer is formed on the particle surface of the metal powder in order to stabilize it chemically. The plate-shaped hexagonal ferrite is a plate-shaped ferromagnetic substance having an axis of easy magnetization in a direction perpendicular to the plate surface, and includes barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, or cobalt-substituted products thereof. Among them, the cobalt-substituted barium ferrite and the cobalt-substituted strontium ferrite are particularly preferable. Further, in order to improve its characteristics as necessary, I
Elements such as n, Zn, Ge, Nb and V may be added.

In order to increase the recording density of the magnetic recording medium of the present invention, it is necessary that the particle size of the plate-shaped hexagonal ferrite powder is small as described above, and at the same time, the saturation magnetization is at least the magnetic property. 50 emu / g or more,
Desirably, it is 53 emu / g. As for the coercive force,
It is 500 Oe or more, preferably 600 to 2200 Oe.

The water content of these ferromagnetic powders is 0.01 to 2
It is preferably set to wt%. It is preferably optimized depending on the type of binder. The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 4 to 12, but preferably 5 to 10. The magnetic layer of the present invention may have a single layer or a multilayer structure. Further, a nonmagnetic layer composed of at least nonmagnetic powder and a binder may be provided between the magnetic layer and the nonmagnetic support.

In the present invention, of the multi-layer structure, the layer closer to the non-magnetic support is referred to as the lower layer and the farther layer is referred to as the upper layer. The lower layer may be a non-magnetic layer or a magnetic layer, but the upper layer is a magnetic layer. The constituent layer of the present invention may contain conductive particles of non-magnetic powder. In particular, it is preferable to use carbon black from the viewpoint of antistatic. Such carbon black has a specific surface area of 5 to 500 m.
² / g, DBP oil absorption is 10 to 1500 ml / 100
g, particle size 5 mμ to 300 mμ, pH 2 to 10, water content 0.1 to 10%, tap density 0.1 to 1 g / C
C is preferable.

Carbon black which can be used is, for example,
You can refer to the “Carbon Black Handbook” edited by the Bonblack Society. Among the non-magnetic powders used in the non-magnetic layer of the present invention, non-magnetic inorganic powders include α-alumina having a α conversion of 90% or more, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, etc. are used alone or in combination. The particle size of these non-magnetic powders is 0.01
However, it is possible to combine non-magnetic powders having different particle sizes, or to use a single non-magnetic powder to broaden the particle size distribution to obtain the same effect.
Tap density is 0.3-2 g / cc, water content is 0.1-5
%, PH 2 to 11, and specific surface area 1 to 30 m ² / g are preferable. The non-magnetic inorganic powder used in the present invention may be needle-shaped, spherical, or dice-shaped.

As the abrasive used for the magnetic layer and the like of the present invention, generally used materials are fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond and garnet. ,
Emery (main components: corundum and magnetite) is used. These abrasives have a Mohs hardness of 5 to 10 and an average particle size of 0.05 to 5 μm are effective, and preferably 0.2 to 1.0 μm. These abrasives are added in the range of 3 to 20 parts by weight with respect to 100 parts by weight of the binder resin. If the amount is less than 3 parts by weight, sufficient durability cannot be obtained, and if the amount is more than 20 parts by weight, the filling degree is reduced and sufficient output cannot be obtained.

These are nonmagnetic powders contained in the nonmagnetic layer,
It is of course possible to change the type, amount and combination of the abrasives in the magnetic layer and use them properly according to the purpose. For example,
In order to improve the durability of the surface of the upper layer, the amount of the polishing agent in the lower layer may be increased, and in the case of improving the durability of the end surface of the upper layer, the amount of the polishing agent in the upper layer may be increased. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

The thickness of the present magnetic recording medium is such that the non-magnetic support is 1 to 100 μm, preferably 3 to 80 μm, and the magnetic layer is usually 0.05 to 5 μm, preferably 0.1 to 3 μm.
μm. The lower non-magnetic layer which may be provided if desired has a thickness of 1 to 5 μm. Further, an undercoat layer may be provided between the non-magnetic support and the lower layer to improve the adhesion. This thickness is 0.01 to 2 μm, preferably 0.1.
05-0.5 μm. Further, a backcoat layer may be provided on one surface of the nonmagnetic support. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and back coat layers can be used. In the case of a disk-shaped magnetic recording medium, the above layer constitution can be provided on one side or both sides. As the dispersant (pigment wetting agent) used in the present invention, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
Stearic acid, behenic acid, oleic acid, elaidic acid,
1 carbon atom such as linoleic acid, linolenic acid and stearolic acid
2 to 18 fatty acids (R ₁ COOH, R ₁ has 11 carbon atoms
~ 17 alkyl or alkenyl groups); a metal soap consisting of the alkali metal (Li, Na, K, etc.) or alkaline earth metal (Mg, Ca, Ba) of the above fatty acids; Compounds; amides of the above fatty acids; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts (alkyl has 1 to 5 carbons, olefins include ethylene, propylene, etc.); and the like are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfuric acid esters and the like can also be used. These dispersants are added in an amount of 0.5 to 20 with respect to 100 parts by weight of the binder resin.
It is added in the range of parts by weight.

As the lubricant, the following compounds may be used in addition to the above fatty acid ester. That is, fatty acid, fatty acid ester, silicon oil, graphite, molybdenum disulfide, boron nitride, graphite fluoride, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate ester, tungsten disulfide and the like.

All or part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, a ferromagnetic powder is used. There are cases where it is added in a kneading step using a binder and a solvent, when it is added in a dispersion step, when it is added after dispersion, and when it is added immediately before coating.

There are no particular restrictions on the non-magnetic support used in the present invention for these lubricants used in the present invention, and any of those commonly used can be used. Examples of materials forming the non-magnetic support include various synthetic resins such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyaramid, polyamide imide, polyimide, polysulfone, polyether sulfone and syndiotactic polystyrene. There may be mentioned films and metal foils such as aluminum foil and stainless steel foil. The non-magnetic support generally has a thickness of 1 to 100 μm, preferably 25 to 85 μm.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methylethylketone, methylisobutylketone, diisobutylketone, cyclohexanone, isophorone, tetrahydrofuran, etc., and methanol.
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc., methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycoacetate -Esters such as glycol, dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, etc. Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. The content of these impurities is preferably 30% by weight or less, more preferably 10% by weight or less. If necessary, the type and amount of the organic solvent used in the present invention may be changed between the upper layer and the lower layer. Use a highly volatile solvent for the upper layer to improve the surface properties, use a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the lower layer to increase coating stability, and fill with a solvent with a high solubility parameter for the upper layer As an example, increasing the degree is not limited to these examples.

The magnetic recording medium of the present invention is kneaded and dispersed by using an organic solvent together with the above-mentioned ferromagnetic powder, a binder resin and, if necessary, other additives, and at least a magnetic coating material is coated on a non-magnetic support. It is obtained by orienting and drying if necessary.

The process for producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each process may be divided into two or more stages. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. In addition, individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

Various kneading machines are used for kneading and dispersing the magnetic paint. For example, two-roll mill, three-roll mill, ball mill, pebble mill, tron mill, sand grinder, Szegvari, attritor, high speed impeller disperser, high speed stone mill, high speed impact mill, disper, kneader, high speed mixer, homogenizer, ultra A sonic disperser or the like can be used.

The non-magnetic paint used in the present invention can be manufactured according to the above magnetic paint.

In order to achieve the object of the present invention, it is needless to say that the conventional known manufacturing techniques can be used as a part of the steps, but in the kneading step, a continuous kneader or a pressure kneader is used. High Br of the magnetic recording medium of the present invention can be obtained by using a material having a strong kneading force such as a dam. When a continuous kneader or a pressure kneader is used, all or part of the ferromagnetic powder and the binder (however, 30% by weight or more of the total binder) and the ferromagnetic powder 10 are used.
Kneading is performed in the range of 15 to 500 parts with respect to 0 parts. For details of these kneading treatments, refer to JP-A-1-10633.
8, JP-A-64-79274. In the present invention, the simultaneous multi-layer coating method as shown in Japanese Patent Laid-Open No. 62-1212933 can be used for more efficient production.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, it is also possible to treat with metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 Kg / cm, more preferably 300 Kg / cm or more.

The magnetic recording medium of the present invention may have a lower layer and an upper layer, and it is easily presumed that the physical properties of the lower layer and the upper layer can be changed according to the purpose.
For example, the elastic modulus of the upper layer is increased to improve running durability, and at the same time, the elastic modulus of the lower layer is made lower than that of the upper layer to improve the contact of the magnetic recording medium with the head.

Further, the composition for each layer is dispersed together with a solvent, the obtained coating solution is coated on a non-magnetic material, and orientation-dried to form a magnetic layer on the non-magnetic support to perform magnetic recording. Get the medium. If necessary, the surface is smoothed or cut into a desired shape to manufacture the magnetic recording medium of the present invention. The use of the magnetic recording medium of the present invention is not particularly limited,
It is particularly suitable for professional video tapes such as the D2 system.

[0063]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. “Parts” in the examples indicates “parts by weight” (Examples and comparative examples) Ferromagnetic alloy powder (composition: Fe 90 atomic%, Co 10 atomic%, Hc 1800 Oe, σs 130 emu / g, crystal Child size 165 Å) 100 parts crushed with an open kneader for 10 minutes,
Next, vinyl chloride resin MR110 (polar group SO ₃ M (M is Na, K) and an epoxy ring) made by Nippon Zeon 8
Parts and 40 parts of methyl ethyl ketone for 60 minutes, and then polyurethane (listed in Table 1) 8 parts (solid content) Abrasive (Al ₂ O ₃ , particle size 0.3 μm) 2 parts carbon black (particle size 40 nm) 2 parts methyl ethyl ketone / Cyclohexanone = 1/1 200 parts was added and dispersed by a sand mill for 120 minutes. To this, polyisocyanate (described in Table 2) 4 parts (solid content) butoxyethyl stearate 1 part Stearic acid amide 1 part Stearic acid 1 part Methyl ethyl ketone 50 parts are added, and after stirring and mixing for a further 20 minutes, an average pore size of 1 μm is obtained. A magnetic paint was prepared by filtering with a filter. The obtained magnetic coating material was applied onto the surface of an aramid support having a thickness of 8 μm using a reverse roll so that the thickness after drying was 2 μm, and the following back liquid was applied and dried at a thickness of 0.5 μm. A non-magnetic support coated with magnetic paint,
Magnetic field orientation is performed with a 3000 gauss magnet while the magnetic paint is undried, and after drying, a five-stage calendering process using a combination of metal rolls (speed 100 m /
min, linear pressure 300 kg / cm, temperature 90 ° C.) and then slit at 200 m / min to prepare various video tapes for evaluation. The results are shown in Table 3. (Back liquid composition) Carbon black (particle size 18 nm) 100 parts Nitrocellulose (RS1 / 2H manufactured by Daicel) 60 parts Polyurethane (N-2301 manufactured by Nippon Polyurethane Co., Ltd.) 60 parts Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co.) 20 parts Methyl ethyl ketone 1000 parts Toluene 1000 parts

[0064]

[Table 1]

However, the abbreviations in the table are as follows. Ad: adipic acid, DEIS: sulfoisophthalic acid ethylene oxide adduct represented by the following structural formula

[0066]

[Chemical 3]

Tg: A film of a binder resin alone having a thickness of 20 μm was formed, and E ″ was formed by vibron (manufactured by Orientec Co., Ltd.).
The peak temperature was measured.

[0068]

[Table 2]

However, in Table 2, the number average molecular weight is a value obtained by measuring the NCO group blocked with a large excess of methanol by GPC.

[0070]

[Table 3]

[Evaluation Method] (1) Electromagnetic conversion characteristics (initial output CN): D2 on the sample tape
Method Video tape recorder (Sony: DVR1)
0) was used to record and reproduce a 32 MHz signal. The reproduction output of 32 MHz recorded on the reference tape (Example 1) is set to 0.
The relative playback output of the tape when measured in dB was measured. (2) Head contact: When the electromagnetic conversion characteristics of (1) were measured, the shape of the envelope was bad, and the good one was good. (3) Surface roughness Ra of the magnetic layer surface: The center line average roughness Ra was determined by an optical interference method using a digital optical profilometer (manufactured by WYKO) under the condition of a cutoff of 0.25 mm. (4) Still durability: Same VTR as (1), 23 ℃, 8% R
The time until the output decreased by 3 dB in the still mode under H environment was measured. 72 hr or more was marked with ⊚, 48 hr to 72 hr was marked with ◯, 24 hr to 48 hr was marked with Δ, and less than 24 hr was marked with x. (5) Still durability after storage: stored in a storage environment of 60 ° C, 90% RH for 7 days in an M64 cassette, then 23C, 8
Still durability was evaluated using the same method as (4) in the% RH environment. 72 hours or more is ◎, 48 hours to 72 hours is ◯, 24 hours
.About.48 hr was designated as .DELTA., And less than 24 hr was designated as X. (6), (9) Repeatability: Using the above VTR, a 64 minute long tape was continuously run 100 times to measure the DO increase and observe the dirt on the video head. I observed.

Dirt on the video head ○: No dirt was observed at all ○ △: Area where 10% or less was dirty △: Area where 30% or less was dirty Thing X ... 30% or more of the area was dirty (7),
(8) Dropout: An initial value was measured using the above VTR, the tape after repeated running was run, and the number of output drops of 5 μsec or more was measured by a dropout counter. (10) Dropout after storage: Stored in a storage environment of 60 ° C, 90% RH for 7 days in an M64 cassette, and then at 23 ° C for the above VT.
Dropout was measured using R. (11) Calendar roll dirt: tape sample length 200m
After being calendered under the above conditions, the metal roll in contact with the magnetic layer surface was wiped with a gauze and the gauze was observed to be dirty.

Those with stains were marked with X, and those without stains were marked with ◯. From the above table, it can be seen that the magnetic recording medium using the binder of the present invention has various properties as compared with the comparative example.

[0074]

INDUSTRIAL APPLICABILITY According to the present invention, the combination of polyurethane and polyisocyanate having a specific structure improves the cross-linking reactivity and forms a unique and uniform three-dimensional network structure, which improves heat resistance and calender moldability. A magnetic recording medium having excellent smoothness can be manufactured. Therefore, the present invention can prevent deterioration of durability due to frictional heat generated by sliding on the magnetic head, especially in commercial metal tapes, etc., improve still durability and reduce scraping. The present invention provides a magnetic recording medium that prevents head contamination such as clogging and has excellent electromagnetic conversion characteristics with less dropout.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-266458 (JP, A) JP-A-1-106317 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/70

Claims (3)

(57) [Claims] 1. A magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder resin and a curing agent on a non-magnetic support, wherein the binder resin comprises polyurethane derived from polyether polyol and polyester polyol. , The number average molecular weight of the curing agent is 1,000 or more 50
00 less than the polyisocyanate only including, the Poriisoshia
A magnetic recording medium having an NCO content of 3 to 35% by weight . 2. The polyurethane has a Tg of at least 2.
The magnetic recording medium according to claim 1, which is a polyurethane having one or more and one of which is 0 ° C or lower and the other of which is 40 ° C or higher. 3. The polyisocyanate is isocyanurate.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is selected from the group consisting of oligomers having a ring and oligomers derived from polymeric MDI.