Membrane and method for transferring a decoration by sublimation using such a membrane

Abstract

The invention relates to a system suitable for the hot transfer of a decoration printed on a sheet with sublimation inks onto a substrate by a sublimation method, the device comprising a flexible membrane (11) bordered at the periphery by a seal (12), the membrane (11) extending in a main plane and the seal (12) extending from an inner face of the membrane (11) in a direction perpendicular to the main plane of the membrane (11), the seal (12) being configured so that when the membrane (11) is pressed against the substrate, this seal cooperates with the substrate to delimit, between the substrate and the inner face of the membrane (11), a sealed space that can be placed under vacuum. The invention also relates to a method for decorating a substrate using sublimation printing.

Description

Description Title of the invention: Membrane and method for transferring a decoration by sublimation using such a membrane Technical field of the invention [1] The technical field of the invention relates to the decoration of objects by transferring a decoration onto the surface of the object by a sublimation process. The invention is particularly applicable to the decoration of large objects and / or objects having three-dimensional surfaces. State of the art [2] In a known manner, the decoration of an object by sublimation consists of transferring a decoration onto a suitable surface of the object, a surface which will subsequently be called a “substrate”. A suitable surface (or a substrate) is a non-porous surface (for example a surface covered with a varnish) or a porous surface (for example the surface of an object made of an organic material such as wood or leather).The decoration is printed on a transfer support sheet (or decoration sheet) with heat-sensitive inks. The transfer is then carried out by applying the sheet to the substrate, heating the transfer support sheet to sublimate the inks and applying pressure to the support sheet to press it onto the substrate and facilitate the transfer of the sublimated inks to the substrate to be decorated. To apply uniform pressure over the entire surface of the decoration to be transferred, D1 = WO0196123 proposes using a mold in the shape of the object to be decorated and a press to apply the necessary pressure while heating. However, the production of a mold is quite expensive so that such a process is interesting for the production of large series of identical objects, but such a process is not suitable for the decoration of small series of objects or for the decoration of objects of various shapes and sizes.Furthermore, the size of a mold (and associated press) that can be produced at a reasonable price is necessarily physically limited, so that this method is not relevant for the decoration of large objects, for example, those larger than 100 cm. [3] In document D2 = WO2004106082, the transfer sheet is shaped into a pocket inside which the object to be decorated is positioned; the pocket is sealed and a vacuum is created inside the pocket so that atmospheric pressure mechanically presses the transfer support onto the outer surface of the object to be decorated during a heating step following the vacuum step, heating carried out in a closed enclosure. After transfer, the transfer support sheet is torn off and discarded.This solution is interesting for decorating small objects that can be enclosed in a pocket and then in a reasonably sized enclosure. of the order of a few centimeters or tens of centimeters, but is not suitable for decorating large objects. Disclosure of the invention [4] The invention proposes a technical solution to overcome all or part of the drawbacks set out above. [5] The invention firstly proposes a system suitable for the hot transfer of a decorprinted onto a sheet with sublimable inks onto a substrate by a sublimation process, a device comprising: - a flexible membrane bordered at the periphery by a seal, the membrane extending in a main plane and the seal extending from an internal face of the membrane in a direction perpendicular to the main plane of the membrane, the seal being configured so as, when the membrane is applied to the substrate, to cooperate with the substrate to delimit between the substrate and the membrane a sealed space capable of being placed under vacuum.[6] The system according to the invention operates in an open environment from a thermal point of view so that the dimensions of the objects capable of being decorated are not limited by the dimensions of an oven. The system according to the invention thus makes it possible to decorate large objects. [7] The flexibility and suppleness of the membrane make it possible to decorate objects having a three-dimensional surface to be decorated, of any shape. [8] Finally, the membrane is reusable, it can be used to decorate several objects one after the other or to transfer several decorations onto the same object. And the flexibility of the membrane makes it possible to decorate objects of different shapes and / or different dimensions with the same membrane.[9] The invention also provides a method for decorating a substrate by ink sublimation, a method using a system as described above and comprising the following steps: - applying a decorative sheet to the substrate to be decorated, sheet on which a decoration is printed with sublimable inks - applying the membrane to the substrate so as to cover the decorative sheet and delimit a sealed space between the substrate and the internal face of the membrane, - creating a vacuum between the membrane and the substrate to be decorated, and - heating the decorative sheet to sublimate the inks.

[10] The method according to the invention does not require the use of a press to apply pressure; it does not require significant means to create a vacuum under the membrane because the volume of air to be sucked in is very limited. The method also does not require bulky and expensive heating means to heat and sublimate the inks.The implementation of the process is thus simple and inexpensive.

[0011] According to one embodiment, after the membrane has been placed, an operator heats the membrane with a heating means external to the transfer system according to the invention. According to another embodiment, the system according to the invention also comprises a heating means adapted to heat the decorative sheet at least locally to sublimate the inks. Presentation of the figures

[12] The invention will be better understood, and other characteristics and advantages of the invention will appear in the light of the following description of examples of implementation of the invention. These examples are given without limitation. The description is to be read in relation to the appended drawings in which: ^ [Fig. 1] is a perspective view of a membrane according to the invention, ^ [Fig. 2] shows a sectional diagram of a detail of the membrane of [Fig. 1], ^ [Fig. 3] schematically shows a transfer system comprising a membrane such as that of [Fig. 1], ^ [Fig.4] schematically shows a step of the transfer method according to the invention.

[0013] In the various figures, identical or similar elements are referenced with the same references. Detailed description

[14] As stated previously, the invention proposes a system suitable for the hot transfer of a decoration printed on a decoration sheet with sublimable inks, transfer to a substrate by a sublimation method. By substrate, is meant throughout the description a surface suitable for implementing a sublimation decoration method. The substrate to be decorated can be an interior surface or an exterior surface of an object, a flat surface or a three-dimensional surface.

[15] The device according to the invention comprises [Fig. 1] a flexible membrane 11 bordered at the periphery by a seal 12; the membrane extends in a main plane and the seal extends from an internal face of the membrane in a direction perpendicular to the main plane.And the seal 12 is configured to, when the membrane is applied to the substrate, cooperate with the substrate to delimit between the substrate and the membrane a sealed space capable of being placed under vacuum. Thus, within the framework of the invention, the vacuum is created between the membrane and the substrate; in other words, a part of the substrate (i.e. the surface of the object to be decorated) forms a part of the walls of a pocket which can be placed under vacuum.

[16] According to one embodiment, the dimensions of the surface of the membrane are such that: - an area of the internal face of the membrane is greater than an area of the decoration to be transferred and. - an area of the inner face of the membrane is less than an area of the substrate onto which the decoration is to be transferred. Thus, the membrane can cover the area of the decoration to be transferred, and can be used even for transferring decorations onto objects with a large surface area. For example, a membrane according to the invention can be used to decorate body parts of motor vehicles such as cars or trucks, or even building walls.

[0017] The seal may have a distal end 12a rounded at least locally [Fig. 2], preferably on the inner side of the membrane. Such a rounding facilitates the rotation and crushing of the seal [Fig.4] when creating a vacuum between the membrane and the substrate to be decorated, to ensure the sealing of the membrane.

[0018] The system shown also comprises a vent 14a allowing the suction of air under the membrane to create a vacuum.According to one embodiment, the vent 14a is made in the membrane [Fig. 1]. According to another embodiment [Fig. 2], the system comprises a pipe 14 taken in the seal 12 and opening onto an internal face of the membrane, an opening of the pipe forming the vent 14a [Fig. 2] and [Fig. 3].

[0019] The flexible membrane is for example made of an elastomeric material, for example a polyaddition silicone elastomer conventionally used for prototyping. The membrane thus has the shape of a flexible sheet; it deforms to adapt to the shape of the substrate and returns to its substantially flat shape when it is moved away from the substrate. The elasticity of the material facilitates the deformation of the membrane and its adaptation to three-dimensional surfaces, in particular during vacuum.

[0020] The material is chosen so that the membrane withstands a temperature of the order of 100 to 140°C and can be reused several times.Also, the material is chosen to be gas-tight to allow a vacuum to be created between the membrane and the substrate to be decorated. As a concrete example, the membrane can be made of polymethylvinylsiloxane.

[0021] The membrane preferably has a thickness of between 0.5 and 4 mm. The thickness of the flexible membrane is chosen so that the membrane has, on the one hand, flexibility allowing it to cover three-dimensional substrates of various shapes, including substrates with significant curvatures, and on the other hand, mechanical strength allowing the same membrane to be reused to carry out several transfers. A thickness of around 2 mm is a good compromise for various applications.

[0022] The joint is preferably made of a material whose hardness is between 20 and 40 Shore A, the choice of hardness being a compromise between flexibility and mechanical strength of the joint, as for the membrane.The tests carried out have shown that a hardness of 30 Shore A is a good compromise for various applications.

[0023] The seal has, in a plane parallel to the main plane of the membrane, a width L [Fig. 2] of between 5 and 15 mm, and preferably between 5 and 10 mm. The seal has, in a direction perpendicular to the membrane, a height H [Fig.2] of between 5 and 17 mm. and preferably between 8 and 12 mm. Preferably, the seal is a lip seal for better airtightness.

[0024] In [Fig. 1], the membrane shown has a generally rectangular shape and a prototype of such a membrane has been produced with dimensions of the order of 30 cm * 50 cm. Such a membrane can be used, for example, to decorate a substrate having the shape of a disc with a radius greater than 60 cm (60 cm being substantially the radius of a circle circumscribed by a rectangle of 30 cm * 50 cm) or a rectangular substrate with a width greater than approximately 35 cm and a length greater than approximately 55 cm. Other shapes and other dimensions can of course be envisaged. For example, other tests have been carried out with a substantially square membrane with dimensions of the order of 2 m by 2 m. The surface area and shape of the membrane must be sufficient for the membrane to cover the sheet 20 [Fig.3], [Fig.4] on which the decoration to be transferred is printed, said sheet having a shape and a surface area themselves adjusted according to the decoration to be transferred. And the shape and the surface area of the membrane must be adapted so that the membrane can be well pressed against the substrate to be decorated and that the vacuum can be created between the membrane and the substrate. For this, the surface area of the membrane must be less than the surface area of the substrate and the membrane must not protrude from the substrate when it is resting on the substrate [Fig. 3].

[0025] Preferably, the shape and the surface area of the membrane are also chosen so that the edge of the membrane, and therefore also the joint, have, in the main plane and at any point of the perimeter of the joint, a radius of curvature R greater than 1 mm. For example, for a membrane of substantially rectangular shape [Fig.1], in the corners the joint has a radius of curvature R equal to 1 mm and, in the areas where the joint is substantially straight, the curvature (1 / R) is zero, the radius of curvature R being very large. This makes it possible to minimize the risk of the joint detaching when a vacuum is created between the membrane and the substrate to be decorated.

[0026] In addition to the membrane described above, the system shown [Fig. 4] also comprises a vacuum pump 30, a suction inlet of which is connected to the membrane via the pipe 14 or directly to the vent 14a of the membrane. The vacuum pump 30 is known elsewhere. It makes it possible to create a vacuum between the membrane and the substrate to be decorated so that the air located outside the membrane applies a pressure of the order of 1 bar (atmospheric pressure) uniformly over the entire membrane.

[0027] The system according to the invention described above is used to print a decoration on a substrate, with the following steps consisting of: - applying a decorative sheet to the substrate to be decorated (50), sheet on which a decoration is printed with sublimable inks - applying the membrane to the substrate so as to cover the decorative sheet and delimit between the substrate and the internal face of the membrane a sealed space, - creating a vacuum between the membrane and the substrate to be decorated, and - heating the decorative sheet at least locally to sublimate the inks.

[0028] The decorative sheet 20 and the sublimable inks with which the sheet is printed are elements known elsewhere for the implementation of conventional sublimation techniques; the sheet is made of a material impermeable to liquids and gases.Thus, when printing the decoration on the sheet, the liquid inks do not migrate inside the material of the sheet and, when heating the sheet, the sublimated, gaseous inks migrate towards the substrate to be decorated, without penetrating into the sheet. The sheet is placed on the object to be decorated and is covered by the membrane.

[0029] The vacuum is created between the membrane and the substrate to be decorated, that is to say in the sealed space delimited by the membrane and the substrate. Due to the vacuum created under the membrane, the atmospheric pressure mechanically presses the membrane and the decorative sheet against the substrate. The flexible membrane thus molds itself to the shape of the substrate to be decorated, with the decorative sheet pinched between the two. In [Fig. 4], the membrane 10 is shown schematically before (4a) and after (4b) having created the vacuum. The atmospheric pressure which is exerted on the membrane causes the transfer of the sublimated inks towards the substrate to be decorated.

[0030] The vacuum pump and the pipe which connects it to the membrane are in the open air and are thus subjected only to atmospheric pressure and a relatively low temperature, in all cases lower than the temperature applied to sublimate the inks.

[0031] The heating means used in the context of the invention is suitable for heating, at least locally, the decorative sheet to sublimate the inks. The heating causes the transformation of the sublimable inks into gas, gases which then penetrate into the substrate to be decorated and solidify again by incorporating themselves into the structure of said substrate. The duration of the heating is of the order of 15s to 5 min, depending on the quantity of inks to be sublimated and the heating temperature.

[0032] According to one embodiment, the heating means is a heating element, for example a heating layer 40a [Fig.4], heating element positioned between the membrane 10 and the sheet 20

[0033] The heating layer is for example made up of heating wires or a sheet of heating wires sandwiched between two layers of fabric preferably coated with an insulating and flexible plastic material such as a silicone material; preferably, the electrical wiring elements of the ends of the heating layer are also integrated between the membrane and the sheet, for example in the seal 12, so that the seal can be maintained during vacuuming. Heating directly at the core of the membrane has the advantage of ensuring uniform distribution of heat over the entire surface covered with the decorative sheet, which makes it possible to obtain an excellent, homogeneous and high-quality transfer.

[0034] The system can be advantageously supplemented by an insulating layer positioned between the internal face of the membrane and the heating layer.Thus, the heat emitted by the heating layer is fully transmitted to the sheet to be heated.

[0035] The system can also advantageously be supplemented by a layer having a smooth surface condition, positioned between the decorative sheet and the heating layer. The. Commercially available heating layers have a more or less textured surface condition (due to the texture of the fabric) which degrades the uniformity of the heat and pressure exerted on the sheet and on the substrate; the quality of the decoration obtained is degraded. The use of a layer having a smooth surface condition makes it possible to obtain a better quality decoration. The layer having a smooth surface condition is for example made of greaseproof paper, impermeable and resistant to the temperatures necessary for the sublimation of the inks,

[0036] A heating means such as a heating layer 40a however has limits, mainly linked to the dependence between the membrane and the heating layer during vacuuming.Indeed, the flexibility and suppleness of the membrane / heating layer assembly are lower than the flexibility and suppleness of the membrane alone, so that the assembly may have difficulty adapting to three-dimensional substrates with abrupt angle changes or very pronounced curves, especially if the angle exceeds 30°. The relative rigidity of the membrane / heating layer assembly may cause difficulties in maintaining close and uniform contact between the membrane and the substrate to be decorated; this may result in poorly printed areas or deformations of the transferred decoration on substrates with complex shapes.

[0037] According to another embodiment, the heating means 40b [Fig. 3] is adapted to produce a blast of hot air applied to the outer face of the membrane, which has several advantages.First of all, the design and production of the membrane itself are simplified because it is not necessary to integrate a heating layer and the associated electrical wiring in or under the membrane. The membrane is more flexible than a membrane / heating layer assembly; the handling of the membrane and its installation are made possible even on substrates with greater angle changes, up to 180°. The membrane is therefore more adaptable to complex substrates to be decorated, such as substrates with curved shapes or with reliefs. Then, it is possible to best and easily adjust the surface area of the heated zone of the membrane, thus making it possible to transfer both small and larger decorations with the same membrane.The hot air flow can be applied, for example, with a heat gun carried by a cobot; the gun can thus be moved to transfer large decorations step by step, in the order of 50 cm to 5 m for example, onto large objects such as motor vehicles or even building walls. Finally, and unlike the use of a heating layer, the use of a blast of hot air allows the creation of a thermal flow between the heat source and the membrane with very little inertia. This thermal flow makes it possible to manage the heating and then cooling phases much more precisely throughout the transfer. By controlling the cooling, the solidification of the sublimated inks can be influenced. This can improve the quality of the transfer, ensure optimal fixation of the inks in the target material and avoid possible defects linked to inappropriate cooling.

[0038] Preferably, the heating means is controlled so that a temperature of the substrate to be decorated remains below 120°C and a temperature of the decorative sheet is higher. at a sublimation temperature of the sublimable inks. This can be achieved by adjusting the temperature and the duration of use of the heating means.

[0039] Since such a temperature of the substrate to be decorated is not very high, the phases of heating up and cooling of the substrate are thus quick and easy to control. Also, with such a temperature, it is possible to decorate more fragile substrates, such as polyamide substrates. It is also possible to decorate objects covered with varnish or paint, such as car body parts. In this case, the sublimated inks become embedded in the varnish and / or paint, which constitute a suitable substrate for a transfer of decoration by sublimation. Finally, the inks, in particular inks without a compound capable of creating a positive azeotrope with water, are less heated and age better.Of course, the invention can also be used to transfer a decoration onto an object made of a more usual material for such a transfer, such as for example porous materials such as leather, wood, porous aluminas, etc.

[0040] In a practical implementation, one preferably works with a high temperature and a low quantity of heat by adjusting the temperature and the flow of hot air so as to have a temperature difference between the decoration sheet and the substrate to be decorated of the order of 30°C to 60°C and preferably between 45 and 55°C. The sublimation of the inks is thus rapid.

[0041] In summary, the invention proposes a new means for decorating objects by a sublimation process, which notably provides the following technical and economic benefits: - a membrane that is easy to produce and inexpensive, - a versatile membrane that can be used to decorate objects of various sizes and shapes, - a membrane that can be used to decorate objects with three-dimensional surfaces, including complex shapes and shapes with significant angles or curvatures, - a membrane that can be used to decorate objects of large, or even very large, dimensions, - an installation that does not require expensive and fixed technical means, such as a press, for example - a transportable installation - excellent transfer quality

[0042] Nomenclature11 Membrane12 seal 12a distal end of the seal 14 pipe 14a vent 20 decorative sheet. vacuum pump a heating layer b means suitable for producing a blast of hot air substrate to be decorated

Claims

Claims

1. System suitable for the heat transfer of a decoration printed on a sheet with sublimable inks onto a substrate by a sublimation process, device comprising a flexible membrane (11) bordered at the periphery by a seal (12), the membrane extending in a main plane and the seal extending from an internal face of the membrane in a direction perpendicular to the main plane of the membrane, the seal being configured to, when the membrane is applied to the substrate, cooperate with the substrate to delimit between the substrate and the membrane a sealed space capable of being placed under vacuum.

2. System according to claim 1 in which an area of the internal face of the membrane is greater than an area of the decoration to be transferred and is less than an area of the substrate onto which the decoration is to be transferred.

3. System according to claim 1 in which the seal has a rounded distal end (12a).

4. System according to one of the preceding claims, also comprising a pipe (14) taken in the seal and opening onto the internal face of the membrane.

5. System according to one of the preceding claims in which the membrane and / or the seal are made of elastomeric material, for example polyaddition silicone, for example polymethylvinylsiloxane.

6. System according to one of the preceding claims in which the membrane has a thickness of between 0.5 and 4 mm and preferably equal to 2 mm.

7. Device according to one of the preceding claims in which the seal has, in a plane parallel to the main plane of the membrane, a width (L) of between 5 and 15 mm, and preferably between 5 and 10 mm.

8. System according to one of the preceding claims in which the seal has, in a direction perpendicular to the main plane of the membrane, a height (H) of between 5 and 17 mm and preferably of between 8 and 12 mm.

9. System according to one of the preceding claims in which the seal has, in the main plane and at any point of its perimeter, a radius of curvature R greater than 1 mm.

10. Membrane according to one of the preceding claims in which the seal is a lip seal.

11. System according to one of the preceding claims also comprising a heating means (40a, 40b) adapted to heat the sheet. of decoration at least locally to sublimate the inks and to cause the transfer of the sublimated inks onto the substrate to be decorated.

12. System according to claim 11 in which the heating means (40b) is adapted to produce a blast of hot air applied to an outer face of the membrane.

13. System according to claim 11 in which the heating means is a heating layer (40a) positioned between the sheet and the membrane.

14. System according to claim 13 also comprising an insulating layer positioned between the inner face of the membrane and the heating layer.

15. System according to claim 12 or 13 also comprising a layer having a smooth surface condition, positioned between the sheet and the heating layer.

16. Method for decorating a substrate by ink sublimation, method using a system according to one of claims 11 to 15 and comprising the following steps: - applying a decorative sheet to the substrate to be decorated (50), sheet on which a decoration is printed with sublimable inks - applying the membrane to the substrate so as to cover the decorative sheet and delimit between the substrate and the internal face of the membrane a sealed space, - creating a vacuum between the membrane and the substrate to be decorated, and - heating the decorative sheet to sublimate the inks.

17. Method according to claim 16 wherein during the heating step, the heating means is controlled so that a temperature of the substrate to be decorated remains below 120°C and a temperature of the decorative sheet is higher than a sublimation temperature of the sublimable inks.

18. A method according to one of claims 16 or 17, in combination with claim 13, wherein a temperature and a flow rate of the hot air are adjusted so that a temperature difference between the decorative sheet and the substrate to be decorated is between 30 and 60°C, and preferably between 45 and 55°C.

19. A method according to one of claims 16 to 18 wherein the vacuum is maintained during heating of the sheet.

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