JPS6262425A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a back coat layer which has good dispersibility of fillers and stable runnability by incorporating a cellulosic resin, cured polyurethane and polyisocyanate into the binder of the back coat layer and incorporating org. powder having 0.01-0.5mum average particle size therein. CONSTITUTION:The binder of the back coat layer consists of the cellulosic resin and polyurethane resin, contains the polyisocyanate and contains the org. powder having 0.01-0.5mum average particle size. The polyurethane resin is synthesized by the reaction of polyol and polyisocyanate and the average mol. wt. thereof is preferably 5,000-200,000. Cellulose ether, org. acid ester of cellulose, etc. are usable for the cellulosic resin. The mixing weight ratio of the polyurethane resin and cellulosic resin is 1/9-8/2, more preferably 2/8-7/3. The polyisocyanate is incorporated as a hardener into the binder and the amt. of the polyisocyanate to be added to the binder is 0.15-0.5 sum of the weights thereof. The org. powder is exemplified by an acryl styrene resin, phthalocyanine pigment, etc.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a magnetic recording medium, and particularly to a magnetic tape.

[Conventional technology]

Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and convenience store fields. Among these, for example, regarding magnetic tape in the video field, magnetic tape stored in a cassette is used to record and play back images.
This cassette is mounted on a video deck, and the tape is scanned along a circuit while its front and back sides are rubbed by an idle ball or an idler roller, and then 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 if 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 does powder drop occur, but the winding shape is disturbed and the edges of the tape become uneven, resulting in poor image or electromagnetic conversion characteristics such as skew, jitter, and chroma S/N. Therefore, a back coat layer is provided on the back side of the magnetic tape support to improve running properties and durability against ``id balls'', ``id rolls'', ``id bins, etc.'', and this back coat layer contains inorganic powder. There is one in which the layer contains as a filler. This is made by roughening the surface of Barafco/H to reduce the contact area with guide poles, etc., and reduce the frictional resistance.
For example, JP-A-57-130234, JP-A No. 58-1611
No. 35, No. 57-53825, No. 58-2415,
Japanese Patent Publication No. 50-3927 all show examples using inorganic powders, and many of these also show those with limited particle sizes. However, even those using these inorganic powders not only do not provide sufficient lubricity, but also
When the backcoat layer, such as the alumina particles described in No. 0-3927, comes into contact with an id pin, it scrapes the id pin, allowing the magnetic tape to be guided smoothly, but impairing the function of the id pin. One of the reasons for this 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. Excessive roughening can also be caused by inorganic powders (e.g. titanium 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 the resin used for bangu, and there are many problems with dispersibility, which causes particles to separate from the resin and cause powder to fall off, for example, staining the video deck, and magnetic This may cause dropouts in the reproduction of the layer's image.9 On the other hand, the binder used for the back coat layer contains a wide variety of additives, mainly magnetic powder, to adjust the electromagnetic characteristics and physical properties of the tape. It is necessary to determine the composition from a different perspective than that of the magnetic layer binder, and using the magnetic layer binder composition as it is is an overtreatment and may even cause warping and unnecessary defects. For example, vinyl chloride
When vinyl acetate copolymer and polyurethane resin are cured with polyisocyanate, the abrasion resistance and toughness are insufficient and the coefficient of friction is large, resulting in an increase in running torque, resulting in tape bending, tape elongation, and scratches. This results in large fluctuations in RF output, leaving concerns about interlayer adhesion, and furthermore, the pot life is unstable due to the process, which may cause reagglomeration of the filler. In this way, if the roughness of the backfoot layer surface, which is the sliding surface with the video deck, is not appropriate and sufficient wear resistance and durability are not achieved, problems such as powder falling off of the magnetic layer may occur, resulting in fluctuations in output. In addition, electromagnetic fluctuation characteristics such as the chroma S/N cannot be improved. In particular, the recent miniaturization and higher density of video equipment has made the path of the magnetic tape more complicated, and there are many opportunities for it to come into contact with (and often be rubbed against) the guide poles, idle rolls, and even magnetic heads of the tape. There is a need for improved running performance and improved wear resistance and durability to prevent powder falling off.

[Objectives of the Invention] The objects of the present invention are as follows: (1) Good dispersibility of the filler, (2) No transfer of surface state from the back coat layer to the magnetic layer, (3) Low chargeability and no dropout. (4) To provide a magnetic recording medium having a back coat 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 layer/inkfoot layer is cellulose-based. tel
(Contains fat, polyurethane curable resin, and polyisoryanate, and has an average particle size of 0.01 to 0.5μ)

This is achieved by a magnetic recording medium characterized by containing an organic powder of [n]. Polyurethane resins are synthesized by a reaction between a polyol and a polyincyanate, but the polyurethane resin of the present invention can be synthesized by selecting a polyol to create a general polyurethane resin in which the main chain of the polyurethane has an ether bond and the adjacent atoms are carbon atoms. The urethane bond may also contain a natural ester bond, a carbonate ester bond, or a combination of two or more thereof. Furthermore, for example, fluorine, silicon or sulfone groups may be introduced into the main chain and side chains in order to improve lubricity or dispersibility. The average molecular weight is preferably 5,000 to 200,000. As the cellulose resin according to the present invention, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, etc. can be used. Examples of cellulose ethers include methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benzylcellulose, cyanoethylcellulose, vinylcellulose, Nitrocarboxymethylcellulose, diethylamide/ethylcellulose, ami7ethylcellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. Cellulose organic acid esters include acetyl cellulose, propionyl cellulose, butyryl cellulose, methacryloyl cellulose, chloroacetyl cellulose, β-oxyprobionyl cellulose, benzoyl cellulose, p-)luenesulfonate cellulose, acetyl propionyl cellulose, acetyl butyl cellulose, Riru cellulose etc. can be used. Among these fiber cord resins, nitrocellulose is preferred. The mixing weight ratio of the polyurethane resin and cellulose resin is 179 to 8/2, preferably 2/8 to 7/3. By using cellulose resin, especially nitrocellulose, as in the present invention, heat resistance, toughness, and block resistance can be improved, and the coefficient of friction is small and it has an outstanding effect on preventing interlayer adhesion, especially at high temperatures. It is possible to improve running stability. 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, polyisocyanate is contained as a curing agent in the binder. Aromatic polyisocyanates that can be used include, for example, tolylene diisocyanate (TDI) and adducts of these polyisocyanates and active hydrogen compounds, and those having an average molecular weight of 100 to a.ooo are preferable. Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic polyisocyanates and adducts of these polyisocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic polyisocyanates, non-alicyclic polyisocyanates and adducts of these compounds and active hydrogen compounds are preferred. The amount of the polyisocyanate added to the binder is preferably 0.1 to 0.7 of the sum of the weights of both.
5 to 0.5. In addition, examples of the organic powder used in the present invention include acrylic styrene (fat), benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment.
Polyolefin resin powder, polyester resin powder,
Polyamide resin powder, polyimide U (fat powder, poly7isoethylene resin powder, etc.) can also be used. The average particle size of the organic powder is 0.01 to 0.5 μm, and if it is smaller than 0.01 μm, the back coat Appropriate roughness cannot be obtained on the surface, and the surface becomes too smooth, increasing the coefficient of dynamic friction and causing problems in running durability.If the roughness is greater than 0.5 μIn, the roughness of the back coat surface will be transferred to the magnetic surface, causing Chroma S /N
Deterioration occurs. Also, the amount of organic powder added is 0.3 based on the weight of the total solid content.
-0.9 preferably 0.4-0.7. Further, carbon black may be added as a light-shielding filler. 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, phosphate esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinates, known surfactants, etc. and these salts,
It is also possible to use salts of polymeric dispersants having negative organic groups (eg -COOHl-PO,H). These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 20 parts by weight per 100 parts by weight of bangu. In addition, lubricants include silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, fatty acids such as lauric acid, palmitic acid, oleic acid, stearic acid, behenic acid, myristic acid, and butyl stearate. Fatty acid esters such as octyl palmitate and octyl palmitate can also be used. These lubricants are used in amounts of 0.2 to 100 parts by weight of magnetic powder.
It is added in an amount of 20 parts by weight. Antistatic agents that may be used include carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin;
7-ion surfactants such as alkylene oxide, glycerin, and glycidol; higher alkyl amines;
Cationic surfactants such as quaternary ammonium salts, pyrinone, other heterocycles, phosphoniums or sulfonites; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester groups, phosphate ester groups, etc. Examples include amphoteric activators such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols. The back coat paint formed as above has a dry thickness of 0.
The coating is applied so that the thickness is preferably 0.5 to 1.5 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 may be a coated magnetic layer using magnetic powder, a binder and dispersion, a lubricant, etc., or may be formed by a vapor deposition method, a sputtering method, a paper deposition method, etc. It may also be a thin film type magnetic layer. Examples of magnetic materials include γ-Fe203, CO-containing-Fe20, Co-coated-Fe201, Fe201,
-0,. Fe30t with COO, Co coated Fe3'04% Cro
2, etc., such as Fe, Ni, Co,
Fe-Ni alloy, Fe Co alloy, Fe-NlP alloy, Fe NiCo alloy, Fe-Mn-Zn alloy, F
e-Ni Zn alloy, Fe-Co-Ni-Cr alloy,
Fe-Co-N1-P alloy, Co-Ni alloy, Co
Examples include various ferromagnetic materials such as P alloy, Co-Cr alloy, and metal magnetic powder containing Fe, Ni, and Co as main components. Additives to these metal magnetic materials include Sl, Cu,
Elements such as Zll, AQ, P, Mn, and Cr, or compounds thereof may be included. Also used are major ferrites such as barium ferrite, and iron nitride. 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 #a fiber resin and vinyl chloride copolymer are used alone, the layer becomes too hard, but this can be prevented by containing the above-mentioned polyurethane. Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. 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. Phenoxy resins can also be used. 7 E/oxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness. These advantages are complementary to the above-mentioned polyurethane, and furthermore, they can significantly improve the stability over time of the physical properties of the tape. Furthermore, in addition to the above-mentioned baingu, mixtures with 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 paint can contain various curing agents, such as incyanate. Examples of the isocyanate include the polyisocyanate used in the back coat layer. The magnetic paint used to form the magnetic layer may contain additives such as dispersants, lubricants, abrasives, matting agents, antistatic agents, and the like, if necessary. As for the above-mentioned dispersant, lubricant, antistatic agent, and management 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 caulking magnetic powder. In addition, as a mantle agent, the above-mentioned organic powder or non-organic powder can be used individually or as a mixture,
Inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide,
Examples include aluminum oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α-Fe201, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide. Commonly used abrasives include solvent alumina, silicon carbide, chromium oxide, corundum, synthetic corundum, diamond, synthetic diamond,
Garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05-5
μIff is used, particularly preferably 0
．． It is 1 to 2 μfn. These abrasives are binder 100
It is added in an amount of 1 to 20 parts by weight. The solvents to be added to the back coat and magnetic paint or the diluting solvents used when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, butanol, etc. ; Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol Sepha ('Qi); Ethers such as glycol dimethyl ether, glyfur monoethyl ether, dioxane, and tetrahydro-7rane; benzene, toluene, xylene, etc. aromatic hydrocarbons; halogenated hydrocarbons such as methylene chloride, ethylene chloride, RZ tetrachloride, chloroform, dichlorobenzene, etc. can be used. In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-7-talate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose guiacetate, and plastics such as polyamide and polycarbonate, but metals such as Cu, All, and Z++. , Plus, BN, Si carbide, ceramics such as porcelain, earthenware, etc. can also be used. The thickness of these supports is approximately 3 to 100μ70 in the case of a film or sheet, preferably 5 to 50μm, and 30μm1 to 1'Or in the case of a disk or card.
If it is drum-shaped, it is used in a cylindrical shape, and its shape is determined depending on the recorder used. A transparent 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 coat, blade coat, air-1-
Iacote, Squeezco), 2-i? Coat, reverse roll coat, trans7T-roll coat, gravure neat, kiss coat, cast foot, spray foot, 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 (1) was thoroughly mixed and dispersed in a ball mill, 5 parts of polyfunctional incyanate was added as a hardening agent, and 1
It was filtered through a μ+N filter and coated with a reverse roll coater to a dry film thickness of 1”75 μIn on a polyethylene Tele7 tanto base to obtain a sample film. The film was then subjected to supercuring treatment. The composition of the material formulation H was dispersed in a ball mill for 5 hours.
It was used as a backfoot paint. The paint was coated on the back side of the sample film with a reverse roll coater to a dry film thickness of 1.0.
A backfoot layer was formed by coating and drying to a thickness of μ11, and each portion was slit to a width of 2 inches to obtain top example sample tapes 1 and 2 and comparative example sample tapes (1) to (4). Formulation 1 (Magnetic paint) (Parts by weight) Contains CO - Fe203100 Polyurethane 12 Vinyl chloride vinyl acetate copolymer 8 Butyl stearate 0.8 Myristic acid 0.8 Alumina 5 Carbon black 5 Lecithin 4 Cyclohexanone 100 Methyl ethyl ketone 50 As above For the sample obtained in
- Check the tape condition, physical properties, and electromagnetic conversion characteristics of the tape (pass), and compare the results as shown in Table 2. (a) Compare Samples 1 and 2 with (1) and (2). Then (
In cases 1) and (2), the particle size of the organic filler is large, 0.8 and V1μ, respectively, so the BC filler falls off, which increases the friction coefficient and increases the amount of back scraping. Furthermore, since the particle size is too large, transfer of the BC surface to the magnetic surface occurs, resulting in deterioration of chroma S/N. Therefore, the filler particle size is suitably 0.01 to 0.5μ. (1)) Comparing samples 1, 2 and (3), (3)
uses an inorganic filler, TiO2, and the particle size is 0.
A value of 1μ is suitable, but the durability itself is poor, and the friction coefficient increases, BC filler falls off, and tape damage occurs to some extent. (c) Comparing Samples 1, 2 and (4), since nitrocellulose was not used in the bainggu, (4) was significantly inferior in durability, had filler falling off, had poor winding appearance, and was frequently damaged by the tape. Furthermore, since the use of vinyl chloride-vinyl acetate copolymer resulted in a slight increase in interlayer adhesion, it is therefore effective to use nitrocellulose for the binder in terms of running durability. Measuring method; (a) BC abrasion To determine the abrasion state, each of the above magnetic tapes was passed through a video deck (NV 6200, manufactured by Matsushita Electric Co., Ltd.) 200 times, and the degree of abrasion of the bank 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. (b) Adhesiveness A sample tape with a length of 1 + n was wound around a glass tube with a diameter of 36 ro + n while applying a load of 1.5 kg, and this was placed in an atmosphere at 60°C and 180% (relative humidity). , leave the tape for 24 hours, then heat at 23°C 155%
The tape was left in an atmosphere of (relative humidity) for 24 hours, and the degree of adhesion was evaluated when the tape was gently unwound. (c) It(lJjtJ friction coefficient・23℃, 60%
R) In I, Yokohama System Co., Ltd. running performance test tl (T
BT-3000), the sample tape was wrapped at 180° around a stainless steel bottle with a diameter of 3.8n+m at an inlet tension of 20g, and the tape was run at 3.3cm/s to determine the exit rotance a.
Gourd resistance (d) Interlaminar friction coefficient...23°C160'R11
Medium, use the same 'JA position as (1+), and set the large mouth tension to 20. Wrap it around a stainless steel drum with a diameter of 62 + n + n with the magnetic layer facing up, and then wrap
A sample tape was wound around the sample tape and the DC surface was run at 0.2 crn/s, and the exit tension was measured and calculated from equation (1). (e) DC surface roughness (Ra)...The sample surface was measured at 2.5+n using a three-dimensional roughness measuring instrument 5E-3PK (Koita Institute).
+o measurement, cut t70,25, vertical magnification 50.00
Measurement was performed at 0x magnification, 50x lateral magnification, and stylus pressure 30 to g. (n ria 7S/N (7) measurement-) IR-7100
(Nippon Hifter) at the maximum recording sensitivity current, 4.
5 Old (Record Z and compare the noise voltage during playback with the reference tape. 0+) Repeated running test...Packed in a VIIS cassette at 20'C. NV-6200 (manufactured by Matsushita Electric Industrial Co., Ltd.) was used in 609 g of RIl, and the test was run repeatedly for 200 passes. At the same time, R
The reduction in F output was also measured. (11) The winding was visually evaluated after the tape had been run 200 times. The same goes for tape 411 scratches.

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 and a polyurethane resin and contains polyisoryanate, And average particle diameter 0.01~
A magnetic recording medium characterized by containing organic powder of 0.5 μm.