JPS6018388A - Thermal magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the titled recording medium capable of recording a large amount of information including magnetic information and visible information, wherein a thermal recording layer consisting of a metal, an alloy or a compound thereof is provided on a magnetic recording layer provided on a base. CONSTITUTION:The magnetic recording layer 3 comprising fine magnetic powders of (Co-coated) gamma-Fe2O3, Fe3O4, Co-Cr or the like and having a thickness of 100Angstrom -1mum is provided on a sheet or plate form base 1 consisting of a synthetic resin, a metal or the like and having a thickness of 0.005-5mm.. Then, the thermal recording layer 4 consisting of a metal, an alloy or a compound thereof, such as Fe, Co, Ni, Fe-Co, Co-V and Co-doped iron oxide, and having a thickness of 100Angstrom -1mum is provided on the layer 3. Accordingly, a thermal and magnetic recording medium can be obtained which enables double checking by magnetic checking and mechanical reading checking and is hard to forge or alterate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thermosensitive magnetic recording medium having a magnetic recording layer and a thermosensitive recording layer.

[Technical background of the invention and its problems] A magnetic recording medium, which is formed by providing a magnetic recording layer on the surface of a base such as plastic 1, is used for credit cards, cash cards, and ID cards.
Widely used as cards, train tickets, commuter passes, magnetic tape, etc.

Such magnetic recording media have a high recording density (and have the advantage that the recorded information cannot be easily read from the outside), but as a result of this, the recorded information is inevitably invisible, so these recording There may be cases where it is necessary to record visible information on a medium.

In such cases, characters, designs, etc. have been printed on the margins on the front surface of the magnetic recording medium or on the back side of the substrate, but since magnetic recording media are generally small in size, the necessary characters cannot be printed. There was a drawback that there was insufficient space to print visible information such as, and it was not possible to print a sufficient amount of information.

Therefore, in recent years, magnetic recording media have appeared on which visible information such as characters and designs are formed by printing means on the magnetic recording layer of the magnetic recording medium. However, since the visible information is formed by various printing means, it has the disadvantage that its contents are uniform and fixed, and there is little change.

In addition, printing individual information such as barcodes, OCR characters, names, expiration dates, etc. on the magnetic recording layer according to individual circumstances increases manufacturing costs.
The drawback was that it was not realistic.

Furthermore, since printing ink of 2 to 5 microns is provided on the magnetic recording layer, the distance between the magnetic recording layer and the magnetic head becomes too narrow, and the magnetic output in that area is lower than that in the non-printed area. It also had the disadvantage of large output fluctuations.

By the way, in recent years, cash cards, credit cards,
Forgery and falsification of magnetic recording media such as commuter passes are becoming a major social problem, and at present little is being done to prevent the forgery and falsification of magnetic recording information.

[Objects of the Invention] The present invention aims to solve the problems associated with the prior art as described above, and the present invention has the following objects.

a) To provide a recording medium that can store more than one amount of information from both magnetic information and visible information.

b) To provide a recording medium that can simply record individual visible information according to individual situations.

C) To provide a recording medium whose magnetic information cannot be easily forged or altered.

d) To provide a recording medium that is capable of double-checking magnetic information and visible information and is difficult to forge or alter.

e) To provide a recording medium in which the magnetic output is less reduced by the visible recording portion provided on the magnetic recording layer.

[Summary of the invention]

The thermosensitive magnetic recording medium according to the present invention is characterized in that a thin film layer made of a metal, an alloy, or a compound thereof is provided as a thermosensitive recording layer on a magnetic recording layer provided on a substrate, and visible information is stored in the thin film layer. It is recorded by destroying it with a heating means such as a laser beam or a thermal head. In the present invention, the metal or alloy is preferably composed of a magnetic metal, and therefore the thin film layer is preferably a magnetic thin film layer.

Furthermore, if necessary, a thin film layer (preferably a magnetic thin film layer)
A colored layer or a protective layer may be provided on top to clarify visible information, and a colored layer may be provided between the thin film layer and the magnetic recording layer, and in some cases,
It is also possible to provide an adhesive layer that increases the adhesive force between each layer and prevents peeling between each layer.

In some cases, a thin film layer made of a metal, an alloy, or a compound thereof (preferably an oxide) is provided on the substrate as a heat-sensitive recording layer, and a magnetic recording layer is provided on this thin film layer to form a heat-sensitive magnetic recording medium. may be configured. In this case, the substrate is transparent and visible information is recorded by destroying the thin film layer with a laser beam. In the present invention, the metal or alloy is preferably composed of a magnetic metal, and therefore the thin film layer is preferably a magnetic thin film layer.

[Detailed description of the invention]

The present invention will be explained below using preferred specific examples shown in the drawings.

In the following specific examples, the case where the layer is a thin 11 momme layer or a magnetic thin film layer will be mainly explained.

A thermosensitive magnetic recording medium 1 according to the present invention, as shown in FIG. The magnetic thin film layer 4 serves as a heat-sensitive recording layer. The magnetic recording layer 3 is provided entirely or partially on the surface of the base 20. Furthermore, the magnetic thin film layer 4 is provided entirely or partially on the surface of the magnetic recording layer 3;
In some cases, as shown in FIG. 2, the magnetic recording film layer 4 may be provided on the surface of the substrate 20 over a wider area than the magnetic recording layer 3.

Another specific example of the thermosensitive magnetic recording medium 1 according to the present invention is shown in FIGS. 3 to 7. The thermosensitive magnetic recording medium 1 shown in FIG.
A magnetic recording layer 3, a magnetic thin film layer 4, and a colored layer 5 are laminated in this order on the substrate 2, and the colored layer 5 has the function of giving contrast to recorded visible information to make it clear. have.

The thermosensitive magnetic recording medium 1 shown in FIG. 4 has a magnetic recording layer 3, a colored layer 5, and a magnetic thin film layer 4 laminated in this order on a substrate 2. It has the function of giving contrast to information.

The thermosensitive magnetic recording medium 1 shown in FIG. 5 has a magnetic recording layer fII 3, a magnetic thin film layer 4, and a protective layer 6 laminated in this order on a base 2, and the protective layer 6 is a magnetic thin film layer. 40 plays a role in protecting the surface.

In the thermosensitive magnetic recording medium J shown in FIG. 6, a magnetic recording layer 3 and a magnetic thin film layer 4 are laminated in this order on a base 21, and there is a space between the magnetic recording layer 3 and the magnetic thin film layer 4. An adhesive layer 7 is provided. This adhesive layer 7 performs an 'lF' function that strengthens the adhesiveness between the magnetic recording layer 3 and the magnetic thin film layer 4 and prevents the two layers from peeling off.

The thermosensitive recording medium 1 shown in FIG. 7 has a magnetic recording layer 3, a first tinted layer 5a, a magnetic thin film layer 4, and a second colored layer 5b laminated in this order on a substrate 2. . By providing two colored layers, if printing is performed by destroying only the magnetic thin film layer 4 by a laser beam or the like, the first colored layer 5a and the second colored layer 5b will appear to overlap in the printed area. On the other hand, when printing is performed by destroying both the second colored layer 5b and the magnetic thin film layer 40 with a laser beam or the like, the printed portion takes on the color of the first colored layer 5a and the color of the surrounding second colored layer 5b. clearly distinguished from

The thermosensitive magnetic recording medium 1 shown in FIG. 8 has a magnetic recording layer 3 and a magnetic thin film layer 4 laminated in this order on both the front and back surfaces of a base 2, and stores a large amount of magnetic information and visible information.
It is now possible to record.

The thermosensitive magnetic recording medium 1 shown in FIG.
A magnetic thin film layer 4 is provided, and a magnetic recording layer 3 is provided on this magnetic thin film layer. Since the magnetic thin film layer 4 of this recording medium 1 is not exposed on the outer surface, it is preferable when the physical strength of the magnetic thin film layer is weak. In this case, writing on the magnetic thin film layer 4, which is a heat-sensitive recording layer, is preferably performed using a laser beam through the transparent substrate 2.

Hereinafter, the method for manufacturing the thermosensitive magnetic recording medium according to the present invention and the materials used will be explained.

In the thermosensitive magnetic recording medium 1 according to the present invention, a magnetic recording layer 3, a magnetic thin film layer 4, and, if necessary, a colored layer 5, a protective layer 6, or an adhesive layer 7 are formed directly on a substrate 2 using a printing method or It can be formed by a direct method such as a coating method.

Moreover, as shown in FIG. 10, once on the transfer substrate 8,
Through the release layer 9, the protective layer 6, the colored layer 5, and the first adhesive layer 7
a. Prepare a transfer laminate 11 in which the magnetic thin film layer 4, the second adhesive layer 7b, the magnetic recording layer 3, and the hot melt adhesive layer 10 are laminated in this order, and prepare the hot melt adhesive layer 10 of this laminate 11. The recording medium 1 according to the present invention can also be formed by a transfer method in which the transfer substrate 8 is adhered onto the surface of the substrate 2 and the transfer substrate 8 is removed by the peeling layer 9.

Furthermore, as shown in FIG. 11, a pasting laminate 13 in which a magnetic recording layer 3 and a magnetic thin film layer 4 are laminated on a pasting base 12 is prepared, and an adhesive layer 14 is placed on the back surface of this laminate 13. By an adhesion method in which the base 2 and the adhesion base 12 are bonded together via the adhesive layer 14,
It is also possible to form a recording medium 1 according to the invention.

The base material 2 has a sheet-like or plate-like shape, and includes nylon, cellulose diacetate, cellulose triacetate, polystyrene, polyethylene,
Polypropylene, polyester, polyimide, polycarbonate) 1! Any plastics, metals such as copper, aluminum, paper, impregnated paper, etc. can be used alone or in combination as a composite. A preferable material may be selected as appropriate from among the above-mentioned materials, taking into consideration the physical properties required for the base material, such as strength, rigidity, hiding power, and light opacity. Note that the thickness of the base material 2 is approximately 0.005 to 5 mm.

The magnetic recording layer 3 is made of γ-Fe203. CO deposited γ-Fe2
03°Fe 304? Cry□t Fe z Fe
-Cr, Fe -Co + Co -Cr +C
o-Ni, MnAl, Ba ferrite, Sr
A dispersion in which conventionally known magnetic fine particles such as ferrite are dispersed in a suitable resin or ink vehicle,
It can be formed on the base material 2 by a conventionally known coating method such as a gravure method, a roll method, or a knife method.

Moreover, the magnetic recording layer 3 is made of Fe, Fe-Cr, Fe-
It can also be formed on the base material 2 by a vacuum evaporation method, a sputtering method, a plating method, etc. using a metal or an alloy such as Co, Co-Cr, or an oxide thereof.

When the magnetic recording layer 3 is formed by a coating method, the film thickness is about 1 to 100 microns, preferably about 5 to 100 microns. Further, when forming the magnetic recording layer 3 by a vacuum evaporation method, a sputtering method, or a plating method, the film thickness is 1
00A to 1 micron, preferably about 500 to 2000A.

Examples of the resin or ink vehicle in which magnetic fine particles such as γ-F e 20a are dispersed include butyral resin, vinyl chloride/vinyl acetate copolymer resin, urethane resin, polyester resin, cellulose resin, acrylic resin, styrene/maleic acid. Copolymer 4☆1 fat etc. are used,
If necessary, a rubber resin such as nitrile rubber or a urethane elastomer is added. In addition, a surfactant, a silane coupling agent, a plasticizer, a surfactant, a silane coupling agent, a plasticizer,
Waxes, silicone oils, carbon and other pigments can also be added.

The magnetic thin film layer 4 is made of Fe, Co, Ni, Fe-Co
, Fe-Cr, Fe-V, Fe-Ni, Fe-
Pt, Fe-Pd, Fe-Cu.

Fe-Zn, Co-Ni, Co-Cr, Co-V
, Co-Cu.

Co-Mn, Co-P, Ni-Cr, Ni-Cu
, Ni-Zn, N1-V, Ni-Mn, Fe-
Co-Ni, Fe-Mn-Co, Fe-Ni-Cr
, Fe-Ni-Mn, Fe-Co-Cr, Co-
Δff1−Ni.

Co-N1-P, r-Fe203. Fe3O4,C
o-doped iron oxide, Co-coated iron oxide, CrO2, Ba0
・6Fe203. It can be formed on the magnetic recording layer provided on the base material 2 using a metal such as SrOφ6Fe203, an alloy, or a mixture thereof by vacuum evaporation, sputtering, plating, or the like. This magnetic thin film layer 4 is
Since it plays a role as a heat-sensitive recording layer, it preferably has a low melting point. In addition, the thickness of the magnetic thin film layer is 1008 ~
1 micron, preferably about 500 to 1000 A.

Cellulose derivatives such as phosphorescent R1!5 &'r, ethyl cellulose, ethyl hydroxyethyl cellulose, cellulose acetate globione), cellulose acetate,
Single or copolymer resin of styrene resin or styrene copolymer resin such as polystyrene, poly-α-methylstyrene, acrylic resin or methacrylic resin such as polymethyl methacrylate, polymethacrylate ether, polyethyl acrylate, polybutyl acrylate, etc. , rosin, rosin-modified maleic acid resin, rosin-modified phenolic resin, rosin ester resin with polymerized rosin, polyvinyl acetate resin, coumaron resin, vinyl toluene resin, vinyl chloride resin, polyester resin, polyurethane resin, butyral resin, etc. binders Various pigments are added depending on the color to be colored, and if necessary, plasticizers, stabilizers,
After adding wax, grease, desiccant, drying aid, curing agent, thickener, and dispersant, a colored paint or ink that is sufficiently kneaded with a solvent or diluent is used, using the normal gravure method or roll. Law, Naifetuji Law.

By coating methods such as offset method or printing method,
It can be formed in any desired part.

The protective layer 6 can be formed by laminating synthetic resin films, by extrusion coating, or by applying synthetic resin paint. The synthetic resin constituting the protective layer may be the same as the synthetic resin used to form the colored layer, depending on the intended use or adhesion with other layers. Using a synthetic resin for the mold is advantageous in terms of surface hardness and prevention of contamination, and it is also preferable to use a paint containing an ultraviolet curable synthetic resin because it can be cured instantly after application. Silicone or the like can also be added to the protective layer to make the surface releasable.

The 1χ adhesive layer 7 is made of vinyl chloride/vinyl acetate copolymer, ethylene/vinyl acetate copolymer, vinyl chloride/propionic acid copolymer, rubber resin, cyanoacrylate resin, cellulose resin, ionomer resin, polyolefin copolymer. After adding plasticizers, stabilizers, curing agents, etc. as necessary to a binder such as 1-coalescence, using a coating for the adhesive layer sufficiently mixed with a solvent or diluent, gravure method, It can be formed on a desired portion of the substrate by a coating method such as a roll method or a knife method. In particular, when providing a contact M layer on a magnetic recording layer, in order to prevent the magnetic recording layer from re-dissolving, a thermoplastic resin is emulsified and applied.
It is preferable to dry it to form a heat-sealable adhesive layer.

Magnetic information is recorded in the magnetic recording layer 3 by a conventional method such as a magnetic head. On the other hand, barcode, OCR
Visible information such as characters, names, and expiration dates are recorded by selectively destroying the magnetic thin film layer using heating means such as a thermal head, laser beam, or hot stamping.

When recording magnetic information and visible information, first
The magnetic information may be recorded in this order, followed by the magnetic information (or the magnetic information may be recorded in the order of the visible information. However, since a heating means is used to record the visible information, the visible If there is a possibility that the temperature of the magnetic recording layer becomes higher than one Curie temperature when recording information, it is preferable to first record visible information and then record magnetic information '1''.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

In the following examples, all "parts" are by weight unless otherwise specified.

Example 1 On a polyethylene terephthalate sheet having a thickness of 188 microns, a magnetic paint having the following composition was applied by gravure coating to form a magnetic recording layer having a thickness of 10 microns. Next, Co-Ni (Co
80% N, 120% (the same applies hereinafter) was deposited to a film thickness of 500 Å as measured by a film thickness measurement method using a quartz crystal resonator to form a magnetic thin film layer which is a heat-sensitive recording layer.

Composition of magnetic paint: 3 parts of Sanren 113114, 3 parts of isopropyl alcohol, part of methyl ethyl ketone, 5 parts of toluene, 50 yen 13 Example 2 A magnetic recording layer and a magnetic thin film layer were formed on a polyethylene terephthalate sheet in the same manner as in Example 1. After that, using a colored paint with the following composition, it was coated to a thickness of 3 by gravure coating.
A micron-sized beach-colored layer was formed.

Composition of colored paint: Pigment 10 parts Methyl ethyl ketone 30 parts Toluene Addition Example 3 After forming a magnetic recording layer on a polyethylene terephthalate sheet in the same manner as in Example 1, the same colored paint as used in Example 2 was used. A colored layer with a thickness of 3 microns was formed by gravure coating. Next, -Co-Ni was deposited thereon to a thickness of soo x by vacuum evaporation to form a magnetic thin film layer serving as a heat-sensitive recording layer.

Example 4 After forming a magnetic recording layer and a magnetic thin film layer on a polyethylene terephthalate sheet in the same manner as in Example 1, a protective layer with a thickness of 1 micron was formed by gravure coating using a protective layer paint with the following composition. did.

Composition of paint for protective layer: Methyl ethyl ketone 3 parts Toluene 30 parts Ethyl acetate 30 parts Example 5 After forming a magnetic recording layer on polyethylene terephthalate in the same manner as in Example 1, a paint for adhesive layer having the following composition was applied. A first adhesive JF5 having a thickness of 0.5 microns was formed using the gravure coating method. Next, Co--Ni was deposited thereon to a thickness of 50 OA by vacuum evaporation to form a magnetic thin film layer serving as a heat-sensitive recording layer.

Example 6 First, a thermal transfer tape having a width of 6.5 mm for forming a magnetic recording layer I and a magnetic thin film Fj on a substrate was prepared as follows.

(a) 25 micron thick polyethylene terephthalate sheet" Second, a release layer with a thickness of 1 micron was formed by gravure coating using a release layer paint having the following composition.

Composition of paint for release layer: (b) Using the same paint for protective layer as used in Example 4,
A 1 micron thick protective layer was formed on the release layer by gravure coating.

(CJ Using the same colored paint as used in Example 2, a colored layer with a thickness of 3 microns was formed on the retention layer by gravure coating.

(d) A second adhesive layer having a thickness of 0.5 microns was formed on the colored layer by gravure coating using an adhesive layer paint having the following composition. This second adhesive eyebrow is for improving the adhesion between the colored layer and the magnetic thin film.

Composition of paint for second adhesive layer: (e) A magnetic thin film was formed by applying Co--Ni to a thickness of 500A on the second adhesive layer by g-vacuum deposition.

(f) Using the same adhesive layer paint as used in Example 5,
A first adhesive layer having a thickness of 0.5 microns was formed on the magnetic thin film by gravure coating.

(g)! Using the same magnetic paint used in 5111,
A magnetic recording layer with a thickness of 10 microns was formed on the first adhesive layer by gravure coating.

(11) A hot melt contact layer having a thickness of 10 microns was formed on the magnetic recording layer 4 by gravure coating using a hot melt contact layer coating composition having the following composition.

Composition of paint for hot melt adhesive layer: Next, the transfer tape produced in this way was thermally transferred onto a vinyl chloride base material, and the length was 86 mm and the width was 0 mm.
, a card with a thickness of 0.8 mm was produced.

Example 7 An Ar laser was applied to the recording medium manufactured according to Examples 1 to 6 above at an energy density of 50 mJ/mm2.
When barcodes, OCR characters, Kanji characters, Roman characters, etc. were printed, the desired pattern was formed on the recording medium. The barcode and OCR characters were clear enough to be read by a machine.

Next, when magnetic recording was performed on this printed recording medium using a magnetic head, a recording density of 420 FRPI (flu
x reversal per 1nch), the reproduction output is 5.9V in the printed area and 6.3V in the non-printed area, and the output decrease due to printing is 6%, and the influence of printing on the reproduction output is within a range that does not pose a practical problem. Met.

〔Effect of the invention〕

Since the thermosensitive magnetic recording medium according to the present invention has a thermosensitive recording layer consisting of a magnetic recording layer and a magnetic thin film layer,
It has the following effects.

a) Both magnetic information and visible information can be recorded on a recording medium, making it possible to record a large amount of information.

b) In addition to magnetic information, individual visible information depending on individual circumstances can be easily recorded.

C) Since the heat-sensitive recording layer made of a magnetic thin film layer is integrally provided on the magnetic recording layer, counterfeiting and tampering of the recording medium is difficult compared to recording media that only have a magnetic recording layer. It is.

d) Magnetic information, barcode, OCR on the recording medium
Since visible information such as characters can be recorded, it is possible to perform a double check using magnetic checking and mechanical readout checking, which also makes it difficult to forge or alter the recording medium.

e) The thickness of the magnetic thin film layer, which is the visible information recording section provided on the magnetic recording layer, is thinner than the visible information recording section provided by the printing means (therefore, the gap between the magnetic head and the magnetic recording layer is thinner than the visible information recording section provided by printing means). Spacing loss is small, and output fluctuations in playback output are small.

[Brief explanation of the drawing]

FIGS. 1 to 9 are cross-sectional views of the thermosensitive magnetic recording medium according to the present invention, and FIGS. It is a sectional view of the body. DESCRIPTION OF SYMBOLS 1... Recording medium, 2... Substrate, 3... Magnetic recording layer, 4... Magnetic thin film layer, 5... Colored layer, 6... Protective layer. Figure 1/L

Claims (1)

[Claims] 1. A thermosensitive magnet, characterized in that a magnetic recording layer is provided on a substrate, and a thin film layer made of a metal, an alloy, or a compound thereof is provided as a thermosensitive recording layer on the magnetic recording layer. recoding media. 2. The thermosensitive magnetic recording medium according to claim 1, wherein the metal or alloy is made of a magnetic metal, and therefore the thin film layer is a magnetic thin film layer. 3. The thermosensitive magnetic recording medium according to claim 1, wherein the compound is an oxide of a magnetic metal or an alloy thereof. 4. The magnetic thin film layer is made of Fe, Co, Ni, Fe-C
o, Fe-Cr, Fe-V, Fe-Ni, Fe
-Pt, Fe-Pd. Fe-Cu, Fe-Zn, Co-Ni, Co-C
r, Co-V. Co-Cu, Co-Mn, Co-P, Ni-C
r, Ni-Cu. Ni-Zn, Ni-, V, Ni-Mn, Fe-Co-N
i, Fe-M(1-CO, Fe-Ni-Cr, Fe-N
i, -Mn, Fe-Co-Cr, Co-Mn-Ni,
Co-N1-P, r-Fe203゜Fe3O4, Co
Doped iron oxide, Co-coated iron oxide. CrO2, BaO・6Fe203. SrO・6Fe20
3. The thermosensitive magnetic recording medium according to claim 2, wherein the thermosensitive magnetic recording medium is selected from the group consisting of 5. The thermosensitive magnetic recording medium according to claim 2, characterized in that a colored layer is provided on the magnetic thin film layer. 6. The thermosensitive magnetic recording medium according to claim 2, characterized in that a colored layer is provided between the magnetic recording layer and the magnetic thin film layer. 7. Thermosensitive magnetic recording according to claim 2, characterized in that a first colored layer is provided between the magnetic recording layer and the magnetic thin film layer, and a second colored layer is provided on the magnetic thin film layer. Medium. 8. The thermosensitive magnetic recording medium according to claim 1, 2, 5, 6, or 7, characterized in that a protective layer is provided as the uppermost layer. 9. The thermosensitive magnetic recording medium according to claim 1, 2, 5, 6, 7, or 8, characterized in that an adhesive layer is provided between each of the layers. 10. A heat-sensitive magnetic recording medium, comprising a thin film layer made of a metal, an alloy, or a compound thereof as a heat-sensitive recording layer spread over a transparent substrate, and a magnetic recording layer provided on the thin film layer. 11. The thermosensitive magnetic recording medium according to claim 10, wherein the metal blank or alloy is made of a magnetic metal, and therefore the thin film layer is a magnetic thin film layer. 12. The thermosensitive magnetic recording medium according to claim 10, wherein the thermosensitive magnetic recording medium is an oxide of a magnetic metal or an alloy thereof. 13. The thermosensitive magnetic recording medium according to claim 10, characterized in that a colored layer is provided between the magnetic thin film layer and the magnetic recording layer. 14. The thermosensitive magnetic recording medium according to claim 9, 10, 11, or 12, characterized in that a protective layer is provided as the uppermost layer. 15. The thermosensitive magnetic recording medium according to claim 9, 10, 11, 12, or 13, characterized in that an adhesive layer is provided between each layer.