JP3656700B2 - Magnetic recording medium - Google Patents

Description

【０１７４】
＜低密度針状ヘマタイト粒子粉末の製造＞
実施例１〜９及び比較例１〜１４
出発原料である針状ゲータイト粒子粉末の種類、焼結防止剤の有無、種類及び添加量、加熱脱水温度及び時間を種々変化させた以外は、前記本発明の実施の形態と同様にして低密度針状ヘマタイト粒子を得た。尚、比較例４で得られた粒子は、ゲータイト粒子である。
【０１７５】
この時の主要製造条件及び諸特性を表２乃至表５に示す。
【０１７６】
【表２】

【０１７７】
【表３】

【０１７８】
【表４】

【０１７９】
【表５】

【０１８０】
＜高密度針状ヘマタイト粒子粉末の製造＞
実施例１０〜１８及び比較例１５〜２７
低密度針状ヘマタイト粒子粉末の種類、高密度化加熱処理の温度及び時間を種々変化させた以外は、前記本発明の実施の形態と同様にして高密度針状ヘマタイト粒子を得た。
【０１８１】
この時の主要製造条件及び諸特性を表６及び表７に示す。
【０１８２】
【表６】

【０１８３】
【表７】

【０１８４】
＜針状ヘマタイト粒子のアルカリ水溶液中における処理＞
実施例１９〜２７及び比較例２８〜３５
高密度針状ヘマタイト粒子粉末の種類、湿式粉砕の有無、アルカリ水溶液中における加熱処理の有無、スラリーのｐＨ値、加熱温度及び加熱時間を種々変化させた以外は、前記本発明の実施の形態と同様にして針状ヘマタイト粒子を得た。
【０１８５】
この時の主要製造条件及び諸特性を表８乃至表１１に示す。
【０１８６】
【表８】

【０１８７】
【表９】

【０１８８】
【表１０】

【０１８９】
【表１１】

【０１９０】
＜針状ヘマタイト粒子の表面被覆処理＞
実施例２８
アルカリ性水溶液中における加熱処理後にデカンテーション法により水洗して得られた実施例１９のｐＨ値が１０．５のスラリーは、スラリー濃度が９８ｇ／ｌであった。このスラリー５ｌを再度加熱して６０℃とし、このスラリー中に１．０Ｎのアルミン酸ナトリウム水溶液２７２ｍｌ（針状ヘマタイト粒子に対しＡｌ換算で１．５ｗｔ％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８．５に調整した。次いで、前記本発明の実施の形態と同様にして濾別、水洗、乾燥、粉砕して粒子表面がアルミニウムの酸化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。
【０１９１】
この時の主要製造条件及び諸特性を表１２及び表１３に示す。
【０１９２】
実施例２９〜３６
針状ヘマタイト粒子粉末の種類、表面処理物の種類及び添加量を種々変化させた以外は、実施例２８と同様にして表面被覆針状ヘマタイト粒子を得た。
【０１９３】
この時の主要製造条件及び諸特性を表１２及び表１３に示す。
【０１９４】
【表１２】

【０１９５】
【表１３】

【０１９６】
＜非磁性下地層の製造＞
実施例３７〜５４及び比較例３６〜５０
実施例１９〜３６で得られた針状ヘマタイト粒子、出発原料Ｅの針状ゲータイト粒子及び比較例３、１５〜１８、２３、２８〜３５で得られた針状ヘマタイト粒子を用いて前記本発明の実施の形態と同様にして非磁性下地層を得た。
【０１９７】
この時の主要製造条件及び諸特性を表１４乃び表１５に示す。
【０１９８】
【表１４】

【０１９９】
【表１５】

【０２００】
＜鉄を主成分とする金属磁性粒子粉末を使用している磁気記録媒体の製造＞
実施例５５〜７２及び比較例５１〜６５
先ず、表１６に示す４種類の鉄を主成分とする金属磁性粒子粉末（ａ）乃至（ｄ）を準備した。
【０２０１】
【表１６】

【０２０２】
非磁性下地層の種類、鉄を主成分とする針状金属磁性粒子粉末の種類を種々変化させた以外は、前記本発明の実施の形態と同様にして鉄を主成分とする金属磁性粉末を使用している磁気記録媒体を製造した。
【０２０３】
この時の主要製造条件及び諸特性を表１７乃び表１８に示す。
【０２０４】
【表１７】

【０２０５】
【表１８】

【０２０６】
【発明の効果】
本発明に係る磁気記録媒体は、前出実施例に示した通り、非磁性下地層用非磁性粉末として、粒子内部にジルコニウムをほぼ均一に含有している針状ヘマタイト粒子からなる特定の粉体ｐＨ値を有するとともに可溶性塩、殊に、可溶性硫酸塩の少ない針状ヘマタイト粒子粉末を用いたことに起因して、基体としての強度とより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、強度が大きいとともに、より表面平滑である磁気記録媒体を得ることができ、しかも、非磁性下地層用非磁性粉末として特定の粉体ｐＨ値を有するとともに可溶性塩、殊に、可溶性硫酸塩の少ない針状ヘマタイト粒子粉末を用いたことに起因して、磁気記録層中のアルミニウムが存在している鉄を主成分とする針状金属磁性粒子粉末の腐蝕に伴う磁気特性の劣化を抑制することができる。
【０２０７】
そして、本発明に係る磁気記録媒体は、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ヘマタイト粒子からなる針状ヘマタイト粒子粉末を用いたこと及び磁気記録層用磁性粒子粉末としてアルミニウムが存在している鉄を主成分とする針状金属磁性粒子粉末を用いたことに起因してより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 metal magnetic particle mainly composed of iron dispersed in a magnetic recording layer, having low light transmittance, high strength, smooth surface and excellent durability. An object of the present invention is to provide a magnetic recording medium having a nonmagnetic underlayer in which deterioration of magnetic properties due to powder corrosion is suppressed.
[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, acicular metal magnetic particle powders mainly composed of iron obtained by heating and reducing acicular goethite particles or acicular hematite particles in a reducing gas as magnetic powders suitable for high output and high density recording have been widely used. in use.
[0007]
The acicular metal magnetic particle powder mainly composed of iron has high coercive force and large saturation magnetization, but the acicular metal magnetic particle powder mainly composed of iron used for magnetic recording media is 1 μm or less, especially about 0.01 to 0.3 μm, so that it is easy to be corroded, magnetic characteristics are deteriorated, and particularly, the saturation magnetization and the coercive force are reduced. is there.
[0008]
Therefore, in order to maintain the characteristics of magnetic recording media that use metal magnetic particle powder containing iron as a main component as a magnetic particle powder over a long period of time, corrosion of acicular metal magnetic particles containing iron as a main component is required. It is strongly required to suppress as much as possible.
[0009]
Next, the thinning of the magnetic recording layer will be described.
[0010]
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.
[0011]
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.
[0012]
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" “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.
[0013]
Secondly, the non-magnetic support such as 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 to run smoothly on the recorder. The improvement is greatly desired.
[0014]
By the way, at present, the end of the magnetic tape of a magnetic recording medium such as a video tape is determined by detecting a portion of the magnetic recording medium having a high light transmittance with a video deck. Magnetic recording layer becomes difficult to detect when the light transmittance of the whole magnetic recording layer increases as the magnetic recording layer 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.
[0015]
However, the addition of a large amount of nonmagnetic carbon black or the like not only inhibits high density recording but also hinders thinning of the magnetic recording layer. In order to further reduce the thickness of the magnetic recording layer by reducing the magnetization depth from the surface of the magnetic recording layer, it is strongly required to reduce the amount of non-magnetic particle powder such as carbon black added to the magnetic recording layer as much as possible. Has been.
[0016]
Therefore, there is a strong demand for a magnetic recording medium having a low light transmittance even when the amount of carbon black added to the magnetic recording layer is reduced. From this point, improvement of the substrate for forming the magnetic recording layer is strongly demanded. ing.
[0017]
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.
[0018]
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 is 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 the magnetic layer tends to peel off after a short period of use. 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.
[0019]
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. At least one underlayer (hereinafter referred to as a nonmagnetic underlayer) in which a nonmagnetic particle powder mainly composed of iron such as hematite particles is dispersed in a binder has been provided, and has already been put into practical use. It has become. (Japanese Patent Publication No. 6-93297, Japanese Patent Laid-Open No. 62-159338, Japanese Patent Laid-Open No. 63-187418, Japanese Patent Laid-Open No. 4-167225, Japanese Patent Laid-Open No. 4-325915, Japanese Patent Laid-Open No. 5-73882, JP-A-5-182177, JP-A-5-347017, JP-A-6-60362, JP-A-9-22524, etc.)
[0020]
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. JP, 8-50718, JP-A-8-255334, JP-A-9-27116, JP-A-9-35245, etc.).
[0021]
[Problems to be solved by the invention]
As the magnetic recording layer is made thinner, as the non-magnetic support is made thinner, the light transmittance is low, the strength is high, the surface is smooth, and the durability is excellent. A magnetic recording medium in which corrosion of metal powders mainly composed of iron dispersed in a magnetic recording layer is suppressed is the most demanded at present, but magnetic recording that sufficiently satisfies these various characteristics. The medium has not yet been obtained.
[0022]
That is, the known magnetic recording medium manufactured using a substrate on which a nonmagnetic underlayer in which nonmagnetic powder is dispersed in a binder resin on a nonmagnetic support has a low light transmittance and a smooth surface. However, although the strength is high, there is a problem that the durability is particularly poor.
[0023]
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.
[0024]
Therefore, the present invention can improve the surface smoothness and strength of the nonmagnetic underlayer. When a magnetic recording layer is provided on the nonmagnetic underlayer, the light transmittance is low and the strength is high. The surface is smoother and more durable, and the deterioration of the magnetic properties due to the corrosion of the metal magnetic particle powder mainly composed of iron dispersed in the magnetic recording layer is suppressed. Obtaining a magnetic recording medium is a technical problem.
[0025]
[Means for solving the problems]
The technical problem can be achieved by the present invention as follows.
[0026]
That is, the present invention relates to a nonmagnetic underlayer comprising a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support and a binder resin, and a magnetic particle powder formed on the nonmagnetic underlayer. In a magnetic recording medium comprising a magnetic recording layer containing a binder resin, the nonmagnetic particle powder is composed of acicular hematite particles containing 0.05 to 50% by weight of zirconium in terms of Zr inside the particles, The average major axis diameter is 0.3 μm or less, the powder pH value is 8 or more, the content of soluble sodium salt is 300 ppm or less in terms of Na, and the content of soluble sulfate is SO_FourIt is acicular hematite particle powder of 150 ppm or less in terms of conversion, and the magnetic particle powder is an acicular metal magnetic particle powder mainly composed of iron in which 0.05 to 10% by weight of aluminum is present in terms of Al. This is a magnetic recording medium.
[0027]
The present invention also provides a nonmagnetic underlayer comprising a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support and a binder resin, and a magnetic particle powder formed on the nonmagnetic underlayer. In a magnetic recording medium comprising a magnetic recording layer containing a binder resin, the non-magnetic particle powder contains 0.05 to 30 wt% zirconium in terms of Zr inside the particle, and an aluminum hydroxide, It consists of acicular hematite particles whose particle surface is coated with at least one of aluminum oxide, silicon hydroxide and silicon oxide, and has an average major axis diameter of 0.3 μm or less, and a powder pH The value is 8 or more, the content of soluble sodium salt is 300 ppm or less in terms of Na, and the content of soluble sulfate is SO_FourIt is acicular hematite particle powder of 150 ppm or less in terms of conversion, and the magnetic particle powder is an acicular metal magnetic particle powder mainly composed of iron in which 0.05 to 10% by weight of aluminum is present in terms of Al. This is a magnetic recording medium.
[0028]
The configuration of the present invention will be described in more detail as follows.
[0029]
First, the nonmagnetic underlayer in the present invention will be described.
[0030]
The nonmagnetic underlayer in the present invention is formed on a nonmagnetic support and is composed of acicular hematite particle powder and a binder resin.
[0031]
Nonmagnetic supports include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, synthetic resin films such as 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 kinds of paper 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, and in the case of polyethylene terephthalate, it is usually 3 to 100 μm, preferably 4 to 20 μm. In the case of polyethylene naphthalate, it is usually 3 to 50 μm, preferably 4 to 20 μm. In this case, it is usually 2 to 10 μm, preferably 3 to 7 μm.
[0032]
The acicular hematite particles in the present invention contain 0.05 to 30% by weight of zirconium in terms of Zr.
[0033]
When the zirconium content is less than 0.05% by weight in terms of Zr with respect to hematite particles containing zirconium, the obtained magnetic recording medium does not have sufficient durability. 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, it is preferably 0.1 to 25% by weight, more preferably 0.5 to 25% by weight, and still more preferably 1.0 to 20% by weight.
[0034]
The hematite particles in the present invention are acicular particles and have 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: 1 or more. Is preferred. Considering the dispersibility in the vehicle, the upper limit is preferably 20: 1, preferably 10: 1. Here, the acicular particles mean not only acicular shapes but also spindle shapes, rice grains, and the like.
[0035]
When the axial ratio is less than 2: 1, it is difficult to obtain a desired coating strength.
[0036]
The average major axis diameter of the acicular hematite particles 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 hematite particles 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.
[0037]
The acicular hematite particles in the present invention preferably have 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.
[0038]
The powder pH value of the acicular hematite particles in the present invention is 8 or more. When the pH value of the powder is less than 8, the metal magnetic particle powder mainly composed of iron contained in the magnetic recording layer formed on the nonmagnetic underlayer is gradually corroded to deteriorate the magnetic characteristics. cause. In consideration of the corrosion prevention effect of the metal magnetic particle powder containing iron as a main component, the powder pH value is preferably 8.5 or more, more preferably 9.0 or more. The upper limit is a powder pH value of 12, preferably a powder pH value of 11, more preferably a powder pH value of 10.5.
[0039]
The content of the soluble sodium salt of the acicular hematite particles in the present invention is 300 ppm or less in terms of Na. When it exceeds 300 ppm, the metal magnetic particle powder mainly composed of iron contained in the magnetic recording layer formed on the nonmagnetic underlayer is gradually corroded to cause deterioration of magnetic properties. In addition, the dispersion characteristics of the hematite particles in the vehicle are liable to be impaired, and the white flower phenomenon may occur in the storage state of the magnetic recording medium, particularly in a high humidity environment. Considering the corrosion prevention effect of the metal magnetic particle powder containing iron as a main component, it is preferably 250 ppm or less, more preferably 200 ppm or less, and still more preferably 150 ppm or less. Considering industrial properties such as productivity, the lower limit is about 0.01 ppm.
[0040]
The content of soluble sulfate in acicular hematite particles in the present invention is SO._FourIt is 150 ppm or less in terms of conversion. When it exceeds 150 ppm, the metal magnetic particle powder mainly composed of iron contained in the magnetic recording layer formed on the nonmagnetic underlayer is gradually corroded to cause deterioration of magnetic properties. In addition, the dispersion characteristics of the hematite particles in the vehicle are liable to be impaired, and the white flower phenomenon may occur in the storage state of the magnetic recording medium, particularly in a high humidity environment. Considering the corrosion prevention effect of the metal magnetic particle powder containing iron as a main component, it is preferably 70 ppm or less, more preferably 50 ppm or less. Considering industrial properties such as productivity, the lower limit is about 0.01 ppm.
[0041]
The acicular hematite particle powder in the present invention has a BET specific surface area value of 35 m.²/ G or more is preferable. 35m²If it is less than / g, the hematite particles are coarse, or the particles are particles that are sintered between the particles, which adversely affects the surface smoothing of the coating film, which is not preferable. Preferably 37m²/ G or more, more preferably 40 m²/ G and the upper limit is 150 m²/ G. Considering dispersibility in the vehicle, preferably 100 m²/ G or less, more preferably 80 m²/ G or less.
[0042]
The acicular hematite particle powder in the present invention preferably has a major axis diameter particle size distribution of 1.5 or less in terms of geometric standard deviation. If it exceeds 1.5, 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 1.48 or less, more preferably 1.45 or less. Considering industrial productivity, the lower limit of the particle size distribution of the major axis diameter of the obtained hematite particles is about 1.01 in terms of geometric standard deviation.
[0043]
The acicular hematite particle powder in the present invention has a high degree of densification. Specific surface area S measured by BET method_BETSurface area S calculated from the major axis and minor axis diameters measured from the values and particles shown in the electron micrograph_TEMWhen it shows by ratio with a value, what has 0.5-2.5 is preferable.
[0044]
S_BET/ S_TEMWhen the value is less than 0.5, the particles adhere to each other by sintering between the particles, the particle diameter is increased, and the surface smoothness of the coating film is not sufficient. S_BET/ S_TEMWhen the value exceeds 2.5, the dispersibility in the vehicle becomes insufficient because there are many pores on the particle surface. Considering the surface smoothness of the coating and the dispersibility in the vehicle, S_BET/ S_TEMIs preferably 0.7 to 2.0, more preferably 0.8 to 1.6.
[0045]
The acicular hematite particle powder in the present invention has a resin adsorption strength of 60% or more, preferably 65% or more, more preferably 68% or more. The upper limit is about 95%.
[0046]
The needle-like hematite particles in the present invention may be coated on the particle surface with at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, if necessary. The acicular hematite particles whose particle surfaces are coated with a coating have good compatibility with the binder resin and have excellent dispersibility in the vehicle.
[0047]
In the case of aluminum hydroxide or aluminum oxide, the amount of the above coating is calculated in terms of Al, and in the case of silicon hydroxide or silicon oxide, SiO.₂It is preferably 0.01 to 50% by weight based on the total weight of the particles. When the amount is less than 0.01% by weight, there is almost no effect of improving dispersibility by coating. When the amount exceeds 50% by weight, the coating effect is saturated, so there is no meaning to add more than necessary. Considering the dispersibility in the vehicle, 0.05 to 20% by weight is more preferable.
[0048]
Average major axis diameter, powder pH value, soluble sodium salt content, soluble sulfate content, axial ratio (major axis), which are various characteristics of acicular hematite particle powder coated with a surface coating on the particle surface Diameter / minor axis diameter), average minor axis diameter, BET specific surface area, particle size distribution of major axis diameter, degree of densification, and the like are substantially the same as acicular hematite particle powder not coated with a surface coating.
[0049]
As binder resins, vinyl chloride-vinyl acetate copolymer, urethane resin, vinyl chloride-vinyl acetate-maleic acid copolymer, urethane elastomer, butadiene-acrylonitrile copolymer, which are currently widely used in the production of magnetic recording media. For example, synthetic rubber resins such as coalescence, polyvinyl butyral, nitrocellulose, polyester resins, polybutadiene, epoxy resins, polyamide resins, polyisocyanates, electron beam curable acrylic urethane resins, and mixtures thereof can be used. In addition, each binder resin has —OH, —COOH, —SO._ThreeM, -OPO₂M₂, -NH₂And the like (where M is H, Na, K). Considering the dispersibility of the particles, polar groups —COOH, —SO_ThreeBinder resins containing M are preferred.
[0050]
The blending ratio of the acicular hematite particle powder and the binder resin in the nonmagnetic underlayer is 5 to 2000 parts by weight, preferably 100 to 1000 parts by weight of the acicular hematite particle powder with respect to 100 parts by weight of the binder resin. .
[0051]
Note that the nonmagnetic underlayer may contain a lubricant, an abrasive, an antistatic agent, etc. used in the production of a normal magnetic recording medium, if necessary.
[0052]
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.
[0053]
The nonmagnetic underlayer containing acicular hematite particle powder not coated with the surface coating in the present invention has a coating film glossiness of 185 to 280%, preferably 190 to 280%, more preferably 195 to 280%. The coating film surface roughness Ra is 2.0 to 10.0 nm, preferably 2.0 to 9.0 nm, and more preferably 2.0 to 8.0 nm.
[0054]
The nonmagnetic underlayer containing acicular hematite particles coated with the surface coating in the present invention has a coating film glossiness of 190 to 280%, preferably 193 to 280%, more preferably 196 to 280%, The coating film surface roughness Ra is 2.0 to 9.0 nm, preferably 2.0 to 8.0 nm, and more preferably 2.0 to 7.4 nm.
[0055]
Next, the magnetic recording medium according to the present invention will be described.
[0056]
The magnetic recording medium according to the present invention is a magnetic recording medium comprising a metal magnetic particle powder mainly composed of iron in which aluminum is present and a binder resin on a nonmagnetic underlayer formed on a nonmagnetic support. And a recording layer.
[0057]
The acicular metal magnetic particles containing iron as a main component in the present invention contain 0.05 to 10% by weight of aluminum in terms of Al.
[0058]
When the aluminum is contained only in the central part of the particles of acicular metal magnetic particles mainly composed of iron, it is almost even from the center to the surface when contained only in the surface layer part. Any of the above cases may be used, or a coating layer may be formed on the surface of the particle, or a combination of these various positions may be used. Considering the surface of the magnetic recording layer and the durability of the magnetic recording medium, the main component is iron, in which aluminum is contained almost uniformly from the center to the surface, and a coating layer is formed on the particle surface. Needle-like metal magnetic particles are preferred.
[0059]
When the abundance of aluminum is less than 0.05% by weight in terms of Al, the resin adsorption in the vehicle of the acicular metal magnetic particles mainly composed of iron is not sufficient and the dispersion becomes difficult, and the object of the present invention Thus, it is impossible to obtain a magnetic recording layer or a magnetic recording medium excellent in durability. Even when the amount exceeds 10% by weight, the effect of improving the durability of the magnetic recording layer or the magnetic recording medium is recognized, but the effect is saturated and does not make sense to exist more than necessary. In addition, the increase in aluminum, which is a nonmagnetic component, impairs the magnetic properties of acicular metal magnetic particles mainly composed of iron.
[0060]
As is well known, the acicular metal magnetic particle powder mainly composed of iron containing aluminum inside the particle is obtained by variously changing the addition timing of the aluminum compound in the above-described acetic acid goethite particle formation reaction step. Acicular goethite particles containing aluminum at desired positions inside the particles are obtained, and acicular shapes containing aluminum at desired positions inside the particles obtained by heating and dehydrating the goethite particles or the goethite particles It can be obtained by heating and reducing hematite particles in a temperature range of 300 to 500 ° C.
[0061]
The acicular metal magnetic particle powder mainly composed of iron whose particle surface is coated with aluminum includes acicular goethite particles whose particle surface is coated with an aluminum compound such as an oxide or hydroxide of aluminum or the needle. Obtained by heating and reducing acicular hematite particles whose particle surface obtained by heating and dehydrating the goethite particles is coated with an aluminum compound such as aluminum oxide or hydroxide in a temperature range of 300 to 500 ° C. .
[0062]
The acicular metal magnetic particle powder containing iron as a main component in the present invention is a particle containing 50 to 99% by weight, preferably 60 to 95% by weight of iron, and if necessary, Co other than iron and Al, Ni, P, Si, B, Nd, La, Y, etc. may be contained in an amount of about 0.05 to 10% by weight. When a magnetic recording medium according to the present invention is manufactured using acicular metal magnetic particle powder mainly composed of iron in which Al and rare earth metals such as Nd, La, and Y are present, the durability is improved. It is preferable that a magnetic recording layer and a magnetic recording medium excellent in the above can be obtained. In particular, acicular metal magnetic particle powder mainly composed of iron in which Al and Nd are present is most preferable.
[0063]
The acicular metal magnetic particle powder containing iron as a main component in the present invention 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 0.00. 0007 to 0.17 μm, preferably 0.003 to 0.10 μm, particles having an axial ratio of 3: 1 or more, preferably 5: 1 or more, and considering the dispersibility in the vehicle, the axial ratio The upper limit of is 15: 1, preferably 10: 1. The shape of the particles may be a needle shape, a spindle shape, a rice grain shape, or the like.
[0064]
In consideration of characteristics such as high density recording, the coercive force is preferably 900 to 3200 Oe, more preferably 1500 to 3200 Oe, and the saturation magnetization is the magnetic property of the acicular metal magnetic particle powder mainly composed of iron. 100-170 emu / g is preferable, More preferably, it is 120-170 emu / g.
[0065]
The acicular metal magnetic particles mainly composed of iron in the present invention have a resin adsorption strength of 65% or more, preferably 68% or more, more preferably 70% or more.
[0066]
As the binder resin used for forming the magnetic recording layer, the binder resin used for forming the nonmagnetic underlayer can be used.
[0067]
The blending ratio of the acicular metal magnetic particle powder containing iron as a main component and the binder resin in the magnetic recording layer is 200 to 200 wt. The amount is 2000 parts by weight, preferably 300-1500 parts by weight.
[0068]
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.
[0069]
The magnetic recording layer may contain a lubricant, an abrasive, an antistatic agent and the like that are usually used as necessary.
[0070]
The magnetic recording medium according to the present invention has a coercive force of 900 to 3500 Oe, preferably 1000 to 3500 Oe, more preferably 1500 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 200 to 300%, preferably 210 to 300%, and the coating film surface roughness Ra is 10.0 nm or less, preferably 2.0 to 9.0 nm. More preferably, it is 2.0 to 8.0 nm, and the linear absorption coefficient of the coating film is 1.10 to 2.00 μm.^-1Preferably 1.20 to 2.00 μm^-1Of the durability, the running durability is 20 minutes or more, preferably 22 minutes or more, more preferably 25 minutes or more, and the scratch resistance is B or more, preferably A. And the corrosion property shown by the change rate (%) of the coercive force is 10.0% or less, preferably 8.0% or less, and the corrosion property shown by the change rate (%) of Bm is 10.0% or less, preferably 8%. 0.0% or less.
[0071]
Next, a method for producing the nonmagnetic underlayer in the present invention will be described.
[0072]
The nonmagnetic underlayer in the present invention is formed by applying a nonmagnetic paint containing the acicular hematite particle powder, the binder resin and the solvent in the present invention on a nonmagnetic support to form a coating film, and then drying. Is obtained.
[0073]
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.
[0074]
The usage-amount of a solvent is 50-1000 weight part in the total amount with respect to 100 weight part of acicular hematite 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.
[0075]
A method for producing acicular goethite particle powder containing almost uniform zirconium inside the particle, which is a precursor of acicular hematite particles containing zirconium uniformly inside the particles in the present invention, will be described.
[0076]
Needle-like goethite particles containing zirconium almost uniformly inside the particles react with ferrous salt and either alkali hydroxide, alkali carbonate, or alkali hydroxide / alkali carbonate, as described in detail later. In order to produce acicular goethite particles by aeration of oxygen-containing gas such as air into a suspension containing iron-containing precipitates such as iron hydroxide and iron carbonate obtained as above, oxygen-containing gas such as air is used. It can be obtained by having a zirconium compound present before aeration. Specifically, it may be added to any one of a ferrous salt aqueous solution, an alkali hydroxide or alkali carbonate aqueous solution, and a suspension containing an iron-containing precipitate, and most preferably a ferrous salt aqueous solution.
[0077]
As the zirconium compound, zirconium sulfate, zirconium oxysulfate, zirconium chloride, zirconium nitrate, zirconium acetate and the like can be used.
[0078]
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.
[0079]
A typical basic reaction of acicular goethite particles is as follows. (1) A suspension containing ferrous hydroxide colloid obtained by adding an aqueous alkali hydroxide solution in an equivalent amount or more to a ferrous salt aqueous solution has a pH value of 11 A method for producing needle-like goethite particles by performing an oxidation reaction by bubbling an oxygen-containing gas at a temperature of 80 ° C. or lower, and (2) obtained by reacting a ferrous salt aqueous solution and an alkali carbonate aqueous solution. FeCO_ThreeA method of producing spindle-shaped goethite particles by performing an oxidation reaction by aeration of an oxygen-containing gas, if necessary, after aging a suspension containing, and (3) a ferrous salt aqueous solution and an alkali carbonate, A suspension containing an iron-containing precipitate obtained by reacting with an alkali hydroxide is aged as necessary, and then a goethite particle having a spindle shape is generated by performing an oxidation reaction by aeration of an oxygen-containing gas. Method (4) Oxidation by passing an oxygen-containing gas through a ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by adding less than an equivalent amount of an alkali hydroxide aqueous solution or an alkali carbonate aqueous solution to a ferrous salt aqueous solution. By performing the reaction, acicular goethite core particles are generated, and then the ferrous salt aqueous solution containing the acicular goethite core particles is added to the Fe ferrous salt aqueous solution.²⁺A method of growing an acicular goethite core particle by aeration of an oxygen-containing gas after adding an alkali hydroxide aqueous solution of an equivalent amount or more to the above, (5) an aqueous alkali hydroxide solution or carbonic acid of less than an equivalent amount in the ferrous salt aqueous solution Acicular goethite core particles are produced by performing an oxidation reaction by bubbling an oxygen-containing gas into a ferrous salt aqueous solution containing ferrous hydroxide colloid obtained by adding an alkaline aqueous solution, and then generating the acicular goethite In the ferrous salt aqueous solution containing the core particles, Fe in the ferrous salt aqueous solution is added.²⁺A method of growing an acicular goethite core particle by aeration of an oxygen-containing gas after adding an alkali carbonate aqueous solution of an equivalent amount or more with respect to (6) an alkali hydroxide or alkali carbonate aqueous solution less than the equivalent of ferrous salt aqueous solution The needle-like goethite core particles are generated by conducting an oxidation reaction by aerating an oxygen-containing gas to an aqueous ferrous salt solution containing ferrous hydroxide colloid obtained by adding, and then in the acidic to neutral region There is a method of growing the acicular goethite core particles.
[0080]
In addition, during the formation reaction of goethite particles, foreign elements such as Ni, Zn, P, and Si that are usually added to improve various characteristics such as the major axis diameter, minor axis diameter, and axial ratio of the particles are added. There is no problem. The obtained acicular goethite particle powder usually has an average major axis diameter of 0.005 to 0.4 μm, an average minor axis diameter of 0.0025 to 0.20 μm, and a BET specific surface area value of 50 to 250 m.²/ G, soluble sodium salt is 300 to 1500 ppm in terms of Na, soluble sulfate is SO_FourContaining 100 to 3000 ppm in terms of conversion.
[0081]
The hematite particles containing zirconium almost uniformly inside the particles can be obtained by heating and dehydrating the goethite particles containing zirconium almost uniformly inside the particles.
[0082]
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 in a temperature range of 550 to 850 ° C. More preferred.
[0083]
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.
[0084]
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 zirconium compounds such as zirconium oxysulfate. Can do.
[0085]
The amount of the sintering inhibitor present on the surface of the acicular goethite particles varies depending on the type and amount of the sintering inhibitor, the pH value in the alkaline aqueous solution, the heat treatment temperature, etc. About 0.05 to 10% by weight is preferable.
[0086]
Needle-like goethite particle powder whose particle surface is coated with a sintering inhibitor is usually 500 to 2000 ppm of soluble sodium salt in terms of Na and SO in soluble sulfate._FourIt contains 300 to 3000 ppm in terms of conversion, and the BET specific surface area value is 50 to 250 m.²/ G or so. The coating treatment with the sintering inhibitor may be performed by adding the sintering inhibitor to an aqueous suspension containing acicular goethite particles, mixing and stirring, and then filtering, washing, and drying.
[0087]
In order to obtain high-density needle-like hematite particles that retain the particle shape of the needle-like goethite particles, the needle-like goethite particles are preliminarily heat-treated at 250 to 550 ° C. at low temperature and contain zirconium inside the particles. It is preferable to obtain density acicular hematite particles and then heat-treat the low density acicular hematite particles at a temperature of 550 to 800 ° C.
[0088]
If the temperature during low-temperature heating is less than 250 ° C., the dehydration reaction takes a long time. When the temperature during low-temperature heating exceeds 500 ° C., a dehydration reaction occurs abruptly, and the shape of the particles tends to collapse, or sintering between particles tends to occur. Low density acicular hematite particles obtained by low-temperature heat treatment are obtained from goethite particles to H₂O is dehydrated and is a low-density particle having many dehydration holes, and the BET specific surface area value is about 1.2 to 2 times that of the acicular goethite particle as a precursor. The low density hematite particle powder usually has an average major axis diameter of 0.005 to 0.30 μm, an average minor axis diameter of 0.0025 to 0.15 μm, and a BET specific surface area value of 70 to 350 m.²/ G, soluble sodium salt is 500 to 3000 ppm in terms of Na, soluble sulfate is SO_FourContaining 300 to 4000 ppm in terms of conversion.
[0089]
Next, the low density hematite particle powder is heated to a high temperature at 550 ° C. or higher to obtain acicular hematite particles that have been densified. The upper limit of the heating temperature is preferably 850 ° C. When the heating temperature is less than 550 ° C., the densification tends to be insufficient, and there are a large number of dehydration pores inside and on the surface of the hematite particles, resulting in insufficient dispersibility in the vehicle. When a nonmagnetic underlayer is formed, a smooth coating film is difficult to obtain. When the heating temperature exceeds 850 ° C., the density of the hematite particles is sufficiently increased. However, since the particles and each other are sintered, the particle diameter is increased, and the coating film having a smooth surface is similarly formed. It is difficult to obtain. High-density hematite particle powder usually has a soluble sodium salt of 500 to 4000 ppm in terms of Na and a soluble sulfate salt of SO._FourIt contains 300 to 5000 ppm in terms of conversion, and the BET specific surface area value is 35 to 150 m.²/ G or so.
[0090]
Next, the high-density needle-like hematite particles are coarsely pulverized by a dry method to loosen the coarse particles, and then slurried, and then wet-pulverized to further loosen the coarse particles. The wet pulverization may be performed using a ball mill, a sand grinder, a colloid mill or the like so as to eliminate coarse grains of at least 44 μm or more. The degree of wet pulverization is 10% or less, preferably 5% or less, and more preferably 0% for coarse particles of 44 μm or more. When coarse particles of 44 μm or more remain exceeding 10%, it is difficult to obtain a treatment effect in an aqueous alkaline solution in the next step.
[0091]
The slurry containing the high-density needle-like hematite particles from which coarse particles have been removed is heated at a temperature of 80 ° C. or higher after adding an alkaline aqueous solution such as sodium hydroxide to the slurry to adjust the pH value to 13 or higher.
[0092]
The concentration of the alkaline suspension having a pH value of 13 or more containing the high-density needle-like hematite particle powder is preferably 50 to 250 g / l.
[0093]
When the pH value in an alkaline suspension containing high-density needle-like hematite particle powder is less than 13, solid cross-linking caused by the sintering inhibitor present on the particle surface of the hematite particles can be effectively removed. Therefore, it is impossible to wash out soluble sodium salts, soluble sulfates, etc. present in the particle interior and on the particle surface. The upper limit of the pH value is about 14. Removal of solid cross-linking caused by sintering inhibitors existing on the surface of hematite particles, the effect of washing out soluble sodium salts, soluble sulfates, etc. Considering the cleaning effect for removal, the pH value is preferably in the range of 13.1 to 13.9.
[0094]
The heating temperature of the alkaline aqueous solution having a pH value of 13 or more containing the high-density needle-like hematite particle powder is preferably 80 ° C. or more, more preferably 90 ° C. or more. When the temperature is lower than 80 ° C., it is difficult to effectively remove the solid crosslinking caused by the sintering inhibitor existing on the surface of the hematite particles. The upper limit of the heating temperature is preferably 103 ° C, more preferably 100 ° C. When the temperature exceeds 103 ° C., the solid cross-linking can be effectively removed, but an autoclave or the like is required, and under normal pressure, the liquid to be treated boils and is not industrially advantageous.
[0095]
High-density needle-shaped hematite particles heat-treated in an aqueous alkaline solution are separated by filtration and washed with water in the usual manner, so that the soluble sodium salt or soluble sulfate salt washed out from the inside of the particle or the surface of the particle, or the hematite particles during the aqueous alkaline treatment The alkali such as sodium attached to the surface is removed and then dried.
[0096]
By the method described above, acicular hematite particles containing zirconium inside the particles in the present invention can be obtained.
[0097]
As a water washing method, if a method commonly used in industry such as a method of washing by decantation, a method of washing by a dilution method using a filter thickener, a method of washing by passing water through a filter press, etc. is used. Good.
[0098]
If the soluble sodium salt or soluble sulfate contained in the high-density hematite particles is washed out with water, the subsequent steps, for example, in the coating treatment step to be described later, on the particle surface of the hematite particles. Even if soluble sodium salt or soluble sulfate is adhered, it can be easily removed by washing with water.
[0099]
The needle-like hematite particles in the present invention are heat-treated in an alkaline aqueous solution, if necessary, and then filtered and washed by a conventional method, and then aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon. It can be coated with at least one of the following oxides.
[0100]
The coating treatment is performed by adding an aluminum compound, a silicon compound or both of the compounds to an aqueous suspension obtained by dispersing a cake, slurry, or dry powder of acicular hematite particles in an aqueous solution, and mixing and stirring, or If necessary, the surface of the needle-shaped hematite particles is coated with aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide by adjusting the pH value. Separately, it may be washed, dried and pulverized. If necessary, a deaeration / consolidation process may be further performed.
[0101]
As the aluminum compound in the present invention, the same as the above-mentioned sintering inhibitor can be used.
[0102]
The addition amount of the aluminum compound is 0.01 to 50% by weight in terms of Al with respect to the acicular hematite particle powder. When the amount is less than 0.01% by weight, the obtained needle-like hematite particle powder is not sufficiently dispersed in the vehicle. When the amount exceeds 50% by weight, the coating effect is saturated. There is no meaning to do.
[0103]
As the silicon compound in the present invention, the same compounds as the above-mentioned sintering inhibitor can be used.
[0104]
The amount of silicon compound added is SiO to acicular hematite particle powder.₂It is 0.01 to 50% by weight in terms of conversion. When the amount is less than 0.01% by weight, the obtained needle-like hematite particle powder is not sufficiently dispersed in the vehicle. When the amount exceeds 50% by weight, the coating effect is saturated. There is no meaning to do.
[0105]
When an aluminum compound and a silicon compound are used in combination, the equivalent amount of Al and SiO₂The total amount with the converted amount is preferably 0.01 to 50% by weight.
[0106]
Next, a method for manufacturing a magnetic recording medium according to the present invention will be described.
[0107]
The magnetic recording medium according to the present invention comprises a nonmagnetic underlayer formed on a nonmagnetic support and a metal magnetic particle powder mainly composed of iron in which aluminum is present, a binder resin, and a solvent. It is obtained by applying a magnetic coating composition to form a coating film and then drying to form a magnetic recording layer.
[0108]
As the solvent used in the production of the magnetic paint, the solvent used for forming the nonmagnetic underlayer can be used.
[0109]
The total amount of the solvent used is 65 to 1000 parts by weight with respect to 100 parts by weight of the metal magnetic particle powder mainly composed of iron in which aluminum is present. If it is less than 65 parts by weight, the viscosity becomes too high when it is used as a 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.
[0110]
DETAILED DESCRIPTION OF THE INVENTION
A typical embodiment of the present invention is as follows.
[0111]
As for the remaining amount of the sieve after wet dispersion, the slurry concentration after wet pulverization is separately obtained, and an amount of slurry equivalent to 100 g of hematite solid content is passed through a sieve of 325 mesh (aperture 44 μm) to leave the hematite remaining in the sieve. It was determined by quantifying the amount of solids.
[0112]
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 indicated by its average value. The axial ratio is the ratio of the average major axis diameter to the average minor axis diameter.
[0113]
Geometric standard deviation of major axis diameter of particle powder (σ_g) Is a value obtained by the following method. That is, the value obtained by measuring 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 values, and the horizontal axis on the log normal 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, from this graph, the value of the major axis diameter corresponding to the number of particles of 50% and 84.13% is read, and the geometric standard deviation value (σ_g) = Long axis diameter at 84.13% under accumulated sieve / Value calculated according to major axis diameter (geometric mean diameter) at 50% under accumulated sieve. The smaller the geometric standard deviation value, the better the particle size distribution of the major axis diameter of the particles.
[0114]
The specific surface area of the particle powder was shown as a value measured by the BET method.
[0115]
As described above, the degree of densification of the acicular hematite particle powder is S_BET/ S_TEMIt showed in. Where S_BETIs the value of the specific surface area measured by the BET method. S_TEMIs a value calculated according to the following formula, assuming that the particles are rectangular parallelepiped using the average major axis diameter lcm and the average minor axis diameter wcm of the particles measured from the electron micrograph.
[0116]
S_TEM(M²/ G) = [(4lw + 2w²) / (Lw²・ Ρ_p)] × 10^-Four
(However, ρ_pIs the true specific gravity of hematite, 5.2 g / cm^ThreeWas used. )
[0117]
The amount of each of Zr, Al, Si, P, B, and Nd present inside or on the surface of acicular hematite particles or acicular metal magnetic particles mainly composed of iron was measured by fluorescent X-ray analysis.
[0118]
The pH value of the powder was measured by weighing 5 g of a sample into a 300 ml Erlenmeyer flask, adding 100 ml of boiled pure water, heating and holding the boiled state for about 5 minutes, then plugging it and letting it cool to room temperature. After adding water corresponding to the above, stoppered again, shaken for 1 minute, allowed to stand for 5 minutes, and then measured the pH of the obtained supernatant according to JIS Z 8802-7. It was.
[0119]
The content of the soluble sodium salt and the content of the soluble sulfate were determined by changing the supernatant prepared for measurement of the powder pH value as No. Filter using 5C filter paper and add Na in the filtrate.⁺And SO_Four ^2-Was measured using an inductively coupled plasma optical emission spectrometer (manufactured by Seiko Instruments Inc.).
[0120]
The viscosity of the paint is measured by using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.), and the shear rate D = 1.92 sec.^-1It was shown by the value in.
[0121]
The resin adsorption strength (T) indicates the degree to which the resin is adsorbed by acicular hematite particles or acicular metal magnetic particles mainly composed of iron, and the T% obtained by the following method is closer to 100. The resin is strongly adsorbed on the surface of acicular hematite particles or acicular metal magnetic particles mainly composed of iron, indicating that the resin is good.
[0122]
First, the resin adsorption amount Wa is obtained.
[0123]
A mixed solvent (27.0 g of methyl ethyl ketone, 16.2 ml of toluene) in which 20 g of acicular hematite particle powder or 20 g of acicular metal magnetic particle powder mainly containing iron and 2 g of vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group are dissolved. 2 g, 10.8 g of cyclohexanone) and 56 g of 3 mmφ steel beads are placed in a 100 ml plastic bottle and mixed and dispersed in a paint shaker for 60 minutes.
[0124]
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 subtracting it from the charged resin amount, and this is based on acicular hematite particle powder or iron as the main component. It is set as resin adsorption amount Wa (mg / g) with respect to acicular metal magnetic particle powder.
[0125]
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 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 surface of acicular hematite particles or acicular metal magnetic particles mainly composed of iron is calculated. Quantify.
[0126]
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 (%).
[0127]
T (%) = [(Wa-We) / Wa] × 100
[0128]
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.).
[0129]
Surface roughness Ra measured the centerline average roughness of the coating film using "Surfcom-575A" (made by Tokyo Seimitsu Co., Ltd.).
[0130]
The durability of the magnetic recording medium was evaluated by determining the following running durability and scratch characteristics.
[0131]
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.
[0132]
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: Some scratches
C: Scratch
D: Severe scratches
[0134]
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.
[0135]
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.
[0136]
The change over time in the magnetic properties of the magnetic recording medium accompanying the corrosion of the metal magnetic particle powder containing iron as a main component in the magnetic recording layer is that the magnetic recording medium is left for 14 days in an environment of a temperature of 60 ° C. and a relative humidity of 90%. The coercive force value and saturation magnetic flux density value before and after standing were measured, and the value obtained by dividing the amount of change by the value before standing was expressed as a percentage.
[0137]
The degree of light transmission is indicated by a linear absorption coefficient calculated by inserting the value of light transmittance measured for a magnetic recording medium using a “self-recording spectrophotometer UV-2100” (manufactured by Shimadzu Corporation) into the following equation. It was. The larger the value of the linear absorption coefficient, the harder it is to transmit light.
[0138]
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.
[0139]
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)
[0140]
The thicknesses of the nonmagnetic support, the nonmagnetic underlayer and the magnetic recording layer constituting the magnetic recording medium were measured as follows.
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. Further, 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.
[0141]
<Production of spindle-shaped hematite particles>
Using a ferrous sulfate aqueous solution, a zirconium oxysulfate aqueous solution, and a sodium carbonate aqueous solution, 2.56% by weight of zirconium in terms of Zr obtained by the above goethite particle production method (2) is uniformly contained inside the particles. Spindle-shaped goethite particles (average major axis diameter 0.189 μm, average minor axis diameter 0.0207 μm, axial ratio 9.1, BET specific surface area value 141.3 m²/ G, soluble sodium salt content is 1380 ppm in terms of Na, soluble sulfate content is SO_FourIn conversion, 821 ppm, powder pH value 5.9 and geometric standard deviation value 1.33) 1200 g were 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 10.0.
[0142]
Next, 30.0 g of No. 3 water glass was gradually added to the alkaline slurry as a sintering inhibitor. After the addition was completed, aging was performed for 60 minutes. Next, a 0.1N acetic acid solution was added to the slurry to adjust the pH value of the slurry to 6.0. Thereafter, filtration, washing, drying, and pulverization were performed by a conventional method to obtain spindle-shaped goethite particle powder in which a silicon oxide was coated on the particle surface. Silicon content is SiO₂It was 0.69% by weight in terms of conversion.
[0143]
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 30 minutes in the air while being rotated to obtain low-density spindle-shaped hematite particles. The obtained low-density spindle-shaped hematite particles containing zirconium have an average major axis diameter of 0.151 μm, an average minor axis diameter of 0.0198 μm, an axial ratio of 7.6, and a BET specific surface area value (S_BET) 159.8m²/ G, density degree S_BET/ S_TEMIs 3.86, the content of soluble sodium salt is 2123 ppm in terms of Na, and the content of soluble sulfate is SO_Four1016ppm in terms of conversion, zirconium content is 2.81% by weight in terms of Zr, silicon content is SiO₂The conversion was 0.75% by weight, the powder pH value was 6.0, and the geometric standard deviation value was 1.34.
[0144]
Next, 850 g of the low-density spindle-shaped hematite particle powder was put into a ceramic rotary furnace, and heat-treated at 650 ° C. for 30 minutes in the air while being driven to rotate, thereby sealing the dehydration holes. The densified spindle-shaped hematite particles have an average major axis diameter of 0.150 μm, an average minor axis diameter of 0.0200 μm, an axial ratio of 7.5, and a BET specific surface area value (S_BET) Is 51.6m²/ G, degree of densification S_BET/ S_TEM1.26, soluble sodium salt content 3104 ppm in terms of Na, soluble sulfate content SO_FourThe conversion was 2656 ppm, the powder pH value was 5.1, and the geometric standard deviation value was 1.34. The zirconium content is 2.81% by weight in terms of Zr, and the silicon content is SiO.₂It was 0.75% by weight in terms of conversion. The resin adsorption strength was 54.5%.
[0145]
After 800 g of the obtained high-density spindle-shaped hematite particle powder was coarsely pulverized in advance with a Nara type pulverizer, it was put into 4.7 l of pure water and peptized for 60 minutes using a homomixer (made by Tokushu Kika Kogyo) did.
[0146]
Next, the obtained slurry of high-density spindle-shaped hematite particles was mixed and dispersed for 3 hours at a shaft rotational speed of 2000 rpm while circulating through a horizontal SGM (Dispamat SL: manufactured by ESC Adchem). The sieve residue in the 325 mesh (aperture 44 μm) of the spindle-shaped hematite particles in the obtained slurry was 0%.
[0147]
The concentration of the resulting high-density spindle-shaped hematite particle slurry was 100 g / l, and 7 l of the slurry was collected. While stirring this slurry, 6N NaOH aqueous solution was added to adjust the pH value of the slurry to 13.5. Next, this slurry was heated with stirring to a temperature of 95 ° C. and held at that temperature for 3 hours.
[0148]
Next, this slurry was washed with water by a decantation method to obtain a slurry having a pH value of 10.5. To ensure accuracy, the slurry concentration at this point was confirmed to be 98 g / l.
[0149]
Next, 2 l of the obtained water washing slurry was filtered using a Buchner funnel, pure water was passed through, and the filtrate was washed with water until the electric conductivity of the filtrate became 30 μs or less. Thus, spindle-shaped hematite particle powder was obtained. The obtained spindle-shaped hematite particle powder uniformly containing 2.81% by weight of zirconium in terms of Zr inside has a major axis diameter of 0.150 μm, a minor axis diameter of 0.0199 μm, and an axial ratio of 7 .5, Geometric standard deviation value σ of particle size (major axis diameter)_g1.34, BET specific surface area value (S_BET) Is 50.9m²/ G, degree of densification (S_BET/ S_TEM) Is 1.23, the powder pH value is 9.3, the content of soluble sodium salt is 96 ppm in terms of Na, and the content of soluble sulfate is SO_FourIt was 21 ppm in terms of conversion. The resin adsorption strength was 76.5%.
[0150]
<Manufacture of nonmagnetic underlayer>
12 g of spindle-shaped hematite particle powder uniformly containing 2.81% by weight of zirconium in terms of Zr obtained above and binder resin solution (vinyl chloride-vinyl acetate copolymer having sodium sulfonate group) 30% by weight of resin, 70% by weight of cyclohexanone) and cyclohexanone were mixed to obtain a mixture (solid content rate 72%), and this mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.
[0151]
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 coating composition.
[0152]
The composition of the paint containing the obtained spindle-shaped hematite particles was as follows.
Spindle-shaped hematite particle powder 100 parts by weight
Has sodium sulfonate group
10 parts by weight of vinyl chloride-vinyl acetate copolymer resin
10 parts by weight of polyurethane resin having sodium sulfonate group
44.6 parts by weight of cyclohexanone
Methyl ethyl ketone 111.4 parts by weight
66.9 parts by weight of toluene
[0153]
The obtained paint containing hematite particles was applied on a polyethylene terephthalate film having a thickness of 12 μm to a thickness of 55 μm using an applicator, and then dried to form a nonmagnetic underlayer. The thickness of the nonmagnetic underlayer was 3.5 μm.
[0154]
The obtained nonmagnetic underlayer had a glossiness of 207%, a surface roughness Ra of 6.3 nm, and a Young's modulus (relative value) of the substrate of 130.
[0155]
<Manufacture of magnetic recording layer>
In the center of the particle, 1.26% by weight in terms of Al, 0.81% by weight in terms of Al in the surface layer part, and 0.96% by weight in terms of Al in the surface coating part, and Nd = 0. Needle-like metal magnetic particle powder containing iron as a main component present in an amount of 56% by weight (average major axis diameter 0.110 μm, average minor axis diameter 0.0146 μm, axial ratio 7.5,
Coercive force 1911 Oe, saturation magnetization 136.5 emu / g, geometric standard deviation 1.36, resin adsorption strength 82.2%) 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 resin solution (30% by weight vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group and 70% by weight cyclohexanone) and Cyclohexanone was mixed to obtain a mixture (solid content ratio 78%), and this mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.
[0156]
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. Then, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker.
[0157]
The composition of the obtained magnetic paint was as follows.
100.0 parts by weight of metal magnetic particle powder mainly composed of iron
Has sodium sulfonate group
Vinyl chloride-vinyl acetate copolymer resin 10.0 parts by weight
10.0 parts by weight of polyurethane resin having sodium sulfonate group
Abrasive (AKP-30) 10.0 parts by weight
Carbon black (# 3250B) 3.0 parts by weight
Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight
Curing agent (polyisocyanate) 5.0 parts by weight
65.8 parts by weight of cyclohexanone
Methyl ethyl ketone 164.5 parts by weight
98.7 parts by weight of toluene
[0158]
After applying a magnetic coating on the nonmagnetic underlayer to a thickness of 15 μm using an applicator, orientation and drying in a magnetic field, followed by calendering, a curing reaction is performed at 60 ° C. for 24 hours. A magnetic tape was obtained by slitting to a width of 0.5 inch. The thickness of the magnetic recording layer was 1.1 μm.
[0159]
The magnetic tape obtained by forming the magnetic recording layer on the nonmagnetic underlayer has an Hc of 1983 Oe, a squareness ratio (Br / Bm) of 0.88, a glossiness of 228%, and a surface roughness Ra of 6. 0.1 nm, Young's modulus (relative value) of 132, linear absorption coefficient of 1.24 μm^-1The running durability was 30 minutes or more, and the scratch property was A.
[0160]
The changes over time in the magnetic properties of the magnetic tape were 3.1% for the coercive force and 2.7% for the saturation magnetic flux density Bm.
[0161]
[Action]
The most important point in the present invention consists of acicular hematite particles containing 0.05 to 30% by weight of zirconium in terms of Zr inside the particles, the average major axis diameter is 0.3 μm or less, The body pH value is 8 or more, the content of soluble sodium is 300 ppm or less in terms of Na, and the content of soluble sulfate is SO_FourWhen the acicular hematite particle powder having a conversion of 150 ppm or less is used as the non-magnetic particle powder for the non-magnetic underlayer, the dispersibility in the binder resin is excellent. The surface smoothness of the base layer and the strength of the substrate can be improved, and a magnetic recording layer using acicular metal magnetic particle powder mainly composed of iron in which aluminum is present is provided on the nonmagnetic underlayer. In this case, the magnetic recording layer has a low light transmittance, a high strength, a smoother surface, and a more durable magnetic recording medium. This is the fact that it is possible to suppress the deterioration of magnetic properties due to the corrosion of the metal magnetic particle powder mainly composed of iron in which the dispersed aluminum is present.
[0162]
Regarding the reason why the surface smoothness of the non-magnetic underlayer and the strength of the substrate could be further improved, the present inventor found that soluble sodium causing high-density acicular hematite particles to be firmly crosslinked and aggregated Due to the fact that the salt and soluble sulfate can be sufficiently washed away, the agglomerates can be unraveled into substantially independent particles, resulting in dispersibility in the vehicle. Is considered to be due to obtaining excellent needle-like hematite particle powder.
[0163]
The fact that the acicular hematite particle powder in the present invention is excellent in dispersibility in the vehicle will be described below.
[0164]
As described above, the acicular goethite particles used as a precursor are produced by various production methods. In any method, when the main raw material for producing acicular goethite particles is ferrous sulfate. Of course, sulfate [SO_Four ^2-] Are present in large quantities.
[0165]
In particular, when producing goethite particles from an acidic solution, Na₂SO_FourThis produces iso-water soluble sulfate and the reaction mother liquor has K⁺, NH_Four ⁺, Na⁺Since it contains an alkali metal such as an alkali metal, a precipitate containing an alkali metal or sulfate is likely to be formed._Three(SO_Four) (OH)₆(R = K⁺, NH_Four ⁺, Na⁺). These precipitates are sparingly soluble sulfur-containing iron salts and cannot be removed by conventional water washing. This hardly soluble salt becomes a soluble sodium salt or soluble sulfate in the subsequent heat treatment step, but this soluble sodium salt or soluble sulfate is in the form of needle-shaped hematite particles in the high temperature heat treatment step for densification. The anti-sintering agent, which is essential to prevent deformation and sintering between particles, is firmly bonded to the inside and the surface of the particles while cross-linking the needle-like hematite particles. Aggregation between them is further strengthened. As a result, in particular, soluble sulfates and soluble sodium salts trapped inside the particles and aggregates are extremely difficult to remove by washing with water by a conventional method.
[0166]
When producing acicular goethite particles in an alkaline aqueous solution using ferrous sulfate and sodium hydroxide, the sulfate produced simultaneously is Na₂SO_FourIn addition, NaOH exists in the mother liquor, and both of them are soluble, so if the needle-like goethite particles are sufficiently washed with water, essentially Na₂SO_FourAnd should be able to remove NaOH. However, since the crystallinity of needle-like goethite particles is generally low, the washing efficiency is poor. When washing with water by a conventional method, soluble sulfate [SO_Four ^2-], Soluble sodium salt [Na⁺] Contains water soluble content. As described above, this water-soluble component is firmly bonded to the inside and the surface of the particles while cross-linking the acicular hematite particles with the sintering inhibitor, thereby further aggregating the acicular hematite particles. Strengthen. As a result, in particular, soluble sulfates and soluble sodium salts trapped inside the particles and aggregates are extremely difficult to remove by washing with water by a conventional method.
[0167]
As described above, high-density acicular hematite particles in which soluble sodium salt or soluble sulfate is strongly bonded to the inside of the particle, the surface of the particle, or the inside of the aggregate via an anti-sintering agent, After loosening, the pH value of the slurry is adjusted to 13 or higher, and heat treatment is performed at a temperature of 80 ° C. or higher. The alkaline aqueous solution sufficiently penetrates into the particles of the high-density needle-like hematite particles. In addition, the binding strength of the sintering inhibitor strongly bonded to the inside of the agglomerates gradually weakens, dissociates from the inside of the particles, the surface of the particles and the inside of the agglomerates, and at the same time, water-soluble sodium salts and water-soluble sulfates can be easily washed away with water. It is considered to be.
[0168]
The reason why the durability of the surface of the magnetic recording layer and the magnetic recording medium has not been improved is not yet clear, but as shown in the Examples below, the present inventors have uniformly contained zirconium inside the particles, Needle-like hematite particles having a pH value of 8 or more and a low content of soluble sodium salt or soluble sulfate are used as non-magnetic particles, and needles mainly composed of iron containing aluminum Due to the synergistic effect with the use of the powdered metal magnetic particle powder as the magnetic particle, the resin adsorption strength of both the acicular hematite particle and the magnetic particle and the binder resin in the vehicle is increased. Increased adhesion between acicular hematite particles and binder resin in magnetic underlayer and adhesion of nonmagnetic underlayer itself to nonmagnetic support, magnetic particles in magnetic recording layer Are believed to be due to the synergistic effect of such that the heightened degree of adhesion with respect to the degree of adhesion and magnetic recording layer nonmagnetic underlayer itself with the binder resin.
[0169]
The present inventor has promoted the corrosion of the metal for the reason that the deterioration of the magnetic properties accompanying the corrosion of the iron-based metal magnetic particle powder in which the aluminum dispersed in the magnetic recording layer is present is suppressed. The main component of iron is that the soluble sodium salt, the soluble sulfate, and the like have a low soluble content in the high-density acicular hematite particles and the acicular hematite particles themselves have a high powder pH value of 8 or more. It is considered that the progress of the corrosion of the metal magnetic particle powder was suppressed.
[0170]
In fact, the present inventor, as shown in the examples and comparative examples described later, when heat-treating the high-density needle-like hematite particles after wet pulverization with an alkaline aqueous solution having a temperature of 80 ° C. or higher and a pH value of less than 13, When the high-density acicular hematite particles after wet pulverization are heat-treated with an alkaline aqueous solution having a temperature of less than 80 ° C. and a pH value of 13 or more, the high-density acicular hematite particles remain coarse without containing the wet pulverization. In any case of heat treatment in an alkaline aqueous solution having a temperature of 80 ° C. or higher and a pH value of 13 or higher, the corrosion of the metal magnetic particle powder mainly composed of iron in which aluminum is present is sufficiently progressed. Confirmed the phenomenon that the progress of corrosion of the metal magnetic particle powder containing iron as the main component can be suppressed by the synergistic effect that the soluble content is low and the powder pH value is 8 or more because it cannot be suppressed. To have.
[0171]
【Example】
Next, examples and comparative examples are given.
[0172]
<Types of acicular goethite particle powder>
The following starting materials A to E were prepared as precursors for producing acicular hematite particles.
[0173]
[Table 1]

[0174]
<Production of low density acicular hematite particle powder>
Examples 1-9 and Comparative Examples 1-14
Low density as in the above-described embodiment of the present invention, except that the type of acicular goethite particle powder as a starting material, the presence or absence of a sintering inhibitor, the type and addition amount, the heat dehydration temperature and time are variously changed. Acicular hematite particles were obtained. The particles obtained in Comparative Example 4 are goethite particles.
[0175]
Tables 2 to 5 show main manufacturing conditions and various characteristics at this time.
[0176]
[Table 2]

[0177]
[Table 3]

[0178]
[Table 4]

[0179]
[Table 5]

[0180]
<Production of high density acicular hematite particle powder>
Examples 10-18 and Comparative Examples 15-27
High-density needle-like hematite particles were obtained in the same manner as in the embodiment of the present invention, except that the kind of low-density needle-like hematite particles, the temperature and time of the densification heat treatment were variously changed.
[0181]
Tables 6 and 7 show the main production conditions and various characteristics at this time.
[0182]
[Table 6]

[0183]
[Table 7]

[0184]
<Treatment of acicular hematite particles in aqueous alkali solution>
Examples 19-27 and Comparative Examples 28-35
Except for various changes in the type of high-density acicular hematite particle powder, presence or absence of wet pulverization, presence or absence of heat treatment in an alkaline aqueous solution, slurry pH value, heating temperature and heating time, Similarly, acicular hematite particles were obtained.
[0185]
Tables 8 to 11 show main manufacturing conditions and various characteristics at this time.
[0186]
[Table 8]

[0187]
[Table 9]

[0188]
[Table 10]

[0189]
[Table 11]

[0190]
<Surface coating treatment of acicular hematite particles>
Example 28
The slurry having a pH value of 10.5 in Example 19 obtained by washing with water by a decantation method after heat treatment in an alkaline aqueous solution had a slurry concentration of 98 g / l. 5 l of this slurry was heated again to 60 ° C., and 272 ml of 1.0 N sodium aluminate aqueous solution (corresponding to 1.5 wt% in terms of Al with respect to acicular hematite particles) was added to this slurry, and held for 30 minutes. Then, the pH value was adjusted to 8.5 using acetic acid. Next, in the same manner as in the above-described embodiment of the present invention, filtration, washing, drying, and pulverization were performed to obtain acicular hematite particle powders whose particle surfaces were coated with aluminum oxide.
[0191]
Tables 12 and 13 show the main production conditions and various characteristics at this time.
[0192]
Examples 29-36
Surface-coated needle-like hematite particles were obtained in the same manner as in Example 28 except that the kind of needle-like hematite particles, the kind of surface-treated product, and the amount added were varied.
[0193]
Tables 12 and 13 show the main production conditions and various characteristics at this time.
[0194]
[Table 12]

[0195]
[Table 13]

[0196]
<Manufacture of nonmagnetic underlayer>
Examples 37-54 and Comparative Examples 36-50
The present invention using the acicular hematite particles obtained in Examples 19 to 36, the acicular goethite particles of the starting material E, and the acicular hematite particles obtained in Comparative Examples 3, 15 to 18, 23, and 28 to 35. A nonmagnetic underlayer was obtained in the same manner as in the above embodiment.
[0197]
Tables 14 and 15 show the main manufacturing conditions and various characteristics at this time.
[0198]
[Table 14]

[0199]
[Table 15]

[0200]
<Manufacture of magnetic recording medium using metal magnetic particle powder containing iron as main component>
Examples 55-72 and Comparative Examples 51-65
First, metal magnetic particle powders (a) to (d) mainly comprising four types of iron shown in Table 16 were prepared.
[0201]
[Table 16]

[0202]
A metal magnetic powder containing iron as a main component is the same as the embodiment of the present invention except that the type of nonmagnetic underlayer and the type of acicular metal magnetic particle powder containing iron as a main component are variously changed. The magnetic recording medium used is manufactured.
[0203]
Tables 17 and 18 show the main manufacturing conditions and various characteristics at this time.
[0204]
[Table 17]

[0205]
[Table 18]

[0206]
【The invention's effect】
The magnetic recording medium according to the present invention is a specific powder composed of acicular hematite particles containing zirconium almost uniformly inside the particles as the nonmagnetic powder for the nonmagnetic underlayer, as shown in the previous examples. Due to the use of needle-like hematite particles having a pH value and a soluble salt, in particular, a low amount of soluble sulfate, it is possible to obtain a nonmagnetic underlayer having superior strength and surface properties as a substrate. In addition, when the nonmagnetic underlayer is used as a magnetic recording medium, it is possible to obtain a magnetic recording medium having low light transmittance, high strength, and smoother surface, and nonmagnetic underlayer for nonmagnetic underlayer. There is aluminum in the magnetic recording layer due to the use of needle-like hematite particles having a specific powder pH value and a low soluble salt, particularly a low amount of soluble sulfate. It is possible to suppress the deterioration of the magnetic properties with the iron being in corrosion of acicular magnetic metal particles as a main component.
[0207]
The magnetic recording medium according to the present invention uses a needle-like hematite particle powder composed of needle-like hematite particles uniformly containing zirconium inside the particle as the non-magnetic particle powder for the non-magnetic underlayer and magnetic recording. Magnetic recording medium for high-density recording because it has superior durability due to the use of acicular metal magnetic particle powder mainly composed of iron in which aluminum is present as the magnetic particle powder for layer Is preferable.

Claims (2)

A nonmagnetic underlayer comprising a nonmagnetic support, a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, and a magnetic particle powder and a binder resin formed on the nonmagnetic underlayer In a magnetic recording medium comprising a magnetic recording layer, the nonmagnetic particle powder is composed of acicular hematite particles containing 0.05 to 30% by weight of zirconium in terms of Zr, and has an average major axis diameter of 0. Acicular hematite particles having a powder pH value of 8 or more, a soluble sodium salt content of 300 ppm or less in terms of Na, and a soluble sulfate content of 150 ppm or less in terms of SO ₄ The magnetic particle powder is a needle-like metal magnetic particle powder whose main component is iron in which 0.05 to 10% by weight of aluminum is present in terms of Al. A nonmagnetic underlayer comprising a nonmagnetic support, a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, and a magnetic particle powder and a binder resin formed on the nonmagnetic underlayer In the magnetic recording medium comprising a magnetic recording layer, the non-magnetic particle powder contains 0.05 to 30% by weight of zirconium in terms of Zr, and is a hydroxide of aluminum, an oxide of aluminum, silicon A needle-like hematite particle whose particle surface is coated with at least one of a hydroxide and a silicon oxide, an average major axis diameter of 0.3 μm or less, a powder pH value of 8 or more, and The acicular hematite particle powder has a soluble sodium salt content of 300 ppm or less in terms of Na and a soluble sulfate content of 150 ppm or less in terms of SO ₄ , and the magnetic particle powder is 0 in terms of Al. A magnetic recording medium, characterized in that it is a needle-like metal magnetic particle powder mainly composed of iron in which 05 to 10% by weight of aluminum is present.