A magnetic recording medium having on a flexible, nonmagnetic support, in order, a lower layer comprising a nonmagnetic powder and a binder, and a magnetic layer comprising a ferromagnetic powder and a binder. The average thickness d of the magnetic layer is 0.02-0.2 xcexcm. The ferromagnetic powder contained in the magnetic layer is a platelike hexagonal ferrite magnetic powder with a mean plate diameter of not more than 40 nm. The nonmagnetic powder contained in the lower layer is an acicular inorganic powder with a mean main axis length of not more than 0.2 xcexcm. Further, the plate ratio of the ferromagnetic powder is not greater than the acicular ratio of the lower layer inorganic powder. A particulate magnetic recording material exhibiting a high C/N in high-density magnetic recording, particularly in reproduction with MR heads is provided.

1. Field of the Invention
The present invention relates to a particulate magnetic recording medium for high-density recording.
2. Description of Related Art
In recent years, recording wavelengths have tended to shorten as recording densities have increased. The problem of self-magnetization losses during recording, where output drops due to the thickness of the magnetic layer, has become significant. Thus, the magnetic layer has been reduced in thickness. However, when a magnetic layer of 2 xcexcm or less is directly coated onto a support, the nonmagnetic support tends to affect the magnetic surface, and deterioration of electromagnetic characteristics and dropout tend to appear.
One means of solving this problem employs a method of forming a magnetic layer by a simultaneous multilayer coating method in which a nonmagnetic lower layer is provided on a support and a high-density magnetic coating solution is thinly applied (Japanese Patent Unexamined Publication Nos. Sho 63-191315 and Sho 63-187418). Such inventions have made it possible to achieve good electromagnetic characteristics with dramatically improved yields.
Magnetoresistive reproduction heads designed to further increase recording density have been brought into practical use with hard disks, and tests on flexible media such as metal evaporation tapes (ME) have been reported (IEEE. Trans. Mag. Vol. 35. No. 2, p. 729 (1999)).
Although magnetic recording media suited to reproduction with MR heads have been examined with regard to metal evaporation tapes (ME), there has not been adequate examination with regard to particulate magnetic recording media with good production and preservation properties.
Accordingly, an object of the present invention is to provide a particulate magnetic recording medium exhibiting a high C/N ratio in high-density magnetic recording, particularly when employing MR heads for reproduction.
The present invention relates to a magnetic recording medium comprising on a flexible nonmagnetic support, in order, a lower layer comprising a nonmagnetic powder and a binder, and a magnetic layer comprising a ferromagnetic powder and a binder, wherein an average thickness of said magnetic layer ranges from 0.02 xcexcm to 0.2 xcexcm; said ferromagnetic powder contained in said magnetic layer is a magnetic powder of platelike hexagonal ferrite with a mean plate diameter equal to or less than 40 nm; said nonmagnetic powder contained in said lower layer is an inorganic acicular powder with a mean major axis length equal to or less than 0.2 xcexcm; and a plate ratio of said ferromagnetic powder is equal to or less than an acicular ratio of said inorganic powder of the lower layer.
The operating mechanism of the present invention will be described here.
Adopting a magnetic layer thickness of 0.02-0.2 xcexcm permits improvement in the C/N resolution of digital recordings with MR heads. This is documented by reports of the results of experiments employing evaporation tapes (IEEE, Trans. Mag. Vol. 35, No. 2, p. 729 (1999) and the Picture Information Media Society Technical Reports, Vol. 23, No. 78, p. 21 (1999)). However, it is difficult to achieve magnetic layer film thicknesses in coated media equivalent to those of thin metal films. Further, in coated media, with magnetic alloy powders yielding high performance with conventional inductance heads, there is significant noise during reproduction with MR heads and saturation tends to occur, precluding high C/N ratios. In the present invention, a magnetic layer with low magnetic nonuniformity can be achieved by providing a magnetic layer comprising a magnetic powder of hexagonal ferrite of small (mean plate diameter=40 nm) particle size over a nonmagnetic lower layer comprising a nonmagnetic powder having a mean major axis length of 0.2 xcexcm or less and an acicular ratio greater than the plate ratio of the magnetic powder.
In the present invention, incorporating a nonmagnetic powder with a higher acicular ratio than the magnetic particles into the nonmagnetic lower layer permits improvement in the flow orientation properties of the lower layer, improvement in the orientation of magnetic material of micrograms tending not to assume orientations, and reduction in the variation in thickness of the magnetic layer. The relation whereby the upper layer acicular ratio is less than or equal to that of the lower layer acicular ratio is disclosed in Japanese Patent Unexamined Publication Nos Hei 8-102037 and Hei 9-106533. However, the present invention has been found to achieve never before seen results by incorporating a microgranular magnetic powder of hexagonal platelike ferrite. That is, since magnetic hexagonal ferrite materials have lower saturation magnetization than magnetic alloy powders, the thixotropic property of the coating solution is low and orientation reversion tends to occur. Accordingly, although mixing with the lower layer takes place during the coating drying process, resulting in significant orientation reversion, the use of the lower layer in the present invention has been found to yield good upper and lower film boundaries and orientation properties. This effect is marked when the platelike, ferromagnetic powder (magnetic material of hexagonal ferrite) is oriented in a vertical direction. Further, the greater the acicular ratio of the lower layer magnetic powder, the better the molding properties during calendering, so it was found that by compensating for the fact that magnetic layers are difficult to form when using microgranular magnetic materials with low void rates in the film-forming stage, good surface properties could be achieved.
The following are desirable forms of the magnetic recording medium of the present invention:
(1) The mean grain volume of the ferromagnetic powder ranges from 1,500 to 15,000 nm3, and the coercivity Hc of the magnetic layer in the longitudinal direction is 167 KA/m (2,100 Oe) or greater;
(2) The squareness of the magnetic layer in the vertical direction SQxe2x8axa5 is 0.3 or greater and the coercivity in the vertical direction Hcxe2x8axa5 is 119 KA/m (1,500 Oe) or greater; and
(3) The mixing in of 10-30 parts of granular particles with a mean primary grain diameter of 50 nm or less and a true specific gravity of 5 or less per 100 parts of acicular material in the nonmagnetic lower layer is desirable to achieve uniform formation of the above-described thin magnetic layer.
The mean grain volume of the ferromagnetic powder is preferably 1,500-15,000 nm3 from the perspective of noise reduction, and the Hc is preferably 167 KA/m (2,100 Oe) or greater to maintain stable recording magnetization. A grain volume of 1,500 nm3 or greater and an Hc of 167 KA/m (2,100 Oe) or greater maintains good thermal stability of recording magnetization. When the grain volume is 15,000 nm3 or less, noise is controlled and an adequate C/N ratio can be achieved. Due to recording principles, a large coercivity Hc is desirable, but when the recording head capacity is considered, 175-279 KA/m (2,200-3,500 Oe) is actually suitable.
An SQxe2x8axa5 in the vertical direction of the magnetic layer of 0.3 or greater and an Hcxe2x8axa5 in the vertical direction of 119 KA/m (1500 Oe) or greater are advantageous to effectively exploit the vertical magnetization component and achieve good resolution.
Further, mixing in 10-30 parts of granular particles with a mean primary grain diameter of 50 nm or less and a true specific gravity of 5 or less per 100 parts of acicular material in the nonmagnetic layer forms voids between the acicular grains in the film, improves forming properties during calendering, and yields good surface properties.
[The Magnetic Layer]
In the magnetic recording medium of the present invention, a suitable average magnetic layer thickness (d) is 0.02-0.2 xcexcm, preferably 0.03-0.15 xcexcm.
The object of the present application can be achieved with a single layer or multilayered magnetic layer. When employing multiple magnetic layers, the technique described in Japanese Patent Unexamined Publication No. Hei 6-139555 can be applied, for example. Since the magnetic layer is thin in the present invention and a saturated recording state occurs, no variation in the thickness of the magnetic layer is desirable. However, so long as the relation between the standard deviation "sgr" in the recording layer thickness and d ("sgr"/d) is equal to or smaller than 0.5, variation can be permitted in practical terms. "sgr"/d is preferably equal to or smaller than 0.3.
An example of a specific method of reducing is to employ a thixotropic magnetic coating solution for the lower layer, as described in Japanese Patent No. 2566096. There is a wet-on-dry method of applying the magnetic upper layer after coating and drying the nonmagnetic lower layer employing an acicular nonmagnetic powder in the lower layer. Employing an acicular nonmagnetic powder of larger acicular ratio than the magnetic material as specified in the present invention and further mixing in microgranular powder with a true specific gravity of 5 or less permits a reduction in the standard deviations "sgr".
The residual magnetization level xcfx86r of the magnetic layer is desirably 5-50 mTxc2x7xcexcm (50-500 Gxc2x7xcexcm). xcfx86r is optimized within the range at which the MR head employed does not saturate. For example, the relation between xcfx86r in an evaporation tape and the saturation magnetization thickness of an MR element is disclosed in Japanese Patent Unexamined Publication No. Hei 10-134306 and the Picture Information Media Society Technical Reports, Vol. 23, No.78, p.21 (1999). The coated (particulate) medium also desirably satisfies the same relation. Examples of methods of setting the residual magnetization level include varying the quantity of binder employed and varying the saturization magnetization of the magnetic material employed. A suitable volume fill rate of the ferromagnetic powder is 30 percent or greater, preferably 35 percent or greater, and still more preferably, 38 percent or greater.
A suitable "sgr"s in the ferromagnetic powder is 50-70 Am2/kg (50-70 emu/g). A suitable average plate diameter is 40 nm or less, preferably 10-35 nm or less. A suitable plate thickness in the ferromagnetic powder is 5-20 nm, preferably 8-15 nm. A suitable acicular ratio (major axis length/minor axis length) in the ferromagnetic powder is 2-15, preferably 3-8.
Substitution products of barium ferrite, strontium ferrite, lead ferrite, and calcium ferrite, Co substitution products or the like, and hexagonal Co powders can be employed as the hexagonal ferrite. Specific examples are magnetoplumbite-type barium ferrite and strontium ferrite, as well as magnetoplumbite type barium ferrite and strontium ferrite partly containing a spinel phase. The following may be incorporated in addition to other prescribed atoms: Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, Nb, and the like. Compounds to which elements such as Coxe2x80x94Ti, Coxe2x80x94Tixe2x80x94Zr, Coxe2x80x94Tixe2x80x94Zn, Nixe2x80x94Tixe2x80x94Zn, and Irxe2x80x94Zn have been added may generally also be employed. The compounds of particular preference are Co substitution products of barium ferrite and strontium ferrite.
The hexagonal ferrite employed in the present invention is normally a hexagonal platelike grain. The grain diameter refers to the width of the plate of the hexagonal grain as measured by electron microscopy. In the present invention, the grain diameter (plate diameter) is specified within the range of 0.01-0.2 xcexcm, more preferably 0.02-0.1 xcexcm. Further, the mean thickness (plate thickness) of the grains is 0.001-0.2 xcexcm, more preferably 0.003-0.05 xcexcm. Further, the plate ratio (grain diameter/plate thickness) is 1-15, more preferably 3-7. The specific surface area (SBET) of the hexagonal ferrite micropowder as measured by the BET method is 25-100 m2/g, more preferably 40-70 m2/g. At less than 25 m2/g, noise increases, and at greater than 100 m2/g, surface properties deteriorate; such levels are thus undesirable. The saturation magnetization ("sgr"s) of the magnetic material is 50 Am2/kg (50 emu/g) or greater, preferably 60 Am2/kg (60 emu/g) or greater. The tap density is preferably 0.5 g/mL or greater, more preferably 0.8 g/mL or greater.
The following atoms may be incorporated into the magnetic powder in addition to other prescribed atoms: Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B and the like. To improve thermal stability, Al, Si, Ta, Y, and the like may be adhered to or solved into the surface. The magnetic powder may be pretreated prior to dispersion with a dispersing agent, lubricant, surfactant, antistatic agent, or the like.
Known binders can be employed in the magnetic layer; examples are described in Japanese Patent Nos. 2566096 and 2571351. These binders preferably incorporate a functional group (SO3M, PO3M, or the like) to promote adhesion to the magnetic powder; incorporation of an epoxy group is also desirable. The molecular weight is 10,000-100,000, preferably 20,000-60,000. The quantity employed is 5-25 parts, preferably 5-20 parts, and more preferably 5-15 parts per 100 weight parts of magnetic powder.
The magnetic layer may also incorporate a known abrasive such as xcex1-alumina or Cr2O3. The mean grain diameter of the abrasive for wet-on-wet application is not less than ⅓ and not more than five times the magnetic layer thickness, and for wet-on-dry application, not less than ⅓ and no more than two times the thickness of the magnetic layer. When excessively large, noise dropout results. Since abrasives especially tend to cause protrusions in wet-on-dry application, a microgranular abrasive is preferred. Known techniques may be employed for pH and surface treatment. In addition, solid lubricants (carbon with a grain diameter of not less than 30 nm) and liquid lubricants such as fatty acids and fatty esters may also be added.
[The Nonmagnetic Layer (Lower Layer)]
The nonmagnetic powder employed as the chief component of the nonmagnetic lower layer is characterized by being acicular, having an average major axis length of not more than 0.2 xcexcm, preferably 0.05-0.15 xcexcm, and having an acicular ratio smaller than that of the magnetic powder in the magnetic layer.
The acicular ratio of the lower layer powder is preferably 5-20, and more preferably satisfies the relation of 0.3xe2x89xa6acicular ratio of upper magnetic material/acicular ratio of lower layer nonmagnetic powderxe2x89xa60.9. Specifically, an acicular metal oxide of not less than pH 5 is particularly desirable in the present application. Such powders disperse well since they have high adhesive properties with the functional group in the binder, and have high mechanical strength in films.
In other preferred forms of the nonmagnetic powder, an oil absorption employing DBP of 5-100 mL/100 g, preferably 10-80 mL/100 g, and more preferably 20-60 mL/100 g is appropriate. The specific gravity is 1-12, preferably 3-6, and the ignition loss is preferably not more than 20 weight percent.
The nonmagnetic powder employed in the present invention desirably has a Mohs hardness of not less than 4. The powder surface desirably has a roughness factor of 0.8-1.5, preferably 0.9-1.2. Stearic acid (SA) absorption is 1-20 xcexcmol/m2, preferably 2-15 xcexcmol/m2. The heat of wetting in water at 25xc2x0 C. of the lower layer nonmagnetic powder desirably ranges from 20-60 xcexcJ/cM2 (200 erg/cm2-600 erg/cm2). Further, solvents falling within this heat of wetting range may also be employed. The number of surface water molecules at 100-400xc2x0 C. is suitably 1-10/100 A.
The pH at the isoelectric point in water is preferably 5-10.
The surface of the powder is preferably treated with Al2O3, SiO2, TiO2, ZrO2, SnO2, Sb2O3 or ZnO. Particularly good dispersability is achieved with Al2O3, SiO2, TiO2, and ZrO2. These may be employed singly or in combination. Depending on the objective, a coprecipitated surface treatment layer may be employed; a structure achieved by an alumina treatment followed by treatment of the surface layer with silica, or the reverse, may be adopted. The surface-treated layer may be a porous layer depending on the objective, but a homogeneous, dense layer is generally preferable. Examples of such acicular powders are oxides and nonmagnetic metals such as TiO2, hematite, xcex1-alumina, xcex3-alumina, ZrO2, CeO2, Cr2O3, and SiO2.
In addition to the above-described acicular nonmagnetic powder, 5-30 parts of a granular powder with a mean grain size of not more than 50 nm, preferably not more than 40 nm, and a true specific gravity of not more than 5 are desirably incorporated into the lower layer per 100 parts of acicular nonmagnetic powder. Oxides, nonmagnetic metals, organic resin fillers, carbon black, and the like, such as TiO2, hematite, alumina, ZrO2, CeO2, Cr2O3, and SiO2 may be employed. Carbon black with a mean grain size of 30 nm or less is particularly suitable.
The same binder as employed in the magnetic upper layer may be employed in the lower layer. However, it is desirable to incorporate a functional group (as described above) to enhance dispersability, and the molecular weight is 20,000-50,000, preferably 30,000-50,000. An excessively high molecular weight tends to compromise calender forming results. Surface treatment with alumina or an aromatic phosphorus compound to promote dispersion in the nonmagnetic material is also desirable.
For details, the descriptions in Japanese Patent Nos. 2566088 and 2634792 may be consulted.
The lower layer is suitably 0.3-3 xcexcm, preferably 0.5-2 xcexcm, in thickness.
The polyisocyanates given below may also be employed as binders in the upper layer and lower layer of the present invention: tolylene diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate or the like, products of these isocyanates with polyalcohols, or polyisocyanates produced by condensation of isocyanates. These isocyanates are commercially available under the following trade names: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR and Millionate MTL, manufactured by Nippon Polyurethane Co. Ltd.; Takenate D-102, Takenate D-110N, Takenate D-200 and Takenate D-202, manufactured by Takeda Chemical Industries Co. Ltd.; Desmodule L, Desmodule IL, Desmodule N and Desmodule HL, manufactured by Sumitomo Bayer Co. Ltd. and so on. They can be used singly or in combinations of two or more by exploiting differences in curing reactivity in both the nonmagnetic layer and the magnetic layer.
Examples of types of carbon black suitable for use in the upper layer of the present invention are: furnace black for rubber, thermal for rubber, black for coloring, and acetylene black. A specific surface area of from 5 to 500 m2/g, an amount of DBP oil absorption of from 10 to 400 mL/100 g, a grain diameter of from 5 nm to 300 nm, a pH of from 2 to 10, a moisture content of from 0.1 to 10 weight percent and a tap density of from 0.1 to 1 g/mL are desirable. Specific examples of types of carbon black employed in the present invention are: BLACK PEARLS 2000, 1300, 1000, 900, 800, 700 and VULCAN XC-72, manufactured by Cabot Corporation; #80, #60, #55, #50 and #35, manufactured by Asahi Carbon Co. Ltd.; #2400B, #2300, #900, #1000, #30, #40 and #10B, manufactured by Mitsubishi Chemical Corp.; and CONDUCTEX SC, RAVEN 150, 50, 40 and 15, manufactured by Columbia Carbon Co. Ltd. The carbon black employed may be surface-treated with a dispersant or grafted with resin, or have a partially graphitized surface. The carbon black may be dispersed in advance into the binder prior to addition to the coating solution. These carbon blacks may be used singly or in combination.
When employing a carbon black, the quantity employed is preferably 0.1-30 weight percent.
Carbon black works to prevent static in the magnetic layer, reduce the friction coefficient, impart light-blocking properties, enhance film strength, and the like; the properties vary with the type of carbon black used. Accordingly, the type, quantity, and combination of carbon black employed in the present invention may be determined separately for the upper magnetic layer and the lower layer, based on the objective and the various characteristics stated above, such as grain size, oil absorption amount, electrical conductivity, and pH. For example, the Carbon Black Handbook compiled by the Carbon Black Association may be consulted for the type of carbon black to employ in the magnetic layer of the present invention.
Chiefly, known materials with a Mohs hardness of 6 or greater may be employed singly or in combination as the abrasive of the present invention. Examples are xcex1-alumina having an xcex1-conversion rate of not less than 90 percent, xcex2-alumina, silicon carbide, chromium oxide, cerium oxide, xcex1-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide and boron nitride. Further, a composite comprising two or more of these abrasives (an abrasive obtained by surface-treating one abrasive with another) may also be used. Although these abrasives may contain compounds and elements other than the main component in some cases, the same effect is obtainable if the content of the main component comprises not less than 90 weight percent. A tap density of 0.3-2 g/mL, a moisture content of 0.1-5 weight percent, a pH of 2-11, and a specific surface area of 1-30 m2/g are desirable. The abrasive employed in the present invention may be acicular, spherical, or cubic in shape, but shapes that are partially angular have good abrasion properties and are thus preferred. Specific examples of abrasives employed in the present invention are: AKP-20, AKP-30, AKP-50, HIT-50, and HIT-100, manufactured by Sumitomo Chemical Co. Ltd.; G5, G7 and S-1, manufactured by Nippon Chemical Industrial Co. Ltd.; and TF-100 and TF-140, manufactured by Toda Kogyo K.K. It is, of course, possible in the present invention to separately determine the type, quantity, and combination of abrasive employed in the magnetic layers (upper and lower layers) of the present invention, based on the objective. These abrasives may be added to the magnetic application solution after being dispersion treated in advance with binder.
Substances having lubricating effects, antistatic effects, dispersive effects, plasticizing effects, or the like, may be employed as additives in the present invention. Examples are: molybdenum disulfide; tungsten graphite disulfide; boron nitride; graphite fluoride; silicone oils; silicones having a polar group; fatty acid-modified silicones; fluorine-containing silicones; fluorine-containing alcohols; fluorine-containing esters; polyolefins; polyglycols; alkylphosphoric esters and their alkali metal salts; alkylsulfuric esters and their alkali metal salts; polyphenyl ethers; fluorine-containing alkylsulfuric esters and their alkali metal salts; monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and metal (e.g., Li, Na, K, Cu) salts thereof; monohydric, dihydric, trihydric, tetrahydric, pentahydric and hexahydric alcohols having 12 to 22 carbon atoms (which may contain an unsaturated bond or be branched); alkoxy alcohols having 12 to 22 carbon atoms; monofatty esters, difatty esters, or trifatty esters comprising a monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or be branched) and any one from among a monohydric, dihydric, trihydric, tetrahydric, pentahydric or hexahydric alcohol having 2 to 12 carbon atoms (which may contain an unsaturated bond or be branched); fatty esters of monoalkyl ethers of alkylene oxide polymers; fatty acid amides having 8 to 22 carbon atoms; and aliphatic amines having 8 to 22 carbon atoms.
Specific examples of compounds suitable for use are: lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linolic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol and lauryl alcohol. It is also possible to employ nonionic surfactants such as alkylene oxide-based surfactants, glycerin-based surfactants, glycidol-based surfactants and alkylphenolethylene oxide adducts; cationic surfactants such as cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums, or sulfoniums; anionic surfactants comprising acid groups, such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester groups, and phosphoric ester groups; and ampholytic surfactants such as amino acids, amino sulfonic acids, sulfuric or phosphoric esters of amino alcohols, and alkyl betaines.
Details of these surfactants are described in xe2x80x9cA Guide to Surfactantsxe2x80x9d (published by Sangyo Tosho K.K.). These lubricants, antistatic agents and the like need not be 100 percent pure and may contain impurities, such as isomers, unreacted materials, by-products, decomposition products and oxides, in addition to the main components. These impurities are preferably comprised not more than 30 percent, and more preferably not more than 10 percent, by weight.
The lubricants and surfactants that are employed in the present invention may be employed differently in the lower layer and magnetic upper layer, as needed, based on type and quantity. For example, it is conceivable to control bleeding onto the surface through the use in the lower layer and the magnetic upper layer of fatty acids having different melting points, to control bleeding onto the surface through the use of esters having different boiling points and polarities, to improve coating stability by adjusting the amount of surfactant, and to enhance the lubricating effect by increasing the amount of the lubricant added to the nonmagnetic layer; this is not limited to the examples given here. All or some of the additives used in the present invention may be added at any stage of the process of manufacturing the magnetic application solution. For example, they may be mixed with the ferromagnetic powder before a kneading step; added during a step of kneading the ferromagnetic powder, the binder, and the solvent; added during a dispersing step; added after dispersing; or added immediately before coating. Part or all of the additives may be applied by simultaneous or sequential coating after the magnetic layer has been applied to achieve a specific purpose. Depending on the objective, the lubricant may be coated on the surface of the magnetic layer after calendering or making slits.
Examples of the trade names of lubricants suitable for use in the present invention are: NAA-102, NAA-415, NAA-312, NAA-160, NAA-180, NAA-174, NAA-175, NAA-222, NAA-34, NAA-35, NAA-171, NAA-122, NAA-142, NAA-160, NAA-173K, hydrogenated castor oil fatty acid, NAA-42, NAA-44, Cation SA, Cation MA, Cation AB, Cation BB, Nymeen L-201, Nymeen L-202, Nymeen S-202, Nonion E-208, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-210, Nonion HS-206, Nonion L-2, Nonion S-2, Nonion S-4, Nonion O-2, Nonion LP-20R, Nonion PP-40R, Nonion SP-60R, Nonion OP-80R, Nonion OP-85R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-60, Anon BF, Anon LG, butyl stearate, butyl laurate, and erucic acid, manufactured by NOF Corp.; oleic acid, manufactured Kanto Chemical Co. Ltd; FAL-205 and FAL-123, manufactured by Takemoto Yushi K.K.; EJLUB LO, EJLUB IPM, and Sansosyzer E4030, manufactured by New Japan Chemical Co. Ltd.; TA-3, KF-96, KF-96L, KF96H, KF410, KF420, KF965, KF54, KF50, KF56, KF907, KF851, X-22-819, X-22-822, KF905, KF700, KF393, KF-857, KF-860, KF-865, X-22-980, KF-101, KF-102, KF-103, X-22-3710, X-22-3715, KF-910 and KF-3935, manufactured by Shinetsu Chemical Co. Ltd.; Armide P, Armide C and Armoslip CP, manufactured by Lion Armour K.K.; Duomine TDO, manufactured by Lion Yushi K.K.; BA-41G, manufactured by Nisshin Oil Mills, Co. Ltd.; Profan 2012E, Newpole PE61, Ionet MS-400, Ionet MO-200, Ionet DL-200, Ionet DS-300, Ionet DS-1000 and Ionet DO-200, manufactured by Sanyo Chemical Industries Co. Ltd.
The organic solvent employed in the present invention may be used in any ratio. Examples are ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran; alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, and methylcyclohexanol; esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; aromatic hydrocarbons, such as benzene, toluene, xylene, cresol, and chlorobenzene; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene; N,N-dimethylformamide; and hexane. These organic solvents need not be 100 percent pure and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides and moisture in addition to the main components. The content of these impurities is preferably not more than 30 percent, more preferably not more than 10 percent. Preferably the same type of organic solvent is employed in the present invention for the magnetic layer coating solution and nonmagnetic layer coating solution. However, the amount added may be varied. The stability of coating is increased by using a solvent with a high surface tension (such as cyclohexane or dioxane) in the nonmagnetic layer. Specifically, it is important that the arithmetic mean value of the upper layer solvent composition be not less than the arithmetic mean value of the lower layer solvent composition. To improve dispersion properties, a solvent having a somewhat strong polarity is desirable. It is desirable that solvents having a dielectric constant of 15 or more are comprised not less than 50 percent of the solvent composition. Further, the dissolution parameter is desirably from 8 to 11.
The thickness of the flexible nonmagnetic support of the magnetic recording medium of the present invention is suitably from 1 to 100 xcexcm, preferably from 3 to 80 xcexcm. An under-coating layer can be provided between the flexible nonmagnetic support and the lower layer to improve adhesion. The thickness of this under-coating layer is from 0.01 to 2 xcexcm, preferably from 0.02 to 0.5 xcexcm. In addition, a backcoat layer may be provided on the opposite side of the nonmagnetic support from the magnetic layer side. The thickness thereof is from 0.1 to 2 xcexcm, preferably from 0.3 to 1.0 xcexcm. Publicly known under-coating layers and backcoat layers can be employed.
Publicly known films can be employed as the flexible nonmagnetic support in the present invention, including polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonates, polyamides, polyimides, polyamidoimides, polysulfones, aramide, and aromatic polyamides.
These supports may be subjected beforehand to corona discharge treatment, plasma treatment, adhesion enhancing treatment, heat treatment, dust removal, and the like.
When the nonmagnetic support employed in the present invention is a tape, Young""s modulus in the MD direction is 3.92-14.7 GPa (400-1,500 kg/ mm2), preferably 4.9-12.75 GPa (500-1,300 kg/mm2). Young""s modulus in the TD direction is 4.9-19.6 GPa (500-2,000 kg/mm2), preferably 6.9-17.6 GPa (700-1800 kg/mm2), and the ratio of TD/MD is 1/1-1/5, preferably 1/1-1/3.
The thermal shrinkage rate at 100xc2x0 C. at 30 minutes in the tape running direction and the crosswise direction of the support is preferably not more than 3% and more preferably not more than 1.5 percent, and at 80xc2x0 C. at 30 minutes, preferably not more than 1 percent, and more preferably 0.5 percent or less. The break strength in both directions is preferably 5-100 kg/mm2.
The process for manufacturing the magnetic application solution for the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step to be carried out, if necessary, before or after the kneading and dispersing steps. Each of the individual steps may be divided into two or more stages. All of the starting materials employed in the present invention, including the ferromagnetic powder, binders, carbon black, abrasives, antistatic agents, lubricants, solvents, and the like, may be added at the beginning or during any of the steps. Moreover, the individual materials may be divided and added during two or more steps; for example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for viscosity adjustment after dispersion.
To achieve the object of the present invention, conventionally known manufacturing techniques may, of course, be utilized for some of the steps. In the kneading step, only by using a kneader having a strong kneading force, such as a continuous kneader or a pressure kneader, it was possible to obtain the high residual magnetic flux density (Br) of the magnetic recording medium of the present invention. When a continuous kneader or pressure kneader is employed, the ferromagnetic powder and all or part of the binder (preferably not less than 30 percent of the entire quantity of binder) are kneaded in the range of from 15 to 500 parts of binder per 100 parts of ferromagnetic powder. Details of the kneading treatment are described in Japanese Patent Unexamined Publication Nos. Hei 1-106338 and Sho 64-79274. When preparing the lower nonmagnetic layer solution, a dispersing medium having a high specific gravity is desirably utilized, with zirconia beads being suitable.
The following are examples of devices and methods for coating the multilayered structure of the magnetic recording medium of the present invention.
1. The lower layer is first applied with a coating device commonly employed to apply magnetic application solutions such as a gravure coating, roll coating, blade coating, or extrusion coating device, and the upper layer is applied while the lower layer is still wet by means of a support pressure extrusion coating device such as is disclosed in Japanese Patent Examined Publication No. Hei 1-46186 and Japanese Patent Unexamined Publication Nos. Sho 60-238179 and Hei 2-265672.
2. The upper and lower layers are applied nearly simultaneously by a single coating head having two built-in slits for passing coating solution, such as is disclosed in Japanese Patent Unexamined Publication Nos. Sho 63-88080, Hei 2-17971, and Hei 2-265672.
3. The upper and lower layers are applied nearly simultaneously using an extrusion coating apparatus with a backup roller as disclosed in Japanese Patent Unexamined Publication No. Hei 2-174965.
To prevent compromising the electromagnetic characteristics or the like of the magnetic recording medium by aggregation of ferromagnetic powder, shear is desirably imparted to the coating solution in the coating head by a method such as disclosed in Japanese Patent Unexamined Publication Nos. Sho 62-95174 or Hei 1-236968. In addition, the viscosity of the coating solution must satisfy the numerical range specified in Japanese Patent Unexamined Publication No. Hei 3-8471. To obtain the magnetic recording medium of the present invention, orientation is conducted following drying. A solenoid of not less than 100 mT (1,000 G) and a cobalt magnet of not less than 200 mT (2,000 G) are desirably employed together in orientation with like poles opposed (in a same manner that the same polarities of those above to each other). It is also desirable to provide a suitable drying step prior to orientation so as to achieve the highest orientation property following drying. Further, when the present invention is being applied as a disk medium, an orientation method achieving random orientation is rather required.
Heat-resistant plastic rollers of epoxy, polyimide, polyamide, polyimidoamide, or the like, are employed as calender processing rollers. Processing may also be conducted with metal rollers. The processing temperature is preferably not less than 70xc2x0 C., more preferably not less than 80xc2x0 C. Linear pressure is preferably 200 kg/cm or more, more preferably 300 kg/cm or more. The friction coefficient for SUS420J of the magnetic layer surface of the magnetic recording medium of the present invention and its opposite surface is preferably not more than 0.5, more preferably not more than 0.3. The surface resistivity is preferably from 104 to 1012 xcexa9/sq, the modulus of elasticity at 0.5% elongation of the magnetic layer in both the running direction and the width direction is preferably 0.98-19.6 GPa (100 to 2,000 kg/mm2) and the break strength is preferably 0.98-29.4 GPa (from 1 to 30 kg/cm2). The modulus of elasticity of the magnetic recording medium in both the running direction and the longitudinal direction is preferably from 0.98-14.7 GPa (100 to 1,500 kg/mm2) and the residual elongation is preferably not more than 0.5 percent. The thermal shrinkage rate at any temperature not greater than 100xc2x0 C. is preferably not greater than 1 percent, more preferably not greater than 0.5%, and most preferably not greater than 0.1%. The glass transition temperature (i.e., the temperature at which the loss elastic modulus of dynamic viscoelasticity is measured at 110 Hz peaks) of the magnetic layer is preferably not less than 50xc2x0 C. and not more than 120xc2x0 C., and that of the lower layer is preferably 0xc2x0 C.-100xc2x0 C. The loss elastic modulus preferably falls within a range of from 1xc3x97107 to 8xc3x97108 N/m2 (1xc3x97108 to 8xc3x97109 dyne/cm2) and the loss tangent is preferably not more than 0.2. Adhesion failure tends to occur when the loss tangent becomes excessively large.
The residual solvent in the magnetic layer is preferably not more than 100 mg/m2 and more preferably not more than 10 mg/m2. The void ratio in both the lower layer and the magnetic layer is preferably not more than 30 volume percent, more preferably not more than 20 volume percent. Although a low void percentage is preferable for attaining high output, there are some cases in which it is better to maintain a certain level. For example, in magnetic recording media for data recording where repeat applications are important, higher void ratios often result in better running durability. As regards the magnetic characteristics of the magnetic recording medium of the present invention, when measured under a magnetic field of 500 mT (5 KOe), squareness in the tape running direction is not less than 0.70, preferably not less than 0.75, and more preferably not less than 0.85.
Squareness in the two directions perpendicular to the tape running direction is preferably not more than 80 percent of the squareness in the running direction. The switching field distribution (SFD) of the magnetic layer is preferably not more than 0.6.
In the roughness spectrum of the surface of the magnetic layer, the power spectrum density of roughness in the. wavelength of from 1 to 5 xcexcm is 0.2 nm2 or less, and the power spectrum density of roughness in the wavelength of from 0.5 to 1.0 xcexcm is 0.02-0.1 nm2. To achieve a good CNR, the lower power spectrum density of roughness the better, but to improve running durability, it is necessary to keep the power spectrum density of roughness in the wavelength of from 0.5 to 1.0 xcexcm to 0.02-1.0 nm2.
The magnetic recording medium of the present invention comprises a lower layer and an upper magnetic layer. It will be readily understood that the physical characteristics of the lower layer and the magnetic layer can be changed based on the objective. For example, the magnetic layer can be imparted with a high modulus of elasticity to improve running durability while at the same time imparting to the lower layer a lower modulus of elasticity than that of the magnetic layer to improve head contact with the magnetic recording medium. What physical characteristics to impart to two or more magnetic layers can be determined by consulting techniques relating to known magnetic multilayers. For example, there are many inventions imparting a higher Hc to the upper magnetic layer than to the lower layer, such as disclosed in Japanese Patent Examined Publication No. Sho 37-2218 and Japanese Patent Unexamined Publication No. Sho 58-56228. However, making the magnetic layer thin, as in the present invention, permits recording on a magnetic layer of comparatively high Hc.
The present invention relates to the subject matter contained in Japanese Patent Application No. 2000-108247, filed on Apr. 10, 2000, which is expressly incorporated herein by reference in its entirety.

Magnetic recording medium having specified acicular ratio relationship between non-magnetic and ferromagnetic particles


The invention concerns glazing sheets with variable absorbing power. The glazing comprises two transparent walls providing an inter-wall space containing one of the two following fluids: either a first transparent fluid, such as air; or a second transparent fluid, absorbing solar energy over a very large part of the spectrum, in particular liquid water or liquid water with added alcohol. The glazing further compromises a circuit for discharging energy in the form of a bead, located at its periphery, preferably consisting of a heat pip-exchanger. The glazing also comprises an apparatus for filling up or emptying the inter-wall space, as well as flexible elements for absorbing the second fluid expansion depending on temperature. The glazing can in particular be used for producing car windows.

The present invention relates to glazings.
Enclosures closed by transparent glazings receive strong solar loads, especially in summer. This is notably the case for the passenger compartment of a vehicle, and also for horticultural greenhouses and house walls exposed to the South or East-West. The temperature inside the enclosure increases and becomes too high for the objects or the plants which are placed therein or for persons who are in there or who are induced to penetrate therein.
It is known that this drawback is partly overcome by staining the glass glazing so that a fraction of the solar load is reflected, without however affecting the transparence and the passengers"" visibility to the outside of the vehicle. Windows with double glazing are also known wherein the internal space thereof is filled with gas having a low thermal conductivity at a relatively low pressure. It is thus possible to substantially reduce heat transfer by convection. U.S. Pat. No. 4,928,448 describes such a device. However, thermal isolation obtained in this way does not provide an obstacle to the solar load transferred through radiation.
Double glazing windows are also known. Depending on insolation, either an insulating liquid is introduced between the walls or the liquid is emptied from the inter-wall space which contains it. U.S. Pat. No. 5,787,652 describes such a vehicle window. The radiated heat is absorbed by the insulating liquid which transfers it to the inside of the vehicle by conduction and by convection.
The object of the present invention is to solve the posed problem by limiting the effects of radiated solar loads, notably in the case of a stopped vehicle when air-conditioning is no longer running. The present invention also aims at finding a remedy for the posed problem without affecting the glazing""s transparence.
The glazing according to the invention has variable absorptivity. It comprises two transparent, notably glass walls. Other transparent materials other than glass may also be contemplated, notably synthetic plastics. These two walls provide an inter-wall space. Depending on the individual case, the latter contains
either a first transparent fluid, notably a gas such as air, transferring solar energy in the transparence wavelength bands of said walls,
or a second fluid transparent in the visible portion of the electromagnetic spectrum, absorbing solar energy on a very wide portion of the electromagnetic spectrum, notably water in the liquid state or water in the liquid state with alcohol added.
In the first case, the glazing""s transparence in the visible portion of the electromagnetic spectrum is not affected and the glazing transfers the major portion of the solar load which it receives.
In the second case, the glazing absorbs the major portion of the solar energy which it receives, while remaining transparent in the visible portion of the electromagnetic spectrum. Indeed, water in the liquid state has the property of transparence, notably when it is in a thin layer under thicknesses from 1 to 2 millimeters. On the other hand, water in the liquid state has properties close to those of a black body absorbing solar radiations. Water in the liquid state as a thin layer does not provide an obstacle to transparence and furthermore, the small thickness of inter-wall space blocks convective motions. Hence, in this second case, the glazing is a radiation shield.
According to another essential characteristic feature of the invention, the glazing comprises a circuit for discharging energy located at its periphery. Preferably, the circuit for discharging energy located at the periphery of the glazing is a bead-shaped exchanger, with a heat pipe effect. Also advantageously, the second fluid absorbing solar energy is under its vapor pressure. It vaporizes and condenses in the free space within the bead. Heat energy absorbed by said second insulating fluid (in the sense of the present description, the expression xe2x80x9cinsulating fluidxe2x80x9d refers to an absorbing fluid or liquid) is thus dissipated at the periphery of the glazing towards the outside. The exchange surface is calculated in order to discharge heat towards the outside, by convection and conduction.
In the configuration of the second case, when the interwall space is filled with the insulating liquid, the glazing is thus well adapted for a stopped vehicle receiving a high solar load. Although the air conditioning is no longer running as the engine is stopped, the temperature inside the vehicle remains moderate. The passenger which now climbs into his vehicle no longer has to wait for the air-conditioning to be running again at its standard rating in order to feel the well-being of a moderate temperature.
Nevertheless, the driver may consider that the shield of water in the liquid state affects his/her visibility and may prefer to drive his vehicle while benefiting from maximum visibility, that obtained in the situation where the fluid filling the inter-wall space is air, or where the second fluid is under its vapor pressure. The effect of the solar load is then compensated by the air-conditioning which has been able to start after starting the engine.
Preferably, according to a complementary feature of the present invention, the glazing further includes means for filling or emptying the inter-wall space in order to fill said space with said second fluid which absorbs solar energy or, according to the case, to empty said space of said second fluid and to substitute said first fluid for it.
Also preferably, the glazing according to the invention is such that the periphery of the glazing includes an expansion volume for absorbing expansions of the second fluid depending on the temperature. This expansion volume may notably be achieved by means of free volume inside the bead located at the upper portion of the glazing.
Advantageously, the thickness of the inter-wall space is larger than or equal to 1 millimeter and less than or equal to 2 millimeters. Such a thickness is sufficiently large so that water in the liquid state may act, with the properties of a back body, it is sufficiently small for blocking convective motions.
The glazing according the present invention may be applied to the thermal preconditioning of the passenger compartment of a vehicle, to the creation of a window in dwelling premises, to the creation of greenhouses.


A self-propelled vacuum-cleaning device for cleaning smooth and textile floor coverings, particularly in the private home sector. The device has a housing, a vacuum blower, an electrically driven cleaning roller, an electrical drive mechanism, control electronics, and a power source. The maximal electric power of the self-propelled vacuum-cleaning tool lies between 150 watts and 300 watts during cleaning operation, whereby between 120 watts and 220 watts are allocated to the vacuum blower, between 10 watts and 40 watts are allocated to the electrical roller drive for the cleaning roller, and between 5 watts and 40 watts are allocated to the drive mechanism, and whereby the control electronics have a power demand of less than 5% of the maximal electric power.

1. Field of the Invention
The invention relates to a self-propelled vacuum-cleaning device for cleaning smooth and textile floor coverings, particularly in the private home sector. The device has a housing, a vacuum blower, an electrically driven cleaning roller, an electrical drive mechanism, control electronics, and a power source.
2. The Prior Art
Self-propelled vacuum-cleaning devices are described in U.S. Pat. No. 5,787,545 and European Patent No. EP 0 803 224 B1, and in various embodiments from practice. The known embodiments have a rechargeable battery as a power source, which is manually or automatically charged in a charging station during breaks in operation. During cleaning, the self-propelled vacuum-cleaning devices are controlled by the control electronics, which act on the electrical drive mechanism. Various contact sensors or sensors that work without contact can be provided to recognize barriers and walls. It is also known to store the traveled path in the memory of the control electronics in the form of an electronic card, thereby making it possible to clean a complete area within as short a time as possible. With a typical power demand of up to 40 watts, the working time until the rechargeable batteries have been discharged is about one hour. According to U.S. Pat. No. 5,787,545, the vacuum-cleaning tool is supposed to have low dimensions and a low maximal electric power of at most 100 watts, whereby typically, at most 5 to 10 watts are allocated to the vacuum blower and 2 to 3 watts are allocated to motors of the drive mechanism. The known vacuum-cleaning tools are suitable for removing coarse, loose particles such as crumbs and lint from smooth floor coverings. However, their cleaning effect on textile floor coverings is insufficient.


A monochrome liquid crystal display device comprises a layer of liquid crystals (1) and a light source (6) arranged for uniformly illuminating the liquid crystal layer. A color filter (8) is provided for changing the spectrum of the light emitted by the liquid crystal display device.

The present invention relates to display devices. More specifically the invention relates to monochrome liquid crystal display devices for use in medical applications, such as radiographic diagnosis.
In radiographic diagnosis it has been common practice for very many years to use photographic film as a medium for recording a radiographic image. Diagnosis is performed by examining the image on the film when placed on a light box.
The film medium is being used for primary diagnosis as well as for communication between radiologist, physicians, doctors, patients and others. The film is furthermore used as an archiving medium.
Several film types have been used. A distinction between the different film types can be made on the basis of the inherent color of the film base. One can distinguish between clear base film and blue base films.
Among radiologist so-called blue base film has become a standard. In order to obtain a blue base radiographic film a blue dye has been added to the substrate of the radiographic film. (see Technik der Rxc3x6ntgendiagnostik, Hanno Poppe, Georg Thieme Verlag, Stuttgart, 1961, p. 571). Blue base film is far more frequently used than clear base film, the use of which has become rather limited.
Although the technical reasons for the claimed advantages of blue base radiographic film are far from convincing, it is a fact that the blue color of the film is considered an aid to diagnosis (see Radiographic processing, D. H. O. John, Focal Press London, page 238-239). Advantages of this so-called blue base film are described by radiologists as xe2x80x98cleanerxe2x80x99, xe2x80x98less fatiguingxe2x80x99, xe2x80x98coldxe2x80x99, xe2x80x98sharperxe2x80x99 and xe2x80x98with more contrast perceptionxe2x80x99.
With the introduction of Picture Archiving and Communication Systems (PACS) and workstation based applications such as computed radiography (CR), magnetic resonance (MR), computed tomography (CT) etc. cathode ray tube (CRT) monitors have more and more been used as a replacement for film.
In order to be able to perform diagnosis of the image displayed on the monitor, specific monitors have been developed and introduced in this market in order to meet the high standards.
Typically, these monitors are high resolution monochrome (grayscale) monitors. Pixels are not formed by addressing a red, green and blue subpixel in various intensity combinations like it is done on color monitors, but by directly writing with an electron beam on the CRT phosphor, without passing through a grid. In this way, higher resolutions can be obtained. However, a consequence is that in such a monitor only one type of phosphor is used to generate the light.
For medical applications, in most cases one of the following two phosphor types are currently being used in these monitors: the P104 and the P45 phosphor.
A P104 phosphor produces a light color, which is very close to neutral white.
A P45 phosphor produces a more blue-like light. The P45 phosphor has been used to generate an overall image look that resembles the overall image look which the radiologist is used to have when he is diagnosing radiographic images on blue-base film.
One of the latest developments in the softcopy environment, is the use of flat panel displays on the basis of liquid crystals.
The development of the technology of grayscale flat panels is leading to an increased use of the medium for diagnostic and viewing applications. The more the quality of these products is improved, the more they will replace the currently used medical grayscale CRT monitors.
The technology of grayscale flat panel display devices is based on another principle than that of CRT monitors.
In these display devices chemical crystals are applied that within a given temperature range (xe2x88x925xc2x0 C.-+65xc2x0 C.) act as anisotrope fluidum whereas above this temperature range they become a clear isotrope fluidum.
In the anistrope range the optical characteristics of these crystals can be changed by applying an electrical field.
In absence of this electrical field, the material is clear whereas at ca. 1 MV/m the material becomes turbid and does no longer transmit light.
The fact that these crystals may act as light valves for the light of an illuminating light source (occasionally provided with a light diffuser) placed behind the layer of liquid crystals is used when building display devices by means of these so-called xe2x80x98liquid crystalsxe2x80x99.
A liquid crystal display device commonly consists of two spaced glass panels in between which a thin layer of liquid crystals is applied. The glass panels are usually covered with a transparent electrode layer which may be patterned in such a way that an array of pixels is created. By energizing the electrodes the liquid crystal layer can be made locally turbid.
Two addressing systems are used to drive the display device: either a passive or an active system.
In the passive system the two electrode layers are patterned in a regular array of stripes. The stripes on one panel are perpendicular to those on the other panel.
The application of a voltage across two opposing stripes causes a change in the optical properties of the liquid crystal material situated at the crossing point of the two stripes, resulting in a change of light transmission through the energized pixels.
In an active system, which greatly improves the performance of the liquid crystal display device, each pixel has its own individual microelectronic switch. This means that such a microswitch is connected to an individual transparent pixel electrode, the planar size of which defines the size of the pixel. The microswitches are individually addressable. Three terminal or two-terminal switching elements exist. Three terminal switches are formed by thin film transistors arrayed in a matrix pattern on one glass platen which together with a glass platen carrying a transparent uniform (non-patterned) electrode layer forms a gap which is filed with the liquid crystal material. In case of a two-terminal switch such as a diode the second platen must also be patterned.
Monochrome as well as color liquid crystal display devices exist.
To impart color reproduction capability to the liquid crystal display device a color filter array element is provided on one of the two glass platens. In an active matrix display device, the color filter is usually provided on the glass platen not carrying the switching elements.
A color filter array for full color reproduction is composed of patches of three primary colors red, green and blue arranged in a given order. For contrast enhancement the color patches may be separated by black contour line patterns delineating the individual color filters.
In order to prevent loss of effective voltage over the liquid crystal material, the color filter is preferably kept out of the electrical circuit, which means that the transparent electrode is deposited on top of the color filter array element.
U.S. Pat. No. 5,128,782 discloses another embodiment of a color liquid crystal display device. The device comprises a liquid crystal display panel. Behind the panel are three flash tubes. The flash tubes are used for sequentially illuminating the panel with three primary colors. For this purpose in front of each of the flash tubes either a red or a green or a blue color filter is provided.
Color separation images of an image to be displayed are generated and applied to the display device. First the red separation image is displayed. For this purpose the red image is retrieved from memory and the transparency of pixels of successive lines of the liquid crystal display panel is controlled in accordance with the data of the red color separation image.
Next the procedure is continued for the green and the blue color separation images.
In medical diagnosis high resolution is extremely important. Another very important aspect is contrast. Monochrome liquid crystal display devices provide increased luminance which results in increased contrast and are therefore preferred over color liquid crystal display devices.
Another element which is very important to make medical diagnosis as reliable as possible is the consistency of the overall outlook of medical (radiographic) images.
A radiologist must be presented with images the overall outlook of which resembles as much as possible the outlook he is trained to see and is expected to see.
In this way it is avoided that his attention would be distracted by overall changed aspects of the image such as a different background color of the image rather than by elements that are of real importance for the diagnosis.
However, the monochrome liquid crystal display devices presently on the market produce a gray shade that is clearbase like because of the spectrum of the light source that is used in such a monochrome liquid crystal display device.
Hence, the image that is displayed on a monochrome liquid crystal display devices does not correspond with the characteristics of the image which the radiologist is used to diagnose. It does not resemble the blue base radiographic film, nor does it resemble the image on a CRT monitor employing a P45 phosphor.
This fact is generally not appreciated by the radiologists.
It is an object of the invention to provide a monochrome liquid crystal display device that is adapted for use in the field of medical diagnosis on displayed radiographic images.
Further object will become apparent from the description hereafter.
The above mentioned objects are realized by a monochrome liquid crystal display device having the specific features defined in claim 1.
A monochrome liquid crystal display device according to the present invention comprises a liquid crystal panel comprising a layer (1) of liquid crystals and a light source (6) arranged for uniformly illuminating the layer (1) of liquid crystals. A color filter (8) is provided for changing the spectrum of the light emitted by said liquid crystal panel.
Preferably the color filter has a spectrum such that the color co-ordinates of the light emitted by the liquid crystal display device correspond with the color co-ordinates of the blue base of a photographic film.
In a specific embodiment the color filter is the blue base of a photographic film.
The color filter is preferably provided between the light source and a viewer. Different positions are possible.
The characteristics of a filter for changing the spectrum of the light emitted by a monochrome liquid crystal display device can be determined as follows.
First the spectrum of the monochrome liquid crystal display device is measured without a filter being present and the color co-ordinates in a predefined color space such as 1931 CIE standard color space, are calculated. The result is referred to as color A.
Next, the spectrum of a blue base of a photographic film is measured on the same light-box. The color co-ordinates in the same color space are calculated. The result is referred to as color B.
Next a filter is calculated having a spectrum C so that color A applied with the filter C can be perceived by the human eye as color B.
Specific features for preferred embodiments of the invention are set out in the dependent claims.
The display device of the present invention is advantageous because it provides an acceptable compromise between two requirements set by the radiologists, namely (1) the need for high contrast which is nowadays provided by monochrome liquid crystal display devices and (2) the need for a displayed image that maximally resembles the overall look of the images the radiologist has been used to see on either radiographic film or on a CRT display device.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.

Monochrome liquid crystal display device utilizing a color filter for changing the spectrum of light emitted from a liquid crystal panel


Systems and methods for processing media files are described. In one embodiment, one or more events are captured having associated event data and associated with a client device, wherein each event is associated with an article and at least one of the articles is a media file, wherein at least one of the events is captured in real time upon the occurrence of the event, at least some of the event data and articles associated with the events are indexed and stored, a search query is received, and the at least one media file is determined as relevant to the search query.

Users generate and access a large number of articles, such as emails, web pages, word processing documents, media files, spreadsheet documents, instant messenger messages, and presentation documents, using a client device, such as a personal computer, personal digital assistant, or mobile phone. Some articles are stored on one or more storage devices coupled to, accessible by, or otherwise associated with the client device(s). Users sometimes wish to search the storage device(s) for articles.
Conventional client-device search applications may significantly degrade the performance of the client device. For example, certain conventional client-device search applications typically use batch processing to index all articles, which can result in noticeably slower performance of the client device during the batch processing. Additionally, batch processing occurs only periodically. Therefore, when a user performs a search, the most recent articles are sometimes not included in the results. Moreover, if the batch processing is scheduled for a time when the client device is not operational and is thus not performed for an extended period of time, the index of articles associated with the client device can become outdated. Conventional client-device search applications can also need to rebuild the index at each batch processing or build new partial indexes and perform a merge operation that can use a lot of client-device resources. Conventional client-device search applications also sometimes use a great deal of system resources when operational, resulting in slower performance of the client device.
Additionally, conventional client-device search applications can require an explicit search query from a user to generate results, and may be limited to examining file names or the contents of a particular application's files.

This patent is subject to a terminal disclaimer.

Methods and systems for processing media files


There is provided a method for operating a basic input/output system (BIOS) of a pay-as-you go computer system. In one example embodiment, the method includes determining if a user password feature is activated on a hard drive and computing a password to unlock the hard drive if the password feature is activated. In another example embodiment, the method includes performing a checksum verification of boot information. In yet another example embodiment, the method includes storing portions of boot information in non-standard locations on the hard drive and combining the portions using operators.

This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
To most people, a computer system is an expensive purchase. This is especially true in developing countries. To reduce the initial cost of the ownership, a "pay-as-you-go" business model has been developed. In the "pay-as-you-go" business model, computer systems are initially sold at a considerable discount. It is anticipated that by selling computer usage time for such computer systems, the cost of providing the computer at the discounted price can be recouped over time.
The pay-as-you-go model is vulnerable, however, to the computer system being hacked in such a way that payment is no longer required for usage. Without safeguards, a user may simply replace the operating system and then use the computer without paying. Additionally, because the computer system is initially sold at a discount, purchasers may try to sell the computer system hardware, such as the hard drive and monitor for example, as component parts in hopes of making a profit over the initial cost of the computer system. One solution requires the use of a cryptographic chip, such as a trusted platform module (TPM). Such a solution, however, is not a zero cost solution, as it incurs cost through the design and manufacture of motherboards and cannot share inventory with current retail models.

System and method for secure operating system boot

Hewlett-Packard Development Company, L.P.