Use of Fe(II) compounds free of water of crystallization as radiation absorbers

Abstract

The invention relates to the use of iron(II) orthophosphate of general formula Fe3(PO4)2 free of water of crystallization or iron(II) metal-orthophosphate, iron(II) metal-phosphonate, iron(II) metal-pyrophosphate, iron(II) metal-metaphosphate of general formula FeaMetb(POc)dFe, free of water of crystallization, where a represents a number from 1 to 5, b represents a number from >0 to 5, c represents a number from 2.5 to 5, d represents a number from 0.5 to 3, and Met represents one or more metals, selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, transition metals (d-block), in particular Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Mn, Cu, Zn, Co, Ni, Ag, Au, the metals and semimetals of the third, fourth, and fifth major groups, in particular B, Al, Ga, In, Si, Sn, Sb, Bi and lanthanides, or combinations of the aforementioned phosphates as absorbers of electromagnetic radiation,where the absorbent is finely distributed or released into the support material.

Description

SUBJECT OF THE INVENTION

[0001] The present invention relates to new uses of anhydrous iron(II) orthophosphate of the general formula Fe 3 (PO 4 ) 2 and anhydrous iron(II) metal orthophosphate, iron(II) metal phosphonate, iron(II) metal pyrophosphate or iron(II) metal metaphosphate of the general formula Fe a Met b (PO c ) d or mixtures of the aforementioned. BACKGROUND OF THE INVENTION

[0002] A wide variety of organic and inorganic absorbers for near-infrared (NIR) radiation, i.e., in the wavelength range of approximately 780 nm to 1400 nm, and their applications are described in the literature. Despite their widespread use, the application of organic NIR absorbers is associated with some disadvantages. For example, the use of so-called leuco dyes requires the addition of thermal acid generators (TAGs). These compounds release protons under the influence of heat and / or lasers, thereby inducing a color change in the leuco dye. Typical examples of such TAG compounds are ammonium salts of organic silicon or boron compounds, or benzyl hydroxybenzoate. Furthermore, organic NIR absorbers often exhibit absorption in the visible light range and thus an inherent coloration that is undesirable in some applications.Furthermore, organic NIR absorbers are usually complex compounds that are difficult to synthesize, their production is costly, and their use is associated with ecological and toxicological concerns. The comparatively low thermal stability of these organic compounds is also a disadvantage and severely limits their range of applications.

[0003] There have therefore long been efforts to replace organic compounds with simple and stable compounds. For example, carbon black is a very readily available and inexpensive, strong absorber. However, the use of carbon black also has some disadvantages. The biggest disadvantage of carbon black is certainly its non-specific absorption over a very broad range of the electromagnetic spectrum, especially absorption in the visible range, which gives it its black color and consequently also leads to an undesirable gray or black discoloration of the substrate into which the absorber is incorporated.

[0004] Alternatively, various inorganic metal oxides, minerals, and complex compounds can be used as NIR absorbers. These generally possess good temperature resistance and are usually easy and inexpensive to produce.

[0005] WO 2012 / 055742 A2 concerns a stretch blow molding process for thermoplastic materials that involves the use of IR-absorbing compounds. In this process, a preform made of a polyolefin composition is produced by injection molding. This preform contains phosphates, condensed phosphates, or hydroxide phosphates of copper, calcium, tin, or iron as IR absorbers. The preform is then heated using IR radiation and stretch blow molded. Copper hydroxide phosphate, Cu₂(OH)PO₄, is mentioned as an IR absorber in the examples. The use of this absorber is intended to improve the wall thickness distribution of the finished product.

[0006] WO 2005 / 052049 relates to thermoplastic polymers containing IR absorbers of the general formula Me x (PO 4 ) y (OH) z, where Me is to consist of one or more elements from the group Cu, Fe, Mn, Sb, Zn, Ti, Ni, Co, V, Mg, Bi, Be, Al, Ce, Ba, Sr, Na, K, Ge, Ga, Ca, Cr, In or Sn and x = 1-18, y = 1-12 and z = 0.2-10. However, the only expressly mentioned and preferred absorbers are monometallic or mixed-metallic copper phosphate compounds, and the embodiments relate, as in WO 2012 / 055742 A2, exclusively to copper hydroxide phosphate, Cu 2 (OH)PO 4 .

[0007] DE 39 17 294 A1 discloses laser-markable polymers containing an additive as an absorber that is said to have no or only a slight inherent color in the visible spectral range from 400 nm to 750 nm and, upon exposure to laser light in the IR spectral range above 900 nm and / or in the UV spectral range below 400 nm, is intended to produce a marking with high color contrast. DE 39 17 294 A1 discloses molybdenum(VI) oxide (MoO₃) and copper hydroxide phosphate as absorbing additives, the latter being particularly suitable. Titanium dioxide, titanium yellow, and red iron oxide are also mentioned as additives, but for the purpose of imparting a white, yellow, or red background color to the polymer and thus to the marking applied to it, corresponding to the inherent color of these substances.

[0008] Copper hydroxide phosphate is also known from numerous other prior art documents as an excellent IR radiation absorber without significant inherent coloration, which is why it has been used as a radiation absorber in a wide variety of applications for many years. Examples include the aforementioned heating of a polymer in stretch blow molding, laser marking, as well as laser welding of thermoplastic materials and other applications where a more or less transparent polymer is required to absorb IR and / or UV radiation, thereby potentially causing a greater or lesser degree of heating of the substrate material, depending on the application. To date, there are hardly any known absorbers that can match the exceptional properties of copper hydroxide phosphate in terms of absorption capacity combined with high thermal and chemical stability and the absence of inherent coloration.Copper hydroxide phosphate exhibits strong absorption in the wavelength range of approximately 800 - 1600 nm.

[0009] One disadvantage of copper hydroxide phosphate, known as an excellent absorber, as well as other copper phosphate compounds, lies in its relatively high production costs. Furthermore, for reasons of water protection, copper should ideally not enter wastewater or must be removed from it at considerable expense, which is why the avoidance of copper compounds is sought in many applications.

[0010] EP 3 176 792 A1 discloses a composition for the production of a conductive structure on a support material comprising a polymer resin, including polycarbonate resin, and an inorganic additive which absorbs electromagnetic radiation in the IR range.

[0011] US 2008 / 241492 A1 discloses an ink for a steel engraving process, wherein the ink comprises a polymeric organic binder and an infrared-absorbing material containing a transition metal compound, which may be selected from Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The anions of the compound include phosphates, silicate, condensed polysilicates, titanate, condensed polytitatanates, vanadate, condensed polyvanadates, molybdate, condensed polymolybdates, tungstate, condensed polytungstates, fluorides, oxides, and hydroxides. The transition metal compounds may also contain alkali or alkaline earth metals.

[0012] WO 2015 / 067545 concerns mixed-metallic phosphate compounds which contain copper as the main metal in a divalent oxidation state in a proportion of at least 70 at% and one or more dopants in a total proportion of dopants of at least 0.01 to at most 30.0 at%. TASK

[0013] The object of the present invention was therefore to provide absorbers for various uses which have advantages over the prior art and are as well suited or possibly even better suited than known absorbers to absorb NIR radiation, while exhibiting high thermal and chemical stability, having no or only slight inherent coloration and being less toxicologically and ecologically problematic. DESCRIPTION OF THE INVENTION

[0014] This problem is solved according to the invention by the use of anhydrous iron(II) orthophosphate of the general formula Fe 3 (PO 4 ) 2 or anhydrous iron(II) metal orthophosphate, iron(II) metal phosphonate, iron(II) metal pyrophosphate or iron(II) metal metaphosphate of the general formula Fe a Met b (PO c ) d , wherein a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and wherein Met represents one or more metals selected from the group consisting of K, Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Mo, W, Mn, Cu, Zn, Ni, B, Al, Ga, In, Si, Sn, Sb, Bi, and the lanthanides, or combinations of the aforementioned phosphates. as an absorber for electromagnetic radiation, wherein the absorber is finely dispersed or dissolved in a carrier material and the carrier material is selected from the group consisting of thermoplastic and thermosetting polymers, oxide ceramics, non-oxide ceramics, glasses, hot melt adhesives, paints, varnishes, silicones, cardboards, papers, pulps and celluloses, wherein the absorber is finely dispersed or dissolved in the carrier material at a concentration of 100 ppm to 20 wt.%, based on the total weight of the carrier material including any additives, including the absorber.

[0015] It was surprisingly found that the anhydrous monometallic iron(II) orthophosphate according to the invention, as well as the anhydrous mixed-metallic iron(II) metal phosphates, iron(II) metal phosphonates, iron(II) metal pyrophosphates and iron(II) metal metaphosphates of the general formula Fe a Met b (PO c ) d according to the invention, have very good absorption properties in the NIR range of the electromagnetic spectrum and at the same time, similar to copper hydroxide phosphate, exhibit only low absorption in the visible wavelength range of 380 - 780 nm and thus have hardly any inherent coloration.

[0016] In one embodiment of the invention, the absorber is anhydrous iron(II) orthophosphate of the general formula Fe 3 (PO 4 ) 2 and has the graftonite crystal structure.

[0017] Other crystal structures are also known for anhydrous Fe3(PO4)2, for example the sarcopside crystal structure, which is isostructural with the olivine-analogous structure of Ni3(PO4)2. In contrast, anhydrous Fe3(PO4)2 in the graftonite crystal structure has proven to be a particularly advantageous absorber with very high absorption in the wavelength range of approximately 800–1250 nm, even better in the wavelength range of 900–1100 nm, and with an absorption maximum at approximately 1000 nm.

[0018] In contrast, the absorption of Fe 3 (PO 4 ) 2 with the sarcopside crystal structure over the wavelength range of 800 - 1250 nm is low compared to anhydrous Fe 3 (PO 4 ) 2 in the graftonite crystal structure.

[0019] Without committing to a specific theory, the inventors assume that the advantageous absorption properties of the Fe(II) compounds according to the invention are not solely attributable to the presence of divalent iron and the phosphate or phosphonate anions, but also to the absence of water of crystallization. Furthermore, it has surprisingly been shown that certain crystal structures are advantageous compared to others, in particular the graftonite crystal structure of anhydrous iron(II) orthophosphate compared to the sarcopside crystal structure also known for iron(II) orthophosphate. Hydrous iron(II) orthophosphates are also known, for example, the octahydrate vivianite Fe₃(PO₄)₂·8H₂O, after which the corresponding vivianite crystal structure is also named. However, this does not exhibit the advantageous absorption properties according to the invention.Iron(III) orthophosphate also does not possess the advantageous absorption properties of the anhydrous iron(II) orthophosphate with graftonite crystal structure according to the invention.

[0020] The graftonite crystal structure of the anhydrous iron(II) orthophosphate of the formula Fe₃(PO₄)₂ according to the invention is named after the mineral graftonite, (Fe,Mn,Ca,Mg)₃(PO₄)₂. The crystal system is monoclinic, the space group is P2 1 / cThe lattice constants are approximately a ≈ 8.81 Å, b ≈ 11.56 Å, c ≈ 6.14 Å, α ≈ 90.00°, β ≈ 99.35°, γ ≈ 90.00°. The unit cell contains 8 formula units of Fe 1.5 PO 4. The phosphorus is tetrahedrally coordinated by oxygen, and iron(II) occurs on 3 different 4-fold (4e) layers, each with different coordination geometries: 1x distorted octahedral, where one of the coordinated oxygen ions is significantly farther away (d ~ 2.68 Å), and 2x trigonal bipyramidal. Thus, in the graftonite system, the iron atoms are coordinated without an inversion center. The strong deviation from a densest packing of the anions probably stems from the optimization of coordinative needs.

[0021] The very good absorption of the anhydrous iron(II) orthophosphate in the graftonite crystal structure in the NIR range and its excellent suitability as an absorber in a wide variety of applications, as described herein, was surprising. Without committing to a specific theory, the inventors explain the good absorption properties as follows.

[0022] The absorption of electromagnetic radiation by transition metal complexes is caused, among other things, by electron transitions within the d-shell. The absorption probability of these transitions is strongly dependent on the structure of the transition metal complexes. Since electronic transitions of equal orbital parity are forbidden in centrosymmetric molecules (Laporte prohibition), their absorption is correspondingly low, as is the case, for example, with iron(III) orthophosphate, FePO₄, in which the iron is octahedrally coordinated.

[0023] However, if the molecule lacks an inversion center, as is the case with the anhydrous iron(II) orthophosphate according to the invention, which has a graftonite crystal structure, but also with the mixed-metal iron(II) compounds of the general formula Fe a Met b (PO c ) d according to the invention, the Laporte prohibition is lifted and the absorption is correspondingly stronger. The absorbers according to the invention are therefore transition metal complexes of iron that have a crystal structure in which the complex lacks an inversion center with respect to the central atom.

[0024] This coordination is surprisingly advantageous compared to the crystal structures of, for example, vivianite, Fe3(PO4)2*8H2O, or anhydrous iron(II) orthophosphate, Fe3(PO4)2, in the sarcopside crystal structure, which exhibit octahedral coordination with an inversion center relative to the central iron atom. As a result, the absorption, particularly in the NIR range, is correspondingly lower than in the compounds according to the invention.

[0025] Corresponding considerations also apply to the anhydrous iron(II) metal orthophosphates, phosphonates, pyrophosphates and metaphosphates of the general formula Fe a Met b (PO c ) d according to the invention, insofar as these have an iron coordination without an inversion center.

[0026] Preferred anhydrous iron(II) metal phosphates according to the invention are the compounds SrFeP₂O₇, BaFeP₂O₇, KFePO₄, K(Fe₀.75Zn₀.25)PO₄ and K(Fe₀.75Mg₀.25)PO₄. For example, SrFeP₂O₇ and BaFeP₂O₇ have a structure defined by trigonal bipyramids and square pyramids, respectively, and simultaneously exhibit very strong absorption in the NIR range at wavelengths of approximately 800–1150 nm and approximately 1800–2500 nm.

[0027] Compounds according to the invention with tetrahedral coordination of the iron(II) atoms also lack an inversion center and exhibit pronounced absorption in the NIR range. Iron(II) metal orthophosphates, iron(II) metal phosphonates, iron(II) metal pyrophosphates, and iron(II) metal metaphosphates with tetrahedral coordination are therefore also preferred according to the invention. Among these, anhydrous KFePO₄, K(Fe 0.75 Zn 0.25 )PO₄, and K(Fe 0.75 Mg 0.25 )PO₄ are particularly preferred. In these anhydrous iron(II) metal phosphates, the absorption in the NIR range is particularly pronounced and extends almost uniformly over the entire IR range from approximately 780 nm to 2500 nm and beyond.Their use is particularly advantageous in application areas where broad absorption across the entire IR range is desired, such as in packaging materials that are intended to protect the packaged products, for example food, from IR radiation.

[0028] The absorber is usually finely dispersed within the carrier material. Depending on the carrier material and the absorber itself, it may also be completely or partially dissolved within the carrier material.

[0029] According to the invention, the absorber is finely dispersed or dissolved in the carrier material at a concentration of 100 ppm to 20 wt.%, preferably at a concentration of 100 ppm to 5 wt.%, based on the total weight of the carrier material including any additives and the absorber. For the purposes of this invention, the total weight of the carrier material always refers to the sum of the mass of the carrier material and the mass of the added substances. If the proportion of absorber is too low, the absorption effect may be insufficient for the intended application. Conversely, an excessively high proportion of absorber may impair the material properties of the carrier material. The selection of the carrier material, the absorber according to the invention, and the required or necessary additives for the respective application is determined by the invention.The person skilled in the art can easily determine the appropriate amount of absorber based on their specialist knowledge and taking into account the examples given below, with knowledge of the invention.

[0030] The compounds of the present invention offer a multitude of advantages compared to other absorbers. They are relatively simple and can be produced at comparatively low cost, and are characterized, for example, by high stability compared to organic or organometallic absorbers. They are anhydrous, meaning that the entire radiation is absorbed by the actual complex and not partially by the water of crystallization. Furthermore, they exhibit particularly high absorption in the NIR range, while showing only weak absorption in the visible range of electromagnetic radiation. As a result, they have no or only slight inherent coloration and do not significantly affect the color of the substrate material, while the complex can be very easily activated by NIR radiation.

[0031] Compounds with an absorption maximum in the wavelength range of short-wave NIR radiation (IR-A) of approximately 780 - 1450 nm have the advantage that a higher amount of energy is absorbed in this IR range than through the absorption of long-wave NIR radiation (IR-B) of approximately 1450 - 3000 nm, and thus, in corresponding applications, for example, a greater heating of the substrate material can be achieved.

[0032] Particularly advantageous compounds according to the invention are those NIR absorbers that exhibit weak absorption in the visible range and strong absorption in the short-wavelength NIR range of the electromagnetic spectrum. Advantageously, the ratio of the maximum absorption of electromagnetic radiation in the short-wavelength NIR range (IR-A) of 780–1450 nm to the maximum absorption of electromagnetic radiation in the visible wavelength range of 380–780 nm (VIS) is at least 1.3, preferably at least 1.6, and particularly preferably at least 1.8.

[0033] In applications according to the present invention, it can be advantageous to use laser light as the source for irradiating the substrate material in which the absorber is finely dispersed or dissolved, preferably laser light with a wavelength in the range of 780 nm to 1500 nm, and particularly preferably in the range of 900 nm to 1200 nm. The use of so-called excimer lasers, such as those known from photolithography, is suitable. Particularly suitable excimer lasers are ArF, KrF, XeCl, XeF, and KrCl lasers. The use of Nd:YAG lasers, such as those known from medical technology, is also advantageous, preferably those with a wavelength of 1064 nm or 946 nm, i.e., in the NIR range. Laser light is particularly suitable for achieving sharp contours of the irradiation and a locally confined high energy input where this is desired or required.Inventive uses in which laser light is particularly advantageous for irradiating the substrate material include, for example, laser welding, laser marking and the production of electrically conductive metal structures, preferably conductor track structures on a non-conductive substrate material (LDS process).

[0034] A carrier material within the meaning of the invention can be any organic or inorganic material that can contain the absorber of the inventive use in a finely dispersed or dissolved form. Preferably, the absorber is uniformly distributed in the carrier material, since such a uniform distribution is very easily achieved using common processing methods such as extrusion. Alternatively, the absorber can be more concentrated in certain areas of the carrier material than in other areas. The absorber can also be contained in the carrier material or in a section of the carrier material with a concentration gradient.Targeted enrichment in a specific area can lead to improved material properties as well as advantageous absorption properties, for example, if absorption is desired specifically in the near-surface area of ​​the substrate material and less so in deeper areas.

[0035] According to the invention, the carrier material is selected from the group consisting of thermoplastic polymers, thermosetting polymers, oxide ceramics, non-oxide ceramics, glasses, hot melt adhesives, paints, varnishes, silicones, papers, pulps, cardboards and celluloses.

[0036] The preferred carrier material is a thermoplastic polymer selected from the group consisting of polyvinyl butyral (PVB), polypropylene (PP), polyethylene (PE), polyamide (PA), polyesters such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyphenylene oxide, polyacetal, polymethacrylate, polyoxymethylene, polyvinyl acetal, polystyrene, acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), polycarbonate, polyethersulfone, polysulfonate, polytetrafluoroethylene, polyurea, formaldehyde resins, melamine resins, polyetherketone, polyvinyl chloride, polylactide, polysiloxane, phenolic resins, epoxy resins, poly(imide), bismaleimide triazine, thermoplastic polyurethane, copolymers and / or mixtures of the aforementioned polymers.

[0037] Thermoplastic polymers are in most cases colorless, and their color and / or transparency is not affected, or only minimally affected, by the addition of the absorber according to the invention, which is particularly advantageous in many applications. The absorbers according to the invention generally possess a long shelf life and high stability. They are very temperature-resistant, so that even compounding or injection molding in conjunction with high-temperature plastics, such as polyaramids or liquid crystal polymers (LCPs), is possible.

[0038] In a preferred embodiment of the invention, the absorber has a mean particle size (d50 value) in the range of 0.01 µm to 50 µm, preferably from 0.1 to 20 µm, and particularly preferably from 1 µm to 10 µm. Excessively small particle sizes have the disadvantage of leading to agglomerates, which then have to be broken up. Excessively large particle sizes have the disadvantage of making it impossible, for example, to produce thin films or very thin components. By incorporating particles of smaller particle sizes, the material properties are less affected than by large particle sizes, a more uniform absorption behavior is achieved, and local overheating is avoided.

[0039] To determine the mean particle sizes, methods commonly used by those skilled in the art, such as light scattering or microscopic techniques, can be employed. The mean particle sizes according to the invention specified herein were determined using a laser particle size analyzer (model LA-950V2 from Horiba; software version 7.2).

[0040] The absorbers according to the invention are particularly temperature-stable compared to many known absorbers. In the context of the present invention, this means that no significant transformation, decomposition, or hydration processes occur within a certain temperature range. To verify the temperature stability of the absorber, a sample of the absorber is exposed to a defined temperature for 16 hours, and after the temperature treatment, the absorption of a defined quantity of the temperature-treated absorber is compared with that of the untreated absorber at a specific wavelength or within a specific wavelength range. Advantageously, the comparison is performed at the wavelength of the absorption maximum of the untreated absorber.An absorber is considered to be temperature-stable if the absorption of the temperature-treated absorber is >80%, preferably >90%, particularly preferably >95% of that of the untreated absorber.

[0041] Advantageously, in the applications according to the invention, the carrier material does not contain any additives that release gas upon heating to 300°C, preferably to 400°C, particularly preferably to 500°C, and / or upon irradiation with electromagnetic radiation, through decomposition, chemical transformation, or reaction with a component of the carrier material or the carrier material itself, at least not in significant quantities that are likely to adversely affect the material properties of the carrier material. The material properties of the carrier material can be deteriorated by the formation and foaming of gas. Therefore, the proportion of gas-releasing additives in the carrier material, if such additives are present at all, is preferably less than 1% by weight, more preferably less than 0.1% by weight, and particularly preferably less than 0.01% by weight of the total mass of the carrier material.

[0042] The present invention comprises the use of the absorber according to the invention for the production of products consisting of or comprising the carrier material, wherein the carrier material contains the absorber in an amount such that it absorbs infrared radiation at at least one wavelength in the range of 780 nm to 1400 nm more strongly than the same polymer without the absorber. Products according to the invention are described in more detail below. a) According to the invention, it is advantageous to use the absorber according to the invention for the production of packaging material for commercial products, wherein the carrier material is a thermoplastic polymer or a thermosetting polymer, preferably a transparent thermoplastic polymer or a thermosetting polymer.

[0043] By using absorbers in packaging materials, radiation-sensitive commercial products, such as food, but also products that change color with prolonged exposure, can be protected from radiation and / or heating caused by light or sunlight. In the case of food, this can significantly extend its shelf life without the need for colored packaging materials. This allows the products to be presented to the consumer through the packaging material while simultaneously protecting them from harmful radiation.

[0044] Furthermore, by blocking radiation, degradation reactions and damage to the packaging material itself, especially thermoplastic or thermosetting plastics, can be reduced, such as cross-linking, embrittlement, fading or brittleness of the material.

[0045] Furthermore, the compounds according to the invention are largely toxicologically and ecologically harmless, which is why, compared to many other NIR absorbers, they are particularly suitable for use as food packaging or for packaging, for example, children's toys. They do not release any substances that are harmful to health or affect taste, and they also do not impair the material properties of the packaging material.

[0046] In a preferred embodiment of this use, the absorber is an iron(II) metal orthophosphate, iron(II) metal phosphonate, iron(II) metal pyrophosphate or iron(II) metal metaphosphate with a tetrahedral structure, preferably KFePO4, Fe(0.75Zn0.25)PO4 or K(Fe0.75Mg0.25)PO4, since these absorbers exhibit high absorption over a very broad, almost the entire range of the NIR spectrum, such as that contained in solar radiation, and thus protect the product and / or the packaging material.

[0047] b) According to the invention, it is also advantageous to use the absorber according to the invention for the production of window panes, wherein the carrier material is expediently transparent thermoplastic polymer, transparent thermosetting polymer or glass.

[0048] When using window panes, especially those made of thermoplastic materials such as polymethyl methacrylate or polycarbonate, sunlight regularly leads to a warming of the interior of rooms enclosed by the window panes. This warming is caused by the absorption of near-infrared (NIR) radiation and its conversion into longer-wavelength thermal radiation by building components behind the window panes, provided the NIR radiation can pass through them unimpeded. Since long-wave thermal radiation is only radiated back outwards to a limited extent, a "greenhouse effect" occurs. To minimize this effect, the transmission of NIR radiation through the window panes should be reduced accordingly. Most NIR absorbers for window panes known in the prior art are based on rare-earth or transition metal compounds, which either have an inherent color or are difficult and expensive to obtain.The iron compounds according to the invention offer the possibility of producing transparent window panes simply and at low cost. By absorbing radiation, the heating effect behind the window panes caused by penetrating radiation is significantly reduced.

[0049] In a preferred embodiment of this use, the absorber is an iron(II) metal phosphate, phosphonate, pyrophosphate or metaphosphate with a tetrahedral structure, preferably KFePO4, Fe(0.75Zn0.25)PO4 or K(Fe0.75Mg0.25)PO4, since these absorbers exhibit high absorption over a very broad, almost the entire range of the IR spectrum, such as that contained in solar radiation, and thus prevent heating by radiation from essentially the entire IR range.

[0050] c) According to the invention, it is also advantageous to use the absorber according to the invention for the production of preforms which are intended and designed for further processing into end products, preferably into containers, particularly preferably into food containers or bottles, in a thermal forming process, preferably in a stretching process or stretch blow molding process, wherein the carrier material is thermoplastic polymer, preferably transparent thermoplastic polymer.

[0051] Thermal polymer forming processes, such as stretching or stretch blow molding, are in most cases complex and energy-intensive processes with low process flexibility. The use of NIR absorbers in polymer processing according to the invention allows such processes to be made more flexible and efficient. The precise application and dosing of IR radiation, both in terms of location and time, enables processing to be adapted to specific requirements and needs at any time. In this context, it is advantageous that the NIR absorbers according to the invention exhibit high temperature resistance.

[0052] d) According to the invention, it is also advantageous to use the absorber according to the invention for the production of end products made of thermoplastic polymer, which are produced in a thermal forming process, preferably in a stretching process or stretch blow molding process;

[0053] Another preferred embodiment of the invention includes the use of the absorber as a heating accelerator and / or polymerization accelerator and / or crosslinking accelerator in thermoplastic or thermosetting plastics, hot melt adhesives, paints, varnishes or silicones under irradiation with electromagnetic radiation, preferably under irradiation with infrared radiation at at least one wavelength in the range of 780 nm to 1400 nm.

[0054] Since the radiation loss due to transmission or light scattering is lower in substrate materials containing the absorber according to the invention than in materials without the additive according to the invention, a higher heating rate can be used for the same radiation power, and consequently the required power of the emitter and / or the radiation duration can be significantly reduced. The high absorption rate can also be used to accelerate chemical polymerization reactions and / or crosslinking reactions. This can be achieved either by the temperature increase resulting from the increased radiation absorption or by the transfer of energy from the IR absorber to a component of the chemical reaction.

[0055] The use of absorbers according to the invention is particularly preferred in thermally induced polymerization or crosslinking reactions, such as radical polymerization, as well as for the NIR curing of coatings, for example clearcoats, which generally absorb very weakly in the NIR range and therefore cure slowly. The use of absorbing additives is known for such applications, but these additives have disadvantages. For example, TiO₂ reflects in the NIR range, whereas carbon black, although exhibiting strong absorption, leads to a color shift in the visible range of light. The use of the absorbers according to the invention is therefore particularly advantageous due to the high belt speeds and low thermal stress on the substrates during the curing process.The curing of varnishes with the absorber according to the invention generally takes place much faster than without the absorber, without the need to use any other adverse additives.

[0056] The present invention also encompasses the use of the absorber according to the invention as an absorber for electromagnetic radiation in laser marking, laser engraving, laser welding, and / or polymer joining. Here, too, transparent or colored thermoplastic or thermoset polymers are generally used as substrate materials. By using lasers in these processes, very narrowly defined areas can be irradiated and locally heated, enabling the achievement of very sharp contours or precise structures in laser marking, laser engraving, and laser welding.

[0057] In a preferred embodiment, the absorber of the invention is used as an absorber for infrared radiation in the production of electrically conductive metal structures, preferably conductor track structures, on a non-conductive substrate material (LDS process).

[0058] The invention will now be further explained with reference to manufacturing examples for absorbers according to the invention, as well as examples of uses according to the invention and the attached figures. Figure 1 shows the X-ray diffractogram of anhydrous Fe₂P₂O₇ produced according to the invention according to production example 1. Figure 2 shows the X-ray diffractogram of a phase mixture of anhydrous Mg₁₅Fe₁₅(PO₄)₂ and Fe₃₄(PO₄)₂ produced according to the invention according to production example 2. Figure 3 shows the X-ray diffractogram of anhydrous Fe₃(PO₄)₂ produced according to the invention according to production example 3. Figure 4 shows the X-ray diffractogram of anhydrous KFe(PO₄)₂ produced according to the invention according to production example 4. Figure 5 shows the X-ray diffractogram of anhydrous KFe₀.90Zn₀.10(PO₄) produced according to the invention according to production example 5. Figure 6 shows the X-ray diffractogram of anhydrous KFe 0.75 Zn 0.25 (PO 4) produced according to the invention in accordance with manufacturing example 6.Figure 7 shows the X-ray diffractogram of anhydrous KFe 0.75 Mn 0.25 (PO 4) produced according to the invention by preparation example 7. Figure 8 shows the X-ray diffractogram of anhydrous BaFeP 2 O 7 produced according to the invention by preparation example 8. EXAMPLES X-ray diffractometry (XRD)

[0059] X-ray diffraction (XRD) measurements were performed on the products manufactured according to the following examples using a D8 Advance A25 diffractometer (Bruker) with CuKα radiation.

[0060] The products and their crystal structures were identified using corresponding reference diffractograms (Powder Diffraction Files; PDFs) from the database of the ICDD (International Centre for Diffraction Data), formerly JCPDS (Joint Committee on Powder Diffraction Standards). Where PDFs were not available for the manufactured products, PDFs of isotypic compounds (compounds of the same structural type) were used. Elementary analysis

[0061] To determine and confirm the stoichiometries of the manufactured products, elemental analyses were carried out using X-ray fluorescence analysis (XRF) with the Axios FAST spectrometer (PANalytical). Production example 1 - anhydrous Fe2P2O7

[0062] A suspension of i) 35.5 kg iron(III) oxide hydroxide [FeO(OH) or Fe₂O₃·1H₂O], ii) 16.5 kg 98% phosphonic acid [H₃PO₃], iii) 26.5 kg 75% phosphoric acid [H₃PO₄] and LM: 220 kg of water was spray-granulated. The resulting granules were heat-treated in a rotary kiln at 700°C with a mean residence time of 4 h under a forming gas atmosphere (5 vol% H₂ in N₂). An almost colorless to pale pink product was obtained. The X-ray diffractogram (XRD) of the product is shown in Figure 1 shown. The product was identified using the PDF card 01-072-1516. Production example 2 - Phase mixture of anhydrous Mg 1.5 Fe 1.5 (PO 4 ) 2 and Fe 3 (PO 4 ) 2

[0063] A suspension of i) 8.45 kg iron(III) oxide hydroxide [FeO(OH) or Fe 2 O 3 1H 2 O], ii) 7.95 kg 98% phosphonic acid [H 3 PO 3 ], iii) 19.6 kg iron (III) phosphate dihydrate [FePO 4 2H 2 O], iv) 8.43 kg magnesium carbonate [MgCO 3 ] and LM: 160 kg of water was spray-granulated. The resulting granules were heat-treated in a rotary kiln at 750°C with a mean residence time of 3 h under a forming gas atmosphere (5 vol% H₂ in N₂). An almost colorless product was obtained. The X-ray diffractogram (XRD) of the product is shown in Figure 2 The product was identified, based on the PDF cards, as a phase mixture consisting of a main phase Mg 1.5 Fe 1.5 (PO 4 ) 2 (PDF card 01-071-6793) and a secondary phase Fe 3 (PO 4 ) 2 (PDF card 00-49-1087). Production example 3 - anhydrous Fe 3 (PO 4 ) 2

[0064] A suspension of i) 21.75 kg iron(III) oxide hydroxide [FeO(OH) or Fe 2 O 3 1H 2 O], ii) 12.15 kg 98% phosphonic acid [H 3 PO 3 ], iii) 10.3 kg iron (III) phosphate dihydrate [FePO 4 2H 2 O] and LM: 140 kg of water was spray-granulated. The resulting granules were heat-treated in a rotary kiln at 750°C with a mean residence time of 90 minutes under a forming gas atmosphere (5 vol% H₂ in N₂). An almost colorless product was obtained. The X-ray diffractogram (XRD) of the product is shown in Figure 3 The product crystallizes in the graftonite structure and was identified using PDF chart 00-49-1087. The product was milled such that 50 wt% of the product had a particle size of less than 3 µm. Production example 4 - Production of anhydrous KFe(PO4)

[0065] A suspension of i) 11.80 kg iron(III) oxide hydroxide [FeO(OH)₂ or Fe₂O₃·1H₂O], ii) 10.70 kg 98% phosphonic acid [H₃PO₃], iii) 24.8 kg iron(III) phosphate dihydrate [FePO₄·2H₂O], IV) 29.8 kg 50% potassium hydroxide solution [KOH], V) 1.0 kg 75% phosphoric acid [H₃PO₄], and LM: 110 kg water were spray-granulated. The resulting granules were heat-treated in a rotary kiln at 650°C with a mean residence time of 3 h under a forming gas atmosphere (5 vol% H₂ in N₂). A pale light green product was obtained. The X-ray diffractogram (XRD) of the product is shown in Figure 4 shown. The product was identified using the PDF card 01-076-4615. Production example 5 - anhydrous KFe 0.90 Zn 0.10 (PO 4 )

[0066] A suspension of i) 10.60 kg iron(III) oxide hydroxide [FeO(OH)₂ or Fe₂O₃·1H₂O], ii) 9.65 kg 98% phosphonic acid [H₃PO₃], iii) 22.30 kg iron(III) phosphate dihydrate [FePO₄·2H₂O], IV) 2.15 kg zinc oxide [ZnO], IV) 29.8 kg 50% potassium hydroxide [KOH], V) 4.15 kg 75% phosphoric acid [H₃PO₄], and LM: 120 kg water were spray-granulated. The resulting granules were heat-treated in a rotary kiln at 600°C with an average residence time of 2 h under a forming gas atmosphere (5 vol% H₂ in N₂). A light gray product was obtained. The X-ray diffractogram (XRD) of the product is in Figure 5 shown. The product is a new structure type that appears to be closely related to the KFe(PO4) structure according to PDF card 01-076-4615. Production example 6 - Crystal water-free KFe 0.75 Zn 0.25 (PO 4 )

[0067] A suspension of i) 8.85 kg iron(III) oxide hydroxide [FeO(OH)₂ or Fe₂O₃·1H₂O], ii) 8.05 kg 98% phosphonic acid [H₃PO₃], iii) 18.60 kg iron(III) phosphate dihydrate [FePO₄·2H₂O], IV) 5.40 kg zinc oxide [ZnO], IV) 29.8 kg 50% potassium hydroxide [KOH], V) 9.30 kg 75% phosphoric acid [H₃PO₄], and LM: 120 kg water were spray-granulated. The resulting granules were heat-treated in a rotary kiln at 600°C with a mean residence time of 2 h under a forming gas atmosphere (5 vol% H₂ in N₂). A light gray product was obtained. The X-ray diffractogram (XRD) of the product is in Figure 6 The product is not known from the literature. It crystallizes isotypically to KZn(PO₄) according to PDF chart 01-081-1034. Production example 7 - Crystal water-free KFe 0.75 Mn 0.25 (PO 4 )

[0068] A suspension of i) 8.85 kg iron(III) oxide hydroxide [FeO(OH) or Fe₂O₃·1H₂O], ii) 8.05 kg 98% phosphonic acid [H₃PO₃], iii) 18.60 kg iron(III) phosphate dihydrate [FePO₄·2H₂O], IV) 8.85 kg manganese carbonate hydrate [MnCO₃·H₂O], IV) 29.8 kg 50% potassium hydroxide [KOH], V) 9.30 kg 75% phosphoric acid [H₃PO₄], and LM: 140 kg water were spray-granulated. The resulting granules were heat-treated in a rotary kiln at 600°C with a mean residence time of 2 h under a forming gas atmosphere (5 vol% H₂ in N₂). A light grey product was obtained. The X-ray diffractogram (XRD) of the product is in Figure 7 The product is not known from the literature. It crystallizes isostructurally to KFe(PO₄) according to PDF chart 01-076-4615. Production example 8 - anhydrous BaFeP 2 O 7

[0069] A suspension of i) 8.70 kg iron(III) oxide hydroxide [FeO(OH)₂ or Fe₂O₃·1H₂O], ii) 8.20 kg 98% phosphonic acid [H₃PO₃], iii) 19.05 kg iron(III) phosphate dihydrate [FePO₄·2H₂O], IV) 63.09 kg barium hydroxide octahydrate [Ba(OH)₂·8H₂O], V) 26.15 kg 75% phosphoric acid [H₃PO₄], and 250 kg water were spray-granulated. The resulting granules were heat-treated in a rotary kiln at 800°C with a mean residence time of 4 h under a forming gas atmosphere (5 vol% H₂ in N₂). A light gray product was obtained. The X-ray diffractogram (XRD) of the product is in Figure 8 shown. The product crystallizes isotypically to BaCoP 2 O 7 according to PDF chart 01-084-1833. Application example 1 (laser welding)

[0070] 2 wt% of the absorber Fe3(PO4)2 according to production example 3 was uniformly distributed in a polyethylene (Lupolen 1800S from BASF) using an extruder (type ZSK18 from Coperion GmbH). Sheets measuring 3 cm x 4 cm x 3 mm were then produced from the extrudate. A sheet of the same dimensions, but without the absorber, was also produced. The sheet without the absorber was placed over the sheet with the absorber, and the sheets were then welded together using an Nd:YAG laser with a wavelength of 1064 nm. Usage example 2 (LDS)

[0071] The inventive absorber material, iron(II) magnesium phosphate, a phase mixture of Mg 1.5 Fe 1.5 (PO 4 ) 2 and Fe 3 (PO 4 ) 2 according to manufacturing example 2, was dry-mixed with 1 wt% sodium dihydrogen pyrophosphate. Subsequently, 5 wt% of the mixture was incorporated into a polyamide 6.6 (Ultramid™< from BASF) using an extruder (type ZSK18 from Coperion GmbH) to produce granules. The granules were further processed into plates measuring 3 cm x 4 cm x 3 mm. The plates were irradiated with an Nd:YAG laser (Trumpf) with a wavelength of 1064 nm, generating antenna structures that could then be used to receive electromagnetic radiation. Usage example 3 (heating rate)

[0072] 5 wt% of the inventive absorber K(Fe 0.75 Zn 0.25 )PO 4 according to production example 6 was uniformly distributed in a polypropylene (HE125MO from Borealis) using an extruder (type ZSK18 from Coperion GmbH). Sheets measuring 3 cm x 4 cm x 3 mm were produced from the extrudate and subsequently irradiated with a commercially available infrared lamp (red light lamp). For comparison purposes, the same polymer body, but without the absorber, was irradiated in the same manner. The temperature of the bodies was recorded over time during irradiation. The polymer body with the added absorber reached a temperature of 77 °C after 1 minute, whereas the polymer body without the absorber only reached a temperature of 77 °C after 5 minutes of irradiation.The temperature absorption curve of the polymer body with the addition of the absorber according to the invention shows a heating rate that is almost twice as fast over the entire timescale as the temperature absorption curve of the polymer body without the addition of the absorber. Example of use 4 (laser marking / laser engraving)

[0073] 2 wt% of the inventive absorber KFe(PO₄) according to manufacturing example 4 was uniformly incorporated into a polyethylene (Lupolen 1800S from BASF) using an extruder (type ZSK18 from Coperion GmbH). Plates measuring 3 cm x 4 cm x 3 mm were then produced from the extrudate. Markings were subsequently created on the surface of the plates by irradiation with an Nd:YAG laser with a wavelength of 1064 nm. For comparison purposes, identical polymer plates, but without the absorber, were laser-marked in the same manner. On the polymer plates with the inventive absorber, the markings were clearly visible even at a laser power of 1 watt and a frequency of 6000 Hz. Under the same conditions, no visible markings were observed on the irradiated reference plate without the absorber. Example of use 5 (heating of preforms using IR radiation)

[0074] Preforms used in the manufacture of beverage bottles were produced from a master batch of polyethylene terephthalate (PET) with 500 ppm K(Fe 0.75 Zn 0.25 )PO 4 according to production example 6. For comparison purposes, identical preforms were produced without the added absorber. The preforms were heated to the glass transition point of the polymer using IR halogen lamps. For the preforms with the added absorber, the required heating energy was approximately 15% lower and the required irradiation time approximately 20% shorter than for the preforms without the added absorber. Example of use 6 (crosslinking of silicone)

[0075] A non-crosslinked silicone compound was mixed with 0.05 wt% anhydrous Fe₃(PO₄)₂ with a graftonite crystal structure according to Production Example 3 and subsequently treated with a commercially available peroxide crosslinker. The silicone compound was then heated over a large area using a VCSEL laser (Phillips) with laser light of a wavelength of 980 nm. For comparison, the same silicone compound without the absorber was treated in the same way. Crosslinking of the silicone with the absorber according to the invention occurred after only 110 seconds, while crosslinking of the silicone without the absorber took 120 seconds. Thus, by adding a small amount of the absorber according to the invention, the energy input required for crosslinking, and therefore the crosslinking time, could be reduced. Application example 7 (laser welding)

[0076] 4 wt% anhydrous Fe₃(PO₄)₂ with a graftonite crystal structure, as described in production example 3, was uniformly incorporated into a polyamide 6.6 (Ultramid™ from BASF) using an extruder (type ZSK18 from Coperion GmbH). A molded part for the automotive industry, used as a rear light in passenger cars, was then produced. A second component, to be joined (welded) to the aforementioned component, was manufactured from the same material but without an absorber. The two components were then welded together using a commercially available diode laser with a wavelength of 940 nm. For comparison, an attempt was made to weld corresponding components, both without absorbers, in the same manner, but this proved impossible without causing damage.

Claims

1. Use of - crystal water-free iron(II) orthophosphate of the general formula Fe3(PO4)2 or - crystal water-free iron(II) metal orthophosphate, iron(II) metal phosphonate, iron(II) metal pyrophosphate or iron(ll) metal metaphosphate of the general formula FeaMetb(POc)d, wherein a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and wherein Met represents one or more metals selected from the group consisting of K, Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Mo, W, Mn, Cu, Zn, Ni, B, Al, Ga, In, Si, Sn, Sb, Bi, and the lanthanoids, or combinations of the aforementioned phosphates as an absorber for electromagnetic radiation, wherein the absorber is finely dispersed or dissolved in a carrier material and the carrier material is selected from the group consisting of thermoplastic and duroplastic polymers, oxidic ceramics, non-oxidic ceramics, glasses, hot-melt adhesives, dyes, varnishes, silicones, cardboards, papers, pulps and celluloses, wherein the absorber is present in the carrier material in a concentration of 100 ppm to 20% by weight finely dispersed or dissolved, based on the total weight of the carrier material with optionally contained additive including the absorber.

2. Use according to any one of the preceding claims, characterized in that the carrier material is a thermoplastic polymer, which is selected from the group consisting of polyvinyl butyral (PVB), polypropylene (PP), polyethylene (PE), polyamide (PA), polyesters such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyphenylene oxide, polyacetal, polymethacrylate, polyoxymethylene, polyvinyl acetal, polystyrene, acryl-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), polycarbonate, polyethersulfone, polysulfone, polytetrafluoroethylene, polyurea, formaldehyde resins, melamine resins, polyetherketone, polyvinyl chloride, polylactide, polysiloxane, phenol resins, epoxide resins, poly(imide), bismaleimide-triazine, thermoplastic polyurethane, copolymers and / or mixtures of the aforementioned polymers.

3. Use according to any one of the preceding claims, characterized in that the absorber has an average particle size (d50 value) in the range from 0.01 µm to 50 µm, preferably from 0.1 to 20 µm, particularly preferably from 1 µm to 10 µm.

4. Use according to any one of the preceding claims, characterized in that the absorber is crystal water-free iron(II) orthophosphate of the general formula Fe3(PO4)2 and has the graftonite crystal structure.

5. Use of the absorber according to any one of the preceding claims for producing products, which consist of the carrier material or comprise it, wherein the carrier material contains the absorber in an amount such that it absorbs infrared radiation at at least one wavelength in the range from 780 nm to 1400 nm more strongly than the same polymer without absorber contained therein, and wherein the products are selected from the group consisting of: - packaging material for commercial products, wherein the carrier material is thermoplastic polymer or duroplastic polymer, preferably transparent thermoplastic polymer or duroplastic polymer; - window panes, wherein the carrier material is transparent thermoplastic polymer, transparent duroplastic polymer or glass; - preforms, which are provided and designed for further processing into end products, preferably into containers, particularly preferably into food containers or bottles, in a thermal reshaping procedure, preferably in a stretching process or stretch blow molding process, wherein the carrier material is thermoplastic polymer, preferably transparent thermoplastic polymer; - end products made of thermoplastic polymer, which are manufactured in a thermal reshaping procedure, preferably in a stretch process or stretch blow molding process.

6. Use of the absorber according to any one of the preceding claims as heating accelerator and / or polymerization accelerator and / or cross-linking accelerator in thermoplastic or duroplastic plastics, hot-melt adhesives, dyes, varnishes or silicones under irradiation with electromagnetic radiation, preferably under irradiation with infrared radiation at at least one wavelength in the range from 780 nm to 1400 nm.

7. Use of the absorber according to any one of the preceding claims as an absorber for electromagnetic radiation in laser marking, laser inscription, laser welding and / or polymer joining.

8. Use of the absorber according to any one of the preceding claims as an absorber for infrared radiation in the manufacture of electrically conductive metal structures, preferably of conductor track structures or antenna structures by means of laser light on a nonconductive carrier material (LDS process).

9. Use according to any one of the preceding claims, characterized in that the absorption maximum of the absorber is at a wavelength in the range from 200 nm to 12,000 nm, preferably 700 nm to 1,500 nm, particularly preferably 900 nm to 1,200 nm, wherein the absorbed radiation comprises laser radiation as well as non-laser radiation.

Images