JPH05143957A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium such as a magnetic disk, magnetic tape or the like having excellent durability and high reliability. CONSTITUTION:The magnetic recording medium consists of a nonmagnetic supporting boty and a magnetic layer comprising a magnetic powder and a binder resin containing a radiationsensitive resin. The binder contains as a whole >=0.5mmol/g radiation sensitive double bonds and >=1.5mmol/g urethane or urea bonds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape having a magnetic layer containing magnetic powder and a binder on a non-magnetic support,
The present invention relates to a magnetic recording medium such as a magnetic disk.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium of this type comprises a non-magnetic support such as a polyester film, a magnetic powder,
A magnetic coating material containing a binder, an organic solvent, and various additives that are added as necessary is applied and dried to form a magnetic layer.The magnetic layer surface is the magnetic head of a recording / reproducing device during recording / reproducing. The magnetic layer is required to have excellent durability because it makes sliding contact with the guide member at a large relative speed.

Therefore, conventionally, a polyisocyanate compound is blended in the binder component of the magnetic layer, whereby the binder resin is cross-linked and cured to increase the mechanical strength of the magnetic layer.
Therefore, a means for improving durability is widely used.

However, when the crosslinking density of the magnetic layer is increased in order to further improve the durability by such means, the amount of the polyisocyanate compound used increases, and the storage stability of the magnetic coating composition deteriorates. The pot life is shortened and the surface treatment and other steps after coating are inevitably carried out in a short time, and long time heating is required for cross-linking and curing after winding. However, there is a problem in that the unevenness easily occurs on the surface of the magnetic layer, and the smoothness of the surface of the magnetic layer deteriorates, resulting in deterioration of electromagnetic conversion characteristics.

On the other hand, as a means for avoiding such difficulties, a method of using a radiation-sensitive resin as a binder of the magnetic layer has already been put into practical use, and various radiation-sensitive resins have been proposed (for example, , JP-A-50-77433, JP-B-63-66846, etc.). According to this radiation-sensitive resin, there is no problem of the pot life of the magnetic coating material such as the above polyisocyanate compound, and further, the crosslinking curing is performed in a short time by the irradiation of ultraviolet rays or electron beams in the continuous process after the coating of the magnetic coating material. Since it can be performed, winding after curing is possible, and the advantage that the above-mentioned blocking and transfer of unevenness can be avoided is obtained.

[0006]

By the way, in recent years, the performance of various audio equipment and commercial and consumer electronic equipment using magnetic recording means such as personal computers and word processors has been improved. Significantly, along with this, it is necessary to further improve the quality of the magnetic recording medium, and in particular, improving the durability of the magnetic recording medium is an important issue for improving the reliability and storage stability of recorded information. There is. However, in terms of this durability, even the means using the above-mentioned conventional radiation-sensitive resin as a binder can no longer meet the severe demands of recent years.

In view of the above situation, it is an object of the present invention to provide a magnetic recording medium having extremely high durability and high reliability.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies in order to achieve the above object, and as a result, have used a radiation-sensitive resin containing a urethane or urea bond as a binder component of a magnetic layer. In addition, when the content of the radiation-sensitive double bond and the urethane or urea bond in the binder as a whole is set to a specific value or more, the magnetic layer becomes extremely tough, and sufficiently copes with the recent severe demands. The inventors have found that a magnetic recording medium having extremely excellent durability can be obtained, and have completed the present invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer formed by binding magnetic powder on a non-magnetic support with a binder containing a radiation sensitive resin, and the binder as a whole. , 0.5 mmol / g or more of a radiation-sensitive double bond and 1.5 mmol / g or more of a urethane or urea bond.

Further, according to the present invention, in the above magnetic recording medium, the radiation-sensitive double bond is contained in the binder in an amount of 0.5.
A composition containing a resin component having a urethane or urea bond content of less than 1.5 mmol / g and a urethane or urea bond content of less than 1.5 mmol / g; and a number average molecular weight of 2, containing a urethane or urea bond content of 4.0 mmol / g or more in the binder. 000 or less resin component and a structure containing a resin component having a number average molecular weight of 10,000 or more containing 2.0 to 4.0 mmol / g of urethane or urea bond, respectively, are preferred embodiments.

[0011]

According to the present invention, as described above, the radiation-sensitive resin containing urethane or urea bond is used as the binder component of the magnetic layer, and the radiation-sensitive double bond as the whole binder is used. Since the content of the urethane or urea bond is set to a specific value or more, the magnetic layer to be formed has a high crosslinking density after curing by irradiation with radiation, and the cohesive force of the layer is significantly increased by the urethane or urea bond. Increased and very tough.

Therefore, in the magnetic recording medium of the present invention, even if the surface of the magnetic layer is repeatedly repeatedly slidably contacted with the magnetic head or the like at the time of recording / reproducing, abrasion or damage of the magnetic layer is unlikely to occur, and good recording / reproducing over a long period of time It can exhibit its characteristics and exhibits extremely excellent durability.

The radiation-sensitive resin constituting the above-mentioned binder has a radiation-sensitive double bond content of 0.5 mmol / g or more and a urethane or urea bond as the whole binder. It is necessary that the rate is 1.5 mmol / g or more. That is, when the radiation-sensitive double bond is less than 0.5 mmol / g, the crosslink density after curing of the magnetic layer becomes insufficient, and when the content of urethane or urea bond is less than 1.5 mmol / g. The cohesive force of the magnetic layer becomes insufficient, and in any case, the toughness of the magnetic layer is insufficient, and the desired excellent durability cannot be obtained.

In the present invention, it is a matter of course that the entire binder can be composed of a single radiation-sensitive resin component having both the content of the radiation-sensitive double bond and the content of the urethane or urea bond above the above specified values. However, it is recommended to use a plurality of types of radiation-sensitive resin components in combination and to set the content of the radiation-sensitive double bond and the urethane or urea bond in the binder as a whole to be the above specified value or more.

In general, in order to sufficiently exhibit the performance as a magnetic layer, the binder resin needs to be a high molecular weight polymer having a certain amount or more, whereas it contains a urethane or urea bond. This is because it is difficult to synthesize a radiation-sensitive resin having a high molecular weight and a high content of both the radiation-sensitive double bond and the urethane or urea bond, due to the reaction mechanism.

Therefore, as the above-mentioned binder, a resin component for increasing the average molecular weight of the magnetic layer as a whole, that is, a high-molecular-weight content of both the radiation-sensitive double bond and the urethane or urea bond is defined as above. It is preferable to use a resin component having a value less than that (hereinafter referred to as resin component A) and a resin component for increasing the content of the radiation-sensitive double bond and the urethane or urea bond as the whole binder.

However, when the above resin component A is used, the other resin component used in combination sets the content of the radiation-sensitive double bond and the urethane or urea bond as the whole binder to the above specified value or more. In the above, it is necessary to make these contents very high. However, the polymer having such a high content must have a very small molecular weight due to the above-mentioned reaction mechanism of the synthesis. If the blending amount of such a resin component having a very small molecular weight becomes large, it may cause inconvenience in the characteristics of the coating film. Therefore, even if the average molecular weight of the binder as a whole is large, the performance as a magnetic layer is likely to deteriorate.

Therefore, as a means for coping with the above problems, a resin component (hereinafter referred to as resin component B) having a very small molecular weight but a remarkably high content of radiation-sensitive double bond and urethane or urea bond, When a resin component having a relatively high molecular weight (hereinafter, referred to as resin component C) having a relatively low content is used in combination with the resin component A, both the content and the average molecular weight of the binder as a whole are increased. At the same time, it is desirable to reduce the proportion of polymer components with very low molecular weight.

As the above-mentioned resin component A, a resin which does not contain one or both of a radiation-sensitive double bond and a urethane or urea bond can be used. For example, a vinyl chloride copolymer, a fibrin resin, A resin component generally used as a binder for magnetic recording media such as polyisobutyral resin, polyester resin, polyacrylic resin, epoxy resin, and phenol resin can be used, but the magnetic layer In carrying out the cross-linking and curing by irradiation with radiation, those having a radiation-sensitive double bond introduced to these resin components to some extent are preferred, and those having a urethane or urea bond introduced to some extent are more preferred. The number average molecular weight of the resin component A is usually 1
It is preferably 10,000 or more.

To introduce a radiation-sensitive double bond into the above resin component A, for example, (a) partially saponified vinyl chloride-vinyl acetate copolymer, vinyl chloride and 3-hydroxypropyl acrylate are used. Method of reacting a hydroxyl group-containing vinyl chloride resin such as a copolymer with a (meth) acrylic compound having a functional group having an isocyanate group (b) For a resin containing one or more epoxy groups in a molecule, ) A method of reacting a compound having a group sensitive to an epoxy group such as acrylic acid and a radiation-sensitive double bond (c) A resin containing at least one carboxyl group in the molecule,
There is a method of reacting a compound having a radiation-sensitive double bond with a group reactive with a carboxyl group such as glycidyl acrylate. In the above method (a), a urethane bond is introduced together with the radiation-sensitive double bond.

As the resin component B, one having a number average molecular weight of 2,000 or less containing 4.0 mmol / g or more of urethane or urea bond is preferable in view of the relationship with the resin component C. Further, the content of the radiation-sensitive double bond in the resin component B is preferably 1 mmol / g or more.

The means for synthesizing the resin component B is not particularly limited, but for example, suitable means include the following components (a) to (d); (a) trimethylolpropane, glycerin, pentaerythritol- Polyols such as 1,4-butanediol and neopentyl glycol (b) Tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate (C) 2-hydroxyethyl acrylate, 2-hydroxymethyl methacrylate, and other organic diisocyanates (c) (meth) acrylic compounds having a functional group having reactivity with an isocyanate group ( d) Among diamines such as ethylenediamine and tolylenediamine or water, at least three components (a), (b) and (c) are reacted, and if necessary, A method of reacting further component (d) Te.

As the resin component C, from the relationship with the resin component B, the number average molecular weight of 10,000 containing a urethane or urea bond of 2.0 to 4.0 mmol / g is 10,000.
The above is preferable. Further, the content of the radiation sensitive double bond of the resin component C is preferably about 0.05 to 0.4 mmol / g.

The means for synthesizing the resin component C is not particularly limited, but, for example, as a suitable means, a polyurethane resin having hydroxyl groups at both terminals containing 2.0 to 4.0 mmol / g of urethane or urea bond, There is a method of reacting a polyurea resin or a polyurethane urea resin with a (meth) acrylic compound having a functional group having an isocyanate group.

The mixing ratio of the resin components A, B and C is
Depending on the structure and properties of those used as each of these resin components, the content of the radiation-sensitive double bond and the urethane or urea bond as the whole binder becomes the above specified value or more, and the performance as the magnetic layer is ensured. It may be adjusted appropriately so as to obtain. Further, for the purpose of improving the dispersibility of the magnetic powder, one or all of these resin components A, B and C are incorporated into the molecule in the form of —SO ₃ M group, —OSO ₃ M group and —PO.
It may have a polar group such as an (OM) ₂ group (where M is hydrogen, an alkali metal, or a hydrocarbon group) and a tertiary amino group.

To manufacture the magnetic recording medium of the present invention,
According to a conventional method, a magnetic paint containing the above-mentioned binder, magnetic powder and various additives to be blended as needed is prepared, and the paint is sprayed or roll-coated on a non-magnetic support such as a polyester film. After applying and drying by a suitable means such as work to form a magnetic layer, and then curing by irradiation with radiation, if necessary, after surface treatment such as calendaring, cut into a desired width or shape. Good. It is also possible to provide a back coat layer on the surface opposite to the above magnetic layer or to provide a magnetic layer on both surfaces. Furthermore, you may perform an orientation process between the said application and drying.

As the above magnetic powder, for example, γ-
Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and Fe ₃ O ₄
Iron oxide in an intermediate oxidation state with, γ-Fe ₂ O ₃ containing Co,
Co-containing _{Fe 3 O 4, CrO 2,} Ba oxide-based magnetic powder such as ferrite, Fe, Co, Fe-Co alloy, Fe
-Ni alloy, Fe-Co-Ni alloy, Fe-Ni-Cr
Any magnetic powder conventionally used for magnetic recording media, such as metal magnetic powder such as alloys and nitride magnetic powder such as iron nitride, can be used.

If these magnetic powders are composed of acicular particles, the average major axis diameter is about 0.2 to 1.0 μm,
An average axial ratio (average major axis diameter / average minor axis diameter) of about 5 to 10 is preferable, and an average plate diameter of plate particles is preferably about 0.07 to 0.3 μm.

As the solvent for the magnetic paint, various organic solvents generally used for magnetic paints such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane and dimethylformamide can be used. You may use 2 or more types together.

Examples of additives to be added to the magnetic paint as required include a cross-linking agent, a lubricant, an abrasive, an antistatic agent, a dispersant, a filler and a coloring agent.

As the non-magnetic support, polyethylene terephthalate, polyethylene naphthalate, polyimide,
Various non-magnetic materials such as aluminum alloys can be used.

The radiation used to cure the magnetic layer is an electron beam from an electron beam accelerator, γ-rays using Co ⁶⁰ as a radiation source, X-rays.
Although there are X-rays, ultraviolet rays, etc. by a ray generator, an electron beam by an electron beam accelerator is preferable from the viewpoints of control of absorbed dose, ease of introduction into a production line, and ease of shielding ionizing radiation.

[0033]

According to the present invention, a radiation-sensitive resin containing a urethane or urea bond is used as the binder component of the magnetic layer, and the radiation-sensitive double bond and the urethane or urea bond as the whole binder are used. Since the content ratio of is set to a specific value or more, the magnetic layer is very tough and hardly wears or damages, good recording and reproduction can be performed over a long period of time, and it has excellent durability. It is possible to provide a highly reliable magnetic recording medium.

The above-mentioned binder contains a resin component having a radiation-sensitive double bond of less than 0.5 mmol / g and a urethane or urea bond of less than 1.5 mmol / g, and a binder. With a number average molecular weight of 2,000 containing urethane or urea bonds of 4.0 mmol / g or more
A number average molecular weight of 1.00 containing 0 or less resin component and 2.0 to 4.0 mmol / g of urethane or urea bond.
According to the structure containing 0 or more resin components, it is easy to set the contents of the radiation-sensitive double bond and the urethane or urea bond, and the original performance of the magnetic layer can be sufficiently ensured. Therefore, it is possible to easily and surely provide a highly reliable magnetic recording medium having the above-mentioned extremely excellent durability.

[0035]

EXAMPLES Next, examples of the present invention will be specifically described in comparison with comparative examples. The resin component B used in the examples
1 to B3 and C1 are synthesized by the following method. In the following, "parts" means "parts by weight".

<Resin Component B1> Trimethylolpropane 50 parts Tolylene diisocyanate 195 parts 2-Hydroxyethyl acrylate 130 parts Hydroquinone 0.1 parts Tin octylate 0.1 parts Methylethylketone 100 parts The above composition Was placed in a flask equipped with a condenser, the atmosphere was sufficiently replaced with nitrogen, and the mixture was reacted at 80 ° C. for 6 hours with stirring to synthesize a resin component B1. This resin component B
No. 1 had a radiation-sensitive double bond of 3.0 mmol / g, a urethane bond of 6.0 mmol / g, and a number average molecular weight of 1,
It was 000.

<Resin Component B2> Pentaerythritol 40 parts Tolylene diisocyanate 205 parts 2-Hydroxyethyl acrylate 137 parts Hydroquinone 0.1 parts Tin octylate 0.1 parts Methyl ethyl ketone 100 parts The resin component B2 was synthesized by reacting the composition in the same manner as the resin component B1. This resin component B2 is
Radiation-sensitive double bond 3.1 mmol / g, urethane bond 6.2 mmol / g, number average molecular weight 1,300
It was.

<Resin component B3> pentaerythritol 40 parts tolylene diisocyanate 256 parts 2-hydroxyethyl acrylate 137 parts ethylenediamine 17 parts hydroquinone 0.1 part tin octylate 0.1 part methyl ethyl ketone 130 Part The resin composition B3 was synthesized by putting the above composition in a flask equipped with a condenser, thoroughly purging with nitrogen, and reacting at 80 ° C. for 6 hours while stirring. This resin component B
In No. 3, the radiation-sensitive double bond was 2.6 mmol / g, the urethane-urea bond was 6.5 mmol / g, and the number average molecular weight was 1,500.

<Resin Component C1> Polybutylene adipate (number average molecular weight 870) 200 parts Tolylene diisocyanate 80 parts Neopentyl glycol 22 parts Hydroquinone 0.1 part Tin octylate 0.1 part Methyl ethyl ketone 200 parts The above composition was put in a flask equipped with a condenser, and after thoroughly substituting with nitrogen, reacted with stirring at 80 ° C. for 6 hours, and then 4 parts of 2-hydroxyethyl acrylate was added to further 80 The resin component C1 was synthesized by reacting at 2 ° C. for 2 hours. This resin component C1 had a radiation-sensitive double bond of 0.1 mmol / g, a urethane bond of 3.0 mmol / g and a number average molecular weight of 22,000.

Example 1 α-Fe magnetic powder (average major axis diameter 0.3 μm) 100 parts Vinyl chloride-vinyl acetate copolymer containing radiation-sensitive double bond 15 parts (radiation-sensitive double bond 0.4 Mmol / g, urethane bond 0.8 mmol / g, —SO ₃ K group 0.05 mmol / g, number average molecular weight 18,000) Resin component B1 7 parts Resin component C1 10 parts Carbon black 10 parts α-Al ₂ O ₃ powder 15 parts Oleyl oleate 7 parts Cyclohexanone 395 parts Toluene 395 parts

A magnetic coating material was prepared by mixing and dispersing the above composition in a ball mill for 72 hours. This paint has a thickness of 6
A 2 μm polyester film is coated on both sides so that the thickness after drying is 2.5 μm, dried to form a magnetic layer, calendered, and then an electro-caten type electron beam accelerator is applied. Use, acceleration voltage 170 Ke
Both sides were irradiated with an electron beam in a nitrogen gas atmosphere under the conditions of V and irradiation dose of 7 Mrad. Then, the film having magnetic layers on both sides was punched into a disk shape and polished to prepare a magnetic disk.

Example 2 A magnetic disk was produced in the same manner as in Example 1 except that the same amount of the resin component B2 was used instead of the resin component B1.

Example 3 A magnetic disk was produced in the same manner as in Example 1 except that the same amount of the resin component B3 was used instead of the resin component B1.

Comparative Example 1 A magnetic disk was produced in the same manner as in Example 1 except that the same amount of trimethylolpropane triacrylate was used instead of the resin component B1.

Comparative Example 2 A magnetic disk was prepared in the same manner as in Example 1 except that the amount of the resin component C1 used was changed to 17 parts and the resin component B1 was not used.

Each of the magnetic disks of Examples 1 to 3 and Comparative Examples 1 and 2 was loaded on a 3.5-inch floppy disk drive, and the magnetic disk was placed under conditions of 0 ° C. and 50 ° C.
The durability under a temperature cycle environment in which it was left alternately for 2 hours and the durability under a high temperature of 50 ° C. were examined. The results are shown in Table 1 together with the contents of the radiation-sensitive double bond and the urethane or urea bond as a whole of the binder used in the magnetic layer of each magnetic disk. The durability is
When the head was driven to the innermost track, the output was shown as the number of times the output decreased by 3 dB with respect to the initial output.

[0047]

[Table 1]

From the results shown in Table 1 above, as the binder of the magnetic layer, the content of both the radiation-sensitive double bond and the urethane or urea bond in the binder as a whole is equal to or more than the specified value. It is clear that (Examples 1 to 3) show markedly superior durability as compared with the magnetic disks (Comparative Examples 1 and 2) in which one of the above two content ratios is not more than the specified value. ..

Claims (3)

[Claims] 1. A magnetic recording medium provided with a magnetic layer comprising a non-magnetic support and magnetic powder bound to said non-magnetic support with a binder containing a radiation-sensitive resin.
A radiation-sensitive double bond of 0.5 mmol / g or more,
A magnetic recording medium having a urethane or urea bond of 1.5 mmol / g or more. 2. The binder contains a resin component having a radiation-sensitive double bond of less than 0.5 mmol / g and a urethane or urea bond of less than 1.5 mmol / g.
The magnetic recording medium according to 1. 3. A number average molecular weight of 2,000 containing 4.0 mmol / g or more of urethane or urea bond in the binder.
A number average molecular weight of 1.00 containing 0 or less resin component and 2.0 to 4.0 mmol / g of urethane or urea bond.
The magnetic recording medium according to claim 1, comprising 0 or more resin components.