JPH0332136B2 - - Google Patents

Description

[Detailed description of the invention]

1 Industrial Application Field The present invention relates to magnetic recording media (e.g. magnetic tape)
The present invention relates to a manufacturing method. 2. Prior Art When manufacturing magnetic recording media such as magnetic tapes, generally a magnetic coating composition consisting of magnetic powder, additives such as a binder, a dispersant, and a solvent is prepared,
After adding a curing agent to this, it is applied onto a support and dried. As the density of magnetic recording has increased in recent years, durability has become necessary for magnetic recording media, and in order to meet this requirement, curable binder compositions have been proposed. According to conventional technology, a curing agent is added at the final stage of creating magnetic paint to prevent a curing reaction from occurring at the stage of creating magnetic paint, but this addition method After addition of the hardener and the magnetic paint, it is necessary to apply it onto the support as quickly as possible. In this case, it is difficult to sufficiently prevent the curing reaction of the binder before coating, and the properties such as squareness ratio and durability of the obtained magnetic recording medium tend to deteriorate. This is particularly problematic when an active hardening agent such as an isocyanate compound or an alloy powder is used as the magnetic powder. Therefore, one method is to
As seen in the specification of the publication, it is conceivable to continuously add a curing agent to the magnetic coating material while coating it on the support. According to this known method, the continuous addition described above can stabilize the magnetic paint and improve the squareness of the resulting magnetic recording medium. However, as a result of the inventor's investigation,
It has been found that the above method has the following defects. In other words, when continuously adding magnetic paint and curing agent, for example, in order to eliminate mistakes in addition amount or adjust viscosity, etc., simply adding magnetic paint and curing agent continuously does not solve these problems. I can't solve it. In other words, it is impossible to simply continuously control the amount added. The publication describes the provision of a buffer tank as follows. However, the method of the above-mentioned publication still has the following defects. (1) In the above method, the mixture is actually put into a buffer tank immediately after the curing agent is added to the magnetic paint, stirred there, and then discharged as a coating solution. During this stagnation, components in the mixed liquid coagulate, resulting in a change in viscosity, for example.
It is not possible to maintain the physical properties required during application. (2) Moreover, the curing reaction by the curing agent tends to proceed during residence in the buffer tank, making it practically difficult to use an active curing agent or magnetic powder. (3) Since the curing agent and magnetic paint are added in predetermined amounts to each other while being put into the buffer tank, the amount added cannot be increased significantly, and therefore the flow rate of the paint that can be applied is low. , mass productivity deteriorates. Under these circumstances, there has been a strong demand for a coating that can be applied in a mass-producible manner while maintaining the physical properties of the coating and suppressing the curing reaction caused by the curing agent. 3. Object of the Invention An object of the invention is to provide a method for manufacturing a magnetic recording medium that can fully satisfy the above requirements. 4. Structure of the Invention That is, the present invention provides a method for applying a magnetic coating material containing aluminum-containing iron-based metal magnetic powder onto a support by applying a predetermined amount of at least a curing agent and/or a curing agent precursor to the magnetic coating material. They are introduced into the mixing section one by one and are added continuously to mix with each other.
A method for manufacturing a magnetic recording medium, characterized in that the mixture is sent through a static mixer, and a portion of the mixture is returned to the mixing section from the downstream side of the static mixer through a reflux conduit. It is. 5 Examples Hereinafter, the present invention will be described in detail with reference to Examples. FIG. 1 shows a first embodiment of the invention. The magnetic paint is dispersed in a disperser 11 by a known method, filtered, and passed through a conduit 12 to a tank 13.
Put it in. Here, the magnetic paint is stirred with a stirrer 14 to prevent agglomeration of the magnetic powder. A curing agent and/or a curing agent precursor (hereinafter simply referred to as a curable component) is placed in a tank 15 and can be stirred with a stirrer 16 . The magnetic paint and curable components are pumped into pumps 17 and 1.
8, a predetermined amount is drawn out from tanks 13, 15, guided through conduits 21, 22 while controlling each flow rate with flow meters 19, 20, and continuously introduced into static mixer 24. The static mixer 24 feeds the magnetic paint and the curable component while mixing them in predetermined amounts. Further, this mixture is passed through a metering pump 26, a disperser 27, a filter 28, and then transferred to an application section 29.
and coated onto the flexible support 30 by a coating roller 34. 31 and 32 in the figure are flowmeters, and these are pumps 17, 18 and 2.
6, a signal is input to the microcomputer 33 so that the flow rate of each liquid is adjusted. A noteworthy feature of the method and apparatus of this embodiment is that a portion of the mixture of the magnetic paint and the curable component is fed to the drain side of the static mixer 24 through a reflux conduit 35. 24, and even during this reflux, the mixed flow from the static mixer 24 to the coating section 29 is kept flowing (that is, constantly supplied in a predetermined amount). By this,
The flow rate of the mixture flowing through the static mixer 24 can be increased, making it possible to increase the amount of each liquid to be mixed per hour.
Moreover, since the mixed stream is constantly flowing, no agglomeration phenomenon due to stagnation occurs as seen in the previously mentioned known methods, and the viscosity of the mixture does not change. In addition, since there is no stagnation, curing by the curing agent can be sufficiently suppressed, making it possible to select a wide range of types of curing agent and magnetic powder. In addition, in the example shown in Fig. 1, of course, magnetic paint and curable components are added in controlled amounts,
Since the materials are mixed, the progress of the curing reaction can be significantly suppressed compared to the case where the materials are mixed and stored in a tank and then supplied. FIG. 2 shows another embodiment in which the above-mentioned static mixer 24 is used as the mixing means.
A combination of a mixer 23 and a normal mixer 23 on the upstream side thereof is adopted. In this example, the same remarkable effects as described in FIG. 1 can be obtained, except that the mixer 23 can perform preliminary mixing of the original mixing operation performed by the static mixer 24. The magnetic paint that can be used in each of the above embodiments may consist of the following components: First, examples of the magnetic powder include iron-based metal magnetic powder containing aluminum, such as Fe-Al. Further, as the binder, a mixture of a thermoplastic resin, a thermosetting resin, a reactive resin, and an electron beam curable resin may be used. As a thermoplastic resin, the curing temperature is 150℃ or less and the average molecular weight is
10,000 to 200,000, with a polymerization degree of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, urethane elastomer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic acid Ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acolylonitrile-butadiene copolymer, nitrocellulose Cellulose resins such as cellulose diacetate, polyvinyl butyral, styrene
Putadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid ester copolymer,
Polyamide resins, various synthetic rubber-based thermoplastic resins, mixtures thereof, and the like 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 that do not soften or dissolve before the resin is thermally decomposed are preferable. Specifically, compounds such as phenolic resin, urethane resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, mixture of methacrylate copolymer and diisocyanate prepolymer, polyol and isocyanate, etc. urea formaldehyde resin, polyamine resin, and mixtures thereof. As electron beam irradiation curable resin,
Unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., or polyfunctional monomers such as ether acrylic type, urethane acrylic type, phosphate ester Examples include acrylic type, aryl type, and hydrocarbon type. The mixing ratio of the magnetic powder and the binder is 5 to 400 parts by weight, preferably 5 to 400 parts by weight of the binder per 100 parts by weight of the magnetic powder.
Used in a range of 10 to 200 parts by weight. If the amount of binder is too large, the recording density of the magnetic recording medium will be reduced, and if it is too small, the strength of the magnetic layer will be poor, resulting in undesirable situations such as decreased durability and powder falling off. The magnetic paint may contain additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, and the like, if necessary. Dispersants used include lecithin, phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic acid esters, known surfactants, and salts thereof. , negative organic groups (e.g. -COOH, _-PO3H )
It is also possible to use salts of polymeric dispersants having . These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 30 parts by weight per 100 parts by weight of the magnetic powder. In addition, as lubricants, silicone oil, graphite, carbon black graphed polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acids having 12 to 16 carbon atoms and carbon atoms of the fatty acids are used. Fatty acid esters consisting of monohydric alcohols having 21 to 23 atoms can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the magnetic powder. Abrasive materials that may be used include commonly used materials such as fused alumina, silicon carbide,
Chromium oxide, corundum, artificial corundum, diamond, artificial diamond, 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.
It is. These abrasives are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic powder. 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. Nonionic surfactants such as alkylene oxide, glycerin, and glycidol; Cationic surfactants such as higher alkyl amines, quaternary ammonium salts, pyridine, other heterocycles, phosphonium or sulfonium; carboxylic acids, Examples include anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols. Examples of solvents for magnetic paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, etc. Esters: ethylene glycol dimethyl ether, diethylene glycol monoethyl ether,
Ethers such as dioxane and etrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene, etc. can be used; Examples of curing agents that can be used include isocyanates, epoxy compounds, and adducts of these with active hydrogen compounds. Examples of isocyanate compounds include those shown in Table 1 below.

【table】

【table】

【table】

[Table] Examples of epoxy compounds include the compounds shown in Table 2 below.

【table】

[Table] In addition, Takenate D-103 (manufactured by Takeda Pharmaceutical Company), Desmodyur L-75 (manufactured by Sumitomo Bayer)
There is. In addition, usable curing agent precursors are added to facilitate the function of the curing agent (e.g., pH adjustment, concentration adjustment).
-X (X is a group that is easily dissociated, such as a halogenated alkyl group or an aryl group), and is then dissociated under appropriate conditions, such as by applying temperature, to form an isocyanate compound (having -NCO).
There is something that says. Further, as another type, nitrile oxide (a compound having a group -CN←O) can be used, and the nitrile oxide can be easily converted into an isocyanate compound. In addition to the above-mentioned curing agents and curing agent precursors, the curing components include curing reaction decomposers (for example, amines such as triethylamine, dibutyltin dilaurate, iron acetylacetonate, and 2-methyl-
tin hexylate, tin naphthenate, tin octylate, tin laurate, tin stearate, etc.
(RCOO) ₂ Sn containing C ₆ to _{C 18} (which may contain branches) may be mentioned, and organic metal compounds and metal salts such as “Hexoate Tin” manufactured by Toei Kako Co., Ltd. may also be added. Further, as the material of the support body 30 mentioned above, polyethylene terephthalate, polyethylene-2,
Polyesters such as 6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polycarbonate, metals such as Al and Zn, glass, silicon nitride, silicon carbide, porcelain, ceramics, etc. Ceramics etc. are used. The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 100 μm.
50μm, and in the case of disk or card shape,
The diameter is about 30 μm to 10 mm, and when it is drum-shaped, it is cylindrical, and its shape is determined depending on the recorder used. Coating methods for forming a magnetic layer by applying the magnetic paint onto the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, and gravure coating. , kiss coat, cast coat, spray coat, etc., and other methods are also possible. The magnetic layer coated on the support by such a method is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried. Further, if necessary, the magnetic recording medium is manufactured by subjecting it to a surface smoothing process or cutting it into a desired shape. Next, the advantages of the present invention will be explained using specific examples. First, for comparison, the following composition was prepared (however, "parts" indicate parts by weight). Using this, the following operation was carried out using the continuous addition method according to the conventional method (using a buffer tank) described above. Co-containing γ-Fe ₂ O ₃ 300 parts Partially hydrolyzed vinyl chloride-vinyl acetate copolymer ("VAGH" manufactured by Union Carbide) 40 parts Polyurethane ("Estan" manufactured by Gutdrich)
5701'' 40 parts Silicone oil 4 parts Triene/Methyl ethyl ketone = 1/1 800 parts The above composition was placed in a ball mill, dispersed for 24 hours, and then filtered through a filter with an average pore size of 3 μm to obtain a magnetic paint (hereinafter referred to as curable component-free). The magnetic paint is called liquid A) and is temporarily stored in a tank (13 in Figure 1). Isocyanate compound ("Coronate L" manufactured by Nippon Polyurethane Co., Ltd.) 25 parts terminal NCO urethane prepolymer 10 parts toluene/methyl ethyl ketone = 1/1 While continuously adding a curable component having a composition of 105 parts, it was applied onto a polyethylene terephthalate film. A magnetic recording material was obtained by applying the magnetic recording material to a dry thickness of 5μ, orienting it, and drying it.The obtained magnetic recording material was subjected to a super calendar roll treatment and slit into 1/2 inch width.
Got the videotape. Coating according to the above method was carried out after a predetermined time (for example, one hour) after the magnetic paint A was passed through and put into a storage tank (13 in FIG. 1). The video sensitivity (5MHz video sensitivity: measured with a VHS type video deck) of the obtained medium was as shown by curve a in FIG. 4. On the other hand, when the magnetic paint is applied while the mixture is refluxed at a rate of 3 to 8 min, as shown by 35 in Fig. 1, the obtained video sensitivity is as shown by curve b in Fig. 3. It was found that this was improved over the above comparative example. A videotape was prepared in the same manner except that the composition of the magnetic paint liquid A was changed as shown below, and the squareness ratio of the videotape coated while continuously adding a hardening agent was as shown in Table 3 below. The squareness ratio of the videotape produced using the apparatus shown in FIG. 1 of the present invention is shown in Table 3 below. Fe-based metal magnetic powder (Fe97%, Al3%) 300 parts Polyester polyurethane 30 parts Epoxy resin (Union Carbide "PKHH") 30 parts Silicone oil 3 parts Myristic acid 4 parts Toluene/Methyl ethyl ketone = 1/1 800 parts

[Table] In addition, when Co-containing γ-Fe ₂ O ₃ is used as the magnetic powder in the above paint composition, the squareness ratio of the videotape produced is 0.87 after 1 hour elapsed time and 0.85 after 20 hours elapsed time. It was hot. This is clearly worse than when Al-containing Fe-based metal magnetic powder is used as in the present invention. Therefore, it can be seen that in the case of the present invention, the stability of the paint was improved by using the Al-containing Fe-based metal magnetic powder. Furthermore, when a videotape was prepared in the same manner using 0.8 parts of iron acetylacetonate added to the curing agent component tank 15, the result was as shown in Table 4 below. (Invention', Comparative').

[Table] Next, for comparison, in place of the Fe-based metal magnetic powder (Fe-97%, Al-3%),
A videotape was made using -97% Ni and -3% metal magnetic powder, but in the same manner as above. As a result, the viscosity change of the magnetic paint from 1 hour to 15 hours is shown in Table 5 below, and the RF output of the magnetic tape coated with the paint after 1 hour is based on the value of the tape in the example ( 0dB), the following table-6
It became a street.

【table】

[Table] This result shows that even with metal magnetic powder, by using Al-containing Fe-based metal magnetic powder as in the present invention, the stability of the paint over time is improved and the output is also improved. In addition, in the above, Fe-97%, Al-3%
When magnetic paint using Fe-based magnetic powder, Fe-97%, Ni-3% Fe-based magnetic powder is intermittently added to the mixer (i.e., under conditions where the mixture is refluxed at a rate of 3 to 8 min. Even if the viscosity was adjusted by adding only the curable component without adding the magnetic paint for 3 to 4 seconds), the viscosity change of the magnetic paint was 2200 centipoise (Fe-Al type) and 2200 centipoise in one hour. (Fe-Ni system), 2980 centipoise (Fe-Al system), 4050 centipoise (Fe-Ni system) in 18 hours, and the change over time does not decrease that much (Fe-Al system).
It was found that -Al type is relatively stable). In addition, in the above, Fe-
A videotape was created in the same manner, except that the magnetic paint containing 97% Al-3% Fe-based magnetic powder and the curable component were mixed using an ordinary mixer without using a static mixer. The squareness ratio obtained was 0.88 after 1 hour and 0.79 after 20 hours. The above facts are clearly considered to reflect the effects such as reduced agglomeration of the paint when the magnetic paint is prepared using the method and apparatus according to the present invention. Although the present invention has been illustrated above, the above-mentioned example can be further modified based on the technical idea of the present invention. For example, the position where the above-mentioned reflux path (35 in the figure) is provided can be arbitrarily selected, and the reflux can be made from a point immediately after the disperser 27. Further, the mixing means is not limited to the above-mentioned one. 6. Effects of the Invention As described above, in the present invention, the magnetic paint mixture is fed by a static mixer and returned from the downstream side to the magnetic paint-curing component mixing section (a reflux path is provided). Accordingly, the flow rate or paint supply amount in the mixing section can be increased, making it suitable for mass production. Furthermore, since the mixture can be processed by being constantly fluidized without stagnation, changes in viscosity and progress of the curing reaction can be effectively suppressed. In addition, since the magnetic paint is prepared by continuous addition using Al-containing Fe-based magnetic powder as the magnetic powder, changes in the paint over time are reduced and properties such as RF output and squareness ratio are improved. .

[Brief explanation of the drawing]

The drawings show examples of the present invention, and FIGS. 1 and 2 are schematic diagrams of three examples of magnetic recording medium manufacturing apparatuses, and FIG. 3 is a graph showing the characteristics of the obtained magnetic tape. be. In addition, in the symbols shown in the drawings, 11, 27... Dispersion machine, 13... Tank for magnetic paint, 15... Tank for curable component, 23... Mixer, 24... Static mixer, 31, 3...
2...Flow meter, 33...Microcomputer, 34...Applying roller, 35...Recirculation conduit.

Claims (1)

[Claims] 1. When applying a magnetic paint containing aluminum-containing iron-based metal magnetic powder onto a support, at least a hardening agent and/or a hardening agent precursor and the magnetic paint are continuously introduced in predetermined amounts into a mixing section. the mixture is sent through a static mixer, and a portion of the mixture is returned to the mixing section from the downstream side of the static mixer through a reflux conduit. A method for manufacturing a recording medium.