Abstract
A composite comprising an upper layer and a substrate layer, wherein the upper layer comprises a shape-memory polymeric material having a glass transition temperature T.sub.g,SMP and being at least partially transparent for light in the VIS-range, characterized in that the upper layer comprises a surface, wherein the surface is at least partially a rough surface having an arithmetic average roughness R.sub.a of at least 0.1 m.
Claims
1. A composite comprising an upper layer and a substrate layer, wherein the upper layer comprises a shape-memory polymeric material having a glass transition temperature T.sub.g,SMP and being at least partially transparent for light, characterized in that the upper layer comprises a surface, wherein the surface is at least partially a rough surface having an arithmetic average roughness R.sub.a of at least 0.1 m.
2. The composite according to claim 1, characterized in that the arithmetic average roughness R.sub.a is at least 0.2 m.
3. The composite according to claim 1, characterized in that the upper layer has a thickness of at most 20.0 m.
4. The composite according to claim 1, characterized in that the T.sub.g,SMP is below 70 C.
5. The composite according to claim 1, characterized in that the T.sub.g,SMP can be lowered by humidity and water, irradiation, organic vapors, amines, metal ions, pH-values, and chemical gases such as ammonia, carbon dioxide, carbon monoxide nitrogen dioxide, nitrogen monoxide, and oxygen.
6. The composite according to claim 1, characterized in that the substrate layer comprises a laminate of at least two sheets.
7. The composite according to claim 6, characterized in that at least one of the sheets of the substrate layer is selected from the group comprising a glass sheet, a polymeric material sheet, a paper and/or paperboard sheet, a metal sheet, a mineral sheet, and a sheet made of ink.
8. The composite according to claim 6, characterized in that the upper layer and/or at least one of the sheets of the substrate layer comprises a CLC polymeric material.
9. The composite material according to claim 8, characterized in that the CLC polymeric material is arranged in a layer and/or a sheet comprising a polymeric material.
10. The composite according to claim 9, characterized in that the CLC polymeric material are CLC particles.
11. The composite according to claim 6, characterized in that at least one sheet of the substrate layer is transparent.
12. A method of manufacturing a composite comprising the following steps: a. providing an upper layer onto a substrate layer, wherein the upper layer comprises a shape-memory polymeric material having a glass transition temperature T.sub.g,SMP and being at least partially transparent for light in the VIS-range, b. heating the composite above the T.sub.g,SMP, c. compressing the upper layer with a stamp having a rough surface, d. cooling down the composite under the T.sub.g,SMP, e. removing the stamp to provide an upper layer comprising a rough surface having an arithmetic average roughness R.sub.a of at least 0.1 m.
13. A method comprising using the composite according to claim 1 as an optical sensor on substrates comprising food, medicine, chemicals, and/or any other temperature sensitive perishable goods.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0059] The following figs. and examples have to be understood as embodiments of the invention and not as limiting features of the invention.
[0060] FIGS. 1A-B: FIG. 1A shows optical micrographs of a composite according to the invention in an initial and the deformed mode, and FIG. 1B shows reflection bands of initial, deformed and heated modes.
[0061] FIGS. 2A-B: FIG. 2A shows Height profiles of the upper layer of the composite of FIG. 1A before deformation and FIG. 2B shows them after deformation.
[0062] FIGS. 3A-C: Photographs of the deformed composite of FIGS. 1A-B obtained at various viewing angles.
[0063] FIGS. 4A-B: FIG. 4A shows optical micrographs of a composite according to the invention in an initial mode, a deformed mode, and a heated mode, and FIG. 4B shows reflection bands of initial, deformed, and heated modes.
[0064] FIGS. 5A-B: FIG. 5A shows optical micrographs of a composite according to the invention in an initial mode, deformed mode, and heated mode, and FIG. 5B shows reflection bands of initial, deformed, and heated modes.
[0065] FIGS. 6A-B: FIG. 6A shows optical micrographs of a composite according to the invention in an initial mode, a deformed mode, and a heated mode, and FIG. 6B shows reflection bands of initial, deformed, and heated modes.
[0066] FIGS. 7A-B: FIG. 7A shows optical micrographs of a composite in a mode before compression (initial) and after compression of the composite and FIG. 7B shows reflection bands of initial and compressed modes.
DETAILED DESCRIPTION OF THE INVENTION
[0067] m FIGS. 1A-B show a composite according to the invention, wherein in FIG. 1A optical micrographs of the composite are shown. The micrographs show the composite in an initial mode (initial), in which the upper layer has an even and uniform surface of ca. 2.5 m thickness, and in a deformed mode (deformed), in which the upper layer has a rough surface. The shown composite comprises CLC polymeric material in the upper layer so that the composite shows a red color in the initial mode and shows a matte grey/green color in the deformed mode. The zoomed micrograph of the deformed mode shows several different colored spots, which shows the increase of light scattering. Additionally, the zoomed micrograph shows also that contamination of particles is uncomplicated as this does not disturb the scattering. Furthermore, FIG. 1B shows the reflection band of the composite in the different modes, in which can be seen that after deformation the reflection bands is flattened and has an increased reflection across all wavelengths, which indicates the increased scattering.
[0068] FIGS. 2A-B shows the height profiles of the surface of the upper layer of the composite shown in FIGS. 1A-B. Thereby, in FIG. 1A the height profile of the composite in the initial mode having an R.sub.a value of 0.02 m (smooth surface) and in FIG. 1B the height profile of the composite in the deformed mode having a R.sub.a value of 0.3 m (rough surface) are shown. The drawings above of the height profiles in FIGS. 2A and 2B depicts schematically a non-scattering (indicated by arrows) even surface (FIG. 2A) and a scattering (indicated by arrows) rough surface (FIG. 2B).
[0069] FIGS. 3A-C shows photographs of the deformed composite of FIGS. 1A-B at various viewing angles. FIG. 3A is made from a nearly perpendicular viewing angle with respect to the plane of the composite (90), FIG. 3B is made from a viewing angle of 60 with respect to the plane of the composite and FIG. 3C is made from a viewing angle of 30 with respect to the plane of the composite. Thereby, the composite exhibits an area which is deformed (matte grey/green, inner region) and an area which is non-deformed (red, outer region). The non-deformed area shows a viewing angle dependent slight color change from red (FIG. 3A) over orange (FIG. 3B) to yellow/green (FIG. 3C).
[0070] FIGS. 4A-B shows a composite according to the invention, wherein in FIG. 4A optical micrographs of the composite are shown. The micrographs show the composite [0071] in an initial mode (initial), in which the upper layer has an even and uniform surface [0072] in a deformed mode (deformed), in which the upper layer has a rough surface, and [0073] in an after heating mode (heated), in which the upper layer has an even and uniform surface again after exceeding the T.sub.g,SMP.
[0074] The shown composite comprises transparent CLC polymeric material in the upper layer so that the composite shows a transparency in the initial mode and an opaqueness in the deformed mode. Further FIG. 4B shows the reflection bands of the composite in the different modes, in which can be seen that after deformation the reflection bands has an increased reflection across all wavelengths (deformed) in view of the reflection in the initial mode (initial) and after heating mode (heated). This increase of reflection across all wavelengths indicates the scattering of the rough surface.
[0075] FIGS. 5A-B shows a composite according to the invention, wherein in FIG. 5A optical micrographs of the composite are shown. The micrographs show the m composite [0076] in an initial mode (initial), in which the upper layer has an even and uniform surface, [0077] in a deformed mode (deformed), in which the upper layer has a rough surface, and [0078] in an after heating mode (heated), in which the upper layer has an even and uniform surface again.
[0079] The shown composite does not comprise CLC polymeric material in the upper layer so that the upper layer is transparent and the red color of the substrate layer becomes visible in the initial mode of the composite. In the deformed mode the composite exhibits an opaqueness. Further FIG. 5B shows the reflection bands of the composite in the different modes, in which can be seen that after deformation (deformed) the reflection band comprises also an peak at the same region as in the initial mode (initial), but the reflection is increased across all wavelengths, which indicates the scattering of light at the rough surface.
[0080] FIGS. 6A-B shows a composite according to the invention, wherein in FIG. 6A optical micrographs of the composite are shown. The micrographs show the composite [0081] in an initial mode (initial), in which the upper layer has an even and uniform surface, and [0082] in a deformed mode (deformed), in which the upper layer has a rough surface.
[0083] The shown composite comprises CLC polymeric material in the upper layer so that the blue/grey color of the CLC-particles becomes visible in the initial mode m of the composite. In the deformed mode the composite exhibits an opaqueness. Further FIG. 6B shows the reflection bands of the composite in the different modes, in which can be seen that after deformation (deformed) the reflection band comprises also a peak at the same region as in the initial mode (initial), but the reflection is increased across all wavelengths and the reflection band is flattened. The increase of reflection across all wavelengths indicates the scattering of light at the rough surface.
[0084] FIGS. 7A-B shows a comparative composite, wherein in FIG. 7A optical micrographs of the composite are shown. The micrographs show the composite in an initial mode (initial), in which the upper layer has an even and uniform surface of ca. 2.5 m thickness, and in compressed mode (compressed), in which the upper layer has a compressed surface. The shown composite comprises CLC polymeric material so that the composite shows in the initial mode a red color. In the compressed mode (compressed) the composite exhibits inhomogeneous color across its dimensions; including areas of a partial color change, and areas where the red color from the initial mode is dominating. In the zoomed micrograph of the compressed mode can be seen that there are spots of intense green color, which belong to particle contamination (e.g. dust). The contamination can also be a reason for the partial color change. Further, FIG. 7B shows the reflection bands of the composite in the different modes, in which can be seen that after compression (compressed) the peak of the initial mode is reduced but not disappeared. In addition, a second blue shifted peak appears (520 nm), which indicates the two appearing colors, as shown in the micrograph (compressed). But, the reflection is not increased or flattened across all wavelengths, thus, scattering is not exhibited in the composite in the compressed mode (compressed).
WORKING EXAMPLES
Example 1 (E.SUB.1.)
[0085] A composite comprising an upper layer made of CLC polymeric material (red color) and a black flexible polyethylene terephthalate (PET) substrate layer, wherein the upper layer has a thickness of approx. 2.5 m measured according to profilometry, was manufactured by depositing a CLC ink on a black flexible polyethylene terephthalate (PET) substrate layer using flexographic printing (IGT Printability Tester F.sub.1 from IGT Testing System Pte Ltd.), and subsequently cured using UV-irradiation. The glass transition temperature (T.sub.g) of the upper layer was determined by differential scanning calorimetry (DSC) to be approx. 15-30 C., with a mid-point at 18.4 C. The layer was subsequently deformed above its T.sub.g (35 C., 30 s, 6 bar) using a hot-embossing stamp (KBA-Metronic GmbH). In the experimental setup, the surface of the upper layer was in direct contact with a roughly structured rubber (R.sub.a1 m), and the upper layer was quickly cooled to room temperature upon removal of the stamp. Since room temperature falls within the T.sub.g range, the upper layer will slowly revert back to its undeformed mode under ambient conditions.
[0086] The optical micrographs of FIG. 1A and reflectivity spectra (obtained using ii Pro from X-Rite inc.) of FIG. 1B shows the composite prior to and after deformation. The upper layer exhibits a homogenous red reflection which is marked by a reflection band centered at 620 nm. Upon deformation, the upper layer appears matte and grey. Closer inspection using an optical microscope (Leica M80) (FIG. 1A, bottom), indicates that the macroscopically uniform deformed upper layer consists of numerous small domains which vary in color. Remarkably, the presence of a particle (center of the image) had no effect on the deformation. The deformation of the upper layer is further marked by a distinct change in reflectivity yielding the optical contrast. First, a decreased reflection is observed at 620 nm which indicates the loss of CLC order upon deformation. Second, a flattening of the reflection band is observed across all wavelengths which is indicative of increased (surface) scattering.
[0087] Profilometry experiments performed on the upper layer of the composite prior to and after deformation reveal the transformation of a smooth surface (Ra=0.02 m; FIG. 2A) to a roughly structured surface (Ra=0.3 m; FIG. 2B), which identifies surface roughness as a source of scattering. After heating, the surface deformation is reversed completely, and the layer returns to its initial red color.
[0088] Further, it is observed that the typical angle-dependent reflection for planar aligned CLC polymeric material is significantly reduced by the deformation-induced scattering (FIG. 3-A-C). Interestingly this effect serves as additional optical contrast between initial and deformed modes (matte grey vs. reflective with strong angular dependency).
Example 2 (E.SUB.2.)
[0089] A composite as in E.sub.1 was used except that the CLC polymeric material and the polyethylene terephthalate (PET) substrate layer are transparent.
[0090] As shown in FIGS. 4A-B, the resulting composite is transparent. According to colorimetry, the reflectivity across all visible wavelengths is <2%. After deformation (as per E.sub.1), the reflectivity increased significantly across all wavelengths, which appeared as increased scattering leading to a largely opaque upper layer. After heating, the deformed upper layer returned completely to its m initial non-scattering transparent mode. This mode of operation can be used to reveal an image, text, or background color.
Example 3
[0091] A composite comprising a transparent shape-memory polymeric material as an upper layer and a clean glass slide as a sheet of a substrate layer and a red-reflecting CLC polymeric material as a further sheet of the substrate layer was manufactured by coating a clean glass slide with a commercially available monoacrylate (DSM), crosslinker, and photoinitiator, and subsequently cured with UV-radiation. The T.sub.g,SMP of the upper layer was determined to be approximately 30 C. The glass slide containing the acrylic coating was subsequently placed on top of the red-reflecting CLC polymeric material used in E.sub.1 as an upper layer.
[0092] Prior to deformation, the reflection spectrum of the transparent acrylic coating with the background of the CLC polymeric material (FIG. 5B) is identical to the reflection spectrum of the initial non-deformed upper layer of the composite of E.sub.1 (FIG. 1B). The upper layer was subsequently deformed using identical conditions as in E.sub.1 and E.sub.2, resulting in a partially opaque appearance. Characterization by colorimetry revealed that the reflection band centered at 620 nm, stemming from the underlying sheet of CLC polymeric material, remained completely intact. This indicates that the CLC order is completely maintained, in contrast to E.sub.1. However, the reflection band is shifted evenly upward across all wavelengths, which indicates that increased surface scattering is in this case the only source of the optical contrast between initial (Ra=0.03 m) and deformed modes (Ra=0.4 m). After heating, the upper layer returned completely to a transparent non-scattering mode.
Example 4
[0093] A composite comprising an upper layer as in E.sub.3 and a glass substrate layer, wherein in the upper layer additionally CLC particles are comprised, was manufactured by coating a clean glass slide with the acrylic coating precursors from E.sub.3 and additionally, a small amount of a CLC particle mixture (according to WO 2015/120950 A1). The CLC particle mixture consisted of green- and blue-reflecting CLC polymer particles, with a T.sub.g of approximately 60-70 C. After coating, the precursors were cured with UV-radiation to result in a particulate upper layer consisting of the CLC particle mixture embedded in the acrylic binder. To prevent scattering (prior to deformation), it was ensured that the refractive index of the CLC particles and acrylic binder were matching (n1.5). The substrate layer containing the upper layer was subsequently placed on top of a black PET background, to reveal a blue tint (FIG. 6A).
[0094] Prior to deformation, the reflection spectrum of the acrylic coating with CLC particles showed two weak reflection bands, centered at 540 nm and 420 nm, corresponding to the green- and blue-reflecting CLC particles, respectively (FIG. 6B). The particulate coating was subsequently deformed using identical conditions as E.sub.1-3, resulting in a partially opaque appearance. It is important to note that the temperature at which the deformation is performed is below the T.sub.g of the CLC particles. In this example therefore, only the T.sub.g,SMP of the acrylic binder in the upper layer is important for achieving optical contrast.
[0095] Colorimetry measurements revealed that the reflection bands broadened slightly, which may be an effect of increased scattering events. At the same time, the reflection band is shifted evenly upward across all wavelengths, indicative of increased surface scattering. After heating, the upper layer returned completely to a transparent non-scattering mode. The advantage of the particulate upper layer approach is that optical contrast can be achieved using a single layer, while the thermomechanical (binder) and optical properties (CLC particles) are decoupled. It is important to note that in principle any dye can be used to generate color within the binder.
Comparative Example 1 (CE.SUB.1.)
[0096] In order to illustrate the advantage of the deformation of the surface of the upper layer of the composite, the effect of compressing the upper layer using a rigid and smooth/uniform (Ra<0.02 m) brass surface in an otherwise identical experimental setup to E.sub.1 is also investigated. In this case, a non-uniform color shift across the composite dimensions after compression is observable (FIG. 7A). Overall a gradient color shift is observed across the composite, which indicates insufficient alignment of the stamp used in the compression. However, since the experimental setup was otherwise unchanged, this finding illustrates that the requirements for achieving a uniform color shift are much more stringent and hence more difficult to achieve in practice. The reflection band obtained in the green area of the compressed sample appears bimodal (FIG. 7B); with one peak unchanged to its initial position (620 nm), and one peak significantly blue-shifted (520 nm). Scattering at non-reflective wavelengths is hardly increased, in contrast to the previous approach. Closer inspection using a microscope reveals that the bimodal reflection spectrum is caused by the existence of a green-reflecting area speckled by red-reflecting domains which have microscopic particles or print imperfections at their center. From this it is deducible that the small height differences caused by these imperfections are prohibitive for the compression of their surrounding area in this approach.
