Abstract:
A PVC film cover is provided including a down and interned marginal portion terminating in a thickened bead, the marginal portion tapering in thickness from the bead toward the central body portion of the cover. 
     The cover is produced through the use of a shape-conforming mold into whose central portion liquid PVC is dispensed while the mold is rotating. The liquid PVC moves over the mold surfaces outward toward the outer marginal portion thereof by centrifugal force and rotation of the mold is terminated and the mold is quickly inverted into a downwardly opening position whereupon the excess liquid PVC at the outer periphery of the mold flows slowly down to a reversely turned edge for forming the bead of the cover. In quick succession, the mold is heated in order to gel and then harden the liquid PVC, mold is cooled and the cover is thereafter removed from the mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a division of application Ser. No. 08/768,629 filed Dec. 18, 1996 now U.S. Pat. No. 5,932,163 
    
    
     STATEMENT REGARDING FEDERAL SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a thin film cover constructed PVC and more specifically to a cover which is approximately 0.0025 inches in thickness throughout a major portion of its plan area, but which includes an open mouth portion defined by a considerably thickened rim or bead and an adjacent marginal portion which tapers in thickness from the bead toward the main body of the cover. Also disclosed is a preferred method for forming the cover. 
     2. Description of Related Art 
     The following prior U.S. Patents disclose articles which are coated through the use of methods which are somewhat similar to the method disclosed in the instant invention: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 2,009,629 
                 2,047,691 
                 2,368,046 
               
               
                 2,442,179 
                 2,569,852 
                 2,770,557 
               
               
                 2,950,990 
                 3,146,873 
                 3,506,431 
               
               
                 3,389,070 
                 3,530,825 
                 3,870,015 
               
               
                 4,101,925 
                 4,148,942 
                 4,201,149 
               
               
                 4,392,805 
                 4,416,213 
                 4,434,113 
               
               
                 4,590,094 
                 4,601,923 
                 4,659,522 
               
               
                 4,680,149 
                 4,794,977 
                 5,040,590 
               
               
                 5,098,628 
                 5,238,878 
                 5,250,116 
               
               
                 5,393,215 
                 5,453,230 
                 5,468,324 
               
               
                   
               
             
          
         
       
     
     However, the coated articles disclosed by the above-noted patents, the articles formed in part by coating and the methods involved in the above-noted prior patents are not equivalent to the article of the instant invention or the method utilized in forming the article. 
     SUMMARY OF THE INVENTION 
     The article of the instant invention is similar to the apparatus or lid disclosed in U.S. Pat. No. 4,901,881 in that it is designed for use as a closure. However, U.S. Pat. No. 4,901,881 discloses a closure formed of a latex elastomeric material and which must be formed utilizing a method which is considerably different from the method by which the closure of the instant invention is formed. 
     The cover of the instant invention is formed of polyvinyl chloride compounded to provide a material which is highly flexible, relatively non-flammable, hard-wearing and resistant to water and corrosion. Polyvinyl chloride is an ethanoid polymer produced as a fine white powder by both emulsion polymerization and suspension polymerization of the gas, vinyl chloride, when liquified under nitrogen pressure. The terms “PVC” and “vinyl” are commonly used with reference not only to the polymer, but to all materials of which polyvinyl chloride is a constituent. PVC composition are prepared by hot mixing the polymer with plasticizers and small proportions of stabilizers, stearate lubricants, and coloring materials to give materials of a wide range of hardness, from rigid (with little or no plastizer) to very soft (equal proportions of plastisizers and polymer), and in a wide range of colors, as well as crystal clear. 
     The polyvinyl chloride utilized in producing the cover or article of the instant invention is termed as a plastisol thermosetting plastic. Once compounded, plastisols need heat to transform them into a solid. They usually are placed in molds and as the heat increases, the plastisol passes from a liquid, through a gel phase and finally becomes a solid. Heat is then continued to cure the solid mass and give it its final properties. 
     The latex elastomeric material utilized in producing the cover disclosed in U.S. Pat. No. 4,901,881 may have minute particles of latex rubbed therefrom by friction and there are many potential environmental uses for a flexible cover and the like for which a latex elastomeric material is not desirable because of the possibility of contamination by minute particles of latex rubber when covers of this material are used. 
     Plastisols, on the other hand, when properly compounded and cured, are reasonably elastic, highly tear-resistant, pliable, and relatively soft to the touch without being excessively resilient. It is also pointed out that the polyvinyl chloride cover of the instant invention may be formed in generally one-half the time required to form a similar cover constructed of a latex elastomeric material, in that the latex elastomeric material requires a considerably longer curing time. 
     The main object of this invention is to provide a flexible cover which will have many uses. 
     Another object of this invention, is to provide a flexible cover which will be at least somewhat elastomeric, thereby enabling a cover, such as that produced for covering an open top container, to be manufactured in different sizes but capable of being usable to cover not only specific sizes of containers but also containers of at least slightly varying sizes. 
     Another important object of this invention, to provide a cover of the thin film type which may be reliably produced, without “pinholes”. 
     Still another object of this invention is to provide a flexible thin film cover incorporating not only a molded thickened peripheral bead (as opposed to a rolled bead) but also an outer marginal portion immediately adjacent the thickened bead which tapers gradually toward the main central body portion of the cover, to thereby provide an outer peripheral portion of the cover which may be more securely sealed relative to an associated container. 
     Another object of this invention is to provide a flexible, film-type cover which may be readily molded against a concave mold surface. 
     Still another object of this invention is to provide a flexible, thin-film cover which may be individually produced over a considerably shorter time period than a similar cover constructed of latex rubber material. 
     Another object of this invention is to provide a method of manufacturing the cover of the instant invention which incorporates not only centrifugal force but also gravity in a manner such that the main body of the cover is of a substantially constant thickness, the open mouth of the cover is defined by a thickened reinforcement bead and a peripheral zone of the cover immediately adjacent the reinforcement bead gradually tapers in thickness from the bead toward the central body portion of the cover. 
     A final object of this invention to be specifically enumerated herein is to provide a cover which will conform to conventional forms of manufacture, be useable in numerous environments, be resistant to light abrading independent of minute particle deterioration and reliable throughout a wide range of usage. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of an apparatus, includes a conveyor system, for carrying out the method of the instant invention for producing a flexible PVC closure or cover, 
     FIG. 2 is an enlarged fragmentary transverse vertical sectional view, illustrating the support chain of the conveyor, a portion of one of the mounting brackets supported from the support chain and a rotary concave mold supported from one end of the support bracket. 
     FIG. 3 is a exploded perspective view of an attaching assembly by which the mold illustrated in FIG. 2 is mounted from the rotary support therefore. 
     FIG. 4 is a fragmentary enlarged vertical sectional view illustrating a modified form of air valve for the mold. 
     FIG. 5 is a front schematic view illustrating the manner in which liquid PVC may be introduced into the mold as the latter is being spun. 
     FIG. 6 is a side schematic view of the structure illustrated in FIG.  5 . 
     FIG. 7 is an end schematic view of one of the inverted rotary molds as it moves through the heating housing. 
     FIG. 8 is a schematic illustrating the manner in which a cover or closure is removed from the mold after the latter has been cooled. 
     FIG. 9 is a fragmentary vertical sectional view illustrating one peripheral portion of the mold with the PVC material therein during spinning. 
     FIG. 10 is a fragmentary vertical sectional view of the opposite peripheral portion of the mold illustrated in FIG.  9 . 
     FIG. 11 is a fragmentary vertical sectional view of the structure in FIG. 9 in inverted position and subsequent to termination of rotation of the mold. 
     FIG. 12 is a fragmentary vertical section view of the structure illustrated in FIG. 10 in inverted position and subsequent to termination of rotation of the mold. 
     FIG. 13 is a schematic sectional view, illustrating the manner in which PVC material may be applied to the concave inner surfaces of a rotating dome-shaped mold. 
     FIG. 14 is a schematic sectional view, illustrating the mold structure of FIG. 13 in inverted position and subsequent to termination of rotation of the mold and as it is moving through the heating housing. 
     FIG. 15 is a vertical sectional schematic view, illustrating the manner in which the article or closure within the mold illustrated FIG. 14 is removed therefrom. 
     FIG. 16 is a vertical sectional view of the article illustrated in FIGS. 14 and 15 after having been removed from the mold. 
     FIG. 17 illustrates a third shape of mold and the manner in which the mold interior may be initially coated with liquid PVC while the mold is being rotated about a horizontal axis. 
     FIG. 18 is a vertical sectional schematic view illustrating the mold shown in FIG. 17 in inverted position for curing the material therein as it passes through the heating housing in an inverted position. 
     FIG. 19 a vertical schematic view illustrating the manner in which the article being formed in the mold illustrated in FIGS. 17 and 18 may be removed therefrom. 
     FIG. 20 is a vertical schematic view similar to FIG. 17, but illustrating a slightly different shaped mold for forming a liner for a tapered container. 
     FIG. 21 is a vertical sectional view illustrating the manner in which the liner formed in the mold illustrated in FIG. 20 may be placed within a paper or plastic container and have a conventional cover snapped downwardly over the combination of the tapered container and liner. 
     FIG. 22 is a fragmentary enlarged vertical sectional view of a cover removed from the mold of FIG.  8 . 
     FIG. 23 is a fragmentary enlarged vertical sectional view of a cover removed from the mold of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now more specifically to the drawings, the numeral  10  generally designates a machine or apparatus by which the several products disclosed hereinafter may be produced. The apparatus  10  includes a framework  12  from which powered and idle sprockets  14  and  16  are journaled. A conveyor chain  18  is trained over the sprockets  14  and  16  and the sprocket  14  is mounted on a power shaft  20  driven by a gear head motor  22  through a drive chain  24 . 
     The conveyor chain  18  supports  12  transverse support arms  26  therefrom (only  5  support arms  26  being shown). The opposite ends of each support arm  26  support a rotary spindle  28  which is tubular, and each spindle  28  includes a drive pulley  30  to be hereinafter more fully set forth. One set of ends of the rotary spindles  28  include air inlet nipples  32  and the other set of ends of the spindles  28  include molds  34  supported therefrom. A mold  34  fragmentarily illustrated in FIG. 2 is generally in the form of an inverted pot cover with a slightly revised (inwardly rolled) mouth rim  38 . In addition, at least one peripheral portion of the outer margin of the mold  34  is provided with a tubular nipple  36  which is open at its inner end and closed at its outer end, the rolled mouth rim  38  of the mold  34  serving a purpose hereinafter more fully set forth. 
     As the molds  34  move along the upper and lower reaches of the chain  18 , the molds  34  first move into registry with downwardly directed PVC discharging nozzles  40  and then pass about the shaft  20  and swing (in inverted positions) into heating housing  42  extending beneath the lower reaches of the chain  18 . The molds  34  enter the heating housings  42  through slots  44  having flexible flaps  46  removably closing the inner ends thereof. In addition, the top walls of the heating housings  42  have slots  48  formed therein through which the rotary spindles  28  are snugly received, the slots  48  having flexible seals  50  operatively associated therewith and between which the rotary spindles  28  are received. The ends of the housings  42  remote shaft  20  are provided with flexible flaps similar to the flaps  46  but which are mounted on the exterior of the heating housings  42 . 
     As the spindles  28  exit the heating housings  42  they pass inwardly through slots  52  formed in cooling housings  54  and the cooling housings  54  are also provided with slots and seals  56  and  58  corresponding to the slots  48 . 
     After exiting the ends of the cooling housings  54  remote from the heating housings  42 , the spindles  28  pass about the shaft  60  from which the idle sprocket  16  is mounted and move into registry with air discharge nozzles  62 , which nozzles  62  may be mounted for limited movement longitudinally of the frame  12  and spring biased (in any convenient manner) toward the end of the frame  12  remote from the heating housings  42 . The movement of the air discharge nozzles  62  longitudinally of the frame  12  will be effected by any suitable spring biased latch or the like mounted on the structure (not shown) which supports the air discharge nozzles  62  for longitudinal movement of the frame  12  and which is engaged by each support arm  26  as it moves from the shaft  60  end of the frame  12  toward the shaft  20  end of the frame  12 . In this manner, the air discharge nozzles  62  will register and move with each spindle for a short distance of its movement along frame  12  and then turn to the start position thereof adjacent the shaft  60  end of the frame  12 . While the nozzles  62  are registered and move with the spindles  28  air from the nozzles  62  is directed upwardly into the air inlet nozzles  32  of the rotary spindles  28 . 
     The interior of each rotary spindle  28  includes a downwardly spring biased valve stem  64  and the upper end of each valve stem  64  includes a valve head  66 , see FIG. 2, seatable with the seat  68  defined at the upper end of a hollow conical form  70  supported within the center of each mold  34  through the utilization of a unique bolt and washer assembly including a shouldered bolt  72  and a non-circular washer  74  having a square central opening  76  formed therein. 
     The shouldered bolt  72  includes a circular shoulder  78  rotatably received through the center opening  80  formed in the mold  34  and a square shoulder  82  receivable through the square opening  76 . Thus, even though the bolt  72  includes a circular head  86  snugly received within the lower end of the conical form  70 , suitable torque applying tools may be applied to the exterior of the washer  74  in order to rotate the same and thus tighten the bolt  72  within the threaded counter-bore  88  formed in the upper end of the spindle  28 . 
     With attention now invited more specifically again to FIG. 1, it may be seen that a drive belt  90  is driven by a gear motor  92  and that the drive belt  90  has one reach thereof disposed for engagement by the drive pulley  30  of each spindle  28  as that spindle approaches the shaft  20  end of the frame  12 . Only the right-hand belt  90  is illustrated in FIG. 1, but the left-hand belt  90  is illustrated in FIG.  2 . 
     With attention now invited to FIGS. 1,  2  and  5 - 8 , as a pair of molds  34  move into registry with the nozzles  40  the corresponding drive pulleys  32  engage the belts  90  and cause the molds  34  to rotate in the manner indicated by the arrows  94  in FIG.  1 . At substantially the same time, the nozzles  40  downwardly discharge the plastisol or liquid PVC downwardly upon the corresponding forms  70 . Plastisol quickly flows by gravity downwardly along the form  70  and as rotating molds  34  move further toward the shaft  20  end of the frame  12 , the nozzles  40  apply additional plastisol between the form  70  and rolled rim  38  of each mold  34  registered with a nozzle  40 . Then, the discharge of plastisol from the nozzles  40  is terminated. The plastisol, designated by the reference numeral  96 , and because of the rotation of the molds  34 , is spun outwardly into the outer rims  98  of the molds  34 . Because of surface tension, the plastisol  96  forms only a thin film (approximately 0.0025 inches) over the main body portion of the inner surface of the mold  34 , and the remainder, or excess, of the plastisol  96  collects in the rim  98  in the manner illustrated at  100  in FIGS. 9 and 10. The plastisol  96  fully fills the interior of the nipple  36 ′ illustrated in FIG. 9 (note that the nipple  36 ′ of FIG. 9 is inclined oppositely relative to the nipple  36  illustrated in FIG.  2 ). When a support arm  26  supporting a pair of molds  34  passes about the shaft  20  to invert the molds  34  and the inverted molds move into the heating housings  42 , the molds  34  have ceased to rotate and the collected plastisol at  100  flows by gravity down into the rolled rim  38  in the manner illustrated in FIGS. 11 and 12. However, because rotation of the molds  34  has terminated, the plastisol collected at  100  tends to flow down the inverted rims  98  of the molds  34  in a manner such that the thickness of the plastisol tapers upwardly away from the inverted rims  38  in the manner illustrated at  102  in FIGS. 11 and 12, the interior of the nipple  36 ′ remaining full of plastisol  96 . However, if a mold  34  is used with an oppositely inclined tubular nipple such as that indicated at  36  in FIG. 2, when the mold  34  is inverted the nipple  36  will be upwardly and outwardly inclined and the excess plastisol spun into the interior of the nipple  36  when the mold  34  is upright and being spun by the belt  90  will drain therefrom when the mold  34  is inverted and before it moves into the heating housing  42  so as to provide a tubular article nipple, opening into the interior of mold  34 . 
     When the mold drive pulleys  30  are engaged with the belts  90 , the molds  34  are rotated at approximately 670 rpm. Furthermore, the chain  18  moves about 3 feet per minute. Also, the interior temperature of the heating housings  42  is approximately 370° F. and the heating housings  42  are approximately 6 feet in length. Thus, the molds  34  remain within the heating housings for approximately two minutes, thereby enabling the molds  34  and the plastisol to reach curing temperatures of approximating 370° F. This curing temperature is sufficient to transform the plastisol into a solid and immediately upon moving from the discharge ends of the heating housings  42  the molds  34  move into the cooling housings  54  in which cool air is directed upon the molds  34  in order to reduce their temperature to approximately 120° F. Upon exiting the ends of the cooling housings  54  remote from the heating housings  42  the molds  34  move about the shaft  60  into positions registered the air inlet nozzles  32  and air under pressure is discharged from the nozzles  62  into the air inlet nozzles  32  whereupon the valves stems  64  are upwardly displaced to elevate the valve heads  66  upwardly from the seats  68  and to allow air under pressure to enter the mold  34  beneath the center portion of the cover or article  106  (see FIG. 8) in order to upwardly displace the center portion of the cover  106  from the mold  34 . Then, a hand-held or machine positioned implement  108  may be used to break one peripheral portion of the bead  110  of the cover  106  from the rolled rim  38  of the mold  34 . It will be noted from FIG. 2 that the valve head  66  includes a peripheral groove  112 . The groove  112  is provided in order that the center conical portion of the cover or article  106  initially formed over the hollow conical form  70  will partially interlock with the valve head. Then, when the cover  106  is initially forced from the mold  34  by the air under pressure being admitted into the mold under the cover  106 , the center conical portion  107  of the cover or article  106  will be turned inside-out such that the conical portion  107  is disposed to the exterior of the cover  106  as opposed to the interior of the cover, as originally formed. 
     With attention now invited more specifically to FIG. 4, the mold  34 ′ illustrated in FIG. 4 is identical to the mold  34 , but the bolt and washer assembly illustrated in FIG. 3 are used without the hollow conical form  70  and outer side of the head  86 ′ of the shouldered bolt  72 ′ is contoured as at  87  in order to form a seat for the modified valve head  66 ′ carried by the upper end of the modified valve stem  64 ′ illustrated in FIG.  4 . Thus, when a cover or article similar to the article  106  is removed from the mold  34 ′ the cover or article thus removed does not include the conical portion  107  of the cover  106 . 
     With attention again invited to FIG. 2, the upper reach of the chain  18  is supported from and rides along a support guide  113  (not shown in FIG. 1) and the support arms  26  each include a roller  114  journaled therefrom which rollingly engage a similar support guide (not shown) mounted beneath at the lower reach of the chain  18 . 
     Referring now more specifically to FIG. 13, there may be seen a modified form of mold  34 ″ supported from a spindle  28  in the same manner the mold  34 ′ is supported from the spindle  28  in FIG.  4 . The mold  34 ″ is very similar to the mold  34 , but differs from the latter in that it is generally in the shape of a bowl as opposed to an inverted pot top. Accordingly, when the mold  34 ″ is spun, excess plastisol collects as at  100 ′ similar to the manner in which the excess  100  collects in FIGS. 9 and 10. Then, when rotation of the mold  34 ″ is terminated and the mold  34 ″ is inverted in the manner illustrated in FIG. 14, the excess plastisol at  100 ′ flows downwardly by gravity into the rolled rim  38 ′ and tapers from the bead  110 ′ upwardly toward the maximum diameter portion of the mold  34 ′ as at  102 ′. Of course, the slot or opening  44 ′ for the heating housing  42 ′ to be used in conjunction with the mold  34 ″ is larger than the opening or slot  44 . Also, after the article  106 ′ has been displaced upwardly from the mold  34 ″ by air pressure therein, see FIG. 15, a manually or mechanically actuated implement  108 ′ may be used to break the bead  110 ′ of the article  106 ′ from the mold  34 ″. The finished article  106 ′ is illustrated in FIG.  16 . 
     With attention now invited more specifically more specifically to FIG. 17, yet another form of mold  134  is disclosed and mounted upon a spindle  128  which is horizontally disposed. The plastisol  96  is injected into the mold  134  from a nozzle  140  and the spindle  128  is rotated so that the initial excess plastisol at  100 ″ collects at the largest diameter portion of the mold  134 . Then, rotation of the mold is terminated and the mold is inverted in a position similar to that illustrated in FIG. 18, whereupon the excess plastisol at  100 ″ flows down into the rolled rim  138  and forms a tapered thickness at  102 ″ of the plastisol from the rolled rim  138  to the maximum diameter zone of the mold  134 . 
     When the mold  134  is used, the upper reach of the attendant conveyor chain must be guidingly twisted approximately 90° and the attendant belt and belt drive assembly for rotating the spindle also must be rotated 90°. Furthermore, the discharge nozzle  140  must be mounted for movement with the spindle  128  during the plastisol injection process and also mounted for longitudinal rectilinear displacement so that the nozzle  140  can be introduced into the mold  134  and subsequently extracted therefrom. This of course also applies to the plastisol discharge nozzle  40 ′ illustrated in FIG.  13 . 
     With attention now invited more specifically FIG. 20, a final form of mold is designated by the reference numeral  234  and may be supported from a rotary spindle  228  similar to the rotary spindle  128 . The mold  234  constantly tapers from its large diameter end to its small diameter end and, therefore, need not be rotated to an inverted position. The plastisol  96  injected into the mold  234  is spun by centrifugal force fully the length of the mold  234  to the rim  238  thereof. Thereafter, mold  234  may be moved through a horizontal side-slotted heating housing (not shown) and subsequently through a similar cooling housing and then into horizontal registry with an air discharge nozzle (not shown) for injecting air through the spindle  228  and into the mold  234  exteriorly of the article formed by the plastisol  96  therein. 
     FIG. 19 illustrates the manner in which the article formed in the mold  134  or the article formed in the mold  234  may be displaced from the corresponding mold through the utilization of air injection from an air discharge nozzle  262 . As the article  206  shown in FIG. 19 is displaced outwardly of the open end of the mold by the injected air, a manually or mechanically actuated implement  208  is utilized to break the bead  210  of the article  206  from the rolled rim  138 . Thereafter, the article  206  may be manually removed from engagement with the mold  134 . Of course, the article formed in the mold  234  may be removed therefrom in the same manner. 
     Each article  206  (formed in the mold  134 ) and  240  (formed in the mold  234 ) may be utilized as a liner for a conventional tapered container  242  (see FIG.  21 ). The article  240  is illustrated in FIG. 21 as received within the container  242  and with the open end of the article  240  rolled back over and downwardly from the upper rim  244  exteriorally of the container  242 . A conventional lid  246  then may be placed downwardly over the open upper end of the container  242  in the conventional manner, the thinness of the liner or article  240  passing about the rim  244  offering little resistance to engagement of the lid  246  downwardly over the open upper end of the container  242  and the article or liner  240 . 
     Also, the article  206  after being removed from the mold  134 , may be used as a liner for the container  242 . The tapering portion  102 ″ of the article  206 , when the article  206  is placed within the container  242 , being that portion of the open end of the article  206  that extends downwardly from the rim  244  of the container  242 . 
     With reference now more specifically to FIG. 22 of the drawings, the article  106  extracted from the mold  34  in the manner illustrated in FIG. 8 includes the aforementioned conical portion  107  disposed to the exterior of the cover. 
     However, if the cover  106  is placed upon an open top food container with the conical portion  107  disposed to the exterior of the cover  106  and placed within a cool environment such as the interior of a refrigerator any air within the container will contract upon becoming cooled and the conical portion  107  will, by greater exterior air pressure be inverted to a position within the cover  106 . 
     The narrow groove  107 ′ (see FIG. 22) formed by the groove  112  indicates an area of the conical portion  107  which may be clipped therefrom if the covered container is to breathe. 
     With attention now invited more specifically to FIG. 23, it may be seen that the cover  106  also includes a hollow peripheral nipple  36 ′ formed in the nipple  36  (see FIG.  2 ). The nipple  36 ′ may be maintained closed and utilized in manually assisting removal of the cover  106  from the mold  34 . On the other hand, inasmuch as the wall thickness of the nipple  36 ′ is very thin, the extreme outer end of the nipple  36 ′ may be cut therefrom. Then, when the cover  106  is stretch over the open top of a container, the tubular nipple  36 ′ will serve as a vent to allow escape of excess air pressure from within the container, but the thinness of the walls of the nipple  36 ′ will allow the latter to droop downwardly when air pressure inside and outside the cover  106  is equal in order to prevent dust or other atmospheric contamination from entering a container over whose open end the cover  106  is secured. 
     It is also pointed out that the gradual thickening of the wall of the cover adjacent and away from the bead  110  as at  102  further reinforces the open marginal portion of the cover  106  in addition to the reinforcement thereof provided by the bead  110 . 
     With attention now invited again to FIGS. 13 through 16, when using the mold  34 ″, as an example only, it is to be understood that the liquid PVC may be injected into the mold  34 ″ as it is rotated generally in the same manner illustrated in FIG. 13, but with the mold  34 ″ and the nozzle  40 ′ inverted. The liquid PVC is discharged into the inverted mold  34 ″ with the nozzle  40 ′ spaced very close to the closed upper end of the inverted mold  34 ″ and only a prescribed amount of liquid PVC is dispensed upwardly on to the opposing center surface of the mold  34 ″. Because the mold  34 ″ is rotating, the liquid PVC immediately moves outwardly and is retained against the inner surface of the mold  34 ″ by surface tension with the result that the excess PVC  100 ′ collects in the maximum diameter portion of the mold  34 ″ in the same manner as illustrated in FIG.  13 . Then, with the mold  34 ″ still inverted, rotation of the mold  34 ″ is terminated and the excess liquid PVC is allowed to flow downward by gravity into the reversely turned rim  38 ′. 
     By using this method of forming the article or cover  106 ′, the end result is the same as that illustrated in FIG.  16 . The article or cover  106  is removed from the mold  34 ″ in the same manner as that illustrated in FIG. 15, but with the mold  34 ″ inverted to a downwardly opening position and it is therefore unnecessary to carry the spindle  28  on a chain such as the conveyor chain illustrated in FIG.  1 . Rather, a plurality of spindles  28  may be carried by a rotating turret and the heating and cooling housings may be made arcuate so as to accommodate the movement of the spindles  28  through a circular path. 
     However, it is important to note that in each disclosed manner of forming the various disclosed covers or articles in the various disclosed molds the liquid PVC is applied to what might be termed concave inner surfaces of a mold as opposed to the outer surfaces of a mold. By using such an internal mold cavity as opposed to external mold surfaces, covers of more varying shapes may be formed. Furthermore, because internal mold cavities used, greater rotational speeds of the molds may be used since there is no chance of excess liquid PVC material being spun from outer surfaces of the mold. 
     The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous other modifications and changes readily will occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.