JPH0453019A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To stabilize traveling property of the medium and to obtain excellent picture quality by providing a back coating layer containing a filler and polyurethane having secondary and/or tertiary hydroxide groups as the side chain on the opposite side of a nonmagnetic supporting body to the magnetic layer side. CONSTITUTION:The magnetic recording medium consists of a nonmagnetic supporting body 1, single-layer magnetic layer 2 on one side of the supporting body 1, and a back coating layer 3 provided on the back surface of the supporting body 1. The layer 3 contains a binder and a filler dispersed in the binder. The binder contains a specified polyurethane, namely, such one containing at least secondary and/or tertiary hydroxide groups at least as the side chain. The filler is carbon black. The nonmagnetic supporting body 9 released from a supply roll 8 is coated with magnetic coating materials for an upper layer and a lower layer by extrusion coaters 10, 11, passed through magnets12,13 provided in the front and rear stages for nonorientation treatment, and then dried with hot air blown from a drier 14. The supporting body 9 is treated in a supercalendering device 16 and dropout is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more particularly, the present invention relates to a magnetic recording medium that has stable running properties, provides excellent image quality, and reduces dropouts. Regarding the medium.

[Prior Art and Problems to be Solved by the Invention] In a magnetic recording medium having a magnetic layer on a non-magnetic support, in order to improve the characteristics, a layer is added to the surface of the non-magnetic support opposite to the magnetic layer. It is known to provide a backcoat layer and to include a filler in this backcoat layer.

However, the dispersibility of the filler in the back coat layer was poor, resulting in unstable running properties, resulting in poor image quality and dropouts.

The present invention has been made to improve the above situation.

That is, an object of the present invention is to provide a magnetic recording medium that stabilizes running properties by improving the dispersibility of the filler in the back coat layer, provides excellent image quality, and reduces dropouts. be.

[Step L for Solving the Problems] To achieve the above objects, the present invention provides a magnetic recording medium having a magnetic layer on a non-magnetic support, which is opposite to the magnetic layer of the non-magnetic support. The magnetic recording medium is characterized in that it has a back coat layer containing a filler and polyurethane having secondary and/or tertiary hydroxyl groups as side chains on the side surface thereof.

The detailed description of the present invention will be given below.

Layer Structure 1 The magnetic recording medium of the present invention basically consists of a non-magnetic support-L
A single layer or a plurality of magnetic layers are provided on the substrate, and a back coat layer is provided on the back surface of the -ll magnetic support.

In the magnetic recording medium shown in FIG. 1(A), one layer of magnetic M2 is provided on a non-magnetic support 1, and a back coat layer 3 is provided on the back surface of the non-magnetic support 1.

Further, in the magnetic recording medium shown in FIG. 1(B), a magnetic layer consisting of, for example, a lower layer 5 and a lunar calendar 6 is provided on a non-magnetic support 4J-, and a back coat layer 7 is provided on the back surface of the non-magnetic support 4. It is provided.

Note that an adhesive layer (an adhesive layer is also included in this concept) or the like may be interposed as an intermediate layer between the nonmagnetic support and the magnetic layer.

Backcoat Layer - The backcoat layer basically consists of a filler dispersed in a binder.

In the present invention, it is important to use a specific polyurethane as the binder.

The specific polyurethane referred to herein is one having at least a secondary and/or tertiary hydroxyl group as a side chain.

Note that this polyurethane may have a primary hydroxyl group at the end of its molecular chain.

In this way, by incorporating a specific polyurethane and a filler described below into the back coat layer, the running properties of the magnetic recording medium are stabilized, excellent image quality can be obtained, and dropouts can be reduced. .

On the other hand, if polyurethane or a resin other than polyurethane that does not meet the above specified conditions is used as a binder, the dispersibility of fillers such as carbon black will be poor and the surface of the back coat layer will be uneven. Therefore, running problems occur and the object of the present invention cannot be achieved.

In order to obtain the above specific polyurethane, a polyvalent isocyanate compound and a polyol (polyneedle, polyester) having a secondary and/or tertiary hydroxyl group in the side chain may be reacted according to a conventional method.

Specific examples of polyols having primary and/or tertiary hydroxyl groups in their side chains include glycerin, l-bis(2-hydroxyethyl)amino-2-propatol, 2-methylpropane-1,2, 3-triol, 3-
Methylpentane 1,3,5-triol, 1,2,6-
Hexanetriol, these ethylene oxides 1~
A 10 molar adduct or the like can be suitably used.

Further, as representative examples of polyvalent isocyanate compounds, for example, toluene diisocyanate, polymethylene diisocyanate, naphthalene-1,5-diisocyanate 4
, 4'-diphenyl diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-triphenylmethane triisocyanate and the like.

Next, as the filler, for example, carbon black, graphite, silver powder, nickel powder, alumina [α-
AM, O, (corundum), etc.], artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), and the like.

Among these, carbon black is particularly preferred for the purposes of the present invention.

The content of these fillers is as follows: polyurethane 1, [1
The amount is usually 40 to 200 parts by weight, preferably 60 to 120 parts by weight.

If the filler content is less than 40 parts by weight, the friction of the back coat layer will be significant and running stability will not be obtained, and if the filler content exceeds 200 parts by weight, the effect of the binder will be reduced. This is not preferable as it may become insufficient.

In addition, the particle size of the filler cannot be determined unconditionally according to its class II, or, for example, if the filler is carbon black, the average particle size is usually 10 to 100 mm.
The range is good.

In the present invention, the following binders may be used together with the polyurethane.

That is, thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, or mixtures thereof, which are conventionally known in the field of magnetic recording bodies, can be used.

Examples of the L-foot thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, donyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester. - Vinylidene chloride copolymer, Nisder methacrylate - Vinylidene chloride copolymer, Nisder methacrylate -
Ethylene copolymer, polyvinyl fluoride, beachloride, lidene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl phthyral, cellulose derivative (cellulose acetate phthalate!-), cellulose diacedate, Examples include cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene phtadiene copolymers, polynisder resins, chlorovinyl ether acrylate copolymers, amino resins, and synthetic rubber-based thermal I'IT plastic resins. I'll come.

These im may be used alone, or two or more types may be used in combination.

Examples of the thermosetting resin or reactive resin include phenolic resin 6-r-boxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polynisder resin, and isocyanate resin. Examples include mixtures with polymers, mixtures of methacrylate copolymers and cyisocyanate brevolimers, urea formaldehyde resins, and polyamine resins.

These may be used alone or in combination of two or more.

Examples of the electron beam irradiation curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type: ether acrylic type. , urethane acrylic type, epoxy acrylic type, phosphate ester acrylic type, aryl type, and pytrocarbon type.

These may be used alone as 111, or 21! The above may be used in combination.

When the polyurethane specified in the present invention and the binder are used together, the amount of the latter is usually 250 parts by weight or less per 100 parts by weight of the former.

If the latter ratio exceeds 250 parts by weight, the effects of the present invention may not be fully expressed.

In the present invention, an aromatic or aliphatic polyisocyanate can be used as a curing agent in combination with the binder.

Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI) and adducts of this with active hydrogen compounds, and have an average molecular weight of 100 to 3000.
Preferably within the range of .

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (HMD I) and combinations thereof with active hydrogen compounds, with an average molecular weight of 10
Those in the range of 0 to 3000 are preferred, and non-alicyclic polyisocyanates and adducts of these with active hydrogen compounds are more preferred.

The amount of the aromatic or aliphatic polyisocyanate added is usually 1.0% by weight relative to the binder resin. /20
~7/IO1 preferably 1/10 to 1/2.

Although the thickness of the back coat layer is not particularly limited in the present invention, it is usually 0.1 to 2.0 μm.

The surface roughness of the back coat layer is defined as Ra (center line average roughness) [defined in JIS, AB 0601 (1976)] of 0. It is preferable that it is old to 0.05.

-Magnetic layer The magnetic layer basically contains ferromagnetic powder and a binder.

Examples of the ferromagnetic powder include Go-containing -Fe, 03 powder, Co-containing FeJn powder, Go-containing Fen, (
4/3 <x<3/2) powder, or Fe-41 metal powder, Fe-Ni metal powder, Fe-Al JNik metal powder Fe-AM-P metal powder, FFe-Ni-3
t-A metal powder, Fe-Ni-8i-^1-11n metal powder, N1-Goo powder, Fe-Mn-Zr1 metal powder, Fe-Xl-Zn metal powder, Fe-Go-N
1-Cr metal powder, FeCo-N1-P metal powder, Co
Examples include fine ferromagnetic metal powders such as -Ni metal powder and Co-P metal powder.

These ferromagnetic powders can be used alone or in combination of two or more.

Among these, preferred is fine Cci-containing γ-F.
It is eJs powder.

Such ferromagnetic powder has large saturation magnetization and coercive force He, and is excellent in high-density recording. Further, by using ferromagnetic powder having a large specific surface area (for example, BET value of 40 m2/g or more), it is possible to easily realize a medium that allows high-density recording and has an excellent S/N ratio.

Next, as the binder to be contained in the magnetic layer, it is preferable to use a resin modified by introducing a functional group, particularly a modified vinyl chloride resin, a modified polyurethane resin, or a modified polyester resin.

Examples of the functional group include -3o, M, OSO, M
, -COOM and MI (In the formula, M is a hydrogen atom or an alkali metal such as lithium or sodium, and Ml and N2 are each a hydrogen atom, lithium, potassium, sodium, or an alkyl group. Ml and N2 ), which may be the same or different from , is preferable.

If the modified resin contains such a functional group, the compatibility between the modified resin and the ferromagnetic powder will be improved, and the dispersibility of the ferromagnetic powder will not only be further improved, but also its agglomeration will be prevented. The stability of the working fluid is further improved, and as a result, the frequency characteristics from high to low frequencies are balanced, and in addition to the electromagnetic conversion characteristics, the durability of the magnetic recording medium is also improved.

The modified resin can be used alone or in combination of two types.

The modified resin is a vinyl chloride resin, a polyurethane resin, or a polynisder resin, and a compound having a negative functional group and chlorine in the molecule, such as c5L-1:H2CH2S.
031d, C-CH2C)1. SO, extinction, C1
-C112COO heel, OM"C look-C)I
It can be produced by condensing with a compound such as 2-P-002 (Tatashi, M, Ml, N2 have the same meanings as above) through a #1 acid removal reaction.

In addition, in the present invention, thermoplastic resins and thermosetting resins conventionally known in the field of magnetic recording media are used.

A reactive resin, an electron beam curable resin, or a mixture thereof can be used, or they can be used in combination with the modified resin.

Their types are the same as those described for the back coat layer.

The blending amount of the binder in the magnetic layer is as follows:
The amount is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight.

If the amount of binder blended is too large, the amount of ferromagnetic powder blended will be reduced, which may reduce the recording density of the magnetic recording medium, and if the blended amount is too small, the strength of the magnetic layer will be reduced. However, the running durability of the magnetic recording medium may be reduced.

In the present invention, also in the magnetic layer, aromatic or aliphatic polyisocyanate-1 can be used as a curing agent in combination with the binder.

The details of the curing agent C are also the same as those described for the back coat layer.

The magnetic layer may contain various additive components, such as a lubricant, nonmagnetic abrasive particles, conductive powder, and surfactant, as necessary.

Examples of the lubricant include silicone oil, graphite, molybdenum disulfide, and
Examples include fatty acid Nisdel, which is composed of about 0 monobasic fatty acids (stearic acid) and --valent alcohols having about 3 to 26 carbon atoms.

Examples of the non-magnetic abrasive particles include alumina [
α-Auzo, + (corundum), etc.], artificial corundum, fused alumina, silicon carbide, WI trichrome diamond, artificial diamond, garnet, emery (main components: corantum and magnetite), etc.

The content of the abrasive particles is preferably 20 parts by weight or less based on the ferromagnetic powder, and the average grain size thereof is 0.5 parts by weight or less.
4m or less is good, 0.4p, m or more is good.

Incidentally, when the lubricant and the non-magnetic abrasive material are included in the outermost magnetic layer, the contact characteristics with the head (sliding performance, wear resistance, etc.) can be significantly improved.

Examples of the conductive powder include carbon black, Graphi l-1 silver powder, nickel powder, etc., and the surfactant includes natural, nonionic, anionic, cationic, and amphoteric surfactants. I can list many things.

By adding these conductive powders and surfactants to the magnetic layer, especially the outermost layer, it is possible to effectively lower the surface electrical resistance. This can be used to prevent outs from occurring.

The thickness of the magnetic layer is not particularly limited in the present invention, and is generally preferably 1 to 5 gm, more preferably 2 to 4 μm.

Also, the surface roughness of the magnetic layer is Ra (center line average roughness).
[1 definition in JISAB 0601 (1976), 0
02 to 0.02 is preferable.

-Non-magnetic support- Examples of the material forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and cellulose such as cellulose triacetate and cellulose diacedate. derivatives, polyamides,
Plastics such as polycarbonate, Cu, Ai, Zr
It can punch metals such as +, glass, boron nitride, Si carbide, ceramics, etc.

The form of the non-magnetic support is not particularly limited, and is mainly tape-like, film-like, sheet-like, or cart-like.

There are disk shapes, drum shapes, etc.

There are no particular restrictions on the thickness of the non-magnetic support; for example, in the case of a film or sheet, it is usually 3 to 1. OOpm
, preferably from 5 to 5[1 pLni], in the case of a disk or cart shape, it is about 30)Lnn to 10 mm, and in the case of a drum shape, it is appropriately selected depending on the recorder, etc.

Note that this nonmagnetic support may have a single layer structure or a multilayer structure.

Further, this nonmagnetic support may be subjected to surface treatment such as corona discharge treatment.

1. Manufacture of Magnetic Recording Medium The method of manufacturing the magnetic recording medium of the present invention is not particularly limited, and may be manufactured in accordance with a known method of manufacturing a magnetic recording medium of a single-layer or multi-layer structure.

For example, generally, a magnetic paint is prepared by cross-dispersing magnetic layer forming components such as ferromagnetic powder and a binder in a solvent, and then this magnetic paint is applied to the surface of a non-magnetic support, and the binder and A paint may be prepared by cross-dispersing backcoat layer forming components such as fillers in a solvent, and this paint may be applied to the back surface of the non-magnetic support.

Examples of molten material include acetone, methyl ethyl ketone (for needles), and methyl isobutyl ketone (MIBK).
Ketones such as , cyclohexanone, alcohols such as methanol, ethanol, propatool, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester systems such as ethylene glycol monoacetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, etc. Aromatic hydrocarbons such as benzene, toluene, xylene, etc.: methylene chlorite, ethylene chloride carbon tetrachloride chloroform, ethylene chloride Halogenated hydrocarbons such as hydrin and dichlorobenzene can be used.

When preparing a magnetic paint, the ferromagnetic powder and other magnetic layer forming components are charged into a kneader simultaneously or individually.

For example, adding the ferromagnetic powder to a solution containing a dispersant,
After kneading for a predetermined time, the remaining components are added and kneading is continued to form a magnetic paint.

Various kneaders can be used for cross-dispersing the magnetic layer-forming components.

This kneading machine includes, for example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a sight grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper kneader-2 high-speed mixer homogenizer, and an ultra-high-speed mixer homogenizer. Examples include sonic dispersers.

Application methods for magnetic paint include, for example, gravure coating, knife coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, and squeegee coating. , kiss coating method, and fantine coating method.

After a magnetic paint is applied to the surface of a non-magnetic support, the undried paint film is generally subjected to a magnetic field orientation treatment, and then a surface smoothing treatment is performed using a super calender roll, etc., and then the desired shape is obtained. By cutting into shapes,
It is possible to obtain magnetic recording media.

The above process will be explained by taking multilayer coating as an example and referring to FIG. 1.Oa,
A dryer in which the lower layer paint and the upper layer paint are layered in a wet-on-wet manner using a wet-on-wet method, and then passed through the first-stage non-orientation magnet 12 and then the second-stage non-orientation magnet 13. 14, where it is dried by being blown with hot air from nozzles arranged above and below.

The nonmagnetic support 9 having the magnetic layer dried in this way is
The sheet is guided to a super calender device 16 consisting of a combination of calender rolls 15, where it is calendered and then wound onto a winding roll 17.

Then, by cutting the obtained raw material into a desired shape and size (not shown), a magnetic recording medium suitable for the intended use can be obtained.

[Example] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

In addition, in the following, "part" means "part by weight".

(Examples 1 to 3, Comparative Examples 1.2) Magnetic paints with the following composition were thoroughly mixed in a ball mill, 6 parts of polyfunctional isocyanate was added as a hardening agent, and 11L
It was filtered with an filter.

Next, apply this paint to a thickness of 141Lm using a reverse roll.
Polyethylene terephthalate film, applied to
While forming a magnetic layer with a thickness of 3 m (after drying),
A back coat layer having a composition shown in Table 1 was formed on the back surface of this base to a thickness of Igm.

Then, the L film was subjected to supercalender treatment.

Go-containing -Fe=mouth, 100 parts Polyurethane 8 parts Vinyl chloride-vinyl acetate copolymer 12 parts Stearic acid Butyl・・・・・・・・・ 0.8 parts myristic acid・・・・・・
・・・・・・ 0.5 part stearic acid ・・・・・・・・・
・・0.5 part alumina・・・・・・・・・・・・・
5 parts carbon black 0.5 parts lecithin 4 parts cyclohexanone 40 parts methyl ethyl ketone
・・・・・・・・・ 60 parts toluene・・・・・・・・・
... 60 copies The original fabric thus obtained was further slit into 1/2 inch width to obtain a videotape.

The surface roughness Ra, dropout (Dlo) after 100 baths, scraping of the back coat layer, scratches on the magnetic layer, and S/N tee force of this videotape were measured.

The results are shown in Table 2.

Table Note: The polyurethanes of Examples 1 to 3 were used as chain extenders.
-Methylpropane-1,2,3ol and methylpropane-1,3-diol were used.

In addition, the polyurethane of Comparative Example 1.2 was used as a chain extender.
-Methylpropane-1,3ol only was used.

[Effects of the Invention] According to the present invention, it is possible to provide a magnetic recording medium that has stable running properties, provides excellent image quality, and reduces dropouts.

[Brief explanation of the drawing]

FIGS. 1A and 1B are schematic cross-sectional views showing different examples of magnetic recording media of the present invention. FIG. 2 shows "Manufacturing for obtaining the magnetic recording medium of the present invention"--
It is a follow chart showing an example of the process. 1... Nonmagnetic support, 2... Single magnetic layer 3...
Back coat layer, 4... Non-magnetic support, 5... Lower layer, 6... Upper layer, 7... Back coat layer, 8... Supply roll, 9... Non-magnetic support, 10 .11...
・Extrusion coater 12...Magnet for non-orientation in the first stage,】
3...Late-stage non-orientation magnet, ]4...Dry smoke device, 1
5... Calendar roll, 16... Super calendar device, 17... Winding roll. Figure 2

Claims (2)

[Claims] (1) In a magnetic recording medium having a magnetic layer on a non-magnetic support, a polyurethane having secondary and/or tertiary hydroxyl groups as side chains on the surface of the non-magnetic support opposite to the magnetic layer. A magnetic recording medium comprising a back coat layer containing a filler and a filler. (2) The magnetic recording medium according to claim 1, wherein the filler is carbon black.