JP2985242B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape 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 of magnetic particles, filling properties, orientation, durability of the magnetic layer, abrasion resistance, heat resistance, adhesiveness with a non-magnetic support, and the like. 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 a magnetic recording medium, in order to improve the s / n ratio (signal-to-noise ratio) and to increase the recording density, the magnetic layer is filled with magnetic particles that are more finely divided. Orientation and smoothing of the mounting surface of the magnetic layer are performed. 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 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 backcoat layer, the worse the running and running durability of the magnetic tape, and the better the durability, abrasion resistance, heat resistance, and adhesion to the non-magnetic support. There is a need for a binder. Conventional binders for magnetic layers and backcoat layers are insufficient for these requirements.

An object of the present invention is to provide a magnetic recording medium having good running properties and running durability by developing a binder having good durability, abrasion resistance, heat resistance and adhesion to a non-magnetic support. is there.

(Means for Solving the Problems) As a result of intensive studies on a polyurethane resin in order to achieve the object of the present invention, the present invention has been reached. 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 non-magnetic support, as a binder component of the magnetic layer and / or Molecular weight as a binder component of the back coat layer provided on the support
A polyurethane resin comprising a polymer polyol having a molecular weight of 500 or more, an organic diisocyanate and, if necessary, a diol compound having a molecular weight of 500 or less, wherein at least 40% by weight of the polymer polyol is an aromatic polyester diol; 30% by mole or more of the component is a tricyclic glycol represented by the following formula:

The hydroxyalkyl group of X ₁ and X ₂ preferably has 1 to 10 carbon atoms.

As the carboxylic acid component of the aromatic polyester diol used in the present invention, terephthalic acid, isophthalic acid,
Orthophthalic acid, 1,5-naphthalic acid, 2,6-naphthalic acid,
Aromatic dicarboxylic acids such as 4,4'-diphenyldicarboxylic acid and 4,4'-diphenylether dicarboxylic acid are exemplified. As the glycol component, 30 of all glycol components
At least mol%, preferably at least 50 mol%, is tricyclic glycol. If it is less than 30 mol%, properties such as heat resistance, durability, and abrasion resistance are insufficient. Other glycol components include 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-pentanediol, cyclohexane dimethanol, ethylene oxide adduct and propylene oxide adduct of bisphenol A,
There are ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. In addition, tri- 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 properties of the polyester resin such as organic solvent solubility and coating workability. May be.

The dicarboxylic acid component and glycol component of the aromatic polyester diol other than the above include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoterephthalic acid, and 2-sodium sulfo-
Those containing a metal sulfonic acid salt such as 1,4-butanediol and 2,5-dimethyl-3-sodium-2,5-hexanediol are exemplified. Sulfonate metal base is magnetic powder
This has the effect of significantly improving the dispersibility of inorganic particles such as 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 dodecane dicarboxylic 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; 1,6-
Examples include polycarbonate polyols derived from hexanediol, neopentyl glycol, cyclohexanedimethanol, and the like.

The difference between the glass transition temperature of the aromatic polyester diol and the other polymer polyol is 80 ° C., preferably 100 ° C.
In the case where only the aromatic polyester diol is used as the high molecular weight polyol component, the glass transition temperature of the obtained polyurethane resin is 70 ° C., preferably 80 ° 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'-biphenylene diisocyanate, 2,4-naphthalenediisocyanate, 3,3'-
Dimethyl-4, diisocyanate, 4,4'-diisocyanatediphenyl-ter, 1,5-m-kilysilylene diisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane, 4,
4'-diisocyanatocyclohexane, 4,4'-diisocyanatocyclohexylmethane, isophorone diisocyanate, and the like.

The diol compound having a molecular weight of 500 or less used as necessary adjusts the urethane group concentration in the polyurethane resin and imparts toughness specific to the polyurethane resin. 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-pentanediol, cyclohexanedimethanol, 1: 1 adduct of neopentyl glycol and hydroxypivalic acid, ethylene oxide adduct and propylene oxide adduct of bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A and And propylene oxide adducts.

The molecular weight of the polyurethane resin used in the present invention is 5000
To 80,000, 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, and the workability and the dispersibility of magnetic powder, abrasives, carbon black and the like deteriorate.

In the present invention, in addition to the polyurethane resin used in the present invention, it is desirable to add another resin or mix a crosslinking agent for the purpose of adjusting flexibility, improving cold resistance and heat resistance, and the like.
Examples of the other resin include a vinyl chloride resin, a cellulose resin, a polyester resin, an epoxy resin, a phenoxy resin, a polyvinyl butyral, an acrylonitrile-butadiene copolymer, and a polyurethane resin other than the polyurethane resin described in the present invention. 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 magnetic 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- Examples include Fe ₂ O ₃ or Fe ₂ O ₄ , 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, potassium 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 sulfo sodium succinate, t-butyl phenol polyethylene ether, sodium ethyl naphthalene 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) By having a tricyclic glycol component, the polyurethane resin of the present invention has a high hardness, a low coefficient of abrasion, and a high flexibility segment copolymerized with the polyurethane resin or other flexible resin is used. Extremely tough by adding. As a result, it is considered that the magnetic recording medium of the present invention has good running properties and running durability.

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

Synthesis Example 1 of Polyurethane Resin A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was charged with 50 parts of polyester diol (A) shown in Table 1, 65 parts of toluene, and 65 parts of methyl ethyl ketone.
Charge 24.3 parts of diphenylmethane diisocyanate,
After heating at 2 ° C. for 2 hours, 50 parts of polyester diol (B),
5 parts of neopentyl glycol and 0.03 part of dibutyltin dilaurate as a reaction catalyst were added. After 6 hours of reaction at 80 ° C., 86 parts of toluene and 86 parts of methyl ethyl ketone were added.
The resulting polyurethane resin 1 solution had a solid content of 30%,
The solution viscosity at 25 ° C. was 80 poise.

 Table 1 shows the characteristics of the polyurethane resin 1.

Synthesis Examples 2 to 6 of polyurethane resin and Comparative Synthesis Examples 1 to
5 In the same manner as in Synthesis Example 1 of polyurethane resin, a polyurethane resin solution was obtained from the raw materials shown in Table 1. Table 1 shows the properties of the obtained polyurethane resin.

In Comparative Synthesis Example 1, when the tricyclic glycol in the aromatic polyester diol was 20 mol% of the total glycol,
Comparative Synthesis Examples 2 and 4 are cases where the aromatic polyester diol containing no tricyclic glycol is used, and Comparative Synthesis Example 3 is a case where the aromatic polyester diol containing the tricyclic glycol is 30% by weight of the high molecular weight polyol. No. 5 is a case where a high molecular weight polyol copolymerized adipic acid.

Abbreviations in the table are as follows.

Polyester composition and molecular weight Polyester A: T / DSN // EG / TCD (97/3 // 20/80 mol%
MW = 2000 Polyester B: Polybutylene adipate, MW = 2000 Polyester C: T / I / DSN // EG / NPG / TCD (50/48/2 // 30/3
0/40 mol% ratio), MW = 2500 Polyester D: T // EG / TCD (100 // 20/80 mol% ratio), MW = 2000 Polyester E: T / I / DSN // EG / NPG / TCD (50/48/2 // 40/4
0/20 mol% ratio), MW = 2500 Polyester F: T / I / DSN // EG / NPG (50/48/2 // 50/50 mol% ratio), MW = 2500 Polyester G: polycaprolactone, MW = 2000 Polyester H: T / AA / DSN // EG / NPG (70/28/2 // 70/30 mol% ratio), MW = 2500, where T; Terephthalic acid I; Isophthalic acid DSN; Dimethyl-5- Sodium sulfoisophthalic acid EG; ethylene glycol TCD; tricyclodecane dimethylol NPG; neopentyl glycol AA; adipic acid diisocyanate MDI; 4,4'-diphenylmethane diisocyanate Polyurethane Industry) as a curing agent.
Five parts, 0.05 part of stearic acid and 0.05 part of butyl stearate as a lubricant were added, and the mixture was further mixed for 1 hour to obtain a magnetic paint. This was applied on a 15 μm-thick polyethylene terephthalate film so that the thickness after drying was 4 μm,
Drying was performed while applying a magnetic field of 2000 gauss to produce a magnetic tape. The resulting magnetic tape was left at 60 ° C. for 1 day and slit to 1/2 inch. The surface gloss and the squareness ratio of the magnetic layer of the obtained tape were measured. Also, 10 ° C on a commercially available VTR deck
And the abrasion state of the magnetic layer after running 100 times at 40 ° C. was observed. Table 4 shows each characteristic.

10 parts of the polyurethane resin solution obtained in Synthesis Example 1 (30 solutions of MEK / toluene = 1/1) Co ferrite magnetic powder (BET 45m ² ) 12 parts Cyclohexanone 5 parts Toluene 10 parts MEK 5 parts Alumina (average particle size) 0.5 μm) 0.5 parts Examples 2 to 4 and Comparative Examples 1 to 5 Magnetic tapes were prepared in the same manner as in Example 1 except that the polyurethane resin described in Table 2 was used instead of the polyurethane resin used in Example 1. Created. Table 2 shows each characteristic.
Shown in

Example 5 A composition having the following composition ratio was dispersed in a sand mill containing glass beads having a diameter of 2 mm for 1 hour, and then 0.5 part of a polyisocyanate compound Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a curing agent. The mixture was further mixed for 1 hour to obtain a back coat paint. This was dried on a polyethylene terephthalate film having a thickness of 15 μm to a thickness of 0.
The magnetic paint obtained in Example 1 was applied and dried on the opposite side of the back coat layer of the polyethylene terephthalate film in the same manner as in Example 1 to obtain a magnetic tape. The same curing treatment as in Example 1,
After slitting, wear coefficient of back coat surface and commercial VT
The wear coefficient at 20 ° C after running 100 times at 40 ° C on an R deck was measured. Table 3 shows the results.

The wear coefficient was measured by attaching a 100 g weight to the magnetic tape and holding it on a mirror-finished stainless steel roll with a diameter of 50 mm.
The test was performed by running at a speed of 1 cm / s at 180 degrees.

100 parts of a solution of the polyurethane resin obtained in Synthesis Example 5 (30% solution of MEK / toluene = 1/1) carbon black 10 parts calcium carbonate (average particle diameter 0.05 μm) 20 parts cyclohexanone 50 parts toluene 50 parts Example 6 -7 and Comparative Examples 6-9 In the same manner as in Example 5, except that the polyurethane resin for the back coat was a polyurethane tape described in Table 3, and a magnetic tape was prepared. The characteristics are shown in Table-3.

Comparative Example 10 The same test as in Example 5 was performed on the magnetic tape (without back coat) obtained in Example 1. Table 3 shows the results.

(Effect of the Invention) By using the polyurethane resin of the present invention having an aromatic polyester diol containing a specific proportion of tricyclic glycol 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.

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 nonmagnetic support opposite to the magnetic layer, 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. A polyurethane resin comprising a diol compound, wherein at least 40% by weight of the high-molecular-weight polyol is an aromatic polyester diol, and at least 30 mol% of all glycol components of the aromatic polyester diol are represented by the following formula: A magnetic recording medium, which is glycol.