US3157528A - Apparatus and method for cast coating sheet material - Google Patents

Description

APPARATUS AND METHOD FOR cAsT COATING SHEET MATERIAL Filed oct. 5. 1951 G. A. sTRAHL Nov. 17, 1964 2 Sheets-Sheet 1 Nov. 17, 19.64 G. A. sTRAHL 3,157,528

APPARATUS AND METHOD FOR CAST COATING SHEET MATERIAL Filed Oct. 5. 1961 2 Sheets-Sheet 2 HOLD DOW/V SSEMBL Y FIG.3

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United States Patent O 3,157,528 APPARATUS AND PJETHGD FR CAST CA'HNG SEEE? MATE George A. Strahl, St. Louis, Mo., assigner to Crown Zellerbach Corporation, San Francisco, Calif., a corporation of Nevada Filed Get. 5, 1%1, Ser. No. 143,190 6 Claims. (Cl. 117-64) This invention relates to an improvement in the art of cast coating wherein fluid coating compositions are ap plied to discrete blanks of sheet material and then solidilied in contact with a casting surface to obtain` a desired finish on the coating after solidication thereof.

The art of obtaining specific surface finishes on coated paper material by means of cast coating is described in Patent No. 1,719,166, dated luly 2, i929, to Eradner. Bradner teaches us that duid coatings maybe solidied in contact with a casting surface, either by chilling in the case of thermo-plastic coatings or by heating in the case of liquid coatings having a volatile carrier. Braclner teaches us further that an essential feature of the cast coating art is that the coating after solidilication must be substantially non-adherent to the casting surface otherwise the coating would be imperfect. A further contribution to the cast coating art is shown in Patent No. 2,437,492, dated March 9, 1948, to Allen. Ah apparatus therein disclosed provides an endless belt in generally horizontal disposition wherein the top surface of the belt may be heated or chilled by an underlying tanks or troughs of water or other suitable liquid heat transfer agents. Materials deposited on the belt surface are solidified thereon.

This apparatus is particularly adapted to the cast coating art and an example of a similar apparatus is shown in the Patents No. 2,892,735, dated lune 3G, 1959, and

2,982,245, dated May 2, 1961, to Curler et al. These patents are directed particularly towards a solution of the problem of obtaining release of discrete paperboard blanks from a casting surface after suitable solidiiication of thermoplastic coatings. The method therein disclosed provides coatings having a determined adhesion to the casting surface whereby the coated blanks separate from the casting surface at the abrupt change in direction of the belt whereat the belt follows a curvilinear return path. There is further shown in these patents an air blast which is directed against the leading edges of the blanks as they separate from the belt at the curvilinear return path to assist in the removal of the blanks from the casting surface.

The known means for separating discrete blanks from casting surfaces also include the use of mechanical devices which have a sharp edge in close adjacency to the belt surface to catch a leading edge of the blank and plow it or lift it from the casting surface. This means, however, has not been entirely satisfactory in that such mechanical devices may either scratch highly polished casting surfaces or on the. other hand may scratch the coating and thereby defeat the purpose of the casting operation. Thebeforementioned Cutler patents, while avoiding this mechanical operation means, are necessarily limited to specific coating compositions which have the required adhesion to the casting surface. However, as the cast coating art is applied to ever expanding contr mercial applications it has been found that various coating formulations having special properties may not 'oe adjusted to the determined adhesion levels and therefore other means of interrupting residual adhesion to the casting surface me required.

The present invention provides a method and apparatus for solving the problem of interrupting a residual adhesion of a coated blank from a planar casting surface. This l Patented Nov. 17, i964 ICC invention more particularly provides for an air blast in closely spaced adjacency to the casting surface in acute angular relation thereto and directed at the casting surface adjacent the side edges of the successive passing coated blanks to interrupt the adhesion thereof. The invention further provides for means for maintaining the thus separated blanks in relative position on the advancing casting surface until they can be removed at the end of the horizontal travel of the belt into an orderly arrangement removed from the casting surface.

The present invention thus provides for positive release of discrete coated blanks from a planar casting surface without deleterious effect on either the finely iinished casting surface or to the nish imparted to the coated blanks. The invention is further adapted to high speed production and is relatively unaected by intermittent running and the resulting variables such as variance in temperature or compositions of the coating material or the temperature of the belt surface which has been a serious disadvantage of prior art methods and apparatus. In this connection it is well to note that in cast coating machines utilizing a continuous belt casting surfaces and having high production capacities, the retention of even a single blank on the casting surface tends to compound the diiliculty and results in annoying and costly work stoppage and the discarding of the resulting defectively coated blanks.

These and other objects and advantages of the invention will become apparent from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a vertical cross-sectional view showing a cast coating machine embodying the invention;

FlGURE 2 is an enlarged vertical cross-sectional view showing the disposition of the air jet nozzle in'relati'on to the planar belt surface and the blank retaining means;

FIGURE 3 is a top perspective view partially broken away to show the disposition of the air jet nozzle in relation to carton blanks in adhered relation to the casting surface;

FIGURE 4 is a cross-sectional view through a carton blank released from the casting surface by an opposed pair of air jets;

FIGURE 5, a cross-sectional view through line 5-5 in FIGURE 2, shows the initial stage of the separation of a blank portion by an air jet directed adjacent one edge thereof.

Referring now to the drawings in detail, the complete cast coating machine embodying the invention is shown in FIGURE 1 where cut and scored discrete paperboard blanks 20 are positioned in stacked relation on a conventional blank feeding apparatus 21 Which successively feeds the bottom blank from a stack into a coating applicator 22. The coating applicator may be of any conventional type, a spray type applicator being diagrammatically shown in the drawing wherein a coating of molten wax composition is sprayed on the applicator rolls 23 and thence transferred to the successive blanks 2l). Metering rolls 24 remove excess coating as the blanks are projected from the coating applicator 22. Alternatively, the coating may be applied by a system of pick-np, transfer and applicator rolls; or by dipping in a fluid coating compositionv and passing through suitable metering means such as paired rollers or doctor blade. The important factor in the coating application being that the coating must be applied and maintained in a fluid or plastic state until the blank 2t) is pressed into intimate contact with the casting surface.

After the blanks are coated with a molten composition, which for example may be a thermo-plastic wax composition, the blanks are fed onto the casting surface at the feed end 25 of the continuous casting belt 26 with the at Vfor imparting the desired finish to the particular coating composition in use, but in the case of thermo-plastic wax belt is preferably stainless steel which is highly vpolished to provide a specular finish. Stainless steel is durable and provides desirable high heat transmission characteristics. One of the sheaves'is power driven to motivate the casting belt 28.

An ironing roll 31 is rotatably positioned over the feed end 2S of the casting belt upper surface 29 and rmly Vstantv pressure under varying conditions. The ironing roll 31 adjustment means 32 may be spring loaded having a springY 33 responsive to the threaded shaft 34 which imparts the desired pressure and spacing to the ironing roll shaft 35. The ironing roll 31 is further provided with a heating means to insure that the thermo-plastic coated blanks will have a greater adherence for the casting belt which is chilled, as described'hereinafter, than for the ironcompositions wherein a high gloss finish is desired, the Y Y supported on a frame not shown. Sheave 4S. is Vdriven to provide substantially synchronous movement of the holding roll. .The heating means, not shown, is preferably internally operative in the ironing roll 31 and may be a circulatinghot oil system having external heating and pumping means, the oil being circulated through the ironingy roll by means of ports in the ends of the ironing roll shaft 35. The temperature is maintained above the melting point of the thermo-plastic coating. YIt is to be noted further that the blanks 20 emitting from-the coating applicator 22 are projected initially against the lower portion ironing roll and thence .almost instantaneously downward onto the casting surface 29. This prevents a sliding action of the blank 2Q bnfthe'casting surface 29 which may be deleterious to the finished coating.

Y' A heat transmitting means is disposed subjacent the casting belt upper surface 29. and comprises troughs 36 wherein is disposed pipe conduits 37 for circulating aYV liquid heat transfer agent ksuch as water. vIn .this case'the water is cooled by refrigerant means not shown and circulated through the conduits 37 to maintain-the water in the troughs and adjacent the belt within a desired temperatureV range. 'In the case of thermo-plastic coatings the temperature range, of course, must be maintained at a lower temperature than the solidiiication temperature of the thermo-plastic coating. A trough 36 and conduit 37 assembly may correspond in length to the belt upper surface 29 intervening theV sheaves 27 and 28, but preferably two or more troughs, as shown, and included cooler cir- Y culation means are used."V It has been found that aiirst 'if closely tothe width'of thecasting surface belt 25. The

belt 26 in passing over the-'troughs 36 is in contacting relation with Vthe upper edges38 of the Vtroughs 36 and the chilled water being under vpressure is presented against Vthe bottom facing of the belt upper surface 29fetfectively vmaintaining the desired temperature-thereof. Previsioni for overliow is providedalongthelongitudinal side edges of the troughs 3d, whereby the excess coolant may be recirculated through the refrigerant' means 'and then returned to the trough 36 through `the conduit orifices 39.

Along the .planar surfaces of the casting belt 26 'adwilibe described hereinafter inmore particular detail.

The carton blank hold-down assembly 42 is disposed over the casting belt concurrent with the air nozzles 40' and comprises an arrangement of one or more belts 43 linearly aligned with the direction of movement ofthe casting Y i belt 26 and mounted on sheaves 44 and 45. The sheaves, as best shown in FIGURE 3,"extend the full width of the belt 26 andare rotable about Vtheir respective shafts 46 down belts 43 and the casting belt 26. This may beconveniently accomplished bythe provision of a protrudingV Y flange on thedriven sheave 45 in contacting relation with the longitudinal rmargin of the casting be1t2'6. The holddown belt sheaves 445are otherwise spaced from the casting belt to permit slight upward movement of the blanks 2li to attain complete .separation thereof from the casting surface 29 and yet retain complete ycontrol and relative disposition ofthe individual-blanksjon the casting belt. Hold-down belt tensioning means 47 are pivotally mounted to a frame and weighted to provide theV desiredY degree of tension. After release from the castingbelt upper surface 29ftl1e blanks are retained ,in relative positionV on the casting surface andare transported by frictional engagement with the casting beltsurface 29 and the hold-down belts 43 outwardly to the take-off end 4l.` of the casting'belt 28. Y i

The blanks 2i) are successively projected onto. an inclined collector belt 48 rotably mounted on sheaves 49-50. The collector' belt may be synchronized to the speed'of the casting belt to receive the blanks 20 in spaced relation thereon so that may be ejected into straight stacking relation as shown at 7i). Other conventional collecting andv stacking means may be used.V

The hold-down assembly 42 is shown injenlarged view i in FIGURE 2. YIt may be kseen that the hold-down belt 43 Y are in closely spaced adjacency to the upper surface 29 of lateral width, but at the same time Vsaid blanks must be l Y restrainedunder'control,and theutter dampened to jacent the take-off end 4I there is disposed one or more v air jet nozzles dil which are precisely related tothe casting Y surface 29 and to the adhered carton blanks 20 thereon as minimize displacement ofthe blanks on thelcasting sursurface. This arrangement thus permits orderly collect-` ing and stacking of the blanks as they'pass from the take- Volf end 4l of the casting belt. The belts of course are Eo disposed laterally of the casting belt 26 that theyV koverlie Y the carton blanks to accomplish the desired purpose as best shown in FIGURE 3.

Y FIGURE 3 shows a preferred commercial embodiment of the invention wherein the blanks, depending on their overall size, may be disposed in two or more longitudinally aligned lines on theY casting surface to obtain Vmaximum utilization of the casting surface available width and consequently maximum production.V The blanks 20 as they.

progress Vfrom the feed end 25 Yof the casting machine and prior to passing the release station 50 at the lair nozzles lil are substantially adhered to the belt surface 29. TheL air jets 51 are directed from the nozzles 40 which are f connected by piping 52 to suitable' air'supply. The'oriiic'e l53 1n each nozzle may be of varied shape, as for'exarnple,

a circular opening approximately '3&4 inch in diameter with a4() pound pressure air supply. The air blast-51v is di- Vrected at the casting surface 29 adjacent the longitudinally aligned edges 54 of the blanks 20 in an acute angular rela-V tion toV the belt'surface 29' preferably in Vthe range ofVVV 15-45 degrees. Here the longitudinal aligned edges are Y to be understood as those parallelV to the direction of travel u 29 and fans out in a deltoid manner intervening the blank edges and the casting surface 29, lifting the same, and progressing inwardly throughout the lateral width of the blank.

The arrangement of the air jets must be adjusted t conform to the particular blanks being cast coated. This may be accomplished by mounting the piping 52 on a lixedly positioned mounting bar-S, not shown, extending across the width of the casting belt 2e in vertically spaced relation thereto. Certain carton blanks which have a flexible protruding free edge portion 56, along the leading edge thereof, which may tend to adhere to the casting surface, can be speciicially provided for by the addition of an intervening nozzle 57 which will serve to break the adhesion of this carton blank portion. Even through this interevning nozzle 57 necessarily exerts downward pressure on the top surface of the blank as the blank passes thereunder it does not interrupt the action of the nozzles disposed adjacent the side edges 54 of the blank and complete separation of the blank is attained. Thereafter, while the blanks are completely separately from the casting surface they are retained in relative position and passed under the driven sheaves and outwardly of the take-off end 4i of the casting belt 26 as before described.

As best shown in FIGURE 4 the blanks are completely separated from the casting surface 29 by the intervention of the air blast 51 between the blank 2t? and said casting surface, but the blanks 2t? are prevented from displacement from their relative position on the casting surface 29 by the hold-down belts 43. The characateristic action of the blank at this point is a fluttering action rather than a sustained disposition against the belts 43 and after passing the turbulence of the release station Sii said blanks are propelled by frictional engagement with the casting surface 29 and the belts 43. The air blast being directed in acute angular relation to the travelling planar surface of the belt fans out in a sharp edged layer on the belt surface 29. This air blast 5l engages the blank edges 54 or protruding portions 56 lifting the same and thence intervenes the edge of the blank and casting surface 32 as shown in FIGURE 5. This provides a substantial and positive force for breaking the residual adhesion of the coated blank to the casting surface Without impairment of the nish imparted to the coating thereon. Thus the blanks are progressively separated from their leading edge continuing to their trailing edge and inwardly from the side edges towards the center or opposite side thereof.

This invention, While being described particularly in respect to a cast coating machine particularly for thermoplastic coated breboard blanks, may obviously be adapted to cast coating of other comparable materials and various types of coatings or solid materials solidified on a casting surface which is heated or chilled to solidify such material as the case may be. This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of disclosure, which do not constitute departures from the spirit and scope of the invention.

What I claim is:

1. The method of cast coating discrete blanks of paperboard material comprising the steps of applying a plastic coating to a succession of discrete blanks, placing the coated blanks into contact on a continuons moving casting belt having a generally horizontal upper surface terminating at opposite ends around circular rotating means, advancingthe casting belt and blanks thereon until the coating is substantially solidified, releasing the blanks upwardly from the horizontal surface of the casting belt by means of one or more high velocity streams of air directed at a margin of said blank at an acute angle to the t belt and in normal relation to the direction of travel thereof, restraining the separated blank from unrestricted displacement from the belt, returning the blank to the horizontal moving belt, moving said separated blank on said belt to the curved end portion thereof where said blank is permanently separated from said belt.

2. ln a cast coating machine for discrete blanks having means for applying a coating to the discrete blanks, means for continuously advancing a casting surface in a horizontal linear path, means for impressing the coated blanks in intimate contact with the casting surface with the side edges of the blanks in substantial alignment with the direction of travel of the casting surface; the improvement comprising means for interrupting the residual adhesion of the coated blanks lto the casting surface comprising at least a pair of air jets oppositely directed and inclined to the casting surface in the linear path thereof at an included angle of about 15 45 said air jets disposed in substantially normal relation -to the direction of travel of the casting surface and impinging thereon in zones adjacent the side edges of the coated blanks and towards said edges, means adjacent the air jets to engage the upper surface of said released blanks for retaining the blanks in relative position on the casting surface after the adhesion is interrupted, and guide means for removing the4 blanks from the casting surface.

3. ln the cast coating machine described in claim 2, the further improvement wherein the means for retaining the blanks comprises longitudinally extending members overlying the blanks and in closely spaced relation to the casting surface.

4. The retaining means in claim 3 wherein the longitudinally extending members comprise belts driven in substantially synchronous movement with the casting surface.

5. ln a machine for cast coating thermo-plastic coated discrete blanks inrsuccession, ythe machine having a continuous advancing belt casting surface disposed in extended horizontal relation with the upper portion providing an essentially planar casting surface and a lower portion following a return path, said upper casting surface having means for chilling the same to solidify the thermo-plastic coating, means for interrupting the residual adhesion of the coated blanks to the casting surface after substantial solidication of the coating comprising at least a pair of air jets oppositely directed and inclined in acute angular relation to the casting surface, said air jets inwardly directed in substantially normal relation to to the direction of travel of the casting surface and irnpinging thereon in zones adjacent the side edges of the successive blanks, means for retaining the blanks in relative position on the casting surface after separation there-V 1,606,554 Wycherley et al. Nov. 9, 1926 2,261,972 Matthews Nov. 11, 1941 2,270,038 Corbin Ian. 13, 1942 2,517,388 Daves Aug. 1, 1950 2,805,898 YWillis Sept. 10, 1957 2,892,735 Curler et al lune 30, 1959 3,013,900 Yezek et al. Dec. 19, 1961

Claims (1)

1. THE METHOD OF CAST COATING DISCRETE BLANKS OF PAPERBOARD MATERIAL COMPRISING THE STEPS OF APPLYING A PLASTIC COATING TO A SUCCESION OF DISCRETE BLANKS, PLACING THE COATED BLANKS INTO CONTACT ON A CONTIMOUOUS MOVING CASTING BELT HAVING A GENERALLY HORIZONTAL UPPER SURFACE TERMINATING AT OPPOSITE ENDS AROUND CIRCLAR ROTATING MEANS, ADVANCING THE CASTING BELT AND BLANKS THEREON UNITL THE COATING IS SUBSTANTIALLY SOLIDIFIED, RELAEASING THE BLANKS UPWARDLY FROM TE HORIZONTAL SURFACE OF THE CASTING BELT

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