JPH02230512A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having large luminance output, excellent film property and traveling durability by utilizing characteristics of a binder that the properties of the binder vary with changes in the glass transition point Tg thereof. CONSTITUTION:If polyurethane resin has high Tg, it has large rigidity, which is advantageous for durability. However, it has poor adhesion property to a supporting body and is liable to cause dropout. If the polyurethane resin has low g, adhesion property becomes good with little dropout, but the resin has low rigidity, which deteriorates traveling durability. These characteristics are made use of for the medium having plural numbers of laminated magnetic layers. Namely, the glass transition point Tg(u) of the binder in the uppermost magnetic layer and the glass transition point Tg(d) of the binder in other magnetic layers except for the uppermost layer have the relation of Tg(u)<=Tg(d). The thickness of the uppermost layer is preferably 0.1 - 1.5mum. Thereby, the obtd. magnetic tape has such the laminated magnetic layers having large luminance output, excellent traveling property and durability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and particularly to a magnetic tape having laminated magnetic layers.

[Prior art]

Magnetic recording media in information processing equipment are extremely useful as recording and reproducing elements, and there is a large demand for them, but at the same time, as recording media, they must have advanced and precise electromagnetic conversion characteristics, rich storage capacity, and high density. It is required that the composition be suitable for ensuring runnability, durability, and durability, that it be inexpensive, and that there be no troubles in production technology from a production standpoint. technical efforts have been made.

In general, in order to obtain good electromagnetic conversion characteristics, it is preferable that the magnetic powder in the magnetic layer be densely packed and that the layer be thin, which is why a thin film type magnetic layer deposited in a vapor phase without a binder is preferred. However, the cost is high and it is difficult to secure production volume.

On the other hand, in the coating type, a magnetic layer is formed by dispersing or suspending magnetic particles and other 7-layers in a binder and applying a magnetic paint containing additives for adjusting various properties to a support.
It is an important means of producing magnetic recording media, especially tape-type recording media, in terms of the diversity of applicable technologies and high productivity.

Magnetic particles, which play a central role in electromagnetic properties in this technical field, have been the subject of much research, development, and improvement regarding their composition, particle shape, size, and surface condition, and their importance cannot be overstated. The selection of a binder for dispersing and suspending magnetic particles and containing various additives has a decisive influence not only on the electromagnetic properties but also on the overall properties of the magnetic tape.

In other words, the magnetic particles of the binder, the dispersion force for fillers, the wettability or Young's modulus, the physical properties of the film such as hardness, the adhesion, and other properties required in production technology all affect the success or failure of the magnetic tape. It affects the

Conventionally used binders include vinyl chloride copolymer resins with excellent strength, abrasion resistance, bending resistance, adhesive properties,
Polyurethane resins with good weather resistance, cellulose resins with good dispersibility, phenoxy resins with good dimensional stability, water resistance, and adhesive properties are used, and these have been used in combination to take advantage of their strengths and compensate for their weaknesses. However, with the aim of further improving properties, modified resins have been proposed in which polar groups or functional groups that form intramolecular salts are introduced for vinyl chloride copolymer resins and polyurethane resins, which are the mainstream binders. There is (Unexamined Japanese Patent Publication No. 6)
No. 0-238309, No. 57-92423, No. 61~
No. 10432, Japanese Patent Application No. 63-288365, etc.).

On the other hand, due to technical requirements, magnetic tapes have appeared that are composed of laminated magnetic layers in which the electromagnetic properties are shared among the magnetic layers for recording. Despite the difference in the roles assigned to the electromagnetic properties and physical properties of the tape film, the method of single-layer construction is followed as it is, and the appropriate binder is not allocated in the appropriate place or selected accordingly.

[Purpose of the invention]

In view of the above situation, the present invention focuses on the glass transition point of the binder, and aims to provide a magnetic recording medium which has a large luminance output and has excellent film properties and running durability.

[Structure of the invention]

As a result of studies in line with the above objectives, we found that, among the knowledge regarding the overall physical properties of various binders used alone or in combination with other binders, and the effects of additives, we found that changes in the glass transition point (Tg) of binder 3 were particularly important. We focused on the change in characteristics depending on the For example, when a polyurethane resin has a high Tg, it has high rigidity and is advantageous for durability, but its adhesion to the support is poor and tends to cause dropouts; conversely, when its Tg is low, it has good adhesion. Although there are fewer dropouts, there is a tendency for the rigidity to be insufficient and the running durability to deteriorate.

The present invention actively reverses this tendency and applies its characteristics to each layer by taking into consideration mechanical disturbance, electromagnetic conversion characteristics related to magnetic field line density, or the physical properties of the film. In a magnetic recording medium having a plurality of magnetic layers on a magnetic support and containing ferromagnetic powder dispersed in a binder, the glass transition point of the uppermost magnetic layer binder of the plurality of magnetic layer stacks is Tg(u), The above-described object of the present invention is achieved by a magnetic recording medium characterized in that, where Tg(d) is the glass transition point of the laminated magnetic layer binder other than the top layer, Tg(u)≦Tg(d). It can be achieved.

In addition, as an aspect of the present invention, the thickness of the uppermost layer is 0.1 to 1.
A range of 5 μm is preferred.

The multilayer coating method for the magnetic tape constituent layers according to the present invention may be a wet-on-wet sequential multilayer method or a simultaneous multilayer method, or a wet-on-dry (wet-on-wet) multilayer coating method. -Dry) may also be used.

In addition, the binder resin according to the present invention may further include a modified binder resin into which a polar group or a functional group forming an inner salt is introduced to adjust the properties, such as a modified vinyl chloride copolymer resin or a modified polyurethane resin. May be used.

The binder according to the present invention includes a vinyl chloride copolymer resin,
Considering the characteristics and degree of polymerization of polyurethane resins, cellulose resins, and other resins, the composition is determined by actually measuring the glass transition point (Tg) of a mixed binder adjusted to a single flow or preferred mixing ratio. are selected and used.

The glass transition point in the present invention was measured by the following method.

:Measurement method of glass transition point (Tg): Vibron DDV-II-EA (manufactured by Toyo Baldwin Co., Ltd.) was used as the measuring device, and the thickness was 30 μm and the width was 10 mm.
, While heating a sample with a length of 25 mm at a rate of 5°O/min in the range of -100°O - +100°C, a sine wave expansion/contraction strain with a frequency of 1 OHz was applied to the edge in the width direction, and a sine wave appearing at the other end was applied. Maximum ta of phase difference δ between both stress vectors
Let Tg be the temperature that gives nδ.

Vinyl chloride copolymers and polyurethane resins are the most widely used binders at present, but in the present invention, the binder of the magnetic layer contains a polar group or a negative functional group forming an inner salt, respectively. A modified vinyl chloride copolymer and/or a modified polyurethane resin introduced into the resin are utilized.

The vinyl chloride copolymer according to the present invention has the following general formula CI)
Those represented by are preferred. Note that the order of block polymerization of the repeating units enclosed in small brackets in the large brackets representing the copolymer of the general formula may be in a specific order or in any order.

General formula [■] In the formula, R1 and R2 are a hydrogen atom or a lower alkyl group (
For example, CH3, CzHs, etc.). Also R. and R
2 may be the same or different in each repeating unit block.

X is (a polar group, a modified group such as a group forming an inner salt)
represents a substituent containing -A-X', Y represents A and B
are linking groups that link an intramolecular base or an epoxy group to the main chain of the copolymer, respectively.

The epoxy group introduced into the copolymer resin is effective in suppressing the occurrence of HCQ removal during heating or aging of the vinyl chloride resin, and the content thereof is 0.5 to 0.05% depending on the Tgz solubility of the resin, etc. It has been found that 3 wt% is appropriate. If it is less than 0.5%, HC4 generation cannot be sufficiently suppressed.
If it exceeds wt%, the physical properties of the resin will deteriorate.

Next, Z is a repeating unit inserted as necessary to improve the properties of the copolymer.

That is, adjusting the solvent solubility, flexibility, compatibility with other resins, and curing and crosslinking properties of the copolymer, or further increasing the dispersibility,
Alternatively, it is added for the purpose of improving characteristics such as improving surface smoothness.

In the copolymer represented by the above general formula CI), when the copolymer is used as a binder for a magnetic recording medium and exhibits the necessary function and effect, the vinyl chloride repeating unit increases the strength of the medium (Young). If the vinyl chloride component is too small, the physical properties required for the medium (Young's modulus) cannot be obtained, and if it is too large, the solubility in the solvent will be poor, and the glass transition temperature of the resin will be reduced. (Tg) tends to be high.

In addition, repeating units containing epoxy groups improve the thermal stability of vinyl chloride and also react with cross-linking curing agents such as incyanate, thereby cross-linking the binder to further increase the molecular weight and use other binder resins such as polyurethane. It participates in bonding with other substances, prevents dehydrochlorination, and increases durability such as thermal stability and abrasion resistance. It also has the effect of controlling the glass transition temperature (Tg) and plasticizing effect of the binder resin by adjusting its content. Therefore, they have a mutually complementary relationship, especially with reactive hydroxyl groups (-OH) such as vinyl alcohol.

In addition, repeating units having an intramolecular base such as a betaine group or a modifying group such as a sulfonic acid group contribute to dispersibility.
If the amount is too small, the effect will be small, and if the amount is too large, it will not contribute to any further improvement in dispersibility, and on the contrary, moisture resistance will deteriorate, leading to a decrease in weather resistance.

Furthermore, in addition to the above-mentioned repeating units, the vinyl chloride copolymer of the present invention contains a carboxy group or its metal substituent (-CO
A repeating unit having a hydrophilic functional group such as OM; M is H or an alkali metal such as Li, Na, or K may be introduced. Carpoxy group is magnetic powder (iron oxide, metal powder)
improves the retention and dispersibility of the binder. O
Introducing H groups contributes to dispersibility, curing and crosslinking properties, compatibility, or solubility.

Next, "polyurethane modified with a polar group or a functional group that forms an inner salt" is mainly produced by reacting a polyisocyanate with a polyol and, if necessary, other copolymers. and/or it may be in the form of a urethane resin or urethane prebolomer containing hydroxyl groups, or it may be in the form of a urethane elastomer which does not contain these reactive end groups (for example in the form of a urethane elastomer).

The amount of modified groups etc. introduced into the polyurethane resin according to the present invention is 0.01 to 1.0 mmoO. /g, more preferably in the range of 0.1 to 0.5 mm of 27 g. The amount of the modified group introduced is 0.01 mmof2/g
If it is less than 20%, sufficient effect on the dispersibility of the ferromagnetic powder will not be recognized.

Furthermore, the amount of the modified group introduced is 1. When Qmmoff/g is exceeded, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make it impossible to use ordinary general-purpose solvents.

The durability of the constituent layers such as the magnetic layer according to the present invention can be improved by blending the vinyl chloride resin and the polyurethane resin, but when a polyurethane resin with a molecular weight of 60,000 or more is used, the magnetic powder particles When the particles become fine, their dispersibility becomes insufficient and the viscosity of the paint also increases.

On the other hand, if a polyurethane resin of 60,000 or less is used in the blend, the dispersibility can be improved and the viscosity of the paint can be lowered.

In addition, in order to improve dispersibility, the vinyl chloride resin needs to account for 30% or more of the total weight of the binder resin including the polyurethane resin used in the blend, and when considering the durability and physical properties of the magnetic coating, it accounts for 80%. This is the preferred range of use. In particular, the mixing ratio of polyurethane resin with a molecular weight of 60,000 or less according to the wood invention is PU (polyurethane resin) / V
CQ (vinyl chloride resin) weight ratio: 80/20
~20/80 is preferred, especially 50/50~30/
70 is desirable. As the polyurethane resin having a molecular weight of 60,000 or less to be blended, resins having conventionally known structures can be used. Examples include polyester polyurethane, polycarbonate polyurethane, polylactone polyurethane, polyether polyurethane, but are not particularly limited to these.

Furthermore, by blending with polyurethane having a molecular weight of 60,000 or less, the crosslinking density of the binder system is improved, and the Young's modulus is also improved.

In the present invention, in addition to the above-mentioned binder, conventionally used unmodified or modified vinyl chloride resins, polyurethane resins, or polyurethane resins in which fluorine-containing groups or silicon-containing groups are simply introduced to improve lubricity may be used as necessary. Polyester resins can be used in combination, and cellulose resins, phenoxy resins, thermoplastic resins with specific usage methods, thermosetting resins, reactive resins, electron beam curable resins, etc. can also be used in combination. good.

In particular, by using nitrocellulose whose molecular weight is specified as falling ball viscosity of 1/8 to 173 seconds, it is possible to improve dispersibility, heat resistance, Young's modulus, and block resistance, and also to reduce the coefficient of friction and prevent interlayer adhesion. It has a remarkable effect and can improve running stability, especially in high temperature and high humidity.

In addition, in terms of productivity, paints containing nitrocellulose disperse the filler more quickly than vinyl chloride paints, making the paint itself more stable and less likely to cause filler reagglomeration, resulting in a good lubricating surface structure. Useful.

In the present invention, the binder contains polyisocyanate as a curing agent.

Aromatic polyisocyanates that can be used include, for example, tolylene diisocyanate (TDI) and adducts of these polyisocyanates and active hydrogen compounds, and those having an average molecular weight of 100 to 3,000 are preferred.

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (HMDI) and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic polyisocyanates and adducts of these polyisocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic polyisocyanates, non-alicyclic polyisocyanates and adducts of these compounds and active hydrogen compounds are preferred.

The amount of the polyisocyanate added is 1/20 to 7/10, more preferably 1/10 of the weight of the binder.
~1/2.

The magnetic paint used to form the magnetic layer may contain additives such as fillers and lubricants, if necessary.

As fillers, organic powders or inorganic powders may be used in addition to carbon black, and these may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene resin powder, penzoguanamine resin powder, melamine resin powder, and lid cyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, and polyamide resin powder are preferred. , polyimide resin powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, α-Fe20
3. Talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

As the lubricant, for example, silicone oil (carboxylic acid modified or ester modified may be used), graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc. can be used. .

These may be used alone or in combination of two or more.

Dispersants used in the magnetic layer according to the present invention include resins, phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic esters, and known surfactants. etc. and their salts; salts of polymeric dispersants having negative organic groups (e.g. COOH, -PO, H) can also be used. These dispersants may be used alone or in combination of two or more.

These dispersants are added in an amount of 1 to 20 weight per 100 weight of the binder.

Examples of the magnetic material used in the magnetic layer according to the present invention include γ-Fe2031 Go-containing γ-Fe203, C
o Deposited γ-Fe20,, Fe30,, Co-containing Fe
30, Co-coated Fe3J, Cry. oxide magnetic materials such as Fe, Ni, Co, Fe-Ni alloy, Fe-Co alloy, Fe-Aff alloy, F-AQ
-Ni alloy, FeNi-P alloy, Fe-Ni-Co
Alloy, Fe-Mn-Zn alloy, Fe-NiZn alloy, Fe-Go-Ni-Cr alloy, Fe-Co-Ni
-P alloy, CoN1 alloy, Co-P alloy, Co-
Examples include various ferromagnetic materials such as Cr alloy, metal magnetic powder mainly composed of Fe, Ni, Go, and A[. Additives to these metal magnetic materials include Si, Cu, Zn,
Elements such as AQ, P, Mn, and Cr or compounds thereof may be included.

Also used are hexagonal ferrites such as barium hepteraite, and iron nitride.

Furthermore, conventionally known antistatic agents, abrasives, and the like can be used for the magnetic layer. Further, conventionally used solvents, supports, or coating methods can be used.

〔Example〕

The glass transition point range of the magnetic layer is determined by the above method.
A magnetic paint with a tailored binder is applied onto a non-magnetic support.

Examples 1 to 7 and Comparative Examples (1) to (4) T listed in Table 1
Using binder resins A and B with different g values for the magnetic paints A and B below, samples were prepared by regulating the film thickness, and their properties were measured. Table 2
It was shown to.

(A) Magnetic paint for top layer Weight part Cor-Fe203 (HC=900 0e, BET 50+n”/g) 100 Abrasive (average particle size 0.2
m) PVC resin containing 5 potassium sulfonate IO resin A5 Carpon black 1 Myristic acid l Stearic acid
l-butyl stearate
l Methyl ethyl ketone
l00 hexanone
100 toluene 10
0 After mixing and dispersing the above magnetic paint, 5 parts of a hardening agent Coronate LCE (Honpolyurethane Kogyo) was added to prepare a sample.

Cor-Fe203 (HC=700 0e, BET
=38m2/g) 100 abrasive (average particle size 0
．． 2m) 5 PVC resin containing potassium sulfonate 10 Resin B5 Carpon black 1 Stearic acid I Stearic acid
l Butylstearley 1.1 Methyl ethyl ketone 1.1 100 hexanone 100 toluene
100 After kneading and dispersing the above magnetic paint, 5 parts of hardening agent Coroichito L (Nippon Polyurethane Industries) was added for adjustment.

As is clear from the table, the samples of the present invention exceed the comparative samples in both electromagnetic properties and physical properties.

Two characteristic measurement methods: (1) Point 100 was recorded on the Y-CN magnetic recording medium using the s-vns method.
% signal at reference level, reproduced RF output signal at NF
Input to Design Block AC ammeter M-170L and read the output level.

(2) Edge breakage A tape with a length corresponding to 5 minutes from the beginning of the cassette was repeatedly run 400 times, and the state of edge damage was visually determined.

◎: No damage ○: No problem in practical use △: Problem in practical use ×: Impossible for practical use XX: Severe damage (3) Young's modulus according to conventional method.

Claims (2)

[Claims] (1) In a magnetic recording medium having a plurality of magnetic layers containing ferromagnetic powder dispersed in a binder on a non-magnetic support, the glass transition point of the uppermost magnetic layer binder of the plurality of magnetic layer stacks is Tg. (u) A magnetic recording medium characterized in that Tg(u)≦Tg(d), where Tg(d) is the glass transition point of the binder laminated magnetic layer other than the top layer. (2) The magnetic recording medium according to claim 1, wherein the thickness of the uppermost layer is 0.1 to 1.5 μm.