Method for fabric printing using dyeing indigo paste and printing system thereof

Abstract

The present invention relates to a fabric printing method and system with reduced dyes, in particular indigo dye. The object of this invention consists in a method for printing a fabric with a dye and a fabric printing system comprising at least one printing module configured to apply dyeing paste to a fabric surface; at least one oxidation chamber comprising an internal cavity filled by an oxidizing gaseous mixture; a fabric-feeding device configured to feed a fabric sheet through the printing module and the oxidation chamber; wherein each printing module comprises a plurality of print heads, at least one main reservoir; a plurality of sub tanks; a main circulation pathway and a recirculation pathway. The proposed invention consists in a fabric printing method and fabric printing system aimed to solve the limitations of industrialized indigo printing.

Description

[0001] DESCRIPTION

[0002] METHOD FOR FABRIC PRINTING USING DYEING INDIGO PASTE AND PRINTING SYSTEM THEREOF

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a fabric printing method and system with reduced dyes, in particular indigo dye.

[0005] PRIOR ART

[0006] Traditional dyeing with indigo for denim manufacturing has long been the industry standard but faces significant challenges in terms of sustainability, flexibility, and operational efficiency.

[0007] One of the main issues with traditional indigo dyeing methods is the high consumption of water, as large volumes of water are required to dissolve the pigment and also to immerse the yarn in multiple dyeing and oxidation baths. This is followed by extensive rinsing steps to remove unfixed dye, which produces highly pollutant wastewater effluent streams that harm the environment. These effluents must be treated thoroughly before they can be discharged into the environment, posing a serious ecological and regulatory burden and increasing energy costs.

[0008] In addition, the fixation of indigo dye using traditional methods is often not efficient, as there is a need for several immersion bath cycles, resulting in an extensive use of chemicals, particularly reducing agents such as sodium hydrosulfite and caustic soda.

[0009] In light of these issues, efforts have been made to apply indigo dyes using digital printing technologies. However, indigo presents unique technical challenges for digital printing, as indigo dyes have poor solubility and have a tendency to aggregate. In addition, the requirement to maintain the indigo dye in a reduced state before oxidation makes it incompatible with conventional inkjet equipment. Moreover, the rapid oxidation of indigo dyes upon exposure to air causes clogging in print heads and result in an inconsistent printed pattern.

[0010] While some inkjet systems have adapted to pigment-based or UV-curable inks, none provide a commercially viable solution for true indigo digital printing on textiles. The current state of the art fails to solve the combined challenges of chemical stability, system contamination, supply chain flexibility, and sustainable dye application for indigo.

[0011] The proposed invention consists in a fabric printing method and fabric printing system aimed to solve the limitations of industrialized indigo printing.

[0012] SUMMARY OF THE INVENTION

[0013] The object of this invention is a method for printing a fabric with a dye, comprising the following steps in succession: i. preparing a first composition by mixing a pigment with water and sodium hydroxide to adjust the pH of said first composition between 10,50 and 12,00; ii. heating the first composition up to 60 °C; iii. adding a reducing agent to the first composition to form a second composition, wherein said second composition comprises three parts by weight of reducing agent for each two by weight parts of pigment contained in said second composition; iv. resting said second composition between 6 to 12 hours; v. adding at least two thickening agents to the second composition to form a dyeing paste, wherein at least one thickening agent is a natural thickening agent and at least one thickening agent is a synthetic thickening agent to obtain a dyeing paste; vi. applying said dyeing paste to a surface of a fabric to form a dyeing pattern in said fabric; vii. exposing said dyeing pattern to an oxidizing gaseous mixture, thereby oxidizing the applied dyeing paste on the fabric surface to form a dyed fabric; and viii. drying the dyed fabric.

[0014] In an advantageous aspect of the present invention, the addition of a reducing agent to the first composition in a 3:2 ratio to the total weight of pigment results in the complete reduction of the pigment, which increases the pigment solubility and reduces the occurrence of insoluble pigment particles that could impact the dyeing pattern upon application of the dyeing paste in the fabric. Another advantageous aspect is the that the resting of the second composition after the addition of the reducing agent allows the pigment in the second composition to stabilize and to remain in a reduced state, so that the dyeing paste is more resistant to immediate oxidation, thus allowing the dyeing paste to be fully applied onto the fabric surface prior to being oxidized and permanently dye the fabric.

[0015] The method for printing a fabric with a dye of the present invention is compatible with traditional fabric printing, using rollers or screens to apply the dyeing paste, and digital fabric printing, using customed ink jet systems to successfully apply the dyeing paste onto a fabric.

[0016] In a preferred embodiment of the present invention, the method for printing a fabric with a dye further comprises a step of applying an oxidizing solution to the fabric surface containing the dyeing pattern, wherein said oxidizing solution comprises at least one non-ionic dispersing agent, at least one cationic surfactant, at least one non-ionic surfactant, hydrogen peroxide and acetic acid to adjust the pH of said oxidizing solution between 3,50 and 5,50. Preferably, the at least one non-ionic dispersing agent comprises polyglycol ether, to prevent the unintended transfer of color from the dyed fabric; the cationic surfactant comprises polyamines, to improve the dyeing paste fixation to the fabric fibers; and the at least one non-ionic surfactant comprises fatty alcohol polyoxyethylene ether, as a diffusing agent and to improve color development. The proposed method enables repeated cycles of applying dyeing paste to a fabric, developing the color through oxidation of the pigment, and drying, which makes it compatible for both traditional printing and digital printing equipment. The proposed method minimizes the water consumption as water is only used during the initial mixture of the pigment, to produce the dyeing paste that is applied directly in the fabric to be dyed without requiring other water consuming steps, thus minimizing the production of wastewater resulting from the fabric printing.

[0017] It is also an object of the present invention a fabric printing system for printing a fabric with indigo dye, comprising: at least one printing module configured to apply dyeing paste to a fabric surface; at least one oxidation chamber comprising an internal cavity filled by an oxidizing gaseous mixture; a fabric-feeding device configured to feed a fabric sheet through the at least one printing module and the at least one oxidation chamber; wherein the at least one printing module comprises a plurality of print heads, each print head comprising a nozzle with an internal diameter of 35 - 55 pm and being configured to eject 15 - 60 pL of dyeing paste onto a fabric surface; at least one main reservoir configured to store the dyeing paste; a plurality of sub tanks, each sub tank being located between the ink reservoir and each print head; a main circulation pathway connecting the main reservoir to the plurality of sub tanks and the plurality of printheads; and a recirculation pathway configured to return excess dyeing paste from each print head to the main reservoir; being the main circulation pathway and the recirculation pathway comprised of channels having an internal diameter of 1,2 and 2,0 mm.

[0018] In an advantageous aspect of the present invention, the internal diameter of the channels in the main circulation pathway and recirculation pathway allows large pigment particles, having a particle size between 3,0 and 8,0 pm to flow freely without clogging the channels, which is particularly relevant for indigo dyes that contain larger pigment particles than other dyes. In addition, the internal diameter of 35 - 55 pm of the nozzle of the print head also allows the larger pigment particles contained in the dyeing paste to be fully ejected without clogging the nozzle, even if the dyeing paste has a viscosity higher than 15 cP. Furthermore, the channels of the main circulation pathway and of recirculation pathway are configured to comprise a smooth internal surface with shallow curvatures to prevent turbulence and particle sedimentation along the channel. In an advantageous aspect of the present invention, the combination of the channels having a wider internal diameter with a smooth internal surface and shallow curvatures improves the flow of thicker dyeing paste having a low water content and minimizes local sedimentation and aggregation of the dyeing paste along the main circulation pathway.

[0019] In another advantageous aspect of the present invention, the recirculation pathway allows excess dyeing paste to return to the ink reservoir so that said excess dyeing paste does not dry while inside the channel and clogs the main circulation pathway.

[0020] The proposed fabric printing system is therefore configured to save water during the dyeing process, as it allows repeated cycles of applying dyeing paste directly to a fabric, developing the color through oxidation of the pigment, and drying of the fabric, without generating wastewater from washing steps of the fabric and also minimizing the need for washing steps of the several components of the printing system exposed to the dyeing paste, by adapting the several print head components to the use of thicker dyeing pastes, containing larger pigment particles than conventional dyes having increased water content. Consequently, decreasing the water consumption also results in decreased energy costs, thus promoting a more sustainable method to produce dyed fabric.

[0021] DESCRIPTION OF THE FIGURES

[0022] Figure 1 - Schematic view of an in-line embodiment of the fabric printing system of the present invention, in which a fabric sheet (1) is fed through several printing modules (2), each one applying dyeing paste to a top surface of the fabric sheet (1) as it is being fed by the fabric-feeding device (4), then passing through an oxidation chamber (3) in which the fabric sheet is exposed to oxidizing conditions to fully oxidize the dyeing paste developing the color of the oxidized pigment comprised in the dyeing paste. The retention time of the fabric sheet (1) inside each oxidation chamber (3) is controlled by either by the feeding speed of the fabric sheet (1) or by the distance traveled by the fabric sheet inside each oxidation chamber (3).

[0023] Figure 2 - A first example of dyeing patterns obtained by the fabric printing method of the proposed invention, mimicking a denim style having a more open thread arrangement.

[0024] Figure 3 - A second example of dyeing patterns obtained by the fabric printing method of the proposed invention, mimicking a denim style having a more closed thread arrangement.

[0025] The dyeing patterns shown in the application represent some of the possible configurations of dyeing patterns obtained by the method of the present invention, in which the dyeing patterns are not limited to the examples presented in the Figures.

[0026] DETAILED DESCRIPTION

[0027] The more general and advantageous configurations of the present invention are described in the Summary of the Invention. Such configurations are detailed below in accordance with other advantageous and / or preferred embodiments of implementation of the present invention.

[0028] Preferably, the method for printing a fabric with a dye further comprises the steps of adding at least one polyol compound to the dyeing paste, followed by gently mixing and resting of the dyeing paste for at least 24 hours to stabilize the dyeing paste to be applied to a fabric surface.

[0029] Polyol compounds reduce the evaporation rate of the dyeing paste, in particular at the surface of the dyeing paste that is in contact with the atmosphere, being therefore prone to become dry and form a film layer that can negatively impact the dyeing of the fabric and introduce imperfections to the dyeing pattern. In addition, the polyol compounds improve the rheological properties of the dyeing paste to better control the viscosity of the dyeing paste and also reduces the oxidation rate of the dyeing paste, allowing it to be maintained in a reduced state for longer periods of time. Preferably, the at least one polyol compound is selected from propane-1, 2-diol, ethylene glycol, butylene glycol and dipropylene glycol.

[0030] Preferably, the method for printing a fabric with a dye further comprises the steps of applying a fixing agent to the dyed fabric, thereby fixing the dye to the fabric, and drying the dyed fabric wherein said fixing agent is selected from polyurethane resins, acrylic resins, epoxy resins, such as epichlorohydrin resin, carbodiimide resins, cationic fixing agents and reactive fixing agents, such as chlorotriazine.

[0031] The preferred pigments for the proposed method comprise any pigment select from natural indigo, synthetic indigo and sulfur-based pigments, being the proposed method optimized for indigo pigments that are soluble while in a reduced state and are fixed to fabric fibers upon oxidation.

[0032] In a preferred aspect of the proposed method, the dyeing paste is applied to said fabric surface so that said dyeing pattern comprises a resolution of at least 600 dpi.

[0033] Preferably, the reducing agent is selected from aminoiminomethanesulfinic acid and sodium formaldehydesulfoxylate.

[0034] Preferably, the dyed fabric is dried at a temperature between 60 °C and 120 °C, wherein the drying conditions are dependent on the size of the dyeing patter, the amount of dyeing paste applied to the fabric surface and relative humidity.

[0035] In addition, the dried fabric may be exposed to vapor for 10 to 30 minutes, having said vapor a relative humidity of 90% to 100% and a temperature of 100 to 105 °C, to improve the fixation of the dye to the fabric fibers, especially if the dried fabric comprises more than one layer of dye, since exposure to vapor improves the dye adherence and the durability of the applied dye. Moreover, vaporization of the dyed fabric softens any minor imperfections of the dyeing pattern occurred during the application of the dyeing paste to the fabric surface, thus resulting in a more homogeneous appearance of the dyeing pattern. Vaporization of the dyed fabric also primes said dyed fabric for further processing, such as washing, finishing processes such as artificial aging, bleaching and other processes performed on the dyed fabric to produce a final product.

[0036] In a preferred embodiment of the fabric printing system of the present invention, said fabric printing system comprises a filtration module positioned within the main circulation pathway and upstream of the sub tanks, wherein said filtration module comprises a filter configured to remove particles having a diameter above 10 pm from the dyeing paste. In a more preferred embodiment of the fabric printing system, each print head comprises an inlet valve and a safety filter located upstream said inlet valve, being said safety filter configured to remove particles having a diameter above 3 pm from the dyeing paste.

[0037] In an advantageous aspect of the present invention, the filter comprised in the filtration module prevents large particles to clog the main circulation pathway, thereby maintaining the flow of dyeing paste down to the print head. Preferably, the safety filter being located upstream of the inlet valve of each print head allows even smaller particles to be removed from the dyeing paste, thereby maintaining the free flow of the dyeing paste down to the nozzle to be then ejected to the fabric surface and form the desired dyeing pattern with high accuracy.

[0038] In a more preferred embodiment of the present invention, the fabric printing system comprises a heating module positioned upstream of the nozzle within each print head, said heating module comprising at least one temperature sensor and at least one ceramic resistance configured to heat the dyeing paste from 20 °C to 110 °C. The controlled heating of the dyeing paste reduces the viscosity of said dyeing paste and improves the flow of the dyeing paste down to the nozzle of the print head. Furthermore, the temperature module allows the fine tuning of the dyeing paste viscosity, especially in colder seasons when ambient temperatures are below 20 °C, which would hinder the flow of the dyeing paste and would increase the possibility of aggregation and clogging of the main circulation pathway.

[0039] The fabric printing system may also comprise at least one degassing module positioned within the main circulation pathway and upstream of the sub tanks, wherein said degassing module comprises a gas-permeable membrane configured to remove at least 90% of dissolved oxygen from the dyeing paste, thereby reducing the risk for unintended and premature oxidation of the dyeing paste within the channels of the main circulation pathway, especially for dyeing pastes comprising indigo pigment, which is highly sensitive to oxidation.

[0040] In addition, each print head may comprise a passive ventilation zone and an exhaust aperture, in which said passive ventilation zone and an exhaust aperture are located upstream of the nozzle and are configured to remove residual gases from the dyeing paste flowing to the nozzle. The passive ventilation of the residual gases from the degassed dyeing paste further decreases the oxidation rate of the dyeing paste flowing to the nozzle, so that said dyeing paste only oxidizes upon the exposure of the dyed fabric to an oxidizing gaseous mixture inside the oxidation chambers.

[0041] In a more preferred embodiment of the fabric printing system, the main reservoir and each sub tank are sealed and pressurized with an inert atmosphere containing gaseous nitrogen, so that the dyeing paste is not exposed to oxygen that would oxidize said dyeing paste within the main circulation pathway, before being ejected in the nozzle and applied to the fabric surface.

[0042] Of course, the preferred embodiments shown above are combinable, in different possible configurations, being the present invention not limited to the embodiments previously described.

Claims

CLAIMS1. A method for printing a fabric with a dye, comprising the following steps in succession: i. preparing a first composition by mixing a pigment with water and sodium hydroxide to adjust the pH of said first composition between 10,50 and 12,00; ii. heating the first composition up to 60 °C; iii. adding a reducing agent to the first composition to form a second composition, wherein said second composition comprises three parts by weight of reducing agent for each two by weight parts of pigment contained in said second composition; iv. resting said second composition between 6 to 12 hours; v. adding at least two thickening agents to the second composition to form a dyeing paste, wherein at least one thickening agent is a natural thickening agent and at least one thickening agent is a synthetic thickening agent to obtain a dyeing paste; vi. applying said dyeing paste to a surface of a fabric to form a dyeing pattern in said fabric; vii. exposing said dyeing pattern to an oxidizing gaseous mixture, thereby oxidizing the applied dyeing paste on the fabric surface to form a dyed fabric; and viii. drying the dyed fabric.

2. Method according to claim 1 further comprising the step of applying an oxidizing solution to the fabric surface containing the dyeing pattern, wherein said oxidizing solution comprises at least one non-ionic dispersing agent, at least one cationic surfactant, at least one non-ionic surfactant, hydrogen peroxide and acetic acid to adjust the pH of said oxidizing solution between 3,50 and 5,50.

3. Method according to any of the previous claims further comprising the steps of:ix. Adding at least one polyol compound to the dyeing paste, followed by gently mixing and resting of the dyeing paste for at least 24 hours; wherein said at least one polyol compound is selected from propane-1, 2-diol, ethylene glycol, butylene glycol and dipropylene glycol.

4. Method according to any of the previous claims further comprising the steps of: x. Applying a fixing agent to the dyed fabric, thereby fixing the dye to the fabric, and drying the dyed fabric; wherein said fixing agent is selected from polyurethane resins, acrylic resins, epoxy resins, carbodiimide resins, cationic fixing agents and reactive fixing agents.

5. Method according to any of the previous claims wherein the pigment is selected from natural indigo, synthetic indigo and sulfur-based pigments.

6. Method according to any of the previous claims wherein the reducing agent is selected from aminoiminomethanesulfinic acid and sodium formaldehydesulfoxylate.

7. Method according to any of the previous claims wherein the dyed fabric is dried at a temperature between 60 °C and 120 °C.

8. Method according to any of the previous claims wherein the dry dyed fabric is exposed to vapor for 10 to 30 minutes, having said vapor a relative humidity of 90% to 100% and a temperature of 100 to 105 °C.

9. A fabric printing system for printing a fabric with indigo dye according to claims 1 - 8, said fabric printing system comprising: at least one printing module configured to apply dyeing paste to a fabric surface;at least one oxidation chamber comprising an internal cavity filled by an oxidizing gaseous mixture; a fabric-feeding device configured to feed a fabric sheet through the at least one printing module and the at least one oxidation chamber; wherein the at least one printing module comprises a plurality of print heads, each print head comprising a nozzle with an internal diameter of 35 - 55 pm and being configured to eject 15 - 60 pL of dyeing paste onto a fabric surface; at least one main reservoir configured to store the dyeing paste; a plurality of sub tanks, each sub tank being located between the ink reservoir and each print head; a main circulation pathway connecting the main reservoir to the plurality of sub tanks and the plurality of printheads; and a recirculation pathway configured to return excess dyeing paste from each print head to the main reservoir; being the main circulation pathway and the recirculation pathway comprised of channels having an internal diameter of 1,2 and 2,0 mm.

10. A fabric printing system according to claim 9 further comprising a filtration module positioned within the main circulation pathway and upstream of the sub tanks; wherein said filtration module comprises a filter configured to remove particles having a diameter above 10 pm from the dyeing paste.

11. A fabric printing system according to any of the claims 9 - 10 wherein each print head comprises an inlet valve and a safety filter located upstream said inlet valve, being said safety filter configured to remove particles having a diameter above 3 pm from the dyeing paste.

12. A fabric printing system according to any of the claims 9 - 11 comprising a heating module positioned upstream of the nozzle within each print head, said heating module comprising at least one temperature sensor and at least one ceramic resistance configured to heat the dyeing paste from 20 °C to 110 °C.

13. A fabric printing system according to any of the claims 9 - 12 comprising at least one degassing module positioned within the main circulation pathway andupstream of the sub tanks; said at least one degassing module comprising a gas- permeable membrane configured to remove at least 90% of dissolved oxygen from the dyeing paste.

14. A fabric printing system according to claims 12 - 13 wherein each print head comprises a passive ventilation zone and an exhaust aperture, being said passive ventilation zone and an exhaust aperture located upstream of the nozzle and configured to remove residual gases from the dyeing paste flowing to the nozzle.

15. A fabric printing system according to any of the claims 9 - 14 wherein the main reservoir and each sub tank are sealed and pressurized with an inert atmosphere containing gaseous nitrogen.

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