JPH02232812A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce dropout and to improve traveling durability of the medium having several numbers of laminated magnetic layers by rendering the glass transition point of the binder incorporated in the uppermost magnetic layer higher than that of binders used for other layers. CONSTITUTION:The magnetic recording medium has several magnetic layers formed on a nonmagnetic supporting body. The glass transition point Tg of the binder in the uppermost magnetic layer is made higher than Tg of binders in other magnetic layers. If a resin such as polyurethane has high Tg, it gives large rigidity and excellent durability, but it is inferior in adhesion property and liable to cause dropout. Therefore, Tg of the uppermost layer is made highest to increase the rigidity of the layer, since the layer is vulnerable to mechanical damaged. On the other hand, Tg in other lower layers is made lower to increase adhesion strength. As for the binder, vinyl chloride copolymer resin, polyurethane resin, cellulosic resin, etc., or mixture of these may be used considering the features and polymn. rates of resins.

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. technological 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 packed with high density 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, magnetic particles and other fillers are dispersed in a binder,
The coating type, in which a magnetic layer is formed by coating a support with a magnetic paint containing suspensions and additives for adjusting various properties, is the most popular method for magnetic coating due to its versatility in applicable technology and high productivity. It is an important means of producing recording media, especially recording media in tape form.

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 partitioning properties, phenoxy resins with good dimensional stability, water resistance, and adhesive properties are used, and these are 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. (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 electromagnetic properties are shared among the magnetic layers for recording, but the binder of these laminated magnetic layers is
Despite the fact that the film position is different and the roles of electromagnetic properties and tape film physical properties are different, the method of single-layer structure is followed as it is, and the appropriate binder material is not allocated in the right place or selected accordingly. ing.

[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 with less dropout and excellent running durability.

[Structure of the invention]

As a result of studies in line with the above objectives, we found that, from among the knowledge regarding the use of various binders alone or in combination with other binders, and the overall physical properties affected by the effects of additives, we found that, in particular, changes in the glass transition point (Tg) of binders. We focused on the corresponding changes in characteristics. For example, when polyurethane resin has a high Tg, it has high rigidity and is advantageous for durability, but its adhesion to the support tends to cause glass dropout, and conversely, when it has a low Tg, it has good adhesion. Although there are fewer dropouts, it tends to lack rigidity and reduce walking durability.

The present invention actively reverses this tendency and divides its characteristics into an upper layer that is susceptible to mechanical damage and a lower layer that is protected by the upper layer and whose electromagnetic properties or film properties can be freely adjusted. 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 of the uppermost magnetic layer binder system of the plurality of magnetic layer stacks is applied. The object of the present invention can be achieved by a magnetic recording medium characterized in that the point is set to be higher than the glass transition point of the binder system of any laminated magnetic layer other than the uppermost layer.

In addition, when a protective layer is provided, the binder composition having the Tg of the uppermost magnetic layer may be applied to the binder, or
Further, when an undercoat layer is provided, the binder composition of any of the laminated magnetic layers other than the uppermost layer, preferably the binder composition of the lowermost layer, may be applied to the binder.

The multilayer coating method of the magnetic tape constituent layers according to the present invention includes wet-on-wet (wet-on-wet).
A sequential layering method or a simultaneous layering method may be used, or a wet-on-dry heavy layering method may 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 system according to the present invention can be selected from among vinyl chloride copolymer resin, polyurethane resin, cellulose resin, and other resins, taking into account the characteristics and degree of polymerization of each type, and can be used alone or in combination at a preferable mixing ratio. In addition, the composition is selected after actually measuring the glass transition point (Tg) as a comprehensive physical property of the binder system containing dispersants, lubricants, etc. (however, no curing agent is added). Incidentally, the Tg of the binder system is determined mostly by the Tg of the binder.

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

Method for measuring glass transition point (Tg): Vibron DDV-II-EA (manufactured by Toyo Baldwin Co., Ltd.) was used as a measuring device, and the thickness was 30 pm.
Samples with a width of 10 mm and a length of 25 mm are heated to -100°C to +1
While heating at 5°C/sin in the range of 00°C, apply a sine wave expansion/contraction strain with a frequency of 10 Hz to the end image in the width direction, and calculate the maximum tan δ of the phase difference angle δ between both vectors of the sine wave stress appearing at the other end. Let the temperature given be Tg.

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 (I)
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 (1) In the formula, Rl and R are hydrogen atoms or lower alkyl groups (
For example, CI, C, H. etc.). Also R, and R
, may be the same or different within each repeating unit block.

X is (a polar group, a modified group such as a group forming an inner salt)
represents a substituent -A-X' containing Y; 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 deHCII during heating or aging of the vinyl chloride resin, and its content is 0.5% based on the Tg and solubility of the resin. It was found that ~3vt% is appropriate. H below 0.5wt%
If CQ generation cannot be sufficiently suppressed and the amount exceeds t% of tricarbonate, the physical properties of the resin will deteriorate.

Next, 2 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,
Or it is added for the purpose of improving properties such as improving surface smoothness. In the copolymer represented by the above general formula (1), when the copolymer is used as a binder for a magnetic recording medium and exhibits the necessary effect, the vinyl chloride repeating unit increases the strength of the medium ( 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 solvents will be poor, and the glass transition of the resin will be affected. The temperature (Tg) tends to increase.

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 point (Tg) and plasticizing effect of the binder resin by adjusting its content. Therefore, they have a mutually complementary relationship with the reactive hydroxyl group (-08) of vinyl alcohol, etc. Also,
Repeating units having an intramolecular base such as a petaine group or a modifying group such as a sulfonic acid group contribute to dispersibility, and if the amount is too small, the effect will be small, and if it is too large, it will It no longer contributes to improving the dispersibility of the material, and on the contrary, moisture resistance worsens, leading to a decrease in weather resistance. In addition to the above-mentioned repeating units, the vinyl chloride copolymer of the present invention has an additional 1,200. Carpoxy group or its metal substituent (1000M
: M is H or an alkali metal such as Li, Na, K, etc.) A repeating unit having a hydrophilic functional group such as M may be introduced. The carboxy group improves the retention and dispersibility of the binder to magnetic powder (iron oxide, metal powder). Introducing an OH group 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 the reaction of polyisocyanate with polyol and other copolymers as necessary, and free incyanate groups are and/or in the form of urethane resins or urethane prebolomers containing hydroxyl groups or without these reactive end groups (for example in the form of turrethane elastomers).

The amount of modified groups introduced into the polyurethane resin according to the present invention is 0.
．． 01” is preferably 1.0 mmoQ/g,
More preferably, it is in the range of 0.1 to 0.5 mOl (17g).When the amount of the modified group introduced is less than 0.0mOl/g, a sufficient effect on the dispersibility of the ferromagnetic powder is observed. It disappears.

Furthermore, if the amount of the modified group introduced exceeds 1.0-o(!/g), intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility but also causes selectivity to the solvent, There is also a risk of L7 failure due to the inability to use 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 the polyurethane resin with a molecular weight of 60,000 or less according to the present invention is PU (polyurethane resin)/V
Cffi (vinyl chloride resin) weight ratio: 80/
20-20/80 is preferred, especially 50/50-3
0/70 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, etc., but are not particularly limited thereto.

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, enoxy resins, thermoplastic resins with specific usage methods, thermosetting resins, reactive base resins, electron beam curable resins, etc. can also be used in combination. Good too.

In particular, by using nitrocellulose whose molecular weight is specified as falling ball viscosity of 178 to 1/3 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 glabella adhesion. It has a remarkable effect, and can particularly improve running stability at high temperatures.

In addition, in terms of properties, paints containing nitrocellulose disperse the filler more quickly than vinyl chloride paints, making the paint itself more stable and less prone to reagglomeration of the 7-layer, creating a good lubricating surface. It is useful for

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

Aromatic polyisocyanates that can be used include, for example, tolylene diisocyanate (TDr) 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 incyanates and 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 aliphatic polyisocyanates, non-alicyclic polyisocyanates and adducts of these compounds with active hydrogen compounds are preferred. The amount of the polyisocyanate added is 1/20 to 7/1O, more preferably 1/1 to the weight of the binder.
It is 0 to l/2.

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

In addition to carbon plaque, organic powder or inorganic powder may be used as the filler, and these may be used individually or in combination.

The organic powder used in the present invention is preferably an acrylic styrene resin, a bezoguanamine resin powder, a melamine resin powder, or a cyanine pigment. ! II powder, polyester resin powder, polyamide resin powder, 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, and oxide. Zinc, tin oxide, aluminum oxide, chromium oxide, disaster silicon, calcium carbide, σ-Fe! 01, talc, kaolin, calcium sulfate,
Examples include 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, a-olefin oxide, etc. may be used. Can be done.

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

Dispersants used in the magnetic layer according to the present invention include lecithin, phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid esters, known surfactants, etc. and salts thereof; salts of polymeric dispersants having negative organic groups (for example -COOH1-POs}l) can also be used. These dispersants are 1
It may be used alone or in combination of two or more types.

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-FejO. , Co-containing γ-”*Os* Co
Deposited γ-Fe, Os, Fe30a, Co-containing Fe,
O. , Co-coated Fe30, , CrOz and other oxide magnetic materials, such as Fe, Ni, Co, Fe-Ni alloy, Fe-Co alloy, Fe-Al2 alloy, F-Am
-Ni alloy, Fe-Ni-P alloy, Fe-Ni-C
o alloy, Fe-Mn-Zn alloy, Fe-NjZn alloy, Fe-Co-Ni-Or alloy, Fe-Co-N
i-P alloy, Co-Ni alloy, Co-P alloy, C
Examples include various ferromagnetic materials such as o-Cr alloys and metal magnetic powders mainly composed of Fe, Ni, Co, and An. Additives to these metal magnetic materials include Si, Cu, and Z.
Elements such as n, AQ, P, Mn, and Cr, or compounds of these elements may be included.

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

For the second magnetic layer, antistatic agents, abrasive agents, etc. known in the United States can be used. 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.
The prepared magnetic paint is applied onto a non-magnetic support.

Examples 1 to 5 and Comparative Examples (1) to (5) T listed in Table 1
Samples were prepared using binder resins A%B with different g values for the following magnetic paint A%B, and their properties were measured and are shown in Table 2. (A) Magnetic paint for top layer (Part) Co-
11F e 20 @ (Hc- 9000eBET=
50m”/g) 100 Abrasive (
Average grain! 0.2 μm) PVC yarn resin containing potassium 5-sulfonate 11tA
5 carpon black
1 myristic acid
l-butyl stearate
l Methyl ethyl ketone
100 cyclohexanone
100 toluene lO
O After kneading and dispersing the above magnetic paint, 5 parts of a hardening agent Coronate L (Nippon Polyurethane Industries) was added to prepare. (B) Magnetic paint other than the top layer (Part) Co
-r-Fe! 0 m (HC-7000e
B ET-38m”/g) 100 Abrasive (
Average particle size: 0.2 μm) 5 PVC thread resin containing potassium sulfonate 10 Resin B5 Carpon black 1 Myristic acid l Stearic acid l Butyl stearate l Methyl ethyl ketone
10G cyclohexanone
100 toluene
100 After mixing and dispersing the magnetic paint described above, 5 parts of a hardening agent (Nippon Polyurethane Industries) was added to coronate to prepare.

Table 1 Table 2 As is clear from Table 2, the samples of the present invention have electromagnetic properties, physical properties,
It has good durability as well.

Method of measuring characteristics in Examples and Comparative Examples〉(1)
100 in a certain section (10 to 30 m) on the dropout magnetic recording medium.
% white signal was input and played back, and at that time, the dropout of 15 μs was measured at a -12 dB level using a Shibasoku Co., Ltd. counter (model VHO I BZ) in 1 minute increments, and the average value of the total length of the measured part was taken as the measured value. do.

(2) White 100 is printed on the RF output magnetic recording medium using the S-VHS method.
% signal at reference level, reproduced RF output signal at NF
Input to Design Block's AC ammeter, M-17OL, and read its output level.

(3) Lumi S/N White lOO on magnetic recording medium by S-VHS method
Input playback video signal with reference level of 9250% signal
/1 [noise meter manufactured by Shibasoku Co., Ltd.] and read the Lumi S/N from the obtained absolute noise value.

(4) Durability A tape with a length corresponding to 5 minutes from the beginning of the cassette was repeatedly run 400 times and the average was determined.

a. Edge damage: Visually determine the deformation of the edge.

b- RF output decrease...Evaluate the RF output after the test as 100% of that before the test.

c. Powder falling... Visually judge the amount of magnetic material adhering to the cylinder and header based on the following criteria.

×: High, △: Slightly high, O: Low (5) Friction coefficient The friction coefficient of 41-chrome bottle was measured at a tape speed of 1-40 cm/sec using a tape running tester [manufactured by Yokohama System]. .

(6) A 2 mm square scratch was made on the magnetic layer side of the adhesive magnetic tape, extending from the surface to the support surface, cellophane tape was applied, it was peeled off at once, and evaluation was made based on the number of base squares that were peeled off.

% of base grains stripped off 1% or less 1-5 6-10 11 or more O △
XX

Claims (1)

[Claims] 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 of the plurality of laminated magnetic layers is the same as that of a layer other than the uppermost layer. A magnetic recording medium characterized in that the temperature is higher than the glass transition point of any of the laminated magnetic layer binder systems.