Method for producing a flexible surface element and a surface element produced thereby

Abstract

The invention relates to a method for producing a flexible surface element (1) with an inner or outer functional layer (3), wherein expandable hollow microspheres (4) with a preferably homogeneous distribution are introduced into a functional layer (6). At least one additional pressure-resistant layer (5) is detachably applied to the functional layer (3). By supplying thermal energy, the hollow microspheres (4) are preferably heated uniformly to a temperature above the expansion temperature and expand, the expansion of the hollow microspheres (4) being limited by the pressure-resistant properties of the pressure-resistant layer (5). The material thickness (D) of the functional layer (3) is reduced by the expansion, and the surface quality is significantly improved. The pressure-resistant layer (5) is then removed from the functional layer (3).

Description

[0001] The invention relates to a method for producing a flexible surface element having at least one inner or outer thermoplastic wear layer into which expandable hollow microspheres are introduced with a preferably homogeneous distribution. Furthermore, the invention relates to a flexible surface element produced in this way.

[0002] It is well known that thermoplastics can be foamed using blowing agents. Expandable hollow microspheres, for example, are used as blowing agents.

[0003] Such expandable hollow microspheres, also known as microspheres, consist of a thin plastic shell, such as polyacrylonitrile or copolymer, and are filled with gas, usually hydrocarbons. The temperature applied during thermoplastic processing causes the plastic shell to soften and the enclosed gas to expand. This causes the hollow microspheres to expand. Combinations of chemical blowing agents and expandable hollow microspheres are also used.

[0004] The production and use of expandable thermoplastic hollow microspheres are disclosed, among others, in US Pat. No. 3,615,972. The unexpanded spheres contain volatile liquid blowing agents that gasify upon application of heat. When heat is applied, the polymer shell softens, and the spheres expand as the blowing agent gasifies.

[0005] EP 0 348 372 B1 describes a process in which the unexpanded hollow microspheres are expanded using a hot air blower and an exhaust device, for example by infrared rays.

[0006] Processes for foaming thermoplastic polyurethanes with blowing agents are also known. In the case of thermoplastic polyurethane, chemical blowing agents result in a comparatively coarse foam structure and increased formation of cavities.

[0007] To remedy this deficiency, EP 0 692 516 A1 describes a process for producing foams based on thermoplastic polyurethane, in which a mixture of chemical blowing agents and hollow microspheres is used as blowing agent.

[0008] US Pat. No. 6,103,152 A relates to a process for producing a polymer foam, wherein a molten polymer composition and expandable polymer microspheres are mixed, which are expanded within the polymer composition before the composition exits the die. After exiting the die, the microspheres can be further expanded by heating the polymer foam. The polymer foam can have a substantially smooth surface and can also be produced as a film.

[0009] US 2006 / 0 219 350 A1 discloses an adhesive composition placed between surfaces or layers and containing two thermoexpandable microsphere species, in which a first species of microspheres serves for curing and a second species of microspheres serves for debinding. The microspheres of the different species can be activated at different temperatures.

[0010] US Pat. No. 5,783,302 A describes a calendering system for producing in-situ foamable thin films. The film contains a liquid blowing agent or expanding agent. The resin matrix may contain hollow glass microspheres.

[0011] EP 2 134 425 B1 relates to the use of an endless belt as a treadmill for running training equipment. Foaming can be carried out by mixing expandable microspheres into the thermoplastic material, whereby the resulting foamed layer can then be applied to the tensile body in a second step by calendering.

[0012] In practice, the limited or even partially varying surface quality of the wear layer often proves to be disadvantageous during the production of flexible surface elements. In particular, unevenness, micropores, or cavities cannot be reliably ruled out. Furthermore, the limited dimensional stability of such surface elements, for example, due to continued expansion of the hollow microspheres after calendering, is a hindrance.

[0013] The invention is based on the object of creating a method for producing a surface element with significantly improved properties of the wear layer. Furthermore, the invention is based on the object of creating a flexible surface element produced thereby with improved properties of the wear layer.

[0014] The first-mentioned object is achieved according to the invention with a method for producing a surface element according to the features of claim 1. The further embodiment of the invention can be found in the subclaims.

[0015] According to the invention, a method is provided for producing a flexible surface element with an outer and / or inner thermoplastic, thermosetting or elastomeric wear layer, in which the expandable hollow microspheres are introduced with a preferably homogeneous distribution, wherein at least one additional pressure-resistant layer is detachably applied to the wear layer and then at least one section of the surface element to be treated is heated by thermal energy supply, preferably uniformly, to a specific temperature within an expansion temperature range below an upper limit temperature of the hollow microspheres, so that at least the hollow microspheres contained in the section to be treated and / or already partially expanded hollow microspheres are at least partially expanded, wherein the expansion of the hollow microspheres is limited by the pressure-resistant properties of the pressure-resistant layer,by establishing an equilibrium between the expansion pressure and the counterpressure of the pressure-resistant layer, whereby the material thickness of the wear layer is reduced by the expansion and the pressure-resistant layer is then removed from the wear layer, at least in sections.

[0016] According to the invention, a pressure-resistant layer is understood to be a flexible, yet tensile-resistant, non-elastic, and at most plastically extensible layer that is capable of withstanding expansion pressure and thus precisely limiting expansion. Due to these properties, the pressure-resistant layer can be described as tensile-resistant.

[0017] In a typical application of the method according to the invention, the flexible surface element and thus the thermoplastic wear layer are heated uniformly. The expansion of the hollow microspheres can lead to compression of the wear layer. The pressure-resistant layer acts as a cover film to counteract this expansion. It has already been shown that this homogenizes even the smallest irregularities on the surface of the wear layer, so that after removal of the pressure-resistant layer, the surface has a so-called mirror surface quality. This opens up completely new application possibilities for the surface element, for example in the printing industry. Furthermore, the material thickness of the surface element can be specifically adjusted by regulating the temperature with high, reproducible accuracy.

[0018] A particularly advantageous embodiment of the invention is achieved by removing the pressure-resistant layer from the wear layer over its entire surface after the expansion of the hollow microspheres. The surface texture of the thus exposed wear layer then corresponds to the surface texture of the facing side of the pressure-resistant layer and, in practice, meets the highest quality standards. Of course, structures or patterns can also be transferred to the wear layer using the pressure-resistant layer as a negative of the corresponding texture of the pressure-resistant layer.

[0019] It has already proven particularly advantageous if the pressure-resistant layer comprises a film, particularly made of polyester, as a key material component and preferably of a constant material thickness. Alternatively, areas with varying material thicknesses can also be provided, for example, to allow limited stretchability of the pressure-resistant layer in individual areas, which leads to local elevations in the wear layer.

[0020] In addition, the pressure-resistant layer can allow certain materials or substances to be transferred onto or into the surface of the wear layer or to remain on the wear layer when the pressure-resistant layer is removed.

[0021] It is conceivable to implement the pressure-resistant layer as a metal foil, which can also be reused if necessary. Particularly preferably, the pressure-resistant layer comprises a biaxially or bidirectionally pre-stretched foil, which can also be used, for example, as a protective film and is removed from the wear layer only before use of the surface element.

[0022] Another, equally promising variant of the process is created by partially or sectionally deviating the energy input when heating the section of the surface element to be treated to a temperature above the expansion temperature. This creates at least one area with a lower energy input and at least one other area with a higher energy input. Depending on the spatial expansion limited by the pressure-resistant layer, this results in different compaction in the various areas and, as a result, in areas of the surface element with different densities. This also results in other mechanical properties, such as flexibility, differing from one area to another. In practice, this can create flexible zones, which prove advantageous, for example, for applications as a conveyor belt in the area of ​​deflections.

[0023] Another particularly practical embodiment of the invention is achieved by removing and / or modifying the pressure-resistant layer partially or in sections before, during, or after heating the wear layer by applying energy. For example, the pressure-resistant layer can be cut out, perforated, or weakened using mechanical tools or laser radiation, so that the wear layer protrudes or takes on a convex shape in these areas. By subsequently modifying the pressure-resistant layer already adhered to the wear layer, individual properties of the wear layer can be created.

[0024] The detachable connection between the pressure-resistant layer and the wear layer is achieved, for example, by an adhesive connection.

[0025] In another advantageous variant of the method according to the invention, several, in particular different, pressure-resistant layers are detachably applied to the wear layer, whereby the different layers can also cover different partial areas. By using several pressure-resistant layers, the expansion of the wear layer and thus the material thickness of the resulting surface element can be adjusted. For example, areas with a smaller number of pressure-resistant layers stand out compared to other areas with a higher number of pressure-resistant layers, allowing local depressions and elevations to be created.

[0026] Similarly, individual pressure-resistant layers can have cutouts or perforations, for example with a pattern that can be transferred to the wear layer accordingly.

[0027] The thermal energy can be selectively introduced into different mutually delimited areas, in particular in tracks running in a longitudinal direction, sections running in a transverse direction and / or in different cross-sectional planes of the surface element with different wavelengths or intensities, so that the hollow microspheres are expanded differently in the different areas.

[0028] By selectively activating the hollow microspheres, which are bound in a material forming the matrix for the hollow microspheres of the surface element, after completion of the surface element, which may, for example, have additional decorative or functional layers in addition to the wear layer, the hollow microspheres expand in a manner dependent on the energy input. In this way, material properties such as damping or dimensional stability can be adjusted with high precision in conjunction with the pressure-resistant layer. The outer contour, especially the thickness, of the surface element is limited by the pressure-resistant layer, thus ensuring high dimensional accuracy of the surface element.For the purposes of the invention, the term "region" is understood to mean a surface area in the plane and / or a plane within the material thickness parallel to the outer surface, whereby full-surface activation is intended to be encompassed by the inventive concept. As an alternative to differentiated activation of different areas with different radiation energies, unexpanded hollow microspheres can be retained in other sub-areas. The invention is not limited to hollow microspheres with specific properties. Rather, hollow microspheres with different properties can be incorporated into the surface element.

[0029] It has already proven particularly useful if the hollow microspheres are introduced into the carrier material in different spatially separated areas in different proportions based on the volume or mass of the hollow microspheres, in order to supply a sufficient quantity of the hollow microspheres, especially to those areas in which activation of the hollow microspheres is intended.

[0030] Another, equally useful embodiment of the method according to the invention is realized by introducing electromagnetic radiation in the infrared spectrum (IR) into the surface element as high-energy radiation. The wavelength of the radiation, for example, simultaneously determines the accessible plane within the layer structure. This allows the high-energy radiation to be selectively restricted to comparatively small, possibly individual point-like areas, thus creating any desired structures.

[0031] It has proven particularly promising if, by selecting specific wavelength ranges, the hollow microspheres are expanded and / or activated in different planes at different distances from the running side and / or in different longitudinal sections, for example edge sections, in order to specifically optimize the properties of the surface element in predetermined sub-areas.

[0032] Furthermore, it is particularly useful to incorporate additional fibrous or strand-like fillers into the wear layer. This can further strengthen the wear layer if necessary, thus further improving the dimensional stability of the surface element being produced. It has already been shown that multilayer fillers with hollow microspheres inserted between them can significantly improve the strength, taking into account the total mass of the resulting composite.

[0033] Furthermore, it is also advantageous if the hollow microspheres contain active or reactive substances that are released by the high-energy radiation and the released substances react with components of the adjacent material of the surface element. For this purpose, the hollow microspheres are expanded until they burst or the respective shell of the hollow microspheres becomes permeable and the filler escapes. The filler thus enters the adjacent areas of the strip material as a gaseous or liquid fluid and reacts with the materials of the surface element present there. For example, a hardener is conceivable, which leads to an irreversible reaction with the material of the wear layer in order to harden it. Alternatively, the expansion of the hollow microspheres can also weaken the shell in such a way that the resulting closure leads to a permeability of the shell during use of the surface element.In this way, the hollow microspheres also serve as carriers for a wear indicator substance. A color change achieved in this way is visually perceptible and can therefore be used as a wear indicator.

[0034] Of course, the dye can also be designed in such a way that it is invisible under ambient conditions and can only be detected by light with a certain wavelength (UV).

[0035] In a substance serving as a contamination indicator, the hollow microspheres contain microorganisms that react with moisture or air, for example, so that upon wear, the microorganisms come into contact and trigger biological reactions. Of course, the reactants of the microorganisms can also originate from the transported goods, for example, food or chemical substances. Conversely, the released substances could also release decontaminating, disinfecting, biocidal, or other active substances to protect the transported goods.

[0036] Of course, hollow microspheres can be mixed with other additives, such as color or conductivity additives, to achieve certain desired properties.

[0037] The energy for expanding the hollow microspheres can be introduced using any heat source, for example, a heat transfer fluid. It is particularly advantageous if the high-energy radiation is introduced using a radiation source with a wavelength adapted to the area to be activated, in particular an adjustable wavelength, so that the radiation source introduces a wavelength, for example, in the infrared range, into the respective area of ​​the surface element in a freely selectable layer plane. Other areas thus remain unaffected by the high-energy radiation, thus preventing heating there.

[0038] The further object of creating a flexible surface element with improved properties of the wear layer is achieved according to the invention in that the flexible surface element has at least one expanded thermoplastic wear layer, produced by the expansion of hollow microspheres of the surface element against the pressure-resistant layer and subsequent at least partial removal of the pressure-resistant layer.

[0039] The possible uses and applications of the surface element according to the invention are unlimited. For example, the surface element is also suitable as a processing or printing belt for transferring printable substances such as dyes. The required compressibility, which is predetermined within narrow tolerance limits, can be optimally adjusted using the pressure-resistant layer.

[0040] According to a particularly expedient embodiment of the invention, the surface element has at least one thermoplastic wear layer and at least one tensile member, so that the wear layer containing the hollow microspheres absorbs no or only slight tensile forces during operation.

[0041] The invention allows for various embodiments. To further clarify its basic principle, one of them is shown in the drawing and is described below. This shows in cross section in Fig. 1 shows a surface element according to the invention with a wear layer during heating of the hollow microspheres contained in the wear layer; Fig. 2 shows the surface element after expansion of the hollow microspheres with a wear layer compressed against a pressure-resistant layer; Fig. 3 shows the surface element after removal of the pressure-resistant layer.

[0042] The method according to the invention for producing a flexible surface element 1 is described below with reference to Figures 1 to 3 explained in more detail. The surface element 1 shown is intended for use in the printing industry, so the highest demands are placed on the surface quality of a thermoplastic wear layer 3 made of TPU on a tensile member 2. Expandable hollow microspheres 4 are evenly distributed in a functional layer 6 with the wear layer 3; to clarify the inventive concept, they are not drawn to scale but are exaggerated. A pressure-resistant layer 5, which does not contain any hollow microspheres 4, is applied to the wear layer 3. Of course, the hollow microspheres 4 can also be unevenly distributed.

[0043] The essential idea of ​​the invention is based on the surface or partial activation of the hollow microspheres 4 by the thermal energy supply of a high-energy radiation 7, in particular an electromagnetic radiation in the infrared spectrum, in order to heat a shell (not shown) of the hollow microspheres 4 above its softening temperature. For this purpose, the radiation 7 penetrates the pressure-resistant layer 5 and the wear layer 3 and is focused or concentrated in the desired cross-sectional plane of the functional layer 6, wherein the pressure-resistant layer 5 and the wear layer 3 are not heated or are heated only very slightly. As a result, the affected hollow microspheres 4 expand, as shown in Figure 2 can be seen.

[0044] The expansion of the hollow microspheres 4 initially leads to changed mechanical properties of the surface element 1, which can thus for the first time be specifically adapted to the respective application.

[0045] However, a further essential aspect of the invention is the compaction of the wear layer 3 against the pressure-resistant layer 5, which acts as a barrier or abutment, thereby reducing its thickness D to a reduced thickness d. At the same time, the compact wear layer 3 thus created acquires excellent surface properties, in particular an optimally smooth surface with mirror-like surface quality. In particular, all surface defects are thereby leveled or removed.

[0046] As in Figure 3 As shown, the pressure-resistant layer is finally removed so that the surface of the wear layer 3 is usable. LIST OF REFERENCE SYMBOLS

[0047] 1Surface element 2Tension member 3Wear layer 4Hollow microsphere 5Compression-resistant layer 6Functional layer 7Radiation DDickness DDickness

Claims

1. A method for producing a flexible surface element (1) with at least one thermoplastic, thermosetting and / or elastomeric wear layer (3), wherein expandable hollow microspheres (4) are introduced into the wear layer (3) and / or a functional layer (6) with a preferably homogeneous distribution, wherein at least one additional pressure-resistant layer (5) is detachably applied to the wear layer (3), and wherein at least one section of the surface element (1) to be treated is then heated by thermal energy supply, preferably uniformly, to a temperature within an expansion temperature range of the hollow microspheres (4), so that at least the hollow microspheres (4) contained in the section to be treated are at least partially expanded and / or already partially expanded hollow microspheres (4) are further expanded, wherein the expansion of the hollow microspheres (4) is limited by the pressure-resistant properties of the pressure-resistant layer (5),which is then removed from the wear layer (3) at least in sections., 2. Method according to claim 1, characterized in that the pressure-resistant layer (5) has a film, in particular polyester, as an essential material component.

3. Method according to claim 1 or 2, characterized in that the pressure-resistant layer (5) comprises a particularly biaxially pre-stretched film.

4. Method according to at least one of the preceding claims, characterized in that the pressure-resistant layer (5) is partially or sectionally removed and / or modified before and / or during heating.

5. Method according to at least one of the preceding claims, characterized in that several, in particular different, pressure-resistant layers (5) are applied to the wear layer (3).

6. Method according to at least one of the preceding claims, characterized in thatthe material thickness (D) of the wear layer (3) is reduced to a material thickness (d) as a result of the expansion of the hollow microspheres (4).

7. Method according to at least one of the preceding claims, characterized in that the energy of a radiation (7) through the pressure-resistant layer (5) selectively acts differently, in particular with different parameters, in different mutually delimited areas and / or in different cross-sectional planes of the wear layer (3) and / or the functional layer (6) of the surface element (1), and the hollow microspheres (4) are thereby expanded differently in the different areas and cross-sectional planes of the surface element (1).

8. Method according to at least one of the preceding claims, characterized in thatthe energy input is achieved by electromagnetic radiation (7), in particular in the infrared spectrum (IR), and is in particular adjusted such that at least individual regions and / or cross-sectional planes of the wear layer (3) are heated, and that the pressure-resistant layer (5) is at least substantially penetrated by the radiation (7) without heating.

9. Flexible surface element (1) with at least one expanded wear layer (3), produced by the expansion of hollow microspheres of the surface element (1) against the pressure-resistant layer (5) and subsequent at least partial removal of the pressure-resistant layer (5).

10. Surface element (1) according to claim 9, characterized in that at least one pressure-resistant layer (5) has cutouts or perforations.