WO2011061701A2

WO2011061701A2 - Chemical suspension sensitive to temperature variations and method for obtainment thereof

Info

Publication number: WO2011061701A2
Application number: PCT/IB2010/055254
Authority: WO
Inventors: Marco Mandelli
Original assignee: Marco Mandelli
Priority date: 2009-11-19
Filing date: 2010-11-18
Publication date: 2011-05-26
Also published as: ITVR20090197A1; WO2011061701A3

Abstract

The present invention relates to a suspension including: - 3% to 12%: a plurality of particles of SSD type that are magnetizable by means of application of a magnetic field thereto and demagnetizable mainly due to Brownian motions, such that said chemical suspension results sensitive to temperature variations, the particles being selected from the groups constituted by magnetite, substituted magnetite and/or ferrite; - 15% to 25%: a polar polymer component selected from the group constituted by polyvinylpyrrolidone and/or polystyrene copolymer; and - at least one polar solvent selected from the group constituted by alcohol having a number of carbon atoms comprised between C₇ and C₁₆, said particles being stably embedded in said at least one solvent, whereas said polar polymer component is configured as a net or mesh being extended in said solvent and engaging said particles, so as to prevent the aggregation thereof, said suspension having a freezing temperature in the range of -18°C to 12°C.

Description

CHEMICAL SUSPENSION SENSITIVE TO TEMPERATURE VARIATIONS AND METHOD FOR THE OBTAINMENT THEREOF

The present invention regards a magnetizable chemical suspension sensitive to temperature variations, particularly adapted for achieving a sensor employable in controlling the correct preservation of products, such as numerous food products and drugs; such preservation requires the peremptory compliance with specific temperature thresholds for processing and/or storage and distribution.

The present invention also regards a measurement device intended to detect the temperature variations sustained by a preserved product and to provide, at the output, a signal indicative of the correspondence (or lack of correspondence) of the product with pre-established preservation standards.

Temperature control in the steps of processing, preservation and distribution of food products, drugs and the like (in particular of the so-called "cold chain") is a real problem, since keeping the product within prescribed temperature ranges in these steps is an indispensable requirement for ensuring the quality and/or safety of the products with respect to the law and production directives or specifications.

On this matter, it should be recalled that the "refrigeration" of a product, e.g. a food product, consists of its cooling to a temperature in the range of -1 °C to +8°C. A refrigerated product can be preserved for brief time periods that can vary from several days to several weeks, since the microbe activities and the chemical, physical and biochemical alterations are considerably slowed at the refrigerated state. Refrigerated products are in any case subject to deterioration since their quality decreases with the increase of the time period in which they are stored in refrigerated condition.

The "freezing" of a product (i.e. its cooling to temperatures at least less than -18°C) slows the biochemical reactions responsible for the alterations of the products more greatly with respect to refrigeration, and consequently the shelf-life of frozen products is longer. Nevertheless, some physical- mechanical changes and some biochemical reactions can occur even at freezing temperatures, particularly if there is an even only temporary increase in temperature, for example above -18°C.

Therefore, it is of great importance to be able to control the compliance with the temperatures prescribed by law, typically during the entire cold chain, and hence to be able to verify good product preservation, particularly concerning frozen or refrigerated products. Generally, the operators in this field are required to:

- comply with suitable hygiene standards in all production steps;

- cool or freeze the products in an appropriate manner immediately after their processing, collection and/or packaging;

- maintain the refrigeration temperature (< +5°C) or freezing temperature (< -18°C) controlled during the preservation and distribution phases;

- maintain the refrigeration temperature (< +5°C) or freezing temperature (< -18°C) controlled in the storage cells and on the sales counters;

- ensure that the transfer of the refrigerated or frozen products is carried out without "interruptions" of the cold chain; and

- carrying out systematic and frequent temperature checks on random samples of the preserved products, also with the aid of appropriate and suitably calibrated instruments.

Currently, the main verification of the state of preservation of a food product or drug is only conducted based on monitoring of the product temperature in some specific step of the cold chain.

The International Agreement on the Transportation of Perishable Goods (ATP) sets the following maximum temperatures for the transportation of refrigerated food products, e.g. +7°C for meats, +6°C for meat-based products and for butter, +4°C for poultry, milk and dairy products, +3°C for offal and +2°C for fish. With regard to frozen food products, their temperature must always be maintained below -18°C and values around -15°C are only tolerated for brief time periods in the transportation and/or distribution phases. The temperature of the refrigerated sales counters must be maintained around -18°C, and in any case must not ever exceed -12°C (even an over-temperature of a few hours could result damaging).

A control means currently available on the market for controlling the compliance with the preservation temperatures of refrigerated or frozen products is represented by the so-called "thermochromic labels". These are adhesive labels applicable to products to be monitored, including substances that irreversibly change color when their temperature - and thus that of the product to which they are applied - exceeds a certain threshold value.

These labels have several serious drawbacks. First of all, they require particular conditions for their storage and handling, since they must be preserved at temperatures lower than the respective threshold temperature, i.e. the temperature at which they change color. Secondly, they are not reusable, since they change color in an irreversible manner once their threshold temperature has been exceeded. In addition, their high production cost justifies their use only for some product types, e.g. medicines, vaccines and costly chemical substances.

A specific limit for the use of thermochromic labels is represented by the fact that while they offer an indication of having exceeded (or not exceeded) a certain threshold temperature, they do not allow an objective and precise quantification of the exposure time of the product at temperatures higher than the threshold temperature. As stated above, exceeding the prescribed temperatures is tolerated in the food and pharmaceutical field, even if only for brief time periods.

The German patent application DE-10301 107A1 teaches an ink that is printable via inkjet, as well as a method for the obtainment thereof. The ink includes ferromagnetic particles with 5nm - 30nm dimensions, obtained from water, polyvinylpyrrolidone (PVP) and water-soluble organic solvents. The ink has a viscosity between 700 mPas - 50000 mPas. The ferromagnetic particles of the ink are coated by means of various compounds, including the PVP, such coating being obtained via heating of the aqueous solution, which determines a so-called grafting reaction towards the particles.

As will be understood, possible polymers (PVP) anchored on the surface of the particles increase the steric hindrances in the contacts with other elements of the composition. They also increase the hydrodynamic radius of the same particles, on which (as is known) the relaxation speed depends. The relaxation speed is non-zero if the magnetic particles are free to move and in turn depends on the cube of the hydrodynamic radius; thus the formulations (inks) taught by DE-10301 107A1 do not undergo modifications following variations (increases) of temperature, so that they are not particularly recommended for the determination of such variations.

The international application WO-90/15666 teaches superparamagnetic magnetic particles, which can be obtained by mixing, for example, a magnetically reactive metal with a polymer intended to coat the particles themselves. The polymer can comprise polyvinylpyrrolidone, among other things. According to this prior art document, the particles are obtained from a series of compounds in aqueous solution, which as stated above causes the coating of the particles by the polymer via heating. For such document, the same considerations made with reference to DE-10301 107A1 hold true.

The international application WO-2006/057467 instead regards nanoparticles obtained from a solution of a metallic salt of a surfactant inside a suitable solvent which gives rise, in the same solvent, to a surfactant-metal complex. A surfactant-metal complex solution is then prepared due to the mixing of the preceding product with another solvent containing a surfactant or a mixture of surfactants. Subsequently, the preparation is heated to a temperature between 100 and 400°C and maintained at that temperature for a time comprised between 1 minute and 24 hours; this leads to the formation of nanoparticles which are then separated from the mother liquid due to a flocculation and further purified via centrifugation and precipitation. The main object of the present invention is to provide a magnetizable chemical suspension that is sensitive to the gradient or to the variations of the temperature of a specific product and is therefore suitable for use as a sensor for detecting the exceeding of threshold values, particularly in the preservation of food products and drugs.

Another object of the present invention is to provide a chemical suspension sensitive to the temperature gradient which is easy to preserve and handle and can be produced at competitive costs.

A further object of the present invention is to provide a chemical suspension sensitive to the temperature gradient which allows acquiring objective information on possible temperature variations.

Another object of the present invention is to provide a temperature variation sensor comprising the chemical suspension, object of the present invention, and intended to be applied on the product or on the package of the product to be monitored.

A further object of the present invention is to provide a temperature gradient sensor which can be reused multiple times.

Still another object of the present invention is to provide a temperature gradient sensor that can be produced at competitive costs.

Another object of the present invention is to provide a temperature gradient sensor that practically cannot be tampered with.

A further object of the present invention is to provide a method for obtaining a chemical suspension that is sensitive to the temperature gradient according to the present invention. Not least object is to provide a device for measuring the temperature gradient adapted for providing, in output, a control signal relative to the correct or incorrect preservation of a product.

According to a first aspect of the present invention, a suspension is provided including:

- 3% to 12%: a plurality of particles of SSD type magnetizable by means of application of a magnetic field thereto, and mainly demagnetizable due to Brownian motions, such that said chemical suspension results sensitive to temperature variations, said particles being selected from the group constituted by magnetite, substituted magnetite and/or ferrite;

- 15% to 25%: a polar polymer component selected from the group constituted by polyvinylpyrrolidone and/or polystyrene copolymer; and

- at least one polar solvent selected from the group constituted by alcohol having a number of carbon atoms comprised between C₇ and Ci₆, said particles being stably embedded in said at least one solvent, while said polar polymer component is configured as a net or mesh, such as a substantially three-dimensional net, being extended in said solvent and engaging said particles, thus preventing the aggregation thereof,

said suspension having a freezing temperature comprised between - 18°C and 12°C.

According to a further aspect of the present invention, a sensor is provided for detecting temperature variations of a product to be monitored, comprising at least one substantially rigid containment element and at least one magnetizable suspension, obtained according to the first aspect of the present invention, contained in said at least one containment element characterized in that said at least one containment element is set to prevent the evaporation of said at least one polar solvent in said at least one magnetizable suspension, towards which it is chemically inert.

According to a third aspect of the present invention, a device is provided for detecting the temperature variations sustained by a sensor according to the present invention, comprising:

- magnetic field sensor means adapted to generate an electrical signal correlated with the intensity of at least one detected magnetic field;

- at least one data processing board set to process at least one electrical signal in order to determine at least one parameter correlated with the intensity of said at least one detected magnetic field and to generate at least one electrical output signal correlated with the exceeding (or non-exceeding) of a predefined threshold temperature by said temperature variation sensor; and

- at least one indicator means activatable in response to said at least one electrical output signal.

Further aspects and advantages of the present invention will be clearer from the following detailed description of several currently preferred embodiments thereof, illustrated as merely exemplifying and non-limiting in the drawing set, in which:

Figure 1 shows, in slightly top perspective view, a temperature variation sensor according to a first embodiment of the present invention;

Figure 2 shows a cross section view of a temperature variation sensor according to a second embodiment of the present invention; Figure 3 shows a cross section view of a temperature variation sensor according to a second embodiment of the present invention;

Figure 4 is a schematic and symbolic view with details in section of an ink according to the present invention, applicable on the sensor of Figure 3;

Figure 5 is a schematic and symbolic view in section of a microcapsule of the ink of Figure 4;

Figure 6 shows, in slightly top perspective view, a device for measuring the temperature variations detected by the sensors of Figure 1 , 2 or 3; and

Figure 7 illustrates a flow-chart relative to the functioning of the measurement device of Fig. 6.

In the drawing set, equivalent or similar parts or components were marked with the same reference numbers.

The present invention provides a magnetizable chemical suspension Ci comprising a ferromagnetic component, at least one polar solvent and a polar polymer compound with anti-aggregating function. The ferromagnetic compound is constituted by particles of SSD (Stable Single Domain) type, i.e. by stable ferromagnetic material particles, which once magnetized by means of exposure to an external magnetic field show a remaining field even after removal of the external magnetic field. As is known, the demagnetization process of SSD particles only occurs at a very slow rate, since such particles remain magnetized for billions of years. The demagnetization time mainly depends on the intensity of the Brownian motions of the particles due to temperature variations. The demagnetization time also depends on the dimensions of the particles of said ferromagnetic material, which must be sufficiently small.

Given a magnetizable chemical suspension Ci obtained from particles of ferromagnetic material with predetermined grain size, the measurement of the demagnetization of the composition Ci depends on the time passed from its first magnetization and on the temperature variations undergone. It is preferably indicated in percentage terms according to logarithmic law:

X_w = A * \og{b * t)

where b is a parameter that can be estimated beforehand, t is the time in minutes and A varies with the temperature in the same manner in which the viscosity of the employed solvent varies with the temperature.

The ferromagnetic component for a magnetizable chemical suspension Ci according to the present invention is selected from the group comprised of magnetite, substituted magnetite and/or ferrite, and is formed by stable particles, i.e. of SSD type, having diameter comprised between about 20 nm and 50 nm, such that said suspension is sensitive to temperature variations.

The ferromagnetic component is also present in the suspension in a percentage by volume comprised between 3% and 12% and contributes to providing a pasty consistency to the suspension, with a solid phase content between about 30% and about 70%; unlike the ferrofluids, which as is known have a solid phase content between 5% and 10%.

Generally, ferrofluids have a much lower viscosity than that of the suspension according to the invention. As is known, the demagnetization time depends proportionally on the viscosity of the solvent means for the ferromagnetic material particles. A low viscosity therefore determines a brief demagnetization time, i.e. on the order of several seconds, which would be unsuitable for the purposes of the present invention.

At the state of the art, it is known to use ferrofluids for diagnostic or therapeutic purposes, or in the speaker field and in that of watertight joints. Ferrofluids are characterized by the presence of superparamagnetic particles with diameter comprised between 6 and 10 nm, necessary for avoiding their agglomeration, which would alter the demagnetization process.

In order to avoid the agglomeration in the suspension of the present invention, the presence of 15% to 25% by volume of a polar polymer component is provided for, which has mainly anti-aggregating function. Advantageously, the anti-aggregating polar polymer is typically comprised of polyvinylpyrrolidone (PVP). Preferably, the PVP used for obtaining the suspension of the present invention has molecular mass comprised between 10000 and 800000 Dalton and is present in a percentage by volume comprised between about 20% and about 40%. Alternatively, the polar polymer component is polystyrene copolymer or a combination of PVP and polystyrene copolymer.

The polar solvent is advantageously constituted by one or more alcohols selected from the group formed by the alcohols having a number of carbon atoms comprised between C7-C16, preferably by the straight chain alcohols having a number of carbon atoms comprised between C7-C16, and preferably n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n- dodecanol and 1 -hexadecanol. The magnetizable chemical suspension Ci is preferably made in a manner so as to be particularly sensitive to variations close to the threshold temperatures T_s relative to the freezing or to the refrigeration of the products to be monitored, in particular to foods or drugs. The suspension must therefore comprise a fluid part having a freezing point close to said threshold temperatures and hence typically -18°C, -15°C, -12°C, -6°C, -1 °C, +4°C +8°C; it must therefore have a freezing temperature comprised between - 18°C and 12°C.

In a suspension according to the present invention, the ferromagnetic component particles are stably embedded in the solvent. In addition, the polar polymer component is configured as a net or mesh that is extended in the solvent and engages the particles, so as to prevent their aggregation. As will be understood, with one such "net" structure, the particles cannot agglomerate together due to the Van der Waals attractions: the Brownian relaxation can only occur if the particles are isolated from each other and do not have stable interactions with other elements of the composition, which limit their movements.

The lattice formed by the polar polymer component allows the ferromagnetic component particles to remain substantially uniformly distributed in the solvent, separated from each other, and at the same time be subjected to the effect of an external magnetic field applied thereto, being magnetized with the direction of the external magnetic field. In the case of significant temperature variations, the particles move out of alignment with the external magnetic field. The lattice formed by the polar polymer component advantageously acts as a separator element between the ferromagnetic component particles: after the application of an external magnetic field, such particles tend to group together due to their residual magnetization.

A suspension such as that described above is obtained according to a method which essentially provides for an operative step of mixing the ferromagnetic component particles with a solution of at least one polar solvent and the polar polymer component until a uniform paste is obtained.

The heating of the mixture, preferably to a temperature comprised between 50°C and 95°C, preferably between 70°C and 95°C, accelerates the mixing step.

During the preparation steps of a suspension according to the present invention, it is important that water is not present; this could cause a so-called grafting reaction towards the particles, as stated above with reference to the German patent application DE-10301 107A1 .

Further aspects of the preparation method will be clearer from the following description of several currently preferred and non-limiting preparation examples of the magnetizable suspension according to the invention. Example 1

2.03 grams of PVP were mixed with 7.68ml of undecanol. The mixture was heated at about 95°C under mechanical stirring and the PVP was dissolved in the solvent. 5 grams of nanopowder F₃O₄ were then added and all is mechanically mixed and then cooled at a cooling speed of at least 10°C/min. A magnetic paste is obtained with the following values of "A": 0.035 at 0°C; 0.13 at 4°C; 0.257 at 8°C.

Example 2

2.08 grams of PVP-PS copolymer were mixed with 7.73ml of dodecanol. The mixture was heated to about 95°C under mechanical stirring and the PVP-PS was dissolved in the solvent. 5 g of nanopowder F₃O were added and all is mechanically mixed and then cooled to at least 10°C/min.

A magnetic paste is obtained with the following values of "A": 0.035 at 0°C; 0.0365 at 4°C; 0.12 at 10.3°C; 0.155 at 13°C; 0.25 at 17°C; 0.323 at 20°C.

In order to prevent a suspension stabilized according to the present invention from drying out after evaporation of the solvent, and in order to obtain an ink that is easy to print, preferably via flexography, a suspension according to the present invention can be microencapsulated.

Microencapsulation is a technique that can be applied in various sectors, including the gradual release of active principles in drugs, the protection of the nucleus of a capsule from various mechanisms of degradation, copy paper without carbon and scented inks.

Microencapsulation can be conducted both with mechanical and chemical methods, the first leading to the obtainment of capsules with dimensions between 200 micron and about 2 millimeters.

The chemical methods are mainly based on an interfacial polymerization process, where the interface is that between the emulsion solvent and the magnetizable suspension drops. Such methods in any case occur in emulsion, under constant stirring.

As will be understood, in order to obtain the microencapsulation, the solvent, the material that will form the walls of the capsule and the material of the nucleus must be substantially insoluble with respect to each other.

Example 3

Microencapsulation of a hexadecanol-based stabilized magnetic suspension comprising the following steps:

1 ) 2,72 g of copolymer PVP-PS in 9,72 g of 1 -hexadecanol were dissolved by heating, at a temperature of 95°C - 130°C, and under mechanical stirring. 4,53g of Fe₃O were added to the mixture, and a good mixing was obtained. The magnetic suspension in melted state was air- nebulized in small drops suitable for obtaining, after solidification, particles with a diameter ranging between 2μηη and 200 μιτι. The composition thus obtained is suitable for showing whether the temperature has been higher than ambient temperature: such a feature is much important for preserving oligomers (thereby preventing their polymerization) and a high number of antibodies.

2) Providing 200 ml_ of solvent liquid, such as water, in which the suspension to be encapsulated is emulsified. Such a liquid, optionally, includes up to 35 g of sodium salt of styrene-maleic anhydride (SMA) copolymer with average molecular weight of 150000 and 2 grams of NaOH. The composition thus obtained was mechanically emulsified for 2 hours at 50°C. Subsequently, pH was brought to about 4,0 - 4,5. 3) Adding the material to be encapsulated to the solvent prepared in point 2) and dispersing it by means of cold mechanically stirring at a temperature between 4°C and 10°C.

4) Adding the prepolymer forming the capsule wall and polymerizing The prepolymer can be obtained by heating and mixing a mixture

(molar ration between 1 :1 and 1 :4) of melamine and aqueous solution having 37% formaldeide at a temperature of 60°C-70°C under poorly alkaline conditions (about pH=8).

A prepolymer was added to the prepared emulsion in point 3), e.g. by means of nebulization, in quantities varying from 5ml_ to 25ml_, and the resulting mixture was mixed. When the whole prepolymer was added, the mixture was heated at temperatures ranging from 50°C to 67°C, and the mixture was kept to such a temperature under constant mixing for a period ranging between 30 min and two hours.

Subsequently, acetic acid was added, thus bringing the PH to 4.0, in a manner so as to interrupt the capsule wall formation reaction. Then 10 grams of urea were added for eliminating the excess formaldehyde.

The microcapsules thus obtained were filtered and dried; they had a diameter between 2 and 100 micron, with a nucleus volume of about 75% of the total volume of the respective microcapsule.

The microcapsules were then ready to be loaded in the ink. Such microcapsules 10 comprise (see Fig. 5) a containment element 2b which encloses the ferromagnetic particles 1 1 embedded in the solvents and maintained disaggregated by means of the net of the polar polymer component 12. The percentage composition of the microcapsules in ink according to the present invention is less than 30% by volume.

As will be understood, with a microencapsulation process according to the present invention, the solvent prepared in point 1 serves to emulsify the suspension to be encapsulated, so as to obtain a plurality of drops or micro- drops dispersed in such solvent. Once such emulsion is obtained, one then adds the prepolymer (point 4 above), which at the end of the microencapsulation method will form a containment cover 2b for the previously obtained drops. In such a manner, a plurality of microcapsules are obtained, which are then extracted from the solvent or "mother liquid" (e.g. via evaporation).

The composition of the ink to which the microcapsules are added preferably comprises a solvent selected from the group constituted by water, oil, alcohols, ethyl acetate, a pigment, a resin selected from the group constituted by nitrocellulose, acrylic resin, vinyl resin, maleic resin, fumaric resin, ketonic resin, polyurethane, polyamide resin.

The resin performs the task of making the ink form a film which can adhere to the substrate (paper, plastic, etc.) on which the ink can be printed. In order to obtain inks printable on paper, the solvent is preferably water, while the resin is nitrocellulose.

If however the ink is intended to be printed on polymer materials, the solvent is preferably comprised of ethyl acetate or a mixture made by mixing one or more of the following alcohols: industrial methylated alcohol, n- propanol, iso-propanol with one or a plurality of the following esters: ethyl acetate, n-propyl acetate, isopropyl acetate. The resin can also be an acrylic resin, vinyl rein, maleic resin, fumaric resin, ketonic resin, polyurethane, polyamide resin.

The ink can also comprise additives, e.g. carnauba wax, dibutyl phthalate or a polyethylene wax.

The pigments can be selected from among the following, for example: carbon black, Lithol (red), pyrazolone (orange), dinitroaniline (orange), Hansa yellow (yellow), indanthrene (blue) or metal oxides (non-magnetic).

The composition of an ink according to the present invention, particularly suitable for printing on polyethylene, comprises: 30% by volume of microcapsules, 5% by volume of carbon black, 5% by volume of nitrocellulose, 15% by volume of polyamide, 1 % by volume of dibutyl phthalate, 1 % by volume of polyethylene wax, 1 % by volume of amide wax, 30% by volume of ethanol, 8% by volume of n-propyl acetate, 4% by volume of propanol.

Other inks according to the present invention may not have a solvent, and hence the same do not dry out due to evaporation of the same, but harden by means of application of UV rays.

Such inks comprise, for example: between 10% and 25% by volume of pigment-microcapsule mixture, 40%-60% monomer, 15% to 25% oligomer and 10%-12% photoinitiator. The monomer, for example, can be isophoryl acrylate or tridecyl acrylate, the oligomer is preferably polyester acrylate, while the photoinitiator is advantageously an aromatic ketone.

An ink thus obtained can for example be printed on a label (e.g. made of paper) or directly on the packages of products which must be maintained at pre-established temperatures (see above) in order to prevent their characteristics from being degraded. As will be understood, this can be obtained due to the microencapsulation of the suspension, since the walls of the microcapsules prevent the solvent of the suspension from evaporating.

The magnetizable chemical suspension Ci according to the present invention can be advantageously employed for making temperature variation sensors applicable to a product or to its package, e.g. food products or drugs, in order to monitor the course of their temperatures, at which the product was maintained, from the time of the production and/or packaging thereof up to the exhibition thereof on the sales counters or refrigerators or the final consumption thereof.

As is illustrated in Figures 1 and 2, a sensor 1 according to the present invention is constituted by a support member 3, e.g. made of paper, cotton or any other suitable material, preferably of thickness comprised between 0.02 mm and 1 .0 mm, intended to support a containment element 2 for containing a pre-established quantity of magnetizable suspension C-i, e.g. not microencapsulated. The containment element 2, in turn, is for example constituted by a Millipore, produced by Millipore Corporate of Billerica, MA (USA), and has a tubular structure, with internal opening which acts as reception seat 2a, typically for several milligrams of chemical suspension C-i, e.g. 0.25 mg ÷ 2.0 mg.

Generally, the containment element 2 can be made of nylon or polyethylene or any other suitable material capable of preventing the evaporation of the polar solvent of the magnetizable suspension Ci contained therein, towards which it is chemically inert. The containment element 2 is, moreover, substantially non-deformable, thus ensuring that the magnetizable suspension Ci contained therein is not altered - not by the chemical interactions with the material of the containment element 2 nor following the evaporation of the solvent, nor also via mechanical deformation of its container, particularly via crushing or friction with other bodies.

It follows that the magnetizable suspension C-i, once magnetized by means of the application of an external magnetic field B, is affected by a residual magnetic field B-i which will diminish over time only due to Brownian phenomena of the suspension d; such phenomena can be accelerated following possible temperature variations sustained by the magnetizable suspension itself.

Advantageously, the containment element 2 can be arranged on the upper face 3c of the support member 3 (Figure 2) or it can be incorporated in a reception seat 3a provided for such purpose, in a manner such to be comprised within the bulk of the support member itself (Figure 1 ).

Suitable fixing means 4 can also be provided for on the lower face 3d of the support member 3, in a manner such that it results applicable to a product to be monitored or to its package. Advantageously, the fixing means 4 comprise a biadhesive material layer of any suitable type.

According to a variant of the present invention, see Figure 3, the containment element of the sensor 1 , indicated with the reference number 2b, is comprised of a plurality of microcapsules embedded in an ink I prepared according to the above-described method, which contain the aforesaid pre- established quantity of magnetizable suspension C-i .

Advantageously, the microcapsules 2b act as "substantially non- deformable" containers for the magnetizable suspension Ci contained therein, and in addition to preventing the evaporation of the solvent of the same, they prevent mechanical alterations of the magnetizable suspension caused by possible impacts or friction. Of course, the microcapsules do not chemically react with the magnetizable suspension Ci, and consequently do not alter the magnetization thereof over time.

The ink I containing the plurality of microcapsules 2b can be advantageously printed, preferably via flexography, at the upper face 3c of the support member of the sensor.

The flexographic technique is preferred with respect to the other printing techniques, since it allows controlling - with minimum margins of error - the quantity of ink printed on the support member 3. Consequently, it also allows controlling the quantity of magnetizable suspension Ci applied to the sensor.

Also in this case, the sensor 1 can provide suitable fixing means 4 on the lower face 3d of the support member 3.

After having been applied to a product to be monitored, the sensor 1 can be activated, as indicated above, by applying an external magnetic field B thereto (typically about 600 Gauss in the case of Fe3O₄ magnetite), e.g. at the end of the product packaging phase. The magnetizable suspension Ci in the sensor 1 , once subjected to the external field B, will be affected by a residual magnetic field Bi intended to diminish over time according to the algorithm (already reported above):

X_RF = A \og(b * t) = a * \og(b_{ * T + c) * \og(b * t) where X_RF represents one hundredth of the percentage decrease of the

(in brief "percentage demagnetization") of the magnetizable suspension Ci and depends:

- on the time t elapsed from the activation of the sensor 1 ;

- on the temperature T at which the sensor 1 is found during the time that elapsed from its activation to time t; and

- on four constants that can be estimated beforehand and which depend on the magnetizable suspension Ci employed in the sensor: a, bi, c and b. More particularly, the constant b is equal to about 1 min^"1. As an example, the progression of X_RF with respect to the log(t) is illustrated below. This is a linear progression at a given temperature (e.g. T_s).

It will be easily understood that once the kinetics of demagnetization of a magnetizable suspension Ci at a given threshold temperature T_s are known, together with the predicted demagnetization {XRF_P) and that which was actually measured XRFm after a certain time t, it is possible to estimate if the sensor 1 and thus the product to which this has been applied came to be above the predefined threshold temperature T_s, and the maximum time of this above-threshold-temperature period.

An illustrative example follows: Example 4

Given the following demagnetization kinetics:

X = 0.041 * Log(\min ^l * f[min]) relative to a suspension described in the preceding Example 2 (at the temperature of +7°C), if the sensor is applied to a product to be preserved at the threshold temperature T_s = 7°C for 2 years, one can calculate that at the end of the 2 years, the predictable demagnetization of the suspension Ci is equal to X_RFp = 0.2468. If, instead, after 2 years one measures a demagnetization greater than X_RFm = 0.64, based on the algorithm it is calculated that the sensor, and therefore the product, was at most for 77 min at a temperature 13°C greater than that provided for (i.e. 20°C), or at most for 9960 min (about one week) at a temperature 6°C greater than that provided for (e.g. 13°C).

It will be understood that with this data available, it is possible to carry out evaluations on the temperatures which a product to be monitored may have been subjected to during a specific time period (temperatures which can exceed or not exceed tolerable intervals At_s and ΔΤ_δ), and therefore deduce state of preservation of the product itself. This in order to establish, independent from that possibly indicated on the product's label, if it is suitable or unsuitable for final use-consumption, or if, for example, it can be used- consumed but only within a specific time period - before the expiry date that might be indicated on the package.

It will be observed that the information acquirable with one such sensor is quantifiable in an objective manner through a suitable detector device; one embodiment of such device will be described below. Nevertheless, the obtainable information is of "cumulative" type, in the sense that with regard to a specific established time period, one can determine if and for how long "overall" a product has exceeded the pre-established threshold temperature T_s. The exceeding of such temperature could have occurred in a continuous manner over time, or over separate intervals within the considered time period. The final information that can be obtained from the sensor 1 is in fact the total time over a temperature threshold.

Returning to the structure of the temperature variation sensor 1 , this can also advantageously provide for a control device D₂, borne by said support member 3, e.g. at a suitable reception seat 3b obtained therein (see, as an example, Figures 1 and 2). The control device D₂ advantageously comprises a second magnetizable suspension C₂ having different characteristics from those of the magnetizable suspension Ci .

The magnetizable suspension C₂ is still comprised of particles of SSD type, but they are now non-demagnetizable due to Brownian motions. This means that once subjected to an external magnetic field B, its particles will result magnetized in a substantially permanent manner (residual field B₂), i.e. the demagnetization of the magnetizable suspension C₂ will occur over much greater time period than that of the magnetizable suspension C-i, over many more years. The application of the magnetizable suspension C2 on the support member 3 will occur after the application of the magnetizable suspension Ci in the respective containment element 2, 2b and the magnetization thereof. In such a manner, if it results from a control that the magnetizable suspension C₂ is magnetized, it can be concluded that the respective sensor has been subjected to at least one subsequent magnetization carried out for the purpose (for example) of reducing the value of X_RF in a manner such that a possible exceeding of the threshold temperature T_s is not detectable. With this configuration, the temperature variation sensor 1 will also have a so- called "anti-tampering" function, i.e. it will allow verifying a possible tampering of the sensor 1 , caused by the application of an external magnetic field B after the activation of the sensor itself.

Alternatively, the control element D₂ can be applied to the sensor and magnetized, along a direction perpendicular to the magnetization direction of the suspension C-i, before the magnetization of the suspension C-i. More particularly, the residual magnetic field B_tot, resulting from the sum of the magnetic fields Bi and B₂ of the two magnetizable suspensions Ci and C₂, will vary in intensity and direction during a specific time period. Specifically, the field Bi will decrease due to the Brownian phenomena and due to possible temperatures greater than the threshold temperature T_s, to which the sensor 1 will be subjected, while the field B₂ will remain nearly constant. The progression of the field B_tot is therefore predictable in the optimal case in which a product is correctly preserved for the prescribed time period (B_optimai tot) and one would expect a total measured magnetic field B_totm having at most an intensity less than or equal to B_optimai tot, if the sensor 1 was subjected to temperatures greater than the threshold temperature T_s.

If, therefore, after a certain time period, a progression of the field Bi is detected that is different from that predicted, in particular of greater intensity, and also a field B₂ is detected with a component aligned like B-i of overly high value, this signifies that the magnetizable suspension Ci has been subjected to an additional external magnetic field B in order to compensate for the decrease of B_tot due to the exceeding of the threshold temperature T_s.

At this point, the product associated with the sensor 1 under examination is to be considered, in fact, tampered with, since it was not detected with certainty if and for how long it was exposed to temperatures greater than the relative threshold temperature T_s. Such information could of course be useful to the operator for evaluating the advisability of assigning the product for final use-consumption or rejecting the product.

However, it is clear that after the use-consumption of the product, the sensor 1 , which if desired can also act as a label, can be removed from the product or from its package and be newly magnetized for the packaging of a new product to be monitored.

Optionally, a temperature variation sensor 1 as described above can also comprise a bar code or a two-dimensional code of the type commonly applicable to products intended for sale. One such bar code or two- dimensional code normally allows keeping track of all the so-called "logistical" information regarding a product associated therewith, e.g. the origin, the production batch, the packaging date etc. A sensor 1 according to the present invention provided with bar code advantageously allows acquiring more data related not only to the logistics of the product to which it is applied, but also related to the state of preservation of the product itself, from the time of its production-packaging up to the delivery to points of sales, etc.

With regard to a device for detecting the temperature variations detected by the sensor, this is illustrated in Figure 3 and is indicated with the letter D. The detection device D is substantially comprised of:

- a containment structure or casing 5, e.g. box-like, magnetic field sensor means 6, preferably Hall effect sensors, e.g. of biaxial or triaxial type, or of magnetoresistive type, like the sensor HMC1021 S sold by Honeywell International Inc. of Morristown, NJ (USA), supported by said containment casing 5 and adapted to generate one or more electrical signals correlated with the intensity of at least one magnetic field B detected at a sensor 1 according to the present invention,

- one or more CPU data processing boards, preferably housed in the containment structure 5, set to process the electrical signal or signals for determining at least one parameter correlated with the intensity of the detected magnetic field (B) and to generate one or more electrical output signals correlated with the exceeding (or non-exceeding) of a predefined threshold temperature (T_s) by the temperature variation sensor 1 ; and

- one or more indicator means (8) activatable in response to the electrical output signals.

The CPU data processing board, or each such board, is preferably electrically connected to bar code reader means 7, from which one can acquire an electrical signal related to "logistical" information concerning the monitored product. Based on such information and on that detectable by the magnetic field sensors 6, the CPU is capable of generating electrical output signals correlated both to the exceeding (or non-exceeding) or a predefined threshold temperature (T_s) and to the determination of an actual expiry date.

The electrical output signals will be subsequently sent to indicator means 8 borne by the containment structure or casing 5. The indicator means 8 preferably comprise a screen, e.g. liquid crystal, intended to display the data extrapolated from the electrical output signal or signals exiting from the CPU calculation unit and/or a plurality of LEDs.

As shown in Figure 4, which schematically illustrates the functioning of the device D, the data displayable by the indicator means 8 also comprises the indication of the correct preservation or incorrect preservation of the product at the time when the measurement is made (Step 1 ).

If the product was not correctly preserved, the CPU calculation unit will proceed with the calculation of the total time period of product exposure to temperatures greater than the pre-established temperatures (Step 2) and with the subsequent comparison with suitable pre-set parameters, in order to obtain an evaluation on whether the monitored product is in any case suitable for use-consumption (Step 3).

If the product does not comply with the specifications and therefore is not to be used-consumed, a suitable warning message will be displayed during Step 4. Otherwise (Step 5), the CPU calculation unit, based on the electrical signals acquired up to that moment and on the calculations made, will calculate (operating a comparison with pre-established threshold values previously stored therein) if the product should be placed on the market as is (display of a suitable message in Step 6) or if it will be necessary to detail the need to use-consume the product before the expiry date provided on its package, or if the use thereof will have to occur in different modes, consumed only upon cooking etc...

In this case, the display means 8 could display a suitable message (Step 7) and the data related to a specific consumption of the product could be sent (Step 8), e.g. by means of a suitable signal sending-receiving unit of any suitable type, preferably of wireless or USB type, to a centralized data collection system (such as a server) for updating the information related to the monitored product.

The documents DE-10301 107A1 and WO-90/15666 do not teach compositions nor inks like those according to the present invention, since the ferromagnetic particles according to such prior art documents are coated and hence "trapped" by the PVP, and thus the same do not undergo modifications following temperature variations, unlike the suspension and the ink according to the present invention. Here, the aggregation of the particles is prevented by the polymer compound, which nevertheless does not enclose the particles themselves; after temperature variations such particles therefore free to rotate via Brown ian relaxation.

With regard instead to the international application WO-2006/057467, this teaches the production of nanopartides starting from a series of compounds, but the final composition does not comprise ferromagnetic particles embedded in the solvent and maintained disaggregated by a polyvinylpyrrolidone net. In such prior art document, moreover, it is specified that the nanopartides are separated from the mother liquid and subsequently centrifuged and precipitated. The magnetizable suspension Ci described above, as well as the method for the obtainment thereof, the temperature variation sensor 1 and the device D for detecting such temperature variations are all susceptible to numerous modifications and variants within the protective scope defined by the contents of the following claims.

Thus, for example, the sensor 1 according to the present invention can be constituted by only the ink I containing a predetermined quantity of microencapsulated magnetizable suspension Ci embedded therein, obtained as indicated above, and printed, e.g. via flexography, directly on the product to be monitored or on its package.

Once an external magnetic field B is applied to such ink I, the microencapsulated particles 2b of the magnetizable suspension Ci contained therein will have a residual magnetic field B-i which will vary in accordance with that described above and will be detectable by a detection device D of the type indicated above.

Claims

1 . A suspension including:

- 3% to 12%: a plurality of particles of SSD type that are magnetizable by means of application of a magnetic field thereto and demagnetizable mainly due to Brownian motions, such that said chemical suspension results sensitive to temperature variations, said particles being selected from the groups constituted by magnetite, substituted magnetite and/or ferrite;

- at least one polar solvent selected from the group constituted by alcohol having a number of carbon atoms comprised between C₇ and Ci₆, said particles being stably embedded in said at least one solvent, whereas said polar polymer component is configured as a net or mesh being extended in said solvent and engaging said particles, so as to prevent the aggregation thereof,

said suspension having a freezing temperature in the range of -18°C to

12°C.

2. A suspension according to claim 1 , characterized in that said particles of SSD type have diameter in the range of about 20 nm to 50 nm.

3. A suspension according to claim 1 or 2, characterized in that said at least one alcohol having a number of carbon atoms comprised between C₇ - C-I6 is selected from the group formed by straight chain alcohols having a number of carbon atoms comprised between C₇-Ci6, and preferably n- heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol and 1 - hexadecanol.

4. A suspension according to any preceding claim, characterized in that said polar polymer component is polyvinylpyrrolidone having molecular mass in the range of 10000 to 800000 Dalton.

5. A suspension according to any preceding claim, characterized in that it is pasty, with a solid phase content in the range of about 30% to about 70%.

6. A method for obtaining a suspension according to any claim 1 to 5, characterized in that it comprises the following steps in sequence:

- mixing said at least one polar solvent and said polar polymer component, so as to obtain a mixture, and

- mixing said ferromagnetic component with said mixture until a uniform paste is obtained.

7. A method according to claim 6, characterized in that said mixture of said at least one polar solvent and said polymer component is heated to a temperature in the range of 50°C to 95°C before the addition of said ferromagnetic component, while after such addition a cooling step is conducted at a cooling speed in the range of 5°C to 40°C per minute.

8. A microcapsule of a suspension according to any claim 1 to 5, characterized in that it comprises a wall for containing said suspension.

9. A microcapsule according to claim 8, characterized in that said containment wall is obtained by means of a prepolymer.

10. A microcapsule according to claim 9, characterized in that said prepolymer is a melamine formaldehyde resin.

1 1 . A method for obtaining microcapsules according to claim 8, 9 or 10, comprising the following steps in sequence:

- providing said suspension and said prepolymer; - providing a liquid intended to emulsify said suspension, said liquid being selected from the group constituted by water or oil;

- adding said suspension to said liquid and emulsifying;

- adding said prepolymer to said emulsion and polymerizing;

- filtering and drying the obtained microcapsules.

12. An ink comprising:

- a plurality of microcapsules according to claim 8, 9 or 10,

- at least one solvent selected from the group constituted by water, a compound of ethyl acetate or a mixture obtained from one or more of the following alcohols: industrial methylated alcohol, n-propanol, iso-propanol with at least one from between ethyl acetate ester, n-propyl acetate ester and isopropyl acetate ester;

- at least one pigment,

- nitrocellulose or at least one acrylic resin, vinyl resin, maleic resin, fumaric resin, ketonic resin, polyurethane and/or polyamide resin, and

- at least one additive.

13. A sensor for detecting temperature variations in a product to be monitored, comprising at least one substantially rigid containment element (2, 2b) and at least one magnetizable suspension (C-i) obtained according to any claim 1 to 12 contained in said at least one containment element (2, 2b) characterized in that

said at least one containment element (2, 2b) is set to prevent the evaporation of said at least one polar solvent is said at least one magnetizable suspension (C-i), towards which it is chemical inert.

14. A sensor according to claim 13, characterized in that it comprises a support member (3) for said at least one containment element (2, 2b).

15. A sensor according to claim 14, characterized in that said support member (3) bears said at least one containment element (2) in a reception seat (3a) provided therein, such that said at least one containment element (2) results comprised in the bulk of said support member (3).

16. A sensor according to any claim 13 to 15, characterized in that it comprises a control device (D₂) supported by said support member (3).

17. A sensor according to claim 16, characterized in that said control device (D₂) comprises particles of SSD type that are non-demagnetizable due to Brownian motions.

18. A sensor according to claim 16 or 17, characterized in that said control device (D₂) is applied before the magnetization of said magnetizable suspension (C-i).

19. A sensor according to claim 16 or 17, characterized in that said control device (D₂) is applied after the magnetization of said magnetizable suspension (C-i).

20. A sensor according to any claim 13 to 19, characterized in that it comprises a two-dimensional code associable with a product to be monitored.

21 . A sensor according to claim 20, characterized in that said two- dimensional code is a bar code.

22. A sensor according to claim 21 , characterized in that said bar code is supported by said support member (3).

23. A sensor according to any claim 13 to 22, characterized in that it comprises means (4) for fixing to a product to be monitored.

24. A sensor according to claim 13 or 14, characterized in that said containment element comprises a plurality of microcapsules (2b) according to any claim 8, 9 and 10, said microcapsules being embedded in an ink (I) according to claim 1 1 .

25. A sensor according to claim 24, when dependent on claim 14, characterized in that it comprises means (4) for fixing to a product to be monitored.

26. A sensor according to claim 24, when dependent on claim 13, characterized in that it is printable on said at least one product to be monitored or on a respective package.

27. A device for detecting the temperature variations sustained by a sensor according to any claim 13 to 26, comprising:

- magnetic field sensor means (6) adapted to generate at least one electrical signal correlated with the intensity of at least one detected magnetic field (B); - at least one data processing board (CPU) set to process at least one electrical signal for determining at least one parameter correlated with the intensity of said at least one detected magnetic field (B) and to generate at least one electrical output signal correlated with the exceeding, or non- exceeding, of a predefined temperature threshold (T_s) by said temperature variation sensor; and

- at least one indicator means (8) activatable in response to said at least one electrical output signal.

28. A device according to claim 27, characterized in that said magnetic field sensor means (6), said at least one data processing board and said at least one indicator means (8) are housed in a containment structure (5).

29. A device according to claim 27 or 28, characterized in that said magnetic field sensor means (6) comprise at least one Hall effect sensor.

30. A device according to claim 29, characterized in that said at least one Hall effect sensor is biaxial or triaxial.

31 . A device according to claim 27 or 28, characterized in that said magnetic field sensor means (6) comprise at least one sensor of magnetoresistive type.

32. A device according to any claim 27 to 31 , characterized in that it comprises at least one means for reading and processing two-dimensional codes.

33. A device according to any claim 27 to 32, characterized in that said at least one electrical output signal is correlated with the time interval during which the temperature variation sensor (1 ) is found at a temperature greater than the threshold temperature (T_s).

34. A device according to any claim 27 to 33, characterized in that said at least one electrical output signal is correlated with a temperature (T) greater than the threshold temperature (T_s), at which said sensor is found.

35. A method for measuring temperature variations sustained by a product to be monitored by means of a device according to any claim 27 to 34, characterized in that it comprises the following operating steps:

applying a sensor according to any claim 13 to 26 to the product to be monitored;

activating said sensor (1 ) via the application of an external magnetic field (B) to said magnetizable suspension (C-i); after a time period has elapsed, measuring the demagnetization (XRFm) of said magnetizable suspension (C-i);

comparing said measured demagnetization (XRFm) with a predetermined value (XRF_p) related to the product to be monitored;

- if XRF_IO > XRF_p, calculating the time interval (At) and temperature interval (ΔΤ) during which said temperature variation sensor (1 ) was found above a predetermined threshold temperature (T_s), comparing the calculated values and the predetermined threshold values (At_s and ΔΤ_δ) and activating said display means (8) for visualizing said calculated values and the results of said comparison;

- if XRFm < XRF_p, activating display means (8) for signaling a possible tampering of the sensor.

36. A method according to claim 35, when the sensor comprises a control device (D₂) according to claims 17 and 18, characterized in that said display means (8) are activated for signaling a tampering of said sensor if X_RFm < XRF_P and the component of the magnetic field (B₂) of the magnetizable suspension (C₂) along the magnetization direction of the magnetic field (B-i) of the magnetizable suspension (C-i) exceeds a specific pre-established value.

37. A method according to claim 35, when the sensor comprises a control device (D₂) according to claims 17 and 19, characterized in that said display means (8) are activated for signaling a tampering of said sensor if the suspension of such control element (D₂) is magnetized.