WO1987005343A1

WO1987005343A1 - Dyeing process and apparatus

Info

Publication number: WO1987005343A1
Application number: PCT/GB1987/000163
Authority: WO
Inventors: Brian Robinson
Original assignee: BROOKE, Rosemary, Hilda (heiress and legal represe; Grant, Paul
Priority date: 1986-03-10
Filing date: 1987-03-09
Publication date: 1987-09-11
Also published as: IE860613L; AU7122987A

Abstract

A process for dyeing a piece of carpet comprising a top layer of fibres anchored in or to a backing layer which comprises applying to the fibre layer a metered amount of printing paste having a dye uniformly distributed therein sufficient to penetrate the top layer of fibres at least to a predetermined depth but insufficient to reach the backing layer, and thereafter exposing the piece of carpet to microwave radiation (7) at an intensity and for a period of time sufficient to evaporate at least some of the liquid therefrom. In one preferred form of the process the period of exposure of the piece of carpet to microwave radiation is sufficient to evaporate substantially all liquid therefrom, thereby to fix the dye in the top layer of fibres.

Description

DYEING PROCESS AND APPARATUS This invention relates to a process for dyeing pieces of carpet, for example carpet tiles or lengths of carpet, and to microwave irradiation apparatus suitable for use therein.

A carpet comprises a top layer of fibres anchored in or to a backing layer. Such fibres may be in the form of threads or yarns which form a pile or they may be in the form of a felted layer. Whereas in pile carpets the pile yarn was usually anchored by a knotting process to a woven backing of hessian or the like in traditional methυds of carpet manufacture, in more recent years methods have been developed for manufacture of pile carpets in which the use of knots to secure the pile yarn in the backing layer has been obviated. In these methods the pile yarn is anchored in the backing layer by application of a layer or layers of a pile anchoring material to the surface of the backing layer that will be on the underside of the carpet in use. Such anchoring material may be applied in the form of a latex or from a hot melt. Typical pile anchoring materials used include natural and synthetic rubber latices, polyamides (nylons), polyvinyl chloride and bituminous materials. A layer of scrim or similar backing fabric may then be added for added protection of the underside of the carpet and to improve its wearing qualities. Various processes for forming such carpets exist; in some cases the pile fabric is incorporated in the carpet at the same time as the backing layer is woven, whils't in others a needle punching method is used to insert loops of pile yarn into an already woven backing layer or through an already formed continuous backing sheet. After weaving or needle punching the exposed loops of pile can either be cut to form a cut pile carpet or left uncut as a looped pile carpet. Carpet tiles are sold, generally in square shapes, for laying directly on a floor without being tacked or otherwise secured thereto. They may have a top layer formed from pile yarn or from a felted layer of fibres. They are particularly useful for areas which are prone to heavy usage, as in entrance halls of public buildings, or where there is danger of staining, for example in kitchens, or in offices where access to underfloor services may be required from time to time. It is a simple matter to take up one or more tiles and to relay them as necessary, for example, to spread the effects of wear, to replace stained tiles, or to facilitate office maintenance. It is, however, essential for satisfactory performance of a carpet tile that it should have a standard size that enables it to be abutted snugly against other carpet tiles to form an essentially continuous floor covering. In addition, it must not twist or curl so that it will lie flat on the floor when laid in place. The main function of the backing layer of a carpet is to provide a stable fabric to anchor the pile. It does not have to satisfy any aesthetic considerations; hence it can be made of relatively cheap materials, such as hessian. On the other hand the pile yarn has to be capable of being readily dyed and to be able to stand up to the expected more or less heavy useage. Typical materials used for pile yarn include wool, synthetic polyamides (nylons), polyacrylonitrile, polyesters, polyolefins, and the like, as well as blends of two or more of these types of fibres. In the case of carpet tiles the preferred pile yarns are made from natural and synthetic polyamide fibres and blends thereof, i.e. wool, nylons and blends thereof. Various natural fibres can be used for manufacturing felted carpets and carpet tiles, including goat's hair.

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For safety reasons there is now a trend towards use of bituminous materials for anchoring the pile because in case of fire such materials emit less noxious fumes than, for example, nylon anchoring materials. As in many fields of textile manufacture, it is desirable to delay dyeing carpet tiles until as late a stage as possible in the manufacturing process. In this way the manufacturer can respond more quickly to demand for a particular pattern of tiles and can reduce the capital cost tied up in unsold stock. Accordingly, it is conventional practice to delay dyeing of carpet tiles until the final manufacturing stages. In such a dyeing step it is normal practice to apply the dye (usually an acid dye) to the exposed surface of the pile by a printing process and then to heat the printed tile in an oven, typically a steam heated oven, to vaporise the water in the printing paste. The steam produced is at approximately 100°C, a temperature which suffices to fix the dye on the pile. Although this procedure can be used successfully to produce carpet tiles in which the pile anchoring material is, for example, a synthetic polyamide, difficulties can arise in producing carpet tiles made with a bituminous material as pile anchoring material, because the bituminous layer can partially melt during the drying process, following printing, which can result in distortion of shape of the carpet tile, particularly if it is handled or otherwise subjected to stress whilst it is still hot. This drying step is also time consuming as it is necessary for the whole tile to reach approximately 100°C and to maintain it at this temperature for a sufficient length of time to evaporate all the water present and to ensure fixation of the dye. Typically this step takes between about 2 and about 3 minutes. It is energy intensive and adds significantly to the cost of producing carpet tiles. Moreover, the longer that the carpet tile is held at elevated temperatures, the greater is the risk of distortion of the backing layer. In addition further time must be allowed for the carpet tiles to cool sufficiently to allow them to be packed without risk of damage.

Similar considerations apply to the dyeing of lengths of carpet. There is accordingly a need to provide a process for dyeing pieces of carpet, such as carpet tiles or lengths of carpet, in which the risks of distortion due to exposure of the backing layer to elevated temperatures can be reduced or substantially obviated. There is also a need to provide a dyeing process for carpet tiles or for lengths of carpet that uses less energy than hitherto used processes.

The present invention accordingly seeks to provide a novel carpet dyeing process, which is suitable for dyeing carpet tiles or lengths of carpet, in which the risk of distortion of the backing layer is substantially avoided. It further seeks to provide a more efficient and less energy consuming method of dyeing carpet tiles and other pieces of carpet. Yet again it seeks to reduce the time required to dye carpet tiles and other pieces of carpet and then to package them.

According to the present invention there is provided a process for dyeing a piece of carpet comprising a top layer of fibres anchored in or to a backing layer which comprises applying to the fibre layer a metered amount of printing paste having a dye uniformly distributed therein sufficient to penetrate the top layer of fibres at least to a predetermined depth but insufficient to reach the backing layer, and thereafter exposing the piece of carpet to microwave radiation at an - -

intensity and for a period of time sufficient to evaporate at least some of the liquid therefrom. Preferably the period of exposure of the piece of carpet to microwave radiation is sufficient to evaporate at least a major portion, e.g. at least about 60% to about 95% or more of the liquid therefrom. In one preferred form of the process the period of exposure of the piece of carpet to microwave radiation is sufficient to evaporate substantially all liquid therefrom, thereby to fix the dye in the top layer of fibres.

Hence the invention further provides a process for dyeing a piece of carpet comprising a top layer of fibres anchored in or to a backing layer which comprises applying to the fibre layer a metered amount of printing paste having a dye uniformly distributed therein sufficient to penetrate the top layer of fibres at least to a predetermined depth but insufficient to reach the backing layer, and thereafter exposing the piece of carpet to microwave radiation at an intensity and for a period of time sufficient to evaporate substantially all liquid therefrom, thereby to fix the dye in the top layer of fibres.

The process may be used with all types of carpet but is of particular advantage for dyeing pieces of carpet with a pile layer. It is preferably used for dyeing pieces of carpet wherein the pile is anchored in or to the backing layer by means of an anchoring material, such as one of the anchoring materials mentioned hereinbefore. In a particularly preferred process the anchoring material comprises a bituminous material. The process of the invention is used to particular advantage with carpet tiles.

The process can be operated as a batch process; in this case a metered amount of printing paste is applied to the top layer of one or more pieces of carpet, then the thus treated piece or pieces is or are placed in a suitable oven enclosure and exposed therein to microwave radiation. Alternatively the process may be operated on a continuous or semi-continuous basis in which the carpet pieces are printed and then carried in turn through a suitable microwave drying apparatus; in this latter case care has to be taken, by means of suitable baffles or otherwise, to prevent the microwaves from escaping into a region where they can affect the plant operatives. Any suitable method can be used for applying the printing paste; one suitable method is by a conventional screen printing process. In this way the paste can be applied uniformly over the entire surface of the carpet piece or to one or more selected areas thereof. When dyeing carpet pieces with a pile layer, the pile may be a cut pile or a looped pile. Preferably the pile comprises polyamide fibres or a blend thereof, for example a synthetic polyamide selected from nylon 6, nylon 6/6, nylon 6/10 or a blend thereof with another fibre, such as wool.

The dye is typically an acid dye or a reactive dye. It is formulated as a printing paste of conventional viscosity and dye content. It may contain any of the usual ingredients, such as salts, pH control agents and the like. The paste is formulated in a liquid dispersing medium such as water or an aqueous solution of a water- miscible solvent, such as methanol, ethanol or acetone. If an aqueous solution of a water-miscible solvent is used, particularly one which forms an azeotrope with water, the proportion of such solvent present should be such that, at least during the final stages of evaporation of the paste, the medium being evaporated is mainly or substantially water so that the resulting vapour reaches a temperature in the region of 100°C. In the process of the invention the printing - -

paste penetrates into the top layer of fibres, e.g. the pile, to a predetermined depth in the area or areas to be printed; the depth of penetration is desirably at least sufficient to ensure that the top surface of the finished carpet tile or piece has a satisfactorily coloured appearance but (at least over the major part of the area thereof) is not so great that the backing layer is wetted. The depth of penetration of the paste needed to give satisfactory results will depend, at least to some extent, upon the depth and nature of the pile or other fibre layer. It is preferred, however, that the paste should not penetrate so far into the top layer of fibres that it reaches to less than about 0.5 mm from the backing layer. Preferably it reaches no nearer to the backing layer than about 1 mm and even more preferably no nearer than about 2 mm. Although it is preferred that none of the backing layer should be wetted, it may prove to be difficult in practice, and in some cases virtually impossible, to prevent wetting of a minor part of the backing layer, particularly if the top layer of fibres is thin, e.g. about 3 mm or less. However, such wetting should be confined to a minor part only of the area of the tile or other carpet piece and preferably it should occur only in isolated spots. Clearly the less wetting of the backing layer that occurs, the less is the danger of distortion in the drying step. Naturally it is best if no wetting at all of the backing layer occurs, but a minor amount of wetting can, in some cases, be tolerated; preferably any wetting of the backing layer is confined to no more than about 5% of the total area of the backing layer, and preferably to less than about 1 or 2% thereof.

The greater the thickness of the top layer is, the easier it is to print it without wetting the backing layer. For example, with a pile carpet having a pile depth of about 4 mm, very satisfactory results can be

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achieved by printing with an amount of paste such that the depth of penetration is about 2mm. In this case the liquid in the paste does not penetrate into the pile nearer than about 2mm from the backing layer. The amount of printing paste to be applied per unit area to the pile or felted layer in the first step of the process will depend, inter alia, upon the length of the pile or upon the depth of the felted layer, as the case may be, upon the viscosity and liquid content of the printing paste, and upon the surface area per unit volume of the fibres from which the top layer of fibres is made; however, it should be noted that this list of factors is not necessarily exhaustive. For a given type of carpet tile or length of carpet it is possible to determine what is a suitable amount of paste to apply by a series of trial and error experiments until satisfactory results are achieved. The screen printing press, or other machine used to apply the printing paste, can then be set to deliver the desired amount of printing paste. It is desirable that not too long a delay should occur between the printing and dyeing steps. Preferably the delay between printing and dyeing does not exceed about 120 seconds and preferably is not more than about 30 seconds to about 60 seconds. The microwave frequency used to irradiate the printed carpet pieces should be tuned to correspond more or less to a molecular vibration of water. A suitable frequency is 2 to 3 GHz. The time required to evaporate the liquid from the printing paste and to fix the dye is, broadly speaking, proportional to the intensity of the microwaves used and to the liquid loading of the printed carpet pieces. This time can be reduced by exposing the printed carpet pieces, as they are irradiated with microwaves, to a forced draught of air or to a partial vacuum so as to assist in removal of the steam and any - 9 -

other vaporised constituents of the printing paste. It has further been found preferable to interpose a layer of plastics material between the source of microwave energy and the carpet tiles to be dried. In a particularly preferred process, the carpet piece is exposed, during or after exposure to microwave radiation, to an atmosphere containing added steam.

The invention further provides microwave irradiation apparatus for subjecting substantially flat items, such as carpet pieces, to microwave radiation comprising an enclosure, means for supporting an item to be irradiated within the enclosure, magnetron means for generating microwave radiation, applicator means for guiding microwaves generated by the magnetron means so as to provide substantially uniform exposure of the item to the microwaves, and means for preventing reflection of microwave energy back to the magnetron means.

In one arrangement the applicator means includes a transducer for converting the circular fields generated by the magnetron to rectangular geometry and a flared horn having an inlet end connected to the transducer and having an outlet end of substantially square cross section.

The means for preventing reflection of microwave energy back to the magnetron means may comprise a water impregnated absorbent support upon which the item to be irradiated is supported. Alternatively it may comprise an oil filled tank behind the item to be irradiated in the path of the microwave energy.

Preferably the apparatus is arranged so that the applicator means directs microwave energy on the top surface of the item to be irradiated.

It is further preferred that apparatus should include conveyor means for conveying the item to be irradiated through the enclosure. Means may be provided within the enclosure to - -

expose the item, during or after exposure to microwave irradiation, to an atmosphere of added steam.

In order that the invention may be clearly understood and readily carried into effect, a preferred process according to the invention, and three forms of apparatus for carrying out the same, will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, wherein:

Figure 1 is a partially cut-away front view of a microwave apparatus for drying carpet tiles;

Figure 2 is a cross section on the line A-A of Figure 1;

Figure 3 is a side view of a transducer/ applicator arrangement for use in the apparatus of Figure 1;

Figure 4 is an end view of the arrangement of Figure 3;

^■Figure 5 is a schematic view of an alternative form of apparatus enabling continuous drying of carpet tiles;

Figure 6 is a schematic horizontal section through the apparatus of Figure 5;

Figure 7 shows a modified form of apparatus incorporating supplementary steam heating; and Figure 8 illustrates a detail of the apparatus of Figures 5 to 7.

Referring to the drawings, and to Figure 1 in particular, a microwave apparatus for drying carpet tiles comprises an r.f. cabinet 1 which is provided with a door 2 (which is in the open position in Figure 1). Carpet tiles to be dried are supported on a turntable 3 which can, if desired, be rotated by means of a motor 4 fitted underneath the bottom of r.f. cabinet 1. A condensation shield 5 is fitted around turntable 3 and an extractor vent 6 is provided for removal of moist air from the space around turntable 3 in r.f. cabinet 1 with the aid of a suitable fan (not shown). A number of magnetrons 7 (four in total in the illustrated apparatus) are mounted within r.f. cabinet 1. These magnetrons 7 emit microwaves of frequency 2.452 Ghz and are each coupled to an applicator 8. Reference numeral 9 indicates an r.f. gasket fitted around the opening to the cabinet 1. A fan 10 is used to cool the magnetrons 7 by means of air drawn through air- vent 11. Shield 5 serves to prevent any possible contaminants from the carpet tiles being dried from reaching the coaxial probe of magnetron 7 and damaging the finely divided layer of rare earths with which such probes are typically covered. Shield 5 is made from a material that is substantially transparent to microwaves in order that as much of the microwave energy from the magnetron 7 can be transmitted to the carpet tiles to be dried.

D.c. power supplies for the magnetron 7 and power supplies for the fans and other items of equipment are indicated at 12. Controls 13 mounted in housing 14 are also shown in Figure 1. Space for ancillary equipment is provided at 15.

As mentioned above, four applicators 8 (which are designated A, B, C and D in Figure 2) are mounted in r.f. cabinet 1. Suitable interlock devices (not shown) are provided so as to ensure that magnetrons 7 are immediately switched off if any attempt is made to open door 2.

Figures 3 and 4 illustrate the construction of the magnetron/applicator arrangement of the apparatus of Figures 1 and 2. The output from magnetron 7 is in a coaxial (cylindrical) geometry. Transducer 16 is designed to convert the circular fields around the coaxial probe on magnetron 7 to a distribution which is compatible with square geometry at the output end 17 of applicator 8; this

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has, for example, a cross sectional area of 12.5 cm x 12.5 cm. In this case the four applicators A, B, C and D of Figure 2 can deliver power essentially uniformly over the entire surface of a 50 cm x 50 cm carpet tile. The rectangular aperture applicator 8 is designed to provide uniform aperture illumination. The length and flare of applicator 8 are carefully selected in order that maximum energy transfer occurs. Both transducer 16 and applicator 8 may be made from brass. It is alternatively envisaged that these components may be made from aluminium or from a metal flashed injection moulded plastics material.

The symmetrical geometry of applicator horn 8 is intended to ensure that substantially equal power arrives at all points across the face of aperture 17. The taper length of applicator 8 gives the desired control for good electrical match of the microwave signal to the load to be exposed (i.e. the wet carpet tiles to be dried) so that maximum energy transfer will occur.

Figure 5 illustrates a continuous apparatus using a process in accordance with the invention.

Reference numeral 20 indicates a housing within which is an r.f. cabinet (not shown) fitted with a number of magnetrons, transducers and applicators of the type illustrated in Figures 3 and 4. A slot 21 is provided at one end of housing 20 and a corresponding slot (not shown) is provided at the other end of the housing to allow passage through the housing of a conveyor belt 22 which passes over guide rollers 23. The conveyor belt 22 is arranged to move in the direction of the arrow B by means of a suitable motor (not shown). Reference numeral 24 indicates a control console, whilst pipes 25 are for the supply of steam for a purpose which will be described below. Printed carpet tiles 26 are placed on conveyor 22 and are conveyed through the r.f. cabinet within housing 20 by means of conveyor 22. Figure 6 is a schematic horizontal section through the housing 20 showing the position of applicators 8. Additional applicators 27 can be provided, if desired. Figure 6 also shows the position of the slot 21 of Figure 5 and the corresponding slot 28 at the other end of the housing which is not visible in Figure 5.

Figure 7 is a schematic view of the interior of the r.f. cabinet within housing 20 with the applicators 8 omitted for the sake of clarity. Steam from pipes 25 is blown on the upper surface of tiles 26 from pipe 29.

Arrow 30 indicates the incident microwave energy supplied by applicators 8. Arrow 31 indicated a laminar air flow. Reference numeral 32 indicates a shield to prevent steam from pipe 29 and constituents evaporated from tiles 26 from reaching and contaminating the magnetrons associated with applicators 8.

In one form of apparatus conveyor 22 has an absorbent upper surface which is wetted prior to passage under applicators 8. The water absorbed by conveyor belt 22 will also absorb any stray microwave energy and cuts down back reflection from the floor of the r.f. cabinet.

In an alternative arrangement shown in Figure 7, a cooling tank 33 with walls which are transparent to microwaves is positioned under conveyor 22. Oil can be circulated through tank 33 by means of inlet 34 and 35 for cooling purposes. Any stray microwave energy is absorbed by the circulating oil and hence back reflection from the floor of the r.f. cabinet is substantially prevented.

Figure 8 shows on a somewhat enlarged scale one possible arrangement for preventing leakage of microwaves from the r.f. cabinet via slot 21. The height h and the distance d are chosen in relation to the microwave operating frequency (2.452 Ghz) so that even though there is no physical obstruction, the slot 21 is opaque to the microwave energy, thereby isolating the microwave power - 14 -

within the r.f. cabinet from the outside world.

The invention is illustrated further in the following Examples in which parts are by weight. EXAMPLE 1 Carpet tiles were printed with a printing paste containing a commercial blue acid dye and formulated as follows:

3 parts powdered dye 1 part formic acid 96 parts water.

The tiles were made by a needle punching technique, using a pile made from 1 to 5 denier nylon 6 fibres, the backing then being coated with two layers of synthetic rubber latex, followed by a layer of bituminous anchoring material, before being backed with scrim. The exposed length of the pile was 6 mm.

The printing paste was applied uniformly to the pile of the tiles at the rate of lcc per 8cm of carpet tile surface area. Upon placing each printed tile individually in an oven enclosure and exposing it to microwaves generated by means of a 650 watt magnetron generator tuned to a frequency of 2.43 GHz, the water in the paste was evaporated and fixation of the dye occurred. The tiles were cool enough to be removed immediately from the enclosure with bare hands at the end of this treatment and could be packaged without any delay. Visual inspection of the tiles indicated that the backing layer had not distorted; in particular no sign of melting of the bituminous layer could be detected. The pile was uniformly dyed to a depth of about 4 mm, i.e. the paste penetrated to a depth which left approximately 2 mm of the pile adjacent the backing layer undyed. Fixation of the dye was tested by soaking the tiles in a dilute aqueous detergent solution; if the solution remained uncoloured or was only faintly coloured, dye fixation was considered to be satisfactory. EXAMPLE 2

Similarly good results to those of Example 1 were obtained when a commercial red acid dye or a commercial yellow acid dye was used in place of the blue dye of Example 1. EXAMPLE 3

The procedure of Example 1 was repeated using a modified printing paste obtained by mixing 40 parts of the printing paste of Example 1 with 60 parts of methanol. In this case dyeing of the tiles took only 45 seconds. Similarly good results were obtained. It was noted, however, that the modified paste of this Example wetted the pile more quickly than the paste of Example 1. EXAMPLE 4

The procedure of Example 1 was repeated using a 1.3 kW magnetron generator tuned to 2.43 GHz. Evaporation of water and dye fixation was in this case achieved in 30 seconds. EXAMPLE 5

Using the procedure of Example 1 carpet tiles made with polyvinyl chloride as anchoring material were successfully dyed.

Claims

CLAIMS :

1. A process for dyeing a piece of carpet comprising a top layer of fibres anchored in or to a backing layer which comprises applying to the fibre layer a metered amount of printing paste having a dye uniformly distributed therein sufficient to penetrate the top layer of fibres at least to a predetermined depth but insufficient to reach the backing layer, and thereafter exposing the piece of carpet to microwave radiation at an intensity and for a period of time sufficient to evaporate at least some of the liquid therefrom.

2. A process for dyeing a piece of carpet comprising a top layer of fibres anchored in or to a backing layer which comprises applying to the fibre layer a metered amount of printing paste having a dye uniformly distributed therein sufficient to penetrate the top layer of fibres at least to a predetermined depth but insufficient to reach the backing layer, and thereafter exposing the piece of carpet to microwave radiation at an intensity and for a period of time sufficient to evaporate substantially liquid therefrom, thereby to fix the dye in the top layer of fibres.

3. A process according to claim 1 or claim 2, in which the carpet piece has a pile layer.

4. A process according to claim 3, in which the pile layer comprises polyamide fibres or a blend thereof with wool.

5. A process according to any one of claims 1 to 4, in which the dye is an acid dye or a reactive dye. - 17 -

6. A process according to any one of claims 1 to 5, in which the carpet piece is exposed, during or after exposure to microwave radiation, to an atmosphere containing added steam.

7. A process according to any one of claims 1 to 6, in which the metered amount of printing paste is sufficient to penetrate the top layer of fibres to a predetermined depth but no nearer to the backing layer than about 0.5 mm.

8. A process according to claim 7, in which the metered amount of printing paste is sufficient to penetrate the top layer of fibres to a predetermined depth but no nearer to the backing layer than about 2 mm.

9. Microwave irradiation apparatus for subjecting substantially flat items to microwave radiation comprising an enclosure, means for supporting an item to be irradiated within the enclosure, magnetron means for generating microwave radiation, applicator means for guiding microwaves generated by the magnetron means so as to provide substantially uniform exposure of the item to the microwaves, and means for preventing reflection of microwave energy back to the magnetron means.

10. Apparatus according to claim 9, in which the applicator means includes a transducer for converting the circular fields generated by the magnetron to rectangular geometry and a flared horn having an inlet end connected to the transducer and having an outlet end of substantially square cross section.

11. Apparatus according to claim 9 or claim 10, in which the means for preventing reflection of microwave - -

energy back to the magnetron means comprises a water impregnated absorbent support upon which the item to be irradiated is supported.

12. Apparatus according to claim 9 or claim 10, in which the means for preventing reflection of microwave energy back to the magnetron means comprises an oil filled tank behind the item to be irradiated in the path of the microwave energy.

13. Apparatus according to any one of claims 9 to

12, in which the applicator means is arranged to direct microwave energy on the top surface of the item to be irradiated.

14. Apparatus according to any one of claims 9 to

13, which further includes conveyor means for conveying the item to be irradiated through the enclosure.

15. Apparatus according to any one of claims 9 to 14, in which means are provided within the enclosure to expose the item, during or after exposure to microwave irradiation, to an atmosphere of added steam.