JP2005228445A - Guaranteed value - Google Patents

Abstract

【Task】
Provided is a valuable guarantee product including a highly reliable identification member for safety and authenticity determination.
[Solution]
It is a valuable guarantee product provided with an identification member, and the identification member has a natural radioactive substance element inside and can detect the radiation dose from the outside and it is difficult to rewrite information recorded once. It is characterized by comprising various radioactive magnetic powders. In this way, by configuring the identification member with a material having both a radioactive function and a magnetic recording function, it is possible to make the best use of both excellent functions, and the anti-counterfeiting effect is highly valuable. A guarantee is obtained.
[Selection figure] None

Description

  The present invention relates to a value-guaranteed product to which forgery / alteration prevention measures have been taken.

  Forgery and banknotes, as well as value-guaranteed items such as cards, electronic devices, and securities having the same value as these, forgery and alteration are prevented by providing an identification member.

For example, by configuring the card with resin and metal powder made of Al, Fe, Co, Pb, etc., there is a functional card that can always emit an α dose of 0.1 to 1000 cph / cm ² from the card itself. It is disclosed. Moreover, by recording the set value of the α dose magnetic powders such as coated _{γ-Fe 2 O 3, Co} -γ-Fe 2 O 3 that on the card, recorded in the magnetic powder α At the same time that the set value of the dose is read, the α dose emitted from the card is detected by the α dose detector, and the authenticity of the card can be determined by comparing these values.

JP-A-8-327792

  However, metal powders made of Al, Fe, and Co usually do not have a radiation function, and if they are not artificially processed, they cannot have a radioactive function. The period of maintaining its function is very short.

  For example, the natural isotopes of Fe are atomic weight 54 (abundance ratio 5.845%), atomic weight 56 (abundance ratio 91.754%), atomic weight 57 (abundance ratio 2.119%), atomic weight 58 (abundance ratio 0.282). %) Are known, none of which emit alpha rays. Although it is possible in principle to irradiate them with artificial isotopes capable of emitting α-rays, it is a dangerous technique because the use of nuclear reactors and accelerators is indispensable. It cannot be said that it is effective as a practical means. Furthermore, the half-life of the artificial isotope obtained in this way is extremely short and cannot have a permanent radioactive function. The situation is the same for Al and Co.

  On the other hand, among the Pb isotopes that exist in nature, there are some nuclides that decay α, but the abundance ratio is only 1.4%, so it is impossible to use these nuclides industrially. Close to.

Further, the α dose emitted from the card having the above elements is set to a very small amount of 0.1 to 1000 cph / cm ² . It is very difficult in practice to accurately measure such a minute value, and authenticity determination based on such a difference in data values is credible.

Furthermore, magnetic powders such as γ-Fe ₂ O ₃ and Co-γ-Fe ₂ O ₃ that are used in combination are materials that can block the α dose, thus hindering the function of the metal powder. It will be.

  Therefore, the present invention provides a value-guaranteed product including an identification member having high safety and authenticity determination.

  The present invention is a valuable guarantee product provided with an identification member, and the identification member has a natural radioactive substance element inside and is capable of detecting a radiation dose from the outside and records information once recorded. It comprises a radioactive magnetic powder that is difficult to rewrite. In this way, by configuring the identification member with a material having both a radioactive function and a magnetic recording function, it is possible to make the best use of both excellent functions, and the anti-counterfeiting effect is highly valuable. A guarantee is obtained.

  The radioactive magnetic powder of the present invention is characterized by exhibiting a nucleation type magnetization reversal behavior. Thereby, it is easy to record the first information, and it is possible to obtain a value-guaranteed item that is difficult to record the information again.

  In the radioactive magnetic powder, information is preferably recorded from the initial demagnetization state, thereby obtaining a valuable guarantee that is difficult to write again.

  In particular, the identification member preferably includes the radioactive magnetic powder inside a coating member having a substantially flat main surface, whereby the radiation dose can be accurately and uniformly confirmed from one surface of the resin coating member. Can do. Moreover, it is preferable that the distance of the said identification member main surface and the said radioactive magnetic powder is the range of 0.01-1.0 micrometer, and can satisfy | fill the safety to a user by this. Further, by adjusting the distance within this range, a valuable guarantee product capable of emitting an arbitrary radiation dose can be obtained.

Further, the general formula is R _x T _100-xy N _y (where R is a rare earth element including at least one kind of Y containing Sm as a main component, and T is at least one transition metal containing Fe as a main ingredient) 5 ≦ x ≦ 20, 5 ≦ y ≦ 30), a typical nucleation-type magnetization reversal behavior is exhibited, and a coercive force that is significant with fine particles of 10 μm or less Therefore, it is very suitable for the present invention and, depending on the manufacturing method, can be made into spherical particles, so that it does not fall off or wear due to rubbing or scratching the coating member. The risk is very low. Furthermore, since this material has a ternary alloy composition, it is possible to incorporate a composition ratio and a crystal structure as the final means of authenticity determination. As a result, the effectiveness of authenticity determination can be further increased.

  As described above, the value-guaranteed material of the present invention is difficult to forge or modify by using a single material capable of emitting radiation and magnetism at the same time, and can easily identify authenticity. Can do. For example, forgery becomes difficult by referring to radiation intensity data in magnetic recording or referring to magnetic information (analog or digital) and radiation intensity data. Moreover, it becomes difficult to modify magnetic information by using a nucleation type magnetic material. On the other hand, even if a person who attempts forgery can specify the composition of the material to be used, complete copying cannot be performed unless the relationship between the radiation dose and the magnetic data can be satisfied. Furthermore, if authentic information is included in the particle shape and particle size distribution of the material used, copying becomes more difficult. In addition, when assuming that counterfeiting is performed using two or more types of materials so that the radiation dose and magnetic data can be simultaneously satisfied, those who try to counterfeit are far more than those who use a single material for compounding and blending. A lot of effort will be spent. This is also a kind of counterfeit effect. In addition, if the correlation between the radiation data and the magnetic data of the value-guaranteed material is changed for each identification member by changing the coating amount and the filling rate, the forgery prevention effect is further enhanced. On the other hand, when viewed from the side of manufacturing a value-guaranteed product, since a single member is used, the security effect can be drastically improved without greatly changing the infrastructure of the conventional coating type magnetic recording material.

Hereinafter, although an embodiment concerning the present invention is explained in full detail, it is an example for materializing the technical thought of the present invention, and is not limited to this.
Embodiment 1 FIG.

  The value guaranteed product of the present invention contains a natural radioactive substance element, and as a result, it is possible to detect the radiation dose from the outside, and at the same time, it is difficult to rewrite the magnetic information recorded once. It has the identification member which comprises. The identification member can be formed of a single layer or multiple layers. In the case of multiple layers, it is sufficient that at least one layer contains radioactive magnetic powder.

(Radiomagnetic powder)
In the radioactive magnetic powder provided in the identification member of the present invention, the natural radioactive element is a natural radionuclide contained in cosmic rays and the earth's crust and building materials, and examples thereof include uranium series nuclides and thorium series nuclides. In particular, K-40, Rb-87, Cd-113, In-115, Te-123, La-138, Nd-144, Sm-147, Gd-152, Lu-176, Hf-174, Re-187, It is preferable to have at least one member selected from the group of Os-186 and Pt-190, so that the radiation dose can be used without artificial activation. Some of these radioactive elements include radiation that is subject to legal regulations, but the radioactive magnetic powder of the present invention is not only composed of these elements, but is also composed of elements such as Fe. Therefore, the radiation dose emitted from the radioactive magnetic powder itself can be diluted. As described above, by using the radioactive magnetic powder having the α-radioactive element having a relatively high specific activity, it becomes possible to control the amount of radiation, and to obtain a value-guaranteed material capable of accurate authenticity determination. .

Moreover, it is preferable that (alpha) ray radiation magnetic powder is comprised inside binder materials, such as resin. This makes it possible to shield a part of the α dose with the binder by appropriately adjusting the material and film thickness of the binder, and to accurately measure the radiation dose without adversely affecting the human body. A valuable guarantee that always radiates is obtained. The radiation dose emitted from the value-guaranteed material of the present invention can be adjusted in the range of 10 cpm to 1000 cpm (600 to 60000 cph) / cm ² , and the radiation dose can be emitted to any place.

  Furthermore, since the present invention aims to retain the authenticity discrimination function for a long period of time, preferably in units of decades, it is necessary to emit radiation for a long period of time. Accordingly, the half-life of the natural radiation substance used in the present invention is preferably at least 10 8 years or more, desirably 10 10 years or more.

  The radioactive magnetic powder of the present invention is not particularly limited as long as it has a natural radioactive substance element and it is difficult to rewrite information recorded once. However, considering these effects, it exhibits a nucleation type magnetization reversal behavior. Those are preferred. Here, the nucleation-type magnetization reversal behavior means that saturation magnetization is easily reached in a low magnetic field, and that once magnetized, magnetization reversal tends to be difficult unless a reverse magnetic field is applied to the true coercive force. Is shown. On the other hand, in the pinning type magnetization reversal behavior, which is a concept that is paired with the nucleation type, it is necessary to apply a magnetic field higher than the true coercive force to reach the saturation magnetization. Therefore, it is extremely disadvantageous from the viewpoint of ease of writing.

  Particularly, the initial magnetization degree of the radioactive magnetic powder is preferably 10% or more, more preferably 20% or more, with respect to the saturation magnetization when the write magnetic field is 5 kOe (400 kA / m). Further, it is more preferable that writing of 30% or more is possible. The coercive force of the radioactive magnetic powder is preferably 3 to 15 kOe (240 to 1200 kA / m), more preferably 4 to 10 kOe (320 to 800 kA / m), still more preferably 4 to 8 kOe (320 to 640 kA). / m). As a result, it becomes almost impossible to write information again with a generally used information writing device for the ferrite magnetic material, and a highly reliable value guarantee product can be obtained.

  The radioactive magnetic powder preferably has information recorded in an initial demagnetized state, so that in the counterfeit material in which the information is forcibly rewritten by applying a strong magnetic field exceeding the coercive force, the residual magnetization is completely It is possible to leave clear counterfeit evidence that it will not be reversed. Here, the initial demagnetization state is a state in which the size and direction of the domain wall are random, and as a result, the initial magnetization is extremely easy. If initial magnetization is easy, it is saturated in a low magnetic field, and as a result, magnetic rewriting becomes difficult.

  Specifically, in the above-described identification member in which information is recorded once in the initial demagnetization state, when the act of forcibly rewriting is performed, information rewriting usually refers to the reversal of magnetization, but writing from the initial demagnetization state. Since the domain wall is almost completely lost when performing the above, it is necessary to apply a magnetic field in the opposite direction to that at the time of writing in order to completely invert the domain wall. If the strength of the magnetic field in the opposite direction is the same as that at the time of writing, as a result, the magnetization (magnetic information) becomes a value close to zero, and it becomes possible to easily identify the falsification.

The radioactive magnetic powder used in the present invention is not particularly limited as long as at least one element is composed of a natural radioactive element. For example, Sm-Fe-N series such as Sm ₂ Fe ₁₇ N ₃ , SmCo ₅ (1- 5 system), Sm ₂ -Co system such as Sm ₂ (Co, Fe, Zr, V) ₁₇ (2-17 system), Nd—Fe—B system such as Nd ₂ Fe ₁₄ B and Nd ₂ Fe ₁₄ B, and Nd—Fe—Ti—N, Nd—Fe—V—N, La—Co, or the like can be used. These radioactive magnetic powders are excellent radioactive magnetic powders having all of the functions of magnetic and radiation, semi-permanent half-life, and adjustable radiation dose.

  In addition, when forming a value-guaranteed product in which a flat identification member is formed on a medium such as a card, it is possible to form a thin film consisting only of radioactive magnetic powder in a flat shape, but industrially a powder. Is preferably dispersed in an organic or inorganic material. In this coating step, the particle size of the radioactive magnetic powder is extremely important, and powders such as Sm—Co magnets, La—Co magnets, Sm—Fe—N magnets, Nd—Fe—B magnets, The particle diameter can be easily adjusted to 10 μm or less.

In particular, when the radioactive magnetic powder is contained in the resin-coated member, the use of a substantially spherical magnetic powder having a uniform particle size and a BET value of 10 m ² / g or less makes it more reliable and valuable. A guarantee is obtained. In particular, Sm _x Fe _100-xy N _y (5 ≦ x ≦ 20, 5 ≦ y ≦ 30) powder formed without going through a pulverization step is a magnetic powder having a smooth surface and a small particle diameter, and is preferably used. be able to.

In Sm _x Fe _{100-xy Ny} powder, a part of Sm is at least one of Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. A part of Fe may be substituted with at least one of Co, Ti, V, Cr, Mn, Ni, Cu, Zn, Zr, Hf, Nb, Ta, Mo, W, Ga, and Al. It may be replaced. In particular, by replacing a part of Fe with at least one of Ti, Mn, and Al, a magnetic powder having a smooth surface state can be obtained. Further, the content x of Sm is preferably 3 to 30 atomic%, more preferably 5 to 20 atomic%, and if it is less than 5 atomic%, an α-Fe phase is formed and the coercive force is particularly reduced, and 20 atomic%. When the amount is larger than that, Sm precipitates and the residual magnetization decreases. Further, the content y of N is preferably 5 to 30 atomic%, and if it is less than 5 atomic%, almost no coercive force is exhibited, and if it exceeds 30 atomic%, it consists of a rare earth metal and a nitride of iron itself. An impure phase is generated, and the magnetic properties are significantly reduced. Furthermore, Ca may be contained inside the magnetic powder, whereby particles having a more preferable surface state can be obtained. The Ca content is preferably 0.001 to 0.30 atomic%. If the Ca content is less than 0.001 atomic%, the magnetic properties cannot be improved. And a preferable surface state cannot be obtained.

  In the present invention, the average particle diameter of the primary particles of the radioactive magnetic powder is preferably 0.1 to 10 μm, more preferably 0.5 to 7 μm, and further preferably 1 to 5 μm. Since the primary particles defined in such a range are excellent in dispersibility in the liquid, the generation of huge secondary particles due to aggregation can be suppressed even when the binder solution is highly packed, and the local particles caused by the magnetic powder can be suppressed. Resin degradation can be prevented. Further, by removing coarse particles exceeding 10 μm, it is possible to prevent the radioactive material from dropping from the identification member due to use deterioration. The average particle size of primary particles in the present specification is measured by a Fisher sub-sizer (FSSS), and is obtained by measuring a specific surface area by an air permeation method. The average value is shown.

Further, BET value of radioactive magnetic powder of the present invention, ^{10 m} 2 / g or less, and more preferably a 0.1~3.0m ² / g. When the BET value exceeds 10 m ² / g, the particle surface is not smooth, and the particle shape is indefinite, such as angular, so that when the coated surface is blended with a resin, the coated surface is smooth. May be damaged, and radioactive materials may fall off or fall off. The smoothness of the coated surface is preferably such that the surface roughness Ra value (Ra: arithmetic average height JIS B 0601-2001) is in the range of 0.01 μm to 0.1 μm, and more preferably 0.01 μm to 0.05 μm. It is desirable to be in range. Further, when the BET value is larger than 10 m ² / g, the interface between the resin and the particle surface becomes complicated, which causes a problem that the flexibility that can cope with the deterioration of use of the valuable guarantee product cannot be ensured. By precisely controlling the BET value with the same particle diameter, the particle shape becomes round, and as a result, the particle shape itself can be used as a material for final authenticity determination. This authenticity determination can be easily performed by observing the surface of the valuable guarantee object with an optical microscope. Here, the BET value is indicated by the specific surface area of the magnetic powder measured by an adsorption method using nitrogen gas.

  Further, the radioactive magnetic powder used in the present invention can be subjected to a surface treatment, and the radiation dose can be controlled to a target amount by appropriately modifying the particle surface. Specifically, by providing a coating layer composed of an inorganic substance and / or an organic substance on the surface of the particle by chemical conversion treatment, plating, vapor deposition, etc., wettability with the binder, environmental resistance, and heat resistance can be improved. it can. For example, a silica film can be formed on the particle surface by mixing radioactive magnetic powder and ethyl silicate and firing them under predetermined conditions. Further, when mixed with a silane coupling agent and fired under predetermined conditions, an organic chain can be formed on the silica film.

  In the present invention, the volume percentage of the radioactive magnetic powder in the identification member is preferably 10 vol% to 55 vol%, more preferably 15 vol%, considering the safe use of radiation, prevention of particle dropout, and flexibility. It is preferably ˜50 vol%, more preferably 20 vol% to 45 vol%.

(Binder member)
In order to form the radioactive magnetic particles used in the present invention in the form of a film, a method in which the radioactive magnetic particles are mixed with a resin, a solvent, etc., and made into a paste or ink, is preferably used. Examples of the resin binder include vinyl chloride resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride. Examples thereof include a combination of at least one selected from a copolymer, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer, and a cellulose resin such as nitrocellulose and a polyurethane resin. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

  In the case of a value-guaranteed product that requires bending strength, it is preferable to use a polymer resin such as a liquid crystal polymer resin, a thermoplastic elastomer, or a thermosetting elastomer. As the plastic elastomer, styrene elastomer (SBC), vinyl chloride elastomer (TPVC), olefin elastomer (TPO), urethane elastomer (TPU), polyester elastomer, nitrile elastomer, polyamide elastomer (TPAE), fluorine elastomer Chlorinated polyethylene (CPE), 1.2 polybutadiene, trans 1.4IR, silicone elastomer, chlorinated ethylene copolymer alloy, ester halogen polymer alloy, and the like. Among thermoplastic elastomers, those having a hard segment with particularly high fiber-based performance are preferable, and examples thereof include polyamide elastomers such as PPA, olefin elastomers such as PPS, polyester elastomers, and chlorinated polyethylene. On the other hand, thermosetting resins can also be used. After dissolving an epoxy resin, diallyl terephthalate resin, silicone resin, phenol resin, unsaturated polyester resin, polyimide resin, melamine resin, urea resin, etc. in a suitable solvent together with a curing agent. Use on paste or ink. Further, as the resin of the present invention, a resin obtained by mixing at least two kinds of thermoplastic resins having different melting points can be used. In such a resin, resin molecules having a high melting point are regularly aligned in a flow state in which resin molecules having a low melting point are melted. Thereby, the melting point range in the whole becomes broad, and the identification member can be formed with high dimensional accuracy.

  It is also effective to perform magnetic field orientation when forming the coating surface for the purpose of enhancing the magnetic signal. At this time, there are a case where the film is oriented perpendicularly to the film surface, a case where the film is oriented parallel to the film surface, and a case where the film is oriented obliquely.

In addition, when using magnetic powder capable of emitting a high-energy radiation dose, in order to increase the reliability of the resin-coated member, the radiation dose is resistant to light, such as Si, Al, Ga, Ti, It is preferable to mix an oxide having one or more of Ge, P, B and alkaline earth metal.
Embodiment 2. FIG.

Further, a translucent inorganic member such as SiO ₂ , Al ₂ O ₃ , MSiO ₃ (M includes Zn, Ca, Mg, Ba, Sr, etc.) is used as the coating member for the identification member. It is also possible. The coating layer in which the radioactive magnetic powder is fixed by SiO ₂ is prepared by adjusting a coating liquid in which the radioactive magnetic powder is uniformly dispersed in a silica sol obtained by mixing an alkyl silicate and a high boiling point organic solvent at a predetermined ratio. It can be formed by spray coating or dispensing so as to cover a part or the entire surface of the valuable guarantee product. The coating layer in which the radioactive magnetic powder is fixed with Al ₂ O ₃ is made of aluminum alcoholate, or uniform distribution of the radioactive magnetic powder in a silica sol obtained by mixing aluminum alkoxide and a high boiling point organic solvent in a predetermined ratio. It can be formed by adjusting the coating liquid dispersed in and spray-coating or dispensing so as to cover a part or the entire surface of the valuable guarantee product. Since the identification member formed in this way is made of only an inorganic material, it has very little radiation deterioration and is suitable when a highly radioactive substance is used.

  The coating member of the present invention can be formed almost easily by applying a mixture of a binder solution and radioactive magnetic powder to a value-guaranteed material by a doctor blade method, an ink jet method, a stencil printing method, a spin coating method, etc. It has a flat main surface. By such a method, the identification member whose surface roughness Ra value (Ra: arithmetic average height JIS B 0601-2001) of the radiation surface is in the range of 0.01 μm to 0.1 μm is obtained.

  Below, the Example concerning the value guarantee thing of this invention is described according to the formation method of this invention.

50 parts by weight of SmCo ₅ powder having an average particle diameter of 2.0 μm and a BET value of 5.5 m ² / g subjected to silane coupling treatment, 20 parts by weight of acrylic resin, 30 parts by weight of vinyl chloride resin, and 100 parts by weight of toluene. Mix in proportions to make a paint. The magnetic powder has a coercive force of 8.7 kOe (696 kA / m).

Next, the said composition is apply | coated to the surface of a value guarantee thing by a stencil printing method, and the identification member with a film thickness of 30 micrometers is formed in 1 layer. The main surface of the identification member is substantially flat, and the Ra value is 0.03 μm. The main surface and the distance between the radiation magnetic powder (the resin coat layer thickness) is 0.08 .mu.m, the total film thickness is adjusted so that the radiation dose in this case is the 100cpm ^/ cm ² ~200cpm ^/ cm 2 Has been. The radiation dose can be adjusted by changing the total film thickness and the resin coating thickness, and can also be adjusted by changing the filling amount of the radioactive magnetic powder.

  Next, magnetic information is written with a recording magnetic field of 5 kOe (400 kA / m) in a demagnetized state having substantially no magnetization. Regarding the remanent magnetization, the ratio of the magnetization value when 20 kOe (1600 kA / m) is applied to the value of 5 kOe (400 kA / m) = σ (5/20) is 0.7. In other words, 70% magnetization was recorded by simply applying a quarter of the magnetic field required to magnetically saturate.

  The value-guaranteed material obtained in this way has a unique radiation dose and magnetic information, and therefore has an excellent anti-counterfeiting effect. Specifically, when another information is written by applying a magnetic field of 5 kOe (400 kA / m) in the opposite direction to the above-mentioned information writing, the residual magnetization is 0.1 on the negative side and σ (5/20) is 0.1. Become. Since rewriting (writing) of information means reversal of magnetization, it cannot be said that complete reversal occurs in this state. In short, this experimental fact shows that it is difficult to rewrite information.

A composition is prepared in the same manner as in Example 1 using Sm ₂ Fe ₁₇ N ₃ -based radioactive magnetic powder having an average particle size of 2.5 μm and a BET value of 0.7 m ² / g as the radioactive magnetic powder. The magnetic powder has a coercive force of 10.2 kOe (816 kA / m).

Next, one layer of the above composition is applied to the surface of the value-guaranteed material by a stencil printing method so as to have a film thickness of 50 μm, and a composition consisting only of acrylic resin is formed on the one layer to a film thickness of 0.1 μm The identification member is formed by applying as described above. The distance between the main surface of the identification member and the radiation magnetic powder is 0.2 μm, and the film thickness is adjusted so that the radiation dose is 50 cpm / cm ^{2 to} 100 cpm / cm ² .

  Next, magnetic information is written with a recording magnetic field of 5 kOe (400 kA / m) in a demagnetized state having substantially no magnetization. σ (5/20) is 0.5. In other words, 50% magnetization is recorded by simply applying a quarter of the magnetic field required to magnetically saturate.

  The value-guaranteed material thus obtained has the same excellent magnetic information rewriting prevention effect as that of Example 1, the BET value of the radioactive magnetic powder is relatively small, and the particle shape is spherical. It can reduce the risk of dropout and peeling due to use, and has excellent reliability.

  In Example 2, the same effect as in Example 2 can be obtained by forming the value guaranteed item in the same manner except that the material of the identification member is kneaded into the value guaranteed item itself.

As a comparative example of the present invention, an identification member for a guaranteed product is formed in the same manner as in Example 1 except that a mixture of ferrite powder and radioactive Pb is used instead of the radioactive magnetic powder. The radiation dose observed from the obtained valuable guarantees fluctuates in the vicinity of the radiation measurement limit, that is, 1 to 50 cpm / cm 2, and cannot be measured accurately. Further, when another information is written by applying the same magnetic field in the opposite direction to the first information writing, the residual magnetization value completely shifts to the negative side. This fact indicates that it is difficult to determine authenticity with radiation dose, and that data can be easily altered.

Claims (5)

A value-guaranteed item having an identification member,
The identification member comprises a radioactive magnetic powder having a natural radioactive substance element inside and capable of detecting a radiation dose from the outside and difficult to rewrite magnetic information once recorded. . The value-guaranteed product according to claim 1, wherein the radioactive magnetic powder exhibits a nucleation-type magnetization reversal behavior. 3. The value-guaranteed product according to claim 1, wherein the radioactive magnetic powder has magnetic information recorded from an initial demagnetized state. 4. The value-guaranteed item according to claim 1, wherein the identification member comprises a coating member having a substantially flat main surface and the radioactive magnetic powder provided in the coating member. The radioactive magnetic powder, general formula _{R x T 100-x-y} N y ( provided that at least 1 R is the rare earth element including at least one Y, T is Fe, a main component composed mainly of Sm The value-guaranteed product according to claim 1, wherein 5 ≦ x ≦ 20 and 5 ≦ y ≦ 30.