INDICATOR MIXTURE

Description

[0001] The invention relates to an indicator mixture according to claim 1 and to a chemical indicator according to claim 6.

[0002] DE 10 2019 004 662 A1 discloses an adhesive film comprising an adhesive, a cationic initiator, and a pH-sensitive dye. Irradiating the adhesive film with UV light in an uncrosslinked state, the initiator generates an acid, which crosslinks the adhesive and causes the dye to undergo a color change. The color change can thus be used to indicate the crosslinking of the adhesive or the irradiation. Since the color change is based on a dynamic reaction, the color of the dye changes over time, for example, due to a change in the amount of reactants and products present.

[0003] It is also known to add a photosensitizer to adhesives that are crosslinked by radiation in order to expand the wavelength range of the radiation within which crosslinking of the adhesive can be achieved. The photosensitizer is completely independent of the dye used, and even small amounts of photosensitizer are sufficient to achieve the desired effect.

[0004] DE 100 63 066 A1 discloses a radiation-sensitive composition comprising a cationically or acid-catalytically polymerizable or crosslinkable compound or a compound that increases its solubility under the action of acid in a developer, as well as at least one diaryliodonium salt. WO 2006 / 008251 A2 discloses a process comprising activating a catalyst by irradiating a mixture containing the catalyst and applying the mixture to a substrate.

[0005] From WO 00 / 22060 A1 a colored adhesive is known which contains a dye which has a first color before irradiation and a second color after irradiation.

[0006] The object of the invention is in particular to provide a generic indicator mixture which has improved properties with regard to

[0007] Identification. The object is achieved according to the invention by the features of claims 1 and 6, while advantageous embodiments and further developments of the invention can be found in the subclaims.

[0008] The invention is based on an indicator mixture with at least one dye, which is intended for joint use with at least one coating composition and at least one crosslinking agent.

[0009] It is proposed that the indicator mixture comprise at least one photosensitizer, wherein the mass ratio of photosensitizer to dye is 10-100:1, advantageously 25-90:1, and particularly advantageously 40-80:1. The stated ratios are to be understood such that one milligram of dye is followed by 10-100, 25-90, or 40-80 milligrams of photosensitizer. In particular, the indicator mixture comprises a fixed mixing ratio of photosensitizer to dye, although different types of indicator mixtures may have different mixing ratios within the stated ratios. This enables long-lasting and reliable identification to be achieved. Advantageously, the dye and the excited photosensitizer can jointly form an exciplex in which the dye has an exciplex color that differs from a base color of the dye.Particularly advantageously, the exciplex, which would degrade after a certain period of time under normal conditions, can be prevented from degrading by crosslinking the coating composition. The large amount of photosensitizer present relative to the dye prevents the dye from being influenced by the crosslinker, as is the case in the prior art.

[0010] The indicator mixture is intended to be mixed with the coating compound in an uncrosslinked state and the crosslinker. Advantageously, the indicator mixture can be used with various types of coating compounds and / or crosslinkers. Particularly advantageously, the indicator mixture is available as a separate product, with different types of indicator mixtures being compatible with different types of coating compounds and / or crosslinkers.

[0011] A "coating compound" is understood to mean a compound intended to be applied in a coating process and subsequently form a layer. It would be conceivable for the coating compound to be intended to form an outer layer, which can, for example, provide a protective function; in particular, the coating compound could be designed as a lacquer compound. Preferably, the coating compound is designed as an adhesive compound, in particular a pressure-sensitive adhesive compound. Particularly preferably, the coating compound, together with the crosslinker, is present in the form of an adhesive film after the coating process. The adhesive film could be intended to bond at least two joining partners together.In this case, a color change of the dye can be used to ensure that the crosslinking of the adhesive film is complete and the joining partners can be moved without having to fear that the joining partners will become detached from one another. Preferably, at least one of the joining partners is at least partially transparent, whereby the color change of the dye can be observed from the outside. Alternatively, the adhesive film could be designed as part of a chemical indicator which is intended to be connected to an object to be irradiated. It would be possible for the chemical indicator to be irreversibly bonded to the object; preferably, the chemical indicator is reversibly bonded to the object. The chemical indicator can be designed, for example, as an adhesive tape, an adhesive film, an adhesive strip, an adhesive plate or an adhesive punched part.Alternatively, the chemical indicator can also be designed as a carrierless transfer adhesive film.

[0012] The coating compound formed as an adhesive mass comprises, in particular, at least one adhesive. The adhesive can be any radiation-crosslinking adhesive. Properties of the adhesive in a crosslinked state and a non-crosslinked state depend in particular on the respective area of ​​application. If the adhesive is intended to bond joining partners, the adhesive can be in liquid form in the non-crosslinked state. Preferably, the adhesive is in solid or highly viscous form in the non-crosslinked state and is particularly preferably pressure-sensitively adhesive in the non-crosslinked state. This allows the chemical indicator to be easily bonded to the object to be irradiated. Alternatively, the adhesive could be free of adhesive surfaces in the non-crosslinked state; in this case, an additional adhesive can be used.The additional adhesive is, in particular, pressure-sensitive and forms either part of the adhesive film or a further adhesive film laminated onto the adhesive film. Preferably, the adhesive is pressure-sensitive in its crosslinked state. It would also be conceivable for the adhesive to be free of adhesive surfaces in its crosslinked state; this is particularly suitable if the adhesive is intended to bond the joining partners. For example, the adhesive could comprise at least one substance from the class of acrylates, polyurethanes, and / or epoxy resins. Furthermore, the adhesive can comprise any desired type and amount of additives, such as fillers, additional dyes, and / or tackifiers.

[0013] The crosslinker is intended to initiate a crosslinking reaction upon irradiation of the adhesive. Advantageously, the crosslinker initiates the crosslinking reaction independently of the photosensitizer; alternatively or additionally, the crosslinker can initiate the crosslinking reaction based on activation energy transferred by the photosensitizer. The composition of the crosslinker depends on the particular adhesive used. For example, the crosslinker could comprise substances with at least one isocyanate group and / or at least one vinyl group. In particular, the crosslinker could comprise at least one anionic initiator.

[0014] The wavelength of the radiation by which the adhesive can be crosslinked can, in particular, be chosen arbitrarily. For example, the adhesive could be crosslinked using infrared radiation, microwave radiation, and / or X-rays. The adhesive is preferably crosslinkable using UV radiation; particularly preferably, an absorption range of the photosensitizer lies in the UV range. An "absorption range" of the photosensitizer is understood to mean a wavelength range, wherein the photosensitizer is capable of absorbing radiation within this wavelength range and thereby reaching the excited state. The photosensitizer is preferably designed to remain at least partially in the excited state and to form the exciplex with the dye.In particular, the photosensitizer remains entirely in the excited state; alternatively, the photosensitizer can partially revert to a ground state, thereby releasing activation energy to the crosslinker to initiate the crosslinking reaction. In this case, the proportion of the photosensitizer that reverts to the ground state decreases, in particular gradually, with at least a large portion of the photosensitizer preferably being present as part of the exciplex after irradiation. For example, the absorption range of the photosensitizer could be in the UV-A range, which is 380-315 nm, or in the UV-C range, which is 280-100 nm. The adhesive can be crosslinked using any desired dose and duration of irradiation, which depends in particular on the specific application of the adhesive, for example, on the thickness of the adhesive film.The adhesive is preferably crosslinkable using a dose of at least 1650 mJ / cm² and a duration of at least 5 seconds. A crosslinking reaction of the adhesive is preferably carried out as a dark reaction; more preferably, an open time within which the adhesive is still tacky enough to bond the joining partners after initiation of the crosslinking reaction is at least 10 seconds, preferably between 10 seconds and 60 minutes. After the open time has elapsed, the crosslinking of the adhesive has progressed to such an extent that, in particular, there is no longer sufficient tack to bond the joining partners. As a result, the indicator mixture can advantageously be used to identify UV irradiation, which is one of the most commonly used types of irradiation, thereby achieving the widest possible range of applications for the indicator mixture.

[0015] The photosensitizer comprises at least one isopropylthioxanthone. In particular, the photosensitizer can comprise precisely one isopropylthioxanthone or a plurality of different isopropylthioxanthones. It is conceivable for the indicator mixture to additionally comprise other photosensitizers; preferably, the indicator mixture is free of other photosensitizers. This enables a stable exciplex and a clearly visible color change.

[0016] The dye contains at least one anthraquinone, in particular 1,4-bis(butylamino)anthraquinone. This enables a stable exciplex and a clearly visible color change. If the photosensitizer is isopropylthioxanthone and the dye contains 1,4-bis(butylamino)anthraquinone, a color change from a blue base color to a yellowish exciplex color can be observed.

[0017] Furthermore, a coating composition is proposed that comprises the indicator mixture and the crosslinker. Advantageously, the dye, the photosensitizer, the crosslinker, and the remaining coating composition are selected such that all components are compatible with each other. This prevents failure of the identification process due to the use of incompatible components. Advantageously, the indicator mixture can be provided as part of a ready-to-use product, eliminating additional steps for the user, such as mixing the components.

[0018] It is also proposed that the coating compound be designed as an adhesive compound and comprise at least one adhesive. This eliminates the need for additional adhesives for attaching a chemical indicator to the indicator mixture. The coating compound can advantageously be used to bond joining partners together.

[0019] It is further proposed that the adhesive comprise at least one epoxy resin. For example, the adhesive may comprise an aromatic epoxy resin, a bisphenol-based epoxy resin, a novolak epoxy resin, a halogenated epoxy resin, an aliphatic epoxy resin, and / or a cycloaliphatic epoxy resin. In particular, the adhesive may comprise just one epoxy resin or a plurality of different epoxy resins. This allows a stable exciplex to be achieved. The exciplex can advantageously be "frozen" in the crosslinked epoxy resin.

[0020] Furthermore, it is proposed that the crosslinker comprise at least one cationic initiator. In particular, the crosslinker may comprise just one cationic initiator or a plurality of different cationic initiators. This allows a crosslinking reaction of the adhesive to be initiated in a simple manner.

[0021] In a further aspect, the invention is based on a chemical indicator which comprises at least one carrier and the indicator mixture. Furthermore, the chemical indicator comprises the coating composition and the crosslinking agent, wherein the coating composition either already contains the indicator mixture or the indicator mixture is only mixed into the coating composition during the production of the chemical indicator. The carrier is intended in particular to receive the indicator mixture in at least one state. For example, the carrier could comprise at least one cellulose and / or at least one plastic. It would be conceivable for the carrier to be designed as a release liner and to be detachably connected to the indicator mixture, which comprises the adhesive and the crosslinking agent and is designed as a carrier-free transfer adhesive film.Alternatively, the carrier could be permanently bonded to the indicator mixture and, in particular, be part of an adhesive tape, an adhesive film, an adhesive strip, an adhesive plate, or an adhesive die-cut part. This would allow for simple and error-free identification.

[0022] It would be conceivable for the carrier to have at least one indentation, groove and / or channel into which the indicator mixture is poured. In order to achieve simple production of the chemical indicator, it is proposed that the indicator mixture be at least part of the adhesive film with which the carrier is coated. If the coating compound comprises the indicator mixture and the crosslinker, the coating compound completely forms the adhesive film. In particular, the chemical indicator can be produced using a roll-to-roll process. Advantageously, the chemical indicator is designed in the form of a web, which can particularly advantageously be later disassembled into individual parts, wherein each individual part can be used for a respective identification purpose. For example, the chemical indicator could be disassembled by tearing it off, preferably at a perforation in the chemical indicator, or by cutting it off.This allows the chemical indicator to be produced on an industrial scale.

[0023] The indicator mixture and the chemical indicator are not intended to be limited to the application and embodiment described above. In particular, the indicator mixture and the chemical indicator may contain a number of individual elements and substances that differs from the number stated herein to fulfill a function described herein.

[0024] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0025] They show: Fig. 1A schematic representation of a chemical indicator according to the invention with an indicator mixture according to the invention in a cross-sectional view.

[0026] Figure 1 shows a chemical indicator 10. The chemical indicator 10 is designed as a single-sided adhesive tape. The chemical indicator 10 is intended to be connected to an object to be irradiated (not shown) and to indicate the irradiation by means of a color change. The irradiation is designed as UV irradiation. The chemical indicator 10 has a carrier 12. The carrier 12 is designed as a paper tape. Alternatively, the carrier 12 could also be made of other materials; for example, the carrier 12 could be designed as a film.

[0027] The chemical indicator 10 has an adhesive film 14. The carrier 12 is coated with the adhesive film 14. The adhesive film 14 comprises an indicator mixture. The indicator mixture comprises a dye. The dye comprises a halochromic substance. The halochromic substance is in the form of an anthraquinone. The halochromic substance is in the form of 1,4-bis(butylamino)anthraquinone. Alternatively or additionally, the dye could comprise other substances that may also be halochromic or thermochromic, photochromic, and / or ionochromic. A basic color of the dye is blue.

[0028] The indicator mixture contains a photosensitizer. One absorption range of the photosensitizer lies in the UV range. The photosensitizer contains isopropylthioxanthone. The photosensitizer contains 2-isopropylthioxanthone. Alternatively or additionally, the photosensitizer can contain other substances whose absorption ranges lie in the UV range. The photosensitizer is in a ground state. When the object to be irradiated is irradiated, the photosensitizer enters an excited state and, together with the dye, forms an exciplex. In the exciplex, the dye exhibits an exciplex color. The exciplex color is greenish-yellow.

[0029] The indicator mixture is part of a coating compound. The coating compound is designed as a pressure-sensitive adhesive and comprises an adhesive. The adhesive is designed as an adhesive that crosslinks using UV radiation. The adhesive is in an uncrosslinked state. The adhesive is pressure-sensitively adhesive. The adhesive has a solid form. Alternatively, the adhesive can also be free of adhesive surfaces; in this case, the chemical indicator 10 could additionally comprise another adhesive film (not shown), which is pressure-sensitively adhesive and is laminated onto the adhesive film 14. After irradiation of the object to be irradiated, the adhesive is in a crosslinked state. In the crosslinked state, the adhesive is free of adhesive surfaces.The adhesive comprises a mixture of aromatic and cycloaliphatic epoxy resins; alternatively, the adhesive could also comprise only one epoxy resin, at least one acrylate, and / or at least one polyurethane. Furthermore, the adhesive comprises a film former, an epoxidized polyether compound, and one or more polyols. Alternatively or additionally, the adhesive may comprise further additives and / or fillers.

[0030] The coating composition comprises a crosslinker. The crosslinker is intended to initiate a crosslinking reaction through activation energy transferred from the photosensitizer to the crosslinker. Alternatively, the crosslinker could also initiate the crosslinking reaction independently of the photosensitizer. The crosslinker comprises a cationic initiator. The cationic initiator is bis(triphenylsulfonium hexafluorophosphate) (Omnicat 432 from IGM Resins). Alternatively or additionally, the crosslinker can comprise other cationic or anionic initiators.

[0031] The mass ratio of photosensitizer to dye in Adhesive Film 14 is 40-80:1, with the same mass ratio also applying when the indicator mixture is considered separately from the adhesive and crosslinker. The following table lists some sample formulations for Adhesive Film 14: Recipe Adhesive [g] Crosslinker [g] Photosensitizer [g] Dye [mg] 1 50 5 0,5 8 2 50 5 0,5 12 3 50 2,5 0,5 8 Reference symbol

[0032] 10Chemical indicator 12Adhesive film 14Carrier

Claims

1. Indicator mixture comprising at least one dye and at least one photosensitizer, configured to be used together with at least one coating mass and at least one curing agent, wherein the dye is an anthraquinone and the photosensitizer is an isopropylthioxanthone and a mass ratio of the photosensitizer and dye is 10-100:1, which is to be understood as 1 milligram of dye being present for every 10-100 milligram of photosensitizer.

2. Coating mass, comprising the indicator mixture according to any of the preceding claims and the curing agent.

3. Coating mass according to claim 2, characterized in that the coating mass is an adhesive mass and comprises at least one adhesive.

4. Coating mass according to claim 3, characterized in that the adhesive comprises at least one epoxy resin.

5. Coating mass according to any of the claims 2 to 4, characterized in that the curing agent comprises at least one cationic initiator.

6. Chemical indicator (10) comprising at least one carrier (12) and the indicator mixture according to claim 1.

7. Chemical indicator (10) according to claim 6, characterized by the adhesive mass according to claim 3 or 4, wherein the adhesive mass forms an adhesive film (14) which is coated onto the carrier (12).