JP3661738B2 - Magnetic recording medium substrate having non-magnetic underlayer and magnetic recording medium using the substrate - Google Patents

Description

【０１２４】
得られた３種類の塗料をそれぞれ厚さ１２μｍのポリエチレンテレフタレートフィルム上にアプリケーターを用いて５５μｍの厚さに塗布し、次いで、乾燥させることにより３種類の非磁性下地層を形成した。非磁性下地層Ａの厚みは３．６μｍであった。非磁性下地層Ｂの厚みは３．５μｍ、非磁性下地層Ｃの厚みは３．３μｍであった。
【０１２５】
非磁性粒子粉末として紡錘状ゲータイト粒子粉末を用いて得られた非磁性下地層Ａは、光沢が１８１％、表面粗度Ｒａが１１．６ｎｍであり、基体のヤング率（相対値）は１３３であった。
【０１２６】
非磁性粒子粉末として低密度紡錘状ヘマタイト粒子粉末を用いて得られた非磁性下地層Ｂは、光沢が１９０％、表面粗度Ｒａが１０．２ｎｍであり、基体のヤング率（相対値）は１３３であった。
【０１２７】
非磁性粒子粉末として高密度紡錘状ヘマタイト粒子粉末を用いて得られた非磁性下地層Ｃは、光沢が２０６％、表面粗度Ｒａが６．９ｎｍであり、基体のヤング率（相対値）は１３５であった。
【０１２８】
＜磁気記録層の製造＞
鉄を主成分とする紡錘状金属磁性粒子粉末（平均長軸径０．１５３μｍ、平均短軸径０．０１９１μｍ、軸比８．０１、保磁力１７１０Ｏｅ、飽和磁化値１２５．３ｅｍｕ／ｇ、幾何標準偏差１．３５）１２ｇ、研磨剤（商品名：ＡＫＰ−３０、住友化学（株）製）１．２ｇ、カーボンブラック（商品名：＃３２５０Ｂ、三菱化成（株）製）０．３６ｇ、結合剤樹脂溶液（スルホン酸ナトリウム基を有する塩化ビニル−酢酸ビニル共重合樹脂３０重量％とシクロヘキサノン７０重量％）及びシクロヘキサノンとを混合して混合物（固形分率７８％）を得、この混合物を更にプラストミルで３０分間混練して混練物を得た。
【０１２９】
この混練物を１４０ｍｌガラス瓶に１．５ｍｍφガラスビーズ９５ｇ、結合剤樹脂溶液（スルホン酸ナトリウム基を有するポリウレタン樹脂３０重量％、溶剤（メチルエチルケトン：トルエン＝１：１）７０重量％）、シクロヘキサノン、メチルエチルケトン及びトルエンとともに添加し、ペイントシェーカーで６時間混合・分散を行って磁性塗料を得た。更に、潤滑剤及び硬化剤を加えた後、ペイントシェーカーで１５分間混合・分散した。
【０１３０】
得られた磁性塗料の組成は下記の通りであった。

【０１３１】
得られた磁性塗料を前記非磁性下地層Ａ、Ｂ及びＣのそれぞれの上にアプリケーターを用いて１５μｍの厚さに塗布した後、磁場中において配向・乾燥し、次いで、カレンダー処理を行った後、６０℃で２４時間硬化反応を行い０．５インチ幅にスリットして磁気テープを得た。磁気記録層の厚みはいずれも１．１μｍであった。
【０１３２】
非磁性下地層Ａの上に磁気記録層を形成させて得られた磁気テープは、Ｈｃが１７７１Ｏｅ、角型比（Ｂｒ／Ｂｍ）が０．８７、光沢度が１９５％、表面粗度Ｒａが１０．２ｎｍ、ヤング率（相対値）が１３６、線吸収係数が１．２３、走行耐久性が２１．２分、すり傷特性がＢであった。
【０１３３】
非磁性下地層Ｂの上に磁気記録層を形成させて得られた磁気テープは、Ｈｃが１７７３Ｏｅ、角型比（Ｂｒ／Ｂｍ）が０．８７、光沢度が２００％、表面粗度Ｒａが８．８ｎｍ、ヤング率（相対値）が１３７、線吸収係数が１．２３、走行耐久性が２４．６分、すり傷特性がＡであった。
【０１３４】
非磁性下地層Ｃの上に磁気記録層を形成させて得られた磁気テープは、Ｈｃが１７８０Ｏｅ、角型比（Ｂｒ／Ｂｍ）が０．８９、光沢度が２１６％、表面粗度Ｒａが７．０ｎｍ、ヤング率（相対値）が１３７、線吸収係数が１．２３、走行耐久性が２７．６分、すり傷特性がＡであった。
【０１３５】
【作用】
本発明において最も重要な点は、Ｚｒ換算で０．０５〜３０重量％のジルコニウムを粒子内部に含有している非磁性粒子粉末、必要により、さらに、アルミニウムの水酸化物、アルミニウムの酸化物、ケイ素の水酸化物及びケイ素の酸化物の少なくとも１種で粒子表面が被覆されている鉄を主成分とする針状非磁性粒子粉末を非磁性下地層用の非磁性粒子粉末として用いた場合には、非磁性下地層の表面平滑性と基体の強度を向上させることができ、当該非磁性下地層の上に磁気記録層を設けた場合に、磁気記録層の光透過率を小さくし、表面平滑で、強度が大きく、且つ、耐久性に優れている磁気記録媒体を得ることができるという事実である。
【０１３６】
非磁性下地層の表面平滑性と基体の強度及び磁気記録媒体の耐久性をより向上させることができた理由について、本発明者は、非磁性粒子のビヒクル中における結合剤樹脂との樹脂吸着強度が高まり、その結果、非磁性下地層中における非磁性粒子と樹脂との密着度や非磁性下地層自体の非磁性支持体への密着度が高まったことによるものと考えている。
【０１３７】
【実施例】
次に、実施例並びに比較例を挙げる。
【０１３８】
＜針状ゲータイト粒子粉末の種類＞
非磁性粒子Ａ１、Ａ８
針状ゲータイト粒子粉末の平均長軸径、平均短軸径、幾何標準偏差値、軸比及びＢＥＴ比表面積、ジルコニウム含有の有無及び量、表面被覆物の有無並びに樹脂吸着強度等が相違する針状ゲータイト粒子粉末２種類を準備した。
【０１３９】
針状ゲータイト粒子粉末Ａ１及びＡ８の主要製造条件を表１に、諸特性を表２に示す。
【０１４０】
＜針状ヘマタイト粒子粉末の種類＞
非磁性粒子Ａ２〜Ａ７、Ａ９〜Ａ１１
出発原料である針状ゲータイト粒子粉末の基本生成反応、焼結防止剤の種類及び量、平均長軸径、平均短軸径、幾何標準偏差値、軸比、比表面積及び密度化の程度、ジルコニウム含有の有無及び量、表面被覆物の有無、種類及び量並びに樹脂吸着強度が種々相違する針状ヘマタイト粒子粉末を準備した。尚、ジルコニウムを含有している針状ヘマタイト粒子は、いずれも粒子内部にジルコニウムを均一に含有している粒子である。
【０１４１】
針状ヘマタイト粒子Ａ２〜Ａ７、Ａ９〜Ａ１１の主要製造条件を表１に、諸特性を表２に示す。
【０１４２】
【表１】

【０１４３】
【表２】

【０１４４】
尚、針状非磁性粒子の表面被覆処理は、非磁性粒子の種類、被覆物の種類及び量を種々変化させた以外は、下記の方法によった。
【０１４５】
非磁性粒子Ａ４を含む濃度が９９ｇ／ｌのスラリー５ｌを加熱して６０℃とし、このスラリー中に１．０ＮのＮａＡｌＯ₂ 溶液１５５．８ｍｌ（針状ヘマタイト粒子に対しＡｌ換算で０．８５重量％に相当する。）を加え、３０分間保持した後、酢酸を用いてｐＨ値を７．５に調整した。次いで、前記発明の実施の形態と同様にして濾別、水洗、乾燥した後、粉砕して粒子表面が被覆物により被覆されている針状ヘマタイト粒子粉末を得た。
【０１４６】
＜非磁性下地層の製造＞
実施例１〜７及び比較例１〜４
非磁性粒子Ａ１〜Ａ１１の針状非磁性粒子粉末を用いて前記発明の実施の形態と同様にして非磁性下地層を得た。
【０１４７】
この時の主要製造条件及び諸特性を表３に示す。
【０１４８】
【表３】

【０１４９】
＜磁気記録媒体の製造＞
実施例８〜２４及び比較例５〜１２
非磁性下地層の種類、磁性粒子粉末の種類を種々変化させた以外は、前記発明の実施の形態と同様にして磁気記録媒体を製造した。
【０１５０】
この時の主要製造条件及び諸特性を表４及び表５に示す。
【０１５１】
【表４】

【０１５２】
【表５】

【０１５３】
【発明の効果】
本発明に係る磁気記録媒体は、粒子内部にジルコニウムをほぼ均一に含有している非磁性粒子粉末であることに起因して、基体としての強度と表面性に優れている非磁性下地層を得ることができ、該非磁性下地層を用いて磁気記録媒体とした場合において光透過率が小さく、表面平滑で、強度が大きい磁気記録媒体を得ることができ、しかも、該磁気記録媒体は、非磁性下地層用非磁性粒子粉末として粒子内部にジルコニウムを均一に含有している針状非磁性粒子粉末を用いたことに起因して耐久性に優れたものであるので、高密度記録用磁気記録媒体として好ましいものである。[0001]
[Industrial application fields]
The present invention provides a substrate for a magnetic recording medium having a nonmagnetic underlayer having a low light transmittance, a smooth surface, a high strength, and excellent durability, and a magnetic recording medium using the substrate. Objective.
[0002]
[Prior art]
In recent years, as video recording and audio magnetic recording / reproducing devices have been recorded for a long time and reduced in size and weight, the performance of magnetic recording media such as magnetic tapes and magnetic disks has been improved, that is, higher recording density and higher output characteristics. In particular, there is an increasing demand for improvement of frequency characteristics and low noise.
[0003]
In order to improve these various characteristics of the magnetic recording medium, various attempts have been made in terms of both high performance of the magnetic particle powder and thinning of the magnetic recording layer.
[0004]
First, the performance enhancement of the magnetic particle powder will be described.
[0005]
A characteristic of the magnetic particle powder suitable for satisfying the above requirements for the magnetic recording medium is that it has a high coercive force and a large saturation magnetization.
[0006]
In recent years, as a magnetic particle powder suitable for high output and high density recording, it is possible to reduce ac-coated magnetic iron oxide particles, acicular goethite particles or acicular hematite particles in which ac is coated on acicular maghemite particles or acicular magnetite particles. Acicular metal magnetic particle powders mainly composed of iron obtained by heat reduction in a gas are widely used.
[0007]
Next, the thinning of the magnetic recording layer will be described.
[0008]
Recently, the demand for higher image quality of video tapes is increasing, and the frequency of the carrier signal to be recorded is higher than that of conventional video tapes. That is, it has shifted to the short wavelength region, and as a result, the magnetization depth from the surface of the magnetic tape is remarkably shallow.
[0009]
In order to improve the high output characteristics of a magnetic recording medium, particularly the S / N ratio, with respect to a short wavelength signal, it is strongly required to make the magnetic recording layer thinner. This is the case, for example, “Development of Magnetic Materials and Highly Dispersed Magnetic Powder Technology” (1982), page 312 published by the General Technology Center Co., Ltd. The high output characteristics can be maintained with low noise with respect to the wavelength signal. For this purpose, both the coercive force Hc and the residual magnetization Br are required to be large and the coating film must be thinner. "..." as described.
[0010]
As the magnetic recording layer becomes thinner, several problems have arisen. First, it is a problem of smoothing and uneven thickness of the magnetic recording layer. As is well known, in order to make the magnetic recording layer smooth and free of uneven thickness, the surface of the base film must also be smooth. . This is the case, for example, published by the Engineering Information Center Publishing Department, "Magnetic Tape-Friction and Wear Occurrence Factors and Trouble Countermeasures for the Head Running System-Comprehensive Technical Documents" (hereinafter referred to as "Comprehensive Technical Documents Collection"). “The surface roughness of the magnetic layer after curing is strongly dependent on the surface roughness of the base (back surface roughness), and the two are almost proportional to each other. As the surface of the base is smoothened, the uniform and large head output is obtained and the S / N is improved.
[0011]
Secondly, the base film is also made thinner like the magnetic layer, and as a result, the strength of the base film has become a problem. This fact is, for example, the above-mentioned “Development of magnetic materials and high dispersion technology of magnetic powder” on page 77 “… ...... High density recording is a major theme imposed on the current magnetic tape. In order to shorten the length of the tape and miniaturize the cassette, it is important for long-time recording, which requires reducing the thickness of the film base. As the tape becomes thinner, the tape stiffness decreases sharply, making it difficult for the recorder to run smoothly. The improvement is greatly desired.
[0012]
By the way, determination of the end of the magnetic tape of a magnetic recording medium such as a video tape is currently performed by detecting a portion of the magnetic recording medium having a high light transmittance with a video deck. Magnetic recording media become difficult to detect if the light transmittance of the entire magnetic recording layer increases as the magnetic recording medium becomes thinner or the magnetic particle powder dispersed in the magnetic recording layer becomes ultrafine. The light transmittance is reduced by adding carbon black or the like to the layer. Therefore, the addition of carbon black or the like to the magnetic recording layer is essential in the current video tape.
[0013]
However, the addition of a large amount of nonmagnetic carbon black or the like not only inhibits high density recording, but also inhibits thinning. In order to further reduce the thickness of the magnetic tape by reducing the magnetization depth from the surface of the magnetic tape, it is strongly required to reduce the nonmagnetic particle powder such as carbon black added to the magnetic recording layer as much as possible. Yes.
[0014]
Therefore, there is a strong demand for a magnetic recording medium having a low light transmittance even if the amount of carbon black added to the magnetic recording layer is reduced. From this point, improvement of the substrate is also strongly demanded.
[0015]
Furthermore, the demand for higher performance of magnetic recording media has not been limited recently, and the surface of the magnetic recording layer and the magnetic recording medium itself have been reduced along with the thinning of the magnetic recording layer and the thinning of the nonmagnetic support described above. Therefore, it is strongly required to improve the durability of the magnetic recording layer surface and the magnetic recording medium itself.
[0016]
This fact is disclosed in Japanese Patent Application Laid-Open No. 5-298679 “In recent years, with the development of magnetic recording, the demand for high image quality and high sound quality has been increasing. There is a demand for higher density, lower noise by smoothing the surface of the magnetic tape, and higher C / N .... However, while the magnetic tape is running, As a result of the increase in the friction coefficient of contact, the magnetic layer of the magnetic recording medium tends to be damaged or peeled off after a short period of use, especially in video tapes, the video head and magnetic recording medium contact at high speed. However, since the ferromagnetic powder tends to fall off from the magnetic layer and cause clogging of the magnetic head, it is desired to improve the running durability of the magnetic layer of the magnetic recording medium. It is clear from the description made.
[0017]
Various attempts have been made to improve the substrate for forming the magnetic recording layer as the magnetic recording layer is thinned or the nonmagnetic support is thinned. It is possible to provide at least one underlayer (hereinafter referred to as a nonmagnetic underlayer) in which nonmagnetic particle powders containing iron as a main component, such as hematite particles and hydrous ferric oxide particles, are dispersed in a binder. Have already been put into practical use (Japanese Patent Publication No. 6-93297, Japanese Patent Application Laid-Open No. 62-159338, Japanese Patent Application Laid-Open No. 63-187418, Japanese Patent Application Laid-Open No. Hei 4-167225, Japanese Patent Application Laid-Open No. Hei 4- No. 325915, JP-A-5-73882, JP-A-5-182177, JP-A-5-347017, JP-A-6-60362, and the like.
[0018]
Further, as the nonmagnetic particle powder for the nonmagnetic underlayer, there is known a nonmagnetic particle whose surface is treated with a zirconium compound or the like for the purpose of improving dispersibility in a vehicle (Japanese Patent No. 2566088). Japanese Patent No. 2571350, Japanese Patent No. 255821, JP-A-6-60362, JP-A-9-22524, JP-A-9-27117, JP-A-5-73883, JP-A-6-60360. No. 8, JP-A-8-50718, JP-A-8-255334, JP-A-9-27116, JP-A-9-27117, JP-A-9-35245).
[0019]
[Problems to be solved by the invention]
Magnetic recording media with low light transmittance, smooth surface, high strength, and excellent durability as well as thin magnetic recording layers are now available. Although most demanded, a magnetic recording medium that sufficiently satisfies these various characteristics has not yet been obtained.
[0020]
That is, a magnetic recording medium manufactured using a substrate having a nonmagnetic underlayer formed by dispersing nonmagnetic powder in a binder resin on a nonmagnetic support has a low light transmittance, a smooth surface, and strength. However, there was a problem that the durability was poor.
[0021]
This fact is disclosed in Japanese Patent Application Laid-Open No. 5-182177, "If the magnetic layer is provided as an upper layer after providing a non-magnetic thick undercoat layer on the support surface, the effect of the surface roughness of the support is described. However, there is a problem that the head wear and durability are not improved because the thermosetting resin is used as a binder as a non-magnetic lower layer, and the lower layer is hardened and magnetic. It is considered that the friction between the layer and the head and the contact with other members are performed in an unbuffered state, and the magnetic recording medium having such a lower layer is slightly inflexible. ... ”As described.
[0022]
Accordingly, it is a technical object of the present invention to obtain a magnetic recording medium having low light transmittance, smooth surface, high strength, and excellent durability.
[0023]
[Means for solving the problems]
The technical problem can be achieved by the present invention as follows.
[0024]
That is, the present invention relates to a magnetic recording medium substrate comprising a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support, and a nonmagnetic underlayer containing a binder resin. Is a needle-like non-magnetic particle powder mainly containing iron containing 0.05 to 30% by weight of zirconium in terms of Zr, and if necessary, further, an aluminum hydroxide, an aluminum oxide, A needle-shaped nonmagnetic particle powder mainly composed of iron, the particle surface of which is coated with at least one of silicon hydroxide and silicon oxide, and having a major axis diameter of the needle-shaped nonmagnetic particle A magnetic recording medium substrate having a nonmagnetic underlayer characterized by having a geometric standard deviation value of 1.50 or less .
[0025]
The present invention also provides a magnetic recording medium in which a magnetic recording layer including magnetic particle powder and a binder resin is provided on a magnetic recording medium substrate having the nonmagnetic underlayer.
[0026]
The configuration of the present invention will be described in more detail as follows.
[0027]
First, a magnetic recording medium substrate having a nonmagnetic underlayer according to the present invention will be described.
[0028]
The nonmagnetic particle powder containing iron as a main component in the present invention is a hydrous ferric oxide particle powder such as acicular goethite (α-FeOOH) particle or an acicular hematite particle powder. These particle powders are converted into Zr. 0.05 to 30% by weight of zirconium is contained almost uniformly inside the particles.
[0029]
When the amount of zirconium contained in the particles is less than 0.05% by weight in terms of Zr with respect to acicular nonmagnetic particles containing iron as a main component, the obtained magnetic recording medium has sufficient durability. do not do. When it exceeds 30% by weight, the obtained magnetic recording medium has sufficient durability, but since the effect is saturated, it is meaningless to contain more than necessary. Considering the durability of the magnetic recording medium, 0.5 to 25% by weight is preferable. More preferably, it is 1.0 to 20% by weight.
[0030]
The acicular nonmagnetic particle powder mainly composed of iron in the present invention has an axial ratio (average major axis diameter: average minor axis diameter, hereinafter simply referred to as “axial ratio”) of 2: 1 or more, preferably 3: One or more particles are preferred. In consideration of the dispersibility in the vehicle, the upper limit is preferably 20: 1 or less, preferably 10: 1 or less. Here, the acicular particles mean not only acicular shapes but also spindle shapes, rice grains, and the like.
[0031]
When the axial ratio is less than 2: 1, it is difficult to obtain a desired coating strength.
[0032]
The average major axis diameter of the acicular nonmagnetic particle powder containing iron as a main component in the present invention is 0.3 μm or less. When the average major axis diameter exceeds 0.3 μm, the particle size is too large, which is not preferable because the surface smoothness of the coating film is impaired. When the average major axis diameter of the acicular nonmagnetic particles containing iron as the main component is less than 0.005 μm, it is difficult to disperse in the vehicle, which is not preferable. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, 0.02 to 0.2 μm is preferable.
[0033]
The acicular nonmagnetic particle powder mainly containing iron in the present invention preferably has an average minor axis diameter of 0.0025 to 0.15 μm. If it is less than 0.0025 μm, it is not preferable because dispersion in the vehicle becomes difficult. When the average minor axis diameter exceeds 0.15 μm, the particle size is too large, which is not preferable because the surface smoothness of the coating film is impaired. In consideration of the dispersibility in the vehicle and the surface smoothness of the coating film, 0.01 to 0.10 μm is preferable.
[0034]
The acicular goethite particle powder as the acicular nonmagnetic particle powder containing iron as a main component in the present invention preferably has a BET specific surface area value of 50 m ² / g or more. If it is less than 50 m ² / g, it adversely affects the surface smoothing of the coating film, which is not preferable. Preferably it is 70 m < ² > / g or more, More preferably, it is 80 m < ² > / g or more, The upper limit is 300 m < ² > / g. Considering the dispersibility in the vehicle, it is preferably 250 m ² / g or less, more preferably 200 m ² / g or less.
[0035]
The acicular hematite particle powder as the acicular nonmagnetic particle powder containing iron as a main component in the present invention preferably has a BET specific surface area of 35 m ² / g or more. When it is less than 35 m ² / g, the hematite particles are coarse, or particles are sintered between the particles, which is not preferable because it adversely affects the surface smoothing of the coating film. Preferably it is 40 m < ² > / g or more, More preferably, it is 45 m < ² > / g or more, The upper limit is 300 m < ² > / g. Considering the dispersibility in the vehicle, it is preferably 100 m ² / g or less, more preferably 80 m ² / g or less.
[0036]
The acicular nonmagnetic particle powder mainly composed of iron in the present invention preferably has a major axis diameter particle size distribution of 1.50 or less in terms of geometric standard deviation. When it exceeds 1.50, the existing coarse particles adversely affect the surface smoothing of the coating film, which is not preferable. Considering the surface smoothness of the coating film, it is preferably 1.40 or less, more preferably 1.35 or less. Considering industrial productivity, the lower limit value of the particle size distribution of the major axis diameter of the acicular nonmagnetic particles mainly composed of iron is 1.01 in terms of geometric standard deviation.
[0037]
The acicular nonmagnetic particles mainly composed of iron in the present invention have a resin adsorption strength of 60% or more, preferably 65% or more, and more preferably 68% or more.
[0038]
The acicular hematite particles in the present invention have a specific surface area calculated from a specific surface area S _BET value obtained by measuring the degree of densification by the BET method and a major axis diameter and a minor axis diameter measured from the particles shown in the electron micrograph. If indicated by the ratio of the S _TEM value, preferably those having a 0.5 to 2.5. In consideration of the surface smoothness of the coating film and the dispersibility in the vehicle, the value of S _BET / S _TEM is preferably 0.7 to 2.0, more preferably 0.8 to 1.6.
[0039]
In the present invention, the surface of the acicular nonmagnetic particles mainly composed of iron is coated with at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide, if necessary. It may be. The acicular non-magnetic particles mainly composed of iron whose particle surfaces are coated with these surface coatings have good dispersibility in the vehicle because they have good compatibility with the binder resin.
[0040]
In the case of aluminum hydroxide or aluminum oxide, the amount of the surface coating is about 0.1% of the total weight of the particles in terms of Al, and in the case of silicon hydroxide or silicon oxide, the amount of SiO _{2 is} converted to SiO ₂ . 01 to 50% by weight is preferred. When the amount is less than 0.01% by weight, it is difficult to obtain the effect of improving the dispersibility by coating. When the amount exceeds 50% by weight, the coating effect is saturated, so there is no need to add more than necessary. Considering the dispersibility in the vehicle, 0.05 to 20% by weight is more preferable.
[0041]
Axial ratio, average major axis diameter, average minor axis diameter, BET specific surface area value, major axis diameter particle size distribution, resin of acicular non-magnetic particle powder whose main component is iron coated with surface coating The adsorption strength and the degree of densification are substantially the same as those of acicular nonmagnetic particle powder mainly composed of iron that is not coated with the surface coating.
[0042]
The nonmagnetic underlayer in the present invention is formed on a nonmagnetic support and is composed of acicular nonmagnetic particle powder mainly composed of iron and a binder resin.
[0043]
As non-magnetic supports, synthetic resin films such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, and polyimide, which are currently widely used for magnetic recording media, metal foils such as aluminum and stainless steel, A board and various papers can be used, and the thickness varies depending on the material, but usually 1.0 to 300 μm, more preferably 2.0 to 200 μm is used. In the case of a magnetic disk, polyethylene terephthalate is usually used as a nonmagnetic support, and the thickness is usually 50 to 300 μm, preferably 60 to 200 μm. In the case of magnetic tape, the thickness varies depending on the material. In the case of polyethylene terephthalate, it is usually 3 to 100 μm, preferably 4 to 20 μm, and in the case of polyethylene naphthalate, it is usually 3 to 50 μm, preferably 4 to 20 μm. In the case of polyamide, it is usually 2 to 10 μm, preferably 3 to 7 μm.
[0044]
The coating thickness of the nonmagnetic underlayer formed on the nonmagnetic support in the present invention is in the range of 0.2 to 10.0 μm. When the thickness is less than 0.2 μm, it is difficult to improve the surface roughness of the nonmagnetic support, and the strength tends to be insufficient. In order to obtain a thin magnetic recording medium, the upper limit is preferably about 10.0 μm, more preferably in the range of 0.5 to 5.0 μm.
[0045]
As binder resin, vinyl chloride-vinyl acetate copolymer resin, urethane resin, vinyl chloride-vinyl acetate-maleic acid copolymer resin, urethane elastomer, butadiene-acrylonitrile copolymer, which are currently widely used in the production of magnetic recording media. Resins, cellulose derivatives such as polyvinyl butyral and nitrocellulose, synthetic rubber resins such as polyester resins and polybutadiene, epoxy resins, polyamide resins, polyisocyanate polymers, electron beam curable acrylic urethane resins, and mixtures thereof can be used. Each binder resin contains polar groups such as —OH, —COOH, —SO ₃ M, —OPO ₂ M ₂ , —NH ₂ (where M is H, Na, K). May be. Considering the dispersibility of the particles, a binder resin containing polar groups —COOH and —SO ₃ M is preferable.
[0046]
The blending ratio of the acicular nonmagnetic particle powder mainly composed of iron and the binder resin in the nonmagnetic underlayer is such that the acicular nonmagnetic particles mainly composed of iron are 5 to 100 parts by weight of the binder resin. The amount is 2000 parts by weight, preferably 100 to 1000 parts by weight.
[0047]
Incidentally, the nonmagnetic underlayer may contain a lubricant, an abrasive, an antistatic agent, etc. used in the production of a normal magnetic recording medium as required.
[0048]
The nonmagnetic underlayer containing acicular nonmagnetic particle powder mainly composed of iron in the present invention has a coating film glossiness of 170 to 280%, preferably 180 to 280%, more preferably 185 to 280%, The coating film surface roughness Ra is 2.0 to 15.0 nm, preferably 2.0 to 13.0 nm, more preferably 2.0 to 12.0 nm, and the Young's modulus is 125 to 150, preferably 127 to 150. Preferably it is 130-150.
[0049]
Next, the magnetic recording medium according to the present invention will be described.
[0050]
In a magnetic recording medium, a magnetic recording layer made of magnetic particle powder and a binder resin is provided on a nonmagnetic underlayer formed on a nonmagnetic support.
[0051]
In the present invention, the magnetic particle powder includes maghemite particle powder, magnetite particle powder, magnetic iron oxide particle powder such as beltride compound particles which are intermediate oxides of maghemite and magnetite, and these magnetic iron oxide particle powders in addition to Fe. , Particles containing different elements such as Al, Ni, P, Zn, Si, B or the like, particles obtained by depositing Co or the like on these magnetic iron oxide particles, metal magnetic particles mainly containing iron, other than iron Iron alloy magnetic particles containing Co, Al, Ni, P, Zn, Si, B, etc., plate-like Ba ferrite particle powder, and divalent metals (Co, Ni, Zn, etc.) 4 Any plate-like composite ferrite particle powder containing a valent metal (Ti, Sn, Zr, etc.) can be used. The magnetic particle powder has an average major axis diameter of 0.01 to 0.50 μm, preferably 0.03 to 0.30 μm, and an average minor axis diameter of 0.0007 to 0.17 μm, preferably 0.00. Particles having a diameter of 003 to 0.10 μm and an axial ratio of 3: 1 or more, preferably 5: 1 or more are preferred. Considering the dispersibility in the vehicle, the upper limit of the axial ratio is 15: 1 or less, preferably 10: 1 or less. The shape of the particles may be any of a spindle shape, a rice grain shape, a cubic shape, a plate shape, etc. as well as a needle shape.
[0052]
The magnetic characteristics of the magnetic particle powder in the present invention are preferably 300 to 3200 Oe, more preferably 700 to 2500 Oe, and a saturation magnetization of 60 to 170 emu / g, considering various characteristics such as high density recording. Is more preferable, and 70-170 emu / g is more preferable.
[0053]
As the binder resin in the magnetic recording layer, the binder resin used to form the nonmagnetic underlayer can be used.
[0054]
The coating thickness of the magnetic recording layer provided on the nonmagnetic underlayer is in the range of 0.01 to 5.0 μm. When the thickness is less than 0.01 μm, uniform coating is difficult and uneven coating tends to occur. When the thickness exceeds 5.0 μm, it is difficult to obtain the electromagnetic conversion characteristics of the magnetic recording medium due to the influence of the demagnetizing field. Preferably it is the range of 0.05-1.0 micrometer.
[0055]
The blending ratio of the magnetic particle powder and the binder resin in the magnetic recording layer is 200 to 2000 parts by weight, preferably 300 to 1500 parts by weight with respect to 100 parts by weight of the binder resin.
[0056]
The magnetic recording layer may contain a lubricant, an abrasive, an antistatic agent and the like that are usually used as necessary.
[0057]
The magnetic recording medium according to the present invention has a coercive force of 300 to 3500 Oe, preferably 500 to 3500 Oe, more preferably 700 to 3500 Oe, and a squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95. The glossiness of the coating film is preferably 180 to 300%, preferably 190 to 300%, and the coating film surface roughness Ra is 12.0 nm or less, preferably 2.0 to 11.0 nm. More preferably, 2.0 to 10.0 nm, Young's modulus is 130 or more, preferably 132 or more, and the linear absorption coefficient of the coating is 1.10 to 2.00 μm ^−1, preferably 1.20 to 2.00 μm ⁻¹ Of the durability, the running durability is 15 minutes or more, preferably 20 minutes or more, more preferably 22 minutes or more, and the scratch resistance is B or more, preferably A.
[0058]
Next, production of acicular goethite particle powder which is the acicular non-magnetic particle powder containing iron as a main component in the present invention and which contains zirconium substantially uniformly inside the particle which is also a starting material of acicular hematite particles State the law.
[0059]
The acicular goethite particles containing zirconium in the inside of the particles substantially uniformly include, as will be described in detail later, a ferrous salt aqueous solution and an alkali hydroxide aqueous solution, an alkali carbonate aqueous solution, or an alkali hydroxide / alkali carbonate aqueous solution. When producing acicular goethite particles by aerating an oxygen-containing gas such as air to a suspension containing iron-containing precipitates such as iron hydroxide and iron carbonate obtained by reaction using the above suspension It can be obtained by allowing a zirconium compound to be present in an amount of 0.04 mol% to 40 mol% in terms of Zr with respect to Fe before venting an oxygen-containing gas such as air.
[0060]
As the zirconium compound, zirconium sulfate, zirconium oxysulfate, zirconium nitrate, zirconium acetate, zirconium chloride and the like can be used.
[0061]
The needle-like goethite particles obtained in this way are particles containing zirconium substantially uniformly from the center of the particle to the particle surface.
[0062]
In addition, as a typical basic reaction of acicular goethite particles, (1) a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution has a pH value. A method of generating acicular goethite particles by conducting an oxidation reaction by bubbling an oxygen-containing gas at a temperature of 11 to 80 ° C., and (2) obtained by reacting a ferrous salt aqueous solution and an alkali carbonate aqueous solution. A method of producing spindle-shaped goethite particles by performing an oxidation reaction by aeration of an oxygen-containing gas after aging the suspension containing FeCO ₃ as required, and (3) an aqueous ferrous salt solution, A suspension containing an iron-containing precipitate obtained by reacting with an alkali carbonate / alkali hydroxide aqueous solution is aged as necessary, and then an oxygen-containing gas is passed through to carry out an oxidation reaction to thereby form a spindle-shaped gate (4) Oxygen-containing gas in ferrous salt aqueous solution containing ferrous hydroxide colloid obtained by adding less than equivalent aqueous alkali hydroxide solution or aqueous alkali carbonate solution to ferrous salt aqueous solution To generate acicular goethite core particles by performing an oxidation reaction, and then the ferrous salt aqueous solution containing the acicular goethite core particles is equivalent to Fe ²⁺ in the ferrous salt aqueous solution. A method of growing the needle-like goethite core particles by adding an oxygen-containing gas after adding the above alkali hydroxide aqueous solution, and (5) adding less than an equivalent amount of an alkali hydroxide aqueous solution or an alkali carbonate aqueous solution to the ferrous salt aqueous solution. The needle-shaped goethite core particles are produced by performing an oxidation reaction by aerating an oxygen-containing gas to a ferrous salt aqueous solution containing the ferrous hydroxide colloid obtained by addition, and then generating the needle-shaped goethite After adding an alkali carbonate aqueous solution equal to or more than the Fe ²⁺ in the ferrous salt aqueous solution to the ferrous salt aqueous solution containing the core particles, the needle-like goethite core particles are grown by ventilating an oxygen-containing gas. And (6) oxidation by introducing an oxygen-containing gas into a ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by adding less than an equivalent amount of alkali hydroxide or alkali carbonate aqueous solution to the ferrous salt aqueous solution. There is a method of generating acicular goethite core particles by performing a reaction, and then growing the acicular goethite core particles in an acidic to neutral region.
[0063]
Next, a method for producing acicular hematite particle powder containing zirconium almost uniformly inside the particles will be described.
[0064]
The acicular hematite particles containing the zirconium in the particles almost uniformly can be obtained by heating and dehydrating the acicular goethite particles containing the zirconium in the particles almost uniformly.
[0065]
The heating dehydration temperature is about 250 to 800 ° C. Considering the degree of densification of acicular hematite particles containing zirconium uniformly in the obtained particles, acicular hematite particles densified by heating and dehydrating at 550 to 800 ° C. are more preferable.
[0066]
In particular, when heat-dehydrating at a high temperature of 550 ° C. or higher, as is well known, the surface of the needle-like goethite particles may be coated with a sintering inhibitor prior to the heat-dehydration of the needle-like goethite particles. preferable.
[0067]
As sintering inhibitors, commonly used phosphorus compounds such as sodium hexametaphosphate, polyphosphoric acid, orthophosphoric acid, No. 3 water glass, silicon compounds such as sodium orthosilicate, sodium metasilicate, colloidal silica, boron such as boric acid Use aluminum salts such as compounds, aluminum acetate, aluminum sulfate, aluminum chloride, and aluminum nitrate, alkali aluminates such as sodium aluminate, aluminum compounds such as alumina sol and aluminum hydroxide, and titanium compounds such as titanium oxysulfate. Can do.
[0068]
The amount of the sintering inhibitor present on the surface of the acicular nonmagnetic particles containing iron as a main component is preferably about 0.05 to 10% by weight with respect to the total weight of the particles.
[0069]
Next, a method for coating the surface of the acicular nonmagnetic particles in the present invention with a surface coating will be described.
[0070]
The coating treatment is performed by adding an aluminum compound, a silicon compound, or both of these compounds to an aqueous suspension obtained by dispersing a cake, slurry, or dry powder of acicular goethite particles or acicular hematite particles in an aqueous solution, and mixing and stirring. By adjusting the pH value if necessary, the surface of the acicular hematite particles is coated with aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. Then, it may be filtered, washed with water, dried and pulverized. If necessary, a deaeration / consolidation process may be further performed.
[0071]
As the aluminum compound in the coating treatment, the same one as the above-mentioned sintering inhibitor can be used.
[0072]
The addition amount of the aluminum compound is 0.01 to 50% by weight in terms of Al with respect to the acicular nonmagnetic particle powder. When the amount is less than 0.01% by weight, the acicular nonmagnetic particle powder obtained is insufficiently compatible with the binder resin expected by coating the aluminum compound, and when the amount exceeds 50% by weight. Does not make sense to add more than necessary because the coating effect is saturated.
[0073]
As the silicon compound in the coating treatment, the same one as the above-mentioned sintering inhibitor can be used.
[0074]
The addition amount of the silicon compound is 0.01 to 50% by weight in terms of SiO ₂ with respect to the acicular nonmagnetic particle powder. When the amount is less than 0.01% by weight, the acicular non-magnetic particle powder obtained is insufficiently compatible with the binder resin expected by coating the silicon compound, and exceeds 50% by weight. Does not make sense to add more than necessary because the coating effect is saturated.
[0075]
When used in conjunction with an aluminum compound and a silicon compound, to acicular non-magnetic particles, 0.01 to 50 wt% in total of Al equivalent amount and SiO ₂ equivalent amount is preferred.
[0076]
Next, a method for producing a magnetic recording medium substrate having a nonmagnetic underlayer according to the present invention will be described.
[0077]
The substrate for a magnetic recording medium according to the present invention is formed by applying a nonmagnetic coating material containing a needle-like nonmagnetic particle powder mainly composed of iron, a binder resin, and a solvent on a nonmagnetic support to form a coating film. Obtained by drying.
[0078]
As the solvent, it is possible to use methyl ethyl ketone, toluene, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, a mixture thereof, and the like that are currently widely used in the production of magnetic recording media.
[0079]
The amount of the solvent used is 50 to 1000 parts by weight in total with respect to 100 parts by weight of the nonmagnetic particle powder. If it is less than 50 parts by weight, the viscosity becomes too high when it is used as a non-magnetic paint, making application difficult. When it exceeds 1000 parts by weight, the volatilization amount of the solvent at the time of forming the coating film becomes too large, which is industrially disadvantageous.
[0080]
Next, a method for manufacturing a magnetic recording medium according to the present invention will be described.
[0081]
In the magnetic recording medium according to the present invention, a coating composition containing magnetic particle powder, a binder resin and a solvent is applied onto a nonmagnetic underlayer to form a coating film, and then dried to form a magnetic recording layer. Can be obtained.
[0082]
As the solvent, it is possible to use methyl ethyl ketone, toluene, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, a mixture thereof, and the like that are currently widely used in the production of magnetic recording media.
[0083]
The total amount of the solvent used is 65 to 1000 parts by weight with respect to 100 parts by weight of the magnetic particle powder. If it is less than 65 parts by weight, the viscosity becomes too high when it is used as a non-magnetic coating material, making application difficult. When it exceeds 1000 parts by weight, the volatilization amount of the solvent at the time of forming the coating film becomes too large, which is industrially disadvantageous.
[0084]
DETAILED DESCRIPTION OF THE INVENTION
A typical embodiment of the present invention is as follows.
[0085]
The average major axis diameter and average minor axis diameter of the particles are the major axis diameter and minor axis diameter of about 350 particles shown in the photograph obtained by enlarging the electron micrograph (× 30000) four times in the vertical and horizontal directions, respectively. Each was measured, and the average value was shown. The axial ratio is the ratio of the average major axis diameter to the average minor axis diameter.
[0086]
The geometric standard deviation value (σg) of the major axis diameter of the particle was indicated by a value obtained by the following method. That is, the value measured for the major axis diameter of the particles shown in the above enlarged photograph is calculated on the basis of the actual major axis diameter and the number of particles calculated from the measured value, and the horizontal axis on the lognormal probability paper according to a statistical method. The major axis diameter of the particles is plotted on the vertical axis, and the cumulative number of particles belonging to each of the predetermined major axis diameter sections (under the integrated sieve) is plotted in percentage on the vertical axis. Then, the value of the major axis diameter corresponding to the number of particles of 50% and 84.13% is read from this graph, and the geometrical standard deviation value (σg) = major axis diameter / integrated at 84.13% under the integrated fluid. The value was calculated according to the major axis diameter (geometric mean diameter) at 50% under the sieve. The smaller the geometric standard deviation value, the better the particle size distribution of the major axis diameter of the particles.
[0087]
The specific surface area was shown by the value measured by BET method.
[0088]
The degree of densification of the acicular hematite particles was indicated by S _BET / S _{TEM as} described above. Here, S _BET is a value of the specific surface area measured by the BET method. S _TEM, the average major axis diameter lcm of particles measured from the electron micrograph, the average particle using short axis diameter wcm assuming cuboid is a value calculated according to the following equation.
[0089]
S _TEM (m ² / g) = [(4lw + 2w ² ) / (lw ² · ρ _p )] × 10 ⁻⁴ (where ρ _p is the true specific gravity of the hematite particles, and 5.2 g / cm ³ was used. .) Since _STEM is the specific surface area of particles with no dehydration holes inside and on the particle surface and smooth surfaces, the closer the value of S _BET / _STEM is to 1, the more dehydrated inside and on the surface of hematite particles. This means that the particles have few pores and have a smooth surface, in other words, high-density particles.
[0090]
The amount of each of Zr, Al and Si present in the inside and the surface of the acicular nonmagnetic particles was measured by fluorescent X-ray analysis.
[0091]
The coating viscosity at 25 ° C. of the obtained coating was measured using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.) and indicated by a value at a shear rate D = 1.92 sec ⁻¹ . .
[0092]
The resin adsorption strength indicates the degree to which the resin is adsorbed to the particles. The closer the value obtained by the following method is to 100, the stronger the resin is adsorbed to the acicular nonmagnetic particles, and the better. .
[0093]
First, the resin adsorption amount Wa is obtained. 100 ml of 20 g of particle powder and 56 g of a mixed solvent (methyl ethyl ketone 27.0 g, toluene 16.2 g, cyclohexanone 10.8 g) in which 2 g of vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group are dissolved, together with 120 g of 3 mmφ steel beads Place in a plastic bottle and mix and disperse in a paint shaker for 60 minutes.
[0094]
Next, 50 g of this coating composition is taken out, put into a 50 ml settling tube, and centrifuged at 10000 rpm for 15 minutes to separate the solid portion and the solvent portion. Then, the resin solid content concentration contained in the solvent portion is quantified by a gravimetric method, and the amount of resin present in the solid portion is obtained by subtraction from the charged resin amount, and this is the resin adsorption amount Wa (mg / g) to the particles. And
[0095]
Next, only the solid part separated previously was taken out into a 100 ml tall beaker, and 50 g of a mixed solvent (methyl ethyl ketone 25.0 g, toluene 15.0 g, cyclohexanone 10.0 g) was added thereto, and ultrasonic dispersion was performed for 15 minutes. After making it into a suspended state, it is placed in a 50 ml settling tube and centrifuged at a rotational speed of 10,000 rpm for 15 minutes to separate the solid portion and the solvent portion. Then, by measuring the resin solid content concentration in the solvent portion, the amount of resin extracted into the solvent phase out of the resin adsorbed on the particle surface is quantified.
[0096]
Further, the operation from taking out the total amount of only the solid portion into a 100 ml tall beaker to determining the amount of the resin dissolved in the solvent phase was repeated twice, and the total amount We (mg of resin extracted in the solvent phase was totaled 3 times. / G), and the value obtained according to the following formula was defined as the resin adsorption strength T (%).
[0097]
T (%) = [(Wa-We) / Wa] × 100
Higher T indicates stronger and better resin adsorption on the powder surface in the vehicle.
[0098]
The glossiness of the coating surface of the nonmagnetic underlayer and magnetic recording layer was determined by measuring the 45 ° glossiness of the coating using “Gloss Meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.).
[0099]
Surface roughness Ra measured the centerline average roughness of the coating film using "Surfcom-575A" (made by Tokyo Seimitsu Co., Ltd.).
[0100]
The durability of the magnetic recording medium was evaluated by determining the following running durability and scratch characteristics.
[0101]
The running durability was evaluated based on the actual moving time at a load of 200 gw and a relative speed of the head and the tape of 16 m / s, using “Media Durability Tester MDT-3000” (manufactured by Steinberg Associates). The longer the actual movable time, the better the running durability.
[0102]
For the scratch characteristics, the surface of the tape after running was observed with a microscope, the presence or absence of the scratch was visually evaluated, and the following four grades were evaluated.
A: No scratch B: Slight scratch C: Scratch D: Severe scratch [0103]
The coating film strength was obtained by measuring the Young's modulus of the coating film using “Autograph” (manufactured by Shimadzu Corporation). The Young's modulus was expressed as a relative value with a commercially available video tape “AV T-120 (manufactured by Victor Company of Japan)”. It shows that it is so favorable that a relative value is high.
[0104]
The magnetic characteristics were measured using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) up to an external magnetic field of 10 KOe.
[0105]
The degree of light transmission is a linear absorption coefficient calculated by inserting the value of light transmittance measured for a magnetic recording medium using “Self-recorded photoelectric spectrophotometer UV-2100” (manufactured by Shimadzu Corporation) into the following equation. Indicated. The larger the value of the linear absorption coefficient, the less light is transmitted.
[0106]
In measuring the value of light transmittance, the same nonmagnetic support as the nonmagnetic support used in the magnetic recording medium was used as a blank.
[0107]
Linear absorption coefficient (μm ⁻¹ ) = [ln (1 / t)] / FT
t: Light transmittance at λ = 900 nm (−)
FT: Thickness (μm) of coating layer of film used for measurement (total thickness of nonmagnetic underlayer and magnetic recording layer)
[0108]
The thicknesses of the nonmagnetic support, the nonmagnetic underlayer and the magnetic recording layer constituting the magnetic recording medium were measured as follows.
[0109]
First, the film thickness (A) of the nonmagnetic support is measured using a digital electronic micrometer K351C (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support (the sum of the thickness of the nonmagnetic support and the nonmagnetic underlayer) was measured in the same manner. To do. Furthermore, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the sum of the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer). ) Is measured in the same manner. The thickness of the nonmagnetic underlayer is indicated by B-A, and the thickness of the magnetic recording layer is indicated by CB.
[0110]
<Production of spindle-shaped goethite particle powder>
Using a ferrous sulfate aqueous solution, a zirconium oxysulfate aqueous solution, and a sodium carbonate aqueous solution, 3.78% by weight of zirconium in terms of Zr obtained by the above-described goethite particle production method (2) is uniformly contained inside the particles. Spindle-shaped goethite particle powder (average major axis diameter 0.150 μm, average minor axis diameter 0.0183 μm, axial ratio 8.2, BET specific surface area value 151.6 m ² / g and geometric standard deviation value 1.36) 1440 g A reaction slurry containing was obtained.
[0111]
This is filtered through a press filter, washed with pure water until the electric conductivity is 30 μs or less, then dried and pulverized, and 1380 g of spindle-shaped goethite particle powder containing zirconium uniformly inside the particles. Got. The resin adsorption strength of the obtained spindle-shaped goethite particle powder was 65.3%. This spindle-shaped goethite particle powder was used as the nonmagnetic particle powder of the nonmagnetic underlayer A described later.
[0112]
<Production of low density spindle-shaped hematite particle powder>
The spindle-shaped goethite particle powder 1200 g was suspended in water to form a slurry, and the solid content concentration was adjusted to 8 g / l. 150 l of this slurry was heated to a temperature of 60 ° C., and 0.1N NaOH aqueous solution was added to adjust the pH value of the slurry to 9.0.
[0113]
Next, 36.0 g of No. 3 water glass was gradually added to the alkaline slurry as a sintering inhibitor, and after the addition was completed, aging was performed for 60 minutes. Next, 0.1N acetic acid solution was added to this slurry, and the pH value of the slurry was adjusted to 6.0, followed by filtration, washing, drying, and pulverization by a conventional method. As a result, 1165 g of spindle-shaped goethite particle powder coated on the surface was obtained. The amount of SiO ₂ was 0.83 wt%.
[0114]
1000 g of the obtained spindle-shaped goethite particle powder was put into a stainless steel rotary furnace and dehydrated by heat treatment at 340 ° C. for 60 minutes in the air while being rotated to obtain low-density spindle-shaped hematite particles.
[0115]
Next, 100 g of the obtained low-density spindle-shaped hematite particles were peptized in 1 l of pure water using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), and then filtered using Nutsche. It washed with water until the electric conductivity became 30 microseconds or less using water. Thereafter, drying and pulverization were performed to obtain 98 g of low density spindle-shaped hematite particle powder.
[0116]
The obtained low-density spindle-shaped hematite particles containing zirconium have an average major axis diameter of 0.116 μm, an average minor axis diameter of 0.0153 μm, an axial ratio of 7.6, and a BET specific surface area value (S _BET ) of 187.6 m. ² / g, degree of _{densification} S _BET / S _TEM was 3.50, Zr content was 4.15 wt% and geometric standard deviation value was 1.36. The resin adsorption strength was 68.8%. This low density spindle-shaped hematite particle powder was used as a nonmagnetic particle powder for a nonmagnetic underlayer B described later.
[0117]
<Production of high-density spindle-shaped hematite particle powder>
850 g of the low density spindle-shaped hematite particle powder was put into a ceramic rotary furnace and heat-treated in air at 670 ° C. for 25 minutes while being rotated, thereby sealing the dehydration holes.
[0118]
100 g of the resulting densified spindle-shaped hematite particle powder was peptized in 1 l of pure water using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), then filtered using Nutsche, and then purified water And was washed with water until the electric conductivity reached 30 μs or less. Thereafter, drying and pulverization were performed to obtain 98 g of high-density spindle-shaped hematite particles.
[0119]
The high-density spindle-shaped hematite particle powder has an average major axis diameter of 0.115 μm, an average minor axis diameter of 0.0155 μm, an axial ratio of 7.4, and a BET specific surface area value (S _BET ) of 60.3 m ² / g, The degree of _{densification} S _BET / S _TEM was 1.14 and the geometric standard deviation value was 1.36. The Zr content was 4.15% by weight. The resin adsorption strength was 73.8%. This high-density spindle-shaped hematite particle powder was used as a nonmagnetic particle powder for a nonmagnetic underlayer C described later.
[0120]
<Manufacture of nonmagnetic underlayer>
Using the spindle-shaped goethite particle powder, low-density spindle-shaped hematite particle powder, and high-density spindle-shaped hematite particle powder obtained above, 12 g of each particle powder and a binder resin solution (vinyl chloride-vinyl acetate having a sodium sulfonate group) 30% by weight of copolymer resin, 70% by weight of cyclohexanone) and cyclohexanone were mixed to obtain a mixture (solid content rate 72%), and this mixture was further kneaded for 30 minutes with a plastmill to obtain three types of kneaded products.
[0121]
Each of these three kinds of kneaded materials is 95 g of 1.5 mmφ glass beads in a 140 ml glass bottle, a binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, 70% by weight of a solvent (methyl ethyl ketone: toluene = 1: 1)), It was added together with cyclohexanone, methyl ethyl ketone and toluene, and mixed and dispersed for 6 hours with a paint shaker to obtain three types of coating compositions.
[0122]
The composition of the paint containing each of the obtained spindle-shaped goethite particle powder, low-density spindle-shaped hematite particle powder, and high-density spindle-shaped hematite particle powder was as follows.
[0123]

[0124]
The three types of coating materials thus obtained were each applied to a polyethylene terephthalate film having a thickness of 12 μm to a thickness of 55 μm using an applicator, and then dried to form three types of nonmagnetic underlayers. The thickness of the nonmagnetic underlayer A was 3.6 μm. The thickness of the nonmagnetic underlayer B was 3.5 μm, and the thickness of the nonmagnetic underlayer C was 3.3 μm.
[0125]
The nonmagnetic underlayer A obtained by using the spindle-shaped goethite particle powder as the nonmagnetic particle powder has a gloss of 181%, a surface roughness Ra of 11.6 nm, and a Young's modulus (relative value) of the substrate of 133. there were.
[0126]
The nonmagnetic underlayer B obtained by using the low density spindle-shaped hematite particle powder as the nonmagnetic particle powder has a gloss of 190%, a surface roughness Ra of 10.2 nm, and the Young's modulus (relative value) of the substrate is 133.
[0127]
The nonmagnetic underlayer C obtained by using high-density spindle-shaped hematite particle powder as the nonmagnetic particle powder has a gloss of 206%, a surface roughness Ra of 6.9 nm, and the Young's modulus (relative value) of the substrate. 135.
[0128]
<Manufacture of magnetic recording layer>
Spindle-like metal magnetic particle powder containing iron as a main component (average major axis diameter 0.153 μm, average minor axis diameter 0.0191 μm, axial ratio 8.01, coercive force 1710 Oe, saturation magnetization 125.3 emu / g, geometric standard Deviation 1.35) 12 g, abrasive (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) 1.2 g, carbon black (trade name: # 3250B, manufactured by Mitsubishi Kasei Co., Ltd.) 0.36 g, binder A resin solution (vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 30% by weight and cyclohexanone 70% by weight) and cyclohexanone were mixed to obtain a mixture (solid content 78%). A kneaded product was obtained by kneading for 30 minutes.
[0129]
This kneaded product is placed in a 140 ml glass bottle with 95 g of 1.5 mmφ glass beads, a binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, 70% by weight of a solvent (methyl ethyl ketone: toluene = 1: 1)), cyclohexanone, methyl ethyl ketone and It was added together with toluene, and mixed and dispersed for 6 hours with a paint shaker to obtain a magnetic paint. Further, after adding a lubricant and a curing agent, the mixture was mixed and dispersed for 15 minutes with a paint shaker.
[0130]
The composition of the obtained magnetic paint was as follows.

[0131]
After applying the obtained magnetic paint on each of the nonmagnetic underlayers A, B and C to a thickness of 15 μm using an applicator, orientation and drying in a magnetic field, and then performing a calendar treatment The magnetic tape was obtained by performing a curing reaction at 60 ° C. for 24 hours and slitting to a width of 0.5 inch. The thickness of each magnetic recording layer was 1.1 μm.
[0132]
The magnetic tape obtained by forming the magnetic recording layer on the nonmagnetic underlayer A has an Hc of 1771 Oe, a squareness ratio (Br / Bm) of 0.87, a glossiness of 195%, and a surface roughness Ra. The Young's modulus (relative value) was 136, the linear absorption coefficient was 1.23, the running durability was 21.2 minutes, and the scratch characteristics were B.
[0133]
The magnetic tape obtained by forming the magnetic recording layer on the nonmagnetic underlayer B has an Hc of 1773 Oe, a squareness ratio (Br / Bm) of 0.87, a glossiness of 200%, and a surface roughness Ra. The Young's modulus (relative value) was 137 nm, the linear absorption coefficient was 1.23, the running durability was 24.6 minutes, and the scratch characteristics were A.
[0134]
The magnetic tape obtained by forming the magnetic recording layer on the nonmagnetic underlayer C has an Hc of 1780 Oe, a squareness ratio (Br / Bm) of 0.89, a glossiness of 216%, and a surface roughness Ra. The Young's modulus (relative value) was 7.0 nm, the linear absorption coefficient was 1.23, the running durability was 27.6 minutes, and the scratch characteristics were A.
[0135]
[Action]
In the present invention, the most important point is that non-magnetic particle powder containing 0.05 to 30% by weight of zirconium in terms of Zr, if necessary, aluminum hydroxide, aluminum oxide, When the needle-like nonmagnetic particle powder mainly composed of iron whose particle surface is coated with at least one of silicon hydroxide and silicon oxide is used as the nonmagnetic particle powder for the nonmagnetic underlayer Can improve the surface smoothness of the nonmagnetic underlayer and the strength of the substrate. When a magnetic recording layer is provided on the nonmagnetic underlayer, the light transmittance of the magnetic recording layer is reduced, and the surface This is the fact that a magnetic recording medium that is smooth, large in strength, and excellent in durability can be obtained.
[0136]
Regarding the reason why the surface smoothness of the nonmagnetic underlayer, the strength of the substrate and the durability of the magnetic recording medium could be further improved, the present inventor stated that the resin adsorption strength with the binder resin in the vehicle of the nonmagnetic particles As a result, it is considered that the degree of adhesion between the nonmagnetic particles and the resin in the nonmagnetic underlayer and the degree of adhesion of the nonmagnetic underlayer itself to the nonmagnetic support increased.
[0137]
【Example】
Next, examples and comparative examples are given.
[0138]
<Types of acicular goethite particle powder>
Nonmagnetic particles A1, A8
Needle-shaped needles with different average major axis diameter, average minor axis diameter, geometric standard deviation value, axial ratio and BET specific surface area, presence or absence of zirconium, presence or absence of surface coating, resin adsorption strength, etc. Two types of goethite particle powder were prepared.
[0139]
Table 1 shows the main production conditions of the acicular goethite particle powders A1 and A8, and Table 2 shows the characteristics.
[0140]
<Types of acicular hematite particle powder>
Nonmagnetic particles A2 to A7, A9 to A11
Basic production reaction of needle-like goethite particle powder as a starting material, type and amount of sintering inhibitor, average major axis diameter, average minor axis diameter, geometric standard deviation value, axial ratio, specific surface area and degree of densification, zirconium Needle-like hematite particle powders having different contents and amounts, presence / absence, type and amount of surface coating, and resin adsorption strength were prepared. The acicular hematite particles containing zirconium are particles that uniformly contain zirconium inside the particles.
[0141]
Table 1 shows the main production conditions of the acicular hematite particles A2 to A7 and A9 to A11, and Table 2 shows the characteristics.
[0142]
[Table 1]

[0143]
[Table 2]

[0144]
The surface coating treatment of the acicular nonmagnetic particles was performed by the following method except that the type of nonmagnetic particles and the type and amount of the coating were variously changed.
[0145]
5 l of a slurry containing nonmagnetic particles A4 having a concentration of 99 g / l is heated to 60 ° C., and 155.8 ml of 1.0 N NaAlO ₂ solution (0.85 weight in terms of Al with respect to acicular hematite particles) Was added and held for 30 minutes, and then the pH value was adjusted to 7.5 using acetic acid. Next, after filtering, washing with water, and drying in the same manner as in the above embodiment of the invention, acicular hematite particle powder having a particle surface covered with a coating was obtained by pulverization.
[0146]
<Manufacture of nonmagnetic underlayer>
Examples 1-7 and Comparative Examples 1-4
Using the acicular nonmagnetic particle powder of nonmagnetic particles A1 to A11, a nonmagnetic underlayer was obtained in the same manner as in the above embodiment.
[0147]
Table 3 shows the main production conditions and various characteristics at this time.
[0148]
[Table 3]

[0149]
<Manufacture of magnetic recording media>
Examples 8-24 and Comparative Examples 5-12
A magnetic recording medium was manufactured in the same manner as in the above embodiment except that the type of the nonmagnetic underlayer and the type of the magnetic particle powder were variously changed.
[0150]
Tables 4 and 5 show the main production conditions and various characteristics at this time.
[0151]
[Table 4]

[0152]
[Table 5]

[0153]
【The invention's effect】
The magnetic recording medium according to the present invention obtains a nonmagnetic underlayer excellent in strength and surface property as a substrate due to the nonmagnetic particle powder containing zirconium substantially uniformly inside the particles. In the case of using the nonmagnetic underlayer as a magnetic recording medium, it is possible to obtain a magnetic recording medium having a low light transmittance, a smooth surface, and a high strength. Magnetic recording medium for high-density recording because it has excellent durability due to the use of acicular non-magnetic particle powder that uniformly contains zirconium as the non-magnetic particle powder for the underlayer Is preferable.

Claims (3)

In a magnetic recording medium substrate comprising a nonmagnetic support, a nonmagnetic underlayer comprising a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, the nonmagnetic particle powder is converted to a Zr equivalent of 0.00. A needle-shaped nonmagnetic particle powder containing iron as a main component and containing 0.5 to 30% by weight of zirconium inside the particle. A magnetic recording medium substrate having a nonmagnetic underlayer, characterized by the following: In a magnetic recording medium substrate comprising a nonmagnetic support, a nonmagnetic underlayer comprising a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, the nonmagnetic particle powder is converted to a Zr equivalent of 0.00. Iron containing 0.5 to 30% by weight of zirconium in the inside of the particle and having the particle surface coated with at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide A magnetic recording medium having a nonmagnetic underlayer, characterized by comprising acicular nonmagnetic particle powder as a main component, and a particle size distribution of major axis diameter of the nonmagnetic particle powder being a geometric standard deviation value of 1.50 or less Substrate. 3. A magnetic recording medium comprising a magnetic recording medium substrate comprising the nonmagnetic underlayer according to claim 1 and a magnetic recording layer containing magnetic particle powder and a binder resin.