JPH01106319A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To suppress drop-out to a low level and to improve traveling durability by specifying the Young's modulus of a magnetic layer and the crack generating elongation of the magnetic layer. CONSTITUTION:A magnetic recording medium such as magnetic tape is constituted by providing the magnetic layer consisting of the magnetic powder, binder and other necessary components on a base such as polyester film. The traveling durability of the medium is improved by harmonizing the two characteristics; the Young's modulus and crack generating elongation of this magnetic layer. Namely, the Young's modulus of the magnetic layer is specified to >=400kg/mm<2>, more preferably >=450kg/mm<2>. The crack generating elongation is specified to >=3%, more preferably >=5%. Edge damage and tape sticking or film exfoliation, etc., are thereby prevented. These characteristics are determined by the mixing ratios of a vinyl chloride resin, polyurethane, isocyanate compd., and pigment which are the constituting components of the magnetic layer. The preferable ratios vary with the Tg (glass transition temp.), etc., of the vinyl chloride resin and polyurethane.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to magnetic recording media such as video tapes, audio tapes, computer tapes, and 70-tuppy disks, and particularly to magnetic recording media with improved running durability. be.

[Conventional technology]

Generally, magnetic powder is placed on a support such as a polyester film.
In magnetic recording media such as magnetic tapes, which have a magnetic layer made of a binder and other necessary components, the magnetic layer comes into sliding contact with a magnetic head or magnetic pad at high speed during recording and reproduction, so the magnetic layer has poor wear resistance. Excellence is required,
Conventionally, attempts have been made to improve the wear resistance of the magnetic layer by incorporating lubricants such as higher fatty acid esters and higher fatty acids into the magnetic layer.

However, magnetic recording media using such technology either have a magnetic layer with a low Young's modulus and good adhesion to the support (i.e., high crack initiation elongation), or have a high Young's modulus. If the Young's modulus is either highly brittle (i.e., crack initiation elongation is small) and the Young's modulus is low, the running durability of the magnetic recording medium deteriorates, causing edge damage or tape sticking, and the Young's modulus decreases. If the magnetic layer is high, the adhesion and brittleness of the magnetic layer to the support will deteriorate, deprinting will occur, and the dropout characteristics will deteriorate.

As a result of research aimed at improving these conventional drawbacks, the present inventors improved running durability by adjusting the two properties of the magnetic layer, Young's modulus and crack initiation elongation, to specific ranges. The present invention was achieved by discovering that it is possible to do so.

[Purpose of the invention]

An object of the present invention is to provide a magnetic recording medium with low dropout and improved running durability.

[Structure of the invention]

An object of the present invention is to provide a magnetic recording medium having a ferromagnetic layer on a non-magnetic support, in which the Young's modulus of the magnetic layer is 400 kg/
This is achieved by a magnetic recording medium characterized in that the magnetic layer has a crack initiation elongation of 3% or more.

The present invention will be explained in detail below.

The Young's modulus of the magnetic layer of the magnetic recording medium of the present invention is 400 kg.
/ff1m” or more, preferably 450kg/m
m” or more.

Furthermore, the crack initiation elongation of the magnetic recording medium of the present invention is 3% or more, preferably 5% or more.

Next, a description will be given of means for manufacturing a magnetic recording medium that satisfies the above-described specific Young's modulus and crack initiation elongation conditions according to the present invention.

The above characteristics can be achieved, for example, by appropriate mixing ratios of vinyl chloride resin, polyurethane, incyanate compound, and pigment in the constituent components of the magnetic layer.

The vinyl chloride resin is preferably a vinyl chloride copolymer having acidic groups, epoxy groups, and hydroxyl groups. These functional groups may exist in any state, but preferably form a part of the copolymer.

A preferable vinyl chloride copolymer can be represented by the following general formula, for example. 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.

In the general formula, R, , R, and R1 represent a hydrogen atom or a lower alkyl group (for example, -CH3, C2H5, etc.).

Further, R, , R2 and R1 may be the same or different in each repeating unit block.

X is a substituent containing acidic groups such as -303M, C00M, PO(OM)1, -A-5o, M, -A'
-COOM, -A"-PO(OM), etc., Y represents a substituent containing an epoxy group -B -CH-CH, and V represents a hydrogen atom \1 - (CHs)qOH or bar ( co, co, o) qo
n (q represents an integer of 1 to 4).

M is a hydrogen atom or an alkali metal atom such as Li, Na or Ni. Further, A, A', A" and B are linking groups that link acidic groups and epoxy groups to the main chain of the copolymer, respectively. Examples of linking groups include the following.

(CHz) , CON Kano cHt% , C0NHCR
s-I However, R6 and R7 are each a hydrogen atom or a carbon number of 1 to 15
represents an alkyl group or a phenyl group, and R represents an alkylene group having 1 to 15 carbon atoms.

r represents an integer from θ to 20.

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 lubricity.

Specific examples of the repeating unit include units having the following structure. .

Here, R4 and R6 each represent H or a lower alkyl group (eg CHs, CzHs).

Represents an integer. ) represents. Moreover, p is an integer of 1-50.

R9 is an unsubstituted hydrocarbon group having 8 or more carbon atoms, such as trickle, tocosyl, eicosyl, nonadecyl, octadecyl, hexadecyl, tridecyl, undecyl, decyl, nonyl, octyl, and the like.

As the compound (Z), any structural unit that can be copolymerized with the compound of the present invention, such as vinylidene chloride, ethylene, styrene, maleic anhydride, maleic acid, and maleic ester, can be used.

In the above general formula, k is 200 to 800, α and α
' represents an integer of 0-100, m represents an integer of 1-100, and n represents an integer of 0-200.

The degree of polymerization (Pn) of the vinyl chloride copolymer according to the present invention is 250≦Pn≦500, and at least one acidic group must be present in the copolymer. Repeating units containing 0.5 to 3 wt%, repeating units containing epoxy groups 0.5 to 4 wt%, repeating units containing hydroxyl groups 0.1 to 7 wt%, and vinyl chloride units 95 to 70 wt%.
It is preferable that

In the copolymer represented by the above general formula, when the copolymer is used as a binder for a magnetic recording medium and exhibits the necessary effect, the vinyl chloride repeating unit contributes to the strength of the medium. However, if the vinyl chloride component is too small, the physical properties (mechanical strength) necessary for the medium cannot be obtained.
If the amount is too large, the solubility in the solvent will deteriorate and the glass transition temperature (Tg) of the resin will also tend 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 isocyanates. It is involved in bonding with other materials 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 controlling the content. In addition, a reactive hydroxyl group (-01() of vinyl alcohol, etc. participates in a crosslinking reaction with incyanate, etc.).

In addition, repeating units having acidic groups contribute to dispersibility, and if the amount is too small, the effect will be small, and if it is too large, it will not contribute to further improvement of dispersibility. On the contrary, the moisture resistance deteriorates, which is not preferable.

Furthermore, repeating units having the effect of improving the resin's strength, solvent solubility, compatibility with other resins, lubricity, or flexibility may be introduced.

Next, specific examples of the copolymers represented by the above general formula will be given.

Compound example CH.

CH.

? H・ Next, the synthesis of the vinyl chloride copolymer will be described.

The copolymer represented by the above general formula has hydrophilic groups -303M, -COOM, -PO(O
M) It can also be synthesized by adding the above-mentioned hydrophilic group or functional group to a copolymer containing -0H group by reaction, such as a vinyl chloride-vinyl alcohol copolymer, which does not have 2.

That is, Q is -505M, -COOM, -PO(
OM) i or an epoxy group, P represents a halogen atom, and R represents a substituted or unsubstituted alkylene group or phenylene group having 1 to 20 carbon atoms, then P-R-Q is an additional element in the above-mentioned addition synthesis. Can be used.

Among these, the case of reacting with a copolymer υ with CQ (CHz) 5OsNa is shown as an example, and the result is OH0(CHi) 5OsNa. Similar reactions can also be obtained when other compounds are used. A predetermined copolymer can be produced by the following steps.

However, since the reaction between the copolymer and the reactive compound is a polymer reaction, there are problems in the presence of unreacted compounds and removal of by-products, and it is also difficult to control the reaction rate. Furthermore, there is a particular problem that the introduced epoxy group reacts with hydrochloric acid during the reaction, or a ring-opening reaction occurs during the synthesis. Therefore, in order to avoid these problems, it is advantageous to copolymerize all monomers as copolymerizable monomers. That is, a predetermined amount of a reactive monomer having an unsaturated bond from which a repeating unit represented by the above general formula is derived is poured into a reaction vessel such as an autoclave, and a general polymerization initiator such as BPO (benzoyl peroxide) or AIBN is added. Polymerization can be carried out using a polymerization initiator such as a radical polymerization initiator such as (azobisisobutyronitrile), a redox polymerization initiator, an anionic polymerization initiator, or a cationic polymerization initiator. Thereafter, it undergoes processing steps such as drying and, if necessary, pulverization, to obtain a mainly white powder.

Specific examples of the reactive monomer for introducing the epoxy group include glycidyl acrylate and glycidyl methacrylate, and specific examples of the reactive monomer for introducing the sulfo group or its salt include vinyl sulfonic acid. , unsaturated hydrocarbon sulfonic acids such as allylsulfonic acid, methacrylsulfonic acid, p-styrenesulfonic acid, and salts thereof. Also included are sulfoalkyl esters of acrylic acid or methacrylic acid, such as sulfoethyl methacrylate and sulfopropyl methacrylate, and salts thereof.

In addition, introduction of a carboxy group or its salt (-COOM
acrylic acid, methacrylic acid, etc.

Acrylic acid and methacrylic acid are also advantageous in introducing a phosphoric acid group or a salt thereof (introducing -PO(OM)2).

Furthermore, examples of the oil-soluble radical polymerization initiator include the following azo compounds or organic peroxides. For example, azo compounds include 2.2'-azobisisobutyronitrile, 2.2'-azobis(2-methylcapronitrile), 2.2'-azobis(2-methylcapronitrile), and 2.2'-azobis(2-methylcapronitrile). '-Azobis(2,3,3-1-limethylbutyronitrile), 2゜21-azobis(2,4-dimethylvaleronitrile), etc. can be used, and as the organic peroxide, for example, acetyl peroxide,
Diacyl peroxides such as propionyl peroxide, imbutyryl peroxide, octanoyl peroxide, lauroyl peroxide, benzoyl peroxide, diisopropyl peroxydicarbonate; t-butyl peroxyisobutyrate, t-butyl peroxybivalate Peroxy esters such as, etc. can be used. Of course, two or more of the above oil-soluble radical polymerization initiators can also be used in appropriate combination.

Among them, azo compounds are preferred from the viewpoint of handling safety and performance, and 2,27-azobisisobutyronitrile or 2,2'-asohis (2,4-dimethylvaleronitrile) is particularly preferred. Although it is difficult to define the amount of the initiator to be used, it is generally used within the range of 0.2 to 2.0% based on the weight of the monomer.

In addition, regarding the pH of the polymerization system, if it is too acidic, it will cause ring opening of the epoxy group during polymerization, and if it is too alkaline, it will cause hydrolysis of the produced polymer.
9, preferably within the range of 2 to 7.

The polymerization temperature will depend on the type of initiator, but the higher the temperature, the more likely the ring-opening reaction of the epoxy group will occur, or a portion of the monomer will be emulsified and undergo emulsion polymerization, resulting in the formation of a latex-like fine polymer. To avoid problems, a temperature range of approximately 80° C. or lower, preferably 40 to 70° C., is recommended.

Although it is desirable to use industrial water as the polymerization medium, there is no problem in coexisting a water-miscible organic solvent or an electrolyte salt.

Examples of the polyurethane include the following. That is, as diols for synthesizing polyurethane, organic dibasic acids such as phthalic acid, adipic acid, duplex sulfuric acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane are used. , hexanetriol, glycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, polyhydric alcohols such as pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. Polyester polyols synthesized by reaction with; or S-caprolactam, σ-methyl-1-caglolactam, S-methyl-8-caprolactam, γ-
Examples include lactone polyester polyols synthesized from lactams such as butyrolactam; or polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. These polyols can be combined with tolylene diisocyanate, hexamethylene diisocyanate, etc. , polyester polyurethanes and polyether polyurethanes which are urethanized by reacting with incyanate compounds such as methylene diisocyanate and metaxylylene diisocyanate, and polycarbonate polyurethanes which are carbonated with phosgene or diphenyl carbonate. These polyurethanes are usually produced primarily by the reaction of polyisocyanates with polyols and contain free incyanate groups.
Alternatively, it may be in the form of a urethane resin or urethane prepolymer containing hydroxyl groups, or it may be in the form of a urethane elastomer that does not contain these reactive end groups.

Further, examples of the polyurethane used in the present invention include polycarbonate polyurethanes that do not have ester bonds (urethane bonds and carbonate bonds are not included), and polyurethanes derived from polyenitel-polyester-polyols.

The polycarbonate polyurethane having no ester bond is, for example, polycarbonate polyol (H(-0-R-0-C-0-) R-OH)I based on the following formula.
Q and polyvalent incyanate (e.g. 0CN-R' -NC
Synthesized by urethanization reaction with 0).

(However, R and R' are aliphatic or aromatic hydrocarbon groups. Q is preferably 50 or less, preferably 1 to 30, in order to lower Tg and prevent stickiness. m is a group that maintains film-forming ability. and 5 to 500 <, 10 to improve solvent solubility.
~300 is desirable. a and m are selected so that the average molecular weight of this polycarbonate polyol polyurethane is desirably 50,000 to 200,000. ) The polycarbonate polyol that can be used here is formed by linking polyols with carbonate bonds, and is obtained, for example, by condensation of a conventionally known polyhydric alcohol with phosgene, chloroformic acid ester, dialkyl carbonate, diallyl carbonate, etc. .

Examples of the polyhydric alcohol include 1.10-decanediol, 1.6-hexanediol, 1.4-butanediol, 1.3-butanediol, neopentyl glycol, 5-bentanediol, and the like. The number of carbon atoms in this polyhydric alcohol, such as diol, is important and is preferably set to 4 to 12.

In the above-mentioned urethanization reaction, it is important that active hydrogen (due to -OH) exists in the polycarbonate, but in addition to the polyhydric alcohols listed above as compounds that supply similar active hydrogen, ethylene Glycol, diethylene glycol, fluoropylene glycol, l,4-butylene glycol, bisphenol A1
Glycerin, 1.3゜6-hexanediol, trimethylolpropane, pentaerythritol, sorbitol, sucrose, dipropylene glycol, methyljetanolamine, ethylbiisopropanolamine, triethanolamine, ethylenediamine, hexamethylenediamine, bis(p- compounds such as aminocyclohexane), tolylenediamine, diphenylmethanediamine, methylenebis(2-chloroaniline), and/or these compounds, ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran,
Examples include polyether polyols obtained by adding one or more types of styrene oxide (hereinafter simply referred to as alkylene oxide).

Next, although the active hydrogen-containing polycarbonate such as the above-mentioned polycarbonate polyol can be used alone, other polyhydric alcohols may be used in combination with the above-mentioned urethanization, and other known chain extenders may be used in combination. For example, when other low-molecular-weight polyhydric alcohols such as hexanediol and butanediol are used together, it can be expected that this will react with an excess amount of the polyisocyanate and promote gelation, but as shown in Figure 3, It is desirable to maintain the proportion of polycarbonate polyol at 80% or more in order to obtain sufficient wear resistance.

Next, as the above-mentioned polyvalent incyanate, aromatic incyanate is preferable, such as tolylene diisocyanate (TDI) (2,4-T old, 2.6-TD
I), dimer of 2,4-tolylene diisocyanate, 4
．． 4-diphenylmethane diisocyanate (MDI)
, xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), naphthylene-
These include 1,5-diisocyanate (NDI), o-tolylene diisocyanate (TODI), and adducts of these incyanates with active hydrogen compounds, and their average molecular weights range from 100 to 3,000. is suitable. Specifically, Sumidur T80, Sumidur 44S1 PF manufactured by Sumidur Urethane Co., Ltd.
, L1 Desmodille T65, 15, R1 RF
1 [L, SL; Takenate 3 manufactured by Takeda Pharmaceutical Co., Ltd.
00S, 500; Mitsui Nisso Urethane Co., Ltd. product rND
IJ, rTODIJ, Nippon Polyurethane Co., Ltd. product Desmodur T100, Millioneroto MR, same MT, Coronate L; Kasei Upjohn Co. product PAPI-135
, TD165, 80, 100, Incyanato 12
Examples include 5M and 143L.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (T
HDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these incyanates and active hydrogen compounds, those with a molecular weight of 100 are preferable.
~3.000. Among the aliphatic incyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

Specifically, for example, Sumidur N1 Desmodur Z 4273 manufactured by Bayer Urethane Co., Ltd., and Duranate 50M1 24A-100 and 24A manufactured by Asahi Kasei Co., Ltd.
-90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd.

There are products such as TMD I manufactured by Hüls. Examples of alicyclic isocyanates among aliphatic isocyanates include methylcyclohexane-2,4-diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), isophorone diisocyanate, and its active hydrogen compound. Examples include adducts of . Specifically, products rlPDIJ and rlPDI manufactured by Huls Chemical Co., Ltd.
-71890J, -H2921, -B1065, etc. Examples of other polyvalent isocyanates include adducts of diisocyanates and trivalent polyols, and pentamers of diisocyanates.

Examples of these include an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, and a pentamer consisting of 2 moles of tolylene diisocyanate. These can be easily obtained through engineering.

Among the polyvalent incyanates mentioned above, aromatic ones act as hard components (hard segments), so
Polycarbonate (Polyol) Desirable as it provides sufficient rigidity of polyurethane.

Adhesion can be kept low by setting the average molecular weight of the polyurethane in the range of 50,000 to 200,000, but in this case, using an aromatic type as the incyanato component of the polyurethane can sufficiently increase the still durability. On the other hand, it can be seen that when aliphatic incyanate is used, the still durability decreases. Among the aromatic incyanates mentioned above, naphthylene-1,5-diisocyanate,
Particularly preferred is diphenylmethane diisocyanate.

The amount of isocyanate used above is such that the NCO group (incyanate group) contained in the polyisocyanate is an active hydrogen-containing compound (e.g. polycarbonate polyol).
It is desirable that the equivalent ratio be 0.8 to 1.2, more preferably 0.85 to 1.1 with respect to the total amount of active hydrogen contained in the active hydrogen.

The above polyether polyester polyol can basically be synthesized from the following three components (a) to (c).

(a) Polytetramethylene glycol (PTMEG)
).

Structural formula 'HO((CH*)40:l nH (however, n=
It is a positive number of 1 to 5G, preferably 4 to 40. ) (b) Ethylene oxide on the phenolic hydroxyl group,
A diol with a molecular weight of 1000 or less formed by adding an oxide such as propylene oxide.

For example, the following structural formula is an ethylene oxide adduct of bisphenol A (BPA -EO)CH3 -O-(-CH,0B20 +nH (however, m and n are each positive numbers of 1 or more, and (m
)≦20. ) (C) Aromatic polybasic acids Heptatalic acid, orthophthalic acid, and isophthalic acid are mentioned. In addition to the above, the following polyols, diols, and polybasic acids can also be used.

1 (% 0CH2CH2%0H CH1 H+0CHCH29〇H HaCI, C120H CH3CHCH2CH2OF+ (1,3-butanediol)〇H HOCH2CH, CH2CH20H (1,4-butanediol) and other ordinary diols When synthesizing urethane resin, conventional When using glycols, the surface flatness of the layer cannot be said to be sufficient, and in particular, the performance of the videotape, that is, the image quality and abrasion resistance (durability), is not satisfactory.Moreover, Conventional urethane resins derived from glycols have poor adhesion to substrates such as polyethylene terephthalate, and in some cases an intermediate layer or subbing layer is required between the support and the magnetic layer to improve adhesion. However, in the present invention, when obtaining a urethane resin, if a tertiary amine type polyhydric alcohol represented by the following general formula is used as a low molecular weight diol, the dispersibility will be improved and the surface flatness will be improved. In addition, a magnetic recording medium with excellent durability and improved adhesion to the substrate can be obtained.

General formula: %Formula% (However, R' and R2 are alkylene groups, and R3 is an alkyl group or an aryl group. In particular, in order to improve adhesive strength, it is desirable that R3 is an aryl group.) These low molecular weight diols A specific example is as follows.

HOCH, CH20H \/ HOCHzCHz CBzCHzO[(\/ CH3CH2N-e-CH2CH20H)zCH3CH
2N + CH2CHCH3) 2■ H Below margins CH, CH.

Next, an aromatic group-containing polyether polyester polyol is obtained using each of the above-mentioned components, such as the compounds (a), (b), and (c) above, and according to a conventional synthesis method. The weight average molecular weight of this polyether polyester polyol is preferably from 500 to 5.000, from 600 to 5.000.
More preferably, it is 3.000. Four types of the obtained aromatic residue-containing polyether polyester polyols (A
, B, C, D) are shown in Table 1 below.

Weight average molecular weight A polyether polyester polyol having a weight average molecular weight of 2,000 is thus obtained.

Polyether polyester polyurethane was synthesized from these polyols according to Synthesis Example 1 shown below.

(Synthesis Example 1) The gas in a reactor equipped with a stirrer and a reflux condenser was replaced with nitrogen gas, 300 parts by weight of methyl ethyl ketone (hereinafter simply referred to as "parts") was put into the reactor, and , polyether polyester polyol (A) 165.0
86.0 parts diphenylmethane diisocyanate 0.03 parts dibutyltin dilaurate were added,
The reaction was carried out at 80°0 for 2 hours. This solution contains 43.2 parts of phenyldiethanolamine and 400 parts of methyl ethyl ketone.
of the mixture was added, and the reaction was further carried out at 80°C for 1 hour.

5.8 parts of 3-methylpentane-1,3,5-triol was added to the obtained solution, and the mixture was reacted at 80°C for 1 hour.

The thermoplastic polyurethane solution thus obtained had a nonvolatile content of 30.2 wt% and a viscosity of 13.100 cps/25°C.
and molecular weight My-79,000, Mn=15,000, Mw/Mn-5 by GPC (in tetrahydro 7 run)
, 4, the softening temperature was 65°C.

In the same manner as Synthesis Example 1, various polyurethanes according to Synthesis Examples 2 to 8 were synthesized as shown in Cloth-2 below.

, -11 or less ゛white Here, PEP type (aromatic polyester polyether)
The synthesis examples are 1, 2, 3.4 and 5, the PC system is synthesis example 7, the PCL system is synthesis example 6, and 1.4RA
The system is Synthesis Example 8.

In addition, in the above, usable polyisocyanates include tolylene diisocyanate (TDI) (2) in addition to diphenylmethane diisocyanate.

4-T old, 2,6-TDI), 2,4-tolylene diisocyanate diiso, xamethylene diisocyanate (XDl), metaxylylene diisocyanate (M
XDI), naphthylene-1,5-diisocyanate (
MDI), 0-tolylene diisocyanate (TODI
) and adducts of these incyanates with active hydrogen compounds, and their average molecular weights range from 100 to 3.
A range of 000 is preferred. Usable aliphatic polyisocyanates include hexamethylene diisocyanate ()IMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (THDI).
, inphorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate (8,2MDI)
, and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these incyanates and active hydrogen compounds, those having a weight average molecular weight of 100 are preferable.
~3000.

As an incyanate compound used as a factor for realizing Young's modulus and crack initiation elongation of the magnetic recording medium of the present invention,
Mention may be made of the following aromatic incyanates and aliphatic incyanates.

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

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these l isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3.000 are preferred. Among the aliphatic incynates, non-alicyclic incynates and adducts of these compounds with active hydrogen compounds are preferred.

The preferred ratio of vinyl chloride resin/polyurethane/isocyanate varies depending on the Tg of the vinyl chloride resin and polyurethane, but for example, if the binder is Tg-6
0°C, Mw -25000 hinyl chloride tree III
, T g =-20°C, Mw-60000 (7) Ho!
When J Utalene and TDI aromatic soicyanate are used, the ratio is vinyl chloride resin/polyurethane -872-476 isocyanate/other binder -1/10 to 40/10, and the total amount of binder to pigment at that time -15~
Preferably it is 30%.

The method for measuring Young's modulus in the present invention is as follows.

Length of sample: 200m Width of sample: 12.65mm Stretching speed: 100+am/win Temperature: 20°C Relative humidity = 50% Measure the load when stretched under the above conditions (Tensile curve),
Young's modulus is determined from the load of 1% elongation.

The method for measuring crack initiation elongation in the present invention is as follows.

Sample size (before testing): Length 100 mm (= L) Width 12.65 mm + Temperature: 20°C Relative humidity: 50% Stretching speed: Very low speed While stretching the test piece under the above conditions, check the surface condition of the test piece. was observed with a microscope (X200), and the crack initiation point was defined as the point at which one or more linear cracks were observed that expanded into a lip shape, and the length of the test piece at this point was L'.
From the length before the test, the crack initiation elongation - ((L' -L
)/L) x 10" to determine the crack initiation elongation.

Generally used techniques can be applied to the magnetic recording medium of the present invention.

Examples of the magnetic material used in the present invention include γ-Fe
2O3, co-containing - Fe2o1, co deposited - Fe2
0s%Fe5Oa, CO gold-containing e50, Co-coated Fe5
0*, oxide magnetic materials such as CrO2, e.g. Fe, Ni1
Fe-Ni alloy, Fe-Co alloy, Fe-N1-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe
-Ni-Zn alloy, Fe-C.

-Ni-Cr alloy, Fe-Co-N1-P alloy, Co-
Examples include various ferromagnetic materials such as P alloy, Go-Cr alloy, metal magnetic powder mainly composed of Fe and Ni5Co. Additives to these metal magnetic materials include Si, Cu, and Z.
Elements such as nxA2qP, Mn, and Cr, or compounds thereof may be included. Also used are hexagonal ferrites such as barium ferrite, and iron nitride.

The magnetic paint used to form the magnetic layer may contain additives such as a dispersant, a lubricant, an abrasive, a matting agent, and an antistatic agent, if necessary.

Dispersants used in the present invention include lecithin, phosphoric esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. and negative organic groups (e.g. -
It is also possible to use salts of polymeric dispersants with COOHl-PO,H). These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 25 parts by weight per 100 parts by weight of the ferromagnetic powder particles.

Further, as the lubricant, silicone oil, gelaphalite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, fatty acid ester consisting of -basic fatty acid and monohydric alcohol, etc. can be used. Among these, fatty acid esters are preferred in the magnetic disk embodiment. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

In addition, antistatic agents include carbon black,
Conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; 9 nonionic surfactants such as alkylene oxide, glycerin, and glycidol; Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums; Anionic surfactants include; amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; methyl acetate, ethyl acetate, butyl acetate,
Esters such as ethyl lactate and ethylene glycol monoacetate; Ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; Aromatic hydrocarbons such as benzene, toluene, and xylene; Methylene chloride, ethylene chloride, carbon tetrachloride, Halogenated hydrocarbons such as chloroform and dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-7-talate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose triacetate, and plastics such as polyamide and polycarbonate, but metals such as Cu, Aff, and Zn, Glass, BN%Si carbide, ceramic, etc. can also be used.

The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
In the case of a disk or card, it is approximately 30 μm-10+mm.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, Can be used include, but are not limited to, a tin coat.

〔Example〕

Next, the present invention will be specifically explained using examples.

Example 1 A magnetic paint was prepared by dispersing the composition shown in Table 1 with a sand mill and then diluting it with a diluted solution of additives.
Dry thickness 4 μm polyethine terephthalate film
．． The material was applied to a thickness of 5 μm, dried, smoothed with a supercalender, and cut into 1/2-inch pieces to prepare magnetic tape samples.

For these samples, tests were conducted to determine the initial number of dropouts, increase in the number of dropouts by continuous running for 100 passes, and tape damage.

These measurement conditions are as follows.

The number of dropouts is 114 at Sibank VHOIBZ.
dB/10 μs, the number of dropouts per minute was measured.

The 100-pass driving test was conducted on a VHR deck at 20°C.

The number of dropouts after repeating reproduction 100 times in a 50% RH atmosphere and the tape damage after running were visually determined.

The results are shown in Table-3. "Parts" in Table 3 indicate "parts by weight". By doing so, maintenance of a low level of dropout and running durability are improved.

〔Effect of the invention〕

According to the present invention, dropout of a magnetic recording medium is suppressed to a low level and running durability is improved.

Applicant: Konishiroku Photo Industry Co., Ltd.

Claims (1)

[Claims] In a magnetic recording medium having a ferromagnetic layer on a non-magnetic support, the Young's modulus of the magnetic layer is 400 kg/mm^2 or more,
A magnetic recording medium characterized in that the magnetic layer has a crack initiation elongation of 3% or more.