JPS6276024A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of a filler and to obtain a back coat layer having good running property without the transfer of the back coat layer by specifying the material quality of a binder for the back coat layer. CONSTITUTION:The binder for the back coat layer consists of a cellulosic resin and polyurethane resin, contains a polyisocyanate and contains org. powder and carbon black. The mixing weight ratio of the polyurethane resin and cellulosic fiber is preferably 3/7-6/4. Wear resistance, toughness and blocking resistance can be improved by using nitrocellulose in particular as the cellulosic fiber. Said resin has a small coefft. of friction and has an outstanding effect of preventing the adhesion between layers, thus contributing to an improvement in running stability particularly at and under a high temp. and high humidity. Acryl styrene resin, etc. are usable as the org. powder and acidic carbon has good affinity to the binder and has the excellent dispersibility as the carbon black.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to magnetic recording media, particularly magnetic tape.

BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic tapes, and magnetic disks are widely used in the audio, video, and computer fields. Among these, for example, magnetic tape stored in a cassette is used to record and play back signals, and the cassette is inserted into a video deck.
The tape travels on a circuit while its front and back sides are rubbed by guide poles and guide rulers, and is rubbed and scanned by a magnetic head. The surface of the magnetic layer is finished to be smooth so that the sliding condition of the magnetic tape against the magnetic head does not change when the magnetic tape runs on a circuit.

However, the side opposite to the magnetic layer of the magnetic tape has a similar effect on the above fluctuations, and when the running performance and durability of the opposite side are poor, excessive tension is applied to the running magnetic tape, causing damage to the magnetic layer. Not only will powder fall off, but the winding will become disordered and the edges of the tape will become uneven, skewed, and
Image quality, chroma S/N, etc. or electromagnetic conversion characteristics deteriorate.

Therefore, a back coat layer is provided on the back side of the magnetic tape support to improve running properties and durability against guide balls, guide rolls, guide pins, etc., and this back coat layer contains inorganic powder. There is one in which the layer contains as a filler. This is a method in which the surface of the back coat layer is made rough to reduce the contact area with guide balls etc., thereby reducing the frictional resistance.
No. 5, No. 57-53825, No. 58-2415, and Japanese Patent Publication No. 50-3927 (all of which show examples using inorganic powder, and many of these also have examples that limit the particle size. However, even those using these inorganic powders not only do not provide sufficient lubricity, but also have problems with the back coat layer, such as the alumina particles described in Japanese Patent Publication No. 50-3927. When the magnetic tape comes into contact with a guide bottle or the like, especially if the guide bottle is made of organic resin, the K will scrape the pin or the like, impairing the function of the guide bottle to smoothly guide and run the magnetic tape.

One of these causes is that inorganic powders generally have a wide variety of particle shapes and are not constant, and also have a wide distribution of particle sizes, which causes the surface of the back coat layer to become rougher than necessary.

In addition, excessive roughening can be caused by inorganic powder (e.g. chikum dioxide/
Coupled with the high hardness of the iron oxide (α-iron oxide, etc.), unevenness is transferred to the magnetic layer, causing problems in various electromagnetic conversion characteristics.

In addition, in general, inorganic powders do not mix well with binder resins (there are many problems with dispersibility, which causes particles to separate from the resin and fall off, for example, staining the video deck, and magnetic This may cause dropouts in the playback of the layer's images.

In place of the above-mentioned inorganic fillers, attempts have been made to use organic fillers whose particle size and particle hardness and softness can be controlled. For example, it is known to use Teflon powder in JP-A-59-112428.

However, Teflon powder has poor compatibility with binders used in recording media (it may not be sufficiently dispersed), and is therefore unsatisfactory as a filler for high-density magnetic recording media.

Furthermore, when used as a filler for a carbon black backfoot layer, which is commonly used as an antistatic agent and/or a light shielding agent, it lacks durability, causes powder to fall off due to repeated running, and is extremely difficult to disperse.

On the other hand, the composition of the binder used in the backfoot layer needs to be determined from a different perspective than the binder for the magnetic layer, which mainly consists of magnetic powder and has a wide variety of additives added to adjust the electromagnetic characteristics and physical properties of the tape. Reusing the magnetic layer binder composition as it is is an excessive treatment and may even cause warping and unnecessary defects. For example, when vinyl chloride-vinyl acetate copolymer and polyurethane resin are cured with polyincyanate, abrasion resistance and toughness are insufficient, leaving concerns about interlayer adhesion, and there is room for improvement.

(Objectives of the Invention) The objects of the present invention are: (2) good dispersibility of the filler; (2) no transfer of surface state from the back coat layer to the magnetic layer; (3) low chargeability and little dropout; (4
) An object of the present invention is to provide a magnetic recording medium having a backfoot layer with stable running properties.

(Structure of the Invention) The object of the present invention is to provide a magnetic recording medium having a magnetic layer on one side of a support and a back coat layer on the other side, in which the binder of the back coat layer is a cellulose resin. , consisting of polyurethane resin and containing polyinsyanate,
This is achieved by a magnetic recording medium characterized by containing organic powder and carbon black.

Next, the present invention will be specifically explained.

Polyurethane resins are synthesized by a reaction between a polyol and a polyinsyanate, and the polyurethane resin according to the present invention can be synthesized by selecting a polyol. The urethane bond may also contain an ester bond, a carbonate ester bond, or a combination of two or more thereof. Furthermore, in order to improve the lubricity or dispersibility of the main chain, side chains, etc., for example, fluorine, silicon, or su/I/hono groups may be introduced.

The average molecular weight is 5,000 to 200. OOO is preferred.

As the cellulose resin according to the present invention 1, cellulose needles, cellulose inorganic acid esters, cellulose organic acid esters, etc. can be used. Examples of cell p-sgoether include methyl cellulose, ethyl cellulose, propyl cellulose, isopropyl cellulose, butyl cellulose,
Methyl ethyl cellulose, methyl ester, ethylhydroquine, ethyl cellulose, carboxymethyl cellulose, carboxymethyl cellulose.
Thulium salt, hydroxyethylcellulose, be/7'
/lucel p-su, cyanoethyl cellulose, vinyl cellulose, nitrocarboxymethyl cellulose, diethylamine ethyl cellulose, amino/ethyl cellulose, etc. As the cellulose inorganic acid ester, 21
r+cellulose, cellulose sulfate, cellulose phosphoric acid p-su, etc. can be used. In addition, examples of cellulose organic acid esters include acetylce'l-lose, propionyl cellulose,
Butyryl cellulose, methacryloyl cellulose, chloracetic acid cellulose, β-oxypropionyl cellulose, benzoyl cellulose, p-toluenesulfonate cellulose, acetyl propionyl cellulose, 7-cetyl butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred.

The mixing weight ratio of the polyurethane resin and cellulose resin is 2.
/8 to 8/2, preferably 3/7 to 6/4.

By using nitrocellulose in the cellulose m fat percentage as in the present invention, abrasion resistance, toughness, and block resistance can be improved, and the coefficient of friction is small and has a simple effect on preventing interlayer adhesion. In particular, running stability in high humidity conditions can be improved.

In addition, in terms of productivity, in paints containing nitrocellulose, the filler is dispersed more quickly than in vinyl chloride paints, the paint itself is stable, and reagglomeration of the filler is less likely to occur.

In the present invention, a curing agent and 1-
1. Polyincyanate is contained.

The aromatic polymers/cyanates used are, for example, tolylene diene (TT) I) and these polyesters.
Examples include adducts of incyanate and active hydrogen compounds, and those having an average molecular weight in the range of 100 to 3,000 are suitable.

In addition, examples of the aliphatic carbon IJ-rn/7-inocyanate include hekydec methylene diisocyanate (I-tMD diisocyanate) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic polyincyanates and adducts of these polyin7no7nates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic polyinsyanates, non-alicyclic polyisocyanates 1 and adducts of these compounds with active hydrogen compounds are preferred.

The amount of the polyincyanate added to the binder is 01 to 07, particularly preferably 0.1 of the weight sum of both.
5 to 0.5.

Examples of organic powders used in the present invention include acrylic styrene resins, benzoguanamine resin powders, melamine resin powders, 2-taloshi7-nino pigments, 7-zo pigments, polyolefin resin powders, polynisdel Also usable are resin powders, polyamide resin powders, polyimide resin powders, polyfluoroethylene resin powders, and the like.

The average particle size of the organic powder is preferably 0.1 to 0.8.
μm, particularly preferably 0.02 to 0.5 μm.

The carbon black used in the present invention is basically acidic carbon, which has good compatibility with Ba-ingu (it has excellent dispersibility, but carbon black does not have sufficient compatibility with organic pigments in the dispersion liquid, etc.). It cannot be grasped only by the so-called catalog data listed in the catalog.The following is a list of the ones that were particularly preferred from those tested, but you may use other than those listed.

Manufactured by Columbia: Raven 5000, Raven
7000.

Raven 3500, Raven 2000, Rav
en 1255, Raven] 250, Raven
1035, C0NDUCTEX 975
, C0NDUCTE SC% C0NDUCTE
X 900% Raven 14 Manufactured by Kabonoto; Blcck Pearls (hereinafter referred to as B, P) 1300, B, P, 1000% B, P, -L, I
GAL 400, VULCANXC-72, S'rBA
LING-V made by Mitsubishi Kasei; #2400B, #2
350, #220OB.

#1000, MA 100, MA 7, MA 8, MA
II The amount of the organic powder and carbon black added is 02 to 0.9, preferably 04 to 0.7, based on the total solid weight, and the organic powder/carbon black is IO/1 to 4.
/6, particularly preferably 9/1 to 515.

The paint used to form the back coat layer may contain additives such as a dispersant, a lubricant, and an antistatic agent, if necessary.

Dispersants used in the back coat layer according to the present invention include lecithin, phosphoric acid ester, amine compound, furkyl sulfate, fatty acid 7amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, and known surfactants. and their salts,
It is also possible to use salts of polymeric dispersants having negative organic groups (for example -COOHl-PO3H). These dispersants may be used alone or in combination of two or more (. These dispersants
It is added in an amount of 1 to 20 parts by weight based on 0M parts.

In addition, lubricants include silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, fatty acids such as lauric acid, valmitic acid, oleic acid, stearic acid, behenic acid, myristic acid, butyl stearate, Fatty acid esters such as octyl palmitate and octyl myritate can also be used.

These lubricants are 0.0% to binder 1001 part.
It is added in an amount of 0.02 to 20 parts by weight.

Examples of antistatic agents that may be used include the carbon black according to the present invention, conductive powders such as graphite, tin oxide-stanmon oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; Natural surfactants; fullkylene oxide type, glycerin type,
7-ion surfactants such as glycidol; cationic surfactants such as higher furkyl 7-mines, quaternary ammonium salts, pyridino, other heterocycles, phosphonium or sulfonium; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid 7 containing acidic groups such as ester groups and phosphoric acid ester groups
Ionic surfactant; amino acid M, 7j nosulfonic acids,
Examples include amphoteric activators such as sulfuric acid or phosphoric acid esters of 7minoalcohols.

The backfoot paint configured as above has a dry thickness of 0.
．． The coating is applied to a thickness of 3 to 2.0 μm, preferably 05 to 15 μm.

In the present invention, conventional techniques can be used to create the magnetic tape of the present invention.

The magnetic layer of the magnetic tape of the present invention includes magnetic powder, 1
It may be a coated magnetic layer using a binder, a dispersion, a lubricant, etc., or a vapor deposition method, a sputtering method, 1.
A thin film type magnetic layer formed by a paper deposition method or the like may be used.

Examples of magnetic materials include 1-Fe2O3, Co-containing rFe2O3, Co-coated 1-Pe203, Fe3
O4, Co-containing Fe3O4, Co-coated Fe3O4, Cr
Oxide magnetic materials such as O2, e.g. Fe, Ni, Co,
Fe-Ni alloy, Pe-Co alloy, Fe-Ni-P
alloy, Fe-Ni-Co alloy, Pe Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni
-Cr alloy, Fe-Co-N1-P alloy, Co-Nj
Gold alloy Co-P alloy, Co-Cr alloy etc. Fe%N1, C
Examples include various ferromagnetic materials such as metal magnetic powder containing o as a main component. As an additive to these metal magnetic materials, S
i, Cu, Zn,, hl, P, Mn.

It may contain an element such as Cr or a compound thereof. Hexagonal ferrite such as barium ferrite and iron nitride are also used.

The binder used in the magnetic layer of the present invention includes abrasion-resistant polyurethane.

It has strong adhesion to other substances, is mechanically strong to withstand repeated stress or bending, and has good abrasion resistance and weather resistance.

Furthermore, if a cellulose resin and a vinyl chloride copolymer are also contained in addition to polyurethane, the dispersibility of the magnetic powder in the magnetic layer will be improved and its mechanical strength will be increased. However, if only the cellulose resin and the vinyl chloride copolymer are used, the material becomes too hard, but this can be prevented by containing the above-mentioned polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, and cellulose organic acid ester. The vinyl chloride copolymer described above may be partially hydrolyzed. Preferable examples of the vinyl chloride copolymer include copolymers containing vinyl chloride and vinyl acetate.

Phenokine resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, and chemical resistance, and good adhesiveness at ℃.

These advantages are complementary to the above-mentioned polyurethane, and also help to significantly improve the stability over time in the physical properties of the tape.

Furthermore, in addition to the binders described above, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

In order to improve the durability of the magnetic layer of the magnetic tape of the present invention, the magnetic coating material can contain various curing agents, such as inseaide. Examples of the incyanate include the polyisocyanate used for the backfoot layer.

The magnetic paint used to form the magnetic layer may contain additives such as a dispersant, a lubricant, an abrasive, a matting agent, and an antistatic agent, if necessary.

Regarding the above-mentioned dispersant, lubricant, antistatic agent, and matting agent, the same ones mentioned in the above-mentioned back coat layer can be used under almost the same conditions.

Incidentally, these dispersants may be used to pre-treat the magnetic powder in advance. In addition, as a matting agent, the above-mentioned organic powder or inorganic powder can be used individually or in combination.
・The inorganic powder includes silicon oxide, titanium oxide,
Aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, pm oxide, silicon carbide, calcium carbide, α-Fe203, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide Can be mentioned.

The abrasives that may be used include commonly used materials such as fused alumina, silicon carbide, oxidized PM, corundum, artificial corundum, diamond, artificial diamond,
Zaku 1 stone, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 005-5
A size of μm is used, particularly preferably 0.1 μm.
~2 μm. These abrasives are added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

The solvent used in the back coat and magnetic paint or the diluting solvent when applying this paint is acetone,
Ketones such as methyl ethyl ketone, methyl imptilktone, and nclohegisanone; alcohols such as methanol, ethanol, purpanol, and methanol; esters such as methyl acetate, ethyl acetate, methyl acetate, ethyl lactate, and ethylene glycol monoacetate; glycol dimethyl ether, and glycols Ethers such as monoethyl ether, dioxane, and tetrahydrofuran; benzene,
Aromatic hydrocarbons such as toluene and xylene; p-genated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyoleins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate, but metals such as Cu%AJ%Zn,
Glass, BN.

Ceramics such as 8i carbide, porcelain, and earthenware can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card shape, the diameter is about 30 μm to 10 μm, and in the case of a drum shape, it is used in a cylindrical shape, and the shape is determined depending on the refuder used.

An intermediate layer for improving adhesion may be provided between the support and the back coat layer or magnetic layer.

The coating method for forming the above layer on the support is as follows:
Air doctor foot, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer rule coat, gravure foot, kiss foot, cast coat, spray coat, etc. can be used, but are not limited to these.

(Example) The present invention will be specifically explained using examples.

Example 1 A magnetic paint having the following formulation I was thoroughly mixed and dispersed in a ball mill, 5 parts of polyfunctional incyanate was added as a hardening agent, and 1
The mixture was passed through a 13 μm thick polyethylene terephthalate base using a reverse roll coater to give a dry film thickness of 5 μm to obtain a sample film. The film was subjected to supercalender treatment.

Next, the compositions of different backcoat paint formulations H for each sample shown in Table 1 were dispersed in a ball mill for 15 hours to obtain backcoat paints for each sample. The paint was applied to the back side of the sample film using a reverse roll coater to a dry film thickness of 1.0 μm, and dried to form a back coat layer on each.
Example sample tapes 1 to 3 were slit into /2 inch width;
and comparative example sample tapes (1) to (4) were obtained.

Formula I (Magnetic paint) (Parts by weight) Co-containing r Fe2O3 100 Polyurethane 12 Vinyl chloride monovinyl acetate copolymer 8 Butyl stearate 0.8 Myristic acid 08 Alumina 5 Carbon black 5 Lecithin 4 Cyclohexanone 100 Methyl ethyl ketone 50 Toluene 10 Formula Coat paint) Table 1 Regarding the samples obtained as described above, the presence or absence of transfer, the first time (0-pass) and after 200 repeated runs (
The tape condition, physical properties, and electromagnetic conversion characteristics of 200-pass) were checked, and the results are listed in Table 2.

Measurement method: (al BC wear Wear condition is measured using video deck (NV)
6200, manufactured by Matsushita Electric Co., Ltd.) with two of each of the above magnetic tapes.
After 00 passes, the degree of abrasion of the back coat layer was observed using an optical microscope. If there was powder falling off, scratches would be visible on the surface of the back coat layer, so it was evaluated based on whether this was more or less.

tbl Dynamic friction coefficient...23°C 160% RJ (inside, Yokohama System Co., Ltd. running performance tester (TBT-300)
D), diameter 3.8 with input roti/john 20,9
A sample tape was wound at 180° around a stainless steel pin of n and run at 3.3 cIn/S, and the outlet tension was measured and calculated from the following formula.

μ= -gn (excretion=Eyuuotto) -f11π
Inlet rotation (c) Interlaminar friction coefficient 23° (!160%T()
Using the same equipment as in (b), the magnetic layer was wound on a stainless steel drum with a diameter of 62 mm at an inlet tension of 20.9 mm, and the sample tape was wound 180° on top of the drum. The BC was run at a speed of 0.2 cm/S, the outlet tension was measured, and it was calculated from equation (1).

(al　roll form　200 bus tape visually inspected and evaluated.

As is clear from Cloth-2, Examples 1 to 3 have lower friction coefficients and less back surface scraping than Comparative Examples.

(Effects of the Invention) In terms of the process, it is possible to obtain a bank coat layer with good dispersibility of the filler, no transfer of the back coat layer, and good runnability.

Claims (1)

[Claims] In a magnetic recording medium having a magnetic layer on one side of a support and a back coat layer on the other side, the binder of the back coat layer is made of a cellulose resin, a polyurethane resin, contains polyisocyanate, and is an organic material. A magnetic recording medium characterized by containing powder and carbon black.