JPH11106571A - Molding material for magnetic recording medium base - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material which can give a magnetic recording medium base excellent in levelness and capable of high speed revolution by using a cyclic hydrocarbon polymer having monocyclic hydrocarbon structures in the main chain or as side chains. SOLUTION: The monocyclic hydrocarbon structure is a usually 4-12 membered, desirably 5-8 membered, more desirably 6-membered ring. The cyclic hydrocarbon polymer having ring structures in the main chain is exemplified by a cyclic conjugated diene polymer. The cyclic hydrocarbon polymer having ring structures as side chains is exemplified by a vinyl cyclic hydrocarbon polymer. It is desirable that, in both cases, the ring carbon-carbon unsaturations have been hydrogenated. It is desirable that the cyclic hydrocarbon polymer has a weight-average molecular weight (Mw) of 10,000-1,000,000 in terms of the polystyrene as measured by GPC and a molecular weight distribution (Mw/Mn) of 6.0 or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel magnetic recording medium substrate and a molding material therefor, and more particularly, to a magnetic recording medium substrate capable of high-speed rotation and a molding material therefor.

[0002]

2. Description of the Related Art In recent years, with the development of computers, the development of magnetic recording media having a large recording capacity has been promoted.
Expectations are being placed on high-density magnetic disks. Also,
As computers themselves become smaller and lighter, there is also a demand for lighter recording media. Under the above circumstances, replacing the magnetic disk substrate with a conventional aluminum substrate,
Attempts have been made to use plastic substrates.
However, such a magnetic disk has a high recording density, even when compared with the highest density and high speed magneto-optical disk substrate (MO).
Since the rotation speed is several times or more, and the recording signal is detected by a magnetic head that is only a few tens of nm away from the substrate, deformation due to moisture absorption of the substrate and blurring (vibration) during rotation of the substrate are serious problems. Become.

Conventionally, it has been known that thermoplastic norbornene resins such as hydrogenated ring-opening polymers of tetracyclododecene monomers are excellent as materials for optical disc substrates because of their excellent low moisture absorption. Furthermore, Japanese Patent Application Laid-Open No. 7-153060 discloses that excellent characteristics can be obtained even when used as a magnetic disk substrate. Japanese Patent Application Laid-Open No. 7-210855 discloses that when a fine particle such as an inorganic filler is mixed with a thermoplastic norbornene-based resin, the elastic modulus of the resin is improved. ing.

However, with the recent increase in the rotational speed of the magnetic disk, the conventional thermoplastic norbornene-based resin is not sufficiently large so that the elastic modulus can follow the rotational speed. Was added to improve the elastic modulus, the surface roughness of the substrate was sometimes reduced depending on the particle size and the amount of the filler.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a substrate for a magnetic recording medium which has excellent flatness on the surface of the substrate and enables high-speed rotation, and a molding material for the substrate.

[0006]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the use of a polymer having a specific structure shows excellent performance. It was completed.

Thus, according to the present invention, there is provided (1) a molding material for a magnetic recording medium substrate comprising a cyclic hydrocarbon polymer having a monocyclic cyclic hydrocarbon structure in a main chain or a side chain. According to the present invention, (2) the cyclic hydrocarbon structure is 6
The molding material according to (1), which is a member ring, is provided. According to the present invention, there is provided (3) the molding material according to (2), wherein the cyclic hydrocarbon-based polymer has a six-membered ring in a side chain. According to the present invention, (4) the cyclic hydrocarbon-based polymer is
The molding material according to any one of (1) to (3), which has an elastic modulus of 20,000 kgf / cm ² or more. According to the present invention, (5) the cyclic hydrocarbon-based polymer has a weight average molecular weight (Mw) and a number average molecular weight (Mn) ratio (Mw / Mn) of 6.0 or less, and a weight average molecular weight (Mw). Mw) is 10,000 to 1,000,000, and the molding material according to any one of (1) to (4) is provided. According to the present invention, there is provided a magnetic recording medium substrate formed by molding the molding material described in (6) (1) to (5). According to the present invention, there is provided (7) a method for producing a substrate for a magnetic recording medium by injection molding the molding material according to any one of (1) to (5). According to the present invention, (8)
A magnetic recording medium provided with a magnetic recording layer on the surface of the magnetic recording medium substrate according to (6) is provided.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below by dividing them into items.

(Molding Material for Magnetic Recording Medium Substrate) In the present invention, a cyclic hydrocarbon polymer having a monocyclic cyclic hydrocarbon structure in a main chain or a side chain is used as a molding material for a magnetic recording medium substrate. .

(Cyclic Hydrocarbon Polymer) The monocyclic cyclic hydrocarbon structure is not particularly limited, but is usually 4-12.
When the ring is a membered ring, preferably a 5- to 8-membered ring, more preferably a 6-membered ring, properties such as heat resistance and strength characteristics are highly balanced and suitable. The structure of the cyclic hydrocarbon may be either saturated or unsaturated, but is preferably a saturated cyclic hydrocarbon from the viewpoint of heat resistance and the like. In the ring structure, the content of the saturated ring structure is usually 80% or more, and preferably 90% or more.
More preferably, it is 95% or more, and substantially 1%.
Most preferably, it is 00%. The ring structure in the polymer is
Any of a main chain and a side chain may be used, but in order to achieve a high balance between elastic modulus and moldability, those having a ring structure in the side chain are preferred.

Specific examples include polymers having a cyclic structure in the main chain, such as cyclopentene and cyclohexene, and monocyclic olefins such as cyclopentadiene and cyclohexadiene.
Or a hydrogenated product thereof; as a polymer having a ring structure in a side chain, a vinylcyclohexene-based or vinylcyclohexane-based polymer, or a hydrogenated product thereof, an aromatic vinyl-based polymer such as polystyrene, or a hydrogenated product thereof No.

The following is an example of the grouping.

[Cyclic hydrocarbon polymer having a cyclic structure in the main chain] Specific examples of the cyclic hydrocarbon polymer having a cyclic structure in the main chain include, for example, a cyclobutene polymer, a cyclopentene polymer, a cyclohexene polymer, Monocyclic olefin addition polymers such as cycloheptene polymer and cyclooctene polymer; and cyclic conjugated diene polymers such as cyclopentadiene polymer, cyclohexadiene polymer, cyclheptadiene polymer and cyclooctadiene polymer. Among these, a 5- to 8-membered ring is preferable for the ring structure in view of the balance between heat resistance, moldability, and strength properties.
Member rings are most preferred. For the same reason, 1,4-addition of a cyclic conjugated diene is preferable to 1,2-addition of a monocyclic olefin for the same reason. Further, the carbon-carbon unsaturated bond in the ring is preferably hydrogenated. From such a viewpoint, among the cyclic hydrocarbons having a cyclic structure in the main chain, hydrogenated cyclohexadiene polymers are most preferred.

[Cyclic Hydrocarbon Polymer Having a Cyclic Structure in the Side Chain] Specific examples of the cyclic hydrocarbon polymer having a cyclic structure in the side chain include, for example, a vinylcyclopentene-based or vinylcyclopentane-based polymer or a vinylcyclopentane-based polymer thereof. Hydrogenated product, vinylcyclohexene-based or vinylcyclohexane-based polymer or hydrogenated product thereof, vinylcycloheptene-based or vinylcycloheptane-based polymer or hydrogenated product thereof, vinylcyclooctene-based or vinylcyclooctane-based polymer or the same Examples include hydrogenated products, aromatic vinyl polymers and hydrogenated products thereof.
Among these, from the balance of heat resistance, moldability and strength properties, the ring structure is preferably a 5- to 8-membered ring, and a vinylcyclohexene-based or vinylcyclohexane-based polymer or a hydrogenated product thereof, an aromatic vinyl-based polymer or hydrogenated A 6-membered ring such as a product is most preferred. Further, it is preferable that the carbon-carbon unsaturated bond in the ring is hydrogenated because the elastic modulus is improved.

Examples of the vinyl cyclic hydrocarbon monomer used to obtain the above-mentioned vinyl cyclic hydrocarbon polymer include styrene, α-methylstyrene, α-ethylstyrene, α-propylstyrene, and the like. α-isopropylstyrene, α-t-butylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,
Styrene-based monomers such as 4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, and 4-phenylstyrene Isomers; vinylcyclohexane-based monomers such as vinylcyclohexane and 3-methylisopropenylcyclohexane; 4-vinylcyclohexene;
Vinylcyclohexene monomers such as isopropenylcyclohexene, 1-methyl-4-vinylcyclohexene, 1-methyl-4-isopropenylcyclohexene, 2-methyl-4-vinylcyclohexene, 2-methyl-4-isopropenylcyclohexene; d-terpene,
Examples include vinylated six-membered ring hydrocarbon monomers such as terpene monomers such as l-terpene and diterpene, and substituted products thereof. When a styrene-based monomer containing an aromatic ring is used, the hydrogenation rate is 80% by the hydrogenation reaction.
% Is preferable. These monomers may be used alone or in combination of two or more.

In the present invention, a monomer other than the above-mentioned monomers may be copolymerized within a range where the repeating unit in the polymer is less than 50% by weight. The copolymerizable monomer is not particularly limited as long as it can be copolymerized in a polymerization method such as radical polymerization, anionic polymerization, or cationic polymerization. Examples thereof include ethylene, propylene, isobutene, and 2-methyl-1-. Α-olefin monomers such as butene, 2-methyl-1-pentene and 4-methyl-1-pentene; cyclopentadiene, 1-methylcyclopentadiene, 2-methylcyclopentadiene, 2-ethylcyclopentadiene, 5- Methylcyclopentadiene,
Cyclopentadiene-based monomers such as 5,5-dimethylcyclopentadiene; cyclobutene, cyclopentene,
Cyclic olefin monomers such as cyclohexene and dicyclopentadiene; butadiene, isoprene, 1,3-
Conjugated diene monomers such as pentadiene, furan, thiophene and 1,3-cyclohexene; nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile; methyl methacrylate, ethyl methacrylate, meta (Meth) acrylate monomers such as propyl acrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate; acrylic acid, methacrylic acid, Unsaturated fatty acid monomers such as maleic anhydride; phenylmaleimide; ethylene oxide, propylene oxide, trimethylene oxide, trioxane, dioxane, cyclohexene oxide, styrene oxide, Cyclic ether monomers such as epichlorohydrin and tetrahydrofuran; heterocyclic-containing vinyl compound monomers such as methyl vinyl ether, N-vinylcarbazole and N-vinyl-2-pyrrolidone; Generally, when the content of the repeating unit derived from a monomer other than the cyclic hydrocarbon monomer increases, the strength and heat resistance of the polymer decrease.

The content of the repeating unit of the cyclic hydrocarbon-based monomer is appropriately selected according to the purpose of use.
It is at least 0% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, most preferably at least 90% by weight. When the content of the cyclic hydrocarbon monomer repeating unit is in the above range, the molding material is excellent in strength properties and heat resistance, and is suitable.

The content of the saturated ring structure in the ring structure (hydrogenation rate when the ring structure is an aromatic ring or a cyclohexene ring) is 80% or more, preferably 90% or more, more preferably 95% or more. It is. When the hydrogenation rate is in this range, the heat resistance is particularly excellent and the composition becomes suitable. Incidentally, the hydrogenation rate can be determined by ¹ H-NMR measurement.

In view of the above, the most preferred cyclic hydrocarbon polymer used in the present invention is a vinyl cyclic hydrocarbon repeating unit having a 6-membered ring structure in a side chain comprising at least 90% by weight of the total repeating units of the polymer. 6 of the repeating unit
The ratio of the saturated ring (vinylcyclohexane ring) in the membered ring structure is 95% or more. Specifically, hydrogenated polystyrenes, hydrogenated styrene-based polymers such as styrene / α-methylstyrene copolymer hydrogenated products; hydrogenated vinylcyclohexene-based polymers such as hydrogenated polyvinylcyclohexene; polyvinylcyclohexane; Examples thereof include a vinylcyclohexane-based polymer.

The glass transition temperature (Tg) of the cyclic hydrocarbon polymer used in the present invention is usually 80 to 300 ° C., preferably 100 to 280 ° C., and more preferably 120 to 2 ° C.
When the glass transition temperature is in the range of 50 ° C. and the glass transition temperature is in the above range, the balance between the strength characteristics (elastic modulus) at high temperature and the moldability is excellent.

The weight average molecular weight (Mw) of the cyclic hydrocarbon polymer used in the present invention is generally 10,000 to 1,000, in terms of polystyrene measured by GPC.
0000, preferably 500,000 to 500,00
When it is 0, more preferably in the range of 100,000 to 300,000, it is excellent in balance between strength characteristics and moldability and is suitable. The molecular weight distribution is usually 6.0 or less, preferably 3 or less, as the ratio (Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) in terms of polystyrene measured by gel permeation chromatography (GPC). .0
Or less, more preferably 2.5 or less, most preferably 2.
0 or less. Mw / M of vinyl-based cyclic hydrocarbon polymer
When n is in the above range, the mechanical strength and heat resistance of the polymer are particularly excellent, and when the weight average molecular weight (Mw) is in the above range, the strength properties, moldability and birefringence of the polymer are balanced, which is preferable. is there.

In the case of a hydrogenated product, if the weight average molecular weight (Mw) of the unhydrogenated polymer is excessively large, the hydrogenation reaction of the ring is difficult, and the hydrogenation reaction is forcibly advanced to nearly 100%. The molecular chain distribution reaction, which is a competitive reaction, progresses and the molecular weight distribution increases, and the low molecular weight component increases, so the strength characteristics and heat resistance decrease.On the contrary, if it is excessively small, the strength characteristics are inferior and the molding is insufficient. Since the product can not be molded, none of them is preferable, when it is in the above range, the mechanical strength,
It is suitable because the heat resistance and the like are highly balanced.

(Production method) As the polymerization method of the cyclic hydrocarbon polymer of the present invention, a conventionally known polymerization method can be used. The method for producing each of the aforementioned cyclic hydrocarbon polymers will be described below.

The method for obtaining the addition polymer of a monocyclic cyclic olefin monomer is not particularly limited.
It can be obtained by a known method using a Ni, Pd complex described in JP-A-96 / 23010 as a polymerization catalyst. The method for obtaining the polymer of the cyclic conjugated diene monomer is not particularly limited.
It can be obtained by a known method using an organic metal of Group Ia of the periodic table described in 1 as a catalyst. As a method for obtaining a polymer such as a vinyl compound having a cyclic hydrocarbon group, for example, a styrene or a vinylcyclohexane derivative,
There is no particular limitation, and it can be obtained by a known method using a suitable one among known radical polymerization catalysts, anion polymerization catalysts, cationic polymerization catalysts and Ziegler-Natta polymerization catalysts as a catalyst. These polymers may be copolymers with other copolymerizable monomers. Furthermore, when a carbon-carbon double bond is contained in the main chain portion and the side chain portion of the above polymer, the polymer may be hydrogenated by a known hydrogenation catalyst. Examples of the hydrogenation catalyst include Ni,
Examples of the catalyst include a catalyst in which Pd is supported on alumina or silica, and a Ni, Pd-based Ziegler catalyst.

Further, a method for producing a vinyl-based cyclic hydrocarbon polymer, which is the most preferred embodiment of the polymer of the present invention, will be described in detail.

As described above, the process for producing the vinyl cyclic hydrocarbon polymer of the present invention comprises radical polymerization, anion polymerization,
It is obtained by performing polymerization using a known polymerization method such as anionic living polymerization, cationic polymerization, and cationic living polymerization.

As the polymerization method, in the case of radical polymerization, polymerization can be performed by a known method using an organic peroxide, and in the case of cationic polymerization, polymerization can be performed by a known method using BF ₃ , PF ₆ or the like.

In order to obtain a polymer having a small molecular weight distribution, it is preferable to carry out polymerization by anionic living polymerization. Specifically, it can be easily obtained by polymerization in a hydrocarbon solvent using an organic alkali metal as an initiator. .

As the organic alkali metal, for example, n-
Monoorganic lithium compounds such as butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium and stilbenelithium; dilithiomethane, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, 1,3 And multifunctional organolithium compounds such as 1,5-trilithiobenzene; sodium naphthalene, potassium naphthalene and the like.
Among these, organolithium compounds are preferred, and monoorganic lithium compounds are particularly preferred.

These organic alkali metals can be used alone or in combination of two or more. The amount of the organic alkali metal used is appropriately selected depending on the required molecular weight of the produced polymer.
0.05 to 100 mmol, preferably 0.10 to 50 mmol, more preferably 0.15 to 2 per 0 parts by weight.
The range is 0 mmol.

The polymerization methods include bulk polymerization, emulsion polymerization,
Although suspension polymerization, solution polymerization and the like can be applied, solution polymerization is preferable in order to continuously carry out the hydrogenation reaction.

The solvent used in the case of solution polymerization is preferably a hydrocarbon-based solvent, and is not particularly limited as long as it does not destroy the above-mentioned initiator. For example, n-butane, n-pentane, aliphatic hydrocarbons such as iso-pentane, n-hexane, n-heptane and iso-octane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane and decalin; benzene, toluene and the like Aromatic hydrocarbons; ethers such as tetrahydrofuran and dioxane; and the like. Among these, the use of aliphatic hydrocarbons and alicyclic hydrocarbons is preferable because the hydrogenation reaction can be performed as it is. These hydrocarbon solvents are used alone or in combination of two or more, and usually have a monomer concentration of 1 to 40% by weight.
It is used at a quantitative ratio such that

The polymerization reaction may be either an isothermal reaction or an adiabatic reaction, usually at -70 to 150 ° C, preferably at -50 ° C.
It is carried out in a polymerization temperature range of ~ 120 ° C. The polymerization time is
It is in the range of 0.01 to 20 hours, preferably 0.1 to 10 hours.

After the polymerization reaction, the polymer can be recovered by a known method such as a steam stripping method, a direct desolvation method, or an alcohol coagulation method. In the present invention, when a solvent inert to the hydrogenation reaction is used at the time of polymerization, the polymer can be directly used for the hydrogenation step without recovering the polymer from the polymerization solution.

The method for hydrogenating the polymer is not particularly limited, and any conventional method may be used. Preferred is a hydrogenation method in which the hydrogenation rate of the aromatic ring is high and the polymer chain is less broken, for example, in an organic solvent, nickel, cobalt,
It can be carried out using a hydrogenation catalyst containing at least one metal selected from iron, titanium, rhodium, palladium, platinum, ruthenium and rhenium. The hydrogenation catalyst is
Among these, a nickel catalyst is particularly preferable because a hydrogenated product having a particularly small Mw / Mn can be obtained. The hydrogenation catalyst may be either a heterogeneous catalyst or a homogeneous catalyst.

The heterogeneous catalyst can be used as it is as a metal or a metal compound, or supported on a suitable carrier. Examples of the carrier include activated carbon, silica, alumina, calcium carbonate, titania, magnesia, zirconia, diatomaceous earth, silicon carbide, and the like. In this case, the amount of the metal supported on the carrier is usually 0.01 to 80. weight%
, Preferably in the range of 0.05 to 60% by weight.

As the homogeneous catalyst, nickel, cobalt, titanium or iron compounds and organometallic compounds, for example,
Catalysts in combination with organoaluminum, organolithium compounds; or rhodium, palladium, platinum, ruthenium,
An organometallic complex such as rhenium can be used. As the nickel, cobalt, titanium or iron compound used for the homogeneous catalyst, for example, acetylacetone salts, naphthenates, cyclopentadienyl compounds, cyclopentadienyl dichloro compounds and the like of various metals are used. Examples of the organic aluminum include alkyl aluminum such as triethyl aluminum and triisobutyl aluminum;
Alkyl aluminum halides such as diethylaluminum chloride and ethylaluminum dichloride; alkylaluminum hydrides such as diisobutylaluminum hydride; and the like are preferably used. Examples of the organometallic complex include metal complexes such as the above-mentioned metals such as γ-dichloro-π-pentene complex, dichloro-tris (triphenylphosphine) complex, and hydride-chloro-tris (triphenylphosphine) complex. .

These hydrogenation catalysts can be used alone or in combination of two or more. The amount of the hydrogenation catalyst used is the amount of the aromatic vinyl polymer 1
Usually, 0.03 to 50 parts by weight, preferably 0.16 to 33 parts by weight, more preferably 0.33 to 1 part by weight per 100 parts by weight.
The range is 5 parts by weight.

Examples of the organic solvent used in the hydrogenation reaction include, for example, alcohols in addition to the solvent used in the above-mentioned polymerization reaction. These organic solvents can be used alone or in combination of two or more. The amount of the organic solvent used is such that the concentration of the aromatic polymer is usually 1 to 50% by weight, preferably 3 to 40% by weight.

In the hydrogenation reaction, the temperature is usually 10 to 250
° C, preferably 50-200 ° C, more preferably 80-
In the range of 180 ° C. and the hydrogen pressure is usually 1 to 300 k
g / cm ² , preferably 5 to 250 kg / cm ² , more preferably 10 to 200 kg / cm ² .

[Compounding agents] The molding material of the present invention may contain various compounding agents, if necessary. The compounding agent is not particularly limited as long as it is generally used in molding materials, and examples thereof include antioxidants such as phenol-based, phosphite-based, and thioether-based agents; ultraviolet absorbers such as hindered phenol-based agents; Release agents such as aliphatic alcohols, aliphatic esters, aromatic esters, triglycerides, fluorine-based surfactants and higher fatty acid metal salts; other lubricants; plasticizers; antistatic agents; These compounding agents can be used alone or in combination of two or more. The amount of the compounding agent used is appropriately selected within a range that does not impair the purpose of the present invention. Further, for the purpose of improving the adhesion to the magnetic recording layer, a small amount of an organic compound having at least one alcoholic hydroxyl group and a long-chain hydrocarbon structure may be added. Specific examples include partial ethers and partial esters of polyhydric alcohols. For the purpose of preventing a decrease in mechanical strength under a high temperature and high humidity environment, a small amount of a rubbery polymer or the like may be added.

The molding material of the present invention may contain a small amount of an inorganic or organic filler for the purpose of further improving the elastic modulus as long as the surface roughness of the molded article is not impaired. The filler is not particularly limited, for example, silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, pumice powder, pumice balloon, basic magnesium carbonate, dowamite, calcium sulfate, potassium titanate, barium sulfate, calcium sulfite , Talc, clay, mica, asbestos, glass fiber, glass flake, glass beads,
Calcium silicate, montmorillonite, bentonite,
Examples include graphite, aluminum powder, molybdenum sulfide, boron fiber, silicon carbide fiber, polyethylene fiber, polypropylene fiber, polyester fiber, and polyamide fiber. Among these fillers, inorganic fillers are preferable, and fine-particle silica is particularly preferable because of excellent heat resistance and surface roughness during molding.

(Substrate for Magnetic Recording Medium) The substrate used for manufacturing the magnetic recording medium of the present invention is a magnetic recording medium for storing data of an information processing apparatus such as a computer, and more specifically, a floppy disk substrate, A magnetic disk substrate and the like can be cited, and a magnetic disk substrate, such as a magnetic disk substrate, which requires particularly high density and high-speed rotation, can be exemplified as one in which the effect of the present invention is remarkably exhibited. The recording density of such a magnetic recording disk is usually 100 megabytes (MB) or more, and the recent one has a recording density of 1 megabyte (MB).
Some are gigabytes (GB) or more. The rotation speed is 3,
2,000 to 8,000 rpm, and the detection of the recording signal
Since the magnetic head is provided only with a gap of about 50 nm from the substrate, if the elastic modulus of the molding material for the substrate is not a sufficient value, the blur at high-speed rotation increases, and the resonance frequency (recording signal can be detected) The maximum rotation speed (without blur): the rotation speed of the servo band) cannot be increased, and the reading speed cannot be improved. Therefore, the elastic modulus of the molding material sufficient to sufficiently increase the resonance frequency is usually 20,000 or more, preferably 24,000 or more, and most preferably 28,000.
0 or more. Further, in recent years, magneto-optical disks such as MOs and DVDs are required to have higher densities than ever before, so that the groove width is reduced, the number of rotations is increased, and the disk is close to the same level as the magnetic disk substrate. However, the molding material of the present invention may be used for these substrates.

[Magnetic Disk Substrate] The above-described magnetic disk has a magnetic recording layer provided on a magnetic disk substrate. The magnetic recording layer is generally composed of an underlayer, a magnetic layer, a protective film, An agent application layer is sequentially provided. Hereinafter, a specific example of the plastic magnetic disk substrate will be described.

The magnetic disk substrate has a substantially disk shape having a diameter of 65 mm and a thickness of 0.8 mm. Specifically, for example, a magnetic disk substrate is formed on a recording region forming portion, and on the inner and outer peripheral sides of the recording region forming portion. It comprises a clamp portion and a landing portion located, but the structure is not limited to these.

The recording area forming part is a part which becomes a recording area when the magnetic disk is used. The data area forming part in which an area for actually recording data is formed, and the address and the position in the recording track are defined. And a servo mark forming section on which servo marks for controlling (tracking) are formed.

An underlayer is formed on the magnetic disk substrate as described above, and a magnetic layer is further formed thereon. Note that a protective film and a lubricant coating layer are formed on the magnetic layer.

[Formation of Substrate] The substrate for a magnetic recording medium is molded by injection molding using the molding material of the present invention. The type of the injection molding machine is not particularly limited as long as it is a conventional injection molding machine for an optical disk substrate. A mold equipped with a stamper for a magnetic disk is used. The molding temperature (resin temperature) is usually 200 to 400 ° C. Preferably 250-3
90 ° C, more preferably 300 to 380 ° C. When the molding temperature is in the above range, characteristics such as surface roughness, transferability, and mechanical characteristics are highly balanced, which is preferable. Mold temperature is usually 70 to 140 ° C, preferably 90 to 140 ° C,
The temperature is more preferably 90 to 130 ° C. When the molding temperature is in the above range, characteristics such as transferability and molding cycle are highly balanced, which is preferable.

[Magnetic Recording Film Layer and Forming Method] An underlayer made of, for example, Cr, Mo or the like is formed on the above-mentioned magnetic disk substrate: about 100 nm on average, CoCrPt, Co, Pt,
Magnetic layer made of Co, Pd, etc .: about 60 nm on average, C
A protective film made of, for example, about 18 nm on average is formed sequentially by sputtering. As a sputtering method, for example, an in-line stationary facing DC magnetron sputtering apparatus is used, and an alloy target is used for the magnetic layer.
The film is formed in an r gas atmosphere. Further, a lubricant (trade name: Fomblin Z) is formed on the protective film by dipping.
-DOL, manufactured by Montecatini Co., Ltd.), but the method is not limited to these methods.

[0050]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

In the examples, "parts" means "parts by weight" unless otherwise specified.

[Production Example] (Production of Molding Material for Magnetic Disk) Production example in which a cyclic hydrocarbon polymer and a norbornene polymer used in a comparative example were produced as molding materials for molding a magnetic disk substrate. Are described below.

(Test Items and Test Conditions) (1) The molecular weight was measured by GPC using toluene as a solvent, and the weight average molecular weight (Mw) in terms of standard polystyrene was determined. (2) The molecular weight distribution was measured by GPC using toluene as a solvent, and the weight average molecular weight (Mw) in terms of standard polystyrene was used.
And the number average molecular weight (Mn) are determined, and the weight average molecular weight (M
w) and the number average molecular weight (Mn) ratio (Mw / Mn) was calculated. (3) The glass transition temperature was measured by a differential scanning calorimeter (DSC). (4) The hydrogenation rate was calculated by measuring ¹ H-NMR.

Production Example 1 (Production of Hydrogenated Product A of Aromatic Vinyl Polymer) A dehydrated cyclohexane 320 was placed in a stainless steel autoclave equipped with an electromagnetic stirrer having a capacity of 1 liter and having been sufficiently dried and purged with nitrogen. Parts, 80 parts of styrene monomer and 1.83 parts of dibutyl ether.
While stirring at 0 rpm, the n-butyllithium solution (15
% Hexane solution) to initiate polymerization. After polymerization for 3 hours under the same conditions, 0.42 parts of isopropyl alcohol was added to stop the reaction. The weight average molecular weight of the produced aromatic vinyl polymer a (M
w) and the number average molecular weight (Mn) were measured.
113,636, Mw = 125,000.

Then, 400 parts of the polymerization solution containing the aromatic vinyl polymer a was added to the stabilized nickel hydrogenation catalyst N16.
3A (manufactured by Nippon Chemical Co., Ltd .; 40% nickel-supported silica)
Alumina carrier (12 parts) was added and mixed, and the mixture was charged into a 1.2-liter stainless steel autoclave equipped with an electric heating device and an electromagnetic stirring device for adjusting the hydrogenation reaction temperature. After completion of the charging, the inside of the autoclave was replaced with nitrogen gas, and the autoclave was stirred at a rotation speed of 700 rpm for 2 hours.
A hydrogenation reaction was performed at 30 ° C. and a hydrogen pressure of 45 kg / cm ² for 8 hours. After completion of the hydrogenation reaction, the hydrogenation catalyst was removed from the reaction solution by filtration, 1200 parts of cyclohexane was added, and the mixture was poured into 10 liters of isopropanol to precipitate a hydrogenated product A of an aromatic vinyl polymer. After the hydrogenated product A was separated by filtration, the product was dried with a reduced-pressure drier to recover the aromatic vinyl polymer hydrogenated product A. The physical properties of the obtained hydrogenated product A were Mn = 48,421 and Mw =
92,000, Mw / Mn = 1.90, hydrogenation rate is 10
0%, Tg = 140 ° C.

Production Example 2 (Production of hydrogenated product B) In a stainless steel autoclave equipped with an electromagnetic stirrer having a content of 1 liter and thoroughly dried and purged with nitrogen, 100 parts of a styrene monomer and azobisisobutyro were added. 0.05 part of nitrile was charged, polymerization was carried out at 70 ° C. for 24 hours while stirring at 400 rpm, 1200 parts of cyclohexane was added, and the mixture was poured into 10 liters of isopropanol to precipitate a polymer. After the polymer was separated by filtration, the polymer was dried with a reduced-pressure drier to obtain 90 parts of polystyrene. Dissolve 80 parts of this polymer in 320 parts of dehydrated cyclohexane,
In the same manner as in Production Example 1, hydrogenation was performed for 12 hours to obtain a hydrogenated product B.
The physical properties of the obtained hydrogenated product B were Mn = 69,565, M
w = 160,000, Mw / Mn = 2.30, the degree of hydrogenation was 99%, and Tg was 140 ° C.

Production Example 3 (Production of hydrogenated product C) Azobisisobutyronitrile 0.04 parts, polymerization temperature was 9
A hydrogenated product C was obtained in the same manner as in Production Example 2 except that the temperature was changed to 0 ° C. The physical properties of the obtained hydrogenated product C were Mn = 25,55.
6, Mw = 92,000, Mw / Mn = 3.60, the degree of hydrogenation was 99%, and Tg = 139 ° C.

Production Example 4 (Production of hydrogenated product D: polymerization of polycyclohexadiene) Addition polymerization of cyclohexadiene and hydrogenation reaction were carried out by a known method described in JP-A-7-258318, and Average molecular weight (Mn) = 4
8,300, weight average molecular weight (Mw) = 72,200,
(Tg = 218 ° C.). The hydrogenation rate of the obtained polymer was 85%.

Production Example 5 (Production of hydrogenated product E: polymerization of thermoplastic norbornene-based polymer) Ring-opening polymerization of 8-ethyltetracyclododecene and hydrogenation by a known method described in JP-A-4-363312. And the number average molecular weight (M
n) = 31,200, weight average molecular weight (Mw) = 55,
800, Tg = 140 ° C.). The hydrogenation rate of the obtained polymer was 99% or more.

[Examples 1 to 4 and Comparative Example 1] (Production of pellets for molding material) Production examples 1 to 5 in a class 1,000 clean room
Of pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] 0.1 as an antioxidant
Part, poly (oxy-2-hydroxyl trimethylene) nonylphenyl ether 0.5 as a recording film adhesion improver
And a 35 mm diameter twin screw extruder (trade name: T
EM35B, manufactured by Toshiba Machine Co., Ltd.)
And extruded in a strand form from a die, and pelletized with a pelletizer. The pellets obtained for each of the polymers A to E of Production Examples 1 to 5 were used as molding material pellets A to
E.

[Comparative Example 2] (Production of Filler-Filled Pellets) Further, a synthetic quartz true spherical filler having an average particle diameter of 0.5 μm and a particle diameter of 0.1 to 1 μm of 95% by weight or more (trade name: Admafine SO) Pellets F were produced using the hydrogenated product E in the same manner as in Comparative Example 1 except that 20 parts of -C2, manufactured by Tatsumori Corporation were added.

(Measurement of Flexural Modulus) As an experiment 1, each of the above-mentioned pellets A to F was injection-molded at a resin temperature of 290 ° C. using an injection molding machine (trade name: FS80, manufactured by Nissei Plastics Industry Co., Ltd.). A test piece for a bending test according to D-790 was formed, and the bending elastic modulus was measured. The results are shown in Table 1.

[0063]

[Table 1]

From Table 1, it can be seen that the test pieces in Examples 1 to 4 and Comparative Example 2 have significantly higher flexural modulus than the test piece in Comparative Example 1.

(Manufacture of Magnetic Disk Substrate) The magnetic disk according to this embodiment has a magnetic disk substrate on which an underlayer, a magnetic layer, a protective film, and a lubricant coating layer are sequentially provided. The magnetic disk substrate is made of the cyclic hydrocarbon-based polymer molding material obtained in the production example, and has a substantially disk shape with a diameter of 65 mm and a thickness of 0.8 mm. It comprises a clamp section and a landing section located on the inner and outer sides of the recording area forming section.

The recording area forming part is a part which becomes a recording area when the magnetic disk is used. The data area forming part in which an area for actually recording data is formed, and an address and a position in a recording track are defined. And a servo mark forming section on which servo marks for controlling (tracking) are formed.

An underlayer is formed on the magnetic disk substrate as described above, and a magnetic layer is further formed thereon. Note that a protective film and a lubricant coating layer are formed on the magnetic layer.

(Molding of Magnetic Disk Substrate) The pellets A to F were injection-molded into a magnetic disk substrate shape. Specifically, at a resin temperature of 340 ° C., an injection molding machine (trade name: DISC-5, manufactured by Sumitomo Heavy Industries, Ltd.) and a mold with a stamper fixed are used, and a mold temperature of 11 is used.
At 0 ° C., injection molding was performed to a diameter of 65 mm and a thickness of 0.8 mm.

Thereafter, an underlayer made of Cr (100 nm), a magnetic layer made of CoCrPt (60 nm), and a protective film made of C (18 nm) were sequentially formed on the magnetic disk substrate by sputtering. The in-line type static facing DC magnetron sputtering apparatus was used for sputtering, and the magnetic layer was formed in an Ar gas atmosphere using an alloy target. Furthermore, a lubricant (trade name: Fomblin Z-DO) is formed on the protective film by dipping.
L, manufactured by Montecatini Co.).

Then, the preformat of the servo mark into the servo mark forming section is performed by setting the magnetic gap to 0.3 μm,
The magnetic disk was completed by a two-step magnetization method using a magnetic head having a track width of 4.0 μm. The magnetic disks obtained as described above were used as sample disks, and 100 of them were prepared.

The characteristics of the sample disk prepared as described above were evaluated.

In Experiment 2, the surface roughness of a mirror surface portion where no groove was formed on the surface of the magnetic disk substrate on the stamper side was examined. As a result, Examples 1 to 4 and Comparative Example 1
In the sample disk No. 2, the surface roughness Rmax was 0.017 μm and the average roughness was 0.002 μm, which was smooth. In the sample disk of Comparative Example 2, the surface roughness Rmax was 0.08 μm, and the average roughness was 0.01 μm, which was poor in smoothness.

Next, as Experiment 3, the resonance frequency was examined.
Table 1 shows the results.

From the above results, it was confirmed that the resonance frequency of the magnetic disk molded with the molding material of the present invention having an elastic modulus of not less than a certain value can be sufficiently improved. When 20 parts of the filler were added, the elastic modulus was improved and the co-vibration frequency could be improved, but it was confirmed that the surface roughness was reduced.

[0075]

According to the present invention, it is possible to provide a magnetic recording medium capable of high-speed rotation and having excellent surface flatness, a substrate for the medium, and a molding material for the substrate.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Haruhiko Takahashi 1-2-1, Yaiko, Kawasaki-ku, Kawasaki-shi, Kanagawa Japan Zeon Corporation General Development Center

Claims (8)

[Claims] 1. A molding material for a magnetic recording medium substrate comprising a cyclic hydrocarbon polymer having a monocyclic cyclic hydrocarbon structure in a main chain or a side chain. 2. The molding material according to claim 1, wherein the cyclic hydrocarbon structure is a six-membered ring. 3. The molding material according to claim 2, wherein the cyclic hydrocarbon-based polymer has a six-membered ring in a side chain. 4. The method according to claim 1, wherein the cyclic hydrocarbon polymer is 20,000.
4. The molding material according to claim 1, which has an elastic modulus of not less than kgf / cm ² . 5. The cyclic hydrocarbon-based polymer has a ratio (Mw / M) between a weight average molecular weight (Mw) and a number average molecular weight (Mn).
n) is 6.0 or less and the weight average molecular weight (Mw) is 1
The molding material according to any one of claims 1 to 4, wherein the molding material is from 000 to 1,000,000. 6. A magnetic recording medium substrate obtained by molding the molding material according to claim 1. 7. A method for producing a substrate for a magnetic recording medium by injection molding the molding material according to claim 1. 8. A magnetic recording medium comprising a magnetic recording layer provided on the surface of the substrate for a magnetic recording medium according to claim 6.