WO2005059240A1

WO2005059240A1 - Process for colour printing on natural tissues

Info

Publication number: WO2005059240A1
Application number: PCT/IT2003/000841
Authority: WO
Inventors: Flavio Lissoni
Original assignee: Zola, Emilio
Priority date: 2003-12-19
Filing date: 2003-12-19
Publication date: 2005-06-30
Also published as: AU2003300740A1

Abstract

A process for colour printing on plant tissues, characterised in that it comprises the following steps: soaking the plant tissue with resin; crosslinking of the mixture applied to the tissue; preparing the paper with the images to be transferred onto said natural tissue; and heat-transferring of said images from said paper to the said treated natural tissue.

Description

A PROCESS FOR COLOUR PRINTING ON NATURAL TISSUES

DESCRIPTION The present invention relates to a process for colour printing on natural tissues and, more preferably, on plant tissues like linen, hemp, cotton, mixed, etc. To lay dyes on plant tissue, like linen, hemp, cotton, blend, etc. a first so-called silk-screen process is known that may be with one or more looms according to the dyes to be used, manual as well as automatic, or with one or more rolls, always according to the number of dyes to be applied. The laying of the dye by this process requires a step of first drying of the inks and, subsequently to the applying thereof, a step of tissue cleaning. The tissue cleaning may be carried out ^Λdry' by solvents, or ^λwet' by detergents. In some cases a further step is required, in which the plant tissue is subjected to finish. Moreover, in another alternative process, known as direct printing from plotter, images are first computer- processed and then sent to the plotter to print them directly onto the tissue. The inks used are acid or solvent-based, and, subsequently to their laying, a fixing of the print with a vaporizer and, casewise, a subsequent cleaning are required. The processes mentioned hereto and still employed to date entail the drawback of having a scarce overall economy owing to the high cost of the systems, of the machinery constituting them and of the preparation of the printing process, making them suitable solely for high- volume printings and high repetitiveness of the printing for a single subject. Moreover, another additional drawback lies in that inks and solvents or toxic and acid chemical material are used, thereby generating toxic wastes to be disposed of. Hence, object of the present invention is to solve said drawbacks by providing a process for colour printing on natural tissues, and preferably on plant tissues, providing a high versatility of application and remarkably reducing system and machinery costs. Another object of the present invention is to provide a process for colour printing on plant tissues providing the use of water-dissolved inks so as to attain a reduced use of toxic substances with respect to analogous processes of the state of the art. A further object of the present invention is to provide a process for colour printing on plant tissues entailing a high operational simplicity and remarkably reducing the preparation costs, as well as a flexibility such as to be applicable both to a small or even unitary printing and to a medium-size production printing. Therefore, the present invention provides a process for colour printing on plant tissues according to claim 1. Advantageously, according to the process of the present invention, the old classic problems of applying dyes to plant tissues are solved with absolutely novel commercially available materials. Furthermore, there is advanced a novel procedure with simple and inexpensive machinery, exhibiting a medium-low energy absorption. Moreover, another advantage of the process of the present invention lies in that it provides the use of products and related operation steps in the full respect of the environment, by virtue of the use of water-soluble resins, water-based inks and plant tissues. Hereinafter, there will be provided a detailed description of a preferred embodiment of the process for colour printing on plant tissues according to the present invention, given by way of a non-limiting example. In the course of the research and testing of the present applicants it has surprisingly been found that by treating the plant tissue with a mixture and by applying the sublimation process to said tissue thus treated, there can be attained certain and positively innovative printing results onto the same tissues, combining operational simplicity and considerable savings on the preparation costs, as well as attaining a flexibility such as to envisage both the small or even unitary printing and the medium-size production printing. More precisely, according to the present invention, the process for colour printing on plant tissues comprises the following steps: a) treating the plant tissue with a mixture comprising resin; b) hot and/or cold crosslinking the mixture applied to the tissue; c) preparing a supporting paper with the images to be transferred onto said tissue; and d) heat-transferring the images from said supporting paper to said plant tissue by a sublimation process. Concerning the step (a) of treating the plant tissue with a mixture, the mixture used for the soaking of the plant tissue is made of resin and additives. For such a mixture the following compounds are used: Resin: - polyester: water-soluble, branched, hydroxylated; - isocyanic: water-soluble aliphatic isocyanate; - melamine: branched, water-soluble As additives the following compounds are used: - flame retardant; - UV absorbers Then, the mixture thus additioned is laid onto the tissue (e.^'g., through a rolling machine). The mixture used should be very viscous, and as it is not water- diluted the tissue is not wetted, thereby avoiding the forming of pile. Optionally, there may be provided a step of drying the tissue thus soaked. The dosage of the mixture deeply influences tissue rigidity once the process is over; influential is also the time elapsed from the rolling process to the crosslinking: the waiting time may be varied in order to obtain a tissue of greater or lesser softness, also with reference to the tactile-visual sensation provided by the original, i.e., untreated, tissue. Concerning the (b) step of crosslinking, the same takes place through a rotary press or the like, heated and/or at room temperature according to the mixture of resin and additives employed, with the use of a fiberglass/Teflon mat contacting the tissue. The fiberglass/Teflon mat has the function of making the surface uniform and smooth. In case a hot crosslinking is carried out, there is provided a temperature ranging from 30°C to 230 °C, preferably near 200 °C according to the kind of tissue. The transfer rate ranges from 0.4 to 1.00 m/min, preferably from 0.5 to 0.8 m/min. The pressure exerted by the press ranges from 1.5kg/cm² to 3 kg/cm². Concerning the (c) step of preparing the paper with the images in order to transfer the latter onto the tissue, the subjects to be printed (e.g. images, writings, drawings, etc.) are brought first of all to the processing by means of computer programs, specific and already known to the art. Then, the images thus processed are sent to a plotter that uses water-dissolved diffusion inks and the former are fixed on paper. It has to be specified that for paper' it is meant the kind of paper usually employed in this field, which is treated with a surface coating to enable inks to remain on the surface thereof. Subsequently, the paper thus printed is used for the final transfer of the subjects (images, etc.) onto the treated plant tissue. The inks used are water-based, i.e. water-soluble, so as to contain no heavy metals and be free from toxic substances, thereby being physiologically acceptable. Concerning the sublimation step (d) , the plant tissue pretreated as above is coupled to the paper preprinted with the preselected subjects, and all is introduced in a press (preferably of the hot rotary kind) thereby attaining the transfer of the images by 'sublimation. According to the kind of tissue and mixture the sublimation process is attained with a temperature ranging from 30°C to 250°C, and more preferably near

220 °C at a conveyor transfer rate of about 2m/min and at a pressure of lkg/cm². Hereinafter, there will be provided some experimental examples implemented by the same applicant. The experiments were performed on ^' plant tissues like linen, hemp, cotton, etc. in which there was selected first a known process of the state of the art and then the process for printing of the present invention. Therefore, in the examples there will be highlighted the advantageous aspects regarding the economy, flexibility, salubrity and simplicity of the machinery used in the process of the present invention, and the overcoming of the several hereto-highlighted problems found to date in the usual processes for printing on plant tissues and on other tissues. It has to be specified that, concerning the preparing of the paper, the same requires no specific preparing step, as it cab be selected from the kind already used in sublimation processes onto synthetic tissues. However, obviously, according to the process of the present invention the quantities of ink on the paper change, and the printing contours and the linearization change as well. Therefore, the main difficulty lies in the treatment of the tissue that, obviously, when carried out with unsuitable processes, leads to the following negative results : tissue with pile, therefore not smooth; • limited pliability; limited life of the printing components; difficulty in transferring the images from the paper to the treated tissue.

Example 1 A normal raw plant tissue is used. The raw plant tissue was initially treated by dipping with a polyester resin in order to enable inks to bind to the tissue fiber. This kind of treatment causes a very serious problem, i.e. the formation of pile, due to the dipping of the tissue in the resin. All this makes the tissue surface rough and ill-suited to take up the transfer of the images from the paper. Then, the plant tissue thus treated in order to eliminate the above problem, i.e. the formation of pile, was subsequently pressed by a flat press, at a temperature of about 160 °C for a time of about 30" and at a pressure of about 4 kg/cm². By a subsequent step of pressing the images were transferred from the paper to the pretreated plant tissue. The operation was carried out always on a flat press at a temperature ranging from 150°C to 175°C, and with a time ranging from 60' to 180' at a pressure ranging from 1 to 3 kg/cm². To this end, subsequent tests with different temperatures, times and pressures were required, as there revealed itself a serious drawback consisting in the difficulty of removing the paper from the treated plant tissue. Then, the plant tissue with the images thus transferred required a further surface treatment with a water-dispersed polyurethane mixture, as the product applied during the first step of dipping in resin did not prove suitable and/or final, the resin being of the primer kind, apt to bind the dye to the plant tissue fiber. The application of water-dispersed polyurethane mixture with thermosetting catalyst was carried out with a semiautomatic spraying system. In order to apply the mixture by spraying, the same had to be diluted with water, yet the presence of the latter led again to the formation of pile onto the tissue surface, due to tissue fiber swelling. Then, subsequently to the spraying of the polyurethane mixture, the tissue required a further pressing, to crosslink the applied mixture as well as to smooth anew the surface of the plant tissue. The temperatures and the times as well as the pressure used for this step are alike those described in the preceding step of pressing. Lastly, to make fire-retardant the plant tissue thus treated there was required a further spraying treatment to apply a phosphate resin. The operation highlighted again the problem of pile formation, tissue puckering and the entailed need to dry up the water in the specific resin. In order to solve the above problems, there was required a further pressing of the tissue, with the same modes of the preceding pressings. To carry out all the operations described there was used a large-sized flat press having an automatic tissue loading/unloading system, a plate heating by diathermic oil, and an engaged power of about lOOk . For the spray application there was used a semiautomatic system with tissue loading/unloading and a suction booth for the fumes purified by scrubbing with water. The printed tissue thus obtained highlighted problems of fastness of the dye on the plant tissue^ ill- defined image contours and subdued colour shadings in the images. There also occurred doubling effects of the images and, partly, of the surface colours, owing to the continual hot-pressing runs on the tissue.

Example 2 While searching for modifications apt to overcome the abovedescribed drawbacks, the mixture used was modified. Moreover, some steps were eliminated and in order to carry out a lower number of hot pressings the ranges of temperature, times and pressure were changed. Despite all that, the results were still less than considerable. In the course of the testing, the products, the machinery and the parameters thus used (temperatures, time, pressure) proved inadequate in the following aspects: a) inaccurate, muddy and unstable printing; b) dye destruction over a short time; c) dye dispersion on the surface; d) difficulty of drying the water present in the application of the mixtures; e) difficulty, at the end of the image transfer, in removing the paper from the tissue; Moreover, to carry out all the described operations, uneconomical machinery was used, not quite amenable to the methodologies applied. In fact, the machinery used is known to be originally costly and, being bulky, requiring wide workspaces, high energy absorption rates and lengthy installation times. Concerning the fume suction system of the spray booth, the required scrubbing and purification of said fumes leads to the formation of toxic wastes to be subsequently disposed of. Example 3 There were overcome the problems and drawbacks generally and notoriously found in the application of dyes to plant tissues according to the preceding examples and according to the process of the present invention. To this end, the operations were carried out with mixtures and machinery differing from the abovedescribed ones, in order to attain the final result both for the treatment of the plant tissue and for the transfer, by sublimation, of the images from the paper to the plant tissue . The plant tissue was initially treated with a polyurethane water-soluble mixture with hot catalysis, by spraying system. In particular, the tissue was laid on wood panels and secured thereto by means of staples. The formation of pile was abated to a minimum, using a mixture requiring no dilution with water and entailed drying thereof. In particular, the resin mixture applied was selected so as to make it viscous, yet anyhow applicable by spraying,^" to have the plant tissue preserve pliability and resistance to mechanical wear (rubbing) and fastness to light. Subsequently, upon being coupled to a mylar (polyester film) the plant tissue was introduced in a rotary press at 165 °C with a pressure of about 2kg/cm² and at a rate of 0.9m/min. At the end of the pressing process the plant tissue proved ready for image transfer (sublimation printing) . Then, the plant tissue coupled to the pre-prepared paper was run in the rotary press at the temperature of about 185 °C at a pressure of about lkg/cm² and at the rate of 1.5m/min. Surprisingly, the results proved excellent just by virtue of the above resin mixtures, yielding as end product a smooth. tissue, with a lesser quantity of water to be removed during the step of soaking in a short time at the temperature of 25°C/30°C. Moreover, remarkably any difficulty in detaching the paper after the step of transferring was eliminated. The images thus obtained are very satisfactory, exhibiting no doubling effects or muddiness.

Example 4 Initially, for the treatment of the plant tissue, there was selected a resin mixture obtained by mixing various commercially available resins, until obtaining a mixture exhibiting a sensibly high viscosity. To such a mixture a flame retardant and an UV absorber were also added, so as to have the end mixture thus obtained allow an excellent image transfer and provide optimal softness and elasticity to the plant tissue, good colour shadings and good fastness thereof over time, and lastly yield a fire-retardant tissue free from surface charges by the flame retardant integral part of the mixture. Advantageously, the obtained viscosity allows to avoid laying the mixture on a plant tissue by a spraying system, using instead a rolling machine. The innovative use of the rolling machine enables to treat the plant tissue in a simple manner, with no addition of water, almost no formation of pile, abatement of the drying time and entailed reduced time of exposure to air of the plant tissue at a temperature of 25°C/30°C. Also the quantity of mixture to be laid off on the plant tissue is adjusted in a simple manner. While operating on the mixture, instead of using a single hot catalysis by means of a suitable hot catalyst, there was added a catalyst for cold catalysis so that, upon ending the hot crosslinking process as well as the image transfer (sublimation) process, the latter trigger a cold crosslinking slowly strengthening the mixture over time . On the other hand, in order to avoid drawbacks, the Mylar was replaced by a fiberglass/Teflon mat. This allows to work continually at elevated temperatures without undergoing surface alterations or breakings during a continuous processing cycle, providing moreover, after the crosslinking, a smooth surface of the plant tissue. Subsequently, the plant tissue was laid on wood panels and anchored thereto with staples, then run in the rolling machine to lay off the mixture. Then, for some minutes (from 1' to 10') the tissue was exposed to air at the temperature of 25°C/30°C. Then, the plant tissue was coupled to the fiberglass/Teflon mat to be run in the rotary press at a rate of 0.6 m/min, at the temperature of 190 °C, with a pressure of 2kg/cm², to obtain the hot crosslinking of the mixture. It is required that the fiberglass/Teflon mat be into contact with the heated roll of the rotary press. The present applicants observed that with regard to the constitution of said mat there proved likewise suitable for use a different combination of different materials with alike physical features, like e.g. polyester film and/or Kevlar. Subsequently, the crosslinked plant tissue, once coupled to the image transfer paper, should be run in the rotary press at a rate of 2.2 m/min, at the temperature of 215°C, with a pressure of 1 kg/cm2. It has to be pointed out that with the process thus described there is attained an excellent and stable image transfer by sublimation by simple and economic operations.

Claims

CLAIMS 1. A process for the colour printing on natural tissues, characterised in that it comprises the following steps : - soaking the natural tissue with a resin; - crosslinking of the resin applied to said natural tissue; - preparing a supporting paper with the images to be transferred onto said natural tissue; and - heat-transferring the images from said paper to said natural tissue.

2. The process for colour printing on natural tissues according to claim 1, wherein said step of soaking the tissue with a resin provides the use of a mixture made of resin and additives, and selected from the group comprising: - water-soluble, or with organic solvent (sov) , or branched, or hydroxylated Polyester. water-soluble aliphatic isocyanate, or with organic solvent Isocyanic: water-soluble, or with organic solvent, or branched Melamine; - water-soluble unsaturated polyester, or with organic solvent, crosslinked by UV rays; and further comprising additives selected in the following group: - flame retardant; - UV absorbers.'

3. The process for colour printing on natural tissues according to claim 1 or 2, wherein said step of soaking the tissue with a resin provides soaking means selected from the group comprising: - a rolling machine; - a spraying system; - a coater; - a dipping tank.

4. The process for colour printing on natural tissues according to claim 1 or 2 or 3, wherein said step of crosslinking takes place in a hot and/or cold condition, and via a hot and/or cold pressing step.

5. The process for colour printing on plant tissues according to the preceding claim, wherein said pressing step is achieved by a rotary and/or a flat press.

6. The process for colour printing on natural tissues according to the preceding claim, wherein said pressing operation provides the use of one or more mats comprising at least one or a combination of materials selected from the following group: - fiberglass; - Teflon; - polyester film; and - Kevlar; said mat having a heat resistance ranging from 100C° to 300C°, and being apt to come into contact with the plant tissue.

7. The process for colour printing on natural tissues according to claim 4, wherein said step of hot crosslinking provides a functional temperature range from 30°C to 250°C.

8. The process for colour printing on natural tissues according to claim 5, wherein said step of crosslinking provides a transfer rate ranging from 0.1 to 5.00 m/min.

9. The process for colour printing on natural tissues according to any one claim 4 to 8, wherein said pressing operation provides a pressure value ranging from O.lkg/c ² to 5 kg/cm².

10. The process for colour printing on natural tissues according to any one of the preceding claims, wherein said step of preparing the supporting paper comprises the printing of images thereon by a plotter.

11. The process for colour printing on natural tissues according to the preceding claim, wherein said paper is of the kind having a surface treatment with a coating.

12. The process for colour printing on natural tissues according to claim 10 or 11, wherein said operation of printing onto said paper provides the use of water-soluble diffusion inks.

13. The process for colour printing on natural tissues according to any one of the preceding claims, wherein said step of heat-transferring images onto said natural tissue provides a sublimation process for said images, by means of coupling the treated tissue to the preprinted paper and subsequent hot pressing said coupled tissue and paper.

14. The process for colour printing on natural tissues according to the preceding claim, wherein said step of hot pressing provides the use of a rotary or a flat press.

15. The process for colour printing on natural tissues according to claim 13 or 14, wherein said sublimation step is attained with a temperature ranging from 30°C to 250°C, and with a transfer rate ranging from 0.1 m/min to 5 m/min, and at a pressure from O.lkg/cm² to 5 kg/cm².

16. The process for colour printing on natural tissues according to any one of the preceding claims, wherein said natural tissue is a plant tissue selected from the group comprising linen, hemp, cotton, mixed, and the like.