US 20150247001A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2015/0247001 A1 Lötzsch et al. (43) Pub. Date: Sep. 3, 2015

(54) THERMOCHROMIC MATERIAL MOLDED (30) Foreign Application Priority Data ARTICLE COMPRISING SAD MATERAL AND USE THEREOF Sep. 24, 2012 (DE) ...... 10 2012 O18813.7 (71) Applicant: FRAUHOFER-GESELLSCHAFT Publication Classification ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG (51) Int. Cl. E.V., Munich (DE) C08G 63/9. (2006.01) (52) U.S. Cl. (72) Inventors: Detlef Lötzsch, Berlin (DE); Ralf CPC ...... C08G 63/912 (2013.01) Ruhmann, Berlin (DE); Arno Seeboth, Berlin (DE) (57) ABSTRACT (73) Assignee: FRAUNHOFER-GESELLSCHAFT The invention relates to a thermochromic material compris ZUR FORDERUNG DER ing at least one biopolymer, at least one natural dye and at ANGEWANDTEN FORSCHUNG least one reaction medium, selected from the group of fatty E.V., München (DE) acids and derivatives thereof, gallic acid and derivatives thereOThereof and mim1Xtures thereOT.hereof. TheThe ththermochrom1C hromi materiaial (21) Appl. No.: 14/430,419 according to the invention is completely based on non-toxic, 1-1. natural products. Processing into materials or molded articles (22) PCT Filed: Aug. 8, 2013 can occur, according to the invention, by means of conven tional extrusion technology in the form offlat film, blown film (86). PCT No.: PCT/EP2013/066604 or sheets or multi-wall sheets. The thermochromic material S371 (c)(1), can be used in particular in the food industry and medical (2) Date: Mar. 23, 2015 technology.

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21 OH C HO O HO Patent Application Publication Sep. 3, 2015 US 2015/0247001 A1

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US 2015/0247001 A1 Sep. 3, 2015

THERMOCHROMIC MATERIAL MOLDED are imprinted with a paint for use in Sun protection or, corre ARTICLE COMPRISING SAD MATERAL sponding to U.S. Pat. No. 4,121,010, polymers are coated AND USE THEREOF with a thermochromic paint, consisting of Sulphates, Sul 0001. The invention relates to a thermochromic material phides, arsenic, bismuth, Zinc and other materials, and the comprising at least one biopolymer, at least one natural dye oxides thereof. As a result, both the field of use is greatly and also at least one reaction medium, selected from the restricted and, as a result of the required additional coating group offatty acids and the derivatives thereof, gallic acid and (printing technique), a cost-reducing continuous technology the derivatives thereof and also mixtures hereof. The thermo is prevented. chromic material according to the invention is thereby based 0007. In DE 103 39 442 B4 and U.S. Pat. No. 7,662,466 entirely on non-toxic natural products. Processing to form B2, thermochromic flat films which are likewise based on the materials or moulded articles can be effected by means of use of the above-mentioned organic dyes are described. conventional extrusion technology in the form of flat films, 0008. This also applies to the invention described in EP 1 blown films or sheets or multiskinsheets. The thermochromic 157 802. Here, in extrusion-blow moulding, thermochromic material is used in particular in the foodstuff industry and in pigments are added only in partial regions of the wall thick medical technology. ness of a plastic material container. This takes place by the 0002 Thermochromism comprises the property of chang addition of a reversible thermochromic pigment in the form of ing the colour of a material, as a function of the temperature, strip-shaped inlays. The thermochromic pigments require in reversibly or irreversibly. This can be effected both by chang addition additional thermostable pigments and are added or ing the intensity and/or the wavelength maximum. Examples fed to the extrudate before discharge from the extrusion head. and theoretical backgrounds relating to the mechanism of the 0009. To date, thermochromic inks, screen printing inks, temperature-controlled colour are described representatively coatings or films have not been used in sensitive areas, such as in Chromic Phenomena by P. Bamfield and M. I. Hutchings the foodstuff sector or medical technology. An essential rea (The Royal Society of Chemistry, 2010) and in Thermochro son is, categorically, the use of toxic compounds. Also the mic Phenomena in Polymers by A. Seeboth and D. Lötzsch most recent thermochromic dyes with a diazapentalene struc (Smithers Rapra Technology, 2008). ture (G. Qian and Z. Y. Wang, Adv. Mater. 24, 2012, page 0003. Materials in the most varied of material forms, 1582) do not offer an approach to the solution. amongst those also polymer films with thermochromic prop 0010 Starting herefrom, it was the object of the present erties, have been patented in the past in various ways. Irre invention to provide a thermochromic material which can be spective of whether the thermochromic effect is of a revers used in many fields of daily life, e.g. in the foodstuff sphere. ible or irreversible nature, inorganic or organic dyes are used, Likewise, the thermochromic material should be produced the latter also in the form of composites with melting agents Such that further processing by means of extrusion technol and/or developers, it is common to all systems that they ogy is possible. always comprise toxic starting materials in Some form. Stan 0011. This object is achieved by the thermochromic mate dard in this respect is the use of bisphenol as developer almost rial having the features of claim 1 and the extruded moulded in all existing organic thermochromic composites. As dyes, articles having the features of claim 11. In claim 13, uses basic structures of triphenylmethane dyes, pyridinium phenol according to the invention are indicated. The further depen betaines, Sulphophthalein structures, thyranines, azo dyes or dent claims reveal advantageous developments. fluoran dyes are used. 0012. According to the invention, a thermochromic mate 0004 Inorganic thermochromic pigments, the colour rial is provided, which material comprises at least one change of which is based on a temperature-controlled change biopolymer, at least one natural dye and also at least one of modification, are based in general on salts of heavy metals. reaction medium selected from the group of fatty acids and A known example is the use of thermochromic inorganic the derivatives thereof, gallic acid and the derivatives thereof pigments as hotspot warning for pans or as Screenprinting for and also mixtures hereof. All the components contained in the bar codes. Encapsulation of heavy metal salts or organic thermochromic material thereby concern components or thermochromic composites likewise does not offer an alter additives which are permitted for foodstuff, i.e. all the com native here; migration effects cannot be stopped permanently. ponents in the dosages used are not toxic. The generally used melamine resins as case for thermochro 0013 Preferably, all the components of the thermochro mic capsules are definitively unsuitable as protective layer mic material are permitted according to the EU regulation No. and in addition are not suitable for extrusion technology. 1333/2008 and corresponding current appendices for food 0005 Thus, the change of a colour effect, based on a stuff and have an E-number. donor-acceptor system, is described in EP 1084 860, which 0014. It is preferred that, as natural dyes, those with an system can be present also in the form of microcapsules with anthocyanidin structure are used. These are subdivided into a diameter of approx. 50 Lum. In EP 1 323 540 A2, a thermo Sugar-free aglycones and glycosides, both Sub-structures chromic material consisting of three components which is being able to be used. As foodstuff additives, anthocyanidins likewise microencapsulated is described. Lack of light stabil with the E-number 163 are permitted. The colour of antho ity of the thermochromic complexes is intended to be coun cyanidins which is dependent upon the pH value in aqueous teracted, corresponding to U.S. Pat. No. 5,527.385, by addi solution is thereby known, whilst the thermochromic proper tives such as hydrazide-, Sulphur- orphosphorus compounds. ties of anthocyanidins have to date not been known. This implies the addition of further toxic compounds. 00.15 Preferred anthocyanidins are cyanidin, delphinidin, 0006. The production of polymeric thermochromic mate aurantinidin, petunidin, peonidin, malvidin, pelargondin, ros rials with the help of imprinting (laminating) of a thermo inidin, europinidin and luteolinidin. The basic structure is chromic paint is a practical solution for Some requirements illustrated in FIG.1. By varying the radicals R to R (R with and wishes of the packaging industry, where toxicity plays a —H. —OH, - OCH), the properties can be widely varied. subordinate role. Thus according to US 2002037421, glasses The formation of dimers, aggregates/chelates, both amongst US 2015/0247001 A1 Sep. 3, 2015

each other and with the biopolymer or the reaction medium, is Applied Chem. 104, 1990, 1310) or also iv) by cooperation of made possible. If a Sugar radical is introduced in positon R. the above-mentioned three effects i, ii, and iii. The process glycoside structures are attained (FIG. 2). can be designed reversibly or irreversibly. As a function of the 0016. As reaction medium, gallic acid and the derivatives temperature, reorientations on a molecular plane are effected, thereof, in particular gallates, saturated, once unsaturated or bonds are reinforced or loosened and a concentration gradient multiply unsaturated fatty acids and the derivatives thereof, in of the natural dye or of the fatty acid and/or gallate in the particular esters, and also branched carboxylic acids are pre polymer volume are enabled reversibly or irreversibly. Thus, ferred. An essential property feature of carboxylic acids is the interaction between the fatty acid and the anthocyanidin is their self-organisation to form dimers. changed as a function of the temperature whilst, at the same 0017. A large number offatty acids can be used to form the time, both compounds change their interaction either respec thermochromism. Advantageously, thermochromic proper tively individually or as acting complex with the polymer ties can be produced within a wide operational field; this is chain. In the individual case, all the compounds are integrated associated interalia with the melting point of the fatty acids in the polymer structure via physicochemical interactions, and can be controlled between -55° and +81° C. by the this thereby changing naturally. In this case, a new Superor specific fatty acids. If required, the operating range can be dinate polymer structure is formed, which cannot be broken widened even further. down further. The interactions between the different mol 0018. As fatty acids, both unsaturated and saturated fatty ecules can be triggered both via the polar and dispersive acids and also mixtures hereof can be used. structural units. The system consequently attains exceptional 0019. The unsaturated fatty acids are preferably selected thermodynamic stability. As a result, the optical macroscopic from the group consisting of petroselinic acid, palmitoleic properties are changed. During differential scanning calorim acid, myristoleic acid, oleic acid, elaidic acid, gadoleic acid, etry (DSC), only one peak is visible in this case which differs undecylenic acid, icosenic acid, vaccenic acid, cetoleic acid, from the peak of the pure polymer. Glycosides are suitable in erucic acid, nervonic acid, cervonic acid, clupanodonic acid, particular for the formation of superordinate structures. By timnodonic acid, linoleic acid, calendic acid, punicic acid, means of the Sugar unit in Rposition (cyanidin-3-glucoside), eleoStearic acid, arachidonic acid and mixtures hereof. an aggregate structure (chelate complex) can be achieved. 0020. The saturated fatty acids are preferably selected This mechanism is used in nature to increase for example also from the group consisting of formic acid, acetic acid, caprylic the light stability of natural dyes. The Sugar radicals are acid, pelargonic acid, caproic acid, laroic acid, myristic acid, disposed in layers which are stabilised in addition by the chair palmitic acid, margaric acid, Stearic acid, arachic acid, pro form. It is obvious that the sugar structure is capable of further pionic acid, butyric acid, Valeric acid, caproic acid, onanthic interaction with fatty acids and/or gallates. acid, behenic acid, lignoceric acid, cerotic acid, montanic 0025. The molar ratio between the starting compounds acid, melissic acid and mixtures hereof. anthocyanidin and fatty acid and/or gallate, including the 0021. It is easily recognisable for the person skilled in the derivatives and mixtures thereof, crucially controls the proton art that also a large number of structural derivatives, such as transfer in the natural dye and hence the thermochromic alpha-, gamma- or beta structures, can be used here or also behaviour. Subsequently, mass ratios are indicated with ester-, amine- or amide structures. It is obvious that the fatty respect to the processing. When using mixtures offatty acids acids or the derivatives thereof can be used also in the form of and gallates, ratios of 1:99 or 99:1 can be used. Fatty acid or mixtures. Thus esters of Stearic acid, palmitic acid, linoleic gallate or the mixture thereofare used with 10- to 50-times acid, erucic acid have proved, inter alia, to be particularly excess, with respect to the anthocyanidin dye, preferably with complex-stabilising. Fatty acids and fatty acid esters are mar 15- to 35-times excess. The anthocyanidin acid (and/or gal keted in the foodstuffsector under the numbers E570 or E304. late) complex is found with 2-38% in the biopolymer, pref 0022. In addition to fatty acids, gallic acids and the deriva erably with 7-15%. tives thereof, in particular ester compounds (gallates), are 0026. Further variables with an influence on the macro preferred for use as reaction medium. Mixtures offatty acids scopic optical behaviour are the molar mass, the MFR value and gallates are likewise usable. Gallates and also fatty acids and the crystalline/amorphous structure of the biopolymers are permitted for foodstuff. For example, E312—dodecylgal which are used. late, E311—octylgallate and E310 propylgallate should be 0027. It is clear for the person skilled in the artin extrusion mentioned. technology that the technological parameters used, such as 0023. As branched carboxylic acids, phytanic acid, isova the temperatures of the respective heating Zones, of the slot leric acid or etheric oils are preferred. die or chill roll, the discharge speed, the screw geometry, 0024. According to the invention, the non-toxic thermo speed of rotation and compound pressure or dwell time have chromic material is made possible by physicochemical inter an additional influence on the resulting thermochromic action between anthocyanidin, biopolymer and fatty acid. A behaviour of the non-toxic polymer materials. temperature-controlled proton transfer in the anthocyanidin 0028 Essential components of the invention are corre structure triggers the change in colour. Both the intensity and spondingly the production of thermochromism by interaction the wavelength maximum can hereby be switched. Thus, a of the used components, including their long-term stability, thermochromic switching effect can be produced via i) the on the one hand, and, on the other hand, the development of a formation or dissolution of hydrogenbridges in the system, ii) technology for producing thermochromic compounds or the formation of domains/aggregates/chelates, preferably batches/master batches. The compound or batch/masterbatch controlled by the interaction of the fatty acid or gallates with can be further processed in the extrusion process to form the polar polymer chain, e.g. with CA/CTA, PHB or PLA. iii) films, sheets, multiskin sheets. The layer thickness of the the formation of ordered structures between biopolymer— films is between 50 and 300 um. Sheets can be up to 5 mm natural dye—fatty acid and/or gallate, as are well known in thick. The thermochromic films and sheets can be coextruded biomaterials as self-orientating systems (see H. Ringsdorf, with further layers. These additional layers can produce fur US 2015/0247001 A1 Sep. 3, 2015 ther functions in the material or the component, such as light cetoleic acid, erucic acid, nervonic acid, cervonic acid, stability, permanent colours and hence introduce a resulting clupanodonic acid, timnodonic acid, linoleic acid, cal subtractive colour system or increased mechanical stability in endic acid, punicic acid, eleostearic acid, arachidonic the material. acid, formic acid, acetic acid, caprylic acid, pelargonic 0029. The subject according to the invention is intended to acid, caproic acid, laroic acid, myristic acid, palmitic be explained in more detail with reference to the subsequent acid, margaric acid, Stearic acid, arachic acid, propionic Figures and the example, without wishing to restrict said acid, butyric acid, Valeric acid, onanthic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, mel subject to the specific embodiment shown here. issic acid, dodecylgallate, octylgallate, propylgallate, 0030 FIG. 1 shows the basic structure of anthocyanidins phytanic acid, isovaleric acid or etheric oils or mixtures with reference to a chemical formula. thereof. 0031 FIG. 2 shows the chemical formula of the basic 4. The thermochromic material according to claim 1, structure of a glycosine. wherein the at least one biopolymer is suitable for flat film or blown film extrusion or for manufacture of sheets. EXAMPLE 5. The thermochromic material according to claim 1, 0032. According to the invention a non-toxic thermochro wherein the at least one biopolymer is selected from the mic biopolymer film can be produced as follows. In a first group consisting of polyhydroxybutanoic acid, cellulose step, a complex consisting of palmitic acid, laurylgallate and acetate, polylactic acid and copolymers and polymer cyanidin chloride in the ratio 1:1.5:0.02 is prepared at a tem blends thereof. perature above 115° C. and a reaction duration of 15 min. In 6. The thermochromic material according to claim 1, a twin-screw compounder, 8.5% by weight of the complex is wherein all the components of the thermochromic material processed with 91.5% by weight of PLA 4060 to form a are permitted for foodstuff according to the EU regula compound at a screw speed of rotation of 20 rpm. The tem tion No. 1333/2008 and corresponding current appendi peratures of the heating zones 1 to 5 are 175° C./185°C./185° ces for foodstuff and have an E-number. C./180° C./160° C. As a result, a colourless compound is 7. The thermochromic material according to claim 1, obtained at room temperature, which compound changes into wherein the thermochromic effect of the material is revers the blue state when heated to approx. 65° C. The effect is ible or irreversible. reversible. In a single-screw extruder, the compound is pro 8. The thermochromic material according to claim 1, cessed into a thermochromic mono-PLA-biopolymer film, wherein thermochromic effect is produced by physico according to the known method, the temperature of the chill chemical interactions of the components. roll being 45°C. The reversible colour change of the film is as 9. The thermochromic material according to claim 1, for the compound at approx. 65° C. wherein the thermochromic material is extrudable. 1. A thermochromic material comprising at least one 10. An extruded moulded article comprising athermochro biopolymer, at least one natural dye and at least one reaction mic material according to claim 1. medium selected from the group of fatty acids and derivatives 11. The moulded article according to claim 10. thereof, gallic acid and derivatives thereof and mixtures wherein the moulded article is a flat film or a blown film. thereof, 12. The moulded article article according to claim 10. wherein all the components of the thermochromic material wherein the moulded article is a sheet or a multiskin sheet. optionally contain components or additives which are 13. A method comprising utilizing the thermochromic permitted for foodstuff. material and molded articles made therefrom in the foodstuff 2. The thermochromic material according to claim 1, industry and medical technology according to claim 1. wherein the at least one natural dye has an anthocyanidin. 14. The thermochromic material according to claim 2, 3. The thermochromic material according to claim 1, wherein the at least one natural dye is selected from the group wherein the at least one reaction medium is selected from consisting of cyanidin, delphinidin, aurantinidin, petunidin, the group consisting of petroselinic acid, palmitoleic peonidin, malvidin, pelargondin, rosinidin, europinidin, acid, myristoleic acid, oleic acid, elaidic acid, gadoleic luteolinidin and mixtures thereof. acid, undecylenic acid, icosenic acid, vaccenic acid,