WO1996029903A1

WO1996029903A1 - Drying a deposit upon a body

Info

Publication number: WO1996029903A1
Application number: PCT/GB1996/000665
Authority: WO
Inventors: Raymond Hanson
Original assignee: British United Shoe Machinery Ltd.; Usm España S.L.
Priority date: 1995-03-30
Filing date: 1996-03-20
Publication date: 1996-10-03

Abstract

A drying apparatus and a method of operating a drying apparatus is described which is particularly suitable for water-based adhesive depositions upon shoes and/or shoe soles (201) during their manufacture. The apparatus and method essentially comprise two stages, in a first stage in a drying chamber (110) the shoe (201) is exposed to air flows directed upon a surface carrying the deposit and to infrared heat on its passage through the drying chamber (110) in order to tease solvent (water) from the deposit without creation of a surface skin or crust, in a second stage the deposit is heated by further infrared heater means in a post-drying station (116) after the drying chamber (110) and without air flows to leave the deposit in a tacky state. The drying chamber (110) means comprises a plurality of appropriately spaced infrared tubes (202) which can provide an approximate planar uniform infrared flux at a displaced distance above the carrier upon which the bodies (shoes) (201) are carried.

Description

_λ DRYING A DEPOSIT UPON A BODY

The present invention relates to a method and apparatus for drying a deposit such as a water-based adhesive upon a 2 body such as a shoe.

In the drying of a deposit of adhesive applied to an article surface, the total drying time can be divided into two separate periods:

10

In a first period the rate of evaporation of the solvent, such as water, is determined by the state of the area immediately adjacent the surface, this rate being constant whilst the surface remains "wet". Thus during this period, l_ which is referred to as the "constant rate period" the rate of drying depends upon the rate of removal of water vapour from the layer of air adjacent to the wet surface.

In the second period, removal of water depends upon the 20 migration of the water through the moist solid to the surface, the resistance to water transfer progressively increases and thus reduces the drying rate. Thus, during this period, which is referred to as the "falling rate period", the controlling factor is the rate of vapour diffusion through the solid.

25

While it is of course possible to allow the water or any other solvent to evaporate off naturally, it is usual for force drying to take place in order to accelerate the rate of evaporation/drying. To this end, the surface to which the

30 deposit has been applied may be heated, e.g. by radiant heaters; alternatively, the surface may be subjected to hot air which is passed over the surface of the body and serves to remove water laden air from adjacent to it. In any event it is generally considered that heat is desirable in both the

35 constant rate period and the subsequent falling rate period, the amount of heat supplied being dependent upon the amount of time which can be allocated to the drying process. It will of course be appreciated that use of heat in this way is expensive in so far as either the energy costs are high if the air is not recirculated, or if the air is recirculated then more complicated and thus expensive apparatus is required, usually also involving thermal insulation panels, as well as a system removing water from the non water-laden air.

In our prior European Patent No. 328923 (British United Shoe .Machinery Limited) a method and apparatus for drying coatings is described which achieves more economic energy use and better preparation of adhesive in shoe manufacture. The method essentially comprises during the constant rate period of drying to merely project ambient temperature air towards the shoe bottom in order that turbulent air picks up the solvent from the adhesive and carries it away from adjacent areas to the shoe bottom and in the falling rate period merely to expose the adhesive to radiant heat without air flow in order to stimulate migration of solvent through the adhesive to the surface. Thus, the inherently expensive activity of heating air for projection towards the shoe bottoms when not necessary i.e. during the constant rate period of drying is avoided whilst stimulation through heat is still achieved in the second falling rate period of drying to remove remaining solvent within the adhesive volume coated on the shoe bottom. Unfortunately, this post-heating approach is inadequate for less volatile water-based adhesives as compared to solvent- based adhesives.

It will be understood that hydrocarbon solvents are generally_far more volatile that water. Thus, it is necessary to input a greater amount of energy in order to cause evaporation of water from a deposited adhesive. However, it is also important that a crust or surface layer of essentially dry deposited adhesive is not created as this will act as a barrier to migration of water from within the deposited adhesive. Essentially, the problem is that water-based adhesives will inherently on a like for like basis take longer to dry as compared to more volatile hydrocarbon solvent based adhesives.

Unfortunately, due to the environmentally damaging effects of hydrocarbon solvents there is a desire to use water-based adhesives in a wide range of manufacturing environments including shoe and footwear fabrication. Obviously such a switch to water-based adhesives should be made with as little detrimental effect on processing times as possible as e.g. a significant proportion of the cost of manufacturing an article such as a shoe is the processing time; less shoes per hour increases the unit cost per shoe.

It is an objective of the present invention to provide an improved method and apparatus for drying a deposit of adhesive or similar material upon a body which significantly reduces the cost and energy consumption as compared with previous systems.

In accordance with a first embodiment of the present invention there is provided an apparatus for drying a deposit upon a body such as a water-based adhesive coating upon a shoe, the apparatus comprising a drying chamber through which carrier means in use transport a body with deposit towards a post-drying station, said carrier means supporting the body in order to transport it through said drying chamber with a regular motion and with the body appropriately presented in the chamber, said drying chamber including air flow means to project air flows towards said body and so collect evaporated solvent from said deposit, . said drying chamber also including infra-red radiant heat means mounted within said drying chamber to ensure said body is exposed to said infra-red radiant heat during its passage through said drying chamber, said post-drying station exposing said body to radiant heat.

Preferably, the body is exposed to infra-red radiant heat for less than half its passage through said drying chamber, the infra-red radiant heat means being mounted either to expose the body to heating at the entry or exit of the drying chamber. Furthermore, the infra-red radiant heat means may expose the body to different infra-red heat intensities as it passes through the drying chamber.

Preferably, the radiant heat means is an array of infra¬ red tubes mounted to project upon the body within the drying chamber. The infra-red tubes may be spaced within the drying chamber in order to create at a fixed distance from said tubes a plane of infra-red flux of substantially uniform density. The infra-red tubes may be spiral heat elements within a quartz tube and provide radiant heat in the frequency range 2-4 μm dependent upon deposit solvent.

Preferably, the post-drying station includes an infra-red planar/modular quartz lamp unit.

Preferably, the infra-red tubes within the drying chamber are protected from air flow by deflector elements.

Preferably, the bodies are exposed within the drying chamber to the heat means for a time period in the range up to 60 seconds and thus the deposit is exposed to an energy uptake in the order of 1 W/cm^.

Preferably the air flow directed towards said body is in excess of 18 m/s, but depends upon air jetting.

The radiant heat means may be so-called calrods appropriately mounted within the drying chamber.

Alternatively, the present invention includes a method of drying a deposit upon a body such as a water-based adhesive coating upon a shoe, the method including;

(a) Placing the body upon carrier means in order that said body is transported through a drying chamber with a regular motion and appropriatly presented to infra-red radiant heaters in said drying chamber;

(b) Presenting environmental temperature air flows directed towards to said body in order to collect evaporated solvent from said deposit and subsequently exhaust said solvent from said drying chamber;

(c) Presenting within said drying chamber infra-red radiant heat directed towards said body as it is transported by the carrier means through said drying chamber; and

(d) Presenting to said body after passage though said drying chamber radiant heat in a post-drying station.

Preferably, the body is exposed to infra-red radiation heat for a time period less than half the time for said body to pass through said chamber.

In addition, it will be appreciated that in accordance with the present invention the infra-red heater in the chamber could be arranged to provide little or no heat to said body, but a radiant heater prior to the heater is provided. Thus, further in accordance with the present invention there is provided a method of drying a coating of solvent-based, especially water-based, adhesive applied to a substrate surface using jets of air at ambient temperature directed against the coating for a first period and thereafter subjecting the coating to radiant heat for a second period, characterised in that prior to and/or during the first period the coating is heated to a temperature which is elevated in relation to that of the jets of air but which is not sufficiently high for a skin to be formed on the coating surface. Also provided is an apparatus for use in carrying out this method comprising a support arrangement for supporting a substrate, to a surface of which an adhesive coating has been applied, with said surface exposed, said support arrangement being mounted for movement along a path, a chamber which is arranged along said path and through which the support arrangement can be moved, said chamber comprising a plurality of nozzles for directing jets of air towards the coated substrate surface as the support arrangement is moved therepast, conveyor means for moving the support arrangement along said path through said chamber, and a radiant heater arrangement arranged along said path "downstream" of the chamber, characterised in that a further radiant heater arrangement is arranged along said path "upstream" of the chamber.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:-

Figure 1 is a perspective view of a drying apparatus;

Figure 2 is a schematic cross-section of a drying arrangement;

Figure 3 is an expanded view of the radiant heater arrangement in a drying chamber of the drying apparatus;

Figure 4 is a graphical representation of the temperature variation of an adhesive deposit as it passes through drying apparatus; and

Figure 5 is an alternative embodiment of the present invention in which a pre-heater is provided before the drying chamber.

In Figure 1 a perspective view of a drying apparatus for drying a deposit of water-based adhesive (or other solvent- based adhesives) applied to the surface of a body such a shoe bottom or a shoe sole is illustrated and is generally similar, except as hereinafter described, to apparatus described in EP- A-0 512 772. Thus, the illustrated apparatus comprises a drying chamber 110 including a plenum chamber 114, in a base plate of which are formed a plurality of nozzles or openings 112 through which air under pressure collected in the plenum chamber 114 can be directed downwardly into the drying chamber 110, as will be referred to hereinafter.

The apparatus illustrated in Figure 1 comprises a shoe transporter or carrier system generally designated 120 comprising a continuous chain 122 entrained at each end about a sprocket mounted for rotation each about an axis 120, the two axes being arranged at opposite ends of the chamber 110. For carrying shoes and/or shoe sole units through the drying chamber 110, therefore, the shoe transporter system 120 comprises a plurality of carriers or supports 130 which form part of the chain and each of which has two upstanding lugs each for supporting a shaft extending across the width of the shoe transporter/carrier system i.e. outwardly at opposite sides of the chain 122. Each shaft in turn supports a support member 138 for pivotal movement about the axis of the shaft, the support members 138 thus supporting by one of the supports 130 constituting a shoe support arrangement of the illustrated apparatus. Furthermore, by reason of members 138 being mounted on the shaft as aforesaid, they are adjustable in order to accommodate shoes of different sizes or to provide a relatively flat support surface for a sole unit.

It will thus be appreciated that shoes and/or sole units supported by the shoe transporter/carrier system 120 can be carried, along the upper region of the chamber 122 along a path extending through the drying chamber 110. It will thus be appreciated that as shoes and/or sole units are conveyed by the shoe transporter/carrier system 120 along said path, they are subjected to jets of air directed thereonto through the nozzles 112 forming the base plate of the plenum chamber 114.

"Downstream" of the drying ch.amber 110 furthermore, is a post heater arrangement 116 comprising a suitable radiant heater arrangement, e.g. an infra-red heater. The shoes and/ or sole units thus pass along their path are subjected to radiant heating by means of the heater arrangement 116. This "downstream" heater arrangement is termed a post-heat station and includes no air jet impingement upon the shoes and/or sole units.

In addition, in the illustrated apparatus there is a control panel generally designated 142 by which various settings may be made (not of particular relevance in relation to the present invention) . In addition, the upper region of the chain 122 and thus the shoe transport/carrier system 120, extends beyond the drying chamber 110 and heater arrangements in order to provide a loading station A and unloading station

B.

In using the apparatus illustrated in Figure 1 and the method in accordance with the present invention, shoes and or sole insoles to which a coating of water-based (or other solvent-based) adhesives have been applied are placed on the shoe transporter/carrier system 120 at the loading station A, generally in the manner disclosed in EP-A-0 512 772. The shoes and/or sole units thus loaded firstly pass through the drying chamber 110 and then are passed on to the post-drying station 116. In the present invention within the drying chamber 110 a heater arrangement is designed preferably to radiate heat upon the shoes and/or sole units for a time period less than half of that time period for these shoes and/ or units to pass through the drying chamber 110. However, it is equally possible to arrange for the shoes and/or insoles to be exposed to infra-red heating for the whole time period of their passage through said chamber 110. Furthermore, the body such as shoes and/or insoles could be exposed to infra-red heating of varying intensity as it passes through the chamber 110. Such variation in infra-red heat intensity may be used to ensure a crust or dry layer is not formed.

The effect of this drying chamber heating arrangement is to elevate the temperature of the adhesive to approximately 36^βC in order to facilitate evaporation of water solvent from the adhesive and to enable air flows directed towards that adhesive to subsequently pick up such evaporated water. The elevated temperature allows water to permeate through the adhesive more readily and thus ensures that the surface of the adhesive remains moist and tacky. It will be appreciated that part of the reason the surface of an adhesive becomes crusted is due to the disparity between the rate of transmission of solvent through the adhesive in comparison with the rate of evaporation. By use of an elevated temperature it is easier to ensure there is a balance between these two effects and thus the surface remains tacky. It has been found that raising the temperature by a relatively modest amount in comparison with environmental or ambient temperature about the drying apparatus has been insufficient to cause a crust or skin to be formed on the surface of the deposited adhesive coating, whilst nevertheless being sufficiently high to achieve adequate removal of solvent from the adhesive in an acceptably short period time for shoe manufacture. In this way, therefore, a temperature gradient is formed in the body of the deposited adhesive coating which favours the migration of water (solvent) to the exposed surface of the coating and thus favours evaporation of the solvent (water) and the drying of the coating.

Within the drying chamber as indicated previously the deposited adhesive coatings are exposed to jets of air. The air temperature is that environmentally i.e. ambient about the drying apparatus. Thus, initially the air temperature is room or ambient temperature but it will be appreciated that as the air is recirculated through the drying apparatus there is an inherent increase in temperature of a few degrees centigrade. The air temperature is slightly elevated in respect of ambient conditions by reason of its repeated contact with the hot adhesive coatings. Following the passage through the drying chamber 110 the surface coatings are then subjected to further heating by the post-drying station 116 prior to being removed from the shoe transporter/carrier system 120 at the unloading station B. The time required for drying adhesive deposited coatings to an appropriate texture and thus the time taken for the shoes and/or sole units to pass from the loading station A to the unloading station B, will vary according to the nature of the adhesive used and also of the substrate (shoe and/or shoe sole) to which the coating is applied. In general, however, the time taken should be in the order of li-2-J minutes. Under such circumstances, therefore, the time period of exposure to the heating arrangement in the drying chamber 110 should be the order of up to 60 seconds. However, it is really the amount of energy input to the shoe and/or shoe sole on passage beneath these heating arrangements in the drying chamber 110 that is of most importance. It has been found that to leave the deposited adhesive coating in an appropriately tacky condition for further fabrication operations that an energy input of 1 W/cπ.2 is reasonable. Typically, to achieve this energy input with infra-red tube lamps made by Hereaus a temperature in the coils of these lamps of 600°C is necessary.

With regard to the time of passage through the drying chamber 110 it will be understood that as disclosed in EP-A-0 328 923 the period is dependent upon the rate of evaporation of solvent (water) . However in the present invention there is at least for a specified time period of passage of the shoe and/or shoe sole within the drying chamber 110 during which the deposited adhesive coating is both heated and exposed to air jets, thus, the complete time period for passage through the chamber 110 may be altered but not significantly. It will typically take a body such a shoe or shoe sole 1 to 1 _ minutes to pass through the drying chamber 110. Finally, the time period during which heating by the post-drying station 116 occurs is preferably in the order 7-12 seconds and it will be understood that this is a period when the rate of evaporation of water (solvent) from the adhesive is diminishing i.e. most solvent will have been depleted from the adhesive by this stage and there is a law of diminishing returns due both to a lower solvent content and also, despite best endeavours. creation of a surface solvent depleted layer, which acts as a barrier to further surface evaporation.

Although the above described method of drying and apparatus has been illustrated with regard to shoe and/or shoe insole components it will be appreciated that other bodies and articles can be dried in accordance with the present invention. Furthermore, in addition to adhesive it may be possible to dry other coatings such as paint, lacquer or plastic material coatings etc.

Figure 2 is a schematic illustration of the drying apparatus in accordance with the present invention. The manner of transportion of bodies 201 such as shoes is as described previously with regard to Figure 1. The bodies 201 pass through the drying chamber 110 upon a carrier system 120. In the example shown the shoes 201 have their bottom or sole surface exposed to jets of air passing through apertures 112 in the plenum chamber 114. These jets of air as indicated previously present and impinge upon the surface of the shoes 201 in a turbulent manner in order to remove water (solvent) evaporating from deposited adhesive coatings. It will be appreciated that these jets of air create significant noise within a factory environment and the level of noise is dependent upon the air flow rate. Typically,, in previous systems as described in European Patent No. 0328923 the rate of air flow has been in the order of 28 m/s. However, as described below with the present drying apparatus it is possible to reduce the rate of air flow to below 20 m/s and preferably 18 m/s, this significantly reduces the noise level created by the present drying apparatus whilst retaining efficiency of deposited adhesive drying to an appropriate tackiness. Furthermore, a lower flow rate for the air jets allows a cheaper fan to be used and so may reduce costs.

Within the drying chamber 110 in accordance with the present invention there are located infra-red radiant heaters such as infra-red tubes appropriately activated to created infra-red radiation in the range of about 2 - 4 μm in order to heat the deposited adhesive upon the bodies 201. The benefit of infra-red heating is that rather than heating the surface of the adhesive it is the interior of the deposited adhesive volume which generates heat through energy loss inherent in bond vibration due^' to such infra-red radiation. This stimulates emigration of solvent from within the deposited adhesive volume to the surface of the adhesive and so helps to inhibit creation of a surface skin or crust by ensuring a balance between evaporation of water (solvent) with solvent migration from within the deposited adhesive to the surface. Typically, the infra-red tubes are those supplied by Hereaus and are of a spiral heat element within a quartz tube type.

It will be appreciated.that the excitation wavelength i.e infra-red wavelength used in any particular heater arrangement is dependent upon the solvent used thus for organic solvents it will be appreciated that an excitation wavelength 3.4 μm is acceptable whilst with water a slightly shorter wavelength would be more appropriate.

It is inherent in the present invention that the bodies 201 are only exposed to radiant infra-red heat for at least a proportion of their passage through the drying chamber 110. This time period of heat exposure is preferably less than half the passage time through the chamber 110 and preferably in the order of 1/3 of the passage time period. Thus, the deposited adhesive upon the bodies 201 is heated in order to tease the water (solvent) from the adhesive rather than cure which could result in hardening of the adhesive and thus be detrimental to the effectiveness of subsequent fabrication stages.

Infra-red heating is the ideal approach in the present invention as it is controllable within the chamber; the air is not heated directly while the deposited adhesive is only heated when exposed to infra-red heating.

Figure 4 illustrates in graphic fashion the adhesive temperature as a body 201 passes through the chamber 110 when the drying/heating arrangement is at the front end of the chamber 110. As can be seen there is a steady increase in temperature between W and X which represents that part of the drying chamber 110 in which the body 201 is exposed to radiant heat from infra-red tubes 202. Between X and Y i.e. where there is no infra-red heating but air flow over the body 201 there is a decrease in temperature possibly due to the latent heat of evaporation of water from the adhesive during this period of passage through the chamber 110. On leaving the drying chamber 110 the bodies 201 enter the post-drying station 116 where a further radiant heater preferably of the planar type 103 again heats the adhesive to tease water (solvent) from the adhesive but without air jets incident upon the adhesive to enhance vapour exhaustion. Thus, between the end of the chamber 110 i.e. position Y and the end of the post-drying station 116 i.e. position Z there is a rapid increase in adhesive temperature. This increase as described in European Patent No. 0328923 is sufficient to remove solvent (water) from the adhesive but is designed to ensure that the deposited adhesive coating remains tacky for further subsequent manufacturing steps.

As indicated above with the heaters 202 positioned at the front of the chamber 110 it is possible to reduce the air flow rate and thus noise about the drying apparatus. Due to the adhesive heating effect of tubes 202 more solvent (water) is teased to the surface of the deposited adhesive and thus less air flow is required to remove this water. However, it will be appreciated that the heating arrangement within the drying chamber 110 may be positioned later in the passage of the body, but it would be advantageous if the solvent teasing effect occurred earlier in the body 201 passage to ensure the full benefits of air flow removal of vapour is achieved. Figure 3 illustrates in schematic expanded view the drying chamber heater arrangement of tubes 202 mounted upon the surface of the pleniary chamber 114 and about jet orifices 112. In order to protect the tubes, and also where necessary provide additional reflectivity, the tubes 202 are protected by valance elements 301. These elements 301 extend along the length of the infra-red tubes 202 and ensure the cooling effect of the air flow on these tubes does not detrimentally effect their-radiant infra-red heat capacity. Furthermore, the elements 301 are angled to ensure there is limited effect on air flow direction towards bodies (not shown) which are transported along the conveyor 120. Alternatively, it may be possible to provide the orifice jets 112 positions at the end of elements 301 between infra-red tubes 202.

As the infra-red tubes 202 are essentially radial emitters of infra-red radiation to heat adhesive deposited coatings it will be understood that by appropriate spacing of the tubes 202 that a substantially consistent planar flux density can be achieved which will give consistent heating over a span of time defined by the passage of a body past the heat arrangement of the drying chamber 110 (Figure 2). Thus in Figure 3 the regular broken line illustrates the appropriate segments of each tube 202 infra-red flux density and the alternate long short broken line an estimate of the substantially planar flux density. As indicated above by appropriate spacing of the tubes 202 the height of this planar infra-red flux density can be chosen dependent upon the height of bodies (not shown) passing through the drying chamber along carrier system 210. Thus, the efficiency of heating of such bodies may be tailored as necessary. Furthermore, by gradually increasing the spacing between the tubes 202 it may be possible to provide a variation or inclined consistent infra-red flux density on passage through the heated section of the drying chamber 110 as necessary.

It will be understood rather than using tubes 202 it may be possible to use a so-called modular quartz lamp unit which essentially comprises a series of tubes mounted in appropriate relay headers to create a planar infra-red flux density. However, such a device would inhibit and/or limit the possibility for air jet nozzles 112 within the drying chamber 110. Furthermore, such lamp units hae a fixed planar infra-red flux density and so variation for body height could not be achieved.

It will be appreciated if air flow rate is reduced in addition to less noise the drying apparatus will use less power and consequently will be more economic and also particularly if lightweight bodies with deposited adhesive coatings are to be dried there is a reduction in the chance of displacement/flotation of those components on passage through the drying chamber 110.

Figure 4 as described previously illustrates a typical graphical temperature change profile of a body 202 passing through the drying apparatus in accordance with the present invention. It will be appreciated that more important that the actual adhesive temperature rise is the amount of energy input to the adhesive by the drier heating arrangement tubes 202. Tests have indicated that an adequate adhesive tackiness is retained if the adhesive is in receipt of about 1 W/cm^ on passage through the drying chamber. However, an energy gain in excess of 0.8 W/cm² may be sufficient depending upon the requirements of future manufacturing stages. In the period W to Y which is equivalent to passage of the body 202 through the drying chamber 110 most of the water (solvent) has been evaporated and collected by the air flows within the chamber 110 and the subsequent post-drying station 116 which is equivalent to Y to Z in Figure 4 achieves increased evaporation rate on the falling side of evaporation as defined previously and due to natural phenomena. Thus, the surface of the deposited adhesive coating after passage through the post- drying station 116 remains reasonably tacky but is not as fluid as would be present with a liquid adhesive as originally applied. Thus, the dried adhesive coating is manageable within the manufacturing process and is tacky enough for component assembly whilst not requiring too great a curing/ setting operation before any bond with the adhesive coating is fixed.

Figure 5 is illustrative of an alternative apparatus for drying a coating of water-based adhesive (or other solvent- based adhesive) applied to the surface of a shoe bottom or of a shoe- sole and is generally similar, except as hereinafter described, to the second apparatus described in EP-A-0 512 772. Thus, the illustrative apparatus comprises a drying chamber 110 comprising a plenum chamber 114, in a base plate of which are formed a plurality of nozzles or openings 112 through which air under pressure collected in the plenum chamber can be directed downwardly into the drying chamber, as will be referred to hereinafter.

The illustrative apparatus also comprises a shoe transporter system generally designated 120 comprising a continuous chain 122 entrained at each end about a sprocket mounted for rotation each about an axis 124, the two axes being arranged at opposite ends of the chamber 110. For carrying shoes and/or shoe sole units through the drying chamber 110, furthermore, the shoe transporter system 120 comprises a plurality of carriers or supports 130 which form part of the chain and each of which has two upstanding lugs each for supporting a shaft extending across the width of the shoe transporter system, i.e. outwardly at opposite sides of the chain 122. Each shaft in turn supports a support member 138 for pivotal movement about the axis of the shaft, the two support members 138 thus supported by one of the supports 130 constituting a shoe support arrangement of the illustrative apparatus. Moreover, by reason of the members 138 being mounted on the shafts as aforesaid, they are adjustable in order to accommodate shoes of different sizes or to provide a relatively flat support surface for a sole unit. Whereas in the illustrative apparatus the members 138 are generally of oval cross section, other support members, e.g. in the form of plate members (as described in EP-A-0 512 772), may alternatively be used, or indeed any other suitable support.

It will thus be appreciated that shoes and/or sole units supported by the shoe transporter system 120 can be carried, along the upper reach of the chain 122, along a path extending through the drying chamber 110. It will thus be appreciated that, as shoes and/or sole units are conveyed by the shoe transporter system 120 along said path, they are subjected to jets of air directed thereonto through the nozzles 112 formed in the base plate of the plenum chamber 114.

"Downstream" of the drying chamber 110, furthermore, is a heater arrangement 116 comprising a suitable radiant heater arrangement, e.g. an infra-red heater. The shoes and/or sole units thus passing along their path are subjected to radiant heating by means of the heater arrangement 116.

A further heater arrangement 140 is also provided at the entry end, i.e. "upstream", of the drying chamber 110. The heater arrangement 140, which is also a radiant heater arrangement, again e.g. an infra-red heater, effects a preliminary heating operation on shoes and/or sole units placed upon the support members 138 and conveyed along their path by the shoe transporter system 120.

In addition, the illustrative apparatus comprises a control panel generally designated 142, by which various settings may be made (not of particular relevance in relation to the present invention) . In addition, the upper reach of the chain 122, and thus of the shoe transporter system 120, extends beyond the drying chamber and heater arrangements in order to provide a loading station A and an unloading station B. In using the illustrative apparatus, in carrying out the illustrative method, shoes and/or sole units to which a coating of a water-based (or other solvent-based) adhesive has been applied are placed on the shoe transporter system 120 at the loading station A, generally in the manner disclosed in EP-A-0 512 772. The shoes and/or sole units thus loaded firstly pass beneath the further heating arrangement 140, at which they are subjected to radiant heat. More particularly, in carrying out the illustrative method, the temperature of the coating is elevated by the application of radiant heat to in the order of 82^βC. This temperature has been found to be insufficient to cause a skin to be formed on the surface of the coating, while nevertheless being significantly higher than ambient conditions. In this way, therefore, a temperature gradient is formed in the body of the coating which favours the migration of the water (solvent) to the exposed surface of the coating and thus favours the evaporation of the solvent water) and the drying of the coating.

Following the preliminary heating operation, the adhesive coatings are then exposed to the jets of air in the drying chamber 110, the air temperature in this case being ambient (although if the air is re-circulated, during the course of a working day clearly it will become slightly elevated in respect of ambient conditions by reason of its repeated contact with the hot adhesive coatings). Following the passage through the drying chamber 110, furthermore, the surface coatings are then subjected to further heating by the heating arrangement 116, prior to being removed from the shoe transporter system 120 at the unloading station B.

The time required for drying coatings, and thus the time taken for the shoes and/or sole units to pass from the loading station A to the unloading station B, will vary according to the nature of the adhesive and also of the substrate (shoe and/or shoe sole) to which the coating is applied. In general, however, the time taken should lie in the order of 1.5 to 2.5 minutes. Under such circumstances, therefore, the passage beneath the further heating arrangement should take in the order of 10-15 seconds. For adequate heating as required in accordance with the invention, therefore, a surface temperature in the order of 300^βC has been found satisfactory for the further heating arrangement 140. With regard to the time of passage through the drying chamber 110, furthermore, this, as disclosed in EP-A-0 328 923, is determined according to the period during which the rate of evaporation of solvent (water) is relatively constant, which of course will also vary according to the nature of the adhesive and the substrate, but in any event should lie in the order of 1-1.5 minutes. Similarly, the period during which heating takes place by the heater arrangement 116 is preferably in the order of 7-12 seconds, being a period during which the rate of evaporation is falling.

It has been found that carrying out the illustrative method a very satisfactory level of drying can be achieved for certain solvent-based adhesives, particularly water-based adhesives, in the times referred to above.

Whereas in the illustrative apparatus a separate further heating arrangement is provided "upstream" of the drying chamber 110, alternatively it would be possible to provide heaters on the underside of the base plate of the plenum chamber 114 for maintaining the temperature of the coating elevated in relation to ambient conditions during the passage of the substrate beneath the jets of air; alternatively again such an arrangement could be used in combination with the further heater arrangement 140.

Moreover, whereas in carrying out the illustrative method the coating has been applied to shoe bottoms and/or sole units, it will be appreciated that methods in accordance with the invention for drying other substrates to the surface of which a coating of adhesive has been applied may be carried out without going beyond the scope of the present invention.

Claims

Claims :

1. An apparatus for drying a deposit upon a body such as a water-based adhesive coating upon a shoe, the apparatus comprising a drying chamber through which carrier means in use transports a body with a deposit towards a post-drying station, said carrying means supporting the body in order to transport it through said drying chamber with a regular motion and with the body appropriately presented in the chamber, said drying chamber including air flow means to project air flows towards said body to turbulently collect evaporated solvent from said deposit, said drying chamber also including infra¬ red heater means mounted about said drying chamber to ensure said body is exposed to said infra-red radiant heat prior to or during its passage through said chamber for a proportion of its passage time span through the apparatus, said post-drying station exposing said body to radiant heat.

2. An apparatus as claimed in Claim 1 wherein the heater means comprises a plurality of infra-red tubes arranged to provide by appropriate spacing a planar or inclined infra¬ red flux density at a displaced distance from said tubes and above the carrier means.

3. An apparatus as claimed in Claim 1 or Claim 2 wherein the infra-red heater means is mounted within said drying chamber to expose said body to said infra-red radiant heat.

4. An apparatus as claimed in Claim 1, 2 or 3 wherein the heater means within the drying chamber is located such that the body in use is heated prior to or immediately upon entry to said drying chamber.

_. 5. An apparatus as claimed in Claim 2 or 3 wherein the infra-red wavelength is in the range 2 to 4 μm dependent upon expected deposit solvent.

6. A method of drying a deposit upon a body such as a water-based adhesive coating upon a shoe, the method including steps of;

a) placing the body upon carrier means in order that said body is transported through a drying chamber with a regular motion and appropriately presented to radiant heaters in said drying chamber;

b) presenting environmental air flows directed towards said body in order to collect evaporated solvent from said deposit and subsequently exhaust said solvent from said drying chamber;

c) presenting just prior to or within said drying chamber infra-red radiant heat as said body is transported by the carrier means through said drying chamber; and,

d) Presenting to said body after passage through said drying chamber radiant heat in a post-drying station.

7. A method as claimed in Claim 6 wherein the deposit is heated to a temperature in the order of 36^βC in the drying chamber and is heated to a temperature in the order of 68^βC in the post-drying station and the air flow rate within the drying chamber is in excess of 18 m/s.

8. A method as claimed in Claim 6 or 7 wherein the body is exposed to heat within the drying chamber for a time period of up to 60 seconds and is subsequently exposed to heat within the post-drying station for a time period of 15-20 seconds.

9. A method as claimed in any of Claims 6, 7 or 8 wherein the body is only exposed to infra-red heat within the drying chamber for a time period less than half the time period for passage of said body through said drying chamber.

10. A method as claimed in any of Claims 6, 7, 8 or 9 wherein the body is only exposed to infra-red heat within the drying chamber for a specified time period either after entry into said chamber or as appropriate before exit from said chamber.