JP3049762B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk.

(Prior Art) Magnetic tapes and floppy disks, which are general-purpose magnetic recording media, disperse needle-like magnetic particles having a major axis of 1 μm or less together with additives such as dispersants, lubricants, and antistatic agents in a binder solution. It is made by making a magnetic paint and applying it to a polyethylene terephthalate film.

Characteristics required for the binder of the magnetic layer include dispersibility, filling property, orientation of the magnetic particles, durability of the magnetic layer, abrasion resistance, heat resistance, adhesiveness to a non-magnetic support, and the like. However, binders play a very important role.

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

As a binder for the magnetic layer or the back coat layer, a mixture of an adipate-type or polycaprolactone-type polyurethane resin and nitrocellulose or a PVC-based copolymer has been mainly used.

(Problems to be solved by the invention) In magnetic recording media, the s / n ratio (signal / ize ratio)
In order to improve the recording density and increase the recording density, the magnetic layer is filled with magnetic particles at a high level and is highly oriented, and the surface of the magnetic layer is smoothed. When the magnetic tape is stored in the form of a roll, the back coat layer is also smooth so that the output of the magnetic tape does not decrease even if the unevenness of the back coat layer is transferred to the magnetic layer. The smoother the surfaces of the magnetic layer and the back coat layer, the worse the running and running durability of the magnetic tape, and the better the bonding of the durability, abrasion resistance, heat resistance, and adhesion to the non-magnetic support. Agents are needed. Conventional binders for magnetic layers and backcoat layers are insufficient for these requirements.

Polyurethane resin containing aromatic polyester diol as one component of high molecular weight polyol is excellent in mechanical strength, abrasion resistance, heat resistance, etc., and is in the direction of improvement for these requirements, but completely solves the problem Has not been reached.
In particular, general-purpose aromatic polyester diols include low molecular weight compounds that do not polymerize during the urethanization reaction. These low molecular weight compounds are mainly cyclic compounds, the presence of which hinders the increasingly sophisticated requirements of magnetic recording media.

The object of the present invention is to improve the running property and running durability by using a polyurethane which has a significantly reduced durability of the low molecular compound, abrasion resistance, heat resistance, and good adhesion to a non-magnetic support. An object of the present invention is to provide a magnetic recording medium.

(Means for Solving the Problems) In order to achieve the object of the present invention, as a result of intensive studies on a polyurethane resin, the present invention has been achieved.

That is, the present invention relates to a magnetic recording medium in which a magnetic material in which a ferromagnetic powder is dispersed in a binder is coated on a nonmagnetic support, as a binder component of the magnetic layer and / or a magnetic layer on the nonmagnetic support. As a binder component of the back coat layer provided on the opposite side, a high molecular weight polyol having a molecular weight of 500 or more, an organic diisocyanate, and if necessary, a molecular weight of 50
A polyurethane resin comprising a polyol compound of 0 or less, wherein at least 30% by weight of the high molecular weight polyol is an aromatic polyester diol, and the glycol component of the aromatic polyester diol is a tricyclic compound represented by the following general formula (I). It is composed of a formula glycol, a glycol having 8 or more carbon atoms (excluding a tricyclic glycol represented by the following general formula (I)) and ethylene glycol, and each glycol is in the range of the following (i) and (ii). A magnetic recording medium characterized by the above-mentioned.

General formula (I) (I) Ethylene glycol 50 mol% or less in all glycols (ii) Molar ratio of tricyclic glycol / glycol having 8 or more carbon atoms 4: 1 to 1: 3 Carboxyl of aromatic polyester diol used in the present invention As the acid component, terephthalic acid, isophthalic acid,
Orthophthalic acid, 1,5-naphthalic acid, 2,6-naphthalic acid,
Aromatic dicarboxylic acids such as 4,4'-diphenyl dicarboxylic acid, 2,2'-diphenyl dicarboxylic acid, and 4,4'-diphenyl ether dicarboxylic acid, and the like, in particular, terephthalic acid, isophthalic acid, and 2,6-naphthalic acid Is desirable. The glycol component comprises a tricyclic glycol represented by the general formula (I), a glycol having 8 or more carbon atoms (excluding the tricyclic glycol represented by the general formula (I)), and ethylene glycol. Examples of the glycol having 8 or more carbon atoms include 1,
8-nonanediol, 2-methyloctanediol, 2,
2,4-trimethyl-1,3-pentaneddiol, dodecanediol, cyclohexanedimethanol, 2-butyl-2
-Ethyl-1,3 propanediol, neopentyl hydroxypivalate, ethylene oxide adduct and propylene oxide adduct of bisphenol A,
There are ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A. Of these, neopentyl hydroxypivalate, cyclohexanedimethanol, and nonanediol are preferred, and neopentyl hydroxypivalate is particularly desirable.

Glycols having 8 or more carbon atoms have a long chain length or bulky side chains and thus are difficult to form a cyclic compound, but reduce the rigidity and heat resistance of the aromatic polyester diol. The tricyclic glycol represented by the following general formula (I) is also difficult to form a cyclic compound, but because of its rigid structure, it can be used for relatively difficult to disperse such as metal magnetic powder, barium ferrite and carbon black. Aptitude worsens. The disadvantage of the tricyclic glycol can be prevented by using a glycol having 8 or more carbon atoms in combination. The combined use of the tricyclic glycol and the glycol having 8 or more carbon atoms makes it possible to reduce the amount of the cyclic compound while maintaining the properties of the aromatic polyester diol.

The molar ratio of the tricyclic glycol to the glycol having 8 or more carbon atoms is in the range of 4: 1 to 1: 3, preferably 3: 1 to 1: 1. When the amount of tricyclic glycol is larger than this range, the dispersibility of fine magnetic powder or carbon black is reduced, and when the amount is smaller, the effect of using the aromatic polyester diol cannot be obtained.

Among the glycol components of the aromatic polyester diol, ethylene glycol is used in an amount of 50 mol% or less, preferably 30 mol% or less of the total glycol. If it exceeds 50 mol%, the proportion of the cyclic compound tends to increase and the durability of the magnetic recording medium tends to decrease.

In addition, tri- or higher-functional compounds such as trimellitic acid and pyromellitic acid are used as a part of the raw material of the polyester diol to improve the properties such as the solubility of the aromatic polyester diol in the organic solvent, the dispersibility of the magnetic powder, and the workability of applying the magnetic paint. You may use it in the range which does not impair.

The dicarboxylic acid component and the glycol component of the aromatic polyester diol other than those described above include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoterephthalic acid, 2-sodium sulfone-1,4-butanediol, 2, Those containing a metal sulfonic acid salt such as 5-dimethyl-3-sodium sulfo-2,5-hexanediol are exemplified. Sulfonate metal bases have the effect of significantly improving the dispersibility of inorganic particles such as magnetic powder, abrasives and carbon black.

Examples of the high-molecular-weight polyol having a molecular weight of 500 or more other than the aromatic polyester diol include succinic acid, adipic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as dodecanedicarboxylic acid and aliphatic polyester polyols obtained from glycols, polycaprolactone, and polycaprolactone. Polylactone polyols such as valerolactone; polyether polyols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol; and polycarbonate polyols derived from 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol, and the like.

Aromatic polyester diol is 30 in polymer polyol
% By weight, preferably 50% by weight or more. 30% by weight
If it is less than 10, the toughness, heat resistance and the like of the polyurethane resin decrease, and the durability of the magnetic recording medium deteriorates.

The difference between the glass transition temperature of the aromatic polyester diol and the other polymer polyol is 80 ° C., preferably 100 ° C.
That is, or when only the aromatic polyester diol is used as the high molecular weight polyol component, the obtained polyurethane resin has a glass transition temperature of 50 ° C., preferably 70 ° C.
The above is preferable for achieving the object of the present invention. When the difference between the glass transition temperatures of the aromatic polyester diol and the other polymer polyol is 80 ° C., the aromatic polyester diol can be used alone as the binder resin. It is desirable to add another resin for the purpose of adjusting flexibility and improving cold resistance.

As the organic diisocyanate component of the polyurethane resin used in the present invention, 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'-biphenylenediisocyanate, 1,5-naphthalenedidisocyanate, 2,6-naphthalenediisocyanate, 3,3'-dimethyl-4,4'-diisocyanate, 4,4'- Diisocyanate diphenyl ether, 1,5-xylylene diisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane, 4,4'-diisocyanatocyclohexane, 4,4'-diisocyanatocyclohexylmethane, isophorone diisocyanate, etc. .

If necessary, a polyol compound having a molecular weight of 500 or less adjusts the urethane group concentration in the polyurethane resin to impart a unique toughness to the polyurethane resin, and a polyol having three or more functions increases reactivity with a curing agent to increase the crosslink density. Has the effect of increasing. For example, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2, 4-trimethyl-1,3
Diol compounds such as pentanediol, cyclohexanedimethanol, neopentylhydroxypivalate, bisphenol A ethylene oxide adduct and propylene oxide adduct, hydrogenated bisphenol A ethylene oxide adduct and propylene oxide adduct, trimethylolpropane Glycerin, pentaerythritol, dipentaerythritol and the like.

A polyol compound having a molecular weight of 500 or less has the effect of adjusting the urethane group concentration and imparting a toughness specific to the polyurethane resin, but if the urethane group concentration is too high, the interaction between the polyurethane resins becomes too strong and magnetic powder or carbon The dispersibility of black decreases. Due to the physical properties of the polyurethane resin itself and the properties of the composite coating film containing inorganic fine particles resulting from the degree of dispersion, the urethane group concentration in the polyurethane resin is preferably in the range of 1500 to 700 equivalents per ton of resin, and more preferably in the range of 1400 to 1000 equivalents.

The molecular weight of the polyurethane resin used in the present invention is from 5000
8000, preferably 10,000 to 40,000. If the molecular weight is less than 5000, the mechanical strength is insufficient, and the running durability is poor. If the molecular weight exceeds 80,000, the solution viscosity increases,
Workability and dispersibility of magnetic powder, abrasives, carbon black, etc. are deteriorated.

In the present invention, in addition to the polyurethane resin used in the present invention, other resins are added and / or a crosslinking agent is mixed for the purpose of adjusting flexibility, improving cold resistance and heat resistance, and the like. Is desirable. Other resins include vinyl chloride resin, cellulose resin, polyester resin, epoxy resin, phenoxy resin, polyvinyl butyral, acrylonitrile / butadiene copolymer and the like.
On the other hand, examples of the crosslinking agent include a polyisocyanate compound, an epoxy resin, a melamine resin, a urea resin, an acid anhydride and the like, and among these, a polyisocyanate compound is particularly preferable.

The ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe ₂ O ₃ , a mixed crystal of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , and γ-Fe coated with cobalt. Examples include ferromagnetic oxides such as ₂ O ₃ or Fe ₂ O ₄ and barium ferrite, and ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni.

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

The magnetic recording medium of the present invention may further include a plasticizer such as dibutyl phthalate and triphenyl phosphate, dioctyl sodium sulfosuccinate, t-butylphenol polyethylene ether, sodium ethylnaphthalene sulfonate, dilauryl succinate, and stearic acid. Lubricants such as zinc, soybean oil lecithin and silicone oil and various antistatic agents can also be added.

(Function) The magnetic recording medium of the present invention has a tricyclic glycol component as a binder component of a magnetic layer and / or a binder component of a back coat layer provided on the side opposite to the magnetic layer on the nonmagnetic support. A polyurethane resin containing at least 30% by weight of a high molecular weight polyol component of an aromatic polyester diol comprising glycol, glycol having 8 or more carbon atoms and ethylene glycol is used.

By using a tricyclic glycol and a glycol having 8 or more carbon atoms in combination, the amount of the cyclic compound can be reduced without losing the properties of the aromatic polyester diol such as rigidity, hardness and heat resistance. As a result, the durability of the magnetic recording medium of the present invention is improved.

(Examples) Hereinafter, the present invention will be specifically illustrated by examples. In the examples, “parts” means “parts by weight”.

Synthesis Example of Polyurethane Resin 1 In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a distillation tube, 50 parts of the polyester diol (A), 50 parts of the polyester diol (B), and 80 parts of toluene shown in Table 1 were placed. After charging and dissolving, 20 parts of toluene was distilled and the reaction system was dehydrated by azeotropic distillation of toluene / water. After cooling to 60 ° C., 15.6 parts of diphenylmethane diisocyanate was added, and the mixture was heated at 80 ° C. for 2 hours. Then, 60 parts of methyl ethyl ketone, 2 parts of trimethylolpropane, and 0.03 part of dibutyltin dilaurate as a reaction catalyst were added. After reaction at 80 ° C for 6 hours, toluene
77.2 parts and 77.2 parts of methyl ethyl ketone were added, and the solid content
30% of polyurethane resin 1 was obtained. Polyurethane resin 1
Table 1 shows the characteristics. In Table 1, the solution viscosity was 25 ° C,
The number average molecular weight was measured by gel permeation chromatography using a tetrahydrofuran solution.

Synthetic Examples 2 to 6 of Polyurethane Resin and Comparative Synthetic Examples 1 to 6 A polyurethane resin solution was obtained from the raw materials shown in Table 1 in the same manner as in Synthetic Example 1 of polyurethane resin. Table 1 shows the properties of the obtained polyurethane resin.

Comparative Synthesis Examples 1 to 3 were obtained when ethylene glycol in the aromatic polyester diol was 65 mol% of the total glycol, and Comparative Synthesis Example 3 was obtained when the aromatic polyester diol was 20% by weight in the high molecular weight polyol. 4 and 5 are cases where the tricyclic glycol and the glycol having 8 or more carbon atoms are out of the claims, and Comparative Synthesis Example 6 is the case where the aromatic polyester diol does not contain the glycol having 8 or more carbon atoms.

Abbreviations in the table are as follows.

Polyester composition, molecular weight Polyester AT / I / DSN // EG / TCD / HPN (50/47/3 // 20/50/30 mol%) MW = 2000 Polyester B polybutylene adipate MW = 2000 Polyester C polycaprolactone MW = 2000 Polyester DT / I / DSN // EG / TCD / 1,9-ND (50/47/3 // 10/60/30 mol%) MW = 30
00 Polyester FT / I / DSN // EG / TCD / HPN (50/47/3 // 65/20/15 mol%) MW = 2000 Polyester GT / I / DSN // EG / TCD / HPN (50/47 / 3 // 30/15/55 mol%) MW = 2000 Polyester HT / I / DSN // EG / TCD / 1,9-ND (50/47/3 // 10/75/15 mol%) MW = 30
00 Polyester IT / DSN // TCD / NPN (98/2 // 50/50 mol%) MW = 1500 where T; terephthalic acid I; isophthalic acid DSN; dimethyl 5-sodium sulfoisophthalic acid EG; ethylene glycol TCD; Cyclodecane dimethylol HPN; neopentyl hydroxypivalate 1,9-ND; 1,9-nonanediol NPG; neopentyl glycol low molecular polyol TMP; trimethylolpropane NPG; neopentyl glycol TMP-CL; TMP-ε-caprolactone adduct, Molecular weight 3
90 Diisocyanate MDI; 4,4'-diphenylmethane diisocyanate Example 1 A composition having the following composition ratio was placed in a ball mill and dispersed for 48 hours, and then a polyisocyanate compound, coronate
0.5 using MR (manufactured by Nippon Polyurethane Industry) as a curing agent
Parts, 0.05 parts of stearic acid and 0.05 parts of butyl stearate as a lubricant were added and mixed for 1 hour to obtain a magnetic paint.
This was applied on a polyethylene terephthalate film having a thickness of 15 μm so that the thickness after drying was 4 μm.
Drying was performed while applying a magnetic field of Gauss to produce a magnetic tape. The resulting magnetic tape was left at 60 ° C. for 1 day and slit to 1/2 inch. Surface gloss of the magnetic layer of the obtained tape,
The squareness ratio was measured. Also, at 10,40 ° C on a commercial VTR deck
The abrasion state of the magnetic layer after running 100 times was observed. The characteristics are shown in Table-4.

Solution of polyurethane resin obtained in Synthetic Example 1 10 (30% solution of MEK / toluene = 1/1) Metal magnetic powder (BET50m ² ) 15 Cyclohexanone 5 Toluene 10 MEK 5 Alumina (average particle size 0.05 μ) 0.5 Example 2 to 5 Comparative Examples 1 to 6 Magnetic tapes were prepared in the same manner as in Example 1 except that the polyurethane resin shown in Table 2 was used instead of the polyurethane resin used. The characteristics are shown in Table-2.

Example 6 A composition having the following composition ratio was placed in a sand grinder containing glass beads having a diameter of 2 m ² 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 for 0.5 hour. 1 additional
After mixing for a time, a paint for a back coat was obtained. This is thickness 15
On a polyethylene terephthalate film having a thickness of 0.5 μm, the coating is dried so that the thickness after drying becomes 0.5 μm, and the magnetic paint obtained in Example 1 is applied and dried on the opposite surface of the polyethylene terephthalate film in the same manner as in Example 1. A magnetic tape was created. After the same curing treatment and slitting as in Example 1, the friction coefficient of the back coat surface and the friction coefficient at 20 ° C. after running 100 times at 40 ° C. on a commercially available VTR deck were measured. The results are shown in Table-3.

The coefficient of friction was measured using a magnetic tape with a weight of 100 g and a mirror-finished stainless steel roll with a diameter of 50 mm.
The test was run at 180 degrees at a speed of 1 cm / s.

Solution of polyurethane resin obtained in Synthesis Example 1 100 (30% solution of MEK / toluene = 1/1) Carbon black 10 Calcium carbonate (average particle size 0.05 μm) 20 Cyclohexanone 50 Toluene 50 Example 7 and Comparative Examples 7 to 9 A magnetic tape was prepared in the same manner as in Example 6, except that the polyurethane resin shown in Table 3 was used instead of the polyurethane resin used for the back coat. Table of characteristics
3 is shown.

Comparative Example 10 The same test as in Example 7 was performed on the magnetic tape (without back coat) obtained in Example 1. The results are shown in Table-3.

In Tables 2 and 3, the polyurethane resin (Z) is a polybutylene adipate-based polyurethane, “Nipporan 2301” manufactured by Nippon Polyurethane Co., Ltd. Abrasion state of magnetic layer ○ --- No damage is observed on the magnetic layer.

.DELTA .-- Scratch is observed in the magnetic layer but small.

× --Scratch is clearly observed in the magnetic layer.

(Effect of the Invention) By using a polyurethane resin having an aromatic polyester diol containing a specific glycol of the present invention in a specific ratio in a molecule as a binder for magnetic particles and a binder for a back coat layer, abrasion resistance is improved. And the change in the coefficient of friction is reduced. As a result, a magnetic recording medium having excellent running durability can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 5/702 C09D 5/23 C09D 175/06 CAPLUS (STN)

Claims (1)

(57) [Claims] 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 the magnetic layer and / or as a binder component of the back coat layer provided on the side opposite to the magnetic layer on the non-magnetic support, a high molecular weight polyol having a molecular weight of 500 or more, an organic diisocyanate, and if necessary, a molecular weight of 500 or less At least 30% by weight of the high molecular weight polyol is an aromatic polyester diol, and the glycol component of the aromatic polyester diol is a tricyclic glycol represented by the following general formula (I): And glycols having 8 or more carbon atoms (excluding tricyclic glycols represented by the following general formula (I)) and ethylene glycol, wherein each glycol is in the range of the following (i) and (ii). Magnetic recording medium. General formula (I) (I) Ethylene glycol 50 mol% or less in total glycol (ii) Molar ratio of tricyclic glycol / glycol having 8 or more carbon atoms 4: 1 to 1: 3