JP2568753B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a coated magnetic tape or a magnetic disk using a ferromagnetic metal powder as a magnetic powder.

2. Description of the Related Art In recent years, in particular, the demand for high-density recording has increased, and in magnetic recording media such as magnetic tapes and magnetic disks used for video, audio equipment, computers and the like, the recording wavelength and track width have been reduced, the magnetic layer and support have been reduced. It is becoming indispensable to realize a thin body.

Therefore, the coercive force (Hc) of the magnetic layer and the residual magnetic flux density (B
r) can be increased, and ferromagnetic metal powders suitable for improving reproduction output in a short wavelength region have been adopted.

However, the ferromagnetic metal powder has a larger saturation magnetization (σ _s ) and a tendency to become finer than conventional oxide-based magnetic powder, so that an agglomerated structure is easily formed in the magnetic paint. In addition, the orientation of the magnetic powder becomes insufficient, the surface properties and mechanical strength of the magnetic layer deteriorate, and it becomes difficult to obtain a high level of electromagnetic conversion characteristics and durability.

Furthermore, the use environment of magnetic recording media is expected to be wider and harsher than ever due to the portable magnetic recording / reproducing device and the spread of the camera body type. Improving is a very important issue.

Therefore, conventionally, for the purpose of improving the dispersibility of the ferromagnetic metal powder, a surfactant has been used as a dispersant and disclosed in JP-A-61-158023 and JP-A-2-35621. -SO ₃ M, -OSO
There has been proposed a method of introducing a polar group such as ₃ M, -COOM, -PO (OM) ₂ (where M is a hydrogen atom or an alkali metal).

Further, in order to improve the durability of the magnetic layer, Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent No. 111325, specifying the mechanical strength (tensile strength, elongation at break) of the binder,
As disclosed in JP-A-60-59522, a method of specifying the molecular weight (Mn) of a binder and further introducing a large number of hard segments such as aromatic rings as a skeleton component of the binder. Has been proposed.

Problems to be Solved by the Invention However, using the conventional method, the dispersibility of the ferromagnetic metal powder is improved, and the surface properties and mechanical strength of the magnetic layer are improved. It is very difficult to provide a magnetic recording medium having high durability and various problems.

For example, the concentration of the polar group introduced into the binder or the amount of the surfactant is determined by the specific surface area of the ferromagnetic metal powder,
The shape, the magnitude of the saturation magnetization (σ _s ), and the like must be determined in full consideration. If the concentration of the polar group is excessively increased, the binder is gelled due to strong interaction between the polar groups, and the amount of the binder adsorbed on the surface of the magnetic powder is reduced, and the dispersibility of the magnetic powder is deteriorated. Further, when the concentration of the polar group is high with respect to the amount of the binder used, there is a possibility that interparticle crosslinking is formed. In addition, these phenomena are not preferable from the viewpoint of workability at the time of paint production and smoothing property at the time of coating. Conversely, when the concentration of the polar group is low, the amount of the binder adsorbed on the magnetic powder decreases, and the dispersibility of the magnetic powder deteriorates.

Furthermore, in order to improve the filling ratio of the magnetic powder in the magnetic layer, the magnetic powder is finely divided, and the specific surface area tends to increase. The amount of the specific adsorption binder contributing to the property is reduced, and as a result, it becomes difficult to improve the surface properties of the magnetic layer. Therefore, in the method of improving the calendering property simply by increasing the amount of the binder used, the excess loss of the binder on the surface of the magnetic layer increases the spacing loss between the tape and the head, and consequently increases the electromagnetic wave. Conversion characteristics will be degraded.

In addition, in order to improve the durability of the magnetic layer, simply specifying the individual properties of the binder is not enough because of the difference in the reaction rate of the binder with the cross-linking agent or the difference in the adsorption ability to the magnetic powder surface. In many cases, such effects cannot be obtained. In particular, in the method of introducing a large number of hard segments such as aromatic rings as the skeleton component of the binder, the glass transition temperature (Tg) of the binder increases, and the calendering property deteriorates. Not only cannot a smooth magnetic layer surface be obtained,
As the reactivity with the cross-linking agent also deteriorates, calender adhesion tends to occur due to the effect of unreacted isocyanate groups (-NCO groups) and hydroxyl groups (-OH groups) remaining in a large amount in the magnetic layer. , Dropout and the like.

The present invention has been made in view of the above problems, and has as its object to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and durability.

Means for Solving the Problems To solve the above problems, the magnetic recording medium of the present invention is
The average value of the glass transition temperature (Tg) of the binder used (weighted according to the blending amount and the averaged glass transition temperature) is 30 to 45 (° C), ferromagnetic metal powder, abrasive, carbon black The ratio of the binder adsorbed on the binder (adsorbed binder) to the binder not adsorbed (non-adsorbed binder) is 1 ± 0.2.
The inclusion of 2 parts by weight is an essential requirement.

The magnetic recording medium of the present invention has the above-described structure, and the surface of the powder particles is uniformly formed with the minimum necessary binder effective for dispersing the powder particles in the magnetic layer such as ferromagnetic metal powder, abrasive, and carbon black. Can be coated. As a result, entanglement (gelling) between polar groups of the binder does not occur, and cross-linking between particles is not formed, so that the dispersion stability of the powder particles can be improved. In addition, the workability at the time of paint production and the smoothing property at the time of coating can be improved. Furthermore, the ferromagnetic metal powder, the abrasive, the non-adsorbed binder not adsorbed and fixed on the surface of carbon black can be increased in an appropriate amount, and the average value of the glass transition temperature (Tg) of the binder is set to be appropriately low. Therefore, the calendering property at a relatively low temperature is improved, the surface property of the magnetic layer is improved, and excellent electromagnetic conversion characteristics can be obtained. In addition, the reactivity with the cross-linking agent is also improved, and a magnetic recording medium having excellent durability can be obtained without causing calendar adhesion which causes dropout.

Embodiment Hereinafter, a magnetic recording medium according to an embodiment of the present invention will be described with reference to the drawings.

As the ferromagnetic metal powder used in the present invention, Fe, F
Needle-like metal powders such as e-Co and Fe-Co-Ni can be mentioned. Further, in consideration of weather resistance, prevention of sintering at the time of production, and the like, a needle-like metal powder containing a small amount of an additional metal such as Al, Cr, or Si can be used.

As the binder, vinyl chloride resin, vinyl chloride-
Vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylic copolymer, polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer, epoxy Resin, polyvinyl acetal resin, polyvinyl butyral resin and the like can be used.

In addition, each part number of the material described in the examples and the comparative examples is the number of parts by weight when the ferromagnetic metal powder is 100.

(Example 1) Ferromagnetic metal powder 100 parts (average major axis diameter 0.17 μm, average axis ratio 1:10, specific surface area 50 m ² / g, saturation magnetization 125 emu / g) Vinyl chloride resin (PVC) 9 parts [Zeon Corporation, MR-110 glass transition temperature 59 ° C] Polyurethane resin (PU) ... 5 parts [Toyobo Co., Ltd., AM-63 glass transition temperature 21 ° C] Polyurethane resin (PU) 4 parts [Nippon Polyurethane Industry Co., Ltd., RM-3 glass transition temperature 5 ° C] Abrasives 7 parts [Sumitomo Chemical Industries, Ltd., AKP-50] Carbon black 2 parts [Tokai Carbon (Ltd., Seist S) Lubricant ... 4 parts Stearic acid ... 2 parts Myristic acid ... 1 part-n-butyl stearate ... 1 part Crosslinking agent ... 4 parts [Nippon Polyurethane Industry Co., Ltd. , Coronate L] Mixed solvent 300 parts (MEK / toluene / cyclohexanone = 3/2/1) First, ferromagnetic metal powder and carbon black were put in a planetary mixer (PLM) under a nitrogen atmosphere (O ₂ concentration: 2% or less), wetted with 10 parts of a mixed solvent, and then vinyl chloride resin. (PV
C), polyurethane resin (PU), polyurethane resin (P
U) and 45 parts of a mixed solvent are added, and kneading is performed for 10 hours. Next, an abrasive and 180 parts of a mixed solvent were added, and the mixture was dispersed by a sand mill to obtain a magnetic coating stock solution. Further, a lubricant, a crosslinking agent and 50 parts of a mixed solvent were added, and mixed and stirred with a dissolver to prepare a magnetic paint. Then, a filter having an average pore size of 0.4 μm (HT-4 manufactured by Nippon Roki Co., Ltd.)
The coating material filtered by 0) was applied on a 10 μm-thick polyethylene terephthalate (PET), and subjected to orientation, drying, and mirror finishing using a super calender. After further curing treatment, a back coat layer mainly composed of carbon black was provided on polyethylene terephthalate on the opposite side of the magnetic layer, and slit to an 8 mm width to prepare an 8 mm VTR metal tape.

The average value of the glass transition temperature (Tg) of the binder used here is 36.4 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(59 × 9) + (21 × 5) + (5 × 4)} / (18) = 3
6.4 In this case, the ratio of the binder (adsorbed binder) adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black to the binder not adsorbed (non-adsorbed binder) is as follows:
It was 0.87.

(Example 2) Instead of the binder in Example 1, vinyl chloride resin (PVC) ... 10 parts [manufactured by Zeon Corporation, MR-110 glass transition temperature 59 ° C] Polyurethane resin (PU) ... 6 Part [Nippon Polyurethane Industry Co., Ltd., RM-3 glass transition temperature 5 ° C] Polyurethane resin (PU) 4 parts [Nippon Polyurethane Industry Co., Ltd., R-104 glass transition temperature 11 ° C] In the same manner as in Example 1, an 8 mm VTR
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 33.2 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(59 × 10) + (5 × 6) + (11 × 4)} / (20) = 3
3.2 In this case, the ratio between the binder adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black (adsorbed binder) and the binder not adsorbed (non-adsorbed binder) is
1.07.

(Example 3) Instead of the binder in Example 1, a vinyl chloride-acrylic copolymer ... 10 parts [Eslek E glass transition temperature, manufactured by Sekisui Chemical Co., Ltd.]
60 ° C] Polyurethane resin (PU) 5 parts [Toyobo Co., Ltd., AM-97 glass transition temperature 32 ° C] Polyurethane resin (PU) 4 parts [Toyobo Co., Ltd., UR-8700 glass Transition temperature −23 ° C.] except that 8 mm VTR was used in the same manner as in Example 1.
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 35.2 (° C.). This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(60 × 10) + (32 × 5) + (− 23 × 4)} / (19) = 35.2 In this case, the binder adsorbed on the ferromagnetic metal powder, the abrasive, and the carbon black (adsorbed binder) The ratio with the non-adsorbed binder (non-adsorbed binder) is
0.98.

(Comparative Example 1) Instead of the binder used in Example 1, vinyl chloride resin (PVC) ... 13 parts [manufactured by Zeon Corporation, MR-110 glass transition temperature 59 ° C] Polyurethane resin (PU) ... 5 Part [Nippon Polyurethane Industry Co., Ltd., RM-3 glass transition temperature 5 ° C] Polyurethane resin (PU) ... 1 part [Nippon Polyurethane Industry Co., Ltd., R-104 glass transition temperature 11 ° C] In the same manner as in Example 1, an 8 mm VTR
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 42.2 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(59 × 13) + (5 × 5) + (11 × 1)} / (19) = 4
2.2 In this case, the ratio of the binder (adsorbed binder) adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black to the binder not adsorbed (non-adsorbed binder) is 1.
It was 35.

(Comparative Example 2) Instead of the binder in Example 1, vinyl chloride resin (PVC) 8 parts [manufactured by Nippon Zeon Co., Ltd., glass transition temperature 59 ° C] Polyurethane resin (PU) 8 Part [Toyobo Co., Ltd., AM-63 glass transition temperature 21 ° C] Polyurethane resin (PU) 5 parts [Nippon Polyurethane Industry Co., Ltd., R-104 glass transition temperature 11 ° C] By the same method as in the first embodiment, an 8 mm VTR
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 33.1 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(59 × 8) + (21 × 8) + (11 × 5)} / (21) = 3
3.1 In this case, the ratio of the binder (adsorbed binder) adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black to the binder not adsorbed (non-adsorbed binder) is
It was 0.74.

(Comparative Example 3) Instead of the binder in Example 1, vinyl chloride resin (PVC) 10 parts [manufactured by Zeon Corporation, glass transition temperature 59 ° C] Polyurethane resin (PU) 5 Part [Toyobo Co., Ltd., UR-8200 glass transition temperature 79 ° C] Polyurethane resin (PU) 4 parts [Nippon Polyurethane Industry Co., Ltd., RM-3 glass transition temperature 5 ° C] By the same method as in the first embodiment, an 8 mm VTR
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 52.9 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(59 × 10) + (79 × 5) + (5 × 4)} / (19) = 5
2.9 In this case, the ratio of the binder (adsorbed binder) adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black to the binder not adsorbed (non-adsorbed binder) is as follows:
It was 1.18.

(Comparative Example 4) Instead of the binder in Example 1, vinyl chloride-acrylic copolymer ... 11 parts [Slec E glass transition temperature, manufactured by Sekisui Chemical Co., Ltd.]
60 ° C] Polyurethane resin (PU) 5 parts [T-5206 glass transition temperature -25 ° C, manufactured by Dainippon Ink and Chemicals, Inc.] Polyurethane resin (PU) 4 parts [Manufactured by Nippon Polyurethane Industry Co., Ltd.] , RM-3 glass transition temperature 5 ° C], except that 8 mm VTR was used.
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 27.8 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (the number of polymerization parts) as shown in the following formula.

{(60 × 11) + (− 25 × 5) + (5 × 4)} / (20) =
27.8 In this case, the ratio of the binder (adsorbed binder) adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black to the binder not adsorbed (non-adsorbed binder) is
It was 0.77.

(Comparative Example 5) Instead of the binder in Example 1, vinyl chloride-acrylic copolymer ... 10 parts [Slek E glass transition temperature, manufactured by Sekisui Chemical Co., Ltd.]
60 ° C] Polyurethane resin (PU) 8 parts [Toyobo Co., Ltd., AM-97 glass transition temperature 32 ° C] Polyurethane resin (PU) 5 parts [Dainippon Ink & Chemicals, T −5206 glass transition temperature −25 ° C.] except that 8 mm VTR was used in the same manner as in Example 1.
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 31.8 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (parts by weight) as shown in the following formula.

{(60 × 10) + (32 × 8) + (− 25 × 5)} / (23) = 31.8 In this case, the binder (adsorbing binder) adsorbing on the ferromagnetic metal powder, abrasive, and carbon black The ratio with the non-adsorbed binder (non-adsorbed binder) is
It was 0.84.

(Comparative Example 6) Instead of the binder in Example 1, vinyl chloride resin (PVC) ... 9 parts [manufactured by Zeon Corporation, MR-110 glass transition temperature 59 ° C] Polyurethane resin (PU) ... 3 Part [Toyobo Co., Ltd., AM-97 glass transition temperature 32 ° C] Polyurethane resin (PU)… 3 parts Except for using [Toyobo Co., Ltd., AM-63 glass transition temperature 21 ° C] By the same method as in Example 1, 8mm VTR
Made metal tape for use.

The average value of the glass transition temperature (Tg) of the binder used here is 46.0 (° C.).

This value is an averaged glass transition temperature weighted by the blending amount (the number of polymerization parts) as shown in the following formula.

{(59 × 9) + (32 × 3) + (21 × 3)} / (15) = 4
6.0 In this case, the ratio of the binder adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black (adsorbed binder) to the binder not adsorbed (non-adsorbed binder) is
0.96.

The calculation method of the ratio between the binder adsorbed on the ferromagnetic metal powder, the abrasive and the carbon black (adsorbed binder) and the binder not adsorbed (non-adsorbed binder) will be described below.

In a 50 ml plastic container, 10 g of the magnetic paint prepared in each of Examples and Comparative Examples and a mixed solvent (MEK / toluene / cyclohexanone = 3/2/1) are charged (at this time, the solid content concentration of the paint was reduced to 10%). Set.), Shake for 15 minutes using Shaker. Thereafter, the diluted paint was centrifuged (4 × 10 ³ r
Perform for 30 minutes under pm conditions. ) Furthermore, the supernatant liquid after centrifugation was collected in a centrifuge tube, and subjected to high-speed centrifugation (2 × 10 ⁴ r).
Perform for 2 hours under pm conditions. ). 10 ml of the supernatant after high-speed centrifugation is collected in an aluminum cup, and the weight is measured. Next, the supernatant is evaporated to dryness on a hot plate, and the weight is measured again. From the above operation,
The amount of binder (non-adsorbed binder) in the supernatant can be calculated, and the amount of binder obtained by subtracting the amount of binder in this supernatant (non-adsorbed binder) from the total amount of binder (combined binder) is the ferromagnetic metal powder. , Abrasive, and the amount of binder adsorbed on carbon black (adsorbed binder amount). Based on the above results, the ratio between the adsorbed binder and the non-adsorbed binder can be determined.

The following measurements were performed on each of the 8 mm VTR metal tapes obtained in the above Examples and Comparative Examples.

(1) Surface roughness WYKO's non-contact three-dimensional surface roughness meter (TOPO-3D)
The measurement was performed using. At this time, as a method of indicating the surface roughness of the magnetic layer, RMS, which is the square root of the value obtained by integrating the square of the deviation from the center line to the roughness curve in the section of the measurement length and averaging the value in the section, was adopted.

(2) C / N (5.0MHz / 4.5MHz) 5.0MHz signal and 4.
The noise ratio at 5 MHz was measured. 8mm VTR for C / N measurement
MVS-5000 (manufactured by KODAK) was used. The recording / reproducing head uses an amorphous alloy.
The C / N of the metal tape for mVTR is shown as a relative value with reference (OdB).

(3) Dropout Using the same 8 mm VTR as for C / N measurement, run 200 passes of each videotape sample in an environment of 40 ° C-80% RH (durability test). For each videotape sample before and after the durability test,
The number per minute at which an output reduction of 16 dB or more occurred over 15 μs was measured.

(4) Head Powder Adhesion The amount of powder adhesion on the magnetic head and the cylinder after the durability test according to the above (3) was observed with a microscope, and the degree of powder adhesion was evaluated on a five-point scale. As the evaluation, 5 was evaluated as having no powder adhesion and having no practical problem at all, and 1 was evaluated as having a large amount of powder adhesion and having a practical problem.

(5) Still life Using an 8 mm VTR modified for still measurement, a still image recorded in advance was reproduced at -10 ° C and a load of 30 g, and the time until the image signal dropped by 6 dB was shown.
Table 1 shows the evaluation results of the 8 mm VTR metal tapes prepared in the examples and comparative examples. FIG. 1 shows the binder in the magnetic paint prepared in each of Examples and Comparative Examples.
Ratio of binder (adsorbed binder) adsorbed to ferromagnetic metal powder, abrasive, carbon black and non-adsorbed binder (specifically adsorbed binder), and magnetic layer surface roughness of 8mm VTR metal tape made using each of the above paints The relationship with RMS was shown. In the drawing, black circles indicate Examples 1 to 3.
, And white circles represent Comparative Examples 1 to 6.

As is clear from Table 1, Examples 1, 2 and 3 were obtained because the average value of the glass transition temperature of the binder, the ratio of the amount of the adsorbed binder to the amount of the non-adsorbed binder, and the number of parts by weight of the binder were appropriate. , The magnetic layer surface becomes smooth and C / N
Was high. As for durability, the amount of powder adhering to the head cylinder after the durability test was small and the still life was long. Furthermore, the dropout was reduced both in the initial stage and after the durability test.

FIG. 1 also shows that the magnetic layer surface roughness RMS is greatly affected by the ratio of the amount of adsorbed binder to the amount of non-adsorbed binder.

In Comparative Example 1, since the ratio of the amount of the adsorbed binder to the specific amount of the adsorbed binder was large, that is, the amount of the non-adsorbed binder contributing to the calendering property was small, the surface roughness of the magnetic layer was extremely poor, and the C / N was considerably low. Value. In Comparative Examples 2 and 4, conversely, since the ratio between the amount of the adsorbed binder and the amount of the non-adsorbed binder was small, the calendering property was improved, and the surface roughness of the magnetic layer was also good. Since the dispersibility of the powder particles in the magnetic layer such as black was poor (the amount of binder adsorbed on the surface of the powder particles was small), the C / N was low. In particular, in the case of Comparative Example 4, since the average value of the glass transition temperature (Tg) of the binder was low,
The durability such as the amount of powder adhered and the still life was significantly deteriorated (dropout after the durability test also increased abnormally). In Comparative Example 3, since the average value of the glass transition temperature (Tg) of the binder was too high, the calendering property was poor, the surface roughness of the magnetic layer was poor, and the C / N was low.
In Comparative Example 5, since the amount of the binder added was large, excess binder was present on the surface of the magnetic layer. As a result, the spacing loss between the tape and the head was increased, and the C / N was reduced. In Comparative Example 6, on the contrary, since the amount of the binder added was small, the dispersibility of the powder particles in the magnetic layer such as the magnetic powder, the abrasive, and the carbon black was deteriorated, and the amount of the binder contributing to the calendering property was also reduced. , C / N decreased. Further, regarding the durability, since the surface of the powder particles could not be sufficiently covered with the binder, the mechanical strength of the magnetic coating film was reduced, powder adhesion was increased, and the still life was shortened.

In the above embodiment, only the metal tape for 8 mm VTR has been described. However, the present invention can be similarly applied to other coating type magnetic tapes and magnetic disks using ferromagnetic metal powder.

Advantages of the Invention As is clear from the above description of the embodiments, according to the magnetic recording medium of the present invention, the average value of the glass transition temperature (Tg) of the binder (weighted by the blending amount and averaged glass transition temperature) ) Is 30 to 45 (° C.), and ferromagnetic metal powder,
The ratio of the binder adsorbed on the abrasive and the carbon black (adsorbed binder) to the binder not adsorbed (non-adsorbed binder) is 1 ± 0.2, and the amount of the binder added is 16 parts by weight based on 100 parts by weight of the ferromagnetic metal powder. With a configuration of about 22 parts by weight, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and durability.

[Brief description of the drawings]

FIG. 1 shows a binder (adsorbing binder) adsorbed on a ferromagnetic metal powder, an abrasive, and carbon black, among binders in a magnetic paint prepared for magnetic recording media of Examples and Comparative Examples of the present invention. 8m made using each of the above magnetic paint
4 is a graph showing a relationship between a magnetic layer surface roughness RMS value of an mVTR metal tape.

Claims (2)

(57) [Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic paint containing a ferromagnetic metal powder, an abrasive, carbon black, and a binder to form a magnetic layer, wherein the binder has a glass transition temperature. The average value weighted by the blending amount of (Tg) is 30 to 45 ° C., and the ratio of the binder adsorbed on the ferromagnetic metal powder, the abrasive, and the carbon block to the binder not adsorbed is 1 ± 0.2. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the binder is contained in an amount of 16 to 22 parts by weight based on 100 parts by weight of the ferromagnetic metal powder.