JPH07262548A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in running durability of the magnetic layer. CONSTITUTION:Polyurethane resin consisting of high molecular polyol having a mol.wt. of >=500 and an org. diisocyanate or further contg. a low mol.wt. compd. having two or more functional groups reacting with isocyanato groups in one molecule and a mol. wt. of <500 is contained as a component of the binder of the magnetic layer of this magnetic recording medium and/or a component of the binder of a back coat layer disposed on the nonmagnetic substrate so that it is made opposite to the magnetic layer. At least 40wt.% of the high molecular polyol is arom. polyester diol and >=20mol% of all the acid components of the arom. polyester diol is an acid component having a naphthalene skeleton.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a magnetic tape or a magnetic disk which has excellent durability, abrasion resistance, heat resistance, dispersibility and filling properties. It is a thing.

[0002]

2. Description of the Related Art A magnetic tape, which is a general-purpose magnetic recording medium,
The floppy disk is prepared by dispersing needle-like magnetic particles with a major axis of 1 μm or less in a binder solution together with additives such as a dispersant, a lubricant and an antistatic agent to prepare a magnetic paint, which is applied to a polyethylene terephthalate film. Has been.

Properties required for the binder of the magnetic layer include dispersibility of magnetic particles, packing properties, orientation, magnetic layer durability, abrasion resistance, heat resistance, and adhesion to a non-magnetic support. The binder plays a very important role.

The back coat layer provided on the side opposite to the magnetic layer on the non-magnetic support affects the running property of the magnetic tape, and the properties required for the binder of the back coat layer are durability and abrasion resistance. Properties, heat resistance, adhesion to a non-magnetic support, and the like, and the binder of the back coat layer also plays a very important role.

The binders that have been conventionally used are:
Vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer, vinyl chloride / vinylidene chloride copolymer, polyurethane resin, polyester resin, acrylonitrile / butadiene copolymer, nitrocellulose, cellulose acetate / butyrate , Epoxy resin, acrylic resin, etc. are used.

Among these resins, the polyurethane resin is superior in toughness and abrasion resistance to other resins due to intermolecular hydrogen bond by urethane bond, but the conventional polyurethane resin is dispersibility of magnetic powder. However, various studies have been conducted to improve this. For example,
One using a urethane resin derived from a polyester polyol containing 2,2-dialkyl-1,3-propanediol (JP-A-2-240177), a polyurethane resin using a polyhydric alcohol having a branched chain (special Kaihei 2-
177020).

[0007]

Magnetic particles used to improve image quality in video tapes and to improve sound quality in audio tapes tend to be finer and have a high coercive force to improve recording density. Magnetic particles are used. The finer the magnetic particles and the higher the coercive force, the more difficult the conventional binder is to disperse, and it is required that the dispersibility of the magnetic particles in the binder is higher. JP-A-2-240177, JP-A-2-240177
Improvement in the dispersibility of the binder in 177020 is recognized, but it is not always satisfactory.

Further, in the magnetic recording medium, the magnetic layer is made to be highly filled and highly oriented with finely-divided magnetic particles for improving the S / N ratio (signal / noise ratio) and increasing the recording density. The surface is made smooth. Further, when the magnetic tape is stored in a roll form, the back coat layer is also smooth so that the output of the magnetic tape is not reduced even if the irregularities of the back coat layer are transferred to the magnetic layer.

The smoother the surface of the magnetic layer and the back coat layer, the worse the running property and running durability of the magnetic tape, and the better the durability, abrasion resistance, heat resistance and adhesion to the non-magnetic support. Binders are needed. Conventional binders for magnetic layers are insufficient to meet these requirements. Therefore, it is an object of the present invention to improve the dispersibility and filling property of finely divided magnetic particles and to provide a magnetic recording medium having excellent durability.

[0010]

Means for Solving the Problems The present invention has been achieved as a result of extensive studies on polyurethane resins for achieving the object of the present invention. That is, the present invention provides a magnetic recording medium in which a magnetic material in which a ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, as a binder component of a magnetic layer and / or a non-magnetic material on the side opposite to the magnetic layer. As a binder component of the back coat layer provided on the support, a high molecular weight polyol having a molecular weight of 500 or more, an organic diisocyanate, and, if necessary, a molecular weight of 50 having two or more functional groups capable of reacting with isocyanate.
An acid component containing a polyurethane resin composed of a low molecular weight compound of less than 0, at least 40% by weight of the polymer polyol is an aromatic polyester diol, and 20 mol% or more of the total acid component of the aromatic polyester diol has a naphthalene skeleton. Is a magnetic recording medium.

The carboxylic acid component of the aromatic polyester diol used in the present invention includes 1,5-naphthalic acid, 2,
Other than those having a naphthalene skeleton such as 6-naphthalic acid, terephthalic acid, isophthalic acid, orthophthalic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenylethercarboxylic acid and the like can be mentioned. Of these aromatic carboxylic acid components, 20 mol% or more, preferably 40 mol% or more 70
Less than% has a naphthalene skeleton. When it is less than 20 mol%, the durability, abrasion resistance and heat resistance properties are insufficient.

As the glycol component, ethylene glycol, propylene glycol, 1,3-propanediol,
Aliphatic glycols such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2,3 -Butylene glycol, 2,2-dimethyl-1,3
-Propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate, 2,2-diethyl-1,3-
Propanediol, 1,4-bis (hydroxymethyl) cyclohexane, ethylene oxide adduct of bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A and propylene oxide adduct, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc. To be Also, trifunctional or higher functional compounds such as trimellitic anhydride, glycerin, trimethylolpropane, and pentaerythritol are used as a part of the raw material of the polyester diol within a range that does not impair the organic solvent solubility and coating workability of the polyester resin. You may.

As the dicarboxylic acid component and glycol component of the aromatic polyester diol other than the above, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoterephthalic acid, 2-sodium sulfo-1,4-butanediol , 2,5-dimethyl-3-sodium
Examples include those containing a metal salt of sulfonic acid such as -2,5-hexanediol. The metal sulfonate base has the effect of significantly improving the dispersibility of inorganic particles such as magnetic powder, abrasives and carbon black.

As the high molecular weight polyol having a molecular weight of 500 or more other than the aromatic polyester diol, an aliphatic polyester polyol obtained from a glycol and an aliphatic dicarboxylic acid such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid, a poly Polylactone polyols such as caprolactone and polyvalerolactone,
Polyethylene glycol, polypropylene glycol,
Examples thereof include polyether polyols such as polytetramethylene glycol, polycarbonate polyols derived from 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol and the like.

The difference between the glass transition temperatures of the aromatic polyester diol and the other high molecular polyol is 80 ° C., preferably 100 ° C. or higher, or when only the aromatic polyester diol is used as the high molecular polyol component, it is obtained. The glass transition temperature of polyurethane resin is 70
C., preferably 80.degree. C. or higher is preferable for achieving the object of the present invention. The difference in glass transition temperature between aromatic polyester diol and other high molecular polyol is 80 ° C.
In the case of, it can be used alone as the binder resin, but when only the aromatic polyester diol is used as the polymer polyol component, for the purpose of adjusting flexibility, improving cold resistance, etc., It is desirable to add other resins.

The high molecular weight polyol component of the polyurethane resin used in the present invention preferably has a molecular weight of 500 or more.
It is more preferably 500 to 5,000. Molecular weight is 5
When it is less than 00, the urethane group concentration becomes too high and the dispersibility of the magnetic powder and the low temperature characteristics deteriorate, and when the molecular weight exceeds 5,000, the characteristics such as toughness and abrasion resistance peculiar to the polyurethane resin deteriorate.

The diisocyanate compound used in the production of the polyurethane resin used in the present invention is 2,
4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane, 4,4'-diisocyanate cyclohexane, 4,4'-diisocyanate cyclohexylmethane, isophorone diisocyanate, etc. It

A low molecular weight compound having two or more functional groups in one molecule which reacts with an isocyanate having a molecular weight of less than 500, which is optionally used in the production of the polyurethane resin used in the present invention, is used for controlling the concentration of urethane groups in polyurethane. it can. A low molecular weight compound having 3 or more functional groups that react with isocyanate in one molecule is effective in improving the reactivity with a general-purpose curing agent.

Specific compounds include ethylene glycol, 1,3-propylene glycol, 1,6-hexanediol, cyclohexanedimethanol, xylylene glycol, diethylene glycol, triethylene glycol,
Linear glycol such as ethylene oxide adduct of bisphenol A, propylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol,
2,2,4-Trimethyl-1,3-pentanediol, branched glycols such as propylene oxide adduct of bisphenol A, amino alcohols such as N-methylethanolamine, monoethanolamine, diethanolamine, trimethylolpropane, glycerin, penta Examples thereof include polyols such as erythritol and dipentaerythritol, and ε-caprolactone adducts of one of these polyols.

The polyurethane resin used in the present invention has a molecular weight of 5,000 to 80,000, preferably 10,000 to 40,000. If the molecular weight is less than 5,000, mechanical strength is insufficient and running durability is poor. Molecular weight 80
If it exceeds 000, the solution viscosity increases, and the workability and the dispersibility of magnetic powder, abrasives, carbon black, etc. deteriorate.
The reaction method may be performed either by melting the raw materials or by dissolving them in a solution.

As the reaction catalyst, stannous octylate, dibutyltin dilaurylate, triethylamine and the like may be used. Further, an ultraviolet absorber, a hydrolysis inhibitor, an antioxidant and the like may be added before, during or after the production of the polyurethane resin.

In the present invention, in addition to the polyurethane resin used in the present invention, for the purpose of controlling flexibility, improving cold resistance and improving durability, other resin is added and / or a polyurethane resin is used. It is desirable to mix compounds that react and crosslink. Examples of other resins include vinyl chloride resins, polyester resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, and the like.

On the other hand, examples of the compound that crosslinks with the polyurethane resin include polyisocyanate compounds, epoxy resins,
There are melamine resins, urea resins and the like, and among these, polyisocyanate compounds are particularly preferable.

Used in the magnetic layer of the magnetic recording medium of the present invention
The magnetic particles used are γ-Fe₂ O ₃ , Γ-Fe₂ O₃ 
And Fe₃ O_Four Crystals, CrO₂ , Γ coated with cobalt
-Fe₂ O₃ Or Fe₃ O_Four , Barium ferrite and
And ferromagnetic alloy powders such as Fe-Co and Fe-Co-Ni,
Pure iron etc. can be mentioned.

In the magnetic recording medium of the present invention, if necessary, a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctylsulfosodium succinate, t-
Butylphenol / polyethylene ether, ethylnaphthalene / sodium sulfonate, dilauryl succinate,
Lubricants such as zinc stearate, soybean oil lecithin, silicone oil and various antistatic agents can also be added.

The inorganic fine particles used in the back coat layer of the magnetic recording medium of the present invention include inorganic lubricants such as calcium carbonate, magnesium carbonate, aluminum oxide, chromium dioxide, silicon dioxide and titanium oxide, carbon black and tin oxide. And the antistatic agent.

[0027]

Since the polyurethane resin of the present invention has a naphthalene skeleton, it is necessary to copolymerize a segment having a high hardness, a small friction coefficient and a large flexibility with the polyurethane resin or adding another soft resin. Makes it extremely tough. As a result, the magnetic recording medium of the present invention is considered to have good running properties and running durability.

[0028]

The present invention will be specifically illustrated by the following examples. In the examples, "parts" means "parts by weight".

Polyurethane Resin Synthesis Example 1 80 parts of polyester diol (A) shown below, 43 parts of toluene and 43 parts of methyl ethyl ketone were charged into a reaction vessel equipped with a thermometer, a stirrer and a reflux condenser, and after dissolution, After adding 24 parts of diphenylmethane diisocyanate and heating at 80 ° C. for 2 hours, 20 parts of polydiol (F), 5 parts of neopentyl glycol, and 0.03 part of dibutyltin dilaurate as a reaction catalyst were added. After reacting at 80 ° C. for 6 hours, 107 parts of toluene and 107 parts of methyl ethyl ketone were added. The resulting polyurethane resin 1 solution had a solid content concentration of 30% and a solution viscosity at 25 ° C. of 84 poises. The characteristics of polyurethane resin 1 are shown in Table 1.

The abbreviations in the table are as follows. Polyester composition and molecular weight Polyester A: 2,6-NDC / T / I / DSN // EG / NPG (50/24/23/3 // 50/50) MW = 2000 Polyester B: 2,6-NDC / I / O / DSN // NPG / DMH (70/12/15/3 // 50/50) MW = 2200 Polyester D: 1,5-NDC / T / I / DSC // CHDM / EG / NPG (30 / 34/34/2 // 20/47/33 MW = 2500 Polyester D: 2,6-NDC / T / I / DSN // EG / NPG (15/43/40/2 // 50/50) MW = 2300 Polyester E: T / I / DSN // NPG / EG (49/48/3 // 50/50) MW = 2200 Polyester E: D // NPG / HD (100 // 40/60) MW = 2000 Polyester G: AA / DSN // NPG / HD (97/3 // 40/60) MW = 2000 Polyester H: 2,6-NDC / T / I // EG / NPG (50/25/25 // 50 / 50) MW = 2200 Polyester I: Polycaprolactone MW = 2000 Polyester J: 2,6-NDC / I / DSN /// NPG / DMH (90/8/2 // 50/50) MW = 2300 2,6- NDC: 2,6-naphthalic acid 1,5-NDC: 1,5-naphthalic acid OPA: orthophthalic acid IPA: isophthalic acid
TPA: terephthalic acid DSN: dimethyl-5-sodium sulfoisophthalic acid HTPA: 1,4-cyclohexanedicarboxylic acid SA: sebacic acid AA: adipic acid NPG: 2,2-dimethyl-1,3-propanediol DMH: 2-butyl -2-Ethyl-1,3-propanediol HPN: 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-
Dimethyl-3-hydroxypropanate CHDM: 1,4-bis (hydroxymethyl) cyclohexane EG: Ethylene glycol MDI: 4,4'-diphenylmethane diisocyanate

Polyurethane Resin Synthesis Examples 2 to 7 and Comparative Synthesis Examples 1 to 4 In the same manner as in Polyurethane Resin Synthesis Example 1, polyurethane resin solutions were obtained from the raw materials shown above. The properties of the obtained polyurethane resin are shown in Table 1. In Comparative Synthesis Example 1, the copolymerization ratio of the acidic component having a naphthalene skeleton in the acidic component of the aromatic polyester diol is less than 20 mol%. In Comparative Synthesis Example 2, the copolymerization ratio of the aromatic polyester diol in the polyester diol component was 40.
If less than wt%. Comparative Synthesis Example 3 is a case where the aromatic polyester diol does not contain a naphthalene skeleton. Comparative Synthesis Example 4 is a case where no aromatic polyester diol was contained. The number average molecular weight in the polyurethane resin was determined by gel permeation chromatography using tetrahydrofuran as a solvent, and the value in terms of standard polystyrene was measured. The gloss of the magnetic layer of the magnetic tape was measured at 60 degrees. The squareness ratio of the magnetic layer was measured by using a vibration test magnetometer and measuring the squareness ratio in the vertical direction. The magnetic layer density was determined by measuring the weight and volume of the magnetic layer. The wear resistance of the magnetic layer is S-VH on the market.
The scratches on the magnetic layer were observed after running 100 times on the S-Video deck at running temperatures of 10 ° C. and 40 ° C., and the degree was evaluated according to the following 6 grades. 6: Almost no scratch 5: Slightly scratched 4: Slightly scratched and slightly noticeable 3: Scratched and noticeable, not reaching the PET film 2: Scratched and noticeable, PET film surface is slightly visible 1: Scratched and noticeable, Many PET film surfaces can be seen

Example 1 A composition having the following blending ratio was placed in a ball mill and dispersed for 48 hours, and then, as a lubricant, stearic acid: 1 part, butyl stearate: 1 part, and an isocyanate compound, Coronate L (Nippon Polyurethane Industry Co., Ltd.). (Manufactured): 6 parts was added as a curing agent, and the dispersion was further continued for 1 hour to obtain a magnetic coating material. This was applied onto a polyethylene terephthalate film having a thickness of 12 μm while applying a magnetic field of 2,000 gauss so that the thickness after drying was 4 μm. After aging at 50 ° C. for 48 hours, it was slit into a 1/2 inch width to obtain a magnetic tape. The characteristics of the magnetic tape obtained are shown in Table 2. 30% solution of polyurethane resin 1 100 parts Metal powder (BET56m ² / g) 120 parts Alumina powder (average particle size 0.2 μm) 5 parts Cyclohexanone 100 parts MEK 50 parts Toluene 50 parts

Examples 2 to 7 Using the binders shown in Table 1, magnetic tapes were obtained in the same manner as in Example 1. Table 2 shows the characteristics of each magnetic tape.

Comparative Examples 1 to 4 Magnetic tapes were obtained in the same manner as in Example 1 except that the binders shown in Table 1 were used. Table 2 shows the characteristics of each magnetic tape.

Example 8 A composition having the following blending ratio was placed in a sand mill containing glass beads having a diameter of 2 mm and dispersed for 1 hour, and then a polyisocyanate compound Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a curing agent. Was added and mixed for 30 minutes to obtain a back coat paint. This was coated and dried on a polyethylene terephthalate film having a thickness of 15 μm so that the thickness after drying would be 0.5 μm, and the magnetic coating material obtained in Example 1 was applied to the opposite side of the back coat layer of this polyethylene terephthalate film. A magnetic tape was prepared by coating and drying in the same manner as in 1. After the same curing treatment and slitting as in Example 1, the coefficient of friction of the back coat surface and the coefficient of friction at 20 ° C. after running 100 times at 40 ° C. on a commercially available VTR deck were measured. The results are shown in the table. The coefficient of friction was measured by attaching a weight of 100 g to the magnetic tape and holding it on a mirror-finished stainless steel roll with a diameter of 50 mm at an included angle of 180.
The vehicle was run at a speed of 1 cm / s. Solution of polyurethane resin obtained in Synthesis Example 1 100 parts (30% solution of MEK / toluene = 1/1) Carbon black 3 parts Calcium carbonate (average particle size 0.05 μm) 20 parts Cyclohexanone 50 parts Toluene 50 parts

Examples 9 to 10 and Comparative Examples 6 to 9 In the same manner as in Example 8 except that the polyurethane resin for the back coat was the polyurethane resin shown in Table 1, magnetic tapes were prepared. The characteristics are shown in Table 3.

Comparative Example 10 The same test as in Example 8 was conducted on the magnetic tape (without back coat) obtained in Example 1. The results are shown in Table 3.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

EFFECTS OF THE INVENTION The polyurethane resin of the present invention having a specific proportion of an aromatic polyester diol containing a naphthalene skeleton in a specific proportion in a molecule is used as a binder for magnetic particles and a binder for a back coat layer to provide abrasion resistance. Is improved,
The change in friction coefficient is small. As a result, a magnetic recording medium having excellent running durability can be obtained.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic material in which ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, and a high molecular weight polyol having a molecular weight of 500 or more and an organic diisocyanate are used as the binder component of the magnetic layer. And a polyurethane resin comprising a low molecular weight compound having a molecular weight of less than 500 and having two or more functional groups which react with an isocyanate in one molecule, at least 40% by weight of the polymer polyol is an aromatic polyester diol,
20% by mol or more of the total acid component of the aromatic polyester diol is composed of an acid component having a naphthalene skeleton. 2. A magnetic recording medium in which a magnetic material in which a ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, and a back coat layer provided on the non-magnetic support opposite to the magnetic layer. As a binder component, a polyurethane resin comprising a high molecular weight polyol having a molecular weight of 500 or more, an organic diisocyanate, and a low molecular weight compound having a molecular weight of less than 500 having two or more functional groups which react with an isocyanate in one molecule, if necessary, is used. A magnetic recording medium characterized in that at least 40% by weight of the molecular polyol is an aromatic polyester diol, and 20 mol% or more of the total acid component of the aromatic polyester diol is an acid component having a naphthalene skeleton.