JP3443912B2 - Magnetic recording media - Google Patents

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 coating type magnetic recording medium having excellent resistance to cracking during slitting.

[0002]

2. Description of the Related Art Recently, in a magnetic recording medium which is often used by being put in a cassette case such as a video tape,
In order to meet the demand for longer recording time, the magnetic tape accommodated in the unit cassette is lengthened by thinning the magnetic tape. However, when the magnetic tape is made thin, the stiffness strength of the magnetic tape as a whole decreases in inverse proportion to the cube of the thickness.
For this reason, V adjusted for a conventional thickness video tape
When a thin video tape is used for a long time in a TR or the like, contact with a limiter post that determines the running reference surface of the magnetic tape, breakage of the end surface of the magnetic tape due to riding, etc., and scraping of the magnetic surface occur. The recorded image or data is significantly damaged due to poor tracking of the image due to these phenomena. In order to prevent such deterioration of running durability, it has been studied to increase the Young's modulus of the binder of the non-magnetic support or the magnetic layer. As an example of the former, a base material such as polyethylene naphthalate or polyimide has been proposed in place of the conventionally used polyethylene terephthalate, but it is much more expensive than the conventional polyethylene terephthalate. In the latter, the loss elastic modulus is increased by increasing the concentration of the aromatic polyester having skeleton such as phthalic acid as the soft segment constituent material of the polyurethane resin which is the main component of the binder of the magnetic recording layer, or the urethane group concentration, A method of increasing the Young's modulus of the magnetic recording layer has been proposed.

[0003]

However, in the magnetic tape using the polyurethane resin in which the loss elastic modulus is increased by increasing the rigidity of the soft segment or increasing the concentration of the urethane group as described above, the flexibility of the coating film is increased. The cracks caused by slitting the magnetic tape to a specified width, especially cracks occur remarkably in the high Young's modulus tape using such a high-rigidity polyurethane resin. There are problems such as deterioration of performance, deterioration of durability, increase of dropout, and clogging of magnetic head. The present invention solves the above problems,
An object of the present invention is to provide a magnetic recording medium having improved cracking resistance during slitting and excellent electromagnetic conversion characteristics, durability, peeling resistance, and coating film surface characteristics.

[0004]

As a result of earnest research, the inventors of the present invention have found that a magnetic recording medium capable of achieving the above object can be obtained by using a polyurethane resin binder composed of specific components and ratios. Found and completed the present invention.

That is, the present invention provides a magnetic recording medium comprising a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, wherein (1) an alkyl group is a side chain as a component of the binder. 10 to 50% by weight of an aliphatic polyester diol (A) obtained by reacting a low molecular weight diol having the above-mentioned with a mixture of more than 85 mol% of adipic acid and 15 mol% or less of 5-sodium sulfoisophthalic acid, Aromatic polyester diol (B) 90 having a glass transition temperature of −3 ° C. or higher obtained by reacting a molecular diol with 70 mol% or more of phthalic acid and 30 mol% or less of adipic acid
Mixed polyester diol with ˜50% by weight, (2)
0.05 based on the solid content of raw materials for polyurethane resin production
A chain extender comprising ~ 1.0 wt% triol, (3)
Polyurethane resin obtained by reacting with organic diisocyanate and having a sodium sulfonate group and / or carboxyl group content of 0.001 to 0.2 mmol / g and a maximum loss elastic modulus of 20 to 60 ° C. The above magnetic recording medium is characterized by containing.

The present invention also provides, as a component of the binder,
A curing agent is added to 100 parts by weight of the polyurethane resin.
The above-mentioned magnetic recording medium further contains 40 to 40 parts by weight.

The present invention will be described in detail below. The aliphatic polyester diol (A) used in the present invention is
A polyester diol having a terminal hydroxyl group obtained by a condensation reaction of a low-molecular diol having an alkyl group in its side chain and an aliphatic dicarboxylic acid, for example, a molecular weight of 5
Those of 00 to 5,000 are preferable. Examples of the low-molecular diol include 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2
-Butyl-2-ethyl-1,3-propanediol, 2
-Methyl-1,5-heptanediol and the like may be mentioned alone or as a mixture of two or more thereof, and the molecular weight thereof is 50 to 400.
Are preferred. The aliphatic dicarboxylic acid is 85
It contains adipic acid in an amount of more than mol% and 5-sodium sulfoisophthalic acid in an amount of 15 mol% or less, preferably 5 mol% or less.

Glass transition point (Tg) used in the present invention
With an aromatic polyester diol (B) having a temperature of −3 ° C. or higher includes a low-molecular diol and phthalic acid (alone), or 70
A polyester diol having a terminal hydroxyl group obtained by a condensation reaction with an aromatic dicarboxylic acid containing a mixture of phthalic acid in an amount exceeding 30 mol% and adipic acid in an amount of 30 mol% or less, preferably 20 mol% or less. Fifty
Those of 0 to 5,000 are preferable. Examples of the low molecular weight diol include 1,2-propanediol, 1,3
-Propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,5-heptane Diol, 1,6
-Hexanediol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol and the like can be mentioned one or a mixture of two or more glycols having 3 to 10 carbon atoms, and a molecular weight of 50 to 400. Is preferred. Examples of the phthalic acid include one or a mixture of two or more of orthophthalic acid, isophthalic acid and terephthalic acid.

The weight ratio of the aliphatic polyester diol (A) to the aromatic polyester diol (B) is 10 to 50% by weight to 90 to 50% by weight, preferably 2%.
0 to 40% by weight to 80 to 60% by weight. When the proportion of the aliphatic polyester diol (A) is less than 10% by weight, the cracking resistance during slitting in the magnetic recording medium production process is adversely affected, and when it is more than 50% by weight, the storage durability is deteriorated. Adversely affect.

The chain extender used in the present invention is a mixed chain extender containing triol. Examples of chain extenders other than triol include 1,2-propanediol, 1,
3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,5- Heptanediol, 1,
Examples thereof include one or a mixture of two or more low molecular weight diols having a molecular weight of 50 to 400 and having 3 or more carbon atoms, such as 6-hexanediol, cyclohexane-1,4-diol, and cyclohexane-1,4-dimethanol. Examples of the triol used as a part of the chain extender in the present invention include one kind or a mixture of two or more kinds such as trimethylolpropane and glycerin. The content is 05 to 1.0% by weight, preferably 0.1 to 0.4% by weight. If the amount of triol is less than this range, the storage durability is adversely affected, and if it is more than this range, the cracking resistance is adversely affected.

Examples of the organic diisocyanate used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate. One or a mixture of two or more of 4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and the like can be mentioned.

In producing the polyurethane resin of the present invention, the NCO / OH molar ratio of the mixed polyester diol and the chain extender to the organic diisocyanate is 0.5 to.
The range of 1.1, especially 0.7 to 1.0 is preferable. If it deviates from this range, it is not preferable because the excellent various properties aimed at by the present invention cannot be obtained.

The temperature at which the maximum loss elastic modulus of the polyurethane resin in the present invention is 20 to 60 ° C., preferably 30 to 50 ° C. If it is lower than this range, the storage durability is adversely affected, and if it is higher than this range, the cracking resistance is adversely affected. The polyurethane resin has a terminal hydroxyl group, and its number average molecular weight is preferably 5,000 to 70,000, particularly preferably 7,000 to 40,000. When the number average molecular weight of the polyurethane resin is less than 5,000, durability is poor. On the other hand, when the number average molecular weight is larger than 70,000, the dispersibility of the magnetic powder is deteriorated and it becomes difficult to form a coating material.

The polyurethane resin may contain sodium sulfonate group and / or carboxyl group, the concentration of which is 0.001 per polymer.
~ 0.2 mmol / g. The sodium sulfonate base is introduced into the polyester diol molecule by using 5-sodium sulfoisophthalic acid as a part of the acid component of the polyester diol (A). As a method of introducing a carboxyl group, bis (2,2
A method of using -hydroxylmethyl) propionic acid as a diol component in the polyester diol, a method of using it as a part of a chain extender, and the like can be mentioned.

Further, in the production of the polyurethane resin, a catalyst, a stabilizer and the like can be used if necessary. Examples of the catalyst include amines such as N-methyldiethanolamine, triethylamine and triethylenediamine, metal salts such as potassium acetate and zinc stearate, and organic metal compounds such as dibutyltin laurate and dibutyltin oxide. By incorporating a stabilizer such as substituted benzotriazoles against ultraviolet rays as a stabilizer and a stabilizer against thermal oxidation such as phenol derivatives, various performances of the polyurethane resin can be remarkably stabilized. Further, in producing this polyurethane resin, any conventionally known method can be adopted,
For example, a solution reaction method in which the reaction is carried out in a single or mixed solvent system of toluene, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, ethyl acetate, etc. can be used.

As the binder in the magnetic recording medium of the present invention, in addition to the polyurethane resin, other binder resins commonly used in magnetic recording media can be used in combination. Examples thereof include a normal type linear polyurethane resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer,
Vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, polyvinyl butyral-based resin, styrene-based resin, fibrin-based resin, polyester resin, epoxy resin, phenoxy resin, and SO ₃ M (M
Is potassium or sodium), and a type in which a hydrophilic polar group such as a carboxyl group is introduced. The binder thus obtained is dissolved in an organic solvent and the magnetic powder is dispersed and applied on a non-magnetic support to form a magnetic layer.

In the present invention, a curing agent can be used if necessary. The curing agent used here is a low molecular weight polyisocyanate containing two or more isocyanate groups,
For example, a compound having a terminal isocyanate group obtained by reacting a low-molecular polyol with an organic diisocyanate, a cyclic trimer compound of an organic diisocyanate, and the like can be mentioned. Specifically, there are Coronate L, Coronate 3041, Coronate HL and the like manufactured by Nippon Polyurethane Industry. 5 to 4 of these curing agents are added to 100 parts by weight of the binder resin.
By adding 0 parts by weight, the mechanical strength, abrasion resistance, heat resistance, solvent resistance and the like of the magnetic layer can be further improved.

Further, in the above-mentioned magnetic layer, in addition to the above-mentioned binder and magnetic powder, an additive such as a dispersant, a lubricant, an abrasive,
Antistatic agents, rust preventives and the like can be used in combination.

[0019]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples.
The "parts" and "%" in the synthetic examples, examples and comparative examples are "parts by weight" and "% by weight" unless otherwise specified. <Synthesis of Polyurethane Resin> Synthesis Example 1 Aliphatic polyester diol A2 having a number average molecular weight of 2,000 is placed in a reaction vessel equipped with a thermometer, a stirrer, and a cooling tube.
(Polyester diol from adipic acid, 5-sodium sulfoisophthalic acid and neopentyl glycol) 5
Aromatic polyester diol B3 of 00 parts and number average molecular weight of 2,000 [glycol (neopentyl glycol / 2-butyl-2-ethyl-1,3-propanediol / cyclohexanedimethanol = 9/4/7 molar ratio) And phthalic acid (terephthalic acid / isophthalic acid = 1/1 molar ratio)] 1,500 parts, neopentyl glycol 50 parts, 2,2-dimethylolpropionic acid 16 parts, trimethylolpropane 4 parts, and 1,673 parts of cyclohexanone was charged and mixed at 50 ° C., then 0.3 parts of dioctyltin dilaurate and 384 parts of 4,4′-diphenylmethane diisocyanate as a urethanization catalyst were added and reacted at 80 ° C. Since the viscosity increases as the reaction progresses, dilute with cyclohexanone, methyl ethyl ketone and toluene at appropriate times.
The disappearance of the peak of the isocyanate group was confirmed in the infrared spectrum, and a uniform transparent liquid was obtained. This polyurethane resin solution 1 has a solid content of 25.0% and a viscosity of 400 cP / 2.
The number average molecular weight was 33,000 at 5 ° C. Table 3 shows the composition and characteristics of the synthesized polyurethane resin 1.

Synthetic Examples 2 to 18 In the same manner as in Synthetic Example 1, the aliphatic polyester diol (A) shown in Table 1, the aromatic polyester diol (B) shown in Table 2 and the kind of the chain extender are used. By changing the amount, the reaction with 4,4'-diphenylmethane diisocyanate was performed to synthesize each polyurethane resin solution. The compositions of the polyurethane resins obtained in the above synthesis examples are shown in Tables 3 to 5. Since the urethanization catalyst and the solvent are the same as those in Synthesis Example 1, their description is omitted in Tables 3 to 5.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

[Table 5]

The glass transition points (Tg) shown in Table 2 are the thermal analysis instruments manufactured by Seiko Denshi Kogyo [Model SSC-500].
0 (station), DSC-200 (analysis module section)] at a heating rate of 10 ° C / min according to JIS
It measured according to K7121. In Tables 3 to 5, the loss elastic modulus (E ″) was measured by coating the release paper with a polyurethane resin solution so as to have a dry film thickness of 100 μm.
Samples dried at ℃ × 30 minutes + 120 ℃ × 120 minutes + room temperature × 1 week, using a rheovibron (manufactured by Toyo Baldwin), frequency: 35 Hz, heating rate: 2 ℃ / mi
The measurement was performed under the condition of n, and the temperature at which the maximum loss elastic modulus (E ″) was exhibited was determined.

<Preparation of Magnetic Paint and Evaluation of Magnetic Coating> Example 1 Using the polyurethane resin solution 1 obtained in Synthesis Example 1,
The magnetic paint obtained by blending in the following proportions and dispersed for 5 hours with a sand grind mill (Igarashi Kikai) was added with Coronate L (Nippon Polyurethane Industry Co., Ltd.) as a curing agent to 100 parts of polyurethane resin in terms of solid content. 20 copies,
After further mixing for 1 hour, a dry coating film of 5 μm was applied on a polyethylene terephthalate base film having a thickness of 15 μm, and immediately after applying a magnetic field for 3 minutes at 80 ° C. and calendering, it was further heated at 50 ° C. for 24 hours. It was cured for a time to obtain a magnetic film. Blend Co-γ-Fe ₂ O ₃ (BET number 38 m ² / g) 100 parts Polyurethane resin (solid content) 25 parts Methyl ethyl ketone 110 parts Toluene 110 parts Cyclohexanone 73 parts Glossiness of the obtained magnetic film, squareness ratio, The running and storage durability, cracking resistance, and peeling resistance were evaluated.
The results are shown in Table 6.

Examples 2-11, Comparative Examples 1-7 Instead of the polyurethane resin solution 1 used in Example 1,
Polyurethane resin solutions 2-1 obtained in Synthesis Examples 2-18
8 was used to evaluate the glossiness, squareness ratio, running and storage durability, cracking resistance, and peeling resistance of the magnetic film in the same formulation as in Example 1. The results are shown in Tables 6-8.

Evaluation method (1) Gloss: The magnetic surface of the obtained magnetic film was measured with a gloss meter (manufactured by Suga Test Instruments Co., Ltd.) at an incident angle of 45 degrees and a reflection angle of 45.
The reflectance in degrees was measured. (2) Squareness ratio: The magnetic conversion characteristics of the obtained magnetic film are as follows: Vibration sample magnetometer VSM-3KA type (manufactured by Toei Industry Co., Ltd.)
Was measured using. (3) Running durability: The tape damage after running 100 passes at + 5 ° C. was visually evaluated using a VHS system VTR. The symbols used in this item are as follows. ◯: Good ×: Tape was broken (4) Storage durability: Magnetic film at 60 ° C × 95% RH
After storage for 4 weeks, the amount of binder extracted by the Soxhlet extraction test (extracting with boiling methyl ethyl ketone for 5 hours) was measured to determine the weight change rate before and after extraction of the binder. The symbols used in this item are as follows. A: Weight change rate of less than 5% O: Weight change rate of 5% or more and less than 10% B: Weight change rate of 10% or more and less than 20% X: Weight change rate of 20% or more (5) Cracking resistance: Obtained magnetic film Was cut with a sharp cutter knife, and the vicinity of the cross section was observed using an electron microscope (manufactured by JEOL Ltd.) for cracks in the magnetic layer. The symbols used in this item are as follows. ⊚: As shown in FIG. 1, magnetic layer cross section 1 and magnetic layer surface 2
No cracks in the circles ○: As shown in FIG. 2, fine cracks 4 are present in the magnetic layer cross section Δ: As shown in FIG. 3, the magnetic layer cross section 1 and the magnetic layer surface 2
A state in which fine cracks 4 are included in the cross section: As shown in FIG. 4, the magnetic layer cross section 1 and the magnetic layer surface 2
State with slightly large cracks (6) Peel resistance: Width 1 on the magnetic surface of the obtained magnetic film
Adhere 8mm polyacetate adhesive tape, JIS K
It measured according to 6301. However, the pulling speed is 30 mm
/ Min. Is. The symbols used in this item are as follows. ○: The adhesive layer of the adhesive tape is peeled off and attached to the magnetic surface. Δ: A part of the magnetic layer is peeled off from the polyethylene terephthalate film, and the magnetic tape is partially attached to the adhesive tape. ×: The entire magnetic layer is polyethylene. Peeled off from the terephthalate film and all magnetic layers adhered to the adhesive tape

[0030]

[Table 6]

[0031]

[Table 7]

[0032]

[Table 8]

The magnetic films of Examples 1 to 11 were superior in performance to the magnetic films of Comparative Examples 1 to 7,
In particular, since the cracking resistance is excellent, it can be seen that magnetic powder does not fall off and the magnetic recording characteristics including the electromagnetic conversion characteristics are excellent.

[0034]

INDUSTRIAL APPLICABILITY The magnetic recording medium of the present invention is excellent in cracking resistance during slitting, electromagnetic conversion characteristics, durability, peeling resistance and coating film surface characteristics, and is required to have high recording density and reliability. It is useful as a video tape, audio tape, computer tape, floppy disk, magnetic card, etc. Further, the polyurethane resin as the binder component in the present invention can be used as an adhesive for film lamination, an ink binder, a surface treatment agent for plastics, other adhesives, and a coating agent.

[Brief description of drawings]

FIG. 1 is a schematic view of a cracking resistance judgment standard with an electron microscope in the vicinity of a cross section of a cut magnetic film.

FIG. 2 is a schematic view of a cracking resistance judgment standard by an electron microscope in the vicinity of a cross section of a cut magnetic film.

FIG. 3 is a schematic view of a cracking resistance determination standard with an electron microscope in the vicinity of a cross section of a cut magnetic film.

FIG. 4 is a schematic view of a cracking resistance judgment standard with an electron microscope in the vicinity of a cross section of a cut magnetic film.

[Explanation of symbols]

1 Magnetic layer cross section 2 Magnetic layer surface 3 base film 4 cracks

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-2-270116 (JP, A) JP-A-5-266458 (JP, A) JP-A-62-241133 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B 5/702

Claims (2)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of magnetic powder and a binder formed on a non-magnetic support, comprising a low-molecular compound having (1) an alkyl group as a side chain as a component of the binder. Molecular diols and more than 85 mol% adipic acid and 1
10 to 50% by weight of an aliphatic polyester diol (A) obtained by reacting with a mixture of 5-sodium sulfoisophthalic acid within 5 mol%, a low molecular diol and 70
A mixed polyester diol with 90 to 50 wt% of an aromatic polyester diol (B) having a glass transition point of −3 ° C. or higher, which is obtained by reacting phthalic acid in an amount of more than mol% and adipic acid in an amount of 30 mol% or less; (2) A sodium sulfonate base obtained by reacting a chain extender containing 0.05 to 1.0% by weight of triol with respect to the solid content of a raw material for producing a polyurethane resin, and (3) an organic diisocyanate. / Or content of carboxyl group is 0.001 ~
The magnetic recording medium according to claim 1, further comprising a polyurethane resin having a temperature of 20 to 60 ° C. that exhibits a maximum loss elastic modulus of 0.2 mmol / g. 2. The magnetic recording medium according to claim 1, further comprising, as a component of the binder, a curing agent in a ratio of 5 to 40 parts by weight with respect to 100 parts by weight of the polyurethane resin.