EP0997918A1 - Preparation of a magnetic layer - Google Patents
Preparation of a magnetic layer Download PDFInfo
- Publication number
- EP0997918A1 EP0997918A1 EP99201371A EP99201371A EP0997918A1 EP 0997918 A1 EP0997918 A1 EP 0997918A1 EP 99201371 A EP99201371 A EP 99201371A EP 99201371 A EP99201371 A EP 99201371A EP 0997918 A1 EP0997918 A1 EP 0997918A1
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- EP
- European Patent Office
- Prior art keywords
- support
- ions
- magnetic layer
- soft magnetic
- process according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/0027—Thick magnetic films
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/14—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates
- H01F41/16—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates the magnetic material being applied in the form of particles, e.g. by serigraphy, to form thick magnetic films or precursors therefor
Definitions
- the present invention relates to the preparation of particular types of magnetic layers and to their use in an anti-theft system.
- H a ferromagnetic sample that is initially demagnetized
- B a particular flux density
- the value of H is decreased again the decreasing flux density does not follow the path of increase but decreases at a rate less than that at which it rose.
- H has reached zero again the value of B is not reduced to zero but to a value called the retentivity or remanence.
- the sample has retained a permanent magnetization.
- the value of B may be reduced to zero by reversing th magnetic field to negative and increasing its value to the so-called coercive force or coercivity.
- H By further increasing H to negative values and then again reversing its direction a hysteresis loop as represented in fig. 1 is completed.
- a so-called soft ferromagnetic material shows a rather low coercive force ; a so-called semi-soft ferromagnetic material shows a rather high coercive force.
- This properties are used in a special type of anti-theft labels, e.g. for preventing the theft from clothes out of shops, called EM-EAS labels ( E lectro M agnetic E lectronic A rticle S urveillance).
- the principle works as follows.
- a label carrier is covered on one side with a soft magnetic layer having a coercive force of about 0.5 Oe, and on the other side with a semi-soft magnetic layer having a coercive force of about 100 Oe.
- the detection zone consists of a transmitter which transmits an alternating magnetic field with a force Z M positioned between 0.5 and 100 Oe, and of a receiver.
- the semi-soft magnetic layer consists of a nickel mesh
- the soft magnetic layer consists of a complex alloy of Ni a Fe b Co c (Mo) d B e .
- the problem with these magnetic layers is the fact that they are nowadays applied by means of sputtering in vacuo, a cumbersome and expensive technique.
- aqueous solution of nickel(II) ions is prepared.
- a most suitable salt is Ni(NO 3 ) 2 .6H 2 O.
- the solution is acidified with a small amount of nitric acid.
- the nickel ions in the solution are reduced to highly dispersed metallic nickel particles of nanosize by means of the addition of a reducing agent.
- a preferred reducing agent is KBH 4 .
- the reducing agent can be added to the original nickel salt solution as a solid powder. More preferably, the reducing agent may be dissolved separately in a second aqueous medium and added to the nickel salt solution according to a single jet or a double jet procedure. Preferably, according to the double jet principle, the aqueous medium containing the nickel ions and the second solution containing the reducing agent are added together to a third aqueous medium.
- the second aqueous solution comprising the reducing agent preferably also contains sulphite ions which strongly enhance the chemical stability of this solution.
- a protective binder is preferably added to one or more of the three aqueous solutions involved.
- this protective binder is added to the third aqueous medium wherein both others are jetted.
- a particularly preferred protective binder is carboxymethylcellulose (CMC).
- CMC carboxymethylcellulose
- Other possible binders include gelatin, arabic gum, poly(acrylic acid), cellulose derivatives and other polysaccharides.
- a complexing agent is present in one of the three aqueous media described above.
- a preferred complexant is simply the well-known ethylenediaminetetraacetic acid (EDTA) or a homologous compound or a salt thereof.
- EDTA ethylenediaminetetraacetic acid
- Another preferred one is citrate, e.g. triammonium citrate.
- Suitable complexants include diethylenetriamine-pentaacetic acid (DTPA), trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), ethyleneglycol-O,O'-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), N-(2-hydroxyethyl)ethylenediamine-N,N,N'-triacetic acid (HEDTA), etc.
- the complexing agent is preferably present in the third aqueous medium to which the other solutions are added according to the double jet principle.
- the superfluous salts are first removed from the aqueous medium by a washing process, preferably involving ultrafiltration and/or diafiltration. Additionally or alternatively centrifugation can be used.
- a so-called dispersing aid can be present.
- this compound is added to the diafiltration liquid at the last stage of the preparation.
- Suitable dispersing aids in the case of nickel are phosphates, more particularly a hexametaphosphate such as sodium hexametaphosphate.
- the hexametaphosphate adsorbs to the surface of the alloy particles so that they become negatively charged. By electrostatic repulsion they are kept in dispersion.
- the phosphate inhibits further oxidation of the surface of the formed nanoparticles.
- the thin nickel oxide shell that will be formed inevitably around the nanoparticles since the reducing medium disappears during the washing step will be passivated by the hexametaphosphate.
- the nickel particles are ultrafiltrated e.g. through a Fresenius F60 cartridge and subsequently diafiltrated against a solution of sodium hexametaphosphate in water/ethanol (98.5/1.5).
- the hexametaphosphate is also preferably added to the third aqueous solution.
- the obtained final colloidal composition is coated on the substrate by means of a conventional coating technique, such as slide hopper, curtain coating and air-knife coating.
- a conventional coating technique such as slide hopper, curtain coating and air-knife coating.
- Suitable coating agents include non-ionic agents such as saponins, alkylene oxides e.g. polyethylene glycol, polyethylene glycol/polypropylen glycol condensation products, polyethylene glycol alkyl esters or polyethylene glycol alkylaryl esters, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkylamines or alkylamides, silicone-polyethylene oxide adducts, glycidol derivaties, fatty acid esters of polyhydric alcohols and alkyl esters of saccharides; anionic agenst comprising an acid group such as a carboxy, sulpho, phospho, sulphuric or phosphoric ester group; ampholytic agents such as aminoacids, aminoalkyl sulphonic acids, aminoalkyl sulphates or phosphates, alkyl betaines, and amine-N-oxides; and cationic agents such as aklylamine salt
- Useful transparent organic resin supports include e.g. cellulose nitrate film, cellulose acetate film, polyvinylacetal film, polystyrene film, polyethylene terephthalate film, polycarbonate film, polyvinylchloride film or poly- ⁇ -olefin films such as polyethylene or polypropylene film.
- the thickness of such organic resin film is preferably comprised between 0.05 and 0.35 mm.
- the support is a polyethylene terephthalate layer provided with a subbing layer. This subbing layer can be applied before or after stretching of the polyester film support.
- the polyester film support is preferably biaxially stretched at an elevated temperature of e.g.
- the stretching may be accomplished in two stages, transversal and longitudinal in either order or simultaneously.
- the subbing layer when present, is preferably applied by aqueous coating between the longitudinal and transversal stretch, in a thickness of 0.1 to 5 mm.
- the subbing layer preferably contains, as described in EP 0 464 906, a homopolymer or copolymer of a monomer comprising covalently bound chlorine. Examples of said homopolymers or copolymers suitable for use in the subbing layer are e.g.
- polyvinyl chloride polyvinylidene chloride; a copolymer of vinylidene chloride, an acrylic ester and itaconic acid; a copolymer of vinyl chloride and vinylidene chloride; a copolymer of vinyl chloride and vinyl acetate; a copolymer of butylacrylate, vinyl acetate and vinyl chloride or vinylidene chloride; a copolymer of vinyl chloride, vinylidene chloride and itaconic acid; a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, etc.
- Polymers that are water dispersable are preferred since they allow aqueous coating of the subbing layer which is ecologically advantageous.
- the support may be opaque, such as a paper support, e.g. a plain paper support or a polyolefin coated paper. Furtheron glass, e.g. thin glass packed on roll can be used.
- the coated substantially pure nickel layer is ferromagnetic of the so-called semi-soft type.
- the nickel ions are not the sole ion type undergoing reduction but they are mixed with one or more other types of ions.
- Preferred types of salts for admixture with the nickel salt are iron salts, cobalt salts or molybdene salts, or mixtures of those.
- soft magnetic layers By choosing the appropriate type(s) of ions and the appropriate admixture ratio(s) so-called soft magnetic layers can be prepared.
- a support preferably a paper support
- a semi-soft magnetic layer based on substantially pure nickel prepared according to the present invention
- a soft magnetic layer based on an admixture of nickel particles with other metal particles prepared according to the present invention.
- the resulting labels can be used in a EM-EAS system ( E lectro M agnetic E lectronic A rticle S urveillance). Furtheron, such a label can also be produced when a semi-soft magnetic layer prepared according to the present invention is applied to a commercially available soft magnetic layer on a support.
- PERMALLOY (trade mark of Western Electric), METGLAS (trade mark of Allied Signal Co.), and ATALANTE (trade mark of IST/Bekaert).
- Particularly useful METGLAS products are type 2705M, consisting of Co 69 Fe 4 Ni 1 B 12 Si 12 , and type 2826MB, consisting of Fe 40 Ni 38 Mo 4 B 12 .
- such a label can also be produced when a soft magnetic layer prepared according to the present invention is applied to a commercially available semi-soft magnetic layer on a support.
- Examples of such commercial products are VICALLOY (trade mark of Telecon Metals Ltd.), AMOKROME (trade mark of Arnold Engineering), and CROVAK (trade mark of Vacuumschmelze GmbH).
- the Ni-Fe-dispersion was prepared as follows:
- solution 1 at a flow rate of 12.4 ml/min was simultaneously added with solution 2 at 12.4 ml /min.
- the NiFe dispersion was ultrafiltrated through a Fresenius F60 cartridge and diafiltrated with a 0.36 % solution of sodium hexametaphosphate in water/ethanol (98.5/1.5).
- the dispersion was stirred and 10 ml of a 12.5% solution of Saponine Quillaya (Schmittmann) in water/ethanol (80/20) was added. This is the Ni-Fe dispersion.
Abstract
Description
- the saturation magnetization Bsat which is proportional to the amount of material;
- the coercive force CM which is dependent on the chemical composition, the particle size, the temperature, etc.;
- the magnetic permeability (susceptibility or permitivity) PM which is dependent on the chemical composition, the degree of deformation of the material, etc..
Solution 1 | |
Ni(NO3)2.6H2O | 41.8 g |
Fe(SO4)2.6H2O | 14.3 g |
water to | 150 ml |
HNO3 | 3ml |
Solution 2 | |
Water | 150 ml |
NH3 (26% in water) | 0.5 ml |
KBH4 | 10 g |
Na2SO3 | 2 g |
Solution 3 | |
Na6P6O18 (2% in water/ethanol (85/15) | 100 ml |
Triammoniumcitrate (70% in water) | 9.1 ml |
Carboxymethylcellulose (3% in water) | 25.5 ml |
The dispersion was stirred and 10 ml of a 12.5% solution of Saponine Quillaya (Schmittmann) in water/ethanol (80/20) was added. This is the Ni-Fe dispersion.
The dispersion was analysed for its particle size distribution (weight average dwa) with the Disc Centrifuge Photosedimentometer BROOKHAVEN BI-DCP. A dwa of 56 nm (swa = 10) was obtained.
Subsequently this dispersion was coated on a substrated PET foil so that an amount of 0.90 g/m2 was obtained.
A Squid magnetometer was used to measure the magnetic properties. A coercive field of 110 Oe was measured.
Claims (13)
- Process for the preparation of a magnetic element comprising a support and at least one magnetic layer, said process comprising the steps of :(1) preparing an aqueous solution containing one or more type of metal ions including nickel(II) ions,(2) chemically reducing said one or more metal ions by means of a reducing agent thus forming a aqueous dispersion of metal particles including nickel,(3) removing all superfluous ions from said aqueous dispersion by means of a washing step or by means of centrifugation,(4) coating the resulting aqueous dispersion onto a support.
- Process according to claim 1 wherein said reducing agent is added by means of a separate second aqueous solution.
- Process according to claim 2 wherein said separate second aqueous solution further contains sulphite ions.
- Process according to any of claims 1 to 3 wherein said reducing agent is KBH4.
- Process according to any of claims 1 to 4 wherein said washing step involves an ultrafiltration and/or diafiltration step.
- Process according to claim 5 wherein a phosphate is present as dispersing aid during the ultrafiltration and/or diafiltration step.
- Process according to claim 6 wherein said phosphate is a hexametaphosphate.
- Process according to any of claims 1 to 7 wherein said metal ions are substantially solely nickel(II) ions thus giving rise after completing steps (1) to (4) to a semi-soft magnetic layer.
- Process according to any of claims 1 to 7 wherein said metal ions beside nickel ions further comprise iron ions, cobalt ions or molybdene ions, or mixtures of those, thus giving rise afer completing steps (1) to (4) to a soft magnetic layer.
- Magnetic material comprising a support and on one side of said support a semi-soft magnetic layer prepared according to the process of claim 8, and on the other side of said support a soft magnetic layer.
- Magnetic material comprising a support and on one side of said support a semi-soft magnetic layer, and on the other side of said support a soft magnetic layer prepared according to the process of claim 9.
- Magnetic material comprising a support and on one side of said support a semi-soft magnetic layer prepared according to the process of claim 8, and on the other side of said support a soft magnetic layer prepared according to the process of claim 9.
- Use of a magnetic material according to any of claims 10 to 12 as a label in a EM-EAS system (Electro Magnetic Electronic Article Surveillance).
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP19990201371 EP0997918B1 (en) | 1998-10-26 | 1999-04-29 | Preparation of a magnetic layer |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP98203868 | 1998-10-26 | ||
EP98203868 | 1998-10-26 | ||
EP19990201371 EP0997918B1 (en) | 1998-10-26 | 1999-04-29 | Preparation of a magnetic layer |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0997918A1 true EP0997918A1 (en) | 2000-05-03 |
EP0997918B1 EP0997918B1 (en) | 2004-07-14 |
Family
ID=26150879
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19990201371 Expired - Lifetime EP0997918B1 (en) | 1998-10-26 | 1999-04-29 | Preparation of a magnetic layer |
Country Status (1)
Country | Link |
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EP (1) | EP0997918B1 (en) |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5767156A (en) * | 1980-10-13 | 1982-04-23 | Nec Corp | Electroless plating bath |
JPS583963A (en) * | 1981-06-29 | 1983-01-10 | Nec Corp | Electroless plating method |
JPH02108221A (en) * | 1988-10-18 | 1990-04-20 | Mitsubishi Kasei Corp | Magnetic recording medium |
EP0793242A1 (en) * | 1996-02-28 | 1997-09-03 | Unitika Ltd. | Magnetic element and process for producing the same |
-
1999
- 1999-04-29 EP EP19990201371 patent/EP0997918B1/en not_active Expired - Lifetime
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5767156A (en) * | 1980-10-13 | 1982-04-23 | Nec Corp | Electroless plating bath |
JPS583963A (en) * | 1981-06-29 | 1983-01-10 | Nec Corp | Electroless plating method |
JPH02108221A (en) * | 1988-10-18 | 1990-04-20 | Mitsubishi Kasei Corp | Magnetic recording medium |
EP0793242A1 (en) * | 1996-02-28 | 1997-09-03 | Unitika Ltd. | Magnetic element and process for producing the same |
Non-Patent Citations (3)
Title |
---|
PATENT ABSTRACTS OF JAPAN vol. 006, no. 143 (C - 117) 3 August 1982 (1982-08-03) * |
PATENT ABSTRACTS OF JAPAN vol. 007, no. 069 (C - 158) 23 March 1983 (1983-03-23) * |
PATENT ABSTRACTS OF JAPAN vol. 014, no. 325 (P - 1075) 12 July 1990 (1990-07-12) * |
Also Published As
Publication number | Publication date |
---|---|
EP0997918B1 (en) | 2004-07-14 |
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