Improved method for manufacturing a leather piece

Abstract

The invention relates to a method for manufacturing a part (2) comprising a step of depositing a coating (2D) using a droplet fluid (12A) by electrohydrodynamic inkjet.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for manufacturing a piece of jewelry, fine jewelry, leather goods or writing instrument, and in particular such a method comprising a step of depositing drops of a fluid onto a surface of the piece of jewelry, fine jewelry, leather goods or writing instrument. TECHNICAL BACKGROUND OF THE INVENTION

[0002] To create a design on a piece of jewelry, leather goods, or writing instruments, pad printing is commonly used. This involves using a pad to transfer an ink pattern onto the object. A typical example is printing a brand or design on the outer surface of the piece. Pad printing is very precise and reproducible, resulting in a highly desirable aesthetic. However, it requires a separate tool for each design, which can make pad printing less cost-effective for small production runs. Furthermore, if multiple colors are needed, more tooling is required.

[0003] Inkjet printing of parts has already been attempted for small production runs that are difficult to make profitable with pad printing. However, the print heads currently available produce droplets with a diameter greater than 25 µm, which is incompatible with the superior aesthetics of pad printing. Indeed, curved lines are not sharp and exhibit a pixelated effect unsuitable for a high-quality part. Furthermore, only relatively low viscosity is compatible with such a print head, limiting the types of fluids that can be used. Finally, the gloss and uneven surface finish (orange peel effect) are significantly lower quality than with pad printing. SUMMARY OF THE INVENTION

[0004] The invention aims to propose a new type of manufacturing of a part comprising a deposition step which offers a precision and a result equivalent or even superior to pad printing while limiting the investment required regardless of the number of parts to be manufactured, the number of different fluids to be deposited or the nature of the fluid to be deposited.

[0005] To this end, the invention relates to a method for manufacturing a leather goods item, characterized in that it comprises the following steps: to obtain a rough draft of the leather goods to be decorated; to deposit a coating on at least part of the rough draft of a droplet fluid by electrohydrodynamic inkjet intended to form at least one decoration on the leather goods.

[0006] Advantageously, the process according to the invention uses an electrohydrodynamic inkjet deposition system that allows for versatile deposition on demand (continuous, semi-continuous, spot, etc.) and with a variety of fluid types (metallic, aqueous, polymeric, ceramic, adhesive, oil) with ideal precision for a wide range of applications. Typically, the same type of part, using the same tooling, can be used to mass-produce a virtually unlimited number of different deposits on each part.Thus, depending on the type of fluid present on each ejection nozzle, a first part can receive a first deposition pattern with a first type of fluid, a second part of the same type can receive a second deposition pattern with the first type of fluid, a third part of the same type can receive the first deposition pattern with a second type of fluid, a fourth part of the same type can receive the first deposition pattern with the first type of fluid and the second deposition pattern with the second type of fluid, etc., without each part being much more expensive to produce than another.

[0007] Furthermore, an electrohydrodynamic nozzle uses a simple potential difference to eject a droplet much smaller than the fluid meniscus at the nozzle outlet. By selectively controlling the potential difference, it is therefore very easy to parameterize the frequency and timing of droplet ejection to a dimension (diameter or height) approximately ten times smaller than with known ejection heads such as the piezoelectric type. This results in a coating that becomes compatible with a wide variety of parts of varying sizes, with resolution and finish at least equivalent to those of pad printing, without the limitations in terms of production costs and fluids.

[0008] Finally, any type of leather goods item can advantageously receive, on all or part of its external surface, the coating thus formed by a droplet deposition according to the invention. It is understood in particular that a wide variety of fluids deposited as droplets – the material of the leather goods item – can be considered to form the decorative coating without being limited to printing solely by electrohydrodynamic inkjet printing, that is to say, in particular combined with another type of printing, while maintaining a result at least equivalent to pad printing, with the advantage of being able, for example, to personalize an item on demand (word, signature, designs, etc.).), but also combined applications that are both technical and aesthetic, such as lubrication, bonding, metallization, or more generally, a selective deposition of a very precise coating that is not necessarily intended to be visible on the final application of the part, such as, for example, to form an authentication pattern that is not visible to the naked eye without magnification and / or special illumination.

[0009] The invention may also include one or more of the following optional features, taken alone or in combination.

[0010] This at least one decoration on the leather goods item can be created solely by depositing the coating using a droplet fluid via an electrohydrodynamic inkjet process. This achieves optimal resolution for each decoration and allows for a wide variety of colors with a higher quality finish than pad printing or conventional inkjet printing (such as piezoelectric or thermal inkjet).

[0011] The deposition step can form a coating with a thickness (vertical direction) of less than 5 µm. Advantageously, according to the invention, the coating can be very thin. Indeed, depending on the desired aesthetic effect, it may be desirable for some of the incident light to be transmitted (partial transparency) through the coating to partially reflect the color of the area beneath the coating, thus creating a particular aesthetic. Conversely, it may be desirable for no incident light to be transmitted (opaque) through the coating to reveal only the coating's color. The deposition step can therefore form a coating of a thickness (vertical direction) equal, for example, to 0.5 µm, 1 µm, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4 µm or 4.5 µm.Of course, depending on the application, the thickness could be greater, such as, for example, between 5 µm and 10 µm, without departing from the scope of the invention.

[0012] At least one partially closed contour of said at least one decoration of the leather goods piece may be formed solely by the step of depositing the coating using an electrohydrodynamic type inkjet drop fluid and the interior of each at least partially closed contour of said at least one decoration of the leather goods piece may be formed solely by a step of depositing another coating using an inkjet drop fluid (piezoelectric or thermal type).

[0013] This variant is preferred for large decorations, such as those with a horizontal dimension of at least 15 µm. Indeed, for the same surface area, electrohydrodynamic inkjet deposition is slower and more expensive to implement compared to piezoelectric or thermal inkjet deposition. Similar to cloisonné enamel, the closed contour(s) (one contour can enclose one or more other contours) are printed in high resolution, and then the interior (main surface) of each contour is printed in low resolution. This allows for a compromise between a finish equivalent to pad printing and a shorter overall printing time, while retaining the advantages mentioned above, such as customizing a leather item on demand (words, signatures, designs, etc.) at a competitive cost.Of course, the outline can also be partial by electrohydrodynamic inkjet deposition so that the missing part of the outline and the inside of the outline are made by conventional inkjet deposition in order to obtain lower production costs and times.

[0014] The deposition step may involve applying several adjacent drops to form a coating in a substantially flat layer on the leather item. The drops will form a pattern in the form of a layer of approximately constant thickness (vertical direction). Such a deposition can be used to create a decorative effect, such as a Superluminova® pattern, to create an electrical trace on the item, or to selectively deposit an adhesive fluid to allow the leather item to be bonded.

[0015] As a substitute for or in addition to the previous deposition, the deposition step may involve applying several overlapping drops to form a raised coating on the leather item. It is understood that the drops will form at least one pattern in the form of a stack of layers of varying thickness (vertical direction) depending on the fluid and the number of drops stacked in the same area.Such a stacking can provide a desired thickness, for example, in relation to an electrical or thermal conduction section to allow welding or brazing, to provide a curved thickness to improve aesthetics (monochromatic or polychromatic) such as, for example, to offer nuances of color, differences in saturation or even textures or artistic effects from the same fluid (at least one first drop being larger than at least one second drop and deposited in the same place) or to activate an epoxy glue by depositing the two constituents in the same location on top of each other to allow the bonding of the part or to deposit a first constituent on a first part and a second constituent on a second part, an activation such as a bonding of the first and second parts of the part being obtained by bringing the first and second constituents into contact.

[0016] The deposition step can apply droplets, each with a dimension (diameter or height) less than or equal to 10 µm, which is defined as the dimension beyond which a human eye, without a magnifying instrument, is no longer able to distinguish two points. Advantageously, a droplet dimension (diameter or height) between 1 µm and 2 µm has been obtained using an electrohydrodynamic inkjet device. The deposition step can therefore apply (deposit) droplets, each with a dimension (diameter or height) equal to, for example, 1 µm, 2 µm, 3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, or 10 µm. Of course, depending on the application such as, for example, bonding or metallization, the size of the drops could be larger such as, for example, between 10 µm and 25 µm, without going out of the scope of the invention.

[0017] The deposition stage can advantageously achieve a resolution of at least 2,500 dpi (dots per inch) according to the invention. This parameter is crucial for creating a high-quality decoration. Advantageously, a resolution of approximately 15,000 dpi has been achieved using an electrohydrodynamic inkjet device. Such a resolution overcomes current limitations and surpasses the human eye's ability to distinguish individual dots. The deposition step can therefore apply (deposit) drops at a resolution equal, for example, to 2500 dpi, 3000 dpi, 3500 dpi, 4000 dpi, 4500 dpi, 5000 dpi, 5500 dpi, 6000 dpi, 6500 dpi, 7000 dpi, 7500 dpi, 8000 dpi, 8500 dpi, 9000 dpi, 9500 dpi, 10000 dpi, 11000 dpi, 12000 dpi, 13000 dpi, 14000 dpi or 15000 dpi.Of course, depending on the application such as, for example, gluing or metallization, in which aesthetics are not a determining factor, the resolution could be less than 2,500 dpi without going out of the scope of the invention.

[0018] The deposition step can apply (deposit) drops each with a volume less than or equal to 1 pL (picoliters). More generally, the drops advantageously obtained according to the invention are on the order of femtoliters (fL) and no longer picoliters (pL), that is to say at least ten times less voluminous than with known ejection heads. The deposition step can therefore apply (deposit) drops with a volume equal to, for example, 0.1 fL, 0.2 fL, 0.3 fL, 0.4 fL, 0.5 fL, 0.6 fL, 0.7 fL, 0.8 fL, 0.9 fL, 1 fL, 2 fL, 3 fL, 4 fL, 5 fL, 6 fL, 7 fL, 8 fL, 9 fL, 10 fL, 20 fL, 30 fL, 40 fL, 50 fL, 60 fL, 70 fL, 80 fL, 90 fL, 100 fL, 150 fL, 200 fL, 250 fL, 300 fL, 350 fL, 400 fL, 450 fL, 500 fL, 550 fL, 600 fL, 650 fL, 700 fL, 750 fL, 800 fL, 850 fL, 900 fL, 950 fL or 1000 fL. Of course, depending on the application such as, for example, bonding or metallization, the volume of each drop could be greater than 1 pL without departing from the scope of the invention.

[0019] Advantageously, according to the invention, the deposition step can be used, for example, in addition to forming at least one decoration on the part, to form at least one electrically conductive layer on the part, to form at least one lubricating layer on the part, or even to form at least one adhesive layer on the part. Of course, other applications are possible without departing from the scope of the invention.

[0020] The fluid is electrically conductive, that is to say, for example, to have an electrical conductivity of at least 0.1 µS·m -1.

[0021] The fluid may include colored pigments in order to give at least one predetermined color to the coating(s).

[0022] The coating can be opaque to the human visible spectrum, that is, no part of the incident light from the human visible spectrum is transmitted through the thickness of the coating to obtain only the tint(s) of the coating(s).

[0023] The blank for the leather goods item can be made of leather. Advantageously, according to the invention, the process can thus be applied to a new blank or a blank belonging to a leather goods item already on the market in order to personalize it. It is understood that the process makes it possible to obtain a decorated leather goods item with a flexible blank.

[0024] Finally, the invention also relates to the use of an electrohydrodynamic type inkjet device for depositing a coating using a droplet fluid on a leather goods item with the advantages and results as explained above for the process of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other features and advantages of the invention will become clear from the description given below, which is by way of example and in no way limiting, with reference to the attached drawings, in which: there figure 1 is a schematic view of an example of a piece of jewelry or precious metalwork according to the invention; the figure 2 is a schematic view of an example of a leather goods item according to the invention; the figure 3 is a schematic view of an example of a writing instrument according to the invention; the figure 4 is a schematic diagram of an electrohydrodynamic nozzle according to the invention; the figure 5 is a schematic view of an example of an electrohydrodynamic inkjet device according to the invention; the figure 6 is a schematic cross-sectional view of an example of a belt with a coating obtained by electrohydrodynamic inkjet deposition according to the invention; the figure 7is a schematic cross-sectional view of a variant of the example of the figure 6 . DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

[0026] In the various figures, identical or similar elements bear the same references, possibly with an additional subscript. Therefore, a description of their structure and function is not systematically repeated.

[0027] In all that follows, orientations are the orientations of the figures. In particular, the terms "upper", "lower", "left", "right", "above", "below", "forward" and "backward" are generally understood in relation to the direction in which the figures are represented.

[0028] Furthermore, the orientation terms are understood with respect to the orthogonal coordinate system taken with reference to the normal orientation of an electrohydrodynamic nozzle 11, represented on the figure 5 and in which we can distinguish: a longitudinal axis X, horizontal extending from back to front; a transverse axis Y, horizontal extending from left to right; and a vertical axis Z, extending from bottom to top.

[0029] The term "horizontal" is defined with respect to the XY plane, the terms "vertical plane" are defined with respect to a horizontal component projected along the vertical Z axis.

[0030] By "human visible spectrum" we mean the range of wavelengths between 380 and 780 nm as defined by the ISO / CIE 11664-3:2019 standard of the International Commission on Illumination "CIE".

[0031] By "opaque" we mean that no part of the incident light is transmitted, for example, through the thickness of the 2D coating to give the leather item 2 only the color(s) of the 2D coating or the 2D, 2E coatings.

[0032] The term "droplet deposition of fluid by inkjet" refers to the droplet ejection stage achieved by a conventional inkjet device, such as piezoelectric or thermal inkjets. For example, a voltage is selectively applied to a piezoelectric nozzle, which uses the contraction / expansion of the piezoelectric material to eject a predetermined quantity of fluid (droplet) contained within the nozzle. More specifically, the piezoelectric nozzle expands under the applied voltage, decreasing the volume of its cavity and forcing a quantity of fluid (droplet) to be expelled from the nozzle's outlet.

[0033] By "deposition of a fluid droplet by electrohydrodynamic inkjet," we mean the droplet ejection step achieved by an electrohydrodynamic inkjet device. An electrohydrodynamic nozzle 11 utilizes the conductivity of the fluids directly within the nozzle 11 (supplied by a conduit 14) and the interactions between electrostatic forces and the fluids. More specifically, the charges of the elements in a solution (possibly colloidal) are split into positive and negative ions with electrical characteristics due to the electrical potential difference between the nozzle 11 and a substrate (which can be part 1, 2, or 4, as in the example of the figure 4 , an intermediate target 3 between the nozzle 11 and the part 1, 2, 4 as in the example of the figure 5 or a target (not visible) positioned so that part 1, 2, 4 is between nozzle 11 and the target).

[0034] After a potential is applied by a voltage generator 13, the difference in this potential between the nozzle 11 and the substrate 1, 2, 3, 4 will cause the electrical repulsive forces to create a substantially spherical curved surface (meniscus 12 at Figures 4 and 5 ) of the fluid at the outlet of the nozzle 11. The charges in the fluid will separate into positive and negative ions due to the strong electrical force in the meniscus 12, so that tiny droplets 12A form in the part furthest from the meniscus 12 (lower dome) relative to the nozzle 11. The resistance and energy required for extraction (ejection) are therefore low and allow better control of the generation of droplets 12A.

[0035] Several types of electrohydrodynamic ejection modes exist, depending on the different fluid properties and the applied potential (voltage) parameters. For example, in a microdroplet mode, the electric field strength at the tip of the nozzle 11 is sufficiently strong to cause the meniscus 12 to form a hemisphere or ellipse. Then, droplets 12A, much smaller than the outer diameter of the nozzle 11, form at the lowest point of the meniscus 12, where the electric field is concentrated. Consequently, the maximum size—specifically, the largest diameter or height—of the droplets 12A can be limited to a few micrometers, thus offering very high deposition accuracy and resolution.Other modes of ejection from an electrohydrodynamic nozzle 11 are also possible such as pulsed conical ejection (droplet from a conical meniscus) or continuous ejection (droplets linked together).

[0036] The term "based on" refers to a material or alloy comprising at least 50% by total mass or weight of a given element, such as 51%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% by total mass. Of course, in the case of a material or alloy comprising at least three elements, the expression "based on a first element" means a material or alloy consisting primarily, by total mass or weight, of that first element, which may in this case be less than 50% of the total mass. In what follows, unless otherwise indicated, all percentages (%) are expressed as percentages by total mass or weight.

[0037] By "polymer" we mean all materials formed from at least one polymer chain, sometimes called a fiber, of varying lengths, which can be of natural or synthetic origin.

[0038] By "ceramic" we mean all materials in crystalline and / or amorphous form based on an oxide, carbide, sulfide or nitride, especially metallic such as aluminium oxide (alumina, Al 2 O 3 ), silicon oxide (SiO 2 ), silicon nitride (SiN) or silicon carbide (SiC ).

[0039] By "piece of jewellery", we mean all types of decorative or ornamental articles that may include a non-precious decorative stone such as a bracelet, a necklace, a belt, etc.

[0040] By "piece of jewelry" we mean all types of decorative or ornamental articles that may include a precious or semi-precious stone such as a bracelet, a necklace, a belt, etc.

[0041] By "leather goods item", we mean all types of leather-based articles such as a bracelet, a bag, a belt, a saddle for example equestrian, a harness for example equestrian, etc.

[0042] By "writing instrument" we mean all types of portable articles that allow one to manually draw a pattern on a surface such as a pen holder, a mechanical pencil, a compass, a fountain pen, a ballpoint pen, a rollerball pen, etc.

[0043] Parts 1, 2, and 4 of the invention have been developed for application in the fields of jewelry, fine jewelry, leather goods, and writing instruments, as illustrated, for example, in figures 1 to 3Thus, part 1 can form all or part of a jewelry item, such as all or part of a necklace 1A, a chain, a bracelet, a pendant 1B, an earring, or a ring. Furthermore, part 2 can form all or part of a leather goods item, such as all or part of a necklace, a bracelet, a belt, a strap 2A, a loop 2B, a clasp 2C such as a buckle and pin set, or a shoulder strap. Finally, part 4 can form all or part of a writing instrument, such as all or part of a main body 4A, a head 4B such as a nib, a cap 4C, or a clip 4D.

[0044] To achieve the purpose of the invention, the process includes a first step intended to obtain a blank 2' of the leather goods piece 2 to be decorated, and then a second step intended to deposit a 2D coating on at least part of the blank 2' to form the decorated leather goods piece 2 which offers a precision and a finish equivalent or even superior to pad printing while limiting the necessary investment without any real aesthetic limitations.

[0045] Preferably, the blank 2' is made of leather, such as bovine or ovine leather, and includes at least a partial surface to be decorated. The blank 2' is thus flexible yet sufficiently firm for the decorative coating 2D, 2E. Advantageously, according to the invention, the process can therefore be applied to a new blank 2' or to a blank 1' from a leather item 2 already on the market in order to personalize it. This sufficient rigidity can be obtained, for example, from a thickness (vertical direction Z) of the blank 2' of at least 0.5 mm.

[0046] Of course, an intermediate layer (between the leather and the 2D, 2E coating) can be used to improve the adhesion (better grip between the leather and the 2D, 2E coating) and / or the aesthetics (better contrast between the leather and the 2D, 2E coating) of the decoration. Such an intermediate layer can be, for example, made of a transparent, semi-transparent, or opaque polymer.

[0047] The invention generally relates to the use of an electrohydrodynamic inkjet device 10 for depositing a droplet fluid 12A onto a leather goods item 2. Typically, the invention relates in particular to a method for manufacturing a leather goods item 2 comprising a step of depositing a 2D coating on at least a part of the blank 2' using an electrohydrodynamic inkjet droplet fluid intended to form at least one decoration of the leather goods item 2.

[0048] Advantageously, the process according to the invention uses an electrohydrodynamic (EHD) inkjet deposition system, which allows for versatile deposition on demand (continuous, semi-continuous, spot, etc.). In other words, the type of droplets (shapes, frequency, dimensions, etc.) can be easily adapted to the requirements. The device is simply controlled by the voltage generator, which induces pulses with a relatively high voltage amplitude, such as, for example, between 1 kV and 5 kV, i.e., for example, 1 kV, 1.5 kV, 2 kV, 2.5 kV, 3 kV, 3.5 kV, 4 kV, 4.5 kV, or 5 kV.

[0049] Thus, the electrohydrodynamic nozzle 11 uses a simple potential difference to eject a droplet 12A much smaller than the meniscus 12 of fluid at the outlet of the nozzle 11, as illustrated in particular in the figure 5By selectively controlling the potential difference, it is therefore very easy to parameterize the frequency and timing at which the 12A droplets are ejected, with a dimension (diameter or height) approximately ten times smaller than with known ejection heads such as the piezoelectric type. This results in a deposit suitable for jewelry, leather goods, or writing in general, with resolution and finish at least equivalent to those of pad printing, without the limitations in terms of production costs and fluids.

[0050] In the example illustrated in the figure 5The electrohydrodynamic inkjet device 10 includes an intermediate target 3 between the nozzle 11 and the part 1, 2, 4. This device 10 is preferred because it allows the part 1, 2, 4 to be completely independent of the device 10. The device 10 can thus be moved above the part 1, 2, 4, or conversely, the part 1, 2, 4 can be moved below the device 10, or even both the part 1, 2, 4 and the device 10 can be mobile relative to each other to obtain the desired deposition pattern for each part 1, 2, 4, which notably allows for lower-cost mass production while enabling a very wide variety of different possible depositions between each part 1, 2, 4.

[0051] Each droplet 12A ejected from the nozzle 11 passes through the intermediate target 3 via at least one through hole 3A in order to be deposited onto the part 1, 2, 4. In such a configuration, the vertical working distance (Z-axis) between the part 1, 2, 4 and the intermediate target 3 can be, for example, between 0.2 mm and 2 mm, i.e., for example, equal to 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or 2.0 mm. Of course, depending on the application, the distance could be less or greater without departing from the scope of the invention.

[0052] The type of fluid is highly varied (metallic, aqueous, polymeric, ceramic). Generally, the fluid used may contain colored pigments (or even a coloring chemical in a variety of materials) in a conductive medium or binder. The binder may be aqueous. In one variation, a UV-sensitive fluid may be formulated to harden when exposed to ultraviolet (UV) light to fix the deposit on part 1, 2, 4. Another variation may involve using a fluid sensitive to a gas such as air (oxidation) to fix the deposit on part 1, 2, 4. Preferably, UV-sensitive fluids are used because they dry very quickly, resulting in sharper and more vibrant designs. Solvent-based fluids that dry rapidly through the evaporation of one or more solvents may also be used.

[0053] Advantageously, the electrohydrodynamic inkjet deposition according to the invention can use fluids of virtually any viscosity. Typically, viscosities ranging from 0.5 to 10,000 cP (1 centiPoise = 1 × 10⁻³ Pa·s) have been successfully tested. However, the fluids used must necessarily be electrically conductive, even with very low polarity, for the process according to the invention to function. By way of non-limiting example, the fluid may have an electrical conductivity of at least 0.1 µS·m⁻¹.

[0054] Typically, the same type of part 1, 2, 4 or not, with the same tooling (same device 10), can mass-produce a number of different deposits on each part 1, 2, 4 without any real limit. Thus, for example, depending on the type of fluid present on each ejection nozzle 11, a first part 1, 2, 4 can receive a first deposit pattern with a first type of fluid, a second part 1, 2, 4 can receive a second deposit pattern with the first type of fluid, a third part 1, 2, 4 can receive the first deposit pattern with a second type of fluid, a fourth part 1, 2, 4 can receive the first deposit pattern with the first type of fluid and the second deposit pattern with the second type of fluid, etc., without each part 1, 2, 4 being significantly more expensive to produce than another.

[0055] The process according to the invention offers an unprecedented technological change by pushing back traditional limits and redrawing the field of possibilities with its droplet viscosity tolerance 12A up to 10,000 cP, droplet sizes 12A less than 1 µm (micrometer) and printheads with several hundred (or even thousands) of nozzles 11 containing one fluid (or several different fluids).

[0056] Finally, any type of part 1, 2, 4 (flat or embossed) can advantageously include, on all or part of its external surface, the 2D coating thus formed by a droplet deposition according to the invention. It is understood in particular that a wide variety of fluids deposited as droplets – the material of part 1, 2, 4 – can be considered to form the decorative coating without being limited to printing solely by electrohydrodynamic inkjet printing, that is to say, in particular combined with another type of printing, while maintaining a result at least equivalent to pad printing, with the advantage of being able, for example, to personalize a part 1, 2, 4 on demand (word, signature, designs, etc.).), but also combined applications that are both technical and aesthetic, such as lubrication, bonding, metallization or more generally a selective deposition of a very precise coating which is not necessarily intended to be visible on the final application of part 1, 2, 4 such as, for example, to form an authentication pattern which is not visible to the naked eye without magnification and / or without special illumination.

[0057] Advantageously, according to the invention, the deposition step can be intended, for example, in addition to forming at least one decoration on the piece 1, 2, 4 such as a motif 5 of the piece 1 of jewelry of the figure 1 , a motif 5 from piece 2 of leather goods from the figure 2 , to form at least one metal ring 9 on the writing piece 4 at the figure 3 , to form at least one decorative lubricating layer on the leather goods piece 2 such as between the clasp 2C and the strap 2A of the figure 2or even to form at least one luminescent adhesive layer on part 1, 2, 4 such as between the loop 2B and the strap 2A of part 2. Of course, other applications are possible without going out of the scope of the invention.

[0058] Said at least one decoration of the leather goods item 2 is preferably formed solely, that is to say exclusively, by the step of depositing the 2D coating using a droplet fluid 12A by electrohydrodynamic inkjet technology as, for example, illustrated in the figure 6 for a belt. We then obtain an optimal resolution of the whole of each decoration formed and it is possible to obtain a decoration with a wide variety of colors with a rendering of better quality than a pad printing or a classic inkjet printing (of the piezoelectric or thermal type).

[0059] According to a variant illustrated in the figure 7For an example of application to a belt, said at least one decoration of the leather goods item 2 is formed by at least one closed contour whose interior is filled. Thus, preferably, said at least one closed contour of said at least one decoration of the leather goods item 2 is formed solely by the step of depositing the coating 2D using an electrohydrodynamic inkjet droplet fluid, and the interior of each closed contour of said at least one decoration of the leather goods item 2 can be formed solely by a step of depositing another coating 2E using an inkjet droplet fluid such as, for example, piezoelectric or thermal.

[0060] This variant is preferred for large decorations, such as those with a horizontal dimension (X and / or Y axis) of at least 15 µm. Indeed, for the same surface area, electrohydrodynamic inkjet deposition is slower and more expensive to implement compared to piezoelectric or thermal inkjet deposition. Similar to cloisonné enamel, the closed contour(s) (one contour can enclose one or more other contours) are printed in high resolution, and then the interior (main surface) of each contour is printed in low resolution. This allows for a compromise between a finish equivalent to pad printing and a shorter overall printing time, while retaining the advantages mentioned above, such as customizing a leather item on demand (words, signatures, designs, etc.) at a competitive cost.

[0061] The deposition step can form a 2D coating with a thickness E (vertical direction Z) of less than 5 µm. Advantageously, according to the invention, the 2D coating can be very thin, which makes it possible, in particular, to faithfully reproduce the reliefs of the upper surface of the blank 2'. Indeed, depending on the desired aesthetic effect, it may be desirable for some of the incident light to be transmitted (partial transparency) through the thickness E of the 2D coating, 2E, to partially reproduce the color of the part beneath the 2D coating, 2E (such as the blank 2' of the leather goods piece 2) to give a particular aesthetic. Conversely, it may be desirable that no part of the incident light be transmitted (opaque 2D coating) through the thickness of the 2D coating to give only the tint(s) of the 2D coating or 2D, 2E coatings.The deposition step can therefore form a 2D coating with a thickness E (vertical direction) equal, for example, to 0.5 µm, 1 µm, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4 µm or 4.5 µm. Of course, depending on the application, the thickness E could be greater, such as, for example, between 5 µm and 10 µm, without departing from the scope of the invention.

[0062] Thus, depending on the thickness E and the ink composition, the 2D,2E decorative coating can be substantially opaque, that is, allow transmission across the entire visible human spectrum through the 2D,2E coating of at most 10%, such as, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%, and preferably at most 5%, such as, for example, 0.25%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5%, 2.75%, 3%, 3.25%, 3.5%. 3.75%, 4%, 4.25%, 4.5%, 4.75%, or 5%.

[0063] The deposition step can be designed to apply several adjacent drops 12A to form the coating 2D, 2E in a substantially flat layer on the leather part 2. It is understood that the drops 12A will form a substantially horizontal pattern (XY plane) in the form of a layer of substantially constant thickness E (vertical Z direction). Such a deposition can be used to create a decoration such as a Superluminova® pattern 5 on part 1, 2, to form a metallic ring 9 on part 4, or to selectively deposit an adhesive fluid to allow the bonding of part 2.

[0064] As a replacement or complement to the previous deposition, the deposition step may be intended to apply several superimposed 12A drops to form the 2D, 2E coating according to a raised layer (thickness along the Z axis not constant) on the part 1, 2, 4. It is understood that the 12A drops will form at least a substantially horizontal pattern (XY plane) in the form of a stack of layers of a thickness (vertical Z direction) variable depending on the fluid and the number of 12A drops stacked in the same place.Such a stacking can provide a desired thickness, for example, in relation to an electrical or thermal conduction section to allow welding or brazing, to provide a curved thickness to improve aesthetics (monochromatic or polychromatic) such as, for example, to offer a gradient of colors from the same fluid (at least one first drop being larger than at least one second drop and deposited in the same place), to activate an epoxy glue by depositing the two constituents of the epoxy glue in the same location on top of each other to allow the bonding of part 1, 2, 4 or to deposit a first constituent on a first organ and a second constituent on a second organ, an activation such as a bonding of the first and second organs of part 1, 2, 4 being obtained by bringing the first and second constituents into contact.

[0065] The deposition step can apply 12A drops, each with a dimension (diameter or height) less than or equal to 10 µm, which is defined as the dimension beyond which a human eye, without a magnifying instrument, is no longer able to distinguish two points. Advantageously, a dimension (diameter or height) of 12A drops between 1 µm and 2 µm has been obtained using an electrohydrodynamic inkjet device. The deposition step can therefore apply (deposit) 12A drops, each with a dimension (diameter or height) equal to, for example, 1 µm, 2 µm, 3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, or 10 µm. Of course, depending on the application such as, for example, bonding or metallization, the size of the 12A drops could be larger such as, for example, between 10 µm and 25 µm, without departing from the scope of the invention.

[0066] By depositing the 2D coating using a 12A droplet fluid via electrohydrodynamic inkjet in a single pass over the surface to be decorated, the thickness E (vertical Z direction) of the 2D coating is typically several hundred nanometers (e.g., between 400 and 600 nm), because the 12A droplets spread across the surface after deposition. Naturally, the thickness E (vertical Z direction) of the 2D coating increases with each subsequent deposition pass. Therefore, the 2D coating deposition step may involve two or more passes in order, for example, to achieve a 2D coating thickness E (vertical Z direction) greater than 1 µm.

[0067] The deposition stage can advantageously achieve a resolution of at least 2,500 dpi (dots per inch) according to the invention. This parameter is crucial for creating a high-quality decoration. Advantageously, a resolution of approximately 15,000 dpi has been achieved using an electrohydrodynamic inkjet device. Such a resolution overcomes current limitations and surpasses the human eye's ability to distinguish individual dots. The deposition step can therefore apply (deposit) 12A drops at a resolution equal, for example, to 2500 dpi, 3000 dpi, 3500 dpi, 4000 dpi, 4500 dpi, 5000 dpi, 5500 dpi, 6000 dpi, 6500 dpi, 7000 dpi, 7500 dpi, 8000 dpi, 8500 dpi, 9000 dpi, 9500 dpi, 10000 dpi, 11000 dpi, 12000 dpi, 13000 dpi, 14000 dpi or 15000 dpi.Of course, depending on the application such as, for example, gluing or metallization, in which aesthetics are not a determining factor, the resolution could be less than 2,500 dpi without going out of the scope of the invention.

[0068] The deposition step can apply (deposit) 12A droplets, each with a volume less than or equal to 1 pL (picoliters). More generally, the droplets advantageously obtained according to the invention are on the order of femtoliters (fL) and no longer picoliters (pL), that is to say, at least ten times less voluminous than with known ejection heads. The deposition step can therefore apply (deposit) 12A drops with a volume equal, for example, to 0.1 fL, 0.2 fL, 0.3 fL, 0.4 fL, 0.5 fL, 0.6 fL, 0.7 fL, 0.8 fL, 0.9 fL, 1 fL, 2 fL, 3 fL, 4 fL, 5 fL, 6 fL, 7 fL, 8 fL, 9 fL, 10 fL, 20 fL, 30 fL, 40 fL, 50 fL, 60 fL, 70 fL, 80 fL, 90 fL, 100 fL, 150 fL, 200 fL, 250 fL, 300 fL, 350 fL, 400 fL, 450 fL, 500 fL, 550 fL, 600 fL, 650 fL, 700 fL, 750 fL, 800 fL, 850 fL, 900 fL, 950 fL or 1000 fL. Of course, depending on the application such as, for example, bonding or metallization, the volume of each drop 12A could be greater than 1 pL without departing from the scope of the invention.

[0069] The initial results, highlighted by routine parameterization tests of device 10 according to the fluid to be deposited, should allow for finer droplet sizes on the order of 0.2 µm.

[0070] By way of example, and by no means limiting the application of the invention, one can imagine obtaining, using the process according to the invention, embossed or flat decorations, printing on flat or curved surfaces, selective metallization, lubricant dispensing, adhesive application, on-demand customization, authentication, etc., without changing the device 10. It is thus possible, in particular, to create diffractive decorations by direct printing on a blank 2' of a part 1, 2, 4, such as a cap 4C of a writing part 4 or a clasp 2C of a leather goods part 2 with submicron structures. One can also imagine creating OLED-type prints using special fluids (for example, quantum dots) on a part 1, 2, 4.It is also possible to directly print submicrometer (or a few micrometers) electrical traces invisible to the naked eye, enabling the inductive charging of a battery, the creation of RFID devices, or solar devices. Finally, the process according to the invention also allows the direct printing of semiconductors and / or focusing microlenses for a solar device comprising, for example, at least one photovoltaic cell.

[0071] The invention is not limited to the embodiments and variations shown, and other embodiments and variations will be obvious to those skilled in the art. Thus, the above embodiments are examples. Simple features of different embodiments can also be combined and / or interchanged to provide other embodiments.

[0072] Furthermore, the invention is not limited to the fields of jewelry, fine jewelry, leather goods, or writing instruments. Thus, the invention could also be applied in other fields such as, for example, watchmaking, tableware, optical instruments, or firearms. LIST OF REFERENCES

[0073] 1 - Jewelry or gemstone item 1A - Necklace 1B - Pendant 2 - Leather goods item 2A - Strap 2B - Loop 2C - Clasp 2D - Coating 2E - Other coating 3 - Intermediate target 3A - Through hole 4 - Writing item 4A - Main body 4B - Head 4C - Cap 4D - Clip 5 - Decorative motif 9 - Metal ring 10 - Electrohydrodynamic inkjet device 11 - Nozzle 12 - Meniscus 12A - Droplet 13 - Pulse voltage generator 14 - Fluid supply line E - Deposition thickness

Claims

1. Method for manufacturing a leather goods item (2), characterized in that It includes the following steps: - to obtain a blank (2') of the leather goods piece (2) to be decorated; - to deposit a coating (2D) on at least part of the blank (2') of a droplet fluid (12A) by electrohydrodynamic inkjet intended to form at least one decoration of the leather goods piece (2).

2. Method according to the preceding claim, wherein said at least one decoration of the leather goods piece (2) is formed solely by the step of depositing the coating (2D) using a droplet fluid (12A) by electrohydrodynamic inkjet.

3. Method according to the preceding claim, wherein the deposition step forms a coating (2D) of a thickness (E) less than 5 µm.

4. Method according to claim 1, wherein at least one at least partially closed contour of said at least one decoration of the leather goods (2) is formed solely by the step of depositing the coating (2D) using a droplet fluid (12A) by electrohydrodynamic inkjet and the interior of each at least partially closed contour of said at least one decoration of the leather goods (2) is formed solely by a step of depositing another coating (2E) using a droplet fluid by inkjet.

5. A method according to any one of the preceding claims, wherein the deposition step is intended to apply several adjacent drops (12A) to form the coating (2D, 2E) in a substantially flat layer on the leather goods piece (2).

6. A method according to any one of the preceding claims, wherein the deposition step is intended to apply several superimposed drops (12A) to form the coating (2D, 2E) in relief layer on the leather goods piece (2).

7. A method according to any one of the preceding claims, wherein the deposition step applies drops (12A) each of a dimension less than 10 µm.

8. A method according to any one of the preceding claims, wherein the deposition step has a resolution of at least 2,500 dpi.

9. A method according to any one of the preceding claims, wherein the deposition step applies drops (12A) each of a volume less than or equal to 1 pL.

10. A method according to any one of the preceding claims, wherein the fluid is electrically conductive and comprises colored pigments.

11. A method according to any one of the preceding claims, wherein the coating (2D, 2E) is opaque over the human visible spectrum.

12. A method according to any one of the preceding claims, wherein the blank (2') of the leather goods piece (2) is leather-based.

13. Use of an electrohydrodynamic type inkjet device (10) for depositing a decorative coating (2D) using a droplet fluid (12A) on a leather goods item (2) intended to form at least one decoration of the leather goods item (2).

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