WO2014037509A1

WO2014037509A1 - Method of drying textile using alternating pressure

Info

Publication number: WO2014037509A1
Application number: PCT/EP2013/068479
Authority: WO
Inventors: Lilian Eva Tang Baltsen
Original assignee: Novozymes AS
Current assignee: Novozymes AS
Priority date: 2012-09-07
Filing date: 2013-09-06
Publication date: 2014-03-13
Anticipated expiration: 2015-03-07

Description

METHOD OF DRYING TEXTILE USING ALTERNATING PRESSURE

FIELD OF THE INVENTION

The present invention relates to the field of drying fabrics. In particular, the invention relates to methods of drying fabrics employing alternating pressure.

DESCRIPTION OF THE RELATED ART

Laundering is in general performed by agitating the fabrics in a detergent solution for a certain period of time followed by rinsing the fabrics in water. Laundering may be carried out using an automatic washing machine or it may be done by hand. Modern detergents are complex compositions comprising a number of components such as; surfactants, builders, bleaches, polymers, enzymes etc. just to mention a few, and are usually formulated as a powder or a liquid.

After laundering textiles they are dryed before use, and a convenient method employs a drying device, in general a device comprising a drum wherein the fabrics are loaded and where relative dry air is flowing through th drum leading to evaporation of water from the fabrics and consequently drying thereof.

Several modifications of the drying process have been suggested to inprove the performance or to reduce energy consumption. This invention relates to such drying processes. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new method for drying an object which unlike conventional methods is grounded on the use of alternating pressure during the drying process. The object is preferable a fabric such as clothes or other textiles that need washing and drying.

In one aspect, the invention relates to a method for drying an object comprising the steps:

(a) placing the object to be dried in an alternating pressure resistant container; (b) applying to the object a stream of relative dry air under conditions of alternating pressure to the container; and (c) removing the dried object from the container when it has reached the desired degree of moisture. Preferably the object is a fabric or a textile.

DETAILED DESCRIPTION OF THE INVENTION

When line drying textile in a room without convection the drying process is dependent on evaporation of water from the surface of the textile. This will with time give a concentration gradient from the inner off the textile towards the surface. The rate of drying is dependent on how fast the water is transported from the inner to the outer part of the textile.

In conventional dryers for texiles, the wet textiles are usually subjected to a stream of relative dry air, often at an elevated temperature, at a constant pressure. The exchange of air through the chamber dries out the textile by fast removal of humidity from the surface of the textile. The exchange is done by air turbulence at even pressure in order to force evaporation of water from the inner fibers.

Often, the drying is accompanied by tumbling or rotating the container, usually a drum, wherein the textile is contained in order to secure that all parts of the textiles are exposed to the drying air and thereby to secure a uniform drying of all the textiles in the container. Conventionally, the whole drying process takes place inside a drying machine that may have a number of different designs based on the specific purpose and the different manufacturers.

Drying process known as freeze drying is a process that is drived by sublimation of water from its solide fase (ice). This is done at low pressure and low temperature. Radiant heating is an important factor for fast evaporation process. However, freexe drying is in general not used for drying textiles.

When alternating the pressure in the chamber with the textile present the air trapped inside and around the fibers changes size. That will force the fibers closer together when increasing the pressure in the chamber. This will ease the exchange of water from the inside of the fibers to the out side. Both by capillary forces and by decreasing the total surface of the textile. Making vacuum will decrease the cooking point and thereby increase the evaporation of water from the surface. Supplying with heat (eg radiant heating) will increase the evaporation. Dissolved air will be undissoled and air bubbles will increase in size when the pressure is decreased in the chamber this will slightly expand the fibers increasing the area of the surface. This will ease the evaporation process. Ventillation in the drying chamber with fans is also of importance for increasing the evaporation rate.

The present invention is based on the observation that when the drying operation is performed under alternating pressure a very efficient drying process can be obtained. Further, the drying process may result in a reduced energy and the mechanical wear on the textile may be reduced compared with a conventional drying process.

Without wishing to be bound by any theory, it is believed that the alternating pressure affects the textile and the water phase differently, which together leads to a more uniform distribution of water throughout the textile sheets. This moisture distribution in the fabric leads to that the water is preferable evaporated from the surface of the fabrics, resulting in a lower temperature of the fabric compared with a similar drying procedure under constant pressure. Further water evaporated from the surface is easier transported from the fabric compared with water evaporated from the inner of the fabrics, meaning that the process may be condicted at a more energy efficient way.

During the drying operation, the textile can be considered a network of fibers arranged in a regular way and the water is located as a more or less continuous phase between the fibers.

When the pressure is decreasing air bubbles trapped inside the textile will expand considerable meaning that water located inside the textile will be forced from the inner of the textile to the surface thereof. Next, when the pressure is increasing again the bubbles will again be reduced in size and thereby draw some of the water into the textile again, but part of the water will reside on the surface of the textile. The textile and water will also be affected by decreasing and increasing pressure, but the impact will be considerably smaller than what is seen for the bubbles. Thus, a cyclus of pressure decrease followed by a pressure increase secures that the water in the fabrics is more uniformly distributed throughout the fabrics.

When alternating the pressure in the chamber with the textile present the air trapped inside and around the fibers changes size. That will force the fibers closer together when increasing the pressure in the chamber. This will ease the exchange of water from the inside of the fibers to the out side. Both by capillary forces and by decreasing the total surface of the textile. Making vacuum will decrease the cooking point and thereby increase the evaporation of water from the surface. Supplying with heat (eg radiant heating or other suitable heating means) will increase the evaporation. Dissolved air will be undissoled and air bubbles will increase in size when the pressure is decreased in the chamber this will slightly expand the fibers increasing the area of the surface. This will ease the evaporation process. Ventillation in the drying chamber (e.g. using fans) is also of importance for increasing the evaporation rate.

In one preferred embodiment, the alternating of the pressure is done in small steps. Before the water content in the chamber is in balance (that the partial pressure is reached) a change in pressure of the chamber is prepared. For example chaning the pressure from vaccum to pressure may be done by first increasing from 0,5 to 0,6 and the release this air by decreasing the pressure again to 0,5 bar; immediately after increase pressure till e.g. 0,8 bar reduce the pressure till 0,5 bar; next increase till 1 bar and escape till 0,5 bar and increase now the pressure till 2 bar over a short time period e.g.1 minute.

The invention may furthermore result in reduced energy consumption compared to a similar conventional drying processe taking place at constant pressures because the need for macro-mechanical action (turning the drum) may be avoided or at least reduced, and the evaporation of water may also consume reduced amount of energy for heating air, because it is easier to evaporate water from the surface of the fabrics than from the inner part of the fabrics.

This have the consequence that the drying according to the invention may be performed on a shorter time achieving same result as would have taken longer time using a conventional drying process.

Additionally, the drying process may be performed under conditions that are gentle to the fabrics being dryed. Due to the alternating pressure and following better distribution of water, the need for tumbling is less than in a conventional dryer, where the tumbling is the main driver for distribution of fabrics and water. Further, because the alternating pressure transports water to the surface of the fabrics, a larger part of the evaporation of the water takes place from the surface of the fabrics compared with a traditional dryer, and the cooling provided by evaporation of water means that the surface of the fabrics will be less impacted by the high temperature of hot air flowing through the drum, which high temperature is known to result in inadvertent effects e.g. such as shrinking of at least some textiles. Thus the drying process of the invention may be conducted in a way that is very gentle to the fabrics and the process may therefore be used for very delicate fabrics.

In the present invention, alternating pressure generates mechanical action on a microscopically level within the hydrodynamic barrier. When the pressure is lowered the dissolved gas present in the water will appear as bubbles which increase in size. Dependent on the viscoelasiticity of the water phase changes in bubble size creates micro-mechanical action both within as well as at the surface of the fabric/textile. This action promotes transport of water away from the textile.

Application of a pressure of 1-2 bars will lead to diminished size of the bubbles in the water. The bubbles will nearly disappear and the liquid film that creates the walls around the bubbles becomes thick, thereby easing the flow of water. Alternating pressure where low and high pressure is applied in turn creates a micro-mechanical action which promotes the transport in the whole fabric/textile surface and since the water will disappear from the surface of the textile/fabrics the net result is transport of water out of the textile/fabrics in addition to themore uniform distribution of the water.

In some embodiments of the invention, the drying comprises at least one cycle of alternating pressure wherein the pressure in turns is reduced and increased or wherein the pressure is in ture increased and decreased. One cycle of alternating pressure correspond to reduced pressure followed by increased pressure or by increased pressure followed by reduced pressure. Alternatively, a time period wherein alternating pressure is performed may be indicated. During this time period one or more cycles of alternating pressures may take place.

The number of cycles of alternating pressure may vary and accordingly it may be 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, or 30 cycles. Alternatively the number of cycles of alternating pressure may vary regularily with a frequency of e.g. 0.1 to 30 cycles prer minute, preferably 0.25 to 15 cycles per minute, more preferred 1 to 45 cycles per minute; such as 0.25, 0.5, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, or 30 cycles pr minut.

Likewise, the time period of alternating pressure may vary and accordingly it may last 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, or 30 minutes. It is preferred that the drying process comprises more than one cycle of alternating pressure.

In some embodiments, the invention relates to a method, wherein the alternating pressure is at least 0.1 bar; at least 0.2 bar; at least 0.3 bar, at least 0.4 bar, at least 0.5 bar, at least 0.6 bar, at least 0.7 bar, at least 0.8 bar, at least 0.9 bar, at least 1.0 bar, at least 1.1 bar, at least 1.2 bar, at least 1.3 bar, at least 1.4 bar, at least 1.5 bar, at least 2.0 bar, at least 2.5 bar, at least 3.0 bar, at least 3.5 bar, at least 4.0 bar, at least 4.5 bar, or at least 5.0 bar.

The temperature during drying according to the method is not critical as long as the temperature is sufficiently high to provide for a reasonable rate of evaporation of water and the temperature is sufficiently low to prevent damages of the fabrics/textile. Generally the temperature is in the range of 0-90°C, 5-50°C, 10-40°C, 15-30°C, 20-25°C.

If the temperature of the air stream through the dryer is selected to be higher than ambient temperature, the dryer will comprise a device for heating the air to the desired temperature. The invention is not limited to any particular heating device, but any such device as known in the art may be applied to the present invention. As examples of suitable heating devices can be mentioned the devises disclosed in EP 1 10881 1 , DE10164102D4, US 2009183386 and WO 2007131531.

The invention described and claimed herein is not to be limited in scope by the specific aspects herein disclosed, since these aspects are intended as illustrations of several aspects of the invention. Any equivalent aspects are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. In the case of conflict, the present disclosure including definitions will control.

Claims

A method for drying an object comprising the steps:

a) placing the object to be dried in an alternating pressure resistant container;

b) applying to the object a stream of relative dry air under conditions of alternating pressure to the container; and

c) removing the dried object from the container when it has reached a desired moisture.

The method of claim 1 , wherein the alternating pressure is at least 0.1 bar; at least 0.2 bar; at least 0.3 bar, at least 0.4 bar, at least 0.5 bar, at least 0.6 bar, at least 0.7 bar, at least 0.8 bar, at least 0.9 bar, at least 1.0 bar, at least 1.1 bar, at least 1.2 bar, at least 1.3 bar, at least 1.4 bar, at least 1.5 bar, at least 2.0 bar, at least 2.5 bar, at least 3.0 bar, at least 3.5 bar, at least 4.0 bar, at least 4.5 bar, or at least 5.0 bar.

The method of any of the preceding claims, wherein the object is: fabrics; textiles; laundry; leather; skin; fur; or hard surfaces.