Technical Field

The invention relates to a transfer printing method for transferring an image consisting of a picture, a letter, a word, a group of words, a photograph, a logo or a pattern to the transfer foil first and then transferring it from said transfer foil to the natural leather.

Prior Art

When we examine the general printing techniques of today, we can sum up the printing methods applied for the purpose of giving a visual characteristic such as images or patterns to the inflexible and uneven surfaces image such as natural leather under two main headings. One of these printing methods is the direct printing and the other one is the transfer printing method.

The direct printing method is used today to provide many visual features such as pattern, color, shape, number, picture to many material surfaces. This printing method is based on the direct transfer of the coloring chemicals used for applying a pattern on the surface to be printed. Techniques for implementing this method are diversified as analog printing techniques such as rotagravure printing technique, flexo printing technique, offset printing technique and digital printing techniques such as inkjet printing technique and laser printing technique.

The common characteristics of materials that can be printed on surfaces by applying direct printing technique are that they must be scaled by a certain mold or shaping method. As far as details are concerned, printing machines that can print with direct printing techniques can print using the two different forms of sorting of the materials they print. These the printing machines that are capable of doing roller to roller printing on rolled state of the material to be applied printing and the layer printing machines that are capable of printing on materials in layers and in shapes and dimensions suitable for industrial printing such as square and rectangular respectively.

It is very difficult to print on a material that has an uneven structure such as natural leather. Natural leather does not have a certain style. Each leather shows dimensional and formal differences. This physical condition of the natural leather makes it difficult to apply printing directly to the leather surface by applying a direct printing technique. Different printing machines have been developed in recent years that use the direct printing technique to solve this problem, which is caused by the formal condition of the natural leather layer and is causing problems for machines that print using existing printing techniques. However, the difficulties in using these machines, developed with the aim of printing on the natural leather surface by direct printing and machine speeds have some difficulties in meeting the requirements regarding to the industrial production demands. Another important drawback apart from speed and production difficulties is the loss of color vividness due to the printing surface in direct printing technique.

The permeable structure of the leather surface causes the ink that is transferred to the leather surface to be absorbed by it. The ink that penetrates deeply through the leather surface creates a negative condition for the formation of vivid colors on the surface. This situation causes loss of color on the leather surface as well as negativity in the quality of the visual desired to be formed on the leather surface by causing mixing of colors into each other.

As a result of all these negativities, natural leather has become recognized in printing industry for many years and the printing technique used has become the transfer printing technique. The transfer printing technique is preferred because it provides the advantage that the printing materials used for transfer can be operated on machines that provide the speed and quantity that can meet the industrial printing needs and provide more vivid colors and clear patterns on the leather surface when compared to the direct printing technique.

The transfer printing technique is a method in which any pattern, shape or number desired to be applied to the surface of the final product is previously printed on another carrier material and transferred from the printed material to the final product by using various methods. Today, many analog and digital printing machines that use printing techniques such as grayscale, offset, digital inkjet and digital laser are used in transfer printing. Surface printing works are performed in many sectors such as textile, advertisement, household goods and furniture sector with the transfer printing method today.

The transfer printing technique, which is used for printing on many materials in the printing sector, has been used in the natural leather printing industry for many years. Non-standardized measurements and surface properties of the natural leather require the use of transfer printing.

In the transfer printing method, a surface larger than the leather surface can be printed. The material that will transfer the print to the final surface is called the transfer film, paper or foil according to the raw material of the material. Transfer films can be rolled or layered on the specified dimensions. In this way, the pressure on the entire surface of the natural leather is transferred perfectly.

The transfer of the print from the printed transfer foil to the natural leather surface is carried out in a pressing machine which applies heat to the sheet or roller roller to a certain degree. The presses that perform the transfer process as a layer are called the layer press, and the transfer presses that perform the transfer process to the roller are called the calender press. Prior to pressing, the thermal glue is applied in the spraying machines so that natural leather that is tanned in the tannery can be printed on the transfer foil. Pre-drying of the glue applied to the natural leather surface is performed in the heat tunnel. Prepared natural leather is ready for transfer operation. The machines that transfer the print from roll-to-roll transfer foils to the natural leather surface work at a certain speed generally in the heat range of 90-140 degrees Celsius. The pre-prepared leather surface is passed between two cylinders which apply heat and pressure in a certain amount to be combined with the printed side of the transfer foil. At the same time, the adhesive property of the glue on the heat applied leather surface is activated. The glue with the adhesion feature activated on the natural leather surface holds the pattern printed on the transfer foil. The transfer foil and natural leather exiting from the pressing section of the machine as a incorporated with each other, pass over the cooling roller at the end of the machine. Cooling rollers shorten the time period required for decreasing to lower temperatures ensuring disappearance of adhesion characteristics of the thermal glue so that the efficiency of the transfer process is increased. After the cooling rollers, the natural leather which is combined with the transfer foil and the surface of is cooled down is removed from the transfer foil manually. In this way, the pattern on the transfer foil is transferred to the natural leather surface and the transfer process is finished.

There are some drawbacks of the rotogravure printing technique which prints the pattern, picture or number on the surface of the transfer foils already used in the natural leather impression process. For example, the preparation of the molds of the rotogravure printing technique requires requires high cost and long time. Every new printing to be done requires new molds. Depending on the characteristic of the printing, the number of these molds usually varies from 1 to 8 (CMYK colors) in most cases. These costs affect the minimum number of prints. The minimum printing quantities a pattern can be tens of thousands of meters due to the mould costs. It has been seen over time by the companies that transfer printing to the natural leather surface that the printed transfer foil, which has to be procured more than their actual needs, has become idle without any usage. This, of course, means a waste product. Since the molds needed to print the transfer foils already used in the natural leather imprinting process on the rotogravure machines take time to prepare, the rehearsal prints and the samples to be prepared require a certain amount of time. This causes temporal disadvantages in the process of product approval.

Especially the digital printing machines, which have started to be used in the field of advertising and printing, long with the developing technology, have started to be used in the leather industry in recent years. The transfer foils used for the transfer printing method, which is used especially in the field of natural leather imprinting, have started to be printed with digital printing machines. Digital machines do not need mold compared to analogue printing machines. As they can print without mold, they allow saving on mold costs. Because it saves from the cost of the mold, it brings the ease of printing even in very low quantities. It does not necessitate printing more than on the required quantity. The ease of printing in lower quantities will also increase the versatility of printing. The diversified end product brings purchasing convenience to the end user. The ease of buying provided is a factor that helps increase the consumption of the product.

In addition, samples can be prepared much faster on digital printing machines than it is on analogue printing machines. The approval process of quickly- prepared samples is shortened and this helps to proceed with the production process more quickly. However, one of the most important advantages of digital printing machines is the increase in printing qualities. Picture clarity and color grading are more outstanding compared to the analogue printing machines. The advantage of being able to play with printing characteristics with different drop sizes is one of the most important advantages of digital printing machines compared to analogue printing machines.

Digital printing machines, which are currently used in the field of natural leather printing and known as transfer printing technology, are printing machines that use solvent ink. Solvent digital printing machines get their name from the ink they use when printing. The 3 types of inks used in digital printing machines are Solvent, UV and latex in the commercial and printing sectors. Machines using solvent based ink are called solvent digital printing machines. Solvent digital printing machines have also been diversified in the name of eco-solvent along with the development of inks formulated with chemicals that contain ecological content in subsequent years. UV inks are inks that are cured with ultraviolet light. Printing machines that use UV ink are called UV digital printing machines. The latex content ink composition is water based. They are called with this name because they use binders in the latex group. Digital printing machines that use a latex content ink composition are called Latex digital printing machines.

In the last few years, transfer foils used in natural leather transfer printing have begun to be printed with digital printing machines that use solvent and eco- solvent printing ink. As a result, prints in lower quantities were possible, and pattern and color diversity was achieved together with higher quality print results. With the advantages it provides, there are also some ink-related disadvantages in the machines that print using solvent and eco-solvent printing ink. For example, transfer foil which is applied transfer printing with solvent and eco-solvent printing ink is produced by a very small number of the manufacturers specially for this technique. Hence, there are difficulties in terms of price and supply. Along with these, the image is transferred from the two-layer transfer foil to the substrate (surface to be printed) by lamination process. In said transfer process a layer of transfer foil is transferred to the substrate (printed surface) together with the print (image).

The printing method subject to the invention is the use of latex digital printing machines which are generally used in advertisement industry and print by using inks that contain water based latex substances for performing printing on the transfer foil using in natural leather transfer printing. It is possible to print on outdoor products event banners, vehicle graphics, backlit products, traffic signs, wall coverings and canvas by using latex printing machines on the canvas. The printing process takes place by transferring the ink containing the latex mixture on fabric or a similar material. However, this mentioned printing and transfer method can not be directly printed on the natural leather surface. In a printing process involving a latex mixture ink, it is possible to print on smooth-edged surfaces that can be rolled up in rolls.

Latex printing machines enable printing with more vibrant colors than solvent and eco-solvent printing machines. In addition, latex-based ink composition has a more flexible structure than its competitors. One of the most important elements that is desired in leather is the flexibility of the leather. Leather can be used in materials such as the shoes, armchairs, accessories etc. where bending and flexing are necessary. The latex containing ink composition has a flexible structure. It is compatible with leather. The latex-containing ink composition must also stretch without cracking along with the stretching on the printed surface. No printing defects occur in situations such as the bending of the leather by printing with a latex containing ink composition. In addition, the latex-containing ink composition contains chemicals that are less harmful to the environment than solvent and eco- solvent inks as it is water-based.

Latex printing machines use a preprinting lacquer called "optimizer" with colorant printing inks. This printing lacquer is transferred to the surface before the latex-containing ink composition reaches to the printing surface, helping the latex- containing ink composition adhere to the surface and creating a clearer pattern and images without causing said composition to flow off the surface. This feature of the latex printing machine offers the advantage of printing on more product surfaces than machines printing with solvent and eco-solvent ink. This eliminates the need for a special coating for the transfer foil to be transfer printed on the natural leather surface. For the transfer foil to be printed with the latex machine, polyester film with the thicknesses of 8-50 microns, with no surface treatment is used. The US patent US20180001685A1, which is incorporated in the present art, discloses transferring a latex containing ink composition onto a surface. In said transfer process, an ink composition containing latex particles is used to form an image on the release paper. In said method, the image is transferred from the transfer paper to a substrate (printing surface) by lamination. During lamination process; the substrate is laminated to a transfer paper and a release paper. Thus, the image is transferred from the printed transfer paper to the substrate. It is possible to print on outdoor products, event banners, vehicle graphics, backlit products, traffic signs, wall coverings and canvas by using latex printing machines on the canvas. The printing process takes place by transferring the ink containing the latex on fabric or a similar material. However, this mentioned printing and transfer method can not be printed on the natural leather surface.

Purpose of the Invention

The purpose of the invention is to create a new transfer printing method that ensures good adhesion to the leather surface, has high light fastness, and high tensile strength.

Another purpose of the invention is to create a new transfer printing method that provides scratch-resistant printing on the leather surface.

Another purpose of the invention is to create a new, ecologic and environment-friendly transfer printing method for printing on the leather surface.

Another purpose of the invention is to create a transfer printing method that allows the leather surface to have a more flexible structure.

Another purpose of the invention is to create a transfer printing method that can be applied quickly. Another purpose of the invention is to create a transfer printing method that enables easy and quick color and pattern revisions to the leather surface.

Another purpose of the invention is to provide to create a transfer printing method that makes it possible to print fewer copies.

Another purpose of the invention is to ensure to make the transfer process without using different molds for natural leather of different size and variety.

Another purpose of the invention is to create a transfer printing method in which only the pattern is transferred, not the pattern of any layer of the transfer foil together with the pattern.

In the method of transfer printing to the natural leather surface developed to realize aforesaid purposes; polyester film is used as transfer foil (40). The polyester film used as transfer foil (40) can withstand the temperatures used in the transfer process thanks to its characteristic structure. After the desired image is transferred onto the non-corona treated transfer foil (40) by using the digital latex printing machine (30), the image is transferred to the surface of the binder applied natural leather (10) through the transfer press (50).

Description of Figures

Figure - 1 attached is the general view of the natural leather (20).

Figure- 2 is a general view of the process of applying heat-active adhesive (20). In this stage, pre-painting of the natural leather surface can be done with heat- active adhesive.

Figure - 3 is a perspective view of the digital latex printing machine (30), which allows the transfer of the print (42) to the transfer foil (40).

Figure - 4 is a side view of the process of transferring the print (42) onto the natural leather (10). Figure-5 is a perspective view of the transfer foil (40) having only the first layer (41).

Figure-6 is a perspective view of printed (42) state of the transfer foil (40) having only the first layer (41).

Figure - 7 is a perspective view showing that only the print (42) is transferred onto the natural leather (10) by the transfer press (50).

Figure 8 is a perspective view of transfer foil (60) having the first layer (61) and second layer (63) used in the present technique.

Figure-9 is a perspective view of printed (62) state of transfer foil (60) having the first layer (61) used in the present technique.

Figure- 10 is a perspective view showing that the second layer (63) has been transferred with the printing (62) in the method used in the present technique.

Numbers and names of main parts mentioned in the figures are given below.

(10) Natural leather (substrate)

(20) Heat-active adhesive

(30) Digital latex printing machine

(40) Transfer foil

(41) The first layer (release paper)

(42) Print (image)

(50) Transfer press

(60) Transfer foil

(61) The first layer (release paper)

(62) Print (image)

(63) The second layer (printed transfer paper)

Detailed Explanation of the Invention

The invention relates to a transfer printing method for transferring an image consisting of a picture, a letter, a word, a group of words, a photograph, a logo or a pattern to the transfer foil (40) first and then transferring it from said transfer foil (40) to the natural leather (10). The developed transfer printing on natural leather (10) process is related to a printing method performed by using transfer printing technique on natural leather (10) by using a latex containing ink composition. The latex-containing ink composition is used in the digital latex printing machine (30). The latex-containing ink composition comprises latex particles and pigment (s).In the latex printing method, a latex-containing ink composition is used, unlike the printing methods in which solvent-based ingredients are used.

An ink composition containing latex is used in natural leather (10) transfer printing process. Said latex is a liquid plant extract in which many substances are present. Latex is also known as natural rubber. It contains protein, starch, alkaloid, sugar, oil, gum, tannin, and resin. In addition to that the polymers having monomers selected from acrylates, methacrylates, vinyls, styrenes, ethylenes, vinyl chlorides, vinylidene chlorides, maleate esters, fumarate esters, itaconate esters, combinations and mixtures thereof may also be included in latex.

The latex-containing ink composition allows vivid colors to be obtained in the print (42). In addition, a flexible printing surface is formed thanks to the latex- based ink composition. The transferred printing surface can even accommodate the harsh physical conditions of the outdoors while adapting to non-rigid surfaces. However, the digital latex printing machines (30) can not be used on the natural leather (10) surfaces as they can only print on smooth-edged surfaces that can be rolled up in rolls.

At the first stage of the printing process, the natural leather (10) is applied binder. Leather binding is a priming process applied to the surface of natural leather (10) as shown in figure-2. The heat-active adhesive (20) is applied together with the binding process. In an alternative embodiment of the invention, said natural leather (10) is painted in a color that provides contrast with the print (42) to be applied before or during the binding process. In the next step, the print (42) containing the contents such as desired picture, letter, word, word group, photo, logo and pattern to be transferred to the surface of the natural leather (10) is printed onto the transfer folio (40) by the digital latex printing machine (30). At least one surface of said transfer foil (40) is not applied the corona treatment. Only the print (42) remains on the surface of the natural leather (10) after the transfer is finished.

After the desired image is transferred onto the non-corona treated transfer foil (40) by using the digital latex printing machine (30), the image is transferred to the surface of the binder applied natural leather (10) through the transfer press (50). Said transfer operation is carried out at a temperature between 90 ° and 140 °. The transfer process here is carried out by printing with the transfer press (50) on the leather (10) on the base.

The transfer foil (60) used in digital latex printing machines (30) in the present technique is composed of two layers which are first layer (61) and the second layer (63). In addition to the two layers mentioned, there is also a print (62), i.e. the image to be transferred. The print (62) is applied on the second layer (63) and the first layer (61) is removed after the transfer printing operation is completed. Thus, the print (62) on the surface to be transferred remains with the second layer (63). As the second layer (63) covers a larger area than the print (62), i.e the image, the print (62) remains within the second layer (63). Figure 9 and Figure 10 clearly show this situation. When examined carefully, the second layer (63) is noticeable on the natural leather surface subject to transfer printing. This creates a negative situation aesthetically. The transfer foil (40) used in the process subject to the invention consists of a single layer. There is no second layer (63) as described in the present art. Furthermore, after the transfer process is completed, the first layer (41) is completely removed and the print (42), which consists of latex-containing ink composition desired to be transferred only on the leather, remains. In this way, both cost advantage is provided by using less material and a high quality result is obtained from the visual point of view. Further, since the digital latex transfer printing machine (30) is used, it is not necessary to use different molds for different products. Thus, transfer printing is desired quantity can be done quickly on the natural leather (10). In the printing method in which the latex containing ink composition is used, transfer foil (40) with at least one non-corona treated surface and the transfer press (50) is used. Transfer foil (40) with at least one non-corona treated surface is taken to the transfer press (50) and it is ensured that the content s transferred to the natural leather (10). Therefore, the print (42) on the transfer foil (40) with at least one non corona treated surface, is transferred to the natural leather (10) in a quality manner.

Polyester film is used as transfer foil (40). The polyester film used as transfer foil (40) can withstand the temperatures used in the transfer process thanks to its characteristic structure. The surface tension values of the polyester film used as transfer foil (40) are in the range of 40-60 dyne / cm and generally have a thickness of 8-50 microns. The latex containing ink composition having a surface tension value lower than 30-60 dyne / cm can be printed on the transfer foil (40) surface from polyester film having higher surface tension even without additional processing such as chemical or electric corona application. The closed surface structure of the transfer foil (40) provides the appropriate surface conditions for the print (42) to be transferred, i.e the image, to be stored for a long time without transfer and then for perfect transfer after the printing process.

The digital latex printing machine (30) applies the latex containing ink composition containing pigment or pigments on the polyester film transfer foil (40) without any corona treatment so that the pattern to be transferred is created. Prior to this application, a pre-printing lacquer is applied from a different channel of the same printing apparatus, which allows the pigment-containing latex-containing ink to adhere to the surface. Thus, the latex containing ink composition ensures that the composition adheres to the surface and forms clearer patterns and images before it reaches the printing surface.

The invention is a method related to the printing of the print (42), i.e. the image composed of contents such as pictures, letters, words, word groups, photos, logo and patterns on a transfer foil (40) by using the digital latex printing machine (30) and transferring it onto the natural leather (10) subsequently and it is composed of following steps,

Preparation of natural leather (10)

- Binding of the natural leather (10) and application of the heat-active adhesive (20)

Printing of the print (42), i.e. the image composed of contents such as pictures, letters, words, word groups, photos, logo and patterns on a single layer transfer foil (40) by using the digital latex printing machine (30) - Transferring of the image composed of contents such as pictures, letters, words, word groups, photos, logo and patterns on the binder applied natural leather (10) from the non-corona treated transfer foil (40) surface by using the transfer press (50). An alternative embodiment of the invention follows from the following process steps;

Preparation of natural leather (10)

Binding of the natural leather (10) and application of the heat-active adhesive (20)

said natural leather (10) is painted in a color that provides contrast with the print (42) to be applied before or during the binding process.

Printing of the print (42), i.e. the image composed of contents such as pictures, letters, words, word groups, photos, logo and patterns on a single layer transfer foil (40) by using the digital latex printing machine (30)

Transferring of the image composed of contents such as pictures, letters, words, word groups, photos, logo and patterns on the binder applied natural leather (10) from the non-corona treated transfer foil (40) surface by using the transfer press (50).