Method of making a plastic container

#Plastic collapsible containers, and in particular squeeze tubes such as are used for toothpaste, gel-type detergents, shampoos, and the like, are made by the hundreds of millions, and constitute an appreciable part of the price of the product. These tubes typically are in the form of a thin walled plastic shell sealed at one end and with dispensing means formed at the opposite end. The dispensing means end usually consists of a conical portion tapering to a nozzle adapted to receive a closure cap of either the screw-on or snap-on variety. In order to form threads for a screw-on cap, or a thickened ring for a snap-on cap, with sufficient strength to retain the cap and to sustain opening and closing torques, the nozzle wall must be made much thicker than the wall of the body portion of the tube.

#Thin walled containers with selected thickened portions have been made heretofore by several processes or by a combination of processes such as extruding, blow molding, cementing, spin-welding, ultra-sonic welding, and the like. For instance, in the extruding art, the R. W. Saumsiegle et al U.S. Pat. No. 3,226,464 starts with a piece of extruded thermoplastic tubing in excess of the final length of the finished product. Die means crush the excess to crudely approximate the conical portion of the product, whereinafter the crushing die is removed and replaced by a heated forming die to mold the thermoplastic crushed portion into a final configuration. Neither the starting raw tube nor the method of forming this tube is related to, or contributes to, the plastic coating art. The disclosures of Bogoslowsky U.S. Pat. No. 2,418,155 and Rohdin U.S. Pat. No. 3,032,454 also show methods of forming plastic sheets into tubes but without regard for the formation of the sheets per se, or the problem of increased wall thickness in specific critical areas. In the electrostatic spray forming art applicant is aware of devices and methods for spray forming bottles, such as disclosed in the patents to Britten U.S. Pat. No. 3,187,381 and to Roe U.S. Pat. No. 3,491,170. However, neither of these devices or methods recognizes the problems of plastic coating so as to enable a product to be formed with varying wall thicknesses. Nor is applicant aware of any other electrostatic spray method or apparatus which recognizes, let alone solves, the problems attendant with manufacturing a plastic container with non-uniform wall thicknesses.

#Generally, the commercially available techniques, all well known to those skilled in the art, for applying a thin coat of plastic in or about a mold or core may be divided into electrostatic and non-electrostatic methods. Electrostatic applications include spraying powder or liquid; dipping into a liquid or a fluidized bed of powder; or dipping into non-fluidized powder. Non-electrostatic applications include the use of heated or unheated liquids which may be applied by various means such as spraying or dipping. Although the invention contemplates the use of all prior art plastic coating and molding techniques, known electrostatic methods of application are presently preferred.

#Reference is now made to the drawings in which the same characters of reference are employed to indicate corresponding or similar parts throughout the several figures of the drawings in which:

#FIG. 1 shows an ordinary plastic squeeze tube with a screw-on cap;

#FIG. 2 is an elevational view of a drum exteriorly carrying cores for electrostatic spray forming of squeeze tubes;

#Referring now to the Figures in greater detail, my invention relates to the manufacture of thermoplastic container shells for containers such as illustrated in FIG. 1, comprising a tube 2, with a sealed lower end 4, a conical portion 6, and a closure receiving nozzle 8 with threads 10 to receive a threaded closure 12. I employ the term "shell" to describe a container before the lower end 4 is sealed. Although any method of plastic coating a mold or core known in the prior art may be used, in the practice of my invention, I prefer to utilize a recently developed method of forming thermoplastic articles wherein products may be molded directly from finely divided plastic resin in a single revolution of a drum 14, FIG. 2, equipped with cores 16. As the drum 14 revolves, it passes over an electrostatically charged fluidized bed, not shown, containing powdered resin particles which are electrostatically attracted to the cores 16, i.e. sprayed on the cores. Thereafter, the powder is fused into a homogeneous layer by applying heat to the cores. As the drum continues to revolve, the cores are cooled and finally the container shell is removed by mechanical, air or vacuum operated pick-off means. In the alternative, as shown in FIG. 3, drum 14 may be provided with mold cavities 15, wherein the products are formed interiorly of the drum rather than exteriorly as shown in FIG. 2. Hereinafter, however, the expression "core" will be used throughout in the specification and claims, it being understood that as so used it is intended to include either a male core or a female mold. The molding methods and apparatus illustrated in FIGS. 2 and 3 are old in the art and I make no claim to either. However, I do propose to use some method of electrostatic forming in the practice of my invention, since to my knowledge it is presently preferable to non-electrostatic plastic application. Unfortunately, the maximum wall thickness which is obtainable with any coating process known to me is in the order of 0.040 inches, while the nozzle wall of a collapsible plastic tube must be approximately twice that thickness and in some cases even greater.

#In a preferred embodiment of the present invention, I solve this problem by providing an improved core, one end of which is provided with a plurality of material increasing extensions to which thermoplastic powdered resin will adhere. As shown in FIG. 4, these material increasing extensions are in the form of a series of concentric grooves 18 and ridges 19 over which may be deposited concentric integrally connected pleats 21 of thermoplastic resin. As further shown in FIG. 4, the core 14 may be provided with a plug 17 of Teflon or similar material, to which the thermoplastic particles will not adhere, so as to leave an aperture at the center of the end of the formed tube. However, the plug may be dispensed with in another embodiment, as shown in FIG. 5, thereby permitting a membrane 21a to bridge the periphery of the innermost pleat. This membrane may be pierced in a subsequent die forming operation, or by the end user when shelf life or sterility requires a hermetically sealed container until actual use. Single doseage disposable medicinal capsules are an example of an application of the embodiment of FIG. 5. The pleats 21 are then heated and squeezed together between dies under pressure to form the desired final shape of the nozzle, there being enough pleats so that their combined thickness is sufficient for this purpose. Other configurations for increasing surface area in the vicinity of the nozzle may also be resorted to, such as the corrugations 56 shown in FIGS. 15 and 16; fins 57, FIG. 18; and honeycombs or other similar geometrical patterns 59, 61 and 63 shown for illustrative purposes in FIGS. 19, 20 and 21, respectively.

#Since the maximum wall thickness that can presently be obtained by the above described processes is approximately 0.040 inches, with the core embodiment of FIG. 4, the nozzle wall thickness is increased four-fold. From the foregoing it is apparent that additional increases in nozzle wall thickness may be obtained by increasing the number of concentric pleats 21, such as shown in FIG. 13.