APPARATUS FOR CONTINUOUS DECATIZING IN AUTOCLAVE

The present invention relates to an apparatus for continuous decatizing in autoclave, which is particularly suitable to allow an optimal decatizing in a short time. It is known that autoclave decatizing is the most effective decatizing for wool, synthetic or mixed fabrics. In fact, temperatures higher than 100 ⁰ C can be reached in an autoclave thus preventing the moisture contained in steam from evaporating due to the effect of the high pressure value in the autoclave, which is usually higher than 1.5 arm.

This characteristic is the reason why autoclave decatizing gives permanent results; in fact, the gloss and the feel provided by decatizing are destroyed neither by washing nor by ironing, nor by the vapour press used by clothing manufacturers. This permanency of the properties cannot be obtained by decatizing treatments carried out in atmospheric pressure environments. In fact, in common decatizing treatments, in an open atmospheric pressure environment, this combination of high temperatures and high humidity cannot exist as the steam, when it exceeds 100°C, looses its moisture by evaporation and is transformed into hot air.

Autoclave decatizing apparatuses are also known which are provided with slots allowing to work in a continuous way. The fabric to be treated is sandwiched between two belts which, upon being put into the autoclave, adhere to a rotatable cylinder. Many of said apparatuses comprise an autoclave provided with a coaxial internal jacket which is heated in order to prevent the formation of condensation.

In the US Patent 6 381 883 an apparatus is disclosed comprising an autoclave wherein there is pressurized air at room temperature in a container which is not heated and contains a heated rotatable cylinder on which the fabric to be treated passes. However, the technical results achieved by said apparatuses are not satisfactory because it is difficult to reproduce in a slotted autoclave pressure, humidity and temperature conditions allowing to reach permanent decatizing results in a short time with a high productivity.

In an apparatus comprising a discontinuous decatizing autoclave without slots the decatizing treatment lasts few minutes, for example 5-6 minutes. The fabric is introduced into the autoclave being wound in rolls. The autoclave is closed, air is

removed and steam is introduced. The maximum temperature in the autoclave is usually close to 132°C corresponding to a vapour pressure of 2 atmospheres. As the treatment time is rather long this temperature is sufficient for ironing and decatizing the fabric which is arranged as a "sandwich" between two layers of technical cloth and wound, and for making the obtained finishing permanent.

On the contrary, in a slotted autoclave of a continuous decatizing apparatus the treatment lasts few seconds. For instance, assuming a fabric velocity of 20 meters per minute and an autoclave internal capacity of 5 meters (i.e. a circumference of the cylinder internal to the autoclave which is equal to 1200 mm plus the path to enter and exit from the autoclave), the residence of the fabric inside the autoclave can be 15 seconds. These data refer to an example of apparatus producing about 1200 meters per hour.

Although the continuous decatizing treatment carried out in a known apparatus with a slotted autoclave, for example such as above described, is characterized by being very quick, it however has the drawback that a fabric with a permanent gloss and feel is not obtained, as the treatment time is excessively short.

If the same results as obtained in a discontinuous autoclave are desired in a slotted autoclave, it is necessary first to work at temperatures and humidity which are higher than usual in order to compensate the shorter residence time. Object of the present invention is thus to provide a continuous autoclave decatizing apparatus and method which are free from the above-mentioned drawbacks and allow a high productivity and at the same time to obtain a fabric characterized by a permanent gloss and feel, such as those achievable in a discontinuous autoclave which operates in remarkably longer times. It is evident in fact that if the velocity is much lower and the fabric remains for a long time in a slotted autoclave, optimal decatizing results would be achieved also without the invention herein described, but the production of such an apparatus would be so low that said apparatus would not be industrially applied. Therefore the continuous autoclave decatizing apparatus and method according to the present invention have the advantage of combining a high productivity with a permanent decatizing result in terms of a gloss and a feel which would be achieved only in

remarkably longer times. This advantage is achieved by the combined heating of the autoclave jacket and the rotatable cylinder which overheat the steam contained in the autoclave along with the contemporaneous injection of overheated steam and/or water into the autoclave. Another advantage of the continuous autoclave decatizing apparatus and method according to the present invention is the possibility to keep the decatizing steam saturated by injecting water into the autoclave in a controlled way.

The injection of water into an autoclave should be considered as overcoming a technical prejudice, since so far the prior art prescribed to remove the water resulting from condensation inside the autoclave.

A further advantage of the continuous autoclave decatizing apparatus and method according to the present invention is the possibility to control the pressure, temperature and humidity values in two different areas inside a single autoclave, so as to achieve an optimal decatizing result. Further advantages and characteristics of the decatizing apparatus and the decatizing method according to the present invention will be evident to those skilled in the art from the following detailed and non-limiting description of an embodiment thereof with reference to the annexed drawings wherein:

Figure 1 shows a schematic sectional view of an embodiment of the continuous autoclave decatizing apparatus according to the present invention; and

Figure 2 shows a sectional view of the autoclave of Fig. 1 wherein the winding of the fabric around the cylinder is represented in more detail.

Figure 1 shows a continuous autoclave decatizing apparatus 1 comprising an autoclave 2 containing a cylinder 3 which is heated and rotatable around its axis. The apparatus 1 further comprises a first conveyor belt 4 and a second conveyor belt 5 which are supported by suitable rolls and are suitable to sandwich between themselves a fabric to be treated 6 and to carry said fabric 6 into the autoclave 2 through an inlet sealing slot 7 and out of the autoclave 2 through an outlet sealing slot T. The inlet sealing slot 7 and the outlet sealing slot T can for example be the nips comprised between suitable sealing rolls 8, 9 and 10. Inside the autoclave 2 one or more rolls 11

can be arranged which are suitable to support the conveyor belts 4 and 5, which sandwich between themselves the fabric to be treated 6. The conveyor belts 4 and 5 are arranged so as to surround the cylinder 3 and adhere on most of the cylindrical lateral surface thereof. As it is known, the autoclave 2 of apparatus 1 can be provided with an internal anti-condensation jacket 13, coaxially arranged relative to the autoclave 2, which can be heated by suitable heating means 14 in order to prevent the formation of condensation inside the autoclave 2.

In the decatizing apparatuses of the prior art wherein the anti-condensation jacket 13 is provided, the latter is heated at most up to a temperature of about 132°C, corresponding to an internal pressure of the autoclave of 2 arm.

On the contrary, according to the present invention the anti-condensation jacket 13 and the cylinder 3 are both heated at temperatures ranging from 160 ⁰ C to 200°C in order to overheat in a combined way the interior of autoclave 2 up to a temperature which is at least higher than 140°C and at a relatively low pressure, of about 2 arm, which would not allow to reach such a steam temperature, in order to achieve appreciable decatizing results. The means 14 for heating the jacket 13 may be formed of passageways wherein diathermic oil flows continuously. The oil may be heated outside the autoclave 2. The apparatus 1 is further provided with means 12 for injecting steam into the autoclave 2. In the embodiment illustrated in Figure 1, the steam injecting means 12 are formed of at least one pipe.

The temperature of the jacket 13 is raised until it reaches 180-200°C. In a preferred embodiment the temperature of the jacket 13 ranges from 160 to 200°C. The heating of the jacket 13 is particularly effective for overheating the steam contained in the autoclave 2 as it is provided of a large heat transfer surface directly exposed to the steam. The heated cylinder 3 has a smaller heat transfer surface than the jacket 13 but it is however essential for heating, in a combined way with the latter, the steam inside the autoclave 2 and heating the fabric 6. According to the present invention, a further heating of the steam inside the autoclave 2 can be obtained by auxiliary heating means 15, for example formed of

electrical resistances or heated coils.

In order to ensure the adhesion and the tension of the conveyor belts 4 and 5 and the fabric 6 on the cylinder, the autoclave 2 can also be provided with pressure rolls (not shown) which are pushed for example by pistons. The pressure rolls press the fabric against the heated cylinder and increase the steam ironing and decatizing effect.

Although there is a limitation to work at relatively low pressures, lower than 2 atm, in order to prevent steam leaks, with the decatizing apparatus 1 according to the present invention it is possible to obtain an overheated but saturated steam preferably at

150-160°C, inside the autoclave 2, by injecting water from the outside. Thus the technical prejudice according to which any presence of water inside the autoclave 2 should be avoided has been overcome. Water is injected into autoclave 2 through suitable injecting means, when the apparatus 1 is working. Preferably, water is injected into the autoclave 2 by means of a volumetric pump 18 and a corresponding injection mouth 19. In the autoclave 2 the water contacts the heated jacket 13 and is instantly vaporized, thus remarkably increasing the steam humidity value inside the autoclave 2.

Similarly, the water could also be injected in the direction of other heated elements arranged between the jacket 13 and the cylinder 3, for example towards said auxiliary heating means 15.

In an alternative embodiment the water could also be injected through steam injecting means 12, for example before they inject steam into the autoclave 2, by means of a volumetric pump 18*.

By adjusting with the volumetric pump the amounts of injected water it is possible to modify the decatizing results.

The means 12 for injecting steam into the autoclave may be provided with one or more non-return valves 20 in order that the amount of injected steam is not influenced by any possible variations in the internal pressure of autoclave 2 which are due to the evaporation of the injected water.

By keeping the steam contained in the autoclave 2 saturated with moisture by a controlled water injection, the pressure inside the autoclave 2 can be kept relatively low, whereby the sealing slots 7 and T are not too stressed.

Referring now to Figure 2 it is observed in more detail that the fabric 6 is

sandwiched between the two continuous conveyor belts 4 and 5. The first conveyor belt 4 directly contacting the heated rotatable cylinder 3 is preferably a common permeable felt belt and the second outer conveyor belt 5 is preferably an impermeable belt, which is usually siliconed. The fabric 6 and the two conveyor belts 4 and 5 sandwiching it, in the portion between the sealing slot 7 and the point where they adhere on the cylinder 3, come into contact with the overheated steam which is in the autoclave and injected by the steam injecting means 12 and/or obtained by heating the water injected by the water injecting means 18, 19. The first permeable belt 4 is impregnated by the steam and transmits moisture to the fabric 6 comprised between the first belt 4 itself and the second impermeable belt 5. As the multilayer structure formed of the first belt 4, fabric 6 and second belt 5 contacts the heated cylinder 3, the steam retained in the fabric 6 and the first permeable belt 4 tends to evaporate and expand. The second impermeable belt 5 is kept very much tensioned so as to generate an additional pressure on the fabric 6 due to the evaporation of the water becoming steam in the portion where the multilayer structure formed of the first belt 4, the fabric 6 and the second belt 5 is in contact with the heated cylinder 3. In said portion an area 21 is created (the dotted area in Figure 2, which is not represented according to real proportions as the first belt 4, the fabric 6 and the second belt 5 actually are in tight contact one with the other and with the cylinder 3) wherein the temperature and pressure values are remarkably higher relative to the rest of the autoclave 2. Therefore, inside a single autoclave 2, the fabric 6 crosses two different areas and thus undergoes two different decatizing treatments, the first one being due to the condition of steam created inside the autoclave, the second one deriving from the higher temperature and pressure obtained through the contact with the heated cylinder. A continuous autoclave decatizing apparatus 1 provided with a single impermeable belt 5 would also be possible, but in such a case the fabric 6 would tend to become longer because, as it is no longer protected on both its sides, it might be subjected to excessive tensioning stresses due to the friction in correspondence with the sealing slots 7 and T when entering and exiting from the autoclave 2. Humidity, temperature and pressure parameters can be adjusted in function of the decatizing velocity, the weight and the composition of the fabric to be treated (for

example wool, mixed-wool fabrics, synthetic fabrics, etc.). Further it is necessary to consider that a higher decatizing velocity implies a shorter treatment time, and that a larger amount of cold material to be heated should be fed into the autoclave.

It is possible to verify that the temperature which is actually reached from the fabric 6 is close to 145-150 ⁰ C for example by means of adhesive thermosensitive papers applied on the cloth.

In the following a non-limiting example of the decatizing parameters for a pure wool fabric is provided.

Example A pure wool fabric 6 weighing 400 grams per linear meter was treated in a continuous autoclave decatizing apparatus according to the present invention whose autoclave 2 had a diameter of 1800 mm. The decatizing velocity was about 20 m/min. The amount of water injected into the autoclave 2 was equal to about 1% of the fabric weight, that is about 80 grams per minute. The temperature of the jacket 13 of the autoclave 2 was equal to about 18O ⁰ C.

The temperature of the cylinder 3 was equal to about 180 ⁰ C.

The steam pressure inside the autoclave 2 was equal to about 1.5 bar.

The temperature reached by the fabric 6 in the first decatizing step, when there is no contact between the belts 4 and 5 and the heated cylinder 3, was estimated to be about 125-130 ⁰ C, while in the second decatizing step, when the belts 4 and 5 sandwiching the fabric between themselves are on the cylinder 3, it was estimated to be about 145-150 ⁰ C.

The permanence of the decatizing treatment of the fabric 6 was verified through the passage of a hot flat iron thereon, while arranging a humid cloth between the flat iron and the fabric 6. It is known in fact that the treatment proves to be permanent if the hot flat iron and the humid cloth do not leave a ring on the fabric 6. Upon passage of the iron on the fabric 6 being decatized by the apparatus 1 according to the above-indicated parameters, no rings were formed and the fabric 6 proved to have permanent properties and optimal feel and gloss.

It should be noted that it is possible to vary the decatizing parameters in order to

achieve different decatizing results. For example, if the amount of water injected in the autoclave 2 is equal to about 1% of the weight of the fabric 6 to be decatized and the fabric 6 is not excessively compressed on the cylinder 3, a more compact decatized fabric 6 is obtained. On the contrary, if the water injected in the autoclave 2 is equal to about 3-4% of the weight of the fabric 6 to be decatized and the fabric 6 is more strongly pressed against the cylinder 3, a fabric which is more compact and having a more "plastic-like" feel is obtained.

By using the apparatus according to the present invention it is also possible to carry out a decatizing wherein the steam to be injected into the autoclave 2 is remarkably overheated outside the autoclave 2 before being injected.

Further, it is possible to feed a previously humidified fabric 6 into the slotted autoclave 2.

Possible variants and/or additions can be made by those skilled in the art to the embodiments of the invention herein described and illustrated remaining within the scope of the following claims.