JPH0568006B2 - - Google Patents

Description

[Detailed description of the invention]

B. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks. B. Prior Art In general, magnetic recording media are manufactured by applying a magnetic paint containing magnetic powder, binder resin, etc. onto a support and drying it. Thus, it is well known to use urethane resin as a binder resin for, for example, a magnetic layer of a magnetic recording medium. 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) A high molecular weight polyol whose main component is an ester of adipic acid. (2) Polycaprolactone diol. (3) High molecular weight polyols whose main component is esters of aromatic carboxylic acids such as terephthalic acid and 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 of the polyurethanes derived from the above-mentioned high molecular weight polyols had the following drawbacks and were not satisfactory. That is, the urethane resin derived from the aliphatic polyester polyol (1) above and the urethane resin derived from polycaprolactone diol (2) above have insufficient heat resistance and moisture resistance, and are hydrophobic. The adhesion to the polyethylene support (especially polyethylene terephthalate substrate) is not sufficient. 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 the segments. . In addition, the urethane resin derived from the polyether-based high molecular weight polyol in (4) above has good hydrolysis resistance, but
The mechanical properties are not satisfactory, the heat resistance is insufficient, and the thermal properties tend to deteriorate. Furthermore, the urethane resin derived from the aromatic carboxylic acid ester in (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. C. Purpose of the Invention The purpose of the present invention is to provide a predetermined layer such as the magnetic layer described above with excellent adhesion to the base, good physical properties of the resin, heat resistance, moisture resistance, hydrolysis resistance, and durability. The object of the present invention is to provide a magnetic recording medium with improved properties. D. Structure of the invention and its effects That is, the present invention provides a magnetic recording medium in which a magnetic layer and/or a back coat layer are provided on a substrate, as a resin of a coating film constituting the magnetic layer and/or back coat layer. A polyether polyester polyol derived from polytetramethylene glycol, a diol formed by adding an alkylene oxide to a phenolic hydroxyl group, and an aromatic polybasic acid, and the following general formula:

[Chemical formula] (However, R ¹ and R ² are alkylene groups, R ³ is an alkyl group or an aryl group) A tertiary amine type polyhydric alcohol,
The present invention relates to a magnetic recording medium characterized by using a urethane resin composed of an isocyanate compound. 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 the molecule,
The features of each of these components can be effectively exhibited, and the drawbacks of each component can be mutually compensated for, thereby fully achieving the above-mentioned object of the present invention. 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[-( _CH2 ) ₄ --O] _o --H (where n=1 to 50, preferably 4 to 40
is a real number. ) (b) Ethylene oxide on the phenolic hydroxyl group,
A diol with a molecular weight of 1000 or less made by adding alkylene oxide such as propylene oxide. For example, ethylene oxide adduct (BPA・EO) of bisphenol A with the following structural formula:

[C] (However, m and n are each real numbers of 1 or more,
(m+n)≦20. ) (c) Aromatic polybasic acids. for example,

Examples include terephthalic acid, orthophthalic acid, and isophthalic acid represented by the formula: In addition to the above, the following polyols, diols, and polybasic acids can also be used. H−OCH ₂ CH ₂ ) _o −−OH

[ka]

[ka] (neopentyl glycol)

[Chemical] (1,3-butanediol) HOCH ₂ CH ₂ CH ₂ CH ₂ OH
(1,4-butanediol) Other ordinary diols

[ka]

[ka]

[C] When synthesizing urethane resin, when conventional glycols are used, the surface smoothness of the layer is not sufficient, especially for videotape performance, such as image quality and abrasion resistance (durability). is 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 is required between the substrate and the magnetic layer to improve adhesion. layers are required. 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:

[Chemical formula] (However, R ¹ and R ² are alkylene groups, and R ³ is an alkyl group or an aryl group. In order to particularly improve adhesive strength, R ³ is preferably an aryl group.) Such low molecular weight Specific examples of diols are as follows.

[ka]

[Chemical] CH ₃ CH ₂ N (−-CH ₂ CH ₂ OH) ₂

[ka]

[ka]

[ka]

[ka]

[ka]

[Chemical formula] Next, each of the above-mentioned components, such as (a), (b), and
Using each compound (c), an aromatic residue-containing polyether polyester polyol is obtained according to a conventional synthesis method. The weight average molecular weight of this polyether polyester polyol is preferably from 500 to 5,000, more preferably from 600 to 3,000. The six types of aromatic group-containing polyether polyester polyols (A, B, C, D, E, F) obtained are shown in Table 1 below.

[Table] * Weight average molecular weight A polyether polyester polyol having a weight average molecular weight of approximately 2000 is thus 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, and 300 parts by weight of methyl ethyl ketone (hereinafter simply referred to as "parts") was placed in the reactor.
Add polyether polyester polyol (A)
165.0 parts diphenylmethane diisocyanate 86.0 parts dibutyltin dilaurate 0.03 parts were added and reacted 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 mixture was further reacted at 80°C for 1 hour. 3-methylpentane-1,
5.8 parts of 3,5-triol was added and reacted at 80°C for 1 hour. The thermoplastic polyurethane solution thus obtained had a non-volatile content of 30.2 wt%, a viscosity of 13100 cps/25°C, and a molecular weight determined by GPC (in tetrahydrofuran) _{of w} = 79,000, _o = 15,000, _w / _w / _o =
5.4, and the softening temperature was 66°C. In the same manner as Synthesis Example 1, various polyurethanes according to Synthesis Examples 2 to 12 were synthesized as shown in Table 2 below (However, Synthesis Examples 8 to 12 are comparative examples). Note that the polyurethane solutions prepared using the aromatic group-containing polyether polyester polyols A to E were uniform, but in the case of F, the resin precipitated during the reaction, making it difficult to obtain a uniform polyurethane solution. Therefore, this product could not exhibit excellent characteristics as a binder resin for the coating film of a magnetic recording medium.

【table】

[Table] Here, PEP-A to D (aromatic polyester polypolyate) are those of the present invention, (synthesis examples 1, 3,
4, 5, 6), PC type (corresponding to synthesis example 8), PCL type (corresponding to synthesis example 7), 1,4BA
The system (corresponding to Synthesis Examples 9 and 10) and PEP-E, F (corresponding to Synthesis Examples 11 and 12) are for comparison. Synthesis Examples 9 and 10 were comparative examples in which a conventional diol was used as the low molecular weight diol and a diol of the present invention having particularly good adhesiveness was used. In addition, in addition to diphenylmethane diisocyanate, usable polyisocyanates include tolylene diisocyanate (TDI) (2,
4-TDI, 2,6-TDI), dimer of 2,4-tolylene diisocyanate, xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), naphthylene-1,5-diisocyanate (NDI), o -tolylene diisocyanate (TODI) and adducts of these isocyanates with active hydrogen compounds, etc., and those having an average molecular weight of 100 to 3000 are suitable.
Usable aliphatic polyisocyanates include:
Examples include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (THDI), isophorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate (H ₁₂ MDI), and adducts of these isocyanates with active hydrogen compounds. I can do it. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a weight average molecular weight in the range 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 is improved and its mechanical strength is 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. The phenoxy resin that can be used is a polymer obtained by polymerizing bisphenol A and epichlorohydrin, and is represented by the following general formula.

[C] (However, n82-13) For example, PKHC manufactured by Union Carbide,
There are PKHH, PKHT, etc. In addition, the above-mentioned vinyl chloride copolymers that can be used have the general formula:

[ka] There is something expressed as in this case,

The molar ratio derived from l and m in the [Formula] unit and [-X] _n -- unit is 95 to 50 mol % for the former unit and 5 to 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. The degree of polymerization expressed as (l+m) is preferably 100 to 600, and the degree of polymerization is 100 to 600.
If it is less than 600, the magnetic layer etc. tends to become sticky.
If it exceeds this, 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
It is called "vinyl chloride-vinyl acetate copolymer." )
are mentioned. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, etc.
Among vinyl acetate copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include "VAGH" and "VYHH" manufactured by Union and Carbide;
"VMCH", "Esretsu A" manufactured by Sekisui Chemical Co., Ltd.,
“Eslec A-5”, “Eslec C”, “Eslec M”, “Denkabinil” manufactured by Denki Kagaku Kogyo Co., Ltd.
1000G", "Denkabinir 1000W", 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. As a thermoplastic resin, the softening temperature is 150℃ or less,
Weight average molecular weight is 10,000 to 200,000, degree of polymerization is approximately 200
~2000, for example, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, 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, phenolic resin, epoxy resin, urea resin, melamine resin,
Alkyd resin etc. Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride types, urethane acrylic types, and polyester acrylic types. 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). Magnetic powders, especially ferromagnetic powders used in the magnetic layer 2 include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ ,
Iron oxide magnetic powder such as Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ ; Fe,
Ni, Co, Fe-Ni-Co alloy, Fe-Mn-Zn alloy,
Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-
Examples include metal magnetic powders containing Fe, Ni, Co, etc. as main components, such as Co-Ni-p alloy and Co-Ni alloy. Here, the specific surface area of the magnetic powder of magnetic layer 2 is 30m ² /gr.
By doing so, the reproduction output and S/N ratio of the medium can be significantly improved (preferably by reducing the particle size). If the specific surface area of this magnetic powder is made larger than necessary, poor dispersion will occur, so
It is desirable to set the upper limit to 100m ² /gr. Furthermore, known dispersants (for example, powdered lecithin), abrasives (for example, fused alumina), etc. may be added to the magnetic layer 2. As an abrasive that can be added, α-
Al ₂ O ₃ (corundum), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond,
Synthetic diamonds, garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05 to 5μ, particularly preferably 0.1 to 2μ.
Further, conductive carbon black or light-shielding carbon black may also be added. As a conductive carbon black, for example, Conductex 975 (specific surface area 250
m ² /g, particle size 24 mμ), Conductex 900 (specific surface area 125 m ² /g, particle size 27 mμ), Cabot Vulcan XC-72 (specific surface area 254
m ² /g, particle size 30 mμ), Raven 1040, 420, #44 manufactured by Mitsubishi Kasei Corporation, etc. Light-shielding carbon black may also be used in conjunction with the light-shielding carbon black, such as Raben 2000 (specific surface area) manufactured by Columbia Carbon.
190 m ² /g, particle size 18 mμ), 2100, 1170, 1000, #100, #75, #40, #35, #30 manufactured by Mitsubishi Kasei Corporation, etc. can be used. Carbon black is 20~
It is preferable to have a particle size of 30 mμ, preferably 21 to 29 mμ, and the oil absorption amount is 90ml (DBP)/100g.
If it is above, it is desirable in that it is easy to form a structured structure and exhibits higher conductivity. The non-magnetic powder contained in the BC layer 3 includes carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide,
Calcium carbide, zinc oxide, α-Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black (especially conductive carbon black) and/or Or one made of titanium oxide can be mentioned. By incorporating these non-magnetic powders into the BC layer, the surface of the BC layer can be appropriately roughened (matted) to improve its surface properties.
In addition, in the case of carbon black, conductivity is imparted to the BC layer, thereby providing an antistatic effect. It is advantageous to use carbon black and other non-magnetic powders in combination, since both the effects of improving surface properties (stabilizing runnability) and improving conductivity can be obtained. 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. (Same below). As the material for the support 1, plastics such as polyethylene terephthalate and polypropylene, metals such as Al and Zn, glass, BN, Si carbide, ceramics such as porcelain and earthenware, etc. are used. In addition, when coating and forming the above magnetic layer and BC layer,
It is desirable to add a predetermined amount of polyfunctional isocyanate as a crosslinking agent to each coating material. Such crosslinking agents include polyfunctional polyisocyanates,
Examples include triphenylmethane triisocyanate, tris-(p-isocyanate phenyl) neophosphite, and polymethylene polyphenyl isocyanate. FIG. 2 shows another magnetic recording medium in which an OC layer 4 is provided on the magnetic layer 2 of the medium in FIG. This OC layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. This OC layer 4 may also contain the urethane resin of the present invention. The surface roughness of the OC layer 4 is Ra≦ especially in relation to color S/N.
It is preferable that Rmax be 0.01 mμ and Rmax≦0.13 mμ. In this case, the surface roughness of the support 1 is Ra≦0.01mμ,
It is desirable that Rmax≦0.13 mμ and that a smooth support 1 be used. FIG. 3 shows a magnetic recording medium configured as a magnetic disk, in which a magnetic layer 2 and an OC layer 4 similar to those described above are provided on both sides of a support 1, respectively. E. Examples The present invention will be described below with reference to specific examples. After dispersing the components shown in Table 4, this magnetic paint was filtered through a 1 mm filter, 5 parts of polyfunctional isocyanate was added, and it was coated on a support to a thickness of 5 mm using a reverse roll coater and supercalendered. , and were slit into 1/2 inch width to make video tapes (corresponding to the numbers of each Example and Comparative Example). However, the numbers after the second column of Table 3 represent parts by weight, and "fruit" after the second column refers to Examples.
"Ratio" represents a comparative example.

[Table] The following measurements were performed on videotapes according to each of the above examples. Chroma S/N: Measured using a color video noise meter "Shibasoku925D/1". Lumi S/N: Same as above RF output: 4MHz using VTR deck for RF output measurement
We measured the RF output at , and after 100 playbacks, the value showed a decrease compared to the initial output.
(Unit: dB). Glossiness: After dispersion, apply the magnetic coating liquid onto the glass plate using an applicator with a gap thickness of 30 mm.
After drying, the reflective gloss at 60° was measured using a gloss meter. Adhesiveness: Glue commercially available adhesive tape to the magnetic layer,
Furthermore, the tape was peeled off and the peeling state of the magnetic layer was compared. 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.

【table】

[Table] * No output was obtained.
From the above results, it can be seen that in the examples in which the magnetic layer was formed according to the present invention, the tape performance was significantly improved. Next, the content ratio of the polyether polyester polyol component in the urethane resin used was examined, and the results shown in FIG. 4 were obtained.
Furthermore, the results shown in FIG. 5 were obtained regarding Br/Bm (squareness 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. Also,
It can be seen that Br/Bm increases when the polyol component is 55% by weight or more. Therefore, it is preferable that the polyol component is contained in the urethane resin in an amount of 40% 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 this, it can be seen that the still durability is improved in the case of a polyol obtained by using a tertiary amine type polyhydric alcohol as a low molecular weight diol. 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 had 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. Heat resistance/moisture resistance Add 5 parts of trifunctional isocyanate to 100 parts of polyurethane resin solid content to create a film made of resin alone, and measure the retention of tensile strength over time at 60°C and 90% constant temperature and humidity. (measured humidity 25℃).

[Table] Resin 〓

[Table] 0 After Post-synthesis Example 1 100 95 92 (PEPA) Resin of the present invention (film production conditions) After curing in a dryer at 80°C for 1 hour, it was cured for 3 days at 20°C and 60%. A film sample with a thickness of 30 μm was obtained, and measurements were made in accordance with JISK-6301.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and
Figures 1, 2, and 3 are enlarged sectional views of a portion of the magnetic tape according to each example, and Figures 4 and 5 are glossiness and squareness ratio depending on the content ratio of the polyether polyester polyol component, respectively. FIG. 6 is a graph showing a comparison of still image life (durability) and output reduction depending on the type of polyol component. In addition, in the symbols used in the drawings, 2
...Magnetic layer, 3...Back coat layer (BC layer), 4
...It is an overcoat layer (OC layer).

Claims (1)

[Scope of Claims] 1. In a magnetic recording medium in which a magnetic layer and/or a back coat layer are provided on a substrate, as a resin of a coating film constituting the magnetic layer and/or back coat layer, polytetramethylene glycol, phenol-based resin is used. Diols with alkylene oxide added to hydroxyl groups and polyether polyester polyols derived from aromatic polybasic acids, and the following general formula: (where R ¹ and R ² are alkylene groups, and R ³ is alkyl or aryl group);
1. A magnetic recording medium characterized by using a urethane resin composed of an isocyanate compound.