JPS63220415A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the lubricity and surface smoothness of a magnetic layer, the stability of a magnetic coating material and the dispersibility of magnetic particles in the magnetic layer by incorporating specified thermoplastic polyurethane resin and a specified ester compd. into the magnetic layer. CONSTITUTION:Thermoplastic polyurethane resin having specified mol.wt., tensile rupture strength, tensile rupture elongation, 100% by formula I are used. In the formula I, each of R1 and R2 is 1-25C straight chain or branched satd. alkyl group, the total number of C atoms in R1 and R2 is 18-34 and R3 is 7-29C straight chain or branched (un)satd. alkyl group. The components are easily converted into a magnetic coating material having superior dispersibility and stability. When the coating material is applied, a magnetic layer having superior smoothness is formed and a magnetic recording medium having superior durability in wide temp. and humidity ranges from low temp. and humidity to high temp. and humidity can be obtd. even in case of a system using no hardening agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media. More specifically, the present invention relates to a magnetic recording medium with improved durability using a polyurethane resin having specific physical properties and a specific ester compound.

[Conventional technology and its problems]

In recent years, magnetic recording media such as VTRs, audio tapes, and floppy disks have become widespread, and their performance requirements are diverse and becoming more stringent. Among these, the demand for recording and reproducing reliability is particularly increasing, and for example, the required performance is the ability to withstand long-term running under various environments, from low temperature and low humidity to high temperature and high temperature.

Conventionally, polyester resins, polyurethane resins, etc. have been widely used as binders for magnetic recording media, but various studies have been conducted to meet the above requirements, and now magnetic layers have good heat resistance and abrasion resistance. In order to improve the durability of magnetic recording media, a binder mainly containing thermoplastic polyurethane resin and polyisocyanate, or a resin having a large number of hydroxyl groups such as vinyl chloride-vinyl acetate copolymer, etc. Binders and the like have been put into practical use.

These thermoplastic polyurethane resins used as binder components of magnetic recording media are disclosed in Japanese Patent Application Laid-Open No. 58-203623.
As shown in the above publications, (I) the mechanical properties and heat resistance of the binder are improved by reacting it with a curing agent (crosslinking agent) such as polyisocyanate to form a wire bond, thereby improving the magnetic layer. A thermoplastic polyurethane resin (containing isocyanate of 115% or less) with a relatively low urethane group concentration that imparts heat resistance and abrasion resistance to (2) mechanical properties such as tensile strength of the film without reacting with a curing agent, Excellent heat resistance,
Utilizing this property, thermoplastic polyurethane resins can be divided into thermoplastic polyurethane resins with a relatively high urethane group concentration (isocyanate content of 15% or more), which can impart heat resistance and abrasion resistance to the magnetic layer.

The thermoplastic polyurethane resin (I) has a low urethane group concentration (isocyanate content of 15% or less), is soft, and has a molecular weight of 10.000 to 50.000, especially 15.00.
A substantially linear thermoplastic polyurethane resin with a molecular weight of 0 to 35,000 is often used, and it is easy to make magnetic paint because of its relatively low molecular weight, but it has poor heat resistance due to its mechanical properties and low flow initiation point. At present, it has poor properties, requires a curing agent, and the magnetic layer after curing still leaves much room for improvement, especially in terms of performance under high-temperature environments.

Further, thermoplastic polyurethane resins having a molecular weight of 50,000 or more deteriorate the dispersibility of magnetic powder extremely, making it difficult to form into paints.

In the case of (2), the urethane group concentration is relatively high (isocyanate content 15 to 40%), the molecular weight is 20.000 to so, which is hard, has a high flow start point, and is almost 100°C or higher.
, ooo thermoplastic polyurethane resin is used, and although it has a relatively low molecular weight, it has excellent mechanical properties and a high flow initiation point, so although it has excellent heat resistance and abrasion resistance, the magnetic layer becomes too hard. Calendar properties are poor due to reasons such as
The surface smoothness deteriorates, and the so-called "
Undesirable phenomena such as "squealing" occur. Also,
Due to the large number of urethane bonds, the attractive force between polyurethane molecules increases, resulting in poor solubility in commonly used toluene, methyl ethyl ketone, etc., resulting in poor stability of magnetic coatings and dispersibility of magnetic particles in magnetic coatings. In many cases, it significantly reduces

Further, in order to particularly impart lubricity to the magnetic layer, fatty acids, oleyl oleate, butoxide stearate, fatty acid amides, liquid paraffin, wax, and the like have been used as lubricants. However, it is currently difficult to say that these lubricants are satisfactory in terms of performance. For example, oleyl oleate, butoxide stearate, etc. are insufficient for improving the durability of the media, while fatty acids such as stearic acid and oleic acid, and hydrocarbon-based lubricants such as liquid paraffin are effective in improving durability. Although effective, it has poor compatibility with the binder, and when used in large quantities, it bleeds from the surface of the magnetic layer and tends to stain the head.

[Means for solving problems]

Therefore, the inventors of the present invention have improved the above-mentioned drawbacks without impairing the excellent performance of thermoplastic polyurethane resins, and have also improved the above-mentioned drawbacks regarding lubricity. As a result of extensive research in order to obtain a magnetic recording medium with significantly improved durability, we developed a thermoplastic polyurethane resin with a specific molecular weight, tensile strength at break, tensile elongation at break, 100% modella, and glass transition temperature. By adopting a specific ester compound,
It is easy to make a magnetic paint, it has excellent dispersibility and stability, and it is possible to obtain a magnetic layer with excellent smoothness after application, and even systems that do not use a hardening agent can be used from low temperature and low humidity to high temperature and high temperature. The present inventors have discovered that a magnetic layer with excellent durability can be obtained over a wide temperature and humidity range, and that the durability of the magnetic layer can be further improved by using it in combination with a low molecular weight polyisocyanate, leading to the completion of the present invention. .

That is, the present invention provides a magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, in which the magnetic layer has a number average molecular weight of 5,000 to 40,000 as determined by gel permeation chromatography, and a tensile strength. Speed 1100n/m
Breaking strength in tensile test of 200kg/cm”
The above-mentioned thermoplastic polyurethane resin has an elongation at break of 100 to 400%, a 100% mode elasticity of 150 kg/cm" or more, a glass transition temperature of 40°C or more as analyzed by dynamic viscoelasticity measurement, and the following general formula (I) (formula In the middle, R2 and R2 have 1 to 25 carbon atoms (however, the sum of the carbon numbers of R and R2 is 18 to 25).
34) having a linear or branched saturated alkyl group,
R8 is a linear or branched saturated or unsaturated alkyl group having 7 to 29 carbon atoms. ) A magnetic recording medium characterized by containing an ester compound represented by the following is provided.

The thermoplastic polyurethane resin used in the present invention is subjected to gel permeation chromatography (column 5ho).
dex A-803, 804 mixed, Showa Denko (+gradation)
The number average molecular weight is 5,000 to 40,000 as analyzed by
The more preferable molecular weight is 10,00
0 to 25,000. The above number average molecular weight is 5
,000 without grooves, the mechanical properties of the magnetic layer and the adhesion to the base material are poor. Furthermore, if the number average molecular weight exceeds 40,000, the dispersibility of the magnetic powder will be poor, and a significant improvement in durability cannot be expected when used in combination with a low molecular weight polyisocyanate.

The tensile strength of the thermoplastic polyurethane resin used in the present invention was measured using Tensilon UTM-■ manufactured by Toyo Sokki ■ at a tensile rate of 10 m/min, and the breaking strength was 200 kg/min.
cm" or more, elongation at break 100 to 400%, 100% modulus 150 kg/cn+" or more, more preferably breaking strength 250 kg/cm or more, elongation at break 100 to 300%, 100% modulus 230 kg.
/cm" or more. Breaking strength is 200kg/c.
If the elongation at break is less than 100% or more than 400% and the 100% modulus is less than 150 kg/cm, the strength of the magnetic layer will be poor and the durability will be disadvantageous.

The glass transition temperature of the thermoplastic polyurethane resin used in the present invention was measured using a dynamic viscoelasticity measuring device (RIIEOVIBR).
ON DDV-1 [[-EA, manufactured by Toyo Baldwin Co., Ltd.] at a measurement frequency of 3.5 Hz and a heating rate of 3°C/m.
measured at 40° C. or higher. Those having a glass transition temperature of less than 40° C. have poor heat resistance when forming a magnetic layer. From the viewpoint of calenderability of the magnetic layer and surface smoothness of the magnetic layer, the glass transition temperature is preferably 65° C. or lower. The glass transition temperature in the present invention is the temperature at which the ratio E"7B' between the loss modulus E'" and the storage modulus E' is maximum in dynamic viscoelasticity measurement.

Both ends of the thermoplastic polyurethane resin used in the present invention may be an isocyanate group, both ends may be a hydroxyl group, or one end may be an isocyanate group and the other end may be a hydroxyl group. It's okay.

Furthermore, from the viewpoint of durability and dispersibility of the magnetic layer, the thermoplastic polyurethane resin of the present invention has (a) a molecular weight of 500 to 3;
Polyester polyol having 000, (b) 2-1
Manufactured from diols having 0 carbon atoms, or diols obtained by adding 2 to 4 moles of ethylene oxide or propylene oxide to bisphenol A1 bisphenol S1 hydroquinone, etc., and (c) diisocyanates having at least one aromatic ring. This is desirable.

Polyester polyols having molecules [500 to 3,000] include ethylene glycol, 2-brobylene glycol, 1,3-propylene glycol, 2,3
-butylene glycol, 1,4-butylene glycol,
2.2-dimethyl-1,3-propanediol, diethylene glycol, ■.

Glycols such as 5-pentamethylene glycol, 1,6-hexamethylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimetatool or a mixture thereof, succinic acid, maleic acid,
dibasic acids such as adipic acid, glutaric acid, pimelic acid, superric acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, and esters of these acids;
Examples include polyester polyols obtained by polycondensation with an acid halide, and further examples include polycaprolactone diols obtained by ring-opening addition polymerization of a lactone such as ε-caprolactone in the presence of a glycol or the like.

Among these, condensation polyester polyols and polycaprolactone polyols of ethylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol alone or as a mixture, and adipic acid or sebacic acid are preferred.

As low molecular weight diols having 2 to 10 carbon atoms,
Glycols used in the production of the polyester polyols may be used alone or in mixtures.

Examples of the diisocyanate having at least one aromatic ring include xylene diisocyanate, toluidine diisocyanate, 2.4-tolylene diisocyanate, 2.
．． 6-) lylene diisocyanate), 4.4''-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-biphenyl diisocyanate, 3,3°-dimethylbiphenyl -4,4
Suitable are diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, and mixtures thereof.

When producing the thermoplastic polyurethane resin used in the present invention, polyester polyol (a) and carbon number 2 to
The molar ratio with low molecular weight polyols etc. (b) having 10 is 47 units = 1/2.5 to 1/20, preferably 1/2.
The range of 4 to 1/8 is desirable, and the molar ratio of 011/NCO of polyol and diisocyanate is 110.85 to 1/8.
1/1.15, preferably 1.010.95 to 1.0
/1.05 is good. These ranges are preferable from the viewpoint of various performances of the obtained magnetic layer.

Furthermore, in producing the thermoplastic polyurethane resin, conventionally known methods can be used, for example,
After thoroughly mixing the reactants, the reaction mixture is poured into a flat plate or vat, heated, cooled, and then crushed, or dimethylformamide, toluene, xylene,
Production methods such as a solution reaction method in which the reaction is carried out in a single or mixed organic solvent such as benzene, dioxane, tetrahydrofuran, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, and butyl acetate can be employed. At this time, a reaction catalyst may be added in order to lower the reaction temperature or shorten the reaction time. Specific examples of reaction catalysts include amine compounds such as triethylenediamine, tetramethylethylenediamine, and tetramethylhexanediamine, and salts thereof, dibutyltin dilaurate, and tin octylate.
．． Examples include organometallic compounds such as lead octylate and manganese octylate, and mixtures thereof. Further, for the purpose of increasing the stability of the polyurethane resin, antioxidants, ultraviolet absorbers, hydrolysis inhibitors, etc. may be added alone or in combination.

Furthermore, in the present invention, in order to further improve the durability of the polyurethane resin, it is preferable to cure the polyurethane resin using an appropriate curing agent. Examples include monomers and polyisocyanate compounds, but low molecular weight polyisocyanate compounds having two or more isocyanate groups are optimal.

Examples of the low molecular weight polyisocyanate having two or more isocyanate groups that can be used in the present invention include, in addition to the organic diisocyanate used in the production of the thermoplastic polyurethane resin, 3 mol of diisocyanate such as tolylene diisocyanate and hexamethylene diisocyanate. and 1 mole of trimethylolpropane, and polyfunctional isocyanate compounds such as modified diphenylmethane diisocyanate and polyphenylenemethane polyisocyanate. These compounds are available from Nippon Polyurethane ■ as “Coronate” and “Coronate 41L”.
”, “Coronate 2030”, U Millionate MRJ,
"Desmodule Shi", "Desmodule N", "Desmodule ILJ", "Desmodule H" are available from Sumitomo Bayer Urethane under product names such as "Millionate MTL J".
LJ, r death module R”, “death module l?F
Takenate D- from Takeda Pharmaceutical Co., Ltd. under product names such as
102J, "Takenate D-11ONJ", "Takenate D-202J", etc., respectively.

By adding 3 to 40 parts by weight of the low molecular weight polyisocyanate to 100 parts by weight of the thermoplastic polyurethane resin and curing it, the mechanical strength, abrasion resistance, heat resistance, moist heat resistance, solvent resistance, and group strength of the magnetic layer can be improved. Adhesion to materials can be significantly improved.

If necessary, the binder component may contain thermoplastic polyurethane resins, cellulose derivatives such as nitrocellulose, cellulose acetate, and cellulose acetate butyrate, which are commonly used as binder components for magnetic recording media; vinyl chloride/vinyl acetate, etc. Polymer, vinyl chloride/vinyl acetate/
Vinyl alcohol copolymer, vinyl chloride/vinyl acetate/
Salt vinyl acetate resin such as maleic acid copolymer; vinylidene chloride/
Vinylidene chloride resins such as vinyl chloride copolymers and vinylidene chloride/acrylonitrile copolymers; alkyd resins,
Polyester resins such as linear polyesters: Acrylic resins such as (meth)acrylic acid/acrylonitrile copolymer, methyl (meth)acrylate/acrylonitrile copolymer; Acetal resins such as polyvinyl acecool and polyvinyl butyral; Phenoxy resin, epoxy resin, polyamide resin, butadiene/acrylonitrile copolymer,
Styrene/butadiene copolymers and the like can also be used alone or in combination.

The ester compound represented by the general formula (I) according to the present invention can be obtained, for example, by an esterification reaction between a branched alcohol and a fatty acid. Specific examples of this ester compound include 2-decyltetradecyl stearate, 2-decyltetradecyl palmitate, 2-decyltetradecyloleate, 2-decyltetradecylisomyristate, 2-decyltetradecyllaurate, 2-
Decyltetradecyl behenate, 2-octylhexadecyl isostearate, 2-dodecylhexadecyllaurate, 2-tetradecyloctadecylcaprylate,
Examples include 2-octyldodecyl oleate.

In the magnetic recording medium of the present invention, in addition to the ester compound represented by the general formula (I), a commonly used lubricant can be used in combination, but the total lubricant is
It is preferable that the ester compound represented by the general formula (I) be contained in an amount of at least 5% by weight, including 0% by weight.

Common lubricants that can be used in combination in the present invention include higher fatty acids, various esters obtained from higher fatty acids and linear alcohols, fatty acid amides, waxes, liquid paraffin, squalene, and the like.

The amount of the ester compound represented by the general formula (I) according to the present invention or the total amount of the ester compound and the general lubricant used is usually 1 to 15% by weight based on the magnetic powder. .

As the ferromagnetic fine powder that can be used in the present invention, TFE! 203, r FezO= and Fe
Examples include mixed crystals with 3O4, Co-modified iron oxide, Cr0z, iron, etc., and other fine alloy powders containing iron as a main component can be preferably used. Regarding the shape of these ferromagnetic fine powders, any shape such as needle, plate, or spherical shape can be used.

Non-magnetic supports used in producing the magnetic recording medium of the present invention include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonates;
Polyvinyl chloride; polyimide; plastics such as aromatic polyamide; metals such as Al and CLI; paper, etc. are used. The form may be a film, tape, sheet, disk, card, drum, etc.

Further, the surface of the support may be treated with corona discharge, radiation, ultraviolet light, etc., or may be precoated with a suitable resin.

〔Example〕

The present invention will be specifically explained below by showing synthesis examples and examples, but the present invention is not limited only to these examples.

In addition, all "parts" in the examples indicate "parts by weight."

Synthesis Example 1 In a reactor equipped with a thermometer, a stirrer, and a reflux condenser, 200 parts of methyl ethyl ketone, 190 parts of cyclohexanone, and a polyester polyol with molecules it 1,000 consisting of adipic acid and 1,6-hexamethylene glycol were placed. 10
0 parts, 2,2-dimethyl-1,3-propanediol 3
2 parts, 8 parts of l,4-butylene glycol, 121 parts of 4,4'-diphenylmethane diisocyanate, and 1-0.3 parts of dibutyltin dilaure as a catalyst were added, and the mixture was reacted at 80°C for 12 hours to form a thermoplastic polyurethane resin. Prepared.

Synthesis Example 2 In a container similar to Synthesis Example 1, 100 parts of methyl ethyl ketone,
140 parts of cyclohexanone, 100 parts of polycaprolactone polyol with a molecular weight of 1,000, 7.3 parts of ethylene glycol, 24 parts of 2,2-dimethyl-1,3-propanediol, 109 parts of 4,4''-diphenylmethane diisocyanate, dibutyltin as a catalyst. Dilaurate 0
．． 3 parts were added and reacted at 85° C. for 10 hours to obtain a thermoplastic polyurethane resin.

Synthesis Example 3 In a container similar to Synthesis Example 1, 116 parts of methyl ethyl ketone,
100 parts of tetrahydrofuran, 100 parts of a polyester polyol with a molecular weight of 1.500 consisting of adipic acid and 1,4-butylene glycol, 2,2-dimethyl-1,3
-35 parts of propanediol, 8.8 parts of 1゜4-butylene glycol, 120 parts of 4,4゛-diphenylmethane diisocyanate, 0 parts of dibutyltin dilaurate as a catalyst
．． 3 parts were added and reacted at 70°C for 15 hours to prepare a thermoplastic polyurethane resin.

Comparative Synthesis Example 1 In Synthesis Example 1, the amount added was 2,2-dimethyl-1,3
A thermoplastic polyurethane resin was prepared in the same manner except that 15 parts of -propanediol, 4.1 parts of 1.4-butylene glycol, and 72 parts of 4.4'-diphenylmethane diisocyanate were used.

Comparative Synthesis Example 2 Molecular weight 1, oo consisting of a diol with 2 moles of propylene oxide added to bisphenol A and adipic acid
Same as Synthesis Example 1 using 100 parts of polyester polyol of o, 22 parts of 2,2-dimethyl-1,3-propanediol, 5.6 parts of 1.4-butylene glycol, and 90 parts of 4.4'-diphenylmethane diisocyanate. A thermoplastic polyurethane resin was prepared using the method described above.

Thermoplastic polyurethane resins obtained in Synthesis Examples 1 to 3 and Comparative Synthesis Examples 1 to 2, and Niraporan N-2 as a commercial product
Number average molecular weight, tensile strength at break,
Table 1 shows the measured values of 100% modulus, elongation at break, and glass transition temperature.

Table 1 Examples 1 to 3 and Comparative Examples 1 to 5 Thermoplastic polyurecne resins obtained in Synthesis Examples 1 to 3 and Comparative Synthesis Examples 1 to 2 and commercially available 2,7 poran N-230
1. Magnetic disks were manufactured by the method shown below using the lubricants shown in Table 2, and their durability was measured.

Table 2 Manufacture and durability evaluation of magnetic disks> r-Feze
3100 parts ・Carbon blank 3 parts ・Lubricant type and amount shown in Table 2 ・Methyl ethyl ketone 200 parts ・Cyclohexanone
100 parts of the above composition was milled in a ball mill for 24 hours.
After kneading for an hour, add 10 parts of curing agent (manufactured by Nippon Polyurethane Co., Ltd.,
Coronate L) was added thereto, and after further kneading for 1 hour, the resulting magnetic paint was coated on a polyethylene terephthalate base film with a thickness of 70 microns to a thickness of 2 microns after drying, and then dried and aged.

The film was then cut into a predetermined magnetic disk size, mounted on a drive, and the durability was evaluated by measuring the time until the playback output decreased to 50% in an environment of 20° C. and 40° C.

The results are shown in Table 3.

Table 3

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer provided on a non-magnetic support, in which the magnetic layer has a number average molecular weight of 5,000 as determined by gel permeation chromatography analysis.
~40,000, breaking strength in a tensile test at a tensile speed of 100 mm/min is 200 kg/cm^2 or more, elongation at break 100-400%, 100% modulus 150k
g/cm^2 or more, a thermoplastic polyurethane resin with a glass transition temperature of 40°C or more as analyzed by dynamic viscoelasticity measurement, and the following general formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) { In the formula, R_1 and R_2 have 1 to 25 carbon atoms (however, R
The sum of the carbon numbers of _1 and R_2 is 18 to 34), and R_3 is a saturated alkyl group having a straight chain or branching, and R_3 is a carbon number of 7 to 34.
It is a saturated or unsaturated alkyl group having 29 straight or branched chains. ) A magnetic recording medium characterized by containing an ester compound represented by: