JPS61104325A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a magnetic layer which is excellent in coating property, thermal stability, etc. by incorporating an urethane resin derived from polyether polyester polyol contg. an arom. residue into a binder of the prescribed layer such as magnetic layer to be provided on a substrate. CONSTITUTION:The urethane resin derived by the condensation of the arom. residue-contg. polyether polyester polyol by the condensation of polyether polyol such as the addition product of ethylene oxide of bisphenol A, arom. dibasic acid such as terephthalic acid or isophthalic acid and polytetramethylene glycol and diphenylmethane diisocyanate, etc. is used as the binder for forming the prescribed layer, more particularly the magnetic layer 2 on the substrate, more particularly hydrophobic substrate 1 consisting of polyethylene terephthalate, etc. The above-mentioned resin added with non-magnetic powder is used for forming a back coat layer 3 or an overcoat layer 4 on the layer 2. The magnetic recording medium having excellent heat resistance, moisture resistance, etc. is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media are manufactured by applying a magnetic paint containing magnetic powder, binder resin, etc. onto a support and drying it.

It is well known that a urethane resin is used as a binder resin in the magnetic layer of such a magnetic recording medium, for example. Conventionally known urethane resins are synthesized from high molecular weight polyols, diisocyanates, chain extenders, and crosslinking agents (used if necessary). Known high molecular weight polyols that can be used include the following (1) to (5).

(1) High molecular weight polyol whose main component is ester of adipic acid.

(2), polycaprolactone diol.

(3) A high molecular weight polyol whose main component is an ester of an aromatic carboxylic acid such as terephthalic acid or isophthalic acid.

(4) High molecular weight polyols whose main component is polyether such as polyethylene glycol, polypropylene glycol, and polybutylene glycol.

(5) Polycarbonate type high molecular weight polyol.

However, all polyurethanes derived from the above-mentioned high molecular weight polyols have the following drawbacks:
It wasn't something I was satisfied with.

That is, the urethane resin derived from the aliphatic polyester polyol in the above (1) and the urethane resin derived from the polycafrolactone diol in the above (2) have insufficient heat resistance and moisture resistance, and Adhesion to hydrophobic supports (especially polyethylene terephthalate substrates) is insufficient. In addition, the urethane resin derived from the polycarbonate-type high molecular weight polyol described in (5) above has relatively good hydrolysis resistance, but has insufficient thermal durability due to the large degree of freedom of segments. . Also, (4) above
Urethane resins derived from polyether-based high-molecular-weight polyols have good hydrolysis resistance, but their mechanical properties are unsatisfactory, and their heat resistance is insufficient and their thermal properties tend to deteriorate. . Furthermore, the urethane resin derived from the aromatic carboxylic acid ester (3) above has better adhesion to a support, heat resistance, and moisture resistance than the other urethane resins mentioned above, but has a high melting point. The calenderability is relatively poor, the solvent solubility is insufficient and precipitation occurs, and the compatibility with other urethane resins is poor, resulting in poor workability.

The object of the present invention is to provide a predetermined layer such as the above-mentioned magnetic layer with excellent adhesion to the base, good physical properties of the resin, heat resistance, moisture resistance, hydrolysis resistance, An object of the present invention is to provide a magnetic recording medium with improved durability.

28 Structure and effects of the invention, namely, the magnetic recording medium according to the present invention is a magnetic recording medium in which a magnetic layer is provided on a substrate, in which a predetermined layer provided on the substrate contains aromatic residues. It is characterized by containing a urethane resin derived from a polyether polyester polyol containing.

According to the present invention, the urethane resin used as a binder resin for a predetermined layer (especially a magnetic layer) on a substrate (especially a hydrophobic support such as polyethylene terephthalate) contains both a polyether component and a polyester component. Moreover, since it is derived from a polyol that also has aromatic residues in its molecule, it can effectively exhibit the features of each component and compensate for the shortcomings of each component. As a result, the above-mentioned object of the present invention is more than fully achieved. In addition, in the urethane resin of the present invention, the aromatic polyester component tends to increase the melting point, but this may be caused by partially copolymerizing an aliphatic ester such as adipic acid ester with the acid component in the polyester, or This problem can be sufficiently resolved by reducing the crystallinity by using long-chain polyether as the alcohol component.
This improves the thermal properties and solubility of the urethane resin.

The method for producing the urethane resin according to the present invention will be explained below.

Usable polyether polyester polyols can basically be synthesized from the following three components (a) to (C).

(a), polytetramethylene glycol (PTMEG)
.

Structural formula: HO+(CH2i0+-=H (however, n=l~
50, preferably a real number from 4 to 40. ) (b) A diol having a molecular weight of 1000 or less, which is obtained by adding an oxide such as ethylene oxide or propylene oxide to a phenolic hydroxyl group.

For example, the ethylene oxide adduct of bispheno-)LEA with the following structural formula (BPA-EO)0-+ CHt
CHz O+TH (However, m and n are each real numbers of 1 or more, and (m+n
)≦20. ) (C), aromatic polybasic acid.

Examples include terephthalic acid, orthophthalic acid, and isophthalic acid.

In addition to the above, the following polyols, diols, and polybasic acids can also be used.

H-';-OCHz CH2hOH OR3 I H-(-OCHCzh OH CH3CH2-OH CH*CHCHzCHzOH (1,3-butanedi■ OH ol) HOCH2CH2CH2CH20H (1,4-butanediol) Other ordinary diols OOH 0 3H urethane resin When conventional glycols are used during synthesis, the surface smoothness of the layer is not sufficient.
In particular, the performance of the videotape, ie, the image quality and abrasion resistance (durability), are not satisfactory. Moreover, conventional urethane resins derived from glycols have poor adhesion to substrates such as polyethylene terephthalate, and in some cases an intermediate layer or undercoat layer is required between the substrate and the magnetic layer to improve adhesion. It becomes necessary. However, in the present invention, when a urethane resin is obtained, if a tertiary amine type polyhydric alcohol represented by the following general formula is used as a low molecular weight diol, dispersibility will be improved and surface smoothness will be improved. A magnetic recording medium with improved adhesion to the substrate and excellent durability can be obtained.

General formula: % formula % (However, R1 and R2 are alkylene groups, R3 is an alkyl group or an aryl group. In particular, to improve adhesive strength,
Preferably, R3 is an aryl group. ) Specific examples of such low molecular weight diols are as follows.

CH3CH2N +CHZ CHZ OH) zCH:
ICHzN-G-CHzCHCR3) 2) Next, using each of the above-mentioned components, such as the compounds +a), (b), and (C1), an aromatic residue-containing polyether polyester polyol is prepared according to a conventional synthesis method. The weight average molecular weight of this polyether polyester polyol is preferably from 500 to 5,000.
It is more preferable to set it to 3000. Four types of the obtained aromatic group-containing polyether polyester polyols (A,
B, C, 'D) are shown in Table 1 below.

Table 1 In this way, a polyether polyester polyol having a weight average molecular weight of about 2000 is obtained.

Polyether polyester polyurethane was synthesized from these polyols according to Synthesis Example 1 shown below.

(Synthesis Example 1) The gas in a reactor equipped with a stirrer and a reflux condenser was replaced with nitrogen gas, 300 parts by weight of methyl ethyl ketone (hereinafter simply referred to as "parts") was put into the reactor, and , polyether polyester polyol (A) 165.0
86.0 parts of diphenylmethane diisocyanate 0.03 parts of dibutyltin dilaurate were added,
The reaction was carried out at 80°C for 2 hours. 43.2 parts of phenyldiethanolamine and 400 parts of methyl ethyl ketone were added to this solution, and the reaction was further carried out at 80°C for 1 hour. 5.8% of 3-methylpentane-1,3゜5-triol was added to the resulting solution.
of the mixture was added, and the mixture was reacted at 80°C for 1 hour.

The thermoplastic polyurethane solution thus obtained had a nonvolatile content of 30.2 wt% and a viscosity of 13,100 cps/25°C.
and molecular weight M by GPC (in tetrahydrofuran) = 7,9000, East = 15,000, Yes/No = 5.4,
The softening temperature was 66°C.

In the same manner as Synthesis Example 1, various polyurethanes according to Synthesis Examples 2 to 10 were synthesized as shown in Table 2 below (however,
Configuration examples 8 to 10 are comparative examples).

(Left below) Here, PEP type (aromatic polyester polyether)
are those of the present invention (corresponding to Synthesis Example 1.3.4.5.6), PC system (corresponding to Synthesis Example 8), PCL system (corresponding to Synthesis Example 7), and 1.4BA system (Synthesis Example 9). .10) is for comparison. Synthesis Examples 9 and 10 were comparative examples in which a conventional diol was used as a low molecular weight diol and a diol of the present invention having particularly good adhesiveness was used.

In the above, usable polyisocyanates include tolylene diisocyanate (TDI) (2,4-TDI, 2.
6-TDI), dimer of 2,4-tolylene diisocyanate, xylylene diisocyanate (XD■), metaxylylene diisocyanate (MXDI), naphthylene-1°5-diisocyanate (NDI), o-tolylene diisocyanate ( TODI) and adducts of these isocyanates with active hydrogen compounds, and the average molecular weight thereof is preferably in the range of 100 to 3,000. As aliphatic polyisocyanate that can be used, hexamethylene diisocyanate (HMD I)
, lysine isocyanate, trimethylhexamethylene diisocyanate (THDI), isophorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate (H+zMDI), and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a weight average molecular weight of 100 to 3.000 are preferred.

In addition, other known urethane resins may be used in combination with the above-mentioned urethane resins as the binder resin. Further, if a phenoxy resin and/or a vinyl chloride copolymer is also contained, the dispersibility of the magnetic powder will be improved and its mechanical strength will be increased. However, if only the phenoxy resin and/or the vinyl chloride copolymer is used, the layer becomes too hard, but this can be prevented by containing polyurethane, and the adhesion to the support or base layer is improved.

Phenoxy resins that can be used include polymers obtained by polymerizing bisphenol A and epichlorohydrin;
It is expressed by the following general formula.

(However, n. 82 to 13) For example, PKHClPKHH manufactured by Union Carbide
, PKHT, etc.

Further, as the above-mentioned vinyl chloride copolymers that can be used, there are those represented by the general formula: In this case, the molar ratio derived from l and m in is 95-50 mol% for the former unit and 5-50 mol% for the latter unit.

Further, X represents a monomer residue copolymerizable with vinyl chloride, and represents at least one member selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like. (l
The degree of polymerization expressed as +m) is preferably from 100 to 6
If the degree of polymerization is less than 100, the magnetic layer etc. will become sticky and if it exceeds 600, the dispersibility will deteriorate.

The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a vinyl chloride-vinyl acetate copolymer (hereinafter referred to as "vinyl acetate").
"vinyl chloride-vinyl acetate copolymer". ). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, etc. Among the copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the vinyl chloride-vinyl acetate copolymers include rlAGHJ, rVYHHJ, manufactured by Union Carbide,
rVMcHJ, “Esretsu A” manufactured by Block Chemical Co., Ltd.
, "S-LEC A-5", "S-RESOC C", "S-LEC M", "Denkabinir 10" manufactured by Denki Kagaku Kogyo Co., Ltd.
0OGJ, Denkabinir 100OWJ, etc. can be used.

In addition to the above, cellulose resins can be used as the binder resin, such as cellulose ethers, cellulose inorganic acid esters, cellulose organic acid esters, and the like. As the cellulose ether, methyl cellulose, ethyl cellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used.

Further, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred.

In addition to the binder resins mentioned above, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used as binder resins for the layers constituting the magnetic recording medium of the present invention.

The thermoplastic resin has a softening temperature of 150°C or less, a weight average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 200 to 2.000, such as acrylic acid ester-acrylonitrile copolymer, Acrylic ester-vinylidene chloride copolymers, acrylic ester-styrene copolymers, etc. are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Moreover, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, urea resin,
These include melamine resin, alkyl resin, etc.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, there are maleic anhydride type, urethane acrylic type, polyester acrylic type, etc.

The layer containing the above-mentioned urethane resin according to the present invention as a binder resin is, for example, the magnetic layer 2 on the support 1, as shown in FIG. A BC layer 3 is provided on the surface opposite to the magnetic layer 2 (the BC layer may or may not be provided).

The magnetic powder used for the magnetic layer 2, especially the ferromagnetic powder, includes T-F+, O=, Co-containing r-FezO*, Fe
Iron oxide magnetic powder such as 3O4, Go-containing Fe, 04; Fe
, Ni, Co, Fe-Ni-Co alloy, Fe-M
n-Zn alloy, Fe-Ni-Zn alloy, Fe-Co
-Ni-Cr alloy, Fe-Co-Ni-p alloy,
Examples include metal magnetic powders containing Fe, Ni, Co, etc. as main components, such as Co--Ni alloys.

Here, the specific surface area of the magnetic powder of magnetic layer 2 is 30 rd / g.
By making the particle size r or more (preferably by reducing the particle size), the reproduction output and S/N ratio of the medium can be significantly improved. If the specific surface area of this magnetic powder is made larger than necessary, poor dispersion will occur, so the upper limit is set at 100 rd/gr.
It is desirable to do so.

Furthermore, known dispersants (for example, lecithin), abrasives (for example, fused alumina), etc. may be added to the magnetic layer 2.

Examples of abrasives that can be added include α-A12O3 (corundum), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. . These abrasives have an average particle diameter of 0.05 to 5μ, particularly preferably 0.1 to 2μ.
It is. Further, conductive carbon black or light-shielding carbon blank may also be added. As the conductive carbon blank, for example, Conductex 975 (specific surface area 250
m7g, particle size 24mμ), Conductex 900 (
Specific surface area 125 nf/g, particle size 27 mμ), Cabot Vulcan
C-72 (specific surface area 254 rr?/g, particle size 30 mμ
), Raven 1040.420, #4 manufactured by Mitsubishi Kasei Corporation
There is a 4th prize.

A light-shielding carbon blank may also be used, and examples of such a light-shielding carbon blank include Laben 2000 (specific surface area: 190 = /
g, particle size 18m, cr), 2100.1170.10
00, #100, #75, #40 manufactured by Mitsubishi Kasei Corporation
, #35, #30, etc. can be used. Carbon black preferably has a particle size of 20 to 30 mμ, preferably 21 to 29 mμ, and its oil absorption is 90 ml!
(D B P ) /100 g or more is desirable because it facilitates formation of a striated structure and exhibits higher conductivity.

The non-magnetic powder contained in the BC layer 3 is as follows:
Carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Ft403, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide,
Examples include those made of calcium carbonate and the like, preferably carbon black (especially conductive carbon blank) and/or titanium oxide. If these non-magnetic powders are included in the BC layer, the surface of the BC layer can be appropriately roughened (matted) to improve its surface properties, and in the case of carbon blanks, it can be made to impart conductivity to the BC layer. Provides antistatic effect. It is advantageous to use a carbon blank and other non-magnetic powder in combination, as it can improve surface properties (stabilize running properties) and improve conductivity. Further, the urethane resin of the present invention may be used as the binder resin of the BC layer 3.

Further, the magnetic recording medium shown in FIG. 1 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may not be provided with an undercoat layer (not shown). Same below).

In addition, the material of the support 1 includes plastics such as polyethylene terephthalate and polypropylene, AI, and Zn.
Metals such as glass, B N % Si carbide, ceramics such as porcelain and earthenware, etc. are used.

Incidentally, when forming the magnetic layer and BC layer by coating, it is desirable to add a predetermined amount of polyfunctional isocyanate as a crosslinking agent to each coating material. Examples of such crosslinking agents include, in addition to polyfunctional polyisocyanates, triphenylmethane triisocyanate, tris-(p-isocyanate phenyl) neophosphite, polymethylene polyphenylisocyanate, and the like.

FIG. 2 shows other magnetic recording media.
A 00 layer 4 is provided on the magnetic layer 2 of the illustrated medium.

This 00 layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. This 00 layer 4 may also contain the urethane resin of the present invention. The surface roughness of the 00 layer 4 is Ra ≦0.01 mμ, Rmax≦0.13 mμ, especially in relation to color S/N.
It is better to In this case, the surface roughness of the support l is Ra
It is preferable to set ≦0.01 mμ, Rmax≦0.13 mμ, and use a smooth support 1.

FIG. 3 shows a magnetic recording medium configured as a magnetic disk, with magnetic layers 2.00 similar to those described above on both sides of the support 1.
A layer 4 is provided respectively.

E, Example Hereinafter, the present invention will be explained with reference to specific examples.

After dispersing the ingredients shown in Table 4, apply 1 m of this magnetic paint.
After filtration with a μ filter, 5 parts of polyfunctional isocyanate was added, coated on a support with a reverse roll coater to a thickness of 5 μm, supercalendered, slit into 2 inch widths, and videotape (each example, comparative (corresponding to the example number). However, the numbers after the second column of Table 3 represent parts by weight, and "actual" after No. 241111 represents an example, and "ratio" represents a comparative example.

(Left below) The following measurements were made on the videotapes from each side described above.

Chroma S/N: Color Video Noise Meter
Measured using 925D/IJ.

Lumi S/N: RF output at 4MHz using the same VTR deck for measuring RF output.
The output was measured, and after 100 playbacks, it showed a value that was lower than the initial output. (Unit: dB).

Glossiness: After dispersion, apply the magnetic coating liquid onto a glass plate using an applicator with a gap thickness of 30mm, and after drying, the gloss is 606.
The reflective glossiness of the sample was measured using a glossmeter.

Adhesiveness 2 A commercially available adhesive tape was adhered to the magnetic layer, and the tape was then peeled off to compare the peeling state of the magnetic layer. In addition, the substrate on the side opposite to the magnetic layer of the magnetic tape was strongly rubbed, and the state in which the magnetic layer peeled off from the substrate was compared.

Table 4 shows the performance of each example videotape.

(The following is a blank space) From the above results, it can be seen that in the examples in which the magnetic layer was formed based on the present invention, the tape performance was significantly improved.

Next, we examined the content ratio of the polyether polyester polyol component in the urethane resin used, and the results shown in FIG. 4 were obtained.

Further, the results shown in FIG. 5 were obtained for Br/8m (square ratio).

From these results, it can be seen that in terms of glossiness, the glossiness is improved (that is, the dispersibility is good) when the polyol component is 40% by weight or more. Further, it can be seen that Br/8m increases when the polyol component is 55% by weight or more. Therefore, the above polyol component is 4% in the urethane resin.
It can be said that the content is preferably 0% by weight or more, and more preferably 55% by weight or more.

Regarding the polyol component itself, results as shown in FIG. 6 were obtained. From now on, as a low molecular weight diol, the third
It can be seen that the still durability is improved in the case of the polyol obtained using the grade amine thread alcohol.

It also shows that the higher the content of aromatic diol, the lower the decrease in output during still durability.

Furthermore, it was determined through the following test that the resin of the present invention has excellent heat resistance and moisture resistance. It can be seen that the decrease in tensile strength is low in the resin of the present invention.

Goods 1: 5 parts of trifunctional isocyanate is added to 100 parts of polyurethane resin solid content to prepare a film of resin alone, and 6
The retention rate of tensile strength was measured over time at 0°C and 90% constant temperature (measurement humidity: 25°C).

0 7 days later 14 days later Resin of Synthesis Example 1 100 95 92 (PE
PA) The present invention (film production conditions) After curing in a dryer at 80°C for 11 hours, it was cured for 3 days at 20°C and 60% to obtain a sample with a film thickness of 30μ, and the measurement was performed according to JIS K- Measured in accordance with 6301.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and include FIG.
Figures 2 and 3 are enlarged cross-sectional views of a portion of the magnetic tape from each side, and Figures 4 and 5 show changes in gloss and squareness ratio depending on the content ratio of the polyether polyester polyol component, respectively. The graph is . In addition, in the symbols used in the drawings, 2----
---・--Magnetic layer 3------Back coat layer (BC layer) 4-
・-・-・-・Overcoat layer (00 layer). Agent Patent Attorney Hiroshi Aisaka 1st degree ('/,) 80 5th figure 0.90 0.60 Drip content ratio fe (1t°/,)

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer is provided on a substrate, a predetermined layer provided on the substrate contains a urethane resin derived from a polyether polyester polyol containing an aromatic residue. A magnetic recording medium characterized by: