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(11) | EP 0 242 419 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Linerless plastic vacuum closure |
| (57) A molded plastic closure cap (1) is disclosed having integrally molded plastic fin
or rib members (7) for sealing a container and also having a layer (9) of a softer
sealing material applied to the members to improve the seal, as, for example, to include
vacuum sealing capability. The softer sealing materials include plastisol formulations
characterized by their having a fusing temperature safely below that which would shrink
the molded closures which include polyolefin closures. |
BACKGROUND OF THE INVENTION
[0001] The present invention relates to improved closure caps for sealing containers formed of glass or plastic or other materials and more particularly to a molded plastic closure cap where the sealing means includes integral sealing ribs or fins molded as an integral portion of the closure cap and covered with a softer sealing material. This is a continuation-in-part of application Serial No. 334,325 dated December 24, 1981.
[0002] Plastic closures with sealing ribs or fins are presently used to seal containers in various packaging applications. A closure of this type is applied to the container's threaded neck and creates a seal when its ribs or fins press against the container finish. Such closures are commonly called linerless closures.
[0003] Certain packages require a seal which retains an extremely airtight seal or a vacuum within the sealed container for preserving the packaged product. Although the general type of plastic closure presently used may maintain vacuum in a certain percentage of sealed packages, the percentage of packages in which the seal fails to maintain vacuum is unacceptably high in many cases.
[0004] Plastic caps with sealing ribs or fins are usually molded in one piece from polyolefin materials, often a polypropylene type. The sealing fins are relatively rigid in comparison to other materials such as plastisol gaskets normally used to seal containers. The polyolefin sealing fins thus lack the softness to attain intimate contact with container finishes such as is necessary to maintain a vacuum especially during the handling of the packages. Although containers are manufactured to specified tolerances, they do not always have perfect finishes due to problems inherent in their manufacturing process.
[0005] Another problem with the materials used to make linerless plastic closures is that adhering other materials to the polyolefin surfaces is very difficult.
[0006] The method of this invention to achieve the improved sealing capability is to place a softer sealing material such as a wax, hot melt, epoxy, or a softer plastic preferably a heat cured plastisol over the sealing ribs or fins of the closure cap. For example, paraffin wax and plastisol have been tested and both have improved the ability of the closure to hold vacuum. When plastisol is used, it is applied as a liquid over the sealing fins and then heated to cause the liquid plastisol to fuse or gel into a solid. The liquid plastisol may be applied to the fins by a stationary nozzle or spray gun while the closure is rotated. A thickness of the plastisol of 0.001" to 0.020" over the ribs or fins has proven useful as described below or thicker plastisol coatings anchored by the fins may be used.
[0007] The invention includes preferred plastisol formulations for use with molded closures such as those molded from polyolefin including polypropylene. The preferred plastisols have uncharacteristically low fusing temperatures thereby eliminating heat damage to the closures such as the shrinking experienced with the prior plastisols requiring relatively high fusing temperatures.
[0008] Accordingly the object of this invention is to improve the sealing ability of linerless plastic closure caps particularly for the retention of a vacuum within sealed packages and thus to provide a molded plastic closure cap suitable for achieving an acceptable percentage of properly sealed vacuum packages where the sealing may be done on automatic sealing machinery at extremely high sealing rates.
[0010] Another object of the present invention is to provide a molded linerless plastic closure incorporating a relatively thin coating of sealing material on the cap sealing members.
[0011] Another object of the present invention is to provide a molded linerless plastic closure having a fused or gelled and relatively thin sealing coating provided on the sealing fins or other sealing members.
[0012] Another object is to provide plastisol formulations having uncharacteristically low fusing temperatures to eliminate heat damage to the molded closures.
[0013] Other and further objects of the present invention will become apparent upon an understanding of the illustrative embodiments about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawings, forming a part of the specification, wherein:
FIG. 1 is a side elevational view, partially in section, illustrating a preferred embodiment of the closure cap.
FIGS. 2 and 3 are enlarged fragmentary detailed sectional views of differing embodiments of the closure cap of the invention sealing a container.
FIGS. 4 and 5 are enlarged fragmentary detailed sectional views of different embodiments of closure caps in accordance with the invention.
FIG. 6 is a side elevational view illustrating a preferred method of applying the soft sealing coating to the sealing members of the closure.
FIG. 7 is an enlarged fragmentary detailed sectional view of another embodiment of the closure cap of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] The closure cap 1, in accordance with the present invention, has a cover 2 and a depending skirt 3 including container engaging threads 4. The outer surface of the skirt 3 may include knurls or other gripping means 5 for applying and removing the closure cap 1 from the container 6. The cover 2, skirt 3 and threads 4, together with a container sealing means comprise a unitary or one-piece molded closure cap formed on conventional cap molding machinery.
[0016] There are a number of suitable integral container sealing means which usually take the form of fins or ribs or rings which extend downwardly from the underside of the closure cap. Sealing means of this general type have been described in prior U.S. patent No. 3,815,771 (S.N. 86,316), dated June 11, 1974. This prior U.S. patent describes projecting ribs or fins which are molded as an integral part of the closure cap and which are positioned for engaging the container rim. The fins or ribs engage the container rim and provide the seal for the contents of the sealed container.
[0017] As illustrated in FIGS. 1 and 2 the sealing fins 7 have an angular alignment with both the closure cap cover 2 and the container rim 8 so that they yield and accommodate themselves against the adjacent container rim 8 in a sealing relationship.
[0018] The improvement of this invention comprises the application of a coating of softer sealing material over the fins 7. Suitable sealing films 9 include easily applied films such as waxes, hot melts, epoxies, or other soft plastic materials and preferably plastisols applied over the fins 7.
[0019] Coatings of these materials have been tested and have been proven to significantly increase the sealing capabilities of molded closures and in particular have increased the ability of the closures to hold a vacuum within the sealed containers.
[0020] When a plastisol is employed, it may be sprayed or otherwise distributed over the sealing fins 7 and heated and fused or gelled into a continuous resilient sealing film over the fins. Relatively thin plastisol films having a thickness of as little as 0.001 to 0.020 inches have been tested and found to be effective in providing the improved sealing action. Such a thin or film-like coating is illustrated in FIG. 3. A heavier coating is illustrated in FIG. 2.
[0021] The fused or gelled plastisol conforms generally to the shape of the plastic sealing fins with the thin coating illustrated in FIG. 3 and is held in the closure by its own adhesive qualities but also by the physical interlock resulting between the film 10 and the sealing fins 7. The thicker coating 9 in FIG. 2 provides the sealing improvements while using more of the sealing material. Even though packages sealed with fins coated in the manner illustrated in FIGS. 2 and 3 were subjected to elevated temperatures, such as those resulting from the use of steam by the vacuum forming sealing apparatus, no significant loss of the improved sealing action of the films has been found to result.
THE PREFERRED PLASTISOL FORMULATIONS
[0022] Preferred low-temperature fusion plastisol formulations for the sealants in linerless plastic closures as described are of the following general type:
[0023] The following are specific examples of ingredients which have been found to be useful in the plastisol formulation.
1. Vinyl Dispersion Resin
[0024] Vinyl dispersion resins include both polyvinyl chloride homopolymer and polyvinyl chloride copolymer resins. Examples of commercially available homopolymer resins include FPC-605 (Occidental Chemical Corp.) and Geon 125 (B.F. Goodrich, Chemical Division). Examples of commercially available copolymer resins containing vinyl actate comonomer include FPC-6338, 4.2% vinyl acetate, (Occidental Chemical Corp.) and Formolon 40, 4.6% vinyl acetate, (Formosa Plastics Corp.). Another copolymer resin is Geon 138, 4% vinyl ester (B.F. Goodrich, Chemical Division) which contains a proprietary vinyl ester comonomer instead of vinyl acetate comonomer. Regardless of the comonomer used, the vinyl copolymer dispersion resins, as a class, are preferred over the homopolymer resins for this type of formulation because plastisols containing copolymer resin fuse at a lower temperature than do those made with homopolymer resins.
2. Fast-Fusing Plasticizer
[0025] Examples of fast-fusing plasticizers include: butyl benzyl phthalate, di-butyl phthalate, and butyl octyl phthalate. Butyl benzyl phthalate is commercially available as Santicizer 160 from Monsanto Industrial Chemicals Co. Butyl octyl phthalate is commercially available as PX-914 from U.S.S. Chemicals. Di-butyl phthalate is commercially available as Palatinol DBP (Badische Corp.), Nuoplaz DBP (Tenneco Chemicals, Inc.), and PX-104 (U.S.S. Chemicals).
3. General Purpose Plasticizer
[0026] Examples of general purpose plasticizers include di-2-ethyl hexyl phthalate (DOP), and di-isodecyl phthalate (DIDP). These plasticizers are both commercially available from a number of companies. DOP is available as Nuoplaz DOP (Tenneco Chemicals, Inc.), PX-138 (U.S.S. Chemicals, Inc.), and Palatinol DOP (Badische Corp.). DIDP is available as Nuoplaz DIDP (Tenneco Chemicals, Inc.) PX-120 (U.S.S. Chemicals), and Palatinol DIDP (Badische Corp.).
[0027] The general purpose plasticizer functions to stabilize the viscosity of the unfused (liquid) plastisol.
4. Stabilizer
[0028] Stabilizers retard the heat degradation of the vinyl resin. There are many stabilizers available as powders, liquids, or pastes. Examples of commercially available stabilizers include Ferro 707X, Zinc, Epoxy, Organic inhibitor paste type, (Ferro Corporation) and Interstab CZL 731, Calcium, Zinc Liquid type, (Interstab Chemicals, Inc.).
5. Filler
[0029] A filler is an inert, powdered material which can be properly dispersed in plastisol, is usually inexpensive, and is included in the formulation to lower the plastisol cost. Often fillers also function synergistically with other ingredients such as lubricants. Examples of commercially available fillers include No. 1 Barytes, barium sulphate, (Pfizer, Inc.) and Mica #279 (Whittaker, Clark, and Daniels).
6. Pigment
[0030] A pigment provides color to the fused plastisol. Examples of commercially available pigments include TI-Pure R-101, titanium dioxide, (E.I. du Pont deNemours & Co.) and BK-5099 Pure Black Iron Oxide (Pfizer, Inc.).
7. Lubricants
[0031] Lubricants cause the fused plastisol to have a slippery surface, reducing friction between the closure's plastisol sealing surface and the container's sealing surface. A slippery plastisol is necessary to lower the torque required to remove the closure. Examples of commercially available lubricants are oleamide, erucamide, and silicone fluid. Oleamide is commercially available as Kemamide U and erucamide as Kemamide E (both from Witco Chemical Corp., Humko Division). Silicone fuid is available as SF-18 (General Electric).
8. Blowing Agent
[0032] Blowing agents decompose during plastisol fusion causing the fused plastisol to have a cellular or foamed structure. Commercially available blowing agents include Celogen OT and Celogen TSH,p,p¹ - oxybis (benzene sulfonyl hydrazide), (both from Uniroyal Chemical Co.) and Nitropore OBSH,p,p¹ - oxybis (benzene sulfonyl hydrazide), (Olin Corp.).
[0033] The ingredients are combined as described below to form a liquid plastisol. The liquid plastisol is deposited into a plastic linerless closure to form a sealing surface for a vacuum package consisting of the closure and container onto which the closure is applied. The container can be made of materials such plastic, glass, or metal.
[0034] The critical property required of the plastisol is that it must fuse at a temperature sufficiently low enough to prevent shrinkage of the plastic closure in which it is fused. Plastisol formulations as disclosed above have the required low-temperature fusion properties by virtue of their containing a combination of (1) vinyl copolymer dispersion resins and (2) fast fusing plasticizers.
[0035] The general purpose plasticizer functions to stabilize the viscosity of the liquid plasticizer, increasing its shelf life. The remaining ingredients are not critical to the low temperature fusion properties of the plastisol.
[0036] Additional ingredients such as surfactants, vinyl blending resins, diluents, thixotropic agents, and solvents may be included in the plastisol without departing from the scope and purpose of the forumlation, which is to provide a plastisol having fusion temperature low enough for fusion in a polyolefin closure.
The Plastisol Mixing and Handling
[0037] The ingredients comprising a plastisol formulation are weighed in the proportions described in Part I. Then the weighed ingredients are combined and thoroughly mixed to form a homogeneous dispersion. This liquid dispersion is called a plastisol. Plastisol mixing and handling are well described in trade literature.
[0038] Mixing is usually done by automatic equipment. Many laboratory and production mixers of various designs are suitable for mixing plastisols and are commercially available. An example is the Double Planetary Mixer manufactured by Charles Ross and Son Co.
[0039] Typically, minor liquid and paste ingredients in the formulation are preblended to form slurries. The slurries are inroduced into the mixer, followed by the remaining powders and resins in the formulation.
[0040] Next, all or part of the general purpose plasticizer can be added. At this point, some of the fast-fusing plasticizer can be added, but it is usually withheld. The purpose of withholding part of the plasticizer is to create a condition of high shear during the initial phase of mixing. The mixer is operated under high shear conditions until all the lumps of dry powder have been broken and dispersed. Finally, the remainder of the plasticizer is added, and mixing is continued until a homogeneous dispersion is obtained. Often, mixing is done in a partial vacuum (25-30 inches Hg) to remove air bubbles from the plastisol.
[0041] Plastisol can be mixed in advance of use and stored until needed. Some plastisols, especially the low-temperature fusion type described in Part I, become more viscous during storage due to plasticizer absorption by the vinyl resin. Storage life can be lengthened by maintaining the storage temperature at 40-50°F and particularly by avoiding temperatures of 80°F or greater.
Lining Closures
[0042] Plastisol is placed into a pressurized tank which is connected to a dispensing nozzle. This nozzle is positioned over a rotating closure into which the plastisol is injected when the nozzle opens. The liquid plastisol is thereby flowed onto the closure's fins in a precisely metered amount. Next, the closure and plastisol are heated to a temperature of less than 330°F for a period of time necessary to sufficiently fuse or flux the plastisol in the closure.
[0043] Examples of preferred plastisols are given below. Tensile strength is used to measure the degree of fusion of the plastisol.
[0044] FIG. 2 as indicated illustrates a coating in accordance with the invention with a middle range of thickness and where the coating material 9 fills the space between the two sealing fins 7. In this case, the coating provides the sealing contact between the closure 2 and the container 6.
[0045] FIG. 3 illustrates a similar closure where a coating 10 is of lesser thickness is used and where the coating is seen to conform more closely to the shape of the sealing fins 7. Nevertheless, such coatings with a thickness near the lower side of the thickness range provide significantly improved sealing capability.
[0046] FIG. 4 illustrates the use of a coating of the type described above on a closure cap 11 having a differing sealing means comprising three sealing fins 12 having differing lengths and having a lesser angle with the cover 13 of the closure 11. This fin and coating combination functions in a similar manner to provide the improved sealing capability.
[0047] FIG. 5 illustrates another embodiment where the closure 14 is in sealing engagement with a container 19 and where a relatively thin coating 16 forms a seal between the slanted fins 15 and the container finish edges 18.
[0048] FIG. 6 shows a preferred method of applying these coatings in controlled thicknesses. The caps are mounted in rotating nests of a typical gasket applying machine. A spray nozzle positioned to direct a coating spray onto the sealing members operates for a sufficient period to apply the desired coating thickness. After the application of the coating, in this case where a plastisol or other material requiring curing has been used, the cap is transferred to a suitable heating means for the curing or gelling step.
[0049] FIG. 7 illustrates another embodiment of the invention as a closure 20. The closure 20 has a molded closure cap shell with a cover 21 and a depending skirt 22 including closure threads 23 for engaging cooperating threads 24 on a container 25. The sealing means for the closure cap 20 comprises a pair of sealing fins 26 having a generally triangular cross-section and depending from the underside 31 of the closure cap cover 21. The fins 26 are inclined at about a 30° angle from the vertical and their angularly aligned sides enclose an angle of about 20°.
[0050] A plastisol is sprayed or flowed around the two sealing fins 26 to form a sealant 28 of generally rectangular cross-section which is confined in a channel 27 comprising the underside 31 of the cap cover 21, the inner and upper wall 29 of the closure skirt 22 and a downwardly extending and generally vertically oriented bead 30. If there is no bead corresponding to the bead 30, the inner edge of the sealant tapers inwardly and upwardly to the cover underside 31. In this embodiment of the closure cap, the two fins 26 and the sealant 28 combine to provide an efficient seal useful for vacuum seals as well as air tight seals of extremely high efficiency. The two fins 26 also cooperate to anchor the sealant 28 in the closure cap shell in combination with the channel firming walls. The sealant is preferably a low temperature fusing plastisol as described herein.
1. In a molded closure cap for sealing a container where the closure cap has a molded
closure cap shell with a cover and a depending skirt and where the skirt has container
engaging means for engaging cooperating means on a container neck and where there
are one or more integrally molded sealing fins on the underside of the closure cap
cover; the improvement comprising:
a sealant of about .001 to .020 inches overlying the said fins and positioned for providing a resilient sealing layer between the container rim and said fins; and said sealant comprising a low temperature fusion plastisol which is fused in place in the closure at the low temperature of less than about 330°F thereby preventing shrinkage of the molded closure cap shell during the fusion heating.
a sealant of about .001 to .020 inches overlying the said fins and positioned for providing a resilient sealing layer between the container rim and said fins; and said sealant comprising a low temperature fusion plastisol which is fused in place in the closure at the low temperature of less than about 330°F thereby preventing shrinkage of the molded closure cap shell during the fusion heating.
2. The closure cap as claimed in Claim 1 in which said fins comprise a plurality of
downwardly projecting members having a generally triangular cross-section and being
positioned for engaging an upwardly facing surface on the container rim.
3. The closure cap as claimed in Claim 1 which further comprises a bead projecting
downwardly from the underside of the container closure cap cover radially inwardly
of said sealing fins to provide a sealant receiving channel.
4. The closure cap as claimed in Claim 1 in which said sealant comprises a relatively
thin layer having a thickness of from about .001 to .020 inches.
5. The closure cap as claimed in Claim 1 in which the sealant comprises a formulation
consisting for essential ingredients thereof of the following ingredients in the part
ranges indicated:
6. The closure cap as claimed in Claim 5 in which the vinyl dispersion resin is FPC-6338.
7. The closure cap as claimed in Claim 5 in which the vinyl dispersion resin is Formolon
40.
8. The closure cap as claimed in Claim 6 or Claim 7 in which the stabilizer is Ferro
707X.
9. The closure cap as claimed in Claim 6 or Claim 7 in which the filler is No. 1 Barytes.
10. The closure cap as claimed in Claim 6 or Claim 7 in which the pigment is Ti-Pure
R-101.
11. The closure cap as claimed in Claim 6 or Claim 7 in which the lubricant is Kemamide
U.
12. The closure cap as claimed in Claim 6 or Claim 7 in which the lubricant is SF-18.
13. The closure cap as claimed in Claim 6 or Claim 7 in which the plasticiser is about
equal parts of Santiciser 160 and PX-120 (DIDP).
14. The closure cap as claimed in Claim 5 in which the formulation consists for essential
ingredients thereof of the following ingredients by parts:
15. The closure cap as claimed in Claim 5 in which the formulation consists for essential
ingredients thereof of the following ingredients by parts:
