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The present invention relates to a plant and a process for the treatment and dyeing of materials wrapped on rigid supports.
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A known type of plant for bath dyeing generally comprises a substantially cylindrical autoclave, with a horizontal or vertical axis, in which the bath (dyeing liquid) is contained, heated by means of a serpentine coil or a shell-and-tube exchanger in which steam or superheated water circulates.
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Inside the autoclave is placed the material to be dyed, which is normally wound on hollow rigid cylindrical supports or contained in special baskets. For example, such supports are beams or bobbins when the horizontal autoclave is intended for dyeing fabrics or yarns, or tubes generally made of plastic or metal placed on a material-holding structure when the autoclave has a vertical axis and is intended for dyeing yarns.
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The bobbins or tubes are stacked on hollow or solid cylindrical spindles with a circular or triangular cross-section of the material-holding structure.
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In the case of rigid cylindrical supports (beams or cylindrical spindles or perforated tubes), these are provided with radial through holes, through which the bath can flow, to pass from the inside to the outside or vice versa, crossing the fabric or the fibres to be dyed.
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Other packages generically known as tops, bumps, cakes; or other materials such as yarns for warp beams or ribbons or zippers are treated on different material holders but according to concepts similar to those provided for fabrics on beams or yarns on bobbins.
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In the case of a vertical axis autoclave, by exploiting the duct inside the hollow spindles and the hollow inner core of the perforated bobbins, a distribution duct for the dyeing fluid is created, capable of then generating a flow of dye bath in a radial direction with respect to the spindles and transverse through the bobbins, from the inside to the outside, which crosses the textile material, dyeing it as uniformly as possible.
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When the textile material is a yarn, it is wound on the perforated bobbin, whereas when the textile material is a fabric, it is wound on the beam or perforated tube, so as to substantially completely cover the lateral surface of the tube.
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The autoclave is connected to a bath circulation pump that carries the liquid inside the autoclave and in particular inside the hollow spindles of the material-holding structure. The plant, in versions with double pump pressurization, also includes an expansion tank, necessary to compensate for the increase in the volume of the bath with temperature and useful for making additions of dye and auxiliary components without stopping the process.
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Furthermore, in versions with air pressurization, the plant provides a pressurization group necessary to bring the internal chamber of the autoclave to the working pressure and also provides control, regulation and command devices for the various dyeing cycles.
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The dyeing of yarns on bobbins and of fabrics and other textile material in general at temperatures lower or higher than that of saturated vapour at atmospheric pressure, has always been carried out on apparatus equipped with devices that allow the liquid state of the water to be maintained even at temperatures higher than that of saturated vapour at atmospheric pressure, including for example between 120 and 150 °C.
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The ways in which known devices allow reaching temperatures higher than that of saturated vapour at atmospheric pressure are substantially two: the first involves the use of a pressurized air cushion that guarantees sufficiently high pressures inside the autoclave to maintain the liquid state of the dye bath, while the second involves the use of a pressurization pump that guarantees the liquid state of the dye bath.
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In both cases, the pressure is used to maintain the liquid state of the dye bath. For this reason, the machines are sized to withstand maximum allowable pressures which, depending on the cases, applications and technologies used, reach up to 7 bar and temperatures up to 150°C.
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An example of such a plant is described in the patent application
WO0073567 in the name of the same applicant.
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The traditional dyeing procedure consists of pumping the dyeing liquid into the autoclave inside the support cylinders of the material, which then exits outwards in a radial manner, falls to the bottom of the autoclave itself and is repumped inside the cylinder. In some cases, inverse cycles are also carried out in which the liquid is pumped to the outside of the cylinder and sucked towards the bottom of the autoclave from inside the hollow cylinder.
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In such traditional procedures, it can happen that the dye does not penetrate in a particularly uniform way inside the fabrics or yarns to be dyed, for example due to poor homogenization of the dyeing liquid that is pumped inside the autoclave. Furthermore, the material wrapped on the rigid supports can undergo stresses that could generate deformations and therefore condition the effectiveness of the dyeing process first and penalize its quality before and after use.
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Over the years, attempts have been made to overcome this drawback of non-uniformity of dyeing, due to the poor homogenization of the dyeing liquid, by adding one or more auxiliary recirculation circuits for the liquid in the autoclave. For example, in patent
EP2659042B1 a second circuit, or recirculation member, is provided to induce sufficient movement of the dyeing fluid inside the autoclave, having a second pump and a switchable valve between an open condition, in which the second pump induces said dyeing fluid to cross at least one bobbin-holder spindle, and a closed condition, in which said bobbin-holder spindle is not crossed by said dyeing fluid.
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The
Italian patent 102019000009276 describes a plant in which a bobbin-holder spindle is present in the autoclave, onto which at least one yarn bobbin can be fitted, so that a first portion of said treatment bath is retained by absorption by the yarn of said bobbin and a remaining, second portion of said treatment bath remains outside said at least one bobbin. An auxiliary recirculation circuit comprises a second pump associated with a second hydraulic circuit passing through the outside of the autoclave has a flow rate such as to cause said second portion of the treatment bath to exit the autoclave and be reintroduced into the autoclave, so as to mix said treatment bath.
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The applicant has observed that in these prior documents, through a more or less sophisticated parallel circuit, an attempt is made to overcome the problem of the homogenization of the temperature and composition of the free bath, i.e., of the bath that by definition is not in the primary circuit upstream and downstream of the main pump and in the bobbins. None of the indicated patents considers the effects on treatment homogeneity caused by a non-uniform flow distribution.
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In these documents, the resistant medium (in particular the bobbin or the beam) is considered a perfect body when, for known reasons related to the formation process of the bobbin or beam, to the behaviour of the fibres as a function of process and chemistry, such cylindrical supports for the material to be dyed are instead not perfect bodies. Furthermore, in these documents and in the proposed solutions, little or no weight is given to the asymmetries of the hydraulic circuit as a whole, imagining localized suction/delivery points, both of the main and secondary circuits.
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In these documents, it is assumed that to obtain an optimal result it is logical to force the circulation through the material to be dyed to the maximum, even in two opposite directions, so as to increase the probability of a uniform distribution in the different points of the fibre and the exchange, always bringing new colour into contact with the fibre to compensate for what has already been absorbed.
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Therefore, to increase the intensity of the circulation it is necessary to increase the flow rate of the pump, or its head. The applicant has observed that this can cause the fabric wound on the beams or the yarn wound on the bobbins to deform, increasing, for example, the non-uniformity of the bobbin and determining the formation of preferential passages, not allowing for correct homogeneity of the dyeing. The bobbin with the wound yarn after treatment may appear deformed, while the beam with the wound fabric may present the fabric itself not perfectly distributed on the beam. In both cases, due to these displacements or deformations, the dyeing may not be optimal.
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The purpose of the present invention is, therefore, to eliminate the lamented technical drawbacks, by creating a plant and a process for the treatment and in particular for the dyeing of material wrapped on a hollow rigid support that allows obtaining high-quality products with regard to dyeing uniformity and the preservation of the geometry of the system and the physical/mechanical characteristics of the material.
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Another purpose of the invention is to create a process that allows obtaining high and, in any case, substantially greater productivity compared to that obtainable with traditional procedures.
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A further purpose of the invention is to create a plant and a process that allow operating at specific flow rates substantially higher than those known and permissible and, consequently, with proportionally shorter process times.
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Not the least purpose of the invention is to create a process for dyeing materials, in particular yarns or fabrics, wrapped on rigid supports, which is substantially simple, safe and reliable as well as at relatively limited costs by virtue of the advantages obtained.
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These and other purposes, according to the present invention, are achieved by creating a plant for the treatment of material wrapped on hollow rigid supports according to claim 1. Other characteristics of the plant and the process are defined in the subsequent claims.
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Advantageously, the process according to the present invention allows reducing process times, increasing the productivity of the plants and simultaneously guaranteeing a high quality of the treated material, as it reduces the deformations determinable by the high specific flow rates. It is also possible to reduce energy consumption, favouring economic and environmental implications.
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The process according to the invention also allows treating and, in particular, dyeing different types of materials including, mainly, natural, artificial and synthetic textile fibres and not only.
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Further characteristics and advantages of a plant and a process for the treatment of materials wrapped on rigid supports, according to the present invention, will become more evident from the following description, exemplary and non-limiting, referring to the attached schematic drawings, in which:
- figure 1 shows a first embodiment of a plant that carries out a process according to the present invention, in particular a plant for dyeing fabrics with air pressurization;
- figure 2 shows a second embodiment of a plant that carries out the process according to the present invention, in particular a plant for dyeing yarns on bobbins with static pump pressurization;
- figure 3a illustrates the bobbin of figure 3c after the dyeing process at a certain flow rate according to the prior art;
- figure 3b illustrates the bobbin of figure 3c after the dyeing process at a certain flow rate according to the present invention;
- figure 3c illustrates a bobbin with a wound yarn before the dyeing process;
- figure 4a illustrates a graph of the parameters set for the dyeing process of the bobbin of figure 3a;
- figure 4b illustrates a graph of the parameters set for the dyeing process of the bobbin of figure 3b.
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With reference to figure 1, an example of a plant is shown that carries out a process for dyeing yarns or fabrics wrapped on hollow rigid supports, according to the invention, indicated overall by the reference number 11.
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The plant 11 comprises an autoclave 12, inside which is inserted a material-holding structure 13 comprising one of said rigid supports for the material to be dyed. In the embodiment illustrated in figure 1, the plant is of the "horizontal" type, as the autoclave has a horizontal axis and the material-holding structure is inserted horizontally into the autoclave and comprises a beam 13 consisting of a hollow tubular element provided with through holes along its entire surface and equipped with end flanges for containing the material to be dyed 14, which is preferably a fabric. In the case of a horizontal axis autoclave, by exploiting the hollow inner core of the beam, a distribution duct for the dyeing fluid is created, capable of then generating a flow of dye bath in a radial direction with respect to the beam itself from the inside to the outside (and vice versa in some cases) that crosses the textile material, dyeing it.
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Inside the autoclave 12 is also located a serpentine heat exchanger 15 for heating the bath; inside the serpentine coil 15 circulates steam or superheated water coming from a boiler, not shown for simplicity. The serpentine heat exchanger can be suitably replaced by a shell-and-tube exchanger located externally on the main circuit. According to this embodiment, the autoclave 12 is connected, by means of pipes 16, to an expansion tank 17, which can absorb the volume variations of the bath following temperature variations.
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From the tank 17, furthermore, ducts 18 depart, connected to a ring recirculation circuit 20, in which a circulation pump 19 is placed. The ring circuit 20 has a first branch 20A, which opens inside the beam 13, and a second branch 20B, which opens into the autoclave 12. The pump 19 can feed the bath inside the material-holding structure (through branch 20A of circuit 20) and aspirate (through branch 20B of circuit 20) the same bath to carry out the dyeing according to a traditional procedure.
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The plant 11 comprises an introduction circuit 21 connected to the ring circuit 20, so as to guarantee the introduction of chemical products contained in one or more tanks V1 and V2; this circuit comprises an introduction pump 211 connected to the ring circuit or to another part of the machine through a regulation circuit 22 of the quantity of such chemical products to be delivered. The plant further comprises a supply circuit 23 for the dye bath, advantageously equipped with a liquid quantity counting sensor 231, connected to said ring circuit 20 and a discharge circuit 25 for said bath from the autoclave 12.
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The plant comprises a steam supply circuit 151 to the serpentine coil 15 provided with thermoregulation elements. Said tank 17 is connected to a pressurization circuit 24 with compressed fluid and air discharge through connection valves. Advantageously, a pressure switch P is present in this pressurization circuit. This pressurization circuit is suitable for maintaining a static pressure in the autoclave higher than the vapour pressure for the dyeing liquid. The plant also comprises a control circuit 26 for the opening and closing (of the state in general) of the lid 121 of the autoclave 12.
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With particular reference to figure 2, a further example of a plant is shown that carries out the process for dyeing yarns wrapped on hollow rigid supports, according to the invention, indicated overall by the reference number 11'. The plant 11' comprises an autoclave 12', inside which is housed a material-holding structure 13' for the yarn to be dyed. In the embodiment illustrated in figure 2, the plant is of the "vertical" type as the autoclave has a vertical axis and the material-holding structure 13' is inserted into the autoclave from above. In the illustrated example, the material to be dyed is a yarn wound on bobbins or tubes 131', generally of plastic or metal, placed on the material-holding structure 13' with a vertical axis. The bobbins or tubes are stacked on hollow spindles 132' of the material-holding structure itself. In the case of a vertical axis autoclave, by exploiting the duct inside the hollow spindles and the hollow inner core of the perforated bobbins, a distribution duct for the dyeing fluid is created, capable of then generating a flow of dye bath in a radial direction with respect to the spindles and transverse through the bobbins, from the inside to the outside (and vice versa) that crosses the textile material, dyeing it.
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Inside the autoclave 12' is also located a serpentine heat exchanger 15' for heating the bath, while inside the serpentine coil circulates steam or superheated water coming from a boiler, not shown for simplicity. The serpentine heat exchanger can be suitably replaced by a shell-and-tube exchanger located externally on the main circuit.
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The plant also comprises a steam supply circuit 151' to the serpentine coil 15' provided with thermoregulation elements. The plant also comprises a ring recirculation circuit 20', in which a circulation pump 19' is placed, which comprises a first branch 20A', which opens inside the material-holding structure, and a second branch 20B', which opens into the autoclave 12'. The pump 19' can feed the bath inside the material-holding structure (through branch 20' of circuit 20') and aspirate (through branch 20B' of circuit 20') the same bath to carry out the dyeing according to a traditional procedure. The plant 11' comprises a pressurization circuit 24' with a static pressurization pump, connected to the ring circuit20' comprising a static pressurization pump 241' that reaches the autoclave through the ring 20'. This circuit is suitable for maintaining a static pressure in the autoclave higher than the vapour pressure for the dyeing liquid. The plant further comprises a supply circuit 23' for the dye bath to the autoclave and a discharge circuit 25' for the bath itself from the autoclave.
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The plant illustrated in figures 1 and 2 is controlled by an electronic processing unit that controls and commands all the hydraulic devices (valves, pumps, sensors and actuators) and sets the various working cycles (dyeing, washing, etc.) by setting the parameters (temperatures, pressures, flow rates and so on) in an automated way according to one or more work programs. According to the process of the present invention, the material-holding structure with the material to be dyed (beam, bobbins stacked on spindles, depending on the type of plant) is inserted inside the autoclave 12 or 12' and subsequently the dyeing fluid and chemical products are introduced. The dye bath crosses the material to be dyed, pushed by the pump 19 or 19', at an absolute flow rate to which a specific flow rate and a crossing speed correspond, which condition the kinetics of the process. The dyeing cycle is generally divided into one or more phases in which the temperature of the liquid is traditionally brought to a process temperature Tp, which can vary between room temperature (20°C) and a maximum temperature of about 140°C, for example around 130°C.
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Furthermore, at this process temperature, to prevent the liquid inside the autoclave from vaporizing, it is necessary that the static pressure inside it is higher than the vapour pressure (or more properly saturated vapour pressure) for that type of liquid, at the process temperature. For example, for a process temperature of 130°C for a given dye bath, the vapour pressure can assume values of about 2.8 Bar. The dyeing cycle (including the relative pre- and post-treatments) is traditionally carried out at a circulation pump flow rate such as to guarantee a homogeneous flow of the dye bath on the material-holding structure and therefore on the material itself. Insufficient flow rates prevent a homogeneous treatment, while excessive flow rates can generate - for example in the case of bobbins - deformations such as those shown in figure 3a. Clearly, the higher the flow rate of the pump, the more the material-holding structure is stressed. As already mentioned previously, in a dyeing cycle at a predetermined process temperature and at a static working pressure just above the vapour pressure, the flow rate can be increased in a limited way, as the stressed yarns or fabrics can deform. For the purposes of the present invention, static working pressure Psa just above the vapour pressure means 5-10% of the value of the vapour pressure and in any case limited by the test pressure of the autoclave. Figure 3a shows a bobbin (illustrated before dyeing in figure 3c) subjected to a dyeing process, in a vertical autoclave like the one illustrated in figure 2. In particular, this bobbin is wound with a textured polyamide yarn of 78/23 X2. The weight of the bobbin used is 1.3 kg. The dyeing cycle was carried out at a temperature of 105°C and at a static pressure of 2.7 bar and the maximum flow rate of the pump reached 90 1/min. The graph in figure 4a shows this dyeing cycle. Therefore, this process was carried out at a predetermined static working pressure Psa just above the vapour pressure and at a predetermined process temperature Tp of 105 °C. The flow rate of the pump was increased until it exceeded a limit value beyond which the mass of dyed yarn and its structure in general were deformed. The graph in figure 4a illustrates the parameters used for this dyeing process according to the prior art. The applicant has perceived that in order to be able to increase the flow rate of the distribution pump and thus make the dyeing process more homogeneous without damaging the mass of yarn wound on the bobbins, it is necessary to increase the static pressure inside the autoclave by at least 20%, preferably 40%, even more preferably 50%, above the value of the vapour pressure at the process temperature. To do this, it is necessary to know, for a given natural (e.g., cotton, wool, cashmere, silk), artificial, or synthetic (Polyester, Polyamide) material wound on its corresponding material-holding support under certain conditions of density and crossing, defined as a package, process parameters such as • MAF (Max Allowed Flow); • mrf (minimum required flow). For the purposes of the present invention, MAF means the maximum allowed flow, i.e., the pump flow rate beyond which, under certain conditions, the package undergoes deformations such as to penalize the quality of the dyeing process, which is preferably expressed in litres per minute per kilogram of material [1/minxKg] or in cycles per minute. Also for the purposes of the present invention, mrf means the minimum flow rate below which the homogeneity of the treatment, i.e., the evenness of the dyeing result or of the process, is lost, which is preferably expressed in litres per minute per kilogram of material [1/minxKg] or in cycles per minute. A further parameter to be taken into account besides the static pressure is the dynamic pressure (Pdiff), i.e., the pressure available for the circulation of the dyeing liquid: its value normally does not exceed 5 - 2.8 = 2.2 bar, more frequently 4.5 - 2.8 = 1.7 bar. Depending on the characteristics of the machine and the material to be treated, a certain dynamic pressure corresponds to a certain flow rate Q measured in m3/h, i.e., 1/min, or 1/minxKg or even cycles/min. The value of the flow rate Q, to avoid damage to the material and ensure homogeneous dyeing, must be comprised between mrf and MAF. Therefore, a preliminary phase of the dyeing process requires establishing at least the MAF for a package. This can be obtained by placing the package in a laboratory plant designed for the purpose or in the plant itself, setting the process temperature Tp, the static working pressure Psa just above the vapour pressure. Subsequently, the flow rate of the circulation pump is progressively increased, thus forcing the flow of dye bath into the package, until a limit flow rate value PL is reached, at which the package itself begins to show irregularities in its structure. Once the MAF (limit flow rate for that package) has been established at a process temperature Tp and at pressure Psa, it is possible to set one or more dyeing cycles, each having a predetermined dyeing time tc, setting the static pressure of the autoclave to at least 20% (preferably 30%, even more preferably 40%) higher than the value Psa (Psa+HS) and setting (or progressively increasing) the flow rate of the circulation pump to a value higher than the limit flow rate PL by at least 10% (preferably 20%, even more preferably 30%). In general, at present the static pressure inside the autoclave is higher than 2.7 bar and can also reach 10 bar. Figure 3b shows a bobbin (illustrated before dyeing in figure 3c) subjected to a dyeing process according to the present invention, in a vertical autoclave like the one illustrated in figure 2. In particular, this bobbin is wound with a textured polyamide yarn of 78/23 X2. The weight of the bobbin used is 1.3 kg. The dyeing cycle was carried out at a temperature of 60°C and a static pressure of 5.5 bar and the maximum flow rate of the pump reached 90 1/min. The graph in figure 4b shows this dyeing cycle. The result is that the bobbin is not deformed, unlike the same bobbin treated with the prior art process and illustrated in figure 3a. Therefore, in substance, the process of the present invention carried out in a plant like the one illustratively shown in figures 1 and 2 comprises the steps of i. for a package of material to be dyed wrapped on said rigid support housed in said material-holding structure (13,13'), obtaining a limit flow rate value (PL) of the circulation pump at a stable process temperature (Tp) and at a static pressure in the autoclave (Psa) just above the vapour pressure for the dye bath defined as maximum allowable flow (MAF), ii. setting at least one dyeing cycle for a predetermined cycle time (tc), setting the static pressure of the autoclave to at least 20% higher than the value of the static pressure (Psa) just above the vapour pressure and setting the flow rate of the circulation pump to a value higher than the limit flow rate (PL) calculated in step i), for example at least 10% higher. Or, alternatively, progressively increasing the flow rate up to identifying the limit flow rate value at a certain pressure Psa + HS, with the new limit flow rate being higher than the original MFA flow rate; and with the new limit flow rate being such as to ensure greater treatment uniformity without harmful side effects. This set dyeing cycle takes place according to the following phases: • introducing a package of material to be dyed wrapped on said rigid support housed in said material-holding structure (13,13'), • introducing into the autoclave a dye bath or liquid, • heating said dye liquid to a process temperature (Tp), • pressurizing said fluid contained in the autoclave to a pressure value (Psa) just above the saturated vapour pressure at said process temperature; • setting the circulation pump to a limit flow rate value (PL) of the circulation pump, • for the predetermined time (tc) of said cycle, setting the static pressure to at least 20% with respect to the value of the static pressure (Psa) just above the vapour pressure and • setting the flow rate of the circulation pump to a value higher than the limit flow rate (PL), for example at least 10%. These phases of the cycle are preferably followed by the phases of: • cooling the dyeing liquid; • depressurizing the dyeing fluid in the autoclave; • draining the dyeing liquid from the autoclave; • removing the material package from the autoclave. In conclusion, the result was obtained as the dyeing process is characterized by static pressures higher than the value used in conventional processes. In particular, by working at static pressures comprised in a range of values between 2.7 and 10 bar and, in particular, equal to 4.5 bar, it was possible to increase the flow rates up to more than twice the conventional ones without thereby damaging the yarn or deforming the bobbin. The bath temperatures reached values between 20 and 150 °C, preferably between 130 and 135 °C. It has been practically found that the process for dyeing yarns or fabrics wrapped on a hollow rigid support, according to the invention, is particularly advantageous because it allows obtaining high-quality products with a productivity higher than that obtainable with traditional procedures. A process for dyeing yarns or fabrics wrapped on a hollow rigid support so conceived is susceptible to numerous further modifications and variations, all falling within the scope of the invention; moreover, all details can be replaced by technically equivalent elements. Finally, the materials used, as well as the dimensions, can be any according to the technical requirements.