Method for dyeing a semi-finished product

Abstract

Method for dyeing a semi-finished textile product, preferably comprising at least 20% cellulosic fibres, and preferably 100% cellulosic fibres comprising the following steps: a phase of making available at least one semi-finished product to be dyed, a step in the preparation of a dye solution, containing at least one chemical compound configured to dye the semi-finished product, a dyeing phase during which at least one semi-finished product to be dyed is brought into contact with the dyeing solution, in which the dyeing phase takes place inside a dyeing machine 2 which includes: a plurality of external walls 6 that defines an internal environment 4 within which the garments and the dyeing solution are directly inserted, The method is also characterized by the fact that the dyeing phase includes a sub-phase of adding at least one alkaline silicate, preferably sodium silicate, inside the container.

Description

[0001] METHOD FOR DYEING A SEMI-FINISHED PRODUCT

[0002] The present invention concerns a method for dyeing a semi-finished product or fabric, in particular for dyeing a semi-finished product or fabric made of natural or artificial fibres, but in particular cellulosic fibres.

[0003] The dyeing of textile products in cellulosic fibers, such as cotton, is a fundamental process in the textile industry. Traditionally, this process requires the use of large amounts of water and the addition of inorganic salts to aid in the absorption of the dye by the fibers. Reactive dyes are widely used for their ability to covalently bind to cellulosic fibers, ensuring good color fastness.

[0004] However, the conventional approach to dyeing cellulosic fiber garments presents several challenges. Firstly, the high water consumption, with bath ratios typically between 1:5 and 1:20, has a significant environmental and economic impact. Secondly, the use of large amounts of inorganic salts, such as sodium chloride or sodium sulphate, contributes to wastewater pollution and requires expensive purification treatments. In addition, the high temperatures often used in the dyeing process result in significant energy consumption.

[0005] A further critical issue is represented by the difficulty of obtaining a uniform and penetrating dye when operating with low bath ratios, especially in the dyeing of ready-made garments. Reducing the volume of liquid can in fact compromise the homogeneous distribution of the dye, leading to unsatisfactory results in terms of uniformity and intensity of the color.

[0006] It has been understood that it would be advantageous to have a method that overcomes one or more of these problems.

[0007] There are known methods for dyeing garments that involve placing the garments to be dyed inside a washing machine together with colored liquid. The washing machine, as is well known, includes a chamber, generally cylindrical or parallelepipedic, inside which a rotating drum with perforated walls is placed. The garments to be dyed are inserted into the drum through an opening, while the dyeing solution is inserted inside the chamber, and enters the drum through the holes inthe walls of the latter.

[0008] However, this solution is not fully satisfactory as it requires the use of large quantities of dyeing solution since this must fill, at least partially, the chamber, and not only the drum. This dye contains chemical compounds that cannot be released into the environment, such as a large amount of salts, bases and coloring compounds. The disposal of these liquids represents a significant cost for companies operating in the sector, as well as presenting risks and complications from an environmental point of view.

[0009] The state of the art also includes US 2005 / 115004, EP 1 566432, CN 115 161 926 and IT 2021 000007826. In particular, these documents show the use of a normal dyeing device, in which the garments are placed in a perforated basket, which in turn is inserted inside a closed container in which the dyeing solution is inserted. However, these solutions are not fully satisfactory as they require the use of high bath ratios, with the consequent problems that have been outlined above.

[0010] The aim of the invention is to propose a method for dyeing a semi-finished product that allows to overcome the drawbacks of the well-known solutions.

[0011] Another purpose of the invention is to propose a method that allows less water to be consumed.

[0012] Another purpose of the invention is to propose a method that allows to reduce the consumption of raw materials.

[0013] Another purpose of the invention is to propose a method that allows to obtain a homogeneous color on semi-finished products.

[0014] Another purpose of the invention is to propose a method that allows the coloring to be fixed.

[0015] Another purpose of the invention is to propose a method that optimizes the use of dyes.

[0016] Another purpose of the invention is to propose a method that decreases the use of bases.

[0017] Another purpose of the invention is to propose a method that is alternative and / or an improvement on the known solutions.

[0018] Another purpose of the invention is to propose a method that allows to create asemi-finished product with a high aesthetic value, giving the user the feeling of being in front of a high quality semi-finished product.

[0019] Another objective of the invention is to create a dyeing process with a low bath ratio that allows to significantly reduce water consumption and environmental impact, while maintaining high dyeing performance in terms of uniformity, intensity and color fastness.

[0020] Another objective of the present invention is to eliminate or drastically reduce the use of inorganic salts that are difficult to treat in the dye bath, thus improving wastewater quality and simplifying downstream treatment processes.

[0021] A further goal of the invention is to provide a dyeing method that can be carried out at lower temperatures than conventional processes, allowing for energy savings and reduced operating costs.

[0022] Another objective of the present invention is to provide a method of garment dyeing of cellulosic fibre products which will make it possible to overcome the above-mentioned drawbacks and in particular to obtain a uniform and high-quality dyeing with reduced water consumption and with less or no use of inorganic salts such as sulphate and sodium chloride, potassium sulphate and chloride and the like easily and immediately.

[0023] All these purposes, and others which will be clearly apparent from the description, are obtained by a method for dyeing a semi-finished product having the characteristics described in claim 1.

[0024] Other structural and functional characteristics of the present innovation and the relative advantages compared to the known technique will be even clearer and evident from an examination of the following description and from the figures, referring to an exemplary and preferred, but not limiting, form of realization of the method for dyeing a semi-finished product covered by this innovation.

[0025] Figure 1 shows in the side section a dyeing machine used for a method according to the invention,

[0026] Figure 2 he shows it in frontal view.

[0027] The present invention concerns a method for dyeing a semi-finished product. In particular, the method according to the invention concerns a method for dyeing asemi-finished product including textile fibers made at least partially of cellulose fiber, and preferably including at least 20% cellulose fiber, and more preferably made of 100% cellulose fiber.

[0028] Below, semi-finished product including textile fibres (or more simply semi-finished product) refers to any object intended to be worn, such as an item of clothing; in addition, it also includes pieces, preferably cut or semi-finished products intended to become clothing, or rolled semi-finished products. In particular, the semi-finished product according to the invention can be made by weaving.

[0029] The main field of application is the industrial dyeing of garments, preferably packaged and preferably made of cellulosic fibers such as cotton, linen, viscose or other. The proposed method offers significant advantages in terms of environmental sustainability and production efficiency.

[0030] A key aspect of the invention is the drastic reduction in water consumption, which in the dyeing phase decreases by 80-90% compared to conventional dyeing methods. This significant reduction is achieved by using a very low liquor ratio, typically around 1:2.

[0031] Another characterizing element is the elimination or strong reduction of inorganic salts in the dye bath. In traditional processes, these salts are used to help deplete the dye on the fiber. The method that is the subject of the invention achieves similar or superior results without the addition of electrolytes, instead exploiting the synergy between the low bath ratio and the use of an alkaline silicate.

[0032] These measures make it possible to obtain an industrial-quality dye, with yields and color fastness comparable to or better than conventional methods, while significantly reducing the environmental impact of the process. In particular, the absence of salinity in the discharges and the lower consumption of water and energy represent significant advantages from an ecological and economic point of view.

[0033] Advantageously, one or more phases of the method according to the invention can be carried out within a dyeing machine 2.

[0034] In particular, the dyeing machine 2 can provide an internal environment 4 within which the semi-finished products to be dyed are placed. The internal environment 4 is delimited by at least one, and preferably by a plurality of internal walls 6, andpreferably has a substantially cylindrical shape with the axis of rotation substantially horizontal. In particular, therefore, substantially the internal walls 6 can define a rotating drum. Preferably the inner walls 6 can be made of thermally conductive material, and, more preferably, of metal, e.g. stainless steel.

[0035] Appropriately, the internal environment 4 can be unique - i.e. it does not have internal subdivisions or sub-chambers. Advantageously, the internal walls 6 can divide the environment in which the semi-finished products to be dyed are placed in a watertight way with respect to the outside. Therefore, during the dyeing operations, substantially all the dyeing solution will be contained within the internal environment 4. Appropriately, the semi-finished products to be dyed can be substantially free to move within the internal environment.

[0036] Advantageously, the internal walls 6 can provide a plurality of reliefs facing inwards, which allow to improve the handling of the semi-finished products to be dyed.

[0037] Furthermore, according to the invention, the machine can include at least one, and preferably a plurality of 6" external walls, configured to define a 6" cavity inside which a heating fluid can pass, or the components of the dyeing machine 2 can be housed, at least partially.

[0038] Appropriately, the dyeing machine 2 may include a central nozzle 7, configured to direct a fluid in the direction of the internal environment 4. Advantageously, moreover, the dyeing machine 2 can include handling means configured to move, and in particular to rotate the internal walls 6. Appropriately, the dyeing machine 2 can also include an opening 8 on the external walls 6 configured to connect the internal environment 4 with the outside of the machine, so as to allow the insertion of the semi-finished products to be dyed. Preferably opening 8 is resealable, and more preferably it can be closed in a watertight way. In particular, opening 8 is configured to be opened during the loading of the semi-finished products, and is configured to be closed again during the dyeing operations, essentially separating the internal environment in which the semi-finished products to be dyed and all the dyeing solution are inserted, from the outside.

[0039] Appropriately, the dyeing machine 2 may also include appropriate heating media configured to heat the outer walls 6, e.g. heating elements. Appropriately, moreover,the machine 2 according to the invention can include a steam generator 10 configured to evaporate water and convey it towards the nozzles 7. Appropriately, machine 2 can include inside the drum materials such as spheres or cylinders or others which, rolling with the semi-finished products, facilitate the penetration and equalization of the dyeing dyes. Appropriately, these materials can be a rolling cylinder around which the fabric is wrapped.

[0040] Preferably the dyeing machine 2 can be for example a drum.

[0041] The dosing of the products can be carried out by parcelling the liquid, or by foaming or simple dosing.

[0042] The method, according to the invention, involves a phase of making available at least semi-finished products to be dyed. Preferably the semi-finished product can be in its raw state and can have the natural color of the fiber with which it is made. Advantageously, the phase of making a semi-finished product available can include the insertion of the semi-finished product itself into the dyeing machine 2.

[0043] Preferably, the method according to the invention involves a washing phase of the semi-finished product, configured to remove any stains and / or residues present on the semi-finished product. Advantageously, the washing phase of the semi-finished product can be carried out inside the dyeing machine 2. Advantageously, this phase can be carried out at room temperature, or at a temperature above 30°C, and preferably above 40°C, and preferably above 50°C, and preferably below 100°C. In addition, the method involves a dyeing phase, configured to deposit on the fibers that make up the semi-finished product to be dyed at least one chemical compound product configured to dye the semi-finished product, hereinafter also called a dye. Appropriately, the dyeing phase can include a sub-phase of preparation of a dye solution, which for example involves the dissolution in water of at least one dye, and a quantity of salt that depends on the shade of the color to be applied, for example a quantity of less than 70 g / l, and preferably equal to 10 g / l for dark dyes, and an amount of about 10 g / l and preferably equal to 5g / l for light colors, as well as other components.

[0044] Advantageously, the dyeing phase can include a dyeing phase during which the dyeing solution is placed in contact with the semi-finished products to be dyed.Advantageously this can be done by injecting the dyeing solution into the internal environment 4 of the dyeing machine 2 through the nozzle 7, or by the opening 8. Advantageously, a quantity of dyeing solution equal to at least the weight of the semi-finished products to be dyed, and preferably equal to at least 1.5 times the weight of the semi-finished products to be dyed, and preferably equal to at least twice the weight of the semi-finished products to be dyed, and preferably less than 10 times the weight of the semi-finished products to be dyed, can be inserted, and preferably less than 5 times the weight of the semi-finished products to be dyed, and preferably less than 3 times the weight of the semi-finished products to be dyed. Appropriately, all the dyeing solution necessary for the dyeing phase can be inserted inside the internal environment 4. Advantageously, the dyeing solution can be recirculated within the environment 4.

[0045] Appropriately, this phase can take place at a temperature above room temperature, preferably it can take place at a temperature above 50°C, and more preferably above 60°C, and more preferably above 70°C, and more preferably above 80°C, and more preferably above 90°C, and more preferably below 100°C. advantageously this can be achieved by heating the internal walls 6, which transfer heat to the dyeing solution and to the semi-finished products to be dyed by conduction, following direct contact with the latter. In particular, therefore, it is clear that the semi-finished products to be dyed are intended to come into contact with the internal walls 6 of the dyeing machine 2 during the dyeing phase.

[0046] Advantageously, during the dyeing phase, the processes of absorption of the dyeing solution by the fibers of the semi-finished product can take place, and the process of dispersion of the dyeing compound along the same fibers, in order to obtain a homogeneous color.

[0047] Appropriately, the method according to the invention may provide, during the dyeing phase, for a mixing sub-phase, during which the semi-finished products to be dyed are mixed by means of a suitable mobile device present within the internal environment 4, for example by means of spheres or cylinders or a rolling cylinder around which the semi-finished products to be dyed are wrapped.

[0048] Appropriately, the method according to the invention can also include a fixing phase,configured to fix the dye on the semi-finished products. Advantageously, this can provide for the conveyance of steam on the semi-finished products to be dyed. Preferably this can be achieved by conveying steam through nozzle 7. Appropriately during this phase, the external walls 6 of machine 1 can be kept at a high temperature, preferably above 60°C, and more preferably above 70°C, and more preferably above 80°C.

[0049] Appropriately, the method according to the invention can also provide for a drying phase, preferably in the air and at room temperature.

[0050] As is clear from what has been said, the method according to the invention is particularly advantageous as it allows to dye semi-finished products of the various fibers through the use of small quantities of dyeing solution and in the case of cellulosic salt.

[0051] The method can therefore comprise, preferably in order, the following steps:

[0052] - a phase of insertion of at least one garment in a container,

[0053] - the dyeing phase, which preferably includes the following sub-phases:

[0054] o a sub-step of inserting a dye solution containing a dye into the container, o and a sub-step of inserting an alkaline silicate inside the container.

[0055] This method allows for a uniform, high-quality dye using a low bath ratio and without the addition of additional inorganic salts, thus significantly reducing water consumption and the environmental impact of the dyeing process.

[0056] The method may be characterized by the fact that the solution does not include inorganic sodium salts other than sodium silicate and sodium carbonate.

[0057] Removing chloride, sulphate or similar anions from the dyeing solution simplifies wastewater salinity treatment, simplifying downstream treatment processes and improving discharge quality.

[0058] The method may be characterized by the fact that the solution includes sodium carbonate.

[0059] The use of sodium carbonate in the dye solution helps maintain the optimal pH for the dye's bonding reaction to the fibers, improving the efficiency of the dyeing process.

[0060] The method may be characterized by the fact that the ratio of garments to solutionby weight is less than 1 :3, and preferably about 1 :2.

[0061] This low bath ratio allows for a dramatic reduction in water consumption compared to conventional methods, while maintaining a high concentration of dye that promotes absorption by the fibers.

[0062] The method can be characterized by the fact that the solution containing a dye does not contain salts other than those of standardization and synthesis of the dyes inserted during the dyeing phase.

[0063] The decrease in the amount of salts in the dyeing solution drastically reduces the problem of saline pollution of wastewater, greatly simplifying purification processes and reducing the environmental impact of the process. Since silicate can simply be precipitated in an acidic environment.

[0064] The method can be characterized by the fact that the sub-phase of adding at least one alkaline silicate is carried out at a temperature below 50°C, and preferably below 40°C.

[0065] The use of lower temperatures during the dye fixing phase reduces the energy consumption of the process and minimizes the risk of thermal damage to fibers and garments.

[0066] The method can be characterized by the fact that it provides for a washing phase following the sub-phase of addition of at least one alkaline silicate.

[0067] The washing phase following the insertion of the alkaline silicate allows you to effectively remove the unfixed dye and silicate residues, ensuring better color fastness and preventing discharge problems during use of the garment.

[0068] The method can be characterized by the fact that the alkaline silicate is sodium silicate.

[0069] The use of sodium silicate as an alkaline agent offers the advantage of providing both the alkalinity necessary for the fixation of the dye and an electrolytic effect that promotes the depletion of the dye bath.

[0070] The method can be characterized by the fact that the pH of the solution during the sub-phase of adding at least one alkaline silicate is greater than 9.

[0071] Maintaining a high pH during the dye fixation phase ensures an efficient reaction between the reactive dye and the cellulosic fibers, improving dyeing yield and colorfastness.

[0072] The method can be characterized by the fact that the sub-phase of adding at least one alkaline silicate is carried out following the absorption of the dye by the garments to be dyed.

[0073] The insertion of alkaline silicate after the initial absorption of the dye allows the fixing process to be optimized, reducing the risk of dye hydrolysis and improving the overall efficiency of the dye.

[0074] The garments are loaded manually or by automated systems within the dyeing machine 2, ensuring that they are evenly distributed to ensure a homogeneous dyeing. It is important to avoid overloading the container, as this may affect the quality of the dye.

[0075] Before insertion, the garments can be pre-moistened with clean water to promote uniform wetting, especially in the case of particularly hydrophobic materials. This pre-wetting can be done directly in the dyeing machine 2 or in a separate step. The dyeing machine 2 used can be equipped with internal recirculation and spraying systems which, combined with the recipe used in the method according to the invention, allow to operate with extremely low bath ratios, up to about 1 :2 (weight of the garment: volume of liquid). These systems ensure uniform wetting of the garments even with minimal volumes of liquid.

[0076] When inserting garments, care should be taken not to damage the fabrics. The garments are handled gently to avoid tearing or deformation. In some cases, protective nets or bags can be used for particularly delicate garments.

[0077] Once the loading is complete, the dyeing machine 2 is hermetically sealed to prevent liquid spillage during the dyeing process. The locking system must be robust and safe, able to withstand the mechanical stresses of rotation.

[0078] The insertion phase of the dye solution involves the preparation of a concentrated dye solution containing the appropriate reactive dye for the type of fiber to be dyed. This solution is prepared by dissolving the dye in a portion of the bath water. It is important to note that the dyeing solution preferably does not contain sodium chloride or other added conductive salts, unlike conventional dyeing methods. Appropriately, the solution can contain a quantity of dye equal to what is necessaryto achieve the desired tone.

[0079] In some examples, the solution may contain sodium carbonate, which acts as an alkalizing agent to aid in the fixation of the dye on the fiber. The amount of soda ash can vary depending on the type of dye and the degree of alkalinity desired.

[0080] To improve the performance of the dyeing process, the dyeing solution may include specific ancillary products.

[0081] These auxiliary products are added in small quantities, typically in the order of a few grams per liter of solution.

[0082] Once prepared, the dyeing solution is placed in the dyeing container containing the garments to be dyed. Insertion takes place in a gradual and controlled manner, ensuring uniform distribution on the garments through the rotating movement of the container and / or by means of internal spraying systems. This approach allows for a homogeneous wetting of the fabric and promotes uniform absorption of the dye. The ratio between the weight of the garments and the volume of the dyeing solution is kept very low, preferably less than 1:3, and more preferably around 1:2. This extremely low liquor ratio helps to increase the effective concentration of dye per unit volume, improving depletion kinetics and reducing the need to add salts to aid in dye absorption.

[0083] The sub-step of adding at least one alkaline silicate is a key step in the dyeing process described. The alkaline silicate used is preferably sodium silicate in aqueous solution. The addition of this compound is preferably done gradually, dividing the total amount into several portions that are introduced into the dye bath at regular intervals. Appropriately, alkaline silicate can be inserted in a quantity greater than 10g / I, and more preferably more than 30g / l, and preferably equal to about 40-50g / l, and more preferably equal to 40g / l.

[0084] The temperature during this phase is maintained between 30 and 40°C. This relatively low temperature range helps to reduce the energy consumption of the process and limit unwanted hydrolysis of the reactive dye.

[0085] The addition of alkaline silicate causes the pH of the dye bath to rise progressively to values between 11 and 11.5. This strongly alkaline environment is necessary to trigger the fixation reaction of the reactive dye on the cellulosic fibers.The total duration of the dyeing phase, including the addition of silicate and subsequent fixation, is 1-12 hours depending on the dyeing temperature. This time is sufficient to allow a complete reaction between the dye and the fibers, ensuring a high degree of fixation and color fastness.

[0086] The use of alkaline silicate in this phase performs multiple functions:

[0087] provides the alkalinity necessary for dye fixation.

[0088] acts as a buffering agent, controlling the gradual release of hydroxide ions and stabilizing the pH.

[0089] It contributes to the ionic strength of the bath, favoring the depletion of the dye on the fiber.

[0090] It can slightly improve the degree of whiteness of the garments thanks to a slight cleansing effect.

[0091] The combination of these effects, combined with the absence of added inorganic salts and the low bath ratio, allows for optimal dyeing results with a reduced environmental impact compared to conventional methods.

[0092] After the sub-phase of adding at least one alkaline silicate and completing the dye fixation reaction, the process involves a washing phase of the dyed garments. This step is useful for removing unfixed dye, neutralizing residual alkalinity, and improving color fastness.

[0093] The wash cycle typically includes the following steps:

[0094] initial rinse with water at room temperature to remove most of the residual components from the dye bath.

[0095] neutralization with an acid, e.g. dilute acetic acid to lower the pH and neutralize the residual alkalinity of the silicate.

[0096] one or two soaping washes at high temperature (about 90°C) with the addition of a specific detergent to remove the unfixed hydrolyzed dye and improve color fastness.

[0097] enzymatic treatment at moderate temperature (about 50°C) to remove any surface fibrils and improve the hand of the fabric. This step uses enzymes specific to the material from which the garments are made.

[0098] Final rinses with warm and cold water to remove all chemical residues andprepare the garments for drying.

[0099] Possible application of a fabric softener to further improve the hand of the fabric.

[0100] The washing phase is carried out in the same container used for dyeing, maintaining a higher bath ratio (typically 1 :8, but which can go as low as 1 :3) to ensure effective residue removal.

[0101] This complete wash cycle ensures that dyed garments are free of unfixed dye, have good colour fastness and are ready for subsequent finishing and packaging steps. Thorough removal of chemical residues and unfixed dye also helps to reduce the environmental impact of process effluents.

[0102] The proposed dyeing method is based on the synergistic interaction of different phases that contribute to the effectiveness and eco-sustainability of the process. The absence of added inorganic salts and the use of an alkaline silicate are fundamental elements of this interaction.

[0103] The initial step of inserting the cellulosic fiber garment into the dyeing container prepares the substrate for the process. Subsequently, the addition of the solution containing the reactive dye, free of salts, allows direct contact between the dye and the fiber. The extremely low bath / material ratio, typically around 1 :2, favors a high concentration of dye near the fiber.

[0104] The absence of salts in the initial dyeing solution might seem counterintuitive, given that traditionally salts promote dye depletion. However, in this method, the high concentration of dye due to the low bath ratio effectively compensates for the lack of added electrolytes.

[0105] The next step of adding at least one alkaline silicate plays a crucial role in the interaction between dye and fiber. Alkaline silicate, typically sodium silicate, provides both the alkalinity necessary for the fixation reaction of the reactive dye, and an adequate amount of sodium ions that contribute to the final depletion of the dye. The gradual introduction of alkaline silicate at relatively low temperatures (below 50°C preferably below 40°C) allows precise control of the pH, which reaches values above 11 , optimal for fixation.

[0106] This combination of factors - low bath ratio, absence of added salts and use ofalkaline silicate - leads to a depletion of the dye even greater than 90%, or in any case to a high depletion compared to the same recipe carried out with a longer bath ratio.

[0107] The interaction between these steps not only optimizes dyeing efficiency, but also contributes to the eco-sustainability of the process. The absence of added salts eliminates a significant source of pollution in wastewater. The low bath ratio dramatically reduces water consumption and the energy required for heating. In addition, the high depletion and fixation of the dye minimizes the amount of residual dye in the effluents.

[0108] The final washing phase, performed after the addition of the alkaline silicate and the completion of the fixation, effectively removes any residues of unfixed dye and chemicals, thanks to the lower presence of salts to be eliminated compared to conventional processes.

[0109] In summary, the interaction between the different phases of the method, characterized by the absence of added salts and the targeted use of alkaline silicate, makes it possible to obtain an efficient and eco-sustainable dyeing process, with dyeing performance comparable to or superior to traditional methods, but with a significantly reduced environmental impact.

[0110] EXAMPLES OF REALIZATION

[0111] Example 1 - Dyeing of salt-free cotton T-shirts at a 1 :2 ratio

[0112] Material: 10 cotton jersey T-shirts (total weight 1 kg, natural color).

[0113] Dye: Reactive Black (bifunctional reactive type) at 3% of the weight of the fabric. Machine: Laboratory dyeing machine 2 of 5 kg, heatable, with internal sprayer. Procedure: The garments are pre-soaked with 1 I of warm water in the dyeing machine 2 in slow rotation for 5 minutes. A solution containing 30 g of Reactive Black dye (previously dissolved in 0.5 I of water at 40°C with 2 g / l of humectant auxiliary) is then added. Leave the dyeing machine 2 in rotation at 30°C for 20 minutes, during which the initially intense bath becomes visibly lighter as the dye absorbs on the T-shirts.

[0114] After this time, an alkaline solution with sodium silicate is prepared: 50 ml of liquid sodium silicate (commercial solution of 40% SiCh) diluted in 200 ml of water. Addthe silicate solution in 4 portions of about 60 ml each, pouring them into the drum every 5 minutes. The pH of the bath, initially about 7, rises to about 11.5 after the last addition. Continue the rotation at 30°C for a further 60 minutes to complete the fixation reaction. It is observed that the final bath is almost colorless, indicating dye depletion of more than 90%. The total initial liquid volume is increased to 2 I (ratio 1:2).

[0115] Then drain the bath and wash it: first wash with 2 I of water at 30°C with neutral detergent (5 g / l) for 10 minutes; second wash with 2 I of water at 60°C with soap agent (2 g / l) for 15 minutes; third and fourth rinse with warm water and finally cold for 5 minutes each.

[0116] Dyed T-shirts have an intense and uniform black color. The fastness tests show: fastness to washing 4-5 (Grey scale), fastness to rubbing 4 (dry) 13-4 (wet), values completely similar to those expected from a conventional process. Despite the absence of salt, there are no defects; The use of silicate ensured good penetration and color fixation.

[0117] Example 2 - Dyeing cotton sweatshirts with blue reactive dye, comparison with conventional method

[0118] Material: 5 cotton sweatshirts (total weight 2.5 kg, bleached).

[0119] Colour: Reactive Blue, medium-dark shade, at 2% of the goods weight.

[0120] Two parallel dyes are performed for comparison:

[0121] (A) Conventional method in 1:10 flask with salt and soda

[0122] (B) Method according to the invention, in a 2 1 :2 dyeing machine with silicate (A) Conventional method: The sweatshirts are dyed in a washing machine with 25 I of bath (1:10) containing 50 g / l of salt (NaCI). After 10 minutes at 40°C add the previously dissolved dye (50 g, 2% of the weight of the goods); continue for 20 minutes then add sodium carbonate (soda) 20 g / l in two parts to fix (T = 60°C, 30 minutes). You unload and wash the sweatshirts with the standard cycles.

[0123] (B) Method according to the invention: The sweatshirts are dyed in a single drum of 3 I of total liquid (ratio about 1 :2 adopted here to maximize water savings). Add 50 g of Reactive Blue dye in 1 I of water, rotate for 15 minutes at 30°C, then put 250 ml of liquid sodium silicate diluted 1:1 in water, dividing the addition into 3 doses. Keep30°C for 1 hour. It is drained and washed as in example 1.

[0124] Results: Both batches of sweatshirts show the same shade of blue, intense and uniform, with no visible differences. The instrumental measurements of color resistance (fastness to light, washing and rubbing) are superimposable between the conventional method and the one according to the invention (all fastness values within 0.5 units of degree). The calculated dyeing yield (percentage of dye fixed on the fiber compared to the dosed) is about 72% for the conventional method (A) and about 78% for the method according to the invention (B), indicating a slight fixation advantage for the latter.

[0125] From an environmental point of view, the exhausted bath of method (A) contained high residual salinity (about 30 g / l of unabsorbed NaCI) and a discharge volume of about 25 I, while the bath (B) had negligible salinity and only about 3 I of volume to be disposed of. This comparative example confirms that the new method according to the invention achieves dyeing performance equivalent to the traditional method, while offering significant benefits in terms of reduction of water and salt used.

Claims

CLAIMS1. Method for dyeing a semi-finished textile product, preferably comprising at least 20% cellulosic fibres, and preferably 100% cellulosic fibres comprising the following steps:a phase of making available at least one semi-finished product to be dyed, a step in the preparation of a dye solution, containing at least one chemical compound configured to dye the semi-finished product,a dyeing phase during which at least one semi-finished product to be dyed is brought into contact with the dyeing solution,in which the dyeing phase takes place inside a dyeing machine (2) which includes:a plurality of external walls (6) that defines an internal environment (4) within which the garments and the dyeing solution are directly inserted,the method being also characterized by the fact that the dyeing phase includes a sub-phase of adding at least one alkaline silicate, preferably sodium silicate, inside the container.

2. Method according to claim 1 characterised by the fact that the dyeing phase is carried out at a temperature of between 50 and 100°C, and more preferably between 60 and 100°C, and more preferably between 70 and 100°C, and more preferably between 80 and 100°C, and more preferably between 90 and 100°C.

3. Method according to one or more of the above claims characterized by the fact that during the dyeing phase, in the internal environment 4 there is a quantity of dyeing solution equal to at least the weight of the semi-finished products to be dyed, and preferably equal to at least 1.5 times the weight of the semi-finished products to be dyed, and preferably equal to at least twice the weight of the semi-finished products to be dyed, and preferably less than 10 times the weight of the semifinished products to be dyed, and preferably less than 5 times the weight of the semi-finished products to be dyed, and preferably less than 3 times the weight of the semi-finished products to be dyed.

4. A method according to one or more of the above claims characterized by the fact that the external walls (6) of the machine are heated, and transmit the heat to the dyeing solution and to the garments to be dyed by direct contact.

5. A method according to one or more of the above claims characterised by the fact that there is a washing phase of the semi-finished product to be dyed prior to the dyeing phase.

6. A method according to one or more of the above claims characterized by the fact that the washing phase is carried out at room temperature, or at a temperature between 30 and 100°C, and preferably between 40 and 100°C, and preferably between 50 and 100°C.

7. A method according to one or more of the above claims characterised by the fact that it involves a fastening phase during which the garments are heated to a temperature above 60°C, and more preferably above 70°C, and more preferably above 80°C.

8. A method according to one or more of the above claims characterized by the fact that during the fixing phase, water vapour is injected into the internal environment (4).

9. Method according to one or more of the above claims characterized by the fact that the dyeing machine (2) is a drum.

10. A method according to one or more of the above claims characterized by the fact that, during the dyeing phase, the semi-finished product to be dyed and the dyeing solution are completely contained within the internal environment (4).

11. A method according to one or more of the previous claims characterized by the fact of providing for an opening opening phase (8) and an opening closing phase (8), essentially separating the internal environment (4) in which the semi-finished products to be dyed and all the dyeing solution are inserted, from the outside.

12. Method according to one or more of the above claims characterized by the fact that during the dyeing operations, substantially all the dyeing solution is contained within the internal environment (4).

13. Method according to one or more of the previous claims characterized by the fact that during the dyeing operations the semi-finished products to be dyed can be substantially free to move within the internal environment.

14. Method according to one or more of the above claims characterized by the fact that the solution does not include sodium chloride.

15. Method according to one or more of the above claims characterized by the fact that the solution includes sodium carbonate.

16. A method according to one or more of the above claims characterized by the fact that the solution containing a dye does not contain salts.

17. Method according to one or more of the above claims characterized by the fact that the sub-phase of adding at least one alkaline silicate is carried out at a temperature below 50°, and preferably below 40°C18. A method according to one or more of the previous claims characterized by the fact that it provides for a washing phase following the sub-phase of addition of at least one alkaline silicate.

19. Method according to one or more of the above claims characterized by the fact that the pH of the solution during the phase of adding at least one alkaline silicate is greater than 11.

20. Method according to one or more of the above claims characterized by the fact that the sub-phase of adding at least one alkaline silicate is carried out following the absorption of the dye by the garments to be dyed.

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