WO2009043948A1

WO2009043948A1 - Method for conditioning mineral materials such as safety additives

Info

Publication number: WO2009043948A1
Application number: PCT/ES2008/000602
Authority: WO
Inventors: Antonio Olmos Ruiz; Jose Mendia Aguilar; Javier Baraja Carracedo; Juan Antonio Rubio Sanz; Miguel Angel Rodriguez Barbero; Jose Francisco Fernandez Lozano
Original assignee: Fabrica Nacional De Moneda Y Timbre - Real Casa De La Moneda
Priority date: 2007-10-04
Filing date: 2008-09-24
Publication date: 2009-04-09
Also published as: ES2317790B1; ES2317790A1

Abstract

The invention relates to: a method for conditioning inorganic materials such as safety additives, the resulting conditioned material, safety paper having a composition containing said conditioned inorganic material and the use of the conditioned inorganic material for the production of safety paper.

Description

METHOD OF CONDITIONING OF MINERAL MATERIALS AS SAFETY ADDITIVES

FIELD OF THE INVENTION

The invention belongs to the field of inorganic materials used as security elements in paper. More specifically, the invention relates to a method for conditioning said inorganic materials as safety additives, as well as to the inorganic conditioned material thus obtained, to a safety paper comprising said inorganic material conditioned in its composition and to the use of the material inorganic conditioning for the manufacture of security paper.

BACKGROUND OF THE INVENTION

The use of identification means in order to ensure the authenticity of documents or objects is very old and today, increasingly sophisticated methods are still used, in order to avoid forgery. These methods involve both the support material and the whole element to be secured. From logo designs to the incorporation of electronic components.

In the case of documents and paper money, it is very important to be able to ensure their authenticity, which is why, for many years, elements that hinder their falsification have been incorporated. More and more complex paper compositions are formulated, watermarks are made, etc. Active components have been used for years to paper, which in small proportions are able to make them active at certain stimuli whether electromagnetic radiation, electrical fields, etc.

Since the 50s, various forms of authentication of documents using optical means, from credit cards (US 3679449), identification cards (US 2704634), to avoid the photocopy of documents (US 3713861), bank documents (US 3886083), identification cards (US 3928226), security paper (US 4183989).

Different authentication methods have been used such as avoiding photocopies generating fluorescent emissions, reflecting the incident radiation, providing magnetic particles, etc. In the end, all this consists in developing some physical property, normally, in some additive or coating to be applied to the security document.

The operative form in the preparation of the products (value documents supported on paper) is always the same: once the physical property to be developed in the document is known, the raw material is defined with the appropriate additives or dopants to design the response of so that it stays in a desired range, whether of frequencies, electric field, magnetic permeability, etc. However, the active material, obtained by synthesis, whose properties of evaluable behavior are known, it is necessary to process it to achieve the precise characteristics to be able to add it to the paper.

US 6344261 describes a series of inorganic materials with luminescent capacity useful as safety elements. The patent also describes the preparation of said materials which, after their synthesis, are incorporated directly into the paper pulp. However, the direct incorporation of the powdered materials into the paper pulp results in an insufficient dispersion of the material in the paper that is desirable to improve.

The inventors of the present invention have developed a method for conditioning inorganic materials for incorporation into paper pastes This is based both on the use of suitable average particle sizes and on the prior dispersion of said particles in a conditioning solution. The method of the present invention allows to obtain clearly improved and more homogeneous dispersions of the inorganic safety material in the paper pulp and therefore higher quality security papers.

DETAILED DESCRIPTION OF THE INVENTION

In the first place, the invention relates to a method for the conditioning of applicable inorganic materials as safety additives in paper comprising: a) Calcination and agglomeration of the inorganic material at a temperature of up to 1600 ° C,

b) Subject the calcined and agglomerated material of a) to one or several grinding stages up to an average particle size between 2-20 μm,

c) Suspension of the material of b) in an aqueous solution with one or more dispersants,

where, optionally, before stage a), another grinding stage can be carried out.

In the context of the present invention, inorganic material is any mineral substance commonly used as a paper safety additive. Normally these minerals have some physical property that allows them to act as such security elements. Inorganic materials used as safety elements are normally capable of being excited at certain wavelengths while emitting luminescence to different lengths. The inorganic materials of the invention are minerals that comprise rare earths since these have the ability to excite in the visible spectral region and have a high level of emission intensity in the near-infrared spectral region. In a preferred embodiment, the inorganic materials of the invention have a perovskite-like structure such as strontium titanate doped with praseodymium or other rare earths. In another preferred embodiment the inorganic material has a garnet-like structure such as ytrium aluminate doped with erbium or other rare earths.

In the first stage of the method the calcination and agglomeration of the inorganic material previously synthesized is carried out. This heat treatment serves to improve certain aspects of the synthesized products such as their chemical stability, degree of crystallinity, their crystallite size and their state of agglomeration. The treatment must be designed according to the material and synthesis method by which it has been synthesized although in general the calcination will be carried out at a temperature not exceeding 1600 ⁰ C. In a preferred embodiment of the invention the calcination will be carried out between 800 and 1300 ⁰ C.

The second stage of the process involves subjecting the agglomerated material to one or several grinding stages up to an average particle size within the range of 2 to 20 μm. These are sizes compatible with the paper preparation. On the one hand the particles cannot be greater than 20 μm so that they are perfectly integrated in the thickness of the sheet of the final paper and to avoid its location and identification because it is a security element. On the other hand, if the concentration of particles less than 2 μm is very high, the effectiveness of the product will be low since during the papermaking process, much of the material will be lost with the water. Therefore, the size ranges must be in a

100% less than 20 μm and 95% greater than 2 μm. That is, there is a 5% error range but only for sizes below the lower limit. There is no mistake, however, in the upper limit since the final finishing of the paper would not be satisfactory for the reasons stated above. In any case, in a preferred embodiment of the invention, the average particle size must be within the range of 3 to 7 μm.

After the heat treatment, the materials are densified, so that before the fine grinding until reaching the desired particle size, it is necessary to start with a previous or broken grinding, which can be carried out by techniques such as breaking the jaws, hammers or of roller. These types of treatments are done dry. In the case of soft agglomerates, high shear agitation systems can be used, taking advantage of this stage for the suspension of the material.

Because the precise granulometry for the paper pulp must be fine as mentioned above, it is necessary to pass through wet grinding systems since the risk of contaminating the material is run through a dry route. For wet milling, methods such as ball mills, attrition grinding systems or in the case that the agglomerates are relatively weak, high shear dispersion systems can be used. Naturally, a combination of all the above-mentioned techniques, both dry and wet, can be used to obtain the desired particle size.

The last step of the method comprises the suspension of the material with the appropriate particle size in water in the presence of one or more dispersing agents. The amount of dispersant must be determined according to the unit of active material to be processed. As a reference unit, the material surface that is the one that makes rheological sense should be used. Therefore, the amount of dispersing agent necessary for the suspension will depend on the specific surface area of the final product. Both organic and inorganic dispersants are valid for the purposes of the present invention. As for the predominant dispersing effect, this may be steric in the case of ammonium or ionic polyacrylate, as in the case of sodium or mixed hexametaphosphate, such as in the case of polyethylene glycol. Both ammonium polyacrylate, such as sodium hexametaphosphate and polyethylene glycol represent the preferred dispersants of the invention although other dispersants may also be valid. Dispersants can be used individually or mixed together.

The method of the invention may include several optional steps depending on the type of material to be processed and the use that is intended to be given to the final conditioning solution.

In the first case, when the material to be agglomerated does not have the appropriate dimensions for calcination, it can be subjected to some previous grinding stage. This grinding can be performed by any of the techniques mentioned above.

In the second case, the circumstance can be given that the conditioned material will be used immediately for the preparation of the paper, so that there would be no problem. However, if the application of the material is to be carried out later and the material must be stored or transported, it can be subjected to a drying stage to remove the water. This drying stage can be carried out by means of a press filter or spray. This last technique is preferable.

When the material is to be incorporated into the pulp of the paper, it must be resuspended in water. The presence of the dispersant in the dried material favors the restoration of the suspension of the inorganic material for its incorporation into the paper pulp. Another aspect of the invention relates to the conditioned inorganic material obtainable according to the method of the invention.

The object of the invention is also a security paper comprising an inorganic conditioned material obtainable according to the method of

The invention

A final aspect of the invention refers to the use of a conditioned inorganic material according to the method of the invention in the preparation of security paper.

The following examples serve to illustrate the present invention although they are not intended to have a limiting character thereof.

Example 1

In the case of a luminescent active substance with a Perovskite-like structure, it is taken, consisting of Strontium titanate doped with Praseodymium, prepared as described in the work of H. Yamamoto, S. Okamoto and H. Kobayashi (Journal of Luminescence 100 (2002) 325-332).

The appropriate quantities of SrCO ₃ , TiO ₂ and PrCI ₃ are homogenized in a dry ball mill and placed in a Cordierita-mullita crucible of low form and of 2 liters capacity. Said crucible is introduced in an electric oven capable of reaching 1500 ⁰ C. It is heated at a speed of 2 ° C / min to 800 ⁰ C to achieve the decomposition of raw materials and subsequently the temperature is raised to 1300 ⁰ C at a speed of 3 ° C / min. It is kept at said temperature for 120 min and cooled at a speed of 3 ° C / min. At 200 ° C the oven opens to accelerate cooling. After this stage, the obtained agglomerated powder is subjected to a previous grinding by means of a jaw crusher to a smaller size 0.5 mm

The powder thus obtained will be broken down into a continuous high shear agitation equipment, of the IKA brand. For this, a mixture consisting of 49.9% by weight of deionized water, 50% by weight of the substance to be deagglomerated and 0.1% of sodium hexametaphosphate is prepared. Said mixture will be processed with the high shear agitator through the system of successive passes to ensure that all the material passes through the deagglomeration chamber. The passes continue until the particle size of the suspension, determined by dispersion of laser radiation indicates that 100% of the population is below 20 micrometers, and the average size between 2 and 7 micrometers, sizes compatible with the manufacture of paper.

The suspension thus obtained can be added to the formulation of the corresponding paper pulp.

If you want to transport it, you proceed to remove the water, for which an impeller atomizer is used, using an air pressure of 6 Kgr / cm ² to move the impeller, an inlet air temperature of 35O ⁰ C.

For subsequent suspension it is sufficient to use the same proportions of dust and water (~ 50:50% weight) and a high speed stirrer.

Example 2

In the case of a luminescent active substance with a garnet structure, it is taken, consisting of Ytrium aluminate doped with Erbium, prepared as described in the work of A. Leleckaite and A. Kareiva (Optical Materials 26 (2004) 123- 128). Suitable amounts of Y ₂ O ₃ , Er ₂ O ₃ and AI (NO ₃ ) ₃ .9H ₂ O are processed as described below. The Ytrium oxide is dissolved in a 0.2 molar solution of acetic acid at 65 ⁰ C. To this solution is added Erbium oxide dissolved in acetic acid. Next, the Aluminum Nitrate, previously dissolved in water, is added. The whole is stirred for 3 hours at 65 ⁰ C. Subsequently 1,2-ethanediol is added as a complexing agent. The solution is concentrated by slow evaporation at 65 ⁰ C until it becomes a transparent gel. The gel is mechanically crushed and introduced into a Cordierita-mullita crucible of low shape and 2 liters capacity. Said crucible is introduced in an electric oven capable of reaching 1500 ⁰ C. It is heated at a speed of 2 ° C / min to 800 ⁰ C where 120 min is maintained to achieve the decomposition and reaction of the raw materials. The agglomerate thus obtained is subjected to a previous grinding by means of a jaw crusher up to a size smaller than 0.5 mm. Subsequently reintroduced into the pot and in the furnace and heated to the temperature of 1000 ⁰ C at a rate of 3 ° C / min. It is maintained at said temperature for 120 min. And it cools at a speed of 3 ° C / min. At 200 ° C the oven opens to accelerate cooling.

After this stage, the obtained agglomerated powder is subjected to a previous grinding by means of a jaw crusher up to a size smaller than 0.5 mm.

The powder thus obtained will be broken down into a continuous high shear agitation equipment, of the IKA brand. For this purpose, a mixture consisting of 54.7% by weight of deionized water, 45% by weight of the substance to be deagglomerated is prepared and 0.3% ammonium polyacrylate is added (Dolapix CE64 Zschimmer & Schwarz GMBH & Co KG) Said mixture will be processed with the high shear agitator through the system of successive passes to ensure that all the material passes through the breakdown chamber. The passes continue until the particle size of the suspension, determined by means of laser radiation dispersion, indicates that 90% of the population is below 100 micrometers. Subsequently, the suspension is introduced into an attrition mill with zirconium oxide balls of 3 mm and thus processed to reach an average size between 3 and 7 micrometers, sizes compatible with papermaking. The suspension thus obtained can be added to the formulation of the corresponding paper pulp.

In case of wanting to transport it, the water is eliminated. To dry the suspension obtained, an impeller atomizer is used, using an air pressure of 6 Kgr / cm ² to move the impeller, an inlet air temperature of 35O ⁰ C.

Claims

1. Method for conditioning applicable inorganic materials as safety additives in paper comprising:

a) Calcination and agglomeration of inorganic material at a temperature of up to 1600 ° C,

where, optionally, before stage a), another grinding stage can be carried out.

2. Method according to claim 1 characterized in that the inorganic material has a perovskite type structure.

3. Method according to claim 2 characterized in that the inorganic material with perovskite type structure is strontium titanate doped with praseodymium or other rare earths.

4. Method according to claim 1 characterized in that the inorganic material has a garnet type structure.

5. Method according to claim 4 characterized in that the inorganic material with garnet type structure is ytrium aluminate doped with erbium or other rare earths.

6. Method according to claim 1 characterized in that the calcination and agglomeration of the inorganic material is carried out at a temperature of between 800-1300 ⁰ C.

7. Method according to claim 1 characterized in that the grinding is carried out by breaking jaws, hammers or rollers; high shear agitation; ball mills; attrition grinding, high shear dispersion; or a combination thereof.

8. Method according to claim 1 characterized in that the grinding can be carried out by dry or wet.

9. Method according to claim 1 characterized in that the average particle size obtained in step b) is between 3-7 μm.

10. Method according to claim 1 characterized in that the dispersant is sodium hexametaphosphate, low molecular weight polyethylene glycol or ammonium polyacrylate or any of its mixtures.

11. Method according to claim 1, which may optionally include a drying step for the storage of the inorganic material or for its transport.

12. Method according to claim 11 characterized in that the drying is carried out by means of a press filter or by atomization.

13. Inorganic material conditioned for incorporation into paper obtainable by the method of any of claims 1-12.

14. Security paper comprising in its composition a conditioned inorganic material according to claim 13.

15. Use of a conditioned inorganic material according to claim 12 in the preparation of security paper.