US 3197324 A
Description (OCR text may contain errors)
July 27, 1965 D. H. BROOKS COATING CONTINUOUS MATERIAL 2 Sheets-Sheet 1 Filed Oct. 20. 1961 I nvenlor pap/9A0 uenea 8W Ratnf Attorney D. H. BROOKS July 27, 1965 COATING CONTINUOUS MATERIAL 2 Sheets-Sheet 2 Filed 001:. 20. 1961 IIIIIIIIH ||umn Inventor w Dona -o uenassr mm a If By A Home y United States Patent 3,197,324 CQATING CQNTINUQUS MATERIAL Donald Herbert Brooks, River Bend, Northdene, District Vanderhijl Park, Republic of South Africa, assignor, by
mesne assignments, to International Protected Metals,
Inc, a corporation of New Jersey Filed 0st. 20, 1961, Ser. No. 146,512 Claims priority, application Republic of South Africa, Nov. 1, 1960, alt/4,438; Nov. 11, 1960, 69/4594 '7 Claims. (Cl. 11721) This is a continuation in part of Serial No. 846,376 filed October 14, 1959, now abandoned, which is in turn a continuation in part of Serial No. 806,931 filed April 16, 1959.
The present invention relates to the coating of continuous, e.g. strip material. More particularly the invention relates to a modification of the coating process described and claimed in the said patent application Serial No. 846,376, which coating process comprises contacting the surface to be coated with a bed of particulate coating material, e.g. a powder, in an adequately mobile state of even aeration for substantially uniform contacting of the surface to be coated with the particulate material intermediate between that of the material in the condition known as a fluidised bed and that of the loosely settled material during at least a substantial part of the coating period while maintaining conditions suitable to cause the adherence of the particles to the surface to be coated, either by rendering the said surface itself adhesive prior to the above-mentioned contacting step or by heating the surface to be coated to a temperature at which the particles become at least plastiform enough to ahere to the surface.
The above-mentioned process, constituting the subject of Serial No. 846,376, oflers considerable advantages over conventional methods utilising true fluidised beds. In a fluidised bed turbulent conditions prevail; in the state of aeration to which Serial No. 846,376 relates, turbulence is substantially absent. The conditions specified in that patent application lead to very even, high quality coatings, the thicknesses of which may be successfully controlled. The process is particularly applicable to the production of coatings with thermoplastic powders, e.g. thermoplastic resin powders.
It has now been found that the said process may also be applied successfully to the coating of continuous materials including wire and cables, but particularly strip materials of various types, composition and texture, in particular strip metal. However, the invention is not limited to this particular application and may, for example, also be applied to the coating of very thin glass sheeting, fabrics, including fibreglass fabrics and textile fabrics or any other suitable material. The invention will be described with particular reference to strip materials. However, those skilled in the art will readily recognise those features of the invention applicable to other continuous materials, as Well as any features peculiar to the coating of strip material to the exclusion of other continuous materials.
In accordance with the present invention the said process of the said patent application Ser. No. 846,376 is modified by the feature that the surface to be coated is the surface of a continuous strip of sheet material or wire or other continuous material and that the said surface is continuouslypassed through a Zone of contact with the bed of particulate coating material in the abovedefined state of aeration.
The movement of the continuous material relative to the bed while in the zone of contact is preferably rectilinear. The said movement may take place in any direction relative to the bed, including from one side to the other, i.e. normally in a substantially horizontal plane.
Preferably, however, the movement of the surface being coated relative to the bed is in a substantially vertical direction, preferably in a vertical upwards direction. The relative movement between the surface to be coated and the bed of particulate material results in a beneficial wiping effect which has already been described in the said earlier patent appplication.
As described in the earlier patent application the said state of aeration intermediate between that of a fluidised bed and the loosely settled material includes two cases. In the one case a fine static balance prevails and the said condition is maintained continuously, when it may be referred to as a static aerate. The continuous surface to be coated in accordance with the present invention is then passed in contact with this static aerate.
In the alternative case the particulate coating material is first fluidised and the fluidised bed formed thereby is then allowed to collapse. Applied to the present invention the collapsing aerated particle bed is continuously supplied to a zone in which the surface to be coated passes in contact with the partly collapsed bed. Both alternatives are essentially equivalent, the main difierence being that a static aerate is a constantly maintained condition, whereas the condition of a collapsing fluidised bed is continuously changing.
The process in its application to the coating of strip material may be carried out in such a manner that only one side of the strip is passed in contact with the particulate coating material, e.g. by causing the strip material to form one lateral limiting surface of a space containing the said bed of particulate coating material, suitable precautions being taken to ensure that there is an adequate seal between the strip material and the remainder of the confining walls or sides of the said space containing the bed of particulate coating material. Such sealing may, for instance, be afiorded by the provision of strips of a felt-like material, e.g. asbestos cloth. The escape of powder may conceivably also be prevented by maintaining a reduced pressure inside the said space, at least in the critical regions, as compared with the outside pressure, or by directing gas jets in a direction opposed to the direction of escape of the powder.
The process is particularly suitable for the coating on both sides of strip material, in which case the strip material is passed right through a bed of the particulate coating material in the defined state of aeration, e.g. through a suitably sealing gap or slot in the bottom of the space containing the bed of particulate coating material. Again the seal may be brought about by m chanical means, alternatively reduced pressure at least in the vicinity of the gap or slot inside the space, as compared with the pressure prevailing outside the slot, or gas jets may be employed to inhibit the escape of coating material. However the term scaling is to be understood in its wide-st sense to include any manner or means of preventing or inhibiting the outflow of coating material. Thus when the continuous material moves very fast upwards, i.e. well over ft./min. say about 300 ft./rnin., the scaling is adequate without additional precautions, even if there is a clearly visible gap between the continuous material and the apparatus.
In order to ensure a continuous supply of particulate coating material to the contact zone at least part of the bottom of the vessel or space containing the said particulate material preferably slopes, the term including stepwise sloping, towards the surface to be coated to an extent which exceeds the angle of repose of the aerated particulate material.
In a preferred apparatus for carrying out the process, the said sloping bottom may itself be gas-pervious and '5 u constitute all or part of a bed support, i.e. a partition between the aerating space proper and a gas box, to which aerating medium is supplied which then passes through the partition into the particulate material.
Also in a preferred apparatus for carrying out the process of the type in which strip material passes vertically upwards through the bottom of the aerating vessel and out through an opening in the top thereof, the seal at the bottom of the vessel between the bottom of the vessel and the strip material is provided by a pair of rollers adapted for the passage of the strip material therebetween.
The process is particularly suitable for the application of thermoplastic coatings to strip material and the like, in which case the material to be coated is suitably preheated prior to and/or heated during its passage in contact with the bed of coating material.
It is preferred to pass the strip or like material through a bed of coating material of relatively shallow depth or a succession of such beds of relatively shallow depth, e.g. 1 /2" to 12', preferably 2" to 6" deep.
Heat may be applied to the material being coated between successive passages through coating material. Heat may for example, be applied by passing the material through an induction zone or by passing a current through the strip or like material. Infrared radiation or hot gas heating may also be employed.
The process described above may be furt er modified or improved so as to comprise aerating a particulate coating material in an aerating space, utilising the powder head in the aerating space to continuously feed the aerated material into a constricted passage sloping downwards with an angle in excess of the angle of repose of the particulate material at least in its aerated condition and rapidly moving the surface of the material to be coated in a substantially vertical upwards direction past the lower end of the said passage in such a manner that the material to be coated substantially forms a barrier across the said end of the passage against which barrier the particulate material descending through the passage is dammed up and accordingly continuously kept in contact with the surface of the material to be coated. The said passage should be as short as possible, say of the order of 10 inches, in order to prevent excessive de-aeration of the particulate material during its movement through the passage.
The said passage preferably slopes at an angle of the order of 50. The spacing between the upper and lower confining planes of the said passageway may be of the order of 2", depending on the rate at which the powder is used up, since the sojourn of the powder in the said passage should not be so long as to result in a complete de-aeration of the powder mass. According to some embodiments it is possible to apply some additional aeration in the said passage itself.
Again, as in the embodiments described further above, involving the use of thermoplastic coating materials, the continuous material may be heated in any suitable manner in order to cause the adherence thereto of the coating material.
The same applies to any subsequent heating which may be necessary to complete the fusion of the thermoplastic material. Induction heating has been found very suitable when coating conducting materials such as strip metal. -Di-electric heating may be applied when coating non-conductors.
The present method is also very suitable for coating both sides of a continuous strip material with two different coating materials or qualities of coating.
The strip or other continuous material may also successively pass in contact in the manner specified with two or more different coating materials so as to result in a multiple layer coating.
Apart from the method and apparatus outlined further above in which strip material to be coated on one side only functions as a side wall of the space containing the coating material, there are other ways of achieving the same end, e.g. masking the side of the strip which is to remain uncoated with a suitable masking member passed through the bed of coating material together with and in sealing relationship with the strip material. For example two continuous strips of material to be coated are passed rear to rear in sealing relationship with one another, along the sides at least, through the bed of coating material. If desired or required the strips may be caused to adhere to one another during their passage through the bed, e.g. by the use of pressure-sensitive adhesive, preferably by the use of two-sided pressure-sensitive adhesive tapes such as silicone-coated tapes. The backing material of the tapes may be metal. The said tapes may be used repeatedly and may, for example be employed in the form of endless belts.
The process may be carried out with an apparatus which comprises an entrance opening at the bottom of the apparatus adapted to allow the entrance of the continuous material to be coated in a vertical direction through, the apparatus in substantially sealing relationship to the said opening, at least one downwardly sloping passage of restricted vertical clearance and limited length terminating at its upper end near the bottom of an aerating vessel and terminating at its lower end, which coincides with the said entrance opening, close against the path of the continuous material through the apparatus, with at least a small clearance provided between the upper confining wall of the passage and the path of the material to be coated.
As will be clear from the description of the method, the slope of the said passage is preferably of the order of 50, the length of the passage being as short as possible and preferably not in excess of 10 inches and the clearance between the upper and lower confining Walls of the passage preferably being of the order of 2 inches.
The said upper and lower confining walls are preferably parallel.
The gap between the upper confining wall and the continuous material is preferably adjustable by means of a shutter or the like.
Provision may be made for the water-cooling of the material confining the entrance opening for the continuous material to be coated. This entrance opening may be confined by sharp edges.
The preferred apparatus comprises two or more of the said passages in succession, one on top of the other, the upper confining wall of one passage preferably constituting the lower confining wall of the next and the upper end of each passage terminating in an aerating vessel. ince there is a certain amount of communication between successive passages at their lower termination, it is advisable to operate the apparatus in such a manner that the pressure head of the powder in each passage is substantially the same. This inhibits the undesirable flow from one passage into the other.
The relative dimensions of the individual passages depend on the relative thicknesses of the individual coating layers, which it is desired to apply, bearing in mind the differences in thermal conductivity, which may arise in practice when applying successive layers of thermoplastic coatings to a hot object, and which necessitate prolonged contacting periods in order to produce successive coating layers of comparable thickness.
The apparatus in accordance with the invention may be adapted to the coating of wires, in which case the said passages will confine funnel-shaped spaces, i.e. concentric funnel-shaped spaces in the case of several successive passages.
When coating stn'p material, e.g. sheet metal the said passages may either approach the path of the strip material from one side only (when it is desired to coat only one side of the strip material) or from both sides, and the arrangement on the two sides may be different if it is desired to apply different coatings to the two sides of the strip material.
The apparatus may also be provided with suitably arranged guide rollers to allow two continuous strips of material to be coated to be guided rear to rear through the apparatus so that each strip is coated on one side only.
In addition the apparatus may comprise one or more endless belts coated on both sides with a heat-resistant pressure sensitive adhesive, e.g. a silicone base pressure sensitive adhesive and a guide system adapted to pass said belt or belts between the two continuous strips of material to be coated passing rear to rear through the apparatus and means for pressing said strips on both sides against the said belt thereby bringing about adhesion and establishing a seal at least along the edges of the said strips.
The scope of the invention also includes in its scope a further mod jication in which the continuous material to be coated is introduced under non-adhesion-favouring conditions from above into an aerated bed of particulate coating material, is then bent upwards well below the surface of the said bed and is hence passed upwards, under conditions causing the adherenw of particulate coating material to the continuous material, and out of the aerated bed of particulate coating material. This embodiment is again particularly applicable to coating with thermoplastic powders in which case the continuous material is introduced to the bed of thermoplastic powder from above at a temperature below the tacky temperature of the coating material, passed around a guide well below the surface of the coating material and hence upwards while heat is simultaneously supplied to the endless material, sufiicient to cause the adherence of coating material to the endless material during its upwards passage. Heating of the continuous material while submerged in the bed of coating material preferably takes place by induction heating, though it is possible to pro-heat the endless material to a temperature below the tacky temperature of the coating material by any suitable means, e.g. hot gas heating, the direct passage of a current through the material by contacting the material with electrical terminals, infra-red eating, or also induction heating.
The above-mentioned process is preferably carried out with an apparatus in accordance with the invention which comprises an aerating vessel adapted for the dense phase aeration of a powder contained therein said aerating vessel being open at the top at least to an extent allowing the introduction from above of an endless material to be coated and the exit through the top of the endless material after its passage through the coating material, means for guiding the endless material down into the vessel and hence upwards and out of the vessel and a heating system, e.g. an induction heating system, adapted for the passage therethrough of the material to be coated between its point of upward turning and its exit from the coating vessel.
If desired or required the surface of the endless material coated by any one of the modifications of the process described above may be embossed, e.g. for decorative purposes. Such embossing is preferably carried out in the case of coating with thermoplastic materials after only partly having fused the thermoplastic material, the fusion being completed after the embossing step only. Accordingly the apparatus for carrying out this form of the process comprises embossing means, e.g. embossing rollers, beyond the point where the material to be coated emerges from the bed of coating material and a post-heating zone beyond the embossing means.
The invention and the manner in which it may be put into practice will be further described by way of example with reference to the accompanying drawings, in which FIG. 1 represents in vertical section an apparatus in accordance with the invention for coating continuous sheet metal with thermoplastic material on both sides.
FIG. 2 represents a vertical section of part of an apparatus similar to the one shown in FIG. 1;
FIG. 3 represents a diagrammatic view of an apparatus 6 for coating two continuous lengths of material each on one side only;
FIG. 4 represents a vertical section through an alternative apparatus in accordance with the invention for coating a continuous material with a thermoplastic material in powder form, which apparatus is also suitable for coating such materials as light gauge expanded metal or wire mesh;
FIG. 5 represents a vertical section through an apparatus for coating sheet metal and similar continuous material with various types of coating;
FIG. 6 represents a vertical section in perspective view of an apparatus similar to the one illustrated in FIG. 5 but adapted for the coating of wire, cables and the like.
Referring to FIG. 1 of the drawings, the apparatus comprises an aerating vessel 1 kept supplied with thermoplastic resin powder 2, e.g. polyethylene powder or polyvinylchloride powder or a thermosetting resin powder having thermo-softenable properties initially, from a hopper 3.
The bottom of the aerating space of the aerating vessel is partly formed by a gas pervious bed support 4 underneath which a gas chamber 5 is provided, which is supplied with compressed air or other suitable gas, e.g. nitrogen through inlet 6. The bottom of the aerating space, partly represented by gas pervious bed support 4, drops steeply in the central portion 7 where the bottom of the vessel is formed by guide and sealing rollers S in sealing relationshi with the remainder of the vessel by means of resilient blades 9.
it represents a continuous length of sheet metal to be coated which travels in the direction of the arrow. Before entering the aerating vessel, between rollers 8, the sheet metal is pre-heated in pre-heating zone 11, which pre-heating zone may employ hot gas heating, radiation heating, induction heating, or conventional resistance heating. Depending on the extent of the pro-heating it may be necessary for the rollers 8 to be water cooled. However, if pro-heating is to a temperature substantially below he temperature at which the resin powder becomes tacky, such cooling will be unnecessary. For bringing the sheet metal to the exact required temperature induction coils 12 are provided in portion 7 of the aerating vessel. The exact temperature depends not only on the resin powder and the speed of travel of the sheet metal 1%} and the desired thickness of the coating, but also on the subsequent aftertreatment to which the coating is subjected; In the present example powder layers 13 are picked up but only partly fused initially. The partly fused layers are then subjected to an embossing treatment between embossing rollers 14, and complete final fusing is brought about by post-heating between induct-ion coils 15. In the case of.
heat sensitive thermoplastic coating compositions it is now important that the temperature be lowered below a temperature at which appreciable heat deterioration takes place as rapidly as possible. This is facilitated by the fact that the heat capacity of sheet met-a1 is comparatively low. In the present example cooling fans 16 are provided for an initial cooling, and final quenching is brought about in a quenching Zone 15a, e.g. with the aid of water jets. It is also possible to employ the embossing rollers 14 for changing the direction of travel of the sheet metal, e.g. in a horizontal or slightly downwards direction, in which case the finished product may also be passed through a quenching bath, before it is rolled up by means not shown in the drawing.
Referring now to FIG. 2, the arrangement may be similar to that in FIG. 1. The gas pervious bed support 4;: in this example slopes inwards towards the sheet metal 10 throughout. Close to the sheet metal 10 the steepness of the gradient increases and in that portion the member 4a is gas-impervious. The gas chamber So has a wedge shape. In this example there is a slight gap between the sheet metal and the coating apparatus at 17, no additional sealing means being provided, because the speed of travel of the sheet metal (say about 300 ft. per minute) is sufii cient to prevent appreciable powder losses through the p- Referring now to FIG. of the drawings, the apparatus enables multilayer coatings to be produced and different coatings on different sides of a length of sheet metal or the like passing through the apparatus. On the right hand side in FIG. 5 there is an aerating vessel 18 filled with thermoplastic powder kept thoroughly aerated by compressed air passed into gas chamber 19 and from there through gas-pervious bed support 2% into the powder mass. Somewhat above bed support 2%} a passage 21 with parallel top and bottom walls and having the width of the sheet metal being coated slopes downwards at an angle of approximately 50. Passage 21 is continuously being supplied with aerated powder from aerating vessel 18, the degree of aeration diminishing as the powder travels downwardsalong the passage. The arrangement is such that at 22 there is contact or at the most a small gap between the sheet metal and the lower confining wall and the passage 21. Between the upper confining wall and the sheet metal a small gap is maintained which is adjustable by means of a shutter 23. Above passage 21 there is a second passage 24 supplied with aerated powder from a second aerating vessel 25 having a bed support 26 and a gas chamber 27 with gas inlet 28. Again the gap between the upper confining wall of the passage 24 and sheet metal 19 is adjustable by means of a shutter 23a. The powders in aerating vessels 1% and 25 are of different composition one for example being a thermoplastic powder particularly suitable as a base layer, the other being suitable for forming a finish layer. The powder level in both parts of the apparatus are so regulated that the pressure head at 23 is approximately the same in both passages. Heating of the sheet metal to cause the adherence of powder layers 13a and 13b may be accomplished by similar means as described with reference to FIG. 1.
Ch the left hand side of FIG. 5 a third aerating vessel 29 in all respects similar to aerating vessel 18 is provided, also having a downwardly sloping passage 30 similar in all respects to passage 21 but leading to the opposite side or" sheet metal it). In the present example it is assumed that aerating vessel 29 is filled with a non-fusable powder. Before sheet metal 10 is brought into contact with the powder supplied by passage 30, a layer 31 of a tacky adhesive is applied by applicator 32. Accordingly a layer 136 of the non-fusable powder will adhere to sheet metal 10.
Referring to FIG. 6 of the drawings, the apparatus is essentially similar to that shown in FIG. 5 except that it is adapted to the coating of wires, cables and the like, denoted 33. There are two concentrically arranged aerating vessels 34 and 35 respectively, each comprising a gas chamber 36 and 3'7 respectively and a gas pervious bed support 38 and 39 respectively. The aerating vessels keep funnel-shaped concentric passages 40 and 41 respectively supplied with the coating material. Heating, quenching and like means which may be similar to those in FIG. 1 have not been shown in this drawing.
Referring to FIG. 3, 42 represents a coating apparatus which could be of the type illustrated in FIG. 1 or FIG. 5. Two continuous lengths of sheet metal 10a and 10b are coated simultaneously, however, each on one side only. The sheet metal is supplied from rolls 43a and 43b and then is fed back to back into the apparatus 42 with one or more endless belts 44 sandwiched in between. The belt 44 is coated on both sides with a pressure sensitive silicone adhesive, renewed whenever necessary, at 45. The two lengths of sheet metal are pressed against the belt or belts by rollers 46 to bring about adhesion and sealing of the edges at least. After passage through the coating apparatus the two lengths of sheet metal are again separated and coiled up at 47a and 47b respectively, the belt 44 continuing its endless path separately, guided by guide rollers 48.
Referring now to FIG. 4, continuous material 10a which may be sheet metal but which could also be wire mesh or light gauge expanded metal is fed in the direction of the arrow around a guide roller 49 into a preheating zone Sii which may be of similar type as preheating zone 121 in FIG. 1. Here the material is preheated below the temperature at which a thermoplastic coating powder subsequently to be applied becomes tacky. This coating powder indicated by 51 is contained in an aerating vessel 52 of conventional design. Just above the bed support 53 of the aerating vessel a guide roller 54 is mounted. The sheet metal 10a after having passed through the pre-heating zone 50 travels steeply down into the aerating vessel 52 around guide roller 54 and hence upwards and out through the top of the aerating vessel. During its upwards travel the sheet metal is heated above the tacky temperature of the powder by means of induction coils 55 and accordingly picks up layers 13 of coating composition. The subsequent treatment may be similar to that described with reference to FIG. 1.
When carrying out the process in accordance with the invention with any one of the apparati described above, conditions are controlled in such a manner that at least the bulk of the coating powder in contact with the continuous material is in a non-turbulent condition, yet is more loosened up than an ordinary loosely settled powder. This condition of intermediate aeration is particularly advantageous because it largely eliminates the disadvantages of a fluidized bed (excessive heat losses, excessive rarification of powder, disturbing eifect of turbulence, higher gas consumption) and yet retains it main advantage (high mobility) to a remarkable degree.
As described in the said application Serial No. 846,376 the said intermediate condition of aeration includes two distinct case in the one case a collapsing bed is produced by first fluidizing the coating powder and then decreasing or ceasing the through flow of aerating medium to cause the collapse of the aerated particle bed. The surface to be coated is then contacted with the aerated bed during that transitory period, after the turbulence characteristic of a fluidized bed has ceased, but while the bed is still collapsing on its own accord and before the powder has reached the loosest condition in which the bed can exist self-supporting, that is, without any gas flow at all.
The other alternative is the static aerate, so-called because the particles of the bed are maintained (by gas fiow) in static equilibrium as against the dynamic equilibrium of a fluidized bed. A most convenient way of producing the static aerate condition is by first completely fluidizing the bed of powder and then reducing the flow of aerating medium through the bed by a regulated amount, sufficiently for turbulence to cease, but insufiiciently for the bed to collapse completely, that is, to a loosely settled self-supporting condition, such as can be maintained for prolonged periods without any gas flow at all. In contrast to the fluidized bed, which has no angle of repose at all, the static aerate exhibits a small angle of repose, which is, however, always less than the angle of repose of a self-supporting loosely settled powder, no matter how loose the latter may be.
What I claim is:
1. A coating process for coating a moving continuous strip material and the like, comprising continuously passing an aerating gas into a bed of particulate solid coating material to form a fluidized bed of the particulate coating material, forming a zone of the particulate solid coating material in open communication with and continuously fed by the fluidized bed and in which zone the degree of aeration is maintained in a state of aeration intermediate between that of a fluidized bed and that of a bed of loosely settled self-supporting particulate solid coating material, passing said moving strip in contact with the particles of said zone exclusive of said aerated bed while applying heat to the strip material as it passes through said zone sufliciently to form in said zone a partly fused layer of the particles onto the strip, thereafter passing this strip between a pair of pressurizing rollers and subsequently completely fusing the partly fused layer.
2. A coating process according to claim 1 comprising passing particles from said fluidized bed into said zone and confining said zone in a downwardly directed passage and into contact with said strip.
3. A coating process according to claim 2 wherein said moving strip maintains a closure at the lower end of said passage while it passes into contact with particles of said zone.
4. A coating process as claimed in claim 1 in which the movement of the surface being coated relative to the bed is in a substantially vertical upwards direction and the particulate coating material in the immediate vicinity of the surface being coated is maintained in a less intensely aerated condition than those adjoining parts of the coating material which are further removed from the surface being coated.
5. A coating process as claimed in claim 1 in which the continuous material is pre-heated to a temperature below the temperature at which the particulate coating material becomes tacky, before coming into contact with said particulate coating material.
6. A coating process for coating a moving continuous strip material and the like, comprising continuously passing an aerating gas into a bed of particulate solid coating material and adjusting the gas flow therethrough to form an aerated bed of the particulate solid coating material in a state of aeration intermediate that of a fluidized bed and that of a bed of loosely settled self-supporting particulate material, forming a Zone of the particulate solid coating material in open communication with and continuously fed by the continuously aerated bed and in which zone the degree of aeration is less than that of the aerated bed, passing said moving strip in contact with the particles of said zone exclusive of said aerated bed 10 while applying heat to the strip material as it passes through said zone sufficiently to form in said Zone a partly fused layer of the particles onto the strip, thereafter passing the strip between a pair of pressurizing rollers and subsequently completely fusing the partly fused layer.
7. A coating apparatus for coating continuous strips with particulate solid coating materials in a dense phase state of aeration comprising a vessel for containing the particulate c-oacting material, a bottom wall in said vessel for supporting the particulate material, an opening in the bottom wail, at least part of the bottom wall being directed downwardly toward and terminating at said opening, guide means positioned below said opening for guiding a pair of continuous strips toward each other and through said opening, an endless belt coated on both sides with a heat-resistant pressure sensitive adhesive, said belt passing between and in adhering contact with said strips, and means for non-destructive'ly separating the trips from said belt after leaving the coating vessel.
References Cited by the Examiner UNITED STATES PATENTS 1,101,178 6/14 Haigh 117-48 1,974,594 9/34 Augier 156-152 X 2,268,673 1/42 Reynolds 117-48 2,938,276 5/60 Doleman et al. 2,971,242 2/61 Doleman et al. 2,987,413 6/61 Dettling et a1 117-21 2,991,550 7/61 Block 117-48 X 3,019,126 1/62 Bartholomew. 3,032,816 5/62 Zimmerli.
FOREIGN PATENTS 833,181 4/60 Great Britain.
VVELLIAM D. MARTIN, Primary Examiner.
RICHARD D. NEVIUS, Examiner.