JPH0261412B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to acicular particles containing surface-treated iron carbide and a magnetic coating composition comprising the same. The present inventors have filed a patent application (Japanese Patent Application No. 1983-1983) for acicular particles containing iron carbide, their manufacturing method, and their uses.
No. 171765 (see Japanese Unexamined Patent Publication No. 60-71509)). Acicular particles containing iron carbide have excellent magnetic properties such as high coercive force, and have magnetic field orientation. However, when processed into magnetic recording media such as magnetic tape, the squareness ratio was around 0.7, leaving room for improvement. Magnetic recording media are required to have a high signal output/noise ratio. If other conditions are the same, the signal output depends on the magnitude of the residual magnetic flux density, which in turn depends on the squareness ratio, so
An improvement in the squareness ratio leads to an improvement in the residual magnetic flux density, which leads to an improvement in the signal output/noise ratio. An object of the present invention is to provide acicular particles containing iron carbide that provide a magnetic recording medium that exhibits an excellent squareness ratio when processed into a magnetic recording medium, and a magnetic coating composition containing the same. It's about doing. The above object can be achieved by surface-treating acicular particles containing iron carbide with a surface-treating agent. Thereby, it is possible to obtain a magnetic recording medium having an improved squareness ratio, and thus a high coercive force and a high residual magnetic flux density. In the present invention, by providing a coating layer of a surface treatment agent on the surface of acicular particles containing iron carbide,
The squareness ratio can be improved by 0.02 or more compared to the case where the coating layer of the surface treatment agent is not provided. Here, the method for preparing the sample for measuring the squareness ratio and the method for measuring the squareness ratio were performed as follows. (i) Sample preparation method 20g of acicular particles containing iron carbide are added to acetone.
The suspension was suspended in 200 g, 0.5 g of the surface treatment agent was added thereto, stirred for 1 hour, filtered, and dried under reduced pressure at room temperature to prepare a sample having a coating layer of the surface treatment agent. (ii) Squareness ratio measurement method The acicular particles of the above sample and the acicular particles without surface treatment were prepared into a paint using the following formulation. Acicular particles 18.25g Vinyl chloride-vinyl acetate copolymer 5.25g Dioctyl phthalate 1.00g Lauric acid 0.2g Toluene 15.0g Methyl isobutyl ketone 15.0g The prepared paint was coated with a doctor knife (gap 100μ).
(m) was applied onto a polyethylene terephthalate film, subjected to orientation treatment using a repulsion and repulsion magnet method, and dried. The magnetic properties of the film thus obtained were measured in the direction perpendicular and parallel to the direction of orientation treatment. In the present invention, the iron carbide-containing acicular particles to be surface treated are
-It is described in No. 171765. That is,
The acicular particles have an average primary particle axis ratio (major axis/minor axis) of usually 3 or more, preferably 3 to 20, and an average particle diameter (long axis) of usually 2 μm or less, preferably 0.1 to 20. 2μ
m, optimally 0.1 to 1.0 μm. put it here,
Primary particles are
Particles that can be observed and identified at magnification Further, the iron carbide contained in the acicular particles is
Fe ₅ C ₂ , Fe ₂ C, and Fe ₂₀ C ₉ (Fe _2.2 C) each singly or as a mixture of two or more, and FexC (2≦x<
3) is appropriate. The presence of iron carbide generally indicates that the X-ray diffraction pattern of iron carbide represented by a known chemical formula (e.g.
This can be confirmed by comparing it with the ASTM X-Ray Powder Date File. However, since the differences in the X-ray diffraction patterns between individual iron carbides are slight, it is possible to confirm the main component iron carbide, but it is almost impossible to confirm other iron carbides that exist in trace amounts. be. However,
A trace amount of iron carbide coexisting can be ignored because it has no effect on magnetic properties and the like. In a preferred embodiment, the lattice spacing in the X-ray diffraction pattern is
2.28, 2.20, 2.08, 2.05 and 1.92 Å. Such iron carbide is considered to correspond to Fe ₅ C ₂ , and Fe ₂ C, Fe ₂₀ C ₉ (Fe _2.2 C), Fe ₃ C, etc. may coexist. Further, when the content of iron carbide in the acicular particles of the present invention is 20% by weight or more, the coercive force of the acicular particles is
It is preferable to have a coercive force of 450 Oe or more, and when it is 50% by weight or more, it is more preferable to have a coercive force of 850 Oe or more. As mentioned above, it is almost impossible to confirm all types of iron carbide contained, and furthermore, it is generally impossible to isolate them, so the amount of iron carbide present cannot be determined. Determine the chemical formula for the main component iron carbide that can be confirmed, and if necessary,
Determine chemical formulas for components other than iron carbide, such as
It can be determined as Fe ₃ O ₄ etc. by combining these chemical formulas, elemental analysis, and scorching heat gain. Further, the acicular particles include not only those containing only iron carbide as a component, but also those containing other components. Components other than iron carbide include components derived from manufacturing raw materials, such as iron oxide, components derived from the manufacturing process, such as elemental carbon, and copper and magnesium derived from other additives to manufacturing raw materials.
Examples include carbides or oxides of manganese, nickel, cobalt, etc., carbonates or oxides of potassium, sodium, etc., and/or oxides of silicon, etc. A preferred method for producing the acicular particles is to contact acicular iron oxyhydroxide or acicular iron oxide with CO or a mixture thereof with H ₂ . Here, the average axial ratio of acicular iron oxyhydroxide or acicular iron oxide is usually 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 2μ
m or less, preferably 0.1 to 2 μm, optimally 0.1 to 1.0 μm
It is m. As will be described later, the average axial ratio and average particle diameter of the acicular particles produced are slightly smaller than those of these raw materials, but there is almost no difference, and this is usually the case for the acicular particles of the present invention in general. This is because something like this is suitable. The acicular iron oxyhydroxide is preferably acicular α-FeOOH (goethite) or acicular γ-FeOOH (lepidocrocite);
Fe ₂ O ₃ (hematite), acicular γ-Fe ₂ O ₃ (maghemite) or acicular Fe ₃ O ₄ (magnetite) are preferred. The particles obtained in the present invention are averagely uniform acicular particles when observed with an electron microscope, and have the same shape as the acicular particles of the raw material acicular iron oxyhydroxide or acicular iron oxide. They are skeletal particles and exist as primary particles. Further, it is clear that the obtained acicular particles contain carbon according to elemental analysis, and further contain iron carbide according to the X-ray diffraction pattern. The X-ray diffraction pattern shows that the interplanar spacing is
2.28, 2.20, 2.08, 2.05 and 1.92 Å are shown. Such a pattern corresponds to Fe ₅ C ₂ , and the iron carbide of the present invention usually consists mainly of Fe ₅ C ₂ , but Fe ₂ C, Fe ₂₀ C ₉
(Fe _2.2 C), Fe ₃ C, etc. may coexist. Therefore, the iron carbide contained in the acicular particles of the present invention is
It is appropriate to express it as FexC (2≦x<3). If carbonization is incomplete, the acicular particles obtained according to the invention also contain iron oxides, mainly Fe ₃ O ₄ . In general, regarding iron oxides, FeO, Fe ₃ O ₄ and γ-Fe ₂ O ₃ are structurally related, and the oxygen atoms in these three have a cubic close-packed structure, and in reality Since the existing Fe ₃ O ₄ varies within these ranges, the above iron oxide is FeOy (1<y≦
1.5) is appropriate. The obtained acicular particles also contain iron carbide or iron oxide in some cases, but when referring to the elemental analysis values of C, H, and N, it is usually calculated using the chemical formula of iron carbide confirmed by the X-ray diffraction pattern. Contains carbon in excess of the amount of carbon used. Such excess carbon is
It is unknown whether it exists in combination with iron or as free carbon. In this sense, elemental carbon may be present in the acicular particles obtained.
Therefore, the obtained particles are acicular particles consisting essentially of iron carbide or iron carbide, iron oxide and/or elemental carbon, and have an average axial ratio of 3 or more in the form of primary particles. . Further, the average axial ratio and average particle diameter of the obtained acicular particles are slightly smaller than those of the raw material acicular iron oxyhydroxide or acicular iron oxide, but there is almost no difference. Therefore, the average axial ratio of the acicular particles obtained by this production method is usually 3 or more, preferably 3 to 20, and the average particle diameter (long axis) is usually 2 μm or less, preferably 0.1
~2 μm, optimally 0.1-1.0 μm. In the present invention, the surface treatment agent includes (1) a silane coupling agent such as γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane; Silane, γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)
Ethyltrimethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrichlorosilane, vinyltriacetate such as oxysilane. (2) Long-chain organic carboxylic acids or their salts, such as oleic acid, coconut oil fatty acids, fatty acids having 12 to 20 carbon atoms such as sodium oleate, or their alkali metal (Na, K, NH ₄ , etc.) salts or alkaline earths. Salts of similar metals (calcium, magnesium, etc.) (3) Phosphate esters, such as lecithin, Garfac [manufactured by Toho Chemical Co., Ltd.], etc. (4) Sorbitan fatty acid esters, such as polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan mono Examples include stearate, polyoxyethylene sorbitan monolaurate, etc. (5) Organic sulfonates such as sodium dialkyl sulfosuccinate, sodium alkylbenzene sulfonate, and the like. In the present invention, the method of treating the acicular particles with a surface treatment agent to form a coating layer of the surface treatment agent can be carried out as appropriate. For example, acicular particles containing iron carbide are generally treated at 10% by weight. A method of suspending the acicular particles in a solvent as shown below, adding a predetermined amount of the processing agent to the suspension and stirring, and adsorbing the processing agent onto the surface of the acicular particles to form a coating layer. Examples include a method in which a predetermined amount of a treatment agent dissolved in a solvent is sprayed to form a coating layer. The amount of the surface treatment agent is preferably about 0.01 to 3% by weight, based on the iron carbide-containing acicular particles. When the amount of the processing agent is within this range, the effects of the present invention are noticeable,
In addition, there is less possibility that the processing agent will leak into the magnetic recording medium and adversely affect various characteristics, which is preferable. The present invention also relates to a magnetic coating material comprising acicular particles containing iron carbide and having a coating layer of the above-mentioned surface treatment agent. The magnetic paint made from the acicular particles of the present invention can be produced by a known method, for example, by dispersing the acicular particles together with a binder in an organic solvent. An antistatic agent and the like can be added as necessary. As the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, etc., and mixtures thereof are used. As a thermoplastic resin, the softening temperature is 150℃ or less,
Average molecular weight is 10000~200000, degree of polymerization is about 200~
2000, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer,
Vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinyldene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic Acid ester styrene copolymer, urethane elastomer,
Polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer,
Polyester resins, chlorovinyl ether acrylic acid ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof 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 when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenolic resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin,
Epoxy-polyamide resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers,
Mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and mixtures thereof, etc. . These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the acicular particles and the binder is 10 to 400 parts by weight, preferably 30 parts by weight, of the binder to 100 parts by weight of the acicular particles.
Used in the range of ~200 parts by weight. Examples of dispersants include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid, etc. having 12 or more carbon atoms.
18 fatty acids (R ¹ COOH, R ¹ is an alkyl group having 11 to 17 carbon atoms); alkali metals (Li,
Na, K, etc.) or alkaline earth metals (Mg, Ca, etc.)
Metal soap consisting of Ba, etc.); lecithin, etc. are used. In addition, higher alcohols with carbon numbers of 12 or more,
In addition to these, sulfuric esters and the like can also be used. These dispersants are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder. As lubricants, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of monobasic fatty acids with 12 to 16 carbon atoms and monohydric alcohols with 3 to 12 carbon atoms, carbon atoms of 17 or more are used. A fatty acid ester consisting of a monobasic fatty acid and a monohydric alcohol having 21 to 23 carbon atoms in total can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder. As the abrasive, commonly used materials such as fused alumina, silicon carbon, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite) are used. These abrasives have an average particle diameter of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm. These abrasives are added in an amount of 7 to 20 parts by weight based on 100 parts by weight of the binder. As an antistatic agent, natural surfactants such as saponin; alkylene oxide type, glycerin type,
Nonionic surfactants such as glycidol; cationic surfactants such as higher alkyl amines, quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, Anionic surfactants containing acidic groups such as phosphate groups;
Ampholytic activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. These antistatic agents may be added alone or in combination. Although these are used as antistatic agents, they are sometimes applied for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids. The present invention will be described below with reference to Examples. Reference example 1 2 g of needle-shaped lepidocrocite particles with an average particle diameter of 0.7 μm (long axis) and an average axial ratio of 10 were placed in a porcelain boat and inserted into a tube furnace, and after replacing the air by flowing nitrogen, ℃, and at that temperature CO/H ₂ (30/70
The mixture was treated for 5 hours while flowing a mixed gas (volume ratio) at a flow rate of 75 ml per minute, and then allowed to cool to room temperature to obtain a black acicular powder. The X-ray diffraction pattern of the product is ASTM X-
Ray Powder Data File 20−509 Fe ₅ C ₂ Iron
Matched with Carbide. Table 1 shows the interplanar spacing (dÅ) and intensity ratio (I/I ₁ ) of the peaks in the pattern.
, ASTM's X-Ram Powder Data File 20
A comparison with those of −509 Fe ₅ C ₂ Iron Carbide is shown.

[Table] Note that no Fe ₃ O ₄ peak was detected. The magnetic properties of the thus obtained powder were measured using a vibrating sample magnetometer VSM 3 model manufactured by Toei Kogyo Co., Ltd. under a measuring magnetic field of 15 kOe. The results are shown below. Coercive force (Hc) 878Oe Residual magnetization (σr) 54.7emu/g Saturation magnetization (σs) 134.4emu/g Examples 1 to 6 and Comparative Example 1 20g of acicular particles obtained in Reference Example 1 were added to 200g of acetone. 0.5g of suspended surface treatment agent listed in Table 2
was added thereto, stirred for 1 hour, filtered, and dried under reduced pressure at room temperature to prepare surface-treated acicular particles. Acicular particles without surface treatment (Comparative Example 1) and acicular particles with various surface treatments were prepared into paints using the following formulations. Acicular particles 18.25g Vinyl chloride-vinyl acetate copolymer 5.25g Dioctyl phthalate 1.00g Lauric acid 0.2g Toluene 15.0g Methyl isobutyl ketone 15.0g Use the prepared paint with a doctor knife (gap 100μm)
The film was coated on a polyethylene terephthalate film, oriented using a repulsive magnet method, and dried. The magnetic properties of the film thus obtained were measured in the directions perpendicular and parallel to the orientation treatment direction, and the coercive force, residual magnetic flux density, and squareness ratio were determined. The results are shown in Table 2. In addition, in the table, A: γ-glycidoxypropyltrimethoxysilane B: Oleic acid C: Garfac RA-600 D: Polyoxyethylene sorbitan monooleate E: Sodium dioctyl sulfosuccinate F: Sodium oleate

【table】

Claims (1)

[Scope of Claims] 1. Acicular particles containing iron carbide and having an average axial ratio of primary particles of 3 or more and having a coating layer of a surface treatment agent sufficient to improve the squareness ratio by 0.02 or more. 2. The particles according to claim 1, wherein the surface treatment agent is a silane coupling agent, a long-chain organic carboxylic acid or a salt thereof, a phosphoric acid ester, a sorbitan fatty acid ester, or an organic sulfonate. 3. A magnetic paint material comprising acicular particles containing iron carbide and having an average axial ratio of primary particles of 3 or more and having a coating layer of a surface treatment agent sufficient to improve the squareness ratio by 0.02 or more. 4. The material according to claim 3, wherein the surface treatment agent is a silane coupling agent, a long-chain organic carboxylic acid or a salt thereof, a phosphoric acid ester, a sorbitan fatty acid ester, or an organic sulfonate.