US3265525A

US3265525A - Method and apparatus for continuous coating of endless metal bands with synthetic resins

Info

Publication number: US3265525A
Application number: US269394A
Authority: US
Inventors: Lichte Albert
Original assignee: Schloemann AG
Current assignee: Schloemann AG
Priority date: 1962-04-04
Filing date: 1963-04-01
Publication date: 1966-08-09
Anticipated expiration: 1983-08-09

Description

Aug. 9, 1966 Filed April 1 1963 LICHTE METHOD AND APPARATUS FOR CONTINUOUS GOATING OF ENDLESS METAL BANDS WITH SYNTHETIC RESINS 2 Sheets-Sheet 1 Aug. 9, 1966 A, LlcHTE METHOD AND APPARATUS FOR CONTINUOUS COATING OF ENDLESS METAL BANDS WITH SYNTHETIC RESINS 2 Sheets--Shee'c 2 Filed April 1, 1963 Ffg z Fig 3 vllllllll..lllllillrlfrlvlrrllf United States Patent O 3,265,525 METHOD AND APPARATUS FOR CONTINUOUS COATIN G OF ENDLESS METAL BANDS WITH SYNTHETIC RESINS Albert Lichte, Wuppertal-Elberfeld, Germany, assignor to Schloemann Aktiengesellschaft, Dusseldorf, Germany,

a German company Filed Apr. 1, 1963, Ser. No. 269,394 Claims priority, application Germany, Apr. 4, 1962, Sch 31,252 4 Claims. (Cl. 117-49) This invention relates to a method of and apparatus for the bubble-free coating of thin layers of synthetic material, in a liquid or pasty condition, in a continuous operation, upon continuously accuring endless metal bands, and for the rapid hardening of the layer of synthetic material so applied.

The synthetic coating material may consist of mixed PVC polymerizates, acrylic resins, alkyds, or certain proprietary preparations of the kind commonly known as plastic lacquers.

The object of the invention is to carry out the coating and hardening in a small space, with simple apparatus and small operative expenditure, in as short a time as possible. In particular, the drying or gelatinising and hardening times are to be short, and a rapid change-over to different materials and orders of magnitude, with dustfree working, is to be rendered possible.

The invention consists in applying the synthetic material, which has been brought into a pasty to liquid condition by means of a solvent of the ketone group for example, to the band to be coated, in a vacuum, and eiecting the hardening or polymerisation of the applied layer in a vacuum, or at least in a treatment chamber at a lowered pressure. (When reference is hereinafter made to vacuum, what is meant is a lowered pressure which is less than atmospheric pressure). Owing to the fact that in a vacuum the fractional distillation of the solvent can be reduced by lowering the boiling points of the participating solvents, the gelatinisiug, drying or polymerising process, which is controlled by the solvents, admits of being considerably shortened.v The usual solvents, for instance methyl ethyl ketone, evaporate in a normal atmosphere at about 80 C. By adopting a slightly lowered pressure, between 100 and 40 Torr (.millimetres of mercury) for example, the boiling point can be shifted to room temperature or lower. This has the advantage that following the vaporisation of the solvents a cooling of the coated band in the conventional sense is no longer required. The entire drying tract for the hardening of the coating is thereby considerably shortened, so that a considerable increase in the speed of passage of the band is possible. Besides the advantages of a greater coating output, the coating materials applied in a vacuum are free from bubbles and free from dust. Additional advantages are yielded by the vacuum treatment, in that the solvent vapours arising from the vaporisation of the solvents can be condensed by appropriate cooling devices and collected. The consumption of solvents can thereby be considerably reduced. Furthermore, in the coating of light metals, aluminium bands for example, there is an advantage, in that no alteration in the technological properties of the aluminium band is brought about, because the drying in a vacuum is eifected below the recrystallisation temperature.

Finally, as compared with conventional coating installations, a substantially smaller consumption of energy is also an advantage, for `only the heat of vaporisation eliminated in the evaporation of the solvents need be resupplied. This supply of heat, which is in any case necessary for the maintenance of the vaporisation temperature,

is however comparatively small.

3,265,525 Patented August 9, 1966 ICC The apparatus for carrying out the process according to the invention, which comprises a vacuum chamber serving for the vacuum treatment, closed in an airtight manner, at both the band-admission and the band-exit ends, in a known manner by vessels containing liquid, is characterised by the feature that at the same level as the sealing-'liquid containers, and between these, treatment vessels are provided, and that the sealing-liquid vessels are in each case connected by way of one connecting tube, but the treatment vessels in each case by way of two connecting tubes, with a vacuum tank arranged above at a higher level, in such `a way that the band to be coated can be carried through the apparatus in a number of vertical loops, the reversing rollers that carry the band, and also the Vactual coating appliances, being arranged partly in the sealing and treatment vessels and partly in the vacuum tank.

The installation costs of this apparatus, as compared with conventional plants, are extremely low. The vacuum chamber, having regard to the purpose for which it is employed, is by this arrangement kept very small, and owing to the vertical tube lconnection of the liquid vessels with the upper vacuum tank, the provision of as high a Vacuum as may be desired is possible, since the column of liquid sucked up by the vacuum in these connecting tubes can be raised as far as may be wished. Independently of the height of the vacuum, therefore, a constantly continuous passage of the band through the apparatus is given. The sealing-liquid baths may at the same time serve as treatment baths, for instance in such a manner that the liquid seal at the band-admission end of the apparatus constitutes at the same time the last cleaning stage of a preparatory treatment of the band, whilst by the liquid seal at the band exit end an after-treatment of the finished band may at the same time take place, for instance in such a manner that the coated band is here coated With a thin protective lm, in order to prevent an electrostatic charging, and therefore an attraction of dust.

These and further details of the process according to the invention, as well as of the apparatus according to the invention, are further explained by reference to a constructional example, which is illustrated in the `accompanying drawings, in which z' FIGURE 1 shows in front elevation theA apparatus according to the invention;

FIGURE 2 is a diagrammatic representation of a coating `appliance known in itself;

FIGURE 3 shows a section on the line III--III in FIGURE 1; yand FIGURE 4 a section on the line IV-IV -in FIGURE 3.

The apparatus illustrated consists essentially of four vessels 1, 2, 3, 4, erected side by side in one plane, a vacuum tank 5 arranged above 4them at a higher level, and six vertically extending connecting

tubes

6, 7, 8, 9, 10, 11, by which the lower vessels 1, 2, 3, 4 are connected with the vacuum tank 5. In order to ensure a satisfactory sealing, that is, a vacuum-tight sealing, of the connecting

tubes

6, 7, 8, 9, 10, 11, each of the lower vessels 1, 2, 3, 4, is equipped with two upwardly directed tubular members or sockets 1a, 1b, 2a, 2b, 3a, 3b, 4a and 4b, whilst the vacuum tank 5 above them has six downwardly directed sockets, c, d, e, f, g and h. The connection of the lower vessels 1, 2, 3, and 4 with the upper vacuum tank 5 is here established by means of the connecting

tubes

6, 7, 8, 9, 10 and 11 in such a way that the band 12 to be coated can be passed through the apparatus in a succession of vertical loops by way of

lower reversing rollers

13, 14, 15, 16 arranged inside the vessels 1, 2, 3 and 4, and by way of

upper reversing rollers

17, 18, 19 journalled in the vacuum tank 5. The open socket 1a of the vessel 1 here serves as an entry into the apparatus, and `the socket 4a of the vessel 4 as an exit from the apparatus. The band admission roller 20, and

the band outlet roller 21, are located at about the same level outside the apparatus itself.

All parts of the apparatus, that is, the lower vessels, the vacuum tank and. the connecting tubes, may fundamentally be made of any Idesired cross section, even square or rectangular. A round or at least oval cross-sectional form is however preferred. The production of the vacuum is eected by vacuum-producers not represented in the drawings, such for instance as pumps, steam-jet ejectors, condensers or the like, which are connected to the upper vacuum tank 5 by way of tank unions 22.

The vessels 1 and 4 both serve -as liquid-containers for the accommodation of sealing liquid, and thus are at the same time sluices for the air-free admission and exit of the band. The sealing medium is in both cases an aqueous solution. The solution in the vessel 1, that is, at the end at which the band enters, may also pertain to the last cleaning stage of the preparatory treatment of the band. The solution in the vessel 4, on the other hand, may be a special solution, which, as the coated band runs through, deposits upon the surface of the band a protective film, by which an electrostatic charging, and therefore an attraction of dust, is prevented.

During the operation, in dependence upon the height of the vacuum in the apparatus, the solutions in the vessels 1 and 4 are drawn upwards by suction linto the vaeuum space, that is, into the connecting tubes 6 and 11. In each of these connecting tubes 6 and 11 a column of liquid corresponding to the vacuum accordingly adjusts itself. On the vessels 1 and 4 are also provided

overflow spouts

23 and 24, by which the solutions in these Vessels tlow away into a collecting receptacle located lower down and not represented in the drawing, to be pumped back again from there into the vessels by way of the sockets or pipe couplings 1a and 4a, which are open to the atmosphere. This has the advantage that the surface level of liquid in the vessels 1 and 4 always maintains a constant height, even if accidental iiuctuations should occur in the vacuum. Furthermore in this way the composition of the Solution can be constantly checked, and can be supplemented or renewed in case of need.

The vessels 2 and 3 serve as treatment vessels, and are subject to vacuum. They contain, besides the lower band-reversing rollers 14 and 15 respectively, the

actual coating devices

26 and 28 respectively, for applying an adhesion-promoting medium and the layer of synthetic material respectively. Similar :

coating devices

25 and 27 are moreover provided in the vacuum tank 5, the coating device 25 being designed for applying an adhesion-promoting medium and the coating device 27 for applying the layer of synthetic material. The adhesion promoting medium may be the proprietary preparation known as mesamol, or some similar primer.

Each coating device, as shown in FIGURE 2, consists of a trough 40 containing the liquid synthetic material or the adhesion-promoting means, a dipping roller 41 dipping into the trough, and an applying roller 42 co-operating with the dipping roller. The entire unit, including its drive, is supported in the vacuum space, and each such unit is arranged in the neighbourhood of one of the

reversing rollers

14, 15, 17 or 13 that guide the band 12, so that during the application of the layer of synthetic material the reversing roller serves as a counter-pressure roller.r

In order to enable the thickness Vof the coating to be accurately adjusted while it is being applied, the entire coating :device is displaceable towards the band, that is, towards the centre of the reversing roller. The troughs 40 containing the liquid synthetic material have each an overow connection as well as an inlet connection. These connections are in communication with a storage vessel, which is arranged outside and underneath the vacuum plant. In order that the coating materials may not dry up, and that their viscosity may be maintained, they are -continuously pumped round. For the maintenance of the vacuum it is however requisite that the connecting pipes should form a U-shaped loop extending vertically downwards and corresponding to lthe height of the Vacuum, s0 as to counteract the suction produced by the vacuum.

The bottoms of the treatment vessels 2 and 3 are so constructed that in a method of working with a rather coarse vacuum `of for instance more than Torr, the solvent condensing on and running down the cooler walls of the

tubes

7, 8, 9 and 10 can be caught underneath. By

special discharge pipes

29 and 30 the condensate is drawn olf, and the surface level of the condensate in the vessels 2 and 3 is maintained constant. The

discharge pipes

29 and 30, like the connecting tubes of the coating devices, are of U-shaped construction and extend vertically downwards, the length of the U-shaped loop having to be adapted to the height of the vacuum. For the satisfactory condensation of the vaporised solvent, cooling devices, for instance cooling coils 31, may if desired be provided in the ltreatment vessels 2 and 3. An external cooling of the vessels 2 and 3, or of the connecting

tubes

7, 8, 9 and 10, is however likewise possible.

The treatment or coating of the band 12 is effected in the treatment vessels 2 and 3 and in the vacuum tank S. The connecting tubes 6 and 11 serve as drying spaces for the drying and hardening of the coating material, so that the length of the drying Atract is determined by the length of the connecting tubes. By increasing the length of the connecting tubes, therefore, the length of the drying tract can be increased in `a very -cheap and simple manner, with out the other structural parts of the apparatus having to be altered. The connecting tubes 6 and 11 communicating with the liquid vessels 1 and 4 serve at the same time as stand-pipes for the columns of sealing liquid sucked upwards by the vacuum.

In order to accelerate the drying and handening or polymerisation of the freshly applied coating, and at the same time to make good the heat removed by vaporisation of the solvents, heating devices 32 are installed in the connecting tubes. Since the transfer of heat in the vacuum can only be effected by radiation, the heating devices 32 are preferably infra-red radiators or similar thermal radiators. These heating devices are located near the band surface just coated, and are so arranged that an intensive irradiating o'f the coating substances is possible.

One form of construction, by way of example, of a heating appliance constructed as a thermal madiator, is shown by FIGURES 3 and 4. The thermal radiator elements are lassembled into Ignoups, each -gr-oup of radiators consisting lof a number of tubes 34 arranged transversely to the direction in which the band passes, and welded in a vacuum-tight manner to the connect-ing tube, for instance to the `t-ube 7 in FIGURES 3 and 4. The thermal radiating tubes 34 yare `open at both ends, so that any desired source yof heat can be fitted in or connected thereto. For the strengthening and intensifying orf the yradi-ating eiIect, reflectors 3S are provided on the side of the thermal radiating tubes 34 remote from the band 12, as shown in FIGURE 4.

If the connecting tubes 7 to 10 are provided throughout their length with such radiating tubes 34, they admit of being used Ioptionally for heating or for cooling. In this way the entire apparatus can be widely adapted to all coating requirements.

The working procedure or coating paratus according to the invention is as follows: T-he band 12 to be coated is introduced, by way of the bandentry 4roller 20, through the open tubular member la, into the liquid vessel 1, and is guided upwards by the reversing roller 13, journalled in the liquid, 'into the connecting tube 6. In` the upper part ofthe connecting tube 6 is mounted a heating device 32, which vaporises drops of water that operation in the aphave remained clinging by adhesion to the surface of the band. Upon the deflection of the band 12 round the upper reversing roller 17, an adhesion-promoting medium is applied to one side off the band by the coating device 25. Upon the further tr-avel of the band this applied layer is irradiated by the heating device 32 located in the connecting tube 7, the solvent evaporating and the coating itself being dried out. In the treatment vessel 2, by means of the coating device 26, the other side ofthe band is then provided with an adhesion-promoting medium, which, upon the band ascending again, is dried in the connecting tube 8. As the band passes round the upper deflecting roller 18, lthe first side of the band is now coa-ted with a synthetic material, which, during the further travel through the connecting tube 9, is hardened or polymerised by the aid of the heating device 32 therein. Then in the treatment vessel 3 the coating of the second side of the band with synthetic material is effected as it passes round the delecting roller 15, the hardening or polymerisation being eifected in the succeeding connecting tube 10. By the upper deflecting roller .19 the band 12 is deflected downwards again, and dips, in the connecting tube 11, into the liquid seal of the liquid-container 4. After deflection of the band by the lower reversing roller 16, journalled in the liquid container 4, the band then leaves the apparatus through the open tubular member 4a to be guided away over the band exit roller 21.

Immediately before the

coating appliances

27, 28 that apply the coating of synthetic material, further heat-radiating devices m-ay be Iprovided, for the purpose :of transiently softening by heat the adhesion-promoting coating already applied. A bet-ter adhesion of the layer of synthetic material can be obtained in this way, according to the consistency of the coating substances.

I claim:

1. Apparatus for applying thin synthe-tic coatings to metal bands and hardening the coatings, comprising: a closed liquid container formedwith an inlet for the band to be coated, a closed liquid container formed with an outlet for the coated band, treatment vessels located between the two liquid containers and at the same level, a vacuum tank located above the liquid containers and treatment vessels, a connecting tube extending upwards from each liquid container to the vacuum tank, two connecting tubes extending upwards from each treatment vessel to the vacuum tank, reversing rollers so a-rranged in the liquid contaliners, treatment vessels and vacuum tank that a band entering the first liquid container through the band inlet can pass round the reversing rollers and through the liquid containers, treatment vessels, vacuum tank and connecting tubes in a plurality of vertical loops to the band outlet, means ttor exhausting air from the vacuum tank,

the treatment vessels and the tubes connecting them w-ith one another, means in the treatment vessels for -applying a solution of synthetic coating material in an atleast semiliquid condition to that side of the band tha-t does not come into contact with the rollers therein, means in the vacuum tank for applying synthetic coating material in an at semi- Iliquid condition to that side of the band that does not come into contact with the reversing nollers in the vacuum tank, and means in the connecting tubes .for heating that side of the band which in each case yhad not come into contact with the preceding reversing roller.

2. Apparatus for aplyin g thin synthetic coatings to metal bands `and hardening the coatings as claimed in claim 1, the heating means in the connecting tubes being infra-red radiators.

3. Apparatus for applying thin synthe-tic coatings to metal bands and hardening the coatings as claimed in claim 1, funther comprising: cooling means for condensing the vapours of the solvent removed from the synthetic coating by the heating means, and discharged pipes for removing excess condensed solvent from the treatment vessels without disturbing the vacuum therein.

4. A method for the bubble-free application of thin coatings of :synthetic material, in a continuous operation, to -a continuously advancing metal band, and for the rapid hardening of the coatings applied, comprising: bringing the synthetic material into an at least semi-liquid condition by means of a solvent, applying this semi-liquid material to the band ina partial vacuum, hardening or polymerizing the coating so applied, still in a partial vacuum,

- the height of the vacuum being such that the vaporization temperature of the solvent is at about room temperature, and replacing the heat of vaporization, which is withdrawn from the synthetic material in the vaporization of the solvent, by thermal radiation from an external source.

References Cited by the Examiner UNITED STATES PATENTS 987,629 3/191'1 Ketchson 117-61 X 1,069,033 7/1913 Rowland 118-61 1,322,327 11/1919 Minton. 1,331,729 2/1920 Taylor 117-61 1,595,236 8/1926 Minton 117-61 1,595,475 8/ 1926 Minton 117-61 2,137,256 11/ 193 8 Waldron 117-6-1 X 2,346,523 4/ 1944 Vincent 117-61 2,894,483 7/1959 Stahl 118-50 2,937,108 5/1960 Toye 117-119 X MURRAY KATZ, Primary Examiner.

JOSEPH B. SPENCER, Examiner.

Claims

1. APPARATUS FOR APPLYING THIN SYNTHETIC COATINGS TO METAL BANDS AND HARDENING THE COATINGS, COMPRISING: A CLOSED LIQUID CONTAINER FORMED WITH AN INLET FOR THE BAND TO BE COATED, A CLOSED LIQUID CONTAINER FORMED WITH AN OUTLET FOR THE COATED TREATMENT VESSELS LOCATED BETWEEN THE TWO LIQUID CONTAINERS AND THE SAME LEVEL, A VACUUM TANK LOCATED ABOVE THE LIQUID CONTAINERS AND TREATMENT VESSELS, A CONNECTING TUBE EXTENDING UPWARDS FROM EACH LIQUID CONTAINER TO THE VACUUM TANK, TWO CONNECTING TUBES EXTENDING UPWARDS FROM EACH TREATMENT VESSEL TO THE VACUUM TANK, REVERSING ROLLERS SO ARRANGED IN THE LIQUID CONTAINERS, TREATMENT, VESSELS AND VACUUM TANK THAT A BAND ENTERING THE FIRST LIQUID CONTAINER THROUGH THE BAND INLET CAN PASS ROUND THE REVERSING ROLLERS AND THROUGH THE LIQUID CONTANERS, TREATMENT VESSELS, VACUUM TANK AND CON-