TITLE

A METHOD TO ALLOW THE REALIZATION OF A PRINT ON A LEATHER

LAYER

Scope of the invention

This present invention relates to the technical field of leather manufacturing.

In particular, the invention relates to an innovative method that enables long-lasting printing on sheets of leather.

Brief overview of the process

At present, the creation of designs, or prints if you prefer, on sheets of leather leaves a lot to be desired in terms of the obtainable quality of the product, in particular when it comes to the durability of the design itself.

The outer surface of the leather, which is referred to as the "grain" in technical jargon, is particularly smooth, impermeable and oily. These external properties of the leather can be attributable to various reasons including, for example, the processing the leather undergoes in order to create the final product.

To this effect, when you try to imprint a design the colours are not actually absorbed and remain on the outer surface. The properties of this outer surface of the leather are such that the design does not take well and very quickly water, cleaning and usage can cause the design to be altered, swiftly turning the leather sheet into waste.

Obviously, when the sheet of leather on which the design is printed is part of a fashion item, accessory, shoe or item of clothing it is clear that the gradual alteration of the design itself makes the overall product unmarketable, also considering the cost of putting these products on the market.

It is precisely for this reason that the majority of companies operating within the industry prefer to avoid producing and marketing leather products that have designs imprinted directly onto the leather.

This is clearly a significant manufacturing limitation .

In addition, creating a design on the leather's outer surface using traditional methods is not satisfactory when the leather is subject to strong traction, for example when it is bent to form the shape of a shoe. When this happens, a cracking effect occurs in the design, which obviously makes the quality of the design itself unacceptable.

Summary of the invention

The scope of this invention is therefore to provide a method for printing or creating a coloured design, if you prefer, on a sheet of leather in a way that resolves the aforementioned technical problems.

In particular, the aim of this invention is to provide a process that is functional and provides a final product, i.e. the design on the leather, that is long lasting and does not crack when subjected to traction.

These objectives, along with others, are therefore achieved using this method for printing or creating a coloured design, if you prefer, on a sheet of leather, in accordance with claim 1.

This method includes the following phases:

Developing of the design through removal, with a laser (100, 101), of a surface layer of the sheet of leather, the removed thickness of which is thinner than the overall thickness of the sheet of leather, so as to brought to the light an underlying layer (A' ) of the leather reproducing the design.

Arranging the sheet of leather in a printing machine (200) which provides to apply a colour or a combination of predetermined colours onto the underlying layer reproducing the design.

The technical properties of the underlying layer that is revealed (referred to as the "flesh" in technical jargon) are very different from those of the surface level (referred to as the "grain" in technical jargon) .

In particular, this underlying layer is not smooth and oily like the external layer, and therefore absorbs the colour much better.

The result is that the colour is perfectly locked in and proves to be long lasting, with no cracking effect in the colour when the sheet of leather is subject to traction .

It is not essential to remove a thick layer as just a few tenths of a millimetre are sufficient, for example from a tenth of a millimetre up to a millimetre and more.

In fact, the thickness of the layer removed is a criterion that can be varied as needed, depending on the requirements and the desired effect.

With a thin layer removed, for example around a tenth of a millimetre, the indent that is formed when material is removed even becomes imperceptible to the touch as it is actually filled with the colouring itself.

In other cases, you may actually want to create this indented effect, or may want to make the bas-relief that determines the composition of the design visible even after it is filled with the colouring.

The removal of the layer using the laser is preferably preceded by the application of a protective layer over a predetermined area of the sheet of leather, preferably the entire sheet of leather, containing at least the area intended to be lasered and the surrounding area.

This prevents damage to or stains on the area of the sheet of leather that surrounds the part due to be lasered and that will not be printed.

There will also preferably be a phase during which a light-coloured colouring, preferably white, is applied to the layer of leather revealed before the actual colouring is applied.

The light colour, for example white, creates a neutral base upon which the colours are more intensified, thus preventing unexpected changes to the colour applied. This is because the colour of the leather revealed is particularly dark and may change the actual tone of the colour later applied, thereby creating a final effect that is different from what was intended.

Further benefits can be inferred from the remaining dependent claims.

Brief description of the designs

Other features and benefits offered by this invention's method will be made clear in the following non-exhaustive description of some examples of its operational forms, with reference to the enclosed designs, in which:

- Figure 1 and Figures 3-8 describe the production phases according to this invention;

- Figure 2 describes a paper tape applied to the sheet of leather being processed;

- Figure 9 outlines, by comparison, a design to be created using the laser machine that differs from the one to be completed with colouring on the printing machine, in such a way that the electronic files of the two designs are preferably two separate files;

- Finally, Figure 10 shows a summary flow chart.

Description of some preferred operational forms

Figure 1, with the number 1, represents a generic sheet of leather whose rectangular shape shown in the illustration is clearly not meant to be limitative.

The sheet of leather could be of any size or, obviously, any thickness.

Very schematically and in thin dotted lines, Figure 1 depicts a design (specifically of a snake) that you may wish to create on the same sheet.

The design is shown in thin lines as during this stage, as outlined below, it has not yet been transferred to the sheet of leather; it is shown in Figure 1 solely to provide an idea of the type of design you may want to create and its position on the sheet.

Obviously, the design can be any shape and size and can depict anything, for example a flower, object or animal. In this sense, the snake is solely illustrative and not limitative.

Given the above, and as outlined in Figure 1, you can then proceed with the application of a protective sheet 2 which is applied to the outer surface of the sheet of leather being printed, that is, on surface 4 with reference to Figure 7.

By way of example, the protective layer could be a simple paper tape, such as those used in the stationer's or the adhesive ones used for car body repairs. This paper tape is schematically shown in Figure 2 in the form of a roll .

Depending on the area being covered, more pieces of tape can be placed alongside each other, or a single larger piece of tape can be used to speed up the process.

It does not need to be transparent and its function is to protect the area of leather not being processed in order to prevent accidental marks.

As outlined below, the protective sheet must therefore have certain impermeable properties in order to prevent the paint product applied from penetrating and being deposited on the surface of the sheet of leather being protected.

Paper tape meets these requirements well and can also be easily removed at the end of the process without leaving any residue.

Once the paper tape has been applied to the entire surface of the leather or to part of it that obviously includes the area due to be processed, the design can then be created.

This design is created using incisions, or by removing material if you prefer, using a Laser 100 machine that emits a laser beam that burns the leather in the targeted zone.

The laser is already widely used for other purposes within the field of leather production, for example to create holes in leather according to a predetermined pattern .

As schematically shown in Figure 3, the machine interfaces with, or is itself equipped with, a computer that acquires a design in electronic form, usually in a CAD format such as ".DXF", to reproduce.

Figure 3 actually shows an example design of a snake that is encoded according to this type of CAD electronic file (or another design software) .

Once the sheet of leather being processed is positioned underneath the head that emits the laser beam 101, this laser beam is moved according to the CAD design inputted into the memory and accurately reproduces the design by making incisions on the leather itself, or by removing an equivalent area.

In fact, Figure 4 shows the CAD design uploaded to the machine 100 that emits a laser 101 onto sheet 1, laid down on the work surface 102.

Of course, the system obtains the initial reference coordinates for a launch that positions the laser beam correctly over the sheet.

However, this in itself is prior art and further details will not be provided here.

The thickness of the removed layer may vary from a tenth of a millimetre to more, but in any case, must be thinner than the total thickness of the leather being processed. To this effect, this method does not involve through holes being created, but rather a bas-relief design that reveals the underlying layer of the leather, referred to as the "flesh" in technical jargon.

Indeed, section B-B of Figure 7 shows the depth of the incision that actually creates the bas-relief that reveals layer 3, in relation to surface 4.

Figure 5 actually shows the snake created by removing a layer of leather in the area marked by the perimeter of the snake itself, thus creating a groove in the shape of a snake.

The enlarged Figure A, included in Figure 6, shows part of this groove and the section in Figure 7 shows its thickness or height.

All you need to do is correctly adjust the strength of the laser beam in order to obtain the desired depth of the incision.

If desired, the depth can vary within the design being created.

Revealing the underlying layer of the leather ensures that the colour that is then applied is able to fully take as the properties of this underlying layer are very different from those of the leather's external surface .

Obviously, when the paper tape is generally arranged in the area of and around the design, the laser beam will burn the local area, including the tape, overall causing a sort of local incineration of both the tape and the leather to the desired depth.

Before the subsequent operations are completed, cleaning should be undertaken in order to eliminate any combustion residues that may be present on the sheet of leather being processed.

This operation can be completed in various ways, for example by placing the sheet being processed in a sandblasting machine that blasts the sheet with jets of air and grains of sand in order to efficiently clean the surfaces of any residue.

This also enables the subsequent phase of the colouring itself to take much better.

Other cleaning machines that use, for example, only jets of air may also be used.

The next phase sees the application of a light paint, preferably white, on the lasered area of incision.

During this stage the protective tape applied previously comes into play as it protects the areas outside of the lasered area from this paint, ensuring that once the tape is removed these areas are intact and are not accidentally marked by the paint applied.

Once the paint is applied, the colouring itself of the bas-relief area created can be completed, now that there is a light base upon which to apply the colour.

To do this, a digital printer 200 (see Figure 8) such as those used to print on T-shirts, for example, is used .

For example, you could use an Epson SureColorF2000 printer .

The advantage of using a digital printer is that they distribute the colours in line with a predefined programme using an electronic design, in this case usually a ".tif" CAD design.

As shown for clarification purposes in Figure 9, the electronic designs used in the laser machine and in the printer, are generally two distinct and separate electronic designs.

This is because within the laser machine the design must delineate the area Bl to be removed and the depth to which it will be removed.

However, the same design within the printer must set other parameters that, as shown in Figure 9, include the various colours to be used to colour the various B2.. Bn sub-areas that make up the design.

Thus, as they are two completely independent designs you have the benefit of being able to quickly change the parameters relating to the laser process or colouring.

For example, you can change the depth of the incision made by changing the design used in the laser machine, whilst leaving the settings relating to the colouring unchanged. Or, in contrast, you can leave the parameters relating to the laser work unchanged whilst modifying the shades used in the colouring process, or even which sub-areas will be coloured as part of the design .

Clearly, although this is more complex, this does not exclude the possibility of using the same electronic file to be transferred from the laser machine to the printer, and vice versa.

In order to centre the sheet precisely within the printer, it is advisable to use a template that serves as a reference point . On the whole, this method enables you to obtain a high quantity of products that are identical to one another, as this is in fact a repeatable industrial process .

The sheet of leather is inserted into the printer, which sprays the colour according to the predefined programme within the areas removed and delineated by the electronic design, therefore directly onto the "flesh" that depicts the design (surface 3 of Figure 7) and leaving the "grain" intact (surface 4 of Figure 7) .

The light or white colour that was previously applied creates a neutral base on the "flesh", which is generally dark in colour, ensuring that the tone of the colours sprayed is not changed by a dark background.

However, it is not essential to apply a light or white colour onto the bas-relief area if you are using, for example, leather that itself is lighter in colour.

The light or white colour can be applied using either a spraying machine or a brush.

The colour then applied to the "flesh", in other words onto the bas-relief, using the printer will take perfectly and will be long lasting.

In addition, the paint will not crack when the leather is subject to traction, and using a digital printer facilitates the production of a high number of items with a high level of reproducibility.

Of course, in theory you could use other methods for carving the design, for example a machine that removes the material using a point. However, in this case acceptable results can be achieved when working with sole leather, which is a tougher leather. For much softer leather the best results are achieved using a laser.

Furthermore, in all cases it is the laser solution that largely provides better results, not only in terms of quality but also in terms of the speed in which the design is created.

Preferably, but not necessarily, it may also be useful to apply a stiffening sheet on the sheet of leather being processed, on the opposite side to the surface on which the bas-relief is being created. For example, you may wish to apply a plasticised sheet.

This sheet limits the buckling of the surface of the leather being processed, enabling the sheet to stay as straight and flat as possible. Thus, the quality of the design and colouring is clearly optimised as the processed surface is kept perfectly flat.

Furthermore, once the sheet of leather has been prepared for processing, therefore fitted with the upper protective sheet and the lower stiffening sheet, you can proceed with the pressing stage in a press in order to ensure that these external sheets fully adhere and to make the surface of the leather being processed perfectly flat and straight.

At the end of the colouring, and therefore of the entire processing, if necessary you can proceed with spraying a brightener that enhances the brightness of the colours before removing the protective tape.

The final figure shows a flow chart that summarises the invention's phases.

The diagram shows the preparation phase of the electronic design for the laser machine, as well as the design for the printer.

You can then proceed with protecting the sheet of leather using, for example, paper tape.

You can then proceed with the lasering phase and subsequent cleaning.

Then, apply the light or white colour within the lasered areas of incision before then proceeding with the colouring itself using the printer.

Finally, move to the drying stage (for example, in still or forced air) and the potential application of a brightener and the removal of the protective covers from the sheet of leather.

In this description, the term "Leather" is intended to refer to all materials derived from animal hide, also including sole leather.