JPH11217539A - Binder resin for magnetic recording medium and coating material composition for magnetic recording medium and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium excellent in running durability, electromagnetic transduction characteristics, or the like, by using a binder good in dispersibility and filling properties of magnetic particles, abrasion and heat resistances, or the like. SOLUTION: The molecular weight distribution of a polyurethaneurea resin is <=6 in the polyurethaneurea resin for a magnetic recording medium comprising (A) a diisocyanate, (B) a high-molecular weight polyol having 500-20,000 number- average molecular weight, (C) a compound containing two primary amino groups or secondary amino groups and at least one or more hydroxyl groups in the molecule and, as necessary, (D) a glycol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder resin, a paint and a magnetic recording medium for a magnetic recording medium such as a magnetic tape and a magnetic disk obtained by using a binder having excellent properties. More specifically, as a resin component of a coating layer such as a magnetic layer, an anchor coat layer, and a back coat layer provided on a nonmagnetic support, a thermoplastic polyurethane urea resin having a specific molecular weight distribution and having a hydroxyl group in a side chain. And a coating material for a magnetic recording medium and a magnetic recording medium containing the resin.

[0002]

2. Description of the Related Art Magnetic tapes, which are general-purpose magnetic recording media,
A floppy disk is made by dispersing needle-shaped magnetic particles having a major axis of 1 μm or less together with additives such as a dispersant, a lubricant and an antistatic agent in a binder solution to form a magnetic paint, and applying this to a polyethylene terephthalate film. It is made.

[0003] The properties required for the binder of the magnetic layer include the dispersibility of magnetic particles, the filling property, the orientation, the durability of the magnetic layer, the abrasion resistance, the heat resistance, the adhesion to the non-magnetic support and the like. And binders play a very important role. As a binder for the magnetic layer, a mixture of an adipate-type or polycaprolactone-type polyurethane resin and nitrocellulose or a PVC-based copolymer has been mainly used.

In Japanese Patent Publication No. 58-41565, it is effective to use a polyurethane resin containing a metal sulfonate in the molecule as a binder in order to improve the dispersibility of magnetic particles and the filling property in a magnetic layer. It is stated that there is.

[0005] In a coating type magnetic recording medium, coating layers such as a magnetic layer, an anchor coat layer and a back coat layer provided on a non-magnetic support have improved wear resistance, improved heat resistance, improved adhesion, and improved solvent resistance. For the purpose of imparting properties and the like, a two-pack type using a curing agent in combination is used. As the curing agent, polyisocyanate, epoxy resin, acid anhydride, melamine resin, urea resin and the like are known. In particular, polyisocyanates are widely used in view of reactivity, workability, performance, and the like.

In order to improve the reactivity with a curing agent in a polyurethane resin, a trifunctional or higher functional component such as glycerin, trimethylolpropane or pentaerythritol is used as a chain extender, or these polyfunctional components are used in combination. By using a polymerized polyol, the reaction point of the polyurethane resin is increased. In addition, special fair 4
No. 8856 describes a polyurethane resin containing, as a raw material, a compound containing two primary amines or secondary amines and at least one hydroxyl group as a coating agent for a magnetic recording medium.

[0007]

In a magnetic recording medium, S
In order to improve the / N ratio (signal / ize ratio) and increase the recording density, it is necessary to smooth the surface of the magnetic layer, or to highly fill the magnetic layer with finer magnetic particles and to perform high orientation. There is a need for these and a binder that has good dispersion of magnetic particles is needed. The smoother the surface of the magnetic layer, the higher the friction coefficient and the worse the running property and running durability of the magnetic tape. Therefore, a binder having good durability, abrasion resistance, heat resistance, and adhesion to a non-magnetic support is desired. In addition, with the general use of magnetic tapes, there is a demand for improvements in durability under various environments from low to high temperatures and from low to high humidity. Further, with the thinning of the magnetic layer, there is a demand for significant improvement in physical properties such as strength, elongation, and elastic modulus of the magnetic layer.

In magnetic recording media, magnetic particles having a high coercive force, such as fine magnetic powder and metal magnetic powder, are used to improve the S / N ratio (signal / noise ratio) and increase the recording density. Although layers are highly filled and highly oriented, it is difficult to disperse these magnetic particles with conventional binders. Poor dispersion not only decreases the electromagnetic conversion characteristics but also increases the porosity in the magnetic layer, and the increase in the porosity deteriorates the running durability of the magnetic layer. Introducing a metal sulfonate group into polyurethane is extremely effective in improving the dispersibility of magnetic powder.However, introduction of a metal sulfonate group alone cannot satisfy the demand for sophistication. Not enough for the request.

[0009] In the back coat layer as well as the magnetic layer, improvement in wear resistance is required for improving running durability. In order to increase the toughness and adhesion of the coating layer, a resin and a curing agent are used in combination to form a crosslinked product. In a two-pack type in which a polyurethane resin and a curing agent are used in combination, a method of increasing the branch point of the polyurethane resin by using a trifunctional or more functional component such as glycerin, trimethylolpropane or pentaerythritol in order to improve the crosslinking property is known. . However, when the crosslinking property of the polyurethane resin is enhanced by this method, the molecular weight distribution of the obtained resin is widened, and the danger of gelation during the production of the polyurethane resin is increased.

In the method described in Japanese Patent Publication No. 4-8856 utilizing the difference in the reaction rate of an amino group and a hydroxyl group to isocyanate, a polyurethane urea resin having a high concentration of a hydroxyl group can be obtained. The reaction vessel has a gel attached and the obtained resin has a wide molecular weight distribution. In pigments, such as magnetic particles and carbon black, which are difficult to disperse, when the molecular weight distribution of the binder resin is widened, the dispersibility is significantly reduced. The decrease in dispersibility deteriorates the characteristics of the magnetic recording medium.

In view of the above situation, an object of the present invention is to use a binder having good dispersibility / filling property of magnetic particles, abrasion resistance, heat resistance, etc. to thereby provide excellent running durability and electromagnetic conversion characteristics. To provide a magnetic recording medium.

[0012]

Means for Solving the Problems As a result of intensive studies on the polyurethane resin, the present inventors have reached the present invention. That is, the present invention provides 1) diisocyanate (A), high molecular weight polyol (B) having a number average molecular weight of 500 to 20,000, and a compound containing two primary amino groups or secondary amino groups and at least one hydroxyl group in the molecule. (C) A binder resin for a magnetic recording medium, wherein the molecular weight distribution of the polyurethane urea resin is 6 or less in the polyurethane urea resin for a magnetic recording medium comprising glycol (D) if necessary. 2) The polyurethane urea resin described in 1) above reacts a raw material other than the compound (C) containing two amino groups and hydroxyl groups to obtain an isocyanate-terminated prepolymer, and then converts the prepolymer to two amino groups. A binder resin for a magnetic recording medium, which is added to and reacted with a compound (C) containing a hydroxyl group. 3) A coating composition for a magnetic recording medium, comprising the polyurethane urea resin described in 1) or 2) above. 4) A magnetic recording medium having a coating layer provided on a nonmagnetic support, wherein the coating layer uses the coating composition for a magnetic recording medium described in 1) or 2) above. Medium. It is.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The binder resin for a magnetic recording medium in the present invention is specifically used for forming a magnetic layer, a back coat layer, an anchor coat layer, and a top coat layer provided on a magnetic layer. The magnetic layer may be a two-layer coat containing nonmagnetic particles in the lower layer.

In general, the reactivity between isocyanate groups and amino groups is much faster than in the case of hydroxyl groups. Therefore, in the case of polyurethane urea, the reaction procedure affects the properties of the resulting resin. In particular, when the production unit becomes large, the characteristics of the resin change due to fluctuations in the charging time of the raw materials. Therefore, when this resin is used as a binder resin for a magnetic recording medium, these fluctuations change the properties of the paint and the properties of the resulting magnetic recording medium.

The polyurethane urea resin used in the present invention will be described in detail. The molecular weight distribution of the polyurethane urea resin of the present invention needs to be 6 or less. It is more preferably 5 or less, further preferably 4 or less. When the molecular weight distribution exceeds 6, the viscosity of the coating material increases, the dispersibility of the inorganic particles deteriorates, and a magnetic recording medium having a uniform coating film cannot be obtained. Here, the molecular weight distribution referred to here is a case where the weight average molecular weight is Mw and the number average molecular weight is Mn,
It shows the value of Mw / Mn. Therefore, the molecular weight distribution is 1 or more.

As a method for producing a thermoplastic polyurethane urea resin, a one-shot method and a prepolymer method are known. In the one-shot method, gelation occurs when the amount of the compound (C) containing two amino groups and hydroxyl groups increases. Further, even in a range where gelation does not occur, the obtained polyurethane urea resin has poor solubility in general-purpose solvents, and insolubles are generated and the reaction vessel is contaminated. In the present invention, the polyurethane urea resin used in the present invention uses a prepolymer method in which the polyurethane urea resin is first reacted with a high molecular weight polyol (B) under an isocyanate excess condition, and then reacted with a chain extender. The polyurethane urea resin used in the present invention is obtained by reacting a raw material other than the compound (C) containing two amino groups and hydroxyl groups with isocyanate to obtain an isocyanate-terminated prepolymer obtained by reacting a compound containing two amino groups and hydroxyl groups ( It is characterized by being added to C) and reacted. Isocyanate terminated prepolymer,
When a compound (C) containing two amino groups and a hydroxyl group is added and reacted, insolubles are generated or the reaction vessel is contaminated, and the molecular weight distribution of the obtained resin is increased. In the method for producing the polyurethane urea resin used in the present invention,
The solubility of the obtained resin is good, and when dissolved in an organic solvent, it does not contain foreign matter or insoluble matter even if it becomes opaque.

The reaction of the polyurethane urea resin used in the present invention can be carried out by melting the raw materials, but is preferably carried out in an organic solvent. Examples of the solvent include at least one of aromatic hydrocarbons such as toluene and xylene, ketones such as methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, and amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. .

The diisocyanate (A) component of the polyurethane urea resin used in the present invention includes 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate. G, diphenylmethane diisocyanate, m-phenylenediisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4 '
-Biphenylene diisocyanate, 1,5-naphthalenedi isocyanate, 2,6-naphthalenedi isocyanate, 3,3'-dimethyl-4,4'-diisocyanate
G, 4,4'-diisocyanate-to-diphenyl ether,
1,5-xylylene diisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane, 4,4'-diisocyanatocyclohexane, 4,4'-diisocyanatocyclohexyl Methane, isophorone diisocyanate and the like can be mentioned.

The high molecular weight polyol (B) of the polyurethane urea resin used in the present invention has a number average molecular weight in the range of 500 to 20,000. Polyester polyols, polyether polyols, polycarbonate polyols, hydroxyl-containing polyolefins and the like are mentioned, and polyester polyols are preferred. In particular, the polyester polyol desirably contains a metal sulfonate group in the molecule for the purpose of the present invention. As a raw material for introducing the metal sulfonate group, 5-sodium sulfoisophthalic acid and 5-potassium sulfoisophthalic acid are used as raw materials. , Sodium sulfoterephthalic acid, 2-sodium sulfo-1,
Examples thereof include dicarboxylic acids and glycols such as 4-butanediol and 2,5-dimethyl-3-sodiumsulfo-2,5-hexanediol, and 5-sodiumsulfoisophthalic acid and 5-potassiumsulfoisophthalic acid are preferred.

The compound (C) containing two primary amino groups or secondary amino groups and at least one hydroxyl group in the molecule used in the production of the polyurethane urea resin used in the present invention includes, for example, , Ethylenediamine, propylenediamine, hexamethylenediamine,
Addition of one or two molecules of ethylene oxide or propylene oxide to a diamine compound such as xylene diamine or phenylenediamine, wherein each amino group is not tertiary. Alternatively, a single molecule addition product of ethylene oxide or propylene oxide to each amino group of a linear amine such as diethylenetriamine and triethylenetetramine may also be mentioned. Further, an adduct of an amino group to a diepoxy compound is also included.

The amount of the compound (C) containing two primary amino groups or secondary amino groups and at least one hydroxyl group in the molecule is attributed to the compound (C) in the obtained polyurethane urea resin. It is desirable to use such that the hydroxyl group is in the range of 300 to 5000 equivalents / 106 g.

Glycol (D) optionally used in producing the polyurethane urea resin used in the present invention.
Is used to impart characteristics such as abrasion resistance and toughness specific to the polyurethane resin. As a specific 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-pentaneddiol, cyclohexanedimethanol, Neopentyl hydroxypivalate, bisphenol A
And diol compounds such as ethylene oxide adducts and propylene oxide adducts, and bisphenol A hydrogenated ethylene oxide adducts and propylene oxide adducts.

The ratio of each raw material used in the production of the polyurethane urea resin used in the present invention is such that the number of moles of diisocyanate (A) is a, the number of moles of high molecular weight polyol (B) is b, primary amino group or 2 Assuming that the number of moles of the compound (C) containing two primary amino groups and at least one hydroxyl group is c and the number of moles of the glycol (D) is d, it is expressed in the following range. Outside this range, gels are formed and the reaction vessel is contaminated. (B + c + d) / a ≧ 1

The molecular weight of the polyurethane urea resin used in the present invention is 5,000 to 50,000, preferably 10
It is preferably from 000 to 30,000. Molecular weight 50
If it is less than 00, the mechanical strength is insufficient and the molecular weight is 50,000.
If the ratio exceeds the above range, the solution viscosity will increase and the flow characteristics will deteriorate, resulting in a decrease in workability.

In the coating composition for a magnetic recording medium and the magnetic recording medium of the present invention, in addition to the polyurethane urea resin used in the present invention, for the purpose of controlling flexibility, improving cold resistance and heat resistance, etc. It is desirable to add a resin of and / or mix a crosslinking agent. Other resins include polyurethane resins, vinyl chloride resins, cellulosic resins, polyester resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, 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, and an acid anhydride. Among these, a polyisocyanate compound is preferable, and an aliphatic or alicyclic polyisocyanate compound is particularly preferable. And characteristics of the magnetic recording medium.

The ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe ₂ O ₃ and γ-Fe
Mixed crystal of ₂ O ₃ and Fe ₃ O ₄ , γ-F coated with cobalt
Examples include ferromagnetic oxides such as e ₂ O ₃ or Fe ₂ O ₄ and barium ferrite, and ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni. The back coat layer may contain fine particles such as carbon black such as channel carbon and furnace carbon, graphite, silica, talc and calcium carbonate.

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

In the coating resin composition for a magnetic recording medium and the magnetic recording medium of the present invention, a high concentration of O
Includes polyurethane urea resins with narrow molecular weight distribution despite containing H groups. Further, since the binder resin for a magnetic recording medium of the present invention has an OH group at a high concentration, it strongly adsorbs to inorganic fine particles. When a curing agent that reacts with a hydroxyl group is used in combination, a cured coating film having a high crosslinking density can be obtained. As a result, when used as a binder for the magnetic layer, the magnetic layer has a high filling degree and good wear resistance. Since it strongly adsorbs to the inorganic fine particles, when used as a lower binder in the multilayer structure, a coating film with less influence of the solvent of the upper magnetic paint can be obtained. When used as a binder for the back coat layer, a coating film having excellent carbon black dispersibility and low abrasion can be obtained. When used as an anchor coating agent, a coating film having good solvent resistance can be formed.

[0029]

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

Analysis and evaluation of the resin were carried out by the following methods. Molecular weight and molecular weight distribution Waters Gel Permeation Chromatography (Mode
l150-C, hereinafter abbreviated as GPC), using polystyrene as a standard substance, and measuring the weight average molecular weight (Mw) and the number average molecular weight (Mn). The molecular weight distribution was calculated by Mw / Mn. GPC measurement conditions are as follows. Column: KF-802 manufactured by Showa Denko KK Solvent: tetrahydrofuran Solvent flow rate: 1 ml / min Temperature: 30 ° C. Sample concentration: 3 mg / ml Sample injection volume: 100 μl Detector: RI

Curability "Coronate HX" (trimer of hexamethylene diisocyanate) manufactured by Nippon Polyurethane Co., Ltd. is added to the resin solution at a ratio of 10% by weight of the resin so that the polyester film has a thickness of 10 microns after drying. It was applied and dried with hot air at 110 ° C. for 5 minutes. After 10 hours at 20 ° C., methyl ethyl ketone (MEK) / toluene / cyclohexanone = 1
The sample was immersed in a mixed solvent of / 1/1 for 1 hour to determine the solvent-insoluble content.

Synthesis Example 1 100 parts of dehydrated polyester diol (a) having a number average molecular weight of 2,000 described in Table 1 and neopentyl glycol (NPG) were placed in a glass reaction vessel equipped with a thermometer, a stirrer, and a cooling tube. 10 parts, methyl ethyl ketone (ME
K) 50 parts and 50 parts of toluene were charged, and after dissolution,
4'-diphenylmethane diisocyanate (MDI) 6
After adding 1 part and reacting at 70 ° C. for 5 hours, MEK102
, And diluted with 102 parts of toluene to obtain an isocyanate-terminated prepolymer solution. In another reaction vessel, 22.5 parts of N, N'-bis (hydroxypropyl) -m-xylenediamine (MXDA-2PO manufactured by Mitsubishi Gas Chemical) are dissolved in 137 parts of cyclohexanone. .5 parts (90 parts of total prepolymer solution)
%) Was added dropwise over 10 minutes. The reaction was completed by heating at 70 ° C. for 3 hours. The obtained resin solution has a solid concentration of 3
0%, pale yellow and transparent. No foreign substance was found in the solution, and no gel was attached to the reaction vessel. Table 1 shows the analysis and evaluation results of the obtained resin.

Comparative Synthesis Examples 1 and 2 In the same glass reaction vessel as in Synthesis Example 1, a number average molecular weight of 20 was added.
100 parts of dehydrated polyester diol (a)
NPG10 parts, MXDA-2PO 25 parts, MEK15
2 parts, toluene 152 parts and cyclohexanone 152
Parts were charged and dissolved. In Comparative Example 1, 61 parts of MDI were added, and in Comparative Example 2, 51 parts were added and heated to 70 ° C. In Comparative Example 1, gelation occurred 30 minutes after the introduction of MDI. In Comparative Example 2, the reaction was completed by heating at 70 ° C. for 10 hours. The solution of Comparative Example 2 was opaque, and the presence of foreign matter was recognized. Also, gel was found to adhere to the reaction vessel. Analysis of the obtained resin
Table 2 shows the evaluation results.

Comparative Synthesis Example 3 In the same glass reaction vessel as in Synthesis Example 1, a number average molecular weight of 20 was prepared.
100 parts of dehydrated polyester diol (a)
10 parts of NPG, 50 parts of MEK and 50 parts of toluene were charged, 61 parts of MDI was added after dissolution, and the mixture was reacted at 70 ° C. for 5 hours, and diluted with 102 parts of MEK and 102 parts of toluene.
An isocyanate-terminated prepolymer solution was obtained. To this prepolymer solution, a solution of MXDA-2PO / cyclohexanone = 25 parts / 152 parts was dropped over 10 minutes.
The reaction was completed by heating at 70 ° C. for 3 hours. The resulting solution was opaque and gel adhesion was observed in the reaction vessel. Table 2 shows the analysis and evaluation results of the obtained resin.

Synthetic Examples 2 to 5 In the same manner as in Synthetic Example 1, an isocyanate-terminated prepolymer was added to an amine to obtain a polyurethane urea. However, the raw materials used were the compounds shown in Table 1. The composition of the solvent was MEK / toluene / cyclohexanone = 1/1/1 wt as in Synthesis Example 1. Table 1 shows the appearance of the solution, contamination of the reaction vessel, and the results of analysis and evaluation of the obtained resin.

Comparative Synthesis Examples 4 and 5 Comparative Synthesis Examples 4 and 5 were carried out using the same raw materials as in Synthesis Examples 4 and 5. However, in Comparative Synthesis Examples 4 and 5, the amine solution was added to the isocyanate-terminated prepolymer solution as in Comparative Synthesis Example 3. In each of the comparative synthesis examples, foreign substances were present in the solution, and the gel adhered to the reaction vessel. Table 2 shows the analysis and evaluation results of the obtained resin.

Comparative Synthesis Example 6 In the same reaction vessel as in Synthesis Example 1, a dehydrated polyester diol (a) 1 having a number average molecular weight of 2,000 as shown in Table 1 was placed.
00 parts, neopentyl glycol (NPG) 10 parts, methyl ethyl ketone (MEK) 50 parts and toluene 50
After dissolution, 55 parts of 4,4′-diphenylmethane diisocyanate (MDI) was added and reacted at 70 ° C. for 5 hours, followed by dilution with 86 parts of MEK and 86 parts of toluene to obtain a prepolymer solution having an isocyanate terminal. In another reaction vessel, 9 parts of glycerin was dissolved in 122 parts of cyclohexanone, and 393.3 parts of the above prepolymer solution (90% of the total prepolymer solution) was added dropwise to this solution over 10 minutes. The reaction was completed by heating at 70 ° C. for 5 hours. The resulting resin solution had a solid content of 30% and was pale yellow and transparent. No foreign matter was found in the solution, but there was gel adhesion to the reaction vessel. Table 2 shows the analysis and evaluation results of the obtained resin.

[0038]

[Table 1]

[0039]

[Table 2]

In the table, PES-1: I / DSN / NPG / CHDM / EG = 97/3/70/20/10 molar ratio Number average molecular weight 2000 However, I: isophthalic acid DSN: 5-sodium sulfoisophthalic acid NPG: neo Pentyl glycol CHDM: 1,4-cyclohexanedimethanol EG: Ethylene glycol PES-2: AA / DSN / HD / NPG Number average molecular weight 2000 AA: Adipic acid HD: 1,6-hexanediol NPG: Neopentyl glycol MXDA- 2PO: N, N-bis (2-hydroxypropyl) -m-xylenediamine manufactured by Mitsubishi Gas Chemical Company MXDA-2EO: N, N'-bis (2-hydroxyethyl) -m-xylenediamine manufactured by Mitsubishi Gas Chemical Company DAPOL : 1,3-diamino-2-propanol MDI: 4,4'-diphenylmethane diisocyanate Reaction order A: Add NCO-containing prepolymer to amine (In Comparative Synthesis Example 6, add NCO-containing prepolymer to glycerin solution Added) B: charged reactants in batch, added MDI C: amine addition to the NCO-containing prepolymer

Example 1 A composition having the following composition ratio was placed in a ball mill and dispersed for 24 hours, and then a polyisocyanate compound, Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a curing agent.
Parts, 0.1 part of stearic acid and 0.1 part of butyl stearate as a lubricant were added and 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, and dried while applying a magnetic field of 2000 gauss.
The magnetic layer was passed through a calender roll at a linear pressure of 200 kg / cm to smooth the surface of the magnetic layer to prepare a magnetic tape. The obtained magnetic tape was left at 60 ° C. for 1 day and slit to イ ン チ inch. The surface gloss of the magnetic layer before calendering and the squareness ratio of the obtained tape were measured. Further, the adhesion between the magnetic layer and the base film and the filling property of the magnetic layer were measured by the methods described below. In addition, one commercially available VTR deck
The state of wear of the magnetic layer after running 100 times at 0.40 ° C. was observed. The results are shown in Table-3.

Solution of polyurethane resin obtained in Synthesis Example 1 10 (30% solution of MEK / toluene / cyclohexanone = 1/1/1) Magnetic powder (cobalt-coated ferrite BET 45 m 2 / g) 15 Cyclohexanone 8 Toluene 8 MEK 8 Alumina (average particle size 0.05μ) 0.5

Adhesive property of magnetic layer A cellophane tape made of Nichiban is adhered to the magnetic layer, and a polyester film is applied at a pulling speed of 100 mm / min.
It was bent at 0 degree and peeled off. The measurement temperature was 20 ° C.

Magnetic Layer Filling Property A precisely weighed magnetic tape (weight W1) was immersed in silicone oil for 30 minutes. After wiping off the silicone oil adhering to the surface of the magnetic tape, the weight (W
2) was precisely weighed. After wiping the magnetic layer with a solvent, the film was precisely weighed (W3) to determine the weight of the magnetic layer. The weight increase due to the silicone oil immersion with respect to the weight of the magnetic layer, that is, (W2-W1) / (W1-W3) was determined.
Silicone oil penetrates into the voids in the magnetic layer, so the weight increase due to silicone oil immersion (expressed as a percentage)
Is smaller, the filling rate of the magnetic layer is higher.

Examples 2 to 4 and Comparative Examples 1 to 6 In the same manner as in Example 1, except that the polyurethane urea resins shown in Tables 3, 4, 5 and 6 were used instead of the polyurethane urea resin used, Created a tape. The characteristics are shown in Tables 3, 4, 5, and 6.

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

[Table 6]

In all of Tables 3, 4, 5, and 6, VAGH: PVC copolymer manufactured by Union Carbide Co., Ltd. Abrasion state of magnetic layer ○: no damage, Δ: little damage is observed, ×: scratched PET film appear.

Example 8 The following composition containing the polyurethane urea resin obtained in Synthesis Example 1 as a binder was coated on the opposite side of the magnetic layer of the magnetic tape obtained in Example 2 to a thickness of 0. The solution was applied to a thickness of 5 μ to form a back coat layer.

10 parts of polyurethane urea solution of Synthesis Example 1 (solid content: 30%, MEK / toluene / cyclohexanone = 1/1/1 solution) 2 parts of carbon black (Conductex SC manufactured by Columbia Carbon Co.) 3 parts of calcium carbonate (Shiraishi Industrial Company Homocal D) Methyl ethyl ketone 10 parts Coronate HX 0.3 parts

The obtained magnetic tape was run 100 times at 10.40 ° C. on a commercially available VTR deck, and the state of abrasion of the back coat layer and the coefficient of kinetic friction with respect to the stainless steel pole were measured to determine changes before and after the running test. The results are shown in Table-7.

Comparative Example 7 In the same manner as in Example 8, except that the resin obtained in Comparative Example 2 was used instead of the resin of Synthesis Example 1 used as a binder for the back coat layer in Example 8, Was formed. Evaluation was performed in the same manner as in Example 8. The results are shown in Table-7.

Comparative Example 8 In the same manner as in Example 8, except that the resin obtained in Comparative Example 3 was used instead of the resin of Synthesis Example 1 used as a binder for the back coat layer in Example 8, Was formed. Evaluation was performed in the same manner as in Example 8. The results are shown in Table-7.

[0056]

[Table 7]

Abrasion state of back coat layer ：: no damage, Δ: scratch is recognized but little, ×: scratched PET film is visible. Dynamic friction coefficient change Dynamic friction coefficient ratio of the back coat layer of the magnetic tape to the stainless steel pole before the running test and after 100 running tests

Example 9 The following composition using the polyurethaneurea resin obtained in Synthesis Example 4 as a binder was applied on a 15 μm polyethylene terephthalate film so as to have a thickness of 1.5 μm after drying, and anchored. After forming a coat layer and drying, continuously,
The magnetic paint obtained in Example 2 was applied on the anchor coat layer in the same manner as in Example 1, and orientation treatment and drying were performed. After the obtained magnetic tape was subjected to the same aging treatment as in Example 1, in addition to the same evaluation as in Example 1, the 60-degree gloss of the anchor coat layer and the surface roughness of the magnetic layer before calendering were measured. The results are shown in Table-8. The second embodiment corresponds to the case where the anchor coat of the ninth embodiment is not provided.
The surface roughness of the magnetic layer before calendering is 0.018μ.
Met.

Polyurethane urea solution of Synthesis Example 10 10 parts (solid content concentration 30%, MEK / toluene / cyclohexanone = 1/1/1 solution) Carbon black 4.5 parts (Conductex SC manufactured by Columbia Carbon Co.) Methyl ethyl ketone 20 parts Millionate MR 1 part (Nippon Polyurethane Co. polyisocyanate)

Comparative Example 9 In the same manner as in Example 9, except that the resin obtained in Comparative Example 4 was used instead of the resin used in Example 9 as a binder for the anchor coat layer, the back coat layer was formed. Was formed. Evaluation was performed in the same manner as in Example 9. The results are shown in Table-8.

[0061]

[Table 8]

Abrasion state of magnetic layer ：: no damage, Δ: scratch is recognized but little, ×: scratched PET film is visible.

[0063]

As is clear from the examples and comparative examples, the polyurethane urea resin used in the present invention not only contains a hydroxyl group at a high concentration, but also has a narrow molecular weight distribution, excellent solvent solubility, magnetic particles and carbon particles. Excellent black dispersibility.
Therefore, the coating layer using a polyurethane urea resin as a binder is not only excellent in pigment dispersibility and filling property, but also excellent in running durability and the like.

Claims (4)

[Claims] 1. A diisocyanate (A), a high molecular weight polyol (B) having a number average molecular weight of 500 to 20,000, and a compound (C) containing two primary or secondary amino groups and at least one hydroxyl group in the molecule. A) a binder resin for a magnetic recording medium, wherein the molecular weight distribution of the polyurethane urea resin is at most 6 in the polyurethane urea resin for a magnetic recording medium, which comprises glycol (D) if necessary. 2. The polyurethane urea resin according to claim 1, wherein a raw material other than the compound (C) containing two amino groups and a hydroxyl group is reacted to obtain an isocyanate-terminated prepolymer. A binder resin for a magnetic recording medium, characterized by being added to and reacted with the compound (C) containing an amino group and a hydroxyl group. 3. A coating composition for a magnetic recording medium, comprising the polyurethane urea resin according to claim 1 or 2. 4. A magnetic recording medium in which a coating layer is provided on a nonmagnetic support, wherein the coating layer uses the binder resin for a magnetic recording medium according to claim 1 or 2. recoding media.