EP3994227A1

EP3994227A1 - Compressible uv-activatable or thermally activatable (semi-) structural adhesive film that changes color after activation and after curing

Info

Publication number: EP3994227A1
Application number: EP20739594.8A
Authority: EP
Inventors: Ruben FRIEDLAND; Victoria RITTER; Johannes Stahl
Original assignee: Lohmann GmbH and Co KG
Current assignee: Lohmann GmbH and Co KG
Priority date: 2019-07-05
Filing date: 2020-07-03
Publication date: 2022-05-11
Also published as: DE102019004662A1; US20220380642A1; WO2021004976A1; CN114080438A; CN114080438B

Abstract

The invention relates to an adhesive film that can be wound and punched, comprising an epoxy-based adhesive compound that can be activated by UV radiation or thermally and an expandable filler admixed to the adhesive compound to produce an adhesive film that is compressible when not yet cured.

Description

Compressible, UV- or thermally activatable (semi-) structural adhesive film with a color change after activation and curing

Technical area

The present invention relates to an adhesive film which can be activated and hardened by ultraviolet radiation (UV) or thermally, can be wound and punched for structural bonds with a color change after activation, which in the non-activated state is compressible and pressure-sensitive. In this sense, when referring to UV activation below, thermal activation is also always implied.

State of the art

The terms used in the following explanations are to be understood as follows:

In the following, “adhesive film” means any form of flat adhesive systems, not just adhesive tapes in the narrower sense, but also adhesive films, adhesive strips, adhesive plates or adhesive punched parts.

"Pressure-sensitive adhesive" is the term used for adhesive connections in which the two parts to be joined are connected to one another by an adhesive layer in between and under pressure. The connection is reversible in such a way that it can be released again without damaging the two parts to be joined because the adhesive seam is the weakest point in the joint.

"Structural" or "semi-structural" are adhesive bonds in which the joining partners are connected to one another in such a way that in the event of a separation the joint is not necessarily loosened at the adhesive seam, but possibly also one of the joining partners at the weakest point may be in the connection and then be damaged by the separation. Structural and semi-structural adhesive connections therefore have high strengths. The strengths, measured in the quasi-static tensile shear test according to DIN EN 1465, are structural Connections over 6 MPa, with semi-structural connections generally> 2 MPa. Usual values that are aimed for for structural adhesive connections of epoxy adhesives are 10 to 20 MPa.

"Radiation hardening" describes a process in which reactive materials are converted from a low molecular to a high molecular state with the help of high-energy radiation.

In the present case, UV radiation is understood to mean “UVA” or “UVC” light. UVA radiation is in the wave range of approx. 380 to 315 nanometers (nm), UVC radiation is in the wave range of approx. 280 to 100 nm. In general, both are electromagnetic radiation with wavelengths that are shorter than visible light . With UVA light the energy input is around 3.26 to 3.95 electron volts (eV), with UVC light it is around 4.43 to 12.40 eV.

"Activation" means the setting in motion of a curing process by irradiation with UV light, i.e. the photoinitiators in the adhesive are activated by exposure to light and trigger the curing process of the adhesive by initiating the formation of polymer chains. UV-curing adhesives are usually irradiated after the adhesive partners have been joined. This requires substrates that are sufficiently transparent to the UV radiation used. The bond is then irradiated until curing has progressed sufficiently, that is, it offers sufficient strength. As a result, only substrates that are UV-permeable can be activated and bonded in this way. The final strength of the adhesive is only achieved after the curing process has been completed.

"Open time" or "open time" is the time between application of the adhesive and bonding. During the open time, for example, a liquid hotmelt adhesive spreads over the surfaces to be bonded and ensures the necessary adhesion. Since the viscosity, i.e. the viscosity of an adhesive, usually increases after application, the open time for adhesives is limited in time.

The "curing time" is the period between the joining of the joint partners and the final strength of the connection.

The term “dark reaction” is used in the following to describe the fact that a curing reaction is triggered (triggered) by brief exposure of the adhesive to UV light and then complete curing can take place without further irradiation. Thermal activation means starting the hardening process by adding an increased temperature, ie in this case a temperature of at least 140 ° C.

“Super acid” means the following: During cationic UV curing, a ring opening takes place on the oxirane and / or oxetane (epoxy resins and vinyl ethers). This is done by photolysis of e.g. diaryliodonium salts, which leads to the generation of strong protic acids, so-called super acids. The acid proton opens the epoxy ring and starts the chain growth and thus the hardening.

In the following, “compressible” means an adhesive film or adhesive film which can be subjected to compression deformation before UV or thermal activation and which returns to its original thickness after the load has been removed.

The basis of UV-curing adhesives often consists of acrylate monomers or oligomers, which cure in a radical chain reaction induced by UV light.

In contrast, UV-curing epoxy adhesives are cured by a cationic photoinitiator. With cationic UV curing, a ring opening takes place on the oxirane and / or oxetane (epoxy resins and vinyl ethers). This is done by photolysis of e.g. diaryliodonium salts, which is based on the generation of strong protic acids. The acid proton opens the epoxy ring and starts the chain growth and thus the hardening.

In contrast to the radical UV curing of acrylates, this leads to a lower

Shrinkage and good adhesion to a wide variety of substrates. Another advantage of cationic hardening is its insensitivity to oxygen, which enables high hardening speeds under normal air conditions. Humidity and alkaline conditions, on the other hand, tend to have a greater influence than with radical UV curing.

In the case of cationic UV initiation, it is possible under certain circumstances to delay chain formation to such an extent that it can finally take place in the dark without further exposure to radiation. It can possibly also be greatly delayed so that it only starts up again or is accelerated through a heat treatment. A “trigger irradiation”, i.e. a brief exposure to radiation, is sufficient to start curing. In the possibly following dark reaction - outside of the UV light - further curing then takes place. It may even be possible that a certain "open time" arises, that is to say that initially on the open adhesive layer is irradiated and then there is still time to make the joint with the second substrate without reducing the final bond properties. This procedure would then also make it possible to join substrates that are not UV-transparent. UV-activatable adhesive tapes are known: WO 2017/174303 A1 shows a pressure-sensitive, radiation-activated adhesive tape consisting of a radiation-activatable polymerizable composition consisting of: 5 to 60 parts by weight of at least one polyurethane polymer film-forming component; 40 to 95 parts by weight of at least one epoxy component; 0.1 to 10 parts by weight of at least one photoinitiator, and optionally 0.1 to 200 parts by weight of at least one additive, in each case based on the radiation-activatable polymerizable composition, the parts by weight of the aforementioned individual components being 100 complete.

WO 2018/153985 A1 shows a rollable and punchable adhesive film with an adhesive based on epoxy which can be activated by UV radiation, the adhesive comprising: 2-40% by weight of film former; 10-70% by weight of aromatic epoxy resins; cycloaliphatic epoxy resins, the cycloaliphatic epoxy resins not exceeding 35% by weight; 0.5-7% by weight of cationic initiators; 0-50% by weight of epoxidized polyether compounds and 0-20% by weight of polyol, the proportions adding up to 100%.

In industrial requirements in general, ever higher demands are made on adhesive connections, for example with regard to breaking strength, temperature resistance, resistance to climatic changes, moisture and heat resistance, etc. The reason for this is that increasingly larger quantities of adhesive tapes are being used in automobile construction, e.g. for weight reasons or because they do not necessarily have to be point-like connections, but rather an even distribution of the joining force via an adhesive seam and not least because the joining partners do not be damaged, as is the case with certain other joining processes such as screwing or riveting.

In many processes, for example in the automotive industry, the activation or curing of the adhesive / adhesive tape must be ensured and verified by the manufacturer of the same. Accordingly, there are high requirements for process control when processing these adhesives. This can be remedied by UV-activatable liquid adhesives that are able to indicate activation by means of a color change. EP 3 105 276 B1, for example, describes an irreversible color change of an epoxy adhesive from blue to yellow.

Also known is the bathochromic effect, also known as red shift, which describes a color shift. This leads to a shift of the absorption spectrum into the longer-wave, lower-energy range of the electromagnetic spectrum (cf. K. Schwetlick: Organikum. 15th edition, VEB Deutscher Verlag der Wissenschaften, Berlin 1976, p. 513f.)

This color shift, in turn, can also be generated by the halochromic effect ("salt color"), which describes the change in color of a substance depending on the charge state of its molecules. An example of this is litmus, which changes its color from red (acidic) to blue (basic) depending on the pH value of an aqueous solution.

By means of the known systems, only the occurrence of activation in the case of liquid adhesives can currently be displayed. Accordingly, there is a need to make such a process control accessible to the structural adhesive films. In addition to the time at which activation begins for process control, there is also a need to determine the time of sufficient curing, which is described in the previously unpublished patent application PCT / EP2018 / 084413.

Also, with none of the adhesive films mentioned, a tolerance compensation of the joining partners to be joined is possible to the same extent as with liquid adhesives. However, since there are always manufacturing-related tolerances with real components, this property is essential.

WO 2014/071334 A1 describes an adhesive film based on epoxy resin, containing core-shell rubber particles and thermally expandable microparticles which expand during curing under the influence of the curing temperature. The disadvantage here is that the joining parts are not optimally wetted before curing due to the joining part tolerances and this only happens during the expansion during curing. In this case, however, the build-up of an adhesion to the joining partner is no longer ensured due to the progressive crosslinking, so that there is often a lack of adhesion to the second joining part. In addition, it is imperative that the temperature be introduced during curing. Presentation of the invention

Based on the known prior art, it is an object of the present invention to provide a rollable and punchable adhesive film which, in the uncured state, can be compressed to compensate for joining tolerances and, after activation by means of UV radiation or temperature, a color change as an indicator of activation and has a renewed color change after hardening and thus enables a process control and also provides a corresponding method for producing such a film.

The object is achieved by a rollable and punchable adhesive film with the features of claim 1. Distributable developments result from the subclaims.

Correspondingly, a rollable and punchable adhesive film is proposed, comprising an epoxy-based adhesive that can be thermally activated by UV radiation. According to the invention, the adhesive comprises a mixed-in dye or a mixed-in pigment to produce a first color change after activation of the adhesive and a second color change after the adhesive has cured, as well as a filler mixed into the adhesive to produce an adhesive film that is compressible in the uncured state.

This enables in-process control which, in addition to identifying the start of activation of the adhesive, additionally identifies the progress of the crosslinking reaction of the adhesive in color, so that the status with regard to the curing can be made visible. The prior art is silent with regard to a UV-activatable, in the uncured state compressible adhesive film based on epoxy resin adhesives, in which, apart from the cationic photoinitiator, no further initiator as a radical starter is necessary for activation and which changes color after activation by adding a dye or pigment which can serve as process control. The open time, storage time and curing speed of the adhesives used are not influenced by the addition of appropriate dyes or pigments.

With the present adhesive film, a complete process control of the UV activation can take place by means of a color change within the joining process of possible applications of the UV-activatable adhesives. For example, by adding the dye Sudan blue, a blue-colored adhesive can be produced which, after UV activation, changes to a shade of pink - purple. Postpones after a duration of approx. 24 hours the color of the adhesive turns back towards blue, which is due to the degradation or reaction of the acid contained in the adhesive. Thus, the user has control over the activation or reactivity status of the adhesive film.

Through the further use of appropriate additives, which lead to an expansion during the production of the adhesive film, an adhesive film is created that can be compressed before the UV or thermal activation.

In this way, the finished adhesive film can be applied to components with manufacturing-related tolerances prior to curing and compensates for these tolerances through the ability to compress like a foam. For this reason, full-surface wetting of real components can be ensured before curing.

The processing and coating of the adhesive can take place via a solvent or hotmelt process. Processing and coating are also possible using so-called syrup technology, in which the film-forming component is only built up from monomers or oligomers during the coating.

In the non-activated state, the adhesive film is pressure-sensitive and can thus be treated like a "normal" pressure-sensitive adhesive tape during processing, i.e. it can be applied with a slight adhesion and, if necessary, repositioned. Stamped parts can be manufactured from the adhesive tape, which can be activated by UV light prior to application on the respective parts to be bonded in order to create a (semi-) structural bond after crosslinking.

Covers (release liners) are usually also part of adhesive tapes. In principle, all well-known types of release liners can be used here.

The curing of the adhesive tapes and punched parts is finally activated by UV light, preferably UVA or UVC light. Only then are the joining partners finally and structurally joined. Since the curing reaction takes place in several steps, there is still a certain period of time after activation during which the parts to be joined can be finally aligned and joined; further activation after curing has been initiated by UV light is no longer necessary.

The duration of the dark reaction depends heavily on various factors, e.g. the resin component used (cycloaliphatic or aromatic epoxy resin), the chain length, the type of initiator, the irradiation time, the irradiation dose (UV wavelength) or the temperature. The curing time after irradiation can be between 10 seconds and 60 minutes, depending on the factors mentioned and their interaction.

In a further preferred embodiment, the adhesive comprises: a. 2 - 50% by weight film former,

b. 10 - 70% by weight aromatic epoxy resins,

c. 0.5 - 7 wt .-% cationic initiator,

d. 0.1 - 70% by weight of an additive responsible for the expansion of the adhesive film (= expandable filler),

d. 0.001-0.2% by weight of dye or pigment,

e. cycloaliphatic epoxy resins, the cycloaliphatic epoxy resins not exceeding 35% by weight

f. 0-50% by weight of epoxidized polyether compounds, and

G. 0-20% by weight of polyol, the proportions adding up to 100%.

After UV activation, the adhesive has an open time of 10 seconds to 60 minutes, during which the film is pressure-sensitive before it is finally completely cured and has reached its final strength.

In a further preferred application, the additive responsible for the expansion has an activation temperature between 30 ° C and 150 ° C and a maximum degree of expansion between 40 ° C and 150 ° C, particularly preferably between 60 ° C and 130 ° C. This allows expansion during the drying of the adhesive film, which can be precisely adjusted. This means that defined layer thicknesses and degrees of compression can be produced that meet the application-specific requirements. Fillers that require a higher activation energy or temperature must also be tempered in a separate step, which is not sensible from an energetic layer.

In a preferred embodiment, the uncured adhesive film has a compression of between 5 and 80%, depending on the filler concentration and the expansion. Through this compression, joining part tolerances can be compensated and thus complete wetting can be achieved. aims to be. However, depending on the compressibility, the strength of the adhesive film decreases, so that with small joint tolerances, a low filler concentration and thus compression is more effective. However, if there is also a thermal shock load in later use, a high compressibility and thus deformability in the direction of the thickness is an advantage to compensate for the stresses caused by the different coefficients of thermal expansion.

In a preferred development, the adhesive film is in the form of a carrierless, UV-activatable, compressible adhesive transfer tape.

In a preferred development, the adhesive film comprises a UV-transparent or UV-opaque carrier. By designing the adhesive film with a UV-transparent or UV-opaque carrier, the adhesive film can be tailored to the customer's application and process conditions. With a UV-opaque carrier it is possible to completely decouple the cross-linking of the two adhesive layers spatially and temporally.

In a preferred embodiment, the adhesive film comprises at least one UV- or thermally activatable adhesive. Because the adhesive film contains at least one thermally activatable adhesive, higher strengths and chemical resistance can be achieved.

In a preferred embodiment, 0.001 to 0.2% by weight, preferably 0.01 to 0.07% by weight and particularly preferably 0.015 to 0.04% by weight of the dye or pigment are mixed into the adhesive. At concentrations less than 0.001% by weight, the coloring of the adhesive can no longer be visually reliably detected; at concentrations greater than 0.2% by weight, the dye or pigment and its / their amine groups or nitrogen compounds create a basic environment, which prevents a reaction of the super acid with the epoxy groups and an azo group.

In a preferred development, the dye or the pigment is an azo dye or an azo pigment. In particular, dyes or pigments which change color under the action of an acid are advantageous. Examples are methyl red, methyl orange, congo red and alizarin yellow R.

Dyes or pigments of the azo group are decisive for the color change. They change color through protonation when the pH value falls below a certain level. This is exemplary shown below for the azo dye methyl red, which is present in acidic media in red and in protonated form (right structure below) and in basic media in yellow and deprotonated (see left structure below).

Under the influence of increased air humidity, the color change is less, since the acid particles that are formed tend to attach themselves to the OH ions in the water and thus less to the dye or pigment. At the same time, in these cases the cured adhesive tape is less closely crosslinked, which is shown in lower strengths in the tensile test and at the same time greater elongation at break.

In a preferred development, the adhesive film comprises different adhesive systems, at least one of which is a UV-activatable system.

In a preferred embodiment, the rollable and punchable adhesive film is particularly suitable for the structural bonding of metals, glass, ceramics, glass fiber plastic (GRP), carbon fiber plastic (CFK) and other higher-energy surfaces.

In a further preferred embodiment, the adhesive film, which can be wound and punched, has strengths of between 6 and 20 MPa during adhesive bonding, depending on formulation details, radiation dose and substrates to be bonded. In a further preferred embodiment, the rollable and punchable adhesive film is suitable for the (semi-) structural bonding of plastics and other low-energy surfaces. Detailed description of preferred exemplary embodiments

The production of an adhesive film and its UV activation are described below. Test specimens were produced using the manufacturing process described herein. The test items were subjected to various tests to test their properties. The results of the investigations are also explained in more detail below.

The present adhesive 1 comprises the following composition: a. 2-50% by weight film former, b. 10-70% by weight of aromatic epoxy resins, c. 0.5-7% by weight of the cationic initiator, i.e. 0.001-0.2% by weight of dye or pigment e. cycloaliphatic epoxy resins, the cycloaliphatic epoxy resins not exceeding 35% by weight f. 0.1 to 70% by weight of at least one additive responsible for the expansion during drying (expandable additive), g. 0-50% by weight of epoxidized polyether compounds, and h. 0-20% by weight of polyol, the proportions adding up to 100%.

After UV activation, the adhesive has an open time of 10 seconds to 60 minutes, during which the film is pressure-sensitive. The dye or pigment is preferably an azo dye or an azo pigment and in particular those azo substances which change color under the action of acid. Some azo dyes are listed as examples in the table below:

Table 1

A color change after UV activation or thermal activation occurs when the amount added is between 0.001 and 0.2% by weight of the dye or pigment. At concentrations less than 0.001% by weight, the coloring of the adhesive can no longer be detected visually with process reliability; at concentrations greater than 0.2% by weight, the dye or pigment and their amine groups or nitrogen compounds create a basic environment, which is a Prevents the superacid from reacting with the epoxy groups and the azo group.

The experiments have shown a preferred range from 0.01 to 0.07% by weight and particularly preferably from 0.015 to 0.04% by weight of the dye or pigment. Under the influence of increased air humidity, the color change is less, since the acid particles that are formed tend to attach themselves to the OH ions in the water and thus less to the dye or pigment. At the same time, the cured adhesive tape is less closely crosslinked in these cases, which is shown in lower strengths in the tensile test and at the same time greater elongation at break. The fillers responsible for expansion are thermo-expandable microspheres, which are produced by encapsulating liquid low-boiling hydrocarbons in thermoplastic polymer shells. These usually have particle sizes from 5 μm to 50 μm and activation temperatures from 30 ° C to 300 ° C.

A preferred temperature range for the maximum degree of expansion between 40 ° C and 150 ° C, particularly preferably between 60 ° C and 130 ° C, has emerged from the experiments. This results in an adhesive film that can be compressed before final curing.

The solvent-based adhesive is applied to a siliconized polyester film (thickness 50 μm) by means of a doctor blade. Then the whole thing is first dried for 10 minutes at room temperature and then for 10 minutes at 80 ° C in a convection oven. The order quantity is adjusted so that after drying (removal of the solvent mixture) there is a tacky film with a thickness of about 150 μm.

No protective measures against UV light are necessary for handling the raw materials, the adhesive or the coating. It is sufficient to work away from the UV lamp in a normal laboratory environment. No further shielding is carried out.

The UV source necessary for the UV activation of the UV-activatable adhesive can be, for example, UV-C light from a discharge lamp or UV-A light from a UV-A LED source.

Experiments with a UV-C lamp are carried out with a UV laboratory system from Beltron with a conveyor belt and UV-C radiator with a radiation maximum of 256 nm. The conveyor belt is operated at 2 m / min. The radiation dose in the UV-C range, measured with a UV Power Puck II from EIT Instrument Market Group, is 197 mJ / cm ² .

Alternatively, the adhesives can also be activated with a UV-LED system, despite a significantly higher wavelength. Irradiation times similar to those of the UV-C system are possible and the results in open time and bond strength are in the same range.

Experiments with a UV-LED system are carried out with an LED spot lamp 100 from Hönle, which comprises a UV-LED (wavelength 365 nm) and an irradiation chamber. The test specimens are irradiated for 15 seconds in the irradiation chamber. The radiation dose, measured with a UV Power Puck II from EIT Instrument Market Group, is 5000 mJ / cm ² .

The terms open time, time to handling strength and curing time as they are to be understood in the present context are explained in more detail below.

Open time is understood to mean the maximum possible time between removal from the irradiation tape (UV-C) or removal from the irradiation chamber (UV-A) and the time of joining with the second substrate. During this time, the parts to be joined can be joined. The open time is defined in such a way that during this time the adhesive layer is still tacky. It is determined by checking the tackiness of the adhesive films with a finger after exposure. Immediately after the irradiation, the adhesive film is still sticky / tacky. After a certain time, a noticeable decrease in tackiness can be noticed, which then quickly up to finally drops off a tack free surface. The open time is fixed at the point in time at which the tack decreases so noticeably that there is no more tack afterwards.

It turns out that as long as the surfaces are still sticky, joining is possible and that the subsequent hardening leads to a homogeneous adhesive bond. As the surfaces gradually lose their tack, the hardening process progresses more and more, so that finally joining is no longer possible. This is then shown in greatly reduced strength values, measured by the quasi-static tensile shear strength.

In addition, the activation can be detected by means of the color change that is new for these adhesive films, and the open time can be determined through the further change in color after activation. The adhesive films are joined directly after the UV activation.

The hardening time is the period between joining and final strength. All sample recipes are fully cured after 24 hours at the latest. For this reason, the user usually waited 24 hours before measuring the quasi-static tensile shear strength. If the value exceeds approx. 6 MPa, one speaks of structural strength or structural bonding. Due to the added dye or pigment, it is possible to determine from the color shade whether the recipe has completely cured. The adhesive has then reacted with respect to the degree of crosslinking in relation to the temperature present during crosslinking.

A sufficient open time is required for the application. Fast handling strength is also advantageous if the bond has to withstand an initial load soon after joining (e.g. when transporting the parts), or in order to be able to dispense with further fixing of the parts. On the other hand, 24 hours are sufficient for complete curing, since experience has shown that the bond is only subjected to final stress after this time (continuous stress or shock stress).

Open time and curing time are consequences of the reaction speed of the curing reaction. This reaction begins with the UV activation and ends with the complete hardening of the adhesive film. Hardening is complete when the adhesive bond has reached its final strength. During the open time and curing time, different phases can take place with different reaction speeds; delays and accelerations can occur, see above that overall a certain open time and curing time result. Open time and curing time can be controlled via the recipe, the type, intensity and duration of irradiation and via the heat management (temperatures) in the bonding process.

The time to handling strength refers to the time that elapses after joining until the strength of the connection is so high that the bonded parts can already be transported and processed. Experience shows that handling strength is reached when the quasi-static tensile shear strength reaches 2 MPa. This is a strength that leaves enough leeway for the loads in an industrial manufacturing process.

The raw materials used are listed in Table 2:

Table 2 Test methods a) Color change

The color change is recorded visually and documented with photos. A detection takes place before activation by means of temperature or UV radiation, immediately after activation and 24 hours after activation. The specified color corresponds to the perception of five different test subjects. b) Quasi-static lap shear test

Tensile shear tests according to DIN EN 1465 (2009) at 23 ° C ± 2 ° C and 50% ± 5% relative humidity are carried out at a test speed of 2 mm / min as a parameter for the strength of the bond on GRP. The substrates are cleaned with isopropanol and then joined. The curing takes place by irradiation with UV light and the mechanical test takes place 24 hours after activation. The results are given in MPa (N / mm ² ). The average value from five measurements including standard deviation is given. c) peel test

The peel resistance of the cured adhesive tapes on a typical automotive paint, for example PPG 2K-ApO clearcoat 1.2 [A-B203512], is based on DIN EN 1939 (1996) at 23 ° C ± 2 ° C and 50% ± 5% relative humidity with a Test speed of 100 mm / min and a peel angle of 90 ° determined. The samples are cured with UV light and tested 24 hours after activation. The results are given in N / mm. The average value of the tear resistance from five measurements including standard deviation is given. d) tensile test

Tensile tests based on DIN EN ISO 527 (2012) at 23 ° C ± 2 ° C and 50% ± 5% relative humidity at a test speed of 10 mm / min are carried out as a parameter for the strength of the pure adhesive film in the cured state. For this purpose, strips with a width of 19 mm and a length of 100 mm are cut from cured adhesive films. The layer thickness in the results shown is 0.2 mm. The samples are cured with UV light and tested 24 hours after activation. The results are given in MPa (N / mm ² ). The average value from five measurements including standard deviation is given. e) expansion

The expansion after drying is carried out by measuring the layer thickness with a thickness measuring device. An unfilled sample, which was produced with the same coating parameters, serves as a reference. On the one hand, measurements were made immediately after the adhesive had been coated and dried, as described above in the area of Production of PSAs. The expansion results from the following formula:

100% thickness of the adhesive film modified with fillers

Expansion [%]

Thickness of the unfilled reference f) Compression The compression is measured using a Keyence VHX-5000 microscope with a magnification of 20x100. For this purpose, an adhesive film is clamped between two metal substrates and the thickness of the film is measured in the unloaded state. Then the clamped adhesive film is loaded with a force of 100 N and the thickness of the film is measured again. The compression results from the following formula:

100% thickness of the loaded adhesive film [mm]

Compression [%]

Thickness of the unloaded adhesive film [mm]

Examples:

Table 3 summarizes examples relating to the compositions in relation to the selection of the expandable fillers, the quantitative data denoting parts by weight. K1 to K3 are formulations according to the invention with expandable fillers. V1 is an adhesive transfer film without the addition of an expandable filler:

Table 3

Table 4 summarizes the results of the lap shear, tensile and peel tests and the associated expansion and compression.

Table 4

The adhesive films K1, K2, K3 and V1 each have the same UV-activatable adhesives. Only the expandable filler was varied in order to show differences in the selection of the expandable filler.

The adhesive films according to K1, K2, K3 and V1 do not differ significantly in terms of the standard deviation in tensile strength. It can thus be shown that the use of the expandable filler to achieve an adhesive film that can be compressed before curing does not have any negative influence on this mechanical parameter. The tensile shear strength of the adhesive films according to K3 and V1 is also within the standard deviation without significant differences. Here the tensile shear strengths of formulations K1 and K2 are somewhat lower, which is due to the influence of expansion.

The adhesive films K1 and K2 show a higher peel resistance than the films K3 and V1, which is due to the positive peeling properties of the compressible adhesive film. The expansion after drying at 90 ° C. for 10 minutes shows clear differences between the fillers used. Thus, the adhesives K1 and K2 with similar expanding fillers have an expansion of about 180% and 200%, respectively, whereas adhesive film K3 like the unfilled reference shows no expansion, which in the case of K3 is due to the different nature of the one used compared to K1 and K2 expanding filler is due.

Due to the test method, the compression could not be measured exactly. It depends very much on the filler concentration, the adhesive film thickness and the previous expansion. For the adhesive films K1 to K2, a compression of approx. 30% was measured after the pre-crosslinking at 90 ° C. for 10 minutes. The adhesives K3 and R1 are not compressible due to the different type of expanding filler or the absence of the same.

As far as applicable, all the individual features that are shown in the exemplary embodiments can be combined with one another and / or exchanged without departing from the scope of the invention.

Claims

Expectations

1. A rollable and punchable adhesive film comprising an epoxy-based adhesive that can be activated by UV radiation and / or thermally, characterized in that the adhesive has a mixed-in dye or a mixed-in pigment for generating a first color change after activation of the adhesive and a second color change after the curing of the adhesive, and an expandable filler mixed into the adhesive for producing an adhesive film that is compressible in the uncured state.

2. Windable and punchable adhesive film according to claim 1, characterized in that the adhesive further comprises: a. 2 - 50% by weight film former,

b. 10 - 70% by weight aromatic epoxy resins,

c. 0.5 - 7 wt .-% cationic initiator,

d. 0.001-0.2% by weight of dye or pigment

f. 0.1 to 70% by weight of at least one expandable filler responsible for expansion during drying,

G. 0-50% by weight of epoxidized polyether compounds, and

H. 0-20% by weight of polyol, the proportions adding up to 100%.

3. Windable and punchable adhesive film according to claim 1 and 2, characterized in that the expanding filler has an activation temperature between 30 ° C and 150 ° C and reaches a maximum degree of expansion between 40 ° C and 150 ° C, particularly preferred between 60 ° C and 130 ° C.

4. Winding and punchable adhesive film according to claims 1 to 3, characterized in that the uncured adhesive film has a compression between 5 and 80% depending on the filler concentration and the expansion.

5. Adhesive film that can be wound and punched according to one of the preceding claims, characterized in that the adhesive film is a carrierless UV-activatable adhesive transfer tape.

6. A wound and punchable adhesive film according to claims 1 to 4, characterized in that the adhesive film comprises a UV-transparent or UV-nontransparent carrier.

7. A rollable and punchable adhesive film according to claims 5 or 6, characterized in that the adhesive film comprises at least one UV- or thermally activatable adhesive.

8. Windable and punchable adhesive film according to one of the preceding claims, characterized in that 0.001 to 0.2 wt .-%, preferably 0.01 to 0.07 wt .-% and particularly preferably 0.015 to 0.04 wt. -% of the dye or the pigment are mixed into the adhesive.

9. A wound and punchable adhesive film according to claim 8, characterized in that the dye or the pigment is an azo dye or an azo pigment.

10. Adhesive film that can be wound and punched according to claim 9, characterized in that the azo dye or the azo pigment are among the azo substances which change color under the action of acid.