GB2578476A

GB2578476A - Embossing

Info

Publication number: GB2578476A
Application number: GB1817657.8A
Authority: GB
Inventors: Hawe Matthew
Original assignee: Jewellery Cards Ltd
Current assignee: Jewellery Cards Ltd
Priority date: 2018-10-29
Filing date: 2018-10-29
Publication date: 2020-05-13
Also published as: GB201817657D0

Abstract

A method and apparatus for embossing a plastics substrate 14 by heating the substrate and/or an embossing tool 16 and embossing the substrate by pressing at least one protrusion 24 of the tool into a surface 28 of the substrate and by subsequently retracting the tool to leave an imprint 26 in the surface that substantially corresponds to the shape and/or depth of the or each protrusion. The invention is characterised by, immediately after retracting the tool, compressing the substrate between opposing surfaces 40 as it cools. This maintains the flatness of the substrate and inhibits/prevents curling or other deformation. The invention is particularly suited to embossing of name cards and the like (60, fig 9) into transparent PETG, which can be edge-lit using an LED (72, fig 10) to form illuminated signage (50, fig 9). An edge-lit display and an electrical circuit formed in a plastic substrate having one or more tracks of conductive material formed by embossing are also provided.

Description

EMBOSSING

This invention relates to an embossing method and apparatus, and in particular, to an embossing method and apparatus suitable for embossing transparent plastics. This invention also relates to products made from plastics that have been embossed using the method described herein.

Embossing is a process whereby a tool, having protrusions on its surface, is pressed into the surface of a substrate. The protrusions deform the substrate's surface and when the tool is retracted, leave an imprint corresponding to the shape and/or depth of the protrusions.

Cold embossing, i.e. where neither the tool nor substrate is heated, involves purely plastic deformation of the substrate, but certain plastics, when subject to cold plastic deformation, can craze or whiten, which degrades their appearance.

Hot embossing, on the other hand, involves heating the tool and/or the substrate such that heat can be used to alleviate stress during the embossing process. In effect, the substrate material is deformed whilst in a softened state, and can therefore flow, to a certain extent, around the protrusions, thereby alleviating the adverse effects of crazing/whitening described above.

Whilst hot embossing can reduce or avoid the incidence of crazing/whitening of the substrate during the embossing process, due to anisotropic cooling of the substrate, warping almost always occurs in the substrate as it cools. This is due to a temperature differential/gradient existing between the surface and the bulk of the substrate, causing differential thermal expansion/contraction throughout the thickness of the substrate, which, in turn, causes it to warp. Warping is especially problematic in thin film plastics, say under lmm thick, where the temperature gradient can be high (for a given temperature differential) due to the thinness of the substrate.

As such, there are competing requirements here, namely the need to use heat during embossing to reduce and/or avoid crazing/whitening of the plastic; versus the need to avoid using heat during embossing to reduce and/or avoid warping of the substrate. For this reason, embossing of thin film plastics, and especially thin film transparent plastics (where warping and crazing are particularly detrimental to the optical properties of the material) is generally contraindicated.

Known solutions to this problem, where embossing or an embossing-like process is required, range from simply accepting a certain amount of optical property degradation, to using alternative forming techniques, such as surface machining.

A need therefore exists for a solution to one or more of the above problems, which this invention aims to provide.

Aspects of the invention are set forth in the appended independent claims. Preferred and/or optional features of the invention are set forth in the appended dependent claims.

According to a first aspect of the invention there is provided a method of embossing a plastics substrate using an embossing tool, the method comprising the steps of: supporting the substrate; heating the substrate and/or the tool; and using the tool to emboss the substrate by: pressing at least one protrusion of the tool into a surface of the substrate; and subsequently retracting the tool to leave an imprint in the surface that substantially corresponds to the shape and/or depth of the or each protrusion, the method being characterised by: immediately after the step of retracting the tool, compressing the substrate between opposing surfaces as it cools.

According to a second aspect of the invention, there is provided an apparatus for embossing a plastics substrate comprising: an embossing tool; a substrate support; means for heating the substrate and/or the embossing tool; a first press; a second press; and a substrate transfer mechanism for transferring the substrate from the first press to the second press, the apparatus being configured, in use, to: using the first press, emboss the substrate by pressing at least one protrusion of the embossing tool into a surface of a substrate supported by the substrate support and subsequently retracting the embossing tool to leave an imprint in the substrate's surface that substantially corresponds to the shape and/or depth of the or each protrusion; using the substrate transfer mechanism, immediately after retracting the embossing tool, transferring the substrate from the substrate support to the second press; and using the second press, compressing the substrate between opposing surfaces of the second press as the substrate cools.

The plastics substrate is suitably a thin plastics substrate. The thin plastics substrate can have any suitable thickness, but it is suitably less then lmm thick, and preferably about 0.6mm thick. The plastics substrate is suitably manufactured from a clear and/or optically transparent plastics material. Preferably, the plastics substrate is PETG having a nominal thickness of 0.6mm.

The embossing tool suitably comprises a planar surface from which the protrusion or protrusions protrude. In one embodiment of the invention, the embossing tool has protrusions formed on a flat, planar surface. In other embodiments, the embossing tool is cylindrical, and has a curved or arcuate surface from which the protrusion or protrusions protrude, and can be used in the manner of a roller. The protrusions have a shape and depth, which produce a desired pattern, graphic, image, design or lettering in the surface of the substrate.

The substrate is supported, preferably on a flat platen, or on a platen whose profile corresponds to the surface of the embossing tool.

Where the substrate is heated, this can be accomplished by heating the platen, which in turn heats the substrate by radiation, convection and/or conduction. In one example, the platen is heated by a thermostatically-controlled electric heating element formed within, or in contact with, it. Other heat sources may equally be used, such as a radiant heater, e.g. an IR heater, a heated fluid pipe within, or in contact with, the platen, etc.. Likewise, the embossing tool may be heated by any one or more of the aforesaid means.

A press is suitably used to press the protrusions of the tool into the surface of the substrate, and/or to subsequently retract it from the substrate. Relative movement of the tool and substrate is all that matters: the tool can be fixed and the substrate/platen moved, or vice-versa, or both.

The at least one protrusion of the tool is pressed into the surface of the substrate and subsequently retracted so as to leave an imprint in the surface that substantially corresponds to the shape and/or depth of the or each protrusion. As will be well-understood by the skilled reader, the imprint formed in the substrate may not exactly correspond to the shape and/or depth of the protrusion or protrusions; and this may be due to elastic deformation of the substrate material, thermal expansion/contraction of the tool and/or substrate and other factors. Nevertheless, the protrusion(s) can be designed/engineered so as to leave behind a desired imprint in the substrate's surface.

The method of the invention is characterised by the step of "immediately" after retracting the tool, compressing the substrate between opposing surfaces as it cools.

By "immediately", in the context of this disclosure, it is meant within a very short time-frame, typically less than 1 second and preferably within less than 1 second, but generally, the sooner thereafter the better.

What is important here is that the substrate is compressed between the opposing surfaces as soon as possible after it starts to cool (i.e. once removed from the (heated) platen and/or once the (heated) tool has been retracted), and ideally whilst it is still above its softening temperature. The reason for this is that if the substrate can be pressed flat before it cools below its softening temperature, it can be re-formed, so as to remove any warping that may have occurred during the embossing process -before its (warped) shape becomes (permanently) set-in.

Whilst it may be possible to re-heat the substrate and press it again to flatten it, any additional heating steps will tend to remove any embossing. As such, by embossing and then clamping/pressing the substrate immediately thereafter (i.e. in one thermal cycle), both the embossing is preserved, and any final/residual warping is reduced or avoided.

Suitably, the plastics substrate is manufactured from transparent PETG and is heated to between about 130-140°C, which is above that material's softening temperature of about 60°C. In ambient temperature conditions of about 20°C, the plastics substrate can cool by between about 8090°C before passing through its softening transition temperature. Empirically, it has been found that if the substrate can be moved from the platen to the press within about 1 second, then there is sufficient time to apply the press and re-flatten the substrate before it cools below its softening temperature (60°C, in this case).

In certain embodiments of the invention, a transfer layer is interposed between the embossing tool and the substrate prior to pressing the at least one protrusion of the tool into the surface of the substrate. Suitably, the transfer layer is a metal foil layer, such as gold leaf or thin silver foil, and this can be pressed into the recesses formed by the embossing tool during the embossing process. The protrusion(s) of the embossing tool can be configured, such as by having sharp edges, to cut the transfer layer as they are pressed into the surface of the substrate and this can result in the recesses formed by the embossing process being completely or partially "lined" with the transfer layer once the tool has been retracted.

The transfer layer has been found to preferentially fuse with, or otherwise adhere to, the recesses formed in the substrate, and so the excess can be removed by a simple wiping procedure. This removes the "negative" of the transfer layer, leaving behind an embossed substrate whose indentations are lined with the transfer layer, but with the remaining areas being exposed substrate surface. By this method, it is possible to form a decorative and/or functional metalized design in the surface of the substrate.

In one possible application, attractive gold or silver embossed lettering can be formed in a clear plastics substrate, which can be used in signage or the like. In another application, conductive tracks or wires of an electrical circuit can be formed in the surface of the substrate, for example, where the imprint corresponds to the configuration of a circuit diagram.

The invention thus has both aesthetic/decorative applications, as well as practical applications; or both aesthetic and decorative applications, where, for example, a circuit is intended to be visible, in a particular article.

The transfer layer can, of course, be manufactured from other materials, such as plastics films, and combinations of metal and plastics films can be used to create a potentially unlimited number of designs of varying complexity.

The excess, negative or non-embossed parts of the transfer layer can be removed prior to or after the pressing step following on from the embossing step. However, to avoid unwanted fusion/adhesion of the negative to the surface of the substrate, the negative/excess is preferably removed prior to the pressing step following on from the embossing step.

As previously mentioned, the excess or "negative" of the transfer layer can be removed via a wiping process. This can be accomplished using a wiper blade, such as a strip of rubber, which passes over the substrate surface as it moves from the platen to the press; or a rotating press cylinder. In certain embodiments of the invention, an "airblade" is used, that is to say, a jet of pressurised air, which removes the excess/"negative" transfer layer from the surface.

One application of the invention is in signage where, for example, lettering and/or an image/other design is embossed into a transparent plastic substrate.

In one particular embodiment, the embossed substrate is used as part of an edge-lit display system, whereby an edge of the transparent plastic substrate is illuminated by a light source. Total internal reflection of the light within the transparent plastic substrate causes the substrate to become illuminated, in particular at the edges and/or where the embossing has been made. This can make the lettering/design stand out distinctively and not only does this aid reading of the text/design, but it also creates a pleasing/striking visual effect. Moreover, in low-light conditions, the embossed lettering/design can be seen because the embossing is preferentially illuminated by the edge lighting. Edge-lit signage is understood and does not require detailed explanation herein.

Nevertheless, one aspect of the invention provides an edge-lit signage system comprising a base unit and an embossed substrate having been embossed using the method described herein. The base unit suitably comprises a slot for receiving an edge of the substrate and an illumination means adapted, in use, to illuminate an edge of the substrate where it extends within the base unit. Accordingly, when the base unit is activated and its light source illuminated, light enters the substrate via one or more of its edges and becomes illuminated by total internal reflection. If there are any edges/indentations in the surface of the substrate, these are preferentially illuminated by the light source within the base unit.

Preferably, the light source within the base unit comprises one or more LEDs as these are low-power devices, which emit relatively large amounts of light for a given electrical power consumption. The light source is preferably battery-powered, and switch means is suitably provided for turning the light source on/off, as needed.

In order to improve the illumination of the substrate, a light dispersion means is suitably interposed between the light source and the edge of the substrate. Suitably, the light dispersion means comprises a Fresnel lens, which collimates light from the light source or sources and directs it edge-wise into an edge of the substrate.

Another aspect of the invention provides an electrical circuit formed in a plastic substrate using the method described herein. The electrical circuit typically comprises tracks of conductive material, which are formed by embossing the substrate surface in the manner previously described with an electrically conductive transfer layer used to "line" the embossing. By this means, electrically conductive "tracks" can be formed in the surface of the substrate, which can be used as part of an electrical circuit. In certain embodiments, a combination of electrically conductive and electrically insulative transfer layers are used to form a circuit comprised of conductive tracks and insulating regions.

In a preferred embodiment of the invention, the electrical circuit so formed can be used in conjunction with an edge-lighting base unit as described herein.

Embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1 to 4 illustrate a schematic sequence illustrating the embossing method of the invention; Figures 5 to 8 illustrate, schematically, the embossing method of the invention with the addition of a transfer layer being applied; Figure 9 is a schematic perspective view of an edge-lit signage system in accordance with the invention; Figure 10 is a schematic, cross-sectional view of Figure 9 on X-X; and Figure 11 is a schematic, plan view of a decorative electrical circuit in accordance with the invention.

Referring firstly to Figures 1 to 4 of the drawings, an embossing method in accordance with the invention is illustrated. The embossing method involves the use of a platen 10, which is heated, internally, by a heating system 12. A substrate 14 is placed on the platen 10 and is heated by the heating system 12, which radiates and/or conducts heat from the platen into the substrate. Once the substrate 14 has been heated to above its softening point, an embossing tool 16 is pressed 18 down onto the substrate 14. The embossing tool 16 has a main body 20 with a generally flat underside surface 22, from which a set of protrusions 24 project in the form of a desired pattern/design.

The platen 10 heats the substrate 14 to a temperature above its softening point, and the embossing tool 16 is pressed down, as shown in Figure 2, so that its protrusions produce corresponding indentations 26 in a substrate 14. Once an impression has been made in the substrate 14, the embossing tool 16 is retracted, as shown in Figure 3 -leaving behind a substrate 14 with indentations 26 therein corresponding to the protrusions 24. As can be seen in Figure 3, once the embossing tool 16 has been retracted, the substrate 14 will begin to cool and as it does so, it will usually tend to warp due to its upper surface 28 (in contact with the air) being relatively cooler than its lower surface 30 (in contact with the heated platen). In addition, warping occurs due to residual strain within the substrate 14 caused by the embossing process. The warping shown in Figure 3 is relatively uniform, but that is rarely the case.

The invention proposes, immediately after retracting the embossing tool 16, to transfer 32 the substrate 14 into a secondary press 34, which comprises upper 36 and lower 38 parts, each having flat pressing surfaces 40.

As shown in Figure 4 of the drawings, the secondary press 34 is engaged with the substrate 14 whilst the substrate 14 is still above its softening point and this re-flattens the substrate 13.

Once the substrate 14 has cooled to below its softening point, the secondary press 34 can be opened and the substrate 14 removed 42.

The result is a substrate 14 with indentations 26 on its surface that correspond to the protrusions 24 of the embossing tool, but which also has a generally flat overall shape, as per the original substrate. The invention thereby overcomes the problem of warping caused by differential thermal expansion and/or by the embossing process itself.

Turning now to Figures 5 to 8 of the drawings, a variation of the aforedescribed method is shown schematically. Identical reference signs have been used to identify identical features to avoid unnecessary repetition.

The process is largely the same as that described previously, except that a transfer layer 44 (for example a gold or silver foil) is interposed between the substrate 14 and the embossing tool 16 prior to the embossing step 18.

As shown in Figure 6 of the drawings, when the embossing tool 16 is pressed down onto the substrate 14, it forms the aforedescribed indentations 26, but also draws portions of the transfer layer 44 into the "wells" created by the protrusions 24 of the embossing tool 16.

When the embossing tool 16 is retracted, as shown in Figure 7 of the drawings, each of the indentations 26 is effectively "lined" with an impression from the transfer layer 44A. The remainder of the transfer layer 44B that was not contacted by the protrusions 24 form a "negative", which lies on top of the upper surface 28 of the substrate 14.

As the substrate 14 is transferred 32 to the secondary press 34, an air blade 46 (in this embodiment) is used to remove the negative 44B from the upper surface 28 of the substrate 14; and the excess 44B is collected in a receptacle 48. Other means may equally be provided for removing the excess 448, such as a straightforward wiper blade, a brush, or a roller.

The process proceeds in the manner previously described, with the substrate 14 being flattened by the secondary press 34, and once removed 42, the substrate 14 has transfer layer-lined indentations 26/44A, but the remainder of the upper surface 28 of the substrate 14 remains clear.

One application for the embossing method is in the field of signage and a "name card" type device is shown, schematically, in Figure 9 of the drawings.

The name card device 50 comprises a base unit 52. In the illustrated embodiment, the base unit 52 is formed from a hollow cube of aluminium, and has a slot 54 cut into its upper surface 56 whose width corresponds to the thickness 58 of a transparent plastics name card 60. The slot 54 is angled backward slightly so that the name card 60 is presented at a non-vertical angle, but this is not essential.

The name card 60 has been formed by the method described in relation to Figures 5 to 8 of the drawings, and has embossed lettering and/or a design 62 formed on an otherwise flat surface 28. The lettering 62 is lined with gold foil, in the illustrated embodiment, using the transfer layer process described previously.

Internally, as shown in Figure 10, the base unit 52 has a hollow interior volume, which houses a circuit board 66 and a battery power supply 68. An on/off switch 70 is provided for switching the circuit on/off. The batteries 68 power a set of surface-mount LEDs 72, which are located slightly behind a Fresnel lens 74. The surface of the Fresnel lens 74 intersects the slot 54 and so a name card 60 inserted into the slot 54 can be edge-lit by the LEDs 72. The Fresnel lens 74 collimates the light from the LEDs, thereby creating a uniform edge-lighting effect.

The light from the LEDs 72 enters a name card 60 via its lower edge 76 and is totally internally reflected within the bulk of the name card. However, when the light reaches the edges 78, or the embossed lettering 62, it can escape and this creates a pleasing visual effect. In effect, the lettering 62 is back lit and the edges 58 of the name card 60 provide a pleasing-looking, illuminated border to the name card 64. The edge-lit effect can be switched on/off using the switch 70 in a manner that would be readily understood by the skilled reader.

An alternative application of the invention is shown in Figure 11 of the drawings, in which a circuit 80 has been formed in the substrate 14 by embossing conductive tracks 82, which are formed by metal foil-lined embossing in the surface 28 of the substrate 14. Contact/connection regions 84 are also provided and these enable external components (not shown) to be connected to the circuit 80. In addition to the functional tracks 82 formed on the substrate, decorative/instructional elements 62 can also be provided.

It will be readily apparent from the foregoing description that the circuit 80 shown in Figure 11 could be supported in a base unit 52 like that shown in Figures 9 and 10 and could, therefore, also be back-lit or otherwise supported.

The invention is not restricted to the details of the foregoing embodiment, which are merely exemplary of the invention.

Claims

CLAIMS1. A method of embossing a plastics substrate using an embossing tool, the method comprising the steps of: supporting the substrate; heating the substrate and/or the tool; and using the tool to emboss the substrate by: pressing at least one protrusion of the tool into a surface of the substrate; and subsequently retracting the tool to leave an imprint in the surface that substantially corresponds to the shape and/or depth of the or each protrusion, the method being characterised by: immediately after the step of retracting the tool, compressing the substrate between opposing surfaces as it cools.
2. An apparatus for embossing a plastics substrate comprising: an embossing tool; a substrate support; means for heating the substrate and/or the embossing tool; a first press; a second press; and a substrate transfer mechanism for transferring the substrate from the first press to the second press, the apparatus being configured, in use, to: using the first press, emboss the substrate by pressing at least one protrusion of the embossing tool into a surface of a substrate supported by the substrate support and subsequently retracting the embossing tool to leave an imprint in the substrate's surface that substantially corresponds to the shape and/or depth of the or each protrusion; using the substrate transfer mechanism, immediately after retracting the embossing tool, transferring the substrate from the substrate support to the second press; and using the second press, compressing the substrate between opposing surfaces of the second press as the substrate cools.
3. The method or apparatus of claim 1 or claim 2, wherein the plastics substrate is less then lmm thick and is manufactured from a clear and/or optically transparent plastics material.
4. The method or apparatus of claim 3, wherein the plastics substrate is manufactured from transparent PETG having a nominal thickness of 0.6mm.
5. The method or apparatus of any preceding claim, wherein the embossing tool comprises a surface from which the protrusion or protrusions protrude, the protrusions have a shape and/or depth, which produce a desired pattern, graphic, image, design or lettering in the surface of the substrate.
6. The method or apparatus of claim 5, wherein the substrate is supported on a platen whose profile corresponds to the surface of the embossing tool.
7. The method or apparatus of any preceding claim, wherein the substrate is compressed between the opposing surfaces within less than 1 second of the embossing tool being retracted.
8. The method or apparatus of any preceding claim, wherein the substrate is compressed between the opposing surfaces whilst the substrate is above its softening temperature.
9. The method or apparatus of claim 7 or claim 8, wherein the embossing and subsequent pressing are performed within one thermal cycle of the substrate.
10. The method or apparatus of any preceding claim, wherein the substrate is embossed whilst the substrate is heated to between about 130-140°C, and wherein the substrate is subsequently pressed whilst the substrate is above about 60°C
11. The method or apparatus of any preceding claim, further comprising interposing a transfer layer between the embossing tool and the substrate prior to pressing the at least one protrusion of the tool into the surface of the substrate.
12. The method or apparatus of claim 11, wherein the transfer layer comprises a metal foil layer, which is pressed into the recesses formed by the embossing tool during the embossing process.
13. The method or apparatus of claim 12, wherein the or each protrusion of the embossing tool is configured to cut the transfer layer as it or they are pressed into the surface of the substrate.
14. The method or apparatus of any of claims 11 to 13, further comprising means for removing a "negative" of the transfer layer and removing the "negative" of the transfer layer before the substrate is compressed between the opposing surfaces.
15. An edge-lit display system comprising: an embossed transparent plastic substrate formed by the method or apparatus of any preceding claim; and a base unit, the base unit comprising a slot for receiving an edge of the substrate; and an illumination means adapted, in use, to illuminate an edge of the substrate where it extends within the base unit.
16. The edge-lit display system of claim 15, wherein, when the base unit is activated and its light source illuminated, light enters the substrate via one or more of its edges and becomes illuminated by total internal reflection, such that edges and/or indentations formed in the surface of the substrate are preferentially illuminated by the light source within the base unit.
17. The edge-lit display system of claim 15 or claim 16, wherein the light source within the base unit comprises one or more battery-powered LEDs, switch means for turning the light source on/off, as needed, and a Fresnel lens interposed between the light source and the edge of the substrate.
18. An electrical circuit formed in a plastic substrate using the method or apparatus of any or claims 12 to 14, the electrical circuit comprising one or more tracks of conductive material, which are formed by embossing the substrate surface with an electrically conductive transfer layer.