JP2007193920A - Magnetic tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic tape low in error rate with less missing pulses, as a coating-type magnetic tape suitable for high-density recording. <P>SOLUTION: In a magnetic tape in which a coating film, which includes a magnetic layer having at most a prescribed thickness, is formed on one face of a nonmagnetic base, the number of projections of over 270 nm in height, which exist on the surface of the magnetic layer forming side of the nonmagnetic base, is 0 - 7.67×10<SP>-5</SP>pieces/2.77 mm<SP>2</SP>, and the number of projections of 0 nm-270 nm in height is 1×10<SP>-4</SP>- 10 pieces/2.77 mm<SP>2</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coating type magnetic tape suitable for high-density magnetic recording.

  Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc., but especially in the field of data backup magnetic tapes (backup tapes), as the capacity of hard disks to be backed up increases, Those having a recording capacity of several hundred GB or more have been commercialized. In the future, it will be indispensable to increase the capacity and recording density of magnetic tape in order to cope with the further increase in capacity of hard disks.

  In order to realize such high-density recording of magnetic tape, it is necessary to shorten the recording wavelength and simultaneously reduce the magnetic layer to suppress demagnetization due to the demagnetizing field at the time of recording and reproduction. Since the influence of the spacing between the magnetic layer and the magnetic head is increased, the surface property of the magnetic layer is important. For example, if there are relatively large protrusions on the surface of the magnetic layer, the output is reduced and the error rate is increased due to spacing loss.

  By the way, a coating type magnetic tape is obtained by applying a magnetic coating material in which magnetic powder is dispersed in a binder onto a nonmagnetic support, or, for example, a nonmagnetic undercoat coating material on the nonmagnetic support. The coating layer is formed on a non-magnetic support (a single-layer type magnetic tape in which only the magnetic layer is provided on the non-magnetic support). If the thickness of the multi-layered magnetic tape in which a plurality of layers including a magnetic layer and an undercoat layer are provided on the magnetic layer and the nonmagnetic support is reduced, the nonmagnetic support The surface property of the film tends to affect the surface property and the uniformity of the thickness of the coating film laminated thereon.

A magnetic recording medium described in Patent Document 1 is related to the surface property of such a nonmagnetic support. This is because a nonmagnetic layer (undercoat layer) containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder are provided in this order on at least one surface of the nonmagnetic support. In the recording medium, the center surface average roughness of the magnetic layer forming surface of the nonmagnetic support is 0.1 to 4.0 nm, and the number of protrusions having a height of 273 nm or more is specified in the range of 0 to 10/100 cm ^2. It is a thing. According to this, an excellent smooth surface can be obtained as the surface of the magnetic layer, and at the same time, the spacing loss between the magnetic recording medium and the recording / reproducing head is suppressed, so that high output and low noise can be realized, and dropout and It is said that thermal asperity can also be prevented (paragraphs [0017] to [0018]).

JP 2003-141708 A

  However, if the coating film formed on the non-magnetic support is thinned in order to achieve high-density recording on the magnetic tape, as described below, among the various protrusions existing on the non-magnetic support surface, It has been found that minute protrusions of a specific height or less, which was not a problem with this type of magnetic tape, affect output characteristics, recording signal loss, error rate, and other characteristics.

  For example, a conventional single-layer type magnetic tape conforming to DDS2, which is one of the magnetic tape standards for storing digital data, has a magnetic layer thickness of 2.0 μm (typical value), and conforms to the next generation DDS3. In the multi-layered type magnetic tape, the magnetic layer thickness = 0.2 μm (typical value) and the undercoat layer thickness = 1.8 μm (typical value). There are various microscopic projections on the surface of the non-magnetic support, but the thickness of the coating film including the magnetic layer formed on the surface is the thickness of the above-mentioned DDS2 or DDS3 magnetic tape. If the number of protrusions having a relatively large height (protrusions having a height of 273 nm or more in the previous Patent Document 1) is kept within a certain range, the surface of this type of support is used. Protrusion formation on the surface of the magnetic layer due to the upper protrusion lifting the surface of the magnetic layer is also suppressed. Therefore, it is possible to avoid the occurrence of errors caused by such protrusions on the surface of the magnetic layer and the occurrence of dropout in the VHS magnetic tape.

  However, a non-magnetic support (thickness is thinner than the former) having the same surface property as the non-magnetic support used in the above-mentioned DDS2 and DDS3 magnetic tapes is used. As a result of prototyping magnetic tapes conforming to DDS4 and DAT72, and examining their characteristics, the number of missing recording signals (missing pulses), even for tapes with a coating containing a magnetic layer under the same coating conditions It was also confirmed that the error rate varies. As a result of investigating the cause, the thickness of the coating film including the magnetic layer is thinner than that of the magnetic tape of DDS3 or DDS4 or DAT72 (for example, in the case of the magnetic tape of DDS4, the magnetic layer thickness = 0.2 μm (typical Value), undercoat layer thickness = 1.1 μm (representative value)), it was found that further minute protrusions existing on the surface of the non-magnetic support influence the output characteristics. As a result, in a magnetic tape having a thin coating film including such a magnetic layer, the surface of the nonmagnetic support is described in Patent Document 1 in order to reduce the error rate and missing pulse. It has been concluded that it is not sufficient to control the number of protrusions having a height of 273 nm or more, and it is necessary to control the number of minute protrusions having a lower height.

  The present invention has been made under such circumstances, and a magnetic tape suitable for high-density recording in which the thickness of a coating film including a magnetic layer provided on one surface of a nonmagnetic support is 1.5 μm or less. An object of the present invention is to provide a magnetic tape that is less likely to cause errors and missing pulses during reproduction of a recorded signal.

  As a result of investigating the relationship between the surface properties of the nonmagnetic support and the output characteristics in a magnetic tape having a thickness of 1.5 μm or less including the magnetic layer provided on one surface of the nonmagnetic support, Even when the number density of protrusions (number per unit area) having a height exceeding 270 nm existing on the surface of the magnetic support on the magnetic layer forming surface side is controlled within a certain range, it is even smaller than the protrusions. It has been found that when the number density of the protrusions exceeds a certain level, the error rate and missing pulse (a kind of dropout in VHS) exceed the allowable value during reproduction. The present invention is configured as follows based on such knowledge.

That is, the invention according to claim 1 is a magnetic tape having a magnetic layer containing a binder and a magnetic powder on one surface of a nonmagnetic support and having a thickness of 0.3 μm or less. The number of protrusions having a height exceeding 270 nm existing on the surface of the support on the magnetic layer forming surface side is 0 to 7.67 × 10 ⁻⁵ per 2.77 mm ^{2, and} the number of protrusions having a height exceeding 0 nm and not more than 270 nm. Is 1 × 10 ⁻⁴ to 10 pieces per 2.77 mm ² .

According to a second aspect of the present invention, an undercoat layer comprising a binder and a nonmagnetic powder and having a thickness of 1.2 μm or less is provided on one surface of a nonmagnetic support. In a magnetic tape having a magnetic layer containing a binder and magnetic powder and having a thickness of 0.3 μm or less, the height present on the surface of the nonmagnetic support on the magnetic layer forming surface side exceeds 270 nm The number of protrusions is 0 to 7.67 × 10 ⁻⁵ per 2.77 mm ² , and the number of protrusions having a height of more than 0 nm and not more than 270 nm is 1 × 10 ⁻⁴ to 10 per 2.77 mm ^2. It is a thing.

In these cases, the number of protrusions (hereinafter referred to as “S1 protrusions”) having a height of more than 0 nm and not more than 270 nm existing on the surface of the nonmagnetic support on the magnetic layer forming surface side is defined. In the case of a magnetic tape having a thin coating film including the magnetic layer provided on the magnetic layer forming surface side of the nonmagnetic support as described above, the number of such protrusions is small. This is because if the amount is large, the surface property and thickness uniformity of the magnetic layer are affected, and as a result, the output characteristics in the high-density recording region are adversely affected. That is, when the number of S1 protrusions existing on the surface of the nonmagnetic support on the magnetic layer forming surface exceeds 10 per 2.77 mm ² (10 / 2.77 mm ² ), the error rate and missing pulse increase. To do. However, if the number of S1 protrusions is less than 1 × 10 ⁻⁴ /2.77 mm ² , the surface of the nonmagnetic support on the magnetic layer forming surface side becomes too smooth, and the nonmagnetic support is produced during the magnetic tape manufacturing process. It becomes easy to be attracted to a conveying means such as a roller used for feeding and winding the body, and as a result, wrinkles are generated on the nonmagnetic support during the conveyance, making smooth conveyance difficult. For this reason, the number of S1 protrusions needs to be 1 × 10 ⁻⁴ pieces / 2.77 mm ² or more.

Further, exceeds the height 270nm present in the magnetic layer forming side of the surface of the nonmagnetic support projections (hereinafter, such a projection is also referred to as "S2 projections") per 2.77 mm ² the number of 0 to 7. The reason why 67 × 10 ⁻⁵ (0 to 7.67 × 10 ^{−5 /} 2.77 mm ² ) was used was that such a relatively large S2 protrusion was 7.67 × 10 ^{−5 on the} surface of the nonmagnetic support. This is because if the number exceeds 2.77 mm ² , the magnetic layer is lifted by this, and noise (missing pulse) is likely to be generated (see Patent Document 1). The occurrence of such noise also causes the error rate to increase.

According to the present invention, in the magnetic tape in which the thickness of the coating film including the magnetic layer provided on one surface of the nonmagnetic support is 1.5 μm or less, the surface of the nonmagnetic support on the magnetic layer forming surface side is provided. The number of S2 protrusions exceeding 270 nm in height was set to 0 to 7.67 × 10 ⁻⁵ /2.77 mm ^2, and the number of minute S1 protrusions exceeding 0 nm in height and equal to or less than 270 nm was 1 × Since 10 ⁻⁴ to 10 pieces / 2.77 mm ² , the error rate and missing pulses (number of missing recording signals) in the high-density recording area can be reduced.

  The magnetic tape of the present invention has a magnetic layer containing at least a ferromagnetic magnetic powder and a binder resin on a nonmagnetic support. In such a magnetic tape, as a particularly preferable configuration for realizing high-density recording, a nonmagnetic undercoat layer (hereinafter referred to as an upper magnetic layer) is provided between a nonmagnetic support and the magnetic layer (hereinafter also referred to as an upper magnetic layer). (Also referred to as a lower nonmagnetic layer). The present invention is preferably applied to a magnetic tape that requires particularly high running reliability. In such a magnetic tape, the back surface of the nonmagnetic support, that is, the magnetic layer formation of the nonmagnetic support is formed. A back coat layer can be provided on the surface opposite to the surface for the purpose of ensuring traveling reliability. Hereinafter, the best mode for carrying out the present invention will be described in detail by taking such a magnetic tape as an example.

<Non-magnetic support>
In the present invention, in the state of the magnetic tape, the number of S2 protrusions having a height exceeding 270 nm existing on the surface on which the magnetic layer is laminated is 0 to 7.67 × 10 ⁻⁵ /2.77 mm ² , Use a non-magnetic support having at least one surface made very smooth so that the number of S1 protrusions having a height of more than 0 nm and not more than 270 nm is 1 × 10 ⁻⁴ to 10 pieces / 2.77 mm ^2. .

The nonmagnetic support used in the magnetic tape of the present invention has a Young's modulus in the longitudinal direction of 5.9 GPa (600 kg / mm ² ) or more and a Young's modulus in the width direction of 3.9 GPa (400 kg / mm ² ) or more. Further, the Young's modulus in the longitudinal direction is more preferably 9.9 GPa (1000 kg / mm ² ) or more, and the Young's modulus in the width direction is more preferably 7.9 GPa (800 kg / mm ² ) or more. The reason why the Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 5.9 GPa (600 kg / mm ² ) or more is that tape running becomes unstable below this. The reason why the Young's modulus in the width direction of the non-magnetic support is preferably 3.9 GPa (400 kg / mm ² ) or more is that the edge damage of the tape is liable to occur below this.

  Nonmagnetic supports satisfying such properties include, for example, biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, and aromatic polyimide film. These nonmagnetic supports may be subjected in advance to corona discharge, easy adhesion treatment and the like.

  The thickness of the nonmagnetic support is usually preferably from 2.0 to 4.6 μm. More preferably, it is 3.4 to 4.1 μm. If the thickness of the non-magnetic support is less than 2.0 μm, it is difficult to form a film, and the tape strength is reduced. If the thickness exceeds 4.6 μm, the total thickness of the tape is increased, and the recording capacity per tape roll is reduced. It is to become. The center line average roughness (Ra) of the surface on the magnetic layer forming surface side of the nonmagnetic support is preferably 2.0 nm or more and 6.5 nm or less, more preferably 3.0 nm or more and 6.5 nm or less. If this Ra is 6.5 nm or less, the unevenness of the surface of the lower nonmagnetic layer and the surface of the magnetic layer is reduced even if the lower nonmagnetic layer is made thinner. However, if this Ra is less than 3.0 nm, the friction coefficient on the surface of the magnetic layer may increase and tape running performance may be deteriorated.

<Upper magnetic layer>
Ferromagnetic magnetic powder is used as the magnetic powder contained in the upper magnetic layer. As such magnetic powder, ferromagnetic iron-based metal powder is particularly preferable. The coercive force of the magnetic powder is preferably 135 kA / m to 360 kA / m (1700 to 4500 Oe), and more preferably 175 kA / m to 290 kA / m (2200 to 3600 Oe). Saturation magnetization is preferably ^{70~200A · m 2 / kg (70~200emu} / g) ^{is, 90~180A · m 2 / kg (} 90~180emu / g) is more preferable. The values indicating these magnetic properties were measured under the condition of an external magnetic field of 1.28 MA / m (16 kOe) using a sample vibrating magnetometer.

  200 nm or less is preferable and, as for the average diameter (average particle diameter of magnetic powder particle) of said ferromagnetic magnetic powder (a ferromagnetic iron type metal powder is included), 20-150 nm is more preferable. If the average diameter is larger than 200 nm, particle noise based on the size of the magnetic powder particles becomes large, and it becomes difficult to improve the C / N characteristics. On the other hand, if the average diameter is less than 10 nm, the coercive force decreases, and at the same time, the cohesive force of the magnetic powder increases, so that it becomes difficult to disperse in the paint. In addition, said average diameter is calculated | required as an average value of the major-axis length and minor-axis length measured as follows. That is, first, a particle photograph taken at 100000 times with a scanning electron microscope (SEM) was subjected to image processing, and the particle shape of the magnetic powder was drawn as a two-dimensional figure. Next, in one magnetic powder of interest, the longest length was set as the long axis length, and the shortest one was set as the short axis length by passing the magnetic powder passing through the center point of the long axis length. The average value of these two was taken as the diameter of the magnetic powder, and the average value per 100 magnetic powders was taken as the average diameter.

The BET specific surface area of the ferromagnetic iron-based metal powder is preferably 35~85m ² / g, more preferably ^{40~80m 2 / g, 50~70m 2 /} g being most preferred.

  The present invention is applied to a magnetic tape having a magnetic layer thickness of 0.3 μm or less. This is because the present invention was made in consideration of DDS4, DAT72, or a new generation magnetic tape standard that follows them, and in these magnetic tapes, the thickness of the magnetic layer was reduced to 0 to achieve higher density recording. It is because it is necessary to make it 0.3 μm or less. However, even if the thickness of the magnetic layer is in the above range, if the thickness is too thin, not only is the manufacturing difficult, but the leakage magnetic field from now on becomes smaller and the head output becomes smaller. Since the head output becomes small due to the thickness loss, the preferable thickness of the magnetic layer is 0.1 to 0.3 μm.

  The coercive force of the upper magnetic layer as a magnetic recording medium is preferably 135 kA / m to 360 kA / m (1700 to 4500 Oe) in the recording / reproducing direction, and the residual magnetic flux density is preferably 0.25 T (2500 G) or more in the head running direction. This range is preferable because when the coercive force is less than 135 kA / m, the output decreases due to the demagnetizing field, and when it exceeds 360 kA / m, writing by the head becomes difficult. The reason why the residual magnetic flux density is preferably 0.25 T (2500 G) or more is that the output is reduced below 0.35 T. Those having a coercive force of 175 kA / m to 290 kA / m (2200 to 3600 Oe) and a residual magnetic flux density of 0.3 T to 0.5 T (3,000 to 5000 G) are more preferable.

When the MR head is used as a reproducing head, the Mrt value, which is the product of the residual magnetic flux density (Mr) in the longitudinal direction of the upper magnetic layer and the magnetic layer thickness (t), is 72 Tnm (6.0 memu / cm ² ). The following is preferable. The reason why Mrt is 72 Tnm or less is that most MR heads are saturated at 72 Tnm or more. The Mrt is more preferably in the range of ^{2 to} 24 Tnm (0.2 to 2.00 memu / cm ² ).

  The center line average roughness Ra of the upper magnetic layer is preferably in the range of 0.2 to 3.0 nm, and more preferably in the range of 0.3 to 2.0 nm. If Ra exceeds 3.0 nm, the short wavelength component of the output may drop sharply and the reproduction resolution may deteriorate. On the other hand, if Ra is less than 0.2 nm, the friction with the head and the traveling guide may be increased and the durability may be deteriorated. In addition, a magnetic recording medium having an upper magnetic layer with an Ra of less than 0.2 nm is difficult to manufacture and is too expensive to process. In addition, this centerline average roughness Ra is a value obtained by measuring a visual field of 5 μm × 5 μm with 512 × 512 pixels using an atomic force microscope (AFM), and arithmetically averaging the absolute values from the average line of each point. It is.

<Lower nonmagnetic layer (undercoat layer)>
In the magnetic tape in which a magnetic layer is provided on a nonmagnetic support via a nonmagnetic undercoat layer (lower nonmagnetic layer), the thickness of the lower nonmagnetic layer is 1.2 μm or less. Applies to something. For magnetic tapes with a thickness of the undercoat underlayer nonmagnetic layer greater than 1.2 μm, even if there are microprojections such as S1 projections on the magnetic layer forming surface of the nonmagnetic support, Since there is a relatively thick lower nonmagnetic layer, the magnetic layer is not affected by microprojections on the surface of the nonmagnetic support, and even if the number of such microprojections is large to some extent, this increases the elalate. This is because an increase in missing pulses is not considered to occur. However, if the lower nonmagnetic layer is thin, coating becomes difficult and productivity is deteriorated. Therefore, the thickness of the lower nonmagnetic layer is preferably 0.01 μm or more, and more preferably 0.05 μm or more. Such a lower non-magnetic layer is provided to prevent a decrease in durability due to a thin magnetic layer, or to appropriately supply a lubricant to the upper magnetic layer.

  The Young's modulus of the lower nonmagnetic layer is preferably 80 to 99% of the Young's modulus of the upper magnetic layer. The reason why the Young's modulus of the lower nonmagnetic layer is preferably lower than that of the magnetic layer is that the lower nonmagnetic layer acts as a kind of cushion during calendar processing.

  The Young's modulus of the coating film composed of the lower nonmagnetic layer and the upper magnetic layer is preferably 40 to 100% of the average value of the Young's modulus in the longitudinal direction and the width direction of the nonmagnetic support. This is because the durability of the tape is large and the tape-head touch is improved. The Young's modulus of the coating film is more preferably in the range of 50 to 100%, and further preferably in the range of 60 to 90%. This range is preferable because if the amount is less than 40%, the durability of the coating film becomes small, and if it exceeds 100%, the tape-head touch becomes poor. In the present invention, as one method for controlling the Young's modulus of a coating film composed of a lower nonmagnetic layer and an upper magnetic layer, a control method based on calendar conditions is used.

  The lower nonmagnetic layer contains a nonmagnetic inorganic powder for the purpose of increasing strength. This inorganic powder is preferably a metal oxide, an alkaline earth metal salt or the like. Further, as the inorganic powder to be added to the lower nonmagnetic layer, iron oxide is preferable, its particle size is preferably 50 to 400 nm, and the addition amount is 35 based on the weight of the total inorganic powder in the lower nonmagnetic device. ~ 83 wt% is preferred. The reason why the particle size is preferable is that uniform dispersion is difficult when the particle size is less than 50 nm, and unevenness at the interface between the lower nonmagnetic layer and the magnetic layer immediately above it increases when the particle size exceeds 400 nm. Further, the addition amount is preferable because if the amount is less than 35% by weight, the effect of improving the coating film strength is small, and if it exceeds 83% by weight, the coating strength is lowered.

  It is preferable to add alumina to the lower nonmagnetic layer. The addition amount of alumina is preferably 2 to 30% by weight, more preferably 8 to 20% by weight, and still more preferably 11 to 20% by weight based on the weight of the total nonmagnetic powder. The particle diameter of the alumina to be added is preferably 100 nm or less, more preferably 10 to 100 nm, further preferably 30 to 90 nm, and further preferably 50 to 90 nm. The alumina of the lower nonmagnetic layer is particularly preferably alumina mainly composed of a corundum phase. The amount of alumina added in the above range is preferable because if the amount is less than 2% by weight, the fluidity of the coating becomes insufficient, and if it exceeds 30% by weight, the unevenness between the lower nonmagnetic layer and the magnetic layer immediately above it becomes large. Also, 100 nm or less of alumina is preferable because, when a non-magnetic support with a low smoothness having a surface roughness of the magnetic layer formation surface of 2.5 nm or more is used, if the particle size of alumina exceeds 100 nm, the lower layer This is because the smoothing effect on the surface of the nonmagnetic layer becomes insufficient. Alumina mainly composed of a corundum phase (α conversion rate: 30% or more) is particularly good because the Young's modulus of the lower nonmagnetic layer is increased in a small amount compared to the case of using σ, θ, γ-alumina, etc. This is because the tape strength is increased. In addition, by increasing the tape strength, output variations due to tape edge undulation (edge weave) are also improved.

  It is not excluded to add 100 to 800 nm of α-alumina with less than 3% by weight based on the weight of the total inorganic powder together with the alumina having the above particle diameter.

  Carbon black (CB) is added to the lower nonmagnetic layer for the purpose of improving conductivity. As CB to be added, acetylene black, furnace black, thermal black or the like can be used. Although those having a particle size of 5 nm to 200 nm can be used, those having a particle size of 10 to 100 nm are preferred. This range is preferable because CB has a structure, so that dispersion of CB is difficult when the particle size is 10 nm or less, and smoothness may be deteriorated when the particle size is 100 nm or more. The amount of CB added varies depending on the particle size of CB, but is preferably 15 to 40% by weight with respect to the total nonmagnetic powder. This is because if the added amount is less than 15% by weight, the effect of improving conductivity is poor, and if it exceeds 40% by weight, the effect is saturated. It is more preferable to use 15 to 35% by weight of CB having a particle size of 15 nm to 80 nm, and it is even more preferable to use 20 to 30% by weight of CB having a particle size of 20 to 50 nm. By adding CB having such a particle size and amount, electric resistance is reduced, and generation of electrostatic noise and tape running unevenness are reduced.

<Abrasive>
It is preferable to add an abrasive to the upper magnetic layer for the purpose of head cleaning and the like. As an abrasive to be added, the average particle size (number average particle size) is 5 to 150 nm, the particle size distribution is 10 nm or less with a standard deviation, and α-alumina or β-alumina having a Mohs hardness of 6 or more is used alone or in combination Are preferably used. Among these, corundum type alumina (α conversion rate: 30% or more) is particularly preferable. This is because the hardness is higher than when σ, θ, γ-alumina, or the like is used, and the head cleaning effect is excellent with a small addition amount. Furthermore, single crystal alumina prepared by the CVD method is particularly preferable since it has a narrow particle size distribution and no sintering. As for the particle size of the alumina abrasive, although it depends on the thickness of the magnetic layer, it is usually more preferable that the average particle size is 20 to 100 nm, more preferably 30 to 90 nm. The addition amount is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic iron-based metal powder. More preferably, it is 8 to 18 parts by weight.

  Here, the reason why alumina having an average particle size of 150 nm or less is preferable is that, when alumina having an average particle size of more than 150 nm is present in the magnetic layer, the head wear resistance is increased. The reason why alumina having an average particle size of 50 nm or more is preferable is that durability and cleaning properties deteriorate when the particle size of alumina present in the magnetic layer is less than 50 nm. Furthermore, the standard deviation of the particle size distribution is preferably 10 nm or less. When alumina having a distribution wider than 10 nm is used, the wear of the head is increased in part where the large particle size alumina exists in the magnetic layer, and small particle size alumina exists. There is a risk that durability and cleaning performance may deteriorate at the portion where the ink is applied. When partial deterioration occurs in this way, the characteristics vary, and eventually sufficient performance cannot be achieved.

  The reason why the amount of alumina added is preferably 5 parts by weight or more is that if the amount is less than 5 parts by weight, the coating strength of the magnetic layer is lowered and the durability may be deteriorated. In addition, since the cleaning performance of the head by the coating film is extremely deteriorated, there is a possibility that the dirt attached to the head cannot be scraped off. The reason why 15 parts by weight or less is preferable is that the C / N characteristic is lowered when the amount exceeds 15 parts by weight.

<Carbon black>
Conventionally known carbon black (CB) can be added to the upper magnetic layer for the purpose of improving conductivity and improving surface lubricity. As CB to be added, acetylene black, furnace black, thermal black or the like can be used. A particle size of 5 to 200 nm is used, but a particle size of 10 to 100 nm is preferable. When the particle size is 10 nm or less, it is difficult to disperse CB. On the other hand, when the particle size is 100 nm or more, it is necessary to add a large amount of CB. In any case, the surface becomes rough, which causes a decrease in output. The addition amount is preferably 0.2 to 5 parts by weight with respect to 100 parts by weight of the ferromagnetic iron-based metal powder. More preferably, it is 0.5 to 4 parts by weight.

<lubricant>
Lubricants with different roles can be added to the lower nonmagnetic layer and the upper magnetic layer. When the lower non-magnetic layer contains 0.5 to 4.0% by weight of higher fatty acid and 0.2 to 3.0% by weight of higher fatty acid ester based on the total inorganic powder, This is preferable because the coefficient of friction with the rotating cylinder or the head island is small. The addition of higher fatty acids in the above range is preferable when the content is less than 0.5% by weight, and the effect of reducing the friction coefficient is small. When the content exceeds 4.0% by weight, the primer layer may be plasticized and the toughness may be lost. Because. In addition, the addition of higher fatty acid esters within the above range is preferable when the content is less than 0.5% by weight, since the effect of reducing the friction coefficient is small, and when the content exceeds 3.0% by weight, the amount transferred into the magnetic layer is too large. This is because side effects such as sticking of the rotating cylinder or the head island may occur.

  When the upper magnetic layer contains 0.2 to 3.0% by weight of fatty acid amide and 0.2 to 3.0% by weight of higher fatty acid ester with respect to the ferromagnetic iron-based metal powder, And the coefficient of friction between the rotating cylinder and the rotating cylinder are small. If the amount of fatty acid amide added is less than 0.2% by weight, direct contact at the head / magnetic layer interface is likely to occur, and the effect of preventing seizure is small. Defects are likely to occur. As the fatty acid amide, amides such as palmitic acid and stearic acid can be used. Further, if the ester addition amount of the higher fatty acid is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, side effects such as sticking of the tape and the rotating cylinder may occur. The mutual movement of the lubricant in the magnetic layer and the lubricant in the lower nonmagnetic layer is not excluded.

<Binder>
The binder used for the lower non-magnetic layer and the upper magnetic layer is vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer. Examples include a combination of at least one selected from a resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, nitrocellulose, and the like, and a polyurethane resin. it can. Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane. These binders are used in the range of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the ferromagnetic iron-based metal powder in the magnetic layer and 100 parts by weight of the total nonmagnetic powder in the lower nonmagnetic layer. It is done. In particular, it is most preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin as a binder.

-COOH as a functional _{group, -SO 3 M, -OSO 3 M} , -P = O (OM) 3, -O-P = O (OM) 2 [ In these formulas, M represents a hydrogen atom, an alkali metal base or An amine salt], -OH, -NR1R2, -N ⁺ R3R4R5 [in these formulas, R1, R2, R3, R4, R5 represent hydrogen or a hydrocarbon group], a chloride consisting of a polymer having an epoxy group Binder resins such as vinyl resins and urethane resins are used. The reason why such a binder resin is used is that the dispersibility of the magnetic powder and the like is improved as described above. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

<Crosslinking agent>
It is desirable to use together with the above-mentioned binder, a thermosetting cross-linking agent that bonds and crosslinks with a functional group contained in the binder. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are usually used at a ratio of 10 to 50 parts by weight with respect to 100 parts by weight of the binder. More preferably, it is 15 to 35 parts by weight.

<solvent>
Organic solvents used in paint for forming the upper magnetic layer (magnetic paint), paint for forming the lower non-magnetic layer, and paint for forming the back coat layer described later include acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone. , Ketones such as cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, alcohols such as methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol glycol Esters such as glycol dimethyl ether, glycol monoethyl ether, dioxane and other glycol ethers, benzene, toluene, xylene, cresol, chlorobenzene, etc. Family hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, chlorobenzene, or dichlorobenzene, N, N- dimethylformamide, may be mentioned hexane. These can be used alone or in admixture at any ratio.

<Back coat layer>
It is preferable to provide a backcoat layer on the back surface of the nonmagnetic support to improve running performance. The thickness of the back coat layer is preferably 0.2 to 0.8 μm. This range is good because if the thickness is less than 0.2 μm, the effect of improving running performance is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the storage capacity per roll becomes small. The back coat layer can be formed by using a conventionally known gravure coating device, roll coating device, blade coating device, die coating device, or the like.

  Carbon black (CB) such as acetylene black, furnace black, and thermal black can be added to the back coat layer. Usually, small particle size carbon black and large particle size carbon black are used. As the small particle size carbon black, those having a particle size of 5 to 200 nm are used, and those having a particle size of 10 to 100 nm are more preferable. This range is more preferable because when the particle size is 10 nm or less, it is difficult to disperse CB, and when the particle size is 100 nm or more, it is necessary to add a large amount of CB. This is because it causes a setback (embossing). When 5 to 15% by weight of the small particle size carbon black and the large particle size carbon black having a particle size of 300 to 400 nm are used as the large particle size carbon black, the surface is not roughened and the effect of improving running performance is increased. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight, more preferably 70 to 95% by weight based on the weight of the inorganic powder. The surface roughness Ra is preferably 3 to 8 nm, and more preferably 4 to 7 nm.

  It is preferable to add iron oxide to the backcoat layer for the purpose of improving the strength. The particle size of the iron oxide to be added is preferably 100 nm to 600 nm, and more preferably 200 nm to 500 nm. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight based on the weight of the inorganic powder.

<Production method>
Examples of the main method for producing the magnetic coating include the following methods. That is, first, using a powerful kneader such as a kneader or a biaxial continuous kneader (extruder), magnetic powder and a small amount of binder resin are kneaded, and a solvent is added to obtain a solid content concentration of 35 to 45%. The mixture is stirred with a weight basis (the same applies hereinafter) to obtain a paste-like mill base. The biaxial continuous kneader used in the kneading step is equipped with a device that can be heated and cooled in the kneading part (barrel), and the temperature of the kneading part is 20 to 50 ° C., preferably 25 to 35 ° C. It is adjusted by controlling. Here, if the temperature of the kneading part is less than 20 ° C., the wettability to the kneaded product cannot be improved and the dispersibility cannot be improved. If the temperature exceeds 50 ° C., the viscosity of the kneaded product decreases. Thus, a desired shear force cannot be applied. The kneading conditions for kneading in the kneading step are preferably that the kneading time is 2 to 5 minutes, and the feed rate of the kneaded product is preferably 5 to 15 kg / h. Next, a dispersion operation is performed by a sand mill or the like to improve the dispersion state of the solid content.

  In order to coat and form an average dry thickness of the upper magnetic layer with an arbitrary thickness of 0.3 μm or less with good accuracy and good productivity, the upper magnetic layer is superimposed immediately above the lower nonmagnetic layer while it is wet. It is preferable to use a wet-on-wet simultaneous multilayer coating method. In this case, the lower non-magnetic layer and the upper magnetic layer are applied almost simultaneously by a single die coating head having two coating liquid passage slits. At this time, in order to increase the coating stability, it is preferable to adjust the surface tension of the solvent used for the lower nonmagnetic layer to be higher than the surface tension of the solvent used for the upper magnetic layer. Examples of the solvent having a high surface tension include cyclohexanone and dioxane.

  After coating and forming the lower non-magnetic layer and the upper magnetic layer, the density and surface state of these layers are made uniform and the density of the magnetic powder in the magnetic layer is improved so that the density is passed between metal rolls and calendered. It is preferable. In this case, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyimide amide or the like can be used as the calender roll. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 × 9.8 N / cm, more preferably 300 × 9.8 N / cm or more, and the speed is in the range of 20 m / min to 700 m / min. The effect of the present invention can be further enhanced by performing the calendar process at a temperature of 80 ° C. or higher and a linear pressure of 300 × 9.8 N / cm or higher.

  The back coat layer is applied in any of the steps before and after the application of the surface coating layer and the calendar process. Further, after coating and forming the surface layer coating layer and the back coat layer and performing the calendar treatment, an aging treatment at 40 ° C. to 80 ° C. may be performed in order to promote curing of the surface layer coating layer and the back coat layer.

  Examples of the present invention will be described below. In addition, "part" in the following component shows a weight part.

[Example 1]
《Backcoat layer paint component》
Carbon black (average particle diameter: 25 nm) 80 parts Carbon black (average particle diameter: 350 nm) 10 parts α-iron oxide (average particle diameter: 100 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin (-SO ₃ 30 parts) Cyclohexanone 290 parts Toluene 680 parts Methyl ethyl ketone 410 parts

  After the coating component for the backcoat layer was dispersed in a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate was added to adjust the coating material for the backcoat layer, and after filtration, an aromatic polyamide film (Young's modulus in the MD direction: 11330 MPa, TD direction Young's modulus: 15380 MPa, thickness: 3.6 μm, product name: Mikutron, manufactured by Toray Industries, Inc.), dried and calendered so that the thickness after calendering is 0.5 μm. Applied and dried.

《Non-magnetic paint component (coating component for undercoat layer)》
(1)
• α-iron oxide (average particle size: 110 nm) 68 parts • α-alumina powder (average particle size: 70 nm) 8.0 parts • Carbon black (average particle size: 75 nm) 24 parts • Stearic acid (SA) 1. 0 parts vinyl chloride - hydroxypropyl acrylate copolymer 8.8 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 eq / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 71 parts ・ Methyl ethyl ketone 120 parts ・ Toluene 26 parts (2)
・ Stearic acid (SA) 1.0 part ・ Butyl stearate (SB) 1.0 part ・ Cyclohexanone 20 parts ・ Methyl ethyl ketone 13 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.3 parts ・ Cyclohexanone 2.0 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 2.0 parts

<Magnetic paint component (magnetic layer paint component)>
(1) Kneading step 100 parts of ferromagnetic iron-based metal powder [Co / Fe: 24 at%,
Y / (Fe + Co): 4.7 at%,
Al / (Fe + Co): 8.2 at%
σs: 155 A · m ² / kg,
Hc: 188 kA / m,
(Average particle diameter: 100 nm)
-12 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin (PU) 5.5 parts (contained -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)
・ Carbon black (average particle size: 25 nm) 2.0 parts ・ Methyl acid phosphate (MAP) 2.5 parts ・ Methyl ethyl ketone 30 parts ・ Toluene 12 parts (2) dilution process ・ α-alumina slurry 22 parts (manufactured by Sumitomo Chemical Co., Ltd.) Α-alumina average particle diameter: 200 nm, content 45%)
-N-butyl stearate (SB) 1.0 part-palmitic acid amide 2.0 part-cyclohexanone 110 parts-methyl ethyl ketone 110 parts-tetrahydrofuran 30 parts-toluene 80 parts (3) compounding process-polyisocyanate 1.9・ Methyl ethyl ketone 12 parts ・ Cyclohexanone 5.0 parts ・ Toluene 5.0 parts

  In the above nonmagnetic paint component, (1) was kneaded with a batch kneader, and then (2) was added and stirred. Next, a dispersion treatment was performed using a sand mill with a residence time of 60 minutes, and after adding (3) to this, stirring and filtering, a nonmagnetic paint for an undercoat layer (lower nonmagnetic layer) was obtained.

  Separately from this, in the components of the magnetic coating, (1) was kneaded with a batch kneader, and then (2) was added and stirred. Next, a dispersion treatment was performed using a sand mill with a residence time of 45 minutes, and after adding (3), stirring and filtering, a magnetic coating material for forming a magnetic layer was obtained.

  On the other side of the non-magnetic support (base film) coated with the back coat paint on one side, the non-magnetic paint is applied so that the thickness after drying and calendering becomes 0.9 μm. An undercoat layer was formed, and the magnetic coating was applied on the undercoat layer by wet-on-wet, and the thickness after magnetic field orientation treatment / drying / calendar treatment (magnetic layer thickness) was 0.25 μm. A magnetic layer was formed as follows. Next, after magnetic field orientation treatment, drying was performed using a dryer and far infrared rays to obtain a magnetic sheet. In the magnetic field orientation treatment, an NN counter magnet (5 kG) is installed in front of the dryer, and two NN counter magnets (5 kG) are spaced from each other at a distance of 50 cm from the front side 75 cm of the position of dry coating of the coating in the dryer. It was installed at. The coating speed was 100 m / min.

The magnetic sheet thus obtained was mirror-finished under the conditions of a temperature of 100 ° C. and a linear pressure of 1.96 × 10 ⁵ N / m using a seven-stage calendar made of a metal roll. Next, after aging at 70 ° C. for 72 hours in a state in which the magnetic sheet is wound around the core, the sheet is cut to a width of 3.81 mm, and the surface of the magnetic layer is polished with a lapping tape while being run at 200 m / min. The magnetic tape was prepared by polishing and wiping with a tissue. The magnetic tape thus obtained was incorporated into a DDS cartridge with a length of 170 m to obtain an evaluation tape, which was produced in the required number of samples.

About each produced tape for evaluation, when the surface center line average roughness Ra on the magnetic layer forming surface side of the nonmagnetic support, the thickness of each layer, and the Young's modulus (MD, TD direction) were measured by the following measurement method, The values were as follows. These are average values of five evaluation tapes (the number of samples is 5).
-Surface centerline average roughness Ra on the magnetic layer forming surface side of the nonmagnetic support: 4.5 nm
-Magnetic layer thickness: 02 μm
・ Undercoat layer thickness: 0.9 μm
-Backcoat layer thickness: 0.4 μm
-Nonmagnetic support thickness: 3.7 nm

“Surface center line average roughness of nonmagnetic support on the magnetic layer forming surface side: Ra”
Scan Length was measured at 5.0 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO. The measurement visual field is 350 μm × 260 μm. The centerline average roughness of the nonmagnetic support surface was determined as Ra.

"Thickness of each layer"
The thickness was measured as follows. First, the obtained magnetic tape was filled with resin, cut out with a diamond cutter (or a peripheral ion beam processing apparatus), and the cross section was 10000 times with a transmission electron microscope (TEM). Photographing is performed to border the boundary between the magnetic layer and the nonmagnetic layer, the nonmagnetic layer and the nonmagnetic support, and the nonmagnetic support and the backcoat layer. Next, the distance between the bordered lines is measured as the thickness at any five locations per photograph, and the magnetic layer thickness, nonmagnetic layer (undercoat layer) thickness, and backcoat layer are determined from the average value thereof. The thickness was determined.

"Measurement of Young's modulus (MD, TD direction) of magnetic tape"
Using a small tensile tester (manufactured by Yokohama System Co., Ltd.), strain and tensile stress in an environment of 23 ° C. and 50% RH were measured. The measured length of the sample was 10 mm, the sample was pulled at a tensile rate of 10% strain / minute, and the 0.3% elongation modulus (Young's modulus) was evaluated based on the value of 0.3% strain of the obtained stress. This evaluation was performed in the longitudinal (MD) direction and the width (TD) direction of the sample.

[Evaluation of properties]
Next, a predetermined number of evaluation tapes prepared as described above were prepared, and the following items were measured for these samples to determine the relationship between the S1 protrusion and the error rate, and the relationship between the S1 protrusion and the missing pulse, respectively. Examined.

“Height and number of protrusions on the surface of non-magnetic support”
It was determined as follows.
1) Aluminum vapor deposition is performed on the magnetic layer forming side of the nonmagnetic support.
2) Observe 4 samples (1 field: 2.77 mm ² ) arbitrarily with a differential interference microscope (50 times magnification) and mark the protrusions.
3) The height of the marked protrusion is measured with KEYENCE PROFILE MICROMETER: VF-7500, 7510 (CR magnification: 2500 times), and the number of protrusions of 0 to 270 nm (S1 protrusion) is counted.
4) Calculate the sum of the four fields of view.
5) The average value of 4 fields of view is the number of protrusions, rounded to the first decimal place, and expressed as an integer.

"Missing Pulse"
A missing pulse is a missing reproduction signal whose peak value (0-P) with respect to 0 V of the voltage of the reproduction signal is 50% or less of the average signal amplitude of a signal having a recording density of 2999.9 ftpmm. judge.
MS4500Series (HPDDS4Drive) manufactured by Media Scope was used as a measuring device for missing pulses.

"Reproduction output (4T output)"
The reproduction output (4T output) was determined by recording (recording density 1499.9 ftpmm) and reproduction using a DDS4 drive manufactured by HP. The output was defined as 100% of the standard tape as a reference, and expressed as a relative value.

"Error rate"
The error rate (ERT) is measured by using a DDS4 drive manufactured by HP and recording and reproducing a random digital signal with a recording track width of 5.4 μm (recording density 5999.7 to 1499.9 ftpmm). Was converted into a rate using the total number of records as a parameter. The population parameter was obtained for each block number per second. The value obtained was defined as 10 relative to the value of the error rate standard tape used as a comparison target in this type of measurement, and finally expressed as a relative value.

〔Evaluation results〕
1 and Table 1 show measurement results regarding the relationship between the S1 protrusion and the missing pulse (MP), and FIGS. 2 and 2 show measurement results regarding the relationship between the S1 protrusion and the error rate (ERT). In this case, the S1 protrusion has a distribution of an average height: about 140 nm, a standard deviation: about 67 nm, a maximum height: 270 nm, and a minimum height: 0 nm. Further, the “range” described in Table 1 and Table 2 is a range between the maximum value and the minimum value in the measurement values of each item.

Looking at these figures and tables, the number of S1 projections (microprojections with a height of more than 0 nm and less than 270 nm present on the surface of the nonmagnetic support on the magnetic layer forming side) per 10.77 mm ² is 10 or less. means a case when (more than 10 /2.77mm ²⁾ and more than 10 or more when /2.77mm ² .10 pieces (10 or more, is used here the words of convenience "or more". It can be seen that there is a significant difference between the missing pulse and the error rate. That is, when the number of S1 protrusions is 10 or less, the 4T output is slightly higher than when the number of S1 protrusions is 10 or more, and when the 4T output is the same, the number of missing pulses is small and the error rate is low. Can also be confirmed.

It is a graph which shows the result of having investigated the relationship between S1 protrusion and missing pulse (MP) using the some tape for evaluation (magnetic tape) produced in the Example of this invention. It is a graph which shows the result of having investigated the relationship between S1 protrusion and an error rate (ERT) using the some tape for evaluation (magnetic tape) produced in this invention Example.

Claims (4)

A magnetic tape having a magnetic layer containing a binder and magnetic powder on one side of a nonmagnetic support and having a thickness of 0.3 μm or less,
The number of protrusions having a height exceeding 270 nm present on the surface of the nonmagnetic support on the magnetic layer forming surface side is 0 to 7.67 × 10 ⁻⁵ per 2.77 mm ² , and the height is more than 0 nm and not more than 270 nm. A magnetic tape characterized in that the number of protrusions is 1 × 10 ⁻⁴ to 10 per 2.77 mm ² . One surface of the non-magnetic support contains an undercoat layer having a thickness of 1.2 μm or less containing a binder and non-magnetic powder, and a binder and magnetic powder provided thereon. A magnetic tape having a magnetic layer with a thickness of 0.3 μm or less,
The number of protrusions having a height exceeding 270 nm present on the surface of the nonmagnetic support on the magnetic layer forming surface side is 0 to 7.67 × 10 ⁻⁵ per 2.77 mm ² , and the height is more than 0 nm and not more than 270 nm. A magnetic tape characterized in that the number of protrusions is 1 × 10 ⁻⁴ to 10 per 2.77 mm ² .   The magnetic tape according to claim 1 or 2, wherein the center line average roughness Ra of the surface of the nonmagnetic support on the magnetic layer forming surface side is 3.0 nm or more and 6.5 nm or less.   The magnetic tape according to any one of claims 1 to 3, wherein the nonmagnetic support has a thickness of 2.0 µm or more and 4.6 µm or less.

Images