WO2020043822A1

WO2020043822A1 - Retroreflective sheeting and article, method of manufacturing and use of a retroreflective sheeting

Info

Publication number: WO2020043822A1
Application number: PCT/EP2019/073086
Authority: WO
Inventors: Christian SECKER; Daniel Berger; Michael J. Hanrahan
Original assignee: Orafol Europe Gmbh
Priority date: 2018-08-29
Filing date: 2019-08-29
Publication date: 2020-03-05

Abstract

This disclosure relates to a retroreflective sheeting comprising a prismatic layer having microprismatic elements and a reflective layer adjacent to the prismatic layer. The layers of the sheeting are arranged such that incident light penetrates the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer. The sheeting further comprises a base layer and an intermediate layer between the base layer and the prismatic layer. The base layer comprises a base layer material, the intermediate layer comprises an intermediate layer material, and the prismatic layer comprises a prismatic layer material. The layers of the sheeting are arranged such that incident light penetrates the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer. A ratio between a thickness of the intermediate layer and a thickness of the base layer is 0.1 or less, and a ratio between the thickness of the intermediate layer and a thickness of the prismatic layer is 0.4 or less, and a ratio between a yield stress of the intermediate layer material and a yield stress of the base layer material is 0.4 or less, and a ratio between the yield stress of the intermediate layer material and a yield stress of the prismatic layer material is 0.1 or less.

Description

RETROREFLECTIVE SHEETING AND ARTICLE,

METHOD OF MANUFACTURING AND USE OF A RETROREFLECTIVE SHEETING

Technical Field

The present disclosure relates to a retroreflective sheeting comprising a base layer, a prismatic layer, and a reflective layer, a retroreflective article comprising such a sheet, a method of manufacturing such a sheet, and to the use of such a sheet.

Technical Background

A retroreflector reflects incoming light back substantively in the direction of the source. In other words, the

reflection direction for incoming light is to a large degree substantively parallel to the direction of income. An

important field of application for retroreflectors relates to traffic, e.g., to road traffic and vehicles, and in

particular to number plates and traffic signs. Known

retroreflectors include microprismatic retroreflectors and so-called glass bead retroreflectors .

Examples of cube-corner retroreflectors are disclosed in US 2013/0034682 A1. Cube-corner retroreflectors comprise a retroreflective sheeting including so-called microprismatic elements that are essentially truncated little cubes

(prisms) . According to one principle of how such corner retroreflectors work, the cube surfaces are metallized surfaces, and the cubes work on the basis of total

reflection. A problem associated with these cube-corner retroreflectors is that their retroreflective efficiency substantively depends on the angle of inclination of light, at least for some angle ranges. According to another

principle of how such corner retroreflectors work, a plurality of hermetically sealed air pockets are provided adjacent to microprismatic elements, and a reflection is effected that is associated with the difference of

diffraction indices of neighboring materials. A disadvantage of these retroreflectors is that the bonds needed to seal the air pockets decreases the overall share of a surface

available to actively contribute to reflective properties. Moreover, these retroreflectors are mechanically sensitive. They may therefore suffer or even be damaged upon being deformed and are, hence, not ideal for three-dimensional applications .

Using cube-corner retroreflectors is known to compromise the isotropic properties of a resulting retroreflective sheeting. This may in general terms be understood to be associated with the pronounced breaking of symmetry by the cube-corner prismatic elements. To increase the isotropy of

retroreflective sheetings comprising corner retroreflectors , different regions including differently oriented cube-corner retroreflectors , respectively, may be provided in a sheet.

For example, surface areas with a first type of cube-corner retroreflectors may be interrupted by stripes including a second type of cube-corner retroreflectors that are oriented in a manner perpendicular to or rotated with respect to the first type. This may increase the overall isotropic

properties of the sheeting but complicates the manufacturing process and introduces another form of anisotropy on a different scale.

Glass bead retroreflectors are known to have higher

retroreflective isotropy than corner retroreflectors . The glass bead retroreflectors comprise little spherical

elements, e.g., elements made of glass. Light is reflected on the curved surfaces of the glass elements. The spherical elements do not (at least not in such a pronounced manner) break symmetries like the corner retroreflectors and thus promote a higher isotropy of resulting retroreflective sheetings. However, the reflectivity of the spherical

elements is not as good as for microprismatic elements due to a larger degree of scattering losses.

One differentiates between glass bead sheetings of

encapsulated type and of embedded type.

Encapsulated glass bead sheetings include glass beads that are metallized on one side, in order to enhance their

reflective properties, and that are included in air pockets. Between the areas filled with air, sealing areas are

provided. These sealing areas decrease the overall share of a surface available to actively contribute to reflective properties. Moreover, such encapsulated glass bead sheetings are relatively thick and mechanically sensitive. They may suffer or even be damaged upon being deformed and are, hence, not ideal for three-dimensional applications. In addition, to produce the metallized glass beads, the glass beads must be partially embedded in a removable carrier, which is then metallized, then the metallized surface is coated with a support layer, the removable carrier sheet is peeled off, and the non-metallized exposed surfaces of the glass beads must then be protected from the impact of dirt and humidity by various further coating and/or sealing steps, which generally involve the use of solvents and other pollutants. In

addition, these steps tend to increase the manufacturing costs .

Embedded glass bead sheetings comprise glass beads that are coated with a plastic material, and said plastic material is metallized. The spherical glass elements must be embedded in a substrate, and the corresponding manufacturing processes involve several coating steps and involve the use of solvents to form layers in intermediate steps. Solvents and certain layers may have to be removed during the manufacturing process. In addition, sometimes formaldehyde and/or other pollutants are produced, and those may need to be removed as well. For all of these reasons, the manufacturing of the glass bead retroreflectors is rather cumbersome and also raises concerns in terms of unsatisfactory environment- friendliness .

Further shortcomings associated with known retroreflective sheetings comprising cube-corner retroreflectors are

associated with their susceptibility for being damaged, especially when deformations of the sheetings are necessary. Known sheetings are particularly prone to be damaged upon being deformed three-dimensionally or upon being applied to an external object followed by three-dimensional deformation.

There is, hence, a need for a retroreflective sheeting and a corresponding manufacturing method suited to address at least one and preferably all of the above-mentioned shortcomings.

In particular, it would be desirable to provide a sheeting that combines a good isotropy in its optical properties with good retroreflectivity and which can be prepared in a cost effective and environment-friendly way. It would also be desirable to provide a sheeting with improved deformation properties .

Summary

Aspects of the above-mentioned objects are achieved by a retroreflective sheeting comprising a prismatic layer having microprismatic elements, a reflective layer adjacent to the prismatic layer, a base layer, and an intermediate layer between the base layer and the prismatic layer.

The base layer comprises a base layer material, the intermediate layer comprises an intermediate layer material, and the prismatic layer comprises a prismatic layer material. Each of the three materials may be a homogeneous material or it may be a compound of two or more components. For example, the respective material may be a certain substance including impurities, or it may be a mix of substances. According to some aspects, the base layer consists of a base layer material, the intermediate layer consists of an intermediate layer material, and the prismatic layer consists of a prismatic layer material.

The layers of the sheeting are arranged such that incident light penetrates the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer.

A ratio between a thickness of the intermediate layer and a thickness of the base layer is 0.1 or less, and a ratio between the thickness of the intermediate layer and a thickness of the prismatic layer is 0.4 or less. In other words, the intermediate layer has a very small thickness as compared to the thicknesses of the base layer and the prismatic layer, respectively. This means that the relative increase of the total thickness of the sheeting, as opposed to the case in which the intermediate layer is omitted, is very small.

A ratio between a yield stress of the intermediate layer material and a yield stress of the base layer material is 0.25 or less, and a ratio between the yield stress of the intermediate layer material and a yield stress of the prismatic layer material is 0.1 or less. The yield stress of the intermediate layer is, in other words, very low as compared relatively to the yield stress of the base layer and the prismatic layer, respectively.

It turns out that the interposing of the intermediate layer between the base layer and the prismatic layer may have a tremendous impact on the overall properties of the sheeting, despite the very small thickness of the intermediate layer. In particular, the yield stress of the sheeting may be significantly lowered in comparison to the case in which the intermediate layer is omitted. The yield stress of the sheeting, in particular, may be lowered by about 15% to 30% by the presence of the intermediate layer.

The pronounced influence on the overall properties may be considered surprising in view of the fact that the intermediate layer is relatively thin compared to the base layer and the prismatic layer, respectively. Moreover, it is remarkable that interposing the intermediate layer which has a yield stress which differs even more from the yield stress of the prismatic layer than the differences between the yield stresses of the base layer and the prismatic layer, has such a strong effect on the yield stress of the entire sheeting. Instead of having a mediating layer between base layer and prismatic layer (mediating layer in the sense of having properties that are in-between the properties of the base layer and the prismatic layer, respectively) , the intermediate layer is interposed which might be considered "even more extreme" than the base layer in terms of its properties and the contrast formed to the properties of the prismatic layer.

The sheeting in accordance with this aspect may have superior deformation properties, both with regard to hot deformations as well as to cold deformations. The sheeting is thus particularly suited to be deformed three-dimensionally and applied to an external object (e.g., with a three-dimensional contour), or to be applied to an external object (e.g., with a three-dimensional contour) and to then be deformed three- dimensionally together with the external object. The suitability for cold deformations is especially high due to the much lower yield stress of the sheeting (as compared to an analogous sheeting in which the intermediate layer is omitted) . This makes it remarkably suited for efficient and easy application to a three-dimensional external object and subsequent deformation, or three-dimensional deformation and subsequent application to an external object. The "yield stress" as used in this application is to be understood as being measured in accordance with the provisions of the norm DIN EN ISO 527-1. When referring to numerical values in this application, reference is made to measurements under this norm using a machine of type "zwickiLine Z0.5 TH Materialprufmaschine mit Xforce HP Kraftaufnehmer, Nennkraft 500N". This is a high precision measurement apparatus with a connection bolt diameter of 8 mm, with a precision class 1 according to ISO 7500-1 starting from IN and with a precision class 0.5 according to ISO 7500- 1 starting from 5N, with a particularly good linearity and typical relative deviations < 0.25% starting from 2N and <1% starting from 0.5N, and with a calibration means in accordance with ISO 7500-1. All measurements leading up to numerical values (and ratios between values) quoted in this application have been performed under normal climate (as defined by the norm DIN EN ISO 139 or DIN EN ISO 291) and in a statistically relevant manner.

The term "microprismatic elements" is in this context used to refer to prismatic elements that are small in the sense that the prismatic elements have a characteristic dimensionality (e.g., height, edge lengths, etc.) lying in the order of magnitude of micrometers.

The microprismatic elements may be cube corner elements (also sometimes referred to as corner retroreflectors .

Keeping the heights of the microprismatic elements very low (and the thickness low of the prismatic layer) may further promote a better flexibility of the sheeting so that (hot or cold) deformations of the sheeting, be it in standalone form or as a component of a product, may be carried out

conveniently and accurately. This may make the sheeting even more suitable for three-dimensional applications, e.g., for being provided on a surface of a product with varying height, i.e., a surface with recesses and/or protrusions. An example for the latter is a German vehicle number plate on which the characters are embossed and stand out from the plane of the number plate. Such three-dimensional supports or deformations pose particular challenges for sheetings applied thereon, and the inventive very flexible sheetings are particularly well suited to master such challenges.

The retroreflective sheeting according to the present

invention can also be manufactured in a more environment- friendly way than at least some of the sheetings known as prior art. In particular, depending on the aspects in

question, the use of solvents to form layers in intermediate steps, and the removal thereof, may not be necessary, so that less waste is generated and the manufacturing may become more cost-efficient and environment-friendly, using solvent-free UV technology. This is remarkable because UV cured materials are normally too brittle for three-dimensional applications of retroreflective sheetings.

According to some aspects, the ratio between the thickness of the intermediate layer and the thickness of the prismatic layer is 0.25 or less. Having an even thinner intermediate layer keeps the overall thickness of the sheeting even lower. Despite this extremely thin intermediate layer, the mentioned properties of the overall sheeting may be significantly improved. In particular, the yield stress of the sheeting may be lowered by about 15 % to 30 % (in practice, values between about 20% and 25% are usually encountered) as compared to the comparative sheeting without the intermediate layer. This implies that a superior hot deformability and, even more so, a superior cold deformability is provided.

According to some aspects, the ratio between the yield stress of the intermediate layer material and the yield stress of the base layer material is 0.3 or less, or even 0.25 or less or 0.20 or less. In case the base layer comprises or consists of casted PVC, a ratio of 0.25 or even 0.20 or less may especially promote the good deformation properties of the sheeting, and in case the base layer comprises or consists of casted polyurethane, a ratio of 0.15 or even 0.10 or less may especially promote the advantageous properties of the sheeting. The increasingly lower ratios may to an increasing degree promote the desired good deformation properties.

According to some aspects, the ratio between the yield stress of the intermediate layer material and the yield stress of the prismatic layer material is 0.07 or less, or even 0.06 or less or 0.05 or less. The increasingly lower ratios may to an increasing degree promote the desired good deformation properties .

According to some aspects, the thickness of the intermediate layer is less than 20 ym, optionally in a range of 1 ym to 15 ym, or in a range of 3 ym to 10 ym. Optionally, the range may be 5 ym to 8 ym. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting.

According to some aspects, the yield stress of the intermediate layer material is in a range of 1 N/mm^ to 2 N/mm^. The range may be 1.2 N/mm^ to 1.8 N/mm^, 1.3 N/mm^ to 1.7 N/mm^, or 1.4 N/mm^ to 1.6 N/mm^. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting.

According to some aspects, the yield stress of the base layer material is in a range of 4

to 18 N/mm^ ^ or 7 N/mm2 to 10 N/mm2 or 13.5 N/mm2 to 16.5 N/mm2. Especially when the base layer comprises or consists of casted PVC, the yield stress of the base layer material may be in a range of

or 7.5 N/mm^ to 9.5 N/mm^. Especially when the base layer comprises or consists of casted polyurethane, the yield stress of the base layer material may be in a range of 12 N/mm^ p₀ ]_ g N/mm2 , or 13 N/mm2 to 17 N/mm2 , or 14 N/mm2 to 16 N/mm^. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting .

According to some aspects, the yield stress of the prismatic

N/mm2. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting .

According to some aspects, a ratio between a Young's modulus of the intermediate layer material and a Young's modulus of the base layer material is 0.2 or smaller, or 0.15 or smaller. Instead thereof or in addition thereto, a ratio between the Young's modulus of the intermediate layer material and a Young's modulus of the prismatic layer material is, according to some aspects, 0.05 or smaller, or 0.04 or smaller, or 0.025 or smaller. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting.

"Young's modulus", as used in this application, is measured in accordance with the provisions of the norm DIN EN ISO 527- 1. When referring to numerical values in this application, reference is made to measurements under this norm using a machine of type "zwickiLine Z0.5 TH Materialprufmaschine mit Xforce HP Kraftaufnehmer, Nennkraft 500N". All measurements are performed under normal climate (as defined by the norm DIN EN ISO 139 or DIN EN ISO 291) and in a statistically relevant manner.

The Young's modulus of the intermediate layer material is, according to some aspects, in a range of 15 to 70 MPa, or a range of 20 to 70 Mpa, or a range of 22 to 60 Mpa, or a range of 25 to 50 MPa. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting.

The Young's modulus of the base layer material is, according to some aspects, in a range of 80 to 800 MPa, or a range of 90 to 700 MPa, or a range of 105 to 600 MPa, or a range of 115 to 570 MPa, or a range of 125 to 550 MPa. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting .

The Young's modulus of the prismatic layer material is, according to some aspects, in a range of 1500 to 4000 MPa, or a range of 1700 to 3800 MPa, or a range of 1850 to 3600 MPa, or a range of 2000 to 3400 MPa, or a range of 2200 to 3200 MPa. The increasingly narrower ranges may to an increasing degree promote the desired good deformation properties of the sheeting .

According to some aspects, a ratio between an elongation at break of the intermediate layer material and an elongation at break of the base layer material is 1.4 or larger, optionally 1.6 or larger, 1.7 or larger, 1.8 or larger, or even 1.9 or larger. The increasingly narrower ranges may to an increasing degree promote the quality of the sheeting as breakage is increasingly prevented to a higher degree of certainty. This may further promote the desired suitability for hot and, even more so, cold deformations, and for application on external objections and preceding or subsequent three-dimensional shape deformations.

"Elongation at break", as used in this application, is measured in accordance with the provisions of the norm DIN EN ISO 527-1. When referring to numerical values in this application, reference is made to measurements under this norm using a machine of type "zwickiLine Z0.5 TH Materialprufmaschine mit Xforce HP Kraftaufnehmer, Nennkraft 500N". All measurements are performed under normal climate (as defined by the norm DIN EN ISO 139 or DIN EN ISO 291) and in a statistically relevant manner.

According to some aspects, a ratio between an elongation at break of the intermediate layer material and an elongation at break of the prismatic base layer material is 100 or larger, optionally 130 or larger, 160 or larger, 180 or larger, or even 200 or larger. The increasingly narrower ranges may to an increasing degree promote the quality of the sheeting as breakage is increasingly prevented to a higher degree of certainty. This may further promote the desired suitability for hot and, even more so, cold deformations, and for application on external objections and preceding or subsequent three-dimensional shape deformations.

The elongation at break of the intermediate layer material is, according to some aspects, in a range of 250% to 700%, optionally in a range of 300% to 600%, 330% to 570%, 360% to 540%, or even 370% to 530%. The increasingly narrower ranges may to an increasing degree promote the quality of the sheeting as breakage is increasingly prevented to a higher degree of certainty. This may further promote the desired suitability for hot and, even more so, cold deformations, and for application on external objections and preceding or subsequent three-dimensional shape deformations.

The elongation at break of the base layer material is, according to some aspects, in a range of 70% to 400%, optionally in a range of 80% to 350%, 80% to 180% or 250% to 350%. When the base layer material comprises or consists of casted PVC, the elongation at break may be in a range of 200% to 400%, optionally in a range of 230% to 370%, or even 250% to 350%. When the base layer material comprises or consists of casted polyurethane, the elongation at break may be in a range of 70% to 220%, optionally in a range of 80% to 200%, or even 80% to 180%. The increasingly narrower ranges may to an increasing degree promote the quality of the sheeting as breakage is increasingly prevented to a higher degree of certainty. This may further promote the desired suitability for hot and, even more so, cold deformations, and for application on external objections and preceding or subsequent three-dimensional shape deformations.

The elongation at break of the prismatic layer material is, according to some aspects, 3% or less, optionally 2.7% or less, 2.5% or less, 2.3% or less, or even 2% or less.

A ratio between a tensile strength of the intermediate layer material and a tensile strength of the base layer material is, according to some aspects, 0.4 or smaller, 0.3 or smaller, 0.2 or smaller, 0.18 or smaller, 0.15 or smaller, 0.12 or smaller, or even 0.1 or smaller. This may to an increasing degree, with narrower ranges, promote more convenience for deformation works to be carried out with the sheeting .

"Tensile strength", as used in this application, is measured in accordance with the provisions of the norm DIN EN ISO 527- 1. When referring to numerical values in this application, reference is made to measurements under this norm using a machine of type "zwickiLine Z0.5 TH Materialprufmaschine mit Xforce HP Kraftaufnehmer, Nennkraft 500N". All measurements are performed under normal climate (as defined by the norm DIN EN ISO 139 or DIN EN ISO 291) and in a statistically relevant manner.

A ratio between the tensile strength of the intermediate layer material and a tensile strength of the prismatic layer material is, according to some aspects, 0.4 or smaller, 0.3 or smaller, 0.2 or smaller, 0.18 or smaller, or even 0.15 or smaller. This may to an increasing degree, with narrower ranges, promote more convenience for deformation works to be carried out with the sheeting. The tensile strength of the intermediate layer material is, according to some aspects, in a range of 1

optionally 3

or even 5 N/mm^ to 8 N/mm^. This may to an increasing degree, with narrower ranges, promote more convenience for deformation works to be carried out with the sheeting.

The tensile strength of the base layer material is, according to some aspects, in a range of 15

optionally 18

or even 21 N/mm^ to 28 N/mm^. This may to an increasing degree, with narrower ranges, promote more convenience for deformation works to be carried out with the sheeting.

The tensile strength of the prismatic layer material is, according to some aspects, in a range of 20 N/mm^ to 50 N/mm^, optionally 24 N/mm^ to 46 N/mm^, 27 N/mm^ to 43 N/mm^, or even 30 N/mm^ to 40 N/mm^. This may to an increasing degree, with narrower ranges, promote more convenience for deformation works to be carried out with the sheeting.

The layers of the sheeting are, according to some aspects, arranged such that incident light penetrates the base layer, the intermediate layer, the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer. This may even further promote the good hot and, even more so, cold deformation properties of the sheeting.

According to some aspects, the microprismatic elements have heights in a range of 15 pm to 40 pm, optionally 22 pm to 38 pm, 23 pm to 36 pm, 23 pm to 34 pm, or even 23 pm to 32 pm.

According to some aspects, the reflective layer is a metallization on at least parts of the prismatic layer. The metallization may be provided on the entire prismatic layer, or it may, for example, be limited to the microprismatic elements .

According to some aspects, the afore-listed optional ranges and values of the tensile strength and/or the elongation of break for base layer, intermediate layer, and prismatic layer, may be combined, especially with increasingly narrow ranges. In other words, all of the former ranges may be combined with each other.

For example, according to some specific aspects, the tensile strength of the intermediate layer material may be in a range of 5 to 6 N/mm^ and the elongation of break of the intermediate layer material may be in a range of 200% to 240%, while the tensile strength of the base layer material may be in a range of 22 to 26 N/mm^ and the elongation of break of the base layer material may be in a range of 200% to 240%, and the tensile strength of the prismatic layer material may be in a range of 30 to 40 N/mm^ and the elongation of break of the base layer material may be below 2%. Taking a thickness of the base layer of about 70 to 110 ym, of the intermediate layer of about 5-8 ym, and of the prismatic layer of about 23 to 36 ym, it turns out that a combination of such a base layer with an intermediate layer provides a composite with a tensile strength in the range of 22 to 26 N/mm^ and an elongation at break of 200% to 240%. Upon additionally adding the prismatic layer, it turns out that the composite (the entire sheeting) has a tensile strength in the range of 10 to 12 N/mm^ (a surprisingly low value in view of the values associated with the individual layers) and an elongation at break of 130% to 170% (a surprisingly high value in view of the values associated with the individual layers) .

Examples of materials of which the base layer, the intermediate layer, and the prismatic layer may be formed follow. These may be freely combined. The base layer may comprise or consist of casted PVC, PU, PE, PP, ethylene vinyl acetate copolymer, alkyd resin systems, and thermoplastic elastomers. These materials are particularly suited for reaching the above-indicated ranges for the tensile strength and the elongation at break as well as for satisfying the indicated thickness range. The intermediate layer may comprise or consist of one or several materials selected from the group consisting of: polyurethane, PVC, or PVC copolymer based coating formulations, and reactive acrylate. These materials are particularly suited for reaching the above- indicated ranges for the tensile strength and the elongation at break as well as for satisfying the indicated thickness range. The prismatic layer may comprise or consist of one or several materials selected from the group consisting of: thermally curable lacquer or radiation curable lacquer such as epoxy resin, polyurethane acrylate, PMMA, PC, polyacrylate, and polyurethane. These materials are particularly suited for reaching the above-indicated ranges for the tensile strength and the elongation at break as well as for satisfying the indicated thickness range. In addition, these materials are particularly suited for allowing the formation of the microprismatic elements by embossing, engraving, or casting.

Particular aspects (satisfying the above-indicated ranges for the respective tensile strengths of the components, the respective elongations at break of the components, and the respective thicknesses of the components, especially towards the respective increasingly narrower ranges) comprise a base layer made of casted PVC (e.g., H62-H72, parts per 100 resin) or casted polyurethane, an intermediate layer made of polyurethane, and a prismatic layer made of isobornyl- /urethane-di-acrylate or vinylcarbonate /penta- erytitrolacrylate /urethane di-acreylate .

As the base layer material, casted PVC may be particularly preferable. Alternatively, casted polyurethane may be

particularly preferable. According to some aspects, the sum of the thicknesses of the base layer, the intermediate layer, and the prismatic layer is in a range of 50 pm to 200 pm, optionally 50 pm to 150 pm, or even 70 pm to 145 pm. This total thickness may even further promote the good three-dimensional deformation properties .

According to some aspects, a thickness of the sheeting is in a range of 50 pm to 500 pm. This thickness may in particular include an adhesive layer with a thickness in a range of 80 pm to 160 pm and/or a a liner with a thickness in a range of 80 pm to 160 pm.

Aspects of the above-mentioned objects are achieved by a retroreflective sheeting comprising a prismatic layer having microprismatic elements and a reflective layer adjacent to the prismatic layer. The layers of the sheeting are arranged such that incident light penetrates the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer. Moreover, the microprismatic elements have heights equal to or smaller than 34 pm. This may further enhance the three-dimensional deformation ability of the retroreflective sheeting.

All of the features relating to the aspects of a retroreflective sheeting provided above may be analogously applicable to this aspect of a retroreflective sheeting. In other words, all of the optional features mentioned above are also optional features of the retroreflective sheeting according to this aspect, and vice versa.

The term "microprismatic elements" is in this context used to refer to prismatic elements that are small in the sense that the prismatic elements have a characteristic dimensionality (e.g., height, edge lengths, etc.) lying in the order of magnitude of micrometers. The microprismatic elements may be cube corner elements (also sometimes referred to as corner retroreflectors .

Their small heights may work to ensure a higher

retroreflective isotropy of the retroreflective sheeting, especially with respect to different directions of incidence (and, hence, due to the retroreflectivity, of reflection) . In other words, the differences of reflective properties in function of the angle of incoming light may be lowered or even abolished over a broad range of angles. In particular, the retroreflectivity may be improved for flat incoming and reflection angles. For this reason, it may no longer be necessary to introduce different regions with different microprismatic elements in the sheeting, e.g., in the form of stripes including a different type of elements in order to promote higher overall retroreflective isotropy.

Specifically, the height of 34 pm or less promotes a wide angled diffraction of light in the retroreflection . This may in turn promote a good visibility for a larger range of angles of incidence and may increase the safety of a device provided with the retroreflective sheeting such as a road sign or a vehicle number plate.

The symmetry breaking effect of the prismatic elements may be understood to take place on a smaller scale than for larger prismatic elements so that the resolution of the

retroreflective properties may be understood to be increased with respect to the prior art. Even although the reflectivity may seemingly be improved by turning to prismatic elements with larger heights, a better compromise between good

reflectivity, as such, and isotropy in terms of

retroreflectivity may be achieved by retroreflective

sheetings in accordance with the present disclosure.

The small heights of 34 pm or less may also promote a better flexibility of the sheeting so that (hot or cold) deformations of the sheeting, be it in standalone form or as a component of a product, may be carried out conveniently and accurately. This may make the sheeting particularly suitable for three-dimensional applications, e.g., for being provided on a surface of a product with varying height, i.e., a surface with recesses and/or protrusions. An example for the latter is a German vehicle number plate on which the

characters are embossed and stand out from the plane of the number plate. Such three-dimensional supports or deformations pose particular challenges for sheetings applied thereon, and the inventive very flexible sheetings are particularly well suited to master such challenges.

The retroreflective sheeting according to the present

question, the use of solvents to form layers in intermediate steps, and the removal thereof, may not be necessary, so that less waste is generated and the manufacturing may become more cost-efficient and environment-friendly, using solvent-free UV technology. This is remarkable because UV cured materials are normally too brittle for applications of retroreflective sheetings .

According to some aspects, at least a part of the

microprismatic elements has been formed by embossing, engraving, or casting. These techniques may be carried out while avoiding or lowering the quantities of use of polluting chemicals so that environment-friendliness may be further promoted .

The prismatic layer may comprise or consist of one or several materials selected from the following list: thermally curable lacquer or radiation curable lacquer such as epoxy resin, polyurethane acrylate, polymethylmethacrylate (PMMA) , polycarbonate (PC), polyacrylate, and polyurethane. These materials may be particularly suited for a precise formation of the sheeting with precision down to the desired micrometer scale .

At least 90% of the microprismatic elements may have heights equal to or smaller than 34 pm. According to some aspects, this may even be the case for 95% or even for 98% (or 100%) of the microprismatic elements. The mentioned isotropy and other advantages may thereby be promoted to a larger extent and/or more consistently throughout a surface extension direction of the sheeting.

According to some aspects, at least 90% (or 95%, 98%, or even 100%) of the microprismatic elements may have heights equal to or smaller than 32 pm, and according to some aspects, they may have heights equal to or smaller than 30 pm,

respectively. In these cases, the isotropy of the

retroreflectivity and the wide-angled diffraction may be particularly promoted, making the respective sheeting

particularly suitable, for example, for three-dimensional applications .

According to some aspects, the microprismatic elements may have heights in a range of 15 to 34 pm, a range of 19 to 34 pm, 22 to 31 pm, 23 to 29 pm, or 24.5 to 26.5 pm. These ranges may, to an increasing degree, respectively promote the isotropy of the retroreflectivity and the wide-angled diffraction may be particularly promoted, making the respective sheetings satisfying the respective height ranges particularly suitable, for example, for three-dimensional applications .

According to some aspects, at least 90%, optionally at least 95%, or even all of the microprismatic elements have the same heights. The isotropy of the retroreflectivity and the wide angled diffraction may be particularly promoted, making the respective sheeting particularly suitable, for example, for three-dimensional applications.

The disclosure encompasses aspects of the sheeting, comprising different types of microprismatic elements that are distributed with the same distribution ratio over at least 90%, and in the case of some aspects 95% or 98%, of the prismatic layer. The higher the percentage of the prismatic layer over which the same distribution ratio is achieved, the higher the homogeneity of the sheeting, and the isotropy of the retroreflective properties may thus be further promoted, and the manufacturing costs may be decreased.

According to some aspects, at least 90%, and in the case of some aspects 95% or 98%, or all of the microprismatic elements are identical. This may further increase the homogeneity of the sheeting, and the isotropy of the retroreflective properties may thus be further promoted, and the manufacturing costs may be decreased.

At least one of the microprismatic elements of aspects of the sheeting may be a cube-corner element with three side surfaces meeting at an apex. According to some aspects, the height of the cube-corner element is defined to be a distance between the apex and a surface defined to contain at least three furthermost points, said furthermost points comprising one or several points, at least one on each side surface, that are furthermost from the apex amongst all points on the respective side surface. According to some aspects, the height of the cube-corner element is defined as a distance between the apex and a surface that is defined to contain at least one furthermost point on a side surface of the cube- corner element that is furthest from the apex amongst all points on the side surfaces of said cube-corner element, and analogous furthermost points of other cube-corner elements which are identical to said cube-corner element.

Some aspects of the sheeting may further comprise a base layer. The layers of these aspects may be arranged such that incident light penetrates the base layer, then the prismatic layer, and is reflected at the interface of the prismatic layer and the reflective layer of the sheeting. Alternatively, the base layer and the prismatic layer are provided on opposite sides of the reflective layer, respectively .

The base layer may stabilize the sheeting. Alternatively or in addition thereto, the base layer may promote the flexibility of the sheeting and/or provide a protection to the optical layer. The base layer may or may not be provided as a top layer (i.e., a surface layer), for example, as a form of protective layer. It may be partially or fully opaque, transparent, and/or colored or it may be printed on.

The base layer may comprise or consist of one or several materials selected from the following list: casted PVC, calendared PVC, casted TPU, extruded TPU, PU, PE, PP, PE-PAA copolymer, PET, PMMA, PC, ethylene vinyl acetate copolymer, alkyd resin systems, PVA, and thermoplastic elastomers.

According to some aspects, the sheeting may comprise an intermediate layer between the base layer and the prismatic layer. The intermediate layer may provide an optical damping effect, may influence the color (both the location of color, the luminance factor and/or the daytime visibility/luminance). It may, in addition thereto or alternatively, be used to add security or quality seals and/or one or several sensors.

The intermediate layer may be manufactured by flexography, digital printing, intaglio, etching, screen printing, and/or gravure printing.

The intermediate layer may comprise a printing color on the basis of water and/or solvent, optionally being thermally curable and/or curable by radiation.

The intermediate layer may comprise one or several materials selected from the group consisting of: acrylate polymer, polyurethane or PVC based colors, reactive acrylate, methacrylate, vinyl ether, and a material comprising epoxide.

The reflective layer may be a metal film applied to the prismatic layer. This may ensure a difference in refractive index between reflective layer and prismatic layer suited to provide a good reflectivity at the interface there-between . According to some aspects, the reflective layer may comprise or consist of one or several metals selected from the following list: aluminum, silver, and gold and/or other metals .

Some aspects of the sheeting may comprise a cover layer. The cover layer may provide protection and/or provide a modification to the surface in terms of, for example, adherence properties, and/or may serve as a possibility to provide color subsequently during a manufacturing process.

The layers of the sheeting may be arranged such that incident light first penetrates the cover layer and then other layers of the sheeting.

The cover layer may comprise or consist of one or several materials selected from the following list: casted PVC, calendared PVC, casted TPU, extruded TPU, PU; PE, PP, PE-PAA copolymer, PET, PMMA, PC, EVAC ethylene vinylacetate copolymer, alkyd resin, PVA, and thermoplastic elastomers.

According to some aspects, the sheeting may comprise an adhesive layer for adhering the sheeting to an external object, the adhesive layer comprising an adhesive configured to be activated chemically, by pressure, and/or heat. The adhesive layer may be particularly useful for adhering the sheeting, e.g., to a plastic material, and/or to a material containing metal and/or an inorganic (e.g., ceramic) material .

The adhesive layer may be provided with a liner on the interior side. This may make the application of the sheeting to an external object particularly convenient.

The adhesive of the adhesive layer may comprise or consist of one or several materials selected from the following list: acrylate, polyurethane, epoxy based substances, and vinyl based substances.

The adhesive layer may be at least partially transparent and/or at least partially pigmented.

This disclosure also relates to a retroreflective article comprising the retroreflective sheeting in accordance with one or any combination of two or more of the previously described aspects of the sheeting. The retroreflective article may, for example, be a vehicle number plate, a traffic sign, a warning mark on a vehicle, or a container, etc. For these articles, aspects in accordance with the present disclosure may be particularly suitable. A reason therefore may lie in the particularly good suitability for three-dimensional applications. For example, the flexibility of the sheeting may be particularly good, and the sheeting may therefore be easily and conveniently deformed (by hot and/or cold deformation, depending on the desired application) . For example, the sheeting can be applied to a material to form a plate, and characters may then be embossed on the plate to produce a vehicle number plate.

The disclosure also encompasses the use of the retroreflective sheeting according to any one or any combination of two or more of the previously described aspects of a sheeting for application to an external object such as a number plate or a traffic sign.

The use may include the step of hot or cold deformation of the sheeting before application to the external object, or, after application, of the step hot or cold deformation of the external object having the sheeting applied thereto.

The use may involve that the surface of the external object has a three-dimensional structure.

Additional advantages and features of the present disclosure, that can be realized on their own or in combination with one or several features discussed above, insofar as the features do not contradict each other, will become apparent from the following description of particular aspects.

Brief Description of the Drawings

For a better understanding of the present disclosure and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Fig. 1 r s

sectional view of an aspect of retroreflective sheeting in accordance with the present disclosure;

Fig . 2 r s

Fig . 3 r s

sectional view of an aspect of retroreflective sheeting in accordance with the present disclosure; Fig. 4 is a sectional view of an aspect of a retroreflective article (a vehicle number plate) in accordance with the present disclosure;

Fig. 5 is a sectional view of an aspect of a retroreflective article (a vehicle number plate) in accordance with the present disclosure;

Fig. 1 depicts a sectional view of an aspect of a

retroreflective sheeting 1 in accordance with the present disclosure .

The arrow P in Fig. 1 represents a direction of incidence of light. In other words, the sheeting 1 is intended to be used such that the lower side in Fig. 1 is the front side, i.e., the side on which light is incident and gets reflected, and the upper side is the back side.

The sheeting 1 comprises a prismatic layer 2 with

microprismatic elements 20. In the case of this aspect, the microprismatic layer 2 comprises UV-cured resins. The

disclosure is, however, not limited thereto.

The sheeting 1 also comprises a reflective layer 3 that is located adjacent to the prismatic layer 2. In the case of the aspect of Fig. 1, the reflective layer 3 is a metal film that is applied to the prismatic layer 2. It comprises aluminum in this case. However, the disclosure is not limited thereto.

As the direction of the arrow P indicates, the layers 2, 3 of the sheeting 1 are arranged such that incident light

penetrates the prismatic layer 2 first, and is then reflected at the interface between the prismatic layer 2 and the reflective layer. The microprismatic elements 20 are cube corner elements with heights smaller than 34 ym. In the case of this aspect, the heights are 26 ym. In this case, the height h is defined as a distance between the apex of a cube corner element 20 and the surface comprising, for each of the elements 20, the

furthermost points from the respective apex. The disclosure is, however, not limited thereto. The cube corner element with these small heights, together with the adjacent

reflective layer 3, provide good reflectivity, and the isotropy of the retroreflective properties of the sheeting 1 is very good. In particular, the small heights imply that a wide-angled diffraction takes place. Specifically, the sheeting 1 is particularly good in terms of isotropy of the retroreflection for a wide range of angles of incidence (and reflection) . The retroreflection is also good for small angles of incidence (and reflection) .

In the case of Fig. 1, the microprismatic elements 20 have been formed by casting. However, in the case of other

aspects, they may be formed differently, e.g., by embossing or engraving, etc. The casting allows for a very good

resolution in the sense of a precise forming down to the order of magnitude of micrometers.

All of the microprismatic elements 20 are identical (same shape and height h, etc.) . In the case of other aspects, there may be two or more types of microprismatic elements 20 provided. Moreover, in the case of this aspect, they are homogeneously spread over the entire sheeting 1. In the case of other aspects, they may be spread over a part of the sheeting 1 only.

Fig. 2 is a sectional view of an aspect of a retroreflective sheeting 1 in accordance with the present disclosure. Also this sheeting 1 comprises a prismatic layer 2 with

microprismatic element 20 and a reflective layer 3 in the form of a metal film on the microprismatic elements 20. The microprismatic elements 20 are cube corner elements with heights h smaller than 34 ym. In the case of this aspect, the heights h are 30 ym. Other aspects may, e.g., have heights of 34 ym (or any other lower value of choice) .

The arrow P in Fig. 2 shows the direction of incidence of light. The small arrows on the left-hand side of Fig. 2 illustrate how the light reaches a microprismatic element 20 and are reflected back in the direction of incidence

(retroreflectivity) .

Fig. 2 depicts a sectional view of an aspect of a

retroreflective sheeting 1 in accordance with the present disclosure .

The prismatic layer 2 and the reflective layer 3 in the form of a metallization on the prismatic layer 2 are analogous as in the case of Fig. 1.

The sheeting 1 of Fig. 2, however, further comprises a base layer 8 and a very thin intermediate layer between the base layer 8 and the prismatic layer 2.

microprismatic element 20 and a reflective layer 3 in the form of a metal film on the microprismatic elements 20.

The microprismatic elements 20 are cube corner elements with heights h smaller than 34 ym. The small thickness of the prismatic layer and the low heights of the microprismatic elements 20 promotes good hot or, even more so, cold

deformability of the sheeting 1. In the present example, the heights are about 28 ym. The base layer 8 of the sheeting of Fig. 2 is made of casted PVC . However, an alternative (which is otherwise the same) comprises a base layer 8 made of casted polyurethane. The thickness of the base layer 8 is, in the case of this

example, 90 ym. However, alternatives with thicknesses in the range of 70 ym to 110 ym behave equivalently. The only difference is that the properties such as the yield stress, the Young's modulus, and the elongation at break are to be scaled accordingly (they behave proportionally in the

sketched ranges) . The thickness of the intermediate layer 7 is, in the case of this example, 6.5 ym. However,

alternatives with thicknesses in the range of 5 ym to 8 ym behave equivalently. The thickness of the prismatic e layer 2 is, in the case of this example, 30 ym. However, alternatives with thicknesses in the range of 23 ym to 36 ym behave equivalently. The tensile strength of the sheeting 1 of Fig. 2, as a whole, is in a range of 10 to 12 N/mm^. The

elongation at break of the sheeting 1 of Fig. 2, as a whole, is in a range of 130% to 170%. The Young's modulus of the sheeting 1 of Fig. 2, as a whole, is about 430 MPa. The yield stress of the sheeting 1 of Fig. 2, as a whole, is about 6.4 N/mm^ _

The sheeting 1 of Fig. 3 further comprises an adhesive layer 4 for adhering the sheeting 1 to an external object, for example, for manufacturing a retroreflective article of interest (e.g., a road sign) . The adhesive layer 4 comprises an adhesive that can be activated by applying pressure. Other aspects may comprise one or several other adhesives, amongst which, e.g., an adhesive that can be activated by heat and/or chemically. The adhesive layer 4 of Fig. 3 comprises

acrylate. However, the disclosure is not limited thereto. The adhesive layer 4 is transparent. Alternatively, it could be at least in some regions or throughout provided with

pigments . The sheeting 1 also comprises a liner 40 on the interior side of the adhesive layer 4 that can be easily removed before sticking the sheeting 1 onto an external object.

The sheeting 1 also comprises a printing 5 provided thereon. In the case of this aspect, the printing 5 has been formed by gravure roll printing. Due to the presence of said printing, light no longer reaches the reflective layer 3 at the

respective locations covered by the printing. The light does therefore at these positions not get reflected at the

reflective layer 3 but passes and thus makes the marked parts with the printing 5 visible. Consequently, one can see the markings appearing as a contrast to the parts where light is reflected .

A casting support layer 7 is stuck to the prismatic layer 2 via another adhesive layer 6. Adjacent to the casting support layer 7, a base layer 8 is provided. The base layer 8 of this aspect comprises casted PVC and PET. However, the disclosure is not limited thereto.

As may be taken from Fig. 3, the layers of the sheeting 1 are arranged such that incident light penetrates the base layer 8, the casting support layer 7, the another adhesive layer 6, and, at those parts where no printing 5 (e.g., a gravure roll printing) is provided that blocks the light's way, the prismatic layer 2, where it is then reflected at the

interface between prismatic layer 2 and the reflective layer 3 in the form of a metal (in this case: aluminum) film within the microprismatic elements 20.

This disclosure also relates to the use of the sheeting 1 in accordance with any of the described aspects for application to an external objection such as a number plate or traffic sign. The disclosure also encompasses retroreflective

articles such as number plates and traffic signs. Fig. 4 depicts a section through a number plate 10 in

accordance with the present disclosure. The number plate 10 comprises a prismatic layer 2 with microprismatic element 20 with heights h of 26 ym (the disclosure is not limited thereto), a reflective layer 3, an adhesive layer 4, and a liner 40. These components are similar to those described for the sheeting 1 of Fig. 1, and a repetition of the description thereof is therefore omitted.

The arrow P in Fig. 4 shows the direction of incidence of light. The small arrows on the left-hand side of Fig. 4 illustrate how the light reaches a microprismatic element 20 and are reflected back in the direction of incidence

(retroreflectivity) .

The number plate 10 is provided with two types of printing, a first printing 5 and a second printing 50, both of them in this case manufactured by using a printing technology, e.g., gravure roll printing.

Moreover, laser gravures 8 have been applied to a part of the prismatic layer 2 of the aspect of Fig. 4. By applying the laser, the reflective layer 3 (in this case: the metallized coating on the respective microprismatic elements 20) has been etched, and some microprismatic elements therefore no longer contribute to retroreflection but have become

transparent (as the reflective layer has been laser etched and light is no longer reflected) . Thus, the parts where the laser gravures 80 have been applied become visible to a consumer looking at the number plate 10 as they stand out due to not contributing to the reflections.

In the form of such laser gravures (laser etchings) , further markings can be added to aspects of products in accordance with the present disclosure. For example, in the case of the aspect of Fig. 4, a security feature has been added in the form of the laser etched parts, i.e., the laser gravures 8. The small arrow in Fig. 4 pointing towards the laser gravures 8 (and the absence of an arrow pointing in the counter directions) symbolizes that the light does not get reflected. Likewise, also the arrow pointing towards a pair of printings 5, 50 symbolizes that light does not get reflected.

In addition, the number plate 10 comprises another adhesive layer 6 and a casting support layer 7.

Fig. 5 depicts a section through a number plate 10 in

accordance with the present disclosure. Its" constitution is similar to the one described for the number plate 10 of Fig. 4. It comprises a prismatic layer 2 with microprismatic element 20 with heights h of 26 ym (the disclosure is not limited thereto), a reflective layer 3, an adhesive layer 4, and a liner 40.

The arrow P in Fig. 5 shows the direction of incidence of light. The small arrows on the left-hand side of Fig. 5 illustrate how the light reaches a microprismatic element 20 and are reflected back in the direction of incidence

(retroreflectivity) .

Also the aspect of Fig. 5 comprises laser gravures 8 applied to a part of the prismatic layer 2. By applying the laser, the reflective layer 3 (in this case: the metallized coating on the respective microprismatic elements 20) has been etched, and some microprismatic elements therefore no longer contribute to retroreflection but have become transparent (as the reflective layer has been laser etched and light is no longer reflected) . Thus, the parts where the laser gravures 80 have been applied become visible to a consumer looking at the number plate 10 as they stand out due to not contributing to the reflections.

In the form of such laser gravures (laser etchings) , further markings can be added to aspects of products in accordance with the present disclosure. For example, in the case of the aspect of Fig. 5, a security feature has been added in the form of the laser etched parts, i.e., the laser gravures 8. The small arrow in Fig. 5 pointing towards the laser gravures 8 (and the absence of an arrow pointing in the counter directions) symbolizes that the light does not get reflected. Likewise, also the arrow pointing towards a pair of printings 5, 50 symbolizes that light does not get reflected.

Most of the structure of the number plate 10 of Fig. 5 is identical to corresponding structure of the number plate 10 of Fig. 4, and repeating the description of corresponding structural components will be omitted. Reference is made to the description associated with Fig. 4.

A difference between the number plate 10 of Fig. 5 and the number plate 10 of Fig. 4 is that the printings 5, 50 of the number plate 10 of Fig. 5 are located adjacent to one another precisely so as to fully overlap, whereas the printings 5, 50 of the number plate 10 of Fig. 4 are shifted with respect to one another. In both cases, the first printing 5 and the second printing 50 have been manufactured using gravure roll printing. The disclosure is by no means limited to such arrangements .

Some examples of sheetings in accordance with the present disclosure were prepared and studied:

* For all of the previous examples, the values for the tensile strength and the elongation at break of the laser markings and the metallization are negligible.

The tensile strength and the elongation at break of the entire sheetings were determined to be:

These results demonstrate that the combination of the base layer and the prismatic layer with the intermediate layer disposed in-between promotes a particularly low overall tensile strength of the sheeting, and a particularly high elongation at break of the sheeting, especially in view of the comparative values of the adjacent prismatic layer.

In addition, a comparative study was performed to compare the yield stress, the elongation at break, the Young's modulus, and the tensile strength of a sheeting comprising a base layer, an intermediate layer, and a metallized prismatic layer, with a sheeting wherein the intermediate layer is omitted .

Examples 6, 7, 8

Sheetings were prepared as examples 6, 7, and 8 which consisted of a base layer made of casted PVC with a thickness of 80 ym (example 6), 90 ym (example 7), and 100 ym (example

8), an intermediate layer made of polyurethane with a thickness of 5 ym (example 6), 6.5 ym (example 7), and 8 ym

(example 8), as well as a prismatic layer with a metallization provided thereto as a reflective layer, the prismatic layer made of isobornyl-di-acrylate and having a thickness of 27 ym (example 6), 30 ym (example 7), and 33 ym (example 8 ) . Comparative Examples 1, 2, 3

Comparative examples 1, 2, 3 were prepared to be the same as examples 6, 7, and 8, but each of them lacking the respective intermediate layer.

The following tables show comparisons between experimental results for the respective sheetings including the intermediate layer and the comparative sheetings without the intermediate layer.

In each case, the presence of the intermediate layer implies a significant decrease of the yield stress (a yield stress of 7 or lower promotes a particularly good suitability for hot, and even more so, for cold deformations of the sheetings either before application to an external object or thereafter) .

Similar results were found for analogous sheetings as examples 6, 7, and 8, but wherein the prismatic layer was made of urethane-di-acrylate (but with otherwise identical setups for the examples and respective comparative examples.

Examples 9, 10, 11

Sheetings were prepared as examples 9, 10, and 11 which consisted of a base layer made of casted polyurethane with a thickness of 45 ym (example 9), 65 ym (example 10), and 85 ym (example 11), an intermediate layer made of polyurethane with a thickness of 5 ym (example 9), 6.5 ym (example 10), and 8 ym (example 11), as well as a prismatic layer with a metallization provided thereto as a reflective layer, the prismatic layer made of isobornyl-di-acrylate and having a thickness of 27 ym (example 9), 30 ym (example 10), and 33 ym (example 11).

Comparative Examples 4, 5, 6

Comparative examples 4, 5, 6 were prepared to be the same as examples 9, 10, and 11, but each of them lacking the respective intermediate layer.

In each case, the presence of the intermediate layer implies a significant decrease of the yield stress (a yield stress of 7 or lower promotes a particularly good suitability for hot, and even more so, for cold deformations of the sheetings either before application to an external object or thereafter) . It is interesting to note that the yield stress of examples 12, 13, and 14 is more or less identical to the yield stress of examples 6, 7, 8, or 9, 10, and 11, respectively, despite the base layer materials" far higher yield stress. However, in these cases, a base layer of a lower thickness was used, so that similarly good results were achieved .

Similar results were found for analogous sheetings as examples 9, 10, and 11, but wherein the prismatic layer was made of urethane-di-acrylate (but with otherwise identical setups for the examples and respective comparative examples.

It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed devices and systems without departing from the scope of the disclosure. Other aspects of the disclosure will be apparent to those skilled in the art from consideration of the

specification and practice of the features disclosed herein. It is intended that the specification and examples be

considered as exemplary only. Many additional variations and modifications are possible and are understood to fall within the framework of the disclosure.

Claims

1. A retroreflective sheeting comprising

a prismatic layer having microprismatic elements, a reflective layer adjacent to the prismatic layer, a base layer, and

an intermediate layer between the base layer and the prismatic layer,

the base layer comprising a base layer material, the intermediate layer comprising an intermediate layer material, and the prismatic layer comprising a prismatic layer material,

wherein the layers of the sheeting are arranged such that incident light penetrates the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer,

wherein a ratio between a thickness of the intermediate layer and a thickness of the base layer is 0.1 or less, and a ratio between the thickness of the intermediate layer and a thickness of the prismatic layer is 0.4 or less, and

wherein a ratio between a yield stress of the intermediate layer material and a yield stress of the base layer material is 0.25 or less, and a ratio between the yield stress of the intermediate layer material and a yield stress of the prismatic layer material is 0.1 or less .

2. The retroreflective sheeting according to claim 1, wherein the ratio between the thickness of the intermediate layer and the thickness of the prismatic layer is 0.25 or less.

3. The retroreflective sheeting according to claim 1 or 2, wherein the ratio between the yield stress of the intermediate layer material and the yield stress of the base layer material is 0.3 or less, and the ratio between the yield stress of the intermediate layer material and the yield stress of the prismatic layer material is 0.07 or less.

4. The retroreflective sheeting according to any one of the previous claims, wherein the thickness of the intermediate layer is less than 20 ym, optionally in a range of 1 ym to 15 ym, or in a range of 3 ym to 10 ym.

5. The retroreflective sheeting according to any one of the previous claims, wherein the yield stress of the intermediate layer material is in a range of 1 N/mm^ to 2 N/mm^ _

6. The retroreflective sheeting according to any one of the previous claims, wherein the yield stress of the base layer material is in a range of 4

and/or wherein the yield stress of the prismatic layer material is in a range of 20 N/mm^ to 45 N/mm^.

7. The retroreflective sheeting according to any one of the previous claims, wherein a ratio between a Young's modulus of the intermediate layer material and a Young's modulus of the base layer material is 0.2 or smaller, and a ratio between the Young's modulus of the intermediate layer material and a Young's modulus of the prismatic layer material is 0.05 or smaller.

8. The retroreflective sheeting according to claim 7, wherein the Young's modulus of the intermediate layer material is in a range of 20 to 70 MPa, and/or the Young's modulus of the base layer material is in a range of 80 to 800 MPa, and/or the Young's modulus of the prismatic layer material is in a range of 1500 to 4000 MPa.

9. The retroreflective sheeting according to any one of the previous claims, wherein a ratio between an elongation at break of the intermediate layer material and an elongation at break of the base layer material is 1.4 or larger, and a ratio between the elongation at break of the intermediate layer material and an elongation at break of the prismatic layer material is 100 or larger.

10. The retroreflective sheeting according to claim 9, wherein the elongation at break of the intermediate layer material is in a range of 250% to 700%, and/or the elongation at break of the base layer material is in a range of 80 % and 400%, and/or the elongation at break of the prismatic layer material is 3 % or less.

11. The retroreflective sheeting according to any one of the previous claims, wherein a ratio between a tensile strength of the intermediate layer material and a tensile strength of the base layer material is 0.4 or smaller, and a ratio between the tensile strength of the intermediate layer material and a tensile strength of the prismatic layer material is 0.25 or smaller.

12. The retroreflective sheeting according to claim 11, wherein the tensile strength of the intermediate layer material is in a range of 1

and/or the tensile strength of the base layer material is in a range of 15

and/or the tensile strength of the prismatic layer material is 20 N/mm^ to 50 N/mm^ _

13. The retroreflective sheeting according to any one of the previous claims, wherein the layers of the sheeting are arranged such that incident light penetrates the base layer, the intermediate layer, the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer.

14. The retroreflective sheeting according to any one of the previous claims, wherein the microprismatic elements have heights equal to or smaller than 34 pm.

15. The retroreflective sheeting according to any one of the previous claims, wherein the reflective layer is a metallization on at least parts of the prismatic layer.

16. The retroreflective sheeting according to any one of the previous claims, wherein the sum of the thicknesses of the base layer, the intermediate layer, and the prismatic layer is in a range of 50 pm to 200 pm, and/or wherein a thickness of the sheeting is in a range of 50 pm to 500 pm.

17. A retroreflective sheeting comprising

a prismatic layer having microprismatic elements, a reflective layer adjacent to the prismatic layer, wherein the layers of the sheeting are arranged such that incident light penetrates the prismatic layer and is reflected at the interface of the prismatic layer and the reflective layer, and

wherein the microprismatic elements have heights equal to or smaller than 34 pm.

18. The retroreflective sheeting according to any one of the previous claims, wherein at least a part of the microprismatic elements has been formed by embossing, engraving, or casting.

19. The retroreflective sheeting according to any one of the previous claims, wherein the prismatic layer comprises or consists of one or several materials selected from the following list: solvent lacquer, radiation curable lacquer, epoxy resin, polyurethane acrylate, PMMA, PC, polyacrylate, and polyurethane.

20. The retroreflective sheeting according to any one of the previous claims, wherein at least 90%, optionally at least 95% or 98% of the microprismatic elements have heights equal to or smaller than 34 pm, optionally equal to or smaller than 32 pm or 30 pm, optionally in a range of 15 to 34 pm, a range of 19 to 34 pm, 22 to 31 pm, 23 to 29 pm, or 24.5 to 26.5 pm, and/or

at least 90%, optionally at least 95%, or all of the microprismatic elements have the same heights.

21. The retroreflective sheeting according to claim 20, wherein different types of microprismatic elements are distributed with the same distribution ratio over at least 90%, optionally 95% or 98%, of the prismatic layer, or

at least 90%, optionally 95% or 98%, or all of the microprismatic elements are identical.

22. The retroreflective sheeting according to any one of the previous claims, wherein at least one of the microprismatic elements is a cube-corner element with three side surfaces meeting at an apex,

wherein, optionally, the height of the cube-corner element is defined to be a distance between the apex and a surface defined to contain at least three furthermost points, said furthermost points comprising one or several points, at least one on each side surface, that are furthermost from the apex amongst all points on the respective side surface, or

optionally, the height of the cube-corner element is defined as a distance between the apex and a surface that is defined to contain at least one furthermost point on a side surface of the cube-corner element that is furthest from the apex amongst all points on the side surfaces of said cube-corner element, and analogous furthermost points of other cube-corner elements which are identical to said cube-corner element.

23. The retroreflective sheeting according to any one of the previous claims, further comprising a base layer, the base layer optionally comprising or consisting of one or several materials selected from the following list: casted PVC, calendared PVC, casted TPU, extruded TPU, PU, PE, PP, PE-PAA copolymer, PET, PMMA, PC, ethylene vinyl acetate copolymer, alkyd resin systems, PVA, and thermoplastic elastomers,

wherein the layers of the sheeting are optionally arranged such that incident light penetrates the base layer, then the prismatic layer, and is reflected at the interface of the prismatic layer and the reflective layer of the sheeting, or

wherein the base layer and the prismatic layer are provided on opposite sides of the reflective layer.

24. The retroreflective sheeting according to claim 23, further comprising an intermediate layer between the base layer and the prismatic layer,

wherein the intermediate layer is optionally manufactured by flexography, digital printing, intaglio, etching, screen printing, and/or gravure printing,

the intermediate layer optionally comprising a printing color on the basis of water and/or solvent, optionally being thermally curable and/or curable by radiation,

the intermediate layer optionally comprising one or several materials selected from the group consisting of: acrylate polymer, polyurethane or PVC based colors, reactive acrylate, methacrylate, vinyl ether, and a material comprising epoxide.

25. The retroreflective sheeting according to any one of the previous claims, wherein the reflective layer is a metal film applied to the prismatic layer and, optionally, comprises or consists of one or several metals selected from the following list: aluminum, silver, and gold, and/or wherein the retroreflective sheeting comprises one or several printings, optionally formed by gravure roll printing, and/or laser gravures formed by etching the reflective layer and/or the prismatic layer using a laser, wherein a thickness of the reflective layer is optionally below 2ym, optionally below 1.3ym.

26. The retroreflective sheeting according to any one of the previous claims, further comprising a cover layer, wherein the layers of the sheeting are optionally arranged such that incident light first penetrates the cover layer and then other layers of the sheeting,

the cover layer optionally comprising or consisting of one or several materials selected from the following list: casted PVC, calendared PVC, casted TPU, extruded TPU, PU, PE, PP, PE-PAA copolymer, PET, PMMA, PC, EVAC ethylene vinylacetate copolymer, alkyd resin, PVA, and thermoplastic elastomers,

wherein a thickness of the reflective layer optionally lies in a range of 20 ym to 150 ym, optionally 35 ym to 130 ym.

27. The retroreflective sheeting according to any one of the previous claims, further comprising an adhesive layer for adhering the sheeting to an external object, the adhesive layer comprising an adhesive configured to be activated chemically, by pressure, and/or heat, the adhesive layer optionally provided with a liner on the interior side,

the adhesive optionally comprising or consisting of one or several materials selected from the following list: acrylate, polyurethane, epoxy based substances, and vinyl based substances,

the adhesive layer optionally being at least partially transparent and/or at least partially pigmented,

wherein a thickness of the adhesive layer optionally lies in a range of 20 ym to 100 ym, optionally 35 ym to 80 ym.

28. A retroreflective article comprising the retroreflective sheeting according to any one of the previous claims, said article optionally being a vehicle number plate or a traffic sign.

29. Use of the retroreflective sheeting according to any one of claims 1 to 28 for application to an external object such as a number plate or a traffic sign.

30. Use according to claim 29, including the step of hot or cold deformation of the sheeting before application to the external object, or, after application, of hot or cold deformation of the external object having the sheeting applied thereto.

31. The use according to claims 29 or 30 wherein the surface of the external object is three-dimensional.