WO2007054241A1

WO2007054241A1 - Nanoparticulate preparation and method of heating it

Info

Publication number: WO2007054241A1
Application number: PCT/EP2006/010575
Authority: WO
Inventors: Hans-Martin Sauer.; Elisabeth Cura; Lars Henning Lie; Rolf Hempelmann; Stefan Spiekermann; Heidi Schweitzer; Melanie Heeg
Original assignee: Sustech Gmbh & Co. Kg.
Priority date: 2005-11-10
Filing date: 2006-11-03
Publication date: 2007-05-18
Also published as: EP1945701A1

Abstract

The invention relates to a nanoparticulate preparation which comprises a coherent phase and, disperse therein, at least one particulate phase of superparamagnetic, nanoscale particles having a volume-averaged diameter in the range from 2 to 100 nm, the particles exhibiting a field shift effect, and to a method of heating a nanoparticulate preparation of this kind, it being possible to set different temperatures via variation in the strength of the applied magnetic DC field.

Description

Nanoparticulate preparation and process for its heating

The invention relates to a nanoparticulate preparation which comprises a coherent phase and at least one particulate phase of superparamagnetic, nanoscale particles having a volume-average particle diameter in the range from 2 to 100 nm dispersed therein, and a method for heating a corresponding nanoparticulate preparation to different temperatures.

From WO 03/054102 A1 ferrites are known. These ferrites have a stoichiometry in which

M ^{a is} selected from Mn, Co, Ni, Mg, Ca, Cu, Zn, Y and V

M ^{b is} selected from Zn and Cd, x is 0.05 to 0.95, preferably 0.1 to 0.8, y is 0 to 0.95, and the sum of x and y is at most 1.

These ferrites can be heated under the conditions described there and in DE 100 37 883 A1 with the simultaneous use of microwave radiation having a frequency in the range of 1 to 300 GHz and a magnetic constant field with a field strength in the range of 0.001 to 10 Tesla.

The microwave radiation causes in conjunction with the DC magnetic field in the substrate embedded in the particles the phenomenon of ferromagnetic resonance (FMR), as indicated in paragraph [0015] to paragraph [0027] of DE 100 37 883 A1, by the energy input from the microwave radiation into the particles leads to the actual heating of the preparation. The application of a DC magnetic field serves to set or optimize the resonance frequency, as described on page 16 of WO 03/054102 A1 or in paragraph [0023] of DE 100 37 883 A1.

Preparations of particles with particle sizes in the nanometer range (nanoscale particles) have found application in many fields of technology. This is especially true for dispersions containing particles with magnetic, ferroelectric or piezoelectric Contain properties that can be heated under the action of magnetic, electrical or electromagnetic alternating fields. These serve, for example, for the production of adhesives and sealants which harden as a result of the heating induced by the application of alternating magnetic, electric or electromagnetic fields or in which an existing adhesive bond is separated. Such adhesives and sealants are used in many industries, especially in the metalworking industry, such. As the aircraft industry, the vehicle industry, in commercial vehicle construction and their supplier industries or in the manufacture of machinery and household appliances and in the construction industry increasingly used to bond the same or different metallic and non-metallic substrates adhesively or sealingly together. This type of joining of components increasingly replaces the classical joining methods, such as riveting, screwing or welding, because they offer a multitude of technological advantages, for example with regard to a possible recycling of the components used.

DE-A 199 23 625 describes a process for the preparation of redispersible metal oxides or metal hydroxides having a volume-weighted average crystallite size in the range of 1 to 20 nm, which are particularly suitable for so-called magnetic fluids (ferrofluids).

DE-A 199 24 138 describes adhesive compositions which contain nanoscale particles with ferromagnetic, ferrimagnetic, superparamagnetic or piezoelectric properties in the binder system and which are suitable for producing releasable adhesive bonds. The adhesive bonds can be heated so high under the action of electromagnetic radiation that a slight solution (detackification) is possible.

WO 01/30932 describes a method for the adhesive separation of adhesive bonds, wherein the adhesive composite comprises a thermally softenable thermoplastic or heat-cleavable thermosetting adhesive layer and a primer layer, wherein the primer layer contains nanoscale particles which can be heated by electromagnetic alternating fields.

WO-A 01/28771 describes a microwave radiation curable composition comprising particles capable of microwave absorption with a curie The temperature which is higher than the curing temperature of the composition contains, for example, the particles capable of microwave absorption may be ferrites.

EP-A-0 498 998 describes a method for microwave heating a polymer material to a predetermined temperature, the polymer material containing dispersed ferromagnetic particles having a Curie temperature corresponding to the temperature desired by the heating. The particle diameter of the ferromagnetic material is in a range of 1 to 100 nm and the Curie temperature in a range of 50 to 700 ⁰ C. The desired heating temperature may be, for example, the curing or melting temperature of the polymer material or for activation act temperature required a cleavage reaction,

WO 01/14490 describes a method for bonding substrates with hotmelt adhesives, wherein these are used in combination with a microwaved (MW) activatable primer.

A disadvantage of the abovementioned nanoparticulate compositions, in particular adhesive compositions, and the method for heating them, is that the various temperatures required for sticking are not readily attainable.

Depending on the application, however, different temperatures must be achieved during curing or during subsequent detackifying in the case of the aforementioned adhesive methods. Thus, the temperature for curing the adhesive is usually smaller than the temperature for detackifying or softening the adhesive.

The adhesives known from the above prior art have nanoparticles, which are in particular ferrites. These ferrites, as stated above, allow the adhesives to be increased by microwave radiation and applying a DC magnetic field to a temperature limited by the Curie temperature. Although the ferrites provide sufficient energy absorption during curing, they are designed to be intrinsic Temperature limitation (Curie temperature) is effective to prevent overheating during curing, so that the same ferrites are not usable as an energy absorber for a higher temperature during detackifying.

A possible variant would be to use two different ferrites, which require a different bias by the magnetic DC field to achieve maximum energy absorption. One of the two ferrites would have a relatively low, but the other a significantly higher limit or end temperature. In this way, could be switched by the choice of the respective magnetic DC fields (bias) between the two ferrites, depending on which limit temperature is required for curing or detackifying. A disadvantage of this, however, would be that the adhesive would have to be added twice the amount of ferrites.

Alternatively, the adjustment of the different temperatures could be carried out by working with a correspondingly lower radiant power during bonding than during later removal. As a result, however, the end temperature would no longer be determined by the intrinsic temperature limitation of the ferrites, at least during bonding, but would result from the heat balance between the microwave absorption and the heat dissipation into the environment. The temperature-limiting effect of the ferrite would thus be dispensed with here. In addition, this process would be slower because the cure temperature would not reach so fast as the radiant power would be reduced.

In contrast, the object of the invention is to provide a nanoparticulate preparation and a method which makes it possible to heat the corresponding nanoparticulate preparation to different temperatures in a simple manner. In particular, the method should allow the curing (sticking) and subsequent softening (detackifying) of adhesive compositions.

This object is achieved by the process shown in claim 14 and by a corresponding nanoparticulate preparation according to claim 1.

Due to the fact that the particles used have a field-shift effect, different temperatures are due to the variation of the field strength of the applied adjustable magnetic field. Thus, it is possible, regardless of the Curie temperature with a single ferrite to reach different final temperatures, without sacrificing the temperature-limiting effect of the ferrite, which is an overheating protection. Thus, by changing the field strength of the bias, the temperature can be "selected" without having to change the microwave radiation power.

If, for example, a low limit temperature is selected via the magnetic field, a particularly steep rise in temperature (until the limit temperature is almost reached) is achieved during the first few seconds of the irradiation process, so that particularly short cycle times during bonding are possible in a production. On the other hand, if a high limit temperature is selected, then the absolute power of the ferrite reaches a maximum only at a fairly high temperature, so that the then very high heat losses are compensated by the heat dissipation.

Apart from these advantages, the system is still not without complete temperature limitation, since all at the latest at the Curie temperature of the ferrite, the microwave absorption decreases again.

Gluing and detacking can be carried out in accordance with the same microwave system, for which only the bias must be changed in each case. If the pre-magnetization generated by permanent magnets, so only these magnets must be replaced. In systems using electromagnets, even only a change in the exciting current of the coil of the electromagnet is sufficient.

Preferably, the particles are selected from at least one electrically neutral ferrite of the general formula (M ^a _1-xy M ^b _x FC y) ¹¹ Fe ₂ ¹¹¹ O ₄ , wherein

M ^{a is} selected from Mn, Co, Ni, Mg, Ca, Cu, Zn, Y and V

M ^{b is} selected from Zn and Cd, x is 0.05 to 0.95, preferably 0.1 to 0.8, y is 0 to 0.95, and the sum of x and y is at most 1. These have proven to be particularly suitable. The particles used preferably have a temperature coefficient of the field-shift effect with a sign-independent value α greater than 0.05 mT / ° C, in particular greater than 0.10 mT / ° C, particularly preferably greater than 0.15 mT / ° C. Thus, by changing the field strength of the bias, particularly large temperature differences can be achieved.

In the case of the prior art methods described, for example, in DE 100 37 833 A1 or WO 03/054102 A1, in order to achieve optimum MW absorption of the ferrite, a static magnetic field or constant magnetic field must be applied to the adhesive seam in addition to the MW radiation whose strength results from the following equation (1) for ferromagnetic resonance:

/ = _Y [B _^ + Bj (1)

where f (eg 2.45 GHz) is the MW frequency, y = 28 GHz / T the gyromagnetic constant, B _ext the strength of the bias field and B _1n , the internal magnetic field defined by the composition of the ferrite , For these ferrites, the limit or final temperature is determined by the Curie temperature.

As already stated in the introduction, the application of the DC magnetic field serves only to adjust or optimize the resonance frequency of the particle or ferrite.

In contrast, in the case of the particles or ferrites preferably used according to the invention, B, _nt additionally depends on the temperature T, so that strictly speaking, equation (1) can be satisfied only for a single temperature:

B _m (T) = B _mt (T ₀ ) + CC (T - T ₀ ) (2)

With

as a temperature coefficient of the internal magnetic field or the field-shift effect. That is, the required bias field can be set to satisfy Equation (1) for room temperature (20 ^° C.):

/ = Y (V _* + A _n , ⁽ T ₀ )) (4)

The external magnetic field for optimal curing of the adhesive is thus calculated as:

On the other hand, an external magnetic field of the following strength is required when detacking, since an increased temperature T ₁ > T _{0 is} necessary for dissolving the adhesive:

BT "'" = flϊ BM) -Cc (T ₁ -T ₀ ) (4B)

When the coefficient D is less than zero, the magnetic field is usually higher when detackifying than when gluing.

If during the heating of the preparation, for. For example, to cure an adhesive composition that raises temperature, Equation (1) is no longer satisfied and MW absorption continues to decrease with increasing temperature. This results in a temperature-limiting effect of the particles used according to the invention or of the preferably used ferrite, which is also independent of the Curie temperature.

To calculate the thermal power generated by ferrites, the heat output generated per adhesive volume in the in the prior art, for. B. in WO 03/054102 A1 described ferrites are given as follows

^' APλ _ πM (T) (APλ

ΛVL ^{~ vo /} Δ * Uv L _ß ⁽⁵⁾ Here are:

(ΔP / ΔV) _th e _rm in a volume element .DELTA.V of the ferrite-containing adhesive or

Polymer due to the absorption of MW generated heat output;

(ΔP / ΔV) MW _, B is the inductive generated by the MW applicator in this volume element

Reactive power;

C _{d is} the volume fraction of the ferrite in the adhesive or polymer (C _VO ι <<0.1);

M (T) the magnetization of ferrite at the given temperature T and

ΔB is the ferromagnetic resonance (FMR) linewidth of the ferrite.

The temperature dependence of M was referred to in WO 03/054102 A1 as the essential mechanism for the intrinsic temperature limitation. The temperature limitation is based in WO 03/054102 A1 on the fact that the magnetization M (T) and thus the heat output generated at the Curie temperature T = T _{c is} zero.

For the present invention, however, this dependence is meaningless, since the selected operating temperature, eg. As in bonding and detackifying, usually is significantly lower than the Curie temperature of the ferrites used.

In a preparation according to the invention in which the particles used (for example ferrites) have a significant field-shift effect, Eq. (5) however, be amended as follows:

With

as the temperature at which the maximum of the MW absorption occurs. Here is:

T _{0 is} the temperature at which the internal magnetic field B _in the particle (ferrite) is specified (eg room temperature); α is the temperature coefficient of the field shift effect according to Eq. (3) and Y is the gyromagnetic constant.

In summary, it is particularly preferred if, in the method, the preparation can be heated independently of the energy introduced by the microwave radiation only up to a maximum temperature independent of the Curie temperature, using mixed oxides with divalent metals selected as nanoscale particles such that the maximum temperature correlated with the field strength of the magnetic DC field, that is adjustable.

"Nanoscale particles" for the purposes of the present application are particles having a volume-average particle diameter of at most 100 nm. A preferred particle size range is 4 to 50 nm, in particular 5 to 30 nm and particularly preferably 6 to 15 nm. Such particles are characterized by a high degree of uniformity The size of the particles is preferably determined by the UPA method (Ultrafine Particle Analyzer), eg by the laser light scattering method.

Methods for producing superparamagnetic nanoscale particles are known in principle. They are based, for example, on precipitation from aqueous solutions of metal salts by raising or lowering the pH with a suitable base or acid. DE-A-196 14 136 describes a process for producing agglomerate-free nanoscale particles using the example of iron oxide particles. DE-A-199 23 625 describes a process for the preparation of nanoscale redispersible metal oxides and hydroxides. The disclosure of these documents is hereby incorporated by reference.

A suitable method for producing superparamagnetic nanoscale particles which can be used according to the invention consists in the precipitation from acidic aqueous metal salt solutions by addition of a base. For this purpose, for example, optionally heated, aqueous hydrochloric acid solutions of metal salts for precipitation with a suitable amount of a heated base can be added. It has proved to be advantageous in precipitation of the particles to maintain a certain temperature range in order to achieve particles with the desired high magnetic field or microwave absorption capability. Preferably, the temperature is at the alkaline precipitation in a range of 20 to 100 ⁰ C, particularly preferably 25 to 95 ⁰ C and in particular 60 to 90 ⁰ C.

In order to substantially prevent agglomeration or coalescence of the nanoscale particles and / or to ensure good dispersibility of the particulate phase in the coherent phase of the preparations according to the invention, the particles used are preferably surface-modified or surface-coated. The particles preferably have on at least part of their surface a single- or multi-layer coating which contains at least one compound having ionogenic, ionic and / or nonionic surface-active groups. The compounds having surface-active groups are preferably selected from the salts of strong inorganic acids, e.g. Nitrates and perchlorates, saturated and unsaturated fatty acids such as palmitic acid, margaric acid, stearic acid, isostearic acid, nonadecanoic acid, lignoceric acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid and elaosteric acid, quaternary ammonium compounds such as tetraalkylammonium hydroxides, e.g. Tetramethylammonium hydroxide, silanes such as alkyltrialkoxysilanes and mixtures thereof. DE-A-197 26 282 describes the surface modification of nanoscale particles with at least two shells surrounding the particles. WO 97/38058 describes the preparation of nanoscale particles which have been surface-modified with silanes. These documents are referred to in their entirety.

If surface-modified nanoparticulate particles are used in the formulations according to the invention, the proportion of surface modifier is generally 1 to 50, preferably 2 to 40 and especially 10 to 30, percent by weight, based on the weight of the particles used.

The coherent phase of the nanoparticulate preparations according to the invention is preferably selected from water, organic solvents, polymerizable monomers, polymers and mixtures thereof.

Suitable organic dispersants are, for example, selected from oils, fats, waxes, esters of C with mono-, di- or trihydric alcohols, saturated acyclic and cyclic hydrocarbons, fatty acids, low molecular weight alcohols, fatty alcohols and mixtures thereof. These include, for example, paraffin and paraffin oils, mineral oils, linear saturated hydrocarbons having usually more than 8 carbon atoms, such as tetradecane, hexadecane, octadecane, etc., cyclic hydrocarbons, such as cyclohexane and decahydronaphthalene, waxes, esters of fatty acids, silicone oils, etc. Preferred are e.g. As linear and cyclic hydrocarbons and alcohols.

Polymerizable monomers and polymers suitable as the coherent phase are mentioned below in the adhesive compositions.

The rheological properties can be advantageously adjusted in a wide range depending on the type and amount of the dispersant. Thus, depending on the desired application form, preparations can be produced which have a liquid to gel-like consistency. "Gel-like consistency" shows agents which have a higher viscosity than liquids and which are self-supporting, that is to say retain the shape given to them without a shape-stabilizing coating The viscosity of such preparations is, for example, in the range from about 1 to 60,000 mPas.

The preparations used on the basis of liquid dispersants according to the invention are generally redispersible, d. H. the dispersed particles can be recovered by drying the preparation and then redispersed, substantially without deteriorating the dispersibility and the magnetic and alternating magnetic field absorbing ability.

The proportion of the nanoscale particles is preferably 1 to 70, in particular 2 to 35 and especially 3 to 10 percent by weight, based on the total weight of the nanoparticulate preparation. Due to the very good ability of the preparations used for energy absorption by absorption of microwaves (MW) according to the invention, the proportion of dispersed particles required to absorb a certain amount of energy can be significantly reduced in comparison with particulate preparations from the prior art.

In a particularly preferred embodiment, the preparation used according to the invention is an adhesive composition. The coherent phase of adhesive compositions comprises at least one polymer suitable for use in adhesives and / or at least one polymerizable one VZ

Monomer.

As a coherent phase (binder matrix) for the adhesives, in principle all polymers suitable for adhesives can be used. Mention should be made by way of example of the thermoplastically softenable adhesives based on ethylene-vinyl acetate copolymers, polybutenes, styrene-isoprene-styrene or styrene-butadiene-styrene copolymers, thermoplastic elastomers, amorphous polyolefins, linear, thermoplastic polyurethanes, copolyesters, polyamide resins, polyamide / EVA copolymers, polyaminoamides based on dimer fatty acids, polyester amides or polyether amides. Furthermore, the known reactive adhesives based on one- or two-component polyurethanes, one- or two-component polyepoxides, silicone polymers (one- or two-component), silane-modified polymers, as described, for example, by G. Habenicht, "Glue: Fundamentals, Technology, Applications ", 3rd edition, 1997 in chapter 2.3.4.4 who described the (meth) acrylate-functional reaction adhesives based on peroxidic hardeners, anaerobic hardening mechanisms, aerobic hardening mechanisms or UV hardening mechanisms are also suitable as adhesive matrix, Concrete examples of the The inclusion of thermally labile groups in reaction adhesives for the purpose of subsequent cleavage of these bonds are the adhesives according to WO 99/07774 in which at least one synthesis component contains di- or polysulfide bonds In a particularly preferred embodiment, these adhesives may still be solid cleavage reagents in crystalline, encapsulated, chemis ch blocked, topologically or sterically inactivated or kinetically inhibited, finely dispersed form, as disclosed in DE-A-199 04 835 on pages 14 to 16, which are also designed such that they only at the higher Entklebungstemperatur, preferably at 140 to 180 ⁰ C unfold their effect. Another possibility is the use of polyurethane adhesives which contain as cleavage agent the amine derivatives disclosed in DE-A-198 32 629. The cleavage agents disclosed in the two aforementioned publications are expressly part of the present invention.

The coherent phase of thermally activatable chemically reactive adhesives generally contains one or more components that are susceptible to polyreaction. These include, for example, adhesives containing polyisocyanates with capped thermally activatable isocyanate groups and a component having isocyanate-reactive groups, such as. As a polyol. In particular, as the coherent phase, an adhesive composition of a thermosetting polymerization adhesive is preferably used, which polymerizes in a temperature range between 40 and 140 ⁰ C and above 140 ⁰ C by a glass phase transition from solid to a softened state or at temperatures above 140 ⁰ C by thermal Damage to the polymer matrix undergoes a significant loss of strength. Examples include the adhesives Ashland Pliogripp 7770, Dow Betamate, Lord Fusor 380/383.

In the context of the present invention, the term "thermosetting" is understood to mean the heat-initiated curing of an adhesive composition which usually employs a separately present crosslinking agent. This is usually referred to by experts as extraneous networking. If the crosslinking agents are already incorporated into the adhesive composition, this is also referred to as self-crosslinking. According to the invention, the crosslinking is advantageous and is therefore preferred.

Is the adhesive composition used in addition to the heat curing with actinic radiation, d. H. Dual cure-curable, it preferably still contains conventional and known actinic radiation-curable binders and crosslinking agents.

As actinic radiation is electromagnetic radiation and corpuscular radiation into consideration. The electromagnetic radiation includes near infrared (NIR), visible light, ultraviolet radiation, x-rays and gamma rays, particularly ultraviolet radiation. The corpuscular radiation comprises electron radiation, alpha radiation, proton radiation and neutron radiation, in particular electron radiation.

Materials curable with actinic radiation include, as is known, radiation-curable low molecular weight, oligomeric and / or polymeric compounds, preferably radiation-curable binders, in particular based on ethylenically unsaturated prepolymers and / or ethylenically unsaturated oligomers, optionally one or more reactive diluents and optionally one or more photoinitiators. Examples of suitable radiation-curable binders are (meth) acryl-functional (meth) acrylic copolymers, polyether acrylates, polyester acrylates, unsaturated polyesters, Epoxy acrylates, urethane acrylates, amino acrylates, melamine acrylates, silicone acrylates and the corresponding methacrylates. Binders which are free of aromatic structural units are preferably used.

Very particular preference is given to the use of preparations with ferrites of the formula (M ^a _1-xy M ^b _x Fe ₇ ) ¹¹ Fe ₂ ¹¹¹ O ₄ as particles, where M ^{a is} selected from manganese or copper and M ^{b is} zinc. In these ferrites, the field-shift effect is particularly high.

In addition, ferrites are still suitable as particles in which up to 10% of the trivalent iron ions are replaced by other trivalent "rare earths" or Al, Cr, etc. Such ferrites have, for example, the following formula: (M ^a _1-xy M ^b _x Fe _y ) "(Fe _2- _Z M ^C _Z )" ¹ O ₄ . Here, z <0.2 and M ^{c is} selected from the group consisting of Al, Cr and the rare earths (Ce, Lu, in particular Gd) or combinations thereof. As a rare

The elements scandium (atomic number 21), yttrium (39) and lanthanum (57) and the 14 lanthanum elements cerium (58), praseodymium (59), neodymium (60), promethium (61), samarium (62 ), Europium (63), gadolinium (64), terbium (65), dysprosium (66), holmium (67), erbium (68), thulium (69), ytterbium (70) and lutetium (71).

For the input of energy, the alternating electromagnetic field of a microwave radiation having a frequency in the range of about 0.1 to 300 GHz is used. The preparation is simultaneously exposed to a DC magnetic field whose field strength is approximately in the range of 0.001 to 10 Tesla.

The frequency of the microwave radiation used is preferably in a range of 100 MHz to 25 GHz. For example, it is possible to use electromagnetic radiation of the so-called ISM (Industrial Scientific and Medical Application) ranges in which the frequencies lie between 100 MHz and 200 GHz. Available frequencies are for example 433 MHz, 915 MHz, 2.45 GHz and 24.125 GHz as well as the so-called mobile phone bands in the range of 890 to 960 MHz and 1710 to 1880 MHz. Further details on electromagnetic alternating fields in the microwave range are described in Kirk Othmer, "Encyclopedia of Chemical Technology", 3rd Edition, Volume 15, chapter "Microwave Technology", which is incorporated herein by reference. I b

Advantageously, the particles preferably used have a linewidth of the FMR absorption maximum ΔB of less than 100 mT, in particular less than 50 mT (compare equation (6)). In these particles, the line width is small enough to be heated particularly specifically even when the field strength of the DC magnetic field changes.

Thus, due to their uniformity, the superparamagnetic, nanoscale particles used in accordance with the invention make it possible to achieve a sharp resonance frequency in the preparations depending on the applied field strength and not, as in the case of particulate preparations from the prior art, a mixture of widely distributed frequencies. In these prior art formulations, the microwave absorption frequencies of the individual nanoparticles are never completely equal, so that only that fraction of the dispersed particles always absorbs microwave energy whose absorption frequency actually corresponds to a radiated frequency. All other particles are inactive, which leads to insufficient utilization of the registered energy.

Particularly preferably used particles have an internal magnetization B _int at 20 ⁰ C of greater than 50 mT, in particular greater than 250 mT. At 120 ^° C., the internal magnetization B _{int should be} greater than 30 mT, in particular greater than 100 mT. Thus, large field-shift effect can be achieved since α is dependent on B _int (see equation 2), so that considerable differences between the adjustable temperatures are made possible.

The process according to the invention is very particularly preferably suitable for bonding and detacking of substrates, at least one adhesive being used for bonding i) to at least one part of a surface

Substrates applies the preparation whose coherent phase at least one

Ii) contacting the substrate surfaces in the area of the applied composition, and iii) the substrates in the region of the applied composition for heating to a first temperature of a microwave radiation with a frequency in the range of 0.1 to 300 GHz and a magnetic DC field with a first

Field strength in the range of 0.001 to 10 Tesla exposes. The adhesive bond can be produced by targeted heating of the adhesive composition (bond-on-command) by introduction of energy in the form of microwave radiation, for example by a chemical reaction between suitable functional groups of the adhesive composition, as described above.

Furthermore, it can also by releasing a curing initiating component, for. As a monomer and / or catalyst, are triggered. For this purpose, the curing triggering components can be dispersed, for example in the form of microcapsules in the adhesive composition. The irradiation can cause a certain heating, which leads to an opening of the microcapsules and release of the components contained. According to this method, it is possible to cure the adhesive composition with a very low energy input since it is not necessary to heat the entire adhesive composition.

In order to solve or ungluble the adhesive bond, this is for heating to a second temperature, which is higher than the first temperature, a microwave radiation having a frequency in the range of 0.1 to 300 GHz and a DC magnetic field with a second field strength in Range from 0.001 to 10 Tesla, which is higher than the first field strength under Hi), wherein the adhesive bond dissolves at the second higher temperature, so that, optionally under mechanical stress, the bonded substrates can be separated from each other.

This release of the adhesive bond by deliberate heating of the cured adhesive composition (disbond-on-command) by means of entry of energy in the form of microwaves can be based, for example, on a reversible or irreversible softening of the adhesive bond. For example, the adhesive used may be a hot melt adhesive which reversibly softens as a result of the heating caused by the action of the radiation. This reversible softening can then be used both for targeted production as well as for targeted release of an adhesive bond (see above).

In the case of thermoplastic adhesive bonds, the heating can take place above the softening point and, in the case of thermosetting adhesive bonds, to one Temperature which causes a cleavage.

Furthermore, the set adhesive may contain thermally labile bonds that are cleaved as a result of the heating caused. The release of the adhesive bond can be carried out in such adhesives without the action of chemicals and under conditions under which the assembled substrates are not significantly heated and thus thermally damaged.

The adhesive composition may also comprise cleavage reagents in thermally activatable, for example encapsulated, crystalline, chemically blocked, topologically or sterically inactivated or kinetically inhibited form (see above). The components causing the cleavage are present, for example, in the form of microcapsules, which are additionally dispersed in the adhesive composition. By irradiation under the action of the second magnetic field for heating to the higher Entklebungstemperatur these microcapsules are thermally opened and thus causes the cleavage of the adhesive preparation. Again, the heating can be limited to just these capsules, so that the energy required energy consumption can be greatly reduced compared with a homogeneous distribution throughout the composition.

The invention will be further illustrated by the following non-limiting examples.

Examples

example 1

a) Preparation of a surface-modified ferrite material

A solution of 608,5g MnSO ₄ * H ₂ O, 258,8g ZnSO ₄ ^* 7 H ₂ O and 2285,1g Fe ₂ (SO ₄ J ₃ ^* H ₂ O and 3700 ml H ₂ OVE was mixed at room temperature, to ensure a uniform mixing. Thereafter, the solution with vigorous stirring was (initially 220 rpm, then 265 rpm) was added to a heated to 85 ⁰ C solution of 1800 g of sodium hydroxide in 13 L of demineralized H ₂ 0 _PU in a 20 L stirred reactor. the temperature stirred at 85 ° C (KPG-stirrer), rose slightly to 90-95 ⁰ C in. then, the mixture was during 40 min. after which the desired product precipitates as a precipitate.

The product was sedimented after precipitation in the reactor with cooling, the supernatant water (10 L) sucked off and the sediment slurried with 9L water. The sedimentation, suction and washing was repeated several times until the pH of the wash water was about 10 and a colloidal suspension of nanoferrite particles in the residual liquor, which can no longer be separated by sedimentation.

The suspension was then heated to 80 ⁰ C and treated at 80 ⁰ C with 1046g of oleic acid under increased agitation.

After about 5 min. the modified ferrite precipitates as precipitate.

It was washed twice with 1OL water and the modified ferrite transferred to a plastic bowl and then dried for 5 hours at 60 ⁰ C under 100 mbar vacuum.

There were obtained 2100 g of a manganese-zinc-ferrite (Mn ₀ , 8Zn ₀ , ₂ Fe ₂ O ₄ ) -ölsäure paste. As stated in WO 03/054102 A1, this ferrite has a Curie temperature of about 240 ⁰ C. b) Preparation of an irradiated ferrite

4.99 g of manganese-zinc ferrite

from step (a) were stirred into 25.65 g of toluene until a homogeneous dispersion is formed. To this was slowly added 15.11 g of finely powdered calcium carbonate (anhydrous). The toluene was then first evaporated in air, then under vacuum (100 mbar), so that finally a solid granules was obtained.

1.18 g of the granules were placed in a flat Teflon dish (20 x 20 mm internal dimensions, 2 mm depth, thickness of the bottom 2 mm) and lightly pressed with the spatula.

The shell is mounted on the face of a rectangular waveguide (standard R26, 43 x 86 mm cross-section) of a MW system (Mügge, MX 2000 series, with R26 waveguide connection), so that when the granules are heated by the MW radiation a controlled heat flow from the granules through the bottom of the Teflon shell in the waveguide is possible. This consists of cast aluminum and has 20 ⁰ C. To measure the temperature, the measuring tip of a glass fiber thermometer is inserted into the granules (Ipitek Lumitherm 500).

c) Irradiation with Microwaves and Verification of the Function According to the Invention Subsequently, the sample is preheated at a MW radiation power of 240 W MW at 2.45 GHz and without premagnetization, after about 2 minutes a temperature equilibrium at about 100 ^° C. in the granules established. This heating is based primarily on the dielectric losses of the microwave radiation in the organic components of the granules and only a small part on the energy absorption of the ferrite.

By switching on the bias (waveguide system is in an electromagnet), the specific MW absorption of the ferrites is activated. At a microwave frequency, the magnitude of the applied magnetic field B _ext (see equation (1)) is between 48 mT and 90 mT, depending on the strength of the internal field B _{int of} the ferrite material. As a result of this additional energy consumption, the temperature in the granules continues to rise (FIG. 1).

Depending on the magnitude of the bias (48 mT, 90 mT), a new one will appear after some time Temperature equilibrium at 160 ⁰ C or 190 ⁰ C reached (see Figure 1). It is essential that the temperature rise rate immediately after switching on the magnet is always the same: The MW absorption at 100 ⁰ C regardless of whether it was pre-magnetized with 48 mT or 90 mT, always the same.

However, the MW absorption at the 48 mT pre-magnetized measurement above 150 ⁰ C decreases sharply, so that 160 ⁰ C are never exceeded. On the other hand, when measuring at 90 mT, the temperature increases by 30 ⁰ C higher.

FIG. 1 shows the heating and cooling curve of the ferrite granules at different premagnetizations.

Thus, it could be shown that with the same ferrite by varying the field strength of the magnetic DC field different limit or final temperatures are adjustable, regardless of the Curie temperature or radiation power.

Example 2:

A ferrite of composition Mn ₀₁₈ Zn ₀₁₂ Fe ₂ O ₄ surface-coated with oleic acid (from Example 1) was exposed to MW irradiation (as above) at different temperatures and biasing.

This ferrite behaves differently due to the temperature dependence of the absorbed MW power at different bias field strengths (Equation (6)): At relatively low bias, MW absorption decreases with increasing temperature. This is the result of a relatively high internal magnetic field (B _int (120 ⁰ C) = 35 mT), which decreases with increasing temperature (B _int (180 ⁰ C) = 10 mT). As a result, to reach the magnetic resonance at 120 ⁰ C, an external magnetic field B _ext only about 52 mT needed, at 180 ⁰ C, however, a field of 78 mT.

Figure 2 shows the MW energy absorption per gram of ferrite for different bias strengths as a function of temperature (bias: 1 A equals 12 mT). The MW absorption decreases with low bias as a function of temperature (at 54 mT: decrease by 0.3 units between 120 and 180 ⁰ C), on the other hand, with strong premagnetization it increases (at 84 mT: increase by 0.6 units between 120 and 180 ^° C)).

Figure 3 shows the MW energy absorption per gram of ferrite for different temperatures as a function of bias (1 A corresponds to 12 mT). At (120 ⁰ C, the absorption maximum is reached with a bias of 5.5 A = 66 mT, at 180 ⁰ C, the maximum is 6.5 A = 78 mT).

From this, a temperature coefficient α = -0.2 mT / ° C for the field shift effect can be calculated on the basis of the equations given above.

Claims

claims

Claims 1. A nanoparticulate preparation comprising a coherent phase and at least one particulate phase of superparamagnetic nanoscale particles having a volume average particle diameter in the range of 2 to 100 nm dispersed therein, characterized in that the particles have a field-shift effect.

2. Nanoparticulate preparation according to claim 1, characterized in that the particles are selected from at least one electrically neutral ferrite of the general formula (M ^a _1-xy M ^b _x Fe _x ) ¹¹ Fe ₂ ¹¹¹ O ₄ , wherein

M ^{a is} selected from Mn, Co, Ni, Mg, Ca, Cu, Zn, Y and V, M ^{b is} selected from Zn and Cd, x is from 0.05 to 0.95, preferably from 0.1 to 0.8 , y is 0 to 0.95 and the sum of x and y is 1 or less.

3. Nanoparticulate preparation according to claim 1 or 2, characterized in that the particles used have a temperature coefficient of the field-shift effect α with a sign independent value greater than 0.05 mT / ° C, in particular greater than 0.15 mT / ° C.

4. Nanoparticulate preparation according to one of claims 1 to 3, wherein the preparation can be heated independently of the energy introduced by the microwave radiation only up to a temperature independent of the Curie temperature maximum temperature, the nanoscale particles are selected with divalent metals selected so, that the maximum temperature correlates with the field strength of the DC magnetic field.

5. Nanoparticulate preparation according to one of the preceding claims, wherein the volume-average particle diameter of the particles in the preparation used in a range of 4 to 50 nm, preferably 5 to 30 nm, more preferably 6 to 15 nm.

6. Nanoparticulate preparation according to one of the preceding claims, wherein the particles of the preparation used on at least part of its surface a single or multi-layer coating containing at least one compound with ionic, ionic and / or nonionic surface-active groups.

A nanoparticulate preparation according to claim 6, wherein the compound having surface-active groups is selected from the salts of strong inorganic acids, saturated and unsaturated fatty acids, quaternary ammonium compounds, silanes and mixtures thereof.

The nanoparticulate composition according to any one of the preceding claims, wherein the coherent phase is selected from water, organic solvents, polymerizable monomers, polymers and mixtures thereof.

A nanoparticulate preparation according to any one of the preceding claims, wherein M ^{a is} selected from Mn and Cu and M ^{b is} Zn.

10. Nanoparticulate preparation according to one of the preceding claims, wherein up to 10% of the Fe ions are replaced by other trivalent rare earths or Al, Cr, in particular according to the formula (M ^a _1-X, _y M ^b _x Fe _y ) (Fe ₂ -zM ^c _z ) " ¹ O ₄ , with z <0.2 and wherein M ^{c is} selected from the group consisting of Al, Cr and the rare earths or combinations thereof.

11. Nanoparticulate preparation according to one of the preceding claims, wherein internal magnetization B _{int of} the particles at 20 ⁰ C is greater than 50 mT, in particular greater than 250 mT.

12. Nanoparticulate preparation according to one of the preceding claims, wherein the preparation comprises between 1 and 10 percent by weight of nanoscale particles.

13. Nanoparticulate preparation according to one of the preceding claims, wherein the line width of the FMR absorption maximum ΔB of the particles used is less than 100 mT, in particular less than 50 mT.

14. A method of heating a nanoparticulate formulation comprising a coherent phase and at least one particulate phase of superparamagnetic nanoscale particles having a volume average particle size dispersed therein Particle diameter in the range of 2 to 100 nm comprises, wherein for heating the preparation simultaneously exposing a microwave radiation having a frequency in the range of 0.1 to 300 GHz and a DC magnetic field with a field strength in the range of 0.001 to 10 Tesla, characterized the particles used have a field-shift effect, so that different temperatures can be set via the variation of the field strength of the applied direct magnetic field.

15. The method according to claim 14, characterized in that the particles are selected from at least one electrically neutral ferrite of the general formula (M ^a i _-xy M ^b _x Fe _x ) ¹¹ Fe ₂ ¹¹¹ O ₄ , wherein

16. The method according to claim 14 or 15, characterized in that the particles used have a temperature coefficient of the field-shift effect α with a sign independent value greater than 0.05 mT / ° C, in particular greater than 0.15 mT / ° C.

17. The method according to any one of claims 14 to 16, wherein the preparation can be heated regardless of the registered by the microwave radiation energy only up to a temperature independent of the Curie temperature maximum temperature, wherein one uses nanoscale particles with divalent metals selected so that the Maximum temperature correlates with the field strength of the DC magnetic field.

18. The method according to any one of the preceding claims, wherein the volume-average particle diameter of the particles in the preparation used in a range of 4 to 50 nm, preferably 5 to 30 nm, more preferably 6 to 15 nm. TO

19. The method according to any one of the preceding claims, wherein the particles of the preparation used on at least part of its surface have a single- or multi-layer coating containing at least one compound with ionic, ionic and / or nonionic surface-active groups.

A process according to claim 19, wherein the compound having surface-active groups is selected from the salts of strong inorganic acids, saturated and unsaturated fatty acids, quaternary ammonium compounds, silanes and mixtures thereof.

21. The method according to any one of the preceding claims, wherein the coherent phase is selected from water, organic solvents, polymerizable monomers, polymers and mixtures thereof.

22. The method according to any one of the preceding claims 14 to 21, wherein M ^{a is} selected from Mn and Cu and M ^{b is} Zn.

23. The method according to any one of the preceding claims 14 to 22, wherein up to 10% of the "Fe ions are replaced by other trivalent rare earths or Al, Cr, in particular according to the formula (M ^a _1-xy M ^b _x Fe _y )" (Fe _{2 -z} M ^c _z ) " ¹ O ₄ , with z <0.2 and wherein M ^{c is} selected from the group consisting of Al, Cr and the rare earths or combinations thereof.

24. The method according to any one of the preceding claims 14 to 23, wherein the line width of the FMR absorption maximum ΔB of the particles used is less than 100 mT, in particular less than 50 mT.

25. The method according to any one of the preceding claims 14 to 24, wherein internal magnetization B _{int of} the particles at 20 ° C is greater than 50 mT, in particular greater than 250 mT.

26. The method according to any one of the preceding claims 14 to 25, wherein the preparation comprises between 1 and 10 percent by weight of nanoscale particles.

27. The method according to any one of the preceding claims 14 to 26, wherein i) on at least a portion of a surface of at least one to be bonded

Substrates applies the preparation whose coherent phase at least one

Adhesive composition comprises, ii) the substrate surfaces in the region of the applied preparation with each other in

Contact brings, and iii) the substrates in the area of the applied preparation for heating to a first

Temperature of microwave radiation having a frequency in the range of 0.1 to 300

GHz and a DC magnetic field with a first field strength in the range of

0.001 to 10 tesla exposes.

28. The method of claim 27, wherein iv) for releasing the adhesive bond this for heating to a second temperature which is higher than the first temperature, a microwave radiation having a frequency in the range of 0.1 to 300 GHz and a DC magnetic field with a second field strength in the range of 0.001 to 10 Tesla, which is higher than the first field strength under iii), and the adhesive bond softens at the second higher temperature, so that, optionally under mechanical stress, the bonded substrates can be separated from each other.

29. Use of a nanoparticulate preparation according to one of claims 1 to 13 in a method for heating, in particular for bonding and de-bonding, in particular according to one of claims 14 to 28.