WO2022073608A1

WO2022073608A1 - Geometrically defined pressure-sensitive adhesive film

Info

Publication number: WO2022073608A1
Application number: PCT/EP2020/078186
Authority: WO
Inventors: Florian DÜMMLER; Ruben FRIEDLAND; Peter Harendt
Original assignee: Lohmann Gmbh & Co. Kg
Priority date: 2020-10-07
Filing date: 2020-10-07
Publication date: 2022-04-14

Abstract

The present invention relates to a geometrically defined pressure-sensitive adhesive film produced by stereolithography processes, the adhesive film being brought into a geometrically defined shape without a subsequent shaping process.

Description

Geometrically defined pressure-sensitive adhesive film

technical field

The present invention relates to a geometrically defined pressure-sensitive adhesive film that was produced using stereolithography processes.

State of the art

To coat adhesives, coating units are used which usually coat the liner over its full width; certain coating geometries (points or strips) are also possible to a narrowly limited extent in such units. In any case, however, it is neither possible to vary the geometries completely freely in a single coating step, nor is it possible to produce different geometries in a single coating step, such as are necessary for gluing emblems consisting of different letters or other symbols. To create such geometries, a stamping process is usually used after the coating process. This procedure has the disadvantage of the often low degree of material utilization, since the production of the stamped parts produces up to 90% waste that cannot be used.

With conventional coating, all known coating processes are available, such as strip polymerisation, hot-melt coating and drying of water-based or solvent-based systems.

An adhesive layer produced in this way is preferably used as a carrierless adhesive tape (transfer tape), but can also form an adhesive layer of an adhesive tape. Adhesive layers that are to be used as a pressure-sensitive adhesive tape and are not provided with a stable backing can be brought into a geometrically defined shape only with difficulty, if at all. All previous attempts to accomplish this with the usual current manufacturing processes result in damage to the tape produced or render it unusable. The new manufacturing process of the Polyjet Modeling process according to the invention falls into the category of the processes known as “rapid prototyping” or “additive manufacturing” and is therefore a “3D printing” application in the broadest sense.

Methods for producing adhesive surfaces using a 3D printing method are already known from the literature. For example, WO 2019/120818 A1 describes in very general terms the production of an adhesive surface by applying an adhesive to at least one surface of a part to be joined or a transfer adhesive carrier using a 3D printing device. The corresponding 3D printing device, which works according to the inkjet principle or is fed by an endless strand, and the method for gluing two parts to be joined are also claimed here. This method is also used for a wide selection of different types of adhesive that can be used here, as well as for both homogeneous and different layer thicknesses.

Special photo-curable resin compositions for 3D printing are the subject of EP 3597668 A1 and EP 3597669 A1, the printing process used here can be a so-called “material jetting” process or a stereolithographic process.

EP 3196000 B1 describes a method for producing a composite material component by printing a component skeleton and introducing a resin into this skeleton. The skeleton can be printed using the PolyJet printing process. WO 2019/1215170 A1 claims an aqueous acrylic adhesive dispersion for 3D printing, WO 2020/146452 A1 an additive manufacturing process using an amine-containing adhesive polymer and finally WO 2020/165193 A1 claims a 3D printing process

Use of a film containing metal powder. Finally, the manufacture of adhesives and adhesive products using additive manufacturing methods is the subject of WO 2017/117035 A1; Here, an adhesive precursor composition is applied to a radiation-permeable surface, and then different sections are irradiated with different radiation doses and for different radiation durations in each case, resulting in an adhesive surface with different properties.

In the project "Resource-efficient production of pressure-sensitive adhesive molded parts through generative printing processes", which was funded by the German Federal Environmental Foundation under file number DBU-AZ 32912/01, a process based on rotogravure printing is described. Here, UV-crosslinking pressure-sensitive adhesives are applied to the liner in the form of the gravure printing process, thus producing geometrically defined printed parts. However, none of these property rights describes the production of a geometrically defined, preferably also solvent-free adhesive layer using a rapid prototyping method, specifically a stereolithography method that saves both starting material and waste, as described in more detail below.

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

In the following, "adhesive film" or "adhesive film" means any form of two-dimensional adhesive systems, i.e. not only adhesive films, but also adhesive tapes, adhesive foils, adhesive strips, adhesive plates or adhesive die-cut parts. Furthermore, the term "adhesive tape" or "adhesive film" also includes so-called "transfer films", ie unsupported adhesive tapes.

Adhesives or adhesive films are referred to as “pressure-sensitive adhesive”, “pressure-sensitively sticky” or “pressure-sensitive” adhesives, which are able to join two joining partners to one another only by applying pressure. In particular, a permanent connection between the joining partners can be realized under relatively weak contact pressure. The connection is reversible, i.e. it can be released again without destroying the parts to be joined.

In the following, “3D printing” means the application of adhesive masses to a liner using the stereolithography process.

“Room temperature” means a temperature of 23 ± 2 °C.

Presentation of the invention

Proceeding from the known prior art, it is an object of the present invention to provide a geometrically defined pressure-sensitive adhesive film which has been produced using a rapid prototyping method, specifically a waste-saving stereolithography method in a discontinuous batch-to-batch process.

A further object is to provide a geometrically defined pressure-sensitive adhesive film which has been produced in the stereolithography process by means of band polymerisation.

The object is achieved by a geometrically defined pressure-sensitive adhesive film having the features of claim 1. Advantageous developments result from the dependent claims. Accordingly, a geometrically defined pressure-sensitive adhesive film based on a generative printing process is specified, the pressure-sensitive adhesive composition particularly comprising acrylates. According to the invention, UV acrylates are processed with the stereolithography method and printed in geometrically defined forms.

Furthermore, in one embodiment, it is possible to produce the geometric shape in all spatial directions, so that not only two-dimensional adhesive tapes with a geometric definition, but also three-dimensional adhesive tapes with a geometric definition can be produced.

In a preferred embodiment, a pressure-sensitive adhesive film has a bond strength of at least 0.2 N/mm. The bond strength is determined here on steel based on DIN EN 1939:1996 at 23° C.±2° C. and 50%±5% relative humidity at a peel-off speed of 300 mm/min and a peel-off angle of 180°. As part of the test, an etched PET film with a thickness of 50 μm is used as the intensifying film. A 25 mm wide measuring strip is bonded to the steel substrate using a 5 kg roller at a temperature of 23 °C ± 2 °C. The adhesive film is pulled off at 300 mm/min 10 minutes after application. The measured value (in N/mm) is the mean of five individual measurements.

Pressure-sensitive adhesives have a permanently tacky effect at room temperature, ie they have a sufficiently low viscosity and high initial tack, so that they wet the surface of the respective substrate even with slight contact pressure. The bondability of the adhesives is based on their adhesive properties and their redetachability on their cohesive properties.

In a preferred embodiment, the geometrically defined pressure-sensitive adhesive film has no backing and is therefore suitable for forming a transfer film.

In the case of a transfer film or transfer adhesive tape, the adhesive mass, which corresponds to the finished adhesive film in the final state, is applied to a flexible material such as a film or between two flexible materials before application. These materials are referred to as release liners, they are provided with a separating layer on the adhesive surface and/or have anti-adhesive properties.

When using two liners, for example, to apply the adhesive film, one liner is first removed and the adhesive film is applied with the adhesive surface now exposed to a first part to be joined. The second liner is then removed and the adhesive surface that is now exposed connected to the second joining part. The adhesive can thus be used directly to connect two surfaces.

With such a contact-adhesive, carrier-free adhesive transfer film, very precise gluing in terms of positioning and metering is made possible.

There is also the possibility of producing adhesive films or adhesive tapes with a combination of different adhesives or adhesive systems. For example, the first layer, a UV acrylate layer, can be provided with a second UV acrylate layer. Thus, a further storage container with a second adhesive and a further post-crosslinking line are connected behind the first storage container and the post-crosslinking line. It is thus possible to implement an asymmetrical adhesive tape structure with all of the adhesives mentioned below by connecting storage containers in series. One of these printed adhesives can also function as a carrier system, so that all imaginable layer structures are technically possible.

Adhesive films or adhesive tapes are also possible in which two liners are not used, but rather only a single liner that is repellent on both sides. In this case, a first side of the adhesive film is covered with one side of the double-sided separating liner and a second side of the adhesive film when it is wound onto a roll or a spool is then covered with the reverse side of the double-sided separating liner.

In a further embodiment, the geometrically defined pressure-sensitive adhesive film has at least one backing. If a backing material is present, it can be provided with a geometrically defined (pressure-sensitive) adhesive on one or preferably both sides.

The carrier material includes all flat structures such as foils, foams, fabrics, scrims, nonwovens and papers or combinations thereof. Different backings can be combined with the adhesives for different applications. In this embodiment, only the carrier material needs to be finished if necessary, which means that the overall waste is significantly reduced compared to the standard coating and punching process.

In a preferred development, the thickness of the geometrically defined PSA, both in the form of an adhesive transfer film and coated on a sheetlike structure, is between 1 μm and 3000 μm, more preferably between 10 μm and 2000 μm and particularly preferably between 50 μm and 1000 μm. Layer thicknesses between 100 μm and 1000 μm are ideally suited for bridging tolerances in the parts to be bonded. Layer thicknesses between 1 μm and 50 μm lead to reduced adhesion on the parts to be joined, but at the same time reduce the amount of material used.

Adhesives used are, on the one hand, all adhesives known to those skilled in the art based on UV acrylates, which can be polymerized by means of UVA, UVB or UVC. Examples of such adhesives are well known and described in adhesive practice and in the literature.

In a preferred development, the adhesives are partially functionalized, resulting in a functional adhesive film. The functionalities can be introduced by means of fillers to produce electrically or thermally conductive adhesive films or adhesive tapes, as well as by introducing medicinal substances or medicinal active substances to produce active substance patches.

In a further preferred embodiment, the functionalization is for coloring the adhesive films, and for functionalization by means of biocides and herbicides.

Short description of the figures

Preferred further embodiments of the invention are explained in more detail by the following description of the figures. show:

FIG. 1 shows a schematic representation of a complex geometrically defined pressure-sensitive adhesive film;

FIG. 2 shows a schematic representation of a discontinuous batch-to-batch process; and

FIG. 3 shows a schematic representation of a production process for a geometrically defined pressure-sensitive adhesive film in a discontinuous roll-to-roll SLA process.

Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. Elements that are the same, similar or have the same effect are provided with identical reference symbols in the different figures, and a repeated description of these elements is sometimes dispensed with in order to avoid redundancies. Production of the geometrically defined pressure-sensitive adhesive layers

To produce the respective geometrically defined pressure-sensitive adhesive layers, the respective pressure-sensitive adhesive masses are placed in the storage container. The pressure viscosity is between 10 mPas and 10 Pas, preferably between 50 mPas and 1 Pas.

The adhesive is then polymerized using a UV light source directed at a high-resolution pixel screen. The pixels required for the respective layer open and close via a controller and thus expose the UV-reactive adhesive mass in the storage container equipped with a UV-transparent base. This polymerizes only in the exposed areas, the other areas remain liquid and can be removed afterwards in a washing process.

The thickness of the exposed layer depends on the distance between the construction platform and the bottom of the storage container and is between 1 μm and 3000 μm, preferably between 10 μm and 2000 μm and particularly preferably between 50 μm and 1000 μm.

To produce the layers of adhesive, i.e. the unsupported pressure-sensitive adhesive tapes, the various adhesives (UV acrylate) are applied to a conventional liner (siliconized polyester film) using the stereolithography process and then irradiated with a UV lamp with UVA, UVB or UVC.

The thickness of the transfer film is then 300 ± 20 μm. The adhesive films produced in this way are each laminated on the open side immediately after the polymerization with a second liner (siliconized polyester film with a lower release force than the first liner).

Exemplary production of the geometrically defined pressure-sensitive adhesive film

In the present example, a standard UV acrylate from Lohmann was used, which consists of 2-ethylhexyl acrylate, acrylic acid and a radical photoinitiator.

This was printed with an Ultimaker S5 in a width of 100mm x 100mm. The shape was chosen analogously to the test specifications described below and thus in the form of test strips with a thickness of about 300 μm (example K1).

At the same time, a more complex geometry analogous to Figure 1 was printed to examine the limitations of the process. The geometrically defined pressure-sensitive adhesive film was produced in a discontinuous batch-to-batch process (FIG. 2). Here, reference number 1 is the SLA printing station and reference number 2 is the storage container equipped with a UV-transparent base.

FIG. 3 shows the production process of a geometrically defined pressure-sensitive adhesive film in a discontinuous roll-to-roll SLA process. Here, reference number 1 is the unwinder, reference number 2 is the SLA printing station with the storage container equipped with a UV-transparent bottom. The excess adhesive is removed in the cleaning station 3 before it is post-crosslinked in a UV post-treatment station 7 . Then the liner with the geometrically defined pressure-sensitive adhesive film 6 printed on it is wound up on the winder 5 .

In parallel, an adhesive film with the identical recipe was coated onto the identical liner in a thickness of 500 μm using a coating system (R1) in order to be able to comparatively assess the mechanical performance of the adhesive film produced using the stereolithography process.

Results of the pressure-sensitive adhesives in terms of thickness, bond strength and shear strength

Adhesion:

The bond strength is determined on steel based on DIN EN 1464:2010 at 23° C.±2° C. and 50%±5% relative humidity at a peel speed of 300 mm/min and a peel angle of 110° in the roller peel test. An etched PET film with a thickness of 50 μm is used as the reinforcing film. A 25 mm wide measuring strip is bonded to the steel substrate using a 5 kg roller at a temperature of 23 °C ± 2 °C. The adhesive film is pulled off at 300 mm/min 10 minutes (initial) or 24 h (24 h) after application. The measured value (in N/mm) is the mean of five individual measurements including the standard deviation.

Shear strength:

Tensile shear tests according to DIN EN 1465 at 23 °C ± 2 °C and 50 % ± 5 % relative humidity are carried out at a test speed of 10 mm/min as a parameter for the strength of the bond on steel. Steels of the alloy 1.4301 are used as test substrates, which are cleaned with acetone on the one hand and subjected to a mechanical surface pretreatment on the other hand by means of cross-polishing. The samples are produced using a 5 kg roller at a temperature of 23°C ± 2°C and tested 24 hours after application. the Results are given in MPa (N/mm ² ). The mean value from five measurements including standard deviation and fracture pattern evaluation is given in each case.

Thickness:

As a parameter for the thickness of the adhesive film, thickness measurements based on DIN EN 1942:2008 are carried out at 23° C. ± 2° C. and 50% ± 5% relative humidity. The results are given in mm. The average of five measurements is given in each case.

The adhesive films K1 and R1 have an identical chemical composition. Only the manufacturing process is varied. Thus, R1 is coated using standard coating processes in a 2-roller application over a width of 450 mm and band-polymerized. In contrast to this, K1 is applied in the width to be tested by means of stereolithography processes and is also band-polymerized.

Within the standard deviation, the adhesives K1 and R1 have the same bond strength both initially and after 24 hours. With regard to the lap shear strength, K1 has a higher lap shear strength than R1, but experience has shown that this is due to the lower adhesive layer thickness. The tensile shear strengths would therefore also be the same within the scope of the standard deviation if the thickness of the adhesive layer was identical. It can thus be said that the geometrically defined pressure-sensitive adhesive layer which was produced using the stereolithography process has the same technical adhesive properties as a conventionally coated adhesive film.

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

Claims

Expectations

1. Geometrically defined pressure-sensitive adhesive film which is produced by means of a stereolithography process, characterized in that the adhesive film is brought into a geometrically defined shape without a subsequent shaping process.

2. Geometrically defined pressure-sensitive adhesive film according to claim 1, characterized in that the adhesive film is produced using stereolithography methods in a discontinuous batch-to-batch process.

3. Geometrically defined pressure-sensitive adhesive film according to claims 1 and 2, characterized in that the adhesive film has geometrically defined forms both in a two- and three-dimensional view.

4. Geometrically defined pressure-sensitive adhesive film according to claim 1, characterized in that UV acrylates can be printed in the viscosity range of 10 mPas and 10 Pas, preferably between 50 mPas and 1 Pas.

5. Geometrically defined pressure-sensitive adhesive film according to claims 1 and 2, characterized in that the adhesive is selectively irradiated by means of a UV light source and a pixel screen and is thus polymerized.

6. Geometrically defined pressure-sensitive adhesive film according to one of the preceding claims, characterized in that the bond strength is at least 0.2 N/mm.

7. Geometrically defined pressure-sensitive adhesive film according to one of the preceding claims, characterized in that the adhesive film is unsupported to form a transfer film.

8. Geometrically defined pressure-sensitive adhesive film according to any one of claims 1 to 5, characterized in that the adhesive film comprises a carrier.

9. Geometrically defined pressure-sensitive adhesive film according to one of the preceding claims, characterized in that the adhesive film consists of several different adhesive film layers, which are variations of different UV acrylates.

10. Geometrically defined pressure-sensitive adhesive film according to one of the preceding claims, characterized in that the adhesive film has a thickness of between 1 μm and 3000 μm, more preferably between 10 μm and 2000 μm and particularly preferably between 50 μm and 1000 μm.

11. Geometrically defined pressure-sensitive adhesive film according to one of the preceding claims, characterized in that the adhesive film is functionalized.

12. Geometrically defined pressure-sensitive adhesive film according to claim 12, characterized in that the functionalization serves to generate thermal or electrical conductivity.

13. Geometrically defined pressure-sensitive adhesive film according to claim 12, characterized in that the functionalization for producing active substance patches is carried out by means of medicinal substances or medicinal active substances.

14. Geometrically defined pressure-sensitive adhesive film according to claim 12, characterized in that the functionalization takes place by means of herbicides and biocides.

15. Geometrically defined pressure-sensitive adhesive film according to claim 12, characterized in that the functionalization serves to color the adhesive films and to produce color effects on the adhesive films.