JPH01205725A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having excellent traveling resistance and traveling durability by superposing 1st and 2nd magnetic layers successively on a nonmagnetic base, incorporating a vinyl chloride copolymer and specific polyurethane resin into the binder of the 1st magnetic layer and incorporating the specific vinyl chloride copolymer and polyisocyanate into the binder of the 2nd magnetic layer. CONSTITUTION:The binder of the lower layer contains the polyurethane resin having >=25,000 number average mol.wt. in addition to the vinyl chloride copolymer and the glass transition temp. of this polyurethane resin is confined to <0 deg.C. The binder of the upper layer contains the vinyl chloride copolymer contg. org. groups having active hydrogen at a ratio of >=3 pieces per 1 molecule and the polyisocyanate and further the polyurethane resin having >=0 deg.C glass transition temp. The org. groups having the active hydrogen are one kind among OH, NH2 and NHR (R is an alkyl group). The recording medium which decreases the generation of drop-outs and has the excellent traveling durability is obtd. by this constitution.

Description

Detailed Description of the Invention [Field of the Invention] The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer, and more particularly to a magnetic recording medium having at least two magnetic layers. It is.

[Background of the Invention] Magnetic recording media are widely used as recording tapes, video tapes, and floppy disks. A magnetic recording medium basically consists of a magnetic layer in which ferromagnetic powder is dispersed in a binder, which is laminated on a non-magnetic support.

Magnetic recording media are required to have high levels of various properties such as electromagnetic conversion properties, running durability, and running performance. That is, audio tapes for music recording and playback are required to have higher original sound playback capabilities. Furthermore, video tapes are required to have excellent electromagnetic conversion characteristics, such as excellent original picture reproduction ability.

In addition to having such excellent electromagnetic conversion characteristics, magnetic recording media are required to have good running durability as described above. And in order to obtain running durability,
Abrasives and lubricants usually play an important role.

However, in order to obtain excellent running durability with abrasives, it is necessary to increase the amount added to some extent.
Therefore, the content of ferromagnetic powder decreases. Further, when an abrasive having a large particle size is used to obtain excellent running durability, the abrasive tends to protrude excessively from the surface of the magnetic layer. Therefore, improvement of running durability using an abrasive material often causes a problem in that the above-mentioned electromagnetic conversion characteristics deteriorate.

Even when the running durability is improved by using a lubricant, it is necessary to increase the amount of the lubricant added, which tends to make the binder more likely to be plasticized and reduce the durability of the magnetic layer.

Another method for improving the running durability is to use a hard binder to increase the hardness of the magnetic layer.

However, as a negative effect of increasing the hardness of the magnetic layer,
The problem is that the magnetic layer becomes more brittle and more easily damaged, resulting in dropouts due to contact with the magnetic head, deterioration of still characteristics, and insufficient improvement in running durability. There is.

Therefore, a magnetic recording medium with sufficiently excellent running durability, such as less occurrence of dropouts and good still characteristics, has not yet been obtained.

[Objective of the Invention] An object of the present invention is to provide a magnetic recording medium with less occurrence of dropouts and good still characteristics, that is, excellent running durability.

[Summary of the Invention] The present invention provides a magnetic recording medium in which a first magnetic layer and a second magnetic layer are provided in this order on the surface of a non-magnetic support, in which the first magnetic layer is made of a vinyl chloride copolymer as a binder. and a vinyl chloride copolymer containing a polyurethane resin with a number average molecular weight of less than 25,000, the second magnetic layer of which has three or more organic groups having active hydrogen as a binder per molecule, and a polyisocyanate. A magnetic recording medium comprising:

Preferred embodiments of the magnetic recording medium of the present invention are as follows.

1) The magnetic recording medium described above, wherein the second magnetic layer contains a polyurethane resin as a binder in addition to a vinyl chloride copolymer, and the polyurethane resin has a number average molecular weight of 25,000 or more.

2) The magnetic recording medium described above, wherein the polyurethane resin contained in the first magnetic layer has a glass transition temperature of less than 0°C.

3) The second magnetic layer contains a polyurethane resin in addition to a vinyl chloride copolymer as a binder, and the glass transition temperature of the polyurethane resin contained in the second magnetic layer is 0°C or higher. The above magnetic recording medium.

4) The magnetic recording medium described above, wherein the organic group having active hydrogen is at least one selected from the group consisting of -0H1-NH2 and -Nl(R (R is an alkyl group).

5) The magnetic recording medium as described above, characterized in that the second magnetic layer contains a polyurethane resin containing three or more organic groups having active hydrogen per molecule.

[Effects of the Invention] As shown above, the present invention provides a magnetic recording medium having at least two magnetic layers, wherein the second magnetic layer contains polyisocyanate and a vinyl chloride copolymer, and This vinyl chloride copolymer has three or more organic groups having active hydrogen per molecule in order to increase the crosslinking density of the second magnetic layer.

In this way, vinyl chloride copolymers that have organic groups with three or more active hydrogens per molecule have high reactivity with polyisocyanates, so there is almost no vinyl chloride copolymer that does not participate in crosslinking. Since the reaction (crosslinking) with the polyisocyanate progresses to a certain extent, the second magnetic layer becomes an extremely strong magnetic layer. This makes it possible to obtain a magnetic recording medium with less occurrence of dropouts and good still characteristics, that is, excellent running durability.

In addition, the first magnetic layer, which is the lower layer, has a binder that has a number average molecular weight of less than 25,000 (preferably a glass transition temperature of 0).
By using a polyurethane-based resin with a temperature of less than 10.degree.

[Detailed Description of the Invention] The magnetic recording medium of the present invention basically has a structure in which at least two magnetic layers containing ferromagnetic powder dispersed in a binder are provided on a non-magnetic support. have

Non-magnetic supports that can be used in the present invention include:
Polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyamide, and polyamideimide. , films or sheets made of synthetic resin such as polyimide: non-magnetic metal foils such as aluminum and copper; metal foils such as stainless steel foils; paper, ceramic sheets, etc.

The thickness of these supports ranges from 2.5 to 100 μm, preferably from 3 to 80 μm.

The magnetic recording medium of the present invention includes a vinyl chloride copolymer as a binder and a number average molecular weight of 25,000 in the first magnetic layer.
The second magnetic layer contains a vinyl chloride copolymer and a polyisocyanate. The vinyl chloride copolymer contained in the second magnetic layer is characterized in that it has three or more organic groups having active hydrogen per molecule.

The second magnetic layer of the present invention contains a polyisocyanate and a vinyl chloride copolymer, and the vinyl chloride copolymer contains an organic group having active hydrogen per molecule in order to increase the crosslinking density of the second magnetic layer. They have three or more. In this way, vinyl chloride copolymers that have organic groups with three or more active hydrogens per molecule have high reactivity with polyisocyanates, so there is almost no vinyl chloride copolymer that does not participate in crosslinking. Since the reaction (crosslinking) with the polyisocyanate progresses to a certain extent, the second magnetic layer becomes an extremely strong magnetic layer. As a result, a magnetic recording medium with less occurrence of dropouts and good still characteristics can be obtained.

The organic group having active hydrogen is -0H1-SH
, -NH2, =NH, -C3NH2, -C3NHR1-
C(=NH)OH1-C(=NH)NHCONH2-N
HNH2, -CONHNH2, -NRNH2%-NHN
HR1=NNH2, -N-NHR, -NHCONH2,
-NHCONHRl-NHCSNH2, -NHCONH
2,-NHCSNH,,-NRCONH2,-NHC
(=NR)NH2, -NHC(=NH)NHR
, biguanidine, biuret (wherein R is an alkyl group), and the like. Preferably -0H1-
NH, and -NHR. One kind of these functional groups may be contained in the polyurethane resin molecule, or two or more kinds thereof may be contained in the polyurethane resin molecule.

In the first magnetic layer of the present invention, it is preferable that the polyurethane resin used has a relatively low molecular weight so that the dispersion part of the ferromagnetic powder and the smoothness of the magnetic layer surface are improved, and the running durability is improved. It is preferable to have a low molecular weight and be flexible from the viewpoint of ease of use.

Therefore, in order to make the first magnetic layer flexible as described above, it is necessary to use a polyurethane resin in addition to the vinyl chloride copolymer as a binder, and the number of It is required that the average molecular weight is less than 25,000.

More preferably, the glass transition temperature is less than 0°C. This improves the adhesion of the magnetic layer to the non-magnetic support, thereby improving durability such as running durability.

Also, in the second magnetic layer of the present invention, it is preferable to use a polyurethane resin as a binder in order to make the magnetic layer even stronger. The polyurethane resin contained in the second magnetic layer preferably has a number average molecular weight of 25,000 or more and a glass transition temperature of 0°C.
It is preferable that it is above. In particular, the polyurethane resin contained in the second magnetic layer preferably has three or more organic groups having active hydrogen per molecule.

As in the present invention, it is a multilayer magnetic recording medium consisting of two magnetic layers, in which a vinyl chloride/vinyl acetate copolymer having active hydrogen, a polyester having two hydroxyl groups, and a polyisocyanate are used as the lower layer, Japanese Patent Laid-Open No. 57-1380 claims that it is possible to provide a magnetic recording medium with less sensitivity unevenness and output fluctuation by sufficiently curing the lower layer.
44 and Japanese Patent Application Laid-open No. 138045/1983. However, although the above invention is the same as the present invention in that it uses a resin containing active hydrogen, the structure is different, and it is used in the upper layer instead of the lower layer, and the purpose is to improve running durability etc. This is qualitatively different from the above-mentioned prior art in that it has improved durability.

Vinyl chloride copolymers that can be used in the present invention include, for example,
Vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinyl acetate/acrylic acid copolymer, vinyl chloride/vinylidene chloride copolymer, vinyl chloride/acrylonitrile copolymer,
Examples include the above-mentioned vinyl chloride copolymers into which polar groups such as hydroxyl group, carboxyl group, phosphoric acid group, phosphoric ester group, -503Na or -5O2Na are introduced.

Further, polyurethane resins that can be used in the present invention include, for example, polyester polyurethane resins, polyether polyurethane resins, hydroxyl groups, carboxyl groups, phosphoric acid groups, phosphate ester groups, -502Na or -5O2Na
Examples include polyurethane resins into which polar groups have been introduced, such as polycarbonate polyurethane resins.

In addition to the above-mentioned vinyl chloride copolymer and polyurethane resin, there are no particular limitations on the binder resin used to form each magnetic layer. Examples include ethylene/vinyl acetate copolymers, cellulose derivatives such as nitrocellulose JFs, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, epoxy resins, and phenoxy resins.

These can be used alone or in combination.

However, the specific vinyl chloride copolymer contained in the first magnetic layer is preferably contained in the binder in an amount of 20% by weight or more, and the specific vinyl chloride copolymer contained in the second magnetic layer is preferably 20% by weight or more. It is preferable that the copolymer is contained in the binder in an amount of 20% by weight or more. If it is less than the above value, the effect of the present invention will not be exhibited.

Further, in the present invention, a polyisocyanate compound is used for the magnetic layer. It is necessary to vibrate the compound in the second magnetic layer, and it is preferable to use it also in the first magnetic layer. The polyisocyanate compound is selected from those commonly used as curing agent components for polyurethane resins and the like. Examples of polyisocyanate compounds include reaction products of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane (e.g., Desmodur L-75 (
Bayer company! ), a reaction product of 3 moles of diisocyanate such as xylylene diisocyanate or hexamethylene diisocyanate and 1 mole of trimethylolpropane, a biuret addition compound of 3 moles of hexamethylene diisocyanate, an isocyanurate compound of 5 moles of tolylene diisocyanate, Range isocyanate 3
Mention may be made of isocyanurate addition compounds of mol and 2 mol of hexamethylene diisocyanate, polymers of isophorone diisocyanate and diphenylmethane diisocyanate.

Further, when performing curing treatment by electron beam irradiation, a compound having a reactive double bond (eg, urethane acrylate) can be used.

As in the present invention, when a polyisocyanate compound is used as a curing agent for a vinyl chloride copolymer (preferably combined with a polyurethane resin) having an organic group having active hydrogen, the vinyl chloride copolymer (preferably used in combination with a polyurethane resin) In addition, the blending weight ratio of polyurethane resin) and polyisocyanate compound is usually 1:0.8 to 1:2 (preferably 1:1).
~1:1.5). By doing so, even when using fine ferromagnetic metal powder with low hardness, it becomes possible to effectively prevent softening of the binder caused by using polyurethane resin.

The total weight of the resin component and curing agent is 100% of the ferromagnetic powder.
It is usually preferably in the range of 5 to 40 parts by weight, more preferably 10 to 20 parts by weight.

Examples of the ferromagnetic powder used in the present invention include γ-Fe2O
Metal oxide-based ferromagnetic powder such as No. 3, dissimilar metal/metal oxide-based ferromagnetic powder such as γ-Fe20) containing other components such as cobalt, and strong magnetic powder such as iron, cobalt or nickel. Examples include fine ferromagnetic metal powders containing magnetic metals.

When using a ferromagnetic metal fine powder, it is a ferromagnetic metal fine powder containing iron, cobalt or nickel, and has a specific surface area of 42 m''/g or more (particularly preferably 45 m''/g).
It is preferable that the powder be ferromagnetic metal fine powder of "7 g or more."

As an example of this ferromagnetic metal fine powder, the metal content in the ferromagnetic metal fine powder is 75% by weight or more, and the metal content is 8% by weight.
0% by weight or more of at least one ferromagnetic metal or alloy (e.g., Fe, Co, Ni, Fe-Co, Fe-Ni
, Co-Ni.

Co-N1-Fe), and other components (e.g., AIL, Si, S, Sc%T
i%V, Cr, Mn%Cu, 2n.

Y%Mo, Rh%Pd%Ag%Sn, Sb, B.

Ba, Ta, W%Re, Au, Hg, Pb, P.

Mention may be made of alloys that may contain (La, Ce, Pr, Nd, Te, Bi). Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide.

Methods for producing these ferromagnetic powders are already known, and the ferromagnetic powder used in the present invention can also be produced according to known methods.

There are no particular restrictions on the shape of the ferromagnetic powder, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used. In particular, it is preferable to use acicular ferromagnetic powder.

The above resin component, curing agent, and ferromagnetic powder are mixed and dispersed together with a solvent (e.g., methyl ethyl ketone, dioxane, cyclohexanone, ethyl acetate) that is normally used in the preparation of magnetic paint to obtain a magnetic paint. Crosstalk dispersion can be performed according to conventional methods.

In addition to the above components, the magnetic paint contains abrasives (e.g. a
-A11202, Cr202), antistatic agents (e.g., carbon black), lubricants (e.g., fatty acids, fatty acid esters, silicone oil), dispersants, and other commonly used additives or fillers (agents). Of course, it is possible.

For coating, a magnetic paint prepared from the above materials is applied onto a non-magnetic support by the following method. First, a coating liquid for the first magnetic layer is prepared by cross-dispersing magnetic layer forming components such as a resin component for the first magnetic layer, a ferromagnetic powder, and a curing agent blended as desired with a solvent. A coating liquid for the second magnetic layer is also prepared in the same manner as for the first magnetic layer.

The method for producing a magnetic recording medium of the present invention includes, for example, applying a coating solution for a first magnetic layer onto the surface of a non-magnetic support under running so that the thickness of the first magnetic layer after drying is preferably 0.1 to 5 μm. While the coated layer is in a wet state, the coating solution for the second magnetic layer is continuously applied on the coated layer so that the layer thickness after drying of the second magnetic layer is 0.1 to 0.1. It is preferable to apply the coating so that the thickness is within the range of 1.5 μm. The method of continuously coating these two layers is, for example, when using an extrusion coater as a coating machine.
It is also possible to apply two extrusion coats in succession so as to sandwich the non-magnetic support running, or the first magnetic layer may be in a wet state (that is, the coating layer still contains solvent and is sticky). It is also possible to install two units with an interval between them within a range that can maintain the condition (indicating 1).

Applicators for applying the above magnetic paint include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat,
reverse roll coat, transfer roll coat,
Gravure coat, kiss coat, cast coat, spray coat, spin cord, etc. can be used. In the present invention, an extrusion coat for simultaneous multilayer coating having two slots as shown in Japanese Patent Application No. 62-124631 is desirable.

The second magnetic layer obtained by using the above manufacturing method has a uniform layer thickness even if it is an extremely thin magnetic layer of 1.5 μm or less, and is coated with an extremely smooth surface. be able to. Thereby, it is possible to manufacture the magnetic recording medium of the present invention which has excellent running durability and does not impair electromagnetic conversion characteristics.

The coating layer of the above-mentioned magnetic paint is coated with the thickness of the magnetic layer of the obtained magnetic recording medium (the total layer J''X of the first magnetic layer and the second magnetic layer).
) is usually within the range of 0.5 to 10 μm.

A backing layer may be provided on the surface of the nonmagnetic support used in the present invention that is not coated with the magnetic paint. Normally, the back layer is formed by applying a back layer forming paint made of particulate components such as abrasives and antistatic agents and a binder dispersed in an organic solvent to the side of the non-magnetic support that is not coated with the magnetic paint. It is a layer provided.

Note that an adhesive layer may be attached to the surface of the nonmagnetic support on which the magnetic paint and the back layer forming paint are applied.

Usually, the coated layer of magnetic paint is dried after being subjected to a treatment for orienting the ferromagnetic powder contained in the coated layer of magnetic paint, that is, a magnetic field orientation treatment.

After being dried in this manner, the coated layer is subjected to surface smoothing treatment. For example, a super calender roll is used for the surface smoothing process. By performing the surface smoothing treatment, the pores generated by the removal of the solvent during drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer increases, making it possible to obtain a magnetic recording medium with high electromagnetic conversion characteristics. can.

The thus cured laminate is then cut into a desired shape.

The cutting can be carried out under normal conditions using a normal cutting machine such as a slitter.

Although the magnetic recording medium of the present invention has been described as having an upper and lower two-layer system, it may have three or more layers as a whole as long as it maintains the above specified properties and includes two magnetic layers.

In the following, the present invention will be explained in more detail with reference to Examples and Comparative Examples. On each side, "r parts" means "parts by weight" unless otherwise specified.

- [Example 1] First magnetic layer coating liquid Co-Y-Fe202 100 parts [11
c:6500e.

5IIET specific surface area=35rIf/g]・Vinyl chloride・
Vinyl acetate/12 parts maleic acid combination (composition ratio: 86:I:1:1, degree of polymerization 350) Polyester polyurethane resin 1 finger 6 parts (Mn = 23000.Tg = -5°C) Carbon black 8 parts Butyl steer Rate 1 part stearic acid
2-part butyl acetate
200 copies 6. Crushed t-Co-y-Fe202 100 parts [+Ic
Near 00 0e.

5UET specific surface area: 40 b/g] Vinyl chloride/vinyl acetate/10 parts maleic acid/vinyl alcohol copolymer composition ratio: 85:1
0:l:4゜-011:18 pieces/molecule, degree of polymerization 400) Polyester polyurethane resin 7 parts (Mn = 2800
0. Tg-3°C.

-OH: 3 pieces/molecule) Polyisocyanate 5 parts (Coronated, manufactured by Nippon Polyurethane) Carbon black
Part 3 α-AIL, o,
5 parts (average particle size: 0.6 μm) Butyl stearate 1 part stearic acid 2 parts butyl acetate
200 parts of each of the above two molding materials were cross-dispersed using a sand mill. 6 parts of polyisocyanate (coronated above) and 40 parts of butyl acetate were added to the resulting dispersion, and 1 μm
A coating solution for forming the first magnetic layer and a coating solution for forming the second magnetic layer were prepared by filtration using a filter having an average pore size of .

The coating solutions for forming the first and second magnetic layers were applied in the following manner using an extrusion coat for simultaneous multilayering having a slot for coating the first magnetic layer and a slot for coating the second magnetic layer.

The obtained coating liquid for the first magnetic layer has a thickness of 3.5 mm after drying.
While running a polyethylene terephthalate support with a thickness of 14 μm at a speed of 60 m/min,
Coat the surface of the support using an extrusion coater having slots for coating the first magnetic layer, and immediately thereafter (while the first magnetic layer is still wet) apply the coating solution for the second magnetic layer to the thickness after drying. is 0
．． The second magnetic layer was coated to a thickness of 5 μm using an extrusion coater having slots for coating, and while the magnetic layer was still wet, it was oriented using the above magnet, and after drying, supercalendering was carried out to give one portion 2 inches wide. was slit to produce videotape.

[Example 2] In Example 1, the vinyl chloride/vinyl acetate/maleic acid/vinyl alcohol copolymer in the coating solution for the second magnetic layer was mixed (composition ratio: 85:10:l:4.-011+18 pieces/ Molecules) from (composition ratio: 88:10:l:1.
A videotape was produced in the same manner as in Example 1, except that OH: 4 pieces/molecule) was used.

[Example 3] In Example 1, vinyl chloride/vinyl acetate/maleic acid/vinyl alcohol copolymer (composition ratio: 85:10:l:4.-011:18 pieces) in the coating solution for the second magnetic layer /
A videotape was produced in the same manner as in Example 1, except that an amino acid-containing vinyl chloride/vinyl acetate copolymer (-Nil, 3 pieces/molecule) was used instead of the amino acid-containing vinyl chloride/vinyl acetate copolymer (-Nil).

[Comparative Example 1] In Example 1, vinyl chloride/vinyl acetate/maleic acid/vinyl alcohol copolymer (composition ratio: 85:10:1:4.-18 leaves) in the coating solution for the second magnetic layer / minute,
A videotape was produced in the same manner as in Example 1, except that a vinyl chloride/vinyl acetate/maleic acid copolymer (composition ratio: 87:12:1, no organic group having active hydrogen) was used instead of Manufactured.

[Comparative Example 2] In Example 1, the polyester polyurethane resin in the coating liquid for the second magnetic layer was (Mn=2:1000.Tg-
-5℃) (Mn= 28000.Tg--5
A videotape was produced in the same manner as in Example 1, except that the temperature was changed to (°C).

Table 1 shows the physical properties of the video tapes obtained in Examples 1 to 3 and Comparative Examples 1 to 2, measured by the following measuring method.

Masahiro Naodada (1) A constant video signal was recorded on a videotape obtained using a still durable VHS video tape recorder (NV-8200 [manufactured by Matsushita Electric Industrial Co., Ltd.]), and the reproduced still images were clear. The time until it was lost was measured.

(Measurements were made at 5°C and 80% RH.) (2) Number of clogging times above Vt (Using an S video tape recorder, a constant video signal was recorded on the obtained videotape, and The vehicle was run repeatedly T10 times, and the number of times the output decreased by 3 dB or more during the run was determined.

(Measurements were made at 5°C and 30% RH.) (3) Adhesive force between nonmagnetic support and magnetic layer Width 1/2 inch, length 5
The force required for 180 degree peeling was measured using a cm videotape, and this was taken as the adhesive force.

Below is the margin Table 1 Active hydrogen Clogging Still Adhesive strength Organic group Number of times Durability (pieces/molecule) (minutes) (g) Example 1
-01l(+8) 0 60<98 Example 2
-011(4) 0 60< 95 Example 3
-Nil 2(3) 0 60 < 96 Comparative Example 1 %Si 20 1 90 Comparative Example 2 -01
l(+8) 2 40 25 As is clear from Table 1 above, the first magnetic layer contains a vinyl chloride copolymer and a polyurethane resin with a number average molecular weight of less than 25,000, and the second magnetic layer contains active hydrogen. The magnetic recording medium of the present invention using a vinyl chloride/vinyl acetate copolymer having three or more 4T organic groups in one molecule has good clogging frequency, still durability, and adhesive strength of the magnetic layer. It can be seen that durability such as running durability is excellent.

On the other hand, conventional magnetic recording media that use vinyl chloride/vinyl acetate copolymers that do not have active hydrogen have poor performance as described above (Comparative Example 1); Even if a polymer is used, if the number average molecular weight of the polyurethane resin contained in the first magnetic layer is 25,000 or more, still durability and adhesive strength are poor (Comparative Example 2)
I understand that.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a first magnetic layer and a second magnetic layer provided in this order on the surface of a non-magnetic support, wherein the first magnetic layer contains a vinyl chloride copolymer and a vinyl chloride copolymer as a binder. Contains a polyurethane resin with a number average molecular weight of less than 25,000, the second magnetic layer contains a vinyl chloride copolymer having three or more organic groups having active hydrogen as a binder per molecule, and polyisocyanate. A magnetic recording medium characterized by the following.