US3603286A

US3603286A - Coating apparatus

Info

Publication number: US3603286A
Application number: US861528*A
Authority: US
Inventors: Howard A Scopp; Thomas F Sincock
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1969-07-30
Filing date: 1969-07-30
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07

Abstract

An apparatus for applying a liquid sealant coating to the surface of a package by forcing it from a reservoir through a porous distributing applicator onto the surface.

Description

0 United States Patent 1 3,603,286

"31 lnwmnn Howard A. Scopp 1561 References Cited H UNIThDSIATES PATENTS p 2543.041 2/1951 Murray 118/401 x 1 2800.881 8/1959 Barfl5c1 111 118/264 )1 gl' :32} 3 35 32 3.041.833 12/1961 Lee 118/264ux S N 66048 A 4 9 7 3.059.393 10 1962 Allied 1. 55/523 )1 s d 'E 6 3.097584 7/1963 Wright..1r 118/266 x 1/1] .iti nun pt. .1 C 3,152,011 10/1964 Gerard 118/211 I 1 Amgn "f 3,201,275 8/1965 Herrick 118/401 x 3.362.640 1/1968 Fainman 1. 222 189 x 3,463,322 8/1969 Gcrarde 3. 222/189 X Primary Examiner-Morris Kaplan Atl0rr1ey.1"---MichaelJv Murphy. James C Logomasini and (54) COATING APPARATUS Herbe" B Roberts 3 Claims, 1 Drawing Fig.

[52] U.S.C1. 1 1 3 1 1 1 1 3 118/64, 118/410 [5 I lnl. C1... B051: 11/10 ABSTRACT: An apparatus for applying a liquid sealant coal- [SOI Field of Search H 1 18/401, ing to the surface of a package by forcing it from a reservoir EFSSURIZED through a porous distributing applicator onto the surfacer PATENTED SE? 7 l9?! QmNEDmmmmm INVENTORS. HOWARD A. SCOPP B THOMAS E SINCOCK W ATTORNEY COATING APPARATUS This is a division of copending application Ser. No. 660,482, filed Aug. l4, I967.

This invention relates to sealed food packages and more particularly to an improved apparatus for applying a liquid sealant to the surface of a package prior to sealing.

Cottage cheese, margarine, butter, fruit salad and other comestible items are normally marketed in a package in the form of a plastic receptacle, or wax coated or impregnated paper container having a lid of similar material which is sealed to the receptacle body so as to minimize the entry of air, or the escape of liquids and gases from the closed package through the sealed joint. Whether or not a hermetically sealed joint is adequate for storing foodstuffs without ingress or egress of moisture through the joint is largely dependent on the quantity and distribution of the amount of sealing material on the package surface. Too little results in a leaking joint, variable thickness will result in squeezing, or a cracked seam, and also leaking.

The industry has in the past had difficulty in consistently depositing an adequate and uniform thickness of adhesive or sealant on a container lid which will effectuate the desired protection of the contents of the assembled package along the seal line, yet which dries in a minimum of time, as required for an economical, continuous sealant application process. in known methods, multiple step offset techniques are generally utilized. These involve passing revolving pickup cylinders into a reservoir of the sealant in order to deposit the liquid on the cylinders, applying the liquid to a plate or other roll from the pickup rolls after removal from the reservoir, followed by final transfer of the sealant to the package surface. In order for the rolls to pickup adequate material to provide the desired coating thickness, a relatively viscous material is required so that the liquid will flow off the rolls or transfer plate by gravity prior to application to the package surface. When the sealant is a heat sealing composition, its solvent system must be generally composed of high boiling, nonvolatile type solvents in order to obtain this viscosity. Such high boiling solvents. however, are often incompatible with conventional packaging materials, require excessive drying times (-20 minutes) which are uneconomical in high speed mass production techniques, and leave a lingering, persistent odor deleterious to the comestible within the container. 0n the otherhand, when a low boiling solvent is used, evaporation occurs rapidly in an offset process, generally open to the atmosphere so that the application cylinders designed to function with a thin film of sealant thereon quickly become coated, gummy and inoperative.

Accordingly, it is a principal object of the present invention to provide an apparatus for the efficient, economical deposition of sealing material on a package surface.

It is a further object of the present invention to provide an improved apparatus for depositing a coating of liquid sealant on a container lid, which is to be thereafter placed across the mouth of a container.

It is a particular object of the present invention to provide an apparatus for applying a relatively thick, uniform coating of a heat sealing solution to the surface of a package to be hermetically sealed.

It is a further object of the present invention to provide a closed system for applying a volatile, fast'drying heat sealing solution on a container lid.

It is an additional object of the present invention to provide an apparatus for applying a relatively thick coating of a fastdrying, low viscosity, sealing composition in a single step, for a predetermined time interval, to the surface of a plastic package during a high speed manufacturing operation.

It is a still further object of the present invention to provide a liquid sealant application system having actuating means initiating almost instantaneous coating flow after indexing a package surface in sealant applying position.

lt is a further object of the present invention to provide an apparatus for solving the previously mentioned deficiencies in the prior art.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

These and other objects are accomplished by providing an apparatus for applying a liquid sealant to the surface of a package, by positioning the surface adjacent a porous applicator in communication with a sealant reservoir, and forcing the liquid from the reservoir through the applicator to distribute the liquid on the surface.

In describing the overall invention, reference will be made to a preferred embodiment illustrated in the accompanying drawing, in which:

The sole FIGURE of drawing is a schematic, partially sectioned, elevational view of the apparatus of the present invention.

With reference to the drawing wherein identical numerals refer to identical parts, there is shown in FIG. 1 a closed scalant reservoir 10 having a top wall 11, a sidewall 12, and a bottom wall [4. Fill nozzle 16 and pressurizing fluid entry port 18 are provided in top wall ll. Reservoir I0 is partially filled with liquid sealant 20. A plurality of passageways 22 are provided in the bottom wall 14 of the reservoir 10 connecting the inner surface 24 thereof with its outer lower surface 26. These passageways extend around the periphery of bottom wall 14 adjacent its junction with sidewall 12 of reservoir 10.

One piece, porous sintered metal applicator 28 is cemented at 30 and 31, along the inner and outer periphery of its upper face, to lower surface 26 of bottom wall [4, adjacent the outer edge of bottom wall 14, and in alignment with passageways 22. The pores in the sides of sintered metal applicator 28, parallel to the sidewall of reservoir 10 are closed off to prevent liquid flow therethrough so that the lower face of applicator 28 is the only exposed porous face through which liquid will flow when the applicator is assembled to reservoir 10 and pressurized. Any cement, for example an epoxy type adhesive, may be utilized to join the applicator to the reservoir, as long as it is compatible with the sealant flowing through the applicator.

Movable support means, comprising a conveyor or indexing table 32 are provided for transporting plastic container lid 34, and aligning and supporting channel 36 in lid 34 beneath reservoir 10, and the attached porous applicator 28. A fixed or movable backup member, not shown, may be used below the surface on which the lid rests, if desired, to provide additional support during the application step hereafter described. Ch annel 36 of lid 34 extends around the periphery of the lid and has a base 38 and short opposed, outwardly divergent sidewalls 40 and 42 extending up from the edges of base 38. Channel 36 is so positioned in lid 34 so as to fit over and enclose an upper rim portion of a container to which it will be later sealed. The width of the lower or outer face of applicator or shoe 28 is sized to fit within sidewalls 40 and 42 of channel 36. Applicator 28, likewise is shaped so as to be enclosable within channel 36 around the full periphery of cover 34 when lowered into application position, as hereinafter described and as schematically depicted in FIG. 1. Applicator or shoe 28 may, however, be formed into any shape depending on the contour of the package surface.

Forced hot air oven 44 is situated downstream of the sealant application station. Oven 44 has an inlet port 46, and an outlet port 48 through which passes endless belt conveyor 32. Forced hot air supply means are connected to oven 44 comprising fresh air entry port 50 in duct 54, which has an enlarged section in which heating coils 52 are mounted. Fresh air entering through inlet 46 is heated by passage across coils 52, leaves through discharge port 56 of duct 54, enters oven 44 and is distributed and directed downwardly through slits 58 at a minimum temperature of about F., and at a velocity through the oven of about 10,000 feet per minute. Spent air leaves oven 44 through the discharge outlet 60. Suitable conventional mechanical means such as a motor driven fan, not shown, are supplied for moving the drying air through oven 44.

ln operation, conveyor or indexing table 32 aligns channel 36 of lid 34 beneath applicator 28, which is initially situated above lid 34. The movable support means 32 is then stopped, and closed reservoir l and applicator 28 are reciprocated downwardly as shown in FIG. I by any suitable conventional activating means, for example, a hydraulically or pneumatically operated piston, not shown, so that applicator 28 fits within channel 36 of cover 34 and the lower, outer face of applicator 28 abuts against base 38 of channel 36 in lid 34. Valve 60 in pressurized fluid supply line 62 is opened either at this time, or shortly before, as the applicator approaches channel 36, either manually, or by other suitable automatic means such as a timed solenoid valve. When communication between line 62 and port 18 is established by opening valve 60, pressurized gas flows through entry port 18 into the open space of reservoir l0 above sealant 20. The pressure developed within reservoir I0 by the pressurizing fluid, such as air, bearing on the sealant liquid surface forces the liquid sealant through passageways 22 in the bottom wall of the reservoir, and then through the communicating pores of sintered metal applicator 28 toward the lower face thereof. When the liquid reaches the pores, or spaces between the metal particles of the outer, lower face of the high surface area sintered metal applicator, it contacts the base of channel 36 at numerous points, that is at essentially each minute area in the channel base which adjoins or is opposite a pore in the applicator surface. After a fraction of a second, valve 60 is closed off from the pressurized fluid supply source, and a suitable conventional vent valve, not shown, situated between the interior and exterior of reservoir is opened either manually or automatically to release the pressure within reservoir 10. The reservoir and applicator are then reciprocated upwardly, and as the outer face of the applicator shoe moves away from base 38 and out of channel 36, the sealant liquid preferentially wets and adheres to the plastic surface rather than the metal shoe surface because of its greater affinity for the plastic. An essentially complete transfer of sealant is thereby obtained, and undesirable dripping from the applicator surface is avoided when the depressurized applicator is moved away from the package surface. Pressure, at least not sulficient to cause flow through the outer face of the applicator, is not applied again to the sealant until the following lid is in place at the sealant application station. The conveyor is restarted at any convenient time after application, to transport cover 34 containing layer 64 of liquid sealant in channel 36 into forced hot air oven 44. The next cover is then indexed beneath the applicator, as previously, and another cycle is begun. The cover is passed slowly through oven 44 while supported on the surface of conveyor 32, wherein the liquid sealant 64 is dried to form a smooth coating within peripheral channel 36 prior to the point where the cover exits the over through discharge opening 48. The cover 34 with the dried sealant thereon is then removed from the conveyor either manually or by any conventional automatic means well known in the art. Typical forced drying times for lacquer type heat seal compositions applied at a wet thickness of about 0.5-5 mil are between about -50 seconds when exposed to drying air temperatures of between about 150 to 200 F., and air velocities of about 3,000 to [0,000 feet per minute. These conditions, however, may vary outside these limits depending on the solvents used in the sealing composition.

When the liquid sealant is a hot melt wax based material which is a solid at room temperature, heating means shown typically and schematically as heating coil 66 in reservoir I!) may be supplied to vary viscosity and maintain the sealant at elevated temperature and in liquid form prior to passage through applicator 28. Applicator 28 may likewise be required to be heated, for example, by resistance heaters surrounding and contacting the inner and/or outer sidewall surfaces to prevent setting up of the hot melt material in the pores of the applicator.

After the comestible being packaged is placed in the container by the vendor, lid or cover 34 is fitted over the container mouth either manually or by conventional automatic capping machines so that sealant layer 64 in lid 34 contacts a peripheral rim portion of the container being sealed. Conventional heat sealing equipment well known to those in the art is then utilized to heat activate coating 64, while forcing the lid against the container, to fuse the lid to the container rim and form the finished, sealed food package.

The above description and particularly the drawing is set forth for illustration purposes only and is in no way to be taken in a limited sense.

As mentioned previously, this invention is directed toward an apparatus for applying a liquid sealant to a package surface, by positioning the surface adjacent a porous applicator in communication with a sealant reservoir, and forcing the sealant from the reservoir through the applicator to distribute the liquid on the surface.

The bonding agents which may be applied by means of the present invention may be either pressure sensitive thermoplastics or other types of pressure sensitive adhesives, relatively nonviscous lacquer compositions having viscosities between about 5 to 2000 c.p.s., or hot melt adhesives which are normally solid at room temperature, and are liquids at elevated temperatures above about I50 F. Lacquer type heat activated sealants, dissolved in a volatile, fast drying solvent system, wherein the composition has a viscosity between about 10-100 c.p.s. are particularly adaptable for use in the present invention.

The amount of sealant required to achieve the desired seal strength varies with the weight of the members being sealed. Dry thickness of the above mentioned materials may readily be applied between about 0.1 to 25 mils and preferably between about 0.3 to l0 mils, which is that generally required to hermetically seal a food package.

When hot melt solutions are utilized, separate heating means must be supplied which otherwise need not be used. Utilization of hot melt materials, however, eliminates the need for a downstream drying step since the sealant sets up almost immediately upon exposure to the atmosphere. Obviously any conventional drying system may be utilized, e.g., radiant heating, convection or conduction systems. Forced drying may even be eliminated when lacquer type sealants are utilized, if high production rates are not required. In such cases, drying times at ambient temperatures, i.e., about 70 to [00 F. generally average about 10-15 minutes.

The porous applicator of the present invention may be constructed of a wide variety of materials as long as the pore size is maintained within the range of about [-500 microns and preferably between about 2-30 microns. Pore sizes in excess of about 500 microns generally result in poor application control because of appreciable gravity flow through the applicator, whereas pore sizes less than about 2 microns give the opposite effect, i.e., essentially no flow even at high forcing pressures.

The porous applicators herein described may be made of any metal such as aluminum, chromium, copper, iron, magnesium, nickel, platinum, tin, tungsten, zinc and the like, alloys such as brass, bronze, steel, stainless steel and the like, ceramics, refractory materials such as alumina, silica, silicon, carbide, tungsten carbide, zircon and the like.

In some applications a certain degree of resiliency may be desired in the applicator, whereupon a form of resilient plastic or other material comprising all or part thereof may be utilized. This may be desired, for example, when the package surface being coated has a series of minute corrugations. For example, an open cell foam plastic having adjacent communicating cells, as opposed to a closed cell material, or a felt wick secured between supporting plates could be used in such a case Sintered metal, particularly stainless steel or brass, is the preferred applicator material of construction, because of its durability and resistance to both chemical and mechanical wear in the present, rather severe, application. Sintered metals are comprised of fused metal powders with air spaces between the particles which form the pores, and are fabricated by conventional powdered metallurgy techniques. For example, ground or crushed metal may be comminuted to the desired extent according to the degree of porosity required. The particles are then thoroughly mixed with a fusible material, for example, powdered glass, and then bound together by fusion of the glass. Porous members may also be made by soldering aggregates of small metal balls of the size of buck shot, by sintering wire matrices, etc.

It should be noted that the porous applicator of this invention may be comprised of two or more layers of the same or different porous materials having the same or different pore sizes, though a uniform pore size is preferred.

The applicator may be of any size or shape, depending on the type of surface to which the sealant is being applied. For example, the applicator may be square, rectangular, round, oval, annular and the like, and may become a portion, or all of a wall of the sealant reservoir. It may be machined from fabricated stock, or when sintered metal is used it may be formed to the shape desired by initially pressing it into shape in a mold and then sintering.

It has also been desirably found that on fabricating a sintered metal applicator from stock and machining it to match the desired contour of the package surface to which the sealant is being applied, the pores in any desired surface portion of the applicator are readily sealed shut by the cutting and machining operation, e.g., by a milling machine. The liquid, therefore, may be directed through selective portions only of the applicator. This affords a particularly simple and useful technique for preventing material from flowing out through the sides of the applicator when flow between the top and bottom faces only is desired, and for conserving sealant material in certain cases where a full peripheral seal may not be desired, in that the sealant need only be applied at selected areas around the lid periphery. Other means, however, may be used for masking off particular portions of the applicator surface.

Application of the sealant to the package surface according to the present invention occurs essentially by a wetting technique, and is dependent on a relationship between the sur face tension of the liquid sealant and the respective surface energies of the applicator and package surface. The surface tension of the liquid sealant is preferably less than or equal to the surface energy of the package surface, and greater than the surface energy of the outer face of the porous applicator. Under these conditions, the liquid sealant preferentially wets and is transferred to the package surface when the applicator and package surface are moved apart, because of the surface tension forces of the liquid, as opposed to being retained on the applicator surface. With an organic liquid sealant, a plastic package surface, and a metal applicator, the sealant preferentially wets the plastic because of its greater affinity for it, than for the metal shoe.

Though it is possible to stop the shoe and surface short of actual contact during application of the sealant, this is difficult to mechanically achieve consistently because of the minute spaced between the surfaces. It is preferred that the applicator, and most preferably the surface of the applicator from which the material is being distributed, contact the package surface during the sealant application step. Perfect and complete contact between the two surfaces is often not possible because of imperfections in the applicator and/or package surface, and slight flow from the pressurized applicator may occur onto the package surface in these areas under these conditions.

The porous applicator of the present invention may be considered as a fixed resistance to flow of liquid sealant, positioned between a sealant supply and the surface upon which it is desired to apply the sealant. Characterizing the applicator in terms of the magnitude of this resistance, it can be said that it must be at least sufficient to prevent sealant flow through it at pressures on its upstream face (i.e., that closest to the sealant supply) above atmospheric pressure. For the ranges of sealant viscosities and pore sizes used in the present invention, the

pressure drop across the porous applicator is generally between about 0. l-l00 p.s.i.g., and preferably between about 0.5-] O p.s.i.g.

The magnitude of the pressure necessary to force the seal ing composition through the porous applicator, is governed by the character of the sealant and of the type and size of the ap plicator and may be applied to the sealant in a variety of forms. In addition to forcing by the application of pressurized gas above the liquid level, alternative pressure means may include a mechanically reciprocating piston, the intermittent imposition of the liquid discharge head of a pump on the surface of the liquid sealant, wherein the pressurizing liquid is lighter (i.e., has a lower specific gravity) than the sealant or by gravity flow by intermittent exposure of the sealant to an open constant liquid head above the sealant. Conventional automatic control systems may be used with all techniques described herein.

The time during which pressure is exerted on the sealant to force it through the applicator, obviously determines the thickness of the coating which will be applied to the package surface. With a pressure range of between about 05-10 p.s.i.g., an applicator pore size of between about 2-30 microns, a sealant viscosity of between about 20-150 cps., and an applicator thickness in a direction parallel to flow of between about one-sixteenth inch to 1 inch, the time required for exposure of the liquid to the pressurizing means to provide wet thicknesses of between about 0.001 to 0.003 inch of heat activated coating is between about 0.25 to [.5 seconds.

The useful thickness, i.e., flow path of the applicator may also be varied widely to suit particular needs. In general, any thickness in excess of that approaching the particle size of the material is adequate and preferably for pore sizes between about 2-30 microns the applicator flow path must be between about one-fourth inch to 1 inch or otherwise insufficient resistance to flow and undesirable dripping will result.

Though the apparatus of the present invention has been described as used in sealing any shape of lid to the mouth ofa container, it is likewise broadly applicable to application of sealant to any package surface which is to be sealed to another surface. Thus, the invention is useful in securing coatings and linings to all types of packages, in securing closures to bottles as well as to securing portions of the same package to each other, e.g., sealing bags, pouches, envelopes and the like.

in a preferred form of the present invention, the porous applicator is contoured to contact the groove or rim of either of the contacting surfaces of the lid or container, to provide a defined layer of sealant material at the exact portion of the package where scaling is necessary. In operation, the spon sored applicator will apply the optimum quantity of sealant composition to the desired location on the package within a cycle time consistent with high speed operations. In a more specific embodiment of this invention, the porous applicator is formed in the shape of a substantially annular ridge or shoe designed to intermesh with a peripheral groove or sealing zone of a package having a sealant confining width of between about (H to 0.4 inch in order to deposit a layer of sealing material on a dry basis of from 0.3 to 25 mils thickness within the specifically defined groove, which after contact with the other portion of the package is sufficient to seal the package without excess sealant flowing beyond and outside the seal area. In the preferred operation, a plastic lid having the above mentioned groove therein is indexed in exact sealant applying position so that the substantially annular shoe fits into place within the groove in a single downward stroke in a high speed operation.

Because of the simplicity of the apparatus involved, the sealant application steps of the present invention may be readily incorporated into a conventional lid and container thermoforming production line without requiring expensive equipment modifications. Multiple sealant application stations may be provided, each having its separate sealant reservoir, reciprocating adjacent a support for a multitude of sealing surfaces. Alternatively, a single reservoir feeding individually movable application shoes, having a quantity of sealant on the side of the applicator opposite to that adjacent the package surface may be provided. It is likewise within the purview of the present invention to maintain the shoe stationary during application and move the surface into it, as well as the reverse operation previously described. The sealant may be applied to the surface of either the lid or the container, either before or after the article forming step, or before or after the step of trimming scrap from the formed parts. it is preferably applied, however, to the container lid and prior to the trimming step.

By means of the present invention a simple, compact, versatile system is provided for applying a wide range of thicknesses of liquid sealant in a single step to package sur' faces which are to be sealed. By merely regulating the pressure used to force the sealant through a porous applicator flow resistor having a fixed pore size and/or the time during which the sealant is exposed to the pressure, the thickness of sealant deposited on the package surface may be widely varied to suit the requirements of the particular comestible being packaged. A single system may be used to accommodate sealants of widely different flow characteristics. The closed system wherein the outer surface of the applicator is the only surface of the system exposed to atmosphere having the sealant thereon is especially useful with sealant compositions in a low boiling solvent systems which evaporate rapidly on exposure to the atmosphere and may be flammable.

Various other modifications and alterations will be readily suggested to persons skilled in the art. It is intended, therefore,

that the foregoing be considered as exemplary only, and that the scope of the invention be ascertained from the following claims.

What is claimed is:

1. Apparatus for applying a liquid sealant to the surface ofa container lid comprising:

a. a closed reservoir containing the sealant, having a bottom wall with a plurality of passageways joining its inner and outer surfaces;

b. a sintered brass applicator shoe having a pore size of between about i to 500 microns shaped to match the contour of the container lid and aligned with said passageways, said shoe being secured around the periphery of its upper face to the outer surface of the bottom wall ofsaid reservoir;

c. reciprocating means for bringing a surface of said shoe into contact with a surface of said lid;

d. pressurized fluid supply means in communications with the interior of said reservoir above the liquid level for forcing the sealant through the applicator onto the surface of the container lid; and

e. means for positioning said lid and applicator adjacent each other.

2. The apparatus of claim I including heating means in the sealant reservoir.

3. The apparatus of claim 1 including forced hot air drying means downstream of said applicator.

Claims

2. The apparatus of claim 1 including heating means in the sealant reservoir.
3. The apparatus of claim 1 including forced hot air drying means downstream of said applicator.