JP4654757B2 - Magnetic recording medium - Google Patents

Description

  The present invention relates to a tape-like magnetic recording medium corresponding to a data backup system for linearly recording / reproducing digital data.

  In recent years, in the field of magnetic recording media, with the rapid development of IT, the data capacity has been increasing and the importance of data to be handled has increased. Accordingly, there is a growing need for data storage products compatible with such systems, such as large capacity, high-speed data transfer, and high reliability.

By the way, as a data storage system using a magnetic tape, a so-called linear storage system in which the tape is passed around the magnetic head portion without being wound when loading and recording / reproducing at the first part of the magnetic tape. Is widely used.
In order to achieve the above-described increase in capacity with respect to a magnetic tape that can cope with such a linear system, first, a method of thinning the magnetic layer is mentioned. As a result, the self-demagnetization loss during recording and the thickness loss during reproduction can be reduced, and the electromagnetic conversion characteristics in the high-density recording area can be effectively improved.

However, as the magnetic layer becomes thinner, the problem of spacing loss due to surface irregularities becomes obvious.
This is a problem that occurs because the surface state of the magnetic layer becomes dependent on the surface properties of the nonmagnetic support when the magnetic layer is thinned, and the surface state of the nonmagnetic support is rough. Then, the surface of the magnetic layer also becomes rough, resulting in deterioration of electromagnetic conversion characteristics and inducing dropout.
Moreover, there is also a problem that running durability is reduced due to the thinning.

Therefore, a multilayer coating type configuration in which a lower nonmagnetic layer is interposed between the magnetic layer and the nonmagnetic support has been proposed.
This multi-layer coating type configuration has the advantage that the surface shape of the magnetic layer does not follow the surface shape of the non-magnetic support because the lower non-magnetic layer is interposed, and the surface can be designed freely. is doing.
In addition, by providing various functions not only to the magnetic layer but also to the lower non-magnetic layer, the linear magnetic recording / reproducing system is characterized by the fixed magnetic head and the sliding of the magnetic tape running on the magnetic head at high speed. It is possible to improve the running durability.

By the way, for magnetic tape media, in order to obtain high reliability in running performance, a back coat layer is usually provided on the main surface opposite to the side on which the magnetic layer is provided.
As a result, the magnetic tape can be stably driven with respect to the running system in the drive, and furthermore, the friction with the guide pin can be controlled by forming predetermined irregularities on the surface of the backcoat layer.
In addition, by forming a backcoat layer, the electrical resistance is reduced, an antistatic effect is obtained, the winding characteristics are improved, random winding during running is prevented, and the strength of the entire magnetic tape is increased. Since it can improve, the shape improvement effect is acquired.

However, in a drive of a linear recording / reproducing system, when a magnetic tape is repeatedly run for a long time, an error rate may increase due to a decrease in output.
This is considered to be due to the effect of head clogging caused by powder falling off of the magnetic tape and the effect of damage to the magnetic layer surface.
When observing with an atomic force microscope (AFM) or a scanning electron microscope (SEM), it was found that the damage on the surface of the magnetic layer was caused by the fact that fine holes were connected in the running direction. A possible cause of the formation of the fine holes is that protrusions on the surface of the backcoat layer are transferred to the surface of the magnetic layer (hereinafter referred to as dents). This dent occurs when high protrusions are scattered on the surface of the backcoat layer, and stress concentrates on the protrusions, and when the magnetic recording medium is wound, it is excessively pressed onto the adjacent magnetic layer surface. To do.
In addition, although such a dent is observed even when not running, after running, a dent that has become a continuous state is observed, and such damage is often seen It was found that the amount of powder falling after running tends to be large.
The following reason can be considered about the mechanism which will be in the state which continued as the above dents drive | worked.
In general, in a linear recording / reproducing system, in order to obtain a high data transfer rate, a magnetic tape travels at a high speed of about several m / s. However, in such a case, in order to maintain traveling stability (straightness). High tension is applied to the magnetic tape. In particular, when reversing the running, the speed and tension of the magnetic tape are unstable, so that a slight winding deviation occurs, and accordingly, the occurrence position of the dent is slightly shifted. By repeating this, it becomes a state in which dents due to shape transfer are continuous.
Then, it is considered that when the continuous dents are formed, the surface of the magnetic layer is destroyed and powder falling occurs.
Therefore, in order to improve the quality of the magnetic tape used in the recording / reproducing system employing the linear method as described above, the surface property of the backcoat layer is specified so as not to damage the magnetic layer side in repeated running. It will be necessary.

  Conventionally, in order to suppress running stability of the magnetic tape and shape transfer from the back coat layer side to the magnetic layer surface, studies have been made on the surface shape of the back coat layer (for example, Patent Documents 1 to 3). 3).

JP 2003-317228 A JP 2004-22103 A JP 2004-22105 A

  However, it is expected that the recording density will increase further in the future, and it is thought that the magnetic layer will become thinner with this, but all the techniques described in the above patent documents are all backed up. Only the height and density of the fine protrusions on the surface of the coating layer have been studied, and it is still sufficient to transfer the shape onto the surface of the magnetic layer, adhere to the magnetic head due to powder falling, and degrade the electromagnetic conversion characteristics over time. It was not realized to avoid.

  Therefore, in the present invention, in view of the above-described circumstances, it can withstand high-speed running and realize high-speed data transfer, suppress damage due to shape transfer from the backcoat layer to the magnetic layer surface, and has high durability and excellent performance. Further, the present invention provides a magnetic recording medium having high reliability capable of maintaining electromagnetic conversion characteristics over a long period of time.

The magnetic recording medium of the present invention includes a nonmagnetic layer containing nonmagnetic powder and a binder on one main surface of a long nonmagnetic support, and a magnetic layer containing magnetic powder and a binder. Is formed on the main surface opposite to the surface on which the magnetic layer is formed, and the surface of the backcoat layer satisfies the following conditions (1) and (2) It shall be.
(1) The protrusions having a height of 40 nm or more have a distribution of 0.841 × 10 ⁻³ pieces / μm ² or less and a standard deviation of the height of 0.010 or less.
(2) The protrusions having a height of 100 nm or more have a distribution of 0.012 × 10 ⁻³ pieces / μm ² or less.

  According to the present invention, by specifying specific numerical values regarding the protrusions on the surface of the backcoat layer, even when running repeatedly for a long time, damage to the magnetic layer side can be reliably suppressed, and excellent It was possible to provide a magnetic recording medium that can maintain electromagnetic conversion characteristics and high running reliability over a long period of time.

Specific embodiments of the magnetic recording medium of the present invention will be described, but the present invention is not limited to the following examples.
FIG. 1 shows a schematic cross-sectional view of an example of the magnetic recording medium of the present invention.
The magnetic recording medium 10 has a configuration in which the magnetic layer 2 is formed on one main surface of the nonmagnetic support 1 via the lower nonmagnetic layer 3 and the backcoat layer 4 is formed on the other main surface. have.
The magnetic recording medium according to the present invention is not limited to the example shown below, and may be any configuration as long as the back coat layer is formed on the main surface opposite to the magnetic layer forming surface. A so-called single-layer coated medium in which the magnetic layer side is composed of only one layer may be used, or a multilayer coated medium in which three or more layers are stacked may be used.

As the nonmagnetic support 1, any base film material for magnetic tape can be applied.
For example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, Polycarbonate, polyimide, polyamideimide and the like can be mentioned.
The nonmagnetic support 1 may have a single layer structure or a multilayer structure. Further, for example, surface treatment such as corona discharge treatment may be performed. The film thickness of the nonmagnetic support is preferably about 2 to 10 μm.

Next, the magnetic layer 2 will be described.
The magnetic layer 2 is composed mainly of a ferromagnetic powder and a binder, and other nonmagnetic reinforcing agents, lubricants, dispersants, antistatic agents, curing agents, and various additives are prepared using predetermined solvents. It shall be formed by applying a magnetic paint.

As the ferromagnetic powder, any of those conventionally applied to a coating type magnetic tape medium can be used. For example, Fe, Co, Ni, Fe—Co, Fe—Ni, Fe—Co—Ni, Co—Ni, Fe—Co—B, Fe—Co—Cr—B, Mn—Bi, Mn—Al, Fe— Co-V and the like may be mentioned, and further, metal components such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added for the purpose of improving these various characteristics.
Of these, the Fe-based magnetic powder has excellent electrical characteristics. In terms of corrosion resistance and dispersibility, Fe-Al, Fe-Al-Ca, Fe-Al-Zn, Fe-Al-Co, Fe-Ni-Si-Al-Zn, Fe-Ni- Fe-Al based alloy powder such as Si-Al-Zn-Mn type is preferred.
The shape of the ferromagnetic powder has an average major axis length of 0.5 μm or less, preferably 0.01 to 0.4 μm, more preferably 0.01 to 0.25 μm, and an axial ratio (average major axis length / average (Short axis length) is preferably 12 μm or less, more preferably 10 μm or less.

The ferromagnetic powder preferably has a saturation magnetization (σs) of 70 emu / g or more. If σs is less than 70 emu / g, there is a possibility that sufficient electromagnetic conversion characteristics cannot be obtained in the finally obtained magnetic recording medium.
From the viewpoint of enabling recording / reproduction in a high-density recording area, the ferromagnetic powder preferably has a specific surface area of 20 to 90 m ² / g by the BET method, and more preferably 20 to 40 m ² / g. More preferably. When the specific surface area is in the above range, the ferromagnetic powder is formed into fine particles and high-density recording becomes possible, and a magnetic recording medium having excellent noise characteristics can be obtained.
In addition, the ferromagnetic powder may use 1 type of the said material, and may use 2 or more types together.
As the ferromagnetic powder, hexagonal ferrite such as barium ferrite, iron nitride, etc. can be used. In barium ferrite, barium ferrite in which a part of Fe is substituted with at least Co and Zn is used. The average grain size (the length of the diagonal line of the hexagonal ferrite plate surface) is 300 to 900 mm, and the plate ratio (the value obtained by dividing the length of the diagonal line of the hexagonal ferrite plate surface by the plate thickness) is 2. Those having 0 to 10.0 and a coercive force Hc of 35 to 120 kA / m are preferable.

Next, the binder constituting the magnetic layer 2 will be described.
Examples of the binder include vinyl chloride, vinyl chloride copolymer, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate ester-acrylonitrile. Copolymer, Acrylate ester-Vinyl chloride-Vinylidene chloride copolymer, Methacrylate ester-Vinylidene chloride copolymer, Polyvinyl fluoride, Vinylidene chloride-Allylonitrile copolymer, Acrylonitrile-butadiene copolymer, Polyamide Resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyurethane resin, polyester tree , Amino resins, synthetic rubbers, and the like. Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, urea formaldehyde resin, and the like.

In addition, in the binder resin, polar functional groups such as —SO ₃ M, —OSO ₃ M, —COOM, and P═O (OM) ₂ are introduced into the molecule for the purpose of improving the dispersibility of the ferromagnetic powder. May be. Here, the M is a hydrogen atom or an alkali metal such as lithium, potassium or sodium.
Further, as the polar functional group, -NR1R2, -NR1R2R3 ⁺ X ^- as the side chain type having an end group of, NR1R2 ⁺ X ^- can be applied as a main chain type.
Here, in the formula R1, R2, R3 is a hydrogen atom or a hydrocarbon group, ⁺ X ^- is fluorine, chlorine, bromine, halogen ion or an inorganic or organic ion of iodine.
Moreover, as a polar functional group, —OH, —SH, —CN, an epoxy group, or the like can be applied.
The amount of the polar functional group is preferably 10 ⁻¹ to 10 ⁻⁸ mol / g, and more preferably 10 ⁻² to 10 ⁻⁶ mol / g.

The above-mentioned binders may be used alone or in combination of a plurality of types.
For example, when a mixture of polyurethane and / or polyester and vinyl chloride resin is used, the weight ratio is preferably 90:10 to 10:90, more preferably 70:30 to 30:70. It shall be a range.

The glass transition temperature Tg of the binder is preferably 50 to 70 ° C.
By selecting the glass transition temperature within the above range, the binder can be filled between fine ferromagnetic powders with good fluidity.
Further, by using a ferromagnetic powder having a pH value of 7 or more and a binder having a glass transition temperature of 50 to 70 ° C., the ferromagnetic powder can be favorably dispersed in the binder.
The binder resin preferably has a number average molecular weight of 5,000 to 200,000, more preferably 10,000 to 100,000. The degree of polymerization is about 50 to 1000.
The amount of the binder resin mixed in the magnetic layer 2 as described above is suitably 8 to 50 parts by weight, more preferably 10 to 25 parts by weight, with respect to 100 parts by weight of the ferromagnetic powder.

Non-magnetic reinforcing agent is added for the purpose of supplementing the coating film strength and improving running durability.
Examples include aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase), etc. And carbon black for the purpose of preventing the magnetic layer from being charged, reducing the friction coefficient, and improving the strength of the coating film.
The addition amount of the nonmagnetic reinforcing agent is 3 to 20 parts by weight, more preferably 5 to 10 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.
The nonmagnetic reinforcing agent particles preferably have a Mohs hardness of 4 or more, preferably 5 or more, and more preferably 6 or more.
Further, the nonmagnetic reinforcing agent particles preferably have a specific gravity of 2 to 6, more preferably 3 to 5.
Furthermore, the particles of the nonmagnetic reinforcing agent preferably have an average primary particle diameter of 0.05 to 0.6 μm, and more preferably 0.05 to 0.3 μm.

Conventionally known lubricants include silicone oil, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing ester, polyolefin, polyglycol, mono-fatty acid ester, di-fatty acid ester, tri-fatty acid ester, fatty acid amide, aliphatic amine, olefin oxide, etc. Any of these may be used, and these may be applied alone or in admixture.
Further, the lubricant may be added to the magnetic coating material, or may be applied to the surface of the magnetic layer by a subsequent process.
Particularly when fatty acids or fatty acid esters are added to the paint, the amount of fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the magnetic powder. Is desirable.
If the amount of fatty acid added is less than 0.2% by weight with respect to the magnetic powder, the runnability of the finally obtained magnetic recording medium will be deteriorated. This is because the surface of 2 may be excessively oozed out, and there is a possibility that the output is reduced or the coating itself is plasticized. Further, when the addition amount of the fatty acid ester is less than 0.2% by weight with respect to the magnetic powder, the still durability of the finally obtained magnetic recording medium is insufficient, whereas when it exceeds 10% by weight, the fatty acid ester This is because it may excessively ooze out on the surface of the magnetic layer 2 and cause a decrease in output and plasticization of the coating film.
The fatty acid and the fatty acid ester are preferably used in combination, and in that case, the ratio of the fatty acid to the fatty acid ester is preferably selected from the range of 10:90 to 90:10 by weight.
Note that in a multilayer coating type magnetic recording medium, the amount of lubricant on the surface of the magnetic layer that contributes to running durability can be adjusted by supplying from the lower nonmagnetic layer 3 side described later. The amount of the lubricant added to the layer 2 and the way of using the lubricant are not limited to the above description.

  As the dispersant, conventionally known compounds such as various materials described in JP-A-4-214218 can be applied. The amount of the dispersant added is preferably 0.5 to 5% by weight with respect to the ferromagnetic powder.

  As the antistatic agent, for example, conventionally known surfactants described in JP-A-4-214218 can be applied. The addition amount of the antistatic agent is preferably 0.01 to 40% by weight with respect to the binder.

As the curing agent, for example, polyisocyanate can be applied.
Examples of polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. It is done.
These polyisocyanates preferably have a weight average molecular weight in the range of 100 to 3,000.

Next, the lower nonmagnetic layer 3 will be described.
The lower nonmagnetic layer 3 is formed by applying a nonmagnetic paint mainly composed of a binder and a nonmagnetic powder.
Non-magnetic powders include, for example, acicular α-iron oxide, carbon black having a structure structure, monodispersed carbon black, Ge title chill type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide, and zinc oxide. , Chromium oxide, cerium oxide, titanium carbide, BN, α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate Etc.
The nonmagnetic powder may be surface-treated with a Si compound, an Al compound, or the like. The surface treatment is preferably performed so that the content of Si, Al or the like is 0.1 to 10% by weight with respect to the nonmagnetic powder.

The shape of the nonmagnetic powder may be acicular or spherical, but is more preferably acicular. By applying the acicular nonmagnetic powder, the surface property of the lower nonmagnetic layer 3 is improved, and as a result, the surface of the magnetic layer 2 can be smoothed.
However, the average major axis diameter, average minor axis diameter, and axial ratio (major axis diameter / minor axis diameter) of the nonmagnetic powder are preferably set in the following ranges.
The average major axis diameter of the nonmagnetic powder is 0.5 μm or less, preferably 0.3 μm or less, and more desirably 0.2 μm.
The average minor axis diameter is 0.1 μm or less, preferably 0.06 μm or less.
The axial ratio shall be 2-20, preferably 5-10.
The specific surface area is 10 to 250 m ² / g, preferably 30 to 100 m ² .
By applying the non-magnetic powder having the average major axis diameter, the average minor axis diameter, the axial ratio, and the specific surface area as described above, the surface property of the magnetic layer 2 formed thereon is controlled to be in a good state. Will be able to.

In addition, the said nonmagnetic powder can also be used independently and may use multiple types together.
When used in combination, it is necessary to pay attention to the size of the particles to be used together. In order to ensure good surface smoothness after coating, the average particle size (average long axis length for needle-like particles) is 0.3 μm. Hereinafter, it is preferably selected to be 0.2 μm or less. The specific surface area is 10 to 250 m ² / g, preferably 30 to 100 m ² .

The mixing amount of the nonmagnetic powder into the lower nonmagnetic layer 3 may be 50 to 99% by weight, more preferably 70 to 95% by weight, based on the total amount of all components constituting the lower nonmagnetic layer 3. preferable.
By setting the mixing amount of the nonmagnetic powder within the above range, the surface properties of the lower nonmagnetic layer 3 and the magnetic layer 2 can be controlled to be in a good state.

As the binder, any binder resin applicable in the magnetic layer 2 described above can be used.
The mixing amount of the binder is preferably 5 to 150 parts by weight, more preferably 10 to 120 parts by weight, with respect to 100 parts by weight of the nonmagnetic powder.

  Further, similarly to the magnetic layer 2, the lower nonmagnetic layer 3 may contain various additives such as a nonmagnetic reinforcing agent, a lubricant, a dispersant, an antistatic agent, and a curing agent. The lubricant may be contained in the layer in the same manner as the magnetic layer 2 or may be applied on the surface in a later step.

Next, the back coat layer 4 will be described.
The backcoat layer 4 is formed by applying a nonmagnetic paint mainly composed of a binder and a nonmagnetic powder.
As the non-magnetic powder, carbon black or graphite is mainly applied for the purpose of antistatic effect. In order to add a predetermined strength, a predetermined nonmagnetic reinforcing agent is applied. Specific examples of the nonmagnetic reinforcing agent include TiO ₂ , TiO, ZnO, CaCO ₃ , CaO, SnO ₂ , SiO ₂ , α-Fe ₂ O ₃ , Cr ₂ O ₃ , α-Al ₂ O ₃ , ZnS. , MoS ₂ , BaSO ₄ , CaSO ₄ , MgCO ₃ , BN, SiC, etc., in particular, one type of carbon black, graphite, ZnO, TiO ₂ , BaSO ₄ , CaSO ₄ , or a combination of two or more types Is preferably used.
The shape of the non-magnetic powder particles is not particularly limited, and various commonly used shapes such as a spherical shape, a needle shape, a plate shape, and a dice shape can be used.

In the finally obtained magnetic recording medium, it is included in the back coat layer 4 in order to avoid the deterioration of the electromagnetic conversion characteristics due to damage on the magnetic layer side caused by the surface protrusion of the back coat layer. The particle size of carbon black or a nonmagnetic reinforcing material was selected, and in the present invention, the surface property of the backcoat layer was defined as follows.
That is, it is assumed that the protrusions formed on the surface of the back coat layer 4 satisfy the height distribution conditions shown in the following (1) and (2).
(1) The protrusions having a height of 40 nm or more have a distribution of 0.841 × 10 ⁻³ pieces / μm ² or less and a standard deviation of the height of 0.010 or less.
(2) The protrusions having a height of 100 nm or more have a distribution of 0.012 × 10 ⁻³ pieces / μm ² or less.

In order to satisfy the above conditions, the carbon black in the backcoat layer is preferably applied in combination with fine particle carbon black having an average particle size of 10 to 50 nm and medium particle size carbon black having an average particle size of 60 to 100 nm. . It is preferable that the mixing ratio of the fine particle carbon black and the medium particle carbon black is 100: 0 to 70:30.
Further, as the nonmagnetic reinforcing material, those having a Mohs hardness of 5 to 9 and an average powder size of 10 to 300 nm are preferable. This is because when the average powder size is smaller than 10 nm, the effect as a reinforcing agent cannot be sufficiently obtained, and when it is larger than 300 nm, the surface property of the backcoat layer 4 is deteriorated.
In addition, if the state of the protrusion on the backcoat layer surface is as described above by a method such as a dispersion step or a calendar treatment step, the above-described particle conditions are not necessarily required.

As the binder and dispersant for the backcoat layer 4, any of those applied in the magnetic layer 2 can be used as long as the surface condition of the backcoat layer 4 satisfies the above conditions.
In particular, it was confirmed that the durability and runnability were improved by using polyester or polyurethane resin in combination, and the performance as a magnetic recording medium was exhibited.
In view of thermal decomposition, hydrolysis stability, etc., polyester polyurethane resins, and further polycarbonate polyurethane resins are preferred.
Further, if a trifunctional isocyanate compound, for example, a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate or an isocyanurate which is a cyclic addition polymer of 3 mol of diisocyanate is used as a crosslinking agent, durability Etc. can be further improved.

As in the case of the magnetic layer 2, an additive such as a lubricant may be added to the back coat layer 4.
The lubricant may be contained in the layer, or may be applied to the layer surface in a later step.

Next, a method for producing the magnetic recording medium 10 will be described.
First, using various materials as described above, the magnetic coating for forming the magnetic layer 2, the lower nonmagnetic layer 3, and the backcoat layer 4, the lower nonmagnetic layer coating, and the backcoat layer coating are adjusted. .

  The magnetic paint is prepared by mixing various additives such as ferromagnetic powder, binder, non-magnetic reinforcing agent, lubricant, dispersant, antistatic agent, curing agent, etc. After adjusting the magnetic paint, it is adjusted by diluting and dispersing with a predetermined solvent.

  The lower non-magnetic layer paint is prepared by mixing the non-magnetic powder, the binder, and various additives exemplified above together with a solvent in the same manner as the magnetic paint, and adjusting the high-concentration non-magnetic paint. It is adjusted by diluting and dispersing using a predetermined solvent.

  The coating material for the back coat layer is the same as the magnetic coating material, after the carbon black powder exemplified above, the nonmagnetic reinforcing agent, the binder, and various additives are kneaded and mixed with a solvent to adjust the high concentration back coating material, It is adjusted by diluting and dispersing using a predetermined solvent.

  Conventionally known organic solvents can be applied as the solvent for adjusting each paint, for example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, and alcohol solvents such as methanol, ethanol, and propanol. Solvents, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, benzene, toluene, xylene, etc. Aromatic hydrocarbon solvents, halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, chlorobenzene and the like can be mentioned, and these are used by mixing them appropriately.

When adjusting the coating material, the kneading step is disclosed in, for example, JP-A-4-214218, such as a continuous biaxial kneader, a continuous biaxial kneader that can be diluted in multiple stages, a kneader, a pressure kneader, and a roll kneader. Any kneading machine can be applied.
In the dispersion step, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, an agitator, a homogenizer, an ultrasonic disperser, or the like can be used.

In the production process of the magnetic tape, the lower magnetic layer 3 and the magnetic layer 2 can be formed by simultaneously applying the adjusted magnetic coating material and the lower layer nonmagnetic layer coating material on the nonmagnetic support 1 simultaneously. it can.
For example, a die coater is used when applying the coating layers simultaneously. Examples of the lip configuration of the die coater include a 2-lip system, a 3-lip system, and a 4-lip system.

In general, when the lower nonmagnetic layer 3 and the magnetic layer 2 are formed on the nonmagnetic support 1, there is a method of applying and drying one layer at a time (so-called wet-on-dry coating method) and a wet state where it is not dried. There is a system (so-called wet-on-wet coating system) in which the magnetic layer 2 is applied on the lower nonmagnetic layer 3 in an overlapping manner.
When manufacturing a magnetic recording medium, it is preferable to perform simultaneous wet multilayer coating by a wet-on-wet multilayer coating system from the viewpoint of coating uniformity, upper and lower interface adhesion, and productivity.

In addition, when the back coat layer 4 is formed on the other main surface of the nonmagnetic support 1, the above-described predetermined paint is applied on the nonmagnetic support 1.
As a coating method, any conventionally known coating method such as a one-lip die coater, a gravure coating method, a blade coating method, or a paint extrusion method can be applied.

  Note that either the magnetic layer / lower nonmagnetic layer and the backcoat layer may be applied first, or a coating apparatus may be provided on both of the nonmagnetic supports 1 and applied simultaneously.

The calender roll device used in the coating film forming system after coating has steel rolls and steel rolls alternately installed, sandwiching the coating roll between them, and applying the raw material constituting the nonmagnetic support while applying pressure and temperature. Although the calendar process is performed by running, a calendar roll apparatus that performs the calendar process may use a combination of a heat-resistant resin roll such as polyamide and epoxy and a steel roll.
The raw roll obtained as described above is put into an oven and cured, and then cut into a predetermined width to obtain a target magnetic tape.

  The magnetic recording medium of the present invention will be described based on specific experimental results, but the present invention is not limited to the examples shown below.

[Example 1]
First, each material component of the coating material for forming the magnetic layer and the coating material for forming the lower non-magnetic layer was weighed according to the composition shown below, and kneaded and dispersed using a kneader and a sand mill to prepare each coating material.
(Coating composition for magnetic layer formation)
P / B ratio = 6
Ferromagnetic iron powder: 100 parts by weight (specific surface area by BET method: 50 m ² / g, coercive force: 2400 Oe)
Sodium sulfonate group-containing polyurethane resin: 4 parts by weight Potassium sulfonate group-containing vinyl chloride resin: 16 parts by weight Carbon black (average particle size 0.03 μm): 4 parts by weight α-alumina (average particle size 0.07 μm): 5 Parts by weight myristic acid: 3 parts by weight butyl stearate: 3 parts by weight heptyl stearate: 3 parts by weight methyl ethyl ketone: 200 parts by weight toluene: 150 parts by weight cyclohexanone: 200 parts by weight (coating composition for forming the lower non-magnetic layer)
P / B ratio = 6
α-Fe ₂ O ₃ : 100 parts by weight (specific surface area by BET method 52 m ² / g)
Sodium sulfonate group-containing polyurethane resin: 4 parts by weight Potassium sulfonate group-containing vinyl chloride resin: 16 parts by weight Carbon black: 20 parts by weight (average particle size 0.02 μm)
α-alumina (average particle size: 0.10 μm): 3 parts by weight Butyl stearate: 3 parts by weight Heptyl stearate: 3 parts by weight Methyl ethyl ketone: 100 parts by weight Toluene: 50 parts by weight Cyclohexanone: 100 parts by weight 10 parts by weight of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to the dispersion of the coating material for coating and the coating material for forming the lower non-magnetic layer.

Moreover, each component of the coating material for backcoat layer formation was measured with the composition shown below, and the coating material was adjusted by carrying out a dispersion treatment for 6 hours using a kneader and a ball mill.
(Coating composition for backcoat layer formation)
Carbon black powder (average particle size: 20 nm): 100 parts by weight Polycarbonate polyurethane (glass transition temperature 55 ° C.): 70 parts by weight Nitrocellulose resin: 30 parts by weight Titanium oxide (average particle size 100 nm): 0.5 parts by weight Methyl ethyl ketone: 600 parts by weight Toluene: 400 parts by weight Further, 10 parts by weight of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to the dispersion of the coating material for forming the back coat layer.

The magnetic layer-forming coating material and the lower non-magnetic layer-forming coating material prepared as described above are dried on a polyethylene terephthalate film having a film thickness of 6.0 μm, with a magnetic film thickness of 0.15 μm and a lower layer. Simultaneous multi-layer coating was applied so that the nonmagnetic layer was 1.0 μm.
At this time, the magnetic coating film was randomly subjected to magnetic field orientation treatment while it was in an undried state, and then dried to form a multilayer coating film.
And the coating material of the backcoat layer was apply | coated to the surface on the opposite side to the side which obtained this multilayer coating film, and the backcoat layer with a dry film thickness of 0.6 micrometer was formed.
Then, the surface smoothing process was performed on the conditions shown below using the calendar apparatus with which the steel roll was installed alternately, and the wide raw fabric roll was obtained.
(Surface smoothing conditions)
Processing temperature: 110 ° C
Processing pressure (linear pressure): 150 N / mm ²
Processing speed: 150m / min
Number of processing: 2 times

The raw roll thus obtained was left to stand in an oven heated to 60 ° C. for 20 hours for curing treatment, and then slitted to a 1/2 inch width to produce a pancake.
Then, the sample was assembled into a predetermined cartridge.

[Example 2]
As a material for the coating material for forming the backcoat layer, 90 parts by weight of carbon black powder having an average particle size of 20 nm and 10 parts by weight of carbon black powder having an average particle size of 80 nm were used.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide original roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

Example 3
As a coating material for forming the back coat layer, 70 parts by weight of carbon black powder having an average particle size of 20 nm and 30 parts by weight of carbon black powder having an average particle size of 30 nm were used in combination, and the dispersion time of the back coating was 10 hours.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide original roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

Example 4
As a coating material for forming the backcoat layer, 60 parts by weight of carbon black powder having an average particle size of 20 nm and 40 parts by weight of carbon black powder having an average particle size of 80 nm are used in combination, and the dispersion time of the back coating is 10 hours. did.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide original roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

[Comparative Example 1]
As materials for the coating material for forming the back coat layer, 70 parts by weight of carbon black powder having an average particle size of 20 nm and 30 parts by weight of carbon black powder having an average particle size of 80 nm were used.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide raw roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

[Comparative Example 2]
As a material for the paint for forming the backcoat layer, 70 parts by weight of carbon black powder having an average particle size of 20 nm and 30 parts by weight of carbon black powder having an average particle size of 20 nm are used together, and the dispersion time of the paint for forming the backcoat layer is 10 hours. did.
The other conditions are the same as in Example 1 and the same as in Example 1 above. After a coating process, a calendering process, and a curing process, a wide original roll is prepared, and after passing through a slitting process, a predetermined cartridge is formed. A built-in sample was made. However, the calendar process was performed only once.

[Comparative Example 3]
As a coating material for forming the back coat layer, 70 parts by weight of carbon black powder having an average particle size of 20 nm and 30 parts by weight of carbon black powder having an average particle size of 30 nm are used in combination, and the dispersion time of the amount for forming the back coat layer is 10 hours. It was.
The amount of the magnetic paint and the lower non-magnetic layer was adjusted in the same manner as in Example 1 above.
These paints are subjected to a coating process, a calendering process, and a curing process using the same coating film forming system as in Example 1 above, and then a wide raw roll is prepared. Although it was an embedded sample, the calendaring temperature was 70 degrees.

[Comparative Example 4]
100 parts by weight of carbon black powder having an average particle size of 80 nm was used as a material for the paint for forming the backcoat layer, and the dispersion time of the paint for forming the backcoat layer was 10 hours.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide original roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

[Comparative Example 5]
As a coating material for forming the backcoat layer, 90 parts by weight of carbon black powder having an average particle size of 20 nm and 10 parts by weight of carbon black powder having an average particle size of 100 nm are used together, and the dispersion time of the coating material for forming the backcoat layer Was 10 hours.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide original roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

[Comparative Example 6]
As a material for the coating material for forming the backcoat layer, 50 parts by weight of carbon black powder having an average particle size of 20 nm and 50 parts by weight of carbon black powder having an average particle size of 100 nm are used together, and the dispersion time of the coating material for forming the backcoat layer Was 10 hours.
The other conditions were the same as in Example 1, and after passing through the coating process, the calendar process, and the curing process, a wide original roll was prepared, and the sample was assembled into a predetermined cartridge through the slit process.

About each sample of Examples 1-4 produced as mentioned above and Comparative Examples 1-6, the projection distribution measurement of the backcoat layer and the running durability test were performed, and evaluation was performed.
Hereinafter, measurement and evaluation methods will be described.

(Protrusion distribution of back coat layer)
Using an optical interference type surface shape measuring device (manufactured by Micromap), measurement was performed by randomly selecting 10 points in a 235.3 μm × 176.8 μm range with respect to the surface of the backcoat layer. Then, the projection height distribution was obtained by image analysis of the total data, and the number of projections per unit area and the standard deviation of the projection height were obtained.
Here, when the depth of the flaws with continuous dents on the surface of the magnetic layer was measured with the same measuring device, the depth was 40 nm or more from the average surface, and thus the surface of the backcoat layer having a height of 40 nm or more. The analysis was conducted focusing on the protrusions.

(Running durability test)
FIG. 2 shows a schematic configuration diagram of a drive device (LTO Ultrium 460 drive (manufactured by HP, USA)) used in the running durability test.
The drive device 20 shown in FIG. 2 includes a supply reel 21 and a take-up reel 22 arranged in parallel, and a magnetic tape is wound between the supply reel 21 and the take-up reel 22. The magnetic tape wound around the supply reel 21 is unwound from the supply reel, travels toward the take-up reel 22, and is taken up. Rotation guides 23 and 24 are provided in the travel path between the reels, and a magnetic head 25 is provided between the rotation guides 23 and 24.
A sample magnetic tape was mounted on the drive device 20, and a test for recording and reproducing 200 GB of recorded data was performed in an environment of a temperature of 25 ° C. and a relative humidity of 60%, and the error rate at that time was measured.
Furthermore, after this running test, the damage state on the surface of the magnetic layer and the powder fall state on the magnetic head in the drive were visually observed and evaluated in three stages.

  The production conditions of the backcoat layer in each sample of Examples 1 to 4 and Comparative Examples 1 to 6 are shown in Table 1 below, and the measurement evaluation results are shown in Table 2 below.

As shown in Tables 1 and 2 above, in the magnetic tapes of Examples 1 to 4, the total number of protrusions of 40 nm or more that is a cause of dents in the protrusion distribution on the surface of the backcoat layer is 0.841 × 10 ^−3. pieces / [mu] m ² or less, 100 nm or more protrusions number 0.012 × 10 ^-3 cells / [mu] m ² or less, the standard deviation of the above projection height 40nm is assumed to be 0.010 or less.
In these, the damage on the surface of the magnetic layer, which is seen as a series of dents, is only slightly generated, and there is very little dust falling on the magnetic head, which is in a practically good state.
In addition, the magnetic tapes of Examples 4 to 4 had an error rate as low as 10 ⁻⁵ units (1.5 × 10 ^{−5 to} 2.2 × 10 ⁻⁵ ), and showed sufficiently good results in practical use.

On the other hand, in Comparative Example 1, the dispersion time of the paint for forming the backcoat layer was shortened as compared with Example 3, and in Comparative Example 2, the number of calendar treatments was reduced as compared with Example 3 to 40 nm. The standard deviation of the above protrusion height is larger than 0.010, and the total number of protrusions of 40 nm or more in the protrusion distribution on the surface of the backcoat layer is more than 0.841 × 10 ⁻³ / μm ² , and 100 nm or more. The number of protrusions was greater than 0.012 × 10 ⁻³ / μm ² .
In these, many damages on the surface of the magnetic layer due to running and powder falling on the magnetic head were observed.
In these cases, the error rate was 10 ⁻⁴ units, which was worse than the above-described embodiment according to the present invention.

In Comparative Example 3, the calendering temperature was lowered as compared with Example 3, the standard deviation of the protrusion height of 40 nm or more was larger than 0.010, and the protrusion distribution of 40 nm or more in the protrusion distribution on the surface of the backcoat layer. The total number of protrusions was greater than 0.841 × 10 ⁻³ / μm ² , and the number of protrusions of 100 nm or more was greater than 0.012 × 10 ⁻³ / μm ² .
In this example, many damages on the surface of the magnetic layer due to running and powder falling on the magnetic head were observed.
Also in this example, the error rate was 10 ⁻⁴ units, which was worse than the above-described example according to the present invention.

In Comparative Examples 4 to 6, the average deviation of the carbon black contained in the backcoat layer and the blending ratio are different from those in the above examples, and the standard deviation of the protrusion height of 40 nm or more is 0.010 or more. In the projection distribution on the back coat layer surface, the total number of projections of 40 nm or more is larger than 0.841 × 10 ⁻³ / μm ² , and the number of projections of 100 nm or more is 0.012 × 10 ⁻³ / μm. More than ² .
In these, since particularly high protrusions were present on the surface of the backcoat layer, damage to the surface of the magnetic layer due to running increased remarkably, and many powder drops on the magnetic head were observed. In addition, the error rate was also markedly deteriorated.

As is clear from the results described above, it was confirmed that the damage on the magnetic layer surface and the powder falling on the magnetic head caused by it cause an increase in the error rate which is a fatal defect for the data backup system. It was.
Then, it was confirmed that the number of protrusions on the surface of the backcoat layer, the number of coarse protrusions, and the standard deviation of the protrusion height were involved as factors causing damage to the magnetic layer surface and occurrence of powder falling of the magnetic head. . Even when the number of protrusions on the surface of the backcoat layer is relatively small, if the standard deviation of the protrusion height is large, the damage on the surface of the magnetic layer increases and the powder of the magnetic head tends to fall off. The reason for this is that if the protrusion height on the surface of the backcoat layer is not uniform, stress concentrates on the protrusion higher than the periphery, and this protrusion excessively presses and damages the surface of the magnetic layer that is in contact with the laminate. To give.

In view of the above, in order to suppress damage to the magnetic layer surface due to protrusions on the surface of the backcoat layer and powder falling off of the magnetic head, the number of protrusions on the surface of the backcoat layer greater than a predetermined height, standard In the present invention, the number of protrusions having a height of 40 nm or more is set to 0.841 × 10 ⁻³ pieces / μm ² or less, and coarse protrusions having a height of 100 nm or more are 0.012 × 10 ^−3. It is necessary to make the number of protrusions / μm ² or less, and by making the protrusions uniform so that the standard deviation of the protrusion height of 40 nm or more is 0.010 or less, the stress applied to the protrusions can be dispersed, The damage on the surface of the magnetic layer was effectively reduced, the amount of powder falling on the magnetic head could be extremely reduced, and the error rate could be reduced, making it practically favorable.

1 is a schematic sectional view of a magnetic recording medium of the present invention. The schematic block diagram of the drive apparatus used for the driving | running | working durability test is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 2 ... Magnetic layer, 3 ... Lower nonmagnetic layer, 4 ... Backcoat layer, 10 ... Magnetic recording medium, 20 ... Drive apparatus, 21 ... Supply reel, 22 ... ... Take-up reel, 23, 24 ... Rotation guide, 25 ... Magnetic head

Claims (3)

A nonmagnetic layer containing nonmagnetic powder and a binder and a magnetic layer containing magnetic powder and a binder are laminated on one main surface of the long nonmagnetic support, A magnetic recording medium having a backcoat layer on the main surface opposite to the surface on which the magnetic layer is formed,
A magnetic recording medium, wherein the surface of the backcoat layer satisfies the following conditions (1) and (2).
(1) Height 40nm or more protrusions, the distribution is not more 0.4 33 × ^{10 -3} cells / [mu] m greater than ² 0.841 × ^{10 -3} cells / [mu] m ² or less, the standard deviation of and height 0.010 nm or less.
(2) The protrusions having a height of 100 nm or more have a distribution of 0.012 × 10 ⁻³ pieces / μm ² or less.   The magnetic recording medium according to claim 1, wherein the backcoat layer is formed by applying a nonmagnetic paint containing at least a nonmagnetic powder and a binder.   The magnetic recording medium according to claim 1, wherein the magnetic recording medium is used in a recording / reproducing system to which a linear method is applied.

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